Variation at position 162 of peroxisome proliferator-activated receptor alpha does not influence the effect of fibrates on cholesterol or triacylglycerol concentrations in hyperlipidaemic subjects.

The fibrate group of drugs are widely used to lower plasma lipid concentrations, especially in diabetic subjects. They exert their effects by activating peroxisome proliferator-activated receptor alpha (PPARalpha), which regulates the transcription of a number of genes involved in hepatic lipid metabolism. The discovery of polymorphisms in the PPARalpha gene raises the possibility that different variants could be associated with different responses to fibrate therapy. We have examined this in a random sample of 96 lipid clinic subjects who showed a wide range of response to fibrates. Of the known polymorphisms in PPARalpha, the only difference detected in this sample was the Leu/Val change at position 162. However, this change did not influence baseline plasma cholesterol or triacylglycerol concentrations, and was not associated with any difference in the effectiveness of fibrate treatment. Thus, there is no evidence that variation in the PPARalpha gene at position 162 is responsible for the differential response to fibrates in non-diabetic hyperlipidaemic subjects.

Polymerase chain reaction for screening clinical isolates of corynebacteria for the production of diphtheria toxin.

AIMS: To assess the performance of the polymerase chain reaction (PCR) when used to screen rapidly large numbers of corynebacteria for toxin production; and to determine the incidence of false positive PCR results with non-toxigenic Corynebacterium diphtheriae isolates. METHODS: Eighty seven recent British isolates of corynebacteria were assayed by PCR. All isolates were assayed from both blood and tellurite agar within a five day period. Thirty three non-toxigenic isolates of C diphtheriae from six countries were also tested by PCR and by the Elek immunodiffusion assay. RESULTS: There was complete concordance between the results of PCR and traditional methods on the recent British isolates, with one exception: an Elek positive "C ulcerans" isolate, which was PCR positive from tellurite but not from blood agar. One of the thirty three (3%) non-toxigenic isolates of C diphtheriae was PCR positive. CONCLUSIONS: These results suggest that PCR compares favourably with traditional methods for the detection of toxigenic corynebacteria and that it represents a powerful new tool in the diagnosis of an old disease.

Polymorphisms in the apolipoprotein(a) gene and their relationship to allele size and plasma lipoprotein(a) concentration.

Genotypes at five previously described polymorphic sites at the apolipoprotein(a) gene locus have been determined for the members of 27 families as well as for unrelated white Caucasian and Asian-Indian subjects, and their relationship with isoform size and plasma lipoprotein(a) concentrations investigated. There was strong linkage disequilibrium between sites at the 5'-region of the gene and also between this region and a site in the coding sequence for Kringle 4-37 on the other side of the polymorphic Kringle 4 repeat region. There was no evidence that changes at any of the sites had any direct effect upon lipoprotein(a) concentration. However, certain haplotypes were present almost exclusively on apolipoprotein(a) alleles within a restricted range of sizes and associated lipoprotein(a) concentrations. After correcting for the effect of allele size, there were clear differences between the lipoprotein(a) concentrations associated with alleles of different haplotypes, suggesting that there may be genetically distinct groups of apolipoprotein alleles of different size and different levels of expression. Factors that regulate expression apparently exchange at a rate similar to the rate of change of Kringle 4 repeat number.

Characterization of multiple enhancer regions upstream of the apolipoprotein(a) gene.

Plasma concentrations of the atherogenic lipoprotein(a) (Lp(a)) are predominantly determined by inherited sequences within or closely linked to the apolipoprotein(a) gene locus. Much of the interindividual variability in Lp(a) levels is likely to originate at the level of apo(a) gene transcription. However, the liver-specific apo(a) basal promoter is extremely weak and does not exhibit common functional variations that affect plasma Lp(a) concentrations. In a search for additional apo(a) gene control elements, we have identified two fragments with enhancer activity within the 40-kilobase pair apo(a)-plasminogen intergenic region that coincide with DNase I-hypersensitive sites (DHII and DHIII) observed in liver chromatin of mice expressing a human apo(a) transgene. Neither enhancer exhibits tissue specificity. DHIII activity was mapped to a 600-base pair fragment containing nine DNase I-protected elements (footprints) that stimulates luciferase expression from the apo(a) promoter 10-15-fold in HepG2 cells. Binding of the ubiquitous transcription factor Sp1 plays a major role in the function of this enhancer, but no single site was indispensable for activity. DHIII comprises part of the regulatory region of an inactive long interspersed nucleotide element 1 retrotransposon, raising the possibility that retrotransposon insertion can influence the regulation of adjacent genes. DHII enhancer activity was localized to a 180-base pair fragment that stimulates transcription from the apo(a) promoter 4-8-fold in HepG2 cells. Mutations within an Sp1 site or either of two elements composed of direct repeats of the nuclear hormone receptor half-site AGGTCA in this sequence completely abolished enhancer function. Both nuclear hormone receptor elements were shown to bind peroxisome proliferator-activated receptors and other members of the nuclear receptor family, suggesting that this enhancer may mediate drug and hormone responsiveness.