Gender Differences in the Response to Short-term Cold Exposure in Young Adults

Impact of temperature variations on burden of lower respiratory infections under climate change (1990-2021)

OBJECTIVES

We aimed to evaluate the global burden and trends of lower respiratory infections (LRIs) attributable to non-optimal temperatures between 1990 and 2021, focusing on age, period, and cohort effects as well as health inequalities to inform targeted public health policies.

METHODS

Using the Global Burden of Disease 2021 database, we obtained the age-standardized mortality rate (ASMR) and disability-adjusted life-years rate (ASDR) for LRIs related to non-optimal temperatures. We calculated estimated annual percentage changes (EAPC) to assess LRIs burden trends and applied age-period-cohort modeling to quantify age, period, and cohort effects. Health inequalities were evaluated using the slope index of inequality and the concentration index.

RESULTS

In 2021, the highest ASDR for LRIs due to high temperatures occurred in children under 5 (347.66/100,000), whereas the highest ASMR for LRIs due to low temperatures occurred in adults aged ≥ 65 (338.49/100,000). Globally, the LRIs burden from non-optimal temperatures declined (EAPC: ASMR -2.48; ASDR -3.33). However, among the five climate zones, the LRIs burden in the boreal zone due to high temperatures increased (EAPC: ASMR 24.14; ASDR 45.14), whereas all other climate zones showed decreasing trends. In lower Sociodemographic Index (SDI) regions, the high-temperature-related LRIs burden was more pronounced. Relative inequities driven by non-optimal temperatures worsened in low-SDI regions.

CONCLUSION

From 1990 to 2021, the global burden of LRIs attributable to non-optimal temperatures declined overall; however, high-temperature-related LRIs increased in boreal zones. These health inequalities underscore the urgent need for targeted climate adaptation policies, such as providing international assistance, improving infrastructure, offering healthcare resources, and promoting vaccine coverage, particularly for vulnerable populations in low-SDI regions and boreal zones.

The interactive effect of extreme weather events and PM2.5 on respiratory health among the elderly: a case-crossover study in a high-altitude city

With climate change posing increasing threats and aging populations, understanding the complex relationship between extreme temperatures, PM2.5 pollution, and respiratory health among the elderly is crucial. While some research exists, there remains a significant gap in studying the combined effects of heat waves, cold spells, and PM2.5 on elderly respiratory health in high-altitude regions. We collected data from Xining (2016-2021), including respiratory disease outpatient visits, meteorological, and pollutant data. Employing a case-crossover design and conditional Poisson regression analysis, we investigated the individual and interactive impacts of heat wave, cold spell, and PM2.5 on outpatient visits for respiratory disease among the elderly. We used the relative excess odds due to interaction (REOI), proportion attributable to interaction (AP), and synergy index (S) as quantitative indicators of interaction. Our analysis revealed significant associations between heat wave, cold spell, PM2.5 exposure, and outpatient visits for respiratory disease among the elderly, with odds ratios of 1.10 (95%CI: 1.06, 1.15) and 1.16 (95%CI: 1.13, 1.20), respectively. Moreover, a synergistic effect between cold spell and PM2.5 was observed, particularly affecting vulnerable groups such as female and those aged ≥ 80. The combined exposure to cold spell and elevated PM2.5 levels was estimated to contribute to up to 0.18 (95%CI: 0.17, 0.27) of respiratory outpatient visits. This study underscores the need for urgent interventions, such as reducing PM2.5 exposure and enhancing extreme weather warning systems, to protect the respiratory health of the elderly, especially in high-altitude regions.

