Diuretics Pharmacology And Medicinal Chemistry PDF

Diuretics Pharmacology and Medicinal Chemistry This slide pack will cover mechanism of action of ALL medications in the Diuretics class. Some of them are used in Cardiovascular Disease, Some in Renal Disease, and some are used in other situations. PHP 327 will cover the therapeuti...

Diuretics Pharmacology and Medicinal Chemistry This slide pack will cover mechanism of action of ALL medications in the Diuretics class. Some of them are used in Cardiovascular Disease, Some in Renal Disease, and some are used in other situations. PHP 327 will cover the therapeutic use of the medications in the diseases covered this semester. BPS 337 Dr. Roberta King University of Rhode Island 1  Learning Objectives (for this slide pack) Learn to distinguish terms: filtration, reabsorption, excretion, secretion Understand the medicinal chemistry of the diuretics, including and pharmacology – Mechanism of action or target for each class of diuretics (which transporters do they affect? How?) – Effect of diuretic drug at each site, modifying normal flow – Where (site) in the nephron each diuretic class works, defined by transporters present at each site – Recognize the important structural features of each class of diuretics, including the pharmacophore features and structure-function information presented in class and in course packet. – Learn structural bases for similarities and differences amongst the several marketed diuretics within each class. Differentiate the difference between efficacy and potency as regards to2 diuretics  A few words about diuretics… These drugs act directly in/on the kidneys to increase urine output. (But they also have wider effects in other organs.) “Diuresis” is increased urine volume (output of pure water from the kidney) – pronounced DYE-you-ree-sis “Natriuresis” is increased sodium ion output from the kidney – NAY-tree-you-ree-sis Both are closely related, and the terms are often used interchangeably, but they are not exactly the same – (volume vs sodium output). 3  Diuretic sub-class names Know these terms! Loop (high-ceiling) – Site of action (loop of Henle in kidney), level of efficacy (high) Thiazide (includes thiazide-like) – Chemical class, based on structure Potassium-sparing – Physiological effect (excrete Na+, not K+) Sodium channel Inhibitors—molecular target (ion channel) – Epithelial Na+ Channel Inhibitors (ENaC) Aldosterone antagonists—molecular target (transcription factor) Osmotic - Physical-chemical characteristic (no molecular target) Vasopressin (ADH) receptor antagonists - molecular target Carbonic anhydrase inhibitors (historical, not used anymore as diuretics, discovered in 1937) - Molecular target (enzyme) Adenosine A1-receptor antagonists—a GPCR molecular target – 4 Somewhat effective as diuretic, natriuretic, but only at relative high doses (600 mg caffeine) – Theophylline, caffeine  Will need to know generic Diuretics by Drug Class drug names in each class Aldosterone Antagonists act in the nephron of the kidneys, (includes thiazide-like) but are in RAAS note system drugs, Eplerenone Sodium channel inhibitors Vasopressin is Also called ADH, AntiDiuretic Hormone Adenosine Adenosine receptor Antagonists antagonists Very weak Not used in cardiovascular diuretics disease any longer Theophylline caffeine 5  Reminder of kidney anatomy Know these terms: Cortex, Medulla, Nephron Names and locations of all portions of nephron The remaining slides Connecting tubule zoom in on the nephron, the cell layer Thick ascending limb forming the wall of the tubule, Thin descending limb the receptors in those cells, and the drug molecules 6 Merck Manual  Nephron The functional unit of the kidney, in which waste products are filtered from the blood and urine is produced. Each component of the nephron… (glomerulus, proximal convoluted tubule, loop of Henle, distal convoluted tubule, collecting duct) contain different molecular targets for the different classes of diuretic agents. The action of the different classes is controlled by the target and its location within the nephron. – Includes which ions affected, total efficacy Within each class of diuretics, structural differences cause variation in potency, onset of action, and duration of action (pharmacodynamics and pharmacokinetics). 