[Metabolic consequences of the nonenzymatic glucosylation of apolipoproteins]

The non enzymatic glucosylation (NEG) of proteins is a complex chemical reaction resulting in the formation of a stable bond between a glucose molecule and a protein aminogroup. In diabetics, hyperglycaemia may induce a large increase of NEG. Although the NEG of apolipoproteins remains moderate because of their short half-life, it may alter some of their properties. The NEG of LDL apo B induces a decrease of their catabolism due to a lowering of their binding to the LDL receptor. Glucosylated LDL can accumulate in macrophages, thereby facilitating the development of foam cells. The LDL NEG may also cause other processes including apo B oxidation and production of anti-LDL antibodies. The HDL NEG which essentially corresponds to that of apo A-I, induces a shortening of their half-life. In vitro, the NEG of apo A-I results in a decrease of its interaction with HDL surface. Finally, the binding of glucosylated HDL3 to HDL receptors is decreased in cultured fibroblasts. Since the level of lipoprotein NEG in vivo is moderate, the question as to whether this process may affect quantitatively the metabolic behaviour of lipoproteins and participate to the development of atheroma in diabetic patients, has not been clearly answered.