Markers of enterocyte damage, microbial translocation and systemic inflammation following 9 hours of heat exposure in young and older adults.

Heat stress induced damage to the gastrointestinal barrier can induce local and systemic inflammatory reactions implicated in heat-stroke. Gastrointestinal barrier damage has been shown to be greater in older relative to young adults following hyperthermia. However, comparisons between young and older adults have been limited to brief exposures (3-h), which may not reflect the duration of heat stress experienced during heat waves. We therefore evaluated markers of intestinal epithelial damage (Log transformed intestinal fatty acid binding protein, IFABPLOG), microbial translocation (soluble cluster of differentiation 14, sCD14LOG), and systemic inflammation (tumour necrosis factor alpha, TNF-αLOG; interleukin 6, IL-6LOG; C-reactive protein, CRP) in 19 young (interquartile range: 21-27 yr; 10 females) and 37 older (68-73 yr; 10 females) adults before and after 9-h of rest in 40°C (9% relative humidity). The magnitude of the increase in IFABPLOG was 0.38 log pg/mL (95% CI, 0.10, 0.65 log pg/mL) greater in the older relative to young cohort (P=0.049) after 9-h heat exposure. At baseline both IL-6LOG and CRP concentrations were higher in the older (IL-6: 2.67 (1.5) log pg/mL, CRP: 0.28 (1.5) mg/mL) relative to the young (IL-6: 1.59 log pg/mL, SD 1.2; CRP: 0.11 mg/mL, SD 1.7) group (both P<0.001). The change in IL-6 and CRP was similar between groups following 9-h heat exposure (IL-6: P=0.053; CRP: P=0.24). Neither sCD14LOG and TNF-αLOG were different between groups at baseline nor altered after 9-h heat exposure. Our data indicate that age may modify intestinal epithelial injury following 9 h of passive heat exposure.

Impaired autophagy following ex vivo cooling of simulated hypothermic temperatures in peripheral blood mononuclear cells from young and older adults.

Hypothermia is a critical consequence of extreme cold exposure that increases the risk of cold-related injury and death in humans. While the initiation of cytoprotective mechanisms including the process of autophagy and the heat shock response (HSR) is crucial to cellular survival during periods of stress, age-related decrements in these systems may underlie cold-induced cellular vulnerability in older adults. Moreover, whether potential sex-related differences in autophagic regulation influence the human cold stress response remain unknown. We evaluated the effect of age and sex on mechanisms of cytoprotection (autophagy and the HSR) and cellular stress (apoptotic signaling and the acute inflammatory response) during ex vivo hypothermic cooling. Venous blood samples from 20 healthy young (10 females; mean [SD]: 22 [2] years) and 20 healthy older (10 females; 66 [5] years) adults were either isolated immediately (baseline) for peripheral blood mononuclear cells (PBMCs) or exposed to water bath temperatures maintained at 37, 35, 33, 31, or 4 °C for 90 min before PBMC isolation. Proteins associated with autophagy, apoptosis, the HSR, and inflammation were analyzed via Western blotting. Indicators of autophagic initiation and signaling (LC3, ULK1, and beclin-2) and the HSR (HSP90 and HSP70) increased when exposed to hypothermic temperatures in young and older adults (all p ≤ 0.007). Sex-related differences were only observed with autophagic initiation (ULK1; p = 0.015). However, despite increases in autophagic initiators ULK1 and beclin-2 (all p < 0.001), this was paralleled by autophagic dysfunction (increased p62) in all groups (all p < 0.001). Further, apoptotic (cleaved-caspase-3) and inflammatory (IL-6 and TNF-α) signaling increased in all groups (all p < 0.001). We demonstrated that exposure to hypothermic conditions is associated with autophagic dysfunction, irrespective of age or sex, although there may exist innate sex-related differences in cytoprotection in response to cold exposure as evidenced through altered autophagic initiation.

Greater hyperthermia in men with type 2 diabetes does not lead to higher serum levels of cellular stress biomarkers following exercise-heat stress.

Type 2 diabetes (T2D) is associated with worsening age-related impairments in heat loss, causing higher core temperature during exercise. We evaluated whether these thermoregulatory impairments occur with altered serum protein responses to heat stress by measuring cytoprotection, inflammation, and tissue damage biomarkers in middle-aged-to-older men (50-74 years) with (n = 16) and without (n = 14) T2D following exercise in 40°C. There were no changes in irisin, klotho, HSP70, sCD14, TNF-α, and IL-6, whereas NGAL (+539 pg/mL, p = 0.002) and iFABP (+250 pg/mL, p < 0.001) increased similarly across groups. These similar response patterns occurred despite elevated core temperature in individuals with T2D, suggesting greater heat vulnerability.

Effect of daylong exposure to indoor overheating on autophagy and the cellular stress response in older adults.

