Sulforaphane protects Microcystin-LR-induced toxicity through activation of the Nrf2-mediated defensive response

Microcystins (MCs), a cyclic heptapeptide hepatotoxins, are mainly produced by the bloom-forming cyanobacerium Microcystis, which has become an environmental hazard worldwide. Long term consumption of MC-contaminated water may induce liver damage, liver cancer, and even human death. Therefore, in addition to removal of MCs in drinking water, novel strategies that prevent health damages are urgently needed. Sulforaphane (SFN), a natural-occurring isothiocyanate from cruciferous vegetables, has been reported to reduce and eliminate toxicities from xenobiotics and carcinogens. The purpose of the present study was to provide mechanistic insights into the SFN-induced antioxidative defense system against MC-LR-induced cytotoxicity. We performed cell viability assays, including MTS assay, colony formation assay and apoptotic cell sorting, to study MC-LR-induced cellular damage and the protective effects by SFN. The results showed that SFN protected MC-LR-induced damages at a nontoxic and physiological relevant dose in HepG2, BRL-3A and NIH 3 T3 cells. The protection was Nrf2-mediated as evident by transactivation of Nrf2 and activation of its downstream genes, including NQO1 and HO-1, and elevated intracellular GSH level. Results of our studies indicate that pretreatment of cells with 10 μM SFN for 12 h significantly protected cells from MC-LR-induced damage. SFN-induced protective response was mediated through Nrf2 pathway.     

Sulforaphane protects against acetaminophen-induced hepatotoxicity

Oxidative stress is closely associated with acetaminophen (APAP)-induced toxicity. Heme oxygenase-1 (HO-1), an antioxidant defense enzyme, has been shown to protect against oxidant-induced tissue injury. This study investigated whether sulforaphane (SFN), as a HO-1 inducer, plays a protective role against APAP hepatotoxicity in vitro and in vivo. Pretreatment of primary hepatocyte with SFN induced nuclear factor E2-factor related factor (Nrf2) target gene expression, especially HO-1 mRNA and protein expression, and suppressed APAP-induced glutathione (GSH) depletion and lipid peroxidation, which eventually leads to hepatocyte cell death. A comparable effect was observed in mice treated with APAP. Mice were treated with 300 mg/kg APAP 30 min after SFN (5 mg/kg) administration and were then sacrificed after 6 h. APAP alone caused severe liver injuries as characterized by increased plasma AST and ALT levels, GSH depletion, apoptosis, and 4-hydroxynonenal (4-HNE) formations. This APAP-induced liver damage was significantly attenuated by pretreatment with SFN. Furthermore, while hepatic reactive oxygen species (ROS) levels were increased by APAP exposure, pretreatment with SFN completely blocked ROS formation. These results suggest that SFN plays a protective role against APAP-mediated hepatotoxicity through antioxidant effects mediated by HO-1 induction. SFN has preventive action in oxidative stress-mediated liver injury.     

In vitro and in vivo hepatoprotective effects of the aqueous extract from Taraxacum officinale (dandelion) root against alcohol-induced oxidative stress

The protective effects of Taraxacum officinale (dandelion) root against alcoholic liver damage were investigated in HepG2/2E1 cells and ICR mice. When an increase in the production of reactive oxygen species was induced by 300 mM ethanol in vitro, cell viability was drastically decreased by 39%. However, in the presence of hot water extract (TOH) from T. officinale root, no hepatocytic damage was observed in the cells treated with ethanol, while ethanol-extract (TOE) did not show potent hepatoprotective activity. Mice, which received TOH (1 g/kg bw/day) with ethanol revealed complete prevention of alcohol-induced hepatotoxicity as evidenced by the significant reductions of serum aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, and lactate dehydrogenase activities compared to ethanol-alone administered mice. When compared to the ethanol-alone treated group, the mice receiving ethanol plus TOH exhibited significant increases in hepatic antioxidant activities, including catalase, glutathione-S-transferase, glutathione peroxidase, glutathione reductase, and glutathione. Furthermore, the amelioration of malondialdehyde levels indicated TOH’s protective effects against liver damage mediated by alcohol in vivo. These results suggest that the aqueous extract of T. officinale root has protective action against alcohol-induced toxicity in the liver by elevating antioxidative potentials and decreasing lipid peroxidation.     

