Lecture 19 Flashcards
(49 cards)
1
Q
what is the endocrine system?
A
composed of glands that secrete chemical messengers (hormones) that interact with specific targets (receptors)
2
Q
what are the two types of endocrine glands?
A
1) exocrine - ducted
2) endocrine - ductless, secrete products into interstitial fluid, diffuse into blood
3
Q
what are included in endocrine glands?
A
- pituitary, thyroid, parathyroid, adrenal, and pineal
4
Q
what parts of the endocrine system are not exclusively endocrine glands?
A
pancreas, ovaries, skin, heart, thymus, adipose tissue, small intestine, liver
5
Q
what are hormones?
A
affect only specific target tissues with specific receptors
6
Q
receptors are:
A
constantly synthesized and broken down
7
Q
what are the chemical classes of hormones?
A
1) lipid soluble -> use transport proteins
- steroid
- thyroid
- nitric oxide
2) water soluble -> circulate in free form
- amine
- peptide/protein
- eicosanoid
8
Q
what are the mechanisms of hormone action and what does it depend on?
A
- response depends on both hormone and target cell
- lipid soluble hormones bind to receptors inside the target cells
- water soluble hormones bind to receptors on the plasma membrane which activates a second messenger system
9
Q
what does the responsiveness of the target cell depend on?
A
- hormone concentration
- abundance of target cell receptors
- influence exerted by other hormones
10
Q
how is hormone synthesis regulated?
A
- signals from nervous system
- chemical changes in the blood
- other hormones
11
Q
what is negative feedback?
A
- most hormonal regulation is by negative feedback
- stimulus causes a substance to be released; once it reaches a specific level, it sends a signal that stops further release
12
Q
what are endocrine disrupters (EDCs)?
A
- exogenous substances that have been shown to act like natural hormones within organisms, leading to a disruption of physiological processes
- EDCs interfere with hormone biosynthesis, metabolism, or action
- EDCs interfere with the normal functions of the endocrine system and lead to problems with reproduction and development
13
Q
what are 3 examples of EDCs?
A
- PCBs
- plastics (bisphenol A)
- fuels
14
Q
What allows many of these EDCs to mimic the behaviour of our natural hormones?
A
their phenolic structure is similar to that of steroid hormones
15
Q
what are 3 key characteristics of EDCs?
A
1) receptor ligand or agonist
2) fate
3) hormone transport
16
Q
how do EDCs interact with hormone receptors?
A
- all hormones act by binding to a specific receptor or receptors
- EDCs that inappropriately bind to and/or activate hormone receptors can produce adverse biological effects
- EDCs can activate oestrogen receptors during development which can increase the risk of infertility in both sexes as well as reproductive tract cancer in women and prostate cancer in men
17
Q
what are 2 examples of EDCs activating hormone receptors?
A
- DDT binds to ERalpha and ERbeta and stimulates ER- dependent transcriptional activation in a variety of species
- Hydroxylated PCB congeners (OH-PCB) can activate human thyroid hormone receptor-beta-mediated transcription
18
Q
how do EDCs antagonize hormone receptors?
A
- EDCs can inhibit or block effects of endogenous hormones by acting as receptor antagonists
19
Q
what are 2 examples of EDCs acting as receptor antagonists?
A
1) DDE inhibits androgen binding to the androgen receptor (AR) and inhibits androgen dependent transactivation of the AR in human and rat prostate cells
2) lindane and dieldrin and insecticide aldrin (OCPs) also inhibit dihydrotestosterone binding the the AR
- as androgens are key regulators of male sexual differentiation during fetal development, disruption of androgen action through AR antagonism in this period can permanently demasculinize male fetuses and lead to malformations of the genital tract
20
Q
how do EDCs alter hormone receptor expression?
A
- hormone receptors mediate hormone actions, therefore their pattern of expression dictates their response to hormone signals
- receptor abundance can determine both the concentration of hormones that produces an effect as well as the magnitude of the effect itself
- EDCs can modulate hormone receptor expression and degradation
21
Q
what is an example of an EDC altering hormone receptor expression?
A
BPA alters the expression of oestrogen, oxytocin, and vasopressin receptors in the brain nuclei
22
Q
how do EDCs alter hormone distribution or circulating levels of hormones?
