Comprehensive analysis of maillard protein modifications in human lenses: effect of age and cataract

Abstract

In human lens proteins, advanced glycation endproducts (AGEs) originate from the reaction of glycating agents, e.g., vitamin C and glucose. AGEs have been considered to play a significant role in lens aging and cataract formation. Although several AGEs have been detected in the human lens, the contribution of individual glycating agents to their formation remains unclear. A highly sensitive liquid chromatography-tandem mass spectrometry multimethod was developed that allowed us to quantitate 21 protein modifications in normal and cataractous lenses, respectively. N(6)-Carboxymethyl lysine, N(6)-carboxyethyl lysine, N(7)-carboxyethyl arginine, methylglyoxal hydroimidazolone 1, and N(6)-lactoyl lysine were found to be the major Maillard protein modifications among these AGEs. The novel vitamin C specific amide AGEs, N(6)-xylonyl and N(6)-lyxonyl lysine, but also AGEs from glyoxal were detected, albeit in minor quantities. Among the 21 modifications, AGEs from the Amadori product (derived from the reaction of glucose and lysine) and methylglyoxal were dominant.

Figures

Figure 1

Verification of C5 lysine amide by collision-induced dissociation (CID) of m/z 295.2 [M + H]+: (a) authentic reference N6-xylonyl lysine and (b) protein workup of normal lenses.

Figure 2

Effect of age on the (a) C4 and (b) C5 lysine amide content in human normal lens protein.

Scheme 1

In the Human Lens, 19 AGEs Are Formed from the Amadori Product (fructose lysine), Methylglyoxal, Glyoxal, and Ascorbic Acid