Pharmacology Flashcards
Drug targets are usually?
Proteins
What do anti-acid drugs target?
Protons
Types of protein targets?
Receptors
Enzymes
Ion channels
Transporters
What is a ligand?
The endogenous molecule that binds to a receptors to illicit a response
Examples of ligands?
Neurotransmitters
Hormones
Growth factors
Cytokines
Metabolites
How do ligands cause a response?
Ligand binds receptor
Receptor activated
Signal transmitted from outside cell to inside cell
Signal relayed to effector proteins via signalling pathway
Effector mediates response
Signals can be relayed from a receptor via?
Protein kinases
GTP-binding proteins or G-proteins
Seconds messengers
Calcium ions
What do protein kinases do?
Add phosphate molecules to amino acids in proteins (protein phosphorylation)
Enzyme function can be regulated by addition or removal of a covalently bonded phosphate group
Two main types of protein kinases?
(a) serine/threonine kinases
(b) tyrosine kinases
How does protein phosphorylation change protein shape?
Each phosphate group carries a 2- charge
Binding to an amino acid causes surround positively charged amino acids to move closer causing a conformational change to the proteins shape
How can phosphorylation affect proteins?
1) change to activity- can affect binding of ligands to proteins, change in shape can effect intrinsic activity
2) mask binding sites- disrupting protein-protein interactions
Picture of the protein kinase cascade
What activity to G-proteins have?
GTPase activity
What is GTPase activity?
An enzymatic activity able to hydrolyse GTP to GDP
What can G-proteins bind?
GTP
GDP
How to tell if G-protein is active or inactive?
Active if bound to GTP
Inactive if bound to GDP
What are second messengers?
Small molecules and ions that relay signals received by cell-surface receptors to effector proteins
Examples of second messengers?
Cyclic AMP (synthesised from ATP by adenylyl cyclase)
Cyclic GMP (synthesised from the nucleotide GTP using guanylyl cyclase)
Nitric oxide
Calcium
Four major classes of receptors?
G Protein-couples receptors (GPCR)(metabotropic)
Ligand gated ion channels (ionotropic)
Enzyme-linked receptors
Nuclear receptors
What is a G protein-coupled receptor?
Ligand binding to receptor activates a G-protein which then activates or inhibits an enzyme or ion channel
What is a ligand gated ion channel?
Ligand binding to ion channel causes it to open or close. Conformation change takes place
What are enzyme-linked receptors?
Ligand binding to the receptor activates the intrinsic enzymes activity of the receptor or associated enzyme. Conformation change takes place
What are nuclear receptors?
Intracellular receptors. Ligand binding activates the receptor which then acts as a transcription factor to alter gene expression
What is steady state?
When the rate the drug enters the plasma is equal to its clearance from plasma
How to calculate constant infusion rate?
Maintenance dose rate/clearance from single IV dose
How many half-lives until steady state is reached?
~5
What can be done if steady state needs to be reached sooner?
Use a loading dose
How to calculate loading dose?
Steady state X volume of distribution
How to calculate steady state with an infusion?
Maintenance dose rate/clearance
How to calculate steady state with an oral drug?
Bioavailability X Maintenance dose rate/clearance
What else needs to be considered with steady state when using intermittent dosing?
Variability of drug concentration
Must be above minimum effective concentration and below minimum toxic concentration
General dosing regimens in relation to half-life?
<30 mins- difficult to maintain therapeutic concentrations
30mins- 8 hours- based upon range of therapeutic index and dosing interval convenience
8 hours -24 hours- most desirable half-life, usually given every half-life
>24 hours- usually once daily, sometimes every several days. Delays in reaching steady state
What is the structure of a GPCR?
Single polypeptide chain
Contain seven alfa-helical transmembrane domains
All are glycoproteins
Why is the 3rd intracellular loop and C-terminal tail of GCPRs important?
Highly variable in length and sequence
Responsible for G protein interaction
Contain sites of phosphorylation
Subunits of a G protein?
Alpha
Beta
Gamma
Which subunits of a G protein form a complex?
Beta and gamma
Form beta-gamma complex, a stable dimer
Which subunits of a G protein associate with the plasma membrane?
Alpha and gamma
What G protein subunit does GTP/GDP bind to?
Alpha
It has GTPase activity
How does GPCR signalling work?
