Therapeutic Opportunities of IL-22 in Non-Alcoholic Fatty Liver Disease: From Molecular Mechanisms to Clinical Applications

Lipid-encapsulated mRNA encoding an extended serum half-life interleukin-22 ameliorates metabolic disease in mice

OBJECTIVE

Interleukin (IL)-22 is a potential therapeutic protein for the treatment of metabolic diseases such as obesity, type 2 diabetes, and metabolic dysfunction-associated steatotic liver disease due to its involvement in multiple cellular pathways and observed hepatoprotective effects. The short serum half-life of IL-22 has previously limited its use in clinical applications; however, the development of mRNA-lipid nanoparticle (LNP) technology offers a novel therapeutic approach that uses a host-generated IL-22 fusion protein. In the present study, the effects of administration of an mRNA-LNP encoding IL-22 on metabolic disease parameters was investigated in various mouse models.

METHODS

C57BL/6NCrl mice were used to confirm mouse serum albumin (MSA)-IL-22 protein expression prior to assessments in C57BL/6NTac and CETP/ApoB transgenic mouse models of metabolic disease. Mice were fed either regular chow or a modified amylin liver nonalcoholic steatohepatitis-inducing diet prior to receiving either LNP-encapsulated MSA-IL-22 or MSA mRNA via intravenous or intramuscular injection. Metabolic markers were monitored for the duration of the experiments, and postmortem histology assessment and analysis of metabolic gene expression pathways were performed.

RESULTS

MSA-IL-22 was detectable for ≥8 days following administration. Improvements in body weight, lipid metabolism, glucose metabolism, and lipogenic and fibrotic marker gene expression in the liver were observed in the MSA-IL-22-treated mice, and these effects were shown to be durable.

CONCLUSIONS

These results support the application of mRNA-encoded IL-22 as a promising treatment strategy for metabolic syndrome and associated comorbidities in human populations.

Novel Insights into Psychosis and Antipsychotic Interventions: From Managing Symptoms to Improving Outcomes

For the past 70 years, the dopamine hypothesis has been the key working model in schizophrenia. This has contributed to the development of numerous inhibitors of dopaminergic signaling and antipsychotic drugs, which led to rapid symptom resolution but only marginal outcome improvement. Over the past decades, there has been limited research on the quantifiable pathological changes in schizophrenia, including premature cellular/neuronal senescence, brain volume loss, the attenuation of gamma oscillations in electroencephalograms, and the oxidation of lipids in the plasma and mitochondrial membranes. We surmise that the aberrant activation of the aryl hydrocarbon receptor by toxins derived from gut microbes or the environment drives premature cellular and neuronal senescence, a hallmark of schizophrenia. Early brain aging promotes secondary changes, including the impairment and loss of mitochondria, gray matter depletion, decreased gamma oscillations, and a compensatory metabolic shift to lactate and lactylation. The aim of this narrative review is twofold: (1) to summarize what is known about premature cellular/neuronal senescence in schizophrenia or schizophrenia-like disorders, and (2) to discuss novel strategies for improving long-term outcomes in severe mental illness with natural senotherapeutics, membrane lipid replacement, mitochondrial transplantation, microbial phenazines, novel antioxidant phenothiazines, inhibitors of glycogen synthase kinase-3 beta, and aryl hydrocarbon receptor antagonists.

Inflammatory liver diseases and susceptibility to sepsis

Patients with inflammatory liver diseases, particularly alcohol-associated liver disease and metabolic dysfunction-associated fatty liver disease (MAFLD), have higher incidence of infections and mortality rate due to sepsis. The current focus in the development of drugs for MAFLD is the resolution of non-alcoholic steatohepatitis and prevention of progression to cirrhosis. In patients with cirrhosis or alcoholic hepatitis, sepsis is a major cause of death. As the metabolic center and a key immune tissue, liver is the guardian, modifier, and target of sepsis. Septic patients with liver dysfunction have the highest mortality rate compared with other organ dysfunctions. In addition to maintaining metabolic homeostasis, the liver produces and secretes hepatokines and acute phase proteins (APPs) essential in tissue protection, immunomodulation, and coagulation. Inflammatory liver diseases cause profound metabolic disorder and impairment of energy metabolism, liver regeneration, and production/secretion of APPs and hepatokines. Herein, the author reviews the roles of (1) disorders in the metabolism of glucose, fatty acids, ketone bodies, and amino acids as well as the clearance of ammonia and lactate in the pathogenesis of inflammatory liver diseases and sepsis; (2) cytokines/chemokines in inflammatory liver diseases and sepsis; (3) APPs and hepatokines in the protection against tissue injury and infections; and (4) major nuclear receptors/signaling pathways underlying the metabolic disorders and tissue injuries as well as the major drug targets for inflammatory liver diseases and sepsis. Approaches that focus on the liver dysfunction and regeneration will not only treat inflammatory liver diseases but also prevent the development of severe infections and sepsis.

