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GONADAL HORMONES: ESTROGENS AND ANDROGENS Synthesis, Metabolism, Mechanism of Action, Clinical Use. Rich Minshall, PhD Associate Professor; Anesthesiology, Pharmacology rminsh@uic.edu Chapter 40. The Gonadal Hormones & Inhibitors. Learning Objectives:
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GONADAL HORMONES:ESTROGENS AND ANDROGENSSynthesis, Metabolism, Mechanism of Action, Clinical Use Rich Minshall, PhD Associate Professor; Anesthesiology, Pharmacology rminsh@uic.edu Chapter 40. The Gonadal Hormones & Inhibitors
Learning Objectives: Understand the metabolic pathway of testosterone, estrogen and progesterone synthesis and know the drugs that stimulate and inhibit their synthesis Be familiar with the use and mechanism of action of androgen synthesis and receptor blockers Be aware of the treatment options for benign prostate hyperplasia and prostate cancer: FinasteridevsFlutamide Know the symptoms of the menopause period and which symptoms have been shown through clinical trials to benefit from hormone replacement therapy (HRT) Know the various estrogenic agents that may be used to treat menopausal symptoms: Premarin, Provera; PremPro Be aware of the protocols and routes of administration of HRT. Understand the rationale for choosing one protocol or route over another. Explain how a selective estrogen receptor modulator can act as an estrogen agonist in one tissue or cell type while acting as an estrogen antagonist in another tissue or cell type: Tamoxifen vs. Anastrazole
The biosynthetic pathwayof the androgens and estrogens19-carbon precursors are synthesized primarily in the ovaries, testes, and adrenals
Control of androgen secretion in males (1) competitive inhibition of LHRH receptors (2) stimulation (+, pulsatile administration) or inhibition via desensitization of GnRH receptors (–, continuous administration) Lupron: synthetic analog of GnRH, (3) decreased synthesis of testosterone in the testis; e.g., Ketocanazole, Anastrazole (4) decreased synthesis of dihydrotestosterone by inhibition of 5a-reductase; e.g., Finesteride (5) competition for binding to cytosol androgen receptors; e.g., Flutamide
Endogenous Mechanism of Feedback Inhibition Sertoli cells in the testis synthesize and secrete a variety of active proteins, including müllerian duct inhibitory factor, inhibin, and activin. • Leydig cells, upon LH stimulation, produce testosterone in the spaces between the seminiferous tubules. As in the ovary, inhibin and activin appear to be the product of three genes that produce a common a subunit and two bsubunits, A and B. • Activin, composed of the twob subunits, stimulates pituitary FSH release Inhibins(A and B), which contain the asubunit and one of theb subunits,in conjunction with testosterone and dihydrotestosterone , are responsible for the feedback inhibition of pituitary FSH secretion
Pharmacologic Uses of Androgens ANDROGEN REPLACEMENT THERAPY IN MEN: Androgen production falls with age in men and may contribute to the decline in muscle mass, strength, and libido. Hypo-pituitarism. USED AS PROTEIN ANABOLIC AGENTS USED AS GROWTH STIMULATORS ANABOLIC STEROID AND ANDROGEN ABUSE IN SPORTS ANDROGEN SUPPRESSION THERAPY IN MEN: benign prostatic hyperplasia; prostatic carcinoma ANDROGEN SUPPRESSION THERAPY IN woMEN: treatment of hirsutism
Androgen Replacement Therapy • To replace or augment endogenous androgen secretion in hypogonadal men • Used rather than gonadotropin except when normal spermatogenesis is desired • For hypo-pituitarism, androgens are not added to the treatment regimen until puberty • Start with long-acting agents such as testosterone enanthate or cypionate, 50 mg IM, initially every 4, then every 3, and finally every 2 weeks, with each change taking place at 3-month intervals • The dose is then doubled to 100 mg every 2 weeks until maturation is complete • Finally, the adult replacement dose is 200 mg at 2-week intervals.