Sulforaphane protects against cytokine- and streptozotocin-induced β-cell damage by suppressing the NF-κB pathway

Sulforaphane (SFN) is an indirect antioxidant that protects animal tissues from chemical or biological insults by stimulating the expression of several NF-E2-related factor-2 (Nrf2)-regulated phase 2 enzymes. Treatment of RINm5F insulinoma cells with SFN increases Nrf2 nuclear translocation and expression of phase 2 enzymes. In this study, we investigated whether the activation of Nrf2 by SFN treatment or ectopic overexpression of Nrf2 inhibited cytokine-induced β-cell damage. Treatment of RIN cells with IL-1β and IFN-γ induced β-cell damage through a NF-κB-dependent signaling pathway. Activation of Nrf2 by treatment with SFN and induction of Nrf2 overexpression by transfection with Nrf2 prevented cytokine toxicity. The mechanism by which Nrf2 activation inhibited NF-κB-dependent cell death signals appeared to involve the reduction of oxidative stress, as demonstrated by the inhibition of cytokine-induced H₂O₂ production. The protective effect of SFN was further demonstrated by the restoration of normal insulin secreting responses to glucose in cytokine-treated rat pancreatic islets. Furthermore, pretreatment with SFN blocked the development of type 1 diabetes in streptozotocin-treated mice.     

Comparison of protein phosphatase inhibition activities and mouse toxicities of microcystins.

Eight naturally purified microcystins (MCs), including MC-LR, -FR, -WR, -RR, [d-Asp(3)]MC-FR, -WR, -RR, and [Dha(7)]MC-RR were utilized to determine the effects of amino acid substitutions and modifications on MC-induced protein phosphatase inhibition activity and mouse toxicity. Catalytic subunits of protein phosphatase 1 (PP-1) and 2A (PP-2A) were purified and subjected to the inhibition assays, and intraperitoneal injection was used to administer MCs into mice for the toxicity assay. It is found that the replacement of the non-polar amino acid l-leucine at the second position of these heptacyclic peptide toxins by a polar l-arginine reduces their mouse toxicities and inhibitory activities against PP-1 and PP-2A to different extends. Demethylation of methyldehydroalanine (Mdha) at the seventh amino acid of MC-RR exhibits the least mouse toxicity and phosphatase inhibition. The loss of a methyl group on the common methylaspartic acid (MeAsp) at the third position of MC-FR, -WR, and -RR does not alter their toxicity levels, but dominantly reduces their activities in PP-1 inhibition compared to other substitutions or modifications. This suggests that the methyl group on MeAsp is also important for MCs inhibition. However, such a tendency is not observed for PP-2A. By comparing the LD(50) values of the mouse toxicity assay and IC(50) values of the PP-1 and PP-2A inhibition assay of eight MCs using linear regression, it is evident that the MC-induced toxicity is much more related to the inhibition of PP-2A than PP-1, which suggests that PP-2A inhibition may play a major role in the MC-induced mouse toxicity.     

Curcumin attenuates isoniazid-induced hepatotoxicity by upregulating the SIRT1/PGC-1α/NRF1 pathway

As a serious infectious disease, tuberculosis threatens global public health. Isoniazid is the first-line drug not only in active tuberculosis but also in its prevention. Severe hepatotoxicity greatly limits its use. Curcumin, extracted from turmeric, has been found to relieve isoniazid-induced hepatotoxicity. However, the mechanism of isoniazid-induced hepatotoxicity and the protective effects of curcumin are not yet understood completely. We established both cell and animal models about isoniazid-induced hepatotoxicity and investigated the new mechanism of curcumin against isoniazid-induced liver injury. The experimental data in our study demonstrated that curcumin ameliorated isoniazid-mediated liver oxidative stress. The protective effects of curcumin were demonstrated and confirmed to be correlated with upregulating SIRT1/PGC-1α/NRF1 pathway. Western blot revealed that while inhibiting SIRT1 by the siRNA1 (a SIRT1 inhibitor), the expressions of SIRT1, PGC-1α/Ac-PGC-1α, and NRF1 decreased, and the protective effect that curcumin exerted on isoniazid-treated L-02 cells was significantly attenuated. Furthermore, curcumin improved liver functions and reduced necrosis of the isoniazid-treated BALB/c mice, accompanied by downregulating oxidative stress and inflammation in liver. Western blot revealed that curcumin treatment activates the SIRT1/PGC-1α/NRF1 pathway in the isoniazid-treated BALB/c mice. In conclusion, we found one mechanism of isoniazid-induced hepatotoxicity downregulating the SIRT1/PGC-1α/NRF1 pathway, and curcumin attenuated this hepatotoxicity by activating it. Our study provided a novel approach and mechanism for the treatment of isoniazid-induced hepatotoxicity.     

