Nicotinamide mononucleotide inhibits hepatic stellate cell activation to prevent liver fibrosis via promoting PGE2 degradation

TGF - β/SMAD signaling pathway and protein molecules in the treatment of liver fibrosis: A natural lipid membrane protein of exosomes

In recent years, exosomes, as an important medium of intercellular information transmission, have received extensive attention for their potential in the treatment of liver fibrosis. The purpose of this study was to investigate the role of exosome natural lipid membrane proteins in the treatment of liver fibrosis, with emphasis on the regulatory mechanism through the TGF-β/SMAD signaling pathway. Exosomes were extracted from healthy human hepatocytes and their membrane protein components were identified by mass spectrometry. Subsequently, the effects of these exosomes and their membrane proteins on the TGF-β/SMAD signaling pathway were examined using in vitro cell models and mouse liver fibrosis models. Western blot, qPCR and immunofluorescence were used to analyze the expression of fibrosis markers and the activity of signaling pathways. In vitro cell experiments, fibrotic cells showed an obvious reversal trend after treating exosome membrane proteins. In a mouse model of liver fibrosis, the injection of exosome membrane proteins significantly improved the degree of fibrosis in liver tissue.

Advancements in NMN biotherapy and research updates in the field of digestive system diseases

Nicotinamide mononucleotide (NMN), a crucial intermediate in NAD + synthesis, can rapidly transform into NAD + within the body after ingestion. NMN plays a pivotal role in several important biological processes, including energy metabolism, cellular aging, circadian rhythm regulation, DNA repair, chromatin remodeling, immunity, and inflammation. NMN has emerged as a key focus of research in the fields of biomedicine, health care, and food science. Recent years have witnessed extensive preclinical studies on NMN, offering valuable insights into the pathogenesis of age- and aging-related diseases. Given the sustained global research interest in NMN and the substantial market expectations for the future, here, we comprehensively review the milestones in research on NMN biotherapy over the past 10 years. Additionally, we highlight the current research on NMN in the field of digestive system diseases, identifying existing problems and challenges in the field of NMN research. The overarching aim of this review is to provide references and insights for the further exploration of NMN within the spectrum of digestive system diseases.

The circAno6/miR-296-3p/TLR4 signaling axis mediates the inflammatory response to induce the activation of hepatic stellate cells

BACKGROUND

Circular RNA (circRNA) is a novel functional non-coding RNA(ncRNA) that plays a role in the occurrence and development of multiple human liver diseases, including liver fibrosis (LF). LF is a reversible repair response after liver injury, and the activation of hepatic stellate cells (HSCs) is the core event. However, the regulatory mechanisms by which circRNAs induce the activation of HSCs in LF are still poorly understood. The circAno6/miR-296-3p/toll-like receptor 4 (TLR4) signaling axis that mediates the inflammatory response and causes the activation of HSCs was investigated in this study.

METHODS

First, a circAno6 overexpression plasmid and small interfering RNA were transfected into cells to determine whether circAno6 can affect the function of HSCs. Second, real-time quantitative polymerase chain reaction (RT-qPCR), enzyme-linked immunosorbent assay (ELISA), western blotting (WB) and immunofluorescence (IF) were used to detect the effects of circAno6 plasmid/siRNA transfection on HSC activation indices, inflammatory markers and the circAno6/miR-296-3p/TLR4 signaling axis. The subcellular position of circAno6 was then examined by nucleo-cytoplasmic separation and fluorescence in situ hybridization (FISH). Finally, a luciferase reporter gene assay was used to identify the relationship between circAno6 and miR-296-3p as well as the relationship between miR-296-3p and TLR4.

RESULTS

CircAno6 was considerably upregulated in HSCs and positively correlated with cell proliferation and alpha-smooth muscle actin (α-SMA), collagen I, NOD-likereceptorthermalproteindomainassociatedprotein 3 (NLRP3), interleukin-1β (IL-1β) and interleukin-18 (IL-18) expression. Overexpression of circAno6 increased the inflammatory response and induced HSC activation, whereas interference resulted in the opposite effects. FISH experiments revealed the localization of circAno6 in the cytoplasm. Then, a double luciferase reporter assay confirmed that miR-296-3p significantly inhibited luciferase activity in the circAno6-WT and TLR4-WT groups.

