The endotoxin-induced increase of cytokines is followed by an increase of cortisol relative to dehydroepiandrosterone (DHEA) in healthy male subjects

Dehydroepiandrosterone (DHEA) and DHEA sulphate (DHEAS) inhibit T-helper lymphocyte type 2 immune reactions and exert anti-inflammatory effects in some chronic inflammatory diseases. Both DHEA and, in particular, DHEAS levels are dramatically decreased in chronic inflammatory diseases whereas cortisol levels remain stable or are elevated. However, the time course of cortisol relative to DHEA production is not known. We tested whether administration of endotoxin to healthy male subjects can induce an early predominance of cortisol relative to DHEA and DHEAS. It is demonstrated that endotoxin induces a dose-dependent increase of cortisol in relation to DHEA (no effect at 0.2 ng endotoxin/kg body weight (b.w.), clear effect at 0.4 and 0.8 ng/kg b.w., p<0.05) and DHEAS (tested at 0.4 ng/kg b.w., P=0.014). The increase of cortisol relative to DHEA appears 4 h after endotoxin injection and 2 h after a strong increase of interleukin (IL)-6 relative to tumour necrosis factor (TNF). In addition, an increase of cortisol relative to 17OH-progesterone was observed. The ratio of serum IL-6/TNF was positively correlated with the ratio of serum cortisol/DHEA (R(Rank)=0.472, P=0.041) and serum cortisol/17OH-progesterone (R(Rank)=0.514, P=0.048). In conclusion, dissociation of cortisol relative to DHEA, DHEAS or 17OH-progesterone appears very early during a systemic inflammatory response which is associated with an increase of IL-6 relative to TNF. As in chronic inflammatory diseases, during an acute inflammatory response with endotoxin, these physiological hormone changes are probably necessary to achieve adequate cortisol levels at the expense of adrenal androgens.

Body weight, the tumor necrosis factor system, and leptin production during treatment with mirtazapine or venlafaxine

Weight gain is a frequent and important side effect of psychopharmacotherapy. Recent studies suggest that the fat-cell-derived hormone leptin and the tumor necrosis factor-alpha (TNF-alpha) cytokine system are pathophysiologically involved. No information is available concerning the influence of the antidepressants mirtazapine and venlafaxine on these immunoendocrine variables. An open-labeled study was performed in 20 patients suffering from major depression treated with either mirtazapine (N = 11) or venlafaxine (N = 9). During 4 weeks, the patients' weight, body mass index (BMI), and plasma levels of leptin, TNF-alpha, sTNF-R p55, and sTNF-R p75 were assessed. Mirtazapine induced a significant increase in weight (mean weight gain: 2.4 kg) that was evident after the first week of treatment. In parallel, the plasma levels of TNF-alpha and both soluble TNF receptors increased. In addition, a slight rise in leptin levels, which occurred slowly and was significant only at the end of the 4 th week of treatment, was observed. Weight decreased slightly but significantly in patients treated with venlafaxine (mean weight loss: 0.4 kg), whereas plasma levels of leptin, TNF-alpha, or soluble TNF receptors did not change significantly. The present results further support the notion that the activation of the TNF-alpha cytokine system is an early, sensitive, and specific marker of weight gain induced by psychotropic agents. In contrast, the effects of such drugs on leptin production seem to be less sensitive with respect to weight gain and more variable.

Endotoxin-induced changes in food consumption in healthy volunteers are associated with TNF-alpha and IL-6 secretion

This study examined the effects of endotoxin administration on food and water consumption in humans, and the associations between these changes and endotoxin-induced secretion of cytokines, cortisol, and fever. Twenty healthy male volunteers received an i.v. injection of Salmonella abortus equi endotoxin (0.8 ng/kg) or saline in two experimental sessions. Blood samples were collected hourly, and rectal temperature was monitored continuously. Food consumption was significantly reduced at 0-4 h and significantly elevated at 4-5 h after the endotoxin injection. Endotoxin administration had no significant effect on water consumption. Endotoxin-induced secretion of TNF-alpha and IL-6 was positively associated with the decrease in food consumption (r=0.61 and 0.68), and negatively associated with the rebound increase in food consumption (r=-0.53 and -0.45). Neither the febrile response, nor the secretion of cortisol was associated with the changes in food consumption. These results suggest that TNF-alpha and IL-6 are involved in endotoxin-induced anorexia in humans.

