Interaction between fatty acid oxidation and ethanol metabolism in liver.

Fatty acid oxidation (FAO) releases the energy stored in fat to maintain basic biological processes. Dehydrogenation is a major way to oxidize fatty acids, which needs NAD+ to accept the released H+ from fatty acids and form NADH, which increases the ratio of NADH/NAD+ and consequently inhibits FAO leading to the deposition of fat in the liver, which is termed fatty liver or steatosis. Consumption of alcohol (ethanol) initiates simple steatosis that progresses to alcoholic steatohepatitis, which constitutes a spectrum of liver disorders called alcohol-associated liver disease (ALD). ALD is linked to ethanol metabolism. Ethanol is metabolized by alcohol dehydrogenase (ADH), microsomal ethanol oxidation system (MEOS), mainly cytochrome P450 2E1 (CYP2E1), and catalase. ADH also requires NAD+ to accept the released H+ from ethanol. Thus, ethanol metabolism by ADH leads to increased ratio of NADH/NAD+, which inhibits FAO and induces steatosis. CYP2E1 directly consumes reducing equivalent NADPH to oxidize ethanol, which generates reactive oxygen species (ROS) that lead to cellular injury. Catalase is mainly present in peroxisomes, where very long-chain fatty acids and branched-chain fatty acids are oxidized, and the resultant short-chain fatty acids will be further oxidized in mitochondria. Peroxisomal FAO generates hydrogen peroxide (H2O2), which is locally decomposed by catalase. When ethanol is present, catalase uses H2O2 to oxidize ethanol. In this review, we introduce FAO (including α-, ß-, and ω-oxidation) and ethanol metabolism (by ADH, CYP2E1, and catalase) followed by the interaction between FAO and ethanol metabolism in the liver and its pathophysiological significance.

Racial differences in the effect of APOE-ε4 genotypes on trail making test B in Alzheimer's disease: A longitudinal study.

OBJECTIVES: The trail making test part B (TMT-B) evaluates executive functions, memory, and sensorimotor functions. No previous study was found to examine the longitudinal effect of APOE-ε4 genotypes on the TMT-B scores in Alzheimer's disease (AD) across racial groups. METHODS: This study used the data from Alzheimer's Disease Neuroimaging Initiative (ADNI): 382 participants with AD, 503 with cognitive normal (CN), 1293 with mild cognitive impairment (MCI) at baseline and follow-up of four years. The multivariable linear mixed model was used to investigate the effect of APOE-ε4 genotypes on changes in TMT-B scores. RESULTS: Compared with Whites, African Americans (AA) and Hispanics had higher TMT-B scores (poor cognitive function). Furthermore, Whites subjects with 1 or 2 APOE-ε4 alleles had significantly higher TMT-B scores compared with individuals without APOE-ε4 allele at baseline and four follow-up visits; however, no differences in TMT-B were found between APOE-ε4 alleles in the Hispanic and AA groups. No APOE-ε4 by visit interactions was found for 3 racial groups. Stratified by AD diagnosis, the APOE-ε4 allele was associated with TMT-B scores only in the MCI group, while there were significant interactions for visit by education, APOE-ε4 allele, and the Mini Mental State Examination (MMSE) score in the MCI group. In addition, TMT-B was significantly correlated with the MMSE, AD Assessment Scale-cognitive subscale 13 (ADAS13), tTau, pTau, Aß42, and hippocampus. CONCLUSIONS: APOE-ɛ4 allele is associated with TMT-B scores in Whites subjects, but not in the Hispanic and AA groups. APOE-ε4 showed interaction with visit in the MCI group.

Alcoholic fatty liver is blunted by rFGF21 administration in mice lacking adipose FGFR1: The role of FGF21 in PPARα-mediated regulation of adipose tissue mass.

Fibroblast growth factor 21 (FGF21) is regulated by peroxisome proliferator activated receptor α (PPARα) in the liver. FGF21 regulates lipid metabolism via fibroblast growth factor receptor 1 (FGFR1). FGF21 protect against alcoholic fatty liver (AFL), however, FGF21 does not exert protective effect through liver FGFR1. We have previously shown that PPARα agonist WY-14,643 induces FGF21 and adipose atrophy but fails to protect against chronic ethanol-induced AFL in mice lacking adipose FGFR1. In this study we tested the direct role of the FGF21 in regulation of adipose tissue mass and ethanol induced-hepatic triglyceride (TG) accumulation in normal control (fgfr1fl/fl) mice and in adipose FGFR1 knockout mice (fgfr1adipoQ-cre). First, we tested whether WY-14,643 effects on adipose atrophy and AFL can be recapitulated in binge alcohol model. As in chronic model, adipose tissue mass and serum free fatty acid (FFA) were decreased by WY-14,643 in the fgfr1adipoQ-cre mice but not in the fgfr1fl/fl mice. However, in contrast to the chronic model, binge ethanol-induced AFL was blunted by WY-14,643 to a greater extent in the fgfr1adipoQ-cre mice than in the fgfr1fl/fl mice. Similarly, circulating FGF21 was elevated by binge ethanol to a greater extent in the fgfr1adipoQ-cre mice than in the fgfr1fl/fl mice on top of WY-14,643 treatment. Accordingly, we tested the involvement of the FGF21 in adipose atrophy and AFL. Consistent with FGFR1-dependent effects of WY-14,643 on adipose atrophy and AFL, recombinant mouse FGF21 (rFGF21) injection induced adipose atrophy, blunted AFL and serum TG elevation to a greater extent in the fgfr1adipoQ-cre mice than in the fgfr1fl/fl mice. These results indicated the consistency of adipose FGFR1 dependent effect of WY-14,643 and FGF21 in PPARα-mediated regulation of adipose tissue mass and fat mobilization from adipose tissues to the liver, suggesting that adipose tissues crosstalk with liver through an interaction between liver PPARα-FGF21 and adipose FGFR1 to maintain adipose tissue mass.

