Decreased production and increased catabolism of apolipoprotein B-100 in apolipoprotein B-67/B-100 heterozygotes

Apolipoprotein (apo) B-67 is a truncated form of apoB-100 due to deletion of an adenine at cDNA 9327. Heterozygotes have one allele making apoB-100; therefore, plasma apoB levels would be predicted to be at least 50% of normal. However, apoB-67 heterozygotes have total plasma apoB levels that are 24% of normal. To determine the mechanisms responsible for the lower-than-expected levels of apoB, in vivo kinetics of apoB-100 were performed in three apoB-67/apoB-100 heterozygotes and compared with those of six control subjects by using a primed-constant infusion of [5,5,5-2H3]leucine in the fed state. Kinetic parameters were calculated by multicompartmental modeling of the data. The mean total apoB plasma concentration of the apoB-67 subjects was 21.8+/-6.1 mg/dL, or 24% of that of control subjects (89.6+/-24.1 mg/dL, P=.002). ApoB-67 subjects had lower mean VLDL apoB-100 production rates (3.6+/-1.2 versus 13.9+/-3.5 mg x kg(-1) x d(-1), P=.002) and lower mean transport rates of apoB-100 into LDL (3.5+/-1.4 versus 12.6+/-4.1 mg x kg(-1) x d(-1), P=.008) compared with control subjects. The transport rate into IDL was not significantly different (1.2+/-0.5 versus 6.2+/-4.0 mg x kg(-1) x d(-1), P=.07). The fractional catabolic rate of VLDL apoB-100 was significantly higher in apoB-67 subjects than in control subjects (18.1+/-8.6 versus 7.6+/-1.6 mg x kg(-1) x d(-1), P=.017). ApoB-100 IDL and LDL fractional catabolic rates were not significantly different. VLDL apoB-100 pool size in apoB-67 subjects was 11% of that of control subjects (15.8+/-7.7 versus 141.6+/-33.7 mg, P=.0004) due to a 74% lower production rate (26% of control values) and a 2.4-fold higher fractional catabolic rate. LDL apoB-100 pool size in apoB-67 subjects was 22% of that of control subjects (665.3+/-192.4 versus 2968.3+/-765.2 mg, P=.002) due primarily to a lower production rate (27% of control values). Thus, both decreased production of VLDL and LDL apoB-100 and increased catabolism of VLDL apoB-100 are responsible for the low levels of apoB-100 in apoB-67 subjects.     

Characterization and quantitation of apolipoprotein B-100 by capillary electrophoresis

The interaction of low density lipoproteins (LDL) with different surfactants was studied by capillary electrophoresis (CE) and sucrose density gradient ultracentrifugation as part of developing a method for quantitation of apoB-100 in serum. A mixture of surfactants consisting of 70% sodium dodecyl sulfate (SDS), 25% sodium myristyl sulfate, and 5% sodium cetyl sulfate was found to delipidate LDL particles more effectively than pure SDS or sodium decyl sulfate. The delipidation products of LDL [apolipoprotein B-100 (apoB-100) and lipids] were resolved as two distinct peaks by CE when using a 3.5 mM 70% SDS mixture, 20% (v/v) aceto nitrile, 50 mM sodium borate, pH 9.1 buffer. This CE method was also used to characterize apoB-100 derived from samples of lipoprotein [a] and very low density lipoproteins (VLDL). A CE-based quantitation method for apoB-100 was developed utilizing the observed linear relationship between apoB-100 concentration and its corrected 214 nm absorbance peak area measured on-line by CE. Concentration values of apoB-100 in LDL and VLDL samples were determined by CE and found to be accurate when compared to values obtained by immunoturbidimetric analysis and the Lowry method. Capillary electrophoresis can be used as a precise, accurate, and specific on-line method for the qualitative and quantitative analysis of the apoB-100 component of VLDL and LDL-related lipoproteins.     

