a search for hepatoprotective agents of natural...
TRANSCRIPT
A search for hepatoprotective agents of natural origin
Department of Chemical Technology, Dr.Babasaheb Ambedkar Marathwada University, Aurangabad
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NATURE always stands as a golden mark to exemplify the
outstanding phenomenon of symbiosis. The plants are indispensable to man
for his life. Nature has provided a complete storehouse of remedies to cure
all ailments of mankind.
In the past, almost all the medicines used were from the plants, the
plant being man's only chemist for ages. Today, vast store of knowledge
concerning therapeutic properties of different plants has accumulated.
The history of herbal medicines is as old as human civilization. The
documents, many of which are of great antiquity, revealed that plants were
used medicinally in China, India, Egypt and Greece long before the beginning
of Christian era.
Ayurveda is believed to be prevalent since last 5000 years in India. It
is one of the most noted systems of medicine in the world. Ayurveda is based
on the hypothesis that everything in the universe is composed of five basic
elements viz. space, air, energy, liquid and solid. They exist in the human
body in combined forms like Vata (space and air), Pitta (energy and liquid)
and Kapha (liquid and solid). Vata, Pitta and Kapha together called Tridosha
(three pillars of life). It is believed that they are in harmony with each other
but in every human being one of them is dominating which in turn is called
as the prakruti of that person1.
Considerable scopes of ethanobotanical studies are found in different
parts of India; mainly use natural plant product directly as drugs to get rid
from various diseases. Much work in the field of medicinal plants has
accumulated in India during 20th century. Therapeutic use of plants for
treatment of human illness dates back many millennia. Evidenced of their
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effectiveness in the diagnosis, cure and prevention of disease state exist in
every culture throughout the world2.
Plants constitute one of the major raw materials for drugs for treating
various ailments of human being, although there has been significant
development in the field of synthetic drug chemistry and antibiotics. In all
over the world now considerable changes have taken place during last two
decades. Due to the awareness of toxicity associated with the long use of
synthetic drugs and antibiotic, the western society prefers the drug from
natural sources than the synthetics.
Moreover modern medicine does not have a suitable answer for many
conditions such as liver disorder and for chronic conditions such as asthma,
arthritis etc. and this leads to increase interest in herbal drugs3.
Today "traditional medicine" characterized by the use of herbs and
other natural products, still remains regular component of health care in
countries such as China, Japan, India, South America and Egypt. Even
today more than 40% of drugs in allopathy have their origin from plants.
Keeping this significant contribution, there is a need that we should
understand the original system of medicine and stop calling them as
"Alternative Systems"4.
Hepatic endothelial and kupffer Cell specific delivery of drugs
Fibrosis or scarring of the liver occurs after damage to liver tissue.
Most chronic liver diseases eventually result in excess scarring leading to
liver cirrhosis. This fatal disease, to date can only be effectively treated with
a liver transplantation. Since this is a costly procedure, hampered by the
lack of donor organs among other technical factors, much effects has been
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put into developing new drugs. The drugs available are not sufficiently
effective and/or cause too many adverse side-effects. Therefore, drug
targeting is an option in trying to maximize efficacy and minimize adverse
drug reactions.
Since drug targeting implies the manipulation of drug distribution in
the whole body, emphasis should be put on in vivo studies. In contrast to in
vitro studies, studies in the intact organism will provide more definite insight
into the cell specificity of carrier systems, the potential toxicity,
immunogenicity and the ability of the carrier system to pass anatomical
barriers enroute to the target cells. Moreover, it is of the utmost importance
that these parameters are also studied in the diseased state, since the
targeting potential of carriers can change dramatically under pathological
conditions. In vitro studies with various liver preparations can be used to
study endocytosis, carrier degradation and intracellular release of the
targeted drug in more detail. In addition, the concept of drug targeting
should also be tested in human tissue.
The Liver
At the crossroads between the digestive tract and the rest of the body
resides the largest solid organ of the body, the liver. Because of its
interposition, the liver has a dual blood supply.
Nutrient-rich blood arrives through the portal vein and oxygen-rich
blood through the hepatic artery. Together these channels import a large
variety of endobiotics and xenobioties, ranging from nutrients to toxic
substances derived from the digestive system. The main function of the
liver, therefore, is to maintain the body’s metabolic homeostasis. This
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includes the efficient uptake of amino acids, carbohydrates, lipids, vitamins
and their subsequent storage, metabolic conversion and release into blood
and bile, synthesis of serum proteins, hepatic biotransformation of
circulating compounds. It is a process which converts hydrophobic
substances into water-soluble derivatives that can be secreted into bile or
urine as well as phagocytosis of foreign macromolecules and particles such
as bacteria.
