Menter J M, Patta A M, Hollins T D, Moore C L, Willis I
Department of Medicine, Morehouse School of Medicine, Atlanta, GA 30310-1495, USA.
Photochem Photobiol. 1998 Oct;68(4):532-7.
Several important clinical conditions can result in close association between the pigment melanin and dermal collagen. Because melanin and its precursors can be chemically reactive in ground and excited states, it is important to know whether the resulting melanin-collagen interaction results in photoprotection or photoaggression. Acidic and neutral air-saturated collagen suspensions (0.033%) were irradiated with 0-2.6 x 10(4) J/m2 UVC or with 0-83 x 10(4) J/m2 solar-simulating UV radiation (SSR). Photochemical destruction of a photolabile collagen fluorophore (lambda em 360 nm) and collagen chain degradation were monitored as functions of irradiation time in the presence and absence of added (0-100 micrograms) sepia eumelanin. Melanin retarded collagen photodamage but did not qualitatively alter the fluorescence fading kinetics. Both H2O2 and O2-. can be produced by UV irradiation of eumelanin. Added H2O2 and KO2 destroyed collagen fluorescence and caused 50% chain degradation at ca 10-20-fold molar excess. Previous studies have demonstrated that eumelanins efficiently scavenge O2-.. We demonstrated that eumelanin also efficiently scavenges H2O2 as evidenced by its ability to (a) compete with scopoletin for peroxide uptake and (b) directly take up H2O2 through a dialysis bag. The latter observation suggests that peroxide scavenging could occur in vivo by melanin sequestered in melanophages. Thus, neither UV-generated O2-. nor H2O2 are likely to be present in concentrations high enough to cause measurable collagen damage. Absorption and/or scattering of excitation radiation away from the target chromophore appears to be the primary photoprotection mechanism, although scavenging of active O2 intermediates may play an important, if subtle role.
几种重要的临床情况可导致色素黑色素与真皮胶原蛋白紧密关联。由于黑色素及其前体在基态和激发态下具有化学反应性，因此了解由此产生的黑色素 - 胶原蛋白相互作用是导致光保护还是光损伤非常重要。用0 - 2.6×10⁴ J/m²的紫外线C（UVC）或0 - 83×10⁴ J/m²的模拟太阳紫外线辐射（SSR）照射酸性和中性空气饱和的胶原蛋白悬浮液（0.033%）。在添加（0 - 100微克）乌贼墨黑色素和未添加的情况下，监测光不稳定胶原蛋白荧光团（发射波长360纳米）的光化学破坏和胶原蛋白链降解随照射时间的变化。黑色素可延缓胶原蛋白的光损伤，但未定性改变荧光衰减动力学。紫外线照射黑色素可产生过氧化氢（H₂O₂）和超氧阴离子（O₂⁻）。添加H₂O₂和超氧化钾（KO₂）可破坏胶原蛋白荧光，并在约10 - 20倍摩尔过量时导致50%的链降解。先前的研究表明，真黑色素能有效清除O₂⁻。我们证明，真黑色素也能有效清除H₂O₂，这体现在其能够（a）与东莨菪素竞争过氧化物摄取，以及（b）通过透析袋直接摄取H₂O₂。后一观察结果表明，被巨噬细胞隔离的黑色素在体内可能发生过氧化物清除。因此，紫外线产生的O₂⁻和H₂O₂浓度可能都不足以导致可测量的胶原蛋白损伤。激发辐射从目标发色团的吸收和/或散射似乎是主要的光保护机制，尽管活性O₂中间体的清除可能也起到重要作用，尽管作用较为微妙。
