Genetics of atherosclerosis: the search for genes acting at the level of the vessel wall

A reduction of 3 g/day from a usual 9 g/day salt diet improves endothelial function and decreases endothelin-1 in a randomised cross_over study in normotensive overweight and obese subjects

BACKGROUND AND AIM

It is unclear if a modest reduction in dietary salt intake has beneficial effects on vascular function. The aim was to compare the effects of 9 g salt/day with 6 g salt/day intake on measures of vascular function and explore mechanisms of effect in overweight and obese adults.

METHODS

Twenty-five overweight/obese subjects (BMI 27-40 kg/m(2)) completed a randomised cross-over study of 6 weeks each on a reduced salt (RS) (6 g/day) and usual salt diet (US) (9 g/day). Flow-mediated-dilatation (FMD), 24 h blood pressure (BP), augmentation index (AIx), pulse wave velocity (PWV), plasma and urinary nitrate/nitrite, asymmetric dimethylarginine (ADMA), renin, aldosterone and endothelin-1 and vascular adhesion molecules were measured after 2 days and 6 weeks. Adherence to the diets was determined from two 24 h urine collections.

RESULTS

Urinary sodium excretion was 155 ± 58 mmol/24 h US vs 113 ± 45 mmol/24 h RS (p = 0.002). Following the RS diet there was a significant improvement in FMD from 3.5 ± 2.8% to 5.6 ± 2.8% (P < 0.001) and decrease in serum endothelin-1 from 1.45 ± 0.38 pg/ml to 1.25 ± 0.39 pg/ml (P < 0.05). Endothelium-independent vasodilatation was also significantly different between treatments (P < 0.05). AIx, PWV, serum ADMA and plasma and urinary nitrate/nitrite concentrations were not different between treatments. Change in FMD was related to the urinary sodium: creatinine ratio (r = -0.47, P < 0.05) and was independent of blood pressure. Aldosterone and renin were unchanged.

CONCLUSIONS

A small reduction in dietary salt intake of 3 g/day improves endothelial function in normotensive overweight and obese subjects. This response may be mediated by serum endothelin-1. This small reduction in salt had no effect on aldosterone and renin concentrations. This trial was registered with the Australian and New Zealand Clinical Trials Registry Unique Identifier: ACTRN12609000321246 http://www.anzctr.org.au/ACTRN12609000321246.aspx.

Smoking and atherosclerotic cardiovascular disease: Part I: atherosclerotic disease process

The normal endothelium inhibits platelet and leukocyte adhesion to the vascular surface maintaining a balance of profibrinolytic and prothrombotic activity. Endothelial function is assessed largely as endothelium-dependent vasomotion, partly based on the assumption that impaired endothelium-dependent vasodilation reflects the alteration of important endothelial functions. Atherosclerotic risk factors, such as hypercholesterolemia, hypertension, diabetes and smoking, are associated with endothelial dysfunction. In the diseased endothelium, the balance between pro- and antithrombotic, pro- and anti-inflammatory, pro- and antiadhesive or pro- and antioxidant effects shifts towards a proinflammatory, prothrombotic, pro-oxidative and proadhesive phenotype of the endothelium. A common mechanism underlying endothelial dysfunction is related to the increased vascular production of reactive oxygen species. Recent studies suggest that inflammation per se, and C-reactive protein in particular, may contribute directly to endothelial dysfunction. The loss of endothelial integrity is a hallmark of atherosclerosis and the causal possible link between each individual risk factor, the development of atherosclerosis and the subsequent clinical events, such as myocardial infarction or stroke.

Integrating genotypic and expression data in a segregating mouse population to identify 5-lipoxygenase as a susceptibility gene for obesity and bone traits

Forward genetic approaches to identify genes involved in complex traits such as common human diseases have met with limited success. Fine mapping of linkage regions and validation of positional candidates are time-consuming and not always successful. Here we detail a hybrid procedure to map loci involved in complex traits that leverages the strengths of forward and reverse genetic approaches. By integrating genotypic and expression data in a segregating mouse population, we show how clusters of expression quantitative trait loci linking to regions of the genome accurately reflect the underlying perturbation to the transcriptional network induced by DNA variations in genes that control the complex traits. By matching patterns of gene expression in a segregating population with expression responses induced by single-gene perturbation experiments, we show how genes controlling clusters of expression and clinical quantitative trait loci can be mapped directly. We demonstrate the utility of this approach by identifying 5-lipoxygenase as underlying previously identified quantitative trait loci in an F(2) cross between strains C57BL/6J and DBA/2J and showing that it has pleiotropic effects on body fat, lipid levels and bone density.

5-lipoxygenase and atherosclerosis

PURPOSE OF REVIEW

5-Lipoxygenase (5LO) was recently identified as a gene that makes an important contribution to atherosclerosis in mice and humans, but the underlying mechanism(s) remains unknown.

RECENT FINDINGS

Studies of the 5LO pathway in other disease areas suggest that 5LO could contribute to atherosclerosis at different levels, such as lesion initiation, growth and cellular proliferation within the lesion, and/or destabilization of plaques that can lead to their rupture.

SUMMARY

Recent advances in our understanding of how 5LO is involved in the atherosclerotic process will have important implications for diagnostic and therapeutic strategies in the future.