W9L1 Mon endocrine disruptor Flashcards
What is an Endocrine Disruptor
Endocrine disruptor: an exogenous agent that interferes with synthesis, secretion, transport, binding + action or elimination of natural hormones in body which are responsible for maintenance of homeostasis, reproduction, development +/or behaviour
Source of endocrine disruptor
§ Natural chemical (phytochemical): from soy, hops, clover; weak + generally act through oestrogen pathway
§ Synthetic chemical (xenochemical): plastics, drugs, household products, pesticides; bioaccumulate in fatty tissues
Exposure to EDC
- Route of exposure: occupational/ agricultural/ service/ commercial industries (nail salon, hairdresser),
ingestion (food – plastics, water – pesticides, cosmetics),
absorption (skin, cosmetics),
inhalation (air, dust)
Controversal with EDC
– Relatively new (1990s)
– Few studies in humans
– Hard to show direct effect, background contamination
– Lab studies usually only use very high doses
– Natural levels difficult to measure
Bisphenols BPA, BPF, BPS)
- Plastic bottles & containers, food can linings, epoxy resins, till receipts
- Few studies on replacers – BPF, BPS. Mainly oestrogenic actions
Parabens
- Preservatives, anti-microbial agents, cosmetics, suncream, personal care products
- Similar structure to bisphenols, 5-fold higher in women. Mainly oestrogenic actions
Phthalates (MEHP, DEHP)
- Soft toys, flooring, medical equipment/tubing, personal care products, food packaging
- Mainly anti-androgenic and oestrogenic actions
Persistent Organic Pollutants (POPs)
- Consists of ‘superfamilies’- PBB, PCB, PCDD, PCDF & PFAS – Some banned since 1979
- Flame retardants, foams, plasticware, paints, lubricants, metal & paper production
- Very long half-life in the environment! Mainly oestrogenic and anti-androgenic actions
Pesticides, Herbicides and Insecticides
- Organochlorines, organophosphates, pyrethroids e.g. DDT/DDE (banned 1972), Atrazine…
- Often chemical mixtures – Oestrogenic, anti-oestrogenic, androgenic, anti-androgenic actions
Mechanisms of Action
endocrine disruptors bind to steroid hormone receptors + mimic hormones = block hormone binding
§ Can alter signalling + gene expression without binding
§ Influence production/metabolism of hormones, hormone receptor production/action + enzyme-related hormone functions
§ Oestrogenic pathway: BPA, DES, methoxychlor
§ Androgenic pathway: DDE, vinclozolin
§ Actions not fully understood; have independent effects outside of normal steroid pathway
* EDCs elicit effects at much lower doses (pM to fM concentration) vs. normal hormones (nM to pM)
Target Organs and Tissues
: brain (sexual behaviour), thyroid (metabolism), thymus (immune system), breast (cancer), pancreas (obesity)
§ Male: testis + penis (hypospadias + cancer)
§ Female: ovarian function (PCOS, endometriosis, cancer) + pregnancy (foetal growth reduction, preterm + still birth)
§ EDCs affect neurons of hypothalamus, pituitary or gonads
Effect of EDCs in wildlife
§ Amphibians + fish living in polluted water = frog deformities/infertility + abnormal ovaries
§ Alligators in Florida (1990s): lake full of DDT + pesticides = feminisation of males (tiny penis, low T4, high E2), abnormal ovaries
§ Bald eagles (1997): DDT (food chain) caused fragile eggshells + failed hatchings
§ Deer, otters + sea lions: PCB + DDT effects on fertility (bioaccumulation in blubber)
§ Issues understanding EDC effects: measure toxic/lethal not subtle effects, length of exposure vs. time of measurement, environment levels difficult to measure, background contamination = hard to show direct effect
EDCs effect During Foetal Development
Most sensitive period of exposure
§ Effects:
-placental function + transfer,
-thyroid function,
-bipotential gonad differentiation,
-deficits in IQ + memory,
-neurobehavioural + delayed neuromuscular development postnatally
EDC effect on adult development
§ Effects:
-thyroid function,
- ↑cancer incidence,
-abnormal production of ovarian steroids + disruption of folliculogenesis,
-organ morphology/function, behavioural differences (feminisation), ↓stress respond
§ Hayes’ study on male frogs + Atrazine: feminised + become hermaphrodites
Many Studies are done on male
EDC effect on Gamete/Embryo Development
§ 4 day exposure of embryo to normal amounts of BPA found in environment can change metabolic profile of embryo (↑obesity)
§ Unknown subtle effects or if effects different b/w males + females