pharmacological principles (week 1-4) Flashcards
(177 cards)
1
Q
List the 3 drug origins
A
- Synthetic chemicals
- Biotech product
- Phytochemical
2
Q
Define and give an example of a drug with a synthetic chemical origin
A
Synthetic chemicals = produced in factories/chemists synthetically.
EXAMPLE: aspirin produced by chemical reactions from starting molecules
3
Q
Define and give an example of a drug with a biotechnology product origin
A
Biotech product
EXAMPLE: recombinant antibodies or recombinant proteins (insulin)
4
Q
Define and give an example of a drug with phytochemical origin
A
Photochemical = from plants
EXAMPLE: morphone and codeine from poppy seeds
5
Q
What is pharmodynamics?
A
Pharmodynamics = what drugs do to your body
6
Q
What is pharmacokinetics?
A
Pharmacokinetics = what the body does to drugs
7
Q
What is a drug target?
A
Drug target = a drug binding site that upon association with a drug leads to a change in a physiological response
8
Q
List and describe 3 examples of drug targets that are NOT proteins
A
- anti-cancer drugs and anti-microbial drugs that bind directly to DNA
- anti-sense oligonucleotides or small interfering RNAs target RNA not protein
- bisphosphonates that bind to calcium salts in the banes
9
Q
In what scenario does a drug NOT have a drug target?
A
Antacid correcting pH balance - technically doesn’t bind anywhere
10
Q
What are the 4 protein targets of drugs?
A
- Receptors
- Ion channels
- Carriers (transporters)
- Enzymes
11
Q
Define a receptor as a drug target, including how it functions and different ways it acts functionally
A
Receptors = biological macromolecules that recognise and respond to endogenous chemical signals or exogenous drugs
It binds to a ligand (molecule that binds to a receptor) at a binding site (where ligand binds to receptor)
Agonist = a ligand that activates a receptor - turns on that receptor and activates some form of signaling pathway
Antagonist = a ligand that binds to a receptor without activity - binds and sits there, blocking whatever normally binds there
12
Q
What are the 4 receptor types?
A
- ligand-gated ion channels (ionotropic receptors)
- g-protein-coupled receptors (metabotropic)
- kinase-linked receptors
- nuclear receptors
All four receptor types are extremely common targets used in pharmaceuticals
13
Q
Describe the process in which ligand-gated ion channels functions
A
- Some sort of channel ions will travel through
- Causes hyperpolarisation or depolarisation of cell - like action potentials and nerves
- Result is cellular effect - very quick effect (milliseconds)
14
Q
List and describe the characteristics of ligand-gated ion channels
A
> Millisecond timescale
> Most often binds extracellularly (gate is on cell surface), but can bind intracellularly
> Ligand binding alters conductance of selective ions through channel resulting in cellular effect
> Tube-like macromolecules w/ protein subunits that pass through plasma membrane
> 3-5 subunits arranged around central aqueous channel (pore)
Acronym: MELTS
M = Milliseconds
E = Extracellular
L = Ligand -> conductance
T = Tube
S = Subunits
15
Q
Give and describe an example of a ligand-gated ion channel
A
Nicotinic Acetylcholine Receptor
> Receptor has 5 subunits: 2x alpha subunits, beta subunit, gamma subunit, delta subunit
> Won’t open without acetylcholine
PROCESS:
1. Alpha subunit is ligand binding domain - where acetylcholine will bind and open up the channel
- Sodium channels will flow into the cell causing an action potentia
16
Q
Describe the process in which G-protein coupled receptors functions
A
- Have GPCR, a seven-trans membrane style receptor, on the outside of that receptor ligand will bind
- On inside of receptor G-protein will couple
- Ligand binds turning on the receptor
- Receptor will turn on a G-protein - an intracellular signalling complex made up of an alpha, and beta and gamma subunits - is normally bound to GDP but when activated is converted to a GTP
- G-protein couples the receptor through to other effector which will often turn on some other signalling, creating a domino effect of signalling - phosphorylation cascade
17
Q
List the structural features of a G-protein coupled receptor
A
> 7 transmembrane regions
> extracellular region - ligand-binding domain
> G-protein alpha and beta-gamma subunits
> effector cell - enzymes, ion channels, transporters, gene transcription regulators
18
Q
List and describe the characteristics of G-protein coupled receptors
A
> These receptors are more general and most abundant (most common) - 33% of targets in 2017 - although other types are starting to catch up
> G-proteins can be stimulatory or inhibitory
> Can couple a range of things (effector) - enzymes, ion channels, transporters, gene transcription regulators
> When effector activates secondary messenger can end up with protein phosphorylation cascade, but ALSO sometimes have changes in calcium depending on what’s happening
> Seconds timescale
19
Q
Give and describe an example of a G-protein coupled receptor
A
Muscarinic Acetylcholine Receptor
PROCESS:
1. Starts with standard GPCR and G-protein with GDP bound = is inactive
- Agonist binding then GTP swaps in for GDP causing the activation of the G-protein
- Alpha unit if g-protein will diffuse away and bind to effector
- Once effector is turned on GTP hydrolyses and get inactive form of G-protein again
- Agonist will come off and process will repeat
20
Q
List and describe the characteristics of kinase-linked receptors
A
> Unlike G-protein coupled (linked to g-proteins) is linked to kinase -
1. Enzymatic Cytosolic Domain = receptor itself has intrinsic kinase action to turn on phosphorylation, OR
2. Link to Adapter Enzymes = is an adapter kinase that will do that
> General result is phosphorylation then gene transcription and protein synthesis
> Takes hours to take effect
> Are single-membrane-spanning proteins - unlike G-protein coupled receptors that have 7 membrane spamming domains = transduce signals by forming dimers, work through modulating phosphorylation
21
Q
List the 3 types of kinase-linked receptors
A
THREE KINASE-LINKED RECEPTOR TYPES:
1. Receptor tyrosine kinases (RTKs)
2. Receptor serine/threonine kinases
3. Cytokine receptors
22
Q
Describe the process in which receptor tyrosine kinase (RTK) would functions
A
Single protein with extracellular ligand binding domain =
- Helix to go through membrane with intrinsic tyrosine kinase domain in the middle
- Once ion binds get dimerisation of two subunits of receptors = tyrosine autophosphorylation
