Lecture 1 Flashcards
Metabolism plays an important role in….
the elimination of drugs and other foreign substances from the body
what is the term for “foreign substances” that are removed through the process of metabolism?
xenobiotics
xenobiotics are relatively ___ soluble
lipid
metabolic reactions covert the relatively lipid soluble xenobiotics to….
water soluble (hydrophilic) compounds that can be excreted
what would happen if lipophilic drugs were not metabolized to more polar, water soluble products?
they would remain in the body indefinitely eliciting their biological effects (bc they would not be readily excretable, water soluble products)
do water soluble drugs need to be metabolized?
no. they are simply filtered and eliminated
metabolism leads to compounds that are…..
generally pharmacologically LESS ACTIVE and relatively nontoxic
as mentioned, metabolism leads to compounds that are generally pharmacologically LESS ACTIVE and relatively nontoxic.
therefore, drug metabolism reactions are also regarded as ____ processes
detoxification
sometimes, the metabolite can be…..
(3 things)
-toxic
-biologically active
-activate an inactive drug
as mentioned, sometimes the metabolite that results from a metabolic reaction can be toxic.
give a specific example of this
acetaminophen is metabolized to N-acetylimidoquinone which is a TOXIC METABOLITE and can cause liver toxicity if too much acetaminophen is taken
as mentioned, sometimes the metabolite that results from a metabolic reaction can be biologically active
give a specific example of this and explain the significance
when diazepam undergoes metabolism, it is converted to an ACTIVE METABOLITE - Oxazepam.
THERFORE, the presence of the parent molecule (diazepam) cannot be used to signal the end of the duration of action, because the metabolite is also active
true or false
it is typical of benzodiazepines to have a metabolite that is biologically active
true.
such is the case for diazepam
as mentioned, sometimes the metabolite from the metabolism of a drug can activate an inactive drug
give a specific example of this
such is the case with prodrugs
protonsil gets bioreduced to produce the active antibiotic – sulfonamide
true or false
drug metabolism is a straightforward detoxification
FALSE.
there are 3 exceptions as mentioned. the metabolite can be toxic, be biologically active, or activate an inactive drug
name the 2 categories of metabolic reactions
phase 1 (functionalization reactions)
phase 2 (conjugation reactions)
true or false
benzene is lipophilic
true
what is the function of phase 1 of drug metabolism
to “functionalize” the starting material that has no functional group
for example, if starting with benzene a hydroxyl group can be added to form phenol. this molecule can then undergo conjugation
if you are starting with a drug molecule that has a phenol functional group, is phase 1 of drug metabolism needed?
usually not, but it depends
in theory, if a molecule already has a “built in” polar functional group, phase 1 shouldn’t be needed.
however, if too much of the drug is ingested, phase 1 might still be needed. this is the case for acetaminophen. It has a built in polar functional group so phase 1 is usually bypassed, but if too much is taken, acetaminophen might undergo phase 1
true or false
diazepam’s metabolite is toxic
FALSE – it is biologically active
the main purpose of functionalization (phase 1) reactions is to _______ into _______
introduce a polar functional group into a xenobiotic (foreign) molecule
as mentioned, the main purpose of functionalization reactions is to introduce a polar functional group into a xenobiotic molecule.
name the most common of these functional groups
-OH (hydroxyl)
-COOH (carboxyl)
-NH2 (amine)
-SH (thiol)
the main organ that handles drug metabolism
the liver
as mentioned, the main purpose of the phase 1 reactions of drug metabolism is to introduce a polar functional group into a xenobiotic molecule
explain how this is accomplishes
mainly through the liver microsomal enzymes through 3 reactions:
-oxidations
-reductions
-hydrolysis
Phase 1 reactions provide a _____ in the form of _____ to undergo_____
phase 1 reactions provide a HANDLE in the form of POLAR FUNCTIONAL GROUPS (-OH, -COOH, -NH2, -SH) to undergo PHASE 2 REACTIONS
Phase 2 reactions are also known as ____ reactions
conjugation
Phase 2 (conjugation) reactions attach ______ to _________
phaase 2 reactions attach POLAR AND IONIZABLE GROUPS to:
-the phase 1 metabolites OR
-the xenobiotics already containing the necessary polar functional groups
to form water soluble CONUJUGATED PRODUCTS devoid of activity
name 3 typical phase 2 reactions
-glucuronic acid conjugation
-sulfate conjugation
-glycine, glutamine, and other amino acid conjugation
glucuronic acid conjugation can also be called…
glucuronidation
sulfate conjugation can also be called…
sulfation - attaching sulfate group to substrate
what are the typical amino acids that undergo phase 2 metabolic reactions?
