Novel genetic insights into the roles of amino acids in metabolic dysfunction-associated steatotic liver disease

Background Previous research has suggested potential links between amino acids and metabolic dysfunction-associated steatotic liver disease (MASLD), but the precise roles of amino acids in MASLD development are not well understood. This study aimed to obtain insights into the relationships between circulating amino acids and MASLD. Methods Utilizing data from the UK Biobank, we examined the observational associations of ten amino acids with MASLD in a cohort of 72,626 MASLD cases and 128,102 controls. Bi-directional two-sample Mendelian randomization (MR) was conducted using genome-wide association study data to investigate the causal relationships between amino acids and MASLD. Multiple MR methods comprising MR-Egger and MR-PRESSO were applied to assess pleiotropy and heterogeneity, and multivariable MR was conducted to evaluate the impacts of body mass index (BMI) on these associations. Survival analysis assessed the link between baseline amino acid levels and the risk of major outcomes. Results We identified nine amino acids significantly associated with MASLD in the observational study. The genetic predisposition towards higher leucine (odds ratio (OR) [95% confidence interval (CI)]: 2.1 [1.4, 3.2]), valine (OR [95% CI]: 1.8 [1.3, 2.7]), and alanine (OR [95% CI]: 1.4 [1.1, 1.8]) levels were significantly associated with MASLD. By contrast, the genetic predisposition for increased MASLD risk was significantly associated with phenylalanine (beta = 0.05, p = 4.0×10-4). Further analysis showed that valine may mediate the association between BMI and MASLD, and may also have an exclusive effect on MASLD in addition to the effect of obesity (beta = 1.3, p = 1.9×10-4). Elevated phenylalanine levels in MASLD patients were linked with an increased risk of metabolic dysfunction-associated steatohepatitis (MASH), hepatocellular carcinoma, cirrhosis, heart failure, stroke, and mortality. Conclusion We found genetic associations between circulating branched-chain amino acids, particularly leucine and valine, and MASLD, independent of obesity. Phenylalanine was identified as a potential biomarker for MASLD prognostic complications. These results highlight the importance of amino acid metabolism in MASLD as well as suggest new possibilities for research and therapeutic intervention. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement J.L. is supported by a Novo Nordisk Postdoctoral Fellowship Programme run in partnership with the University of Oxford. Y. Z is supported by Discipline Cluster of Oncology, Wenzhou Medical University, China (No.z2-2023024). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: All participants provided electronically signed informed consent, and the study was approved by the North West Multi-centre Research Ethics Committee, Patient Information Advisory Group, and Community Health Index Advisory Group. The current study is part of UK Biobank project 61054. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes UK Biobank data are publicly available to bona fide researchers upon application at http://www.ukbiobank.ac.uk/using-the-resource/. Publicly available summary statistics are obtained from https://gwas.mrcieu.ac.uk/ andhttps://www.ebi.ac.uk/gwas/. Other sources of data or web sources were clarified in the methods.