Social isolation stress enhanced liver metastasis of murine colon 26-L5 carcinoma cells by suppressing immune responses in mice

Augmentation and proliferation of T lymphocytes and Th-1 cytokines by Withania somnifera in stressed mice

Stress has been associated with reports of both greater severity and prolongation of diseases in patients with the infectious origin as well as other immune-mediated diseases. Withania somnifera, an Indian medicinal plant used widely in the treatment of many clinical conditions in India, was investigated for its anti-stress properties using BALB/c mice subjected to chronic stress. The study aimed to investigate chronic stress-induced alterations on Th1 lymphocyte subset distribution and corresponding cytokine secretion patterns. Oral administration of chemically standardized and identified aqueous fraction of W. somnifera root (WS) at the graded doses of 25, 50, 100 and 200 mg/kg p.o. caused significant increase in the stress-induced depleted T-cell population and increased the expression of Th1 cytokines in chronically stressed mice.

Optimization of chronic stress paradigms using anxiety- and depression-like behavioral parameters

Chronic stress is a risk factor for psychiatric illnesses, such as anxiety and depression disorders. To understand the underlying mechanism regarding how chronic stress triggers such psychiatric dysfunctions, restraint-based chronic stress models have been attempted in the past. However, total durations of repeated restraint stress and the evaluation time points used after the last restraint application vary from experiment to experiment. One reason for these methodological heterogeneities is related to considerable ambiguity concerning the definition of chronic stress, particularly in animal models. In the present study, we used behavioral traits, anxiety and depression, as stress-assessment parameters that meet operationally useful requirements for the definition of the chronic stress state. We demonstrate that restraint treatment for 2 or 8 hr daily for 14 days is enough to produce anxiety- and depression-like behaviors, whereas a 2 hr-10 days restraint was marginally effective. cDNA microarray analysis identified 34 genes in the hippocampus and 72 genes in the amygdala with expression levels that were up- or down-regulated by >2.0-fold. Among the wide range of genes identified in this analysis, genes required for energy metabolism, signal transduction, transcription, synaptic plasticity, and remodeling of the brain architecture were notable. Our results suggest that the psychiatric criteria of anxiety and depression can be used as chronic stress-assessment parameters and that a restraint stress paradigm consisting of restraint treatment for 2 or 8 hr daily for 14 days could be used as a prototype paradigm for chronic stress studies.

Effect of Triphala on oxidative stress and on cell-mediated immune response against noise stress in rats

Stress is one of the basic factors in the etiology of number of diseases. The present study was aimed to investigate the effect of Triphala (Terminalia chebula, Terminalia belerica and Emblica officinalis) on noise-stress induced alterations in the antioxidant status and on the cell-mediated immune response in Wistar strain male albino rats. Noise-stress employed in this study was 100 dB for 4 h/d/15 days and Triphala was used at a dose of 1 g/kg/b.w/48 days. Eight different groups of rats namely, non-immunized: control, Triphala, noise-stress, Triphala with noise-stress, and corresponding immunized groups were used. Sheep red blood cells (5 x 10(9) cells/ml) were used to immunize the animals. Biochemical indicators of oxidative stress namely lipid peroxidation, antioxidants superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), ascorbic acid in plasma and tissues (thymus and spleen) and SOD, GPx and corticosterone level in plasma were estimated. Cell-mediated immune response namely foot pad thickness (FPT) and leukocyte migration inhibition (LMI) test were performed only in immunized groups. Results showed that noise-stress significantly increased the lipid peroxidation and corticosterone level with concomitant depletion of antioxidants in plasma and tissues of both non-immunized and immunized rats. Noise-stress significantly suppressed the cell-mediated immune response by decreased FPT with an enhanced LMI test. The supplementation with Triphala prevents the noise-stress induced changes in the antioxidant as well as cell-mediated immune response in rats. This study concludes that Triphala restores the noise-stress induced changes may be due to its antioxidant properties.

Does stress exacerbate liver diseases?

