Cardiac Glycosides PharmD 200 (Nov. 2024) PDF

CARDIAC GLYCOSIDES BY PHARM. EVANS PAUL KWAME AMEADE DEPT. OF PHARMACOGNOSY AND HERBAL MEDICINE SCHOOL OF PHARMACY AND PHARMACEUTICAL SCIENCES UNIVERSITY FOR DEVELOPMENT STUDIES PHARM.D, LEVEL 300 NOVEMBER, 2024  Outli...

CARDIAC GLYCOSIDES BY PHARM. EVANS PAUL KWAME AMEADE DEPT. OF PHARMACOGNOSY AND HERBAL MEDICINE SCHOOL OF PHARMACY AND PHARMACEUTICAL SCIENCES UNIVERSITY FOR DEVELOPMENT STUDIES PHARM.D, LEVEL 300 NOVEMBER, 2024  Outline What are cardiac glycosides Sources of cardiac glycosides Structure of cardiac glycosides Biogenesis of cardiac glycosides Plant drug containing cardiac glycosides Test for cardiac glycosides What are cardiac glycosides They are naturally occurring secondary metabolites which in appropriate small quantities has beneficial effect on the heart but can become toxic in high concentration. Plants containing cardiac steroids have been used as poisons and as cardiotonic agents which are widely used in the modern treatment of congestive heart failure and for treatment of atrial fibrillation and flutter Congestive heart failure Heart diseases can be primarily grouped into three major disorders: cardiac failure, ischemia and cardiac arrhythmia. Cardiac failure can be described as the inability of the heart to pump blood effectively at a rate that meets the needs of the body because the muscles of the heart especially the ventricles which are to contract to force blood out of the heart are performing weakly. Reduced contraction of heart leads to reduced heart output but new blood keeps coming in resulting in the increase in heart blood volume. The heart feels congested. Hence the term congestive heart failure (CHF). CHF leads to lowered blood pressure and poor renal blood flow which results in oedema in the lower extremities and the lung (pulmonary oedema). Renal failure ultimately occurs in unmanaged CHF. Sources of cardiac glycosides Cardiac glycosides occurs in several parts of the plants including the seeds, leaves, stems, roots or barks. More than 400 naturally occurring cardiac glycosides have been identified The also occur in only some genera in plant families such as Apocynaceae (Apocynum, Nerium, Strophantus, Thevetia) Scrophularaceae (Digitalis) Liliaceae (Convallaria, Urginea) Ranunculaceae (Adonis, Helleborus) Crassulaceae (Cotyledon, Kalanchoe) Brassicaceae (Erysimum) Celastraceae (Euonymus) Asclepiadaceae (Asclepias, Calotropis, Cryptostegia, Periploca, Xysmalobium)  Notable plants that are known to produce cardiac glycosides are Common oleander (Nerium oleander) Yellow oleander (Thevetia peruviana) Purple Foxglove (Digitalis purpurea) Lily of the valley (Convallaria majalis) Kalanchoe (Bryophyllum spp.) Azalea (Rhododendron spp.) Woolly foxglove (Digitalis lanata) Ouabain (Strophanthus gratus) Squill bulb (Drimia maritima [syn. Urginea maritima]) Kombe arrow poison (Strophanthus kombe) Common oleander Yellow oleander Lily of the valley Kalanchoe Azalea Structure and types of cardiac glycosides The basic structure of cardiac glycosides is composed of a sterol nucleus an unsaturated conjugated lactone ring attached to the C17 position, a hydroxyl group at the C3 position of the nucleus with a sugar. The basic structure of the steroidal part is cyclopentano perhydrorphenanthrene nucleus, to which a lactone ring is attached  Other important features in the structure include 14 β – OH group at C – 14 The four rings of the steroidal nucleus are fused differently B/C ring is trans, C/D ring and A/B ring are mostly cis Such ring fusion gives the aglycone nucleus of cardiac glycosides the characteristic 'U' shape U-shape of the aglycone molecule of cardiac glycoside  Additional OH groups at C-5, C – 11 and C – 16 may be present Depending on the type of unsaturated lactone ring attached to the C17 position of the cardiac glycoside, they are classified into two types type A (a five-membered unsaturated lactone ring) type B (a six-membered unsaturated lactone ring). The type A (a five-membered unsaturated lactone ring) is called the Cardenolide The type B (a six-membered unsaturated lactone ring) is referred to as Bufadienolide  Plants and animals such as toads (Bufonidae) and some insects can produce both cardenolides and bufadienolides.  