Sex differences in amino acids lost via sweating could lead to differential susceptibilities to disturbances in nitrogen balance and collagen turnover

Abstract

Fluid collected during sweating is enriched with amino acids derived from the skin’s natural moisturising factors and has been termed “faux” sweat. Little is known about sex differences in sweat amino acid composition or whether faux sweat amino acid losses affect nitrogen balance. Faux sweat collected by healthy adults (n = 47) after exercise, and at rest by chronic fatigue patients, was analysed for amino acid composition. Healthy females had higher total amino acid concentrations in sweat (10.5 ± 1.2 mM) compared with healthy males (6.9 ± 0.9 mM). Females had higher levels of 13 amino acids in sweat including serine, alanine and glycine. Higher hydroxyproline and proline levels suggested greater collagen turnover in females. Modelling indicated that with conservative levels of exercise, amino acid losses in females via faux sweat were triple than those predicted for urine, whereas in males they were double. It was concluded that females were more susceptible to key amino acid loss during exercise and/or hot conditions. Females reporting chronic fatigue had higher levels of methionine in faux sweat than healthy females. Males reporting chronic fatigue had higher levels of numerous amino acids in faux sweat compared to healthy males. Higher amino acid loss in faux sweat associated with chronic fatigue could contribute to a hypometabolic state. Depending on activity levels, climatic conditions and gender, amino acid losses in sweat and skin leachate could influence daily protein turnover where periods of continuously high turnover could lead to a negative net nitrogen balance.

Modelling of protein turnover provides insight for metabolic demands on those specific amino acids utilised at disproportionately faster rates than other amino acids

“…de Koning et al (2003) Present in sweat and urine at significantly higher concentrations than found in plasma Dunstan et al (2016Dunstan et al ( , 2017) Source Non-essential as it can be synthesised by the body Serine synthesis can be insufficient to meet body demands leading to sub-optimal growth Maxwell et al (1956) Addition of non-essential serine can instigate improved growth in human cells Eagle (1959) Classified as conditionally essential Histidine Used as the precursor for urocanic acid which is a humectant working as part of the natural moisturising factor on the skin Scott et al (1982), Rawlings and Harding (2004) Is an essential amino acids in humans Required for synthesis of haemoglobin Kopple and Swendseid (1975) Deficit in diet can lead to anaemia Clemens et al (1984), Cooperman and Lopez (2002) Histidine can stabilise oxyhaemoglobin and C)-bound haemoglobin Required for the formation of carnosine Bauchart et al (2007), Tamaki et al (1984) Carnosine is highly concentrated in the muscles and brain Acts as an anti-oxidant, chelating agent, Reddy et al (2005) Acts as an anti-glycating agent to reduce the rate of progression of certain degenerative diseases Hobart et al (2004) Required for the formation of histamine Facilitates inflammatory immune response Stimulates gastric secretion Neurotransmission roles Nieto-Alamilla et al (2016) Histidine is a major component in actin and myosin families of muscle proteins Methylated to form 3-methyl-histidine Anti-inflammatory and anti-secretory properties Histidine acts as an anti-oxidant by scavenging the hydroxyl radical and singlet oxygen Raghavan et al (1989), Wade and Tucker (1998) Present in sweat and urine at significantly higher concentrations than found in plasma Dunstan et al (2016Dunstan et al ( , 2017 Activated sympathetic neurotransmission to adipose tissues and accelerated energy expenditure Konishi et al (2015) Decreased food intake (appetite suppression) Increased fat utilisation in brown adipose tissue Present in sweat at significantly higher concentrations than found in plasma Dunstan et al (2016) Source Non-essential as it can be synthesised by the body Ornithine synthesis can be insufficient to meet body demands leading to Sub-optimal nitrogen excretion Inefficient energy metabolism Could be classified as conditionally essential…”

“…Represents 11.5% of all amino acids Wu (2010a, b) Represents 20% of the amino acids in proteins Represents 33% of amino acids in collagen which is the most abundant family of proteins in the body Wu (2009) Used as a humectant in the natural moisturising factor in the skin Scott et al (1982) Inhibitory nerve transmitter Rajendra et al (1997) Glycine modulates Ca 2+ levels in leukocytes and macrophages regulating the production of cytokines, and the generation of superoxide for immune function Zhong et al (2003) Conjugation with bile acids with a key role in digestion and absorption of fatty acids, lipophilic nutrients and lipid-soluble vitamins Hafkenscheid and Hectors (1975) Found in major pathways of metabolism Hall (1998) Purines for generating nucleosides, nucleotides, RNA and DNA Haem for haemoglobin and cytochromes critical for oxygen transport/CO 2 removal and mitochondrial electron transport Dai et al (2013) Creatine which participates in energy metabolism within muscles and nerves Glutathione which is the most abundant low molecular weight thiol and the major anti-oxidant in cells Wu et al (2004) Present in sweat and urine at significantly higher concentrations than found in plasma Dunstan et al (2016Dunstan et al ( , 2017) Source It is technically classified as non-essential as it can be synthesised by the body Darling et al (1999), Wu (2010a) Glycine synthesis can be insufficient to meet body demands leading to sub-optimal growth, impaired immune responses…”

“…These amino acids were identified as histidine, serine, glycine, ornithine, lysine, and aspartic acid. The concentrations of these amino acids were higher in sweat from females compared with males, suggesting that females may be more susceptible to fatigue from altered nitrogen homeostasis (Dunstan et al 2017). It was also shown that the average losses of histidine, glycine, serine, and lysine comprised nearly 60% of amino acids excreted through urine (Dunstan et al 2017).…”

“…The concentrations of these amino acids were higher in sweat from females compared with males, suggesting that females may be more susceptible to fatigue from altered nitrogen homeostasis (Dunstan et al 2017). It was also shown that the average losses of histidine, glycine, serine, and lysine comprised nearly 60% of amino acids excreted through urine (Dunstan et al 2017). The combined losses of these key amino acids from urination and sweating were modelled under various scenarios ranging from sedentary-to medium-level exertion.…”

“…The combined losses of these key amino acids from urination and sweating were modelled under various scenarios ranging from sedentary-to medium-level exertion. It was demonstrated that the losses of these amino acids become very extensive, as exertion levels rise (Dunstan et al 2017).…”