Prostaglandins

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This is a presentation giving basics of PGs & a review of a research paper on the same.

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Prostaglandins

  1. 1. PROSTAGLANDINS Bhumika Sharma BMS III year
  2. 2. INTRODUCTION <ul><li>These are a class of eicosanoids and were discovered through their effect on smooth muscle. </li></ul><ul><li>Produced & released by nearly all mammalian cells; (Except RBCs) </li></ul><ul><li>Perform a variety of functions </li></ul><ul><li>These are produced in minute amounts and are not stored. </li></ul>
  3. 3. CLASSIFICATION Cyclooxygenase Lipoxygenase
  4. 4. STRUCTURE <ul><li>The structure of PG is based on hypothetical 20C parent saturated acid called “Prostanoic Acid” </li></ul><ul><li>All naturally occuring PGs are 20C fatty acids containing a cyclopentane ring. </li></ul><ul><li>All PGs have: </li></ul><ul><ul><li>-OH group at 15 th position </li></ul></ul><ul><ul><li>trans double bond at 13 th position </li></ul></ul>
  5. 5. CLASSIFICATION OF PGS <ul><li>PG-E group: PGE-1, PGE-2 & PGE-3 </li></ul><ul><ul><li>Functional group: β hydroxyketone </li></ul></ul><ul><li>PG-F group: PGF1 α , PGF2 α & PGF3 α </li></ul><ul><li>Functional group: 1,3-diols </li></ul><ul><li>PG-A group: PGA-1, PGA-2 & 19-OH PGA-1 </li></ul><ul><ul><ul><li>Functional group: β unsaturated ketone </li></ul></ul></ul><ul><li>PG-B group: PGB-1, PGB-2 & 19-OH PGB-1 </li></ul>
  6. 6. BIOSYNTHESIS <ul><li>Synthesized aerobically from polyunsaturated fatty acids. </li></ul><ul><li>Multienzyme complex called Prostaglandin H Synthase (PGHS) </li></ul><ul><li>PGHS has two components Cyclo-oxygenase system & Peroxidase system </li></ul><ul><li>PGHS is present as two isozymes PGHS 1 & PGHS 2 </li></ul><ul><li>Acyl Hydrolase ( phospholipase A2), released from the cell membrane/ lysosome hydrolyses membrane phospholipids into lysophospholipids & arachidonic acid. </li></ul><ul><li>Arachidonic acid is converted to PG by oxidative cyclization with Cyclooxygenase of PGHS ( ER, Microsomes & cell membrane) </li></ul><ul><li>This system forms the first unstable cyclic endopreoxide PG-G2. </li></ul><ul><li>PG-G2 is converted into PG-H2 by Peroxidase enzyme of peroxidase component of PGHS System. </li></ul><ul><li>PG-H2 is the precursor of Prostanoids </li></ul>
  7. 7. CELL ARACHIDONIC ACID CYCLIC-ENDO-PEROXIDES Diet Peroxidase
  8. 9. PHYSIOLOGICAL EFFECT
  9. 11. CYTOTEC <ul><li>Also known as misoprostol, manufactured by Searle (pfizer) </li></ul><ul><li>Cytotec was approved 12 years ago by the FDA for its intended purpose: to prevent ulcers in people who take non-steroidal anti-inflammatory drugs like aspirin or naproxen. misoprostol is a synthetic PGE 1 analogue </li></ul><ul><li>When administered, misoprostol </li></ul><ul><li>stimulates increased secretion of the protective mucus that lines the gastrointestinal tract </li></ul><ul><li>increases mucosal blood flow, thereby increasing mucosal integrity. </li></ul><ul><li>It is sometimes co-prescribed with non-steroidal anti-inflammatory drugs (NSAIDs) to prevent the occurrence of gastric ulceration, a common adverse effect of the NSAIDs. </li></ul><ul><li>Used for inducing labor at or near term : 0.5mg/ml </li></ul><ul><li>Used for terminating pregnancy: 5 μ g/ml </li></ul>
  10. 12. PHYSIOLOGICAL EFFECTS
  11. 13. PHYSIOLOGICAL EFFECT <ul><li>Platelet Aggregation & Thrombosis </li></ul><ul><li>PGI2: ( Inhibit Aggregation) </li></ul><ul><li>Released by endothelial cells </li></ul><ul><li>Responsible for non-adherence of platelets to healthy blood vessels </li></ul><ul><li>PGE2 & TXA2: ( Promote Clotting Process) </li></ul><ul><li>Produced by platelets, accounts for spontaneous aggregation of platelets to thrombin, collagen at the site of injury </li></ul>
  12. 14. . Eicosanoid Major Site(s) of Synthesis Major Biological Activities PGD 2 mast cells inhibits platelet and leukocyte aggregation, decreases T-cell proliferation and lymphocyte migration and secretion of IL-1&ALPHA; and IL-2; induces vasodilation and production of cAMP PGE 2 kidney, spleen, heart increases vasodilation and cAMP production, enhancement of the effects of bradykinin and histamine, induction of uterine contractions and of platelet aggregation; decreases T-cell proliferation and lymphocyte migration and secretion of IL-1&ALPHA; and IL-2 PGF2 α kidney, spleen, heart increases vasoconstriction, bronchoconstriction and smooth muscle contraction PGH 2 many sites a short-lived precursor to thromboxanes A 2 and B 2 , induction of platelet aggregation and vasoconstriction PGI 2 heart, vascular endothelial cells inhibits platelet and leukocyte aggregation, decreases T-cell proliferation and lymphocyte migration and secretion of IL-1&ALPHA; and IL-2; induces vasodilation and production of cAMP TXA 2 platelets induces platelet aggregation, vasoconstriction, lymphocyte proliferation and bronchoconstriction TXB 2 platelets induces vasoconstriction
  13. 15. CATABOLISM OF PG <ul><li>Rapidly removed from circulation. </li></ul><ul><li>Upto 90% PGs are destroyed in liver. </li></ul>
