Nrf2 pathway activation contributes to anti-fibrosis effects of ginsenoside Rg1 in a rat model of alcohol- and CCl4-induced hepatic fibrosis

Aim:

To investigate the anti-fibrosis effects of ginsenoside Rg1 on alcohol- and CCl₄-induced hepatic fibrosis in rats and to explore the mechanisms of the effects.

Methods:

Rats were given 6% alcohol in water and injected with CCl₄ (2 mL/kg, sc) twice a week for 8 weeks. Rg1 (10, 20 and 40 mg/kg per day, po) was administered in the last 2 weeks. Hepatic fibrosis was determined by measuring serum biochemical parameters, HE staining, Masson''s trichromic staining, and hydroxyproline and α-SMA immunohistochemical staining of liver tissues. The activities of antioxidant enzymes, lipid peroxidation, and Nrf2 signaling pathway-related proteins (Nrf2, Ho-1 and Nqo1) in liver tissues were analyzed. Cultured hepatic stellate cells (HSCs) of rats were prepared for in vitro studies.

Results:

In the alcohol- and CCl₄-treated rats, Rg1 administration dose-dependently suppressed the marked increases of serum ALT, AST, LDH and ALP levels, inhibited liver inflammation and HSC activation and reduced liver fibrosis scores. Rg1 significantly increased the activities of antioxidant enzymes (SOD, GSH-Px and CAT) and reduced MDA levels in liver tissues. Furthermore, Rg1 significantly increased the expression and nuclear translocation of Nrf2 that regulated the expression of many antioxidant enzymes. Treatment of the cultured HSCs with Rg1 (1 μmol/L) induced Nrf2 translocation, and suppressed CCl₄-induced cell proliferation, reversed CCl_4- induced changes in MDA, GPX, PCIII and HA contents in the supernatant fluid and α-SMA expression in the cells. Knockdown of Nrf2 gene diminished these actions of Rg1 in CCl₄-treated HSCs in vitro.

Conclusion:

Rg1 exerts protective effects in a rat model of alcohol- and CCl₄-induced hepatic fibrosis via promoting the nuclear translocation of Nrf2 and expression of antioxidant enzymes.     

基于Nrf2/HO-1信号通路的中药有效成分缓解肝损伤研究进展

近年研究已证实,氧化应激是造成肝损伤的重要因素,研究发现核因子E2相关因子2（Nrf2）/血红素氧合酶-1（HO-1）可以通过调控氧化应激以缓解肝损伤。中药单体或中药复方可以通过调控该信号通路减少氧化应激、铁死亡、炎症和细胞焦亡的发生以缓解肝损伤。对中药中的黄酮类、多糖、酚酸、甾体类等有效成分通过 Nrf2/HO-1信号通路在氧化应激与肝损伤之间的相互作用进行综述,对于寻求靶向 Nrf2/HO-1信号通路发挥缓解肝损伤作用的中药提供依据,同时为中药治疗肝损伤作用机制的深入研究提供参考。     

Protective effects of diallyl disulfide on carbon tetrachloride‐induced hepatotoxicity through activation of Nrf2

This study was conducted to investigate the potential effects of diallyl disulfide (DADS) on carbon tetrachloride (CCl₄)‐induced acute hepatotoxicity and to determine the molecular mechanisms of protection offered by DADS in rats. DADS was administered orally at 50 and 100 mg/kg/day once daily for 5 consecutive days prior to CCl₄ administration. The single oral dose of CCl₄ (2 mL/kg) caused a significant elevation in serum aspartate and alanine aminotransferase activities, which decreased upon pretreatment with DADS. Histopathological examinations showed extensive liver injury, characterized by extensive hepatocellular degeneration/necrosis, fatty changes, inflammatory cell infiltration, and congestion, which were reversed following pretreatment with DADS. The effects of DADS on cytochrome P450 2E1 (CYP2E1), the major isozyme involved in CCl₄ bioactivation, were also investigated. DADS pretreatment resulted in a significant decrease in CYP2E1 protein levels in dose‐dependent manner. In addition, CCl₄ caused a decrease in protein level of cytoplasmic nuclear factor E2‐related factor 2 (Nrf2) and suppression of nuclear translocation of Nrf2 concurrent with downregulation of detoxifying phase II enzymes and a decrease in antioxidant enzyme activities. In contrast, DADS prevented the depletion of cytoplasmic Nrf2 and enhanced nuclear translocation of Nrf2, which, in turn, upregulated antioxidant and/or phase II enzymes. These results indicate that the protective effects of DADS against CCl₄‐induced hepatotoxicity possibly involve mechanisms related to its ability to induce antioxidant or detoxifying enzymes by activating Nrf2 and block metabolic activation of CCl₄ by suppressing CYP2E1. © 2013 Wiley Periodicals, Inc. Environ Toxicol 30: 538–548, 2015.     

