DETOXIFICATION

2. Xenos
Xenobiotic Compound that is
foreign to body
Stranger

3.  As part of normal metabolism, body produces
toxins which have to be eliminated.
 Humans are constantly exposed to
exogenous & endogenous toxins.
 Biotransformation is the process whereby a
substance is changed from one chemical to
another by a chemical reaction in body.

4.  Definition:
 Detoxification is the process by which toxic
substances are converted into more soluble &
less toxic substances, which are mainly
eliminated through urine & bile.
 Takes place in the “liver”.
 The compounds to be detoxified include
Drugs – antibiotics, cardiac drugs, steroids, etc.

5.  Carcinogens – food dyes, preservatives,
artificial sweeteners, alcohols, chemicals &
cosmetics etc.

7.  Many endogenous & Xenobiotics are lipophilic.
 They can easily cross lipid bilayers & transported by
lipoproteins.
 Metabolism of endogenous compounds & xenobiotics
allows organisms to convert lipophilic compounds to
more water soluble forms which facilitates excretion
 Many xenobiotic compounds contain aromatic rings &
heterocyclic ring structures, that we are unable to
degrade or recycle.
 These structures are hydrophobic

8.  Metabolism of foreign compounds occurs as
a results phase-I & phase-II reactions.
 Phase-I reactions are
 Oxidation
 Reduction
 Hydrolysis
 Phase II is conjugation reactions of phase I
compounds.
 Direct conjugation can also occur.

9.  The cytochrome P450 is involved.
 Approximately 50% of the drugs are
metabolized by isoforms of cytochrome P 450
 Use of O2 that one atom of oxygen enters R-
OH and one atom enters water
 This dual fate of Oxygen accounts for former
naming of mono-oxygenases as mixed
function oxidases

10. Conjugating agent Active form
Glucuronic acid UDP-glucuronic acid
Sulfate PAPS
Cysteine Glutathione
Acetic acid AcetylCoA

11. 1.Oxidation
2.Reduction
3.Hydrolysis

13.  Phase I metabolism adds functional group on
the molecule & increases water solubility.
 Phase II metabolism adds an endogenous
substrate to produce a water-soluble
conjugate & is easily excreted.
 Phase I activity is located in microsomal
fraction of the cell.
 Phase II activity is located in the cytosolic
fraction of the cell.

15.  Liver
 Kidneys
 Gastrointestinal tract
 Skin
 Testes
 Ovaries
 Adrenals
 Placenta

16.  Detoxification by oxidation:
 Foreign substances - alcohols, aldehydes,
amines, anilides, aromatic hydrocarbons &
certain drugs are destroyed in the body by
oxidation.
 It occurs predominantly in liver & kidney.
 CYT P450, ADH, Aldehyde DH & mono amine
oxidase are involved.

17.  Oxidation of Alcohols:
 These are oxidized to corresponding acids.
CH3-CH2-OH
Ethyl alcohol
NAD+ NADH + H+
CH3-CHO
Acetaldehyde
Benzyl alcohol Benzoic acid
Ethanol Acetic acid
Methyl alcohol Formic acid

18.  Oxidation of Aldehyde:
 Oxidized to corresponding acids.
CH3-CHO
Acetaldehyde
NAD+
-CHO -COOH
Benzaldehyde Benzoic acid
NADH + H+
CH3-COOH
Acetic acid
NAD+ NADH + H+

19.  Detoxification of Amines:
 These are oxidized to corresponding acids.
Benzylamine Benzoic acid + urea
Chloral Trichloroacetic acid
 Aromatic hydrocarbons:
 These are oxidized to phenols or phenolic
compounds, which are then conjugated with
sulphuric & glutamic acids.

20.  Anilides:
 These are oxidized to corresponding phenols
Acetanilide Aminophenol
 Drugs:
 Chloral is partly oxidized to trichloroacetic
acid, which excreted as its salts.
 Sulfur compounds:
 Organic sulfur is oxidized to sulfuric acid.

21.  Certain aldehydes e.g., chloral, undergoes
reduction to form corresponding alcohol,
which is then conjugated with D-glucuronic
acid & excreted as corresponding
glucuronides.
Chloral
Trichloroethanol + D-glucuronic
acid (excreted as corresponding
glucuronides)

22. OH
I
-NO2
I
NO2
O2N-
OH
I
-NH2
I
NO2
O2N-
H2O
Picric acid Picramic acid

23.  Aromatic nitro compounds, e.g., p-
nitrobenzaldehyde is reduced to
corresponding amines & excreted after
conjugation
3. Hydrolysis
 The hydrolysis of bonds - ester, glycoside
& amide.
 Usually occurs in liver.

24. Acetanilide
Atropine
Procaine
Aspirine Salicylic acid + Aspirin acid
Aniline + Acetic acid
Tropic acid + tropine
PABA + Diethylaminoethanol

25.  Definition:
 It is a process by which the foreign molecules
or its metabolites are coupled with a
conjugating agent & converted to soluble,
nontoxic derivatives & easily excreted in urine.
 Features:
 Conjugating agents are available in the body &
some of them are synthesized in the body.