PPARα agonist WY-14,643 induces the PLA2/COX-2/ACOX1 pathway to enhance peroxisomal lipid metabolism and ameliorate alcoholic fatty liver in mice.

Peroxisome proliferator-activated receptor α (PPARα) regulates fatty acid oxidation (FAO). Usually, very-long chain fatty acids are first activated by acyl-CoA synthetase (ACS) to generate acyl-CoA for oxidation by acyl-CoA oxidase (ACOX) in peroxisomes, and the resultant shorter chain fatty acids will be further oxidized in mitochondria. ACS long-chain family member 4 (ACSL4) preferentially uses arachidonic acid (AA) as substrates to synthesize arachidonoyl-CoA. Arachidonoyl-CoA is usually esterified into phospholipids. When AA is released by phospholipase A2 (PLA2) from phospholipids, it will be used for prostaglandin synthesis by cyclooxygenases (COX). In this study, when PPARα agonist WY-14,643 was mixed in liquid Lieber-DeCarli ethanol or control diets and fed to mice, liver PLA2, COX-2, and ACOX1 were induced but ACSL4 was inhibited, suggesting that AA released by PLA2 from phospholipid will be metabolized to prostaglandin via COX-2 instead of being synthesized into acyl-CoA by ACSL4. However, liver prostaglandin E2 (PGE2), a major component of prostaglandin, was not increased with the induced COX-2 but decreased by WY-14,643. ACOX1 specific inhibitor mixed in the liquid diets restored both the WY-14,643-suppressed liver TG and PGE2, but COX-2 specific inhibitor celecoxib mixed in the liquid diets reversed the WY-14,643-suppressed liver TG but not liver PGE2 contents. These results suggest that induction of PLA2, COX-2 and ACOX1 orchestrates to increase oxidation of AA/PGE2, which constitutes one new mechanism by which PPARα induces peroxisomal FAO and inhibits ethanol-induced liver fat accumulation.

High-fat diet induces fibrosis in mice lacking CYP2A5 and PPARα: a new model for steatohepatitis-associated fibrosis.

Obesity is linked to nonalcoholic steatohepatitis. Peroxisome proliferator-activated receptor-α (PPARα) regulates lipid metabolism. Cytochrome P-450 2A5 (CYP2A5) is a potential antioxidant and CYP2A5 induction by ethanol is CYP2E1 dependent. High-fat diet (HFD)-induced obesity and steatosis are more severe in CYP2A5 knockout (cyp2a5-/-) mice than in wild-type mice although PPARα is elevated in cyp2a5-/- mice. To examine why the upregulated PPARα failed to prevent the enhanced steatosis in cyp2a5-/- mice, we abrogate the upregulated PPARα in cyp2a5-/- mice by cross-breeding cyp2a5-/- mice with PPARα knockout (pparα-/-) mice to create pparα-/-/cyp2a5-/- mice. The pparα-/-/cyp2a5-/- mice, pparα-/- mice, and cyp2a5-/- mice were fed HFD to induce steatosis. After HFD feeding, more severe steatosis was developed in pparα-/-/cyp2a5-/- mice than in pparα-/- mice and cyp2a5-/- mice. The pparα-/-/cyp2a5-/- mice and pparα-/- mice exhibited comparable and impaired lipid metabolism. Elevated serum alanine transaminase and liver interleukin-1ß, liver inflammatory cell infiltration, and foci of hepatocellular ballooning were observed in pparα-/-/cyp2a5-/- mice but not in pparα-/- mice and cyp2a5-/- mice. In pparα-/-/cyp2a5-/- mice, although redox-sensitive transcription factor nuclear factor erythroid 2-related factor 2 and its target antioxidant genes were upregulated as a compensation, thioredoxin was suppressed, and phosphorylation of JNK and formation of nitrotyrosine adduct were increased. Liver glutathione was decreased, and lipid peroxidation was increased. Interestingly, inflammation and fibrosis were all observed within the clusters of lipid droplets, and these lipid droplet clusters were all located inside the area with CYP2E1-positive staining. These results suggest that HFD-induced fibrosis in pparα-/-/cyp2a5-/- mice is associated with steatosis, and CYP2A5 interacts with PPARα to participate in regulating steatohepatitis-associated fibrosis.