Sex-specific response of the human plasma lipidome to short-term cold exposure

Cold-induced lipolysis is widely studied as a potential therapeutic strategy to combat metabolic disease, but its effect on lipid homeostasis in humans remains largely unclear. Blood plasma comprises an enormous repertoire in lipids allowing insights into whole body lipid homeostasis. So far, reported results originate from studies carried out with small numbers of male participants. Here, the blood plasma's lipidome of 78 male and 93 female volunteers, who were exposed to cold below the shivering threshold for 2 h, was quantified by comprehensive lipidomics using high-resolution mass spectrometry. Short-term cold exposure increased the concentrations in 147 of 177 quantified circulating lipids and the response of the plasma's lipidome was sex-specific. In particular, the amounts of generated glycerophospholipid and sphingolipid species differed between the sexes. In women, the BMI could be related with the lipidome's response. A logistic regression model predicted with high sensitivity and specificity whether plasma samples were from male or female subjects based on the cold-induced response of phosphatidylcholine (PC), lysophosphatidylcholine (LPC), and sphingomyelin (SM) species. In summary, cold exposure promotes lipid synthesis by supplying fatty acids generated after lipolysis for all lipid classes. The plasma lipidome, i.e. PC, LPC and SM, shows a sex-specific response, indicating a different regulation of its metabolism in men and women. This supports the need for sex-specific research and avoidance of sex bias in clinical trials.

Sex differences in autonomic functions and cognitive performance during cold-air exposure and cold-water partial immersion

Introduction

This study investigated the differences between males and females in autonomic functions and cognitive performance during cold-air exposure and cold-water partial-immersion compared to a room temperature-air environment. Although several studies have investigated the effects of cold-air or cold-water exposures on autonomic function and cognitive performance, biological sex differences are often under-researched.

Methods

Twenty-two males and nineteen females participated in the current study. Subjects completed a battery of cognitive tasks based upon those used within the Defense Automated Neurobehavioral Assessment (DANA), consisting of five subtasks that assess simple and procedural reaction time, spatial manipulation, attention, and immediate memory. In total, subjects took the battery within a 15-minute period across 30-minute intervals throughout the duration of environmental exposure. Across three separate days, subjects were exposed to three different environmental conditions: room temperature air (23°C), cold air (10°C), and cold water (15°C; in which subjects were immersed up to their necks). Room temperature and cold-air conditions consisted of five sessions (about 2.5 h), and the cold-water condition consisted of three sessions (about 1.5 h). During each experimental condition, physiological data were collected to assess autonomic function, including electrodermal activity (EDA) data and heart rate variability (HRV) derived from electrocardiogram signals.

Results

Females showed slower reaction time in spatial manipulation tasks, immediate memory, and attention during cold-air exposures compared to room temperature air, whereas the performance of males were similar or better during cold-air exposures compared to room temperature air. Cold-water immersion affected the immediate memory performance of males. Both males and females exhibited smaller EDA amplitudes during cold-air and cold-water conditions compared to room temperature air. For HRV, only male subjects exhibited significantly greater values in low-frequency and very-low-frequency components during cold air exposure compared to the normal condition.

Discussion

Sex introduces important differences in cognitive performance and autonomic functions during exposure to cold-air and cold-water. Therefore, sex should be considered when assessing the autonomic nervous system in cold environments and when establishing optimal thermal clothing for performance in operational environments. Our findings can assist with determination of operational clothing, temperature in operating environment, and personnel deployment to operational sites, particularly in settings involving both males and females.

Pre-exercise cryotherapy reduces myoglobin and creatine kinase levels after eccentric muscle stress in young women

Introduction: The aim of this study was to investigate the effect of pre-exercise whole-body cryotherapy (WBC) on muscle damage indicators following eccentric treadmill exercise in young women. Methods: Twenty-seven participants underwent two 1-h downhill treadmill runs, replicating 60% of their maximal oxygen uptake, with a 4-week intermission for recovery and treatment application. In this intermission, one group underwent 20 sessions of WBC, delivered five times a week at -120°C for 3 min each, while the comparison group received no such treatment. Markers of muscle injury-serum myoglobin concentration, creatine kinase and lactate dehydrogenase activity and also uric acid, and cell-free DNA concentration-were measured before and after downhill runs. Results: The study observed a notable reduction in post-exercise myoglobin and CK levels in the WBC group after the second running session. Discussion: The results suggest that WBC can have a protective effects against muscle damage resulting from eccentric exercise.

