Polymorphisms in the TNF-alpha and TNF-receptor genes in patients with coronary artery disease

Real-time PCR-based genotyping assay for CXCR2 polymorphisms

BACKGROUND

The human chemokine receptor CXCR2 (IL8RB) is a high affinity receptor for interleukin-8 as well as other CXC chemokines, and is involved in the chemotaxis of immune cells. Genetic variants of CXCR2 have potential relevance in various inflammatory human disorders. We developed a real-time polymerase chain reaction (PCR)-based allelic discrimination assay for the detection of the CXCR2 single nucleotide polymorphisms (SNPs) C785T, T1208C and G1440A.

METHODS

Polymorphisms were delineated using PCR amplification of specific alleles (PASA). Allele-specific primers were developed for both wild-type and mutant alleles. An additional nucleotide mismatch at the third position from the 3' end of each primer was used to improve amplification specificity and to prevent generation of nonspecific products. Genotypes were assigned based on PCR growth curves and melt curve analysis performed on a SmartCycler using SYBR Green I chemistry.

RESULTS

Genotyping assignments were successfully performed in a set of 20 human DNA samples, and were validated by comparison with results from direct DNA sequencing and agarose gel electrophoresis of PCR products.

CONCLUSIONS

Due to its rapid and relatively inexpensive performance and accuracy, the presented allelic discrimination assay for CXCR2 polymorphisms has wide applicability, especially for high-throughput sample analysis in large population genotyping studies.

TNF-α promoter, Nod2 and toll-like receptor-4 polymorphisms and the in vivo and ex vivo response to endotoxin

Humans exhibit substantial inter-individual differences in TNF-alpha production upon endotoxin stimulation. To determine to what extent the lipopolysaccharide-induced TNF-alpha production capacity in vivo and ex vivo is determined by polymorphisms in toll-like receptor-4 (TLR4), the TNF-alpha promoter region and Nod2, we screened for two TLR4 polymorphisms, a Nod2 polymorphism and the TNF-alpha promoter polymorphisms. We measured the perioperative endotoxemia and TNF-alpha production and the TNF-alpha production capacity of each patient in a whole-blood stimulation assay using blood drawn before anesthesia, using various LPS concentrations, in patients undergoing elective cardiac surgery. This operation represents a major surgical trauma associated with ischemia-reperfusion injury and triggers an endotoxemia and profound inflammatory response. In vivo TNF-alpha production was positively correlated with the level of endotoxemia after aortic declamping; thus TNF-alpha levels were higher in patients having endotoxemia compared to patients without endotoxemia. This correlation was observed in patients with any of the genotypes studied, and did not differ between the various genotypes. In vivo TNF-alpha levels correlated best with those ex vivo after stimulation with 1000 ng/mL LPS, and the estimated maximal TNF-alpha release capacity. Subjects with the wild-type TLR4 gene had similar levels of TNF-alpha upon LPS stimulation ex vivo as compared with patients carrying Asp299Gly and/or the Thr399Ile TLR4 polymorphism. Our results indicate that polymorphisms in the TLR4 receptor, Nod2 and TNF-alpha promoter region are not strongly associated with in vivo and ex vivo TNF-alpha production capacity upon endotoxin stimulation. This suggests that in this model of natural LPS release, the variation between individuals in TNF-alpha release can only modestly be determined by genetic background (TNF-alpha promoter, Nod2 and TLR4) of the individual.

Genetic risk for coronary artery disease in individuals with or without type 2 diabetes

Given that a substantial proportion of individuals with coronary artery disease (CAD) also have type 2 diabetes, it is important to identify genes that confer susceptibility to CAD independently in subjects with type 2 diabetes and in those without this condition. A large-scale association study was performed to identify genes that confer susceptibility to CAD in either the absence or presence of type 2 diabetes. The study population comprised 5207 unrelated Japanese individuals, including 3085 subjects with CAD and 2122 controls. Among all subjects, 1704 individuals had type 2 diabetes and 3503 individuals did not have this condition. The genotypes for 33 polymorphisms of 27 candidate genes were determined with a fluorescence- or colorimetry-based allele-specific DNA primer-probe assay system. Multivariate logistic regression analysis with adjustment for age, body mass index, and the prevalence of smoking, hypertension, hypercholesterolemia, and hyperuricemia revealed that the following polymorphisms were significantly (P < 0.005) associated with CAD: the 1019C -->T of the connexin 37 gene for men with type 2 diabetes; the 2445G -->A in the fatty acid-binding protein 2 gene for women with this condition; the -863C-->A in the tumor necrosis factor-alpha gene, the -219G-->T in the apolipoprotein E gene, the 1019C-->T in the connexin 37 gene for men without type 2 diabetes; and the -482C-->T in the apolipoprotein C-III gene for women without this condition. Genotyping of these polymorphisms may prove informative for assessment of the genetic risk for CAD in the absence or presence of type 2 diabetes.

Polymorphism R92Q of the tumour necrosis factor receptor 1 gene is associated with myocardial infarction and carotid intima-media thickness – The ECTIM, AXA, EVA and GENIC Studies

The TNFRSF1A gene was screened for polymorphisms in 95 subjects with premature myocardial infarction (MI), who also had one parent who had an MI. A total of 10 polymorphisms were found: three in the promoter region, two in exons and five in introns. All polymorphisms were genotyped in ECTIM, a case-control study of MI (1815 subjects). The nonsynonymous 92Q allele was found in 1.8, 1.0 and 1.7% of controls from Strasbourg, Belfast and Glasgow - respectively; in cases: 4.2, 2.2 and 3.2%. The population-adjusted odds ratio (OR) for MI associated with allele Q carrying was 2.15 (95% CI: 1.09-4.23). To check its possible implication in atherosclerosis, this polymorphism was then genotyped in the AXA Study (ultrasound examinations of carotid and femoral arteries in the context of an employment medical examination, 733 subjects), the EVA Study (ultrasound examinations of carotid arteries in a study of cognitive and vascular ageing, 1092 subjects) and the GENIC Study (on brain infarction (BI), 912 subjects). In the AXA Study, among smokers, carrying the 92Q allele was positively associated with the presence of a carotid plaque (OR 5.07; 95% CI: 1.64-15.63) and with a thickening of the carotid intima-media thickness (IMT) (0.59 (0.11) vs 0.54 (0.11), P=0.045). In the EVA Study, carriers of allele 92Q had an increased mean carotid IMT (0.70 (0.09) vs 0.67 (0.13), P=0.02). No significant association of the 92Q allele was found with BI in the GENIC Study. Overall, these results may suggest that carriers of the 92Q allele may be at increased risk of atherosclerosis.