Immobilization of the irreversible thrombin inhibitor D-Phe-Pro-Arg-chloromethylketone: a concept for hemocompatible surfaces?

Steps Toward Recapitulating Endothelium: A Perspective on the Next Generation of Hemocompatible Coatings

Endothelium, the lining in this blood vessel, orchestrates three main critical functions such as protecting blood components, modulating of hemostasis by secreting various inhibitors, and directing clot digestion (fibrinolysis) by activating tissue plasminogen activator. No other surface can perform these tasks; thus, the contact of blood and blood-contacting medical devices inevitably leads to the activation of coagulation, often causing device failure, and thromboembolic complications. This perspective, first, discusses the biological mechanisms of activation of coagulation and highlights the efforts of advanced coatings to recapitulate one characteristic of endothelium, hereafter single functions of endothelium and noting necessity of the synergistic integration of its three main functions. Subsequently, it is emphasized that to overcome the challenges of blood compatibility an endothelium-mimicking system is needed, proposing a synergy of bottom-up synthetic biology, particularly synthetic cells, with passive- and bioactive surface coatings. Such integration holds promise for developing advanced biomaterials capable of recapitulating endothelial functions, thereby enhancing the hemocompatibility and performance of blood-contacting medical devices.

TMPRSS2 inhibitor discovery facilitated through an in silico and biochemical screening platform

The COVID-19 pandemic has highlighted the need for new antiviral targets, as many of the currently approved drugs have proven ineffective against mitigating SARS-CoV-2 infections. The host transmembrane serine protease TMPRSS2 is a highly promising antiviral target, as it plays a direct role in priming the spike protein before viral entry occurs. Further, unlike other targets such as ACE2, TMPRSS2 has no known biological role. Here we utilize virtual screening to curate large libraries into a focused collection of potential inhibitors. Optimization of a recombinant expression and purification protocol for the TMPRSS2 peptidase domain facilitates subsequent biochemical screening and characterization of selected compounds from the curated collection in a kinetic assay. In doing so, we demonstrate that serine protease inhibitors camostat, nafamostat, and gabexate inhibit through a covalent mechanism. We further identify new non-covalent compounds as TMPRSS2 protease inhibitors, demonstrating the utility of a combined virtual and experimental screening campaign in rapid drug discovery efforts.

Improving Hemocompatibility: How Can Smart Surfaces Direct Blood To Fight against Thrombi

Nature utilizes endothelium as a blood interface that perfectly controls hemostasis, preventing the uncontrolled formation of thrombi. The management of positive and negative feedback that finely tunes thrombosis and fibrinolysis is essential for human life, especially for patients who undergo extracorporeal circulation (ECC) after a severe respiratory or cardiac failure. The exposure of blood to a surface different from healthy endothelium inevitably initiates coagulation, drastically increasing the mortality rate by thromboembolic complications. In the present study, an ultrathin antifouling fibrinolytic coating capable of disintegrating thrombi in a self-regulated manner is reported. The coating system is composed of a polymer brush layer that can prevent any unspecific interaction with blood. The brushes are functionalized with a tissue plasminogen activator (tPA) to establish localized fibrinolysis that solely and exclusively is active when it is required. This interactive switching between the dormant and active state is realized through an amplification mechanism that increases (positive feedback) or restores (negative feedback) the activity of tPA depending on whether a thrombus is detected and captured or not. Thus, only a low surface density of tPA is necessary to lyse real thrombi. Our work demonstrates the first report of a coating that self-regulates its fibrinolytic activity depending on the conditions of blood.

The use of CD47-modified biomaterials to mitigate the immune response

Addressing the aberrant interactions between immune cells and biomaterials represents an unmet need in biomaterial research. Although progress has been made in the development of bioinert coatings, identifying and targeting relevant cellular and molecular pathways can provide additional therapeutic strategies to address this major healthcare concern. To that end, we describe the immune inhibitory motif, receptor-ligand pairing of signal regulatory protein alpha and its cognate ligand CD47 as a potential signaling pathway to enhance biocompatibility. The goals of this article are to detail the known roles of CD47-signal regulatory protein alpha signal transduction pathway and to describe how immobilized CD47 can be used to mitigate the immune response to biomaterials. Current applications of CD47-modified biomaterials will also be discussed herein.

