9. Ecosonoids_MBBS Lecture Series.pptx

Pharmacology of Eicosanoids:Role in health, disease & Therapeutics Dr Bassi PU NBBS Lecture Series  CASE STUDY A 40-year-old woman presented to her to the clinic with a 6-month history of increasing shortness of breath. This was associated with poor a...

Pharmacology of Eicosanoids:Role in health, disease & Therapeutics Dr Bassi PU NBBS Lecture Series  CASE STUDY A 40-year-old woman presented to her to the clinic with a 6-month history of increasing shortness of breath. This was associated with poor appetite and ankle swelling. On physical examination, she had elevated JVP distention, a soft tricuspid regurgitation murmur, clear lungs, and mild peripheral edema. An echo revealed tricuspid regurgitation, severely elevated pulmonary pressures, and RV enlargement. Cardiac catheterization confirmed the severely elevated pulmonary pressures. She was commenced therapies. Which of the eicosanoid agonists have been demonstrated to reduce both morbidity and mortality in patients with such a diagnosis? What are the modes of action?  Eicosanoids: Definitions The eicosanoids are an important group of endogenous fatty acid autacoids that are produced from arachidonic acid, a 20- carbon fatty acid (Plasma Phospholipids) in cell membranes Prostaglandins and related compounds are collectively known as eicosanoids. Mostly produced from arachidonic acid, a 20-carbon polyunsaturated fatty acid (5,8,11,14-eicosatetraenoic acid). Short half-lives (10 secs – 5 mins) so that functions are usually limited to actions on nearby cells. Bind to specific cell surface G-protein coupled receptors, and generally increase cAMP levels.  What are Eicosanoids Major families of eicosanoids include the straight-chain derivatives (leukotrienes) and cyclic derivatives (prostacyclin, prostaglandins, and thromboxane). 1.The prostaglandins 2.Thromboxanes 3.Leukotrienes 4.The epoxyeicosatrienoic acids.(hydroperoxyeicosatetraenoic acids (HPETEs) ) They have various roles in inflammation, fever, regulation of blood pressure, blood clotting, immune system modulation, control of reproductive processes and tissue growth, and regulation of the sleep/wake cycle. BIOSYNTHESIS OF EICOSANOIDS  Main sites of eicosanoid biosynthesis Endothelial cells Leukocytes Platelets Kidney Unlike histamine, eicosanoids are NOT synthesized in advance and stored in granules – when needed, they can be produced very quickly from arachidonate released from membranes  Eicosanoid biosynthesis  Arachidonic acids is the precursor of Eicosanoids  In most tissues, arachidonic acids is esterfied in phospholipid pool.  The Principal ecosonoids if Prostaglandis, the thromboxanes and the leucotrines.  other derivatives of arachidonic acids, Lipoxins are also produced.  The term Protanoids is used to encompass Prostaglandins and Thromboxane. 1. The prostaglandin H synthase (COX, cyclooxygenase) pathway produces: A. thromboxane B. the primary prostaglandins  i. prostaglandin E, or PGE  ii.prostaglandin F, or PGF  iii.prostaglandin D, or PGD) C. prostacyclin (PGI 2 ) 2. The lipoxygenase pathway produces:  iv. HPETEs  v.HETEs  vi. leukotrienes  Main steps of Eicosanoid Biosynthesis 1) Activation of phospholipase A2 (PLA2) The rate limiting step in ecosonoids synthesis is the liberation of arachidonic acids, either in one step process or two step process as seen in diaggrams next slides, from phospholipids by phospholipase A2.. – PLA2 -mediated production from membrane phospholipids; this pathway is inhibited by Glucocorticoids. 2) Release of arachidonate from membrane phospholipids by PLA 2 – Arachidonic acid, the most common precursor of the eicosanoids, is formed by two pathways: The prostaglandin H synthase (COX, cyclooxygenase) and Throboxane (Lipooxygenase) pathways the primary prostaglandins  i. prostaglandin E, or PGE  ii. prostaglandin F, or PGF  iii. prostaglandin D, or PGD) The lipoxygenase pathway produces:  i. HPETEs  ii. HETEs   Arachidonate release for eicosanoid synthesis From membrane phospholipids – mainly by the action of phospholipase A2: Arachidonate release from phospholipids can be blocked by the anti- inflammatory steroids!  