Biomedical subjects

D J Rader

Publications and source records attributed to D J Rader.

At least 91 records · Page 5Linked to original sources

PubMed1994

Quantitation of plasma apolipoproteins in the primary and secondary prevention of coronary artery disease.

PURPOSE: To review current knowledge of apolipoprotein quantitation used in the clinical management of persons with or at risk for the development of premature coronary artery disease. DATA SOURCES: The English-language literature was analyzed using MEDLINE (1975 to 1993) with key words "apolipoproteins," "quantitation," and "coronary artery disease." Article bibliographies were also reviewed to obtain additional references. STUDY SELECTION: Published, peer-reviewed retrospective and prospective studies relevant to the association of plasma apolipoprotein levels with coronary artery disease in humans. DATA SYNTHESIS: Most studies concerned apolipoprotein A-I (apo A-I), apolipoprotein B (apo B), and lipoprotein(a) [Lp(a)]. In retrospective cross-sectional studies, apo A-l levels were not substantially more predictive of coronary artery disease than were high-density lipoprotein (HDL) cholesterol levels. In contrast, levels of apo B and Lp(a) were often more strongly associated with coronary artery disease than were traditional lipid measurements. In studies of the relation between apolipoprotein levels in children and premature coronary artery disease in their parents, Lp(a) levels, but not apo A-l and apo B levels, were consistently predictive of familial coronary artery disease. Prospective studies have yielded variable results for all three apolipoproteins. Low apo A-l levels were consistently associated with coronary artery disease in six prospective studies but were not more predictive than HDL levels. Apolipoprotein B levels were strongly associated with coronary artery disease in four of five prospective studies but were more predictive of coronary artery disease than were total cholesterol levels in only two of the four studies. Lipoprotein(a) levels were strongly associated with coronary artery disease in five of seven prospective studies but were not associated in two of the four largest studies. CONCLUSIONS: Too few large prospective studies of apolipoprotein quantitation using validated assay methods, both in general unselected populations and in subgroups of persons with premature coronary artery disease or family histories of premature coronary artery disease, are available to make definitive recommendations concerning clinical utility. The data do not support use of apolipoprotein quantitation as a screening tool to predict coronary artery disease risk in the general population. However, the data suggest that quantitation of apo B and Lp(a) may be indicated in subgroups of persons with premature coronary artery disease or with family histories of premature coronary artery disease. In these persons, an increased apo B or Lp(a) level or both could be a clinical indication for more aggressive treatment of low-density lipoprotein cholesterol.

Apolipoproteins↗

PubMed1994

Oestrogen and inhibition of oxidation of low-density lipoproteins in postmenopausal women.

Oxidative modification of low-density lipoprotein (LDL) may be atherogenic. We studied the time of onset of LDL oxidation (lag) in 18 postmenopausal women before and after intraarterial infusion of 17 beta-oestradiol, after 3 weeks' patch administration in 12 of these women, and 1 month after discontinuation in 10. The lag increased from baseline after acute infusion (from 134 [SD41] to 167 [36] min, p = 0.01) and after the patch (132 [31] to 178 [45] min, p = 0.009). After discontinuation of oestradiol, the lag returned to baseline. This study shows an antioxidant effect of physiological levels of 17 beta-oestradiol, which may contribute to an anti-atherogenic action.

Administration, Cutaneous↗

PubMed1994

A comparison of Lp(a) levels in fresh and frozen plasma using ELISAs with either anti-apo(a) or anti-apoB reporting antibodies.

