Evaluation of the Potential Association between NOS Gene Polymorphisms (iNOS G-954C and eNOS G894T) and Psoriasis

Dear Editor:

Psoriasis is a common chronic skin disease that affects 0.1%~3% of the world population. The exact pathomechanism of this disease has not yet been fully elucidated. Most hypotheses assume that the disease is an immune-mediated disorder involving multigenic components and environmental factors1.

Nitric oxide (NO) acts as an intercellular messenger contributing to the pathogenesis of various autoimmune diseases via cell proliferation, differentiation, and apoptosis2. Several lines of evidence indicate that NO is important in the pathogenesis of psoriasis and promotes skin microvasculature formation, keratinocyte proliferation, and keratinocyte differentiation3.

NO is synthesized by a group of enzymes called nitric oxide synthases (NOSs). The NOS family consists of three isoforms, neuronal NOS, endothelial NOS (eNOS), and inducible NOS (iNOS). Recently, Ormerod et al.4 have shown high levels of eNOS and iNOS expression in psoriatic lesions, suggesting their involvement together with NO in the occurrence and further development of psoriasis4. Considering the important role played by iNOS and eNOS in the production of NO and in the pathogenesis of psoriasis, we hypothesized that iNOS and eNOS gene polymorphisms may be associated with the risk of psoriasis. Therefore, we investigated the potential association of the iNOS G-954C and eNOS G894T polymorphisms with psoriasis and attempted to correlate the results with the clinical features in this study.

Sommer et al.5 have shown that patients with psoriasis have a higher risk of developing hypertension than individuals without psoriasis. It has also been reported that eNOS gene polymorphisms are associated with hypertension susceptibility6. These findings led us to question whether any susceptibility genes are common between psoriasis and hypertension. Therefore, we studied the association of the eNOS G894T polymorphism and psoriasis with hypertension to investigate the mechanism underlying the relationship between psoriasis and hypertension.

The study included 212 Han Chinese patients who had psoriasis and visited the Department of Dermatology, WestChina Hospital, Sichuan University. One hundred and seventy eight age- and sex-matched Han Chinese healthy volunteers were used as the control group. For all individuals, age, sex, and history of psoriasis and hypertension were recorded. This study was approved by the organization is the Clinical Trials and Biomedical Ethics Committee of West China Hospital Sichuan University (No. 2015158).

The genes polymorphisms were determined using the polymerase chain reaction (PCR)-restriction fragment length polymorphism method. DNA was isolated from venous blood samples using a DNA extraction kit (Jingbo, Chengdu, China). PCR was used to amplify the fragments that contained the polymorphic sites. The primers for iNOS G-954C were as follows: 5'-ACTTGGTACTGAGGAAGGCGCTCT-3' (forward) and 5'-TAGCAAAGCCCCGTTTCAACAA-3' (reverse). eNOS G894T was amplified with the primers 5'-CATGAGGCTCAGCCCCAGAAC-3' (forward) and 5'-GTCAATCCCTTTGGTGCTCAC-3' (reverse), as previously reported7, 8. The lengths of the amplified PCR products for iNOS G-954C and eNOS G894T polymorphisms were 680 bp and 206 bp, respectively. We used the restriction enzymes BsaI and MboI (New England Biolabs, Beverly, MA, USA) to delineate iNOS G-954C and eNOS G894T polymorphisms, respectively. Cleavage by these enzymes resulted in 490-bp and 190-bp fragments for the iNOS G-954C G allele and 119-bp and 87-bp fragments for the eNOS G894T C allele.

Statistical analyses were performed using SPSS ver. 16.0 (SPSS Inc., Chicago, IL, USA). Results are presented as mean±standard deviation. The proportions of the alleles and genotypes between patients and controls were compared using the chi-square test. A two-tailed p-value of 0.05 or less was considered statistically significant.

Baseline characteristics of patients and controls are summarized in Table 1. The results of the genotype and allele frequencies are presented in Table 2. No significant differences in the genotype and allele distributions were observed between patients and controls. Similarly, there were no significant differences according to the age of onset, the clinical types of psoriasis, family history, and joint involvement. In addition, patients with or without hypertension are no associations with the eNOS G894T polymorphism (data not shown).

Table 1
Clinical characteristics of the psoriatic patients and controls

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Table 2
Genotype and allele frequencies (%) for the control, psoriasis and psoriatic clinical features groups

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To the best of our knowledge, this study is the only casecontrol study to date to investigate iNOS G-954C polymorphisms in psoriasis, although these gene polymorphisms have been already been implicated in diseases such as rheumatoid arthritis, diabetes5. However, our present data did not support a relationship between this gene polymorphism and susceptibility to psoriasis in the Han Chinese population. Further, our stratification analysis of clinical features showed that none of the phenotypes of psoriasis were associated with the iNOS G-954C polymorphism.

In 2006, Senturk et al.8 were the first to report that the eNOS G894T polymorphism is implicated in Turkish patients with psoriasis However, Coto-Segura et al.9 have shown contradictory results in Spanish patients. Considering the above differing conclusions, we aimed to assess the association between the eNOS G894T polymorphism and psoriasis in the Han Chinese population. Our study showed that there was no significant correlation between the gene polymorphism and psoriasis susceptibility, contrary to the reports of Senturk et al.8, which indicated that the association may vary with the patients such as ethnicities, regions, clinical features. Moreover, in our study, none of the phenotypes of psoriasis were associated with the eNOS G894T polymorphism, similar to the findings for iNOS G-954C.

There is accumulating evidence that hypertension is common among patients with psoriasis, and the eNOS G894T polymorphism has been associated with hypertension5, 6. Although our study indicated that the eNOS G894T polymorphism had no association with psoriasis accompanying hypertension, the possible involvement of other eNOS loci cannot be excluded.

Thus, our study may be useful in further understanding the correlation between psoriasis and NOS gene polymorphisms. However, our study has some limitations. Since the study was conducted in a single population and with a limited number of participants, it requires further confirmation in larger groups and populations.