NNMT aggravates hepatic steatosis, but alleviates liver injury in alcoholic liver disease

NNMT/1-MNA protects against hepatic ischemia-reperfusion injury through the AKT/FOXO1/ANGPT2/JNK axis

Hepatic ischemia‒reperfusion injury (HIRI) occurs during liver surgery, contributing to postoperative complications such as liver failure, prolonged hospital stays, and increased morbidity and mortality rates. Yet, the mechanism underlying HIRI remains unclear. Nicotinamide N-methyltransferase (NNMT) facilitates the conversion of nicotinamide into N1-methylnicotinamide (1-MNA) and plays crucial roles in various pathophysiological processes. In this study, we find a decrease in hepatic NNMT expression and serum 1-MNA levels during HIRI. Both NNMT overexpression and exogenous 1-MNA treatment alleviate HIRI in male mice HIRI models and primary hepatocytes H/R models. Mechanistically, NNMT/1-MNA plays key roles in inflammation, apoptosis, and vascular injury during HIRI through the AKT/FOXO1/ANGPT2/JNK axis. Hepatic-specific depletion of NNMT leads to increased ANGPT2 expression and exacerbates HIRI, effects that can be mitigated by ANGPT2 knockdown. Our findings suggest that NNMT/1-MNA/ANGPT2 may regulate HIRI via the JNK signaling pathway. In summary, we present the function of NNMT and its underlying mechanism in liver injury, providing potential new therapeutical strategies for addressing HIRI.

SMPD3 Inhibition Contributes to Nicotinamide-Ameliorated Hepatic Steatosis in Chronic Alcohol-Fed Mice

Alcohol-associated liver disease (ALD) is characterized by the reduction of hepatic nicotinamide adenine dinucleotide (NAD+), which exacerbates hepatic steatosis. The present study was conducted to investigate the protective role of nicotinamide (NAM), a foodborne precursor of NAD+ biosynthesis, in ALD. C57BL/6N mice were employed to establish the ALD model and were administered NAM by gavage. Our results showed that NAM supplementation significantly ameliorated alcohol-induced NAD+ reduction and lipid accumulation in both mice liver and cultured AML-12 hepatocytes and improved lipid metabolism-associated gene disorders. Alcohol-induced liver injury and oxidative stress were also blocked by NAM administration. Further transcriptomics analysis and validation revealed that alcohol-stimulated sphingomyelin phosphodiesterase 3 (SMPD3) was significantly reversed by NAM, along with the reduction of hepatic ceramide levels. Importantly, SMPD3 was upregulated in the livers of ALD patients. Genetically silencing SMPD3 alleviated alcohol-induced lipid accumulation in hepatocytes. ChIP assay identified SMPD3 as a direct downstream target of hypoxia-inducible factor 1 alpha (HIF-1α). Liver-specific Hif1α knockdown reduced the level of hepatic SMPD3 expression in mice. Activation of HIF-1α abolished the prevention of intrahepatic liver lipid deposition by NAM, while SMPD3 knockdown reversed HIF-1α activation-stimulated lipid accumulation, indicating that a HIF-1α-regulated SMPD3 pathway was involved in the beneficial role of NAM. NAM improved liver oxidative stress, while antioxidant MitoQ administration rescued HIF-1α/SMPD3 activation in ALD mice, implying that the antioxidant effect of NAM contributed to its inhibitory role on the HIF-1α/SMPD3 pathway. In conclusion, NAM ameliorates chronic alcohol intake-induced hepatic steatosis by inhibiting SMPD3. This study provides new insights into the mechanistic understanding of ALD and highlights NAM as a therapeutic choice for ALD treatment.