Classically the liver has been divided into hexagonal lobules centered
around the terminal hepatic venules. Blood enters the liver through the
portal tracts that are situated at the corners of the hexagon. The portal tracts
are triads of a portal vein, an hepatic artery and a common hepatic bile duct.
The vast expanse of hepatic tissue, mostly consisting of parenchymal cells
(PC) or hepatocytes, is serviced via terminal branches of the portal vein and
hepatic artery, which enters the tissue at intervals. The hepatocytes are
organized into cords of cells radially disposed about the central hepatic
venule. Between these cords are vascular sinusoids that transport the blood
to the central hepatic venules. The blood is collected through the hepatic
venules into the hepatic vein which exits the liver into the inferior vena cava
(Figure 1.1)
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Figure 1.1 Representation of architecture of liver
Blood enters the liver through the portal vein (PV) and hepatic
arteries (HA), flows through the sinusoids and leaves the liver again via the
central vein (CV), Kupffer cells (KC), sinusoidal endothelial cells (SEC),
hepatic stellate cells (HSC) and bile duct (BD).
The Sinusoids are lined by the discontinuous and fenestrated
SEC that demarcate the extrasinusoidal space of Disse. The abundant
microvilli of the hepatocytes protrude into this space, which also contains the
fat-containing lipocyte or HSC. At a strategic position along the luminal side
of the endothelial cells are the resident tissue macrophages, which are KC.
Also located on the endothelial lining is the Pit cell that corresponds to the
large granular lymphocytes with natural killer activity. Between the abutting
hepatocytes are bile canaliculi, channels in between the plasma membranes
of facing hepatocytes that are delineated from the vascular space by tight
junctions. These intercellular spaces constitute the outermost reaches of the
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biliary tree. The canaliculi emanate from the centriobular regions,
progressively drain into the canals of Hering at the fringes of the portal
tracts, and biliary fluid finally collects in the interlobular bile ducts.
The Parenchymal Cell (PC)
The liver consists mainly of parenchymal cells (PC) or hepatocytes.
Most drug-targeting preparations designed for liver targeting of therapeutic
compounds are directed towards this cell type, generally aiming at the
asialoglycoprotein receptor using galactose residues coupled to a core
molecule for binding 5-7.
Hepatocytes make up 60-70 % of the total number of liver cells. They
have a well-organized intracellular structure with huge numbers of cell
organelles to maintain the high metabolic profile. At the apical side or
canalicular membrane the cell is specialized for the secretion of bile
components. There are several ATP dependent transport carriers located on
this side of the membrane, which transport bile salts, lipids and xenobiotics
into the canaliculus. On the sinusoidal side, the cells specialize in uptake
and secretion of a wide variety of components. To increase the surface of the
membrane for this exchange with the bloodstream, the sinusoidal domain of
the membrane is equipped with irregular microvilli. The microvilli are
embedded into the fluid and matrix components of the space of Disse and are
in close contact with the sinusoidal blood because of the discontinuous and
fenestrated SECs. To facilitate its metabolic functions numerous membrane
transport mechanisms and receptors are situated in the membrane.
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The Sinusoidal Endothelial Cell (SEC)
The endothelial lining of the sinusoids in the liver differs from the
other capillaries in the body and is adapted to form a selective barrier
between blood and hepatocytes. The basement membrane is composed of
non-fibril-forming collagens including types IV, VI and XIV glycoproteins and
proteoglycans. The lining is discontinuous and the SECs are perforated by
numerous fenestrae that lack diaphragms. This allows direct contact of the
hepatocytes with most plasma proteins in the space of Disse, but prevents
direct contact with blood cells, large chylomicrons, bacteria and viruses.
SECs play an important role in the pathogenesis of several acute and chronic
inflammatory liver diseases. Consequently they are attractive target cell for
anti-inflammatory therapies.
The SECs account for 20% of all liver cells and are the first cells,
together with the KCs to encounter potentially harmful materials present in
the portal blood. They are therefore equipped with scavenger capabilities
and certain defense mechanisms to prevent damage to other cell types. The
SECs have an active scavenging system for the majority of physiological and
foreign soluble (waste) macromolecules8,9. Clearance mechanisms include
receptor mediated endocytosis, transcytosis and phagocytosis. To regain
local homeostasis after ingestion of injurious substances and after other
determental events, the SECs can also produce cytokines, eicosanoids and
adhesion molecules for the mobilization of their hepatic cell types and cells of
the immune system.
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Receptor-mediated Endocytosis
Targeting to SECs should be directed at specific receptors present on
this cell type-A wide range of proteins and other molecules can be taken up
by SECs through receptor-mediated endocytosis. For example, SECs play an
important role in the uptake of degradation products of the extracellular
matrix. For this purpose they have hyaluronan10, procollagen and
fibronectin receptors11. The first two receptors are uniquely located on SECs.