Sandwich ELISAs with an anti-apo(a) trapping antibody and either an anti-apolipoprotein B or anti-apolipoprotein(a) reporting antibody, were used to measure the concentrations of Lp(a) in 230 plasma samples that were either freshly drawn or stored at -20 degrees C for 4-6 weeks. The assays produced significantly different results for the fresh and frozen samples, however, the magnitudes of these differences were small, about 8% higher for the frozen samples, and independent of total cholesterol, HDL cholesterol, triglyceride, apolipoprotein B or Lp(a) concentration or assay configuration. A similar difference was seen for a freshly drawn plasma sample assayed at the time as the fresh and frozen samples, indicating the differences were due to inherent differences in the assays at the times the assays were performed. The assay configuration was an important factor in determining the Lp(a) concentrations for identically treated samples. ELISAs using the apoB reporting antibody yielded concentrations that were significantly less than those determined by ELISAs using the anti-apo(a) reporting antibody. The assay differences did not correlate with total cholesterol, HDL cholesterol, triglyceride, or apoB concentration. However, the magnitude of the difference did correlate well with Lp(a) amount. Low Lp(a) concentrations produced greater assay differences than high Lp(a) concentrations.

Antibodies↗

PubMed1994

Decreased plasma levels of lipoprotein(a) in patients with hypertriglyceridemia.

Lipoprotein(a) (Lp(a)) is an atherogenic lipoprotein which is similar in structure to, but metabolically distinct from, LDL. Factors modulating plasma Lp(a) concentrations are poorly understood. To investigate the possible interaction of Lp(a) with triglycerides, we determined the apo(a) phenotype, Lp(a) concentration, and distribution of Lp(a) in a group of patients with triglycerides > 400 mg/dl (n = 60) compared with a control group (n = 128). Lp(a) concentrations were significantly lower in hypertriglyceridemic patients (mean +/- S.E., 13 +/- 4 mg/dl; median, 6 mg/dl; 25/75 percentile, 2-13 mg/dl) as compared with the controls (mean, 22 +/- 2 mg/dl; median, 10 mg/dl; 25/75 percentile, 7-30 mg/dl). Plasma Lp(a) concentrations in the hypertriglyceridemic patients correlated negatively with triglyceride levels (r = -0.69, P = 0.03). The difference in Lp(a) levels between patients and controls was maintained when subjects were stratified by apo(a) phenotype and type of hyperlipidemia. After subdividing the hypertriglyceridemic patients into one group with apo(a) isoforms < or = S2 and one group with apo(a) isoforms > or = S3, we found that the differences in plasma Lp(a) concentrations between patients and controls were more pronounced in the group with the lower molecular weight apo(a) isoforms. These data indicate that hypertriglyceridemia is associated with lower plasma Lp(a) concentrations and suggest that increased levels of triglyceride-rich lipoproteins may influence the metabolism of Lp(a).

Adolescent↗

PubMed1994

Effect of antioxidant vitamins on low density lipoprotein oxidation and impaired endothelium-dependent vasodilation in patients with hypercholesterolemia.

