pharm - lab - basic principles

8/8/2019 PHARM - LAB - Basic Principles

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BASIC PRINCIPLESPharmacology. Defined as a science that deals with thestudy of substances that activate or inhibit the normal bodyprocesses upon their interaction with living systems.

Medical pharmacology: is dealing with prevention,diagnosation and treatment of diseases.Have therapeutical effect in patients or toxic effect on parasites.

Toxicology: is branch of pharmacology that dealing with harmfuleffects of substances on living systems.

pharmacon (from Greek: pharmakos) which originally denoted amagical substance or drug.


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PRINCIPLES OF THERAPY

- CURATIVE

- SUPRESSIVE

- PREVENTIVE

antibioticsantibiotics

drugs for treatmentdrugs for treatment

of hypertension,of hypertension,diabetes etc.diabetes etc.

malaria,malaria,

anticoncipientsanticoncipients


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Natural, semisynthetic and synthetic

Agonists, antagonists.

Endogenous: synthesise within the body(hormones(hormones,, transmitterstransmitters))

or xenobiotics (xenos= stranger) out the body.

Poisons are drugs synthesized by plants, animals

or of metals origin such as lead and arsenic.

Solid, liquid (nicotine) or gases (nitrous oxide)

SHOULD BE TRANSPORTED,SHOULD BE TRANSPORTED,INACTIVATED/EXCRETEDINACTIVATED/EXCRETED

THE NATURE OF DRUGS


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Physical properties

- solid, liquid, gas (may decide theroute of

administration)

- organic compounds;

proteins, carbohydrates, fats

- weak acids/bases

Size of the molecules- mol wt: 7-59 000; the majority 100-

1000

CHARACTER OF THE PHARMACONS


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DRUG-RECEPTOR BONDSElectrostatics ( strong between charged ionic molecules,

weaker (H bond) and very weak (van der Waals : dipol

interactions) are most common. Covalent

(phenoxybenzamine, alkylating agents)Hydrophobic

DRUG-BODY INTERACTIONS

Pharmacodynamic: The actions of the drugs on the body or onmicroorganisms or parasites within or on the body .

Pharmacokinetic: The actions of the body on the drugs. Is abranch of pharmacology dealing with the fate of drugs

administered externally to a living organism.


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DRUG-RECEPTOR INTERACTIONSK+1

K-1A + R AR

AR* RESPONSE

K+1

K-1

B + R BR NO RESPONSE

A= Agonist

B= Antagonist


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AGONIST : is a drug when binds to receptorsalters their activities and leads to a biological

response.Types of agonists:- Full agonist

- Partial agonist (Buprenorphine at , Pindolol at -receptors)

- Mixed (agonist + antagonist; Nalorphine antagonist at and

partial at )


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ANTAGONIST: Binds to receptors without

causing biological response.

Types of antagonists:- Competetive antagonism (reversible or irreversible)

- Noncompetetive antagonists

(reversible or irreversible)- Physiological antagonism ( Histamine Omeprazole;

glucocorticoids Insulin)

- Chemical antagonism (Heparine protamine sulfate)- Pharmacokinetic antagonism (warfarinPhenobarbital)


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TARGETS(CLPONTOK) FORDRUG ACTION

A drug is a chemical that affects normal

bodily function.

TARGET PROTEINS:

- RECEPTORS (RECEPTOR FAMILIES)

- ENZYMES

- ION CHANNELS

- CARRIERS


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Fulvestrantbreast cancer in

postmenopausal women

EthinylestradiolOestrogenreceptor

Naloxone,

Naltrexone

Morphine, DAMGOOpioid (-receptor)

PropranololNE, Isoprenaline-adrenoceptor

Tubocurarine

-Bungarotoxine

Acetylcholine

Nicotine

Nicotine ACh

receptor

ANTAGONISTSAGONISTSRECEPTORS


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BenzodiazepinesPicrotoxinGABA-gated

chloride channels

Cromakalim

Sulphonylureas

ATPATP-sensitive K

channels

4-AminopyridineVoltage-gated Kchannels

DihydropyridinesDivalent cations

Cd2+Voltage-gated

Ca-channel

AldosteroneAmilorideRenal tubule Na

channels

VeratridineLocal anaestheticsTetrodotoxin

Voltage-gated Nachannels

MODULATORSBLOCKERSION CHANNELS


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Didanosine

Zidovudine

Revers

transcriptase

SaquinavirHIV protease

AciclovirThymidine kinase

MethyldopaCarbidopaDopa

decarboxylase

AsprineCyclooxygenase

HemicholineCholine

acetyltransferase

Neostigmine

Organophosphate

Acetylcholinestrase

FALSE SUBSTRATESINHIBITORSENZYMES


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OmeprazoleProton pump

(stomach)