Androgen Suppression Therapy • Inhibition of Steroid Precursor Conversion to Androgens • Ketoconazole-an inhibitor of adrenal and gonadal steroid synthesis • Abiraterone- inhibits the 17-hydroxylation of progesterone or pregnenolone to androgens • Finasteride-steroid-like orally active inhibitor of 5a-reductase that causes a reduction in dihydrotestosterone levels. Moderately effective in reducing prostate size in men with benign prostatic hyperplasia and is approved for this use in the USA. The dosage is 5 mg/d. • Dutasteride- a similar orally active steroid derivative with a slow onset of action and a much longer half-life than finasteride. The dose is 0.5 mg daily. • Anastrazole- blocks aromatase and inhibits conversion of androgens to estrogen • Receptor Inhibitors • Flutamide- potent anti-androgen that has been used in the treatment of prostatic carcinoma. Although not a steroid, it behaves like a competitive antagonist at the androgen receptor. • Cyproterone and cyproterone acetate are effective anti-androgens that inhibit the action of androgens at the target organ • Bicalutamide and nilutamide- potent orally active anti-androgens that can be administered as a single daily dose and are used in patients with metastatic carcinoma of the prostate.Spironolactone- a competitive inhibitor of aldosterone that also competes with dihydrotestosterone for the androgen receptor in target tissues. It also reduces 17-hydroxylase activity, lowering plasma levels of testosterone and androstenedione. It is used in dosages of 50–200 mg/d in the treatment of hirsutism in women and appears to be as effective as finasteride, flutamide, or cyproterone in this condition. • GOSSYPOL- cottonseed extract, abandoned as a candidate male contraceptive
Use of Anti-Androgen Therapy to treat BPH and Prostate Cancer The glandular cells of the Prostate produce a milky fluid, and during sex the smooth muscles contract and squeeze this fluid into the urethra. Here, it mixes with sperm and other fluids to make semen. Finasteride (Proscar, generic) and dutasteride (Avodart) are drugs used to treat benign prostatic hypertrophy (BPH). They block 5 alpha-reductase, which is the enzyme that converts testosterone to dehydroepiandrosterone (DHEA) that is known to stimulate growth of the prostate.
Treatment of Prostate Cancer Orchiectomy-surgical removal of the testicles (surgical castration) is the single most effective method of reducing androgens. When combinded with radical prostatectomy, this will delay progression in patients with cancers that have spread only to the pelvic lymph nodes. Orchiectomy increases the risk for osteoporosis LHRH Agonists The primary drugs used for suppressing androgens are LHRH agonists which block the pituitary gland from producing LH that stimulates testosterone production. Leuprolide (Lupron, Leuprogel), goserelin (Zoladex), and buserelin. Side effects: hot flashes and nipple and breast tenderness. Anti-Androgens Anti-androgens are drugs used to block the effects of testosterone at the receptor. Flutamide (Eulexin, Drogenil), nilutamide (Nilandron), and bicalutamide (Casodex). Side effect: diarrhea
Control of ovarian secretion and the actions of its hormones In the follicular phase, the ovary produces mainly estrogens; In the luteal phase, it produces estrogens and progesterone. SERMs, selective estrogen receptor modulators
Consider the normal menstrual cycle: 1) Estrogen released from the ovary - increases the expression of estrogen receptors. 2) Estrogen increases the expression of progesterone receptors. 3) Progesterone down regulates the expression of estrogen receptors. 4) With the progesterone-elicited decrease in estrogen receptor numbers - there will be a decrease in the ability of estrogen to stimulate the production of progesterone receptors - in this way - progesterone turns itself off.
