Genotoxicity of photoilluminated riboflavin in the presence of Cu(II)

Riboflavin - properties, occurrence and its use in medicine

Riboflavin is built on an isoalloxazin ring, which contains three sixcarbon rings: benzoic, pyrazine and pyrimidine. Riboflavin is synthesized by some bacteria, but among humans and animals, the only source of flavin coenzymes (FAD, FMN) is exogenous riboflavin. Riboflavin transport in enterocytes takes place via three translocators encoded by the SLC52 gene. Deficiency of dietary riboflavin has wide ranging implications for the efficacy of other vitamins, the mechanism of cellular respiration, lactic acid metabolism, hemoglobin, nucleotides and amino acid synthesis. In studies it was found that, pharmacologic daily doses (100 mg) have the potential to react with light, which can have adverse cellular effects. Extrene caution should be exercised when using riboflavin as phototherapy in premature newborns. At the cellular level, riboflavin deficiency leads to increased oxidative stress and causes disorders in the glutathione recycling process. Risk factors for developing riboflavin deficinecy include pregnancy, malnutrition (including anorexia and other eating disorders, vegitarianism, veganism and alcoholism. Furthermore, elderly people and atheletes are also at risk of developing this deficiency. Widespread use of riboflavin in medicine, cancer therapy, treatment of neurodegenerative diseases, corneal ectasia and viral infections has resulted in the recent increased interest in this flavina.

Riboflavin ameliorates cisplatin induced toxicities under photoillumination

Background

Cisplatin is an effective anticancer drug that elicits many side effects mainly due to induction of oxidative and nitrosative stresses during prolonged chemotherapy. The severity of these side effects consequently restricts its clinical use under long term treatment. Riboflavin is an essential vitamin used in various metabolic redox reactions in the form of flavin adenine dinucleotide and flavin mononucleotide. Besides, it has excellent photosensitizing property that can be used to ameliorate these toxicities in mice under photodynamic therapy.

Methods and Findings

Riboflavin, cisplatin and their combinations were given to the separate groups of mice under photoilluminated condition under specific treatment regime. Their kidney and liver were excised for comet assay and histopathological studies. Furthermore, Fourier Transform Infrared Spectroscopy of riboflavin-cisplatin combination in vitro was also conducted to investigate any possible interaction between the two compounds. Their comet assay and histopathological examination revealed that riboflavin in combination with cisplatin was able to protect the tissues from cisplatin induced toxicities and damages. Moreover, Fourier Transform Infrared Spectroscopy analysis of the combination indicated a strong molecular interaction among their constituent groups that may be assigned for the protective effect of the combination in the treated animals.

Conclusion

Inclusion of riboflavin diminishes cisplatin induced toxicities which may possibly make the cisplatin-riboflavin combination, an effective treatment strategy under chemoradiotherapy in pronouncing its antineoplastic activity and sensitivity towards the cancer cells as compared to cisplatin alone.

Synchronous fluorescence as a rapid method for the simultaneous determination of folic acid and riboflavin in nutritional beverages

A rapid synchronous spectrofluorimetric method was first developed for the simultaneous determination of folic acid and riboflavin in nutrimental beverages. Folic acid could be detected by using H(2)O(2) plus Cu(II) as oxidation system to produce pterine-6-carboxylic acid, which had strong fluorescence in aqueous solution, and riboflavin itself was obviously fluorescent. Various operational parameters were thoroughly discussed in terms of their effects on the fluorescence signals, including instrumental parameters, concentration of the oxidation system, and pH. Under optimum conditions, the calibration curves were linear in the ranges of 100-250 μg/L for folic acid and 1-250 μg/L for riboflavin, and the detection limits were 2.0 and 0.014 μg/L, respectively. In addition, this method was applied to the determination of folic acid and riboflavin in nutrimental beverages with satisfactory results.

Ameliorative effect of riboflavin on the cisplatin induced nephrotoxicity and hepatotoxicity under photoillumination

Cisplatin is a widely used anticancer drug. It is documented that it elicits major side effects like nephrotoxicity and hepatotoxicity due to oxidative stress forcing the patients to limit its clinical use in long term treatment. Riboflavin (vitamin B(2)) is a strong photosensitizer because it generates reactive oxygen species (ROS) upon photoillumination. We have tried to trap its photosensitizing property to ameliorate the cisplatin induced nephrotoxicity and hepatotoxicity in mice. They were treated with riboflavin and cisplatin separately as well as with their combination under photoilluminated condition. The status of major antioxidant enzymes, antioxidant proteins, functional markers, lipid peroxidation and protein oxidation was studied in liver, kidneys and serum samples of all the groups. Cisplatin treated group showed significantly compromised level of antioxidant enzymes and the proteins with higher extent of lipid and protein oxidation. Similar but less pronounced pattern was observed in the riboflavin treated group. The groups treated with the combination of cisplatin and riboflavin showed all the parameters tended towards normal levels in a dose dependent manner. Hence, it can be hypothesized that riboflavin shows ameliorative effect on the cisplatin induced nephrotoxicity and hepatotoxicity under the mentioned treatment conditions.

Hemolysis of human red blood cells by riboflavin-Cu(II) system: enhancement by azide

Photoactivated riboflavin in the presence of Cu(II) generates reactive oxygen species (ROS) which can hemolyze human red blood cells (RBC). In the present work we examined the effect of sodium azide (NaN3) on RBC in the presence of riboflavin and Cu(II). The addition of NaN3 to the riboflavin-Cu(II) system enhanced K+ loss and hemolysis. The extent of K+ loss and hemolysis were time and concentration dependent. Bathocuproine, a Cu(I)-sequestering agent, inhibited the hemolysis completely. Among various free radical scavengers used to identify the major ROS involved in the reaction, thiourea was found to be the most effective scavenger. Thiourea caused almost 85% inhibition of hemolysis suggesting that *OH is the major ROS involved in the reaction. Using spectral studies and other observations, we propose that when NaN3 is added to the riboflavin-Cu(II) system, it inhibits the photodegradation of riboflavin resulting in increased *OH generation. Also, the possibility of azide radical formation and its involvement in the reaction could not be ruled out.

Hemolysis of human red blood cells by combination of riboflavin and aminophylline

The effect of aminophylline on human red blood cells (RBC) has been studied. Under in vitro condition, aminophylline alone does not hemolyse RBC. However, in the presence of riboflavin and visible light, aminophylline causes hemolysis of RBC. This hemolysis depends on the concentration of both riboflavin and aminophylline. Using different free radical scavengers we show that RBC hemolysis is caused by reactive oxygen species. Studies using bovine serum albumin show that riboflavin-aminophylline combination can also cause protein degradation in vitro.

Hemolysis of human red blood cells by riboflavin-Cu(II) system

The photodynamic action of riboflavin is generally considered to involve the generation of reactive oxygen species, whose production is enhanced when Cu(II) is present in the reaction. In the present study we report that photoactivated riboflavin causes K(+) loss from fresh human red blood cells (RBC) in a time dependent manner. Addition of Cu(II) further enhances the K(+) loss and also leads to significant hemolysis. Riboflavin in a 2:1 stoichiometry with Cu(II) leads to maximum K(+) loss and up to 45% hemolysis. Bathocuproine, a specific Cu(I)-sequestering agent, when present in the reaction, inhibits the hemolysis completely. Free radical scavengers like superoxide dismutase, potassium iodide and mannitol inhibited the hemolysis up to 55% or more. However, thiourea was the most effective scavenger showing 90% inhibition. These results suggest that K(+) leakage and hemolysis of human RBC are basically free radical mediated reactions.