The effects of cold exposure (cold water immersion, whole- and partial- body cryostimulation) on cardiovascular and cardiac autonomic control responses in healthy individuals: A systematic review, meta-analysis and meta-regression

BACKGROUND

Cryostimulation and cold-water immersion (CWI) have recently gained widespread attention due to their association with changes in cardiovascular and cardiac autonomic control responses. Therefore, the aim of the present systematic review and meta-analysis was to identify the global impact of such cold exposures on cardiovascular and cardiac autonomic activity.

METHODS

Three databases (PubMed, Embase, Web-of-Science) were used. Studies were eligible for inclusion if they were conducted on healthy participants using cryostimulation and/or CWI. The outcomes included measurements of blood pressure (BP), heart rate (HR), and heart rate variability (HRV) indices: RR interval (RR), Root mean square of successive RR interval differences (RMSSD), low frequency band (LF), high frequency band (HF), and LF/HF ratio.

RESULTS

Among the 27 articles included in our systematic literature review, only 24 were incorporated into the meta-analysis. Our results reveal a significant increase in HRV indices: RMSSD (Standardized mean difference (SMD) = 0.61, p < 0.001), RR (SMD = 0.77, p < 0.001), and HF (SMD = 0.46, p < 0.001), as well as significantly reduced LF (SMD = -0.41, p < 0.001) and LF/HF ratio (SMD = -0.25, p < 0.01), which persisted up to 15 min following cold exposure. Significantly decreased heart rate (SMD = -0.16, p < 0.05), accompanied by slightly increased mean BP (SMD = 0.28, p < 0.001), was also observed. These results seem to depend on individual characteristics and the cooling techniques.

CONCLUSION

Our meta-analysis suggests that cryostimulation and/or CWI exposure enhance parasympathetic nervous activity. There is scarce scientific literature regarding the effect of individual characteristics on cold-induced physiological responses.

Cold exposure, gut microbiota and health implications: A narrative review

Temperature has been recognized as an important environmental factor affecting the composition and function of gut microbiota (GM). Although research on high-temperature impacts has been well studied, knowledge about the effect of cold exposure on GM remains limited. This narrative review aims to synthesize the latest scientific findings on the impact of cold exposure on mammalian GM, and its potential health implications. Chronic cold exposure could disrupt the α-diversity and the composition of GM in both experimental animals and wild-living hosts. Meanwhile, cold exposure could impact gut microbial metabolites, such as short-chain fatty acids. We also discussed plausible biological pathways and mechanisms by which cold-induced changes may impact host health, including metabolic homeostasis, fitness and thermogenesis, through the microbiota-gut-brain axis. Intriguingly, alterations in GM may provide a tool for favorably modulating the host response to the cold temperature. Finally, current challenges and future perspectives are discussed, emphasizing the need for translational research in humans. GM could be manipulated by utilizing nutritional strategies, such as probiotics and prebiotics, to deal with cold-related health issues and enhance well-being in populations living or working in cold environments.

SCD1 sustains brown fat sympathetic innervation and thermogenesis during the long-term cold exposure

Brown fat adipose tissue (BAT) is a therapeutic potential target to improve obesity, diabetes and cold acclimation in mammals. During the long-term cold exposure, the hyperplastic sympathetic network is crucial for BAT the maintain the highly thermogenic status. It has been proved that the sympathetic nervous drives the thermogenic activity of BAT via the release of norepinephrine. However, it is still unclear that how the thermogenic BAT affects the remodeling of the hyperplastic sympathetic network, especially during the long-term cold exposure. Here, we showed that following long-term cold exposure, SCD1-mediated monounsaturated fatty acid biosynthesis pathway was enriched, and the ratios of monounsaturated/saturated fatty acids were significantly up-regulated in BAT. And SCD1-deficiency in BAT decreased the capacity of cold acclimation, and suppressed long-term cold mediated BAT thermogenic activation. Furthermore, by using thermoneutral exposure and sympathetic nerve excision models, we disclosed that SCD1-deficiency in BAT affected the thermogenic activity, depended on sympathetic nerve. In mechanism, SCD1-deficiency resulted in the unbalanced ratio of palmitic acid (PA)/palmitoleic acid (PO), with obviously higher level of PA and lower level of PO. And PO supplement efficiently reversed the inhibitory role of SCD1-deficiency on BAT thermogenesis and the hyperplastic sympathetic network. Thus, our data provided insight into the role of SCD1-mediated monounsaturated fatty acids metabolism to the interaction between thermogenic activity BAT and hyperplastic sympathetic networks, and illustrated the critical role of monounsaturated fatty acids biosynthetic pathway in cold acclimation during the long-term cold exposure.

Chronic cold environment regulates rheumatoid arthritis through modulation of gut microbiota-derived bile acids

The pathologies of many diseases are influenced by environmental temperature. As early as the classical Roman age, people believed that exposure to cold weather was bad for rheumatoid arthritis (RA). However, there is no direct evidence supporting this notion, and the molecular mechanisms of the effects of chronic cold exposure on RA remain unknown. Here, in a temperature-conditioned environment, we found that chronic cold exposure aggravates collagen-induced arthritis (CIA) by increasing ankle swelling, bone erosion, and cytokine levels in rats. Furthermore, in chronic cold-exposed CIA rats, gut microbiota dysbiosis was identified, including a decrease in the differential relative abundance of the families Lachnospiraceae and Ruminococcaceae. We also found that an antibiotic cocktail suppressed arthritis severity under cold conditions. Notably, the fecal microbiota transplantation (FMT) results showed that transplantation of cold-adapted microbiota partly recapitulated the microbiota signature in the respective donor rats and phenocopied the cold-induced effects on CIA rats. In addition, cold exposure disturbed bile acid profiles, in particular decreasing gut microbiota-derived taurohyodeoxycholic acid (THDCA) levels. The perturbation of bile acids was also associated with activation of the TGR5-cAMP-PKA axis and NLRP3 inflammasome. Oral THDCA supplementation mitigated the arthritis exacerbation induced by chronic cold exposure. Our findings identify an important role of aberrant gut microbiota-derived bile acids in cold exposure-related RA, highlighting potential opportunities to treat cold-related RA by manipulating the gut microbiota and/or supplementing with THDCA.

Effects of different extreme cold exposure on heart rate variability

Frequent extreme cold events in recent years have brought serious threats to outdoor workers and rescuers. Changes in ambient temperature are associated with altered cardiac autonomic function. The study aims to investigate heart rate variability(HRV) and its relationship to other physiological parameters under extreme cold exposures. 12 males underwent a 30-minute preconditioning phase in a neutral environment followed by a 30-minute cold exposure(-5 °C, -10 °C, -15 °C, and -20 °C). Time-domain indexes(meanRR, SDNN, RMSSD, and pNN50), frequency domain indexes(Log(HF), Log(LF), and low frequency/high frequency(LF/HF)), parasympathetic nervous system(PNS), and sympathetic nervous system(SNS) were analyzed. Results showed all HRV indexes of four cold exposures were significant. The decrease in temperature was accompanied by progressive PNS activation with SNS retraction. SDNN was the most sensitive HRV index and had good linear relationships with blood pressure, pulse, and hand temperature. The results are significant for formulating safety protection strategies for workers in extremely cold environments.

Influence of cold-stimulated adipocyte supernatant on the expression of adhesion-related molecules in Schwann cell line

Bell's palsy is the most common form of facial nerve palsy. This study aimed to explore the pathogenesis of Bell's palsy by investigating the effect of cold-stimulated adipocyte supernatant on adhesion molecule expression in Schwann cell line. Schwann cells were cultured in regular or adipocyte-conditioned medium and analyzed using RNA sequencing. The mRNA expression of Schwann cell adhesion molecules melanoma cell adhesion molecule (MCAM), protocadherin 9 (PCDH9), and intercellular cell adhesion molecule 1 (ICAM1) was determined using real-time reverse-transcription polymerase chain reaction. Differentially expressed genes were identified, and Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses were conducted. Compared with Schwann cells in 37 °C, the expression of MCAM, PCDH9, and ICAM1 was downregulated in Schwann cells treated with cold-stimulated adipocyte supernatant compared with Schwann cells in 37 °C. Adipocytes subjected to cold exposure may weaken the adhesion capacity of Schwann cells and disrupt the local homeostasis of Schwann cell-axon interactions by affecting the expression of MCAM, PCDH9, and ICAM1, ultimately leading to the development of demyelinating lesions.

Exercise in cold: Friend than foe to cardiovascular health

Exercise has been proven to benefit human health comprehensively regardless of the intensity, time, or environment. Recent studies have found that combined exercise with a cold environment displays a synergistical beneficial effect on cardiovascular system compared to exercise in thermoneutral environment. Cold environment leads to an increase in body heat loss, and has been considered a notorious factor for cardiovascular system. Exercise in cold increases the stress of cardiovascular system and risks of cardiovascular diseases, but increases the body tolerance to detrimental insults and benefits cardiovascular health. The biological effects and its underlying mechanisms of exercise in cold are complex and not well studied. Evidence has shown that exercise in cold exerts more noticeable effects on sympathetic nervous activation, bioenergetics, anti-oxidative capacity, and immune response compared to exercise in thermoneutral environment. It also increases the secretion of a series of exerkines, including irisin and fibroblast growth factor 21, which may contribute to the cardiovascular benefits induced by exercise in cold. Further well-designed studies are needed to advance the biological effects of exercise in cold. Understanding the mechanisms underlying the benefits of exercise in cold will help prescribe cold exercise to those who can benefit from it.

