Directing role of organic anion transporters in the excretion of mercapturic acids of alkylated polycyclic aromatic hydrocarbons.
Excretion of mercapturic acids of a xenobiotic is a good indicator for the formation of electrophilic intermediates. However, the route of excretion, urine or feces, is important for usage of a given mercapturic acid as a biomarker in humans. In the present study we investigated the excretion routes of 1-methylpyrenyl mercapturic acid (MPMA) and 1,8-dimethylpyrenyl mercapturic acid (DMPMA) formed from the corresponding benzylic alcohols in rats. Whereas MPMA was primarily excreted in urine (72% of the total urinary and fecal level), DMPMA clearly preferred the fecal route (88%). We then examined interactions of these mercapturic acids with renal basolateral organic anion transporters (OATs) using HEK293 cells stably expressing human OAT1 and OAT3. The uptake rates of MPMA by OAT1- and OAT3-expressing cells were 2.8- and 1.7-fold, respectively, higher than that by control cells. MPMA was a competitive inhibitor of p-aminohippurate uptake by OAT1 and estrone sulfate uptake by OAT3 with K(i) values of 14.5 microM and 1.5 microM, respectively. In contrast, DMPMA was not transported by OAT1 and only modestly transported by OAT3 (1.25-fold over control). Thus, we suspect that the substrate specificities, alone or together with other factors, played a directing role in the excretion of MPMA and DMPMA. Although the mechanistic link requires verification, our results clearly show that a minute structural difference (the presence or absence of an additional methyl group in an alkylated four-ring polycyclic hydrocarbon) can strongly affect the interaction with transporter proteins and direct the excretion route of mercapturic acids.
Bakhiya
Nadiya
N
German Institute of Human Nutrition Potsdam-Rehbrücke, Arthur-Scheunert-Allee 114-116, 14558 Nuthetal, Germany.
Batke
Monika
M
Laake
Janet
J
Monien
Bernhard H
BH
Frank
Heinz
H
Seidel
Albrecht
A
Engst
Wolfram
W
Glatt
Hansruedi
H
D000111:Acetylcysteine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000652:urine; D000818:Animals; D002460:Cell Line; D005243:Feces / Q000737:chemistry; D006801:Humans; D008297:Male; D027362:Organic Anion Transport Protein 1 / Q000378:metabolism*; D029362:Organic Anion Transporters, Sodium-Independent / Q000378:metabolism*; D011721:Pyrenes / Q000378:metabolism* / Q000493:pharmacokinetics*; D051381:Rats; D017208:Rats, Wistar
C524821:1,8-dimethylpyrenylmercapturic acid; C524819:1-hydroxymethyl-8-methylpyrene; C524820:1-methylpyrenylmercapturic acid; D027362:Organic Anion Transport Protein 1; D029362:Organic Anion Transporters, Sodium-Independent; D011721:Pyrenes; C114338:organic anion transport protein 3; C065833:1-hydroxymethylpyrene; D000111:Acetylcysteine