[Leptin and psychiatric disorders]

As early as the beginning of the 20th century, changes in appetite and weight were recognized as important symptoms of severe psychiatric disorders. Particularly in the last decade, understanding of the regulation of appetite and weight has made major progress. In this context, the discovery of the adipose tissue hormone leptin, which signals the size of the peripheral fat stores to the CNS, was crucial. In addition, leptin is also involved in a number of CNS networks regulating behavior and thus of great importance for the pathophysiology of psychiatric disorders. Apart from sexual behavior, those networks include motor activity, sleep, and cognition. Moreover, leptin seems to be involved in the development and maturation of the brain. The present paper summarizes current studies which suggest that, in psychiatric disorders, leptin could be of importance not only for disease-associated or drug-related changes in appetite and weight but also for alterations in behavior and cognition.

In vitro cytokine secretion in individuals with schizophrenia: results, confounding factors, and implications for further research

The present paper reviews the results of all publications on in vitro cytokine secretion in patients with schizophrenia, as published by March 2001. The authors supply easy to read tables with respect to the individual cytokines and soluble cytokine receptors investigated, the in vitro methodology used, characterization of the patient samples, and the results on cytokine secretion as stated in these studies. Inconsistent results, e.g., regarding in vitro secretion of IL-2 with 11/18 studies finding decreased secretion, 5/18 finding no change, and 2/18 finding increases, cannot systematically be correlated with any methodological procedures nor any diagnostic subtypes, per se. However, factors such as medication and cigarette smoking are likely to play a role. The authors suggest that more hypothesis-driven research, together with more carefully designed studies, as well as better communication between basic or animal researchers and clinicians might help to answer the question of whether there are meaningful peripheral changes in the immune system related to schizophrenia.

[On the clinical relevance of clozapine-triggered release of cytokines and soluble cytokine-receptors]

Cytokines are pivotal mediators of the interaction between immunocompetent cells. Moreover, they mediate the interaction between the immune system and other physiological systems, including the CNS. It has been shown recently that the antipsychotic drug clozapine stimulates in vivo the release of cytokines and soluble cytokine receptors. This holds true for the tumor necrosis factor(TNF)-system, the interleukin(IL)-2-system, IL-6, and granulocyte colony-stimulating factor (G-CSF). The present paper discusses the clinical relevance of these findings for the pathophysiology of clozapine-induced side-effects. It is very probable that TNF-alpha plays an important role in clozapin-induced fever and in the hematopoetic side effects, including agranulocytosis. Moreover, it is likely that TNF-alpha and other cytokines are involved in metabolic (weight gain, diabetes), cardiac (myocarditis), CNS (sedation) and other rare side effects. The mechanisms underlying clozapine-induced immunomodulation are unknown. Hence, further studies are very important to enhance our understanding of clozapins's side effects and to develop strategies for prevention and treatment.

Effects of sleep on endotoxin-induced host responses in healthy men

OBJECTIVE

To examine whether increased sleep during viral or bacterial infections supports host defense mechanisms.

METHODS

To test this assumption in humans, healthy male subjects were assigned either to sleep from 2300 to 0700 hours (n = 10) or to stay awake through the night (n = 10). In the sleeping subjects Salmonella abortus equi endotoxin (0.4 ng/kg) or placebo were intravenously injected in balanced order during the first SWS episode. The age-matched, sleep-deprived subjects were injected at the same time point.

RESULTS

As expected, endotoxin significantly increased rectal temperature, the plasma levels of cortisol, tumor necrosis factor-alpha (TNF-alpha), the soluble TNF receptors p55 and p75, Interleukin (IL)-6, the IL-1 receptor antagonist (RA), leukocyte, and granulocyte counts in both sleeping and sleep-deprived subjects, whereas lymphocyte and monocyte counts were transiently reduced. Time courses of endotoxin-induced host responses did not differ between the sleep and sleep deprivation groups. Endotoxin did not affect the amount of nocturnal wakefulness, nonrapid-eye-movement (NREM) sleep, or rapid-eye-movement (REM) sleep across the total night compared with placebo, but significantly increased electroencephalogram-arousals (EEG-arousals) in stage 2 and decreased arousals in SWS. In addition, the amount of SWS, spectral EEG-delta and -theta power was increased at the beginning and at the end of the sleep period, respectively, when the degree of immune activation was relatively low.

CONCLUSION

The present results support the notion that short-term sleep deprivation is unlikely to harm the immune system as far as unspecific acute responses are concerned. The effects of endotoxin on sleep in this case support prior observations that in humans, enhanced SWS and intensified NREM sleep occur when host defense activation is subtle.