Cardiac glycosideNa+/K+ pump

FurosemideNa+/K+/Cl- co-

transporter (loop

of Henle)

ReserpineNE uptake

(vesicular)

Tricyclic

antidepressants

Cocaine

Noradrenaline

uptake 1

HemicholineCholine carrier

(nerve terminal)

FALSE

SUBSTRATES

INHIBITORSCARRIERS


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TYPES OF DOSE RESPONSE

CURVES

- Graded-dose response curveNull dose response curves

Cummalative- Quantal


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DOSE-RESPONSE

RELATIONSHIPS

Potency: Potencies or activities of

compounds are Expressed by EC50 orIC50 (in vitro); ED50 or ID50 (in vivo) and

defined as the amount of agonist needs to

produce 50% effect.

Efficacy: is the magnitude of the response

resulted upon the interaction of agonistswith the receptors.


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Relations between drug concentration and drug effect (panel A) or receptor-bound

drug (panel B).The drug concentrations at which effect or receptor occupancy is half-

maximal are denoted EC50 and KD, respectively. (2001 The McGraw Hill Companies, Inc.)


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Experimental demonstration of spare receptors, using different concentrations of an irreversible

antagonist. Curve Ashows agonist response in the absence of antagonist. After treatment with a low

concentration of antagonist (curve B), the curve is shifted to the right; maximal responsiveness is preserved,however, because the remaining available receptors are still in excess of the number required. In curve C,produced after treatment with a larger concentration of antagonist, the available receptors are no longer "spare";

instead, they are just sufficient to mediate an undiminished maximal response. Still higher concentrations ofantagonist (curves Dand E) reduce the number of available receptors to the point that maximal response is

diminished. The apparent EC50 of the agonist in curvesD

andE

may approximate the KD that characterizes thebinding affinity of the agonist for the receptor. (2001 The McGraw Hill Companies, Inc.)


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Spare receptors increase sensitivity to drug. In panel A, the free concentration of agonist is equal to the KDconcentration; this is sufficient to bind 50% of the four receptors present, resulting in the formation of twoagonist-receptor complexes. (Note:When the agonist concentration is equal to the KD, half the receptors will beoccupied. Remember that B/Bmax = C/[C + KD].) Agonist occupancy of these two receptors changes their

conformation so that they bind to and activate two effector molecules, resulting in a response. Because two offour effectors are stimulated by agonist-receptor complexes, the response is 50% of maximum. In panel B, the

receptor concentration has been increased tenfold (not all receptors are shown), and the KD for binding of agonistto receptors remains unchanged. Now a very much smaller concentration of free agonist (= 0.05 KD) suffices tooccupy two receptors and consequently to activate two effector molecules. Thus, the response is 50% ofmaximum (just as in panel A), even though the agonist concentration is very much lower than the K

D

. (2001 TheMcGraw Hill Companies, Inc.)


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Changes in agonist concentration-effect curves produced by a competitive antagonist

(panel A) or by an irreversible antagonist (panel B). In the presence of a competitiveantagonist, higher concentrations of agonist are required to produce a given effect; thus theagonist concentration (C') required for a given effect in the presence of concentration [I] of an

antagonist is shifted to the right, as shown. High agonist concentrations can overcome inhibitionby a competitive antagonist. This is not the case with an irreversible antagonist, which reduces the

maximal effect the agonist can achieve, though it may not change its EC50. (2001 The McGraw

Hill Companies, Inc.)