To protect vulnerable populations during heat waves, public health agencies recommend maintaining indoor air temperature below ∼24-28 °C. While we recently demonstrated that maintaining indoor temperatures ≤26 °C mitigates the development of hyperthermia and cardiovascular strain in older adults, the cellular consequences of prolonged indoor heat stress are poorly understood. We therefore evaluated the cellular stress response in 16 adults (six females) aged 66-78 years during 8 h rest in ambient conditions simulating homes maintained at 22 °C (control) and 26 °C (indoor temperature upper limit proposed by health agencies), as well as non-air-conditioned domiciles during hot weather and heat waves (31 and 36 °C, respectively; all 45% relative humidity). Western blot analysis was used to assess changes in proteins associated with the cellular stress response (autophagy, apoptosis, acute inflammation, and heat shock proteins) in peripheral blood mononuclear cells harvested prior to and following exposure. Following 8 h exposure, no cellular stress response-related proteins differed significantly between the 26 and 22 °C conditions (all, P ≥ 0.056). By contrast, autophagy-related proteins were elevated following exposure to 31 °C (p62: 1.5-fold; P = 0.003) and 36 °C (LC3-II, LC3-II/I, p62; all ≥2.0-fold; P ≤ 0.002) compared to 22 °C. These responses were accompanied by elevations in apoptotic signaling in the 31 and 36 °C conditions (cleaved-caspase-3: 1.8-fold and 3.7-fold, respectively; P ≤ 0.002). Furthermore, HSP90 was significantly reduced in the 36 °C compared to 22 °C condition (0.7-fold; P = 0.014). Our findings show that older adults experience considerable cellular stress during prolonged exposure to elevated ambient temperatures and support recommendations to maintain indoor temperatures ≤26 °C to prevent physiological strain in heat-vulnerable persons.

Changes in surrogate markers of intestinal epithelial injury and microbial translocation in young and older men during prolonged occupational heat stress in temperate and hot conditions.

PURPOSE: Exertional heat stress can cause damage to the intestinal epithelium and disrupt gastrointestinal barrier integrity, leading to microbial translocation (MT) linked to the development of heat stroke. This study aimed to assess age-related differences in markers of intestinal epithelial injury and MT following non-heat stress and high-heat stress exercise in healthy young and older men. METHODS: Markers of intestinal epithelial injury (intestinal fatty acid-binding protein-'IFABP') and MT (soluble cluster of differentiation 14-'sCD14'; and lipopolysaccharide-binding protein-'LBP') were assessed in healthy young (18-30 y, n = 13) and older (50-70 y) men (n = 12). Blood samples were collected before, after 180 min of moderate-intensity (metabolic rate: 200 W/m2) walking and following 60 min recovery in either a non-heat stress [temperate: 21.9 °C, 35% relative humidity (RH)] or high-heat stress (hot: 41.4 °C, 35% RH) environment. RESULTS: There were no differences in IFABP and sCD14 between the young and older groups in the temperate condition, while LBP was greater in the older group (+ 0.66 ug/mL; + 0.08 to + 1.24 ug/mL). In the hot condition, the older group experienced greater increases in IFABP compared to the young group (+ 712 pg/mL/hr; + 269 to + 1154 pg/mL/hr). However, there were no clear between-group differences for sCD14 (+ 0.24 ug/mL/hr, - 0.22 to + 0.70 ug/mL/hr) or LBP (+ 0.86 ug/mL/hr, - 0.73 to + 2.46 ug/mL/hr). CONCLUSION: While older men may experience greater intestinal epithelial injury following exercise in the heat; this did not lead to a greater magnitude of microbial translocation relative to their younger counterparts.

Physiological responses to 9 hours of heat exposure in young and older adults. Part III: Association with self-reported symptoms and mood state.

