Modulation of P-glycoprotein-mediated doxorubicin resistance in canine cell lines.

OBJECTIVE: To characterize the chemosensitivity of wild type and multidrug resistant canine cell lines and determine the relative potency of the P-glycoprotein (Pgp) modulators verapamil, tamoxifen and a cyclosporin-A analog (PSC833). METHODS: The dose required to reduce cell proliferation to 50% of control (ED50) for doxorubicin (DOX) and cisplatin was determined for canine cell lines 4TG11-50c, OS2.4wt, OS2.4DX and the human cell line MCF7/DX. The effect of Pgp chemomodulators on cytotoxicity was quantified by determining the dose modifying factor [DMF = (ED50 of Dox alone)/(ED50 of Dox + Modulator)]. Relative potency of modulators was defined as DMFMOD1/DMFMOD2. Pgp function was assessed by DiOC2 dye retention and by accumulation of DOX after chemomodulator addition. RESULTS: All cell lines were equally cisplatin sensitive but varied in doxorubicin resistance. PSC833 was 12X, 5X and 2X more potent than tamoxifen in 4TG11-50c, OS2.4WT and OS2.4DX, respectively. Dye retention was a better indicator of chemomodulator-enhanced cytotoxicity than was DOX accumulation. CONCLUSIONS: Pgp inhibition is cell line, modulator and concentration dependent but the cytotoxic potency of a modulator may be predicted by the extent of dye retention in canine drug resistant cell lines.

Evaluation of intestinal permeability and gluten sensitivity in Soft-Coated Wheaten Terriers with familial protein-losing enteropathy, protein-losing nephropathy, or both.

OBJECTIVE: To evaluate intestinal permeability and gluten sensitivity in a family of Soft-Coated Wheaten Terriers (SCWT) affected with protein-losing enteropathy (PLE), protein-losing nephropathy (PLN), or both. ANIMALS: 6 affected adult dogs. PROCEDURE: Intestinal biopsy specimens, urine protein-to-creatinine ratio, serum concentrations of albumin and globulin, and concentration of alpha1-protease inhibitor in feces were evaluated before, during, and 13 weeks after daily administration of 10 g of gluten for 7 weeks. Eosinophils and lymphocytes-plasmacytes were enumerated in intestinal biopsy specimens. Intestinal permeability was evaluated before and during the sixth week of gluten administration via cellobiose-mannitol and chromium-EDTA absorption tests. RESULTS: Serum globulin concentration decreased significantly after prolonged administration of gluten. Although not significant, there was an increase in lymphocytes-plasmacytes and a decrease in eosinophils in intestinal biopsy specimens. Furthermore, these counts were greater than those reported for clinically normal dogs. Gluten administration did not increase intestinal permeability. CONCLUSIONS AND CLINICAL RELEVANCE: Daily administration of gluten was associated with a significant decrease in serum globulin concentration in SCWT affected with PLE or PLN, but other variables remained unchanged. Although enhanced wheat-gluten sensitivity may be one factor involved in the pathogenesis of PLE or PLN in SCWT, this syndrome does not appear to be the result of a specific sensitivity to gluten.

Food hypersensitivity reactions in Soft Coated Wheaten Terriers with protein-losing enteropathy or protein-losing nephropathy or both: gastroscopic food sensitivity testing, dietary provocation, and fecal immunoglobulin E.