OBJECTIVES: The aims of this study were to determine whether antioxidant vitamins could reduce the susceptibility of low density lipoprotein (LDL) to oxidation and improve endothelium-dependent vasodilator responsiveness in patients with hypercholesterolemia. BACKGROUND: Animals and humans with hypercholesterolemia have exhibited impaired endothelium-dependent vasodilation. In vitro studies suggest that oxidatively modified LDL can impair nitric oxide production. METHODS: Forearm blood flow was measured with strain gauge plethysmography and brachial artery drug infusions in 19 patients, aged 52 +/- 9 years, with hypercholesterolemia (mean +/- SD total cholesterol 283 +/- 22 mg/dl, LDL 197 +/- 31 mg/dl) and in 14 subjects, aged 48 +/- 8 years, with normal cholesterol levels (total cholesterol 169 +/- 20 mg/dl, LDL 102 +/- 25 mg/dl). Acetylcholine (7.5, 15 and 30 micrograms/min) was utilized as an endothelium-dependent vasodilator, and sodium nitroprusside (0.8, 1.6 and 3.2 micrograms/min) was used to test endothelium-independent vasodilation. Oxidative susceptibility of LDL was measured by a spectrophotometric assay of conjugated diene production after the addition of copper chloride. Hypercholesterolemic patients then received daily antioxidant vitamin supplements (beta-carotene [30 mg], ascorbic acid [vitamin C] [1,000 mg], vitamin E [800 IU]) for 1 month, with repeat measurement of both forearm blood flow responsiveness to the same agonists and LDL oxidizability. RESULTS: The maximal flow in response to acetylcholine was impaired in patients compared with that in normal subjects (9.8 +/- 7.8 vs. 15.9 +/- 8.1 ml/min per 100 ml, p = 0.03), with similar maximal flow responses to sodium nitroprusside (9.5 +/- 4.2 vs. 9.0 +/- 2.8 ml/min per 100 ml, p = 0.72). After 1 month of vitamin therapy, the onset of LDL oxidation was prolonged over baseline measurements by 71 +/- 67%, and the maximal rate of oxidation was decreased by 26 +/- 25% (both p < 0.001). However, the maximal forearm blood flow response to acetylcholine remained unchanged from baseline values (maximal flow after acetylcholine 9.0 +/- 6.2 vs. 9.8 +/- 7.8 ml/min per 100 ml, p = 0.57). This study had 80% power (alpha = 0.05) to exclude a 45% increase over baseline value in acetylcholine-stimulated flow during vitamin therapy. CONCLUSIONS: Although 1 month of administration of antioxidant vitamin supplements in hypercholesterolemic patients reduced the susceptibility of LDL to oxidation, impairment in endothelial function remained unaltered. The use of nonvitamin antioxidants or concomitant reduction in LDL levels, as well as more sensitive techniques for measuring vascular responsiveness, may be required to show a beneficial effect on endothelial vasodilator function.

Acetylcholine↗

PubMed1994

Markedly accelerated catabolism of apolipoprotein A-II (ApoA-II) and high density lipoproteins containing ApoA-II in classic lecithin: cholesterol acyltransferase deficiency and fish-eye disease.

Classic (complete) lecithin:cholesterol acyltransferase (LCAT) deficiency and Fish-eye disease (partial LCAT deficiency) are genetic syndromes associated with markedly decreased plasma levels of high density lipoprotein (HDL) cholesterol but not with an increased risk of atherosclerotic cardiovascular disease. We investigated the metabolism of the HDL apolipoproteins (apo) apoA-I and apoA-II in a total of five patients with LCAT deficiency, one with classic LCAT deficiency and four with Fish-eye disease. Plasma levels of apoA-II were decreased to a proportionately greater extent (23% of normal) than apoA-I (30% of normal). In addition, plasma concentrations of HDL particles containing both apoA-I and apoA-II (LpA-I:A-II) were much lower (18% of normal) than those of particles containing only apoA-I (LpA-I) (51% of normal). The metabolic basis for the low levels of apoA-II and LpA-I:A-II was investigated in all five patients using both exogenous radiotracer and endogenous stable isotope labeling techniques. The mean plasma residence time of apoA-I was decreased at 2.08 +/- 0.27 d (controls 4.74 +/- 0.65 days); however, the residence time of apoA-II was even shorter at 1.66 +/- 0.24 d (controls 5.25 +/- 0.61 d). In addition, the catabolism of apoA-I in LpA-I:A-II was substantially faster than that of apoA-I in LpA-I. In summary, genetic syndromes of either complete or partial LCAT deficiency result in low levels of HDL through preferential hypercatabolism of apoA-II and HDL particles containing apoA-II. Because LpA-I has been proposed to be more protective than LpA-I:A-II against atherosclerosis, this selective effect on the metabolism of LpA-I:A-II may provide a potential explanation why patients with classic LCAT deficiency and Fish-eye disease are not at increased risk for premature atherosclerosis despite markedly decreased levels of HDL cholesterol and apoA-I.

Adult↗

PubMed1994

The inverse association of plasma lipoprotein(a) concentrations with apolipoprotein(a) isoform size is not due to differences in Lp(a) catabolism but to differences in production rate.