Older adults are at greater risk of heat-related morbidity and mortality during heat waves, which is commonly linked to impaired thermoregulation. However, little is known about the influence of increasing age on the relation between thermal strain and perceptual responses during daylong heat exposure. We evaluated thermal and perceptual responses in 20 young (19-31 yr) and 39 older adults (20 with hypertension and/or type 2 diabetes; 61-78 yr) resting in the heat for 9 h (heat index: 37°C). Body core and mean skin temperature areas under the curve (AUC, hours 0-9) were assessed as indicators of cumulative thermal strain. Self-reported symptoms (68-item environmental symptoms questionnaire) and mood disturbance (40-item profile of mood states questionnaire) were assessed at end-heating (adjusted for prescores). Body core temperature AUC was 2.4°C·h [1.0, 3.7] higher in older relative to young adults (P < 0.001), whereas mean skin temperature AUC was not different (-0.5°C·h [-4.1, 3.2] P = 0.799). At end-heating, self-reported symptoms were not different between age groups (0.99-fold [0.80, 1.23], P = 0.923), with or without adjustment for body core or mean skin temperature AUC (both P ≥ 0.824). Mood disturbance was 0.93-fold [0.88, 0.99] lower in older, relative to young adults (P = 0.031). Older adults with and without chronic health conditions experienced similar thermal strain, yet those with these conditions reported lower symptom scores and mood disturbance compared with young adults and their age-matched counterparts (all P ≤ 0.026). Although older adults experienced heightened thermal strain during the 9-h heat exposure, they did not experience greater self-reported symptoms or mood disturbance relative to young adults.NEW & NOTEWORTHY Despite experiencing greater cumulative thermal strain during 9 h of passive heat exposure, older adults reported similar heat-related symptoms and lower mood disturbance than young adults. Furthermore, self-reported symptoms and mood disturbance were lower in older adults with common age-associated health conditions than young adults and healthy age-matched counterparts. Perceptual responses to heat in older adults can underestimate their level of thermal strain compared with young adults, which may contribute to their increased heat vulnerability.

Temperature-Dependent Relationship of Autophagy and Apoptotic Signaling During Cold-Water Immersion in Young and Older Males.

Autophagy is a crucial cytoprotective mechanism preventing the accumulation of cellular damage, especially during external stimuli such as cold exposure. Older adults poorly tolerate cold exposure and age-related impairments in autophagy may contribute to the associated reductions in cold tolerance. The purpose of this investigation is to evaluate the effect of different intensities of in vivo cold-water immersion and in vitro cold exposure on autophagic and apoptotic signaling in young and older males. Peripheral blood mononuclear cells (PBMCs) are isolated at baseline, end-cold exposure, and after 3 h of thermoneutral recovery. Additionally, PBMCs are treated with rapamycin and bafilomycin prior to in vitro cold exposure equivalent to in vivo core temperatures (35-37 °C). Proteins associated with autophagy, apoptosis, the heat shock response, and inflammation are analyzed via Western blotting. Moderate cold stress (0.5 °C decrease in core temperature) increased autophagic and heat shock protein activity while high cold stress (1.0 °C decrease in core temperature) augmented apoptosis in young males. In older males, minimal autophagic activation during both cold-water exposures are associated with increased apoptotic and inflammatory proteins. Although in vitro cold exposure confirmed age-related dysfunction in autophagy, rapamycin-induced stimulation of autophagic proteins underlie the potential to reverse age-related vulnerability to cold exposure.

The intensity-dependent effects of exercise and superimposing environmental heat stress on autophagy in peripheral blood mononuclear cells from older men.

Autophagy is a vital cellular process, essential to maintaining cellular function during acute physiological stressors including exercise and heat stress. We previously showed that autophagy occurs during exercise in an intensity-dependent manner in peripheral blood mononuclear cells (PBMCs) from young men, with elevated responses in the heat. However, given autophagy declines with age, it is unclear whether a similar pattern of response occurs in older adults. Therefore, we evaluated autophagy and the cellular stress response [i.e., apoptosis, inflammation, and the heat shock response (HSR)] in PBMCs from 10 healthy older men [mean (SD): aged 70 yr (5)] in response to 30 min of semirecumbent cycling at low, moderate, and vigorous intensities [40, 55, and 70% maximal oxygen consumption (V̇o2max), respectively] in a temperate (25°C) environment, with an additional vigorous-intensity bout (70% of V̇o2max) performed in a hot environment (40°C). Responses were evaluated before and after exercise, as well as throughout a 6-h seated recovery period performed in the same environmental conditions as the respective exercise bout. Proteins were assessed via Western blot. Although we observed elevations in mean body temperature with each increase in exercise intensity, autophagy was only stimulated during vigorous-intensity exercise, where we observed elevations in LC3-II (P < 0.05). However, when the same exercise was performed in the heat, the LC3-II response was attenuated, which was accompanied by significant p62 accumulation (P < 0.05). Altogether, our findings demonstrate that older adults exhibit autophagic impairments when the same vigorous-intensity exercise is performed in hot environments, potentially underlying heat-induced cellular vulnerability in older men.NEW & NOTEWORTHY We demonstrate that autophagic stimulation occurs in response to short-duration (30-min) vigorous-intensity exercise in peripheral blood mononuclear cells from older adults; however, no changes in autophagy occur during low- or moderate-intensity exercise. Moreover, older adults exhibit autophagic impairments when the same vigorous-intensity exercise is performed in hot ambient conditions. When paired with an attenuated heat shock response, as well as elevated apoptotic responses, older men may exhibit greater cellular vulnerability to exertional heat stress.

Elevations in serum brain-derived neurotrophic factor following occupational heat stress are not influenced by age or common chronic disease.