Preliminary investigation of nicotinamide N-methyltransferase as an HBV-specific biomarker for hepatocellular carcinoma diagnosis

BackgroundNicotinamide N-methyltransferase (NNMT), a metabolic enzyme in the liver, has been implicated in various biological processes, and its high expression in hepatocellular carcinoma has been linked to tumor metastasis and poor prognosis. However, its potential as a serum biomarker for hepatocellular carcinoma diagnosis remains unexplored.MethodsA total of 172 subjects were included in this study, consisting of 71 hepatocellular carcinoma patients (64 with hepatitis B virus (HBV)-associated hepatocellular carcinoma and 7 with non-HBV-associated hepatocellular carcinoma), as well as 70 healthy controls and 31 HBV-infected individuals. Serum NNMT levels were measured, and clinical-pathological correlations were analyzed. The diagnostic efficacy of serum NNMT for HBV-related hepatocellular carcinoma was evaluated using receiver operating characteristic (ROC) curve analysis.ResultsSerum NNMT levels were significantly elevated in HBV-infected individuals and correlated with poorer prognosis, including reduced overall survival and shorter disease-free survival. Kaplan-Meier analysis revealed that low NNMT expression was associated with longer overall survival (75 vs. 12 months, P < 0.0001) and disease-free survival (21.5 vs. 5 months, P < 0.01). In HBV-related hepatocellular carcinoma patients, NNMT levels correlated with biochemical markers including alfa-fetoprotein, aspartate transaminase, triglycerides, total cholesterol, low-density lipoprotein, apolipoprotein B, TB, and albumin, with decreased albumin, and high-density lipoprotein levels promoting NNMT expression. ROC analysis showed that NNMT outperformed alfa-fetoprotein (area under the curve (AUC) 0.869 vs. 0.775), with a sensitivity of 95.2%, specificity of 87.9%, and a combined AUC of 0.947, demonstrating its superior diagnostic value for HBV-related hepatocellular carcinoma.ConclusionsSerum NNMT is a promising biomarker for predicting the risk of hepatocellular carcinoma in HBV-infected individuals and may serve as an indicator for the prognosis of hepatocellular carcinoma patients.

Genetic inhibition of nicotinamide N-methyltransferase and prevention of alcohol-associated fatty liver in humans

Recent studies of animal models reported Nicotinamide N-methyltransferase (NNMT) as a potential therapeutic target for preventing alcohol-associated fatty liver (AFL), yet its efficacy and safety in humans remain unknown. We aim to estimate the effectiveness and safety of inhibiting NNMT in humans. We leveraged Electronic Medical Records (EMRs) data coupled with genetic information to perform a retrospective drug target validation study. We examined longitudinal clinical data from 612 individuals with excessive alcohol consumption. Two variants lowering NNMT protein levels were combined to calculate a weighted NNMT genetic score that could mimic mild inhibition of NNMT. Participants with an NNMT score above the median were classified as genetically inhibited, while others were considered non-inhibited. We then evaluated whether genetic inhibition of NNMT would affect the incidence of AFL or the risk of liver injury, to illuminate the effectiveness and safety of genetic inhibition of NNMT respectively. NNMT genetic inhibition correlated with a reduced AFL risk (hazard ratio [HR] 0.67, 95% confidence interval [CI] 0.49-0.90, P = 0.009) without a significant increase in serum aminotransferase levels (P > 0.10). Notably, elevated ALT and AST levels were observed (P < 0.05) in the genetically inhibited group prior to alcohol exposure. These findings suggest NNMT inhibition is a promising avenue for AFL prevention among individuals with excessive alcohol intake. They also underscore the need for precise target population identification to mitigate potential adverse effects.

Nicotinamide n-methyltransferase inhibitor synergizes with sodium-glucose cotransporter 2 inhibitor to protect renal tubular epithelium in experimental models of type 2 diabetes mellitus

AIMS

We aim to explore the potential of nicotinamide n-methyltransferase (NNMT) as a sensitive marker of renal tubular injury and the possibility of an NNMT inhibitor to combine with sodium-glucose cotransporter 2 (SGLT2) inhibitor to protect proximal tubular epithelium in vivo and in vitro model of Type 2 diabetes mellitus (T2DM), respectively.

