l-Ornithine attenuates corticotropin-releasing factor-induced stress responses acting at GABAA receptors in neonatal chicks

L-Citrulline: A novel hypothermic amino acid promoting thermotolerance in heat-exposed chickens

With global warming becoming of increasing concern, poultry farms are experiencing a concomitant increase in heat stress. Chickens are very sensitive to high ambient temperature (HT), so the development of novel nutrients that will help deal with the challenge posed by heat stress is vital. We revealed that L-citrulline (L-Cit) can reduce body temperature in chickens. Orally administered L-Cit solution has been found to provide heat tolerance in chickens and to result in reduced food intake. Heat exposure and oral administration of L-Cit led to increased levels of plasma insulin, whereas heat stress led to a decline in plasma thyroxine. Dietary administration of L-Cit was also shown to be effective to reduce heat stress in broiler chickens. Moreover, L-Cit was found to be metabolized in the liver within 1 h of its administration, and in L-Cit-treated broiler chicks, the Cit-Arginine cycle and the Krebs cycle were found to be active. L-Cit has not yet been approved for inclusion in the poultry diet, so it is important to find alternative sources of L-Cit. Taken together, these findings suggest that L-Cit may serve as an important novel nutrient with the ability to produce heat tolerance in chickens under HT.

Central Taurine Attenuates Hyperthermia and Isolation Stress Behaviors Augmented by Corticotropin-Releasing Factor with Modifying Brain Amino Acid Metabolism in Neonatal Chicks

The objective of this study was to determine the effects of centrally administered taurine on rectal temperature, behavioral responses and brain amino acid metabolism under isolation stress and the presence of co-injected corticotropin-releasing factor (CRF). Neonatal chicks were centrally injected with saline, 2.1 pmol of CRF, 2.5 μmol of taurine or both taurine and CRF. The results showed that CRF-induced hyperthermia was attenuated by co-injection with taurine. Taurine, alone or with CRF, significantly decreased the number of distress vocalizations and the time spent in active wakefulness, as well as increased the time spent in the sleeping posture, compared with the saline- and CRF-injected chicks. An amino acid chromatographic analysis revealed that diencephalic leucine, isoleucine, tyrosine, glutamate, asparagine, alanine, β-alanine, cystathionine and 3-methylhistidine were decreased in response to taurine alone or in combination with CRF. Central taurine, alone and when co-administered with CRF, decreased isoleucine, phenylalanine, tyrosine and cysteine, but increased glycine concentrations in the brainstem, compared with saline and CRF groups. The results collectively indicate that central taurine attenuated CRF-induced hyperthermia and stress behaviors in neonatal chicks, and the mechanism likely involves the repartitioning of amino acids to different metabolic pathways. In particular, brain leucine, isoleucine, cysteine, glutamate and glycine may be mobilized to cope with acute stressors.

Potential Role of Amino Acids in the Adaptation of Chicks and Market-Age Broilers to Heat Stress

Increased average air temperatures and more frequent and prolonged periods of high ambient temperature (HT) associated with global warming will increasingly affect worldwide poultry production. It is thus important to understand how HT impacts poultry physiology and to identify novel approaches to facilitate improved adaptation and thereby maximize poultry growth, health and welfare. Amino acids play a role in many physiological functions, including stress responses, and their relative demand and metabolism are altered tissue-specifically during exposure to HT. For instance, HT decreases plasma citrulline (Cit) in chicks and leucine (Leu) in the embryonic brain and liver. The physiological significance of these changes in amino acids may involve protection of the body from heat stress. Thus, numerous studies have focused on evaluating the effects of dietary administration of amino acids. It was found that oral l-Cit lowered body temperature and increased thermotolerance in layer chicks. When l-Leu was injected into fertile broiler eggs to examine the cause of reduction of Leu in embryos exposed to HT, in ovo feeding of l-Leu improved thermotolerance in broiler chicks. In ovo injection of l-Leu was also found to inhibit weight loss in market-age broilers exposed to chronic HT, giving rise to the possibility of developing a novel biotechnology aimed at minimizing the economic losses to poultry producers during summer heat stress. These findings and the significance of amino acid metabolism in chicks and market-age broilers under HT are summarized and discussed in this review.

