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395
Introduction
Carbonic anhydrase (CA, E.C.4.2.1.1), an enzyme puri-fied from erythrocytes for the first time in 19931, plays an important role in mammals, in processes such as pH control, gas balance, ion transport, calcification, secretion of electrolytes, and tumourigenesis among others2. CAs, of which many diverse isoforms are currently known, effectively catalyze a slow, but fundamental physiological reaction, the conversion of carbon dioxide to bicarbonate and protons3,4. CAs are classified in five distinct classes, the α, β, γ, δ and ζ families5. These types of CAs are pres-ent in different organisms, but the α-CAs are the only such enzymes found in mammals. The β-class is mainly found in plants, fungi and prokaryotes; γ-CAs were iden-tified in Archaea and some bacteria6. The ε-CA class was
reclassified as a different type of β-CA based on crystal-lographic data7,8, which showed a nearly identical fold to those of the canonical, archaeal (cab-type) and plant-type (Pisum sativum) β-CAs9–11. In ζ-CA, the geometry of the active site is nearly identical to that of β-CAs, and there is also some similarity in the protein fold, but these enzymes contain Cd(II) at their active site, not Zn (II) as the other genetic CA families6, although they function also with Zn(II) or Co(II) replacing the cadmium ion.
In mammals, 16 different CA isoenzymes have been described so far2. Some of these isozymes are cytosolic (CA I, CA II, CA III, CA VII and CA XIII), others are mem-brane bound (CA IV, CA IX, CA XII and CA XIV), two are mitochondrial (CA VA and CA VB) and one is secreted in saliva and milk (CA VI12). Human and most mammalian
RESEARCH ARTICLE
Inhibition of carbonic anhydrase isozymes I and II with natural products extracted from plants, mushrooms and honey
Huseyin Sahin1, Zehra Can1, Oktay Yildiz1, Sevgi Kolayli1, Alessio Innocenti2, Gabriele Scozzafava,3 and Claudiu T. Supuran2
1Karadeniz Technique University, Department of Chemistry, Trabzon, Turkey, 2Università degli Studi di Firenze, Polo Scientifico, Laboratorio di Chimica Bioinorganica, Rm. 188, Via della Lastruccia 3, Sesto Fiorentino, Florence, Italy, and 3Università degli Studi di Firenze, Dipartimento di Economia, Ingegneria, Scienze e Tecnologie Agrarie e Forestali (D.E.I.S.T.A.F.), Firenze, Italy
AbstractDifferent natural products and secondary metabolites from mushrooms, teas, honeys, mosses, plants and seaweeds were investigated for their in vitro inhibitory effects on human carbonic anhydrase (hCA, E.C.4.2.1.1) isoforms I and II. Inhibition data were correlated with the total phenol content in the extract and investigated with the pure compounds believed to be responsible for this activity. Methanolic extracts were prepared for 17 such pure chemicals present in the natural products and for 41 diverse natural products. The IC50 values were in the range of 0.11–66.50 μg/mL against hCA I and of 0.09–54.54 μg/mL against hCA II, respectively. The total phenol content was in the range of 0.02–1318.96 (as milligrams of gallic acid equivalents) per gram of sample. These data offer new insights on possible novel classes of CA inhibitors based on natural products, possessing a range of chemical structures not present in the classical inhibitors with pharmacological applications, such as the sulfonamides and sulfamates.Keywords: Carbonic anhydrase, natural products, phenol, inhibition, isoform I and II
Address for Correspondence: Huseyin Sahin, Karadeniz Technique University, Department of Chemistry, Trabzon, Turkey. Tel.: +90 462 377 36 64, Fax: +90 462 325 31. E-mail: [email protected], or Claudiu T. Supuran, Università degli Studi di Firenze, Polo Scientifico, Laboratorio di Chimica Bioinorganica, Rm. 188, Via della Lastruccia 3, Sesto Fiorentino, Florence, Italy. Tel.: +39-055–4573005, Fax: +39-055–4573385. E-mail: [email protected]
(Received 11 May 2011; revised 28 May 2011; accepted 30 May 2011)
Journal of Enzyme Inhibition and Medicinal Chemistry, 2012; 27(3): 395–402© 2012 Informa UK, Ltd.ISSN 1475-6366 print/ISSN 1475-6374 onlineDOI: 10.3109/14756366.2011.593176
Journal of Enzyme Inhibition and Medicinal Chemistry
2012
27
3
395
402
11 May 2011
28 May 2011
30 May 2011
1475-6366
1475-6374
© 2012 Informa UK, Ltd.
