Modification of glutathione content in platelet concentrates by the use of acivicin

The effect of gamma irradiation on platelet redox state during storage

BACKGROUND

As a method with insignificant adverse effects on in vitro quality of platelet concentrates (PCs), gamma irradiation is applied to abrogate the risk of transfusion-associated graft-vs-host disease in vulnerable recipients. However, there is some evidence of lower posttransfusion responses and proteomic alterations in gamma-irradiated platelets (PLTs), which raises some questions about their quality, safety, and efficacy. Since reactive oxygen species (ROS) are considered as markers of PLT storage lesion (PSL), the study presented here investigated oxidant state in gamma-irradiated PCs.

STUDY DESIGN AND METHODS

PLT-rich plasma PC was split into two bags, one kept as control while other was subjected to gamma irradiation. Within 7 days of storage, the levels of intra-PLT superoxide, H₂ O₂ , mitochondrial ROS, P-selectin expression, and phosphatidylserine (PS) exposure were detected by flow cytometry while intracellular reduced glutathione (GSH), glucose concentration, and lactate dehydrogenase (LDH) activity were measured by enzymocolorimetric method.

RESULTS

GSH decreased, while ROS generation and LDH activity increased, during storage. Gamma irradiation significantly attenuated GSH whereas increased ROS generation in earlier and later stages of storage associated with either P-selectin or PS exposure increments.

CONCLUSION

Gamma irradiation can significantly increase cytosolic ROS generation in two distinct phases, one upon irradiation and another later in longer-stored PCs. While earlier ROS influx seems to be governed by direct effect of irradiation, the second phase of oxidant stress is presumably due to the storage-dependent PLT activation. Intriguingly, these observations were also in line with early P-selectin increments and increased PS exposure in longer-stored PLTs. Given the mutual link between ROS generation and PLT activation, further investigation is required to explore the effect of gamma irradiation on the induction of PSL.

Production of cysteinyl-dopamine during intravenous dopamine therapy

BACKGROUND

Oxidized dopamine rapidly forms thiol-conjugates with --SH groups on cysteine, glutathione, and proteins. We used cysteinyl-dopamine production as an index of thioester production during intravenous dopamine treatment of critically ill patients.

METHODS

Cysteinyl-dopamine and catecholamines were measured by high-performance liquid chromatography with electrochemical detection. The production of cysteinyl-dopamine by purified human neutrophils was measured using dopamine (1 micromol/L) and cysteine (1 mmol/L) concentrations similar to those found during dopamine treatment. To examine the impact of endotoxic shock on cysteinyl-dopamine production, anesthetized rats were given dopamine (12 to 15 microg/kg/min intravenously) with or without endotoxin (50 mg/kg intravenously).

RESULTS

In vitro, neutrophils converted 26% of dopamine to cysteinyl-dopamine (30 min at 37 degrees C). Activating neutrophils with zymogen increased dopamine consumption from 26 to 68%, but only 36% appeared as cysteinyl-dopamine. The remainder may have been oxidized to other cysteinyl derivatives. Endotoxin increased cysteinyl-dopamine in rat plasma from 2.5 nmol/L (range <0.2 to 11) to 9.7 nmol/L (range <0.3 to 31, P = 0.1). After four hours, with or without endotoxin, cysteinyl-dopamine was <0.3 nmol/L in cerebrospinal fluid. In the plasma of eight patients receiving dopamine (6 to 20 microg/kg/min for 1 to 3 days), dopamine was 0.5 to 9.9 micromol/L, and cysteinyl-dopamine was 48 to 1660 nmol/L. Cysteinyl-dopamine was 4.3 to 22.6% of dopamine and correlated with leukocyte count (r(2) = 0.388, P = 0.099).

CONCLUSIONS

A significant fraction of exogenously administered dopamine reacts with -SH groups of cysteine and probably also with -SH groups on peptides and proteins. During brief dopamine treatment of endotoxic shock in rats, neither dopamine nor cysteinyl-dopamine crossed the blood-brain barrier.

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).