Spectral characterization of advanced glycation end products in human hemoglobin, serum albumin, and erythrocytes.

As final products of the Maillard reaction, the formation of advanced glycation end products (AGEs) is associated with pathological complications of diabetes mellitus (DM) and aging. Since some AGEs are fluorescent, fluorescent advanced glycation end products (fAGEs) have been used as biomarkers for characterizing the degree of tissue glycation. While many studies focus on using 370 nm as the excitation source and 440 nm as the detection wavelength for fAGE, there is an advantage to consider other spectral ranges, especially for in vivo detection, where longer wavelengths allow detection at greater depths. In this study, we attempt to obtain a full spectral characterization of fAGEs in the visible range by using artificially glycated human blood samples of serum albumin, hemoglobin, and erythrocytes, from the treatment of ribose, fructose, galactose, and glucose. For the case of D-ribose, we found that monosaccharide-treated sample solutions have a broad absorption spectrum spanning from 420 nm to 680 nm. Moreover, by varying the excitation wavelengths of 373, 405, 473, 532, and 644 nm, we found the fAGE spectral range to be in the 380-700 nm range, with the peaks of fluorescence emission changing as a function of excitation wavelength. This observation suggests the existence of multiple-fAGE species. Detailed spectral analysis suggests that there are multiple fAGE species in the above spectral range. Our results suggest that, due to reduced scattering, longer wavelengths should be used in developing clinical diagnostic tools for fAGEs in tissues.