Thermoregulatory responses to lipopolysaccharide in the mouse: dependence on the dose and ambient temperature

Impact of thermoneutral acclimation on a murine model of polymicrobial peritonitis

To examine the effects of ambient temperature on the reproducibility and translation of a murine sepsis model, we hypothesized that acclimation of mice in temperatures within their thermoneutral zone would alter immune responses and outcomes compared to standard housing temperatures. Mice housed for one week in thermoneutral (30°C) as compared to standard (22°C) conditions displayed lower counts of circulating neutrophils (0.52 ± 0.20 vs. 1.10 ± 0.54 x103/μL; p = 0.011) and peritoneal macrophages (0.80 ± 0.57 vs. 1.62 ± 0.62 x 105/μL; p = 0.002) as well as reduced in vitro production of IFN-γ by stimulated splenocytes (0.38 ± 0.68 vs 2.55 ± 0.76 x104 pg/mL, respectively, p = 0.004). After one week of temperature acclimation followed by CLP, the 7-day mortality was significantly lower under thermoneutral as compared to standard temperatures (80% vs 30%, respectively; p = 0.012), although core body temperature was preserved (average for 24 hours: 36.4 ± 1.3°C vs 31.7 ± 4.7°C; p < 0.0001). The lower survival was accompanied by increased systemic IL-6 levels (3.8 ± 3.3 vs 1.9 ± 1.3 x103 pg/mL; p = 0.04) and less robust influx of neutrophils into the peritoneum (1.68 ± 1.07 vs. 4.20 ± 2.46 x105/μL, respectively; p = 0.0003). Overall, thermoneutral temperatures impacted innate immune parameters before and after CLP, producing distinctly different outcomes. Therefore, ambient temperature is an important variable that could impact model reproducibility and should be reported for the acclimation period and experimentation phases of murine sepsis studies.

Fluoxetine mitigates hypothermia and inflammatory responses in lipopolysaccharide-induced systemic inflammation: Insights into serotonergic and hypothalamic thermoregulatory mechanisms

An abnormally elevated mortality rate is evident in cases of sepsis. To study specific mechanisms of sepsis experimentally, lipopolysaccharide (LPS) systemically administered has been used as a model, in which an exaggerated immune response, neurochemistry settings, and fever following hypothermia take place. Notably, systemic inflammation (SI) can modulate the central serotonergic pathways and being influenced by it. This influence extends to the hypothalamus, which holds a hierarchical significance in the control of body temperature (Tb). This study investigates the potential impact of orally administered fluoxetine (FLX), a selective serotonin reuptake inhibitor (SSRI) given orally for 7 days before on LPS-induced SI (1.5 mg/kg, i.v.) in rats. The assessment involved monitoring Tb, heat loss index (HLI), along non-shivering thermogenesis assessed by oxygen consumption. Cytokine levels in the spleen and blood, along with nitric oxide (NO), and prostaglandins (PGs) E2 and D2, levels were also measured. The findings reveal increased plasma NO, cytokines in plasma and spleen, and hypothalamus PGE2 levels during SI. Interestingly, FLX mitigated LPS-induced hypothermia, accompanied by a reduction in plasma and splenic NO, interleukins (IL) 6, and 10. Additionally, the results align with the hypothesis that hypothermia, blunted by FLX, develops in fact in a regulated form, as an adaptive strategy.

Hypothermia protects against ventilator-induced lung injury by limiting IL-1β release and NETs formation

Although mechanical ventilation is a critical intervention for acute respiratory distress syndrome (ARDS), it can trigger an IL-1β-associated complication known as ventilator-induced lung injury. In mice, we found that LPS and high-volume ventilation, LPS-HVV, leads to hypoxemia with neutrophil extracellular traps (NETs) formation in the alveoli. Furthermore, Il1r1 -/- LPS-HVV mice did not develop hypoxemia and had reduced NETs, indicating that IL-1R1 signaling is important for NETs formation and hypoxemia. Therapeutic hypothermia (TH) is known to reduce the release of inflammatory mediators. In LPS-HVV mice, TH (32 °C body temperature) prevented hypoxemia development, reducing albumin leakage, IL-1β, gasdermin D (GSDMD) and NETs formation. We also observed that LPS-primed macrophages, when stimulated at 32°C with ATP or nigericin, release less IL-1β associated with reduced GSDMD cleavage. Thus, hypothermia is an important modulating factor in the NLRP3 inflammasome activation, IL-1β release and NETs formation, preventing LPS-HVV-induced acute respiratory failure.

Ambient temperature leads to differential immune strategies in the subterranean rodent Ctenomys talarum

Animal thermoregulation may have significant costs and compete directly or indirectly with other energetically demanding processes, such as immune function. Although the subterranean environment is characterized by thermally stable conditions, small changes in ambient temperature could be critical in shaping immunity. However, little is known about the effects of ambient temperature, in naturally varying ranges, on immunity of wild species. Therefore, to evaluate the effect of short-term exposure to ambient temperatures on energy metabolism and body temperature during the acute phase immune response (APR) in the subterranean rodent Ctenomys talarum, 70 adult animals were divided into three experimental groups and exposed twice for 1 h to 15, 25 or 32°C (below, at or near the upper limit of the thermoneutral zone, respectively) before and after injection with saline (control) or lipopolysaccharide (LPS, which induces the APR). Animals exposed to 25 and 32°C showed a similar APR pattern, characterized by fever (average: 37.1 and 37.7°C, respectively), a 16% increase in O2 consumption and an increase in the neutrophil/lymphocyte ratio (N/L). Body mass loss and symptoms of sickness behavior were detected from 3 and 1 h post-injection, respectively. Individuals exposed to 15°C increased their metabolic rate by 60%, showed frequent hypothermia (34.3°C on average) and the characteristic N/L increase was attenuated. Body mass loss and sickness behavior were mostly detected 24 h post-injection. Our results suggest that the thermoregulation costs in C. talarum may limit the energy available for immunity, leading to different strategies to cope with infection.

Synthesis and physiological effects of new 4-aminophenol derivatives as paracetamol analogues

Paracetamol has antipyretic and analgesic properties and it is widely used for fever and pain. However, paracetamol is partially metabolized to N-acetyl-p-benzoquinoneimine, which in overdose leads to liver necrosis, urging for safer paracetamol analogues. As the latter, new para-aminophenol derivatives containing fragments of acetic acid, saturated fatty acids and monoethanolamine were synthesized. The obtained compounds at equimolar doses of paracetamol (0.5 mmol/kg) have been shown to have modulating effect on thermoregulatory (in experimental fever) and nociceptive (in experimental arthritis) reactions. The studied derivatives in rats with LPS-induced fever leveled the first phase of the febrile response and reduced the increase in core body temperature in the second phase by three times. The synthesized compounds in rats with zymosan-induced arthritis suppressed the nociceptive response in Randall-Selitto test and Hot plate test by 21-48 % and 8-42 %, respectively.

Mathematical model of the inflammatory response to acute and prolonged lipopolysaccharide exposure in humans

One in five deaths worldwide is associated with sepsis, which is defined as organ dysfunction caused by a dysregulated host response to infection. An increased understanding of the pathophysiology of sepsis could provide improved approaches for early detection and treatment. Here we describe the development and validation of a mechanistic mathematical model of the inflammatory response, making use of a combination of in vitro and human in vivo data obtained from experiments where bacterial lipopolysaccharide (LPS) was used to induce an inflammatory response. The new model can simulate the responses to both acute and prolonged inflammatory stimuli in an experimental setting, as well as the response to infection in the clinical setting. This model serves as a foundation for a sepsis simulation model with a potentially wide range of applications in different disciplines involved with sepsis research.

Thermoregulation and survival during sepsis: insights from the cecal ligation and puncture experimental model

BACKGROUND

Sepsis remains a major global health concern due to its high prevalence and mortality. Changes in body temperature (Tb), such as hypothermia or fever, are diagnostic indicators and play a crucial role in the pathophysiology of sepsis. This study aims to characterize the thermoregulatory mechanisms during sepsis using the cecal ligation and puncture (CLP) model and explore how sepsis severity and ambient temperature (Ta) influence Tb regulation and mortality. Rats were subjected to mild or severe sepsis by CLP while housed at thermoneutral (28 °C) or subthermoneutral (22 °C) Ta, and their Tb was monitored for 12 h. Blood and hypothalamus were collected for cytokines and prostaglandin E2 (PGE2) analysis.

RESULTS

At 28 °C, febrile response magnitude correlated with sepsis severity and inflammatory response, with tail vasoconstriction as the primary heat retention mechanism. At 22 °C, Tb was maintained during mild sepsis but dropped during severe sepsis, linked to reduced UCP1 expression in brown adipose tissue and less effective vasoconstriction. Despite differences in thermoregulatory responses, both Ta conditions induced a persistent inflammatory response and increased hypothalamic PGE2 production. Notably, mortality in severe sepsis was significantly higher at 28 °C (80%) compared to 22 °C (0%).

