Questionable role of leukotriene B4 in monosodium urate (MSU)-induced synovitis in the dog

Kinetic gait and subjective analysis of the effects of a tachykinin receptor antagonist in dogs with sodium urate-induced synovitis

OBJECTIVE

To examine the ability of preemptive administration of a proprietary neurokinin-1 (NK(1)) receptor antagonist to attenuate limb dysfunction associated with monosodium urate-induced synovitis in the stifle joints of dogs.

ANIMALS

16 clinically normal adult mixed-breed dogs (8 males and 8 females).

PROCEDURES

A crossover study was conducted in 2 phases. Dogs were assigned to 2 groups (8 dogs/group) and orally administered an NK(1) receptor antagonist (3 mg/kg) or a control substance once daily for 4 days. Synovitis was then induced in the left stifle joint by intra-articular injection of monosodium urate. Investigators were not aware of treatment group assignments. Dogs were evaluated by use of subjective lameness scores during standing, walking, and trotting and by use of ground reaction force data 3, 6, 9, 12, and 24 hours after urate injection. After a 21-day washout period, the experiment was repeated with each dog administered the other treatment and injected with monosodium urate in the contralateral stifle joint.

RESULTS

No significant differences were detected between the NK(1) receptor antagonist and control treatments with regard to peak vertical force, vertical impulse area, or subjective evaluations of lameness during standing, walking, or trotting, except during walking 24 hours after monosodium urate injection.

CONCLUSIONS AND CLINICAL RELEVANCE

Preemptive administration of an NK(1) receptor antagonist failed to significantly improve subjective or objective outcome measures in dogs with monosodium urate-induced synovitis.

Concentrations of cartilage oligomeric matrix protein in dogs with naturally developing and experimentally induced arthropathy

OBJECTIVE

To assay concentrations of cartilage oligomeric matrix protein (COMP) in canine sera and synovial fluid (SF), to compare COMP concentrations in clinically normal dogs and dogs with joint disease, and to analyze changes in COMP concentrations in dogs with experimentally induced acute synovitis.

ANIMALS

69 control dogs without joint disease, 23 dogs with naturally occurring aseptic arthropathy, and 6 dogs with experimentally induced synovitis.

PROCEDURE

Serum (n = 69) and SF (36) were obtained from control dogs. Samples of serum (n = 23) and SF (13) were obtained from dogs with naturally occurring aseptic arthropathy with or without radiographic features of osteoarthritis (OA). Serum and SF were obtained before and 1, 2, 3, and 7 days after induction of synovitis. The COMP concentrations were determined by use of an inhibition ELISA that had canine cartilage COMP and monoclonal antibody against human COMP.

RESULTS

Concentrations of COMP in serum and SF of control dogs were 31.3+/-15.3 and 298.7+/-124.7 microg/ml, respectively. In naturally occurring OA, COMP concentrations in serum (44.9+/-177 microg/ml) and SF (401.7+/-74.3 microg/ml) were significantly higher than corresponding concentrations in control dogs. The COMP concentration in SF peaked 24 and 48 hours after induction of synovitis, whereas concentration in serum peaked on day 3.

CONCLUSIONS AND CLINICAL RELEVANCE

These results supported the hypothesis that COMP concentration in serum and SF of dogs may be altered after cartilage degradation or synovitis. Measurement of COMP concentrations can be useful when differentiating arthropathies in dogs.

Altered arachidonic acid metabolism in urate crystal induced inflammation

Gout is an acute rheumatic disorder that occurs in connection with the deposition of monosodium urate (MSU) crystals in the joints. This disease is characterized by intermittent episodes of severe pain and inflammatory joint swelling which are seemingly driven by prostaglandins. In this study we investigated the effect of MSU crystals on arachidonic acid (AA) metabolism in the mouse. We have demonstrated that prostaglandins and other AA metabolites were transiently formed after MSU crystal injection with peak levels occurring after 10 min. In contrast, free AA levels remained high for 2-4 hours after MSU crystal injection. By contrast, when exogenous AA was administered instead of MSU crystals, both the eicosanoids and AA diminished at the same high rates. The metabolism of exogenously administered AA to eicosanoids was inhibited by pretreatment with MSU crystals. No inhibition of AA metabolism was observed when mice were pretreated with AA itself, Ca2+ ionophore (A23187), or zymosan. We conclude that the MSU crystal treatment of mice results in a transient eicosanoid production which is followed by attenuated AA metabolism. It could be that MSU crystals similarly inhibit AA metabolism in gout and thereby limit the duration of gout attacks.

Lipoxygenase products in inflammatory synovial fluids and other exudates

Forty six synovial fluid samples from 42 patients with inflammatory joint disease were analysed by reversed phase high performance liquid chromatography to determine 5-lipoxygenase products, specifically dihydroxyeicosatetraenoic acids (diHETEs). Twenty eight per cent of the fluids which were assayed had one or more products of 5-lipoxygenase activation. Seven fluids contained leukotriene B4 (0.1-28.1 ng/ml); three fluids had low concentrations of 20 carboxy/hydroxy-leukotriene B4 (0.01-0.05 ng/ml); three samples had leukotriene B4 isomers (1.5-2.4 ng/ml); and four fluids contained 5,15-diHETE (2.3-16.4 ng/ml). There was a poor correlation between synovial fluid white blood cell counts and evidence of 5-lipoxygenase activation. Several fluids contained unidentified compounds with spectra similar in shape to that of trienes, but the lambda max values of these unidentified compounds were different from those of known leukotrienes. A septic peritoneal exudate and a septic pleural fluid had concentrations of leukotriene B4 and leukotriene B4 isomers and metabolites in a range similar to those found in synovial fluids.

Inhibition of leucotriene B4 synthesis by BW 755c does not reduce polymorphonuclear leucocyte (PMNL) accumulation induced by monosodium urate crystals

Monosodium urate (MSU) crystals induce an inflammatory response when injected into the rat subcutaneous air pouch, which is characterised by polymorphonuclear leucocyte (PMNL) accumulation and plasma leakage. The arachidonic acid metabolites leucotriene B4 (LTB4), prostaglandin E2 (PGE2), 6-oxo-prostaglandin F1 alpha, (6-oxo-PGF1 alpha), and thromboxane B2 (TXB2) are found in increased concentrations in MSU induced exudates compared with animals injected with phosphate buffered saline (PBS). Pretreatment of animals with BW 755c significantly reduced the concentration of both lipoxygenase and cyclo-oxygenase derived arachidonic acid metabolites. Although BW 755c reduced MSU crystal induced plasma leakage, it did not affect PMNL accumulation. Pretreatment of animals with indomethacin selectively inhibited the generation of cyclo-oxygenase derived arachidonic acid metabolites and reduced MSU crystal induced plasma leakage but had no effect on PMNL accumulation. The inhibition of plasma leakage by either BW 755c or indomethacin was reversed by prostaglandin E2 (1 microgram/ml), which itself produced a significant increase in plasma leakage. The injection of purified LTB4 (4 ng/ml or 40 ng/ml) did not induce either plasma leakage or PMNL accumulation within the air pouch. These data suggest that although MSU crystals stimulate LTB4 production, LTB4 is not the mediator of MSU crystal induced PMNL accumulation. Cyclo-oxygenase products of arachidonic acid metabolism (e.g., PGE2), however, appear to play a part in MSU crystal induced plasma leakage.