Summary molecular toxicology
Inhoud
Summary molecular toxicology ............................................................................................................... 1
Chapter 1 ................................................................................................................................................. 3
Level 1 .............................................................................................................................................. 3
Level 2 .............................................................................................................................................. 4
Chapter 2 ................................................................................................................................................. 5
Level 3 .............................................................................................................................................. 5
Chapter 3/4 transporters and toxicokinetics ........................................................................................... 9
Organ-selective uptake, distribution, accumulation: .......................................................................... 9
Organ-specific metabolism and bio-activation .................................................................................. 10
Tissue specific molecular targets....................................................................................................... 10
Cellular transport and selective accumulation of potentially toxic xenobiotics............................ 12
Chapter 5 ............................................................................................................................................... 16
Name common groups of reactive metabolites and couple them to the metabolic enzymes that
make them......................................................................................................................................... 16
........................................................................................................................................................... 16
Explain the relation between drug metabolism and organ-species-interindividual selectivity in
toxicity (incl.polymorphisms) ............................................................................................................ 17
Explain under which circumstances reactive metabolites can be formed from Phase II conjugation
products............................................................................................................................................. 18
Explain how the enterohepatic circulation can increase exposure to a xenobiotic compound ........ 19
Explain why the kidney is prone to be the target of toxicity by glutathion conjugates .................... 20
Explain the relation between drug metabolism and organ- species-interindividual selectivity in
toxicity (incl. ...................................................................................................................................... 20
polymorphisms)................................................................................................................................. 20
Explain (molecular) mechanisms of induction and inhibition ........................................................... 21
Chapter 6 ............................................................................................................................................... 22
- Define oxidative stress .................................................................................................................... 23
Discuss endogenous (ETC, immunecellen) and exogenous sources of (xenobiotics, UV) ................. 23
Explain what is REDOX cycling and its effects .................................................................................... 24
Describe the action of ROS scavengers ............................................................................................. 24
Explain the role of transition metals in oxidative stress .................................................................... 25
Explain the cytoprotective effect of GSH........................................................................................... 26
Explain the consequence of oxidative stress for cellular macromolecules ....................................... 27
Explain the mechanism of signal transduction and its role in cell survival ....................................... 27
Chapter 10 covalent binding of reactive metabolites to cellular macromolecules ............................... 30
, Understand why certain electrophiles react with certain nucleophiles ............................................ 30
Explain what are the down-stream effects of protein adduct formation.......................................... 31
Discuss why it is difficult to causally relate covalent protein binding to toxicity .............................. 31
Understand why canalicular proteins are a frequent target of electrophile attack ......................... 32
Discuss the possible effects of covalent DNA binding ....................................................................... 32
Chapter 11 immune mechanisms, chapter 12 cytokine mediated toxicity ........................................... 35
Explain immunosuppression and stimulation by xenobiotics ........................................................... 35
Explain how the innate immune system contributes to damage by a toxic insult ............................ 35
Explain the role of chemokines in the induction of an immune response ........................................ 36
Distinguish different kinds of cytokines............................................................................................. 37
Explain the function of TNFa ............................................................................................................. 37
Understand the dual role of TNF in promoting cell surviving and apoptosis .................................... 37
Explain how hapten formation can induce an immune response ..................................................... 38
Chapter 17 disruption of the mitochondrial function and mitochondrial mediated toxicity................ 40
Explain the most common mechanisms of mitochondrial toxicity and its consequences ................ 40
Explain why mitochondrial DNA is very sensitive to toxicity ............................................................. 41
Explain why mitochondrial damage in some cases can be acute, whereas in some cases damage is
delayed .............................................................................................................................................. 41
Explain the mechanism of organ specific sensitivity to mitochondrial injury ................................... 42
Idiosyncratic drug reactions .................................................................................................................. 43
Discusses different hypotheses about how a low molecular drug can induce an adaptive immune
response (hapten theory, P-I hypothesis, altered peptided repertoire) ........................................... 44
Hapten ............................................................................................................................................... 45
pI concept how is an adaptive immune response induced by a low molecular drug? ..................... 46
Altered peptide repertoire ................................................................................................................ 48
Factors that explain idiosyncrasy ....................................................................................................... 49
Lecture Nano ......................................................................................................................................... 53
,Learning points Ing kennen, ken prinicpe, niet per se de voorbeelden.
