Visible Light Anaerobic Photoconversion of Tyrosine Sensitized by Riboflavin. Cytotoxicity on Mouse Tumoral Cells (original) (raw)
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Amino Acids, 2012
The results of the present investigation show the susceptibility of tyrosine to undergo visible lightinduced photomodification to 3-nitrotyrosine in the presence of nitrite and riboflavin, as sensitizer. By changing H 2 O by D 2 O, it could be established that singlet oxygen has a minor role in the reaction. The finding that nitration of tyrosine still occurred to a large extent under anaerobic conditions indicates that the process proceeds mainly through a type I mechanism, which involves the direct interaction of the excited state of riboflavin with tyrosine and nitrite to give tyrosyl radical and nitrogen dioxide radical, respectively. The tyrosyl radicals can either dimerize to yield 3,3 0-dityrosine or combine with nitrogen dioxide radical to form 3-nitrotyrosine. The formation of 3-nitrotyrosine was found to increase with the concentration of nitrite added and was accompanied by a decrease in the recovery of 3,3 0-dityrosine, suggesting that tyrosine nitration competes with dimerization reaction. The riboflavin photosensitizing reaction in the presence of nitrite was also able to induce nitration of tyrosine residues in proteins as revealed by the spectral changes at 430 nm, a characteristic absorbance of 3-nitrotyrosine, and by immunoreactivity using 3-nitrotyrosine antibodies. Since riboflavin and nitrite are both present endogenously in living organism, it is suggested that this pathway of tyrosine nitration may potentially occur in tissues and organs exposed to sunlight such as skin and eye.
Sensitized Photooxidation of Di and Tripeptides of Tyrosine
Photochemistry and Photobiology, 1998
This paper studies the dye-sensitized photooxidation of tyrosine (tyr) and tyr di- and tripeptides (tyr-tyr and tyr-tyr-tyr) mediated by singlet molecular oxygen (O,[l]) in alkaline media. Photooxidation quantum efficiencies (φr) were obtained by determining the overall and reactive rate constants of interaction with the oxidative species, employing the time-resolved O,(l) phosphorescence detection method and static-photolysis actinometric method, respectively. The interaction of O,(l)-tyr derivatives occurs through an intermediate encounter complex with polar character. Ionization of the phenolic OH group of tyr derivatives and the polarity of the solvent favors the overall interaction. Nevertheless, & values decrease when changing from water to MeCN-water medium. This indicates that the reactive deactivation of the encounter complex, probably an entropy-controlled step, may be affected by solvent polarity in the same way as those processes in which charg- es are neutralized along the reaction pathway. Photooxidation quantum efficiencies indicate that the contribution to O,(′) physical quenching (a second alternative deactivation route for the encountered complex [O,(′)-tyr derivatives]) increases with the complexity of the peptide. As a result, the selfprotection of the peptidic entity against physical quenching also increases. The information obtained from the fractional consumption mol OJmol tyr derivative (in tyr, the di- and tripeptides and the respective methyl ester of tyr and the tripeptide), together with the evolution (either consumption and/or generation) of primary amino groups upon photosensitized irradiation of the same compounds clearly indicates that the photooxidation of di- and tri-tyr peptides proceeds with the breakage of peptidic bonds. As a consequence, in the final balance each tyr unity behaves as an independent photooxidizable target.
Visible light effects on tumoral cells in a culture medium enriched with tryptophan and riboflavin
Journal of Photochemistry and Photobiology B: Biology, 1994
When NS0/2 myeloid cell line and teratocarcinoma F9 cells were irradiated in Dulbecco's modified Eagle medium enriched with tryptophan and riboflavin, toxic photoproducts for these tumoral cells were generated. The active participation of 'Or and *OH was established using specific scavengers and quenchers. A cytotoxic effect was also observed when unirradiated tumoral cells were incubated in a previously irradiated culture medium enriched with tryptophan and riboflavin. When irradiated medium was used alone, enriched only with tryptophan or only with riboflavin, no toxic effect was observed. The relevance of charge transfer processes between triplet riboflavin and tryptophan in the generation of cytotoxic photoproducts is discussed.
