Human beta-myosin heavy chain mRNA prevalence is inversely related to the degree of methylation of regulatory elements.

OBJECTIVE: Methylation of cytosine in CG dinucleotides within regulatory elements is believed to silence gene expression. These dinucleotides occur in certain important regulatory elements in the promoter region of the human beta-myosin heavy chain (beta-MHC) gene. We therefore investigated whether methylation of these elements correlates with beta-MHC gene transcription in human 'expressing' (right atrial) and 'non-expressing' (peripheral blood leucocytes) cells. METHODS: We employed 2 techniques to assess promoter methylation: (i) analysis of the susceptibility to digestion of a particular CCGG restriction site in the promoter region when genomic DNA is cleaved with the restriction endonucleases MspI (methylation-insensitive) and HpaII (methylation-sensitive), and (ii) the bisulphite-PCR method to examine in detail the methylation patterns of 3 important regulatory elements that contain CG dinucleotides. beta-MHC mRNA expression in right atrium and leucocytes was assessed using reverse-transcription-PCR with specific primers that do not detect alpha-MHC cDNA. RESULTS: The digestion pattern observed with MspI or HpaII indicated that the CCGG site was almost completely methylated in leucocytes, but relatively unmethylated in atrial myocardium from the same patients. When methylation was examined with the bisulphite-PCR method we found a reciprocal relationship between the level of beta-MHC mRNA expression in leucocytes and atrial myocardium and the degree of methylation of CG dinucleotides in the 5' regulatory elements of the gene. CONCLUSIONS: Tissue-specific methylation of the human beta-MHC gene promoter may play a role in determining the pattern of expression of this gene. Furthermore, alteration of the level of methylation may underlie the changes in transcription of this gene that occur, for example, when atrial or ventricular myocardium hypertrophies.

Analysis of terfenadine in human plasma using microbore high-performace liquid chromatography-electrospray ionisation mass spectrometry.

An assay based on combined microbore high-performance liquid chromatography-positive ion electrospray ionisation mass spectrometry with selected ion recording has been developed for the measurement of the antihistamine drug terfenadine in human plasma. A deuterated analogue of terfenadine was synthesised for use as an internal standard and extraction of terfenadine was carried out on C18 solid phase extraction columns. The limit of detection of terfenadine in plasma is 0.1 ng/ml and the intra-assay coefficient of variation at 1 ng/ml is 10.1%. Plasma concentrations of terfenadine measured in six normal subjects following a 120 mg oral dose are reported.

The cardiac effects of terfenadine after inhibition of its metabolism by grapefruit juice.

OBJECTIVE: To determine whether the pharmacokinetics and electrocardiographic pharmacodynamics of terfenadine are affected by the concomitant administration of grapefruit juice. METHODS: Six healthy volunteers were recruited for a balanced cross-over study. Each volunteer received 120 mg terfenadine 30 min after drinking 300 ml of either water or freshly squeezed grapefruit juice. The alternative treatment was administered on the second study day 2 weeks later. Measurements of the area under the terfenadine plasma concentration-time curve (AUC), maximum terfenadine concentration (Cmax) and the time to maximum concentration (tmax) were made, and the corrected QT (QTc) interval was measured from the surface electrocardiogram. RESULTS: Terfenadine was quantifiable in plasma in all 6 subjects on both study days for up to 24 h post-dosing. The AUC of terfenadine was significantly increased by concomitant grapefruit administration (median values 40.6 vs 16.3 ng.ml-1.h), as was the Cmax (median values 7.2 vs 2.1 ng.ml-1). The tmax was not significantly increased and there was no significant change in the median QTc interval despite the increased terfenadine levels. The 95% confidence interval for the difference in the change in QTc interval at Cmax was -13 to +38 ms. CONCLUSION: Administration of grapefruit juice concomitantly with terfenadine may lead to an increase in terfenadine bioavailability, but the increase observed in this study did not lead to significant cardiotoxicity in normal subjects. However, this does not exclude the risk of cardiotoxicity in high-risk subjects given greater doses of grapefruit juice over longer periods of time.

Hypertensive cardiac hypertrophy--is genetic variance the missing link?

1. Hypertensive cardiac hypertrophy is a major independent predictor of adverse cardiovascular events. In man the cardiac response to increased afterload is very variable, even when ambulatory blood pressure monitoring is used. Analysis of breeding experiments using normotensive and hypertensive rat strains, human twin studies and other data indicate that genetic factors play a significant role in regulating cardiac mass; in other words, a large component of total variability is accounted for by genetic variance. 2. The observation that some patients with only mild-to-moderate hypertension exhibit gross left ventricular hypertrophy (LVH) similar to the inherited hypertrophic cardiomyopathies such as familial hypertrophic cardiomyopathy (FHC) and Friedreich's ataxia (FA) has prompted us to investigate the hypothesis that genetic factors associated with excessive myocardial hypertrophy, viz. mutations in FHC and FA genes alter the hypertrophic response of the heart to pressure overload. Here we review briefly three lines of study: (i) association analysis to test whether the allele frequencies differ in hypertensive patients with or without left ventricular hypertrophy; (ii) characterization of the cardiac manifestations of FA to understand the mechanism by which the heart is affected in a disease associated with pathology in a subgroup of neurons, and (iii) creation of transgenic models to facilitate the investigation of the interaction between hypertrophic stimuli and underlying genetic predisposition. 3. Information on the nature of the cardiac-mass-modifying genes involved may be useful not only for selecting high risk patients in strategies aimed at preventing the development of LVH, but also in opening new avenues of research on the reprogramming of cardiac myocytes to encourage them to hypertrophy in situations where cardiac muscle has been damaged or is hypoplastic.

Staphylococcal tricuspid valve endocarditis in patients with structurally normal hearts and no evidence of narcotic abuse.

We report four cases of staphylococcal tricuspid valve endocarditis in patients with structurally normal hearts and no evidence of intravenous drug abuse. The only risk factor was superficial skin sepsis in three of these patients. Medical therapy was successful in all four cases.