- End up with twho knase domains that come into proximity and phosphorylate each other and turn on the receptor
- Receptor/phosphorylation intracellularly is what’s turning on signaling cascade - get cascaded phosphorylation
- Results in activation of transcription factors and change in gene expression - happening over hours
23
Q
Describe the process in which receptor serine/threonine kinases would functions
A
Same process as receptor tyrosine kinase (RTK) - EXCEPT, instead of tyrosine have a serine or threonine getting phosphorylated
24
Q
Describe the process in which cytokine receptors would functions
A
Operates differently to tyrosine/serine/threonine kinases =
- Cytokine binding to receptor on extracellular domain
- Alpha helix through membrane but doesn’t have enzymatic activity on the inside
- Instead recruit Jak (in this case) - a cytosolic kinase that does the same thing as enzymatic activity in other kinase-linked receptors
- Turns on phosphorylation
- Phosphorylation can be recognised by trascription factor Stat (in this case)
This is referred to as “JACKSTAT” signaling pathway - commonly presented, generic mechanism that’s activated by cytokines
25
List and describe the characteristics of nuclear receptors
> Are intracellular receptors (as compared to surface style or extracellular receptors)
> Don't have to be IN nucleus - but action happens within nucleus
> Generally monomeric proteins = 1 subunit - often this will dimerise once activated
> Since are intracellular drug must get inside the cell - drugs commonly lipophilic
> Nuclear receptor class can:
- be transcription regulatory factors
- have enzymatic activity
- sit within cytoplasm or nucleus
> going to affect gene transcription - resulting in changes in protein synthesis and cellular effects
> Similarly to kinase-linked receptors will take hours (as is at gene transcription level)
26
Give and describe an example of a nuclear receptor
Estrogen Receptors (ER) - Steroid Hormone Receptors =
1. Is initially in cytoplasm of the cell
2. Steroid is lipophilic molecule that can easily pass through lipid bilayer of cell
3. Once gets intracellular will bind to receptors - which is typically kept in a complex and inactive state
4. Once activated (often dimerising) - translocates into the nucleus binding to DNA and changing transcription
NOTE: Doesn't always have to change transcription through binding directly to DNA, can bind to other transcription factos
27
Define an ion channel as a drug target, including how it functions and different ways it acts functionally
> This type of drug target is not mutually exclusive from ligand-gated ion channels - can overlap in terms of definition, is also a type of ion channel
> All ion channels are gateways for through cell membranes for ions
> Very selective of ions allowed through channel - important for membrane excitability = stimulation of action potentions, hyperpolarisation and depolarisation
28
List the two main types of ion channels
1. Ligand-gated channels = type of receptor, open in response to ligand binding - block ion channel itself
2. Voltage-gated channels = open in response to changes in transmembrane voltage - moldulate conductivity of ion channel
29
Define a carrier/transporter as a drug target, including how it functions and different ways it acts functionally
> Gateways for passage of polar and small molecules and ions - not ion channels, are active transporters to get things across liipophilic cell membrane = pumps
> As are pumps, need an energy source = can use ions and electrochemical grandients to exploit their energy to transport something else as well - OR use classic energy, ATP, hydrolising it for energy
> Because are pumps can pump drugs into and out of the cell
> Explain how different people react differently to drugs that are 'pharmacokinetics' - if one individual has lots of a pump may pump drug all the way out of all cells, someone else might have different expression levels and not pump it all out of the cell = different responses
30
Name an example of a carrier/transporter receptor
Selective serotonin reuptake inhibitors (SSRIs)
31
Define an enzyme as a drug target, including how it functions and different ways it acts functionally
> Enzymes are targeted by mimicking endogenous substrate - normally enzyme will chop up something to do something = if give a substrate that looks a lot like endogenous substrate it will bind in same area but won't be able to do what it typically does
> Typically will act as competitive inhibitor
> Sometimes binding can be non-competitive or can be irreversible - but most of drugs will bind to receptors and come off
> Typically won't be positive or a permanent change to enzyme/drug target
32
Name an example of an irreversible enzyme targeting drug
EXAMPLE: Aspirin - binds irreversibly, covalently attaching to target enzyme, cyclooxygenase (COX)
33
What is a pro-drug, and what's an example of a drug that has an enzyme as it's target as a pro-drug
Some drugs require enzymatic activation - pro-drugs
--> ie. given inactive drug that once gets to certain area of the body where you want it to work enzyme there will convert it to the right drug you want
EXAMPLE: Codeine - not particularly active itself but body will convert it into morphine as active compound within body that will have opiate effect
34
Describe an enzymes function surrounding drug metabolism
Enzymes are very important for metabolism and drugs will often be metabolised - can have negative effect though as many are metabolised into toxic compounds
EXAMPLE: paracetamol - high doses is toxic not because paracetamol is toxic but because its converted into something toxic
35
What is the importance of selectivity for drugs?
> Drugs are rarely entirely selective - selectivity for target depends on affinity (dosage, concentration etc.)
> More selective a drug is the less likely it is to bind to things we don't want it to and have adverse effects
> Different tissues and cell types may express same drug type - important to consider how drugs move around the body (pharmacokinetics
36
What is an example demonstrating the importance of drug selectivity?
Antidepressant was initially nonselective - tricyclic antidepressant (TCA) could cause respiratory depression - SSRIs now more selective for certain receptors and less dangerous
37
Define 'pharmacodynamics'
Effect of drugs on the body
38
What is the binding and cell activation process for an agonist?
