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Apolipoprotein E phenotype and dietary responsiveness in hyperlipidemic subjects
Tuesday 11 October 1994: Poster Abstracts Dyslipoproteinemias
strated that LDL particles are heterogeneous in size and lipid composition. In this study, we analyzed the binding of LDL to the LDL receptor in subjects with various types of hyperlipoproteinemia and investigated the effects of variations in LDL size and lipid composition on affinity for the receptor. In several subjects, we also examined the influence of a lipid-lowering drug (bezafibrate) on the characteristics of LDL and on cholesteryl ester transfer protein (CETP) activity. LDL binding was assayed by measuring the competition between 1251-labelednormal LDL and sample LDL for binding to LDL receptors on human fibroblasts, the binding affinity being expressed as the concentration of sample LDL required to inhibit 50% of ‘251-labeled LDL binding (IC50). The IQ0 of LDL from patients with type IIa hyperlipoproteinemia was similar to that of LDL from normal controls. In subjects with hypertriglyceridemia (type IIb and type IV hyperlipoproteinemia), LDL had a low affinity for the LDL receptor and the reduction in affinity was in proportion to the severity of hypertriglyceridemia. The LDL from hypertriglyceridemic patients was rich in protein and triglycerides, poor in cholesterol and phospholipids, and smaller than control LDL. A significant inverse correlation was observed between the IC5,-,value and LDL particle size. LDL receptor binding improved when the lipid composition and particle size were normalized by treatment with bezatibrate. Although it is reported that decreased CETP activity results in the formation of small LDL, plasma CETP activity was normal in our hypertriglyceridemic patients and the improvement of LDL by bezafibrate therapy was not accompanied by an increase in CETP activity. Our results suggest that the abnormal chemical composition and/or small particle size of LDL from patients with hypertriglyceridemia might cause a decrease of affinity for the LDL receptor. These structural and functional abnormalities were reversed by treatment with bezafibrate.
pJ Cobb,
Apolipoprotein E phenotype and dietary responsiveness in hyperlipidemic subjects Risch N, Teitlebaum HS, The Rockefeller Univ. NY,
NY and Yale Univ. New Haven, CT, USA
The genetic predictors of lipoprotein change, or ‘responsiveness’ to a diet crossover are controversial, due partially to dietary variation. In a retrospective analysis, we sought to determine whether apolipoprotein E (apo E) phenotype predicts lipoprotein ‘responsiveness’ to a metabolic diet crossover in normolipidemic subjects, Type II patients, and two patients with rare Type III hyperlipidemia (apo El/4 and 2/2). All groups were fed two contrasting, metabolically controlled diets, separated by a washout. One diet had a low polyunsaturated to saturated fatty acid ratio (P:S), the other a high P:S ratio. Two statistical indices of dietary responsiveness were employed: change in absolute amounts (mg/dl), and percentage change (%A) in lipoprotein levels from baseline. The very low density lipoprotein cholesterol (VLDL-C) ‘response’ to the diet crossover among the Type 111swas dramatically greater, in terms of an absolute decrease (mg/dl), while the low density lipoprotein cholesterol (LDL-C) ‘response’ was greater in the Type II group than in the normolipidemic subjects. Apo E phenotype failed to predict VLDL-C or LDL-C ‘responsiveness,’ expressed as percentage change (%A), to the metabolic diet crossover among the Type II, Type III and normolipidemic subjects. Among the Type III subjects, LDL-C in the apo El/4 patient fell by a degree comparable to that in the normolipidemic apo E4/x subjects, while the apo E2Y2subject showed a rise in LDL-C. In summary, we found that apo E phenotype predicted clinically meaningful reductions in VLDL-C in the Type III subjects and LDL-C levels among the Type II patients. The current study reaffirms the lack of correlation between apo E phenotype and lipoprotein ‘response’ (%A) among the apo E phenotypes, but
131
confirms the correlation of apo E phenotype with baseline lipoprotein levels and absolute changes. Four new deletions of LDL-receptor gene in Italian FH patients Bertolini S, Garuti R, Rolleri M, ws, Dept. of Biomedical
11531
Sciences and Int. Med., Univs. of Modena and Geneva, Italy
