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Biomedical subjects

R E Gregg

Publications and source records attributed to R E Gregg.

108 records · Page 6Linked to original sources
PubMed1984

Apolipoprotein E metabolism in normolipoproteinemic human subjects.

Human apolipoprotein E (apoE) is a constituent of plasma very low density and high density lipoproteins and is important in modulating the catabolism of remnants of triglyceride-rich lipoproteins. There are three common isoforms of apoE, designated apoE-2, E-3, and E-4, which are coded by three separate alleles (epsilon 2, epsilon 3, and epsilon 4) at a single genetic locus and inherited in the population in a co-dominant fashion. ApoE-3 is the predominant apoE isoform in the normolipidemic population, and epsilon 3 has been proposed to be the normal allele. ApoE-3 metabolism was studied in nine normolipidemic subjects homozygous for the epsilon 3 allele. In these subjects, the plasma apoE-3 concentration was 4.8 +/- 1.2 mg/dl (mean +/- SD), the plasma apoE-3 residence time was 0.73 +/- 0.18 days, and the plasma apoE-3 production rate was 3.4 +/- 1.5 mg/kg-day. The apoE in males, when compared to females, tended to have a shorter residence time (0.63 +/- 0.15 days versus 0.83 +/- 0.16), a higher production rate (4.20 +/- 1.73 mg/kg-days versus 2.60 +/- 0.78), but a similar plasma concentration (5.1 +/- 1.5 mg/dl versus 4.5 +/- 0.8). ApoE-3 had a more rapid catabolism from plasma than other apolipoproteins previously studied (apolipoproteins A-I, A-II, A-IV, B-100, C-II, and C-III) except for apolipoprotein B-48. The catabolism of apoE-3 in the individual lipoprotein subfractions was also examined and apoE was shown to be catabolized most rapidly from the VLDL and slowest from the HDL. The results of the kinetic analysis of apoE metabolism are consistent with apoE being important in the catabolism of triglyceride-rich lipoproteins and with HDL serving as a reservoir for apoE to reassociate with newly secreted triglyceride-rich lipoproteins.

Adult↗
PubMed1983

Macula halo syndrome. Variant of Niemann-Pick disease.

The macula halo syndrome is the name proposed to describe patients with a unique ring-form opacity about the foveolas and a histiocytic storage disease. Since sphingomyelinase deficiency has now been found in the three patients in whom it was sought (including two in the present report), the entity may be classified as a variant of Niemann-Pick disease. A secondary hyperlipidemia may also be present. The macula halos consisting of symmetric crystalloid opacities with little or no visual impairment are pathognomonic of the entity.

Adult↗
PubMed1983

Initial diagnosis of lipoprotein lipase deficiency in a 75-year-old man.

Lipoprotein lipase deficiency, characterized by recurrent pancreatitis, profound hypertriglyceridemia, and delayed clearance of chylomicrons, is generally first diagnosed in childhood. Although patients with this condition have died during episodes of acute pancreatitis in the fourth and fifth decades, no patient older than 50 years has been previously reported. The de novo diagnosis of lipoprotein lipase deficiency in a 75-year-old man illustrates important points about this disease. This inborn error in metabolism may have a relatively benign clinical course resulting in normal life span, particularly if there is strict adherence to a low-fat diet and abstinence from alcohol. Moreover, measurement of lipoprotein lipase activity in persons with severe hypertriglyceridemia and recurrent abdominal pain, even in elderly patients, should lead to the correct diagnosis and treatment of this condition.

Abdomen↗
PubMed1983

Apolipoprotein EBethesda: a new variant of apolipoprotein E associated with type III hyperlipoproteinemia.

Apolipoprotein E (apoE) is associated with plasma lipoproteins and is important in modulating the catabolism of remnants of triglyceride-rich lipoproteins. ApoE is a polymorphic protein, and homozygosity for the E2 allele is associated with type III hyperlipoproteinemia. A variant of apoE, apoEBethesda, was found that migrates in the E1 position on isoelectric focusing. Evaluation of the proband and her family showed that both individuals with apoEBethesda had type III hyperlipoproteinemia, and the analysis was consistent with the concept that apoEBethesda was coded by a new E allele and that this allele was expressed in a codominant fashion. The discovery of apoEBethesda and its association with type III hyperlipoproteinemia provides additional evidence for the genetic heterogeneity of the E allele and suggests that a number of different structural mutations of the E apolipoprotein may be associated with the type III phenotype.

Adult↗
PubMed1983

NIH conference. Type III hyperlipoproteinemia: diagnosis, molecular defects, pathology, and treatment.