Estrogen production from progesterone and testosterone via Aromatase: Treatment of estrogen-dependent Breast Cancer with • Aromatase inhibitors, Ketocanazole, Anastrazole
AP-1 Sp1
Elimination of Estrogens 17-estradiol is primarily converted by 17b-hydroxysteroid dehydrogenase to estrone, and converted by 16a-hydroxylation and 17-keto reduction to estriol, which is the major urinary metabolite; sulfate and glucuronide conjugates also are excreted in the urine. Estrone also is converted to the catechol estrogen, or 2-hydroxyestrone which is methylated to 2-methoxyestrone
Therapeutic Use and Dose of E2: • pharmacological considerations for E use in OC and HRT are different because of the dose • conjugated estrogens for HRT (0.625 mg/day for most women; 1.25 mg in some patients) • combination oral contraceptives in current use employ 20 to 35 mg/day of ethinylestradiol • Conjugated estrogens and ethinylestradiol differ widely in their oral potencies; for example, a dose of 0.625 mg of conjugated estrogens generally is considered equivalent to 5 to 10 mg of ethinylestradiol
Alters liver metabolism Affects on clotting and fibrinolysis - fibrinogen levels - synthesis of clotting factors (VII, IX, X, XIII) - plasminogen levels - plasminogen activator inhibitor Alters metabolism of lipoproteins - HDL - TG - LDL - total cholesterol Other - increases angiotensinogen and transport proteins Physiological Effects of Estrogen
Physiological Effects of Estrogen Alters vascular reactivity (endothelial mediators of contraction and relaxation) - endothelin-1 - TXA2 receptors - angiotensin II receptors - superoxide free radicals - nitric oxide synthase expression and activity therefore nitric oxide
ANTI-ESTROGENS • tamoxifen and clomiphene used primarily for treatment of breast cancer and female infertility, respectively • can produce estrogenic as well as anti-estrogenic effects • competitively block estradiol binding to its receptor; act as antagonists, agonists, or partial agonists depending upon the context in which they are used
Pharmacological Effects: • enlargement of the ovaries • ovulation in many patients with amenorrhea, Stein-Leventhal syndrome, and dysfunctional bleeding. • Clomiphene is used in conjunction with human menotropins and CG to induce ovulation • Tamoxifenexhibits anti-estrogenic, estrogenic, or mixed activity depending upon the species and endpoint measured; inhibits the proliferation of cultured human breast cancer cells, but stimulates proliferation of endometrial cells • estrogen-like effect to enhance bone density • does not seem to exhibit antiestrogenic effects on lipoprotein profiles • tamoxifen and clomiphene produce hot flashes in some women, the expected vasomotor effect
Mechanism of Action • Clomiphene and tamoxifen bind ER and prevent binding of E • the drugs and estradiol may interact with overlapping but slightly different regions of the ligand binding site • depending upon the specific cellular context and gene in question, anti-estrogen binding may yield a receptor complex that has full, partial, or no intrinsic activity • best considered as functional competitive receptor antagonists in breast cancer cells and the pituitary • Clomiphene can stimulate ovulation in women with an intact hypothalamic-pituitary-ovarian axis and adequate endogenous estrogens who have failed to ovulate; opposes the negative feedback of endogenous E resulting in increased gonadotropin secretion and ovulation • clomiphene increases the amplitude of LH and FSH pulses, without a change in pulse frequency, acting largely at the pituitary level to block inhibitory actions of E on gonadotropin release from the gland and/or is somehow causing the hypothalamus to release larger amounts of GnRH per pulse • Clomiphene also used in men to stimulate gonadotropin release and enhance spermatogenesis • the effects of tamoxifen on proliferation of breast cancer cells appear to result largely from estrogen receptor blockade • mammary tumors that contain ERs show a higher frequency of response to antiestrogens than do tumors without appreciable receptor levels
Multiple Outcomes of Raloxifene Evaluation (MORE) • Double Blind Placebo-Controlled Trial • 7705 PMP women aged 31 to 80 • Raloxifene 60 mg/d or 120 mg/d or placebo • Follow-up for 36 months for efficacy and 40 months for adverse events • Increased BMD in femoral neck by 2.1% (60 mg) and by 2.4% (120 mg) • Increased BMD in spine by 2.6% (60 mg) and by 2.7% (120 mg) • Increased risk of VTE (RR=3.1) • Conclusions: Raloxifene increases BMD in spine and femoral neck and reduces risk of vertebral fracture – but increases risk of venous thromboembolism
Tamoxifen vs. Anastrazole ? Nat Rev Cancer. 2003 Nov;3(11):821-31. Aromatase inhibitors for breast cancer: lessons from the laboratory. Johnston SR, Dowsett M.
