The immune and neuroendocrine systems are closely involved in the regulation of metabolism at peripheral and central hypothalamic levels. In both physiological (meals) and pathological (infections, traumas and tumors) conditions immune cells are activated responding with the release of cytokines and other immune mediators (afferent signals). In the hypothalamus (central integration), cytokines influence metabolism by acting on nucleus involved in feeding and homeostasis regulation leading to the acute phase response (efferent signals) aimed to maintain the body integrity. Peripheral administration of cytokines, inoculation of tumor and induction of infection alter, by means of cytokine action, the normal pattern of food intake affecting meal size and meal number suggesting that cytokines acted differentially on specific hypothalamic neurons. The effect of cytokines-related cancer anorexia is also exerted peripherally. Increase plasma concentrations of insulin and free tryptophan and decrease gastric emptying and d-xylose absorption. In addition, in obesity an increase in interleukin (IL)-1 and IL-6 occurs in mesenteric fat tissue, which together with an increase in corticosterone, is associated with hyperglycemia, dyslipidemias and insulin resistance of obesity-related metabolic syndrome. These changes in circulating nutrients and hormones are sensed by hypothalamic neurons that influence food intake and metabolism. In anorectic tumor-bearing rats, we detected upregulation of IL-1beta and IL-1 receptor mRNA levels in the hypothalamus, a negative correlation between IL-1 concentration in cerebro-spinal fluid and food intake and high levels of hypothalamic serotonin, and these differences disappeared after tumor removal. Moreover, there is an interaction between serotonin and IL-1 in the development of cancer anorexia as well as an increase in hypothalamic dopamine and serotonin production. Immunohistochemical studies have shown a decrease in neuropeptide Y (NPY) and dopamine (DA) and an increase in serotonin concentration in tumor-bearing rats, in first- and second-order hypothalamic nuclei, while tumor resection reverted these changes and normalized food intake, suggesting negative regulation of NPY and DA systems by cytokines during anorexia, probably mediated by serotonin that appears to play a pivotal role in the regulation of food intake in cancer. Among the different forms of therapy, nutritional manipulation of diet in tumor-bearing state has been investigated. Supplementation of tumor bearing rats with omega-3 fatty acid vs. control diet delayed the appearance of tumor, reduced tumor-growth rate and volume, negated onset of anorexia, increased body weight, decreased cytokines production and increased expression of NPY and decreased alpha-melanocyte-stimulating hormone (alpha-MSH) in hypothalamic nuclei. These data suggest that omega-3 fatty acid suppressed pro-inflammatory cytokines production and improved food intake by normalizing hypothalamic food intake-related peptides and point to the possibility of a therapeutic use of these fatty acids. The sum of these data support the concept that immune cell-derived cytokines are closely related with the regulation of metabolism and have both central and peripheral actions, inducing anorexia via hypothalamic anorectic factors, including serotonin and dopamine, and inhibiting NPY leading to a reduction in food intake and body weight, emphasizing the interconnection of the immune and neuroendocrine systems in regulating metabolism during infectious process, cachexia and obesity.
Neuropeptide Y (NPY) is a potent central appetite stimulant whose concentrations rise markedly in hypothalamic appetite-regulating regions in food-deprived rats. To determine whether increased energy expenditure also affects hypothalamic NPY, we studied the effects of intense physical exercise in rats (n = 10) running voluntarily on a large-diameter exercise wheel. Running was initiated by restricting food intake but stabilized at an average of 8 km/day when food intake was matched to that in 11 nonexercised, freely fed controls [23.9 +/- 1.9 (SE) g/day vs. 24.7 +/- 1.3 g/day; P > 0.5]. Running expended approximately 40% of daily energy intake, and weight gain was significantly inhibited. A separate group (n = 10) of nonexercised rats was food restricted (approximately 15 g/day) to match the weights of the exercised rats. The rats were killed after 40 days, when both experimental groups weighed 30% less than controls (P < 0.01). Hypothalamic NPY concentrations showed significant (P < 0.01) increases of 30-70% in specific regions (arcuate and dorsomedial nuclei and medial preoptic and lateral hypothalamic areas) in both the running and food-restricted groups, compared with controls. There were no significant differences between the two experimental groups in NPY concentrations in any hypothalamic region. These findings suggest that negative energy balance, whether caused by reduced energy intake or increased expenditure, increases hypothalamic NPYergic activity. As NPY acts on the hypothalamus to increase body weight, these data support the postulated homeostatic role of NPY in maintaining nutritional state.