Determinants of the kinetics of very low-density lipoprotein apolipoprotein B-100 in non-obese men

1. Apolipoprotein B-100 (ApoB) is the principal structural and functional protein of the pro-atherogenic lipoproteins. Elevated plasma apoB is an independent risk factor for coronary artery disease. In the present study we aimed to assess the factors that determine the kinetics of apoB in the very low-density lipoprotein (VLDL) in healthy men. 2. We studied 17 non-obese men who were consuming an ad libitum diet and had the following characteristics: mean (+/-SD) age 45.5 +/- 9.7 years, body mass index (BMI) 25.1 +/- 1.4 kg/m2, waist:hip ratio 0.91 +/- 0.04, serum cholesterol 5.2 +/- 0.6 mmol/L, triglycerides 1.08 +/- 0.53 mmol/L and high-density lipoprotein-cholesterol 1.24 +/- 0.31 mmol/L. Daily dietary intake was as follows: total fat 76 +/- 26 g, carbohydrate 238 +/- 67 g, protein 103 +/- 33 g and alcohol 20 +/- 16 g. 3. The kinetics of VLDL ApoB were studied using a primed, constant infusion (1 mg/kg per h) of 1-[13C]-leucine over 8 h with measurement of isotopic enrichment of ApoB using gas chromatography/mass spectrometry. The fractional turnover rate of VLDL ApoB was estimated using a monoexponential function. The mean (+/-SD) absolute hepatic secretion rate (ASR) of ApoB was 8.5 +/- 4.6 mg/kg per day and the fractional catabolic rate (FCR) was 7.9 +/- 5.6 pools/day. The ASR was significantly correlated with the waist:hip ratio (r = 0.60; P = 0.04), but not with age, BMI, weight or nutrient intake. The FCR was significantly and inversely correlated with plasma triglycerides (r = -0.53; P = 0.03) and alcohol intake (r = -0.48; P = 0.05). 4. In conclusion, the hepatic secretion of VLDL ApoB in nonobese, healthy men is primarily determined by the waist:hip ratio, a measure of visceral fat. This is consistent with the hypothesis that the rate of lipid substrate supply in the liver regulates the output of ApoB. The fractional catabolism of VLDL ApoB may, however, be inversely related to alcohol intake and appears to determine the plasma concentration of triglycerides.     

Increased hepatic secretion of very-low-density lipoprotein apolipoprotein B-100 in cholesteryl ester storage disease

Using a stable isotope method, we measured the hepatic secretion rate of very-low-density lipoprotein apolipoprotein B-100 (VLDL apoB) in a 26-year-old women who had dyslipidemia due to cholesteryl ester storage disease (CESD) and in five normolipidemic subjects. [1-13C]Leucine was administered by a primed constant intravenous infusion and the enrichment of VLDL apoB was determined by gas chromatography-mass spectrometry. The absolute secretion rate (ASR) of VLDL apoB in the patient was more than twice the mean ASR of the normolipidemic group (17.1 vs 8.0 +/- 0.8 mg/kg body wt. per day). The plasma mevalonic acid concentration, a measure of intrahepatic cholesterol synthesis, was also greater in the patient than in the normolipidemic subjects (8.3 vs 4.4 +/- 1.8 micrograms/L). The findings are consistent with the hypothesis that in CESD increased intrahepatic synthesis of cholesterol stimulates hepatic secretion of VLDL apoB and this may partly account for the dyslipidemia.     

Incidence of familial defective apolipoprotein B-100 in cases of patients diagnosed with familial hypercholesterolemia

Familial Hypercholesterolemia (FH) and Familial Defective Apolipoprotein B-100 (FDB) are monogenic, autosome, dominantly inherited diseases appearing as type II/a primary hypercholesterolemia. The frequency of the heterozygositic forms is 1:700-1:500 in European population. Both forms of hypercholesterolemia causes early onset coronary heart diseases (CHD). According to the recommendations of the international MED-PED program (Make Early Diagnoses--Prevent Early Death), we found 73 FH cases and their 377 first relatives (parents, siblings, children) were also assessed. 156 patients were diagnosed clinically FH (131 alive and 25 deceased), and 31.8% of the males and 32.4% of females suffered from early onset CHD. One family with FH consists of 5.46 members on the average and there are 2.39 FH patients in one family. In our FH cohort four patients with FDB (R3500Q mutation) were diagnosed with allelspecific PCR, and the mutation was detectable also in 9 cases out of 11 living family members. The plasma total cholesterol level of the FDB patients--especially at younger age--was very close to the normal values, which is in contrast to the findings in FH patients. Nevertheless, FDB can be one of the independent causes of the early onset CHD. Therefore, in families with high frequency of cardiovascular diseases the R3500Q mutation has to be considered.     

