Gallium-67 complexes as radioactive markers to assess gastric and colonic transit.

UNLABELLED: Constipation and gastroparesis are gastrointestinal tract disorders that can be assessed by using radioactive markers in conjunction with scintigraphic techniques. Indium-111-DTPA is the radiopharmaceutical of choice for treating colonic transit in constipated patients, but it is an expensive product and its availability has been unreliable. Indium-113m-DTPA was the tracer used in our study to determine the liquid gastric emptying rate in dual-isotope solid/liquid emptying studies, however, cessation of the 113Sn/113mIn generator production makes it unavailable. Thus, development of alternative tracers to 111In-DTPA and 113mIn-DTPA was essential. METHODS: Gallium-67-citrate and 67-Ga-EDTA were compared to 111In-DTPA to assess their efficacy for exclusive retention in the Gl tract. These markers were orally administered into rats and their three-day cumulative fecal excretion, urine excretion and carcass retention were measured. An in vitro gastric emptying model was used to determine liquid phase partitioning of 113mIn-DTPA, 67Ga-citrate and 67Ga-EDTA at 37 degrees. RESULTS: Gallium-67-citrate was predominantly excreted in the feces (97.2% +/- 0.2%) after three days, with negligible urine excretion (0.1% +/- 0.0%) and carcass retention (0.6% +/- 0.2%). These results are analogous to those obtained for 111In-DTPA for fecal excretion (96.7% +/- 2.6%), urine excretion (0.6% +/- 0.0%) and retention in the carcass (0.2% +/- 0.0%). Gallium-67-EDTA showed similar partitioning in the liquid phase of the gastric emptying model compared with 113mIn-DTPA. CONCLUSION: Gallium-67-citrate is an economical and readily available alternative to 111In-DTPA as a colonic transit radiopharmaceutical. Gallium-67-EDTA is also an alternative to 113mIn-DTPA for assessing liquid-phase emptying in a dual-isotope solid/liquid gastric emptying study.

Kit preparation of technetium-99m-mercaptoacetyltriglycine: analysis, biodistribution and comparison with technetium-99m-DTPA in patients with impaired renal function.

Technetium-99m-mercaptoacetyltriglycine (99mTc-MAG3) was prepared by a frozen solution method, enabling the preparation of kits yielding a product substantially free of lipophilic impurities (96% 99mTc-MAG3). However, biliary activity was not completely eliminated as HPLC-purified 99mTc-MAG3 was also excreted by that route. Sequential 99mTc-DTPA and 99mTc-MAG3 renal scans were performed in 15 patients with renal dysfunction, including renal transplant recipients. In all cases, the 99mTc-MAG3 kit preparation provided superior images to 99mTc-DTPA at all levels of renal function due to a higher target-to-background ratio and a plasma clearance twice as fast as 99mTc-DTPA. Interpretation of delayed 99mTc-MAG3 images, however, was complicated by biliary excretion which will limit quantitative estimates of renal clearance. A 99mTc-MAG3 kit is likely to be of value in renal transplant assessment and in cases of significant renal impairment but would not appear to offer major advantages over 99mTc-DTPA in routine renal imaging.

Radiochemical characterization of modified Technegas.

The aim of this study was to characterize modified Technegas, employing radiochemical analyses and qualitative rabbit organ imaging techniques. Electrophoresis, thin layer chromatography and imaging studies, found modified Technegas to behave like sodium [99mTc]pertechnetate (pertechnetate). Our data indicate that modified Technegas is a pertechnetate aerosol, which results from the presence of 3% oxygen in the reaction atmosphere of the Technegas generator.

Radiolabeling and biodistribution of amiodarone and desethylamiodarone.

The antiarrhythmic drug amiodarone and its metabolite desethylamiodarone, were radiolabeled with sodium [123I]-iodide in > 98% yield using the exchange labeling method. Biodistribution studies with 123I-amiodarone in mice showed high liver and lung uptake. Heart uptake of 0.98% of the injected dose (id) peaked at 5 min, with clearance seen over 60 min to 0.44% id. 123I-Desethylamiodarone (123I-DEA) showed heart uptake of 0.58% id peaking at 5 min, with slower clearance seen over 60 min to 0.43% id. These results indicate that both agents have poor selectivity as myocardial imaging tracers. Low 123I-DEA brain uptake at 5 min (0.49% id) and rapid washout after 60 min indicate that 123I-desethylamiodarone has limited application as a brain imaging agent.

99mTc-alafosfalin: an antibiotic peptide infection imaging agent.

