Utilization of the Zucker Diabetic Fatty (ZDF) Rat Model for Investigating Hypoglycemia-related Toxicities.

Glucokinase (GK) catalyzes the initial step in glycolysis and is a key regulator of glucose homeostasis. Therefore, glucokinase activators (GKa) have potential benefit in treating type 2 diabetes. Administration of a Bristol-Myers Squibb GKa (BMS-820132) to healthy euglycemic Sprague-Dawley (SD) rats and beagle dogs in 1 mo toxicology studies resulted in marked and extended hypoglycemia with associated clinical signs of toxicity and degenerative histopathological changes in the stomach, sciatic nerve, myocardium, and skeletal muscles at exposures comparable to those expected at therapeutic clinical exposures. To investigate whether these adverse effects were secondary to exaggerated pharmacology (prolonged hypoglycemia), BMS-820132 was administered daily to male Zucker diabetic fatty (ZDF) rats for 1 mo. ZDF rats are markedly hyperglycemic and insulin resistant. BMS-820132 did not induce hypoglycemia, clinical signs of hypoglycemia, or any of the histopathologic adverse effects observed in the 1 mo toxicology studies at exposures that exceeded those observed in SD rats and dogs. This indicates that the toxicity observed in euglycemic animals was secondary to the exaggerated pharmacology of potent GK activation. This study indicates that ZDF rats, with conventional toxicity studies, are a useful disease model for testing antidiabetic agents and determining toxicities that are independent of prolonged hypoglycemia.

Improved liquid-liquid extraction with inter-well volume replacement dilution workflow and its application to quantify BMS-927711 in rat dried blood spots by UHPLC-MS/MS.

An UHPLC-MS/MS method was developed and validated to quantify BMS-927711, a drug candidate to treat migraine, in rat dried blood spots (DBS). The DBS samples were extracted using an improved liquid-liquid extraction (LLE) strategy involving in the sonication of DBS punches in 20% MeOH aqueous solution containing the internal standard, [(13)C2, D4]-BMS-927711, and then with a 100mM NH4OAc buffer solution, followed by an automated LLE with EtOAc-hexane (70:30, v/v). The presence of 20% MeOH as an organic modifier in the elution solution significantly improved the analyte elution efficiency and assay performance. A novel inter-well volume replacement dilution workflow was introduced for DBS sample dilution before LLE step. This was a simple two-step process, firstly a small portion of the DBS blank solution was discarded, and then the same volume of a concentrated DBS sample solution was spiked into the leftover blank solution to achieve a desired dilution. Chromatographic separation was achieved on an Acuity UPLC(®) BEH C18 column (2.1mm×50mm, 1.7µm) and the analyte was detected by selected reaction monitoring (SRM) with positive electrospray ionization on an AB Sciex Triple Quad 5500 mass spectrometer. The standard curve was linear from 5.00 to 5000ng/mL with assay precision ≤4.9% CV, and assay accuracy within ±3.1%Dev of the nominal values. Accurate sample dilution was achieved by using inter-well volume replacement with a precision of ≤4.2% CV and an accuracy of ±3.3% for dilution QC at 50,000ng/mL with 100-fold dilution (n=18). This robust UHPLC-MS/MS assay has been successfully applied to the non-clinical studies in rats. By using inter-well volume replacement workflow, accurate dilution was demonstrated using only one DBS blank sample for a typical dilution of <50-fold, and using only two blank DBS samples for a dilution of up to 625-fold. Moreover, this new workflow makes it easier to automate DBS sample dilution.

Cannabinoid receptor antagonist-induced striated muscle toxicity and ethylmalonic-adipic aciduria in beagle dogs.

Ibipinabant (IBI), a potent cannabinoid-1 receptor (CB1R) antagonist, previously in development for the treatment of obesity, causes skeletal and cardiac myopathy in beagle dogs. This toxicity was characterized by increases in muscle-derived enzyme activity in serum and microscopic striated muscle degeneration and accumulation of lipid droplets in myofibers. Additional changes in serum chemistry included decreases in glucose and increases in non-esterified fatty acids and cholesterol, and metabolic acidosis, consistent with disturbances in lipid and carbohydrate metabolism. No evidence of CB1R expression was detected in dog striated muscle as assessed by polymerase chain reaction, immunohistochemistry, Western blot analysis, and competitive radioligand binding. Investigative studies utilized metabonomic technology and demonstrated changes in several intermediates and metabolites of fatty acid metabolism including plasma acylcarnitines and urinary ethylmalonate, methylsuccinate, adipate, suberate, hexanoylglycine, sarcosine, dimethylglycine, isovalerylglycine, and 2-hydroxyglutarate. These results indicated that the toxic effect of IBI on striated muscle in beagle dogs is consistent with an inhibition of the mitochondrial flavin-containing enzymes including dimethyl glycine, sarcosine, isovaleryl-CoA, 2-hydroxyglutarate, and multiple acyl-CoA (short, medium, long, and very long chain) dehydrogenases. All of these enzymes converge at the level of electron transfer flavoprotein (ETF) and ETF oxidoreductase. Urinary ethylmalonate was shown to be a biomarker of IBI-induced striated muscle toxicity in dogs and could provide the ability to monitor potential IBI-induced toxic myopathy in humans. We propose that IBI-induced toxic myopathy in beagle dogs is not caused by direct antagonism of CB1R and could represent a model of ethylmalonic-adipic aciduria in humans.