A
- hormones typically circulate throughout the body in the blood at low concentrations
- a circulating hormone is either transported ‘free’ (not bound to serum protein) with or without conjugation (such as glucuronidation or sulfation) or is circulated bound to various proteins
- EDCs can alter hormone bioavailability by interfering with the distribution of hormones in hormone-responsive tissues or with the circulation of hormones, including by displacing hormones from their serum binding proteins, which can lead to impaired active hormone delivery to target tissues
23
Q
what are 2 examples of EDCs altering hormone distribution?
A
1) BPA has been found to lead to a decrease in circulating levels of testosterone in male rats and men
2) pesticide malathion reduces testosterone levels in serum
24
Q
how do EDCs alter hormone metabolism or clearance?
A
- the different hormone types are inactivated differently
- EDCs can alter the rates of inactivation, including the metabolic degradation or clearance, of hormones, which could alter hormone concentrations and ultimately their activity
25
what is an example of EDCs altering hormone metabolism or clearance?
EDCs can activate glucuronidases, which increase thyroid hormone clearance from the blood
26
how are different types of hormones inactivated?
- after secretion, protein hormones are inactivated when they are broken down by proteases in the blood
- steroid and thyroid hormones are metabolized by enzymes that render them hormonally inactive and increase their water solubility so that they can be removed from the bloodstream and excreted
27
what are the contaminant associations with thyroid hormones?
- contaminants such as PCBs and their hydroxylated metabolites (OH-PCB) measured in tissues of marine mammals have been found to disrupt thyroid homeostasis
- correlations have been reported between POP levels and alterations in TH and other aspects involved in the growth and development of marine mammals, however the results are conflicting
- increased hormone levels vs. decreased hormone levels
- a reduction in TH levels associated with POPs has been reported in several species such as Largha and ribbon seals
- early studies on harbour seals fed PCB-contaminated fish found significant reduction in plasma TH and retinol levels. the decreased TH levels could be reversed when seals were fed non-contaminated fish for 6 months
28
what are the associations between reproductive hormones and POPs?
- testosterone was negatively associated with PCBs in polar bears
- progesterone levels were altered by PCBs in female polar bears
29
what were the endocrine associated effects in marine mammals?
- multiple endocrine associated effects have been found in marine mammals, which includes reproductive defects such as uterine occlusions, leiomyomas, adrenal lesions, and thyroid perturbations
- effects on reproductive tissues and correlations of POP concentrations have been widely reported in pinnipeds and cetaceans
- EDCs can pose a significant threat to wildlife because of their ability to affect reproduction, brain function, and the endocrine and immune system, which are crucial for wildlife survival
- for long lived species, reductions in reproductive success can have high consequences in many of these species due to their low reproductive rate, slow time to achieve reproductive competence, and high mortality of young
30
what were the cortisol related effects in marine mammals?
cortisol was negatively associated with PCBs and total pesticides in polar bears
31
what tissues can be used for hormone measurements?
- plasma/serum
- blubber
- liver
- feces
- saliva
- blow
longitudinal hormonal profiles:
- pinniped claws
- baleen plates
- hair
- teeth
32
what are the 4 methods used to measure hormone levels?
1) enzyme linked immunosorbent assays (ELISA)
2) radio-immunoassays (RIAs): a large amount of sample is required for the determination of an individual hormone
3) high performance liquid chromatography (HPCL)
4) liquid chromatography tandem mass spectrometry (LC/MS/MS): ability to use a relatively small amount of sample for the determination of multiple analytes
33
what is ELISA/EIAs?
- antibody of interest is absorbed onto plastic surface
- antigen is recognized by specific antibody
- the antibody is recognized by second antibody which has the enzyme attached ('enzyme linked')
- substrate reacts with enzyme to produce product, usually coloured
- read on a plate reader
34
what is the basic principle of ELISA?
- use an enzyme to detect the binding of antigen (Ag) to antibody (Ab)
- the enzyme converts a colourless substrate into a coloured product, indicating the presence of Ag:Ab binding
- an ELISA can be used to detect the presence of Ag or Ab in a sample depending on how the test is designed
35
what are the pros and cons of immunoassays (ELISA and RIA)?
pros:
- established and commonly used
- relatively simple and cost-effective
cons:
- large sample mass requirement
- limited by cross-reactivity, leading to potential false positives/negatives
36
what are the pros and cons on analytical techniques (GC-MS, LC-MS)?
pros:
- high specificity and accuracy
- small sample size requirement
cons:
- requires specialized equipment and expertise
- limited number of studies in marine mammals
37
what are vitamins?
