Is bariatric surgery resolving NAFLD via microbiota-mediated bile acid ratio reversal? A comprehensive review

PIM1 alleviated liver oxidative stress and NAFLD by regulating the NRF2/HO-1/NQO1 pathway

AIMS

Non-alcoholic fatty liver disease (NAFLD) has risen as a significant global public health issue, for which vertical sleeve gastrectomy (VSG) has become an effective treatment method. The study sought to elucidate the processes through which PIM1 mitigates the advancement of NAFLD. The Pro-viral integration site for Moloney murine leukemia virus 1 (PIM1) functions as a serine/threonine kinase. Bioinformatics analysis revealed that reduced PIM1 expression in NAFLD.

METHODS

To further prove the role of PIM1 in NAFLD, an in-depth in vivo experiment was performed, in which male C57BL/6 mice were randomly grouped to receive a normal or high-fat diet for 24 weeks. They were operated or delivered the loaded adeno-associated virus which the PIM1 was overexpressed (AAV-PIM1). In an in vitro experiment, AML12 cells were treated with palmitic acid to induce hepatic steatosis.

KEY FINDINGS

The results revealed that the VSG surgery and virus delivery of mice alleviated oxidative stress, and apoptosis in vivo. For AML12 cells, the levels of oxidative stress, apoptosis, and lipid metabolism were reduced via PIM1 upregulation. Moreover, ML385 treatment resulted in the downregulation of the NRF2/HO-1/NQO1 signaling cascade, indicating that PIM1 mitigates NAFLD by targeting this pathway.

SIGNIFICANCE

PIM1 alleviated mice liver oxidative stress and NAFLD induced by high-fat diet by regulating the NRF2/HO-1/NQO1 signaling Pathway.

Energy expenditure related biomarkers following bariatric surgery: a prospective six-month cohort study

BACKGROUND

Mitochondria dysfunction is one of the major causes of insulin resistance, and other countless complications of obesity. PGC-1α, and UCP-2 play key roles in energy expenditure regulation in the mitochondrial thermogenesis. However, the effects of bariatric surgery on the level of PGC-1α and UCP-2 and their relationships are unclear.

OBJECTIVE

This study aimed to investigate the effect of bariatric surgery on key pathways in energy, and to assess the potential predictive role of body composition and metabolic parameters in this regard.

SETTINGS

Hazrat-e Rasool General Hospital, Center of Excellence of International Federation for Surgery of Obesity.

METHODS

This prospective cohort study was carried out on 45 patients with morbid obesity who underwent Roux-en-Y gastric bypass surgery. The patients have evaluated three-time points at baseline, three, and six months after the surgery. Body composition components, the levels of PGC-1α, UCP-2, and metabolic parameters were measured three times during this study.

RESULTS

Significant changes in TWL%, EBMIL%, and metabolic lab tests were observed at three- and six months post-surgery (P < 0.001). The PGC-1α and UCP-2 had a significant increase three and then six-month post-operation compared with the baseline (P < 0.001). Moreover, multivariate linear regression analysis identified that the changing trend of PGC-1α was associated with insulin, uric Acid, HOMA-IR, fat mass and trunk fat mass. UCP-2 was associated with TSH, AST, fat mass and FFM.

CONCLUSIONS

Bariatric surgery has been shown to have a positive effect on UCP-2 and PGC-1α levels, as well as body composition and metabolic parameters. As a result, it is believed that bariatric surgery could improve thermogenesis and energy expenditure by enhancing mitochondrial biogenesis and function. However, further studies are needed to fully understand the precise mechanisms and possible causal relationship.