Type III hyperlipoproteinemia is characterized by increased plasma levels of triglycerides and cholesterol, palmar-tuberoeruptive xanthoma, and premature cardiovascular disease. Three major classes of molecular defects will predispose patients to develop type III hyperlipoproteinemia: a deficiency in apolipoprotein E, a structural defect in the E apolipoprotein, and a functional defect in the liver receptor system. Most patients with type III hyperlipoproteinemia have a structural defect in apolipoprotein E associated with increased synthesis and decreased catabolism of apolipoprotein E, delayed catabolism of chylomicron remnants, and development of plasma lipoprotein abnormalities characteristic of type III hyperlipoproteinemia. Analysis of cardiovascular disease in patients with type III hyperlipoproteinemia showed extensive coronary and peripheral vascular atherosclerosis indistinguishable from the atherosclerosis of non-hyperlipidemic and other dyslipoproteinemic patients. The xanthoma and elevated plasma cholesterol and triglyceride levels in patients with type III hyperlipoproteinemia respond to dietary and drug therapy.

Adolescent↗
PubMed1983

Presence of two forms of apolipoprotein B in patients with dyslipoproteinemia.

Current information suggests that the major forms of the human B apolipoproteins, B-100 and B-48, are under separate genetic control and are synthesized by the liver and intestine, respectively. The apolipoprotein B composition of plasma lipoproteins has been determined in order to gain insight into the metabolic defects in patients with dyslipoproteinemias. Patients with type I and type V hyperlipoproteinemia can be separated into two groups based on apolipoprotein composition and triglyceride concentration. The first group had markedly elevated plasma triglycerides with B-48 in the 1.006 g/ml density fraction and only B-100 within IDL and LDL. The second group had plasma triglycerides less than 1200 mg % and only B-100 in all density fractions. Patients with type III hyperlipoproteinemia had B-48 in only the density less than 1.006 g/ml with B-100 in IDL and LDL; the type III hyperlipoproteinemic patient with apolipoprotein E deficiency, however, had B-48 in density less than 1.006 g/ml fraction, IDL, and LDL. Patients with type IIa, IIb, and IV hyperlipoproteinemia had only B-100 in all density fractions. These combined results are interpreted as indicating that B-48 is associated with triglyceride-rich lipoproteins synthesized by the intestine and that patients with phenotypes I, III, and V have defects in chylomicron remnant metabolism. In addition, in patients with types I and V hyperlipoproteinemia, mild hypertriglyceridemia appears to be associated with lipoprotein particles of liver origin.

Apolipoproteins↗
PubMed1983

Heterogeneity of lipoprotein electrophoretic patterns in patients with type IIa hyperlipoproteinemia.

Previous evaluations of plasma lipoproteins from patients with type IIa hyperlipoproteinemia have demonstrated quantitative but not qualitative differences from lipoproteins isolated from normal subjects. Using a reproducible, sensitive, high-resolution agarose gel electrophoretic system, we evaluated the plasma lipoprotein of 22 consecutive, untreated, unrelated patients with type IIa hyperlipoproteinemia. Five distinct electrophoretic patterns were observed. This electrophoretic heterogeneity in type IIa hyperlipoproteinemia reflects subtle charge differences in the lipoproteins from these patients, which were not detected with paper electrophoresis or with lipoprotein quantification. There was little, if any, difference in total plasma cholesterol, low- or very-low-density lipoproteins, plasma triglycerides, or concentrations of apolipoproteins A-I, A-II, B, C-II, or E in these subgroups. However, unique clinical features were correlated with the electrophoretic patterns. These findings support the concept that the type IIa hyperlipoproteinemic phenotype includes several molecular defects that are reflected in subtle differences in lipoprotein charge.

Adult↗
PubMed1982

Phenotype study of apolipoprotein E isoforms in hyperlipoproteinaemic patients.

It has been suggested that apolipoprotein E (apoE) is inherited at a single genetic locus with three common alleles designated E2, E3, and E4. The products of these three alleles are apoE2, apoE3, and apoE4. The apoE phenotypes of 74 normal subjects and 226 hyperlipoproteinaemic subjects were ascertained by gel isoelectrofocusing. Patients with type I, type IIa, type IIb, and type IV hyperlipoproteinaemia had an apoE phenotypic distribution which was similar to that of normal subjects, with 40.0 to 60.0% being homozygous for E3. In contrast, 75% of type III patients had an E2 phenotype and 25% were E2/3 heterozygotes. Among type V patients 31.4% had an E4 phenotype, and 42.9% were E4 heterozygotes. No type III patient and only 5.7% of type V patients had E3 phenotype. The results suggest that apoE2 and apoE4 are associated with two distinctly different dyslipoproteinaemias and that apoE has at least two different physiological functions.

