Lack of PPARα exacerbates lipopolysaccharide-induced liver toxicity through STAT1 inflammatory signaling and increased oxidative/nitrosative stress

Recent advances in small molecule design strategies against hepatic fibrosis

Hepatic fibrosis, a widespread pathological process observed across various liver diseases, is acknowledged as a potentially reversible condition. In recent years, liver fibrosis has garnered extensive research attention, with a primary emphasis on developing drugs that can directly block or reverse this condition. This paper presents a comprehensive review of the design strategies for various anti-hepatic fibrosis agents that have been many efficacious small-molecule drugs. This review encompasses the synthesis and design of nuclear receptor ligands (such as VDR and Nurr7), kinase inhibitors (including ALK5 and JAK1), selective PDE inhibitors, small-molecule monomers derived from natural products, and other small molecules. The aim of this review is to provide promising avenues and valuable insights for the continued development of anti-hepatic fibrosis drugs.

Design, synthesis, and biological evaluation of piperazine derivatives as pan-PPARs agonists for the treatment of liver fibrosis

Liver fibrosis is commonly occurred in chronic liver diseases, but there is no approved drug for clinical use. The nuclear receptor peroxisome proliferator-activated receptors (PPARs) could not only regulate metabolic homeostasis but also possess anti-inflammatory and antifibrotic effects, and pan-PPARs agonist was considered as a potential anti-liver fibrosis agent. In this study, a series of novel piperazine pan-PPARs agonists were developed, and the preferred compound 12 displayed potent and well-balanced pan-PPARs agonistic activity. Moreover, compound 12 could dose-dependently stimulate the PPARs target genes expression and showed high selectivity over other related nuclear receptors. Importantly, compound 12 exhibited excellent pharmacokinetic profiles and good anti-liver fibrosis effects in vivo. Collectively, compound 12 holds promise for developing an anti-liver fibrosis agent.

Derivation and comprehensive analysis of ageing-related genes in intervertebral disc degeneration for prediction and immunology

Intervertebral disc degeneration (IDD) is triggered primarily by ageing, a process characterized by intrinsic, multifaceted and progressive characteristics. Regarding the crucial senescence genes and underlying regulatory mechanisms leading to the etiology of IDD, there is still some uncertainty. In this study, we used gene expression patterns from the GEO database to create a diagnostic model of IDD using differential ageing-related genes (DARG). We examine the relative dynamics of immune cells by single-sample gene set. On the basis of transcription factor (TF) miRNA and miRNA-mRNA pairs, the regulatory network for transcription and post-transcriptional processes was built. The active therapeutic components and Chinese herbal remedies of the main ageing genes were investigated using a network pharmacology approach. 20 DARGs were combined to create a diagnostic model, and both the training and validation sets had an area under the ROC curve of 1. We found alterations in many cell types in IDD tissue, but mainly in activated dendritic cells, type 17 T helper cells, and mast cells. We identified a regulatory axis for STAT1/miR-4306/PPARA based on the correlations between gene expression and targeting. Active substances (Naringenin and Quercetin) and herbs (Aurantii fructus and Eucommiae cortex) targeting PPARA for the treatment of IDD were discovered through network pharmacology. These results provide a theoretical framework for identifying and treating IDD. For the first time, we were able to diagnose IDD patients using 20 ageing-related indicators. At the same time, TF-miRNA-mRNA in conjunction with network pharmacology enabled the identification of prospective therapeutic targets and pharmacological processes.

Saroglitazar, a dual PPAR-α/γ agonist, alleviates LPS-induced hepatic and renal injury in rats

BACKGROUND

Lipopolysaccharide (LPS), an endotoxin within gram-negative bacteria, is associated with systemic acute inflammatory response after invading living tissues and results in sepsis. The liver and kidney are both major target organs in sepsis. Septic acute hepatic-renal injury is a serious clinical condition with high risk of morbidity and mortality. Nevertheless, effective treatment is still lacking.

AIM

This study highlights saroglitazar (SAR), a dual PPAR-α/γ agonist, as a proposed prophylactic drug against LPS-induced hepatic-renal injury.

