PHM 431 Exam 1

drug addiction definition and causes

• Chronic disease characterized by drug seeking and use that is compulsive despite harmful consequences

  • starts voluntarily

  • addiction develops after repeated use

• Factors in addition development

  • Biology (predispositions)

  • Environment (exposure)

  • Development (combination of both)

Classification of drug addiction

• DSM-5

• “Substance use disorder” recognized as official clinical diagnosis

  • range of severity with symptoms

• “addiction” common term applied to severe symptoms

Is addiction psychological or physical?

• Psychological?

  • Craving behaviors that dominate multiple areas of life

    • socioeconomic status

    • coping skills

    • environment

• Physical?

  • Change in the structure/function of cells, tissues, and organs

    • Genetics

    • early exposure

    • exposure frequency

Principles of Drug addiction

• Likely to be addictive if they produce euphoria

• Euphoria is reinforcing, subject wishes to take drug repeatedly

• Dependence can lead to addiction, but dependence does not equal addiction

• Withdrawal can occur in dependence or addiction states

• All drugs can produce dependence but not all drugs are addictive

Principles of drug addiction

• Physical dependence → biological and is a state that develops due to tolerance (adaptation) to drug effects.

  • resetting of mechanisms maintaining homeostasis

• Signs and symptoms of withdrawal are generally opposite to the responses caused by drug administration

• Avoidance of withdrawal → part of reinforcing profile → potentiates addiction

• withdrawal signs are unpleasant → continue to use to achieve euphoria and avoid withdrawal

Reward circuitry

• Prefrontal cortex

• nucleus accumbens

  • Main hub for reward, motivation, and action selection

• ventral tegmental area

  • Neurons in midbrain that serve as primary dopamine producing region

Common definitions in pharmacology

• Drug: any substance that brings about a change in biologic function through its chemical actions

• Xenobiotic: any substance not produced by your body

• Dose: amount of a drug administered

• Potency: concentration of drug needed to elicit a specific response

• Efficacy: specific outcome of drug treatment’

• Agonist: compound that activates a receptor

• Antagonist: compound that blocks a receptor from activation

Cell membranes

• Composed of lipid bilayer → semi-permeable

• Drugs with charge (ionized) are unable to pass through this membrane

• Unionized or lipophilic drugs can pass through easily into the cell (via simple diffusion)

Cell surface receptors

• Ligand gated ion channel

• G protein coupled receptors (GPCR)

• Receptors with intrinsic enzymatic activity

• Receptors that associate with enzymes

Ligand gated ion channels

• Transmembrane proteins with 2 domains

  • Ligand binding domain (LBD)

  • Membrane spanning domaine (pore)

• With ligand bound ions move down the conc gradient

G protein coupled receptors

• G protein is a trimer, G and alpha, beta, and gamma

• When ligand binds → beta and gamma release → leaves G and alpha alone

• If Gai → inhibits adenylate cyclase (no reaction)

• If Gas → stimulates adenylate cyclase

Dose Response Curve

• Potency vs Efficacy (efficacy Y, potency on X)

Which opiate has the highest potency? What about efficacy?

• China white highest potency → has the highest ED50

• All have the same efficacy

Terminology for PK/PD

• Pharmacokinetics

  • ADME

  • What the body does to the drugs

• Pharmacodynamics

  • Agonist, antagonist, receptor targeted

  • What drugs do to the body

ADME

• absorption: drug is taken into the body and moves from site of exposure to blood

• distribution: movement of drug from the blood to the tissues/interstitial fluid

• metabolism: metabolized in the liver, becomes a metabolite, if not a pro-drug it will be eliminated

• elimination: bye bye leave the body now

Route of administration

• Oral

• IV

• Intranasal

• SQ

• IM

• IP

• Suborbital

Oral drug administration

• Slow onset, takes time for drug to be digested and absorbed in small intestine

  • As a result, has a large latency period

  • Latency: the time between administration of a substance to the peak plasma concentration

• First pass effect

  • Drug enters portal vein and is shuttled to the liver, liver metabolizes and deactivates drug prior to systemic circulations

  • happens in IP administration too

IM and SQ Administration

• Has a long latency too, has to slowly diffuse out into blood stream

• SQ is similar to IM, but SQ does have a longer latency than IM

IV Administration

• Shortest latency (right into circulation, immediate effect)

• Has the highest potential for reaching toxicity threshold due to sharp spike

Absorption and distribution

• Site of administration has the highest concentration initially → rapid equilibrium between SOA, circulation, and target tissue

Drug distribution, tissues vs BBB

• Peripheral tissues have gap junctions in between cells, which allows some charged drugs to make it through

• BBB has tight junctions between cells stitched together by proteins

• Glial cells surround the endothelium of the BBB, adds even more cell membrane to pass through

What is this slide illustrating?