1. Binding to receptor (either on surface or within the cell)
2. Stimulus occurs within the cell promoting a change in cellular biochemsitry
3. Change in cellular biochemistry causes a response and change in cell behaviour
39
Define Affinity as a drug property
Likelihood or tendency of ligand to bind to receptor - measure of the attraction of a ligand for biological target
40
Define Efficacy as a drug property
Chance that a bound ligand will induce a signaling change within the cell - strength of a drug in evoking a response of tissue
41
What effects the likelihood of binding and then a response occuring?
Binding likelihood increases when there is an increased amount of the ligand or increased receptors
- Affinity
- Efficacy
- Potency
NOTE: Just because a ligand binds doesn't mean it will produce an effect - antagonists
42
How is affinity quantified?
Equilibrium dissociation constant - Ka for agonists, Kb for antagonists
Ka/Kb = off-rate / on-rate
Off-rate = amount of drug coming off receptor
On-rate = amount of drug bound to receptor
Higher affinity drugs have a lower Ka/Kb value - equilibrium is dynamic
43
What are the characteristics of a ligand with high affinity for a target?
1. Quick on-rate - will bind quickly
2. Slow off-rate - will bind for longer
3. Low Ka/Kb - inversely proportional
Even at low concentration will have more ligands bound to target than a ligand with low affinity
44
Define receptor occupancy
= governed by law of mass action - rate of chemical reaction is proportional to concentration of reactants
Forward rate = [A] x [receptor] x constant (on-rate)
Backward rate = [drug-bound receptors] x constant (off-rate)
At equilibrium they are equivalent
45
Define fractional receptor occupancy
= for any concentration of drug there's an amount of bound receptor and total number of receptors in the system
If [drug] = Ka then fractional receptor occupancy is half, BECAUSE Ka = value at a certain concentration that half of the receptors are occupied (at equilibrium)
46
What factors does efficacy depend on in an agonist?
Ability to:
1. induce activation of receptor (intrinsic efficacy)
2. stimulus-response coupling from receptor activation to tissue response
47
What is a drug with 0 efficacy?
A drug with no ability to activate a receptor - an antagonist
48
What are the x and y axes on a drug response curve?
x-axis = logarithmic drug concentration with linear numbers [log M]
y-axis = % of maximal effect
49
What are the two main parameters for a concentration response curve?
1. Maximum response (Emax) = maximal response or effect drug can produce - sigmoid curve plateaus
2. Potency = concentration of the drug required to give an effect of a certain size (often 50%)
50
Why can't a response curve be used to measure affinity?
Response isn't directly proportional to receptor occupancy
51
Define potency as a drug property
The drug concentration required to elicit a given effect
52
What is EC50 and why is it used?
Drug concentration that can elicit a 50% response - 50% mark on concentration response curve
Use EC50 to compare potency between different drugs - lower EC50 = higher potency
EXAMPLE: On a curve if [log M] at 50% effect is logEC50 = -7.6, EC50 is 10^-7.6 = 25 nanomolar (nM)
53
How does potency effect a concentration response curve?
Higher potency shifts to the left, lower potency shifts to the right
54
How does efficacy of a partial agonist differ to a fill agonist?
Partial agonists typically have lower Emax
55
Why isn't response directly proportional to receptor occupancy?
Receptor reserve = mechanisms that links receptor binding and response has a reserve capacity - system maintains spare receptors
For a full agonist receptor pool is larger than needed for full response
56
Define desensitisation/tachyphylaxis
Short acting: When the effect of a drug diminishes upon continuous administration over minutes or less - the tissue or cell can adapt to the drug
57
Define tolerance
Long acting: When effect of a drug slowly diminishes upon repeated administration and exposure over hours, days, weeks etc.
58
What 4 factors causes desensitisation and tolerance?
1. Receptor loss: receptor being internalised within the cell, degraded, or recycled
2. Change in expression level of receptors: get more or less receptors over time
3. Exhaustion of mediators within the cell that do signaling
4. Physiological adaptation
Drug can rebound and recover from desensitisation and tolerance if the drug is removed
59
What are characteristics of a good therapeutic agonist?
- Aren't always drugs with high affinity, high potency, high efficacy
- High selectivity is desired - affinity at target receptor vs non-target receptor
- Balance of benefits and adverse effects
Partial agonists may be preferred
60
What is an example of a partial agonist 'good' therapeutic drug?
EXAMPLE: Salbutamol targeting beta-2 adrenosceptors to treat asthma - is a partial agonist = causes less desensitisation so disappearance of receptors known to happen with long period of stimulation doesn't happen
61
What is a receptor antagonists and what are the the types of more specific antagonists branching off it?
receptor antagonists = bind to same receptor as agonist
orthosteric site and allosteric site branch off from receptor antagonists
62
What is a orthosteric site and what are the the types of more specific antagonists branching off it?
orthosteric site = binding side is exactly the same receptor as the agonist
reversible and irreversible competitive antagonists branch off from orthosteric site
63
What is a allosteric site and what are the the types of more specific antagonists branching off it?
allosteric site = binding to a different site on the same receptor
reversible and irreversible non-competitive antagonists branch off from allosteric site
64
What is a non-receptor antagonist and what are the the types of more specific antagonists branching off it?
non-receptor antagonist = binds elsewhere from the agonist
chemical and functional antagonists branch off from non-receptor antagonist
65
What are the characteristics of a reversible competitive antagonist?
Most common and important type of antagonism in lab and clinic - high potency and selectivity achievable
Competitive Antagonist (reversible) = binds to agonist binding side (orthosteric site) and doesn't activate the receptor - is competing with agonist - doesn't stay bound, will dissociate and rebind continuously
66
What is an example of a reversible competitive antagonist?