Evaluating and defining sample preparation procedures for DBS LC-MS/MS assays.

BACKGROUND: A defined approach to develop and validate an LC-MS/MS assay using dried blood spot (DBS) samples is of great interest to many scientists who are adopting this technology. We have evaluated three distinct sample preparation procedures of DBS samples for LC-MS/MS assay development. RESULTS: A new term 'elution efficiency' is introduced to evaluate the effectiveness of eluting compounds from the DBS cards into the liquid phase. Three different types of DBS cards were studied as part of the sample preparation procedures. A DBS LC-MS/MS method was developed, qualified and then applied to a toxicokinetics study. CONCLUSION: Organic extraction and protein precipitation resulted in significant ion suppression and/or enhancement for FTA(®) Classic or FTA(®) Elute cards. Liquid-liquid extraction produced the least ion suppression/enhancement. Both protein precipitation and liquid-liquid extraction effectively eluted the probe compound from the DBS cards under the conditions tested. However, organic extraction by pure solvents resulted in low elution efficiency.

Pooled sample strategy in conjunction with high-resolution liquid chromatography-mass spectrometry-based background subtraction to identify toxicological markers in dogs treated with ibipinabant.

Metabolomics with chromatography-mass spectrometry is often challenging and relies on statistical tools to discern changes in a metabolome. A pooled sample strategy was proposed, consisting of (1) identification of potential marker candidates by detecting changes of metabolites in a few pooled samples between treated and control groups and (2) validation of markers of statistically significant changes with a large set of individual samples. This strategy was enabled by applying a thorough background subtraction approach based on high-resolution mass spectrometry. In a proof-of-principle study, plasma samples were generated and pooled in a 6-week investigational study to identify potential toxicological markers for an observed muscle toxicity associated with the treatment of ibipinabant in dogs. With pooled control samples as backgrounds, potential marker candidates were revealed in the background-subtracted profiles of the pooled ibipinabant-treated samples. After further cleaning with the use of mass defect filtering to exclude drug metabolites and the comparison of profiles between pooled treated samples to eliminate inconsistent peaks, the major biomarker candidates in the profiles were identified to be 19 acylcarnitines. A total of 3 of the 19 acylcarnitines were measured on the set of individual samples to allow for statistical analysis. The results confirmed the significance of acylcarnitine elevations in ibipinabant-treated dogs and indicated that the acylcarnitines could be early markers for the dog-specific toxicity. The advantages of the pooled sample strategy and its potential limitations for metabolomics are discussed.

Reductive isoxazole ring opening of the anticoagulant razaxaban is the major metabolic clearance pathway in rats and dogs.

Razaxaban is a selective, potent, and orally bioavailable inhibitor of coagulation factor Xa. The molecule contains a 1,2-benzisoxazole structure. After oral administration of [(14)C]razaxaban to intact and bile duct-cannulated rats (300 mg/kg) and dogs (20 mg/kg), metabolism followed by biliary excretion was the major elimination pathway in both species, accounting for 34 to 44% of the dose, whereas urinary excretion accounted for 3 to 13% of the dose. Chromatographic separation of radioactivity in urine, bile, and feces of rats and dogs showed that razaxaban was extensively metabolized in both species. Metabolites were identified on the basis of liquid chromatography/tandem mass spectrometry and comparison with synthetic standards. Among the 12 metabolites identified, formation of an isoxazole-ring opened benzamidine metabolite (M1) represented a major metabolic pathway of razaxaban in rats and dogs. However, razaxaban was the major circulating drug-related component (>70%) in both species, and M1, M4, and M7 were minor circulating components. In addition to the in vivo observations, M1 was formed as the primary metabolite in rat and dog hepatocytes and in the rat liver cytosolic fraction. The formation of M1 in the rat liver fraction required the presence of NADH. Theses results suggest that isoxazole ring reduction, forming a stable benzamidine metabolite (M1), represents the primary metabolic pathway of razaxaban in vivo and in vitro. The reduction reaction was catalyzed by NADH-dependent reductase(s) in the liver and possibly by intestinal microflora on the basis of the recovery of M1 in feces of bile duct-cannulated rats.