Lipoprotein(a) (Lp[a]) is an atherogenic lipoprotein which is similar in structure to low density lipoproteins (LDL) but contains an additional protein called apolipoprotein(a) (apo[a]). Apo(a) is highly polymorphic in size, and there is a strong inverse association between the size of the apo(a) isoform and the plasma concentration of Lp(a). We directly compared the in vivo catabolism of Lp(a) particles containing different size apo(a) isoforms to establish whether there is an effect of apo(a) isoform size on the catabolic rate of Lp(a). In the first series of studies, four normal subjects were injected with radio-labeled S1-Lp(a) and S2-Lp(a) and another four subjects were injected with radiolabeled S2-Lp(a) and S4-Lp(a). No significant differences in fractional catabolic rate were found between Lp(a) particles containing different apo(a) isoforms. To confirm that apo(a) isoform size does not influence the rate of Lp(a) catabolism, three subjects heterozygous for apo(a) were selected for preparative isolation of both Lp(a) particles. The first was a B/S3-apo(a) subject, the second a S4/S6-apo(a) subject, and the third an F/S3-apo(a) subject. From each subject, both Lp(a) particles were preparatively isolated, radiolabeled, and injected into donor subjects and normal volunteers. In all cases, the catabolic rates of the two forms of Lp(a) were not significantly different. In contrast, the allele-specific apo(a) production rates were more than twice as great for the smaller apo(a) isoforms than for the larger apo(a) isoforms. In a total of 17 studies directly comparing Lp(a) particles of different apo(a) isoform size, the mean fractional catabolic rate of the Lp(a) with smaller size apo(a) was 0.329 +/- 0.090 day-1 and of the Lp(a) with the larger size apo(a) 0.306 +/- 0.079 day-1, not significantly different. In summary, the inverse association of plasma Lp(a) concentrations with apo(a) isoform size is not due to differences in the catabolic rates of Lp(a) but rather to differences in Lp(a) production rates.

Adult↗

PubMed1994

In vivo metabolism of apolipoproteins A-I and E in patients with abetalipoproteinemia: implications for the roles of apolipoproteins B and E in HDL metabolism.

The metabolism of high density lipoproteins (HDL) is tightly linked to the metabolism of apoB-containing lipoproteins through the exchange and transfer of lipids and apolipoproteins within the plasma compartment. Abetalipoproteinemia (ABL), a genetic disease in which apoB is absent from the plasma and HDL are the sole plasma lipoproteins, is a model for the investigation of HDL metabolism without modification by apoB-containing lipoproteins. Apolipoproteins A-I and E are two of the major apolipoproteins in HDL. Plasma apoA-I levels, but not apoE levels, have been reported to be decreased in patients with ABL. Furthermore, HDL from ABL patients is enriched in apoE compared with normal subjects. The purpose of the present study was: 1) to elucidate the metabolic basis of the low apoA-I levels in ABL; 2) to determine whether in vivo apoE production rates are normal in the absence of apoB-lipoprotein secretion; and 3) to test the hypothesis that apoE influences apoA-I and HDL catabolism in ABL. 131I-labeled apoA-I and 125I-labeled apoE were reassociated with autologous lipoproteins and injected into two unrelated ABL patients and control subjects. The mean residence time of apoA-I in ABL (2.4 days) was significantly decreased by nearly 50% compared with control subjects (4.7 +/- 0.6 days). ApoA-I production rates were also significantly decreased by 40% in ABL (7.1 mg/kg-d) compared with control subjects (11.8 +/- 1.7 mg/kg-d). The mean residence time of apoE in ABL (0.50 days) was somewhat shorter than that of control subjects (0.66 +/- 0.15 days), whereas the mean apoE production rate in ABL (2.14 mg/kg-d) was not substantially different from that of control subjects (1.55 +/- 0.62 mg/kg-d). HDL subfractions LpA-I and LpA-I:A-II were isolated using immunoaffinity chromatography. In contrast to the normal metabolism, apoA-I in LpA-I:A-II particles was catabolized at a faster rate than apoA-I in LpA-I, accounting for the greater decrease of plasma LpA-I:A-II relative to LpA-I in the ABL patients. HDL subfractions with and without apoE were also isolated using anti-apoE immunoaffinity chromatography. Labeled apoA-I in apoE-containing HDL was catabolized faster than that in HDL without apoE. Among the three different forms of apoE, the apoE monomer was catabolized at the fastest rate, the apoE homodimer at an intermediate rate, and the apoE-A-II heterodimer had the slowest rate of catabolism.(ABSTRACT TRUNCATED AT 400 WORDS)