can other amino acids participate in phase 2 reactions?
typical: glycine and glutamine
the conjugation of other amino acids is possible, but it depends on the species involved
explain the metabolites that result from the 3 most common conjugation reactions (listed above)
they are GENERALLY pharmacologically inactive,
VERY POLAR and are readily excreted in the urine
besides:
-glucuronic acid conjugation
-sulfate conjugation
-glycine, glutamine, and other amino acid conjugation
name 3 other phase 2 reactions
glutathione conjugation
acetylation
methylation
what is GSH
glutathione
explain the main purpose of glutathione conjugation
give a specific example of how it accomplishes this purpose
to protect the body against chemically reactive metabolites/xenobiotics
for example, the metabolite of acetaminophen (N-Acetylimidoquinone) is chemically reactive and can cause liver toxicity.
glutathione intercepts this chemically reactive metabolite. Several steps occur and acylated cysteine is added to the molecule. Also, the carbonyl gets reduced to an alcohol (OH). – forms MERCAPTURIC ACID
this molecule is now STABLE
what are 2 brand names of acetaminophen?
tylenol, tempra
name for a benzene ring with a carbonyl at the 1 and 4 positions
1,4-benzoquinone
what is the name of the metabolite of acetaminophen? how is it formed?
N-Acetylimidoquinone
produced under several steps via oxidation
in GSH conjugation, how are the metabolites excreted?
GSH derivatives are not excreted this way. they undergo further biotransformation to form MERCAPTURIC ACID DERIVATIVES which THEN are excreted
what are the 2 phase 2 reactions whose primary goal is to terminate biological activity?
acetylation and methylation
what 3 phase 2 reactions are different from typical conjugation reactions?
explain how they’re different
GSH conjugation, acetylation, and methylation
do not significantly increase water solubility or produce water soluble metabolites
for which 3 conjugation reactions is the primary goal to terminate biological activity?
GSH conjugation, acetylation, and methylation
there are 3 “typical” conjugation pathways and 3 “nontypical” conjugation pathways.
name them
typical – produce biologically inactive, water soluble molecules:
-glucuronic acid conjugation
-sulfate conjugation
-glycine, glutamine, and other amino acid conjugation
nontypical - DONT ENHANCE WATER SOLUBILITY - just terminate biological activity
-GSH conjugation
-methylation
-acetylation
do any of the 3 “nontypical” conjugation reactions ever DO produce polar/water soluble metabolites?
yes.
methylation can lead to a water soluble metabolite when a QUATERNARY AMMONIUM DERIVATIVE IS FORMED (very rare)
explain the structure of quaternary ammonium
Nitrogen with 4 substituents attached and thus has a + charge
____ is a tripeptide
GSH (glutathione)
what does MFOS stand for
mixed function (mono)oxidase system
what does the MFO system require?
- An oxygenating agent
- a reducing cofactor
the MFO system requires:
-an oxygenating agent
-a reducing cofactor
typically, what is used to serve these 2 functions?
molecular oxygen is typically used as an oxygenating agent, all depending on the presence of oxygen molecules.
the reducing cofactor is typically NADPH
what are the enzymes involved in MFOS?
-cytochrome p450
-NADPH-cytochrome P-450 reductase
-NADH-cytochrome b5 reductase
the mixed function oxidase system is part of phase ___ of drug metabolism
ONE
explain what MFO does
inserts only ONE ATOM of oxygen into the substrate (drug) and the other oxygen atom ends up in H2O.