10.3109/14756366.2011.593176
GENZ
593176
Jour
nal o
f E
nzym
e In
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tion
and
Med
icin
al C
hem
istr
y D
ownl
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d fr
om in
form
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lthca
re.c
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396 H. Sahin et al
Journal of Enzyme Inhibition and Medicinal Chemistry
red blood cells comprise two CA isozymes, CA I (slow enzyme of low catalytic efficiency) and human CA (hCA II; rapid, highly effective catalysts for the CO
2 hydration
reaction13). hCA I and hCA II are two of the most abun-dant protein (after hemoglobin) in human erythrocytes.
The catalytic mechanism of CAs is understood in detail. In all enzyme classes, a metal hydroxide species of the enzyme is the catalytically active species, acting as a strong nucleophile on the CO
2 molecule bound in a
hydrophobic pocket nearby2. This metal hydroxide spe-cies is generated from water coordinated to the metal ion, which is found at the bottom of the active site cav-ity. The active centre normally comprises M (II) ions in tetrahedral geometry, with three protein ligands (L) in addition to the water molecule/hydroxide ion, but Zn(II) and Co(II) were also observed in trigonal bipyramidal or octahedral coordination geometries2,14–18.
The inhibition of CA is a well understood process, with most (but not all) classes of inhibitors binding to the metal centre19–29. Inhibition can be achieved by four different mechanisms. First, coordination of the inhibi-tor to the Zn(II) ion by replacing the zinc-bound water/hydroxide ion, leading to a tetrahedral geometry of Zn(II). Second mechanism is addition of the inhibitor to the metal coordination sphere, when the Zn(II) ion is in a trigonal bipyramidal geometry12,30. Third type of inhibi-tion consists of the anchoring of the inhibitor molecule to the Zn (II)-bound solvent molecule, a water or hydroxide ion31. The fourth type of inhibition is achieved by occlu-sion of the entrance to the active site cavity, when the inhibitors bind in the activator binding region32–36. Many CA inhibitors were synthesized and evaluated in the last decades, whereas natural product compounds started to be investigated only recently37. For this reason, the pri-mary objective of this study was the screening of in vitro inhibitory effects on the cytosolic, widely spread iso-forms hCA I and hCA II of some natural product extracts and the corresponding pure chemicals species present in them. Most of these compounds are known to possess antioxidant effects.
Materials and methods
ReagentsAnalytical grade methanol was obtained from Merck Co. (Merck, Darmstadt, Germany). Buffers and other reagents were of the highest purity grade, from Sigma-Aldrich (Milan, Italy). CA isozymes were recombinant ones obtained as reported earlier. Folin-Ciocalteu’s phe-nol reagent was from Fluka Chemie GmbH (Switzerland). Polytetrafluoroethylene membranes (porosity 0.2 μm) for the filtration of the extracts were obtained from Sartorius (Goettingen, Germany).
Samples and preparation of extractsAll samples were prepared in methanol. Because chemi-cals can be dissolved completely in methanol, an extrac-tion process was not used. The natural products were
continuously stirred with a shaker at 60°C for 24 h. The suspension was removed by filtration then centrifuged at 10,000g for 15 min. The supernatant was concentrated in a rotary evaporator under reduced pressure, and the residue resolved in a minimal volume of the same sol-vent and kept in 4°C until use.
CA catalytic activity and inhibitionAn Applied Photophysics stopped-flow instrument has been used for assaying the CA catalysed CO
2 hydration
activity. Phenol red (at a concentration of 0.2 mM) has been used as an indicator, working at the absorbance maximum of 557 nm, with 20 mM HEPES (pH 7.5) as buf-fers and 20 mM Na
2SO
4 (for maintaining constant ionic
strength), following the initial rates of the CA-catalysed CO
2 hydration reaction for a period of 10–100 s. The CO
2
concentrations ranged from 1.7 to 17 mM for the deter-mination of the kinetic parameters and inhibition con-stants. For each sample, at least six traces of the initial 5–10% of the reaction have been used for determining the initial velocity. The uncatalyzed rates were determined in the same manner and subtracted from the total observed rates. Solutions of extracts (10 mM) were prepared in dis-tilled, deionized water and diluted up to 0.01 nM thereaf-ter with distilled, deionized water. Inhibitory sample and enzyme solutions were preincubated together for 15 min at room temperature before assay to allow for the forma-tion of the enzyme–inhibitor complex. The IC
50 represents
the concentration of inhibitor producing a 50% decrease of the catalytic rate and was obtained by nonlinear least-squares methods using PRISM 3 and represent the mean from at least three different determinations.
