OXYRADICALS FROM PHOTOIRRADIATED HAIR 177 12 10 a b c Figure 5. Effects of additives on HTA production from irradiated bleached hair: 0.2 g bleached hair (1-mm long) in 2 mM TA at pH 7.6, irradiated for 90 min. a. Ethanol added (1 M). b. Azide added (10 mM). c. No additives. metal-sulfur complexes, which have considerable reactivity, and thus provide another pathway for oxyradical production (20,37). The sequence given in Scheme 2 has been suggested to explain the fate of thiyl radicals produced during the autoxidation of cysteine (38,39). In our spin trapping studies, irradiation was not carried out in the ESR cavity, and we find no evidence for the presence of transient sulfur radicals. Among the free radicals involved in these reactions, superoxide, hydroxyl, and hydrogen peroxide are most cytotoxic species induced by ionizing radiation and photosensitized
178 JOURNAL OF COSMETIC SCIENCE 10 Gauss Figure 6. ESR spectrum of the DMPO-OH adduct from irradiated hair. A 0.015-g sample of hair was irradiated for 10 min in 1 ml 20 mM DMPO, after which the sample solution phase was transferred to the quartz fiat cell. Spectrometer settings: microwave power, 20 mw sweep width, 100 G modulation am- plitude, 1 G receiver gain, 1.25 x 104 number of scans, 5. a. DMPO blank (no hair). b. Brown hair. c. Red hair. d. Bleached hair. oxidations. Additional reactions result in the oxidation of amino acids, most notably tryptophan, within the hair matrix. Thus, photodamaged hair (and wool) is characterized by reduced tryptophan and increased cysteic acid (5,6,50,41). The reduced fiber strength of weathered hair appears to be the consequence of the scission of disulfide bonds and their conversion to cysteic acid residues. Tryptophan photodamage appears to precede disulfide photooxidation. In cysteine-containing protein such as keratin, the disulfide bond contributes strongly to the overall stability and integrity of the structure. With the destruction of disulfide bonds, the hair may lose its natural elasticity, become more porous, and, hence, become more sensitive to changes in humidity. Degradation of
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176 JOURNAL OF COSMETIC SCIENCE 12 10 0 a b c d Figure 4. HTA production from human hair: 0.2 g hair (1-mm long) in 2 ml of 2 mM TA at pH 7.6, irradiated for 90 min. a. Brown hair. b. Blond hair. c. Red hair. d. Bleached hair. cysteinyldopa and its isomers (present in smaller quantities) (34). It would appear from photobleaching studies that the sulfur-containing benzothiazine unit of pheomelanin is more resistant to oxidation than the indolic units of eumelanin (35). Therefore, eumela- nin seems to be more efficient than pheomelanin as a scavenger of reduced oxygen species. Hence the amount of 02 ß -/OH' that is available to reach the spin traps (DMPO or TA) (Figures 4, 6 reference 25) is greater for red hair and red hair melanin. The greater ability to scavenge free radicals for eumelanin suggests that the eumelanin has a better photoprotective effect with regard to hair structure than pheomelanin. This is consistent with the fact that brown hair is more easily photobleached than either red (35) or black hair (36). As shown from the experiments with wool keratin (Figure 3), the structural component of hair produces oxyradicals even in the absence of melanin. In addition to carbon- and oxygen-centered radicals, it has been reported that sulfur-centered radicals were also produced from irradiated wool keratin (17). This involves thiyl radicals, generated via
OXYRADICALS FROM PHOTOIRRADIATED HAIR 177 12 10 a b c Figure 5. Effects of additives on HTA production from irradiated bleached hair: 0.2 g bleached hair (1-mm long) in 2 mM TA at pH 7.6, irradiated for 90 min. a. Ethanol added (1 M). b. Azide added (10 mM). c. No additives. metal-sulfur complexes, which have considerable reactivity, and thus provide another pathway for oxyradical production (20,37). The sequence given in Scheme 2 has been suggested to explain the fate of thiyl radicals produced during the autoxidation of cysteine (38,39). In our spin trapping studies, irradiation was not carried out in the ESR cavity, and we find no evidence for the presence of transient sulfur radicals. Among the free radicals involved in these reactions, superoxide, hydroxyl, and hydrogen peroxide are most cytotoxic species induced by ionizing radiation and photosensitized

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