Complete intensive material on cox enzymes, types, physiology, drugs associated and pharmacological modulation, interactions, toxicities & recent concepts

1. COX ENZYMES
PHYSIOLOGY AND PHARMACOLOGICAL
MODULATION
DR. SIDDHARTHA DUTTA
POST GRADUATE RESIDENT
MAMC, NEW DELHI

2. CONTENTS
• INTRODUCTION
• COX TYPES
• FUNCTION
• MECHANISM
• PROSTANOIDS- ACTIONS AND PHYSIOLOGICAL ROLE
• NEED IN THERAPY
• COX BLOCKERS
• ASPIRIN AND SOME IMPORTANT COX BLOCKERS
• ADVERSE EFFECTS
• DRUG INTERACTIONS
• SUMMARY

3. EICOSANOIDS
• Precursor essential fatty acids(PUFA) contain 20
carbons
• Why named prostaglandin and leucotrienes ??
• Arachidonic acid(AA) aka 5,8,11,14 eicosa tetra enoic
acid
• In humans, AA, the most abundant precursor is
either derived from dietary linoleic acid or ingested
directly as a dietary constituent
• Prostanoid synthesis- cyclisation of AA

4. HISTORY
• In 1930, Kurzrok and Lieb
• In 1935, von Euler identified the active material and
named prostaglandin
• Samuelsson, Bergström and their colleagues elucidated
the structures of prostaglandin E1 (PGE1) and
prostaglandin F1 (PGF1) in 1962
• In 1964, Bergström and coworkers and van Dorp and
associates, independently achieved biosynthesis of PGE2
from arachidonic acid
• Nobel Prize of von Euler in 1970
• Bergström, Samuelsson, and John Vane in 1982

5. COX
• 3 types- COX-1, COX-2, COX-3(?)
• PG G/H synthase
• COX-3 – A COX-1 SPLICE VARIANT 1 (COX-1V1)
• “COX-3” is a variant of COX-2 that includes the
COX-2-specific carboxy terminus
• “COX-3” should be reserved for the product of an
independent third COX gene which clearly has not
been yet identified

6. COX-1 vs. COX-2

8. COX 1 AND COX -2
• PGs, mostly by COX-1, are constitutively expressed in almost
all tissues; COX-2 appears to only be constitutively expressed
in the brain, kidney, bones, reproductive organs, and some
neoplasms
• Under normal physiologic conditions, PGs play an essential
homeostatic role in cytoprotection of gastric mucosa,
hemostasis, renal physiology, gestation, and parturition
• In platelets there is only COX-1exist (converts arachidonic acid
to TxA2)
• COX-1 predominant in gastric mucosa (source of
cytoprotective PGs)
• The production of PGs, (inducible COX-2 activity >> COX-1) at
sites of inflammation propagate pain, fever

9. MECHANISM

10. MECHANISM

11. PGE₂ PGI₂ PGF₂α TXA₂
CVS Vasodilation,↑cap
permeability, patent
PDA
Vasodialator
Potent
Vasoconstrictor
BP,HR (minor)
Vasoconstrictor
Smooth muscle
mitogen
PLATELETS ---- Inhibits Agg. ----- Aggregation
UTERUS Contracts(in vivo)
Relaxes non preg.
Contracts preg.(in
vitro)
Dysmenorrhoea
Contracts(both
in vivo and vitro)
preg. and non
preg
Dysmenorrhoea
BRONCHIAL
MUSCLE
Relaxes Relaxes Contracts Contracts
GI TRACT ↓ acid secretion
↑ mucus production
& mucosal blood
flow .
Contracts gut muscle
Watery diarrhoea
↓ acid
secretion
Same as
PGE2 .
Opposes
propulsive
action of
PGE2
KIDNEY Natriuresis
Vasodilation
Same as
PGE2 except
vasocontrictor

12. PGE₂ PGI₂ PG2α TXA₂
Male G.U. system High conc in
semen (E1 &
E2)
Penile erection
↑ sperm
motility
Present but
very less
quantity
CNS Pyrogenic
PNS Sensitises nerve ending at the
site of inflamation
EYE ↓ IOP ↓ IOP
NEOPLASIA Pro oncogenic
in colon

13. PROSTANOIDS
PGI₂
• PGI₂(prostacyclin) is located
predominantly in vascular endothelium.
• Main effects: vasodilatation &
inhibition of platelet aggregation
TXA₂
• TXA₂ is found in the platelets.
• Main effects: platelet aggregation
& vasoconstriction