Suppressed hepatocyte proliferation via a ROS-HNE-P21 pathway is associated with nicotine- and cotinine-enhanced alcoholic fatty liver in mice.

CYP2A5 is a major enzyme responsible for nicotine and cotinine metabolism in mice. Nicotine and cotinine enhance alcoholic fatty liver in wild type (WT) mice but not in CYP2A5 knockout (KO) mice, and reactive oxygen species (ROS) generated during the CYP2A5-mediated metabolism contributes to the enhancing effect. In combination with ethanol, nicotine and cotinine increased lipid peroxidation end product 4-hydroxynonenal (HNE) in WT mice but not in KO mice. In ethanol-fed KO mice, only 5 and 10 genes were regulated by nicotine and cotinine, respectively. However, in ethanol-fed WT mice, 59 and 104 genes were regulated by nicotine and cotinine, respectively, and 7 genes were up-regulated by both nicotine and cotinine. Plin 2 and Cdkn1a are among the 7 genes. Plin2 encodes adipose differentiation-related protein (ADRP), a lipid droplet-associated protein, which was confirmed to be increased by nicotine and cotinine in WT mice but not in KO mice. Cdkn1a encodes P21 and elevated P21 in nuclei was also confirmed. HNE can increase P21 and P21 inhibit cell proliferation. Consistently, hepatocyte proliferation markers proliferating cell nuclear antigen (PCNA) and Ki67 were decreased in WT mice but not in KO mice by nicotine/ethanol and cotinine/ethanol, respectively. These results suggest that inhibition of liver proliferation via a ROS-HNE-P21 pathway is involved in nicotine- and cotinine-enhanced alcoholic fatty liver.

CYP2A6 is associated with obesity: studies in human samples and a high fat diet mouse model.

BACKGROUND/OBJECTIVES: CYP2A6 (CYP2A5 in mice) is mainly expressed in the liver. Hepatic CYP2A6 expression is increased in patients with non-alcoholic fatty liver disease (NAFLD). In mice, hepatic CYP2A5 is induced by high fat diet (HFD) feeding. Hepatic CYP2A5 is also increased in monosodium glutamate-induced obese mice. NAFLD is associated with obesity. In this study, we examined whether obesity is related to CYP2A6. SUBJECTS/METHODS: Obesity genetic association study: The SAGE is a comprehensive genome-wide association study (GWAS) with case subjects having a lifetime history of alcohol dependence and control subjects never addicted to alcohol. We used 1030 control individuals with self-reported height and weight. A total of 12 single nucleotide polymorphisms (SNP) within the CYP2A6 gene were available. Obesity was determined as a BMI ≥30: 30-34.9 (Class I obesity) and ≥35 (Class II and III obesity). Animal experiment study: CYP2A5 knockout (cyp2a5-/-) mice and wild type (cyp2a5+/+) mice were fed HFD for 14 weeks. Body weight was measured weekly. After an overnight fast, the mice were sacrificed. Liver and blood were collected for biochemical assays. RESULTS: Single marker analysis showed that three SNPs (rs8192729, rs7256108, and rs7255443) were associated with class I obesity (p < 0.05). The most significant SNP for obesity was rs8192729 (odds ratio (OR) = 1.94, 95% confidence intervals = 1.21-3.10, p = 0.00582). After HFD feeding, body weight was increased in cyp2a5-/- mice to a greater extent than in cyp2a5+/+ mice, and fatty liver was more pronounced in cyp2a5-/- mice than in cyp2a5+/+ mice. PPARα deficiency in cyp2a5-/- mice developed more severe fatty liver, but body weight was not increased significantly. CONCLUSION: CYP2A6 is associated with human obesity; CYP2A5 protects against obesity and NAFLD in mice. PPARα contributes to the CYP2A5 protective effects on fatty liver but it opposes to the protective effects on obesity.

Nicotine enhances alcoholic fatty liver in mice: Role of CYP2A5.

