Autophagy And Apoptosis After Foot And Neck Cooling In Older Adults Exposed To Extreme Heat

We recently showed that a brief 2 h access to air conditioning during a 9 h simulated heat wave caused a robust reduction in core temperature in older adults. However, the changes were transient with core temperature returning to levels similar to their non-cooled counterparts within 2 h of re-entry to the heat. However, it did preserve cytoprotective autophagy and prevented apoptotic cell death, that could play a critical role in reducing heat-induced cellular injury. It remains unclear if alternative home-based cooling interventions (e.g., foot immersion, cool wet towels on the neck) would elicit comparable benefits. PURPOSE: To evaluate cellular responses in older adults during a prolonged heat wave simulation while either immersing the feet in cool water with and without applying a cool wet towel to the neck compared to no-cooling. METHODS: 17 participants (9 females, median age 72 [IRQ, 69-74] years) completed 3, 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 the last 40-min of each hour or foot immersion with a cool wet towel (20 °C) around the neck. Core (rectal) temperature was measured continuously, while proteins associated with autophagy (LC3-II) and apoptosis (caspase-3) were assessed in peripheral blood mononuclear cells before and after each exposure via Western blot. Data are presented as relative quantity (RQ) from baseline and were analyzed via a one-way ANOVA with Bonferroni correction (α = 0.05). RESULTS: Elevations in core temperature were not different between conditions (+1.1 °C; all P > 0.99). No differences in LC3-II were observed following foot immersion with (2.0 RQ [SD 1.9]) or without neck cooling (1.2 RQ [0.4]) compared to no-cooling (1.7 RQ [1.1]; both P ≥ 0.21). Similarly, caspase-3 did not differ from no-cooling at end-exposure (1.3 RQ [0.4]) with either cooling intervention (without neck cooling: 1.39 RQ [0.83]; with neck cooling: 1.42 RQ [0.8]; P ≥ 0.91). CONCLUSION: Foot immersion with and without neck cooling had minimal impact on autophagy or apoptosis during a 6 h passive heat exposure and therefore, may not be effective in alleviating cellular stress in older adults when exposed to extreme heat. Supported by: Canadian Institutes of Health Research, Health Canada