No abstract

In this review, recent methodological developments for the benchmark dose (BMD) methodology are summarized. Specifically, we introduce the advances for the main steps in BMD derivation: selecting the procedure for defining a BMD from a predefined benchmark response (BMR), setting a BMR, selecting a dose-response model, and estimating the corresponding BMD lower limit (BMDL). Although the last decade has shown major progress in the development of BMD methodology, there is still room for improvement. Remaining challenges are the implementation of new statistical methods in user-friendly software and the lack of consensus about how to derive the BMDL.

Dermal absorption is a key parameter in non-dietary human safety assessments for agrochemicals. Conservative default values and other criteria in the EFSA guidance have substantially increased generation of product-specific in vitro data and in some cases, in vivo data. Therefore, data from 190 GLP- and OECD guideline-compliant human in vitro dermal absorption studies were published, suggesting EFSA defaults and criteria should be revised (Aggarwal et al., 2014). This follow-up article presents data from an additional 171 studies and also the combined dataset. Collectively, the data provide consistent and compelling evidence for revision of EFSA's guidance. This assessment covers 152 agrochemicals, 19 formulation types and representative ranges of spray concentrations. The analysis used EFSA's worst-case dermal absorption definition (i.e., an entire skin residue, except for surface layers of stratum corneum, is absorbed). It confirmed previously proposed default values of 6% for liquid and 2% for solid concentrates, irrespective of active substance loading, and 30% for all spray dilutions, irrespective of formulation type. For concentrates, absorption from solvent-based formulations provided reliable read-across for other formulation types, as did water-based products for solid concentrates. The combined dataset confirmed that absorption does not increase linearly beyond a 5-fold increase in dilution. Finally, despite using EFSA's worst-case definition for absorption, a rationale for routinely excluding the entire stratum corneum residue, and ideally the entire epidermal residue in in vitro studies, is presented.

Epidemiological data indicate that intake of estrogens and isoflavones may be beneficial for the prevention of colorectal cancer (CRC). Based on this data, the aim of the study was to investigate estrogen receptor (ER) subtype-specific effects on intestinal homeostasis. Ovariectomized (OVX) female Wistar rats were either treated with 17β-estradiol (4 μg/kg body wt/day) (E2), an ERα-specific agonist (ALPHA) (10 μg/kg body wt/day), an ERβ-specific agonist (BETA) (100 μg/kg body wt/day) or genistein (GEN) (10 mg/kg body wt/day) for three weeks. Vehicle-treated OVX and SHAM animals and those cotreated with BETA and the pure antiestrogen Fulvestrant (ICI 182780) (100 μg/kg body wt/day and 3 mg/kg body wt/day) served as controls. GEN and BETA treatment but not E2 and ALPHA administration reduced proliferation in ileal and colonic mucosa cells. The rate of apoptosis in the small intestine and colon was increased by treatment with BETA and GEN, but not by E2. BETA induced antiproliferative and proapoptotic activity also in SHAM animals. The effects were antagonized by the pure antiestrogen Fulvestrant. Polymerase chain reaction gene array analysis revealed that BETA resulted in the downregulation of the oncogene transformation-related protein 63 (p63). Our data indicate that activation of the ERβ by specific ERβ agonists and GEN induces antiproliferative and proapoptotic effects in the intestinal tract. This observation can be taken as an indication that intake of GEN and specific ERβ agonists may protect the ileal and colonic epithelium from tumor development via modulation of tissue homeostasis.

Estrogen-like effects of the heavy metal cadmium have been reported in both in vitro and in vivo studies. Yet, the molecular mechanisms involved in the hormonal activity of cadmium ions have not been fully elucidated. There are extensive data on cross-talk between aryl hydrocarbon receptor (AhR) and estrogen receptor (ER). Recently, 17β-estradiol (E(2)) was found to modulate the expression of AhR and AhR-regulated genes in rat uterus (Kretzschmar et al. in Mol Cell Endocrinol 321:253-257, 2010). Thus, we hypothesized that cadmium may also affect AhR signaling and examined whether cadmium or E(2) modulate AhR-associated genes via the ER in rat uterus. Ovariectomized Wistar rats received E(2) (0.5 mg/kg bw) or cadmium chloride (0.05 and 2 mg/kg bw i.p.) alone and in combination with the pure anti-estrogen ZK191703. We also co-treated a group with E(2) and cadmium 2 mg/kg bw to assess how they act in concert. Uterus wet weight, uterus epithelial height, complement C3 mRNA, and progesterone receptor (PR) protein expression served as estrogen response parameters, and expression of Mt1a mRNA was analyzed as a cadmium responsive gene. The expression of AhR protein and AhR-associated gene expression, i.e., Ahr, Arnt1, Arnt2, Cyp1a1, and Gsta2, were analyzed to examine effects on AhR-mediated signaling pathways in the uterus of all groups. Both, E(2) and cadmium induced C3 and PR expression, and this was antagonized by ZK191703. Mt1a expression was clearly induced by cadmium but slightly reduced by E(2) compared to controls. Uterine Ahr, Arnt1, Arnt2, and Cyp1a1 expression was modulated by E(2) via the ER since down-regulation by E(2) was reversed by anti-estrogen. Cadmium apparently also modulated Cyp1a1 expression via the ER. Furthermore, cadmium-induced AhR was antagonized by E(2,) and anti-estrogen-induced Gsta2 expression was antagonized by cadmium. Together our findings provide evidence for cross-talk of ER and AhR in the rat uterus.