Multiphoton imaging of glucose, galactose, and fructose-induced formation of fluorescent advanced glycation end products in tissues

Blood glucose and HbA1c, intermediate glycation products of hemoglobin, remain the two clinical biomarkers for monitoring disease progression in diabetics. However, the formation of advanced glycation end products (AGEs) has been implicated in diabetic pathogenesis and the use of AGEs in tissues as long-term glycemic markers may be of value in the clinical setting. Therefore, it is necessary to understand how different tissue constituents respond to dietary monosaccharides. In this study, we studied the in vitro rate of fluorescent AGEs (fAGEs) formation with multiphoton microscopy in different porcine tissues (aorta, cornea, kidney, dermis, and tendon). These tissues were treated with D-glucose, D-galactose, and D-fructose, three primary monosaccharides found in human diets. We found that the use of D-fructose resulted in the highest glycation rate, followed by D-galactose and then D-glucose. Moreover, compared to non-collagen tissue constituents such as elastic fibers and cells, the rate of tissue glycation was consistently higher in collagen, suggesting that collagen is a more sensitive target for fAGE formation. However, we also found that collagen in different tissues exhibits different rates of fAGE formation, with slower rates observed in tightly packed tissues such as cornea and tendon. Our study suggests that for fAGE to be developed into a long-term glycemic biomarker, loosely organized collagen tissues located in the proximity of vasculature may be the best targets.