COX gene is closely related to the cause of ischemic stroke. COX-1 gene locates on chromosomes 9q32-q33.3 and contains 11 exons, COX-2 gene located on chromosomes 1q25.2-q25.3 and contains 10 exons.[34] COX-1 participates in the normal physiological metabolism of the body and regulates platelet function and blood coagulation.[10] COX-2 expression is 10–20 times higher in patients with atherosclerotic plaques or inflammatory stimuli than in asymptomatic patients with arterial stenosis.[35]
As for COX-1, our results showed that rs1330344 and rs3842788 appeared to contribute significantly to the occur of ischemic stroke, but the genotype and allele frequencies at rs5788 had no significant difference between ischemic stroke group and the control group. On one hand, at rs1330344, AA genotype may reduce the susceptibility of ischemic stroke, and CES or SVO. Meanwhile, the A allele carriers also may reduce the susceptibility of ischemic stroke, LAA or CES. On the other hand, at rs3842788, the susceptibility of ischemic stroke was fivefold higher in the AA genotype than in the G allele carrier genotype (GG+GA, recessive model);the susceptibility of CES was higher by about 9.8 times; the risk of SVO was higher by about 4.6 times. Our finding matches a study of 859 ischemic stroke patients indicated the rs5788 locus is not related to ischemic stroke in China.[24] They also suggested that the homozygotes of the minor allele at rs1330344 increase the risk of ischemic stroke recurrence, which was inconsistent with our findings. This difference may caused by the type of ischemic stroke patients that we included was different from them. Their study included patients with recurrent ischemic stroke, and all of the patients were classified as one type. Instead, our study included patients who had their first onset of ischemic stroke and grouped by the TOAST classification. In addition, another study of 196 ischemic stroke patients in Korea revealed that the rs3842788 locus is not associated with ischemic stroke, and a study of 469 ischemic stroke patients in USA also got the same results, both of which were inconsistent with our results.[25] This may because these studies all had relatively small samples and involving different ethnic population.
As for COX-2, our results showed that the genotype and allele frequencies at rs20417 had no significant difference between the ischemic stroke group and the control group. This conclusion is consistent with a meta-analysis of rs20417[26] and two studies (411 ischemic stroke patients in China, 469 ischemic patients in USA) which indicated that rs20417 is not associate with ischemia stroke .[36, 37] However, research of rs20417 remains controversial. Francesco et al. [22]observed that the GC and CC genotypes of rs20417 are related to the pathogenesis of ischemic stroke, and C allele may be a genetic protective factor that reduces the incidence of ischemic stroke. Conversely, a study showed that the GC and CC genotypes were commonly found in African–American and European populations affected by ischemic stroke and suggested that COX-2 is an ischemic stroke-susceptible gene.[23] In our study, the difference between ischemic stroke group and control group at rs20417 was not significant, this may due to the difference between our population and genetic heterogeneity. Furthermore, at COX-2(rs689466), we found the AA genotype carriers had a higher risk of LAA, compared to the G allele carriers genotype (GG+GA). Our finding proved that rs689466 was associated with susceptibility to ischemic stroke in China which matched the results of two studies of Chinese population (Zhejiang Province-224 patients with LAA and 329 patients with SVO,[27] Beijing-93 patients with LAA and 117 patients with SVO[41]) . But the effects of these two studies were confined to SVO among the stroke subtypes rather than to LAA which was dissimilar to our study. This may be caused by their small amount of patients. Otherwise, another study of 572 Chinese patients showed that rs689466 was not associated with ischemic stroke and its subtypes[42], this may also because the small amount of patients. Therefore, we need more large samples and multiethnic studies to be conducted to verify the association of rs689466 with ischemia stroke in China.
There were some differences observed in genotype and allele frequencies between the diabetes/smoking group and control group, and this difference remained significant in multivariate analysis by adjusting for age, gender and traditional risk factors. Inflammation may play a role in the pathogenesis of type 2 diabetes, COX generates prostaglandins, which negatively modulate glucose-stimulated insulin secretion, which indicated that COX may associate with diabetes. [43] Konheim et al. identified that there was no association of COX2 rs689466 with type 2 diabetes.[44] Their conclusion matched another hospital-based case-control study in Turkey.[45] However, our study found that COX-1 rs1330344 and COX-2 (rs20417, rs689466) were associated with diabetes. The racial difference may cause this inconsistent. Since smoking increases the activity of inflammatory mediators through an increase in leukotriene synthesis essential in atherosclerosis pathogenesis, COX functions as a mediator of the inflammatory response and is also essential in a atherosclerosis pathogenesis.[46] Our study found that COX-1 rs5788 and COX-2 rs3842788 were associated with smoking, this evidence may explain that the pathogenesis of COX associate with smoking. We had got some statistically significant positive results from the single gene polymorphism research of COX-1 and COX-2 gene. But these results were not entirely consistent with existing research and cannot fully explain the association between each polymorphism in the same gene. Therefore,we conducted a study on the interaction between multiple loci in ischemic stroke. Our study found that COX-1(rs1330344, rs3842788) and COX-2 rs689466 are associated with SVO. Compared with those patients who do not carry any of the variants, individuals carrying one variant, two variants, and three variants had no significant difference between the ischemic stroke and the control groups. Our previous results showed that rs1330344 reduces the risk of ischemic stroke, including CES and SVO, whereas rs3842788 increases the risk of ischemic stroke, including CES and SVO, rs689466 increases the risk of LAA, and the three loci interact with SVO. Our study also had several limitations. First of all, our study only included the Han population in the southwest of China. Secondly, our study only examined two and three loci of the candidate genes and thus may be unable to cover the entire gene linkage disequilibrium signal. Hence, a linkage disequilibrium map of the gene should be constructed to clarify the relationship between this gene and the pathogenesis of ischemic stroke. Thirdly, this study was limited to two genes and three loci to explore the gene–gene interaction in ischemic stroke. The quantification of the environmental factors of ischemic stroke was relatively difficult. Thus, the role of the interaction of environmental factors was not considered in our study. Therefore, future studies on gene interaction should include environmental and epigenetic factors and should also be performed to enhance our understanding of the genetic structure of ischemic stroke, to investigate the molecular mechanism of ischemic stroke, and to provide a new angle for the diagnosis and treatment of ischemic stroke.