CONCLUSION

This study suggests that circAno6 and miR-296-3p/TLR4 may form a regulatory axis and regulate the inflammatory response, which in turn induces HSC activation. Targeting circAno6 may be a potential therapeutic strategy to treat LF.

Advances in the Synthesis and Physiological Metabolic Regulation of Nicotinamide Mononucleotide

Nicotinamide mononucleotide (NMN), the direct precursor of nicotinamide adenine dinucleotide (NAD+), is involved in the regulation of many physiological and metabolic reactions in the body. NMN can indirectly affect cellular metabolic pathways, DNA repair, and senescence, while also being essential for maintaining tissues and dynamic metabolic equilibria, promoting healthy aging. Therefore, NMN has found many applications in the food, pharmaceutical, and cosmetics industries. At present, NMN synthesis strategies mainly include chemical synthesis and biosynthesis. Despite its potential benefits, the commercial production of NMN by organic chemistry approaches faces environmental and safety problems. With the rapid development of synthetic biology, it has become possible to construct microbial cell factories to produce NMN in a cost-effective way. In this review, we summarize the chemical and biosynthetic strategies of NMN, offering an overview of the recent research progress on host selection, chassis cell optimization, mining of key enzymes, metabolic engineering, and adaptive fermentation strategies. In addition, we also review the advances in the role of NMN in aging, metabolic diseases, and neural function. This review provides comprehensive technical guidance for the efficient biosynthesis of NMN as well as a theoretical basis for its application in the fields of food, medicine, and cosmetics.

Recruitment or activation of mast cells in the liver aggravates the accumulation of fibrosis in carbon tetrachloride-induced liver injury

Liver diseases caused by viral infections, alcoholism, drugs, or chemical poisons are a significant health problem: Liver diseases are a leading contributor to mortality, with approximately 2 million deaths per year worldwide. Liver fibrosis, as a common liver disease characterized by excessive collagen deposition, is associated with high morbidity and mortality, and there is no effective treatment. Numerous studies have shown that the accumulation of mast cells (MCs) in the liver is closely associated with liver injury caused by a variety of factors. This study investigated the relationship between MCs and carbon tetrachloride (CCl4)-induced liver fibrosis in rats and the effects of the MC stabilizers sodium cromoglycate (SGC) and ketotifen (KET) on CCl4-induced liver fibrosis. The results showed that MCs were recruited or activated during CCl4-induced liver fibrosis. Coadministration of SCG or KET alleviated the liver fibrosis by decreasing SCF/c-kit expression, inhibiting the TGF-β1/Smad2/3 pathway, depressing the HIF-1a/VEGF pathway, activating Nrf2/HO-1 pathway, and increasing the hepatic levels of GSH, GSH-Px, and GR, thereby reducing hepatic oxidative stress. Collectively, recruitment or activation of MCs is linked to liver fibrosis and the stabilization of MCs may provide a new approach to the prevention of liver fibrosis.

SIRT3: A potential therapeutic target for liver fibrosis

Sirtuin3 (SIRT3) is a nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylase located in the mitochondria, which mainly regulates the acetylation of mitochondrial proteins. In addition, SIRT3 is involved in critical biological processes, including oxidative stress, inflammation, DNA damage, and apoptosis, all of which are closely related to the progression of liver disease. Liver fibrosis characterized by the deposition of extracellular matrix is a result of long termed or repeated liver damage, frequently accompanied by damaged hepatocytes, the recruitment of inflammatory cells, and the activation of hepatic stellate cells. Based on the functions and pharmacology of SIRT3, we will review its roles in liver fibrosis from three aspects: First, the main functions and pharmacological effects of SIRT3 were investigated based on its structure. Second, the roles of SIRT3 in major cells in the liver were summarized to reveal its mechanism in developing liver fibrosis. Last, drugs that regulate SIRT3 to prevent and treat liver fibrosis were discussed. In conclusion, exploring the pharmacological effects of SIRT3, especially in the liver, may be a potential strategy for treating liver fibrosis.

