Effects of SCH 34826, an orally active inhibitor of atrial natriuretic peptide degradation, in healthy volunteers Atrial natriuretic peptide is cleared from plasma by clearance receptors and by enzymatic degradation by way of a neutral metalloendopeptidase. Inhibition of neutral metalloendopeptidase activity appears to provide an interesting approach to interfere with metabolism of atrial natriuretic peptide to enhance the renal and haemodynamic effects of endogenous atrial natriuretic peptide. In this study, the effects of SCH 34826, a new orally active neutral metalloendopeptidase inhibitor, have been evaluated in a singleblind, placebo-controlled study involving eight healthy volunteers who had maintained a high sodium intake for 5 days. SCH 34826 had no effect on blood pressure or heart rate in these normotensive subjects. SCH 34826 promoted significant increases in excretion of urinary sodium, phosphate, and calcium. The cumulative 5-hour urinary sodium excretion was 15.7 k 7.3 mmol for the placebo and 22.9 k 5,26.7 6 (p < 0.05), and 30.9 2 6.8 mmol @ < 0.01) for the 400,800, and 1600 mg SCH 34826 doses, respectively. During the same time interval, the cumulative urinary phosphate excretion increased 0.3 (p < 0.01), and 2.4 k 0.4 by 0.3 -t- 0.4 mmol after placebo and by 1.5 k 0.3 (p< 0.01), 1.95 mmol (p < 0.001) after 400, 800, and 1600 mg SCH 34826, respectively. There was no change in diuresis or excretion of urinary potassium and uric acid. The natriuretic response to SCH 34826 occurred in the absence of any change in plasma atrial natriuretic peptide levels but was associated with a dosedependent elevation of urinary atrial natriuretic peptide and cyclic guanosine monophosphate. These results demonstrate that neutral metalloendopeptidase inhibition with SCH 34826 can produce natriuresis and phosphate excretion in volunteers receiving a high-salt diet maybe by reducing the renal atrial THER1991;50: 181-91.) natriuretic peptide metabolism. (CLINPHARMACOL
*
*
Michel Burnier, MD, Martin Ganslmayer, MD, Franqois Perret, MD, Marinette Porchet, RN, Teddy Kosoglou, PharmD, Ann Gould, PhD, Jurg Nussberger, MD, Bernard Waeber, MD, and Hans R. Brunner, MD Lausanne, Switzerland, and Kenilworth, N J .
Atrial natriuretic peptides (ANP) induce natriuresis, diuresis, and vasodilation and shift volume from the intravascular to the extravascular compartment.'-4 In some circumstances, they also suppress the activity of the renin-angiotensin-aldosterone system.23"hus ANP constitutes a new hormonal system that contributes to the physiologic regulation of body fluid and
From the Division of Hypertension, University Hospital, Lausanne, and the Schering-Plough Corporation, Kenilworth. Supported by grants from the Swiss National Science Foundation, the Cardiovascular Research Foundation, and Schering-Plough Corporation, Kenilworth, N.J. Received for publication Feb. 5, 1991; accepted April 21, 1991. Reprint requests: M. Bumier, MD, Division of Hypertension, CHUV, 1011 Lausanne, Switzerland. 13/1/30463
cardiovascular homeostasis, counterbalancing the vasoconstrictor and sodium-retaining effects of the renin-angiotensin-aldosterone system.6 Plasma ANP levels are increased in several diseases such as cardiac arrhythmias,7 congestive heart failre,^.'' chronic renal f a i l ~ r e , " ~ ~ % c c l m ~ s i aand ,'~ sometimes essential hypertension.14 This suggests that ANP may also be involved in the pathophysiology of these disorders. Several investigators have administered ANP to patients with such diseases in an attempt to enhance salt and water excretion and possibly correct the hemodynamic abnormalities. A natriuretic and diuretic response to exogenous ANP has been obtained in patients with hypertension and In patients with essential hypertension, blood pressure was significantly reduced during a prolonged 5-day infusion of low-dose A N P . ' ~In patients with congestive
CLIN PHARMACOL THER AUGUST 1991
182 Bumier et al. Table I. SCH 34826 in normal volunteers: results of a four-way crossover study Placebo 0 Hours
2 Hours
SCH 34826, 400 rng 0 Hours 2 Hours
Renal effects
GFR (mllmin) U . V (mllmin) U,, . V (pmollmin) U, . V (pmollmin) U,, . V (pmollmin) U,, . V (pmolimin) Up . V (pmollmin) U,,, . V (pmollmin) Hormonal effects
ANP (pmol1L) cGMP (pmollml) UANP . V (pglmin) U,,,, . V (pmolimin) Data are mean values ? SEM (n = 8 in each group). GFR, Glomemlar filtration rate as reflected by the creatinine clearance; U, urinary; V , volume; ANP, atr~alnatriuretic peptides; P, plasma. * D < 0.05 versus time zero. t p < 0.01 versus time zero. $ p < 0.001 versus time zero 8 p < 0.05 versus placebo. 11 p < 0.01 versus placebo
SUBJECTS AND METHODS heart failure, a renal response to the infusion of ANP could also be obtained, sometimes in association with Eight male volunteers with high intakes of sodium a decrease in capillary wedge pressure and systemic were enrolled in this single-blind, placebo-controlled, blood In patients with chronic renal failfour-way crossover study. The subjects were submitted to a complete physical and biologic evaluation beure, the ANP-induced diuresis and natriuresis apfore and after being included in the study. To increase peared to be blunted.20 their baseline plasma ANP levels, they received a The therapeutic benefits that could be derived from treatment with exogenous ANP still need to be demhigh-sodium diet for 5 days before each study day by onstrated. Unfortunately, the clinical use of ANP is the addition of 6 gm NaCl to their regular food. The protocol of these experiments had been reviewed and limited by its very short half-life and its peptidic structure, which does not allow oral admini~tration.~' approved by the local ethics committee (CHUV, LauPharmacologic inhibition of ANP degradation appears sanne, Switzerland). to provide a rational approach to enhance the activity On the day of the experiment, after an overnight of endogenous ANP. ANP is cleared from plasma by fast, each subject was placed in the supine position. A three mechanisms: glomerular filtration, clearance revenous catheter was inserted in a forearm vein for ceptors, and enzymatic processing by the neutral metblood drawing, and each subject received an oral waalloendopeptidase E.C. 3.4.24.1 1 (NEP). Recently, ter load of 10 mllkg to ensure a high urine output. several inhibitors of NEP have been d e v e ~ o ~ e d . ~ ~ .Each ~ ~ subject was asked to empty his bladder spontaWhen administered intravenously, these compounds neously every 30 minutes. After each urine collection, have been shown, in both animal models and humans, the excreted volume was replaced by an equivalent volume of water, augmented by another 30 ml water to retard ANP breakdown and to potentiate the renal and hormonal effects of A N P . ~ ~ . ~ ' to compensate for insensible losses (1 mllmin). When This study is the first evaluation of the renal and two consecutive urinary volumes were within a range systemic hemodynamic effects of SCH 34826, a new of ? 1 mllmin, the volunteer was considered to be in orally active inhibitor of the neutral metalloendopeptisteady state. The end of the second of these two uridase, in normotensive volunteers with high sodium innary collection periods was taken as time zero. From that time on, a fixed amount of water was given orally takes.