Does working in an extremely cold environment affects lung function?: 10 years follow-up

OBJECTIVE

The aim of this study is to investigate whether there is an association between brief but repeated exposures to extremely cold temperatures over many years and pulmonary function.

METHODS

We performed a retrospective analysis of the data collected over 10 years in the context of the extended medical examinations of storeworkers exposed to extremely cold temperatures. We considered forced vital capacity (FVC), forced expiratory volume in one second (FEV1), Tiffeneau-Pinelli index (FEV1/FVC), CO diffusion capacity (DL,CO) and Krogh-factor (CO diffusion capacity relative to recorded alveolar volume, DL,CO/VA) reported as %-predicted. We analysed trends in outcome parameters with linear mixed models.

RESULTS

46 male workers participated in at least two extended medical examinations between 2007 and 2017. Overall 398 measure points were available. All lung function parameters had values above the lower limit of normality at the first examination. In the multivariate model including smoking status and monthly intensity of cold exposure (≤ 16 h/month vs. > 16 h/month) FEV1%-predicted and FVC %-predicted had a statistically significant positive slope (FEV1, 0.32% 95% CI 0.16% to 0.49% p < 0.001; FVC 0.43% 95% CI 0.28% to 0.57% p < 0.001). The other lung function parameters (FEV1/FVC %-predicted, DL,CO %-predicted, DL,CO/VA %-predicted) showed no statistically significant change over time.

CONCLUSIONS

Long term intermittent occupational exposure to extreme cold temperatures (-55 °C) does not appear to cause irreversible deleterious changes in lung function in healthy workers, thus the development of obstructive or restrictive lung diseases is not expected.

Functional expression of the thermally activated transient receptor potential channels TRPA1 and TRPM8 in human myotubes

Transient potential (TRP) ion channels expressed in primary sensory neurons act as the initial detectors of environmental cold and heat, information which controls muscle energy expenditure. We hypothesize that non-neuronal TRPs have direct cellular responses to thermal exposure, also affecting cellular metabolism. In the present study we show expression of TRPA1, TRPM8 and TRPV1 in rat skeletal muscle and human primary myotubes by qPCR. Effects of TRP activity on metabolism in human myotubes were studied using radiolabeled glucose. FURA-2 was used for Ca2+ imaging. TRPA1, TRPM8 and TRPV1 were expressed at low levels in primary human myotubes and in m. gastrocnemius, m. soleus, and m. trapezius from rat. Activation of TRPA1 by ligustilide resulted in an increased glucose uptake and oxidation in human myotubes, whereas activation of TRPM8 by menthol and icilin significantly decreased glucose uptake and oxidation. Activation of heat sensing TRPV1 by capsaicin had no effect on glucose metabolism. Agonist-induced increases in intracellular Ca2+ levels by ligustilide and icilin in human myotubes confirmed a direct activation of TRPA1 and TRPM8, respectively. The mRNA expression of some genes involved in thermogenesis, i.e. peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), uncoupling protein (UCP) 1 and UCP3, were downregulated in human myotubes following TRPA1 activation, while the mRNA expression of TRPM8 and TRPA1 were downregulated following TRPM8 activation by menthol and icilin, respectively. Cold exposure (18 °C) of cultured myotubes followed by a short recovery period had no effect on glucose uptake and oxidation in the basal situation, however when TRPA1 and TRPM8 channels were chemically inhibited a temperature-induced difference in glucose metabolism was found. In conclusion, mRNA of TRPA1, TRPM8 and TRPV1 are expressed in rat skeletal muscle and human skeletal muscle cells. Modulation of TRPA1 and TRPM8 by chemical agents induced changes in Ca2+ levels and glucose metabolism in human skeletal muscle cells, indicating functional receptors.

Cold-induced adaptive thermogenesis is impaired by exposure of Asian sand dust in mice

Desertification and desert sandstorms caused by the worsening global warming pose increasing risks to human health. In particular, Asian sand dust (ASD) exposure has been related to an increase in mortality and hospital admissions for respiratory diseases. In this study, we investigated the effects of ASD on metabolic tissues in comparison to diesel particulate matter (DPM) that is known to cause adverse health effects. We found that larger lipid droplets were accumulated in the brown adipose tissues (BAT) of ASD-administered but not DPM-administered mice. Thermogenic gene expression was decreased in these mice as well. When ASD-administered mice were exposed to the cold, they failed to maintain their body temperature, suggesting that the ASD administration had led to impairments in cold-induced adaptive thermogenesis. However, impaired thermogenesis was not observed in DPM-administered mice. Furthermore, mice fed a high-fat diet that were chronically administered ASD demonstrated unexplained weight loss, indicating that chronic administration of ASD could be lethal in obese mice. We further identified that ASD-induced lung inflammation was not exacerbated in uncoupling protein 1 knockout mice, whose thermogenic capacity is impaired. Collectively, ASD exposure can impair cold-induced adaptive thermogenic responses in mice and increase the risk of mortality in obese mice.

Cold exposure protects against medial arterial calcification development via autophagy

Medial arterial calcification (MAC), a systemic vascular disease different from atherosclerosis, is associated with an increased incidence of cardiovascular events. Several studies have demonstrated that ambient temperature is one of the most important factors affecting cardiovascular events. However, there has been limited research on the effect of different ambient temperatures on MAC. In the present study, we showed that cold temperature exposure (CT) in mice slowed down the formation of vitamin D (VD)-induced vascular calcification compared with room temperature exposure (RT). To investigate the mechanism involved, we isolated plasma-derived exosomes from mice subjected to CT or RT for 30 days (CT-Exo or RT-Exo, respectively). Compared with RT-Exo, CT-Exo remarkably alleviated the calcification/senescence formation of vascular smooth muscle cells (VSMCs) and promoted autophagy by activating the phosphorylation of AMP-activated protein kinase (p-AMPK) and inhibiting phosphorylation of mammalian target of rapamycin (p-mTOR). At the same time, CT-Exo promoted autophagy in β-glycerophosphate (β-GP)-induced VSMCs. The number of autophagosomes and the expression of autophagy-related proteins ATG5 and LC3B increased, while the expression of p62 decreased. Based on a microRNA chip microarray assay and real-time polymerase chain reaction, miR-320a-3p was highly enriched in CT-Exo as well as thoracic aortic vessels in CT mice. miR-320a-3p downregulation in CT-Exo using AntagomiR-320a-3p inhibited autophagy and blunted its anti-calcification protective effect on VSMCs. Moreover, we identified that programmed cell death 4 (PDCD4) is a target of miR-320a-3p, and silencing PDCD4 increased autophagy and decreased calcification in VSMCs. Treatment with CT-Exo alleviated the formation of MAC in VD-treated mice, while these effects were partially reversed by GW4869. Furthermore, the anti-arterial calcification protective effects of CT-Exo were largely abolished by AntagomiR-320a-3p in VD-induced mice. In summary, we have highlighted that prolonged cold may be a good way to reduce the incidence of MAC. Specifically, miR-320a-3p from CT-Exo could protect against the initiation and progression of MAC via the AMPK/mTOR autophagy pathway.

Characteristics of glucose and lipid metabolism and the interaction between gut microbiota and colonic mucosal immunity in pigs during cold exposure

BACKGROUND

Cold regions have long autumn and winter seasons and low ambient temperatures. When pigs are unable to adjust to the cold, oxidative damage and inflammation may develop. However, the differences between cold and non-cold adaptation regarding glucose and lipid metabolism, gut microbiota and colonic mucosal immunological features in pigs are unknown. This study revealed the glucose and lipid metabolic responses and the dual role of gut microbiota in pigs during cold and non-cold adaptation. Moreover, the regulatory effects of dietary glucose supplements on glucose and lipid metabolism and the colonic mucosal barrier were evaluated in cold-exposed pigs.

RESULTS

Cold and non-cold-adapted models were established by Min and Yorkshire pigs. Our results exhibited that cold exposure induced glucose overconsumption in non-cold-adapted pig models (Yorkshire pigs), decreasing plasma glucose concentrations. In this case, cold exposure enhanced the ATGL and CPT-1α expression to promote liver lipolysis and fatty acid oxidation. Meanwhile, the two probiotics (Collinsella and Bifidobacterium) depletion and the enrichment of two pathogens (Sutterella and Escherichia-Shigella) in colonic microbiota are not conducive to colonic mucosal immunity. However, glucagon-mediated hepatic glycogenolysis in cold-adapted pig models (Min pigs) maintained the stability of glucose homeostasis during cold exposure. It contributed to the gut microbiota (including the enrichment of the Rikenellaceae RC9 gut group, [Eubacterium] coprostanoligenes group and WCHB1-41) that favored cold-adapted metabolism.

CONCLUSIONS

The results of both models indicate that the gut microbiota during cold adaptation contributes to the protection of the colonic mucosa. During non-cold adaptation, cold-induced glucose overconsumption promotes thermogenesis through lipolysis, but interferes with the gut microbiome and colonic mucosal immunity. Furthermore, glucagon-mediated hepatic glycogenolysis contributes to glucose homeostasis during cold exposure.

