Week 7C: Drug metabolism and detoxification, Glucuronyltransferases, Treatment Concepts Liver Disease Flashcards
HC 43, 44, 45
HC43: Why evolution of detoxification pathways
Clearance of toxic or beneficial plant metabolites
> plants have large variety of secondary metabolites which can be useful or toxic
Nagoya protocol for drug discovery from plants
Part of profit back to people who live near resources to maintain it
Cabbages contain metabolites like…
-Glucosinolates: can be converted to cyanates which are toxic
-Also: indoles, which activate AHR nuclear receptors, involved in inflammation gene programs
Toxic compounds of plants are poisonous dependent on the …
Dose
Detoxification deals with endogenous compounds as well, like…
Hormones
Detoxification molecule types
-Xenobiotics: in food or drugs etc
-Endogenous compunds like hormones and heme
Excretion mechanisms
-Feces via liver or stomach
-Urine via kidney
Detoxification phases
-Absorption and distribution
-Oxidation reactions by CYP enzymes and ADH for example (can be skipped) > introduction reactive groups
-Conjugation reaction by sulfotransferases or UDP-glucuronosyltransferase (can be skipped) > make more hydrophilic with sugar groups
-Excretion
Principal site drug biotransformation and other sites
Main: Liver
Other: gut, lungs, skin, kidneys
First passage contents from GI tract in blood
Liver via portal vein
Portal triad and flows in liver lobule
Portal triad: portal vein, bile duct, arteria hepatica
Blood flow: Portal vein / arteria hepatica > sinusoids > central vein
Bile flow: bile canaliculli > bile duct (reverse flow)
Phases drug metabolism
Phase I metabolism: oxidation (in intestine, kidney, liver)
(Phase 0 elimination: direct elimination)
Phase II metabolism: conjugation: add hydrophilic group
(Phase III) Elimination because increased water solubility (in intestine, kidney, liver)
Phase I metabolism: oxidation, by which enzymes
CYP isoforms
Why do similar doses have different effects in humans>
Polymorphisms in enzymes like CYP enzymes: higher or lower activity/expression
Acetaminophen (paracetamol) detoxification
Normally: acetaminophen (nontoxic) is conjugated to a sulfate group or glucuronide group. (nontoxic)
> when overdose, a part is oxidized by CYP2E1 to NAPQI (a reactive, toxic intermediate)
> Glutathione (reduced) used to neutralize NAPQI
> deprivation glutathione, ROS less neutralized > oxidative stress
NAPQI toxic effects
Protein adducts, oxidative stress
Acetaminophen toxicity is main cause liver failure. Which antidote can prevent the toxicity?
Addition N-acetyl cysteine to acetaminophen tablets
> N-acetyl cysteine as antidote
Glutathione ROS neutralization
2 GSH (reduced) + H2O2 > GSSG + 2 H2O (glutathione peroxidase)
> regeneration by NADPH
> glutathione depletion is toxic!
High concentration drug metabolites in bile (canaliculus) compared to plasma, what does this mean? Why can it vary between individuals?
Pumping molecules against concentration gradient > costs ATP
> ABC transporters
> a lot of ABC transporters have polymorphisms, different rates of detoxification.
When can diet give problems to ABC transporters in drug metabolism?
If they contain substrates for the transporter which occupy it.
Abcg2 -/- mice have burned ears, when?
Diet with chlorophyll (plants) > fermentation product made which is toxic
Why do people with dry ear wax have better body smell? ABCC11 pathway
ABCC11 transports SG-3MSH into cell in skin
> conjugated and excreted > cleaved by bacteria in skin > 3-MSH release which smells bad
> Dry ear wax: defect ABCC11
Regulation drug metabolism through nuclear receptors: Name four of these with their dimerization partner and ligand
All bind with RXR on DNA
-LXR binds oxysterols
-FXR binds bile salts
-PXR binds xenobiotics
-CAR binds xenobiotics
Activation PXR
PXR binds xenobiotic PXR ligand in cytosol
> to nucleus and dimerization with RXR
> Bind response element
> upregulate CYP3A isoforms
Role AHR in drug metabolism
Nuclear receptor
> regulates CYP1A1 and involved in programs for excretion drugs (of its ligand)
> present in immune cells and intestinal cells
-regulate barrier function (think defect in IBD or barrier for leakage bacterial contents in gut)
> activation by dietary and microbial compounds positively affects barrier function
Drug interactions: Why does St. Johns Wort with Ciclosporin lead to acute heart transplant rejection
-Transplant patients treated with immunosuppressive drug cyclosporine
> metabolized by CYP3A4 and transported by MDR1 Pgp (ABCB1) (Regulation via PXR)
> Hypericin, active compound in St Johns Wort activates PXR
> PXR controls expression of CYP3A4 and MDR1
> MDR1 rejects enterohepatic cycling by pumping from portal vein back into intestine and from liver to bile canaliculli
> lower cyclosporin in blood, metabolism increased by St. Johns Wort > rejection transplant
Grapefruit Juice drug interactions (GFJ)
GFJ inhibits CYP3A4 activity in enterocytes
> overdose of the drug when taking GFJ
> no metabolism of drug in enterocytes > too much of the drug, the hepatocytes cannot metabolize everything on their own
Amazonian psychedelic brew ayahuasca
Contains psychedelic compound DMT and an inhibitor of its metabolism: inhibitor of MAO (monoamine oxidase) (mixture two plants with each one)
> In serotonin neurons: serotonin receptor agonist (MAO degrades serotonin) > more release
> Hermaline inhibits MAO’s so that DMT is not metabolized
> higher levels DMT (agonist serotonin receptor)
HC44: Marker of liver damage
ALT: alanine aminotransferase
> normally not in blood
Tara flour, found in now banned vegan foods contained baikiain which is ..
