Biotransformation II

Question 1

List all the stages of biotransformation

Answer 1

Phase I: Reduction, oxidation, hydrolysis
Phase II: Sulfation, Acetylation, Methylation, Glutathione conjugation, glucuronidation

Question 2

Describe reduction reaction of anti-cancer drug doxorubicin that leads to adverse effects

Answer 2

NADPH reductase carries 1 e reduction of quinone forming semiquinone which is very reactive

the introduction of the oxygen will cause the semi quinone to transfer back into quinone and the oxygen will then pick up an electron turning it into hydroxyl radical which can kill cells

Question 3

In the biotransformation of doxorubicin, what is NADPH and how can it cause a secondary result of the bio transformed drug?

Answer 3

NADPH is a reductive enzyme that can use NADPH or NADP in the reductive reaction

Question 4

Why is the reductive reaction involving quinone reductase a detoxification pathway

Answer 4

It will form a hydroquinone and direct the quinone away from hydro toxic pathways avoiding the scenario of killing macromolecules

Question 5

What is the significance of epoxide hydrolase in relation to epoxides?

Answer 5

Epoxides are molecules that attack hydrophilic sites and bind covalently to proteins and nucleic acids leading to cytotoxicity

Epoxide hydrolase can mediate this reaction and set off this reaction

Question 6

How does Epoxide hydrolase intercept the epoxide covalent reaction?

Answer 6

Epoxide forms from P450 enzyme reaction and Epoxide hydrolase catalyze reaction with water and hydrolyze epoxide into dihydrodiol metabolite

Question 7

What enzyme is involved in glucuronidation?
Where is it located

Answer 7

UDP-glucuronosyltransferase (UGT)
It is anchored to the Endoplasmic Reticulum luminal side

Question 8

What are some examples of functional groups/drugs that are glucuronidated?

Answer 8

acetaminophen and morphine.
Functional groups: hydroxyl, carboxyl, amine, sulfhydryl,

Question 9

What is the co-factor involved in glucuronidation

Answer 9

Uridine diphosphate-glucuronic acid (UDPGA)

Question 10

Describe the process of glucuronidation

Answer 10

1. UDP moves into the cytoplasm and is phosphorylated to become UTP
2. the UTP reacts with glucose 1 phosphate which converts into UDPGA

Question 11

What exactly is glucuronic acid (UDPGA)

Answer 11

This is the molecule that will be added to the drug in order to make it more water soluble

Question 12

What happens if someone has a genetic deficiency in glucuronidation

Answer 12

it can lead to hyperbilirubinemia or impaired drug clearance of drug-chloramphenicol which can lead to aplastic anemia which damages bone marrow

Question 13

Why do some newborns have jaundice

Answer 13

because of the general deficiency of glucuronidation

Question 14

list the enzymes, substrates, and co-factors of phase II glutathione conjugation

Answer 14

enzyme: glutathione s-transferase
substrates: electrophilic enters like epoxides, nitro groups , or hydroxyl amines, ethacrynic acid, bromobenzene
Co-factor: reduced glutathione (GSH)

Question 15

How does the enzyme GST work in bio transforming drugs?

Answer 15

It will attack electrophilic part of drug and form glutathione conjugate that will neutralize the electrophilic part

Question 16

Explain the process of conjugation with glutathione

Answer 16

1. GST will catalyze reaction bringing together the glutathione and drug by a sulfhydro group
2. GGTP where glutamic acid os removed (GLU) leaving cysteine and glycine with sulfhydro-drug group
3. Remove glycine through cysteinyl glycinose
4. Acetylate the drug and this form of drug will be excreted

Question 17

List the enzyme, substrates, and co factor of phase 2 sulfation conjugation?

Answer 17

enzyme: sulfotransferase
Location: found in the cytoplasm
substrate: phenols and aliphatic alcohols. acetaminophen and steroid hormones
co-factor: 3’-phosphoadenosine-5’ phosphosulfate (PAPs)

Question 18

explain how PAPs is produced

Answer 18

1. sulphate reacts with ATP to produce APs with a phosphate on the 5’ end
2. The APS reacts with ATP to place the phosphate on the 3’ end

Question 19

what are the normal routes of biotransformation of acetaminophen at regular doses

Answer 19

acetaminophen can be glucuronidated into nontoxic glucuronide or it can be sulphated into a nontoxic sulphate

Question 20

how do large doses of acetaminophen lead to hepatotoxicity?

Answer 20

if you have too much acetaminophen in your body, the glucuronidation and sulfation channels will become saturated so there will be some drug that does not bind to these channels leaving them open to be biotransformed into reactive toxic intermediated by P450s in the liver, CYP3A4 and CYP2E1

Question 21

What process does NAPQ1 trigger?

Answer 21

because it is electrophilic it can covalently bond to macromolecules and trigger liver cell death

Question 22

In this cell death guaranteed after the production of NAPQ1?

Answer 22

no, if there is enough glutathione production, NAPQ1 can be biotransformed into mercapturic acid conjugate

Question 23

List the enzyme, substrate, and co-factors of phase II acetylation conjugation

Answer 23

enzyme: n-acetlytransferase (NAT/NAT1/2)
location: cytosolic
substrates: aromatic amine and hydrazine groups
co-factor:acetyl-coenzyme A

Question 24

how do genetics influence fast/slow acetylators?

Answer 24

because of allele encoding of NATs some people can be fast or slow acetylators

Question 25

how is NAT formed

Answer 25

acetate reacting with coenzyme A

Question 26

How does NAT attach to the drug

Answer 26

the acetyl group can be attached to amine group

Question 27

list the enzyme, substrate, and cofactors of phase II methylation conjugation

Answer 27

enzyme: methyltransferase
location: cytosolic
substrate: phenol, catechol, levodopa, 6-mercaptopurine
cofactor: s-adenosylmethionine (SAM)

Question 28

what two phase II processes do not bio transform drugs into more water soluble drugs

Answer 28

acetylation and methylation

Question 29

explain the methylation process of anti-cancer drug 6-mercaptopurine

Answer 29

1. formation of SAM by adding ATP to 2-methionine
2. The drug will bind to 1 methyl group from SAM forming 6-methylmercaptopurine

Question 30

how is methylation involved in the detoxification process of 6-mercaptopurine

Answer 30

methylation helps protect against cytoplasmic effects of 6-mercaptopurine