CONCLUSIONS

Our findings reveal that ambient temperature and the inflammatory burden critically influence thermoregulation and survival during early sepsis. These results emphasize the importance of considering environmental factors in preclinical sepsis studies. Although rodents in experimental settings are often adapted to cold environments, these conditions may not fully translate to human sepsis, where cold adaptation is rare. Thus, researchers should carefully consider these variables when designing experiments and interpreting translational implications.

Behavioral responses during sickness in amphibians and reptiles: Concepts, experimental design, and implications for field studies

In ectothermic vertebrates, behavioral fever, where an individual actively seeks warmer areas, seems to be a primary response to pathogens. This is considered a broad and evolutionarily conserved response among vertebrates. Recent population declines in amphibians are associated with an increase of infectious disease driven largely by climate change, habitat degradation, and pollution. Immediate action through research is required to better understand and inform conservation efforts. The literature available, does not provide unifying concepts that can guide adequate experimental protocols and interpretation of data, especially when studying animals in the field. The aim of this review is to promote common understanding of terminology and facilitating improved comprehension and application of key concepts about the occurrence of both sickness behavior or behavioral fever in ectothermic vertebrates. We start with a conceptual synthesis of sickness behavior and behavioral fever, with examples in different taxa. Through this discussion we present possible paths to standardize terminology, starting from original use in endothermic tetrapods which was expanded to ectothermic vertebrates, particularly amphibians and reptiles. This conceptual expansion from humans (endothermic vertebrates) and then to ectothermic counterparts, gravitates around the concept of 'normality'. Thus, following this discussion, we highlight caveats with experimental protocols and state the need of a reference value considered normal (RVCN), which is different from experimental control and make recommendations regarding experimental procedures and stress the value of detailed documentation of behavioral responses. We also propose some future directions that could enhance interaction among disciplines, emphasizing relationships at different levels of biological organization. This is crucial given the increasing convergence of fields such as thermal physiology, immunology, and animal behavior due to emerging diseases and other global crises impacting biodiversity.

Temperature-dependent differences in mouse gut motility are mediated by stress

Researchers have advocated elevating mouse housing temperatures from the conventional ~22 °C to the mouse thermoneutral point of 30 °C to enhance translational research. However, the impact of environmental temperature on mouse gastrointestinal physiology remains largely unexplored. Here we show that mice raised at 22 °C exhibit whole gut transit speed nearly twice as fast as those raised at 30 °C, primarily driven by a threefold increase in colon transit speed. Furthermore, gut microbiota composition differs between the two temperatures but does not dictate temperature-dependent differences in gut motility. Notably, increased stress signals from the hypothalamic-pituitary-adrenal axis at 22 °C have a pivotal role in mediating temperature-dependent differences in gut motility. Pharmacological and genetic depletion of the stress hormone corticotropin-releasing hormone slows gut motility in stressed 22 °C mice but has no comparable effect in relatively unstressed 30 °C mice. In conclusion, our findings highlight that colder mouse facility temperatures significantly increase gut motility through hormonal stress pathways.

LG, Cruz-Neto AP. Combined effects of ambient temperature and food availability on induced innate immune response of a fruit-eating bat (Carollia perspicillata)

Resilience of mammals to anthropogenic climate and land-use changes is associated with the maintenance of adequate responses of several fitness-related traits such as those related to immune functions. Isolated and combined effects of decreased food availability and increased ambient temperature can lead to immunosuppression and greater susceptibility to disease. Our study tested the general hypothesis that decreased food availability, increased ambient temperature and the combined effect of both factors would affect selected physiological and behavioral components associated with the innate immune system of fruit-eating bats (Carollia perspicillata). Physiological (fever, leukocytosis and neutrophil/lymphocyte ratio) and behavioral (food intake) components of the acute phase response, as well as bacterial killing ability of the plasma were assessed after immune challenge with lipopolysaccharide (LPS: 10 mg/kg) in experimental groups kept at different short-term conditions of food availability (ad libitum diet or 50% food-deprived) and ambient temperature (27 and 33°C). Our results indicate that magnitude of increase in body temperature was not affected by food availability, ambient temperature or the interaction of both factors, but the time to reach the highest increase took longer in LPS-injected bats that were kept under food restriction. The magnitude of increased neutrophil/lymphocyte ratio was affected by the interaction between food availability and ambient temperature, but food intake, total white blood cell count and bacterial killing ability were not affected by any factor or interaction. Overall, our results suggest that bacterial killing ability and most components of acute phase response examined are not affected by short-term changes in food availability and ambient temperature within the range evaluated in this study, and that the increase of the neutrophil/lymphocyte ratio when bats are exposed to low food availability and high ambient temperature might represent an enhancement of cellular response to deal with infection.

Active immunotherapy for C5a-mediated inflammation using adjuvant-free self-assembled peptide nanofibers

The terminal protein in the complement cascade C5a is a potent inflammatory molecule and chemoattractant that is involved in the pathology of multiple inflammatory diseases including sepsis and arthritis, making it a promising protein to target with immunotherapies. Active immunotherapies, in which patients are immunized against problematic self-molecules and generate therapeutic antibodies as a result, have received increasing interest as an alternative to traditional monoclonal antibody treatments. In previous work, we have designed supramolecular self-assembling peptide nanofibers as active immunotherapies with defined combinations of B- and T-cell epitopes. Herein, the self-assembling peptide Q11 platform was employed to generate a C5a-targeting active immunotherapy. Two of three predicted B-cell epitope peptides from C5a were found to be immunogenic when displayed within Q11 nanofibers, and the nanofibers were capable of reducing C5a serum concentrations following immunization. Contrastingly, C5a's precursor protein C5 maintained its original concentration, promising to minimize side effects heretofore associated with C5-targeted therapies. Immunization protected mice against an LPS-challenge model of sepsis, and it reduced clinical severity in a model of collagen-antibody induced arthritis. Together, this work indicates the potential for targeting terminal complement proteins with active immunotherapies by leveraging the immunogenicity of self-assembled peptide nanomaterials. STATEMENT OF SIGNIFICANCE: Chronic inflammatory diseases such as rheumatoid arthritis, psoriasis, and inflammatory bowel disease are currently treated primarily with monoclonal antibodies against key inflammatory mediators. While helpful for many patients, they have high non-response rates, are costly, and commonly fail as anti-drug antibodies are raised by the patient. The approach we describe here explores a fundamentally different treatment paradigm: raising therapeutic antibody responses with an active immunotherapy. We employ innovative supramolecular peptide nanomaterials to elicit neutralizing antibody responses against complement component C5a and demonstrate therapeutic efficacy in preclinical mouse models of sepsis and rheumatoid arthritis. The strategy reported may represent a potential alternative to monoclonal antibody therapies.

Omics analysis of the effect of cold normal saline stress through gastric gavage on LPS induced mice

Cold stress is a significant environmental stimulus that negatively affects the health, production, and welfare of animals and birds. However, the specific effects of cold stimulation combined with lipopolysaccharide (LPS) on the mouse intestine remain poorly understood. Therefore, we designed this research to explore the effect of cold stimulation + LPS on mice intestine via microbiome and microbiota sequencing. Forty-eight mice were randomly divided into four experimental groups (n = 12): Control (CC), LPS-induced (CL), cold normal saline-induced (MC) and LPS + cold normal saline-induced (ML). Our results showed body weight was similar among different groups of mice. However, the body weight of mice in groups CC and CL were slightly higher compared to those in groups MC and ML. The results of gene expressions reflected that CL and ML exposure caused gut injury and barrier dysfunction, as evident by decreased ZO-1, OCCLUDIN (P < 0.01), and CASPASE-1 (P < 0.01) expression in the intestine of mice. Moreover, we found that cold stress induced oxidative stress in LPS-challenged mice by increasing malondialdehyde (MDA) accumulation and decreasing the antioxidant capacity [glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), total and antioxidant capacity (T-AOC)]. The cold stress promoted inflammatory response by increased IL-1β in mice treated with cold normal saline + LPS. Whereas, microbiome sequencing revealed differential abundance in four phyla and 24 genera among the mouse groups. Metabolism analysis demonstrated the presence of 4,320 metabolites in mice, with 43 up-regulated and 19 down-regulated in CC vs. MC animals, as well as 1,046 up-regulated and 428 down-regulated in ML vs. CL animals. It is Concluded that cold stress enhances intestinal damage by disrupting the balance of gut microbiota and metabolites, while our findings contribute in improving management practices of livestock in during cold seasons.