Associations of ambient temperature with creatine kinase MB and creatine kinase: A large sample time series study of the Chinese male population

Previous evidence has associated non-optimal ambient temperature with an increased risk of myocardial infarction. However, no studies have shown an association between ambient temperature and biomarkers in the myocardium. This study aimed to investigate the association of ambient temperature with creatine kinase MB (CK-MB) and creatine kinase (CK). A total of 94,784 men aged 20-50 years were included in this study. We performed blood biochemical tests on the participants and used the daily average temperature to represent ambient temperature. The daily average ambient temperature was calculated by hourly observational data from meteorological indicators in Beijing. Lag effects were observed within 0-7 days. General additive models were used to observe nonlinear associations of ambient temperature with CK-MB and CK. Linear models were used to fit the associations of cold or heat with CK-MB and CK, respectively, after confirming the inflection point of ambient temperature. The OR value of abnormal CK-MB (CK) for a 1 °C increase or decrease was calculated by logistic regression. In the results, a V-shaped relationship between CK-MB and ambient temperature and a linear relationship between CK and ambient temperature were observed. Cold exposure was associated with increased CK-MB and CK levels. For a 1 °C decrease, CK-MB increased by 0.044 U/L (95 % CI: 0.017, 0.070 U/L) at lag day 0, and CK increased by 1.44 U/L (0.44, 2.44 U/L) at lag day 4 (the lag day with the strongest effect). The OR of high CK-MB was 1.047 (1.017, 1.077) at lag day 0, and the OR of high CK was 1.066 (1.038, 1.095) at lag day 4 for a 1 °C decrease. No heat-related elevation of CK-MB or CK was observed. In general, cold exposure is associated with increased levels of CK-MB and CK in humans, which may be associated with myocardial injury. Our findings illustrate the possible adverse effects of cold exposure on the myocardium from a biomarker perspective.

Potential role of ambient temperature as a trigger for intracerebral hemorrhage: a time-stratified case-crossover study in Tianjin, China

The adverse effects of ambient temperature on human health are receiving increasing attention, yet evidence of its impact on intracerebral hemorrhage (ICH) onset is limited. Here, the relationship between ambient temperature and ICH was evaluated. A time-stratified case-crossover analysis was performed based on 4051 ICH patients admitted to five stroke units in Tianjin between January 2014 and December 2020. Conditional logistic regression was applied to evaluate the associations between the daily mean temperature (Tm) or daily temperature range (DTR) and ICH onset. We found a negative association between Tm and ICH onset (OR = 0.977, 95% CI 0.968-0.987) but not between DTR and ICH onset. In stratified analyses, men and individuals aged ≥ 60 years were more susceptible to low-ambient temperature effects; corresponding adjusted ORs were 0.970 (95% CI 0.956-0.983) and 0.969 (95% CI 0.957-0.982), respectively. Tm significantly affected patients with deep ICH (OR = 0.976, 95% CI 0.965-0.988), but had no effect on lobar ICH. There was also seasonal heterogeneity in the effect of Tm on ICH onset, with Tm being negatively associated with ICH onset only in the warm season (OR = 0.961, 95% CI 0.941-0.982). Results suggest that the low-ambient temperature might trigger ICH onset, especially for the male and elderly population, providing important health guidance to prevent cold exposure-induced ICH.

Improvement of thermal perceptions and physiological responses using torso heating under short-term cold exposure

Short-term cold exposure (<1 h) may adversely affect human thermal comfort and health. Few studies have investigated the effectiveness of body heating in providing thermal protection to the torso against sharp temperature decreases, as well as the optimal operation modes of torso heating equipment. In this study, 12 male subjects were acclimatised in a room at 20 °C, then exposed to a cold environment at -2.2 °C, and finally returned to the room for recovery; each phase lasted 30 min. During cold exposure, they wore uniform clothing with an electrically heated vest (EHV) operated under these modes: no heating (NH), stage-regulated heating (SH), and intermittent alternating heating (IAH). Variations in subjective perceptions, physiological responses, and temperatures set for heating were recorded during the experiments. Torso heating mitigated the adverse effects of the large temperature down-step and continuous cold exposure on thermal perception and decreased the occurrence of three symptoms: cold hands or feet, running or stuffy noses, and shivering during cold exposure. After torso heating, the same skin temperature of the non-directly heated parts corresponded to a higher local thermal sensation, which was attributed to an indirect effect of the improved overall thermal state. The IAH mode could achieve thermal comfort at a reduced energy level, and it outperformed SH in subjective perception enhancement and self-reported symptom relief at lower heating temperatures. Additionally, under the same heating setting temperatures and power capacity, it could achieve an approximately 50 % longer usage time than SH could. The results suggest that intermittent heating protocol can be an efficient way to achieve thermal comfort and energy savings for personal heating devices.

The effects of exposure to cold during incubation on developmental stability, fear, growth, and carcass traits in Japanese quails

The aim of this study was to determine the effects of 6 h/day cold (35.0 °C) acclimatization between the 9^th and 15^th days of incubation of Japanese quail embryos on hatchability, livability, chick quality, developmental stability, fear response, live weight, and slaughter-carcass characteristics. Two homologous incubators and a total of 500 hatching eggs were used in the study. Randomly selected half of the eggs were exposed to cold according to the eggshell temperature. The cold acclimation of Japanese quail embryos had no adverse effects on all mentioned traits, except for chick quality. Chicks in the control group had higher Tona scores (99.46) than those exposed to cold (99.00) (P < 0.05). In addition, there were differences among the treatment groups in terms of the parameters of mature weight (β₀), instantaneous growth rate (β₂), and inflection point coordinates of the Gompertz growth model (P < 0.05 for all). It was found that exposing embryos to cold during the incubation changed the shape of the growth curve. As the development of embryos exposed to cold slows down, a compensatory growth occurs in the early posthatch period. Thus, the growth rate increased in the period before the inflection point of the growth curve.

Cold exposure alters lipid metabolism of skeletal muscle through HIF-1α-induced mitophagy

BACKGROUND

In addition to its contractile properties and role in movement, skeletal muscle plays an important function in regulating whole-body glucose and lipid metabolism. A central component of such regulation is mitochondria, whose quality and function are essential in maintaining proper metabolic homeostasis, with defects in processes such as autophagy and mitophagy involved in mitochondria quality control impairing skeletal muscle mass and function, and potentially leading to a number of associated diseases. Cold exposure has been reported to markedly induce metabolic remodeling and enhance insulin sensitivity in the whole body by regulating mitochondrial biogenesis. However, changes in lipid metabolism and lipidomic profiles in skeletal muscle in response to cold exposure are unclear. Here, we generated lipidomic or transcriptome profiles of mouse skeletal muscle following cold induction, to dissect the molecular mechanisms regulating lipid metabolism upon acute cold treatment.

RESULTS

Our results indicated that short-term cold exposure (3 days) can lead to a significant increase in intramuscular fat deposition. Lipidomic analyses revealed that a cold challenge altered the overall lipid composition by increasing the content of triglyceride (TG), lysophosphatidylcholine (LPC), and lysophosphatidylethanolamine (LPE), while decreasing sphingomyelin (SM), validating lipid remodeling during the cold environment. In addition, RNA-seq and qPCR analysis showed that cold exposure promoted the expression of genes related to lipolysis and fatty acid biosynthesis. These marked changes in metabolic effects were associated with mitophagy and muscle signaling pathways, which were accompanied by increased TG deposition and impaired fatty acid oxidation. Mechanistically, HIF-1α signaling was highly activated in response to the cold challenge, which may contribute to intramuscular fat deposition and enhanced mitophagy in a cold environment.

CONCLUSIONS

Overall, our data revealed the adaptive changes of skeletal muscle associated with lipidomic and transcriptomic profiles upon cold exposure. We described the significant alterations in the composition of specific lipid species and expression of genes involved in glucose and fatty acid metabolism. Cold-mediated mitophagy may play a critical role in modulating lipid metabolism in skeletal muscle, which is precisely regulated by HIF-1α signaling.

Role of bile acid receptor FXR in development and function of brown adipose tissue

Bile acids act as signalling molecules that contribute to maintenance of energy homeostasis in mice and humans. Activation of G-protein-coupled bile acid receptor TGR5 induces energy expenditure in brown adipose tissue (BAT). However, a role for the nuclear bile acid receptor Farnesoid X receptor (FXR) in BAT has remained ambiguous. We aimed to study the potential role of FXR in BAT development and functioning. Here we demonstrate low yet detectable expression of the α1/2 isoforms of FXR in murine BAT that markedly decreases upon cold exposure. Moderate adipose tissue-specific FXR overexpression in mice induces pronounced BAT whitening, presenting with large intracellular lipid droplets and extracellular collagen deposition. Expression of thermogenic marker genes including the target of Tgr5, Dio2, was significantly lower in BAT of chow-fed aP2-hFXR mice compared to wild-type controls. Transcriptomic analysis revealed marked up-regulation of extracellular matrix formation and down-regulation of mitochondrial functions in BAT from aP2-hFXR mice. In addition, markers of cell type lineages deriving from the dermomyotome, such as myocytes, as well as markers of cellular senescence were strongly induced. The response to cold and β3-adrenergic receptor agonism was blunted in these mice, yet resolved BAT whitening. Newborn cholestatic Cyp2c70^-/- mice with a human-like bile acid profile also showed distinct BAT whitening and upregulation of myocyte-specific genes, while thermogenic markers were down-regulated. Ucp1 expression inversely correlated with plasma bile acid levels. Therefore, bile acid signalling via FXR has a role in BAT function already early in tissue development. Functionally, FXR activation appears to oppose TGR5-mediated thermogenesis.