The Association Between Concentrations of Arginine, Ornithine, Citrulline and Major Depressive Disorder: A Meta-Analysis

Alterations in the peripheral (e.g., serum, plasma, platelet) concentrations of arginine and its related catabolic products (i.e., ornithine, citrulline) in the urea and nitric oxide cycles have been reported to be associated with major depressive disorder (MDD). The meta-analysis herein aimed to explore the association between the concentration of peripheral arginine, its catabolic products and MDD, as well as to discuss the possible role of arginine catabolism in the onset and progression of MDD. PubMed, EMBASE, PsycINFO and Web of Science were searched from inception to June 2020. The protocol for the meta-analysis herein has been registered at the Open Science Framework [https://doi.org/10.17605/osf.io/7fn59]. In total, 745 (47.5%) subjects with MDD and 823 (52.5%) healthy controls (HCs) from 13 articles with 16 studies were included. Fifteen of the included studies assessed concentrations of peripheral arginine, eight assessed concentrations of ornithine, and six assessed concentrations of citrulline. Results indicated that: (1) the concentrations of arginine, ornithine, and citrulline were not significantly different between individuals with MDD and HCs when serum, plasma and platelet are analyzed together, (2) in the subgroups of serum samples, the concentrations of arginine were lower in individuals with MDD than HCs, and (3) concurrent administration of psychotropic medications may be a confounding variable affecting the concentrations of arginine, ornithine, and citrulline. Our findings herein do not support the hypothesis that arginine catabolism between individuals with MDD and HCs are significantly different. The medication status and sample types should be considered as a key future research avenue for assessing arginine catabolism in MDD.

Nutritional Characteristics and Functions of D-Amino Acids in the Chicken

D-Amino acids occur in modest amounts in bacterial proteins and the bacterial cell wall, as well as in peptide antibiotics. Therefore, D-amino acids present in terrestrial vertebrates were believed to be derived from bacteria present in the gastrointestinal tract or fermented food. However, both exogenous and endogenous origins of D-amino acids have been confirmed. Terrestrial vertebrates possess an enzyme for converting certain L-isomers to D-isomers. D-Amino acids have nutritional aspects and functions, some are similar to, and others are different from those of L-isomers. Here, we describe the nutritional characteristics and functions of D-amino acids and also discuss the future perspectives of D-amino acid nutrition in the chicken.

An acute increase in water temperature can increase free amino acid concentrations in the blood, brain, liver, and muscle in goldfish (Carassius auratus)

Water temperature directly affects the body temperature in fish, so increasing water temperatures in oceans and rivers will lead to increases in fish body temperatures. Whilst a range of responses of fish to increases in water temperature have been measured, amino acid metabolism in a fish under high water temperature (HT) conditions has not been investigated. The aim of this study was to determine the effects of an acute increase in water temperature on oxygen consumption, plasma cortisol concentrations, and free amino acid concentrations in plasma and several tissues in goldfish (Carassius auratus). Oxygen consumption and plasma cortisol concentrations were increased in goldfish exposed to HT (30 ± 1 °C) for 200 min compared with goldfish at a control water temperature (CT 17 ± 1 °C). Oxygen consumption and plasma cortisol concentrations in both groups of fish combined were positively correlated. When goldfish were exposed to HT for 300 min oxygen consumption and plasma concentrations of 15 free amino acids were increased compared with goldish at CT. Concentrations of several free amino acids were increased to varying extents in the brain, liver, and muscle tissues. In conclusion, an acute increase in water temperature affected amino acid metabolism differently in the brain, liver, and muscle tissues. Goldfish will be a useful species for further studies of the possible roles of various amino acids in the brain, muscle, and liver during acute increases in water temperature in fish.

Decreased stress-induced depression-like behavior in lactating rats is associated with changes in the hypothalamic-pituitary-adrenal axis, brain monoamines, and brain amino acid metabolism

Depression-like behavior during lactation may relate to changes in the hypothalamic-pituitary-adrenal (HPA) axis, brain monoamines, and brain amino acid metabolism. This study investigated how the behavior, HPA axis activity, brain monoamines, and brain free amino acid metabolism of rats were changed by stress or lactation period. Rats were separated into four groups: (1) control lactating (n = 6), (2) stress lactating (n = 6), (3) control virgin (n = 7), and (4) stress virgin (n = 7) and restrained for 30 min a total of ten times (once every other day) from postnatal day (PND) 1. Depression-like behavior in the forced swimming test (FST) on PND 10 and concentration of corticosterone in plasma, as well as monoamines and L-amino acids including β-alanine, γ-aminobutyric acid, cystathionine, 3-methyl-histidine and taurine in the prefrontal cortex and hypothalamus on PND 19 were measured. The plasma corticosterone concentration, measured just after restraint stress, was significantly higher in the stress groups, versus the control groups, but there were no significant differences between control and stress lactating groups. Depression-like behavior (immobility) in the FST was significantly lower in the lactating groups, versus the virgin groups. Stress enhanced dopamine and glutamate, and decreased threonine and glycine concentrations in the hypothalamus. In addition, 3-methoxy-4-hydroxyphenylglycol (MHPG), threonine and ornithine concentrations in the prefrontal cortex were significantly higher in the lactating groups compared with the virgin groups. Changes in plasma corticosterone concentration, monoamine, and amino acid metabolism may relate to stress-induced depression-like behavior in lactating rats. Lay summary This study revealed that reduced depression-like behavior in lactating, relative to virgin rats, was associated with changes in monoamine and amino acid metabolism in the prefrontal cortex of the brain. In addition, the effect of stress on monoamine and amino acid metabolism is prominently observed in the hypothalamus and may be related to neuroendocrine stress axis activity and secretion of corticosterone. This study suggested that stress-induced depression-like behavior may be associated with several changes in the stress axis, brain monoamines, and brain amino acid metabolism. These parameters were associated with attenuated depression-like behavior in lactating rats.

