Drug Action 1 Flashcards
What are drug targets?
Proteins
What proportion of drugs interfere with membrane receptors?
30-50%
What is the primary site of drug interference?
Membrane receptors
How many categories of drug receptors are there?
Four
What are the four broad categories of receptor?
Ligand gated ion channels, GPCR receptors, kinase-linked and nuclear receptors
What is the fastest receptor?
Ligand gated ion channels
What is the one common feature to all receptors?
Binding domain
Approximately how many asthma sufferers are there in the UK?
5.4 million
Describe the early phase of an asthma attack.
Mast cells in lungs secrete histmines; these signal other immune cells (causes late phase; shortness of breath, especially when breathing out; cough
Describe the late phase of an asthma attack.
Secondary inflammatory immune response; inflammation of the airways
Describe bronchial hyper-reactivity.
Long term changes in the lungs - mast cells migrate to smooth muscle layer which increases long term sensitivity
What is the effect of mast cell migration to the smooth muscle layer of the lungs?
Increased long term sensitivity
What is the term given to the situation where mast cells have migrated to the smooth muscle layer of the lungs?
Bronchial hyper-reactivity
What are the two main anti-asthmatic drug groups?
Bronchodilators and anti-inflammatory agents
Give one example of a bronchodilator.
Salbutamol
Give two examples of anti-inflammatory agents.
Pednisolone & omalizumab
How does omalizumab work?
A humanised antibody, it stops mast cells from responding
What reduces the efficacy of bronchodilators?
Polymorphisms in ß2-adrenoceptors
What do polymorphisms in ß2-adrenoceptors cause?
Reduced efficacy of bronchodilators
What kind of disease is myathenia gravis?
Autoimmune disease
How common is myasthenia gravis?
1 in 2000
What is the main symptom of myasthenia gravis?
Muscle weakness
What is the main cause of myasthenia gravis?
Decreased nAChR in neuromuscular junctions
What does NMJ stand for?
Neuromuscular junction
What is the primary treatment for myasthenia gravis?
Anti-cholinesterase and immunosuppressants
What are the two steps involved in agonist function?
Bind to the receptor, cause a response
Define affinity.
The strength of interaction between agonist/antagonist and receptor
What value defines how well an agonist/antagonist bind a receptor?
K+1
What is the value K+1?
How well an agonist/antagonist BINDS a receptor
What value defines how well an agonist/antagonist UN-binds a receptor?
K-1
What is the value K-1?
How well an agonist/antagonist UNBINDS a receptor
How is K-A calculated?
(K+1) / (K-1)
What does a K-A value indicate?
Strength of interaction between a drug and its receptor, i.e. constant
What is the strength of interaction between a drug and its receptor often referred to as?
K-D
How is K-D calculated?
1 / K-A
What does a high K-D value indicate?
Low affinity
What does a low K-D value indicate?
High affinity
Would a drug with low affinity have a high or low K-D value?
High
Would a drug with high affinity have a high or low K-D value?
Low
Define occupancy.
How many receptors are occupied at any one point
How is occupancy calculated?
[Receptor/Drug-Complex] / [Receptor]
What two ions are used in the radio ligand binding assay?
H-3 or I-125
What are the five steps in the radio ligand binding assay?
Prepare cells; place cells on filters; add radioligand and leave to equilibrate; remove excess radioligand; count radioactivity on filter - directly proportional to radioactive ligand
What are the two main problems with radio ligand binding assays?
Non-specific binding, radioligand must be pure and specific
How is non-specific binding in radio ligand assays overcome?
Add anti-adsorbants; use two tubes - one with RL and one with RL + L - L displaces RL from receptors, leaving only adsorbed RL - subtract this from first tube to give only bound RL
What must a radioligand be?
Pure and specific
What is the main issue with radioligands, and how is it overcome?
Degradation - overcome by including free-radical scavenger in the drug solution, storing it at cold temp, avoiding light or the incorporation of an antioxident
Why must a radioligand be specific?
To be able to use very low concentrations to avoid excessive adsorbance to other sufraces
What are the advantages to using H-3 as a radioligand?
Labelled product indistinguishable from natural compound, high specificity, good stability, long half life
What is the half life of H-3?
12.5 years
what are the disadvantages to using H-3 as a radioligand?
Specialised labs required, labelling is expensive and difficult
What are the advantages to using I-125 as a radioligand?
