The antioxidant Trolox restores mitochondrial membrane potential and Ca²⁺-stimulated ATP production in human complex i deficiency

Malfunction of mitochondrial complex I caused by nuclear gene mutations causes early-onset neurodegenerative diseases. Previous work using cultured fibroblasts of complex-I-deficient patients revealed elevated levels of reactive oxygen species (ROS) and reductions in both total Ca²⁺ content of the endoplasmic reticulum (ER_Ca) and bradykinin(Bk)-induced increases in cytosolic and mitochondrial free Ca²⁺ ([Ca²⁺] _C; [Ca²⁺]_M) and ATP ([ATP]_C; [ATP]_M) concentration. Here, we determined the mitochondrial membrane potential (Δψ) in patient skin fibroblasts and show significant correlations with cellular ROS levels and ER_Ca, i.e., the less negative Δψ, the higher these levels and the lower ER_Ca. Treatment with 6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (Trolox) normalized Δψ and Bk-induced increases in [Ca²⁺] _M and [ATP]_M. These effects were accompanied by an increase in ER_Ca and Bk-induced increase in [Ca²⁺] _C. Together, these results provide evidence for an integral role of increased ROS levels in complex I deficiency and point to the potential therapeutic value of antioxidant treatment.