Heat Stress Biomarker Amino Acids and Neuropeptide Afford Thermotolerance in Chicks

With global warming, heat stress is becoming a pressing concern worldwide. In chickens, heat stress reduces food intake and growth, and increases body temperature and stress responses. Although it is believed that young chicks do not experience heat stress as they need a higher ambient temperature to survive, our series of studies in young chicks showed that they are sensitive to heat stress. This review summarizes current knowledge on amino acid metabolisms during heat stress, with special emphasis on the hypothermic functions of l-citrulline (l-Cit) and l-leucine (l-Leu), and the functions of neuropeptide Y (NPY) in terms of body temperature and heat stress regulation in chicks. Amino acid metabolism is severely affected by heat stress. For example, prolonged heat stress reduces plasma l-Cit in chicks and l-Leu in the brain and liver of embryos. l-Cit and l-Leu supplementation affords thermotolerance in young chicks. NPY expression is increased in the brains of heat-exposed chicks. NPY has a hypothermic action under control thermoneutral temperature and heat stress in chicks. The NPY-sub-receptor Y5 is a partial mediator of the hypothermic action of NPY. Further, NPY stimulates brain dopamine concentrations and acts as an anti-stress agent in heat-exposed fasted, but not fed chicks. In conclusion, young chicks can serve as a model animal for the study of heat stress in chickens. l-Cit, l-Leu, and NPY were identified as biomarkers of heat stress, with the potential to afford thermotolerance in chicks.

L-Ornithine is a potential acute satiety signal in the brain of neonatal chicks

Recently, we observed that neonatal chicks exhibit feeding behavior characterized by frequent food intake and short resting intervals, with changes detected in the brain amino acid and monoamine concentrations. In this study, we aimed to clarify further the relationship between the appetite of neonatal chicks and brain amino acid metabolism. In Experiment 1, changes were investigated in free amino acids in the brain under conditions of regulated appetite induced by fasting and subsequent short-term re-feeding. Chicks (5 days old) were distributed into four treatment groups--namely, fasting for 3h, and fasting for 3h followed by re-feeding for 10, 20 or 30 min. Brain samples were collected after treatment to analyze free amino acid concentrations. Amino adipic acid and proline in all brain parts as well as arginine and ornithine in all brain parts--except mesencephalic arginine and cerebellar ornithine--were increased in a time-dependent manner following re-feeding. In Experiment 2, we further examined the effect of exogenous administration of some amino acids altered in association with feeding behavior in Experiment 1. We chose L-arginine and its functional metabolite, L-ornithine, to analyze their effects on food intake in chicks. Intracerebroventricular injection (2 μmol) of L-ornithine, but not L-arginine, significantly inhibited food intake in neonatal chicks. In Experiment 3, we found that central injection of L-ornithine (2, 4, and 6 μmol) dose-dependently suppressed food intake in chicks. These results suggested that L-ornithine may have an important role in the control of food intake as an acute satiety signal in the neonatal chick brain.

Randomised controlled trial of the effects of L-ornithine on stress markers and sleep quality in healthy workers

Background

L-ornithine is a non-essential, non-protein amino acid. Although L-ornithine is contained in various foods, the amount is usually small.

Recently, studies have shown that orally administered L-ornithine reduced the stress response in animals.

From these findings, we speculated that L-ornithine may play a role in the relieve of stress and improve sleep and fatigue symptoms in humans. Through a randomised, double-blind, placebo-controlled clinical study, we asked if L-ornithine could be beneficial to stress and sleep in healthy workers.

Method

Fifty-two apparently healthy Japanese adults who had previously felt slight stress as well as fatigue were recruited to be study participants and were randomly divided into either the L-ornithine (400 mg/day) or placebo group. They orally consumed the respective test substance every day for 8 weeks. Serum was collected for the assessment of cortisol and dehydroepiandrosterone-sulphate (DHEA-S). Perceived mood and quality of sleep were measured by the Profile of Mood States (POMS), Athens Insomnia Scale (AIS), and Ogri-Shirakawa-Azumi sleep inventory MA version (OSA-MA).

Results

Serum cortisol levels and the cortisol/DHEA-S ratio were significantly decreased in the L-ornithine group in comparison with the placebo group. Also, anger was reduced and perceived sleep quality was improved in the L-ornithine group.

Conclusion

L-ornithine supplementation has the potential to relieve stress and improve sleep quality related to fatigue, both objectively and subjectively.