Melatonin and elimination of kynurenines in children with Down's syndrome

Heightened activity of superoxide dimutase is an effect derived from the gene dose in the trisomy of Down's syndrome (DS), and has been related to the increased production of hydrogen peroxide and with greater lipid peroxidation. Many of the degenerative changes observed in patients with DS have been associated with the pathological effects of free radicals, and for this reason it is of interest to determine the levels present in these patients of powerful antioxidant molecules such as melatonin, and of metabolites with important neuroprotector and neurotoxic consequences such as those derived from the kynurenine pathway.

A study was made of 15 children with DS, together with a control group of 15 non-DS children, matched for age and sex, examined at the Hospital Costa del Sol, Marbella, Spain. Serum melatonin and serotonin were analyzed by RIA; urinary tryptophan metabolites (kynurenine pathway) were determined during periods of light and darkness (09.00-21.00 h and 21.00-9.00 h) by thin-layer chromatography.

The mean values of serotonin and melatonin were found to be lower in the patients with DS, although the level of nocturnal secretion of melatonin was higher. Urinary excretion of kynurenine was lower in the patients with DS, although greater quantities of kynurenic acid and anthranilic acid were excreted.

Patients with DS present levels of plasma melatonin and urinary kynurenine that are lower than the corresponding levels in the control population, together with higher values of kynurenic acid and anthranilic acid. These circumstances constitute an added risk to these patients of damage by free radicals.