Hormone Action and Clinical Pharmacology of Hormones Flashcards
Steroid vs peptide hormones
Steroid hormone (e.g. androgen) - 18-21 carbons (small)
Protein hormone (e.g. FSH) - large, multiple moieties, alpha/beta subunits (e.g. FSH alpha subunit 92 AAs!, beta subunit 118 AAs!)
Basics re: steroid hormones
- Derived from cholesterol
- 3 x 6-C rings + 1 x 5-C ring
Types of receptors
- Ion channels: simple, ion diffusion through gated channel
- G-protein coupled: transmembrane
- Intrinsic enzyme activity (e.g. tyrosine kinase): also transmembrane
- Intracellular (*steroid hormone receptors)
- Other (LDL, PRL)
Steroid hormone receptors mechanism of action
- Steroid hormone diffusion across cell membrane lipids
- Steroid hormone binds to receptor protein directly either:
- In cytoplasm: glucocorticoid, mineralocorticoid, androgen receptors
- In nucleus: estrogen and progesterone receptors
*binding of steroid hormone to its receptor causes dissociation of heat shock protein 90 (hsp90) and subsequent conformational change in receptor
**Many hormones require dimerization of the receptor here for activation
- Steroid hormone-receptor complex travels to nucleus if not there already > binds directly to DNA at hormone-responsive element
- In nucleus: gene activation > transcription of mRNA > transport to ribosomes
- In cytoplasm: translation > protein synthesis > specific cellular activity
Basic structure of steroid hormone receptor
- A/B: regulatory domain
- C: DNA-binding domain
- D: Hinge region
- E: Hormone-binding domain/pocket
- F: F region
- A/B: regulatory domain: most variable region, can bind transcription factor (TF) to activate receptor without ligand (steroid hormone) binding (e.g. TAF-1 on the estrogen receptor)
- C: DNA-binding domain: essential to activate transcription, most homologous region, contains zinc fingers
- D: Hinge region: localizes receptors to nucleus, a rotational site for conformational change
- E: Hormone-binding domain (pocket): where ligand binds, also may be site of hs90 protein, dimerization, co-factor binding, TAF-2 for ER
- F: F region: conformational change impacts receptor activity
Which region of the steroid hormone receptor is most variable? Most homologous?
Most variable - A/B regulatory domain (F region also variable)
Most homologous: C DNA-binding domain
Structure of ER alpha vs ER beta receptors
ER alpha (chromosome 6) - A/B region contains TAF-1 binding site, 1/2-life is 4-7 hours (found in uterus, bone, pituitary)
vs
ER beta (chromosome 14) (found in granulosa cells)
*Both contain on E-region (hormone-binding region): hs90 protein, TAF-2 binding region
TAF-1
- Transcription activating function-1
- Binds to A/B region of ER alpha receptor
- Can activate transcription after binding to ER alpha receptor without estrogen binding
- Helps explain how estrogen can have different actions in different tissues (depends on which receptor is present in the tissue)
SERM:
- E.g. tamoxifen binding to TAF-1 on ER alpha in breast, uterus, bone, pituitary > acts as agonist: stimulatory (effect of TAF-1 in these tissues overcomes TAF-2 inhibitory effects in these tissues)
Tamoxifen binding to TAF-2 > acts as competitive antagonist: inhibitory (normally overrides TAF-1 activation in most tissues)
Compare effects of SERMs on breast, uterus, bone, VTE, lipids, hot flushes:
- Estrogen
- Clomiphene
- Tamoxifen
- Raloxifene
- Bazedoxifene
Breast: Estrogen is + (all others are -)
Uterus: Estrogen and Tamoxifen are + (bazedoxifene is –)
Bone: All are +
VTE: All are +
Lipids: All are -
Hot flushes: Estrogen is - (all others are +)
Structure of progesterone receptor alpha vs beta
PR alpha - A/B regulatory domain contains TAF-3 binding region
Where is the androgen receptor gene located? How does this affect inheritance of certain disorders?
X chromosome (Xq11-12)
AIS is an X-linked recessive disorder because it involves defects in the androgen receptor gene on the X chromosome
Tissues derived from Wolffian ducts respond to ___
Hair follicles and UG sinus/tubercle respond to __
Tissues derived from Wolffian ducts respond to testosterone (internal male genitalia development)
Hair follicles and UG sinus/tubercle respond to DHT (testosterone must be converted > 5 alpha reductase > DHT) (external male genitalia development)
DHT has much higher affinity (more potent) for its receptor than testosterone
What is the mechanism of action of mifepristone?