Development of a Chimeric Protein BiPPB-mIFNγ-tTβRII for Improving the Anti-Fibrotic Activity in Vivo by Targeting Fibrotic Liver and Dual Inhibiting the TGF-β1/Smad Signaling Pathway

Excessive production of transforming growth factor β1 (TGF-β1) in activated hepatic stellate cells (aHSCs) promotes liver fibrosis by activating the TGF-β1/Smad signaling pathway. Thus, specifically inhibiting the pro-fibrotic activity of TGF-β1 in aHSCs is an ideal strategy for treating liver fibrosis. Overexpression of platelet-derived growth factor β receptor (PDGFβR) has been demonstrated on the surface of aHSCs relative to normal cells in liver fibrosis. Interferon-gamma peptidomimetic (mIFNγ) and truncated TGF-β receptor type II (tTβRII) inhibit the TGF-β1/Smad signaling pathway by different mechanisms. In this study, we designed a chimeric protein by the conjugation of (1) mIFNγ and tTβRII coupled via plasma protease-cleavable linker sequences (FNPKTP) to (2) PDGFβR-recognizing peptide (BiPPB), namely BiPPB-mIFNγ-tTβRII. This novel protein BiPPB-mIFNγ-tTβRII was effectively prepared using Escherichia coli expression system. The active components BiPPB-mIFNγ and tTβRII were slowly released from BiPPB-mIFNγ-tTβRII by hydrolysis using the plasma protease thrombin in vitro. Moreover, BiPPB-mIFNγ-tTβRII highly targeted to fibrotic liver tissues, markedly ameliorated liver morphology and fibrotic responses in chronic liver fibrosis mice by both inhibiting the phosphorylation of Smad2/3 and inducing the expression of Smad7. Meanwhile, BiPPB-mIFNγ-tTβRII markedly reduced the deposition of collagen fibrils and expression of fibrosis-related proteins in acute liver fibrosis mice. Furthermore, BiPPB-mIFNγ-tTβRII showed a good safety performance in both liver fibrosis mice. Taken together, BiPPB-mIFNγ-tTβRII improved the in vivo anti-liver fibrotic activity due to its high fibrotic liver-targeting potential and the dual inhibition of the TGF-β1/Smad signaling pathway, which may be a potential candidate for targeting therapy on liver fibrosis.

Technology and functional insights into the nicotinamide mononucleotide for human health

Nicotinamide mononucleotide (NMN), a naturally occurring biologically active nucleotide, mainly functions via mediating the biosynthesis of NAD⁺. In recent years, its excellent pharmacological activities including anti-aging, treating neurodegenerative diseases, and protecting the heart have attracted increasing attention from scholars and entrepreneurs for production of a wide range of formulations, including functional food ingredients, health care products, active pharmaceuticals, and pharmaceutical intermediates. Presently, the synthesis methods of NMN mainly include two categories: chemical synthesis and biosynthesis. With the development of biocatalyst engineering and synthetic biology strategies, bio-preparation has proven to be efficient, economical, and sustainable methods. This review summarizes the chemical synthesis and biosynthetic pathways of NMN and provides an in-depth investigation on the mining and modification of enzyme resources during NMN biosynthesis, as well as the screening of hosts and optimization of chassis cells via metabolic engineering, which provide effective strategies for efficient production of NMN. In addition, an overview of the significant physiological functions and activities of NMN is elaborated. Finally, future research on technical approaches to further enhance NMN synthesis and strengthen clinical studies of NMN are prospected, which would lay the foundation for further promoting the application of NMN in nutrition, healthy food, and medicine in the future. KEY POINTS: • NMN supplementation effectively increases the level of NAD⁺. • The chemical and biological synthesis of NMN are comprehensively reviewed. • The impact of NMN on the treatment of various diseases is summarized.

DNMT3a-mediated methylation of TCF21/hnRNPA1 aggravates hepatic fibrosis by regulating the NF-κB signaling pathway

Hepatic fibrosis is caused by liver damage as a consequence of wound healing response. Recent studies have shown that hepatic fibrosis could be effectively reversed, partly through regression of activated hepatic stellate cells (HSCs). Transcription factor 21 (TCF21), a member of the basic helix-loop-helix (bHLH) transcription factor, is involved in epithelial-mesenchymal transformation in various diseases. However, the mechanism by which TCF21 regulates epithelial-mesenchymal transformation in hepatic fibrosis has not been elucidated. In this research, we found that hnRNPA1, the downstream binding protein of TCF21, accelerates hepatic fibrosis reversal by inhibiting the NF-κB signaling pathway. Furthermore, the combination of DNMT3a with TCF21 promoter results in TCF21 hypermethylation. Our results suggest that DNMT3a regulation of TCF21 is a significant event in reversing hepatic fibrosis. In conclusion, this research identifies a novel signaling axis, DNMT3a-TCF21-hnRNPA1, that regulates HSCs activation and hepatic fibrosis reversal, providing a novel treatment strategy for hepatic fibrosis. The clinical trial was registered in the Research Registry (researchregistry9079).

