The role of microglia in 67NR mammary tumor-induced suppression of brain responses to immune challenges in female mice

It is poorly understood how solid peripheral tumors affect brain neuroimmune responses despite the various brain-mediated side effects and higher rates of infection reported in cancer patients. We hypothesized that chronic low-grade peripheral tumor-induced inflammation conditions microglia to drive suppression of neuroinflammatory responses to a subsequent peripheral immune challenge. Here, Balb/c murine mammary tumors attenuated the microglial inflammatory gene expression responses to lipopolysaccharide (LPS) and live Escherichia coli (E. coli) challenges and the fatigue response to an E. coli infection. In contrast, the inflammatory gene expression in response to LPS or a toll-like receptor 2 agonist of Percoll-enriched primary microglia cultures was comparable between tumor-bearing and -free mice, as were the neuroinflammatory and sickness behavioral responses to an intracerebroventricular interleukin (IL)-1β injection. These data led to the hypothesis that Balb/c mammary tumors blunt the neuroinflammatory responses to an immune challenge via a mechanism involving tumor suppression of the peripheral humoral response. Balb/c mammary tumors modestly attenuated select circulating cytokine responses to LPS and E. coli challenges. Further, a second mammary tumor/mouse strain model (E0771 tumors in C57Bl/6 mice) displayed mildly elevated inflammatory responses to an immune challenge. Taken together, these data indicate that tumor-induced suppression of neuroinflammation and sickness behaviors may be driven by a blunted microglial phenotype, partly because of an attenuated peripheral signal to the brain, which may contribute to infection responses and behavioral side effects reported in cancer patients. Finally, these neuroimmune effects likely vary based on tumor type and/or host immune phenotype.

Dimethyl Fumarate Alleviates NLRP3 Inflammasome Activation in Microglia and Sickness Behavior in LPS-Challenged Mice

NLRP3 inflammasome activation contributes to several pathogenic conditions, including lipopolysaccharide (LPS)-induced sickness behavior characterized by reduced mobility and depressive behaviors. Dimethyl fumarate (DMF) is an immunomodulatory and anti-oxidative molecule commonly used for the symptomatic treatment of multiple sclerosis and psoriasis. In this study, we investigated the potential use of DMF against microglial NLRP3 inflammasome activation both in vitro and in vivo. For in vitro studies, LPS- and ATP-stimulated N9 microglial cells were used to induce NLRP3 inflammasome activation. DMF’s effects on inflammasome markers, pyroptotic cell death, ROS formation, and Nrf2/NF-κB pathways were assessed. For in vivo studies, 12–14 weeks-old male BALB/c mice were treated with LPS, DMF + LPS and ML385 + DMF + LPS. Behavioral tests including open field, forced swim test, and tail suspension test were carried out to see changes in lipopolysaccharide-induced sickness behavior. Furthermore, NLRP3 and Caspase-1 expression in isolated microglia were determined by immunostaining. Here we demonstrated that DMF ameliorated LPS and ATP-induced NLRP3 inflammasome activation by reducing IL-1β, IL-18, caspase-1, and NLRP3 levels, reactive oxygen species formation and damage, and inhibiting pyroptotic cell death in N9 murine microglia via Nrf2/NF-κB pathways. DMF also improved LPS-induced sickness behavior in male mice and decreased caspase-1/NLRP3 levels via Nrf2 activation. Additionally, we showed that DMF pretreatment decreased miR-146a and miR-155 both in vivo and in vitro. Our results proved the effectiveness of DMF on the amelioration of microglial NLRP3 inflammasome activation. We anticipate that this study will provide the foundation consideration for further studies aiming to suppress NLRP3 inflammasome activation associated with in many diseases and a better understanding of its underlying mechanisms.

Metabolomics: Impact of Comorbidities and Inflammation on Sickness Behaviors for Individuals with Chronic Wounds

