[Pharmacological studies of N-(2-mercapto-2-methylpropionyl)-L-cysteine (SA 96). VI. Effects on vitamin B6, metals and skin collagen in rats]

Reversible disulfide formation of the glutamate carboxypeptidase II inhibitor E2072 results in prolonged systemic exposures in vivo

E2072 [(3-2-mercaptoethyl)biphenyl-2,3'-dicarboxylic acid] is a novel, potent and selective thiol-based glutamate carboxypeptidase II (GCP-II) inhibitor that has shown robust analgesic and neuroprotective efficacy in preclinical models of neuropathic pain and chemotherapy-induced peripheral neuropathy. For the first time, we describe the drug metabolism and pharmacokinetic profile of E2072 in rodents and primates. Intravenously administered E2072 was found to exhibit an unexpectedly long terminal half-life (105 ± 40 h) in rats. The long half-life was found to be the result of its ability to rapidly form reversible homo- and possibly heterodisulfides that served as a continuous E2072 depot. The half-life of reversible homodisulfides was 208 ± 81 h. In further support, direct intravenous administration of the E2072-homodisulfide in rats resulted in the formation of E2072, with both E2072 and its disulfide detected in plasma up to 7 days after dose. The observed long exposures were consistent with the sustained efficacy of E2072 in rodent pain models for several days after dose cessation. It is noteworthy that a shorter t(½) of E2072 (23.0 ± 1.2 h) and its homodisulfide (21.0 ± 0.95 h) was observed in primates, indicating interspecies differences in its disposition. In addition, E2072 was found to be orally available with an absolute bioavailability of ∼30% in rats and ∼39% in monkeys. A tissue distribution study of E2072 and its homodisulfide in rats showed good tissue penetration, particularly in sciatic nerve, the presumed site of action for treatment of neuropathy. Metabolic stability and the correlation between pharmacokinetic profile and pharmacological efficacy support the use of this GCP-II inhibitor in the clinic.

The utility of chelating agents as antidotes for nephrotoxicity of gold sodium thiomalate in adjuvant-arthritic rats

The effects of 2,3-dimercaptopropane sulphonate (DMPS) and N-(2-mercapto-2-methylpropanoyl)-L-cysteine (bucillamine) against the renal damage induced by gold sodium thiomalate (AuTM) in adjuvant-arthritic rats were studied. Arthritic rats induced by adjuvant using Mycobacterium butyricum were injected intraperitoneally with a chelating agent (0.6 mmol/kg) immediately after intramuscular injection of AuTM (0.066 mmol/kg) every other day for 21 days. Treatment with DMPS and bucillamine prevented increases in the urinary excretion of protein, aspartate aminotransferase, and glucose and blood urea nitrogen level after AuTM injection. AuTM prevented the increase in both adjuvant-injected and uninjected hind-feet volumes. The prevention of these inflamed lesions by AuTM was not affected by DMPS and bucillamine. These chelating agents decreased the gold concentration in the kidney and liver after AuTM administration, but did not affect the hepatic and renal concentrations of copper, zinc, iron, and calcium except the renal copper level after AuTM. These findings suggest that DMPS and bucillamine are very useful antidotes for gold toxicity.

Differences in the effects of the antirheumatic drugs, bucillamine and D-penicillamine, on mitogen-induced proliferation of mouse spleen cells

The effect of bucillamine [N-(2-mercapto-2-methylpropionyl)-L-cysteine], a new antirheumatic drug, on the concanavalin A (Con A)-induced proliferation of mouse spleen cells was compared with the effect of D-penicillamine (D-pen). Bucillamine inhibited the Con A-induced incorporation of thymidine (TdR) into mouse spleen cells in a dose-dependent fashion. At the concentration of 10(-4) M, bucillamine inhibited the incorporation by approximately 80%. The inhibitory effect of bucillamine was not enhanced by the addition of copper. In contrast, D-pen showed the same degree of inhibition only in the presence of copper. (4R)-7,7-Dimethyl-6-oxo-tetrahydro-3H-1,2,5-dithiazepine-4-carboxy lic acid (SA981), an intramolecular disulfide derivative of bucillamine, also showed the same degree of inhibition as bucillamine in the absence and presence of copper, whereas D-penicillamine disulfide did not show the inhibitory effect even in the presence of copper. The inhibitory effects of bucillamine and SA981 were not abolished significantly by the addition of catalase which restored the inhibition by D-pen plus copper. The mechanism of inhibition by D-pen plus copper is believed to involve the production of hydrogen peroxide resulting from the oxidation of D-pen. The results in this study, however, indicated that the inhibitory effect of bucillamine is not due to the production of hydrogen peroxide.