Normal plasma levels of orexin A (hypocretin-1) in narcoleptic patients

Deficient orexin signaling has been shown to cause narcolepsy-like conditions in animals. In human narcolepsy, CSF levels of orexin A (hypocretin-1) were reported to be low in most cases. The authors measured CSF and plasma orexin A levels in patients with narcolepsy and in controls. Confirming earlier studies, they found CSF orexin A levels to be extremely low in patients with narcolepsy. However, plasma orexin A levels did not differ from those observed in controls. These results suggest that orexin deficiency in patients with narcolepsy is a phenomena restricted to the CNS.

Cytokine-associated emotional and cognitive disturbances in humans

BACKGROUND

Infectious, autoimmune, and neurodegenerative diseases are associated with profound psychological disturbances. Studies in animals clearly demonstrate that cytokines mediate illness-associated behavioral changes. However, the mechanisms underlying the respective psychological alterations in humans have not been established yet. Therefore, we investigated the effects of low-dose endotoxemia, a well-established and safe model of host-defense activation, on emotional, cognitive, immunological, and endocrine parameters.

METHODS

In a double-blind, crossover study, 20 healthy male volunteers completed psychological questionnaires and neuropsychological tests 1, 3, and 9 hours after intravenous injection of Salmonella abortus equi endotoxin (0.8 ng/kg) or saline in 2 experimental sessions. Blood samples were collected hourly, and rectal temperature and heart rate were monitored continuously.

RESULTS

Endotoxin had no effects on physical sickness symptoms, blood pressure, or heart rate. Endotoxin caused a mild increase in rectal temperature (0.5 degrees C), and increased the circulating levels of tumor necrosis factor alpha (TNF-alpha), soluble TNF receptors, interleukin (IL)-6, IL-1 receptor antagonist, and cortisol. After endotoxin administration, the subjects showed a transient significant increase in the levels of anxiety (effect size [ES] = 0.55) and depressed mood (ES = 0.66). Verbal and nonverbal memory functions were significantly decreased (ES = 0.55 to 0.64). Significant positive correlations were found between cytokine secretion and endotoxin-induced anxiety (r = 0.49 to r = 0.60), depressed mood (r = 0.40 to r = 0.75), and decreases in memory performance (r = 0.46 to r = 0.68).

CONCLUSIONS

In humans, a mild stimulation of the primary host defense has negative effects on emotional and memory functions, which are probably caused by cytokine release. Hence, cytokines represent a novel target for neuropsychopharmacological research.

Experimental immunomodulation, sleep, and sleepiness in humans

Infection, inflammation, and autoimmune processes are accompanied by serious disturbances of well-being, psychosocial functioning, cognitive performance, and behavior. Here we review those studies that have investigated the effects of experimental immunomodulation on sleep and sleepiness in humans. In most of these studies bacterial endotoxin was injected intravenously to model numerous aspects of infection including the release of inflammatory cytokines. These studies show that human sleep-wake behavior is very sensitive to host defense activation. Small amounts of endotoxin, which affect neither body temperature nor neuroendocrine systems but slightly stimulate the secretion of inflammatory cytokines, promote non-rapid-eye-movement sleep amount and intensity. Febrile host responses, in contrast, go along with prominent sleep disturbances. According to present knowledge tumor necrosis factor-alpha (TNF-alpha) is most probably a key mediator of these effects, although it is likely that disturbed sleep during febrile host responses involves endocrine systems as well. There is preliminary evidence from human studies suggesting that inflammatory cytokines such as TNF-alpha not only mediate altered sleep-wake behavior during infections, but in addition are involved in physiological sleep regulation and in hypnotic effects of established sedating drugs.