Activation of Nrf2 pathway and inhibition of NLRP3 inflammasome activation contribute to the protective effect of chlorogenic acid on acute liver injury

Chlorogenic acid (CGA), a kind of polyphenol found in coffee, fruits and vegetables, has potent anti-oxidant and anti-inflammatory properties. Our previous studies showed CGA could efficiently alleviate liver fibrosis in rats. However, whether CGA regulates nuclear factor erythroid-2-related factor 2 (Nrf2) anti-oxidant pathway and NLRP3 inflammasome activation and protects against carbon tetrachloride (CCl₄)-induced acute liver injury are unknown. We found that CGA could increase Nrf2 activation and expression of Nrf2-related anti-oxidant genes, including HO-1, NQO1 and GCLC. Pretreatment with CGA could reduce CCl₄-induced elevation of serum transaminases and alleviate liver pathological abnormalities. CGA also reversed CCl₄-induced increase in MDA level and decrease in the levels of GSH, SOD and CAT in liver tissues. Meanwhile, CGA inhibited NLRP3 inflammasome activation, as indicated by the reduced protein expression of NLRP3, Pro-Caspase-1, Caspase-1, Pro-IL-1β and IL-1β. Moreover, CGA reduced serum levels and liver mRNA expression of TNF-α, IL-6 and IL-1β. These results demonstrate that CGA protects against CCl₄-induced acute liver injury probably through enhancing Nrf2-mediated anti-oxidant pathway and inhibiting NLRP3 inflammasome activation.     

Dibenzoylmethane Protects Against CCl4-Induced Acute Liver Injury by Activating Nrf2 via JNK,AMPK, and Calcium Signaling

Oxidative stress is an important pathogenic factor in various hepatic diseases. Nuclear factor-erythroid 2-related factor-2 (Nrf2), which coordinates the expression of an array of antioxidant and detoxifying genes, has been proposed as a potential target for prevention and treatment of liver disease. Dibenzoylmethane (DBM) is a minor ingredient in licorice that activates Nrf2 and prevents various cancers and oxidative damage. In the present study, the mechanisms by which DBM activates Nrf2 signaling were delineated, and its protective effect against carbon tetrachloride (CCl₄)-induced liver injury was examined. DBM potently induced the expression of HO-1 in cells and in the livers of mice, but this induction was diminished in Nrf2-deficient mice and cells. Overexpression of Nrf2 enhanced DBM-induced HO-1 expression, while overexpression of a dominant-negative fragment of Nrf2 inhibited this induction. DBM treatment resulted in dissociation from Keap1 and nuclear translocation of Nrf2. Moreover, DBM activated Akt/protein kinase B, mitogen-activated protein kinases, and AMP-activated protein kinase and increased intracellular calcium levels. Inhibition of JNK, AMPK, or intracellular calcium signaling significantly suppressed the induction of HO-1 expression by DBM. Finally, DBM treatment significantly inhibited CCl₄-induced acute liver injury in wild-type but not in Nrf2-deficient mice. Taken together, our results revealed the mechanisms by which DBM activates Nrf2 and induces HO-1 expression, and provide molecular basis for the design and development of DBM and its derivatives for prevention or treatment of liver diseases by targeting Nrf2.     

Naringenin attenuates CCl4‐induced hepatic inflammation by the activation of an Nrf2‐mediated pathway in rats

The possible protective effects of naringenin, a naturally occurring citrus flavonone, on carbon tetrachloride (CCl₄)‐induced liver injury in rats and the mechanism underlying its effects were investigated. Forty rats were divided into five groups. Rats in Groups I and II served as the normal and injured liver groups, respectively; Group III rats were treated with the standard drug silymarin as a positive control; and rats in Groups IV and V (naringenin‐treated groups) were administrated 50 mg/kg, p.o., naringenin for 7 days. Liver samples were collected to evaluate mRNA and protein expression, histological changes and oxidative stress. Naringenin inhibited lipid peroxidation and reduced serum levels of hepatic enzymes induced by CCl₄. In addition, naringenin increased the liver content of reduced glutathione and the activity of anti‐oxidant enzymes in rats treated with CCl₄. Naringenin attenuated liver inflammation by downregulating CCl₄‐induced activation of tumour necrosis factor (TNF)‐α, inducible nitric oxide synthase (iNOS) and cyclo‐oxygenase (COX‐2) at both the protein and mRNA levels. Naringenin treatment significantly increased NF‐E2‐related factor 2 (Nrf2) and heme oxygenase (HO‐1) expression in injured livers. In rats treated with CCl₄ alone, decreases were seen in nuclear Nrf2 expression and in the mRNA levels of its target genes (e.g. HO‐1, NQO1 and glutathione S‐transferase alpha 3 (GST‐a3)). Together, the results suggest that naringenin can protect the liver against oxidative stress, presumably by activating the nuclear translocation of Nrf2 as well as attenuating the TNF‐α pathway to elicit an anti‐inflammatory response in liver tissue.     

