In vitro effects of nonsteroidal anti-inflammatory drugs on cyclooxygenaseactivity in dogs

Objective-To establish an in vitro assay and determine the differential sup pressive activity of non steroidal anti-inflammatory drugs (NSAID) on cyclo oxygenase (COX)-1 and COX-2 isoenzymes in dogs. Procedure-COX activity was evaluated in the presence and absence of 4 NSAID (meloxicam, tolfenamic acid, carprofen, and ketoprofen), using a canine mo nocyte/macrophage cell line that constitutively expresses COX-1, but can be induced to express COX-2 when incubated with lipopolysaccharide. inhibitio n of prostaglandin E-2 (PGE(2)) synthesis by each NSAID was measured by enz yme immunoassay and attributed to specific COX-1 or COX-2 activity through assessment of COX messenger RNA expression by use of northern blot analysis and reverse transcription-polymerase chain reaction (RI-PCR). The COX sele ctivity of each drug was evaluated from dose-response curves by calculating a ratio (COX-1:COX-2) of inhibitory concentration values on the basis of c oncentrations that reduced PGE, by 50% in each COX model. Results-Meloxicam and tolfenamic acid preferentially inhibited COX-2, with meloxicam inhibiting COX-2 activity 12 times more effectively than COX-1 ac tivity. Carprofen was only 1.75 times more selective for COX-2 than for COX -1, and ketoprofen was slightly more selective for COX-1. Conclusions-COX-1 and COX-2 were differentially sensitive to inhibition in vitro by NSAID. Meloxicam and tolfenamic acid were selective for COX-2. Eff ects of carprofen and ketoprofen approached equipotency against both isoenz ymes. Selective COX-2 inhibitors are a new class of drugs with anti-inflamm atory effects similar to conventional NSAID but with fewer adverse effects. Development of these agents for veterinary use would be facilitated by the convenience of using a canine cell line as a model system to screen COX-1 and COX-2 inhibitor activities in vitro.