Sequences within apolipoprotein(a) kringle IV types 6-8 bind directly to low-density lipoprotein and mediate noncovalent association of apolipoprotein(a) with apolipoprotein B-100

Lipoprotein(a) [Lp(a)] particle formation is a two-step process in which initial noncovalent interactions between apolipoprotein(a) [apo(a)] and the apolipoprotein B-100 (apoB-100) component of low-density lipoprotein (LDL) precede disulfide bond formation. To identify kringle (K) domains in apo(a) that bind noncovalently to apoB-100, the binding of a battery of purified recombinant apo(a) [r-apo(a)] species to immobilized human LDL has been assessed. The 17K form of r-apo(a) (containing all 10 types of kringle IV sequences) as well as other truncated r-apo(a) derivatives exhibited specific binding to a single class of sites on immobilized LDL, with Kd values ranging from approximately 340 nM (12K) to approximately 7900 nM (KIV5-8). The contribution of kringle IV types 6-8 to the noncovalent interaction of r-apo(a) with LDL was demonstrated by the decrease in binding affinity observed upon sequential removal of these kringle domains (Kd approximately 700 nM for KIV6-P, Kd approximately 2000 nM for KIV7-P, Kd approximately 5100 nM for KIV8-P, and no detectable specific binding of KIV9-P). Interestingly, KIV9 also appears to participate in the noncovalent binding of apo(a) to LDL since the binding of KIV5-8 (Kd approximately 7900 nM) was considerably weaker than that of KIV5-9 (Kd approximately 2000 nM). Finally, it is demonstrated that inhibition of Lp(a) assembly by proline, lysine, and lysine analogues, as well as by arginine and phenylalanine, is due to their ability to inhibit noncovalent association of apo(a) and apoB-100 and that these compounds directly exert their effects primarily through interactions with sequences contained within apo(a) kringle IV types 6-8. On the basis of the obtained data, a model is proposed for the interaction of apo(a) and LDL in which apo(a) contacts the single high-affinity binding site on apoB-100 through multiple, discrete interactions mediated primarily by kringle IV types 6-8.     

Immunoreactivity of apolipoprotein B-100 and binding to LDL-receptor of phospholipase A2-treated low density lipoproteins

Lipid--protein particles were obtained by treatment of low density lipoproteins (LDL) with phospholipase A2 from bee venom. Under these conditions, half of the phosphatidylcholine (PC) of LDL was changed to lysophosphatidylcholine (LPC). At the same time, the composition of other lipids and the apoprotein structure were unaffected. Three monoclonal antibodies (MAbs) against various apo B epitopes were used to test immunoreactivity of phospholipase A2-treated LDL (pl-LDL). The apo B epitope interacting with MAb 4C11 (amino acid residues 2377-2658) showed significantly decreased immunoreactivity. Increase in MAb 4C11 binding was demonstrated to depend on oxidation degree of LDL. Thus, changing of half of PC to LPC modified apo B translocation in the lipoprotein globule in an opposite manner as compared with changes induced by oxidative modification. A minor increase in immunoreactivity of pl-LDL with 1D1 MAb against a large middle part of apo B (residues 1297-3249) may be due to the effect of the change of surface lipid composition on the extent of immersion of apo B into the hydrophobic phase. No changes in the interaction of pl-LDL with MAb 2G8 (residues 3748-4306) were observed in comparison with native LDL. This fact demonstrates that 50% phospholipolysis of LDL does not affect the expression of apo B C-terminal residues in pl-LDL. Twofold increase in pl-LDL affinity to immobilized LDL-receptor was shown in contrast to LDL. The data indicate that LPC accumulation in LDL results in better elimination of LDL from the blood stream than in case of accumulation of oxidative products.     

