Relationship between smoking, clinical, inflammatory, and radiographic parameters in patients with ankylosing spondylitis

Ankylosing spondylitis (AS) is an autoimmune multisystemic disease that attacks the spine, sacroiliacs, and often causes asymmetrical peripheral oligoarthritis. It results from the interaction between the genetic factors mainly Human Leukocyte Antigen B27 (HLA B27) and environmental factors. Current smoking has been reported to be a major risk factor for the incidence and progression of ankylosing spondylitis. So, we aim to explore the relationship between smoking and each of the clinical, inflammatory markers, functional limitation, and radiographic progression in ankylosing spondylitis patients. Fifty ankylosing spondylitis patients were included in this study. Comparisons of clinical data, radiographic, and inflammatory markers among smokers and nonsmokers revealed that AS current smokers showed a statistically significant decrease in chest expansion, increase in the occiput to wall distance (p < 0.001**), higher inflammatory marker, higher disease activity indices (Ankylosing Spondylitis Disease Activity Score, Bath Ankylosing Spondylitis Disease Activity Index), higher Bath Ankylosing Spondylitis functional index, and modified Stoke Ankylosing Spondylitis Spine Score than nonsmokers (P < 0.001**). The smoking index was positively correlated with BASFI, ASDAS, (mSASSS) (r = 0.584, p = 0.005*) and negatively correlated with chest expansion. Current smoking in ankylosing spondylitis patients is associated with higher disease activity, inflammatory markers, functional disability, and radiological progression. This may add to the disease burden and thus interferes with the personal daily activities, physical mobility, life quality, and the response to TNFi therapy. So, stopping smoking is a mandatory step in controlling the disease activity and having favorable outcome.

to examine if smoking carries extraburden to the disease.

Methods
The current study is an observational cross sectional study, including 50 adult ankylosing spondylitis patients diagnosed according to the modified New York criteria [4]. Patients were selected from the outpatient clinic and the inpatients of the Internal Medicine and Rheumatology Department. The study included current smokers, exsmokers (stopped smoking more than 1 year), and nonsmokers ankylosing spondylitis patients with ages > 18 years.
Using PASS 11 program for sample size calculations at setting power 80%, significance level 0.05 and by reviewing the results of studies showed the mean and SD of Schober's test in patients with ankylosing spondylitis in smokers vs nonsmokers were (1.4 ± 1.2 vs 2.5 ± 1 respectively) based on that the sample size needed will be at least 40 patients to be sufficient to achieve study objective.
Exclusion criteria: Other seronegative spondyloarthropathy and associated systemic diseases cardiac, respiratory, other autoimmune diseases (systemic lupus erythematosis, rheumatoid arthritis, scleroderma), and shisha smokers were excluded from the study.
Full history taking including articular, extraarticular disease manifestations, and smoking history were obtained. A quantitative measure for smoking was calculated (one pack years = twenty cigarettes/day for 1 year) age, gender, disease duration, anti-tumor necrosis factor (TNF) medication used at the time of evaluation. All patients provided written consent.

Disease activity, functional assessment, and radiographic parameters
The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) [5], The Bath Ankylosing Spondylitis functional index (BASFI) [6], Ankylosing Spondylitis Disease Activity Score (ASDAS) [7]. Measuring erythrocyte sedimentation rate (ESR mm/h) and C-reactive protein (CRP mg/dl), and complete blood picture for each patient. Human Leukocytic Antigen B27 (HLA-B27) test was obtained from the patients who essentially performed it for their diagnosis.
Plain radiographs of sacroiliac joints, lumbosacral, and cervical spine including anteroposterior and lateral views were performed. The radiographic damage severity was tested by the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS) [8]. Radiographs were scored by an experienced radiologist.

Statistical analysis
Obtained data were analyzed. Quantitative data were illustrated as mean ± standard deviation (SD). Qualitative data were illustrated as frequency and percentage.
The following tests were done: Independent-samples t test of significance. Chi-square (x 2 ) test of significance. Pearson's correlation coefficient (r) test was used to assess the degree of association between two sets of variables. The p value was considered significant as the following: Probability (P value) ≤ 0.05 was significant, P value ≤ 0.001 was highly significant, P value > 0.05 was considered insignificant.

