Brief Reports
BIOLPSYC~rnATRY
539
1990;28:535--539
ical metabolism in schizophrenia. Biol Psychiatry 25:169A. Pall HS, Williams AC, Blake DR, Lunec J (1987): Evidence of enhanced lipid peroxidation in the cerebrospinal fluid of patients taking phenothiazines. Lancet ii:596-599. Prilipko LL (1984): Activation of lipid peroxidation under stress and in schizophrenia. In Kemali D, Morozov PV, Toffano G (eds), New Research Strategies in Biological Psychiatry. Bioiogwal
Psychiatry--New Prospects: 3. London: John Lib-
bey.
Saito T, Ishizaw,~H, Tsuchiya F, Ozawa H, Takahata N (1986): Neurochemical findings in the cerebrospinal fluid of schizophrenic patients with tardive dyskinesia and neuroleptic-induced parkinsonism. Jpn J Psychiatr Neurol 40:189-194. Schooler NR, Kane JM (1982): Research diagnosis for tardivedyskinesia.Arch Gen Psychiatry 39:486-487.
Effects of Low-Dose 4-Fluorotranylcypromine on Rat Brain Monoamine Oxidase and Neurotransmitter Amines R.L. Sherry, G.B. Baker, and K.T. Cou~is
Introduction Tranylcyprornine (TCP), a nonhydrazine monoamine oxidase (MAO) inhibitor with a close structural simil~_,'ity to amphetamine, is a clinically efficacious antidepressant (Himmelhoch et al. 1982.; Quitk~,~ et al. 1979; Whi~,e et al. 1984). Studies have shown :hat in both experimental animals (Fuentes et al. 1976; Calverley et al. 1981; Hampson et al. ~986) and humans (Baser et al. 1977; Lang et ~1. 1979; Weber et al. 1984; Edwards et al. 1985; Mallinger et al. 1986), the turnover rage of TCP is relatively
From the Heurochemical Research Unit and PMHAC Resean:h Unit, Depaiament of Psychiatry and Fac,!ty of Pharmacy rind Pharmaceutical Sciences, University of Alberta, Edmonton, Alberta. Canada. Address reprint requests to Dr. Glen Baker, Neurochemical Research Unit, Department of Psychiatry, Mackenzie Centre, University of Alberta, Edmonton, Alberta, Canada, T6G2B7. Received October 31, !989, revised March 23, 1990.
© 1990 Society of Biological Psychiatry
rapid. It has been demonstrated that TCP under° goes ring hydroxylation in the rat (Baker et ai. 1986; Nazarali et al. 1987; Kang and Chung 1984). In an effort to increase its short elimination half-life and provide for higher, more sustained brain levels, we have synthesized a number of TCP analogues in which there is a chemical substitution at the 4-position of the phenyl ring (Rao et al. 1986), thereby preventing metabolism at that position. Of the analogues tested, fluorotranylcypmmine (FI'CP) was of particular interest because it is stcucturally very similar to TCP (fluorine is similar in atomic: volume to hydrogen) and it has been shown to be a mote potent inhibitor of brain MAO than is TCP in vitro (Rao et al. 1986). Initial studies (Coutts e~.al. 1987) indicated that at a relatively high dose (0.1 mmol/kg, i.p.), FTCP attained higher brain and liver levels and thus provided greater availability than did TCP
0006-3223/90/$03.50
540
Brief Reports
BIOLPSYCHIArRY "9~;28:539-543
after injection of an equimolar amount. These studies have now been extended in order to monitor the effects of FI'CP on inhibition of MAO ex vivo as well as its influence on levels of neumtransmitter amines and their acid metabolites in the brain following administration of clinically relevant doses. T , e results of some of those studies are reported here.
Materials and Methods Chemicals
All samples were stored at - 80°C until the time of analysis. Frozen tissues were allowed to thaw partially and were cut in half and weighed. One half was homogenized in 5 vol of ice-cold isotonic KCI solution and aliquots were kept for MAO assays. The other half was homogenized in 0.1 M perch!oric acid containing 10.0 mg% disodium EDTA and was centrifuged at 12,000 × g for 15 min at 0-4°C.
