191
Clinica Chimica Acta, 61 (1975) 191-197 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
CCA 7066
AN IMPROVED RADIOIMMUNOASSAY USING COMMERCIAL KIT
OF SERUM GASTRIN
MANJULA S. KUMAR and SHqj3AD D. DEODHAR Department Foundation,
of Immunopathology, Division of Laboratory Cleveland, Ohio 44106 (U.S.A.)
Medicine,
Cleveland
Clinic
(Received November 22, 1974)
Summary Our experience with a commercially available kit for the measurement of serum gastrin has been reported. Significant non-specific interference was noted by the addition of serum contents in the assay which lead to erroneous results. Use of gastrin free serum as a diluent in the standard curve was found to improve the mean recovery of added gastrin. With this modification the procedure was evaluated for its clinical application. In 30 normal subjects, the fasting mean gastrin level was 78.7 f 31.9 (S.D.) pg/ml; in 18 of these individuals the postprandial mean level was 118.3 + 26.7 (S.D.) pg/ml. In 15 patients with pernicious anemia the mean level was 912 f 779 pg/ml; and in 4 patients with Zollinger-Ellison (ZE) syndrome the mean gastrin level was 1950 * 379 (S.D.) pg/ml. A significant rise in gastrin level was noted in patients with kidney failure during and after dialysis (p < 0.05).
Introduction In 1964 Gregory and his co-workers first reported the isolation, chemical identification and synthesis of gastrin. Since then, several reports of production of antiserum to porcine and synthetic human gastrin have been published. Trudeau and McGuigan [l] reported the first radioimmunoassay sufficiently sensitive to measure physiological concentrations of gastrin in human serum. Subsequently, other groups have reported on assays with similar sensitivity. It is clear now that this sensitive technique provides rapid and specific measurement of serum gastrin and an earlier and more definitive diagnosis of ZollingerEllison (ZE) syndrome. Other clinical uses of serum gastrin levels can be anticipated in pathological states such as peptic ulcer and pernicious anemia. This report describes a reliable and rapid radioimmunoassay for gastrin using commercially available reagents and also describes studies on the clinical applications of this assay.
192
Materials and Methods The gastrin Immutope Kit for the measurement of serum gastrin levels by radioimmunoassay was obtained from Squibb Co., New Jersey and contained the following reagents: One vial of gastrin antiserum, which was produced in rabbits against synthetic human gastrin I (2-17) coupled to bovine serum albumin. One vial of labelled synthetic gastrin (l-17) I’ ” (spec. act. 800-1000 pCi/c(g); one vial each of standard gastrin A and B (synthetic human gastrin I (l-17), and one vial each of barbital buffer mixture, egg albumin powder and ion-exchange resin (Amberlite CG-4B). Gastrin-free serum was prepared by removing the endogenous gastrin by adsorption with charcoal. To 100 ml of normal human serum 10 g charcoal (Nort-A-Amend Drug Co.) was added, mixed well, then incubated for 30 min at room temperature. Charcoal was removed by centrifugation three times at 13 000 rpm for 1 h. The procedure removed more than 99% of added ’ * ’ I-labelled gastrin and did not significantly affect the total protein concentration. Assay procedure The assay was performed in duplicates in 12 mm X 75 mm disposable plastic tubes (Falcon Plastics). The [’ * ’ I] gastrin was diluted to 4500 cpm/ml in barbital buffer (0.02 M, pH 8.3) containing egg albumin (2.5 mg/ml). 0.9 ml of this solution was added to each tube, and this was followed by the addition of 50 or 100 ~1 of serum samples (unknowns) and 50 ~1 of antiserum. 50 1.11of gastrin-free normal human serum together with standards (synthetic human gastrin) 5 to 200 pg. were used to prepare standard curves. The assay mixture was agitated in a vortex mixer and incubated for 3 h at room temperature. Free and bound gastrin were separated by adding 0.2 ml Amberlite resin CG4B suspension in barbital buffer (0.02 M, pH 8.3), immediately vortexed and then centrifuged for 10 min at 3000 rpm. Supernatant was decanted and counted in a well-type gamma counter (Nuclear Chicago). Results Effect of serum proteins on the assay Two standard curves were run simultaneously, one in buffer only, and another with 50 ~1 of gastrin free serum added to the buffer (Fig. 1). Addition of the serum shifted the curve toward the higher side, and the mean recovery of added gastrin was also significantly improved. The actual results on recovery experiments are tabulated in Table I. Conditions for incubation The effects of temperature and time on the antigen-antibody reaction were checked. Incubation was done at 4”C, room temperature (25”C), and 37°C. Fig. 2 illustrates the results obtained. The equilibrium between antibody bound and free labelled antigen was more rapid at room temperature and 37°C as compared to 4°C incubation. For convenience, 3 h incubation time at room temperature was selected.
