OECD validation of the rodent Hershberger assay using three reference chemicals; 17α-methyltestosterone, procymidone, and p,p′-DDE

Key learnings from the Endocrine Disruptor Screening Program (EDSP) Tier 1 rodent uterotrophic and Hershberger assays

In 2009, companies began screening compounds using the US Environmental Protection Agency's Endocrine Disruptor Screening Program (EDSP). EDSP has two tiers: Tier 1 includes 11 assays to identify compounds with potential endocrine activity. This article describes two laboratories' experiences conducting Tier 1 uterotrophic and Hershberger assays. The uterotrophic assay detects estrogen receptor agonists through increases in uterine weight. The advantages of the uterotrophic rat models (immature vs. adult ovariectomized) and exposure routes are discussed. Across 29 studies, relative differences in uterine weights in the vehicle control group and 17α-ethynylestradiol–positive control group were reasonably reproducible. The Hershberger assay detects androgen receptor (AR) agonists, antagonists, and 5α-reductase inhibitors through changes in accessory sex tissue (AST) weights. Across 23 studies, AST weights were relatively reproducible for the vehicle groups (baseline), testosterone propionate (TP) groups (androgenic response), and flutamide + TP groups (antiandrogenic response). In one laboratory, one and four compounds were positive in the androgenic and antiandrogenic portions of the assay, respectively. Each compound was also positive for AR binding. In the other laboratory, three compounds showed potential antiandrogenic activity, but each compound was negative for AR binding and did not fit the profile for 5α-reductase inhibition. These compounds induced hepatic enzymes that enhanced testosterone metabolism/clearance, resulting in lower testosterone and decreased capacity to maintain AST weights. The Hershberger androgenic and antiandrogenic performance criteria were generally attainable. Overall, the uterotrophic and Hershberger assays were easily adopted and function as described for EDSP screening, although the mode of action for positive results may not be easily determined.

DDT and malaria prevention: addressing the paradox

BACKGROUND

The debate regarding dichlorodiphenyltrichloroethane (DDT) in malaria prevention and human health is polarized and can be classified into three positions: anti-DDT, centrist-DDT, pro-DDT.

OBJECTIVE

We attempted to arrive at a synthesis by matching a series of questions on the use of DDT for indoor residual spraying (IRS) with literature and insights, and to identify options and opportunities.

DISCUSSION

Overall, community health is significantly improved through all available malaria control measures, which include IRS with DDT. Is DDT "good"? Yes, because it has saved many lives. Is DDT safe as used in IRS? Recent publications have increasingly raised concerns about the health implications of DDT. Therefore, an unqualified statement that DDT used in IRS is safe is untenable. Are inhabitants and applicators exposed? Yes, and to high levels. Should DDT be used? The fact that DDT is "good" because it saves lives, and "not safe" because it has health and environmental consequences, raises ethical issues. The evidence of adverse human health effects due to DDT is mounting. However, under certain circumstances, malaria control using DDT cannot yet be halted. Therefore, the continued use of DDT poses a paradox recognized by a centrist-DDT position. At the very least, it is now time to invoke precaution. Precautionary actions could include use and exposure reduction.

CONCLUSIONS

There are situations where DDT will provide the best achievable health benefit, but maintaining that DDT is safe ignores the cumulative indications of many studies. In such situations, addressing the paradox from a centrist-DDT position and invoking precaution will help design choices for healthier lives.

Myosin heavy chain expression pattern as a marker for anabolic potency: desoxymethyltestosterone (madol), norandrostenedione and testosterone repress MHC-IIb expression and stimulate MHC-IId/x expression in orchiectomized rat gastrocnemius muscle