With global warming, workers are increasingly exposed to strenuous occupations in hot environments. Given age- and disease-associated declines in thermoregulatory function, older workers are at an elevated risk of developing heat-related injuries. Brain-derived neurotrophic factor (BDNF) is thought to confer neuroprotection during acute exercise, however, the influence of environmental heat on BDNF responses during prolonged work remains unclear. Therefore, we evaluated serum BDNF concentrations before and after 180 min of moderate-intensity treadmill walking (200 W/m2) and after 60 min of post-exercise recovery in temperate (wet-bulb globe temperature (WBGT) 16°C) and hot (WBGT 32°C) environments in 13 healthy young men (mean [SD; 22 [3] years), 12 healthy older men (59 [4] years), 10 men with hypertension (HTN) (60 [4] years), and 9 men with type 2 diabetes (T2D) (60 [5] years). In the temperate condition, all but one participant (1 HTN) completed the 180 min of exercise. While exercise tolerance in the heat was lower in older men with HTN (117 min [45]) and T2D (123 min [42]) compared to healthy older men (159 min [31]) (both p ≤ 0.049), similar end-exercise rectal temperatures (38.9°C [0.4]) were observed across groups, paralleled by similar elevations in serum BDNF across groups at end-exercise (+1106 pg/mL [203]) and end-recovery (+938 pg/mL [146]; all p ≤ 0.01) in the heat. No changes in serum BDNF were observed in the temperate condition. Our findings indicate similar BDNF responses in individuals with HTN or T2D compared to their healthy counterparts, despite exhibiting reduced tolerance to heat.

Brief ambient cooling preserves autophagy in peripheral blood mononuclear cells from older adults during 9 h of heat exposure.

Heat waves can cause dangerous elevations in body temperature that can compromise cellular function and increase the risk of heat stroke and major cardiovascular events. Visiting a cooling center or other air-conditioned location is commonly recommended by health agencies to protect heat-vulnerable older persons but the associated cellular effects remain underexplored. We evaluated cellular stress responses in peripheral blood mononuclear cells (PBMC) from 19 older adults [71 (SD 2) yr; 9 females] before and after a 9-h heat exposure [40.3°C and 9.3% relative humidity (RH)], with participants moved to a cool room (∼23°C) for hours 5 and 6 (cooling group). Responses were compared with 17 older adults [72 (4) yr; 7 females] who remained in the heat for the entire 9 h (control group). Changes in proteins associated with autophagy, apoptotic signaling, acute inflammation, and the heat shock response (HSR) were assessed via Western blot. Although both groups experienced similar elevations in physiological strain before the cooling center intervention, brief cooling resulted in stark albeit transient reductions in core temperature and heart rate. At end-exposure, autophagy proteins LC3-II and p62 were elevated 1.9-fold [95% CI: 1.2, 2.8] and 2.3-fold [1.4, 3.8], respectively, in the control group relative to cooling group. This was paired with a 2.8-fold [1.6, 4.7] greater rise in apoptotic protein cleaved-caspase-3 in the control group compared with the cooling group. Our findings indicate that 2 h of ambient cooling midway through a 9-h simulated heat wave may preserve autophagy and mitigate heat-induced cellular stress in older adults.NEW & NOTEWORTHY Heat waves can lead to dangerous elevations in body temperature, increasing the risk of life-threatening health conditions. Visiting a cooling center or other air-conditioned location is commonly recommended to protect heat-vulnerable older persons, although the effects on the cellular stress response remain unknown. We found that 2 h of ambient cooling midway through a 9 h simulated heat wave preserves autophagy, a vital cellular survival mechanism, and mitigates accompanying pathways of cellular stress in older adults.

Physiological responses to 9 hours of heat exposure in young and older adults. Part II: Autophagy and the acute cellular stress response.