Elevated levels of serum hyaluronan and fibronectin that are often found in
liver disease12 are usually the result of dysfunction of the clearance capacity
of SECs combined with an increased production by HSCs13.
Scavenger receptors on the SECs are instrumental in another
important endocytic mechanism. They recognize and endocytose modified
proteins that have a high net negative charge13. SECs predominantly express
two type of scavenger receptors viz. the class AI and the class AII scavenger
receptor14. Physiological substrates for these receptors were found to be the
N-terminal propeptides of types I and III procollagen and the lipid A moiety of
endotoxin15,16. The SECs are further equipped with a receptor that
specifically interacts with mannose and N-acetylglucosamine terminated
glycoproteins. Unlike the scavenger receptor, binding of ligands to this so-
called mannose receptor is Ca2+- dependent, but is also followed by rapid
endocytosis and degradation in lysosomes17. The receptor is thought to be
involved in the uptake of microorganisms like yeasts, bacteria and parasites,
but has also been shown to be involved in uptake of tissue-type plasminogen
activator18,19. In addition, the receptor is involved in antigen uptake for
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subsequent antigen presentation. This indicated that SECs may also be
involved in cell-mediated immune responses in the liver20.
Phagocytosis and Transcytosis
SECs are normally able to internalize only small particles (up to 0.23
µ) in conditions of impaired KC function. However, they have also been
found to phagocytose larger particles21. They are also responsible for the
receptor mediated transcytosis of several compounds such as insulin22 and
transferrin23.
Regulation of the Inflammatory Process by SECs
Exposure of the SECs to pathogens or cytokines produced by other
cells during stress induces activation of the SECs and subsequent
production of cytokines, eicosanoids, and/or adhesion molecules. For
instance, after activation with LPS, a main component of the walls of gram
negative bacteria and a major inducer of inflammation and non-specific
immune functions24, SECs produce a number of pro and anti-inflammatory
cytokines. Pro-inflammatory cytokines shown to be produced were a) tumor
necrosis factor alpha (TNFα)25, b) interleukin-1 alpha/beta(IL-1α/β)26, c) the
major inducer of acute phase proteins interleukin-6 (IL-6)27 and d) the
neutrophil chemo-attractant interleukin-828. Anti-inflammatory cytokines
shown to be produced were interleukin-1026 (IL-10) and hepatocyte growth
factor (HGF) 29.
Eicosanoids are the oxidative metabolites derived from the cell
membrane component arachidonic acid. Arachidonic acid is released from
the cell membrane by phospholipase A2 and enzymatically converted to either
prostaglandins (PGs) by cyclo-oxygenase or leukotrienes (LTs) by
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lipoxygenase. Eicosanoids is the collective name of prostaglandins and
leukotrienes. SECs and KCs are the major sources of eicosanoids, whereas
the PCs are considered to be the most important target cells for them. The
main eicosanoid produced by SECs was found to be PGE230, although PGD2
has also been reported to be a major product31. The type of PG released may
be a result of the difference in the induction stimulus used. Eicosanoid
production is induced by many circulating substances; LPS interferon
gamma (IFNγ), TNFα and platelet activating factor (PAF). PGE2 is postulated
to be involved in liver regeneration32 and inhibition of hormone-stimulated
glycogenolysis30, PGD2 was found to induce glycogenolysis33.
SECs, like the vascular endothelium, play an active part in the control
of leucocyte recruitment in cases of acute and chronic inflammatory
conditions. Leucocyte recruitment from the blood compartment is a crucial
determinant for the induction of immunity and inflammation. SECs control
this process by producing cytokines that activate leucocytes and by
expressing adhesion molecules. Under inflammatory conditions upregulation
of intracellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion
molecule 1 (VCAM-1)34, 35 as well as expression of E-selectin and P-selectin36
were found. Together with the expression of CD4 on SECs it has been
postulated that these adhesion molecules might also be involved in the
adhesion of KC cells to the sinusoidal wall24.
The Kupffer Cell (KC)
Kupffer cells are the largest reservoir of fixes tissue macrophages and
are quantitatively the most important cell type for the removal of circulating
micro organisms, LPS, tumor cells, immune complexes, other circulating
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tissue and microbial debris37. They account for about 15% of the liver cell
population in number and they are preferentially located in the periportal
areas38.