Abetalipoproteinemia↗

PubMed1993

Very low high-density lipoproteins without coronary atherosclerosis.

Epidemiological studies have established that concentrations of plasma high-density lipoproteins (HDL) are inversely associated with premature atherosclerosis, but the physiological basis of this relationship remains unknown. We investigated 5 probands with very low plasma HDL. None had clinical or biochemical findings typical of the known genetic disorders with low HDL nor had evidence of premature coronary atherosclerosis by sensitive diagnostic methods. All 5 probands and the son of 1 of them had rapid catabolism of the HDL apolipoproteins A-I and A-II. These results indicate that not all people with low HDL are necessarily at risk of premature coronary heart disease and that further investigation is required before decisions can be made about their management.

Adult↗

PubMed1993

Cloning and gene defects in microsomal triglyceride transfer protein associated with abetalipoproteinaemia.

The microsomal triglyceride transfer protein (MTP), which catalyses the transport of triglyceride, cholesteryl ester and phospholipid between phospholipid surfaces, is a heterodimer composed of the multifunctional protein, protein disulphide isomerase, and a unique large subunit with an apparent M(r) of 88K (refs 1-3). It is isolated as a soluble protein from the lumen of the microsomal fraction of liver and intestine. The large subunit of MTP was not detectable in four unrelated subjects with abetalipoproteinaemia, a rare autosomal recessive disease characterized by a defect in the assembly or secretion of plasma lipoproteins that contain apolipoprotein B (ref. 6). We report here the isolation and sequencing of complementary DNA encoding the large subunit of MTP. A comparison of this sequence to corresponding genomic sequences from two abetalipoproteinaemic subjects revealed a homozygous frameshift mutation in one subject and a homozygous nonsense mutation in the other. The results indicate that a defect in the gene for the large subunit of MTP is the proximal cause of abetalipoproteinaemia in these two subjects, and that MTP is required for the secretion of plasma lipoproteins that contain apolipoprotein B.

Abetalipoproteinemia↗

PubMed1993

Abetalipoproteinemia. New insights into lipoprotein assembly and vitamin E metabolism from a rare genetic disease.

Abetalipoproteinemia is a rare genetic disease that has provided important new insights into the physiology of lipoprotein assembly and vitamin E metabolism. Forty-two years after its initial description, a molecular etiology of ABL has been reported to be a deficiency of a microsomal transfer protein, thus suggesting that this protein plays a key role in lipoprotein particle assembly and secretion both in the intestine and in the liver. Furthermore, studies in patients with ABL have established the critical role of hepatic secretion of VLDL in the delivery of vitamin E to peripheral tissues and the essential role of vitamin E in the maintenance of normal physiological function of multiple tissues. The systematic investigation of this rare genetic disease has provided insights that have substantially enhanced our understanding of human physiology.

Abetalipoproteinemia↗

PubMed1993

Increased production of apolipoprotein A-I associated with elevated plasma levels of high-density lipoproteins, apolipoprotein A-I, and lipoprotein A-I in a patient with familial hyperalphalipoproteinemia.