7 Preview – Simple diagram of nephron and where some diuretics work The formation of urine involves four basic processes: 1. Filtration of plasma in the glomerulus 2. Reabsorption of water and solutes from the filtrate 3. Secretion of selected solutes into the tubular fluid 4. The fluid that remains flows into the Calix to be collected in the bladder and excreted as urine. 8  Preview: All types of Diuretics and location of action Na+ 8 Aquaporin 1 Carbonic anhydrase inhibitors Via Aquaporins NaKCl Transport inhibitors Aquaporin 2, 3 NaCl Transport inhibitors Aquaporin 1 Arrows indicate normal flow. Vasopressin antagonists antagonists Drug blocks this normal flow! 9 8 Epithelial Na Channel Katzung, Diuretics Chapter  Targets (receptors) of Diuretic drugs, Where does each fit in the classification? Enzyme, lyase TF GPCRs Today’s lecture will focus on the Ion Channels, Transporters, GPCR, and Transcription Factor (TF) targets for the Diuretic class of medications 10  Animated movie: Diuretic action in the kidney Designed by Dr. King and URI student, Steven Barbara – 9 minutes – Part 1: nephron flow—filtration, excretion, reabsorption – Part 2: loop diuretics—molecular action, sequence – Part 3: thiazide diuretics—molecular action, sequence – Part 4: sodium channel inhibitors—molecular action, sequence Watch on the “Big Screen” in class, review outside of class http://www.youtube.com/watch?v=6Wc4f2KnbYo Or Search: URIanimation, Diuretic Action in the Kidney 11 Have the sound ON  Sites of Na+ reabsorption within the nephron Efferent Arteriole Afferent Arteriole Juxtaglomerular cells Peritubular capillary Note terms: Note terms: proximal, distal, convoluted, Loop of Henle Filtration, ascending, descending, loop, Reabsorption, connecting, collecting, Secretion. 12 juxtaglomerular, afferent, efferent Excretion.  Watch the beginning of the movie Part 1 (0-3:50): nephron flow—filtration, excretion, reabsorption Pause movie at 3:49, just before part 2. Show slides 14-15 to explain terms, then continue through Part 2 (3:50-6:00): loop diuretics—molecular action, sequence Then return to slides http://www.youtube.com/watch?v=6Wc4f2KnbYo Or Search: URIanimation, Diuretic Action in the Kidney 13 Have the sound ON  Loop diuretics Bind to and inhibit the Na+/K+/2Cl- co- transporter (NKCC2) This transporter is mainly located on the luminal membrane of the thick ascending limb of the loop of Henle See movie for sequence of movements in… – Absence of loop diuretic 3:50-5:25, stop. show slides 15-16, 17 Loop of Henle – Presence of loop diuretic 5:25-6:00, stop, show slides 17, 18-21 14 Transporters present in the thick ascending limb loop of Henle Luminal membrane Anti-luminal membrane Na+ / K+ / 2Cl- co-transporter Secondary active transport, Secondary active transport, dependent on gradient of Cl- established by Na/K/ATPase and NKCC2 dependent on gradient of Na+ Which was established by Na/K/ATPase Chloride channel Periubular capillary Potassium channel Secondary active transport, dependent on gradient of K+ 3 Na+ / 2 K+ ATPase Which was established by Na/K/ATPase Can drive up concentration gradient. ACTIVE Paracellular junction transport See movie for sequence (note terms: luminal & anti-luminal membrane, paracellular junction) 15  Result of normal action in thick ascending limb + 3K+ Periubular capillary 3K+ + See movie for sequence and transporters responsible 16 Result in presence of loop diuretic in thick ascending limb No transport through blocked Na+ / K+ / 2Cl- co-transporter Periubular capillary See movie for sequence 17  Loop diuretics Be able to understand why… Cause increased renal loss of Na+, Cl-, and K+ (and Ca2+, Mg2+). Therefore, potential adverse effect is hypo each ion NOTE: Hypokalemia side effect of loop diuretics is caused by two processes. 