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Biomedical subjects

R J Havel

Publications and source records attributed to R J Havel.

At least 55 records · Page 3Linked to original sources
PubMed1994

Postprandial hyperlipidemia and remnant lipoproteins.

Improved methods for quantification of organ-specific contributions to postprandial hyperlipidemia indicate substantial increases in the concentration and altered properties of hepatogenous VLDL, in addition to accumulation of chylomicron remnants. Recent clinical studies support the hypothesis that small chylomicron remnants characterized by apolipoprotein (apo)B48 and VLDL remnants characterized by apolipoprotein B100 are atherogenic lipoproteins.

Apolipoprotein B-100↗
PubMed1994

Triglyceride-rich lipoproteins isolated by selected-affinity anti-apolipoprotein B immunosorption from human atherosclerotic plaque.

We isolated and characterized immunoreactive apolipoprotein B (apoB)-containing lipoproteins from human atherosclerotic plaque and plasma to determine whether very-low-density lipoprotein (VLDL) can enter and become incorporated into the atherosclerotic lesion and how plaque apoB-containing lipoproteins differ from apoB-containing lipoproteins isolated from plasma. Atherosclerotic plaques were obtained during aortic surgery and processed immediately. Lipoproteins were extracted from minced plaque in a buffered saline solution (extract A). In selected cases a second extraction was done after plaque was incubated with collagenase (extract B). Lipoproteins were then isolated from the extracts by anti-apoB immunosorption and separated into VLDL + intermediate-density lipoprotein (IDL) (d < 1.019 g/mL) and low-density lipoprotein (LDL) (1.019 < d < 1.070 g/mL) fractions by ultracentrifugation. The VLDL + IDL fractions from plaque contained more than one third of the total apoB-associated lipoprotein cholesterol in both extracts A and B. The lipid composition of VLDL + IDL in both extracts was related to that of plasma VLDL + IDL. By electron microscopy mean particle diameters of VLDL + IDL from extracts A and B were 9% and 23%, respectively, greater than VLDL + IDL diameters from plasma. Mean diameters of LDL from extracts A and B were 11% and 31% greater than LDL diameters from plasma. The apoE-apoB ratio of extract A VLDL + IDL was nearly twice that of plasma VLDL + IDL and severalfold higher than that of extract A LDL. Immunoblots of both VLDL + IDL and LDL from extract A demonstrated minimal fragmentation of apoB.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1994

Analysis of angiographic trial data in women.

There are few angiographic trials of cholesterol lowering in women. Two trials have included a sufficient number of women for meaningful assessment of lesion change, as determined by quantitative coronary angiography. In the University of California, San Francisco Specialized Center of Research in Arteriosclerosis (UCSF SCOR) trial, 72 patients (57% women) with familial hypercholesterolaemia (90% of whom had no overt coronary heart disease) were randomised to receive either diet and intensive drug therapy (combinations of colestipol, nicotinic acid and lovastatin) or diet and modest doses of colestipol, according to baseline low density lipoprotein cholesterol level. Coronary angiograms were obtained at 2-year intervals. Change in percentage area of stenosis (the primary end-point) in women receiving intensive drug treatment was -2.06% compared with +1.07% for the controls (p = 0.05). For the intensively treated men, corresponding values were -0.88% compared with +0.41% for the controls (difference not significant). In a recently completed trial in Canada, 269 men and 62 women with established coronary heart disease were randomised to receive either diet alone, or diet and lovastatin (up to 80 mg daily). In men, the increase in percentage diameter of stenosis was reduced by 43% (p = 0.05), and in women by 40% (not significant). By contrast, new lesions appeared in 4% of women assigned to intensive drug treatment, compared with 45% of those randomised to diet (p < 0.001). In men, new lesions appeared in 18% and 29% of patients, respectively (p = 0.047). These data suggest that coronary artery lesions in women respond at least as well as those in men to cholesterol lowering.

Arteriosclerosis↗
PubMed1994

Role of hepatic lipase in the uptake and processing of chylomicron remnants in rat liver.

