Lens cholesterol biosynthesis inhibition: A common mechanism of cataract formation in laboratory animals by pharmaceutical products.

CJ-12,918, a 5-lipoxygenase (5-LO) inhibitor, caused cataracts during a 1-month safety assessment studies in rats whereas the structurally similar ZD-2138 was without effect. For CJ-12,918 analogs, blocking different sites of metabolic liability reduced (CJ-13,454) and eliminated (CJ-13,610) cataract formation in both rats and dogs. Using this chemical series as a test set, models and mechanisms of toxicity were first explored by testing the utility of ex vivo rat lens explant cultures as a safety screen. This model overpredicted the cataractogenic potential of ZD-2138 due to appreciably high lens drug levels and was abandoned in favor of a mechanism-based screen. Perturbations in lens sterol content, from a decline in lathosterol content, preceded cataract formation suggesting CJ-12,918 inhibited lens cholesterol biosynthesis (LCB). A 2-day bioassay in rats using ex vivo LCB assessments showed that the level of LCB inhibition was correlated with incidence of cataract formation in animal studies by these 5-LO inhibitors. Thereafter, this 2-day bioassay was applied to other pharmaceutical programs (neuronal nitric oxide synthase, sorbitol dehydrogenase inhibitor, squalene synthetase inhibitor and stearoyl-CoA desaturase-1 inhibitors/D4 antagonists) that demonstrated cataract formation in either rats or dogs. LCB inhibition >40% was associated with a high incidence of cataract formation in both rats and dogs that was species specific. Bioassay sensitivity/specificity were further explored with positive (RGH-6201/ciglitazone/U18666A) and negative (tamoxifen/naphthalene/galactose) mechanistic controls. This body of work over two decades shows that LCB inhibition was a common mechanism of cataract formation by pharmaceutical agents and defined a level of inhibition >40% that was typically associated with causing cataracts in safety assessment studies typically ≥1 month.

Assessment of endogenous 25-hydroxyvitamin D serum concentrations by liquid chromatography-tandem mass spectrometry in various animal species.

BACKGROUND: Mass spectrometry (MS) has become the preferential method for the analysis of vitamin D in the clinic, yet no single platform is utilized for preclinical species in drug development studies. For vitamin D, the MS platform can provide certain benefits such as applicability of a single assay for multiple species, low cost, and high specificity. OBJECTIVES: A quantitative liquid chromatography-tandem MS (LC-MS/MS) assay for 25-hydroxyvitamin D3 (25OHD3 ) and D2 (25OHD2 ) was validated for rat, dog, mouse, and monkey, and suitability for drug development studies was assessed. METHODS: Standards were used to determine intra- and inter-assay accuracy and precision for LC-MS/MS. Extraction recovery and carryover due to instrumentation were determined. Repeat analyses of pooled serum samples from rat, dog, mouse, and monkey were assessed for precision, and other serum samples were used to determine the normal range in each species and detect biologically relevant changes. RESULTS: For both 25OHD3 and 25OHD2 , inaccuracy was ≤ 6%, and imprecision was ≤ 13%. Extraction recovery was 75% for 25OHD3 and 72% for 25OHD2 , and carryover was ≤ 0.1%. Measurable concentrations of 25OHD3 were recorded in serum samples from all species tested, but no 25OHD2 as diets were only fortified with 25OHD3 . This dataset provides preliminary information for the determination of RIs for 25OHD3 in rat, dog, mouse, and monkey with the LC-MS/MS platform. CONCLUSIONS: The LC-MS/MS assay was accurate and precise for determination of endogenous concentrations of 25OHD3 in serum samples from drug development studies in rat, dog, mouse, and monkey.

An underlying role for hepatobiliary dysfunction in cyclosporine A nephrotoxicity.

Renal-derived cysteinyl leukotrienes (cysLT), such as leukotrienes C(4) (LTC(4)) and D(4) (LTD(4)) are thought to mediate acute and chronic cyclosporine A (CSA) nephrotoxicity. However, whole-body cysLT elimination is regulated primarily by hepatobiliary excretion. Since CSA is known to alter hepatobiliary function, the effects of CSA on whole-body cysLT elimination were investigated in vivo, with respect to hepatobiliary and renal function. Male rats were anesthetized and cannulated (jugular vein, bile duct, and urinary bladder). A tracer dose of tritiated LTC(4) ((3)H-LTC(4)) was administered systemically (i.v.) immediately following vehicle and then 90 min later after vehicle or CSA. In vehicle/vehicle controls, hepatobiliary (3)H-cysLT elimination predominated over renal elimination without altering glomerular filtration rate (GFR), bile flow, and urine production. (3)H-cysLT elimination kinetics were comparable between each 90 min collection period. In vehicle/CSA-treated rats, an acutely nephrotoxic dose of CSA (20 mg/kg, i.v.) reduced urine flow 74+/-9% and caused a transient reduction in GFR, while total bile flow decreased 40+/-13%. Hepatobiliary and renal (3)H-cysLT elimination was also impaired 59+/-5 and 61+/-18%, respectively. In contrast, a non-nephrotoxic dose (2 mg/kg i.v.) increased renal (3)H-cysLT elimination due to impaired hepatobiliary elimination without affecting GFR, bile flow or urine production. Both doses caused (3)H-cysLT retention in hepatic and renal tissue. These findings demonstrate that CSA alters whole-body handling of cysLT by disrupting hepatobiliary cysLT elimination. This disruption leads to increased renal exposure to systemically derived cysLT and renal cysLT tissue retention. Renal exposure to and accumulation of systemically derived cysLT products may be underlying factors in CSA nephrotoxicity.