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Andrographolide is a potent anti-inflammatory agent found in Andrographis paniculata. Endothelin 1 (ET-1) is an endothelium-derived vasoconstrictor with pro-inflammatory properties secreted in response to hypoxia. Mitogen-activated protein kinase phosphatase 5 (MKP-5) is a dual-specificity phosphatase that dephosphorylates threonine and tyrosine residues of MAPKs. We showed previously that hypoxia-induced HIF-1α expression and ET-1 secretion are dependent on p38 MAPK in EA.hy926 cells. Here, we investigate what role MKP-5 plays in andrographolide's inhibition of hypoxia-induced expression of HIF-1α and ET-1. Hypoxic conditions were created using the hypoxia-mimetic agent CoCl2 . Andrographolide enhanced HO-1 and MKP-5 expression and cellular cGMP content in addition to inhibiting hypoxia-induced ROS generation. Concomitantly, the HO-1 byproduct CO and the cGMP analogue 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP) increased MKP-5 expression, and pretreatment with CO and 8-Br-cGMP inhibited hypoxia-induced HIF-1α and ET-1 expression. Transfection of HO-1 siRNA or pretreatment with the HO-1 inhibitor ZnPP-9 or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, a specific inhibitor of soluble guanylate cyclase, reduced andrographolide-induced MKP-5 expression. Moreover, silencing MKP-5 or treatment with the phosphatase inhibitor vanadate abrogated andrographolide's suppressing hypoxia-induced p38 MAPK activation and HIF-1α expression. The inhibition of hypoxia-induced HIF-1α and ET-1 expression by andrographolide is likely associated with HO-1/CO/cGMP/MKP-5 pathways, which is involved in inhibiting hypoxia-induced p38 MAPK activation.

Inflammation plays a key role in the development of cardiovascular disease (CVD), and docosahexaenoic acid (DHA) is recognized to fight against CVD. PPARα belongs to the nuclear hormone receptor superfamily and can interfere with inflammatory processes. Autophagy can degrade inflammasome proteins and counteract inflammation. Overexpression of intercellular adhesion molecule (ICAM) 1 in endothelial cells contributes to monocyte migration into the vascular intima. Here we investigated the mechanisms by which DHA inhibits TNFα-induced ICAM-1 expression in EA. hy926 endothelial cells. DHA markedly activated PPARα and suppressed TNFα-induced ICAM-1 expression, ICAM-1 promoter activity, p65 nuclear translocation, NFκB and DNA binding activity, and THP-1 cell adhesion. PPARα knockdown abolished the ability of DHA to inhibit TNFα-induced ICAM-1 expression and THP-1 cell adhesion. The PPARα antagonist GW6471 reversed the inhibitory effect of DHA on TNFα-induced ICAM-1 expression, p65 nuclear translocation, NFκB and DNA binding activity, and THP-1 cell adhesion. DHA significantly activated autophagy as evidenced by the formation of autophagosomes and increased LC3II protein expression. By contrast, wortmannin, which inhibits autophagy, abrogated DHA-induced autophagy and the inhibition of TNFα-induced ICAM-1 protein expression by DHA. Our results suggest that DHA likely inhibits TNFα-induced ICAM-1 expression by activating PPARα and autophagy.

Soy isoflavones (SI) are phytochemicals with various biological activities. Acetaminophen can cause acute liver injury when overdosed. In this study, to investigate the effects of SI on the metabolism and toxicity of acetaminophen in liver, rats were fed a controlled diet with or without 120 mg/kg SI-rich product for 2 weeks and were then intraperitoneally injected with acetaminophen. Cytochrome P-450 (CYP), phase II enzymes, membrane transporters, and glutathione in liver were evaluated. Acetaminophen-induced elevations in plasma alanine aminotransferase activity and decreases in liver glutathione levels were ameliorated in rats treated with SI. SI reduced hepatic CYP2E1 and CYP3A activities and acetaminophen-protein adduct contents. Hepatic UDP-glucuronosyltransferase activity and urinary acetaminophen excretion were increased by SI after acetaminophen treatment. Protein expression of multidrug-resistance-associated protein 2/3 and connexin 32 in liver, however, was not changed by SI. Our results indicate that SI-rich product may act as functional food which can reduce acetaminophen-induced hepatotoxicity.

