The influence of glutathione depleting agents on human platelet function

Inflammation: Is It a Healer, Confounder, or a Promoter of Cardiometabolic Risks?

Inflammation is the body's non-specific response to injury or infection. It is a natural defense mechanism that helps to maintain homeostasis and promotes tissue repair. However, excessive inflammation can lead to cellular, tissue, or organ dysfunction, as well as contribute to the development of acute vascular events and diseases like Crohn's disease, psoriasis, obesity, diabetes, and cancer. The initial response to injury involves the activation of platelets and coagulation mechanisms to stop bleeding. This is followed by the recruitment of immune cells and the release of cytokines to promote tissue repair. Over time, the injured tissue undergoes remodeling and returns to its pre-injury state. Inflammation is characterized by the activation of inflammatory signaling pathways involving cytokines, chemokines, and growth factors. Mast cells play a role in initiating inflammatory responses. Pattern recognition receptors (PRRs) such as Toll-like receptors (TLRs) and nucleotide-binding domain (NOD)-like receptors (NLRs) are involved in the activation of these inflammatory pathways. Inflammasomes, which are cytoplasmic complexes, also contribute to inflammation by activating cytokines. Inflammation can also be triggered by factors like dietary components and the composition of the gut microbiota. Dysregulation of the gut microbiome can lead to excessive inflammation and contribute to diseases like atherosclerosis and irritable bowel syndrome (IBS). The immune system and gut-associated lymphoid tissue (GALT) play crucial roles in the inflammatory response and the development of conditions like colorectal cancer. Anti-inflammatory therapy can play a significant role in reducing or inducing the remission of inflammatory diseases such as Crohn's disease and ulcerative colitis. The fetal origin of adult diseases theory suggests that conditions during fetal development, such as low birth weight and maternal obesity, can influence the risk of cardiometabolic diseases later in life. All of the known risk factors associated with cardiometabolic diseases such as hypertension, excess weight, obesity, type-2 diabetes, and vascular diseases are accompanied by chronic low-grade inflammation. Inflammation seems to have a role in precipitating even acute vascular events such as heart attacks and stroke. Common markers of inflammation associated with cardiometabolic disease include interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF-α), C-reactive protein (CRP), and soluble TNF receptors such as sTNFR1 and sTNFR2. These markers serve as indicators of systemic inflammation. However, these markers are not disease-specific but provide an insight into the overall chronic inflammatory status. In fact, inflammation has been identified as a potential target for future treatments to reduce or reverse the risk of atherosclerosis-related complications. The regulation of inflammation is complex, and further research is needed to better understand its mechanisms and develop strategies for managing inflammatory disorders. In summary, inflammation is a natural response to injury or infection, but excessive or prolonged inflammation can lead to the progression of various diseases. Understanding the underlying mechanisms of inflammation is important for developing treatments and preventive measures for inflammatory disorders.

Thioredoxin reductase activity may be more important than GSH level in protecting human lens epithelial cells against UVA light

This study compares the abilities of the glutathione (GSH) and thioredoxin (Trx) antioxidant systems in defending cultured human lens epithelial cells (LECs) against UVA light. Levels of GSH were depleted with either L-buthionine-(S,R)-sulfoximine (BSO) or 1-chloro-2,4-dinitrobenzene (CDNB). CDNB treatment also inhibited the activity of thioredoxin reductase (TrxR). Two levels of O2 , 3% and 20%, were employed during a 1 h exposure of the cells to 25 J cm(-2) of UVA radiation (338-400 nm wavelength, peak at 365 nm). Inhibition of TrxR activity by CDNB, combined with exposure to UVA light, produced a substantial loss of LECs and cell damage, with the effects being considerably more severe at 20% O2 compared to 3%. In contrast, depletion of GSH by BSO, combined with exposure to UVA light, produced only a slight cell loss, with no apparent morphological effects. Catalase was highly sensitive to UVA-induced inactivation, but was not essential for protection. Although UVA light presented a challenge for the lens epithelium, it was well tolerated under normal conditions. The results demonstrate an important role for TrxR activity in defending the lens epithelium against UVA light, possibly related to the ability of the Trx system to assist DNA synthesis following UVA-induced cell damage.