MFO activates molecular oxygen which, in turn, OXIDIZES the substrate
true or false
dioxygenase enzymes are used in the MFO system
FALSE - only involves the transfer of 1 atom of oxygen.
involves mono oxygenases (cytochrome P450)
explain the structure of Cytochrome P-450
it contains:
heme portion - made of iron containing porphyrin. IDENTICAL throughout all the Cytochrome P-450 isozymes. it actually delivers the oxygen atom to the substrate.
protein portion - apoprotein.
serves as the drug binding site and provides SELECTIVITY for different isozymes of cytochrome p450
what is the main catalytic place of MFOS?
the heme portion of cytochrome P450
what is the drug binding site of MFO system?
the protein portion of cytochrome P450
why is Cyt P-450 given that name?
when the heme portion of the enzyme containing ferric (Fe+3) is reduced to ferrous (Fe2+) and reacts with carbon monoxide (typically in a lab setting) the enzyme gives a characteristic absorption at 450nm
true or false
the MFO system does not express much versatility
FALSE –
xenobiotics with diverse structures can be metabolized by the MFO system by a VARIETY of oxidative reactions
with base substrate as RH, R can be alkyl, aryl, etc
also not limited to just C-H bonds
how is the MFO system able to have such versatility?
it has broad substrate specificity and also has multiple isozymes (isoforms) of cytochrome p450
where is the MFO system found in high concentrations?
in the liver
besides the liver, where else is the MFO system found?
lungs, kidney, adrenal cortex, skin, placenta, intestine
where SPECIFICALLY is the MFO system found? (not an organ)
it is a MEMBRANE BOUND ENZYME and is in the endoplasmic reticulum
MFO system is a membrane bound enzyme in the endoplasmic reticulum.
what kind of environment is this? (lipophilic or hydrophilic)
WHY?
LIPOPHILIC
lipophilic substrates are taken in to be metabolized by MFO
what is the S9 fraction?
contains CYt P-450 enzymes.
used to represent in vitro phase 1 reaction in the lab setting
give the general chemical reaction for the MFO system
R-H + NADPH + O2 +H+ —> R-OH + NADP+ + H2O
which portion of Cytochrome P-450 has interaction with the activated oxygen species?
the heme portion (catalytic portion)
they’re in very close proximity.
the drug is bound to the substrate binding site (apoprotein portion of cytp450) and the reactive O is inserted between the R and H to form ROH
what is another name for the heme portion of cytochrome p450
protoporphyrin IX
STEP 1: cytochrome p450 forms a complex with what? what kind of complex is it?
the ferric (+3) ion in the heme portion of cytochrome p450
BINARY COMPLEX. contains 2 components - ferric and substrate
STEP 2: after the drug (substrate) forms a binary complex with ferric, what happens?
the coenzyme (NADPH) participates by donating an electron via the Cytochrome p450 reductase enzyme.
this reduces ferric (+3) to ferrous (+2)
this is ALWAYS the first electron donation step (the second step has 2 potential options)
STEP 3:
what happens after NADPH has donated an electron to reduce ferric to ferrous?
ferrous interacts with molecular oxygen (O2) to form a TERTIARY COMPLEX:
-O2
-P450 with ferrous
-substrate
before this step occurs is when the binary complex (ferrous (fe2+)) can react with carbon monoxide in the lab produce a complex with CO. complex is now p450 with ferrous + substrate+ CO
this chromophore (molecule that absorbs light at a particular wavelength) absorbs characteristically at 450nm.
After the binary complex reacts with molecular oxygen to form a tertiary complex, what happens next?
another electron is provided from 1 of 2 sources:
-from NADPH through cytochrome p450 reductase OR
-From NADH through cytochrome b5 reductase
this produces an ACTIVATED tertiary complex and ferrous is oxidized back to ferric
what happens after the second electron is added?
2 electrons are provided - 1 from NADPH and 1 from the oxidation of ferrous back to ferric.
this pair of electrons, with 1 atom from the bound molecular oxygen, forms a WATER MOLECULE
this produces an ACTIVATED OXYGEN SPECIES:
p-450 connected to ferric, O, RH at the substrate binding site
this activated oxygen species then oxidizes the product and it is released, forming R-OH
how are the cytochrome p450s named?
CYP-number-capital letter-number
the cytochrome p450sare named with
CYP-number-capital letter-number
explain this further
1st number = family
Capital letter = subfamily
next # = individual enzyme in a subfamily
how are the families and subfamilies of the cytochrome p450 enzymes determined?
by amino acid sequence homology
what is one of the most common cytochrome p450 enzymes that handles most drugs?
CYP3A4
Approximately how many of the P-450 gene families are identified in mammals?
~14 families
for liver metabolism (in humans), there are ______ main cytochrome p450 families:
3 main families:
CYP1, 2, and 3
