Human evidence for the involvement of insulin-induced gene 1 in the regulation of plasma glucose concentration.

AIMS/HYPOTHESIS: Insulin-induced gene 1 (INSIG1) is a protein that blocks proteolytic activation of sterol regulatory element-binding proteins (SREBPs), transcription factors that activate genes regulating cholesterol and fatty acid metabolism and possibly genes involved in glucose homeostasis. In search of genetic regulation of these processes we examined human INSIG1 for common polymorphisms and analysed their associations with biochemical parameters related to lipid and glucose metabolism. METHODS: Associations between common polymorphisms in INSIG1 and several biochemical parameters were analysed in a group of 618 healthy, 50-year-old men. A replication analysis was performed in a cohort of 472 healthy, middle-aged men. The impact of one promoter polymorphism on oral glucose tolerance was analysed in a subset of 181 subjects. Small interfering RNA (siRNA) inhibition was used to test the significance of INSIG1 for gene expression in human Huh7 hepatoma cells. RESULTS: A potentially functional polymorphism, a C to T substitution at position -169, was discovered in a highly conserved section of the promoter. Significant relationships between the -169C>T polymorphism and plasma glucose concentration were found in two cohorts of healthy, middle-aged men (p < 0.01 and p < 0.02, respectively). The -169T allele was associated with significantly lower post-load plasma glucose concentrations. A significant (p = 0.02) reduction in expression of phosphoenolpyruvate carboxykinase (PCK2) was observed following siRNA inhibition of INSIG1 in human Huh7 hepatoma cells. CONCLUSIONS/INTERPRETATION: Population studies demonstrate that INSIG1 plays a role in glucose homeostasis. Experiments with siRNA suggest that this action of INSIG1 is related to SREBP-mediated regulation of PCK2.

Human evidence that the apolipoprotein a-II gene is implicated in visceral fat accumulation and metabolism of triglyceride-rich lipoproteins.

BACKGROUND: Apolipoprotein (apo) A-II is a major structural protein of plasma HDLs, but little is known regarding its functions. METHODS AND RESULTS: To investigate the physiological role of apoA-II in humans, we screened the promoter region of the apoA-II gene for a functional polymorphism and used this polymorphism as a tool in association studies. A common, functional polymorphism in the promoter region of the apoA-II gene, a T to C substitution at position -265, was found. Electrophoretic mobility shift assays demonstrated that the -265T/C polymorphism influences the binding of nuclear proteins, whereas transient transfection studies in human hepatoma cells showed a reduced basal rate of transcription of the -265C allele compared with the -265T allele. The -265C allele was associated with decreased plasma apoA-II concentration and decreased waist circumference in healthy 50-year-old men. In addition, oral fat tolerance tests provided evidence that the -265C allele enhances postprandial metabolism of large VLDLs. CONCLUSIONS: ApoA-II appears to promote visceral fat accumulation and impair metabolism of large VLDLs.

Functional characterization of 4 polymorphisms in promoter region of hepatic lipase gene.

Hepatic lipase (HL) is a lipolytic enzyme involved in the metabolism of plasma lipoproteins, especially high density lipoproteins. Association studies have provided strong evidence for relations of common mutations in the promoter region of the HL gene to postheparin plasma HL activity and the plasma high density lipoprotein cholesterol concentration, but the functional relevance of these polymorphisms has not been evaluated to date. We analyzed the physiological significance of 4 common polymorphisms (-250G/A, -514C/T, -710T/C, and -763A/G, all in strong linkage disequilibrium) in the promoter of the HL gene by use of electrophoretic mobility shift assays and transient transfection studies in HepG2 cells. No consistent evidence was found for a significant contribution of any of these polymorphisms to the basal rate of transcription of the HL gene. These data suggest that the 4 polymorphisms in the promoter region of the HL gene are in linkage disequilibrium with >/=1 as-yet-unknown functional polymorphisms in the HL gene locus with a significant effect on HL metabolism and/or enzymatic activity.

Two common, functional polymorphisms in the promoter region of the beta-fibrinogen gene contribute to regulation of plasma fibrinogen concentration.