基于Nrf2/Keap1信号通路探讨金盏银盘水提液对四氯化碳诱导急性肝损伤小鼠抗氧化应激作用

目的 探究金盏银盘Bidens biternata(Lour.)Merr.&Sherff.水提液对四氯化碳诱导的急性肝损伤改善作用及其机制。方法 将60只雄性昆明小鼠随机分为对照组、模型组、水飞蓟素（0.15 g/kg）组和金盏银盘低、高剂量（3.9、7.8 g/kg）组,每组12只。各组小鼠连续ig给予相应药物7 d,末次给药后除对照组外均ip 0.4%四氯化碳构建急性肝损伤小鼠模型。24 h后收集小鼠血清及肝脏组织。用生化试剂盒检测血清中天门冬氨酸氨基转移酶（AST）、丙氨酸氨基转移酶（ALT）、超氧化物歧化酶（SOD）活性及丙二醛（MDA）含量,并取肝组织匀浆检测谷胱甘肽过氧化物酶（GSH-Px）活性。采用苏木精–伊红染色（HE）切片观察小鼠肝脏病理变化。Western blotting测定肝组织中核因子E2相关因子2(Nrf2)、抗体Kelch样ECH相关蛋白1(Keap1)、血红素氧合酶1(HO-1)蛋白的表达情况。结果 与模型组比较,金盏银盘水提液组小鼠组织病理学观察发现肝脏炎症细胞浸润明显减少,血清AST、ALT、MDA水平降低,血清SOD和肝组织GSH-Px活性...     

Delayed liver injury and impaired hepatocyte proliferation after carbon tetrachloride exposure in BPOZ2-deficient mice

BPOZ2 is a tumor suppressive mediator in PTEN signaling pathway and plays an important role in cell proliferation. In this study, we investigated the physiology functions of BPOZ2 in CCl₄-induced liver injury and hepatocyte proliferation afterwards. After acute CCl₄ administration, BPOZ2 null mice exhibited delayed liver injury and impaired hepatocyte proliferation, which was accompanied by altered kinetics of CYP2E1 protein expression, compromised cyclin D1 expression and shortened duration of ERK activation. These results for the first time define that BPOZ2 is an important regulator involved in the injury and repair process induced by acute CC1₄ administration in mouse liver.     

The involvement of Nrf2 in the protective effects of diallyl disulfide on carbon tetrachloride-induced hepatic oxidative damage and inflammatory response in rats

This study investigated the potential effect of diallyl disulfide (DADS) against carbon tetrachloride (CCl₄)-induced oxidative hepatic damage and inflammatory response in rat liver. DADS at doses of 50 and 100 mg/kg/day was administered orally once daily for 5 days, prior to CCl₄ administration. Pretreatment with DADS attenuated CCl₄-induced elevated serum transaminase activities and histopathological alterations in liver. It prevented the hepatocellular apoptotic changes with induction of Bcl-2-associated X (Bax), cytochrome c, and caspase-3 caused by CCl₄. An increase in the nuclear translocation of nuclear factor-kappaB (NF-κB) and phosphorylation of I kappaB alpha (IκBα) was observed in the livers of CCl₄-treated rats that coincided with induction of inflammatory mediators or cytokines. In contrast, DADS inhibited NF-κB translocation and IκBα phosphorylation, and that subsequently decreased inflammatory mediators. Furthermore, DADS prevented CCl₄-induced depletion of cytosolic nuclear factor E2-related factor 2 (Nrf2) and suppression of nuclear translocation of Nrf2, which, in turn, up-regulated phase II/antioxidant enzyme activities. Taken together, these results demonstrate that DADS increases the expression of phase II/antioxidant enzymes and simultaneously decreases the expression of inflammatory mediators in CCl₄-induced liver injury. These findings indicate that DADS induces antioxidant defense mechanism by activating Nrf2 pathway and reduces inflammatory response by inhibiting NF-κB activation.     