Both supplements of L-tryptophan and 5-HTP have been used in the treatment of depression, but the use of 5-HTP may offer the advantage of bypassing the conversion of L-tryptophan into 5-HTP by the enzyme tryptophan hydroxylase, which is the rate-limiting step in the synthesis of serotonin. Tryptophan hydroxylase can be inhibited by numerous factors, including stress, insulin resistance, vitamin B6 deficiency, and insufficient magnesium... Moreover, 5-HTP easily crosses the blood–brain barrier, and unlike L-tryptophan, does not require a transport molecule to enter the central nervous system (Green et al., 1980; Maes et al., 1990). Besides serotonin, other neurotransmitters and hormones, such as melatonin, dopamine, norepinephrine, and beta-endorphin have also been shown to increase following oral administration of 5-HTP. All of these compounds are thought to be involved in the regulation of mood as well as sleep and may represent mechanistic pathways stimulated by 5-HTP administration.
l-5-HTP has definitely got antidepressant effect in patients of depression. Antidepressant effect was seen within 2weeks of treatment and was apparent in all degrees of depression. The therapeutic efficacy of l-5-HTP was considered as equal to that of fluoxetine.
Mood: 5-HTP is helpful to managing depression and anxiety. SSRIs plug the serotonin leak, while 5-HTP and tryptophan helps fill the tank. While an increase in synaptic serotonin can be achieved with SSRIs, either increasing serotonin synthesis, or identifying postsynaptic serotonin receptor agonist are additional anxiolytic strategies. In this regard, dietary supplementation with tryptophan and 5-HTP, which crosses the blood-brain barrier, increases brain serotonin… and produces anxiolytic effects.
Sleep: Tryptophan administered at night is known increase physiological concentrations of both serotonin and melatonin, which makes it a useful supplement for improving sleep latency in mild insomniacs.
Evidence suggests that stress and/or a dietary lack of tryptophan may make deficiencies of serotonin and melatonin common. In addition, older animals and human beings have a reduced ability to synthesize melatonin. Disorders of melatonin levels and rhythms are suggested to be a cause of affective disease, abnormal sleep, Alzheimer's disease, and some age related disorders. If these ideas prove to be true, then preventive measures are possible.
The effects of 3 g L-tryptophan on sleep, performance, arousal threshold, and brain electrical activity during sleep were assessed in 20 male, chronic sleep-onset insomniacs (mean age 20.3 +/- 2.4 years). Following a sleep laboratory screening night, all subjects received placebo for 3 consecutive nights (single-blind), ten subjects received L-tryptophan, and ten received placebo for 6 nights (double-blind). All subjects received placebo on 2 withdrawal nights (single-blind). There was no effect of L-tryptophan on sleep latency during the first 3 nights of administration. On nights 4-6 of administration, sleep latency was significantly reduced. Unlike benzodiazepine hypnotics, L-tryptophan did not alter sleep stages, impair performance, elevate arousal threshold, or alter brain electrical activity during sleep.
Over the past 20 yr, 40 controlled studies have been described concerning the effects of L-tryptophan on human sleepiness and/or sleep. The weight of evidence indicates that L-tryptophan in doses of 1 g or more produces an increase in rated subjective sleepiness and a decrease in sleep latency (time to sleep). There are less firm data suggesting that L-tryptophan may have additional effects such as decrease in total wakefulness and/or increase in sleep time. Best results (in terms of positive effects on sleep or sleepiness) have been found in subjects with mild insomnia, or in normal subjects reporting a longer-than-average sleep latency. Mixed or negative results occur in entirely normal subjects--who are not appropriate subjects since there is no room for improvement. Mixed results are also reported in severe insomniacs and in patients with serious medical or psychiatric illness.
Modulating central serotonergic function by acute tryptophan depletion (ATD) has provided the fundamental insights into which cognitive functions are influenced by serotonin. It may be expected that serotonergic stimulation by tryptophan (Trp) loading could evoke beneficial behavioural changes that mirror those of ATD. The current review examines the evidence for such effects, notably those on cognition, mood and sleep. Reports vary considerably across different cognitive domains, study designs, and populations. It is hypothesised that the effects of Trp loading on performance may be dependent on the initial state of the serotonergic system of the subject. Memory improvements following Trp loading have generally been shown in clinical and sub-clinical populations where initial serotonergic disturbances are known. Similarly, Trp loading appears to be most effective for improving mood in vulnerable subjects, and improves sleep in adults with some sleep disturbances. Research has consistently shown Trp loading impairs psychomotor and reaction time performance, however, this is likely to be attributed to its mild sedative effects. (c) 2009 Elsevier Ltd. All rights reserved.
