Abstract
Curcumin is a bifunctional antioxidant derived from Curcuma longa. This study identifies curcumin as a neuroprotectant against hemin-induced damage in primary cultures of cerebellar granule neurons (CGNs) of rats. Hemin, the oxidized form of heme, is a highly reactive compound that induces cellular injury. Pretreatment of CGNs with 5–30 μM curcumin effectively increased by 2.3–4.9 fold heme oxygenase-1 (HO-1) expression and by 5.6–14.3-fold glutathione (GSH) levels. Moreover, 15 μM curcumin attenuated by 55% the increase in reactive oxygen species (ROS) production, by 94% the reduction of GSH/glutathione disulfide (GSSG) ratio, and by 49% the cell death induced by hemin. The inhibition of heme oxygenase system or GSH synthesis with tin mesoporphyrin and buthionine sulfoximine, respectively, suppressed the protective effect of curcumin against hemin-induced toxicity. These data strongly suggest that HO-1 and GSH play a major role in the protective effect of curcumin. Furthermore, it was found that 24 h of incubation with curcumin increases by 1.4-, 2.3-, and 5.2-fold the activity of glutathione reductase, glutathione S-transferase and superoxide dismutase, respectively. Additionally, it was found that curcumin was capable of inducing nuclear factor (erythroid-derived 2)-like 2 (Nrf2) translocation into the nucleus. These data suggest that the pretreatment with curcumin induces Nrf2 and an antioxidant response that may play an important role in the protective effect of this antioxidant against hemin-induced neuronal death.
Highlights
The use of natural products has been a general approach for regulating antioxidant homeostasis in cells
It has been shown that curcumin induces endogenous antioxidant defense mechanisms by modulating transcription factors such as nuclear factor-like 2 (Nrf2) [4], activator protein-1 (AP-1), and nuclear factor kappa B (NFκB) [12]
It was shown that cerebellar granule neurons (CGNs) exposure to hemin induced a decrease in the viability in a concentration-dependent way from 20 to 50 μM after 1 h of incubation, using two methods: FDA fluorescence and MTT reduction (Figures 1(a) and 1(b))
Summary
The use of natural products has been a general approach for regulating antioxidant homeostasis in cells. Curcumin has shown to be an effective anticarcinogenic, antiviral, antioxidant [2,3,4,5], and anti-inflammatory substance in human, cell cultures and animal models [6, 7]. Curcumin acts as a direct and an indirect antioxidant since it scavenges reactive oxygen and nitrogen species [8, 9] and induces cytoprotective enzymes such as glutathione-Stransferase (GST), γ-glutamyl cysteine ligase (γ-GCL), heme oxygenase-1 (HO-1), among others [10, 11]. It has been shown that curcumin induces endogenous antioxidant defense mechanisms by modulating transcription factors such as nuclear factor (erythroidderived 2)-like 2 (Nrf2) [4], activator protein-1 (AP-1), and nuclear factor kappa B (NFκB) [12]. Modification of Keap 1 by oxidation or alkylation (e.g., curcumin interaction) releases
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