1. Mechanisms of female reproductive toxicity
Helena Taskinen
Finnish Institute of Occupational Health

2. Critical points of female fertility
libido, sexual behaviour
oogenesis
hormonal function
fertilization
transportation
implantation

3. Developmental toxicity
gameto-, embryo- and fetotoxicity
abortion, stillbirth
teratogenic effetcs
intrauterine growth retardation
functional defects
impaired mental and physical postnatal development up to puberty
childhood cancer

4. Hypothalamo-pituitary-ovarian axis
Hypothalamus: hypothalamic-releasing factor, gonadotropin-releasing hormone
Pituitary: Gonadotropin-releasing hormone, gonadotropins: follicle stimulating hormone (FSH) and luteinizing hormone (LH)
Ovary: estrogen and progesterone
Agents that disturb the axis can disrupt ovarian function
- Every pregnant women with a female fetus is a “half-a-grand-mother”, since the oocytes of the child are developed during the pregnancy. Thus, damage in the daughter’s oocytes may have been born from maternal ocupational exposure! -

5. Hypothalamo-
Pituitary-
Ovarian
axis
Hypothalamus
Hypothalamic factors
Progesteron,
estrogen
Pituitary gland
Gonadotropins, prolactin
Ovary

6. Mechanisms of toxins 1
Direct acting toxins: structurally similar or chemically reactive
Direct damage to cells, organelles, DNA/RNA, enzymatic and biochemical pathways
alkylating compunds, metals (boron, cadmium, lead, mercury) and ionizing radiation
Toxicant causes a cellular or molecular event which
disrupt the flow of matter
or information
Direct damage to cells, subcellular compartments (i.e. various organelles), molecular loci (DNA, RNA), or enzymatic or biochemical compartments

7. Indirect toxins: metabolic activation produces reactive intermediates:
cyclophosphamide, DDT, PAH, dibromochloropropane

8. Mechanisms of toxins 2 Hormone agonists or antagonists
oral contraceptives, DDT, methoxychlor, polychlorinated biphenyls, polybrominated biphenyls, organochlorine pesticides
Cellular (oocyte) death: necrosis
pesticides, PAH in cigarette smoke, chemotherapeutic agents, ionizing radiation, nitrosamines, lead, mercury, cadmium, 4-vinylcyclohexene

9. Mechanisms of toxins 4 Apoptosis, programmed cellular death
is preceded by activation of calcium/ magnesium-dependent endonuclease enzyme
change in the cellular environment
hyperthermia and radiation can trigger
also a physiological form of cell death
poorly understood, toxins possible, e.g. chemotherapeutics cisplatin and vinblastine

10. Oogenesis
A single follicle becomes graafian follicle, which releases the oocyte
Toxicants interfering the oocyte maturation in the graafian follicle impair reproduction - recovery in next cycle possible
Toxicants affecting primordial or primary follicle may lead to shortened reproductive life span and premature ovarian failure

11. Oocyte toxicants Polycyclic aromatic hydrocarbons can
destroy primordial follicles
cause ovarian tumors
induce chromosomal aberrations in oocyte meiosis
Busulfan and antineoplastic agents can
destroy primordial germ cells or developing follicles, and mutate preovulatory follicles

12. Toxicants 2
DDT and diethylstilbestrol (DES), estrogenic compounds, suppress ovarian progesterone production
General anesthesia during periovulatory period lowers progesterone levels
Benzo(a)pyrene in cigarette smoke inhibits corpora lutea formation and thus progesterone production

13. Toxicants 3 The hypothalamo-pituitary unit is disturbed by
anesthetics, stimulants, analgetics, hallucinogens, marihuana, morphine, cocaine
estrogenic chemicals, e.g. diethylstilbestrol (DES)

14. Toxicity of diethylstilbestrol
a synthetic estrogen, used to prevent spontaneous abortions in
proven ineffective in later studies!
mutagenic and carcinogenic effects mediated through production of reactive metabolites, DNA adducts
clear cell vaginal carcinoma in daughters
18 % of offspring (f) abnormal of the cervix
to 2 million pregnant women received the trtment in US
Later clinical trial showed that DES was ineffective in preventing miscarriages and premature birth!
DES daughters are at high risk for miscarriages, ectopic pregnancy, stillbirth and premature birth

