Green tea polyphenol epigallocatechin-3-gallate mediates an antioxidant response via Nrf2 pathway in heat-stressed poultry: A review

Heat stress is a critical challenge in the poultry industry. It arises when birds are exposed to elevated ambient temperatures beyond their thermoneutral zone, often exacerbated by high humidity and inadequate ventilation. This condition disrupts the birds' ability to maintain thermal homeostasis, leading to physiological and behavioral changes such as increased panting, reduced feed intake, and elevated water consumption. These responses aim to dissipate heat but often result in energy imbalances, oxidative stress, and impaired immune function. Green tea polyphenols (GTPs) mitigate heat stress in poultry birds by modulating oxidative stress pathways, primarily by scavenging reactive oxygen species (ROS) and enhancing antioxidant defense mechanisms. These pathways play a pivotal role in neutralizing ROS generated during oxidative stress, inflammation, and exposure to electrophilic compounds. This action helps restore cellular balance and enhances overall antioxidant defense mechanisms by converting harmful free radicals into less reactive molecules, such as water and oxygen. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) plays a significant character in the activation of the enzymatic antioxidants network. It translocates to the nucleus upon activation, binds to antioxidant response elements (AREs) in the promoter regions of target genes, and upregulates the expression of key antioxidant enzymes. Therefore, the regulation of Nrf2 is considered a critical molecular marker in mitigating the effects of heat stress, as its activation enhances the expression of antioxidant and detoxification enzymes, protecting against oxidative damage and inflammation induced by elevated temperatures. This exploratory review summarizes the antioxidant mechanisms and anti-oxidative stress effects of GTPs in mitigating heat stress in poultry. It highlights the cytoprotective molecular basis of epigallocatechin-3-gallate (EGCG), particularly its role in modulating Nrf2-mediated cellular pathways, which enhance antioxidant defense systems and protect against oxidative damage.