Comparison of Cryotherapy Performed With Ice or Gel and Superficial Skin Cooling of Older Women: A Randomized, Crossover, Clinical Trial

BACKGROUND AND PURPOSE

Cryotherapy is an affordable and popular treatment of soft tissue injuries, which can reduce inflammation and pain. Studies have specifically addressed young adults and athletes, and these findings have been extended to older adults in clinical practice. Aging is associated with changes in the skin, including collagen degradation, decreased fat layer thickness, and reduced blood flow, which can alter the skin response to stress. Because of age-related changes, there are concerns about the direct use of ice on the skin of older individuals. Skin injuries were also observed after cryotherapy. This study aimed to assess the most effective and safe cryotherapy for superficial skin cooling among older women.

METHODS

Eighteen older women were enrolled in this blinded, randomized, crossover, clinical trial. The mean values (SD) of their age, height, and weight were 70.0 years (6.0), 156.0 cm (9.1), and 72.8 kg (19.5), respectively. The participants underwent cryotherapy using bagged ice, bagged ice plus a wet towel, or gel pack for 20 minutes. The surface temperature of the skin was measured at the end of a 20-minute cryotherapy session using an infrared thermometer. Repeated-measures analysis of variance was conducted to analyze the effect of cryotherapy modalities and time, as well as the interaction between these 2 factors. The secondary outcome was the presence of cryotherapy-induced lesions.

RESULTS AND DISCUSSION

Cryotherapy modalities had significant effects on superficial skin temperature (P = .001). Time points after application also had an effect (P = .0001), and no interaction was observed between cryotherapy modalities and time points (P = .051). Bonferroni post hoc evaluation showed that bagged ice (P = .008) and gel (P = .007) were more effective in decreasing the superficial skin temperature than bagged ice plus wet towel. No difference was observed between bagged ice and gel (P = .32). Three of the 18 patients experienced adverse effects with the gel pack.

CONCLUSION

This study of older women found that ice and gel cooled the skin more effectively than ice wrapped in towels. However, the gel pack had some adverse effects. Therefore, bagged ice is recommended for cryotherapy in older women.

Global burden study of lower respiratory infections linked to low temperatures: an analysis from 1990 to 2019

Low temperature conditions have been linked to a heightened susceptibility to lower respiratory infections (LRIs). Yet, our comprehension of the LRIs' disease burden due to such conditions remains limited, especially when considering the diverse socio-demographic indexes (SDIs) and climate types across various nations and regions. We examined the variations over time and space in the impact of LRIs due to low temperatures across a diverse set of 204 nations and regions, each with unique SDIs and climate types, spanning the years 1990 to 2019. Data from the Global Burden of Disease Study 2019 was used for this retrospective analysis. The burden of LRIs attributable to low temperatures was estimated by stratifying by sex, age, country, climate type, and SDI, including age-standardized mortality rate (ASMR) and age-standardized disability-adjusted life year rate (ASDR). We employed Joinpoint models to compute the annual average percent changes (AAPCs) in order to evaluate the trends in LRIs burden due to low temperatures from 1990 to 2019. Furthermore, we utilized Poisson age-period-cohort models to forecast the global and income-specific trends in LRIs burden due to low temperatures for the period 2020-2044. Generalized additive mixed models were used to fit changes in the disease burden of different climate regions. The relationship between SDI and both ASMR and ASDR was determined using models grounded in Gaussian process regression. In general, since the year 1990, there has been a significant reduction in the worldwide impact of LRIs due to low temperatures. This decrease is particularly noticeable among infants and the elderly, as well as in regions with a boreal climate and those with an average SDI. In 2019, LRIs induced by low temperatures showed an ASMR of 2.2 (95% CI: 1.34, 3.07) and an ASDR of 53.73 (95% CI: 17.5, 93.22) for every 100,000 individuals. A global reduction was observed in the ASMR and ASDR for LRIs over the period from 1990 to 2019, showing a decrease of 60.27% and 77.5%, in that order. For ASMR and ASDR, the AAPC values were found to be - 3.3 (95% CI: - 3.4, - 3.1) and - 5 (95% CI: - 5.2, - 4.9), in that order. However, a contrasting pattern was observed in southern Latin America, where an increase was noted in the ASMR for LRIs induced by low temperatures [AAPC: 0.5; 95% CI: (0.3, 0.8)]. Low temperature has decreased as an environmental risk factor for LRIs globally over 30 years, especially in middle SDI regions and boreal climates, but remains important for infants and the elderly population.