VOLUME SO NUMBER 2
SCH 34826, 800 mg 0 Hours 2 Hours
A n inhibitor of atrial natriu~eticfactor degradation 183
SCH 34826, 1600 mg 2 Hours
0 Hours
every 30 minutes, and the volume of this compensation was calculated as the steady-state urine volume + 1 mltmin. At time zero, the subjects were randomly assigned to receive orally either a placebo or 400, 800 or 1600 mg SCH 34826 ((S)-N-(N(- 1(((2,2-dimethyl- l,3-dioxolan-4yl)methoxy)carbonyl)-2-phenylethyl)-L-phenyla1anine)-~-alanine).~~ The placebo and the three single doses of SCH 34826 were given to all subjects at 1-week intervals. After administration of the drug, urine samples were collected every 30 minutes for 5 hours for the measurements of urine volume and urinary electrolyte, cyclic guanosine monophosphate (cGMP) and ANP excretions. Blood pressure and heart rate were monitored at 30-minute intervals. Plasma cGMP and ANP and plasma renin activity (PRA) were determined 30 minutes before administration and at time zero and were repeated 30, 60, 120, 180, 240, and 300 minutes after drug intake. Blood for the determination of serum creatinine and plasma electrolytes was also drawn at time zero and at 60, 120, and 240 minutes. The methods used to measure plasma and urine electrolytes , 3 plasma renin activity,28 and immunoreactive ANP (irANP) levels29 have been described previously. Extracted ANP in urine was determined by radioimmunoassay (Peninsula Laboratories, Inc., Belmont, Calif.). With this method, the mean recovery of added ANP to urine samples was 74.6% -+ 1.7%. The within-assay and between-assay coefficients of variation (CV) were 6.2% and 9. I%, respectively. cGMP in plasma and urine was measured according to the
nonacetylation protocol of Amersham Corp., Arlington Heights, Ill. The mean recovery of added cGMP to plasma or urine was 107.1% :? 4.7%. The withinassay CV of 17 plasmas was 8.9% and the betweenassay CV was 10.4%. The CV from 50 urine samples was 6.8% within assays and 10 9% between assays, respectively. Cumulative urinary sodium, potassium, and phosphate excretions were calculated as the amount of sodium, potassium, or phosphate eliminated during 5 hours after subtraction of the steadystate excretion. Statistics. The statistical evaluation of the results was based on a two-way analysis of variance followed by a least significant difference test when appropriate. Both the differences within and between the doses were examined. The results are expressed as mean values ? SEM. RESULTS During the 5 hours of observation there was no significant modification of blood pressure and heart rate in these normotensive subjects after the administration of 400, 800, or 1600 mg SCH 34826. The baseline and peak renal and hormonal effects of SCH 34826 are presented in Table I, and the statistical analysis of the curves corresponding to the various doses is shown in Table 11. Creatinine clearance was unchanged during NEP inhibition. As shown in Fig. 1, upper panel, a significant and dose-dependent increase in urinary sodium excretion was observed after administration of the NEP inhibitor. Over 5 hours, the cumulative sodium excretion was increased with all
C I J N I'HARMACOL THER AUGUST 1991
Urinary sodium (umol/mln)
Cumulative Na excretion (mmol)
1
35 30 -
25 20 15105-
01 0
I
1
2
3
4
5
Hours Fig. 1. Effects of placebo (0) or of 400 (A), 800 (A), and 1600 mg (@) SCH 34826 on urinary sodium excretion in eight volunteers with high intakes of sodium. The excretion rate is shown in the upper panel and the cumulative sodium excretion over baseline in the lower panel. When compared with time zero, significant increases in sodium excretion rate were observed with 400 @ < 0.05), 800 @ < 0.001), and 1600 mg SCH 34826 @ < 0.01). The statistical analysis of the lower panel is shown in Table 11. All values are mean 2 SEM. For the purpose of clarity, SEM are indicated only for the placebo and the 1600 mg dose.
three doses of SCH 34826 compared with the placebo (+ 15.7 5 7.3 mmol) but only with the two highest doses of 800 (+26.7 + 6 mmol, p < 0.05) and 1600 mg (+30.9 5 6.8 mmol, p < 0.01) did the changes
achieve statistical significance (Fig. 1, lower panel). The peak natriuretic effect of SCH 34826 was reached at 2 hours after drug administration. The duration of the natriuresis was longer after the dose of 1600 mg
VOLUME 50 NUMBER 2
A n inhibitor of atrial natriureticfactor deg-radation 185
than the duration after the smaller doses. A dosedependent elevation of the urinary sodiumicreatinine ratio was seen at peak effect with the 3 doses of SCH 34826. Indeed, the sodiumicreatinine ratio increased within 2 hours from 30.4 + 5.8 to 34.1 +- 3.1 in the placebo group compared with 30.8 ? 3.2 to 40.2 2 2.8 at 400 mg, 29.2 + 2.6 to 40 F 3.9 at 800 mg, and 36.7 + 5.2 to 52.9 ? 10 at 1600 mg SCH 34826. The diuretic effect of SCH 34826 was weak in this study. Urine output increased from 13.6 + 1 to 16.1 + 1.3 mlimin with the highest dose of SCH 34826, but the difference did not reach statistical significance when compared with the placebo group (Tables I and 11). SCH 34826 had no effect on potassium excretion. In contrast, urinary phosphate and calcium excretions were significantly increased after administration of the 3 doses of SCH 34826, as illustrated in Fig. 2. Over 5 hours, the cumulative phosphate excretion was 0.28 2 0.4 mmol with the placebo and 1.55 2 0.3 (p < 0.01), 1.95 + 0.3 ( p < 0.01), and 2.41 -+ 0.43 mmol 0, < 0.01) for the 400, 800, and 1600 mg SCH 34826 doses, respectively. In contrast to sodium excretion, the SCH 34826-induced increase in phosphate excretion was still present 5 hours after the administration of the drug. Uric acid excretion was unaffected by the administration of SCH 34826. Interestingly, plasma irANP levels did not increase with NEP inhibition by SCH 34826 whatever the dose (Fig. 3, upper panel). In the urine, however, a clear dose-dependent elevation of irANP excretion was found during the period of observation (Fig. 3, lower panel). Plasma cGMP levels were significantly increased between the second and the fourth hour after the administration of 800 and 1600 mg SCH 34826 (Fig. 4, upper panel). A significant and dosedependent increase in urinary cGMP was observed during inhibition of NEP with SCH 34826 (Fig. 4, lower panel). A significant correlation was obtained between the urinary excretion of irANP and cGMP (r = 0.52, n = 384, p < 0.001). Plasma electrolytes, glucose, creatinine, liver function tests, or routine hematology and urinary indexes were unchanged after administration of SCH 34826. One volunteer experienced an hypotensive malaise 5 hours after the 1600 mg SCH 34826 dose. No other adverse symptom was reported by any of the subjects.
DISCUSSION SCH 34826 is the orally active pro-drug of the NEP inhibitor SCH 32615. This latter has been shown to inhibit purified kidney and brain NEP effectively with ~ spontaneously hypertensive a ki of 19 n m o l l ~In. ~the
Table 11. Statistical evaluation of the dose effect of SCH 34826 by comparing the entire curves to the placebo in a two-way analysis of variance SCH 34826 400 mg
U .V UN, . v
Na cumulative U,, U,
.V
.V u,., . v
Up . V
Uurlc x t d
.V
GFR pANP pcGMP UANP. v U'CMP ' V
KO0 mg
1600 trig
NS 0.05 NS NS NS 0.01 NS NS NS NS NS 0.05 0.05
U , Urinary: V . volume: NS. not \~pnilicant. P. plasma. GFR. glomerular filtration rats: ANP. atrlal natriuretlc pcpt~des.
rat, SCH 34826 (10 to 90 mgikg, administered subcutaneously) potentiates both the hypotensive and the renal effects of ANP, whereas in the deoxycorticosterone acetate- sodium hypertensi~e rat, SCH 34826 (10 or 90 mglkg, administered orally) significantly reduces blood pressure.25 The results of the present study demonstrate that orally administered SCH 34826 produces a significant increase in urinary sodium, phosphate, and calcium excretion in normotensive volunteers with high sodium intakes without affecting the renal handling of potassium and uric acid and in the absence of any change in systemic blood pressure. Moreover, they also show that the renal response to SCH 34826 can occur without any concurrent rise in plasma ANP levels, but with a significant elevation of urinary ANP and cGMP excretion. SCH 34826 caused a dose-dependent increase in sodium excretion with a marked and sustained effect at the 1600 mg dose. With all doses, the peak effect on renal electrolyte excretion was observed between 1YZ and 2Y2 hours after administration of the drug. Increasing the dose seemed to prolong the natriuretic effect. By comparison, the maximal urinary sodium excretion obtained with 1600 mg SCH 34826 corresponds to the natriuresis obtained previously in volunteers on a high-salt diet with the infusion of exogenous ANP at a dose of 0.5 @min." SCH 34826 does not appear to promote sodium excretion primarily by a hemodynamic effect because glomerular filtration rate, estimated by the changes in creatinine clearance, was unaffected even by the high
CIJN PHARMACOL THER AUGUSI' 1991
Urinary phosphate (umol/mln)
Urinary calcium
Hours
(umol/mIn)
41
Moan f SEM
Hours
Fig. 2. Changes in urinary phosphate (upper panel) and calcium (lower panel) excretion induced by a placebo (0)or by 400 (A), 800 (A), and 1600 mg ( 0 ) SCH 34826 in volunteers with high intakes of sodium. The statistical analysis of the curves is given in Table 11. When compared with time zero, significant increases in phosphate excretion were found with 400 (p < 0.05), 800 (p < 0.01), and 1600 mg SCH 34826 (p < 0.01). Increases in calcium excretion were significant with only the 400 mg (p < 0.01) and 1600 mg doses @ < 0.01).
