(HealthDay News) – A new biomarker is associated with osteoarthritis severity at the hip but not the knee, according to a study published in the Feb. 10 issue of the Journal of Biological Chemistry.

Noting that aging extracellular proteins undergo modifications that accumulate over time, Jonathan B. Catterall, PhD, from the Duke University Medical Center in Durham, NC, and colleagues examined possible hotspots for deamidation within the cartilage oligomeric matrix protein (COMP). They then determined whether the modified protein was present in osteoarthritis patients.

The researchers identified asparagine 64 as a possible hot spot for deamidation (conversion to aspartate) within COMP. Serum levels of deamidated COMP (D-COMP), but not total COMP, fell significantly after joint replacement. D-COMP was associated with osteoarthritis severity at the hip but not the knee, while total COMP was associated with osteoarthritis severity at the knee but not the hip. Levels of D-COMP were found to be higher in hip cartilage nearest the lesions.

“This study demonstrates the presence of D-COMP in articular cartilage and the systemic circulation, and to our knowledge, it is the first biomarker to show specificity for a particular joint site,” Catterall and colleagues conclude. “We believe that enrichment of deamidated epitope in hip osteoarthritis cartilage indicates a lesser repair response of hip osteoarthritis compared with knee osteoarthritis cartilage.”

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