Tobacco and alcohol are often co-abused. Nicotine can enhance alcoholic fatty liver, and CYP2A6 (CYP2A5 in mice), a major metabolism enzyme for nicotine, can be induced by alcohol. CYP2A5 knockout (cyp2a5-/-) mice and their littermates (cyp2a5+/+) were used to test whether CYP2A5 has an effect on nicotine-enhanced alcoholic fatty liver. The results showed that alcoholic fatty liver was enhanced by nicotine in cyp2a5+/+ mice but not in the cyp2a5-/- mice. Combination of ethanol and nicotine increased serum triglyceride in cyp2a5+/+ mice but not in the cyp2a5-/- mice. Cotinine, a major metabolite of nicotine, also enhanced alcoholic fatty liver, which was also observed in cyp2a5+/+ mice but not in the cyp2a5-/- mice. Nitrotyrosine and malondialdehyde (MDA), markers of oxidative/nitrosative stress, were induced by alcohol and were further increased by nicotine and cotinine in cyp2a5+/+ mice but not in the cyp2a5-/- mice. Reactive oxygen species (ROS) production during microsomal metabolism of nicotine and cotinine was increased in microsomes from cyp2a5+/+ mice but not in microsomes from cyp2a5-/- mice. These results suggest that nicotine enhances alcoholic fatty liver in a CYP2A5-dependent manner, which is related to ROS produced during the process of CYP2A5-dependent nicotine metabolism.

Signalling via the osteopontin and high mobility group box-1 axis drives the fibrogenic response to liver injury.

OBJECTIVE: Liver fibrosis is associated with significant collagen-I deposition largely produced by activated hepatic stellate cells (HSCs); yet, the link between hepatocyte damage and the HSC profibrogenic response remains unclear. Here we show significant induction of osteopontin (OPN) and high-mobility group box-1 (HMGB1) in liver fibrosis. Since OPN was identified as upstream of HMGB1, we hypothesised that OPN could participate in the pathogenesis of liver fibrosis by increasing HMGB1 to upregulate collagen-I expression. DESIGN AND RESULTS: Patients with long-term hepatitis C virus (HCV) progressing in disease stage displayed enhanced hepatic OPN and HMGB1 immunostaining, which correlated with fibrosis stage, whereas it remained similar in non-progressors. Hepatocyte cytoplasmic OPN and HMGB1 expression was significant while loss of nuclear HMGB1 occurred in patients with HCV-induced fibrosis compared with healthy explants. Well-established liver fibrosis along with marked induction of HMGB1 occurred in CCl4-injected OpnHep transgenic yet it was less in wild type and almost absent in Opn-/- mice. Hmgb1 ablation in hepatocytes (Hmgb1ΔHep) protected mice from CCl4-induced liver fibrosis. Coculture with hepatocytes that secrete OPN plus HMGB1 and challenge with recombinant OPN (rOPN) or HMGB1 (rHMGB1) enhanced collagen-I expression in HSCs, which was blunted by neutralising antibodies (Abs) and by Opn or Hmgb1 ablation. rOPN induced acetylation of HMGB1 in HSCs due to increased NADPH oxidase activity and the associated decrease in histone deacetylases 1/2 leading to upregulation of collagen-I. Last, rHMGB1 signalled via receptor for advanced glycation end-products and activated the PI3K-pAkt1/2/3 pathway to upregulate collagen-I. CONCLUSIONS: During liver fibrosis, the increase in OPN induces HMGB1, which acts as a downstream alarmin driving collagen-I synthesis in HSCs.

High mobility group box-1 (HMGB1) participates in the pathogenesis of alcoholic liver disease (ALD).

Growing clinical and experimental evidence suggests that sterile inflammation contributes to alcoholic liver disease (ALD). High mobility group box-1 (HMGB1) is highly induced during liver injury; however, a link between this alarmin and ALD has not been established. Thus, the aim of this work was to determine whether HMGB1 contributes to the pathogenesis of ALD. Liver biopsies from patients with ALD showed a robust increase in HMGB1 expression and translocation, which correlated with disease stage, compared with healthy explants. Similar findings were observed in chronic ethanol-fed wild-type (WT) mice. Using primary cell culture, we validated the ability of hepatocytes from ethanol-fed mice to secrete a large amount of HMGB1. Secretion was time- and dose-dependent and responsive to prooxidants and antioxidants. Selective ablation of Hmgb1 in hepatocytes protected mice from alcohol-induced liver injury due to increased carnitine palmitoyltransferase-1, phosphorylated 5'AMP-activated protein kinase-α, and phosphorylated peroxisome proliferator-activated receptor-α expression along with elevated LDL plus VLDL export. Native and post-translationally modified HMGB1 were detected in humans and mice with ALD. In liver and serum from control mice and in serum from healthy volunteers, the lysine residues within the peptides containing nuclear localization signals (NLSs) 1 and 2 were non-acetylated, and all cysteine residues were reduced. However, in livers from ethanol-fed mice, in addition to all thiol/non-acetylated isoforms of HMGB1, we observed acetylated NLS1 and NLS2, a unique phosphorylation site in serine 35, and an increase in oxidation of HMGB1 to the disulfide isoform. In serum from ethanol-fed mice and from patients with ALD, there was disulfide-bonded hyperacetylated HMGB1, disulfide-bonded non-acetylated HMGB1, and HMGB1 phosphorylated in serine 35. Hepatocytes appeared to be a major source of these HMGB1 isoforms. Thus, hepatocyte HMGB1 participates in the pathogenesis of ALD and undergoes post-translational modifications (PTMs) that could condition its toxic effects.

