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Cyp450 Pavitraraj
 

Cyp450 Pavitraraj

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CYTOCHROME P450 for physicians....a ppt. that give you a brief overview about the much talked about enzyme system.

CYTOCHROME P450 for physicians....a ppt. that give you a brief overview about the much talked about enzyme system.

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  • Cytochrome P450steroid hormone biosynthesis from cholesterolmetabolism of Xenobiotics-compounds which are not normally found in the bodyDrugsCompounds in food produced by cooking (polyaromatic hydrocarbons, also in tobacco smoke) or microorganisms typically organic molecules which are poorly soluble in water
  • Location – SER / CytosolSite – liver ,kid lungs…/ hepatic plasmaEnzymes Reaction catalysednote
  • *Reactions *Enzymes involvedPhase I - CYP450 , FMO , hydroxylases (alcdehydrogenase , xanthineoxidase , MAO)Phase II – conjugation - ….
  • The figure shows increasingly microscopic levels of detail, sequentially expanding the areas within the black boxes. CYPs embedded-phospholipidbilayerof the endoplasmic reticulum (ER). located on the cytosolic surface of the ER. NADPH-cytochrome P450 oxidoreductase, transfers electrons to the CYPA single NADPH-CYP oxidoreductase species transfers electrons to all CYP isoforms in the ER. Each CYP contains a molecule of iron-protoporphyrin IX that functions to bind and activate O2. Substituents on the porphyrin ring are methyl (M), propionyl (P), and vinyl (V) groups.
  • Existence of inter-individual differences in DNA sequences coding for one specific gene, giving rise to different functional and (or) morphological traitsGene – made of DNA containing exons & introns which have coding n non coding sequenceChromosome– contains multiple copies of genes or many genesChromatin – condensed chromosomesAllele – (e.g. Aa)one member of a pair or a series of different forms of a gene.(members of a gene that produce different traits in gene charesteristics)Could be coding or non coding sequence. Genotype for the gene is the set of alleles that the individual posses.Diploid organisms (2 chromosomes) 2 alleles make up the genotype.A phenotype is any observable characteristic or trait of an organism: such as its morphology, development, biochemical or physiological properties ...The genotype is the characteristic that cannot be observed. The genotype is the genetic constitution of a cell, an organism, or an individual
  • CYP3A4- inducers macrolides ,glucocorticoids , rifampin (ocp failure) , st johns wort (cycloporin)CYP2E1 – inducer chralc , INH (paracetamol)CYP1A2 – inducer non pharmacological agents charcoal boriled meat , smoke , PAHC
  • Patients with alcohol dependence are at increased risk of acetaminophen toxicity!
  • This analgesic antipyretic drug is quite safe in therapeutic doses (1.2 g/d for an adult). It normally undergoes glucuronidation and sulfation to the corresponding conjugates, which together comprise 95% of the total excreted metabolites. The alternative P450-dependent GSH conjugation pathway accounts for the remaining 5%. When acetaminophen intake far exceeds therapeutic doses, the glucuronidation and sulfation pathways are saturated, and the P450-dependent pathway becomes increasingly important.
  • REVERSIBLE INHIBITION
  • Astemizole (torsades de pointes )Terfenadine (active metabolite fexofenadineprolonged QT interval , torsades de pointes ,polymorphic ventricular tachycardia due to blockage of the delayed rectifer K ch in the heart) Cisapride (ventricular arrhythmias) Felodipine (vascular selective Ca ch block dihydropyridine , long t1/2) Cyclosporine (immunosuppressant - nephrotoxicitySaquinavir (PI)TriazolamTheophylline (cvscnsrs)
  • Interactions become a problem when multiple drugs are simultaneously administered, for example in elderly patients, who on a daily basis may take prescribed antiinflammatory drugs, cholesterol-lowering drugs, blood pressure medications, a gastric acid suppressant, an anticoagulant, and a number of over-the-counter medications.

Cyp450 Pavitraraj Cyp450 Pavitraraj Presentation Transcript

  • Cytochrome P450
    The P450 enzymes have unique spectral properties, and the reduced forms combine with carbon monoxide to form a “PINK” compound (hence 'P') with absorption peaks near 450nm (range 447-452nm).
    Dr. Pavitra Raj Dewda
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  • Dr. Pavitra Raj Dewda
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    Contents
  • 1.BIOTRANSFORMATION
    What is it?
    What are the Components?
    What is the Process?
    Dr. Pavitra Raj Dewda
    3
    xenobiotics metabolism
    substances absorbed across the lungs or skin or, more commonly, ingested either unintentionally as compounds present in food and drink or deliberately as drugs for therapeutic or "recreational" purposes.
