Targeting local mediators. Flashcards
1
Q
What is inflammation resolution and why is it important?
A
- Resolution involves:
1. Removal of pro-inflammatory mediators
2. Neutrophil apoptosis
3. Release of pro-resolving mediators
4. Transformation of M1 (inflammatory) macrophages to M2 (phenotype) - Needed to limit damage done by inflammatory process.
- Failure of resolution leads to chronic inflammation.
2
Q
What is the role of neutrophils?
A
- Neutrophils play an important role in resolution of inflammation.
- Drugs such as NSAIDs that block neutrophil function may trigger chronic pain
- Drugs such as paracetamol help control pain without impacting neutrophil function and prevent development of chronic pain
3
Q
List some local mediators.
A
- Prostaglandins and Leukotrienes
- Platelet activating factor (PAF)
- Histamine
- 5-hydroxytryptamine
- Nitric oxide
- Neuropeptides
- Bradykinin
- Adenosine and Purines
- Complement
- Cytokines
4
Q
What are the features of the local mediator: histamine.
A
- Originally chemically synthesised then Isolated from many tissues and named histamine.
- Found to stimulate smooth muscle and to have vaso-depressor action (1911).
- Synthesised from histidine by histidine decarboxylase and Metabolised by histaminase.
- Released by injured tissue.
- Highest concentration in lungs, skin and GIT and found in Mast cells and Basophils.
- It is also a CNS neurotransmitter.
5
Q
Discuss histamine release.
A
- It is stored in intracellular granules.
- Release is triggered by binding of IgE to receptors on mast cells.
- Also released by binding of complement fragments C3a and C5a to receptors.
- Release occurs following a rise in intracellular Ca and is inhibited by an increase in cAMP.
- Non-receptor release also occurs e.g. morphine
6
Q
What are the histamine receptors and where are they found?
A
- H1 receptors (Gq): main peripheral receptor found on smooth muscle and causes a rise in intracellular Ca.
- H2 receptors (Gs): found in the acid-secreting cells of the gut and activate adenylate cyclase.
- H3 receptors (Gi): found in CNS pre-synaptic.
- H4 receptors (Gi) are found on haematopoietic cells.
7
Q
What are the effects of histamines?
A
- Causes capillary vasodilation
- Acts on post-capillary venules to cause contraction of endothelial cells leading to increased permeability & oedema.
- During anaphylaxis large amounts of histamine are released.
- Blood pools in small vessels whose permeability increases decreasing plasma volume leading to decreased cardiac output and shock.
8
Q
What is a triple response?
A
- Occurs with injected histamine.
- Reddening of the skin due to direct vasodilation by histamine (0-1min)
- Larger brighter red spot or flare and itch due to axon mediated vasodilation via histamine.
- Formation of a wheal due to localised oedema (1-2 min)
9
Q
What are the antagonistic properties of histamines?
A
- Actions and uses of histamine antagonists depend on 3 properties:
1. Selectivity for H1 over H2 receptors.
2. Anti-muscarinic effects cause sedation in CNS and dry mouth and blurred vision in periphery.
3. Ability to cross the blood brain barrier causes sedation and anti-emesis. - Agents are inverse agonists rather than antagonists.
10
Q
Discuss antihistamines and their categories.
A
- First generation cross the blood brain barrier:
- Diphenhydramine
- Can have anti-muscarinic activity
- More side-effects: Drowsiness & Dry mouth - Second generation do not cross the blood-brain barrier:
- Cetirizine
- Loratidine
- Fewer side-effects
- Some members withdrawn from the market due to arrhythmias
11
Q
What are the uses of antihistamines?
A
- Most effective in allergic rhinitis and conjunctivitis.
- In other conditions: asthma and anaphylaxis used as adjunct therapy.
- 1st generation are old drugs with lack of good quality clinical studies.
- Ideal compounds are second generation.
** Only first generation antagonists can be used for motion sickness.
12
Q
What are the benefits of H1 antagonists?
A
- They down-regulate allergic inflammation mainly through the H1-receptor.
- May potentially cause adverse effects not only through H1-receptors in the central nervous system but also through the muscarinic, α- adrenergic, and serotonin receptors and cardiac ion channels.
13
Q
What is anaphylaxis?
A
14
Q
Discuss anaphylaxis management.
A
- Anti-histamines: block the action of the primary mediator of anaphylaxis but only effective if used early
- Adrenaline: Immediate increases heart rate and causes vasoconstriction leading to resolution of
hypotension - Steroids: used to reduce the inflammation
- Anti-IgE (omalizumab): Used to prevent immune complex binding to mast cells used for prophylaxis
15
Q
What is serotonin/ 5- hydroxytryptamine?
