C242T polymorphism of the p22 phox gene is not associated with peripheral arterial occlusive disease

Peripheral Arterial Disease Genetics: Progress to Date and Challenges Ahead

PURPOSE OF REVIEW

In this paper, we review the progress made thus far in research related to the genetics of peripheral arterial disease (PAD) by detailing efforts to date in heritability, linkage analyses, and candidate gene studies. We further summarize more contemporary genome-wide association studies (GWAS) and epigenetic studies of PAD. Finally, we review current challenges and future avenues of advanced research in PAD genetics including whole genome sequencing studies.

RECENT FINDINGS

Studies have estimated the heritability of PAD to be moderate, though the contribution to this heritability that is independent of traditional cardiovascular risk factors remains unclear. Recent efforts have identified SNPs associated with PAD in GWAS analyses, but these have yet to be replicated in independent studies. Much remains to be discovered in the field of PAD genetics. An improved understanding of the genetic foundation for PAD will allow for earlier diagnosis of disease and a more complete pathophysiological understanding of the mechanisms of the disease leading to novel therapeutic interventions. Future avenues for success will likely arise from very large-scale GWAS, whole genome sequencing, and epigenetic studies involving very well-characterized cohorts.

Association between rs4673 (C/T) and rs13306294 (A/G) haplotypes of NAD(P)H oxidase p22phox gene and severity of stenosis in coronary arteries

Phagocytic NADH/NADPH oxidase is an important enzyme producing reactive oxygen species within subendothelial space of vessels. Findings have shown that p22phox subunit is an essential element related to the enzyme activity. Since some p22phox polymorphisms are thought to have functional roles in the enzyme thus, we studied the association between rs4673 (C242T) and rs13306294 (A/G) haplotypes and the severity of stenosis in coronary arteries. One hundred eighty-two subjects undergoing coronary angiography were recruited on the base of study design. Patients (n=114) had at least a stenosed coronary artery (>50% stenosis) and subdivided into three subgroups; SVD (n=28), 2VD (n=31) and 3VD (n=55) while controls (n=68) had the normal coronary arteries (<5% stenosis). The direct haplotyping technique of SNPs was performed using ARMS-RFLP-PCR method. Furthermore, alphabet-based tools predicted the changes of secondary structure at the rs4673 position. All haplotypes being proposed theoretically were found in the study population. The distribution of two-allele haplotypes had no significant difference between patients and controls (P=0.1). Although the rs4673 allele frequency was not significant between the groups (P>0.5), chi square test and multinomial regression analysis showed an observed high risk for rs13306294 A allele among patients. The bioinformatics tools predicted that the p22phox secondary structure is not changed due to the substitution of Tyr→His at the rs4673 position. We concluded that the polymorphisms have no allele linkage on the chromosome. In addition, the rs13306294 A allele is a potential factor of stenosis of coronary arteries that increases susceptibility for the extent of disease.

Association between chromosome 9p21 variants and the ankle-brachial index identified by a meta-analysis of 21 genome-wide association studies

BACKGROUND

Genetic determinants of peripheral arterial disease (PAD) remain largely unknown. To identify genetic variants associated with the ankle-brachial index (ABI), a noninvasive measure of PAD, we conducted a meta-analysis of genome-wide association study data from 21 population-based cohorts.

METHODS AND RESULTS

Continuous ABI and PAD (ABI ≤0.9) phenotypes adjusted for age and sex were examined. Each study conducted genotyping and imputed data to the ≈2.5 million single nucleotide polymorphisms (SNPs) in HapMap. Linear and logistic regression models were used to test each SNP for association with ABI and PAD using additive genetic models. Study-specific data were combined using fixed effects inverse variance weighted meta-analyses. There were a total of 41 692 participants of European ancestry (≈60% women, mean ABI 1.02 to 1.19), including 3409 participants with PAD and with genome-wide association study data available. In the discovery meta-analysis, rs10757269 on chromosome 9 near CDKN2B had the strongest association with ABI (β=-0.006, P=2.46×10(-8)). We sought replication of the 6 strongest SNP associations in 5 population-based studies and 3 clinical samples (n=16 717). The association for rs10757269 strengthened in the combined discovery and replication analysis (P=2.65×10(-9)). No other SNP associations for ABI or PAD achieved genome-wide significance. However, 2 previously reported candidate genes for PAD and 1 SNP associated with coronary artery disease were associated with ABI: DAB21P (rs13290547, P=3.6×10(-5)), CYBA (rs3794624, P=6.3×10(-5)), and rs1122608 (LDLR, P=0.0026).

