Ileitis promotes MASLD progression via bile acid modulation and enhanced TGR5 signaling in ileal CD8+ T cells

BACKGROUND & AIMS

Clinical evidence substantiates a link between inflammatory bowel disease, particularly Crohn's disease (CD), and metabolic dysfunction-associated steatotic liver disease (MASLD). This study aims to explore the underlying molecular mechanisms responsible for this association.

METHODS

MASLD was induced by administering high-fat and western diets, while inflammatory bowel disease was induced using DSS (dextran sulfate sodium) and the Il10 knockout (KO) mouse model. The investigation into the role of secondary bile acids (SBAs) in ileitis involved employing metagenomic sequencing, conducting metabolomics detection, performing fecal microbiota transplantation, and constructing CD8+ T cell-specific gene knockout mice.

RESULTS

In MASLD+DSS and Il10 KO MASLD mice, we observed ileitis characterized by T-cell infiltration and activation in the terminal ileum. This condition resulted in decreased bile acid levels in the portal vein and liver, inhibited hepatic farnesoid X receptor (FXR) activation, and exacerbated MASLD. Metagenomic and metabolomic analysis of ileal contents revealed increased Clostridium proliferation and elevated SBA levels in MASLD-associated ileitis. Experiments using germ-free mice and fecal microbiota transplantation suggested an association between SBA and MASLD-related ileitis. In vitro, SBAs promoted CD8+ T-cell activation via the TGR5, mTOR, and oxidative phosphorylation pathways. In vivo, TGR5 KO in CD8+ T cells effectively alleviated ileitis and reversed the MASLD phenotype. Clinical data further supported these findings, demonstrating a positive correlation between ileitis and MASLD.

CONCLUSION

MASLD-induced changes in intestinal flora result in elevated levels of SBAs in the ileum. In the presence of a compromised intestinal barrier, this leads to severe CD8+ T cell-mediated ileitis through the TGR5/mTOR/oxidative phosphorylation signaling pathway. Ileitis-induced tissue damage impairs enterohepatic circulation, inhibits hepatic FXR activation, and exacerbates the MASLD phenotype.

IMPACT AND IMPLICATIONS

Our study provides a comprehensive investigation of the interplay and underlying mechanisms connecting ileitis and metabolic dysfunction-associated steatotic liver disease (MASLD). Secondary bile acids produced by intestinal bacteria act as the critical link between MASLD and ileitis. Secondary bile acids exert their influence by disrupting liver lipid metabolism through the promotion of CD8+ T cell-mediated ileitis. In future endeavors to prevent and treat MASLD, it is essential to thoroughly account for the impact of the intestinal tract, especially the ileum, on liver function via the enterohepatic circulation.

Are we ready for genetic testing in metabolic dysfunction-associated steatotic liver disease?

Metabolic dysfunction-associated steatotic liver disease (MASLD), with its steadily increasing prevalence, represents now a major problem in public health. A proper referral could benefit from tools allowing more precise risk stratification. To this end, in recent decades, several genetic variants that may help predict and refine the risk of development and progression of MASLD have been investigated. In this review, we aim to discuss the role genetics in MASLD plays in everyday clinical practice. We performed a comprehensive literature search of PubMed for relevant publications. Available evidence highlights the emergence of genetic-based noninvasive algorithms for diagnosing fatty liver, metabolic dysfunction-associated steatohepatitis, fibrosis progression and occurrence of liver-related outcomes including hepatocellular carcinoma. Nevertheless, their accuracy is not optimal and application in everyday clinical practice remains challenging. Furthermore, susceptible genetic markers have recently become subjects of great scientific interest as therapeutic targets in precision medicine. In conclusion, decisional algorithms based on genetic testing in MASLD to facilitate the clinician decisions on management and treatment are under growing investigation and could benefit from artificial intelligence methodology.

Calorie Restriction Using High-Fat/Low-Carbohydrate Diet Suppresses Liver Fat Accumulation and Pancreatic Beta-Cell Dedifferentiation in Obese Diabetic Mice

In diabetes, pancreatic β-cells gradually lose their ability to secrete insulin with disease progression. β-cell dysfunction is a contributing factor to diabetes severity. Recently, islet cell heterogeneity, exemplified by β-cell dedifferentiation and identified in diabetic animals, has attracted attention as an underlying molecular mechanism of β-cell dysfunction. Previously, we reported β-cell dedifferentiation suppression by calorie restriction, not by reducing hyperglycemia using hypoglycemic agents (including sodium-glucose cotransporter inhibitors), in an obese diabetic mice model (db/db). Here, to explore further mechanisms of the effects of food intake on β-cell function, db/db mice were fed either a high-carbohydrate/low-fat diet (db-HC) or a low-carbohydrate/high-fat diet (db-HF) using similar calorie restriction regimens. After one month of intervention, body weight reduced, and glucose intolerance improved to a similar extent in the db-HC and db-HF groups. However, β-cell dedifferentiation did not improve in the db-HC group, and β-cell mass compensatory increase occurred in this group. More prominent fat accumulation occurred in the db-HC group livers. The expression levels of genes related to lipid metabolism, mainly regulated by peroxisome proliferator-activated receptor α and γ, differed significantly between groups. In conclusion, the fat/carbohydrate ratio in food during calorie restriction in obese mice affected both liver lipid metabolism and β-cell dedifferentiation.