Bacteroides and NAFLD: pathophysiology and therapy

Non-alcoholic fatty liver disease (NAFLD) is a prevalent chronic liver condition observed globally, with the potential to progress to non-alcoholic steatohepatitis (NASH), cirrhosis, and even hepatocellular carcinoma. Currently, the US Food and Drug Administration (FDA) has not approved any drugs for the treatment of NAFLD. NAFLD is characterized by histopathological abnormalities in the liver, such as lipid accumulation, steatosis, hepatic balloon degeneration, and inflammation. Dysbiosis of the gut microbiota and its metabolites significantly contribute to the initiation and advancement of NAFLD. Bacteroides, a potential probiotic, has shown strong potential in preventing the onset and progression of NAFLD. However, the precise mechanism by which Bacteroides treats NAFLD remains uncertain. In this review, we explore the current understanding of the role of Bacteroides and its metabolites in the treatment of NAFLD, focusing on their ability to reduce liver inflammation, mitigate hepatic steatosis, and enhance intestinal barrier function. Additionally, we summarize how Bacteroides alleviates pathological changes by restoring the metabolism, improving insulin resistance, regulating cytokines, and promoting tight-junctions. A deeper comprehension of the mechanisms through which Bacteroides is involved in the pathogenesis of NAFLD should aid the development of innovative drugs targeting NAFLD.

What are the common downstream molecular events between alcoholic and nonalcoholic fatty liver?

Liver fat storage, also called hepatic steatosis, is increasingly common and represents a very frequent diagnosis in the medical field. Excess fat is not without consequences. In fact, hepatic steatosis contributes to the progression toward liver fibrosis. There are two main types of fatty liver disease, alcoholic fatty liver disease (AFLD) and nonalcoholic fatty liver disease (NAFLD). Although AFLD and NAFLD are similar in their initial morphological features, both conditions involve the same evolutive forms. Moreover, there are various common mechanisms underlying both diseases, including alcoholic liver disease and NAFLD, which are commonalities. In this Review, the authors explore similar downstream signaling events involved in the onset and progression of the two entities but not completely different entities, predominantly focusing on the gut microbiome. Downstream molecular events, such as the roles of sirtuins, cytokeratins, adipokines and others, should be considered. Finally, to complete the feature, some new tendencies in the therapeutic approach are presented.

B. longum CKD1 enhances the efficacy of anti-diabetic medicines through upregulation of IL- 22 response in type 2 diabetic mice

The gut microbiota plays a pivotal role in metabolic disorders, notably type 2 diabetes mellitus (T2DM). In this study, we investigated the synergistic potential of combining the effects of Bifidobacterium longum NBM7-1 (CKD1) with anti-diabetic medicines, LobeglitazoneⓇ (LO), SitagliptinⓇ (SI), and MetforminⓇ (Met), to alleviate hyperglycemia in a diabetic mouse model. CKD1 effectively mitigated insulin resistance, hepatic steatosis, and enhanced pancreatic β-cell function, as well as fortifying gut-tight junction integrity. In the same way, SI-CKD1 and Met- CKD1 synergistically improved insulin sensitivity and prevented hepatic steatosis, as evidenced by the modulation of key genes associated with insulin signaling, β-oxidation, gluconeogenesis, adipogenesis, and inflammation by qRT-PCR. The comprehensive impact on modulating gut microbiota composition was observed, particularly when combined with MetforminⓇ. This combination induced an increase in the abundance of Rikenellaceae and Alistipes related negatively to the T2DM incidence while reducing the causative species of Cryptosporangium, Staphylococcaceae, and Muribaculaceae. These alterations intervene in gut microbiota metabolites to modulate the level of butyrate, indole-3-acetic acid, propionate, and inflammatory cytokines and to activate the IL-22 pathway. However, it is meaningful that the combination of B. longum NBM7-1(CKD1) reduced the medicines' dose to the level of the maximal inhibitory concentrations (IC50). This study advances our understanding of the intricate relationship between gut microbiota and metabolic disorders. We expect this study to contribute to developing a prospective therapeutic strategy modulating the gut microbiota.

