Differential involvement of IL-6 in the early and late phase of 1-methylnicotinamide (MNA) release in Concanavalin A-induced hepatitis

Integrated metabolomics and network pharmacology revealing the mechanism of arsenic-induced hepatotoxicity in mice

Endemic arsenic (As) poisoning is a severe biogeochemical disease that endangers human health. Epidemiological investigations and animal experiments have confirmed the damaging effects of As on the liver, but there is an urgent need to investigate the underlying mechanisms. This study adopted a metabolomic approach using UHPLC-QE/MS to identify the different metabolites and metabolic mechanisms associated with As-induced hepatotoxicity in mice. A network pharmacology approach was applied to predict the potential target of As-induced hepatotoxicity. The predicted targets of differential metabolites were subjected to a deep matching for elucidating the integration mechanisms. The results demonstrate that the levels of ALT and AST in plasma significantly increased in mice after As exposure. In addition, the liver tissue showed disorganized liver lobules, lax cytoplasm and inflammatory cell infiltration. Metabolomic analysis revealed that As exposure caused disturbance to 40 and 75 potential differential metabolites in plasma and liver, respectively. Further investigation led to discovering five vital metabolic pathways, including phenylalanine, tyrosine, and tryptophan biosynthesis and nicotinate and nicotinamide metabolism pathways. These pathways may responded to As-induced hepatotoxicity primarily through lipid metabolism, apoptosis, and deoxyribonucleic acid damage. The network pharmacology suggested that As could induce hepatotoxicity in mice by acting on targets including Hsp90aa1, Akt2, Egfr, and Tnf, which regulate PI3K Akt, HIF-1, MAPK, and TNF signaling pathways. Finally, the integrated metabolomics and network pharmacology revealed eight key targets associated with As-induced hepatoxicity, namely DNMT1, MAOB, PARP1, MAOA, EPHX2, ANPEP, XDH, and ADA. The results also suggest that nicotinic acid and nicotinamide metabolisms may be involved in As-induced hepatotoxicity. This research identified the metabolites, targets, and mechanisms of As-induced hepatotoxicity, offering meaningful insights and establishing the groundwork for developing antidotes for widespread As poisoning.

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.

Nicotinamide N-methyltransferase protects against deoxynivalenol-induced growth inhibition by suppressing pro-inflammatory cytokine expression

Deoxynivalenol (DON) is an inevitable contaminant in cereals for infants. Indeed, children's growth retardation caused by widespread DON pollution has become a global problem that cannot be ignored. Accumulating evidence has shown that DON stunts growth in children through pro-inflammatory cytokines. An exogenous increase of methylnicotinamide, a metabolite produced by nicotinamide N-methyltransferase (NNMT), has anti-inflammatory effects, but it is not clear whether NNMT has the same effect, and the role of NNMT in DON-induced inflammation and growth impairment remains indistinct. The present research reports that NNMT is an inflammatory self-protective factor in DON-exposed L02 cells. DON promoted the production of pro-inflammatory cytokines. Furthermore, DON increased NNMT to reduce pro-inflammatory cytokines, including interleukin (IL)-1β, IL-11 and IL-6, and thus increased IGF-1 and cell viability, alleviating the cell growth inhibition induced by DON. Interestingly, NNMT negatively regulated the expression of IL-1β through Sirtuin type 1 (SIRT1). Collectively, these findings provide new mechanistic insights into the toxicity of DON-induced growth retardation and inflammatory responses in children.

