Activation of thyroid hormone receptor-β improved disease activity and metabolism independent of body weight in a mouse model of non-alcoholic steatohepatitis and fibrosis

Cross-Talk Between Thyroid Disorders and Nonalcoholic Fatty Liver Disease: From Pathophysiology to Therapeutics

The medical community acknowledges the presence of thyroid disorders and nonalcoholic fatty liver disease (NAFLD). Nevertheless, the interconnection between these two circumstances is complex. Thyroid hormones (THs), including triiodothyronine (T3) and thyroxine (T4), and thyroid-stimulating hormone (TSH), are essential for maintaining metabolic balance and controlling the metabolism of lipids and carbohydrates. The therapeutic potential of THs, especially those that target the TRβ receptor isoform, is generating increasing interest. The review explores the pathophysiology of these disorders, specifically examining the impact of THs on the metabolism of lipids in the liver. The purpose of this review is to offer a thorough analysis of the correlation between thyroid disorders and NAFLD, as well as suggest potential therapeutic approaches for the future.

Beneficial effects of MGL-3196 and BAM15 combination in a mouse model of fatty liver disease

BACKGROUND AND AIM

Metabolic dysfunction-associated steatohepatitis (MASH) is a metabolic disorder with limited treatment options. The thyroid hormone receptor (THR)-β agonist resmetirom/MGL-3196 (MGL) increases liver fat oxidation and has been approved for treating adult MASH. However, over 60% of patients receiving MGL treatment do not achieve MASH resolution. Therefore, we investigated the potential for combination therapy of MGL with the mitochondrial uncoupler BAM15 to improve fatty liver disease outcomes in the GAN mouse model of MASH.

METHODS

C57BL/6J male mice were fed GAN diet for 38 weeks before stratification and randomization to treatments including MGL, BAM15, MGL + BAM15, or no drug control for 8 weeks. Treatments were admixed in diet and mice were pair-fed to control for drug intake. Treatment effectiveness was assessed by body weight, body composition, energy expenditure, glucose tolerance, tissue lipid content, and histological analyses.

RESULTS

MGL + BAM15 treatment resulted in better efficacy versus GAN control mice than either monotherapy in the context of energy expenditure, liver fat loss, glucose control, and fatty liver disease activity score. Improvements in ALT, liver mass, and plasma cholesterol were primarily driven by MGL, while improvements in body fat were primarily driven by BAM15. No treatments altered liver fibrosis.

CONCLUSIONS

MGL + BAM15 treatment had overall better efficacy to improve metabolic outcomes in mice fed GAN diet than either monotherapy alone. These data warrant further investigation into combination therapies of THR-β agonists and mitochondrial uncouplers for the potential treatment of disorders related to fatty liver, obesity, and insulin resistance.

Current Progress and Challenges in the Development of Pharmacotherapy for Metabolic Dysfunction-Associated Steatohepatitis

Metabolic dysfunction-associated steatohepatitis (MASH), a severe form of metabolic dysfunction-associated steatotic liver disease (MASLD), poses a significant threat to global health. Despite extensive research efforts over the past decade, only one drug has received market approval under accelerated pathways. In this review, we summarise the pathogenesis of MASH and present a comprehensive overview of recent advances in phase 2-3 clinical trials targeting MASH. These trials have highlighted considerable challenges, including low response rates to drugs, limitations of current surrogate histological endpoints, and inadequacies in the design of MASH clinical trials, all of which hinder the progress of MASH pharmacotherapy. We also explored the potential of non-invasive tests to enhance clinical trial design. Furthermore, given the strong association between MASLD and cardiometabolic disorders, we advocate for an integrated approach to disease management to improve overall patient outcomes. Continued investigation into the mechanisms and pharmacology of combination therapies may offer valuable insights for developing innovative MASH treatments.

Liver-specific thyroid hormone receptor-β agonism alleviates alcoholic steatohepatitis (ASH) in mice

Alcoholic steatohepatitis (ASH) represents a critical stage in alcoholic liver disease (ALD), which significantly increases the risk of developing alcoholic hepatitis and cirrhosis. Currently, corticosteroids and alcohol abstinence remain the only available strategy to prevent or reverse ASH progression with no FDA approved drug therapy till date. Given the notable pathological similarities between ASH and metabolic dysfunction-associated steatohepatitis (MASH), repurposing drugs approved for MASH presents an attractive therapeutic approach to treat ASH. In this context, we evaluated the efficacy of Resmetirom, a recently approved drug for MASH, in a mouse model of ASH. Our findings demonstrate that Resmetirom, a liver-specific thyroid hormone analog, not only reduces hepatic steatosis but also markedly alleviates liver injury, oxidative stress, and inflammation associated with ASH. In summary, this study provides a proof-of-concept for the potential use of MASH drugs in treating ASH and establishes a foundation for future testing and clinical trials of Resmetirom, in patients with ASH.

Thyroid hormone receptor-beta agonist HSK31679 alleviates MASLD by modulating gut microbial sphingolipids

BACKGROUND & AIMS

As the first approved medication for metabolic dysfunction-associated steatohepatitis (MASH), the thyroid hormone receptor-β (THR-β) agonist MGL-3196 (resmetirom) has garnered much attention as a liver-directed, bioactive oral drug. However, studies on MGL-3196 have also identified remarkable heterogeneity of individual clinical efficacy and its interference with gut microbiota in host hepatoenteral circulation remains to be elucidated.

METHODS

We compared MASH attenuation by MGL-3196 and its derivative drug HSK31679 between germ-free (GF) and specific-pathogen free (SPF) mice to evaluate the role of gut microbiota. Then cross-omics analyses of microbial metagenome, metabolome and single-cell RNA-sequencing were applied to a randomized, double-blind, placebo-controlled multiple ascending dose cohort receiving HSK31679 treatment (n = 32) or placebo (n = 8), to comprehensively investigate the altered gut microbiota metabolism and circulating immune signatures.

RESULTS

HSK31679 outperformed MGL-3196 in ameliorating MASH diet-induced steatohepatitis of SPF mice but not GF mice. In the multiple ascending dose cohort of HSK31679, the relative abundance of B. thetaiotaomicron was significantly enriched, impairing glucosylceramide synthase (GCS)-catalyzed monoglucosylation of microbial Cer(d18:1/16:0) and Cer(d18:1/24:1). In contrast to the non-inferior effect of MGL-3196 and HSK31679 on MASH resolution in GFBTΔGCS mice, HSK31679 led to superior benefit on steatohepatitis in GFBTWT mice, due to its steric hindrance of R123 and Y401 of gut microbial GCS. For participants with high fecal GCS activity, the administration of 160 mg HSK31679 induced a shift in peripheral compartments towards an immunosuppressive niche, characterized by decreased CD8α+ dendritic cells and MINCLE+ macrophages.

CONCLUSIONS

This study provided novel insights into the gut microbiota that are key to the efficacy of HSK31679 treatment, revealing microbial GCS as a potential predictive biomarker in MASH, as well as a new target for further microbiota-based treatment strategies for MASH.

IMPACT AND IMPLICATIONS

Remarkable heterogeneity in individual clinical efficacy of thyroid hormone receptor-β agonists and their interferences with the microbiome in host hepatoenteral circulation are poorly understood. In our current germ-free mouse models and a randomized, double-blind, multiple-dose cohort study, we identified microbial glucosylceramide synthase as a key mechanistic node in the resolution of metabolic dysfunction-associated steatohepatitis. Microbial glucosylceramide synthase activity could be a predictive biomarker of response to HSK31679 treatment or a new target for microbiota-based therapeutics in metabolic dysfunction-associated steatohepatitis.

Resmetirom and Metabolic Dysfunction-Associated Steatohepatitis: Perspectives on Multidisciplinary Management from Global Healthcare Professionals

PURPOSE OF REVIEW

The approval of resmetirom brings great hope to patients with metabolic dysfunction-associated steatohepatitis (MASH). The purpose of this review is to explore its impact on the global health environment. The implementation of multidisciplinary management MASH is proposed.