5-HTP (Hydroxytryptophan) and tryptophan have been examined to see whether these treatments are effective, safe and acceptable in treating unipolar depression in adults. The researchers reported that the symptoms of depression decreased when 5-HTP and tryptophan were compared to a placebo (non-drug). However, side effects had occurred (dizziness, nausea and diarrhoea). They also reported that tryptophan has been associated with the development of a fatal condition. More evidence is needed to assess efficacy and safety, before any strong and meaningful conclusions can be made. Until then, the reviewers propose that the use of antidepressants which have no known life threatening side effects remain more attractive. The review sets out the required methodology for effectively studying these substances in proper controlled studies.
Mood: Consuming tryptophan increases the concentration of tryptophan in the brain and synthesis of serotonin. “The neurotransmitter, serotonin (5-HT), synthesized in the brain, plays an important role in mood alleviation, satiety, and sleep regulation. Although certain fruits and vegetables are rich in 5-HT, it is not easily accessible to the CNS due to blood brain barrier. However the serotonin precursor, tryptophan, can readily pass through the blood brain barrier. Tryptophan is converted to 5-HT by tryptophan hydroxylase and 5-HTP decarboxylase, respectively, in the presence of pyridoxal phosphate, derived from vitamin B6. Hence diets poor in tryptophan may induce depression as this essential amino acid is not naturally abundant even in protein-rich foods.”
Neuroprotection: Other benefits of melatonin include general neuroprotective effects, as melatonin is a powerful antioxidant. Melatonin also has several anti-cancer properties, and is currently being investigated for its role in fighting breast cancer. “Both in vitro studies and in vivo studies have shown that melatonin is a potent scavenger of the highly toxic hydroxyl radical and other oxygen- centered radicals, suggesting that it has actions not mediated by receptors.31 In one study, melatonin seemed to be more effective than other known anti- oxidants (e.g., mannitol, glutathione, and vitamin E) in protecting against oxidative damage. There- fore, melatonin may provide protection against dis- eases that cause degenerative or proliferative changes by shielding macromolecules, particularly DNA, from such injuries. However, these antioxidant effects require concentrations of melatonin that are much higher than peak nighttime serum concentrations. Thus, the antioxidant effects of melatonin in humans probably occur only at pharmacologic concentrations….The decrease in nighttime serum melatonin concentrations that occurs with aging, together with its multiple biologic effects, has led several investigators to suggest that melatonin has a role in aging and age-related diseases. Studies in rats and mice suggest that diminished melatonin secretion may be associated with an acceleration of the aging process. Melatonin may provide protection against aging through attenuation of the effects of cell damage induced by free radicals or through immunoenhancement. However, the age-related reduction in nighttime melatonin secretion could well be a consequence of the aging process rather than its cause, and there are no data supporting an antiaging effect of melatonin in humans.”
Light suppresses melatonin while darkness stimulates its synthesis. Many people have trouble falling asleep. Delayed sleep phase syndrome results in late sleep onset, despite normal sleep architecture and total sleep duration. Melatonin has been shown to improve sleep latency (the time it takes to fall asleep) in several randomized controlled studies. Rather than immediately prior to sleeping, melatonin works best when given two hours before sleeping. Melatonin is also useful for jet lag, irregular sleep-wake rhythms, and shift work sleep disorder. Exogenously administered melatonin has phase shifting properties, and the effect follows a phase- response curve (PRC) that is about 12 h out of phase with the PRC [phase response curve] of light Melatonin administered in the afternoon or early evening will phase advance the circadian rhythm, whereas melatonin administered in the morning will phase delay the circadian rhythm (Fig. 2). The magnitude of phase shifts is time-dependent, and the maximal phase shifts result when melatonin is scheduled around dusk or dawn. The effect of exogenous melatonin is minimal when administered during the night, at least during the first-half of the night.