The microsomal triglyceride transfer protein catalyzes the post-translational assembly of apolipoprotein B-100 very low density lipoprotein in McA-RH7777 cells

In cells in which the lipoprotein assembly process had been inactivated by brefeldin A (BFA), membrane-associated apoB-100 disappeared without forming lipoproteins or being secreted, indicating that it was degraded. Reactivation of the assembly process by chasing the cells in the absence of BFA, gave rise to a quantitative recovery of the membrane-associated apoB-100 in the very low density lipoprotein (VLDL) fraction in the medium. These results indicate that the membrane-associated apoB-100 can be converted to VLDL. A new method was developed by which the major amount (88%) of microsomal apoB-100 but not integral membrane proteins could be extracted. The major effect of this method was to increase the recovery of apoB-100 that banded in the LDL and HDL density regions, suggesting that the membrane-associated form of apoB-100 is partially lipidated. We also investigated the role of the microsomal triglyceride transfer protein (MTP) in the assembly of apoB-100 VLDL using a photoactivatable MTP inhibitor (BMS-192951). This compound strongly inhibited the assembly and secretion of apoB-100 VLDL when present during the translation of the protein. To investigate the importance of MTP during the later stages in the assembly process, the cells were preincubated with BFA (to reversibly inhibit the assembly of apoB-100 VLDL) and pulse-labeled (+BFA) and chased (+BFA) for 30 min to obtain full-length apoB-100 associated with the microsomal membrane. Inhibition of MTP after the 30-min chase blocked assembly of VLDL. This indicates that MTP is important for the conversion of full-length apoB-100 into VLDL. Results from experiments in which a second chase (-BFA) was introduced before the inactivation of MTP indicated that only early events in this conversion of full-length apoB-100 into VLDL were blocked by the MTP inhibitor. Together these results indicate that there is a MTP-dependent "window" in the VLDL assembly process that occurs after the completion of apoB-100 but before the major amount of lipids is added to the VLDL particle. Thus the assembly of apoB-100 VLDL from membrane-associated apoB-100 involves an early MTP-dependent phase and a late MTP-independent phase, during which the major amount of lipid is added.     

Salt-wasting congenital adrenal hyperplasia: detection of mutations in CYP21B gene in a Chilean population

The steroid 21-hydroxylase deficiency (21OHD) is the most frequent cause of congenital adrenal hyperplasia. We have characterized the disease-causing mutations in the 21-hydroxylase genes of 63 patients with salt-wasting congenital adrenal hyperplasia from a Chilean population of Hispanic origin, a group that has been scarcely evaluated. Using allele-specific PCR, lesions were identified in 97 chromosomes out of 126 tested (77%). The most frequent findings were the gene deletion or large gene conversion (LGC) = 22.9%, I2 splice = 19%, R357W = 12.7%, and Q319X = 10.5%. We did not find alleles with the mutation F308insT and we found three alleles with the cluster E6. The frequency of the point mutation R357W was at least two times more frequent than the one found in Caucasians populations, but similar to that communicated in Asian populations; this finding may be explained by the Asian ancestry of our South-Amerindian population. The frequency of Q319X was also high, similar only to those patients studied in Italy and in a neighboring Argentinian population. In summary, this is a genetic characterization of 21OHD made in an almost pure Hispanic population in Latin America. The high frequency of deletion of CYP21B gene, I2 splice, R357W, and Q319X mutations probably reflects the European-Caucasian-Spanish influence of the conquerors, mixed with Amerindians of Asian ancestry and modulated by other European immigrations.     

Inhibition of N-linked glycosylation results in retention of intracellular apo[a] in hepatoma cells, although nonglycosylated and immature forms of apolipoprotein[a] are competent to associate with apolipoprotein B-100 in vitro

