James Medchem Lecture 2 (Powerpoint 2)

Question 1

In phase 2 reactions, a functional group in the drug combines with a…

Answer 1

“small, usually water-soluble, endogenous molecule (co-substrate)”

Question 2

The product of most (not all) phase 2 reactions is _______ at physiological pH

Answer 2

anionic

Question 3

Most phase 2 metabolites are either excreted into _____ by a combination of glomelular filtration or into _______ by active transport

Answer 3

Urine; bile

Question 4

What are the 5 important phase 2 reactions?

Answer 4

Glucuronide conjugation
Sulfonation
Glutathione conjugation
Acetylation
Amino acid conjugation

Question 5

Glucuronide conjugation is catalyzed by which enzyme

Answer 5

UDP-glucuronosyltransferases, or UGT

Question 6

What co-substrate is required for glucuronide

Answer 6

UDP-glucuronic acid

Question 7

True or False: Most glucuronides are not biologically active

Answer 7

True

Question 8

Glucuronides are anions at what pH?

Answer 8

7.4

Question 9

To what atoms can UGT add UDP-glucuronic acid to? AKA RXH - what X’s?

Answer 9

O, N, S, or acidic C

Question 10

What group of glucuronic acid is anionic at pH 7.4, facilitating excretion?

Answer 10

Carboxyl group (COO-)

Question 11

Where is there an inversion of configuration during glucuronidation reactions?

Answer 11

At the glucuronic acid carbon, where the RX group adds

Question 12

Acyl glucuronides (carbon group + carboxyl group at the end reacting with UGT) are chemically reactive. Further reaction of these metabolites may lead to the drug being ___________. This may trigger __________.

Answer 12

Bound to proteins; an immune response

Question 13

What functional groups can undergo sulfate conjugation?

Answer 13

Alcohols, phenols, and amines

Question 14

Why don’t carboxylic acid groups form sulfate conjugates?

Answer 14

It is an unstable product

Question 15

What enzyme catalyzes sulfonation?

Answer 15

PAPS-sulfotransferase enzyme family, or SULT

Question 16

What co-substrate is required for sulfonation?

Answer 16

3’-phosphoadenosine-5’-phosphosulfate (PAPS)

Question 17

What is the final product of a sulfonation reaction?

Answer 17

RXH + PAPS = RX-sulfonic acid group

Question 18

At a low dose of drug, which is most likely to occur: Sulfonation or Glucuronidation?

Answer 18

Sulfonation

Question 19

At a high dose of drug, which is most likely to occur: Sulfonation or Glucuronidation?

Answer 19

Glucuronidation

Question 20

What enzyme catalyzes glutathione conjugation?

Answer 20

Glutathione-transferases, or GST

Question 21

What co-substrate is required for glutathione conjugation?

Answer 21

γ-glutamyl-cysteinyl-glycine, aka glutathione (abbreviated GSH)

Question 22

________ groups in drugs form glutathione conjugates

Answer 22

Electrophilic

Question 23

What are some examples of electrophilic groups?

Answer 23

Alkyl halides, some aryl halides, α,β-unsaturated ketone, and epoxides

Question 24

Electrophilic groups are only found on drugs that are used to…

Answer 24

Kill cells, such as cancer cells

Question 25

The product of glutathione conjugation is not secreted as such. It is further metabolized in several steps to the final metabolite, ___________.

Answer 25

N-acetyl-cysteine conjugate. Also known as mercapturic acid

Question 26

GSH conjugation is very often a _________ reaction, as it protects the cell from damage caused by ________.

Answer 26

Detoxification; electrophiles

Question 27

What reaction detoxifies the reactive metabolite produced by a minor pathway of acetaminophen?

Answer 27

GSH conjugation

Question 28

What enzyme catalyzes acetylation?

Answer 28

N-acetyl-transferases, abbreviated NAT

Question 29

What co-substrate is needed for acetylation?

