Download Comparison of Rabbit Scintigrams: Electrolysis vs SnCl2-Reduced Tc-99m Preparations and more Lecture notes Nuclear medicine in PDF only on Docsity!
Reduced by Electrolysis and by SnCI2:
Concise Communication
Joseph Steigman, Edward V. Chin, and Nathan A. Solomon
Downstate Medical Center, Brooklyn, New York
[@‘Tc]pertechnetate was reduced electrolytically with a carbon cathode and plati num anode: a) in 1% DTPA at pH 4-5; b) in 4% sodium pyrophosphate at pH 7; c) in 1% HEDP at 7.3; and d) in 5% sodium gluconate at pH 9.2. Chromatography on Biogel P-JO showed that the various complexes were prepared in high yield. Rabbits were injected in pairs, one receiving the electrolyzed preparation, and the other receiving the conventional SnCI2-ligand-@TcO4 preparation. In the DTPA, pyro phosphate, and HEDP solutions, the two types ofpreparation gave similar scintiphotos, but decreased body background was seen with the electrolyzed solutions. With glucon ate the technetium in both preparations went to the kidneys initially, but with the electrolyzed material the renal activity virtually disappeared within 30 mm, whereas itpersistedfor at least an hour with the SnC12 preparation. The injection of electrolyzed Tc-gluconate, when followed within minutes by injection of a sodium gluconate-SnC solution, fixed the activity in the kidneysjust as it did with the ordinary tin-technetium gluconate kit, but with an hour between injections it produced the same effect as the electrolyzed solution alone. We suggest that tin compounds in the blood change the permeability of various membranes and cause the retention of technetium by the kidneys that is seen with the usual Tc-99m(Sn)glucoheptonate preparations. It is concluded that the reduction of pertechnetate by SnCI2 is not necessaiy for the for mation of the four labeled complexes that we studied, at least in relation to gel chromatographic analysis and scintigrams. The more general question ofthe existence of mixed tin-technetium complexes is briefly discussed. J Nuci Med 20: 766—770, 1979
Recently, Russell reported that he had succeeded in labeling both tetracycline and EDTA with Tc 99m by the reduction of @FcO4at a mercury-pool cathode using a controlled potential (1). This fol lowed his polarographic and voltametric studies
Received Nov. 9, 1978;revision accepted Jan. 17, 1979. For reprints contact: Joseph Steigman, Div. of Nuclear Mcd icine, SUNY Downstate Medical Ctr. , 450 Clarkson Ave., Brooklyn, NY 11203.
of the reduction of @‘FcO4at platinum, gold, glassy carbon, and mercury cathodes, in solutions of dif ferent pH. For each cathode he measured the range of potential available for the reduction of @TcO before the onset of hydrogen evolution, in the pres ence of a large number of potential ligands for the reduced technetium. These studies were then ap plied to the reduction of @TcO4 in solutions of EDTA and tetracycline at the most negative applied potentials at which molecular hydrogen did not form. He concluded that SnCl2 was not necessary
766 THE JOURNAL OF NUCLEAR^ MEDICINE
Scintlphotos In Rabbits Made with Tc-99m Preparations
BASIC SCIENCES RADIOCHEMISTRY AND RADIOPHARMACEUTICALS
for the formation of these two Tc-99m complexes. We had started a more limited investigation of the electrolytic reduction of 99―TcO4before the publication of Russell's comprehensive article. Our immediate goals were the preparation by electrol ysis of several Tc-99m radiopharmaceuticals, an analysis of their yields by gel chromatography, and comparison of rabbit scans made with the electro lyzed solutions and with SnCl2-reduced radiophar maceuticais. In agreement with Russell, we felt that inert cathodes with a high hydrogen overvoltage would be preferable to platinum, since hydrogen evolution on platinum would start virtually at the theoretical equilibrium potential (2) and might pro duce much smaller yields of reduced technetium. Electrolyses were not conducted at controlled po tentials. A simple regulated voltage supply was used, and voltmeter readings were recorded for the applied voltage at which satisfactory yields of the various Tc-99m complexes were obtained. All but one of the experiments reported here were carried out with a graphite cathode.
