Butein up-regulates the expression of the π class of glutathione S-transferase in rat primary hepatocytes through the ERK/AP-1 pathway

Modulatory Role of Curcumin on Cobalt-Induced Memory Deficit, Hippocampal Oxidative Damage, Astrocytosis, and Nrf2 Expression

Chemical overexposure is a growing environmental risk factor for many medical issues. Cobalt toxicity from environmental, industrial, and medical exposure has previously been linked to neurological impairment. Hence, the current study looked into the neuroprotective potential of curcumin, a natural polyphenol contained in the spice turmeric, against cobalt-induced neurotoxicity. Adult rats were randomly divided into six groups as follows: control, 40 mg/kg cobalt chloride (CoCl₂) only, 240 mg/kg curcumin only, 120 mg/kg or 240 mg/kg curcumin, or 100 mg/kg vitamin C co-administered with CoCl₂. The administration was via oral route daily for 4 weeks. After that, neurobehavioral tests were undertaken to evaluate short-term spatial memory. Biochemical investigation was performed to determine the hippocampal levels of status via measures of SOD, CAT, GST, and LPO. Furthermore, immunohistochemical assessment of the expression of GFAP and Nrf2 in the hippocampus was carried out. In the CoCl₂ group, the results showed altered behavioral responses, a decrease in antioxidant activities, increased expression of GFAP and the number of activated astrocytes, and decreased immunoexpression of Nrf2. These effects were mitigated in the curcumin- and vitamin C-treated groups. These results collectively imply that curcumin enhances memory functions in rats exposed to cobalt possibly by attenuating oxidative responses, mitigating astrocytosis, and modulating Nrf2 signaling.

Glutathione S-transferases P1-mediated interleukin-6 in tumor-associated macrophages augments drug-resistance in MCF-7 breast cancer

Glutathione S-transferase P1 (GSTP1), a phase II detoxifying enzyme, is overexpressed and plays an important role during breast cancer drug resistance. Tumor-associated macrophages (TAMs), representing most of the leukocyte population in solid tumors, are involved in cancer cell resistance to chemotherapy. Although GSTP1 exists in TAMs, whether GSTP1 in TAMs promotes drug resistance is still unclear. In the current study, we found a novel mechanism that GSTP1 in TAMs contributes breast cancer cell drug resistance. GSTP1 is aberrantly expressed in TAMs from breast cancer tissues of patients after chemotherapy than that without chemotherapy. Adriamycin (ADR) time-dependently induced the expression of GSTP1 in TAMs in vitro. Conditional medium of TAMs significantly inhibited ADR-induced cell death of MCF-7 breast cancer cells. Meanwhile, overexpression of GSTP1 in TAMs promoted the expression and release of interleukin-6 (IL-6) associated with reduced ADR-induced breast cell death, which was reversed by IL-6 antibody. Mechanistically, GSTP1 interacted with inhibitor of nuclear factor κB kinase β (IKKβ) to activate nuclear factor-κB (NF-κB) to induced the expression and release of IL-6 in TAMs. Moreover, IL-6 further upregulated GSTP1 through c-Jun, and ultimately mediated drug resistance in MCF-7 cells. Taken together, our data demonstrated for the first time that GSTP1 in TAMs promoted ADR-resistance in breast cancer by regulating interleukin-6 release.

Acute microplastic exposure raises stress response and suppresses detoxification and immune capacities in the scleractinian coral Pocillopora damicornis