Andrographolide, the main bioactive component of the medicinal plant Andrographis paniculata, has been shown to possess potent anti-inflammatory activity. Endothelin 1 (ET-1), a potent vasoconstrictor peptide produced by vascular endothelial cells, displays proinflammatory property. Hypoxia-inducible factor 1α (HIF-1α), the regulatory member of the transcription factor heterodimer HIF-1α/β, is one of the most important molecules that responds to hypoxia. Changes in cellular HIF-1α protein level are the result of altered gene transcription and protein stability, with the latter being dependent on prolyl hydroxylases (PHDs). In this study, inhibition of pro-inflammatory ET-1 expression and changes of HIF-1α gene transcription and protein stability under hypoxia by andrographolide in EA.hy926 endothelial-like cells were investigated. Hypoxic conditions were created using the hypoxia-mimetic agent CoCl2. We found that hypoxia stimulated the production of reactive oxygen species (ROS), the expression of HIF-1α mRNA and protein, and the expression and secretion of ET-1. These effects, however, were attenuated by co-exposure to andrographolide, bilirubin, and RuCO. Silencing Nrf2 and heme oxygenase 1 (HO-1) reversed the inhibitory effects of andrographolide on hypxoia-induced HIF-1α mRNA and protein expression. Moreover, andrographolide increased the expression of prolyl hydroxylases (PHD) 2/3, which hydroxylate HIF-1α and promotes HIF-1α proteasome degradation, with an increase in HIF-1α hydroxylation was noted under hypoxia. Inhibition of p38 MAPK abrogated the hypoxia-induced increases in HIF-1α mRNA and protein expression as well as ET-1 mRNA expression and secretion. Taken together, these results suggest that andrographolide suppresses hypoxia-induced pro-inflammatory ET-1 expression by activating Nrf2/HO-1, inhibiting p38 MAPK signaling, and promoting PHD2/3 expression. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 918-930, 2017.

oxLDL is involved in the pathogenesis of atherosclerotic lesions through cholesterol accumulation in macrophage foam cells. Andrographolide, the bioactive component of Andrographis paniculata, possesses several biological activities such as anti-inflammatory, anti-oxidant, and anticancer functions. Scavenger receptors (SRs), including class A SR (SR-A) and CD36, are responsible for the internalization of oxLDL. In contrast, receptors for reverse cholesterol transport, including ABCA1 and ABCG1, mediate the efflux of cholesterol from macrophage foam cells. Transcription factor liver X receptor [Formula: see text] (LXR[Formula: see text] plays a key role in lipid metabolism and inflammation as well as in the regulation of ABCA1 and ABCG1 expression. Because of the contribution of inflammation to macrophage foam cell formation and the potent anti-inflammatory activity of andrographolide, we hypothesized that andrographolide might inhibit oxLDL-induced macrophage foam cell formation. The results showed that andrographolide reduced oxLDL-induced lipid accumulation in macrophage foam cells. Andrographolide decreased the mRNA and protein expression of CD36 by inducing the degradation of CD36 mRNA; however, andrographolide had no effect on SR-A expression. In contrast, andrographolide increased the mRNA and protein expression of ABCA1 and ABCG1, which were dependent on LXR[Formula: see text]. Andrographolide enhanced LXR[Formula: see text] nuclear translocation and DNA binding activity. Treatment with the LXR[Formula: see text] antagonist GGPP and transfection with LXR[Formula: see text] siRNA reversed the ability of andrographolide to stimulate ABCA1 and ABCG1 protein expression. In conclusion, inhibition of CD36-mediated oxLDL uptake and induction of ABCA1- and ABCG1-dependent cholesterol efflux are two working mechanisms by which andrographolide inhibits macrophage foam cell formation, which suggests that andrographolide could be a potential candidate to prevent atherosclerosis.

