Ezetimibe and Thyroid Hormones Overview
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Questions and Answers

Which iodine-containing compound is formed by the condensation of two DIT molecules?

  • rT3
  • T3
  • T4 (correct)
  • MIT

    • What role does the hypothalamic-pituitary-thyroid axis play in thyroid hormone synthesis?

  • It provides iodine directly to the thyroid gland.
  • It produces T3 and T4 directly.
  • It catalyzes the condensation of DIT molecules.
  • It regulates the feedback mechanisms for hormone synthesis. (correct)

    • Which thyroid hormone is considered more active?

  • rT3
  • T3
  • T4 (correct)
  • MIT

    • What is a characteristic of the chemical structure of T3?

    <p>It contains a phenolic OH group.</p> Signup and view all the answers

    Levothyroxine is primarily used for which purpose?

    <p>Treatment of hypothyroidism.</p> Signup and view all the answers

    What is the mechanism of action for anti-thyroid drugs?

    <p>They prevent incorporation of iodine in thyroxine precursors.</p> Signup and view all the answers

    What is the primary action of ezetimibe in the body?

    <p>Inhibits absorption of cholesterol</p> Signup and view all the answers

    Which of the following hyperlipidemias is ezetimibe useful for?

    <p>Type IIa</p> Signup and view all the answers

    Which condition may necessitate the use of anti-thyroid drugs prior to surgery?

    <p>Hyperthyroidism</p> Signup and view all the answers

    What role do thyroid hormones play in metabolism?

    <p>Increase calorigenesis and oxygen consumption</p> Signup and view all the answers

    What is a common effect of thyroid hormones on metabolism?

    <p>Increase the absorption of glucose.</p> Signup and view all the answers

    Which mineral is essential for the synthesis of thyroid hormones?

    <p>Iodine</p> Signup and view all the answers

    What is the initial step in the production of iodinated amino acids within thyrocytes?

    <p>Synthesis of thyroglobulin</p> Signup and view all the answers

    Which reaction is catalyzed by thyroperoxidase during thyroid hormone synthesis?

    <p>Oxidation of iodide to iodine</p> Signup and view all the answers

    How do thyroid hormones affect carbohydrate metabolism?

    <p>Accelerate insulin degradation and increase gluconeogenesis</p> Signup and view all the answers

    What effect do thyroid hormones have on the cardiovascular system?

    <p>Increase sensitivity to catecholamines</p> Signup and view all the answers

    What is the primary function of α-glucosidase inhibitors?

    <p>To inhibit the absorption of monosaccharides</p> Signup and view all the answers

    What side effects can result from the use of α-glucosidase inhibitors?

    <p>Diarrhea and flatulence</p> Signup and view all the answers

    How do incretins function in the body?

    <p>By enhancing insulin release from beta cells</p> Signup and view all the answers

    What characterizes meglitinides compared to sulfonylureas?

    <p>They do not have toxic effects</p> Signup and view all the answers

    What is the primary mechanism through which diuretics achieve their effect?

    <p>Direct inhibition of Na transport in the nephron</p> Signup and view all the answers

    What role does α-glucosidase play in carbohydrate digestion?

    <p>It breaks down polysaccharides into disaccharides</p> Signup and view all the answers

    Why should patients using α-glucosidase inhibitors avoid glucose intake?

    <p>They are unaffected by these drugs</p> Signup and view all the answers

    What is a potential outcome of increased saccharides in the colon due to α-glucosidase inhibitors?

    <p>Colonic distress symptoms</p> Signup and view all the answers

    What is primarily lost during acidosis?

    <p>HCO-3</p> Signup and view all the answers

    Which compound is considered the prototype for heterocyclic sulfonamides?

    <p>Acetazolamide</p> Signup and view all the answers

    What characteristic is essential for the diuretic activity of sulfonamides?

    <p>Sulfamoyl group</p> Signup and view all the answers

    How does substitution of a methyl group on one of acetazolamide's ring nitrogens affect its activity?

    <p>It increases its carbonic anhydrase inhibitory potency.</p> Signup and view all the answers

    Which of the following is not capable of inhibiting carbonic anhydrase?

    <p>Most antibacterial sulfonamides except sulfanilamide</p> Signup and view all the answers

    What is the significance of the sulfamoyl nitrogen atom remaining unsubstituted?

    <p>To retain carbonic anhydrase inhibitory activity.</p> Signup and view all the answers

    Which property of sulfonamide derivatives is related to the carbonic anhydrase inhibitory and diuretic activity?

    <p>High lipid/water partition coefficient</p> Signup and view all the answers

    Which characteristic must be present in the moiety to which the sulfamoyl group is attached?

    <p>Aromatic character</p> Signup and view all the answers

    Which diuretic is NOT included in the site 3 diuretics list?

    <p>Furosemide</p> Signup and view all the answers

    What is the significance of position 3 in the structure activity relationship of diuretics?

    <p>It plays a critical role in potency and duration of action.</p> Signup and view all the answers

    Which functional group is associated with the acryloyl group that forms an adduct with sodium/potassium ATPase?

    <p>Acrylic</p> Signup and view all the answers

    What type of structural modification can position 2 tolerate according to the structure activity relationship?

    <p>Small alkyl groups like CH3</p> Signup and view all the answers

    Which of the following is a characteristic feature of site 3 diuretics?

    <p>They are generally less potent than loop diuretics.</p> Signup and view all the answers

    Which compound is used in the synthesis of ethacrynic acid and involves AlCl3?

    <p>ClCH2COOH</p> Signup and view all the answers

    What is the role of the sodium/potassium ATPase system in the loop of Henle?

