Highly active antiretroviral therapy (HAART)-associated lactic acidosis: in vitro effects of combination of nucleoside analogues and protease inhibitors on mitochondrial function and lactic acid production.

Lactic acidosis is a rare but potentially life-threatening and poorly understood sequelae among HIV-infected patients on highly active antiretroviral therapy (HAART). Mitochondrial DNA depletion and inhibition of respiratory complexes have been hypothesized to be involved in HAART-associated lactic acidosis. Although mitochondrial toxicity and increased plasma lactates are associated with long-term exposure to nucleoside analogue reverse transcriptase inhibitors (NRTI), reports of lactic acidosis are now emerging among HIV-infected patients exposed to combination therapy that includes not only NRTI but also protease inhibitors (PI). We therefore investigated the effects of clinically relevant NRTI and PI combinations on mitochondrial membrane potential, uncoupling of mitochondrial respiration from oxidative phosphorylation and lactic acid production. Our study demonstrated that treatment of HepG2 cells with a combination of nucleoside analogues and PI, decreased mitochondrial membrane potential (delta psi m) within 24 hr, followed by increased lactic acid production after 9 days of treatment. However, loss of delta psi m and increased lactates were not associated with mitochondrial uncoupling or ATP production. Our findings suggested that not only NRTI but also PI are capable of increasing lactic acid production in vitro, and probably involve early biochemical changes in mitochondrial function such as loss of mitochondrial membrane potential.