Cytoprotective Properties of Carnosine against Isoniazid-Induced Toxicity in Primary Cultured Rat Hepatocytes

Background: Drug-induced liver injury is a critical clinical complication. Hence, finding new and safe protective agents with potential clinical application is of value. Isoniazid (INH) is an antituberculosis agent widely used against Mycobacterium tuberculosis infection in human. On the other hand, hepatotoxicity is a clinical complication associated with isoniazid therapy. Oxidative stress and its associated events are major mechanisms identified for INH-induced liver injury. Carnosine is an endogenously found peptide widely investigated for its hepatoprotective effects. On the other hand, robust antioxidant and cytoprotective effects have been attributed to this peptide. Methods: The current study designed to evaluate the potential cytoprotective properties of carnosine against INH-induced cytotoxicity in drug-exposed primary cultured rat hepatocytes. Primary cultured rat hepatocytes were incubated with INH (1.2 mM). Results: INH treatment caused significant increase in cell death and lactate dehydrogenase (LDH) release. On the other hand, it was found that markers of oxidative stress including reactive oxygen species were significantly increased in INH-treated cells. Cellular glutathione reservoirs were also depleted in INH-treated group. Carnosine treatment (50 and 100 µM) significantly diminished INH-induced oxidative stress and cytotoxicity. Conclusion: These data mention carnosine as a potential protective agent with therapeutic capability against INH hepatotoxicity.

Acidosis-induced downregulation of hepatocyte mitochondrial aquaporin-8 and ureagenesis from ammonia

It has been proposed that, during metabolic acidosis, the liver downregulates mitochondrial ammonia detoxification via ureagenesis, a bicarbonate-consuming process. Since we previously demonstrated that hepatocyte mitochondrial aquaporin-8 channels (mtAQP8) facilitate the uptake of ammonia and its metabolism into urea, we studied whether mtAQP8 is involved in the liver adaptive response to acidosis. Primary cultured rat hepatocytes were adapted to acidosis by exposing them to culture medium at pH 7.0 for 40 h. Control cells were exposed to pH 7.4. Hepatocytes exposed to acid medium showed a decrease in mtAQP8 protein expression (–30%, p < 0.05). Ureagenesis from ammonia was assessed by incubating the cells with 15N-labeled ammonia and measuring 15N-labeled urea synthesis by nuclear magnetic resonance. Reduced ureagenesis was found in acidified hepatocytes (–31%, p < 0.05). In vivo studies in rats subjected to 7 days acidosis also showed decreased protein expression of hepatic mtAQP8 (–50%, p < 0.05) and reduced liver urea content (–35%; p < 0.05). In conclusion, our in vitro and in vivo data suggest that hepatic mtAQP8 expression is downregulated in acidosis, a mechanism that may contribute to decreased ureagenesis from ammonia in response to acidosis.