環境化学物質：保健・生物医学分野の研究デザイン

要旨

ジェンダード・イノベーション・プロジェクトは、欧州委員会から、第7次欧州研究開発フレームワーク計画（FP7）のいくつかのプロジェクトを分析するよう依頼された。このケーススタディでは、「女性における環境化学物質の生殖への影響」（REEF）プロジェクトについて取り上げる。性差分析によるイノベーション、セックス/ジェンダー分析の手法、そしてジェンダード・イノベーション手法の活用によって「付加価値」が生まれる可能性がある点について明らかにする。

課題：

環境化学物質がヒトの生殖の健康に及ぼす潜在的影響については、これまで主に男性を対象として研究が行われてきた。世界保健機関（WHO）に対して、専門家グループは「女性の生殖機能の発達も内分泌の干渉を受けやすい」という事実があるにもかかわらず、「女性の生殖機能の健康の変化傾向については、男性と比較してはるかに研究が進んでいない」と報告している（Damstra et al., 2002,）。

方法：保健・生物医学研究のデザイン

研究者たちは、環境化学物質が女性の生殖機能に及ぼす影響に関する科学的知見の空白を埋めることを目的として、実験を計画した。対照実験で動物のメスをサンプリングすることにより、環境化学物質への曝露の生理的および遺伝的影響に関する新しい知見が得られた。また、研究者は妊娠中のメスもサンプリングしており、妊娠結果を評価項目に用いることが可能になっている。さらに、妊娠中のメスを研究することで、環境化学物質の胎内曝露が女性および男性の胎児に及ぼす影響を調査し、感受性における性差を解明するという貴重な研究成果が得られている。

ジェンダード・イノベーション：

• 1. REEFプロジェクトは、環境中の化学物質への曝露が妊娠中の女性およびその男性・女性の子孫に与える影響に焦点を当てたプロジェクトである。
  
• 2. REEFプロジェクトでは、性差の分析を行うことで、ヒトを含め、雌雄それぞれに対する胎内での環境化学物質の影響を比較した。さらに、出生後の動物を研究することは、ヒトにおける環境化学物質の影響のモニタリングにも役立つ可能性がある。
  

ジェンダード・イノベーション手法による研究への付加価値の可能性

• 1. 妊娠と環境化学物質の影響の潜在的相互作用の調査
  
• 2. 環境化学物質のヒトへの影響における、性差、年齢、職業、地理的位置、社会

ケーススタディの詳細はこちら

Background: The European Union Framework Programme 7 (FP7) Reproductive Effects of Environmental Chemicals in Females (REEF) Project
Gendered Innovation 1: Studying the Effects of Environmental Chemicals (ECs) in Pregnant Females and Their Offspring
Method: Designing Health and Biomedical Research
Gendered Innovation 2: Comparing EC Effects in Females and Males
Method: Analyzing Sex
Potential Value Added to Future Research through the Future Application of Gendered Innovations Methods
Value Added 1: Investigating Possible Interactions between Pregnancy and EC Effects
Value Added 2: Understanding the Influence of Sex, Age, Occupation, Geographic Location, Socioeconomic Status, and Body Composition in Potential EC Effects on Humans
Method: Intersectional Approaches
Conclusions
Works Cited

 

Background

The REEF project is a study of the effects of environmental chemicals (ECs, including endocrine disruptors) on mammals, with the potential to improve human health by identifying possible risks posed by ECs. REEF researchers' "ultimate concern is to determine how the developing human female fetus might be affected by exposure to ECs" (REEF, 2009b). This project also studies male fetuses (Fowler et al., 2008). The diagram below shows relationships between a subset of REEF experiments:

In "EC cocktail" experiments, environmentally-relevant EC doses were obtained using a cohort of sheep grazing on sewage-sludge-treated pastures; these animals were exposed to a complex mixture of compounds which may mirror human exposure patterns better than laboratory experiments involving a single test chemical (NECTAR, 2009). The effects of ECs may be additive—that is, exposure to two or more chemicals at given concentrations may produce adverse effects, even if exposure to any single chemical at the same concentration would not be harmful. Further, effects may be synergistic—that is, the effects of exposure to two or more chemicals may be greater or different than the simple sum of their effects in isolation (Kortenkamp et al., 2011; Crews et al., 2003). In the context of this case study, EC exposure includes intentional exposure (for example, though tobacco smoking)—see diagram.