Microbiota dynamics preceding bariatric surgery as obesity treatment: a comprehensive review

The review present data on the intricate relationship between bariatric surgery, gut microbiota, and metabolic health in obesity treatment. Bariatric surgery, is recognized as an effective intervention for managing morbid obesity, including various techniques with distinct mechanisms of action, efficacy, and safety profiles including Roux-en-Y Gastric Bypass (RYGB), Sleeve Gastrectomy (SG), Laparoscopic Adjustable Gastric Banding (LAGB), and Biliopancreatic Diversion (BPD). RYGB and SG are the most prevalent procedures globally, inducing gut microbiota changes that influence microbial diversity and abundance. Post-surgery, alterations in bacterial communities occur, such as the increased of Escherichia coli inversely correlated with fat mass and leptin levels. During digestion, microbiota produce physiologically active compounds like bile acids (Bas) and short-chain fatty acids (SCFAs). SCFAs, derived by microbial fermentation, influence appetite, energy metabolism, and obesity-related pathways. Bas, altered by surgery, modulate glucose metabolism and insulin sensitivity. Furthermore, SG and RYGB enhance incretin secretion, particularly glucagon-like peptide 1 (GLP-1). Therefore, understanding microbiota changes after bariatric surgery could be crucial for predicting metabolic outcomes and developing targeted interventions for obesity management.

Bariatric surgery in the prevention of obesity-associated cancers: mechanistic implications

Obesity is associated with an increased risk of at least 13 different cancers, as well as worse cancer outcomes and increased cancer mortality. As rates continue to rise both in the United States and worldwide, obesity is poised to become the leading lifestyle-related risk factor for cancer. Currently, the most effective treatment for patients with severe obesity is bariatric surgery. Multiple cohort studies have demonstrated a consistent >30% decreased risk of cancer incidence in women, but not men, following bariatric surgery. However, the physiologic mechanisms driving obesity-associated cancer and the cancer-protective effect of bariatric surgery are not clearly defined. In this review, we highlight emerging concepts in the mechanistic understanding of obesity-associated cancer. Evidence from both human studies and preclinical animal models suggest that obesity drives carcinogenesis through dysregulation of systemic metabolism, immune dysfunction, and an altered gut microbiome. Additionally, we present related findings to suggest that bariatric surgery may disrupt and even reverse many of these mechanisms. Finally, we discuss the use of preclinical bariatric surgery animal models in the study of cancer biology. The prevention of cancer is emerging as an important indication for bariatric surgery. Elucidating the mechanisms through which bariatric surgery limits carcinogenesis is critical to developing a variety of interventions that intercept obesity-driven cancer.

The Role Bariatric Surgery and Endobariatric Therapies in Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease worldwide. Disease spectrum varies from steatosis, steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. Currently, there are no approved medical therapies, and weight loss through lifestyle modifications remains a mainstay of therapy. Bariatric surgery is the most effective therapy for weight loss and has been shown to improve liver histology. Recently, endoscopic bariatric metabolic therapies have also emerged as effective treatments for patients with obesity and NAFLD. This review summarizes the role of bariatric surgery and endoscopic therapies in the management of patients with NAFLD.

Mechanisms linking bariatric surgery to adipose tissue, glucose metabolism, fatty liver disease and gut microbiota

PURPOSE

In the last 20 years, bariatric surgery has achieved an important role in translational and clinical research because of obesity comorbidities. Initially, a tool to lose weight, bariatric surgery now has been shown to be involved in several metabolic pathways.

METHODS

We conducted a narrative review discussing the underlying mechanisms that could explain the impact of bariatric surgery and the relationship between obesity and adipose tissue, T2D, gut microbiota, and NAFLD.

RESULTS

Bariatric surgery has an impact in the relation between obesity and type 2 diabetes, but in addition  it induces the white-to-brown adipocyte trans-differentiation, by enhancing thermogenesis. Another issue is the connection of bariatric surgery with the gut microbiota and its role in the complex mechanism underlying weight gain.

CONCLUSION

Bariatric surgery modifies gut microbiota, and these modifications influence lipid metabolism, leading to improvement of non-alcoholic fatty liver disease.