LC-IMS-HRMS for identification of biomarkers in untargeted metabolomics: The effects of pterostilbene and resveratrol consumption in liver steatosis, animal model

Untargeted metabolomics with the combination of ion mobility separation coupled to high resolution mass spectrometry (IMS-HRMS) was applied to investigate the impact of resveratrol and pterostilbene supplementation on the metabolic fingerprint of the Wistar rats liver with induced liver steatosis. RP-LC and HILIC in both ionisation modes were employed to analyse the liver samples (n = 40) from Wistar rats fed with a high-fat and high-fructose diet, supplemented or not with resveratrol and pterostilbene. After univariate and multivariate statistical analysis, 34 metabolites were highlighted in the different diets and elucidated. Despite the structural similarity, different alterations in liver metabolism were observed by the supplementations. Resveratrol treatment was characterised by the alteration in metabolism of 17 lysophospholipids, while pterostilbene affected some vitamins and derivatives, among others. IMS has demonstrated great potential in the elucidation process thanks to the additional structural descriptor the CCS (Ų), providing more confidence in the identification.

Hepatoprotective effects of parsley (Petroselinum Crispum) extract in rats with bile duct ligation

BACKGROUND AND STUDY AIMS

This study aimed to investigate the possible protective effects of parsley extract (Petroselinum Crispum; PC) against oxidative liver damage caused by bile obstruction in rats.

MATERIAL AND METHODS

Bile duct ligation (BDL) method was used to induce liver injury in rats. The rats were divided into the three groups each consisting of 8 rats; Sham-operated control (C), bile duct ligated + saline treated (BDL), and BDL + PC treated groups. PC extract was given at a dose of 2 g/kg orally for 28 days. Aspartate amino transferase (AST), alanin amino transferase (ALT), and bilirubin levels were analyzed in sera. In order to determine free radicals in liver injury, luminol and lucigenin chemiluminescence tests used. Oxidative stress was evaluated through superoxide dismutase, glutathione, malondialdehyde, Na⁺/K⁺-ATPase and 8-hydroxy guanosine levels. Furthermore, inflammation marker myeloperoxidase, apoptosis marker caspase-3, and fibrosis markers TGF- β and hydoxyproline were investigated. The liver tissues were also examined for histological evaluations.

RESULTS

While PC treatment decreased AST and ALT levels which increased with BDL, oxidant damage parameters also decreased with this treatment.

CONCLUSION

The present study, which is the first research for PC extract on cholestasis induced liver damage, demonstrated that PC extract could be a potential therapeutic agent against liver fibrosis and need further studies.

The Ultrastructure of Hepatic Stellate Cell-Macrophage Intercellular Crosstalk as a New Morphological Insight into Phenomenon of Fibrogenesis in Pediatric Autoimmune Hepatitis

The aim of the study was the pioneering retrospective ultrastructural evaluation of respective forms of hepatic stellate cells (HSCs) and analysis of their crosstalk with other adjacent nonparenchymal cells (NPCs), especially Kupffer cells/macrophages (KCs/MPs), in pediatric autoimmune hepatitis (AIH).

METHODS

Ultrastructural assessment of the HSC population and NPCs was performed in transmission electron microscopy (TEM) using pretreatment liver biopsies from 25 children (8 boys and 17 girls) aged 4-17 with clinic-pathologically diagnosed untreated AIH.

RESULTS

Submicroscopic evaluation allowed easy identification of numerous HSCs in the form of transitory cells, i.e., T-HSCs, accompanied by signs of fibrosis. T-HSCs included cells with features of activation initiation (iHSCs) and activation perpetuation (pHSCs), indicating high HSC activation plasticity. The pHSCs were markedly elongated and mainly showed a distinct loss of lipid cytoplasmic material, expanded and dilated channels of granular endoplasmic reticulum, and linear bundles of microfilaments beneath the cell membrane. They were surrounded by usually mature collagen fibers. Frequently activated KCs/MPs adhered directly to T-HSCs. Between them, tight intercellular junctions were formed by means of point desmosomes.