Indirect Calorimetry to Assess Energy Balance in Mice: Measurement and Data Analysis

Understanding the factors affecting body weight regulation requires careful measurement of food intake and metabolic rates. Modern indirect calorimetry systems are designed to record these features. Here, we describe our approach for reproducible analysis of energy balance experiments performed using indirect calorimetry. CalR, a free online web tool, calculates both instantaneous and cumulative totals for metabolic variables including food intake, energy expenditure, and energy balance making it an excellent start for analyzing energy balance experiments. Energy balance may be one of the most important metrics that CalR calculates as it provides a clear picture of metabolic trends resulting from experimental interventions. Because of the complexity of indirect calorimetry devices and the frequency of mechanical breakdowns, we place a heavy emphasis on the importance of data refinement and visualization. Plots representing energy intake or energy expenditure versus body mass or physical activity can help to identify a malfunctioning apparatus. We also introduce a critical visualization of experimental quality control: a plot of the change in energy balance versus the change in body mass, which simultaneously represents many of the essential components of indirect calorimetry. These analyses and data visualizations allow the investigator to make inferences about experimental quality control and the validity of experimental results.

Proper regulation of β-adrenergic signal requires Btg2 gene for lipolysis and thermogenesis in response to starvation or cold acclimation in female mice

Mammals maintain constant body temperature in cold environment by activating thermogenesis via adrenergic/protein kinase A (PKA) signaling. B-cell translocation gene 2 (BTG2^/Tis21), induced by PKA signaling, regulates glucose and lipid metabolism in liver, yet its role in lipolysis and in thermogenesis is not explored. Here, Btg2-knockout (KO) mice failed to maintain body temperature under starvation, or in cold acclimation. And norepinephrine-induced thermogenic response was turned off earlier in the KO mice. Gender specifically, gonadal white adipose tissues (gWAT) of female-KO were very active in lipolysis in fed state, however, the fat degradation was diminished upon fasting or cold acclimation. Also, insulin sensitivity was increased in female-KO, but not in male-KO mice, along with the low bone mineral density and small brown adipose tissues (BAT). In the mechanistic aspect, expressions of UCP1 and lipases (LPL, ATGL, HSL) in gWAT of female-KO mice were significantly reduced in response to adrenergic signals. Here, we present some data that Btg2 gene is essential for properly respond to β-adrenergic signals, and plays as a negative regulator of insulin signaling in female mice.

DEPTOR loss impairs brown adipocyte development in vitro but has limited impacts in mice

OBJECTIVES

The mechanistic target of rapamycin (mTOR) is a serine/threonine kinase that regulates growth and metabolism. In mice, activation of mTOR controls cold adaptation by promoting the recruitment and the activation of brown adipose tissue (BAT). DEP-domain containing mTOR-interacting protein (DEPTOR) interacts with mTOR to modulate its activity. Whether DEPTOR levels are modulated by cold in BAT and whether this protein regulates brown adipocyte development and thermogenic activation has never been tested.

METHODS

DEPTOR levels were measured in mouse tissues upon cold exposure and in brown preadipocytes following the induction of adipogenesis. Lentiviruses expressing short-hairpin RNA were used to repress DEPTOR expression in brown preadipocytes in vitro. Conditional deletion of DEPTOR in brown preadipocytes and in mature brown fat cells was achieved by crossing DEPTOR floxed mice with either Myf5-Cre or Ucp1-Cre^ERT2 mice. These animals were exposed to cold and extensively phenotyped.

RESULTS

DEPTOR is highly expressed in BAT and its levels are induced by chronic cold exposure, a condition that triggers BAT expansion and activation. Supporting a role for DEPTOR in brown fat cell recruitment, we found that DEPTOR is induced during brown adipocyte development and that its depletion impairs adipogenesis in vitro. This adipogenic lesion was associated with defects in both Akt activation and the expression of key adipogenic regulators. Conditional deletion of DEPTOR in brown preadipocytes or mature brown fat cells did not impact BAT recruitment and thermogenesis in mice but slightly reduced the expression of adipogenic and lipogenic genes.

CONCLUSIONS

DEPTOR is highly expressed in BAT and its levels are dynamically regulated during brown fat cell development and upon cold exposure. Although DEPTOR depletion severely represses brown fat adipogenesis in vitro, its deletion is dispensable for BAT development, recruitment, and thermogenic activation in mice.

A prospective study on local cold injuries in northern Sweden

The study aimed to determine the prevalence and incidence proportion of local cold injuries in northern Sweden, and identify associated factors. It was based on prospective data from surveys in 2015 and 2021 sent to a population-based sample in northern Sweden. Multiple binary logistic regression was performed. The study included 5,017 subjects (response rate 44.4%). The prevalence of cold injuries in the hands was 11.4%, feet 12.6%, and face 19.9%, while the incidence proportion was 1.0%, 1.0%, and 0.9%, respectively. Male gender was associated with incident cold injuries in the hands (OR 1.69; 95% CI 1.31-1.28), feet (OR 1.34; 95% CI 1.04-1.73), and face (OR 1.53; 95% CI 1.15-2.03); mental stress with cold injuries in the hands (OR 1.55; 95% CI 1.16-2.05) and feet (OR 1.39; 95% CI 1.04-1.88); previous stroke with cold injuries in the hands (OR 2.64; 95% CI 1.09-6.40) and face (OR 3.09; 95% CI 1.26-7.56); and Raynaud's phenomenon with cold injuries in the hands (OR 2.48; 95% CI 1.80-3.41) and feet (OR 2.07; 95% CI 1.50-2.87). We conclude that male gender, mental stress, previous stroke, and Raynaud's phenomenon increased the probability of contracting local cold injuries.

The positive effects of combined breathing techniques and cold exposure on perceived stress: a randomised trial

A pranayama-inspired breathing technique, cold exposure, and their combined application were assessed for their potential to reduce perceived stress in adults and compared to a control group. An experiment involving four groups was conducted, yielding separate cells for breathing technique-only and cold exposure-only, as well as a combined treatment and a control group. Eighty-six individuals participated in the study. Perceived stress is measured employing the 10-item version of the Perceived Stress Scale (PSS-10) and the 20-item version of the Perceived Stress Questionnaire (PSQ). The instruments exhibit a substantial correlation (r = 0.842, p < 0.001). The combined group exhibited a medium to large positive effect on perceived stress compared to the control group. The breathing technique and cold exposure on their own were not found to yield substantial effects, indicating synergies between both exercises. Combinations of breathing techniques and cold exposure may be employed to decrease individuals' perceived stress.

Cold exposure induces lipid dynamics and thermogenesis in brown adipose tissue of goats

Background

Adaptive thermogenesis by brown adipose tissue (BAT) is important to the maintenance of temperature in newborn mammals. Cold exposure activates gene expression and lipid metabolism to provide energy for BAT thermogenesis. However, knowledge of BAT metabolism in large animals after cold exposure is still limited.

Results

In this study, we found that cold exposure induced expression of BAT thermogenesis genes and increased the protein levels of UCP1 and PGC1α. Pathway analysis showed that cold exposure activated BAT metabolism, which involved in cGMP-PKG, TCA cycle, fatty acid elongation, and degradation pathways. These were accompanied by decreased triglyceride (TG) content and increased phosphatidylcholine (PC) and phosphatidylethanolamine (PE) content in BAT.

Conclusion

These results demonstrate that cold exposure induces metabolites involved in glycerolipids and glycerophospholipids metabolism in BAT. The present study provides evidence for lipid composition associated with adaptive thermogenesis in goat BAT and metabolism pathways regulated by cold exposure.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08765-5.

Experimental Models for Cold Exposure of Muscle in vitroand in vivo

Work in cold environments may have a significant impact on occupational health. In these and similar situations, cold exposure localized to the extremities may reduce the temperature of underlying tissues. To investigate the molecular effects of cold exposure in muscle, and since adequate methods were missing, we established two experimental cold exposure models: 1) In vitroexposure to cold (18°C) or control temperature (37°C) of cultured human skeletal muscle cells (myotubes); and 2) unilateral cold exposure of hind limb skeletal muscle in anesthetized rats (intramuscular temperature 18°C), with contralateral control (37°C). This methodology enables studies of muscle responses to local cold exposures at the level of gene expression, but also other molecular outcomes. Graphical abstract.

Occupational cold exposure in relation to incident airway symptoms in northern Sweden: a prospective population-based study

Objective

To determine if occupational exposure to cold environments is associated with incident airway symptoms in previously healthy workers.

Methods

A prospective, survey-based, closed-cohort study was conducted on a sample of 5017 men and women between 18 and 70 years of age, living in northern Sweden. Data on occupation, occupational and leisure-time cold exposure, airway symptoms, general health, and tobacco habits were collected during the winters of 2015 (baseline) and 2021 (follow-up). Stepwise multiple logistic regression was used to determine associations between baseline variables and incident airway symptoms.

Results

For individuals working at baseline, without physician-diagnosed asthma or chronic obstructive pulmonary disease, reporting any occupational cold exposure was associated with incident wheeze (OR 1.41; 95% CI 1.06–1.87) and incident productive cough (OR 1.37; 95% CI 1.06–1.77), but not incident long-standing cough (OR 0.98; 95% CI 0.74–1.29), after adjusting for age, body mass index, daily smoking, and occupational physical workload. Detailed analysis of the occupational cold exposure rating did not reveal clear exposure–response patterns for any of the outcomes.

Conclusions

Occupational cold exposure was robustly associated with incident wheeze and productive cough in previously healthy workers. This adds further support to the notion that cold air is harmful for the airways, and that a structured risk assessment regarding occupational cold exposure could be considered for inclusion in the Swedish workplace legislation. Further studies are needed to elaborate on exposure–response functions, as well as suggest thresholds for hazardous cold exposure.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00420-022-01884-2.

