SAT-396 A Non-Surgical Animal Model of Hypoparathyroidism for Testing PTH Analogues

Abstract

BACKGROUND:In vivo animal models for testing the pharmacokinetics and bioactivity of PTH and its analogues require parathyroidectomy by surgery (1, 2). As the parathyroid glands of rodents are very small the surgery often includes thyroidectomy, making this animal model time-limited, single use, complex, and expensive. We have developed a non-surgical rodent model of hypoparathyroidism using the Type II calcimimetic compound, Cinacalcet-HCl, to suppress PTH and thereby serum calcium levels.Methods:Normal male Wistar rats were gavaged with 30 mg/kg Cinacalcet-HCl (or vehicle only). To test the effect of PTH 1–34, animals were dosed immediately after Cinacalcet-HCl gavage with either a single subcutaneous injection of PTH at 20 nmol/kg or given as same dose repeated every hour for 6 hrs or vehicle only. Serum samples were analysed for ionised calcium (iCa) using an EasyLyte, fully automated electrolyte analyser (Medica Corporation) and phosphate using a Phosphorus Detection Assay Kit (Pars Azmun, IRAN) and an Hitachi 917 Clinical Chemistry Analyser.Results:Rats gavaged with 30 mg/kg Cinacalcet-HCl produced a significant reduction in iCa levels between 2-24hrs returning to baseline at 48-72hrs post dose with the nadir at 8 hours (ANOVA P < 0.0001). This equated to a 25% reduction in iCa at 8 hrs: mean±SD, iCa 1.19 ± 0.09 mmol/L at predose and 0.891 ± 0.04 mmol/L at 8 hours (t-test P < 0.0001). For phosphate there was an initial lowering within the first 2 hrs in all test groups but then a rise such that phosphate was at higher levels than control from 8–24 hrs (ANOVA, ns), returning to baseline at 48 hrs. PTH at 20 nmol/kg given as a single sc dose abrogated the Cinacalcet-HCl induced fall in iCa for up to 2 hrs (AUC±SD (mmol/L).hr, 0.076 ±0.047 versus 0.168±0.0874, t-test P=0.0289).Conclusions:We have shown that the administration of Cinacalcet-HCl provides a robust and reproducible lowering of calcium which is line with current published data (3). These studies demonstrate that the use of Cinacalcet-HCl in normal rats produces a hypocalcemic state that can be abrogated by the addition of PTH. This non-surgical animal model of hypoparathyroidism will be of value in testing the pharmacodynamics of PTH analogues.