- essential nutrients that are not produced endogenously and are generally acquired through diet
- in all mammals, the physiology of vitamins (dietary hormones) are highly regulated within the body to ensure constant availability during fluctuating intake
38
what are 2 essential nutrients required for a number of biological functions and what functions are they required for?
- vitamin A and vitamin E
- required for growth, development, reproduction, and protection against tissue damage
39
what is vitamin A?
- vitamin A is a collective name for a group of lipophilic compounds, also referred to as retinoids, that are essential to growth, development, reproduction, and immune function
- circulatory concentrations of vitamin A are kept within close ranges by a transport complex shared with thyroid hormone, consisting of a retinol-binding protein and transthyretin, and excess amounts are stored in the liver
40
how do mammalian neonates get vitamin A?
- they are born with very low liver stores of vitamin A due to minimal placenta transfer for retinol
- they receive greater amounts of vitamin A via milk during the nursing period
- thus, time is needed to build up a cumulative body store of vitamin A via nursing and foraging following weaning
41
what are the contaminant associations with vitamins A and E?
- PCBs, PCDDs, and PCDFs can interfere with vitamin A transport, storage, and metabolism, thereby promoting more rapid excretion
- vitamins A and E have been found to be disrupted by PCBs in arctic belugas, NE pacific harbour seals, california sea lions, baltic ringed and grey seals, and greendland killer whales
42
what are the methods used to measure vitamin levels?
- can be measured in variety of marine mammal tissues including blubber, liver, and plasma/serum
- storage at -80 degrees C
- high performance liquid chromatography (HPCL)
43
what are cell line cultures and how are they used?
- cell cultures can be used as a model system of an entire animal, organ, or tissue for an almost unlimited number of tests under precisely controlled conditions
- marine mammal cell cultures have the potential to be a multifunctional instrument in physiological, biochemical, genetic, and ecotoxicological studies, replacing the use of whole animals
44
what are marine mammal cell lines and how are they used?
- live immune cells are difficult to acquire for many marine mammal species
- thus, relevant immortalized cell lines can be invaluable for in vitro risk assessment
- established marine mammal cell lines exist for nonimmune, skin/fibroblast cell lines
- one marine mammal specific immune cell line does exist (harbour seal 11B7501 lymphoma B cell line) and it has been used to characterize the immunotoxic effects of heavy metals and pharmaceuticals
45
what alternatives have been used for marine mammals to assess toxicity?
- AhR CALUX assay - eg. rat cell line
- PPARg-bla assay - metabolic disorders
- AREc32 assay - oxidative stress hormone
- bioassays for activation of hormone receptors - endocrine disruption effects: ER (estrogenicity), AR (androgenicity), GR (glucocorticoid receptor), PR (progesterone receptor)
46
what is the freeze-filtration method for assessing marine mammal toxicity?
- can be used to retain contaminants from marine mammal blubber that removes lipids and can be used to facilitate the generation of realistic animal-derived mixtures that can be used for in vitro experiments
- cannot provide information of which individual compound is causing effects
- provides a unique, species specific method to assess immunotoxicity in marine mammal studies that are difficult to study in vivo
- minimally invasive method to study marine mammal health
47
what are baselines or reference intervals (RI)?
- baselines have been established for serum chemistry values for free-ranging beluga whales, harp seals, and ringed seals, as well as for managed-care marine mammals including beluga whales and killer whales
- procedures for establishing RIs based on the reference sample size and distribution have been recommended by the american society for veterinary clinical pathology for wildlife species, with sample sizes ranging from n=20 up to n>120
48
what are 3 challenges with obtaining baselines?
- obtaining an adequate sample size to establish an RI for a particular biomarker
- proper tissue/sample to collect
- proper tissue storage
49
what are the knowledge gaps/future needs with hormone and vitamin analysis?
- understanding the normal range, or reference intervals, for important physiologic endpoints in wildlife
- establish multispecies assessments that assess linkages between EDC exposure, body burden, and adverse health effects
- evaluate other environmental stressors that can affect the uptake and accumulation of EDCs, as well as health effects