Both 19-norandrostenedione (estr-4-ene-3,17-dione, NOR) and desoxymethyltestosterone (17alpha-methyl-5alpha-androst-2-en-17beta-ol, DMT or "madol") are 'designer steroids' misused for doping purposes in the bodybuilding scene. We have previously characterized the pharmacological profile of madol and identified potential adverse side effects. The aim of this study was to investigate the anabolic potency of NOR, madol and the reference substance testosterone propionate (TP). Besides wet weight of the M.levator ani (LA), we examined the effects on muscle fiber type composition and myosin heavy chain (MHC) expression in the M.gastrocnemius (Gas) muscle as additional markers for anabolic potency. A Hershberger assay was performed, where orchiectomized (orchi) male Wistar rats were treated subcutaneously with NOR, madol, TP or vehicle control (all 1 mg/kg BW/day) for 12 days. Wet weights of the Gas, LA, prostate and seminal vesicle were examined to determine anabolic and androgenic effects. Fiber type composition of the Gas muscle was analyzed using ATPase staining, and MHC protein profiles were determined by silver stain and Western blot analysis. NOR and madol exhibited strong anabolic and weak androgenic potency by stimulating growth of the LA but not the prostate and seminal vesicle. Skeletal muscle fiber type composition characterized by ATPase staining was not significantly altered between the treatment groups, although there was a tendency toward lower levels of type IIB and increased type IIA fibers in all treatment groups relative to orchi. MHC protein expression determined by Western blot and silver stain analysis revealed that MHC IId/x was significantly up-regulated, while MHC IIb was significantly down-regulated in NOR, madol and TP groups relative to orchi. There were no significant differences for MHC IIa and MHC I expression between groups. Results suggest that the observed MHC expression shift could serve as a molecular marker to determine anabolic activity of anabolic steroids at least in skeletal muscle of orchi rats. The molecular mechanisms as well as the androgen-dependent regulation of MHC expression in intact skeletal muscle remain to be further investigated.

OECD validation of phase-3 Hershberger assay using the stimulated weanling male rat in Korea

The OECD has proposed a new, validated test guideline with the stimulated weanling male Hershberger assay to avoid the surgical castration step. In the present study, we assessed the relevance and reliability of the stimulated weanling Hershberger assay in four stages. All chemicals except for testosterone propionate (TP) were orally administered to sexually immature male rats of 22 days old for 10 days. The weights of four mandatory accessory sex organs, two additional reproductive tissues and optional systemic organs were evaluated. At the first two stages, TP, as reference androgen, significantly increased the weights of epididymides and accessory sex organs (ASO) at 1.0 mg kg(-1) and flutamide (FLU), as a positive anti-androgen control, decreased the TP-stimulated organ weights at 3.0 mg kg(-1). At stage 3, trenbolone (40 mg kg(-1)), an anabolic steroid, significantly increased ASO weights, and weak anti-androgens (DDE and linuron) decreased the TP-stimulated ASO weights at each high dose. The above results were confirmed in a blind test with coded substances provided by OECD. Compared with results from our previous castrated male assay, the intact weanling version is less sensitive than the castrated male version, in terms of a smaller response at the reference dose of TP or FLU. However, this study suggests that the stimulated weanling Hershberger assay can detect the effects of both potent and weak anti-androgens on androgen-producing and androgen-dependent tissues.

OECD validation of phase 3 Hershberger assay in Korea using surgically castrated male rats with coded chemicals

As a participating laboratory for the OECD Hershberger validation program, we conducted a phase 3 trial to test the reliability of the Hershberger assay using coded substances. Male Sprague-Dawley rats were castrated at 6 weeks of age and allowed to recover for 8 days. All the coded substances were administered orally once daily for 10 consecutive days. In the antagonist version of the assay, 0.4 mg kg(-1) of testosterone propionate (TP), a reference androgen, was co-administered with the coded compounds C, D, H, I or K, by a subcutaneous injection. As anticipated, TP alone produced statistically significant increases in the five mandatory accessory sex organ weights. The coded substance L (trenbolone 40 mg kg(-1)), the test agonist, caused significant increases in the weights of the androgen-dependent tissues. The five coded compounds, p,p'-DDE at two doses (codes C and I), linuron at two doses (codes D and K) and flutamide (code H), all significantly decreased the weights of the TP-stimulated sex organs. These results suggest the OECD Hershberger assay to be a reliable screening method for detecting androgen agonists and antagonists.