Determination of total phenolicsTotal phenolic (TP) content was determined by the Folin-Ciocalteu procedure38 using gallic acid as standard. In brief, 20 μL of various concentrations of gallic acid and samples (20 μL), 400 μL of 0.5 N Folin-Ciocalteu reagent and 680 μL of distilled water was added, and the con-tents were vortexed. After 3 min incubation, 400 μL of Na
2CO
3 (10%) solution was added, and after vortexing,
the mixture was incubated for 2 h at 25°C with intermit-tent shaking. The absorbance was measured at 760 nm at the end of the incubation period. The concentration of TP compounds was calculated as milligrams of gallic acid equivalents (GAE) per gram of 100 g FW, by using a standard graph for gallic acid in the concentration range between 0.015 and 0.5 mg/mL (r2 = 0.9997).
Statistic analysisResults ate presented as mean values of two replicates. Data and regression analyses were tested using SPSS for Windows Release 10 (SPSS Inc.).
Results and discussion
Many natural products are rich in phenolic com-pounds and possess antioxidant, antibacterial,
Jour
nal o
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Inhibition of carbonic anhydrase isozymes I and II 397
© 2012 Informa UK, Ltd.
Tab
le 1
. Th
e n
ame
of s
amp
les
and
thei
r co
des
.C
ode
Typ
e of
sam
ple
sSa
mp
les’
nam
eC
omp
any
or p
lace
of o
rigi
nC
ode
Typ
e of
sam
ple
sSa
mp
leC
omp
any
or p
lace
of o
rigi
nC
1C
hem
ical
2 ci
s 4
tran
s ab
scis
ic a
cid
Sigm
a (S
t. L
ouis
, MO
, USA
)H
4H
oney
Ch
estn
ut H
oney
Turk
ey-R
ize
C2
Ch
emic
alB
enzo
ic a
cid
Sigm
a (S
t. L
ouis
, MO
, USA
)H
5H
oney
Ch
estn
ut H
oney
Turk
ey-T
rabz
onC
3C
hem
ical
Ap
igen
inSi
gma
(St.
Lou
is, M
O, U
SA)
H 6
Hon
eyC
hes
tnu
t Hon
eyTu
rkey
-Zon
guld
akC
4C
hem
ical
Cat
ech
inSi
gma
(St.
Lou
is, M
O, U
SA)
H 7
Hon
eyFl
ower
Hon
eyTu
rkey
-Tra
bzon
C5
Ch
emic
alC
hlo
roge
nic
aci
dSi
gma
(St.
Lou
is, M
O, U
SA)
H 8
Hon
eyFl
ower
Hon
eyTu
rkey
-Riz
eC
6C
hem
ical
Epic
atec
hin
Sigm
a (S
t. L
ouis
, MO
, USA
)H
9H
oney
Flow
er H
oney
Turk
ey-Z
ongu
ldak
C7
Ch
emic
alR
ham
net
inSi
gma
(St.
Lou
is, M
O, U
SA)
N 1
Mos
sR
hyn
chos
tegi
um
rot
un
difo
liu
mTu
rkey
-Riz
e-Ç
ayel
iC
8C
hem
ical
Kae
mp
fero
lSi
gma
(St.
Lou
is, M
O, U
SA)
N 2
Mos
sC
ampl
yopu
s p
yrif
orm
isTu
rkey
-Tra
bzon
-Sü
rmen
eC
9C
hem
ical
m-h
ydro
xyb
enzo
ic a
cid
Sigm
a (S
t. L
ouis
, MO
, USA
)N
3M
oss
Hyp
nu
m c
upr
essi
form
eTu
rkey
-Tra
bzon
-Sü
rmen
eC
10C
hem
ical
o-co
um
aric
aci
dSi
gma
(St.
