Microsomal triglyceride transfer protein polymorphisms and lipoprotein levels in type 2 diabetes

Abstract

Background: Microsomal triglyceride transfer protein (MTP) regulates the assembly of chylomicrons in the intestine and very-low-density lipoprotein (VLDL) in the liver. Common polymorphisms have been described that do not affect lipoproteins in non-diabetic subjects. Their effect in diabetes has not been described in a Caucasian population. Aim: To investigate the association of these three common polymorphisms with lipoproteins in type 2 diabetes. Methods: Eighty-two patients consumed a high-fat test meal. Chylomicron and VLDL apoB48, apoB100, cholesterol, triglycerides and phospholipids were measured fasting, and at 4 and 6 h postprandially. MTP genotyping was performed by PCR-RFLP. Results: Thirty-three subjects were heterozygous for the -493G/T substitution. These patients had significantly lower LDL cholesterol (3.0 ± 0.2 vs. 3.5 ± 0.1 mmol/l, p<0.02). In the postprandial period, they had higher levels of apoB48 in the VLDL fraction (4 h, 7.0 ± 1.4 vs. 2.9 ± 0.4 μg/ml plasma, p<0.002; 6 h, 6.4 ± 1.0 vs. 3.5 ± 0.5 μg/ml plasma, p<0.05). In the VLDL fraction there was significantly less cholesterol at 4 and 6 h (p<0.05). The -40OA/T substitution gave very similar lipoprotein results, but there was significant linkage dysequilibrium between the two polymorphisms. No association was found between the -164T/C polymorphism and either plasma lipids or the postprandial lipid profile. ApoE genotype was also examined, but did not influence the above results. Discussion: The common -493G/T MTP polymorphism is associated with changes in VLDL and LDL in Type 2 diabetic patients. The importance of the changes in apoB48-containing small particles requires further investigation. The significantly lower LDL cholesterol suggests that this polymorphism may confer protection against atherosclerosis in type 2 diabetes. © Association of Physicians 2004; all rights reserved.