The efficacy of foot and neck cooling on autophagy and cellular stress responses in peripheral blood mononuclear cells from older adults exposed to extreme heat.

Abstract

With rising average global temperatures, extreme heat events are becoming more frequent and intense, placing heat-vulnerable older adults at an elevated risk of mortality and morbidity. We recently showed that a brief 2 h access to air-conditioning during a simulated heatwave confers cytoprotective benefits in older adults; however, air-conditioning is inaccessible to many. Although foot immersion and neck cooling have been proposed as alternative cooling strategies, their effects on cellular stress are unclear. We evaluated cellular responses (autophagy, apoptosis, acute inflammation, and heat shock proteins) in peripheral blood mononuclear cells from 17 participants (9 females, median age: 72 [IQR, 69-74] yr) who completed three, 6-h heat exposures at 38°C (35% relative humidity) with either no-cooling (control), submersion of the feet (mid-calf) in 20°C water for 40-min each hour or foot immersion with a cool wet towel (20°C) around the neck. Core (rectal) temperature was measured continuously. Western blot analysis was used to assess changes in protein responses at baseline and end exposure. Despite similar elevations in core temperature between conditions, p62 concentrations were elevated in the control compared with both foot immersion with [mean difference: 0.4 relative quantity (RQ); P = 0.046] and without (0.6 RQ; P = 0.026) neck cooling. Furthermore, HSP70 concentrations were elevated in control compared with foot immersion (0.7 RQ; P = 0.030). No changes between conditions were observed for apoptotic or inflammatory proteins. Although foot immersion with or without neck cooling had minimal impact on core temperature, these strategies may improve autophagic responses in older adults when exposed to extreme heat.NEW & NOTEWORTHY As the incidence and severity of heatwaves continue to rise, there is an urgent need to develop accessible and sustainable heat-alleviation strategies. We evaluated the use of foot immersion in cool water with or without the addition of a damp towel around the neck on cellular stress responses in older adults exposed to extreme heat. Although neither cooling intervention reduced elevations in core temperature, both cooling strategies may improve autophagic responses in older adults.