• Albumin bound drugs cannot pass through into tissues, too large of a molecule, this means the bound drug cannot have an effect

• When two drugs enter the system they compete for the same amount of albumin → there is now more free drug allowed to circulate in the blood → pass into tissues and leads to toxicity

Metabolism

• A family of enzymes (CYP450) principally in the liver but in other tissues as well acts on drugs and other XBs to inactivate these compounds

• Sometimes CYPs increase pharmacological activity of a drug: an inactive molecule may be transformed into an active compound or toxic metabolite

• Drug enters phase 1 metabolism → oxidation, reduction, hydrolysis → part of the drug is metabolized (hydrophilic)

• Drug enters phase 2 metabolism → conjugation → part of the drug is metabolized (hydrophilic)

• TWO drugs enter metabolism → competition and inhibition → much more Drug 1 + Drug 2 left unmetabolized → toxicity

Factors affecting metabolism

• Competition: For enzymes by co-administration drugs will lead to increased levels of both drugs

• Induction: increased enzyme activity as a result of previous same/different) drug exposure

• Natural products + Herbal products over the counter: interfere with metabolism of prescription drugs and changes the effects of these drugs

• Drug-Drug interactions: issues for elderly patients

• Inhibition: decreased enzyme activity as a result of previous drug exposure

First order kinetics

• T1/2 = half life

• Kel = elimination rate constant (0.693/t1/2)

• Cp0 = plasma concentration at t=0

• First order elimination kinetics (most drugs) → 1st order because the amount of elimination is proportional to the concentration of drugs

• The derivative of the slope is a straight line

Zero order kinetics

• Rate of elimination is constant per unit time: alcohol

• Keep an eye on axises (should see rate of change on y, concentration on x)

• rate of change vs conc should be a straight line, if a derivative it is a straight horizontal line

• Alchohol = 120mg/kg/hr

Pharmacodynamics

• Interaction of a drug with its site of action

• Drug can have two effects

  • Non-receptor mediated actions → usually unintended

  • Receptor mediated actions → specific high affinity binding site for drug

    • Act as an agonist → binds with high affinity and activates a receptor

    • Antagonist → binds with high affinity but does not activate a receptor, blocks binding or activation by an agonist

Quantitative description of drug-receptor interaction affinity/efficacy

• K1 is forward reaction, K2 is reverse reaction, Ka = K2/K1

• Affinity: Small Ka values = high affinity for a receptor = high potency

• Efficacy: Agonists have efficacy

  • antagonists do not have efficacy

  • agonists can vary in their transduction efficiency there are high efficacy agonists (full agonists) and low efficacy agonists (partial agonists)

Dose Response Curve

• Top of the sigmoidal curve is the Emax → maximal effect (measurement of efficacy) plateaus here

• Middle of curve → Emax/2 or EC50 (measures potency) → amount needed for ½ max effect in 50% of people

Dose response curve - Agonist vs antagonist

• Agonist → binds receptor → causes change response

• Antagonist → binds receptor → prevents change in response

• imagine the graph with the full, partial, antagonist, and inverse agonist

Dose response curve - potency vs efficacy

• Potency increases from right to left, as the curves shift to the left their EC50 decreases

• Efficacy increases from bottom to top, the higher the top of the curve → higher maximal effect

  • EC50 is relevant to each individual drugs max efficacy. A has highest Emax, so its EC50 will appear higher on Y axis but they are equal

Agonist efficacy vs potency

• Agonist B > A in efficacy

• Agonist B is a full agonist

• Agonist A is a partial agonist

• Potency: agonist A > agonist B

Therapeutic Index

• Equal to EC50 toxic/ EC50 therapeutic

• We want a large therapeutic index between curves so we can ensure the drug is safe blah blah

Antagonism

• There are two kinds of antagonism

  • Chemical

  • Physiological

• Competitive antagonism

  • binds reversibly to the same receptors site as an agonist

  • effects can be overcome by a higher concentration

  • shifts dose-response curve to the right without altering maximum response

• Non-competitive antagonism

  • binds to different site or irreversibly to same site

  • effects cannot be fully overcome by increasing agonist

  • reduces maximum possible response (efficacy)