Content of stress granules reveals a sex difference at the early phase of cold exposure in mice

Adaptive thermogenesis is a vital physiological process for small endotherms. Female animals usually are more sensitive to cold temperature due to anatomical differences. Whether there is a sex difference at a molecular level is unclear. Stress granules (SGs) are dynamic organelles in which untranslated mRNAs reside during cellular stress. We hypothesize that the prompt response of SGs to cold stress can reveal the molecular difference between sexes. By analyzing the content in SGs of brown adipose tissue (BAT) at the early phase of cold stress for both sexes, we found more diverse mRNAs docked in the SGs in male mice and these mRNAs representing an extensive cellular reprogramming including apoptosis process and cold-induced thermogenesis. In female mice, the mRNAs in SGs dominantly were comprised of genes regulating ribonucleoprotein complex biogenesis. Conversely, the proteome in SGs was commonly characterized as structure molecules and RNA processing for both sexes. A spectrum of eukaryotic initiation factors (eIFs) was detected in the SGs of both female and male BAT, while those remained unchanged upon cold stress in male mice, various eIF3 and eIF4G isoforms were found reduced in female mice. Taken together, the unique features in SGs of male BAT reflected a prompt uncoupling protein-1 (UCP1) induction which was absent in female, and female, by contrast, were prepared for long-term transcriptional and translational adaptations.NEW & NOTEWORTHY The proteome analysis reveals that stress granules are the predominant form of cytosolic messenger ribonucleoproteins of brown adipose tissue (BAT) at the early phase of cold exposure in mice for both sexes. The transcriptome of stress granules of BAT unveils a sex difference of molecular response in early phase of cold exposure in mice, and such difference prepares for a prompt response to cold stress in male mice while for long-term adaptation in female mice.

Molecular Mechanisms of Lipid-Based Metabolic Adaptation Strategies in Response to Cold

Temperature changes and periods of detrimental cold occur frequently for many organisms in their natural habitats. Homeothermic animals have evolved metabolic adaptation strategies to increase mitochondrial-based energy expenditure and heat production, largely relying on fat as a fuel source. Alternatively, certain species are able to repress their metabolism during cold periods and enter a state of decreased physiological activity known as torpor. By contrast, poikilotherms, which are unable to maintain their internal temperature, predominantly increase membrane fluidity to diminish cold-related damage from low-temperature stress. However, alterations of molecular pathways and the regulation of lipid-metabolic reprogramming during cold exposure are poorly understood. Here, we review organismal responses that adjust fat metabolism during detrimental cold stress. Cold-related changes in membranes are detected by membrane-bound sensors, which signal to downstream transcriptional effectors, including nuclear hormone receptors of the PPAR (peroxisome proliferator-activated receptor) subfamily. PPARs control lipid metabolic processes, such as fatty acid desaturation, lipid catabolism and mitochondrial-based thermogenesis. Elucidating the underlying molecular mechanisms of cold adaptation may improve beneficial therapeutic cold treatments and could have important implications for medical applications of hypothermia in humans. This includes treatment strategies for hemorrhagic shock, stroke, obesity and cancer.

Temperature variability increases the onset risk of ischemic stroke: A 10-year study in Tianjin, China

Background

Epidemiological evidence suggests a correlation between ambient temperature and ischemic stroke. However, evidence on the impact of daily temperature variability on the onset of ischemic stroke is lacking and limited.

Objective

We aimed to investigate the short-term association between temperature variability and ischemic stroke occurrence in Tianjin.

Methods

We performed a 10-year analysis of ischemic stroke patients hospitalized in two affiliated hospitals of Tianjin Medical University from 2011 to 2020. Daily meteorological data were collected from the Tianjin Meteorological Bureau. Temperature variability was calculated from the standard deviation (SD) of daily minimum and maximum temperatures over exposure days. A quasi-Poisson generalized linear regression combined with distributed lag non-linear model (DLNM) was used to estimate the effect of temperature variability on daily stroke onset, while controlling for daily mean temperature, relative humidity, long-term trend and seasonality, public holiday, and day of the week.