Plasma fibrinogen is a major risk factor for coronary heart disease, stroke, and peripheral artery disease. There is evidence that genetic variation in the beta-fibrinogen gene contributes to the rate of synthesis of fibrinogen, but the molecular mechanism underlying the genetic heritability of the plasma fibrinogen concentration is largely unknown. We evaluated the physiological roles of 5 common nucleotide substitutions in the promoter region of the beta-fibrinogen gene at positions -148, -249, -455, -854, and -993 from the transcriptional start site. Electrophoretic mobility shift assays revealed distinct differences in the binding characteristics of nuclear proteins between wild-type and mutant fragments of both the -455G/A and -854G/A polymorphisms, whereas no clear differences were observed for the -148C/T, -249C/T, and -993C/T sites. Transfection studies in HepG2 cells showed increased basal rates of transcription for both the G-to-A substitution at position -455 (+50%, P<0.05) and the G-to-A substitution at -854 (+51%, P<0.05). Additional transfection studies using proximal promoter constructs confirmed that both the -455A and -854A alleles independently enhance the basal rate of transcription of the beta-fibrinogen gene. The rare alleles of the nonrelated -455G/A and -854G/A polymorphisms were also associated with significantly increased plasma fibrinogen levels in healthy middle-aged men. Overall, the 2 polymorphisms together explained approximately 11% of the variation in plasma fibrinogen concentration. It is concluded that the -455G/A and -854G/A polymorphisms of the beta-fibrinogen gene are physiologically relevant mutations with a significant impact on the plasma fibrinogen concentration.

A functional polymorphism in the apolipoprotein B promoter that influences the level of plasma low density lipoprotein.

Apolipoprotein (apo) B is the structural protein moiety of plasma low density lipoprotein (LDL), an important risk factor for coronary heart disease (CHD). There is evidence that the rate of synthesis of apoB-containing lipoproteins may play an important role in the regulation of plasma LDL levels. However, it is generally thought that transcriptional regulation of the apoB gene is not a significant determinant of the synthesis of apoB-containing lipoproteins, and by inference, of the regulation of the plasma LDL concentration. Here we report the discovery of a common polymorphism in the promoter region of the apoB gene, a C to T substitution at position -516. The -516T allele is associated with an increase in the basal transcription of the apoB gene (+41%, P < 0.05) in vitro in transfected HepG2 cells. Healthy middle-aged men who are homozygous for the -516T allele have 12% higher plasma LDL cholesterol levels than healthy homozygotes for the -516C allele (P < 0.05). The frequency of the -516T allele is significantly higher in young postinfarction patients (0.38) than in population-based controls (0.30) when the comparison is restricted to subjects without severe hypercholesterolemia who are homozygous for the apoE3 allele (P < 0.05). It is concluded that variation in the rate of transcription of the apoB gene can affect plasma LDL levels and influences the risk of CHD in middle-aged men.

A common functional polymorphism (C-->A substitution at position -863) in the promoter region of the tumour necrosis factor-alpha (TNF-alpha) gene associated with reduced circulating levels of TNF-alpha.

Tumour necrosis factor-alpha (TNF-alpha) plays a key role in orchestrating the complex events involved in inflammation and immunity. Accordingly, TNF-alpha has been implicated in a wide range of autoimmune and infectious diseases, but also in conditions such as obesity and insulin resistance. The regulation of TNF-alpha expression in man is indicated to be partly genetically determined. We therefore screened a 1263 bp section of the proximal promoter of the TNF-alpha gene for common genetic variants affecting the transcriptional activity of the gene. Here we report the characterization of a common functional polymorphism in the promoter region of the TNF-alpha gene, a C-->A substitution at position -863. Electromobility shift assays provided evidence for a distinct difference in the binding of monocytic and hepatic nuclear factors to the -863C and -863A alleles. The rare -863A allele was associated with 31% lower transcriptional activity ( P < 0.001) in chloramphenicol acetyltransferase (CAT) reporter gene studies in human hepatoblastoma (HepG2) cells, indicating that the-863C/A polymorphism influences the basal rate of transcription of the TNF-alpha gene in vitro. Allele frequencies were 0.83/0.17 amongst 254 apparently healthy men of Swedish origin, aged 35-50 years. In 156 men, the -863C/A polymorphism was associated with the serum TNF-alpha concentration, carriers of the rare A allele having a significantly lower TNF-alpha level ( P < 0.05). It is concluded that the common-863C/A polymorphism in the promoter region of the TNF-alpha gene is functional in vitro in monocytic and hepatic cells and influences the serum TNF-alpha concentration in vivo in healthy middle-aged men.

