Alterations of tryptophan metabolism induced by sleep deprivation

Acute sleep deprivation during pregnancy in rats: Rapid elevation of placental and fetal inflammation and kynurenic acid

The kynurenine pathway (KP) is the dominant pathway for tryptophan degradation in the mammalian body and emerging evidence suggests that acute episodes of sleep deprivation (SD) disrupt tryptophan metabolism via the KP. Increases in the neuroactive KP metabolite kynurenic acid (KYNA) during pregnancy may lead to a higher risk for disrupted neurodevelopment in the offspring. As pregnancy is a critical period during which several factors, including sleep disruptions, could disrupt the fetal environment, we presently explored the relationship between maternal SD and KP metabolism and immune pathways in maternal, placenta, and fetal tissues. Pregnant Wistar rat dams were sleep deprived by gentle handling for 5 h from zeitgeber time (ZT) 0 to ZT 5. Experimental cohorts included: i) controls, ii) one session of SD on embryonic day (ED) 18 or iii) three sessions of SD occurring daily on ED 16, ED 17 and ED 18. Maternal (plasma, brain), placental and fetal (plasma, brain) tissues were collected immediately after the last session of SD or after 24 h of recovery from SD. Respective controls were euthanized at ZT 5 on ED 18 or ED 19. Maternal plasma corticosterone and fetal brain KYNA were significantly elevated only after one session of SD on ED 18. Importantly, maternal plasma corticosterone levels correlated significantly with fetal brain KYNA levels. In addition, placental levels of the proinflammatory cytokines interleukin-1β (IL-1β) and interleukin-6 (IL-6) were increased following maternal SD, suggesting a relationship between placental immune response to SD and fetal brain KYNA accumulation. Collectively, our results demonstrate that sleep loss during the last week of gestation can adversely impact maternal stress, placental immune function, and fetal brain KYNA levels. We introduce KYNA as a novel molecular target influenced by sleep loss during pregnancy.

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Prenatal sleep deprivation influences kynurenine pathway metabolism in utero.

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Fetal brain kynurenic acid (KYNA) is elevated after maternal sleep deprivation.

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Maternal plasma corticosterone is increased after sleep deprivation.

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Prenatal sleep deprivation induces placental and fetal brain cytokines.

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These data support an interplay with stress, in utero inflammation, and KYNA.

Acute Kynurenine Challenge Disrupts Sleep-Wake Architecture and Impairs Contextual Memory in Adult Rats

Study Objectives

Tryptophan metabolism via the kynurenine pathway may represent a key molecular link between sleep loss and cognitive dysfunction. Modest increases in the kynurenine pathway metabolite kynurenic acid (KYNA), which acts as an antagonist at N-methyl-d-aspartate and α7 nicotinic acetylcholine receptors in the brain, result in cognitive impairments. As glutamatergic and cholinergic neurotransmissions are critically involved in modulation of sleep, our current experiments tested the hypothesis that elevated KYNA adversely impacts sleep quality.

Methods

Adult male Wistar rats were treated with vehicle (saline) and kynurenine (25, 50, 100, and 250 mg/kg), the direct bioprecursor of KYNA, intraperitoneally at zeitgeber time (ZT) 0 to rapidly increase brain KYNA. Levels of KYNA in the brainstem, cortex, and hippocampus were determined at ZT 0, ZT 2, and ZT 4, respectively. Analyses of vigilance state-related parameters categorized as wake, rapid eye movement (REM), and non-REM (NREM) as well as spectra power analysis during NREM and REM were assessed during the light phase. Separate animals were tested in the passive avoidance paradigm, testing contextual memory.

Results

When KYNA levels were elevated in the brain, total REM duration was reduced and total wake duration was increased. REM and wake architecture, assessed as number of vigilance state bouts and average duration of each bout, and theta power during REM were significantly impacted. Kynurenine challenge impaired performance in the hippocampal-dependent contextual memory task.

Conclusions

Our results introduce kynurenine pathway metabolism and formation of KYNA as a novel molecular target contributing to sleep disruptions and cognitive impairments.

