L03 Toxicokinetics (ADME) PDF

6/6/2024 L03 Toxicokinetics (ADME) Absorption-Distribution-Metabolism-Excretion Timo Hamers 1 Setup Toxicokinetics - ADME  Absorption = Uptake  Distribution  Metabolism = Biotransformation  Excretion...

6/6/2024 L03 Toxicokinetics (ADME) Absorption-Distribution-Metabolism-Excretion Timo Hamers 1 Setup Toxicokinetics - ADME  Absorption = Uptake  Distribution  Metabolism = Biotransformation  Excretion 2 2 1  6/6/2024 Fate and effect of chemical compounds Exposure Toxicokinetics What does the body do to the compound? Toxicodynamics Wat does the compound do to the body? 3 3 Toxicokinetics: fate of a compound after exposure  ADME Absorption Distribution Metabolism Excretion Klaassen, 2008 Casarett & Doull’s Toxicology 7th edition 4 4 2  6/6/2024 Setup Toxicokinetics - ADME  Absorption = Uptake GI tract Lung  Distribution  Metabolism = Biotransformation  Excretion 5 5 Absorption after oral intake  Enterohepatic circulation Repeat of absorption, conjugation (=metabolism), elimination, deconjugation, absorption, etc.  Presystemic elimination Elimination before systemic distribution can take place.  Portal vein 6 6 3  6/6/2024 Absorption after intake by inhalation: gasses Source: Patterns in Assistive Technology Training and Services http://webschoolsolutions.com/patts/systems/heart.htm 7 7 Absorption of gasses in the lungs Alveoli cavity Ibrahim & Garcia-Contreras, 2013 Therapeutic Delivery 4: 8 Can be very fast (ether) Depending on air:water partitioning constant (Henry coefficient = pair / Cwater) 8 8 4  6/6/2024 Absorption of inhaled particles 5-30µm 1-5µm Cigarette smoke contains 0.16 µg per cigarette 0.3 x 25 x 0.16 = 1.2 µg/day > 25 cigarettes per day Outdoor air 0.3 x 20 x 0.002 = 0.012 µg/day > 0.002 µg per m3 > 20 m3 per day Food 0.06 x 0.6 x 50 = 1.8 µg/day > 50 µg per kg > 600 g per day Drinking water 0.06 x 2 x 1 = 0.12 µg/day > 1 µg/l > 2 l per dag + 3.312 µg/day 11 11 Setup Toxicokinetics - ADME  Absorption = Uptake  Distribution Accumulation Barriers  Metabolism = Biotransformation  Excretion 12 12 6  6/6/2024 Accumulation in tissue other than target e.g. lipophilic compounds  Lipophilic = Fat-loving, for example PCB Cl Cl  Accumulate in fat tissue Cl Cl  Excretion Cl Cl Slowly through blood → urine Quickly through breastmilk 13 13 Loosing weight increases bioavailability of lipophilic compounds! 14 14 7  6/6/2024 Accumulation  Lipophilic compounds (high Kow) in fat tissue Released during fat mobilization, e.g. loosing weight Risk in case of small fat deposits (foetus, infant)  Pb++, Sr++ and F- in bones Exchange with Ca++ or OH- Has effect (Sr++ and F-) or no effect (Pb++) on bones Released during Ca-mobilization  Cadmium in liver and kidneys Efficient binding to metallothionein Cd-MT complex itself is also nephrotoxic 15 15 Accumulation (in summary)  Selective binding or uptake into specific tissues Sometimes in an “accumulation organ” (POPs) Sometimes in the “target organ” (Sr++ and F-)  Accumulation In most cases not biologically available, i.e. not toxic Can be mobilized from deposit Dynamic equilibrium with concentration in blood 16 16 8  6/6/2024 Barriers in distribution  Blood-Brain Barrier (BBB)  Placenta 17 17 Blood-brain barrier  Endothelial cells tight junctions efflux by transporter proteins > multidrug resistant proteins (mdr) > multiresistant drug proteins (mrd) No pinocytosis Biotransformation capacity  Astrocytes (gliacells) Physical support Efflux by transporter proteins? Biotransformation capacity?  