With rising global temperatures, heat-related mortality is increasing, particularly among older adults. Although this is often attributed to declines in thermoregulatory function, little is known regarding the effect of age on the cellular processes associated with mitigating heat-induced cytotoxicity. We compared key components of the cellular stress response in 19 young (19-31 yr; 10 female) and 37 older adults (61-78 yr; 10 female) during 9 h of heat exposure (40°C, 9% relative humidity). Mean body temperature (Tbody) was calculated from core and skin temperatures. Changes in proteins associated with autophagy, apoptotic signaling, acute inflammation, and the heat shock response were assessed via Western blot in peripheral blood mononuclear cells harvested before and after exposure. Tbody increased by 1.5 (SD 0.3)°C and 1.7 (0.3)°C in the young and older adults, respectively. We observed similar elevations in autophagy-related proteins (LC3-II and LC3-II/I) in young and older adults (both P ≥ 0.121). However, the older adults displayed signs of autophagic dysfunction, evidenced by a 3.7-fold [95% CI: 2.4, 5.6] greater elevation in the selective autophagy receptor p62 (P < 0.001). This was paired with elevations in apoptotic responses, with a 1.7-fold [1.3, 2.3] increase in cleaved caspase-3 in the older relative to young adults (P < 0.001). Older adults also exhibited diminished heat shock protein 90 responses (0.7-fold [0.5, 0.9] vs. young, P = 0.011) and, at any given level of thermal strain (Tbody area under the curve), elevated tumor necrosis factor-α (1.5-fold [1.0, 2.5] vs. young, P = 0.008). Attenuated autophagic responses may underlie greater vulnerability to heat-induced cellular injury in older adults.NEW & NOTEWORTHY We demonstrate for the first time that peripheral blood mononuclear cells from older adults exhibit signs of autophagic impairments during daylong (9 h) heat exposure relative to their younger counterparts. This was paired with greater apoptotic signaling and inflammatory responses, and an inability to stimulate components of the heat shock response. Thus, autophagic dysregulation during prolonged heat exposure may contribute to age-related heat vulnerability during hot weather and heat waves.

Physiological responses to 9 hours of heat exposure in young and older adults. Part I: Body temperature and hemodynamic regulation.

Aging is associated with an elevated risk of heat-related mortality and morbidity, attributed, in part, to declines in thermoregulation. However, comparisons between young and older adults have been limited to brief exposures (1-4 h), which may not adequately reflect the duration or severity of the heat stress experienced during heat waves. We therefore evaluated physiological responses in 20 young (19-31 yr; 10 females) and 39 older (61-78 yr; 11 females) adults during 9 h of rest at 40°C and 9% relative humidity. Whole body heat exchange and storage were measured with direct calorimetry during the first 3 h and final 3 h. Core temperature (rectal) was monitored continuously. The older adults stored 88 kJ [95% confidence interval (CI): 29, 147] more heat over the first 3 h of exposure (P = 0.006). Although no between-group differences were observed after 3 h [young: 37.6°C (SD 0.2°C) vs. older: 37.7°C (0.3°C); P = 0.216], core temperature was elevated by 0.3°C [0.1, 0.4] (adjusted for baseline) in the older group at hour 6 [37.6°C (0.2°C) vs. 37.9°C (0.2°C); P < 0.001] and by 0.2°C [0.0, 0.3] at hour 9 [37.7°C (0.3°C) vs. 37.8°C (0.3°C)], although the latter comparison was not significant after multiplicity correction (P = 0.061). Our findings indicate that older adults sustain greater increases in heat storage and core temperature during daylong exposure to hot dry conditions compared with their younger counterparts. This study represents an important step in the use of ecologically relevant, prolonged exposures for translational research aimed at quantifying the physiological and health impacts of hot weather and heat waves on heat-vulnerable populations.NEW & NOTEWORTHY We found greater increases in body heat storage and core temperature in older adults than in their younger counterparts during 9 h of resting exposure to hot dry conditions. Furthermore, the age-related increase in core temperature was exacerbated in older adults with common heat-vulnerability-linked health conditions (type 2 diabetes and hypertension). Impairments in thermoregulatory function likely contribute to the increased risk of heat-related illness and injury seen in older adults during hot weather and heat waves.

Efficacy of Cooling Centers for Mitigating Physiological Strain in Older Adults during Daylong Heat Exposure: A Laboratory-Based Heat Wave Simulation.

BACKGROUND: Health agencies, including the U.S. Centers for Disease Control and Prevention and the World Health Organization, recommend that heat-vulnerable older adults without home air-conditioning should visit cooling centers or other air-conditioned locations (e.g., a shopping mall) during heat waves. However, experimental evidence supporting the effectiveness of brief air-conditioning is lacking. OBJECTIVE: We evaluated whether brief exposure to an air-conditioned environment, as experienced in a cooling center, was effective for limiting physiological strain in older adults during a daylong laboratory-based heat wave simulation. METHODS: Forty adults 64-79 years of age underwent a 9-h simulated heat wave (heat index: 37°C) with (cooling group, n=20) or without (control group, n=20) a cooling intervention consisting of 2-h rest in an air-conditioned room (∼23°C, hours 5-6). Core and skin temperatures, whole-body heat exchange and storage, cardiovascular function, and circulating markers of acute inflammation were assessed. RESULTS: Core temperature was 0.8°C (95% CI: 0.6, 0.9) lower in the cooling group compared with the control group at the end of the cooling intervention (p<0.001; hour 6), and it remained 0.3°C (95% CI: 0.2, 0.4) lower an hour after returning to the heat (p<0.001; hour 7). Despite this, core temperatures in each group were statistically equivalent at hours 8 and 9, within ±0.3°C (p≤0.005). Cooling also acutely reduced demand on the heart and improved indices of cardiovascular autonomic function (p≤0.021); however, these outcomes were not different between groups at the end of exposure (p≥0.58). DISCUSSION: Brief air-conditioning exposure during a simulated heat wave caused a robust but transient reduction in core temperature and cardiovascular strain. These findings provide important experimental support for national and international guidance that cooling centers are effective for limiting physiological strain during heat waves. However, they also show that the physiological impacts of brief cooling are temporary, a factor that has not been considered in guidance issued by health agencies. https://doi.org/10.1289/EHP11651.