Although anecdotal comments on detrimental effects of psychosocial stress on liver diseases can be found even in the early literature, only recently has scientific evidence been reported. The present article reviewed such evidence to demonstrate how stress exacerbates liver diseases. A search of the literature from the last two decades was performed using MEDLINE by pairing 'psychological stress' with 'liver' or 'hepatitis.' Additional research was conducted by screening the bibliographies of articles retrieved in the MEDLINE search. The search results showed that the principal effectors of the activated hypothalamic-pituitary-adrenal (HPA) axis, glucocorticoids, can exert a facilitative effect on the hepatic inflammatory response and even increase the risk of developing hepatocellular carcinoma. For certain liver diseases, defective HPA axis activation, which probably contributed to the exacerbation of the liver disease, has been reported. The efferent sympathetic/adrenomedullary system mainly contributes to the stress-induced exacerbation of liver diseases via its neurotransmitters, the catecholamines. In contrast, the efferent parasympathetic nervous system elicits an inhibitory effect on the development of hepatic inflammation. In conclusion, the pathophysiological interaction between stress and the liver appears to be regulated by the complex, dynamic networks of both the endocrine and autonomic nervous systems, which implies a further need for basic research into the involved mechanisms and for clinical evidence to apply psychosocial support to patients with chronic liver diseases.

Effects of social isolation stress on immune response and survival time of mouse with liver cancer

AIM: To investigate the effects of isolation stress on mouse with liver cancer and possible associated mechanisms.

METHODS: Transplantable murine hepatoma22 (H22) model was used to evaluate the effects of social isolation stress on murine liver cancer. Mice were immunized with sheep red blood cell (SRBC) and intraperitoneally inoculated with H22 cell, then divided into two groups, one reared individually as group (I) and the other reared in groups as group (G). Titer of antibody to SRBC and interleukin 2 (IL-2) in serum was monitored. The survival time of mouse with liver cancer was observed.

RESULTS: The titer of antibody to SRBC in group (G) was 1:24.5 and that in group (I) was 1:11.2. There was a significant difference between these two groups (t = 2.60, P = 0.02). A significant difference in IL-2 concentration was observed between group (G) (39.6 ng/L) and group (I) (47.1 ng/L, t = 2.14, P = 0.046). The survival time in group (G) (16.5 d) was markedly longer than that in group (I) (13.2 d, t = 3.46, P = 0.002).

CONCLUSION: Our study suggests that survival time of the mouse bearing H22 tumor is affected by the social isolation stress and the associated mechanism may be the immunological changes under the social isolation stress.

Role of melatonin in reducing water avoidance stress-induced degeneration of the liver

Melatonin, a pineal secretory product, is a potent scavenger of a variety of free radicals. We investigated the role of melatonin on water avoidance stress (WAS)-induced degenerations of the liver parenchyme. Wistar albino rats were exposed to acute WAS (aWAS group) or chronic WAS (cWAS group). Before exposing animals to acute (aWAS + mel group) or chronic WAS (cWAS + mel group), 10 mg/kg melatonin was injected i.p. The liver samples were investigated under light and transmission electron microscope. Malondialdehyde (MDA) and glutathione (GSH) levels were also determined. Prominent vascular congestion and dilated sinusoids, activated Kupffer cells with prominent morphology, dilated granular endoplasmic reticulum membranes, and focal picnotic nuclei were observed in the aWAS group; these morphological changes were severe in the cWAS group. MDA level was increased and GSH level was decreased significantly in the cWAS group. The morphology of liver parenchme in both the aWAS + mel and the cWAS + mel group showed that melatonin significantly reduced the degeneration in liver; besides, a significant decrease in MDA and an increase in GSH levels were observed in the cWAS + mel group. Based on the results, melatonin treatment significantly prevented WAS-induced morphological and biochemical changes in liver parenchyma.