Familial hyperalphalipoproteinemia (FHA) is a heritable trait associated with elevated plasma concentrations of high-density lipoprotein (HDL) cholesterol and possibly with longevity and protection against coronary heart disease (CHD). The metabolic basis and molecular etiology of FHA have not been established in most kindreds. The proband of a kindred with FHA and possible longevity was found to have elevated plasma levels of HDL cholesterol, apolipoprotein (apo) A-I, and lipoproteins containing apo A-I without apo A-II (Lp A-I), but normal levels of apo A-II and lipoproteins containing apo A-I with apo A-II (Lp A-I:A-II). The in vivo kinetics of apo A-I and apo A-II were studied in the FHA proband and in control subjects using both exogenous radiotracer (125I-apo A-I and 131I-apo A-II) and endogenous stable isotope (primed constant infusion of 13C6-phenylalanine) labeling techniques. The production rate (PR) of apo A-I was markedly increased in the FHA subject (28.9 mg/kg.d) compared with the control subjects (12.0 +/- 2.1 mg/kg.d), whereas the apo A-II PR was not substantially increased. The primary sequence of the proband's apo A-I gene, including 1.2 kb of the 5'-flanking sequence, was normal. We conclude that a selective upregulation of apo A-I production is one metabolic cause of FHA, and results in high plasma concentrations of HDL cholesterol, apo A-I, and Lp A-I and possibly in protection from atherosclerotic CHD.

Apolipoprotein A-I↗

PubMed1993

Variation in lipoprotein(a) concentrations among individuals with the same apolipoprotein (a) isoform is determined by the rate of lipoprotein(a) production.

Lipoprotein(a) [Lp(a)] is an atherogenic lipoprotein which is similar in structure to, but metabolically distinct from, LDL. Factors regulating plasma concentrations of Lp(a) are poorly understood. Apo(a), the protein that distinguishes Lp(a) from LDL, is highly polymorphic, and apo(a) size is inversely correlated with plasma Lp(a) level. Even within the same apo(a) isoform class, however, plasma Lp(a) concentrations vary widely. A series of in vivo kinetic studies were performed using purified radiolabeled Lp(a) in individuals with the same apo(a) isoform but different Lp(a) levels. In a group of seven subjects with a single S4-apo(a) isoform and Lp(a) levels ranging from 1 to 13.2 mg/dl, the fractional catabolic rate (FCR) of 131I-labeled S2-Lp(a) (mean 0.328 day-1) was not correlated with the plasma Lp(a) level (r = -0.346, P = 0.45). In two S4-apo(a) subjects with a 10-fold difference in Lp(a) level, the FCR's of 125I-labeled S4-Lp(a) were very similar in both subjects and not substantially different from the FCRs of 131I-S2-Lp(a) in the same subjects. In four subjects with a single S2-apo(a) isoform and Lp(a) levels ranging from 9.4 to 91 mg/dl, Lp(a) concentration was highly correlated with Lp(a) production rate (r = 0.993, P = 0.007), but poorly correlated with Lp(a) FCR (mean 0.304 day-1). Analysis of Lp(a) kinetic parameters in all 11 subjects revealed no significant correlation of Lp(a) level with Lp(a) FCR (r = -0.53, P = 0.09) and a strong correlation with Lp(a) production rate (r = 0.99, P < 0.0001). We conclude that the substantial variation in Lp(a) levels among individuals with the same apo(a) phenotype is caused primarily by differences in Lp(a) production rate.

Adult↗

PubMed1993

Rapid in vivo transport and catabolism of human apolipoprotein A-IV-1 and slower catabolism of the apoA-IV-2 isoprotein.

