Sex hormone-regulated renal transport of perfluorooctanoic acid

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Abstract

The biological half-life (t1/2) of perfluorooctanoic acid (PFOA) in male rats is 70 times longer than that in female rats. The difference is mainly due to the difference in renal clearance (CLR), which was significantly reduced by probenecid, suggesting that PFOA is excreted by organic anion transporter(s). Castration of male rats caused a 14-fold increase in the CLR of PFOA, which made it comparable with that of female rats. The elevated PFOA CLR in castrated males was reduced by treating them with testosterone. Treatment of male rats with estradiol increased the CLR of PFOA. In female rats, ovariectomy caused a significant increase in CLR of PFOA, which was reduced by estradiol treatment. Treatments of female rats with testosterone reduced the CLR of PFOA as observed in castrated male rats. To identify the transporter molecules that are responsible for PFOA transport in rat kidney, renal mRNA levels of organic anion transporter 1 (OAT1), OAT2, OAT3, organic anion transporting polypeptide 1 (oatp1), oatp2 and kidney specific organic anion transporter (OAT-K) were determined in male and female rats under various hormonal states and compared with the CLR of PFOA. The level of OAT2 mRNA in male rats was only 13% that in female rats. Castration or estradiol treatment increased the level of OAT2 mRNA whereas treatment of castrated male rats with testosterone reduced it. In contrast to OAT2, mRNA levels of both oatp1 and OAT-K were significantly higher in male rats compared with female rats. Castration or estradiol treatment caused a reduction in the levels of mRNA of oatp1 and OAT-K in male rats. Ovariectomy of female rats significantly increased the level of OAT3 mRNA. Multiple regression analysis suggests that the change in the CLR of PFOA is, at least in part, due to altered expression of OAT2 and OAT3.

Introduction

Perfluorooctanoic acid (PFOA) is a potent synthetic surfactant that is used in a variety of industrial processes [1]. This chemical has been identified as a major contributor to organic fluorine in human serum [2], and the subsequent studies have revealed that serum levels of organic fluorine in plant workers occupationally exposed to this chemical were 10- to 50-fold higher than that in the general public [3]. The biological half-life (t1/2) in humans has been estimated to be 18–24 months following analysis of the serum from a plant worker [3].

The effects of PFOA on biological systems have been extensively studied in rodents. PFOA causes peroxisome proliferation as well as induction of various enzymes involved in lipid metabolism [4], [5], [6], [7], [8]. Toxic effects of PFOA have been reported, such as induction of fatty liver [5] and uncoupling of the mitochondrial respiratory chain [9]. PFOA also affects the serum levels of various hormones, i.e. reducing thyroid hormone and testosterone, and increasing estradiol in rats [10], [11]. Although these findings suggest that PFOA affects hormonal states and metabolism of lipids in human, to date, no significant correlation has been observed between serum levels of PFOA and any biological parameters in plant workers [12], [13], [14].

PFOA, once absorbed by the body, is predominantly eliminated in urine and the rate of fecal elimination is far less than that of urinary elimination in rats [15], [16]. Urinary elimination, therefore, is critical for detoxification of PFOA. We and other investigators have shown that urinary elimination of PFOA is markedly faster in female rats compared with male rats [15], [16], [17], [18], [19]. There are also significant sex differences in the metabolism of some chemicals and drugs [20], [21], [22]. Since PFOA is metabolically inert [16], [23], [24], sex-related difference observed in the biological effects of PFOA is not due to a difference in metabolism of PFOA. In the previous study, we observed that perfluorocarboxylic acid (PFCA) with a shorter carbon chain length was more rapidly eliminated in urine [15]. This suggests that PFCA are recognized and transported into urine by certain biological systems, although little is known about the molecular mechanism responsible for PFOA transport. Recently, several transporters have been cloned, by which various organic anions are transported across biological membranes, in various tissues including liver, kidney, intestine and brain [25], [26], [27], [28], [29], [30], [31], [32], [33]. These transporters have broad substrate specificities and transport various drugs as well as endogenous substrates [34]. Regulation of the expression of these transporters by sex hormones, however, has not been fully investigated yet. We have hypothesized, therefore, that PFOA is transported into urine by a transporter whose expression is regulated by sex hormones. In the present study, we investigated in detail the activities of renal PFOA transport under various hormonal states in male and female rats. Furthermore, the activities were compared with renal levels of mRNA of various organic anion transporters to identify potential candidates for PFOA transporters.