MAIN METHODS

Rats were pretreated with SAR (2 and 4 mg/kg/day) for 15 days, while sepsis was induced by LPS injection (10 mg/kg) on day 15 one hour following SAR oral administration.

KEY FINDINGS

SAR pretreatment could successfully mitigate LPS-induced hepatic-renal injury, evidenced by enhancement of renal and hepatic functions and a decrease of tissue pathological injury. Meanwhile, SAR alleviated LPS-induced oxidative stress; it reduced malondialdehyde (MDA) levels and ameliorated decreased levels of superoxide dismutase (SOD) and glutathione (GSH). LPS-induced elevations in hepatic and renal nuclear factor-kappa B (NF-κB), phosphorylated inhibitor of kappa B alpha (p-IκBα), interferon-beta (IFN-β), and hepatic high mobility group box-1 (HMGB-1) contents were significantly attenuated in SAR-treated groups. SAR showed an advantageous impact against LPS-induced activation of non-canonical inflammasome and pyroptosis via a significant reduction in cysteinyl aspartate-specific proteinase-11 (Caspase-11) and gasdermin D (GSDMD) expressions. Moreover, Nucleotide-Binding Oligomerization Domain (NOD)-Like Receptor Protein 3 (NLRP3) inflammasome activation with concomitant expression and activation of caspase-1 and release of interleukin-1beta (IL-1β) were considerably diminished following SAR pretreatment.

SIGNIFICANCE

SAR could be considered a prophylactic anti-inflammatory antioxidant drug against LPS-induced liver and kidney injury.

Salvia miltiorrhiza Bge. (Danshen) in the Treating Non-alcoholic Fatty Liver Disease Based on the Regulator of Metabolic Targets

Non-alcoholic fatty liver disease (NAFLD) is rapidly prevalent due to its strong association with increased metabolic syndrome such as cardio- and cerebrovascular disorders and diabetes. Few drugs can meet the growing disease burden of NAFLD. Salvia miltiorrhiza Bge. (Danshen) have been used for over 2,000 years in clinical trials to treat NAFLD and metabolic syndrome disease without clarified defined mechanisms. Metabolic targets restored metabolic homeostasis in patients with NAFLD and improved steatosis by reducing the delivery of metabolic substrates to liver as a promising way. Here we systematic review evidence showing that Danshen against NAFLD through diverse and crossing mechanisms based on metabolic targets. A synopsis of the phytochemistry and pharmacokinetic of Danshen and the mechanisms of metabolic targets regulating the progression of NAFLD is initially provided, followed by the pharmacological activity of Danshen in the management NAFLD. And then, the possible mechanisms of Danshen in the management of NAFLD based on metabolic targets are elucidated. Specifically, the metabolic targets c-Jun N-terminal kinases (JNK), sterol regulatory element-binding protein-1c (SREBP-1c), nuclear translocation carbohydrate response element–binding protein (ChREBP) related with lipid metabolism pathway, and peroxisome proliferator-activated receptors (PPARs), cytochrome P450 (CYP) and the others associated with pleiotropic metabolism will be discussed. Finally, providing a critical assessment of the preclinic and clinic model and the molecular mechanism in NAFLD.

Contributing Roles of CYP2E1 and Other Cytochrome P450 Isoforms in Alcohol-Related Tissue Injury and Carcinogenesis

The purpose of this review is to briefly summarize the roles of alcohol (ethanol) and related compounds in promoting cancer and inflammatory injury in many tissues. Long-term chronic heavy alcohol exposure is known to increase the chances of inflammation, oxidative DNA damage, and cancer development in many organs. The rates of alcohol-mediated organ damage and cancer risks are significantly elevated in the presence of co-morbidity factors such as poor nutrition, unhealthy diets, smoking, infection with bacteria or viruses, and exposure to pro-carcinogens. Chronic ingestion of alcohol and its metabolite acetaldehyde may initiate and/or promote the development of cancer in the liver, oral cavity, esophagus, stomach, gastrointestinal tract, pancreas, prostate, and female breast. In this chapter, we summarize the important roles of ethanol/acetaldehyde in promoting inflammatory injury and carcinogenesis in several tissues. We also review the updated roles of the ethanol-inducible cytochrome P450-2E1 (CYP2E1) and other cytochrome P450 isozymes in the metabolism of various potentially toxic substrates, and consequent toxicities, including carcinogenesis in different tissues. We also briefly describe the potential implications of endogenous ethanol produced by gut bacteria, as frequently observed in the experimental models and patients of nonalcoholic fatty liver disease, in promoting DNA mutation and cancer development in the liver and other tissues, including the gastrointestinal tract.