Analysis of chemokines and reactive oxygen species formation by rat and human neutrophils induced by microcystin-LA, -YR and -LR.

Microcystins (MC), a family of heptapeptide toxins produced by some genera of Cyanobacteria, have potent hepatotoxicity and tumor-promoting activity. Leukocyte infiltration in the liver was observed in MC-induced acute intoxication. Although the mechanisms of hepatotoxicity are still unclear, neutrophil infiltration in the liver may play an important role in triggering toxic injury and tumor development. The present study reports the effects of MC-LA, MC-YR and MC-LR (1 and 1000 nM) on human and rat neutrophils functions in vitro. Cell viability, DNA fragmentation, mitochondrial membrane depolarization and intracellular reactive oxygen species (ROS) levels were measured by flow cytometry. Extracellular ROS content was measured by lucigenin-amplified chemiluminescence, and cytokines were determined by ELISA. We found that these MC increased interleukin-8 (IL-8), cytokine-induced neutrophil chemoattractant-2alphabeta (CINC-2alphabeta) and extracellular ROS levels in human and rat neutrophils. Apart from neutrophil presence during the inflammatory process of MC-induced injury, our results suggest that hepatic neutrophil accumulation is further increased by MC-induced neutrophil-derived chemokine.     

Microcystin-Induced Immunotoxicity in Fishes: A Scoping Review

Cyanobacteria (blue-green algae) have been present on Earth for over 2 billion years, and can produce a variety of bioactive molecules, such as cyanotoxins. Microcystins (MCs), the most frequently detected cyanotoxins, pose a threat to the aquatic environment and to human health. The classic toxic mechanism of MCs is the inhibition of the protein phosphatases 1 and 2A (PP1 and PP2A). Immunity is known as one of the most important physiological functions in the neuroendocrine-immune network to prevent infections and maintain internal homoeostasis in fish. The present review aimed to summarize existing papers, elaborate on the MC-induced immunotoxicity in fish, and put forward some suggestions for future research. The immunomodulatory effects of MCs in fish depend on the exposure concentrations, doses, time, and routes of exposure. Previous field and laboratory studies provided strong evidence of the associations between MC-induced immunotoxicity and fish death. In our review, we summarized that the immunotoxicity of MCs is primarily characterized by the inhibition of PP1 and PP2A, oxidative stress, immune cell damage, and inflammation, as well as apoptosis. The advances in fish immunoreaction upon encountering MCs will benefit the monitoring and prediction of fish health, helping to achieve an ecotoxicological goal and to ensure the sustainability of species. Future studies concerning MC-induced immunotoxicity should focus on adaptive immunity, the hormesis phenomenon and the synergistic effects of aquatic microbial pathogens.     