RECENT FINDINGS

Resmetirom has benefits in the treatment of MASH, and its safety and effectiveness have been studied. The adverse events (AEs) need to be noticed. To improve patient outcomes, a multimodal approach with medication such as resmetirom, combined with metabolic and bariatric surgery (MBS) and lifestyle interventions can be conducted. MASH, a liver disease linked with obesity, is a challenging global healthcare burden compounded by the absence of any approved pharmacotherapy. The recent conditional approval by the Food and Drug Administration (FDA) in the United States of resmetirom, an oral, liver-directed, thyroid hormone receptor beta-selective agonist, marks a significant milestone, offering a treatment option for adults with non-cirrhotic MASH and who have moderate to advanced liver fibrosis. This narrative review discusses the efficacy and safety of resmetirom and its role in the therapeutic landscape of MASH treatment. Despite the promising hepatoprotective effect of resmetirom on histological liver endpoints, its use need further research, particularly regarding ethnic differences, effectiveness and cost-effectiveness, production scalability, social acceptance and accessibility. In addition, integrating resmetirom with other multidisciplinary therapeutic approaches, including lifestyle changes and MBS, might further improve clinical liver-related and cardiometabolic outcomes of individuals with MASH. This review highlights the importance of a comprehensive treatment strategy, supporting continued innovation and collaborative research to refine treatment guidelines and consensus for managing MASH, thereby improving clinical patient outcomes in the growing global epidemic of MASH. Studies done to date have been relatively short and ongoing, the course of the disease is highly variable, the conditions of various patients vary, and given this complex clinical phenotype, it may take many years of clinical trials to show long-term benefits.

Resmetirom's approval: Highlighting the need for comprehensive approaches in NASH therapeutics

The recent FDA approval of Rezdiffra (resmetirom), an oral partial agonist of the thyroid hormone receptor-beta (THR-beta), for the treatment of noncirrhotic non-alcoholic steatohepatitis (NASH) with moderate to advanced fibrosis, has challenged conventional approaches to NASH drug development. Despite extensive efforts targeting typical pathways involved in NASH progression, such as lipogenesis, oxidative stress, and inflammation, these approaches have yet to yield any approved therapies. The success of resmetirom highlights the potential advantages of targeting THR-beta, which exerts pleiotropic effects on multiple pathways involved in NASH pathogenesis, including lipid metabolism, glucose homeostasis, and inflammation. In the phase 3 MAESTRONASH trial, resmetirom significantly improved NASH resolution, fibrosis, and LDL cholesterol levels compared to placebo, with a favorable safety profile. The tissue-specific action of resmetirom may also contribute to its efficacy and safety. The approval of resmetirom has opened new avenues for NASH drug development, emphasizing the importance of exploring novel mechanisms of action, developing targeted therapies, and embracing a more comprehensive approach to treatment. As the global burden of NASH continues to grow, the lessons learned from the success of resmetirom should inform future drug development strategies, offering hope to the millions of patients affected by this disease worldwide.

Exploring Varied Treatment Strategies for Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD)

Metabolic dysfunction-associated steatotic liver disease (MASLD) represents a liver disorder characterized by steatosis with underlying metabolic risk factors. The prevalence of MASLD continues to rise, leading to increased patient risk of various complications. Recent research has been focused on new therapeutic strategies to reduce the incidence of MASLD and provide effective treatment plans to prevent further irreversible liver damage. The treatment approach is multifactorial, with a primary focus on weight loss and management of underlying comorbidities through lifestyle modifications, pharmacotherapy, or surgical options. Ongoing research is exploring new pharmacological therapies that could enhance the treatment of MASLD.

The first MASH drug therapy on the horizon: Current perspectives of resmetirom

The rising prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD) poses a significant global health challenge, affecting over 30% of adults worldwide. MASLD is linked to increased mortality rates and substantial healthcare costs, primarily driven by its progression to metabolic dysfunction-associated steatohepatitis (MASH), which can lead to severe liver complications including cirrhosis and hepatocellular carcinoma. Despite its growing burden, effective pharmacotherapy for MASLD/MASH has been lacking until the recent conditional approval of resmetirom by the FDA. Resmetirom, a liver-targeted thyroid hormone receptor-β selective drug, has shown promise in clinical trials for treating non-cirrhotic MASH with moderate to advanced fibrosis. It has demonstrated efficacy in reducing hepatic fat content, improving liver histology (both MASH resolution and fibrosis improvement), and ameliorating biomarkers of liver damage without significant effects on body weight or glucose metabolism. Notably, resmetirom also exhibits favourable effects on circulating lipids, potentially reducing cardiovascular risk in MASLD/MASH patients. The safety profile of resmetirom appears acceptable, with gastrointestinal adverse events being the most common, though generally mild or moderate. However, long-term surveillance is warranted to monitor for potential risks related to thyroid, gonadal, or bone diseases. Clinical implementation of resmetirom faces challenges in patient selection and monitoring treatment response, and will heavily rely on non-invasive tests for liver fibrosis assessment. Nonetheless, resmetirom represents a landmark breakthrough in MASLD/MASH treatment, paving the way for future therapeutic strategies aiming to mitigate the multifaceted risks associated with this complex metabolic liver disease.

The gut-liver axis: emerging mechanisms and therapeutic approaches for nonalcoholic fatty liver disease and type 2 diabetes mellitus

Nonalcoholic fatty liver disease (NAFLD), more appropriately known as metabolic (dysfunction) associated fatty liver disease (MAFLD), a prevalent condition in type 2 diabetes mellitus (T2DM) patients, is a complex condition involving hepatic lipid accumulation, inflammation, and liver fibrosis. The gut-liver axis is closely linked to metabolic dysfunction, insulin resistance, inflammation, and oxidative stress that are leading to the cooccurrence of MAFLD and T2DM cardiovascular diseases (CVDs). The purpose of this review is to raise awareness about the role of the gut-liver axis in the progression of MAFLD, T2DM and CVDs with a critical analysis of available treatment options for T2DM and MAFLD and their impact on cardiovascular health. This study analysed over 100 articles on this topic, using online searches and predefined keywords, to understand and summarise published research. Numerous studies have shown a strong correlation between gut dysfunction, particularly the gut microbiota and its metabolites, and the occurrence and progression of MAFLD and type 2 diabetes mellitus (T2DM). Herein, this article also examines the impact of the gut-liver axis on MAFLD, T2DM, and related complications, focusing on the role of gut microbiota dysbiosis in insulin resistance, T2DM and obesity-related cardiovascular complications. The study suggests potential treatment targets for MAFLD linked to T2DM, focusing on cardiovascular outcomes and the molecular mechanism of the gut-liver axis, as gut microbiota dysbiosis contributes to obesity-related metabolic abnormalities.

In NASH with liver fibrosis, resmetirom improved NASH resolution and reduced fibrosis at 1 y

SOURCE CITATION

Harrison SA, Bedossa P, Guy CD, et al. MAESTRO-NASH Investigators. A phase 3, randomized, controlled trial of resmetirom in NASH with liver fibrosis. N Engl J Med. 2024;390:497-509. 38324483.

Resmetirom: First Approval

Resmetirom (Rezdiffra™) is an oral thyroid hormone receptor-β (THR-β) agonist being developed by Madrigal Pharmaceuticals, Inc., to target the key underlying causes of metabolic dysfunction associated steatohepatitis (MASH) [previously known as nonalcoholic steatohepatitis (NASH)]. In March 2024, resmetirom was approved for use (under accelerated approval) in conjunction with diet and exercise for the treatment of adults with noncirrhotic NASH with moderate to advanced liver fibrosis (consistent with stages F2 to F3 fibrosis) in the USA. Resmetirom is also under regulatory review in the EU for the treatment of MASH/NASH. This article summarizes the milestones in the development of resmetirom leading to this first approval for the treatment of adults with MASH/NASH.

Intrahepatic hypothyroidism in MASLD: Role of liver-specific thyromimetics including resmetirom

BACKGROUND AND AIMS

Thyroid hormones are important regulators of hepatic lipid homeostasis and whole-body energy expenditure. Recent evidence suggests that euthyroid individuals with metabolic dysfunction-associated steatohepatitis (MASH) develop intrahepatic hypothyroidism that promotes progression of MASH.