Two common functional polymorphisms in the promoter region of the coagulation factor VII gene determining plasma factor VII activity and mass concentration.

Recent studies have provided evidence for associations between common polymorphic markers in the coagulation factor VII (FVII) gene and plasma FVII levels. Here we describe two common, nonrelated, functional polymorphisms in the promoter region of the FVII gene, a G to T substitution at position -401 and a novel G to A substitution at position -402. Both polymorphisms strongly influence the binding properties of nuclear protein(s). The rare -401T allele is associated with a reduced basal rate of transcription of the FVII gene in human hepatoblastoma cells and with reduced plasma concentrations of total FVII (VIIag) and fully activated FVII molecules (VIIa). In contrast, the rare -402A allele confers increased transcriptional activity and is associated with increased plasma FVII levels. Together, the two polymorphisms explained 18% and 28% of the variation in VIIag and VIIa, respectively, in a group of 183 healthy, middle-aged men. It is concluded that these polymorphisms are important for the regulation of the plasma levels of FVII and that they are likely to be useful genetic markers to resolve the issue of whether a causal relationship exists between FVII levels and risk of coronary heart disease.

Separation of VLDL subfractions by density gradient ultracentrifugation.

To assess the presence and composition of very-low-density lipoprotein (VLDL) in various types of hyperlipoproteinemia, a method of density gradient ultracentrifugation has been developed. After 2 hours of density gradient ultracentrifugation, human serum VLDL is separated into two distinct VLDL cholesterol peaks (VLDL1 and VLDL2). The two VLDL subfractions were detected in the serum samples from all subjects in the study, including subjects with normolipidemia (n = 10), familial dysbetalipoproteinemia (n = 12), and type IIa (n = 8), type IIb (n = 12), and type IV/V (n = 10) hyperlipoproteinemia. The cholesterol profiles obtained by the density gradient ultracentrifugation technique resembled the band patterns after electrophoresis of identical serum samples on 2% to 16% nondenaturing polyacrylamide gradient gel: VLDL1 represents relatively large VLDL particles (diameter of about 67 nm) and VLDL2 represents relatively small VLDL particles (diameter of about 38 nm). Recentrifugation of isolated VLDL1 and isolated VLDL2 did not result in any change in their density distribution. In all groups studied, the fluidity of VLDL1 was significantly higher than that of VLDL2, in accordance with the finding that VLDL1 particles were relatively rich in triglycerides and VLDL2 particles were relatively rich in cholesteryl esters. These results indicate that the two VLDL subfractions isolated represent distinct VLDL subclasses. The density gradient ultracentrifugation technique presented in this study allows the rapid isolation and characterization of VLDL subfractions from the serum samples of normolipidemic individuals and patients with hyperlipoproteinemia.

Allele-specific increase in basal transcription of the plasminogen-activator inhibitor 1 gene is associated with myocardial infarction.

Increased plasminogen-activator inhibitor 1 (PAI-1) activity is a common finding in patients with coronary heart disease. Here we provide evidence for an independent, etiological role of PAI-1 in myocardial infarction. The 4G allele of a recently described common 4/5-guanine-tract (4G/5G) polymorphism in the PAI-1 promoter is associated with higher plasma PAI-1 activity. The prevalence of the 4G allele is significantly higher in patients with myocardial infarction before the age of 45 than in population-based controls (allele frequencies of 0.63 vs. 0.53). Both alleles bind a transcriptional activator, whereas the 5G allele also binds a repressor protein to an overlapping binding site. In the absence of bound repressor, the basal level of PAI-1 transcription is increased.

Plasma lipoproteins in familial dysbetalipoproteinemia associated with apolipoproteins E2(Arg158-->Cys), E3-Leiden, and E2(Lys146-->Gln), and effects of treatment with simvastatin.