Lou
is, M
O, U
SA)
N 4
Mos
sH
omal
othe
ciu
m s
eric
eum
Turk
ey-R
ize-
Çay
eli
C11
Ch
emic
alIs
orh
amn
etin
Sigm
a (S
t. L
ouis
, MO
, USA
)N
5M
oss
Pla
giom
niu
m u
ndu
latu
mTu
rkey
-Tra
bzon
-Sü
rmen
eC
12C
hem
ical
Pro
pylp
arab
enSi
gma
(St.
Lou
is, M
O, U
SA)
N 6
Mos
sSy
ntr
ichi
a in
term
edia
Turk
ey-R
ize-
Çay
eli
C13
Ch
emic
alFi
seti
nSi
gma
(St.
Lou
is, M
O, U
SA)
N 7
Pla
nt
Tili
a ru
bra
subs
. Cau
scas
ica
(L
ind
en tr
ee)
Turk
ey
C14
Ch
emic
alP
roto
cate
chu
ic a
cid
Sigm
a (S
t. L
ouis
, MO
, USA
)N
8P
lan
tR
osm
arin
us
offici
nal
is (
Ros
emar
y)Tu
rkey
C15
Ch
emic
alR
uti
nSi
gma
(St.
Lou
is, M
O, U
SA)
N 9
Pla
nt
Men
tha
pipe
rita
(M
int)
Turk
eyC
16C
hem
ical
Van
illic
aci
dSi
gma
(St.
Lou
is, M
O, U
SA)
N 1
0Fr
uit
Pru
nu
s la
uro
cera
sus
Turk
eyC
17C
hem
ical
t-ci
nn
amic
aci
dSi
gma
(St.
Lou
is, M
O, U
SA)
N 1
1V
eget
able
Alli
um
cep
a (O
nio
n)
Turk
eyM
1M
ush
room
Lact
ariu
s pi
pera
tus
Turk
eyN
12
Veg
etab
leA
lliu
m s
ativ
um
(G
arlic
)Tu
rkey
M 2
Mu
shro
omH
eric
ium
eri
nac
eus
Turk
eyN
13
Veg
etab
leA
piu
m g
rave
olen
s (C
eler
y)Tu
rkey
M 3
Mu
shro
omP
leu
rotu
s er
yngi
iTu
rkey
N 1
4V
eget
able
Alli
um
am
pelo
pras
um
var
. por
rum
(L
eek)
Turk
ey
M 4
Mu
shro
omM
orch
ella
esc
ula
nta
Turk
eyN
15
Pla
nt
Lau
rus
nob
ilis
(Sw
eet b
ay)
Turk
eyM
5M
ush
room
Gan
oder
ma
luci
dum
(R
eish
i)Ja
pan
N 1
6Fr
uit
Pho
enix
dac
tyli
fera
(D
ate)
Sau
di A
rab
iaM
6M
ush
room
Len
tin
ula
edo
des
(Sh
iita
ke)
Jap
anN
17
Seaw
eed
Pad
ina
pavo
nic
aTu
rkey
T 1
Tea
Bla
ck T
eaTu
rkey
-Riz
eN
18
Seaw
eed
Ente
rom
orph
a li
nza
Turk
eyT
2Te
aG
reen
Tea
Turk
ey-R
ize
N 1
9Se
awee
dU
lva
rigi
daTu
rkey
T 3
Tea
Wh
ite
Tea
Turk
ey-R
ize
N 2
0Se
awee
dC
lado
phor
a gl
omer
ata
Turk
eyH
1H
oney
Mad
Hon
eyTu
rkey
-Riz
eN
21
Seaw
eed
Cys
tose
ira
barb
ata
Turk
eyH
2H
oney
Mad
Hon
eyTu
rkey
-Tra
bzon
N 2
2Se
awee
dC
eram
ium
cil
iatu
mTu
rkey
H 3
Hon
eyM
ad H
oney
Turk
ey-Z
ongu
ldak
N 2
3Se
awee
dC
oral
lin
a offi
cin
alis
Turk
ey
Jour
nal o
f E
nzym
e In
hibi
tion
and
Med
icin
al C
hem
istr
y D
ownl
oade
d fr
om in
form
ahea
lthca
re.c
om b
y D
r C
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uran
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pers
onal
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398 H. Sahin et al
Journal of Enzyme Inhibition and Medicinal Chemistry
Tab
le 2
. To
tal p
hen
olic
con
ten
t (T
Ps)
an
d in
hib
itor
y eff
ects
of s
amp
les
agai
nst
hC
A I
and
hC
A II
(as
IC50
-s)
from
thre
e d
iffer
ent d
eter
min
atio
ns.