Gendered Innovation 1: Studying the Effects of ECs in Pregnant Females and Their Offspring

REEF has developed new strategies for studying the effects of ECs on both pregnant females and their offspring, with relevance to environmental monitoring and legislation. Researchers combined a wide range of established approaches, including 1) methodologies, 2) research subjects, 3) generational cohorts, 4) exposure routes, and 5) endpoints—see chart.

Studies have also increased basic understanding of pregnancy, particularly of the functions and epigenetics of endometrial tissue (Sandra et al., 2010). Certain of these findings are described in Gendered Innovation 2.

Method: Designing Health and Biomedical Research

REEF researchers designing experiments using sheep, mice, and humans have sampled both females and males, as well as pregnant and non-pregnant females (Pocar et al., 2012a; Pocar et al., 2012b). This design allows detection of sex-specific effects of chemical exposure (for example, ovarian atresia in females and poor sperm quality in males). Further, it allows sex differences in EC effects to be identified or ruled out.

View General Method

 

Gendered Innovations 2: Comparing EC Effects in Females and Males

REEF researchers have identified similarities and differences in the effects of ECs on female and male animals. These include:

• 1. Sex similarities and differences in EC effects on bone homeostasis: Ewes and rams grazing on EC-contaminated pastures fertilized with sewage sludge similarly display defects in bone homeostasis, but "the bone tissue is more sensitive in rams than in ewes to pollutants present in sewage sludge." In particular, rams show increases in bone mineral density, decreases in cross-sectional area, and shrinking of the marrow space to a greater degree than ewes (Lind et al., 2009).
  
• 2. Sex differences in the inter-generational transmission of EC effects: When pregnant mice are exposed to a given concentration of polychlorinated biphenyls (PCBs), their offspring will show sex-specific developmental defects-for example, follicular atresia in females and reduced sperm viability in males. However, the heritability of these effects differs: only first-generation females are affected, but males are affected up to the third generation (Pocar et al., 2012b). Pregnant females in this experiment were fed up to 100 μg/kg/day of a mixture of PCB congeners 101 and 118. Both congeners have been assigned toxicity equivalence factors (TEFs) of 0.00003 (U.S. EPA, 2009; Van den Berg et al., 2005). Therefore, this exposure corresponds to 0.03 μg toxic equivalent (TEQ) /kg/day, or 30,000 pg TEQ/kg/day, which is far higher than typical human intakes, estimated at 1 pg TEQ/kg/day (Judd et al., 2004).
  
• 3. Sex similarities and differences in possible EC effects on human fetal liver development: Researchers examining mRNA transcription and protein expression in the fetal liver found differences between fetuses from mothers who smoked tobacco and fetuses from non-smoking mothers. In some cases, the observed effect was the same in smoke-exposed fetuses of both sexes; both expressed higher levels of EPHX1 than non-exposed fetuses. In other cases, observed effects were different by sex; smoke-exposed male fetuses showed depressed expression of GGT1, CYP2R1, and CAR, whereas no genes were observed to be depressed in smoke-exposed female fetuses (O'Shaughnessy et al., 2011a)—see diagram.
  

Method: Analyzing Sex

By studying animals of both sexes, researchers identified both similarities and differences in EC effects (Pocar et al., 2012a; Lind et al., 2009). Many REEF studies have utilized both females and males in a given experiment, avoiding the difficulties in evaluating sex differences through meta-analysis of single-sex studies (Fowler et al., 2011; O'Shaughnessy et al., 2011a).

Potential Value Added to Future Research through the Future Application of Gendered Innovations Methods

Value Added 1: Investigating Possible Interactions between Pregnancy and EC Effects

Researchers may gain additional knowledge by analyzing factors intersecting with sex. For females, pregnancy may be an important determinant of EC exposure and its consequences. Many REEF studies have compared male animals to non-pregnant females, and other studies have examined pregnant females in detail, but no studies specifically compare pregnant and non-pregnant females. Such comparisons could provide information about pregnancy's effects on absorption, mobilization, and metabolism of ECs.

Value Added 2: Understanding the Influence of Sex, Age, Occupation, Geographic Location, Socioeconomic Status, and Body Composition in Potential EC Effects on Humans

If the REEF project is expanded to include epidemiological studies of human populations, many variables apart from sex may be important to understanding EC exposures and effects.

