medicine Medicine is the science and Praxis (process), practice of caring for a patient, managing the diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment, Palliative care, palliation of their injury or disease, and Health promotion ...

, glycoprotein IIb/IIIa (GPIIb/IIIa, also known as integrin α_IIbβ₃) is an

integrin Integrins are transmembrane receptors that facilitate cell-cell and cell-extracellular matrix (ECM) adhesion. Upon ligand binding, integrins activate signal transduction pathways that mediate cellular signals such as regulation of the cell cycle, ...

complex found on

platelet Platelets, also called thrombocytes (from Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby i ...

s. It is a receptor for

fibrinogen Fibrinogen (factor I) is a glycoprotein complex, produced in the liver, that circulates in the blood of all vertebrates. During tissue and vascular injury, it is converted enzymatically by thrombin to fibrin and then to a fibrin-based blood ...

and

von Willebrand factor Von Willebrand factor (VWF) () is a blood glycoprotein involved in hemostasis, specifically, platelet adhesion. It is deficient and/or defective in von Willebrand disease and is involved in many other diseases, including thrombotic thrombocytop ...

and aids platelet activation. The complex is formed via calcium-dependent association of gpIIb and gpIIIa, a required step in normal platelet aggregation and endothelial adherence. Platelet activation by

ADP Adp or ADP may refer to: Aviation * Aéroports de Paris, airport authority for the Parisian region in France * Aeropuertos del Perú, airport operator for airports in northern Peru * SLAF Anuradhapura, an airport in Sri Lanka * Ampara Air ...

(blocked by

clopidogrel Clopidogrel — sold under the brand name Plavix, among others — is an antiplatelet medication used to reduce the risk of heart disease and stroke in those at high risk. It is also used together with aspirin in heart attacks and following ...

) leads to the aforementioned conformational change in platelet gpIIb/IIIa receptors that induces binding to fibrinogen. The gpIIb/IIIa receptor is a target of several drugs including

abciximab Abciximab, a glycoprotein IIb/IIIa receptor antagonist manufactured by Janssen Biologics BV and distributed by Eli Lilly under the trade name ReoPro, is a platelet aggregation inhibitor mainly used during and after coronary artery procedures li ...

, eptifibatide, and

tirofiban Tirofiban, sold under the brand name Aggrastat, is an antiplatelet medication. It belongs to a class of antiplatelets named glycoprotein IIb/IIIa inhibitors. Tirofiban is a small molecule inhibitor of the protein-protein interaction between fibr ...

gpIIb/IIIa complex formation

Once platelets are activated, granules secrete clotting mediators, including both

and

TXA2 Thromboxane A2 (TXA2) is a type of thromboxane that is produced by activated platelets during hemostasis and has prothrombotic properties: it stimulates activation of new platelets as well as increases platelet aggregation. This is achieved by a ...

. These then bind their respective receptors on platelet surfaces, in both an

autocrine Autocrine signaling is a form of cell signaling in which a cell secretes a hormone or chemical messenger (called the autocrine agent) that binds to autocrine receptors on that same cell, leading to changes in the cell. This can be contrasted with p ...

and

paracrine Paracrine signaling is a form of cell signaling, a type of cellular communication in which a cell produces a signal to induce changes in nearby cells, altering the behaviour of those cells. Signaling molecules known as paracrine factors diffuse ove ...

fashion (binds both itself and other platelets). The binding of these receptors result in a cascade of events resulting in an increase in intracellular calcium (e.g. via G_q receptor activation leading to Ca²⁺ release from platelet endoplasmic reticulum Ca²⁺ stores, which may activate PKC). Hence, this calcium increase triggers the calcium-dependent association of gpIIb and gpIIIa to form the activated membrane receptor complex gpIIb/IIIa, which is capable of binding fibrinogen (factor I), resulting in many platelets "sticking together" as they may connect to the same strands of fibrinogen, resulting in a clot. The

coagulation Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanis ...

cascade then follows to stabilize the clot, as

thrombin Thrombin (, ''fibrinogenase'', ''thrombase'', ''thrombofort'', ''topical'', ''thrombin-C'', ''tropostasin'', ''activated blood-coagulation factor II'', ''blood-coagulation factor IIa'', ''factor IIa'', ''E thrombin'', ''beta-thrombin'', ''gamma- ...

(factor IIa) converts the soluble fibrinogen into insoluble fibrin strands. These strands are then cross-linked by factor XIII to form a stabilized blood clot.

Pathology

Defects in glycoprotein IIb/IIIa cause Glanzmann's thrombasthenia. Autoantibodies against IIb/IIIa can be produced in

immune thrombocytopenic purpura Immune thrombocytopenic purpura (ITP), also known as idiopathic thrombocytopenic purpura or immune thrombocytopenia, is a type of thrombocytopenic purpura defined as an isolated low platelet count with a normal bone marrow in the absence of othe ...

Medicine

Glycoprotein IIb/IIIa inhibitors In medicine, glycoprotein IIb/IIIa inhibitors, also GpIIb/IIIa inhibitors, is a class of antiplatelet agents. Several GpIIb/IIIa inhibitors exist: * abciximab (abcixifiban) (ReoPro) * eptifibatide (Integrilin) * tirofiban (Aggrastat) * roxifi ...

can be used to prevent blood clots in an effort to decrease the risk of

heart attack A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which m ...

or stroke.

References

External links

* Integrins {{gene-17-stub

gpIIb/IIIa complex formation

Pathology

Medicine

See also

References

External links