An investigation of the mitochondria as a potential source of racial differences in reactive oxygen species production and cellular respiration in peripheral blood mononuclear cells of healthy adults

Abstract

Background: Non-Hispanic Black (NHB) adults exhibit a higher prevalence of cardiovascular disease (CVD) compared to Non-Hispanic White (NHW) adults. Vascular oxidative stress may be one contributing factor to these racial disparities. Peripheral blood mononuclear cells (PBMCs) are primary contributors to systemic oxidative stress with documented racial differences in PBMC-derived reactive oxygen species (ROS) production. However, it is unclear whether the racial differences in PBMC-derived ROS are associated with alterations in mitochondrial function. Therefore, the purpose of this study was to investigate potential racial differences in protein expression for mitochondrial complexes, antioxidant defenses, superoxide-generating NADPH oxidase subunits, and cellular respiration in PBMCs isolated from NHB and NHW adults. Methods: PBMCs were isolated as an ancillary subproject for the “Neighborhood Disadvantage, Sleep, and Vascular Health: Racial Disparities in Cardiometabolic Health and Blood Pressure” Study (NCT04576338) from healthy, young participants (17 NHB & 24 NHW). PBMCs were cultured 14-18 hrs prior to cell respiration and protein harvest. A Clark Electrode measured rate of basal, leak, maximal, and non-mitochondrial respiration. Formulas were also used to determine coupling efficiency, adenosine triphosphate (ATP) demand, spare respiratory capacity, and OCR metabolic potential. Western blotting was used to measure antioxidant modulators of oxidative stress (superoxide dismutase [SOD] isoforms 1 & 2; acetylated SOD2 [AcSOD2], inactivate form; NAD-dependent deacetylase Sirtuin-3 [SIRT3]), superoxide-generating enzyme NADPH oxidase subunits (p47phox and gp91phox), and mitochondrial complexes I – V. Non-adjusted differences between groups were analyzed with a student’s t-test or Man-Whitney U test, if they showed non-normal distributions. Results: There were no racial differences in the modulators of oxidative stress or superoxide-generating NADPH oxidase subunits. PBMCs isolated from NHBs adults exhibited a significantly higher expression for Complex I (p=0.014). There were no sex differences in NADPH oxidase subunits or mitochondrial complexes. However, PBMCs isolated from females exhibited a greater expression for the antioxidant enzyme SIRT3 (p=0.038). PBMCs isolated from NHBs adults exhibited a significantly lower rates for basal respiration, leak respiration, and non-mitochondrial respiration (p=0.017, p=0.009, p=0.014 respectively). Finally, there were no sex differences in cell respiration. Conclusion: While speculative, the lower respiration rates (basal, leak, and non-mitochondrial derived) and higher protein expression for Complex I in PBMCs isolated from NHB adults may contribute to elevated ROS production. While no racial differences were found in the redox regulating proteins, additional information are needed on SOD activity, NADPH oxidase activity, mitochondrial damage, and changes in metabolic phenotype in activated PBMCs.