Involvement of Th2 cytokines in the mouse model of flutamide-induced acute liver injury

Drug‐induced liver injury is a growing concern for pharmaceutical companies and patients because numerous drugs have been linked to hepatotoxicity and it is the most common reason for a drug to be withdrawn. Flutamide rarely causes liver dysfunction in humans, and immune allergic reactions have been suggested in some cases. In this study, we investigated the mechanisms of flutamide‐induced liver injury in BALB/c mice. Plasma alanine aminotransferase and aspartate aminotransferase levels were significantly increased 3, 6 and 9 h after flutamide (1500 mg kg^?1, p.o.) administration. The biomarker for oxidative stress was not changed, but Th2‐dominant immune‐related factors, such as interleukin (IL)‐4, IL‐5, STAT6 and GATA‐binding protein (GATA)‐3, were induced in flutamide‐administered mice. The pre‐administration of monoclonal‐IL‐4 antibody suppressed the hepatotoxicity of flutamide. In addition, we investigated the effect of 13,14‐dihydro‐15‐keto‐PGD₂ (DK‐PGD₂; 10 µg per mouse, i.p.) administration on flutamide‐induced acute liver injury. Coadministration of DK‐PGD₂ and flutamide resulted in a significant increase in alanine aminotransferase and a remarkable increase of macrophage inflammatory protein‐2. In conclusion, we demonstrated that flutamide‐induced acute liver injury is mediated by Th2‐dominant immune responses in mice. Copyright © 2011 John Wiley & Sons, Ltd.     

MiR‐146a regulates PM1‐induced inflammation via NF‐κB signaling pathway in BEAS‐2B cells

Exposure to particulate matter (PM) leads to kinds of cardiopulmonary diseases, such as asthma, COPD, arrhythmias, lung cancer, etc., which are related to PM‐induced inflammation. We have found that PM_2.5 (aerodynamics diameter <2.5 µm) exposure induces inflammatory response both in vivo and in vitro. Since the toxicity of PM is tightly associated with its size and components, PM₁ (aerodynamics diameter <1.0 µm) is supposed to be more toxic than PM_2.5. However, the mechanism of PM₁‐induced inflammation is not clear. Recently, emerging evidences prove that microRNAs play a vital role in regulating inflammation. Therefore, we studied the regulation of miR‐146a in PM₁‐induced inflammation in human lung bronchial epithelial BEAS‐2B cells. The results show that PM₁ induces the increase of IL‐6 and IL‐8 in BEAS‐2B cells and up‐regulates the miR‐146a expression by activating NF‐κB signaling pathway. Overexpressed miR‐146a prevents the nuclear translocation of p65 through inhibiting the IRAK1/TRAF6 expression, and downregulates the expression of IL‐6 and IL‐8. Taken together, these results demonstrate that miR‐146a can negatively feedback regulate PM₁‐induced inflammation via NF‐κB signaling pathway in BEAS‐2B cells.     

Icaritin activates Nrf2/Keap1 signaling to protect neuronal cells from oxidative stress

Our earlier study indicated that icaritin (ICT) protected mice from cerebral ischemic injury by inhibiting oxidative stress, and this study aimed to investigate its mechanism using a H₂O₂‐treated SH‐SY5Y cells model. Cell viability was assessed by cell counting kit 8 (CCK‐8). Oxidative stress parameters were detected by flow cytometry, and signaling pathways were analyzed by immunoblotting. We found that ICT alleviated apoptosis and intracellular and mitochondrial reactive oxygen species (ROS) levels, decreased the expressions of Bax and cleaved caspase‐3, and increased the expressions of Bcl‐2 compared to H₂O₂ group. ICT increased mitochondrial membrane potential (ΔΨm) and blocked the opening of mitochondrial membrane permeability transporter (MPT), and increased the activity of glutathione peroxidase (GSH‐px), catalase (CAT), and superoxide dismutase (SOD), meanwhile, decreased the activity of malondialdehyde (MDA) compared to H₂O₂ group. Further investigation revealed that ICT significantly up‐regulated the expressions of nuclear factor erythroid 2‐related factor 2 (Nrf2), heme oxygenase 1 (HO‐1) and NAD(P)H‐quinone oxidoreductase 1 (NQO‐1). The anti‐apoptosis and antioxidative effects of ICT were blocked bay ML385, a Nrf2/Keap1 signaling pathway inhibitor. These results indicate that ICT can play a neuroprotective role against oxidative stress injury by activating Nrf2/Keap1 signaling pathway.     

