Two Members of Vitamin-K-Dependent Proteins, Gla-Rich Protein (GRP) and Matrix Gla Protein (MGP), as Possible New Players in the Molecular Mechanism of Osteoarthritis

Kurtuluş B, Atilgan N, Yilmaz M, Dokuyucu R · Journal of Clinical Medicine

Puts a second vitamin-K-dependent protein beside matrix Gla protein and measures both in the joint, and both are higher where the disease is. Gla-rich protein came to 419.6 ± 70.1 ng/mL in osteoarthritic synovial fluid against 382.2 ± 62.3 in the controls (p = 0.037), matrix Gla protein to 67.8 ± 11.4 against 53.5 ± 18.3 (p = 0.001), and calcium to 12.89 ± 3.43 mg/dL against 9.51 ± 2.15 (p = 0.0001). The authors read the two inhibitors as rising in response to the calcium rather than failing to hold it down. Matrix Gla protein tracks age (R = +0.335, p = 0.011) and Gla-rich protein does not (p = 0.486), which is the paper's argument for preferring it as a marker.

Population

26 people undergoing knee replacement for grade 4 primary osteoarthritis, mean age 62.0, against 31 having arthroscopy for a meniscal tear or an ACL rupture with no cartilage disease, mean age 47.7

Intervention

Knee synovial fluid assayed by ELISA for Gla-rich protein, matrix Gla protein and calcium

Comparator

The non-osteoarthritic knees

Limitations

A single measurement in two surgical groups, so nothing here says which way cause runs, and every osteoarthritic knee was grade 4 — the authors name that as their main limitation. The comparison group is not healthy knees but knees being repaired after a meniscal tear or an ACL rupture. The osteoarthritic group is 14 years older on average (p = 0.0001), which is the variable matrix Gla protein correlates with. The paper describes itself in its methods as a double-blind randomised clinical trial, which it is not, and reports concentrations above the detection ceiling its own assay section states. No declared conflicts.