Results

Temperature variability was positively associated with ischemic stroke. A 1°C increase in temperature variability at 0-1 days (TV_0-1) was associated with a 4.1% (1.9-6.3%) increase of ischemic stroke onset. In a stratified analysis, men, people aged ≤65 years, and individuals with pre-existing hypertension, hyperlipidemia, hyperhomocysteinemia were more susceptible to temperature variability. Furthermore, the influence pattern of temperature variability on ischemic stroke was different in the cold season (November-April) and the warm season (May-October).

Conclusion

Our findings suggested that short-term temperature variability exposure could increase the risk of ischemic stroke, which may provide new insights into the impact of climate change on health.

Kinetics of lipid indicators in response to short- and long-duration whole-body, cold-water immersion

Cold exposure-induced secretion of stress hormones activates cold-defense responses and mobilizes substrates for increased energy demands to fuel thermogenesis. However, it is unclear whether acute cold exposure-induced stress hormone response kinetics affect circulating lipid parameter kinetics. Therefore, we aimed to investigate the 2-day kinetics of stress hormones (i.e., cortisol, epinephrine, and norepinephrine) and the lipid profile (i.e., total cholesterol [TC], high-density lipoprotein [HDL] cholesterol, low-density lipoprotein [LDL] cholesterol, and triglycerides) in response to whole-body long- (intermittent 170 min; 170-CWI) or short-duration (10 min; 10-CWI) cold-water immersion (CWI; 14 °C water) in 17 healthy, young, adult men. Both CWI trials induced a marked release of the stress hormones, epinephrine, and norepinephrine, with higher concentrations detected after 170-CWI (p < 0.05) and a disrupted diurnal peak of cortisol lasting for a few hours. 170-CWI increased triglyceride levels from immediately after until 2 h after CWI, thereafter the concentration decreased at 4 h, 6 h, 1 day and 2 days after CWI (p < 0.05). Furthermore, the HDL-cholesterol level increased immediately after and at 6 h after 170-CWI (p < 0.05), while TC and LDL-cholesterol levels were not altered within 2 days. Lipid parameters were not affected within the 2 days after 10-CWI. Although both CWIs decreased deep body temperature and increased stress hormone levels for a few hours, only long-duration CWI induced changes in the circulating lipid profile within 2 days after CWI. This should be considered when discussing therapeutic protocols to improve circulating lipid profiles and ameliorate diseases associated with such profiles.

Sex Difference in Female and Male Ice Swimmers for Different Strokes and Water Categories Over Short and Middle Distances: A Descriptive Study

Background

Winter swimming developed from a national tradition into a health-improving sport with international competitions. The difference in performance between women and men was thoroughly examined in various sporting disciplines; however, there is little data on winter swimming events. Therefore, this study aims to compare the sex differences in female and male winter swimmers for a distinct stroke over distances of 25 m and 200 m in ice water, freezing water and cold water in the multiple stages of the Winter Swimming World Cup, hosted by the International Winter Swimming Association (IWSA) since 2016.

Methods

All data included in this study were obtained from the official results of the Winter Swimming World Cup, published on the “International Winter Swimming Association” (IWSA) website. The Mann–Whitney U test was used to compare race time between sexes in different swimming strokes and categories of water. In contrast, the Kruskal–Wallis H test was used to compare differences between swimming strokes or water categories for the same sex.

Results

For 25 m and 200 m events of the “IWSA World Cup,” male athletes were faster than female athletes, regardless of stroke and water temperature category. However, the effect size of the difference between the sexes was greater in 25 m than in 200 m for all strokes and water temperatures. Swimming speed for the same-sex differed between the swimming stroke in relation to the water temperature category. Head-up breaststroke was found to be the slowest stroke (p < 0.05).

Conclusion

In water temperatures between − 2° and + 9 °C, men were faster than women in all stages of the “IWSA World Cup,” regardless of the swimming stroke, but the effect size of the difference between the sexes was greater in shorter than in longer events.