Eicosanoid Biosynthesis In almost all cell types (except for red blood cells) 3 pathways: – A) cyclooxygenase (COX) – produces prostaglandins and thromboxanes – B) lipoxygenase (LO) – produces leukotrienes, lipoxins, 12- and 15-HETEs, and hepoxilins – C) cytochrome P450s (monooxygenases) – produce the other HETEs (20-HETE); principal pathway in the proximal tubules Eicosanoid Biosynthesis  The Cyclooxygenase Pathway: Prostanoids  Prostaglandin H 2 (PGH2) Synthase production of PGs, PGI 2 & TXA 2  PGH 2 synthase & Cyclooxygenase (COX) are used as synonyms  PGs endoperoxides (PGG 2 & PGH 2 ) are more potent & long-acting than the PGs to which they decompose  TXA 2 formed mainly in platelets by TX synthase mediating vasoconstriction & platelet aggregation  PGI 2, formed mainly in endothelium by PGI synthase opposes TXA 2  A) Cyclooxygenase (COX) pathway Prostaglandin H synthase, present as two isoenzymes (PGHS- 1/COX-1, PGHS-2/COX-2), each possessing two activities: – cyclooxygenase – catalyzes addition of two molecules of O2 to the arachidonic acid molecule, forming PGG2 – hydroperoxidase – converts the hydroperoxy function of PGG2 to an OH group (of PGH2) The enzyme is also capable of self-catalyzed destruction! Mostly, a given cell type produces 1 type of prostanoids: platelets produce almost exclusively thromboxanes, vascular endothelial cells prostacyclins, heart muscle makes PGI2, PGE2, PGF2  The Cyclooxygenase Pathway Two isoforms of COX exists: COX-1 (constitutive form) & COX-2 (inducible form), COX-1 is constitutively expressed at low levels in many cell types COX-2 is constitutively expressed in kidney & CNS – COX-2 gene transcription is stimulated by growth factors, cytokines, & endotoxins A COX-1 variant, named COX-3, plays a significant role in pain sensation in paracetamol-sensitive way  Prostanoids Biologic Effects Cardiovascular System PGI 2/D 2/E 2 → Potent dilator of Blood vessels (dilation of arterioles, pre-capillary sphincters & post-capillary veins → increased blood flow & cardiac output) TXA 2 is a potent vasoconstrictor TXA 2 & PGI 2 are potent platelet aggregation inducer & inhibitor respectively (blood fluidity) PGI 2 de-aggregate platelets clumps & reduces myocardial infarct size & ischemic organ damage PGI 2, PGE 2, & NO are simultaneously released from endothelium PGE 2 inhibits B- & T-lymphocyte activation & proliferation,  Functions Of Prostaglandins Prostaglandins have numerous and diverse functions. Antihypertensive action : The prostaglandins (PGE,PGA and PGI 2) are vasodilators. Increased blood flow and decreased peripheral resistance so there is a fall in blood pressure. PGs are used in treatment of hypertension. Role of PG in inflammation: PGE1 and PGE2 induce the symptoms of inflammation (redness, swelling,edema) due to arteriolar vasodilation. PG are considered as natural mediators of inflammatory reactions of rheumatoid arthritis psoriasis(skin),conjunctivitis(eyes).  Corticosteroids are frequently used to inhibit the inflammatory response PG and Reproduction PGE 2 and PGF2 are widely used for medical termination of pregnancy and induction of labour, it increases the uterine contraction.  