Age and sex shape plasma lipid associations to skeletal muscle mitochondrial respiration and H₂O₂ emission

Aging changes the lipidome and mitochondrial function in a sex-dependent manner, yet their associations remain poorly understood. Twenty-four younger (7M/17F) and forty-three older (21M/22F) adults underwent blood draws and skeletal muscle biopsies for this cross-sectional investigation. Plasma lipidomic profiling was performed via liquid chromatography-tandem mass spectrometry, while peak mitochondrial O₂ utilization (OXPHOS) and hydrogen peroxide (H₂O₂) emission were assessed using high-resolution respirometry. Plasma lipidomic analysis annotated 535 lipid species across 28 different lipid classes. Lipid-age associations were identified in four lipid classes for both sexes with twelve lipid classes demonstrating sex-specific associations, including triglycerides (TG), carnitines (CAR), and fatty acids (FA). For lipid-OXPHOS interactions, the primary lipid class and species associated with higher OXPHOS exclusively in males were ceramides (CER) and dimethyl cholesterol esters (dimethyl-CE), while TG were the primary lipid species associated with impaired OXPHOS in females. For lipid-H₂O₂ interactions, the primary lipid class and species associated with higher H₂O₂ were methyl desmosteryl esters (methyl-DE), methyl cholesterol esters (methyl-CE), FA and TG in males whereas females exhibited 10 (CE, SM, LPC, dihexosylceramides (Hex2Cer), LPE, PI, HexCer, LPI, CAR, and hexosyl-N-acetylneuraminyl-ceramides (Hex2NeuAcCer)) lipid classes associated exclusively with H₂O₂ emission. These findings establish novel age- and sex-specific relationships between age-related changes in plasma lipids and skeletal muscle mitochondrial function, revealing distinct lipid signatures for respiration and H₂O₂ emission in males and females.