Alteration of cytochrome oxidase subunit I labeling is associated with severe mitochondriopathy in NRTI-related hepatotoxicity in HIV patients

Liver mitochondrial toxicity induced by nucleoside reverse transcriptase inhibitors (NRTI) in human immunodeficiency virus (HIV) patients has been associated with a wide range of liver involvement ranging from low-grade hepatotoxicity, asymptomatic lactacidemia to severe liver insufficiency, with massive steatosis and life-threatening lactic acidosis. Considerable efforts have been made in the last few years to establish clinical guidelines to avoid life-threatening NRTI-associated lactic acidosis. However, the important issue of low-grade NRTI-associated hepatotoxicity still needs to be unravelled since its natural history is largely unknown. We have recently reported a series of 13 monoinfected HIV patients with low-grade NRTI-associated toxicity. Our results outlined the heterogeneity of NRTI-induced hepatotoxicity and raised the question of its diagnosis. The present study evaluates the expression of cytochrome oxidase (COX) subunits I and IV, encoded by mitochondrial and nuclear DNA, respectively, in NRTI hepatotoxicity. The aim of our study was to compare the detection rate of mitochondrial abnormalities of immunohistochemistry for COX subunit I with electron microscopy. COX subunit I and IV labeling was performed together with light microscopy and ultrastructural analysis in a series of 55 liver biopsies from HIV monoinfected and HIV-hepatitis C virus coinfected patients. Clinical data were also recorded. Our major findings were: (i) decreased COX subunit I labeling is associated with severe ultrastructural mitochondrial alterations and may represent overt NRTI-induced mitochondrial cytopathy; (ii) mild ultrastructural damage associated with normal COX subunit I labeling is of unknown clinical significance. The results of the study suggest that COX subunit I labeling may be a valuable tool for the diagnosis of mitochondrial liver disease in HIV patients.