Furosine Induced Apoptosis by the Regulation of STAT1/STAT2 and UBA7/UBE2L6 Genes in HepG2 Cells

As a typical product in the Miallard reaction, research on the quantitative detection of furosine is abundant, while its bioactivities and toxic effects are still unclear. Our own work recently demonstrated the induction of furosine on apoptosis in HepG2 cells, while the related mechanism remained elusive. In this study, the effects of furosine on cell viability and apoptosis were detected to select the proper dosage, and transcriptomics detection and data analysis were performed to screen out the special genes. Additionally, SiRNA fragments of the selected genes were designed and transfected into HepG2 cells to validate the role of these genes in inducing apoptosis. Results showed that furosine inhibited cell viability and induced cell apoptosis in a dose-dependent manner, as well as activated expressions of the selected genes STAT1 (signal transducer and activator of transcription 1), STAT2 (signal transducer and activator of transcription 2), UBA7 (ubiquitin-like modifier activating enzyme 7), and UBE2L6 (ubiquitin-conjugating enzyme E2L6), which significantly affected downstream apoptosis factors Caspase-3 (cysteinyl aspartate specific proteinase-3), Bcl-2 (B-cell lymphoma gene-2), Bax (BCL2-Associated gene X), and Caspase-9 (cysteinyl aspartate specific proteinase-9). For the first time, we revealed furosine induced apoptosis through two transcriptional regulators (STAT1 and STAT2) and two ubiquitination-related enzymes (UBA7 and UBE2L6).

Acyl-CoA Thioesterase 1 (ACOT1) Regulates PPARα to Couple Fatty Acid Flux With Oxidative Capacity During Fasting

Hepatic acyl-CoA thioesterase 1 (ACOT1) catalyzes the conversion of acyl-CoAs to fatty acids (FAs) and CoA. We sought to determine the role of ACOT1 in hepatic lipid metabolism in C57Bl/6J male mice 1 week after adenovirus-mediated Acot1 knockdown. Acot1 knockdown reduced liver triglyceride (TG) as a result of enhanced TG hydrolysis and subsequent FA oxidation. In vitro experiments demonstrated that Acot1 knockdown led to greater TG turnover and FA oxidation, suggesting that ACOT1 is important for controlling the rate of FA oxidation. Despite increased FA oxidation, Acot1 knockdown reduced the expression of peroxisome proliferator-activated receptor α (PPARα) target genes, whereas overexpression increased PPARα reporter activity, suggesting ACOT1 regulates PPARα by producing FA ligands. Moreover, ACOT1 exhibited partial nuclear localization during fasting and cAMP/cAMP-dependent protein kinase signaling, suggesting local regulation of PPARα. As a consequence of increased FA oxidation and reduced PPARα activity, Acot1 knockdown enhanced hepatic oxidative stress and inflammation. The effects of Acot1 knockdown on PPARα activity, oxidative stress, and inflammation were rescued by supplementation with Wy-14643, a synthetic PPARα ligand. We demonstrate through these results that ACOT1 regulates fasting hepatic FA metabolism by balancing oxidative flux and capacity.

Peroxisome proliferator-activated receptor alpha mediates C/EBP homologous protein to protect mice from acute liver failure

OBJECTIVE

Peroxisome proliferator-activated receptor α (PPARα) activation has been reported to ameliorate liver injury in cases of acute liver failure (ALF). However, its intrinsic protective molecular mechanisms remain largely undetermined. C/EBP homologous protein (CHOP) is an important mediator of lipopolysaccharide (LPS)-induced inflammation. The aim of the present study was to test the hypothesis that PPARα activation alleviates liver inflammation to protect mice from acute liver failure (ALF) mediated by CHOP.

