Frequency of the XbaI, EcoRI, PvuII and MspI polymorphisms of the apolipoprotein B gene in relation to hypercholesterolaemia in the general population.

In this study the frequencies of the genotypes of four restriction fragment length polymorphisms in the apolipoprotein B gene (XbaI, EcoRI, PvuII and MspI) are compared between groups of normolipidaemic and diet resistant hypercholesterolaemic individuals as possible markers for the influence of this gene on plasma cholesterol levels. In the first part of the study genotypes of all four markers were determined in 92 normolipidaemic (mean cholesterol 5.6 + 0.8 mmol/l) and 79 diet resistant hypercholesterolaemic (mean cholesterol 7.8 + 0.7 mmol/l) individuals seen in a local health centre screening programme for coronary heart disease risk factors. No significant difference was seen in the frequencies of the EcoRI and PvuII genotypes between the two groups. There was significant enrichment of both the XbaI X2 (presence of cutting site) allelic frequency and of the MspI M1M2 (M2 absence of cutting site, rarer allele) genotype frequency in the hypercholesterolaemic group. In the second part of the study an independent larger group of individuals, seen in a multicentre screening programme across the city of Glasgow, were genotyped for the two potentially significant polymorphic sites (XbaI and MspI). From this second screening programme 188 age matched normolipidaemic males (mean cholesterol 5.0 +/- 0.8 mmol/l) were compared with 186 males who were still hypercholesterolaemic (mean 8.2 +/- 0.6 mmol/l) after three months dietary intervention. The hypercholesterolaemic individuals in this second study did not show a significant enrichment of the XbaI X2 allele but again showed a highly significant enrichment of the MspI M1M2 genotype. This genetic effect may relate directly to the charge change from arginine to glutamine at amino acid 3611 caused by the MspI mutation or to an as yet unknown functionally significant mutation in linkage disequilibrium with this site.

A novel truncated apolipoprotein B (apo B55) in a patient with familial hypobetalipoproteinemia and atypical retinitis pigmentosa.

We have identified an apolipoprotein (apo) B mutation in a patient with an atypical form of retinitis pigmentosa (RP). In the family the eye disease is characterised by late age of onset and autosomal dominant inheritance. In addition to RP, the proband has low total cholesterol (4.5 mmol/l) and LDL-cholesterol (2.0 mmol/l) levels characteristic of the autosomal codominant apolipoprotein (apo) B deficiency disease hypobetalipoproteinemia (HBL). Using a monoclonal antibody directly against apo B and immunoblots of SDS polyacrylamide gel separated plasma, a normal apo B100 and a truncated apo B species with an estimated size of apo B54 was identified in the proband and his RP-affected sister. The location of the mutation in the apo B gene was identified using chemical cleavage of mismatch and this was confirmed by direct sequencing of an amplified fragment of DNA spanning the estimated site of the mutation. The mutation is a C----T transition at nucleotide 7692 which changes the CGA arginine2495 codon to a STOP codon resulting in the premature termination of apo B100. The truncated apo B protein is 2494 amino acids long with a predicted size of apo B55. Using allele specific oligonucleotides and oligonucleotide melting techniques, the proband, his sister and two other relatives out of a total of 20 family members, screened for the presence of the apo B55 mutation, were heterozygous for the mutation. The segregation of the apo B55 allele was confirmed in the family using the 3' variable number of tandem repeats of the apo B gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma triglyceride and low density lipoprotein metabolism.

This study examines the relationship between plasma triglyceride and low density lipoprotein (LDL) levels by measuring the turnover of the native and 1,2 cyclohexanedione-treated lipoprotein in 25 healthy adults. Plasma triglyceride showed a strong positive correlation with circulating LDL apoprotein (apo LDL) mass. In order to achieve a satisfactory fit to the kinetic data it was necessary to postulate the existence of two plasma apo LDL pools (A and B). When subjects were grouped in quintiles on the basis of circulating apo LDL mass, pool A predominated in those in the lowest quintile. The fractional catabolic rate (FCR) of apo LDL from this pool was high (FCR = 0.57 +/- 0.06 pools day-1). As plasma triglyceride and apo LDL mass rose, apoprotein accumulated in the more slowly metabolized pool B as a result of an increase in the rate of input of apo LDL into the latter. The fractional clearance rate of protein from this pool remained unchanged at 0.26 +/- 0.04 pools day-1. Synthesis of apo LDL into pool B correlated with plasma triglyceride (r = 0.553, P less than 0.01), suggesting that the protein in this pool was derived from large, triglyceride-rich very low density lipoprotein.

Acipimox in combination with low dose cholestyramine for the treatment of type II hyperlipidaemia.

1. This study was designed to examine the effects of acipimox 250 mg three times daily and cholestyramine 4 g three times daily on plasma lipids and lipoproteins in 28 hypercholesterolaemic individuals in a prospective double-blind placebo controlled parallel group fashion. 2. Combined treatment with the two agents produced a mean reduction of 27% in plasma total cholesterol and a 32% fall in LDL cholesterol. Plasma triglyceride was reduced by 13% due to a 38% decrement in VLDL cholesterol. 3. In comparison treatment with cholestyramine alone resulted in a 12% fall in plasma cholesterol and a 15% fall in LDL cholesterol. In this group triglycerides and VLDL showed no significant change. 4. Studies of HDL subfraction mass showed that the addition of acipimox to resin therapy produced a mean increment of 45% in HDL2. 5. These results demonstrate the effectiveness of such a well tolerated low dosage combination therapy.

