Recent findings suggest that inflammatory cytokines are involved in sleep regulation. In part, this idea is based on studies showing that systemic levels of interleukin-6 (IL-6) are affected by sleep and sleep deprivation. However, intravenous (IV) catheters used for repetitive blood sampling were reported to increase local IL-6 production, which might confound sleep-dependent or circadian changes in the plasma concentrations of this cytokine. To further examine the effects of blood drawing procedures on IL-6 plasma levels, 12 healthy young male subjects participated in a 24-h cross-over study protocol involving sleep and sleep deprivation. Blood was collected half-hourly through an IV line and one additional sample was taken by a simple needle stick from the contralateral arm in parallel to the last sample from the catheter. Difficulties in blood sampling, the plasma levels of IL-6, cortisol and subjective sleepiness were quantified. In samples from the IV line there was a linear increase in IL-6 levels in both conditions, whereas the amount of IL-6 detected in the needle stick sample at the end did not differ from baseline. IL-6 levels were significantly higher in samples rated as difficult and those difficulties were more frequent during sleep compared to nocturnal wakefulness. IL-6 levels did not correlate to variations in sleepiness or cortisol levels. We conclude that variations in IL-6 plasma levels measured in samples from an IV catheter are caused, at least in part, by changes in local cytokine production rather than by physiological changes in circulating IL-6 levels.
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.
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.
BACKGROUND: The concentration of C-reactive protein (CRP) in otherwise healthy subjects has been shown to predict future risk of myocardial infarction and stroke. CRP is synthesized by the liver in response to interleukin-6, the serum concentration of which is subject to diurnal variation.
METHODS: To examine the existence of a time-of-day effect for baseline CRP values, we determined CRP concentrations in hourly blood samples drawn from healthy subjects (10 males, 3 females; age range, 21-35 years) during a baseline day in a controlled environment (8 h of nighttime sleep).
RESULTS: Overall CRP concentrations were low, with only three subjects having CRP concentrations >2 mg/L. Comparison of raw data showed stability of CRP concentrations throughout the 24 h studied. When compared with cutoff values of CRP quintile derived from population-based studies, misclassification of greater than one quintile did not occur as a result of diurnal variation in any of the subjects studied. Nonparametric ANOVA comparing different time points showed no significant differences for both raw and z-transformed data. Analysis for rhythmic diurnal variation using a method fitting a cosine curve to the group data was negative.
CONCLUSIONS: Our data show that baseline CRP concentrations are not subject to time-of-day variation and thus help to explain why CRP concentrations are a better predictor of vascular risk than interleukin-6. Determination of CRP for cardiovascular risk prediction may be performed without concern for diurnal variation.
STUDY OBJECTIVES: This study sought to establish the effects of caffeine on sleep inertia, which is the ubiquitous phenomenon of cognitive performance impairment, grogginess and tendency to return to sleep immediately after awakening.
DESIGN: 28 normal adult volunteers were administered sustained low-dose caffeine or placebo (randomized double-blind) during the last 66 hours of an 88-hour period of extended wakefulness that included seven 2-hour naps during which polysomnographical recordings were made. Every 2 hours of wakefulness, and immediately after abrupt awakening from the naps, psychomotor vigilance performance was tested.
MEASUREMENTS AND RESULTS: In the placebo condition, sleep inertia was manifested as significantly impaired psychomotor vigilance upon awakening from the naps. This impairment was absent in the caffeine condition. Caffeine had only modest effects on nap sleep.
CONCLUSIONS: Caffeine was efficacious in overcoming sleep inertia. This suggests a reason for the popularity of caffeine-containing beverages after awakening. Caffeine's main mechanism of action on the central nervous system is antagonism of adenosine receptors. Thus, increased adenosine in the brain upon awakening may be the cause of sleep inertia.
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.
BACKGROUND: The extent to which sleep loss may predispose astronauts to a state of altered immunity during extended space travel prompts evaluation with ground-based models.
OBJECTIVE: We sought to measure plasma levels of selected cytokines and their receptors, including the putative sleep-regulation proteins soluble TNF-alpha receptor (sTNF-alpha R) I and IL-6, in human subjects undergoing 2 types of sleep deprivation during environmental confinement with performance demands.
METHODS: Healthy adult men (n = 42) were randomized to schedules that varied in severity of sleep loss: 4 days (88 hours) of partial sleep deprivation (PSD) involving two 2-hour naps per day or 4 days of total sleep deprivation (TSD). Plasma samples were obtained every 6 hours across 5 days and analyzed by using enzyme-linked immunoassays for sTNF-alpha RI, sTNF-alpha RII, IL-6, soluble IL-2 receptor, IL-10, and TNF-alpha.
RESULTS: Interactions between the effects of time and sleep deprivation level were detected for sTNF-alpha RI and IL-6 but not for sTNF-alpha RII, soluble IL-2 receptor, IL-10, and TNF-alpha. Relative to the PSD condition, subjects in the TSD condition had elevated plasma levels of sTNF-alpha RI on day 2 (P =.04), day 3 (P =.01), and across days 2 to 4 of sleep loss (P =.01) and elevated levels of IL-6 on day 4 (P =.04).