Impacts of age, diabetes, and hypertension on serum endothelial monocyte-activating polypeptide-II after prolonged work in the heat.

BACKGROUND: With rising temperature extremes, older workers are becoming increasingly vulnerable to heat-related injuries because of age- and disease-associated decrements in thermoregulatory function. Endothelial monocyte-activating polypeptide-II (EMAP-II) is a proinflammatory cytokine that has not yet been well-characterized during heat stress, and which may mediate the inflammatory response to high levels of physiological strain. METHODS: We evaluated serum EMAP-II concentrations before and after 180 min of moderate-intensity work (200 W/m2 ) in temperate (wet-bulb globe temperature [WBGT] 16°C) and hot (WBGT 32°C) environments in heat-unacclimatized, healthy young (n = 13; mean [SD]; 22 [3] years) and older men (n = 12; 59 [4] years), and unacclimatized older men with hypertension (HTN) (n = 10; 60 [4] years) or type 2 diabetes (T2D) (n = 9; 60 [5] years). Core temperature and heart rate were measured continuously. RESULTS: In the hot environment, work tolerance time was lower in older men with HTN and T2D compared to healthy older men (both p < 0.049). While core temperature and heart rate reserve increased significantly (p < 0.001), they did not differ across groups. End-exercise serum EMAP-II concentrations were higher in young men relative to their older counterparts due to higher baseline levels (both p ≤ 0.02). Elevations in serum EMAP-II concentrations were similar between healthy older men and older men with HTN, while serum EMAP-II concentrations did not change in older men with T2D following prolonged work in the heat. CONCLUSION: Serum EMAP-II concentrations increased following prolonged moderate-intensity work in the heat and this response is influenced by age and the presence of HTN or T2D.

Serum klotho concentrations in older men with hypertension or type 2 diabetes during prolonged exercise in temperate and hot conditions.

PURPOSE: Klotho is a cytoprotective protein that increases during acute physiological stressors (e.g., exercise heat stress), although age-related declines in klotho may underlie cellular vulnerability to heat stress. The present study aimed to compare serum klotho in healthy older men and men with type 2 diabetes (T2D) or hypertension (HTN) during prolonged exercise in temperate or hot conditions. METHODS: We evaluated serum klotho in 12 healthy older men (mean [SD]; 59 years [4]), 10 men with HTN (60 years [4]), and 9 men with T2D (60 years [5]) before and after 180 min of moderate-intensity (fixed metabolic rate of 200 W/m2; ~ 3.4 METs) exercise and 60 min of recovery in temperate (wet-bulb globe temperature (WBGT) 16 °C) and hot (WBGT 32 °C) environments. Core temperature (rectal), heart rate (HR), and heart rate reserve (HRR) were measured continuously while klotho was measured at the end of baseline, exercise, and recovery. RESULTS: Total exercise duration was reduced during the hot condition in older men with HTN and T2D than healthy older men (both p ≤ 0.049), despite similar core temperatures, HR, and HRR. Klotho was higher than rest following exercise in the heat in healthy older men (+ 191 pg/mL [189]; p < 0.001) and responses were greater (p = 0.036) than men with HTN (+ 118 pg/mL [49]; p = 0.030), although klotho did not increase in men with T2D (+ 4 pg/mL [71]; p ≥ 0.638). CONCLUSION: Given klotho's role in cytoprotection, older men with HTN and especially T2D may be at increased cellular vulnerability to prolonged exercise or physically demanding exercise in the heat.

Involvement of nitric oxide synthase and reactive oxygen species in TRPA1-mediated cutaneous vasodilation in young and older adults.

