Download Phase 1

Metabolism
•Chemical transformaion of xenobiotics
•Occurs in mostly in liver (enzymatic prosesses)
•Convertion into more hydrophil. subst. - excretion urine
•May convert procarciogenics into cytotox., muthagenic compounds
•Different persons may have differences in methabolism (genetic diff., physiol. factors)
•Methabolism of one xenobiotic may influence metab. of amother
Xenobiotics
•Drugs
•Other foreign non-essential compounds
Metabolism in non-hepatic tissue
•Intestine mucosa
•Kidney
•Lung
•Bacteria in GI-tract
First-pass metabolism:
Xenobiotic metabolized before reaching
general circulation
First-pass metabolism:
Xenobiotic metabolized before reaching general circulation
A) Metab. lungs (inhaled subst)
Intestine mucosa, GI bacteria
B)
General
Circulation
GI
Liver
Absorb under tung
Absorbfrom rectum
Pathways of metabolism
Phase 1: Biotransformation
Attachment of new functional groups, transformation of exist. funct. groups
oxidation, reduction, hydroxylation, hydrolysis etc.
Phase 2: Conjugation.
Masking of an exist. funct. group by for instance
acetylation, glycosylation, attachment amino acid etc
More hydrophilic drug
Renal excretion
N
CH3
NH
NH
Conjugation
glucuronic acid
Demethylation
HO
O
Morphine
OH
Phase 1
HO
O
OH
Phase 2
HO
O
O
HO
OH
O
OH
CO2H
Phase 1
Metabolism by cytochrome P450 enzyme systhem (CYP450)
•Located in endoplasmatic reticulum (liver and other cells)
•Electron transport systhem - oxidation, monooxygenase
•Heme protein + flavoprotein
•Capablee of oxidation - many differen xenobiotics
Cystein
S
N
Fe3+
N
N
N
H
O
CHEMICAL REVIEWS
Volume 104, Issue 9 (September 8, 2004)
3947-3980 Mechanism of Oxidation Reactions Catalyzed by Cytochrome P450 Enzymes
Bernard Meunier, Samuël P. de Visser, and Sason Shaik
<http://dx.doi.org/10.1021/cr020443g>http://dx.doi.org/10.1021/cr020443g
H
Flavoprotein
FMNH2
red. form
NAD
ox. form
Flavoprotein
FMN
ox. form
NADH
red. form
Heme protein
Fe3+
ox. form
Substrate-red. form
Heme protein
Fe2+
red. form
Substrate-ox.form
Flavin mononucleotide
Nicotinamid adenine dinucleotide
O
NH2
NH2
N
O
HO
N
O
O
OH
HO
O PO
OH
N
N
N
O
HO
NH2
O
NH2
N
NAD
OH
OH
HO
P
O
O
HO
O
O
P
O
H H O
O P O
OH
N
N
O
HO
N
H3C
N
H
H
H
NH
N
OH
NADH
O
H3C
N
N
H
OH
OH
OH
H
H
H
OH
OH
OH
-
OPO3 2
FMN
N
N
H3C
H
N
O
H3C
NH
O
-
OPO3 2
FMNH2
CYP450 families and sub-families
Family 1:
CYP1A1
Aromatic hydrocarbon hydroxylase, metabol. PAH etc.
OH
O
OH
Nu
More hydrophilic
not tox.