METHODS

In a murine model induced by D-galactosamine (D-GalN, 700 mg/kg) and LPS (10 μg/kg), Wy-14643 (6 mg/kg) was administered to activate PPARα. The mice of different groups were killed 6 h after D-GalN/LPS injection, and the liver and blood were collected for analysis. To find out whether PPARα activation protects the liver from injury due to inflammation by regulating CHOP, we used expression plasmid to increase CHOP expression and demonstrated how PPARα mediated CHOP to regulate inflammation in vivo and in vitro.

RESULTS

The expression of PPARα was downregulated and the expression of CHOP was upregulated with the development of D-GalN/LPS-induced liver injury. The protective molecular mechanisms of PPARα activation were dependent on the expression of CHOP. Indeed, (1) PPARα activation decreased the expression of CHOP; on the other hand, PPARα knockdown increased the expression of CHOP in vivo; (2) the depressed liver inflammation by PPARα activation was due to the downregulation of CHOP expression, because overexpression of CHOP by transfect plasmid reversed liver protection and increased liver inflammation again; (3) in vitro, PPARα inhibition by siRNA treatment increased the expression of proinflammatory cytokines, and CHOP siRNA co-transfection reversed the expression of proinflammatory cytokines.

CONCLUSIONS

Here, we demonstrated that PPARα activation contributes to liver protection and decreases liver inflammation in ALF, particularly through regulating CHOP. Our findings may provide a rationale for targeting PPARα as a potential therapeutic strategy to ameliorate ALF.

Hepatocyte-specific PPARA expression exclusively promotes agonist-induced cell proliferation without influence from nonparenchymal cells

Peroxisome proliferator-activated receptor-α (PPARA) is a nuclear transcription factor and key mediator of systemic lipid metabolism. Prolonged activation in rodents causes hepatocyte proliferation and hepatocellular carcinoma. Little is known about the contribution of nonparenchymal cells (NPCs) to PPARA-mediated cell proliferation. NPC contribution to PPARA agonist-induced hepatomegaly was assessed in hepatocyte (Ppara△Hep)- and macrophage (Ppara△Mac)-specific Ppara null mice. Mice were treated with the agonist Wy-14643 for 14 days, and response of conditional null mice was compared with conventional knockout mice (Ppara-/- ). Wy-14643 treatment caused weight loss and severe hepatomegaly in wild-type and Ppara△Mac mice, and histological analysis revealed characteristic hepatocyte swelling; Ppara△Hep and Ppara-/- mice were protected from these effects. Ppara△Mac serum chemistries, as well as aspartate aminotransferase and alanine aminotransferase levels, matched wild-type mice. Agonist-treated Ppara△Hep mice had elevated serum cholesterol, phospholipids, and triglycerides when compared with Ppara-/- mice, indicating a possible role for extrahepatic PPARA in regulating circulating lipid levels. BrdU labeling confirmed increased cell proliferation only in wild-type and Ppara△Mac mice. Macrophage PPARA disruption did not impact agonist-induced upregulation of lipid metabolism, cell proliferation, or DNA damage and repair-related gene expression, whereas gene expression was repressed in Ppara△Hep mice. Interestingly, downregulation of inflammatory cytokines IL-15 and IL-18 was dependent on macrophage PPARA. Cell type-specific regulation of target genes was confirmed in primary hepatocytes and Kupffer cells. These studies conclusively show that cell proliferation is mediated exclusively by PPARA activation in hepatocytes and that Kupffer cell PPARA has an important role in mediating the anti-inflammatory effects of PPARA agonists.