Obesity amplifies influenza virus-driven disease severity in male and female mice

Influenza virus-induced respiratory pneumonia remains a major public health concern. Obesity, metabolic diseases, and female sex are viewed as independent risk factors for worsened influenza virus-induced lung disease severity. However, lack of experimental models of severe obesity in female mice limits discovery-based studies. Here, via utility of thermoneutral housing (30 °C) and high-fat diet (HFD) feeding, we induced severe obesity and metabolic disease in female C57BL/6 mice and compared their responses to severely obese male C57BL/6 counterparts during influenza virus infection. We show that lean male and female mice have similar lung edema, inflammation, and immune cell infiltration during influenza virus infection. At standard housing conditions, HFD-fed male, but not female, mice exhibit severe obesity, metabolic disease, and exacerbated influenza disease severity. However, combining thermoneutral housing and HFD feeding in female mice induces severe obesity and metabolic disease, which is sufficient to amplify influenza virus-driven disease severity to a level comparable to severely obese male counterparts. Lastly, increased total body weights of male and female mice at time of infection correlated with worsened influenza virus-driven disease severity metrics. Together, our findings confirm the impact of obesity and metabolic disease as key risk factors to influenza disease severity and present a novel mouse experimental model suitable for future mechanistic interrogation of sex, obesity, and metabolic disease traits in influenza virus-driven disease severity.

[Thermoneutrality and animal study]

Animal models remain important for the study of human pathologies. The most widely used model (mouse) is an endothermic mammal like humans, maintained at ambient temperatures (22 °C). Its energy metabolism is overactivated, a situation rarely observed in humans thanks to various adaptations (clothing, heating…). The thermoneutral zone is defined as a range of ambient temperatures that allows an organism to regulate body temperature without using additional thermoregulatory processes. There are many examples of divergent results between studies conducted at 22 °C or at 30 °C (thermoneutrality for mice). Therefore, it seems essential to take into account the housing temperature both for animal welfare and for the relevance of the results.

Hyperthermia elevates brain temperature and improves behavioural signs in animal models of autism spectrum disorder

BACKGROUND

Autism spectrum disorders (ASD) are predominantly neurodevelopmental and largely genetically determined. However, there are human data supporting the idea that fever can improve symptoms in some individuals, but those data are limited and there are almost no data to support this from animal models. We aimed to test the hypothesis that elevated body temperature would improve function in two animal models of ASD.

METHODS

We used a 4 h whole-body hyperthermia (WBH) protocol and, separately, systemic inflammation induced by bacterial endotoxin (LPS) at 250 µg/kg, to dissociate temperature and inflammatory elements of fever in two ASD animal models: C58/J and Shank3B- mice. We used one- or two-way ANOVA and t-tests with normally distributed data and Kruskal-Wallis or Mann-Whitney with nonparametric data. Post hoc comparisons were made with a level of significance set at p < 0.05. For correlation analyses, data were adjusted by a linear regression model.

RESULTS

Only LPS induced inflammatory signatures in the brain while only WBH produced fever-range hyperthermia. WBH reduced repetitive behaviours and improved social interaction in C58/J mice and significantly reduced compulsive grooming in Shank3B- mice. LPS significantly suppressed most activities over 5-48 h.

LIMITATIONS

We show behavioural, cellular and molecular changes, but provide no specific mechanistic explanation for the observed behavioural improvements.

CONCLUSIONS

The data are the first, to our knowledge, to demonstrate that elevated body temperature can improve behavioural signs in 2 distinct ASD models. Given the developmental nature of ASD, evidence that symptoms may be improved by environmental perturbations indicates possibilities for improving function in these individuals. Since experimental hyperthermia in patients would carry significant risks, it is now essential to pursue molecular mechanisms through which hyperthermia might bring about the observed benefits.

Icilin, a cool/cold-inducing agent, alleviates lipopolysaccharide-induced septic sickness responses in mice

Sepsis is a significant global public health challenge, resulting in millions of human deaths annually. Transient receptor potential melastatin 8 (TRPM8), a non-selective ion channel, is the primary cold sensor in humans; however, its effects on endotoxin-induced inflammation remain unclear. We previously reported that TRPM8 knockout mice exhibited more severe physiological and behavioral endotoxemia responses upon a high-dose injection with lipopolysaccharide (LPS). In the present study, we investigated whether icilin, a TRPM8 agonist, was a target for the suppression of sickness responses using a mouse model of LPS-induced sepsis. A peripheral high-dose injection of LPS at 5 mg/kg showed a maximal body temperature decrease of 5.1 °C in mice subcutaneously pretreated with vehicle and 1.5 °C in icilin-pretreated animals. The decline in locomotor activity was attenuated in icilin-pretreated mice and its recovery was faster; however, the high-dose LPS injection rapidly decreased locomotor activity regardless of the icilin pretreatment. Furthermore, the icilin pretreatment attenuated LPS-induced decreases in body weight and food and water intakes and accelerated recovery from these sickness responses. Therefore, the present results demonstrated that the icilin pretreatment alleviated LPS-induced sickness responses or decreases in body temperature, locomotor activity, body weight loss, and food and water intakes, suggesting its potential as a therapeutic target for sepsis.

Varying intensity of simulated infection partially affects the magnitude of the acute-phase immune response in the subterranean rodent Ctenomys talarum

The acute phase response (APR), coordinated by a complex network of components of the immune and neuroendocrine systems, plays a key role in early immune defense. This response can be elicited by a wide variety of pathogens at different intensities (frequencies and doses), hence experimental immune challenges with antigen gradients makes it possible to evaluate sickness progression with a better representation of what occurs in natural systems. However, how infection intensity could shape the APR magnitude in wild species is still poorly understood. Here, the immune response was activated in the subterranean rodent Ctenomys talarum with a gradient of lipopolysaccharide (LPS) doses (0.5, 1, 1.5, and 2 mg/kg of body mass). Changes in body temperature, body mass, and energetic costs were evaluated over time. We also assessed cortisol levels, white blood cells counts and neutrophil: lymphocyte ratios, before and after injection. Results indicated that during the APR, C. talarum shows a hyperthermic response, which is maintained for 6 h, with slight differences among antigen doses in the pattern of thermal response and body mass change. A maximum increase in body temperature of 0.83°C to 1.63°C was observed during the first hour, associated with a metabolic cost that ranged from 1.25 to 1.41 ml O₂ /gh. Although no clear effects of treatment were detected on leukocyte abundance, we found increments in neutrophil: lymphocyte ratios and gradual increases in cortisol levels corresponding to the intensity of simulated infection, which may indicate redistribution of immune cells and enhancement of immune function. An evident sickness syndrome was observed even at the lowest LPS dose that was characterized by an increase in body temperature, energy expenditure, and N: L ratio, as well as a dose-dependent increase in cortisol levels. Although in nature, other constraints and challenges could affect the magnitude and costs of immune responses, C. talarum mounts an effective APR with a low increase in their daily energy expenditure, regardless of LPS dose.

Microbial and Host Metabolites at the Backstage of Fever: Current Knowledge about the Co-Ordinate Action of Receptors and Molecules Underlying Pathophysiology and Clinical Implications

Fever represents an elevation of body temperature, that exerts a protective effect against pathogens. Innate immune cells and neurons are implicated in the regulation of body temperature. Pathogen-associated molecular patterns, i.e., lipopolysaccharides from Gram-negative bacteria and peptidoglycan and lipoteichoic acid from Gram-positive bacteria are exogenous pyrogens, that bind to Toll-like receptors on immune and non-immune cells. The subsequent release of pro-inflammatory cytokines [interleukin-1 (IL-1), IL-6 and Tumor necrosis factor-alpha] and their passage through the brain trigger the febrile response. In fact, neurons of the pre-optic area produce prostaglandin E2 (PGE2), that, in turn, bind to the PGE2 receptors; thus, generating fever. Apart from classical non-steroidal anti-inflammatory drugs, i.e., aspirin and acetaminophen, various botanicals are currently used as antipyretic agents and, therefore, their mechanisms of action will be elucidated.

Prostaglandin production in brain endothelial cells during the initiation of fever

The initiation of fever has been a matter of controversy. Based on observations of little or no induction of prostaglandin synthesizing enzymes in the brain during the first phase of fever it was suggested that fever is initiated by prostaglandin released into the circulation from cells in the liver and lungs. Here we show in the mouse that prostaglandin synthesis is rapidly induced in the brain after immune challenge. These data are consistent with our recent findings in functional experiments that prostaglandin production in brain endothelial cells is both necessary and sufficient for the generation of all phases of fever.

