ABCG2 Transports the Flukicide Nitroxynil and Affects Its Biodistribution and Secretion into Milk

Abstract

The ABCG2 transporter plays a key role in pharmacological and toxicological processes, affecting bioavailability, tissue accumulation and milk secretion of its substrates. This protein is expressed in several biological barriers acting as a protective mechanism against xenobiotic exposure by pumping out a broad range of compounds. However, its induced expression during lactation in alveolar cells of mammary gland represents a relevant route for active transport of unwanted chemicals into milk. This work aimed to characterize the involvement of ABCG2 in systemic exposure and milk secretion of the flukicide nitroxynil. Using MDCK-II cells overexpressing the transporter, we showed that nitroxynil is an in vitro substrate of different species variants of ABCG2. Moreover, using wild-type and Abcg2^-/- mice, we showed that murine Abcg2 clearly affects plasma levels of nitroxynil. We also reported differences in nitroxynil accumulation in several tissues, with almost 2-fold higher concentration in kidney, small intestine and testis of Abcg2^-/- mice. Finally, we proved that nitroxynil secretion into milk was also affected by Abcg2, with a 1.9-fold higher milk concentration in wild-type compared with Abcg2^-/- mice. We conclude that ABCG2 significantly impacts nitroxynil biodistribution by regulating its passage across biological barriers.

Keywords: ABC transporter; biological barriers; milk secretion; nitroxynil; pharmacokinetics; tissue distribution.

Figure 1

Transepithelial in vitro transport of nitroxynil at 10 µM in the absence (A) or presence (B) of the specific inhibitor of ABCG2, Ko143 (1 µM) in MDCK-II cells overexpressing murine, ovine, bovine and human variants of the ABCG2 transporter (mAbcg2, oABCG2, bABCG2 and hABCG2, respectively). Nitroxynil concentration at different time points was determined by HPLC and transport across monolayers was related to the total drug added at beginning of the experiment in the donor compartment_. Results are presented as means and error bars indicate SD. The relative efflux transport ratio (apically directed transport percentage divided by the basolaterally directed translocation percentage) at 4 h is indicated. (*) p ≤ 0.05, significant differences in transport ratio compared to parental MDCK–II cells (Student’s t-test, normally distributed data) (n = 3–8).

Figure 2

Plasma concentration of nitroxynil in wild-type and Abcg2^−/− male mice at 0.5, 3, 4.5, 6, 24, 48 and 96 h after subcutaneous administration of Distomicide^® at a dose of 10 mg/kg body weight. Results are presented as means and error bars indicate SD. (*) p ≤ 0.05, significant differences compared to wild-type mice (Student’s t-test, normally distributed data) (n = 4–5).

Figure 3

Nitroxynil concentration in plasma and milk samples from wild-type and Abcg2^−/− mice 30 min after intravenously administration of 10 mg/kg bw of Distomicide^®. Milk-to-plasma ratio is included. Results are presented as means and error bars indicate SD. (*) p ≤ 0.05, significant differences compared to wild-type mice (Student’s t-test, normally distributed data) (n = 10–11).