Receptor-mediated Endocytosis
Similar to the targeting of compounds to SECs drug targeting
preparations designed to modify KC functions have to be directed at KC-
specific receptors. KCs are able to remove numerous soluble and particulate
substances from the circulation and they possess many receptor systems
that mediate this clearance, some of which have also been described for
SECs Like SECs, they possess fibronectin receptors, mannose receptors, Fe
receptors, CD14 receptors and the scavenger receptors class AI and AII39. In
addition to these receptors, KCs also possess the novel member of the class A
scavenger receptor family, the macrophage receptor with collagenous
structure (MARCO) 40. Besides these types of scavenger receptors, they also
have macrosialin scavenger receptors for the uptake of oxidized LDL and
scavenger receptors class BI for the removal of high-density lipoproteins
(HDL)41. For the uptake of unmodified LDL, KCs also have special LDL
receptors42.
Mannose receptors on KCs essentially recognize the same
molecules as the mannose receptors present on SECs, but they exhibit
different kinetics43. Besides the mannose receptors, KCs have two other
carbohydrate-specific receptors. One is the galactose particle receptor,
recognizing galactose terminated oligosaccharides on particles and mediating
endocytosis of desialylated erhyhrocytes44. The other is the fucose receptor
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which interacts not only with fucose terminated glycoproteins, but also with
galactose exposing neoglycoproteins45.
KCs also possess receptors for the complement components Clq and
C3ba46,47. The complement system is one of the main defense mechanisms of
the body against invading pathogens. It is composed of a group of serum
proteins that are part of a multienzymatic cascade. Activation of complement
generates membranolytic components and protein fragments that enhance
phagocytosis and mediate immune responses. KCs have the optimal capacity
to remove complexes coated with complement from the circulation.
Phagocytosis
Not all KCs are phagocytic to the same extent; periportal KCs
generally have a higher level of phagocytic activity than those in other
regions of the liver48. Prior to phagocytosis, particulate material like viruses,
bacteria and erythrocytes may be opsonized and bound by specific receptors,
but this is not essential for phagocytosis49.
Hepatic Inflammation and Fibrosis
Virtually any insult to the liver can cause hepatocyte destruction and
parenchymal inflammation. If the insult is minor and occurs only once, local
restoration mechanisms will suffice to repair the damage. If however, the
insult is major or persistent, an inflammatory response will be generated.
This inflammation is the result of cytokine-mediated activation of sinusoidal
cells, their subsequent release of pro-inflammatory cytokines and their
expression of adhesion molecules for the recruitment of circulating
leucocytes. Once the damage is under control and the inciting insult has
been eliminated, the inflammatory process will end and local mechanisms
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will proceed until the damage is repaired. Usually little scar tissue will be
detectable, because of extracellular matrix remodeling. During conditions of
chronic liver injury, however, the repair process does lead to scar tissue
formation, which is deposited with in the liver until impairment of liver
function occurs. This process is called liver fibrogenesis and the end stage,
or irreversible stage, is referred to as liver cirrhosis (Figure 1.2)
Figure 1.2 Diagram outlining the pathogenesis of liver fibrosis.
Injury to PC results in the activation of KC and SEC and the recruitment of
IC. These cells release cytomines, growth factors and reactive oxygen species
that induce activation and proliferation of HSC. HSCs gradually transform
into MF, the major producers of ECM proteins.
After damage or infection, monocytes and KCs in the area
detect the damaged cells or infectious agent and respond with release of
primary mediators such as TNFα, IL-1 and some IL-6. These cytokines
activate the surrounding cells that respond with a secondary amplified
release of cytokines. This second wave includes large amounts of IL-6 which
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induce the synthesis of acute phase proteins in hepatocytes and
chemoattractants such as IL-8 and MCP-1. These events will then lead to the
typical inflammatory reactions. Both IL-1 and TNFα activate the central
regulatory protein of many reactions involved in immunity and inflammation,
nuclear factor kappa B (NFkB). These cytokines cause dissociation of NFkB
from its inhibitor IkB, which makes translocation of NFkB to the nucleus
possible. In the nucleus active NFkB induces the transcription of the
‘Second wave’ cytokines.
The release of TNFα and IL-1 also upregulates adhesion molecules like
ICAM-1 and VCAM-1 on SECs that are subsequently responsible for the
adhesion and recruitment of circulating neutrophils. KCs and PCs release
IL-8, which is a potent neutrophil chemoattractant. The attracted neutrophils
and KCs are stimulated to release large amounts of reactive oxygen species
(ROS: hydrogen peroxide, superoxide anion and nitric oxide (NO) radicals).
The production of NO is also mediated through the NFkB pathway. The
enzyme responsible for the increased synthesis of NO, inducible NO
synthetase (i-NOS), is increasingly ex-pressed through NFkB mediated
stimulation of the i-NOS promoter region.