Omega-9 Oleic Acid Induces Fatty Acid Oxidation and Decreases Organ Dysfunction and Mortality in Experimental Sepsis

Sepsis is characterized by inflammatory and metabolic alterations, which lead to massive cytokine production, oxidative stress and organ dysfunction. In severe systemic inflammatory response syndrome, plasma non-esterified fatty acids (NEFA) are increased. Several NEFA are deleterious to cells, activate Toll-like receptors and inhibit Na⁺/K⁺-ATPase, causing lung injury. A Mediterranean diet rich in olive oil is beneficial. The main component of olive oil is omega-9 oleic acid (OA), a monounsaturated fatty acid (MUFA). We analyzed the effect of OA supplementation on sepsis. OA ameliorated clinical symptoms, increased the survival rate, prevented liver and kidney injury and decreased NEFA plasma levels in mice subjected to cecal ligation and puncture (CLP). OA did not alter food intake and weight gain but diminished reactive oxygen species (ROS) production and NEFA plasma levels. Carnitine palmitoyltransferase IA (CPT1A) mRNA levels were increased, while uncoupling protein 2 (UCP2) liver expression was enhanced in mice treated with OA. OA also inhibited the decrease in 5' AMP-activated protein kinase (AMPK) expression and increased the enzyme expression in the liver of OA-treated mice compared to septic animals. We showed that OA pretreatment decreased NEFA concentration and increased CPT1A and UCP2 and AMPK levels, decreasing ROS production. We suggest that OA has a beneficial role in sepsis by decreasing metabolic dysfunction, supporting the benefits of diets high in monounsaturated fatty acids (MUFA).

Inhibition of glycogen synthase kinase 3β promotes autophagy to protect mice from acute liver failure mediated by peroxisome proliferator-activated receptor α

Our previous studies have demonstrated that inhibition of glycogen synthase kinase 3β (GSK3β) activity protects mice from acute liver failure (ALF), whereas its protective and regulatory mechanism remains elusive. Autophagy is a recently recognized rudimentary cellular response to inflammation and injury. The aim of the present study was to test the hypothesis that inhibition of GSK3β mediates autophagy to inhibit liver inflammation and protect against ALF. In ALF mice model induced by D-galactosamine (D-GalN) and lipopolysaccharide (LPS), autophagy was repressed compared with normal control, and D-GalN/LPS can directly induce autophagic flux in the progression of ALF mice. Autophagy activation by rapamycin protected against liver injury and its inhibition by 3-methyladenine (3-MA) or autophagy gene 7 (Atg7) small interfering RNA (siRNA) exacerbated liver injury. The protective effect of GSK3β inhibition on ALF mice model depending on the induction of autophagy, because that inhibition of GSK3β promoted autophagy in vitro and in vivo, and inhibition of autophagy reversed liver protection and inflammation of GSK3β inhibition. Furthermore, inhibition of GSK3β increased the expression of peroxisome proliferator-activated receptor α (PPARα), and the downregulated PPARα by siRNA decreased autophagy induced by GSK3β inhibition. More importantly, the expressions of autophagy-related gene and PPARα are significantly downregulated and the activity of GSK3β is significantly upregulated in liver of ALF patients with hepatitis B virus. Thus, we have demonstrated the new pathological mechanism of ALF that the increased GSK3β activity suppresses autophagy to promote the occurrence and development of ALF by inhibiting PPARα pathway.

Mitochondrial dysfunction and tissue injury by alcohol, high fat, nonalcoholic substances and pathological conditions through post-translational protein modifications

Mitochondria are critically important in providing cellular energy ATP as well as their involvement in anti-oxidant defense, fat oxidation, intermediary metabolism and cell death processes. It is well-established that mitochondrial functions are suppressed when living cells or organisms are exposed to potentially toxic agents including alcohol, high fat diets, smoking and certain drugs or in many pathophysiological states through increased levels of oxidative/nitrative stress. Under elevated nitroxidative stress, cellular macromolecules proteins, DNA, and lipids can undergo different oxidative modifications, leading to disruption of their normal, sometimes critical, physiological functions. Recent reports also indicated that many mitochondrial proteins are modified via various post-translation modifications (PTMs) and primarily inactivated. Because of the recently-emerging information, in this review, we specifically focus on the mechanisms and roles of five major PTMs (namely oxidation, nitration, phosphorylation, acetylation, and adduct formation with lipid-peroxides, reactive metabolites, or advanced glycation end products) in experimental models of alcoholic and nonalcoholic fatty liver disease as well as acute hepatic injury caused by toxic compounds. We also highlight the role of the ethanol-inducible cytochrome P450-2E1 (CYP2E1) in some of these PTM changes. Finally, we discuss translational research opportunities with natural and/or synthetic anti-oxidants, which can prevent or delay the onset of mitochondrial dysfunction, fat accumulation and tissue injury.