Analytical Procedures
¢_+)-TCF HCI, 2-phenylethylamine (PEA) HCI, High-pressure liquid chromatography with elec(-)-norepinephrille (NE) HCI, dopamine (DA) trochemical detection (HPLC-EC) was used to HCI, 5-hydroxyindole-3-acetic acid (5-HIAA), dete,rmine the neurotransmitter amines and the 3,4-dihydroxyphenylacetic acid (DOPAC), acid metabolites (NE, DA, 5-I-P~, HVA, DOhomovanillic acid (HVA), and 5-bvdroxytrypPAC, and 5-HIAA) according to ",he procedure tamine (5-HT) creatinine sulfate we~:; purchased of Baker et al. (1987). from Sigma Chemical Co. (St. Louis, Mo.) {5Monoamine oxidase activity was determined [ELhyl-! 14C]-phenyie~ylamine hydrc~rhlofide radiochemically ~!,ag a modification of the pro(55.0 mCi/mmol) and 5-[2-14C]-hydroxytryp cedure of Wurtraa~ and Axelrod (1963). m4C-5tamine binoxalate (55 mCi/nunol) were purHT and ~4C-PEA diluted with the ~opropriate chased from New England Nuclear (Boston, authentic L,nine were used as specific substrates Mass.). All oLh¢r chemic~ds and solvents were for MAO-A ~ d i~L~O-B is~nzymes, ~ p e c of the higne ~ purity conunercially available. tively. Water was eouble-distilled in an all-glass disData were analyzed by analysis of variance t':Ration apparatus. FTCP was synthesized in our followed by the Newman-Kculs test (eL= 0.05). laboratories, as previously described (Courts et al. 1987).
Results and Discussion Drug Administration Male Sprague-Dawley rats (220-280 g) were obtained from Bio-Sciences (l~lierslie, Albert,a, Canada) and were gxoup-housed on a 12b_r light/dark cycle at a temperature of 20°C. Food and water were freely available. Animals were injected i.p. with the saline vehicle or various doses of either TCP.HCI or FTCP.HCI dissolved in physiological saline. Groups of rats were killed at predetermined time intervals by cervical dislocation and decapitation.
Tisst:e Collection Each brain was removed immediately and frozen solid in isopentane on solid carbon dioxide.
In an initial study I hr after drug injec~on, four concentrations of FTCP were investigated for their effects on inhibition of MAO; a dose-response effect was observed. The mean % inhibitiot: values observed were as follows (for doses of 0.4, 1.2, 3.7, and 37 ttmol/kg, respectively): MAO-A, 29.5, 60.0, 86.5, and 97.9; MAO-B~ 35;8~ 75~7~ 86,62 and ¢;7.0 Two of these doses, 1.2 and 3.7 p,mol/kg, were chosen for further investigation and ~br comparison to equi~nolar doses of TCP. At the higher dose, which is equivalent on a :_~.~g basis to that n o m ~ l y used in human subjects, the two drugs do =,.3t differ in their de~ee c,,~ ~'~ibition of MAO-A or MAO-B 1 hr after injection (Figure 1), although at this dose FTCP c~uses a signify. icantly greater increase in brain col~c~ntrations
Brief Reports
B[OLPSYCHIATRY 1990;28:539--543
TCP i 100
% INHIBITION
MAO-A
541
FTCP I
r/////~4
AND MAO-B
9O 80 70
Oe ee
T "
6O 50 40 3O 20
lO ! o 1.2
3.7
1.2
3.7
D O S E (umol/kg)
F i g ~ 1. Effects of equimolar doses of TCP and FTCP on inhibition of MAO-A (left half of figure) and MAG-B (right half of tigure) at l hr after drug injection. Values represent means +- SEM (n = 12) **p < 0.01, compared to TCP.