Management of metabolic-associated fatty liver disease: The diabetology perspective

The metabolic syndrome as a consequence of the obesity pandemic resulted in a substantial increase in the prevalence of metabolic-associated fatty live disease (MAFLD) and type 2 diabetes mellitus (T2DM). Because of the similarity in pathobiology shared between T2DM and MAFLD, both disorders coexist in many patients and may potentiate the disease-related outcomes with rapid progression and increased complications of the individual diseases. In fact, awareness about this coexistence and the risk of complications are often overlooked by both hepatologists and diabetologists. Management of these individual disorders in a patient should be addressed wholistically using an appropriate multidisciplinary team approach involving both the specialists and, when necessary, liaising with dieticians and surgeons. This comprehensive review is to compile the current evidence from a diabetologist's perspective on MAFLD and T2DM and to suggest optimal management strategies.

Increased plasma genistein after bariatric surgery could promote remission of NAFLD in patients with obesity

Background

Bariatric surgery is associated with a positive effect on the progress of non-alcoholic associated fatty liver disease (NAFLD). Although weight loss is the obvious mechanism, there are also weight-independent mechanisms.

Methods

We collected blood samples from 5 patients with obesity before and 3 months after surgery and performed an LC-MS-based untargeted metabolomics test to detect potential systemic changes. We also constructed sleeve gastrectomy (SG) mice models. The plasma, liver and intestine samples were collected and analyzed by qPCR, ELISA and HPLC. Cohousing experiments and feces transplantation experiments were performed on mice to study the effect of gut microbiota. Genistein administration experiments were used to study the in vivo function of the metabolites.

Results

Plasma genistein (GE) was identified to be elevated after surgery. Both clinical data and rodent models suggested that plasma GE is negatively related to the degree of NAFLD. We fed diet-induced obese (DIO) mice with GE, and we found that there was significant remission of NAFLD. Both in vivo and in vitro experiments showed that GE could restrict the inflammation state in the liver and thus relieve NAFLD. Finally, we used co-housing experiments to alter the gut microbiota in mice, and it was identified that sleeve gastrectomy (SG) mice had a special gut microbiota phenotype, which could result in higher plasma GE levels. By feces transplantation experiment (FMT), we found that only feces from the SG mice (and not from other lean mice) could induce higher plasma GE levels.

Conclusion

Our studies showed that SG but not calorie restriction could induce higher plasma GE levels by altering the gut microbiota. This change could promote NAFLD remission. Our study provides new insights into the systemic effects of bariatric surgery. Bariatric surgery could affect remote organs via altered metabolites from the gut microbiota. Our study also identified that additional supplement of GE after surgery could be a therapy for NAFLD.

Gut microbiota modulation in patients with non-alcoholic fatty liver disease: Effects of current treatments and future strategies

Non-alcoholic fatty liver disease (NAFLD) is frequently associated with metabolic disorders, being highly prevalent in obese and diabetic patients. Many concomitant factors that promote systemic and liver inflammation are involved in NAFLD pathogenesis, with a growing body of evidence highlighting the key role of the gut microbiota. Indeed, the gut-liver axis has a strong impact in the promotion of NAFLD and in the progression of the wide spectrum of its manifestations, claiming efforts to find effective strategies for gut microbiota modulation. Diet is among the most powerful tools; Western diet negatively affects intestinal permeability and the gut microbiota composition and function, selecting pathobionts, whereas Mediterranean diet fosters health-promoting bacteria, with a favorable impact on lipid and glucose metabolism and liver inflammation. Antibiotics and probiotics have been used to improve NAFLD features, with mixed results. More interestingly, medications used to treat NAFLD-associated comorbidities may also modulate the gut microbiota. Drugs for the treatment of type 2 diabetes mellitus (T2DM), such as metformin, glucagon-like peptide-1 (GLP-1) agonists, and sodium-glucose cotransporter (SGLT) inhibitors, are not only effective in the regulation of glucose homeostasis, but also in the reduction of liver fat content and inflammation, and they are associated with a shift in the gut microbiota composition towards a healthy phenotype. Even bariatric surgery significantly changes the gut microbiota, mostly due to the modification of the gastrointestinal anatomy, with a parallel improvement in histological features of NAFLD. Other options with promising effects in reprogramming the gut-liver axis, such as fecal microbial transplantation (FMT) and next-generation probiotics deserve further investigation for future inclusion in the therapeutic armamentarium of NAFLD.

