Dr Henderson - Inflammation Flashcards
What are the two kinds of stimuli that can excite action potentials in primary afferent nerve fibres?
External stimuli
Internal stimuli - Released by tissue damage eg ATP and NO
What causes flare? How is this shown?
Neurogenic inflammation
Denervated or anaesthetised tissue does not show flare
What is the effect of stimulation of a nociceptor?
APs travel to the CNS causingthe perception of pain
APs also invade branch terminals of the afferent nerve fibre, from which they release neuropeptides substance P and CGRP
These activate mast cells = inflammatory factors eg histamine
How do bacterial/ viral/ fungal infections cause inflammation?
Releasing toxin
Lysing host cells = release of bradykinin and ATP
Draw the simple flow diagram depicting the response to injury, invasion and noxious stimuli
Well done
What are the major chemotactic factors?
C5a, LTB4, IL-8 and PAF
What are the direct and indirect actions of IL-1 and TNF on endothelial cells?
Direct - Increase in permeability of the junctions between endothelial cells
Indirect - Trigger production of further inflammatory mediators (bradykinin, PGE2) which cause further increases in vascular permeability and vasodilation and activation of sensory neurons
What effect do thrombin and plasmin have on the complement cascade?
They stimulate the production of c3b
What is an autocoid?
Local hormones that act upon the cell type from which they were released
What are the ways by which mast cells can become activated?
By components of the complement cascade or by an allergen binding to an immunoglobulin and in turn an Fc receptor on the mast cell membrane
Also activated by Substance P or CGRP
Where is histamine found?
Mast cells
Basophils
Enterochromaffin-like cells of oxyntic glands in the stomach
Histaminergic neurons in the CNS
What causes an increase in histamine release? How is this achieved?
Increase in intracellular calcium through binding of C3a/C5a or Fc receptor
What are the actions of histamine?
Contraction of smooth muscle
Dilation of small arterioles
Increased permeability of posst-capillary venules
Sensitises nerve endings, leading to itching
Classic triple response of Lewis
What are the pathophysiological roles of histamine?
Involved in various allergic conditions eg allergic rhinitis and urticaria
Response include swelling, itching, nasal congestion and watery eyes
Can cause anaphylaxis
May play a role in chronic inflammatory conditions
What is the role of adrenaline in histamine release?
It increases cAMP and so inhibits histamine release
What are the drugs which inhibit degranulation of mast cells?
β2 agonists
Methylxanthines (PDE inhibitor)
Sodium cromoglycate (Ca2+ channel blockers = prevents exocytosis)
Sodium cromoglycate?
Ca2+ channel blocker - inhibits exocytosis from mast cells
Used to prevent histamine release from mast cells
What are the types of histamine receptor and to which kind of G protein are they coupled?
H1 - Gq = inflammation
H2 - Gs = gastric acid secretion
H3 - Gi = Important in CNS
H4 - Gq = Unknown role
Upon which receptor do antihistamines act?
H1
How were antihistamines improved (second generation)?
More selective for the H1 receptor and could not cross the BBB so did not cause drowsiness
Mepyramine
First generation histamine receptor antagonist
Low selectivity and had actions in the CNS = drowsiness
Promethazine
First generation histamine receptor antagonist
Low selectivity and had actions in the CNS = drowsiness
Terfenadine
Second generation histamine receptor antagonist = more selective
Could not cross BBB therefore no drowsiness
Prodrug and is metabolised to its active form fexofenadine
What is terfenadine poisoning?
Under conditions of reduced activity of cytochrome P450, terfenadine is not metabolised sufficiently and can affect the heart via block of HERG channel (Kv11.1) = potentially fatal arrhythmias
Why can terfenadine’s break down be interfered with?
Metabolised by the 3A4 isoform of cytochrome P450 and this is susceptible to inhibition by various drugs
Fexofenadine
Third generation antagonist H1 receptor antagonist
Fewer CNS effects and no action on the heart (lower affinity for Kv11.1)
Loratidine
Third generation antagonist H1 receptor antagonist
Fewer CNS effects and no action on the heart (lower affinity for Kv11.1)
What is the other use of H1 receptor antagonists (other than anti-inflammatory)?
Anti motion sickness drugs
Dimenhydrinate?
