metabolism of xenobiotics
DESCRIPTION
Metabolism of xenobiotics. Seminar No. 8. Q. 2. 1 . Phase of biotransforma tion = mainly oxidations. oxidations. Rea ctions occur mainly in ER, some in cytosol. Q. 3. A. 3. The s yst em of cytochrom e P-450 is composed from: - PowerPoint PPT PresentationTRANSCRIPT
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Metabolism of xenobiotics
Seminar No. 8
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Q. 2
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1. Phase of biotransformation = mainly oxidations
Reaction Xenobiotic (example)
Hydroxylation
Sulfooxidation
Dehydrogenation
Reduction
Hydrolysis
aromatic hydrocarbons
disulfides (R-S-R)
alcohols
nitro compounds (R-NO2)
esters
Reactions occur mainly in ER, some in cytosol
oxidations
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Q. 3
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A. 3
NADP+
FAD
FADH2
Fe++
hem
Fe+++
hem
NADPH H++
2 H+
cyt. reduktasa cyt P-450
RH
R OH
O2
H2O
The system of cytochrome P-450 is composed from:
• two enzymes (cytochrome reductase, cytochrome P-450)
• three cofactors (NADPH, FAD, hem)
• in ER, mitochondria
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Q. 4 + 5
R-H + O2 +
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A. 4 + 5 Hydroxylation
R-H + O2 + NADPH + H+ R-OH + H2O + NADP+
• substrate R-H reacts with O2
• monooxygenase = from O2 one atom O is inserted into substrate
(between carbon and hydrogen atom)
• the second O atom makes H2O, 2H come from NADPH+H+
• dioxygen is reduced to -OH group and water
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Q. 6
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A. 6
• Inducer may act on several levels:
• Inducer in complex with intracellular receptor enters
nucleus and binds to DNA enhances the transcription of
mRNA
• Decreases the degradation of mRNA and/or CYP
• Influences the poststranscription modifications of mRNA
• May cause the hypertrophy of ER
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insufficient effectof applied drug
CYP inducer
higher levels of drugunwanted effects
overdosing
CYP inhibitor no interference
normal (expected)
effect of remedy
optimal therapy
Influence of CYP inducers/inhibitors on the effect of drug (remedy)
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Q. 7
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A. 7
• if concurrently aplied inducer + medicament metabolized with
the same CYP isoform remedy is catabolized faster
is less effective
• diclofenac is less effective
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Q. 8
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A. 8
• if concurrently aplied inhibitor + medicament metabolized
with the same CYP isoform remedy is catabolized more
slowly higher concentration in blood adverse effects
(overdosing)
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Q. 9
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A. 9 - II. Phase of biotransformation
• conjugation – synthetic character
• xenobiotic after I. phase reacts with conjugation reagent
• the product is more polar – easily excreated by urine
• conjugation reactions are endergonnic – they require energy
• reagent or xenobiotic has to be activated
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A. 9 Overview of conjugation reactions
Conjugation Reagent Group in xenobiotic
Glucuronidation
Sulfatation
Methylation
Acetylation
By GSH
By amino acid
-OH, -COOH, -NH2
-OH, -NH2, -SH
-OH, -NH2
-OH, -NH2
Ar-halogen
-COOH
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A. 9 Overview of conjugation reactions
Conjugation Reagent Group in xenobiotic
Glucuronidation
Sulfatation
Methylation
Acetylation
By GSH
By amino acid
UDP-glucuronate
PAPS
SAM
acetyl-CoA
glutathione
glycine, taurine
-OH, -COOH, -NH2
-OH, -NH2, -SH
-OH, -NH2
-OH, -NH2
Ar-halogen
-COOH
GSH = glutathione, PAPS = phosphoadenosine phosphosulfate
SAM = S-adenosyl methionine
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PAPS is sulfatation reagentphospho adenosine phospho sulfate
O
OHO
O
P
PO
O
OSO
O
O
O
O
O
N
N
N
N
NH2
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The conjugation reactions of phenol
konjugace
O glukuronát O sulfát
H
hydroxylace (CYP 450)
OH
glucuronide sulfate
conjugation
hydroxylation
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Glutathione (GSH)
HOOCN
N COOH
O
H
CH2
SH
O
H
NH2
R-X + GSH R-SG + XH
R-X halogen alkanes (arenes)
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Conjugation with aminoacids
• glycine, taurine
• xenobiotics with -COOH groups
• the products of conjugation are amides
• endogenous substrates – bile acids
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Biotransformation of toluene (sniffers)
CH3 CH2OH COOH
toluen benzylalkohol benzoová kys.
C
OH
O glycin
C
NH
O
CH2 C
OH
O
benzoová kys. hippurová kyselina(N-benzoylglycin)
toluene benzyl alcohol benzoic acid
benzoic acid
glycine
hippuric acid
(N-benzoylglycine)
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EthanolHow can you calculate the level of alcohol in blood?
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alcohol in blood (‰) = fm
m
body
alcohol
(kg)
(g)
0.67 (males)0.55 (females)
Per milles of alcohol in blood‰ = per mille = 1/1000
How do you calculate malcohol ?