Mifepristone (RU-486) is a selective progesterone receptor modulator (“SPERM”)
Mostly acts as a progesterone receptor ANTAGONIST (in the presence of progesterone); however, acts as an agonist in the absence of progesterone
Weak anti-glucocorticoid and anti-androgen activity
FDA-approved for medical abortion, non-FDA clinical use for miscarriage
Mechanism of action of ulipristal acetate?
SPERM (selective progesterone receptor modulator)
Works primarily as an ANTAGONIST at the uterus, cervix, ovaries, hypothalamus
Weak anti-mineralocorticoid and anti-androgen activity
FDA-approved for emergency contraception (30 mg dose), non-FDA approved for fibroids (5 mg dose)
Mechanism of action of spironolactone?
Aldosterone antagonist
Competitive inhibitor of testosterone at androgen receptor (but not completely antagonistic effect; dose-dependent competition, 20% affinity)
*Interferes with multiple cypP450 enzymes including 5-alpha reductase, SCC, 17 alpha hydroxylase, 17,20-lyase, 3 beta HSD, 11 beta hydroxylase, 21 hydroxylase, aldosterone synthase
*SE: HYPERkalemia (diuretic)
*Contraindications: teratogenic
Mechanism of action of flutamide?
Pure anti-androgen
Blocks androgen effect by competitive inhibition
*SE: liver toxicity
*Contraindications: teratogenic
Mechanism of action of finasteride?
5-alpha reductase inhibitor (inhibits conversion of testosterone > DHT)
Tx for: hirsutism
*Contraindicaitons: teratogenic
Steroid analogues
- Ethinyl estradiol
Ethinyl estradiol: addition of ethinyl group to increase oral bioavailability and increase half-life, but prevents detection by standard estrogen assays
- Most common estrogen in OCP
- 5 mcg dose of EE = 1 mg 17-beta-E2 (Estrace)
Norethinedrone
- Which generation?
- Androgenic/Estrogenic?
- What is it derived from?
- What is another name?
- Classified as?
- One of the oldest synthetic progestins
- Derived from testosterone
- 19-nor testosterone (NO 19th C, unlike testosterone)
- Addition of ethinyl group
- 1st generation
- Androgenic (binds to androgen receptor)
- “Estrane”
Levonorgestrel
- Which generation?
- Androgenic/Estrogenic?
- Compare to norethinedrone
- Classified as?
- 2nd generation
- Most potent and more androgenic than norethinedrone due to longer half-life > makes a good progestin for IUD (packaged small amount)
- One additional C compared to norethinedrone
- “Gonane”
Norgestimate
Desogestrel > (and Etonogestrel metabolite)
Gestodene
- Which generation?
- Androgenic/Estrogenic?
- Concerns?
- 3rd generation
- Designed to be less androgenic
- Some concern re: higher DVT risk
Drospirenone
- Which generation?
- Androgenic/Estrogenic?
- Concerns?
- 4th generation
- Agonist at progesterone receptor
- Antagonist at androgen and mineralocorticoid receptors > mild diuretic effect
- Some concern re: higher DVT risk
Medroxyprogesterone acetate (Provera)
- Derived from?
- Acts on which receptor?
- Concerns?
- Classified as?
- NOT derived from androgen, but progesterone itself
- Potent progesterone agonist at high doses
- Can suppress FSH at high doses (negative feedback) > decrease E2 production, amenorrhea, bone loss (e.g. Depo-Provera)
- “Pregnane”
Megestrol acetate (Megace)
- Derived from?
- Acts on which receptor?
- Derived from progesterone
- Potent progesterone receptor agonist
- Tx of endometrial hyperplasia
Norethinedrone acetate (Aygestin)
- Similar to norethinedrone with added acetyl group
- Tx: 5 mg for AUB, lower doses in OCP
- Metabolized at a low rate > ethinyl estradiol ! Therefore, can be used as sole HRT (for endo, for GnRH agonist add-back)
Which region of the steroid hormone receptor contains zinc fingers?
