The role of l-thyroxine and hepatic reductase activity in isoniazid-induced hepatotoxicity in rabbits

Protective effect of picroliv against hydrazine-induced hyperlipidemia and hepatic steatosis in rats

The protective effect of picroliv (PIC) obtained from Picrorhiza kurroa (family: Scrophulariaceae) against hydrazine (Hz)-induced hyperlipidemia was evaluated in rats. Hz administration (50 mg/kg, i.p.) caused an increase in triglyceride (TG), cholesterol (CHO), free fatty acids (FFA), and total lipids (TL) in both the plasma and liver tissue of rats accompanied by a fall in phospholipids (PL) in the liver tissue 24 h after its administration, indicating its hyperlipidemic property. The above abnormality was prevented by simultaneous treatment of PIC (50 mg/kg, p.o.) with Hz. Hz treatment also caused an increase in the mobility of TG and TL from adipose tissue, and these results indicate that Hz administration could cause hepatic steatosis by nonhepatocellular factors (such as mobilization of depot fats). This effect was also prevented by simultaneous treatment of PIC with Hz. PIC-alone treatment, however, did not produce any change in the status of all the lipid parameters evaluated in plasma, liver, and adipose tissues. These results indicate that increased mobilization of depot fats from adipose tissue may contribute to the development of hepatic steatosis in addition to decreased lipoprotein secretion, increased hepatic TG biosynthesis, and increased hepatic uptake of FFA. These have been reported as the mechanism responsible for the development of Hz-induced hepatic steatosis. PIC prevents Hz-induced hyperlipidemia, hepatic steatosis, and mobilization of lipids from depot fats, but the mechanism behind the protective effect of PIC remains to be elucidated.

The Effect of pyrazinamide and rifampicin on isoniazid metabolism in rats

Hepatotoxicity is the main concern during tuberculosis chemotherapy with the first-line drugs isoniazid (INH), rifampicin (RMP) and pyrazinamide (PYR). Since these hepatotoxic events have been associated with INH metabolites, the study aimed to measure the area under curve (AUC) parameter for INH and its metabolites acetylisoniazid (AcINH), hydrazine (Hz) and acetylhydrazine (AcHz), when groups of rats were pre-treated for 21 days with INH alone or in combination with RMP and/or PYR, in the following amounts per kg body weight: INH 100 mg; INH 100 mg + RMP 100 mg; INH 100 mg + PYR 350 mg; INH 100 mg + PYR 350 mg + RMP 100 mg. It was found that co-administration of RMP, PYR and RMP + PYR caused a significant decrease in the AUC for INH. Co-administration of PYR was the only treatment that caused a significant increase in the AUC for Hz and a decrease in the AUC for its acetylated product AcHz. The AUC for AcINH was not significantly altered in any experimental group. In conclusion, the increased metabolism of INH in all the drug combinations and the significantly higher production of Hz in the group INH + PYR might be linked with exacerbated hepatotoxic effects of these drug associations.

Energy metabolism and biotransformation as endpoints to pre-screen hepatotoxicity using a liver spheroid model

The current study investigated liver spheroid culture as an in vitro model to evaluate the endpoints relevant to the status of energy metabolism and biotransformation after exposure to test toxicants. Mature rat liver spheroids were exposed to diclofenac, galactosamine, isoniazid, paracetamol, m-dinitrobenzene (m-DNB) and 3-nitroaniline (3-NA) for 24 h. Pyruvate uptake, galactose biotransformation, lactate release and glucose secretion were evaluated after exposure. The results showed that pyruvate uptake and lactate release by mature liver spheroids in culture were maintained at a relatively stable level. These endpoints, together with glucose secretion and galactose biotransformation, were related to and could reflect the status of energy metabolism and biotransformation in hepatocytes. After exposure, all of the test agents significantly reduced glucose secretion, which was shown to be the most sensitive endpoint of those evaluated. Diclofenac, isoniazid, paracetamol and galactosamine reduced lactate release (P <0.01), but m-DNB increased lactate release (P <0.01). Diclofenac, isoniazid and paracetamol also reduced pyruvate uptake (P <0.01), while galactosamine had little discernible effect. Diclofenac, galactosamine, paracetamol and m-DNB also reduced galactose biotransformation (P <0.01), by contrast, isoniazid did not. The metabolite of m-DNB, 3-NA, which served as a negative control, did not cause significant changes in lactate release, pyruvate uptake or galactose biotransformation. It is concluded that pyruvate uptake, galactose biotransformation, lactate release and glucose secretion can be used as endpoints for evaluating the status of energy metabolism and biotransformation after exposure to test agents using the liver spheroid model to pre-screen hepatotoxicity.