Abstract
Background
Exercise training (ET) and statin treatment both alter skeletal muscle function.
Purpose
We investigated the effects of a combined exercise and statin use on skeletal muscle mitochondrial oxidative phosphorylation (OxPhos) and metabolic alterations in obese rats.
Methods
Eight-week-old male Wistar rats were used. A total of 14 animals received standard chow, while 46 rats were fed a high-fat diet (HFD) for 20 weeks. After 8 weeks, the rats were randomized into 6 groups: sedentary (n=8), ET (n=6), sedentary with HFD (n=11), ET with HFD (n=11), statin with HFD (n=13) and ET with HFD and statins (n=11). Simvastatin (10mg/d/kg) was added to the drinking water. ET was performed for 12 weeks, 5 days/week for 1 h/day at 18 m/min in a motorized running wheel. OxPhos was assessed by complex-specific antibodies and targeted metabolomics using the Biocrates p180 kit. All experiments were done on frozen samples of the M. gastrocnemicus. An ANOVA with fixed effects for diet, exercise, statin treatment and statin-exercise interaction was used to identify significantly different metabolites.
Results
Statin use was associated with significantly lower cholesterol levels, but did not affect exercise duration and intensity compared to none-use. In sedentary animals, HFD increased OxPhos complex II (succinate dehydrogenase), complex IV (cytochrome-c-oxidase) and V (ATP synthase) while statin treatment diminished this increase in all complexes. HFD increased complex IV independent of statin treatment but had no effect on complex II and V in ET rats. Complex IV was increased due to ET only in HFD fed rats compared to rats on normal chow but decreased in contrast to sedentary animals on a HFD. With regards to metabolomics, we found 57 metabolites which were influenced by HFD while no metabolites were identified with a significant effect for ET. A significant statin-exercise interaction was found for three lysophosphatidylcholines (lysoPC a C26.0, lysoPC a C26.1, lysoPC a C24.0), one phosphatidylcholine (PC aa C42.6) and one sphingomyelin (SM C16.1). HFD decreased the concentration of all mentioned metabolites compared to standard chow fed animals. Likewise, ET increased the concentration of metabolites compared to sedentary animals on HFD. Statin treatment led to an increase, while statin in combination with ET did not rescue this effect.
Conclusion
HFD induced severely impaired skeletal muscle OxPhos independent of ET and statin treatment. Our findings suggest a limiting rate of NADH production in the tricarboxylic acid cycle as a potential mechanism. However, ET prevented the increase in cytochrome-c-oxidation while statins blocked the HFD induced increase in ATP synthase. Our metabolomics results imply that future research should consider the lipotoxic effects of a HFD when assessing skeletal muscle alterations due to ET or statins. Of particular interest could be the 5 metabolites that have been shown to be impacted by a statin-exercise interaction.
Application of modular kinetic analysis to mitochondrial oxidative phosphorylation in skeletal muscle of birds exposed to acute heat stress
