Genetics of phase II metabolism Flashcards
what are the 3 types of Glutathione S-transferases (GST) polymorphisms
- GSTM1 = loss of activity
- GSTT1 = loss of activity
- GSTP1 = small change in catalytic activity
what is GSTM1 and what is it involved in
- expressed in many tissues
- involved in reactions such as detoxication of benzo[a]pyrene diol epoxide
how does GSTM1 activity differ between populations
- approx 50% of white europeans lack this enzyme activity
- small number (1% of saudi Arabians) have duplication
What type of substrate does theta class GST (GSTT1) prefer
smaller molecule (e.g. dichloromethane)
what _% of caucasians lack GSTT1 due to a _
20
deletion
what is the percentage of europeans who are
a) GSTM1 null
b) GSTT1 null
a) 50%
b)15%
what is the percentage of African americans who are
a) GSTM1 null
b) GSTT1 null
a) 30%
b) 22%
what is the percentage of Polynsians who are GSTM1 null
81%
what is the percentage of japanese who are GSTM1 null
48%
what is the percentage of East Asians who are GSTT1 null
60%
what does N-acetyltransferases do and where is it found
- NATs transfer acetyl group to hydroxyl group
- both human NATs found in cytosol, NAT1 expressed in most tissue and NAT2 mainly in liver and intestine
NAT are inducible T/F
false
which NAT is polymorphic
NAT2
how was NAT2 identified
Isoniazid metabolism
- mutation = slow acetylators
- normal = fast acetylators
what is the wildtype allele for NAT2 and why is that?
*4
because 1-3 are WT in different animal species
what NAT2 alleles produced reduced activity and which produced effectively mo activity
*5 = reduced
*6 + *7 = no activity
what would someone with a NAT2 genotype of 5/7 be called
slow acetylators
what percent of europeans are slow acetylators
- what is the most common allele in this populations
50%
5/6
what percent of east asians are slow acetylators
- what is the most common allele in this populations
10%
*7
N-acetylation does not influence the pharmacological activity of caffeine -T/F
T
what is the most widely used phase II reaction and what enzyme is involved
glucuronidation
UDP-glucuronosyltransferases (UGTs)
what is conjugated by UGTs and what is needed as a cofactor
steriods, vitamins, bile acids and bilirubin
UDP-glucuronic acid
what is the issue with UGT1A1 absence in newborn
Crigler-Najjar syndrome
- Haem gets converted to bilirubin which is insoluble, and requires glucuronidation to become soluble prior to excretion.
- Accumulation becomes toxic to organs and tissues.
what is Gilbert syndrome
small increase inn plasma bilirubin but has no adverse clinical consequences
what is the most common UGT polymorphism in caucasians
(TA)7TAA in TATA box instead of (TA)6TAA
appears to affect transcriptional levels
what is a UGT polymorphism that effects some asians
amino acid substitution in exon 1 (gives same phenotype)
what drug does UGT polymorphism effects the metabolism for
irinotecan (anti cancer drug)
what are the two alleles of UGT2B7 involved in C161T polymorphism
C allele = *1
T allele = *2
TT suggested to be associated with increased morphine 6-glucuronidation in vivo
what are the 2 types of polymorphism involved in SULT1A1
- copy number variation
- 3’-untranslated region involving regulation by miRNA
How many copies do caucasians people normally have of SULT1A1
2 copies
How many copies do Indian & Japanese people normally have of SULT1A1
2 copies
How many copies do African-American
and south African people normally have of SULT1A1
more than 2
how does miRNA and 3’UTR affect gene expression
they’re binding reduces gene expression by inhibiting translation or by mRNA cleavage
what polymorphism is 3’UTR of SULT1A1
C973T
decreased enzyme activity in those carrying one or two T alleles
what is the allele frequency of T allele in SULT1A1. What is the % of white US population homologous for T alleles
0.44
20%
how is luciferase used to investiagte SULT1A1 C/T allele
- constructs containing C at 973 will show lower extent of miRNA binding, and hence more luciferase activity; more miRNA binding with T at 973, less luciferase activity
- Predicted using computer program that miR-631 would downregulate SULT1A1 expression more robustly in subjects carrying 973T than in those with C allele
how is 6-mercaptopurine metabolised
by methyltransferase at the thiol group
S-adenosylmethionine donates _ group
methyl
how many caucasians lack S-adenosylmethionine
0.3%
if your treated with anti cancer drugs what do you have to do first
be genotyped
what is Catechol-O-methyltransferase involved in
- Catecholamine metabolism
- Noradrenaline -> normetanephrine
- L-DOPA
what is the common genetic polymorphism in Catechol O-methyltransferase
Codon - G158A - Val to Met substitution
Met form of enzyme more thermolabile than Val and associated with lower activity