The participation of hepatic lipase in the initial uptake and processing of chylomicron remnants was studied in the isolated, perfused rat liver. Hepatic lipase activity was either reduced by preperfusion of livers with heparin or inhibited with specific rat hepatic lipase antibodies. [3H]palmitate-labeled chylomicron remnants were recirculated through control and treated livers for 15 min; the livers were then flushed, homogenized, and endosome-rich fractions were isolated. Depletion of hepatic lipase activity by both methods reduced the uptake of chylomicron remnants and hydrolysis of their component triglycerides by perfused rat livers, but at the same time significantly increased the rate of endocytosis of those chylomicron remnants taken up. We conclude that hepatic lipase facilitates, but is not essential for, the initial uptake of chylomicron remnants by rat liver. Furthermore, endocytosis of chylomicron remnants does not require binding to hepatic lipase or the associated hydrolysis of remnant lipids.

Animals↗
PubMed1994

Three consecutive pregnancies in a patient with glycogen storage disease type IA (von Gierke's disease).

Glycogen storage disease type IA is associated with metabolic abnormalities that can compromise fetal outcome. Normal outcome can be achieved by maintaining euglycemia throughout gestation. We report three consecutive pregnancies in a patient with glycogen storage disease type IA. The patient, a 35-year-old woman, has been maintained on a regimen of nightly nasogastric or cornstarch feedings for the past 12 years with improving metabolic control, reduced liver size, and no progression of multiple hepatic adenomas. On confirmation of each pregnancy, early in the first trimester nightly feeding was changed from cornstarch ingestion to Polycose by nasogastric intubation, with good metabolic control. During the last trimester of each pregnancy metabolic control showed further improvement, with lowering of lactate, urate, and triglyceride levels. During the first pregnancy unexpected fetal death occurred at 33 weeks. During the last two pregnancies, the patient was admitted at 33 and 34 weeks, respectively, for closer supervision of metabolic status and fetal monitoring. She underwent a cesarean section at 35 weeks 4 days of gestation and was delivered of a girl. She underwent a repeat cesarean section at 35 weeks 2 days for the subsequent gestation and was delivered of a boy. Both infants are healthy and appear to be unaffected by von Gierke's disease. Hepatic adenomas did not enlarge during the pregnancies. Meticulous management resulted in normal pregnancy outcomes in two consecutive gestations. Rapid fetal growth late in the third trimester may require particularly careful supervision to maintain euglycemia.

Adult↗
PubMed1993

Relationships between the responses of triglyceride-rich lipoproteins in blood plasma containing apolipoproteins B-48 and B-100 to a fat-containing meal in normolipidemic humans.

The concentration of triglyceride-rich lipoproteins containing apolipoprotein (apo) B-48 (chylomicrons) and apo B-100 (very low density lipoproteins) was measured in blood plasma of healthy young men after an ordinary meal containing one-third of daily energy and fat. Plasma obtained in the postabsorptive state and at intervals up to 12 hr after the meal was subjected to immunoaffinity chromatography against a monoclonal antibody to apo B-100 that does not bind apo B-48 and a minor fraction of apo B-100 rich in apo E. Measurements of the concentrations of components of the total and unbound triglyceride-rich lipoproteins separated from plasma by ultracentrifugation showed that about 80% of the increase in lipoprotein particle number was in very low density lipoproteins containing apo B-100 and only 20% was in chylomicrons containing apo B-48 that carry dietary fat from the intestine. The maximal increments and the average concentrations of apo B-48 and B-100 during the 12 hr were highly correlated (r2 = 0.80), suggesting that preferential clearance of chylomicron triglycerides by lipoprotein lipase leads to accumulation of hepatogenous very low density lipoproteins during the alimentary period. The composition of the bulk of very low density lipoproteins that were bound to the monoclonal antibody changed little and these particles contained about 90% of the cholesterol and most of the apo E that accumulated in triglyceride-rich lipoproteins. The predominant accumulation of very low density lipoprotein rather than chylomicron particles after ingestion of ordinary meals is relevant to the potential atherogenicity of postprandial lipoproteins.

Adult↗
PubMed1993

Plasma lipoproteins and progression of coronary artery disease evaluated by angiography and clinical events.

