Increased glycosylation of proteins from cataractous lenses in diabetes

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Abstract
The rates of glycosylation of lens proteins were determined in extracts of human ‘diabetic’ and ‘senile’ cataractous lenses by a method employing thiobarbituric acid. Incubation of soluble lens proteins (6,500×g supernatant of homogenates) in vitro with various concentrations of D-glucose in sodium phosphate buffer (50 mmol/l, pH 7.2) resulted in a gradual glycosylation which was time and concentration dependent. Glycosylated proteins from the cataractous lenses of 21 senile and 12 diabetic subjects afforded 0.72 ±0.22 and 1.84±0.44 nmol 5-hydroxymethylfurfural/mg protein (mean±SD), respectively. The value is significantly higher in the diabetic than in the senile group (pp<0.01). These results indicate that human lens proteins can be glycosylated both in vitro and in vivo, and that hyperglycaemia can accelerate the non-enzymatic glycosylation of lens proteins in diabetic patients.