Osteopontin binding to lipopolysaccharide lowers tumor necrosis factor-α and prevents early alcohol-induced liver injury in mice.

UNLABELLED: Although osteopontin (OPN) is induced in alcoholic patients, its role in the pathophysiology of alcoholic liver disease (ALD) remains unclear. Increased translocation of lipopolysaccharide (LPS) from the gut is key for the onset of ALD because it promotes macrophage infiltration and activation, tumor necrosis factor-α (TNFα) production, and liver injury. Since OPN is protective for the intestinal mucosa, we postulated that enhancing OPN expression in the liver and consequently in the blood and/or in the gut could protect from early alcohol-induced liver injury. Wild-type (WT), OPN knockout (Opn(-/-)), and transgenic mice overexpressing OPN in hepatocytes (Opn(HEP) Tg) were fed either the control or the ethanol Lieber-DeCarli diet. Ethanol increased hepatic, plasma, biliary, and fecal OPN more in Opn(HEP) Tg than in WT mice. Steatosis was less in ethanol-treated Opn(HEP) Tg mice as shown by decreased liver-to-body weight ratio, hepatic triglycerides, the steatosis score, oil red-O staining, and lipid peroxidation. There was also less inflammation and liver injury as demonstrated by lower alanine aminotransferase (ALT) activity, hepatocyte ballooning degeneration, LPS levels, the inflammation score, and the number of macrophages and TNFα(+) cells. To establish if OPN could limit LPS availability and its noxious effects in the liver, binding studies were performed. OPN showed binding affinity for LPS which prevented macrophage activation, reactive oxygen, and nitrogen species generation and TNFα production. Treatment with milk OPN (m-OPN) blocked LPS translocation in vivo and protected from early alcohol-induced liver injury. CONCLUSION: Natural induction plus forced overexpression of OPN in the liver or treatment with m-OPN protect from early alcohol-induced liver injury by blocking the gut-derived LPS and TNFα effects in the liver.

Synergistic toxic interactions between CYP2E1, LPS/TNFα, and JNK/p38 MAP kinase and their implications in alcohol-induced liver injury.

The mechanisms by which alcohol causes cell injury are not clear. Many pathways have been suggested to play a role in how alcohol induces oxidative stress. Considerable attention has been given to alcohol-elevated production of lipopolysaccharide (LPS) and TNFα and to alcohol induction of CYP2E1. These two pathways are not exclusive of each other; however, associations and interactions between them, especially in vivo, have not been extensively evaluated. We have shown that increased oxidative stress from induction of CYP2E1 in vivo sensitizes hepatocytes to LPS and TNFα toxicity and that oxidative stress, activation of p38 and JNK MAP kinases, and mitochondrial dysfunction are downstream mediators of this CYP2E1-LPS/TNFα potentiated hepatotoxicity. This Review will summarize studies showing potentiated interactions between these two risk factors in promoting liver injury and the mechanisms involved including activation of the mitogen-activated kinase kinase kinase ASK-1 as a result of CYP2E1-derived reactive oxygen intermediates promoting dissociation of the inhibitory thioredoxin from ASK-1. This activation of ASK-1 is followed by activation of the mitogen-activated kinase kinases MKK3/MKK6 and MKK4/MMK7 and subsequently p38 and JNK MAP kinases. Synergistic toxicity occurs between CYP2E1 and the JNK1 but not the JNK2 isoform as JNK1 knockout mice are completely protected against CYP2E1 plus TNFα toxicity, elevated oxidative stress, and mitochondrial dysfunction. We hypothesize that similar interactions occur as a result of ethanol induction of CYP2E1 and TNFα.

Osteopontin induces ductular reaction contributing to liver fibrosis.

OBJECTIVE: In human chronic liver disease, there is association between ductular reaction (DR) and fibrosis; yet, the mechanism triggering its onset and its role in scar formation remains unknown. Since we previously showed that osteopontin (OPN) is highly induced during drug-induced liver fibrosis, we hypothesised that OPN could drive oval cells (OC) expansion and DR and signal to hepatic stellate cells (HSC) to promote scarring. RESULTS: In vivo studies demonstrated increased OPN expression in biliary epithelial cells (BEC) and in OC in thioacetamide (TAA)-treated mice. OPN ablation protected mice from TAA and bile duct ligation-induced liver injury, DR and scarring. This was associated with greater hepatocyte proliferation, lower OC expansion and DR along with less fibrosis, suggesting that OPN could activate the OC compartment to differentiate into BEC, which could then signal to HSC to enhance scarring. Since TAA-treated wild-type mice and cirrhotic patients showed TGF-ß(+) BEC, which were lacking in TAA-treated Opn(-/-) mice and in healthy human explants, this suggested that OPN could regulate TGF-ß, a profibrogenic factor. In vitro experiments confirmed that recombinant OPN (rOPN) decreases hepatocyte proliferation and increases OC and BEC proliferation. To evaluate how BEC regulate collagen-I production in HSC, co-cultures were established. Co-cultured BEC upregulated OPN and TGF-ß expression and enhanced collagen-I synthesis by HSC. Lastly, recombinant TGF-ß (rTGFß) and rOPN promoted BEC proliferation and neutralisation of OPN and TGF-ß reduced collagen-I expression in co-cultured HSC. CONCLUSIONS: OPN emerges as a key matricellular protein driving DR and contributing to scarring and liver fibrosis via TGF-ß.