Gut microbiota-mediated IL-22 alleviates metabolic inflammation

Low-grade chronic inflammation, also known as metabolic inflammation, promotes the development of metabolic diseases. Increasing evidence suggests that changes in gut microbes and metabolites disrupt the integrity of the gut barrier and exert significant effects on the metabolism of various tissues, including the liver and adipose tissue, thereby contributing to metabolic inflammation. We observed that IL-22 is a key signaling molecule that serves as a bridge between intestinal microbes and the host, effectively alleviating metabolic inflammation by modulating the host immunomodulatory network. Here, we focused on elucidating the underlying mechanisms by which the gut microbiota and their metabolites reduce inflammation via IL-22, highlighting the favorable impact of IL-22 on metabolic inflammation. Furthermore, we discuss the potential of IL-22 as a therapeutic target for the management of metabolic inflammation and related diseases.

Supplementation with the Probiotic Strains Bifidobacterium longum and Lactiplantibacillus rhamnosus Alleviates Glucose Intolerance by Restoring the IL-22 Response and Pancreatic Beta Cell Dysfunction in Type 2 Diabetic Mice

Type 2 diabetes (T2D) is known as adult-onset diabetes, but recently, T2D has increased in the number of younger people, becoming a major clinical burden in human society. The objective of this study was to determine the effects of Bifidobacterium and Lactiplantibacillus strains derived from the feces of 20 healthy humans on T2D development and to understand the mechanism underlying any positive effects of probiotics. We found that Bifidobacterium longum NBM7-1 (Chong Kun Dang strain 1; CKD1) and Lactiplantibacillus rhamnosus NBM17-4 (Chong Kun Dang strain 2; CKD2) isolated from the feces of healthy Korean adults (n = 20) have anti-diabetic effects based on the insulin sensitivity. During the oral gavage for 8 weeks, T2D mice were supplemented with anti-diabetic drugs (1.0-10 mg/kg body weight) to four positive and negative control groups or four probiotics (200 uL; 1 × 109 CFU/mL) to groups separately or combined to the four treatment groups (n = 6 per group). While acknowledging the relatively small sample size, this study provides valuable insights into the potential benefits of B. longum NBM7-1 and L. rhamnosus NBM17-4 in mitigating T2D development. The animal gene expression was assessed using a qRT-PCR, and metabolic parameters were assessed using an ELISA assay. We demonstrated that B. longum NBM7-1 in the CKD1 group and L. rhamnosus NBM17-4 in the CKD2 group alleviate T2D development through the upregulation of IL-22, which enhances insulin sensitivity and pancreatic functions while reducing liver steatosis. These findings suggest that B. longum NBM7-1 and L. rhamnosus NBM17-4 could be the candidate probiotics for the therapeutic treatments of T2D patients as well as the prevention of type 2 diabetes.

Bacteriophage targeting microbiota alleviates non-alcoholic fatty liver disease induced by high alcohol-producing Klebsiella pneumoniae

Our previous studies have shown that high alcohol-producing Klebsiella pneumoniae (HiAlc Kpn) in the intestinal microbiome could be one of the causes of non-alcoholic fatty liver disease (NAFLD). Considering antimicrobial resistance of K. pneumoniae and dysbacteriosis caused by antibiotics, phage therapy might have potential in treatment of HiAlc Kpn-induced NAFLD, because of the specificity targeting the bacteria. Here, we clarified the effectiveness of phage therapy in male mice with HiAlc Kpn-induced steatohepatitis. Comprehensive investigations including transcriptomes and metabolomes revealed that treatment with HiAlc Kpn-specific phage was able to alleviate steatohepatitis caused by HiAlc Kpn, including hepatic dysfunction and expression of cytokines and lipogenic genes. In contrast, such treatment did not cause significantly pathological changes, either in functions of liver and kidney, or in components of gut microbiota. In addition to reducing alcohol attack, phage therapy also regulated inflammation, and lipid and carbohydrate metabolism. Our data suggest that phage therapy targeting gut microbiota is an alternative to antibiotics, with potential efficacy and safety, at least in HiAlc Kpn-caused NAFLD.

