Abstract
Recent reports show that the worldwide incidence of autism spectrum disorder (ASD) is dramatically increasing, although ASD etiology and pathogenesis are still far to be fully elucidated. Some dietary-derived essential compounds, such as the amino acid tryptophan, appear to be impaired in patients with ASD. Tryptophan (Trp) plays a significant role in the human organism and serves as a precursor for a wide range of bioactive compounds, including major neurotransmitters. Research indicates that tryptophan might be deficient in subjects with ASD. Deficiency in the tryptophan level can be retrieved by investigating Trp levels or its major metabolite kynurenine in urines. The purpose of the present study is to quantify tryptophan content in urine samples (n = 236) of ASD patients, who underwent a supplemented dietary panel with B vitamins and magnesium, compared to controls (without this diet regimen). The samples were analyzed with gas chromatography-mass spectrometry. Additionally, the correlation between body mass index (BMI) and the level of this amino acid in urine was accomplished. Basic parameters of urine samples were also evaluated. Statistical evaluations in the concentration of tryptophan in ASD patients with different severity of symptoms were reported. A significant difference in tryptophan levels in all groups was observed. Supplementation with B vitamins and magnesium has an influence on the Trp concentration. Furthermore, no correlation between BMI and tryptophan levels was found. These results assess that the Trp level in ASD subjects is critical and that intake of B vitamins and magnesium with diet might influence its metabolic homeostasis.
Highlights
L-tryptophan is an essential amino acid, which plays a significant role even in neurodegeneration if its catabolism isMetab Brain Dis (2017) 32:1585–1593 functionally impaired (Morris et al 2016a, b)
Tryptophan levels in urine can help researchers to highlight the relationship between this amino acid and its relationship with catabolites such as kynurenine with neurological and cognitive disorders associated with immune-related pathology (Gabbay et al 2010; Keegan et al 2016)
Precursors of L-tryptophan can be found in eggs, meat, cereal, milk, bananas, fish, seafood and plums, though the amino acid is synthesized by gut microflora, which should contribute to altered tryptophan metabolism, yielding increased levels of indolyl 3-acetic acid and indolyl lactate (Richard et al 2009; Gevi et al 2016)
Summary
L-tryptophan is an essential amino acid, which plays a significant role even in neurodegeneration if its catabolism isMetab Brain Dis (2017) 32:1585–1593 functionally impaired (Morris et al 2016a, b). The increase in the indolamine-2,3dioxygenase (IDO), the tryptophan-metabolizing enzyme, has been associated with immunological and inflammatory disorders, at least in animal models (Wirthgen et al 2016). Tryptophan levels in urine can help researchers to highlight the relationship between this amino acid and its relationship with catabolites such as kynurenine with neurological and cognitive disorders associated with immune-related pathology (Gabbay et al 2010; Keegan et al 2016). Precursors of L-tryptophan can be found in eggs, meat, cereal, milk, bananas, fish, seafood and plums, though the amino acid is synthesized by gut microflora, which should contribute to altered tryptophan metabolism, yielding increased levels of indolyl 3-acetic acid and indolyl lactate (Richard et al 2009; Gevi et al 2016). Tryptophan plays a role in the serotonin and kynurenine pathway, protein synthesis, and bacterial degradation, as current literature reported evidence about the role of tryptophan metabolites, especially serotonin, in the pathophysiology of the gut, through the many mechanisms underlying these connections are still far to be elucidated (Peters 1991; Keszthelyi et al 2009; Gevi et al 2016)
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