Angiogenesis in two animal models of osteoarthritis

We have previously described angiogenesis at the osteochondral junction and in synovium of knees from patients with osteoarthritis (OA), but little is known about how closely animal models of OA resemble human disease with respect to vascular growth. This study aimed to characterise two animal models of knee OA with particular respect to osteochondral and synovial angiogenesis.

We examined the spontaneous Dunkin-Hartley (DH) guinea pig and medial meniscal transection (MNX) rat models of OA. Vessels at the osteochondral junction and in the synovium were identified by lectin immunohistochemistry and quantified by computer-assisted image analysis. Disease severity was assessed using a scoring system.

Blood vessels crossed the osteochondral junction in juvenile rats and guinea pigs, with higher densities in the lateral than medial tibial plateau, the number decreasing with maturation in the absence of other OA changes. In the rat model, increased vascular density was observed both at the osteochondral junction and in the synovium, whilst osteochondral vascularity in control rats decreased with maturation, OA rats showed a persistence of blood vessels at the osteochondral junction. In rat synovium, blood vessel fractional area was increased in the hypertrophied synovium 14 days after surgery, then decreased to control levels by day 28. Significant differences in vascularity were not observed between affected (medial) and spared (lateral) compartments of guinea pig knees.

The rat meniscal transection model of OA reproducibly displays both osteochondral and synovial angiogenesis comparable to our previous observations in human knee OA. DH guinea pigs, by contrast, display low vascularity throughout their protracted course of OA development. Changes in vascularisation occur early during the development of OA in the rat, and may contribute to the pathogenesis of OA.