METHODS

A literature search was performed with Medline (PubMed), Scopus and Google Scholar electronic databases from inception till March 2024, using the following keywords: hypothyroidism and nonalcoholic fatty liver disease; MASLD and thyroid function; intrahepatic hypothyroidism; TRβ agonists; and resmetirom. Relevant studies were extracted that described pathogenesis of MASH in the context of thyroid functions.

RESULTS

In euthyroid individuals with MASH, there is decreased conversion of prohormone thyroxine (T4) to bioactive tri-iodothyronine (T3) and increased conversion of T4 to inactive metabolite reverse T3 (rT3). Consequently, reduced levels of T3 results in impaired intrahepatic TRβ signaling, a state of intrahepatic hypothyroidism, which promotes progression of MASH. Hepatic TRβ activation leads to metabolically beneficial effects in the liver including mitochondrial fatty acid uptake and β-oxidation, mitochondrial biogenesis, increasing surface low-density lipoprotein (LDL) receptor density and lowering of circulatory LDL-cholesterol. In recent years, selective thyroid hormone mimetics that exhibit TRβ-selective binding and liver-selective uptake have been designed. Resmetirom, a liver-specific thyromimetic, improves intrahepatic TRβ signaling and in clinical trials significantly improved liver inflammation, fibrosis and lipid profile in patients with MASH.

CONCLUSIONS

In euthyroid individuals with MASH, development of intrahepatic hypothyroidism results in further progression of the disease. In clinical trials, resmetirom treatment results in a significant improvement in steatosis, inflammation and fibrosis and is the first drug approved by the US Food and Drug Administration (FDA) for the treatment of noncirrhotic MASH with moderate to advanced fibrosis.

A revisit of drugs and potential therapeutic targets against non-alcoholic fatty liver disease: learning from clinical trials

PURPOSE

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease, with a worldwide prevalence of 25%. Although numerous clinical trials have been conducted over the last few decades, an effective treatment has not been approved yet. Extensive research has accumulated a large amount of data and experience; however, the vast number of clinical trials and new therapeutic targets for NAFLD make it impossible to keep abreast of the relevant information. Therefore, a systematic analysis of the existing trials is necessary.

METHODS

Here, we reviewed clinical trials on NAFLD registered in the mandated federal database, ClinicalTrials.gov, to generate a detailed overview of the trials related to drugs and therapeutic targets for NAFLD treatment. Following screening for pertinence to therapy, a total of 440 entries were identified that included active trials as well as those that have already been completed, suspended, terminated, or withdrawn.

RESULTS

We summarize and systematically analyze the state, drug development pipeline, and discovery of treatment targets for NAFLD. We consider possible factors that may affect clinical outcomes. Furthermore, we discussed these results to explore the mechanisms responsible for clinical outcomes.

CONCLUSION

We summarised the landscape of current clinical trials and suggested the directions for future NAFLD therapy to assist internal medicine specialists in treating the whole clinical spectrum of this highly prevalent liver disease.

Drug targets regulate systemic metabolism and provide new horizons to treat nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH), is the advanced stage of nonalcoholic fatty liver disease (NAFLD) with rapidly rising global prevalence. It is featured with severe hepatocyte apoptosis, inflammation and hepatic lipogenesis. The drugs directly targeting the processes of steatosis, inflammation and fibrosis are currently under clinical investigation. Nevertheless, the long-term ineffectiveness and remarkable adverse effects are well documented, and new concepts are required to tackle with the root causes of NASH progression. We critically assess the recently validated drug targets that regulate the systemic metabolism to ameliorate NASH. Thermogenesis promoted by mitochondrial uncouplers restores systemic energy expenditure. Furthermore, regulation of mitochondrial proteases and proteins that are pivotal for intracellular metabolic homeostasis normalize mitochondrial function. Secreted proteins also improve systemic metabolism, and NASH is ameliorated by agonizing receptors of secreted proteins with small molecules. We analyze the drug design, the advantages and shortcomings of these novel drug candidates. Meanwhile, the structural modification of current NASH therapeutics significantly increased their selectivity, efficacy and safety. Furthermore, the arising CRISPR-Cas9 screen strategy on liver organoids has enabled the identification of new genes that mediate lipid metabolism, which may serve as promising drug targets. In summary, this article discusses the in-depth novel mechanisms and the multidisciplinary approaches, and they provide new horizons to treat NASH.

Recent advances in age-related metabolic dysfunction-associated steatotic liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) affects approximately 25% of the world's population and has become a leading cause of chronic liver disease. In recent years, an increasing amount of data suggests that MASLD is associated with aging. As the population ages, age-related MASLD will become a major global health problem. Targeting an aging will become a new approach to the treatment of MASLD. This paper reviews the current studies on the role of aging-related factors and therapeutic targets in MASLD, including: Oxidative stress, autophagy, mitochondrial homeostasis, bile acid metabolism homeostasis, and dysbiosis. The aim is to identify effective therapeutic targets for age-related MASLD and its progression.

The Free Triiodothyronine, Gamma-Glutamyl Transpeptidase and Spontaneous Bacterial Peritonitis Index: A Novel Model for Predicting 1-Year Mortality in Patients with HBV-Related Hepatic Encephalopathy

Background and Aims

Hepatic encephalopathy (HE) is characterized by neuropsychiatric manifestations in patients with decompensated cirrhosis (DC) and/or liver failure. This study aimed to investigate the predictive value of thyroid hormone in patients with HE.

Methods

Patients with DC and HE were enrolled, and multivariate logistic analysis was conducted to analyze the risk factors for 1-year mortality.

Results

Among the 81 patients with HBV-related DC and HE, 9 (11.1%) died within 3 months, and 15 (18.5%) died within the first year. More patients with FT3 < 3.5pmol/L had ascites (33.3% vs 8.9%, P<0.01) and higher model for end-stage liver disease (MELD) (Z=3.669, P<0.01). Additionally, free triiodothyronine (FT3) levels were lower in the non-survivor group (P<0.01). FT3 exhibited a negative correlation with international normalized ratio and MELD (both P<0.05). Multivariate analysis revealed that FT3, gamma-glutamyl transpeptidase (GGT), and spontaneous bacterial peritonitis (SBP) were independent risk factors for 1-year mortality of HE. A new model incorporating FT3, GTT, and SBP demonstrated superiority to MELD based on the AUROC (0.9 and 0.752, P=0.04).

Conclusion

Low FT3, but not thyroid-stimulating hormone and free tetraiodothyronine, was identified as an independent risk factor for 1-year mortality in patients with DC and HE. The newly proposed prognostic model, which includes FT3, GTT, and SBP, holds significant predictive value.

Design, synthesis, and biological evaluation of deuterated indolepropionic acid derivatives as novel long-acting pan PPARα/γ/δ agonists

Metabolic syndrome is a complex disease with diverse symptoms, but current pharmacological interventions have limited efficacy. Indeglitazar, a pan-agonist targeting the three-peroxisome proliferator activated receptors (PPAR), exhibits significant therapeutic effects on both diabetic and fatty liver animal models. However, its short half-life limits the in vivo efficacy, which might be attributed to the β-oxidation of indolepropionic acid at Indeglitazar. To overcome this metabolic instability, two deuterium atoms were introduced to the α-position of indolepropionic acid to block the β-oxidation. In this study, several deuterated derivatives were found to sustain PPARs activity and extend the half-life of liver microsomes. In oral glucose tolerance tests, I-1 exhibited the strongest glucose-lowering effect on ob/ob mice in this series. In db/db mice, I-1 reduced lipid levels, liver steatosis and promoted UCP1 expression in white adipose tissue. Mechanistic studies further revealed that I-1 exerts stronger effects than Indeglitazar on the regulation of genes related to lipid metabolism, mitochondrial function, and oxidative stress. Furthermore, I-1 significantly reduced liver steatosis, hepatocellular ballooning, inflammation, and fibrosis in NASH model induced by HFD + CCl4, and even exerted better therapeutic effect than that of Indeglitazar. With the above attractive efficacy, deuterated derivative I-1 is considered as a promising treatment for metabolic syndrome.

