Serum hyaluronan levels increase with the total number of osteoarthritic joints and are strongly associated with the presence of knee and finger osteoarthritis.

PURPOSE: Although serum hyaluronan (HA) levels increase in patients with osteoarthritis (OA), the association between OA severity and elevation of serum HA levels is not clear. Our purpose was to investigate the relationship between serum HA levels and OA in various anatomical sites and to detect which joints are strongly correlated with elevated serum HA levels. METHODS: Seven hundred and ten individuals from the general population who participated in the Iwaki Health Promotion Project in 2008 were involved. Kellgren-Lawrence grade 2 or higher in the knee, hip, lumbar spine, finger and wrist was defined as OA. Serum HA levels were determined on the same day. Spearman's correlation coefficients between serum HA levels and total number of joints affected by OA were calculated. Linear regression was analysed with serum HA levels as the independent variable; age, gender, presence of OA and intake of supplements were used as dependent variables. RESULTS: Prevalence of knee OA was 30.7 %, hip 16.8 %, lumbar spine 65.1 %, wrist 9.0 % and finger 22.0 %. Serum HA levels had a positive correlation with the number of involved joints, and the correlation coefficient was 0.410 (p < 0.001). Serum HA was significantly affected by age (ß = 0.382), knee OA (ß = 0.163) and finger OA (ß = 0.164). CONCLUSION: Although this biomarker reflects a systemic condition, higher serum HA levels were associated with total number of OA joints. Knee and finger OA were key joints related to increased serum HA levels. These results are valuable in understanding characteristics of serum HA levels as a biomarker for osteoarthritis.

Role of prostaglandin I2 in the gene expression induced by mechanical stress in spinal ligament cells derived from patients with ossification of the posterior longitudinal ligament.

Ossification of the posterior longitudinal ligament of the spine (OPLL) is characterized by ectopic bone formation in the spinal ligaments, and mechanical stress has been suggested to play an important role in the progression of OPLL. To identify the genes that participate in OPLL, the differential display reverse transcription-polymerase chain reaction (RT-PCR) method was used. A 283-base pair cDNA fragment corresponding to prostaglandin I2 (PGI2) synthase was highly expressed in OPLL cells compared with non-OPLL cells. To examine the effect of mechanical stress on the expression of PGI2 synthase, cells were subjected to uniaxial cyclic stretch (0.5 Hz, 20% stretch), and PGI2 synthase mRNA expression was assessed by quantitative RT-PCR. Cyclic stretch induced an increase in PGI2 synthase in OPLL cells in a time-dependent manner, whereas no change was observed in non-OPLL cells. Cyclic stretch for 9 h also induced a 2.86x increase in PGI2 production. Beraprost (a stable PGI2 analog) and dibutyryl cAMP (a membrane-permeable cAMP analog) increased the mRNA expression of alkaline phosphatase (ALP) as a marker for osteogenic differentiation up to 240 and 200%, respectively, in OPLL cells, whereas no change was observed in non-OPLL cells. The increases in ALP mRNA induced by beraprost and cyclic stretch were both inhibited by SQ22536, a potent adenylate cyclase inhibitor. These data suggest that the increase in PGI2 synthase induced by mechanical stress plays a key role in the progression of OPLL, at least in part through the induction of osteogenic differentiation in spinal ligament cells via the PGI2/cAMP system.