A study of nonenzymatic-glycosylated-low-density-lipoprotein binding using the calf adrenocortical low-density lipoprotein receptor.

In vitro studies have shown that nonenzymatic glycosylation of low-density lipoprotein (LDL) reduces its ability to bind the LDL receptor. It has been suggested that this may contribute to the increased risk of atherosclerosis associated with diabetes, since modified LDL is cleared from plasma by atherogenic pathways. In order to test the ability of LDL from diabetics to bind to the LDL receptor, a competitive binding assay was developed in which the calf adrenocortical LDL receptor was used as the binder. The ability of LDL to bind to the receptor was determined indirectly by its ability to displace control $\sp{125}$I-LDL from the receptor. It was shown that the calf adrenocortical LDL receptor is an acceptable substitute for the human LDL receptor for studying human LDL binding. It demonstrated the same binding specificity towards human lipoprotein fractions and had a similar dissociation constant (8.8 $\pm$ 1.0 $\mu$g $\sp{125}$I-LDL/mL) as the human LDL receptor. Furthermore, the calf adrenocortical receptor was able to distinguish between LDL preparations with different extents of nonenzymatic glycosylation. The LDL receptor was purified to a semi-pure solubilized form in order to minimize the number of steps required in the purification and yet allow simple binding assays to be performed. The binding assay of the present study of nonenzymatic glycosylated LDL required shorter incubation periods and fewer steps than binding assays of previous studies which used intact cultured cells. $\sp{125}$I-LDL displacement of LDL isolated from subjects values did not correlate very well with any of the indicators of glycemic control (plasma glucose and fructosamine, and glycosylated hemoglobin). Correlation coefficients were $-$0.173, $-$0.133, and $-$0.067, respectively. LDL from subjects (whether diabetic or not) whose plasma triglyceride concentrations were greater than 5.0 mmol/L had a reduced ability to bind to the LDL receptor when compared to LDL from subjects whose plasma triglyceride concentrations were less than 5.0 mmol/L. The data suggests that hypertriglyceridemia rather than hyperglycemia plays a role in affecting LDL binding to the LDL receptor in diabetics.Dept. of Chemistry and Biochemistry. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1992 .C389. Source: Dissertation Abstracts International, Volume: 54-05, Section: B, page: 2479. Thesis (Ph.D.)--University of Windsor (Canada), 1992