MASLD treatment-a shift in the paradigm is imminent

MASLD prevalence is growing towards the leading cause of end-stage liver disease. Up to today, the most effective treatment is weight loss. Weight loss interventions are moving from lifestyle changes to bariatric surgery or endoscopy, and, more recently, to a new wave of anti-obesity drugs that can compete with bariatric surgery. Liver-targeted therapy is a necessity for those patients who already present liver fibrosis. The field is moving fast, and in the near future, we will testify to a disruptive change in MASLD treatment, similar to the paradigm-shift that occurred for hepatitis C almost one decade ago with direct antiviral agents.

Thyroid Hormone and Mitochondrial Dysfunction: Therapeutic Implications for Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD)

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly termed nonalcoholic fatty liver disease (NAFLD), is a widespread global health concern that affects around 25% of the global population. Its influence is expanding, and it is anticipated to overtake alcohol as the leading cause of liver failure and liver-related death worldwide. Unfortunately, there are no approved therapies for MASLD; as such, national and international regulatory health agencies undertook strategies and action plans designed to expedite the development of drugs for treatment of MASLD. A sedentary lifestyle and an unhealthy diet intake are important risk factors. Western countries have a greater estimated prevalence of MASLD partly due to lifestyle habits. Mitochondrial dysfunction is strongly linked to the development of MASLD. Further, it has been speculated that mitophagy, a type of mitochondrial quality control, may be impaired in MASLD. Thyroid hormone (TH) coordinates signals from the nuclear and mitochondrial genomes to control mitochondrial biogenesis and function in hepatocytes. Mitochondria are known TH targets, and preclinical and clinical studies suggest that TH, thyroid receptor β (TR-β) analogs, and synthetic analogs specific to the liver could be of therapeutic benefit in treating MASLD. In this review, we highlight how mitochondrial dysfunction contributes to development of MASLD, and how understanding the role of TH in improving mitochondrial function paved the way for innovative drug development programs of TH-based therapies targeting MASLD.

Current Therapeutical Approaches Targeting Lipid Metabolism in NAFLD

Nonalcoholic fatty liver disease (NAFLD, including nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH)) is a high-prevalence disorder, affecting about 1 billion people, which can evolve to more severe conditions like cirrhosis or hepatocellular carcinoma. NAFLD is often concomitant with conditions of the metabolic syndrome, such as central obesity and insulin-resistance, but a specific drug able to revert NAFL and prevent its evolution towards NASH is still lacking. With the liver being a key organ in metabolic processes, the potential therapeutic strategies are many, and range from directly targeting the lipid metabolism to the prevention of tissue inflammation. However, side effects have been reported for the drugs tested up to now. In this review, different approaches to the treatment of NAFLD are presented, including newer therapies and ongoing clinical trials. Particular focus is placed on the reverse cholesterol transport system and on the agonists for nuclear factors like PPAR and FXR, but also drugs initially developed for other conditions such as incretins and thyromimetics along with validated natural compounds that have anti-inflammatory potential. This work provides an overview of the different therapeutic strategies currently being tested for NAFLD, other than, or along with, the recommendation of weight loss.

Solubility determination, dissolution properties and solid transformation of resmetirom (form A) in heptane and seven alcohols

In this work, the solubility of resmetirom (form A) was initially measured in heptane and seven alcohol solvents by gravimetric methods. Then, the transformation temperature between form A and ethanol solvate was determined at 333.76 K. Subsequently, some commonly used models were applied to fit the solubility data, and it was found that the modified Apelblat equation and the Jouyban-Acree-van't Hoff (J-A-V) model achieved the highest correlation accuracy for those in mono-solvents and heptane + propanol, respectively. And the average relative deviation (ARD) values of models were less than 0.5%, indicating a good agreement with the experimental results. Additionally, through density functional theory calculation and the analysis of solvent parameters, it was observed that hydrogen-bonding played primary roles in the dissolution process of resmetirom. The multiple factors such as the polarity of solvent, active site interaction, the molecular size and free volume all affect the solubility of resmetirom. Furthermore, by comparing the experimental and simulated infrared spectra of form A and two alcohol solvates, five characteristic bands were selected for quantification. Partial least squares regression (PLSR), a multivariate statistical analysis method, was used to extract quantitative information. The quantitative analysis model was established based on specific wavelength intervals, which were associated with inter-molecular interactions. Combined with PLSR, a new high-precision quantitative method was established to study the solid transformation process between form A and solvates. From 303.15 to 323.15 K, the rate of transformation from form A to methanol solvate or ethanol solvate was decreased with increasing temperature, revealing that the transformation process was driven by the solubility difference between form A and solvates under the studied conditions. This research will definitely afford necessary solubility data and solvent selection for the design of the crystallization process of resmetirom (form A) in industry, and provide basic data for the production of resmetirom (form A) in the pharmaceutical industry.

Obesity, non-alcoholic fatty liver disease and hepatocellular carcinoma: current status and therapeutic targets

Obesity is a global epidemic and overwhelming evidence indicates that it is a risk factor for numerous cancers, including hepatocellular carcinoma (HCC), the third leading cause of cancer-related deaths worldwide. Obesity-associated hepatic tumorigenesis develops from nonalcoholic fatty liver disease (NAFLD), progressing to nonalcoholic steatohepatitis (NASH), cirrhosis and ultimately to HCC. The rising incidence of obesity is resulting in an increased prevalence of NAFLD and NASH, and subsequently HCC. Obesity represents an increasingly important underlying etiology of HCC, in particular as the other leading causes of HCC such as hepatitis infection, are declining due to effective treatments and vaccines. In this review, we provide a comprehensive overview of the molecular mechanisms and cellular signaling pathways involved in the pathogenesis of obesity-associated HCC. We summarize the preclinical experimental animal models available to study the features of NAFLD/NASH/HCC, and the non-invasive methods to diagnose NAFLD, NASH and early-stage HCC. Finally, since HCC is an aggressive tumor with a 5-year survival of less than 20%, we will also discuss novel therapeutic targets for obesity-associated HCC and ongoing clinical trials.

A new NASH model in aged mice with rapid progression of steatohepatitis and fibrosis

Non-alcoholic fatty liver disease (NAFLD) has a high prevalence worldwide, with a significant proportion of patients progressing into non-alcoholic steatohepatitis (NASH) and further into cirrhosis and hepatocellular carcinoma (HCC). Most of the current animal models of NASH have limitations, such as incompatibility with human pathogenesis characteristics or long induction periods, which severely limit the development of new drugs and preclinical studies for NASH. We investigated the progression of NASH and fibrosis, as well as metabolic indicators, at different time points in aged mice induced by the Gubra Amylin NASH (GAN) diet, a high-fat, high-sugar, high-cholesterol diet, and attempted to establish a rapid and useful mouse model of NASH. Young and aged C57BL/6 mice were induced on a normal chow or GAN diet for 12 and 21 weeks, respectively. After 12 weeks of induction, aged mice developed NASH, including hepatic steatosis, lobular inflammation and hepatic ballooning, and the phenotype was more severe compared with young mice. After 21 weeks of induction, aged mice developed hepatic fibrosis, which greatly shortened the induction time compared with young mice. Furthermore, analysis of immune cell infiltration in the liver by flow cytometry elucidated the changes of multiple immune cells during the pathogenesis of NASH. These findings suggest that aged mice may develop NASH and fibrosis more rapidly under GAN diet induction, which may significantly shorten the period for preclinical studies of NASH.

Discovery of a natural small-molecule AMP-activated kinase activator that alleviates nonalcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is a primary cause of cirrhosis and hepatocellular carcinoma. Unfortunately, there is no approved drug treatment for NASH. AMP-activated kinase (AMPK) is an important metabolic sensor and whole-body regulator. It has been proposed that AMPK activators could be used for treating metabolic diseases such as obesity, type 2 diabetes and NASH. In this study, we screened a marine natural compound library by monitoring AMPK activity and found a potent AMPK activator, candidusin A (CHNQD-0803). Further studies showed that CHNQD-0803 directly binds recombinant AMPK with a KD value of 4.728 × 10-8 M and activates AMPK at both molecular and intracellular levels. We then investigated the roles and mechanisms of CHNQD-0803 in PA-induced fat deposition, LPS-stimulated inflammation, TGF-β-induced fibrosis cell models and the MCD-induced mouse model of NASH. The results showed that CHNQD-0803 inhibited the expression of adipogenesis genes and reduced fat deposition, negatively regulated the NF-κB-TNFα inflammatory axis to suppress inflammation, and ameliorated liver injury and fibrosis. These data indicate that CHNQD-0803 as an AMPK activator is a novel potential therapeutic candidate for NASH treatment.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-023-00168-z.

