Sunlight induces N epsilon-(carboxymethyl)lysine formation from glycated polylysine-iron(III) complex

Sunlight was found to strongly induce the formation of N epsilon-(carboxymethyl)lysine (CML) from glycated polylysine in the presence of Fe(III) ion. The initial step of this Fe(III)-catalyzed CML formation was noted to be similar to that of blueprint photography as was confirmed by the production of Turnbull's blue in sunlight-exposed glycated human serum albumin ferricyanide solution in the presence of Fe(III). Based on this, photoinduced oxidative C-C bond cleavage of the Amadori compound was assumed to be initiated by photochemical single electron transfer front ligand to Fe(III) in the Fe(III)-Amadori compound complex affording the Fe(II)-Amadori compound radical intermediate, which eventually yields either CML or active oxygen species. CML is thus a useful oxidative stress marker. The mechanism proposed here would explain the high accumulation of CML in lens protein and skin actinic elastosis.