Phosphocitrate reduced cartilage degeneration in non-calcification induced osteoarthritis

Abstract

Purpose: It was believed that phosphocitrate (PC) exerted its disease modifying effect on calcification-induced osteoarthritis (OA) by inhibiting the formation of calcium crystals within the joints. However, recent studies suggest that PC exerts its disease modifying effect on OA, at least in part, through a crystal-independent mechanism. This study sought to investigate the disease-modifying effect of PC on partial-meniscectomy induced OA or non-calcification induced OA and test the hypothesis that PC is not only potentially a disease modifying drug for calcification-induced OA therapy but also potentially a disease-modifying drug for non-calcification-inducted OA therapy. Methods: Male Hartley guinea pigs of 4 weeks old were subjected to intraperitoneal injections of PC and physiological saline respectively. Two months later, partial medial meniscectomy was performed on the right knee of all guinea pigs to remove the anterior horn (calcification site) of the medical meniscus. After the surgery, injections of PC and saline were resumed. Five months later, these guinea pigs were euthanized and hind limbs were collected. Meniscal calcification and cartilage degeneration was examined with digital x-ray, Indian ink and safranin O staining. Matrix metaloproteinse-13 (MMP-13), ADAM metallopeptidase with thrombospondin type 1 motif 5 (ADAMTS5), chemokine (C-C motif) ligand 5 (CCL5), cyclooxygenase 2 (Cox-2) and type X collagen were examined with immunostaining. Results were are expressed as the mean ± standard deviation. The differences between PC-treated and untreated groups were analyzed using Student’s t test or Wilcoxon rank sum test. Results: Meniscal calcification in the medial meniscus was absent in the partial-meniscectomy performed right knees. PC treatment significantly reduced the severity of cartilage degeneration and cartilage thinning in the partial-meniscectomy induced OA or non-calcification-induced OA. The reductions in cartilage degeneration and cartilage thinning were accompanied with significantly decreased protein levels of MMP-13, ADAMTS5 and CCL5. Conclusions: PC is not only potentially a disease modifying drug for calcification-induced OA therapy but also potentially a disease-modifying drug for non-calcification-inducted OA therapy. PC exerts its disease modifying activity on non-calcification-induced OA mainly by targeting the production of extracellular matrix-degrading enzymes through a crystal-independent mechanism. These findings provide further support for the development of PC or its analogues as disease-modifying drugs for human OA therapy.Figure 2. Mean histological scores of the tibia plateaus. Left bar group: Mean histological scores of the medial tibia plateaus of the rights knees in the untreated and PC-treated guinea pigs. Right bar group: Mean histological scores of the lateral tibia plateaus of the right knees in the untreated and PC-treated guinea pigs. * = P < 0.05 PC-treated versus the untreated guinea pigs.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 3. Cartilage thickness. Left: thickness of the medial tibia cartilage in the untreated guinea pigs. Right: thickness of the medial tibia cartilage in the PC-treated guinea pigs.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 4. Immunostaining scores. Left bar group: MMP-15 immunostaining. Middle bar group: ADAMTS5 immunostaining. Right bar group: CCL-5 immunostaining.View Large Image Figure ViewerDownload Hi-res image Download (PPT)