METHODS

In vivo, immunohistochemical staining, Masson's trichrome staining and Sirius red staining were used to observe the changes of NNMT expression, renal tubular injury and interstitial fibrosis in renal tissue from the db/db mice. Bioinformatic analysis was also conducted to broaden the range of data validation. In vitro, Western Blot and quantitative RT-PCR were used to measure the degree of damage of HK-2 cells.

RESULTS

Our in vivo data showed upregulation of NNMT expression paralleled renal tubular damage and interstitial fibrosis. Our in vitro data revealed both NNMT inhibitors and SGLT2 inhibitors can protect against the injury as assessed by extracellular matrix (ECM) synthesis and profibrotic phenotype transition of HK-2 cells, and the combination of these two agents can further reduce these injuries.

CONCLUSIONS

The present study is the first to show that NNMT is a promising marker of renal tubular injury in diabetic nephropathy (DN) and NNMT inhibitors can synergize with SGLT2 inhibitors to protect HK-2 better. Our findings will provide the insight and pave the way of developing novel therapeutic strategies for chronic renal tubular injury associated with T2DM.

Exploring NNMT: from metabolic pathways to therapeutic targets

Cellular metabolism-related epigenetic modulation plays a pivotal role in the maintenance of cellular homeostasis. Nicotinamide N-methyltransferase (NNMT) serves as a crucial link between cellular metabolism and epigenetics by catalyzing nicotinamide methylation using the universal methyl donor S-adenosyl-L-methionine. This direct connection bridges the methylation-mediated one-carbon metabolism with nicotinamide adenine dinucleotide levels. Numerous studies have revealed tissue-specific differences in NNMT expression and activity, indicating that its varied physiological and pathological roles depend on its distribution. In this review, we provide an overview of the NNMT involvement in various pathological conditions, including cancer, liver disease, obesity, diabetes, brain disease, pulmonary disease, cardiovascular disease, and kidney disease. By synthesizing this information, our article aims to enhance our understanding of the cellular mechanisms underlying NNMT biology related to diverse diseases and lay the molecular groundwork for developing therapeutic strategies for pharmacological interventions.

Discovery of a novel lipid metabolism-related gene signature to predict outcomes and the tumor immune microenvironment in gastric cancer by integrated analysis of single-cell and bulk RNA sequencing

Gastric cancer (GC) is a pressing global clinical issue, with few treatment options and a poor prognosis. The onset and spread of stomach cancer are significantly influenced by changes in lipid metabolism-related pathways. This study aimed to discover a predictive signature for GC using lipid metabolism-related genes (LMRGs) and examine its correlation with the tumor immune microenvironment (TIME). Transcriptome data and clinical information from patients with GC were collected from the TCGA and GEO databases. Data from GC samples were analyzed using both bulk RNA-seq and single-cell sequencing of RNA (scRNA-seq). To identify survival-related differentially expressed LMRGs (DE-LMRGs), differential expression and prognosis studies were carried out. We built a predictive signature using LASSO regression and tested it on the TCGA and GSE84437 datasets. In addition, the correlation of the prognostic signature with the TIME was comprehensively analyzed. In this study, we identified 258 DE-LMRGs in GC and further screened seven survival-related DE-LMRGs. The results of scRNA-seq identified 688 differentially expressed genes (DEGs) between the three branches. Two critical genes (GPX3 and NNMT) were identified using the above two gene groups. In addition, a predictive risk score that relies on GPX3 and NNMT was developed. Survival studies in both the TCGA and GEO datasets revealed that patients categorized to be at low danger had a significantly greater prognosis than those identified to be at high danger. Additionally, by employing calibration plots based on TCGA data, the study demonstrated the substantial predictive capacity of a prognostic nomogram, which incorporated a risk score along with various clinical factors. Within the high-risk group, there was a noticeable abundance of active natural killer (NK) cells, quiescent monocytes, macrophages, mast cells, and activated CD4 + T cells. In summary, a two-gene signature and a predictive nomogram have been developed, offering accurate prognostic predictions for general survival in GC patients. These findings have the potential to assist healthcare professionals in making informed medical decisions and providing personalized treatment approaches.

