Objective—To determine whether there is a relationship
between species-specific mitochondrial DNA
(mtDNA), especially canine and feline mtDNA, and
detectable amounts of pentobarbital in previously
analyzed dog food samples.
Sample Population—31 dog food samples previously
analyzed for pentobarbital (limit of detection, 1 µg/kg).
Procedure—Polymerase chain reaction (PCR) analysis
was performed on dog food samples by use of
PCR primers specific for either canine, feline, equine,
bovine, porcine, ovine, or poultry mtDNA.
Results—PCR amplicons specific for feline or canine
mtDNA at a 0.007% (70 µg/g [wt/wt basis]) or
0.0007% (7 µg/g) level, respectively, were not found
in the 31 dog food samples. Most of the 31 dog food
samples had a PCR amplicon on PCR analysis when a
PCR primer set capable of simultaneously detecting
mtDNA of cows, pigs, sheep, goats, deer, elk, and
horses was used. Results of PCR analysis by use of
primers specific for bovine, swine, sheep and goat, or
horse mtDNA revealed amplicons specific for bovine
or swine mtDNA only in 27 of the 31 samples.
Analysis of the remaining 4 samples failed to yield
amplicons for any mammalian mtDNA. Pentobarbital
was detected in 2 of these 4 samples. Results of PCR
analysis correlated with the stated ingredient list for
most, but not all samples.
Conclusions and Clinical Relevance—Because
canine and feline mtDNA were not found in a set of
retail dog food samples, these results indicate that
the source of pentobarbital in dog food is something
other than proteins from rendered pet remains. ( Am J Vet Res 2004;65:99–103)
Objective—To develop in genetically engineered mice an alternative screening method for evaluation of P-glycoprotein substrate toxicosis in ivermectin-sensitive Collies.
Animals—14 wild-type C57BL/6J mice (controls) and 21 genetically engineered mice in which the abcb1a and abcb1b genes were disrupted and the mutated canine ABCB1 gene was inserted.
Procedures—Mice were allocated to receive 10 mg of ivermectin/kg via SC injection (n = 30) or a vehicle-only formulation of propylene glycol and glycerol formal (5). Each was observed for clinical signs of toxic effects from 0 to 7 hours following drug administration.
Results—After ivermectin administration, considerable differences were observed in drug sensitivity between the 2 types of mice. The genetically engineered mice with the mutated canine ABCB1 gene had signs of severe sensitivity to ivermectin, characterized by progressive lethargy, ataxia, and tremors, whereas the wild-type control mice developed no remarkable effects related to the ivermectin.
Conclusions and Clinical Relevance—The ivermectin sensitivity modeled in the transgenic mice closely resembled the lethargy, stupor, disorientation, and loss of coordination observed in ivermectin-sensitive Collies with the ABCB1–1Δ mutation. As such, the model has the potential to facilitate toxicity assessments of certain drugs for dogs that are P-glycoprotein substrates, and it may serve to reduce the use of dogs in avermectin derivative safety studies that are part of the new animal drug approval process.
Objective—To identify biomarkers of P-glycoprotein (P-gp) substrate neurotoxicity in transgenic mice expressing the mutant canine ABCB1 gene (ABCB1-1Δ).
Animals—8 ABCB1 knock-in and knock-out transgenic mice expressing the ABCB1-1Δ gene and 8 control mice expressing the wild-type canine ABCB1 gene (ABCB1-WT).
Procedures—Groups including 2 ABCB1-1Δ mutant mice and 2 ABCB1-WT mice were administered the P-gp substrates ivermectin (10 mg/kg, SC), doramectin (10 mg/kg, SC), moxidectin (10 mg/kg, PO), or digoxin (1.53 mg/kg, SC). A toxicogenomic approach based on DNA microarrays was used to examine whole-genome expression changes in mice administered P-gp substrates.
Results—Compared with control ABCB1-WT mice, ABCB1-1Δ mutant mice developed neurotoxic signs including ataxia, lethargy, and tremors similar to those reported for dogs with the ABCB1-1Δ mutation. Microarray analysis revealed that gene expression was altered in ABCB1-1Δ mutant mice, compared with findings for ABCB1-WT mice, following administration of the same P-gp substrates. Gene pathway analysis revealed that genes with a ≥ 2-fold gene expression change were associated with behavior and nervous system development and function. Moreover, 34 genes were altered in the ABCB1-1Δ mutant mice in all 4 drug treatment groups. These genes were also associated with behavior, which was identified as the top-ranked gene network.
Conclusions and Clinical Relevance—These study data have facilitated understanding of the molecular mechanisms of neurotoxicosis in ABCB1-1Δ mutant mice following exposure to various P-gp substrates. Some genes appear to be potential biomarkers of P-gp substrate neurotoxicity that might be used to predict the safety of those drugs in dogs with the ABCB1-1Δ mutation.