Evaluation of selective inhibition of canine cyclooxygenase 1 and 2 by carprofen and other nonsteroidal anti-inflammatory drugs

OBJECTIVE

To evaluate the activity of carprofen and other nonsteroidal anti-inflammatory drugs (NSAID) against isozymes of canine cyclooxygenases (COX1 and COX2).

PROCEDURE

Constitutive COX1 was obtained from washed canine platelets, and COX2 was obtained from a canine macrophage-like cell line that was induced with endotoxin. Activity of carprofen and other NSAID against COX1 and COX2 was compared. Dose-response curves were plotted, and calculations were performed to identify concentrations that caused 50% inhibition (IC50 [microM]) for each isozyme. Ratio of the COX1-to-COX2 IC50 was used as a measure of isozyme selectivity.

RESULTS

Of the compounds evaluated, carprofen had the greatest selectivity for COX2. Potency of carprofen for canine COX2 was more than 100-fold greater than for canine COX1. Inhibition of canine COX2 (IC50, 0.102 microM) for the racemic mixture of carprofen (S and R stereoisomers) was primarily attributable to the S enantiomer (IC50, 0.0371 microM), which was approximately 200-fold more potent than the R enantiomer (IC50, 5.97 microM). Nimesulide had the next highest selectivity for COX2 (38-fold), and tolfenamic acid and meclofenamic acid had 15-fold selectivity for COX2. The other compounds tested did not have substantial selectivity for canine COX2 or were more selective for canine COX1.

CONCLUSIONS

Carprofen was found to be a potent inhibitor of canine COX2. Of the compounds tested, carprofen had the highest selectivity for canine COX2.

CLINICAL RELEVANCE

The selectivity of carprofen for canine COX2 may be an important factor for its use in dogs.

In vitro microbiological characterization of novel macrolide CP-163,505 for animal health specific use

A novel 16-membered-ring macrolide agent (CP-163,505, a reductive amination derivative of repromicin) was identified as an antibacterial against Pasteurella haemolytica, P. multocida and Actinobacillus pleuropneumoniae, important etiological agents of livestock respiratory disease. In vitro MIC50/90 analysis revealed that CP-163,505 was more potent (4x) than tilmicosin against P. multocida, and equivalent to tilmicosin against P. haemolytica and A. pleuropneumoniae. In time kill kinetic studies, CP-163,505 showed bactericidal activity against P. haemolytica, P. multocida and A. pleuropneumoniae and bacteriostatic activity against E. coli at 8 times its MIC. In vitro, CP-163,505 was more potent in alkaline pH (16 approximately 32 x ) and less potent in the presence of excess cations (Mg+2 and Ca+2, 4x). EDTA and PMBN increased CP-163,505 potency against E. coli (4x) but not against the other species. Similar results were obtained with erythromycin A and tilmicosin, which were used as controls. From our data, we hypothesize that Pasteurella and Actinobacillus have an outer membrane significantly different from that of the typical enteric Gram-negative bacterium E. coli.

Structure-activity relationships of hygromycin A and its analogs: protein synthesis inhibition activity in a cell free system

Several analogs of hygromycin A were tested in an Escherichia coli cell free protein synthesis inhibition assay and in a Serpulina hyodysenteriae whole cell assay. The aminocyclitol moiety is essential for antibacterial activity in both cell free and whole cell assays. However a 4'-O-allyl ether of hygromycin A aglycone showed an equivalent MIC to hygromycin A, while having a less potent IC50 in the cell free assay. Hence 6-deoxy-5-keto-D-arabino-hexofuranose can be replaced by a hydrophobic allyl group and still retain antibacterial activity. However, this replacement reduces the intrinsic protein synthesis inhibition activity. The loss of intrinsic activity with replacement by the allyl group may be compensated for by better transport into the bacterial cell. In addition to the SAR analysis, we demonstrated that the ineffectiveness of hygromycin A against Gram-negative enteric bacteria such as Escherichia coli is mainly due to the efflux mechanism (Acr A/B pump) existing widely among the enteric bacteria rather than the impermeable barrier of the outer membrane.