Apolipoprotein[a] (apo[a]) is a highly polymorphic glycoprotein that forms a covalent complex with apolipoprotein B-100 (apoB-100), producing a lipoprotein species referred to as lipoprotein[a] (Lp[a]). We have studied the effects of alterations in glycosylation of apo[a] on its intracellular processing and secretion as well as its ability to associate with low density lipoprotein (LDL) apoB-100. HepG2 cells transfected with a 6 kringle IV (6 K-IV) apo[a] minigene were treated with tunicamycin, an inhibitor of N-linked glycosylation, which eliminated apo[a]-B-100 complexes from the media. Tunicamycin treatment also reduced secretion of the 6 K-IV apo[a] protein from transfected McA-RH7777 cells by approximately 50%, but completely eliminated secretion of apo[a] species containing 9 and 17 K-IV repeats. Mixing experiments, performed with radiolabeled media (+/-tunicamycin) from transfected McA-RH7777 cells, demonstrated no alteration in the extent of association of apo[a] with human LDL. Similar mixing experiments using culture media from glycosylation-defective mutant chinese hamster ovary (CHO) cells transfected with the same apo[a] minigene showed identical results. Apo[a] secretion was demonstrated in all mutant cell lines in the absence of either N- or O-linked (or both) glycosylation. The mechanisms underlying the reduced secretion of apo[a] from transfected hepatoma cells were examined by pulse-chase radiolabeling and apo[a] immunoprecipitation. Tunicamycin treatment altered the efficiency of precursor apo[a] processing from the ER by increasing its ER retention time. The increased accumulation of precursor apo[a] in the ER was associated with alterations in the kinetics of association with two resident endoplasmic reticulum (ER) chaperone proteins, calnexin and BiP. These findings suggest that the glycosylation state and size of apo[a] appear to play a role in regulating its efficient exit from the endoplasmic reticulum. However, neither N- nor O-linked glycosylation of apo[a] exerts a major regulatory role in its covalent association with apoB-100.     

Genetic variability of apolipoprotein E in a Polish population

Apolipoprotein E (apoE, protein; APOE, gene) is a component of very low density lipoprotein and high-density lipoprotein and plays an important role in lipoprotein metabolism. There are three common alleles of APOE (*2, *3, and *4), which encode the E2, E3, and E4 isoforms of the protein. Distribution of apoE isoforms shows marked variation among various ethnic groups. Direct phenotyping of human APOE in plasma was used to estimate APOE allele frequencies in 137 unrelated blood donors from 3 regions of Poland. The relative frequencies observed for the APOE*2, APOE*3, and APOE*4 alleles were 0.055, 0.839, and 0.106, respectively. The data have been compared with data found in other population groups. The frequency of the APOE*2 allele in Poles was among the lowest in Europe.     

Lack of association of the apolipoprotein A-I-C-III-A-IV gene XmnI and SstI polymorphisms and of the lipoprotein lipase gene mutations in familial combined hyperlipoproteinemia in French Canadian subjects

Familial combined hyperlipoproteinemia (FCH) is a common familial lipoprotein disorder characterized by elevated plasma cholesterol and triglyceride levels with segregation in first-degree relatives. Most affected subjects with FCH have elevated plasma levels of apolipoprotein (apo) B. The disorder results from oversecretion of hepatic apoB-containing lipoprotein particles. The genetic defect(s) are unknown. Previous work has suggested that genetic polymorphisms of the apoA-I gene and functional abnormalities of the lipoprotein lipase (LPL) gene are associated with FCH. We investigated the XmnI and SstI restriction fragment length polymorphisms (RFLP) of the apoA-I gene in FCH subjects of French Canadian descent. We also investigated three common functional mutations of the lipoprotein lipase (LPL) gene (LPLGly188Glu, LPLPro207Leu, and LPLAsp250Asn) in French Canadians that account for approximately 97% of cases of complete LPL deficiency in the province of Québec, Canada. We identified and characterized 54 FCH probands in lipid clinics and examined at least one first-degree relative. There were 37 men and 17 women (mean age 48 +/- 9 and 58 +/- 8 years, respectively). None of the probands had diabetes mellitus; mean plasma glucose was 5.5 mmol/L. High blood pressure was diagnosed in 32% of men and 29% of women. The body mass index (weight (kg)/height(m2)) was elevated in probands (27 +/- 4 for men and 26 +/- 4 for women). Mean plasma levels of cholesterol (C) was 7.6 +/- 1.5 mmol/L, triglycerides 3.5 +/- 1.6 mmol/L, LDL-C 4.9 +/- 1.2 mmol/L, HDL-C 1.0 +/- 0.3 mmol/L, and apoB 1.83 +/- 0.67 g/L in the probands. Allele frequency of the rare alleles of the XmnI and SstI RFLP was not significantly different from a healthy reference group. In several families studied, the XmnI and SstI RFLP did not unequivocally segregate with the FCH phenotype. There was no significant effect of the presence or absence of the XmnI or SstI RFLP's on plasma lipids, lipoprotein cholesterol or apoB levels. Only one FCH proband was found to have a mutation of the LPL gene (Gly188Glu), and this did not segregate with the FCH phenotype in the family. We conclude that in our highly selected group of FCH subjects of French Canadian descent, the XmnI and SstI RFLPs of the apoA-I gene and common functional mutations of the LPL gene resulting in complete LPL deficiency are not associated with FCH.     