EXAMPLE: Naloxone = opioid receptor antagonist that can reverse effect of morphine and other opioids - will compete with morphine/opioid, reversing effect of morphine when treating overdose
67
What are the effects of a partial agonist when it is combined with a full agonist?
The partial agonist will act as an antagonist to the full agonist, decreasing the potency of the agonist resulting in a higher EC50. It will eventually be surmountable, producing the same Emax
68
Which way does a concentraiton curve shift when an antagonist is added and how does this effect the potency?
Shifts curve (parallel when antangonist is competitive and reversible) to the right and apparent potency of the agonist is reduced
69
What is an example of an irreversible competitive antagonist?
EXAMPLE: Phenoxybenzamine = covalently binds to alpha adrenoceptors (non-selectively) blocking the effects of catecholamines - used in treatment of tumours in adrenal medulla
70
What is an example of a partial agonist acting as an antagonist?
EXAMPLE: Buprenorphine = partial opioid receptor agonist - can be used as an analgesic to reduce opioid withdrawal symptoms - if someone took morphine at the same time (full agoinst) buprenorphine wound act as an antagonist to the morphine
71
How does an allosteric modulator function and what are the effects it has?
Allosteric modulation bind to an AG protein coupled receptor whereas an agonist binds in one pocket and allosteric modulator binds in another - both bind to and effect the same receptor but at different sites.
When allosteric modulator (antagonist) binds it causes conformational change in receptor causing effects that are:
- NEGATIVE - can act as inhibitor of agonist
- POSITIVE - can act as potentiator increasing agonist action
THEREFORE, can increase/decrease affinity or efficacy of agonist to site
72
What is an example of an allosteric modulator?
EXAMPLE: Benzodiazepines = positive allosteric modulators of GABA-A receptors - potentiates effects of GABA which is an inhibitory neurotransmitter causing anxiolutic sedative and anti-convulsant effects
73
What are the clinical applications of allosteric modulators?
Can change coupling receptors to different pathways = biased algorithm - can direct receptor towards different intracellular signaling pathways
74
What is a chemical antagonist?
A molecule that binds to or destroys the ligand itself - agonist can no longer bind to target because it is destroyed
Uncommon for small molecule drugs - common for therapeutic antibodies though
75
What is an example of a chemical antagonist?
EXAMPLE: Mepolizumab = anti-IL-5 antibody - binds to ligand IL-5 and stops it from binding to the receptor, having an anti-asthma effect
76
What is a functional (physiological) antagonist?
Opposes the biological effect of an agonist by acting on a different site on a different receptor - may be an antagonist to the cell effect being targeted can be an agonist at the receptor it's binding to
77
What is an example of a functional/physiological antagonist?
EXAMPLE: Salbutamol = used to treat asthma - acts as an agonist at beta-2-adrenoseptor causing relaxation in smooth muscle relaxing airways - antagonises the contradictory pathway of contractile agonists acting on other receptors = ie. acetylcholine at muscarinic receptors
78
Aside from being used for therapeutics how can antagonists be used? (as tools?)
Antagonists are used to understand: physiology of systems, biochemistry of systems, immunology, neuroscience, any biomedical discipline
Used to discover new signaling pathways and new receptors - if agonist works on a cell type we know of, then antagonist is added and it can only interfere with someone of response and some is unchanged can potentially discover new receptors and different receptors an agonist may be acting on
79
What is the action of somatic neurons?
Innovate skeletal muscle and regulate skeletal muscle contraction
80
Where does the sympathetic divison of the ANS originate?
Fight or flight: cell bodies originate in thracic and lumbar portion of the spinal cord - ganglion is closer to the cell body
81
Where does the parasympathetic division of the ANS originate?
Rest & digest: nerves originating from cranial and sacral portion of spinal cord and brain - ganglion closer to effector cell
82
What are the tissues of the sympathetic nervous system that are of sympathetic innovation?
1. Adrenal medula = on top of kidney, secretes noradrenaline and adrenaline (neurotransmitter and hormone)
2. Most peripheral blood vessels and sweat glands
83
What are the tissues of the parasympathetic nervous system that are of parasympathetic innovation?
The lungs = predominantly parasympathetic innovation - sympathetic more regulares airway dilation through adrenaline not lungs themselves
84
What is a complimentary effect of the sympathetic and parasympathetic divisions of the ANS?
Saliva = sympathetic secretes mucus and ensymes, parasympathetic = responsible for watery secretion
85
What is the junction at the end of skeletal muscle cells called?
Neuromuscular junction
86
What is the junction at the end of the ANS cells called?
Neuroeffector junctions
87
What are the steps in chemical transmission? (neurotransmitter transmission)
1. Action potential propagation and depolarisation of pre-synaptic nerve terminal - change in the membrane voltage allows...
2. Opening of voltage-gated calcium channels = channels permeable to calcium - since extracellular calcium concentration is higher than inside the nerve terminal will have an influx of calcium as goes down electrochemical gradient into nerve terminal
3. Increase of Calcium concentration leading to fusion of vesicle with plasma membrane = increase in intracellular calcium needed for exocytosis/calcium dependent vesicular exocytosis - when have fusion of synaptic vesicle containing neurotransmitters to plasma membrane of the terminal, allowing...
4. Neurotransmitter release into synapse or junction - binding and activating post-synaptic/post-junctional receptors creating a cellular response
88
In what cell(s) is acetylcholine the neurotransmitter released?
skeletal muscles, parasympathetic nerves, sweat glands, adrenal cells, preganglionic neurons
89
In what cell(s) is noradrenaline the neurotransmitter released?
sympathetic nerves
Has a feedback loop from noradrenaline (NA) of when there is enough or too much NA released
90
What is an acetylcholine receptor called?
Cholinoceptor -
1. Nicotinic (ligand-gated ion channels) (nAChR) = ganglionic transmission, skeletal muscles - fast response
2. Muscarinic (G-protein) (mAChR) = parasympathetic nerves - intermediate response
91
What is a noradrenaline receptor called?