H1 receptor antagonist - CNS effects
Used as an anti motion sickness drug
What is the effect of histamine on the GI tract?
Parietal cells express H2 receptors, stimulation of which causes a rise in cAMP that in turn regulates activity and location of the H+/K+ pump
Cimetidine
H2 selective antagonist used in the treatment of gastric ulceration - reduces acid secretion
Does produce drug-drug interaction
Ranitidine
H2 selective antagonist used in the treatment of gastric ulceration - reduces acid secretion
What are the older and newer treatments for peptic ulcers?
Older:
Antacids, cholinergic blockade and vagotomy
Newer:
H2 selective antagonist, proton pump inhibitor, eradication of H. pylori
Omeprazole
Proton pump inhibitor used in the treatment of gastric ulcers
Clarithromycin
Drug used to eradicate H. pylori
Metronidazole
Drug used to eradicate H. pylori
What are the peptide mediators of inflammation?
Kinins, tachykinins, cytokines and NGF
What is the role of of kallikrien?
Protease which cleaves bradykinin from high-molecular weight kininogen or low-molecular weight kininogen
How is kallikrien activated?
By tissue damage
What are the two types of bradykinin? What is the difference between them?
Bradykinin (in blood, made from high-molecular weight kininogen)
Lys-bradykinin/kallidin (in tissue, made from low-molecular weight kininogen)
Upon which receptors do bradykinin and kallidin act? What are the features of these receptors?
B(2) receptors
Constitutively expressed
Gq coupled - release IP(3), increasing intracellular calcium and activating eNOS
=smooth muscle relaxation
Draw a diagram depicting bradykinin and kallidins actions (via B(2))
WELL DOOONE
What is the role of the B(1) receptor, where is it present and what activates it?
B(1) - Gq coupled = same effects as B(2) ie activation of eNOS and smooth muscle relaxation
Up-regulated in inflammation
Activated by the bradykinin which has had its C-terminal arginine removed by kininase I
What causes inactivation of bradykinin?
Removal of the C-terminal Phe (after removal of arg) by kininase II (AKA ACE)
What are the roles of kinins?
Generates plasmin from plasminogen
Causes vasodilation (smooth muscle contraction)
Activates nociceptors
What is the natural inhibitor of kallikrien?
C1 esterase inhibitor (C1-INH)
What is Hereditary Andioedema? What is the treatment?
A rare acute inflammatory condition caused by low levels of C1-INH (C1 esterase inhibitor) and characterised by episodes of severe swelling
A kallikrien inhibitor ecallantide (Kalitor) has been developed (mimic the binding domain of an antibody)
What are tachykinins?
Substances P (AKA NK1) Substance K (AKA NK2) Neurokinin B (AKA NK3)
What is the effect of activation of tachykinin receptors?
Gq coupled so an increase in Ca2+
What is unusual about cytokines?
Not stored by are produced on demand by gene transcription and released by a process of vesicle shedding
Which cells produce cytokines?
Macrophages, T cells and monocytes
Which cytokines are proinflammatory?
IL-1,2,6 and TNF-α
Which cytokines inhibit the production of other cytokines?
IL-4 and 10
Nerve Growth Factor?
Released from activated macrophages
Potent cause of pain in osteoarthritis
Glucocorticoid?
Inhibit the transcription of genes involved in inflammation
Tanezumab?
Antibody which targets NGF
Potent analgesic in osteoarthritis - so effective that patient overuse their joints!
Draw the cleavage sites of phospholipases
WEFEWF
How are lipid-derived mediators of inflammation made?
Produced on demand from membrane phospholipids via the action of phospholipases
What are the common features of the fatty acids on the glycerol backbone?
FA at location 1 is saturate
FA at location 2 is often arachidonic acid (cis double bonds at 5, 8, 11 and 14 positions)
What is generated by the action of phospholipase A2?
Arachidonic acid and lyso-phosphatidylcholine
What happens to arachidonic acid in inflammation?
It is converted to inflammatory mediators by cyclo-oxygenase enzymes or by 5-,12- or 15-lipoxygenase
What is activation of PLA2 dependent on?
A rise in intracellular calcium and activation of GPCRs such as B1 or B2 (= phosphorylation of PLA2)
12-HETE
Chemotactic messenger employed in the migration of leukocytes to the site of injury
Leukotrienes?