Iodination is easy in most labs, its cheap, high specificity, easy to attach to aromatic compounds
What are the disadvantages to using I-125 as a radioligand?
More readily degraded, activity can easily be reduced, short half life
What methods are employed to separate bound radioligands from free?
Filtration, centrifugation, dialysis, column chromatography, precipitation, absorption
What is the major problem with bound/free radioligand separation?
Rate of dissociation of ligand-receptor complex
What shape is the radioligand assay curve?
Sigmoid
Why does the specific binding curve in a radioligand assay level off?
Only a fixed number of receptors
How is K-D deriven from a graph?
50% occupency
What is a scatchard plot?
Straight line on a bound/free against bound graph
What does the slope on a scatchard plot represent?
minus 1 / K-d
What does the x-axis intercept on a scatchard plot represent?
B-max
Define the equation of the scatchard line.
SEE PAD 6
Is 50% occupancy required for 50% response?
No
Why is % occupancy not always the same as % response?
Secondary messengers amplify the response
What determines the response of a drug?
Downstream activation
What is the receptor ‘reserve’ and what purpose does it serve?
Extra receptors that are no necessarily needed - means that they can be lost without losing function, and more chance of a vew low [agonist] will cause a response
What is X-a?
[agonist]
Define response as an equation.
SEE PAD 9
Define bound receptors as an equation.
SEE PAD 8
What does the phrase ‘higher affinity’ mean?
Better at binding receptor
What does the hprase ‘higher efficacy’ mean?
Better at causing change
What is a partial agonist?
Agonist that cannot cause 100% response of the tissue
What does a partial agonist need to get its full response?
100% occupancy
Define what an antagonist is.
Drug that prevents the agonist response
What are the 6 different classes of antagonism?
Chemical, biological, pharmacokinetic, physiological, non-competitive, competitive antagonism
What is chemical antagonism?
Combination of antagonist and agonist in solution so the effects of the active drug are lost, i.e. agonist is chemically altered
What is a chelation agent?
Drug that combines with heavy metals in the body to inactivate their pharmacoogical effects
What is biological antagonism?
Antagonism of endogenous mechanisms in the body
What does omalizumab bind to?
IgE
What is pharmacokinetic antagonism?
Increased clearing of the drug from the system
What are the three main pharmacokinetic antagonistic pathways?
Reduction of absorption, reduction of renal excretion, change in drug metabolism
What is physiological antagonism?
Interaction of two drugs with the body causing opposing actions
Give an example of physiological antagonism.
Noradrenaline and histamine on BP
How do opiates act as general pharmacokinetic antagonists?
They reduce drug absorption
How does aspirin generally interact pharmacokinetically with other drugs in the body?
Reduces the rate of renal excretion, thus increases drug half life
Give an example of a drug interaction that increases an agonist’s metabolism.
Antibiotics can trigger Warfarin metabolism
What is non-competitive antagonism?
Blocking a step in the process between receptor activation and response - does not compete with the agonist for the receptor site
What is competitive antagonism?
Competition with the agonist for a receptor, which can be reverse by increasing [agonist]
What does an increase of competitive agonist concentration cause?
Shift to the right on concentration/response curve, effectively increasing K-d
What is a dose ratio?
Comparison of the EC-50 with and without antagonist
Define the dose ratio equation.
SEE PAD 10
What is pA2?
The negative logarithm to the base 10 of the molar concentration of antagonist that makes it necessary to double the concentration of agonist needed to elicit the original submaximal response.
Define the pA2 equation.
SEE PAD 11
How is [antagonist] required to create a DR of 2 deriven?
SEE PAD 12
What is irreversible competitive antagonism?
Time-dependent antagonism that cannot be washed out or effected by [agonist]
What is the only way to counter irreversible competitive antagonism?
Re-synthesis receptors
What is tachyphylaxis?
Acute down turn in drug response
What is tachyphylaxis also known as?
Densensitisation
What causes tachyphylaxis?
Loss of receptors by internalisation/recycling/degradation; altered receptors through phosphorylation/decreased effector coupling; exhausted mediators; increased degradation of drug; physiological adaptation
What does drug effect depend on?
Mechanism of action, physicochemical properties, concentration
What are physicochemical properites?
Affinity, efficacy and potency
What two methods do drugs distribute themselves through the body?
