Current Drug Targets - Cardiovascular & Haematological Disorders, Volume 4, Number 4, 2004
Contents
Exogenous Factors Affecting Cardiovascular and Hematological Targets
Guest
Editor: R. Manjunatha Kini
Platelet Aggregation and
Exogenous Factors From Animal Sources Pp.301-325
R. Manjunatha Kini
Disintegrins Pp.327-355
Mary Ann McLane, Elda E. Sanchez, Alice Wong,
Carrie Paquette-Straub and John C. Perez
C-type Lectin-related
Proteins from Snake Venoms Pp.357-373
Takashi Morita
Antihemostatic Strategies of
Blood-Feeding Arthropods Pp.375-396
Donald E. Champagne
Snake Venom Prothrombin
Activators Similar to Blood Coagulation Factor Xa Pp.397-416
Jeremiah S. Joseph and R. Manjunatha Kini
a−Fibrinogenases Pp.417-435
S. Swenson, C.F. Toombs, L. Pena, J.
Johansson and F.S. Markland Jr.
Hypotensive Agents from
Snake Venoms Pp.437-459
Roy Joseph, Susanta Pahari, Wayne C. Hodgson
and R. Manjunatha Kini
Abstracts
[Back to top] Platelet Aggregation and Exogenous
Factors From Animal Sources
R. Manjunatha Kini
Platelet aggregation plays a crucial role in thrombosis. This review
describes exogenous factors isolated from various animal sources, including
venoms and the salivary glands that interfere in platelet aggregation. Some of these
factors induce platelet aggregation or agglutination, whereas others inhibit
platelet aggregation. These proteins range from small molecular weight peptides
to large proteins. Some of these proteins exhibit various enzymatic activities,
while others are nonenzymatic. These exogenous factors affect platelet
aggregation by various mechanisms and thus they have been classified based on
their mechanism of action. Many of these proteins have evolved through both
convergent and divergent evolution. For example, platelet aggregation
inhibitors, which interfere in the interactions between fibrinogen and its
receptor, the glycoprotein IIb/IIIa complex, show extreme structural diversity
but they share the common functional site of Arg-Gly-Asp (RGD) tripeptide segment.
On the other hand, C-type lectin related proteins exhibit diverse biological
effects by interacting with different proteins, but share common structural
scaffold. Thus the mechanistic and structure-function studies of these
exogenous proteins have contributed significantly to the understanding of
molecular mechanisms of platelet aggregation and to the development of potent
antiplatelet agents, respectively. A number of new exogenous factors have been
identified recently and the search is still on for novel factors that interfere
with platelet aggregation. Further studies in this area will help in the
development of novel strategies for treating cardiovascular and hematological
disorders.
[Back to top]
Disintegrins
Mary Ann McLane, Elda E. Sanchez, Alice Wong,
Carrie Paquette-Straub and John C. Perez
The existence of disintegrins, non-enzymatic, small molecular weight
proteins from viper venom, has been known for 2 decades, and their impact on
cellular research has been substantial and far-reaching. Disintegrins have been
the molecular scaffold used in the design of therapeutics for the prevention of
thrombosis and cancer. Their sequencing has provided insights into the evolution
of proteins over millennia. Production of recombinant disintegrin mutants and
fusion proteins has allowed investigations into molecular mechanisms at work in
cell-extracellular matrix interactions. Structural homologies with non-snake
proteins have shown disintegrin-like molecules in species ranging from slime
mold to humans. Intracellular signaling events have been elucidated through the
use of venom disintegrins, including events related to programmed cell death,
motility, cell proliferation and viral pathogenesis. Disintegrin sequences
(protein or genes) have been placed in microbubbles and liposomes and been
found to target neovascular endothelium and metastatic tumors in two mouse
models. The purpose of this review is to highlight the members of this disintegrin
family discovered since 1998 as well as the increased understanding of their
usefulness in therapeutics and technical assays.
[Back to top]
C-type Lectin-related Proteins from Snake Venoms
Takashi Morita
C-type lectin-like proteins (CLPs) of snake venom have a variety of
biological properties, acting for example as anticoagulants, procoagulants, and
agonists/antagonists of platelet activation. The structural and functional studies
of the first identified CLP, factor IX/factor X-binding protein, have led to an
understanding how new functionally heterodimeric CLPs from monomeric C-type
lectin related proteins may have evolved by 3D domain swapping, and have
contributed to our understanding of the significance of magnesium ions in the
blood coagulation cascade reaction. Two metallo-proteases, carinactivase and
RVV-X (factor X activator of a snake venom), with C-type lectin-like domains,
were isolated, characterized, and found to be useful in the study of the
properties of prothrombin and coagulation factor X. There are also several
unique CLPs belong to agonists and antagonists of platelet receptors, platelet
glycoprotein Ib and glycoproteins Ia/IIa and VI, collagen receptors and the
following CLPs that modulate platelet function. These CLPs may provide the new
insights into platelet function: alboaggregin-B, echicetin, botrocetin,
bitiscetin, flavocetin-A, aggretin/rhodocytin, convulxin, and agkistin.