of 5-HT and a significantly greater decrease in brain concentrations of the acid metabolites DOPAC, HVA, and 5-HIAA than does TCP. Levels of the neurochemicals (expressed as mean % of control _+ SEM, n = 10-11) for TCP and FTCP, respectively, were as follows: DOPAC 46.3 _-4=.6.3, 5,6 +- 1.4; HVA 68.3 _.+ 4.5, 32.8 _+. 5.7; 5-HT 120.5 +_ 8.5, 187.8 - 4.0; and 5-HIAA 80.3 -- 8.7, 47.1 +_ 4.4. At the lower dose (1.2 !xmol/kg), more potent inhibition of ~ h MAO-A and MAO-B by FTCP than by TCP is evident (Fi.gure 1). Fu~her studies conducted at 1, 2, 4, and 8 hr after injection indicated that at this lower dose, this diffezence was evident at all time ~ntervals (p < 0.01 at all times, except 8 hr ~n the case of MAO-B, where p < 0.05). Mean % inhibition values (__.SEM, n = 5 - ! 0 ) wi~h TCP and FTCP, respectively, were as follows: MAO-A: 1 hr, 33.7 -+ 2.7, 59.0 _ 3.0; 2 hr, 30.7 _4=_2.9, 89.5 +_ 1.1; 4 hr, 35.3 -+ 2.5, 65.1 - 8.3; 8 hr, 27.2 __. 6.t, 46.4 ± 6.2. For MAO-B, the corre-
sponding values were as follows: I hr 43.0 +_ 5.4, 75.7 -+ 3.1; 2 hr, 36.2 _ 2.5, 88.2 +_ 1.7; 4 hr, 35.0 _ 2.8, 70.9 - 5.0; 8 hr, 18.3 _+ 1.6, 69.5 4- 3.1. Doses of TCP of 37-14g ,Lmol/kg a,~ use~ freouentl,, in animal studies reported in the literature, but the 3.7 !,~aol/kg dose is equivalent, on a mg/kg basis., to t,hat use,d in ~ e clinical situation. FTCP was synthesized with the aim of effectively lowering th ~. dose required to inhibit MAO as compared to the dose of TCP needed for the same degree of enzyme inhibition. The fluorinated drug is protected from hydroxylation at the 4 position of the phenyl ring by virtue of its fluorine group and thus should a~-~.ai'n!ongcr-lasting and more consistent concentrations in brain than do~s TCP. Lowering the clinical dose in this manner ~a~ reduce the incidence of :~ide effects apparently contributed to the action of TCP ou uptake and release of neurotransmRter amines (Hendley and Snyder 1968; Schil ~d~,xau~ i970;
542
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BIOL PSYCHIATRY 1990;28:539-543
Horn and Snyder 1972; Baker et al. 1978, 1980; Tuomisto and Smith 1986), although comp~hensive comparisons of effects of TCP and FTCP on uptake and release of these amines in vitro and ex vivo in brain and heart will be necessary to clarify this situationo Other studies on FTCP in our labo~tories have in0Acated that it is much stronger than TCP at inhibiting brain MAO in vitro (Rao et al. 1986) and that it achieves longer-lasting brain levels than TCP when the two ,&rugs are administe,,ed at equimolar doses (Courts et al. 1987). A chronic administration experiment indicated that, like TCP, low doses of ,~I'CP pr~:]~:e downregulation of a2-adrenoceptors (Greenshaw et al. 1988). Mallinger et al. (1986) found that in human subjects, mean plasma TCP concentrations were correlated with mean orthostatic drop of systolic blood pressuye and rise of pulse rate. The authors suggested tkat patients who have hypotensive reactions to this drug may benefit from dose regimen changes ain~ed at mLnLmizing peak TCP levels. However, such adjustments could be problematic considering the relatively short half-life of TCP (Edwards et al. 1985; Mallinger et al. 1986). This problem might be overcome with a drug such as FI~CP due to its longer half-life and increased MAOinhibiting potency (i.e., lower doses of FTCP are required to produce the same degree of inhibition as TCP). .The above results indicate that FTCP is a more potent inh':bitor of MAO~ both ex vivo and in vitro, than is TCP. The effects on MAO observed in the current study with FTCP at a dose approximately one-third S a t of the clinical dose of TCP, together with other reports showing that FTCP has a longer half-life in rat brain than does TCP, suggest that ~rther studies on the effects of both acute and chronic administration of F I C P on inhib~.tion of MAO and levels of neurotransrrfitter amines in brain (and heart) are warranted.
search. RLS is the recipient of an Alberta Mental Health Research Fm,,dscholarship.