a direct hepatotoxin
Causes unexpected drug toxicity
-Polymorphisms in drug metabolizing enzymes or drug-drug interactions
Functions of CYP2E1
Metabolism of ethanol and acetamoniphen
-Ethanol
> Ethanol to acetoaldehyde (then to acetate with two oxidation reactions creating NAD+, this first conversion can also be done by ADH)
-Acetaminophen
> to toxic NAPQI when high dose
Effect acute ethanol consumption after overdose acetaminophen
Beneficial
> compete for CYP2E1 activity, less toxic NAPQI made
Chronic alcohol consumption and acetaminophen cause problems. Why?
Chronic alcohol consumption upregulates the expression of CYP2E1 to deal with the ethanol.
> More conversion acetaminophen to toxic NAPQI
Alcohol flush response
Defect in the ALDH enzyme (aldehyde dehydrogenase) for conversion acetaldehyde (from ethanol metabolism) to acetate.
> accumulation acetaldehyde: toxic
> leads to crosslinking of DNA: possibly defects in birth.
Function UDP-glucuronyltransferases (UGTs)
Catalyze the conjugation of a wide variety of substrates with glucuronic acid
> UDP-glucuronic acid is the sugar donor
> glucuronidation of substrates renders them more water-soluble > facilitate excretion
Effects glucuronidation
More water-soluble and less bio-active drugs
> in most drugs performed
UGTs and odorant signal termination
Conjugate substances which interact with olfactory receptors
> also, the epithelial layer of the nose contains UGTs which conjugates the compounds to be excreted and removed
UGTs conjugate drugs and odorants. But what elso?
-Inactivate steroid hormones
-Inactivate bilirubin
UGT polymorphisms in testosterone doping
-Ratio testosterone to epitestosterone is measured (T/E ratio: if too high: doping)
> urine samples
> usually around 1:1
-Polymorphism in UGT2B17: deletion, T/E ratio does not increase after testosterone doping.
UGT reaction
Substrate + UDPGA > Subtrate-glucuronide + UDP
Some drugs can become active after conjugation, like …
Morphine
Heme detoxification to bilirubin
Senescent erythrocytes taken up by macrophages
> release hemoglobin > to heme
> Heme + O2 + NADPH > Biliverdin (green) + ferric iron Fe3+ + CO (heme oxygenase)
> Biliverdin > bilirubin (yellow) (BVR, biliverdin reductase)
In heme degradation, iron is salvaged and the rest is …
excreted
Heme: part hemoglobin and CYP enzymes
Heme oxidation to biliverdin generates CO, this is toxic. But other function?
Regulator of many physiologic processes
Bilirubin transport in plasma
Bund to albumin
Which compound of heme metabolism may play a role in detoxification?
Bilirubin
Glucuronidation of bilirubin
In liver by UGT1A1 (ER)
> BR > BMG and BDG (conjugated)
> first: BR from cytosol to ER.
> conjugated bilirubin
Bilirubin accumulation causes…
Jaundice, yellowish skin
Bilirubin metabolism in colon
Metabolism to urobilinogens > this makes feces brown
What happens with feces of patients with severe bile flow obstruction (cholestasis)
White feces
Crigler-Najjar disease
Partial or complete absence of bilirubin UGT > unconjugated hyperbilirubinemia, severe toxicity and jaundice
Gilbert syndrome, and the danger of chemotherapy
Polymorphisms in bilirubin UGT promotor reduce expression > neonatal jaundice and possible high toxicity of chemotherapeutic irinothecan
> that is normally conjugated by the BR UGT
> irinotecan converted to SN-38 which is glucuronidated and detoxified
> deficient: SN-38 metabolized to neurotoxic compounds
Polymorphism in Gilbert syndrome
The TATA box in bilirubin UGT promotor has 6 or 7 TAs. > 7 TA variant has lower activity
Combination 7TA BR UGT with deficiency glucose 6 phosphate dehydrogenase (G6PD).
G6PD (PPP committed enzyme!, make NADPH, for glutathione and reducing oxidative stress) > high erythrocyte turnover
> more heme to metabolize
> life threatening high serum bilirubin at birth
Which form of bilirubin is neurotoxic?