FXR and NASH: an avenue for tissue-specific regulation

NASH is within the spectrum of NAFLD, a liver condition encompassing liver steatosis, inflammation, hepatocyte injury, and fibrosis. The prevalence of NASH-induced cirrhosis is rapidly rising and has become the leading indicator for liver transplantation in the US. There is no Food and Drug Administration (FDA)-approved pharmacological intervention for NASH. The farnesoid X receptor (FXR) is essential in regulating bile acid homeostasis, and dysregulation of bile acids has been implicated in the pathogenesis of NASH. As a result, modulators of FXR that show desirable effects in mitigating key characteristics of NASH have been developed as promising therapeutic approaches. However, global FXR activation causes adverse effects such as cholesterol homeostasis imbalance and pruritus. The development of targeted FXR modulation is necessary for ideal NASH therapeutics, but information regarding tissue-specific and cell-specific FXR functionality is limited. In this review, we highlight FXR activation in the regulation of bile acid homeostasis and NASH development, examine the current literature on tissue-specific regulation of nuclear receptors, and speculate on how FXR regulation will be beneficial in the treatment of NASH.

Current, emerging, and potential therapies for non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) has been identified as the most common chronic liver disease worldwide, with a growing incidence. NAFLD is considered the hepatic manifestation of a metabolic syndrome that emerges from multiple factors (e.g., oxidative stress, metabolic disorders, endoplasmic reticulum stress, cell death, and inflammation). Non-alcoholic steatohepatitis (NASH), an advanced form of NAFLD, has been reported to be a leading cause of cirrhosis and hepatic carcinoma, and it is progressing rapidly. Since there is no approved pharmacotherapy for NASH, a considerable number of therapeutic targets have emerged with the deepening of the research on NASH pathogenesis. In this study, the therapeutic potential and properties of regulating metabolism, the gut microbiome, antioxidant, microRNA, inhibiting apoptosis, targeting ferroptosis, and stem cell-based therapy in NASH are reviewed and evaluated. Since the single-drug treatment of NASH is affected by individual heterogeneous responses and side effects, it is imperative to precisely carry out targeted therapy with low toxicity. Lastly, targeted therapeutic agent delivery based on exosomes is proposed in this study, such that drugs with different mechanisms can be incorporated to generate high-efficiency and low-toxicity individualized medicine.

Discovery of Highly Potent and Selective Thyroid Hormone Receptor β Agonists for the Treatment of Nonalcoholic Steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a progressive stage of nonalcoholic fatty liver disease (NAFLD) and is characterized by steatosis, inflammation, hepatocyte ballooning, and fibrosis. While there are currently no approved therapies for NASH, the thyroid hormone receptor β (THR-β), primarily expressed in the liver, is emerging as an effective molecular target for the treatment of NASH. However, the adverse cardiac and bone effects mediated by thyroid hormone receptor α (THR-α) need to be minimized. Herein, we reported the discovery of a series of novel THR-β agonists featuring pyrrolo[3,2-b]pyridin-5-one skeletons based on structure-based drug design. Further optimization led to compound 15, which exhibited higher potency and selectivity for THR-β over THR-α compared to clinical drug MGL-3196. More significantly, an excellent liver-to-serum ratio of 93:1 was observed for compound 15. We believe that the high hepatic concentration of compound 15 may result in no cardiotoxicity.

Immunometabolic factors contributing to obesity-linked hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a major public health concern that is promoted by obesity and associated liver complications. Onset and progression of HCC in obesity is a multifactorial process involving complex interactions between the metabolic and immune system, in which chronic liver damage resulting from metabolic and inflammatory insults trigger carcinogenesis-promoting gene mutations and tumor metabolism. Moreover, cell growth and proliferation of the cancerous cell, after initiation, requires interactions between various immunological and metabolic pathways that provide stress defense of the cancer cell as well as strategic cell death escape mechanisms. The heterogenic nature of HCC in addition to the various metabolic risk factors underlying HCC development have led researchers to focus on examining metabolic pathways that may contribute to HCC development. In obesity-linked HCC, oncogene-induced modifications and metabolic pathways have been identified to support anabolic demands of the growing HCC cells and combat the concomitant cell stress, coinciding with altered utilization of signaling pathways and metabolic fuels involved in glucose metabolism, macromolecule synthesis, stress defense, and redox homeostasis. In this review, we discuss metabolic insults that can underlie the transition from steatosis to steatohepatitis and from steatohepatitis to HCC as well as aberrantly regulated immunometabolic pathways that enable cancer cells to survive and proliferate in the tumor microenvironment. We also discuss therapeutic modalities targeted at HCC prevention and regression. A full understanding of HCC-associated immunometabolic changes in obesity may contribute to clinical treatments that effectively target cancer metabolism.

Potential use of TG68 - A novel thyromimetic - for the treatment of non-alcoholic fatty liver (NAFLD)-associated hepatocarcinogenesis

Introduction

Several lines of evidence suggest that the thyroid hormone signaling pathway is altered in patients with NAFLD and that pharmacological strategies to target the thyroid hormone/thyroid hormone nuclear receptor axis (TH/THR) in the liver may exert beneficial effects. In this study, we investigated the effect of TG68, a novel THRβ agonist, on rat hepatic fat accumulation and NAFLD-associated hepatocarcinogenesis.

Methods

Male rats given a single dose of diethylnitrosamine (DEN) and fed a high fat diet (HFD) were co-treated with different doses of TG68. Systemic and hepatic metabolic parameters, immunohistochemistry and hepatic gene expression were determined to assess the effect of TG68 on THRβ activation.

Results

Irrespectively of the dose, treatment with TG68 led to a significant reduction in liver weight, hepatic steatosis, circulating triglycerides, cholesterol and blood glucose. Importantly, a short exposure to TG68 caused regression of DEN-induced preneoplastic lesions associated with a differentiation program, as evidenced by a loss of neoplastic markers and reacquisition of markers of differentiated hepatocytes. Finally, while an equimolar dose of the THRβ agonist Resmetirom reduced hepatic fat accumulation, it did not exert any antitumorigenic effect.

Discussion

The use of this novel thyromimetic represents a promising therapeutic strategy for the treatment of NAFLD-associated hepatocarcinogenesis.

CS27109, A Selective Thyroid Hormone Receptor-β Agonist Alleviates Metabolic-Associated Fatty Liver Disease in Murine Models

BACKGROUND/AIM

Thyroid hormone receptor-β (THR-β) agonists play crucial roles in dyslipidemia and metabolic associated fatty liver disease (MAFLD). We developed a novel oral and liver-targeted THR-β agonist, CS27109, and evaluated its efficacy in the treatment of metabolic disorders.

MATERIALS AND METHODS

We evaluated in vitro and in vivo efficacy and/or safety of CS27109 along with MGL3196 (a phase III THR-β agonist).

RESULTS

CS27109 showed pronounced activity and selectivity to THR-β and favorable PK properties, which was equivalent to MGL3196. In the hamster model, animals treated with a high dose of CS27109 showed equivalent reductions in serum TC and LDL-c with groups treated with MGL3196. In the rat model, CS27109 and MGL3196 reduced serum ALT, TC, TG, LDL-c, liver weight ratio, and liver steatosis. CS27109 simultaneously decreased liver TG and TC, and MGL3196 additionally reduced AST. In the mouse model, CS27109 dose-dependently reduced serum AST, ALT, liver inflammation, and NAS score, and also downregulated TC, LDL-c, liver steatosis, and fibrosis, but not in a dose-dependent manner. MGL3196 revealed an equivalent effect with CS27109 in that model. CS27109 also exhibited tolerable toxicity to the heart.

CONCLUSIONS

CS27109 shows comparative in vitro and in vivo efficacy with MGL3196, suggesting its potential therapeutic application in the treatment of MAFLD such as dyslipidemia and steatohepatitis.