CONCLUSIONS

Genome-wide association studies in more than 40 000 individuals identified 1 genome wide significant association on chromosome 9p21 with ABI. Two candidate genes for PAD and 1 SNP for coronary artery disease are associated with ABI.

Peripheral artery disease and genetics: is there a cause-and-effect relationship?

Peripheral artery disease (PAD) is a major health problem worldwide, affecting millions of patients. Although cardiovascular risk factors, such as diabetes, tobacco use, hypertension, and hypercholesterolemia have been associated with the development of PAD, the possible existence of an inherited genetic predisposition to PAD has been investigated in numerous familial aggregation studies. A link between genetics and PAD may open new avenues for the prevention of this morbid and mortal disorder. This is an overview of the potential association between genetics and PAD.

A field synopsis and meta-analysis of genetic association studies in peripheral arterial disease: The CUMAGAS-PAD database

In an electronic search of the literature, the authors systematically retrieved all published studies that investigated genetic susceptibility to peripheral arterial disease (PAD). They created a comprehensive database of all eligible studies, collecting detailed genetic and bioinformatics data on each polymorphism. Data from eligible studies were synthesized using meta-analysis techniques. Gene variants were classified into distinct pathophysiologic pathways, and their potential involvement in PAD pathogenesis was determined. Forty-one publications that examined 44 gene polymorphisms were included. For 37 polymorphisms, the variant form had a functional effect. Twenty-three polymorphisms in 22 potential PAD candidate genes (F2, FGB, MTHFR, ITGB3, ACE, AGT, IL6, CCL2, ICAM1, SELE, MMP9, PPARG, MMP1, ADD1, P2RY12, LIPC, PLA2G7, SCARB1, MMP3, MTTP, LPA, CHRNA3) showed a significant association in individual studies. Eighty-eight percent of the studies had statistical power of less than 50%, and in 15 studies the genotype distribution in the control group did not conform to Hardy-Weinberg equilibrium. Data on 12 polymorphisms (F5 1691 G/A, MTHFR 677C/T, F2 20210 G/A, ITGB3 1565 T/C, ACE I/D, AGT 704C/T, AGT -6G/A, AGT 733C/T, IL6 -174 G/C, MMP9 -1562C/T, ICAM1 1462A/G, CHRNA3 831C/T) were synthesized, and a positive association was found for 3 (IL6 -174 G/C, ICAM1 1462A/G, CHRNA3 831C/T).

NADPH oxidase CYBA polymorphisms, oxidative stress and cardiovascular diseases

Oxidative stress plays a key role in the pathophysiology of several major cardiovascular diseases, including atherosclerosis, hypertension, heart failure, stroke and diabetes. ROS (reactive oxygen species) affect multiple tissues either directly or through NO depletion. ROS induce cardiovascular dysfunction by modulating cell contraction/dilation, migration, growth/apoptosis and extracellular matrix protein turnover, which contribute to vascular and cardiac remodelling. Of the several sources of ROS within the cardiovascular system, a family of multisubunit NADPH oxidases appears to be a predominant contributor of superoxide anion. Recent findings suggest a significant role of the genetic background in NADPH oxidase regulation. Common genetic polymorphisms within the promoter and exonic sequences of CYBA, the gene that encodes the p22(phox) subunit of NADPH oxidase, have been characterized in the context of cardiovascular diseases. This review aims to present the current state of research into these polymorphisms in their relationship to cardiovascular diseases.

Genetic susceptibility to peripheral arterial disease: a dark corner in vascular biology

Peripheral arterial disease (PAD) is characterized by reduced blood flow to the limbs, usually as a consequence of atherosclerosis, and affects approximately 12 million Americans. It is a common cause of cardiovascular morbidity and an independent predictor of cardiovascular mortality. Similar to other atherosclerotic diseases, such as coronary artery disease, PAD is the result of the complex interplay between injurious environmental stimuli and genetic predisposing factors of the host. Genetic susceptibility to PAD is likely contributed by sequence variants in multiple genes, each with modest effects. Although many of these variants probably alter susceptibility both to PAD and to coronary artery disease, it is likely that there exists a set of variants specifically to alter susceptibility to PAD. Despite the prevalence of PAD and its high societal burden, relatively little is known about such genetic variants. This review summarizes our limited present knowledge and gives an overview of recent, more powerful approaches to elucidating the genetic basis of PAD. We discuss the advantages and limitations of genetic studies and highlight the need for collaborative networks of PAD investigators for shedding light on this dark corner of vascular biology.