THE INTESTINAL MICROBIOME IN PATIENTS UNDERGOING BARIATRIC SURGERY: A SYSTEMATIC REVIEW

BACKGROUND

Dysbiosis of the gut microbiota is frequently found in cases of obesity and related metabolic diseases, such as type 2 diabetes mellitus. The composition of the microbiota in diabetics is similar to that of obese people, thereby causing increased energy uptake efficiency in the large intestine of obese people, maintenance of a systemic inflammatory state, and increased insulin resistance. Bariatric surgery seems to entail an improvement in gut dysbiosis, leading to an increased diversity of the gut microbiota.

AIMS

This study aimed to present a literature review on obesity-associated gut dysbiosis and its status post-bariatric surgery.

METHODS

A systematic review of primary studies was conducted in PubMed, SciELO, BIREME, LILACS, Embase, ScienceDirect, and Scopus databases using DeCS (Health Science Descriptors) with the terms "obesity," "intestinal dysbiosis," "bariatric surgery," and "microbiota."

RESULTS

We analyzed 28 articles that had clinical studies or literature reviews as their main characteristics, of which 82% (n=23) corresponded to retrospective studies. The sample size of the studies ranged from 9 to 257 participants and/or fecal samples. The epidemiological profile showed a higher prevalence of obesity in females, ranging from 24.4 to 35.1%, with a mean age of around 25-40 years. There was a variation regarding the type of bariatric surgery, migrating between the Roux-en-Y bypass, adjustable gastric banding, and vertical gastrectomy. Of the 28 studies, 6 of them evaluated the gut microbiota of obese patients undergoing bariatric surgery and their relationship with type 2 diabetes mellitus/glucose metabolism/insulin resistance.

CONCLUSIONS

The intestinal microbiota is an important influencer in the regulation of the digestive tract, and obese individuals with comorbidities (diabetes mellitus, hypercholesterolemia, and metabolic syndrome) present important alterations, with an unbalance normal state, generating dysbiosis and the proliferation of bacterial species that favor the appearance of new diseases. Patients who undergo bariatric surgery present an improvement in the intestinal microbiota imbalance as well as reversibility of their comorbidities, increasing their life expectancy.

Gut microbiome and microbial metabolites in NAFLD and after bariatric surgery: Correlation and causality

Non-alcoholic fatty liver disease (NAFLD) is currently related to a heavy socioeconomic burden and increased incidence. Since obesity is the most prevalent risk factor for NAFLD, weight loss is an effective therapeutic solution. Bariatric surgery (BS), which can achieve long-term weight loss, improves the overall health of patients with NAFLD. The two most common surgeries are the Roux-en-Y gastric bypass and sleeve gastrectomy. The gut-liver axis is the complex network of cross-talking between the gut, its microbiome, and the liver. The gut microbiome, involved in the homeostasis of the gut-liver axis, is believed to play a significant role in the pathogenesis of NAFLD and the metabolic improvement after BS. Alterations in the gut microbiome in NAFLD have been confirmed compared to that in healthy individuals. The mechanisms linking the gut microbiome to NAFLD have been proposed, including increased intestinal permeability, higher energy intake, and other pathophysiological alterations. Interestingly, several correlation studies suggested that the gut microbial signatures after BS become more similar to those of lean, healthy controls than that of patients with NAFLD. The resolution of NAFLD after BS is related to changes in the gut microbiome and its metabolites. However, confirming a causal link remains challenging. This review summarizes characteristics of the gut microbiome in patients with NAFLD before and after BS and accumulates existing evidence about the underlying mechanisms of the gut microbiome.