Using a density-gradient ultracentrifugation technique, we analyzed in detail the plasma lipoprotein profiles of 18 patients with familial dysbetalipoproteinemia (FD) who had apolipoprotein (apo) E2(Arg158-->Cys) homozygosity (the E2-158 variant, n = 6), apoE3-Leiden heterozygosity (the E3-Leiden variant, n = 6), or apoE2(Lys146-->Gln) heterozygosity (the E2-146 variant, n = 6), with average plasma cholesterol concentrations of 8.99 +/- 1.34 mmol/L, 9.29 +/- 1.55 mmol/L, and 8.46 +/- 1.10 mmol/L, respectively. No significant differences in sex, age, body mass index, dietary habits, and standard laboratory tests between the three groups were observed. The lipoprotein profiles of all FD patients were characterized by higher concentrations of very-low-density lipoprotein (VLDL) 1, VLDL2, and intermediate-density lipoprotein (IDL) and a higher cholesteryl ester content of VLDL1 and VLDL2 than in 6 normolipidemic control subjects with an average plasma cholesterol concentration of 5.90 +/- 0.53 mmol/L. Major differences between the plasma lipoprotein profiles of patients with the E2-158 variant, the E3-Leiden variant, and the E2-146 variant and the normolipidemic control subjects were in IDL cholesterol concentration (1.70 +/- 0.26, 1.50 +/- 0.26, 1.05 +/- 0.36, and 0.47 +/- 0.14 mmol/L, respectively), LDL cholesterol concentration (1.83 +/- 0.50, 3.09 +/- 0.32, 3.79 +/- 0.76, and 3.77 +/- 0.56 mmol/L, respectively), and the molar ratio of IDL cholesterol to LDL cholesterol (0.98 +/- 0.28, 0.48 +/- 0.04, 0.28 +/- 0.09, and 0.12 +/- 0.03, respectively). After 10 weeks of simvastatin treatment the concentrations of plasma cholesterol, VLDL2 cholesterol, IDL cholesterol, and LDL cholesterol in 3 patients with the E2-158 variant fell significantly, by 46%, 56%, 53%, and 48%, respectively; they also fell in 3 patients with the E3-Leiden variant, by 48%, 54%, 57%, and 52%, respectively, and in 3 patients with the E2-146 variant, by 38%, 55%, 46%, and 35%, respectively. Simvastatin therapy lowered plasma activity of cholesteryl ester transfer protein but had no significant effect on plasma activity of lecithin:cholesterol acyltransferase. It is concluded that patients with FD due to various apoE variants have different lipoprotein profiles, mainly with regard to IDL and LDL levels, although they have a number of similar features of dysbetalipoproteinemia. Simvastatin therapy effectively reduced the plasma concentrations of total cholesterol, VLDL2 cholesterol, IDL cholesterol, and LDL cholesterol in the three groups of patients studied. It is proposed that apoE-dependent defects of the conversion of IDL to LDL may be an important mechanism in the pathophysiology of FD.

Plasma lipoprotein profiles of normocholesterolemic and hypercholesterolemic homozygotes for apolipoprotein E2(Arg158-->Cys) compared.

We compared plasma lipoprotein profiles of 15 individuals with normocholesterolemic (plasma cholesterol 4.81 +/- 0.90 mmol/L) familial dysbetalipoproteinemia (NFD) and 15 patients with hypercholesterolemic (plasma cholesterol 10.61 +/- 2.32 mmol/L) familial dysbetalipoproteinemia (HFD), matched for age and sex. All subjects were homozygous for apoE2(Arg158-->Cys). Compared with 15 normolipidemic controls (plasma cholesterol 5.47 +/- 0.92 mmol/L), subjects with NFD and HFD had greater cholesterol concentrations of large very-low-density lipoprotein (VLDL1), small VLDL (VLDL2), and intermediate-density lipoprotein, each of which was correlated to their plasma total cholesterol concentration. VLDL1 and VLDL2 subfractions were enriched in cholesteryl ester, and plasma cholesteryl ester transfer protein activities were increased in both NFD and HFD; however, absolute changes were larger in HFD than in NFD. Concentrations of low-density lipoprotein cholesterol were lower in HFD (1.89 +/- 0.48 mmol/L) and NFD (1.56 +/- 0.36 mmol/L) than in normolipidemic controls (3.35 +/- 0.73 mmol/L). We conclude that all subjects homozygous for apoE2(Arg158-->Cys) show features of dysbetalipoproteinemia.

Screening for familial defective apolipoprotein B-100 with improved U937 monocyte proliferation assay.