Functions Of Prostaglandins Renal System PGs enhance urine formation, natriuresis, & kaliuresis via action on renal blood flow & tubules Intravenous infusion of PGE and PGA produces substantial increase in renal plasma flow. Increase in GFR PGD 2, PGE 2, PGI 2 stimulate renin release PGs inhibit water re- absorption under ADH effect increased urinary flow Nervous system – Hypertehermia by PGE 2, related pyrogen-induced fever. Antipyretic action of ASA & NSAIDs is via inhibition of COX-1, -2 & -3 – Algesia induction & pain sensitization to histamine, BK or mechanical  Prostanoids Biologic Effects Respiratory System Smooth muscle of the Bornchi:   Bronchial muscle relaxation by PGE 2 & PGI 2, but constriction by TXA 2, LTC 4 & LTD 4  PGE is a bronchodilator whereas PGF acts as bronchoconstrictor of smooth muscles. PGE and PGF oppose the action of each other in the lungs. PGE 1 and E2 are used in the treatment of asthma.  Prostanoids Biologic Effects GIT: PGE s & PGI 2 Stomach -Decrease (inhibit) Gastric acid secretion, increase mucus production by PGE2, -Decrease acid (Pepsin) secretion and mucosal vasodilatation by PGI2 Intestine - Contracts longitudinal and relaxes circular muscle, Increase peristalsis/cl --Increased electrolyte/water movement into intestinal lumen (diarrhea) -They increase bicarbonate, mucus & blood flow   TXA 2 is pro-ulcerogenic  Prostanoids Biologic Effects Role of PG in inflammation: Effect of PG on pain and fever  Pyrogens (fever producing agents)promote PG synthesis leading to the formation of PGE 2 in the hypothalamus, the site for regulation of body temperature. PGE1 and PGE2 induce the symptoms of inflammation (redness, swelling,edema) due to arteriolar vasodilation. PG are considered as natural mediators of inflammatory reactions of rheumatoid arthritis psoriasis(skin),conjunctivitis(eyes). PGE 2 along with histamine and bradykinin causes pain. Migraine is due to PGE 2. Aspirin and other non steroidal drugs inhibit PG synthesis and  Prostanoids Biologic Effects PG and Reproduction PGE 2 and PGF2 are widely used for medical termination of pregnancy and induction of labour, it increases the uterine contraction Endocrine system- PGE2-Release of ant pituitary hormones, steroids, insulin, TSH like action Release of gonadotropins and prolactin, luteolysis (in animals)-PGF2 Metabolism- Antilipolytic, insulin like action, mobilization of bone calcium – PGE2  Prostanoids Biologic Effects Effect on metabolism PGE inhibits lipolysis. PGE has also some insulin like effects on carbohydrate metabolism.  The Lipoxygenase Pathway Lipoxygenase, catalze the addition of O 2 to double bond(s) of arachidonic acid forming hydroperoxy-eicosatetraenoic acid (HPETE) 5-, 12- & 15- lipoxygenases → 5-, 12- & 15- HPETEs respectively 5-HPETE is converted to leukotriene-A 4 (LTA 4 ), which in turn may be converted to various other leukotrienes LTA 4 is converted into LTB 4 in PMNLs & to LTC 4 in mast cells 12-HPETE is converted to the hydroperoxide; hepoxilins A & B 15-HPETE is converted to the lipoxins; LXA  B) Lipoxygenase (LO) pathway 12-lipoxygenase 15-lipoxygenase 3 different lipoxy-genases insert oxygen into the 5, 12, or 15 position of arachidonate; the first product is the hydroperoxy-eicosatetraenoic acid Hepoxilins 5-lipoxygenase (HPETE) (HXA3) Only 5-lipoxygenase produces leukotri- enes; requires protein FLAP 5-lipoxygenase se 15-lipoxygena Gly–Cys–Glu Leukotriene D4 -Gly Leukotriene E4 -Glu peptidoleukotrienes  Thromboxanes Thromboxanes are also derived from prostanoic acid but instead of 5- carbon cyclopentane ring of PG ,thromboxanes have a 6- membered oxane ring  Function Of Thromboxanes Thromboxanes are synthesized in platelets and upon release cause vasoconstriction and platelet aggregation. It stimulates steroid production by adrenal cortex. Exerts PTH like effects on bone,it causes increased mobilization of calcium from bones.  Prostacyclins VsThromboxanes Effects on Target Prostacyclins (PG I Thromboxane's organs 2) Coronary Artery Dilates constrict Blood Pressure Lowers Raises Platelet Aggregations inhibits stimulates Cyclic AMP In target Decrease Increase cells  Leukotrienes(LTs) They are a family of conjugated trienes formed from eicosanoic acids in leukocytes,mast cells and macrophages by lipoxygenase pathway in response to immunologic and non inflammatory stimuli. They have no ring in their structure but have three conjugated double bonds LTs are produced mainly in leukocytes  Functions Of Leukotrienes LTs act as mediators of inflammation and anaphylaxis.