dose of SCH 34826. This observation is supported by a recent dog study in which no change in glomerular filtration rate was observed during NEP inhibiti~n.~' Nonetheless, it is impossible to rule out the occurrence of subtle changes in glomerular filtration rate which might have been undetectable by the usual cre-
atinine clearance technique. The increase in the urinary sodiurn/creatinine ratio is compatible with an elevation of the fractional excretion of sodium and therefore points to a tubular effect of SCH 34826. In the absence of specific markers for the proximal reabsorption of sodium, it is not possible to determine
VOLUME SO NUMBER 2
An inhibitor of atrial natn'ureticfactor degradation 18 7
Plasma ANP
-2
0
2
Urinary ANP
i
6
8
10
Hours
(pg/min) 40 1
Hours Fig. 3. Effect of SCH 34826 on plasma (upper panel) and urinary atrial natriuretic peptide (ANP; lower panel). Only the changes in plasma ANP observed under placebo (0)or 1600 mg ( 0 ) SCH 34826 are shown. Significant increases in urinary ANP were found with 400 mg (A; p < 0.05), 800 mg (A; p < 0.01), and 1600 mg SCH 34826 @ < 0.001) when compared with time zero. The statistical analysis of the curves is shown in Table 11.
whether the drug-induced natriuresis observed in this study is caused by a proximal or a distal tubular effect of the compound. A clear dose-dependent increase in phosphaturia was found with NEP inhibition in our volunteers. The effect of SCH 34826 on phosphate excretion is more prolonged than that on sodium excretion and follows
closely the profile of cGMP excretion. The mechanism whereby SCH 34826 promotes phosphate excretion cannot be appreciated precisely from our findings. The ability of a neutral endopeptidase inhibitor to increase phosphaturia therefore deserves further specific investigations. On the other hand, a slight but significant increase in urinary calcium excretion was no-
CLIN PHARMACOL TIIEK AUGUST 1991
188 Bumieretal.
Hours Urinary cGMP
Mean f SEM
Hours
Fig. 4. Effect of SCH 34826 on plasma (upper panel) and urinary cyclic guanosine monophosphate (cGMP; lower panel). Isolated significant increases in plasma cGMP were observed with the 800 mg (A) and 1600 mg (@) doses when compared with placebo (0). When compared with time zero, significant increases in urinary cGMP were found at 400 (A; p < 0.05), 800 ( p < 0.01), and 1600 mg @ < 0.001). The statistical evaluation of the curves is given in Table 11.
ticed. The pattern of electrolyte excretion observed in this study suggests that the renal response to NEP inhibition is similar to that obtained with the infusion of a low dose of exogenous ANP. Interestingly, the natriuresis induced by oral administration of SCH 34826 occurred in the absence of any
change in plasma ANP levels, whereas there was at the same time a dose-dependent increase in urinary ANP and cGMP excretion. This hormonal response to SCH 34826 contrasts with the results published for other NEP inhibitors in normal subjects and patients with congestive heart f a i l ~ r e . ~In~ these . ~ ~ studies,
V O L U M E SO NUMBER 2
A n inhibitor of atrial natriuretic factor depadation
189
plasma ANP levels were significantly increased during lated to an increase in renal ANP activity. Urinary NEP inhibition. However, our observation is in accorcGMP increased markedly and dose-dependently at a dance with the results of several animal studies in time when plasma cGMP was only slightly elevated. which SCH 34826 or analog compounds produced a This observation may indicate that cGMP like ANP is natriuresis without affecting plasma ANP ~ e v e l s . ~ ~ - ~ ' generated within the kidney because both NEP and This discrepancy does not seem to be specific to SCH guanylate cyclase- linked ANP receptors have been 34826 because a similar phenomenon has now been described at this site.36 Finally, the natriuretic effect reported with other NEP inhibitor^.^',^^ of SCH 34826 is not likely to be attributable to the inhibition of other enzymatic processes, in particular the There are several potential explanations for the disinhibition of angiotensin converting enzyme. Indeed, sociation between plasma and urinary ANP. The first hypothesis postulates that inhibition of ANP metaboin vitro, SCH 32615, the active metabolite of SCH 34826, is devoid of any activity against angiotensin lism by SCH 34826 occurs only at critical sites, for example, in the brush border of the proximal tubule. converting enzyme at concentrations up to 10 prnoli~.~~ The consecutive elevation of local tissue and urinary ANP could then mediate the response to the inhibitor. SCH 34826 had a weak, if any diuretic effect in our subjects, who had ingested large amounts of water. Recent experimental studies in the rat, in which urinary cGMP increased when plasma ANP levels This poor effect on diuresis is certainly not explained by the high baseline urine output because urine volwere not altered, tend to support this idea.25,31 The ume can increase up to 20 mllmin in normal volunlack of change in plasma ANP under NEP inhibition ~ , ~observa~ teers, as shown in previous s t ~ d i e s .This may also be accounted for by the ability of an efficient tion is more likely caused by a weak potentiation of C-receptor mechanism to clear ANP from the plasma endogenous ANP. As mentioned earlier, the natriafter inhibition of its enzymatic degradation. Recent uretic response to 1600 mg SCH 34826 is approxistudies in which the pharmacokinetics of ANP were mately equivalent to that obtained in similar condievaluated during separate or combined inhibition of tions with the infusion of 0.5 pglmin ANP. At this NEP and C-receptors tend to support this latter hydose of exogenous ANP, the natriuresis was obtained p~thesis.~~ in the absence of any change in urine flow rate." What kind of evidence do we have that SCH 34826 Finally, SCH 34826 had no influence on blood acted mainly by an ANP-mediated mechanism? Bepressure and heart rate in our normotensive subjects. sides ANP, the neutral metalloendopeptidase 24.1 1 is This is not surprising if one considers that decreases in involved in the metabolism of several other peptides blood pressure have, in our experience, been observed including kinins, angiotensins, enkephalins, and neuonly with rather high doses of exogenous ANP. Nevrot ens in^.^^ It could thus be argued that part of the ertheless, one volunteer experienced a malaise 5 hours drug-induced natriuresis is caused by an effect of SCH after the administration of 1600 mg SCH 34826. This 34826 on these hormonal systems. Although such a episode was similar to those seen previously during possibility cannot be entirely ruled out, there is some ANP infusions. evidence that the contribution, if any, of other pepIn conclusion, the findings of this study demontides is small. In spontaneously hypertensive rats, strate that the orally active NEP inhibitor SCH 34826 SCH 34826 does not modify the blood pressure repromotes sodium excretion in normotensive volunteers sponse to angiotensin I, angiotensin 11, or bradykinin, with high intakes of sodium. This effect is associated whereas thiorphan, a dual ACE and NEP inhibitor, with increases in urinary phosphate and calcium expotentiates the depressor response to bradykinin.25,35 cretion but with no change in kaliuresis. The renal reFurthermore, administration of a bradykinin antagosponse to SCH 34826 appears to be related mainly to nist failed to alter the fall in blood pressure induced by the potentiation of endogenous ANP in the kidney as SCH 34826 in deoxycorticosterone acetate-sodium suggested by the marked elevation of urinary ANP hypertensive rats." In our normal volunteers, several and cGMP excretion when plasma ANP is unchanged. observations also point to a main impact of SCH 34826 on ANP metabolism. Thus, positive correlations were found not only between urinary ANP and References cGMP but also between urinary cGMP and sodium 1. De Bold AJ, Borenstein HB, Veress AT, Sonnenberg and phosphate excretion. These correlations do not asH. A rapid and potent natriuretic response to intravecertain a causal relationship but nevertheless support nous injection of atrial myocardial extracts in rats. Life Sci 1981;28:89-94. the idea that the renal effects of SCH 34826 are re-