    Organs of Biotransformation
    LIVER (hepatocytes)
    kidney (proximal tubule)
    lungs (type II cells)
    testes (Sertoli cells)
    skin (epithelial cells)
    intestines (microbial flora)
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  • Clinical CorrelateMetabolites can alter the pharmacological action of drug qualitatively
    TerfenadineFexofenadine
    FluoxetineNorfluoxetine
    Dr. Pavitra Raj Dewda
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    METABOLITE
    CYP3A4
    Blocks histamine H 1 receptors only & not cardiac K+ channels
    Non sedating antihistaminic
    Can Block K+ Channel Cause Arrhythmias
    METABOLITE -demethylated
    T1/2 – 50 hrs
    T1/2 – 10 days , COMPETES for hepatic oxidases with TCA ect..days after administration of the parent drug has been stopped.
    CYP2D6
  • 2.Cytochrome P450 isoenzymes (CYPs)
    What are they?
    Nomenclature
    CYP reaction
    Dr. Pavitra Raj Dewda
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    In its reduced (Fe2+) form, it binds carbon monoxide to give a complex that absorbs light maximally at 450 nm
    Proteins with at least 40% amino acid sequence homology.
    In humans up to 21 families have been described.
    • In humans - 21 families, 20 subfamilies and 57 genes
    • Of these CYP 1, 2 and 3 constitute 70% of total hepatic CYPs which responsible for 94% of drugs metabolism
    • Xenobiotic metabolising - 12 CYPs (CYP1A1, 1A2, 1B1, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4, and 3A5)
    • Some show genetic polymorphism while others can be induced or inhibited
    >55 amino acid sequence homology & 57 such isotype
    40-55% amino acid sequence homology & about 20 subfamilies are imp in man
  • What are CYPs ?
    Superfamily of haemoprotein enzymes found on the membrane of SER
    The heme is a cofactor which contains iron-protoporphyrin IXthat functions to bind & activate Oxygen and transfer electrons.
    CYPs are also known as
    Mixed function oxidases
    Poly substrate Mono-oxygenases
    Location
    liver , intestine , lungs , kidneys , brain etc.
    Dr. Pavitra Raj Dewda
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  • CYP Oxidation Reaction
    Dr. Pavitra Raj Dewda
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  • Dr. Pavitra Raj Dewda
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    NADPH +H++ O2+RH
    NADP++H2O+R-OH
  • Microsomal drug oxidations
    Reaction
    step 1
    Oxidized (Fe3+) P450 combines with a drug substrate to form a binary complex.
    step 2
    NADPH donates an electron to the flavoprotein P450 reductase, which in turn reduces the oxidized P450-drug complex .
    step 3
    A second electron is introduced from NADPH via the same P450 reductase, which serves to reduce molecular oxygen and to form an "activated oxygen"-P450-substrate complex”
    step 4
    This complex in turn transfers activated oxygen to the drug substrate to form the oxidized product
    Sometimes the oxidised product is a Epoxide (highly reactive electrophiles that can bind to cellular nucleophiles found in protein, RNA, and DNA, resulting in cell toxicity and transformation)
    EpoxideHydrolaseshydrolyse such epoxides
    microsomalepoxidehydrolase (mEH)
    soluble epoxidehydrolase (sEH)
    Dr. Pavitra Raj Dewda
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  • Carbamazepine v/s newer antiepileptics
    Carbamazepine (prodrug)
    CYP3A
    Carbamazepine -10,11-epoxide (active)
    mEH
    Dihydrodiol (inactive)
    Newer – Gabapentine & Levetiracetamare metabolized only by CYP’s
    Dr. Pavitra Raj Dewda
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    CYP3A4
    • Drowsiness
    • Headaches
    • Migraines
    • Motor coordination impairment
    • Upset stomach
    Valnoctamide
    Valproic acid
  • 3.Genetic Polymorphism
    What is it?
    Phenotypic (allelic) variants
    Examples
    New approach to personalized Rx
    PRINCIPLE
    Testing for Polymorphisms (genotyping) could predict therapeutic failures or ADRs therefore used to optimize drug choice, avoid serious ADRs and decrease medical costs!
    Dr. Pavitra Raj Dewda
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  • Genetic Polymorphism of CYP450
    Polymorphism - www.imm.ki.se/CYPalleles/
    Is Genetic variations in a population when both gene or allelic variants exist with a frequency of at least one percent
    CYP enzymes in families 1-3 are polymorphic
    CYP2D6, CYP2C19 and CYP2C9 –main polymorphic forms responsible for almost 40% of P450 metabolism
    Homozygous mutations in the CYP1B1 gene are associated with primary congenital glaucoma
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  • P450 Phenotypes based on the allelic variation & clinical importance
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  • From impossible to possible
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  • The AmpliChip (Roche Molecular Systems, Inc.)
