43/44 - Bilirubin & Antioxidants Flashcards
Chain-Breaking Antioxidants
act by reacting with PEROXYL RADICALS
ROO*
DONOR Antioxidant
tocopherol (VIT E) // VIT C // Uric Acid
makes a less reactive radical
SACRIFICAL Antioxidant
Nitric Acid
does NOT form a radical –> LOONO / DNIC
How is UROBILIGINOGEN formed?
Conjugated Bilirubin
Transported to the INTESTINES
VVVVVV
Hydrolyzed & Reduced by
BACTERIA in the GUT
VVVVVV
UROBILIGINOGEN
colorless compound
What happens to the FREE IRON?
from the breakdown of HEME –> Biliverdin + CO
by HO1?
Heme + HO1 –> CO + Biliverdin
+ Fe2+
Used for
Ferritin = Storage
Iron-Sulfur Clusters = Electron Transfer
Heme Recycled = Catalytic Activity
Characteristic of a GOOD
CHAIN-BREAKING ANTIOXIDANT
BOTH Antioxidant + ATRadical should be generally UNREACTIVE
ATRadical should decay to harmless products
does NOT add O2 to make a peroxyl radical
Recylced/renewed
MIDDLE OF THE PECKING ORDER
of redox potentials
Redox Potentials
Higher the Redox Potential = Greater the OXIDANT
FERRIC Iron = Fe3+ is a GOOD OXIDANT
readily accepts electron –> ferrous iron Fe2+
Iron bound to Transferrin or Ferritin
DOES NOT Redox cycle
PREVENTATIVE Antioxidants
that act by Removing Hydroperoxides
- *Glutathione Peroxidases**
- slow on its own*, but FAST when Coupling Enzyme Reactions + GSH
- *Acetaminophen toxicity –> glutatione depletion**
Catalase
Pyruvate
2 Classes of Antioxidants
- *PREVENTATIVE**
- *intercept** oxidizing species before damange is done
- *Deactivate metals** // Remove Hydroperoxides // Quench O’s
CHAIN BREAKING
slow or stop oxidative processes after they begin
by intercepting the chain-carrying radicals
Vitamin E –> lipid peroxidation
Donor or Sacrificial
Lipid Peroxidation
type of Oxidative Stress
RADICAL CHAIN REACTION** + **AUTOOXIDATION
- *1 Free Radical (OH.)** leads to
- *many oxidized lipids**
PROPAGATION
Free Hydroxyl leads to:
DNA Strand Breaks
BASE Modifications
Protein OXIDATIONS
Lipid PEROXIDATIONS
PREVENTATIVE Antioxidants
that act by Deactivating Metals
- *Biological Chelators**
- *Transferrin_ & _FERRITIN**
Chemical Chelators
Desferal / Detapac / EDTA
Fenton Reaction
OCCURS FAST
Fe2+ + H2O2 -> HO• + OH- + Fe3+
IRON + other metals
Catalyze the formation of the
OH RADICAL:
causes nonspecific oxidation & damage to:
Nucleic Acids / Lipids / proteins
Where do ANTIOXIDANTS lie in the
Pecking Order of REDOX POTENTIALS?
and why?
MIDDLE
enough reducing power to react w/ Reactive oxidizing species
but at the same time are:
t_oo WEAK_ to initiate reductive reactions
VITAMIN E & VITAMIN C
E is a better oxidant/higher vs C
Vitamin C can recycle Vit E because it is a better reductant
What is OXIDATIVE STRESS?
General term to describe an IMBALANCE in the relative levels of
PROOXIDANTS & ANTIOXIDANTS
in which the levels of
Prooxidants >>> Antioxidants
How and Where is
Bilirubin transported to?
Biliverdin 9 + BVR(NADPH) –>
Bilirubin
(water-insoluble / unconjugated)
vvvvv
released from macrophages
vvvvv
bound tightly to ALBUMIN
vvvvv
brought to the LIVER
WHY is Bilirubin bound to albumin?
- *INCREASE ITS SOLUBILITY**
- *UN-conjugated bilirubin** is water-insoluble
Albumin has
2 binding sites for Bilirubin
HIGH & low affinity sites
How does NITRIC OXIDE act as an Antioxidant?
Sacrificial antioxidant –> TERMINATES the Chain
Iron sequestration
Fe(2)+NO*—-> DNIC = dinitrosyl iron complexes
less redox active
reacts with the chelatable iron pool = CIP/LIP
- *LOO*** + NO* –> LOONO = nitrolipid
- not as reactive*
What happens to BILIRUBIN in the LIVER?
Hepatic Phase:
Bilirubin is REMOVED from ALBUMIN
VVVVVV
CONJUGATED TWICE
UDPGT w/ 2x UDP-Glucuronic Acid
VVVVVV
Conjugated Bilirubin Diglucuronide
Define
PROOXIDANT
any substances that
GENERATE OXIDANTS
or
INHIBIT Anti-oxidant Systems
Excess Prooxidants >> anti-oxidants = OXIDATIVE STRESS
Define Antioxidant
any molecule that
- *Delays / prevents / Removes**
- *oxidative damage to a target molecule**
Ex.