Oxidative Stress in Liver Pathophysiology and Disease

The liver is an organ that is particularly exposed to reactive oxygen species (ROS), which not only arise during metabolic functions but also during the biotransformation of xenobiotics. The disruption of redox balance causes oxidative stress, which affects liver function, modulates inflammatory pathways and contributes to disease. Thus, oxidative stress is implicated in acute liver injury and in the pathogenesis of prevalent infectious or metabolic chronic liver diseases such as viral hepatitis B or C, alcoholic fatty liver disease, non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH). Moreover, oxidative stress plays a crucial role in liver disease progression to liver fibrosis, cirrhosis and hepatocellular carcinoma (HCC). Herein, we provide an overview on the effects of oxidative stress on liver pathophysiology and the mechanisms by which oxidative stress promotes liver disease.

Autophagy, Oxidative Stress, and Alcoholic Liver Disease: A Systematic Review and Potential Clinical Applications

Ethanol consumption triggers oxidative stress by generating reactive oxygen species (ROS) through its metabolites. This process leads to steatosis and liver inflammation, which are critical for the development of alcoholic liver disease (ALD). Autophagy is a regulated dynamic process that sequesters damaged and excess cytoplasmic organelles for lysosomal degradation and may counteract the harmful effects of ROS-induced oxidative stress. These effects include hepatotoxicity, mitochondrial damage, steatosis, endoplasmic reticulum stress, inflammation, and iron overload. In liver diseases, particularly ALD, macroautophagy has been implicated as a protective mechanism in hepatocytes, although it does not appear to play the same role in stellate cells. Beyond the liver, autophagy may also mitigate the harmful effects of alcohol on other organs, thereby providing an additional layer of protection against ALD. This protective potential is further supported by studies showing that drugs that interact with autophagy, such as rapamycin, can prevent ALD development in animal models. This systematic review presents a comprehensive analysis of the literature, focusing on the role of autophagy in oxidative stress regulation, its involvement in organ-organ crosstalk relevant to ALD, and the potential of autophagy-targeting therapeutic strategies.

A human liver organoid screening platform for DILI risk prediction

BACKGROUND & AIMS

Drug-induced liver injury (DILI), both intrinsic and idiosyncratic, causes frequent morbidity, mortality, clinical trial failures and post-approval withdrawal. This suggests an unmet need for improved in vitro models for DILI risk prediction that can account for diverse host genetics and other clinical factors. In this study, we evaluated the utility of human liver organoids (HLOs) for high-throughput DILI risk prediction and in an organ-on-chip system.

METHODS

HLOs were derived from three separate iPSC lines and benchmarked on two platforms for their ability to model in vitro liver function and identify hepatotoxic compounds using biochemical assays for albumin, ALT, AST, microscopy-based morphological profiling, and single-cell transcriptomics: i) HLOs dispersed in 384-well-formatted plates and exposed to a library of compounds; ii) HLOs adapted to a liver-on-chip system.

RESULTS

Dispersed HLOs derived from the three iPSC lines had similar DILI predictive capacity as intact HLOs in a high-throughput screening format, allowing for measurable IC50 values of compound cytotoxicity. Distinct morphological differences were observed in cells treated with drugs exerting differing mechanisms of toxicity. On-chip HLOs significantly increased albumin production, CYP450 expression, and ALT/AST release when treated with known hepatoxic drugs compared to dispersed HLOs and primary human hepatocytes. On-chip HLOs were able to predict the synergistic hepatotoxicity of tenofovir-inarigivir and displayed steatosis and mitochondrial perturbation, via phenotypic and transcriptomic analysis, on exposure to fialuridine and acetaminophen, respectively.

CONCLUSIONS

The high-throughput and liver-on-chip systems exhibit enhanced in vivo-like functions and demonstrate the potential utility of these platforms for DILI risk assessment. Tenofovir-inarigivr-associated hepatotoxicity was observed and correlates with the clinical manifestation of DILI observed in patients.