BACKGROUND: There is considerable evidence that remnants of triglyceride-rich lipoproteins may be particularly atherogenic. METHODS AND RESULTS: Levels of lipoprotein lipids and of apolipoprotein B in low-density lipoproteins were measured in 335 men and women enrolled in a study in which quantitative coronary angiography was carried out at 2-year intervals. Clinical events related to coronary disease occurred in 129 patients during the trial and in the subsequent follow-up period of 4 to 6 years. In multivariate analysis controlled for a number of nonlipid risk factors, high-density lipoprotein cholesterol was inversely related to the mean percentage increase in coronary artery stenosis in both men and women. Neither plasma triglycerides nor low-density lipoprotein cholesterol, triglycerides, or apolipoprotein B was related to change in stenosis, but a measure of remnants of triglyceride-rich lipoproteins, which included cholesterol in intermediate-density lipoproteins, was directly related to lesion progression. The same relations for these measures of plasma lipoprotein concentrations were found to hold for clinical events related to coronary artery atherosclerosis. CONCLUSIONS: In patients with established coronary heart disease, increased levels of remnants of triglyceride-rich lipoproteins and decreased levels of high-density lipoproteins appear to promote progression of coronary artery atherosclerosis, which in turn may lead to an untoward clinical event. No such relation could be shown for the level of components of low-density lipoproteins. These and other observations call for reevaluation of relations between particular species of lipoproteins containing apolipoprotein B and the pathogenesis of coronary artery atherosclerosis and coronary heart disease.

Adult↗
PubMed1992

Relation of plasma lipid and apoprotein levels to progressive intimal hyperplasia after arterial endarterectomy.

BACKGROUND: To examine the relation of plasma lipoproteins to the proliferative response after arterial injury in humans, we examined the plasma lipid, lipoprotein, and apoprotein levels of 20 patients with early recurrent stenosis caused by intimal hyperplasia after carotid endarterectomy. These were compared with 20 controls who had no evidence of recurrent stenosis by duplex ultrasound scanning. METHODS AND RESULTS: By univariate analysis, the reoperated patients had higher levels of plasma cholesterol (251 versus 225 mg/dl, p less than 0.05), total triglycerides (173 versus 105 mg/dl, p less than 0.03), and low density lipoprotein (LDL) apoprotein B (99.8 versus 77.2 mg/dl, p less than 0.003). The ratio of cholesterol to apoprotein B in LDL was lower in patients with restenosis (p less than 0.04), suggesting LDL of smaller diameter. High density lipoprotein (HDL) cholesterol level was reduced (45 versus 55 mg/dl, p less than 0.01) in patients with restenosis. With statistical adjustment for the correlations between these variables by multivariate analysis, both LDL apoprotein B and HDL cholesterol were independent predictors of the risk of restenosis. Ten patients with restenosis but only two controls had one or two apolipoprotein E4 alleles. CONCLUSIONS: Elevated lipid levels usually associated with an increased risk of atherosclerosis may predispose patients to an increased incidence of intimal hyperplasia after endarterectomy.

Aged↗
PubMed1992

Properties of an apolipoprotein E-enriched fraction of triglyceride-rich lipoproteins isolated from human blood plasma with a monoclonal antibody to apolipoprotein B-100.

A monoclonal antibody to apolipoprotein (apo) B-100 (JI-H) with unique binding properties has been used to separate a population of triglyceride-rich lipoproteins from blood plasma of normotriglyceridemic individuals and patients with various forms of hypertriglyceridemia. This antibody fails to recognize an apoE-rich population of very low density lipoproteins (VLDL) containing apoB-100 as well as all triglyceride-rich lipoproteins containing apoB-48, but it binds other VLDL that contain apoE and almost all lipoproteins that contain apoB-100, but no apoE. The unbound triglyceride-rich lipoproteins separated by ultracentrifugation after separation from plasma by immunoaffinity chromatography contained 10-13% of the apoB of triglyceride-rich lipoproteins from three normotriglyceridemic individuals, 10-29% of that from five patients with endogenous hypertriglyceridemia, 40-48% of that from three patients with familial dysbetablipoproteinemia, and 65% of that from a patient with lipoprotein lipase deficiency. In all cases, the unbound triglyceride-rich lipoproteins contained more molecules of apoE and cholesteryl esters per particle than those that were bound to monoclonal antibody JI-H, and they were generally depleted of C apolipoproteins. These properties resemble those described for partially catabolized remnants of chylomicrons and VLDL. The affinity of the unbound lipoproteins for the low density lipoprotein (LDL) receptor varied widely, and closely resembled that of the total triglyceride-rich lipoproteins from individual subjects. Our results demonstrate that remnant-like chylomicrons and a population of remnant-like VLDL can be isolated and quantified in blood plasma obtained in the postabsorptive state from normotriglyceridemic and hypertriglyceridemic individuals alike.