OH
Nu
CYP1A2
Ox of arylamines, nitrosamines, aromatic hydrocarbons
Family 2:
Family 3:
CYP2A6
CYP3A4
CYP2B6
CYP2C
CYP2D6: Often enantioselective, lipophil. amines
CYP2E1: Halogenated hydrocarbons, other org solvents
CYP450 / Mechanisms of metobolic transformations
Hydroxylation of alkane
Dehydrogenation of alkane
R-O-H
R-H
+
Fe3+
H2O
CYP450
CYP450
Fe3+
Fe4+ OH
Fe3+ OH
H
CYP450
CYP450
R
R-H
NADPH
R
=
H
Fe5+ O
CYP450
Fe2+
R-H
CYP450
R-H
H2O
O2
2H
Fe3+ O2
Fe2+
CYP450
R-H
O2
CYP450
e
Fe3+
R-CH3
CYP450
R-CH2OH
Other enzymes
O2
CYP450
R-CO2H
R-H
R-H
Allylic alchohol
Proposed mech. ox of alkenes
OH
Fe3+
Radical
-complex
Alkene, aromatic
-complex
H
R
R
R
Fe4+ O
Fe5+
O
Fe3+
O
O
1,2 migration
R
alkynes
R
O
R
O
Fe3+ O
Fe3+
R
R
Fe3+ O
R
O
H2O
O
R
OH
Proposed mech. ox of aromatics
R
O
R
Fe3+
Fe3+
R
R
R
Fe4+ O
R
R
R
taut
R=H
Fe3+ O
O H H
Fe5+ O
Fe3+
HO
Proposed mech. react. on heteroatom cont. compounds
H
Fe5+
O
H
X
R
X
R
O
Fe4+
X
R
X
R
Fe4+ OH
OH
i.e. N oxide
Fe3+
Fe3+
OH
O
X
R
+ HX-R
i.e. hemiacetal
N, O, S dealkylation
cleav. of small alkylgroups (Me)
Dehalogenation: HX + carbonyl comp.
Proposed mech. react. on heteroatom cont. compounds
H
O
H
N
R
N
R
N
R
N
R
N-oxide
Fe5+
O
Fe4+
Fe4+ OH
OH
sulfide ox, see FMO
Fe3+
R''
O
N
R
Stable if R, R' R''° H
R'
H
OH
O
N
R'
H
H
H
N
O
N
R
Rearrang.
OH
R
N
R'
R'
hydroxylamine
O
H
N
nitroso comp.
hemiaminal
O
R
H N
R'
CYP450 Induction / inhibition by xenobiotics
Xenobiotics may enhance metabol. of them selvs as well as other comp. taken at the same time
Induce transcript CYP450 mRNA - Synth. CYP450 enzymes (enzyme induction)
•Drugs
•Ethanol
•Organic solvents
•Components in cig. smoke
•
OH
N
H
OH
O
OH
R
HO
HO
R=H:
Hypericin
R=OH
Pseudohypericin
St. Johns Worth
(Johannesurt, prikkperikum)
OH
O
OH
CYP450 Inhibitors
Reversible CYP enzyme inhibitors: Several drugs
ex. antimycotic azoles
Squalene
epoksidsyklase
Squalene
epoksidase
HO
O
Squalene
Antimycotic
allylamines
H
Lanosterol
CYP450: Lanosterol
14a-demetylase
Klotrimazole
Canesten etc
Antimycotic azoles
N
N
Cl
HO
HO
Ergosterol
H
Cell wall component fungi
H
H
HO
Kolesterol
H
CYP450 Inhibitors
Complexation inhibitors
ex. metabolites from alkylamines
CYP450
R-NMe2
Alkylamine
No inhib. activity
R-N=O
Nitrosoalkane
Irreversible complexation with
Fe(II) heme in CYP sub families
Mechanism based inhibitors (suicide inhib)
ex. alkynes
O
H2O
R
FeO3+
R
R
R
O
CYP450
OH
H
H
H
HO
Ethynyl estradiol
OH
O
NH2-Enzyme
R
N
H
Enzyme
Phase 1 react. not involving CYP450
Other microsomal enzymes
Azoreductase
O
H2N S
O
N
H2N
N
NH2
Prontocil
O
H 2N S
O
NH2
Sulfanilamide
Nitroreductase
R NO2
R NH2
Flavinmonooxygenase-FMO (N and S-ox.)
