Blood-vessel-on-a-chip technology has revealed anti-inflammatory and anti-thrombotic for “parmodulins.”
The inflammatory response of the human body is essential for fighting diseases and repairing injuries, but it can also lead to serious health problems such as the formation of blood clots due to overproduction of the coagulant protein thrombin. The current treatment in these cases involves administration of activated protein C (APC), a naturally occurring anticoagulant protein with anti-inflammatory and other protective effects, but this approach is used selectively because it can over-inhibit thrombin and thus prevent normal blood coagulation and clotting.
Researchers at Harvard University’s Wyss Institute and the Division of Hemostasis and Thrombosis at Beth Israel Deaconess Medical Center (BIDMC) have found a potential, promising solution – “parmodulins”, synthetic APC-mimicking small molecules that provide anti-inflammatory and anti-thrombotic protection to endothelial cells similar to APC’s but without preventing normal blood clotting and coagulation. This information was obtained using Wyss Institute’s Organ-on-a-Chip technology to model thrombosis within a human blood vessel in vitro.
The activity of the parmodulins on endothelium was first evaluated by incubating human endothelial cells with parmodulin 2 in vitro for 4 hours and then exposing them to lipopolysaccharide (LPS) or tumor necrosis factor-α (TNF-α), two thrombin-inducing inflammatory agents. In the cells exposed to parmodulin 2, generation of thrombin was reduced by over 50% compared to non-treated cells and the activity of proteins involved in blood coagulation (factor V or factor X) were not inhibited.
Endothelial cells were chosen for this first study because APC and parmodulins affect the activity of protease-activated receptor 1 (PAR1), a transmembrane protein present on both endothelial cells and platelets that circulate through the blood and promote clotting. PAR1 is a receptor for thrombin, but when it is activated by APC on endothelial cells, anti-inflammatory, anti-apoptotic, and barrier-fortifying pathways that protect cells from the negative effects of inflammation are triggered.
APC, however, also inhibits the generation of thrombin, which, if excessive, can lead to uncontrolled bleeding. The goal of the research was to use parmodulins to activate endothelial PAR1 without over-reducing thrombotic responses.
The initial results suggested that this goal was possible. As a next step, the researchers used Wyss-developed blood-vessel-on-a-chip technology. In the chip, parallel microfluidic channels are embedded in a clear polymer. They are coated with collagen and lined with human endothelial cells. Whole blood is perfused through the channels to mimic blood flow within human blood vessels. In the study, different pro- and anti-inflammatory compounds were added to the whole blood and the response of the endothelium evaluated.
Endothelial cells exposed to parmodulin 2 and then TNF-α experienced inhibited platelet accumulation followed by resumption of normal endothelium function, suggesting that parmodulin exposure blocks the thrombotic response of endothelium to inflammatory stimuli without affecting blood coagulation in humans.
Other in vitro tests performed by the researchers confirmed that parmodulin 2’s activation of PAR1 also induces cytoprotective responses in endothelial cells by inhibiting apoptosis (programmed cell death) induced by thrombin, TNF-α, and the apoptotic alkaloid staurosporine. In vivo studies in mice also showed that parmodulin 2 reduces the binding of white blood cells to blood vessels and impairs platelet and fibrin accumulation at injury sites during the inflammatory response. In addition, parmodulin 2 did not interact with many of APC’s other binding partners, and thus it should be a more targeted treatment with reduced side effects.
“The discovery of an anti-inflammatory molecule that prevents endothelial thrombosis but also preserves normal blood coagulation is a major step toward an alternative and better approach to treating inflammatory disease,” says Rob Flaumenhaft, M.D., Ph.D., and Professor of Medicine at Harvard Medical School and Chief of the Division of Hemostasis and Thrombosis at BIDMC. “Furthermore, nearly all other pharmaceuticals that target transmembrane PAR1-like receptors bind to the exterior side of the receptor; parmodulin 2 represents a paradigm shift for compounds targeting these receptors because it acts on the cellular side of the protein. We are excited to see if we can advance it to clinical trials.”