Ethanol plus the Jo2 Fas agonistic antibody-induced liver injury is attenuated in mice with partial ablation of argininosuccinate synthase.

BACKGROUND: Argininosuccinate synthase (ASS) is an enzyme shared by the urea cycle and the l-citrulline/nitric oxide (NO·) cycle. ASS is the rate-limiting enzyme in the urea cycle and along with nitric oxide synthase 2 (NOS2), it endows cells with the l-citrulline/NO· salvage pathway to continuously supply l-arginine from l-citrulline for sustained NO· generation. Thus, ASS conditions NO· synthesis by NOS2. Because of the relevance of NOS2 activation for liver injury, we examined the contribution of ASS to NO· generation and how it impacts liver injury. METHODS: Wild-type (WT) mice and Ass(+/-) mice (Ass(-/-) mice are lethal) were intraperitoneally injected with ethanol (EtOH) at a dose of 2.5 g/kg of body weight twice a day for 3 days. Two hours after the last dose of EtOH, mice were administered the agonistic Jo2 anti-mouse Fas monoclonal antibody (Ab) at a dose of 0.2 µg/g of body weight. Mice were sacrificed 8 hours after the Jo2 Ab injection. Markers of nitrosative and oxidative stress as well as liver damage were analyzed. RESULTS: EtOH plus Jo2 injection induced liver injury as shown by serum alanine aminotransferase and aspartate aminotransferase activity, liver pathology, TUNEL, and cleaved caspase-3 were lower in Ass(+/-) mice compared with WT mice, suggesting that ASS contributes to EtOH plus Jo2-mediated liver injury. CYP2E1 induction, glutathione depletion, and elevated thiobarbituric acid reactive substances were comparable in both groups of mice, suggesting that CYP2E1-mediated oxidative stress is not linked to ASS-induced liver injury. In contrast, NOS2 induction, 3-nitrotyrosine adducts formation and elevated nitrites, nitrates, and S-nitrosothiols were higher in livers from WT mice than from Ass(+/-) mice. CONCLUSION: Decreased nitrosative stress causes lower EtOH plus Jo2-induced liver injury in Ass(+/-) mice.

Cellular and molecular mechanisms of hepatic ischemia-reperfusion injury: The role of oxidative stress and therapeutic approaches.

Ischemia-reperfusion (IR) or reoxygenation injury is the paradoxical exacerbation of cellular impairment following restoration of blood flow after a period of ischemia during surgical procedures or other conditions. Acute interruption of blood supply to the liver and subsequent reperfusion can result in hepatocyte injury, apoptosis, and necrosis. Since the liver requires a continuous supply of oxygen for many biochemical reactions, any obstruction of blood flow can rapidly lead to hepatic hypoxia, which could quickly progress to absolute anoxia. Reoxygenation results in the increased generation of reactive oxygen species and oxidative stress, which lead to the enhanced production of proinflammatory cytokines, chemokines, and other signaling molecules. Consequent acute inflammatory cascades lead to significant impairment of hepatocytes and nonparenchymal cells. Furthermore, the expression of several vascular growth factors results in the heterogeneous closure of numerous hepatic sinusoids, which leads to reduced oxygen supply in certain areas of the liver even after reperfusion. Therefore, it is vital to identify appropriate therapeutic modalities to mitigate hepatic IR injury and subsequent tissue damage. This review covers all the major aspects of cellular and molecular mechanisms underlying the pathogenesis of hepatic ischemia-reperfusion injury, with special emphasis on oxidative stress, associated inflammation and complications, and prospective therapeutic approaches.

Hepatocyte-Specific PEX16 Abrogation in Mice Leads to Hepatocyte Proliferation, Alteration of Hepatic Lipid Metabolism, and Resistance to High-Fat Diet (HFD)-Induced Hepatic Steatosis and Obesity.