Thermogenic responses to different clamped skin temperatures in cold-exposed men and women

Despite many decades of research examining thermoregulatory responses under varying cold stresses in humans, very little is known about the variability in metabolic heat production and shivering activity. Here, we used a novel closed-loop mean skin temperature clamping technique with a liquid-conditioned suit to isolate the effects of mean skin temperature on the subjective evaluation of thermal sensation, heat production, shivering responses, and oxidative fuel selection in young, lean and healthy men (n = 12) and women (n = 12). Our results showed a skin temperature-dependent increase in metabolic heat production (5.2±1.0 kJ/min, 5.9±1.0 kJ/min and 7.0±1.0 kJ/min with skin temperature maintained at 31°C, 29°C and 27°C, respectively; P< 0.0001) and shivering intensity in both men and women (0.6±0.1 %MVC, 1.1±0.4 %MVC and 2.5±0.7 %MVC, respectively; P<0.0001), including sex-dependent differences in heat production at all three temperatures (P < 0.005). Even when controlling for lean body mass and fat mass, sex differences persisted (P = 0.048 and P = 0.004, respectively), whereas controlling for differences in body surface area eliminated these differences. Interestingly, there were no sex differences in the cold-induced change in thermogenesis. Despite clamping skin temperature, there was tremendous variability in the rate of heat production and shivering intensity. Collectively this data suggests that many of the inter-individual differences in thermogenesis and shivering may be explained by differences in morphology and body composition.

Adaptive metabolic responses in a thermostabilized environment: Transgenerational trade-off implications from tropical tilapia

Relatively warm environments caused by global warming enhance the productivity of aquaculture activities in tropical/subtropical regions; however, the intermittent cold stress (ICS) caused by negative Arctic Oscillation can still result in major economic losses. In contrast to endotherms, ectothermic fishes experience ambient temperature as an abiotic factor that is central to performance and survival. Therefore, the occurrence of extreme temperatures caused by climate change has ignited a surge of scientific interest from ecologists, economists and physiologists. In this study, we test the transgenerational effects of rearing cold-experienced (CE) and cold-naïve (CN) strains of tropical tilapia. Our results show that compared to CN tilapia, the CE strain preferentially converts carbohydrates into lipids in liver at a regular temperature of 27 °C. Besides, at a low temperature of 22 °C, the CE strain exhibits a broader aerobic scope than CN fish, and their metabolite profile suggests a metabolic shift towards the utilization of glutamate derivatives. Therefore, in response to thermal perturbations, this transgenerational metabolic adjustment provides evidence into the adaptive trade-off mechanisms in tropical fish. Nevertheless, global warming may result in less thermal variation each year, and the stabilized ambient temperature may cause tropical tilapia to gradually exhibit lower energy deposits in liver. In addition to those habitants in cold and temperate regions, a lack of cold exposure to multiple generations of fish may decrease the native cold-tolerance traits of subtropical/tropical organisms; this notion has not been previously explored in terms of the biological effects under anthropogenic climate change.

Analysis of Thermogenesis Experiments with CalR

Modern indirect calorimetry systems allow for high-frequency time series measurements of the factors affected by thermogenesis: energy intake and energy expenditure. These indirect calorimetry systems generate a flood of raw data recording oxygen consumption, carbon dioxide production, physical activity, and food intake among other factors. Analysis of these data requires time-consuming manual manipulation for formatting, data cleaning, quality control, and visualization. Beyond data handling, analyses of indirect calorimetry experiments require specialized statistical treatment to account for differential contributions of fat mass and lean mass to metabolic rates.Here we describe how to use the software package CalR version 1.2, to analyze indirect calorimetry data from three examples of thermogenesis, cold exposure, adrenergic agonism, and hyperthyroidism in mice, by providing standardized methods for reproducible research. CalR is a free online tool with an easy-to-use graphical user interface to import data files from the Columbus Instruments' CLAMS, Sable Systems' Promethion, and TSE Systems' PhenoMaster. Once loaded, CalR can quickly visualize experimental results and perform basic statistical analyses. We present a framework that standardizes the data structures and analyses of indirect calorimetry experiments to provide reusable and reproducible methods for the physiological data affecting body weight.

Effect of BMI on the Thermogenic Response to Cold Exposure and Associated Changes in Metabolism and Browning Markers in Adult Humans

INTRODUCTION

Brown adipose tissue (BAT) serves to produce heat by nonshivering thermogenesis. Activation of BAT increases energy expenditure and is seen as a putative strategy to treat obesity. There are conflicting data on the capacity for cold-induced thermogenesis in individuals with higher BMI.

METHODS

To investigate the effect of BMI on cold-induced stimulation of energy expenditure, changes in the metabolic profile, and the expression of browning markers in subcutaneous white adipose tissue (scWAT), healthy adults (N = 173, 50.9% females) with a median age of 26.0 (interquartile range [IQR]: 23.0; 28.0) years and a median body mass index (BMI) of 23.6 [IQR: 21.9; 26.6] kg/m2 were exposed to short-term mild cold exposure (CE). Resting energy expenditure (REE) was measured by indirect calorimetry and blood sampling was conducted at baseline and after CE. In a subgroup of participants with obesity, subcutaneous abdominal fat biopsies were taken before and after CE.

RESULTS

The cold-induced median increase in REE was 74 (IQR: -28; 241) kcal/day (p < 0.001). This increase negatively correlated with BMI (p < 0.001). Participants with BMI 18.5-24.9 kg/m2 displayed a significant median increase of 103 kcal/day (p < 0.001), participants with overweight or obesity were not able to increase REE (23, p = 0.468 or -30 kcal/day, p = 0.917, respectively). In participants with obesity, expression of cell death activator in scWAT after CE was upregulated in females (p = 0.034).

CONCLUSIONS

Persons with overweight and obesity do not increase REE in response to CE, presumably reflecting lower BAT activity. Likewise, the metabolic response to cold is diminished in participants with elevated BMI.

Cold exposure aggravates pulmonary arterial hypertension through increased miR-146a-5p, miR-155-5p and cytokines TNF-α, IL-1β, and IL-6

BACKGROUND

Cold temperatures can aggravate pulmonary diseases and promote pulmonary arterial hypertension (PAH); however, the underlying mechanism has not been fully explored.

AIM

To explore the effect of chronic cold exposure on the production of inflammatory cytokines and microRNAs (miRNAs) in a monocrotaline (MCT)-induced PAH model.

METHODS

Male Sprague Dawley rats were divided into a Control (23.5 ± 2 °C), Cold (5.0 ± 1 °C for ten days), MCT (60 mg/kg body weight i.p.), and MCT + Cold (ten days of cold exposure after 3 weeks of MCT injection). Hemodynamic parameters, right ventricle (RV) hypertrophy, and pulmonary arterial medial wall thickness were determined. IL-1β, IL-6, and TNF-α levels were determined using western blotting. miR-21-5p and -3p, miR-146a-5p and -3p, and miR-155-5p and -3p and plasma extracellular vesicles (EVs) and mRNA expression of Cd68, Cd163, Bmpr2, Smad5, Tgfbr2, and Smad3 were determined using RT-qPCR.

RESULTS

The MCT + Cold group had aggravated RV hypertrophy hemodynamic parameters, and pulmonary arterial medial wall thickness. In lungs of the MCT + Cold, group the protein levels of TNF-α, IL-1β, and IL-6 were higher than those in the MCT group. The mRNA expression of Cd68 and Cd163 were higher in the MCT + Cold group. miR-146a-5p and miR-155-5p levels were higher in the plasma EVs and lungs of the MCT + Cold group. Cold exposure promoted a greater decrease in miR-21-5p, Bmpr2, Smad5, Tgfbr2, and Smad3 mRNA expression in lungs of the MCT + Cold group.

CONCLUSION

Cold exposure aggravates MCT-induced PAH with an increase in inflammatory marker and miRNA levels in the plasma EVs and lungs.

Overheating or overcooling: heat transfer in the spot to fight against the pandemic obesity

The prevalence of obesity has nearly doubled worldwide over the past three and a half decades, reaching pandemic status. Obesity is associated with decreased life expectancy and with an increased risk of metabolic, cardiovascular, nervous system diseases. Hence, understanding the mechanisms involved in the onset and development of obesity is mandatory to promote planned health actions to revert this scenario. In this review, common aspects of cold exposure, a process of heat generation, and exercise, a process of heat dissipation, will be discussed as two opposite mechanisms of obesity, which can be oversimplified as caloric conservation. A common road between heat generation and dissipation is the mobilization of Free Faty Acids (FFA) and Carbohydrates (CHO). An increase in energy expenditure (immediate effect) and molecular/metabolic adaptations (chronic effect) are responses that depend on SNS activity in both conditions of heat transfer. This cycle of using and removing FFA and CHO from blood either for heat or force generation disrupt the key concept of obesity: energy accumulation. Despite efforts in making the anti-obesity pill, maybe it is time to consider that the world's population is living at thermoneutrality since temperature-controlled places and the lack of exercise are favoring caloric accumulation.

