Differential Effects of PB125 and MitoQ Supplementation and Limb Immobilization on Mitochondrial Respiration and Protein Expression in Skeletal Muscle

Mitochondrial dynamics and respiratory capacity contribute to the regulation of cellular redox state and metabolism. Disuse upregulates reactive oxygen species (ROS), disrupting physiological pathways and impairing mitochondria. This study investigated the effects of PB125 (a nuclear factor erythroid-2-like 2 [Nrf2] activator) and MitoQ (a mitochondria-targeted antioxidant) with two weeks of supplementation and two weeks of limb immobilization on mitochondrial respiration and protein expression. We hypothesized that both supplements would decrease ROS and improve mitochondrial respiration. Twenty-four participants (15F/9M, 27±7 years old) were randomly assigned to Placebo (n=8, 6F/2M), PB125 (n=9, 4F/5M), or MitoQ (n=7, 5F/2M). Skeletal muscle biopsies were taken from the vastus lateralis at baseline (V1), after 2 weeks of supplementation (V2), and after 2 weeks of limb immobilization with supplementation (V3). Mitochondrial respiration and ADP sensitivity (apparent K m ) were measured in permeabilized muscle fibers via high-resolution respirometry. Protein levels of mitochondrial complexes and mitochondrial dynamics were assessed by western blot. Skeletal muscle superoxide levels were assessed by electron paramagnetic resonance spectroscopy using mitoTEMPO-H. After 2 weeks of supplementation (V1-V2), State 3 complex I respiration (7.0±2.4 pmol/s/mg to 12.4±3.7 pmol/s/mg, p=0.030) and maximal respiration (59.1±12.5 pmol/s/mg to 73.8±14.5 pmol/s/mg, p=0.050) were enhanced with MitoQ, with no effect in PB125 or placebo (both, p>0.05). There was a differential effect of supplementation on K m , where those receiving placebo had an increase in K m from V1 to V3 (237±85 to 406±194 µM ADP, p=0.032), MitoQ had a decrease from V2 to V3 (612±259 to 345±88 µM ADP, p=0.032), and there was no effect on PB125 (p>0.05). From V1-V2, both PB125 and MitoQ improved only one mitochondrial protein. PB125 supplementation increased Drp1 (10.7%, p=0.031), while MitoQ supplementation increased complex I (30.0%, p=0.036). Following disuse (V2-V3), both PB125 and MitoQ saw a decrease in multiple mitochondrial proteins. PB125 had a decrease in Mfn2 (-20.0%, p=0.012), complex III (-50.7%, p=0.035), and complex V (-34.0%, p=0.046), while with MitoQ, there was a decline in PGC1α (-24.5%, p=0.035), Parkin (-10.2%, p=0.009), and complex IV (-10.7%, p=0.037). No significant changes in mitochondrial superoxide were observed for any supplementation (all, p>0.05). MitoQ supplementation enhanced mitochondrial respiration, likely through complex I upregulation, however, neither PB125 nor MitoQ fully protected against reductions in mitochondrial proteins following disuse. R01HL142603VA Merit I01CX001999 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.