    • Tests the DNA from a patient's white blood cells collected in a standard anticoagulated blood sample for 29 polymorphisms and mutations for the CYP2D6 gene and 2 polymorphisms for the CYP2C19
    • According to FDA labeling, "Information about CYP2D6 genotype may be used as an aid to clinicians in determining therapeutic strategy and treatment doses for therapeutics that are metabolized by the CYP2D6 product"
    Dr. Pavitra Raj Dewda
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  • CYP450 Enzyme Induction
    What is enzyme induction?
    What are the consequences of enzyme induction?
    What is the mechanism of enzyme induction?
    Examples
    Dr. Pavitra Raj Dewda
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  • What is enzyme induction?
    Increase in the CYP450 metabolizing capacity
    Requires repeated drug administration
    Onset & Duration of induction
    Depends on ‘kinetics ’ & ‘half life’ of the drug (ranges from 1-6 days)
    Peak induction4-14 days
    On withdrawing inducer the CYP returns to their original level in 1-3 weeks
    Mechanism
    Enhancing the rate of its synthesis*
    Increasing transcription
    Reducing its rate of degradation /substrate stabilization
    Increasing translation
    Dr. Pavitra Raj Dewda
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  • What is the mechanism of enzyme induction?
    Is incompletely understood but is similar to a steroid that bind to nuclear receptors (induction/regulatory receptors).
    Drugs bind to the ligand binding domain of a soluble protein, termed the aromatic hydrocarbon (Ah) receptor which is cytosolic in nature.
    This binding leads to conformational change in receptor
    Transportation of this complex to the nucleus by an Ah-receptor nuclear translocater
    In the DNA binds Ah-receptor response elements thereby promoting transcription of the gene
    Dr. Pavitra Raj Dewda
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    Non-transcriptional mechanisms
    Protein / Substrate stabilization or increased protein translation i.e. decreased degradation.
    e.g. CYP2E 1 by ethanol and isoniazide
    CYP3A by clotrimazole
  • Pharmacological induction
    Oral contraceptives & steroids
    Rifampicin
    Inactivated & Excreted
    Result
    Contraceptive Failure
    Dr. Pavitra Raj Dewda
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    Other CYP3A inducers
    • Glucocorticoids
    • Anticonvulsants
    Induction
    CYP3A4
  • Pharmacological induction/Herbal Drug
    Cyclosporin
    St. Johns Wort
    Metabolite
    Result
    Impaired Immune response
    Rejection
    Dr. Pavitra Raj Dewda
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    Induction
    CYP3A4
  • Pharmacological induction
    Paracetamol
    Ethanol(chronic)
    INH
    Toxic Metabolite(N-acetylbenzoiminoquinone)
    Result
    Hepatotoxicity
    Dr. Pavitra Raj Dewda
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    Induction
    CYP2E1
  • Pharmacological induction - paracetamol cont…
    Dr. Pavitra Raj Dewda
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  • Cigarette smoke Benzpyrene
    CYP1A27-8epoxidation
    Dr. Pavitra Raj Dewda
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    Non Pharmacological (CYP1A2) inducers
    activates
    +induces
    synthesis +
    • Polycyclic hydrocarbons-Epoxide formation
    • Charcoal – barbecued food
    • Plasticizers (polychlorinated biphenyls)
    • High dosing requirements of drugs like ‘Theophylline’ in smokers
    Carcinogen
  • Enzyme Inhibition
    What is enzyme inhibition?
    What are the types?
    Specific examples
    Dr. Pavitra Raj Dewda
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  • What is enzyme inhibition?
    Certain substrates can block P450 enzyme isoforms (specifically) that metabolize other drugs/substrates
    A drug may inhibit one P450 isoenzyme while being metabolized its self by another.
    E.g. Quinidine metabolized by CYP3A4 and inhibits CYP2D6
    Also some times a product of drug’s oxidation may inhibit its own metabolism  “Suicide Inhibitor”
    E.g. Chloramphenicol , Spironolactone etc…
    Unlike induction (1-3 weeks for onset) , enzyme inhibition usually begins with the first dose of the inhibitor and has a fast time course.