Redox regulation of morphology, cell stiffness, and lectin-induced aggregation of human platelets

Redox regulation and carbohydrate recognition are potent molecular mechanisms which can contribute to platelet aggregation in response to various stimuli. The purpose of this study is to investigate the relationship between these mechanisms and to examine whether cell surface glycocalyx and cell stiffness of human platelets are sensitive to the redox potential formed by glutathione. To this end, human platelets were treated with different concentrations (0.05 μM to 6 mM) and ratios of reduced or oxidized glutathione (GSH or GSSG), and platelet morphological, mechanical, and functional properties were determined using conventional light microscopy, atomic force microscopy, and lectin-induced cell aggregation analysis. It was found that lowering the glutathione redox potential changed platelet morphology and increased platelet stiffness as well as modulated nonuniformly platelet aggregation in response to plant lectins with different carbohydrate-binding specificity including wheat germ agglutinin, Sambucus nigra agglutinin, and Canavalia ensiformis agglutinin. Extracellular redox potential and redox buffering capacity of the GSSG/2GSH couple were shown to control the availability of specific lectin-binding glycoligands on the cell surface, while the intracellular glutathione redox state affected the general functional ability of platelets to be aggregated independently of the type of lectins. Our data provide the first experimental evidence that glutathione as a redox molecule can affect the mechanical stiffness of human platelets and induce changes of the cell surface glycocalyx, which may represent a new mechanism of redox regulation of intercellular contacts.

Trivalent methylated arsenical-induced phosphatidylserine exposure and apoptosis in platelets may lead to increased thrombus formation

Trivalent methylated metabolites of arsenic, monomethylarsonous acid (MMA(III)) and dimethylarsinous acid (DMA(III)), have been found highly reactive and toxic in various cells and in vivo animal models, suggesting their roles in the arsenic-associated toxicity. However, their effects on cardiovascular system including blood cells, one of the most important targets for arsenic toxicity, remain poorly understood. Here we found that MMA(III) and DMA(III) could induce procoagulant activity and apoptosis in platelets, which play key roles in the development of various cardiovascular diseases (CVDs) through excessive thrombus formation. In freshly isolated human platelets, treatment of MMA(III) resulted in phosphatidylserine (PS) exposure, a hallmark of procoagulant activation, accompanied by distinctive apoptotic features including mitochondrial membrane potential disruption, cytochrome c release, and caspase-3 activation. These procoagulant activation and apoptotic features were found to be mediated by the depletion of protein thiol and intracellular ATP, and flippase inhibition by MMA(III), while the intracellular calcium increase or reactive oxygen species generation was not involved. Importantly, increased platelet procoagulant activity by MMA(III) resulted in enhanced blood coagulation and excessive thrombus formation in a rat in vivo venous thrombosis model. DMA(III) also induced PS-exposure with apoptotic features mediated by protein thiol depletion, which resulted in enhanced thrombin generation. In summary, we believe that this study provides an important evidence for the role of trivalent methylated arsenic metabolites in arsenic-associated CVDs, giving a novel insight into the role of platelet apoptosis in toxicant-induced cardiovascular toxicity.

Protein S-glutathionylation and platelet anti-aggregating activity of disulfiram

Blood platelets are central to haemostasis, and reactions in platelets involving sulfhydryl groups play important roles in platelet function. Reduced glutathione (GSH) plays an important role in platelet aggregation and glutathione-depleting chemicals inhibit platelet aggregation. The lipophilic drug disulfiram, because of its affinity for sulfhydryl groups, is a highly thiol-reacting agent. As a consequence, GSH and sulfhydryl groups of protein cysteines in human platelets, in analogy to other components of human blood, are a potential target of disulfiram. In the present study, we have shown that exposure of human platelets to disulfiram causes the depletion of platelet GSH and augmentation of mixed disulfides between GSH and protein sulfhydryl groups to form protein-glutathione mixed disulfides (S-glutathionylated proteins). The depletion of platelet GSH and the increase in S-glutathionylated proteins occurred at concentrations of disulfiram that inhibited platelet aggregation, suggesting that protein S-glutathionylation is involved in the inhibition of platelet aggregation caused by disulfiram.