Produced predominantly by inflammatory cells such as mast cells and macrophages
What is the role of LTB4?
Stimulates neutrophil and macrophage adherence, chemotaxis and proliferation and cytokine production by macrophages and lymphocytes
What are the cysteinyl-leukotrienes? What do they do?
LTC4, LTD4 and LTE4
‘slow reacting substances of anaphylaxis’
Constrict coronary vessels but increase blood flow and vascular permeability elsewhere
Powerful spasmogens
In what conditions are cysteinyl-leukotrienes important?
Asthma and other inflammatory disorders
they cause bronchospams
Zileuton
A 5-lipoxygenase inhibitor used to prevent the production of cysteinyl-leukotrienes in asthma/ other inflammatory disorders
Zafirlukast
A specific cysteinyl leukotriene receptor antagonist used in the treatment of asthma and other inflammatory conditions
What stimuli result in the production of cysteinyl leukotrienes?
Exercise, dry cold air Adenosine Allergens Aspirin in NSAID-intolerant patients PAF SO2
How is platelet activating factor produced? What is its role?
By replacing the carboxylic acid linker at position 1 with an ether bond
It is a potent platelet aggregator
Also a vasodilator and chemotactic agent for leukocytes
How is platelet activating factor degraded?
Rapidly degraded in vivo by acetyl hydrolase which removed the 2-position acteyl group
What molecule is made by the replacement of the carboxylic acid at position 1 with an ether bond?
Platelet activating factor
What are prostanoids derived from?
Arachidonic acid by cyclo-oxygenase enzymes
What is the life span of a prostanoid?
~1min
What is the role of cyclooxygenase?
It catalyses two distinct reactions
Firstly a cyclo-oxygenase reaction leading to PGG and secondly a peroxidase reaction resulting in PGH2
What is the action of NSAIDs?
Inhibit COX’s production of PGG
Draw the pathway of prostaglandin production and action in platelets
AA => PGH2
Txs converts this to TxA(2)
Transported out of cell by PGT
Acts on TPβ receptor on vascular smooth muscle to cause vasoconstriction
Acts on TPα receptor on platelets to cause aggregation
Draw the pathway of prostaglandin production and action in endothelial cells
AA => PGH(2)
PGH(2) => PGI(2) via the action of PGIS
PGI(2) then acts upon IP receptor on vascular smooth muscle to cause vasodilation
PGI(2) also acts on IP receptors on platelets to cause declumping
Draw the pathway of prostaglandin production and action in mast cells
AA => PGH(2)
PGH(2) => PGD(2) via the action of PGDS
PGD(2) transported out of the cell by PGT
PGD(2) then acts upon DP2 receptors on Th2 lymphocytes to cause chemotaxis
PGD(2) also acts upon DP1 receptors on lung epithelial cells to cause allergic asthma
Draw the pathway of prostaglandin production and action in most cells
AA => PGH(2)
PGH(2) => PGE(2) via PGES
PGE(2) transported out of the cell by PGT
PGE(2) then acts on…
EP(4) receptors on osteoclasts = bone reabsorption
EP(3) receptors on OVLT neurons = fever generation
EP(2) receptors on ovarian cells = maturation for ovulation/fertilisation
EP(2/4) receptors on spinal neurons = Pain response
What is the role of COX1?
Constitutively expressed and is involved in the secretion of stomach acid as well as the production of prostanoids in tissues
What are the inflammatory effects of prostaglandins?
Swelling - PGI(2) acting on IP receptors
= increase in cAMP = smooth muscle relaxation = ^ blood flow
Fever - PGE2 locally produced in the hypothalamus acting locally on neurones via EP3 receptor
= v cAMP
Pain - PGE(2) effects on EP(2/4) receptors
= increase in cAMP = enhances sensory fibre response to other painful signals (hyperalgesia)
What is the action of prostanoids on blood vessel and in platelet aggregation?
PGI(2) produced by endothelial cells has vasodilatory and anti aggregatory action
TXA(2) produced by platelets has vasoconstrictor and pro-aggregatory actions
= produce during endothelial damage to alter the balance in favour of platelet aggregation to seal damage vessels
TXA(3) derived from eicosapentaenoic acid (from fish oil) has lower pro-aggregatory actions so lower probability of thrombus
What happens when there is damage to the endothelium?