Illness, cytokines, and depression

Various medical conditions that involve activation of the immune system are associated with psychological and neuroendocrine changes that resemble the characteristics of depression. In this review we present our recent studies, designed to investigate the relationship between the behavioral effects of immune activation and depressive symptomatology. In the first set of experiments, we used a double-blind prospective design to investigate the psychological consequences of illness in two models: (1) vaccination of teenage girls with live attenuated rubella virus, and (2) lipopolysaccharide (LPS) administration in healthy male volunteers. In the rubella study, we demonstrated that, compared to control group subjects and to their own baseline, a subgroup of vulnerable individuals (girls from low socioeconomic status) showed a significant virus-induced increase in depressed mood up to 10 weeks after vaccination. In an ongoing study on the effects of LPS, we demonstrated significant LPS-induced elevation in the levels of depression and anxiety as well as memory deficits. These psychological effects were highly correlated with the levels of LPS-induced cytokine secretion. In parallel experiments, we demonstrated in rodents that immune activation with various acute and chronic immune challenges induces a depressive-like syndrome, characterized by anhedonia, anorexia, body weight loss, and reduced locomotor, exploratory, and social behavior. Chronic treatment with antidepressants (imipramine or fluoxetine) attenuated many of the behavioral effects of LPS, as well as LPS-induced changes in body temperature, adrenocortical activation, hypothalamic serotonin release, and the expression of splenic TNF-alpha mRNA. Taken together, these findings suggest that cytokines are involved in the etiology and symptomatology of illness-associated depression.

Low leptin levels but normal body mass indices in patients with depression or schizophrenia

Appetite, food intake and weight are frequently altered in psychiatric disorders such as major depression and schizophrenia. The few studies investigating weight and the body mass index (BMI) have yielded variable results. Leptin, a fat cell-derived hormone signalling to the brain the size of the adipose tissue, plays a pivotal role in the regulation of weight and food intake. Moreover, leptin is involved in the control of other behaviors and in brain development. There is almost no information about the amounts of circulating leptin in major depression or schizophrenia. We investigated the BMI and plasma leptin levels in patients with major depression (n = 62), schizophrenia (n = 42), and in healthy controls (n = 64). Mean BMIs did not differ between groups. However, leptin levels were significantly lower in both patient groups compared to healthy controls. Moreover, patients suffering from schizophrenia showed significantly lower leptin levels than depressed patients. Decreased leptin levels were independent of psychotropic medication. We conclude that depression and schizophrenia go along with decreased systemic leptin concentrations that cannot be explained by medication or an altered BMI. Hence, leptin might play an important pathophysiological role in these psychiatric disorders that deserves further scientific attention.

Mediators of inflammation and their interaction with sleep: relevance for chronic fatigue syndrome and related conditions

In humans, activation of the primary host defense system leads to increased or decreased NREM sleep quality, depending on the degree of early immune activation. Modest elevations of certain inflammatory cytokines are found during experimental sleep loss in humans and, in addition, relatively small elevations of cytokines are seen following commencement of pharmacological treatments with clozapine, a CNS active antipsychotic agent, known to have immunomodulatory properties. Cytokines such as TNF-alpha, its soluble receptors, and IL-6, present in the periphery and the CNS, comprise a link between peripheral immune stimulation and CNS-mediated behaviors and experiences such as sleep, sleepiness, and fatigue. The debilitating fatigue experienced in chronic fatigue syndrome and related diseases may also be related to altered cytokine profiles.

[The physiopathology of weight regulation during treatment with psychotropic drugs]

Weight changes during pharmacological treatment are a well-known phenomenon and they have been an object of research since the 1950's. Weight gain occurs during treatment with drugs of different chemical structures and is an important problem when patients are treated with antidepressants, antipsychotics, or mood stabilizers. The clinical relevance of drug-induced weight changes is due to increased rates of morbidity and reduced treatment compliance. Regarding the underlying causes, the important role of neurotransmitter systems and in particular the blockade of serotonin and histamine receptors has been discussed since decades. Only recently, however, research has been started on the effects of psychotropic agents on major neuroendocrine systems involved in appetite and weight regulation. These studies suggest that the fat-cell derived hormone leptin might play an important role. Leptin signals to the brain the size of the adipose tissue and is probably the most important peripheral signal for the long-term regulation of weight. In addition to the neuroendocrine systems, weight gain induced by psychotropic agents might also involve immune modulators, in particular the proinflammatory cytokine tumor-necrosis-factor-alpha (TNF-alpha) and soluble TNF-receptors. Some psychotropic agents influence the TNF system very rapidly, already prior to any obvious increases in weight. Hence, changes in the TNF-alpha system might be of predictive value for drug-induced weight gain. Strategies to minimize or to counteract weight gain induced by psychotropic agents include psychotherapeutic and pharmacological approaches. Although numerous psychotherapeutic approaches are available, they are only of limited usefulness in severely ill psychiatric patients. Fortunately, a number of promising pharmacological approaches to reduce weight have been introduced into clinical practice during the last years; however, so far there is no knowledge on pharmacodynamic and -kinetic interactions with psychotropic drugs, and there is no clinical data on the usefulness and safety of such drug combinations.

