Reversal of hypercholesterolemia in low density lipoprotein receptor knockout mice by adenovirus-mediated gene transfer of the very low density lipoprotein receptor

We have used the technique of adenovirus-mediated gene transfer to study the in vivo function of the very low density lipoprotein receptor (VLDLR) in low density lipoprotein receptor (LDLR) knockout mice. We generated a replication-defective adenovirus (AdmVLDLR) containing mouse VLDLR cDNA driven by a cytomegalovirus promoter. Transduction of cultured Hepa (mouse hepatoma) cells and LDLR-deficient CHO-ldlA7 cells in vitro by the virus led to high-level expression of immunoreactive VLDLR proteins with molecular sizes of 143 kDa and 161 kDa. Digestion of the cell extract with the enzymes neuraminidase, N-glycanase, and O-glycanase resulted in the stepwise lowering of the apparent size of the 161-kDa species toward the 143-kDa species. LDLR (-/-) mice fed a 0.2% cholesterol diet were treated with a single intravenous injection of 3 x 10(9) plaque-forming units of AdmVLDLR. Control LDLR (-/-) mice received either phosphate-buffered saline or AdLacZ, a similar adenovirus containing the LacZ cDNA instead of mVLDLR cDNA. Comparison of the plasma lipids in the 3 groups of mice indicates that in the AdmVLDL animals, total cholesterol is reduced by approximately 50% at days 4 and 9 and returned toward control values on day 21. In these animals, there was also a approximately 30% reduction in plasma apolipoprotein (apo) E accompanied by a 90% fall in apoB-100 on day 4 of treatment. By FPLC analysis, the major reduction in plasma cholesterol in the AdmVLDLR animals was accounted for by a marked reduction in the intermediate density lipoprotein/low density lipoprotein (IDL/LDL) fraction. Plasma VLDL, IDL/LDL, and HDL were isolated from the three groups of animals by ultracentrifugal flotation. In the AdmVLDLR animals, there was substantial loss (approximately 65%) of protein and cholesterol mainly in the IDL/LDL fraction on days 4 and 9. Nondenaturing gradient gel electrophoresis indicates a preferential loss of the IDL peak although the LDL peak was also reduced. When 125I-IDL was administered intravenously into animals on day 4, the AdmVLDLR animals cleared the 125I-IDL at a rate 5-10 times higher than the AdLacZ animals. We conclude that adenovirus-mediated transfer of the VLDLR gene induces high-level hepatic expression of the VLDLR and results in a reversal of the hypercholesterolemia in 0.2% cholesterol diet-fed LDLR (-/-, mice. The VLDLR overexpression appears to greatly enhance the ability of these animals to clear IDL, resulting in a marked lowering of the plasma IDL/LDL. Further testing of the use of the VLDLR gene as a therapeutic gene for the treatment of hypercholesterolemia is warranted.

Effect of 764-3 on aggregation and calcium movements in aequorin-loaded human platelets

Washed human platelets were loaded with the Ca(2+)-sensitive photoprotein, aequorin, using hypoosmotic shock treatment-technique. Then aggregation and cytoplasmic ionized calcium concentration ([Ca2+]i) changes in response to collagen or thrombin were measured simultaneously in the aequorin-loaded human platelets with a Platelet Ionized Calcium Aggregometer. 764-3, an active component isolated from the Chinese medicinal herb Salvia Miltiorrhiza Bge, inhibited platelet [Ca2+]i rise as well as aggregation evoked by collagen or thrombin in the presence of extracellular Ca2+. After the extracellular Ca2+ was removed by addition of EGTA, collagen or thrombin, causing no aggregation, still elicited platelet [Ca2+]i rise which reflected Ca2+ mobilization from intraplatelet stores. Under this condition, 764-3 could also suppress platelet [Ca2+]i rise. Analysis shows that 764-3 inhibits platelet Ca2+ influx and Ca2+ mobilization with similar potency, which accounts for its suppression of platelet [Ca2+]i rise, and must contribute to its inhibition of platelet aggregation.