Stress, depression, the immune system, and cancer

The links between the psychological and physiological features of cancer risk and progression have been studied through psychoneuroimmunology. The persistent activation of the hypothalamic-pituitary-adrenal (HPA) axis in the chronic stress response and in depression probably impairs the immune response and contributes to the development and progression of some types of cancer. Here, we overview the evidence that various cellular and molecular immunological factors are compromised in chronic stress and depression and discuss the clinical implications of these factors in the initiation and progression of cancer. The consecutive stages of the multistep immune reactions are either inhibited or enhanced as a result of previous or parallel stress experiences, depending on the type and intensity of the stressor and on the animal species, strain, sex, or age. In general, both stressors and depression are associated with the decreased cytotoxic T-cell and natural-killer-cell activities that affect processes such as immune surveillance of tumours, and with the events that modulate development and accumulation of somatic mutations and genomic instability. A better understanding of the bidirectional communication between the neuroendocrine and immune systems could contribute to new clinical and treatment strategies.

Stress causes a further decrease in immunity to herpes simplex virus-1 in immunocompromised hosts

Physical or psychological stress can modulate immune responses in normal subjects. The effects of stress on immunity in immunocompromised hosts, however, have not been extensively investigated. Here we assess relationships among footshock stress (FS), infection with herpes simplex virus-1 (HSV-1), and immunosuppression by cyclophosphamide (CY) during the active immune response to virus in BALB/c mice. Without FS, CY significantly decreased survival and body weight gain, splenic leukocyte numbers, in vivo serum cytokine level and in vitro splenocyte cytokine production during HSV-1 infection. FS alone also significantly inhibited cell mediated anti-viral responses to HSV-1. However, FS in combination with certain CY doses led to a further significant decrease in host responses compared to either CY or FS treatment alone, including decreased survival rate, increased weight loss, lowered leukocyte numbers, reduced cytokine production in vivo and in vitro, and decreased numbers of cytokine-producing cells (IL-12 and IFNgamma). In contrast, CY, but not FS, significantly reduced in vivo anti-HSV-1 antibody secretion. These data support the hypothesis that stress can further reduce host immune responses in immunocompromised individuals. Thus, stress levels of patients should be taken into consideration prior to clinical treatment with immunosuppressants.

24-hour pattern of circulating prolactin and growth hormone levels and submaxillary lymph node immune responses in growing male rats subjected to social isolation

To assess the effect of social isolation of growing rats on 24-h rhythmicity of circulating prolactin and growth hormone (GH) levels and submaxillary lymph node immune responses, male Wistar rats were either individually caged or kept in groups (4-5 animals per cage) for 30 d starting on d 35 of life. Plasma prolactin and GH levels, and submaxillary lymph node lymphocyte subset populations, interferon (IFN)-gamma release and mitogenic responses to concanavalin A (Con A) and lipopolysaccharide (LPS) were determined at six time intervals during the 24 h span. Social isolation brought about changes in mean values and 24-h pattern of plasma prolactin and GH levels and lymph node immune responses. After isolation, prolactin and GH mean values decreased, and lymph node T, B, non T-non B, CD8+, and CD4+-CD8+ cells augmented, whereas lymph node CD4+/CD8+ ratio, IFN-gamma release and mitogenic responses decreased. Social isolation resulted in disruption of 24 h rhythmicity of every immune parameter tested. CD4+/CD8+ ratio, IFN-gamma release and Concanavalin A (Con A) and lipopolysaccharide (LPS) responses correlated significantly with plasma prolactin or GH levels while T/B ratio correlated with plasma prolactin levels only. B, non T-non B, and CD4+-CD8+ cells correlated negatively with plasma prolactin. Modifications in mean value and 24-h rhythmicity of plasma prolactin and GH levels are presumably involved in the effect of social isolation on immune responsiveness.