Apolipoproteins↗
PubMed1982

Increased prevalence of apolipoprotein E4 in type V hyperlipoproteinemia.

Type V hyperlipoproteinemia (HLP) is characterized clinically by hepatosplenomegaly, occasional eruptive xanthomas, and an increased incidence of pancreatitis. These patients have striking hypertriglyceridemia due to increased plasma chylomicron and very low density lipoprotein concentrations in the fasting state, without a deficiency of lipoprotein lipase or its activator protein, apolipoprotein (apo) C-II. ApoE, a protein constituent of triglyceride-rich lipoproteins, has been implicated in the receptor-mediated hepatic uptake of these particles. ApoE has three major alleles: E2, E3, and E4, and the products of these alleles are apoE2, apoE3, and apoE4, respectively. ApoE phenotypes were determined in 30 type V HLP patients as well as in 37 normal volunteers. Among the type V patients, 33.3% were noted to be homozygous, and 40.0% heterozygous for E4 (normal, 2.7 and 21.6%, respectively). These data suggest that apoE4 may play a role in the etiology of the hyperlipidemia in a significant number of type V HLP patients.

Apolipoprotein E4↗
PubMed1981

Type III hyperlipoproteinemia: defective metabolism of an abnormal apolipoprotein E.

The apolipoprotein E isolated from plasma of individuals with type III hyperlipoproteinemia (HLP) shows an abnormal pattern when it is examined by isoelectric focusing. Compared to apolipoprotein E from normal subjects, apolipoprotein E isolated from subjects with type III HLP had a decreased fractional catabolic rate in vivo in both type III HLP patients and normal individuals. The delayed catabolism of apolipoprotein E in type III HLP patients may be responsible for the lipid and lipoprotein abnormalities characteristic of these patients.

Apolipoproteins↗
PubMedDate not supplied

Morphologic features of the liver in abetalipoproteinemia.

Liver tissue of a newly diagnosed 30-year-old patient with abetalipoproteinemia was studied by light and electron microscopy. Despite accumulation of large quantities of lipid droplets in hepatocytes, the lobular architecture remained intact, and there was no fibrosis. Acanthocytes were readily identified in sinusoids by scanning electron microscopy. Profiles of rough endoplasmic reticulum, smooth endoplasmic reticulum and Golgi apparatus appeared normal by transmission electron microscopy. Lipid droplets were not bound to membranes and were not associated with the endoplasmic reticulum or Golgi apparatus. In abetalipoproteinemia, these morphological features are consistent with defective apolipoprotein B synthesis. This prevents assembly of lipoproteins that can be secreted through the normal intracellular communicating tubular network and, consequently, fat accumulates in the cytoplasm of the hepatocytes.

Abetalipoproteinemia↗
PubMedDate not supplied

Characterization of a human hepatic receptor for high density lipoproteins.

Characterization of the membrane receptor for the low density lipoproteins (LDL) has led to insights into cellular receptor physiology as well as mammalian lipid transport. Result with LDL have stimulated the search for specific receptors for other plasma lipoproteins. Receptors for high density lipoproteins (HDL) have been identified in human fibroblasts and smooth muscle cells. Specificity for this receptor has been difficult to define since normal HDL contains several apolipoproteins, and particles containing apolipoproteins B and E have been shown to compete for HDL binding. In the present study, we demonstrate that HDL isolated from a patient devoid of apolipoprotein E was bound specifically by human hepatic membranes. This binding reached saturation within 2 hours and was EDTA-resistant. Assuming a single receptor model, we found that 2.9 x 10(15) receptors/mg membrane protein bound with an affinity KD = 3.5 x 10(-7) M at 0 to 4 degrees C and KD = 1.9 x 10(-7) M at 37 degrees C. The binding was effectively competed with intact HDL3, with HDL3 that had undergone selective arginine and lysine residue modification, and with antibodies to apolipoproteins A-I and A-II. However, LDL, asialofetuin, and HDL3 which had undergone tyrosine modification by nitration, and anti-apolipoprotein B did not compete with apo A-I HDL binding. In contrast to LDL binding, the human hepatoma cell line, HEPG2, increased HDL binding with cholesterol loading that was specific for HDL3. Thus, hepatic tissue can modulate its recognition of HDL. Finally, hepatic membranes from a patient lacking normal hepatic LDL receptors bound apo A-I HDL normally. These data indicate that a saturable, specific regulatable receptor for apo E-free HDL is present in human liver.