Frostegård et al. (J Lipid Res 1990;31:37-44) demonstrated that the proliferation of the human monocyte cell line U937 is critically dependent on the uptake of low-density lipoprotein (LDL) via the apo B, E (LDL) receptor, a characteristic that was used to detect patients with familial defective apolipoprotein B-100 (FDB). Here we applied this principle to develop a simple and reproducible assay for the detection of patients with functionally defective LDL. We added serum to U937 cells in cholesterol-free incubation medium and determined the increase in cell number after a 72-h incubation at 37 degrees C by using an electronic cell counter. Sera from 10 normolipidemic individuals and from 34 patients with type IIa hyperlipoproteinemia stimulated the growth of U937 cells in proportion to the exogenous cholesterol concentration (r = 0.83, P < 0.001) and the LDL-cholesterol concentration (r = 0.81, P < 0.001). However, sera from 16 patients with FDB stimulated less cell proliferation than did sera from patients with type IIa hyperlipoproteinemia with equal LDL-cholesterol concentrations. With a 15% reduction in growth as the cutoff value, this test had a sensitivity and specificity for diagnosis of FDB of 87.5% and 100%, respectively. The improved U937 monocyte proliferation assay can be used for screening hypercholesterolemic patients to detect individuals with functionally defective LDL.

Lipoprotein profiles in a family with two mutants of apolipoprotein E: possible association with hypertriglyceridaemia but not with dysbetalipoproteinaemia.

1. The plasma lipoprotein profiles of eight members of a Dutch pedigree spanning three generations where two rare apolipoprotein E mutants, APOE*3(Cys-112-->Arg; Arg-251-->Gly) and APOE*2(Val-236-->Glu), segregate were analysed to determine whether the APOE mutants were associated with dyslipidaemia. 2. The proband, a 51-year-old Caucasian male, was a carrier of APOE*3(Cys-112-->Arg; Arg-251-->Gly) and his spouse was a carrier of APOE*2(Val-236-->Glu). Four other family members were carriers of one or both of the mutant APOE genes. 3. The plasma cholesterol and triacylglycerol concentrations were markedly elevated in the proband and were classified as type IV hyperlipoproteinaemia. The plasma triacylglycerol concentration was moderately increased in a sister, who was a carrier of APOE*3(Cys-112-->Arg; Arg-251-->Gly), and in the son, who was a compound heterozygote for both mutant APOE alleles. Normal plasma lipid levels were observed in all other family members. In the plasma samples of the proband and his family members beta-very-low-density lipoprotein was not detectable and the molar ratio of very-low-density lipoprotein-cholesterol to very-low-density lipoprotein-triacylglycerol was less than 0.9. The concentration of intermediate-density lipoprotein was within normal limits. 4. None of the family members carrying APOE*3-(Cys-112-->Arg; Arg-251-->Gly) and/or APOE*2(Val-236-->Glu) exhibited lipoprotein abnormalities characteristic of familial dysbetalipoproteinaemia, although three family members carrying APOE*3-(Cys-112-->Arg; Arg-251-->Gly) showed hypertriglyceridaemia.

Changes of lipoprotein profile in familial dysbetalipoproteinemia with gemfibrozil.

PURPOSE: This prospective study was undertaken to evaluate the effects of gemfibrozil on the lipoprotein profile of patients with familial dysbetalipoproteinemia (type III hyperlipoproteinemia). PATIENTS AND METHODS: Eight patients with well-defined familial dysbetalipoproteinemia associated with the apolipoprotein (apo) E2/2 phenotype were treated with gemfibrozil (Lopid) at a dose of 600 mg twice daily for a period of 10 months. Blood samples were taken at baseline, after 4 and 5 weeks, after 3 months, and after 10 months. The separation of serum lipoprotein (sub)fractions was performed by a recently developed density gradient ultracentrifugation technique. RESULTS: After 4 weeks of gemfibrozil therapy, the concentrations of serum total cholesterol and serum total triglyceride had decreased by 45% (from 11.87 to 6.51 mmol/L, p < 0.01) and by 63% (from 6.08 to 2.23 mmol/L, p < 0.001), respectively. The cholesterol concentrations of very-low-density lipoprotein-1 (VLDL1) (large VLDL), VLDL2 (small VLDL), and intermediate-density lipoprotein (IDL) had decreased significantly by 73%, 74%, and 34%, respectively. The low-density lipoprotein (LDL)-cholesterol level remained unchanged, whereas the particle size of LDL showed a small but significant increase (from 24.09 nm to 24.43 nm, p < 0.01). The concentrations of high-density lipoprotein (HDL)-cholesterol, apo A-I, and apo A-II had increased significantly by 23%, 13%, and 29%, respectively. Only minor changes in the composition of the lipoprotein (sub)fractions were observed. After 3 months of treatment with gemfibrozil, the concentrations of serum total cholesterol and serum total triglyceride were 5.95 mmol/L and 2.06 mmol/L, respectively, and after 10 months of treatment with gemfibrozil, the concentrations of serum total cholesterol and serum total triglyceride were 6.19 mmol/L and 2.27 mmol/L, respectively. CONCLUSION: Gemfibrozil treatment in patients with familial dysbetalipoproteinemia resulted in a marked reduction of the concentrations of large VLDL, small VLDL, and IDL, and an increase in the levels of HDL, apo A-I, and apo A-II. These changes are considered to exert an antiatherosclerotic effect in these patients.