CLIN PHARMACUL THEK AUGUST 1991
2. Richards AM, Ikram H, Yandle TG, Nicholls MG, Webster MWI, Espiner EA. Renal, haemodynamic and hormonal effects of human a-atrial natriuretic peptide in healthy volunteers. Lancet 1985;1:545-548. 3. Biollaz J, Nussberger J, Porchet M, et al. Four-hour infusion of synthetic atrial natriuretic peptide in normal volunteers. Hypertension 1986;8(suppl II):II96-11105. 4. Fluckiger JP, Waeber B, Matsueda GR, Delaloye B, Nussberger J, Brunner HR. Effect of atriopeptin I11 on hematocrit and volemia of nephrectomized rats. Am J Physiol 1986;251:H880-H883. 5. Tikkanen I, Fyhrquist F, Metsarinne K, Leidenius R. Plasma atrial natriuretic peptide in cardiac disease and during infusion in healthy volunteers. Lancet 1985;2:66-9. 6. Espiner EA, Richards AM. Atrial natriuretic peptide. An important factor in sodium and blood pressure regulation. Lancet 1989;1:707-10. 7. Tikkanen I, Metsarinne K, Fyhrquist F. Atrial natriuretic peptide in paroxysmal supraventricular tachycardia. Lancet 1985;2:40-1. 8. Bumett JC, Kao PC, Hu DC, et al. Atrial natriuretic peptide elevation in congestive heart failure in the human. Science 1986;231: 1145-7. 9. Cody RJ, Atlas SA, Laragh JH, et al. Atrial natriuretic factor in normal subjects and heart failure patients. Plasma levels and renal, hormonal and hemodynamic responses to peptide infusion. J Clin Invest 1986;78:1362-74. 10. Raine AEG, Erne P, Burgisser E, et al. Atrial natriuretic peptide and atrial pressure in patients with congestive heart failure. N Engl J Med 1986;315:533-7. 11. Saxenhofer H, Gnadinger MP, Weidmann P, et al. Plasma levels and dialysance of atrial natriuretic peptide in terminal renal failure. Kidney Int 1987;32:55461. 12. Shenker Y, Port FK, Swartz RD, Gross MD, Grekin RJ. Atrial natriuretic hormone secretion in patients with renal failure. Life Sci 1987;41:1635-44. 13. Fievet P, Fournier A, De Bold A, et al. Atrial natriuretic factor in pregnancy-induced hypertension and preeclampsia: increased plasma concentrations possibly explaining these hypovolemic states with paradoxical hyporeninism. Am J Hypertens 1988;1: 16-22. 14. MacGregor GA, Sagnella GA, Markandu ND, et al. Raised plasma levels of atrial natriuretic peptide in subjects with untreated essential hypertension. J Hypertens 1986;4:(suppl 6):S567-S568. 15. Richards AM, Nicholls MG, Espiner EA, et al. Effects of a-human atrial natriuretic peptide in essential hypertension. Hypertension 1985;7:812-7. 16. Weidmann P, Gnadinger MP, Ziswiler HR, et al. Cardiovascular, endocrine and renal effects of atrial natiuretic peptide in essential hypertension. J Hypertens 1986;4(suppl 2):S7 1-S83. 17. Petrillo A, Scherrer U, Gonvers JJ, et al. Atrial natriuretic peptide administered as intravenous infusion or
bolus injection to patients with liver cirrhosis and ascites. J Cardiovasc Pharmacol 1988;12:279-85. 18. Janssen WMT, De Zeeuw DD, Vanderhern GK, De Jong PE. Antihypertensive effect of a 5-day infusion of atrial natriuretic factor in humans. Hypertension 1989;131640-6. 19. Goy JJ, Waeber B, Nussberger J, et al. Infusion of atrial natriuretic peptide to patients with congestive heart failure. J Cardiovasc Pharmacol 1988;12:562-70. 20. Burnier M, Mooser V, Wauters JP, et al. Bolus injections of synthetic atrial natriuretic peptide in patients with chronic renal failure or nephrotic syndrome. J Cardiovasc Pharmacol 1989;13:682-90. 21. Biollaz J, Callahan LT, Nussberger J , et al. Pharmacokinetics of synthetic atrial natriuretic peptides in normal man. CLINPHARMACOL THER1987;4 1:67 1-7. 22. Chipkin RE, Berger JG, Billard W, lorio LC, Chapman R, Barnett A. Pharmacology of SCH 34826, an orally active enkephalinase inhibitor analgesic. J Pharmacol Exp Ther 1988;245:829-38. 23. Seymour AA, Fennel1 SA, Swerdel JN. Potentiation of renal effects of atrial natriuretic factor-(99-126) by SQ 29072. Hypertension 1989;14:87-97. 24. Northridge DB, Jardine AG, Alabaster CT, et al. Effect of UK 69578: a novel atriopeptidase inhibitor. Lancet 1989;2:591-3. 25. Sybertz EJ, Chiu PJS, Vemulapalli S, Watkins R, Haslanger MF. Atrial natriuretic factor-potentiating and antihypertensive activity of SCH 34826, an orally active neutral metalloendopeptidase inhibitor. Hypertension 1990; 15: 152-61. 26. Richards M, Espiner E, Frampton C, et al. Inhibition of endopeptidase EC 24.11 in human. Renal and endocrine effects. Hypertension 1990;16:269-76. 27. Gros C, Souque A, Schwartz JC, et al. Protection of atrial natriuretic factor against degradation: diuretic and natriuretic responses after in vivo inhibition of enkephalinase (EC 3.4.24.1 1) by acetorphan. Proc Natl Acad Sci USA 1989;86:7580-4. 28. Nussberger J, Fasanella d'Amore T, Porchet M, et al. Repeated administration of the converting enzyme inhibitor cilazapril to normal volunteers. J Cardiovasc Pharmacol 1987;9:39-44. 29. Nussberger J, Mooser V, Maridor G, Juillerat L, Waeber B, Brunner HR. Caffeine induced diuresis and atrial natriuretic peptides. J Cardiovasc Pharmacol 1990;15:685-91. 30. Margulies KB, Cavero PG, Seymour AA, Delaney NG, Burnett JC Jr. Neutral endopeptidase inhibition potentiates the renal actions of atrial natriuretic factor. Kidney Int 1990;38:67-72. 31. Sybertz EJ, Chiu PJS, Vemulapalli S, et al. SCH 39370, a neutral metalloendopeptidase inhibitor potentiates biological responses to atrial natriuretic factor and lowers blood pressure in desoxycorticosterone acetatesodium hypertensive rats. J Pharmacol Exp Ther l989;250:624-3 1.
VOLUME 50 NUMBER 2
A n inhibitor of atrial natriuretic factor de~radation 191
32. Olins GM, Krieter PA, Trapani AJ, Spear KL, Bovy PR. Specific inhibitors of endopeptidase 24.11 inhibit the metabolism of atrial natriuretic peptides in vitro and in vivo. Mol Cell Endocrinol l989;6 1:20 1-8. 33. Sybertz EJ, Chiu PJS, Watkins RW, Vemulapalli S. Neutral metalloendopeptidase inhibition: a novel means of circulatory modulation. J Hypertens [In press]. 34. Erdos EG, Skidgel RA. Neutral endopeptidase 24.1 1 (enkephalinase) and related regulators of peptide hormones. FASEB J 1989;3:145-51. 35. Baum T, Becker FT, Sybertz EJ, Sabin C, Desiderio
DM. Enkephalinase "A" inhibition by thiorphan: central and peripheral cardiovascular effects. Eur J Pharmacol 1983;94:85-91. 36. Shima M, Seino Y , Torikai S, Imai M. Intrarenal localization of degradation of atrial natriuretic peptide in isolated glomeruli and cortical nephron segments. Life Sci 1988;43:357-63. 37. Biollaz J, Bidiville J, DiCzi J , et al Site of the action of a synthetic atrial natriuretic peptide evaluated in humans. Kidney Int 1987;32:537-46.
