ApoE-2/E-3 ratio of very low density lipoprotein in diabetes mellitus

Apolipoprotein E genotyping methods for the clinical laboratory

To select the best method for detecting apolipoprotein E (apo E) genotypes determined by the three common alleles epsilon 2, epsilon 3 and epsilon 4, we compared the radiolabeled allele-specific oligonucleotide (ASO) probe assay and the nonisotopic restriction isotyping assay. Leukocytic DNA was extracted from the blood of 93 patients after which the region containing two mutation points coding amino acid residues 112 and 158 was amplified by using the polymerase chain reaction (PCR). Amplified DNA fragments were spotted on nylon membranes, then hybridized for the ASO probe assay. The amplified DNA fragments were also digested with restriction endonuclease Hhal, followed by polyacrylamide gel electrophoresis for the restriction isotyping assay. The apo E genotypes determined by both methods for every specimen studied were in complete agreement. Although the radiolabeled ASO probe method was 10 times more sensitive than restriction isotyping on polyacrylamide gel, the two were comparable in accuracy. Additionally, because it is simpler to perform, is less time consuming, and is less expensive, we conclude that the restriction isotyping assay is the more suitable of these two methods for use in a clinical laboratory.

Metabolism by human endothelial cells of very low density lipoprotein subfractions isolated from type 1 (insulin-dependent) diabetic patients

The very low density lipoprotein (VLDL) fraction was isolated from 11 normolipidaemic Type 1 (insulin-dependent) diabetic patients in good to fair glycaemic control and from 11 age-, sex- and race-matched, non-diabetic, control subjects. The rate of receptor-mediated degradation by human endothelial cells was significantly greater (p < 0.02) for the total VLDL fraction isolated from diabetic patients compared to control subjects and averaged 1008 +/- 300 and 717 +/- 150 ng.mg cell protein-1.16 h-1, respectively. The total VLDL fraction was separated into three subfractions: VLDL-I, Sf 100-400 (Sf = Svedberg units); VLDL-II, Sf 60-100; VLDL-III, Sf 20-60. Rates of receptor-mediated degradation of VLDL-I and VLDL-II isolated from diabetic patients were significantly greater than the comparable subfraction isolated from control subjects and averaged 1023 +/- 279 vs 361 +/- 122 (p < 0.01) and 433 +/- 70 vs 294 +/- 70 ng.mg cell protein-1.16 h-1 (p < 0.03), respectively. Rates of receptor-mediated degradation of the V-III subfraction isolated from the two groups did not differ significantly. There were no significant differences in the chemical composition or in the plasma concentrations of the VLDL subfractions isolated from diabetic patients compared to control subjects. There was a significant increase in the apoprotein E content of VLDL-I (p < 0.01) and VLDL-II (p < 0.05) isolated from diabetic patients. There was a significant increase in the ratio of apoprotein C compared to apoprotein E (p < 0.03) in VLDL-I isolated from control subjects compared to the diabetic patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal lipoprotein and apolipoprotein pattern in lipoprotein glomerulopathy

Recently, two cases of renal disease were observed in which there was an abnormal accumulation of lipids, "lipoprotein thrombi," in the glomerular capillary lumen. This disease has been designated as lipoprotein glomerulopathy. Four other cases have been diagnosed independently by renal histology in other clinical laboratories. All six patients showed proteinuria (1.6 to 10 g/d), normal lecithin-cholesterol acyltransferase (LCAT) activity, type III hyperlipoproteinemia-like lipoprotein profiles, and significantly (P less than 0.01) higher levels of plasma apolipoprotein (apo) E (greater than 10 mg/dL) compared with the control patients with hyperlipidemic nephrotic syndrome without lipoprotein thrombi and type IIb hyperlipoproteinemia without renal disease. Lipoprotein glomerulopathy is not familial type III hyperlipoproteinemia (dysbetalipoproteinemia), because apolipoprotein E3 is present. Apo E isoforms were all rare: five cases of E2/3 and one case of E4/4. These results suggest that excessive apo E is associated with apo E isoform and lipoprotein metabolic derangement in such a renal disease. Further studies are needed on the relationship between the apo E hyperlipoproteinemia and the formation of lipoprotein thrombi.

Apolipoprotein E phenotyping: a word of caution

Using two different techniques, phenotyping and genotyping, we have studied allelic variation at amino acids 112 and 158 of the apolipoprotein E gene locus in 52 patients with insulin-dependent diabetes and in 58 non-diabetic controls. Phenotypes were determined by isoelectric focusing and immunoblotting of delipidated, neuraminidase-treated plasma. Genotypes were determined by using the polymerase chain reaction to amplify a 227 base pair fragment of the apolipoprotein E gene spanning both allelic sites. This was then digested with the restriction endonuclease CfoI and the alleles identified by polyacrylamide gel electrophoresis. Discrepancies between phenotype and genotype were observed in 16 (15%) of the individuals studied, 7 (13%) in the diabetics and 9 (17%) in the controls. From these results it is concluded that isoelectric focusing can lead to the erroneous assignment of apolipoprotein E phenotype even after pretreatment with neuraminidase. It is suggested that genotyping by DNA analysis is the method of choice in determining apolipoprotein E status.

