Aggregation as a consequence of glycation: insight into the pathogenesis of arthritis

Advanced glycation end products (AGEs) as a result of Maillard reaction are currently at the heart of the pathogenesis of several diseases and hence are the objective of numerous investigations. Glycation of proteins has been an implication in long-term complications. Collagen is the most abundant protein in the human body. The purpose of this study was to monitor and characterize the oligomeric aggregates and AGEs of human collagen on addition of glyoxal using ultraviolet, fluorescence, circular dichroism (CD) spectroscopy, docking studies, ITC, and microscopy. Collagen was incubated for varying time periods up to 21 days with three different concentrations (5, 20, and 40 mM) of glyoxal. Collagen exists as molten globule at day 6, evident from native-like secondary structure, altered tryptophan, and high ANS fluorescence due to surface-exposed hydrophobic residues. Glycated collagen as AGEs and aggregates was observed at day 18 and 21, respectively. Formation of AGE and aggregates were confirmed by UV and fluorescence spectroscopy. The obtained AGEs were characterized with respect to the extent of side chain modifications (lysine and arginine) forming the Schiff base, the carboxymethyl lysine, and carbonyl content. Non-tryptophan fluorescence for AGEs was also monitored as the emission peak at 400 and 440 nm, respectively. SEM and TEM confirmed the oligomeric nature of aggregates. Glyoxal at 40 mM shows maximum alterations in protein structure followed by 20 and 5 mM concentration. In the present paper, we propose that a high concentration of glyoxal for a prolonged time results in the formation of harmful aggregates and AGEs.