A systems biology approach utilizing a mouse diversity panel identifies genetic differences influencing isoniazid-induced microvesicular steatosis.

Isoniazid (INH), the mainstay therapeutic for tuberculosis infection, has been associated with rare but serious hepatotoxicity in the clinic. However, the mechanisms underlying inter-individual variability in the response to this drug have remained elusive. A genetically diverse mouse population model in combination with a systems biology approach was utilized to identify transcriptional changes, INH-responsive metabolites, and gene variants that contribute to the liver response in genetically sensitive individuals. Sensitive mouse strains developed severe microvesicular steatosis compared with corresponding vehicle control mice following 3 days of oral treatment with INH. Genes involved in mitochondrial dysfunction were enriched among liver transcripts altered with INH treatment. Those associated with INH treatment and susceptibility to INH-induced steatosis in the liver included apolipoprotein A-IV, lysosomal-associated membrane protein 1, and choline phosphotransferase 1. These alterations were accompanied by metabolomic changes including reduced levels of glutathione and the choline metabolites betaine and phosphocholine, suggesting that oxidative stress and reduced lipid export may additionally contribute to INH-induced steatosis. Finally, genome-wide association mapping revealed that polymorphisms in perilipin 2 were linked to increased triglyceride levels following INH treatment, implicating a role for inter-individual differences in lipid packaging in the susceptibility to INH-induced steatosis. Taken together, our data suggest that INH-induced steatosis is caused by not one, but multiple events involving lipid retention in the livers of genetically sensitive individuals. This work also highlights the value of using a mouse diversity panel to investigate drug-induced responses across a diverse population.

Liver biomarker and in vitro assessment confirm the hepatic origin of aminotransferase elevations lacking histopathological correlate in beagle dogs treated with GABAA receptor antagonist NP260.

NP260 was designed as a first-in-class selective antagonist of α4-subtype GABAA receptors that had promising efficacy in animal models of pain, epilepsy, psychosis, and anxiety. However, development of NP260 was complicated following a 28-day safety study in dogs in which pronounced elevations of serum aminotransferase levels were observed, although there was no accompanying histopathological indication of hepatocellular injury. To further investigate the liver effects of NP260, we assayed stored serum samples from the 28-day dog study for liver specific miRNA (miR-122) as well as enzymatic biomarkers glutamate dehydrogenase and sorbitol dehydrogenase, which indicate liver necrosis. Cytotoxicity assessments were conducted in hepatocytes derived from dog, rat, and human liver samples to address the species specificity of the liver response to NP260. All biomarkers, except ALT, returned toward baseline by Day 29 despite continued drug treatment, suggesting adaptation to the initial injury. In vitro analysis of the toxicity potential of NP260 to primary hepatocytes indicated a relative sensitivity of dog>human>rat, which may explain, in part, why the liver effects were not evident in the rodent safety studies. Taken together, the data indicate that a diagnostic biomarker approach, coupled with sensitive in vitro screening strategies, may facilitate interpretation of toxicity potential when an adaptive event masks the underlying toxicity.