Disparity between apolipoprotein E phenotypes and genotypes (as determined by polymerase chain reaction and oligonucleotide probes) in patients with non-insulin-dependent diabetes mellitus

Apolipoprotein (apo) E phenotype and genotype frequencies, due to allelic variation at amino acids 112 and 158, have been investigated in 95 Caucasian non-insulin dependent diabetic patients (NIDDM). Phenotypes were determined by one-dimensional isoelectric focussing (IEF). In this sample, the frequency of the epsilon 2 allele was higher (0.122) and the frequency of the epsilon 4 allele lower (0.101) than previously reported in Caucasian populations (P less than 0.05). Genotypes were assigned using the technique of polymerase chain reaction and allele specific oligonucleotide probes. By contrast, the frequencies of the alleles determined by genotyping was similar to previously reported in Caucasian populations (apo epsilon 2, 0.095; epsilon 3, 0.758; epsilon 4, 0.147; P greater than 0.1). It is possible that in patients with NIDDM post-translational modification of apo E may lead to disparities, with phenotypes being unrepresentative of allelic variation at this gene locus.

Isoform patterns of apolipoprotein E in diabetes mellitus

Apolipoproteins in delipidated VLDL preparations from normal, diabetic, and non-diabetic hyperlipidaemic subjects were analysed by SDS-polyacrylamide gel electrophoresis, and by isoelectric focusing. On electrophoresis, diabetic VLDL contained more apolipoprotein E (17.3 +/- 7.3 (+/- SD) %, n = 54) than did VLDL from hyperlipidaemic (13.4 +/- 4.2%, n = 52; p less than 0.005) or normal (12.4 +/- 2.6%, n = 29; p less than 0.001) subjects. Apolipoprotein E excess was also seen when subgroups were characterized by apolipoprotein E phenotype. In diabetic patients of E3/E3 phenotype, apolipoprotein E was 16.4 +/- 6.0% (n = 25), compared with 12.9 +/- 2.5% in control subjects (n = 14; p = 0.008). Acidic isoforms were more common in 44 diabetic patients with E3/E3 phenotype; E3, E2, E1, and E1' as percentage of total E apolipoprotein were 58.3 +/- 7.6, 24.5 +/- 4.4, 13.7 +/- 4.5, and 3.8 +/- 4.3% respectively, compared with 63.5 +/- 10.4 (p = 0.034), 19.1 +/- 5.3 (p less than 0.001), 13.7 +/- 6.5 (NS), and 3.7 +/- 2.1% (NS) in 21 normal subjects. In 31 diabetic patients, of apolipoprotein E3/E3 phenotype, E3, E2, E1 and E1' were 60.2 +/- 7.3, 23.4 +/- 9.4, 11.1 +/- 4.1, and 5.4 +/- 3.7%, respectively, compared with 68.0 +/- 7.1 (p less than 0.001), 21.9 +/- 6.4 (NS), 6.3 +/- 3.9 (p less than 0.001), and 3.7 +/- 2.5 (p less than 0.05) % in 32 hyperlipidaemic patients. Diabetic patients of E3/E2 phenotype showed less apolipoprotein E3 than normal or hyperlipidaemic subjects, with a similar trend for apolipoprotein E4 in those of E4/E3 phenotype.(ABSTRACT TRUNCATED AT 250 WORDS)

Appearance of multidisperse low density lipoprotein and altered lipoprotein composition in non-insulin-dependent diabetes with type IIa hyperlipoproteinemia

The purpose of the present study is to elucidate the characteristics of lipoprotein disorders in diabetes mellitus. By analytical ultracentrifugation, non-insulin-dependent diabetic patients (NIDDM) with type IIa hyperlipoproteinemia (HLP) showed significantly higher incidence of multidisperse low density lipoprotein (LDL) than non-diabetics with type IIa HLP. Furthermore, LDL multidispersity in diabetic subjects seemed to be directly related to neither triglyceride (TG) levels in very low density lipoprotein (VLDL) nor the degree of glycemic control. Diabetics with multidisperse LDL had a lipoprotein profile that was different from the subjects with paucidisperse LDL as follows: (1) enrichment in the cholesterol content of VLDL, (2) TG-rich LDL with small flotation coefficient, (3) low cholesterol levels in high density lipoprotein2 along with enrichment in TG, and (4) high plasma concentrations of apoprotein B. Although the underlying mechanism behind the prevalence of multidisperse LDL in NIDDM with type IIa HLP remains unknown, it seems important that lipoprotein disorders in diabetics with multidisperse LDL were potentially atherogenic.

Apo E 2 phenotypes in type II diabetics with and without insulin therapy

In 106 type II diabetics with persisting hyperlipidemia (i.e. persistently increased triglycerides greater than 200 mg/dl during intensive diabetes therapy) the Apo E polymorphism was examined in relation to IDDM (n = 68) and NIDDM (n = 38). It was shown that Apo E2 phenotypes are more (22.6% vs. 14.5%, p less than 0.05) and Apo E3 phenotypes less frequent in type II diabetics than in non-diabetic controls (86.8% vs. 94.7%, p less than 0.001). Looking at the increase in Apo E2 phenotypes it could be proved that the phenotype composition was distinctly different between diabetics with and in those without insulin therapy. While in NIDDM the increase was consequent to a higher concentration of Apo E2 homozygotes (p less than 0.005) it was caused by Apo E2 heterozygotes in IDDM (p less than 0.025) accompanied by a simultaneous decrease in Apo E3 homozygotes (p less than 0.025). Regarding blood lipids there was an increase in total cholesterol due only to VLDL cholesterol in IDDM as well as in NIDDM. It is concluded that in spite of similar hyperlipidemias in type II diabetics the increase in Apo E2 phenotypes is different; it is induced by heterozygotes in IDDM and by homozygotes in NIDDM.