The Protective Role of IL-36/IL-36R Signal in Con A-Induced Acute Hepatitis

The IL-36 family, including IL-36α, IL-36β, IL-36γ, and IL-36R antagonist, belong to the IL-1 superfamily. It was reported that IL-36 plays a role in immune diseases. However, it remains unclear how IL-36 regulates inflammation. To determine the role of IL-36/IL-36R signaling pathways, we established an acute hepatitis mouse model (C57BL/6) by i.v. injection of the plant lectin Con A. We found that the levels of IL-36 were increased in the liver after Con A injection. Our results demonstrated the infiltrated neutrophils, but not the hepatocytes, were the main source of IL-36 in the liver. Using the IL-36R-/- mouse model (H-2b), we surprisingly found that the absence of IL-36 signals led to aggravated liver injury, as evidenced by increased mortality, elevated serum alanine aminotransferase and aspartate aminotransferase levels, and severe liver pathological changes. Further investigations demonstrated that a lack of IL-36 signaling induced intrahepatic activation of CD4+ and CD8+ T lymphocytes and increased the production of inflammatory cytokines. In addition, IL-36R-/- mice had reduced T regulatory cell numbers and chemokines in the liver. Together, our results from the mouse model suggested a vital role of IL-36 in regulating T cell function and homeostasis during liver inflammation.

Endothelial SIRT1 as a Target for the Prevention of Arterial Aging: Promises and Challenges

ABSTRACT

SIRT1, a member of the sirtuin family of longevity regulators, possesses potent activities preventing vascular aging. The expression and function of SIRT1 in endothelial cells are downregulated with age, in turn causing early vascular aging and predisposing various vascular abnormalities. Overexpression of SIRT1 in the vascular endothelium prevents aging-associated endothelial dysfunction and senescence, thus the development of hypertension and atherosclerosis. Numerous efforts have been directed to increase SIRT1 signaling as a potential strategy for different aging-associated diseases. However, the complex mechanisms underlying the regulation of SIRT1 have posed a significant challenge toward the design of specific and effective therapeutics. This review aimed to provide a summary on the regulation and function of SIRT1 in the vascular endothelium and to discuss the different approaches targeting this molecule for the prevention and treatment of age-related cardiovascular and cerebrovascular diseases.

Overexpression of Nicotinamide N-methyltransferase mainly covers stroma of colorectal cancer and correlates with unfavorable survival by its product 1-MNA

Background: Accumulating evidence indicates that Nicotinamide N-methyltransferase (NNMT) is abnormally expressed in tumor tissues of several cancers including colorectal cancer (CRC) and associated with cancer progression. However, the distribution characteristics and the clinical value of each part of NNMT expression in CRC are still not fully understood. The purpose of this study is to determine the distribution of NNMT expression and its association with survival in CRC. Methods: By using the cancer genome atlas (TCGA) and clinical proteomic tumor analysis consortium (CPTAC), we firstly analyzed the difference of gene and protein levels of NNMT between CRC and normal colorectal tissue. Then, NNMT protein expressions were detected in 18 intraepithelial neoplastic samples and 177 CRC tumor samples through immunohistochemistry in our study cohort. Furthermore, the relationship between NNMT expression and clinicopathological characteristics, overall survival (OS) and disease-free survival (DFS) of CRC patients were analyzed by Pearson χ2 test and log-rank test, respectively, in public datasets and our study cohort. Lastly, the function of NNMT and its product 1-methyl-nicotinamide (1-MNA) on migration and invasion in colorectal cancer cells was analyzed by wound healing assay and transwell assay. Results: We determined that higher NNMT expression in CRC tissues than normal tissues in both gene and protein level in TCGA and CPTAC datasets (all p < 0.05). In addition, the strong relationships of NNMT expression with stromal cells were found in the TCGA cohort. Fortunately, our cohort could validate that the expression of NNMT in tumor stroma cell was significantly higher than that in tumor cell (p < 0.0001), and both of them were significantly higher than that in adjacent normal tissue (ANT) (p < 0.0001 and p < 0.0001, respectively). Furthermore, the positive NNMT expression in tumor cell and stromal cell were associated with series of unfavorable clinical characteristics, including advanced TNM stage, lymph node metastasis, distant metastasis (all p < 0.05). Also, higher NNMT was associated with unfavorable survival both in our study and public datasets, including TCGA and two Gene Expression Omnibus (GEO) datasets (GSE33113 and GSE17538). Moreover, the functional experiments showed that stromal cells with high NNMT expression can secret 1-MAN to promote migration and invasion of CRC cells in vitro. Conclusions: In CRC, NNMT is overexpressed in tumor cells and stroma cells, and then mainly expressed in tumor stroma cells. Overexpression of NNMT in tumor cell and stroma cell both are associated with metastasis and unfavorable survival. Besides, stromal cells with high NNMT expression secrets 1-MAN to promote migration and invasion of CRC cells. Therefore, NNMT may be a potential prognostic indicator in CRC patients.

