Biomedical subjects

J C Cohen

Publications and source records attributed to J C Cohen.

At least 55 records · Page 3Linked to original sources

PubMed1994

Variation at the hepatic lipase and apolipoprotein AI/CIII/AIV loci is a major cause of genetically determined variation in plasma HDL cholesterol levels.

Genetic factors have been shown to play an important role in determining interindividual variation in plasma HDL-C levels, but the specific genetic determinants of HDL cholesterol (HDL-C) levels have not been elucidated. In this study, the effects of variation in the genomic regions encoding hepatic lipase, apolipoprotein AI/CIII/AIV, and the cholesteryl ester transfer protein on plasma HDL-C levels were examined in 73 normotriglyceridemic, Caucasian nuclear families. Genetic factors accounted for 56.5 +/- 13% of the interindividual variation in plasma HDL-C levels. For each candidate gene, adjusted plasma HDL-C levels of sibling pairs who shared zero, one, or two parental alleles identical-by-descent were compared using sibling-pair linkage analysis. Allelic variation in the genes encoding hepatic lipase and apolipoprotein AI/CIII/AIV accounted for 25 and 22%, respectively, of the total interindividual variation in plasma HDL-C levels. In contrast, none of the variation in plasma HDL-C levels could be accounted for by allelic variation in the cholesteryl ester transfer protein. These findings indicate that a major fraction of the genetically determined variation in plasma HDL-C levels is conferred by allelic variation at the hepatic lipase and the apolipoprotein AI/CIII/AIV gene loci.

Apolipoprotein A-I↗

PubMed1994

Genetic analysis of a polymorphism in the human apolipoprotein A-I gene promoter: effect on plasma HDL-cholesterol levels.

Previous studies have indicated that a G to A substitution at position -76 in the gene encoding apolipoprotein A-I (apoA-I) confers increased plasma high density lipoprotein cholesterol (HDL-C). Increased HDL-C may be a direct consequence of the A allele, or may reflect the action of a locus in linkage disequilibrium with the A allele. To elucidate this question, we examined the effect of this polymorphism in a large sample (n = 409) of unrelated Caucasians and their nuclear families (n = 22). To eliminate the confounding effects of hypertriglyceridemia, individuals with triglyceride levels greater than 150 mg/dl were excluded from the study. ApoA-I genotype was determined by polymerase chain reaction (PCR) amplification of genomic DNA and restriction digestion with Msp I. Individuals were grouped by genotype (GG, GA or AA) and mean adjusted HDL levels of the three groups were compared by one-way analysis of variance. Our analysis indicates that HDL-C levels do not vary by genotype, and no gene dosage effect is apparent in men or in women. Analysis of 22 informative Caucasian nuclear families showed no significant difference between individuals with the A allele and their GG siblings. These data suggest that polymorphism at -76 in the apoA-I gene does not directly affect HDL levels. Therefore, the increased HDL-C levels reported in other populations must reflect linkage disequilibrium between the A allele and a putative HDL-raising allele. As we find no evidence for association between the A allele and high HDL levels, this putative allele must occur at a low frequency in the population sampled in this study.

Adenine↗

PubMed1993

cDNA equalization for reverse transcription-polymerase chain reaction quantitation.

Reverse transcription coupled with the polymerase chain reaction has been increasingly utilized to study gene expression. However, most previously published quantitative techniques are limited by accurate initial RNA quantitation and do not account well for the relative efficiency of reverse transcription. We have developed a technique of labeling and quantitating the random-primed cDNA product of a reverse transcription reaction. Using the polymerase chain reaction in conjunction with template dilutions or with an internal competitive template, we show that by normalizing the cDNA input into the polymerase chain reaction, we get accurate quantitation of gene expression. We call this procedure cDNA equalization of reverse transcriptase-polymerase chain reaction. This method is ideal for small clinical samples where accurate quantitation of input RNA is difficult.

Animals↗

PubMed1993

Molecular definition of the extreme size polymorphism in apolipoprotein(a).