1. Less reabsorption of K+ right in the loop. 2. increased delivery of Na+ to the distal tubule which causes activation of RAAS (Goodman & Gillman). Four agents in use (furosemide, bumetanide, torsemide, ethacrynic acid): – All Quick onset of action (about 30 min) – All Relatively short duration of action (about 5-8 hr). – All Highly bioavailable (about 80-100%) – All loops: 8-10 times greater diuretic efficacy than thiazides – All Loop diuretics have approximately equal (and relatively high) diuresis efficacy! 18 Lecture question: What is measured to determine diuretic efficacy? Water to urine  Sulfonamide-based Loop Diuretics Prior to 2022, it was thought that the sulfonamide and sulfonylurea functional groups of bumetanide and furosemide most important for binding to the receptor. However, in 2022 the new cryo-electron micrograph (cryo-EM) structure showed that the carboxyl group is most important and binds where the K+ would bind! 19 , 2022  Sulfonamide-based Loop Diuretics Furosemide (Lasix) (fyoor OH se mide): Oral or injected. Has free carboxylic acid group. Side effect: systemic acidosis caused by off-target carbonic anhydrase inhibition in proximal tubule which increases bicarbonate excretion. (1966) Bumetanide (Bumex) (byoo MET a nide): Oral or injected. Has free carboxylic acid group. 40-fold more potent diuretic than furosemide. Also has off-target carbonic anhydrase inhibition and systemic acidosis side effect. (1983) Torsemide (Demadex) (TORE se mide): Oral only. Sulfonamide replaced by sulfonylurea. Does not increase phosphate or bicarbonate excretion because does not act on carbonic anhydrase (no systemic acidosis side effect). 2-3- fold more potent diuretic than furosemide. (1993) All Loop diuretics have approximately equal (and relatively high) efficacy! 20  NEW: Structure Biology of Na-K-2Cl transporter Ion path (Na+, K+, 2 Cl-) Extracellular The helices “twist” to open the channel Cell Furosemide binds mem- directly inside the brane channel Purple (K+) and green (Cl-) spheres are ions trapped in the channel Intracellular 21 , 2022 Details of Bumetanide binding The carboxylate (COO) binds with K+ and the backbone Nitrogen of a methionine residue Lipophilic interactions for the aromatic ring and butyl chain. 22  Another Loop Diuretic: Non-sulfonamide Ethacrynic acid (Edecrin) (eth a KRIN ik AS id): (1967) – not structurally related to others: phenoxyacetic acid derivative. – Has free carboxylic acid group. Oral or injected. 23 , 2022  Diuretics—potency vs. efficacy Efficacy: maximal ability of the drug (at tolerated dose) to cause increased Diuresis and Natriuresis (increase excretion of water and sodium caused by decreased reabsorption of Na+). Compare diuretic efficacy of agents between classes. – eg., loop diuretics are more efficacious than Na+ channel blockers. Potency: dose amount (mg, mmol) of the drug required to produce a specified diuretic response (water loss). Compare potency of agents within each class. – bumetanide is most potent followed by torsemide then furosemide (compare loops diuretics to each other) – hydrochlorothiazide is more potent than chlorothiazide (thiazide class) These are the pharmacology definitions. Clinical use of these terms do not always follow these definitions (warning) 24  Thiazide diuretics (includes sub-classes of thiazide-like and hydrothiazide) Inhibit Na+/Cl- co- transporter (NCC) This transporter is located on luminal membrane of the distal convoluted tubule Compete for Cl- binding site See movie for sequence of movements in… – Absence of loop diuretic 6:00-6:46 – Presence of loop diuretic Loop of Henle 6:46-7:04 25  Restart the movie – Part 3: thiazide diuretics—molecular action, sequence Absence of loop diuretic 6:00-6:46 Presence of loop diuretic 6:46-7:04 – Then return to slides. 