Significance: Approximately 6.5 million people in the United States suffer from chronic wounds. The chronic wound population is typically older and is characterized by a number of comorbidities associated with inflammation. In addition to experiencing wound-related pain, individuals with chronic wounds commonly experience multiple concurrent psychoneurological symptoms such as fatigue and depression, which delay wound healing. However, these distressing symptoms have been relatively overlooked in this population, although their adverse effects on morbidity are well established in other chronic disease populations. Recent Advances: Inflammation is involved in multiple pathways, which activate brain endothelial and innate immune cells that release proinflammatory cytokines, which produce multiple symptoms known as sickness behaviors. Inflammation-based activation of the kynurenine (KYN) pathway and its metabolites is a mechanism associated with chronic illnesses. Critical Issues: Although putative humoral and neuronal routes have been identified, the specific metabolic variations involved in sickness behaviors in chronic wound patients remain unclear. To improve health outcomes in the chronic wound population, clinicians need to have better understanding of the mechanisms underlying sickness behaviors to provide appropriate treatments. Future Directions: This article presents a synthesis of studies investigating associations between inflammation, metabolic pathways, and sickness behaviors in multiple chronic diseases. The presentation of a theoretical framework proposes a mechanism underlying sickness behaviors in the chronic wound population. By mediating the immune system response, dysregulated metabolites in the KYN pathway may play an important role in sickness behaviors in chronic inflammatory conditions. This framework may guide researchers in developing new treatments to reduce the disease burden in the chronic wound population.

Immune-Endocrine Links to Gregariousness in Wild House Mice

Social interactions are critically important for survival and impact overall-health, but also impose costs on animals, such as exposure to contagious agents. The immune system can play a critical role in modulating social behavior when animals are sick, as has been demonstrated within the context of “sickness behaviors.” Can immune molecules affect or be affected by social interactions even when animals are not sick, therefore serving a role in mediating pathogen exposure? We tested whether markers of immune function in both the blood and the brain are associated with gregariousness, quantified as number of animals interacted with per day. To do this, we used remote tracking of social interactions of a wild population of house mice (Mus musculus domesticus) to categorize animals in terms of gregariousness. Blood, hair, brain and other tissue samples from animals with extreme gregariousness phenotypes were collected. We then tested whether the levels of three important cytokines (TNF-α, IFN-γ and IL-1β) in the serum, cortex and hypothalamus of these animals could be explained by the gregariousness phenotype and/or sex of the mice. Using the hair as a long-term quantification of steroid hormones, we also tested whether corticosterone, progesterone and testosterone differed by social phenotype. We found main effects of gregariousness and sex on the serum levels of TNF-α, but not on IFN-γ or IL-1β. Brain gene expression levels were not different between phenotypes. All hair steroids tended to be elevated in animals of high gregariousness phenotype, independent of sex. In sum, elements of the immune system may be associated with gregariousness, even outside of major disease events. These results extend our knowledge of the role that immune signals have in contributing to the regulation of social behaviors outside periods of illness.

Protective effect of Panax ginseng in cisplatin-induced cachexia in rats

AIM

This study investigated the protective effect of a standardized extract of Panax ginseng on multiple cisplatin-induced 'sickness behaviors' (model of cancer-induced cachexia) in rats.

MATERIALS & METHODS

Cisplatin was administered twice weekly (1-2 mg/kg, intraperitoneal) for 5 consecutive weeks. Panax ginseng extract (0, 25 and 50 mg/kg, intragastric) was administered daily over the 5-week period of cisplatin exposure. Malaise, bodyweight and temperature, pain sensitivity, and endurance running were recorded at baseline and at 5 weekly intervals.

RESULTS

Treatment with cisplatin produced severe signs of malaise, marked loss of bodyweight, hypothermia, hyperalgesia and reduction in running time. Treatment with Panax ginseng extract completely prevented all cisplatin-induced alterations.

CONCLUSION

These data indicate that treatment with Panax ginseng extract exerted a protective effect in a rat model of cachexia and suggest that Panax ginseng extract may be a therapeutic promising tool for supportive care in oncology.

Sleep disturbance, cytokines, and fatigue in women with ovarian cancer

Pro-inflammatory cytokines, such as interleukin-6 (IL-6), have been implicated in the underlying processes contributing to sleep regulation and fatigue. Despite evidence for sleep difficulties, fatigue, and elevations in IL-6 among women with ovarian cancer, the association between these symptoms and IL-6 has not been investigated. To address this knowledge gap, we examined relationships between sleep disturbance, fatigue, and plasma IL-6 in 136 women with ovarian cancer prior to surgery. These relationships were also examined in 63 of these women who were disease-free and not receiving chemotherapy one year post-diagnosis. At both time-points, higher levels of IL-6 were significantly associated with sleep disturbances (p<0.05), controlling for potentially confounding biological and psychosocial covariates. Higher IL-6 was significantly associated with fatigue prior to surgery (p<0.05); however, when sleep disturbance was included in the model, the relationship was no longer significant. IL-6 was not significantly associated with fatigue at one year. Changes in sleep over time were significantly associated with percent change in IL-6 from pre-surgery to one year, adjusting for covariates (p<0.05). These findings support a direct association of IL-6 with sleep disturbances in this population, whereas the relationship between IL-6 and fatigue prior to surgery may be mediated by poor sleep. As this study is the first to examine cytokine contributions to sleep and fatigue in ovarian cancer, further research is warranted to clarify the role of biological correlates of sleep and fatigue in this population.