( Elicits erythema and wheal and flare reaction and increases vascular permeability). Leukotrienes are very potent constrictors of the bronchial airway muscles: (LTC4, LTD4, and LTE4). inhalation of LTs causes bronchospasm. LTs-C4 and D4 are potent stimulators of mucus secretion. They cause attraction (LTB4) and activation of leukocytes (primarily eosinophils and monocytes), promote diapedesis , enhance phagocytosis They regulate vasoconstriction They increase vascular permeability LTs in host defense : (induction of gene expression) (activation of NADPH oxidase) (synthesis of iNOS) (release from neutrophils) (receptors for LTs)  Overproduction of LTB4 Overproduction of LTB4 was demonstrated in: Crohn's disease rheumatoid arthritis psoriasis cystic fibrosis Leukotrienes are also suspected of participating in atherosclerosis development Excessive bronchoconstriction can be found in some forms of asthma Slow Reacting Substance Of Anaphylaxis SRS-A : is a mixture of thionyl peptidesLTC4, LTD4 &LTE4. More potent than histamine Constrictor of bronchial airway musculature. Increase vascular permeability. Attraction and activation of leucocytes  Lipoxins They are a group of compounds produced by leukocytes. They are conjugated tetraenes. They are formed by the combined action of more than one lipoxygenase. Lx A4 is the most common type, it is chemotactic in nature.  The Epoxygenase Pathway A cytochrome P450 epoxides double bonds of the precursor FA (arachidonate) into mono-epoxide FA; epoxy eicosatetraenoic acids (EPETEs) EPETEs are involved in vascular tone modulation, ion transport, hemostasis &hematopoiesis  Effects of Eicosaniods Induction of inflammation Mediation of pain signals Induction of fever Smooth muscle contraction (including uterus) Smooth muscle relaxation Protection of stomach lining Simulation of platelet aggregation Inhibition of platelet aggregation Sodium and water retention  USES of Eicosanoids 1. Abortion 2. Induction/ augmentation of labour 3. Cervical priming (ripening) 4. Postpartum haemorrhage (PPH)- carboprost 5. Peptic ulcer- Misoprostol 6. Glaucoma- latanoprost, travoprost, bimatoprost 7. Maintain patency of ductus arteriosus- Alprostadil 8. Avoid platelet damage -Epoprostenol 9. Peripheral vascular disease- rest pain, healing of ischemic 10.Impotency- Alprostadil Inhibitors mediators of inflammations Cyclooxygenase & Drugs Affecting the Prostanoid Pathway  Therapeutic uses 1. Induction of labor at term.  Induction of labor is produced by: – infusion of PGF 2 (carboprost tromethamine) [Hemabate] or – PGE 2 (dinoprostone) [Prostin E]. Therapeutic Abortion i. A. Inducing abortion in the second trimester: 44 – Infusion of carboprost tromethamine or – Administration of vaginal suppositories containing dinoprostone ii. B. inducing first-trimester abortion: – these prostaglandins are combined with mifepristone (RU486)  Therapeutic uses III. Maintenance of ductus arteriosus is produced by PGE 1 [Prostin VR] infusion  IV. PGE 1 will maintain patency of the ductus arteriosus, which may be desirable before surgery. V. Treatment of peptic ulcer. VI. Misoprostol [Cytotec] a methylated derivative of PGE 1 is approved for use in patients taking high doses of nonsteroidal antiinflammatory drugs (NSAIDs) to reduce gastric ulceration  Erectile dysfunction Alprostadil (PGE 1 ) can be injected directly into the corpus cavernosum or administered as a transurethral suppository to cause vasodilation and Injected directely into the corpus cavernosum enhance tumescence. injected directly into the Transurethral Suppositories corpus cavernosum transurethral suppository  Adverse effects of eicosanoids local pain and irritation  bronchospasm  gastrointestinal disturbances: nausea, vomiting, cramping, and diarrhea.  