26  Transporters present in distal convoluted tubule Na+ / Cl - co-transporter Chloride channel Periubular capillary 3 Na+ / 2 K+ ATPase Potassium channel Luminal membrane Anti-luminal membrane See movie for sequence Note: channels and NCC, move ions “down the concentration gradient”; no energy input needed. 27 ATPase hydrolyzes ATP to give energy to drive against gradient  Result of normal action in distal convoluted tubule Na+ / Cl- co-transporter Chloride channel, 3 Cl- Periubular capillary 3 Na+ / 2 K+ ATPase Potassium channel Water to follow isotonicity See movie for sequence and transporters responsible 28  Result in presence of thiazide diuretic in distal convoluted tubule No transport through blocked Na+/Cl- co-transporter X Periubular capillary 3Na+ 3Cl- X Water to follow isotonicity water See movie for sequence 29 NOTE: Hypokalemia side effect of thiazide diuretics is not explainable directly. Rather, hypokalemia is explained by increased delivery of Na+ to the distal tubule, and activation of RAAS (Goodman & Gillman) Thiazide (and hydrothiazide, thiazide-like) diuretics Named for their chemical class (all contain a thiazide). – All 3 types included in more general term “thiazides” Bind at the chloride binding site of the Na+/Cl- co-transporter on luminal membrane of the early distal convoluted tubule. Cause increased renal loss of Na+, Cl–, and water. – Also Decrease Ca2+, uric acid excretion – Increase bicarbonate excretion Intermediate efficacy (1-2 L/24 hr) between loop (4 L/24 hr) and potassium-sparing diuretics. 30  Pharmacophore Structural features affecting activity of thiazide and thiazide-like diuretics Hydrochlorothiazide Chlorothiazide Chlorthalidone (1959) Methylclothiazide Indapamide Metolazone Color coded: Note portion of structure that Brown: Hydrothiazides are more potent than thiazides makes them hydrothiazides! Green: Sulfonamide group at position 7 is required for diuretic activity Blue: electron-withdrawing group essential for diuretic activity, usually a Chloro- Black: The thiazide-like diuretics replace the ring-sulfamoyl group with other electronegative group 31  Structure of Na, Cl transporter published 2023 Very similar to the Na-K-2Cl transporter structure, but K+ does not bind because amino acid change. The chloro group of hydrochlorothiazide overlaps with the proposed Cl−-binding site of the NCC (Extended Data Fig. 7b), corroborating reports that thiazide diuretics compete with Cl− for binding42,43,44. 32  Na+ channel (ENaC) inhibitors (Potassium-sparing) Bind to and inhibit distal tubule and sodium channels collecting duct On the luminal membrane of distal tubule and collecting duct Physically blocks the luminal opening of the Na+ channel. See movie for sequence of movements in… – Absence of loop diuretic – Presence of loop diuretic Loop of Henle Restart the movie Part 3: Na+ channel diuretics—molecular action, sequence 33 Then return to slides. Transporters present in distal tubule and collecting ducts distal tubule and collecting duct Potassium channel Periubular capillary 3 Na+ / 2 K+ ATPase Sodium channel 34  Result of normal action in collecting tubules Potassium channel Periubular capillary 3 Na+ / 2 K+ ATPase Sodium channel See movie for sequence, calculate the overall result Under “normal” conditions, potassium is secreted. Under high Na+ delivery to collecting tubules, even more K+ is secreted35 than “normal”, results in hypo-kalemia side effect of thiazides and loops. Result in presence of sodium channel inhibitors in collecting tubules Potassium channel Periubular capillary 3 Na+ / 2 K+ ATPase Sodium channel See movie for sequence, calculate the overall result (Whole sequence is blocked: no sodium reabsorbed, no potassium secreted, even under “high Na+” conditions) 36  Epithelial Na+ channel (ENaC) inhibitors (Potassium-sparing) triamterene, amiloride Block reabsorption of sodium (resulting in excretion of sodium) Block secretion of potassium (resulting in retention of potassium) Net result is increased sodium excretion and almost no potassium secretion. Side effect of all Na+ channel inhibitor diuretics: hyperkalemia, increased retention of potassium. Offered in combination with hydrochlorothiazide to balance the potassium effects. 