Peroxidases
microsome: Artefactual
spherical particle, not present in the living cell,
derived from pieces of the endoplasmic reticulum present in homogenates of tissues or cells:
microsomes sediment from such homogenates when centrifuged at 100 000 g and higher:
the microsomal fraction obtained in this way is often used as a source of mono-oxygenase enzymes.
Flavinmonooxygenase-FMO
Cont. FAD
Flavin mononucleotide
Flavin adenine dinucleotide
O
H3C
N
H3C
N
NH
N
H
H
H
OH
OH
OH
O
NH2
N
O
O
O P O
O
OH OH
H
N
H3C
N
FADH2
O
N
R
O
HO
HO
NH2
O
O P O
OH
N
N
N
O
OR
OH
HO
O PO
OH
R=H NAD
R=Phosphate: NADP+, NADPH
N
N
H
OH
OH
OH
H
H
H
H3C
N
H3C
N
FMNH2
H
H
H
N
N
OH
OH
OH
OH
HO
HO
OR
OH
Adenine
(Vit. B4)
N
O
N
O
HO
O
N
N
N
N
NH
N
Nicotinic acid / Niacin
(Vit. B3)
CO2H
NADH
N
NH
O
OPO3 2
NH2
NH2
N
O
HO
O
P
O
H 3C
OH
OH
OH
O
NH2
N
OH
O
Riboflavin
(Vit B2)
H H O
O
N
FMN
OH
N
HO
N
-
NH2
P
H3C
NH
OPO3 2
O
O
N
H
H
H
Nicotinamid adenine dinucleotide
O
H3C
O N
O
H
N
O
H 3C
O
NH
N
N
HO
FAD
H3C
-
Flavinmonooxygenase-FMO
Ox of soft Nu
R
O
H
Peroxide
Peracid
Substrate
H3C
H3C
OH
O
H O
N
N
R
N
+ ROH
O Nu
O
N-oxide
Sulfoxide
Nu
Substrate-O
H
N
H3C
NH
H3C
O
N
R
OH
O
H2O
NH
N
O
O
H3C
N
H3C
N
R
FAD
H3C
H3C
O2
H
N
O
N
R
N
H
NH
FADH2
•Amine: ox. to N-oxide / hydroxylamine
•Sulfide: ox to sulfoxide , furter to sulfone
O
•Thiol:
R-SH
R-S-S-R
R-S-S-R
NADPH
O
NADP+
NH
N
O
Non-microsomal enzymes
•Enzymes in mitokondria
•Enzymes in soubile tissue fractions
Alchohol dehydrogenase
(NAD cont.)
aldehyde / ketone
R-OH
R
O
Aldehyde dehydrogenase
O
R
H
OH
prim or sec.
CH3OH
Alcohol dehydrogenase
Aldehyde dehydrogenase
CH2O
HCO2H
rel. fast
Slow
EtOH cometitive substr.
