Background/Purpose:

High serum urate (SUA) is a risk factor for metabolic disease, including hypertension and coronary artery disease. However, SUA has an antioxidant effect and can play a role in protecting against diseases characterised by high oxidative stress, such as neurodegenerative disease. Osteoporosis, a condition defined by bone loss and fragility fractures, is also characterised by high oxidative stress levels, mediated through increased osteoclastic activity. Therefore, antioxidants are of considerable interest due to theoretical protective properties against bone loss. Existing literature examining SUA and its impact on bone mineral density (BMD), particularly in axial spondyloarthropathy (axSpA), is limited. The aim of this study is to examine the relationship between SUA and BMD in a well-characterised axSpA cohort.

Methods:

Patients fulfilling modified New York (mNY) or Assessment of SpondyloArthritis International Society (ASAS) criteria were consecutively recruited from 2 centres in this cross-sectional study. Patients underwent a detailed assessment: demographics, disease-related variables (validated measures of disease activity included BASDAI, ASDAS-CRP, BASMI), clinical examination, laboratory parameters (routine bloods, SUA, CRP, vitamin D). BMD was assessed using dual-energy x-ray absorptiometry of the lumbar spine and hip (total hip and femoral neck). SUA >360 µmol/L (>6 mg/dL) was considered high. Analysis was performed using SPSS.

Results:

A total of 107 patients were included: 76% male, 81% fulfilling mNY criteria, median (IQR) age 51.5 (17.8) years, disease duration 23.5 (20.4) years. Median BMI was 27.6 (6.5) kg/m^2, with 31% of the cohort obese. The median (interquartile range [IQR]) BASDAI was 3.9 (3.6), ASDAS-CRP 2.1 (1.5) and BASMI 4.1 (3.2). Low BMD was present in 38.5% of the cohort and 44% had a previous fracture.

Median (IQR) SUA in the cohort was 312 (119) µmol/L, with a SUA >360 µmol/L present in 34% (n=36). More men than women had high SUA (94% v 5.6%, p<0.01). BMI was significantly higher in those patients with SUA above 360 µmol/L than patients with normal levels (mean difference 4.2 kg/m^2, 95% CI 2.1-6.3). Age, disease duration, axSpA disease severity, psoriasis prevalence, vitamin D and CRP were equal in patients with high and normal levels of SUA.

SUA correlated positively (p<0.01) with BMD at the spine (r=0.3) and total hip (r=0.3). The cohort was subsequently examined in 3 groups of SUA: <300 µmol/L (43% of cohort), 300-360 µmol/L (23%) and >360 µmol/L (34%); mean BMD increased at the spine and total hip across the 3 groups (p<0.05), but not at the femoral neck.

Patients with a high SUA had significantly less osteopenia or osteoporosis (19%) than patients with a normal SUA (46%) (OR 3.5, 95% CI 1.4-9.3).

In univariate logistic regression analysis, low SUA and low BMI were associated with low BMD. After correcting for obesity, patients with high SUA remained independently associated with normal BMD compared to those patients with a normal SUA (OR 3.4, 95% CI 1.2-9.6).

Conclusion:

This study demonstrates that high SUA levels are independently associated with normal BMD, suggesting a protective effect of SUA against osteoporosis in axSpA patients.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/higher-serum-uric-acid-levels-protect-against-osteoporosis-in-patients-with-axial-spondyloarthropathy/