Apolipoprotein (apo) A-IV is a polymorphic, intestinally derived apolipoprotein that is genetically linked to and similar in structure to apoA-I, the major apolipoprotein in high density lipoproteins (HDL). ApoA-IV plays a potentially important role in lipoprotein metabolism and reverse cholesterol transport, but its in vivo metabolism is poorly understood. In order to gain insight into factors modulating apoA-IV metabolism in humans, the in vivo kinetics of the two major human apoA-IV isoproteins apoA-IV-1 and apoA-IV-2 were investigated in normolipidemic human subjects. 131I-apoA-IV-1 and 125I-apoA-IV-2 were reassociated with autologous plasma and injected into study subjects. Analysis of the kinetic data revealed a rapid mean fractional catabolic rate (FCR) for apoA-IV-1 of 2.42 +/- 0.11 d-1. The mean production, or transport, rate of apoA-IV-1 was 16.3 +/- 1.4 mg/kg per d. Plasma apoA-IV concentrations were highly correlated with apoA-IV production rate (r = 0.84, P < 0.001) and not correlated with apoA-IV fractional catabolic rate (r = 0.25, P = NS). The mean FCR of apoA-IV-2 was 2.21 +/- 0.10 d-1. In the ten subjects in whom 131I-apoA-IV-1 and 125I-apoA-IV-2 were simultaneously injected, the FCR of apoA-IV-2 was significantly slower by paired t test (P = 0.003). The FCR of apoA-IV-2 in an apoA-IV-2/2 homozygote was only 1.49 d-1, substantially slower than in all other subjects. We conclude that: (a) apoA-IV is a rapidly catabolized apolipoprotein in humans, with a fractional catabolic rate more than 10 times greater than that of apoA-I; (b) apoA-IV has a high absolute transport rate similar to that of apoA-I; (c) plasma levels of apoA-IV are primarily determined by apoA-IV production rate in normolipidemic subjects; and (d) the fractional catabolic rate of the common variant apoA-IV-2 is slower than that of the wild-type apoA-IV-1.

Adult↗

PubMed1993

Delayed catabolism of high density lipoprotein apolipoproteins A-I and A-II in human cholesteryl ester transfer protein deficiency.

Deficiency of the cholesteryl ester transfer protein (CETP) in humans is characterized by markedly elevated plasma concentrations of HDL cholesterol and apoA-I. To assess the metabolism of HDL apolipoproteins in CETP deficiency, in vivo apolipoprotein kinetic studies were performed using endogenous and exogenous labeling techniques in two unrelated homozygotes with CETP deficiency, one heterozygote, and four control subjects. All study subjects were administered 13C6-labeled phenylalanine by primed constant infusion for up to 16 h. The fractional synthetic rates (FSRs) of apoA-I in two homozygotes with CETP deficiency (0.135, 0.134/d) were found to be significantly lower than those in controls (0.196 +/- 0.041/d, P < 0.01). Delayed apoA-I catabolism was confirmed by an exogenous radiotracer study in one CETP-deficient homozygote, in whom the fractional catabolic rate of 125I-apoA-I was 0.139/d (normal 0.216 +/- 0.018/d). The FSRs of apoA-II were also significantly lower in the homozygous CETP-deficient subjects (0.104, 0.112/d) than in the controls (0.170 +/- 0.023/d, P < 0.01). The production rates of apoA-I and apoA-II were normal in both homozygous CETP-deficient subjects. The turnover of apoA-I and apoA-II was substantially slower in both HDL2 and HDL3 in the CETP-deficient homozygotes than in controls. The kinetics of apoA-I and apoA-II in the CETP-deficient heterozygote were not different from those in controls. These data establish that homozygous CETP deficiency causes markedly delayed catabolism of apoA-I and apoA-II without affecting the production rates of these apolipoproteins.

Adult↗

PubMed1993

Evaluation of apoA-I kinetics in humans using simultaneous endogenous stable isotope and exogenous radiotracer methods.