A
- Clotted blood produces a serum vasoconstrictor which was named serotonin and later identified as 5- hydroxytryptamine.
- Mainly found in GIT enterochromaffin cells.
- Also found in platelets and CNS.
- Synthesised in cells, except platelets which accumulate it from GIT.
16
Q
What are the actions of 5-HT?
A
- Increases gastrointestinal motility.
- Vasoconstriction of large blood vessels due to action on smooth muscle cells.
- Vasodilation due to direct action on endothelial cells which release NO.
- Dilation of arterioles; constriction of venules increased capillary permeability.
- Enhances platelet aggregation.
- 5-HT released from platelets causes vasodilation in undamaged vessels but vasoconstriction in damaged vessels.
- May play a role in peripheral vascular disease.
- Causes pain and itching by direct action on sensory nerves.
- Major driver of organ dysfunction in sepsis.
**IV 5-HT: initial increase in blood pressure followed by a decrease.
17
Q
What are 5 HT receptors?
A
- 7 families of 5-HT receptor all G-protein linked except 5-HT3.
- 5-HT1 receptors (A-F): found in CNS except for 5-HT1D which causes cerebral vasoconstriction, decrease cAMP
- 5-HT2 receptors (A-C): found in smooth muscle cells and platelets. Increase IP3.
- 5-HT3 peripheral nervous system: involved in nociception. Ion channel linked.
- 5-HT4 found in GIT, increases peristalsis. Increase cAMP.
- Also 5-HT5, 5-HT6, 5-HT7,
18
Q
What are the major therapeutic roles of 5 HT?
A
- 5-HT1A agonists in anxiety (eg busiprone)
- 5-HT1D agonists in migraine
- 5-HT2 antagonists in hypertension (ketanserin)
- 5-HT3 antagonists for emesis (eg ondansetron)
19
Q
Discuss neurogenic inflammation.
A
- It is due to release of inflammatory mediators (especially neuropeptides) from small- diameter primary afferent C- fibres rather than immune cells causing vasodilation.
- Calcitonin gene-related peptide (CGRP)
- Migraine is the classic example of neurogenic inflammation.
20
Q
What is calcitonin gene-related peptide (CGRP)?
A
- A highly potent vasodilator.
- CGRP is primarily released from sensory nerves and thus is implicated in pain pathways.
21
Q
What are triggers of neurogenic inflammation?
A
22
Q
What causes migraines?
A
- Provoked by infusion of calcitonin gene-related peptide (CGRP).
- CGRP, a neuropeptide released from activated trigeminal sensory nerves, dilates intracranial and extra-cranial blood vessels and centrally modulates vascular nociception.
23
Q
Discuss methods for targeting CGRP.
A
- Anti-CGRP receptor antibodies: Erenumab
- Anti-CGRP antibodies: Fremanezumab, Galcanezumab, Eptinezumab.
- Small molecule CGRP antagonists, Ubrogepant, Rimegepant
24
Q
Discuss the treatment of acute migraine treatment.
A
- NSAIDS and/or paracetamol
- Anti-emetic if required
- Triptans: 5-HT1agonists
- Frovatriptan
- Zolmitriptan - Ergotamine (ergot alkaloid):
- 5-HT1agonist
- Adverse effects due to activity on other 5-HT receptors, noradrenergic and dopaminergic receptors.
- Cannot be used in patients with coronary artery disease.
- Sumatriptan, an agonist is very effective but expensive.
- Ubrogepant (CGRP antagonist)
- Lasmiditan (5HT1F agonist)
25
Discuss migraine prophylaxis.
- Avoid triggers
- β-adrenoreceptor antagonists
- Amitriptyline (anti-depressant)
- Topiramate (anti-psychotic)
- Onabotulinumtoxin A (Botulinum toxin, Botox):
*chronic migraine only
- Anti-Calcitonin Gene-Related Peptide treatment – Erenumab (anti-CGRP receptor antibody)
- Fremanezumab (anti-CGRP antibody)
26
What is Endothelium-derived relaxing factor (EDRF)?
- Acetylcholine relaxes aorta strips pre-contracted with noradrenaline.
- Relaxation does not occur if the endothelium is damaged.
- Endothelium-derived relaxing factor (EDRF) is involved.
- It is released by Ach, Substance P, ADP, bradykinin, histamine, 5- HT.
27
What is Nitric oxide (NO)?
- NO is a gas and is different from Nitrous oxide the aneasthetic.
- NO is a free radical and is therefore unstable with a short half life.
