Decreased insulin binding of mononuclear leukocytes in diabetic patients with hyperlipidemia

The effects of lipoproteins on 125I-insulin binding activity of mononuclear leukocytes were investigated in 22 diabetic patients and eight healthy adults. There was a significant negative relationship between insulin binding activity and levels of plasma beta-lipoprotein (r = 0.70, p < 0.01). The inhibition of insulin binding activity was also observed by in vitro addition of LDL to the assay system of insulin binding activity of mononuclear leukocytes. Double fluorescent staining techniques demonstrated that insulin receptors and LDL receptors are located very close to each other on the cell-surface. These results indicate that LDL intereferes with insulin binding activity in mononuclear leukocytes in vivo and in vitro, presumably because of the close localization of receptors for insulin and LDL on the cell surface. It is concluded that hyperlipoproteinemia is responsible for the decrease in insulin binding activity in diabetic patients.