Tox. effects:
Acidosis
Blindness
Dietary folic acid
O
O
HN
O
N
H
H
N
N
H
HCO2H
CO2H
N
H
N
H
Tetrahydrofolate
O
O
CO2H
HN
O
N
H
N
H
H
N
N
H
CO2H
N
H
O
CO2H
10-Formyl-THF
dehydrogenase
CO2
Non-microsomal enzymes (Phase 1)
Molybdenum Hydroxylases
•Aldehyde oxidase
•Xantine oxidase
•Xantine dehydrogenase
Xanthine oxidase
Electron transfer:
Cont. Mo in cat. site
Cont FAD and 2 Fe/s clusters
Use H2O not O2
FAD - Fe2S2ˇI - Fe2S2ˇII - Moco - Substrate
Active form
•Aldehyde oxidase
O
R
O
H
R
N
N
OH
H2N
O
Aldehyde oxidase
Esterase / hydrolysis
N
N
H2N
N
N
H
N
HO
AcO
OH
N
HO
AcO
N
N
HN
O
Famciclovir
Antiviral (Herpes etc)
Pro-drug
Aza heterocycle
•Xantine oxidase
xanthine oxidoreductase
•Xantine dehydrogenase
O
O
(requires NAD+)
N
N
HN
O
HN
N
N
H
O
Hypoxanthine
N
H
HN
N
H
O
Xanthine
O
HN
N
N
N
H
Allopurinol
HN
O
N
N
H
H
N
O
N
H
N
H
Uric acid
Treatment of gout (podagra)
O
Penciclovir
N
H
Alloxanthine
Inhib. enzyme
Non-microsomal enzymes (Phase 1)
Oxidative deamination of amines
•Monoamine oxidase (MAO)
•Diamine oxidase (DAO)
R-CH2-NH2 + O2
O
NH2
HO
MAO
R-CHO + NH4+
[R-CH=NH]
HO
N
H
N
H
Serotonin
5-Hydroksotryptamin (5-HT)
Serotonine:
•Neurotransmittor; temp. control, mood
•Depresion: Low serotonine activity
•MAO Inhibitors - Older antidepresants
(low selectivity)
Moklobemid
Aurorix® Moklobemid®
O
O
N
N
H
Cl
Other MAO substrates:
HO
HO
OH H
N
Not MAO substrates (subst at -C):
HO
H
NH2
NH2
Noradrenaline
HO
Dopamine
(S)-amfetamin
Low dopamine conc. ≈ Parkinston
Non-selective monoamine re-uptake inhib.
Tricyclic antidepressants
SSRI (selective serotonine re-uptake inhib.)
“Lykkepiller” Prozac etc (Fontex)
-Arylam
X
H2 N
Active transport re-uptake transmittor
(not Acetylcholine)
- -Arylamin
Y
Z
R

H N

O
F3 C
N
Stor gruppe / sterisk hinding
Hindrer reopptak
-Arylaminer
HO
HO

HO
OH
NH2

DA
HO
HO
NH2
NH2
NE
N
H
5-HT
Non-microsomal enzymes (Phase 1)
Oxidative deamination of amines
•Monoamine oxidase (MAO)
•Diamine oxidase (DAO)
HN
Oxidize diamines, histamine
N
NH2
MAO like enzymes in plants
NH2
HN
N
N
N
N
H
N
N
N
BAP
CYtokinin (Plant growth hormone)
N
H
N
N
+
O
N
N
H
N
N
N
N
H
N
N
N
CK analogs, Anders Bråthe
N
H
Non-microsomal enzymes (Phase 1)
Miscellaneous react.
Reductions
Hydrolysis - Esterases
R S S R
R-SO-R
R-SH
O
R-S-R (i.e.DMSO)
R
O
R'
O
R-CO-R
R-CHOH-R
R-NO-R
R-NH-R
R-CH=CH-R
R
O
R
N
R''
R'
R-CH2-CH2-R
R-OH
R-H
Ar-OH
Ar-H
OH
Esters as pro-drugs
-Oxidation
R-CH2-CH2-CO2H
R-CH2-CH2-CO-S-CoA
R-CO2H
+
NH2
N
N
O
S
H
N
OH
H
N
O
O OO O
P
P
O
O
O
Acetyl-CoA
N
N
O
O
Nu
PO3
Acetyl-CoA
CHa-CO-S-CoA
OH
R-CO-S-CoA
Pathways of metabolism
Phase 1: Biotransformation
Attachment of new functional groups, transformation of exist. funct. groups
oxidation, reduction, hydroxylation, hydrolysis etc.
Phase 2: Conjugation.