1) hormone binds to receptor and causes conformation change in receptor
2) activated receptor binds to alpha subunit of G protein
3) binding causes conformational change in alpha subunit, GDP dissociates and is replaced by GTP
4) alpha subunit dissociates from beta-gamma complex
5) alpha subunit binds to effector protein activating or inhibiting it
What is the effector protein for Gs?
Adenylyl cyclase
What does Gs stand for?
Stimulatory
What is the second messenger for Gs?
Increased cAMP
What does Gi stand for?
Inhibitory
What is the effector protein for Gi?
Adenylyl cyclase
What is the second messenger for Gi?
Decreased cAMP
What is the effector protein for Gq?
Phospholipase C
What are the second messengers for Gq?
IP3 and DAG
Examples of GsPCRs and drugs that bind?
B-receptors- salbutamol, propranolol
H2- ranitidine
Glucagon
Some 5HT- amitriptyline
What does cAMP activate?
Protein kinase A
The Gs protein is activated by which toxin?
Cholera
What do phosphodiesterase do?
Turn cAMP to 5’AMP
Examples of GiPCRs and drugs that bind?
Alpha-2 clonidine
Opioid receptor codeine
Some 5HT sumatriptan
What toxin inactivates Gi?
Pertussis
What does the beta-gamma complex do in GiPCRs/GsPCRs?
Regulates ion channels
Which is faster? G-protein gated ion channels or ligand gated ion channels
Ligand gated
Examples of GqPCRs?
Some 5-HT
Adrenergic alpha-1
Vasopressin type 1
Angiotensin II type 1
H1
M1 M3 M5
Examples of drugs that target GsPCRs?
Propranolol
Salbutamol
Ranitidine
Amitriptyline
Examples of drugs that target GiPCRs?
Clonidine
Codeine
Sumatriptan
Examples of receptors and drugs that target GqPCRs?
H1 Loratadine
Alpha-1 doxazosin
Angiotensin II Losartan
IP3 promotes an increase in?
Intracellular calcium
What does DAG activate?
Protein kinase C
What does PIP2 do?
Gets cleaved to IP3 and DAG
What does PIP2 stand for?
Phosphatidyl inositol 4, 5 bisphosphate
What does IP3 stand for?
Inositol 1, 4, 5-trisphosphate
What does DAG stand for?
Diacylglycerol
What is receptor desensitization?
Where repeated exposure of the agonist leads to a decreased response
Most common ligand of ligand-gated ion channels?
Neurotransmitters
Examples of ligand-gated ion channel receptors?
GABA receptors
Some 5-HT
NMDA receptors
Examples of drugs that target ligand-gated ion channel receptors?
Benzodiazepines
Z drugs
Memantine
Ketamine
Mirtazapine
The two domains of ligand-gated ion channels?
Transmembrane domain including the ion pore
Extracellular domain containing the ligand binding location
Three families of ligand-gated ion channels?
Cys-loop
Ionotropic glutamate receptors
ATP-gated channels
Ligand-gated ion channel structure?
Pentameric- made up of five subunits
Beta, delta, gamma and 2 x alpha
What type of ligand-gated ion channels are stimulatory?
Cation selective
What type of ligand-gated ion channels are inhibitory?
Anion selective
Example of a cation selective ligand-gated ion channel?
Nicotinic acetylcholine receptor (nAchR)
Example of a anion selective ligand-gated ion channel?
GABAa
How many different classes of enzyme linked receptors are there?
Seven
Two important classes of enzyme linked receptors?
Receptor tyrosine kinases (RTKs)
Cytokine receptors
What kind of activity do receptor tyrosine kinases have?
Intrinsic tyrosine kinase- they phosphorylate their substrate proteins on the amino acid tyrosine
What do receptor tyrosine kinases respond to?
Peptide/protein ligands
Common structure of receptor tyrosine kinases?
N-terminal extracellular ligand-binding domain
Single transmembrane alpha helix
Cytosolic C-terminal domain with protein kinase activity
Usually a single polypeptide
Example of a receptor tyrosine kinase that is not a single polypeptide?
Insulin- a dimer
What are mitogens?
Ligands that stimulate cell division
What are growth factors?
Ligands that stimulate cell growth
Activation of receptor tyrosine kinases?
1) ligand binds and causes dimerisation of receptor
2) activation of tyrosine kinase domain by trans-autophosphorylation, creating binding sites for proteins
4) proteins bind and are activated
5) proteins relay signal downstream leading to response
What does MAPK stand for?