Sexual Dimorphism in Brown Adipose Tissue Activation and White Adipose Tissue Browning

The present narrative review gathers the studies reported so far, addressing sex differences in the effects of cold exposure, feeding pattern and age on brown adipose tissue (BAT) thermogenesis and white adipose tissue (WAT) browning. In rodents, when exposed to decreasing temperatures, females activate thermogenesis earlier. Results obtained in humans go in the same line, although they do not provide results as solid as those obtained in rodents. Regarding the effects of overfeeding, interesting sex differences on BAT thermogenic capacity have been reported, and the greater or lower sensitivity of each sex to this dietary situation seems to be dependent on the type of feeding. In the case of energy restriction, females are more sensitive than males. In addition, sex differences have also been observed in thermogenesis changes induced by phenolic compound administration. During sexual development, an increase in BAT mass and BAT activity takes place. This phenomenon is greater in boys than in girls, probably due to its relation to muscle-mass growth. The opposite situation takes place during ageing, a lifespan period where thermogenic capacity declines, this being more acute in men than in women. Finally, the vast majority of the studies have reported a higher susceptibility to developing WAT browning amongst females. The scarcity of results highlights the need for further studies devoted to analysing this issue, in order to provide valuable information for a more personalised approach.

miR-375 is cold exposure sensitive and drives thermogenesis in visceral adipose tissue derived stem cells

Activation of brown adipose tissue may increase energy expenditure by non-shivering thermogenesis. Cold exposure is one of the options to activate brown adipocytes. To link changes in energy metabolism with microRNA expression (miRNAs), we analyzed 158 miRNAs in serum of 169 healthy individuals before and after cold exposure. Validating the results of a miRNA array, a significant down-regulation of miR-375 after cold exposure (P < 0.0001) was detected. These changes went along with a significant negative correlation between miR-375 and visceral adipose tissue (VAT) mass (P < 0.0001), implicating a specific function of miR-375 in this depot. Significantly higher expression levels of miR-375 were found in VAT in comparison to subcutaneous fat (SAT). Using in silico prediction, we identified putative miR-375 target genes involved in the thermogenesis pathway. Cold-stimulation of subcutaneous and visceral pre-adipocytes (PACs) led to significantly higher expression levels of FABP4, FGF21, PPARGC1A and PRDM16 in VC-PACs. Analyzing miR-375 knock down and cold stimulated VC-PACs revealed a significant up-regulation of thermogenesis associated genes PPARGC1A, ELOVL3 and PRDM16. In summary, our findings identified miR-375 as a potential adipogenic and thermogenesis-associated miRNA exclusively acting in visceral adipose tissue.

Cold-Induced Thermogenesis Shows a Diurnal Variation That Unfolds Differently in Males and Females

CONTEXT

Cold exposure mobilizes lipids to feed thermogenic processes in organs, including brown adipose tissue (BAT). In rodents, BAT metabolic activity exhibits a diurnal rhythm, which is highest at the start of the wakeful period.

OBJECTIVE

We investigated whether cold-induced thermogenesis displays diurnal variation in humans and differs between the sexes.

METHODS

This randomized crossover study included 24 young and lean male (n = 12) and female (n = 12) participants who underwent 2.5-hour personalized cooling using water-perfused mattresses in the morning (7:45 am) and evening (7:45 pm), with 1 day in between. We measured energy expenditure (EE) and supraclavicular skin temperature in response to cold exposure.

RESULTS

In males, cold-induced EE was higher in the morning than in the evening (+54% ± 10% vs +30% ± 7%; P = 0.05) but did not differ between morning and evening in females (+37% ± 9% vs +30% ± 10%; P = 0.42). Only in males, supraclavicular skin temperature upon cold increased more in morning than evening (+0.2 ± 0.1 °C vs -0.2 ± 0.2 °C; P = 0.05). In males, circulating free fatty acid (FFA) levels were increased after morning cold exposure, but not evening (+90% ± 18% vs +9% ± 8%; P < 0.001). In females, circulating FFA (+94% ± 21% vs +20% ± 5%; P = 0.006), but also triglycerides (+42% ± 5% vs +29% ± 4%, P = 0.01) and cholesterol levels (+17% ± 2% vs 11% ± 2%; P = 0.05) were more increased after cold exposure in morning than in evening.

CONCLUSION

Cold-induced thermogenesis is higher in morning than evening in males; however, lipid metabolism is more modulated in the morning than the evening in females.