Huganbuzure Granule Attenuates Concanavalin-A-Induced Immune Liver Injury in Mice via Regulating the Balance of Th1/Th2/Th17/Treg Cells and Inhibiting Apoptosis

In Uygur medicine, Huganbuzure granule (HBG) is one of the classical prescriptions for liver protection. However, its role in immune liver injury remains unknown. This study evaluates the effect of HBG on concanavalin-A- (ConA-) induced immune liver injury and investigates its protective underlying mechanism. BALB/c mice were randomly divided into five groups (n = 24 mice per group): control, ConA, 1.6 g/kg HBG + ConA, 3.2 g/kg HBG + ConA, and 6 mg/kg prednisolone + ConA. HBG was intragastrically administrated once daily for ten consecutive days, prior to ConA (20 mg/kg) injection. The levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin (TBIL), superoxide dismutase (SOD), and malondialdehyde (MDA) in mouse serum were measured after ConA injection. Moreover, liver-related mRNA levels were evaluated by qPCR. The detection of liver-related proteins was assessed by immunohistochemistry and western blot analysis. Compared with the ConA group, HBG reduced the mRNA expression of IL-17A and IFN-γ and the protein expression of T-bet and ROR-γt. In addition, HBG increased the mRNA expression of IL-4 and TGF-β and protein expression of GATA3 and Foxp3, indicating that HBG regulated the balance of Th1/Th2 and Th17/Treg. Furthermore, HBG alleviated immune liver injury by reducing oxidative stress, inhibiting apoptosis, and decreasing the expression of p-JNK, p-ERK, p-p38, p-JAK1, p-STAT1, p-STAT3, and IRF1. Our data suggested that HBG attenuated ConA-induced immune liver injury by regulating the immune balance and inhibiting JAK1/STATs/IRF1 signaling, thereby reducing apoptosis induced by JNK activation. The findings indicate that HBG may be a promising drug for immune liver injury.

Nicotinamide N-methyltransferase in endothelium protects against oxidant stress-induced endothelial injury

Nicotinamide N-methyltransferase (NNMT, EC 2.1.1.1.) plays an important role in the growth of many different tumours and is also involved in various non-neoplastic disorders. However, the presence and role of NNMT in the endothelium has yet to be specifically explored. Here, we characterized the functional activity of NNMT in the endothelium and tested whether NNMT regulates endothelial cell viability. NNMT in endothelial cells (HAEC, HMEC-1 and EA.hy926) was inhibited using two approaches: pharmacological inhibition of the enzyme by NNMT inhibitors (5-amino-1-methylquinoline - 5MQ and 6-methoxynicotinamide - JBSF-88) or by shRNA-mediated silencing. Functional inhibition of NNMT was confirmed by LC/MS/MS-based analysis of impaired MNA production. The effects of NNMT inhibition on cellular viability were analyzed in both the absence and presence of menadione. Our results revealed that all studied endothelial lines express relatively high levels of functionally active NNMT compared with cancer cells (MDA-MB-231). Although the aldehyde oxidase 1 enzyme was also expressed in the endothelium, the further metabolites of N1-methylnicotinamide (N1-methyl-2-pyridone-5-carboxamide and N1-methyl-4-pyridone-3-carboxamide) generated by this enzyme were not detected, suggesting that endothelial NNMT-derived MNA was not subsequently metabolized in the endothelium by aldehyde oxidase 1. Menadione induced a concentration-dependent decrease in endothelial viability as evidenced by a decrease in cell number that was associated with the upregulation of NNMT and SIRT1 expression in the nucleus in viable cells. The suppression of the NNMT activity either by NNMT inhibitors or shRNA-based silencing significantly decreased the endothelial cell viability in response to menadione. Furthermore, NNMT inhibition resulted in nuclear SIRT1 expression downregulation and upregulation of the phosphorylated form of SIRT1 on Ser47. In conclusion, our results suggest that the endothelial nuclear NNMT/SIRT1 pathway exerts a cytoprotective role that safeguards endothelial cell viability under oxidant stress insult.

