Non-enzymatic glycosylation of human serum lipoproteins Elevated ϵ-lysine glycosylated low density lipoprotein in diabetic patients

Abstract

The ‘minor hemoglobins’ (Hb AI,,.) were the first examples to show that glucose can react non-enzymatically with proteins in the human body to form stable glycosyl-protein adducts. Other proteins have been observed to undergo non-enzymatic glycosylation, such as the eye lens crystallins [I], red cell membrane proteins [2,3], serum albumin [4-61. The amount of HbA,,-, is increased in diabetic patients depending on the level of,hyperglycemia; this holds also for glycosylated albumin [7,8], and erythrocyte membrane proteins [2,3]. Apart from the diagnostic value of HbAr and glycosyl-albumin as tools for long-term control of diabetes, protein glycosylation has attracted special interest with regard to the role it may play in the development of the late complications of diabetes. In these studies we have found that glucose is covalently bound to e-amino groups of lysine of human apo-lipoproteins upon incubation, in vitro. Moreover, we could show that the level of glycosylated apoprotein B (apo-B) of the low density lipoproteins (LDL) is increased in the serum from diabetic patients.