Apolipoprotein A-I is the major apolipoprotein constituent of high density lipoproteins (HDL). Methods used to investigate in vivo kinetics of apoA-I include exogenous labeling with radioiodine and endogenous labeling with stable isotopically labeled amino acids. We report here a direct comparison of these methods to determine the in vivo kinetics of apoA-I in four normal subjects. Purified apoA-I was labeled with 125I, reassociated with autologous plasma, and injected into study subjects. At the same time, [13C6]phenylalanine was administered as a primed constant infusion for up to 14 hours. The kinetic parameters of apoA-I were determined from the 125I-labeled apoA-I plasma curves. For the analysis of data from stable isotope studies, very low density lipoprotein (VLDL) apoB-100, VLDL apoB-48, and total apoA-I were isolated by ultracentrifugation and subsequent preparative NaDodSO4-PAGE, hydrolyzed, and derivatized. The tracer/tracee ratio was determined by gas chromatography-mass spectrometry. Monoexponential function analysis was used to determine the tracer/tracee curves of VLDL apoB-100 and VLDL apoB-48, and total apoA-I. The mean plateau tracer/tracee ratio of VLDL apoB-100 (primarily liver-derived) was 5.19%, whereas that of VLDL apoB-48 (intestinally derived) was only 3.74%. Using the VLDL apoB-100 plateau tracer/tracee ratio as the estimate of the precursor pool enrichment for apoA-I, the mean apoA-I residence time (RT) was 5.14 +/- 0.41 days, compared with 4.80 +/- 0.30 days for the exogenous labeling method. The apoA-I RTs using these two methods were highly correlated (r = 0.874).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

Two different allelic mutations in the lecithin:cholesterol acyltransferase (LCAT) gene resulting in classic LCAT deficiency: LCAT (tyr83-->stop) and LCAT (tyr156-->asn).

The molecular defects in the lecithin:cholesterol acyltransferase (LCAT) gene have been identified in a 52-year-old patient with classic LCAT deficiency, presenting with corneal clouding and proteinuria. Plasma total cholesterol was normal, triglycerides were elevated, whereas high density lipoprotein (HDL) cholesterol (8 mg/dl) and plasma cholesteryl esters (6% of total cholesterol) were markedly reduced. Plasma cholesterol esterification rate (pCER) was zero, alpha-LCAT activity, assayed using an HDL-like proteoliposome substrate was reduced to 1.6% of control, and LCAT mass was 3.7% of normal plasma levels. DNA sequence analysis of the proband's LCAT gene identified a C to A substitution, converting tyr83 to a stop codon, and a T to A transition, replacing tyr156 by asn. Restriction analysis of PCR-amplified DNA from the proband, a control and his four children using the enzymes Acc I and Rsa I established that the patient is a compound heterozygote for both mutations. The two children, heterozygous for the stop codon defect, were phenotypically indistinguishable from the two with the tyr156 defect. In vitro expression of LCAT (tyr156-->asn) in human embryonic kidney-293 cells established the functional significance of this mutation. The secreted translation product had only 6% of control mass and no detectable CER; however, the residual LCAT mass of the in vitro expressed LCAT (tyr156-->asn) demonstrated a specific alpha-LCAT activity of 30% of control, suggesting that this amino acid substitution results in a mutant enzyme that retains some enzymic activity, but may be rapidly catabolized. In summary, we have identified two unique defects in the LCAT gene that lead to the expression of classic LCAT deficiency in this kindred.

Alleles↗

PubMed1992

Absence of microsomal triglyceride transfer protein in individuals with abetalipoproteinemia.

Abetalipoproteinemia is a human genetic disease that is characterized by a defect in the assembly or secretion of plasma very low density lipoproteins and chylomicrons. The microsomal triglyceride transfer protein (MTP), which is located in the lumen of microsomes isolated from the liver and intestine, has been proposed to function in lipoprotein assembly. MTP activity and the 88-kilodalton component of MTP were present in intestinal biopsy samples from eight control individuals but were absent in four abetalipoproteinemic subjects. This finding suggests that a defect in MTP is the basis for abetalipoproteinemia and that MTP is indeed required for lipoprotein assembly.

Abetalipoproteinemia↗