Discovery of a novel, liver-targeted thyroid hormone receptor-β agonist, CS271011, in the treatment of lipid metabolism disorders

INTRODUCTION

Thyroid hormone receptor β (THR-β) plays a critical role in metabolism regulation and has become an attractive target for treating lipid metabolism disorders in recent years. Thus, in this study, we discovered CS271011, a novel THR-β agonist, and assessed the safety and efficiency of CS271011 compared to MGL-3196 in vitro and in vivo.

METHODS

We conducted luciferase reporter gene assays to assess the activation of THR-β and α in vitro. C57BL/6J mice were fed a high-fat diet for 12 weeks, CS271011 was administered by gavage at the dose of 1 mg/kg and 3 mg/kg, and MGL-3196 was administered at the dose of 3 mg/kg for 10 weeks. Body weight, food intake, serum and hepatic parameters, histological analysis, pharmacokinetic studies, RNA sequencing of the liver and heart, and expression of hepatic lipid-metabolic genes were determined to evaluate the safety and efficiency of CS271011.

RESULTS

Compared with MGL-3196, CS271011 showed higher THR-β activation in vitro. In the diet-induced obesity mice model, CS271011 demonstrated favourable pharmacokinetic properties in mice and was enriched in the liver. Finally, CS271011 improved dyslipidaemia and reduced liver steatosis in the diet-induced obesity murine model. Mechanistically, CS271011 and MGL-3196 showed potent regulation of lipid metabolism-related genes.

CONCLUSIONS

CS271011 is a potent and liver-targeted THR-β agonist for treating lipid metabolism disorders.

The correlation between triiodothyronine and the severity of liver fibrosis

BACKGROUND

The severity of liver fibrosis is an important predictor of death in patients with non-alcoholic fatty liver disease (NAFLD) and type 2 diabetes mellitus (T2DM). However, there is still no definite conclusion on the relationship between triiodothyronine (T3) and the severity of liver fibrosis. Thus, the aim of this study was to analyze the correlation between T3 level and the severity of liver fibrosis.

METHODS

We performed a cross-sectional study of 2072 T2DM patients with normal thyroid function from January 2017 to January 2020. NAFLD fibrosis score (NFS), Fibrosis index based on the 4 factors (FIB-4) and BARD score (BARD) were used to assess the severity of fibrosis in T2DM patients, and linear regression analyses were used to determine the factors independently associated with liver fibrosis. Further experiments were performed to assess the impact of low T3 on fibrosis progression in mice model and explore possible mechanisms.

RESULTS

Free triiodothyronine (fT3) levels had significantly inverse correlations with NFS and FIB-4, and BARD in T2DM patients (P < 0.05). In multiple linear regression analyses, decreased fT3 level was an independent risk factor for the severity of liver fibrosis of T2DM patients (P < 0.01). Findings from in-vivo experiment using mice model proved that hypothyroidism mice had more severe of liver fibrosis than those mice with normal thyroid function. We also found that T3 could inhibit the profibrotic TREM2⁺CD9⁺ macrophage, which had been identified an important player in the progression of liver fibrosis.

CONCLUSION

The findings from this study proved an inverse correlation between T3 level and the severity of liver fibrosis, and lower fT3 level within the normal range was an independent risk factor for severe liver fibrosis.

Shedding light on non-alcoholic fatty liver disease: Pathogenesis, molecular mechanisms, models, and emerging therapeutics

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disorder globally impacting an estimated 25% of the population associated with severe consequences such as cirrhosis, hepatocellular carcinoma (HCC), and overall mortality. Fatty liver disease is triggered through multiple pathways, but the most prominent cause is either diabetes or obesity, or a combination of both. Therefore, hepatic glucose, insulin and fatty acid signaling becomes a dire need to understand which is well elaborated in this review. This review summarizes the popular two-hit pathogenesis of NAFLD, the molecular mechanisms underlying hepatic insulin resistance. As fatty liver disease gets advanced, it requires in-vitro as well as in-vivo models closer to disease progression in humans for better understanding the pathological state and identifying a novel therapeutic target. This review summarizes in-vitro (2D cell-culture/co-culture, 3D spheroid/organoid/liver-on-a-chip) models as well as in-vivo (genetically/dietary/chemically induced fatty liver disease) research models. Fatty liver disease research has gathered lots of attention recently since there is no FDA approved therapy available so far. However, there have been numerous promising targets to treat fatty liver disease including potential therapeutic targets under clinical trials are listed in this review.

NAFLD and thyroid function: pathophysiological and therapeutic considerations

Nonalcoholic fatty liver disease (NAFLD) is a worldwide rising challenge because of hepatic, but also extrahepatic, complications. Thyroid hormones are master regulators of energy and lipid homeostasis, and the presence of abnormal thyroid function in NAFLD suggests pathogenic relationships. Specifically, persons with hypothyroidism feature dyslipidemia and lower hepatic β-oxidation, which favors accumulation of triglycerides and lipotoxins, insulin resistance, and subsequently de novo lipogenesis. Recent studies indicate that liver-specific thyroid hormone receptor β agonists are effective for the treatment of NAFLD, likely due to improved lipid homeostasis and mitochondrial respiration, which, in turn, may contribute to a reduced risk of NAFLD progression. Taken together, the possible coexistence of thyroid disease and NAFLD calls for increased awareness and optimized strategies for mutual screening and management.

TSH-SPP1/TRβ-TSH positive feedback loop mediates fat deposition of hepatocyte: Crosstalk between thyroid and liver

Aims

We conducted this study with two aims: (1) whether TRβ could be damaged by NAFLD, thereby represent thyroid hormone resistance-like manifestation and (2) to analyze the potential role of SPP1 in TH signaling pathway on the process of NAFLD. This study is expected to provide a new perspective on the therapeutic mechanism in the pathological course of NAFLD.

Methods

A total of 166 patients diagnosed with type 2 diabetes mellitus (T2DM) were enrolled in this study. All patients had a BMI above 24 kg/m2 and were stratified into two groups: NAFLD and Non-NAFLD groups. Ages, gender, BMI, duration of diabetes and biochemical markers were obtained from participants' records. We downloaded the dataset GSE48452 from GEO. The Pathview library was used to make the thyroid hormone signaling pathway visualization. The CIBERSORT algorithm was applied to calculate the infiltrated immune cells in obese NAFLD patients. C57BL/6 mice were randomly selected to constitute the normal control (NC) group and were fed a normal chow diet; the rest of the mice were fed a high-fat diet (HFD). After 12 weeks HFD feeding, the mice were sacrificed by cervical dislocation, and blood samples were collected. Mouse livers were also collected; one part of each liver was fixed in 10% formalin for histological analysis, and the other part was snap-frozen for subsequent molecular analyses. To explore the relationship between SPP1, TRβ and lipid deposition in hepatocytes, HepG2 cells were treated with 50 μ M concentration of PA and/or 20 ng/ml concentration of rh-SPP1 for 48h. In addition, the PC3.1-TRβ plasmid was constructed for further validation in HepG2 cells. We used THP-1 cells to construct an M1 macrophage model in vitro. We then analyzed THP-1 cells treated with various concentrations of PA or TSH.

Results

(1) After adjusting for all factors that appeared P value less than 0.1 in the univariate analysis, BMI, TSH, and FT3 were significant independent risk factors of NAFLD (ORs were 1.218, 1.694, and 2.259, respectively); (2) A further analysis with BMI stratification indiacted that both FT3 and TSH had a significant change between individuals with NAFLD and Non-NAFLD in obesity subgroup; however, there was no statistic difference in over-weight group; (3) Bioinformatics analysis of GSE48452 had shown that several key molecular (including TRβ) of thyroid hormone pathway affected by NAFLD induced transcriptomic changes and the expression levels of SPP1, FABP4 and RPS4Y1 were significantly higher, while the expression levels of PZP and VIL1 were significantly decreased in NAFLD patients(adjusted p < 0.05, |logFC| > 1.0). The CIBERSORT algorithm showed increased M0 and M1, decreased M2 macrophage infiltration in NAFLD with comparison to healthy obese group; (4) After 12 weeks of HFD-feeding, the obesity mice had significantly higher serum TSH and In IHC-stained liver sections of obesity group, the intensity of SPP1 had a significantly increased, while TRβ reduced; (5) In vitro studies have shown SPP1 aggravated lipid deposition in hepatic cells dependent on down-regulating the expression of TRβ and TSH acts to promote secretion of SPP1 in M1 macrophage cells.