The relationship between serum cholesterol and serum thyrotropin, thyroxine and tri-iodothyronine concentrations in suspected hypothyroidism.

The relationship between serum cholesterol, thyrotropin, thyroxine and tri-iodothyronine was investigated in 1018 female patients over 40 years of age with suspected hypothyroidism. The correlation between serum thyrotropin and cholesterol (r = 0.398) and between thyroxine and cholesterol (r = -0.217) were both highly significant (P less than 0.001), but the correlation between tri-iodothyronine and cholesterol (r = -0.011) was not significant. Only in patients with a serum thyrotropin in excess of 40 mU/L was there a clinically appreciable increase in the serum cholesterol. In 139 patients treated for hypothyroidism by thyroxine replacement there was a highly significant correlation (P less than 0.001) between the decrease in serum thyrotropin and cholesterol (r = 0.593). The correlation between increase in serum thyroxine and decrease in cholesterol (r = -0.401) was also highly significant (P less than 0.001), but there was an even stronger correlation between the increase in serum tri-iodothyronine and the decrease in serum cholesterol (r = -0.529).

Effect of combined therapy with bezafibrate and cholestyramine on low-density lipoprotein metabolism in type IIa hypercholesterolemia.

This study was designed to examine the influence of combined therapy with bezafibrate and cholestyramine on plasma lipids and on the metabolism of low-density lipoprotein (LDL). Twenty-one type II hyperlipidemic subjects were treated with bezafibrate alone or in combination with cholestyramine. A 17% fall in plasma cholesterol was seen with bezafibrate, and addition of cholestyramine produced an additional 9% reduction in this lipid. The effectiveness of the combination therapy was mediated through a 47% decrement in very-low-density lipoprotein (VLDL) cholesterol, a 37% reduction in LDL cholesterol, and a 15% increase in the level of that lipid in high-density lipoprotein (HDL). Plasma triglyceride fell 43% when bezafibrate was given alone, and did not change further when cholestyramine was added. The metabolism of LDL was examined in nine individuals to determine the mechanism underlying these changes. No significant modification in LDL synthetic rate was incurred with either drug regimen, whereas the fractional catabolic rate of LDL via the receptor pathway rose by 66% with bezafibrate alone and by 79% (compared to baseline) following the addition of cholestyramine. Plasma HDL rose during bezafibrate therapy due to an increase in the HDL3 subfraction. Compositional analysis of LDL showed a reduction in cholesterol ester and an increase in triglyceride and phospholipid during combined drug therapy. These results demonstrate that combined therapy with bezafibrate and cholestyramine markedly improves the lipoprotein profile in type II hyperlipidemia. The drugs appear to be complementary in their actions upon the LDL receptor pathway.

Catabolic rate of low density lipoprotein is influenced by variation in the apolipoprotein B gene.

This study examines the potential influence of genetic variation on the metabolism of LDL. Restriction fragment length polymorphisms (RFLP) of the gene coding for apo B were identified using the endonucleases Xba I, Eco RI, and Msp I in a group of 19 subjects with moderate hyperlipidemia. There was a significant association between the Xba I polymorphism and the total fractional clearance rate (FCR) of LDL. The individuals with the X1X1 genotype had, on average, a 22% higher FCR (P less than 0.025) than those with the genotype X2X2 (X2 allele = presence of Xba I cutting site). This difference was attributable to increased clearance by the receptor-mediated pathway of LDL catabolism. In this group of subjects, there was no association of LDL kinetic parameters and RFLPs of the LDL receptor gene or the AI- CIII- AIV gene cluster. The data suggest that variation in apo B itself, presumably acting through variable binding to the LDL receptor, makes a significant contribution to the rate of catabolism of LDL.

Rapid, sensitive detection of plasma IL-1 by extraction and bioassay.

A method for separating IL-1 from plasma inhibitors by silica extraction has been developed and coupled to a highly sensitive bioassay using the LBRM TG6 cell line and the I1-2 dependent HT2A cell line. Using this assay we have detected IL-1 activity in plasma from patients undergoing elective surgery.

Thyroid dysfunction and hypercholesterolaemia in the general population of Glasgow, Scotland.

As part of a screening programme for coronary heart disease risk factors, fasting plasma cholesterol was measured in 2,250 people from the east-end of Glasgow. Plasma thyrotropin (TSH) was measured in the 90 individuals (4% of the population studied) who had a cholesterol level greater than or equal to 8.0 mmol/l. Four had unequivocal biochemical evidence of hypothyroidism-TSH greater than 34 mU/l and a low plasma thyroxine (T4) less than or equal to 45 nmol/l. A further 8 were found to have raised TSH levels suggesting they may have subclinical hypothyroidism. These data indicate that thyroid dysfunction may make a significant contribution to hypercholesterolaemia in the general population.

Influence of etofibrate on low density lipoprotein metabolism.

This study examined the effect of single dose etofibrate (1.0 g/day) on plasma lipids and lipoproteins in a group of eleven hypercholesterolemic individuals. The drug lowered plasma triglyceride and cholesterol by 32% and 14%, respectively (P less than 0.005). The cholesterol reduction came from a decrement in both VLDL and LDL. The cholesterol content of HDL did not change although its mass as determined by analytical ultracentrifugation rose by 29%. LDL metabolism was followed before and during drug therapy. Treatment increased catabolism of this lipoprotein by 14%, without affecting synthesis. The increased clearance resulted from activation (64%) of the LDL receptor pathway. There was a reciprocal decrease in the amount of lipoprotein channelled into the receptor-independent route.