The role of 4- and 5-aminosalicylic acids in a riboflavin-photosensitised process
Journal of Photochemistry and Photobiology A: Chemistry, 2003
A kinetic study on the effect of the therapeutic anti-oxidative drugs 4-and 5-aminosalicylic acids (ASA) in a Vitamin B2 (riboflavin (Rf))-photosensitised process was performed. Employing Rf 0.01-0.02 mM and ASA 0.5-1 mM both in the excited singlet and triplet states of the pigment are quenched by ASA with rate constant values slightly lower than the diffusional ones. From the latter states singlet molecular oxygen and Rf •− are generated and subsequently scavenged with the concomitant degradation of ASA, mainly by means of superoxide radical anion. As a consequence, the photodegradation of the vitamin is impeded due to the electron transfer process from Rf − to ground state dissolved oxygen.
The riboflavin-mediated photooxidation of doxorubicin
Cancer Chemotherapy and Pharmacology, 2000
Purpose: Previously, it was shown that exposing doxorubicin (ADR) to 365 nm light resulted in the loss of its cytotoxic activity as well as its absorbance at 480 nm. These processes were much enhanced when mediated by ribo¯avin. In the present study we investigated the quantitative and qualitative aspects of riboavin-mediated photodegradation of ADR. Methods: ADR solutions containing variable concentrations of ribo¯avin and other agents were exposed to 365 nm light for variable time periods and then the absorbance spectrum of ADR was measured by a double beam spectrophotometer. These measurements were used to calculate the half-time of the ADR degradation process. The degraded ADR solutions were analyzed by chromatography and mass spectrometry. Results: Analysis of the ribo¯avin eect indicated that a maximal rate of photolytic degradation of ADR was obtained only after most of the ADR molecules had formed bimolecular complexes with ribo¯avin. The retardation of lumichrome formation by ADR and the inhibition of ADR bleaching by excess of ascorbic acid suggested that ADR was degraded by a photooxidation process. Similar spectral changes occurred when ADR was exposed to strong oxidizers such as sodium hypochlorite and dipotassium hexachloroiridate. Cyclic voltammetry revealed that the oxidation-reduction process of ADR was not electrochemically reversible and therefore the oxidation potential could not be determined accurately; however its value should be between 0.23 and 0.78 V. Analysis of the photooxidative process revealed that it was not mediated by the formation of singlet oxygen, superoxide anion radicals, hydrogen peroxide or hydroxyl radicals, and it is suggested that ADR was oxidized directly by the excited triplet ribo¯avin. The mass spectrograms and the HPLC chromatograms of photooxidized ADR indicate that the central ring of ADR was opened and that 3-methoxysalicylic acid was produced by this cleavage. Conclusions: The ribo¯avinmediated photodegradation of ADR is an oxidative process resulting in the cleavage of the anthraquinone moiety. 3-Methoxysalicylic acid was identi®ed as one of the resulting fragments. It is possible that some of the large fractions of the ADR metabolites that are nonuorescent are the result of an in vivo oxidation of ADR and that 3-methoxysalicylic acid may play a role in the dierent biological activities of ADR.
A study of simultaneous photolysis and photoaddition reactions of riboflavin in aqueous solution
Journal of Photochemistry and Photobiology B: Biology, 2004
The photodegradation reactions of riboflavin (RF) in the presence of 0.05-2.00 M phosphate (pH 7.0) have been studied using a specific multicomponent spectrophotometric method. The reactions involve simultaneous photolysis (intramolecular photoreduction) and photoaddition (intramolecular photoaddition) leading to lumichrome (LC) and cyclodehydroriboflavin (CDRF), respectively, as major products. The contribution of each reaction in the overall photodegradation depends upon the phosphate concentration, i.e., higher the phosphate concentration higher the extent of photoaddition. The apparent first-order rate constants for the photodegradation of RF and for the formation of LC and CDRF at 0.25-2.00 M phosphate concentration range from 0.65 to 3.03 Â 10 À2 , and from 0.41 to 0.99 Â 10 À2 and 0.12 to 1.63 Â 10 À2 min À1 , respectively. The second-order rate constants for the phosphate catalysed photodegradation of RF and for the formation of LC and CDRF are 2.12 Â 10 À4 and 0.61 Â 10 À4 and 1.41 Â 10 À4 M À1 s À1 , respectively. Since the formation of CDRF by photoaddition is catalysed by HPO 2À 4 ions [Eur. J. Biochem. 57 (1975) 35], it is suggested that H 2 PO À 4 ions may be involved in the formation of LC by photolysis. Thus, both H 2 PO À 4 and HPO 2À 4 ions may catalyse the two major reaction pathways of riboflavin photodegradation, respectively.