193
120 ,L
I00
L.
80
, -
4c )-
2c )-
CI-
r
I
IO
5 AMOUNT
50
20
OF GASTRIN
ADDED
!
100
200
(Pg)
Fig. 1. Displacement curves of gastrin in buffer and in the presence of 50 ~1 of gastrin free human serum. I1 2511 Gastrin bound to antibody in buffer in absence of stable gastrin (40%) had been set equal to 100, and the remaining data were expressed as percent of this value. TABLE
I
RESULTS
ON RECOVERY
TO STANDARD Gastrin added (pg/mI)
0 100 200 500
EXPERIMENTS
WITH AND WITHOUT
GASTRIN
FREE SERUM
ADDED
CURVE Without gastrin free serum in standard curve
With gastrin free serum in standard curve
gastrin @g/ml) (mean f SD.)
gastrin (pglml) (mean f S.D.)
79.6 t 136.3 196.6 356
1.5
* 5.5 f 15.3 f 42.7
INCUBATION
% mean recovery _
96.6
56.7 58.0 55.2
TIME
194 297 533
*
3
f 5.3 f 6.4 f 30.5
% mean recovery 97.4 100.3 87.3
(HOURS)
Fig. 2. Effect of time and temperature of incubation on the antibody reaction. 4OC, room temperature and at 37’C from 1 to 6 h; % labelled gastrin bound against time of incubation.
Tubes were incubated at to antibody was plotted
194 TABLE
II
KECOVERY The
rrsults
OF of
ADDED
SYN1’HF:TIC
determinations
Gastnn
Indimtlual’s
added
(P~irnl)
HUhlAN
IIf known values
in 8 differrnt
1
GASTRIN
amount
of
gastrin
addrd
to srrum
assays
sample
Gastrm
nwasured
“A w ..
:.:.: . ... . . .. .. ... .. ::::: :::;:i ::;::: +A :.:.:. :::;:i .:.:.
IO0
0
f
DURING
PRE-DIALYSIS
DIALYSIS Fig.
4. Serum
carcinoid
gastrin
type.
POST DIALYSIS
levels in 10 patients with renal disease (narrow vertical bars represent * 1 S.E.M).
After
the surgery, the postoperative
gastrin level dropped
to 65
pg/ml. The tumor was extracted with phosphate buffered saline (pH 7.5). It was homogenized first in the Waring blender, and then in a glass homogenizer. The whole mixture was centrifuged twice for 1 h at 13 000 rpm. The supernatant was tested in the gastrin assay and was found to contain 32 pugof gastrin/g of tumor.
Gastrin levels in renal disease In ten dialysis was after dialysis dialysis (p < cantly higher
patients with severe renal disease, the mean gastrin level before 219 f 87.9 pg/ml, during mid-dialysis was 274 t 105.1, and just 303 * 117 (Fig. 4). A significant rise was noted during and after 0.05) in 9 of these patients, and only one of them had a signifilevel of gastrin than normals at predialysis stage.
