Recent advances in understanding/management of non-alcoholic steatohepatitis

Evaluation of Human Hepatocyte Drug Metabolism Carrying High-Risk or Protection-Associated Liver Disease Genetic Variants

Metabolic-dysfunction-associated steatotic liver disease (MASLD), which affects 30 million people in the US and is anticipated to reach over 100 million by 2030, places a significant financial strain on the healthcare system. There is presently no FDA-approved treatment for MASLD despite its public health significance and financial burden. Understanding the connection between point mutations, liver enzymes, and MASLD is important for comprehending drug toxicity in healthy or diseased individuals. Multiple genetic variations have been linked to MASLD susceptibility through genome-wide association studies (GWAS), either increasing MASLD risk or protecting against it, such as PNPLA3 rs738409, MBOAT7 rs641738, GCKR rs780094, HSD17B13 rs72613567, and MTARC1 rs2642438. As the impact of genetic variants on the levels of drug-metabolizing cytochrome P450 (CYP) enzymes in human hepatocytes has not been thoroughly investigated, this study aims to describe the analysis of metabolic functions for selected phase I and phase II liver enzymes in human hepatocytes. For this purpose, fresh isolated primary hepatocytes were obtained from healthy liver donors (n = 126), and liquid chromatography-mass spectrometry (LC-MS) was performed. For the cohorts, participants were classified into minor homozygotes and nonminor homozygotes (major homozygotes + heterozygotes) for five gene polymorphisms. For phase I liver enzymes, we found a significant difference in the activity of CYP1A2 in human hepatocytes carrying MBOAT7 (p = 0.011) and of CYP2C8 in human hepatocytes carrying PNPLA3 (p = 0.004). It was also observed that the activity of CYP2C9 was significantly lower in human hepatocytes carrying HSD17B13 (p = 0.001) minor homozygous compared to nonminor homozygous. No significant difference in activity of CYP2E1, CYP2C8, CYP2D6, CYP2E1, CYP3A4, ECOD, FMO, MAO, AO, and CES2 and in any of the phase II liver enzymes between human hepatocytes carrying genetic variants for PNPLA3 rs738409, MBOAT7 rs641738, GCKR rs780094, HSD17B13 rs72613567, and MTARC1 rs2642438 were observed. These findings offer a preliminary assessment of the influence of genetic variations on drug-metabolizing cytochrome P450 (CYP) enzymes in healthy human hepatocytes, which may be useful for future drug discovery investigations.

Sphingosine-1-Phosphate Metabolism in the Regulation of Obesity/Type 2 Diabetes

Obesity is a pathophysiological condition where excess free fatty acids (FFA) target and promote the dysfunctioning of insulin sensitive tissues and of pancreatic β cells. This leads to the dysregulation of glucose homeostasis, which culminates in the onset of type 2 diabetes (T2D). FFA, which accumulate in these tissues, are metabolized as lipid derivatives such as ceramide, and the ectopic accumulation of the latter has been shown to lead to lipotoxicity. Ceramide is an active lipid that inhibits the insulin signaling pathway as well as inducing pancreatic β cell death. In mammals, ceramide is a key lipid intermediate for sphingolipid metabolism as is sphingosine-1-phosphate (S1P). S1P levels have also been associated with the development of obesity and T2D. In this review, the current knowledge on S1P metabolism in regulating insulin signaling in pancreatic β cell fate and in the regulation of feeding by the hypothalamus in the context of obesity and T2D is summarized. It demonstrates that S1P can display opposite effects on insulin sensitive tissues and pancreatic β cells, which depends on its origin or its degradation pathway.

Harnessing Human Microphysiology Systems as Key Experimental Models for Quantitative Systems Pharmacology

Two technologies that have emerged in the last decade offer a new paradigm for modern pharmacology, as well as drug discovery and development. Quantitative systems pharmacology (QSP) is a complementary approach to traditional, target-centric pharmacology and drug discovery and is based on an iterative application of computational and systems biology methods with multiscale experimental methods, both of which include models of ADME-Tox and disease. QSP has emerged as a new approach due to the low efficiency of success in developing therapeutics based on the existing target-centric paradigm. Likewise, human microphysiology systems (MPS) are experimental models complementary to existing animal models and are based on the use of human primary cells, adult stem cells, and/or induced pluripotent stem cells (iPSCs) to mimic human tissues and organ functions/structures involved in disease and ADME-Tox. Human MPS experimental models have been developed to address the relatively low concordance of human disease and ADME-Tox with engineered, experimental animal models of disease. The integration of the QSP paradigm with the use of human MPS has the potential to enhance the process of drug discovery and development.

