Corticosteroid and immune responses of mice following mini-osmotic pump implantation

Repetitive orogastric gavage affects the phenotype of diet-induced obese mice

Interest in pharmacological intervention to combat metabolic syndrome and its complications is increasing as the prevalence of obesity is reaching epidemic proportions. The potential efficacy of drugs is often tested in animal models; however, the method of drug delivery is frequently overlooked and may act as a confounder due to stress. We hypothesized that long-term orogastric gavage would negatively influence the development of hepatic steatosis and the metabolic syndrome in a murine model of diet-induced obesity. C57BL/6J male mice were fed a high fat diet and were gavaged with a vehicle once or twice daily for 9 weeks. A group without orogastric gavaging served as control. A similar experiment was performed using leptin deficient ob/ob mice that were fed a standard diet for 4 weeks. Food intake was monitored, insulin resistance determined, and steatosis was assessed by histology and quantified via magnetic resonance spectroscopy. After 9 weeks, control C57BL/6J mice exhibited significantly more weight gain, insulin resistance and hepatic steatosis, compared to mice that were gavaged daily, or twice daily. This effect was likely due to decreased food consumption associated with gavage-induced stress. In contrast, the phenotype of leptin deficient ob/ob mice was not affected by orogastric gavage. Therefore, we concluded that orogastric gavage may lead to increased stress, thereby affecting food intake and the development of diet-induced obesity in a murine model. The effects of what may seem to be trivial laboratory routines, such as orogastric gavage, should be taken into account when designing animal studies for drug development.

No detrimental effect from chronic exposure to buprenorphine on corticosteroid-binding globulin and corticosensitive immune parameters

Opioid drugs reportedly regulate the immune system via their effects on the hypothalamic- pituitary-adrenal (HPA) axis. The present study was carried out to assess the effects of chronic exposure to buprenorphine on HPA axis activation, corticosteroid-binding globulin (CBG), the main glucocorticoid (GC) carrier, and the immune system. Results show that buprenorphine, delivered by osmotic pump subcutaneously in C57BL/6 male mice during a 10-day period, caused a marked decrease in total corticosterone (CORT) levels at day 1 of exposure. CORT levels then increased with maximal values observed at day 5 of exposure. After day 5, total CORT levels gradually decreased and returned to control values. No significant changes were observed in CBG protein levels and mRNA expression in the liver. Since CBG levels remained unchanged, the percentage of free CORT values in buprenorphine mice did not differ from control values. Thus, the variations observed in the amount of free CORT were related only to changes measured in total CORT. These endocrine changes did not have a significant impact on the immune parameters measured. Total CD(4)+ and CD(8)+ splenic and thymic populations were not modulated by buprenorphine. However, splenocytes from mice exposed to buprenorphine after 5 days exhibited greater proliferation upon anti-TCR monoclonal antibody stimulation than saline-exposed mice. These results indicate that buprenorphine can be safely used because it did not have significant effects on GC availability for immune corticosensitive cells.

Stress and the immune system

Stressors can positively or adversely affect immune and inflammatory responses. However, the current understanding of these effects at the cellular and molecular levels is not sufficient to allow prediction of the effects of a particular stressor on a particular immune or inflammatory function. Three complementary conceptual frameworks are presented that may prove useful in developing such an understanding. In addition, specific examples of the action of particular stress mediators on particular immune or inflammatory end points are discussed, and the relationship of these observations to the conceptual frameworks is indicated. Several of the effects discussed are relevant clinically, and the prospects for pharmacological intervention to prevent adverse effects of stressors on the immune system are discussed. Finally, some of the factors that can (sometimes unexpectedly) influence the outcome of stress-immunology studies and some of the pitfalls that continue to make this area of research controversial in some circles are discussed.

Effects of spaceflight and PEG-IL-2 on rat physiological and immunological responses

Sprague-Dawley rats were subjected to two 8-day spaceflights on the space shuttle. Rats housed in the National Aeronautics and Space Administration's animal enclosure were injected (iv or sc) with pegylated interleukin-2 (PEG-IL-2) or a placebo. We tested the hypothesis that PEG-IL-2 would ameliorate some of the effects of spaceflight. We measured body and organ weights; blood cell differentials; plasma corticosterone; colony-forming units (macrophage and granulocyte macrophage); lymphocyte mitogenic, superantigenic, and interferon-gamma responses; bone marrow cell and peritoneal macrophage cytokine secretion; and bone strength and mass. Few immunological parameters were affected by spaceflight. However, some spaceflight effects were observed in each flight. Specifically, peritoneal macrophage spontaneous secretion of tumor necrosis factor-alpha occurred in the first but not in the second flight. A significant monocytopenia and lymphocytopenia were detected in the second but not in the first flight. The second mission produced bone changes more consistent with past spaceflight investigations. PEG-IL-2 did not appear to be beneficial; however, this was mostly due to the lack of spaceflight effects. These studies reflect the difficulty in reproducing experimental models by using current space shuttle conditions.