[Characterization of platelet activation induced by CD9 McAbs]

The platelet activation induced by two anti-human platelet P24/CD9 McAbs was investigated. The results showed that the pathways of platelet aggregation induced by the two McAbs (HI117 and SJ9A4) were different and HI117 and SJ9A4 induced the phosphorylation of platelet proteins (40,000 and 20,000) when platelets were activated. However, HI117 did not cause a rise in intracellular Ca2+ concentration in activated platelets in comparison with SJ9A4 and the epitope recognized by HI117 and SJ9A4 was different and this might explain why the two CD9 McAbs played different roles in platelet activation in addition, McAbs HI117 and SJ9A4 could not promote associations of other proteins (eg: GP II b/III a) with P24/CD9 on activated human platelets. All these results indicate that the mechanisms of platelet activation induced by HI117 or SJ9A4 are different from each other. It suggests that CD9 antigen plays an importent and complex role in platelet activation.

Phenotypic correction of hypercholesterolemia in apoE-deficient mice by adenovirus-mediated in vivo gene transfer

To investigate the potential use of apoE in gene therapy of hyperlipidemias, an adenoviral vector was constructed that contained the human apoE3 cDNA under the control of the RSV promoter (Av1RE). Transduction of HepG2 cells resulted in the overexpression of human apoE secreted into the culture medium. Intravenous injection of 5 x 10(11) Av1RE vector particles into apoE-deficient mice resulted in expression of human apoE3 in mouse plasma at levels of 1.2 +/- 0.4 micrograms/L (mean +/- SEM, n = 5) 7 days after injection. Mice injected with the control vector Av1Lacz4 did not express detectable levels of human apoE. Average plasma cholesterol concentrations were reduced approximately eightfold from 737.5 +/- 118 mg/dL (mean +/- SEM, n = 6) to 98.2 +/- 4.4 mg/dL (mean +/- SEM, n = 5) and were unaffected in the control vector group. Expression of human apoE resulted in a shift in the plasma lipoprotein distribution from primarily VLDL and LDL in the control mice to predominantly HDL in the Av1RE-treated group. Western blot analysis of fast protein liquid chromatography-fractionated mouse plasma showed that the human apoE protein was associated with VLDL, LDL, and HDL. Correction of the hyperlipidemic condition found in the apoE-knockout mouse strain by direct in vivo gene transfer establishes the potential of this approach for treatment of hyperlipidemia caused by apoE deficiency or malfunction in human disease.

Adenovirus-mediated gene transfer of rat apolipoprotein B mRNA-editing protein in mice virtually eliminates apolipoprotein B-100 and normal low density lipoprotein production

Apolipoprotein (apo) B-100 is the major protein component in low density lipoprotein (LDL); it contains the binding domain for the LDL receptor and the attachment site for apolipoprotein(a) in lipoprotein(a). ApoB-48 is colinear with the amino-terminal half of apoB-100 and misses the part of the molecule required for LDL receptor interaction and lipoprotein(a) formation. ApoB-48 mRNA is produced by the editing of apoB-100 mRNA, a process by which the codon CAA for Gln-2153 is changed to UAA, an in-frame stop codon. We used the cloned catalytic component of the rat apoB mRNA-editing enzyme (REPR) to construct a replication-defective recombinant adenoviral vector containing REPR cDNA (AvREPR) and a control vector (Av1LacZ4) containing a beta-galactosidase cDNA to investigate the effect of REPR gene delivery in C57BL/6 mice. Intravenous injection of AvREPR in mice resulted in efficient transduction of liver cells, where REPR mRNA and protein were overexpressed, reaching a peak at 7 and 12 days, returning toward control levels at 39 days after AvREPR administration. ApoB mRNA editing activity in liver extracts showed changes parallel to those of REPR mRNA expression; the proportion of edited apoB mRNA in the total hepatic apoB mRNA increased from approximately 60% to more than 90% at the peak of REPR expression. The proportion of plasma apoB-100 in AvREPR-transduced animals decreased from approximately 50% to < 10% of total plasma apoB concentration. Plasma very low density lipoproteins were polydisperse in control animals with an average diameter of 54.9 +/- 20.6 nm (uninjected control) and 54.7 +/- 16.8 nm (Av1LacZ4-treated), respectively. They became much smaller (average diameter 39.3 +/- 12.7 nm) and more uniform in size at day 12 following AvREPR administration. On the same day, the normal plasma LDL (26.2-25.5 nm) was almost completely eliminated in treated animals. Adenovirus-mediated transfer of the REPR cDNA is an efficient method to reduce plasma apoB-100 and normal LDL production.