Ethical consideration
Approval of the study conduction was obtained from the Ethical Committee, the aim of this study was explained to all participants, and confidentiality was assured, written informed consent was obtained.

Results
Fifty Ankylosing Spondylitis patients were included in the study. This study showed that 27 (54%) patients were never smoked, 20 (40%) were current smokers, and 3 (6%) were past smokers. In the study, they were categorized into 2 groups, group I, which included current smokers, and group II, the non-smokers including past and never smokers. The smoking index for current smokers ranged from 1 to 18 years (mean 7.33 ± 5.29). Descriptive data (demographic, clinical, laboratory, and radiographic data) of the patients are shown in Table 1.
Comparisons of clinical, radiographic, and acute phase reactants between group I and group II are demonstrated in Table 2 which shows a statistically significant decrease in chest expansion (p < 0.001**) and increase in the occiput to wall distance (p < 0.001**) in smokers than non-smokers. Regarding disease activity indices, it demonstrates that smokers had a significantly higher BASDAI (P < 0.001**), BASFI (P < 0.001**), and ASDAS (P < 0.001**) compared with non-smokers which reflects more functional disability and disease progression in smokers AS patients. Additionally, most of the smokers had grade IV sacroiliitis while most of the non-smokers had grade III. Also, there was a highly statistically significant difference between the two groups as regards mSASSS (p < 0.001**) which reflects more radiographic progression in smokers. Regarding acute phase reactants ESR (P = 0.029*) and CRP (P < 0.001**), they were significantly higher in smokers in comparison with nonsmokers. As regards uveitis, we found 3 patients only had uveitis. There was an insignificant difference between them.