MATERIALSAND METHODS Equipment. A regulated power supply (range 0— 8 volts) was the source of applied voltage and a multimeter was used to measure current. An elec trolytic H-cell (a two-compartment cell with a sin tered disc and an agar plug saturated with KCI be tween compartments) was the electrolysis vessel. The capacity of the cathode compartment was about 20 ml, and that of the anode compartment 30 ml. The cathodes were ¼-inch-thick graphite rods of moderate purity. The anode was a platinum bas ket and wire. For the chromatographic determina tions, Tc-99m activity was measured in an auto matic well counter. Chromatography was performed with a conventional saline and benzyl alcohol eluant, using Biogel P-b (100—200mesh) in a 0.9- by 30-cm glass column, and fractions collected. Activities injected into the rabbits were measured in a dose calibrator. Animal scans were done with an Anger camera. Chemicals. 1, 1 Hydroxyethylidene diphosphon ate (HEDP) was obtained commercially. Mercury was triple-distilled and nitrogen gas was pre-puri fled. All other chemicals—including gluconolac tone, DTPA, and sodium pyrophosphate—were of reagent grade. Pertechnetate-99m was eluted with normal saline from a generator and diluted as needed. Animals. New Zealand White male rabbits, weighing 6—8lb were used. Procedures. Before electrolysis, the cathode com partment received 10 ml of a previously de-aerated
solution of ligand and [@Tc] pertechnetate in nor mal saline that had been brought to the desired pH. Ten milliliters of normal saline were added to the anode compartment. The catholyte was de-aerated with nitrogen for 30 mm before the electrolysis was started. A small magnetic bar stirred the solution, and nitrogen was passed through it during electrol ysis. At the end, samples were withdrawn either for animal injection or for analysis by column chro matography. The saline eluant and the columns were kept under nitrogen. Two rabbits of approximately equal size were injected i.v. for each run. One was injected in the ear with 1—2ml of an electrolyzed solution, and the other with an equal volume of a solution containing 1 mg SnCl2/ml, with the same ligand, saline, and Tc-99m concentrations as those of the electrolyzed solution. Virtually identical doses, from 250 to 500 @tCi,were administered to the two animals. Each was strapped on a retaining board before injection, and scintigraphed with the camera. For this pur pose, a small target area was selected, the time to reach 2000 counts was recorded, and all images of that particular rabbit were run with that exposure time. When bone-scanning agents were injected, scintigrams were taken 2 hr after injection. Imaging was started within 1 mm after injection of the renal scanning agents. RESULTS Table 1 shows the operating conditions and ana lytical results of electrolyses with a carbon cathode and a platinum anode. In each of the four pairs of radiopharmaceuticals, the Biogel P-b elution pat terns were the same for the electrolytically reduced and the SnC12-reduced preparations. The currents were measured approximately. They averaged 4 mA at 3 volts, 8.6 mA at 4 volts, and 180 mA at 5 volts. Gas bubbles were evolved at each electrode, increasing in rate of formation with increasing cur rent. Figure 1 shows the scintiphotos of two rabbits injected with Tc-99m HEDP preparations (left = electrolytic, right = SnCl2—see Table 1). Images similar to those in Fig. 1 were obtained with Tc-99m pyrophosphate preparations. Figure 2 shows scintiphotos of two rabbits in jected with Tc-99m DTPA preparations (left = elec trolytic, right = SnC12). Figure 3 shows scintiphotos of two rabbits in jected with Tc-99m gluconate preparations (left = electrolytic, right = SnCl2). If an electrolyzed Tc gluconate solution and SnCl2 were injected into the same rabbit within 5 mm of each other, regardless of the order of the injection, the scintiphoto made 1 hr later was indis
Volume 20, Number (^7 )
BASICSCIENCES
RADIOCHEMISTRY AND RADIOPHARMACEUTICALS
preparations yielded images that, at least visually, showed better target-to-nontarget ratios than those from tin. General body backgrounds were lower, and the scans appeared sharper and clearer. That is, soft-tissue uptake was more marked with tin. With gluconate, however, the scintigrams made with the electrolytically generated Tc-99m complex were very different from those made with tin. Ini tially (i.e., 1 mm after injection) there was little difference in kidney uptake. After ½hr, most of the electrolytically reduced technetium had left the kidneys, whereas the tin-reduced compound still showed the same activity. After 1 hr, the difference between them was even more marked. This is cvi dent in Fig. 3. If a SnC12 solution (containing glu conate) and an electrolytically reduced Tc-glucon ate preparation were separately injected into the same animal within 5 mm of one another, the scm tiphoto showed strong activity in the kidneys 1 hr after the two injections, as with the SnCl2-reduced technetium gluconate preparation (see Fig. 3F). The order of injection made no difference to the result. However, if 1 hr elapsed between an injection of SnCl2 and an injection of electrolytically reduced technetium gluconate, the image made 30 mm after the second injection showed very little activity re maining in the kidneys, like that shown in Fig. 3C. It is likely that the tin is producing this retention of technetium activity in the kidneys with the glucon ate preparation. This may be related to the false positive brain scans that are sometimes seen when pertechnetate is injected after a bone scan has been done (3,4). It is possible that tin compounds in the blood change the permeability of various mem branes and that this is the cause of the retention of activity by the kidney that is seen with the usual Tc-99m(Sn)glucoheptonate preparations. If this is so, apparently the renal effect is operative withi'n 5 mm of the injection of the SnCl2-gluconate solu tion, but has been either diluted out or nullified after an hour. We conclude that reduction of pertechnetate by electrolysis on a carbon cathode produces radi opharmaceuticals that are equivalent to those formed by SnC12 reduction in the presence of the four ligands investigated. Reduction by SnCl2 is not necessary for the formation of labeled compounds, at least from the point of view of gel chromato graphic analysis and of scintigrams with the same solutions. This does not prove that SnCl2 fails to form mixed complexes with Tc-99m in these prep arations. It may do so, but if it is, these mixed complexes are not essentially different from the electrolyzed materials in the two respects listed above. The question of mixed-metal complex for mation is a chemical question, and must ultimately
B
4
A
C
E F
FIG. 3. Scintiphotos of two rabbits injected with Tc-99m gluconate preparations. A, C, and E were made with the electrolyzed preparation; B, 0 and F with the SnCl2 prepa ration. A and B were made within 1 mm after injection; C and D 30 mm later; and E and F 1 hr after injection.