Bulk flow transfer through the bloodstream and diffusion through lipids, channels and carriers
What is lipid solubility defined as?
Partition coefficient
What is the partition coefficient?
Lipid solubility of a drug
What is diffusivity defined as?
Diffusion coefficient
What is the diffusion coefficient?
Diffusivity of a drug
What is the most important property of a drug?
Partition coefficient - how soluble in lipids they are
What three characteristics mean non-polar molecules are the best drugs?
Increased rate of absorption form the gut, increased penetration into the brain and other tissues, increased renal elimination
What is the BBB?
Blood brain barrier - endothelial cells lining blood vessels in the CNS forming tight junctions that are impermeable to water molecules
What substances does the BBB restrict and allow?
Restricts water soluble molecules, allows lipid soluble molecules
What happens to the BBB during inflammation? Give an example.
Tight junctions can become leaky, such as during meningitis, hence why it can be treated by IV penicillin
What three major factors affect drug distribution?
BBB, binding to plasma proteins, partition into specific tissues
How does albumin interact with drug affinity?
Binds to mainly acidic drugs, restricting their binding to receptors
What are the six methods of drug delivery?
Oral/rectal, percutaneous, intravenous, intramuscular, intrathecal, inhalation
What does intrathecal mean?
Through the CNS (i.e. CSF)
What is CSF?
Cerebrospinal fluid
What are the four methods of drug excretion?
Urine, faeces, milk/sweat, expired air
What are the two main biochemical reactions in drug metabolism?
Phase 1 - catabolic (which can produce more reactive compounds); phase 2 - synthetic (conjugation to produce inactive product)
What are pro-drugs?
Must cross the hepatic plasma membrane and be metabolised to activate
What role does metabolism of a drug have in its life span?
End, alter or prolong pharmacological actions
What does the molecular weight of a drug affect?
Rate of diffusion
Why does pH and ionisation affect many drugs?
Many drugs are weak acids or bases, and only uncharged species can cross the lipid barrier; only during the correct pH are these drugs un-ionised and able to diffuse and activate
What three systems comprise the ANS?
Sympathetic, parasympathetic and enteric
What does ANS stand for?
Autonomic nervous system
What does SS stand for?
Sympathetic nervous system
In what three systems do the SS and PSS oppose each other?
GI smooth muscle, heart rate and bladder control
What system controls sweat glands and most blood vessels?
SS
What system controls sweat glands?
SS
What nervous system controls most blood vessels?
SS
What nervous system controls the ciliary muscle of the eye?
PSS
What nervous system controls the salivary gland?
PSS + SS
What effects do the PSS and SS have on the salivary gland?
Exactly the same - stimulate release
What is the neuronic pathway from CNS to blood vessels?
To cholinergic ganglion then on to adrenergic end point
What is the neuronic pathway from CNS to sweat glands?
To cholinergic ganglion then on to cholinergic (muscarinic) end point
What is the neuronic pathway from CNS to adrenal medulla?
To cholinergic (nicotinic) end point
What is the neuronic pathway from CNS to salivary glands?
To cholinergic (nicotinic) ganglion then on to cholinergic (muscarinic) end point
What is Dale’s criteria?
That a neuron releases the same NT at every terminal branch
What does NT stand for?
Neurotransmitter
What are the 5 steps in synaptic transmission?
NT synthesis, storage in synaptic vesicles, release upon neuronal activation, post-synaptic receptor activation, breakdown and/or reuptake
What are the 5 principal targets for drugs?
Receptors, transmitter synthesis, transmitter breakdown, transmitter reuptake/packaging, exocytosis
What two types receptors are used in the ANS?
Ligand gated ion channels (ionotropic) and GPCRs (metabotropic)
What flavour of ligand gated ion channels are in the ANS?
Nicotinic cholinergic receptors
What flavours of GPCRs are in the ANS?
Alpha 1, 2; beta 1, 2; muscarinic receptors 1-5
What does nAChr mean?
Nicotinic cholinergic receptor
What does mAChr mean?
Muscarinic cholinergic receptor
How many distinct GPCR receptors exist?
> 1000
What does GPCR stand for?
G-protein coupled receptor
What are GPCRs often referred to as?
Metabotropic
What are ligand gated ion channels often referred to as?
Ionotropic
Describe the structure of GPCRs.
