Phase 1 and 2 metabolic conversions and CYP enzymes Flashcards
what are CYP enzymes
- contain a heme group
- membrane bound and associated with p450 reductase
- large lipophilic cavity
- no specificity
p450 reductase role
NADPH binds to p450 and electrons are shuttled through
6 phase 1 cyp mediated reactions
hydroxylation, dealkylation, dehydrogenation, epoxidation, epoxidation and dihydroxylation, monohydroxylation
where can hydroxylation take place
at any carbon
MOA of hydroxylation
- drug enters enzyme
- Fe5+ is very reactive and takes e- from =O to form fe4+
- radical formed, picks up OH from cyp 450
- Fe3+ is reformed
where can dealkylation take place
at any carbon next to a heteroatom
MOA of dealkylation
- hydroxylation takes place
- OH bond of hydroxylation breaks, forming =O
- =O breaks the bond with the rest of the molecule
where can dehydrogenation take place
alkanes
MOA of dehydrogenation
- radical formed by hydroxylation
- radical forms double bond
- elimination reaction reduces Fe4+ and removes one group
where can epoxidation take place
alkenes
epoxidation MOA
- double bond breaks to form a radical and breaks double bond in Fe5+=O
- radical reduces Fe4+ x2
- 2nd bond formed between radical and oxygen
where can epoxidation and dihydroxylation of aromatics take place
on aromatic rings with no substituents
MOA of aromatic epoxidation and monohydroxylation
- pi bond forms covalent bond with O
- reduces Fe5+ and forms C radical
- radical binds to O to form epoxide and reduce Fe4+
- epoxide hydrolase breaks epoxide
where can monohydroxylation take place
on aromatic rings with 2 unsubstituted carbons
monohydroxylation MOA
- hydroxylation forms a radical
- radical reduces Fe4+ and forms bond to O
- Fe3+ breaks bond with O causing shift in benzene
- =O finds free H+ to form OH
phase 1 non-cyp metabolism
epoxide hydrolase and ethanol metabolism
why are epoxides dangerous
covalently bond to N7 guanine in bases causing mutations and caner (apurinic DNA)
epoxide hydrolase MOA
catalyses nucleophilic addition on presence of water (-O to 2x -OH)
ethanol metabolism MOA
ethanol - alcohol dehydrogenase -> ethanal - aldehyde dehydrogenase -> ethanoic acid
what is alcohol aversion therapy
disulfiram - inhibits aldehyde dehydrogenase leading to an increase in ethanal = increase in side effects
other drugs that inhibit alcohol dehydrogenase
metronidazole, nitrofurantoin
phase 2 metabolism reactions
glucuronidation, sulphation and glutathione conjugation
what is glucuronidation
metabolite is conjugated with glucuronic acid
MOA of glucuronidation
UDP + glucuronic acid cleaved by UDP-glucuronyl transferase and glucuronic acid is attached to an electron rich atom in the drug (N,O,S)
what is sulphation
addition of SO3- to a drug, catalysed by sulfotransferase, requires PAPS
what is PAPS
SO4 2- + ATP –> PAPS + ADD + PPI (3’phosphoadenosine-5’phosphosulfate)
which molecules can undergo sulphation
usually phenols, sometimes alcohols
what is glutathione conjugation
addition of glutathione to the molecule to neutralise it
glutathione structure
gly-cys-glu
MOA of glutathione conjugation
S in Cys is a strong nucleophile, with the help of glutathione-s-transferase, it is conjugated to the molecule
factors affecting drug metabolism
- drug metabolising enzyme polymorphisms
- drug - drug interactions
- age
- gender
- disease
how do enzyme polymorphisms affect drug metabolism
- SNIP - single nucleotide polymorphism can change the protein structure of the enzyme causing, no, increased or decreased enzyme activity
how do drug-drug interactions affect drug metabolism
they can inhibit or induce the effects of other drugs
how do drug-drug interactions inhibit metabolism
- CYP450 inhibition!
- by competitive/non-competitive inhibition, formation of inactive complexes or cyp450 destruction
how do drug-drug interactions induce metabolism
induce the enzyme to work faster
how does age affect drug metabolism
very young - not fully metabolically competent, virtually no phase 2 and limited phase 1
very old - decreased action, diminished enzyme induction and usually drug-drug interactions
how does gender affect metabolism
first observed in rats, males metabolise faster - less significant in humans but thought to be due to sex hormones
how does disease affect metabolism
endocrine, liver, infections can all alter metabolism
what is alcoholic liver disease
prolonged alcohol exposure leading to inflammation - results in cirrhosis and fibrosis
alcoholic liver disease effects on drug metabolism
acute exposure - inhibits
chronic exposure - induces
cirrhosis - inhibits
what is cirrhosis
liver tissue is replaced by fibrous tissue resulting in metabolism inhibition (esp. CYP450)
