Influence of gender on prednisolone effects on whole blood T-cell deactivation and trafficking in rats

Abstract

Prednisolone (5 mg/kg intravenous) was administered to adrenalectomized male and female Sprague-Dawley rats (250-350 g) to assess the effects of gender on disposition and pharmacoimmunodynamics. Plasma concentrations of prednisolone were determined by high-performance liquid chromatography. Incorporation of [3H]thymidine (3H-TDR) was used to determine whole blood T-cell (WBTC) trafficking and deactivation following stimulation with Concanavalin-A. Whole blood T-cell trafficking was determined indirectly by using the glucocorticoid receptor antagonist RU-40555 (250 ng/mL) added to ex vivo cultures of whole blood from animals dosed with prednisolone. Mean (+/- SD) prednisolone clearance values were 3.22 +/- 0.88 and 3.46 +/- 0.96 L/h/kg in males and females, respectively. After administration of prednisolone, relative T-cell counts decreased slowly with time to reach a nadir at 3-5 h and returned to baseline levels by 8 h. Fitting data using an indirect response model yielded mean prednisolone 50% inhibitory concentration for inhibition of WBTC trafficking (IC50T) that was lower in males compared with females (0.14 +/- 0.16 versus 1.03 +/- 0.06 ng/mL; p < 0.05). In the absence of RU-40555, an immediate and complete inhibition of 3H-TDR incorporation into WBTC was observed (deactivation) and baseline levels were recovered slowly as prednisolone was cleared from blood. The mean 50% inhibitory concentration for inhibition of WBTC deactivation (IC50D) based on an inhibitory Imax model was similar in males and females (0.20 +/- 0.24 versus 0.18 +/- 0.12 ng/mL). Although male and female rats have similar exposure to prednisolone after 5-mg/kg doses, males are more sensitive to the inhibition of WBTC trafficking, whereas no gender effects on deactivation of WBTC exist.

Figure 1

Pharmacodynamic model for the effects of prednisolone on whole blood T-cell trafficking and deactivation. Cells egress from blood to extravascular (EV) tissues with rate constant k_out, and the rate constant for return to blood is k_in. The IC_50T reflects prednisolone inhibition of k_in and IC_50D reflects the inhibition of mitogen-stimulated activation of whole blood T-cells.

Figure 2

Mean (±SD) plasma concentration versus time profiles of prednisolone for males and females after iv administration of prednisolone 5 mg/kg. Symbols represent experimental data and lines are least-squares regression fittings.

Figure 3

[³H]Thymidine incorporation into whole blood T-cells as a function of time at baseline for male and females. Symbols represent mean (±SD) of data from four animals.

Figure 4

Joint effects of RU-40555 and prednisolone on whole blood T-cell deactivation in vitro. Key: (open bars) prednisolone + RU-40555 (250 mg/mL); (shaded bars) prednisolone alone; (*) p < 0.05 comparing single versus dual agents.

Figure 5

Mean (±SD) [³H]thymidine incorporation into whole blood T-cells as a function of time in male and female rats after administration of prednisolone. Symbols are experimental data and lines represent fittings to the pharmacodynamic model. Key: (○) [³H]thymidine incorporation in the presence of RU-40555 (trafficking); (●) [³H]thymidine incorporation in absence of RU-40555 (deactivation). AUC_BL = A + B; AUC_E = B, and AUC_SR = B/(A + B).