Adult↗
PubMed1991

Acid hydrolases in early and late endosome fractions from rat liver.

We have examined the distribution of the cation-independent mannose 6-phosphate receptor and five acid hydrolases in early and late endosomes and a receptor-recycling fraction isolated from livers of estradiol-treated rats. Enrichment of mannose 6-phosphate receptor mass relative to that of crude liver membranes was comparable in membranes of early and late endosomes but was even greater in membranes of the receptor-recycling fraction. Enrichment of acid hydrolase activities (aryl sulfatase, N-acetyl-beta-glucosaminidase, tartrate-sensitive acid phosphatase, and cholesteryl ester acid hydrolase) and cathepsin D mass was also comparable in early and late endosomes but was considerably lower in the receptor-recycling fraction. The enrichment of two acid hydrolases, acid phosphatase and cholesteryl ester acid hydrolase, in endosomes was severalfold greater than that of the other three examined, about 40% of that found in lysosomes. Acid phosphatase and cholesteryl ester acid hydrolase were partially associated with endosome membranes, whereas cathepsin D was found entirely in the endosome contents. These findings raise the possibility that lysosomal enzymes traverse early endosomes during transport to lysosomes in rat hepatocytes and suggest that the greater enrichment of some acid hydrolases in endosomes is related to their association with endosome membranes. Despite the substantial enrichment of lysosomal enzymes in hepatocytic endosomes, we found that two, cholesteryl ester acid hydrolase and cathepsin D, did not degrade cholesteryl esters and apolipoprotein B-100 of endocytosed low density lipoproteins in vivo, presumably because they are inactive at the pH within endosomes.

Acetylglucosaminidase↗
PubMed1991

Trafficking of the epidermal growth factor receptor and transferrin in three hepatocytic endosomal fractions.

Hepatocytes rapidly internalize epidermal growth factor (EGF) and transferrin by receptor-mediated endocytosis. Both EGF and its receptor are thought to be targeted for destruction in lysosomes, leading to down-regulation of the receptor, whereas transferrin, after unloading iron within the cell, is thought to recycle to the cell surface bound to its receptor. Previously, we isolated three endosomal fractions from livers of estradiol-treated rats and examined their roles in cellular trafficking of low density lipoproteins (LDL) and the LDL receptor, which cycles constitutively (Belcher, J. D., Hamilton, R. L., Brady, S. E., Hornick, C. A., Jäckle, S., Schneider, W. J., and Havel, R. J., Proc. Natl. Acad. Sci. U. S. A. (1987) 84, 6785-6789). In the current study we have taken advantage of the distinct trafficking of the EGF receptor and transferrin to evaluate further the functions of these endosome fractions. Intravenous injection of a saturating amount of EGF into estradiol-treated rats induced internalization of a single population of EGF receptors, which rapidly accumulated in the endosome fraction of intermediate density ("compartment of uncoupling of receptor and ligand" (CURL)) and subsequently in the low density endosome fraction (multivesicular bodies (MVBs)). The high density endosome fraction, whose membranes contain a high concentration of recycling receptors (designated receptor-recycling compartment (RRC)), failed to accumulate EGF receptors after injection of EGF. In livers of rats not given exogenous EGF, EGF receptors were found in small but comparable concentrations in RRC, CURL, and MVB membranes, consistent with other evidence that targeting of the EGF receptor to lysosomes is mediated by ligand-induced phosphorylation. Transferrin also accumulated first in CURL and later in MVBs, but it also accumulated rapidly in the RRC fraction, consistent with the proposed function of this fraction in receptor recycling. Since transferrin is not degraded during its endocytic cycle, these observations indicate that apotransferrin and its receptor recycle from late endosomes (MVBs) located at the apical pole of hepatocytes, as well as from early endosomes near the sinusoidal pole.

Animals↗
PubMed1991

Familial chylomicronemia (type I hyperlipoproteinemia) due to a single missense mutation in the lipoprotein lipase gene.