Protective effects of puerarin on carbon tetrachloride-induced hepatotoxicity

Puerarin, the main isoflavone glycoside found in the root of Pueraria lobata, has been used for various medicinal purposes in traditional Chinese medicine for thousands of years. The purpose of this study was to investigate the protective effects of puerarin against hepatotoxicity induced by carbon tetrachloride (CCl4) and the mechanism of its hepatoprotective effect. In mice, pretreatment with puerarin prior to the administration of CCl4 significantly prevented the increased serum enzymatic activity of alanine aspartate aminotransferase and hepatic malondialdehyde formation in a dose-dependent manner. In addition, pretreatment with puerarin significantly prevented both the depletion of reduced glutathione (GSH) content and the decrease in glutathione S-transferase (GST) activity in the liver of CCl4-intoxicated mice. Hepatic GSH levels and GST activity were increased by treatment with puerarin alone. CCl4-induced hepatotoxicity was also prevented, as indicated by liver histopathology. The effects of puerarin on cytochrome P450 (CYP) 2E1, the major isozyme involved in CCl4 bioactivation, were also investigated. Treatment of the mice with puerarin resulted in a significant decrease in the CYP2E1-dependent aniline hydroxylation in a dose-dependent manner. Consistent with these observations, the CYP2E1 protein levels were also lowered. Puerarin exhibited anti-oxidant effects on FeCl2-ascorbate induced lipid peroxidation in mouse liver homogenates, and on superoxide radical scavenging activity. These results suggest that the protective effects of puerarin against the CCl4-induced hepatotoxicity possibly involve mechanisms related to its ability to block CYP-mediated CCl4 bioactivation, induction of GST activity and free radical scavenging effects.     

Secretory phospholipase A₂-mediated progression of hepatotoxicity initiated by acetaminophen is exacerbated in the absence of hepatic COX-2

We have previously reported that among the other death proteins, hepatic secretory phospholipase A₂ (sPLA₂) is a leading mediator of progression of liver injury initiated by CCl₄ in rats. The aim of our present study was to test the hypothesis that increased hepatic sPLA₂ released after acetaminophen (APAP) challenge mediates progression of liver injury in wild type (WT) and COX-2 knockout (KO) mice. COX-2 WT and KO mice were administered a normally non lethal dose (400 mg/kg) of acetaminophen. The COX-2 KO mice suffered 60% mortality compared to 100% survival of the WT mice, suggesting higher susceptibility of COX-2 KO mice to sPLA₂-mediated progression of acetaminophen hepatotoxicity. Liver injury was significantly higher at later time points in the KO mice compared to the WT mice indicating that the abatement of progression of injury requires the presence of COX-2. This difference in hepatotoxicity was not due to increased bioactivation of acetaminophen as indicated by unchanged cyp2E1 protein and covalently bound ¹⁴C-APAP in the livers of KO mice. Hepatic sPLA₂ activity and plasma TNF-α were significantly higher after APAP administration in the KO mice. This was accompanied by a corresponding fall in hepatic PGE₂ and lower compensatory liver regeneration and repair (³H-thymidine incorporation) in the KO mice. These results suggest that hindered compensatory tissue repair and poor resolution of inflammation for want of beneficial prostaglandins render the liver very vulnerable to sPLA₂-mediated progression of liver injury. These findings are consistent with the destructive role of sPLA₂ in the progression and expansion of tissue injury as a result of continued hydrolytic breakdown of plasma membrane phospholipids of perinecrotic hepatocytes unless mitigated by sufficient co-induction of COX-2.     

Protective effects of silica hydride against carbon tetrachloride-induced hepatotoxicity in mice

The protective effects of MegaHydrate™ silica hydride against liver damage were evaluated by its attenuation of carbon tetrachloride (CCl₄)-induced hepatotoxicity in mice. Male ICR mice were orally treated with silica hydride (104, 208 and 520 mg/kg) or silymarin (200 mg/kg) daily, with administration of CCl₄ (1 mL/kg, 20% CCl4 in olive oil) twice a week for eight weeks. The results showed that oral administration of silica hydride significantly reduced the elevated serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), triglyceride (TG), and cholesterol and the level of malondialdehyde (MDA) in the liver that were induced by CCl₄ in mice. Moreover, the silica-hydride treatment was also found to significantly increase the activities of superoxide dismutase (SOD), catalase, and glutathione peroxidase (GSH-Px), as well as increase the GSH content, in the liver. Liver histopathology also showed that silica hydride reduced the incidence of liver lesions induced by CCl₄. The results suggest that silica hydride exhibits potent hepatoprotective effects on CCl₄-induced liver damage in mice, likely due to both the increase of antioxidant-defense system activity and the inhibition of lipid peroxidation.     