Immune changes during acute cold/restraint stress-induced inhibition of host resistance to Listeria

Experiments were conducted to delineate the cellular changes modulated by acute cold/restraint stress (ACRS), a physical and psychological stressor, in response to a Listeria monocytogenes(LM) infection. In addition to wild type (WT) BALB/c mice, CD4-deficient (CD4-/-) BALB/c mice, which have no effective adaptive immunity, were used to determine the involvement of adaptive versus innate immunity. ACRS-induced suppression of host resistance to LM was not observed in CD4-/- mice, suggesting the involvement of CD4+T cells in the acute cold/restraint stress (ACRS)-induced inhibition. The in vivo splenic leukocyte phenotypes and activities of WT BALB/c mice after infection and in vitro lymphocyte responses to heat-killed LM (HKLM) also were examined. There were no significant differences in the numbers of splenic T and B lymphocytes, natural killer cells, macrophages, or neutrophils between nonstressed and ACRS-treated WT mice. However, higher levels of activated T cells and non-T lymphocytes were observed in the ACRS-treated mice; beta-adrenergic receptor (beta-ADR) antagonists (propranolol and atenolol) eliminated these elevated levels of activation, as well as the ACRS-induced suppression of host resistance. ACRS and control mice also had equivalent activation of macrophages. With in vitro HKLM stimulation, splenocytes from ACRS-treated mice produced significantly higher levels of IFNgamma and slightly higher levels of IL-6 in comparison with the nonstressed mice, although equivalent levels of lymphocyte proliferation were obtained. Additionally, ACRS-treated mice showed comparable elevation of serum nitric oxide after infection, indicating macrophage bactericidal activity similar to nonstressed mice. Thus, it appears that ACRS inhibits host resistance through regulatory CD4+ T cells and/or effector cell functions downstream of CD4+ T cell activation, as well as through beta-ADR signaling, in that blockage of these receptors appears to aid host defenses by means other than elevation of helper T cell activity. Because CD4 T cell deficiency and beta-ADR blockage produced equivalent effects, beta-ADR+ CD4+ T cells may have a negative role on host defenses after ACRS.

The effect of emotional stress on the primary humoral immunity of rats

The effect of exposure to emotional stress on humoral immune function after injection with ovalbumin, a novel antigen, was studied in adult male Wistar rats. Emotional stress was induced by randomly giving empty water bottles to rats trained to drink water at set times. The results showed that emotional stress induced the decrease in spleen weight and specific immunoglobulin G antibody level to ovalbumin, and increased levels of epinephrine, norepinephrine and corticosterone. A decrease of antibody levels correlated negatively with an increase in plasma norepinephrine levels. These findings suggest that emotional stress can modulate immune function, and that sympathetic nervous system may be involved in this immunomodulation.

Individual housing induces altered immuno-endocrine responses to psychological stress in male mice

Social isolation and lack of social support have deleterious effects on health, thus being regarded as one of the most relevant causes of diseases in human and other mammalian species. However, only few are the studies aimed at evaluating the psychoneuroimmunological functions of individually housed subjects. The present study was designed to understand how the behavior and the physiology of male house mice might be affected by individual housing. We first analyzed whether individual housing of different duration (1-42 days) would result in immuno-endocrine dysfunction (experiment 1). Then we investigated whether housing conditions would affect the reaction to an acute mild psychological stress (experiments 2 and 3). There were three main findings: first, individually housing mice for increasing time periods did not induce any major immuno-endocrine effects compared to a stable sibling group housing. Therefore, prolonged isolation does not seem to dramatically impair mice immuno-endocrine functions. Second, when exposed to a mild acute stress, i.e. forced exposure to a novel environment, isolated mice showed higher basal corticosterone and lower type 1 (IL-2) and type 2 (IL-4) cytokines as well as splenocytes proliferation compared to group housed male mice. Finally, when faced with a free choice between a novel environment and their home cage, individually housed mice showed reduced neophobic responses resulting in increased exploration of the novel environment, thus suggesting a low anxiety profile. Altogether, our findings suggest that individual housing in itself does not change immunocompetence and corticosterone level, but does affect reactivity to a stressor. In fact, individually housed mice showed high behavioral arousal, as well as altered immuno-endocrine parameters, when challenged with mild psychological novelty-stress.