OBJECTIVE: To investigate the nitric oxide synthase (NOS) and reactive oxygen species (ROS) contributions of the cutaneous vasodilator response to transient receptor potential ankyrin-1 channel (TRPA1) activation in young and older adults. MATERIALS AND METHODS: In sixteen young (20 ± 2 years, 8 females) and sixteen older adults (61 ± 5 years, 8 females), cutaneous vascular conductance normalized to maximum vasodilation (%CVCmax) was assessed at four dorsal forearm skin sites continuously perfused via microdialysis with: 1) vehicle solution (Control, 2 % dimethyl sulfoxide, 2 % Ringer, 96 % propylene glycol), 2) 10 mM Ascorbate (non-specific ROS inhibitor), 3) 10 mM L-NAME (non-specific NOS inhibitor), or 4) Ascorbate+L-NAME. The TRPA1 agonist cinnamaldehyde was co-administered at all sites [0 % (baseline), 2.9 %, 8.8 %, 26.4 %; ≥ 30 min per dose]. RESULTS: %CVCmax was not different between groups for Control, L-NAME, and Ascorbate (all p > 0.05). However, there were significant main dose effects for each site wherein %CVCmax was greater than baseline from 2.9 % to 26.4 % cinnamaldehyde for Control and Ascorbate, and at 26.4 % cinnamaldehyde for L-NAME and Ascorbate+L-NAME (all p < 0.05). For Ascorbate+L-NAME, there was a significant main group effect, wherein perfusion was 6 %CVCmax [95% CI: 2, 11, p < 0.05] greater in the older compared to the young group across all cinnamaldehyde doses. There was a significant main site effect for area under the curve wherein L-NAME and Ascorbate+L-NAME were lower than Control and Ascorbate across groups (all p < 0.05). CONCLUSION: The NOS-dependent cutaneous vasodilator response to TRPA1 activation is maintained in older adults, with no detectable contribution of ascorbate-sensitive ROS in either age group.

The serum irisin response to prolonged physical activity in temperate and hot environments in older men with hypertension or type 2 diabetes.

Current labor demographics are changing, with the number of older adults increasingly engaged in physically demanding occupations expected to continually rise, which are often performed in the heat. Given an age-related decline in whole-body heat loss, older adults are at an elevated risk of developing heat injuries that may be exacerbated by hypertension (HTN) and type 2 diabetes (T2D). Elevated irisin production may play a role in mitigating the excess oxidative stress and acute inflammation associated with physically demanding work in the heat. However, the effects of HTN and T2D on this response remain unclear. Therefore, we evaluated serum irisin before and after 3-h of moderate intensity exercise (metabolic rate: 200 W/m2) and at the end of 60-min of post-exercise recovery in a temperate (wet-bulb globe temperature (WBGT) 16 °C) and high-heat stress (WBGT 32 °C) environment in 12 healthy older men (mean ± SD; 59 ± 4 years), 10 men with HTN (60 ± 4 years), and 9 men with T2D (60 ± 5 years). Core temperature (Tco) was measured continuously. In the heat, total exercise duration was significantly lower in older men with HTN and T2D (both, p ≤ 0.049). Despite Tco not being different between groups, Tco was higher in the hot compared to the temperate condition for all groups (p < 0.001). Similarly, serum irisin concentrations did not differ between groups under either condition but were elevated relative to the temperate condition during post-exercise and end-recovery in the heat (+93.9 pg/mL SEM 26 and + 70.5 pg/mL SEM 38 respectively; both p ≤ 0.014). Thus, our findings indicate similar irisin responses in HTN and T2D compared to healthy, age-matched controls, despite reduced exercise tolerance during prolonged exercise in the heat. Therefore, older workers with HTN and T2D may exhibit greater cellular stress during prolonged exercise in the heat, underlying greater vulnerability to heat-induced cellular injury.

Autophagic response to exercise in peripheral blood mononuclear cells from young men is intensity-dependent and is altered by exposure to environmental heat.

Autophagy is essential to maintaining cellular homeostasis in all eukaryotic cells and to tolerance of acute stressors such as starvation, heat, and recovery after exercise. Limited information exists regarding the exercise intensity-dependent autophagic response in humans, and it is unknown how environmental heat stress may modulate this response. Therefore, we evaluated autophagy and accompanying pathways of cellular stress [the heat-shock response (HSR), apoptosis, and acute inflammation] in peripheral blood mononuclear cells (PBMCs) from 10 young men (mean [SD]; 22 [2] years) before, immediately after and up to 6-h postexercise recovery from 30 min of low-, moderate-, and high-intensity semirecumbent cycling [40%, 55%, and 70% of maximal oxygen consumption (V̇o2max), respectively] in a temperate environment (25°C) and at 70% of V̇o2max in a hot environment (40°C). Changes in protein content were analyzed via Western blot. Each increase in exercise intensity was associated with elevations in mean body temperature. LC3-II increased after moderate-intensity exercise, with further increases after high-intensity exercise (P < 0.05). However, an increase in beclin-2 and ULK1, with a decrease in p62 was only observed after high-intensity exercise, which was paralleled by elevated TNF-α and cleaved-caspase-3, with the HSR peaking at 6 h after exercise (P < 0.05). When exercise was performed in the heat, greater LC3-II and cleaved-caspase-3 accumulation were observed; however, beclin-2 declined in recovery (P < 0.05). Therefore, our findings indicate that autophagy in PBMCs during exercise may be associated with greater heat strain exhibited during increasing exercise intensities, which is modulated by exposure to heat.

