Single nucleotide polymorphisms in the CYP2J2 and CYP2C8 genes and the risk of hypertension :

Association studies offer a potentially powerful approach to identify genetic variants that influence susceptibility to common disease, but are plagued by the impression that they are not consistently reproducible. In principle, the inconsistency may be due to false positive studies, false negative studies or true variability in association among different populations. The critical question is whether false positives overwhelmingly explain the inconsistency. We analyzed 301 published studies covering 25 different reported associations. There was a large excess of studies replicating the first positive reports, inconsistent with the hypothesis of no true positive associations (P < 10(-14)). This excess of replications could not be reasonably explained by publication bias and was concentrated among 11 of the 25 associations. For 8 of these 11 associations, pooled analysis of follow-up studies yielded statistically significant replication of the first report, with modest estimated genetic effects. Thus, a sizable fraction (but under half) of reported associations have strong evidence of replication; for these, false negative, underpowered studies probably contribute to inconsistent replication. We conclude that there are probably many common variants in the human genome with modest but real effects on common disease risk, and that studies using large samples will convincingly identify such variants.

Assessing the association between DNA variants and disease has been used widely to identify regions of the genome and candidate genes that contribute to disease. However, there are numerous examples of associations that cannot be replicated, which has led to skepticism about the utility of the approach for common conditions. With the discovery of massive numbers of genetic markers and the development of better tools for genotyping, association studies will inevitably proliferate. Now is the time to consider critically the design of such studies, to avoid the mistakes of the past and to maximize their potential to identify new components of disease.

Endothelial cells release several compounds, including prostacyclin, NO, and endothelium-derived hyperpolarizing factor (EDHF), that mediate the vascular effects of vasoactive hormones. The identity of EDHF remains unknown. Since arachidonic acid causes endothelium-dependent relaxations of coronary arteries through its metabolism to epoxyeicosatrienoic acids (EETs) by cytochrome P450, we wondered if the EETs represent EDHFs. Precontracted bovine coronary arteries relaxed in an endothelium-dependent manner to methacholine. The cytochrome P450 inhibitors, SKF 525A and miconazole, significantly attenuated these relaxations. They were also inhibited by tetraethylammonium (TEA),an inhibitor of Ca2+-activated K+ channels, and by high [K+]0 (20 mmol/L). Methacholine also caused hyperpolarization of coronary smooth muscle (-27 +/- 3.9 versus -40 +/- 5.1 mV), which was completely blocked by SKF 525A and miconazole. In vessels prelabeled with [3H] arachidonic acid, methacholine stimulated the release of 6-ketoprostaglandin F1alpha, 12-HETE, and the EETs. Arachidonic acid relaxed precontracted coronary arteries, which were also blocked by TEA, charybdotoxin, another Ca2+-activated K+ channel inhibitor, and high [K+]0. 14,15-EET, 11,12-EET, 8,9-EET, and 5,6-EET relaxed precontracted coronary vessels (EC50, 1 X 10(-6) mol/L). The four regioisomers were equally active. TEA, charybdotoxin, and high [K+]0 attenuated the EET relaxations. 11,12-EET hyperpolarized coronary smooth muscle cells from -37 +/- 0.2 to -59 +/- 0.3 mV. In the cell-attached mode of patch clamp, both 14,15-EET and 11,12-EET increased the open-state probability of a Ca2+-activated K+ channel in coronary smooth muscle cells. This effect was blocked by TEA and charybdotoxin. These data support the hypothesis that the EETs are EDHFs.