Molecular cloning of an apolipoprotein B messenger RNA editing protein

Mammalian apolipoprotein B (apo B) exists in two forms, each the product of a single gene. The shorter form, apo B48, arises by posttranscriptional RNA editing whereby cytidine deamination produces a UAA termination codon. A full-length complementary DNA clone encoding an apo B messenger RNA editing protein (REPR) was isolated from rat small intestine. The 229-residue protein contains consensus phosphorylation sites and leucine zipper domains. HepG2 cell extracts acquire editing activity when mixed with REPR from oocyte extracts. REPR is essential for apo B messenger RNA editing, and the isolation and characterization of REPR may lead to the identification of other eukaryotic RNA editing proteins.

Evolution of intestinal apolipoprotein B mRNA editing. Chicken apolipoprotein B mRNA is not edited, but chicken enterocytes contain in vitro editing enhancement factor(s)

Mammalian intestinal apolipoprotein B (apoB) messenger RNA (mRNA) undergoes posttranscriptional editing, changing codon 2153 from CAA in apoB100 mRNA to an in-frame translational stop codon (UAA) in apoB48 mRNA. By contrast, chicken intestinal apoB cDNA contains a CAA codon at the corresponding site and apoB mRNA from chicken enterocytes, kidney, and liver is unedited. The cDNA sequence of chicken apoB spanning the edited base is divergent from mammalian apoB cDNA sequence, with 70% homology over the conserved 29-nucleotide sequence (6662-6690) flanking codon 2153. Efficient in vitro editing of both human and rat, but not chicken, synthetic apoB RNA was achieved using rat enterocyte S-100 extracts. By contrast, chicken enterocyte S-100 extracts failed to edit chicken, rat, or human synthetic apoB RNA. Mixing experiments, however, revealed that chicken enterocyte S-100 extracts enhance the in vitro editing activity of rat, pig, and human enterocyte S-100 extracts upon homologous RNAs. The editing enhancement activity of chicken enterocyte S-100 extracts is tissue-specific, heat-sensitive, substrate-saturable, and sensitive to proteinase K, but resistant to micrococcal nuclease. The activity was partially purified by Q-Sepharose chromatography and has an average molecular mass of 49 kDa when analyzed by gel filtration chromatography. We conclude that the evolutionary adaptation of intestinal apoB mRNA editing requires both a requisite RNA motif and tissue-specific factors which mediate the site-specific modification.

Apolipoprotein B messenger RNA editing is developmentally regulated in pig small intestine: nucleotide comparison of apolipoprotein B editing regions in five species

Apolipoprotein B (apo B) mRNA undergoes a posttranscriptional tissue-specific editing reaction which changes codon 2153 from glutamine (CAA) in apoB-100 mRNA to an in-frame stop codon (UAA) in apoB-48 mRNA. Small intestinal apo B mRNA was found to be predominantly (greater than 90%) unedited in fetal (40-day gestational age) piglets but greater than 95% edited in neonatal, suckling and adult animals. By contrast, both fetal, neonatal and adult pig liver contained greater than 99% unedited, apo B-100 mRNA. The nucleotide sequence spanning the edited region in apo B mRNA was found to be highly conserved. We speculate that the regulation of apo B mRNA editing may be developmentally modulated in pig small intestine.