The effect of acute intradermal administration of ascorbate on heat loss responses in older adults with uncomplicated controlled hypertension.

NEW FINDINGS: What is the central question of this study? Does acute intradermal administration of the antioxidant ascorbate augment local forearm cutaneous vasodilatation and sweating via nitric oxide synthase (NOS)-dependent mechanisms during exercise-heat stress in older adults with uncomplicated controlled hypertension? What is the main finding and its importance? Relative to the control site, ascorbate had no effect on forearm cutaneous vascular conductance (CVC) and sweat rate, although CVC was reduced with NOS inhibition in older adults with hypertension. Acute local administration of ascorbate to forearm skin does not modulate heat loss responses during exercise-heat stress in older adults with hypertension. ABSTRACT: Nitric oxide synthase (NOS) contributes to the heat loss responses of cutaneous vasodilatation and sweating during exercise. However, the contribution of NOS may be attenuated in individuals with uncomplicated, controlled hypertension due to elevated oxidative stress, which can reduce NO bioavailability. We evaluated the hypothesis that the acute local intradermal administration of the antioxidant ascorbate would enhance cutaneous vasodilatation and sweating via NOS-dependent mechanisms during an exercise-heat stress in adults with hypertension. Habitually active adults who were normotensive (n = 14, 7 females, 62 ± 4 years) or had uncomplicated, controlled hypertension (n = 13, 6 females, 62 ± 5 years) performed 30 min of moderate-intensity (50% of their pre-determined peak oxygen uptake) semi-recumbent cycling in the heat (35°C, 20% relative humidity). Cutaneous vascular conductance (CVC) and sweat rate were assessed at four forearm skin sites continuously perfused with (1) lactated Ringer solution (Control), (2) 10 mM antioxidant ascorbate, (3) 10 mM NG -nitro-l-arginine methyl ester (l-NAME), a non-selective NOS inhibitor, or (4) a combination of ascorbate and l-NAME. Relative to Control, no effect of ascorbate was observed on CVC or sweating in either group (P = 0.619). However, l-NAME reduced CVC relative to Control in both groups (P ≤ 0.038). No effect of any treatment on sweating was observed (P ≥ 0.306). Thus, acute local administration of ascorbate to forearm skin does not enhance the activation of heat loss responses of cutaneous vasodilatation and sweating in older adults, and those with hypertension during an exercise-heat stress.

Effect of extracellular hyperosmolality during normothermia and hyperthermia on the autophagic response in peripheral blood mononuclear cells from young men.

Heat-stress-induced dehydration is associated with extracellular hyperosmolality. To counteract the associated stress, cells employ cytoprotective mechanisms, including autophagy; however, the autophagic response to hyperosmotic stress has yet to be evaluated in humans. Thus, we investigated autophagy and associated cellular stress pathways [the heat shock response (HSR), apoptosis, and the acute inflammatory response] to isosmotic and hyperosmotic conditions with and without hyperthermia in 12 young men (mean [SD]; 25 [5] yr). Participants received a 90-min intravenous infusion of either isosmotic (ISO; 0.9% NaCl; serum osmolality of 293 [4] mosmol/kgH2O) or hyperosmotic (HYP; 3.0% NaCl; 300 [6] mosmol/kgH2O) saline, followed by passive whole body heating using water perfused suit to increase esophageal temperature by ∼0.8°C. Peripheral blood mononuclear cells were harvested at baseline (preinfusion), postinfusion, and after heating, and changes in protein content were analyzed via Western blotting. Post infusion, the LC3-II/I ratio was higher in HYP compared with ISO infusion (P < 0.001), although no other protein changes were observed (all P > 0.050). Following passive heating, autophagy increased in HYP, as demonstrated by an increase in LC3-II from baseline (P = 0.004) and an elevated LC3-II/I ratio compared with ISO (P = 0.035), and a decrease in p62 when compared with the ISO condition (P = 0.019). This was accompanied by an elevation in cleaved caspase-3 following heating in the HYP condition (P < 0.010); however, the HSR and acute inflammatory response did not change under any condition (all P > 0.050). Taken together, our findings indicate that serum hyperosmolality induces autophagy and apoptotic signaling during mild hyperthermia with minimal autophagic activation during normothermia.NEW & NOTEWORTHY We demonstrate that a physiologically relevant increase in serum osmolality causes minimal activation of the autophagic response. However, the combined stressors of serum hyperosmolality and mild hyperthermia causes activation of both autophagy and apoptotic signaling. Thus, changes in osmotic homeostasis appear to influence the cell's cytoprotective ability during periods of heat stress, highlighting the importance of considering osmotic status when examining autophagic responses in vivo.