Answer 29

Acetyl-coenzyme A

Question 30

What was the enzyme listed that first showed genetic polymorphism in people?

Answer 30

NAT enzymes (NAT-2)

Question 31

Which metabolite given in the powerpoint is the only one that is not anionic after the phase 2 reaction?

Answer 31

Acetylated metabolites

Question 32

Describe the discovery of amino acid conjugates

Answer 32

Benzoic acid was fed to horses and a white crystalline substance was isolated from the horse urine. The substance was known to be an acid, and was named "hippuric acid" (hippos = horse). The substance was shown to be benzoylglycine.

Question 33

What are the substrates of amino acid conjugation? (what is reacted with)

Answer 33

Carboxylic acids

Question 34

What are the two steps in amino acid conjugation?

Answer 34

Formation of a coenzyme A intermediate (replace the OH of a carboxyl group with S-CoenzymeA) Formation of the conjugate (replace the S-CoenzymeA with glycine, which is N-CH2-COOH)

Question 35

What enzymes catalyze the two steps of amino acid conjugation?

Answer 35

First: acyl-coenzyme A ligase Second: acyl-coA-amino acid N-acyltransferase

Question 36

What conjugates are very good substrates for transporters?

Answer 36

Amino acid conjugates

Question 37

What are the relative percentages of each phase 2 reaction?

Answer 37

``` UGT's 45% SULTs 20% GSTs 15% NATs 5% Amino acid conjugation 5% ```

Question 38

What are the minor phase 2 reactions? Why are they different?

Answer 38

Methylation, Fatty acid conjugation, Cholesterol ester formation They don't increase the water solubility

Question 39

Drugs with the ____________ group are common substrates for Methylation reaction

Answer 39

Catechol (two alcohols on an aromatic ring)

Question 40

What enzymes catalyze methylation?

Answer 40

S-adenosine-methyl transferase

Question 41

What co-substrate is necessary for methylation?

Answer 41

S-adenosylmethionine (SAM)

Question 42

What enzyme catalyzes the O-methylation of a catechol group?

Answer 42

Catechol O-methyltransferase

Question 43

Why isn't esterification with endogenous fatty acids/alcohols easy to follow?

Answer 43

Because the products are more fat soluble so they are stored in fatty tissue

Question 44

Which minor phase 2 reaction may contribute to prolonged duration of action of some drugs?

Answer 44

Esterification with endogenous fatty acids or alcohols

Question 45

What happens during fatty acid conjugation?

Answer 45

The carboxylic acid goes from COOH to COO-CH2-CH2-Cl-

Question 46

What enzyme is used to catalyze cholesterol ester formation?

Answer 46

Ester hydrolase

Question 47

What enzyme is used to catalyze fatty acid conjugation?

Answer 47

Ester hydrolase

Question 48

What are Phase III reactions?

Answer 48

The process of transporter protein-aided removal of drugs and drug metabolites out of the cell "phase III" pathways

Question 49

What are SLC's?

Answer 49

Solute carrier proteins They are involved in uptake AND efflux No ATP required

Question 50

What are ABC's?

Answer 50

ATP binding cassette protein Only involved in efflux ATP required

Question 51

Why are ABC's related to resistance of anti-cancer drugs?

Answer 51

Cancer cells start overproducing efflux protein, and pumps out the anti-cancer drug, preventing it from killing the tumor cell

Question 52

What is MDR1?

Answer 52

Multi-Drug Resistance protein 1 aka p-glycoprotein | Transport protein that can take neutral or weakly cationic drugs and efflux them out of the cell, with energy from ATP

Question 53

Some anionic metabolites can be effluxed from cells with the aid of...

Answer 53

MRP2

Question 54

What are OATs?

Answer 54

A family of SLC's

Question 55

OAT1 transporter is found in kidney tubules, where it facilitates uptake of _______ from the blood into the kidney tubule.

Answer 55

Glycine conjugates