Bound volumes available to subscribers
Bound volumes of CLINICAL PHARMACOLOGY & THERAPELTICS are available to subscribers (only) for the 1991 issues from the Publisher, at a cost of $43.00 for domestic, $59.01 for Canadian, and $56.00 for international subscribers for Vol. 49 (Januarp-June) and Vol. 50 (July-December). Shipping charges are included. Each bound volume contains a subject and author index and all advertising is removed. Copies are shipped within 60 days after the publication of the last issue of the volume. The binding is durable buckram with the journal name, volume number, and year stamped in gold on the spine. Payment must accompamy all mden. Contact Mosb!l-Year Book, Inc., Subscription Services, 11830 Westline Industrial Drive, St. Louis, MO 63146-3318, USA; phone (800)325-4177, ext. 4351. Subscriptions must be in force to qualify. Bound volumes are not available in place of a regular journal subscription.
*
*
Michel Burnier, MD, Martin Ganslmayer, MD, Franqois Perret, MD, Marinette Porchet, RN, Teddy Kosoglou, PharmD, Ann Gould, PhD, Jurg Nussberger, MD, Bernard Waeber, MD, and Hans R. Brunner, MD Lausanne, Switzerland, and Kenilworth, N J .
Atrial natriuretic peptides (ANP) induce natriuresis, diuresis, and vasodilation and shift volume from the intravascular to the extravascular compartment.'-4 In some circumstances, they also suppress the activity of the renin-angiotensin-aldosterone system.23"hus ANP constitutes a new hormonal system that contributes to the physiologic regulation of body fluid and
From the Division of Hypertension, University Hospital, Lausanne, and the Schering-Plough Corporation, Kenilworth. Supported by grants from the Swiss National Science Foundation, the Cardiovascular Research Foundation, and Schering-Plough Corporation, Kenilworth, N.J. Received for publication Feb. 5, 1991; accepted April 21, 1991. Reprint requests: M. Bumier, MD, Division of Hypertension, CHUV, 1011 Lausanne, Switzerland. 13/1/30463
cardiovascular homeostasis, counterbalancing the vasoconstrictor and sodium-retaining effects of the renin-angiotensin-aldosterone system.6 Plasma ANP levels are increased in several diseases such as cardiac arrhythmias,7 congestive heart failre,^.'' chronic renal f a i l ~ r e , " ~ ~ % c c l m ~ s i aand ,'~ sometimes essential hypertension.14 This suggests that ANP may also be involved in the pathophysiology of these disorders. Several investigators have administered ANP to patients with such diseases in an attempt to enhance salt and water excretion and possibly correct the hemodynamic abnormalities. A natriuretic and diuretic response to exogenous ANP has been obtained in patients with hypertension and In patients with essential hypertension, blood pressure was significantly reduced during a prolonged 5-day infusion of low-dose A N P . ' ~In patients with congestive
CLIN PHARMACOL THER AUGUST 1991
182 Bumier et al. Table I. SCH 34826 in normal volunteers: results of a four-way crossover study Placebo 0 Hours
2 Hours
SCH 34826, 400 rng 0 Hours 2 Hours
Renal effects
GFR (mllmin) U . V (mllmin) U,, . V (pmollmin) U, . V (pmollmin) U,, . V (pmollmin) U,, . V (pmolimin) Up . V (pmollmin) U,,, . V (pmollmin) Hormonal effects
ANP (pmol1L) cGMP (pmollml) UANP . V (pglmin) U,,,, . V (pmolimin) Data are mean values ? SEM (n = 8 in each group). GFR, Glomemlar filtration rate as reflected by the creatinine clearance; U, urinary; V , volume; ANP, atr~alnatriuretic peptides; P, plasma. * D < 0.05 versus time zero. t p < 0.01 versus time zero. $ p < 0.001 versus time zero 8 p < 0.05 versus placebo. 11 p < 0.01 versus placebo
SUBJECTS AND METHODS heart failure, a renal response to the infusion of ANP could also be obtained, sometimes in association with Eight male volunteers with high intakes of sodium a decrease in capillary wedge pressure and systemic were enrolled in this single-blind, placebo-controlled, blood In patients with chronic renal failfour-way crossover study. The subjects were submitted to a complete physical and biologic evaluation beure, the ANP-induced diuresis and natriuresis apfore and after being included in the study. To increase peared to be blunted.20 their baseline plasma ANP levels, they received a The therapeutic benefits that could be derived from treatment with exogenous ANP still need to be demhigh-sodium diet for 5 days before each study day by onstrated. Unfortunately, the clinical use of ANP is the addition of 6 gm NaCl to their regular food. The protocol of these experiments had been reviewed and limited by its very short half-life and its peptidic structure, which does not allow oral admini~tration.~' approved by the local ethics committee (CHUV, LauPharmacologic inhibition of ANP degradation appears sanne, Switzerland). to provide a rational approach to enhance the activity On the day of the experiment, after an overnight of endogenous ANP. ANP is cleared from plasma by fast, each subject was placed in the supine position. A three mechanisms: glomerular filtration, clearance revenous catheter was inserted in a forearm vein for ceptors, and enzymatic processing by the neutral metblood drawing, and each subject received an oral waalloendopeptidase E.C. 3.4.24.1 1 (NEP). Recently, ter load of 10 mllkg to ensure a high urine output. several inhibitors of NEP have been d e v e ~ o ~ e d . ~ ~ .Each ~ ~ subject was asked to empty his bladder spontaWhen administered intravenously, these compounds neously every 30 minutes. After each urine collection, have been shown, in both animal models and humans, the excreted volume was replaced by an equivalent volume of water, augmented by another 30 ml water to retard ANP breakdown and to potentiate the renal and hormonal effects of A N P . ~ ~ . ~ ' to compensate for insensible losses (1 mllmin). When This study is the first evaluation of the renal and two consecutive urinary volumes were within a range systemic hemodynamic effects of SCH 34826, a new of ? 1 mllmin, the volunteer was considered to be in orally active inhibitor of the neutral metalloendopeptisteady state. The end of the second of these two uridase, in normotensive volunteers with high sodium innary collection periods was taken as time zero. From that time on, a fixed amount of water was given orally takes.
