1- toxicity mechanism Flashcards
what are 2 things that happen after delivery and before cellular dysfunction and injury
interaction with target molecule and alteration of biological environment
what happens after a toxicant does interaction with target molecule and alteration of biological environment
it causes cellular dysfunction and injury
what can cellular dysfunction and injury lead to (2)
inappropriate repair and adaptation, toxicity
what does inappropriate repair and adaptation lead to
toxicity
what 4 things are important in the delivery of the toxicant
absorption, distribution toward target, reabsorption (tubules), toxication
what is toxication
when some molecules become more toxic by bodily processes
what are 4 things that reduce delivery of the toxicant
presynaptic elimination, distribution away from target, excretion, detoxication
what is detoxication
when your body tries to make something less toxic and remove it
what is the ultimate toxicant
chemical that reacts with an endogenous molecule or alters the biological environment resulting in toxicity, may be a metabolite or byproduct of the primary toxicant to which the organism is exposed
what are the 4 main steps of toxicity
1-delivery
2-interaction with target molecule
3-cellular dysfunction, injury
4-inappropriate tissue repair and adaptation, non functionality of organ
is the consumed toxicant the same as the one that interacts with the body
sometimes, but they can be different
what is toxication
biotransformation into a harmful product
what are electrophiles
usually positively charged (full or partial), attracted to negative charges, electron deficient
what happens to chemical reactivity with toxication
increased
what are nucleophiles
electron rich, donate electron pair, can be negatively charged
what are ROS RNS
oxygen/nitrogen containing things with one or more unpaired electrons in outer orbital
what is detoxication
biotransformation that eliminates ultimate toxicant or prevents its formation
what are 3 things that are made with toxication
electrophiles, ROS/RNS, nucleophiles (more uncommon)
which is the relatively uncommon toxication pathway
nucleophiles
how are electrophiles usually produced and what does it make (2 production ways, 3 products)
when an oxygen is inserted resulting in a ketone, aldehyde or epoxide, or due to heterolytic cleavae (uneven distribution of electrons that formed the bond)
what is the charge of the carbon in ketones, aldehydes and epoxides
usually partially + cause of electron withdrawal
what are electrophiles
molecules containing an electron-deficient atom with a full or partial charge
what happens once an oxygen is inserted resulting in a ketone/aldehyde/epoxide?
it produces an electrophile
what is produced if there is heterolytic cleavage in which there is an uneven distribution fo the electrons that form the bond
electrophiles
what is a reactive oxygen species
a molecule containing oxygen that contains one or more unpaired electrons in its outer orbital
what is so bad about ROS
they are highly reaction, and like to interct with proteins DNA lipids
where are ROS most found
in mitochondria via ETC (normal)
Are ROS found naturally in the body and where
yes, esp in in mitochondria via ETC
if ROS is found naturally, why dont we die earlier
because the body has a healthy balance between production and destruction of ROS but this can change when cells are stressed
what can cause a change in the healthy balance between production and destruction of ROS
cells are stressed
what are 3 examples of ROS
superoxide anion (O2*-) hydroxyl radical (OH*) hydrogen peroxide is kinda (H2O2)
what is the deal with superoxide anion (O2*-) (when does it occur, what happens once its formed)
it happens when rxns are incomplete, produce ETC, can travel far and last long
what is the deal with hydrogen peroxide (H2O2) (what happens once its formed)
powerful oxidizer, feeds into pathways that generates ROS. it is not a ROS itself (check)
what is the deal with hydroxyl radical (OH*)
) (what happens once its formed)
very reactive with a short half life, significant local damage, doesnt travel far
which ROS travels far
superoxide anion (O2*-)
which ROS doesn’t travels far
hydroxyl radical (OH*)
what are 3 major sources of ROS
- mitochondrial reduction of oxygen during ATP production
- reduction of H2O2 by transition metal ions (fenton)
- redox cycling
why can mitochondrial reduction of oxygen during ATP production lead to ROS production? what is supposed to happen
it usually ends up in H2O but a small % ends up as ROS
what is the fenton reaction (Definition)
reduction of H2O2 by transition metal ions
what is redox cycling
quinones and bipyridyls contributing to a never ending process of ROS production
what is the specific reaction i the Fenton reaction
HOOH + transition state metal (Fe Cu Mn Cr Ni) –> HOOH- –> OH* + OH-
what does superoxide dismutase do
turn superoxide anion (O2*-) into hydrogen peroxide
what happens if superoxide anion (O2-) and NO join
it forms peroxynitrite (ONOO-)
what can happen to peroxynitrite (ONOO-)
spontaneous rxn with CO2 to form nitrosoperoxy carbonate (ONOOCO-2)
what happens to nitrosoperoxy carbonate (ONOOCO-2)
spontaneous cleavage into NO2* and CO3* (both damaging)
what happens after the fenton reaction to HOOH-
homolytic cleavage into OH* (damaging) and OH- (not reactive)
what are 2 example of toxification paths from O2*-
fenton reaction to OH* then the peroxynitrite side to make NO2* and CO3-*
what does redox cycling generate
free radicals
how do drugs contribute to redox cycling (paraquat, doxorubicin, nitrofurantoin)
they pick up electron from cofactor then donate it to oxygen
what are 2 things that contribute to toxicity in redox cycling
the creation of ROS but also the running out of cofactors (like NADPH)
what enzyme helps out in redox cycling
P450 reductase
what is an example reaction of what P450 reductase can do