The Transcriptomic Signature Of Disease Development And Progression Of Nonalcoholic Fatty Liver Disease

A longitudinal molecular model of the development and progression of nonalcoholic fatty liver disease (NAFLD) over time is lacking. We have recently validated a high fat/sugar water-induced animal (an isogenic strain of C57BL/6 J:129S1/SvImJ mice) model of NAFLD that closely mimics most aspects of human disease. The hepatic transcriptome of such mice with fatty liver (8 weeks), steatohepatitis with early fibrosis (16–24 weeks) and advanced fibrosis (52 weeks) after initiation of the diet was evaluated and compared to mice on chow diet. Fatty liver development was associated with transcriptional activation of lipogenesis, FXR-RXR, PPAR-α mediated lipid oxidation and oxidative stress pathways. With progression to steatohepatitis, metabolic pathway activation persisted with additional activation of IL-1/inhibition of RXR, granulocyte diapedesis/adhesion, Fc macrophage activation, prothrombin activation and hepatic stellate cell activation. Progression to advanced fibrosis was associated with dampening of metabolic, oxidative stress and cell stress related pathway activation but with further Fc macrophage activation, cell death and turnover and activation of cancer-related networks. The molecular progression of NAFLD involves a metabolic perturbation which triggers subsequent cell stress and inflammation driving cell death and turnover. Over time, inflammation and fibrogenic pathways become dominant while in advanced disease an inflammatory-oncogenic profile dominates.

Pre-clinical and clinical investigations of metabolic zonation in liver diseases: The potential of microphysiology systems

The establishment of metabolic zonation within a hepatic lobule ascribes specific functions to hepatocytes based on unique, location-dependent gene expression patterns. Recently, there have been significant developments in the field of metabolic liver zonation. A little over a decade ago, the role of β-catenin signaling was identified as a key regulator of gene expression and function in pericentral hepatocytes. Since then, additional molecules have been identified that regulate the pattern of Wnt/β-catenin signaling within a lobule and determine gene expression and function in other hepatic zones. Currently, the molecular basis of metabolic zonation in the liver appears to be a 'push and pull' between signaling pathways. Such compartmentalization not only provides an efficient assembly line for hepatocyte functions but also can account for restricting the initial hepatic damage and pathology from some hepatotoxic drugs to specific zones, possibly enabling effective regeneration and restitution responses from unaffected cells. Careful analysis and experimentation have also revealed that many pathological conditions in the liver lobule are spatially heterogeneous. We will review current research efforts that have focused on examination of the role and regulation of such mechanisms of hepatocyte adaptation and repair. We will discuss how the pathological organ-specific microenvironment affects cell signaling and metabolic liver zonation, especially in steatosis, viral hepatitis, and hepatocellular carcinoma. We will discuss how the use of new human microphysiological platforms will lead to a better understanding of liver disease progression, diagnosis, and therapies. In conclusion, we aim to provide insights into the role and regulation of metabolic zonation and function using traditional and innovative approaches. Impact statement Liver zonation of oxygen tension along the liver sinusoids has been identified as a critical liver microenvironment that impacts specific liver functions such as intermediary metabolism of amino acids, lipids, and carbohydrates, detoxification of xenobiotics and as sites for initiation of liver diseases. To date, most information on the role of zonation in liver disease including, non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), cirrhosis, and hepatocellular carcinoma (HCC) have been obtained from animal models. It is now possible to complement animal studies with human liver, microphysiology systems (MPS) containing induced pluripotent stem cells engineered to create disease models where it is also possible to control the in vitro liver oxygen microenvironment to define the role of zonation on the mechanism(s) of disease progression. The field now has the tools to investigate human liver disease progression, diagnosis, and therapeutic development.

Review article: novel methods for the treatment of non-alcoholic steatohepatitis - targeting the gut immune system to decrease the systemic inflammatory response without immune suppression

BACKGROUND

The systemic immune system plays a role in inflammation and fibrogenesis associated with non-alcoholic steatohepatitis (NASH) and has become a potential target for drug development. In particular, the gut immune system has been suggested as a means for generating signals that can target the systemic immune system.

AIM

To describe seven novel methods being developed for the treatment of NASH that target the gut immune system for alleviation of the systemic inflammatory response, including oral administration of fatty-liver-derived proteins, anti-CD3 antibodies, tumour necrosis factor fusion protein, anti-lipopolysaccharide antibodies, glucosylceramide, delayed-release mercaptopurine, and soy-derived extracts.

METHODS

A search for these methods for oral immunotherapy for NASH was conducted.