Inhibition of the COX pathway Aspirin inhibits the COX activity of both PGHS-1 and PGHS-2 (by acetylation of a distinct Ser of the enzyme) Other nonsteroidal anti-inflammatory drugs (NSAIDs) also inhibit the COX activity (ibuprofen competes with arachidonate) Transcription of PGHS-2 can be blocked by anti-inflammatory corticosteroids  ? Mechanisms of Action of NSAIDs Inhibits production of prostaglandins and thromboxanes Inhibit COX enzymes Reduce pain, fever and inflammation But… Side effects of some NSAIDs in some people - include gastrointestinal irritation, ulcers, bleeding, etc. - if untreated, lead to death - led to hunt for better anti-inflammatory drug  Effects of aspirin and other pain killers Aspirin works on both COX-1 and COX-2 to inhibit Arachidonic acid’s entry into the active site of the enzyme - acetyl group of aspirin binds to serine in COX - by blocking the activity of the COX enzymes, this relieves some of the effects of pain and fever -”nonselective” --many side effects Tylenol—thought to have effects through inhibiting the activity of COX-3, an alternatively spliced form of COX-1  Low dose aspirin therapy Low dose aspirin therapy: - Aspirin irreversibly inhibits COX-1 (and COX-2) - Has a short half-life - New platelets are constantly being made - Will therefore reduce but not abolish the ability for blood to clot, thereby reducing heart attacks and stroke  Short History of COX-2 Inhibitors 1970’s - aspirin target identified as cyclo-oxygenase (COX) 1980’s - Two forms of COX identified: COX-1, constitutive COX-2, induced at sites of inflammation - Hypothesis: selective inhibition of COX-2 might reduce inflammation without the GI side effects. 1990’s - Rational design of COX-2 inhibitors  COX-2 inhibitors Coxibs – a new class of NSAIDs Rofecoxib – withdrawn from sale by Merck, in 2004 Merck Etoricoxib – successor to rofecoxib? Not (yet) approved by FDA Celebrex (celecoxib) – FDA recommended ‘black box’ warning label Pfizer Bextra (valdecoxib) –withdrawn from the market, 2005  PG analogues PG analogues are used clinically to mimic endogenous bioactivity. Montelukast and zafirlukast specifically inhibit activation of cysteinyl leukotriene receptor 1. Inhibitors of soluble epoxide hydrolase (sEH) reduce inactivation of epoxyeicosatrienoic acids (EETs) as well as HXs. LX, resolvin and protectin mimetics (orange box) are being developed for the treatment of ocular, periodontal and cardiovascular diseases  Summary Points In mammalian cells, eicosanoid biosynthesis is usually initiated by the activation of phospholipase A2 and the release of arachidonic acid (AA) from membrane phospholipids. The AA is subsequently transformed by cyclooxygenase (COX) and lipoxygenase (LO) pathways to prostaglandins, thromboxane and leukotrienes collectively termed eicosanoids. Eicosanoid production is considerably increased during inflammation. Both COX and LO pathways are of particular clinical relevance. The COX pathway is the major target for non-steroidal anti- inflammatory drugs (NSAIDs), the most popular medications used to treat pain, fever and inflammation.  Summary Points In 1991, it was discovered that COX exists in two distinct isozymes, COX-1 and COX-2, of which COX-2 is primarily expressed at sites of inflammation and produces pro- inflammatory eicosanoids. COX-2 selective inhibitors (COXIBs) have been developed recently as anti- inflammatory agents to minimize the risk of GI toxicity. Recently, some COX-2 selective inhibitors have shown adverse cardiovascular side effects, resulting in the withdrawal of rofecoxib and valdecoxib from the market. Selective inhibition of COX-2 without reducing COX-1-mediated thromboxane production could alter the balance between prostacyclin and thromboxane and promote a prothrombotic state, thereby explaining the observed COX-2 cardiovascular risk. Thank You