The determination of differences in hind paw weight distribution in the rat MIA model of OA is a technically straightforward, reproducible method that is predictive of the effects of anti-inflammatory and analgesic agents. This system may be useful for the discovery of novel pharmacologic agents in human OA.

Osteoarthritis (OA) is a degenerative joint disease characterized by joint pain and a progressive loss of articular cartilage. Studies to elucidate the pathophysiology of OA have been hampered by the lack of a rapid, reproducible animal model that mimics both the histopathology and symptoms associated with the disease. Injection of mono-iodoacetate (MIA), an inhibitor of glycolysis, into the femorotibial joint of rodents promotes loss of articular cartilage similar to that noted in human OA. Here, we describe the histopathology in the subchondral bone and cartilage of rat (Wistar) knee joints treated with a single intra articular injection of MIA (1 mg) and sacrificed at 1, 3, 5, 7, 14, 28, and 56 days postinjection. Histologically, the early time points (days 1-7) were characterized by areas of chondrocyte degeneration/necrosis sometimes involving the entire thickness of the articular cartilage in the tibial plateaus and femoral condyles. Changes to the subchondral bone, as evidenced by increased numbers of osteoclasts and osteoblasts, were noted at by day 7. By 28 days, there was focal fragmentation and collapse of bony trabeculae with fibrosis and increased osteoclastic activity. By 56 days there were large areas of bone remodeling evidenced by osteoclastic bone resorption and newly formed trabeculae with loss of marrow hematopoietic cells. Subchondral cysts and subchondral sclerosis were present in some rats. In conclusion, intra-articular injection of MIA induces loss of articular cartilage with progression of subchondral bone lesions that mimic those of OA. This model offers a rapid and minimally invasive method to reproduce OA-like lesions in a rodent species.

The role of inflammation in cardiovascular disease and especially in thrombogenesis has become increasingly recognized as an important component of the overall disease process. Plaque rupture promotes activation of the inflammatory response and increased expression of tissue factor (TF), which in turn acts as one of the major initiators of extrinsic coagulation. It is becoming apparent that the expression of TF on endothelial cells, underlying smooth muscle cells and monocytes is regulated, in part, by proinflammatory cytokines including tumor necrosis factor and IL-1. In addition to initiating coagulation, interaction of TF with the adhesion molecule, P-selectin, has been demonstrated to accelerate the rate and extent of fibrin formation and deposition. P-selectin is expressed on activated platelets and endothelium and serves as the receptor for the endogenous ligand, P-selectin glycoprotein-1 (PSGL-1), expressed on various leukocytic cell types. In addition to mediating transient interactions between endothelial cells and leukocytes, P-selectin has been reported to mediate adherence of platelets to monocytes and neutrophils via specific interaction with PSGL-1. P-selectin is rapidly cleaved off the surface of the platelet membrane and appears in the circulation as a soluble form, which has been reported to be elevated in patients with acute coronary syndromes including unstable angina and non-Q-wave myocardial infarction. This review will focus on the role of cytokines in mediating TF expression and also explore the significance of the relationship between P-selectin and tissue factor in thrombus generation. In addition, possible pharmacological mechanisms to interrupt this disease process will be discussed.

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The rat medial meniscal tear (MMT) model mimics both nociceptive and neuropathic OA pain and is responsive to both a selective cylooxygenase-2 (COX-2) inhibitor commonly utilized for OA pain (rofecoxib) and a widely prescribed drug for neuropathic pain (gabapentin). The rat MMT model may therefore represent a predictive tool for the development of pharmacologic interventions for the treatment of the symptoms associated with OA.