Dietary Exposure to Antibiotic Residues Facilitates Metabolic Disorder by Altering the Gut Microbiota and Bile Acid Composition

Antibiotics used as growth promoters in livestock and animal husbandry can be detected in animal-derived food. Epidemiological studies have indicated that exposure to these antibiotic residues in food may be associated with childhood obesity. Herein, the effect of exposure to a residual dose of tylosin-an antibiotic growth promoter-on host metabolism and gut microbiota was explored in vivo. Theoretical maximal daily intake (TMDI) doses of tylosin were found to facilitate high-fat-diet-induced obesity, induce insulin resistance, and perturb gut microbiota composition in mice. The obesity-related phenotypes were transferrable to germfree recipient mice, indicating that the effects of a TMDI dose of tylosin on obesity and insulin resistance occurred mainly via alteration of the gut microbiota. Tylosin TMDI exposure restricted to early life, the critical period of gut microbiota development, altered the abundance of specific bacteria related to host metabolic homeostasis later in life. Moreover, early-life exposure to tylosin TMDI doses was sufficient to modify the ratio of primary to secondary bile acids, thereby inducing lasting metabolic consequences via the downstream FGF15 signaling pathway. Altogether, these findings demonstrate that exposure to very low doses of antibiotic residues, whether continuously or in early life, could exert long-lasting effects on host metabolism by altering the gut microbiota and its metabolites. IMPORTANCE This study demonstrates that even with limited exposure in early life, a residual dose of tylosin might cause long-lasting metabolic disturbances by altering the gut microbiota and its metabolites. Our findings reveal that the gut microbiota is susceptible to previously ignored environmental factors.

The Problem of Appetite Loss After Major Abdominal Surgery

Objective:

To systematically review the problem of appetite loss after major abdominal surgery.

Summary of Background Data:

Appetite loss is a common problem after major abdominal surgery. Understanding of etiology and treatment options is limited.

Methods:

We searched Medline, Cochrane Central Register of Controlled Trials, and Web of Science for studies describing postoperative appetite loss. Data were extracted to clarify definition, etiology, measurement, surgical influence, pharmacological, and nonpharmacological treatment. PROSPERO registration ID: CRD42021224489.

Results:

Out of 6144 articles, we included 165 studies, 121 of which were also analyzed quantitatively. A total of 19.8% were randomized, controlled trials (n = 24) and 80.2% were nonrandomized studies (n = 97). The studies included 20,506 patients undergoing the following surgeries: esophageal (n = 33 studies), gastric (n = 48), small bowel (n = 6), colon (n = 27), rectal (n = 20), hepatobiliary (n = 6), and pancreatic (n = 13). Appetite was mostly measured with the Quality of Life Questionnaire of the European Organization for Research and Treatment of Cancer (EORTC QLQ C30, n = 54). In a meta-analysis of 4 randomized controlled trials gum chewing reduced time to first hunger by 21.2 hours among patients who had bowel surgery. Other reported treatment options with positive effects on appetite but lower levels of evidence include, among others, intravenous ghrelin administration, the oral Japanese herbal medicine Rikkunshito, oral mosapride citrate, multidisciplin-ary-counseling, and watching cooking shows. No studies investigated the effect of well-known appetite stimulants such as cannabinoids, steroids, or megestrol acetate on surgical patients.

Conclusions:

Appetite loss after major abdominal surgery is common and associated with increased morbidity and reduced quality of life. Recent studies demonstrate the influence of reduced gastric volume and ghrelin secretion, and increased satiety hormone secretion. There are various treatment options available including level IA evidence for postoperative gum chewing. In the future, surgical trials should include the assessment of appetite loss as a relevant outcome measure.