Familial Mediterranean fever at the millennium. Clinical spectrum, ancient mutations, and a survey of 100 American referrals to the National Institutes of Health

Regarded as the most common and best understood of the hereditary periodic fever syndromes, familial Mediterranean fever (FMF) is a recessively inherited disease of episodic fever with some combination of severe abdominal pain, pleurisy, arthritis, and a characteristic ankle rash. The flares typically last for up to 3 days at a time, and most patients are completely asymptomatic between attacks; if untreated with prophylactic colchicine, some patients later develop amyloidosis and renal failure. The recent cloning of the FMF gene on the short arm of chromosome 16p, and the subsequent finding that its tissue expression is limited to granulocytes, has helped to explain the dramatic accumulation of neutrophils at the symptomatic serosal sites; the wild-type gene likely acts as an upregulator of an anti-inflammatory molecule or as a downregulator of a pro-inflammatory molecule. For nearly half a century, FMF was thought to cluster primarily in non-Ashkenazi Jews, Arabs, Armenians, and Turks, although the screening of the 8 known mutations in an American cohort has identified substantial numbers of people from the Ashkenazi Jewish and Italian populations in the United States who also have this disease. Nevertheless, the symptoms often go unrecognized and patients remain undiagnosed for years, not receiving the highly efficacious colchicine therapy; their histories often include multiple laparotomies, laparoscopies, and psychiatric evaluations. The combinations of clinical manifestations among FMF patients are quite heterogeneous, but our American cohort did not establish any connections between individual mutations and specific clinical pictures--as is seen in other diseases like cystic fibrosis, in which distinct genotypes target certain organ systems. Specifically, the data from our American series are insufficient to evaluate the hypothesis that the M694V/M694V genotype confers a more severe phenotype, or increases the risk of amyloidosis; but both our data and the recent literature (160) indicate that amyloidosis can occur in FMF patients with only 1 copy, or no copies, of the M694V mutation. It appears that specific MEFV mutations are probably not the sole determinants of phenotype, and that unknown environmental factors or modifying genes act as accomplices in this disease. Although we hope the discovery of the FMF gene will allow the diagnosis of FMF to become genetically accurate, the reality is that both clinical and genetic tools must still be used together unless mutations are identified on both of a patient's chromosomes. Physicians should be careful not to rule out the diagnosis in patients of high-risk ethnic backgrounds just because of atypical clinical features, as our data indicate that MEFV mutations are sometimes demonstrable in such patients. At the same time, physicians cannot yet rely solely on a genetic diagnosis because we have not yet identified a sufficient spectrum of mutations, and it is not currently feasible to examine every patient's full DNA sequence for the entire gene; screening an ethnically consistent and clinically positive patient for the 8 known mutations frequently identifies a mutation on only 1 chromosome, and genetic analysis of other classic cases will often reveal none of the 8 mutations. Still, our data suggest that ethnic background is an important predictor of finding 1 of the presently known mutations, and the knowledge of ancestries atypical for FMF can suggest the diagnosis of other hereditary periodic fever syndromes. As the list of FMF-associated MEFV mutations is expanded, and/or new sequencing technologies permit more rapid screening, the value and interpretation of genetic testing for FMF will become more straightforward. Moreover, as the pathophysiology of this disorder becomes less of a hypothesis and more of an understood entity, it is likely that treatment options will broaden beyond the use of daily prophylactic colchicine. (ABSTRACT TRUNCATED)     