Modulation of Host-Microbe Metabolism by Cholera Toxin

In order for successful fecal-oral transmission, enteric bacterial pathogens have to successfully compete with the intestinal microbiota and reach high concentrations during infection. Vibrio cholerae requires cholera toxin (CT) to cause diarrheal disease, which is thought to promote the fecal-oral transmission of the pathogen. Besides inducing diarrheal disease, the catalytic activity of CT also alters host intestinal metabolism, which promotes the growth of V. cholerae during infection through the acquisition of host-derived nutrients. Furthermore, recent studies have found that CT-induced disease activates a niche-specific suite of V. cholerae genes during infection, some of which may be important for fecal-oral transmission of the pathogen. Our group is currently exploring the concept that CT-induced disease promotes the fecal-oral transmission of V. cholerae by modulating both host and pathogen metabolism. Furthermore, the role of the intestinal microbiota in pathogen growth and transmission during toxin-induced disease merits further investigation. These studies open the door to investigating whether other bacterial toxins also enhance pathogen growth and transmission during infection, which may shed light on the design of novel therapeutics for intervention or prevention of diarrheal diseases.

Troxerutin attenuates insulin resistance via pancreatic IL-22/JAK1/STAT3 signaling activation in dihydrotestosterone-induced polycystic ovary syndrome rats

Polycystic ovary syndrome (PCOS) is an extremely common endocrine-metabolic disorder and the main cause of infertility in premenopausal women, thus targeted treatments are sorely needed. Accumulative evidence showed that exogenous supplementation of IL-22 in PCOS mice may be of significant positive effect on insulin resistance (IR), a root causative factor for this condition, but much remained unknown about its mechanism. According to our previous study, troxerutin, a common anticoagulant and thrombolytic agent in clinic, alleviated various PCOS-like phenotypes in dihydrotestosterone (DHT)-treated rat model with unclear mechanism. Here, glucose tolerance tests (GTTs), insulin tolerance tests (ITTs), and homeostatic model assessment of insulin resistance (HOMA-IR) analyses revealed that troxerutin treatment in DHT-treated rats also significantly improved insulin resistance and enhanced serum IL-22 levels, which thereby activated IL-22R1/Janus kinase 1 (JAK1)/signal transducer and activator of transcription-3 (STAT3) signaling pathway in pancreatic islet. This protective effect of troxerutin on insulin resistance improvement was blocked by an inhibitor of p-STAT3, S3I-201. Troxerutin administration to DHT rats decreased the relative abundance of Bifidobacterium and enhanced secondary bile acid profiles, which were positively correlated with serum IL-22 concentration. Conclusively, the present study reported that troxerutin is an endogenous enhancer of IL-22 and the effect of troxerutin on insulin resistance improvement was via IL-22R1/JAK1/STAT3 signaling activation in a DHT-induced PCOS rat model. These insights may be translated into a primary therapeutic agent for PCOS with insulin resistance and hyperandrogenism.NEW & NOTEWORTHY Troxerutin decreased the relative abundance of Bifidobacterium, along with enhancement of secondary bile acids/IL-22 system, which thereby activated its downstream IL-22R1/JAK1/STAT3 signaling pathway in pancreatic β cells, subsequently attenuated insulin resistance (IR), hyperandrogenism and PCOS-like phenotypes in DHT-induced PCOS rat models. Troxerutin is an endogenous IL-22 enhancer and may be of therapeutic value for PCOS with insulin resistance.

Hepatic macrophage mediated immune response in liver steatosis driven carcinogenesis

Obesity confers an independent risk for carcinogenesis. Classically viewed as a genetic disease, owing to the discovery of tumor suppressors and oncogenes, genetic events alone are not sufficient to explain the progression and development of cancers. Tumor development is often associated with metabolic and immunological changes. In particular, obesity is found to significantly increase the mortality rate of liver cancer. As its role is not defined, a fundamental question is whether and how metabolic changes drive the development of cancer. In this review, we will dissect the current literature demonstrating that liver lipid dysfunction is a critical component driving the progression of cancer. We will discuss the involvement of inflammation in lipid dysfunction driven liver cancer development with a focus on the involvement of liver macrophages. We will first discuss the association of steatosis with liver cancer. This will be followed with a literature summary demonstrating the importance of inflammation and particularly macrophages in the progression of liver steatosis and highlighting the evidence that macrophages and macrophage produced inflammatory mediators are critical for liver cancer development. We will then discuss the specific inflammatory mediators and their roles in steatosis driven liver cancer development. Finally, we will summarize the molecular pattern (PAMP and DAMP) as well as lipid particle signals that are involved in the activation, infiltration and reprogramming of liver macrophages. We will also discuss some of the therapies that may interfere with lipid metabolism and also affect liver cancer development.

Pathogenesis from Inflammation to Cancer in NASH-Derived HCC

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer and one of the deadliest cancers worldwide. As opposed to the majority of patients with HCC, approximately 20–30% of cases of non-alcoholic steatohepatitis (NASH)-derived HCC develop malignant tumours in the absence of liver cirrhosis. NASH is characterized by metabolic dysregulation, chronic inflammation and cell death in the liver, which provide a favorable setting for the transformation of inflammation into cancer. This review aims to describe the pathogenesis and the underlying mechanism of the transition from inflammation to cancer in NASH.