Nonapnea sleep disorders: Nonapnea sleep disorder In humans, melatonin secretion increases soon after the onset of darkness, peaks in the middle of the night (between 2 and 4 a.m.), and gradually falls during the second half of the night
Taurine has a variety of actions in the body such as cardiotonic, host-defensive, radioprotective and glucose-regulatory effects. However, its action in the central nervous system remains to be characterized. In the present study, we tested to see whether taurine exerts anti-anxiety effects and to explore its mechanism of anti-anxiety activity in vivo. The staircase test and elevated plus maze test were performed to test the anti-anxiety action of taurine. Convulsions induced by strychnine, picrotoxin, yohimbine and isoniazid were tested to explore the mechanism of anti-anxiety activity of taurine. The Rotarod test was performed to test muscle relaxant activity and the passive avoidance test was carried out to test memory activity in response to taurine. Taurine (200 mg/kg, p.o.) significantly reduced rearing numbers in the staircase test while it increased the time spent in the open arms as well as the number of entries to the open arms in the elevated plus maze test, suggesting that it has a significant anti-anxiety activity. Taurine's action could be due to its binding to and activating of strychnine-sensitive glycine receptor in vivo as it inhibited convulsion caused by strychnine; however, it has little effect on picrotoxin-induced convulsion, suggesting its anti-anxiety activity may not be linked to GABA receptor. It did not alter memory function and muscle activity. Taken together, these results suggest that taurine could be beneficial for the control of anxiety in the clinical situations. Copyright (c) 2007 S. Karger AG, Basel.
Excitatory amino acid stimulation of phosphatidylinositol (PI) hydrolysis has been associated with development of the CNS. Normally minimally ineffective in stimulating PI hydrolysis in the neonatal rat cerebellum, N-methyl-D-aspartate (NMDA) increased levels of PI hydrolysis 82.3 +/- 5.5% above basal values in the presence of 1 microM baclofen, a gamma-aminobutyric acidB (GABAB) receptor agonist. This effect was observed at day 7 but not in adult cerebellum. The effect of baclofen could be mimicked by low dose GABA and taurine, actions which were blocked by prior application of a specific GABAB antagonist. Therefore, the ability of NMDA to stimulate PI hydrolysis in neonatal cerebellar tissue may be regulated by the degree of GABAB receptor stimulation.
The interactions of taurine with GABAB receptors were studied in membranes from the brain of the mouse by measuring the binding of [3H]baclofen and that of [3H]GABA in the presence of isoguvacine. Taurine displaced ligand binding to GABAB receptors concentration-dependently with an IC50 in the micromolar range. The effects of baclofen on the release of taurine and GABA from slices of cerebral cortex of the mouse were assessed using a superfusion system. Potassium-stimulated release of both [3H]taurine and [3H]GABA was unaffected by baclofen but potentiated by delta-aminovalerate. The enhancement of release of [3H]taurine by delta-aminovalerate was partially antagonized by baclofen, suggesting that baclofen-sensitive receptors could modify the release.
Taurine, an inhibitory amino acid, potently acts on a subclass of gamma-aminobutyric acid type A (GABAA) receptors. Taurine competitively inhibits [3H]muscimol binding to purified GABAA receptors with an average IC50 value of 50 microM, and enhances [3H]flunitrazepam binding to GABAA-linked benzodiazepine receptors with an EC50 of about 10 microM and with maximal extent lower than that for GABA. Taurine shows variable affinities (low micromolar to near millimolar) for muscimol binding sites in different brain regions as measured by autoradiography. The taurine-sensitive GABA sites are enriched in dentate gyrus, substantia nigra, cerebellum molecular layer, median thalamic nuclei, and hippocampal field CA3; these areas are also enriched in mRNA for the GABA-binding beta 2 subunit subtype. Taurine shows differential affinities for the multiple muscimol-GABA binding polypeptides present in purified GABAA receptors, notably a higher affinity for a beta 55 than a beta 58 polypeptide; these probably represent beta 2 and beta 3 clones, respectively. This work defines a significant target of taurine's inhibitory activity as some GABAA receptor GABA sites, lending support to the hypothesis that this endogenous substance may have a physiological action.
Anxiety & Sleep: Taurine helps with both sleep and anxiety through reducing excitatory neurotransmission. It increases GABA in the brain, can bind to GABA receptors, and indirectly suppresses NMDA signaling. It also acts on glycine receptors, which contributes to its anti-anxiety effects.
