Environmental Endocrine Disruptors

1960’s

• Eagles

– Eggshells

– DDT affected reproduction

• Mink – Lake Michigan

– Repro failure

– Fed lake fish

– Those fed fish from other sources normal

1970’s

• Fish-eating birds – Gulf Coast, Great Lakes

– Abnormalities of repro structures/functions

– Malformed offspring

• Women

– DES daughters

– Repro cancers

• Rare cell changes – vagina, oviducts, uteri

– Repro organ dysfunction/disfigurement

– Estrogen replacement repro effects

• (DES

– Potent estrogenic

– Growth stimulant in cattle

– Miscarriage prevention in women)

• Men

– DES sons

• Abnormalities of genitalia, sperm

• Testicular cancer

• Undescended testicles

– Kepone spill

• Low sperm count

1980’s

• Male alligators

– DDT

– 1/2 testosterone

– Small penis size

– Repro capacity??

1990’s

• Male wildlife

– Various cmpds in water

– Sea gulls

• Eggs exposed to DDT female

– Turtles

• Eggs exposed to PCB’s female

– Male-producing temps

– Same as estrogen exposure

– Fish

• Polluted water

• Vitellogenin

– Egg yolk protein

– Female fish-laying eggs

– Abs’d into ovaries

• Remains in tissue of males

• Also female fish masculinized

• Used as biomarker

• Laboratory Animal Studies

– Drugs/toxins @ diff stages neonatal dev’t

– Sensitive @ spec times of dev’t

– Irreversibility

– Too much/too little may be harmful

• Too little testosterone testicular feminization

– “Behavior sex” of brain

• If no androgens phenotypic female

• Estrogen masculinizes brain

– Brief exposure ONLY

• Affects repro ability later in life

– Detox low doses tolerable

• BUT higher doses overwhelm metab

• Human sperm count depleted??

– 50% drop 1938-1990??

• Incr’d human prostate, testicular cancers reported

• Poss female repro dysfunctions

– Incr’d human breast, ovarian cancer rates

– Incr’d PolyCystic Ovarian Disease

• Related to neonatal androgenization (rodents)

early onset estrus acyclicity

What Are Endocrine Disruptors?

• EPA

– “Exogenous substance that changes endocrine function and causes adverse effects at the level of the organism, its progeny and/or (sub)populations of organisms”

• May act like endogenous hormones

– OR metabolites can act like hormones

– OR can block effects of opp sex hormones, growth factors, other hormones

Estradiol DDT

DES Kepone

Bisphenol A

Nonylphenol

Tributyl tin(androgenic inInvertebrates)

Characteristics of Endocrine “Mimics”

• Persistence

• Bioaccumulation

• High potency

• Critical periods of vulnerability

• Absence of permanent exposure markers

• Transgenerational effects

• Subtle biological outcomes

• “Natural” signal sent by “unnatural” molecule

• Don’t alter genes

• Do change way genes expressed

How Natural Estrogens Work

• Target organs

– Breast

– Bone

– Liver

– Repro organs

– Cardiovascular system

• Chemical signals

• Steroid hormones

– Prod’d from cholesterol

– Synth’d from testosterone

– Secr’d from ovaries, testes when brain hormone signals

– Transported att’d to transport proteins

• Fat soluble

– Pass directly into cells

– Receptors in cytoplasm, nucleus

Testosterone: an androgen, male sex hormone synthesized in the testes, responsible for secondary male sex characteristics, produced from progesterone precursor 

Estradiol: an estrogen, principal female sex hormone, produced in the ovary, responsible for secondary female sex characteristics 

Progesterone: a progestin, produced directly from pregnenolone and secreted from the corpus luteum, responsible for changes associated with luteal phase of the menstrual cycle, differentiation factor for mammary glands

• Estrogen receptor

– Large protein

– In target cells only

– At least two ()

– Two binding sites

• Estrogen

• DNA

• Estrogen+receptor complex nucleus

– Binds regulatory regions of specific genes

– At DNA regulatory site

• “Estrogen Response Element”

– Gene promoter near ERE

– Activates, represses expression

• Through proteins bound to promoter

• Effects transcription of gene

– Gene expr’n modulated for duration receptor bound to ERE

– Examples of estrogenic genes

• Progesterone receptor gene

• Growth factor genes

• Growth factor receptor genes

Environmental Estrogen Binding to Estrogen Receptor

• Receptor apparently not completely specific

– Not all estrogenics “look like” estrogen

– Some atomic structures/distances impt

• Binding of mimics may

– Estrogenic activity

– Inhib’n natural estrogen binding (antiestrogenic)

• Most bind weakly BUT to strong effect

– Receptor binding strength not correlated w/ estrogenicity

• Binding extracell prot’s may be impt (ex: DES)

– Binds estrogen receptor weakly

– BUT binds serum binding prot less tightly than nat’l estrogen

• More DES avail to enter cell

• Some must be act’d metabolically (ex: PAH’s)

– Hydroxylation nec to mimic estrogen

– Enhances affinity for receptor

Estrogenics

• Synergism possible

– Ex: Study of dieldrin, endosulfan, toxaphene, chlordane

– Weakly estrogenic alone

– In combination estrogenicty incr’d 160-1600 fold

• Some physically combine

– Form more estrogen-like molecule

• Some bind sites other than estrogen receptor

– May be @ site other than estrogen binding site

– Probably interactive

– Stronger response when both occupied (perhaps one w/ endogenous estrogen)

• Some may bind subunits of receptor together more strongly functioning unit

– Dimer may bind ERE

• May affect synthesis natural estrogen

• May affect release of nat’l estrogen into circulation

• May alter synth pathways, metab of natural hormones

Growth Factors Affect Estrogen Activity

• Estrogens act through EGF, IGF, TFG

• Cell membr receptors bind factors

• Get series intracell biochem rxns

• One endpoint of signal cascades is estrogen receptor transcr’n

• Estrogenics may affect growth factors

– Interaction w/ factors

– Binding of factor receptors

• Overall change estrogenicity

Is There a Problem?

• Public opinion against regulation/study

– Wildlife effects “esoteric”

– Not enough scientific evidence

– Too alarmist

• Public opinion for regulation/study

– Effects are clear

– Human-wildlife link believable

– Cancers, birth defects, red’d sperm ct frightening

• Risks to humans/wildlife/environment

– Need 5x amt DES to equal estradiol

– Admin DES @250-350 mg/kg during pregnancy

• Mother breast cancer 0.35 risk

• Daughter cerv. cancer 0.001 risk

• Daughter birth defect 0.3 risk

• Not only isolated chem’s at work in wildlife

– Evidence mostly relates to persistent substances (DDT, kepone)

• No longer legal

• Removal not related to hormonal effects

• Effects mostly related to specific sites

– Difficult to prove one chem. effect

• Wildlife studies isolated

– Magnitude of doses

– Synergism?

– Fish studies showed vitellogenesis in vitro, not in field tests

• Lab animals good models?

• Tissue culture samples valid?

EPA Task Force

• Food Quality Protection Act, Safe Drinking Water Act

• Best models

• Best cmpds to test

• Validity analytical techniques

• End points assigned

• Risk vs. cost

Large-Scale Clean-Up??

• Much $$$

• Nec for societal overall health, well-being?

• Nec for public health? Environmental health?

• Nec for wildlife propagation?