Potential ability of morphine to inhibit the adhesion, invasion and metastasis of metastatic colon 26-L5 carcinoma cells

Morphine is frequently used for cancer patient's terminal medical care to relieve cancer pain. In the present study, we examined the inhibitory effect of morphine on experimental lung metastasis and invasion of colon 26-L5 cells. Morphine was found to significantly reduce the number of tumor colonies and the weight of the tumor-containing lung. Morphine inhibited the adhesion and migration of colon 26-L5 cells to extracellular matrix components and invasion into reconstituted basement membrane Matrigel, without affecting the cell proliferation in vitro. Notably, naloxone, an antagonist of morphine, abrogated morphine-induced inhibition of tumor cell adhesion, but did not affect the inhibitory effect on the production of matrix metalloproteinases (MMPs) from tumor cells. These results suggest that morphine inhibited the adhesive and invasive properties of tumor cells by different inhibitory mechanisms that involved the mediation of an opioid receptor.

Seasonal dependency of the effects of rotational stress and cyclophosphamide in mice bearing lewis lung carcinoma

The antitumor effects of cyclophosphamide were previously shown to be markedly reduced by the application of restraint stress in mice bearing Lewis lung carcinoma. The aim of this work was to determine the effects of rotational stress on the antitumor action of cyclophosphamide in the same animal-tumor system. Since the effects of rotational stress on metastasis were found to display a circannual rhythm, with a maximum in summer and a minimum in winter, the experiments were performed in June and February. Groups of 10 young female mice were kept under low stress housing conditions, with a 12-12 h light/dark cycle, starting 2 weeks before and during each experiment. Rotational stress caused an increase of metastasis volume to 361% of nonstressed controls in June and a decrease to 32.4% in February. In both seasons, the treatment with cyclophosphamide (240 mg/kg/day for 6 days) caused the absence of detectable metastasis at sacrifice in all mice; its combination with rotational stress caused the presence of metastases in similar proportions (6/10 and 10/10 for June vs February, respectively). The survival time of control mice was approximately twice as long in February as in June and was not appreciably modified by rotational stress; cyclophosphamide was similarly active in both seasons (4/10 and 6/10 long-term survivors for June vs February, respectively), and the number of long-term survivors was reduced to 0/10 in both seasons by rotational stress. The survival of the different experimental groups inversely correlated with the number of metastases as determined at sacrifice at the end of treatment and also with the number of CD3(+) and CD4(+) splenic T-lymphocyte subsets. These results do not appear to depend on the disruption of the circadian organization of the mice by rotational stress or by seasonal differences in cyclophosphamide activity. On the other hand, they can be interpreted assuming that cyclophosphamide reduces tumor metastasis and that T-lymphocyte-mediated immune responses of the host, amenable to modulation by stress and displaying seasonal differences uncoupled from circadian rhythms, further contribute to the tumor inhibitory effects of the drug. The observed differences in tumor metastasis caused by rotational stress and survival time in two different seasons, and the marked attenuation of cyclophosphamide antitumor action by rotational stress, appear of interest for their experimental and clinical implications.

Psychosocial stress augments tumor development through beta-adrenergic activation in mice

Housing conditions affect behavioral and biological responses of animals. We investigated the effect of same-sex-grouped (G), crowded (GC) and isolated (I) conditions on the growth of B16 melanoma or Meth A fibrosarcoma implanted in the footpad of syngeneic male C57BL / 6 or BALB / c mice. Differential housing altered host resistance to tumor growth. The host responses to stress were reflected in thymic atrophy, which was lowest in the G mice, highest in the GC mice and intermediate in the I mice. The GC condition was a more stressful social environment than the I condition in both male C57BL / 6 and BALB / c mice. Reflecting the extent of psychosocial stress, tumor growth was augmented in the order of GC, I and G condition, and a negative mass correlation between tumor and thymus was observed, thus clearly indicating that the host resistance to tumors was attenuated by psychosocial stress. Furthermore, the stress-enhanced tumor growth and thymus atrophy were completely abrogated by the oral administration of the non-selective beta-adrenergic antagonist, propranolol. On the contrary, the chronic administration of corticosterone significantly induced the atrophy of thymus and spleen without affecting tumor growth. These results suggest an interrelationship among psychosocial stress, tumor growth and beta-adrenergic activation.