The enhancement of riboflavin-mediated photo-oxidation of doxorubicin by histidine and urocanic acid
Cancer Chemotherapy and Pharmacology - CANCER CHEMOTHER PHARMACOL, 2001
Purpose: Previously we have shown that doxorubicin (Adriamycin, ADR) can be inactivated by light-excited riboflavin. The inactivation of the drug results from its direct oxidation by the excited triplet riboflavin in a type I photosensitization reaction, and 3-methoxysalicylic acid is an ADR breakdown product. In the present study, we investigated the enhancement of this process by histidine and some other imidazole analogs. Methods: ADR solutions containing various concentrations of riboflavin and other agents were exposed to 365 nm light for various time periods and then the absorbance spectrum of ADR was measured by a double beam spectrophotometer. These measurement were used to calculate the half-time of the ADR degradation process. The degraded ADR solutions were analyzed by HPLC. Results: The rate of bleaching of ADR by light-excited riboflavin was enhanced in the presence of histidine in a concentration-dependent manner. This enhancement was more pronounced at higher riboflavin concentrations. Histidine also enhanced the riboflavin-mediated photobleaching of N,N-dimethyl-4-nitrosoaniline (RNO), a compound known to be resistant to oxidation by singlet oxygen but sensitive to oxidation by the trans-annular peroxide of histidine. RNO was found to block the histidine enhancement of the riboflavin-mediated photobleaching of ADR in a competitive manner. Among the imidazole analogs of histidine tested, urocanic acid was found to be the most efficient enhancer of the riboflavin-mediated photobleaching of ADR. Superoxide anion radicals which retard the oxidation of ADR were quenched by urocanic acid but not by histidine. It was shown that the oxidation of ADR by the trans-annular peroxide of histidine resulted in the formation of 3-methoxysalicylic acid. Conclusions: In contrast to singlet oxygen, the trans-annular peroxide, formed by the interaction of histidine and the singlet oxygen produced by photoexcited riboflavin, is an efficient oxidizer of ADR. The enhancement of the riboflavin-mediated photobleaching of ADR by histidine analogs depends on the rate of their conversion to a trans-annular peroxide and on the efficiency of these products in oxidizing ADR. However, for some analogs of histidine, as shown for urocanic acid, other mechanisms could also be involved. The presence of urocanic acid in the skin suggests that significant degradation of ADR could occur in the presence of biologically relevant concentrations of riboflavin if patients treated with ADR are exposed to sunlight. The finding that histidine also enhanced the degradation of ADR to 3-methoxysalicylic acid, suggests that the process of ADR oxidation by the trans-annular peroxides is similar to the direct oxidation of ADR by excited triplet riboflavin.
Pheomelanin Effect on UVB Radiation-Induced Oxidation/Nitration of l-Tyrosine
International Journal of Molecular Sciences, 2021
Pheomelanin is a natural yellow-reddish sulfur-containing pigment derived from tyrosinase-catalyzed oxidation of tyrosine in presence of cysteine. Generally, the formation of melanin pigments is a protective response against the damaging effects of UV radiation in skin. However, pheomelanin, like other photosensitizing substances, can trigger, following exposure to UV radiation, photochemical reactions capable of modifying and damaging cellular components. The photoproperties of this natural pigment have been studied by analyzing pheomelanin effect on oxidation/nitration of tyrosine induced by UVB radiation at different pH values and in presence of iron ions. Photoproperties of pheomelanin can be modulated by various experimental conditions, ranging from the photoprotection to the triggering of potentially damaging photochemical reactions. The study of the photomodification of l-Tyrosine in the presence of the natural pigment pheomelanin has a special relevance, since this tyrosine ...