The protein disulphide isomerase inhibitor CxxCpep modulates oxidative burst and mitochondrial function in platelets

MITOCDNB DECREASES PLATELET ACTIVATION THROUGH ITS SELECTIVE ACTION ON MITOCHONDRIAL THIOREDOXIN REDUCTASE

Platelet inhibition is a fundamental objective to prevent and treat thrombus formation. Platelet activation depends on mitochondrial function. This study aims to identify a new mitochondria-targeting compound with antiplatelet activity at safe concentrations in vitro. Cytotoxicity and viability tests were performed on human platelets from volunteer donors, together with experiments on aggregation, platelet activation, mitochondrial function, mitochondrial respiration, and thioredoxin reductase 2 (TrxR2) enzymatic activity in isolated platelet mitochondria. The compound MitoCDNB, corresponding to the molecule 5-chloro-2,4-dinitrophenylamino linked with triphenylphosphonium cation (TPP+) by a butyl chain and methanesulfonate as the counterion, was evaluated. MitoCDNB demonstrates potent, high mitochondria-selective antiplatelet effects that provide a novel approach to platelet inhibition with potentially minimized systemic risks. Here, we describe the first compound that inhibits platelet activation by decreasing TrxR2 enzymatic activity and collagen-stimulated maximal mitochondrial respiration, preventing aggregation and platelet activation. These results can be used to develop new antiplatelet drugs targeting mitochondria.

Linking triphenylphosphonium cation to a bicyclic hydroquinone improves their antiplatelet effect via the regulation of mitochondrial function

Platelets are the critical target for preventing and treating pathological thrombus formation. However, despite current antiplatelet therapy, cardiovascular mortality remains high, and cardiovascular events continue in prescribed patients. In this study, first results were obtained with ortho-carbonyl hydroquinones as antiplatelet agents; we found that linking triphenylphosphonium cation to a bicyclic ortho-carbonyl hydroquinone moiety by a short alkyl chain significantly improved their antiplatelet effect by affecting the mitochondrial functioning. The mechanism of action involves uncoupling OXPHOS, which leads to an increase in mitochondrial ROS production and a decrease in the mitochondrial membrane potential and OCR. This alteration disrupts the energy production by mitochondrial function necessary for the platelet activation process. These effects are responsive to the complete structure of the compounds and not to isolated parts of the compounds tested. The results obtained in this research can be used as the basis for developing new antiplatelet agents that target mitochondria.

An Overview of Two Old Friends Associated with Platelet Redox Signaling, the Protein Disulfide Isomerase and NADPH Oxidase

Oxidative stress participates at the baseline of different non-communicable pathologies such as cardiovascular diseases. Excessive formation of reactive oxygen species (ROS), above the signaling levels necessary for the correct function of organelles and cells, may contribute to the non-desired effects of oxidative stress. Platelets play a relevant role in arterial thrombosis, by aggregation triggered by different agonists, where excessive ROS formation induces mitochondrial dysfunction and stimulate platelet activation and aggregation. Platelet is both a source and a target of ROS, thus we aim to analyze both the platelet enzymes responsible for ROS generation and their involvement in intracellular signal transduction pathways. Among the proteins involved in these processes are Protein Disulphide Isomerase (PDI) and NADPH oxidase (NOX) isoforms. By using bioinformatic tools and information from available databases, a complete bioinformatic analysis of the role and interactions of PDI and NOX in platelets, as well as the signal transduction pathways involved in their effects was performed. We focused the study on analyzing whether these proteins collaborate to control platelet function. The data presented in the current manuscript support the role that PDI and NOX play on activation pathways necessary for platelet activation and aggregation, as well as on the platelet signaling imbalance produced by ROS production. Our data could be used to design specific enzyme inhibitors or a dual inhibition for these enzymes with an antiplatelet effect to design promising treatments for diseases involving platelet dysfunction.

The Use of Triphenyl Phosphonium Cation Enhances the Mitochondrial Antiplatelet Effect of the Compound Magnolol

Although platelets are anucleated cells, they have fully functional mitochondria, and currently, it is known that several processes that occur in the platelet require the action of mitochondria. There are plenty of mitochondrial-targeted compounds described in the literature related to cancer, however, only a small number of studies have approached their interaction with platelet mitochondria and/or their effects on platelet activity. Recent studies have shown that magnolia extract and mitochondria-targeted magnolol can inhibit mitochondrial respiration and cell proliferation in melanoma and oral cancer cells, respectively, and they can also induce ROS and mitophagy. In this study, the effect of triphenylphosphonium cation, linked by alkyl chains of different lengths, to the organic compound magnolol on human-washed platelets was evaluated. We demonstrated that the addition of triphenylphosphonium by a four-carbon linker to magnolol (MGN4) considerably enhanced the Magnolol antiplatelet effect by a 3-fold decrease in the IC50. Additionally, platelets exposed to MGN4 5 µM showed several differences from the control including increased basal respiration, collagen-induced respiration, ATP-independent respiration, and reduced ATP-dependent respiration and non-mitochondrial respiration.

Protein disulfide isomerase-A1 regulates intraplatelet reactive oxygen species-thromboxane A2 -dependent pathway in human platelets

BACKGROUND

Platelet-derived protein disulfide isomerase 1 (PDIA1) regulates thrombus formation, but its role in the regulation of platelet function is not fully understood.

AIMS

The aim of this study was to characterize the role of PDIA1 in human platelets.

METHODS

Proteomic analysis of PDI isoforms in platelets was performed using liquid chromatography tandem mass spectometry, and the expression of PDIs on platelets in response to collagen, TRAP-14, or ADP was measured with flow cytometry. The effects of bepristat, a selective PDIA1 inhibitor, on platelet aggregation, expression of platelet surface activation markers, thromboxane A2 (TxA2 ), and reactive oxygen species (ROS) generation were evaluated by optical aggregometry, flow cytometry, ELISA, and dihydrodichlorofluorescein diacetate-based fluorescent assay, respectively.

RESULTS

PDIA1 was less abundant compared with PDIA3 in resting platelets and platelets stimulated with TRAP-14, collagen, or ADP. Collagen, but not ADP, induced a significant increase in PDIA1 expression. Bepristat potently inhibited the aggregation of washed platelets induced by collagen or convulxin, but only weakly inhibited platelet aggregation induced by TRAP-14 or thrombin, and had the negligible effect on platelet aggregation induced by arachidonic acid. Inhibition of PDIA1 by bepristat resulted in the reduction of TxA2 and ROS production in collagen- or thrombin-stimulated platelets. Furthermore, bepristat reduced the activation of αIIbβ3 integrin and expression of P-selectin.

CONCLUSIONS

PDIA1 acts as an intraplatelet regulator of the ROS-TxA2 pathway in collagen-GP VI receptor-mediated platelet activation that is a mechanistically distinct pathway from extracellular regulation of αIIbβ3 integrin by PDIA3.