Background Osteoarthritis (OA) involves degenerative changes in articular cartilage, remodelling of subchondral bone and limited synovial inflammation. Osteoarthritic changes in articular cartilage are associated with progressive proteolytic degradation of the extracellular matrix (ECM), which is composed mainly of type II collagen and aggrecan. Their destruction leads to eventual cartilage loss that is accompanied by phenotypic hypertrophy-related changes in chondrocytes.
Objectives Here we studied the effects of the iron chelator deferoxamine (DFO) on collagen cleavage, inflammation and chondrocyte hypertrophy in relation to energy metabolism-related gene expression in OA articular cartilage. We hypothesised that DFO treatment of human OA articular cartilage explants might decrease collagen cleavage activity, generation of pro-inflammatory cytokines and recover an often-altered chondrocyte phenotype by changing the cellular energy balance in favour of improving of mitochondrial function and restoring an anabolic matrix phenotype. We tested this hypothesis in cultured OA cartilage while also examining and comparing whole-body AMPK expression by peripheral blood mononuclear cells (PBMCs) in OA versus normal patients.
Methods Full-depth explants of human OA knee articular cartilage from arthroplasty were cultured with exogenous DFO (1–50μM). Type II collagen cleavage and phospho-adenosine monophosphate activated protein kinase (pAMPK) concentrations were measured using ELISAs. Gene expression studies in the knee articular cartilage employed real-time PCR and included AMPK analyses in PBMCs.
Results In OA explants collagen cleavage was frequently downregulated by 10–50 μM DFO. PCR analysis of five OA patient cartilages revealed that 10 μM DFO suppressed expression of MMP-1, IL-1b and TNFa, and a marker of chondrocyte hypertrophy, COL10A1. No changes were observed in the expression of glycolysis-related genes. In contrast, expressions of genes associated with the mitochondrial citric acid cycle (TCA) and AMPK were upregulated. Gene expressions of HIF1α and COL2A1 were also upregulated in individual patients but not significantly in the whole group. AMPK gene expression was reduced in OA cartilage and increased in PBMCs from the same patients compared to healthy controls.
Conclusions Our studies demonstrate that DFO is capable of suppressing excessive collagenase-mediated type II collagen cleavage in OA cartilage and reversing phenotypic changes. The concomitant upregulation of pro-anabolic TCA-related gene expressions points to a potential for availability of energy generating substrates required for matrix repair by end-stage OA chondrocytes. This might normally be prevented by high whole-body energy requirements indicated by elevated AMPK expression in PBMCs of OA patients.
Disclosure of Interest E. Tchetina: None declared, G. Markova: None declared, A. Poole Consultant for: IBEX, Montreal, Canada