AGE-breakers cleave model compounds, but do not break Maillard crosslinks in skin and tail collagen from diabetic...

Advanced glycation end products (AGE), formed by nonenzymatic Maillard reactions between carbohydrate and protein, contribute to the increase in chemical modification and crosslinking of tissue proteins with age. Acceleration of AGE formation in collagen during hyperglycemia, with resultant effects on vascular elasticity and basement membrane permeability, is implicated in the pathogenesis of diabetic complications. AGE-breakers, such as N-phenacylthiazolium (PTB) and N-phenacyl-4,5-dimethylthiazolium (PMT) halides, have been proposed as therapeutic agents for reversing the increase in protein crosslinking in aging and diabetes. We have confirmed that these compounds, as well as the AGE-inhibitor pyridoxamine (PM), cleave the model AGE crosslink, phenylpropanedione, and have studied the effects of these compounds in reversing the increased crosslinking of skin and tail collagen isolated from diabetic rats. Crosslinking of skin collagen, measured as the half-time for solubilization of collagen by pepsin in 0.5M acetic acid, was increased approximately 5-fold in diabetic, compared to nondiabetic rats. Crosslinking of tail tendon collagen, measured as insolubility in 0.05 N acetic acid, was increased approximately 10-fold. Collagen preparations were incubated in the presence or absence of AGE-breakers or PM in phosphate buffer, pH 7.4, for 24h at 37 degrees C. These treatments did not decrease the half-time for solubilization of diabetic skin collagen by pepsin or increase the acid solubility of diabetic tail tendon collagen. We conclude that, although AGE-breakers and PM cleave model crosslinks, they do not significantly cleave AGE crosslinks formed in vivo in skin collagen of diabetic rats.