N1-Methylnicotinamide: An Anti-Ovarian Aging Hormetin?

Ovarian aging occurs due to the reduction of the quality and quantity of the oocytes, and is regulated by mitochondrial survival and apoptotic signals. Reactive Oxygen Species (ROS) are one of those signals considered detrimental to cellular homeostasis. Nowadays, ROS are regarded as a regulatory factor at low levels as it induces the stress resistance which in turn increases the longevity. It is believed that the main mechanism for the life-promoting role of the ROS mediated by the 5' Adenosine Monophosphate-activated Protein Kinase (AMPK). N1-Methylnicotinamide (MNAM) is well known for its anti-diabetic, anti-thrombotic, and anti-inflammatory activity. Aldehyde oxidase 1 (AOX1) is a detoxifying enzyme, which metabolizes the MNAM and produces two metabolites including N1-methyl-2-pyridone-5- carboxamide (2py) and N1-methyl-4-pyridone-3-carboxamide (4py). The activity of AOX1 enhances the production of ROS and improves the longevity. It has been reported that the MNAM could postpone the aging through the induction of low-level stress. It has been documented that the production of MNAM is significantly higher in the cumulus cells of the patients with Polycystic Ovary Syndrome (PCOS) and its administration on the rat model of PCOS has been shown to alleviate the hyperandrogenism and successfully activate the ovarian AMPK. Therefore, it can be hypothesized that the anti-ovarian aging effects of the MNAM are possibly based on the activation of AMPK through transient elevation of the ROS.

Abnormal Expression of ERα in Cholangiocytes of Patients With Primary Biliary Cholangitis Mediated Intrahepatic Bile Duct Inflammation

ERα, one of the classical receptors of estrogen, has been found to be abnormally up-regulated in patients with primary biliary cholangitis (PBC), which is an important factor leading to ductopenia. ERα-mediated signaling pathways are involved in proliferation of human intrahepatic biliary epithelial cells (HiBECs) and portal inflammation. Our previous studies have shown that the expression levels of ERα in the liver tissues of PBC patients are positively correlated with the levels of serum pro-inflammatory cytokines. The present study was designed to assess the relationship between abnormal ERα expression in small bile ducts and the progression of PBC. We examined the levels of multiple cytokines and analyzed their relationship with clinical parameters of livers functions in a cohort of 43 PBC patients and 45 healthy controls (HC). The levels of ERα expression and the relation with the levels of cytokines were further assessed. The localization of cytokines and ERα-mediated signaling pathways in liver were examined using immunohistochemistry. The possible underlying mechanisms of these alterations in PBC were explored in vitro. Our results demonstrated that the levels of IL-6, IL-8, and TNF-α were increased in PBC patients, and positively correlated with the serum AKP levels and ERα expression levels. Moreover, the expression of these cytokines were up-regulated in HiBECs that were stimulated with 17β-estradiol and PPT (an ERα agonist) and they also were positive in intrahepatic bile duct of PBC patients. The ERα-mediated expression of pro-inflammatory cytokines was induced by JNK, P38, and STAT3 phosphorylation in HiBECs. In addition, the CD54 expression was increased in HiBECs after ERα activation, which induced peripheral blood monouclear cells (PBMCs) recruitment. In conclusion, the present study highlighted a key role of abnormal ERα expression in inducing an inflammatory phenotype of HiBECs, which was critical in the development of inflammation and damage in small bile duct.