    Dr. Pavitra Raj Dewda
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  • The determinant of potency of an inhibitor is the strength of the bond between the prosthetic heme iron and the lone electron pair of inhibitors
    30
    H2-receptor antagonist has a imidazole ring which binds competitively binding to the H 2 receptor & also selectively to the heme prosthetic group of CYP3A4 and 2D6
    imidazole-containing antifungal & CYP3A4 inhibitor
    Ketoconazole (/Itraconazole>fluconazole )is a more potent inhibitor because of higher lipophilicity resulting in stronger hydrophobic interactions to CYP3A4
    Ketoconazoleinhibits metabolism of anti-HIV viral protease inhibitors
  • Dr. Pavitra Raj Dewda
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    e.g. of Irreversible Inhibition due to formation of a MI
    Inhibitors
    Erythromycin, Clarithromycin (but not azithromycin)
    Grape fruit juice (furanocoumarins)
    Metabolism of drugs Inhibited (increasing Bioavalibility)
    Astemizole
    Terfenadine
    Cisapride
    Felodipine
    Cyclosporine
    Saquinavir
    Theophylline
    Triazolam
    Illustrative Case
    A 47-year-old man recently diagnosed with HIV infection visited his physician with flushing, dizziness and swelling of the feet and ankles. He had been taking sustained-release nifedipine for treatment of hypertension for about three years. Approximately two weeks earlier, his physician had prescribed a combination of lamivudine, zidovudine and the protease inhibitor ritonavir.
    Ritonavir (inhibitor CYP3A)increases the Bioavalibility of Nifedipine
    Erythromycin - oxidised by CYP3A4
    Nitroso Metabolite + Haem portion of the CYP enzyme
    Stable MI complex is inactive
    CYP3A4
    (torsades de pointes / prolonged QT interval)
    (ventricular arrhythmias ;
    the new drug ITOPRIDE is metaboilsed by FMO3)
    nausea, diarrhea, increase in heart rate, arrhythmias, and CNS excitation
  • Suicide inhibitors—inactivators that attack the heme or the protein moiety—includes ;
    Steroids (ethinyl estradiol, norethindrone, and spironolactone)
    Fluroxene
    Allobarbital
    The analgesic sedatives allylisopropylacetylurea
    Diethylpentenamide
    Ethchlorvynol
    Carbon disulfide
    Chloramphenicol
    Grapefruit furanocoumarins
    Deprenyl
    Phencyclidine
    Ticlopidine and clopidogrel
    Ritonavir
    Propylthiouracil
    Dr. Pavitra Raj Dewda
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  • e.g. of drugs inhibiting CYP2D6
    In order of inhibiting potency
    Paroxetine(is also metabolized)>Fluoxetine>Sertaline
    Dr. Pavitra Raj Dewda
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    CYP2D6
    (substrates)
    If combined with Trazadone
    Postural Hypotension & probably Pirpaism
    If combined with TCAs
    Cardio toxicity
    Convulsions
    Coma
  • Dr. Pavitra Raj Dewda
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  • ROLE OF DRUG METABOLISM IN THE DRUG DEVELOPMENT PROCESS
    Efficacy and Safety ; Both depend on drug metabolism
    It is necessary to determine how and by which enzymes a potential new drug is metabolized
    drug-drug interactions
    genetic polymorphisms
    Ideally, the best drug for a trial would be -
    metabolized by several CYPs so that variability in expression levels of one CYP or drug-drug interactions would not significantly impact its metabolism and pharmacokinetics
    Dr. Pavitra Raj Dewda
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  • Summary
    Most important CYPs involved in drug metabolism are CYP3A4/5, CYP1A2, CYP2D6, CYP2C9, CYP2C19, CYP2E1
    Knowledge about polymorphisms in CYPs (CYP2D6, CYP2C9, CYP2C19), enzyme induction & inhibition helps filtering out drugs for clinical trials and prevents unnecessary patient drug and drug interactions .
    Dr. Pavitra Raj Dewda
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    Chapter 15
    Text 14
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    Have a great day!
  • Extra
    Dr. Pavitra Raj Dewda
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  • How can we demonstrate a role for cytP450 in biotransformation of a XB?
    cytP450 activity increases after exposure to XB
    Enzymatic inhibitors of cytP450 (e.g. aminobenzotriazole) have an effect
    Absorption spectrum of cytP450 is modified in presence of XB
    Reaction can be reconstituted with components of the catalytically cycle (e.g. NADPH)
    Dr. Pavitra Raj Dewda
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  • Hydroxylation of substrates by cytochrome P450-Deactivation (detoxication)
    Dr. Pavitra Raj Dewda
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  • Role of cytochrome P450 and peroxidase in activation of benzene in bone marrow
    Dr. Pavitra Raj Dewda
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    PHS – prostaglandin H synthase
  • Halothane hepatitis and activation by oxidation and reduction
    Dr. Pavitra Raj Dewda
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  • Reactions catalyzed by cytochrome P450
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    CYP450 ENZYME & SUBSTRATES
  • Some inducers of cytochrome P450 isozymes
    Dr. Pavitra Raj Dewda
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  • Some inhibitors of cytochrome P450 isozymes
    Dr. Pavitra Raj Dewda
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