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Hepatotoxic agents including alcohol and high fat elevate nitroxidative stress.

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Increased nitroxidative stress promotes post-translational protein modifications.

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Post-translational protein modifications of many proteins lead to their inactivation.

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Inactivation of mitochondrial proteins contributes to mitochondrial dysfunction.

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Mitochondrial dysfunction contributes to necrotic or apoptotic tissue injury.

The Mechanism of Interferon Refractoriness During Hepatitis C Virus Infection and Its Reversal with a Peroxisome Proliferator-Activated Receptor α Agonist

Patients who respond poorly to therapies for hepatitis C virus (HCV) infection display a characteristic phenotype with high basal hepatic interferon-stimulated gene (ISG) expression, but limited induction following interferon (IFN) treatment. The molecular pathways that mediate this refractory state are not known. We examined whether the AMPK activator metformin, the PPARγ agonist pioglitazone, or the PPARα agonist WY-14643 could potentiate IFN responses, reverse IFN refractoriness, and enhance viral eradication in hepatocytes. WY-14643 demonstrated the strongest antiviral synergy with IFN-α and so was tested in the context of chronic IFN activation. Cells rendered refractory to IFN by IFN-α pretreatment were resensitized by WY-14643, as demonstrated by improved STAT1 phosphorylation, promoter activation, and ISG expression. WY-14643 treatment reduced the expression of key negative regulators of IFN signaling: the AXL receptor tyrosine kinase, suppressor of cytokine signaling (SOCS) 1 and 3, which are upregulated in the IFN-refractory state. AXL is a novel regulator of IFN-α signaling that is induced by HCV infection in vitro and which may drive SOCS3 expression. Our data suggests that PPARα agonists could be a useful adjunct treatment for chronic HCV infection by reducing the expression of AXL/SOCS and increasing the sensitivity to IFN.

Peroxisome proliferator-activated receptor α activation attenuates the inflammatory response to protect the liver from acute failure by promoting the autophagy pathway

Peroxisome proliferator-activated receptor α (PPARα) has been reported to induce a potent anti-inflammatory response. Autophagy is a recently recognized rudimentary cellular response to inflammation and injury. The aim of the present study was to test the hypothesis that PPARα activation mediates autophagy to inhibit liver inflammation and protect against acute liver failure (ALF). PPARα expression during ALF and the impact of PPARα activation by Wy-14 643 on the hepatic immune response were studied in a D-galactosamine/lipopolysaccharide-induced mouse model. Autophagy was inhibited by 3-methyladenine or small interfering RNA (siRNA) against Atg7. In both the mouse model and human ALF subjects, PPARα was significantly downregulated in the injured liver. PPARα activation by pretreatment with Wy-14 643 protected against liver injury in mice. The protective effect of PPARα activation relied on the suppression of inflammatory mechanisms through the induction of autophagy. This hypothesis is supported by the following evidence: first, PPARα activation suppressed proinflammatory responses and inhibited phosphorylated NF-κBp65, phosphorylated JNK and phosphorylated ERK pathways in vivo. Second, protection by PPARα activation was due to the induction of autophagy because inhibition of autophagy by 3-methyladenine or Atg7 siRNA reversed liver protection and inflammation. Third, PPARα activation directly induced autophagy in primary macrophages in vitro, which protected cells from a lipopolysaccharide-induced proinflammatory response. Here, for the first time, we have demonstrated that PPARα-mediated induction of autophagy ameliorated liver injury in cases of ALF by attenuating inflammatory responses, indicating a potential therapeutic application for ALF treatment.