26.  D-glucuronic acid
 Certain amino acids as glycine, cysteine.
 Conjugation occurs mainly in liver & some
extent in kidney
 Conjugation produces less toxic, more
soluble compounds which are excreted..
 Conjugation occurs independently or it can
follow oxidation, reduction or hydroxylation

27. 1.Methylation
2.Acetylation
3.Conjugation with Sulfuric acid
4.Conjugation with D-glucuronic acid
5.Conjugation with Amino acids
6.Conjugation with Glutamine
7.Conjugation with Glutathione

28.  Detoxification by methylation is limited
 Usual methyl donor is SAM (active methionine)
 Methylation of heterocyclic N- atom compounds of the
pyrimidine & Quinoline types. e.g, Nicotin amide
-CONH2
-CONH2
CH3N
Nicotinamide N Methyl Nicotinamide
SAM

29.  Acetyl coA, takes part in conjugation reactions
 Conjugation with acetic acid occurs only with
aromatic amino groups
 Sulpha drugs are conjugated by acetylation &
excreted as acetylated derivatives.
Sulfanilamide
Acetyl CoA
PABA
Acetyl CoA
Acetylated sulfanilamide
Acetyl derivative of PABA
• Acetylation is catalyzed by acetyl transferase.

30.  PAPS is the sulfate group donor
 Sulfuric acid is used for detoxification of phenolic &
hydroxyl groups
 Substances like phenol, cresol, indole are formed in
the gut by the action of intestinal bacteria are
absorbed & transported to liver, where they are
conjugated with sulfate to form Ethereal sulfates,
which are excreted in urine, less toxic & more acidic.

31. Phenol
Active sulfate
OH
I
O
II
O-S-O
I II
O
Phenyl sulfuric acid

32.  It is most important & commonest
detoxification process.
 D-glucuronic acid is participated in this
reaction, as its active form UDP-glucoronic
acid which is formed in uronic acid pathway

33.  Bilirubin to form bilirubin diglucuronide
 Aromatic acids, e.g. benzoic acid
 Phenols & other secondary & tertiary aliphatic
alcohols.
 Certain drugs like morphine, menthol,
pyramidon, acetalinide, sulfa pyridine, etc.
 Antibiotics like chloramphenicol

34.  Hormones:
 Thyroid hormones & derivatives of steroids.
 Glucuronic acid form two types of linkages
 An ether linkage, e.g. in phenyl glucuronide
 An ester linkage, e.g. in benzoyl glucuronide
 Formation of glucuronides play an important
role in detoxification of exogenous &
endogenous compound & their excretion as
corresponding glucuronides.

35.  Glycine combines with harmful substances -
aromatic carboxylic acids to form harmless
derivatives which are excreted in urine.
 Ex. Benzyl Co A is conjugated with glycine to
form hippuric acid.
Benzyl CoA + Glycine Hippuric acid
Nicotinic acid + Glycine Nicotinuric acid

36.  L-Cysteine: Aromatic compounds are
conjugated with L-cysteine in the presence of
acetic acid to form mercapturic acids.
Bromobenzene + L-cysteine + acetic acid
Bromophenyl mercapturic acid
Bromobenzene + L-cysteine + acetic acid
Naphthyl mercapturic acid

37.  Glutamine conjugates phenyl acetic acid to
form phenylacetyl glutamine & excreted in
urine
 Accounts for mousy odour of urine in PKU.
Phenyl acetic acid + Glutamine
Phenyl acetyl Glutamine

38.  It is a tripeptide.
 Potentially toxic electrophilic xenobiotics
(carcinogens) are conjugated to the
nucleophilic GSH
 Glutathione S-transferase is involved.
 Present in liver cytosol & other tissues.
 Exhibit different substrate specifities

39.  P 450 = absorption peak at 450 nm
 The cytochrome P450 contain large group of enzymes.
 CYPs are major enzymes involved in drug metabolism.
 The most common reaction catalyzed by cytochrome
P450 is a monooxygenase reaction (Oxidation), e.g.
insertion of one atom of oxygen into an organic
substrate (RH) while the other oxygen atom is reduced
to water.
 RH + O2 + 2H+ + 2e– → ROH + H2O

40.  Oxygen
 NADPH
 Embedded in lipid bilayer next to
cytochrome P450 oxido-reductase.
 Monooxygenase is also called as mixed
function oxidase, is associated with
microsomes.

41.  About 150 isoforms are present.
 CYP denotes a cytochrome P450
 CYP1A1
 CYP=CytochromoP450
 1=Family
 A=Subfamily
 1=is the first individual member of that
subfamily.

42.  Involved in phase I of the metabolism.
 Involved in the metabolism of many endogenous
compounds (e.g. steroids).
 All are hemoproteins.
 Exhibit broad substrate specificity.
 Extremely versatile catalysts, catalyzing about 60
types of reactions.
 They catalyze reactions involving introduction of one
atom of oxygen into the substrate & one into water.

43.  Their hydroxylated products are more water soluble
& facilitating their excretion.
 Present in liver & also in intestine, brain & lungs.
 Located in smooth endoplasmic reticulum or in
mitochondria
 In some cases their products are mutagenic or
carcinogenic
 Many have a molecular mass of about 55kDa.
 Their activities may be altered in diseased tissues
(e.g. cirrhosis), affecting drug metabolism.

44.  Harper’s Biochemistry – 25th edition
 Medical Biochemistry – AR Aroor
 Text book of Biochemistry – DM Vasudevan