Prolonged exposure to hyperthermic stress augments neutrophil recruitment to lung during the post-exposure recovery period

Higher Temperatures, Higher Solar Radiation, and Less Humidity Is Associated With Poor Clinical and Laboratory Outcomes in COVID-19 Patients

Background: The COVID-19 pandemic varies between countries, with suggestions that weather might contribute to the transmission mode, disease presentation, severity, and clinical outcomes. Yet the exact link between climate and COVID-19 is still not well-explored. Objectives: This study aimed to evaluate the effect of hot geographical region weather [like United Arab Emirates (UAE)] on COVID-19 clinical profile and outcomes. Temperature, wind speed, cloud cover, precipitation, and other weather-related variables were studied concerning COVID-19 patients outcomes and laboratory results. Methodology: A total of 434 COVID-19 positive patients admitted between January and June 2020, were recruited from Al Kuwait Hospital, Dubai, UAE. Temperature, wind speed, cloud cover, and precipitation rate were retrieved from history+ for the day when COVID-19 patients presented to the hospital. These weather parameters were correlated with COVID-19 clinical and laboratory parameters. Results: Our results showed that patients needed admission in days with higher temperatures, higher solar radiation, and less humidity were associated with higher deaths. This association can be linked to the association of these weather parameters with age at diagnosis; higher C-reactive protein (CRP), neutrophil count, white cell count (WCC), aspartate aminotransferase (AST), and alkaline phosphatase (ALP); and lower lymphocyte count, estimated glomerular filtration rate (eGFR), hemoglobin (Hb), Na, and albumin, all of which are considered poor prognostic factors for COVID-19. Conclusion: Our study highlighted the importance of weather-related variables on the dynamics of mortality and clinical outcomes of COVID-19. The hot weather might makes some people, especially those with comorbidities or older ages, develop aggressive inflammation that ends up with complications and mortality.

Shifts in temperature within the physiologic range modify strand-specific expression of select human microRNAs

Previous studies have revealed that clinically relevant changes in temperature modify clinically relevant gene expression profiles through transcriptional regulation. Temperature dependence of post-transcriptional regulation, specifically, through expression of miRNAs has been less studied. We comprehensively analyzed the effect of 24 h exposure to 32°C or 39.5°C on miRNA expression profile in primary cultured human small airway epithelial cells (hSAECs) and its impact on expression of a targeted protein, protein kinase C α (PKCα). Using microarray, and solution hybridization-based nCounter assays, with confirmation by quantitative RT-PCR, we found significant temperature-dependent changes in expression level of only five mature human miRNAs, representing only 1% of detected miRNAs. Four of these five miRNAs are the less abundant passenger (star) strands. They exhibited a similar pattern of increased expression at 32°C and reduced expression at 39.5°C relative to 37°C. As PKCα mRNA has multiple potential binding sites for three of these miRNAs, we analyzed PKCα protein expression in HEK 293T cells and hSAECs. PKCα protein levels were lowest at 32°C and highest at 39.5°C and specific miRNA inhibitors reduced these effects. Finally, we analyzed cell-cycle progression in hSAECs and found 32°C cells exhibited the greatest G1 to S transition, a process known to be inhibited by PKCα, and the effect was mitigated by specific miRNA inhibitors. These results demonstrate that exposure to clinically relevant hypothermia or hyperthermia modifies expression of a narrow subset of miRNAs and impacts expression of at least one signaling protein involved in multiple important cellular processes.

Fever, immunity, and molecular adaptations

The heat shock response (HSR) is an ancient and highly conserved process that is essential for coping with environmental stresses, including extremes of temperature. Fever is a more recently evolved response, during which organisms temporarily subject themselves to thermal stress in the face of infections. We review the phylogenetically conserved mechanisms that regulate fever and discuss the effects that febrile-range temperatures have on multiple biological processes involved in host defense and cell death and survival, including the HSR and its implications for patients with severe sepsis, trauma, and other acute systemic inflammatory states. Heat shock factor-1, a heat-induced transcriptional enhancer is not only the central regulator of the HSR but also regulates expression of pivotal cytokines and early response genes. Febrile-range temperatures exert additional immunomodulatory effects by activating mitogen-activated protein kinase cascades and accelerating apoptosis in some cell types. This results in accelerated pathogen clearance, but increased collateral tissue injury, thus the net effect of exposure to febrile range temperature depends in part on the site and nature of the pathologic process and the specific treatment provided.

Fever, hyperthermia and the heat shock response

The heat shock response is a highly conserved primitive response that is essential for survival against a wide range of stresses, including extremes of temperature. Fever is a more recently evolved response, during which organisms raise their core body temperature and temporarily subject themselves to thermal stress in the face of infections. The present review documents studies showing the potential overlap between the febrile response and the heat shock response and how both activate the same common transcriptional programme (although with different magnitudes) including the stress-activated transcription factor, heat shock factor-1, to modify host defences in the context of infection, inflammation and injury. The review focuses primarily on how hyperthermia within the febrile range that often accompanies infections and inflammation acts as a biological response modifier and modifies innate immune responses. The characteristic 2-3 °C increase in core body temperature during fever activates and utilises elements of the heat shock response pathway to modify cytokine and chemokine gene expression, cellular signalling and immune cell mobilisation to sites of inflammation, infection and injury. Interestingly, typical proinflammatory agonists such as Toll-like receptor agonists modify the heat shock-induced transcriptional programme and expression of HSP genes following co-exposure to febrile range hyperthermia or heat shock, suggesting a complex reciprocal regulation between the inflammatory pathway and the heat shock response pathway.