Apolipoprotein B messenger RNA editing is developmentally regulated and widely expressed in human tissues

Apolipoprotein B (apoB) messenger RNA (mRNA) undergoes posttranscriptional (C to U) editing, producing tissue-specific forms of apoB from the unedited (apoB100) and edited (apoB48) transcripts. ApoB mRNA editing is developmentally regulated in human fetal small intestine, producing parallel changes in the synthesis and secretion of apoB100 and apoB48. Neither fetal nor adult liver contained detectable levels (less than 1%) of edited apoB mRNA. By contrast, apoB mRNA is incrementally edited during development in several extraintestinal fetal tissues. These tissues demonstrated significant differences, however, in both the extent and developmental profile of apoB mRNA editing. Additionally, while apoB100 synthesis and secretion was demonstrated in these tissues, apoB48 synthesis was confined to the small intestine. Thus, although the molecular mechanism underlying this process remains unclear, the capacity to edit apoB mRNA is widely distributed among both fetal and adult tissues. We speculate that the asynchronous and developmentally modulated induction of apoB mRNA editing may provide a novel mechanism for regulating lipoprotein biogenesis in both the developing fetus and adult human.

Adipose tissue glyceride synthesis in patients with hyperapobetalipoproteinemia

Adipose tissue was obtained at thoracotomy in five control patients with valvular heart disease, all of whom were free of coronary artery disease and all of whom were normolipidemic with normal low density lipoprotein apolipoprotein B levels, and eight patients with coronary artery disease, all of whom had hyperapobetalipoproteinemia. In both groups, the rates at which linoleic acid and palmitic acid were incorporated into diglyceride and triglyceride were determined in vitro. The data indicate that fatty acid incorporation into adipose tissue glycerides was twice as rapid in controls as in patients with hyperapobetalipoproteinemia. By contrast there was no difference between the groups in the rate of net lipolysis of adipocyte glyceride. The data at hand do not establish the mechanism responsible for the difference in synthesis between normal subjects and patients with hyperapobetalipoproteinemia, but this may explain the delayed chylomicron triglyceride clearance previously observed in the disorder.

Kinetics of LDL subfractions

After injecting 125I- or 131I-labeled lipoproteins, plasma was subjected to discontinuous density gradient centrifugation, which separates low-density lipoproteins (LDL) into three subfractions. Analysis of changes in apolipoprotein B-specific activity with time showed that light LDL is normally the product of intermediate-density lipoprotein and the precursor of heavy LDL, which is subsequently converted to heavier LDL. In hyperapobetalipoproteinemia these relationships are maintained but there is overproduction of light and heavy LDL secondary to increased synthesis of very low-density lipoprotein. In familial hypercholesterolemia, light LDL is produced normally but its conversion into heavy LDL is reduced and independent synthesis of the latter is apparent. These observations suggest that the LDL receptor normally plays a role in the conversion of light into heavy LDL. They also provide an explanation for previously documented differences in LDL composition between hyperapobetalipoproteinemia, in which there is a relative increase in cholesterol-depleted heavy and heavier subfractions, and familial hypercholesterolemia, in which there is a relative increase in the cholesterol-enriched light subfraction.

Hyperapobetalipoproteinemia. Plasma lipoprotein responses to oral fat load

To better define lipid transport in patients with hyperapobetalipoproteinemia (HyperapoB), the response to an oral fat load was studied in six normotriglyceridemic patients with the disorder. Plasma triglycerides; Sf greater than 400, and Sf 20 to 400 triglycerides; Sf greater than 20 B100; total HDL and HDL subfractions (HDL2 and HDL3) were measured serially for a 7-hour period after an oral fat load and changes in these parameters were compared to those observed in six normolipidemic controls. In addition, plasma triglyceride levels and HDL2 and HDL3 cholesterol were also determined in seven patients with Type IV hyperlipoproteinemia: three with normal LDL apo B levels and four with HyperapoB. When the two normotriglyceridemic groups were compared, the patients with HyperapoB had significantly higher fasting levels of SF greater than 400 lipoproteins and higher fasting VLDL and LDL levels than the normal patients. After the fat load, Sf 20 to 400 triglycerides and Sf greater than 20 B100 levels increased in both groups. Plasma triglycerides rose to a higher level in the HyperapoB patients than in the normal group, but more strikingly, remained elevated in the HyperapoB patients, an elevation due principally to a persistant increase in Sf greater than 400 triglycerides. On the other hand, HDL2 cholesterol dropped substantially in the HyperapoB patients but not in the normal patients. Finally, in the hypertriglyceridemic group, after the fat load, HDL2 cholesterol levels did not change in the patients with normal LDL apo B levels but did decrease in those with elevated plasma LDL apo B.