Altered serum levels of kynurenine metabolites in patients affected by cluster headache

Background

The reported efficacy of memantine in the treatment of patients with cluster headache (CH) suggests that NMDA receptors are involved in mechanisms of nociceptive sensitization within the trigeminal system associated with CH. NMDA receptors are activated or inhibited by neuroactive compounds generated by tryptophan metabolism through the kynurenine pathway. In the accompanying manuscript, we have found that serum levels of all kynurenine metabolites are altered in patients with chronic migraine. Here, we have extended the study to patients affected by episodic or chronic CH as compared to healthy controls.

Method

We assessed serum levels of kynurenine (KYN), kynurenic Acid (KYNA), anthranilic acid (ANA), 3-hydroxy-anthranilic acid (3-HANA), 3-hydroxykynurenine (3-HK), xanthurenic acid (XA), quinolinic acid (QUINA), tryptophan (Trp) and 5-hydroxyindolacetic acid (5-HIAA) by means of a liquid chromatography/tandem mass spectrometry (LC/MS-MS) method in 21 patients affected by CH (15 with episodic and 6 with chronic CH), and 35 age-matched healthy subjects. Patients with psychiatric co-morbidities, systemic inflammatory, endocrine or neurological disorders, and mental retardation were excluded.

Results

LC/MS-MS analysis of kynurenine metabolites showed significant reductions in the levels of KYN (-36 %), KYNA (-34 %), 3-HK (-51 %), 3-HANA (-54 %), XA (-25 %), 5-HIAA (-39 %) and QUINA (-43 %) in the serum of the overall population of patients affected by CH, as compared to healthy controls. Serum levels of Trp and ANA were instead significantly increased in CH patients (+18 % and +54 %, respectively). There was no difference in levels of any metabolite between patients affected by episodic and chronic CH, with the exception of KYN levels, which were higher in patients with chronic CH.

Conclusion

The reduced levels of KYNA (an NMDA receptor antagonist) support the hypothesis that NMDA receptors are overactive in CH. A similar reduction in KYNA levels was shown in the accompanying manuscript in patients affected by chronic migraine. The reduced levels of XA, a putative analgesic compound, may contribute to explain the severity of pain attacks in CH. These data, associated with the data reported in the accompanying manuscript, supports a role for the kynurenine pathway in the pathophysiology of chronic headache disorders.

A review of lifestyle factors that contribute to important pathways associated with major depression: diet, sleep and exercise

Research on major depression has confirmed that it is caused by an array of biopsychosocial and lifestyle factors. Diet, exercise and sleep are three such influences that play a significant mediating role in the development, progression and treatment of this condition. This review summarises animal- and human-based studies on the relationship between these three lifestyle factors and major depressive disorder, and their influence on dysregulated pathways associated with depression: namely neurotransmitter processes, immuno-inflammatory pathways, hypothalamic-pituitary-adrenal (HPA) axis disturbances, oxidative stress and antioxidant defence systems, neuroprogression, and mitochondrial disturbances. Increased attention in future clinical studies on the influence of diet, sleep and exercise on major depressive disorder and investigations of their effect on physiological processes will help to expand our understanding and treatment of major depressive disorder. Mental health interventions, taking into account the bidirectional relationship between these lifestyle factors and major depression are also likely to enhance the efficacy of interventions associated with this disorder.

The urinary excretion of tryptophan and tryptophan metabolites in the chronic ethanol-fed rat