Bariatric Surgery and Solid-Organ Transplantation

Morbid obesity and being overweight are a growing problem worldwide. They also affect patients with end-stage solid-organ disease and patients after transplant. Bariatric surgery is the most effective available weight loss procedure. Bariatric surgery can be helpful for the treatment of some conditions, such as nonalcoholic fatty liver disease or nonalcoholic steatohepatitis, which may lead to transplant, and weight loss can improve or even reverse them. In other cases, morbid obesity is a limitation to accessing a transplant program, so bariatric surgery can serve as a conduit to transplant. After transplant, obesity and obesity-related comorbidities can be a significant health problem that may be treated, as in patients without a transplant, with bariatric surgery. There are some specific conditions and issues to be considered in patients with end-stage solid-organ disease who are candidates for bariatric surgery, such as increased morbidity and mortality. After transplant, immunosuppressant regimens and technical limitations may be also significant.

Obesity and Gallstones

BACKGROUND

The prevalence of obesity has been increasing globally and represents the main risk factor for the development of gallstone disease (GD).

SUMMARY

Excess body weight represents the main cause for the development of GD; nevertheless, there have been described multiple risk factors for its development, among them modifiable risk factors as diet, lifestyle, physical inactivity, and non-modifiable risk factors as ethnicity, female sex, advanced age, parity, and genetic mutations. Body mass index, abdominal perimeter, and waist-hip index have been used to determine the degree of adiposity of a person. Hence, central abdominal fat has been mostly associated with insulin resistance with the consequent increase in the hepatic cholesterol secretion; contributing as one of the multiple mechanisms associated with the development of gallstones. This disease has a low mortality; however, it has been associated with multiple diseases such as cardiovascular diseases, carotid atherosclerosis, metabolic associated fatty liver disease, and gallbladder cancer, probably because they share many of the risk factors.

KEY MESSAGES

GD continues to be considered a disease with a high medical burden, in which it is sought to intervene in modifiable risk factors to reduce its development.

Bariatric Surgery and Liver Disease: General Considerations and Role of the Gut-Liver Axis

Weight loss is a therapeutic solution for many metabolic disorders, such as obesity and its complications. Bariatric surgery aims to achieve lasting weight loss in all patients who have failed after multiple dietary attempts. Among its many benefits, it has been associated with the regression of non-alcoholic fatty liver disease (NAFLD), which is often associated with obesity, with evidence of substantial improvement in tissue inflammation and fibrosis. These benefits are mediated not only by weight loss, but also by favorable changes in systemic inflammation and in the composition of the gut microbiota. Changes in microbial metabolites such as short-chain fatty acids (SCFAs), capable of acting as endocrine mediators, and bile acids (BAs) as well as modifications of the gut-brain axis, are among the involved mechanisms. However, not all bariatric surgeries show beneficial effects on the liver; those leading to malabsorption can cause liver failure or a marked worsening of fibrosis and the development of cirrhosis. Nevertheless, there are still many unclear aspects, including the extent of the benefits and the magnitude of the risks of bariatric surgery in cirrhotic patients. In addition, the usefulness and the safety of these procedures in patients who are candidates to or who have undergone liver transplant need solid supporting evidence. This paper aims to review literature data on the use of bariatric surgery in the setting of chronic liver disease.

Bariatric Surgery Affects Plasma Levels of Alanine Aminotransferase Independent of Weight Loss: A Registry-Based Study

Patients that undergo bariatric surgery experience weight loss and a reduction in the plasma levels of the hepatic enzymes alanine aminotransferase (ALT) and aspartate aminotransferase (AST). We used the Israeli national bariatric registry, which includes demographic, clinical, and biochemical data on 19,403 patients, of which 1335 patients had two-year follow-up data on ALT, AST, A1C, and BMI, to test the dependence of the reduction in the levels of ALT and AST on weight loss. The data were analyzed using regression models, retrospective matching, and time course analyses. Changes in liver enzymes did not correlate with change in BMI, and linear regression models did not demonstrate that the change in ALT and AST values were dependent on pre-operative levels of BMI or the extent of weight loss. ALT and AST levels were reduced two years after surgery compared with a cohort of retrospectively matched patients for ethnicity, sex, age, BMI, and A1C. Finally, patients who regained weight displayed a reduction in levels of liver enzymes. Our results suggest that bariatric surgery affects AST and ALT levels via weight loss dependent and independent mechanisms. Mechanistic studies that will identify the nature of this effect and the clinical relevance of ALT and AST levels to the post-bariatric liver function are warranted.