Association of quinone-induced platelet anti-aggregation with cytotoxicity

Various anti-platelet drugs, including quinones, are being investigated as potential treatments for cardiovascular disease because of their ability to prevent excessive platelet aggregation. In the present investigation 3 naphthoquinones (2,3-dimethoxy-1,4-naphthoquinone [DMNQ], menadione, and 1,4-naphthoquinone [4-NQ]) were compared for their abilities to inhibit platelet aggregation, deplete glutathione (GSH) and protein thiols, and cause cytotoxicity. Platelet-rich plasma, isolated from Sprague-Dawley rats, was used for all experiments. The relative potency of the 3 quinones to inhibit platelet aggregation, deplete intracellular GSH and protein thiols, and cause cytotoxicity was 1,4-NQ > menadione >> DMNQ. Experiments using 2 thiol-modifying agents, dithiothreitol (DTT) and 1-chloro-2,4-dintrobenzene (CDNB), confirmed the key roles for GSH in quinone-induced platelet anti-aggregation and for protein thiols in quinone-induced cytotoxicity. Furthermore, the anti-aggregative effects of a group of 12 additional quinone derivatives were positively correlated with their ability to cause platelet cytotoxicity. Quinones that had a weak anti-aggregative effect did not induce cytotoxicity (measured as LDH leakage), whereas quinones that had a potent anti-aggregative effect resulted in significant LDH leakage (84-96%). In one instance, however, p-chloranil demonstrated a potent anti-aggregative effect, but did not induce significant LDH leakage. This can be explained by the inability of p-chloranil to deplete protein thiols, even though intracellular GSH levels decreased rapidly. These results suggest that quinones that deplete GSH in platelets demonstrate a marked anti-aggregative effect. If this anti-aggregative effect is subsequently followed by depletion of protein thiols, cytotoxicity results.

Endogenous glutathione and platelet function in platelet concentrates stored in plasma or platelet additive solution

Platelet function was studied in platelet concentrates by assay of the thrombin-induced release of endogenous serotonin and presence of the swirling phenomenon in relation to endogenous glutathione (GSH) and cysteine. In platelets stored in plasma, addition of cysteamine resulted in only a moderate fall in GSH after 5 days of storage, from an average of 14.91 to 11.46 nmol per 109 platelets. Exogenously added GSH had no effect, and addition of buthionine sulfoximine (BSO) resulted in almost complete depletion of GSH, to an average of 0.65 nmol per 109 platelets. Addition of cysteamine or GSH resulted in increased endogenous cysteine whereas BSO had no effect. In platelets stored in a platelet additive solution (T-sol), complete depletion of GSH was found in the presence of cysteamine, GSH and BSO. Endogenous serotonin was unchanged during storage both in plasma and in additive solution (2.8 nmol per 109 platelets). Despite almost total depletion of endogenous GSH, the thrombin-induced release of serotonin after 5 days' storage was significantly affected only in the presence of BSO in platelets stored in additive solution (mean values 72.3% vs. 63.3% of endogeneous serotonin, P < 0.05). Similarly, addition of cysteamine or GSH had no significant effect on swirling but BSO reduced the swirling score after 5 days' storage in platelet additive solution compared with plasma. After 10 days' storage, there was a significant reduction in swirling in the concentrates where BSO was added (P < 0.05).

Minor thiols cysteine and cysteinylglycine regulate the competition between glutathione and protein SH groups in human platelets subjected to oxidative stress