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Panel A:The percentage of receptor occupancy resulting from full agonist (present at a single concentration) binding to receptors in the presence ofincreasing concentrations of a partial agonist. Because the full agonist (filled squares) and the partial agonist (open squares) compete to bind to the samereceptor sites, when occupancy by the partial agonist increases, binding of the full agonist decreases. Panel B:When each of the two drugs is used aloneand response is measured, occupancy of all the receptors by the partial agonist produces a lower maximal response than does similar occupancy by thefull agonist. Panel C:Simultaneous treatment with a single concentration of full agonist and increasing concentrations of the partial agonist producesthe response patterns shown in the bottom panel. The fractional response caused by a single concentration of the full agonist (filled squares) decreases

as increasing concentrations of the partial agonist compete to bind to the receptor with increasing success; at the same time the portion of the responsecaused by the partial agonist (open squares) increases, while the total responseie, the sum of responses to the two drugs (filled triangles)gradually

decreases, eventually reaching the value produced by partial agonist alone (compare panel B). (2001 The McGraw Hill Companies)


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Graded dose-responsecurves for four drugs,

illustrating different

pharmacologic potencies

and different maximal

efficacies.


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Quantal dose-effect

plots. Shaded boxes(and the accompanying

curves) indicate the

frequency distribution

of doses of drugrequired to produce a

specified effect; ie, the

percentage of animalsthat required a

particular dose toexhibit the effect. Theopen boxes (and the

corresponding curves)

indicate the cumulative

frequency distributionof responses, which are

lognormally distributed.


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RECEPTOR FAMILIES Intracellular receptors: the ligand must get into the cells.

e.g. ( nitric oxide (NO), corticosteroids,

mineralocorticoids, sex steroids, vitamin D and thyroidhormone). The observed response needs 30 minutes ormore.

Ligand-Regulated Transmembrane Enzymes Including

Receptor Tyrosine Kinases (insulin, epidermal growthfactor EGF, platelet-derived growth factor PDGF, atrialnatriuretic factor ANF, transforming growth factor- TGF, other trophic hormones).

Ligand-Gated ion chanels. The response very fast (fewms)e.g. Nicotinic, GABA receptors

G Protein-coupled receptors (response second to mins)


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Known transmembrane signaling mechanisms:

1:A lipid-soluble chemical signal crosses the plasma membrane and acts on an intracellular receptor (which may

be an enzyme or a regulator of gene transcription);

2:the signal binds to the extracellular domain of a transmembrane protein, thereby activating an enzymatic

activity of its cytoplasmic domain;

3:the signal binds to the extracellular domain of a transmembrane receptor bound to a protein tyrosine kinase,which it activates;

4:the signal binds to and directly regulates the opening of an ion channel;

5:the signal binds to a cell-surface receptor linked to an effector enzyme by a G protein. (R, receptor; G, Gprotein; E, effector [enzyme or ion channel].) (2001 The McGraw Hill Companies)


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Mechanism of glucocorticoid action.

The glucocorticoid receptor polypeptide

is schematically depicted as a protein

with three distinct domains. A heat-shock

protein, hsp90, binds to the receptor in

the absence of hormone and prevents

folding into the active conformation of

the receptor. Binding of a hormone ligand

causes dissociation of the hsp90 stabilizer

and permits conversion to the active

configuration.


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Mechanism of activation of the EGF receptor, a representative

receptor tyrosine kinase.The receptor polypeptide has extracellular

and cytoplasmic domains, depicted above and below the plasmamembrane. Upon binding of EGF (circle), the receptor converts from

its inactive monomeric state (left) to an active dimeric state (right), in

which two receptor polypeptides bind noncovalently in the plane ofthe membrane. The cytoplasmic domains become phosphorylated (P)on specific tyrosine residues (Y) and their enzymatic activities areactivated, catalyzing phosphorylation of substrate proteins (S). /2001The McGraw Hill Companies, Inc./


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Cytokine receptors, like receptor tyrosine

kinases, have extracellular and intracellular

domains and form dimers. However, afteractivation by an appropriate ligand, separate mobileprotein tyrosine kinase molecules (JAK) are

activated, resulting in phosphorylation of STAT

molecules. STAT dimers then travel to the nucleus,

where they regulate transcription.(2001 The McGraw Hill Companies)


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The nicotinic

acetylcholine receptor, a

ligand-gated ion channel.The receptor molecule is

depicted as embedded in a

rectangular piece of plasma

membrane, with

extracellular fluid above

and cytoplasm below.Composed of five subunits

(two a, one b, one g, and

one d), the receptor opens a

central transmembrane ionchannel when acetylcholine

(ACh) binds to sites on the

extracellular domain of its a

subunits.(2001 The McGraw Hill

Companies, Inc. )


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G-PROTEIN-COUPLED RECEPTORS Consist of extracellular N-terminal and intracellular C-terminal domain connected

by a single peptide chain passing the plasma membran seven times and thus formsthe extra and intracellular loops. The third intracellular loop is the region to whichG-proteins are coupling.