Microcystin congener- and concentration-dependent induction of murine neuron apoptosis and neurite degeneration

Cyanobacterial microcystins (MCs) represent a toxin group with > 100 variants, requiring active uptake into cells via organic anion-transporting polypeptides, in order to irreversibly inhibit serine/threonine-specific protein phosphatases. MCs are a human health hazard with repeated occurrences of severe poisonings. In the well-known human MC intoxication in Caruaru, Brazil (1996), patients developed signs of acute neurotoxicity, e.g., deafness, tinnitus, and intermittent blindness, as well as subsequent hepatotoxicity. The latter data, in conjunction with some animal studies, suggest that MCs are potent neurotoxins. However, there is little data to date demonstrating MC neuron-specific toxicity. MC exposure-induced cytotoxicity, caspase activity, chromatin condensation, and microtubule-associated Tau protein hyperphosphorylation (epitopes serine199/202 and serine396) were determined. Neurite degeneration was analyzed with confocal microscopy and neurite length determined using image analysis. MC-induced apoptosis was significantly increased by MC-LF and MC-LW, however, only at high concentrations (≥ 3μM), whereas significant neurite degeneration was already observed at 0.5μM MC-LF. Moreover, sustained hyperphosphorylation of Tau was observed with all MC congeners. The concentration- and congener-dependent mechanisms observed suggest that low concentrations of MC-LF and MC-LW can induce subtle neurodegenerative effects, reminiscent of Alzheimer's disease type human tauopathies, and thus should be taken more seriously with regard to potential human health effects than the apical cytotoxicity (apoptosis or necrosis) demonstrated at high MC concentrations.     

Sulforaphane suppressed LPS-induced inflammation in mouse peritoneal macrophages through Nrf2 dependent pathway

Sulforaphane (SFN) is a natural isothiocyanate that is present in cruciferous vegetables such as broccoli and cabbage. Previous studies have shown that SFN is effective in preventing carcinogenesis induced by carcinogens in rodents, which is related in part to its potent anti-inflammation properties. In the present study, we compared the anti-inflammatory effect of SFN on LPS-stimulated inflammation in primary peritoneal macrophages derived from Nrf2 (+/+) and Nrf2 (−/−) mice. Pretreatment of SFN in Nrf2 (+/+) primary peritoneal macrophages potently inhibited LPS-stimulated mRNA expression, protein expression and production of TNF-α, IL-1β, COX-2 and iNOS. HO-1 expression was significantly augmented in LPS-stimulated Nrf2 (+/+) primary peritoneal macrophages by SFN. Interestingly, the anti-inflammatory effect was attenuated in Nrf2 (−/−) primary peritoneal macrophages. We concluded that SFN exerts its anti-inflammatory activity mainly via activation of Nrf2 in mouse peritoneal macrophages.     

联苯双酯对他克林引起的肝损伤的保护作用

目的　观察联苯双酯(DDB)对他克林(THA)诱发小鼠肝损伤的保护作用。方法　小鼠一次poTHA(56mg·kg^-1) ,观察12h内动物血清ALT ,肝脏MDA和动物体温的改变;分光光度法测定小鼠脑乙酰胆碱酯酶活性;酶动力法测定小鼠肝微粒体7-乙氧基香豆素脱乙基酶和UDP葡糖醛酸转移酶(UDPGT)的活性;荧光法测定线粒体膜电位的改变。结果　DDB 200 mg·kg^-1 可明显保护THA引起的小鼠体温下降、血清ALT和肝脏MDA的升高。DDB(100 μmol·L^-1 )可减轻THA造成的大鼠线粒体膜电位降低。DDB还可提高小鼠肝微粒体7-乙氧基香豆素脱乙基酶的活性,但对UDPGT无影响。结论　DDB似通过降低肝脏脂质过氧化反应、提高线粒体膜稳定性、调节THA代谢酶活性发挥其肝保护作用     

The Aggravation of Clozapine-Induced Hepatotoxicity by Glycyrrhetinic Acid in Rats