• Chemical antagonism

  • direct chemical interaction between drugs

  • forms inactive complexes

  • neutralizes drug before reaching target site

  • albumin → binds to drugs in circulation + not allowing drug to get anywhere

• Physiological antagonism

  • opposing physiological effects through different mechanisms

  • acts on different receptors or pathways

  • counteracts functional outcome

Physiological antagonism

• Both drugs bind and interact to cardiac muscles in the same pathway but induce opposite effects

Drug tolerance

• Defined as a decrease in sensitivity to a drug after repeated administration

  • Graph: Drug user can still feel the effects but the potency required to reach that same effect a naive person feels is much higher

• Innate tolerance: occurs with genetic variations in drug metabolizing enzymes which lead to efficient inactivation of a drug or genetic variations in receptors (or other drug targets) which make those receptors less responsive to a drug

3 types of acquired tolerances

1. Pharmcokinetic tolerance: changes in drug sensitivity due to changes in the distribution and metabolism of the drug.

   1. ex: alcohol induces enzymes responsible for detox → tolerance to high amounts of alcohol through this change in metabolism

2. Pharmacodynamic tolerance: changes in the system in response to repeated drug administration.

   1. Ex: down regulation of receptors/their associated effector molecules

3. Learned tolerance: skills developed through experience with drugs, common with alcohol but can occur with non-abused drugs

   1. Ex: being good at drunk driving

Two forms of desensitization (pharmacodynamic tolerance)

• Two forms of desensitization

  • Internalization: receptor is pulled into the cell and stored within an endosome → happens within minutes to hours → short term desensitization

  • Downregulation: receptor is pulled into the cell and destroyed by a lysosome → decrease in the total number of receptors over hours to days → longterm desensitization

• Receptor or effector molecules can be downregulated!

Cross tolerance

• Morphine binds to opiate receptors in the brain → receptor (or effector) downregulation over time → meperidine is a new drug but also binds to opiate receptors → system is desensitized to this drug due to morphine abuse → no effect

Unique structures of neurons

• Cell body → soma

• Axon terminals at the end of the presynaptic neuron interacts with dendrites on post-neuron

• Axonal transport: transport of secretory components and intracellular communication

• Cell machinery in soma produces proteins and components for NTs

• transport down axon to terminal prior to final packaging

What are the two aspects of neural communication

• Neurotransmitter release

• Electrochemical potentiation

Resting membrane potential

• Nerve cells generate and propagate electrical signals, typically sit at around -60mV at rest (negative resting membrane potential)

• Intracellular concentrations: impermeable nucleic acids and proteins (negative charges) and K+

• Extracellular concentration: Na+, Cl-, Ca2+

• Na+/K+ pump → Energy dependent process that pumps 3 Na+ out and 2K+ in, works to restore -60mV

• Also contains K+ leak channels, Cl- pump (both out of cell)

• At rest, a neuron can passively release/absorb K+

Membrane Potential of an activated neuron

1. Resting membrane potential (-60mV)

2. Rising phase → Influx of Na+ ions → increase in Vm

3. Overshoot → peak of membrane potential

4. Falling phase → cells allows K+ to flow out to restore the -60mV

5. Undershoot → Falls below -60mV → cell utilizes Na/K pump to restore balance and increase back up to -60

• As the rising phase begins, there is a point called the “threshold”, once the mV reaches that threshold it is at the “point of no return” → it is going to fire

Saltatory Conduction and action potential propagation

• Unmyelinated axon: .5-1 m/s

• Myelinated axon

  • myelin sheath → increases speed of conduction (150 m/s)

  • nodes of ranvier: high concentration of Na+ channels

• Vesicles carrying NTs reach the axon terminal → in order for vesicles to fuse with the presynaptic membrane there must be an influx of Ca ions!

• Additionally, SNARE proteins are involved in NT release → imbedded in membranes → activated by Ca release → pull two cells together for NT release

Agents that affect nerve transmission

• Botulinum

• tetrodotoxin

• charybdotoxin

• margatoxin

• dendrotoxin

• conotoxin

Clostridial botulinum (botox)

• Attacks snare proteins at cholinergic nerve endings → blocks NT release of acetylcholine → prevents contraction

Tetrodotoxin

• Pufferfish one

• voltage-gated Na+ channel blocker → inhibit the rising phase of action potential → dead ;(

Charybdotoxin, Margatoxin (scorpion), dendrotoxin (mamba)

• K+ channel blockers → K+ cannot exit the cell fast enough → prolongs the falling phase of action potential

Conotoxin

• Blocks nerve terminal Ca channels → vesicles cannot bind with presynaptic membrane → no transmission of signals

