Name 6 types of reactions that happen in phase 1 metabolism
1) oxidations (esp CYP450)
2) hydrolysis
3) hydration
4) dethioacetylation
5) isomerisation
6) reduction (rare)
Name 3 things that the enzyme xanthine oxidase metabolises
1) theophylline
2) theobromine (in tea)
3) caffeine
What’s the purpose of phase 1 metabolism?
Functionalisation/activation of drugs
Which CYP enzyme metabolises warfarin on the aliphatic branch?
CYP3A4, R-isomer, slower
Which CYP enzyme metabolises warfarin on the aromatic part?
CYP2C9, S isomer, faster
What’s CYP450 enzymes
Membrane bound enzymes involved in metabolism of hydrophobic drugs
List briefly how P450 enzymes work
1) substrate binds to protein causing iron low spin to high spin
2) (6-5) now a vacant site for O2 binding
3) reduction by P450 reductase is required before dioxygen binds
4) second reduction step occurs following dioxygen binding
5) hydroxylation (>1?)
What happens in an uncoupled reaction?
NADPH and dioxygen are consumed but substrate is not oxidised. (Under most conditions these reactions are small proportion of catalytic cycles)
What is an enzyme super family?
The whole group of enzymes that catalyse the same or similar type if reaction using a similar mechanism and are related by primary sequence homology or identity
What does homology mean
When sequences are aligned, an amino acid in a particular position is conserved by type e.g leucine could be substituted for isoleucine or valine but not arginine
What is meant by identity?
When sequences are aligned, an amino acid in a particular position is always the same e.g leucine must be leucine
Name three enzyme super families
1) CYP enzymes (various oxidative reactions)
2) UDP-glucoronsyl transferases (glucoronidation)
3) glutathione-S-transferase (conjugation with glutathione)
Name 5 INTRINSIC factors affecting drug metabolism
1) Age
2) hormonal and gender differences
3) genetic variability of CYP enzymes
4) differences between races/populations and sub-population
5) individual differences
Name 6 EXTERNAL factors that affect drug metabolism
1) diet and nutritional status
2) method of cooking
3) alcohol and smoking
4) co-admin of drugs
5) exposure to drugs, solvents
6) diseases e.g alcoholism- liver
What is the aim of phase 2 metabolism?
Detoxify drugs and/or allow excretion by adding a water solubilising group
Name 6 reactions involved in phase 2 metabolism
1) glucoronidation (nucleophiles)
2) glutathione conjugation (electrophiles)
3) amino acid conjugation
4) sulfation
5) acetylation
6) methylation (rare)
What’s the most common phase 2 reaction and why is it the most common?
Glucoronidation, due to availability of UDP-glucuronic acid
What is the reaction glucoronidation performed by?
UDP-glucuronosyl transferase
At what MW are drugs excreted in urine?
What MW do drugs have to possess in order to be excreted in bile
MW >200Da
What is glutathione important for?
Maintenance of reducing environment (protection against radicals, reactive oxygen species etc)
Are cytosolic enzymes trimers?
No they’re dimers, microsomal enzymes are trimers
How many isoforms of GST (glutathione-s-transferase) are found in humans?
20isoforms
Which exon is variable in UGTs?
Exon 1
Where are CYP enzymes mainly found
Liver
What are CYP enzymes involved in
Metabolism of hydrophobic drugs