Hepatoprotectants
≈hepatics
1. Inhibitors of nuclear transcription factor B (NF-κB)
2. Antifibrotics
3. Antioxidants
4. Compounds which interfere with apoptosis
●most of compounds have multiple mechanisms of action
© assoc. prof. Oldřich Farsa, Ph.D., 2011
Nuclear transcription factor B (NF-κB)
= a protein activating the immunity response of Kupfer cells of liver to
harmful stimuli
●permanent or excessive activation leads to unwanted changes ofi liver
tissue (cirrhosis, fibrosis)
●
under different circumstances, activation of NF-κB can lead also to liver
regeneration
e
Activation of nuclear transcription factor B (NF-κB) by tumor necrosis factor α (TNF-α) and
interleukin 1 (IL-1)
NF-κB is in the cytoplasma in its inactive form linked with protein IκB (inhibitor κB); this interaction disables transfer
of NF-κB into the cell nucleus. NF-κB is activated if TNF-α or IL-1 are bound to their receptors, that leads to
activation of intracellular signals and adaptor proteins, such as MyD88 (gene of primary myeloid diferentiation
response 88), IRAK (IL-1R-asociated kinase) and TRAF-6 (TNF-asociated factor 6) for receptor IL-1 and TRADD
(TNF-asocioated protein of death domain), RIP (receptor-interacting protein) and TRAF2 (TNF-asociated factor 2) for
receptor TNF-α. These changes enable activation of IKKK (kinase of IκB kinase), which phosphorylates a activates
IKK (IκB kinase), consisted from regulation subunit (IKK-γ) and two kinase subunits (IKK-α, IKK-β), that are
responsible for phosphorylation of IκB. Then IκB is degraded by nuclear localisation signal and free NF-κB reaches
the nucleus where it is bound to κB enhancing elements of target gene and induce their transcription.
Silymarin
= a mixture of flavanolignans gained by extraction of seeds of milk thistle(Silybum marianum;
first referred by Pliny the Elder (= Gaius Plinius Secundus (23 AD – August 25, 79 AD) in 77 AD
●content in seeds 1.5 – 3.5 %
●most of hepatoprotective activity is attributed to silybine (A+B) = silibinin; it represents 60 – 70
% of silymarin
●in silybin, hepatoprotective activity in liver damage by death cap (mushroom) (Amanita
phalloides), ethanol, paracetamol, CCl4
etc. was demonstrated.
R
2
R
1O
O
R
3
R
4
H
O
O
OH
OH
OH
silybin A: R1
=R4
=-H
R2
=-CH2OH
R3
= OH
O
CH3
silybin B: R1
=-CH2OH
R2
=R3
=-H
R4
= OH
O
CH3
H
O
O OH
OH
OH
OH
O
OHOCH3
O
OH
silychristin
HO
OH
O
HH
O
OH
OH
O
OH
H
H
OH
O CH3
silydianin
Effects of silymarin and their mechanisms
●
inhibition of activation of NF-κB was demonstrated on hepatoma and lymphoma cells;
probably main mechanism of action
●antioxidation effect: enhances superoxide dismutase activity in lymphocytes and
erythrocytes, inhibits lipoperoxidation
●increses glutathione level
●anticancerogenic effect in prostate carcinoma
H
O
O
O
O
CH3
O
H
O
O
O
H
O
H
O
H
H
H
isosilybin A+B (= isosilibinin A+B)
●
preparations Flavobion®
, Lagosa®
, Legalon®
, Silygal®
, Silymarin AL 50®
PhEur: Silybi mariani extractum siccum
rafinatum et normatum
●silikristin + silidianin 20 – 45 %
●silibinin A + B 40 – 65 %
●isosilibinin A + B 10 – 20 %
Resveratrol
OH
OH
OH
H
H
5-[(E)-2-(4-hydroxyphenyl)ethenyl]benzene-1,3-diol
3,5,4´-trans-trihydroxystilbene
resveratrol
●Arachis (peanut), Vitis vinifera (grapevine)
●effects: antioxidant, anti-inflammatory, cancer prevention
●prevention of fibrose development
●protection before paracetamol toxicity and fibrosis caused by
tetrachloromethane was demonstrated in vitro
●methylation of -OH does not decrease protective effects in vivo
●
mechanism of action: inhibition of NF-κB activation
Curcuminoids
●Curcuma longa, Zingiberaceae
O OH
OH OH
R
1
R
2
O O
OH OH
R