CONCLUSIONS: Total sleep loss produced significant increases in plasma levels of sTNF-alpha RI and IL-6, messengers that connect the nervous, endocrine, and immune systems. These changes appeared to reflect elevations of the homeostatic drive for sleep because they occurred in TSD but not PSD, suggesting that naps may serve as the basis for a countermeasures approach to prolonged spaceflight.
Recently, hypocretins have been implicated in the pathophysiology of narcolepsy, a sleep disorder characterized particularly by the occurrence of excessive daytime sleepiness and cataplexy. Hypocretins, which stimulate food intake, have been reported to be absent in the cerebrospinal fluid (CSF) of the majority of patients suffering from narcolepsy. Because these patients also display an increased body mass index (BMI), it has been suggested that disturbances in metabolism and food intake regulation may be present. To further investigate these presumed alterations, we studied the production of leptin, a fat-cell-derived hormone signaling to the brain the size of the adipose tissue. We measured the levels of leptin in serum and CSF from 15 narcoleptic patients and compared the results to those from age-, sex- and BMI-matched control groups of depressive patients and patients suffering from a noninflammatory neurological disorder. Compared to both control groups, leptin levels in serum, but not in the CSF, were significantly reduced in narcoleptic patients by more than 50%. These results support the hypothesis that human narcolepsy is accompanied by complex alterations of the regulation of food intake and metabolism. The significance of these alterations for the core symptomatology of narcolepsy should be a target of future research.
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.
The role of the central nervous system in the host response to infection and inflammation and modulation of these responses by the hypothalamic-pituitary-adrenal system are well established. In animals, activation of host defense mechanisms increases non-rapid eye movement (NREM) sleep amount and intensity, which, in turn, are thought to support host defense, or the body's ability to defend itself against challenges to its immune system. In humans, the evidence is conflicting. Therefore, we investigated the effects of three placebo-controlled doses of endotoxin on host response, including nocturnal sleep in healthy volunteers. Administered before nocturnal sleep onset, endotoxin dose dependently increased rectal temperature, heart rate, and the plasma levels of tumor necrosis factor (TNF)-alpha, soluble TNF receptors, interleukin (IL)-1 receptor antagonist, IL-6, and cortisol. The lowest dose reliably increased circulating levels of cytokines and soluble cytokine receptors, but it did not affect rectal temperature, heart rate, or cortisol. This subtle host defense activation increased deep NREM sleep amount, often referred to as slow-wave sleep (stages 3 and 4), and intensity (delta power). Conversely, the highest dose of endotoxin disrupted sleep. Whereas it is well established that the endocrine and thermoregulatory systems are very sensitive to endotoxin, this study shows that human sleep-wake behavior is even more sensitive to activation of host defense mechanisms.
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.
Numerous animal studies suggest that cytokines such as interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) mediate increased sleep amount and intensity observed during infection and are, moreover, involved in physiological sleep regulation. In humans the role of cytokines in sleep-wake regulation is largely unknown. In a single-blind, placebo-controlled study, we investigated the effects of granulocyte colony-stimulating factor (G-CSF, 300 microgram sc) on the plasma levels of cytokines, soluble cytokine receptors, and hormones as well as on night sleep. G-CSF did not affect rectal temperature or the plasma levels of cortisol and growth hormone but did induce increases in the plasma levels of IL-1 receptor antagonist and both soluble TNF receptors within 2 h after injection. In parallel, the amount of slow-wave sleep and electroencephalographic delta power were reduced, indicating a lowered sleep intensity. We conclude that G-CSF suppresses sleep intensity via increased circulating amounts of endogenous antagonists of IL-1beta and TNF-alpha activity, suggesting that these cytokines are involved in human sleep regulation.
The 24-hour sleep/wake distributions of untreated patients with narcolepsy-cataplexy and matched normal habitual nappers were compared using home ambulatory monitoring. Subjects followed their usual sleep patterns including, for the habitual nappers, a self-selected daytime nap. There were no differences in 24-hour totals of sleep between groups other than a small increase in SWS in narcolepsy. Narcolepsy showed greater amounts of day sleep (stages 2, SWS, REM and total sleep) and less night sleep (stage 2, total sleep). Data were collapsed into 5 min epochs and entered into a matrix. The data in the two groups were then "wrapped" (re-aligned) around the 24 hours with phase 0 as each of the times of: evening sleep onset, onset of SWS, mid-point of night sleep and moment of morning awakening. In habitual nappers alignment beginning at morning wake-up produced the highest amplitude, least temporal dispersion and greatest kurtosis of daytime sleep (naps). The 24-hour sleep/wake distribution curves of both subject groups (data aligned at morning wake-up) based on collapsed data into 5 min bins then underwent curve fitting using 15th order polynomial regression. As with visual analyses of the raw data, the curve fits confirmed that the peak in daytime sleep propensity in narcoleptics was earlier by about 40 (2.66 hours). It was concluded that decreased daytime amplitude of a circadian arousal system was the most parsimonious explanation for the increased amount, broader temporal distribution and relative phase advance of day sleep in narcolepsy and that, as well, such a mechanism could explain a number of other features of the disease.
