Jerry Phelps

Mono-2-ethylhexyl phthalate, a metabolite of di-(2-ethylhexyl) phthalate, causally linked to testicular atrophy in rats

Acute testicular atrophy results when appropriate dosages of di-(2-ethylhexyl) phthalate (DEHP) or its hydrolysis product mono-2-ethylhexyl phthalate (MEHP) are given to male rats. Events thought to be involved in this pathological effect also occur in cultures of testicular cells in vitro, but require MEHP rather than DEHP. Primary cultures of hepatocytes, Sertoli cells, and Leydig cells were incubated with 14C-labeled MEHP [8 microM] for up to 24 hr. No significant reduction in viability was produced under these conditions. In contrast to the hepatocytes, which extensively metabolized MEHP to a variety of products in 1 hr, the testicular cell cultures were apparently unable to metabolize MEHP (beyond a slight hydrolysis to phthalic acid by Sertoli cells) in 18-24 hr. MEHP was efficiently taken up by hepatocytes, but much less so by testicular cells. These results, combined with related observations from the literature, support the hypothesis that MEHP itself is the metabolite of DEHP responsible for testicular atrophy in rats.

The effects of mono-(2-ethylhexyl)-phthalate on rat Sertoli cell-enriched primary cultures

There is considerable evidence from in vivo studies that the Sertoli cell is an initial target cell for the actions of phthalates in the rodent testis. Because this metabolically active cell type plays a central role in spermatogenesis, we examined the effects of a toxic phthalate, mono-(2-ethylhexyl)-phthalate (MEHP), on the secretory and synthetic activities of primary testicular cell cultures isolated from 18-day-old rats. These cultures were 78-84% Sertoli cells. Exposure to MEHP decreased cellular ATP by ca. 20%, decreased production of radiolabeled 14CO2 from acetate, and decreased media levels of pyruvate, while it increased media levels of lactate and intracellular lipid. Protein synthesis, evaluated by radiolabeled leucine incorporation, was not affected by MEHP. Mitochondrial succinate dehydrogenase activity was decreased in the presence of MEHP. Michaelis-Menton kinetic analysis indicated this was a mixed inhibition. There was no apparent change in mitochondrial Rhodamine 123 uptake. These data are consistent with the concept that mitochondria are one target for the actions of MEHP in the Sertoli cell.

The Interaction of Sertoli and Leydig Cells in the Testicular Toxicity of Tri-o-cresyl Phosphate

Previous studies have shown that after dosing with tri-o-cresyl phosphate (TOCP), the testis contains more active intermediate (saligenin cyclic-o-tolyl phosphate; SCOTP) than do other organs or blood. SCOTP is produced by a cytochrome P450-dependent reaction, and the Sertoli cells, although containing little P450, are the testicular cells that show the first signs of damage after TOCP administration. The present studies evaluated (i) whether testicular Leydig cell production of SCOTP might explain the elevated testicular concentration of SCOTP, (ii) if this production affected testosterone secretion, and (iii) if Sertoli cells cocultured over TOCP-exposed Leydig cells would show effects similar to those found after SCOTP exposure of Sertoli cells in vitro, indicating a cell interaction. Previous data showed that a target enzyme for SCOTP in Sertoli cells, nonspecific esterase (NSE), was inhibited by exposure in vitro to SCOTP, but not to TOCP. In the present experiments, HPLC analysis identified SCOTP in media from Leydig cells cultured with radiolabeled TOCP, demonstrating activation. TOCP addition to Leydig cells decreased testosterone output after stimulation with hCG, an effect that was replicated by subsequent in vivo experiments. Addition of various intermediates in the testosterone biosynthesis pathway indicated that both mitochondrial- and microsomal-based steps in the pathway were affected. Collectively, these data indicate that Leydig cells can activate TOCP. To model whether this activation might affect Sertoli cells in vivo, Sertoli cells were plated in culture-well inserts suspended above (cocultured with) isolated Leydig cells in the presence of TOCP. Sertoli NSE activity was diminished, while remaining unchanged when cultured in the presence of TOCP but without Leydig cells, or over Leydig cells alone. These results show that the Leydig cells in the testis are capable of activating TOCP to SCOTP, and that this can produce effects in Sertoli cells. This in situ activation of TOCP to SCOTP may help explain why the testis contains high concentrations of SCOTP after in vivo dosing with TOCP, and why the testis is a target organ for TOCP toxicity.