37  Na+ channel inhibitors (Potassium-sparing) Triamterene 1964 (Dyrenium): – quick onset of action (30 min), – duration of action greater than 24 hours(!) because some metabolites are active. Amiloride 1967 (Midamor): – open-chain analogue of triamterene, – Long duration of action 10-24 hours. – Approximately 50% of amiloride is excreted unchanged in urine (not metabolized), thus renal impairment could increase its half-life. Both positively charged at physiologic pH. Bind to Na+ binding site on the Na channel 38  2018: Structure Biology of ENaC Ion path (Na+) This Na+ channel is opened/closed by small proteins binding to the extracellular portion (bright red in below image) Extracellular Cell mem- brane Not yet known where the drugs bind Intracellular 39 Noreng S, et al, Structure of the human epithelial sodium channel by cryo-electron microscopy. Elife. 2018 Sep 25;7:e39340. doi: 10.7554/eLife.39340.  Review: Common features of ALL Na+ transport inhibitors All inhibit transporters located on the luminal membrane of nephron tubule (renal) – Na+/K+/2Cl– in loop of Henle (loop diuretics) – Na+/Cl– in distal convoluted tubule (thiazide diuretics) – Na+ channel in collecting duct, connecting tubule (Na+ channel inhibitors) Transport at all three sites initiated and driven by active transport through 3Na+/2K+-ATPase – Different replenishing mechanism at each site is blocked All directly cause decreased reabsorption of sodium – Indirect actions include decreased reabsorption of water – Indirect effects on other ions 40  Cause of different efficacies of diuretics The most efficacious diuretics (4 L/24 hr) (high ceiling/loop) act at the ascending loop of Henle. Loop of Henle Diuretics that act at the most distal sites (Na+ channel blockers, aldosterone antagonists) are least efficacious (weak diuretics) because most of the sodium/water has already been reabsorbed before reaching these sites. Diuretics that act at the early distal tubule (thiazide and thiazide-like) have intermediate efficacy (1-2 L/24 hr). Diuretics that act primarily on the proximal tubule are VERY weak diuretics because the sodium/water is simply left to be reabsorbed in the loop (carbonic anhydrase inhibitors, not used anymore). 41  Other types of diuretics Vasopressin receptor antagonists – Tolvaptan – Conivaptan See next few slides for Osmotic diuretics mechanism and structures – Mannitol – Etc Aldosterone antagonists Moved to RAAS module – Spironolactone – Eplerenone Adenosine antagonists (not cover) 42  Osmotic diuretics Examples: Mannitol, glycerin, isosorbide (bicyclic form of sorbitol), urea Effect: Inhibit water reabsorption and maintain urine flow (promote diuresis, natriuresis). No molecular target, act simply by osmosis. – Low molecular-weight compounds that are freely filtered in the glomerulus. Not reabsorbed because high water solubility. – But the osmotic water movement is through aquaporin channels Mannitol and urea are not orally effective (80% absorbed). 43  Osmotic diuretics, example of mechanism Osmosis: water moving from high concentration of water (low concentration of solutes) to low concentration of water. Mannitol is administered iv as hypertonic solution (higher than normal solute plasma concentration). To balance the high concentration, water moves into the capillaries (osmosis) and blood volume increases. The blood flows through the kidney, and mannitol is nearly completely filtered by the glomerulus, resulting in high mannitol concentration in the filtrate (lower water concentration in filtrate). Lower water concentration in the filtrate means less water is reabsorbed via osmosis). Results in less sodium reabsorbed and elevated urinary flow rate (natriuresis and diuresis). Occurs at nephron sites indicated on next slide, where normally water can freely reabsorb (via aquaporin channels). The osmosis occurs through “water channels” which are called aquaporins. These aquaporins are present in the portions of nephron noted in next slide. Thus, osmotic diuretics act at these sites. 