Progesterone Receptor • Progestins are lipophilic and diffuse freely into cells where they bind to the PR (PR-A and PR-B) • PRs are ligand-activated nuclear transcription factors that interact with a progesterone response element in target genes to regulate their expression • PRs are expressed in the female reproductive tract, the mammary gland, the CNS (including the pulse generator in the hypothalamus), and the pituitary • expression of PRs is induced by estrogens; its presence is a common marker for E action • A single PR gene yields two forms of the receptor, the so-called A and B forms that arise from two translational start codons; the physiological and pharmacological significance of the two forms is unknown, but may relate to intracellular vs cell surface membrane PR • progestins enhance differentiation and oppose the actions of E to stimulate cell proliferation by decreasing ER levels, increasing local metabolism of estrogens to less active metabolites, or induction of gene products that blunt cellular responses to estrogenic agents
Menopause • Vasomotor instability (hot flashes), night sweats • Increase incidence of cardiovascular disease • Osteoporosis • Genitourinary atrophy • Metabolic changes – fat redistribution • Skin changes • Insomnia, fatigue, dysphoria, anxiety • Loss of memory? Susceptibility to dementia?
Menopause TimetableWomen may enter menopause earlier than they realize. Estrogen levels usually drop before menopausal symptoms are seen. Below, the typical ages for various symptoms. SYMPTOM AGE -35 40 45 50 55 60 65 70 Dropping estrogen levels Menstrual irregularity Mood swings Loss of concentration Hot flashes Vaginal dryness Last period Osteoporosis Heart Disease Sources: “Perimenopause: Preparing for the Change” by Nancy Lee Teaff and Kim Wright (Prima Publishing, 1996); “Perimenopause: Changes in Women’s Health After 35” by Drs. James E. Huston and L. Darlene Lanka (New Harbinger, 1997).
Hormone Replacement Therapy Menopause: cessation of menses; loss of ovarian function leading to a state of permanent amenorrhea Ovarian follicle no longer responds to gonadotropin, thus estrogen is not produced Lack of negative feedback results in increased levels of gonadotropins (FSH and LH) Amenorrhea lasting 1 year – average age 51.4 years (2 yrs earlier in smokers) Climacteric: series of physiologic, endocrinologic and psychologic changes that signify the transition from reproductive to non-reproductive life that spans several years – perimenopausal
Routes and Compounds • Oral Estrogens • Premarin, Cenestin • Esterified estrogen • Ethinyl estradiol • Estrone sulfate • Micronized estrogen • Transdermal Estrogens • Less effects on liver – no first pass effect • Patches, creams • Vaginal Estrogens • Vaginal creams – including premarin • Vaginal ring • Parenteral Estrogens • Estrogen esters • Progesterones • Medroxyprogesterone acetate • Norethindrone – etc. • Micronized progesterone
Examples of HRT Preparations • Prempro – continuous combined Premarin and Provera Premphase - continuous sequential Premarin 14 days then Premarin plus Provera for next 14 days • FEMHRT – continuous combined ethinyl estradiol plus norethindrone • Ortho-Prefest – continuous combined; 6 day cycle – day 1-3 micronized estradiol and day 4-6 micronized estradiol with norgestimate
Proposed Benefits of HRT • Cardiovascular • Decreased incidence of cardiovascular disease • Improved lipid profiles • Vasodilatory effects • Antiplatelet activity • Decreased fibrinogen levels • Direct myocardial effects • Antioxidant activity • Non-Cardiovascuclar • Prevention of bone loss* • Treatment of vasomotor symptoms (hot flashes)* • Prevention of colon cancer • Prevention of Alzheimer’s disease • Prevention of urinary incontinence • Alleviation of sleep disorders * known effects of estrogen
Relative Risk for Estrogen Use and Coronary Heart Disease Reproduced with Permission. Stampfer, M. & Colditz, G. Estrogen replacement therapy and coronary heart disease: A quantitative assessment of the epidemiologic evidence. Preventive Medicine. 1991;20, 47-63. Study Type Hospital Case-Control Pop Case-Control Prospective Internal Control Cross-Sectional Prospective External Control All Studies Combined Prospective Internal Control and Cross Sectional 2 0 1.5 1 RR 0.5