Ferratin / bilirubin
Define OXIDANTS
molecules that GAIN ELECTRONS in redox chemical rxns
& promote oxidation of target molecules
Biological oxidants RELATIVE to OXIDATIVE STRESS:
ROS & RNS
PREVENTATIVE Antioxidants
that act by Quenching Singlet oxygen
BILIRUBIN
Beta-Carotene
Lycopene
What happens after BILIRUBIN CONJUGATION?
Conjugated Bilirubin (diglucuronide)
INCREASED Solubility + decreased toxicity
VVVVVV
ACTIVELY TRANSPORTED
against a concentration gradient
VVVVVV
BILE DUCT
VVVVVV
INTESTINES
What does this enzyme do?
HEME OXYGENASE 1
HO1
Catalyzes
- *HEME** —-> BILIVERDIN IX + ( CO & Fe2+ )
- —-> bilirubin*
Vitamin C and COLDS
- *LARGE DOSE ONCE –> NOT EFFECTIVE**
- but*
- *constant doses** can _shorten the duration of cold_
there is a
Maximum oral dose of VITAMIN C –>
we can only have a higher plasma concentration from IV INJECTION
How does BILIRUBIN cause toxicity?
displaced Bilirubin (by drugs, disease) / unconjugated bilirubin (UCB)
causes MITO DYSFUNCTION:
diminished activitiy of Complex 5
–> releasing Cytochrome C
–> activated caspase-9
= TRIGGER the initiation of APOPTOSIS
ROS + RNS
reactive oxygen/nitrogen species
What DRUGS affect BILIRUBIN?
& HOW?
SULFANAMIDES** // **ABx** // **Salicylates
COMPETE with bilirubin for ALBUMIN BINDING
these drugs with displace bilirubin –> allowing it to enter the brain in neonates
–> increased risk of kernicterus
What is the problem with FREE IRON?
- *OXIDATIVE STRESS**
- *Fenton Rxn + Haber-Weiss Rxn** –> Hydroxyl radicals
TOO REACTIVE to be useful in enzyme, protein itself suffers damage from redox rxns
Only Fe // Cu // Mo should be used for redox reactions
and there are naturally only a LITTLE of them
so….
Excess –> TOO REACTIVE when not bound
How does FERRITIN / TRANSFERRIN act like an
ANTIOXIDANT?
Iron bound to Ferritin / Transferrin has a very low Redox Potential
which PREVENTS the
HABER-WEISS REACTION
What does this enzyme do?
Biliverdin Reductase
BVR
- Heme + HO1 –>*
- *BILIVERDIN_ —> _BILIRUBIN**
BVR = NADPH-dependent
How is STERCOBILIN formed?
Urobilinogen in GUT (from bacteria)
VVVVVV
Oxidized
by intestinal bacteria
VVVVVV
STERCOBILIN
BROWN in STOOLS
- *What is the RATE LIMITING STEP of**
- *Hepatic Bilirubin Metabolism?**
Conjugated Bilirubin formed in LIVER —> BILE DUCT
This is an ENERGY-DEPENDENT STEP
requires Active Transport across a concentration gradient by:
MRP2 or MOAT
multidrug resistance-protein 2 // multispecific organic anion transporter
Haer-Weiss Reaction
•O2- + H2O2 → •OH + HO- + O2
Occurs SLOWLY
but in the presence of METALS = CATALYTIC
Fenton + H-W = Fast reaction
generates a HYDROXYL RADICAL –> OXIDATIVE STRES
Vitamin C & E as CO-ANTIOXIDANTS
Vit C = Ascorbate can help recycle
TO Radicalback toTOH(Vit E)
since it is more reducing / less oxidizing
Vitamin C = Water Soluble
Vitamin E = Lipid Soluble
How is UROBILIN formed?
UROBILINOGEN
in the gut, formed by bacteria
VVVVVV
some of it is REABSORBED
into the portal blood
VVVVVV
KIDNEY
VVVVVV
YELLOW UROBILIN
HOW is Bilirubin CONJUGATED?
in the LIVER, after removing it from ALBUMIN
UDPGT
conjugates on 2x UDP-Glucoronic Acid
VVVVVV
Conjugated Bilirubin
(water-soluble & POLAR, +diglucuronide)
- *How do we solve / fix** this CHAIN REACTION from the
- *lipid peroxidation**?
TERMINATION
by
VITAMIN E
(lipid-soluble)
Vitamin E = antioxidant that will produce a NON-Radical Product
- -> alkylperoxide
- *stopping the chain reaction**
HOW is Conjugated Bilirubin removed from the KIDNEYS?
- *MRP2_ or _MOAT**
- *active transport,** also rate-limiting step
Hepatocytes –> Canaliculi –> BILE DUCT