Obesity results in hepatic fat accumulation, i.e., steatosis. In addition to fat overload, impaired fatty acid ß-oxidation also promotes steatosis. Fatty acid ß-oxidation takes place in the mitochondria and peroxisomes. Usually, very long-chain and branched-chain fatty acids are the first to be oxidized in peroxisomes, and the resultant short chain fatty acids are further oxidized in the mitochondria. Peroxisome biogenesis is regulated by peroxin 16 (PEX16). In liver-specific PEX16 knockout (Pex16Alb-Cre) mice, hepatocyte peroxisomes were absent, but hepatocytes proliferated, and liver mass was enlarged. These results suggest that normal liver peroxisomes restrain hepatocyte proliferation and liver sizes. After high-fat diet (HFD) feeding, body weights were increased in PEX16 floxed (Pex16fl/fl) mice and adipose-specific PEX16 knockout (Pex16AdipoQ-Cre) mice, but not in the Pex16Alb-Cre mice, suggesting that the development of obesity is regulated by liver PEX16 but not by adipose PEX16. HFD increased liver mass in the Pex16fl/fl mice but somehow reduced the already enlarged liver mass in the Pex16Alb-Cre mice. The basal levels of serum triglyceride, free fatty acids, and cholesterol were decreased, whereas serum bile acids were increased in the Pex16Alb-Cre mice, and HFD-induced steatosis was not observed in the Pex16Alb-Cre mice. These results suggest that normal liver peroxisomes contribute to the development of liver steatosis and obesity.

Milk osteopontin, a nutritional approach to prevent alcohol-induced liver injury.

Alcohol consumption is a leading cause of liver disease worldwide; thus, there is an urgent need to develop novel therapeutic interventions. Key events for the onset and progression of alcoholic liver disease result in part from the gut-to-liver interaction. Osteopontin is a cytokine present at high concentration in human milk, umbilical cord, and infants' plasma with beneficial potential. We hypothesized that dietary administration of milk osteopontin could prevent alcohol-induced liver injury perhaps by maintaining gut integrity and averting hepatic inflammation and steatosis. Wild-type mice were fed either the control or the ethanol Lieber-DeCarli diets alone or in combination with milk osteopontin for 3 wk, and parameters of gut and liver damage were measured. Milk osteopontin protected the stomach and the gut by increasing gland height, crypt cell plus enterocyte proliferation, and mucin content in addition to lowering macrophages, plasmacytes, lymphocytes, and neutrophils in the mucosa and submucosa in alcohol-fed mice. Milk osteopontin targeted the gut-liver axis, preserving the expression of tight-junction proteins in alcohol-fed mice thus maintaining intestinal integrity and permeability. There was protection from liver injury since transaminases, the activity scores, triglyceride levels, neutrophil infiltration, 3-nitrotyrosine residues, lipid peroxidation end products, translocation of gram-negative bacteria, lipopolysaccharide levels, and tumor necrosis factor-α were lower in cotreated than in ethanol-fed mice. Furthermore, milk osteopontin diminished ethanol-mediated liver injury in OPN knockout mice. Milk osteopontin could be a simple effective nutritional therapeutic strategy to prevent alcohol hepatotoxicity due, among others, to gut protective, anti-inflammatory, and anti-steatotic actions.

Fibromodulin, an oxidative stress-sensitive proteoglycan, regulates the fibrogenic response to liver injury in mice.

BACKGROUND & AIMS: Collagen I deposition contributes to liver fibrosis, yet little is known about other factors that mediate this process. Fibromodulin is a liver proteoglycan that regulates extracellular matrix organization and is induced by fibrogenic stimuli. We propose that fibromodulin contributes to the pathogenesis of fibrosis by regulating the fibrogenic phenotype of hepatic stellate cells (HSCs). METHODS: We analyzed liver samples from patients with hepatitis C-associated cirrhosis and healthy individuals (controls). We used a coculture model to study interactions among rat HSCs, hepatocytes, and sinusoidal endothelial cells. We induced fibrosis in livers of wild-type and Fmod(-/-) mice by bile duct ligation, injection of CCl(4), or administration of thioacetamide. RESULTS: Liver samples from patients with cirrhosis had higher levels of fibromodulin messenger RNA and protein than controls. Bile duct ligation, CCl(4), and thioacetamide each increased levels of fibromodulin protein in wild-type mice. HSCs, hepatocytes, and sinusoidal endothelial cells produced and secreted fibromodulin. Infection of HSCs with an adenovirus that expressed fibromodulin increased expression of collagen I and α-smooth muscle actin, indicating increased activation of HSCs and fibrogenic potential. Recombinant fibromodulin promoted proliferation, migration, and invasion of HSCs, contributing to their fibrogenic activity. Fibromodulin was sensitive to reactive oxygen species. HepG2 cells that express cytochrome P450 2E1 produced fibromodulin, and HSCs increased fibromodulin production in response to pro-oxidants. In mice, administration of an antioxidant prevented the increase in fibromodulin in response to CCl(4). Coculture of hepatocytes or sinusoidal endothelial cells with HSCs increased the levels of reactive oxygen species in the culture medium, along with collagen I and fibromodulin proteins; this increase was prevented by catalase. Fibromodulin bound to collagen I, but the binding did not prevent collagen I degradation by matrix metalloproteinase 13. Bile duct ligation caused liver fibrosis in wild-type but not Fmod(-/-) mice. CONCLUSIONS: Fibromodulin levels are increased in livers of patients with cirrhosis. Hepatic fibromodulin activates HSCs and promotes collagen I deposition, which leads to liver fibrosis in mice.