The radiolabeled antibiotic peptide (99m)Tc-alafosfalin was assessed as an infection imaging agent in a rat model by comparison with (99m)Tc-DTPA and (99m)Tc-leukocytes. (99m)Tc-alafosfalin was prepared via an instant cold kit and (99m)Tc-leukocytes were prepared using (99m)Tc-stannous fluoride colloid in an ex vivo labeling procedure of whole blood. In separate experiments, the three radiotracers were administered to rats infected with staphylococcus aureus. Quantitative biodistribution studies were performed as well as scintigraphic images and histopathology. (99m)Tc-alafosfalin is a stable product, obtained in high radiochemical purity (>95%). This agent was mainly renally excreted, with low liver, spleen and bone uptake, and resulted in a mean ratio of infected/non-infected thighs of 4.3/1.0 at 4 hr post radiotracer injection. (99m)Tc-DTPA gave a corresponding ratio of 1.9/1.0 and (99m)Tc-leukocytes gave 20.0/1.0 at the same time point. An in vitro assay found the level of (99m)Tc-alafosfalin binding to staphylococcus aureas higher than (99m)Tc-DTPA (10% versus 1% respectively). (99m)Tc-alafosfalin accumulates at sites of infection in a rat model better than the perfusion molecule (99m)Tc-DTPA, yet less than (99m)Tc-leukocytes. The distribution characteristics of this (99m)Tc-antibiotic peptide would be an advantage in imaging abdominal and soft tissue infection.

Increased permeability of psoriatic skin to the protein, plasminogen activator inhibitor 2.

The penetration and permeation of the recombinant protein plasminogen activator inhibitor type 2 (PAI-2) in two formulations, one containing a penetration enhancer, into the psoriatic and uninvolved skin of eight patients with plaque-type psoriasis were investigated. Penetration and permeation of PAI-2 were measured by gamma counting and imaging following radiolabelling of a fraction of the applied PAI-2 with (123)I. The feasibility of topical delivery of drug to psoriatic plaques was confirmed by the finding that the permeability of psoriatic plaques to radiolabelled PAI-2 (P=0.007) and free (123)I (P=0.001) was approximately tenfold higher than the permeability of uninvolved skin. The addition of a penetration enhancer improved the permeation of PAI-2 into psoriatic plaques from an average of 35% to 46% (P=0.005). Occlusion decreased the permeation amount of PAI-2 from 46% to 15% due to losses on the occlusive dressing (P=0.001).

99Tcm-tetrofosmin: evaluation of fractionated cold kits and two new methods of quality control.

The fractionation of Myoview into 1:5 was followed by storage at -80 degrees C for 3 months. The kits were reconstituted with 3.5 GBq 99Tcm-pertechnetate and the average radiochemical purity (RCP) was maintained at 96.5 +/- 1.6% (n = 24) for 24 h. There was no difference in biodistribution between the 1:5 fraction and the full kit, especially with respect to myocardial uptake. These observations show that it is possible to fractionate and store Myoview kits at -80 degrees C and produce a product that is stable over 3 months. This provides a cost-effective method for using 99Tcm-tetrofosmin. Two new methods of determining RCP were also examined and found to give results that were not significantly different from the recommended manufacturer's method. A mini paper chromatography (MPC) method using Whatman 17 paper and a solvent mixture of ethyl acetate: acetone (1:9) and an Amprep SAX cartridge method using absolute ethanol as the solvent were found to be more rapid and reliable methods of quality control for this product.

Validation of a column method for technetium-99m exametazime quality control.

OBJECTIVE: The purpose of this study was to investigate if an octadecyl (18C) minicolumn could be applied successfully for quality control of 99mTc exametazime (HMPAO). METHODS: The 18C column system using saline eluent was validated against the Whatman 17 method in calculating the percent radiochemical purity of 99mTc-HMPAO. The behavior of 99mTc-pertechnetate (99mTc04-) and hydrolyzed-reduced 99mTc (99mTc02) on the column was examined, as well as method reproducibility. RESULTS: The column method is reproducible and yields results that are highly comparable to the Whatman 17 method. Technetium-99m-pertechnetate is associated with the eluent, and some 99mTc02 is retained by the column but this level is insignificant to the final patient dose. CONCLUSION: The minicolumn system is safe, simple, rapid and reliable for the quality control analysis of routine 99mTCHMPAO preparations.

The pharmacokinetics of salicylate in the pregnant Wistar rat.

Sodium salicylate, in a single dose of 50 mg/kg, was administered by iv injection to nonpregnant female and 20-day pregnant Wistar rats. Blood samples (for serum) and urine were collected and analyzed for salicylate, gentisic acid, salicyluric acid, and salicyl glucuronides by HPLC. Pregnant rats showed a significant decrease in body weight-normalized total clearance but no change in absolute total clearance of salicylate. On a body weight-adjusted basis there was a slight increase in the apparent volume of salicylate distribution in pregnancy but this increase becomes highly significant if expressed in absolute terms. The biological half-life of salicylate was significantly increased in late pregnancy. Serum protein binding of salicylate is decreased in pregnancy relative to nonpregnant females but in both groups binding shows a concentration dependence. The partial clearances of both salicyluric and gentisic acids were reduced by pregnancy in the rat whereas that of the salicyl glucuronides appeared unchanged. This latter result in intact pregnant animals contrasts with previously reported decreases in glucuronyltransferase activity in isolated liver preparations from pregnant rats.