Lipoprotein(a) [Lp(a)], an atherogenic lipoprotein, consists of an LDL particle complexed with a large glycoprotein, apolipoprotein(a) [apo(a)]. Apo(a) is one of the most polymorphic expressed sequences in the human genome. The glycoprotein varies in size over a approximately 500 kDa range due to length polymorphisms in the apo(a) gene. The region of the apo(a) gene responsible for this size polymorphism was cloned and characterized. Apo(a) alleles of different length were found to contain varying numbers of a subset of a tandemly-repeated, 5.5 kilobase, kringle IV-encoding sequences. A total of 34 apo(a) alleles and glycoproteins could be distinguished using pulsed-field gel electrophoresis and genomic blotting and immunoblotting. Molecular analysis of a newly-generated apo(a) allele of different length suggests that the high degree of length polymorphism is in part due to recombination between sister chromatids.

Alleles↗

PubMed1993

Sequence polymorphisms in the apolipoprotein (a) gene. Evidence for dissociation between apolipoprotein(a) size and plasma lipoprotein(a) levels.

Apolipoprotein(a) [apo(a)], an apolipoprotein unique to lipoprotein(a) [Lp(a)], is highly polymorphic in size. Previous studies have indicated that the size of the apo(a) gene tends to be inversely correlated with the plasma level of Lp(a). However, several exceptions to this general trend have been identified. Individuals with apo(a) alleles of identical size do not always have similar plasma concentrations of Lp(a). To determine if these differences in plasma Lp(a) concentrations were due to sequence variations in the apo(a) gene, we examined the sequences of apo(a) alleles in 23 individuals homozygous for same-sized apo(a) alleles. We identified four single-strand DNA conformation polymorphisms (SSCPs) in the apo(a) gene. Of the 23 homozygotes, 21 (91%) were heterozygous for at least one of the SSCPs. Analysis of a family in which a parent was homozygous for the same-sized apo(a) allele revealed that each allele, though identical size, segregated with different plasma concentrations of Lp(a). These studies indicate that the apo(a) gene is even more polymorphic in sequence than was previously appreciated, and that sequence variations at the apo(a) locus, other than the number of kringle 4 repeats, contribute to the plasma concentration of Lp(a).

Alleles↗

PubMed1992

PCR amplification of HIV-1 proteinase sequences directly from lab isolates allows determination of five conserved domains.

HIV-1 replication requires limited proteolysis of gag and gag-pol encoded precursor proteins by a specific viral proteinase (PR). Sequences of 20 different HIV-1 strains were compared in order to determine regions of conservation and variability within the PR gene. Viral strains included: (a) five new ones derived from New Orleans patient isolates, (b) four established ones grown in our laboratory, (c) eight, whose sequences were published in the Los Alamos Data Base (1990), (d) one Ugandan, and (e) two Brazilian isolates. In the first two groups, HIV proviral DNA extracted from infected lymphocytes was grown in tissue culture and directly amplified by PCR using specific primers flanking the PR gene. Amplified DNA was directly sequenced using a modified di-deoxy sequencing procedure. Sequence data showed a 25% variation among the 20 different HIV strains studied at the amino acid level, including 8% nonconservative changes and 17% conservative changes. Moreover, five noncontiguous regions were able to be delineated in which the PR showed no amino acid changes. These areas included amino acids (I) 1-9 (amino terminal sequence); (II) 21-32 (sequence around the active site); (III) 47-56 (top of the flap); (IV) 78-88; and (V) 94-99 (carboxy terminal sequence). Our results are consistent with those obtained from X-ray crystallography studies as well as single site mutational analysis.

Acquired Immunodeficiency Syndrome↗

PubMed1992

Cloning of the human cholesterol 7 alpha-hydroxylase gene (CYP7) and localization to chromosome 8q11-q12.

Cholesterol 7 alpha-hydroxylase (7 alpha-hydroxylase) is a microsomal cytochrome P450 that catalyzes the first step in bile acid synthesis. In this paper, we describe the cloning, characterization, and chromosomal mapping of the human 7 alpha-hydroxylase gene (CYP7). The gene spans 10 kb and contains six exons and five introns. The exon-intron boundaries are completely conserved between the human and rat genes. Sequencing of the 5' flanking region revealed consensus recognition sequences for a number of liver-specific transcription factors. The human CYP7 gene was mapped to chromosome 8q11-q12 using both mouse-human somatic cell hybrids and in situ chromosomal hybridization studies. A total of four single-stranded conformation-dependent DNA polymorphisms and an Alu sequence-related polymorphism were identified. Of the individuals analyzed, 80% were heterozygous for at least one of these five polymorphisms. The localization and characterization of the human 7 alpha-hydroxylase gene, as well as the identification of polymorphisms, provide the molecular tools necessary to investigate the role of this gene in disorders of cholesterol and bile acid metabolism.