14. PGE₂
• Inhibition of gastric acid secretion
• Contraction of pregnant uterus
• Contraction of GI smooth muscles
PGF₂α
• Contraction of bronchi
• Contraction of myometrium

15. NEED IN THERAPY
Abortion and cervical ripening
• Dinoprostone(PGE₂)-intravaginally
• Misoprostol(PGE₁)- Abortifacient
• Carboprost(PGF₂α)-Intraamniotic,
I.M.- Controls bleeding in PPH
Peptic ulcer
• Misoprostol(PGE₁)-200μgm 4 times daily
• Enprostil(PGE₂)-NSAIDS induced ulcers

16. USES CONTINUED..
Platelet aggregation
Epoprostenol(PGI₂)- Renal dialysis,CP bypass,
platelet storage
Pulmonary hypertension-
Epoprostenol(PGI₂) I.V.
Treprostinil(PGI₂) I.V./S.C.
Ductus arteriosus-
Alpostadil(PGE₁) & Epoprostenol(PGI₂)
Peripheral vascular disease-
Beraprost(PGI₂) Oral
Glaucoma –
latanoprost(PGF₂α), Bimatoprost, Travoprost,
Unoprostone
Male impotence-
Alprostadil(PGE₁)

17. SIDE EFFECTS
• Vomiting, diarrhoea, fever bronchoconstriction
• Hypotension, syncope, dizziness, flushing(PGE₂)
• Anaphylactic shock, cvs collapse(PGF₂α)
• PGF₂α Analogues in glaucoma – blurred vision,
brown iris

18. COX BLOCKERS
1. NON SELECTIVE 2. PREFERENTIAL COX-2
ASPIRIN NIMESULIDE
KETOROLAC MELOXICAM
SULFASALAZINE ETODOLAC
OSALAZINE NABUMETONE
METHYL SALICYLATE
INDOMETHACIN 3. SELECTIVE COX-2
IBUPROFEN CELECOXIB
NAPROXEN ROFECOXIB
MEFENAMIC ACID VALDECOXIB
PIROXICAM ETORICOXIB
DICLOFENAC PARECOXIB
ACECLOFENAC
SULINDAC 4. COX-3(?) INHIBITOR
DIFUNISAL PARACETAMOL
METAMIZOL

19. HISTORY OF SALICYLATE
• Salicylates were first discovered when the observation was made
that chewing willow bark could relieve pain
• Hippocrates: Willow bark as a pain killer during childbirth
• Edmund Stone (1700) Extract of willow bark to reduce fever
• Piria (1838) Isolation of salicin from willow bark
• Kolbe (1853) Synthesis of salicylate from salicin
• Von Gerhardt at Beyer Pharmaceutical Co.
synthesized acetyl SA (ASA) in 1850
• Hoffman, at Beyer gave ASA to his father
• Beyer started testing Aspirin on animals 1899

20. MECHANISM OF ACTION
• ASA covalently and irreversibly modifies both COX-1 and COX-2 by
acetylating serine-529 in the active site
• Acetylation results in a steric block, preventing arachidonic acid from
binding
• Important distinction from all other NSAIDS
• In contrast to aspirin, salicylic acid has no acetylating capacity It is a weak,
reversible, competitive inhibitor of COX
• Acetylation of COX-2 retains the COX activity although the reaction
produces a different product, 15-R-HETE(Hydroxyeicosatetraenoic acid)

21. ASPIRIN
ARE WE ALTERING THE NORMAL
PHYSIOLOGY?

24. THERAPEUTIC USES
1. Analgesia – 324-1000mg oral every 6 hrs
2. Antipyresis- same as analgesic dose
3. Antiinflammatory action-3-4gm/day
4. Antithrombotic action-81-125mg/day
5. Closure of ductus arteriosus
6. Relief in dysmenorrhoea
7. Miscellaneous – colonic and rectal cancer
preeclampsia (PGF₂α)
FAP
niacin induced flushing
retards cataract progression

25. Adverse effects
• Gastric mucosal damage(COX-1 & Ion trapping)
• Respiratory alkalosis with compensatory metabolic
acidosis
• Salicylism – headache, vertigo, tinnitus, hyperventilation,
nausea, vomiting.
• Bleeding
• Hypersensitivity(LOX)
• Uric acid excretion
• Analgesic nephrophathy
• Reye syndrome