Balance is altered in favour of aggregation
= release of TXA(2) and reduced release of PGI(2)
How do fish oils help to reduce the propensity of heart attacks?
Contain eicosapentaenoic acid
Replaces eicosatetranoic acid during prostaglandin synthesis and so produces products containing an extra bond
= reduced pro-aggregatory action of thromboxane A3 compared to A2
What is the effect of prostaglandins on tumour growth?
Believed to enhance tumour growth (in some cases) probably by inhibiting apoptosis, promoting invasion and stimulating angiogenesis
Relates to increase risk of stomach cancer with chronic helicobacter pylori infection
What are non-inflammatory/non thrombotic effects of prostaglandins?
Smooth muscle => contraction or relaxation of smooth muscle (non vascular)
In the kidney => regulates renin release
=> modifies tubular reabsorption
In the stomach => stimulates mucus and bicarbonate secretion
=> Inhibits acid secretion from parietal cells
Where is COX present in the cell?
Attached to the endoplasmic reticulum
How to COX-2 selective drugs achieve their selectivity?
This is due to the fact that they are too bulky to enter the narrower COX-1 channel
Why is paracetamol toxic at high doses?
It is normally eliminated by conjugation, but some of it is converted in the liver to N-acetyl-p-benzoquinone (NAPQI)
NAPQI is normally conjugated to glutathione but in overdose there is insufficient NAPQI
NAPQI oxidises thiol groups on proteins, killing cells
Why is paracetamol overdose often fatal?
Sign do not appear until 24-48hrs = serious hepatic damage can already have taken place
For whom can the toxic dose for paracetamol be lower?
In those with induced liver enzymes through regular use of drugs or alcohol, in people who are malnourished (low levels of glutathione)
What are the adverse effects of NSAIDs? (non including those specific to aspirin)
Nephropathy, prolonged gestation, GI damage, ulceration, bleeding and anaemia
What are the side effects specific to aspirin?
Salicylate poisoning, Reye’s syndrome, hypersensitivity reactions
What are the pharmacological strategies employed to reduce the GI effects of NSAIDs?
Enteric coating NSAID prodrug NSAID + NO NSAID + misoprostol NSAID + proton pump inhibitor NSAID + Vit C Selective COX-2 inhibitors Inhibition of COX and 5-LOX
How does an enteric coating aim to reduce the GI side effects of NSAIDs?
Reduces topical damage (Released more slowly)
Doesn’t work (Sorensen HT et al)
How does an NSAID prodrug aim to reduce the GI side effects of NSAIDs?
Minimises level of active drug in gastric mucosa
How does using NSAID + NO aim to reduce the GI side effects of NSAIDs?
Slow release of gastroprotective NO
How does an NSAID + misoprostol aim to reduce the GI side effects of NSAIDs?
PG substitute
How does use of an NSAID + proton pump inhibitor aim to reduce the GI side effects of NSAIDs?
Prevents acid secretion (reduces risk of gastric ulceration/ GI bleeding)
How does using an NSAID + Vit C aim to reduce the GI side effects of NSAIDs?
Antioxidant effect
Celecoxib
COX-2 selective NSAID - selectivity due to bulky side groups
Increased risk of ulcer rupture due to COX-2’s role in healing
Ibuprofen
Weakly COX-1 selective NSAID
Rofecoxib
COX-2 selective NSAID - selectivity due to bulky side groups
Increased risk of ulcer rupture due to COX-2’s role in healing
Also increased risk of MI (withdrawn)
Paracetamol
Antipyretic and analgesic
May act on COX-3 isoform in brain
Shown to selectively inhibit COX-2 ( Hinz, Chermina and Bruce 2007)
AM404 may act through endogenous cannabinoig system to reduce amanaditine reuptake = activation and desensitization
AM404 can also inhibit Na+ channels (like local anaesthetics)
Also acts on spinal TRPA1 = depolarising block
What is the metabolic pathway for the synthesis of serotonin its breakdown?
