Xenobiotics ( Xenos = strange) are Xenobiotics ( Xenos = strange) are compounds that are foreign to the compounds that are foreign to the body.body.

It includes drugs, food additives, It includes drugs, food additives, pollutants etc.pollutants etc.

Understanding how xenobiotics are Understanding how xenobiotics are handled at the cellular level is handled at the cellular level is important in learning how to cope important in learning how to cope with the chemical attack.with the chemical attack.

The goal of xenobiotics metabolism is make xenobiotics less poisonous or nontoxic metabolite.

Activities of xenobiotics metabolism Activities of xenobiotics metabolism affected by species, genetic factors, affected by species, genetic factors, gendergender, age., age.

Intake phenobarbital or certain Intake phenobarbital or certain hydrocarbons can cause enzyme hydrocarbons can cause enzyme induction.induction.

BLOOD

XENOBIOTIC

BIOTRANS-FORMATION

EX

CR

ET

ION

DNAdamage

Somaticeffect

Detoxification

ActivationNon-toxicmetabolite

Toxicmetabolite

DefinitionBiotransformation is the sum of all processes,whereby a compound is transformed chemicallywithin a living organism

1. Xenobiotik hidrofilik masuk ke dalam sel pada kisi membran hepatosit melalui sistem transpor menggunakan protein karier.

2. Xenobiotik lipofilik (hampir 70-80%); mudah larut di dalam pelarut organik juga fosfolipid lapis ganda ( bilayer) dari membran sel sehingga tidak mengalami halangan yang berarti untuk berinteraksi dengan sel atau organel lainnya mengikuti hukum difusi non ionik.

Bound

Free

Bound

Free

Bound

Free

Target organ

Depot

Absorption

Excretion

Adipose tissuesInert membranesLipoprotein micellsLysosomesSkeleton (endo or exo)

UrineFaeces (gall)Lungs or gillsSecretion from surface

1. Biotransformasi : a. Reaksi melalui 2 fase b. Adaptasi enzimatik

2. Detoksifikasi amonia dan netralisasi bikarbonat a. Siklus Urea / Siklus Glutamin

b. Netralisasi bikarbonat

3. Degradasi Alkohol

4. Sistem Retikuloendotelial

5. Pemusnahan Radikal Bebas dan Antioksidan

Merupakan perubahan di dalam substansi biokimia melalui proses auto metabolik.

Proses biotransformasi / katabolisme xenobiotik berlangsung dalam 2 fase

yaitu; a. Fase 1 : Pengaktifan/ insersi gugus reaktif ke dalam

molekul substansi seperti lipofilik yang terlarut di dalam

air. Reaksi penting: oksidasi, reduksi, hidrolisis.

b. Fase 2 : Metabolit fase 1 mengalami konjugasi dengan substansi endogenus melalui transferasi

spesifik.

The overall purpose of the two phThe overall purpose of the two phasasee

is to increase their water is to increase their water solubility( polarity) and thus excretion solubility( polarity) and thus excretion from the body.from the body.

XenobiXenobiootics are protics are pro--drugs or prodrugs or pro--carcinogens.carcinogens.

Detoxification is usually used as terms Detoxification is usually used as terms to metabolism of xenobiotics.to metabolism of xenobiotics.

Terdapat 4 Mekanisme yang melibatkan adaptasi enzim:

1. Penginduksian Enzim

2. Penghambatan Enzim

3. Pengaktifan dan inaktifasi enzim

4. Reduksi di dalam perubahan enzim

Outline of metabolic activation and detoxification pathways

Enzyme Phase I Phase II

Types of reactions HydrolysisOxidationReduction

Conjugations

Increase inhydrophilicity

Small Large

General mechanism Exposes functionalgroup

Polar compound addedto functional group

Consquences May result inmetabolic activation

Facilitates excretion

XENOBIOTICPRIMARYPRODUCT

SECUNDARYPRODUCT

Expose or addfunctional group

OxidationReductionHydrolysis

PHASE I PHASE II

EXCRETION

Conjugation

LIPOPHILIC HYDROPHILIC

Phase I and phase II reactions

CONJUGATION REACTIONCONJUGATION REACTION

GlucuronidationGlucuronidation SulfationSulfation Conjugation with glutathioneConjugation with glutathione Acetylation e.g. in INH( isohydrazid)Acetylation e.g. in INH( isohydrazid) Methylation Methylation

Important phase I enzymes

Enzyme Co-factor Substrate

Mixed-function oxidases NADPH Most lipophilic substances(cytochrome P-450) (NADH) with M.wt < 800

Carboxyl esterases Unknown Lipophilic carboxyl esters

’A’ esterases Ca++ Organophosphate esteresEpoxide hydrolases Unknown Organic epoxids

Reduktases NADH Organic nitrous compoundsNADPH Organic halogens

Hemoprotein, like hemoglobin.Hemoprotein, like hemoglobin. Widely distributed across species.Widely distributed across species. Present in highest amount in liver and Present in highest amount in liver and

small intestines, mainly in the membranes small intestines, mainly in the membranes of the smooth endoplasmic reticulum.of the smooth endoplasmic reticulum.

Substrate speSubstrate specciificificity.ty. NADPH is involved in reaction mechanism NADPH is involved in reaction mechanism

in cyt P450.in cyt P450. Lipids also components of cyt P450 Lipids also components of cyt P450

system.system. Most of cyt P450 are inducible.Most of cyt P450 are inducible.

Certain isoforms of cyt P450 involved Certain isoforms of cyt P450 involved in metabolism of PAH( polycyclic in metabolism of PAH( polycyclic aromatic hydrocarbons) and called aromatic hydrocarbons) and called AHH( aromatic hydrocarbon AHH( aromatic hydrocarbon hydroxylases).hydroxylases).

Certain cyt P450 exist in polymorphic Certain cyt P450 exist in polymorphic forms.forms.

P-450 system in the endoplasmic reticulum

REDUCTASE

P-450P-450

Xenobiotic

NADPH

NADP+

Fp oxidized

Fp reduced

(RH)-P450-(Fe2+)

(RH)-P450-(Fe3+)

(RH)-P450-(Fe2+) ·O2

P450 (Fe3+)

O2

RH

ROH

+H2O

e-

e-

Cytochrome P-450’s catalytic cycle

CYT P- 450

Fe3+ Fe3+

NADPH

NADP

CYT P-450 reductase

+e-

Fe2+

O2

Fe2+

e-NADPH

NADP

Fe3+

H2O

Fe3+

HC(inducer)

Ah receptor-hsp90

HC

P450 mRNAP450 protein

• Bioactivation• Detoxification

Toxicity

Elimination

Cell

HC-AhR

hsp90

HC-AhR

XRE

P450 gen

Nucleus

Induction of cytochrome P-450

HC: Hydrocarbon (inducer)XRC: Regulator gene (stimulates transcription of P-450 gene)

Aliphatic hydroxylation

Aromatic hydroxylation

R R OH

R - CH CH - R’ R - CH - CH - R’

Epoxidation O

N-, O-, or S-dealkylation

R - (N, O, S) - CH3H

N - hydroxylation

Deamination

R - C - H + NH3 O

OO

R - NH - C – CH3 R - NOH - C – CH3

R - C - H R - C OH R - C -H + HXOX X

H H

R - S - R’ R - S - R’

Sulphur oxidation

S

R1R2P - X R1R2P - X + S

ODe-sulphurnation

Oxidative dehalogenation

Examples of oxidations catalysed by P-450

R - CH2 – CH2 – CH3 R – CH2 – CHOH – CH3

R – (NH2, OH, SH) + CH2O

R – CH2 – NH2