Clozapine (CLZ) was reported to be associated with hepatotoxicity. Glycyrrhetinic acid (GA) has a liver protective effect. Our preliminary experiments showed that GA aggravated rather than attenuated CLZ-induced hepatotoxicity in primary cultured rat hepatocytes. The study aimed to describe the enhancing effect of GA on CLZ-induced hepatotoxicity in vivo and in vitro. Data from primary cultured rat hepatocytes showed the decreased formation of metabolites demethylclozapine (nor-CLZ) and clozapine N-oxide (CLZ N-oxide). The results in vivo showed that 7-day CLZ treatment led to marked accumulation of triglyceride (TG) and increase in γ-glutamyl transpeptidase (γ-GT) activity, liver weight, and serum AST in rats. Co-administration of GA enhanced the increases in hepatic TG, γ-GT, liver weight, and serum total cholesterol induced by CLZ. GA decreased plasma concentrations of nor-CLZ and CLZ N-oxide. Compared with control rats, hepatic microsomes of GA rats exhibited the decreased formations of nor-CLZ and CLZ N-oxide, accompanied by decreases in activities of CYP2C11 and CYP2C19 and increased activity of CYP1A2. QT-PCR analysis demonstrated that GA enhanced expression of CYP1A2, but suppressed expression of CYP2C11 and CYP2C13. All these results support the conclusion that GA aggravated CLZ-induced hepatotoxicity, which was partly via inhibiting CYP2C11 and CYP2C13 or inducing CYP1A2.     

Benzyl alcohol protects against acetaminophen hepatotoxicity by inhibiting cytochrome P450 enzymes but causes mitochondrial dysfunction and cell death at higher doses

Acetaminophen (APAP) hepatotoxicity is a serious public health problem in western countries. Current treatment options for APAP poisoning are limited and novel therapeutic intervention strategies are needed. A recent publication suggested that benzyl alcohol (BA) protects against APAP hepatotoxicity and could serve as a promising antidote for APAP poisoning. To assess the protective mechanisms of BA, C56Bl/6J mice were treated with 400 mg/kg APAP and/or 270 mg/kg BA. APAP alone caused extensive liver injury at 6 h and 24 h post-APAP. This injury was attenuated by BA co-treatment. Assessment of protein adduct formation demonstrated that BA inhibits APAP metabolic activation. In support of this, in vitro experiments also showed that BA dose-dependently inhibits cytochrome P450 activities. Correlating with the hepatoprotection of BA, APAP-induced oxidant stress and mitochondrial dysfunction were reduced. Similar results were obtained in primary mouse hepatocytes. Interestingly, BA alone caused mitochondrial membrane potential loss and cell toxicity at high doses, and its protective effect could not be reproduced in primary human hepatocytes (PHH). We conclude that BA protects against APAP hepatotoxicity mainly by inhibiting cytochrome P450 enzymes in mice. Considering its toxic effect and the loss of protection in PHH, BA is not a clinically useful treatment option for APAP overdose patient.     

Role of CYP2E1 in thioacetamide-induced mouse hepatotoxicity

Previous experiments showed that treatment of mice and rats with thioacetamide (TAA) induced liver cell damage, fibrosis and/or cirrhosis, associated with increased oxidative stress and activation of hepatic stellate cells. Some experiments suggest that CYP2E1 may be involved in the metabolic activation of TAA. However, there is no direct evidence on the role of CYP2E1 in TAA-mediated hepatotoxicity. To clarify this, TAA-induced hepatotoxicity was investigated using Cyp2e1-null mice. Male wild-type and Cyp2e1-null mice were treated with TAA (200 mg/kg of body weight, single, i.p.) at 6 weeks of age, and hepatotoxicity examined 24 and 48 h after TAA treatment. Relative liver weights of Cyp2e1-null mice were significantly different at 24 h compared to wild-type mice (p<0.01). Serum levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP) and lactate dehydrogenase (LDH) in Cyp2e1-null mice were significantly different at both time points compared to wild-type mice (p<0.01). Histopathological examination showed Cyp2e1-null mice represented no hepatototoxic lesions, in clear contrast to severe centriobular necrosis, inflammation and hemorrhage at both time points in wild-type mice. Marked lipid peroxidation was also only limited to wild-type mice (p<0.01). Similarly, TNF-alpha, IL-6 and glutathione peroxidase mRNA expression in Cyp2e1-null mice did not significantly differ from the control levels, contrasting with the marked alteration in wild-type mice (p<0.01). Western blot analysis further revealed no increase in iNOS expression in Cyp2e1-null mice. These results reveal that CYP2E1 mediates TAA-induced hepatotoxicity in wild-type mice as a result of increased oxidative stress.