Mitogen activated protein kinase pathway
What is the Mitogen activated protein kinase pathway
Activated growth factor receptors can activate a G-protein calles Ras
Ras activates a protein kinase cascade
Promotes cell division
Mutant Ras is associated with?
Cancer
Types of tyrosine kinase inhibitors?
Small molecule TK inhibitors
Monoclonal antibodies
Where do small molecule TK inhibitors target?
ATP-binding cleft
Where do monoclonal antibodies target?
Extracellular ligand binding domain or the ligand
Examples of small molecule TK inhibitors?
Imatinib
Sunitinib
Example of monoclonal antibodies?
Trastuzumab
Cetuximab
What are cytokine receptors stably associated with?
Janus kinases
What does JAKs stand for?
Janus kinases
JAKs activate transcription factors called?
Signal transducers and activators of transcription
What does STATs stand for?
Signal transducers and activators of transcription
Cytokine receptor activation?
1) ligand binds and leads to dimerisation of receptor
2) this activates JAK
3) JAK phosphorylates itself and the receptor and STATs
4) STATs translocate to nucleus, bind DNA and regulate gene expression
Where can cytokine receptors be targeted?
The binding domain
The ligand
Examples of cytokine based drugs?
Anakinra
Peginterferon alpha
Adalimumab
Basiliximab
Tocilizumab
Where is noradrenaline release from?
Adrenergic neurones and adrenal gland
Where is adrenaline release from?
Adrenal gland
What type of receptors are adrenergic receptors?
GPCRs
What are catecholamines?
Compounds containing a catechol moiety and an amine side chain
What is a catechol moiety?
A benzene ring with two adjacent hydroxyl groups
What amino acid are catecholamines synthesised from?
Tyrosine
Catecholamine synthesis?
What happens when smooth vascular muscle alpha receptors are activated?
Vasoconstriction
What happens when heart muscle beta-1 receptors are activated?
Increase force of myocardial contraction
Increased heart rate
What happens when airway smooth muscle b-2 receptors are activated?
Bronchodilation
What happens when B-3 receptors are activated?
Lipolysis
What happens when smooth muscle A-1 receptors are activated?
Increase intracellular calcium and contraction apart from smooth muscle where it relaxes
What happens when a-2 receptors are activated at pre-synaptic neurones?
Decrease calcium and contraction
Example of a B-receptor agonist?
Isoprenaline
Adrenaline
Noradrenaline
Example of a B receptor antagonist?
Propranolol
Example of a B-2 receptor agonist?
Salbutamol
Example of an a-1 receptor antagonist?
Doxazosin
Alfuzosin
Example of an a-2 antagonist?
Clonidine
Guanfacine
How do a-1 receptor antagonist work?
Relax smooth muscle in arteries and veins thus decrease systemic arterial blood pressure
How do a-2 receptor agonists work?
Reduce noradrenaline release to decrease both heart rate and blood pressure
What type of G-protein do a-1 receptors have?
Gq
What type of G-protein do a-2 receptors have?
Gi
What type of G-protein do B receptors have?
Gs
Where are most a-1 receptors found?
Smooth muscle
Where are most a-2 receptors found?
Presynaptic nerves
Where are most b-1 receptors found?
Heart
Where are most b-2 receptors found?
Smooth muscle
Where are most b-3 receptors found?
Fat tissue
Examples of a-1 agonists?
Phenylephrine
Metaraminol
How do a-2 agonists reduce noradrenaline release?
Cause hyperpolarisation by K+ efflux from a G-protein gated channel, therefore reducing neuronal activity
How does theophylline work?
PDE 3 and 5 inhibitor
What are sympathomimetic drugs?
Produce similar action to adrenaline and noradrenaline. Also called adrenergic drugs
What are sympatholytic drugs?
Interfere with actions of sympathetic nervous system stimulation, also called anti-adrenergic drugs
Example of a selective B-1 agonist?
Dobutamine
What do cholinesterase do?
Break down acetylcholine
What are the two forms of cholinesterase?
Acetylcholinesterases
Plasma cholinesterases
Acetylcholine is hydrolysed to?
Choline and acetic acid
What do anticholinesterases do?
Slow or prevent the degradation of acetylcholine released at synapses
Three groups of anticholinesterases?