VOLUME SO NUMBER 2
SCH 34826, 800 mg 0 Hours 2 Hours
A n inhibitor of atrial natriu~eticfactor degradation 183
SCH 34826, 1600 mg 2 Hours
0 Hours
every 30 minutes, and the volume of this compensation was calculated as the steady-state urine volume + 1 mltmin. At time zero, the subjects were randomly assigned to receive orally either a placebo or 400, 800 or 1600 mg SCH 34826 ((S)-N-(N(- 1(((2,2-dimethyl- l,3-dioxolan-4yl)methoxy)carbonyl)-2-phenylethyl)-L-phenyla1anine)-~-alanine).~~ The placebo and the three single doses of SCH 34826 were given to all subjects at 1-week intervals. After administration of the drug, urine samples were collected every 30 minutes for 5 hours for the measurements of urine volume and urinary electrolyte, cyclic guanosine monophosphate (cGMP) and ANP excretions. Blood pressure and heart rate were monitored at 30-minute intervals. Plasma cGMP and ANP and plasma renin activity (PRA) were determined 30 minutes before administration and at time zero and were repeated 30, 60, 120, 180, 240, and 300 minutes after drug intake. Blood for the determination of serum creatinine and plasma electrolytes was also drawn at time zero and at 60, 120, and 240 minutes. The methods used to measure plasma and urine electrolytes , 3 plasma renin activity,28 and immunoreactive ANP (irANP) levels29 have been described previously. Extracted ANP in urine was determined by radioimmunoassay (Peninsula Laboratories, Inc., Belmont, Calif.). With this method, the mean recovery of added ANP to urine samples was 74.6% -+ 1.7%. The within-assay and between-assay coefficients of variation (CV) were 6.2% and 9. I%, respectively. cGMP in plasma and urine was measured according to the
nonacetylation protocol of Amersham Corp., Arlington Heights, Ill. The mean recovery of added cGMP to plasma or urine was 107.1% :? 4.7%. The withinassay CV of 17 plasmas was 8.9% and the betweenassay CV was 10.4%. The CV from 50 urine samples was 6.8% within assays and 10 9% between assays, respectively. Cumulative urinary sodium, potassium, and phosphate excretions were calculated as the amount of sodium, potassium, or phosphate eliminated during 5 hours after subtraction of the steadystate excretion. Statistics. The statistical evaluation of the results was based on a two-way analysis of variance followed by a least significant difference test when appropriate. Both the differences within and between the doses were examined. The results are expressed as mean values ? SEM. RESULTS During the 5 hours of observation there was no significant modification of blood pressure and heart rate in these normotensive subjects after the administration of 400, 800, or 1600 mg SCH 34826. The baseline and peak renal and hormonal effects of SCH 34826 are presented in Table I, and the statistical analysis of the curves corresponding to the various doses is shown in Table 11. Creatinine clearance was unchanged during NEP inhibition. As shown in Fig. 1, upper panel, a significant and dose-dependent increase in urinary sodium excretion was observed after administration of the NEP inhibitor. Over 5 hours, the cumulative sodium excretion was increased with all
C I J N I'HARMACOL THER AUGUST 1991
Urinary sodium (umol/mln)
Cumulative Na excretion (mmol)
1
35 30 -
25 20 15105-
01 0
I
1
2
3
4
5
Hours Fig. 1. Effects of placebo (0) or of 400 (A), 800 (A), and 1600 mg (@) SCH 34826 on urinary sodium excretion in eight volunteers with high intakes of sodium. The excretion rate is shown in the upper panel and the cumulative sodium excretion over baseline in the lower panel. When compared with time zero, significant increases in sodium excretion rate were observed with 400 @ < 0.05), 800 @ < 0.001), and 1600 mg SCH 34826 @ < 0.01). The statistical analysis of the lower panel is shown in Table 11. All values are mean 2 SEM. For the purpose of clarity, SEM are indicated only for the placebo and the 1600 mg dose.
three doses of SCH 34826 compared with the placebo (+ 15.7 5 7.3 mmol) but only with the two highest doses of 800 (+26.7 + 6 mmol, p < 0.05) and 1600 mg (+30.9 5 6.8 mmol, p < 0.01) did the changes
achieve statistical significance (Fig. 1, lower panel). The peak natriuretic effect of SCH 34826 was reached at 2 hours after drug administration. The duration of the natriuresis was longer after the dose of 1600 mg
VOLUME 50 NUMBER 2
A n inhibitor of atrial natriureticfactor deg-radation 185
than the duration after the smaller doses. A dosedependent elevation of the urinary sodiumicreatinine ratio was seen at peak effect with the 3 doses of SCH 34826. Indeed, the sodiumicreatinine ratio increased within 2 hours from 30.4 + 5.8 to 34.1 +- 3.1 in the placebo group compared with 30.8 ? 3.2 to 40.2 2 2.8 at 400 mg, 29.2 + 2.6 to 40 F 3.9 at 800 mg, and 36.7 + 5.2 to 52.9 ? 10 at 1600 mg SCH 34826. The diuretic effect of SCH 34826 was weak in this study. Urine output increased from 13.6 + 1 to 16.1 + 1.3 mlimin with the highest dose of SCH 34826, but the difference did not reach statistical significance when compared with the placebo group (Tables I and 11). SCH 34826 had no effect on potassium excretion. In contrast, urinary phosphate and calcium excretions were significantly increased after administration of the 3 doses of SCH 34826, as illustrated in Fig. 2. Over 5 hours, the cumulative phosphate excretion was 0.28 2 0.4 mmol with the placebo and 1.55 2 0.3 (p < 0.01), 1.95 + 0.3 ( p < 0.01), and 2.41 -+ 0.43 mmol 0, < 0.01) for the 400, 800, and 1600 mg SCH 34826 doses, respectively. In contrast to sodium excretion, the SCH 34826-induced increase in phosphate excretion was still present 5 hours after the administration of the drug. Uric acid excretion was unaffected by the administration of SCH 34826. Interestingly, plasma irANP levels did not increase with NEP inhibition by SCH 34826 whatever the dose (Fig. 3, upper panel). In the urine, however, a clear dose-dependent elevation of irANP excretion was found during the period of observation (Fig. 3, lower panel). Plasma cGMP levels were significantly increased between the second and the fourth hour after the administration of 800 and 1600 mg SCH 34826 (Fig. 4, upper panel). A significant and dosedependent increase in urinary cGMP was observed during inhibition of NEP with SCH 34826 (Fig. 4, lower panel). A significant correlation was obtained between the urinary excretion of irANP and cGMP (r = 0.52, n = 384, p < 0.001). Plasma electrolytes, glucose, creatinine, liver function tests, or routine hematology and urinary indexes were unchanged after administration of SCH 34826. One volunteer experienced an hypotensive malaise 5 hours after the 1600 mg SCH 34826 dose. No other adverse symptom was reported by any of the subjects.
DISCUSSION SCH 34826 is the orally active pro-drug of the NEP inhibitor SCH 32615. This latter has been shown to inhibit purified kidney and brain NEP effectively with ~ spontaneously hypertensive a ki of 19 n m o l l ~In. ~the
Table 11. Statistical evaluation of the dose effect of SCH 34826 by comparing the entire curves to the placebo in a two-way analysis of variance SCH 34826 400 mg
U .V UN, . v
Na cumulative U,, U,
.V
.V u,., . v
Up . V
Uurlc x t d
.V
GFR pANP pcGMP UANP. v U'CMP ' V
KO0 mg
1600 trig
NS 0.05 NS NS NS 0.01 NS NS NS NS NS 0.05 0.05
U , Urinary: V . volume: NS. not \~pnilicant. P. plasma. GFR. glomerular filtration rats: ANP. atrlal natriuretlc pcpt~des.
rat, SCH 34826 (10 to 90 mgikg, administered subcutaneously) potentiates both the hypotensive and the renal effects of ANP, whereas in the deoxycorticosterone acetate- sodium hypertensi~e rat, SCH 34826 (10 or 90 mglkg, administered orally) significantly reduces blood pressure.25 The results of the present study demonstrate that orally administered SCH 34826 produces a significant increase in urinary sodium, phosphate, and calcium excretion in normotensive volunteers with high sodium intakes without affecting the renal handling of potassium and uric acid and in the absence of any change in systemic blood pressure. Moreover, they also show that the renal response to SCH 34826 can occur without any concurrent rise in plasma ANP levels, but with a significant elevation of urinary ANP and cGMP excretion. SCH 34826 caused a dose-dependent increase in sodium excretion with a marked and sustained effect at the 1600 mg dose. With all doses, the peak effect on renal electrolyte excretion was observed between 1YZ and 2Y2 hours after administration of the drug. Increasing the dose seemed to prolong the natriuretic effect. By comparison, the maximal urinary sodium excretion obtained with 1600 mg SCH 34826 corresponds to the natriuresis obtained previously in volunteers on a high-salt diet with the infusion of exogenous ANP at a dose of 0.5 @min." SCH 34826 does not appear to promote sodium excretion primarily by a hemodynamic effect because glomerular filtration rate, estimated by the changes in creatinine clearance, was unaffected even by the high
CIJN PHARMACOL THER AUGUSI' 1991
Urinary phosphate (umol/mln)
Urinary calcium
Hours
(umol/mIn)
41
Moan f SEM
Hours
Fig. 2. Changes in urinary phosphate (upper panel) and calcium (lower panel) excretion induced by a placebo (0)or by 400 (A), 800 (A), and 1600 mg ( 0 ) SCH 34826 in volunteers with high intakes of sodium. The statistical analysis of the curves is given in Table 11. When compared with time zero, significant increases in phosphate excretion were found with 400 (p < 0.05), 800 (p < 0.01), and 1600 mg SCH 34826 (p < 0.01). Increases in calcium excretion were significant with only the 400 mg (p < 0.01) and 1600 mg doses @ < 0.01).