Pyridine nucleotide involvement in rat hepatic drug metabolism. The influence of NADH on the NADPH kinetics of phenobarbital pre-treated rat microsomes.

Apparent kinetic constants for NADPH have been calculated for NADPH-cytochrome P450 reductase and demethylase activity in the presence of aminopyrine and ethylmorphine with hepatic microsomal preparations from phenobarbital pre-treated rats. The presence of NADH changed Km values but not the V values for cytochrome P450 reductase. In addition, NADH reduced Km values for demethylase activity and had a biphasic effect on V values; elevating them at high and depressing them at low concentrations. The V values at different NADH concentrations appeared to correlate with the concentration of reduced cytochrome b5 that the added NADH could sustain during the incubation period. Tetrahydronicotinamide adenine dinucleotide (NADH3), a structural analogue of NADH, reduced demethylase activity without affecting NADPH-cytochrome P450 reductase activity or the concentration of reduced cytochrome b5. As this analogue cannot reduce biological systems, the depressed V values for demethylation suggest that in the presence of NADH3 and NADPH there exists an alternative mechanism for the supply of electrons from NADPH to the partially reduced oxygenated cytochrome P450-substrate complex.

Pyridine nucleotide involvement in rat hepatic drug metabolism: pyridine nucleotide kinetics of aniline parahydroxylation.

Apparent kinetic constant (NADPH) have been calculated for NADPH-cytochrome P450 reductase and parahydroxylase in the presence of aniline with hepatic microsomes from both phenobarbital pre-treated and untreated rats. The addition of NADH gave similar stimulation of both aniline parahydroxylation and NADPH-cytochrome P450 reductase activity in the presence of aniline. It is proposed that the increase in aniline metabolism with NADH is due to an increase in the NADPH-cytochrome P450 reductase activity which is rate limiting in microsomes from both phenobarbital and untreated rats.

Antipyrine pharmacokinetics in the pregnant rat.

Pronounced differences in pharmacokinetic parameters of antipyrine have been found in the 20-day pregnant hooded Wistar rat when compared with nonpregnant controls. Total body clearance falls significantly from 5.93 to 3.5 ml/min/kg in the pregnant rat whereas no significant increase in antipyrine volume of distribution occurs. These changes result in an increase in antipyrine half-life from 109 to 223 min in the pregnant rat. This study demonstrates that reduced hepatic mono-oxygenase capacity exists in the pregnant rat and that this can markedly affect drug clearance in there animals.

The preparation of 99mTc-tertiarybutylisonitrile (99mTc-TBI) by a method suitable for routine clinical use.

The myocardial imaging agent technetium-99m-hexakis (tertiarybutylisonitrile) (99mTc-TBI) was prepared by the reaction of [99mTc]pertechnetate with TBI in 50% ethanol/0.9% saline at 100 degrees C, using stannous chloride as the reducing agent. A study of the reaction parameters enabled the yield to be optimized to better than 90%, although this was reduced to approximately 60% if a purification step was carried out. Chromatographic analysis on ITLC-SG medium showed the final product to be of high radiochemical purity. Biological studies comprising biodistribution in mice over a 2-h period, imaging studies in animals and sub-acute toxicity testing in mice indicated that 99mTc-TBI prepared as here described is a suitable agent for routine clinical use in humans.

The effect of lipophilic substituents on the biological properties of EDTA complexes containing paramagnetic metal ions.

Complexes of the radioactive paramagnetic metal ions 51Cr(III), 54Mn(II), 59Fe(III), 57Co(II), 64Cu(II) and 153Gd(III) were prepared with EDTA and its derivative containing the lipophilic 1-(4-methylphenyl)-group (MPEDTA), together with the corresponding 99mTc-compounds. The formation of these complexes was verified by electrophoresis and they were screened for potential use as MRI hepatobiliary contrast agents by biodistribution studies in mice. In this series, the MPEDTA complexes of 54Mn(II) and 64Cu(II) showed increased urinary excretion compared to the unsubstituted EDTA complexes, while the MPEDTA complexes of 99mTc, 59Fe, 57Co, 153Gd and particularly 51Cr demonstrated improved hepatobiliary excretion. Further lipophilic substitution should enhance this property but the preparation of such ligands is complicated by cyclisation reactions.