Short and long-term effects of high-intensity interval training applied alone or with whole-body cryostimulation on glucose homeostasis and myokine levels in overweight to obese subjects

Background: COVID-19 pandemic has exacerbated the problem of physical inactivity and weight gain. Consequently, new strategies to counteract weight gain are being sought. Because of their accessibility, interval training and cold therapy are the most popular such strategies. We here aimed to examine the effect of 6 units of high-intensity interval training (HIIT), applied alone or in combination with 10 sessions of whole-body cryotherapy (WBC; 3 min at -110 ∘C per session) on incretins, myokines, and adipokines levels. Materials and methods: The study involved 65 subjects (body mass index of approximately 30 kg•m^-2). The subjects were randomly divided into training group (TR; n = 27) and training supported by WBC group (TR-WBC; n = 38). Blood samples were collected before, immediately following, and 4 weeks after the intervention. Results: Fibroblast growth factor 21 (FGF21) levels significantly increased (p = 0.03) and adiponectin levels increased in the TR group (p = 0.05) compared with those recorded in TR-WBC group 24 h after the end of experimental protocol. Beneficial changes in the lipid profile (p = 0.07), a significant drop in visfatin levels (p < 0.05), and the improvement in β-cell function (HOMA-B; p = 0.02) were also observed in the TR group in the same time point of study. While TR-WBC did not induce similar changes, it ameliorated blood glucose levels (p = 0.03). Changes induced by both interventions were only sustained for 4 weeks after treatment. Conclusion: Collectively, HIIT, alone and in combination with WBC, positively affects metabolic indicators, albeit, most likely, different mechanisms drive the beneficial effects of different treatments.

Effect of cold exposure and capsaicin on the expression of histone acetylation and Toll-like receptors in 1,2-dimethylhydrazine-induced colon carcinogenesis

Previous studies have indicated that capsaicin-rich diet and cold weather have shown strong association with tumor incidence. Thus, we investigated the effects of capsaicin and cold exposure in 1,2-dimethylhydrazine (DMH)-induced colorectal cancer as well as the mechanisms underlying capsaicin and cold-induced CRC. Rats were randomly divided into four groups and received cold still water and capsaicin via intragastric gavage until the end of the experiment. The rat's body weight, thymus weight, and food intakes were assessed. Global levels of histone H3K9, H3K18, H3K27, and H4K16 acetylation and histone deacetylase (HDACs) in colon mucosa were assessed by western blot. Expression levels of Toll-like receptors 2 (TLR2) and Toll-like receptors 4 (TLR4) were measured by western blot and reverse-transcriptase quantitative polymerase chain reaction (qPCR). We found that cold and low-dose capsaicin increased tumor numbers and multiplicity, although there were no differences in tumor incidence. Additionally, rat exposure to cold water and capsaicin display further higher levels of histone H3 lysine 9 (H3K9AC), histone H3 lysine 18 (H3K18AC), histone H3 lysine 27 (H3K27AC), and HDACs compared with the DMH and normal rats. In contrast, a considerable decrease of histone H4 lysine 16 (H4K16AC) was detected in the colon mucosa. Cold and low-dose capsaicin exposure groups were also increased TLR2 and TLR4 protein levels and mRNA levels. These results suggest that chronic cold exposure and capsaicin at a low-dose intervention exacerbate ectopic expression of global histone acetylation and TLR level, which are crucial mechanisms responsible for the progression of colorectal cancer in rats.

Occupational cold exposure is associated with increased reporting of airway symptoms

OBJECTIVE

To determine if exposure to cold environments, during work or leisure time, was associated with increased reporting of airway symptoms in the general population of northern Sweden.

METHODS

Through a population-based postal survey responded to by 12627 subjects, ages 18-70, living in northern Sweden, the occurrence of airway symptoms was investigated. Cold exposure during work or leisure time was self-reported on numerical rating scales. Binary logistic regression was used to determine the statistical association between cold exposure and airway symptoms.

RESULTS

For currently working subjects (N = 8740), reporting any occupational cold exposure was associated to wheeze (OR 1.3; 95% CI 1.1-1.4); chronic cough (OR 1.2; 95% CI 1.1-1.4); and productive cough (OR 1.3; 95% CI 1.1-1.4), after adjusting for gender, age, body mass index, daily smoking, asthma, and chronic obstructive pulmonary disease. Leisure-time cold exposure was not significantly associated to reporting airway symptoms.

CONCLUSIONS

Occupational cold exposure was an independent predictor of airway symptoms in northern Sweden. Therefore, a structured risk assessment regarding cold exposure could be considered for inclusion in the Swedish workplace legislation.

Study on the experimental verification and regulatory mechanism of Rougui-Ganjiang herb-pair for the actions of thermogenesis in brown adipose tissue based on network pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Cinnamomum cassia Presl (Rougui) has character of xin、gan、wen, belongs to Jing of heart、lung、bladder, and has the effect of dispersing cold and relieving pain. It is widely used to resolve the exterior and dissipate cold in Treatise on Febrile Diseases (Shang Han Lun), such as Chaihu Guizhi Ganjiang Tang and Guizhi Renshen Tang. Both these two prescriptions contain Cinnamomum cassia Presl and Zingiber officinale Rosc (Ganjiang). Rougui-Ganjiang herb-pair (RGHP) can warm viscera and remove cold, which is widely used in Shang Han Lun. And in modern times, recent studies have showed that cinnamon and ginger also have the effect of thermogenesis and regulating the body temperature, respectively.

AIM OF THE STUDY

To maintain the body thermal homeostasis and prevent cold invasion of main organs, in this study, we assessed the underlying physiological changes induced by RGHP in mice exposed to -20 °C and explored the mechanisms for the thermogenic actions of RGHP in brown adipose tissue (BAT) by network pharmacology and molecular docking.

MATERIALS AND METHODS

Male Kunming (KM) mice were fed normal diet with orally administration of distilled water or ethanol RGHP extract (three doses: 375,750 and 1500 mg/kg) for 21 days, once per day and then exposed to -20 °C for 2 h. The core temperature, activity ability and the degree of frostbite in mice, morphological and ATP content of adipocytes were measured. In addition, the network pharmacology was employed to predict the targets of RGHP' s thermogenesis effect on BAT. Pathway analysis and biological process with key genes was carried out through KEGG and GO analysis, respectively. Furthermore, the core ingredients and targets obtained by network pharmacology were verified by molecular docking and Western blot assays.

RESULTS

RGHP can significantly increase the core body temperature, reduce the degree of frostbite and enhance the activity ability of mice after cold exposure. Meanwhile, it can also improve the lipid morphology and decrease ATP production in BAT. A network pharmacology-based analysis identified 246 ingredients from RGHP (two herbs), which related to 222 target genes. There were 8 common genes between 222 compounds target genes and 62 thermogenesis associated target genes, which linked to 49 potential compounds. There are 24 ingredients which degree are greater than the average. Among them, we found that oleic acid, EIC, 6-gingerol, eugenol, isohomogenol and sitogluside could be detected in mice plasma. The cAMP-PPAR signaling pathway was enriched for thermogenesis after KEGG analysis with 8 genes. Molecular docking analysis and Western blot assay further confirmed that oleic acid, 6-gingerol, eugenol and isohomogenol were potential active ingredients for RGHP's heat production effect. And UCP1, PGC-1α, PPARα and PPARγ are key thermogenesis proteins.

CONCLUSIONS

RGHP treatment can significantly maintain the rectal temperature of mice by enhancing the BAT heat production. RGHP exhibited the heat production effect, which might be mainly attributed to increasing thermogenesis through the cAMP-PPAR signaling pathway in cold exposure mice. Oleic acid, 6-gingerol, eugenol and isohomogenol might be considered the potential therapeutic ingredients which affect the key targets of thermogenesis effect.

Cold exposure and capsaicin promote 1,2-dimethylhyrazine-induced colon carcinogenesis in rats correlates with extracellular matrix remodeling

BACKGROUND

Extracellular matrix (ECM) remodeling and stiffening, which are correlated with tumor malignancy, drives tumor development. However, the relationship between ECM remodeling and rat experimental model of 1,2-dimethylhyrazine (DMH)-induced colorectal cancer (CRC) imposed by cold and capsaicin exposure remains unclear.

AIM

To explore the effects of cold exposure and capsaicin on ECM remodeling and ECM enzymes in DMH-induced CRC.

METHODS

For histopathological analysis, the sections of colon tissues were stained with hematoxylin and eosin, Masson’s trichrome, Picrosirius red, and Weigert’s Resorcin-Fuchsin to observe the remodeling of collagen and elastin. Additionally, the protein expression level of type I collagen (COL I), type 3 collagen (COL III0, elastin, matrix metalloproteinase (MMP) 1, MMP2, MMP9, and tissue-specific matrix metalloproteinase 1 (TIMP1) was assessed by immunohistochemistry. The messenger RNA (mRNA) levels of COL I, COL III, elastin, and lysyl oxidase-like-2 (LOXL2) in the colon tissues of rats was measured by reverse-transcriptase quantitative polymerase chain reaction.

RESULTS

Although no differences were observed in the proportion of adenomas, a trend towards the increase of invasive tumors was observed in the cold and capsaicin group. The cold exposure group had a metastasis rate compared with the other groups. Additionally, abnormal accumulation of both collagen and elastin was observed in the cold exposure and capsaicin group. Specifically, collagen quantitative analysis showed increased length, width, angle, and straightness compared with the DMH group. Collagen deposition and straightness were significantly increased in the cold exposure group compared with the capsaicin group. Cold exposure and capsaicin significantly increased the protein levels of COL I, elastin, and LOXL2 along with increases in their mRNA levels in the colon tissues compared with the DMH group, while COL III did not show a significant difference. Furthermore, in immunohistochemical evaluations, MMP1, MMP2, MMP9, and TIMP1 staining increased in the cold exposure and capsaicin group compared with the DMH group.

CONCLUSION

These results suggest that chronic cold and capsaicin exposure further increased the deposition of collagen and elastin in the colonic tissue. Increased COL I and elastin mRNA and protein levels expression may account for the enhanced ECM remodel and stiffness variations of colon tissue. The upregulated expression of the LOXL2 and physiological imbalance between MMP/TIMP activation and deactivation could contribute to the progression of the CRC resulting from cold and capsaicin exposure.