References
Baker GB, Courts RT, Rao TS (1987): Neumpharmacolog~cal and neurochemical properties of N(2-cyanoethyl)-2-phenylethylamine, a pmdrug of 2-phenylethylamine. Br J Pharmacol 92:243-255. Baker GB, Hampson DR, Coutts RT, Micetich RG, Hall TW, Rao TS (1986): Detection and quantiration of a ring-hydroxylated metabolite of the _:m6depressant d~ag trany!cypmmine. J Neural Transm 65:233--244. Baker GB, Hiob LE, Dewhurst WG (1980): Effects of monoamine oxidase inhibitors on release of dopamine and 5-hydroxytryptamine from rat striamm in vitro. Cell Mol Biol 26:132-186. Baker GB, McKim HR, Ca!vefley DG, Dewhurst WG (1978): Effects of the monoamine oxidase intdb~tors tranylcypmmine, phenelzlne and pheniprazine on the uptake of catecholamines in slices from rat brain regions. Proc Fur Soc Neurochem 1:536. Baser RC, Stewart CB, Shaskan E (i977): Determination of serum and urine concentratim,s of wanylcypromine by electron-capture gas-liqfid chromatography. J Anal Toxicol 1:215-2|7. Calverley DG, Baker GB, Courts RT, Dewhurst WG (1981): A method for the meas~eement of trany]cypromine in rat brair~ regions using gas chromatography with electron capture detection. Biochem Pharmacol 30:861-867. Coups RT, Rao TS, Baker GB, Micetich RC, H~! TWE (1987): Neurochemical and neuropharmacological properties of 4-fluorotranylcypromine. Cell Mol Neurobiol 7:271-290. Edwards DJ, Mallinger AG, K~opf S, Himmelhoch J (1985): Determination of tranylcypromine in plasma using gas chromatography-chemical ionization mass spectrometry. J Chrom Biomed Appl 344:356-361. Fuentes JA, Oleshansky MA, Neff NH (1976): Comparison of the antidepressant activity of ( - ) and (+) tranylcyp~mine in an animal model. Biochem Pharmaco! 25;801-804. Greemnaw AJ, ~az~,~,~i AJ, Rao TS, Baker GB, Coutts RT (1998): Chronic tranylcyprominc treatment induce~ functional a2-adrenoceptor downregulation in rats. E~r J Pharmacol 154:67-72. Hamp~oe DR, Beker GR, Courts RT (1986): A comSupportedby, he AlbertaProvincialMentalHealthAdvisory parison of the neurochemical and pharmacological Council (PlVltlAC),t|~eMedicalResearchCouncil 6f Canproperties of the stereoisomers of tranylcyp~mada aqd the Alberta Heritage Foundation for Medical Reine. C,ll Mol 8~ol 32:333-341.
Brief Reports
Hendley El), Snyder SH (1968): The relationship between the action of monoamine oxidase inhibitors on the noradrenaline uptake system and their antidepressant efficacy. Nature 220:1330-1331. Himmelhoch JM, Fuchs ,--,~, " * ,-,.v ~.......... ...... ~ B3 (1982): A double-blind study of tra,3ylcyprow,ine t'eatment of maj,~r anergic depression. J Nerv Merit Dis 170:628-634. Horn AS, Snyder SH (1972): Steric requirements for catecholamine uptake by rat brain synaptosomes, studies with rigid analogues of amphetanfine. ,/ Pharmacol Exp Ther 180:523-530. Kang GI, Chung SY (1984): Mech~i_~ms of monoamine oxidase inhibRion. 1. Identification of Nacetyl- and hydroxylated N-acetyltranylcypromine from tranylcypromine-dosed rat urine. Arch Pharm Res 7:65-68. tang VA, Geissler HE, Mutschier E (1979): Bestimmung und Vergleich der Plasma und Urinkonzentrationen nach gabe yon (+)- und (-)-tranylcypromin. Arzneimittelforschung 29:154-157. Mallinger AG, Edwards DJ, Himmelhoch JM, Knopf S, Elher .I (1986): Pharmacokinetics of tranylcypromine/in patients who are depressed: Relation° ~hip to cardiovascular effects. Clin Pharmacol Ther 40:444~50. ~azarali AJ, Baker GB, Coutts RT, Greenshaw A! (!987): Para-hydroxytranylcypromine: Presence
BIOLPSYCHIATRY 1990;28:539-543
543
in rat brain and heart following administration of trany!cypromine and an N-cyanoethyl analogue. Eur J Drug Metab l.'~,-w,~co~.'inet!2:207-214. Quitkin F, Rifkin A, Klein DF ¢1979): Monoamine oxidase inbibitors: A review of ~h;depressant effectiveness. Arch Gen P~ch!atry 36:749-760. Rao TS, Coutts RT, Baker GB Hall TW, Micetich RG (1986): ~aalogs of traLylcypromine: Comparison of effects on monoamine oxidase in vitro. Proc West Pharmacol Soc 29:~79-281. Schildkraut JJ (1970): TranylcyproL~ine: Effects on norepinephrine metabolism in rat brain. Am J Psychiatry 126:925-931. Tuomisto J, Smith DF (1986): Effects of tranylcypromir,e enantiomers on monoamine uptake and release and imipramine binding. ,/Neural Transm 65:135-145. Weber H, Spahn H, Mahrke W, Mutchler E (1984): Pharmacokinetics of trai~ylcypmmine enantiomers in healthy volunteers. J Pharm Pharmaco136:50W. White K, l~azani J, Cadow B, et al. (1984): Tranylcypmmine vs nortriptyline vs placebo in dep~s~,ed ¢atpatients: A controlled trial. Psychopharmacology 82:258-262. Wurtman iLL Axeirod J (19o3): A sensitive and specific afsay for the estimation of monoamine oxidase. B iochem Pharmacol 12:1439--1440.