Section snippets

Materials

PFOA was purchased from Sigma Aldrich Japan (Tokyo, Japan). Inulin and probenecid were purchased from Sigma Chemical Co. (St. Louis, MO). Testosterone propionate and β-estradiol-3-benzoate were purchased from Wako Pure Chemical Ind. (Osaka, Japan). All other chemicals were of analytical grade. 3-Bromoacetyl-7-methoxycoumarin (BrAMC) was synthesized as described previously [35].

Animals

Male and female Wistar rats were obtained from SLC (Hamamatsu, Japan) and subjected to experiments when 9 weeks old

Sex-related difference in PFOA clearance in rats

Fig. 1 shows plasma concentration-time profiles of PFOA after intravenous injection in male and female rats. Plasma PFOA fell rapidly in female rats whereas it one decreased gradually in male rats. Toxicokinetic analysis revealed that the total clearance of PFOA in female rats was 44 times higher than that in male rats (Table 2). In female rats, the t1/2 was calculated to be 0.08 day, 1/70 that in male rats.

Renal clearance of PFOA in rats

The CLR of PFOA in female rats was markedly higher than that in male rats (Table 3)

Discussion

Recent studies have shown that PFOA accumulates to a high degree in the human body and the t1/2 was estimated to be 18–24 months [3]. Since this chemical is widely used in industrial applications, it is plausible that long-term exposure to this chemical results in its accumulation in humans, which may lead to toxic effects in biological systems. PFOA is not metabolized in biological systems and is eliminated in urine and feces as the free carboxylic acid in experimental animals [16], [23], [24]

Acknowledgements

This research was supported in part, by a Grant-in-Aid for Scientific Research (C) from the Ministry of Education, Science, Sports and Culture, Japan and Sasagawa Scientific Research Grant.

References (49)

  • H. Saito et al.

    Cloning and functional characterization of a novel rat organic anion transporter mediating basolateral uptake of methotrexate in the kidney

    J. Biol. Chem.

    (1996)
  • T. Sekine et al.

    Expression cloning and characterization of a novel multispecific organic anion transporter

    J. Biol. Chem.

    (1997)
  • K. Inui et al.

    Cellular and molecular aspects of drug transport in the kidney

    Kidney Int.

    (2000)
  • T. Ohya et al.

    Determination by high-performance liquid chromatography of perfluorinated carboxylic acids in biological samples

    J. Chromatogr. B

    (1998)
  • Z. Dische et al.

    A new spectrophotometric method for the detection and determination of keto sugars and trioses

    J. Biol. Chem.

    (1951)
  • N. Kudo et al.

    Induction by perfluorinated fatty acids with different carbon chain length of peroxisomal β-oxidation in the liver of rats

    Chemico-Biol. Interact.

    (2000)
  • A.W. Smith et al.

    Evidence for the active renal secretion of S-pentachlorophenyl-N-acetyl-l-cysteine by female rats

    Biochem. Pharmacol.

    (1983)
  • W.E. Tucker et al.

    Sex- and species-related nephropathy of 6-(1-aminocyclohexanecarboxamino)penicillamic acid (cyclacillin) and its relationship to the metabolic disposition

    Toxicol. Appl. Pahrm.

    (1974)
  • W.S. Guy et al.

    Organic fluorocompounds in human plasma: prevalence and characterization

  • R.A. Guethner et al.

    Surface active materials from perfluorocarboxylic acid

    Ind. Eng. Chem. Proc. Res. Dev.

    (1962)
  • F.A. Ubel et al.

    Health status of plant workers exposed to fluorochemicals—a preliminary report

    Am. Ind. Hyg. Assoc. J.

    (1980)
  • N. Kudo et al.

    Fish oil-feeding prevents perfluorooctanoic acid-induced fatty liver in mice

    Toxicol. Appl. Pharm.

    (1998)
  • H. Permadi et al.

    Effects of perfluoro fatty acids on xenobiotic-metabolizing enzymes which detoxify reactive form of oxygen and lipid peroxidation in mouse liver

    Biochem. Pharmacol.

    (1992)
  • A. Langley

    Effects of perfluoro-n-decanoic acid on the respiratory activity of isolated rat liver mitochondria

    J. Toxicol. Environ. Health

    (1990)
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