Two Fluorescent Wavelengths,440 ex /520 em nm and 370 ex /440 em nm,Reflect Advanced Glycation and Oxidation End Products in Human Skin Without Diabetes

Abstract

Background:

Advanced glycation end products (AGEs) and oxidation products (OPs) play an important role in diabetes complications, aging, and damage from sun exposure. Measurement of skin autofluorescence (SAF) has been promoted as a noninvasive technique to measure skin AGEs, but the actual products quantified are uncertain. We have compared specific SAF measurements with analytically determined AGEs and oxidative biomarkers in skin collagen and determined if these measurements can be correlated with chronological aging and actinic exposure.

Methods:

SAF at four excitation (ex)/emission (em) intensities was measured on the upper inner arm (“sun protected”) and dorsal forearm (“sun exposed”) in 40 subjects without diabetes 20–60 years old. Skin collagen from the same sites was analyzed by liquid chromatography–tandem mass spectrometry for three AGEs—pentosidine, carboxymethyllysine (CML), and carboxyethyllysine (CEL)—and the OP methionine sulfoxide (MetSO).

Results:

There was poor correlation of AGE-associated fluorescence spectra with AGEs and OP in collagen, with only pentosidine correlating with fluorescence at 370_ex/440_em nm. A little-studied SAF (440_ex/520_em nm), possibly reflecting elastin cross-links, correlated with all AGEs and OPs. Levels of CML, pentosidine, and MetSO, but not SAF, were significantly higher in sun-exposed skin. These AGEs and OPs, as well as SAF at 370_ex/440_em nm and 440_ex/520_em nm, increased with chronological aging.

Conclusions:

SAF measurements at 370_ex/440_em nm and 335_ex/385_em nm, except for pentosidine, which correlated with fluorescence at 370_ex/440_em, correlate poorly with glycated and oxidatively modified protein in human skin and do not reflect actinic modification. A new fluorescence measurement (440_ex/520_em nm) appears to reflect AGEs and OPs in skin.