The acute phase response in bats (Carollia perspicillata) varies with time and dose of the immune challenge

The acute phase response (APR) is a core component of the innate immune response and represents the first line of immune defense used in response to infections. Although several studies with vertebrates reported fever, a decrease in food intake and body mass, and an increase in neutrophil/lymphocyte ratio and total white blood cell count after lipopolysaccharide (LPS) inoculation, there was great variability in the magnitude of these responses. Some of these differences might reflect, to some extent, differences in the time of endotoxin inoculation (during active or rest periods) and dose. Therefore, our study tested the interplay between LPS dose and time of injection on selected physiological (fever and increase in total white blood cell count and neutrophil/lymphocyte ratio) and behavioral (food intake) components of the APR using a Neotropical fruit-eating bat (Carollia perspicillata) as a model organism. We predicted that LPS would trigger a dose- and time-dependent response in APR components. APR components were assessed in rest and active periods after injection of three doses of LPS (5, 10 and 15 mg kg-1 LPS). The results indicate a more robust decrease in food intake at higher doses during the active period, while increased neutrophil/lymphocyte ratio was more robust during the active period regardless of dose. Furthermore, the skin temperature increase lasted longer at higher doses regardless of the timing of injections. Our study offers important insights into the dependence of time as well as the LPS dosage effect in the APR of bats, and how they deal with the magnitude of infections at different times of day.

Browning of the white adipose tissue regulation: new insights into nutritional and metabolic relevance in health and diseases

Adipose tissues are dynamic tissues that play crucial physiological roles in maintaining health and homeostasis. Although white adipose tissue and brown adipose tissue are currently considered key endocrine organs, they differ functionally and morphologically. The existence of the beige or brite adipocytes, cells displaying intermediary characteristics between white and brown adipocytes, illustrates the plastic nature of the adipose tissue. These cells are generated through white adipose tissue browning, a process associated with augmented non-shivering thermogenesis and metabolic capacity. This process involves the upregulation of the uncoupling protein 1, a molecule that uncouples the respiratory chain from Adenosine triphosphate synthesis, producing heat. β-3 adrenergic receptor system is one important mediator of white adipose tissue browning, during cold exposure. Surprisingly, hyperthermia may also induce beige activation and white adipose tissue beiging. Physical exercising copes with increased levels of specific molecules, including Beta-Aminoisobutyric acid, irisin, and Fibroblast growth factor 21 (FGF21), which induce adipose tissue browning. FGF21 is a stress-responsive hormone that interacts with beta-klotho. The central roles played by hormones in the browning process highlight the relevance of the individual lifestyle, including circadian rhythm and diet. Circadian rhythm involves the sleep-wake cycle and is regulated by melatonin, a hormone associated with UCP1 level upregulation. In contrast to the pro-inflammatory and adipose tissue disrupting effects of the western diet, specific food items, including capsaicin and n-3 polyunsaturated fatty acids, and dietary interventions such as calorie restriction and intermittent fasting, favor white adipose tissue browning and metabolic efficiency. The intestinal microbiome has also been pictured as a key factor in regulating white tissue browning, as it modulates bile acid levels, important molecules for the thermogenic program activation. During embryogenesis, in which adipose tissue formation is affected by Bone morphogenetic proteins that regulate gene expression, the stimuli herein discussed influence an orchestra of gene expression regulators, including a plethora of transcription factors, and chromatin remodeling enzymes, and non-coding RNAs. Considering the detrimental effects of adipose tissue browning and the disparities between adipose tissue characteristics in mice and humans, further efforts will benefit a better understanding of adipose tissue plasticity biology and its applicability to managing the overwhelming burden of several chronic diseases.

Human total, basal and activity energy expenditures are independent of ambient environmental temperature

Lower ambient temperature (Ta) requires greater energy expenditure to sustain body temperature. However, effects of Ta on human energetics may be buffered by environmental modification and behavioral compensation. We used the IAEA DLW database for adults in the USA (n = 3213) to determine the effect of Ta (-10 to +30°C) on TEE, basal (BEE) and activity energy expenditure (AEE) and physical activity level (PAL). There were no significant relationships (p > 0.05) between maximum, minimum and average Ta and TEE, BEE, AEE and PAL. After adjustment for fat-free mass, fat mass and age, statistically significant (p < 0.01) relationships between TEE, BEE and Ta emerged in females but the effect sizes were not biologically meaningful. Temperatures inside buildings are regulated at 18-25°C independent of latitude. Hence, adults in the US modify their environments to keep TEE constant across a wide range of external ambient temperatures.

How murine models of human disease and immunity are influenced by housing temperature and mild thermal stress

At the direction of The Guide and Use of Laboratory Animals, rodents in laboratory facilities are housed at ambient temperatures between 20°C and 26°C, which fall below their thermoneutral zone (TNZ). TNZ is identified as a range of ambient temperatures that allow an organism to regulate body temperature without employing additional thermoregulatory processes (e.g. metabolic heat production driven by norepinephrine), thus leading to mild, chronic cold stress. For mice, this chronic cold stress leads to increased serum levels of the catecholamine norepinephrine, which has direct effects on various immune cells and several aspects of immunity and inflammation. Here, we review several studies that have revealed that ambient temperature significantly impacts outcomes in various murine models of human diseases, particularly those in which the immune system plays a major role in its pathogenesis. The impact of ambient temperature on experimental outcomes raises questions regarding the clinical relevance of some murine models of human disease, since studies examining rodents housed within thermoneutral ambient temperatures revealed that rodent disease pathology more closely resembled that of humans. Unlike laboratory rodents, humans can modify their surroundings accordingly - by adjusting their clothing, the thermostat, or their physical activity - to live within the appropriate TNZ, offering a possible explanation for why many studies using murine models of human disease conducted at thermoneutrality better represent patient outcomes. Thus, it is strongly recommended that ambient housing temperature in such studies be consistently and accurately reported and recognized as an important experimental variable.

Acute-Phase Immune Response Involves Fever, Sickness Behavior, and an Elevated Metabolic Rate in the Subterranean Rodent Ctenomys talarum

AbstractThe acute-phase response (APR) is an induced innate response and may involve pronounced physiological and behavioral changes. One of the most common assays to study the APR involves the use of a lypopolysaccharide (LPS) from the cell wall of gram-negative bacteria. In this study, we determined the energetic costs of the APR in the subterranean rodent Ctenomys talarum, as well as the effects of the exposure to LPS on body temperature, body mass loss, and behavior in this species. Furthermore, we monitored levels of circulating endotoxin after LPS exposure. Our results suggest that in C. talarum, the APR is energetically costly, resulting in a 14% increase in metabolic rate. Animals exposed to LPS experienced a short-term thermal response, weight loss, and changes in their behavior that included more time spent resting and with their eyes totally or partially closed. However, the magnitude of the effects of LPS exposure varied between sexes and among animals. Also, there was a clear peak in circulating endotoxin levels in plasma 3 h postinjection (hpi) and a significant decrease of these levels 24 hpi, but peak endotoxin concentration values recorded were highly variable among animals. In light of these results, ecological determinants of immune function variation in tuco-tucos are discussed considering the roles of pace of life, habitat, and degree of pathogen exposure in these subterranean rodents.

Reliable and Remote Monitoring of Absolute Temperature during Liver Inflammation via Luminescence-Lifetime-Based Nanothermometry

Temperature of tissues and organs is one of the first parameters affected by physiological and pathological processes, such as metabolic activity, acute trauma, or infection-induced inflammation. Therefore, the onset and development of these processes can be detected by monitoring deviations from basal temperature. To accomplish this, minimally invasive, reliable, and accurate measurement of the absolute temperature of internal organs is required. Luminescence nanothermometry is the ideal technology for meeting these requirements. Although this technique has lately undergone remarkable developments, its reliability is being questioned due to spectral distortions caused by biological tissues. In this work, how the use of bright Ag₂ S nanoparticles featuring temperature-dependent fluorescence lifetime enables reliable and accurate measurement of the absolute temperature of the liver in mice subjected to lipopolysaccharide-induced inflammation is demonstrated. Beyond the remarkable thermal sensitivity (≈ 3% °C^-1 around 37 °C) and thermal resolution obtained (smaller than 0.3 °C), the results included in this work set a blueprint for the development of new diagnostic procedures based on the use of intracorporeal temperature as a physiological indicator.