Activation of the nicotinamide N-methyltransferase (NNMT)-1-methylnicotinamide (MNA) pathway in pulmonary hypertension

Background

Pulmonary arterial hypertension (PAH) is associated with inflammatory response but it is unknown whether it is associated with alterations in NNMT activity and MNA plasma concentration. Here we examined changes in NNMT-MNA pathway in PAH in rats and humans.

Methods

PAH in rats was induced by a single subcutaneous injection of MCT (60 mg/kg). Changes in NNMT activity in the lungs and liver (assessed as the rate of conversion of nicotinamide (NA) to MNA), changes in plasma concentration of MNA and its metabolites (analyzed by LC/MS) were analyzed in relation to PAH progression. PAH was characterized by right ventricular hypertrophy (gross morphology), cardiac dysfunction (by MRI), lung histopathology, lung ultrastructure, and ET-1 concentration in plasma. NO-dependent and PGI₂-dependent function in isolated lungs was analyzed. In naive patients with idiopathic pulmonary hypertension (IPAH) characterized by hemodynamic and biochemical parameters MNA and its metabolites in plasma were also measured.

Results

MCT-injected rats developed hypertrophy and functional impairment of the right ventricle, hypertrophy of the pulmonary arteries, endothelial ultrastructural defects and a progressive increase in ET-1 plasma concentration—findings all consistent with PAH development. In isolated lung, NO-dependent regulation of hypoxic pulmonary vasoconstriction was impaired, while PGI₂ production (6-keto-PGF_1α) was increased. NNMT activity increased progressively in the liver and in the lungs following MCT injection, and NNMT response was associated with an increase in MNA and 6-keto-PGF_1α concentration in plasma. In IPAH patients plasma concentration of MNA was elevated as compared with healthy controls.

Conclusions

Progression of pulmonary hypertension is associated with the activation of the NNMT-MNA pathway in rats and humans. Given the vasoprotective activity of exogenous MNA, which was previously ascribed to PGI₂ release, the activation of the endogenous NNMT-MNA pathway may play a compensatory role in PAH.

MRI-based assessment of liver perfusion and hepatocyte injury in the murine model of acute hepatitis

OBJECTIVE

To assess alterations in perfusion and liver function in the concanavalin A (ConA)-induced mouse model of acute liver failure (ALF) using two magnetic resonance imaging (MRI)-based methods: dynamic contrast-enhanced MRI (DCE-MRI) with Gd-EOB-DTPA contrast agent and arterial spin labelling (ASL).

MATERIALS AND METHODS

BALB/c mice were studied using a 9.4 T MRI system. The IntraGateFLASH^TM and FAIR-EPI pulse sequences were used for optimum mouse abdomen imaging.

RESULTS

The average perfusion values for the liver of the control and ConA group were equal to 245 ± 20 and 200 ± 32 ml/min/100 g (p = 0.008, respectively). DCE-MRI showed that the time to the peak of the image enhancement was 6.14 ± 1.07 min and 9.72 ± 1.69 min in the control and ConA group (p < 0.001, respectively), while the rate of the contrast wash-out in the control and ConA group was 0.037 ± 0.008 and 0.021 ± 0.008 min^-1 (p = 0.004, respectively). These results were consistent with hepatocyte injury in the ConA-treated mice as confirmed by histopathological staining.

CONCLUSIONS

Both the ASL and DCE-MRI techniques represent a reliable methodology to assess alterations in liver perfusion and hepatocyte integrity in murine hepatitis.