In vitro effects of nonsteroidal anti-inflammatory drugs on cyclooxygenase activity in dogs.
OBJECTIVE
To establish an in vitro assay and determine the differential suppressive activity of non steroidal anti-inflammatory drugs (NSAID) on cyclooxygenase (COX)-1 and COX-2 isoenzymes in dogs.


METHODS
COX activity was evaluated in the presence and absence of 4 NSAID (meloxicam, tolfenamic acid, carprofen, and ketoprofen), using a canine monocyte/macrophage cell line that constitutively expresses COX-1, but can be induced to express COX-2 when incubated with lipopolysaccharide. Inhibition of prostaglandin E2 TPGE2) synthesis by each NSAID was measured by enzyme 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 (RT-PCR). The COX selectivity 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 concentrations that reduced PGE2 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 activity. 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. Effects of carprofen and ketoprofen approached equipotency against both isoenzymes. Selective COX-2 inhibitors are a new class of drugs with anti-inflammatory 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.
Kay-Mugford
P
P
Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Canada.
Benn
S J
SJ
LaMarre
J
J
Conlon
P
P
D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology*; D015152:Blotting, Northern; D002227:Carbazoles / Q000494:pharmacology; D002460:Cell Line; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology*; D004247:DNA / Q000737:chemistry; D017931:DNA Primers / Q000737:chemistry; D015232:Dinoprostone / Q000032:analysis / Q000096:biosynthesis*; D004285:Dogs / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004587:Electrophoresis, Agar Gel; D015971:Gene Expression Regulation, Enzymologic; D007124:Immunoenzyme Techniques; D007527:Isoenzymes / Q000187:drug effects / Q000235:genetics; D007660:Ketoprofen / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000737:chemistry; D000077239:Meloxicam; D011451:Prostaglandin-Endoperoxide Synthases / Q000187:drug effects* / Q000235:genetics; D012313:RNA / Q000737:chemistry / Q000302:isolation & purification; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013843:Thiazines / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D062367:ortho-Aminobenzoates / Q000494:pharmacology
D000894:Anti-Inflammatory Agents, Non-Steroidal; D002227:Carbazoles; D016861:Cyclooxygenase Inhibitors; D017931:DNA Primers; D007527:Isoenzymes; D008070:Lipopolysaccharides; D013843:Thiazines; D013844:Thiazoles; D062367:ortho-Aminobenzoates; C009500:tolfenamic acid; D012313:RNA; D004247:DNA; D007660:Ketoprofen; D011451:Prostaglandin-Endoperoxide Synthases; C007005:carprofen; D015232:Dinoprostone; D000077239:Meloxicam