Interindividual variability in human drug glucuronidation What we know and what we need to know Laboratory of Comparative and Molecular Pharmacogenomics Department of Pharmacology and Experimental Therapeutics Tufts University School of Medicine Michael H Court, BVSc, PhD
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Interindividual variability in human
drug glucuronidationWhat we know and what we need to know
Laboratory of Comparative and Molecular PharmacogenomicsDepartment of Pharmacology and Experimental TherapeuticsTufts University School of Medicine
Michael H Court, BVSc, PhD
Michael H. Court 2010
Why study drug glucuronidation?
Main identified metabolic clearance pathway (after CYP) for top 200 prescribed drugs in the USA.
May be more frequently encountered since selecting drug candidates for CYP stability
(Williams et al: DMD, 32:1201-1208,2004.)
Enzymes known to be involved in the metabolism of the top 200
prescribed drugs in USA
UGTs
CYPs
Michael H. Court 2010
Advantages of glucuronidation over oxidation?
Glucuronides are “stable” = non-reactive Except some acylglucuronides
Less potential for DDI Typically low affinity (high Km) enzymes Broad, overlapping substrate specificities
Less interindividual variability in activity??
Michael H. Court 2010
Objectives
Brief overview of the UGTs
Characteristics of the Tufts human liver bank
What is the extent of interindividual variability in glucuronidation? For different UGTs? Versus CYPs?
What inherent factors determine UGT variability? Gender; age; genetics; epigenetics
What external factors influence UGT variability? Smoking; alcohol; other drugs; disease
Michael H. Court 2010
UDP-glucuronosyltransferases
Substrates Drug or Phase I metabolite (also hormones, toxins, etc) -OH; -COOH; amino; (rarely -SH; -CH)
Glucuronides generally inactive except: Morphine-6-glucuronide Acyl-glucuronides (esp. NSAIDs)
10 genes expressing 19 unique UGTs Subfamilies UGT1A, 2A, 2B involved in drug metabolism [Subfamily UGT3A - bile acid UDP-N-acetylglucosaminyltransferase]
Drug + UDP-glucuronic acid Drug-glucuronide + UDP
Michael H. Court 2010
UGT gene structures
Chr. 2q37
Differential splicing of unique exon 1 to shared exons 2-5
Anova: Anova: Anova: Anova:**P < 0.001 P = 0.14 P = 0.56 P = 0.16
0
5
10
15
20
25
30
pm
ole
s /
min
/ m
g p
rote
in
S-Lorazepam
|-*p < 0.05-|
|----*p < 0.05----|
0
5
10
15
20
25
0
2
4
6
8
10
0
50
100
150
200
250
0
1
2
3
4
5
6
7
8
9
10
pm
ole
s /
min
/ m
g p
rote
in
R-Lorazepam
0
1
2
3
4
5
6
pm
ole
s /
min
/ m
g p
rote
in
E-4OH-Tamoxifen
0
100
200
300
400
500
600
700
800
pm
ole
s /
min
/ m
g p
rote
in
5OH-Rofecoxib
(Court: Methods Enzymol. 400:104-16, 2005)
Lorazepam
Lorazepam glucuronide
(Chung et al: CPT, 2005)
Time after dose (hrs)
Michael H. Court 2010
A common UGT2B7 haplotype (*1C) is associated with
higher AZT glucuronidation and clearance
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
nm
ole
s/m
in/m
g p
ro
tein
P = 0.021
Noncarrier Carrier
UGT2B7*1C
AZT
glu
curo
nida
tion
Human liver bank
0
20
40
60
80
100
120
140
No
rm
alized
CL
/F (
mL
/min
/kg
)
P = 0.007
Noncarrier Carrier
UGT2B7*1C
AZT
cle
aran
ce
PK study
(Kwara et al: JClinPharm, 2009)
Michael H. Court 2010
Fetal liver
(n=63)
8% of adult
Adult liver
(n=47)
All UGTs
Effect of age on UGT expressionFetal livers do not express any UGT1As
Liver, adult (n=47)
1A1
1A3
1A4
1A61A9
2A3
2B4
2B7
2B10
2B11
2B152B17
Liver, fetal (n=63)
2B4
2B7
2B10
2B11 2A3
2B15
(Court et al, unpublished)
Michael H. Court 2010
Effect of age on UGT activities
Lower UGT1A activity in children/teens (<21 years)
No effect of old age (>60 years)
0
0.5
1
1.5
2
2.5
Est
radio
l-3-U
GT
Triflu
operaz
ine-U
GT
Ser
otonin
-UG
T
Pro
pofol-U
GT
Zidovu
dine-
UG
T
S-o
xazepam
-UG
T
2-20 yrs
21-40 yrs
41-60 yrs
61+ yrs
* * *
Act
ivity
rela
tive
to m
ean
of a
ll liv
ers
(Court: Drug Metabolism Reviews, 2010)
n = 9, 18, 14, 13
UGT1A UGT2B
Michael H. Court 2010
Smoking/alcohol history and UGT activities
0
0.5
1
1.5
2
2.5
3
Est
radio
l-3-U
GT
Trifl
uop
eraz
ine-
UGT
Ser
otoni
n-UGT
Pro
pofo
l-UGT
Zidov
udin
e-UGT
S-o
xaze
pam
-UGT
Non-smoker
Smoker
Act
ivity
rel
ativ
e to
mea
n of
all
liver
s
*
0
0.5
1
1.5
2
2.5
3
3.5
Est
radio
l-3-U
GT
Trifl
uop
eraz
ine-
UGT
Ser
otoni
n-UGT
Pro
pofo
l-UGT
Zidov
udin
e-UGT
S-o
xaze
pam
-UGT
2 or less drinks/day
>2 drinks/day
Act
ivity
rel
ativ
e to
mea
n of
all
liver
s
*
** *
(Court: Drug Metabolism Reviews, 2010)
Michael H. Court 2010
Alcohol history and UGT activitiesSubjects 21 years and over
0
0.5
1
1.5
2
2.5
3
3.5
Est
radio
l-3-U
GT
Triflu
operaz
ine-U
GT
Ser
otonin
-UG
T
Pro
pofol-U
GT
Zidovu
dine-
UG
T
S-o
xazepam
-UG
T
2 or less drinks/day
>2 drinks/day
Act
ivity
rela
tive
to m
ean
of a
ll liv
ers
** *
Michael H. Court 2010
Conclusions
The human liver bank is a useful tool for characterizing interindividual variability in drug glucuronidation
Interindividual variability in drug glucuronidation is comparable to CYP mediated drug metabolism BUT variability is dependent on UGT isoform UGT1A1 and UGT2B15 have highest variability
Genetics, sex and age affect drug glucuronidation UGT1A1 and UGT2B15 - genetic polymorphism Male>female for UGT2B15/17 – sex steroids? Lower UGT1A glucuronidation in infants/children – epigenetics? Alcohol effect on UGT1A – transcription factor?? Role for regulation via protein-protein interaction (UGT-i2)??
Michael H. Court 2010
Acknowledgements
NIH grant R01-GM61834 (2000 – 2011)
Pfizer Global Research and Development
BD Gentest
David Greenblatt and Lisa von Moltke (Tufts Pharmacology)
Chantal Guillemette (Laval University, Quebec)
Court lab - past and present personnel Soundar Krishnaswamy Qin Hao Su Duan Su Hazarika