Elevated Cell-Free Mitochondrial DNA in Filtered Plasma Is Associated With HIV Infection and Inflammation

Abstract

BACKGROUND: Increased cell-free DNA levels are associated with poor health outcomes, and cell-free mitochondrial DNA (cf-mtDNA) has proinflammatory properties. Given that HIV infection is associated with chronic inflammation, we investigated the relationship between cf-mtDNA and proinflammatory cytokine interleukin-6 (IL-6) in the context of HIV infection. We also optimized separation of cell-free plasma from blood. SETTING: In this retrospective cross-sectional study, we collected blood, demographic information, and clinical data from 99 HIV-infected and 103 HIV-uninfected adults and children enrolled in the Children and Women: AntiRetrovirals and Markers of Aging pan-Canadian (CARMA) cohort. METHODS: Plasma was separated from blood by 14,000g centrifugation followed by 0.45-μm filtration to remove cells and platelets. Cf-mtDNA and cell-free nuclear DNA were quantified simultaneously via monochrome, multiplex, quantitative polymerase chain reaction. IL-6 was measured using enzyme-linked immunosorbent assay. RESULTS: Higher speed centrifugation and filtration was necessary to isolate truly cell-free plasma. Higher cf-mtDNA levels were univariately associated with HIV infection, elevated IL-6 levels, younger age, higher white blood cell count, and higher cell-free nuclear DNA levels but not blood mtDNA content or HIV viral load. In a multivariable model, HIV infection (P < 0.001), elevated IL-6 (P = 0.021), younger age (P < 0.001), and higher blood nDNA levels (P = 0.007) were independently associated with higher cf-mtDNA. CONCLUSIONS: People living with HIV have higher levels of circulating cf-mtDNA than their uninfected peers. Increased levels of inflammatory marker IL-6 are associated with elevated cf-mtDNA, independent of the effect of HIV infection. Higher cf-mtDNA levels and white blood cell count in younger people may reflect higher cell turnover in that population.