Amino Acid Sequence↗

PubMed1992

Normal postprandial lipemia in men with low plasma HDL concentrations.

To examine the relation between postprandial lipemia and high density lipoprotein (HDL) concentrations, we measured the plasma triglyceride and retinyl palmitate responses to 50-g fat meals of 1) 25 men with low HDL cholesterol concentrations (less than 36 mg.dl-1) and normal fasting triglyceride concentrations, 2) 25 men with normal HDL cholesterol (greater than 40 mg.dl-1) and normal fasting triglyceride concentrations, and 3) 20 men with mild to moderate fasting hypertriglyceridemia (250-347 mg.dl-1). The average magnitude of postprandial lipemia induced by the fat meals was markedly higher in the hypertriglyceridemic men (593 +/- 311 mg.dl-1.8 hr) than in either of the normolipidemic groups. In normotriglyceridemic men with low HDL cholesterol, mean postprandial lipemia (303 +/- 158 mg.dl-1.8 hr) was similar to the corresponding value of men with normal HDL (283 +/- 130 mg.dl-1.8 hr). Postprandial plasma retinyl palmitate concentrations, which reflect chylomicron remnant metabolism, also were similar in normal-HDL and low-HDL groups. These data suggest that defects in chylomicron-triglyceride clearance that give rise to excess postprandial lipemia are not a common occurrence in normolipidemic men with low HDL cholesterol concentrations. Accordingly, the low HDL cholesterol concentrations measured in the normotriglyceridemic men in this study must be attributable to factors other than an exaggerated postprandial lipemia.

Adult↗

PubMed1990

Chylomicron remnant clearance from the plasma is normal in familial hypercholesterolemic homozygotes with defined receptor defects.

The retinyl palmitate fat tolerance test was used to measure chylomicron remnant clearance in 10 normal subjects (apolipoprotein E [apo E] isotypes 3 or 4 only), 6 normolipidemic apo E2/2 homozygotes and 5 familial hypercholesterolemic homozygotes. Skin fibroblasts with fully upregulated LDL receptors from the latter subjects degraded rabbit 125I-beta VLDL in vitro at rates ranging from less than 10-48% of normal. Experiments in vivo revealed no significant differences between the normal and homozygous familial hypercholesterolemic (FHH) subjects in chylomicron remnant clearance assessed on the basis of "areas under the curves" for retinyl palmitate levels present in post-prandial serum, chylomicron remnants (Sf. less than 1,000), or chylomicrons (Sf. greater than 1,000). Remnant clearance was greatly decreased at all times in the apo E2/2 homozygotes, indicative of an important degree of flux control exerted by a receptor-mediated step involving apo E as ligand. The absence of any excess remnant accumulation in FHH subjects with varying "impairment" of LDL receptor-mediated degradation of apo E-containing lipoproteins, permits the conclusion that chylomicron remnants are initially cleared from the plasma by apo E-recognizing receptors which are genetically distinct from LDL receptors.

Adolescent↗

PubMed1990

Effects of glucose ingestion on postprandial lipemia and triglyceride clearance in humans.