Gut Microbiota in Metabolic-associated Fatty Liver Disease and in Other Chronic Metabolic Diseases

The gut microbiome plays a key role in the health-disease balance in the human body. Although its composition is unique for each person and tends to remain stable throughout lifetime, it has been shown that certain bacterial patterns may be determining factors in the onset of certain chronic metabolic diseases, such as type 2 diabetes mellitus (T2DM), obesity, metabolic-associated fatty liver disease (MAFLD), and metabolic syndrome. The gut-liver axis embodies the close relationship between the gut and the liver; disturbance of the normal gut microbiota, also known as dysbiosis, may lead to a cascade of mechanisms that modify the epithelial properties and facilitate bacterial translocation. Regulation of gut microbiota is fundamental to maintaining gut integrity, as well as the bile acids composition. In the present review, we summarize the current knowledge regarding the microbiota, bile acids composition and their association with MAFLD, obesity, T2DM and metabolic syndrome.

Mining Gut Microbiota From Bariatric Surgery for MAFLD

The progression of metabolic dysfunction associated fatty liver disease (MAFLD) leads to steatohepatitis, liver fibrosis and hepatocellular carcinoma. Thus far, there have been no FDA-approved medications for MAFLD. Bariatric surgery (BS) has been found to improve insulin resistance, steatohepatitis and liver fibrosis but is not recommended for treating MAFLD due to its invasiveness. Recent studies suggest the improved glucose metabolism after BS is a result of, at least partly, alterations to the gut microbiota and its associated metabolites, including short chain fatty acids and bile acids. It makes sense the improved steatohepatitis and fibrosis after BS are also induced by the gut microbiota that involves in host metabolic modulation, for example, through altering bile acids composition. Given that the gut-liver axis is a path that may harbor unexplored mechanisms behind MAFLD, we review current literatures about disentangling the metabolic benefits of MAFLD after BS, with a focus on gut microbiota. Some useful research tools including the rodent BS model, the multiomics approach, and the human microbiota associated (HMA) mice are presented and discussed. We believe, by taking advantage of these modern translational tools, researchers will uncover microbiota related pathways to serve as potential therapeutic targets for treating MAFLD.

iPSC-derived hepatocytes generated from NASH donors provide a valuable platform for disease modeling and drug discovery

Non-alcoholic fatty liver disease (NAFLD) affects 30-40% of adults and 10% of children in the US. About 20% of people with NAFLD develop non-alcoholic steatohepatitis (NASH), which may lead to cirrhosis and liver cancer, and is projected to be a leading cause of liver transplantation in the near future. Human induced pluripotent stem cells (iPSC) from NASH patients are useful for generating a large number of hepatocytes for NASH modeling applications and identification of potential drug targets. We developed a novel defined in vitro differentiation process to generate cryopreservable hepatocytes using an iPSC panel of NASH donors and apparently healthy normal (AHN) controls. iPSC-derived hepatocytes displayed stage specific phenotypic markers, hepatocyte morphology, with bile canaliculi. Importantly, both fresh and cryopreserved definitive endoderm and hepatoblasts successfully differentiated to pure and functional hepatocytes with increased CYP3A4 activity in response to rifampicin and lipid accumulation upon fatty acid (FA) treatment. End-stage hepatocytes integrated into three-dimensional (3D) liver organoids and demonstrated increased levels of albumin secretion compared to aggregates consisting of hepatocytes alone. End-stage hepatocytes derived from NASH donors demonstrated spontaneous lipidosis without FA supplementation, recapitulating a feature of NASH hepatocytes in vivo Cryopreserved hepatocytes generated by this protocol across multiple donors will provide a critical cell source to facilitate the fundamental understanding of NAFLD/NASH biology and potential high throughput screening applications for preclinical evaluation of therapeutic targets.