Changes in the concentrations of protein-mixed disulfides (XS-SP) of glutathione (GSH), cysteine (CSH), and cysteinylglycine (CGSH) were studied in human platelets treated with diamide and t-BOOH in timecourse experiments (time range, 1-30 min) in order to understand the contribution of minor thiols CSH and CGSH to the regulation of glutathione-protein mixed disulfides (GS-SP). Diamide was much more potent than t-BOOH in altering the platelet thiol composition of XS-SP (threshold dose: diamide, 0.03 mM; t-BOOH, 0.5 mM) and caused reversible XS-SP peaks whose magnitude was related to the concentration of free thiols in untreated cells. Thus maximum levels of GS-SP (8 min after 0.4 mM diamide) were about 16-fold higher than those of controls (untreated platelets, GS-SP = 0.374 nmol/10(9) platelets), whereas those of CS-SP and CGS-SP were only 4-fold increased (untreated platelets, CS-SP = 0.112 nmol/10(9) platelets; CGS-SP = 0.024 nmol/10(9) platelets). The greater effects of diamide with respect to t-BOOH were explained on the basis of the activities of fast reactive protein SH groups for diamide and glutathione reductase (GR) and glucose-6-phosphate dehydrogenase (G-6-PDH) for t-BOOH. The addition of cysteine (0.3 mM, at 4 min) after treatment of platelets with 0.4 mM diamide increased the rate of reversal of GS-SP peaks to normal values, but also caused a relevant change in CGS-SP with respect to that of platelets treated with diamide alone. An increased gamma-glutamyltranspeptidase activity was found in platelets treated with diamide. Moreover, untreated platelets were found to release and hydrolyze GSH to CGSH and CSH. Ratios of thiols/disulfides (XSH/XSSX) and activities of GR and G-6PDH were also related to a high reducing potential exerted by GSH but not by minor thiols. The lower mass and charge of minor thiols is a likely requisite of the regulation of GS-SP levels in platelets.

Physical proximity and functional association of glycoprotein 1balpha and protein-disulfide isomerase on the platelet plasma membrane

Platelet function is influenced by the platelet thiol-disulfide balance. Platelet activation resulted in 440% increase in surface protein thiol groups. Two proteins that presented free thiol(s) on the activated platelet surface were protein-disulfide isomerase (PDI) and glycoprotein 1balpha (GP1balpha). PDI contains two active site dithiols/disulfides. The active sites of 26% of the PDI on resting platelets was in the dithiol form, compared with 81% in the dithiol form on activated platelets. Similarly, GP1balpha presented one or more free thiols on the activated platelet surface but not on resting platelets. Anti-PDI antibodies increased the dissociation constant for binding of vWF to platelets by approximately 50% and PDI and GP1balpha were sufficiently close on the platelet surface to allow fluorescence resonance energy transfer between chromophores attached to PDI and GP1balpha. Incubation of resting platelets with anti-PDI antibodies followed by activation with thrombin enhanced labeling and binding of monoclonal antibodies to the N-terminal region of GP1balpha on the activated platelet surface. These observations indicated that platelet activation triggered reduction of the active site disulfides of PDI and a conformational change in GP1balpha that resulted in exposure of a free thiol(s).

The relative importance of oxidative stress versus arylation in the mechanism of quinone-induced cytotoxicity to platelets

Our previous studies demonstrated that menadione is cytotoxic to rat platelets. In an attempt to assess the relative contributions of enzymatic redox cycling versus arylation in menadione-induced cytotoxicity, we have studied three quinones with different mechanisms of action: 2,3-dimethoxy-1,4-naphthoquinone (DMNQ; pure redox cycler), menadione (both redox cycler and arylator), and 1,4-benzoquinone (BQ; pure arylator). BQ was more toxic to rat platelets than menadione, while DMNQ did not cause LDH leakage at all. Cellular uptake kinetics revealed that DMNQ concentration taken up by the cells was equivalent to that decreased in incubation medium. On the other hand, the concentrations of BQ and menadione taken into the cells were significantly lower than the decreases in concentrations seen in the incubation medium. This suggests indirectly that BQ and menadione may have undergone arylation, binding to glutathione (GSH) or protein thiols. The difference in arylation capacity between BQ and menadione was well correlated with their relative cytotoxicity (LDH leakage) observed in platelets. All three quinones caused a rapid, extensive depletion of intracellular GSH in platelets. Treatments with BQ and menadione did not result in formation of oxidized glutathione (GSSG), whereas DMNQ showed a time-dependent increase in GSSG. Altogether, these results suggest that enzymatic redox cycling does not play a critical role in quinone-induced cytotoxicity in rat platelets, while arylation is likely to be quinone's primary mechanism of action.