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malcohol is calculated from volume and density
malc (g) = Valc (ml) × 0.8 (g/ml)
volume of pure alcohol is
calculated from volume fraction
beer 3-6 %
wine 6-12 %
liquors 40-50 %
density
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Metabolism of ethanol
Enzyme Subcellular localization
Alcohol dehydrogenase (AD) cytosol
MEOS endoplasmic reticulum (ER)
Catalase (hem) peroxisome
Acetaldehyde dehydrogenase cytosol / mitochondria
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Write AD and AcD reactions
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H3C C
H
H
O
H
+ NAD H3C C
H
O+
alkoholdehydrogenasa
aldehyddehydrogenasa
+ H2O H3C C
OH
H
O
H
H3C C
OH
ONAD- 2H
NADH+H
H3C C
H
O
acetaldehyd
aldehyd-hydrát octová kyselina
acetaldehyd dehydrogenase
(AcD)
alcohol dehydrogenase (AD)
acetaldehyde
acetaldehyde hydrate acetic acid
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Alternative pathway of alcohol biotransformation
occurs in endoplasmic reticulum
MEOS (microsomal ethanol oxidizing system, CYP2E1)
CH3-CH2-OH + O2 + NADPH+H+ CH3-CH=O + 2 H2O + NADP+
activated at higher consumption of alcohol = higher blood level of alcohol
(> 0.5 ‰) - chronic alcoholics
increased production of acetaldehyde
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Q. 11
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A. 11
Acetate is converted to acetyl-CoA
A) in liver synthesis of FA TAG VLDL
B) in other tissues CAC CO2 + energy
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ml1000
ml1058,0
(l)1
(ml)058,0
(l)1
(g)046,0
(l)1
(mmol)1
0,06 ‰
A. 13
Mr = 46 density = 0,8 g/ml
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Q. 14
Metab. feature Change Explanation
NADH/NAD+
Lactate/pyruvate
CAC
Glycolysis
Gluconeogenesis
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A. 14
Metab. feature Change Explanation
NADH/NAD+ NADH overproduction in AD/AcD reactions
Lactate/pyruvate NADH excess in cytosol in removed by LD reaction
CAC NADH is allost. inhibitor of ICDH and 2-OGDH
Glycolysis shortage of NAD+
Gluconeogenesis shortage of pyruvate + OA (= predominate lactate + malate)
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Q. 15
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A. 15
A) Decreased gluconeogenesis due to lack of oxaloacetate –
hypoglycemia especially after fasting ingestion of alcohol
(+ usually poor dietary habits in chronic alcoholics)
B) Excess of lactate in cytosol increased lactate in blood plasma
lactic acidosis
C) Excess of acetyl-CoA synthesis of FA +TAG liver steatosis
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Consider that
• ethanol is soluble both in polar water and non-polar lipids
• easily penetrates cell membranes
• goes through hydrophilic protein channels or pores
• as well as hydrophobic phospholipid bilayer
!
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Metabolic consequences of EtOH biotransformation
Ethanol
ADH
MEOS
acetaldehyde
(hangover)part. soluble in membrane
PL
toxic effects on CNS
adducts with proteins, NA, biog. amines
acetate
acetyl-CoA
FA/TAG synth. liver steatosis
ADH
excess of NADH in cytosol
reoxidation by pyruvate
lactic acidosis
hypoglycaemia
various products
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Acetaldehyde reacts with biogenic amines
to tetrahydroisoquinoline derivatives
NH2HO
HO
HC
O
CH3
HO
HO
N
CH3
H
salsolinol
6,7-dihydroxy-1-methyl-1,2,3,4-tetrahydroisoquinoline
dopamine
- H2O
acetaldehyde
Neurotoxin ?
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Nicotine - the main alkaloid of tobacco
N
N
CH3
3-(1-methylpyrrolidin-2-yl)pyridine
On cigarette box:
Nicotine: 0.9 mg/cig.
Tar: 11 mg/cig.
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Cigarette smoke contains a number of different compounds
• free nicotine – binds to nicotine receptors in brain and other
tissues
• CO – binds to hemoglobin carbonylhemoglobin
• nitrogen oxides – can generate free radicals
• polycyclic aromatic hydrocarbons (PAH)
(pyrene, chrysene), main components of tar, attack and
damage DNA, carcinogens
• other substances (N2, CO2, HCN, CH4, terpenes, esters …)
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Biotransformation of nicotine
N
NCH3
N
NH
N
NCH3
OH
N
NCH3
O
nikotin
nornikotin 5-hydroxynikotin
kotinin
nikotin-N-glukuronát
kotinin-N-glukuronát
Example
nicotine
nicotine-N-glucuronide
nornicotine5-hydroxynicotine
cotinine
cotinine-N-glucuronide
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Biochemical markers of liver diseases
Liver function / condition Biochemical marker
Integrity of hepatocyte membrane
Necrosis of liver
Bile excretion
Proteosynthesis disorder
Detoxification functions
Disorder of AA metabolism
Disorder of glucose metabolism
Disorder of lipid metabolism
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Biochemical markers of liver diseases
Liver function / condition Biochemical marker
Integrity of hepatocyte membrane ALT, GMT, ALP
Necrosis of liver AST, GMD
Bile excretion ALP, bilirubin, bile ac., urobilinogen
Proteosynthesis disorder (pre)albumin, CHS, coag. factors
Detoxification functions caffeine test (p.o.) – metabolites in urine
Disorder of AA metabolism urea, NH4+
Disorder of glucose metabolism glucose
Disorder of lipid metabolism TAG, HDL
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Selected biochem. markers of liver damage (in serum)
Serum analyte Reference values Change
ALT
GMD
GMT
Bilirubin
Ammonia
Urobilinogens (urine)
------------------------------
Pseudocholinesterase
Urea
Albumin
0,1 - 0,8 kat/l
0,1 - 0,7 kat/l
0,1 - 0,7 kat/l
5 - 20 mol/l
5 - 50 mol/l
up to 17 mol/l
---------------------
65 - 200 kat/l
3 - 8 mmol/l
35 - 53 g/l
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