Mono or dimeric, 7TM alpha-helices with a ligan binding domain in extracellular loop or buried within TM2&3
What does the 3rd intracellular loop and C-terminal tail of a GPCR do?
Highly variable in length and sequence, responsible for G protein interaction and are sites of phosphorylation
How many classes of GPCR are there?
Four
What are the four general classes of GPCR?
Class 1 - rhodopsin like; class 2 - secretin related; class 3 - metabotropic glutamate like; class 4 - frizzled
What signalling function do GPCRs serve?
Transducers
How many subunits comprise a GPCR, and term defines this?
3 - heterotrimeric
Which subunit defines a GPCR, and why?
Alpha - it binds the GDP/GTP
What do beta/gamma subunits do in GPCRs?
Anchor GPCR to inner surface of PM
Which two GPCR subunits form a tight complex?
Beta/gamma
What kind of control does adenylyl cyclase GPCRs have?
Bidirectional control
What terms are given to GPCRs for both sides of the bidirectional adenylyl cyclase control?
G-i - inhibitory; G-s - stimulatory
What terms are given to both alpha subunits of the bidirectional adenylyl cyclase control?
Alpha-s - stimulatory; alpha-i - inhibitory
What kind of control does phospholipase C GPCRs have?
Unidirectional
What term is given to the phospholipase C GPCR?
G-q - stimulatory
What term is given to the phospholipase C GPCR alpha subunits?
Alpha-q - stimulatory
What is PIP2?
Phosphatidyl inositol 4,5 bisphosphate
What is IP3?
Inositol 1,4,5 trisphosphate
What is DAG?
Diaglycerol
Describe the phospholipase C unidirectional GPCR pathway.
GPCR activation leads to PIP2 hydolysis, which generates two more messengers - DAG and IP3
How do you terminate GPCR signalling?
Remove agonist, GTPase activity of alpha subunit, desensitisation of receptor
How is GTPase activity in G-alpha initiated?
RGS-proteins
What are RGS-proteins?
Regulators of G-protein signalling
How are GPCRs desensitised?
Phosphoralysed or internalised
Which GPCRs are adrenergic?
Alpha 1, 2; beta 1, 2
Which GPCRs are muscarinic?
M1-5
Which receptors associate with G-s?
Alpha 1; beta 1, 2
Which receptors associate with G-i/o?
Alpha 2
Which receptors associate with G-i alone?
M2 + M4
Which receptors associate with G-q?
M1, M3 and M5
What are NSAIDs?
Non-steroidal anti-inflammatory drugs
What do NSAIDs do?
Anti-inflammatory - modify inflammatory reaction; analgaesic - reduce certain sorts of pain; anti-pyretic - lower raised temperature
How are NSAIDs anti-inflammatory?
Decrease vasodilation, and in turn oedema
What are NSAIDs ineffective against?
Mediators that contribute to tissue damage associated with chronic inflammatory conditions
How are NSAIDs analgaesic?
Decrease PG production in damaged and inflamed tissue which would otherwise sensitises nociceptors to inflammatory mediators
Name two inflammatory mediators.
Bradykinin, serotonin (5-HT)
How are NSAIDs antipyretic?
Thermostat in hypothalamus activated via IL-1 induced COX2 production of PGE
What is COX?
Cyclooxygenase
What occurs in the COX active site?
Oxidation of arachidonic acid
Describe the structure of COX.
Made up of two identical subunits, each with two catalytic sites
What are the two kinds of catalytic site found on COX?
Peroxidase and cyclooxygenase sites
Where is COX active?
ER membrane
How does aspirin interact with COX?
Binds covalently to Ser residue, preventing arachadonic acid from reaching cyclooxygenase site
What are the five main side effects of NSAIDs?
GIT problems, renal failure, liver damage, bronchospasm, skin rashes
What doe GIT stand for?
Gastrointestinal tract
What GIT problems occur as side effects of NSAIDs?
Dyspepsia, diarrhoea, nausea, vomiting, gastric bleeding, ulceration
What can be co-administered with NSAIDs to protect the GIT?
Misoprostol
What is misoprostol co-administered with, and why?
NSAIDs to protect the GIT
What is dyspepsia?
Indigestion
What is misoprostol and analogue for?
PGs
What does PG stand for?
Prostaglandin
What pathway does COX contribute to?
Inflammatory