TGFβ and TNFα produced by KCs and PDGF produced by SECs
subsequently play an important role in the activation HSCs. TGFβ appears
to be the most important cytokine in stimulating the production of scar
tissue components like collagens by HSCs. The mechanism of activation is
probably via the IGF-II/M6P receptor, which is also increasingly expressed
on activated HSCs. As yet unknown factors produced by KCs stimulate
expression of PDGF receptors on the surface of HSCs. In the presence of
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PDGF the HSC will now proliferate as well. On chronic stimulation HSC
stimulation, but substances directly released by PCs are also found to be
mitogenic50.
Since not every insult necessarily results in liver fibrosis, counter-
regulatory mechanisms must also exist. During inflammation, elimination of
ROS by SECs and KCs is enhanced via increased expression of radical
scavengers like superoxide dismutases and glutathione peroxidase. The
radical nitric oxide itself also has an anti-inflammatory role. It has been
described to prevent leucocyte adhesion to the endothelium51 and to block an
activation pathway of thrombocytes by stimulating guanylyl cyclase52.
Furthermore, both PGE2 and IL-10 can downregulate cytokine produced by
macrophages53,54 and can also inhibit the antigen-presenting properties of
SECs and KCs20,55. HGF produced by KCs, SECs and quiescent HSCs is a
potent mitogen for PCs and stimulates liver regeneration. It is probably aided
by PGE2 which also stimulates DNA synthesis in PCs56. Finally, scar tissue
formation is not only regulated by production of extracellular matrix
components, but also by the degradation of matrix components. Activated
and quiescent HSCs, KCs and SECs produce matrix metalloproteinase that
are responsible for matrix degradation57.
Liver Cirrhosis: Causes and Therapy
Cirrhosis is among the top 10 causes of death in the Western World.
This is largely the result of alcohol abuse, viral hepatitis and biliary
diseases58. The causes for cirrhosis can be roughly divided into six
categories;
1. Chronic exposure to toxins such as alcohol, drugs or chemicals
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2. Viral hepatitis resulting from infection with the Hepatitis B,C
or D viruses
3. Metabolic disorders such as Wilson’s disease (copper storage
disease) and haemochromatosis (iron overload disease)
4. Autoimmune disease such as primary biliary cirrhosis (PBC),
primary selerosing cholangitis (PCS) and autoimmune hepatitis
5. Venous outflow obstruction
6. Cirrhosis of unknown causes
Obviously the best treatment for cirrhosis is removal of the injurious
event. In the case of viral hepatitis, viral load can at least be temporarily
reduced with anti-viral agents such as lamivudine, ribavirin and/or IFNα59.
Unfortunately, complete removal of the injurious event is frequently not
possible. Moreover, by the time cirrhosis is diagnosed the fibrotic process has
usually progressed beyond the point of no return and removal of the
injurious event will have little effect. Successful pharmacological treatment to
reverse the fibrotic process is not yet available. Several drugs have been
tested in clinical trials, by the most effective treatment remains a liver
transplantation.
The bile acid ursodeoxycholic acid has shown some promise in
slowing down the fibrotic process in cholestatic patients, especially those
suffering from PBC and PSC60,61. Its mechanism of action, however, is still a
matter of debate.
Penicillamine, an inhibitor of collagen cross linking, was evaluated in
PBC, but failed to demonstrate any efficacy62. More promising results were
found for colchicine, which inhibits collagen synthesis and secretion and
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enhances collagenase activity. Long-term use of colchicines prolonged
survival in patients with mild to moderate cirrhosis, regardless of the
cause60,63. Other types of collagen synthesis inhibitors like the prolyl
hydroxylase inhibitors have been studied in experimental animal models64,
but have not yet found their way into the clinic.
Several types of immunosuppression have also been tried.
Azathioprine alone was found to have no effect on PBC65, but additional
beneficial effects were found in combination with ursodeoxycholic acid and
corticosteroids61.Cyclosporine showed some success, especially in
corticosteroid-resistant autoimmune hepatitis66, but its use is generally
considerably limited by severe side-effects. Corticosteroids were effective in
the management of several types of autoimmune chronic active hepatitis67,68
and in the management of acute alcoholic hepatitis69. Their use, however,
has to be brief in order to minimize side-effects. In the treatment of PBCs,
corticosteroids alone were found to be toxic and had only limited efficacy60.
A promising new development in drug therapy is the endothelin-
antagonists70,71.Though not yet clinically tested, these compounds show
potential in the management of portal hypertension, a hallmark of cirrhosis.
Again, uptake of these antagonists by other parts of the body hampers their
applicability72, which might be circumvented by drug targeting.