Relationship between apolipoprotein E and low density lipoprotein particle size.

The relationships between the particle size of low density lipoproteins (LDL) and various lipid parameters, including apolipoprotein (apo) E concentration and apo E phenotype, were analyzed in plasma samples obtained from 196 apparently healthy 35-year-old males. The LDL particle size was determined by gradient gel electrophoresis. Using stepwise multiple regression analysis it was found that LDL particle size correlated negatively to the plasma concentrations of triglyceride (r = -0.497, P < 0.001), apo E (r = -0.415, P < 0.001), apo B (r = 0.395, P < 0.001) and cholesterol (r = -0.235, P < 0.001) and correlated positively to the plasma concentrations of apo A-I (r = 0.297, P < 0.001) and apo A-II (r = 0.145, P < 0.05). However, the LDL particle size did not differ significantly among the different apo E phenotypes. Indeed, when entered as a variable in the multiple regression analysis, the apo E phenotype was not correlated to the LDL particle size. It is concluded that the LDL particle size is related to the plasma concentrations of triglyceride, apo E, apo B, apo A-I, apo A-II and cholesterol and is not affected by the apo E phenotype in healthy 35-year-old males.

Identification of a splice-site mutation in the low density lipoprotein receptor gene by denaturing gradient gel electrophoresis.

We have applied the denaturing gradient gel electrophoresis (DGGE) technique to detect sequence variations in exon 9 of the low density lipoprotein receptor (LDLR) gene in individuals with heterozygous familial hypercholesterolemia (FH). A fragment containing exon 9 and 25 base pairs (bp) of the intron boundary sequence at either side was amplified. To this fragment a 40-bp GC-clamp was attached by the polymerase chain reaction (PCR). We have analyzed a total of 165 DNA samples of FH patients and have detected a mutation in three cases. Two patients were found to have the previously described "South African" G to A transition in codon 408. In a third patient, we observed a different banding pattern of the DNA fragments on DGGE indicating a different mutation. The mutant homoduplex band of this sample was purified from the gel, cloned in an AT-vector and sequenced. Sequence analysis demonstrated a G to A transition of the consensus G-nucleotide at the intron 9 splice donor site. Cosegregation between this mutation and elevated plasma cholesterol levels was observed in family members of this FH patient. This mutation probably prevents normal splicing of the mRNA and represents the first identified splice-site mutation in the LDLR gene. We conclude that the use of DGGE of GC-clamped PCR-amplified exon sequences offers a general strategy for the detection of disease-producing mutations in the LDLR gene.

Characterization of five new mutants in the carboxyl-terminal domain of human apolipoprotein E: no cosegregation with severe hyperlipidemia.

Assessment of the apolipoprotein E (apoE) phenotype by isoelectric focusing of both hyperlipidemic and normolipidemic individuals identified five new variants. All mutations were confined to the downstream part of the APOE gene by using denaturing gradient gel electrophoresis (DGGE). Sequence analysis revealed five new mutations causing unique amino acid substitutions in the carboxyl-terminal part of the protein containing the putative lipid-binding domain. Three hyperlipoproteinemic probands were carriers of the APOE*2(Val236-->Glu) allele, the APOE*3(Cys112-->Arg; Arg251-->Gly) allele, or the APOE*1(Arg158-->Cys; Leu252-->Glu) allele. DGGE of the region encoding the receptor-binding domain was useful for haplotyping the mutations at codons 112 and 158. Family studies failed to demonstrate cosegregation between the new mutations and severe hyperlipoproteinemia, although a number of carriers for the APOE*3(Cys112-->Arg; Arg251-->Gly) allele and the APOE*1(Arg158-->Cys; Leu252-->Glu) allele expressed hypertriglyceridemia and/or hypercholesterolemia. Two other mutant alleles, APOE*4-(Cys112-->Arg; Arg274-->His) and APOE*4+(Ser296-->Arg), were found in normolipidemic probands. The lack of cosegregation of these new mutations with severe hyperlipoproteinemia suggests that these mutations do not exert a dominant effect on the functioning of apoE.