Chapter 1
After this lecture:
you understand the different levels at which
molecular mechanisms of toxicity can be
explained:
(book chapter 1 an 2)
- Level of toxicokinetics
- Level of toxicodynamics
- Level of biological response
Molecular toxicology mechanisms of toxicity
Required to:
- Estimate the risk of HUMAN toxicity after
exposure to a potentially toxic compound
- Determine toxicity thresholds
- Develop antidotes against acute toxicity
- Facilitate development of safe pharmaceuticals
- Develop biomarkers of exposure or toxicity
What do we need to get toxicity?
Lack of adaption to the insult (=cells not adapt)
Level 1
Toxicokinetics
toxicity and exposure
Toxicokinetics describes the changes of the concentrations of a compound
in the organism over time (or ‘what the body does to a chemical’).
→ADME e.g. selective uptake and accumulation of xenobiotic (=foreign compound) in a specific tissue or cell type can lead
to toxicity that doesn’t occur in other tissues or cells.
Paracelsus ca 1500 said ‘all compounds are poisons, but it’s the dose that determines if something is toxic’
! But→ compounds have different potentency to be toxic.
LD50: lethal dose 50%, tells you the dose of a substance required to kill 50% of a test
population under controlled conditions.
LD50 is different for compounds ethyl alcohol beer low, but botlinium toxin is lower.
Message here→ toxicity depends on the dose!! Potency is related to different things->
other targets are for example more vulnerable e.g. nerves system.
Also the route of administration is important! When you avoid the first pass effect by
injection a compound can be more toxic compared to oral administration of e.g. ricin.
Because drug is partly metabolized by the intestine and low absorption of the drug in
the blood.
So, (internal) exposure determines toxicity
‘All substance are poisons, it is the EXPOSURE (of the target) that determines if a substance is toxic or not’.
Molecular mechanisms of toxicity
Toxicokinetic factors:
Factors concerning
-absorption
-distribution
-metabolism/(de)toxification
-excretion
What does the body do with the toxic compound?
Together they determine:
What is the exposure “of the target”? (to the ultimate toxicant
, Metabolism and toxicity
Sometimes:
- Metabolites are more toxic than parent compound
= toxification or bioactivation
Sometimes:
- Metabolites less toxic than parent compound
= detoxification
Graph
A is less toxic compared to B
B and C do have a threshold, below the threshold no toxicity occurs.
A compound that does not have a threshold is for example a
compound that causes one molecular modification in DNA that can
lead to cancer no threshold is here.
Level 2
Toxicodynamics: interaction with the target
Toxicodynamics describes the dynamic interactions of a compound
with a biological target and its downstream biological effects (what
the drug does to the body) e.g. covalent interaction of xenotbiotic
with a macromolecule of the cell or interaction nand activation of a cellular receptor, can be linked with toxicity.
Molecular mechanisms of toxicity
Toxicodynamic factors:
What is the “target” of this compound?
(e.g protein, phospholipid membrane, mitochondria, DNA, cellular receptor).
Aspecific to highly specific!
What kind of interaction does the compound
undergo with the target? (And what are downstream effects?)
“What does the compound do to the body?
A very specific target (high affinity binding sites, often receptors located on the cell (plasma membrane receptor) or in the
cytoplasm/nucleus (nuclear receptor))is for example beta blokkers that bind to the beta receptor. Xenobiotic can induce an
agonist response or prevent the physiological ligand from binding to the receptor thus inducing antagonist response by
inhibiting receptor function. Other high affinity targets that specially bind to a foreign substance are enzymes,
transmembrane transporters (carriers or ion channels), or binding proteins that transport endogenous compounds. Another
type of highly specific interaction can occur between a structural moiety of a foreign molecule matching with a specific
target site of a macromolecule. Xenobiotics may not necessarily be reactive by itself and damage the endogenous
macromolecule but due to its high affinity and persistent binding may prevent the macromolecule, or parts of it, from
interacting with other physiological molecules. The toxic compound inhibits a vital physiological process or interferes with a
regulatory step. E.g. thalidomide with regions of DNA->disrupt gene activation an thus inhibit differentiation and growth.
A aspecific target is a electrophilic compound that binds to DNA or causes ROS damage.
Intrinsic properties e.g. LogP, electrophilicity, shape of the molecule all
determine the action with the target.