the back-EMF generated by the products of dcc trolysis. No attempt was made to determine this true potential. A one-compartment cell cannot be used because oxygen, formed at the anode, will have to be re duced again at the cathode. Figures 1 and 2 show that the scans made with electrolytically reduced Tc-99m compounds were like those of the usual SnCl2-reduccd preparations in the case of DTPA, pyrophosphate, and HEDP preparations, with one difference. The electrolyzed
Volume 20, Number (^7 )
.,,@‘..
D@
STEIGMAN, CHIN, AND SOLOMON
be answered in chemical terms for each technetium compound. In our view, it is extremely unlikely that such mixed complexes exist in all pertechne tate formulations with SnC12, at least in aqueous solution. Two tin-technetium complexes have been reported. One is a tin-technetium-99 complex of dimethylglyoxime that crystallized after long stand ing out of ethanol, not water (5). The other is a mixed Tc(III)-Tc(IV)-Sn(II) complex with ortho phosphate, formed in aqueous solution (6). With respect to the ligands reported here, pyrophosphate in water forms a complex with Tc(III), by electro lytic reduction on mercury, whose spectrum is the same as that formed by SnCl2 reduction (6). Glu conate forms a Tc(V) complex whose spectrum is the same whether formed by the addition of the stoichiometric quantity of SnCl2 required for the reduction, or whether it is formed in the presence of an excess of SnC12(7). If mixed-metal complexes had formed, one would have expected a shift in the spectrum. The question is still unresolved for the DTPA and HEDP complexes of Tc-99, although Russell's conclusions about the EDTA complex can almost certainly be applied to that of the DTPA complex (1). The electrolytically formed gluconate and DTPA complexes were injected on several occasions at least 1 hr after they had been drawn up in the syringes. The scans were not different from those obtained with freshly prepared material. These so
lutions without excess reducing agent were more stable against air oxidation than one might have expected.
ACKNOWLEDGMENT We thank Al Romito and David Giangrande for their most helpful technical assistancewith the scintigrams.
REFERENCES I. RUSSELL CD: Carrier electrochemistry of pertechnetate: Ap plication to radiopharmaceutical labelling by controlled po tential electrolysis at chemically inert electrodes. J mt i AppI Radiat Isotopes 28: 241—249, 1977
2. PAGE JA: Electrogravimetry. In Handbook of Analytical Chemistry, Meites L, ed. New York City, McGraw-Hill, 1963, pp 5— 3. WALKER AG: Effect of Tc-99m-Sn bone scan agents on sub sequent pertechnetate brain scans J Nuc! Med 16: 579, 1975 (Abst)
- CHANDLER WM, SHUCK LD: Effects of tin on pertechnetate distribution. J Nuc! Med 16: 690, 1975 5. DEUTSCH E, ELDER RC, LANGE BA, et al: Structural char acterization of a bridged @‘Tc-Sn-dimethylglyoximecomplex: Implications for the chemistry of @“Tc-radiopharmaceuticals prepared by the Sn(II) reduction of pertechnetate. Proc Nat! Acad Sci USA 73: 4287—4289, 1976
- STEIGMAN J, MEINKEN 0, RICHARDS P: The reduction of pertechnetate-99by stannous chloride. II. The stoichiometry of the reaction in aqueous solutions of several phosphorus **(V) compounds. mt i App! Isotopes 29: 653—660, 1978
- STEIGMANJ, HWANG L, SoLoMoN NA: Complexesof re** duced Tc-99 with polyhydric compounds. J Labelled Cmpd Radiopharm 13: 160, 1977 (abst)
NEW ENGLAND CHAPTER
THE SOCIETY OF NUCLEAR MEDICINE
FALL MEETING
Oct. 13-14, 1979 Downtown Howard Johnsons Boston, Massachusetts
The New England Chapter of the Society of Nuclear Medicine announces its Fall Meeting to be held Oct. 13-14, 1979, at the Downtown Howard Johnsons in Boston, Massachusetts.
Topics for lectures to be presented on Saturday include: a) Differential diagnosis of bone lesions, b) Early detection of gastrointestinal bleeding, c) Liver disease and biliary imaging, and d) Pediatric osteomyelitis and genito-urinary reflux. Workshop sessions will be concerned with Bone, Heart, Pediatrics, and Techniques.
On Sunday, following the presentation of the Blumgart Award to Dr. David Kuhl, there will be a symposium on “TomographicImaging.―
For further information contact:
Dr. H. William Strauss Dept. of Radiology Div. of Nuclear Medicine Massachusetts General Hospital Boston, MA 021 14
770 THE^ JOURNAL^ OF^ NUCLEAR^ MEDICINE
