Role of P-glycoprotein in the distribution of the HIV protease inhibitor atazanavir in the brain and male genital tract

Abstract

The blood-testis barrier and blood-brain barrier are responsible for protecting the male genital tract and central nervous system from xenobiotic exposure. In HIV-infected patients, low concentrations of antiretroviral drugs in cerebrospinal fluid and seminal fluid have been reported. One mechanism that may contribute to reduced concentrations is the expression of ATP-binding cassette drug efflux transporters, such as P-glycoprotein (P-gp). The objective of this study was to investigate in vivo the tissue distribution of the HIV protease inhibitor atazanavir in wild-type (WT) mice, P-gp/breast cancer resistance protein (Bcrp)-knockout (Mdr1a-/-, Mdr1b-/-, and Abcg2-/- triple-knockout [TKO]) mice, and Cyp3a-/- (Cyp) mice. WT mice and Cyp mice were pretreated with a P-gp/Bcrp inhibitor, elacridar (5 mg/kg of body weight), and the HIV protease inhibitor and boosting agent ritonavir (2 mg/kg intravenously [i.v.]), respectively. Atazanavir (10 mg/kg) was administered i.v. Atazanavir concentrations in plasma (Cplasma), brain (Cbrain), and testes (Ctestes) were quantified at various times by liquid chromatography-tandem mass spectrometry. In TKO mice, we demonstrated a significant increase in atazanavir Cbrain/Cplasma (5.4-fold) and Ctestes/Cplasma (4.6-fold) ratios compared to those in WT mice (P<0.05). Elacridar-treated WT mice showed a significant increase in atazanavir Cbrain/Cplasma (12.3-fold) and Ctestes/Cplasma (13.5-fold) ratios compared to those in vehicle-treated WT mice. In Cyp mice pretreated with ritonavir, significant (P<0.05) increases in atazanavir Cbrain/Cplasma (1.8-fold) and Ctestes/Cplasma (9.5-fold) ratios compared to those in vehicle-treated WT mice were observed. These data suggest that drug efflux transporters, i.e., P-gp, are involved in limiting the ability of atazanavir to permeate the rodent brain and genital tract. Since these transporters are known to be expressed in humans, they could contribute to the low cerebrospinal and seminal fluid antiretroviral concentrations reported in the clinic.

FIG 1

Atazanavir plasma concentrations over time in WT and TKO mice. Atazanavir plasma concentrations (ng/ml) were measured over time following an i.v. bolus administration of 10 mg/kg atazanavir to WT mice and TKO (Mdr1a^−/−, Mdr1b^−/−, and Abcg2^−/−) mice. The inset shows atazanavir plasma concentrations over time (0 to 24 h) in WT and TKO mice. Results are shown as the mean ± SEM for each time point (n = 4 animals per time point per group). Solid black line and dashed black line, atazanavir C_plasma data fitted to a two-compartment i.v. bolus pharmacokinetic model for WT mice and TKO mice, respectively.

FIG 2

Atazanavir tissue concentrations over time in WT and TKO mice. Atazanavir C_brain (A) and C_testes (B) (ng/g of tissue) were measured over time following i.v. bolus administration of 10 mg/kg atazanavir to WT mice and TKO mice. Results are shown as the mean ± SEM for each time point (n = 4 animals per time point per group).

FIG 3

Atazanavir tissue-to-plasma concentration ratios in WT mice (squares and solid line) and TKO mice (triangles and dashed line). (A) C_brain/C_plasma; (B) C_testes/C_plasma. Results are shown as the mean ± SEM (n = 4 animals per time point per group). Statistically significant differences are indicated (*, P < 0.05).

FIG 4

Effect of elacridar on atazanavir tissue-to-plasma concentration ratios in WT and TKO mice. Atazanavir C_brain/C_plasma (A) and C_testes/C_plasma (B) ratios at 15- and 60-min time points in WT mice in the absence (vehicle) or in the presence of elacridar (5 mg/kg i.v.) are shown. Results are expressed as the mean tissue concentration/plasma concentration ratio ± SEM (n = 4 mice per time point per group). Statistically significant differences are indicated (*, P < 0.05).

FIG 5

Effect of ritonavir on atazanavir tissue-to-plasma concentration ratios in WT and TKO mice. Atazanavir C_brain/C_plasma (A) and C_testes/C_plasma (B) ratios at 60 min in Cyp mice in the absence (vehicle) or the presence of ritonavir (2 mg/kg i.v.) are shown. Results are expressed as the mean tissue concentration/plasma concentration ratio ± SEM (n = 4 mice per time point per group). Statistically significant differences are indicated by an asterisk (*, P < 0.05).