15. Cadmium (Cd)
Structural similarity with zinc - Cd can displace zinc in zinc-dependent enzymes
in rats: follicular atresia, changes in uterine microcirculation; decreased uterine, ovarian and pituitary weights
zinc-dependent enzymes crucial for metabolic processes
e.g. carbonic anhydrase, thymidine kinase, DNA-dependent RNA polymerase, DNA polymerase
Low doses (environmental level, 0.18 mg CdCl2 /kg s.c.) - no major seffects on human female fertility

16. Developmental abnormalities
Major malformation at birth among 3 %
Problems of developmental origin among % by 1 year of age
Among % by school age

17. Causes of developmental abnormalities
% familial genetic defect
% external exposure (environmental, drugs, nutritional)
0 - 23% multifactorial cause
% unknown cause (Wilson 1977; Nelson and Holmes 1989)

18. Species differences
Mammalian embryogenesis and fetal development relatively similar among all species
Differences btw. species due to differences in xenobiotic absorption and metabolism
e.g. thalidomide not soluble in rat blood - no teratogenecity in tests! When solubility was increased, teratogenic in low doses

19. Examples of agents causing toxic effects early in the development
Ionizing radiation
Methylnitrosourea
Medroxyprogesterone acetate
Nickel chloride
Ethylene oxide
Nitrous oxide
Isoflurane
Methylnitrosourea’s effect to blastocysts so weak that nonlethal mutations may play a role in poor fetal outcome
Ethylene oxide (and other chemicals): primary damage epigenetic, leads to disruption in the normal programming of gene expression during early embryogenesis
Anesthetic gases: direct effects, but mechanism unknown
- nitrous oxide marginally toxic, only in early cleavage stages
- isoflurane: decreased fertilization and pregnancy rates in patients receiving this anesthetic during the oocyte retrieval!

20. Anesthetic gases: direct effects, but mechanism unknown
Methylnitrosourea’s effect to blastocysts weak, nonlethal mutations may play a role in poor fetal outcome
Ethylene oxide (and other chemicals): primary damage epigenetic, leads to disruption in the normal programming of gene expression during early embryogenesis
Anesthetic gases: direct effects, but mechanism unknown
- nitrous oxide marginally toxic, only in early cleavage stages
- isoflurane: decreased fertilization and pregnancy rates in patients receiving this anesthetic during the oocyte retrieval!

21. Placenta
Provides nutrients, gas exchange and hormones for maintenance of pregnancy
Placenta is a liver, kidney, lung, ovary, pituitary and hypothalamus in one organ!
Acts as a barrier for toxicants, metabolizes them into less or more detrimental compounds

22. Cadmium and placenta
Cadmium induces placental necrosis at lower doses than renal toxicity
deposited in placenta, little into fetus
blocks nutrient and blood flow: growth retardation, fetal death
interferes with zinc
responsible for the growth retardation caused by smoking

23. Other effects on placenta
Cholinergic system regulates amino acid transport in the placenta
Nicotine, carbon monoxide, cyanide, nitrites (all present in cigarette smoke) inhibit amino acid uptake by placenta by blocking the cholinergic receptor
Risks: preeclampsia, growth retardation, premature delivery, and perinatal mortality
Cholinergic system regulates amino acid transport in the placenta
Morphine inhibits placental acetylcholine release
Cocaine blocks calcium-mediated acetylcholine release
They also cross placenta
Alcohol potentiates the vasoconstrictive effect of nicotine (preeclampsia, growth ret., abortion)

24. 2-methoxyethanol (2-ME) & 2-ethoxyethanol (2-EE) and their acetates
alcohol and aldehyde dehydrogenase enzymes active; if inhibited with 4-methylpyrazole, no malformations
Teratogenic alcoxy acid metabolites:
2-methoxyacetaldehyde and methoxy acetic acid from 2-ME
ethoxyacetaldehyde and ethoxyacetic acid from 2-EE

25. Heavy work
Intraabdominal pressure rises, decreases intrauterine blood flow
Growth retardation
In women 17 % fat needed for menstruation; 22 % for fertility
hypoestrogenism
In men <5 % body fat decreases testosterone and prolactin in the serum