P. Kay-mugford et al., In vitro effects of nonsteroidal anti-inflammatory drugs on cyclooxygenaseactivity in dogs, AM J VET RE, 61(7), 2000, pp. 802-810
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.