Drug Targeting to the Liver
With no effective drugs available and the unacceptable side-effect
profile of those drugs which have been studied so far, liver cirrhosis might
benefit from the targeting of drugs to cells within the liver. There are several
ways to intervene in the fibrotic process. One way is the targeting of drugs to
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SECs and KCs to modulate their release of pro-inflammatory mediators. This
may arrest the inflammatory process leading to cirrhosis. Another way is the
delivery of drugs to HSCs to inhibit collagen production or to enhance their
extracellular matrix degrading capabilities. Drug targeting to the liver focuses
on targeting to KCs and SECs to influence the inflammatory process that is
the basis of most forms of liver cirrhosis. As mentioned before these cells
have a number of specific entry mechanisms that could be used for cell-
specific delivery of drugs. By either enclosing drugs in particles or by
coupling drugs to macromolecular carriers with high affinity for certain
uptake mechanisms, drugs can be concentrated in the target cells without
causing side-effects else where in the body. The choice for a type of carrier is
determined by a number of considerations, depending on the specificity of
the carrier, the potency of the drug and the entry mechanism during
pathological conditions. The possible carriers directed to KCs and SECs show
a considerable overlap, because these cells share many receptor mediated
endocytotis uptake mechanisms, such as uptake mediated by scavenger
receptors of mannose receptors. Most of the carriers directed to SECs and
KCs are designed for these receptors.
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References
1. Kokate C.K.; Purohit, A.P.; Gokhale, S.B.; “ Pharmacognacy” Nirali prakashan, 1998, pp. 1-4.
2. Kapur, S.K.; Indian Drugs; 50, 1991,210.
3. Naik, S.R.; Eastern Pharmacist, 29:36, 1986, 346. 4. Narauan, D.B.; Eastern pharmacist, 21, 1998,487. 5. Flume, L.; Di Stefano, G.; Busi C.; Mattioli, A.; Bonino, F.; Torrani-
cerenxi; M.; Bertini M.; Gervasi G,B.; J.Viral. hepat. 4, 1997, 363-370.
6. Smith, R.M.; Wu G.Y.; Liver Dis., 19, 1999, 83-92. 7. Meijer, D.K.F.; Molema, G.; Liver Dis., 15, 1995, 202-256. 8. Martinez, I.; Sveinbjornsson, B.; Vidal Vanaclocha, F.; Asumendi, A.;
Smedsr onari, J.; Gorry, F.; Boillot, O. Biochem. Biophys. Res. Commun., 27, 1995.
9. Melkko, J.; Hellevik, T.; Risteli, L.; Risteli, J.; Smedsrod, B.; J. Exp.
Med. 179, 1994, 405-412. 10. Mcgary, C.T.; Yannariello-Brown, J.; Kim, D.W.; Stinson, T.C.; Weigel,
P.H.; Hepatology 18,1993, 1465-1476. 11. Smedsrod, B.; De Bleser, P.J.; Braet, F.; Lovisetti, P.p; Vanderkerken,
K.; Wisse, E.; Geerts, A.; Gut, 35, 1994,1509-1516. 12. Ichida, T.; Sugitani, S.; Satoh, T.; Matsuda, Y.; Sugiyama, M.; Yonekura,
K.; Ishikawa, T.; Asakura, H.; Liver, 16, 1996, 365-371. 13. Smedsrod, B.; Pertoft, H.; Gustafson, S.; Laurent, T.C.; Biochem. J.,
266, 1990, 313-327. 14. Van Oosten, M.; van de Bilt E.; Van Berkel T.J.C.; Kuiper, J.; Infect.
Immun. 66, 1998, 5107-5112. 15. Smedsrod, B.; Melkko, J.; Araki, N.; Sano, H.; Horiuchi, S.; Biochem.
J., 322, 1997, 567-573. 16. Hampton, R.Y.; Golenbock, D.T.; Penman, M.; Krieger, M.; Raetz, C.R.;
Nature, 352, 1991, 342-344. 17. Magnusson, S.; Berg, T.; Biochem. J., 257, 1989, 651-656.
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18. Ezekowitz, R.A.B.; Williams, D.J.; Koziel, H.; Armstrong, M.Y.K.; Warner, A.; Richards, F.F.; Rose, R.M. Nature, 351,1991,155-158.
19. Noorman, F.; Rijken, D.C.; Fibrin. Proteol. , 11, 1997, 173-186. 20. Knolle, P.A.; Uhrig, A.; Hegabnarth, S.; Loser, E.; Schmitt, E.; Gerken,
G.; Lohse, A.W.; Clin. Exp. Immunol., 114, 1998, 427-433. 21. Kanai, M.; Murata, Y.; Mabuchi, Y.; Kawahashi, N.; Tanaka, M.; Ogawa,
T.; Doi M.; Soji, T.; Herbert, D.C.; Anat. Rec., 244,1996, 175-181. 22. Bergman, R.N.; Recent. Prog. Horm. Res., 52, 1997, 359-385. 23. Omoto, E.; Minguell, J.J.; Tavassoli, M.; Pathobiology, 60, 1992, 284-
288. 24. Scoazes, J.Y.; Feldman, G.; Hepatology, 14, 1991, 789-797.