Complete deficiency of lipoprotein lipase (LPL) causes the chylomicronemia syndrome. To understand the molecular basis of LPL deficiency, two siblings with drastically reduced postheparin plasma lipolytic activities were selected for analysis of their LPL gene. We used the polymerase chain reaction to examine the nine coding LPL exons in the two affected siblings and three relatives. DNA sequence analysis revealed a single nucleotide change compared with the normal LPL cDNA: a G----A substitution at nucleotide position 680. This transition caused a replacement of glutamic acid for glycine at amino acid residue 142 of the mature LPL protein. Amino acid sequence comparisons of the region surrounding glycine-142 indicated that it is highly conserved among lipases from different species, suggesting a crucial role of this domain for the LPL structure. Expression studies of the mutant LPL cDNA in COS-7 cells produced normal amounts of enzyme mass. However, the mutated LPL was not catalytically active, nor was it efficiently secreted from the cells. This established that the Gly----Glu substitution at amino acid 142 is sufficient to abolish enzymatic activity and to result in the chylomicronemia syndrome observed in these patients.

Amino Acid Sequence↗
PubMed1991

De novo production of low density lipoproteins: fact or fancy.

Many investigators, observing an apparent dilution in the plasma specific activity (SA) of apolipoprotein B-100 (apoB) in low density lipoprotein (LDL) as compared with that in very low density lipoprotein (VLDL) after injection of radiolabeled VLDL, have formulated kinetic hypotheses incorporating the concept of de novo production of LDL to explain their data in humans and other mammals. These hypotheses, with rare exception, do not account for the kinetic heterogeneity known to exist in the apoB of human VLDL on the basis of size and in the apoB of rabbit VLDL on the basis of size and presence of apolipoprotein E. When a logical analysis of such kinetic heterogeneity of apoB in plasma VLDL is performed, it becomes clear that the apparent dilution of the SA of apoB in LDL relative to that in VLDL can be explained without the requirement for de novo production of LDL. Although this alternative hypothesis, incorporating the concept of kinetic heterogeneity of apoB in VLDL, does not exclude the process of de novo production of LDL, which so many investigators have invoked to explain their data, it does raise a question as to the existence of such a process since an alternative hypothesis can explain such data just as well. Clearly, more experimental data on the kinetic heterogeneity of human and other mammalian VLDL are needed before a reasonable choice can be made between these two hypotheses.

Animals↗
PubMed1991

Isolation and characterization of three endosomal fractions from the liver of normal rats after lipoprotein loading.

In earlier research we isolated and characterized three endosomal fractions from livers of estradiol-treated rats (1987. Belcher et al. Proc. Natl. Acad. Sci. USA. 84: 6785; 1989. Jäckle et al. Proc. Natl. Acad. Sci. USA. 86: 1880). We now describe the isolation of comparable endosomal fractions from untreated rats. The fraction of lowest density was composed almost exclusively of lipoprotein-filled multivesicular bodies (MVBs); the intermediate density fraction was composed of smaller lipoprotein-filled vesicles that were also multivesicular and had more numerous membranous appendages; the fraction of highest density was composed of membranes resembling the appendages of the two vesicular fractions. The paucity of contamination of these fractions with nonendosomal organelles is supported by their ultrastructural characteristics and by the proteins, lipids, and marker enzymes of their membranes. Only small amounts of MVBs could be separated from untreated rats not given a load of lipoproteins. However, after injection of large amounts of beta-very low density lipoproteins (beta-VLDL) from cholesterol-fed rabbits, the mass of MVBs increased dramatically. Under these conditions radiolabeled beta-VLDL and epidermal growth factor taken up by the liver accumulated in isolated endosomes at rates similar to those found for LDL in estradiol-treated rats. Although chylomicrons and chylomicron remnants were rapidly taken up by the liver of normal rats, chylomicrons and chylomicron remnants accumulated in endosomes at a lower rate than beta-VLDL. These findings, which differ from earlier data in estradiol-treated rats (1989 Jäckle et al., Proc. Natl. Acad. Sci. USA. 86: 1880) that showed equivalent rates of processing of chylomicron remnants and beta-VLDL, suggest that extracellular processing of chylomicron remnants in the liver normally ; precedes endocytosis.

Administration, Oral↗