Theanine supplementation prevents liver injury and heat shock response by normalizing hypothalamic-pituitaryadrenal axis hyperactivity in mice subjected to whole body heat stress

Thermal stress evokes heat shock response and activates hypothalamic-pituitaryadrenal (HPA) axis. Additionally, liver injury is an important adverse effect of thermal stress. Considering the anti-stress effects of theanine, an amino acid found in tea plants, we hypothesized that theanine may protect against heat stress. Mice were administered intragastrically with theanine prior to whole body thermal exposure. Theanine prevented the heat-induced upregulation of heat shock proteins and reduced the heat-induced liver damage and oxidative stress. Theanine significantly prevented the heat-induced effects on inflammatory and acute phase responses as measured by plasma inflammatory cytokine concentrations, hepatic inflammatory cytokine mRNA levels, plasma nitric oxide and C-reactive protein levels. Additionally, theanine supplementation suppressed heat stress-related disorders associated with normalizing HPA axis hyperactivity. These findings suggest that theanine can have beneficial effects against heat stress and may be an attractive dietary application for people who are at high risk of developing heat stress.