Adrenoceptor
α- and β-adrenoceptors (G-protein) = sympathetic nerves - intermediate response
92
What is co-transmission?
The release of more than one neurotransmitter at the same time (usually a dominant one) all go bind to their own receptors to produce a combined certain effect
Can have pre and post junctional neuromodulators to increase or decrease the amount of neurotransmitters released from the nerve terminal
93
What steps of chemical transmission can be targeted by drugs, and how?
All steps in chemical transmission can be pharmacologically targeted:
1. Can inhibit voltage-gated calcium channel so there's no influx of calcium into nerve terminal
2. Can inhibit or increase synthesis of neurotransmitter - if increase have greater capacity to release more and visa versa
3. Can affect storage of neurotransmitters - if neurotransmitters aren't stored in vesicles can undergo metabolism making less available for release from synapse
4. Can modulate release of calcium dependent vesicular exocytosis
5. Can inhibit or activate post-junctional receptors
6. Affect reuptake of neurotransmitters - recycling of neurotransmitters back into nerve terminal for re-releasing - can inhibit or increase this
7. Can inhibit degradation of neurotransmitters in nerve terminal and junctional space
94
What are the characteristics of noradrenaline?
- most often neurotransmitter, can be hormone if gets into blood
- produced in sympathetic nerve terminal, little bit in adrenal glands
95
What are the characteristics of adrenaline?
- circulating hormone
- produced in adrenal gland primarily
- similar structure to noradrenaly with methyl group on nitrogen - therefore have similar pharmacological properties
96
What is a catacolamine?
Adrenergic mediators (noradrenaline and adrenaline) are catacolamines
- they come with a catacol group (benzene right with hydroxyl groups and amide side chain)
97
What is the SYNTHESIS process for a catecholamine in the sympathetic nerve terminal?
In the nerve terminal = noradrenaline
1. L-tyrosine, an amino acid is transported into nerve cell via transporter
2. L-DOPA is produced when L-tyrosine undergoes hydroxylation by enzyme tyrosine hydroxylase
3. Dopamine (DA) is the product of L-DOPA being converted by the enzyme DPA decarboxylase
4. Dopamine is transported into synaptic vesicle by V-MAT
5. Noradrenaline is synthesised by dopamine-beta-hydroxylase in synaptic vesicle
98
Once synthesised how is a catecholamine in the sympathetic nerve terminal RELEASED?
When an AP is triggered nuclear fusion releases NA into synapse or neuro-effector junction
99
How is a catecholamine in the synmpathetic nerve terminal STORED?
Stored in vesicle - this controls neurotransmitter release and protects them from metabolistic enzymes in nerve terminal
100
What is the SYNTHESIS process for a catecholamine in the chromaffin cells?
In chromaffin cell = adrenaline
SAME FIRST 5 STEPS AS NORADRENALINE:
transported into nerve cell via transporter
2. L-DOPA is produced when L-tyrosine undergoes hydroxylation by enzyme tyrosine hydroxylase
3. Dopamine (DA) is the product of L-DOPA being converted by the enzyme DPA decarboxylase
4. Dopamine is transported into synaptic vesicle by V-MAT
5. Noradrenaline is synthesised by dopamine-beta-hydroxylase in synaptic vesicle
FURTHER STEPS:
6. Adrenaline formed when noradrenaline is converted by PNMT
101
How is a catecholamine in the chromaffin cells STORED?
Once synthesised adrenaline is transported into neurosecretory granules for storage
102
Once synthesised how is a catecholamine in the chromaffin cells RELEASED?
Adrenaline is released into circulation following the activation of nicotinic receptors on plasma membrane (acetylcholine (ACh) binding to nicotinic receptors)
103
What does the drugs L-DOPA & Carbipoda modulate and how?
TARGETING NEUROTRANSMITTER SYNTHESIS
L-DOPA increases dopamine synthesis by providing more substrate.
Carbipoda is a DOPA decarboxylase inhibitor (what turns L-DOPA into Dopamine)
This is used to treat diseases like Parkinsons that lack dopaminergic neurons in the CNS and therefore need increased dopamine output to counteract it.
L-DOPA can cross the blood-brain barrier into the CNS where needed. Carbipoda can't. Therefore Carbipoda prevents increase in dopamine in peripheral nerves where it is not needed to prevent adverse effects. It can't prevent dopamine increase in the CNS though as it can't cross that blood-brain barrier - only get effect where it's wanted (CNS) not in peripheral NS
104
What does the drug Reserpine modulate and how?
TARGETING NEUROTRANSMITTER SYNTHESIS
Inhibits the release fo catecholamines (VMAT) = VMAT inhibitor
Binds to inhibit vesicular monoamine transporters, preventing dopamine from synthesising into noradrenaline
Often used as tool to deplete neurotransmitter storage
105
How is inactivation primarily caused in the sympathetic nervous system?
Inactivation primarily through reuptake of noradrenaline via:
1. (PRIMARY) high affinity norepinephrine transporter (NET)
2. (SECONDARY) extraneuronal uptake via low-affinity organic cation transporter (OCT3)
Noradrenaline can then be re-released
106
How is inactivation primarily caused in cholinergic systems (that release acetylcholine)?
Inactivation primarily through degrading acetylcholine (ACh) - enzyme degrades
107
What do the drugs Tricyclic Antidepressants (TCAs) modulate and how?
Inhibits noradrenaline (norepinephrine) transporters (NET) in CNS
Allows more noradrenaline to stay in junction for longer and bind to receptors causing a greater and more prolinged response
108
What does a MAO inhibitor modulate and how?
Inhibits the metabolistic action of monoamine oxidase (MAO) - preventing the breakdown of noradrenaline in the cytoplasm
More can then be take up by the vescle, or can leak out into the juction having a greater effect
109
What is an indirectly acting sympathomimetic drug?