Apolipoprotein A-I↗
PubMedDate not supplied

Apolipoprotein E polymorphism and atherosclerosis.

The apo E locus contributes to determining the variation in plasma cholesterol levels of healthy and diseased populations. It also influences the expression of hyperlipidemia and appears to modulate the susceptibility to atherosclerosis in a complex multifactorial interaction. There is evidence that the presence of apo E2 is protective, whereas that of apo E4 predisposes to coronary artery disease. The burden of proof, however, lies on future, well-designed clinical trials and prospective studies. The study of the biological significance of the apo E polymorphism in humans has emphasized the importance of gene-gene and gene-environment interactions in the pathogenesis of hyperlipidemia and atherosclerosis. The apo E polymorphism involves the coding region of the apo E gene and results in alterations of the gene product which, in turn, either directly or secondarily affect the metabolic fate of the lipoprotein particles. Rapid advances in knowledge over the last decade have provided a metabolic explanation for the observation of the opposite effects of the epsilon 4 and the epsilon 2 alleles on lipoprotein levels. Apo E2 has lower receptor binding affinity which results in delayed clearance of apo E2-bearing lipoprotein particles from plasma. Apo E4 is distributed differently from apo E3 between VLDL and HDL, is degraded more rapidly than apo E3, and may enhance the catabolism of E4-bearing particles, leading to other alterations in lipoprotein metabolism which result in elevated levels of LDL. In view of the significant opposite impacts of the epsilon 4 and the epsilon 2 alleles on plasma LDL cholesterol concentrations, it is evident that determination of the apo E phenotype will become a useful adjunct to the assessment of the cardiovascular risk profile of an individual. In addition, the relationship between the epsilon 2 allele and type III hyperlipoproteinemia provides a valuable model for the study of complex genetic interactions in the pathogenesis of hyperlipidemia. The further study of apo E and its interactions shows great promise for a deeper comprehension of the pathogenesis of atherosclerosis.

Alleles↗
PubMedDate not supplied

Enhanced apolipoprotein E production with normal hepatic mRNA levels in the Watanabe heritable hyperlipidemic rabbit.

The Watanabe heritable hyperlipidemic rabbit (WHHL) provides an experimental animal model for the low density lipoprotein (LDL) receptor defect present in patients homozygous for familial hypercholesterolemia (FH). Both WHHL rabbits and FH patients have a four- to sevenfold increase in plasma levels of apolipoprotein E (apo E). To determine the etiology for the elevated apo E concentrations, kinetic studies of radiolabeled apo E were conducted in WHHL and control New Zealand White (NZW) rabbits. The sites of apo E synthesis in the WHHL rabbit were evaluated by quantitating apo E mRNA levels in 12 tissues by dot-blot analysis of total RNA from each tissue with an apo E cDNA probe. Compared to the NZW rabbit, the WHHL rabbit had a twofold increase in the plasma apo E residence time, a fourfold increase in apo E production rate, and normal apo E mRNA levels in the liver and all other major apo E synthetic tissues. However, a fivefold increase in WHHL aortic apo E mRNA levels was observed. The elevated level of aortic apo E mRNA indicated a potential role for apo E in modulating atherogenesis in the WHHL rabbit. These results established that the increased plasma apo E in the WHHL rabbit was due to increased synthesis and delayed catabolism. Moreover, the fourfold increase in apo E synthesis with normal tissue apo E mRNA levels may reflect a translational or posttranslational regulation of apo E synthesis.

Animals↗
PubMedDate not supplied

An approach to the management of hyperlipoproteinemia.

Recent clinical trials indicate that reduction of plasma cholesterol concentrations in individuals with increased levels of low-density lipoproteins reduces their risk of myocardial infarction and death. Therefore, the question of "whether to treat" should be shifted to "whom to treat" and "how best to treat". The understanding of normal lipid transport via the plasma lipoproteins has grown to a sophisticated level over the past 20 years. Plasma cholesterol, required for cellular membrane integrity, and plasma triglycerides, the primary mammalian energy source, are carried in lipoprotein particles that vary in size, density, lipid composition, and apolipoprotein content. Some lipoprotein particles (low-density lipoproteins) play a causal role in the atherosclerotic process, while other particles (high-density lipoproteins) appear to prevent this process. Utilizing this understanding of the plasma lipoproteins, a systematic approach to the management of the patient with hyperlipoproteinemia has been developed which may lead to the normalization of plasma lipoprotein concentrations in the majority of hyperlipoproteinemic patients.

Anticholesteremic Agents↗