Argininosuccinate synthase conditions the response to acute and chronic ethanol-induced liver injury in mice.

UNLABELLED: Argininosuccinate synthase (ASS) is the rate-limiting enzyme in both the urea and the L-citrulline/nitric oxide (NO·) cycles regulating protein catabolism, ammonia levels, and NO· generation. Because a proteomics analysis identified ASS and nitric oxide synthase-2 (NOS2) as coinduced in rat hepatocytes by chronic ethanol consumption, which also occurred in alcoholic liver disease (ALD) and in cirrhosis patients, we hypothesized that ASS could play a role in ethanol binge and chronic ethanol-induced liver damage. To investigate the contribution of ASS to the pathophysiology of ALD, wildtype (WT) and Ass(+/-) mice (Ass(-/-) are lethal due to hyperammonemia) were exposed to an ethanol binge or to chronic ethanol drinking. Compared with WT, Ass(+/-) mice given an ethanol binge exhibited decreased steatosis, lower NOS2 induction, and less 3-nitrotyrosine (3-NT) protein residues, indicating that reducing nitrosative stress by way of the L-citrulline/NO· pathway plays a significant role in preventing liver damage. However, chronic ethanol-treated Ass(+/-) mice displayed enhanced liver injury compared with WT mice. This was due to hyperammonemia, lower phosphorylated AMP-activated protein kinase alpha (pAMPKα) to total AMPKα ratio, decreased sirtuin-1 (Sirt-1) and peroxisomal proliferator-activated receptor coactivator-1α (Pgc1α) messenger RNAs (mRNAs), lower fatty acid ß-oxidation due to down-regulation of carnitine palmitoyl transferase-II (CPT-II), decreased antioxidant defense, and elevated lipid peroxidation end-products in spite of comparable nitrosative stress but likely reduced NOS3. CONCLUSION: Partial Ass ablation protects only in acute ethanol-induced liver injury by decreasing nitrosative stress but not in a more chronic scenario where oxidative stress and impaired fatty acid ß-oxidation are key events.

Osteopontin, an oxidant stress sensitive cytokine, up-regulates collagen-I via integrin α(V)ß(3) engagement and PI3K/pAkt/NFκB signaling.

UNLABELLED: A key feature in the pathogenesis of liver fibrosis is fibrillar Collagen-I deposition; yet, mediators that could be key therapeutic targets remain elusive. We hypothesized that osteopontin (OPN), an extracellular matrix (ECM) cytokine expressed in hepatic stellate cells (HSCs), could drive fibrogenesis by modulating the HSC pro-fibrogenic phenotype and Collagen-I expression. Recombinant OPN (rOPN) up-regulated Collagen-I protein in primary HSCs in a transforming growth factor beta (TGFß)-independent fashion, whereas it down-regulated matrix metalloprotease-13 (MMP13), thus favoring scarring. rOPN activated primary HSCs, confirmed by increased α-smooth muscle actin (αSMA) expression and enhanced their invasive and wound-healing potential. HSCs isolated from wild-type (WT) mice were more profibrogenic than those from OPN knockout (Opn(-/-)) mice and infection of primary HSCs with an Ad-OPN increased Collagen-I, indicating correlation between both proteins. OPN induction of Collagen-I occurred via integrin α(v)ß(3) engagement and activation of the phosphoinositide 3-kinase/phosphorylated Akt/nuclear factor kappa B (PI3K/pAkt/NFκB)-signaling pathway, whereas cluster of differentiation 44 (CD44) binding and mammalian target of rapamycin/70-kDa ribosomal protein S6 kinase (mTOR/p70S6K) were not involved. Neutralization of integrin α(v) ß(3) prevented the OPN-mediated activation of the PI3K/pAkt/NFκB-signaling cascade and Collagen-I up-regulation. Likewise, inhibition of PI3K and NFκB blocked the OPN-mediated Collagen-I increase. Hepatitis C Virus (HCV) cirrhotic patients showed coinduction of Collagen-I and cleaved OPN compared to healthy individuals. Acute and chronic liver injury by CCl(4) injection or thioacetamide (TAA) treatment elevated OPN expression. Reactive oxygen species up-regulated OPN in vitro and in vivo and antioxidants prevented this effect. Transgenic mice overexpressing OPN in hepatocytes (Opn(HEP) Tg) mice developed spontaneous liver fibrosis compared to WT mice. Last, chronic CCl(4) injection and TAA treatment caused more liver fibrosis to WT than to Opn(-/-) mice and the reverse occurred in Opn(HEP) Tg mice. CONCLUSION: OPN emerges as a key cytokine within the ECM protein network driving the increase in Collagen-I protein contributing to scarring and liver fibrosis.