26. GASTRIC TOXICITY

27. Afferent
arteriole
Efferent
arteriole
ACEI/
ARB
 NSAIDS,
 Low
volume
 Poor renal
perfusion
normal
Effects on Renal Function
PGs not participated
PGs vasodilator when
angiotensin II or
catercholamines elevated

29. ASPIRIN OVERDOSE
• Effect on Respiration: triphasic
• Low doses: uncoupling phosphorylation → ↑
CO2 → stimulates respiration
• Direct stimulation of respiratory center →
Hyperventilation → resp. alkalosis → renal
compensation
• Depression of respiratory center and
cardiovascular center → ↓ BP, respiratory
acidosis, no compensation + metabolic acidosis
also

30. Dose-Dependent Effects:
Low: < 100mg
blocks platelet aggregation
Intermediate: 300-2400mg/day
antipyretic and analgesic effects
High: 2400-4000mg/day
anti-inflammatory effects
Salicylism

31. DRUG INTERACTIONS

32. PARACETAMOL
• Phenacetin in 1887, analgesic nephropathy
• Paracetamol-effective analgesic and antipyretic
• Lacks anti-inflammatory properties
• No effect on uric acid levels
• lacks platelet-inhibiting properties
• Useful in mild to moderate pain: headache, myalgia,
postpartum pain

33. Cont..
Preferred drug in
• Patients allergic to Aspirin & hemophilia
• History of peptic ulcer, bronchospasm & in children
with viral infections
Inadequate therapy for inflammatory conditions such as
rheumatoid arthritis, although it may be used as an
adjunct with other analgesics

34. PARACETAMOL
WHY ISN’T AN ANTI-INFLAMMATORY?

35. ACUTE PARACETAMOL POISONING
Occurs especially in small children.
If a large dose (> 150 mg/kg or > 10 g in adult)
The letal dose is 250 mg/kg.
N-acetyl-p-benzoquinoneimine (NABQI) is a highly
reactive arylating metabolite of paracetamol which detoxicated
by conjugation with glutathione
Large doses of paracetamol are taken, more NABQI is formed hepatic
glutathione is depleted and NABQI binds covalently to proteins in liver cells
(and renal tubules) causing necrosis.
In chronic alcoholics even 5-6 g/d taken for a few days can result in
hepatotoxicity because ethanol induces CYP 2E2, that metabolizes
paracetamol, to NABQI.
Treatment- activated charcoal, given orally, and N-acetylcysteine (150
mg/Kg by i.v. infusion) oral loading dose of 140mg/kg then 70mg/kg every 4
hrs for 17 doses

37. INDOMETHACIN
• Potent than aspirin(20x)
• Inhibit PMN motility
• Good antiinflammatory, analgesic and antipyretic
• Conc. In synovial fluid is high
• 90% plasma protein bound
• Enterohepatic circulation
• Reserved drug- Ank. Spondylitis, psoriatic arthropathy,
acute gout, destructive arthropathy 3

38. Cont..
• Dosage- 50 mg BD
• Closure of PDA(0.1-0.25mg/kg)
every 12 hrs for 3 doses
• GI toxicity very common
• Toxic doses- uncoupler
• CNS S/E- Frontal headache(m/c), dizziness, vertigo,
mental confusion, siezures, depression, psychosis,
hallucination
• C/I in psychiatric patients, drivers, epileptics
• Leukopenia and hypersensitivity
• Antagonises antihypertensives(diuretics, ace inhibitors,
AT1 receptor antagonist, β-receptor antagonist)

39. IBUPROFEN
• Oral, I.V.
• Safest t NSAIDS by ADR reporting system in U.K.
• Inflammatory disorders- 800 mg 4 times a day
• Primary dysmenorrhoea- 400 mg 4 times a day
• Adverse effects- GI s/e, thrombocytopenia, rashes, blurred
vision, toxic amblyopia, fluid retention & edema 1

40. OTHER PROPIONIC ACID DERIVATIVES
• Naproxen- absorbed completely(food delays the
rate) & Prominent inhibitory effects on leukocyte
function- efficacious in acute gout
• 500-750 mg BD, better compliance
• Ketoprofen-stabilize lysosomal membranes and
antagonize the actions of bradykinin
• Oxaprozin- t 1 /2 of 40-60 hours allows for once-
daily administration
• Flurbiprofen-oral & ophthalmic solution