Associations between the CYBA 242C/T and the MPO –463G/A Polymorphisms, Oxidative Stress and Cardiovascular Disease in Chronic Kidney Disease Patients

Genetic variations in the NADPH/MPO system in chronic kidney disease (CKD) patients might lead to altered activity of these enzymes, and thus to altered risk for oxidative stress (OS) and cardiovascular disease (CVD). We evaluated the impact of 242C/T CYBA and -463G/A MPO polymorphisms on OS and CVD mortality in stage 5 CKD patients starting dialysis. Two hundred and fifty-seven patients were genotyped using Pyrosequencing. Plasmalogen [dimethylacetal (DMA) 16/C16:0] was used as OS marker. CVD was assessed from patient history and clinical symptoms. Prevalence of CVD was higher (35%) in GG patients (MPO) compared to AG (26%) and AA (0%) patients (p < 0.01). Patients with CC genotype (CYBA) had lower levels of DMA 16/C16:0 (ratio 0.071 +/- 0.003) compared to TT patients (0.089 +/- 0.006; p < 0.05). These patients also had increased CVD mortality compared to CT and TT patients (chi(2) 2.19; p < 0.05). We conclude that genetic variations in the NADPH/MPO system are associated with OS, presence of CVD and CVD-related mortality in CKD patients.

Impact of NAD(P)H oxidase p22 phox gene polymorphism on vascular aging in Korean centenarian and nonagenarian

BACKGROUND

Oxidative stress, the imbalance between production and removal of reactive oxygen species (ROS), is implicated in the process of cardiovascular aging. Membrane-associated NAD(P)H oxidase system is the most important source of ROS in vascular cells. p22(phox), a critical component of the NAD(P)H oxidase, has a polymorphic site on exon 4, associated with variable enzyme activity. The goal of this study is to investigate the effect of the p22(phox) C242T polymorphism on cardiovascular aging.

METHODS

We investigated, in a cross-sectional study, the distribution of the p22(phox) genotypes and its impact on vascular aging in elderly Korean subjects (N=123, mean age+/-SD: 97.0+/-5.0). p22(phox) C242T polymorphism was determined by PCR and restriction fragment length polymorphism analysis. The p22(phox) genotype and allele frequencies were also compared with younger Korean subjects (N=363, mean age+/-SD: 49.0+/-10.3).

RESULTS

No significant difference was identified in p22(phox) genotype frequency according to the subject's age. However, the prevalence of CT+TT genotype was significantly less frequent in normotensive extremely elderly compared with younger subjects. Furthermore, the prevalence of the CT+TT genotype was significantly more frequent in hypertensive subjects (21.9%) than in the normotensive group (6.0%, P=0.016) in extremely elderly subject. The association was more significant in systolic hypertension rather than diastolic hypertension. Mean systolic blood pressure and pulse pressure were also significantly higher in subjects with CT+TT genotype. In contrast, there was no significant association between p22(phox) genotype and hypertension in younger-aged group.

CONCLUSION

These results suggest an association between the p22(phox) C242T polymorphism and vascular aging, which might be mediated by the increase of oxidative stress.

The C242T CYBA polymorphism of NADPH oxidase is associated with essential hypertension

OBJECTIVE

Oxidative stress is implicated in hypertension. The reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidases are the main source of superoxide in phagocytic and vascular cells. The C242T polymorphism of CYBA, the human gene that encodes p22phox, has been found to be functionally associated with vascular NADPH oxidase activity in atherosclerotic patients. We investigated the association of the C242T polymorphism with hypertension and its potential impact on NADPH oxidase activity. We also analysed the interaction of C242T polymorphism with the -930A/G CYBA variant.

DESIGN

Case-control study in a random sample of 623 subjects (326 hypertensive patients and 297 normotensive controls) from the general population.

METHODS

CYBA polymorphisms were determined by restriction fragment length polymorphism (RFLP) or allelic discrimination. NADPH oxidase activity and p22phox expression were quantified in phagocytic cells by chemiluminescence and by northern and western blots, respectively.

RESULTS

The prevalence of the CC genotype and the C allele frequency were significantly higher (P < 0.05) in hypertensives than in normotensives. CC genotype remained associated with hypertension after adjusting for potential confounders in a logistic regression analysis. Increased phagocytic NADPH oxidase activity was observed in CC hypertensives compared with CT and TT hypertensives (P < 0.05). Enhanced plasma levels of von Willebrand factor were found in CC hypertensives compared with TT hypertensives (P < 0.05). The C242T polymorphism was not in linkage disequilibrium with the -930A/G CYBA promoter variation, which also associates with hypertension.