Genetic analysis of plasma sitosterol, apoprotein B, and lipoproteins in a large Amish pedigree with sitosterolemia

We previously reported the finding of phytosterolemia, xanthomatosis, and hyperapobetalipoproteinemia (hyperapoB) in five siblings in a large Amish pedigree ascertained through a 13-year-old boy who died suddenly from advanced coronary atherosclerosis. Here, we present further analyses of the plasma levels of the plant sterol, sitosterol, of low density (beta) lipoprotein (LDL) sterol, and of LDL B protein. Of 254 relatives and spouses of the proband, 90.5% were examined. A series of genetic models were explored using a pedigree analysis where parameters reflecting frequency, transmission, and penetrance of putative genotypes were examined simultaneously using a maximum likelihood approach. Segregation analysis of the sitosterol levels showed that the phenotype of sitosterolemia was controlled by a rare autosomal recessive gene. There was also significant familial correlation in plasma sitosterol levels that was attributed to a polygenic component under a mixed model but could also be due to shared environments such as diets. The recessive model was supported by our finding that the plasma sitosterol levels in the parents and in six children born to three of the five sitosterolemics were less than 1 mg/dl, well within the normal range. The phenotype of hyperapoB is based on an elevated level of LDL B protein in the presence of a normal LDL cholesterol level (low LDL sterol to LDL B ratio). For both LDL sterol and LDL B, a polygenic model showed a slightly greater improvement in ln likelihood than did the Mendelian single locus model when both were compared to a sporadic model. Similar results were obtained for sterol levels of high density (alpha) lipoprotein (HDL) sterol. When segregation analysis was performed using the ratio of LDL sterol to LDL B, the Mendelian single locus model gave a slightly better fit to the data than did the polygenic model. While the analyses presented here provided unequivocal evidence for the recessive phenotype of phytosterolemia, we also identified a possible single gene factor that could account for the major portion of the strong familial aggregation in the ratio of LDL sterol to LDL B, and to a lesser extent LDL B. However, there is clear evidence of familial aggregation for these traits in this pedigree beyond that due to Mendelian components.

Metabolic basis of hyperapobetalipoproteinemia. Turnover of apolipoprotein B in low density lipoprotein and its precursors and subfractions compared with normal and familial hypercholesterolemia

The turnover of apolipoprotein B (apo B) in very low density, intermediate density, and low density lipoproteins (VLDL, IDL, and LDL) and in the light and heavy fractions of LDL was determined in seven patients with hyperapobetalipoproteinemia (hyperapo B), six normolipidemic subjects, and five patients with heterozygous familial hypercholesterolemia (FH). After receiving an injection of 125I-VLDL, hyperapo B patients were found to have a higher rate of synthesis of VLDL-apo B than controls (40.1 vs. 21.5 mg/kg per d, P less than 0.05) but a reduced fractional catabolic rate (FCR) (0.230 vs. 0.366/h, P less than 0.01). After receiving an injection of 131I-LDL, hyperapo B patients had higher rates of LDL-apo B synthesis than controls (23.1 vs. 13.0 mg/kg per d, P less than 0.001), as did FH patients (22.7 mg/kg per d). The FCR of LDL was similar in hyperapo B patients and controls (0.386 vs. 0.366/d) but was markedly decreased in FH patients (0.192/d). Most subjects exhibited precursor-product relationships between VLDL and IDL, and all did between IDL and light LDL; an analogous relationship between light and heavy LDL was evident in most hyperapo B patients and controls but not in FH patients. Simultaneous injection of differentially labeled LDL fractions and deconvolution analysis showed increased light LDL synthesis with normal conversion into heavy LDL in hyperapo B, whereas in FH conversion of light LDL was reduced and there was independent synthesis of heavy LDL. These data show that the increased concentration of LDL-apo B in hyperapo B is solely due to increased LDL synthesis, which is secondary to increased VLDL synthesis; in contrast, in FH there is both an increase in synthesis of LDL (which is partly VLDL-independent) and reduced catabolism.

