Primary cultures of porcine aortic endothelial cells were used to detect injurious agents in diabetic rat serum. Media containing normal or diabetic serum (streptozotocin-induced) were incubated with subconfluent primary cultures of endothelial cells. Cells exposed to 17% diabetic serum were severely contracted and permeable to trypan blue after 18 h. Cultures in normal serum contained significantly more protein (P < 0.005) than cultures in diabetic serum after 1 day. When normal and diabetic serum were mixed in different proportions and added to cells at 17% total serum concentration, a 50% reduction from growth in normal serum occurred at a ratio of 1 part diabetic serum to 9 parts normal serum. The toxicity of diabetic serum was not altered by heat inactivation. Administration of insulin to diabetic rats reversed both cytotoxicity and elevated triglyceride levels. Serum triglyceride levels were inversely correlated with endothelial cell growth (r = −0.878, P < 0.001). In vitro addition of up to 1 U/ml insulin to cultures in diabetic serum did not alter toxicity. Ultracentrifugal flotation of diabetic serum demonstrated the toxic substance to be entirely localized in the very-low-density lipoprotein fraction (d < 1.006 g/ml). A pool of d > 1.006 fractions from diabetic serum supported growth equivalent to normal serum. Diabetic serum contains a substance localized in the very-low-density lipoprotein fraction that is severely toxic to aortic endothelial cells in vitro. Very-low-density lipoprotein injury of endothelial cells may play an important role in the development of arterial vascular disease in insulin-dependent diabetes.

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