Impact of Peroxisome Proliferator-Activated Receptor Agonists on Myosteatosis in the Context of Metabolic Dysfunction-Associated Steatotic Liver Disease

Background: Metabolic dysfunction-associated steatotic liver disease (MASLD), and more specifically steatohepatitis may be associated with fat infiltration of skeletal muscles which is known as myosteatosis. Pan-peroxisome proliferator-activated receptor (PPAR) agonists have been shown to promote metabolic dysfunction-associated steatohepatitis (MASH) remission. However, the effect of PPAR agonists on myosteatosis remains to be determined. The aim of this review is to evaluate the effect that PPAR agonists alone or in combination, have on myosteatosis in the context of MASLD. Methods: Original research reports concerning the impact of PPAR agonists on muscle fat in MASLD were screened from PUBMED and EMBASE databases following the PRISMA methodology. Results: Eleven original manuscripts were included in this review. Two preclinical studies assessed the impact of the PPAR alpha agonist on fat content in the quadriceps muscle and the liver by extracting triglycerides in rats fed a high-fat diet and in insulinresistant mice. Both models showed muscle and liver triglyceride content reduction using WY14643. Fenofibrate had no significant impact on soleus intramyocellular lipids or liver fat content in insulin-resistant subjects based on proton magnetic resonance spectroscopy. Treatment with PPAR delta agonists increased the expression of genes involved in fatty acid oxidation in two studies on muscle cell culture. PPAR gamma agonists were investigated in two preclinical studies and one clinical study using spectroscopy and computed tomography respectively. In the first preclinical study in Zucker diabetic fatty rats, rosiglitazone reduced muscle lipids and hepatic steatosis. In a second preclinical study using the same animal model, pioglitazone reduced tibialis anterior intramyocellular lipids. In contrast, computed tomography analyses in patients with type 2 diabetes revealed a surface area increase of low-density muscles (suggesting an increase in muscle fat content) after a one-year treatment with rosiglitazone. Varying combinations of PPAR agonists (cevoglitazar, fenofibrate/pioglitazone and muraglitazar) were evaluated in two preclinical studies and one clinical study. In rats, these treatments showed variable results for muscle and liver depending on the combinations studied. In type 2 diabetic patients, treatment with muraglitazar (a PPAR alpha/gamma agonist) reduced the intramyocellular lipid content of tibialis anterior as well as liver fat content following spectroscopy assessment. Conclusion: The combination of different PPAR agonists could have a positive impact on reducing myosteatosis, in addition to their effect on the liver. Some discrepancies could be explained by the different techniques used to assess muscle lipid content, the muscles assessed and the possible adipogenic effect of PPAR gamma agonists. Further clinical research is needed to fully assess the efficacy of these treatments on both MASLD progression and associated myosteatosis.