Morphine analgesia suppresses tumor growth and metastasis in a mouse model of cancer pain produced by orthotopic tumor inoculation

The present study was conducted to clarify whether relief from cancer pain by morphine would suppress tumor growth and metastasis. When given orthotopic inoculation of B16-BL6 melanoma cells into the hind paw, C57BL/6 mice showed moderate and marked hyperalgesia on days 7-10 and from day 14 post-inoculation, respectively. The volume of inoculated hind paw was increased exponentially as a function of time from day 8 post-inoculation, a phenomena being due to melanoma growth. Lung metastasis was apparent after day 12 post-inoculation. On day 16 post-inoculation, the hyperalgesia was completely inhibited by subcutaneous injection of morphine hydrochloride (5 and 10 mg/kg). The tumor growth and lung metastasis were markedly inhibited by repeated administration of morphine (5 and 10 mg/kg daily for 6 days) and also by the neurectomy of sciatic nerve innervating the inoculated region. The results suggest that relief from cancer pain by morphine inhibits tumor growth and metastasis.

Effects of separation and separation with supplemental stroking in BALb/c infant mice

The purpose of this pilot study was to investigate selected stress, immune, and growth consequences of maternal separation and separation with supplemental stroking in neonatal BALB/c infant mice and their dams. Three groups of 5 litters each (7 pups per litter) were studied. Control litters were undisturbed. Separated litters experienced 3 h of daily maternal deprivation on postnatal days 6 to 10. Separated/stroked litters were separated also, but for 2 h, which was then followed by 1 h of stroking with a wet paintbrush to simulate maternal tactile stimulation. After the experimental period, all animals were returned to the nest and left undisturbed for 5 additional days. One pup from each litter was sacrificed on postnatal days 6, 8, 10, and 15. Spleens and thymuses were removed, weighed, and homogenized for cell sorting, cytokine analysis, and proliferation studies. Blood was drawn for corticosterone levels and hematocrit. Hematocrits and thymus weights were lower in separated mice, suggesting decreased growth and protein synthesis. Separated/stroked pups had increased splenic proliferation responses to conconavalin A and phytohemagglutinin at day 15. Separated dams' proliferative response to ConA was lower than control dams at day 15. Day 15 decreases in thymic CD8 cells occurred in pups, with an increased thymic H:S ratio in separated pups. CD90 cells were higher at day 15 in separated/stroked pups as were CD25s at day 10 in spleen and thymus. However, gene expression of cytokines was not measurable in spleen and thymic cells, with the exception of gamma-IFN in separated/stroked animals. Pooled organ homogenates were used in this preliminary work, and further studies are needed to more precisely analyze the stress, immune, and growth effects of these interventions.

"Host factors"--evolution of concepts of individual sensitivity and susceptibility

The detection of a rapidly increasing number of genetic polymorphisms in xenogen-metabolizing enzymes, of hereditary as well as acquired individual differences in DNA repair, and of the close associations between central nervous structures, the endocrine, and the immune system provides a challenge to develop an evidence-based, comprehensive model of susceptibility. Reviewing the evolution of respective approaches from 400 B.C. until today, this article proposes a conceptional framework that integrates the diverse, and sometimes puzzling contributions from all different fields of life science.

Alterations induced by chronic stress in lymphocyte subsets of blood and primary and secondary immune organs of mice

BACKGROUND

The immune system is particularly sensitive to stress. Although acute stress generally has positive effects, chronic stress typically provokes immunosuppression. The elucidation of the mechanisms involved in immunosuppression are of interest for the design of therapeutic approaches to avoid the appearance of stress disorders. This study aimed to investigate chronic stress-induced alterations on lymphocyte subset distribution and percentages. The experiments were performed with C57BL/6 mice subjected to chronic immobilization stress.