Functional roles of protein nitration in acute and chronic liver diseases

Nitric oxide, when combined with superoxide, produces peroxynitrite, which is known to be an important mediator for a number of diseases including various liver diseases. Peroxynitrite can modify tyrosine residue(s) of many proteins resulting in protein nitration, which may alter structure and function of each target protein. Various proteomics and immunological methods including mass spectrometry combined with both high pressure liquid chromatography and 2D PAGE have been employed to identify and characterize nitrated proteins from pathological tissue samples to determine their roles. However, these methods contain a few technical problems such as low efficiencies with the detection of a limited number of nitrated proteins and labor intensiveness. Therefore, a systematic approach to efficiently identify nitrated proteins and characterize their functional roles is likely to shed new insights into understanding of the mechanisms of hepatic disease pathophysiology and subsequent development of new therapeutics. The aims of this review are to briefly describe the mechanisms of hepatic diseases. In addition, we specifically describe a systematic approach to efficiently identify nitrated proteins to study their causal roles or functional consequences in promoting acute and chronic liver diseases including alcoholic and nonalcoholic fatty liver diseases. We finally discuss translational research applications by analyzing nitrated proteins in evaluating the efficacies of potentially beneficial agents to prevent or treat various diseases in the liver and other tissues.

Role of adipose triglyceride lipase (PNPLA2) in protection from hepatic inflammation in mouse models of steatohepatitis and endotoxemia

Hepatic inflammation is a key feature of progressive liver disease. Alterations of fatty acid (FA) metabolism and signaling may play an important role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD) and its progression to nonalcoholic steatohepatitis (NASH). Moreover, FAs activate peroxisome proliferator-activated receptor α (PPARα) as a key transcriptional regulator of hepatic FA metabolism and inflammation. Since adipose triglyceride lipase (ATGL/PNPLA2) is the key enzyme for intracellular hydrolysis of stored triglycerides and determines FA signaling through PPARα, we explored the role of ATGL in hepatic inflammation in mouse models of NASH and endotoxemia. Mice lacking ATGL or hormone-sensitive lipase (HSL) were challenged with a methionine-choline-deficient (MCD) diet as a nutritional model of NASH or lipopolysaccharide (LPS) as a model of acute hepatic inflammation. We further tested whether a PPARα agonist (fenofibrate) treatment improves the hepatic phenotype in MCD- or LPS-challenged ATGL-knockout (KO) mice. MCD-fed ATGL-KO mice, although partially protected from peripheral lipolysis, showed exacerbated hepatic steatosis and inflammation. Moreover, ATGL-KO mice challenged by LPS showed enhanced hepatic inflammation, increased mortality, and torpor, findings which were attributed to impaired PPARα DNA binding activity due to reduced FABP1 protein levels, resulting in impaired nuclear FA import. Notably, liganding PPARα through fenofibrate attenuated hepatic inflammation in both MCD-fed and LPS-treated ATGL-KO mice. In contrast, mice lacking HSL had a phenotype similar to the WT mice on MCD and LPS challenge.

CONCLUSION

These findings unravel a novel protective role of ATGL against hepatic inflammation which could have important implications for metabolic and inflammatory liver diseases.

Activation of PPARα by Wy-14643 ameliorates systemic lipopolysaccharide-induced acute lung injury

Acute lung injury (ALI) is a major cause of mortality and morbidity worldwide. The activation of peroxisome proliferator-activated receptor-α (PPARα) by its ligands, which include Wy-14643, has been implicated as a potential anti-inflammatory therapy. To address the beneficial efficacy of Wy-14643 for ALI along with systemic inflammation, the in vivo role of PPARα activation was investigated in a mouse model of lipopolysaccharide (LPS)-induced ALI. Using age-matched Ppara-null and wild-type mice, we demonstrate that the activation of PPARα by Wy-14643 attenuated LPS-mediated ALI. This was evidenced histologically by the significant alleviation of inflammatory manifestations and apoptosis observed in the lung tissues of wild-type mice, but not in the corresponding Ppara-null mice. This protective effect probably resulted from the inhibition of LPS-induced increases in pro-inflammatory cytokines and nitroxidative stress levels. These results suggest that the pharmacological activation of PPARα might have a therapeutic effect on LPS-induced ALI.

