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In the last few decades, a substantial body of evidence underlined the pivotal role of bradykinin in certain types of angioedema. The formation and breakdown of bradykinin has been studied thoroughly; however, numerous questions remained open regarding the triggering, course, and termination of angioedema attacks. Recently, it became clear that vascular endothelial cells have an integrative role in the regulation of vessel permeability. Apart from bradykinin, a great number of factors of different origin, structure, and mechanism of action are capable of modifying the integrity of vascular endothelium, and thus, may participate in the regulation of angioedema formation. Our aim in this review is to describe the most important permeability factors and the molecular mechanisms how they act on endothelial cells. Based on endothelial cell function, we also attempt to explain some of the challenging findings regarding bradykinin-mediated angioedema, where the function of bradykinin itself cannot account for the pathophysiology. By deciphering the complex scenario of vascular permeability regulation and edema formation, we may gain better scientific tools to be able to predict and treat not only bradykinin-mediated but other types of angioedema as well.

Most therapeutic agents used for treating brain malignancies face hindered transport through the blood-brain barrier (BBB) and poor tissue penetration. To overcome these problems, we developed peptide conjugates of conventional and experimental anticancer agents. SynB3 cell-penetrating peptide derivatives were applied that can cross the BBB. Tuftsin derivatives were used to target the neuropilin-1 transport system for selectivity and better tumor penetration. Moreover, SynB3-tuftsin tandem compounds were synthesized to combine the beneficial properties of these peptides. Most of the conjugates showed high and selective efficacy against glioblastoma cells. SynB3 and tandem derivatives demonstrated superior cellular internalization. The penetration profile of the conjugates was determined on a lipid monolayer and Transwell co-culture system with noncontact HUVEC-U87 monolayers as simple ex vivo and in vitro BBB models. Importantly, in 3D spheroids, daunomycin-peptide conjugates possessed a better tumor penetration ability than daunomycin. These conjugates are promising tools for the delivery systems with tunable features.

Tissue-on-a-chip technologies are more and more important in the investigation of cellular function and in the development of novel drugs by allowing the direct screening of substances on human cells. Constituting the inner lining of vessel walls, endothelial cells are the key players in various physiological processes, moreover, they are the first to be exposed to most drugs currently used. However, to date, there is still no appropriate technology for the label-free, real-time and high-throughput monitoring of endothelial function. To this end, we developed an optical biosensor-based endothelial label-free biochip (EnLaB) assay that meets all the above requirements. Using our EnLaB platform, we screened a set of plasma serine proteases as possible endothelial cell activators, and first identified the endothelial cell activating function of three important serine proteases – namely kallikrein, C1r and mannan-binding lectin-associated serine-protease 2 (MASP-2) – and verified these results in well-established functional assays. EnLaB proved to be an effective tool for revealing novel cellular mechanisms as well as for the high-throughput screening of various compounds on endothelial cells.

Mannan-binding lectin-associated serine protease 1 (MASP-1), the most abundant enzyme of the complement lectin pathway, is able to stimulate human umbilical vein endothelial cells (HUVECs) to alter the expression of several cytokines and adhesion molecules. This study has assessed to what extent MASP-1 is able to modify the transcriptional pattern of inflammation-related (IR) genes in HUVECs. We utilized Agilent microarray to analyse the effects of recombinant MASP-1 (rMASP-1) in HUVECs, on a set of 884 IR genes. Gene Set Enrichment Analysis showed an overall activation of inflammation-related genes in response to rMASP-1. rMASP-1 treatment up- and down-regulated 19 and 11 IR genes, respectively. Most of them were previously unidentified, such as genes of chemokines (CXCL1, CXCL2, CXCL3), inflammatory receptors (TLR2, BDKRB2) and other inflammatory factors (F3, LBP). Expression of IR genes changed early, during the first 2 hours of activation. Both p38-MAPK inhibitor and NFκB inhibitor efficiently suppressed the effect of rMASP-1. We delineated 12 transcriptional factors as possible regulators of rMASP-1-induced IR genes. Our microarray-based data are in line with the hypothesis that complement lectin pathway activation, generating active MASP-1, directly regulates inflammatory processes by shifting the phenotype of endothelial cells towards a more pro-inflammatory type.

The complement system and neutrophil granulocytes are indispensable in the immune response against extracellular pathogens such as bacteria and fungi. Endothelial cells also participate in antimicrobial immunity largely by regulating the homing of leukocytes through their cytokine production and their pattern of cell surface adhesion molecules. We have previously shown that mannan-binding lectin-associated serine protease-1 (MASP-1), a complement lectin pathway enzyme, is able to activate endothelial cells by cleaving protease activated receptors, which leads to cytokine production and enables neutrophil chemotaxis. Therefore, we aimed to investigate how recombinant MASP-1 (rMASP-1) can modify the pattern of P-selectin, E-selectin, ICAM-1, ICAM-2, and VCAM-1 adhesion molecules in human umbilical vein endothelial cells (HUVEC), and whether these changes can enhance the adherence between endothelial cells and neutrophil granulocyte model cells (differentiated PLB-985). We found that HUVECs activated by rMASP-1 decreased the expression of ICAM-2 and increased that of E-selectin, whereas ICAM-1, VCAM-1 and P-selectin expression remained unchanged. Furthermore, these changes resulted in increased adherence between differentiated PLB-985 cells and endothelial cells. Our finding suggests that complement MASP-1 can increase adhesion between neutrophils and endothelial cells in a direct fashion. This is in agreement with our previous finding that MASP-1 increases the production of pro-inflammatory cytokines (such as IL-6 and IL-8) and chemotaxis, and may thereby boost neutrophil functions. This newly described cooperation between complement lectin pathway and neutrophils via endothelial cells may be an effective tool to enhance the antimicrobial immune response.

Hereditary angioedema (HAE) with C1-inhibitor deficiency (C1-INH-HAE) is a rare bradykinin-mediated disease characterized by recurrent subcutaneous and/or submucosal angioedematous attacks (HAE attacks), which occur unpredictably. The recurrent HAE attacks do not respond to conventional treatments, and may evolve into a life-threatening condition; therefore, special therapy is required.The agents used so far for the acute management of HAE attacks act by blocking the release of bradykinin, or its binding to its receptor. By contrast, the investigational medicinal products under evaluation in Phase I and II clinical trials are targeted at the prevention of HAE attacks. Chemically, these new drugs are small synthetic molecules, oligonucleotides, or antibodies, which inhibit either kallikrein, or Factor XII.The key considerations for the development of new medicinal products include more straightforward dosing, self-administration, longer duration of action, and keeping the patient attack-free. This review summarizes the status and the findings of the currently ongoing Phase I and Phase II clinical trials of C1-INH-HAE.