Inhoud
Summary molecular toxicology ............................................................................................................... 1
Chapter 1 ................................................................................................................................................. 3
Level 1 .............................................................................................................................................. 3
Level 2 .............................................................................................................................................. 4
Chapter 2 ................................................................................................................................................. 5
Level 3 .............................................................................................................................................. 5
Chapter 3/4 transporters and toxicokinetics ........................................................................................... 9
Organ-selective uptake, distribution, accumulation: .......................................................................... 9
Organ-specific metabolism and bio-activation .................................................................................. 10
Tissue specific molecular targets....................................................................................................... 10
Cellular transport and selective accumulation of potentially toxic xenobiotics............................ 12
Chapter 5 ............................................................................................................................................... 16
Name common groups of reactive metabolites and couple them to the metabolic enzymes that
make them......................................................................................................................................... 16
........................................................................................................................................................... 16
Explain the relation between drug metabolism and organ-species-interindividual selectivity in
toxicity (incl.polymorphisms) ............................................................................................................ 17
Explain under which circumstances reactive metabolites can be formed from Phase II conjugation
products............................................................................................................................................. 18
Explain how the enterohepatic circulation can increase exposure to a xenobiotic compound ........ 19
Explain why the kidney is prone to be the target of toxicity by glutathion conjugates .................... 20
Explain the relation between drug metabolism and organ- species-interindividual selectivity in
toxicity (incl. ...................................................................................................................................... 20
polymorphisms)................................................................................................................................. 20
Explain (molecular) mechanisms of induction and inhibition ........................................................... 21
Chapter 6 ............................................................................................................................................... 22
- Define oxidative stress .................................................................................................................... 23
Discuss endogenous (ETC, immunecellen) and exogenous sources of (xenobiotics, UV) ................. 23
Explain what is REDOX cycling and its effects .................................................................................... 24
Describe the action of ROS scavengers ............................................................................................. 24
Explain the role of transition metals in oxidative stress .................................................................... 25
Explain the cytoprotective effect of GSH........................................................................................... 26
Explain the consequence of oxidative stress for cellular macromolecules ....................................... 27
Explain the mechanism of signal transduction and its role in cell survival ....................................... 27
Chapter 10 covalent binding of reactive metabolites to cellular macromolecules ............................... 30
, Understand why certain electrophiles react with certain nucleophiles ............................................ 30
Explain what are the down-stream effects of protein adduct formation.......................................... 31
Discuss why it is difficult to causally relate covalent protein binding to toxicity .............................. 31
Understand why canalicular proteins are a frequent target of electrophile attack ......................... 32
Discuss the possible effects of covalent DNA binding ....................................................................... 32
Chapter 11 immune mechanisms, chapter 12 cytokine mediated toxicity ........................................... 35
Explain immunosuppression and stimulation by xenobiotics ........................................................... 35
Explain how the innate immune system contributes to damage by a toxic insult ............................ 35
Explain the role of chemokines in the induction of an immune response ........................................ 36
Distinguish different kinds of cytokines............................................................................................. 37
Explain the function of TNFa ............................................................................................................. 37
Understand the dual role of TNF in promoting cell surviving and apoptosis .................................... 37
Explain how hapten formation can induce an immune response ..................................................... 38
Chapter 17 disruption of the mitochondrial function and mitochondrial mediated toxicity................ 40
Explain the most common mechanisms of mitochondrial toxicity and its consequences ................ 40
Explain why mitochondrial DNA is very sensitive to toxicity ............................................................. 41
Explain why mitochondrial damage in some cases can be acute, whereas in some cases damage is
delayed .............................................................................................................................................. 41
Explain the mechanism of organ specific sensitivity to mitochondrial injury ................................... 42
Idiosyncratic drug reactions .................................................................................................................. 43
Discusses different hypotheses about how a low molecular drug can induce an adaptive immune
response (hapten theory, P-I hypothesis, altered peptided repertoire) ........................................... 44
Hapten ............................................................................................................................................... 45
pI concept how is an adaptive immune response induced by a low molecular drug? ..................... 46
Altered peptide repertoire ................................................................................................................ 48
Factors that explain idiosyncrasy ....................................................................................................... 49
Lecture Nano ......................................................................................................................................... 53
,Learning points Ing kennen, ken prinicpe, niet per se de voorbeelden.