25. Nagano, 1.; Kita, 1.; Tanaka, N.; Int. J. Exp.Pathol., 73,1992, 675-683.
26. Rieder, H.; Meyer zum Btischenfelde K.H.; Ramadori, G.;J. Hepatol.15, 1992,237-250.
27. Knolle, P.A.; Loser, E.; Protzer, U.; Duchmann, R.; Schmitt, E.;
Zumbuschenfelde, K.H.M.; Rosejohn, S.; Gerken, G.; Clin. Exp. Immunol., 107, 1997, 555-561.
28. Ohkubo, K.; Masumoto, 1.; Horiike, N.; Onji, M.; J. Gastroemerol.
Hepatol. 13, 1998, 696-702. 29. Noji, S.; Tashiro, K.; Koyama, E.; Nohno, 1.;, Ohyama, K.; Taniguchi, S.;
Nakamura, 1.; Biochem. Biophys. Res., 173, 1990, 42-47.
30. Hashimoto, N.; Watanabe, 1.; Shiratori, Y.; Ikeda, Y.; Kato, H.; Han, K.; Yamada, H.; Toda, G.; Kurokawa, K.; Hepatology, 21, 1995,1713-1718.
31. Kuiper, J.; Zijlstra, F.; Kamps, J.A.; Van, Berkel, T.J.; Biochem.
Biophys. Acta, 959, 1988, 143-152. 32. Tsujii, H.; Okamoto, Y.; Kikuchi, E.; Matsumoto, M.; Nakano, H.;
astroenterology, 105, 1993, 495-499. 33. Kuiper, J.; De Rijke Y.B.; Zijlstra, F.J.; Van Waas, M.P.; Van Berkel,
T.J.; Biochem. Biophys. Res., 157, 1988, 1288-1295. 34. Van Oosten, M.; van de, Bilt E.; de Vries H.E.; Van Berkel T.J.C.; J,
Hepatology, 22, 1995, 1538-1546. 35. Steinhoff, G.; Behrend, M.; Schrader, B.; Duijvestijn, A.M.; Wonigeit, K.;
Am. J. Pathol., 142, 1993, 481-488.
A search for hepatoprotective agents of natural origin
Department of Chemical Technology, Dr.Babasaheb Ambedkar Marathwada University, Aurangabad
21
36. Lopez, S.; Prats, N.; Marco, A.J.; Am. J. Pathol., 155, 1999, 1391-1397. 37. West, M.A.; Heaney, M.L.; In: Hepatocyte and Kupffer Cell
Interactions (Eds. Billiar TR, Curran RD), CRC Press, London, Tokyo 1992 pp. 209-241.
38. Bioulac Sage, P.; Kuiper, J.; Van Berkel T.J.; Balabaud, C.;
Hepatogastroenterology, 43,1996, 4-14. 39. Toth, C.A.; Thomas, P.; Hepatology, 16, 1992, 255-266. 40. van der Laan, L.J.; Dopp, E.A.; Haworth, R.; Pikkarainen, 1.; Kangas,
M.; Elomaa, 0.; Dijkstra, C.D.; Gordon, S.; Tryggvason, K.; Kraa,l G.; J. Immunology., 162, 1999, 939-947.
41. Fluiter, K.; vanderWesthuijzen, D.R. Vanberkel, T.J.C.; J. Biol. Chem., 273, 1998, 8434-8438.
42. Kamps, J.A.; Kruijt, J.K.; Kuiper, J.; Van Berkel, T.J.; Biochem. J., 276, 1991, 135-140.
43. Sano, A.; Taylor, M.E.; Leaning, M.S.; Summerfield, J.A.; J. Hepatol.,
10, 1990, 211-216.
44. Shimada, K.; Kamps, J.A.A.M.; Regts, J.; Ikeda, K.; Shiozawa, T.; Hirota, S.; Scherphof, G.L.; BBA-Biomembranes, 1326, 1997,329-341.
45. Biessen, E.A.; Bakkeren, H.F.; Beuting, D.M.; Kuiper, J.; Van Berkel
T.J.; Biochem. J., 299, 1994, 291-296. 46. Armbrust, T.; Nordmann, B.; Kreissig, M.; Ramadori, G.; Hepatology,
26, 1997, 98-106. 47. Maruiwa, M.; Mizoguchi, A.; Russell, G.J.; Narula, N.; Stronska, M.;
Mizoguchi, E.; Rabb, H.; Arnaout, M.A.; Blum, A.K. J.Immunol., 150, 1993, 4019-4030.