During the survey of 350 Italian FH patients we identified four new deletions in the LDL-receptor (LDL-r) gene. All of them were found in FH heterozygotes. FH-Roma is a 12 kb deletion extending from intron 2 to the Y/end of intron 10. Reverse transcription and amplification (RT-PCR) of the proband’s LDL-r mRNA showed that in mutant mRNA exon 2 joined exon 11; that causes a shift in the reading frame leading to the production of a short peptide of 42 amino acids. FH-Genova is a 4 kb deletion from intron 10 to intron 12. RT-PCR of the proband’s LDL-r mRNA showed that in mutant mRNA exon 10 joined exon 12, with a frame shift leading to the formation of a truncated protein (556 amino acids). FH-Roma is a 4.7 kb deletion from intron 12 to intron 14, thus eliminating exons 13-14. RT PCR failed to show the mutant mRNA, which suggests that deletion of exons 13-14 might decrease the stability of LDL-r mRNA. Finally, FH-Padova is a 2 kb deletion from intron 15 to intron 16. RT-PCR of the proband’s RNA showed that in the mutant mRNA exon 15 was followed by exon 17, with no shift in the reading frame but simply an internal deletion of 26 codons. The translation of this mutant mRNA produces a protein of 813 amino acids which is devoid of the last 18 amino acids of the O-linked sugar domain and the first 8 amino acids of the transmembrane domain. It is most likely that internal deletion of several hydrophobic amino acids of the membrane domain and their replacement by more hydrophobic amino acids prevents the proper insertion of the receptor into the plasma membrane. Is there sexual dimorphism for coronary artery disease in homozygous familial hypercbolesterolemia? Evidence from a kindred of a 60.year-old woman homozygous for W66G mutation in the LDL-receptor gene &udet D, Moorjani S, Tremblay G, Perron P, Gag& C, Lupien P-J, Lipid Clinic, Chicoutimi Hospital and Lipid Res. Center,
11541
Lava1 Univ. Hospital, 305 St-Vallier St., Chicoutimi, Qc, Canada, G7H 5H6
Sex-linked dimorphism is well documented for differential expression of coronary artery disease (CAD) in heterozygous (HTZ) familial hypercholesterolemia (FH), but it is not a feature of homozygous (HMZ) FH. We describe a kindred in which CAD expression is delayed in HMZ females relative to HMZ males, and in whom the timing of this expression is similar to that in HTZ males. The proband is a 60-year-old woman, HMZ for missense W66G mutation in the LDL receptor gene, with LDL-C of 18.8 mmol/l. Her 47-year-old sister is also HMZ for the same mutation and has an LDL-C level of 11.2 mmolll. Both have tendinous, tuberous and interdigital xanthomas, characteristic of HMZ FH. In the proband, CAD was documented at the age of 45 years; she had triple vessel stenosis, for which she underwent coronary artery bypass surgery twice, at 46 and 52 years. Presently she has mild symptoms of stable angina pectoris (II/IV). Her HMZ sister is clinically asymptomatic for CAD. The proband’s two brothers are presumed to have been HMZ for FH, based on characteristic xanthomatosis, and both died from CAD at 31 and 32 years. Also, 4 age-matched HTZ first-degree male relatives of the proband had symptomatic CAD before the age of 50 and two of them died from CAD before the age of 56.
Atherosclerosis X, Montreal, October 1994
strated that LDL particles are heterogeneous in size and lipid composition. In this study, we analyzed the binding of LDL to the LDL receptor in subjects with various types of hyperlipoproteinemia and investigated the effects of variations in LDL size and lipid composition on affinity for the receptor. In several subjects, we also examined the influence of a lipid-lowering drug (bezafibrate) on the characteristics of LDL and on cholesteryl ester transfer protein (CETP) activity. LDL binding was assayed by measuring the competition between 1251-labelednormal LDL and sample LDL for binding to LDL receptors on human fibroblasts, the binding affinity being expressed as the concentration of sample LDL required to inhibit 50% of ‘251-labeled LDL binding (IC50). The IQ0 of LDL from patients with type IIa hyperlipoproteinemia was similar to that of LDL from normal controls. In subjects with hypertriglyceridemia (type IIb and type IV hyperlipoproteinemia), LDL had a low affinity for the LDL receptor and the reduction in affinity was in proportion to the severity of hypertriglyceridemia. The LDL from hypertriglyceridemic patients was rich in protein and triglycerides, poor in cholesterol and phospholipids, and smaller than control LDL. A significant inverse correlation was observed between the IC5,-,value and LDL particle size. LDL receptor binding improved when the lipid composition and particle size were normalized by treatment with bezatibrate. Although it is reported that decreased CETP activity results in the formation of small LDL, plasma CETP activity was normal in our hypertriglyceridemic patients and the improvement of LDL by bezafibrate therapy was not accompanied by an increase in CETP activity. Our results suggest that the abnormal chemical composition and/or small particle size of LDL from patients with hypertriglyceridemia might cause a decrease of affinity for the LDL receptor. These structural and functional abnormalities were reversed by treatment with bezafibrate.