Examples of Cardenolide Digitalis glycosides Digoxin Digitoxin Gitoxin Strophanthus gratus glycoside Ouabain Strophanthus Kombe glycoside : K- strophanthin Although best studied in leaves, cardenolides can occur in all plant tissues. The latex seem to have the highest concentration of cardenolides in some plant species. Digoxin Gitoxin Digitoxin Ouabain K- strophanthin  Example of bufadienolide: Squill bulb glycoside Scillaren Venenum bufonis bufalin, cinobufagin, and resibufogenin  One to 4 sugars are found to be present in most cardiac glycosides attached to the 3 β-OH group. The glycone portions determine the pharmacodynamic and pharmacokinetic activities of each cardiac glycoside but possess no biological activity The commonly found sugars include Glucose, Galactose, Mannose, Rhamnose, Digitalose, Digitoxose, Digginose, Vallarose, Fructose The most common monosaccharides found in cardiac glycosides are however glucose, rhamnose and 6-deoxy monosaccharides Whenever glucose is part of the glycone, it is always at the terminal end Glucose at the terminal position of the glycone unit  The names of the aglycone are derived from the name of the cardiac glycosides which are commonly named after the plant from which they occur. The term 'genin' at the end refers to only the aglycone portion of a cardiac glycoside (there are exceptions) From the Digitalis purpurea comes the cardiac glycoside ‘Digitoxin’ which has the aglycone ‘Digitoxigenin” and three sugar moieties forming the glycone. Other aglycone molecules include digoxigenin, gitoxigenin, strophanthidin and bufalin.  The "backbone" U shape of the steroid nucleus appears to be very important since sugar molecules and lactone alone do not have any activity. The lactone ring even if joined to the steroid molecule is not absolutely required since its replacement with unsaturated nitrile (C=C-CN group) found the cardiac glycoside to have little or no loss in biological activity. Structures with C/D trans fusion are inactive whilst conversion of A/B from cis to trans system leads to a marked drop in activity. The C14 -OH groups is dispensable since a skeleton without C14 -OH group but with C/D cis rings fusion remained active.  Although lactone alone is inactive, the unsaturated 17-lactone plays an important role in receptor binding since saturation of the lactone ring dramatically reduced the biological activity. More lipophilic Cardiac glycosides are absorbed faster and exhibit longer duration of action as a result of slower urinary excretion rate. Lipophilicity is strongly influenced by the number of sugar residues and the number of hydroxyl groups on the aglycone part of the glycoside. For example, digitoxin and digoxin structures differ only by an extra OH group in digoxin at C-12, yet their partition coefficients differ by as much as 15 % General characteristics of Cardiac glycoside Colourless or white crystals (rarely amorphous) Solubility is determined by the number of sugar moieties; aglycones – soluble in organic solvents, insoluble in water; but glycosides – soluble in water and slightly soluble in ethanol and chloroform Optically active compounds Undergo hydrolysis (acid, enzymatic and alkaline) Biogenesis of Cardiac glycosides Cardenolides are derived from mevalonic acid via phytosterol and pregnane intermediates The cholesterol is formed by the joining of 3,3- dimethylally pyrophosphate (DMAPP) or its isomer isopentenyl-pyrophosphate (IPP) produced in the mevalonate pathway Pregnenolone formed by a mitochondrial cytochrome P450-dependent side chain cleaving enzyme is modified through several steps to produce the genin.  