BIOLPSYC~rnATRY
539
1990;28:535--539
ical metabolism in schizophrenia. Biol Psychiatry 25:169A. Pall HS, Williams AC, Blake DR, Lunec J (1987): Evidence of enhanced lipid peroxidation in the cerebrospinal fluid of patients taking phenothiazines. Lancet ii:596-599. Prilipko LL (1984): Activation of lipid peroxidation under stress and in schizophrenia. In Kemali D, Morozov PV, Toffano G (eds), New Research Strategies in Biological Psychiatry. Bioiogwal
Psychiatry--New Prospects: 3. London: John Lib-
bey.
Saito T, Ishizaw,~H, Tsuchiya F, Ozawa H, Takahata N (1986): Neurochemical findings in the cerebrospinal fluid of schizophrenic patients with tardive dyskinesia and neuroleptic-induced parkinsonism. Jpn J Psychiatr Neurol 40:189-194. Schooler NR, Kane JM (1982): Research diagnosis for tardivedyskinesia.Arch Gen Psychiatry 39:486-487.
Effects of Low-Dose 4-Fluorotranylcypromine on Rat Brain Monoamine Oxidase and Neurotransmitter Amines R.L. Sherry, G.B. Baker, and K.T. Cou~is
Introduction Tranylcyprornine (TCP), a nonhydrazine monoamine oxidase (MAO) inhibitor with a close structural simil~_,'ity to amphetamine, is a clinically efficacious antidepressant (Himmelhoch et al. 1982.; Quitk~,~ et al. 1979; Whi~,e et al. 1984). Studies have shown :hat in both experimental animals (Fuentes et al. 1976; Calverley et al. 1981; Hampson et al. ~986) and humans (Baser et al. 1977; Lang et ~1. 1979; Weber et al. 1984; Edwards et al. 1985; Mallinger et al. 1986), the turnover rage of TCP is relatively
From the Heurochemical Research Unit and PMHAC Resean:h Unit, Depaiament of Psychiatry and Fac,!ty of Pharmacy rind Pharmaceutical Sciences, University of Alberta, Edmonton, Alberta. Canada. Address reprint requests to Dr. Glen Baker, Neurochemical Research Unit, Department of Psychiatry, Mackenzie Centre, University of Alberta, Edmonton, Alberta, Canada, T6G2B7. Received October 31, !989, revised March 23, 1990.
© 1990 Society of Biological Psychiatry
rapid. It has been demonstrated that TCP under° goes ring hydroxylation in the rat (Baker et ai. 1986; Nazarali et al. 1987; Kang and Chung 1984). In an effort to increase its short elimination half-life and provide for higher, more sustained brain levels, we have synthesized a number of TCP analogues in which there is a chemical substitution at the 4-position of the phenyl ring (Rao et al. 1986), thereby preventing metabolism at that position. Of the analogues tested, fluorotranylcypmmine (FI'CP) was of particular interest because it is stcucturally very similar to TCP (fluorine is similar in atomic: volume to hydrogen) and it has been shown to be a mote potent inhibitor of brain MAO than is TCP in vitro (Rao et al. 1986). Initial studies (Coutts e~.al. 1987) indicated that at a relatively high dose (0.1 mmol/kg, i.p.), FTCP attained higher brain and liver levels and thus provided greater availability than did TCP
0006-3223/90/$03.50
540
Brief Reports
BIOLPSYCHIArRY "9~;28:539-543
after injection of an equimolar amount. These studies have now been extended in order to monitor the effects of FI'CP on inhibition of MAO ex vivo as well as its influence on levels of neumtransmitter amines and their acid metabolites in the brain following administration of clinically relevant doses. T , e results of some of those studies are reported here.