An investigation was made into the hypothesis that chronic ethanol ingestion disturbs the metabolism of tryptophan which is reflected by alterations in the urinary excretion of the metabolites 5-hydroxyindoleacetic acid (5-HIAA), anthranilic acid (AA) and indoleacetic acid (IAA). In particular, we investigated whether experimental chronic alcoholism is associated with a decrease in the tryptophan metabolite ratios as suggested in the literature. Male Wistar rats were chronically fed a nutritionally-complete liquid diet in which ethanol comprised 35% of total calories: controls were pair-fed identical amounts of the same diet in which ethanol was replaced by isocaloric glucose. At 6 weeks, 24 h urine samples were collected for the analysis of tryptophan, 5-HIAA, AA and IAA by HPLC. During ethanol-feeding there were reductions in the daily urinary excretion (i.e. mumol/24 h) of tryptophan (-57%, P = 0.026) and concomitant increases in 5-HIAA excretion (62%, P = 0.057). Expression of data in terms of lean tissue mass (i.e. urinary creatinine) revealed identical conclusions. An analysis was performed on the molar ratios of these urinary analytes. The tryptophan: total metabolite ratio was significantly decreased (by -53%), but the AA: total metabolite ratio was not significantly altered (P = 0.102). The ratios 5-HIAA/AA and 5-HIAA/IAA were slightly increased, but they did not attain statistical significance (P > 0.351). It was concluded that chronic ethanol feeding is associated with significant changes in the urinary excretion of tryptophan and its related metabolites.(ABSTRACT TRUNCATED AT 250 WORDS)

A review of the biological effects of total sleep deprivation in man

This biologically oriented review attempts to complement earlier and more psychological performance based reviews of total sleep deprivation. Also, the effects of total sleep deprivation are interpreted, here, from a function of human sleep perspective, rather than from the more usual stress viewpoint. It would appear that total sleep deprivation does not produce any major changes in biochemical and physiological measures of somatic functioning. Such a conclusion would not seem to support an hypothesis that human sleep is for body restitution. Although there are equivocal results amongst several of the more psychophysiological measures, EEG does show a pronounced change. This latter finding, together with many reports of psychological performance detriment, would appear to sustain a CNS or cerebral restitutional role for human sleep. However, before definitive conclusions can be drawn from the biochemical and physiological findings of total sleep deprivation, the following qualifications of experimental methodology are made: (1) Apart from sleep loss, many studies have provided unnatural regimes which may have ameliorated possible effects of total sleep deprivation. (2) Most studies are of relatively short duration and may not have been sufficiently long for effects to develop. (3) Measures are often limited in range and depth of analysis. (4) Subjects are mostly fit, young adult, intelligent males and there is little constitutional variability. (5) Reported changes of statistical significance may be of no physiological significance and changes of possible physiological significance may be obscured by statistical procedures. (6) Intervening behavioural variables, such as novelty and anticipation of the sleep deprivation situation, may confound real effects.

Changes in blood tryptophan level during sleep deprivation

Prolonged sleep deprivation elicits a significant elevation of the plasma level of free tryptophan which appears to be involved in increased excretion of 5-HIAA during this state through enhanced 5-HT synthesis.

Rapid eye movement (rem) sleep deprivation: effect on acid mucopolysaccharides in rat brain

The effect of rapid eye movement (REM) sleep deprivation on the total content and proportion of different mucopolysaccharides (AMPS) containing uronic acid in rat brain was studied. REM sleep deprivation was induced by the water tank methods. Five experimental groups of animals were used: control, stressed, REM sleep deprived, post-stress sleeping and post-deprivation sleeping rats. No changes of AMPS were observed in any of the experimental groups when the whole brain was analysed. A significant increase of AMPS was found in the cerebral hemispheres of stressed and REM deprived rats. A significant decrease of AMPS was observed in the cerebellum and brain stem. A further increase of AMPS was found in the cerebral hemispheres after the rebound of REM sleep following its deprivation, and after the recovery sleep following the stress. A significant increase of AMPS was found in the brain stem of rats allowed to recuperate after REM deprivation or stress as compared with the stressed and REM deprived animals. Recovery sleep induced a significant increase of AMPS in the cerebellum in previously stressed rats, while previously REM deprived rats exhibited a further decrease of AMPS from control values. The possible functional meaning of these results is discussed in relation to the role of REM sleep in protein synthesis and learning and memory processes. Intriguing, well-controlled positive findings and the fact that no experimental design is known where stress is minimal while REM deprivation is 100 per cent, justify and encourage continued efforts in studying the biochemical state of the brain during sleep and/or its alterations.