Photosensitized Oxidation of Tryptophan: Effect on Liver and Brain Tryptophan

Abstract

Toxic products are formed when tryptophan is irradiated with light in the presence of photosensitizers such as riboflavin. In order to further investigate this phenomenon, solutions of tryptophan (48 mumol.mL-1) were irradiated with broad spectrum fluorescent light in the presence or absence of riboflavin (0.01 mg.mL-1). Solutions of riboflavin were similarly irradiated; control solutions were the respective solutions not exposed to light. Two-week-old suckling gerbils were then assigned to receiving 7 days of intraperitoneal injections of the light-exposed or non-light-exposed solutions. There were significant differences in the concentrations of tryptophan in serum, liver, and brain; activity of gamma-glutamyl transferase (GGT) as well as liver protein were also significantly different among the groups. Body and liver weights were also significantly different among the groups. In order to identify the photoproducts responsible for these changes, solutions of tryptophan that had been irradiated with light in the presence of riboflavin were then fractionated based on time of elution during high-pressure liquid chromatography and the fractions were then injected into the gerbils as before. GGT responses to one of the fractions was similar to that of the parent compound. Chromatographic studies indicated the presence of numerous photoadduct compounds of tryptophan and riboflavin after exposure to light. Both the presence of riboflavin and the exposure of the solutions to light alter brain concentrations of tryptophan in the developing gerbil indicating differing availability to the brain of this serotonin precursor. Clinical implications of the infusion of amino acids in the presence of photosensitizers and light must be considered.

Lichtschutz für Lösungen zur parenteralen Ernährung von Säuglingen und Kindern bis zum Alter von 2 Jahren

“…Aminosäuren reduzieren bzw. verhindern in Mischlösungen mit Lipidemulsionen oder Multivitaminpräparaten die Peroxidbildung [9], werden hierbei aber oxidiert [16,17]. Die Bildung von Peroxiden in Lipidemulsionen ist bei Raumlicht gering, bei Fototherapielicht erheblich [7].…”

Flavins Act as a Critical Liaison Between Metabolic Homeostasis and Oxidative Stress in the Retina

“…These species are further prone to decomposition in presence of redox active metal ions to yield alkoxyl radicals, which can add to the oxidative damage (Cardoso et al, 2012). Detailed investigations have revealed that among all the amino acids, tryptophan is most susceptible to such flavin-sensitized photooxidation in an oxygen-independent mechanism (Bhatia et al, 1991;Silva et al, 1991Silva et al, , 1994Garcia and Silva, 1997;Fuentes-Lemus and Lopez-Alarcon, 2020). Excited state riboflavin binds to tryptophan under a light-induced reaction and leads to cytotoxicities like axonal degeneration and further cascade of photo-adduct formation (Silva et al, 1991;Lucius et al, 1998;Lopez-Alarcon et al, 2014).…”