Electrorotation measurements of diamide-induced platelet activation changes

Electrorotation is a special dielectric spectroscopic technique capable of measuring the polarizability of single platelets. The rotational speed of the particles is recorded as a function of the frequency of the applied rotating electric field. As previously shown, the speed of electrorotation in the range of the first characteristic frequency (anti-field rotation) decreased upon activation and was correlated with [14C]serotonin release and an increase of the TMA-DPH-induced fluorescence. Diamide upon activation and was correlated with [14C]serotonin release and an increase of the TMA-DPH-induced fluorescence. Diamide incubation induced morphological changes in control platelets. These changes were accompanied by a shift of the first characteristic frequency of electrorotation toward higher values and a parallel increase of the anti-field rotation. This was explained by a decrease of membrane conductivity and by the changed polarizability of platelet interior due to the observed internal platelet structure changes. Diamide inhibited activation assessed by both electrorotation and TMA-DPH fluorescence in the case of all activators except the ionophore A 23187. Because diamide largely inhibited the A 23187-induced serotonin release, it was concluded that, despite the diamide treatment, the direct increase of cytoplasmic Ca2+ was still able to induce membrane conductivity changes accessible by electrorotation, but this did not complete the final release step of the activation process.

The action of the glutathione transferase substrate, 1-chloro-2,4-dinitrobenzene on synaptosomal glutathione content and the release of hydrogen peroxide

We studied the action of the glutathione transferase substrate, 1-chloro-2,4-dinitrobenzene (CDNB) on the synaptosomal production of H2O2. We found that CDNB (30-40 microM) readily depletes the cytosolic glutathione but is almost without effect on the mitochondrial fraction. The depletion of the cytosolic glutathione induced by CDNB affords the detection in the extracellular space of H2O2 produced intrasynaptosomally upon increasing the cytosolic Ca2+ concentration that is otherwise destroyed by glutathione peroxidase. Higher concentrations of CDNB induce a H2O2 production which is not related to the glutathione content. This H2O2 is of mitochondrial origin and requires that NAD be reduced. The primary product of the mitochondrial CD-NB-dependent oxygen reduction is at least in part the superoxide anion.

Formation of lipoxins and leukotrienes during receptor-mediated interactions of human platelets and recombinant human granulocyte/macrophage colony-stimulating factor-primed neutrophils

The generation of lipoxygenase products of arachidonic acid is considered an important event in inflammation. This study demonstrates the levels of both lipoxins and leukotrienes (LTC4, LTD4, LTB4, and omega-oxidized LTB4) generated from endogenous sources of arachidonate by PMN primed with recombinant human granulocyte/macrophage colony-stimulating factor and in coincubations with platelets (1:1 to 1:100 ratio). Upon exposure to receptor-mediated stimuli (FMLP and thrombin), the levels of lipoxins generated were within the range of both LTB4 and LTC4. Co-incubation of [1-14C]arachidonate-labeled platelets with primed polymorphonuclear leukocytes (PMN) followed by addition of thrombin and FMLP led to the formation of both 5- and 15-LO products that carried 14C label. Thus, in addition to the transcellular conversion of LTA4 to platelet-derived lipoxins and LTC4, PMN can use platelet-derived arachidonate to generate lipoxygenase products. These results are the first to document the relationship between the levels of lipoxins and leukotrienes generated by receptor-mediated activation of cytokineprimed PMN interacting with platelets. Moreover, they indicate that PMN-platelet interactions utilize bidirectional transcellular routes to contribute to lipoxin formation.

Role of glutathione and glutathione peroxidase in human platelet arachidonic acid metabolism

Selective removal of intracellular glutathione (GSH) and inhibition of the GSH-dependent peroxidase (GSH-Px) by 1-chloro-2,4-dinitrobenzene (CDNB) was used to evaluate the role of GSH and GSH-Px in arachidonic acid (AA) metabolism in human platelets. Although total conversion of AA through the lipoxygenase pathway is lowered by GSH depletion, significant 12-HETE formation was observed suggesting that GSH and GSH-Px are not required for the generation of 12-HETE in human platelets. Prolonged treatment of platelets with CDNB (2 h) completely destroyed GSH-Px activity creating a model in which the effects of GSH alone could be determined. Platelet homogenates replenished with GSH, but lacking GSH-Px activity converted significantly higher amounts of AA to 12-HPETE and 12-HETE than control. Platelet cytosolic metabolism of 15-HPETE to 15-HETE decreased after CDNB, while the membrane metabolism remained similar to control due to high GSH-independent peroxidase activity associated with the membranes. These results indicate that GSH and GSH-Px function to enhance lipoxygenase activity, rather than catalyse the reduction of 12-HPETE to 12-HETE.