Discussion
Ankylosing spondylitis (AS), one of the spondyloarthropathy, is a chronic inflammatory autoimmune disease that mainly affects spine and sacroiliac joints. In the past, before the rising of biologic therapy, it can cause spine fusion [9]. Immune cells and chemical cytokines have been proved to be important in the pathogenesis of AS, especially human leukocyte antigen (HLA)-B27 and the interleukin-23/17 axis [10].
Cigarette smoking is incriminated in the etiology of numerous diseases and took a serious interest worldwide from the current healthcare givers. Also, it has an impact on both innate and adaptive immunity and plays a dual role in dysregulating immunity through either hyperactivation of pathogenic immune responses or weakened defensive immunity [11]. And so, there is a complicated association between smoking and spondyloarthropathy [12]. Although some findings are suggesting increased severity of the disease with smoking [13,14], the mechanism is still unclear [15].
In the present study, we have studied the relationship between smoking and each of the clinical data, inflammatory markers, functional limitation, and radiographic progression in patients with ankylosing spondylitis. Regarding the clinical examination, the smokers had highly statistically significant decrease in chest expansion and increase in occiput to wall distance which reflects more disease progression. This was in acceptance with Kaan and Ferda [16], and Averns et al. [17].
Akyol et al. [18] reported that AS decreases and limits the expansion of the chest by affecting costosternal and costovertebral joints, thereby leading to restrictive respiratory distress. Pleuropulmonary tissue was also found to be injured and fibrosis could occur because of inflammatory processes within the lung parenchyma in AS patients. Smoking can also lead to an increase in inflammatory mediators and pain perception due to the effect of nicotine and indirect toxic effects of vasoconstriction or hypoxia [19].
We found insignificant differences between AS patients who currently smoke and AS patients who do not smoke as regards the presence of uveitis (as extraarticular manifestation); three of the studied patients only were having uveitis, and this small number of patients could not reflect the effect of smoking on developing uveitis as extraarticular manifestation of the disease. However, Yeun et al. [20] found that the incidence of new-onset uveitis increased among current smokers compared to never smokers. Also, there are several pathologic mechanisms that may explain the connection between smoking cigarette and uveitis based on longterm exposure to the high concentration of oxidants and polycyclic aromatic hydrocarbons in the serum of cigarette smokers which lead to an increase in the inflammatory mediators [21,22]. One of those is increasing the transcription of the leukocyte chemoattractant IL-8. Elevated concentrations of IL-8, as observed in the aqueous of the eye in uveitis, act together with IL-6 and TNF-α to promote the migration and activation of macrophages that attack the uvea [23]. Regarding laboratory data, the current smoker AS patients had higher mean ESR and highly significant CRP values. This finding is reflecting the presence of higher level of inflammatory markers in smokers AS patients. This was in agreement with Bazzano et al. [24]; Fröhlich et al. [25] who showed that smoking is significantly associated with elevated inflammatory markers especially CRP. Contrary to our results, Klingberg et al. [26] reported no differences in the level of erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) between smoking based groups. ESR and CRP have been used in combination to diagnose and monitor multiple conditions for many years. CRP is somewhat preferred as a serological marker for acute inflammatory disease [27].
Smoking increases the prevalence of low backache and degenerative diseases of the spine, which may participate in the negative impact of smoking in AS patients [36].
In addition, cigarette smoking was proven to reinforce the manufacturing of numerous pro-inflammatory cytokines such as TNF-α, IL-1, IL-6, IL-8, and GM-CSF (Granulocyte-macrophage colony-stimulating factors), and lower the levels of anti-inflammatory cytokine including IL-10. This inhibitory effect of anti-inflammatory cytokines production is thought to be due to the direct toxic effect of nicotine [37].
Talbot et al. [38] showed that smoking results in aggravation of arthritis and increases the rate of production of Th17 cells in animal models [38]. Th17cells is responsible for regulating the immune response that leads to clearance of extracellular pathogens including bacteria and fungi, and inducing tissue inflammation [38,39]. IL17 is a main cytokine released fromTh17, which takes critical role in the AS pathogenesis [40]. Subsequently, smoking results in increasing IL-17 which affects bone metabolism by activating the release of matrix metalloproteinases from macrophages and the receptor activator of NF-κB ligand (RANKL) presented by osteoblasts. Furthermore, IL-17 directly affects osteoclasts and activates osteoclastogenesis [40].
Recently, Sakellario et al. [41] demonstrated that smoking enhances the release of the vascular endothelial growth factor (VEGF), which is considered a signaling protein that performs a critical function in angiogenesis. The latter has a role in osteogenesis as well as the incidence of sacroiliitis, enthesitis, and syndysmophytes formation [41].
This may suggest that smoking was related to progressive structural damage in AS because the patients who currently smoke had significantly more syndesmophytes than those who had never smoked [42].
Dulger et al. [43] and Jones et al. [32] showed that smoking cessation improves chest expansion, disease Although most of the studied patients received TNF inhibitors (etanercept and adalimumab), the AS smoker patients had very high mean disease activity by ASDAS score in comparison to those in non-smokers. This was similar to a Swiss cohort study which concluded that current AS smokers had worse response rates versus non-smoker AS patients treated with TNFi [44]. Also, they found that current smokers revealed no improvement in disease activity scores (BASDAI and ASDAS scores) upon treatment with TNFi [44].
Demirjian et al. [45] showed that cigarette smoking activates human macrophages and induces the release of TNF-α [45] and increased matrix metalloproteinase levels [36,46,47] which may have negative effects and decrease the response to TNFi therapy in AS smoker patients.
In addition, the present study showed a highly statistically significant positive connection between the smoking index and each of BASFI, ASDAS, and mSASSS. A significant negative correlation was also noticed between Smoking Index and chest expansion. This was in agreement with prior studies of Reed et al. [48], Ward et al. [49], and Zhang et al. [33]. All reported that "The greater intensity of smoking is linked with worse outcomes in AS" [33].
Poddubny et al. [50] and Jiang et al. [51] reported that the sequel of smoking on disease activity, functional limitation, development of structural damage in the spine, and the radiographic spinal progression in axSPA is dependent on the intensity of smoking and appears to be caused by upsurge systemic systemic inflammation in smokers.
Finally, regarding the duration of symptoms, there was no significant difference between the smoker and nonsmoker AS patients. This was consistent with the results found by Kaut et al. [52] and Gaber et al. [53]. However, Sakellariou et al. [35] found that smoking is positively associated with the duration of inflammatory backache.

Conclusion
Current smoking carries an extraburden on ankylosing spondylitis patients and was associated with higher disease activity, inflammatory markers, functional disability, and radiological progression, and thus interferes with the personal daily activities, physical mobility, quality of life, and the response to TNFi therapy. So, stopping smoking is a mandatory step in controlling the disease activity and having favorable outcome.

Limitation of study
We have only 3 patients who stopped smoking; we need more patients to assess the effect of smoking stoppage in improving disease outcome.