CONCLUSION

The C242T CYBA polymorphism is associated with essential hypertension. Furthermore, hypertensives carrying the CC genotype of this polymorphism exhibit features of NADPH oxidase-mediated oxidative stress and endothelial damage.

A beneficial effect of simvastatin on DNA damage in 242T allele of the NADPH oxidase p22phox in hypercholesterolemic patients

BACKGROUND

The effect of simvastatin on DNA damage in hypercholesterolemic patients was investigated, and the relationship between the C242T polymorphism of the NADPH oxidase p22phox gene and the antioxidant effects of simvastatin was examined.

METHODS

Simvastatin (20-40 mg /day) was administered for 8 weeks in 72 hypercholesterolemic patients. DNA damage in lymphocytes was quantified using single-cell gel electrophoresis (COMET assay) by measuring tail DNA (%), tail length (microm) and tail moment (tail length x % tail DNA/100).

RESULTS

Simvastatin significantly reduced DNA damage as expressed by tail DNA (%, p< 0.001), tail length (mum, p<0.001) and tail moment on the DNA in lymphocytes (p<0.001) after 8 weeks. The frequencies of the C242T genotypes for CC, TC, and TT were 75.0%, 23.6% and 1.4% in the subjects. In the presence of the 242T allele, there were higher levels of baseline DNA damage and also a greater improvement in the DNA damage after 8 week simvastatin treatment compared with the CC homozygotes.

CONCLUSION

Simvastatin significantly reduced DNA damage of hypercholesterolemic patients. This study showed that simvastatin has a beneficial effect on the improvement of DNA damage in patients with the 242T allele of NADPH oxidase p22phox gene.

Functional effects of NAD(P)H oxidase p22phox C242T mutation in human leukocytes and association with thrombotic cerebral infarction

BACKGROUND

Previous study showed that polymorphism of the NAD(P)H oxidase p22(phox) gene is associated with atherosclerosis, although others could not confirm such association. We investigated the association between p22(phox) C242T polymorphism and thrombotic cerebral infarction and the role of this polymorphism on superoxide-production activity in human neutrophils and promyelocytic HL-60 cells as a model system.

METHODS

PCR-RFLP analysis revealed that genotype and allele frequencies of C242T polymorphism in 120 patients with thrombotic cerebral infarction and 177 control subjects. The superoxide-production activity in neutrophils was determined by cytochrome c reduction assay. To clarify the role of p22(phox) C242T polymorphism on NAD(P)H oxidase activity, we used transgenic HL-60 cells transfected with expression plasmids carrying p22(phox) cDNAs with or without C242T polymorphism.

RESULTS

Genotype and allele frequencies of C242T polymorphism in patients and control subjects were not significantly different. The superoxide-production activity in neutrophils with T allele was higher than in neutrophils without T allele. Moreover, expression analysis showed that superoxide-production activity in p22(phox) C242T-expressing HL-60 cells were significantly higher than in p22(phox)-expressing HL-60 cells.

CONCLUSIONS

We conclude that C242T of p22(phox) gene is not involved in thrombotic cerebral infarction but more likely in increased NAD(P)H oxidase activity in phagocytes.

NAD (P) H oxidase p22 phox C242T polymorphism affects LDL particle size and insulin resistance in Japanese subjects

Elevated cardiovascular risk is associated with an increased number of small, dense low-density lipoprotein (LDL) particles, which exhibit increased susceptibility to lipid oxidation, however, the mechanism determining LDL particle size has never been fully elucidated. We have examined the association between the C242T polymorphism of the p22 phox gene, which is a small subunit of vascular NAD(P)H oxidase, and both LDL particle size and clinical characteristics in 260 healthy subjects. Peak LDL particle diameter (LDL-PPD) was measured by continuous disk polyacrylamide gel electrophoresis. Twenty-one of the 217 subjects with the CC genotype showed pattern B (median LDL-PPD under 25.5 nm), whereas, none of the 43 subjects with TC + TT genotypes showed pattern B. The pattern B fraction was significantly larger in the CC group than in the TC + TT group (p = 0.030). The subjects with the CC genotype also showed a significantly higher fasting glucose level, plasma insulin level, and insulin resistance index of homeostasis model assessment (HOMA-R) than those with the TC + TT genotype. Our data demonstrate that variation in the small NAD(P)H oxidase subunit p22 phox gene substantially influences LDL particle size and may also reflect differences in the insulin sensitivity of non-diabetic subjects.