A Novel Score Based on Controlled Attenuation Parameter Accurately Predicts Hepatic Steatosis in Individuals With Metabolic Dysfunction Associated Steatotic Liver Disease: A Derivation and Independent Validation Study

INTRODUCTION

In metabolic dysfunction-associated steatotic liver disease, the diagnostic efficacy of controlled attenuation parameter (CAP) was not very accurate in evaluating liver fat content. The aim of this study was to develop a score, based on CAP and conventional clinical parameters, to improve the diagnostic performance of CAP regarding liver fat content.

METHODS

A total of 373 participants from 2 independent Chinese cohorts were included and divided into derivation (n = 191), internal validation (n = 75), and external validation (n = 107) cohorts. Based on the significant difference index between the 2 groups defined by the magnetic resonance imaging-proton density fat fraction (MRI-PDFF) in derivation cohort, the optimal model (CAP-BMI-AST score [CBST]) was screened by the number of parameters and the area under the receiver operating characteristic curve (AUROC). In the internal and external validation cohorts, the AUROC and corresponding 95% confidence intervals (CIs) were used to compare the diagnostic performance of CBST with that of CAP.

RESULTS

We constructed the CBST = -14.27962 + 0.05431 × CAP - 0.14266 × body mass index + 0.01715 × aspartate aminotransferase. When MRI-PDFF was ≥20%, ≥10%, and ≥5%, the AUROC for CBST was 0.77 (95% CI 0.70-0.83), 0.89 (95% CI 0.83-0.94), and 0.93 (95% CI 0.88-0.98), which was higher than that for CAP respectively. In the internal validation cohort, the AUROC for CBST was 0.80 (95% CI 0.70-0.90), 0.95 (95% CI 0.91-1.00), and 0.98 (95% CI 0.94-1.00). The optimal thresholds of CBST were -0.5345, -1.7404, and -1.9959 for detecting MRI-PDFF ≥20%, ≥10%, and ≥5%, respectively.

DISCUSSION

The CBST score can accurately evaluate liver steatosis and is superior to the CAP.

Therapeutic management of metabolic dysfunction associated steatotic liver disease

The incidence and prevalence of non-alcoholic fatty liver disease (NAFLD) have been steadily increasing worldwide, with a huge societal and economic burden. Recently, NAFLD and non-alcoholic steatohepatitis have been renamed and redefined as metabolic dysfunction associated steatotic liver disease (MASLD) and steatohepatitis (Metabolic Dysfunction Associated Steatohepatitis (MASH)), which result from an imbalance between metabolic and inflammatory stress (mainly as a consequence of adipose tissue dysfunction and insulin resistance) and the defence and repair mechanisms of the steatotic liver. Once MASLD progresses to end-stage of liver disease, treatment efficacy becomes limited and may require liver transplantation. Early detection and intervention are crucial. Lifestyle modification is consequently the cornerstone of its management. Timely consideration of bariatric surgeries should be given to patients meeting specific criteria. A multidisciplinary approach is warranted, starting from the concept that MASLD/MASH is at the centre of the cardiovascular-liver-metabolic syndrome. In some cases, pharmacological treatment can complement lifestyle modification. Several drugs used to treat the cardiometabolic co-morbidities have some potential efficacy in slowing Down disease progression, and some have demonstrated efficacy on histological endpoints that are likely to translate into long-term clinical benefits. Optimising the use of these drugs within their licenced indications is thus paramount for patients with MASLD. Several MASH-specific drugs are on the horizon and are likely to enrich our therapeutic armamentarium in the near future, particularly in non-cirrhotic stages of the disease. Much work still needs to be done to understand the specific features of MASH cirrhosis and develop efficacious treatments for this disease stage.

Molecular Mechanisms of Curcumin in the Pathogenesis of Metabolic Dysfunction Associated Steatotic Liver Disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a multifactorial condition characterized by insulin resistance, oxidative stress, chronic low-grade inflammation, and sometimes fibrosis. To date, no effective pharmacological therapy has been approved for the treatment of metabolic-associated steatohepatitis (MASH), the progressive form of MASLD. Recently, numerous in vitro and in vivo studies have described the efficacy of nutraceutical compounds in the diet has been tested. Among them, curcumin is the most widely used polyphenol in the diet showing potent anti-inflammatory and antifibrotic activities. This review aims to summarize the most important basic studies (in vitro and animal models studies), describing the molecular mechanisms by which curcumin acts in the context of MASLD, providing the rationale for its effective translational use in humans.