Pregnenolone may be considered as the starting point for cardenolide formation regardless of the assumed sterol precursor The most common sequence of the individual biosynthetic steps leading to 5β-cardenolides is not yet clear and more than one pathway may be operative. Formation of the sterol from DMAPP and IPP  The aglycones (secondary cardenolides) are glucosylated by cytoplasmatic glucosyltransferases and actively transported into the vacuole by a primary glycosidetranslocase in Digitalis. In Digitalis, cardenolides can be interconverted between the cardiac glycoside (primary cardenolides) the form principally stored in the cell vacuoles and the aglycone form. Glucosidation could enhance the polarity of the cardenolide and therefore prevent its passive efflux out of the vacuole. Importance of cardiac glycosides to life These same compounds have been applied to poison arrows in human warfare They are used by plants to protect themselves against herbivory Some insects sequester cardiac glycosides for protection against their predators. Activity of cardiac glycoside Cardiac glycosides affect the heart both directly and indirectly in a series of complex actions, some of which oppose one another. The direct effect is to inhibit the membrane-bound sodium– potassium adenosine triphosphatase (Na +K+ATPase) enzyme that supplies energy for the system that pumps sodium out of and transports potassium into contracting and conducting cells. The indirect effect is to enhance vagal activity by complex peripheral and central mechanisms. The clinically important consequences are on: the contracting cells: increased contractility and excitability SA and AV nodes and conducting tissue: decreased impulse generation and propagation. Mechanisms of action of cardiac glycosides as drugs The most important use of the cardiac glycosides is its effects in treatment of cardiac failure. In cardiac failure, or congestive heart failure, heart cannot pump sufficient blood to maintain body needs. During each heart contraction, there is an influx of Na + and an outflow of K+. Before the next contraction, Na+K+ ATPase must reestablish the concentration gradient pumping Na + out of the cell against a concentration gradient. This process requires energy, which is obtained from hydrolysis of ATP to ADP by Na+ K+‐ATPase.  Cardiac glycosides inhibit Na+ K+‐ATPase, and consequently increase the force of myocardial contraction By inhibiting the Na+/K+ ATPase, cardiac glycosides cause intracellular sodium concentration to increase. This then leads to an accumulation of intracellular calcium via the Na+-Ca2+ exchange system. In the heart, increased intracellular calcium causes more calcium to be released by the sarcoplasmic reticulum, thereby making more calcium available to bind to troponin-C, which increases contractility (inotropy)  Cardiac glycosides also increase vagal efferent activity to the heart, reducing sinoatrial firing rate (causing bradycardia) and conduction velocity of electrical impulses through the atrioventricular (AV) node. Hence digoxin also used for the the treatment of supra-ventricular arrhythmias, particularly atrial fibrillation Plant drug containing Cardiac glycosides Some plants are known to contain cardiac glycosides of commercial value and they include: Digitalis - Digitalis purpurea leaves (foxglove), Digitalis lanata leaves - white flowers Strophanthus vine seeds Urginea bulbs (squill) Convallaria leaves (lily of the valley) Digitalis Digitalis is a genus of about 20 species of herbaceous, perennials, shrubs and biennials commonly called foxgloves Biological source It is obtained from dried leaves of Digitalis purpurea Digitalis lanata is another source of cardiac glycosides Chemical constituents Digitalis contain 0.2 to 0.45% of both primary glycosides. and secondary Digitalis purpurea contains Primary glycosides: Purpurea glycosides A glucogetaloxin and B, Secondary: digitoxin, gitoxin and getaloxin. Primary glycosides are less stable and less significant secondary glycosides. than Purpurea glycosides A and B constitute the principal active constituent of the fresh leaves. Digitalis lanata contains Digitoxin, gitoxin, digoxin. Lanatoside A, B, C, D & E Lanatoside is acetylated products of purpurea glycosides  Digitalis lanata Digitalis purpurea - Purple foxglove Strophanthus glycosides Strophanthus, which is of the Apocynaceae family, is a flowering plant that grows in tropical Africa, South Africa, southern India, the Philippines, Laos, Vietnam, and South China. The name Strophanthus is derived from the Greek strophos (a twisted cord or rope) and anthos (a flower). e.g. Strophanthus kombe, Strophanthus gratus  Strophantus gratus Strophantus kombe Chemical constituents A mixture of cardiac glycosides isolated from Strophantus kombe mainly contains K-strophanthin-β and K- strophanthozide. K-Strophanthin-β consists of the aglycone of strophanthidin and a sugar residue made up of cymarose- β-d-glucose. K-strophantozide has a sugar residue of three units: cymarose-β-d-glucoso-α-d-glucose. Use of the term strophanthin generally refers to all glucosides of this series Strophantus gratus contains the cardioactive glycoside (Ouabain) or G- strophanthin.  