Two polymorphisms in the fracalkine receptor CX3CR1 are not associated with peripheral arterial disease

OBJECTIVE

CX(3)CR1 is a novel chemokine receptor located on monocytes. Recently, two polymorphisms were linked to coronary artery disease (CAD), V249I and T280M. Carriers of at least one I-allele or one M-allele were found less frequently among patients with CAD compared to controls. The aim of the present study was to investigate the influence of these polymorphisms on the development of peripheral arterial disease (PAD).

METHODS

522 human subjects with documented PAD and 522 age and sex matched controls were genotyped by polymerase chain reaction followed by restriction digestion.

RESULTS

Adjusted odds ratio (OR) of carriers of the I-allele for PAD was 1.34 (95% confidential interval (CI) from 0.86 to 2.09; P=0.19). The OR associated with the M-allele for PAD was 0.65 (95% CI from 0.41 to 1.04; P=0.07), when tested in the same regression analysis with the V249I genotypes. The genotypes were not linked to age at onset or severity of the disease. A subgroup of 137 CAD patients of whom 131 could be genotyped and who did not differ in baseline parameters from the remaining PAD patients, showed VV-genotype in 52.0%, VI in 42.7% and II in 5.3% CAD (OR associated with the I-allele for CAD: 1.29; 95% CI: 0.66-2.51; P=0.46). The distribution of the T280M genotypes was 67.1, 29.8, 3.1% (TT, TM, MM) also showing no association with CAD (OR=0.77; 95% CI 0.36-1.46; P=0.37).

CONCLUSION

In this study we could not detect a difference in genotype frequencies of the V249I and T280M polymorphisms in CX(3)CR1 between PAD patients and controls. CAD concomitant with PAD was also not affected by the I- or the M-allele.

Association of NAD(P)H oxidase p22 phox gene variation with advanced carotid atherosclerosis in Japanese type 2 diabetes

OBJECTIVE

To evaluate the association between the C242T polymorphism of the p22 phox gene, an essential component of NAD(P)H oxidase in the vasculature, with intima-media thickness (IMT) of the carotid artery and risk factors for atherosclerosis in type 2 diabetic subjects.

RESEARCH DESIGN AND METHODS

C242T polymorphism of the p22 phox gene was detected by polymerase chain reaction-restriction fragment-length polymorphism in 200 Japanese type 2 diabetic subjects and 215 nondiabetic subjects. We examined the association with this mutation and carotid atherosclerosis as well as the patients' clinical characteristics and the level of 8-hydroxy-2'deoxyguanosine (8-OHdG) as an index of oxidative DNA damage.

RESULTS

The diabetic subjects with the TC+TT genotypes displayed a significantly lower average IMT (1.13 +/- 0.31 vs. 1.31 +/- 0.34 mm; P = 0.0099) and a not significantly lower serum 8-OHdG level than those with the CC genotype, despite no difference in the risk factors. Stepwise multiple regression analysis showed that the risk factors for increased IMT in the diabetic subjects were systolic blood pressure (P = 0.0042) and p22 phox CC genotype (P = 0.0151). In nondiabetic subjects, the average IMT of the TC+TT group was not different from that of the CC group (0.85 +/- 0.14 vs. 0.94 +/- 0.30 mm, P = 0.417). Fasting plasma insulin concentration (41.4 +/- 15.6 vs. 64.2 +/- 59.4 pmol/l, P = 0.0098) and insulin resistance index of homeostasis model assessment (HOMA-R) (1.58 +/- 0.66 vs. 2.60 +/- 2.56, P = 0.0066) were significantly lower in the TC+TT group than in the CC group.

CONCLUSIONS

These results show that the C242T mutation in the p22 phox gene is associated with progression of asymptomatic atherosclerosis in the subjects with type 2 diabetes and is also associated with insulin resistance in nondiabetic subjects.

Genetic determinants of vascular reactivity

Blood pressure is controlled by a complex combination of processes that influence cardiac output and peripheral vascular resistance. Multiple genes potentially influence each parameter involved in the control of blood pressure, and individuals with the same blood pressor level do not necessarily have the same genotype at relevant loci, nor do individuals with the same genotype at particular loci necessarily have the same blood pressure. Nevertheless, pharmacogenetic studies of vascular reactivity will certainly allow the analysis of the mechanisms affected by genes, and lead to a better understanding of the epidemiologic observations seen in large groups of patients. Polymorphisms in the genes of the renin-angiotensin system allow definition of the "genetic profile" associated with a higher risk of cardiovascular disease, and can also be linked to significant changes in vascular reactivity in arteries isolated from patients carrying the polymorphisms.