Genetics of Non CYP450 mediated phase I metabolism

Question 1

what is Flavin linked monooxygenases

Answer 1

Microsomal enzymes with FAD as prosthetic group, important in oxidation reactions at nitrogen, sulphur and phosphorous centres

Question 2

what is Trimethylamine (TMA)

Answer 2

an unpleasant smelling compound that is a breakdown product of a number of precursors (such as L-carnitine) present in a range of foods – gut bacteria are involved in TMA formation

Question 2

how many different forms of Flavin linked mono-oxygenases

Answer 2

At least 5 different forms but FMO3 is the major hepatic isoform in humans

Question 2

what normally happends to TMA ?

Answer 2

Normally undergoes conversion to trimethylamine N-oxide (TMAO) by FMO3
- TMAO is less volatile and loses odur

Question 3

Who suffers from fish odour syndrome and why

Answer 3

individuals who lack functional FMO3 as TMA isn’t converted to TMAO

Question 4

what is the occurrence rate of subjects with fish odour syndrome

Answer 4

1/100 approx are heterozygous and shows defects in TMA metabolism

Question 5

what is the most common mutation which can cause Fish odour syndrome

Answer 5

Pro153Leu (complete loss of activity)
Proline has a structural role in proteins by “breaking up” areas of alpha helix. Amino acid change to leucine is therefore functionally significant

Question 6

what is the other mutation can be responsible for lack TMA oxidation

Answer 6

N61S

Question 7

True or false - P153L + N61S have an effect on methimazole metabolism

Answer 7

Flase - there is no effects

Question 8

what mutation is responsible for mild fish odour syndrome in children

Answer 8

E158K/E308G in FMO3 polymorphism

Question 9

how does polymorphism in FMO3 effect sulindac metabolism

Answer 9

• Better outcome in those with polymorphism due to slower metabolism
• sulindac is a prodrug but is activated by gut flora prior to absorption)
• Produced sulindac sulphide which is active, The inactive metabolite of sulindac (the sulfone) is subject to enterohepatic recirculation.
• Both S and R epimers show anti cancer activity
• Low FMO3 higher conc in the gut and active metabolite = better effects in good

Question 10

what hydrolysis organophosphates in the liver and serum

Answer 10

Arylesterase - paraoxonase

Question 11

what is PON1 associated with

Answer 11

high density lipoprotein (HDL) in serum and may protect against atherosclerosis. Hydrolyses oxidised LDL-associated cholesterol, with potential protective effects

Question 12

what % of europeans have low activity for paraoxon hydrolysis in serum and why?

Answer 12

50, due to a polymorphism at codon 192 with a Arg to Gln amino acid substitution

Question 13

the effects of PON1 polymorphisms are _ dependent

Answer 13

substrate
Paraoxon: low activity with Gln form. Phenylacetate: no effect. Diazoxon: higher activity with Gln form

Question 14

what are the variation of PON1 genotypes between continents

Answer 14

• 50% of Europeans are homozygous for Gln (low activity with paraoxon)
• 10% of North Africans were RR homozygotes,
• whilst a mixed ancestry South African population were 15.8% QQ
• 15% of Japanese are Gln homozygotes

Question 15

what type of role does PON1 genotype have in CHD

Answer 15

Protective ? (some evidence)
- Low PON1 activity was associated with increased risk of CHD, but this cannot be linked to a particular polymorphism
-Low PON1 activity was associated with polymorphisms in the promoter region in the patient group, but there was no association between these polymorphisms and CHD

Question 16

What is Butyrylcholinesterase

Answer 16

Plasma esterase which hydrolyses the muscle relaxant succinylcholine - high levels in plasma

Question 17

what % of the population is heterogenous + poor hydrolysis of succs

Answer 17

5

Question 18

butyrylcholinesterase polymorphisms is _ specific. therefore most individuals with deficient hydrolysis of succinylcholine show _ hydrolysis of other substrates

Answer 18

substrate
normal

Question 19

what is used to detect individuals with deficiency phenotypically by inhibition pattern of benzoylcholine hydrolysis

Answer 19

dibucaine number

Question 20

how do you measure the dibucaine number

Answer 20

• take plasma samples with varying levels of dibucaine and add benzoylcholine
  -Dibucaine number is % inhibition of benzoylcholine by 10 micromolar dibucaine.
• The majority of people show approx 80% inhibition.
• The atypical reaction shows 10-20% inhibition.

Question 21

what is the muattion responsible for the atypical form assocated with abnormal dibucaine inhibition

Answer 21

Asp70Gly

Question 22

what are the 3 main forms of cholinesterase deficiency

Answer 22

Atypical
fluoride-sensitive
silent

Question 23

what is the difference between CES1 and CES2

Answer 23

CES1 - high levels in liver which is important in metabolism (Tamiflu)
CES2 - mainly expressed in intestine and in other extra hepatic tissues

Question 24

what are the polymorphism involved in CES1

Answer 24

• Gly143Glu = low activity
• Asp260fS = No activity (Rare)

Question 25

what is Dihydropyrimidine dehydrogenase (DPYD)

Answer 25

Metabolic enzyme that converts uracil and thymine to dihydro metabolites facilitating further metabolism to amino acids

Question 26

what drug is metabolised by Dihydropyrimidine dehydrogenase

Answer 26

5-fluorouracil (5FU)is an important anticancer drug

Question 27

Dihydropyrimidine dehydrogenase deficiency is caused by what, normally ?

Answer 27

Most common variant allele associated with deficiency has G to A base change in intron 14 (position 1) resulting in skipping of exon 14 and truncated protein

Question 28

if an individual is heterozygous for DPYD mutation then they are at risk of what ?
what is the occurance of heterozygous ?

Answer 28

• toxicity if 5FU is given
• 2-3% of europeans

Question 29

what does aldehyde dehydrogenese do ?

Answer 29

converts acetyaldehyde to acetate (from ethanol)

Question 30

what are the two forms of aldehyde dehydrogenase

Answer 30

ALDH1 (cytosolic) and ALDH2 (mitochondrial enzymes)

Question 31

why do east asians suffer from flushing/nausea when they consume alcohol

Answer 31

• amino acid substitution in ALDH2 of Glu487Lys at C-terminal end of protein
• results in unstable protien
• Dominant inheritance means subjects can be heterozygous
• flushing/nausea is due to accumulation of acetaldehyde