IMPACT AND IMPLICATIONS

Idiosyncratic (spontaneous, patient-specific) drug-induced liver injury (DILI) is difficult to study due to the lack of liver models that function as human liver tissue and are adaptable for large-scale drug screening. Human liver organoids grown from patient stem cells respond to known DILI-causing drugs in both a high-throughput and on a physiological "chip" culture system. These platforms show promise for researchers in their use as predictive models for novel drugs before entering clinical trials and as a potential in vitro diagnostic tool. Our findings support further development of patient-derived liver organoid lines and their use in the context of DILI research.

1-Methylnicotinamide promotes hepatic steatosis in mice: A potential mechanism in chronic alcohol-induced fatty liver disease

Alcohol abuse and its related diseases are the major risk factors for human health. Alcohol-related liver disease (ALD) is a leading cause of morbidity and mortality worldwide. Although the mechanism of ALD has been widely investigated, liver metabolites associated with long-term alcohol intake-induced hepatic steatosis have not been well explored. In this study, we aimed to investigate the role and mechanisms of 1-methylnicotinamide (1-MNA), a metabolite during nicotinamide adenine dinucleotide (NAD⁺) metabolism, in the pathogenesis of ALD. C57BL/6 wild-type mice were subjected to chronic alcohol feeding with or without 1-MNA (50 mg/kg/day). Our data showed that 1-MNA administration significantly enhanced chronic alcohol consumption-induced hepatic steatosis. Mechanistic studies revealed that alcohol-increased hepatic protein levels of sterol regulatory element-binding transcription factor (SREBP-1c), a key enzyme that regulates lipid lipogenesis, were enhanced in mice administered with 1-MNA, regardless of alcohol feeding. Consistently, alcohol-increased mRNA and protein levels of hepatic diacylglycerol o-acyltransferase 2 (DGAT2) and very low-density lipoprotein receptor (VLDLR) were also exacerbated by 1-MNA administration. Alcohol-induced hepatic endoplasmic reticulum (ER) stress was enhanced by 1-MNA administration, which was evidenced by increased protein levels of binding immunoglobulin protein (BIP), phosphorylated- protein kinase r-like ER kinase (PERK), activating transcription factor 4 (ATF4), and C/EBP-homologous protein (CHOP) in the mouse liver. Overall, this study demonstrated that 1-MNA serves as a pathogenic factor in the development of ALD. Targeting liver 1-MNA levels may serve as a promising therapeutic approach for improving hepatic steatosis in ALD.

Fu brick tea alleviates alcoholic liver injury by modulating the gut microbiota-liver axis and inhibiting the hepatic TLR4/NF-κB signaling pathway

This study first evaluated the protective effects of Fu brick tea water extracts (FTE) on alcoholic liver injury and its underlying mechanism in C57BL/6J mice. Oral administration of FTE by oral gavage (400 mg per kg bw) for 12 weeks significantly alleviated lipid metabolism disorder, reduced the activities of serum ALT and AST, decreased the expression of the liver CYP2E1 gene, and enhanced the antioxidant capacities of the livers in alcohol-fed mice (p < 0.05). FTE also relieved alcohol-induced gut microbiota dysbiosis by promoting the proliferation of probiotics such as Muribaculaceae and Lactobacillus, and subsequently increased the cecal levels of short-chain fatty acids (SCFAs) and decreased the tryptophan content of alcohol-fed mice (p < 0.05). Importantly, FTE was found to improve the alcohol-impaired gut barrier function by up-regulating the expression of the epithelial tight junction protein. Accordingly, FTE decreased the circulating lipopolysaccharide (LPS) and thus inhibited the hepatic TLR4/NF-κB signaling pathway to ameliorate alcoholic liver injury. Cumulatively, these findings shed light on the important role of the gut microbiota-liver axis behind the protective efficacy of FTE on alcoholic liver injury.