CRISPR/Cas9-mediated inactivation of the phosphatase activity of soluble epoxide hydrolase prevents obesity and cardiac ischemic injury

INTRODUCTION

Although the physiological role of the C-terminal hydrolase domain of the soluble epoxide hydrolase (sEH-H) is well investigated, the function of its N-terminal phosphatase activity (sEH-P) remains unknown.

OBJECTIVES

This study aimed to assess in vivo the physiological role of sEH-P.

METHODS

CRISPR/Cas9 was used to generate a novel knock-in (KI) rat line lacking the sEH-P activity.

RESULTS

The sEH-P KI rats has a decreased metabolism of lysophosphatidic acids to monoacyglycerols. KI rats grew almost normally but with less weight and fat mass gain while insulin sensitivity was increased compared to wild-type rats. This lean phenotype was more marked in males than in female KI rats and mainly due to decreased food consumption and enhanced energy expenditure. In fact, sEH-P KI rats had an increased lipolysis allowing to supply fatty acids as fuel to potentiate brown adipose thermogenesis under resting condition and upon cold exposure. The potentiation of thermogenesis was abolished when blocking PPARγ, a nuclear receptor activated by intracellular lysophosphatidic acids, but also when inhibiting simultaneously sEH-H, showing a functional interaction between the two domains. Furthermore, sEH-P KI rats fed a high-fat diet did not gain as much weight as the wild-type rats, did not have increased fat mass and did not develop insulin resistance or hepatic steatosis. In addition, sEH-P KI rats exhibited enhanced basal cardiac mitochondrial activity associated with an enhanced left ventricular contractility and were protected against cardiac ischemia-reperfusion injury.

CONCLUSION

Our study reveals that sEH-P is a key player in energy and fat metabolism and contributes together with sEH-H to the regulation of cardiometabolic homeostasis. The development of pharmacological inhibitors of sEH-P appears of crucial importance to evaluate the interest of this promising therapeutic strategy in the management of obesity and cardiac ischemic complications.

Association Between Adipose Tissue Proton Density Fat Fraction, Resting Metabolic Rate and FTO Genotype in Humans

BACKGROUND

The difference of proton density fat fraction (PDFF) between supraclavicular and gluteal adipose tissue might indicate the presence of brown adipose tissue (BAT). Aim of this cross-sectional study was to investigate the association between PDFF over the supraclavicular fat region as a proxy of BAT proportion and resting metabolic rate (RMR). In addition, the association between the single nucleotide polymorphism (SNP) rs1421085 at the fat mass and obesity associated (FTO) gene locus and both PDFF and RMR was investigated.

METHODS

Anthropometric, clinical, and lifestyle data from 92 healthy adults (66.3% females, mean age: 36.2 ± 13.0 years, mean body mass index: 24.9 ± 5.4 kg/m²) were included in the analysis. The RMR was measured by indirect calorimetry. The magnetic resonance imaging (MRI) was used for the measurement of visceral and subcutaneous adipose tissue (VAT, SAT) volumes and for the measurement of adipose tissue PDFF.

RESULTS

Mean RMR of the whole group was 1 474.8 ± 242.2 kcal. Genotype data was available for 90 participants. After adjustment for age, sex, weight change and fat-free mass (FFM), no association was found between supraclavicular PDFF (p = 0.346) and gluteal PDFF (p = 0.252), respectively, and RMR, whereas statistically significant evidence for a negative association between delta PDFF (difference between gluteal PDFF and supraclavicular PDFF) and RMR (p = 0.027) was obtained. No statistically significant evidence was observed for per FTO risk allele change in RMR, gluteal and supraclavicular PDFF maps or volumes of VAT and SAT.

CONCLUSIONS

Supraclavicular PDFF as a surrogate marker of BAT presence is not a determinant of RMR under basal conditions. In the present study, the FTO rs1421085 variant is not associated with either RMR or PDFF. Further studies are needed to elucidate the effect of BAT on RMR.

Sex differences in brown adipose tissue activity and cold-induced thermogenesis

INTRODUCTION

Brown adipose tissue (BAT) is suggested to exhibit a sexual dimorphism and thus contributes to the observed sex differences in cardiometabolic risk observed between women and men. Clinical data supporting this hypothesis are however scarce. The aim of this study was to investigate the relationship between BAT activity and sex using positron emission tomography (PET) - the current gold-standard for BAT quantification.