Short-acting
Medium acting
Irreversible
How do short-acting anticholinesterases work?
They are mono-quaternary ammonium alcohols. They bind to the anionic site of cholinesterases and competitively replace acetylcholine from the site
Example of a short-acting anticholinestrase?
Edrophonium (used as diagnostic aid for myasthenia gravis)
How do medium-acting anticholinesterases work?
Interact with serine hydroxyl of the esteratic site to give a carbamylated produced which is hydroxylated slower
Example of a medium-acting anticholinestrase?
Pyridostigmine
Neostigmine
How do irreversible anticholinesterases work?
Phosphorylates the serine hydroxyl group of esteratic site. Takes days to regenerate the enzymes.
Example of an irreversible anticholinestrase?
Organophosphates (chemical weapons and insecticides)
Antidote for irreversible anticholinesterases?
Pralidoxime
Uses of anticholinesterases?
Reversal of NMBAs
Myasthenia gravis
Alzheimer’s (donepezil)
What causes myasthenia gravis?
Circulating antibodies that block acetylcholine from binding to nicotinic reception at the neuromuscular junction
What type of receptors do cholinergic transmitter act on?
Nicotinic
Muscarinic
Where are nicotinic receptors found?
Neuromuscular junctions in skeletal muscle
Autonomic ganglia
Postsynaptic at both sites
Examples of nicotinic agonists that act at the neuromuscular junction?
Suxamethonium
Examples of nicotinic agonists that act at the autonomic ganglia?
Nicotine
Varenicline
Examples of nicotinic antagonists that act at the neuromuscular junction?
Rocuronium
Pancuronium
Atracurium
Examples of nicotinic antagonists that act at the autonomic ganglia?
Timethaphan
Hexamethonium
Examples of nicotinic antagonists that act at the autonomic ganglia?
Trimethaphan (hypertensive emergencies)
Why are neuromuscular blocking agents given intravenously?
Most are quaternary ammonium compounds which penetrate cell membranes poorly
Effects of muscarinic receptor agonists?
1) smooth muscle contraction
2) pupillary constriction, ciliary muscle contraction
3) decrease rate and force of heart
4) increases glandular secretion
5) increases gastric acid secretion
6) vasodilation through release of nitrous oxide
7) inhibition of neurotransmitter release
Effects of muscarinic receptor antagonists?
1) inhibition of secretion
2) increase heart rate
3) papillary dilation
4) relaxation of smooth muscle
5) inhibition of gastric secretion
6) antiparkinson action
7) anti-emetic action
Example of muscarinic receptor agonist?
Pilocarpine
Example of muscarinic receptor antagonist?
Atropine
Hyoscine
Ipratropium
Tiotropium
Oxybutynin
Tropicamide
Effects of B-2 stimulation in the airways?
Bronchodilation
Inhibition of cytokine and leukotriene release
Inhibit plasma exudation
Inhibit cholinergic transmission
Increase mucus clearance
Order of affinity of neurotransmitters to alpha receptors?
Adrenaline=noradrenaline>isoprenaline
Order of affinity of neurotransmitters to beta receptors?
Isoprenaline>adrenaline>noradrenaline
How do depolarising NMDAs work?
Activate the nicotinic receptor and produces initial contraction of muscle fibre. The maintained depolarisation event leads to the inactivation of sodium channels. Preventing further action potentials
How do non-depolarising NMBAs work?
Act as competitive antagonists at nicotinic receptor sites. Competes with acetylcholine to block transmission
What type of receptors are nicotinic receptors?
Inonotropic
What kind of receptors are muscarinic receptors?
GPCRs
What receptor does clonidine bind to?
Alpha 2
Activation of Gq receptors?
Ligand binds receptor
Phospholipase C becomes active
Alpha unit dissociations
PIP-2 cleaved to IP3 and DAG
IP3 binds SER to release Ca2+
DAG binds protein kinase C
Protein kinase C phosphorylates target proteins
Activation of Gs receptors?
Ligand binds receptor
Adenylyl cyclase activated and alpha subunit dissociates
Increase cAMP
cAMP binds protein kinase A
Target proteins phosphorylated
Activation of Gi receptors?
Ligand binds receptor
Adenylyl cyclase becomes active and alpha subunit dissociates
Reduction in cAMP so cannot bind protein kinase A
