Quenchers of Singlet Oxygen

Current interest in the carotenoids as putative inhibitors of carcinogenesis (Connett et al., 1989) stems from the evidence that carotenoids can function as quenchers of singlet oxygen (Anderson and Krinsky, 1973) and oxygen-centred free radicals (Krinsky and Deneke, 1982). 

As shown in Figure 13.3, oxidation of ascorbic acid, for example, by the reduction of superoxide to hydrogen peroxide or Fe + to Fe +, and similar reduction of other transition metal ions, proceeds by a one-electron process, forming the monodehydroascorbate radical. The radical rapidly disproportionates into ascorbate and dehydroascorbate. Most tissues also have both nicotinamide adenine dinucleotide phosphate (NADPH) and glutathione-dependent monodehydroascorbate reductases, which reduce the radical back to ascorbate. Ascorbate is thus an effective quencher of singlet oxygen and other radicals. 

D Belus. Quenchers of Singlet Oxygen A Critical Review. In B Ranby and IF Rabeck, Eds. Singlet Oxygen, Reactions with Organic Compounds and Polymers. New York lohn Wiley and Sons, 1978, p. 61. 

The main treatment of the diseases mentioned earlier is, whenever possible, to stop exposure to photosensitizing substances or substances that initiate endogenous production of photosensitizers. In cases in which this is impractical or impossible, quenchers of singlet oxygen, such as P-carotene, can help if photodynamic processes are involved (Poh-Fitzpatrick, 2000). Other treatments of porphyrias, lupus erythematosus, and pellagra are described in textbooks of dermatology. 

The amino acid histidine is used as a bulking agent for lyophilization and can additionally serve as a buffer (histidine/histidine hydrochloride) and stabilizer in the formulation (Nema et al., 2002). Histidine is a rather efficient quencher of singlet oxygen and a scavenger of hydroxyl radicals (Halliwell and Gutteridge, 1985). Thus, the presence of histidine in the parenteral formulation can be very important for the photochemical stability of the product. 

Similar results have been reported by Felder and Schumacher (3, Bellus, Lind, and Wyatt (9). The results indicate that among the tested compounds, the most efficient quencher of singlet oxygen is the N-methyl-substituted piperidine derivative, followed by nickel chelates and nitroxyl compounds of the hindered amines. The 2,2,6,6-tetramethylpiperidines themselves were of relatively low efficiency. 

Bellus, D. Quenchers of singlet oxygen - a critical review. In Singlet oxygen. Reactions... 

Carotenoids are by far the most widely spread-out class of compounds that were recognized as quenchers of singlet oxygen. 

Astaxanthin has demonstrated strong antioxidant behavior in a variety of in vitro studies. In organic solutions, astaxanthin is a potent quencher of singlet oxygen, an effective inhibitor of peroxyl radical-dependent lipid peroxidation, and an efficient peroxyl... 

Pinto, E. Catalani, L.H. Lopes, N.P. Di Mascio, P. Colepicolo, P. Peridinin as the major biological carotenoid quencher of singlet oxygen in marin algae gonyaulex poly-edra. Biochem. Biophys. Res. Comm. 2000, 268, 496. 

Polybutadiene.—Sensitized photo-oxidation of polybutadiene and butadiene -styrene copolymers has demonstrated the suceptibility of such polymers to attack by singlet oxygen/ " Conversely, quenchers of singlet oxygen act as stabilizers for the photo-oxidative decomposition of polymers containing unsaturation. Rabek and Lala have shown that a number of carotoneoids are effective stabilisers for polybutadiene. Nitroxides and their precursors have been shown to be effective antioxidants. Kelleher and co-workers found that in ABS copolymers deterioration occurs in the butadiene segments. They have also found that carbon black is an effective stabilizer. ... 

Apart from its function as a cofactor in enzymes, over the past decade researchers found that vitamin Bg could have the role in preventing oxidative stress of cells and that it is an important quencher of singlet oxygen, with quenching rates comparable to those of vitamins C and E (Ehrenshaft et al. 1999 Bilski et al. 2000). 

Vitamin Bg is essential for more than 100 enzymes involved in protein metabolism. Pyridoxal-5 -phosphate is covalently bound to enzymes via a SchifFs base with an e-amino group of lysine in the enzyme. PLP-dependent enzymes are involved in important steps of amino acid metabolism, hemoglobin formation and chlorophyll biosynthesis. Vitamin Bg could have a role in preventing oxidative stress of the cells and is an impotent quencher of singlet oxygen. 

Recent studies clarified novel functions of vitamin Bg forms. All forms are strong quenchers of singlet oxygen. Pyridoxamine reduces the incidence of diabetic complications. PLP prevents the progression of diabetic nephropathy. 

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