Exceptions, e.g. methylmercury (MeHg+) 18 18 9  6/6/2024 Minamata, Japan 1956 (MeHg) 19 19 Placenta  No a true “barrier”  Many lipophilic compounds diffuse through the placenta!  Defense by Active transport (mdr and oct proteins) Biotransformation capacity 20 20 10  6/6/2024 Setup Toxicokinetics - ADME  Absorption = Uptake  Distribution  Metabolism = Biotransformation Phase I, II, III Bioactivation Enzyme properties  Excretion 21 21 Sleeping Beauty Blood levels of a sleeping pill agent in time 22 22 11  6/6/2024 What is metabolism?  Biotransformation = Biochemical transformation AFTER uptake  GOAL (in case of toxic compounds): Accelerated excretion Detoxification  SIDE EFFECT Bioactivation = activation of compounds into more toxic compounds 23 23 Process of biotransformation Three phases: I. Hydrolysis/reduction/oxidation to create a reactive “handle” to the compound (-OH), (=O); (-COOH) II. Conjugation, coupling of a water soluble molecule to the handle of the compound III. Elimination/excretion: removal of the conjugated product from the body 24 24 12  6/6/2024 Phases in the biotransformation XENOBIOTIC Hydrophilic Polar Lipophilic Very lipophilic and persistent SEQUESTRATION storage in fat tissue PHASE I Oxidation, reduction or hydrolysis PHASE II Conjugation to water soluble molecule PHASE III Extracellular mobilization Excretion via bile Renal excretion 25 25 Phase I reactions  Oxidation Oxygen as electron acceptor (oxygenases and oxydases) NAD(P)+ as electron acceptor  Hydrolysis (breaking of the bond by H2O)  Reduction 26 26 13  6/6/2024 Biotransformation: example of a Phase I reaction OH CYP1A1 pyrene 1-OH-pyrene Oxidation of pyrene into 1-OH-pyrene 27 27 Phase I Oxidation Oxygen as electron acceptor (= oxidant)  Oxygenase (incorporating oxygen from O2 in substrate) E.g. Cytochrome P450 (CYP) E.g. Flavin monooxygenase (FMO) 28 28 14  6/6/2024 29 29 Examples of CYP mediated reactions  Hydroxylation  Epoxidation  Dealkylation 30 30 15  6/6/2024 Negative effect of biotransformation  Product of phase I may be very reactive  bio-activation  Reacts with macromolecule before it can be detoxified in phase II  Upon reaction with DNA: chemical mutagenesis  Basis for carcinogenicity of polycyclic aromatic hydrocarbons, vinyl chloride etc.  Model chemical: benzo(a)pyrene (BaP) 31 31 Three metabolite types formed upon biotransformation of BaP Diol-epoxides Phenols Casarett & Doull’s Toxicology Quinones 32 32 16  6/6/2024 DNA adduct of benzo(a)pyrene-diol epoxide  Local disturbtion in DNA double helix structure  Hampering proper DNA replication  leads to a change in nucleotide order in the DNA chain, inherited by daughter cells (mutation) 33 33 Phase II Conjugation Examples of groups that can be conjugated to reactive Phase I metabolites:  Glutathion by glutathion-S-transferase (GST)  Glucuronic acid by uridine difosfaat glucuronyl transferase (UGT)  Methylgroup by methyltransferase (COMT, NMT)  Sulfate group by sulfotransferase (SULT) 34 34 17  6/6/2024 Co-substrate and conjugating group (Phase II) The group that ultimately conjugates to the reactive Phase I metabolite is shown in blue, except for glutathione, where the whole tripeptide is conjugated 35 35 Phase II Most important conjugations Type Enzyme Co-substrate Glucuronidation UGT UDPGA Sulfonation SULT PAPS Glutathione coupling GST glutathione Methylation MT SAM 36 36 18  6/6/2024 From Phase I to Phase II Phase I Phase II 37 37 Phase II: Conjugation of paracetamol (acetaminophen) 40-60% 20-40%