Microplastics are widespread emerging contaminants that have been found globally in the marine and freshwater ecosystem, but there is limited knowledge regarding its impact on coral reef ecosystem and underpinning mechanism. In the present study, using Pocillopora damicornis as a model, we investigated cytological, physiological, and molecular responses of a scleractinian coral to acute microplastic exposure. No significant changes were observed in the density of symbiotic zooxanthellae during the entire period of microplastic exposure, while its chlorophyll content increased significantly at 12 h of microplastic exposure. We observed significant increases in the activities of antioxidant enzymes such as superoxide dismutase and catalase, significant decrease in the detoxifying enzyme glutathione S-transferase and the immune enzyme alkaline phosphatase, but no change in the other immune enzyme phenoloxidase during the whole experiment period. Transcriptomic analysis revealed 134 significantly up-regulated coral genes at 12 h after the exposure, enriched in 11 GO terms mostly related to stress response, zymogen granule, and JNK signal pathway. Meanwhile, 215 coral genes were significantly down-regulated at 12 h after exposure, enriched in 25 GO terms involved in sterol transport and EGF-ERK1/2 signal pathway. In contrast, only 12 zooxanthella genes exhibited significant up-regulation and 95 genes down-regulation at 12 h after the microplastic exposure; genes regulating synthesis and export of glucose and amino acids were not impacted. These results suggest that acute exposure of microplastics can activate the stress response of the scleractinian coral P. damicornis, and repress its detoxification and immune system through the JNK and ERK signal pathways. These demonstrate that microplastic exposure can compromise the anti-stress capacity and immune system of the scleractinian coral P. damicornis, despite the minimal impact on the abundance and major photosynthate translocation transporters of the symbiont in the short term.

Induction of the pi class of glutathione S-transferase by carnosic acid in rat Clone 9 cells via the p38/Nrf2 pathway

Induction of phase II enzymes is important in cancer chemoprevention. We compared the effect of rosemary diterpenes on the expression of the pi class of glutathione S-transferase (GSTP) in rat liver Clone 9 cells and the signaling pathways involved. Culturing cells with 1, 5, 10, or 20 μM carnosic acid (CA) or carnosol (CS) for 24 h in a dose-dependent manner increased the GSTP expression. CA was more potent than CS. The RNA level and the enzyme activity of GSTP were also enhanced by CA treatment. Treatment with 10 μM CA highly induced the reporter activity of the enhancer element GPEI. Furthermore, CA markedly increased the translocation of nuclear factor erythroid-2 related factor 2 (Nrf2) from the cytosol to the nucleus after 30 to 60 min. CA the stimulated the protein induction of p38, nuclear Nrf2, and GSTP was diminished in the presence of SB203580 (a p38 inhibitor). In addition, SB203580 pretreatment or silencing of Nrf2 by siRNA suppressed the CA-induced GPEI-DNA binding activity and GSTP protein expression. Knockdown of p38 or Nrf2 by siRNA abolished the activation of p38 and Nrf2 as well as the protein induction and enzyme activity of GSTP by CA. These results suggest that CA up-regulates the expression and enzyme activity of GSTP via the p38/Nrf2/GPEI pathway.

Inhibition and induction of glutathione S-transferases by flavonoids: possible pharmacological and toxicological consequences

Many studies reviewed herein demonstrated the potency of some flavonoids to modulate the activity and/or expression of glutathione S-transferases (GSTs). Because GSTs play a crucial role in the detoxification of xenobiotics, their inhibition or induction may significantly affect metabolism and biological effects of many drugs, industrials, and environmental contaminants. The effect of flavonoids on GSTs strongly depends on flavonoid structure, concentration, period of administration, as well as on GST isoform and origin. Moreover, the results obtained in vitro are often contrary to the vivo results. Based on these facts, the revelation of important flavonoid-drug or flavonoid-pollutant interaction has been complicated. However, it should be borne in mind that ingestion of certain flavonoids in combination with drugs or pollutants (e.g., acetaminophen, simvastatin, cyclophosphamide, cisplatine, polycyclic aromatic hydrocarbons, chlorpyrifos, acrylamide, and isocyanates), which are GST substrates, could have significant pharmacological and toxicological consequences. Although reasonable consumptions of a flavonoids-rich diet (that may lead to GST induction) are mostly beneficial, the uncontrolled intake of high concentrations of certain flavonoids (e.g., quercetin and catechins) in dietary supplements (that may cause GST inhibition) may threaten human health.

Activation of Nrf2 is required for up-regulation of the π class of glutathione S-transferase in rat primary hepatocytes with L-methionine starvation

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.