PHOTOPROTECTION OF MAMMALIAN ACID-SOLUBLE COLLAGEN BY CUTTLEFISH SEPIA MELANIN IN-VITRO

Several important clinical conditions can result in close association between the pigment melanin and dermal collagen. Because melanin and i ts precursors can be chemically reactive in ground and excited states, it is important to know whether the resulting melanin-collagen intera ction results in photoprotection or photoaggression, Acidic and neutra l air-saturated collagen suspensions (0.033%) were irradiated with 0-2 .6 x 10(4) J/m(2) WC or with 0-83 x 10(4) J/m(2) solar-simulating UV r adiation (SSR), Photochemical destruction of a photolabile collagen fl uorophore (lambda (em) 360 nm) and collagen chain degradation were mon itored as functions of irradiation time in the presence and absence of added (0-100 mu g) sepia eumelanin, Melanin retarded collagen photoda mage but did not qualitatively alter the fluorescence fading kinetics. Both H2O2 and O-2(-.) can be produced by UV irradiation of eumelanin, Added H2O2 and KO2 destroyed collagen fluorescence and caused 50% cha in degradation at ca 10-20-fold molar excess, Previous studies have de monstrated that eumelanins efficiently scavenge O-2(-.). We demonstrat ed that eumelanin also efficiently scavenges H2O2 as evidenced by its ability to (a) compete with scopoletin for peroxide uptake and (b) dir ectly take up H2O2 through a dialysis bag. The latter observation sugg ests that peroxide scavenging could occur in vivo by melanin sequester ed in melanophages, Thus, neither UV-generated O-2(-.) nor H2O2 are li kely to be present in concentrations high enough to cause measurable c ollagen damage, Absorption and/or scattering of excitation radiation a way. from the target chromophore appears to be the primary photoprotec tion mechanism, although scavenging of active O-2 intermediates may pl ay an important, if subtle role.