Masking of an exist. funct. group by for instance
acetylation, glycosylation, attachment amino acid etc
More hydrophilic drug
Renal excretion
N
CH3
NH
NH
Conjugation
glucuronic acid
Demethylation
HO
O
Morphine
OH
Phase 1
HO
O
OH
Phase 2
HO
O
O
HO
OH
O
OH
CO2H
Phase 2: Conjugation
Most comp. excreted as cojugates, ionic, hydrophilic groups added,
most common glucuronation
•Glucuronic acid conjugation
•Sulfate conjugation
•Conjugation with amino acids
•Acetylation
•Glutathione conjugation
•Methylation
Phase 2: Conjugation
•Glucuronic acid conjugation
Substrates:
RXH: Xenobiotic / Phase 1 metabolite
•Alchohols
•Phenols
X R
CO2H
O
OH
HO
OH
•Amines
OH
•Sulfides
O
OH
OH
Glucose
H
OH
O
N
O
P
O
OH
O N
P
CO2H X
O
OH
OH
R
OH
UDP-Glucuronate
HO
OH
•Carboxylic acids
•1,3-Dicarbonyls
RXH
CO2H X
O
OH
OH
R
Kidney
OH
OH
Poor reabsorb.
Bile (galle)
Reabsorb
Entro-hepatic recycling
Important for many hormones etc
RXH
Urive excretion
CO2H X
O
OH
OH
OH
CO2H X
O
OH
R
Intestine
OH
R
O
Hydrolysis
O
H
R
O
O
H
CO2H
O
OH
OH
O
OH
P
O
R
P
CO2H O
O
OH
Uridine
OH
R
HNu
Macromolecule
OH
UDP-Glucuronate
Relatively labile
Acyl migr.
Nu
Macromolecule
R
O
Altered protein (hapten)
Unwanted immune responce / allergic react.
ex. NSAIDs
Urine
pH<7
Phase 1
Ar-NH2
Ar-NH-OH
Ar-NH-OH-Glu
Ar-N
Ar-NH-OH
H2O
Nitrene
(c.f. carbene)
Bladder cancer
Phase 2: Conjugation
•Sulfate conjugation: Phenols, (alcohols, N-compounds)
NH2
N
ATP
HO
N
O
O N
O S O P
N
O
O
OH
HO3P
O
O
S
O O
OH
PAPS
•Conjugation with amino acids (Most ofthen Gly): Carboxylic acids
O
R-CO2H
R
H2N
S
CoA
O
CO2H
R
N
H
CO2H
No tox. conjugates known
Phase 2: Conjugation
•Acetylation: N-compounds
O
H3C
NH
S
O
CoA
N
•Glutathione conjugation: Electrophilic species
•Alkylhalides
•Epoxides
•Michael acceptors etc
O
R-X
+
HS
O
CO2H
N
H
HN
OH
H2O
OH
HN
NH2
O
Mercapturic acid der.
O
O
HN
HN
HS-R
SR
Paracetamol
S
CO2H
O
Glutathione conjugate
N
Phase 1
CYP450
N
H
HN
NH2
O
HN
O
R
S
O
O
CO2H
R
CO2H
may otherwise
alkylate biomolecules
O
O
H
SR
OH
Br
H2N Liver Protein
Br
S
RSH
Br
S R
Liver dammage
Nu
(i.e. DNA)
Phase 2: Conjugation
•Methylation (O and N- compd)
Prod. may be more lipophilic
React. mainly aimed at converting endogenic compouds
O.Metylation by COMT (catecol O-methyl transferase)
HO
CO2H
H2N
NH2
N
N
N
ATP
S
O
H3C
HO
HO
HO
N
OH
SAM (S-adenocyl methionine)
SAM may also methylate N-comp.
O
H3C
OH
HO
OH
NH2
MAO
HO
HO
OH
CHO
Aldehyde
Dehydrogenase
HO
HO
CO2H
HO
Noradrenaline
(Norepinephrine)
COMT
COMT
OH
OH
H3CO
MAO
NH2
Aldehyde
Dehydrogenase
H3CO
HO
HO
OH
NH2
Ephedrine
Adrenerg agonist
CO2H