Cell migration plays an important role in angiogenesis and wound repair. Vascular endothelial growth factor (VEGF) is an endothelial cell-specific mitogen that is essential for endothelial cell survival, proliferation, and migration. Docosahexaenoic acid (DHA), an n-3 polyunsaturated fatty acid, shows both anti-inflammatory and antioxidant activities in vitro and in vivo. This study investigated the molecular mechanism by which DHA down-regulates VEGF-induced cell migration. HUVECs were used as the study model, and the MTT assay, Western blot, wound-healing assay, and phosphatase activity assay were used to explore the effects of DHA on cell migration. GPR120 is the putative receptor for DHA action. The results showed that DHA, PD98059 (an ERK1/2 inhibitor), and GW9508 (a GPR120 agonist) inhibited VEGF-induced cell migration. In contrast, pretreatment with okadaic acid (OA, a PP2A inhibitor) and S-nitroso-N-acetyl-DL-penicillamine (an NO donor) reversed the inhibition of cell migration by DHA. VEGF-induced cell migration was accompanied by phosphorylation of ERK1/2 and eNOS. Treatment of HUVECs with DHA increased PP2A enzyme activity and decreased VEGF-induced phosphorylation of ERK1/2 and eNOS. However, pretreatment with OA significantly decreased DHA-induced PP2A enzyme activity and reversed the DHA inhibition of VEGF-induced ERK1/2 and eNOS phosphorylation. These results suggest that stimulation of PP2A activity and inhibition of the VEGF-induced ERK1/2/eNOS signaling pathway may be involved in the DHA suppression of VEGF-induced cell migration. Thus, the effect of DHA on angiogenesis and wound repair is at least partly by virtue of its attenuation of cell migration.

Scope Oxidative stress plays a pivotal role in the pathophysiology of cardiovascular diseases. Oxidized low-density lipoprotein (oxLDL) is a key contributor to atherogenesis through multiple mechanisms. In this study, we investigated the protection by three structurally related isothiocyanates, i.e., sulforaphane (SFN), benzyl isothiocyanate (BITC), and phenethyl isocyanate (PEITC), against oxLDL-induced leukocyte adhesion to vascular endothelium and the mechanism involved. Methods and results The protection against oxLDL-induced endothelial dysfunction by isothiocyanates was studied in human umbilical vein endothelial cells (HUVECs). oxLDL increased reactive oxygen species (ROS) production, stimulated nuclear factor-kappaB (NFκB) activation, and enhanced intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), and E-selectin expression in HUVECs, which led to promotion of monocyte adhesion to HUVECs. Treatment with SFN, BITC, and PEITC (0–10 μM) dose-dependently induced heme oxygenase (HO)-1, glutamate cysteine ligase (GCL) catalytic and modifier subunit expression, intracellular glutathione content, and antioxidant response element (ARE)-luciferase reporter activity. SFN, BITC, and PEITC pretreatment reversed oxLDL-induced ROS production, NFκB nuclear translocation, κB-reporter activity, ICAM-1, VCAM-1, and E-selectin expression, and monocyte adhesion to endothelial cells. Both heme oxygenase 1 (HO-1) and nuclear factor erythroid 2-related factor 2 (Nrf2) knockdown attenuated the isothiocyanate inhibition of oxLDL-induced ROS production, κB-reporter activity, and adhesion molecule expression. Conclusion SFN, BITC, and PEITC protect against oxLDL-induced endothelial damage by upregulating Nrf2-dependent HO-1 and GCL expression, which leads to inhibition of NFκB activation and ICAM-1, VCAM-1, and E-selectin expression.