Mimic the effect of sympathetic nervous system indirectly - without acting as an agonist at the receptor, instead increasing noradrenaline available
110
What are examples of indirectly acting sympathomimetics (IAS)?
Tricyclic antidepressants, MAO inhibitors, ephedrine, tyramine
111
What is tyramine and how does it function as a drug?
Drug-food interaction - is found in many foods and is the substrate for monoamine oxidase = competes with noradrenaline for metabolism therefore inhibiting monoamine ocidase (MAO)
112
What is a directly acting sympathomimetic drug? What is an example?
Binds and stimulates adrenoceptor
EXAMPLE: exogenous (grown and created outside of an organism) adrenaline
113
What are the 4 subtypes of adrenoceptors?
alpha 1, alpha 2, beta 1, beta 2
114
How does a beta subtype adrenoceptor act?
Noradrenaline binds to beta 1 or beta 2 which are linked to a G-protein alpha subunit (Gas) (s=stimulatory)
G-protein subunit after being activated can stimulate adenylate cyclase (AC) - membrane bound enzyme that converts ATP to cyclic AMP (cAMP)
cAMP is a secondary messenger that activates futher enzymes that create a response
115
How does an alpha subtype adrenoceptor act?
ALPHA 1:
Linked to G-alpha-Q protein - stimulates a membrane-bound enzyme - phospholipase C (PLC)
PLC is responsible for conversion of POP2 into 2 important sickling molecules - IP3 and DAG causing an increase in calcium concentration
Increased calcium in smooth muscle causes contraction
ALPHA 2:
Linked to G-alpha-i proteins - inhibitory protein that inhibits membrane bound enzyme adenylate cyclase (AC)
Decreases cAMP
Often located pre-junctionally and act as a negative feedback system restricting NA release
116
What tissue/organs does alpha 1 effect and what does it do?
= most blood vessels (smooth muscle) - constriction
Also: pupil dilation and relaxation of gastrointestial system
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What tissue/organs does alpha 2 effect and what does it do?
= pre-junctional synapse - NA negative feedback system
Also: sometimes post-junctionally
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What tissue/organs does beta 1 effect and what does it do?
= heart muscle - increases HR and contraction
Also: renin secretion in kidney
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What tissue/organs does beta 2 effect and what does it do?
= bronchi - bronchodilation, relaxation
Also: blood vessels and gastrointestinal dilation, glycogenolysis in liver
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What is an example of an alpha 1 agonist drug?
Phenylephrine = nasal decongestant - constriction of blood vessels in nose
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What is an example of an alpha 1 antagonist drug?
Prazosin = anti-hypertensive, lowers blood pressure
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What is an example of an alpha 2 agonist drug?
Clonidine = anti-hypertensive through CNS action
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What is an exampe of an alpha 1 and 2 combined antagonist drug?
Phentolamine = manage hypertension
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What is an example of a beta 2 agonist drug?
Salbutamol = asthma bronchodilator
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What is an example of a beta 1 agonist drug?
Dobutamine = acute heart failure preventative - increases heart strength
126
How is acetylcholine (ACh) synthesised?
1. Choline enters the cell via choline transporters
2. Choline acetyltransferase (cHAT) takes the acetyl from acetyl coenzyme A and adds it to the choline to make acetylcholine
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How is acetylcholine (ACh) stored?
Once synthesised acetylcholine (ACh) is stored in vesicles, which it is transported into bi vesicular acetylcholine (against concentration gradient)
128
How is acetylcholine (ACh) released?
1. Vesicle with membrane protein synaptobrevin docks at presynaptic membrane
2. Synaptobrevin forms SNARE complex with SNAP 25 and syntaxin
3. Calcium enters nerve terminal and binds to synaptotagmin on vesicle
4. Synaptotagmin triggers membrane fusion between vesicle and terminal membrane - causing ACh release
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How is acetylcholine (ACh) metabolised?
Metabolised through acetylcholinesterase (AChE) - outside the cell and breaks down ACh metabolising it
130
How do drugs modulate cholinergic activity?
1. Prevent the formation of acetylcholine in the cell through breaking down the SNARE complex
EXAMPLE: botulin toxin
2. Inhibiting aceytcholinesterase (AChE) and causing more ACh in the junction eliciting a greater effect
EXAMPLE: anticholinesterases
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What are the acetylcholine (ACh) receptors and receptor subtypes?
1. Muscarinic receptors (M1-5) MAChR
- G-proteins
- M2 and M3 are only ones relevant
2. Nicotinic receptors (N1-2) NAChR
- ligand-gated ion channel
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What is an example of an antagonist with selective activity at the ACh receptors (one for each receptor)?
Muscarinic antagonist
EXAMPLE: atropine
- competitive reversible antagonist
- 'anti-DUMBELS' - CNS effects = restlessness
- doesn't discriminate muscarinic subtypes
- reduced secretion during anaesthesia
Nicotinic antagonist
EXAMPLE: d-tubocurarine
- competitive reversible antagonist
- acts at neuromuscular junction but ganglia at higher concentrations - less selectivity
- neuromuscular blocking drug for surgical paralysis
- adverse effects = hypotension due to ganglion block
133
What are examples and effects of reversible anticholinesterases?
Medium-duration anticholinesterases:
EXAMPLE: Physostigmine - selective for parasympathetic junctions
- causes increased parasympathtic effects
- used for glaucoma (eye disease from blockage of draining system)
EXAMPLE: Neostigmine - selective for neuromuscular junction
- causes increased muscular response
- reverse competitive neuromuscular block - myasthenia gravis (muscle weakness fron antibodies degrading nicotinic receptors)
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What are examples and effects of irreversible anticholinesterases?