To determine whether the metabolism of diet-derived triglycerides (TG) is acutely regulated by the consumption of insulinogenic carbohydrates, we measured the effects of glucose ingestion on oral and intravenous fat tolerance, and on serum triglyceride concentrations obtained during duodenal fat perfusion. Postprandial lipemia was diminished by the ingestion of 50 g (148 +/- 121 mg.dl-1 x 7 h-1 vs 192 +/- 124 mg.dl-1 x 7 h-1, P less than 0.05) and 100 g (104 +/- 106 mg.dl-1 x 7 h-1 vs 171 +/- 104 mg.dl-1 x 7 h-1, P less than 0.05) glucose. Peak postprandial TG concentrations occurred later after meals containing glucose and fat than after meals containing fat alone. This effect could be reproduced when an iso-osmotic quantity of urea was substituted for glucose in the test meal. Starch ingestion had no discernible effect on postprandial lipemia. Intravenous fat tolerance was similar before (4.9 +/- 1.2%.min-1) and 2 h (4.4 +/- 1.3%.min-1) and 4 h (4.8 +/- 1.5%.min-1) after 50 g glucose ingestion. During duodenal fat perfusion, glucose ingestion caused a progressive decrease in plasma triglyceride concentrations. These data suggest that glucose ingestion diminishes postprandial lipemia in a dose-dependent manner, but that this effect is not due to increased clearance of triglyceride from the circulation. The hypotriglyceridemic effects of glucose appear to reflect delayed gastric emptying and decreased hepatic secretion of triglyceride.

Adult↗

PubMed1989

Replication of baboon endogenous virus in human cells. Kinetics of DNA synthesis and integration.

For the baboon endogenous virus to infect human cells a specific region on chromosome 6 is required for viral DNA replication and integration. In studying the kinetics of baboon endogenous virus DNA replication we show that linear DNA was synthesized as the predominant species after infection and that unintegrated DNA persisted after many cell passages. Examination of integrated DNA revealed the failure of the virus to integrate at early passages. With continuous replication, however, virus integration was observed, but at multiple sites in the host cell.

Animals↗

PubMed1989

Polymorphism in the 5'-flanking region of the insulin gene and its potential relation to cardiovascular disease risk: observations in a biracial community. The Bogalusa Heart Study.

The gene frequencies of a polymorphism in the 5'-flanking region of the insulin gene and its relationship to cardiovascular disease risk were studied in a well defined population of children (mean age 5.5 years) from a biracial community. The BglII endonuclease was used for digestion of the DNA around this polymorphic region. The risk factors studied included parental and grandparental self-reported histories of myocardial infarction and diabetes mellitus, fasting glucose and insulin levels, lipoprotein, cholesterol, and triglyceride levels, and skinfold thicknesses and weight. Four alleles were observed at this locus, with the class 2 allele being significantly more common among blacks than whites. Among white children, the class 3 allele was associated with increased risk for grandparental diabetes mellitus. White children with 2 copies of the class 3 allele had significantly higher levels of glucose. Black children with a copy of the class 3 allele had significantly higher levels of insulin. This study indicates that the class 3 allele is potentially associated with risk for diabetes mellitus and coronary heart disease that can be observed in childhood.

Alleles↗

PubMed1989

Chylomicron triglyceride clearance: comparison of three assessment methods.

Three indirect methods for assessing chylomicron-triglyceride clearance were compared in 12 normolipidemic men. Oral and intravenous fat tolerance tests and a duodenal fat perfusion were performed in each subject by standard methods. Mean values for postprandial lipemia (2.27 +/- 1.8 mmol), Intralipid half-life (13.7 +/- 5.2 min), and chylomicron-triglyceride half-life (4.5 +/- 2.6 min) were similar to corresponding values reported previously for normolipidemic men. The sample correlation coefficient (r) was 0.84 between oral and intravenous fat-tolerance tests, 0.84 between the oral fat-tolerance test and the duodenal-perfusion method, and 0.82 between the intravenous fat-tolerance and the duodenal perfusion methods. All three methods showed a strong correlation between chylomicron-triglyceride clearance and fasting triglyceride concentrations. These findings indicate that the oral and intravenous fat-tolerance tests and the duodenal-perfusion method yield qualitatively similar assessments of chylomicron-triglyceride clearance in normolipidemic men.

Adult↗

PubMed1989

Postprandial lipemia and chylomicron clearance in athletes and in sedentary men.