CONCLUSIONS

Our qualitative TEM observations indicate a key role of T-HSCs in liver fibrogenesis in pediatric AIH, with the essential involvement of activated KCs/MPs that directly adhere to them. Tight intercellular junctions, being the ultrastructural exponent of the specific cellular mechanisms of the crosstalk between NPCs, can play a vital role in hepatic collagen fibroplasia. A better understanding of HSC population morphology at the ultrastructural level in AIH seems important not only to improve the disease morphological diagnostics but to also provide new insights into therapeutic interventions for the phenomenon of liver fibrogenesis.

MiR-690 treatment causes decreased fibrosis and steatosis and restores specific Kupffer cell functions in NASH

Nonalcoholic steatohepatitis (NASH) is a liver disease associated with significant morbidity. Kupffer cells (KCs) produce endogenous miR-690 and, via exosome secretion, shuttle this miRNA to other liver cells, such as hepatocytes, recruited hepatic macrophages (RHMs), and hepatic stellate cells (HSCs). miR-690 directly inhibits fibrogenesis in HSCs, inflammation in RHMs, and de novo lipogenesis in hepatocytes. When an miR-690 mimic is administered to NASH mice in vivo, all the features of the NASH phenotype are robustly inhibited. During the development of NASH, KCs become miR-690 deficient, and miR-690 levels are markedly lower in mouse and human NASH livers than in controls. KC-specific KO of miR-690 promotes NASH pathogenesis. A primary target of miR-690 is NADK mRNA, and NADK levels are inversely proportional to the cellular miR-690 content. These studies show that KCs play a central role in the etiology of NASH and raise the possibility that miR-690 could emerge as a therapeutic for this condition.

Nicotinamide Mononucleotide Administration Restores Redox Homeostasis via the Sirt3-Nrf2 Axis and Protects Aged Mice from Oxidative Stress-Induced Liver Injury

Altered adaptive homeostasis contributes to aging and lifespan regulation. In the present study, to characterize the mechanism of aging in mouse liver, we performed quantitative proteomics and found that the most upregulated proteins were related to the oxidation-reduction process. Further analysis revealed that malondialdehyde (MDA) and protein carbonyl (PCO) levels were increased, while nuclear Nrf2 and downstream genes were significantly increased, indicating that oxidative stress induced Nrf2 activation in aged mouse liver. Importantly, nicotinamide mononucleotide (NMN) administration decreased the oxidative stress and the nuclear Nrf2 and Nrf2 downstream gene levels. Indeed, aged mice treated with NMN improved stress resistance against acetaminophen (APAP)-induced liver injury, indicating that NMN restored Nrf2-mediated adaptive homeostasis. Further studies found that NMN increased Sirt3 activities to deacetylate age-associated acetylation at K68 and K122 in Sod2, while its effects on nuclear Nrf2 levels were diminished in Sirt3-deficient mice, suggesting that NMN-enhanced adaptive homeostasis was Sirt3-dependent. Taken together, we demonstrated that Nrf2-regulated adaptive homeostasis was decreased in aged mouse liver and NMN supplementation restored liver redox homeostasis via the Sirt3-Nrf2 axis and protected aged liver from oxidative stress-induced injury.

The Clock-NAD+ -Sirtuin connection in nonalcoholic fatty liver disease

Nonalcoholic or metabolic associated fatty liver disease (NAFLD/MAFLD) is a hepatic reflection of metabolic derangements characterized by excess fat deposition in the hepatocytes. Identifying metabolic regulatory nodes in fatty liver pathology is essential for effective drug targeting. Fatty liver is often associated with circadian rhythm disturbances accompanied with alterations in physical and feeding activities. In this regard, both sirtuins and clock machinery genes have emerged as critical metabolic regulators in maintaining liver homeostasis. Knockouts of either sirtuins or clock genes result in obesity associated with the fatty liver phenotype. Sirtuins (SIRT1-SIRT7) are a highly conserved family of nicotinamide adenine dinucleotide (NAD+)-dependent deacetylases, protecting cells from metabolic stress by deacetylating vital proteins associated with lipid metabolism. Circadian rhythm is orchestrated by oscillations in expression of master regulators (BMAL1 and CLOCK), which in turn regulate rhythmic expression of clock-controlled genes involved in lipid metabolism. The circadian metabolite, NAD+ , serves as a crucial link connecting clock genes to sirtuin activity. This is because, NAMPT which is a rate limiting enzyme in NAD+ biosynthesis is transcriptionally regulated by the clock genes and NAD+ in turn is a cofactor regulating the deacetylation activity of sirtuins. Intriguingly, on one hand the core circadian clock regulates the sirtuin activity and on the other hand the activated sirtuins regulate the acetylation status of clock proteins thereby affecting their transcriptional functions. Thus, the Clock-NAD+-Sirtuin connection represents a novel "feedback loop" circuit that regulates the metabolic machinery. The current review underpins the importance of NAD+ on the sirtuin and clock connection in preventing fatty liver disorder.