Materials and Methods Chemicals
All samples were stored at - 80°C until the time of analysis. Frozen tissues were allowed to thaw partially and were cut in half and weighed. One half was homogenized in 5 vol of ice-cold isotonic KCI solution and aliquots were kept for MAO assays. The other half was homogenized in 0.1 M perch!oric acid containing 10.0 mg% disodium EDTA and was centrifuged at 12,000 × g for 15 min at 0-4°C.
Analytical Procedures
¢_+)-TCF HCI, 2-phenylethylamine (PEA) HCI, High-pressure liquid chromatography with elec(-)-norepinephrille (NE) HCI, dopamine (DA) trochemical detection (HPLC-EC) was used to HCI, 5-hydroxyindole-3-acetic acid (5-HIAA), dete,rmine the neurotransmitter amines and the 3,4-dihydroxyphenylacetic acid (DOPAC), acid metabolites (NE, DA, 5-I-P~, HVA, DOhomovanillic acid (HVA), and 5-bvdroxytrypPAC, and 5-HIAA) according to ",he procedure tamine (5-HT) creatinine sulfate we~:; purchased of Baker et al. (1987). from Sigma Chemical Co. (St. Louis, Mo.) {5Monoamine oxidase activity was determined [ELhyl-! 14C]-phenyie~ylamine hydrc~rhlofide radiochemically ~!,ag a modification of the pro(55.0 mCi/mmol) and 5-[2-14C]-hydroxytryp cedure of Wurtraa~ and Axelrod (1963). m4C-5tamine binoxalate (55 mCi/nunol) were purHT and ~4C-PEA diluted with the ~opropriate chased from New England Nuclear (Boston, authentic L,nine were used as specific substrates Mass.). All oLh¢r chemic~ds and solvents were for MAO-A ~ d i~L~O-B is~nzymes, ~ p e c of the higne ~ purity conunercially available. tively. Water was eouble-distilled in an all-glass disData were analyzed by analysis of variance t':Ration apparatus. FTCP was synthesized in our followed by the Newman-Kculs test (eL= 0.05). laboratories, as previously described (Courts et al. 1987).
Results and Discussion Drug Administration Male Sprague-Dawley rats (220-280 g) were obtained from Bio-Sciences (l~lierslie, Albert,a, Canada) and were gxoup-housed on a 12b_r light/dark cycle at a temperature of 20°C. Food and water were freely available. Animals were injected i.p. with the saline vehicle or various doses of either TCP.HCI or FTCP.HCI dissolved in physiological saline. Groups of rats were killed at predetermined time intervals by cervical dislocation and decapitation.
Tisst:e Collection Each brain was removed immediately and frozen solid in isopentane on solid carbon dioxide.
In an initial study I hr after drug injec~on, four concentrations of FTCP were investigated for their effects on inhibition of MAO; a dose-response effect was observed. The mean % inhibitiot: values observed were as follows (for doses of 0.4, 1.2, 3.7, and 37 ttmol/kg, respectively): MAO-A, 29.5, 60.0, 86.5, and 97.9; MAO-B~ 35;8~ 75~7~ 86,62 and ¢;7.0 Two of these doses, 1.2 and 3.7 p,mol/kg, were chosen for further investigation and ~br comparison to equi~nolar doses of TCP. At the higher dose, which is equivalent on a :_~.~g basis to that n o m ~ l y used in human subjects, the two drugs do =,.3t differ in their de~ee c,,~ ~'~ibition of MAO-A or MAO-B 1 hr after injection (Figure 1), although at this dose FTCP c~uses a signify. icantly greater increase in brain col~c~ntrations
Brief Reports
B[OLPSYCHIATRY 1990;28:539--543
TCP i 100
% INHIBITION
MAO-A
541
FTCP I
r/////~4
AND MAO-B
9O 80 70
Oe ee
T "
6O 50 40 3O 20
lO ! o 1.2
3.7
1.2
3.7
D O S E (umol/kg)
F i g ~ 1. Effects of equimolar doses of TCP and FTCP on inhibition of MAO-A (left half of figure) and MAG-B (right half of tigure) at l hr after drug injection. Values represent means +- SEM (n = 12) **p < 0.01, compared to TCP.