C - DNA-binding domain
G-protein coupled receptors
- Peptide hormone receptor
- 7 membrane spanning domains
- 3 intracellular, 3 extracellular loops
- Several subunits
Describe cAMP 2nd messenger pathway for G-coupled protein receptors
- What types of G-protein receptors use this pathway?
- Name examples
Adenylate cyclase
cAMP
Protein kinase A
Gs (stimulatory) vs Gi (inhibitory)
FSH, LH, hCG, TSH, ACTH
CRH, Somatostatin, GHRH
Describe phospholipase C 2nd messenger pathway for G-coupled protein receptors
Phospholipase C (PLC)
DAG
IP3
Protein kinase C (sustained response)
Calmodulin (acute response)
Ca2+ dependent reactions
Gq
GnRH (Ca2+ dependent), TRH, oxytocin, kisspeptin
Pathophysiology of McCune Albright Syndrome
- Constitutive activation of the Gs receptor (in absence of ligand)
Manifestations:
- Constitutively active FSH-R > increased estrogen production
- Constitutively active MSH-R > skin pigmentation
Kisspeptin mutation leading to hypo/hypo and absent puberty is a mutation in what gene?
Kisspeptin receptor (GPR54) mutation in Gq receptor > prevents kisspeptin binding and downstream PLC pathway > hypo hypo / absent puberty
Tyrosine kinase receptor
- Typical process
- Examples
- Peptide binds to receptor
- Often involves receptor dimerization
- Receptors phosphorylate themselves (tyrosine residues) or are phosphorylated by other protein kinases > conformational change
- Stimulate other intracellular signaling
Examples: insulin receptor, IGF-1, VEGF, EGF
Pathophysiology behind insulin resistance?
- Resistance: insulin continues to bind, but ceases to have the same biologic effect
- Decreased phosphorylation of tyrosine residues vs
- Increased phosphorylation of serine residues
What effect does insulin have on the theca cells of the ovary?
Increases androgen production
Cytokine receptor
- JAK-STAT hormone pathway
- Ex: growth hormone, prolactin, hPL, leptin
Serine/threonine kinase
Activin
Inhibin
Describe the structure of gonadotropins
FSH, LH, hCG, TSH - glycoprotein hormones
Heterodimers: common alpha subunit, unique beta subunit (alpha-beta subunits connected via disulfide bonds)
Where does glycosylation of gonadotropins occur?
What is the effect of glycosylation?
Golgi apparatus
Adding carbohydrate > alters metabolic clearance/half-life (the higher sialic acid > the longer the half-life)
E.g. hCG has near identical beta subunit, but has much more sialic acid/glycosylation, so its half-life is significantly longer than LH
Heterogeneity of glycoproteins
Multiple isoforms of gonadotropins exist (e.g. hyperglycosylated hCG in GTD) due to differences in DNA promoter action, RNA splicing, post-translational modifications (e.g. glycosylation)
Another example: recombinant (1 isoform, Follistim, Gonal-F from Chinese hamster ovary cells, need mammalian cells for post-translational modification in the Golgi apparatus, cannot use bacteria) vs purified gonadotropins (multiple isoforms, e.g. Menopur from urine). Clinical impact?
Regulation of tropic hormones:
Describe desensitization
- Homologous
- Heterogeneous
vs
Down-regulation
DESENSITIZATION: Prolonged exposure to agonist > DECREASED RESPONSE via auto-phosphorylation of cytosolic portion of receptor > loss of signaling
- Homologous desensitization: affects only single receptor
- Heterogeneous desensitization: affects multiple receptors on the membrane
DOWN-REGULATION: Prolonged exposure to agonist > internalization of receptor via clathrin pits > decreased # of receptors / decreased response to hormone
**prolonged exposure causes both desensitization and down-regulation
Describe structure of GnRH
How does it differ from GnRH agonist?
GnRH antagonist?
- GnRH is a decapeptide
- GnRH has a short half-life due to AA cleavage
- GnRH agonist (leuprolide acetate or Lupron): replacement of AA at #6 position (Gly > Leu) > longer half-life > metabolic stability
- GnRH antagonist: multiple AA substitutions > competitive blockade of GnRH receptor > immediate decline in gonadotropin levels with immediate therapeutic effect (70% suppression of LH, 30% suppression of FSH after only 6 hours)