41. DICLOFENAC
• Oral, topical, transdermal, i.v.
• Selectivity for COX-2 resembles coxibs
• High first pass metabolism(50%), half life-1-2 hrs
• Plasma protien bound 99%
• Good tissue permeability
• Accumulates in synovial fluid- extended therapeutic effect 3

42. • Toxicities- GI toxicities, liver toxicity
• Reversible rise in aminotransferases
Therapeautic uses:
Congeners:
• Aceclofenac - Chondroprotective
• Bromofenac (severe liver toxicity)- withdrawn in 2005
• Nefafenac – ophthalmic solution
• Lumiracoxib- withdrawn due to liver toxicites in 2007
Rheumatoid arthritis
Osteoarthritis
Ank. Spondylitis
Bursitis
Toothache
Dysmenorrhoea
Renal colic
Post traumatic
Post inflammatory conditions

43. NIMESULIDE
• Weak inhibitor of PG synthesis
• Reduced generation of superoxide by neutrophils
• ↓Synthesis and TNFa release, free radical scavanging, inhibition of
metalloproteinase activity in cartilage
• Fulminant hepatic failure
• Most asthamtics and those who develop bronchospasm or
intolerance to aspirin or other NSAIDs do not cross react with
nimesulide
• UK, US, Australia, Canada, Portugal, Israel, Spain and Turkey the
overall safety of this drug especially in children, has been questioned

44. PIROXICAM
• Long acting, potent- once daily
• Antiinflammatory, analgesic and antipyretic
• Additionally blocks neutrophil activation & inhibits
proteoglycanase & collagenase
• Enterohepatic circulation
• Glucuronidation conjugation, excreted in urine & bile
• Extensive plasma protein bound(99%) 3

45. • Less suited for acute analgesia, half life-50 hrs (variable),
steady state conc. 7-12 days
• Suited for gout, osteoarthritis, rheumatoid arthritis
• Rash, pruritus, reversible azotemia and edema
Congeners:
• Meloxicam- more COX-2 selectivity, less GI side effects
• Lornoxicam, cinnoxicam, sudoxicam, and tenoxicam
• Lornoxicam a unique enolic acid derivative - rapid onset of
action and a relatively short t1 /2 (3-5 hours) 1

46. KETOROLAC
• Potent analgesic
• Moderately effective antiInflammatory
• I.M., I.V., Oral, topical(ophthalmic solution)
• Used with morphine
• Post-operative, dental, acute musculoskeletal,
Renal colic, migrane, bony mets
• Dosage- 15-30 mg i.m./i.v. 6 hrly
• Adverse effects- G.I., somnolence, dizziness, renal,
bleeding, and hypersensitivity reactions

47. NABUMETONE
• Prodrug, active metabolite 6-methoxy-2-naphthylacetic acid
• Only basic preferential COX-2 inhibitor
• Good efficacy in rheumatoid arthritis and osteoarthritis
• Plasma half life- 24 hrs
• Relatively low incidence of side effects
• 1000 mg given once daily
• Off-label use in the short-term treatment of soft-tissue injuries

48. COX-2 SELECTIVE DRUGS
• COX-2 can be up-regulated in the CNS and plays an
essential role in the mediation of pain and the febrile
response
• COX-2 selective inhibitors are generally larger molecules
than NSAIDs and therefore preferentially inhibit COX-2
compared to COX-1 because the hydrophobic channel of
COX-2 is larger
• COX-2 selective inhibitors are too bulky to access the
binding pocket of the COX-1 enzyme
• Celecoxib, etoricoxib, parecoxib are available in India
• Etoricoxib- highest COX-2 selectivity, OD dosing
• Parecoxib- prodrug of valdecoxib

49. • Celecoxib is now the only selective COX-2 inhibitor
available in the US
• Withdrawal of rofecoxib (Vioxx, Merck & Co) Sept 2004
• Withdrawal of valdecoxib (Bextra, Pfizer) Apr 2005
• Celecoxib includes a boxed warning, highlighting the
potential for increased risk of cardiovascular events

50. • Platelet Dysfunction
• Gastritis and peptic ulceration with bleeding
• Acute Renal Failure
• Sodium+ water retention and edema
• Analgesic nephropathy
• Prolongation of gestation and inhibition of
labor.
• Hypersenstivity (not immunologic but due to
PG inhibition)

52. SUMMARY

53. THANK YOU