ABSTRACT
Inhibition of liver mitochondrial beta-oxidation by pharmaceuticals may lead to safety concerns including mitochondrial dysfunction, lipid accumulation, inflammation and necrosis. In this study, the consequences of mitochondrial beta-oxidation inhibition by pharmaceuticals is investigated in human and rat liver slices. The fatty acid oxidation inhibitors Etomoxir and CPI975, inhibit the rate limiting mitochondrial beta-oxidation enzyme carnitine palmitoyltransferase I, while FOX988 and SDZ51-641, sequester mitochondrial coenzyme A to inhibit carnitine palmitoyltransferase II. Mitochondrial dysfunction was evident by a significant decrease of liver slice ATP levels and mitochondrial injury was verified by ultrastructural changes in morphology, manifested as enlarged mitochondria, C- or O-shaped mitochondria, and granular or crystalline inclusions. Gene expression changes were evident prior to changes in mitochondrial morphology. Time- and concentration dependent changes in mitochondrial genes linked with respiration and mitochondrial fatty acid beta-oxidation were associated with an up-regulation of peroxisome fatty acid oxidation genes, likely as a compensatory mechanism for the inhibition of the mitochondrial pathways. Gene expression changes preceding the decline of liver slice ATP and GSH levels included an up-regulation of stress response and oxidative stress gene expression, as well as genes linked with transcription, transporters, proliferation, cell matrix and signaling. In association with the decline of liver slice ATP and GSH was increased apoptosis and inflammation. Caspase activity, a functional indicator of apoptosis, was significantly increased as well as an up-regulation of genes linked with apoptosis. The increased gene and protein expression of the pro-inflammatory cytokine IL-8, produced by endothelial cells, is likely in response to the manifestation of oxidative stress and GSH depletion; further amplifying the oxidative stress response induced by the fatty acid oxidation inhibitors and triggering an inflammatory response. In summary, human and rat liver slices exhibited similar effects to the inhibitors of mitochondrial beta-oxidation, and the mitochondrial injury is associated with apoptosis and inflammation in the liver slices.