Lipoproteins in familial dysbetalipoproteinemia. Variation of serum cholesterol level associated with VLDL concentration.

Patients with familial dysbetalipoproteinemia (FD) associated with the apo E2/2 phenotype exhibit a marked interindividual variability in serum cholesterol and triglyceride concentrations. It has been proposed that this variability is due to a combination of the apo E2/2 phenotype and additional genetic factors implicated in diseases like familial hypercholesterolemia, familial combined hyperlipoproteinemia, and familial hypertriglyceridemia. To further explore the nature of this variability, the lipoprotein profiles of 17 patients with FD associated with the apo E2/2 phenotype were analyzed by a density-gradient ultracentrifugation technique and by 2-16% polyacrylamide gel electrophoresis. It was found that all patients with FD were characterized by 1) markedly increased cholesterol concentrations of large very low density lipoprotein (VLDL) (VLDL1) (2.98 +/- 3.08 versus 0.08 +/- 0.03 mmol/L), small VLDL (VLDL2) (4.68 +/- 1.93 versus 0.27 +/- 0.13 mmol/L), and intermediate density lipoprotein (IDL) (2.25 +/- 0.72 versus 0.39 +/- 0.16 mmol/L); 2) decreased low density lipoprotein (LDL) cholesterol level (1.84 +/- 0.54 versus 3.36 +/- 0.53 mmol/L); and 3) altered composition (enrichment by cholesteryl ester) of VLDL1 and VLDL2 compared with normolipidemic control subjects. The cholesterol levels of IDL and LDL showed minor interindividual variabilities and were not correlated with serum cholesterol and triglyceride levels. The compositions of VLDL1 and VLDL2 were independent of the concentrations of lipids in serum. However, the cholesterol concentrations of VLDL1 and VLDL2 showed considerable interindividual variabilities and were positively correlated with the serum cholesterol concentration (r = 0.84 and r = 0.95, respectively, both p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Potential of 99mTc-LDLs labeled by two different methods for scintigraphic detection of experimental atherosclerosis in rabbits.

In this study we evaluated two different 99mTc-labeling techniques to produce 99mTc-low density lipoprotein (99mTc-LDL) suitable for the scintigraphic delineation of experimental atherosclerotic lesions. The two methods are 1) a procedure that uses stannous chloride and sodium borohydride (borohydride method) and 2) a procedure that uses sodium dithionite as a reducing agent and that has been successfully applied in previous scintigraphic atherosclerosis detection (dithionite method). 99mTc-LDL produced by either method was injected into New Zealand White rabbits with diet-induced atherosclerotic plaques and in control rabbits. Scintigraphic images were taken 10 minutes (t = 0) and 1, 4, 8, 16, and 24 hours after injection. Clearance of plasma radioactivity was also studied. Stability of the 99mTc-LDL complex in the circulation was examined by size exclusion chromatography of plasma samples. After scintigraphy, the animals were killed, and the biodistribution of radioactivity was determined. The thoracic and abdominal aortas appeared in scintigraphic images to accumulate 99mTc over their entire length with either 99mTc-LDL preparation. The sparse imaging of focal atherosclerosis was found to be due to the fact that the aortas were covered with confluent atherosclerotic lesions. Scintigraphic image analysis showed that 24 hours after injection, the accumulated radioactivity in the abdominal aorta of the atherosclerotic rabbits was 57% and 54%, respectively, of the accumulated radioactivity in the abdominal aorta at t = 0 when the borohydride versus the dithionite method was used. In the control animals this value was 25% for the dithionite method, whereas in the borohydride method the aortas could not be detected in the images at t = 24 hours.(ABSTRACT TRUNCATED AT 250 WORDS)