Avocado/soybean unsaponifiables prevent the inhibitory effect of osteoarthritic subchondral osteoblasts on aggrecan and type II collagen synthesis by chondrocytes

Abstract

Objective: To determine the effects of avocado/soybean unsaponifiables (ASU) on osteoblast-induced dysregulation of chondrocyte metabolism.

Methods: Human chondrocytes were isolated from osteoarthritis (OA) cartilage and cultured in alginate beads for 4 or 10 days in the absence or presence of osteoblasts isolated from nonsclerotic (NSC) or sclerotic (SC) zones of OA subchondral bone plate in monolayer. Before co-culture, osteoblasts were incubated or not with 10 microg/ml ASU for 72 hours. Aggrecan, type II collagen, matrix metalloproteinase-3 (MMP-3) and MMP-13, tissue inhibitor of metalloproteinase (TIMP-1), transforming growth factor-beta1 (TGF-beta1) and TGF-beta3, inducible NO synthase (iNOS), and cyclooxygenase-2 (COX-2) mRNA levels in chondrocytes were quantified by RT-PCR. Aggrecan, osteocalcin, TGF-beta1, interleukin 1beta (IL-1beta), and IL-6 production were assayed by immunoassays.

Results: In co-culture, SC osteoblasts induced a significant inhibition of matrix protein production and a significant increase of MMP synthesis by chondrocytes. In contrast, SC osteoblasts did not modify TIMP-1, TGF-beta1 and TGF-beta3, iNOS, or COX-2 mRNA levels in chondrocytes. The pretreatment of SC osteoblasts with ASU fully prevented the inhibitory effects of SC osteoblasts on matrix component production, and even significantly increased type II collagen mRNA level over the control (chondrocytes alone) value. In contrast, pretreatment of SC osteoblasts with ASU did not significantly modify the expression of MMP, TIMP-1, TGF-beta1, TGF-beta3, iNOS, or COX-2 gene by chondrocytes.

Conclusion: ASU prevent the osteoarthritic osteoblast-induced inhibition of matrix molecule production, suggesting that this compound may promote OA cartilage repair by acting on subchondral bone osteoblasts. This finding constitutes a new mechanism of action for this compound, known for its beneficial effects on cartilage.