Unconjugated
Crigler-Najjar problem onset
Deficient UGT1A1
> problems directly after birth
> phototherapy as only cure
Gunn rat model
Defect UGT1A1 activity: Crigler-Najjar model > jaundice
Gunn rats become infertile after diet with …
soy
> contains phytoestrogens, resemble and act like estrogen
> insufficient glucuronidation > infertility
HC45: Liver disease symtoms
Fatigue, itch, jaundice, pain, fever, infection, anxiety, higher risk for cancer
Types of liver diseases
- Lifestyle related: alcohol, MASLD
- Infection related: viral hepatitis
- Drug related: acetaminophen, herbal supplements, mushrooms
- Autoimmuity related: AIH (auto-immune hepatitis), PSC (primary sclerosing cholangitis, scar formation), PBC
- Inherited/inborn: structural and functional defects
Problems when liver disease
- Acute liver failure
- Cirrhosis
- Cancer
Types of medication for liver disease
-Drug concepts
-Symptomatic relief
Types of treatment liver disease
- Lifestyle modifications
- Preventive measures: vaccination (HebA/HebB), screenings (liver function tests)
- Medications
- Surgery and procedures: transplantation, resection etc
- Lifestyle support
Drug categories
- Chemicals
- Derived from living organisms: biologics
- Mixtures: Plant/animal mixtures
Viral hepatitis
-Lifestyle related for western world
-HBV, HCV, HDV, HEV
> HEV in meat, problem when immunocompromised
Acute liver failure
-Varices bleeding due to hypertension
-Ascites: belly with fluids due to hypertension
-Hepatic encephalopathy: process that brain does not work well anymore due to hyperammonia
-Kidney dysfunction: toxic substances accumulate since liver does not detoxify.
Drugs that cure
Cause total elimination of the disease
> on infection area
> antibiotics
> chemotherapy
> antiviral HCV drugs which eliminate virus entirely
> organ/cell transplantation (does require immunosuppressive drugs as well)
> boosting own immune system
HCV treatment
Harvoni: combination tablet ledipasvir and sofosbuvir.
> inhibit the nucleotide polymerase
» for certain genotypes of HBC
HBV treatment
No treatment
> HBV docks to transporter
> research working on inhibiting docking receptor > mix different targets
Types of monoclonal antibodies (biologicals)
-Omab: mouse antibody
-Zumab: only the hypervariable region is non-human
-Umab: fully human
> mAbs become cheaper once off patent
Biosimilars
Similar function as the original drug (like mAb) but made by competitor company , same function, but cheaper
aCD20 mAb
Eliminate B-cells in autoimmunity
mAbs in liver disease
Efficient against liver tumors, not for liver damage
Gene therapy for liver disease: two types for two problems
-Defect in each hepatocyte > gene therapy for all cells
-Secreted protein lacks: transduce smaller amounts of hepatocytes until enough secretion to be functional > or enzymatic conversions for bilirubin detoxification for example
AAV mediated gene therapy pros and cons
Advantages
> Low immunogenecity
> High transduction efficiency
> Tropism: certain favourite cell type: hepatocyte
> Non-integrating
Disadvantages
> Tropism
> Non-integrating: you can lose it
> Packaging size: cannot fit very large genes
> Neutralizing antibodies
Why can gene therapy only be done once?
Second dose: recognized and neutralized by own immune response
Gene editing types
DNA or RNA editing
DNA editing
CRISPR-Cas9
> to prevent disease
> for example bile salt transporter NTCP where HBV docks > edit NTCP
CCR5 gene editing
Prevent HIV infection because mutation in CCR5 gene prevents it
Risk CCR5 variants (homozygous CCR5 delta 32)
Higher risk dying when infected with West Nile Virus
Non heritable gene editing types
RNA editing
> mRNA
> Antisense RNA
> RNAi
> Aptamers
> Adenosine deaminases acting on RNA (ADARs)
RNA vaccine
Package RNA to get it into cells
> mRNA in LNPs in liver disease (nanoparticles)
> dampen fibrosis in repeated damage models or stimulate regeneration after acetaminophen intoxication for example
LNP components
Coat to target the right cell (monolayer phospholipids)
> hepatcyte, stellate cell, Kupffer cell, sinuoidal endothelial cell
> seperate receptors
ADAR
RNA deaminases to target the mRNA
> change the A (adenosine) to I
> I is recognized as G (guanine) by ribosomes
> G>A mutation account for most single nucleotide variants (SNVs, 28%)
> make protein inactive like CCR5 or NTCP
Liver surgery
-Resection and ablation
-Cystectomy
-Bypassing
-Transjugular intrahepatic portosystemic shunt (TIPS)
> bypass a plot
> branch of portal vein and hepatic vein connected
> hypertension resolved, no ascites (swelled belly)
-Transplantation
Transplantation liver: integrated perfusion machine
-Keeps transplant liver in healthy state
> surgery can be done next day
> better preparation of recipient and surgeons
> liver uses lots of oxygen: highly oxygenated
> shock with temperature and oxygen while on the pump
> livers not suitable for transplantation may seem suitable afterwards
> liver is outside body: factors to stimulate regeneration in body of the liver to make full liver out of liver transplants is researched
Symptom relieve for liver disease
Itch, anxiety, fever
Drug: plant/food mixtures
Can contain metabolites which include toxins which need to be detoxified
> batch-to-batch variation: hard to study efficacy
> possible toxicity
> easy administration
