The Role of Catechins in Cellular Responses to Oxidative Stress

Exploring the potential benefit of natural product extracts in paraquat toxicity

Paraquat dichloride, a herbicide used for weed and grass control, is extremely toxic to humans and animals. The mechanisms of toxicity involve the redox cycling of paraquat resulting in the generation of reactive oxygen species and the depletion of the cellular NADPH. The major cause of death in paraquat poisoning is respiratory failure due to its specific uptake by and oxidative insult to the alveolar epithelial cells and inflammation with subsequent obliterating fibrosis. Paraquat also causes selective degeneration of dopaminergic neurons in the substantia nigra pars compacta, reproducing an important pathological feature of Parkinson disease. Currently, there are no antidotes for the treatment of paraquat poisoning and therapeutic management is mostly supportive and directed towards changing the disposition of the poison. The lack of effective treatments against paraquat poisoning has led to the exploration of novel compounds with antioxidant and/or anti-inflammatory properties. Recently, there is an interest in plant compounds, particularly those used in traditional medicine. Phytochemicals have been highlighted as a possible therapeutic modality for a variety of diseases due to their putative efficacies and safety. In this review, the status of plant extracts and traditional medicines in ameliorating the toxicity of paraquat is discussed.

Antioxidant and pro-oxidant mechanisms of (+) catechin in microsomal CYP2E1-dependent oxidative stress

The objectives of this work were to evaluate the effects of catechin on cytochrome P450 2E1 (CYP2E1)-dependent oxidative stress. Microsomes co-expressing human CYP2E1 with NADPH cytochrome P450 reductase and cytochrome b5 were incubated with NADPH and DTPA at pH 7.0. Superoxide anion generation was specifically detected by spin-trapping with DEPMPO. Generation of the DEPMPO-OOH adduct was not observed in the absence of CYP2E1 and in the presence of superoxide dismutase (SOD) or catechin, while catalase was ineffective. Reactive oxygen species generation was detected with 1-hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine (CPH) by the EPR-detection of its oxidation product, 3-carboxy-proxyl radical (CP^●). CP^● generation was not observed in the absence of CYP2E1 and in the presence of SOD, while catalase was ineffective. In contrast, catechin increased CPH oxidation, an effect that was not observed in the absence of CYP2E1 or in the presence of SOD (but not catalase), and was not associated with an increase in oxygen consumption. Catechin also increased the non-specific oxidation of the probes CPH and hydroethidine by the superoxide anion-generating system xanthine plus xanthine oxidase. Catechin oxidized CPH in the presence of horseradish peroxidase plus hydrogen peroxide, a catechin radical-generating system. In conclusion, catechin exhibits both antioxidant (superoxide-scavenging) and pro-oxidant effects under CYP2E1-dependent oxidative stress.

Overexpression of miR-153 promotes oxidative stress in MPP+-induced PD model by negatively regulating the Nrf2/HO-1 signaling pathway

Increasing evidence points to oxidative stress as a chief mediator of Parkinson's disease (PD) characterized by progressive loss of dopamine neurons in the pars compacta of the substantia nigra. At present, microRNAs (miRNAs) have been recognized as important regulators in oxidative stress. Furthermore, miRNAs were also involved in the neuropathology of neurodegenerative disorders, including PD. In this study, we aimed to explore the influences of miR-153 and Nrf2 in oxidative stress during the development of PD. It was found that the expression of miR-13 and Nrf2 detected by qRT-PCR were significantly increased and decreased, respectively, in serum of PD patients and MPP⁺-induced SH-SY5Y cells. The target relationship between miR-153 and Nrf2 was determined by dual-luciferase assay. Moreover, after transfecting with miR-153 mimics and inhibitor, the expressions of Nrf2 in mRNA and protein were down-regulated and up-regulated, respectively. The indexes of oxidative stress were examined by biochemical methods. The data revealed that miR-153 could facilitate oxidative stress by negatively regulating Nrf2 in MPP⁺-treated SH-SY5Y cells. Finally, it was observed that miR-153 could suppress the Nrf2/HO-1 signaling pathway in MPP⁺-treated SH-SY5Y cells. Therefore, these findings indicated that overexpression of miR-153 could promote oxidative stress in PD by targeting the Nrf2/HO-1 signaling pathway, possibly providing a new way to treat PD.