METHODS

In this study, we included 95 subjects with a wide BMI range (20-55 kg/m²) aged from 18 to 50 years. Avoiding shivering, participants were cooled with a water-perfused vest to achieve adequate BAT activation. BAT activity was determined by ¹⁸F-fluorodeoxyglucose PET/computed tomography (¹⁸F-FDG PET/CT). Cold-induced thermogenesis (CIT) was quantified by indirect calorimetry.

RESULTS

BAT was present in 44.6% of pre-menopausal women and in 35.9% of men (p = 0.394). CIT was significantly higher in women (p = 0.024). Estradiol levels were positively associated with CIT independent of age, sex, body fat and other sex hormones (b = 0.360, p = 0.016). In women, CIT decreased during the menstrual cycle, with lower levels in the luteal phase similar to median concentrations in men.

CONCLUSION

The prevalence of cold-activated BAT is slightly but non-significantly higher in pre-menopausal women than men. CIT is increased in females and independently associated with estradiol, suggesting that sex hormones may play a role in different thermogenic responses between men and women.

MECHANISMS IN ENDOCRINOLOGY: Human brown adipose tissue as a therapeutic target: warming up or cooling down?

Excessive accumulation of white adipose tissue leads to obesity and its associated metabolic health consequences such as type 2 diabetes and cardiovascular disease. Several approaches to treat or prevent obesity including public health interventions, surgical weight loss, and pharmacological approaches to reduce caloric intake have failed to substantially modify the increasing prevalence of obesity. The (re-)discovery of active brown adipose tissue (BAT) in adult humans approximately 15 years ago led to a resurgence in research into whether BAT activation could be a novel therapy for the treatment of obesity. Upon cold stimulus, BAT activates and generates heat to maintain body temperature, thus increasing energy expenditure. Activation of BAT may provide a unique opportunity to increase energy expenditure without the need for exercise. However, much of the underlying mechanisms surrounding BAT activation are still being elucidated and the effectiveness of BAT as a therapeutic target has not been realised. Research is ongoing to determine how best to expand BAT mass and activate existing BAT; approaches include cold exposure, pharmacological stimulation using sympathomimetics, browning agents that induce formation of thermogenic beige adipocytes in white adipose depots, and the identification of factors secreted by BAT with therapeutic potential. In this review, we discuss the caloric capacity and other metabolic benefits from BAT activation in humans and the role of metabolic tissues such as skeletal muscle in increasing energy expenditure. We discuss the potential of current approaches and the challenges of BAT activation as a novel strategy to treat obesity and metabolic disorders.

Examining the benefits of cold exposure as a therapeutic strategy for obesity and type 2 diabetes

The pathogenesis of metabolic diseases such as obesity and type 2 diabetes are characterized by a progressive dysregulation in energy partitioning, often leading to end-organ complications. One emerging approach proposed to target this metabolic dysregulation is the application of mild cold exposure. In healthy individuals, cold exposure can increase energy expenditure and whole body glucose and fatty acid utilization. Repeated exposures can lower fasting glucose and insulin levels and improve dietary fatty acid handling, even in healthy individuals. Despite its apparent therapeutic potential, little is known regarding the effects of cold exposure in populations for which this stimulation could benefit the most. The few studies available have shown that both acute and repeated exposures to the cold can improve insulin sensitivity and reduce fasting glycemia in individuals with type 2 diabetes. However, critical gaps remain in understanding the prolonged effects of repeated cold exposures on glucose regulation and whole body insulin sensitivity in individuals with metabolic syndrome. Much of the metabolic benefits appear to be attributable to the recruitment of shivering skeletal muscles. However, further work is required to determine whether the broader recruitment of skeletal muscles observed during cold exposure can confer metabolic benefits that surpass what has been historically observed from endurance exercise. In addition, although cold exposure offers unique cardiovascular responses for a physiological stimulus that increases energy expenditure, further work is required to determine how acute and repeated cold exposure can impact cardiovascular responses and myocardial function across a broader scope of individuals.