Andrographolide, a diterpenoid, is the most abundant terpenoid in Andrographis paniculata, a popular Chinese herbal medicine. Andrographolide displays diverse biological activities including hypoglycemia, hypolipidemia, anti-inflammation, and anti-tumorigenesis. Recent evidence indicates that andrographolide displays anti-obesity property by inhibiting lipogenic gene expression, however, the underlying mechanisms remain to be elucidated. In this study, the effects of andrographolide on transcription factor cascade and mitotic clonal expansion in 3T3-L1 preadipocyte differentiation into adipocyte were determined. Andrographolide dose-dependently (0-15μM) inhibited CCAAT/enhancer-binding protein α (C/EBPα) and C/EBPβ mRNA and protein expression as well as peroxisome proliferator-activated receptor γ (PPARγ) protein level during the adipogenesis of 3T3-L1 cells. Concomitantly, fatty acid synthase and stearoyl-CoA desaturase expression and lipid accumulation were attenuated by andrographolide. Oil-red O staining further showed that the first 48h after the initiation of differentiation was critical for andrographolide inhibition of adipocyte formation. Andrographolide inhibited the phosphorylation of PKA and the activation of cAMP response element-binding protein (CREB) in response to a differentiation cocktail, which led to attenuated C/EBPβ expression. In addition, ERK and GSK3β-dependent C/EBPβ phosphorylation was attenuated by andrographolide. Moreover, andrographolide suppressed cyclin A, cyclin E, and CDK2 expression and impaired the progression of mitotic clonal expansion (MCE) by arresting the cell cycle at the Go/G1 phase. Taken together, these results indicate that andrographolide has a potent anti-obesity action by inhibiting PKA-CREB-mediated C/EBPβ expression as well as C/EBPβ transcriptional activity, which halts MCE progression and attenuates C/EBPα and PPARγ expression.

Andrographolide, the main bioactive component of the medicinal plant Andrographis paniculata, has been shown to possess potent anti-inflammatory activity. Endothelin 1 (ET-1), a potent vasoconstrictor peptide produced by vascular endothelial cells, displays proinflammatory property. Hypoxia-inducible factor 1α (HIF-1α), the regulatory member of the transcription factor heterodimer HIF-1α/β, is one of the most important molecules that responds to hypoxia. Changes in cellular HIF-1α protein level are the result of altered gene transcription and protein stability, with the latter being dependent on prolyl hydroxylases (PHDs). In this study, inhibition of pro-inflammatory ET-1 expression and changes of HIF-1α gene transcription and protein stability under hypoxia by andrographolide in EA.hy926 endothelial-like cells were investigated. Hypoxic conditions were created using the hypoxia-mimetic agent CoCl

Chrysin, apigenin, and luteolin are flavones that differ in their number of hydroxyl groups in the B ring. In this study, we investigated the protection by chrysin, apigenin, and luteolin against tert-butyl hydroperoxide (tBHP)-induced oxidative stress and the possible mechanisms involved in rat primary hepatocytes. Chrysin, apigenin, and luteolin dose-dependently up-regulated the protein expression of heme oxygenase 1 (HO-1) and glutamate cysteine ligase (GCL) catalytic (GCLC) and modifier subunit (GCLM) and increased the intracellular glutathione (GSH) content and the ratio of GSH to oxidized GSH. Among the flavones studied, chrysin showed the greatest induction of HO-1, GCLC, and GCLM protein expression and GSH content. Cellular reactive oxygen species production induced by tBHP was attenuated by pretreatment with chrysin, apigenin, and luteolin (P