Semen Analysis and Fertility Assessment in Rabbits: Statistical Power and Design Considerations for Toxicology Studies

Semen analysis is commonly used in evaluating human response to reproductive toxicants. Serial semen samples can be collected from rabbits and fertility assessed by artificial insemination, hence this species is potentially well suited for male reproductive toxicity studies that might be extrapolated to humans. However, the size and cost of rabbits often restricts the number of animals used, reducing the sensitivity of such studies. Therefore, it was of interest to optimize study design for semen analysis and fertility assessment in rabbits. Semen samples were collected weekly from sexually mature New Zealand white rabbits and a range of parameters was analyzed (Semen--pH, volume, osmolality; Sperm--number and concentration, morphology, viability, percentage motility, motion characteristics; Seminal plasma--fructose, citric acid, carnitine and protein concentrations, acid phosphatase activity). Male fertility was assessed by inseminating female rabbits with the minimum number of motile sperm required for normal fertility, determined to be one million. The within- and between-buck variabilities were determined for all parameters and used to calculate the statistical power of different study designs. The variability of sperm number and concentration was decreased when measured in four ejaculates collected within a short period of time rather than in a single ejaculate; this was not true of other endpoints measured. In addition, use of preexposure observations further increased the statistical power for all of the parameters. These data can be used to determine the optimum design for studies of male reproductive toxicity using rabbits, with particular regard to cost and the number of animals used.

Toxicology studies of a chemical mixture of 25 groundwater contaminants: III. Male reproduction study in B6C3F1 mice

A mixture of chemicals has been developed that models contaminated groundwater around hazardous waste sites. We investigated the effects of this mixture on spermatogenesis in B6C3F1 mice. The animals consumed three different concentrations of this mixture for 90 days, after which time they were euthanatized. Although there was a concentration-related decrease in the amount of fluid consumed at the higher two concentrations, there were no differences in body weight among the groups. Similarly, there was no effect of mixture consumption upon the histology of liver, kidney, testis, epididymis, or seminal vesicles or upon the absolute organ weights of these organs. Kidney weight relative to body weight was increased in the high dose group. Epididymal sperm number and testicular spermatid count were not affected by treatment. These studies show that, at exposure levels that decrease fluid intake and increase adjusted kidney weight, there were no effects of this mixture on gametogenesis in male mice.

Conceptual model of comprehensive research metrics for improved human health and environment.

Objective Federal, state, and private research agencies and organizations have faced increasing administrative and public demand for performance measurement. Historically, performance measurement predominantly consisted of near-term outputs measured through bibliometrics. The recent focus is on accountability for investment based on long-term outcomes. Developing measurable outcome-based metrics for research programs has been particularly challenging, because of difficulty linking research results to spatially and temporally distant outcomes. Our objective in this review is to build a logic model and associated metrics through which to measure the contribution of environmental health research programs to improvements in human health, the environment, and the economy. Data sources We used expert input and literature research on research impact assessment. Data extraction With these sources, we developed a logic model that defines the components and linkages between extramural environmental health research grant programs and the outputs and outcomes related to health and social welfare, environmental quality and sustainability, economics, and quality of life. Data synthesis The logic model focuses on the environmental health research portfolio of the National Institute of Environmental Health Sciences (NIEHS) Division of Extramural Research and Training. The model delineates pathways for contributions by five types of institutional partners in the research process: NIEHS, other government (federal, state, and local) agencies, grantee institutions, business and industry, and community partners. Conclusions The model is being applied to specific NIEHS research applications and the broader research community. We briefly discuss two examples and discuss the strengths and limits of outcome-based evaluation of research programs.

The effects of Tri-o-cresyl phosphate and metabolites on rat Sertoli cell function in primary culture

A neurotoxic organophosphate, tri-o-cresyl phosphate (TOCP) is also a testicular toxicant. Histopathologic damage in the testis is first seen in Sertoli cells. TOCP and its activated metabolite saligenin cyclic-o-tolyl phosphate (SCOTP) were evaluated for effects on rat Sertoli cells in primary culture. SCOTP, but not TOCP, caused minor morphologic effects on the cells and increased levels of lactate in the spent medium with no change in pyruvate levels, synthesis of cellular or secreted proteins, or the cyclic AMP response to FSH stimulation. SCOTP was the metabolite of TOCP that produced the largest decrease in nonspecific esterase activity in Sertoli cells (up to 80%), when tested in the concentration range found in vivo. This decrease is consistent with previous in vivo evidence. These in vitro experiments replicate previously observed in vivo biochemical effects and suggest that SCOTP is the metabolite responsible for at least some of the biochemical effects seen in the testis after TOCP exposure.