• analgesic medication

The synapse

• Presynaptic terminal

  • NT

  • synthesis

  • breakdown

• Postsynaptic terminal

  • receptors

  • effectors

Primary dopamine pathways in the brain

• DA is the biggest NT responsible for developing dependence

1. Mesolimbic/mesocortical pathway

2. nigrostriatal pathway

3. tuberoinfundibular pathway (hormone release)

DA Synthesis in nerve terminals to release and breakdown

• Precursor AA is tyrosine → tyrosine hydroxylase → DA → VMAT for packaging into vesicles → release into synapse

  • can bind to D1 or D2 DA receptors

  • D1 → Gs+ → activate adenylate cyclase

  • D2 → Gi- → inhibits adenylate cyclase

• → brought back into presynaptic cell by DAT → 1 of 2 possibilities

  • 1. → DA goes back to VMAT and repeats the above cycle

  • 2. → goes to MAO enzyme and is broken down

Norepinephrine neurons/ pathways in the brain

• Locus coeruleus pathway

• reaches cortex, hypothalamus, and cerebellum

• NE neurons in the peripheral nervous system

  • cells bodies in the autonomic ganglia send fibers out to target tissues

NE/Epinephrine synthesis to release/breakdown

• Begins with tyrosine → tyrosine hydroxylase → becomes DA → dopamine B hydroxylase → NE → reaction occurs in adrenal glands to convert NE finally into EPI

  • note that all three of these NTs utilize tyrosine

  • DA → NE happens within vesicle in pre neuron

• NE synthesized → packaged by VMAT → released → undergoes post or pre synaptic binding (interacts with alpha and beta receptors on pre or post neuron) → uptaken by NET into pre neuron → either back to VMAT or goes to MAO for breakdown

Serotonin systems in the brain

• Two main groups of SER projections

  • Caudal raphe nuclei

    • project down into spinal cord

  • Rostral raphe nuclei

    • project into cortex and hypothalamus

Serotonin synthesis

• Begins with L-tryptophan synthesis → tryptophan hydroxylase → VMAT → release → bind to 5-HT receptors 4,6,7 (Gs+) or receptors 1 and 5 (Gs-) → reabsorbed by SERT → go back to VMAT or eventually broken down by MAO

Cholinergic receptors

• pedunculopontine pontine nucleus

• lateral dorsal tegmental area

• Ach receptors

  • nicotinic receptors (ligand gated ion channels)

  • muscarinic receptors (GPCR)

Ach synthesis and breakdown

• Glucose → pyruvate that enters mitochondria → acteyl coA + choline → choline acteyltransferase → yields Ach → enters synapse → Ach in synapse is broken down by acetylcholineesterase into choline and acetate!! only NT that is broken down in the synapse!!

  • This choline molecule can get reused in pre neuron for further synthesis of Ach

Types of neurons

• Interneurons are local → transmit signals within the same region of brain

• Projection neurons are long distance → transmit into another area of brain

Drugs acting on cholinergic neurons

• Curare plant prevents Ach from binding to post nicotinic receptors → no muscle contraction (competitive antagonist)

• Mushrooms with muscarine like compound → increases the activation of muscarinic receptors (agonist)

Glutamate synapse

• Glutamine precursor → glutaminase → vGlut packages → binds to NMDA, AMPA, and mGluR receptors → EAAT takes back into cell for recycling → back into glutamine

GABA synapse

• Glutamine → glutaminase → glutamate → glutamic acid decarboxylase (GAD) → GABA → binds to GABAa and GABAb

• enters pre neuron again via GABA transporter → glutamine

Phase 1 clinical trials

• Healthy human volunteers (20-100) → small short studies done in a few subjects

• Test escalating single doses to multiple doses

• PD and PK studies

• Safety and tolerance are the endpoints

Phase 2 clinical trials

• Several hundred patients with the target disease, can involve multiple institutions

• placebo controlled, double blind study (gold standard)

• endpoints: efficacy and safety

Phase 3 clinical safety

• Hundreds to thousands (300-3000) of patients with disease at multiple institutions

• placebo double blind

• Endpoint: dosing, must show clinical efficacy

  • key point in drug development

Concurrent work with phase 3 trials

• drug interactions studies in healthy volunteers

• long term toxicology: chronic? repro? teratogenic?

• manufacturing considerations (can we actually make it?)

• prep the market

The funnel

• high thorough output screens millions of drugs on immortalized cell line → pre clinical development → clinical development → approval