Cod
eSa
mp
les’
nam
eT
Ps
(mgG
AE
/g
sam
ple
)IC
50 V
alu
e (µ
g/m
L)C
ode
Sam
ple
TP
s
(mgG
AE
/g s
amp
le)
IC50
Val
ue
(µg/
mL)
hC
A I
hC
A II
hC
A I
hC
A II
C1
2 ci
s 4
tran
s ab
scis
ic a
cid
2.92
± 1
.12
28.2
21.
08H
4C
hes
tnu
t Hon
ey0.
90 ±
0.0
517
.00
10.5
2C
2B
enzo
ic a
cid
11.5
8 ±
0.3
71.
311.
12H
5C
hes
tnu
t Hon
ey0.
50 ±
0.0
34.06
3.78
C3
Ap
igen
in78
2.42
± 3
.91.
221.
14H
6C
hes
tnu
t Hon
ey0.
75 ±
0.0
67.
455.
25C
4C
atec
hin
863.
47 ±
1.3
51.
440.
52H
7Fl
ower
Hon
ey0.
24 ±
0.0
39.
756.
40C
5C
hlo
roge
nic
aci
d51
5.23
± 1
.95
0.98
0.88
H 8
Flow
er H
oney
0.53
± 0
.02
9.60
5.14
C6
Epic
atec
hin
856.
55 ±
1.6
31.
471.
02H
9Fl
ower
Hon
ey0.
57 ±
0.0
918
.27
15.8
6C
7R
ham
net
in13
18.96
± 1.00
0.72
0.55
N 1
Rhy
nch
oste
giu
m r
otu
ndi
foli
um
0.46
± 0
.07
21.3
514
.73
C8
Kae
mp
fero
l72
5.71
± 2
.70
1.24
0.87
N 2
Cam
plyo
pus
pyr
ifor
mis
0.45
± 0
.05
22.4
613
.76
C9
m-h
ydro
xyb
enzo
ic a
cid
828.
84 ±
1.7
21.
331.
00N
3H
ypn
um
cu
pres
sifo
rme
0.12
± 0
.07
4.03
2.59
C10
o-co
um
aric
aci
d71
9.11
± 1
.44
0.93
0.22
N 4
Hom
alot
heci
um
ser
iceu
m0.
10 ±
0.0
66.
144.
76C
11Is
orh
amn
etin
1189
.53
± 1
.30
0.95
0.86
N 5
Pla
giom
niu
m u
ndu
latu
m0.
47 ±
0.0
34.
333.
92C
12P
ropy
lpar
aben
58.9
8 ±
1.4
20.
840.
82N
6Sy
ntr
ichi
a in
term
edia
0.16
± 0
.07
4.97
4.48
C13
Fise
tin
376.
49 ±
0.9
90.
830.
76N
7Ti
lia
rubr
a su
bsp
. cau
scas
ica
(Lin
den
tree
)17
.54
± 0
.03
66.5
054
.54
C14
Pro
toca
tech
uic
aci
d11
18.0
0 ±
1.3
51.
311.
15N
8R
osm
arin
us
offici
nal
is (
Ros
emar
y)36
.53
± 1
.52
2.00
1.78
C15
Ru
tin
513.
49 ±
1.6
30.
520.
36N
9M
enth
a pi
peri
ta (
Min
t)37
.38
± 0.01
1.94
1.70
C16
Van
illic
aci
d66
6.95
± 2
.09
0.47
0.42
N 1
0P
run
us
lau
roce
rasu
s0.
02 ±
0.0
15.
054.
11C
17t-
cin
nam
ic a
cid
0.76
± 0
.37
0.11
0.09
N 1
1A
lliu
m c
epa
(On
ion
)0.
18 ±
0.0
22.
322.
18M
1La
ctar
ius
pipe
ratu
s0.
81 ±
0.0
98.
998.
62N
12
Alli
um
sat
ivu
m (
Gar
lic)
0.41
± 0
.03
10.6
69.
26M
2H
eric
ium
eri
nac
eus
0.80
± 0
.07
1.07
1.04
N 1
3A
piu
m g
rave
olen
s (C
eler
y)0.
56 ±
0.0
95.
084.
25M
3P
leu
rotu
s er
yngi
i3.