Familial persistent hyperinsulinemic hypoglycemia of infancy and mutations in the sulfonylurea receptor

BACKGROUND: Corneal HLA-DR antigens are going to be lost during organ culture storage. This study investigated if this phenomenon is based on down-regulation of the HLA-DR antigen, or on a loss of the HLA-DR-positive corneal Langerhans cells (LCs). MATERIAL AND METHODS: Corneal LCs were stained in situ by the method of fluorescence-associated immunohistochemistry, and the organ culture mediums underwent flow cytometric analysis for HLA-DR-positive corneal LC at the end of the storage period. RESULTS: All stored corneas were negative for HLA-DR after 14 days and HLA-DR antigens could be detected in culture medium at the end of the storage time. CONCLUSION: Flow cytometry showed that organ culture storage leads to loss of HLA-DR-positive cells and not only to a loss of antigen presentation.     

Familial aggregation of colorectal cancer in the general population

To investigate the familial aggregation of colorectal cancer in Denmark, parents and siblings of colorectal cancer patients diagnosed below age 60 years in the years 1982-1984 were identified through population registries. For 1,470 probands with families eligible for tracing, 1,376 mothers, 1,303 fathers and 3,259 siblings were identified. They contributed 222,634 person-years, and 325 cases of colorectal cancer were observed during the follow-up period 1943-1992. All data were retrieved from population registries and consequently were free from any reporting bias. The overall standardized morbidity ratio (SMR) compared with the Danish population was 2.02 (95% confidence interval [CI] 1.81-2.25), significantly different between the parents (1.78, 95% CI 1.55-2.04) and the siblings (2.65, 95% CI 2.21-3.17). A strong dependence on the proband's age at diagnosis was seen for the sibling risk; siblings of probands less than 50 years old at diagnosis had a 5-fold risk compared with the general population. This dependence was not seen for parents, but the risk tended to be higher for parents of younger ages. No other factor was seen to influence the relative risk. The observation of an 80% increased risk among the parents and a 170% increased risk among the siblings indicates that the genetic component is one source, but probably not the only one, of familial aggregation of colorectal cancer. The cost benefit of screening siblings of colorectal cancer patients is substantially higher than that for the total population.     

A simultaneous study of the metabolism of apolipoprotein B and albumin in nephrotic patients

BACKGROUND: The nephrotic syndrome is characterized by proteinuria, hypoalbuminemia and hyperlipidemia. Despite intensive research it is not clear at present what the causal links are between these pathological findings. METHODS: Stable isotope labeled amino acid tracer kinetic analysis was used to simultaneously investigate the metabolism of four apolipoprotein B-containing lipoproteins (VLDL1, VLDL2, IDL and LDL) and albumin in seven patients with nephrotic syndrome and marked hypercholesterolemia, in two additional nephrotic patients with concomitant renal failure and mixed hyperlipidemia, and in a matched group of normolipidemic controls. RESULTS: Increased concentrations of VLDL2, IDL and LDL were due to (a) impaired VLDL2 and IDL delipidation, (b) reduced LDL catabolism, and (c) a trend towards an increased rate of total apolipoprotein B production. The rate of fractional albumin elimination was three times higher in patients than in controls and the rate of albumin synthesis was increased by 45%. No correlations were detectable between rates of apolipoprotein B production and the rate of albumin synthesis. CONCLUSIONS: The results of this study suggest that hyperlipidemia in nephrotic syndrome is predominantly the result of delayed lipoprotein delipidation and catabolism. There is no evidence that it is driven by a general increase of the rate of hepatic protein synthesis.     