EXAMPLE: Organophosphates
- binds and covalently modifies AChE so enzyme can no longer be activated
- causes muscarinic effects
- can treat organophosphates poisoning with muscarinic receptor antagonist
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What are the characteristics of a muscarinic receptor and it's subtypes? (signal transfuction mechanism)
Muscarinic receptors (M1-5) MAChR
- G-proteins
- M2 and M3 are only ones relevant
- M2 = coupled to Gai (inhibitory G-protein) - decreases cAMP causing decreased contractile force - is located in the heart = activation causes decrease in HR, bradycardia
- M3 = coupled with Gaq - activating PLC enzymes that convert PIP2 into IP3 and DAG - increases intracellular calcium and leads to smooth muscle contraction, or on sweat glands increases secretion - on smooth muscle and sweat gland
136
What are the characteristics of a nicotinic receptor and it's subtypes? (signal transfuction mechanism)
Nicotinic receptors (N1-2) NAChR
- ligand-gated ion channel (iontropic)
- composition of subunits varies which forms subtypes with differing properties (specificity, oermeability of ion, physiological response)
- N1 = neruomuscular junction
- N2 = autonomic ganglia
137
What is the difference between dose and concentration?
Dose is how much of a drug is given whilst concentration is the amount that actually ends up being present in the body at the target
138
What factors determine concentration of a drug in the body?
A.D.M.E
A - Absorption
D - Distribution
M - Metabolism
E - Excretion
139
What is the difference between local and systemic drug actions?
Local = drug exerts effect on target at or near site of administration - has access to limited tissue etc.
= less adverse effects
Systemic = drug enters the bloodstream to access the target and in doing so will access many tissues (musct cross membranes to access target)
= more potential for adverse effects
140
How can drugs, small and large molecule be absorbed and cross membranes?
Small molecules:
1. Diffusion through lipid
2. Diffusion through aqueous channels
3. Carrier
Large molecules:
4. pinocytosis - attracted to part of the membrane they can invaginate
141
What properties effect absorption?
1. pH (most drugs are weak acids or bases)
2. aqueous solubility (must be in solution)
3. lipid solubility (to cross cell membrane)
142
How does pH effect absorption?
- uncharged small molecules are more likely to be lipid soluble and well absorbed - passive lipid diffusion
- If charged can't be lipid soluble and will likely need a carrier - more energy and time demanding
- If it is charged like charges will absorb better - EXAMPLE: inflammatory environments are very acidic so an acidic drug would best be absorbed over a basic drug
- There are varying pH levels throughout the gastrointestinal track (although most absorption is done through the small intestine)
143
How does lipid solubility effect absorption?
- If being distributed systemically and taken orally as a drug need to cross 2 membranes - in gastrointestinal lining and blood vessel lining
- easier to get through these linings which are lipid membranes if is lipid soluble
144
What are some important considerations with orally administered drugs?
PROS
- most convenient route (therefore most common)
- variety of forms dose can be put in
CONS
Drugs will go through first pass metabolism after oral absorption:
- exposed to enzymes in saliva and gastrointestinal fluid that could break down drugs
- first pass hepatic metabolism - will pass through liver, the major organ for drug metabilism before reaching circulation
NOTE: metabolism can also be used in the favour of drugs - prodrugs (need to be metabolised to then be in active form)
145
What are some important considerations with injectable routes of drug administration?
4 injectable routes:
1. subcutaneous (sc)
2. intramuscular (im)
3. intradermal (id)
4. intravenous (iv)
- drug instantaneously enters blood stream
- more precise amount of drug enters blood stream, no absorption required
- BUT even once in blood stream still need to get to target - dose still won't be same as concentration
- concentration determined by bioavailability
146
What is bioavailability (F) and what is it affected by?
= proportion of active drug that enters systemic circulation
- is 100% following iv administration - less than 100% for other routes, some lost along the way
- impacted by how much drug is absorbed - pH, lipid solubility etc.
- impacted by how much undergoes first pass metabolism by enzymes both in the liver and in other locations throughout the body
147
What is distribution in relation to drug administration?
= drug reaching the target - how it is spread through the body
- driven by circulation of blood
- can be affected by molecular size, lipid solubility, plasma protein binding (free drug has tissue access, more difficult if binds to plasma protein in blood)
- distribution is rarely uniform - concentrated or excluded from areas (especially due to pH - changes influence lipid solubility) - affinity
- being distributed and eliminated at the same time but distribution is faster
- drugs reach a "distribution equilibrium"
148
What dictates absorption rate?
Slowest rate of reaction - lots of processes going on but slowest one will limit it
149
What is volume distribution?
Volume of body water in which the drug appears to be dissolved in after it has distributed through the body quickly
- constant that relates amount of the drug in the body to plasma concentration (determined during development phase)
EQUATION = amount in body (dose) / plasma concentration (initial concentration)
- important as relates dose to what could be initial concentration in the plasma
- is an apparent value - smaller for drugs that bind to plastma protein, larger for drugs that distribute to tissues or taken up into cells
- need to be careful with what you use value for - the subset of people results were gathered don't represent everyone especially when they're all often men
-
150
What is precision medicine?
A move away for "one size fits all" medical approach - fitting drugs to the patients = personalised medicine
- need to ensure drugs aren't too effective and toxic, but also not too ineffective and a waste of time - balance is needed
151
What is pharmacogenomics, why is it important?
How variation in genes influences the effect of drugs
Important:
- economic issues - huge cost to patients, pharma industry and healthcare system (which subsidizes medicine use)
152
What causes variabilities within the population in drug response?
DNA polymorphisms:
- germ line mutation (inherited)
- somatic mutation (cancer)
Often single nucleotide polymorphism (SNPs)
153
What changes to SNPs cause in drug responsitivity?