Rg1 Attenuates alcoholic hepatic damage through regulating AMP-activated protein kinase and nuclear factor erythroid 2-related factor 2 signal pathways

Rg1 has shown multiple pharmacological activities and been considered to be evaluated for hepatic protective activity, as Rg1 could modulate different pathways in various diseases. Herein we assessed its effect and potential mechanism in a newly modified ethanol model. C57BL/6 mice were fed with Lieber-DeCarli liquid diet containing ethanol or isocaloric maltose dextrin as control diet with or without Rg1. Meanwhile, bicyclol was treated as positive drug to compare the efficacy of Rg1 against alcoholic hepatotoxicity. According to our data, Rg1 indeed improved the survival rate and lowered the abnormal high levels of serum parameters. H&E and Oil Red O staining indicated that the condition of liver damage was mitigated by Rg1 administration. Furthermore, AMPK and Nrf2 pathways were all modulated at both RNA and protein levels. In accordance with these findings, Rg1 effectively protected against alcoholic liver injury, possibly by modulating metabolism, suppressing oxidative stress, and enhancing oxidant defense systems of Nrf2 pathway. In vitro, Rg1 has no cell toxicity and promotes Nrf2 translocate into nuclear. In summary, we demonstrate that Rg1 is a potent activator of Nrf2 pathway, and could therefore be applied for prevention of hepatic damage.     

6-Gingerol ameliorates sepsis-induced liver injury through the Nrf2 pathway

Sepsis-induced liver injury is very common in intensive care units. Here, we investigated the effects of 6-gingerol on sepsis-induced liver injury and the role of the Nrf2 pathway in this process. 6-Gingerol is the principal ingredient of ginger that exerts anti-inflammatory and antioxidant effects. Using cecal ligation and puncture (CLP) to induce polymicrobial sepsis and related liver injury, we found that mice pre-treated with 6-Gingerol showed less incidences of severe liver inflammation and death than untreated CLP groups. 6-Gingerol administration also inhibited the expression of pyroptosis-related proteins, including NOD-like receptor protein 3 (NLRP3), IL-1β, and caspase-1. Consistent with these findings, 6-gingerol reduced the effects of pyroptosis induced by lipopolysaccharide (LPS) and adenosine 5′-triphosphate (ATP) in RAW 264.7 cells, as evidenced by IL-1β and caspase-1 protein levels in the supernatant and propidium iodide (PI) staining. 6-Gingerol was shown to activate the Nrf2 pathway in vivo and in vitro. Notably, Nrf2 siRNA transfection nullified the inhibitory effects of 6-gingerol on pyroptosis in vitro. In summary, these findings suggested that 6-gingerol alleviated sepsis-induced liver injury by inhibiting pyroptosis through the Nrf2 pathway.     

Protective effect of curcumin,a Curcuma longa constituent,in early colonic inflammation in rats

Curcumin, a polyphenol derived from the plant, Curcuma longa, has a variety of pharmacological effects, including chemotherapeutic, anti‐inflammatory, antiangiogenic, and antioxidant activities. To gain a better understanding of the effects and mechanisms of action of curcumin on the acute injury caused by intra‐colonic administration of acetic acid (AA) in rats, inflammation was assessed by histology and myeloperoxidase activity (MPO; an index of neutrophil infiltration in the mucosa); Th1 and Th2 cytokine production; histological and histochemical analysis of the lesions; nitrite production in colon mucosa; and the expression of iNOS, COX‐1 and ‐2 using Western blotting and inmmunohistochemistry. We also studied the involvement of the p38 MAPK/JNK signalling pathway in the protective effect of curcumin in acute colonic inflammation. Curcumin (50–100 mg/kg/day) reduced the degree of colonic injury, the index of neutrophil infiltration and Th1 cytokine secretion, and increased IL‐10 production, reduced colonic levels of nitrites, and reduced COX‐2 and iNOS overexpression. A reduction in the activation of p38 and JNK MAPKs was also observed. Thus, we show that the widely used food additive, curcumin reduced the development of AA‐induced colitis and alleviated the inflammatory response. Inhibition of MAPK signalling by curcumin could explain the changes on the cytokine Th1/Th2 profile, the reduction of COX‐2 and iNOS signaling, as well as the decreased nitrite production in colonic mucosa, suggesting that curcumin may be useful in the treatment of ulcerative colitis. Drug Dev Res, 2009. © 2009 Wiley‐Liss, Inc.