Deep phenotyping of patients with MASLD upon high-intensity interval training

Background & Aims: Exercise is a key component of lifestyle management in patients with metabolic dysfunction-associated steatotic liver disease (MASLD), but neither its therapeutic effect on the active stage of the disease, that is metabolic dysfunction-associated steatohepatitis (MASH) nor the mediating mechanisms have been characterized. Therefore, we performed multi-omic phenotyping of patients with MASLD-MASH on an exercise program. Methods: ) and MRI-determined liver fat were compared with a control group of patients with MASLD (n = 22). RNA sequencing was performed on liver, muscle, and fat biopsies of patients in the exercise group. Stool was analyzed by shotgun metagenomics and untargeted metabolomics was performed on plasma, urine, adipose, and stool. Results: increased significantly in the exercise group compared with controls. Histologically, no reduction in steatosis, MASH, or liver fibrosis was observed; however, transient elastography tended to improve. MRI-determined liver fat did not change in the exercise group compared with controls. HIIT induced changes in mRNA expression of genes related to beiging of adipose tissue and fibrogenesis in liver. In addition, specific gut microbial taxa and metabolites changed. Conclusions: HIIT increased cardiorespiratory fitness and induced beneficial gene expression changes in muscle, adipose tissue, and liver, but without translation into histological improvement of MASLD. Longer exercise intervention trials are warranted to validate or refute current recommendations for exercise as a cornerstone treatment for MASLD-MASH. Impact and implications: Despite exercise being considered as a key component of lifestyle management for steatotic liver disease, neither the clinical effects nor the mechanisms involved are completely understood. We show that a high-intensity interval training (HIIT) program in 15 patients with metabolic dysfunction-associated steatotic liver disease (MASLD) improved cardiorespiratory fitness, compared with 22 control patients with MASLD who did not participate in an exercise program, however, it did not improve MASLD. HIIT induced a positive effect on fat tissue and muscle metabolism which was accompanied with changes in certain gut bacteria and metabolites in blood and urine. These findings improve our understanding of the effects of exercise on the whole-body metabolism in relation to steatotic liver disease. As such, this study provides a basis for future exercise interventions in patients with MASLD, required to thoroughly test current guideline advice for exercise as a cornerstone treatment for MASLD of all stages. Clinical trial registry: Dutch Trial Register (registration number NL7932).