Objective—To demonstrate efficacy of flow cytometric evaluation of expression and activity of P-glycoprotein (P-gp) and multidrug resistance–associated protein (MRP) efflux pumps and characterize and correlate their expression and activity in grossly normal canine nodal lymphocytes.
Sample Population—Nodal lymphocytes from 21 clinically normal dogs.
Procedures—Pump expression was assessed by use of fluorescent-labeled mouse antihuman P-gp (C494) and MRP1 (MRPm6) antibodies and expressed as median values (antibody value divided by isotype control value). The P-gp and MRP activities were assessed by measuring cellular retention of rhodamine 123 and 5(6)-carboxyfluorescein diacetate in the absence and presence of inhibitors (verapamil and PSC833 for P-gp, probenecid and MK-571 for MRP). Protein activity was expressed as median fluorescence of cells with inhibitors divided by that without inhibitors.
Results—Expression of P-gp was (mean ± SEM) 50.62 ± 13.39 (n = 21) and that of MRP was 2.16 ± 0.25 (13). Functional activity was 1.27 ± 0.06 (n = 21) for P-gp and both inhibitors and 21.85 ± 4.09 (21) for MRP and both inhibitors. Function and expression were not correlated.
Conclusions and Clinical Relevance—Use of flow cytometry effectively assessed P-gp and MRP expression and activity in canine lymphocytes. Optimization of the flow cytometric assay was determined for evaluating activity and expression of these pumps in canine lymphoid cells. Evaluation of expression or activity may offer more meaning when correlated with clinical outcome of dogs with lymphoproliferative diseases. Cell overexpression of P-gp and MRP can convey drug resistance.
Objective—To assess kinetic 2-([18F]fluoro)-2-deoxy-d-glucose (18FDG) uptake in the brain of anesthetized healthy adult dogs by use of positron emission tomography (PET) and to determine whether 18FDG uptake differs among anatomic regions of the brain.
Animals—5 healthy Beagles.
Procedures—Each isoflurane-anesthetized dog was administered 18FDG IV (dose range, 3.0 to 5.2 mCi), and PET data were acquired for 2 hours. A CT scan (without contrast agent administration) was performed to allow more precise neuroanatomic localization. Defined regions of interest within the brain were drawn on reconstructed image data. Standard uptake values (SUVs) for 18FDG were calculated to generate time-activity curves and determine time to peak uptake.
Results—Time-activity curve analysis identified 4 regional uptake patterns: olfactory, gray matter, white matter, and other (brainstem, cerebellum, and occipital and frontal regions). The highest maximum SUVs were identified in the olfactory bulbs and cerebral gray matter, and the lowest maximum SUV was identified in cerebral white matter. Mean time to peak uptake ranged from 37.8 minutes in white matter to 82.7 minutes in the olfactory bulbs.
Conclusions and Clinical Relevance—Kinetic analysis of 18FDG uptake revealed differences in uptake values among anatomic areas of the brain in dogs. These data provide a baseline for further investigation of 18FDG uptake in dogs with immune-mediated inflammatory brain disease and suggest that 18FDG-PET scanning has potential use for antemortem diagnosis without histologic analysis and for monitoring response to treatment. In clinical cases, a 1-hour period of PET scanning should provide sufficient pertinent data.
Objective—To determine 2-deoxy-2-fluoro (fluorine 18)-d-glucose (18FDG) biodistribution in the coelom of bald eagles (Haliaeetus leucocephalus).
Animals—8 healthy adult bald eagles.
Procedures—For each eagle, whole-body transmission noncontrast CT, 60-minute dynamic positron emission tomography (PET) of the celomic cavity (immediately after 18FDG injection), whole-body static PET 60 minutes after 18FDG injection, and whole-body contrast CT with iohexol were performed. After reconstruction, images were analyzed. Regions of interest were drawn over the ventricular myocardium, liver, spleen, proventriculus, cloaca, kidneys, and lungs on dynamic and static PET images. Standardized uptake values were calculated.
Results—Kidneys had the most intense 18FDG uptake, followed by cloaca and intestinal tract; liver activity was mild and slightly more intense than that of the spleen; proventricular activity was always present, whereas little to no activity was identified in the wall of the ventriculus. Activity in the myocardium was present in all birds but varied in intensity among birds. The lungs had no visibly discernible activity. Mean ± SD standardized uptake values calculated with representative regions of interest at 60 minutes were as follows: myocardium, 1. 6 ± 0.2 (transverse plane) and 1.3 ± 0.3 (sagittal plane); liver, 1.1 ± 0.1; spleen, 0.9 ± 0.1; proventriculus, 1.0 ± 0.1; cloaca, 4.4 ± 2.7; right kidney, 17.3 ± 1.0; left kidney, 17.6 ± 0.3; and right and left lungs (each), 0.3 ± 0.02.
Conclusions and Clinical Relevance—The study established the biodistribution of 18FDG in adult eagles, providing a baseline for clinical investigation and future research.
OBJECTIVE To determine the pharmacokinetics of orally administered rapamycin in healthy dogs.
ANIMALS 5 healthy purpose-bred hounds.
PROCEDURES The study consisted of 2 experiments. In experiment 1, each dog received rapamycin (0.1 mg/kg, PO) once; blood samples were obtained immediately before and at 0.5, 1, 2, 4, 6, 12, 24, 48, and 72 hours after administration. In experiment 2, each dog received rapamycin (0.1 mg/kg, PO) once daily for 5 days; blood samples were obtained immediately before and at 3, 6, 24, 27, 30, 48, 51, 54, 72, 75, 78, 96, 96.5, 97, 98, 100, 102, 108, 120, 144, and 168 hours after the first dose. Blood rapamycin concentration was determined by a validated liquid chromatography–tandem mass spectrometry assay. Pharmacokinetic parameters were determined by compartmental and noncompartmental analyses.
RESULTS Mean ± SD blood rapamycin terminal half-life, area under the concentration-time curve from 0 to 48 hours after dosing, and maximum concentration were 38.7 ± 12.7 h, 140 ± 23.9 ng•h/mL, and 8.39 ± 1.73 ng/mL, respectively, for experiment 1, and 99.5 ± 89.5 h, 126 ± 27.1 ng•h/mL, and 5.49 ± 1.99 ng/mL, respectively, for experiment 2. Pharmacokinetic parameters for rapamycin after administration of 5 daily doses differed significantly from those after administration of 1 dose.
CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that oral administration of low-dose (0.1 mg/kg) rapamycin to healthy dogs achieved blood concentrations measured in nanograms per milliliter. The optimal dose and administration frequency of rapamcyin required to achieve therapeutic effects in tumor-bearing dogs, as well as toxicity after chronic dosing, need to be determined.