48. Bouwens, L.; Baekeland, M.; De Zanger, R.B.; Wisse, E.; Hepatology, 6, 1986, 718-722.
49. Coleman, D.L. Eur. J. Clin. Microbiol., 5, 1986,1-5. 50. Gressner A.M.; J. Hepatol., 22, 1995, 28-36. 51. Kanwar, S.; Kubes, P.; New. Horiz., 3, 1995, 93-104. 52. Radziszewski, W.; Chopra, M.; Zembowicz, A.; Gryglewski, R.; Ignarro, L
diol., 51, 1995, 211-220.
A search for hepatoprotective agents of natural origin
Department of Chemical Technology, Dr.Babasaheb Ambedkar Marathwada University, Aurangabad
22
53. Goss, J.A.; Mangino, M.J.; Callery, M.P.; Flye, M.W.; Am. J. Physiol., 264, 1993, 601-608.
54. Goss, J.A.; Mangino, M.J.; Flye, M.W.; J. Surg. Res., 52, 1992, 422-428.
55. Fennekohl, A.; Schieferdecker, H.L.; Jungermann, K.; Puschel, G.P.; J.Hepatol., 30, 1999, 38-47.
56. Callery, M.P.; Mangino, M.J.; Flye, M.W.; Hepatology, 14, 1991, 368-372.
57. Alcolado, R.; Arthur, M.J.P.; lredale, J.P.; Clin. Sci., 92, 1997, 103-112s.
58. Scholmerich, J.; Holstege, A.; Drus., 40 (Suppl. 3) ,1990, 3-22. 59. Hoofnagle, J.H.; Digestion, 59, 1998, 563-578. 60. Kaplan, M.M.; Semiln.Liver. Dis., 17, 1997, 129-136.
61. Wolfhagen, F.H.; van Hoogstraten, H.J.; van Buuren, H.R.; Berge-Henegouwen, G.P.; Ten Kate, F.J.; Hop WC, van der Hoek, E.W.;
Kerbert M.J.; van Lijf, H.H.; den Ouden, J.W.; Smit A.M.; de Vries, R.A.; van Zanten R.A.; Schalm S.W.; J. Hepatol., 29, 1998, 736-742.
62. Messner, M.; Brissot, P.; Drugs, 40 (Suppl. 3), 1990, 45-57.
63. Kershenobich, D.; Vargas, F.; Garcia-Tsao, G.; Perez, T.R.; Gent, M.; Rojkind, N.; N.Engl. J. Med., 318, 1988, 1709-1713.
64. Bickel, M.; Baringhaus, K.H.; Gerl, M.; Gunzler, V.; Kanta, J.; Schmidts, L.; Stapf, M.; Tschank, G.; Weid-mann, K.; Werner, U.; Baringhaus, K.H.; Gunzler, V.; Hepatology, 28, 1998, 404-411.
65. Crowe, J.; Christensen, E.; Smith, M.; Cochrane, M.; Ranek, L.; Watkinsol Tygstrup, N.; Williams, R. Gastroenterology, 78, 1980, 1005-1010.
66. Fernandes, N.F.; Redeker, A.G.; Vierling, J.M.; Villamil, F.G.; Fong,
T.L.; Am. J. Gastroenterol., 94, 1999, 241-248.
67. Chazouilleres, O.; Wendum, D.; Serfaty, L.; Montembault, S.; Rosmorduc, O.; Poupon, R.; Hepatology, 28, 1998, 296-301.
68. Czaja, A.J.; Ann. Intern. Med., 125, 1996, 588-598.
A search for hepatoprotective agents of natural origin
Department of Chemical Technology, Dr.Babasaheb Ambedkar Marathwada University, Aurangabad
23
69. Batey, R.G.; Alcohol Suppl., 2, 1994, 327-333.
70. Kawada, N.; Seki, S.; Kuroki, T.; Kaneda, K.; Biochem. Biophys. Res. Commun., 266, 1999, 296-300.
71. Baveja, R.; Kresge, N.; Bian X.; Yokoyama, Y.; Sonin N.V.; Clemens, M.G.; Zang, J.X.; Hepatology, 30, 1999, 232A.
72. Poo, J.L.; Jimenez, W.; Maria, M.R.; Bosch-Marce. M.; Bordas, N.; Morales-Ruiz, M.; Perez, M.; Deulofeu, R.; Sole, M.; Arroyo, V.; Rodes, J.; Gastroenterology, 116, 1999, 161-167.