dose of SCH 34826. This observation is supported by a recent dog study in which no change in glomerular filtration rate was observed during NEP inhibiti~n.~' Nonetheless, it is impossible to rule out the occurrence of subtle changes in glomerular filtration rate which might have been undetectable by the usual cre-
atinine clearance technique. The increase in the urinary sodiurn/creatinine ratio is compatible with an elevation of the fractional excretion of sodium and therefore points to a tubular effect of SCH 34826. In the absence of specific markers for the proximal reabsorption of sodium, it is not possible to determine
VOLUME SO NUMBER 2
An inhibitor of atrial natn'ureticfactor degradation 18 7
Plasma ANP
-2
0
2
Urinary ANP
i
6
8
10
Hours
(pg/min) 40 1
Hours Fig. 3. Effect of SCH 34826 on plasma (upper panel) and urinary atrial natriuretic peptide (ANP; lower panel). Only the changes in plasma ANP observed under placebo (0)or 1600 mg ( 0 ) SCH 34826 are shown. Significant increases in urinary ANP were found with 400 mg (A; p < 0.05), 800 mg (A; p < 0.01), and 1600 mg SCH 34826 @ < 0.001) when compared with time zero. The statistical analysis of the curves is shown in Table 11.
whether the drug-induced natriuresis observed in this study is caused by a proximal or a distal tubular effect of the compound. A clear dose-dependent increase in phosphaturia was found with NEP inhibition in our volunteers. The effect of SCH 34826 on phosphate excretion is more prolonged than that on sodium excretion and follows
closely the profile of cGMP excretion. The mechanism whereby SCH 34826 promotes phosphate excretion cannot be appreciated precisely from our findings. The ability of a neutral endopeptidase inhibitor to increase phosphaturia therefore deserves further specific investigations. On the other hand, a slight but significant increase in urinary calcium excretion was no-
CLIN PHARMACOL TIIEK AUGUST 1991
188 Bumieretal.
Hours Urinary cGMP
Mean f SEM
Hours
Fig. 4. Effect of SCH 34826 on plasma (upper panel) and urinary cyclic guanosine monophosphate (cGMP; lower panel). Isolated significant increases in plasma cGMP were observed with the 800 mg (A) and 1600 mg (@) doses when compared with placebo (0). When compared with time zero, significant increases in urinary cGMP were found at 400 (A; p < 0.05), 800 ( p < 0.01), and 1600 mg @ < 0.001). The statistical evaluation of the curves is given in Table 11.
ticed. The pattern of electrolyte excretion observed in this study suggests that the renal response to NEP inhibition is similar to that obtained with the infusion of a low dose of exogenous ANP. Interestingly, the natriuresis induced by oral administration of SCH 34826 occurred in the absence of any
change in plasma ANP levels, whereas there was at the same time a dose-dependent increase in urinary ANP and cGMP excretion. This hormonal response to SCH 34826 contrasts with the results published for other NEP inhibitors in normal subjects and patients with congestive heart f a i l ~ r e . ~In~ these . ~ ~ studies,
V O L U M E SO NUMBER 2
A n inhibitor of atrial natriuretic factor depadation
189
plasma ANP levels were significantly increased during lated to an increase in renal ANP activity. Urinary NEP inhibition. However, our observation is in accorcGMP increased markedly and dose-dependently at a dance with the results of several animal studies in time when plasma cGMP was only slightly elevated. which SCH 34826 or analog compounds produced a This observation may indicate that cGMP like ANP is natriuresis without affecting plasma ANP ~ e v e l s . ~ ~ - ~ ' generated within the kidney because both NEP and This discrepancy does not seem to be specific to SCH guanylate cyclase- linked ANP receptors have been 34826 because a similar phenomenon has now been described at this site.36 Finally, the natriuretic effect reported with other NEP inhibitor^.^',^^ of SCH 34826 is not likely to be attributable to the inhibition of other enzymatic processes, in particular the There are several potential explanations for the disinhibition of angiotensin converting enzyme. Indeed, sociation between plasma and urinary ANP. The first hypothesis postulates that inhibition of ANP metaboin vitro, SCH 32615, the active metabolite of SCH 34826, is devoid of any activity against angiotensin lism by SCH 34826 occurs only at critical sites, for example, in the brush border of the proximal tubule. converting enzyme at concentrations up to 10 prnoli~.~~ The consecutive elevation of local tissue and urinary ANP could then mediate the response to the inhibitor. SCH 34826 had a weak, if any diuretic effect in our subjects, who had ingested large amounts of water. Recent experimental studies in the rat, in which urinary cGMP increased when plasma ANP levels This poor effect on diuresis is certainly not explained by the high baseline urine output because urine volwere not altered, tend to support this idea.25,31 The ume can increase up to 20 mllmin in normal volunlack of change in plasma ANP under NEP inhibition ~ , ~observa~ teers, as shown in previous s t ~ d i e s .This may also be accounted for by the ability of an efficient tion is more likely caused by a weak potentiation of C-receptor mechanism to clear ANP from the plasma endogenous ANP. As mentioned earlier, the natriafter inhibition of its enzymatic degradation. Recent uretic response to 1600 mg SCH 34826 is approxistudies in which the pharmacokinetics of ANP were mately equivalent to that obtained in similar condievaluated during separate or combined inhibition of tions with the infusion of 0.5 pglmin ANP. At this NEP and C-receptors tend to support this latter hydose of exogenous ANP, the natriuresis was obtained p~thesis.~~ in the absence of any change in urine flow rate." What kind of evidence do we have that SCH 34826 Finally, SCH 34826 had no influence on blood acted mainly by an ANP-mediated mechanism? Bepressure and heart rate in our normotensive subjects. sides ANP, the neutral metalloendopeptidase 24.1 1 is This is not surprising if one considers that decreases in involved in the metabolism of several other peptides blood pressure have, in our experience, been observed including kinins, angiotensins, enkephalins, and neuonly with rather high doses of exogenous ANP. Nevrot ens in^.^^ It could thus be argued that part of the ertheless, one volunteer experienced a malaise 5 hours drug-induced natriuresis is caused by an effect of SCH after the administration of 1600 mg SCH 34826. This 34826 on these hormonal systems. Although such a episode was similar to those seen previously during possibility cannot be entirely ruled out, there is some ANP infusions. evidence that the contribution, if any, of other pepIn conclusion, the findings of this study demontides is small. In spontaneously hypertensive rats, strate that the orally active NEP inhibitor SCH 34826 SCH 34826 does not modify the blood pressure repromotes sodium excretion in normotensive volunteers sponse to angiotensin I, angiotensin 11, or bradykinin, with high intakes of sodium. This effect is associated whereas thiorphan, a dual ACE and NEP inhibitor, with increases in urinary phosphate and calcium expotentiates the depressor response to bradykinin.25,35 cretion but with no change in kaliuresis. The renal reFurthermore, administration of a bradykinin antagosponse to SCH 34826 appears to be related mainly to nist failed to alter the fall in blood pressure induced by the potentiation of endogenous ANP in the kidney as SCH 34826 in deoxycorticosterone acetate-sodium suggested by the marked elevation of urinary ANP hypertensive rats." In our normal volunteers, several and cGMP excretion when plasma ANP is unchanged. observations also point to a main impact of SCH 34826 on ANP metabolism. Thus, positive correlations were found not only between urinary ANP and References cGMP but also between urinary cGMP and sodium 1. De Bold AJ, Borenstein HB, Veress AT, Sonnenberg and phosphate excretion. These correlations do not asH. A rapid and potent natriuretic response to intravecertain a causal relationship but nevertheless support nous injection of atrial myocardial extracts in rats. Life Sci 1981;28:89-94. the idea that the renal effects of SCH 34826 are re-