Safety and health risks for workers exposed to cold thermal environments: A frozen food processing industry perspective

BACKGROUND

Environmental temperatures in the fresh food industry vary from 0°C to 10°C, and go below -20°C for the frozen food industry, representing risk for the health and safety of workers involved.

OBJECTIVE

The aim of this work was to evaluate the cold thermal stress risks for workers working in a frozen food industry.

METHODS

A total of 27 acclimatized workers (13 male and 14 female) participated in a study which was conducted during 11 working days. The thermal sensation questionnaire and the cold work health questionnaire (CWHQ) were applied to all participants. Additionally, 4 workers were chosen to be fully monitored with a thermometer telemetry capsule for measuring the intra-abdominal temperature and 8 skin temperature sensors.

RESULTS

The lowest recorded hand temperature was 14.09°C, lowest forehead 18.55°C, mean skin temperature had variations of 1.10 to 3.20°C along the working period. Highest and most frequent fluctuations were found in the hand and forehead skin temperatures, small changes were found in mean skin temperature.

CONCLUSIONS

Answers to the CWHQ increase concern on clinical forms of "a frigore", and in two cases the mean body temperature decreased below 35.0°C, which is defined in the current literature as a mild form of hypothermia.

The effect of cold exposure on serum cholesterol is dependent upon ApoE

BACKGROUND

Several lines of evidence indicate that cold stimulation may not only activate brown adipose tissue (BAT) and the white adipose tissue (WAT), but also regulate the lipid metabolism and influence the development of atherosclerosis. However, the study of cold exposure affecting cholesterol metabolism have opposite results in different experiments, and Apolipoprotein E (ApoE) may play an important role. There is still a lack of complete research to illustrate this problem.

METHODS

In this study, we first analyzed and discussed the activation of interscapular brown adipose tissue (iBAT), inguinal white adipose tissue (iWAT) and epididymal white adipose tissue (eWAT) under cold exposure (4 °C) in male wild-type C57BL/6 J (WT) and ApoE-deficient mice (ApoE-/-) fed high-fat diet (HFD) for 4 weeks. Subsequently, we investigated the effect of cold exposure on blood lipid profiles in both models. We further explored whether cold exposure can reduce serum cholesterol.

RESULTS

In both WT and ApoE-/- mice, cold exposure activates iBAT and iWAT, as well as hardly affects eWAT. In WT mice,4 weeks cold exposure (4 °C) reduces serum triglyceride by 28%, cholesterol by 30% and LDL-cholesterol by 63%. In ApoE-/- mice, cold stimulation decreases serum triglyceride by 59%, but increases cholesterol by 20% and LDL-cholesterol by 25%.

CONCLUSIONS

Based on these findings, we conclude that cold exposure decreases serum cholesterol is dependent upon the existence of ApoE.

Novel methods for cold exposure of skeletal muscle in vivo and in vitro show temperature-dependent myokine production

Proteins secreted from skeletal muscle serving a signalling role have been termed myokines. Many of the myokines are exercise factors, produced and released in response to muscle activity. Cold exposures affecting muscle may occur in recreational, occupational and therapeutic settings. Whether muscle temperature independently affects myokine profile, is still to be elucidated. We hypothesized that manipulating muscle temperature by means of external cooling would change myokine production and release. In the present study we have established new models for cold exposure of muscle in vivo and in vitro where rat hind limb or cultured human myotubes were cooled to 18 °C. After a recovery period, muscle tissue, cells and culture media were harvested for further analysis by qPCR and immunoassays. Expression of several myokine genes were significantly increased after cold exposure in both models: in rat muscle, mRNA levels of CCL2 (p = 0.04), VEGFA (p = 0.02), CXCL1 (p = 0.02) and RBM3 (p = 0.02) increased while mRNA levels of IL-6 (p = 0.03) were decreased; in human myotubes, mRNA levels of IL6 (p = 0.01), CXCL8 (p = 0.04), VEGFA (p = 0.03) and CXCL1 (p < 0.01) were significantly increased, as well as intracellular protein levels of IL-8 (CXCL8 gene product; p < 0.01). The corresponding effect on myokine secretion was not observed, on the contrary, IL-8 (p = 0.02) and VEGF (VEGFA gene product) p < 0.01) concentrations in culture media were reduced after cold exposure in vitro. In conclusion, cold exposure of muscle in vivo and in vitro had an effect on the production and release of several known exercise-related myokines. Myokine expression at the level of mRNA and protein was increased by cold exposure, whereas secretion tended to be decreased.

Human physiological responses of exposure to extremely cold environments

Extremely cold events have occurred more frequently in the past few years. People exposed to extremely cold exposure could suffer the threats of human health and safety like cold stress and injury. This study aims to investigate human physiological responses of exposure to extremely cold environments and the moment of temperature step. The experiments of 12 subjects exposed to three different cold exposure conditions (-5 °C, -10 °C, -15 °C) were carried out in a climate chamber. Most critical physiological parameters, including the core temperature, local skin temperature, blood pressure, heart rate, respiration rate and blood oxygen saturation, were measured to evaluate human physiological responses. In the particular short term study, the results show that the local skin temperature and blood pressure are the most significant indexes for evaluating the risk of cold strain in extremely cold environment. The finger temperature is a critical index of hand and finger flexibility, and it will lead to serious injuries and reduced manual performance when exposed to below -5 °C for more than 20 min. The high physiological strain at the very beginning moment of cold exposure can significantly affect the ability to make correct judgment and action, and it is suggested that the personnel adapt for 3 min after entering into the extremely cold environment to stabilize physiological parameters and thus enhancing the safety and occupational performance. The experimental data of this study is also of great significance for the development and validation of thermophysiological models.

Quantitative model analysis of the resting membrane potential in insect skeletal muscle: Implications for low temperature tolerance

Abiotic stressors, such as cold exposure, can depolarize insect cells substantially causing cold coma and cell death. During cold exposure, insect skeletal muscle depolarization occurs through a 2-stage process. Firstly, short-term cold exposure reduces the activity of electrogenic ion pumps, which depolarize insect muscle markedly. Secondly, during long-term cold exposure, extracellular ion homeostasis is disrupted causing further depolarization. Consequently, many cold hardy insects improve membrane potential stability during cold exposure through adaptations that secure maintenance of ion homeostasis during cold exposure. Less is known about the adaptations permitting cold hardy insects to maintain membrane potential stability during the initial phase of cold exposure, before ion balance is disrupted. To address this problem it is critical to understand the membrane components (channels and transporters) that determine the membrane potential and to examine this question the present study constructed a mathematical "charge difference" model of the insect muscle membrane potential. This model was parameterized with known literature values for ion permeabilities, ion concentrations and membrane capacitance and the model was then further developed by comparing model predictions against empirical measurements following pharmacological inhibitors of the Na⁺/K⁺ ATPase, Cl^- channels and symporters. Subsequently, we compared simulated and recorded membrane potentials at 0 and 31 °C and at 10-50 mM extracellular [K⁺] to examine if the model could describe membrane potentials during the perturbations occurring during cold exposure. Our results confirm the importance of both Na⁺/K⁺ ATPase activity and ion-selective Na⁺, K⁺ and Cl^- channels, but the model also highlights that additional electroneutral flux of Na⁺ and K⁺ is needed to describe how membrane potentials respond to temperature and [K⁺] in insect muscle. While considerable further work is still needed, we argue that this "charge difference" model can be used to generate testable hypotheses of how insects can preserve membrane polarization in the face of stressful cold exposure.

Distribution of Brown Adipose Tissue Radiodensity in Young Adults: Implications for Cold [18F]FDG-PET/CT Analyses

PURPOSE

Nowadays, 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) positron emission tomography (PET)/X-ray computed tomography (CT) is considered the best available technique to in vivo determination of human BAT volume. The most used Hounsfield unit (HU) threshold for BAT quantification is from - 250 to - 50 HU. Therefore, the main objective of the present study is (i) to examine the influence of SUV and HU thresholds on BAT quantification by [¹⁸F]FDG-PET/CT scan, (ii) to identify the proportion of BAT which is not detected by [¹⁸F]FDG-PET/CT scan when limiting the range between - 10 and - 50 HU, and (iii) to describe the distribution of BAT radiodensity by weight status and sex in young healthy individuals.

PROCEDURES

We measured 125 individuals after a personalized cooling protocol with a static [¹⁸F]FDG-PET/CT scan. We quantified BAT using different combination of threshold in every single HU for all participants.

RESULTS

We observed that the SUV threshold influences BAT quantification by [¹⁸F]FDG-PET/CT scans more than the HU range. We found that the range from - 50 to - 10 HU had the highest proportion of total BAT volume (43.2 %), which represents 41.4 % of the total BAT metabolic activity in our cohort. We also observed that BAT volume was not different between categories of body mass index, as well as BAT activity (SUV_mean). In addition, BAT was less dense in women than in men, although the BAT activity (SUV_mean) was higher in all ranges of HU. We also observed that the radiodensity of BAT located in the cervical area was mainly in the range from - 50 to - 10 HU.

CONCLUSION

Therefore, all future human studies using static [¹⁸F]FDG-PET/CT scans should include BAT in the radiodensity range from - 50 to - 10 HU.