Modulation of apolipoprotein B antigenic determinants in human low density lipoprotein subclasses

To investigate the effect of low density lipoprotein (LDL) heterogeneity on the conformation of LDL apolipoprotein B (apo-B), the immunoreactivities of 6 monoclonal antibodies against LDL apo-B were measured in 3 LDL subfractions isolated by equilibrium density gradient ultracentrifugation. To ensure a broad range of LDL particles, the LDL subfractions were prepared from normal subjects and patients with hyperapobetalipoproteinemia. With 3 of the antibodies, 1D1, 5E11, and 3A10, LDL fractions 1 (the most buoyant), 2 (the intermediate), and 3 (the densest) were equally immunoreactive and competed similarly with reference whole LDL. In contrast, with 3 other antibodies, 2D8, 3F5, and 4G3, fraction 1 was significantly more reactive than fraction 3; that is for each in turn, 290, 250, and 150% more of the densest LDL protein was required to achieve the same displacement as with fraction 1. Further, the immunoreactivities of the 3 LDL fractions with antibodies 2D8, 3F5, and 4G3 were negatively correlated with their LDL cholesterol to LDL protein ratio with r values of 0.727, 0.898, and 0.870, respectively, suggesting that as LDL particle size decreases, the conformation of the LDL apo-B changes progressively. It is of interest that the antigenic determinants recognized by 3F5 and 4G3 are close to the LDL receptor recognition site on LDL apo-B. Therefore, it is possible that the reduced immunoreactivity of these determinants in dense LDL may be the in vitro correlate of the reduced fractional catabolics rate of dense LDL compared to buoyant LDL previously observed in vivo.

Surface morphology of Asian cadaveric hips

The joint surfaces of 60 hips obtained from the cadavers of elderly Asians were studied to determine the incidence, the grade and the distribution of both non-progressive (age-related) and progressive degenerative changes. It was observed that in the Asian population of 40 to 90 years of age, non-progressive changes were common, being seen in 66% of the acetabular specimens and 50% of the femoral heads. Only one specimen of the 60 showed unexplained progressive degenerative change. We conclude that primary osteoarthritis of the hip is rare in Asians.

Familial aggregation and early expression of hyperapobetalipoproteinemia

Family history is an important predictor of coronary risk. However, this relation, in large part, is not explained by the known risk factors such as systemic hypertension or hyperlipidemia. In the present study, plasma lipid, lipoprotein lipid, and plasma low-density lipoprotein (LDL) apoB levels were measured in 66 offspring (myocardial infarction [MI] offspring) of 24 families in which an index parent had premature coronary artery disease and hyperapobetalipoproteinemia. These results were compared to those obtained in 207 control children and young adults. Univariate analysis revealed that plasma LDL apoB and all other lipid and lipoprotein levels except high-density lipoprotein cholesterol were significantly higher in the MI offspring. Multivariate analysis showed plasma LDL apoB and LDL cholesterol best differentiated the MI offspring from control children and young adults. Of the 66 children, 22 had hyperapobetalipoproteinemia, of whom only 7 had clearly abnormal LDL cholesterol or plasma triglyceride levels. Thus, a substantial portion of children born to a parent with premature coronary artery disease and hyperapobetalipoproteinemia have the same disorder of lipoprotein metabolism.

Gait analysis in cerebral palsy

Ambulation problems in cerebral palsy have been very difficult to analyse because it is the central control system rather than the motor system that is at fault. Until recently, decisions regarding surgical management has been made on clinical grounds, which by and large, have been subjective. Attempts to remedy this situation has resulted in the setting up of Gait Analysis Laboratories to provide a more objective method of evaluation of disorders of human motion. We have recently been using an opto-electronic computer-based gait analysis system to analyse normal as well as abnormal gait. Gait analysis can provide information regarding movements of both lower limbs in three planes, ground reaction forces, joint torque and dynamic electromyography. Children with various types of Cerebral Palsy have been assessed. The results of four clinical gait assessment cases are presented and discussed. Information provided by the Gait Analysis Laboratory has introduced more objectivity in pre-operative planning for these children.