The seeds are the part of the plant used as arrow poison as it is extremely poisonous Indications: Atrial fibrillation, Atrial flutter, Cardiac arrhythmia, Left ventricular failure, Ventricular arrhythmia Squill Contain about 15 glycosides; 0.1% to 2.4% total bufadienolides It is the dry fleshy inner scales of the bulb of the white variety of Urginea maritima (synonymous to Drimia maritima ) (Fam. Liliaceae): Mediterranean squill. There is also the red squill which is also known as sea onion, is obtained in the powder form from a plant Urginea indica. : Indian squill. The dried powders of red squill have been used for the control of rodents since the 13th century. Although red squill has many alkaloids, scilliroside is the most toxic and provides rodenticidal activity. White squill (Drimia maritima) Chemical constituents White variety: average 0.2%-0.4% proscillaridin A scillaren A glucoscillaren A (aglycone: scillarenin), scilliphaeoside Scilliglaucoside Red variety: < 0.1% scilliroside and glucoscilliroside (aglycone: scillirosidin); proscillaridin A scillaren A Uses Squill glycosides have similar action to digitalis glycosides, but they have a, more rapid action (rapid onset of action), but less used. diuretic action and expectorant. The red bulb is used as rat poison and not as cardiac glycoside. It kills rats only and not other animals. Red squill is 100-500 times more toxic to rats than is the white variety Chemical tests for cardiac glycosides: Raymond’s test: To the drug, add a few ml of 50% ethanol and 0.1 ml of 1 % solution of m- dinitrobenzene in ethanol. To this solution, add 2-3 drops of 20% sodium hydroxide solution. Violet colors appears, this is due to presence of active methylene group. Legal test: To the drug, add few ml of pyridine and 2drops of nitroprusside and a drop of 20% sodium hydroxide solution. A deep red colour is produced. Keller killiani test: Glycoside is dissolved in a mixture of 1 % ferric sulphate solution in (5%) glacial acetic acid. Add one or two drop of concentrated sulphuric acid. A blue colour develops due to the presence of deoxy sugar. Xanthydrol test: The crude is heated with 0.1 to 5% solution of Xanthydrol in glacial acetic acid containing 1% hydrochloric acid. A red colour is produced due to the presence of 2-deoxysugar. Baljet test: Take a piece of lamina or thick section of the leaf and add sodium picrate reagent. If glycoside is present yellow to orange colour will be seen.  Kedde test: A solution of glycosides is treated with a small amount of Kedde reagent (Mix equal volumes of a 2% solution of 3, 5 dinitrobenzoic acid in menthol and a 7.5% aqueous solution of KOH). Development of a blue or violet colour that faded out in l to 2 hrs shows it presence of cardenolides. Antimony trichloride test: To a solution of glycoside add a solution of antimony tri-chloride and tri-chloroacetic acid, and then heat the mixture. Appearance of blue or violet colour show presence of cardenolides and bufanolides References https://www.sciencedirect.com/topics/neuroscience/card iac-glycosides http://www.yourarticlelibrary.com/pharmacognosy/photo chemical-screening/cardiac-glycosides-types-chemical-t est-and-other-details/49451 https://www.sciencedirect.com/topics/neuroscience/deox y-sugars https://www.sciencedirect.com/topics/biochemistry-gene tics-and-molecular-biology/bufadienolide http://www.people.vcu.edu/~urdesai/car.htm Kreis, W., Hensel, A., & Stuhlemmer, U. (1998). Cardenolide Biosynthesis in Foxglove1. Planta Medica, 64(06), 491-499. THANKS FOR YOUR ATTENTION