NADH + H+ –> NAD+
what are 3 drug examples that create redox cycling
paraquat, doxorubicin, nitrofurantoin
what is paraquat
a herbicide
what kind of bad thing does paraquat do
redox cycling
what are 3 targets of ROS
lipids proteins DNA
what does ROS do to lipids (1 word)
peroxidation
what is peroxidation (general)
breakdown of lipids into small and reactive fragments
what are 3 things that ROS can do to proteins
protein carboneyls, crosslnks, fragmentation
what are protein carbonyls
aldehydes and ketone formation as a result of modification by lipid fragments
what are 3 things that ROS can do to DNA
oxidation of nucleobases, single strand breaks, crosslinks
what is peptide fragmentation
when the backbone of peptide is attacked
what are the main product name formed with lipid peroxidation
α,β-unsaturated aldehydes
what are 2 examples of α,β-unsaturated aldehydes
4-ONE and 4-HNE
peroxidation of what causes the formation of 4-ONE and 4-HNE
omega-6 polyunsaturated fats, linoleic acid and arachidonic acid
What do 4-ONE and 4-HNE do in cell and why (simple)
damage a lot because they are reactive electrophiles
why are 4-ONE and 4-HNE electrophiles (structurally, where in molecule is the electrophilicity)
carbonyl group + hydroxy or ketone results in electron poor environment centered around the 2-3 double bond (C3 become strongly electrophilic)
what often happens to C3 in reactive aldehydes and by who
nucleophilic attack by the side chains of cysteine, lysine, histidine from the nucleophile N/S
why are cysteine, lysine, histidine able to do nucleophilic attack on C3
because of their nitrogens and sulfers
what produces 4-ONE and 4-HNE (generally)
lipid peroxidation
are 4-ONE and 4-HNE reactive
highly yes
can 4-ONE and 4-HNE act at a distance and why
yes because they are amphiphilic so can cross lipid bilayers and attack cytoplasmic proteins at site distant from origin
can adjacent cells not involved in lipid peroxidation be damaged by 4-ONE and 4-HNE
yes because they are amphiphilic so can travel (cross bilayers)
what is the main detoxification pathway for 4-ONE and 4-HNE
conjugation with glutathione
do 4-ONE and 4-HNE have formal charges
no, they are amphililic
what are the main amino acid targets for covalent bonding of lipid aldehyde
cysteine, lysine, histitine
what results in 4-ONE or 4-HNE binding to a protein
introduction of a free carbonyl group
what is michael addition
conjugation of α,β-unsaturated aldehydes to cysteine, lysine or histidine via nucleophilic attack on C3 of the unsaturation aldehyde
what is a schiff base
conjugation of α,β-unsaturated aldehydes to lysine residues in proteins via nucleophilic attack by amino group of lysine on the aldehyde carbon of α,β-unsaturated aldehydes
where does the nucleophilic attack happen in michael addition
C3 of α,β-unsaturated aldehyde
where does the nucleophilic attack happen in schiff base
aldehyde carbon of α,β-unsaturated aldehyde
which amino acids are involved in michael addition
cyteine, lysine or histidine
which amino acids are involved in schiff base
lysine
what happens with a schiff base formation with lysine (like what forms)
pyrrole ring! carbons 1 and 2 fold in on themselves and cyclize
what can form with michael addition
a lactol if it cyclizes
what % of all carbonyl adducts does michael adduction account for
80%
what % of all carbonyl adducts does schiff base adduction account for
20%
how can a cyclized michael adduct cause protein crosslinking
the hydroxyl group is reactive so it can react again, like with a nitrogen on lysine and cause crosslinking
what are the 2 pathways to crosslinking of 4-HNE modification of protein
- no cyclization michael adduct + schiff base
- 4-HNE followed by michael cyclization then crosslink
how does the non cyclized michael protein crosslink happen (3 steps)
- 2 nucleophilic residues to start with
- one gets michael adduct (not cycled)
- schiff base crosslink
how does the cyclized Michael protein crosslink happen (1 step, name reaction and how product forms)
- cyclized michael adduct, add Lys
- then the OH groups reacts and crosslinks with new protein
what is the net result of protein crosslinking (simple)
dysfunctional proteins
what functional groups seem to be especially sensitive to reactive aldehyde modification and why
sulfhydryl groups (SH) because the microenvironment of some active sites appear to make them so sensitive (and they are numerous in many active sites of enzymes)
what does 4-HNE and 4-ONE do to cell life (which is more toxic)
it causes cell death, with ONE seeming more toxic
what is apoptosis
a type of cell death characterized by an ordered, programmed process
how does 4-HNE do to apoptosis
induce the process by interfereing with a protein that normallyinhibits apoptosis
where does bcl-2 reside
in mitochondrial membrane
what is the normal role of bcl-2
anti-apoptosis
how dies bcl-2 prevent apoptosis
inhibits the opening of a mitochondrial channel that releases proteins into the cytoplasm which are a signal for apoptosis to commence
what controlls bcl-2 gene expression
transcription factor NF-KB
what are p50 and p65
part of NF-KB
what holds NF-KB in the cytoplasm
IBK (inhibitor of KB)
how does 4-HNE effect NF-KB pathway
it inhibits IKB degradation, keeping NF-KB bound and inactive (doesnt go to nucleus and do anti-apoptotic stuff)
how does 4-HNE also effect bcl-2 (last point on slide)
inactivation by increasing ability of IKK to phosphorylate BCL-2
what does IKK do
phosphorylates Bcl-2 (to inactivate it)
what happens when Bcl-2 is phosphorylated
it becomes inactive
if 4-HNE increases apoptosis, why is it linked to cancer?
4-HNE has pro or anti cancer effects depending on cell type and the modified targets (sometimes 4-HNE suppresses tumour suppressor proteins)
what does linoleic acid peroxidation form
4-ONE
what does arachidonic acid peroxidation form
4-HNE
