Mitochondrial (mt)DNA changes in tissue may not be reflected by depletion of mtDNA in peripheral blood mononuclear cells in HIV-infected patients

Abstract

Objectives: Most data on mitochondrial toxicity have been derived from peripheral blood mononuclear cells (PBMCs). However, whether mitochondrial DNA (mtDNA) content in PBMCs reflects the mitochondrial state in tissues remains elusive. We report herein on mitochondrial toxicity in skeletal muscle in HIV-infected patients naive to antiretroviral treatment (ART [HIV+ART-naive]; n = 10) patients exposed to nucleoside reverse transcriptase inhibitors (NRTIs [HIV+NRTI+]; n = 24) and healthy controls (n = 11), and compare these tissue data with mtDNA in PBMCs.

Methods: Muscle biopsies were examined for (i) mtDNA and nuclear DNA (nDNA) content using TaqMan real-time PCR system, (ii) mtDNA deletions using long expand PCR with subsequent gel electrophoresis, and (iii) mitochondrial myopathy expressed as cytochrome c oxidase (COX)-deficient muscle fibres.

Results: The mt/n DNA ratio in muscle from HIV+NRTI+ patients was reduced compared with HIV-negative controls (P = 0.028). Moreover, mtDNA deletions were more frequent in HIV+NRTI+ patients than in both HIV-negative controls (P = 0.009) and HIV+ART-naive patients (P = 0.005). HIV+NRTI+ also tended to have more COX-deficient fibres than HIV-negative controls (P = 0.076). COX-deficient fibres were positively correlated with mtDNA deletions in HIV+NRTI+ patients (r = 0.83, P < 0.001). Patients with current use of didanosine (ddl) had more frequent mtDNA deletions and COX-deficient fibres than HIV+NRTI+ not on current treatment with ddl. It should be noted that mitochondrial alterations were not correlated with mtDNA/cell in PBMCs in any group.

Conclusions: In skeletal muscle, HIV+NRTI+ had a reduced mt/n DNA ratio, more frequent mtDNA deletions and possibly more COX-deficient muscle fibres than HIV-negative controls. However, the mtDNA/cell in peripheral blood was decreased in both HIV+NRTI+ and HIV+ART-naive patients. Thus, mtDNA in peripheral blood may not be a relevant marker of mitochondrial toxicity in organ-specific tissue.