Numerous genes expression is regulated in response to amino acid shortage, which helps organisms adapt to amino acid limitation. The expression of the π class of glutathione (GSH) S-transferase (GSTP), a highly inducible phase II detoxification enzyme, is regulated mainly by activates activating protein 1 (AP-1) binding to the enhancer I of GSTP (GPEI). Here we show the critical role of nuclear factor erythroid-2-related factor 2 (Nrf2) in up-regulating GSTP gene transcription. Primary rat hepatocytes were cultured in a methionine-restricted medium, and immunoblotting and RT-PCR analyses showed that methionine restriction time-dependently increased GSTP protein and mRNA expression over a 48 h period. Nrf2 translocation to the nucleus, nuclear proteins binding to GPEI, and antioxidant response element (ARE) luciferase reporter activity were increased by methionine restriction as well as by l-buthionine sulfoximine (BSO), a GSH synthesis inhibitor. Transfection with Nrf2 siRNA knocked down Nrf2 expression and reversed the methionine-induced GSTP expression and GPEI binding activity. Chromatin immunoprecipitation assay confirmed the binding of Nrf2 to the GPEI. Phosphorylation of extracellular signal-regulated kinase 2 (ERK2) was increased in methionine-restricted and BSO-treated cells. ERK2 siRNA abolished methionine restriction-induced Nrf2 nuclear translocation, GPEI binding activity, ARE-luciferase reporter activity, and GSTP expression. Our results suggest that the up-regulation of GSTP gene transcription in response to methionine restriction likely occurs via the ERK-Nrf2-GPEI signaling pathway.

The anticarcinogenic effect of dietary organosulfur compounds has been partly attributed to their modulation of the activity and expression of phase II detoxification enzymes. Our previous studies indicated that garlic allyl sulfides upregulate the expression of the pi class of glutathione S-transferase (GSTP) through the activator protein-1 pathway. Here, we examined the modulatory effect of sulforaphane (SFN) and alpha-lipoic acid (LA) or dihydrolipoic acid (DHLA) on GSTP expression in rat Clone 9 liver cells. Cells were treated with LA or DHLA (50-600 micromol/L) or SFN (0.2-5 micromol/L) for 24 h. Immunoblots and real-time PCR showed that SFN, LA, and DHLA dose dependently induced GSTP protein and mRNA expression. Compared with the induction by the garlic organosulfur compound diallyl trisulfide (DATS), the effectiveness was in the order of SFN > DATS > LA = DHLA. The increase in GSTP enzyme activity in cells treated with 5 micromol/L SFN, 50 micromol/L DATS, and 600 micromol/L LA and DHLA was 172, 75, 122, and 117%, respectively (P < 0.05). A reporter assay showed that the GSTP enhancer I (GPEI) was required for GSTP induction by the organosulfur compounds. Electromobility gel shift assays showed that the DNA binding of GPEI to nuclear proteins reached a maximum at 0.5-1 h after SFN, LA, and DHLA treatment. Super-shift assay revealed that the transcription factors c-jun and nuclear factor erythroid-2 related factor 2 (Nrf2) were bound to GPEI. These results suggest that SFN and LA in either its oxidized or reduced form upregulate the transcription of the GSTP gene by activating c-jun and Nrf2 binding to the enhancer element GPEI.

Epidemiologic studies have demonstrated that chronic arsenic exposure is associated with the incidence of chronic diseases. This association is partly related to the increase in reactive oxygen species (ROS) overload and protein oxidation that result from arsenic exposure. In this study, we intended to identify proteins susceptible to oxidative carbonylation by sodium arsenite and the impact of carbonylation on the function of these proteins in human umbilical vein endothelial cells (HUVECs). The 2,4-dinitrophenylhydrazine (DNPH) dot-blot assay revealed that arsenite (0-50 μM) dose-dependently increased protein carbonylation. Consistent with these findings, the cellular ROS level as measured by 2',7'-dichlorofluorescein diacetate (DCHF-DA) assay was increased in cells exposed to arsenite. By two-dimensional gel electrophoresis and matrix assist laser desorption ionization time of flight mass spectrometry (MALDI-TOF/MS), one glycolytic enzyme, enolase-α, two cytoskeleton proteins, fascin (F-actin associated protein) and vimentin, and two protein quality control proteins, HSC70 (heat-shock cognate protein 70), and PDIA3 (protein disulfide isomerase family A, member 3) were identified to be arsenic-sensitive carbonlyated proteins. Accompanied by carbonylation, enolase-α activity was dose-dependently decreased and the F-actin filament network was disturbed. Taken together, our results suggest that arsenite exposure results in the generation of carbonylated proteins, and the resultant changes in energy metabolism and in the cytoskeletal network may partly lead to cell damage.