Effects of space flight and IGF-1 on immune function

We tested the hypothesis that insulin-like growth factor-1 (IGF-1) would ameliorate space flight-induced effects on the immune system. Twelve male, Sprague-Dawley rats, surgically implanted with mini osmotic pumps, were subjected to space flight for 10 days on STS-77. Six rats received 10 mg/kg/day of IGF-1 and 6 rats received saline. Flight animals had a lymphocytopenia and granulocytosis which were reversed by IGF-1. Flight animals had significantly higher corticosterone levels than ground controls but IGF-1 did not impact this stress hormone. Therefore, the reversed granulocytosis did not correlate with serum corticosterone. Space flight and IGF-1 also combined to induce a monocytopenia that was not evident in ground control animals treated with IGF-1 or in animals subjected to space flight but given physiological saline. There was a significant increase in spleen weights in vivarium animals treated with IGF-1, however, this change did not occur in flight animals. We observed reduced agonist-induced lymph node cell proliferation by cells from flight animals compared to ground controls. The reduced proliferation was not augmented by IGF-1 treatment. There was enhanced secretion of TNF, IL-6 and NO by flight-animal peritoneal macrophages compared to vivarium controls, however, O2(-) secretion was not affected. These data suggest that IGF-1 can ameliorate some of the effects of space flight but that space flight can also impact the normal response to IGF-1. Grant Numbers: NAGW-1197, NAGW-2328.

The in vivo effects of opioid peptides on the murine immune response

We have previously reported that met-enkephalin has dual immunomodulatory properties in vitro. We have continued this investigation using an in vivo system. In this study, Alzet miniosmotic pumps were loaded with either met-enkephalin, DTLET or FK 33-824 and were surgically implanted into BAF1/J mice. Twenty-four hours after pump implantation, mice were challenged with sub-optimal, optimal or supraoptimal immunizing doses of antigen. The immune response was assessed 4 or 5 days after primary immunization. FK 33-824, a met-enkephalin analogue, had no effect on the response of mice challenged with a suboptimal antigen dose. However, FK 33-824, at a pump concentration of 10(-3) M, suppressed the response against optimal challenge doses of antigen. At a pump concentration of 10(-8) M, FK 33-824 suppressed, enhanced or had no effect on the supraoptimal antigen dose-induced immune response. The suppressive effect of FK 33-824 in mice immunized with either optimal or supraoptimal doses of antigen was blocked by naloxone. Met-enkephalin and its delta opioid receptor specific analogue, DTLET, had no effect on the immune response to optimal antigen immunization. These results indicate that FK 33-824 has in vivo immunomodulatory activity and provide evidence that opioid peptides may either upregulate or downregulate the in vivo immune response depending on the strength of the response.

The role of chemical-induced stress responses in immunosuppression: a review of quantitative associations and cause-effect relationships between chemical-induced stress responses and immunosuppression

Although there is an increasing awareness that drugs and chemicals can modulate the immune system by indirect mechanisms, few compounds have been thoroughly evaluated in this regard. Several environmentally relevant chemicals induce stresslike responses, as indicated by elevated glucocorticoid levels. Comparable glucocorticoid levels induced by physical or psychological stressors are consistently associated with suppression of one or more immunological parameters. Thus, it seems likely that stress-related neuroendocrine mechanisms are important in immunosuppression by some environmental chemicals. Distinguishing direct and indirect (stress-related) mechanisms of immunosuppression is generally possible, and this could be done as a routine part of immunotoxicity assessment. Although it is clear that glucocorticoids can contribute to such immunosuppression, it is also clear that several other neuroendocrine mediators associated with stress responses can be immunomodulatory. Thus, correlation between glucocorticoid levels and immunosuppression does not conclusively demonstrate a cause-effect relationship. Demonstrating such relationships has been difficult, but it has been done in a few cases of drug-induced thymic hypoplasia by monitoring several parameters known to be affected by glucocorticoids and by measuring the ability of a glucocorticoid antagonist (RU 486) or adrenalectomy to block changes in these parameters. A similar strategy might be useful for evaluation of the role of glucocorticoids in drug- or chemical-induced suppression of a variety of immune functions, but the effects of RU 486 on neuroendocrine feedback circuits and the possibility of consequent immunological changes must be considered when the data are interpreted. This approach could also be applied to evaluation of the roles in chemical-induced immunosuppression of other neuroendocrine mediators for which antagonists or agents that block the synthesis or release of the mediator are available. However, it is likely that a comprehensive (and perhaps predictive) understanding of the relationship between chemically induced stress responses and immunosuppression will require more detailed and quantitative elucidation of the mechanisms and regulation of neuroendocrine-immune interactions.