Composition and distribution of low density lipoprotein fractions in hyperapobetalipoproteinemia, normolipidemia, and familial hypercholesterolemia

Hyperapobetalipoproteinemia is defined as the combination of a normal low density lipoprotein (LDL) cholesterol in the face of an increased LDL apolipoprotein B (apoB) protein. To examine the physical basis for the apparent disproportion between LDL cholesterol and apoB characteristic of this syndrome, we used density gradient ultracentrifugation to isolate LDL fractions from 10 normal subjects, from 20 patients with hyperapobetalipoproteinemia (10 normotriglyceridemic and 10 hypertriglyceridemic), and from 7 patients with familial hypercholesterolemia. In familial hypercholesterolemia, more LDL was in fraction 1--"light" LDL--and this LDL was relatively enriched in cholesterol and poor in protein. By contrast, it was fraction 2--"heavy" LDL--that differed in hyperapobetalipoproteinemia, being denser, depleted of cholesterol (particularly cholesteryl ester), and relatively enriched in apoB. These findings were more pronounced in the hypertriglyceridemic patients than in the normotriglyceridemic patients with hyperapobetalipoproteinemia. Thus this study confirms that considerable heterogeneity exists between LDL subfractions within individuals but, in addition, indicates there are also marked--and apparently characteristic--differences in LDL composition amongst normal subjects and patients with hyperapobetalipoproteinemia or familial hypercholesterolemia.

Association of hyperapobetalipoproteinemia with endogenous hypertriglyceridemia and atherosclerosis

Researchers disagree on whether plasma triglyceride levels are an independent risk factor for atherosclerotic coronary artery disease. We hypothesized that patients with endogenous hypertriglyceridemia would differ: Some would have normal values of plasma low-density lipoprotein (LDL) B protein; others, despite their normal level of LDL cholesterol, would have increased levels of LDL B protein. We believe the latter patients--those with hyperapobetalipoproteinemia--would be the ones at risk for atherosclerosis. We studied two populations. Group 1, consisting of 162 patients with type IV lipoprotein patterns, was divided into two groups. One subgroup (A), which included 38 patients with elevated plasma LDL B atherosclerotic disease than the other subgroup (B) of 36 patients with normal levels of plasma LDL B protein (10 patients versus two, p less than 0.02). Group 2 consisted of 100 patients who had had myocardial infarction. Eighty-one percent of the 47 hypertriglyceridemic and 70% of the 53 normotriglyceridemic patients had elevated plasma LDL B protein levels (129 mg/dL or greater)--a proportion significantly higher than that in Group 1 (p less than 0.001). Thus, an elevated plasma level of LDL B protein not only identifies subgroups of patients with type IV lipoprotein patterns, but also may be an important marker for atherosclerotic disease.

Hyperapobetalipoproteinaemia in two families with xanthomas and phytosterolaemia

The death of a 13-year-old boy from coronary atherosclerosis prompted the study of an Amish family. Five of his twelve sibs had tendon and tuberous xanthomas, and increased plasma plant sterols, particularly beta-sitosterol. The plasma level of the major apoprotein of low density lipoprotein (LDL), the B protein, was very high (mean 173 mg/dl) in these five sibs, while the LDL cholesterol level was moderately increased (209 mg/dl). Four other sibs and both parents had an increased LDL B protein level with a normal or mildly raised plasma total and LDL cholesterol level (hyperapobeta-lipoproteinaemia). Evidence for coronary artery disease was found in both parents and three xanthomatous sibs. The original family with beta-sitosterolaemia and xanthomatosis, described in 1974, was re-examined. The proband and her sister had persistent phytosterolaemia and normocholesterolaemia but increased LDL B protein levels. Both parents, two uncles, and three of four grandparents had increased LDL B protein levels and normal total and LDL cholesterol levels. The proband's father had atypical angina pectoris. People with the full syndrome (phytosterolaemia, xanthomas, and hyperapobetalipoproteinaemia) are most probably homozygous for a mutant allele. An increased LDL B protein level permits the identification of heterozygotes in these families, even though in the fasting state they show no phytosterolaemia. The homozygote and probably the heterozygote are at increased risk for cardiovascular atherosclerotic disease.