Tryptophan
tryptophan hydroxylase
5-hydroxytryptophan
L-aromatic acid decarboxylase
5-HT
Monoamine oxidase
Aldehyde dehydrogenase
5-HIAA
Name the types of antiemetic drugs
5-HT antagonists eg ondansetron
D2 antagonist eg metoclopramide, phenothiazines
Muscarinic antagonist eg scopolamine
Non-selective H1 antagonist eg mepyramine
Ondansetron
Anti emetic drug
5-HT antagonist
Metoclopramide
D2 antagonist used as an antiemetic
Phenothiazines
D2 antagonists used as antiemetics
Scopolamine
Muscarinic receptor antagonist used as antiemetic
Mepyramine
Non-selective H(1) antagonist used as an antiemetic
Draw the areas of the body and receptors involved in emesis
Add on where antiemetic drugs act
DIAGRAM IN NOTES
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What are the three theories as to the cause of migraines?
Vascular hypothesis
Brain hypothesis
Sensory nerve hypothesis
What are the three phases of a migraine?
The premonitory phase
The aura phase
The headache phase
How did the vascular hypothesis originate?
When it was found that interfering with the meningeal blood vessels during surgery caused headache.
What is the Vascular Hypothesis of migraines?
Theory suggests that constriction of intracerebral arteries produces aura and rebound extracerebral vasodilation produces headache
What happens in the premonitory phase of a migraine?
Symptoms include fatigue, irritability, difficulty concentrating, mood change, yawning, stiff neck, phonophobia and nausea
What happens in the aura phase of a migraine?
Cortical spreading depression causing activation of nociceptive pathways - hypothesised that CSD can be a direct cause of headache
What is the evidence again cortical spreading depression as the cause of headache?
Studies into the timing of migraine relative to aura indicates that headache and other migraine symptoms commonly occur simultaneously with aura
What is the evidence and counter evidence for the involvement of vasodilation in migraine?
Studies showed that both the middle meningeal artery and middle cerebral artery were slightly dilated on the same side as migraine evoked by infusion of calcitonin gene-related peptide
BUT
MRI studies show that migraine headache was not correlated with any significant dilation of cerebral or meningeal arteries
What might be the reason for the discrepancy in evidence regarding the role of vasodilation in migraines?
May the result of different techniques or a reflection of different triggers that were used to evoke migraine
What is the brain hypothesis of migraines?
Links migraine to a wave of cortical spreading depression ie neural inhibition associated with ionic imbalances
What is the sensory nerve hypothesis of migraines?
Sensory nerve hypothesis suggests that activation of trigeminal nerve terminals innervating meningeal blood vessels release neuropeptides eg CGRP causing neurogenic inflammation and vasodilation of meningeal blood vessels
Explain the stage of Cortical Spreading Depression and Trigeminovascular Nociception
CSD is initiated by local elevations of extracellular K+ above a critical level as a result of hyperactive neuronal circuits in the cerebral cortex
CSD is a slowly propagating wave of strong neuronal and glial depolarisation
Other noxious mediators such as H+, NO, AA and 5-HT are released (aswell as neurotransmitters)
These substance may activate trigeminal nociceptors innervating pial blood vessels and via axon collaterals, dural trigeminal afferents
= meningeal afferents after disruption of the BBB, leading to activation of central trigeminovascular neurons
= release of proinflammatory vasoactive neuropeptides (including CGRP, substance P and neurokinin A)
= neurogenic inflammation in the dura (and sensitisation)
What is the role of 5-HT in migraines
Thought to be involved because 5-HT(1D) agonists are remarkably effective in suppressing migraine
What are the drugs treatments for migraines?
To terminate the attack:-
NSAIDs, triptans (5-HT(1) agonists) eg sumatriptans; alkaloids (nonspecific 5-HT(1) agonists) eg ergotamine
Preventative:-
Valproic acid; β-adrenoceptor blockers; Ca2+ channel blockers
Sumatriptan?
Triptan 5-HT(1) agonist used in the treatment of migraines
Ergotamine?
Ergot alkaloid - non-specific 5-HT(1) agonists used in the treatment of migraines
Valproic acid
Used as a preventative measure against migraines
May act through the blockade of voltage dependent sodium channels and increased GABA levels
What are the potential target receptors in the treatment of migraines?
5-HT(1B) receptors => vascular smooth muscle constriction
5-HT(1D) receptors => on sensory nerves = inhibition of peptide release from trigeminal neurons (CGRP etc)
Also development of CGRP antagonists