LPS induces rapid increase in GDF15 levels in mice, rats, and humans but is not required for anorexia in mice

Growth differentiation factor 15 (GDF15), a TGFβ superfamily cytokine, acts through its receptor, cell line-derived neurotrophic factorfamily receptor α-like (GFRAL), to suppress food intake and promote nausea. GDF15 is broadly expressed at low levels but increases in states of disease such as cancer, cachexia, and sepsis. Whether GDF15 is necessary for inducing sepsis-associated anorexia and body weight loss is currently unclear. To test this we used a model of moderate systemic infection in GDF15KO and GFRALKO mice with lipopolysaccharide (LPS) treatment to define the role of GDF15 signaling in infection-mediated physiologic responses. Since physiological responses to LPS depend on housing temperature, we tested the effects of subthermoneutral and thermoneutral conditions on eliciting anorexia and inducing GDF15. Our data demonstrate a conserved LPS-mediated increase in circulating GDF15 levels in mouse, rat, and human. However, we did not detect differences in LPS-induced anorexia between WT and GDF15KO or GFRALKO mice. Furthermore, there were no differences in anorexia or circulating GDF15 levels at either thermoneutral or subthermoneutral housing conditions in LPS-treated mice. These data demonstrate that GDF15 is not necessary to drive food intake suppression in response to moderate doses of LPS.NEW & NOTEWORTHY Although many responses to LPS depend on housing temperature, the anorexic response to LPS does not. LPS results in a potent and rapid increase in circulating levels of GDF15 in mice, rats, and humans. Nevertheless, GDF15 and its receptor (GFRAL) are not required for the anorexic response to systemic LPS administration. The anorexic response to LPS likely involves a myriad of complex physiological alterations.

Changes in Body Surface Temperature Play an Underappreciated Role in the Avian Immune Response

AbstractFever and hypothermia are well-characterized components of systemic inflammation. However, our knowledge of the mechanisms underlying such changes in body temperature is largely limited to rodent models and other mammalian species. In mammals, high dosages of an inflammatory agent (e.g., lipopolysaccharide [LPS]) typically leads to hypothermia (decrease in body temperature below normothermic levels), which is largely driven by a reduction in thermogenesis and not changes in peripheral vasomotion (i.e., changes in blood vessel tone). In birds, however, hypothermia occurs frequently, even at lower dosages, but the thermoeffector mechanisms associated with the response remain unknown. We immune challenged zebra finches (Taeniopygia guttata) with LPS, monitored changes in subcutaneous temperature and energy balance (i.e., body mass, food intake), and assessed surface temperatures of and heat loss across the eye region, bill, and legs. We hypothesized that if birds employ thermoregulatory mechanisms similar to those of similarly sized mammals, LPS-injected individuals would reduce subcutaneous body temperature and maintain constant surface temperatures compared with saline-injected individuals. Instead, LPS-injected individuals showed a slight elevation in body temperature, and this response coincided with a reduction in peripheral heat loss, particularly across the legs, as opposed to changes in energy balance. However, we note that our interpretations should be taken with caution owing to small sample sizes within each treatment. We suggest that peripheral vasomotion, allowing for heat retention, is an underappreciated component of the sickness-induced thermoregulatory response of small birds.

Beneficial effects of QTC-4-MeOBnE in an LPS-induced mouse model of depression and cognitive impairments: The role of blood-brain barrier permeability, NF-κB signaling, and microglial activation

Clinical and preclinical investigations have suggested a possible biological link betweenmajor depressive disorder (MDD) and Alzheimer's disease (AD). Therefore, a pharmacologic approach to treating MDD could be envisioned as a preventative therapy for some AD cases. In line with this, 1-(7-chloroquinolin-4-yl)-N-(4-methoxybenzyl)-5-methyl-1H-1,2,3-triazole-4 carboxamide (QTC-4-MeOBnE) is characterized as an inhibitor of β-secretase, glycogen synthase kinase 3β, and acetylcholinesterase and has also shown secondary effects underlying the modulation of neurogenesis and synaptic plasticity pathways. Therefore, we investigated the effects of QTC-4-MeOBnE treatment (0.1 or 1 mg/kg) on depressive-like behavior and cognitive impairments elicited by repeated injections of lipopolysaccharide (LPS; 250 μg/kg) in mice. Injections of LPS for seven days led to memory impairments and depressive-like behavior, as evidenced in the Y-maze/object recognition test and forced swimming/splash tests, respectively. However, these impairments were prevented in mice that, after the last LPS injection, were also treated with QTC-4-MeOBnE (1 mg/kg). This effect was associated with restoring blood-brain barrier permeability, reducing oxidative/nitrosative biomarkers, and decreasing neuroinflammation mediated NF-κB signaling in the hippocampus and cortex of the mice. To further investigate the involvement with NF-κB signaling, we evaluated the effects of QTC-4-MeOBnE on microglial cell activation through canonical and non-canonical pathways and the modulation of the involved components. Together, our findings highlight the pharmacological benefits of QTC-4-MeOBnE in a mouse model of sickness behavior and memory impairments, supporting the novel concept that since this molecule produces anti-depressant activity, it could also be beneficial for preventing AD onset and related dementias in subjects suffering from MDD through inflammatory pathway modulation.

Housing of A350V IQSEC2 pups at 37 °C ambient temperature prevents seizures and permits the development of social vocalizations in adulthood

OBJECTIVES

Mutations in the human IQSEC2 gene are associated with drug-resistant epilepsy and severe behavioral dysfunction. We have focused on understanding one human IQSEC2 missense mutation (A350V) for which we have created a corresponding A350V IQSEC2 mouse model by CRISPR which demonstrates seizures when the mice are 15-20 days old and impaired social vocalizations in adulthood. We observed that a child with the A350V mutation stops having seizures when experiencing a fever of greater than 38 °C. In this study, we first sought to determine if we could recapitulate this phenomenon in A350V 15-20 day old mice using a previously established protocol to raise body temperature to 39 °C achieved by housing the mice at 37 °C. We then sought to determine if mice in whom seizure activity had been prevented as pups would develop social vocalization activity in adulthood.

METHODS

15-20 day old A350V male mice were housed either at 37 °C or 22 °C. Ultrasonic vocalizations of these mice were assessed at 8-10 weeks in response to a female stimulus.

RESULTS

Housing of 15-20 day old A350V mice at 37 °C resulted in a reduction in lethal seizures to 2% (1/41) compared to 45% (48/108) in mice housed at 22 °C, p = 0.0001. Adult A350V mice who had been housed at 37 °C as pups displayed a significant improvement in the production of social vocalizations.

CONCLUSION

Raising the body temperature by raising the ambient temperature might provide a means to reduce seizures associated with the A350V IQSEC2 mutation and thereby allow for an improved neurodevelopmental trajectory.

Role of TRPM8 in switching between fever and hypothermia in adult mice during endotoxin-induced inflammation

Transient receptor potential melastatin 8 (TRPM8) functions in the sensing of noxious and innocuous colds; however, its significance in pathogen-induced thermoregulation remains unclear. In the present study, we investigated the role of TRPM8 in the regulation of endotoxin-induced body temperature control. The peripheral administration of low-dose lipopolysaccharide (LPS) at 50 ​μg/kg generated fever in wild-type (WT) mice, whereas it caused hypothermia in TRPM8 knockout (KO) animals. LPS-induced sickness responses such as decrease in body weight, and food and water intake were not different between WT and TRPM8 KO mice. TRPM8 KO mice exhibited more severe hypothermia and lower locomotor activity following the peripheral administration of high-dose LPS at 5 ​mg/kg compared with WT ones. An intracerebroventricular (i.c.v.) injection of either LPS at 3.6 ​μg/kg or interleukin-1β at 400 ​ng/kg elicited hypothermia in TRPM8 KO mice, in contrast to fever in WT animals. The peripheral administration of zymosan at 3 ​mg/kg also induced hypothermia in contrast to fever in WT mice. An i.c.v. injection of prostaglandin E₂ at 16 or 160 ​nmol/kg induced normal fever in both WT and TRPM8 KO mice. Infrared thermography showed significant decline of the interscapular skin temperature that estimates temperature of the brown adipose tissue, regardless of no alteration of its temperature in WT animals. Fos immunohistochemistry showed stronger Fos activation of hypothalamic thermoregulation-associated nuclei in TRPM8 KO mice compared with WT animals following the peripheral administration of low-dose LPS. Therefore, the present study indicates that TRPM8 is necessary for switching between fever and hypothermia during endotoxin-induced inflammation.

A Kinetic Response Model for Standardized Regression Analyses of Inflammation-Triggered Hypothermic Body Temperature-Time Courses in Mice

LPS is frequently used to induce experimental endotoxic shock, representing a standard model of acute inflammation in mice. The resulting inflammatory response leads to hypothermia of the experimental animals, which in turn can be used as surrogate for the severity of systemic inflammation. Although increasingly applied as a humane endpoint in murine studies, differences between obtained temperature-time curves are typically evaluated at a single time point with t-tests or ANOVA analyses. We hypothesized that analyses of the entire temperature-time curves using a kinetic response model could fit the data, which show a temperature decrease followed by a tendency to return to normal temperature, and could increase the statistical power. Using temperature-time curves obtained from LPS stimulated mice, we derived a biologically motivated kinetic response model based on a differential equation. The kinetic model includes four parameters: (i) normal body temperature (T _n ), (ii) a coefficient related to the force of temperature autoregulation (r), (iii) damage strength (p ₀), and (iv) clearance rate (k). Kinetic modeling of temperature-time curves obtained from LPS stimulated mice is feasible and leads to a high goodness-of-fit. Here, modifying key enzymes of inflammatory cascades induced a dominant impact of genotypes on the damage strength and a weak impact on the clearance rate. Using a likelihood-ratio test to compare modeled curves of different experimental groups yields strongly enhanced statistical power compared to pairwise t-tests of single temperature time points. Taken together, the kinetic model presented in this study has several advantages compared to simple analysis of individual time points and therefore may be used as a standard method for assessing inflammation-triggered hypothermic response curves in mice.

