Protective Effect of Boldo and Tea Infusions on the Visible Light–mediated Pro-oxidant Effects of Vitamin B2, Riboflavin¶

Abstract

The effect of Boldo and black tea infusions on the pro-oxidant effects of vitamin B2, riboflavin (RF), when exposed to the action of visible light was studied. The amounts of antioxidants present in Boldo and tea infusions were evaluated by a procedure based on the bleaching of preformed 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cations and were expressed as 6-hydroxy-2,5,7,8-tetramethyl-chroman-2-carboxylic acid equivalent concentrations. The quenching rate constants of singlet oxygen (1O2; [kq]Boldo = 6.0 x 10(7) M(-1) s(-1) and [kq]Tea = 3.2 x 10(7) M(-1) s(-1)) and triplet RF (3RF; [3RFkq]Boldo = 10 x 10(8) M(-1) s(-1) and [3RFkq]TEA = 3.2 x 10(8) M(-1) s(-1)) with Boldo and tea were determined by flash photolysis. These data allow a quantitative interpretation of the results obtained. Our data suggest that most of the oxygen consumption observed in the photolysis of RF in the presence of tea and Boldo infusions is caused by 1O2 reactions. The oxygen consumption quantum yield is considerably smaller than the fraction of RF triplets trapped by the additives (AH) present in the infusion, indicating that their interaction with 3RF does not lead to chemical reactions or that the AH*+ radical ions initially formed participate in secondary processes that do not consume oxygen. Boldo and tea infusions have a significant protective effect when a system containing RF and tryptophan (Trp) is exposed to visible light, not only by quenching the 1O2 and interfering with the Type-I mechanism but also by repairing the damage to Trp molecules associated with the latter mechanism.

Direct identification of phenolic constituents in Boldo Folium (Peumus boldus Mol.) infusions by high-performance liquid chromatography with diode array detection and electrospray ionization tandem mass spectrometry

“…Boldo hydroalcoholic extract present a relevant hepatoprotective effect and boldine was at least partially responsible for the reported liver protecting but not for the anti-inflammatory effect [10]. The in vitro antioxidant effect of herbal teas consumed in Chile, including P. boldus leaf infusion was reported [9,11,12]. In a previous communication [7], we showed that catechin was one of the antioxidant compounds of boldo leaves, and that the relative concentration of alkaloids and phenolics in boldo extracts suggested that free-radical scavenging effect is mainly due to catechin and flavonoids rather than to the aporphine alkaloids content.…”

Riboflavin Crystals with Extremely High Water Solubility

“…Rf is an excellent natural photosensitizer that generates reactive oxygen species under light irradiation and can induce amino acid and protein oxidation . Namely, it is involved in the photodecomposition of free or protein-bound amino acids including tryptophan and tyrosine , and the photoinactivation of enzymes including lysozymes. In addition, it promotes the photodegradation of folic acid to 6-carboxypterin .…”

Endogenous Photosensitizers in Human Skin

“…In addition, lumichromes are formed as products during the photochemical reactions of riboflavin. Triplet state riboflavin mediates the photodegradation of free or protein-bound amino acids such as tryptophan and tyrosine , and initiates the photoinactivation of enzymes such as lysozyme. Although the FAD/FAD •– couple can vary greatly depending on the protein, FAD* is high enough in energy (∼2.5 V) to readily oxidize Trp and Tyr, but not Phe, whose redox potential is substantially higher (>2.2 V, Table ) and may exceed that of the peptide backbone .…”