Discussion Addition of gastrin-free serum to the standards was found to be helpful in improving recovery of gastrin added to serum samples. The mechanism of this effect is not clear, but since it improves the accuracy of the test procedure, the addition of gastrin free serum to the standards was considered a desirable step. The normal fasting levels found in this study agree in general with those previously reported [2-41. Lower levels were reported by Stadil and Rehfeld [ 51 and Yalow and Berson [6], and higher values were reported by Byrnes et al. [ 71, and Chan Yip and Jordan [ 81. The gastrin levels in ZE syndrome and in pernicious anemia are also comparable to previously reported values. In one patient with ZE syndrome, the serum gastrin level dropped to normal range after removal of a pancreatic
197
tumor. The tumor extract was found to contain about 400 times higher immunoreactive gastrin than the levels found by Greider and McGuigan [9] in normal pancreatic extract. The high level was comparable to the results reported by others in ZE tumor extract [lo]. In three other patients with ZE syndrome total gastrectomy did not affect the gastrin level significantly, probably indicating autonomous gastrin release from the pancreatic non-beta islet cell tumor. A significant rise in the serum gastrin level was noted in the patients with severe renal disease. Whether this is a-result of impaired renal degradation of gastrin or increased secretion of gastrin as a consequence of a uremic state is not known at this time. The most important clinical benefit of gastrin radioimmunoassay is in the definitive diagnosis of ZE syndrome. Future studies may indicate other areas of application such as in evaluation of patients with gastric or duodenal ulcers, pernicious anemia, and other diseases. Acknowledgement We wish to thank Mrs Celia Cruz for her technical assistance. This study was supported in part by the Carl T. Reinberger Fund. References 1 2 3 4 5 6 7 8 9 10
W.L. Trudeau and J.E. McGuigan, Gastroenterology, 59 (1970) 6 W.L. Trudeau and J.E. McGuigan, New Engl. J. Med., 284 (1971) 408 P.C. Ganguli and W.M. Hunter, J. Physiol., 220 (1972) 499 E. Schrumpf and T. Sand, Stand. J. Gastroenterol.. 7 (1972) 683 F. Stadil and J.E. Rehfeld. Stand. J. Gastroenterol., Suppl. 9 (19’71) 61 R.S. Yalow and S.A. Berson, Gastroenterology, 59 (1970) 6 D.J. Bymes, J.D. Young, D.J. Chishold and L. Lazarus, Br. Med. J., 2 (1970) 626 B.S.S. Chan Yip and P.H. Jordan, Jr, Proc. Sot. Exp. Biol. Med. (New York), 134 (1970) M.H. Greider and J.E. McGuigan. Diabetes, 20 (1971) 389 S.A. Berson and R.S. Yalow, Gastroenterology, 60 (1971) 215
380
Clinica Chimica Acta, 61 (1975) 191-197 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
CCA 7066
AN IMPROVED RADIOIMMUNOASSAY USING COMMERCIAL KIT
OF SERUM GASTRIN
MANJULA S. KUMAR and SHqj3AD D. DEODHAR Department Foundation,
of Immunopathology, Division of Laboratory Cleveland, Ohio 44106 (U.S.A.)
Medicine,
Cleveland
Clinic
(Received November 22, 1974)
Summary Our experience with a commercially available kit for the measurement of serum gastrin has been reported. Significant non-specific interference was noted by the addition of serum contents in the assay which lead to erroneous results. Use of gastrin free serum as a diluent in the standard curve was found to improve the mean recovery of added gastrin. With this modification the procedure was evaluated for its clinical application. In 30 normal subjects, the fasting mean gastrin level was 78.7 f 31.9 (S.D.) pg/ml; in 18 of these individuals the postprandial mean level was 118.3 + 26.7 (S.D.) pg/ml. In 15 patients with pernicious anemia the mean level was 912 f 779 pg/ml; and in 4 patients with Zollinger-Ellison (ZE) syndrome the mean gastrin level was 1950 * 379 (S.D.) pg/ml. A significant rise in gastrin level was noted in patients with kidney failure during and after dialysis (p < 0.05).
Introduction In 1964 Gregory and his co-workers first reported the isolation, chemical identification and synthesis of gastrin. Since then, several reports of production of antiserum to porcine and synthetic human gastrin have been published. Trudeau and McGuigan [l] reported the first radioimmunoassay sufficiently sensitive to measure physiological concentrations of gastrin in human serum. Subsequently, other groups have reported on assays with similar sensitivity. It is clear now that this sensitive technique provides rapid and specific measurement of serum gastrin and an earlier and more definitive diagnosis of ZollingerEllison (ZE) syndrome. Other clinical uses of serum gastrin levels can be anticipated in pathological states such as peptic ulcer and pernicious anemia. This report describes a reliable and rapid radioimmunoassay for gastrin using commercially available reagents and also describes studies on the clinical applications of this assay.