Nicotinamide Mononucleotide Administration Amends Protein Acetylome of Aged Mouse Liver

It is known that the activities of nicotine adenine dinucleotide (NAD⁺)-dependent deacetylase decline in the aging mouse liver, and nicotinamide mononucleotide (NMN)-mediated activation of deacetylase has been shown to increase healthspans. However, age-induced changes of the acetylomic landscape and effects of NMN treatment on protein acetylation have not been reported. Here, we performed immunoprecipitation coupled with label-free quantitative LC-MS/MS (IPMS) to identify the acetylome and investigate the effects of aging and NMN on liver protein acetylation. In total, 7773 acetylated peptides assigned to 1997 proteins were commonly identified from young and aged livers treated with vehicle or NMN. The major biological processes associated with proteins exhibiting increased acetylation from aged livers were oxidation-reduction and metabolic processes. Proteins with decreased acetylation from aged livers mostly participated in transport and translation processes. Furthermore, NMN treatment inhibited the aging-related increase of acetylation on proteins regulating fatty acid β oxidation, the tricarboxylic acid (TCA) cycle and valine degradation. In particular, NAD (P) transhydrogenase (NNT) was markedly hyperacetylated at K70 in aged livers, and NMN treatment decreased acetylation intensity without altering protein levels. Acetylation at cytochrome 3a25 (Cyp3a25) at K141 was also greatly increased in aged livers, and NMN treatment totally arrested this increase. Our extensive identification and analysis provide novel insight and potential targets to combat aging and aging-related functional decline.

Common Pathogenetic Mechanisms Underlying Aging and Tumor and Means of Interventions

Recently, there has been an increase in the incidence of malignant tumors among the older population. Moreover, there is an association between aging and cancer. During the process of senescence, the human body suffers from a series of imbalances, which have been shown to further accelerate aging, trigger tumorigenesis, and facilitate cancer progression. Therefore, exploring the junctions of aging and cancer and searching for novel methods to restore the junctions is of great importance to intervene against aging-related cancers. In this review, we have identified the underlying pathogenetic mechanisms of aging-related cancers by comparing alterations in the human body caused by aging and the factors that trigger cancers. We found that the common mechanisms of aging and cancer include cellular senescence, alterations in proteostasis, microbiota disorders (decreased probiotics and increased pernicious bacteria), persistent chronic inflammation, extensive immunosenescence, inordinate energy metabolism, altered material metabolism, endocrine disorders, altered genetic expression, and epigenetic modification. Furthermore, we have proposed that aging and cancer have common means of intervention, including novel uses of common medicine (metformin, resveratrol, and rapamycin), dietary restriction, and artificial microbiota intervention or selectively replenishing scarce metabolites. In addition, we have summarized the research progress of each intervention and revealed their bidirectional effects on cancer progression to compare their reliability and feasibility. Therefore, the study findings provide vital information for advanced research studies on age-related cancers. However, there is a need for further optimization of the described methods and more suitable methods for complicated clinical practices. In conclusion, targeting aging may have potential therapeutic effects on aging-related cancers.

