Branched chain amino acid metabolism profiles in progressive human nonalcoholic fatty liver disease

Amino Acid Metabolism is Altered in Adolescents with Nonalcoholic Fatty Liver Disease-An Untargeted, High Resolution Metabolomics Study

OBJECTIVE

To conduct an untargeted, high resolution exploration of metabolic pathways that was altered in association with hepatic steatosis in adolescents.

STUDY DESIGN

This prospective, case-control study included 39 Hispanic-American, obese adolescents aged 11-17 years evaluated for hepatic steatosis using magnetic resonance spectroscopy. Of these 39 individuals, 30 had hepatic steatosis ≥5% and 9 were matched controls with hepatic steatosis <5%. Fasting plasma samples were analyzed in triplicate using ultra-high resolution metabolomics on a Thermo Fisher Q Exactive mass spectrometry system, coupled with C18 reverse phase liquid chromatography. Differences in plasma metabolites between adolescents with and without nonalcoholic fatty liver disease (NAFLD) were determined by independent t tests and visualized using Manhattan plots. Untargeted pathway analyses using Mummichog were performed among the significant metabolites to identify pathways that were most dysregulated in NAFLD.

RESULTS

The metabolomics analysis yielded 9583 metabolites, and 7711 with 80% presence across all samples remained for statistical testing. Of these, 478 metabolites were associated with the presence of NAFLD compared with the matched controls. Pathway analysis revealed that along with lipid metabolism, several major amino acid pathways were dysregulated in NAFLD, with tyrosine metabolism being the most affected.

CONCLUSIONS

Metabolic pathways of several amino acids are significantly disturbed in adolescents with elevated hepatic steatosis. This is a novel finding and suggests that these pathways may be integral in the mechanisms of NAFLD.

MicroRNA Expression Relating to Dietary-Induced Liver Steatosis and NASH

Health issues associated with excessive caloric intake and sedentary lifestyle are driving a modern “epidemic” of liver disease. Initially presenting in the clinic as an excessive accumulation of fat within hepatocyte cells (steatosis), the progression to more severe non-alcoholic steatohepatitis (NASH) in which liver damage and inflammation are overt features, is becoming increasingly common. Often developing as a sequela of obesity, non-alcoholic fatty liver disease (NAFLD) arises in almost one-third of people initially carrying excess hepatic fat and is likely the result of the liver’s limited capacity to cope with the modern-day levels of dietary fatty acids circulating in the blood. While routine imaging can readily assess the presence and level of “extra-hepatic fat”, a proper diagnosis of disease progression to NASH is currently only possible by liver biopsy. A general reluctance to undergo such screening means that the prevalence of NASH is likely to be under reported and, thus, risk assessment for future metabolic syndrome (MetS) markedly compromised. The seemingly inevitable progression to overt insulin resistance that characterizes MetS may in part be the consequence of the body’s attempt to cope with NAFLD by driving systemic insulin sensitivity and, thus, fatty acid breakdown. The potential significance of miRNAs in both physiological homeostasis and pathogenesis is increasingly appreciated and in the liver may contribute specifically to the regulation of lipid pathways and NAFLD progression. As such, they may have utility as molecular indicators for the accurate profiling of both initial risk and disease progression from simple steatosis to NASH, and further to fibrosis/cirrhosis.

Adipose Tissue Dysfunction and Altered Systemic Amino Acid Metabolism Are Associated with Non-Alcoholic Fatty Liver Disease

Background

Fatty liver is a major cause of obesity-related morbidity and mortality. The aim of this study was to identify early metabolic alterations associated with liver fat accumulation in 50- to 55-year-old men (n = 49) and women (n = 52) with and without NAFLD.

Methods

Hepatic fat content was measured using proton magnetic resonance spectroscopy (¹H MRS). Serum samples were analyzed using a nuclear magnetic resonance (NMR) metabolomics platform. Global gene expression profiles of adipose tissues and skeletal muscle were analyzed using Affymetrix microarrays and quantitative PCR. Muscle protein expression was analyzed by Western blot.

Results

Increased branched-chain amino acid (BCAA), aromatic amino acid (AAA) and orosomucoid were associated with liver fat accumulation already in its early stage, independent of sex, obesity or insulin resistance (p<0.05 for all). Significant down-regulation of BCAA catabolism and fatty acid and energy metabolism was observed in the adipose tissue of the NAFLD group (p<0.001for all), whereas no aberrant gene expression in the skeletal muscle was found. Reduced BCAA catabolic activity was inversely associated with serum BCAA and liver fat content (p<0.05 for all).

Conclusions

Liver fat accumulation, already in its early stage, is associated with increased serum branched-chain and aromatic amino acids. The observed associations of decreased BCAA catabolism activity, mitochondrial energy metabolism and serum BCAA concentration with liver fat content suggest that adipose tissue dysfunction may have a key role in the systemic nature of NAFLD pathogenesis.

Transcriptional networks implicated in human nonalcoholic fatty liver disease

The transcriptome of nonalcoholic fatty liver disease (NAFLD) was investigated in several studies. However, the implications of transcriptional networks in progressive NAFLD are not clear and mechanisms inducing transition from nonalcoholic simple fatty liver (NAFL) to nonalcoholic steatohepatitis (NASH) are still elusive. The aims of this study were to (1) construct networks for progressive NAFLD, (2) identify hub genes and functional modules in these networks and (3) infer potential linkages among hub genes, transcription factors and microRNAs (miRNA) for NAFLD progression. A systems biology approach by combining differential expression analysis and weighted gene co-expression network analysis (WGCNA) was utilized to dissect transcriptional profiles in 19 normal, 10 NAFL and 16 NASH patients. Based on this framework, 3 modules related to chromosome organization, proteasomal ubiquitin-dependent protein degradation and immune response were identified in NASH network. Furthermore, 9 modules of co-expressed genes associated with NAFL/NASH transition were found. Further characterization of these modules defined 13 highly connected hub genes in NAFLD progression network. Interestingly, 11 significantly changed miRNAs were predicted to target 10 of the 13 hub genes. Characterization of modules and hub genes that may be regulated by miRNAs could facilitate the identification of candidate genes and pathways responsible for NAFL/NASH transition and lead to a better understanding of NAFLD pathogenesis. The identified modules and hub genes may point to potential targets for therapeutic interventions.

Cholestatic liver injury model of bile duct ligation and the protection of Huang-Lian-Jie-Du decoction by NMR metabolomic profiling

Bile duct ligation (BDL) induced cholestasis in rats and the treatment effects of Huang-Lian-Jie-Du decoction (HLJDD) were investigated by NMR-based metabolomics approach: biphasic feature of BDL model and bilateral adjustment of HLJDD were found.