of 5-HT and a significantly greater decrease in brain concentrations of the acid metabolites DOPAC, HVA, and 5-HIAA than does TCP. Levels of the neurochemicals (expressed as mean % of control _+ SEM, n = 10-11) for TCP and FTCP, respectively, were as follows: DOPAC 46.3 _-4=.6.3, 5,6 +- 1.4; HVA 68.3 _.+ 4.5, 32.8 _+. 5.7; 5-HT 120.5 +_ 8.5, 187.8 - 4.0; and 5-HIAA 80.3 -- 8.7, 47.1 +_ 4.4. At the lower dose (1.2 !xmol/kg), more potent inhibition of ~ h MAO-A and MAO-B by FTCP than by TCP is evident (Fi.gure 1). Fu~her studies conducted at 1, 2, 4, and 8 hr after injection indicated that at this lower dose, this diffezence was evident at all time ~ntervals (p < 0.01 at all times, except 8 hr ~n the case of MAO-B, where p < 0.05). Mean % inhibition values (__.SEM, n = 5 - ! 0 ) wi~h TCP and FTCP, respectively, were as follows: MAO-A: 1 hr, 33.7 -+ 2.7, 59.0 _ 3.0; 2 hr, 30.7 _4=_2.9, 89.5 +_ 1.1; 4 hr, 35.3 -+ 2.5, 65.1 - 8.3; 8 hr, 27.2 __. 6.t, 46.4 ± 6.2. For MAO-B, the corre-
sponding values were as follows: I hr 43.0 +_ 5.4, 75.7 -+ 3.1; 2 hr, 36.2 _ 2.5, 88.2 +_ 1.7; 4 hr, 35.0 _ 2.8, 70.9 - 5.0; 8 hr, 18.3 _+ 1.6, 69.5 4- 3.1. Doses of TCP of 37-14g ,Lmol/kg a,~ use~ freouentl,, in animal studies reported in the literature, but the 3.7 !,~aol/kg dose is equivalent, on a mg/kg basis., to t,hat use,d in ~ e clinical situation. FTCP was synthesized with the aim of effectively lowering th ~. dose required to inhibit MAO as compared to the dose of TCP needed for the same degree of enzyme inhibition. The fluorinated drug is protected from hydroxylation at the 4 position of the phenyl ring by virtue of its fluorine group and thus should a~-~.ai'n!ongcr-lasting and more consistent concentrations in brain than do~s TCP. Lowering the clinical dose in this manner ~a~ reduce the incidence of :~ide effects apparently contributed to the action of TCP ou uptake and release of neurotransmRter amines (Hendley and Snyder 1968; Schil ~d~,xau~ i970;
542
Brief Reports
BIOL PSYCHIATRY 1990;28:539-543
Horn and Snyder 1972; Baker et al. 1978, 1980; Tuomisto and Smith 1986), although comp~hensive comparisons of effects of TCP and FTCP on uptake and release of these amines in vitro and ex vivo in brain and heart will be necessary to clarify this situationo Other studies on FTCP in our labo~tories have in0Acated that it is much stronger than TCP at inhibiting brain MAO in vitro (Rao et al. 1986) and that it achieves longer-lasting brain levels than TCP when the two ,&rugs are administe,,ed at equimolar doses (Courts et al. 1987). A chronic administration experiment indicated that, like TCP, low doses of ,~I'CP pr~:]~:e downregulation of a2-adrenoceptors (Greenshaw et al. 1988). Mallinger et al. (1986) found that in human subjects, mean plasma TCP concentrations were correlated with mean orthostatic drop of systolic blood pressuye and rise of pulse rate. The authors suggested tkat patients who have hypotensive reactions to this drug may benefit from dose regimen changes ain~ed at mLnLmizing peak TCP levels. However, such adjustments could be problematic considering the relatively short half-life of TCP (Edwards et al. 1985; Mallinger et al. 1986). This problem might be overcome with a drug such as FI~CP due to its longer half-life and increased MAOinhibiting potency (i.e., lower doses of FTCP are required to produce the same degree of inhibition as TCP). .The above results indicate that FTCP is a more potent inh':bitor of MAO~ both ex vivo and in vitro, than is TCP. The effects on MAO observed in the current study with FTCP at a dose approximately one-third S a t of the clinical dose of TCP, together with other reports showing that FTCP has a longer half-life in rat brain than does TCP, suggest that ~rther studies on the effects of both acute and chronic administration of F I C P on inhib~.tion of MAO and levels of neurotransrrfitter amines in brain (and heart) are warranted.
search. RLS is the recipient of an Alberta Mental Health Research Fm,,dscholarship.
References
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