Regulation of platelet activation and thrombus formation by reactive oxygen species

Abstract

Reactive oxygen species (ROS) are generated within activated platelets and play an important role in regulating platelet responses to collagen and collagen-mediated thrombus formation. As a major collagen receptor, platelet-specific glycoprotein (GP)VI is a member of the immunoglobulin (Ig) superfamily, with two extracellular Ig domains, a mucin domain, a transmembrane domain and a cytoplasmic tail. GPVI forms a functional complex with the Fc receptor γ-chain (FcRγ) that, following receptor dimerization, signals via an intracellular immunoreceptor tyrosine-based activation motif (ITAM), leading to rapid activation of Src family kinase signaling pathways. Our previous studies demonstrated that an unpaired thiol in the cytoplasmic tail of GPVI undergoes rapid oxidation to form GPVI homodimers in response to ligand binding, indicating an oxidative submembranous environment in platelets after GPVI stimulation. Using a redox-sensitive fluorescent dye (H2DCF-DA) in a flow cytometric assay to measure changes in intracellular ROS, we showed generation of ROS downstream of GPVI consists of two distinct phases: an initial Syk-independent burst followed by additional Syk-dependent generation. In this review, we will discuss recent findings on the regulation of platelet function by ROS, focusing on GPVI-dependent platelet activation and thrombus formation.

ROS scavenger, N‐acetyl‐l‐cysteine and NOX specific inhibitor, VAS2870 reduce platelets apoptosis while enhancing their viability during storage

“…Alternatively, these findings indicated that ROS generation can hamper platelet viability during storage. It is known that excessive ROS generation can damage mitochondria in different cell types, whereas reducing ROS generation may benefit mitochondrial function . But of interest here is the observation that showed better preservation of mitochondrial function in the presence of VAS2870 compared with NAC as a general scavenger that removes ROS formed by all production sources, including NOX.…”

“…NAC has proven to be an effective ROS scavenger that successfully enhances redox states in different conditions . VAS2870 is also reported to be a specific inhibitor of NOX 1/2 which are recognized as dominate variants of these enzymes in platelets . Importantly, the specific interaction of VAS2870 with NOX provides valuable advantages rather than the use of nonspecific inhibitors of NOX, such as diphenylene‐iodonium (DPI), which can also interfere with the function of other flavin‐containing enzymes, including nitric oxide synthase, xanthine oxidase, P‐450 NADPH reductase, and mitochondrial respiratory chain complex I .…”

“…However, platelets exposure with excessive levels of exogenous ROS (for example H 2 0 2 ) or inflated generation of intracellular ROS caused by non‐physiological or experimental conditions can result in exaggerated activation, which may lead to dramatic changes in platelet phenotype and function . Generally, platelet stimulation with different agonists or other stimulators, including adhesion molecules, induce ROS generation mainly through the activation of NADPH oxidase 1 and 2 (NOX1/2) complexes . Mitochondrial oxidative metabolisms are considered as another source for ROS, whereas mitochondrial‐originated ROS may also amplify their generation by NOX activation, or vice versa .…”

“…On the other hand, upon platelet stimulation, ROS generated by NOX activation can diminish the mitochondrial membrane potential, resulting in mitochondrial ROS formation and subsequent activation of NOX. This process consequently increases total intracellular ROS production in a vicious circle . Platelet storage has also been shown to be associated with a significant rise of intracellular ROS and its correlation with the increased levels of platelet activation markers, including P‐selectin and CD40 ligand (CD40L) expression or release .…”

Antioxidant Activity and Hepatotoxicity of Flavonoids and Their Metal Complexes Through Co‐Administration of β‐Cyclodextrin

“…The observation of CAT and SOD activity can serve as a gateway for understanding the mode of action of antioxidants . The serum ROS levels are expected to be higher in ROS‐related disease such as liver disease, cardiovascular disease, cancer, and diabetes . Any antioxidant substance would result in decrease of ROS level in serum.…”