Conclusions

SPP1 secretion induced by M1 macrophage polarization, which may down-regulates TRβ in hepatocytes via paracrine manner, on the one hand, the lipid deposition aggravating in liver, on the other hand, a compensatory increase of TSH in serum. The increased TSH can further lead to the following SPP1 secretion of M1 macrophage. The positive feedback crosstalk between thyroid and liver, may be plays an important role in maintaining and amplifying pathological process of NAFLD.

Molecular mechanisms of metabolic associated fatty liver disease (MAFLD): functional analysis of lipid metabolism pathways

The metabolic-associated fatty liver disease (MAFLD) is a condition of fat accumulation in the liver in combination with metabolic dysfunction in the form of overweight or obesity and insulin resistance. It is also associated with an increased cardiovascular disease risk, including hypertension and atherosclerosis. Hepatic lipid metabolism is regulated by a combination of the uptake and export of fatty acids, de novo lipogenesis, and fat utilization by β-oxidation. When the balance between these pathways is altered, hepatic lipid accumulation commences, and long-term activation of inflammatory and fibrotic pathways can progress to worsen the liver disease. This review discusses the details of the molecular mechanisms regulating hepatic lipids and the emerging therapies targeting these pathways as potential future treatments for MAFLD.

Thyroid hormones as a disease modifier and therapeutic target in nonalcoholic steatohepatitis

INTRODUCTION

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease worldwide and closely interconnected to the metabolic syndrome. Liver-specific and systemic signaling pathways orchestrating glucose and fatty acid metabolism contribute to intrahepatic accumulation of lipids and inflammatory processes eventually causing disease progression to nonalcoholic steatohepatitis (NASH), liver fibrosis, and cirrhosis. Since a high number of key regulatory genes regarding liver homeostasis are directly mediated via thyroid hormone (TH) signaling, targeting TH receptors (TRs) represent a promising therapeutic potential for the treatment of NAFLD.

AREAS COVERED

In this review, we elucidate the effects of TH on metabolic regulations in the liver via local availability and actions. We discuss recent advances and the potential impact of thyromimetics in basic research and clinical trials including liver-targeted and TRβ-specific agents for the treatment of NAFLD.

EXPERT OPINION

Unselective TR targeting can be accompanied by negative side effects due to high TRβ expression in other organs and TRα-mediated effects. Recent advances in drug development and the introduction of liver-targeted thyromimetics selectively activating TRβ such as Resmetirom (MGL-3196) and VK2809 bring new hope of translating the knowledge on local TH effects into effective hepatic lipid-clearing therapies against NASH.

Targeted therapeutics and novel signaling pathways in non-alcohol-associated fatty liver/steatohepatitis (NAFL/NASH)

Non-alcohol-associated fatty liver/steatohepatitis (NAFL/NASH) has become the leading cause of liver disease worldwide. NASH, an advanced form of NAFL, can be progressive and more susceptible to developing cirrhosis and hepatocellular carcinoma. Currently, lifestyle interventions are the most essential and effective strategies for preventing and controlling NAFL without the development of fibrosis. While there are still limited appropriate drugs specifically to treat NAFL/NASH, growing progress is being seen in elucidating the pathogenesis and identifying therapeutic targets. In this review, we discussed recent developments in etiology and prospective therapeutic targets, as well as pharmacological candidates in pre/clinical trials and patents, with a focus on diabetes, hepatic lipid metabolism, inflammation, and fibrosis. Importantly, growing evidence elucidates that the disruption of the gut-liver axis and microbe-derived metabolites drive the pathogenesis of NAFL/NASH. Extracellular vesicles (EVs) act as a signaling mediator, resulting in lipid accumulation, macrophage and hepatic stellate cell activation, further promoting inflammation and liver fibrosis progression during the development of NAFL/NASH. Targeting gut microbiota or EVs may serve as new strategies for the treatment of NAFL/NASH. Finally, other mechanisms, such as cell therapy and genetic approaches, also have enormous therapeutic potential. Incorporating drugs with different mechanisms and personalized medicine may improve the efficacy to better benefit patients with NAFL/NASH.

Influence of Altered Thyroid Hormone Mechanisms in the Progression of Metabolic Dysfunction Associated with Fatty Liver Disease (MAFLD): A Systematic Review

We performed a systematic review of the mechanisms of thyroid hormones (THs) associated with metabolic dysfunction associated with fatty liver disease (MAFLD). This systematic review was registered under PROSPERO (CRD42022323766). We searched the MEDLINE (via PubMed) and Embase databases from their inception to March 2022. We included studies that assessed thyroid function by measuring the serum level of THs and those involved in MAFLD. We excluded reviews, case reports, editorials, letters, duplicate studies and designed controls. Forty-three studies included MAFLD, eleven analyzed THs, and thirty-two evaluated the mechanisms of THs in MAFLD. Thyroid hormones are essential for healthy growth, development and tissue maintenance. In the liver, THs directly influence the regulation of lipid and carbohydrate metabolism, restoring the homeostatic state of the body. The selected studies showed an association of reduced levels of THs with the development and progression of MAFLD. In parallel, reduced levels of T3 have a negative impact on the activation of co-regulators in the liver, reducing the transcription of genes important in hepatic metabolism. Overall, this is the first review that systematically synthesizes studies focused on the mechanism of THs in the development and progression of MAFLD. The data generated in this systematic review strengthen knowledge of the impact of TH changes on the liver and direct new studies focusing on therapies that use these mechanisms.

Pathogenesis and Therapeutic Strategies Related to Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD), one of the most common types of chronic liver disease, is strongly correlated with obesity, insulin resistance, metabolic syndrome, and genetic components. The pathological progression of NAFLD, consisting of non-alcoholic fatty liver (NAFL), non-alcoholic steatohepatitis (NASH), and liver cirrhosis, is characterized by a broad spectrum of clinical phenotypes. Although patients with mild NAFL are considered to show no obvious clinical symptoms, patients with long-term NAFL may culminate in NASH and further liver fibrosis. Even though various drugs are able to improve NAFLD, there are no FDA-approved medications that directly treat NAFLD. In this paper, the pathogenesis of NAFLD, the potential therapeutic targets, and their underlying mechanisms of action were reviewed.

Combinations of an acetyl CoA carboxylase inhibitor with hepatic lipid modulating agents do not augment antifibrotic efficacy in preclinical models of NASH and fibrosis

Dysregulated hepatocyte lipid metabolism is a hallmark of hepatic lipotoxicity and contributes to the pathogenesis of nonalcoholic steatohepatitis (NASH). Acetyl CoA carboxylase (ACC) inhibitors decrease hepatocyte lipotoxicity by inhibiting de novo lipogenesis and concomitantly increasing fatty acid oxidation (FAO), and firsocostat, a liver‐targeted inhibitor of ACC1/2, is under evaluation clinically in patients with NASH. ACC inhibition is associated with improvements in indices of NASH and reduced liver triglyceride (TG) content, but also increased circulating TG in subjects with NASH and preclinical rodent models. Here we evaluated whether enhancing hepatocyte FAO by combining ACC inhibitors with peroxisomal proliferator‐activated receptor (PPAR) or thyroid hormone receptor beta (THRβ) agonists could drive greater liver TG reduction and NASH/antifibrotic efficacy, while ameliorating ACC inhibitor–induced hypertriglyceridemia. In high‐fat diet–fed dyslipidemic rats, the addition of PPAR agonists fenofibrate (Feno), elafibranor (Ela), lanifibranor (Lani), seladelpar (Sela) or saroglitazar (Saro), or the THRb agonist resmetirom (Res), to an analogue of firsocostat (ACCi) prevented ACCi‐induced hypertriglyceridemia. However, only PPARα agonists (Feno and Ela) and Res provided additional liver TG reduction. In the choline‐deficient high‐fat diet rat model of advanced liver fibrosis, neither PPARα (Feno) nor THRβ (Res) agonism augmented the antifibrotic efficacy of ACCi. Conclusion: These data suggest that combination therapies targeting hepatocyte lipid metabolism may have beneficial effects on liver TG reduction; however, they may not be sufficient to drive fibrosis regression.

