Effects of a metalloproteinase inhibitor on osteochondral angiogenesis, chondropathy and pain behavior in a rat model of osteoarthritis

Abstract

Objective: To investigate the effects of a matrix metalloproteinase (MMP) inhibitor on joint pathology and pain behavior in the rat meniscal transection (MNX) model of osteoarthritis (OA) and evaluate which aspects of structural disease modification contribute to symptom improvement.

Methods: OA pathology was induced in male Lewis rats, by transecting the medial collateral ligament with (MNX) or without (SHAM) a full thickness cut through the meniscus. MNX animals were orally administered an equipotent MMP 2, 8, 9, 12, 13 inhibitor (0.25, 1 and 5 mg/kg/day) or vehicle from day 1. Chondropathy, osteophytosis, osteochondral vascularity were assessed from toluidine blue stained coronal sections of the total knee joint and weight-bearing asymmetry by incapacitance. Group differences were evaluated using 1-way analysis of variance (ANOVA) and associations as Spearman's correlation coefficients.

Results: Treatment with the MMP inhibitor reduced weight-bearing asymmetry from day 14 onwards, and attenuated chondropathy (both P<0.05). Osteochondral vascularity was elevated in MNX compared with SHAM-operated animals (P<0.001) and reduced, dose-dependently, by MMP inhibitor treatment (r=-0.89, P<0.05). Reduced osteochondral vascularity and chondropathy were associated with the amelioration of weight-bearing asymmetry (both P<0.05).

Conclusion: Here we show that treatment with a MMP inhibitor reduces joint damage, osteochondral angiogenesis and behavioral evidence of pain. The association between osteochondral angiogenesis and pain behavior may be explained by perivascular nerve growth or stimulation of subchondral nerves following loss of osteochondral integrity. Our data suggest that targeting angiogenesis may have utility in the treatment of pain associated with structural damage in OA.

Fig. 1

A). Representative image of the medial tibial plateau of a menisectomised (MNX) animal at 35 days post surgery showing full thickness cartilage fibrillation and proteoglycan loss (arrows). A large osteophyte (circled) has formed at the joint margin. B). Representative image of the medial tibial plateau of a sham (SHAM) operated animal at 35 days. There is no evidence of proteoglycan loss or fibrillation of the cartilage surface. The joint margin appears normal. Scale bars 100 μm.

Fig. 2

A). Representative image of the medial tibial plateaux of MNX animal showing loss of proteoglycan and cartilage fibrillation (large arrows) vascular channels arising from the subchondral bone are evident at the osteochondral junction (small arrows). B). Medial tibial plateu from an MNX animal treated with 5.0 mg/kg/day M503092. The cartilage surface shows no fibrillation but there is some proteoglycan loss as evidence by diminished toluidine blue staining. Fewer vascular channels (small arrow) are seen in treated animals. C). SHAM-operated animal showing intact cartilage and no vascular channels in this section. Sections were stained with toluidene blue and imaged with a small diameter substage diaphragm to demonstrate blood vessels as refractile structures within channels. Scale bars 100 μm.

Fig. 3

The effect of increasing doses of a MMP inhibitor, in the rat MNX model of OA, on chondropathy (Panel A), osteophytosis (Panel B) and the number of vessels crossing the osteochondral junction (Panel C). Treatment with 0.5 and 2.5 mg bid resulted in significant decreases in the chondropathy scores (P < 0.05) and in the number of blood vessels crossing the osteochondral junction (P < 0.001).There was no significant effect on osteophytosis.

Fig. 4

Time course showing the effect of increasing doses of a MMP inhibitor on pain behavior, as measured by a difference in weight bearing, in the MNX and SHAM animals. Vehicle-treated animals continued to show pain behavior but this behavior was dose-dependently decreased by increasing doses of M503092. SHAM animals returned to normal weight bearing over the course of the experiment. Values for 0.125 mg/kg/bid and 2.5 mg/kg/bid have been offset by 0.5 days to increase the clarity of presentation by preventing overlap of error bars. Areas under the curve were calculated for the 10 individual animals in each treatment group and a mean with 95% CI's computed. Differences between groups were sought with 1-way ANOVA with Bonferroni corrections.