Method: Intersectional Approaches

Variables to consider include:

• 1. Age at Exposure: While adults are mainly exposed to ECs through foods, children may consume such substances when they put their fingers in their mouths (Sexton et al., 2004). Airborne ECs (gases, aerosols, and particulates) tend to be most concentrated near the ground, and so children’s shorter height may increase their risk of EC inhalation (Moya et al., 2004). Age influences the consequences of exposure as well as patterns of exposure. ECs may produce different effects on developing fetuses, infants, pre-pubescent children, and adults (Barker, 2004).

• Age may interact with sex. For example, among people exposed to inorganic arsenic through drinking water, women metabolize highly-toxic inorganic arsenic into less-toxic dimethylarsenic compounds significantly more efficiently than men. This observed sex difference interacts with age; women's metabolic advantage disappears after menopause (Lindberg et al., 2008).
  

• 2. Occupation: Gendered divisions in labor influence exposure to ECs in agriculture. In areas where farming is mechanized, such as in the U.S. and Europe, the majority of agricultural workers are men (U.S. Department of Labor Employment and Training Association, 2010; NationMaster Labor Statistics, 2010). In these countries, most occupational exposure to pesticides occurs in men (Rusiecki et al., 2004). In Africa, by contrast, 75% of agricultural workers are women (London et al., 2002; NationMaster Labor Statistics, 2010). Gender inequalities contribute to other problems: women in developing countries are often less educated than men and hence less able to read pesticide label warnings. In many countries, women were also less likely than men to have access to protective equipment such as gloves and face masks (London et al., 2002).

• Gender roles influence patterns of both paid and unpaid labor, and therefore may influence the risk of EC exposures through domestic work (Snijder et al., 2012). Recent studies suggest that women perform between 65% and 75% of all domestic housecleaning in the United States (Coltrane, 2000). Housecleaning is a potential source of exposure to Nonylphenol, as “nonylphenol […] and its ethoxylates are used widely as surfactants in industrial and household cleaners” (Wilson et al., 2007). However, existing studies of nonylphenol levels in urine show no significant sex differences (Calafat et al., 2005).
  

• 3. Socio-Economic Status: Measures of socio-economic status, such as household income, correlate in some cases with measures of EC exposure. For example, among U.S. residents, urinary concentrations of triclosan, "a synthetic chemical with broad antimicrobial activity that has been used extensively in consumer products, including personal care products, textiles, and plastic kitchenware," are highest in people with the highest household incomes (Calafat et al., 2008a). Another class of environmental chemicals—the plasticizers Bisphenol A and 4-tertiary-Octylphenol—show the opposite pattern, with urinary concentrations highest in low-income groups (Calafat et al., 2008b). Low socio-economic status may increase exposure to pollutants—for example, in the U.S., people with low incomes are disproportionately likely to live in undesirable areas with high levels of pollution—for example, areas surrounding trash incinerators (Mohai et al., 2009). Researchers in England investigated the relationship between environmental pollution in a given area and the socio-economic status of residents. The relationships involved are complex, and trends observed are sensitive to ways of measuring both pollution and wealth (Briggs et al., 2008).
  
• 4. Geographic Location: Location can determine exposure to environmental chemicals—for example, people living near agricultural areas may be exposed to pesticides through aerial spraying, even if they are not agricultural workers (Ward et al., 2000).
  
• 5. Body Composition: Adults with higher BMIs in the United States have significantly higher concentrations of BPA in their urine than people with lower BMIs, and BPA levels are correlated with BMI over a wide range (Lang et al., 2008). Though it is well established that BPA exposure can cause obesity in animal models, people who are obese may also accumulate higher BPA levels because the compound—like many ECs—is lipophilic (Vandenberg et al., 2007).
  

Conclusions:

EC effects cannot be fully understood in females or males without studying pregnancy and fetal development, due to the unique characteristics of the in utero environment and the susceptibility of fetuses to certain forms of EC exposure. A key objective of REEF researchers is "to integrate the mouse and sheep exposure studies with […] human" studies (REEF, 2009b). Such integration requires consideration of social factors—such as gender roles and socioeconomic status—in addition to biological factors such as age, sex, and body composition.

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