Targeting Thyroid Hormone/Thyroid Hormone Receptor Axis: An Attractive Therapy Strategy in Liver Diseases

Thyroid hormone/thyroid hormone receptor (TH/TR) axis is characterized by TH with the assistance of plasma membrane transporters to combine with TR and mediate biological activities. Growing evidence suggests that TH/TR participates in plenty of hepatic metabolism. Thus, this review focuses on the role of the TH/TR axis in the liver diseases. To be specific, the TH/TR axis may improve metabolic-associated fatty liver disease, hepatitis, liver fibrosis, and liver injury while exacerbating the progression of acute liver failure and alcoholic liver disease. Also, the TH/TR axis has paradoxical roles in hepatocellular carcinoma. The TH/TR axis may be a prospecting target to cure hepatic diseases.

Updates on novel pharmacotherapeutics for the treatment of nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a progressive form of nonalcoholic fatty liver disease (NAFLD), characterized with hepatocellular steatosis, ballooning, lobular inflammation, fibrotic progression, and insulin resistance. NASH may progress to cirrhosis and hepatocellular carcinoma (HCC), which are the major indications for liver transplantation and the causes for mortality. Thus far, there are no approved pharmacotherapeutics for the treatment of NASH. Given the complexity of NASH pathogenesis at multifaceted aspects, such as lipotoxicity, inflammation, insulin resistance, mitochondrial dysfunction and fibrotic progression, pharmacotherapeutics under investigation target different key pathogenic pathways to gain either the resolution of steatohepatitis or regression of fibrosis, ideally both. Varieties of pharmacologic candidates have been tested in clinical trials and have generated some positive results. On the other hand, recent failure or termination of a few phase II and III trials is disappointing in this field. In face to growing challenges in pharmaceutical development, this review intends to summarize the latest data of new medications which have completed phase II or III trials, and discuss the rationale and preliminary results of several combinatory options. It is anticipated that with improved understanding of NASH pathogenesis and critical endpoints, efficient pharmacotherapeutics will be available for the treatment of NASH with an acceptable safety profile.

Bile acid and receptors: biology and drug discovery for nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD), a series of liver metabolic disorders manifested by lipid accumulation within hepatocytes, has become the primary cause of chronic liver diseases worldwide. About 20%-30% of NAFLD patients advance to nonalcoholic steatohepatitis (NASH), along with cell death, inflammation response and fibrogenesis. The pathogenesis of NASH is complex and its development is strongly related to multiple metabolic disorders (e.g. obesity, type 2 diabetes and cardiovascular diseases). The clinical outcomes include liver failure and hepatocellular cancer. There is no FDA-approved NASH drug so far, and thus effective therapeutics are urgently needed. Bile acids are synthesized in hepatocytes, transported into the intestine, metabolized by gut bacteria and recirculated back to the liver by the enterohepatic system. They exert pleiotropic roles in the absorption of fats and regulation of metabolism. Studies on the relevance of bile acid disturbance with NASH render it as an etiological factor in NASH pathogenesis. Recent findings on the functional identification of bile acid receptors have led to a further understanding of the pathophysiology of NASH such as metabolic dysregulation and inflammation, and bile acid receptors are recognized as attractive targets for NASH treatment. In this review, we summarize the current knowledge on the role of bile acids and the receptors in the development of NAFLD and NASH, especially the functions of farnesoid X receptor (FXR) in different tissues including liver and intestine. The progress in the development of bile acid and its receptors-based drugs for the treatment of NASH including bile acid analogs and non-bile acid modulators on bile acid metabolism is also discussed.

Cytoskeleton alterations in non-alcoholic fatty liver disease

BACKGROUND

Due to its extremely high prevalence and severity, non-alcoholic fatty liver disease (NALFD) is a serious health and economic concern worldwide. Developing effective methods of diagnosis and therapy demands a deeper understanding of its molecular basis. One of the strategies in such an endeavor is the analysis of alterations in the morphology of liver cells. Such alterations, widely reported in NAFLD patients and disease models, are related to the cytoskeleton. Therefore, the fate of the cytoskeleton components is useful to uncover the molecular basis of NAFLD, to further design innovative approaches for its diagnosis and therapy.

MAIN FINDINGS

Several cytoskeleton proteins are up-regulated in liver cells of NAFLD patients. Under pathological conditions, keratin 18 is released from hepatocytes and its detection in the blood emerges as a non-invasive diagnosis tool. α-Smooth muscle actin is up-regulated in hepatic stellate cells and its down-regulation has been widely tested as a potential NALFD therapeutic approach. Other cytoskeleton proteins, such as vimentin, are also up-regulated.

CONCLUSIONS

NAFLD progression involves alterations in expression levels of proteins that build the liver cytoskeleton or associate with it. These findings provide a timely opportunity of developing novel approaches for NAFLD diagnosis and therapy.

DNA Methylation Patterns According to Fatty Liver Index and Longitudinal Changes from the Korean Genome and Epidemiology Study (KoGES)

The role of differentially methylated regions (DMRs) in nonalcoholic fatty liver disease (NAFLD) is unclear. This study aimed to identify the role of DMR in NAFLD development and progression using the Korean Genome and Epidemiology Study (KoGES) cohort. We used laboratory evaluations and Illumina Methylation 450 k DNA methylation microarray data from KoGES. The correlation between fatty liver index (FLI) and genomic CpG sites was analyzed in 322 subjects. Longitudinal changes over 8 years were confirmed in 33 subjects. To identify CpG sites and genes related to FLI, we obtained enrichment terms for 6765 genes. DMRs were identified for both high (n = 128) and low (n = 194) groups on the basis of FLI 30 in 142 men and 180 women. To confirm longitudinal changes in 33 subjects, the ratio of follow-up and baseline investigation values was obtained. Correlations and group comparisons were performed for the 8 year change values. PITPNM3, RXFP3, and THRB were hypermethylated in the increased FLI groups, whereas SLC9A2 and FOXI3 were hypermethylated in the decreased FLI groups. DMRs describing NAFLD were determined, and functions related to inflammation were identified. Factors related to longitudinal changes are suggested, and blood circulation-related functions appear to be important in the management of NAFLD.

Microsomal triglyceride transfer protein inhibitor lomitapide-induced liver toxicity is ameliorated by Triiodothyronine treatment following improved bile homeostasis and β-oxidation

Dyslipidemia or its severe version like familial hypercholesterolemia causes a high risk for cardiovascular diseases. Lomitapide, a microsomal triglyceride transfer protein inhibitor, is approved to treat familial hypercholesterolemia, associated with liver fat accumulation. In this work, we investigated the effect of the combination of lomitapide and triiodothyronine (T₃) in Zucker fatty rats. Lomitapide (1 mg/kg, PO), or T₃ (13 μg/kg, PO), or their combination, were given to these rats once daily for fourteen days. Body weight and food intake were recorded once daily during the treatment period. Serum and hepatic lipids, glucose tolerance, serum aminotransferases, bile fluids, hepatic gene expression, and liver histology were assessed at the end of the treatment. Lomitapide treatment reduced body weight, food intake, glucose intolerance, and serum lipids, and elevated serum aminotransferases and liver lipids. When combined with T₃, lomitapide showed an enhanced reduction in body weight, food intake, serum cholesterol, serum LDL, and glucose intolerance. The combination treatment increased bile flow rate and biliary cholesterol excretion rate. Combining T₃ with lomitapide attenuated the elevation of serum aminotransferases and liver lipids. Hepatic ABCB11, ABCG5, ABCG8, CYP7A1, CPT1, and ACOX1 expressions were increased with combination treatment. Histological analysis indicated that T₃ attenuated hepatic fat accumulation caused by lomitapide. These data suggests that combining lomitapide with T₃ may reduce lomitapide-induced hepatic toxicity and provide additional benefits in obesity and glucose intolerance.