CLIN PHARMACUL THEK AUGUST 1991
2. Richards AM, Ikram H, Yandle TG, Nicholls MG, Webster MWI, Espiner EA. Renal, haemodynamic and hormonal effects of human a-atrial natriuretic peptide in healthy volunteers. Lancet 1985;1:545-548. 3. Biollaz J, Nussberger J, Porchet M, et al. Four-hour infusion of synthetic atrial natriuretic peptide in normal volunteers. Hypertension 1986;8(suppl II):II96-11105. 4. Fluckiger JP, Waeber B, Matsueda GR, Delaloye B, Nussberger J, Brunner HR. Effect of atriopeptin I11 on hematocrit and volemia of nephrectomized rats. Am J Physiol 1986;251:H880-H883. 5. Tikkanen I, Fyhrquist F, Metsarinne K, Leidenius R. Plasma atrial natriuretic peptide in cardiac disease and during infusion in healthy volunteers. Lancet 1985;2:66-9. 6. Espiner EA, Richards AM. Atrial natriuretic peptide. An important factor in sodium and blood pressure regulation. Lancet 1989;1:707-10. 7. Tikkanen I, Metsarinne K, Fyhrquist F. Atrial natriuretic peptide in paroxysmal supraventricular tachycardia. Lancet 1985;2:40-1. 8. Bumett JC, Kao PC, Hu DC, et al. Atrial natriuretic peptide elevation in congestive heart failure in the human. Science 1986;231: 1145-7. 9. Cody RJ, Atlas SA, Laragh JH, et al. Atrial natriuretic factor in normal subjects and heart failure patients. Plasma levels and renal, hormonal and hemodynamic responses to peptide infusion. J Clin Invest 1986;78:1362-74. 10. Raine AEG, Erne P, Burgisser E, et al. Atrial natriuretic peptide and atrial pressure in patients with congestive heart failure. N Engl J Med 1986;315:533-7. 11. Saxenhofer H, Gnadinger MP, Weidmann P, et al. Plasma levels and dialysance of atrial natriuretic peptide in terminal renal failure. Kidney Int 1987;32:55461. 12. Shenker Y, Port FK, Swartz RD, Gross MD, Grekin RJ. Atrial natriuretic hormone secretion in patients with renal failure. Life Sci 1987;41:1635-44. 13. Fievet P, Fournier A, De Bold A, et al. Atrial natriuretic factor in pregnancy-induced hypertension and preeclampsia: increased plasma concentrations possibly explaining these hypovolemic states with paradoxical hyporeninism. Am J Hypertens 1988;1: 16-22. 14. MacGregor GA, Sagnella GA, Markandu ND, et al. Raised plasma levels of atrial natriuretic peptide in subjects with untreated essential hypertension. J Hypertens 1986;4:(suppl 6):S567-S568. 15. Richards AM, Nicholls MG, Espiner EA, et al. Effects of a-human atrial natriuretic peptide in essential hypertension. Hypertension 1985;7:812-7. 16. Weidmann P, Gnadinger MP, Ziswiler HR, et al. Cardiovascular, endocrine and renal effects of atrial natiuretic peptide in essential hypertension. J Hypertens 1986;4(suppl 2):S7 1-S83. 17. Petrillo A, Scherrer U, Gonvers JJ, et al. Atrial natriuretic peptide administered as intravenous infusion or
bolus injection to patients with liver cirrhosis and ascites. J Cardiovasc Pharmacol 1988;12:279-85. 18. Janssen WMT, De Zeeuw DD, Vanderhern GK, De Jong PE. Antihypertensive effect of a 5-day infusion of atrial natriuretic factor in humans. Hypertension 1989;131640-6. 19. Goy JJ, Waeber B, Nussberger J, et al. Infusion of atrial natriuretic peptide to patients with congestive heart failure. J Cardiovasc Pharmacol 1988;12:562-70. 20. Burnier M, Mooser V, Wauters JP, et al. Bolus injections of synthetic atrial natriuretic peptide in patients with chronic renal failure or nephrotic syndrome. J Cardiovasc Pharmacol 1989;13:682-90. 21. Biollaz J, Callahan LT, Nussberger J , et al. Pharmacokinetics of synthetic atrial natriuretic peptides in normal man. CLINPHARMACOL THER1987;4 1:67 1-7. 22. Chipkin RE, Berger JG, Billard W, lorio LC, Chapman R, Barnett A. Pharmacology of SCH 34826, an orally active enkephalinase inhibitor analgesic. J Pharmacol Exp Ther 1988;245:829-38. 23. Seymour AA, Fennel1 SA, Swerdel JN. Potentiation of renal effects of atrial natriuretic factor-(99-126) by SQ 29072. Hypertension 1989;14:87-97. 24. Northridge DB, Jardine AG, Alabaster CT, et al. Effect of UK 69578: a novel atriopeptidase inhibitor. Lancet 1989;2:591-3. 25. Sybertz EJ, Chiu PJS, Vemulapalli S, Watkins R, Haslanger MF. Atrial natriuretic factor-potentiating and antihypertensive activity of SCH 34826, an orally active neutral metalloendopeptidase inhibitor. Hypertension 1990; 15: 152-61. 26. Richards M, Espiner E, Frampton C, et al. Inhibition of endopeptidase EC 24.11 in human. Renal and endocrine effects. Hypertension 1990;16:269-76. 27. Gros C, Souque A, Schwartz JC, et al. Protection of atrial natriuretic factor against degradation: diuretic and natriuretic responses after in vivo inhibition of enkephalinase (EC 3.4.24.1 1) by acetorphan. Proc Natl Acad Sci USA 1989;86:7580-4. 28. Nussberger J, Fasanella d'Amore T, Porchet M, et al. Repeated administration of the converting enzyme inhibitor cilazapril to normal volunteers. J Cardiovasc Pharmacol 1987;9:39-44. 29. Nussberger J, Mooser V, Maridor G, Juillerat L, Waeber B, Brunner HR. Caffeine induced diuresis and atrial natriuretic peptides. J Cardiovasc Pharmacol 1990;15:685-91. 30. Margulies KB, Cavero PG, Seymour AA, Delaney NG, Burnett JC Jr. Neutral endopeptidase inhibition potentiates the renal actions of atrial natriuretic factor. Kidney Int 1990;38:67-72. 31. Sybertz EJ, Chiu PJS, Vemulapalli S, et al. SCH 39370, a neutral metalloendopeptidase inhibitor potentiates biological responses to atrial natriuretic factor and lowers blood pressure in desoxycorticosterone acetatesodium hypertensive rats. J Pharmacol Exp Ther l989;250:624-3 1.
VOLUME 50 NUMBER 2
A n inhibitor of atrial natriuretic factor de~radation 191
32. Olins GM, Krieter PA, Trapani AJ, Spear KL, Bovy PR. Specific inhibitors of endopeptidase 24.11 inhibit the metabolism of atrial natriuretic peptides in vitro and in vivo. Mol Cell Endocrinol l989;6 1:20 1-8. 33. Sybertz EJ, Chiu PJS, Watkins RW, Vemulapalli S. Neutral metalloendopeptidase inhibition: a novel means of circulatory modulation. J Hypertens [In press]. 34. Erdos EG, Skidgel RA. Neutral endopeptidase 24.1 1 (enkephalinase) and related regulators of peptide hormones. FASEB J 1989;3:145-51. 35. Baum T, Becker FT, Sybertz EJ, Sabin C, Desiderio
DM. Enkephalinase "A" inhibition by thiorphan: central and peripheral cardiovascular effects. Eur J Pharmacol 1983;94:85-91. 36. Shima M, Seino Y , Torikai S, Imai M. Intrarenal localization of degradation of atrial natriuretic peptide in isolated glomeruli and cortical nephron segments. Life Sci 1988;43:357-63. 37. Biollaz J, Bidiville J, DiCzi J , et al Site of the action of a synthetic atrial natriuretic peptide evaluated in humans. Kidney Int 1987;32:537-46.
Bound volumes available to subscribers
Bound volumes of CLINICAL PHARMACOLOGY & THERAPELTICS are available to subscribers (only) for the 1991 issues from the Publisher, at a cost of $43.00 for domestic, $59.01 for Canadian, and $56.00 for international subscribers for Vol. 49 (Januarp-June) and Vol. 50 (July-December). Shipping charges are included. Each bound volume contains a subject and author index and all advertising is removed. Copies are shipped within 60 days after the publication of the last issue of the volume. The binding is durable buckram with the journal name, volume number, and year stamped in gold on the spine. Payment must accompamy all mden. Contact Mosb!l-Year Book, Inc., Subscription Services, 11830 Westline Industrial Drive, St. Louis, MO 63146-3318, USA; phone (800)325-4177, ext. 4351. Subscriptions must be in force to qualify. Bound volumes are not available in place of a regular journal subscription.