Fatigue and herpesvirus latency in women newly diagnosed with breast cancer

Fatigue is a notable clinical problem in cancer survivors, and understanding its pathophysiology is important. The current study sought to determine biomarkers of fatigue that exist before cancer treatment. Relationships between the expression of latent Epstein-Barr virus (EBV) and cytomegalovirus (CMV) and fatigue were examined in 158 women newly diagnosed with breast cancer or awaiting a positive diagnostic result. Higher CMV antibody titers, but not EBV antibody titers, were associated with a greater likelihood of being fatigued. Associations between fatigue and higher CMV antibody titers remained after controlling for alcohol use, smoking, comorbidities, depressive symptoms, age, BMI, cancer stage, and sleep problems. More sleep problems and higher levels of depressive symptoms were also associated with a greater likelihood of being fatigued. CMV antibody titers, but not EBV antibody titers, were associated with higher levels of C-reactive protein (CRP), but CRP was not associated with fatigue. When the cellular immune system is compromised, reactivation of latent herpesviruses may fuel chronic inflammatory responses. Prior work has suggested that fatigue may be related to inflammation and its associated sickness behaviors; accordingly, our findings may be tapping into this same physiological substrate.

Anti-inflammatory agents attenuate the passive responses of guinea pig pups: evidence for stress-induced sickness behavior during maternal separation

A previous study found that intracerebroventricular (ICV) infusion of 25 microg of alpha-MSH reduced the passive responses (crouched stance, eye-closing, piloerection) of guinea pig pups during a 3-h isolation in a novel environment. Because alpha-MSH has broad anti-inflammatory properties, the results suggested that proinflammatory factors play a role in mediating the behavior of isolated infants. The present study further investigated this possibility. In Experiment 1, injection of lipopolysacchride (LPS) increased the number of 60-s intervals in which pups expressed the same three responses during a 1-h test, and ICV infusion of alpha-MSH significantly reduced the effect of LPS on crouching and piloerection. In Experiment 2, the prostaglandin synthesis inhibitor indomethacin (10 mg/kg) reduced the number of 60-s intervals in which pups exhibited both crouching and the full suite of passive responses during a 3-h isolation in a novel environment. Together these results provide further support for the hypothesis that the passive behaviors exhibited during prolonged isolation are "stress-induced sickness behaviors" mediated by proinflammatory factors.

Pineal-dependent and -independent effects of photoperiod on immune function in Siberian hamsters (Phodopus sungorus)

Siberian hamsters (Phodopus sungorus) exhibit reproductive and immunological responses to photoperiod. Short (<10-h light/day) days induce gonadal atrophy, increase leukocyte concentrations, and attenuate thermoregulatory and behavioral responses to infection. Whereas hamster reproductive responses to photoperiod are dependent on pineal melatonin secretion, the role of the pineal in short-day induced changes in immune function is not fully understood. To examine this, adult hamsters were pinealectomized (PINx) or sham-PINx, and transferred to short days (9-h light/day; SD) or kept in their natal long-day (15-h light/day; LD) photoperiod. Intact and PINx hamsters housed in LD maintained large testes over the next 12 weeks; sham-PINx hamsters exhibited gonadal regression in SD, and PINx abolished this effect. Among pineal-intact hamsters, blood samples revealed increases in leukocyte, lymphocyte, CD62L+ lymphocyte, and T cell counts in SD relative to LD; PINx did not affect leukocyte numbers in LD hamsters, but abolished the SD increase in these measures. Hamsters were then treated with bacterial lipopolysaccharide (LPS), which induced thermoregulatory (fever), behavioral (anorexia, reductions in nest building), and somatic (weight loss) sickness responses in all groups. Among pineal-intact hamsters, febrile and behavioral responses to LPS were attenuated in SD relative to LD. PINx did not affect sickness responses to LPS in LD hamsters, but abolished the ameliorating effects of SD on behavioral responses to LPS. Surprisingly, PINx failed to abolish the effect of SD on fever. In common with the reproductive system, PINx induces the LD phenotype in most aspects of the immune system. The pineal gland is required for photoperiodic regulation of circulating leukocytes and neural-immune interactions that mediate select aspects of sickness behaviors.