Antithrombin nanoparticles improve kidney reperfusion and protect kidney function after ischemia-reperfusion injury

In the extension phase of acute kidney injury, microvascular thrombosis, inflammation, vasoconstriction, and vascular endothelial cell dysfunction promote progressive damage to renal parenchyma after reperfusion. In this study, we hypothesized that direct targeting and pharmaceutical knockdown of activated thrombin at the sites of injury with a selective nanoparticle (NP)-based thrombin inhibitor, PPACK (phenylalanine-proline-arginine-chloromethylketone), would improve kidney reperfusion and protect renal function after transient warm ischemia in rodent models. Saline- or plain NP-treated animals were employed as controls. In vivo 19F magnetic resonance imaging revealed that kidney nonreperfusion was evident within 3 h after global kidney reperfusion at 34 ± 13% area in the saline group and 43 ± 12% area in the plain NP group and substantially reduced to 17 ± 4% (∼50% decrease, P < 0.05) in the PPACK NP pretreatment group. PPACK NP pretreatment prevented an increase in serum creatinine concentration within 24 h after ischemia-reperfusion, reflecting preserved renal function. Histologic analysis illustrated substantially reduced intrarenal thrombin accumulation within 24 h after reperfusion for PPACK NP-treated kidneys (0.11% ± 0.06%) compared with saline-treated kidneys (0.58 ± 0.37%). These results suggest a direct role for thrombin in the pathophysiology of AKI and a nanomedicine-based preventative strategy for improving kidney reperfusion after transient warm ischemia.

Hemocompatibility of Chitosan/poly(acrylic acid) Grafted Polyurethane Tubing

The activation and adhesion of platelets or whole blood exposed to chitosan (CH) grafted surfaces is used to evaluate the hemocompatibility of biomaterials. The biomaterial surfaces are polyurethane (PU) tubes grafted with an inner poly(acrylic acid) (PAA) and an outer CH or quaternary ammonium modified CH (CH-Q) brush. The CH, CH-Q and PAA grafted layers were characterized by ellipsometry and fluorescence microscopy. Material wear tests demonstrate that CH (CH-Q) is stably grafted onto PU tubes upon exposure to saline solution for 7 days. Using quartz-crystal microbalances with dissipation (QCM-D), in-situ adsorption of blood plasma proteins on CH and CH-Q compared to a silicon oxide control was measured. The QCM-D results showed that the physically adsorbed plasma protein layer on CH-Q and CH surfaces is softer and more viscous than the protein layer on the SiO2 surface. The CH-Q layer thus has the weakest interaction with plasma proteins. Whole blood and platelet adhesion was reduced by ~92% on CH-Q, which showed the weakest interaction with plasma protein but more viscous adsorbed plasma protein layer, compared to SiO2. Last, to examine the biologic response of platelets and neutrophils to biomaterial surfaces, CH (CH-Q)/PAA, PAA and PU tubes were tested using a Chandler Loop apparatus as an ex vivo model and flow cytometry. The blood adhesion and biologic response results showed that CH and CH-Q reduced adhesion and activation of platelets and neutrophils and improved hemocompatibility relative to other surfaces (PU and PAA). Our studies demonstrated that the properties of physically adsorbed plasma protein layer on biomaterial surfaces correlates with blood coagulation on biomaterial surfaces.

Diminished adhesion and activation of platelets and neutrophils with CD47 functionalized blood contacting surfaces

CD47 is a ubiquitously expressed transmembrane protein that, through signaling mechanisms mediated by signal regulatory protein alpha (SIRPα1), functions as a biological marker of 'self-recognition'. We showed previously that inflammatory cell attachment to polymeric surfaces is inhibited by the attachment of biotinylated recombinant CD47 (CD47B). We test herein the hypothesis that CD47 modified blood conduits can reduce platelet and neutrophil activation under clinically relevant conditions. We appended a poly-lysine tag to the C-terminus of recombinant CD47 (CD47L) allowing for covalent linkage to the polymer. SIRPα1 expression was confirmed in isolated platelets. We then compared biocompatibility between CD47B and CD47L functionalized polyvinyl chloride (PVC) surfaces and unmodified control PVC surfaces. Quantitative and Qualitative analysis of blood cell attachment to CD47B and CD47L surfaces, via scanning electron microscopy, showed strikingly fewer platelets attached to CD47 modified surfaces compared to control. Flow cytometry analysis showed that activation markers for neutrophils (CD62L) and platelets (CD62P) exposed to CD47 modified PVC were equivalent to freshly acquired control blood, while significantly elevated in the unmodified PVC tubing. In addition, ethylene oxide gas sterilization did not inhibit the efficacy of the CD47 modification. In conclusion, CD47 modified PVC inhibits both the adhesion and activation of platelets and neutrophils.