  14. 16. INHIBITORS Inhibitor Example Mode of Action False substrates 5,8,11,14-eicosatetraynoic acid (TYA) - Mepacrine - Inhibits phospholipase A Gluco-corticoids Cortisol, Betamethasone Inhibit the transcription of PGHS-2 NSAIDS Aspirin, indomethacin, ibuprofen Inhibit COO Cu++ & dihydrolipoamide Inhibit PGE formation but increses PGF
  15. 17. STIMULANTS <ul><li>Trauma, hypoxia, angiotensin II, bradikinin, Vassopressin, increase PG synthesis by activating Phospholipase A2 </li></ul><ul><li>Catecholamines enhance PG synthesis by activating COO </li></ul><ul><li>Addition of G-SH stimulates synthesis of PGE </li></ul>
  16. 18. NSAID: ASPIRIN <ul><li>Acetyl salicylic acid (Aspirin) is an effective anti-platelet aggregator. </li></ul><ul><li>It irreversibly acetylates the platelets COO system and inhibits it thus hampering in formation of Thromboxane A2 </li></ul><ul><li>At time same time it opposes the formation of PGI2 in the endothelial cells, which is a vasodilator. </li></ul><ul><li>CLINICAL USES: </li></ul><ul><li>Management of angina & MI </li></ul><ul><li>Prevention of stroke & cerebral ischemic attacks </li></ul>
  17. 20. Source: 1971, Nature
  18. 21. <ul><li>The aim of the study was to work out the mechanism of action of aspirin like drugs. </li></ul><ul><li>In studies carried out by Piper & Vane (1969), it was discovered that on being challenged sensitized lungs of guinea pigs release a substance called RCS (rabbit aorta contracting substance) along with histamine, prostaglandins (PGE2 & PGF2 α ) </li></ul><ul><li>Experiment : Guinea pig lung synthesize PGs from arachidonic acid. </li></ul><ul><li>Lungs from a guinea pig were excised rapidly and washed with ice cold buffer. </li></ul><ul><li>The tissue was homogenized and centrifuged and the supernatant was used. </li></ul>
  19. 22. <ul><li>The homogenate was incubated with arachidonic acid for 30’ at 37°C with gentle shaking . </li></ul><ul><li>A zero time sample was taken. </li></ul><ul><li>The reaction was stopped by heating the flask till the proteins coagulated, then diluted in 0.9% saline. </li></ul><ul><li>The samples were assayed on isolated stomach strips & colon of rat. </li></ul><ul><li>The activity was assayed by bracketing the contractions induced by sample between smaller and larger contractions induced by the standards. </li></ul><ul><li>It was found that PGE2 contracted the stomach strips and had no effect on colon </li></ul><ul><li>PGF2 α contracted the colon and had weaker effect on stomach . </li></ul>
  20. 23. <ul><li>In some experiments, the reaction was terminated by decreasing the pH to 3 with HCl, and then extracting the sample. </li></ul><ul><li>The extracts were dried under reduced pressure. The residue was chromatographed on TLC plates with markers of authentic PGE2 & PGF2α. The area on the strip corresponding with the marker was scraped in a test shaken with a medium. It was then assayed on rat colons & stomach strips. </li></ul><ul><li>The zero time activity of PGE2 was 120-750ng and that of PGF2 α was 60-150ng. </li></ul><ul><li>This activity didn’t increase when cell extract was incubated without arachidonic acid. </li></ul><ul><li>On incubation with arachidonic acid, the activity of PGE2 increased by 100-500ng/ml and 220-520ng/ml for PGF2 α . </li></ul>
  21. 24. <ul><li>Experiment : Test for Inhibition </li></ul><ul><li>To test the inhibition of prostaglandin synthesis, varying amount of indomethacin, sodium acetylsalicylate, sodium salicylate were added to the incubation flask. The inhibitor of generation by a drug is expressed as the percentage inhibition of the control generation. </li></ul><ul><li>Indomethacin, sodium acetylsalicylate, sodium salicylate all inhibited the generation of PG like activity. </li></ul><ul><li>By calculating the ID50 it was inferred that indomethacin was 23 times more potent than aspirin as an inhibitor of synthesis of PGF2 α and sodium salicylate was less potent than aspirin for the same purpose. </li></ul><ul><li>Similar results were obtained for PGE2 activity on stomach strips. </li></ul>
  22. 26. <ul><li>Two different lung homogenate enzyme samples were taken and incubated with arachidonic acid. </li></ul><ul><li>The zero time activity for PGF2 α was 40ng/ml and that of PGE2 was 5ng/ml. </li></ul><ul><li>After 30’ incubation activity increased to 160ng/ml for PGF2 α and 50ng/ml for PGE2. </li></ul><ul><li>After incubation with indomethacin or aspirin there was no increase in the activity of PGs over zero time. </li></ul><ul><li>The results show that the three anti-inflammatory acids inhibit the synthesis of prostaglandins . </li></ul>
  23. 28. CONCLUSION <ul><li>The generation of prostaglandins by a cellfree enzyme preparation in vitro was measured by bioassay. Aspirin-like drugs inhibited the formation of prostaglandins. This enzyme inhibition was proposed as the mechanism of therapeutic action and side effects of aspirin-like drugs, implicating prostaglandins in inflammation . </li></ul>

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