Effects of dexamethasone on cytokine plasma levels and white blood cell counts in depressed patients

In major depression, alterations of some aspects of the host defense system and the hypothalamo-pituitary-adrenal (HPA) system have been reported. Both systems are closely related, but their interaction in major depression has not yet been explored. Moreover, little is known about the effects of glucocorticoids on the circulating amounts of cytokines in humans in the absence of immunological challenges. Therefore, we investigated the effects of dexamethasone (DEX) in 17 depressed patients who underwent a combined DEX-suppression and corticotropine-releasing-hormone (CRH)-stimulation test on white blood cell counts, and on the plasma levels of granulocyte colony-stimulating factor (G-CSF), interleukin (IL)-6, IL-10, tumor necrosis factor (TNF)-alpha, and soluble TNF-receptors (sTNF-R) p55 and p75. DEX induced an increase in granulocyte counts, which was positively correlated with increases in the circulating amounts of G-CSF and paralleled by decreased lymphocyte and monocyte counts. Moreover, DEX reduced the plasma levels of IL-6, TNF-alpha and sTNF-R p75. The levels of sTNF-R p55 and IL-10 were not affected. DEX-induced changes in immunological parameters did not differ between patients who had different amounts of HPA-system alteration, and were neither related to the severity of depressive symptomatology or to other clinical features. We conclude that a single oral dose of DEX, even in the absence of infection and inflammation, affects the circulating amounts of cytokines and soluble cytokine receptors, further supporting the pivotal role of these immune-mediators in glucocorticoid-induced immunomodulation. Neuroendocrinological alterations associated with major depression seem to be independent from these processes.

Changes in dehydroepiandrosterone (DHEA) and DHEA-sulfate plasma levels during experimental endotoxinemia in healthy volunteers

Dehydroepiandrosterone (DHEA) and DHEA-sulfate (DHEA-S) have immunomodulatory effects in vitro and in vivo. Additionally, their plasma levels are altered during chronic infection and inflammation. However, it remains unknown whether these steroids are involved in early host responses to infection in humans. We examined DHEA and DHEA-S levels during experimental endotoxinemia, a well established pathophysiological model of bacterial infections in humans. Purified Salmonella abortus equi endotoxin (0.2, 0.4, or 0.8 ng/kg body weight) was injected in a single-blind, placebo-controlled experiment to 17 healthy male volunteers. During the following 12 h, rectal temperature and the plasma levels of ACTH, cortisol, DHEA, DHEA-S, interleukin 6, and tumor necrosis factor alpha were determined. Confirming earlier studies, temperature and cytokine levels showed monophasic, dose-dependent increases in response to endotoxin. In contrast, endocrinological effects of endotoxin showed a complex, biphasic pattern: cortisol levels were not affected by 0. 2 ng/kg but significantly increased during the first 6 h following 0. 4 and 0.8 ng/kg endotoxin, whereas ACTH and DHEA levels were significantly enhanced during the first 6 h following 0.8 ng/kg only. ACTH, DHEA, and cortisol secretion was blunted 6-12 h following 0.8 ng/kg. DHEA-S levels were unaffected during the first 6 h following all dosages, but between 6-12 h after injection they were significantly increased following 0.2 ng/kg, unaffected by 0.4 ng/kg, and significantly decreased following 0.8 ng/kg endotoxin. The present results suggest that similarly to glucocorticoids, the adrenal androgens DHEA and DHEA-S play an important role during early host responses to bacterial infections in humans.

Effects of antipsychotic drugs on cytokine networks

It has been known since the 1950s that phenothiazines have immunomodulatory effects. This review summarizes recent evidence suggesting that antipsychotic drugs, in particular chlorpromazine and the atypical compound clozapine, influence the production of cytokines. Cytokines, organized in networks of related peptides with pleiotropic functions, are pivotal humoral mediators of infection and inflammation, and they play an important role in hematopoiesis and autoimmunity. Therefore, the effects of antipsychotic drugs on cytokine networks are important for the understanding of immune-mediated side effects of these drugs, e.g. agranulocytosis. In addition, modulation of cytokine production by antipsychotic agents suggests that these drugs might be useful for the treatment of diseases which primarily involve the immune system. Moreover, because cytokines are known to have numerous effects on the CNS, they may mediate effects of antipsychotic drugs on brain functions. Finally, the influence of antipsychotic drugs on cytokine networks is an important confounding factor in studies investigating disease-related immunopathology in psychiatric disorders. This review provides a synopsis of the data published on these topics and outlines future research perspectives.