49 ±
0.3
50.52
0.49
N 1
4A
lliu
m a
mpe
lopr
asu
m v
ar. p
orru
m (
Lee
k)0.
20 ±
0.1
79.
237.
24M
4M
orch
ella
esc
ula
nta
2.50
± 0
.21
25.5
27.
04N
15
Lau
rus
nob
ilis
(Sw
eet b
ay)
16.2
4 ±
2.2
59.
716.
74M
5G
anod
erm
a lu
cidu
m0.
94 ±
0.1
52.
482.
38N
16
Pho
enix
dac
tyli
fera
(D
ate)
2.06
± 0
.04
13.7
812
.17
M 6
Len
tin
ula
edo
des
0.57
± 0
.05
3.32
2.80
N 1
7P
adin
a pa
von
ica
0.31
± 0
.01
27.66
15.3
6T
1B
lack
Tea
59.7
1 ±
1.2
736
.66
24.0
2N
18
Ente
rom
orph
a li
nza
0.47
± 0
.08
31.7
212
.07
T 2
Gre
en T
ea83
.63
± 1
.30
14.5
910
.63
N 1
9U
lva
rigi
da0.
12 ±
0.0
145
.81
8.26
T 3
Wh
ite
Tea
602.
92 ±
1.0
911
.38
3.04
N 2
0C
lado
phor
a gl
omer
ata
1.57
± 0
.11
20.2
315
.65
H 1
Mad
Hon
ey0.
20 ±
0.0
116
.68
12.8
0N
21
Cys
tose
ira
barb
ata
0.36
± 0
.02
35.2
96.32
H 2
Mad
Hon
ey0.
35 ±
0.0
44.
284.
20N
22
Cer
amiu
m c
ilia
tum
0.38
± 0
.02
44.7
220
.18
H 3
Mad
Hon
ey0.
17 ±
0.1
515
.13
6.25
N 2
3C
oral
lin
a offi
cin
alis
0.22
± 0
.06
60.0
253
.01
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anti-inflammatory, antiallergic and antithrombotic activities37,39,40. As far as we know, such products have never been tested for their inhibitory activities against the CA family of enzymes. Indeed, CA inhibitors, especially aromatic and heterocyclic sulfonamides, have been and are used clinically for more than 50 years in the treatment of a variety of diseases such as glaucoma, epilepsy, obesity, mountain sickness, gas-tric and duodenal ulcers, osteoporosis and acid–base disequilibria2. Recently, some sulfonamide CA inhibi-tors were demonstrated to possess relevant antitumour and antimetastatic effects41,42.
We have prepared some pure chemical standards and natural compounds, most of which are aromatic derivatives based on the flavone core structure, various substituted phenols/polyphenols and phenolic aromatic acids as methanolic extracts and measured their TP con-tent (Tables 1 and 2). Total phenols were expressed in milligrams of gallic acid per gram of sample. Especially, rhamnetin, protocatechuic acid and catechin extracts
showed higher phenolic content than other prepara-tions. It may be observed that in the chemical samples, the total polyphenol contents were between 0.76 ± 0.37
O
O
OH
R1
R2
R3
R4
R5
Code Name R1
R2
R3
R4
R5
C3 Apigenin -OH -OH -H -H -HC7 Rhamnetin -OCH
3-OH -OH -OH -H
C8 Kaempferol -OH -OH -OH -H -HC11 Isorhamnetin -OH -OH -OH -H -OHC13 Fisetin -OH -H -OH -H -OHC15 Rutin -OH -OH -Rutinose -H -OH
Code Name R1
R2
R3
R4
R5
C2 Benzoic acid -H -H -COOH -H -HC9 m-hydroxybenzoic acid -H -H -OH -H -COOHC10 o-coumaric acid -H -H -OH -(CH
2)
2COOH -H
C12 Propylparaben -H -OH -H -H -COO(CH2)
2CH
3
C14 Protocatechuic acid -OH -OH -H -H -COOHC16 Vanillic acid -H -OH -OCH
3-H -COOH
C17 t-cinnamic acid -H -H -(CH2)
2COOH -H -H
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and 1318.96 ± 1.00 mgGAE/g of sample, whereas for the mushrooms 0.57 ± 0.05 and 3.49 ± 0.35, teas 59.71 ± 1.27 and 602.92 ± 1.09, honeys 0.20 ± 0.01 and 0.90 ± 0.05, natural compounds 0.05 ± 0.01 and 37.58 ± 0.01 mgGAE/g sample (Table 2).