[Back to top]
Antihemostatic
Strategies of Blood-Feeding Arthropods
Donald E. Champagne
Arthropods in at least 23 different families or orders, distributed
between two classes (Insecta and Arachnida), feed on vertebrate blood. They are
able to do this despite constraints imposed by a sophisticated array of
hemostatic defenses, due to the presence of a wide range of antihemostatic
molecules in their saliva, including vasodilators, antiplatelet factors, and
anticoagulants. Vasodilators include amines, prostaglandins, peptides,
proteins, and even a mechanism to store large amounts of nitric oxide and
deliver it into the skin. Platelet aggregation inhibitors include nitric oxide,
prostaglandins, apyrase, molecules that sequester ADP, and a range of peptides
and proteins that interact specifically with integrin receptors. Anticoagulants
include a wide variety of inhibitors that target thrombin and factor Xa, as
well as proteins that disrupt the "tenase", prothrombinase, and
tissue factor/FVIIa complexes. The potential complexity of saliva is
illustrated with the example of Rhodnius prolixus, which contains a
large array of compounds, many of which affect more than one target in the
hemostatic process. Finally a brief discussion of a new approach (sialomics) to
the discovery of pharmacological agents in arthropod saliva is presented.
[Back to top] Snake
Venom Prothrombin Activators Similar to Blood Coagulation Factor Xa
Jeremiah S. Joseph and R. Manjunatha Kini
Activation of prothrombin to mature thrombin in vivo occurs by
the proteolytic action of the prothrombinase complex consisting of serine
proteinase factor Xa, and cofactors that include factor Va, Ca2+
ions and phospholipids. Several exogenous prothrombin activators are found in
snake venom. Among these, Group C prothrombin activators resemble the factor
Xa-factor Va complex, while Group D activators are structurally and
functionally similar to factor Xa. This review provides a detailed description
of current knowledge on Group D prothrombin activators and highlights the
importance of studying this family of proteins in enhancing our understanding
of structure-function relationships in the mammalian prothrombinase complex.
[Back to top] a−Fibrinogenases
S. Swenson, C.F. Toombs, L. Pena, J. Johansson and F.S. Markland Jr.
Snake venoms contain a number of serine and metalloproteinases, included
among these are the fibrinolytic metalloproteinases. When the fibrinolytic
enzymes were first isolated from viper venoms it was postulated that there may
be a clinical application for these enzymes in the treatment of occlusive
thrombi, such as those occurring in the great arteries and veins of cardiac and
cerebral circulation as well as peripheral arteries and veins. In the ensuing
years a substantial body of literature has been generated on the identification
and characterization of the fibrinolytic enzymes from a broad spectrum of snake
species. In this report we describe the biological properties and positive
clinical features of the class of enzymes known as a-fibrinogenases.
Fibrolase, a fibrinolytic metalloproteinase originally isolated from Agkistrodon
contortrix contortrix venom, is the representative fibrinolytic enzyme used
for the description and characterization of the a-fibrinogenases
in this chapter. The biochemical and physiochemical properties and in vivo
activity of the enzyme aredescribed as well as in vitro studies using a
platelet avid chimera of fibrolase. The chimera was formed by coupling
fibrolase to an Arg-Gly-Asp (RGD) like peptide imparting inhibitory activity on
platelet aggregation and thrombus formation, while maintaining full
fibrinolytic activity. Fibrolase has also been modified through the adduction
of polyethylene glycol to reduce the rate of clearance from the circulation.
In this review we also include a description of alfimeprase, a
recombinant fibrinolytic enzyme derived from fibrolase, and follow the
development of the enzyme as a potential clinical agent in the clearance of
occlusive thrombi. Alfimeprase is presently in clinical trials for two indications:
the treatment of peripheral arterial occlusions (in which phase II is nearing
successful completion), and for use in the clearance of occluded vascular
access catheters in direct competition with plasminogen activators.
[Back to top] Hypotensive Agents from
Snake Venoms
Roy Joseph, Susanta Pahari, Wayne C. Hodgson
and R. Manjunatha Kini
Many snake venoms contain toxins which produce profound cardiovascular effects.
The site of action of these toxins includes cardiac muscle, vascular smooth
muscle and the capillary vascular bed. Some snake venoms, for example, contain
peptides that inhibit angiotensin converting enzyme and potentiate the
biological actions of bradykinin. Other snake venoms contain structural and
functional equivalents of mammalian natriuretic peptides. Sarafotoxins are
short peptide toxins found in the venoms of snakes from Atractaspis spp.
which display potent vasoconstriction properties. These peptides, which share a
high degree of sequence identity with endothelins, recognize and bind to
endothelin receptors. Snakes have also evolved toxins which block L-type Ca2+
currents (eg. calciseptine, FS2 toxins, C10S2C2
and S4C8). Snake venom proteins have also been shown to
increase vascular permeability. One such protein, increasing capillary
permeability protein (ICPP) has recently been isolated from the venom of Vipera
lebetina. ICPP is an extremely potent permeability factor with a structure
similar to vascular endothelial growth factor (VEGF). Thus there is a vast
array of snake toxins with potent cardiovascular activity. Some of these
proteins and peptides have proven to be highly selective tools in the study of
physiological processes. Others have been used as probes of potential
therapeutic targets or as lead compounds in the development of therapeutic
agents. Therefore these and other related snake venom proteins hold great
promise in the future understanding and treatment of cardiovascular diseases.