192
Materials and Methods The gastrin Immutope Kit for the measurement of serum gastrin levels by radioimmunoassay was obtained from Squibb Co., New Jersey and contained the following reagents: One vial of gastrin antiserum, which was produced in rabbits against synthetic human gastrin I (2-17) coupled to bovine serum albumin. One vial of labelled synthetic gastrin (l-17) I’ ” (spec. act. 800-1000 pCi/c(g); one vial each of standard gastrin A and B (synthetic human gastrin I (l-17), and one vial each of barbital buffer mixture, egg albumin powder and ion-exchange resin (Amberlite CG-4B). Gastrin-free serum was prepared by removing the endogenous gastrin by adsorption with charcoal. To 100 ml of normal human serum 10 g charcoal (Nort-A-Amend Drug Co.) was added, mixed well, then incubated for 30 min at room temperature. Charcoal was removed by centrifugation three times at 13 000 rpm for 1 h. The procedure removed more than 99% of added ’ * ’ I-labelled gastrin and did not significantly affect the total protein concentration. Assay procedure The assay was performed in duplicates in 12 mm X 75 mm disposable plastic tubes (Falcon Plastics). The [’ * ’ I] gastrin was diluted to 4500 cpm/ml in barbital buffer (0.02 M, pH 8.3) containing egg albumin (2.5 mg/ml). 0.9 ml of this solution was added to each tube, and this was followed by the addition of 50 or 100 ~1 of serum samples (unknowns) and 50 ~1 of antiserum. 50 1.11of gastrin-free normal human serum together with standards (synthetic human gastrin) 5 to 200 pg. were used to prepare standard curves. The assay mixture was agitated in a vortex mixer and incubated for 3 h at room temperature. Free and bound gastrin were separated by adding 0.2 ml Amberlite resin CG4B suspension in barbital buffer (0.02 M, pH 8.3), immediately vortexed and then centrifuged for 10 min at 3000 rpm. Supernatant was decanted and counted in a well-type gamma counter (Nuclear Chicago). Results Effect of serum proteins on the assay Two standard curves were run simultaneously, one in buffer only, and another with 50 ~1 of gastrin free serum added to the buffer (Fig. 1). Addition of the serum shifted the curve toward the higher side, and the mean recovery of added gastrin was also significantly improved. The actual results on recovery experiments are tabulated in Table I. Conditions for incubation The effects of temperature and time on the antigen-antibody reaction were checked. Incubation was done at 4”C, room temperature (25”C), and 37°C. Fig. 2 illustrates the results obtained. The equilibrium between antibody bound and free labelled antigen was more rapid at room temperature and 37°C as compared to 4°C incubation. For convenience, 3 h incubation time at room temperature was selected.
193
120 ,L
I00
L.
80
, -
4c )-
2c )-
CI-
r
I
IO
5 AMOUNT
50
20
OF GASTRIN
ADDED
!
100
200
(Pg)
Fig. 1. Displacement curves of gastrin in buffer and in the presence of 50 ~1 of gastrin free human serum. I1 2511 Gastrin bound to antibody in buffer in absence of stable gastrin (40%) had been set equal to 100, and the remaining data were expressed as percent of this value. TABLE
I
RESULTS
ON RECOVERY
TO STANDARD Gastrin added (pg/mI)
0 100 200 500
EXPERIMENTS
WITH AND WITHOUT
GASTRIN
FREE SERUM
ADDED
CURVE Without gastrin free serum in standard curve
With gastrin free serum in standard curve
gastrin @g/ml) (mean f SD.)
gastrin (pglml) (mean f S.D.)
79.6 t 136.3 196.6 356
1.5
* 5.5 f 15.3 f 42.7
INCUBATION
% mean recovery _
96.6
56.7 58.0 55.2
TIME
194 297 533
*
3
f 5.3 f 6.4 f 30.5
% mean recovery 97.4 100.3 87.3
(HOURS)
Fig. 2. Effect of time and temperature of incubation on the antibody reaction. 4OC, room temperature and at 37’C from 1 to 6 h; % labelled gastrin bound against time of incubation.