Ablation of PDE4B protects from Pseudomonas aeruginosa-induced acute lung injury in mice by ameliorating the cytostorm and associated hypothermia

Pseudomonas aeruginosa is a frequent cause of hospital-acquired lung infections characterized by hyperinflammation, antibiotic resistance, and high morbidity/mortality. Here, we show that the genetic ablation of one cAMP-phosphodiesterase 4 subtype, PDE4B, is sufficient to protect mice from acute lung injury induced by P aeruginosa infection as it reduces pulmonary and systemic levels of pro-inflammatory cytokines, as well as pulmonary vascular leakage and mortality. Surprisingly, despite dampening immune responses, bacterial clearance in the lungs of PDE4B-KO mice is significantly improved compared to WT controls. In wildtypes, P aeruginosa-infection produces high systemic levels of several cytokines, including TNF-α, IL-1β, and IL-6, that act as cryogens and render the animals hypothermic. This, in turn, diminishes their ability to clear the bacteria. Ablation of PDE4B curbs both the initial production of acute response cytokines, including TNF-α and IL-1β, as well as their downstream signaling, specifically the induction of the secondary-response cytokine IL-6. This synergistic action protects PDE4B-KO mice from the deleterious effects of the P aeruginosa-induced cytostorm, while concurrently improving bacterial clearance, rather than being immunosuppressive. These benefits of PDE4B ablation are in contrast to the effects resulting from treatment with PAN-PDE4 inhibitors, which have been shown to increase bacterial burden and dissemination. Thus, PDE4B represents a promising therapeutic target in settings of P aeruginosa lung infections.

Naturally occurring hypothermia promotes survival in severe anaphylaxis

Although hypothermia has received substantial attention as an indicator of severity in anaphylaxis, it has been neglected from the perspective of whether it could act as a disease-modifying factor in this condition. Here, the impact of naturally occurring (spontaneous) hypothermia on anaphylaxis was evaluated in a murine model of ovalbumin (OVA)-induced allergy. Nonextreme changes in the ambient temperature (T_a) were used to modulate the magnitude of spontaneous hypothermia. At a T_a of 24°C, challenge with OVA intraperitoneally or intravenously resulted in a rapid, transient fall in body core temperature, which reached its nadir 4-6°C below baseline in 30 min. This hypothermic response was largely attenuated when the mice were kept at a T_a of 34°C. The T_a-dependent attenuation of hypothermia resulted in a survival rate of only 30%, as opposed to survival of 100% in the condition that favored the development of hypothermia. The protective effect of hypothermia did not involve changes in the rate of mast cell degranulation, as assessed by the concentration of mast cell protease-1 in bodily fluids. On the other hand, hypothermia improved oxygenation of the brain and kidneys, as indicated by higher NAD⁺/NADH ratios. Therefore, it is plausible to propose that naturally occurring hypothermia makes organs more resistant to the anaphylactic insult.

Fever During Localized Inflammation in Mice Is Elicited by a Humoral Pathway and Depends on Brain Endothelial Interleukin-1 and Interleukin-6 Signaling and Central EP3 Receptors

We examined the signaling route for fever during localized inflammation in male and female mice, elicited by casein injection into a preformed air pouch. The localized inflammation gave rise to high concentrations of prostaglandins of the E species (PGE2) and cytokines in the air pouch and elevated levels of these inflammatory mediators in plasma. There were also elevated levels of PGE2 in the cerebrospinal fluid, although there was little evidence for PGE2 synthesis in the brain. Global deletion of the PGE2 prostaglandin E receptor 3 (EP3) abolished the febrile response as did deletion of the EP3 receptor in neural cells, whereas its deletion on peripheral nerves had no effect, implying that PGE2 action on this receptor in the CNS elicited the fever. Global deletion of the interleukin-1 receptor type 1 (IL-1R1) also abolished the febrile response, whereas its deletion on neural cells or peripheral nerves had no effect. However, deletion of the IL-1R1 on brain endothelial cells, as well as deletion of the interleukin-6 receptor α on these cells, attenuated the febrile response. In contrast, deletion of the PGE2 synthesizing enzymes cyclooxygenase-2 and microsomal prostaglandin synthase-1 in brain endothelial cells, known to attenuate fever evoked by systemic inflammation, had no effect. We conclude that fever during localized inflammation is not mediated by neural signaling from the inflamed site, as previously suggested, but is dependent on humoral signaling that involves interleukin actions on brain endothelial cells, probably facilitating PGE2 entry into the brain from the circulation and hence representing a mechanism distinct from that at work during systemic inflammation.

Anti-inflammatory activity of 2-((3-(chloromethyl)benzoyl)oxy)benzoic acid in LPS-induced rat model

INTRODUCTION

Salicylic acid derivate is very popular for its activity to suppress pain, fever, and inflammation. One of its derivatives is acetylsalicylic acid (ASA) which has been reported repeatedly that, as a non-steroidal anti-inflammatory drug (NSAID), it has a cardioprotective effect. Although ASA has various advantages, several studies have reported that it may induce severe peptic ulcer disease. We recently synthesized a new compound derived from salicylic acid, namely 2-((3-(chloromethyl)benzoyl)oxy)benzoic acid (3-CH2Cl) which still has the benefit of acetylsalicylic acid as an analgesic and antiplatelet, but lacks its harmful side effects (Caroline et al., 2019). In addition, in silico studies of 3-CH2Cl showed a higher affinity towards protein receptor cyclooxygenase-2 (COX-2; PDB: 5F1A) than ASA. We hypothesized that 3-CH2Cl inhibits the COX-2 activity which could presumably decrease the inflammatory responses. However, no knowledge is available on the anti-inflammatory response and molecular signaling of this new compound. Hence, in this study, we investigated the potential functional relevance of 3-CH2Cl in regulating the inflammatory response in lipopolysaccharide (LPS)-induced rats. The results of this study show that this compound could significantly reduce the inflammatory parameter in LPS-induced rats.

MATERIAL AND METHODS

Rats were induced with LPS of 0.5 mg/kg bw intravenously, prior oral administration with vehicle (3% Pulvis Gummi Arabicum / PGA), 500 mg/60 kg body weight (bw; rat dosage converted to human) of 3-CH2Cl and ASA. The inflammatory parameters such as changes in the temperature of septic shock, cardiac blood plasma concentrations of IL-1β and TNF-α (ELISA), blood inflammation parameters, white blood cell concentrations, and lung histopathology were observed. Meanwhile, the stability of 3-CH2Cl powder was evaluated.

RESULT

After the administration of 500 mg/60 kg bw of 3-CH2Cl (rat dosage converted to human) to LPS-induced rats, we observed a significant reduction of both TNF-α (5.70+/-1.04 × 103 pg/mL, p=<0.001) and IL-1β (2.32+/-0.28 × 103 pg/mL, p=<0.001) cardiac blood plasma concentrations. Besides, we found a reduction of white blood cell concentration and the severity of lung injury in the 3-CH2Cl group compared to the LPS-induced rat group. Additionally, this compound maintained the rat body temperature within normal limits during inflammation, preventing the rats to undergo septic shock, characterized by hypothermic (t = 120 min.) or hyperthermic (t = 360 min) conditions. Furthermore, 3-CH2Cl was found to be stable until 3 years at 25°C with a relative humidity of 75 ± 5%.

CONCLUSION

3-CH2Cl compound inhibited inflammation in the LPS-induced inflammation response model in rats, hypothetically through binding to COX-2, and presumably inhibited LPS-induced NF-κβ signaling pathways. This study could be used as a preliminary hint to investigate the target molecular pathways of 3-CH2Cl as a novel and less toxic therapeutical agent in alleviating the COX-related inflammatory diseases, and most importantly to support the planning and development of clinical trial.