We investigated cytokine levels (interleukin [IL]-1beta, IL-1ra, IL-2, IL-6, tumor necrosis factor [TNF]-alpha, TNF-beta) in plasma and secreted by mitogen-stimulated blood monocytes and lymphocytes; T-cell subsets; and natural killer cell activity in patients with narcolepsy and in human leukocyte antigen (HLA)-DR2 matched controls. The only significant finding was higher IL-6 secretion by monocytes of patients than by those of the HLA-DR2-positive controls. In conclusion, we found no major abnormalities of T-cell function in patients with narcolepsy, but slight alterations of monocyte function deserving further investigation.
Clozapine is an atypical antipsychotic agent with immunomodulatory properties. We hypothesized that in vitro immune parameters of peripheral blood mononuclear cells (PBMC) are affected in the course of clozapine treatment and that clozapine per se, added in vitro to PBMC cultures of clozapine-treated patients, exerts differential effects in the timecourse of treatment in vivo. We measured proliferation and cytokine secretion of PBMC, serum autoantibodies, and immunoglobulin levels in 17 patients before and during the first 6 weeks of clozapine treatment. Independent of clozapine dosage and rectal temperature, clozapine treatment in vivo suppressed proliferation and shedding of sIL-2r by PBMC, and the addition of clozapine in vitro induced, relative to unstimulated conditions, PBMC proliferation and secretion of IL-6 and sIL-2r. Serum IgG levels were increased; whereas, autoantibody pattern was unaffected. Thus, clozapine treatment and the addition of clozapine in vitro exert differential effects on various in vitro immune parameters independent of clozapine dosage and rectal temperature in the course of treatment.
Sleepiness is a common symptom of infectious diseases. However, the peculiarities and causes of impaired vigilance during host defense activation are largely unknown. It has been shown earlier that mild host defense activation by endotoxin does not affect daytime sleepiness and non-rapid eye movement (NREM) sleep in humans. In the present study we investigated the effects of a more intensive stimulation of the host defense by Salmonella abortus equi endotoxin (0.8 ng/kg), administered 12 h following host response priming by granulocyte colony-stimulating factor (300 micrograms s.c.), on daytime sleep and sleepiness in a placebo-controlled design in ten healthy men. Six equidistant polysomnographically monitored naps were scheduled across the day and the time course of subjective sleepiness was assessed. Endotoxin induced prominent increases in rectal temperature, and in the plasma levels of tumor necrosis factor-alpha, interleukin-6, interleukin-1 receptor antagonist, and cortisol. In the first nap, 1 h following endotoxin administration, total sleep time and NREM sleep stage 2 were reduced, whereas wakefulness and sleep onset latency were increased. Following this nap sleepiness transiently increased peaking prior to the second nap. However, this nap and the following ones were not influenced by endotoxin. These results suggest that prominent host defense activation reduces daytime NREM sleep and increases sleepiness. One cause of daytime sleepiness during infections may be prior sleep disruption and this kind of sleepiness may not necessarily be associated with an increased sleep pressure.
Polysomnographic studies on the effects of clozapine, an atypical antipsychotic agent with strong sedative properties, on night sleep report inconsistent results. Most of these studies did not include baseline recordings and were not controlled for clozapine-induced fever, which is known to alter nocturnal sleep. We conducted a 2-week longitudinal polysomnographic investigation in 10 long-term drug-free schizophrenic patients prior to and at the end of the first and second weeks of clozapine treatment. Rectal temperature was measured daily and patients with fever (> 37.9 degrees C) were excluded. Clozapine significantly improved sleep continuity. In addition, non-rapid eye movement (NREM) sleep and in particular stage 2 sleep increased significantly, while the amounts of stage 4 and slow-wave sleep decreased significantly. Clozapine increased significantly REM density, but it did not affect the amount of REM sleep. We conclude that in patients who do not experience clozapine-induced fever, clozapine has strong sleep consolidating effects resulting from an increase in stage 2 NREM sleep.
Shortened REM latency and increased REM density are frequently observed in both narcolepsy and depression, suggesting a common mechanism of REM sleep disinhibition in these disorders. We compared night sleep recordings of 24 depressive and 24 narcoleptic patients. The amount of REM sleep and REM density did not differ between the patient groups; however, REM latency distributions differed significantly. Whereas in narcoleptic patients REM episodes started either immediately at sleep onset or following at least 60 min of non-REM sleep, in depressives two thirds of REM latencies were in the range from 1 to 60 min. In narcoleptic patients, short as compared to long REM latencies were associated with longer total sleep time, greater sleep efficiency, reduced amounts of wakefulness, and increased amounts of slow-wave sleep. In depressive subjects the reverse pattern was seen. We conclude that a common mechanism of REM sleep disinhibition in narcolepsy and depression is very unlikely.