RESULTS

Stress caused a marked increase in apoptosis inside the thymus, and a reduction in the total number of thymocytes. Furthermore, the proportion of immature thymocytes declined significantly suggesting that the increased apoptosis mainly affected cells of immature phenotype. In blood, the total number of lymphocytes diminished but not all lymphocyte populations showed the same tendency: while the relative proportion of B cells declined slightly, the relative proportion of circulating CD3+ cells, and particularly some T cell subsets showing an immature phenotype (CD3+PNA+), increased under stress. The spleen and lymph nodes show a marked reduction in cellularity, but the relative proportion of T cells increased, while no change or only a slight reduction was observed in the relative proportion of B cells. Similarly, the relative proportion of T cells increased in bone marrow.

CONCLUSIONS

Detailed data on the alterations of lymphoid cell subsets occurring under immobilization stress, both in the bloodstream and in different lymphoid tissues, are obtained. In general, T cells are more affected than B cells and, in particular, a marked increase in the percentage of a subset of circulating PNA+CD3+ T cells is observed.

Social isolation stress impairs the resistance of mice to experimental liver metastasis of murine colon 26-L5 carcinoma cells

Our previous study has demonstrated that the exposure of male BALB/c mice to social isolation stress caused a suppressed immune response and enhanced liver metastasis of colon 26-L5 carcinoma cells. To more precisely understand the influence of psychosocial factors on the metastatic process, here we have investigated the effect of social isolation stress on the vulnerability of the host to develop liver metastasis of colon 26-L5 cells, including the time span and incidence of metastatic formation, survival time and chemotherapy response. Isolation stress decreased the time period required for the metastasis formation relative to that in controls. On day 7 after the tumor injection, the 75% incidence of tumor metastasis in the stressed mice was 5 times the 15% incidence in the unstressed mice. When exposed to the challenge of lower cell numbers (0.025, 0.05, 0.1 x 10(4)/mouse) of colon 26-L5 cells, mice subjected to isolation stress developed an elevated incidence of metastasis (33.3, 66.6, and 100%, respectively) as compared with the controls (0, 33.3 and 50%, respectively). The survival time following the tumor inoculation was also shorter in the stressed mice (21.83 +/- 1.59d) than in the control mice (24.08 +/- 1.68 d). Furthermore, the response of liver metastasis to chemotherapy consisting of 2 mg/kg cisplatin (CDDP) was worse in the stressed mice than that in unstressed mice. These findings suggested that social isolation stress could significantly impair the resistance of mice to the development of metastasis.

Social isolation stress augments angiogenesis induced by colon 26-L5 carcinoma cells in mice

We have previously shown that tumor necrosis factor-alpha (TNF-alpha), which is an important angiogenesis-related factor, was over-secreted in male BALB/c mice under social isolation stress as compared with the control, and closely associated with a remarkable elevation of tumor invasion and metastasis of colon 26-L5 carcinoma cells. In the present study, we explored the effect of isolation stress on the angiogenesis caused by colon 26-L5 carcinoma cells in vivo and in vitro. Social isolation lead to the enhancement of tumor growth after intrahepatic implantation with a fragment of colon 26-L5 tumor. Angiogenic response (number of vessels oriented towards tumor mass) and tumor growth (size) were significantly increased in the socially isolated mouse relative to that in the group-housed mice. Furthermore, higher protein level of hepatic TNF-alpha was found in the stressed mice than that in the control. Expression of mRNA for vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) were also elevated in the tumor regions and liver tissues of the stressed mice in comparison with that in group-housed mice. On the other hand, hepatic sinusoidal endothelial (HSE) cells treated with TNF-alpha exhibited a marked promotion of the migration, invasion, expression of mRNA for matrix metalloproteinase (MMP)-9, and tube-like formation, but no cytotoxicity against the cells in vitro. The above data suggest that the social isolation stress augmented the tumor-induced angiogenesis probably by up-regulating the angiogenesis-related factors, including TNF-alpha, VEGF and HGF, and consequently mediating the functions of endothelial cells such as migration, invasion, and tube-like formation.