Non-canonical Caspase-1 Signaling Drives RIP2-Dependent and TNF-α-Mediated Inflammation In Vivo

Pro-inflammatory caspase-1 is a key player in innate immunity. Caspase-1 processes interleukin (IL)-1β and IL-18 to their mature forms and triggers pyroptosis. These caspase-1 functions are linked to its enzymatic activity. However, loss-of-function missense mutations in CASP1 do not prevent autoinflammation in patients, despite decreased IL-1β production. In vitro data suggest that enzymatically inactive caspase-1 drives inflammation via enhanced nuclear factor κB (NF-κB) activation, independent of IL-1β processing. Here, we report two mouse models of enzymatically inactive caspase-1-C284A, demonstrating the relevance of this pathway in vivo. In contrast to Casp1^-/- mice, caspase-1-C284A mice show pronounced hypothermia and increased levels of the pro-inflammatory cytokines tumor necrosis factor alpha (TNF-α) and IL-6 when challenged with lipopolysaccharide (LPS). Caspase-1-C284A signaling is RIP2 dependent and mediated by TNF-α but independent of the NLRP3 inflammasome. LPS-stimulated whole blood from patients carrying loss-of-function missense mutations in CASP1 secretes higher amounts of TNF-α. Taken together, these results reveal non-canonical caspase-1 signaling in vivo.

In a model of SAH-induced neurogenic fever, BAT thermogenesis is mediated by erythrocytes and blocked by agonism of adenosine A1 receptors

Neurogenic fever (NF) after subarachnoid hemorrhage (SAH) is a major cause of morbidity that is associated with poor outcomes and prolonged stay in the neurointensive care unit (NICU). Though SAH is a much more common cause of fever than sepsis in the NICU, it is often a diagnosis of exclusion, requiring significant effort to rule out an infectious source. NF does not respond to standard anti-pyretic medications such as COX inhibitors, and lack of good medical therapy has led to the introduction of external cooling systems that have their own associated problems. In a rodent model of SAH, we measured the effects of injecting whole blood, blood plasma, or erythrocytes on the sympathetic nerve activity to brown adipose tissue and on febrile thermogenesis. We demonstrate that following SAH the acute activation of brown adipose tissue leading to NF, is not dependent on PGE₂, that subarachnoid space injection of whole blood or erythrocytes, but not plasma alone, is sufficient to trigger brown adipose tissue thermogenesis, and that activation of adenosine A1 receptors in the CNS can block the brown adipose tissue thermogenic component contributing to NF after SAH. These findings point to a distinct thermogenic mechanism for generating NF, compared to those due to infectious causes, and will hopefully lead to new therapies.

Thermoneutrality and Immunity: How Does Cold Stress Affect Disease?

One of the major challenges the scientific community faces today is the lack of translational data generated from mouse trials for human health application. Housing temperature-dependent chronic cold stress in laboratory rodents is one of the key factors contributing to lack of translatability because it reveals major metabolic differences between humans and rodents. While humans tend to operate at temperatures within their thermoneutral zone, most laboratory rodents are housed at temperatures below this zone and have an increased energy demand to generate heat. This has an impact on the immune system of mice and thus affects results obtained using murine models of human diseases. A limited number of studies and reviews have shown that results obtained on mice housed at thermoneutrality were different from those obtained from mice housed in traditional housing conditions. Most of those studies, focused on obesity and cancer, found that housing mice at thermoneutrality changed the outcomes of the diseases negatively and positively, respectively. In this review, we describe how thermoneutrality impacts the immune system of rodents generally and in the context of different disease models. We show that thermoneutrality exacerbates cardiovascular and auto-immune diseases; alleviates asthma and Alzheimer’s disease; and, changes gut microbiome populations. We also show that thermoneutrality can have exacerbating or alleviating effects on the outcome of infectious diseases. Thus, we join the call of others in this field to urge researchers to refine murine models of disease and increase their translational capacity by considering housing at thermoneutrality for trials involving rodents.

Hypothermic Effect of Acute Citral Treatment during LPS-induced Systemic Inflammation in Obese Mice: Reduction of Serum TNF-α and Leptin Levels

Citral is a mixture of monoterpenes present in the essential oil of several plants, such as Cymbopogon citratus and Zingiber officinale, possessing anti-inflammatory, anti-ulcerogenic, and antipyretic actions. We investigated the action of citral on body temperature (Tb) and inflammatory signaling in eutrophic and obese mice during Systemic Inflammation (SI) induced by Lipopolysaccharide (LPS). Thus, we assessed the effect of citral (25, 100, and 300 mg/kg) and ibuprofen in LPS-induced SI in Swiss male mice fed a standard diet (SD) or high-fat diet (HFD) for 12 weeks. Following SI induction, we measured Tb and collected the serum, hypothalamus, and gastric mucosa for biochemical measurements. Acute treatment with citral decreased the Tb of both SD and HFD-fed animals. Citral (300 mg/kg) treatment caused a significantly lower Tb variation in HFD-fed animals than in those fed the SD. Citral reduced peripheral levels of tumor necrosis factor (TNF)-α in SD and HFD mice and decreased serum leptin concentration in HFD mice 90 min after the LPS challenge. Furthermore, citral also reduced interleukin (IL)-6 levels in the hypothalamus of obese mice. In summary, citral effectively reduced Tb during SI by reducing inflammatory mediators with a distinct action profile in HFD mice when compared with SD.

Impact of ambient temperature on inflammation-induced encephalopathy in endotoxemic mice-role of phosphoinositide 3-kinase gamma

BACKGROUND

Sepsis-associated encephalopathy (SAE) is an early and frequent event of infection-induced systemic inflammatory response syndrome. Phosphoinositide 3-kinase γ (PI3Kγ) is linked to neuroinflammation and inflammation-related microglial activity. In homeotherms, variations in ambient temperature (Ta) outside the thermoneutral zone lead to thermoregulatory responses, mainly driven by a gradually increasing sympathetic activity, and may affect disease severity. We hypothesized that thermoregulatory response to hypothermia (reduced Ta) aggravates SAE in PI3Kγ-dependent manner.

METHODS

Experiments were performed in wild-type, PI3Kγ knockout, and PI3Kγ kinase-dead mice, which were kept at neutral (30 ± 0.5 °C) or moderately lowered (26 ± 0.5 °C) Ta. Mice were exposed to lipopolysaccharide (LPS, 10 μg/g, from Escherichia coli serotype 055:B5, single intraperitoneal injection)-evoked systemic inflammatory response (SIR) and monitored 24 h for thermoregulatory response and blood-brain barrier integrity. Primary microglial cells and brain tissue derived from treated mice were analyzed for inflammatory responses and related cell functions. Comparisons between groups were made with one-way or two-way analysis of variance, as appropriate. Post hoc comparisons were made with the Holm-Sidak test or t tests with Bonferroni's correction for adjustments of multiple comparisons. Data not following normal distribution was tested with Kruskal-Wallis test followed by Dunn's multiple comparisons test.

RESULTS

We show that a moderate reduction of ambient temperature triggers enhanced hypothermia of mice undergoing LPS-induced systemic inflammation by aggravated SAE. PI3Kγ deficiency enhances blood-brain barrier injury and upregulation of matrix metalloproteinases (MMPs) as well as an impaired microglial phagocytic activity.

CONCLUSIONS

Thermoregulatory adaptation in response to ambient temperatures below the thermoneutral range exacerbates LPS-induced blood-brain barrier injury and neuroinflammation. PI3Kγ serves a protective role in suppressing release of MMPs, maintaining microglial motility and reinforcing phagocytosis leading to improved brain tissue integrity. Thus, preclinical research targeting severe brain inflammation responses is seriously biased when basic physiological prerequisites of mammal species such as preferred ambient temperature are ignored.

Study of thermo-regulation as a worsening marker of experimental sepsis in an animal model

Objective:

to analyze variations in body temperature and in plasma nitrate and lactate concentrations in rats submitted to the experimental sepsis model.

Method:

a total of 40 rats divided equally into five groups. The induction of endotoxemia was performed with intravenous administration of lipopolysaccharide, 0.5 mg/Kg, 1.5 mg/Kg, 3.0 mg/Kg, and 10 mg/Kg, respectively. The control group received 0.5 mL of saline solution. The experiment lasted six hours, with evaluations performed at 0 (baseline data), 2^nd, 4^th, and 6^thhours.

Results:

The animals that received doses up to 3.0 mg/kg showed a significant increase in body temperature compared to the group with 10 mg/kg, which showed a decrease in these values. The increase in plasma nitrate and lactate concentrations in the groups with lipopolysaccharide was significantly higher than in the group that received the saline solution and was correlated with the increase in body temperature.

Conclusion:

the variations in body temperature observed in this study showed the dose-dependent effect of lipopolysaccharide and were correlated with the increase in the concentrations of nitrate and plasma lactate biomarkers. The implications of this study are the importance of monitoring body temperature, together with the assessment of these pathophysiological markers, which suggest worsening in the prognosis of sepsis.