Chapter 1
After this lecture:
you understand the different levels at which
molecular mechanisms of toxicity can be
explained:
(book chapter 1 an 2)
- Level of toxicokinetics
- Level of toxicodynamics
- Level of biological response
Molecular toxicology mechanisms of toxicity
Required to:
- Estimate the risk of HUMAN toxicity after
exposure to a potentially toxic compound
- Determine toxicity thresholds
- Develop antidotes against acute toxicity
- Facilitate development of safe pharmaceuticals
- Develop biomarkers of exposure or toxicity
What do we need to get toxicity?
Lack of adaption to the insult (=cells not adapt)
Level 1
Toxicokinetics
toxicity and exposure
Toxicokinetics describes the changes of the concentrations of a compound
in the organism over time (or ‘what the body does to a chemical’).
→ADME e.g. selective uptake and accumulation of xenobiotic (=foreign compound) in a specific tissue or cell type can lead
to toxicity that doesn’t occur in other tissues or cells.
Paracelsus ca 1500 said ‘all compounds are poisons, but it’s the dose that determines if something is toxic’
! But→ compounds have different potentency to be toxic.
LD50: lethal dose 50%, tells you the dose of a substance required to kill 50% of a test
population under controlled conditions.
LD50 is different for compounds ethyl alcohol beer low, but botlinium toxin is lower.
Message here→ toxicity depends on the dose!! Potency is related to different things->
other targets are for example more vulnerable e.g. nerves system.
Also the route of administration is important! When you avoid the first pass effect by
injection a compound can be more toxic compared to oral administration of e.g. ricin.
Because drug is partly metabolized by the intestine and low absorption of the drug in
the blood.
So, (internal) exposure determines toxicity
‘All substance are poisons, it is the EXPOSURE (of the target) that determines if a substance is toxic or not’.
Molecular mechanisms of toxicity
Toxicokinetic factors:
Factors concerning
-absorption
-distribution
-metabolism/(de)toxification
-excretion
What does the body do with the toxic compound?
Together they determine:
What is the exposure “of the target”? (to the ultimate toxicant
, Metabolism and toxicity
Sometimes:
- Metabolites are more toxic than parent compound
= toxification or bioactivation
Sometimes:
- Metabolites less toxic than parent compound
= detoxification
Graph
A is less toxic compared to B
B and C do have a threshold, below the threshold no toxicity occurs.
A compound that does not have a threshold is for example a
compound that causes one molecular modification in DNA that can
lead to cancer no threshold is here.
Level 2
Toxicodynamics: interaction with the target
Toxicodynamics describes the dynamic interactions of a compound
with a biological target and its downstream biological effects (what
the drug does to the body) e.g. covalent interaction of xenotbiotic
with a macromolecule of the cell or interaction nand activation of a cellular receptor, can be linked with toxicity.
Molecular mechanisms of toxicity
Toxicodynamic factors:
What is the “target” of this compound?
(e.g protein, phospholipid membrane, mitochondria, DNA, cellular receptor).
Aspecific to highly specific!
What kind of interaction does the compound
undergo with the target? (And what are downstream effects?)
“What does the compound do to the body?
A very specific target (high affinity binding sites, often receptors located on the cell (plasma membrane receptor) or in the
cytoplasm/nucleus (nuclear receptor))is for example beta blokkers that bind to the beta receptor. Xenobiotic can induce an
agonist response or prevent the physiological ligand from binding to the receptor thus inducing antagonist response by
inhibiting receptor function. Other high affinity targets that specially bind to a foreign substance are enzymes,
transmembrane transporters (carriers or ion channels), or binding proteins that transport endogenous compounds. Another
type of highly specific interaction can occur between a structural moiety of a foreign molecule matching with a specific
target site of a macromolecule. Xenobiotics may not necessarily be reactive by itself and damage the endogenous
macromolecule but due to its high affinity and persistent binding may prevent the macromolecule, or parts of it, from
interacting with other physiological molecules. The toxic compound inhibits a vital physiological process or interferes with a
regulatory step. E.g. thalidomide with regions of DNA->disrupt gene activation an thus inhibit differentiation and growth.
A aspecific target is a electrophilic compound that binds to DNA or causes ROS damage.
Intrinsic properties e.g. LogP, electrophilicity, shape of the molecule all
determine the action with the target.