Pharmacology and Potential Implications of Nicotinamide Adenine Dinucleotide Precursors

Coenzyme I (nicotinamide adenine dinucleotide, NAD⁺/NADH) and coenzyme II (nicotinamide adenine dinucleotide phosphate, NADP^+/NADPH) are involved in various biological processes in mammalian cells. NAD⁺ is synthesised through the de novo and salvage pathways, whereas coenzyme II cannot be synthesised de novo. NAD⁺ is a precursor of coenzyme II. Although NAD⁺ is synthesised in sufficient amounts under normal conditions, shortage in its supply due to over consumption and its decreased synthesis has been observed with increasing age and under certain disease conditions. Several studies have proved that in a wide range of tissues, such as liver, skin, muscle, pancreas, and fat, the level of NAD⁺ decreases with age. However, in the brain tissue, the level of NADH gradually increases and that of NAD⁺ decreases in aged people. The ratio of NAD⁺/NADH indicates the cellular redox state. A decrease in this ratio affects the cellular anaerobic glycolysis and oxidative phosphorylation functions, which reduces the ability of cells to produce ATP. Therefore, increasing the exogenous NAD⁺ supply under certain disease conditions or in elderly people may be beneficial. Precursors of NAD⁺ have been extensively explored and have been reported to effectively increase NAD⁺ levels and possess a broad range of functions. In this review article, we discuss the pharmacokinetics and pharmacodynamics of NAD⁺ precursors.

Dual inhibition of reactive oxygen species and spleen tyrosine kinase as a therapeutic strategy in liver fibrosis

Hepatic stellate cells (HSCs) play key roles in liver fibrosis (LF) and hepatocellular carcinoma (HCC). We previously reported that spleen tyrosine kinase (SYK) is critical for HSCs activation, however, the mechanisms are insufficiently understood. In the present study, we found that SYK facilitated autophagy to promote HSCs activation by enhancing reactive oxygen species (ROS) generation. However, SYK inhibitor GS-9973 could efficiently reduce HSCs ROS generation in vitro but not in vivo. Mechanistically, hepatocytes (HCs) would release ROS outside and then diffuse into HSCs to promote autophagy and activation in vitro in the context of inflammation. We then further examined the ROS contents in liver sections and primary liver cells of carbon tetrachloride (CCl4) induced mice treated with or without different doses of Silybin, a natural compound characterized by a well-established antioxidant and hepatoprotective properties, and found that ROS intensities in both liver sections and their deprived primary cells were efficiently inhibited in a dose-dependent fashion. Lastly, we evaluated the rational combination of Silybin and GS-9973 in the treatment of CCl4 induced mice and found that this combination is well tolerated and acts synergistically against HSCs activity, LF and HCC. The combinational use of Silybin and GS-9973 could be a promising therapeutic strategy in patients suffering from LF and even HCC.

Curc-mPEG454, a PEGylated curcumin derivative, as a multi-target anti-fibrotic prodrug

Our previous studies demonstrated that Curc-mPEG454, a curcumin derivative modified with short-chain polyethylene glycol (PEG), not only increased the blood concentration of curcumin, but also retained its anti-inflammatory activity. Here, we aimed to evaluate the anti-fibrotic effect of Curc-mPEG454 on a rat liver fibrosis model induced by carbon tetrachloride (CCl₄), and to explore the underlying mechanisms by integrating our total liver RNA sequencing (RNA-seq) data with recent liver single-cell sequencing (scRNA-seq) studies. 50 mg/kg and 100 mg/kg Curc-mPEG454 treatment significantly reduced the elevation of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) induced by CCl₄, and the incidence of liver cirrhosis decreased from 75% to 37% and 35%, respectively. RNA-seq analysis revealed that Curc-mPEG454 significantly upregulated aldehyde oxidase 1 (AOX1) while downregulated cytochrome p450 26A1 (CYP26A1) and cytochrome p450 26B1 (CYP26B1) resulting in restoring liver retinoic acid (RA) level, increased glutamate-cysteine ligase catalytic subunit (GCLC) and glutamate-cysteine ligase modifier subunit (GCLM) expression to synthesize hepatic glutathione (GSH), and inhibited liver inflammation via down-regulating the Prostaglandin E Synthase 2 (PTGES2)/prostacyclin E2 (PGE2) signaling. Integrating scRNA-seq data revealed that Curc-mPEG454 effectively inhibited the expansion of scar-associated macrophage subpopulation and scar-producing myofibroblasts in the damaged liver, and remodeled the fibrotic niche via regulation of ligand-receptor interactions including platelet-derived growth factor-B (PDGF-B)/platelet-derived growth factor receptor-α (PDGFR-α) signaling. As a multi-target prodrug, PEGylated curcumin deserves further attention and research.