Four new mutations in the apolipoprotein B gene causing hypobetalipoproteinemia, including two different frameshift mutations that yield truncated apolipoprotein B proteins of identical length

Magnetic resonance imaging is frequently complicated by the presence of motion and susceptibility gradients. Also, some biologic tissues have short T2s. These problems are particularly troublesome in fast spin-echo (FSE) imaging, in which T2 decay and motion between echoes result in image blurring and ghost artifacts. The authors reduced TE in conventional spin-echo (SE) imaging to 5 msec and echo spacing (E-space) in FSE imaging to 6 msec. All magnetic gradients (except readout) were kept at a maximum, with data sampling as fast as 125 kHz and only ramp waveforms used. Truncated sinc radio-frequency pulses and asymmetric echo sampling were also used in SE imaging. Short TE (5.8 msec) SE images of the upper abdomen were compared with conventional SE images (TE = 11 msec). Also, FSE images with short E-space were compared with conventional FSE images in multiple body sites. Short TE significantly improved the liver-spleen contrast-to-total noise ratio (C/N) (7.9 vs 4.1, n = 9, P < .01) on T1-weighted SE images, reduced the intensity of ghost artifacts (by 34%, P < .02), and increased the number of available imaging planes by 30%. It also improved delineation of cranial nerves and reduced susceptibility artifacts. On short E-space FSE images, spine, lung, upper abdomen, and musculoskeletal tissues appeared crisper and measured spleen-liver C/N increased significantly (6.9 vs 4.0, n = 12, P < .01). The delineation of tissues with short T2 (eg, cartilage) and motion artifact suppression were also improved. Short TE methods can improve image quality in both SE and FSE imaging and merit further clinical evaluation.     

Arylsulfatase A pseudodeficiency-associated mutations: population studies and identification of a novel haplotype

Pseudodeficiency of arylsulfatase A is characterized by reduction of arylsulfatase A activity without neurodegeneration, making it an important complication when diagnosing metachromatic leukodystrophy. Two DNA substitutions are associated with arylsulfatase A pseudodeficiency. One, 1788A-->G, results in the loss of an N-glycosylated asparagine in the protein, and the second, 2723A-->G, removes the polyadenylation signal site of the mRNA. Previously, the polyadenylation signal site variant was observed only in the presence of the N-glycosylation site variant, although the latter has been reported to occur in the absence of the polyadenylation signal site variant. We investigated the frequencies of these alleles and their linkage disequilibrium in a number of populations and in psychiatric patients. While the N-glycosylation site variant had a high frequency in the Bantu-speaking people from Southern Africa (0.44), the San of Southern Africa (0.22), African Americans (0.37), and Cheyenne Indians (0.375), the polyadenylation signal site variant was absent in these groups. The mutated polyadenylation signal site was found only in the Caucasian groups surveyed. Two Caucasian sibs were identified with the pseudodeficiency polyadenylation signal site variant in the absence of the N-glycosylation site variant, indicating that linkage disequilibrium between the two polymorphisms is not perfect.     

Modulation of the expression of human LDL-Apo B-100 epitopes by lipids and apolipoproteins

The purpose of the present study was to determine the immunochemical properties of apolipoprotein (apo) B-100 associated with low density lipoprotein (LDL) in relation to lipid and apolipoprotein composition. LDLs were isolated by sequential ultracentrifugation (1.019 < d < 1.050 g/mL) from two healthy volunteers and 21 dyslipidemic patients to obtain heterogeneous samples of LDL. Lipid (free cholesterol, cholesteryl esters, triglycerides, and phospholipids) and apolipoprotein contents (apo B, apo C-III, apo E) were determined in each LDL sample. Immunoreactivities of apo B were tested in solid-phase competitive-binding radioimmunoassays using seven monoclonal anti-LDL antibodies that reacted with defined epitopes of apo B-100. The relation between lipid and/or protein variables and the immunoreactivity of apo B was evaluated by successive use of Spearman's rank simple correlation, partial correlation, and canonical correlation analyses. The canonical correlation analysis showed that apo B-100 immunoreactivity on LDL is highly dependent on lipid and apolipoprotein composition simultaneously. The results confirmed the influence of surface and core lipids on the expression of the apo B-100 epitopes, independent of their location on the molecule. However, the lipid requirement of LDL strongly influences the expression of epitopes mapped in the LDL receptor-recognition domain. In contrast to apo E, apo C-III does not seem to influence the expression of the apo B-100 epitopes in the LDL range studied.(ABSTRACT TRUNCATED AT 250 WORDS)