Oxidized low-density lipoprotein (oxLDL) is a key contributor to atherogenesis through multiple mechanisms, including the reactive oxygen species (ROS)-mediated nuclear factor-kappaB (NFκB) signaling pathway. Although shikonin, one of the main active components isolated from the Chinese herb Lithospermum erythrorhizon, has been shown to possess cardioprotective, antioxidative, and anti-inflammatory effects, the mechanisms underlying these actions are not well understood. In this study, we used EA.hy926 endothelial-like cells to examine the anti-atherogenic activity of shikonin. Shikonin (0-1 μM) concentration-dependently induced heme oxygenase-1, glutamate cysteine ligase modifier subunit, catalase, superoxide dismutase 1, glutathione peroxidase 1, and glutathione reductase protein and mRNA expression and glutathione content via activation of the phosphatidylinositol 3-kinase (PI3K)/Akt/Nrf2 signaling pathway. In the presence of oxLDL (40 μg/ml), shikonin pretreatment reversed oxLDL-induced ROS production, antioxidant response element reporter activity, NFκB nuclear translocation, and intercellular adhesion molecule (ICAM)-1 and E-selectin expression and suppressed the increase of monocyte adhesion to endothelial cells. Nrf2 knockdown by using RNA interference attenuated the ability of shikonin to inhibit oxLDL-induced NFκB DNA binding activity, adhesion molecule expression, and monocyte adhesion. Taken together, these results suggest that shikonin protects against oxLDL-induced endothelial damage by suppressing ROS/NFκB-mediated ICAM-1 and E-selectin expression via up-regulation of PI3K/Akt/Nrf2-dependent antioxidant enzyme expression.

Andrographolide, a bioactive diterpenoid, is identified in Andrographis paniculata. In this study, we investigated the pharmacokinetics and bioavailability of andrographolide in rats and studied whether andrographolide enhances antioxidant defense in a variety of tissues and protects against carbon tetrachloride-induced oxidative damage. After a single 50-mg/kg administration, the maximum plasma concentration of andrographolide was 1μM which peaked at 30min. The bioavailability of andrographolide was 1.19%. In a hepatoprotection study, rats were intragastrically dosed with 30 or 50mg/kg andrographolide for 5 consecutive days. The results showed that andrographolide up-regulated glutamate cysteine ligase (GCL) catalytic and modifier subunits, superoxide dismutase (SOD)-1, heme oxygenase (HO)-1, and glutathione (GSH) S-transferase (GST) Ya/Yb protein and mRNA expression in the liver, heart, and kidneys. The activity of SOD, GST, and GSH reductase was also increased in rats dosed with andrographolide (p

The effect of commercially available green tea (GT) and black tea (BT) drinks on drug metabolizing enzymes (DME) and oxidative stress in rats was investigated. Male Wistar rats were fed a laboratory chow diet and GT or BT drink for 5 weeks. Control rats received de-ionized water instead of the tea drinks. Rats received the GT and BT drinks treatment for 5 weeks showed a significant increase in hepatic microsomal cytochrome P450 (CYP) 1A1 and CYP1A2, and a significant decrease in CYP2C, CYP2E1 and CYP3A enzyme activities. Results of immunoblot analyses of enzyme protein contents showed the same trend with enzyme activity. Significant increase in UDP-glucuronosyltransferase activity and reduced glutathione content in liver and lungs were observed in rats treated with both tea drinks. A lower lipid peroxide level in lungs was observed in rats treated with GT drink. Electrophoretic mobility shift assay revealed that both tea drinks decreased pregnane X receptor binding to DNA and increased nuclear factor-erythroid 2 p45-related factor 2 binding to DNA. These results suggest that feeding of both tea drinks to rats modulated DME activities and reduced oxidative stress in liver and lungs. GT drink is more effective on reducing oxidative stress than BT drink.