G-proteins consists of three subunits , and . GTP and GDP bind to -subunit. At rest GDP is binding to (GDP-, trimer). Upon attachment of agonist toreceptor catayses the conversion of GDP to GTP ( then -GTP complex dissociates from-complex and interacts with a target protein, eg enzyme Adenylate cyclase). The GTPaseactivity of the -subunit is enhanced when -GTP complex binds to the target protein andthus results in hydrolysis of GTP to GDP.

-GTP and complexes are the active forms of G-proteins.

Main classes of G-protein: Gs, Gi, Gq

Cholera toxin acts only on Gs persistent activation Pertussis toxin acts on Gi Targets For G-proteins: second messengers (adenylate

cyclase switch on by Gs (cAMP production) ;

Phospholipase C (generates IP3 and DAG) ; Ion channels(Ca2+, K+). e.g. adrenaline, acetylcholine, dopamine,serotonin, opioids.


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PIP2phospholipase C

DAGIP3

Activation of protein

kinase CRelease of intracellularCa2+

PIP2= Phosphatidylinositolbiphosphate


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The guanine nucleotide-dependent activation-inactivation cycle of G proteins.The agonistactivates the receptor (R),which promotes release of GDP from the G protein (G), allowing entry of

GTP into the nucleotide binding site. In its GTP-bound state (G-GTP), the G protein regulatesactivity of an effector enzyme or ion channel (E).The signal is terminated by hydrolysis of GTP,

followed by return of the system to the basal unstimulated state. Open arrows denote regulatory

effects. (Pi, inorganic phosphate.) /2001 The McGraw Hill Companies/


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Transmembrane topology of a typical serpentine receptor.The receptor's amino (N) terminal is extracellular (above theplane of the membrane), and its carboxyl (C) terminal intracellular. The terminals are connected by a polypeptide chain thattraverses the plane of the membrane seven times. The hydrophobic transmembrane segments (light color) are designated byroman numerals (I-VII).The agonist (Ag) approaches the receptor from the extracellular fluid and binds to a site surroundedby the transmembrane regions of the receptor protein. G proteins (G) interact with cytoplasmic regions of the receptor,especially with portions of the third cytoplasmic loop between transmembrane regions Vand VI.The receptor's cytoplasmic

terminal tail contains numerous serine and threonine residues whose hydroxyl (-OH) groups can be phosphorylated. Thisphosphorylation may be associated with diminished receptor-G protein interaction. (2001 The McGraw Hill Companies, Inc. )


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Possible mechanism for desensitization of the .... () (). . . () ( , ) () . , (),

. , () (), . 2001


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The cAMP second

messenger pathway.

Key proteins include hormone

receptors (Rec), a stimulatory

G protein (Gs), catalytic

adenylyl cyclase (AC),

phosphodiesterases (PDE)that hydrolyze cAMP, cAMP-

dependent kinases, with

regulatory(R) and catalytic (C)

subunits, protein substrates

(S) of the kinases, andphosphatases (P'ase),which

remove phosphates from

substrate proteins. Open

arrows denote regulatory

effects.

The McGraw Hill Companies,Inc. 2001.


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The Ca2+-

phosphoinositide

signaling pathway.

Key proteins include

hormone receptors (R), a G

protein (G), aphosphoinositide-specific

phospholipase C (PLC),protein kinase C (PK-C),

substrates of the kinase (S),calmodulin (CaM), and

calmodulin-binding enzymes(E), including kinases,phosphodiesterases, etc.

(PIP2, phosphatidylinositol-

4,5-bisphosphate; DAG,

diacylglycerol. Asteriskdenotes activated state. Open

arrows denote regulatoryeffects.)

2001 The McGraw HillCompanies, Inc.


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Possible relations between the therapeutic and toxic effects of

a drug, based on different receptor-effector mechanisms.


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The relationship between dose and effect can be separated into pharmacokinetic (dose-concentration)

and pharmacodynamic (concentration-effect) components. Concentration provides the link between

pharmacokinetics and pharmacodynamics and is the focus of the target concentration approach to

rational dosing. The three primary processes of pharmacokinetics are absorption, distribution, and

elimination.

pharm - lab - basic principles

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