1
R
2
R1
=R2
=-OCH3
curcumin
R1
=-H R2
=-CH3
demethoxycurkumin
R1
=R2
=-H bisdemethoxycurcumin (syn. curcumin III)
●
mechanisms of action : inhibition of NF-κB, TNF-α and IL-1β
●strong antioxidant activity, scavengers of many ROS
●lower cell membrane peroxidation
●curcumin is also the approved food additive (E 100, C.I. 75300)
Caffeic acid
OH
O
OH
OH
3-(2,3-dihydroxyphenyl)prop-2-enoic acid
caffeic acid
●protection against damage by CCl4
●mechanisms of action: 1. inhibition of lipoxygenase 5 (which produces leucotriens
damaging the liver)
2. inhibition NF-κB activation
3. free radicals scavenging
Pyrrolidine-2-carbodithioic acid
N
H S
SH
●syn. pyrrolidine-2-dithiocarboxylic acid,“pyrrolidine dithiocarbamate“,
„prolinedithiocarbamate“, PDTC, dithioproline
●known at least since 1958 (Zuman, Zahradník)
●mechanisms of action: 1.antioxidant by complexation of metal cations which
catalyse generation of free radicals
2. inhibits activation of NF-κB
Thalidomide and its analogues
N
O
O
N
H
O
O
N
O
O
NH2
O
O
O
CH3
CH3
2-(2,6-dioxopiperidine-3-yl)-1H-isoindole-1,3(2H)-dion
α -(N-phtalimido)glutarimide
thalidomide
3-(3,4-dimethoxyphenyl)-3-(1,3-dioxo-1,3-dihydro-2H
-isoindol-2-yl)propanamide
3-(phtalimido)-3-(3,4-dimethoxyphenyl)propanamide
PDP
●originally hypnotic
●
strong teratogene (Contergan®
)
●
abandoned in 1970th
, now tested for cancer therapy
●anti-inflammatory, antifibrotic and anticirrhotic activity
●
účinný inhibitor NF-κB
2. Antifibrotics
●angiotensin II (AT-II) a ACE play probably important roles in formation of liver
firbrose
●
transforming growth factor β (TGF-β) plays a dominat role in fibrose initiation; it
can be supported by AT-II
●angiotensin receptor 1 antagonists lowers the portal pressure in hepatic cirrhosis
●
hypothesis: inhibition of AT-II leads to NF-κB inactivation
N
O
SH
OOH
CH3
(2S)-1-[(2S)-2-methyl-3-sulfanylpropanoyl]pyrrolidine-2-carboxylic acid
captopril
(normally used as an anti-hypertensive agent)
3. Antioxidants
OH
O
S
S
5-(1,2-dithiolan-3-yl)pentanoic acid
thioctic acid
lipoic acid
●
inhibition of apoptosis of hepatocytes which had been induced by actinomycine D and TNF-α
was demonstrated
●mechanism of action:activation of the insulin receptor by binding to thyrosinkinase domain
●
used and authorised for long time as a drug for diabetic polyneuropathy (Thioktacid®
,
Thiogamma®
)
4. Compounds which interfere with apoptosis
CH3
S
+
H
NH2
O
-
O
H
O
H
H
OH
H
OH
N
N
N
N
NH2
S-adenosylmethionine
SAME, SAM, AdoMet
●endogenous compound, a donor of methyl
●synthesized from Met and ATP by the reaction catalyzed by methionine
adenosyltransferase (MAT)
●regulates liver growth
●anti-apoptic in normal cells, induces apoptosis in cancer cells; a mechanism of action
related to proteins Bcl-x was proposed (Bcl-x belong to BCl-2c family, members of this
family are central regulators of apoptosis); posttranslation splicing of Bcl-x protein can
lead to Bcl-xL
, that is anti-apoptic, or to Bcl-xS
which is proapoptic; SAME and
methionyladenosin (MTA) induced selectively Bcl-xS
in HepG2 cancer cells; the
alternative splicing is modulated by proteinphosphatase 1 (PP1) and its inhibitors block
the ability of SAME and MTA induce Bcl-xS
●SAME and MTA increased the amount of mRNA for the catalytic subunit PP1 in HepG2
cells, but not in normal hepatocytes
●SAME is freely available in food supplements in the USA
CH3
S H
O
H
H
OH
H
OH
N
N
N
N
NH2
methylthioadenosine (MTA)
5´-deoxy-5´-methylsulfanyladenosine
●a side product of SAME metabolism gained in polyamines synthesis
The hepatal metabolism of S-adenosylmethionine (SAME)
methionine adenosyltransferase
S-adenosyl homocysteine