Summary. PCA-III, a phosphocitrate analog, acts not only as a potent calcification inhibitor but also as a protective agent for extracellular matrices. PCA-III has potential as a disease-modifying drug in the treatment of primary osteoarthritis and posttraumatic osteoarthritis in humans. Introduction. Phosphocitrate (PC) inhibits the development of primary osteoarthritis (OA) in Hartley guineas pigs but not menisectomy-induced OA in rabbits (1). We sought to examine the molecular mechanisms underlying the disease-modifying activity of PC, and evaluate the effect of PCA-III, a PC analog (PCA), on the development of primary and secondary OA. Patients & Methods. Meniscal explant and microarray. OA menisci were obtained from OA patients undergoing joint replacement surgery. OA meniscal explants were cultured in medium containing PC (three wells) and medium without PC (three wells). Total RNA was extracted from the explant, and subjected to microarray analysis. RT-PCR. OA fibroblast-like synoviocytes were treated with basic calcium phosphate (BCP) crystals in the absence or presence of PCA-III. RNAs were extracted, and subjected to semi-quantitative RT-PCR to examine the expression of MMP1 and IL-1b. Micromass culture. A droplet of OA chondrocyte suspension was placed in each well of a 24-well plate. After placing all droplets, the wells were fed with chondrogenesis medium with PCA-III (five wells) and without PCA-III (five wells). The production of proteoglycans was examined by alcian blue staining. Animal treatment. The first group of Hartley guinea pigs (n=5) received injections of PCA-III and the second group received injections of saline as control. Two months later, partial-menisectomy surgery was performed on the right knee of all guinea pigs. After the surgery, injections of PCA-III and saline were resumed. All animal were euthanatised four months later, and both knees were examined. Results. PC inhibited the expression of many genes classified into the molecular function group of MMP activity. Of the 23 genes classified into MMP activity, the expression of 16 genes, including CPM, ADAM28, MMP7, MMP10, MMP1, MMP3, ADAMTS5, ADAMTS1, and ADAMTS9, was inhibited. In contrast, the expression of many genes classified into the molecular function group of extracellular matrix structural constituents, was induced by PC, including COL2A1, COL11A1, COL1A1 and ACAN. PC also inhibited the expression of numerous genes classified into the biological process of inflammatory response (data not shown). PCA-III, similar to PC, inhibited BCP crystals-induced expression of MMP1 and IL-1b). In addition, PC-III strongly stimulated the production of proteoglycans by OA chondrocytes while inhibiting calcium deposition (not shown). Microscopic examination of the Indian ink stained medial tibia plateau of the left knees (non-surgery knee) of the guinea pigs indicated that PCA-III inhibited the development of primary OA in the Hartley guinea pigs. Microscopic examination also indicated that PCA-III inhibited the development of partial-menisectomy-induced OA or posttraumatic OA in the post-operative knees. Discussion/Conclusion. PC is thought to act as a potential structural disease-modifying drug for crystal-associated OA by inhibiting crystal deposition within the OA joints. However, PC and its analogs are not only potent calcification inhibitors, but also protective agents for extracellular matrices. Our findings indicate that PCA-III has potential as a disease-modifying drug for both human crystal-associated OA and posttraumatic OA