- NO can be produced enzymatically or chemically
28
What is the use nitric oxide?
- Effects of administered nitrates - nitroglycerin or sodium nitroprusside is due to generation of NO*
- Endothelium is not required for their effects
- Potent vasodilators
29
Does EDRF = NO?
Compare:
- Both have short half life (3-5 sec)
- Both are inhibited by superoxide anion, methylene blue and hemoglobin
- Both lead to an increase in cGMP levels
- Conclusion EDRF=NO
30
How is nitric oxide produced?
- Gβ subunit is responsible for activation
- Produced by Nitric oxide synthase (NOS)
- Exogenous NO comes from spontaneous or enzymatic degradation of NO donors e.g., nitrates
- NO diffuses from endothelial cells to smooth muscle cells.
31
What is the function of NO synthase?
- Converts arginine to citrulline
- Requires tetrahydrobiopterin as a cofactor
- Requires heme as a cofactor
- NOS is activated by Ca2+/calmodulin
- Also activates guanyl cyclase.
32
What are NOS isoforms?
Different isoforms of NOS:
- nNOS/NOS 1 found in neurons
- eNOS/NOS3 found in endothelial cells
- nNOS and eNOS are constitutive
- iNOS/NOS2 is inducible
33
What are the effects of cGMP?
- Acts directly on ion channels, e.g., inhibits Na+ channel in kidney.
- Phosphorylation by cGMP - dependent kinase PKGe.g., decrease in Ca2+ in platelets and smooth muscles.
- cGMP: stimulated phosphodiesterase (II): decrease in cAMP
- cGMP-inhibited phosphodiesterase(III): cAMP increase e.g. Ca2+ in platelets
34
What is the role of phosphodiesterase (PDE)?
- Phosphodiesterase (PDE) breaks down cGMP and cAMP.
- PDEs are dimeric
- There are 11 PDE’s
- PDE4,7&8 are specific for cAMP
- PDE 5, 6 & 9 are specific for cGMP
- PDE 1, 2, 3, 10 & 11 are non-specific
35
What is the role of PDE5?
- cGMP&Zn2+-binding PDE
- Binding of cGMP to catalytic site increases binding of cGMP to the allosteric sites
- cGMP binding leads to phosphorylation by PKG which increase PDE activity
36
What is the role of PDE 6 & 9?
- PDE6 is found in both the cone and rod
- Plays an important role in vision
- Activated by a G-protein (transducin)
- PDE9 is not a cGMP-binding PDE
- PDE9 is widely distributed, function unknown
37
What are the physiological effects of NO?
- Vascular effects: vasodilation & inhibition of platelet aggregation.
- Immunological effects: inhibition of neutrophils & monocytes.
- Found in the brain. It is produced after stimulation with NMDA. May play a role in gastric emptying, memory, appetite control and nociception
38
What are the effects of NO in sex?
- Plays an important role in generating an erection.
- NO from nitrergic nerves induces vasodilation.
- NO may play a similar role in females where it may cause erection of the clitoris?
39
What are the pathological effects of NO?
- NO radical binds to O2- radical to form the peroxynitrite (ONOO-) radical.
- Peroxynitrite radical produces the OH radical.
- Peroxynitrite and OH radicals can destroy invading microorganisms but can also be cytotoxic.
40
What are NO donors?
- Compounds that act by releasing NO
- Include nitro-vasodilators:
1. Amyl nitrite
2. Glyceryl trinitrate
3. Isosorbide dinitrate
4. Sodium nitroprusside
- Mechanism of NO release is unknown but is enhanced by cysteine and glutathione
41
What is the use of NO donors?
- Prevents reperfusion injury (infarct size, stunning and ventricular fibrillation) in the heart by inhibiting neutrophils.
- Dilates large coronary vessels and diverts blood flow in collateral vessels to ischeamic area as in angina.
42
What is nitrate tolerance?
- Tolerance to nitrates develops requiring nitrate free periods.
- Can be due to increased superoxide production
- Nitrate treatment also leads to up-regulation of PDE1A1 in SMC.
43
What are PDE5 inhibitors?
- Inhibition of PDE5 prevents breakdown of cGMP, prolonging its action
- Sildenafil is a selective PDE5 inhibitor approved in 1998.
- Can be used with Iloprost in primary pulmonary hypertension and also used for altitude sickness.
44
Discuss Sildenafil dosing.
1. Viagra:
- 50mg 1 hr before sex
- Max 100 mg daily
- For erectile dysfunction
2. Revatio:
– 20mg 3x daily
– For Pulmonary hypertension
