The document discusses the process of detoxification in the body. It explains that detoxification occurs in two phases - phase I and phase II reactions. Phase I reactions like oxidation, reduction and hydrolysis make toxins more reactive, while phase II conjugation reactions make them water soluble for excretion. The liver is a major organ of detoxification, using enzymes like cytochrome P450 and conjugating agents like glucuronic acid and glutathione to convert fat-soluble toxins into water-soluble compounds that can be removed from the body. The document provides details of various phase I and II reactions and conjugating agents involved in the metabolic breakdown and elimination of both endogenous and exogenous toxic compounds.

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