P4402Effect of carnitine supplementation on progression of carotid plaque in the metabolic syndrome: the ECoM study

Background/Introduction

L-carnitine (L-C) has been investigated as a potential therapy for cardiovascular (CV) disease, but its direct effects on human atherosclerosis are unknown. Epidemiological studies suggest a possible reduction of CV risk factors following treatment, whereas animal studies have shown that L-C may increase pro-atherogenic metabolites.

Purpose

The purpose of this study was to determine whether L-C therapy led to atherosclerosis progression or regression by direct quantification of carotid atherosclerotic lesions in patients with metabolic syndrome (MetS).

Methods

This study was a Phase 2, prospective, parallel, double blinded, randomized, placebo-controlled, two-center trial. MetS was defined according to the International Diabetes Federation harmonized definition, where presence of any 3 of the 5 following risk factors constituted a diagnosis: elevated waist circumference; elevated triglycerides; reduced HDL or treated; elevated blood pressure or treated; elevated glucose or HbA1c or treated. Participants with a baseline carotid total plaque volume (TPV) ≥50 mm3 were randomized to placebo or 2 g L-C daily for 6 months. Plaque progression was quantified by 3D carotid ultrasound for change in TPV and reduction in vessel lumen area (% area stenosis, Fig. 1). Absolute differences were assessed on the raw scale, while percent change on the log scale. Analysis of covariance (ANCOVA) was used to assess within- and between-arm differences.

Results

Of the 177 participants randomized, 157 completed the study (L-C n=76, placebo n=81). No statistically significant difference between arms was found in the primary outcome (TPV). However, there was progression of plaque stenosis in the treatment arm: the L-C group had an increase in stenosis of 9.8% (p=0.01) higher than the placebo arm, and a 2.7% (p=0.03) greater absolute change. Total cholesterol and LDL levels (0.10 mmol/L and 0.05 mmol/L, respectively) were higher in the intervention arm compared to the placebo arm (−0.06 mmol/L and −0.07 mmol/L).

Figure 1

Conclusions

We observed progression of atherosclerosis with L-C therapy compared to placebo in patients with MetS. The clear lack of benefit of L-C therapy in this population raises serious concerns for its further use as a potential therapy. Given its association with pro-atherogenic metabolites our study offers further understanding of the atherosclerotic process.

Acknowledgement/Funding

Heart and Stroke Foundation of Canada

PIF1 DNA helicase from Saccharomyces cerevisiae. Biochemical characterization of the enzyme

Overexpressed PIF1 DNA helicase was purified from mitochondria to near homogeneity. Its ATPase and unwinding properties were characterized. The enzyme specifically utilizes ATP (or dATP) and MgCl2 (and to a lesser extent MnCl2). ATPase activity requires single-stranded DNA as an effector, duplex DNA being 100-fold less effective. The Keff, defined as the concentration of DNA required to achieve half-maximal ATPase activity, does not depend on single-stranded DNA length. Long duplex DNAs are poorly unwound and, moreover, dilution of the enzyme and its DNA substrate in the assay decreases DNA helicase activity. These data indicate that PIF1 helicase is a distributive enzyme, frequently turning from one DNA molecule to another. When forked substrates are used, unwinding by PIF1 is markedly stimulated. The enzyme has a sedimentation coefficient of 6.5 S, suggesting that it exists as a monomer in solution.

PIF1: a DNA helicase in yeast mitochondria

The PIF1 gene is involved in repair and recombination of mitochondrial DNA (mtDNA). In this study, the PIF1 gene product, which cannot be identified in normal yeast cells, has been overproduced from the GALI promoter to detectable protein levels. Location of PIF1 in mitochondria has been shown by immunoelectron microscopy and in vivo import experiments using ts mas1 mutants deficient in the mitochondrial matrix-localized processing protease. Overproduction of PIF1 protein in pif1 mutants restores mtDNA recombination proficiency but is toxic to yeast cells as observed by slower growth. The overproduced PIF1 protein, which is firmly associated with insoluble mitochondrial structures, has been partially purified in a mitochondrial nuclease deficient nuc1 strain by a procedure including solubilization by urea and renaturation by dialysis at alkaline pH. PIF1 is a single-stranded (ss) DNA-dependent ATPase and a DNA helicase which unwinds partially DNA duplexes in a 5' to 3' direction with respect to the ss DNA on which it binds first.

Cloning and sequencing of the PIF gene involved in repair and recombination of yeast mitochondrial DNA

The nuclear gene PIF of Saccharomyces cerevisiae is required for both repair of mitochondrial DNA (mtDNA) and recognition of a recombinogenic signal characterized by a 26-bp palindromic AT sequence in the ery region of mtDNA. This gene has been cloned in yeast by genetic complementation of pif mutants. Its chromosomal disruption does not destroy the genetic function of mitochondria. The nucleotide sequence of the 3.5-kb insert from a complementing plasmid reveals an open reading frame encoding a potential protein of 857 amino acids and Mr = 97,500. An ATP-binding domain is present in the central part of the gene and in the carboxy-terminal region a putative DNA-binding site is present. Its alpha helix-turn-alpha helix motif is found in DNA-binding proteins such as lambda and lactose repressors which recognize symmetric sequences. Significant amino acid homology is observed with yeast RAD3 and E. coli UvrD (helicase II) proteins which are required for excision repair of damaged DNA.