Abstract
N-Acetylcysteine (NAC) is a sulfhydryl-containing compound that produces a dramatic acceleration of urinary methylmercury (MeHg) excretion in poisoned mice, but the molecular mechanism for this effect is poorly defined. MeHg readily binds to NAC to form the MeHg-NAC complex, and recent studies indicate that this complex is an excellent substrate for the basolateral organic anion transporter (Oat)-1, Oat1/Slc22a6, thus potentially explaining the uptake from blood into the renal tubular cells. The present study tested the hypothesis that intracellular MeHg is subsequently transported across the apical membrane of the cells into the tubular fluid as a MeHg-NAC complex using the multidrug resistance-associated protein-2 (Mrp2/Abcc2). NAC markedly stimulated urinary [14C]MeHg excretion in wild-type Wistar rats, and a second dose of NAC was as effective as the first dose in stimulating MeHg excretion. In contrast with the normal Wistar rats, NAC was much less effective at stimulating urinary MeHg excretion in the Mrp2-deficient (TR-) Wistar rats. The TR- rats excreted only ∼30% of the MeHg excreted by the wild-type animals. To directly test whether MeHg-NAC is a substrate for Mrp2, studies were carried out in plasma membrane vesicles isolated from livers of TR- and control Wistar rats. Transport of MeHg-NAC was lower in vesicles prepared from TR- rats, whereas transport of MeHg-cysteine was similar in control and TR- rats. These results indicate that Mrp2 is involved in urinary MeHg excretion after NAC administration and suggest that the transported molecule is most likely the MeHg-NAC complex.
Footnotes
-
This study was supported in part by National Institutes of Health Grants DK48823 and ES06484, by National Institute of Environmental Health Sciences Center Grant ES01247, and by Environmental Toxicology Training Grant ES07026.
-
M.S.M. and D.A.A. contributed equally to this work.
-
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
-
doi:10.1124/jpet.107.122812.
-
ABBREVIATIONS: MeHg, methylmercury; DMPS, dimercaptopropanesulfonate; NAC, N-acetyl-l-cysteine; Oat, organic anion transporter; Mrp2, multidrug resistance-associated protein-2; ABC, ATP binding cassette; TR-, transport-deficient.
- Received March 14, 2007.
- Accepted April 10, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|