RESULTS

Oral administration of these compounds provides an opportunity for immune modulation without immune suppression, with the advantage of being independent of a single molecular/inflammatory pathway. These modes of oral immune therapy demonstrate superior safety profiles, such that the patient is not exposed to general immune suppression. Moreover, these approaches target the whole spectrum of the disease and may serve as adjuvants to other therapies, such that they provide a platform for treatment of concomitant disorders in patients with NASH, including diabetes and hyperlipidaemia. Most of the compounds reviewed are currently in phase II trials, and it is anticipated that the acquisition of more clinical data in the next few years will enable the use of this new class of drugs for the treatment of NASH.

CONCLUSION

Oral immunotherapy may provide a novel platform for the treatment of NASH.

Nuclear receptor FXR: A potential therapeutic target for non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) has become a very common chronic liver disease all over the world. The high incidence of NAFLD is closely related to obesity, diabetes and metabolic disorders. Insulin resistance and dyslipidemia following the hepatic proinflammatory response and fibrosis are the primary features of NAFLD deterioration. Nuclear receptor farnesoid X receptor (FXR) regulates lipid metabolism and homeostasis. Clarification of FXR function and features can provide a better understanding of the pathophysiological characteristics of non-alcoholic steatohepatitis (NASH) and illuminate the mechanism of NAFLD/NASH potential therapeutic targets. FXR activation can inhibit the de novo hepatic lipogenesis, improve insulin sensitivity and protect against bile acid-induced cytotoxicity. Clinical studies indicated that FXR agonists or modulators are very promising for the clinical treatment of NAFLD and NASH. This review focuses on the important regulatory role of FXR in NASH.

Sparstolonin B attenuates early liver inflammation in experimental NASH by modulating TLR4 trafficking in lipid rafts via NADPH oxidase activation

Although significant research data exist on the pathophysiology of nonalcoholic steatohepatitis (NASH), finding an efficient treatment regimen for it remains elusive. The present study used sparstolonin B (SsnB), a novel TLR4 antagonist derived from the Chinese herb Sparganium stoloniferum, as a possible drug to mitigate early inflammation in NASH. This study used an early steatohepatitic injury model in high-fat-fed mice with CYP2E1-mediated oxidative stress as a second hit. SsnB was administered for 1 wk along with bromodichloromethane (BDCM), an inducer of CYP2E1-mediated oxidative stress. Results showed that SsnB administration attenuated inflammatory morphology and decreased elevation of the liver enzyme alanine aminotransferase (ALT). Mice administered SsnB also showed decreased mRNA expression of proinflammatory cytokines TNF-α, IFN-γ, IL-1β, and IL-23, while protein levels of both TNF-α and IL-1β were significantly decreased. SsnB significantly decreased Kupffer cell activation as evidenced by reduction in CD68 and monocyte chemoattractant protein-1 (MCP1) mRNA and protein levels with concomitant inhibition of macrophage infiltration in the injured liver. Mechanistically, SsnB decreased TLR4 trafficking to the lipid rafts, a phenomenon described by the colocalization of TLR4 and lipid raft marker flotillin in tissues and immortalized Kupffer cells. Since we have shown previously that NADPH oxidase drives TLR4 trafficking in NASH, we studied the role of SsnB in modulating this pathway. SsnB prevented NADPH oxidase activation in vivo and in vitro as indicated by decreased peroxynitrite formation. In summary, the present study reports a novel use of the TLR4 antagonist SsnB in mitigating inflammation in NASH and in parallel shows a unique molecular mechanism of decreasing nitrative stress.

Genistein Attenuates Nonalcoholic Steatohepatitis and Increases Hepatic PPARγ in a Rat Model

Nonalcoholic steatohepatitis (NASH) has become a global chronic liver disease, but no effective medicine has been proven to cure it. This study investigated the protective effects of genistein, a phytoestrogen, on NASH and examined whether it has any effect on hepatic PPARγ. Male Sprague-Dawley rats were divided into four groups: control group fed ad libitum with standard rat diet, NASH group fed ad libitum with high-fat diet to induce NASH and NASH + Gen8 group and NASH + Gen16 group fed with high-fat diet plus intragastric administration of 8 or 16 mg/kg genistein once daily. After 6 weeks, liver samples were collected to determine MDA, TNF-α, PPARγ, and histopathology. The findings were that levels of hepatic MDA and TNF-α increased in NASH group, but 16 mg/kg genistein reduced these levels significantly. Downregulation of hepatic PPARγ was observed in NASH group, but genistein significantly upregulated the expression of PPARγ in both NASH + Gen groups. The histological appearance of liver in NASH group presented pathological features of steatohepatitis which were diminished in both NASH + Gen groups. The results suggest that genistein attenuates the liver histopathology of NASH with upregulation of hepatic PPARγ, reduction of oxidative stress, and inhibition of inflammatory cytokine.