Robust protein nitration contributes to acetaminophen-induced mitochondrial dysfunction and acute liver injury

Acetaminophen (APAP), a widely used analgesic/antipyretic agent, can cause liver injury through increased nitrative stress, leading to protein nitration. However, the identities of nitrated proteins and their roles in hepatotoxicity are poorly understood. Thus, we aimed at studying the mechanism of APAP-induced hepatotoxicity by systematic identification and characterization of nitrated proteins in the absence or presence of an antioxidant, N-acetylcysteine (NAC). The levels of nitrated proteins markedly increased at 2h in mice exposed to a single APAP dose (350mg/kg ip), which caused severe liver necrosis at 24h. Protein nitration and liver necrosis were minimal in mice exposed to nontoxic 3-hydroxyacetanilide or animals co-treated with APAP and NAC. Mass-spectral analysis of the affinity-purified nitrated proteins identified numerous mitochondrial and cytosolic proteins, including mitochondrial aldehyde dehydrogenase, Mn-superoxide dismutase, glutathione peroxidase, ATP synthase, and 3-ketoacyl-CoA thiolase, involved in antioxidant defense, energy supply, or fatty acid metabolism. Immunoprecipitation followed by immunoblot with anti-3-nitrotyrosine antibody confirmed that the aforementioned proteins were nitrated in APAP-exposed mice but not in NAC-cotreated mice. Consistently, NAC cotreatment significantly restored the suppressed activity of these enzymes. Thus, we demonstrate a new mechanism by which many nitrated proteins with concomitantly suppressed activity promotes APAP-induced mitochondrial dysfunction and hepatotoxicity.

Ethanol potentiates hepatitis B virus replication through oxidative stress-dependent and -independent transcriptional activation

Excessive alcohol intake accelerates disease progression in chronic hepatitis B virus (HBV) infection, but the mechanisms by which ethanol worsens the prognosis of chronic hepatitis B (CHB) are not fully understood. The aim of this study was to investigate whether HBV replication is augmented by alcohol or alcohol-induced cytochrome p450 2E1 (CYP2E1), and if so, whether oxidative stress is involved in the process. Ethanol treatment promoted HBV replication in HepAD38 cells that permit the conditional viral replication. Luciferase reporter assays confirmed that HBV core, preS1 and preS2/S promoter activities were augmented by ethanol. Ethanol did not induce oxidative stress in HepAD38 cells with minimal expression of CYP2E1. However, over-expression of CYP2E1 induced oxidative stress and amplified transcriptional activation of HBV by ethanol. Antioxidant glutathione treatment attenuated CYP2E1-mediated augmentation of HBV replication in ethanol-treated cells. In conclusion, ethanol enhances transcriptional activity of HBV promoters in human hepatoma cells in an oxidative stress-independent manner; and CYP2E1-mediated oxidative stress potentiates the ethanol-induced transactivation of HBV.

Post-translational modifications of mitochondrial aldehyde dehydrogenase and biomedical implications

Aldehyde dehydrogenases (ALDHs) represent large family members of NAD(P)+-dependent dehydrogenases responsible for the irreversible metabolism of many endogenous and exogenous aldehydes to the corresponding acids. Among 19 ALDH isozymes, mitochondrial ALDH2 is a low Km enzyme responsible for the metabolism of acetaldehyde and lipid peroxides such as malondialdehyde and 4-hydroxynonenal, both of which are highly reactive and toxic. Consequently, inhibition of ALDH2 would lead to elevated levels of acetaldehyde and other reactive lipid peroxides following ethanol intake and/or exposure to toxic chemicals. In addition, many East Asian people with a dominant negative mutation in ALDH2 gene possess a decreased ALDH2 activity with increased risks for various types of cancer, myocardial infarct, alcoholic liver disease, and other pathological conditions. The aim of this review is to briefly describe the multiple post-translational modifications of mitochondrial ALDH2, as an example, after exposure to toxic chemicals or under different disease states and their pathophysiological roles in promoting alcohol/drug-mediated tissue damage. We also briefly mention exciting preclinical translational research opportunities to identify small molecule activators of ALDH2 and its isozymes as potentially therapeutic/preventive agents against various disease states where the expression or activity of ALDH enzymes is altered or inactivated.