To examine the effects of exercise on postprandial serum triglyceride (TG) metabolism, we measured oral and intravenous fat tolerance and chylomicron-TG half-life in highly trained endurance athletes and in a sedentary control group matched for body weight and fasting serum TG concentration. Postprandial lipemia was lower in athletes after meals containing 40 g fat (1.5 +/- 0.7 vs 2.6 +/- 1.5 mmol.L-1.8 h-1, p less than 0.001) or 140 g fat (2.5 +/- 1.2 vs 6.1 +/- 1.9 mmol.L-1.8 h-1, p less than 0.001). The disappearance of an intravenous bolus of Intralipid was faster in athletes (5.4 +/- 1.2%/min) than in sedentary men (4.3 +/- 0.8%/min, p less than 0.01). The half-life of chylomicron-TG was shorter in athletes (3.0 +/- 0.8 min) than in sedentary men (4.0 +/- 1.0 min, p less than 0.05). These findings indicate that chronic exercise decreases postprandial lipemia by reducing chylomicron-TG's half-life. This effect is due partly to reduced fasting serum TG pool size and partly to a direct effect of exercise on the serum TG removal system.

Adult↗

PubMed1989

Protein ingestion does not affect postprandial lipaemia or chylomicron-triglyceride clearance.

The effects of protein ingestion on postprandial lipaemia and intravenous fat tolerance were examined in 15 normolipidaemic young men and women. Mean postprandial lipaemia was similar after meals containing 100 ml dairy cream (containing 40 g fat) and after meals containing 100 ml dairy cream and 23 g protein (in the form of casein). The rate of disappearance of an intravenous bolus of Intralipid was similar before and after the ingestion of 23 g casein. These findings indicate that dietary protein does not significantly affect postprandial lipaemia or chylomicron-triglyceride clearance.

Adult↗

PubMed1988

Hypotheses for testing deviations from random integration: evidence for nonrandom retroviral integration.

The use of a recently developed in vitro model for retroviral integration provides a means of statistically testing hypotheses concerning the distribution of integration sites and hypotheses about the sequence of proviral orientations. In this study, three null hypotheses are formulated and applied to previously published data. Statistical analyses of these data suggest that the distribution of integration sites may not be uniform, and the sequence of proviral orientations is not random. On the basis of these results and the observed clustering of orientations, it was postulated that if a DNA sequence was involved in nonrandom proviral integration, that sequence would be found in the regions where the orientations change direction with respect to the target DNA ("I" regions). Computer analyses for homologous and complementary DNA sequences were performed on all possible pairs of identifiable "I" regions. A common sequence (at least 8 bp in size) was found in three out of four regions and that sequence was absent elsewhere in the target DNA. A model, with features of recombination reminiscent of chi sequences in bacteria, is proposed that may account for these results.

Biometry↗

PubMed1988

Two-stage reimplantation of septic total knee arthroplasty. Report of three cases using an antibiotic-PMMA spacer block.

The management of an infected total knee implant is a major challenge to the orthopaedic surgeon. This article reviews the use of antibiotic-PMMA spacer block in two-stage reimplanation of septic total knee arthroplasties. In addition to serving as an antibiotic delivery system between the time of component removal and reimplantation, the antibiotic-impregnated spacer block imparts mechanical stability to the joint and decreases the morbidity during the period before reimplantation. This temporary "interposition arthroplasty" facilitates the patient's ambulation and also simplifies dissection at the time of reimplantation. Furthermore, osteoporotic bone at the time of resection becomes firm, good-quality bone by the time of reimplantation.

Aged↗

PubMed1988

Serum triglyceride responses to fatty meals: effects of meal fat content.

To determine the dose response of serum triglyceride concentrations to fat feeding, serum triglyceride responses to meals containing 40, 80, and 120 g fat (in the form of dairy cream) were measured in 12 normotriglyceridemic men. Mean postprandial lipemia (measured as the integrated area under the curve of serum triglyceride concentration plotted against time) was 251 +/- 129 mg.dL-1.8 h-1 (2.83 +/- 1.46 mmol.L-1.8 h-1) after the 40-g-fat meal, 503 +/- 233 mg.dL-18 h-1 (5.68 +/- 2.63 mmol.L-1.8 h-1) after the 80-g-fat meal, and 712 +/- 281 mg.dL-1.8 h-1 (8.04 +/- 3.17 mmol.L-1.8 h-1) after the 120-g-fat meal. These data indicate that in normotriglyceridemic men the magnitude of lipemia that follows the ingestion of a fat meal is directly proportional to the fat content of the meal. The results also suggest that the mechanism whereby triglyceride is removed from the intravascular compartment is not saturated by meals containing the amounts of fat typically consumed by men following a Western diet.

Adult↗