Cumulative Effects of In Utero Administration of Mixtures of “Antiandrogens” on Male Rat Reproductive Development

Although risk assessments are typically conducted on a chemical-by-chemical basis, the 1996 Food Quality Protection Act (FQPA) required the Environmental Protection Agency (EPA) to consider cumulative risk of chemicals that act via a common mechanism of toxicity. To this end, we are conducting studies with mixtures to provide a framework for assessing the cumulative effects of “antiandrogenic” chemicals. Rats were dosed during pregnancy with antiandrogens singly or in pairs at dosage levels equivalent to about one half of the ED50 for hypospadias or epididymal agenesis. The pairs include: AR antagonists (vinclozolin plus procymidone), phthalate esters (DBP plus BBP and DEHP plus DBP), a phthalate ester plus an AR antagonist (DBP plus procymidone), and linuron plus BBP. We predicted that each chemical by itself would induce few malformations; however, by mixing any two chemicals together, about 50% of the males would be malformed. All binary combinations produced cumulative, dose-additive effects on the androgen-dependent tissues. We also conducted a mixture study combining seven “antiandrogens” together. These chemicals elicit antiandrogenic effects at two different sites in the androgen signaling pathway (i.e., AR antagonist or inhibition of androgen synthesis). In this study, the complex mixture behaved in a dose-additive manner. Our results indicate that compounds that act by disparate mechanisms of toxicity display cumulative, dose-additive effects when present in combination.

Evaluation of the rodent Hershberger bioassay: testing of coded chemicals and supplementary molecular-biological and biochemical investigations

Under the auspices of the Organization for Economic Cooperation and Development (OECD) the Hershberger assay is being validated as an in vivo screen for compounds with (anti)androgenic potential. We participated in the final activity, the testing of coded chemicals. Test compounds included trenbolone (TREN; 1.5, 40 mg/kg), testosterone propionate (TP; 0.4 mg/kg), flutamide (FLUT; 3mg/kg), linuron (LIN; 10, 100mg/kg), 1,1-bis-(4-chlorophenyl)-2,2-dichloroethylene (p,p'-DDE; 16, 160 mg/kg), and two negative reference substances, i.e., compounds not considered to affect androgen-sensitive tissue weights (ASTWs) in the Hershberger assay, namely 4-nonylphenol (NP; 160 mg/kg) and 2,4-dinitrophenol (DNP; 10mg/kg); TREN, LIN, p,p'-DDE, NP, and DNP being used under code. Compounds were administered for 10 days by oral intubation or subcutaneous injection (TP). Additional investigations not mandatorily requested by OECD included organ gravimetry of the liver, gene expression analysis in prostate using quantitative RT PCR for prostate specific binding protein polypeptide C3 (PBPC3) and ornithine decarboxylase 1 (ODC1) and determination of testosterone metabolizing and phase II conjugating enzymes in the liver. After submission of all study reports to OECD by participants uncoding revealed the following results: (A) When assessing androgenic potential in castrated rats, administration of TREN increased the weights of ventral prostate (VP), seminal vesicles (SV), glans penis, levator ani and bulbocavernosus muscles, and Cowper's glands at the high dose. A similar or stronger (VP, SV) increase of ASTWs was observed for TP; NP and DNP were ineffective. TREN dose-dependently increased gene expression of ODC1 and PBPC3, TP induced expression of these genes even more strongly (almost) to the level of untreated intact animals, whereas NP and DNP were inactive. Liver enzyme activities depending on physiological androgen levels were lower in castrated than in intact rats and could not be restored by androgen treatment. (B) When assessing antiandrogenic potential in TP-supplemented castrated rats, administration of LIN and p,p'-DDE decreased ASTWs only at the high dose. FLUT even more effectively decreased ASTWs, NP and DNP were again without effect. Decreases in androgen-responsive gene expression in the prostate corresponding to the organ weight changes were only observed for p,p'-DDE (high dose) and flutamide (PBPC3 only). p,p'-DDE dose-dependently induced liver weights and most liver enzyme activities including androgen-dependent ones. Our study accurately reproduced ASTW changes obtained in previous studies also under code suggesting that the Hershberger assay is a robust tool to screen for an (anti)androgenic potential. Assessment of ODC1 and PBPC3 gene expression in prostate, however, may only represent a sensitive tool for the detection of an androgenic potential. Finally, p,p'-DDE may affect ASTWs by several mechanisms including enhanced testosterone metabolism.