Experimental OA Research Articles

The canine ‘groove’ model of osteoarthritis is more than simply the expression of surgically applied damage

Recently a new canine model of osteoarthritis (OA; the 'groove' model) has been described. This model is based on surgically applied mechanical damage of the articular cartilage followed by transient forced loading of the affected joint. Ten weeks after surgery this model shows characteristics of OA, mimicking human OA. To establish whether the observed characteristics of degeneration in this model represent the surgically applied damage, or are the results of progressive features of OA, we evaluated this 'groove' model shortly after surgery. In 20 female Beagle dogs, articular cartilage of the weight-bearing areas of the femoral condyles in the right knee was damaged without affecting the underlying bone. After surgery dogs were let out on a patio 5 days/week for 4 h/day. The dogs were forced to load the experimental joint by fixing the contralateral control limb to the trunk 3 days/week. The severity of OA was evaluated at 3 (n = 10) or 10 weeks (n = 10) after surgery. Synovial inflammation, cartilage damage and cartilage matrix turnover were determined. Ten weeks after surgery osteoarthritic features were found, as described previously. Proteoglycan (PG) synthesis, percentage release of newly formed PG, and that of total amount of PG were enhanced, whereas PG content was significantly diminished (all P < 0.05). Importantly, 3 weeks after surgery these characteristics of OA were not yet evident. The present results clearly show that the characteristics observed 10 weeks after induction of joint degeneration in the groove model are not just the expression of the surgically applied damage but are the result of progressive features of (experimental) OA.

Early and stable upregulation of collagen type II, collagen type I and YKL40 expression levels in cartilage during early experimental osteoarthritis occurs independent of joint location and histological grading

While morphologic and biochemical aspects of degenerative joint disease (osteoarthritis [OA]) have been elucidated by numerous studies, the molecular mechanisms underlying the progressive loss of articular cartilage during OA development remain largely unknown. The main focus of the present study was to gain more insight into molecular changes during the very early stages of mechanically induced cartilage degeneration and to relate molecular alterations to histological changes at distinct localizations of the joint. Studies on human articular cartilage are hampered by the difficulty of obtaining normal tissue and early-stage OA tissue, and they allow no progressive follow-up. An experimental OA model in dogs with a slow natural history of OA (Pond–Nuki model) was therefore chosen. Anterior cruciate ligament transection (ACLT) was performed on 24 skeletally mature dogs to induce joint instability resulting in OA. Samples were taken from different joint areas after 6, 12, 24 and 48 weeks, and gene expression levels of common cartilage molecules were quantified in relation to the histological grading (modified Mankin score) of adjacent tissue. Histological changes reflected early progressive degenerative OA. Soon after ACLT, chondrocytes responded to the altered mechanical conditions by significant and stable elevation of collagen type II, collagen type I and YKL40 expression, which persisted throughout the study. In contrast to the mild to moderate histological alterations, these molecular changes were not progressive and were independent of the joint localization (tibia, femur, lateral, medial) and the extent of matrix degeneration. MMP13 remained unaltered until 24 weeks, and aggrecan and tenascinC remained unaltered until 48 weeks after ACLT. These findings indicate that elevated collagen type II, collagen type I and YKL40 mRNA expression levels are early and sensitive measures of ACLT-induced joint instability independent of a certain grade of morphological cartilage degeneration. A second phase of molecular changes in OA may begin around 48 weeks after ACLT with altered expression of further genes, such as MMP13, aggrecan and tenascin. Molecular changes observed in the present study suggest that dog cartilage responds to degenerative conditions by regulating the same genes in a similar direction as that observed for chondrocytes in late human OA.

1182 EXPERIMENTAL MODELS OF MICROVESICULAR FATTY CHANGE IN RAT LIVER

An association of microvesicular hepatic fatty change with hyperammonemia and orotic aciduria (OAuria) has been noted in several pediatric conditions, including Reye's syndrome. Experimental OA supplementation produces fatty changes in rat liver. In the present study severe hyperammonemia (2-3 mg%), without OAuria was produced by repeated administration of urease (25 U/kg) for periods up to 24 hrs. The hyperammonemic rats were found to have hyperglycemia (374±21 mg%: controls: 172±6 mg%), elevated plasma FFA (815±62 μEq/1: controls 491±25 μEq/1) and hepatic triglycerides (15.6±1.4 mg/gm: controls: 2.7±0.2 mg/gm) (SEM). Liver sections stained with oil red O showed microvesicular fatty changes. To evaluate the role of OA in the development of fatty changes, conversion of OA to uridine monophosphate (UMP) was blocked with azauridine. Under these conditions fatty changes resulting from urease-induced hyperammonemia were markedly less than those observed without azauridine. It is concluded that increased availability of carbamyl phosphate in hyperammonemia leads to overproduction of OA and that the conversion of increased amounts of OA to UMP rather than OA elevation was an essential prerequisite to the induction of hepatic microvesicular fatty changes.