Andrographolide (1), an active constituent of Andrographis paniculata, decreased tumor necrosis factor-α (TNF-α)-induced intercellular adhesion molecule-1 (ICAM-1) expression and adhesion of HL-60 cells onto human umbilical vein endothelial cells (HUVEC), which are associated with inflammatory diseases. Moreover, 1 abolished TNF-α-induced Akt phosphorylation. Transfection of an activated Akt1 cDNA vector increased Akt phosphorylation and ICAM-1 expression like TNF-α. In addition, 1 and LY294002 blocked TNF-α-induced IκB-α degradation and nuclear p65 protein accumulation, as well as the DNA-binding activity of NF-κB. Compound 1 exhibits anti-inflammatory properties through the inhibition of TNF-α-induced ICAM-1 expression. The anti-inflammatory activity of 1 may be associated with the inhibition of the PI3K/Akt pathway and downstream target NF-κB activation in HUVEC cells.

Butein and phloretin are chalcones that are members of the flavonoid family of polyphenols. Flavonoids have well-known antioxidant and anti-inflammatory activities. In rat primary hepatocytes, we examined whether butein and phloretin affect tert -butylhydroperoxide (tBHP)-induced oxidative damage and the possible mechanism(s) involved. Treatment with butein and phloretin markedly attenuated tBHP-induced peroxide formation, and this amelioration was reversed by l -buthionine- S -sulfoximine [a glutamate cysteine ligase (GCL) inhibitor] and zinc protoporphyrin [a heme oxygenase 1 (HO-1) inhibitor]. Butein and phloretin induced both HO-1 and GCL protein and mRNA expression and increased intracellular glutathione (GSH) and total GSH content. Butein treatment activated the ERK1/2 signaling pathway and increased Nrf2 nuclear translocation, Nrf2 nuclear protein–DNA binding activity, and ARE–luciferase reporter activity. The roles of the ERK signaling pathway and Nrf2 in butein-induced HO-1 and GCL catalytic subunit (GCLC) expression were determined by using RNA interference directed against ERK2 and Nrf2. Both siERK2 and siNrf2 abolished butein-induced HO-1 and GCLC protein expression. These results suggest the involvement of ERK2 and Nrf2 in the induction of HO-1 and GCLC by butein. In an animal study, phloretin was shown to increase GSH content and HO-1 expression in rat liver and decrease carbon tetrachloride-induced hepatotoxicity. In conclusion, we demonstrate that butein and phloretin up-regulate HO-1 and GCL expression through the ERK2/Nrf2 pathway and protect hepatocytes against oxidative stress.

Understanding the molecular events underlying gene regulation by amino acids has attracted increasing attention. Here, we explored whether the mechanism by which methionine restriction affects the expression of the pi class of glutathione S-transferase (GSTP) is related to oxidative stress initiated by glutathione (GSH) depletion. Rat primary hepatocytes were cultured in an L-15-based medium in the absence or presence of 200 muM L-buthionine sulfoximine (BSO) or in a methionine-restricted L-15 medium supplemented with 20 muM L-methionine up to 72 h. BSO and methionine restriction time-dependently induced GSTP mRNA and protein expression in a similar pattern accompanied by a decrease in the cellular GSH level. The phosphorylation of extracellular signal-regulated kinase (ERK), but not of c-Jun NH(2)-terminal kinase and p38, was stimulated by methionine restriction and BSO. Electromobility gel shift assay showed that the DNA-binding activity of nuclear activator protein-1 (AP-1) increased in cells exposed to methionine restriction or BSO. With the ERK inhibitor FR180204, AP-1 activation and GSTP expression were abolished. Moreover, the induction of GSTP by methionine restriction and BSO was reversed by GSH monoethyl ester and N-acetylcysteine. Our results suggest that methionine restriction up-regulates GSTP gene expression, which appears to be initiated by the ERK-AP-1 signaling pathway through GSH depletion in rat hepatocytes.