Role of bile salts in colchicine-induced hepatotoxicity. Implications for hepatocellular integrity and function.

Colchicine, a microtubule-disrupting agent, induces hepatotoxicity in experimental animals at the doses commonly employed to explore vesicular transport in the liver. The effect of manipulations of the bile salt pool on colchicine-induced hepatotoxicity was studied in rats to determine the role of bile salts in this phenomenon. Leakage of enzyme markers of liver-cell damage into plasma and bile induced by colchicine pre-treatment displayed a sigmoidal log dose-effect curve, the half-maximal effect being reached at 0.12 micromol per 100 g body wt. Lumicolchicine, instead, showed no harmful effect. Maximal increment of biliary LDH discharge induced by colchicine was reduced from 950 +/- 124% to 216 +/- 29% by bile diversion leading to a marked reduction in bile salt output, and this parameter was further decreased to 100 +/- 13% and 157 +/- 39% by subsequent repletion of the bile salt pool with the hydrophilic bile salts taurodehydrocholate and tauroursodeoxycholate, respectively. Conversely, infusion of taurocholate into non-bile salt depleted, colchicine-treated rats led to cholestasis and massive discharge of enzymes into both blood and bile. Our data show conclusively that colchicine-induced hepatotoxicity depends on the magnitude and composition of the bile salt flux traversing the liver. They also support the view that functional integrity of vesicular mechanisms presumably involved in membrane repair are indispensable to protect the hepatocytes from the damaging effect of bile salts during normal bile formation.

Studies related to the use of colchicine as a neurotoxin in the septohippocampal cholinergic system.

Colchicine has been shown to be neurotoxic to cholinergic neurons in the medial septum 1 week following intracerebroventricular injections. The experiments described here were designed to examine the selectivity of this effect over a longer time course, and to examine the role of axoplasmic transport in the neurotoxic effect. As previously reported, 1 week after intracerebroventricular injections of colchicine, the numbers of choline acetyltransferase (ChAT)-immunoreactive neurons in the medial septum-diagonal band complex (MSDB) were reduced to 38% of control; this reduction was stable 2 and 3 weeks post injection. Injections of colchicine placed into the body of the fornix produced similar results. GAD-immunoreactive somata, the other major population of neurons in the MSDB, were unaffected 3 weeks following colchicine, as previously reported 1 week following similar injections. The normal AChE staining pattern in the hippocampus, particularly the dentate gyrus, was depleted following either ICV or intrafornical injections of colchicine. This depletion was more severe with longer survival times. Injections of lumicolchicine, an isomer of colchicine which does not bind tubulin, had no effect on ChAT-immunoreactive neurons in the MSDB or on AChE staining in the hippocampus. Injections of colchicine, but not of lumicolchicine, partially blocked the retrograde transport of the fluorescent dye Fluoro-Gold from the hippocampus to the MSDB. In addition, the content of NGF in the hippocampus rose 84% above control values 2 weeks following colchicine and remained elevated at three weeks. Together these results indicate that colchicine is selectively toxic for cholinergic neurons in the septohippocampal system, and suggest that the alkaloid's neurotoxic effects work via the blockade of axoplasmic transport.

Behavioral investigation of neurotoxicity: the effects of colchicine, lumicolchicine and vincristine sulfate on goldfish optic nerve regeneration.

Experiments were carried out to investigate a behavioral method of assessing neurotoxicity. The proposition is that developing or regenerating neurons. The regenerating optic nerve in goldfish was examined as a preparation for investigating the effects of chemicals on neuronal development. Restoration of optic nerve connections following crushing of the optic nerve, as detected by a noninvasive behavioral technique permitting sequential testing of individual fish, occurred within 17 days. The effect on regeneration of biweekly, intraperitoneal administration of alkaloid neurotoxins was investigated. Regeneration was inhibited by colchicine and vincristine sulfate but not by lumicolchicine. The potency of vincristine was approximately twice that of colchicine. Neither drug had a detectable effect on the maintenance of optic nerve function in sham-operated fish. The results suggest that the behavioral protocol can be used to identify chemical agents which impair neuronal development in vivo, and to estimate their relative neurotoxicity.

The effects of colchicine and vinblastine on memory in chicks.

Colchicine, injected bilaterally into the forebrain of day-old chicks at times before and after one-trial avoidance learning, produced transient amnesia for one to three hours after learning, that could not be accounted for as a perceptual or attentional defect. The amnesia was dose dependent and was produced only when injections occurred within a limited period before and after learning. No amnesia occurred when injections were given 120 min before or 60 min later than the learning trial, nor at times prior to the retrieval test. During the amnesic period, new learning could occur and be retrieved 15 min later. The amnesia could be overcome by retention-testing or by a new, related, learning experience before or up to 30 min after onset of amnesia. Control birds injected with saline or lumicolchicine, a biologically inactive derivative of colchicine, showed normal retention. Vinblastine sulphate, which also interrupts microtubular networks and hence axonal flow, had no amnesic properties. Colchicine injections had no effect on the levels of acetylcholinesterase, choline acetyltransferase, glutamic acid decarboxylase, and muscarinic acetylcholine receptors in the whole forebrain or in forebrain synaptosomes during the amnesic period. Nor did colchicine injections affect amino acid uptake and protein or glycoprotein synthesis before or during the amnesic period, although there was 10-20% inhibition of protein synthesis 5 h after injection. Thus over the amnesic period, there was no evidence of gross perturbation of brain function. Electron microscopy showed microtubules intact within 1 mm of the injection site 2.5 after injection. Oedema was found at this time in chicks injected with a high dose (100 micrograms) shown to disturb behaviour grossly, but not with a low dose (5 micrograms) which caused amnesia. Transient amnesia for one-trial avoidance learning is most probably caused by secondary effects of colchicine on nerve cell function. We suggest that the amnesic episode represents destruction of one of the stages of a multiple independent parallel process of memory consolidation.