Impact of an intermittent and localized cooling intervention on skin temperature, sleep quality and energy expenditure in free-living, young, healthy adults

Where people live and work together it is not always possible to modify the ambient temperature; ways must therefore be found that allow individuals to feel thermally comfortable in such settings. The Embr Wave® is a wrist-worn device marketed as a 'personal thermostat' that can apply a local cooling stimulus to the skin. The aim of the present study was to determine the effect of an intermittent mild cold stimulus of 25 °C for 15-20 s every 5 min over 3.5 days under free-living conditions on 1) skin temperature, 2) perception of skin temperature, 3) sleep quality and 4) resting energy expenditure (REE) in young, healthy adults. Ten subjects wore the device for 3.5 consecutive days. This intervention reduced distal skin temperature after correcting for personal ambient temperature (P < 0.05), but did not affect the subjects' the perception of skin temperature, sleep quality or REE (all P ≥ 0.051). Thus, this intermittent mild cold regime can reduce distal skin temperature, and wearing it under free-living conditions for 3.5 days does not seem to impair the perception of skin temperature and sleep quality or modify REE.

Cinnamomum cassia extract promotes thermogenesis during exposure to cold via activation of brown adipose tissue

ETHNOPHARMACOLOGICAL RELEVANCE

Cinnamomum cassia (L.) J.Presl (Lauraceae), a widely used traditional Chinese medicine, is well known to exert hot property. It is recorded as dispelling cold drug in ancient Chinese monographs, such as Synopsis of golden chamber published in Han dynasty. According to Chinese Pharmacopoeia (2015), Cinnamomum cassia (L.) J.Presl (Cinnamon) has the functions of dispersing cold, relieving pain, warming meridians and promoting blood circulation.

AIM OF THE STUDY

The aim of this study is to evaluate the effect of Cinnamon extract (CE) on cold endurance and the mechanism of thermogenesis activity.

MATERIALS AND METHODS

The improving effect of hypothermia were evaluated with body temperature by infrared camera and multi-thermo thermometer. In vivo, the thermogenic effect was observed with energy metabolism and substrate utilization. The activation of brown adipose tissue (BAT) was evaluated with the histomorphology and expression of thermogenic protein. In vitro, the uncoupling effect on mitochondrial was evaluated with Seahorse and fluorescent staining. The mechanism of thermogenesis was explored in brown adipocyte.

RESULTS

The body temperature and energy expenditure were significantly increased by CE administration in cold environment. In morphology, lipid droplets were reduced and the number of mitochondrial was increased. CE significantly increased the non-shivering thermogenesis via upregulating the expression of thermogenic protein. In vitro, the uncoupling effect was obviously along with the decreased mitochondrial membrane potential and ATP production. It was confirmed that the thermogenesis effect was induced via lipolysis and energy metabolism. In addition, CE also alleviated myocardium injury in the morphology in cold environment. Moreover, the major constituent was identified as (1) coumarin, (2) cinnamic acid, (3) cinnamaldehyde and (4) 2-methoxy cinnamaldehyde.

CONCLUSIONS

The mechanism of improving cold tolerance was related to lipolysis and activation of BAT. Meanwhile, we provided a kind of potential prevention methods for cold injury.

Effects of workload on human cognitive performance of exposure to extremely cold environment

Many jobs like outdoor work and emergency rescue have to be exposed to extremely cold environments. The combined effects of the cold exposure and work intensity on human cognitive performance remain unclear. In this paper, the experiments of six Chinese young men exposed to an extremely cold environment (-10 °C) were conducted in a climatic chamber. The work intensity level was graded according to the metabolic rate corresponding to three walking speeds. Nine cognitive functions and one perceived were recorded to evaluate the subjects' cognitive performance, including NCTB (seven items), Stroop, and RPE were measured. The increase of workload from moderate to high could lead to the acceleration of fatigue speed and the aggravation of fatigue degree 5 min earlier. Moderate work intensity is a noteworthy work level in extremely cold environment, which is an inflection point in the impact of fatigue and cognitive levels. The manual dexterity significantly increases by the workload intensity, and the high work intensity makes the hands more dexterous (29% increase). Extremely cold environment has a significant effect on short-term memory (decreased 33%). The selective attention was reduced by 16% in the extremely cold environment. With the moderate work intensity in extremely cold environment, the perceived judgment response speed would decrease. The combined effects of the extremely cold environment and the workload on the cognitive functions of psychomotor ability and attention or sensorimotor speed should be paid more attention to.

UCP1-dependent and UCP1-independent metabolic changes induced by acute cold exposure in brown adipose tissue of mice

BACKGROUND

Brown adipose tissue (BAT) is a site of metabolic thermogenesis mediated by mitochondrial uncoupling protein 1 (UCP1) and represents a target for a therapeutic intervention in obesity. Cold exposure activates UCP1-mediated thermogenesis in BAT and causes drastic changes in glucose, lipid, and amino acid metabolism; however, the relationship between these metabolic changes and UCP1-mediated thermogenesis is not fully understood.

METHODS

We conducted metabolomic and GeneChip array analyses of BAT after 4-h exposure to cold temperature (10 °C) in wild-type (WT) and UCP1-KO mice.

RESULTS

Cold exposure largely increased metabolites of the glycolysis pathway and lactic acid levels in WT, but not in UCP1-KO, mice, indicating that aerobic glycolysis is enhanced as a consequence of UCP1-mediated thermogenesis. GeneChip array analysis of BAT revealed that there were 2865 genes upregulated by cold exposure in WT mice, and 838 of these were upregulated and 74 were downregulated in UCP1-KO mice. Pathway analysis revealed the enrichment of genes involved in fatty acid (FA) β oxidation and triglyceride (TG) synthesis in both WT and UCP1-KO mice, suggesting that these metabolic pathways were enhanced by cold exposure independently of UCP1-mediated thermogenesis. FA and cholesterol biosynthesis pathways were enhanced only in UCP1-KO mice. Cold exposure also significantly increased the BAT content of proline, tryptophan, and phenylalanine amino acids in both WT and UCP1-KO mice. In WT mice, cold exposure significantly increased glutamine content and enhanced the expression of genes related to glutamine metabolism. Surprisingly, aspartate was almost completely depleted after cold exposure in UCP1-KO mice. Gene expression analysis suggested that aspartate was actively utilized after cold exposure both in WT and UCP1-KO mice, but it was replenished from intracellular N-acetyl-aspartate in WT mice.

CONCLUSIONS

These results revealed that cold exposure induces UCP1-mediated thermogenesis-dependent glucose utilization and UCP1-independent active lipid metabolism in BAT. In addition, cold exposure largely affects amino acid metabolism in BAT, especially UCP1-dependently enhances glutamine utilization. These results contribute a comprehensive understanding of UCP1-mediated thermogenesis-dependent and thermogenesis-independent metabolism in BAT.

Efficacy of warming systems in mountain rescue: an experimental manikin study

Mountain accident casualties are often exposed to cold and windy weather. This may induce post-traumatic hypothermia which increases mortality. The aim of this study was to assess the ability of warming systems to compensate for the victim's estimated heat loss in a simulated mountain rescue operation. We used thermal manikins and developed a thermodynamic model of a virtual patient. Manikins were placed on a mountain rescue stretcher and exposed to wind chill indices of 0 °C and - 20 °C in a climatic chamber. We calculated the heat balance for two simulated clinical scenarios with both a shivering and non-shivering victim and measured the heat gain from gel, electrical, and chemical warming systems for 3.5 h. The heat balance in the simulated shivering patient was positive. In the non-shivering patient, we found a negative heat balance for both simulated weather conditions (- 429.53 kJ at 0 °C and - 1469.78 kJ at - 20 °C). Each warming system delivered about 300 kJ. The efficacy of the gel and electrical systems was higher within the first hour than later (p < 0.001). We conclude that none of the tested warming systems is able to compensate for heat loss in a simulated model of a non-shivering patient whose physiological heat production is impaired during a prolonged mountain evacuation. Additional thermal insulation seems to be required in these settings.

Angiopoietin-like protein 4(E40K) and ANGPTL4/8 complex have reduced, temperature-dependent LPL-inhibitory activity compared to ANGPTL4

We previously demonstrated that angiopoietin-like 8 (ANGPTL8) forms a localized complex with ANGPTL4 to reduce its lipoprotein lipase (LPL)-inhibitory activity and enable increased postprandial uptake of fatty acids (FA) into adipose tissue. Because prolonged cold exposure may increase adipose tissue FA uptake and decrease circulating triglycerides (TG) by reducing ANGPTL4 expression and inducing ANGPTL8 expression (and thus ANGPTL4/8 expression), we investigated the effect of temperature on ANGPTL4 and ANGPTL4/8 LPL-inhibitory activities in vitro. As the ANGPTL4(E40K) mutation results in decreased TG, we also characterized ANGPTL4(E40K) and ANGPTL4(E40K)/8 complex LPL-inhibitory activities. Interestingly, while ANGPTL3, ANGPTL3/8, and ANGPTL4 showed similar LPL inhibition at 37 °C and 22 °C, the already reduced LPL-inhibitory activity of ANGPTL4/8 at 37 °C was even more decreased at 22 °C. At 37 °C, ANGPTL4(E40K) manifested decreased LPL-inhibitory activity compared to ANGPTL4/8, while ANGPTL4(E40K)/8 had even further reduced potency. Remarkably, ANGPTL4/8, ANGPTL4(E40K), and ANGPTL4(E40K)/8 were each actually capable of stimulating LPL activity at 22 °C. Together, these results indicate that ANGPTL4/8 stimulation of LPL activity at low temperatures may represent an additional mechanism for further increasing adipose tissue FA uptake during cold exposure, beyond that already occurring due to decreased ANGPTL4 expression and increased ANGPTL8 expression. In addition, because ANGPTL4(E40K) has decreased LPL-inhibitory activity compared to ANGPTL4/8, our findings also suggest why ANGPTL4(E40K) carriers have decreased circulating TG levels.