    <p>It is essential for ionic transport.</p> Signup and view all the answers

    Which of the following compounds is a thiazide-like diuretic?

    <p>Metolazone</p> Signup and view all the answers

    Study Notes

    Ezetimibe

    • Approved in 2002
    • Reduces LDL, total cholesterol, and triglycerides
    • Increases HDL
    • Prevents cholesterol absorption from diet
    • Useful in hyperlipidemias (type IIa, IIb, III, IV, and V)

    Thyroid Hormones

    • Crucial for growth and development
    • Stimulates metabolism in most tissues (except adult brain)

    Thyroid Hormone Function

    • Increases mitochondrial oxidative phosphorylation
    • Maintains amino acid and electrolyte transport into cells
    • Increases calorigenesis and oxygen consumption
    • Stimulates protein synthesis (structural & enzymatic)
    • Regulates carbohydrate metabolism (accelerates insulin degradation & increases gluconeogenesis)
    • Stimulates lipid metabolism (reduces plasma cholesterol)
    • Increases cardiovascular and nervous system sensitivity to catecholamines (leading to increased heart rate, cardiac output, and arousal)

    Thyroid Hormone Synthesis Requirements

    • Requires tyrosine (amino acid) and iodine (trace mineral)
    • Begins with thyroglobulin synthesis, which is post-translationally modified in unique biochemical reactions

    Thyroid Hormone Biosynthesis Process

    • Iodide is oxidized to iodine by thyroperoxidase (TPO) in the presence of hydrogen peroxide (H2O2)
    • Iodine binds to the 3' position in the tyrosyl ring, forming 3-monoiodotyrosine (MIT)
    • Another iodine binds to the 5' position of MIT, creating 3,5-diiodotyrosine (DIT)
    • T4 is formed by the condensation of two DIT molecules
    • T3 and reverse T3 (rT3) are formed by the condensation of DIT and MIT
    • These biosynthetic processes are controlled by the hypothalamic-pituitary-thyroid axis feedback mechanism

    Thyroid Hormone Drugs

    • Used as replacement therapy in thyroid gland deficiency
    • T3: L-3,3,5-triiodothyronine
    • T4: L-3,5,3,5-tetraiodothyronine (thyroxine)

    Thyroid Hormone Drug Structure-Activity Relationships

    • Contain two aromatic molecules (A & B) linked via a heteroatom (O or S)
    • Ring B contains an amino acid side chain with at least three carbons
    • Ring A must be perpendicular to ring B with a 120° angle
    • Ring B must be substituted at positions 3 and 5 with halogen (lipophilic group) (iodine is most active)
    • Ring A must be substituted at position 3 with halogen
    • T3 (3 iodines) is less active than T4 (4 iodines)
    • Ring A must contain phenolic OH for receptor binding

    Levothyroxine Sodium

    • Obtained from domesticated animal thyroid glands
    • Also prepared synthetically
    • Treats decreased thyroid function

    Liothyronine Sodium

    • Same uses as levothyroxine, including:
      • Hypothyroidism treatment
      • Male infertility
      • Certain gynecological disorders

    Anti-Thyroid Drugs

    • Used for hyperthyroidism (excess thyroid hormone production)
    • Preparation for surgery
    • Thiourea and related compounds are toxic
    • Useful drugs include 2-thiouracil derivatives and 2-thioimidazole derivatives
    • These drugs prevent iodine incorporation into thyroxine and triiodothyronine precursors

    α-Glucosidase Inhibitors

    • Acarbose inhibits the breakdown of complex saccharides in the intestine by α-glucosidase
    • Mimics sugar structure and binds to the enzyme with higher affinity than the natural substrate
    • Decreases monosaccharide absorption and postprandial blood glucose peaks
    • Useful for postprandial hyperglycemia
    • Avoid consuming glucose
    • Can cause colonic distress (diarrhea, flatulence, and cramping)

    Meglitinides

    • Similar mechanism of action to sulfonylureas, but without toxicities

    Incretins

    • Gastrointestinal hormones that increase insulin release from pancreatic beta cells after eating
    • Inhibit glucagon release from alpha cells

    Diuretics

    • Increase urine formation
    • Inhibit sodium reabsorption in the kidney
    • Acidosis occurs due to loss of bicarbonate (HCO3-)

    Heterocyclic Sulfonamides

    • Examples include acetazolamide (Diamox) and methazolamide (Neptazane)

    Diuretic Structure-Activity Relationships

    • Acetazolamide is the prototype
    • Higher lipid/water partition coefficient and lower pKa lead to greater carbonic anhydrase inhibition and diuretic activity
    • Sulfamoyl group is essential for activity
    • Sulfamoyl nitrogen must remain unsubstituted
    • Methyl substitution on one of the ring nitrogens increases potency
    • Sulfamoyl group must be attached to an aromatic moiety

    Ethacrynic Acid Synthesis

    • Involves a series of reactions including Friedel-Crafts acylation and amination with methylamine

    Site 3 Diuretics: Thiazide and Thiazide-like Diuretics

    • Include chlorothiazide, hydrochlorothiazide (HCTZ), benzthiazide, cyclothiazide, indapamide, chlorthalidone, bendroflumethizide, metolazone, etc.

    Thiazide Structure-Activity Relationships

    • Position 2 tolerates small alkyl groups (e.g., CH3)
    • Position 3 is critical for potency and duration of action

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    Description

    This quiz covers essential details about Ezetimibe, a medication approved in 2002 for managing cholesterol levels, as well as thyroid hormones and their crucial functions in metabolism. Explore how these hormones affect growth, energy consumption, and overall cardiovascular health. Additionally, understand the synthesis requirements for thyroid hormones.

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