Toward the Assessment of Scientific and Public Health Impacts of the National Institute of Environmental Health Sciences Extramural Asthma Research Program Using Available Data

Background In the past 15 years, asthma prevalence has increased and is disproportionately distributed among children, minorities, and low-income persons. The National Institute of Environmental Health Sciences (NIEHS) Division of Extramural Research and Training developed a framework to measure the scientific and health impacts of its extramural asthma research to improve the scientific basis for reducing the health effects of asthma. Objectives Here we apply the framework to characterize the NIEHS asthma portfolio’s impact in terms of publications, clinical applications of findings, community interventions, and technology developments. Methods A logic model was tailored to inputs, outputs, and outcomes of the NIEHS asthma portfolio. Data from existing National Institutes of Health (NIH) databases are used, along with publicly available bibliometric data and structured elicitation of expert judgment. Results NIEHS is the third largest source of asthma-related research grant funding within the NIH between 1975 and 2005, after the National Heart, Lung, and Blood Institute and the National Institute of Allergy and Infectious Diseases. Much of NIEHS-funded asthma research focuses on basic research, but results are often published in journals focused on clinical investigation, increasing the likelihood that the work is moved into practice along the “bench to bedside” continuum. NIEHS support has led to key breakthroughs in scientific research concerning susceptibility to asthma, environmental conditions that heighten asthma symptoms, and cellular mechanisms that may be involved in treating asthma. Conclusions If gaps and limitations in publicly available data receive adequate attention, further linkages can be demonstrated between research activities and public health improvements. This logic model approach to research impact assessment demonstrates that it is possible to conceptualize program components, mine existing databases, and begin to show longer-term impacts of program results. The next challenges will be to modify current data structures, improve the linkages among relevant databases, incorporate as much electronically available data as possible, and determine how to improve the quality and health impact of the science that we support.

Scientific and public health impacts of the NIEHS Extramural Asthma Research Program: insights from primary data

A conceptual model was developed to guide evaluation of the long-term impacts of research grant programs at the National Institutes of Health, National Institute of Environmental Health Sciences. The model was then applied to the extramural asthma research portfolio in two stages: (1) the first used extant data sources, (2) the second involved primary data collection with asthma researchers and individuals in positions to use asthma research in development of programs, policies, and practices. Reporting on the second stage, this article describes how we sought to broaden the perspectives included in the assessment and obtain a more nuanced picture of research impacts by engaging those involved in conducting or using the research.

Conceptual model of comprehensive research metrics for improved human health and environment

Performance measurement predominantly consisted of near-term outputs measured through bibliometrics, but the recent focus is on accountability for investment based on long-term outcomes. Our objective is to build a logic model and associated metrics through which to measure the contribution of environmental health research programs to improvements in human health, the environment, and the economy. We developed a logic model that defines the components and linkages between extramural environmental health research grant programs and the outputs and outcomes related to health and social welfare, environmental quality and sustainability, economics, and quality of life, focusing on the environmental health research portfolio of the National Institute of Environmental Health Sciences (NIEHS) Division of Extramural Research and Training and delineates pathways for contributions by five types of institutional partners in the research process. The model is being applied to specific NIEHS research applications and the broader research community. We briefly discuss two examples and discuss the strengths and limits of outcome- based evaluation of research programs.A avaliacao de desempenho compreendia predominantemente resultados de curto prazo avaliados atraves de bibliometria, mas recentemente a enfase voltou-se a prestacao de contas dos investimentos com base em resultados a longo prazo. Nosso objetivo e criar um modelo logico e metricas associadas atraves dos quais possamos avaliar a contribuicao de programas de pesquisa em saude ambiental para melhorar a saude humana, o meio ambiente e a economia. Desenvolvemos um modelo logico que define os componentes e elos entre os programas de pesquisa em saude ambiental extramuros subsidiados e os resultados relacionados a saude e ao bem-estar social, qualidade ambiental e sustentabilidade, economia e qualidade de vida, com enfase no portfolio de pesquisa em saude ambiental do National Institute of Environmental Health Sciences (NIEHS), divisao de pesquisa e treinamento extramuros, delineando caminhos para as contribuicoes de cinco tipos de parceiros institucionais no processo de pesquisa. O modelo esta sendo usado em aplicacoes especificas do NIEHS e na comunidade de pesquisa como um todo. Analisamos brevemente dois exemplos e os pontos fortes e limitacoes da avaliacao baseada em resultados dos programas de pesquisa.