Early-Onset Endocrine Disruptor–Induced Prostatitis in the Rat

Environmental pollutants and industrial chemicals disrupt—and have the potential to alter—the action of gonadal steroid hormones by virtue of their antiandrogenic or estrogenic properties and, in so doing, effect hormonal balance (Foster 2006; Foster and McIntyre 2002; Kelce and Wilson 1997). During fetal and neonatal life, reproductive tract development is hormonally regulated, and the reproductive tract is in an undifferentiated state, lacking compensatory homeostatic mechanisms to prevent adverse effects of endocrine-disrupting chemicals (EDCs) (Cunha et al. 1992; Prins 1997). Thus, the organizational effects of EDCs on the developing reproductive tract can be permanent and irreversible. Dissimilar to prostate cancer (PCa) and benign prostate hyperplasia (BPH), which predominantly affect aging men, prostate inflammation (prostatitis) affects 9% of men of all ages (McNaughton-Collins et al. 2007). Most (> 90%) prostatitis cases are ascribed to unknown (nonbacterial) origins, and the symptoms, both acute and chronic, are common, bothersome, and burdensome in terms of health-related quality of life (McNaughton Collins et al. 2001; Turner et al. 2005). The economic impact of prostatitis includes an estimated annual expenditure in the United States of > $84 million for diagnosis and management, excluding subsequent pharmaceutical costs (Calhoun et al. 2004; Litwin and Saigal 2007; McNaughton-Collins et al. 2007). Because there are extensive gaps in our understanding of prostatitis etiology, many of these current expenditures may be ineffective and a waste of resources. Thus, it is imperative that we better understand this disease, one that has received relatively little attention compared with BPH and PCa. Although increased levels of developmental or environmental estrogens have been linked to the increased incidence of prostate disease (Coffey 2001; Harkonen and Makela 2004), chemicals with antiandrogenic activity are potentially of greater importance because androgens are critical to establishing the male phenotype. Vinclozolin [3-(3,5-dichloro-phenyl)-5-methyl-oxazolidine-2,4-dione] is an antiandrogenic systemic dicarboximide fungicide used widely throughout Europe and the United States to control diseases caused by Botrytis cinerea, Sclerotinia sclerotiorum, and Moniliniam spp. Vinclozolin is degraded to the metabolites 2-[(3,5-dichlorophenyl)-carbamoyl]oxy-2-methyl-3-butenoic acid (M1) and 3′,5′-dichloro-2-hydroxy-2-methyl-but-3-enanilide (M2), which are competitive antagonists of androgen receptor (AR) ligand binding, rather than 5α-reductase enzyme inhibitors (Kelce et al. 1994; Wong et al. 1995). When sprayed as Ronilan (a 50% mixture of vinclozolin; BASF AG, Research Triangle Park, NC, USA) on soil, vinclozolin has a half-life of 23 days (Szeto et al. 1989). Previous reports show that vinclozolin exposure in rodents during reproductive tract development induces malformations such as cryptorchidism, hypospadias, and Leydig cell hyperplasia, and permanent changes in sexually dimorphic structures, such as anogenital distance (AGD) and areola/nipple retention (Gray et al. 1994). These effects occur before formation of the hypothalamic–pituitary–gonadal axis and long after vinclozolin has been cleared from the pup; thus, these effects are organizational rather than due to interruption of a feedback loop via the pituitary. Recent interest in vinclozolin arose from a report that transient embryonic exposure in the rat during embryonic gonadal sex determination [gestation days (GD) 8–14] appears to alter the male germline epigenome and subsequently promotes transgenerational adult-onset disease, including testis and immune abnormalities, prostate and kidney disease, and tumor development (Anway et al. 2005). In a preliminary report, Anway et al. (2006) stated that prostate disease, including inflammation and epithelial atrophy, occurred in aged rats (12–14 months of age) prenatally exposed to vinclozolin, although the incidence of prostatic lesions across four generations of male rats was only 10%. Although the low incidence of prostatic lesions is not compelling, at the same time these findings were controversial because of the vinclozolin purity and the timing and route of its administration in utero. The purity of vinclozolin was not demonstrated by Anway et al. (2006), and vinclozolin, when purchased commercially, requires purification and recrystallization to obtain > 99% purity to ensure that effects are not caused by contaminants. Human exposure to vinclozolin occurs by oral ingestion, enabling metabolism to the more potent AR antagonists (M1 and M2). Direct intraperitoneal administration runs the risk of producing effects not observed by the conventional oral route, such as uterine irritation and changes in uterine blood flow. The timing of vinclozolin exposure also varies the effect on male reproductive tract development in rodents. A window of sensitivity for prostate development occurs when ARs are activated between GD14 and GD19, rather than during embryonic gonadal sex determination around GD8–GD14 (Wolf et al. 2000). Commonly, the outcomes of any transient in utero treatments are examined in aging animals. However, antiandrogenic effects also manifest at other times, including pre- and postpuberty, when hormone action is critical for normal prostate maturation and function. Altogether, these variations in treatment protocol may account for the low incidence of prostatic lesions reported by Anway et al. (2005), who used intraperitoneally administered unpurified vinclozolin during GD8–GD14 and did not study outcomes until 12–14 months of age. Therefore, the aim of this study was to evaluate effects of fetal exposure to purified vinclozolin, administered orally to pregnant rats during the period of male reproductive tract development (GD14–GD19), on pre-and postpubertal prostate gland function in male offspring.