The purpose of this study was to evaluate Soft Coated Wheaten Terriers (SCWTs) affected with protein-losing enteropathy (PLE) or protein-losing nephropathy (PLN) or both for allergy to food. We performed gastroscopic food-sensitivity testing, a provocative dietary trial, and measurement of fecal immunoglobulin E (IgE) in 6 SCWTs affected with PLE or PLN or both. Positive gastroscopic food-sensitivity test reactions were noted in 5 of 6 dogs. Positive reactions were found to milk in 4 dogs, to lamb in 2 dogs, and to wheat and chicken each in 1 dog. Adverse reactions to food (diarrhea, vomiting, or pruritus) were detected in all 6 dogs during the provocative dietary trial. Adverse reactions were found to corn in 5 dogs, to tofu in 3 dogs, to cottage cheese in 2 dogs, to milk in 2 dogs, to farina cream of wheat in 2 dogs, and to lamb in 2 dogs. Serum albumin concentrations significantly decreased and fecal alpha1-protease inhibitor concentration significantly increased 4 days after the provocative trial when compared with baseline values. Antigen-specific fecal IgE varied throughout the provocative trial, with peak levels following ingestion of test meals. We conclude that food hypersensitivities are present in SCWTs affected with the syndrome of PLE/PLN. Mild inflammatory bowel disease was already established in the 6 SCWTs of this report at the time of study, making it impossible to determine if food allergies were the cause or result of the enteric disease.

Phase I and pharmacokinetic analysis of high-dose tamoxifen and chemotherapy in normal and tumor-bearing dogs.

PURPOSE: To determine whether tamoxifen plasma concentrations capable of blocking P-glycoprotein (Pgp) in vitro can be safely achieved in dogs and whether doxorubicin pharmacokinetic alterations occur when tamoxifen is coadministered. METHODS: Tamoxifen dose escalation studies were conducted in 7 normal dogs and in 19 tumor-bearing dogs receiving full-dose chemotherapy. Plasma tamoxifen and serum doxorubicin disposition were analyzed for putative drug interactions. RESULTS: Steady-state plasma concentrations of tamoxifen and N-desmethyl tamoxifen (NDMT) were 5-10 microM following oral tamoxifen administration at 600 mg/m2 every 12 h for 7 days to normal and tumor-bearing dogs. Mild-moderate gastrointestinal toxicity (diarrhea, anorexia) and reversible neurotoxicity were observed in dogs receiving chemotherapy plus high-dose tamoxifen. Myelosuppression was not affected by combined treatment in tumor-bearing dogs. High-dose tamoxifen decreased the clearance and volume of distribution of full-dose doxorubicin. CONCLUSIONS: Concentrations of tamoxifen/ NDMT sufficient to inhibit Pgp may be achieved in dogs receiving full-dose chemotherapy with a moderate but acceptable increase in gastrointestinal toxicity. Tamoxifen affects doxorubicin metabolism in dogs at high doses resulting in increased serum exposure. Pharmacologic manipulation of Pgp expression or function in normal and tumor tissue in dogs may facilitate investigation of novel anticancer treatment strategies in humans.

Use of carbamylated hemoglobin concentration to differentiate acute from chronic renal failure in dogs.

OBJECTIVE: To determine usefulness of carbamylated hemoglobin (CarHb) concentration for differentiation of acute renal failure (ARF) from chronic renal failure (CRF) in dogs. SAMPLE POPULATION: Samples from dogs with ARF or CRF and from nonazotemic control dogs. PROCEDURE: CarHb concentration was determined in heparinized blood samples by measuring the micrograms of valine hydantoin (VH) per gram of hemoglobin (Hb), using a high-performance liquid chromatography assay, in which carbamyl valine is converted to VH via acid hydrolysis. RESULTS: CarHb concentration was significantly higher in dogs with ARF and CRF, compared with values in control dogs (ARF vs control, P < 0.05; CRF vs control, P < 0.001). Furthermore, CarHb concentration was significantly (P < 0.001) higher in dogs with CRF, compared with that in dogs with ARF. Carbamylated hemoglobin concentration did not correlate with serum urea nitrogen or creatinine concentration. Using a cutoff value of 100 micrograms of VH/g of Hb, the sensitivity and specificity of CarHb concentration for differentiating ARF from CRF was 96.1 and 84.2%, respectively. CONCLUSIONS: CarHb concentration was useful in the differentiation of ARF from CRF in the dogs of this study. CLINICAL RELEVANCE: CarHb concentration may be used to increase the accuracy of identifying ARF, so that early, aggressive management can be instituted, thereby increasing the chance of recovery.