| Objective: Ankylosing spondylitis (AS) was a chronic autoimmune disease. In addition to joints and systems involved, there was a high incidence of osteopenia or osteoporosis(OP) and fracture in AS. The mechanism of OP involved in AS was not entirely clarified. Recent studies suggest that osteoclasts (OC) played an important role in bone metabolism. Macrophage- colony stimulating factor (M-CSF), interleukin-6 (IL-6), calcitonin (CT) were important factors in regulating OC. The aim of this study was to investigate the mechanism of bone metabolism in AS through determining bone mineral density(BMD),the serum level of M-CSF, IL-6, CT, bone alkaline phosphatase (BALP) and tartrate resistant acid phosphatase 5b (TRACP-5b).Methods: This cross-sectional study included 30 patients with AS and 20 age- and sex-matched normal controls. All the patients included were consistent with the American College of Rheumatology (ACR) 1984 revised classification criteria of AS. All patients were never continuously treated with glucocorticoid(GC) or disease modifying antirheumatic drugs (DMARDs). The BMD of lumbar vertebra, greater trochanter, femoral neck and intertrochanter of AS patients were measured through dual-energy X-ray absorptiometry (DXA) and the levels of serum M-CSF, IL-6, CT, BALP and TRACP5b were determined by avidin biotin peroxidase complex enzyme-linked immunosorbent assay (ABC-ELISA). The clinical data of AS patients were collected such as age, disease duration, erythrocyte sedimentation rate (ESR), c-reactive protein (CRP), platelet(PLT), levels of serum calcium (Ca), phosphorus (P), alkaline phosphatase (ALKP),etc.All the data were analyzed with SPSS11.5 for Windows statistical software. Quantitative data were expressed as ( x±s). The t or t'test was adopted for comparison between two groups.χ2 test was adopted for comparison between groups for numeration data. Linear correlation analysis was performed for correlationship. P value<0.05 was considered significant.Results: 1. General information description: 30 patients with AS were male, the mean age was (28.30±7.65) years, the mean disease duration at presentation was (81.3±82.25) months. In normal control group, 20 cases were male, the mean age was (30.20±5.20) years. There were no differences between the patients and normal subjects in age and gender (P>0.05). In AS group, the positive rate of HLA-B27 was 86.7% (26 cases), the mean value of ESR was (42.53±26.25) mm/h and CRP was (35.35±46.53) mg/L.2. The BMD condition in AS group: The incidence of normal BMD, osteopenia and OP in 30 AS patients were 16.67% (5 patients),46.67% (14 patients)and 36.67% (11 patients). The incidence of OP in lumbar vertebra, greater trochanter, femoral neck and intertrochanter were 13.3% (4 patients), 26.7% (8 patients), 0% (0 patients), 6.7% (2 patients). The incidence of osteopenia in lumbar vertebra, greater trochanter, femoral neck and intertrochanter were 53.3% (16 patients), 43.3% (13 patients), 16.7% (5 patients), 26.7% (8 patients). The incidence of low BMD was varying in different sites and the maxlmum site was greater trochanter (70.0%).3. The correlation between BMD and clinic index: According to correlation analysis, the BMD of greater trochanter, femoral neck and intertrochanter were positively correlated with BMI (P<0.05).4. The serum level of index of bone metabolism: The levels of M-CSF, IL-6 and TRACP-5b in AS group were (83.99±86.55) pg/ml, (1043.59±1345.90) pg/ml and (1.87±1.40)U/L, and the levels of these indexes in control group were (44.01±36.13) pg/ml, (194.02±248.74) pg/ml and (0.96±0.17) U/L. Compared with normal controls, The levels of M-CSF, IL-6 and TRACP-5b in AS group increased significantly (P <0.05). The levels of CT and BALP in AS group were (1.48±0.62) ng/ml and (28.44±14.56) U/L, and the levels of these indexes in control group were (1.58±0.40) ng/ml and (27.77±6.0) U/L, and there was no significant difference between the two groups. (P>0.05).5. The correlation between index of bone metabolism and clinic index: According to correlation analysis, the level of M-CSF was positively correlated with the level of IL-6 (r=0.911,P=0.000) in control group. In AS group, the level of M-CSF was positively correlated with WBC(r=0.385,P=0.036), the level of IL-6 was positively correlated with the level of TRACP-5b(r=0.625,P=0.000), the level of CT was positively correlated with the level of IgM(r=0.448,P=0.032), the level of BALP was positively correlated with BMI(r=0.464,P=0.011), and the level of BALP was positively correlated with the level of ALKP (r=0.393,P=0.032).6. The correlation between index of bone metabolism and BMD: According to correlation analysis, the serum level of IL-6 was positively correlated with the BMD of lumbar vertebra(r=0.579,P=0.002).7.AS patients were divided into two groups: OP group (11 cases) and non-OP group (19 cases) according to the complication with OP or not for further comparison. There was no significant difference between the two groups except the serum level of BALP. It was significant lower in OP group than non-OP group (P>0.05).Conclusion: 1. Varying degrees of bone loss were found in AS patients. Most patients were complicated with osteopenia or OP. The degree of bone loss was varying in different measurement sites. For a better overall evaluating of the BMD, it was necessary to measure BMD in multiple sites and make a comprehensive analysis. Low BMI was one of the predisposing factors of OP.2. There was abnormality in bone metabolism of AS, and enhancement of bone resorption was an important cause of osteopenia or OP. There was a strong positive correlation between the serum level of IL-6 and TRACP-5b, and it suggested that IL-6 was an important factor to reflect bone resorption.3. There was no strong correlation between bone metabolism indexes and clinic parameters, and also BMD and clinic parameters, suggesting that OP may be caused by multiple factors and long-term effectiveness. |
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