Comparison of bacterial lipopolysaccharide-induced sickness behavior in rodents and humans: Relevance for symptoms of anxiety and depression

Increasing evidence from animal and human studies suggests that inflammation may be involved in mood disorders. Sickness behavior and emotional changes induced by experimental inflammatory stimuli have been extensively studied in humans and rodents to better understand the mechanisms underlying inflammation-driven mood alterations. However, research in animals and humans have remained compartmentalized and a comprehensive comparison of inflammation-induced sickness and depressive-like behavior between rodents and humans is lacking. Thus, here, we highlight similarities and differences in the effects of bacterial lipopolysaccharide administration on the physiological (fever and cytokines), behavioral and emotional components of the sickness response in rodents and humans, and discuss the translational challenges involved. We also emphasize the differences between observable sickness behavior and subjective sickness reports, and advocate for the need to obtain both subjective reports and objective measurements of sickness behavior in humans. We aim to provide complementary insights for translational clinical and experimental research on inflammation-induced behavioral and emotional changes, and their relevance for mood disorders such as depression.

Thermoneutral Housing Temperature Improves Survival in a Murine Model of Polymicrobial Peritonitis

Regulatory guidelines mandate housing for laboratory mice at temperatures below their thermoneutral zone, creating chronic cold stress. However, increases in housing temperature could alter immune responses. We hypothesized housing mice at temperatures within their thermoneutral zone would improve sepsis survival and alter immune responses. Male C57BL/6 mice were housed at 22°C or 30°C after cecal ligation and puncture (CLP) for 10 days. Survival of mice housed at 30°C (78%) after CLP was significantly increased compared with mice housed at 22°C (40%). Experimental groups were repeated with mice euthanized at 0, 12, 24, and 48 h post-surgery to examine select immune parameters. Raising housing temperature minimally altered systemic, peritoneal, or splenic cell counts. However, IL-6 levels in plasma and peritoneal lavage fluid were significantly lower at 12 h post-surgery in mice housed at 30°C compared with 22°C. Bacterial colony counts from peritoneal lavage fluid were significantly lower in mice housed at 30°C and in vivo studies suggested this was the result of increased phagocytosis by neutrophils. As previously demonstrated, adoptive transfer of fibrocytes significantly increased sepsis survival compared with saline at 22°C. However, there was no additive effect when adoptive transfer was performed at 30°C. Overall, the results demonstrated that thermoneutral housing improves survival after CLP by increasing local phagocytic activity and technical revisions may be necessary to standardize the severity of the model across different housing temperatures. These findings stress the pronounced impact housing temperature has on the CLP model and the importance of reporting housing temperature.

Reduced immune responsiveness contributes to winter energy conservation in an Arctic bird

Animals in seasonal environments must prudently manage energy expenditure to survive the winter. This may be achieved through reductions in the allocation of energy for various purposes (e.g. thermoregulation, locomotion, etc.). We studied whether such trade-offs also include suppression of the innate immune response, by subjecting captive male Svalbard ptarmigan (Lagopus muta hyperborea) to bacterial lipopolysaccharide (LPS) during exposure to either mild temperature (0°C) or cold snaps (acute exposure to −20°C), in constant winter darkness when birds were in energy-conserving mode, and in constant daylight in spring. The innate immune response was mostly unaffected by temperature. However, energy expenditure was below baseline when birds were immune challenged in winter, but significantly above baseline in spring. This suggests that the energetic component of the innate immune response was reduced in winter, possibly contributing to energy conservation. Immunological parameters decreased (agglutination, lysis, bacteriostatic capacity) or did not change (haptoglobin/PIT54) after the challenge, and behavioural modifications (anorexia, mass loss) were lengthy (9 days). While we did not study the mechanisms explaining these weak, or slow, responses, it is tempting to speculate they may reflect the consequences of having evolved in an environment where pathogen transmission rate is presumably low for most of the year. This is an important consideration if climate change and increased exploitation of the Arctic would alter pathogen communities at a pace outwith counter-adaption in wildlife.

Housing temperature influences exercise training adaptations in mice

Exercise training is a powerful means to combat metabolic diseases. Mice are extensively used to investigate the benefits of exercise, but mild cold stress induced by ambient housing temperatures may confound translation to humans. Thermoneutral housing is a strategy to make mice more metabolically similar to humans but its effects on exercise adaptations are unknown. Here we show that thermoneutral housing blunts exercise-induced improvements in insulin action in muscle and adipose tissue and reduces the effects of training on energy expenditure, body composition, and muscle and adipose tissue protein expressions. Thus, many reported effects of exercise training in mice are likely secondary to metabolic stress of ambient housing temperature, making it challenging to translate to humans. We conclude that adaptations to exercise training in mice critically depend upon housing temperature. Our findings underscore housing temperature as a critical parameter in the design and interpretation of murine exercise training studies.

Exercise has been shown to be an effective approach to ameliorate metabolic disease in mice housed at ambient temperatures, a condition of mild cold stress to mice. Here the authors show that molecular and metabolic adaptations to exercise are blunted when mice are housed in thermoneutral conditions.

The generation of immune-induced fever and emotional stress-induced hyperthermia in mice does not involve brown adipose tissue thermogenesis

We examined the role of brown adipose tissue (BAT) for fever and emotional stress-induced hyperthermia. Wild-type and uncoupling protein-1 (UCP-1) knockout mice were injected with lipopolysaccharide intraperitoneally or intravenously, or subjected to cage exchange, and body temperature monitored by telemetry. Both genotypes showed similar febrile responses to immune challenge and both displayed hyperthermia to emotional stress. Neither procedure resulted in the activation of BAT, such as the induction of UCP-1 or peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) mRNA, or reduced BAT weight and triglyceride content. In contrast, in mice injected with a β₃ agonist, UCP-1 and PGC-1α were strongly induced, and BAT weight and triglyceride content reduced. Both lipopolysaccharide and the β₃ agonist, and emotional stress, induced UCP-3 mRNA in skeletal muscle. A β₃ antagonist did not attenuate lipopolysaccharide-induced fever, but augmented body temperature decrease and inhibited BAT activation when mice were exposed to cold. An α₁ /α_2b antagonist or a 5HT_1A agonist, which inhibit vasoconstriction, abolished lipopolysaccharide-induced fever, but had no effect on emotional stress-induced hyperthermia. These findings demonstrate that in mice, UCP-1-mediated BAT thermogenesis does not take part in inflammation-induced fever, which is dependent on peripheral vasoconstriction, nor in stress-induced hyperthermia. However, both phenomena may involve UCP-3-mediated muscle thermogenesis.

Neurons and astrocytes of the chicken hypothalamus directly respond to lipopolysaccharide and chicken interleukin-6

In 4-5-month-old chicken, intravenous injections of bacterial lipopolysaccharide (LPS) induced a dose-dependent fever response and a pronounced increase of circulating interleukin-6 (IL-6). To assess a possible role for IL-6 in the brain of birds, a hypothalamic neuro-glial primary culture from 1-day-old chicken was established. Each well of cultured hypothalamic cells contained some 615 neurons, 1350 astrocytes, and 580 microglial cells on average. Incubation of chicken hypothalamic primary cultures with 10 or 100 µg/ml LPS induced a dose-dependent release of bioactive IL-6 into the supernatant. Populations of hypothalamic neurons (4%) and astrocytes (12%) directly responded to superfusion with buffer containing 10 µg/ml LPS with a transient increase of intracellular calcium, a sign of direct cellular activation. Stimulation of hypothalamic cultures with buffer containing 50 ng/ml chicken IL-6 induced calcium signaling in 11% of neurons and 22% of astrocytes investigated. These results demonstrate that IL-6 is produced in the periphery and in the hypothalamus in response to LPS in chicken. The observed cellular responses of hypothalamic cells to chicken IL-6 indicate that this cytokine may readily be involved in the manifestation of fever in the avian hypothalamus.

Micturition video thermography in awake, behaving mice

BACKGROUND

Our understanding of the neural circuits controlling micturition and continence is constrained by a paucity of techniques for measuring voiding in awake, behaving mice.

NEW METHOD

To facilitate progress in this area, we developed a new, non-invasive assay, micturition video thermography (MVT), using a down-facing thermal camera above mice on a filter paper floor.

RESULTS

Most C57B6/J mice void infrequently, with a stereotyped behavioral sequence, and usually in a corner. The timing of each void is indicated by the warm thermal contrast of freshly voided urine. Over the following 10-15 min, urine cools to ∼3 °C below the ambient temperature and spreads radially in the filter paper. By measuring the area of cool contrast comprising this "thermal void spot," we can derive the initially voided volume. Thermal videos also reveal mouse behaviors including a home-corner preference apart from void spots, and a stereotyped, seconds-long pause while voiding.

COMPARISON WITH EXISTING METHODS AND CONCLUSIONS

MVT is a robust, non-invasive method for measuring the timing, volume, and location of voiding. It improves on an existing technique, the void spot assay, by adding timing information, and unlike the cystometrogram preparation, MVT does not require surgical catheterization. Combining MVT with current neuroscience techniques will improve our understanding of the neural circuits that control continence, which is important for addressing the growing number of patients with urinary incontinence as the population ages.