Arthritis & Rheumatism, Volume 60,
October 2009 Abstract Supplement

The 2009 ACR/ARHP Annual Scientific Meeting
Philadelphia October 16-21, 2009.


Association of Plasma n-3 and n-6 Fatty Acids with Synovitis in the Knee: The MOST Study

Baker1,  K., Matthan2,  N. R., Lichtenstein2,  A. H., Grainger3,  A., Niu4,  J., Clancy4,  M., Lewis5,  C.

BUMC, Boston, MA
Tufts University, Boston, MA
U Leeds, Leeds, United Kingdom
BUSM, Boston, MA
UAB, Birmingham, AL
U Iowa, Iowa City, IA
UCSF, SF, CA
Boston University School of Medicine, Boston, MA

Purpose:

Studies have shown that fatty acids modulate the inflammatory response by multiple mechanisms. Specifically the n-6 fatty acid arachidonic acid (AA) and the n-3 fatty acids eicospentaenoic (EPA) and docosahexaenoic (DHA) can serve as precursors for the synthesis of bioactive lipid mediators including eicosanoids. Eicosanoids produced from AA induce eicosanoind-mediated inflammation while those produced from EPA and DHA inhibit inflammation. Synovitis represents an inflammatory process in the knee and has been shown to be a common feature in those with or at high risk of knee OA. We assessed the relationship of plasma n-6 and n-3 fatty acids with knee synovitis.

Methods:

The MOST study is a NIH-funded longitudinal study of risk factors for knee OA in persons age 50–79 with or at high risk of knee OA. Participants were those who volunteered to obtain a 1.5 contrast enhanced MRI of one knee and had fasting blood drawn at the 30-month clinic visit. Synovitis was scored 0–3 in 4 compartments (suprapatellar pouch, medial and lateral parapatellar recesses and infrapatellar fat pad) and 0–1 in 2 compartments (medial and lateral posterior condylar) (Rheumatol 44:1569 2005). Synovitis in the whole knee was categorized as "extensive" (>= 1 compartment scored 3), "a lot" (>= 2 compartments scored 2 but no 3s), "some" (>= 4 compartments scored 1 or 1 scored 2), "none/questionable" (< 4 compartments scored as 1). Inter-reader kappa was 0.9 (p<.001). Plasma samples stored at -80°C were measured for fatty acid concentrations using gas chromotagraphy. We analyzed the concentration of 3 fatty acids, AA, EPA, and DHA in quartiles, with synovitis using a logistic regression model adjusting for age, sex, BMI, MRI bone marrow lesions.

Results:

Of 500 subjects with a fatty acid measure, 28 were excluded, 11 were missing synovitis variables and 17 were taking fatty acid supplements. Mean age was 59.9 ± 7.3 years, mean BMI 29.5 ± 4.8 kg/m2, and 50% were women. 49% had "some" synovitis and 16%"a lot/extensive". The odds of having "a lot/extensive# synovits was 3.4 times more (95% CI 1.4, 10.5) in the highest quartile of AA versus the lowest. Levels of EPA and DHA were not associated with synovitis.

Conclusion:

These data suggest that higher tissue levels of AA may be associated with synovitis in the knee. The lack of a relationship of synovitis with EPA and DHA may be due to relatively low dietary intakes relative to those achieved with supplementation, which has resulted in decreased inflammatory mediators. Our findings indicate the potential for dietary manipulation as a therapy for synovitis.

 Arachidonic Acid 
Synovitis4.99–9.17 (n=120)9.19–10.41 (n=118)10.42–11.82 (n=115)11.85–17.66 (n=119) 
None/Questionable47 (39%)42 (35%)43 (37%)38 (32%) 
Some59 (49%)61 (52%)54 (47%)54 (45%) 
A lot/extensive14 (12%)15 (13%)18 (16%)27(23%)P for trend
Adj OR for some vs no synovitis (95% CI)1.01.1 (0.6, 1.9)1.1 (0.6, 2.0)1.2 (0.7, 2.2)0.5
Adj OR for a lot/extensive vs. no synovitis (95% CI)1.01.7 (0.5, 5.1)2.1 (0.7, 5.8)3.4 (1.4, 10.5)0.01

To cite this abstract, please use the following information:
Baker, K., Matthan, N. R., Lichtenstein, A. H., Grainger, A., Niu, J., Clancy, M., et al; Association of Plasma n-3 and n-6 Fatty Acids with Synovitis in the Knee: The MOST Study [abstract]. Arthritis Rheum 2009;60 Suppl 10 :202
DOI: 10.1002/art.25285

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