Multidrug resistance protein 1 protects the oropharyngeal mucosal layer and the testicular tubules against drug-induced damage

Abstract

The multidrug resistance protein 1 (MRP1) gene encodes a transporter protein that helps to protect cells against xenobiotics. Elevated levels of MRP1 in tumor cells can result in active extrusion of a wide range of (anticancer) drugs with different cellular targets, a phenomenon called multidrug resistance (MDR). To explore the protective function of the mouse mrp1 protein during drug treatment, we investigated the toxicity caused by the anticancer drug etoposide-phosphate (ETOPOPHOS) in mice lacking the mrp1 gene (mrp1(-/-) mice). We show here that the lack of mrp1 protein results in increased etoposide-induced damage to the mucosa of the oropharyngeal cavity and to the seminiferous tubules of the testis. The high concentrations of mrp1 that we find in the basal layers of the oropharyngeal mucosa and in the basal membrane of the Sertoli cells in the testis apparently protect wild-type mice against this tissue damage. We also find drug-induced polyuria in mrp1(-/-) mice, which correlates with the presence of mrp1 protein in the urinary collecting tubules, the major site of kidney water reabsorption. Our results indicate that specific inhibitors of MRP1 used to reverse MDR, in combination with carcinostatic drugs transported by MRP1, might lead to drug-induced mucositis, (temporary) infertility, and diabetes insipidus.

Figure 1

Hematoxylin and eosin–stained paraffin sections of tissues from ETOPOPHOS-treated wild-type and mrp1-deficient mice. Wild-type (A, C, E, and G) and mrp1-deficient (B, D, F, and H) mice 7 d after ETOPOPHOS administration. (A and B) Sections of the oropharyngeal cavity through the tongue, molars, and palatum showing a degeneration of the mucosal layers of the tongue and cheek (B). (C and D) Higher magnification showing at the bottom the tongue and mucosal layer. (E and F) Higher magnification of A and B showing at the bottom the tongue and mucosal layer, and above it the mucosal layer of the cheek. (G and H) Sections through the stomach pyloric region. The dark staining reveals a regeneration of crypts (H). Same magnification in A and B (bar, 200 μm), and in C–H (bar, 100 μm).

Figure 2

Hematoxylin and eosin–stained paraffin sections of testis and epididymis from ETOPOPHOS-treated wild-type and mrp1-deficient mice. Wild-type (A and C) and mrp1-deficient (B and D) mice 7 d after ETOPOPHOS administration. (A and B) Sections of the testis showing vacuoles and disrupted spermatogenesis (B). (C and D) Sections of the epididymis showing reduced numbers of intact spermatids in the lumen (D). Bar, 100 μm.

Figure 3

mrp1 staining of frozen sections of drug-naive wild-type and mrp1-deficient tissues. Sections were counterstained with hematoxylin. Wild-type (A, C, E, and G) and mrp1-deficient (B, D, F, and H) mice. (A and B) Sections of the tongue showing mrp1 staining in the mucosal layer (A). (C and D) Sections of the mucosal layer of the cheek. (E and F) Sections of the esophagus. (G and H) Sections of the lung. Bar, 50 μm.

Figure 4

mrp1 staining of frozen sections of drug-naive wild-type and mrp1-deficient tissues. Sections were counterstained with hematoxylin. Wild-type (A, C, E, and G) and mrp1-deficient (B, D, F, and H) mice. (A–D) Sections of the kidney showing mrp1 staining in the limb of Henle and urinary collecting ducts, and the absence of staining in the glomeruli and proximal convoluted tubules (C and D). (E–H) Sections of the testis showing mrp1 staining in the Leydig and Sertoli cells. (G and H) Higher magnification of E and F. Same magnification in A–D (bar, 100 μm), in E and F (bar, 50 μm), and in G and H (bar, 50 μm).