Reproductive
Toxicology
Developmental Toxicity
Occurrence of adverse effects on the developing organism occurring anytime during the lifetime of the organism that may result from exposure to environmental agents prior to conception (either parent), during prenatal development, or postnatally until the time of puberty.
Sequence of Human Development
1 2 3 4 5 6 7 8 12 16 20 38
ImplantationPrenatal
Death
Emryonic period
Major Morphological abnormalities
Fetal PeriodPhysiological and Functional
Defects
Central Nervous System
Heart
Ears
Eyes
Limbs
Palate
External Genetalia
Red - most sensitive, Gray - Less
Reproduction – issues associated with the egg and sperm
Pregnancy – the critical environment of early development
Development of the infant.
Three Areas
Many ancient cultures had fertility goddess
Many ancient documentation of malformations
Malformations rich aspect of mythology 6500 BC – Turkey - figurine of
conjoined twins 4000-5000 BC – Australia drawings of
twins 2000 BC - Tablet of Nineveh –
describes 62 malformations and predicts the future
Ancient Awareness
15th-16th centuries malformations caused by the Devil, mother and child killed
1830’s - Etienne Geoffroy Saint-Hilaire experimented with chicken eggs
1900’s began acceptance of malformations related to genetics
1940’s - Josef Warkany – environmental factors affect rat development
Historical Awareness
1941 – Human malformations linked to rubella virus
1960’s – Thalidomide (a sedative and anti-nausea drug) found to cause human malformations
1950’s – Methylmercury recognized as developmental toxicant
1970’s – Alcohol related to developmental effects – Fetal Alcohol Syndrome (FAS)
Historical Events
• Approximately 80,000 chemicals listed by EPA
• Most of these chemicals have not been tested for developmental toxicity
• For example, High Production Volume (HPV) Chemicals
• Chemicals produced at >1 million lbs/year• Approximately 3,000 chemicals
identified internationally• Few tested for both reproductive and
developmental toxicity
Current Chemical Facts
• 50% of pregnancies end in miscarriage or spontaneous abortion often before pregnancy is recognized
• 15% of couples of reproductive age are infertile
Human Reproductive Facts
• The occurrence of biologically adverse effects on the reproductive systems of females or males that may result from exposure to environmental agents.
• The toxicity may be expressed as alterations to the female or male reproductive organs, the related endocrine system, or pregnancy outcomes.
Reproductive Toxicity
Reproductive EndpointsREPRODUCTIVE ToxicityReproductive toxicity involves toxic damage to either male or female reproductive system. Toxic effects may causeDecrease LIBIDO and IMPOTENCEINFERTILITYInterrupted pregnancy ( abortion, fatal death, or premature delivery)Infant death or childhood morbidityAltered sex ratio and multiple birthChromosome abnormalities and birth defectsChildhood cancer.
Endocrine disruptorsDDT, Dioxin, Phthalates
Heavy metalsLead (decreased sperm)
Organic SolventsToluene, benzene
DrugsAlcohol
Reproductive Toxicants
• Cardiovascular• Increased - cardiac output heart rate,
blood pressure, blood volume expands • Oxygen consumption increases by
15-20%• Urine volume increases• Gut absorption changes
• Increases in iron and calcium (toxic lead substitutes for calcium)
• Liver metabolism decreases for some drugs or chemicals (caffeine)
Pregnancy Effects the Women
Teratology (physical malformations)
Birth weight Growth Neurobehavioral
Decreased intelligence Decreases learning and
memory
Developmental Endpoints
Effects Amplified
Lower doses toxic effectsRepro system more sensitive to ~33%
toxicants evaluated
Female Reproduction
Three structures› Hypothalamic-pituitary-gonadal axis› Ovary› Fallopian tube
Hypothalamic-Pituitary-Gonadal Axis
Signals ovulationDisrupted by
XenobioticsExcess hormonesInsufficient hormones
Cyclic production of gonadotropins
› FSH, LH, prolactin produced, released Feedback loops controlled by endogenous
hormones BUT environmental chemicals can influence
feedback loops
Neuronal influences› Affected by anesthetics, cannabinols,
sedatives
Ovary
Site of gamete maturation Controls proliferation
› Endometrium› Oviductal function› Uterus
Oocytes at birth› Suspended meiosis (birth to maturity)
Recruitment at maturity Meiosis Release at ovulation
Primary oocytes during suspended meiosis› Susceptible to drugs, environmental agents› PAH’s toxic to ovary, oocytes
Dose toxic to mouse oocytes sim to mutagenic/carcinogenic dose
Dependent on strain, species, age, dose, metabolism
Some agents act indirectly› DES, DDT
› PAH= Polycyclic aromatic hydrocarbons
Activation of some toxins reactive intermediates
Ex: DES- Diethylstilbestrol activation› Harmful to developing fetus› infertility in mature females
Ex: Benzopyrene› Systemic and ovarian metabolism› Some metabolites ootoxic› Cigarette smoking linked to disruption
reproduction
Fallopian Tube, Uterus
Gamete propulsion, fertilization, implantation of embryo
Congenital structural problems› May be linked to xenobiotic exposure› DES- Diethylstilbestrol
Hormonal imbalance, immunologic alterations› Xenobiotics??› Unexplained infertility
Preimplantation embryo in oviduct› Signals endometrium biochemically› Site for interruption
Disruption implantation Improper hormones Improper hormone levels @ crucial time
Male Reproduction
Sperm count decrease?› 1951 – 44% subjects > 100x106/mL› -- 5% < 20x106/mL› 1975 – 24% subjects > 100x106/mL› -- 7% < 20x106/mL
Other indicators decreasing following repro toxicants› Libido› Impotence
FORMS fertile sperm, deliver to female tract› Must be functional
DiBromoChloroPropane (DBCP) (1970’s)› Azoospermia› Oligospermia› Incr’d plasma LH, FSH› Atrophy seminiferous tubular epithelium
Human testes affected Sim in lab animals, but to lesser extent
› Recovery w/in 18-21 mos
Testes
Convoluted seminiferous tubules arranged in lobules
Surrounded by interstitial cells (Leydig cells)
Lined w/› Germ cells
Proliferative Mature to spermatozoa
Migrate basement membr tubule lumen w/ maturation› Sertoli cells
“Hold” sperm Form blood-testis barrier
Help protect sperm from some toxicants
Sperm dev’t prior to release from Sertoli cells› Flagellum develops› Nucleus condenses› Acrosomal cap w/
digestive enzymes develops
Hormones Regulate Testicular Activity
GnRH (hypothalamus)› FSH
From anterior pituitary Required to initiate spermatogenesis
› LH From anterior pituitary Stim’s testosterone synth/release from
Leydig cells
Testosterone› Spermatogenesis progression, maturation,
maintenance› Accessory sex glands› Negative feedback to anterior pituitary
Alterations› Anesthetics, Stimulants, Drugs of Abuse
Alter hypothal-pit-gonadal (so GnRH, FSH, LH)› Exogenous Steroids, Alcohol
Interfere w/ steroid metabolism May affect hormonal balance
Xenobiotics Affect Spermatogenesis
Toxicants selective for sperm dev’t stage(s)
DNA repair mech’s stage-specific Sperm metabolism alteration may
affect fertilizing capacity
Cd› Testicular necrosis› Concentrates in interstitial tissues
Polyaromatic Hydrocarbons› Metabolized in testes› Cyt P450’s.› Metabolites may be toxic
DES -Diethylstilbestrol
› Hypoplastic testes› Microphallus› Cryptorchidism› Oligospermia› Azoospermia