Tubes were incubated at to antibody was plotted
194 TABLE
II
KECOVERY The
rrsults
OF of
ADDED
SYN1’HF:TIC
determinations
Gastnn
Indimtlual’s
added
(P~irnl)
HUhlAN
IIf known values
in 8 differrnt
1
GASTRIN
amount
of
gastrin
addrd
to srrum
assays
sample
Gastrm
nwasured
“A w ..
:.:.: . ... . . .. .. ... .. ::::: :::;:i ::;::: +A :.:.:. :::;:i .:.:.
IO0
0
f
DURING
PRE-DIALYSIS
DIALYSIS Fig.
4. Serum
carcinoid
gastrin
type.
POST DIALYSIS
levels in 10 patients with renal disease (narrow vertical bars represent * 1 S.E.M).
After
the surgery, the postoperative
gastrin level dropped
to 65
pg/ml. The tumor was extracted with phosphate buffered saline (pH 7.5). It was homogenized first in the Waring blender, and then in a glass homogenizer. The whole mixture was centrifuged twice for 1 h at 13 000 rpm. The supernatant was tested in the gastrin assay and was found to contain 32 pugof gastrin/g of tumor.
Gastrin levels in renal disease In ten dialysis was after dialysis dialysis (p < cantly higher
patients with severe renal disease, the mean gastrin level before 219 f 87.9 pg/ml, during mid-dialysis was 274 t 105.1, and just 303 * 117 (Fig. 4). A significant rise was noted during and after 0.05) in 9 of these patients, and only one of them had a signifilevel of gastrin than normals at predialysis stage.
Discussion Addition of gastrin-free serum to the standards was found to be helpful in improving recovery of gastrin added to serum samples. The mechanism of this effect is not clear, but since it improves the accuracy of the test procedure, the addition of gastrin free serum to the standards was considered a desirable step. The normal fasting levels found in this study agree in general with those previously reported [2-41. Lower levels were reported by Stadil and Rehfeld [ 51 and Yalow and Berson [6], and higher values were reported by Byrnes et al. [ 71, and Chan Yip and Jordan [ 81. The gastrin levels in ZE syndrome and in pernicious anemia are also comparable to previously reported values. In one patient with ZE syndrome, the serum gastrin level dropped to normal range after removal of a pancreatic
197
tumor. The tumor extract was found to contain about 400 times higher immunoreactive gastrin than the levels found by Greider and McGuigan [9] in normal pancreatic extract. The high level was comparable to the results reported by others in ZE tumor extract [lo]. In three other patients with ZE syndrome total gastrectomy did not affect the gastrin level significantly, probably indicating autonomous gastrin release from the pancreatic non-beta islet cell tumor. A significant rise in the serum gastrin level was noted in the patients with severe renal disease. Whether this is a-result of impaired renal degradation of gastrin or increased secretion of gastrin as a consequence of a uremic state is not known at this time. The most important clinical benefit of gastrin radioimmunoassay is in the definitive diagnosis of ZE syndrome. Future studies may indicate other areas of application such as in evaluation of patients with gastric or duodenal ulcers, pernicious anemia, and other diseases. Acknowledgement We wish to thank Mrs Celia Cruz for her technical assistance. This study was supported in part by the Carl T. Reinberger Fund. References 1 2 3 4 5 6 7 8 9 10
W.L. Trudeau and J.E. McGuigan, Gastroenterology, 59 (1970) 6 W.L. Trudeau and J.E. McGuigan, New Engl. J. Med., 284 (1971) 408 P.C. Ganguli and W.M. Hunter, J. Physiol., 220 (1972) 499 E. Schrumpf and T. Sand, Stand. J. Gastroenterol.. 7 (1972) 683 F. Stadil and J.E. Rehfeld. Stand. J. Gastroenterol., Suppl. 9 (19’71) 61 R.S. Yalow and S.A. Berson, Gastroenterology, 59 (1970) 6 D.J. Bymes, J.D. Young, D.J. Chishold and L. Lazarus, Br. Med. J., 2 (1970) 626 B.S.S. Chan Yip and P.H. Jordan, Jr, Proc. Sot. Exp. Biol. Med. (New York), 134 (1970) M.H. Greider and J.E. McGuigan. Diabetes, 20 (1971) 389 S.A. Berson and R.S. Yalow, Gastroenterology, 60 (1971) 215
380