Celecoxib reduces hepatic vascular resistance in portal hypertension by amelioration of endothelial oxidative stress

The balance between endothelial nitric oxide (NO) synthase (eNOS) activation and production of reactive oxygen species (ROS) is very important for NO homeostasis in liver sinusoidal endothelial cells (LSECs). Overexpression of cyclooxygenase‐2 (COX‐2), a major intravascular source of ROS production, has been observed in LSECs of cirrhotic liver. However, the links between low NO bioavailability and COX‐2 overexpression in LSECs are unknown. This study has confirmed the link between low NO bioavailability and COX‐2 overexpression by COX‐2‐dependent PGE2‐EP2‐ERK1/2‐NOX1/NOX4 signalling pathway in LSECs in vivo and in vitro. In addition, the regulation of COX‐2‐independent LKB1‐AMPK‐NRF2‐HO‐1 signalling pathway on NO homeostasis in LSECs was also elucidated. The combinative effects of celecoxib on diminishment of ROS via COX‐2‐dependent and COX‐2‐independent signalling pathways greatly decreased NO scavenging. As a result, LSECs capillarisation was reduced, and endothelial dysfunction was corrected. Furthermore, portal hypertension of cirrhotic liver was ameliorated with substantial decreasing hepatic vascular resistance and great increase of portal blood flow. With the advance understanding of the mechanisms of LSECs protection, celecoxib may serve as a potential therapeutic candidate for patients with cirrhotic portal hypertension.

Nicotinamide Mononucleotide Alleviates LPS-Induced Inflammation and Oxidative Stress via Decreasing COX-2 Expression in Macrophages

Macrophage activation is an important process in controlling infection, but persistent macrophage activation leads to chronic inflammation and diseases, such as tumor progression, insulin resistance and atherosclerosis. Characterizing metabolic signatures of macrophage activation is important for developing new approaches for macrophage inactivation. Herein, we performed metabolomic analysis on lipopolysaccharide (LPS)-activated macrophages and identified the associated changes in metabolites. Notably, the cellular Nicotinamide adenine dinucleotide⁺ levels were decreased while NADPH was increased, proposing that NAD⁺ restoration can inhibit macrophage activation. Indeed, supplementation of nicotinamide mononucleotide (NMN) increased cellular NAD⁺ levels and decreased cytokine productions in LPS-activated cells. Quantitative proteomics identified that nicotinamide mononucleotide downregulated the expressions of LPS-responsive proteins, in which cyclooxygenase-2 (COX-2) expression was significantly decreased in NMN-treated cells. Consequently, the cellular levels of prostaglandin E₂ (PGE₂) was also decreased, indicating that NMN inactivated macrophages via COX-2-PGE₂ pathway, which was validated in activated THP-1 cells and mouse peritoneal macrophages. In conclusion, the present study identified the metabolic characteristics of activated macrophages and revealed that NMN replenishment is an efficient approach for controlling macrophage activation.

Reduced Nicotinamide Mononucleotide (NMNH) Potently Enhances NAD+ and Suppresses Glycolysis, the TCA Cycle, and Cell Growth

Decreased cellular NAD⁺ levels are causally linked to aging and aging-associated diseases. NAD⁺ precursors in oxidized form such as nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR) have gained much attention and been well studied for their ability to restore NAD⁺ levels in model organisms. Less is known about whether NAD⁺ precursors in reduced form can also efficiently increase the tissue and cellular NAD⁺ levels and have different effects on cellular processes than NMN or NR. In the present study, we developed a chemical method to produce dihydronicotinamide mononucleotide (NMNH), which is the reduced form of NMN. We demonstrated that NMNH was a better NAD⁺ enhancer than NMN both in vitro and in vivo, mediated by nicotinamide mononucleotide adenylyltransferase (NMNAT). Additionally, NMNH increased the reduced NAD (NADH) levels in cells and in mouse livers. Metabolomic analysis revealed that NMNH inhibited glycolysis and the TCA cycle. In vitro experiments demonstrated that NMNH induced cell cycle arrest and suppressed cell growth. Nevertheless, NMNH treatment did not cause an observable difference in mouse weight. Taken together, our work demonstrates that NMNH is a potent NAD⁺ enhancer and suppresses glycolysis, the TCA cycle, and cell growth.