pJ Cobb,
Apolipoprotein E phenotype and dietary responsiveness in hyperlipidemic subjects Risch N, Teitlebaum HS, The Rockefeller Univ. NY,
NY and Yale Univ. New Haven, CT, USA
The genetic predictors of lipoprotein change, or ‘responsiveness’ to a diet crossover are controversial, due partially to dietary variation. In a retrospective analysis, we sought to determine whether apolipoprotein E (apo E) phenotype predicts lipoprotein ‘responsiveness’ to a metabolic diet crossover in normolipidemic subjects, Type II patients, and two patients with rare Type III hyperlipidemia (apo El/4 and 2/2). All groups were fed two contrasting, metabolically controlled diets, separated by a washout. One diet had a low polyunsaturated to saturated fatty acid ratio (P:S), the other a high P:S ratio. Two statistical indices of dietary responsiveness were employed: change in absolute amounts (mg/dl), and percentage change (%A) in lipoprotein levels from baseline. The very low density lipoprotein cholesterol (VLDL-C) ‘response’ to the diet crossover among the Type 111swas dramatically greater, in terms of an absolute decrease (mg/dl), while the low density lipoprotein cholesterol (LDL-C) ‘response’ was greater in the Type II group than in the normolipidemic subjects. Apo E phenotype failed to predict VLDL-C or LDL-C ‘responsiveness,’ expressed as percentage change (%A), to the metabolic diet crossover among the Type II, Type III and normolipidemic subjects. Among the Type III subjects, LDL-C in the apo El/4 patient fell by a degree comparable to that in the normolipidemic apo E4/x subjects, while the apo E2Y2subject showed a rise in LDL-C. In summary, we found that apo E phenotype predicted clinically meaningful reductions in VLDL-C in the Type III subjects and LDL-C levels among the Type II patients. The current study reaffirms the lack of correlation between apo E phenotype and lipoprotein ‘response’ (%A) among the apo E phenotypes, but
131
confirms the correlation of apo E phenotype with baseline lipoprotein levels and absolute changes. Four new deletions of LDL-receptor gene in Italian FH patients Bertolini S, Garuti R, Rolleri M, ws, Dept. of Biomedical
11531
Sciences and Int. Med., Univs. of Modena and Geneva, Italy
During the survey of 350 Italian FH patients we identified four new deletions in the LDL-receptor (LDL-r) gene. All of them were found in FH heterozygotes. FH-Roma is a 12 kb deletion extending from intron 2 to the Y/end of intron 10. Reverse transcription and amplification (RT-PCR) of the proband’s LDL-r mRNA showed that in mutant mRNA exon 2 joined exon 11; that causes a shift in the reading frame leading to the production of a short peptide of 42 amino acids. FH-Genova is a 4 kb deletion from intron 10 to intron 12. RT-PCR of the proband’s LDL-r mRNA showed that in mutant mRNA exon 10 joined exon 12, with a frame shift leading to the formation of a truncated protein (556 amino acids). FH-Roma is a 4.7 kb deletion from intron 12 to intron 14, thus eliminating exons 13-14. RT PCR failed to show the mutant mRNA, which suggests that deletion of exons 13-14 might decrease the stability of LDL-r mRNA. Finally, FH-Padova is a 2 kb deletion from intron 15 to intron 16. RT-PCR of the proband’s RNA showed that in the mutant mRNA exon 15 was followed by exon 17, with no shift in the reading frame but simply an internal deletion of 26 codons. The translation of this mutant mRNA produces a protein of 813 amino acids which is devoid of the last 18 amino acids of the O-linked sugar domain and the first 8 amino acids of the transmembrane domain. It is most likely that internal deletion of several hydrophobic amino acids of the membrane domain and their replacement by more hydrophobic amino acids prevents the proper insertion of the receptor into the plasma membrane. Is there sexual dimorphism for coronary artery disease in homozygous familial hypercbolesterolemia? Evidence from a kindred of a 60.year-old woman homozygous for W66G mutation in the LDL-receptor gene &udet D, Moorjani S, Tremblay G, Perron P, Gag& C, Lupien P-J, Lipid Clinic, Chicoutimi Hospital and Lipid Res. Center,
11541
Lava1 Univ. Hospital, 305 St-Vallier St., Chicoutimi, Qc, Canada, G7H 5H6
Sex-linked dimorphism is well documented for differential expression of coronary artery disease (CAD) in heterozygous (HTZ) familial hypercholesterolemia (FH), but it is not a feature of homozygous (HMZ) FH. We describe a kindred in which CAD expression is delayed in HMZ females relative to HMZ males, and in whom the timing of this expression is similar to that in HTZ males. The proband is a 60-year-old woman, HMZ for missense W66G mutation in the LDL receptor gene, with LDL-C of 18.8 mmol/l. Her 47-year-old sister is also HMZ for the same mutation and has an LDL-C level of 11.2 mmolll. Both have tendinous, tuberous and interdigital xanthomas, characteristic of HMZ FH. In the proband, CAD was documented at the age of 45 years; she had triple vessel stenosis, for which she underwent coronary artery bypass surgery twice, at 46 and 52 years. Presently she has mild symptoms of stable angina pectoris (II/IV). Her HMZ sister is clinically asymptomatic for CAD. The proband’s two brothers are presumed to have been HMZ for FH, based on characteristic xanthomatosis, and both died from CAD at 31 and 32 years. Also, 4 age-matched HTZ first-degree male relatives of the proband had symptomatic CAD before the age of 50 and two of them died from CAD before the age of 56.
Atherosclerosis X, Montreal, October 1994