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.

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 2h access to air-conditioning during a simulated heatwave confers cytoprotective benefits in older adults, however air-conditioning is inaccessible to many. While 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, heat shock proteins) in peripheral blood mononuclear cells from 17 participants (9 females, median age 72 [IRQ, 69-74] years) who completed 3, 6h 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 to both foot immersion with (mean difference: 0.4 relative quantity [RQ]; P=0.046) and without (0.6 RQ; P=0.026) neck cooling. Further, HSP70 concentrations were elevated in control compared to foot immersion (0.7 RQ; P=0.030). No changes between conditions were observed for apoptotic or inflammatory proteins. While 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.