44  Three Locations of osmotic diuretic action Na+ 8 Aquaporin 1 Carbonic anhydrase inhibitors Via Aquaporins NaKCl Transport inhibitors Aquaporin 2, 3 NaCl Transport inhibitors Aquaporin 1 Vasopressin antagonists Arrows indicate normal flow. antagonists 45 flow! Drug blocks this normal 8 Epithelial Na Channel Katzung, Diuretics Chapter  Anti Diuretic Hormone (ADH) what does it do? Antidiuretic hormone, ADH – Also called vasopressin – Also called arginine vasopressin (AVP) – A nine amino acid peptide – Agonist for the V2-vasopressin receptor in the collecting duct of the nephron in kidney – The agonist (ADH) is Anti-diuretic (water retaining). Arrows indicate normal flow. Drug blocks this normal flow  Vasopressin receptor antagonists tolvaptan conivaptan Vasopressin, also called antidiuretic hormone, ADH In the kidneys, V2-receptor antagonists are a natriuretic and weak diuretic VR antagonists used for the treatment of hyponatremia – Tolvaptan (tol-VAP-tan, 2009) – Conivaptan (KOE-ni-VAP-tan, 2004) Arrows indicate normal flow. Drug blocks this normal flow  Mechanism of action Vasopressin (ADH) receptors are GPCRs, two kinds V2, V2 V2 receptors are present in the kidneys. Activation (agonist) increases reabsorption of water by the kidneys (at V2, Gs mechanism). This is why it is called ADH, Anti-Diuretic Hormone – Antagonism of the V2 receptor in kidney by tolvaptan & conivaptan promotes the excretion of free water (without loss of serum electrolytes, Na+) resulting in net fluid loss, increased urine output, decreased urine osmolality, and subsequent restoration of normal serum sodium levels. Vasopressin antagonists are used to treat hypo-natremia particularly in congestive heart failure patients. V1 receptors are in the vascular smooth muscle (V1=V1a, V3=V1b) – Activation (agonist) causes vasoconstriction (at V1, Gq mechanism) This is why it is called vasopressin V1 antagonists cause vasodilation 48 Vasopressin V2 receptor Cryo-EM structure of the AVP–vasopressin receptor 2–Gs signaling complex Cell Research volume 31, pages932–934 (2021) Extracellular Cell membrane Intracellular 49  CVR Uses of Diuretics Covered in PHP 327 50  Diuretics also used for other diseases Altitude sickness (Diamox, acetazolamide, carbonic anhydrase inhib) Glaucoma (acetazolamide, mannitol) Fast weight (fluid) loss – Edema (furosemide) Raised intracranial pressure – (mannitol) Liver disease, ascites in cirrhosis – (spironolactone, furosemide) 51  Review: All types of Diuretics and location of action Na+ 8 Aquaporin 1 Carbonic anhydrase inhibitors Via Aquaporins NaKCl Transport inhibitors Aquaporin 2, 3 NaCl Transport inhibitors Aquaporin 1 Arrows indicate normal flow. Vasopressin antagonists antagonists Drug blocks this normal flow! 52 8 Epithelial Na Channel Katzung, Diuretics Chapter  Learning Objectives–did we meet them? Learn to distinguish terms: filtration, reabsorption, excretion, secretion Understand the medicinal chemistry of the diuretics, including and pharmacology – Mechanism of action or target for each class of diuretics (which transporters do they affect? How?) – Effect of diuretic drug at each site, modifying normal flow – Where (site) in the nephron each diuretic class works, defined by transporters present at each site – Recognize the important structural features of each class of diuretics, including the pharmacophore features and structure-function information presented in class and in course packet. – Learn structural bases for similarities and differences amongst the several marketed diuretics within each class. Differentiate the difference between efficacy and potency as regards to diuretics 53