SBT-020

Mitochondrial creatine kinase (mtCK) regulates the "fast" export of phosphocreatine to support cytoplasmic phosphorylation of ADP to ATP which is more rapid than direct ATP export. Such "creatine-dependent" phosphate shuttling is attenuated in several muscles, including the heart, of the D2.mdx mouse model of Duchenne muscular dystrophy at only 4 weeks of age. However, the degree to which creatine-dependent and -independent systems of phosphate shuttling progressively worsen or potentially adapt in a hormetic manner throughout disease progression remains unknown. Here, we performed a series of proof-of-principle investigations designed to determine how phosphate shuttling pathways worsen or adapt in later disease stages in D2.mdx (12 months of age). We also determined whether changes in creatine-dependent phosphate shuttling are linked to alterations in mtCK thiol redox state. In permeabilized muscle fibres prepared from cardiac left ventricles, we found that 12-month-old male D2.mdx mice have reduced creatine-dependent pyruvate oxidation and elevated complex I-supported H₂O₂ emission (mH₂O₂). Surprisingly, creatine-independent ADP-stimulated respiration was increased and mH₂O₂ was lowered suggesting that impairments in the faster mtCK-mediated phosphocreatine export system resulted in compensation of the alternative slower pathway of ATP export. The apparent impairments in mtCK-dependent bioenergetics occurred independent of mtCK protein content but were related to greater thiol oxidation of mtCK and a more oxidized cellular environment (lower GSH:GSSG). Next, we performed a proof-of-principle study to determine whether creatine-dependent bioenergetics could be enhanced through chronic administration of the mitochondrial-targeting, ROS-lowering tetrapeptide, SBT-20. We found that 12 weeks of daily treatment with SBT-20 (from day 4-∼12 weeks of age) increased respiration and lowered mH₂O₂ only in the presence of creatine in D2.mdx mice without affecting calcium-induced mitochondrial permeability transition activity. In summary, creatine-dependent mitochondrial bioenergetics are attenuated in older D2.mdx mice in relation to mtCK thiol oxidation that seem to be countered by increased creatine-independent phosphate shuttling as a unique form of mitohormesis. Separate results demonstrate that creatine-dependent bioenergetics can also be enhanced with a ROS-lowering mitochondrial-targeting peptide. These results demonstrate a specific relationship between redox stress and mitochondrial hormetic reprogramming during dystrophin deficiency with proof-of-principle evidence that creatine-dependent bioenergetics could be modified with mitochondrial-targeting small peptide therapeutics.

Chemotherapy‐induced peripheral neuropathy (CIPN) is a major side effect of several anticancer agents including paclitaxel, a chemotherapeutic drug widely used in cancer treatment. CIPN deteriorates patients' quality of life and compromises cancer treatment. Dysfunction or injury of mitochondria has been suggested to be involved in the induction of this neuropathy. SS‐20 is a tetrapeptide that targets mitochondria and restores mitochondrial bioenergetics. This study was aimed to examine the protective effect of SS‐20 against paclitaxel‐induced peripheral neuropathy using a murine model. Repeated administration of paclitaxel to mice induced peripheral neuropathy as demonstrated by the presence of mechanical allodynia and the loss of intraepidermal nerve fibers in the hind paw. Concomitant administration of SS‐20 protected against the development of the neuropathy. Our results suggest that SS‐20 may be a drug candidate for the prevention of CIPN.