1. Direct effect
- change in protein structure/function: change binding of drug, alternative splice (different drug protein synth), more or less modulated by drug
2. Gene transcription effect
- change in gene transcription and hence quantity of protein produced - polymorphism in promoter regions
154
What are potential single nucleotide polymorphisms (SNPs)?
1. silent mutation - base change with no effect (same amino acid)
2. conservative missense mutation - makes a different amino acid but no change in effect
3. nonconservative missense mutation - different amino acid that changes function
4. frame-shift mutation - insertion of nucleotide throwing everything off and greatly impacting function and expression
All above factors can change how drug interacts - potentially causing advers reactions
155
What are other motential mutations that can have consequences that aren't single nucleotide polymorphisms (SNPs) with an example?
Exchange different chromosomal regions
- often associated with cancer
EXAMPLE: Philadelphia chromosome - exhcnage on chromosomal level leads to increased cancer formation
156
What is a consequence of single nucleotide polymorphisms (SNPs) for proteins?
Ubiquitin pathway = ubiquitin picks up on polymorphisms and degrades prteins - then just don't have functional proteins
157
How can polymorphisms be detected?
- DNA sequencing (genome/exome)
- microarray - for known SNPs
158
How does the body effect drugs when polymorphism has occured? (pharmacokinetics)
1. Can reduce formation of active compounds if drug is a pro-drug
2. Can influence half life of drug
3. With reduced enzyme activity drug may reach higher plasma concentration for longer periods - toxicity
4. If enzyme is TOO active may not achieve therapeutic concentration at target
159
What is an example of drugs having varying effects for different people?
EXAMPLE: Suxamethonium = supposed to be a short duration skeletal muscle relaxant used in surgery
Cholinesterase is the enzyme that metabolises suxamethonium - is found in plasma
Polymorphic fors found to have varying effects
1. increased activity of plasma cholinesterase = wears of faster and doesn't have significant effect even in high dosages
2. decreased activity/inactivity of plasma cholinesterase = wears of slowly and even in small doses has a significant and prolonged effect
Dosage to be titrated for individuals to ensure consistent effect
160
What are the impacts of polymorphisms in anti-cancer drugs?
- germline and tumour genomes can broadly effect the efficacy/safety of anti-cancer drugs
- chemotherapy drugs consider epidermal growth factor receptor (EGFR) polymorphism to predict success with kinase inhibitors in certain lung cancers
161
What are the feasible factors surrounding pharmacogenomics in the future?
- has become a lot cheaper
- has been successful for some drugs
162
What are some infeasible factors surrounding pharmacogenomics in the future?
- interpretation of sequence is problematic
- healthcare workers not trained in understanding genome sequences and how to best help patients
- old pharm companies "one size fits all" model doesn't fit for profits - drug would get more expensive?
- ethics of how OTHER stuff they find will be managed? other issues in sequence
163
What are the main factors involved in how drugs get out of the body? (elimination)
- Metabolism (liver)
- Excretion (kidney)
164
What is the characteristics and purpose of metabolism?
Set up the drug to be able to disappear in urine in two phases (through salicyclic acid or glucuronide)
- mainly occurs in liver but also in most tissues
- increases water solubility to facisitate excretion
- enzyme-catalysed reactions
165
Describe the mechanisms behind phase 1 of drug metabolism
1. BREAK DOWN DRUGS TO MAKE SOLUBLE
Cytochrome P450 = enzymes responsible for many phase 1 drug metabolism reactions - metabolise anything we injest to maximuse nutrient benefits and minimise harm
- depending on drug-drug and drug-food reactions alongside other variables can have idiosyncratic effects = unexpected response
166
Describe the mechanisms behind phase 2 of drug metabolism
2. MAKE WATER SOLUBLE
Big molecules get added that are water soluble and relatively stable
EXAMPLE: glutathione conjugation - protects against many things including reactive oxygen species
167
What is the different processes of drug elimination for hydrophobic vs hydrophilic drugs?
Hydrophilic: don't go through phase 1 or 2 metabolite - straight to excretion
Hydrophobic: can go through phase 1 metabolite and then phase 2 or just straight to phase 2
Excreted mainly by kidney
168
What are the 3 processes of renal excretion?
1. Glomerular filtration
2. Tubular secretion
3. Tubular reabsorption
169
What are the mechanisms of glomerular filtration?
Fenestrated capillaries has gaps - size filter where most things (small enough) will go through to get drug OUT of the blood
However, drugs can't leave the blood in this way if they're protein bound in blood, free form drugs can get through tissues more easily
170
What are the mechanisms of tubular secretion?
If can't get through glomerular filtration because too big active carriers can move OUT of the blood stream for excretion through active transport
171
What are the mechanisms of tubular reabsorption?
Drugs will get BACK INTO the blood due to lipid solubility just as they can get into tissue and out of blood to bind to targets - can also get out of the kidney
Consequently why it is important to ensure they're water soluble - so they're in a form that keeps them in the urine
affected by:
- passove movement across membrane
- pH
Can be manipulated - ie. can make urine more basic in aspirin overdose to decrease absorption and increase excretion
172
Define clearance in relation to elimination
= how efficiently we remove the drug from the blood stream (volume of blood cleared by drug/unit time) - CONCEPTUAL
Helps to determine dose rate to achieve a steady state [plasma] - not too much but also not too much being lost
173
What is drug half-life?
= how long a drug exists
In first order processes decay is proportional to amount you have - concentration in plasma
Irrespective of starting point of concentration time to get to half of initial level is the same
174
How many half-lifes is it to remove 95% of a drug after a single dose?
4 half lives
175
How many half-lifes is it until a steady state is reached with chronic dosing
6 half lives
176
Why is half- life important?
Helps determin the frequency at which a dose should be given
177
What is the exception to half-life principles?
Zero-order - half-life is difficult to predict as concentration changes are not consistent = require regular monitoring
Is zero-order because process is saturated
EXAMPLE: Alcohol - enzymes saturated quickly and effectively