AhR Activation Leads to Attenuation of Murine Autoimmune Hepatitis: Single-Cell RNA-Seq Analysis Reveals Unique Immune Cell Phenotypes and Gene Expression Changes in the Liver

The aryl hydrocarbon receptor (AhR) is a ubiquitously expressed ligand-activated transcription factor. While initially identified as an environmental sensor, this receptor has been shown more recently to regulate a variety of immune functions. AhR ligands vary in structure and source from environmental chemicals such as 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and indoles found in cruciferous vegetables to endogenous ligands derived from tryptophan metabolism. In the current study, we used TCDD, a high affinity AhR ligand to study the impact of AhR activation in the murine model of autoimmune hepatitis (AIH). Primarily, we used single-cell RNA-sequencing (scRNA-seq) technology to study the nature of changes occurring in the immune cells in the liver at the cellular and molecular level. We found that AhR activation attenuated concanavalin A (ConA)-induced AIH by limiting chemotaxis of pro-inflammatory immune cell subsets, promoting anti-inflammatory cytokine production, and suppressing pro-inflammatory cytokine production. scRNA-seq analysis showed some unusual events upon ConA injection such as increased presence of mature B cells, natural killer (NK) T cells, CD4+ or CD8+ T cells, Kupffer cells, memory CD8+ T cells, and activated T cells while TCDD treatment led to the reversal of most of these events. Additionally, the immune cells showed significant alterations in the gene expression profiles. Specifically, we observed downregulation of inflammation-associated genes including Ptma, Hspe1, and CD52 in TCDD-treated AIH mice as well as alterations in the expression of migratory markers such as CXCR2. Together, the current study characterizes the nature of inflammatory changes occurring in the liver during AIH, and sheds light on how AhR activation during AIH attenuates liver inflammation by inducing phenotypic and genotypic changes in immune cells found in the liver.

The Molecular Mechanism of Hepatic Lipid Metabolism Disorder Caused by NaAsO2 through Regulating the ERK/PPAR Signaling Pathway

Chronic arsenic exposure is a risk factor for human fatty liver disease, and the ERK signaling pathway plays an important role in the regulation of liver lipid metabolism. However, whether ERK plays a role in the progression of arsenic-induced liver lipid metabolism disorder and the specific mechanism remain unclear. Here, by constructing a rat model of liver lipid metabolism disorder induced by chronic arsenic exposure, we demonstrated that ERK might regulate arsenic-induced liver lipid metabolism disorders through the PPAR signaling pathway. Arsenic could upregulate the expression of PPARγ and CD36 in the rat liver, decrease the expression of PPARα and CPT-1 in the rat liver, increase the organ coefficient of the rat liver, decrease the content of TG in rat serum, and promote fat deposition in the rat liver. In the arsenic-induced rat model of hepatic lipid metabolism disorder, we found that the expression of p-ERK was increased. In order to further explore whether the ERK signaling pathway was involved in arsenic-induced liver lipid metabolism disorder, we exposed L-02 cells to different arsenic concentrations, and the results showed that arsenic significantly increased the expression of P-ERK in L-02 cells in a dose-dependent manner. We further treated L-02 cells with ERK inhibitors and found that the expression of TG, PPARα, and CPT-1 in L-02 cells increased, while the expression of P-ERK, PPARγ, and CD36 decreased. In conclusion, ERK may be involved in arsenic-induced liver lipid metabolism disorder by regulating the PPAR signaling pathway. These findings are expected to provide a new targeting strategy for arsenic-induced liver lipid metabolism disorder.

Pharmacotherapy for Non-Alcoholic Fatty Liver Disease: Emerging Targets and Drug Candidates

Non-alcoholic fatty liver disease (NAFLD), or metabolic (dysfunction)-associated fatty liver disease (MAFLD), is characterized by high global incidence and prevalence, a tight association with common metabolic comorbidities, and a substantial risk of progression and associated mortality. Despite the increasingly high medical and socioeconomic burden of NAFLD, the lack of approved pharmacotherapy regimens remains an unsolved issue. In this paper, we aimed to provide an update on the rapidly changing therapeutic landscape and highlight the major novel approaches to the treatment of this disease. In addition to describing the biomolecules and pathways identified as upcoming pharmacological targets for NAFLD, we reviewed the current status of drug discovery and development pipeline with a special focus on recent evidence from clinical trials.