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

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

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

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! -

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

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

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

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

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

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

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

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

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

Toxicity of diethylstilbestrol a synthetic estrogen, used to prevent spontaneous abortions in 1938-1971 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 500 000 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

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

Developmental abnormalities Major malformation at birth among 3 % Problems of developmental origin among 6 -7 % by 1 year of age Among 12 - 14 % by school age

Causes of developmental abnormalities 20 - 28 % familial genetic defect 10 - 3 % external exposure (environmental, drugs, nutritional) 0 - 23% multifactorial cause 70 - 43 % unknown cause (Wilson 1977; Nelson and Holmes 1989)

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

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!

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!

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

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

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)

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

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