Neuroprotection of quercetin on central neurons against chronic high glucose through enhancement of Nrf2/Glo-1 mediated by phosphorylation regulation / 中国药理学与毒理学杂志

ABSTRACT

OBJECTIVE To investigate the neuroprotective effects of quercetin on central neurons against chronic high glucose in central neurons, in relation to Nrf2/ARE/Glo-1 activation. METHODS SH- SY5Y cells were cultured with high glucose (HG, 70 mmol · L- 1), 4- fold of the normal glucose (17.5 mmol · L- 1). Quercetin was set three concentrations (5, 10, 20 μmol · L- 1), with Nrf2 activator sulforaphane (SFN) as a positive group (2.5 μmol·L-1). After 72 h, cells were collected for glyoxalase 1 (Glo-1) activity and GSH level were by spectrophotometry; advanced glycation end-products (AGEs) as well as nuclear Nrf2 and p-Nrf2 levels by immunofluorescence; Glo-1, γ-glutamycysteine synthase (γ-GCS), Nrf2 and p-Nrf2 protein levels by Western blotting, and Glo-1 and γ-GCS mRNA levels by real-time qPCR. RESULTS Quercetin increased the cell viability of SH-SY5Y cells, and upregulated the levels of Glo-1 activity, protein, and mRNA in SH-SY5Y cells cultured with HG, accompanied by the elevated levels of glutathione, a cofactor of Glo-1 activity, and the reduced levels of AGEs. Meanwhile, quercetin could increase p- Nrf2 and Nrf2 levels in nucleus as well as p- Nrf2 levels in cytosol of SH-SY5Y cells exposed to chronic HG, accompanied by the elevated protein expression and mRNA levels of γ- GCS, a known target gene of Nrf2/ARE signaling. Moreover, a PKC activator or a p38 MAPK inhibitor pretreatment could significantly increase the protein expression of γ-GCS in HG condition, but an alkylating agent for sulfydryl of cysteine in Keap 1, a negative regulator of Nrf2, pretreatment only showed an increased tendency of γ-GCS protein, compared with without pretreatment; however, after pretreatment with those tool drugs, co-treatment with quercetin and HG had similar results to those of single tool drug pretreatment followed by HG exposure. CONCLUSION Firstly, quercetin can enhance Glo-1 function in central neurons, which is mediated by activation of Nrf2/ARE pathway, then exerts the neuroprotection against HG induced damage; moreover, PKC and p38 MAPK pathways may be involved in Nrf2 inactivation in chronic HG condition.