Tolerance for chronic heat exposure is greater in female than male mice

PURPOSE

Chronic heat exposure in mice has cellular and physiological effects that improve thermal tolerance [1], but also modifies innate immune responses with potential adverse consequences [2]. While male and female mice are known to respond differently to acute exposure to severe hyperthermia, sex-based differences in responses to chronic moderate heat exposure have not been reported. The major objective of this study was to compare the tolerance of male and female mice for chronic heat exposure.

MATERIALS AND METHODS

We used a mouse model of 5-day moderate heat exposure (ambient temperature ∼37°C) to compare the physiological and cellular heat shock response in male and female mice. Core temperature, heart rate, and activity were monitored telemetrically and heat shock protein levels were measured in brain and lung by western blotting.

RESULTS

Adult CD-1 female mice maintained a 1.2°C lower core temperature (38.31 ± 0.64 versus 39.51 ± 0.72°C; p = 0.002), experienced less weight loss (1.54 ± 0.45 versus 4.54 ± 1.97 g; p = 0.0007), and had improved survival (16/16 survived versus 13/21, p < 0.006) than male mice of the same age. After 5 days of moderate heat exposure Hsp72 levels in brain and lung increased 2.1-fold (p = 0.007) and 5-fold (p = 0.048) in male mice compared with 1.3- (p = 0.054) and 1.5-fold (p = 0.134) in female mice.

CONCLUSIONS

This study reveals previously unknown and potentially important differences between male and female mice in physiological and cellular responses to chronic heat exposure, which had consequences for survival. Future studies may identify biomarkers of differential heat tolerance and treatments to improve heat tolerance in humans.

Toll-like receptor agonists and febrile range hyperthermia synergize to induce heat shock protein 70 expression and extracellular release

Heat shock protein (Hsp) 70 expression can be stimulated by febrile range temperature (FRT). Hsp70 has been shown to be elevated in serum of patients with sepsis, and when released from cells, extracellular Hsp70 exerts endotoxin-like effects through Toll-like receptor 4 (TLR4) receptors. Circulating TLR agonists and fever both persist for the first several days of sepsis, and each can activate Hsp70 expression; however, the effect of combined exposure to FRT and TLR agonists on Hsp70 expression is unknown. We found that concurrent exposure to FRT (39.5 °C) and agonists for TLR4 (LPS), TLR2 (Pam3Cys), or TLR3 (poly(IC)) synergized to increase Hsp70 expression and extracellular release in RAW264.7 macrophages. The increase in Hsp70 expression was associated with activation of p38 and ERK MAP kinases, phosphorylation of histone H3, and increased recruitment of HSF1 to the Hsp70 promoter. Pretreatment with the p38 MAPK inhibitor SB283580 but not the ERK pathway inhibitor UO126 significantly reduced Hsp70 gene modification and Hsp70 expression in RAW cells co-exposed to LPS and FRT. In mice challenged with intratracheal LPS and then exposed to febrile range hyperthermia (core temperature, ∼39.5 °C), Hsp70 levels in lung tissue and in cell-free lung lavage were increased compared with mice exposed to either hyperthermia or LPS alone. We propose a model of how enhanced Hsp70 expression and extracellular release in patients concurrently exposed to fever and TLR agonists may contribute to the pathogenesis of sepsis.

Febrile-range hyperthermia augments reversible TNF-α-induced hyperpermeability in human microvascular lung endothelial cells

Fever commonly occurs in acute lung injury (ALI) and ALI occurs in 25% of victims of heat stroke. We have shown in mouse models of ALI that exposure to febrile-range hyperthermia (FRH), 39.5°C, increases non-cardiogenic pulmonary oedema. In this study we studied the direct effects of FRH on endothelial barrier integrity using human microvascular endothelial cells (HMVEC-Ls). We analysed the effect of exposure to culture temperatures between 38.5° and 41°C with and without tumour necrosis factor-α (TNF-α) up to 250 U/mL for 6-24 h. We found that exposure to 2.5-250 U/mL TNF-α increased HMVEC-L permeability by 4.1-15.8-fold at 37°C. Exposure to 39.5°C alone caused variable, modest, lot-specific increases in HMVEC-L permeability, however raising culture temperature to 39.5°C in the presence of TNF-α increased permeability an additional 1.6-4.5-fold compared with cells incubated with the same TNF-α concentration at 37°C. Permeability occurred without measurable cytotoxicity and was reversible upon removal of TNF-α and reduction in temperature to 37°C. Exposure to 39.5°C or TNF-α each stimulated rapid activation of p38 and ERK but the effects were not additive. Treatment with inhibitors of ERK (U0126) or p38 (SB203580) each reduced TNF-α-induced permeability in 39.5°C monolayers to levels in 37°C cells, but did not alter TNF-α-induced permeability in the 37°C cells. These results demonstrate that FRH directly increases paracellular pathway opening through a process that requires ERK and p38 MAPKs. A better understanding of this mechanism may provide new understanding about how fever may contribute to the pathogenesis of ALI and provide new therapeutic targets to improve clinical outcomes.