Region-specific growth effects in the developing rat prostate following fetal exposure to estrogenic ultraviolet filters

Abstract

Background and objectives: Exposure to environmental endocrine disruptors is a potential risk factor for humans. Many of these chemicals have been shown to exhibit disruption of normal cellular and developmental processes in animal models. Ultraviolet (UV) filters used as sunscreens in cosmetics have previously been shown to exhibit estrogenic activity in in vitro and in vivo assays. We examined the effects of two UV filters, 4-methylbenzylidene camphor (4-MBC) and 3-benzylidene camphor (3-BC), in the developing prostate of the fetal rat.

Methods: Pregnant Long Evans rats were fed diets containing doses of 4-MBC and 3-BC that resulted in average daily intakes of these chemicals corresponding to the lowest observed adverse effects level (LOAEL) and the no observed adverse effects level (NOAEL) doses in prior developmental toxicity studies. Using digital photographs of serial sections from postnatal day 1 animals, we identified, contoured, and aligned the epithelial ducts from specific regions of the developing prostate, plus the accessory sex glands and calculated the total volume for each region from three-dimensional, surface-rendered models.

Results: Fetal exposure to 4-MBC (7.0 mg/kg body weight/day) resulted in a significant increase (p < 0.05) in tissue volume in the prostate and accessory sex glands. Treated males exhibited a 62% increase in the number of ducts in the caudal dorsal prostate. Increased distal branching morphogenesis appears to be a consequence of exposure in the ventral region, resulting in a 106% increase in ductal volume.

Conclusions: 4-MBC exposure during development of the male reproductive accessory sex glands exhibited classical growth effects associated with estrogenic endocrine disruptors. The different regional responses suggest that the two developmental processes of ductal outgrowth and branching morphogenesis are affected independently by exposure to the environmental chemicals.

Keywords: 4-methylbenzylidene camphor (4-MBC); UV filters; endocrine disruptors; prostate development.

Figure 1

3-D serial section reconstruction of accessory reproductive organs in male PND1 Long Evans rats after systemic and developmental in utero exposure to 7.0 mg/kg bw 4-MBC. Abbreviations: DT, distal tip; PD, proximal duct, VMP, ventral mesenchymal pad. (A) Right lateral view of the surface-rendered anatomical reconstruction of the UGS and ASG structures in a control male. Individual structures are identified by color. (B) Reconstruction of the right lateral and cranial views of the UGS from a 4-MBC–treated male and untreated control male illustrating the significant regional growth differences in ducts of the caudal dorsal prostate and branching morphogenesis development in the ventral region. (C) Additional anatomical views of the prostatic ducts of a control male and a 4-MBC treated male showing the regional growth patterns. (D) Representative histological views of distal-tip budding in the ventral prostate region. Initial bifurcation is the primary feature of the control male, whereas extensive secondary branching morphogenesis has occurred in the 4-MBC–treated male (stained with hematoxylin and eosin; bar = 100 μm). (E) Anatomical view of the UGS, ventral ducts, and VMP showing that the distal tips of the ducts in the control male have made initial contact with the VMP. In the 4-MBC–treated male, the distal tips have penetrated the mesenchymal tissue and undergone later stages of branching morphogenesis. (F) Lateral and dorsal view of the UGS. Shape of the UGS (gray arrow) and bladder neck region of the urethra (black arrow) are changed in the 4-MBC–treated male.

Figure 2

Comparative volume analyses of individual and combined regions of the ASGs in PND1 males after prenatal exposure to various doses of UV filter compounds. Significant effects were observed only in the 7.0 mg/kg bw–treated males. Values shown are mean ± SE (n = 4 for all groups). *p < 0.05, **p < 0.01, ^#p < 0.005, and ^##p < 0.001 compared with control males.

Figure 3

Comparative volume analyses of specific regions of the developing prostate in PND1 males after prenatal exposure to various doses of UV filter compounds. Significant effects were observed only in the dorsal and ventral regions of the 7.0 mg/kg bw–treated males. Values shown are mean ± SE (n = 4 for all groups). *p < 0.05, and **p < 0.01 compared with control males.

Figure 4

Effects of prenatal exposure to UV filter compounds on prostate duct development in PND1 males. A significant increase in the number of developing ducts was observed in the combined dorsolateral prostate region (DLP). This increase was due specifically to an increase in the number of ducts in the caudal region of the dorsal prostate. Values shown are mean ± SE (n = 4 for all groups). *p < 0.05 compared with control males.

Figure 5

Effect of prenatal exposure to 4-MBC (7.0 mg/kg bw) on VMP tissue volume in PND1 males. Values shown are mean ± SE (n = 4 for all groups). *p < 0.05 compared with control males.