We measured thereafter the inhibitory effects of these samples against the purified cytosolic CA iso-forms hCA I and II, which are among the physiologically most relevant such enzymes2. The inhibition results are expressed as IC
50 and were found to be in the range of
0.11–66.50 μg/mL for hCA I and 0.09–54.54 μg/mL for hCA II (Table 2). The meaning of IC
50 is the concentration
of compound (molarity or in this specific case, expressed in mg/mL) that reduces the CA activity by 50%. Among all the investigated samples, it may be observed that the extraction method highly influenced the CA inhibitory activity against both isoforms. Because the components are pure chemicals belonging to the polyphenol class, they are expected to show some inhibition against hCA I and II, and phenols are highly investigated as CA inhibi-tors37. Rhamnetin showed the highest value of total poly-phenol content, according to the gallic acid standard, and it was also a potent inhibitor of hCA I and II. trans-Cinnamic acid (C17) was the best inhibitor, with IC
50 val-
ues of 0.11–0.09 μg/mL (Table 2). It should be mentioned that 2-hydroxy-trans-cinnamic acid was recently discov-ered to be a CA inhibitor, being formed from coumarin (a prodrug) by active-site–mediated hydrolysis33,34. This compound binds in a particular manner to the enzyme, at the entrance of the active site cavity, as shown by X-ray crystallography. Coumarins also led to highly isoform-selective CA inhibitors33,34, and one such compound has notable antitumour and antimetastatic properties, being in preclinical evaluation as an anticancer drug41.
White tea is prepared from young tea leaves or buds covered with tiny, silvery hairs, which are harvested only once a year in the early spring. It is richer in phe-nolic compounds, especially catechin and its derivatives, compared with mature tea43. Pleurotus eryngii contains various phenolic components especially catechin, simi-lar to white tea44. Because of the high catechin content, white tea (T3), among the tea species and P. eryngii (M3) among the mushrooms, showed the lowest IC
50 and
highest total polyphenol value among the investigated extracts (Table 2).
Different honey types contain diverse components that have antioxidant, antimicrobial, antiviral, and anti-fungal effects, by mechanisms not well elucidated yet45–47. Chestnut honey is one type of honey known for its excel-lent properties. Küçük et al.45 reported that chestnut honey contains superior amounts of the total polyphenols (which are responsible for the antioxidant effects) com-pared with rhododendron and flower honeys. Chestnut honey (H5) investigated here showed the best value on hCA I and II inhibition among the various honeys.
Phenolic compounds were investigated in Mentha piperita by Areias et al.48 According to this study, M. piperita contains a high percentage of phenolic
compounds such as eriodictyol, luteolin, hesperetin, apigenin, and rosmarinic acid, etc.48 These compounds might be responsible for the inhibition of hCA I and II observed in the current study, but this hypothesis must be verified.
Marine algae are potentially prolific sources of highly bioactive secondary metabolites that might represent useful leads in the development of new pharmaceutical agents49. According to Chewa et al.50, Padina pavonica contains a high amount of polyphenols50. However, our results show that the value of TP compounds is similar to each other among all investigated seaweeds (Table 2). This also may explain the CA inhibition effects of the algal extracts, which were similar to each other (Table 2).
In conclusion, we report that a CA I and II inhibition study with natural product compounds that contain polyphenols and flavones, extracted from various plants, mushrooms and honey. Many of these rather effective inhibitors detected here can be used as lead compounds for developing novel classes of CA inhibitors, presum-ably with a new mechanism of inhibition, which may be similar to that of the coumarins, newly discovered class of inhibitors of these enzymes.
Acknowledgments
We also thank Assoc. Prof. Dr. Turan ÖZDEMIR for providing and identifying the moss sample Biology Department, Karadeniz Technical University, and also thanks to Assoc. Prof. Dr. Ömer ERTÜRK for pro-viding and identifying the seaweeds sample Biology Department, Ordu University. Work from Supuran lab was financed by two FP7 EU projects (Metoxia and Gums and Joints).
Declaration of interest
This study was supported by Research Fund of Karadeniz Technical University (Project No: 2009.111.002.5). One of the authors (H. Sahin) would like to thank TUBİTAK, BİDEB, TURKEY, for the financial support given to him.
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