Singlet oxygen (1O(2)) disrupts platelet aggregates

Anticoagulant activity of singlet oxygen released from a water soluble endoperoxide by thermal cycloreversion

Singlet oxygen generated by photosensitization has limited potential in vivo due to light attenuation in tissues. However, controlled chemical generation of this reactive oxygen species is likely to open new therapeutic spaces to explore. The fact that its activity is limited by the rate of cycloreversion reaction and the diffusion distance of the excited state molecular oxygen species, is a clear advantage, considering the serious side effects of off-target anticoagulants. In this work, we present novel 1,4-naphthalene endoperoxides as potential anti-coagulant agents due to thermal release of singlet oxygen.

Singlet oxygen generated by the cycloreversion of endoperoxides has anti-coagulant activity.

Au-Cu@PANI Alloy Core Shells for Aerobic Fibrin Degradation under Visible Light Exposure

Fibrin plays a critical role in wound healing and hemostasis, yet it is also the main case of cardiovascular diseases and thrombosis. Here, we show the unique design of Au-Cu@PANI alloy core-shell rods for fibrin clot degradation. Microscopic (transmission electron microscopy (TEM), scanning transmission electron microscopy-energy-dispersive X-ray (STEM-EDX)) and structural characterizations (powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS)) of the Au-Cu@PANI hybrid material reveal the formation of Au-Cu heterogeneous alloy core rods (aspect ratio = 3.7) with thin Cu₂O and PANI shells that create a positive surface charge (ζ-potential = +22 mV). This architecture is supported by the survey XPS spectrum showing the presence of Cu 2p, N 1s, and C 1s features with binding energies of 934.8, 399.7, and 284.8 eV, respectively. Upon photolysis (λ ≥ 495 or 590 nm), these hybrid composite nanorods provide sufficient excited-state redox potential to generate reactive oxygen species (ROS) for degradation of model fibrin clots within 5-7 h. Detailed scanning electron microscopy (SEM) analysis of the fibrin network shows significant morphology modification including formation of large voids and strand termini, indicating degradation of fibrin protofibril by Au-Cu@PANI. The dye 1,3-diphenylisobenzofuran (DPBF) used to detect the presence of ¹O₂ shows a 27% bleaching of the absorption at λ = 418 nm within 75 min of irradiation of an aqueous Au-Cu@PANI solution in air. Moreover, electron paramagnetic resonance (EPR) spin-trapping experiments reveal a hyperfine-coupled triplet signature at room temperature with intensities 1:1:1: and g-value = 2.0057, characteristic of the reaction between the spin probe 4-Oxo-TEMP and ¹O₂ during irradiation. Controlled ¹O₂ scavenging experiments by NaN₃ show 82% reduction in the spin-trapped EPR signal area. Both DPBF bleaching and EPR spin trapping indicate that in situ generated ¹O₂ is responsible for fibrin strand scission. This unique nanomaterial function via use of ubiquitous oxygen as a reagent could open creative avenues for future in vivo biomedical applications to treat fibrin clot diseases.

Microbicidal activity of N-chlorotaurine in combination with hydrogen peroxide

N-chlorotaurine (NCT) and hydrogen peroxide are powerful endogenous antiseptics. In vivo, the reaction between hydrogen peroxide and metal ions leads to the formation of free hydroxyl radicals, which have an increased bactericidal activity. This study examined whether there is an additive antimicrobial effect of NCT combined with hydrogen peroxide. Additionally, it was tested if the additive effect is based on the formation of free radicals. We found by luminometry that, in the presence of H₂O₂, NCT caused a slow and long-lasting production of singlet oxygen in contrast to HOCl, where this burst occurred instantaneously. Both NCT and hydrogen peroxide (1.0 and 0.1%) demonstrated bactericidal and fungicidal activity. At pH 7.1 and 37 °C, hydrogen peroxide (1%, 294 mM) showed a stronger bactericidal and particularly fungicidal activity than NCT (1%, 55 mM), whereas at pH 4.0 and also in the presence of 5.0% peptone NCT revealed a stronger bactericidal activity. A combination of NCT and hydrogen peroxide led to an increased bactericidal but no increased fungicidal activity compared to both substances alone. The additive effect against bacteria was not removed in the presence of the radical scavengers NaN₃, DMSO, or peptone. As a conclusion, NCT and hydrogen peroxide used concurrently interact additive against a range of microorganisms. However, the results of this study suggest that the additive effect of NCT combined with hydrogen peroxide is rather not based on the formation of free radicals.

Point of Care: Diagnostics in Hemostasisthe Wrong Direction?

Point-of-care-testing (POCT) is performance of a laboratory assay outside the laboratory by nontrained personnel. The advantages of POCT are: more rapid medical decisions, avoidance of long sample transports, and small samples. The disadvantages of POCT are: no laboratory personnel, insufficient calibration, quality control and maintenance, poor documentation, high costs, difficult comparability POCT/central laboratory. Therefore, disposing of a 24-hour central laboratory, the POCT spectrum should be limited to the vital parameters: K+, Ca++, Na+, glucose, creatinine, blood gases, hemoglobin or hematocrit, NH3, lactate. POCT offers no advantages, if the hospital has a rapid transport system such as a pneumatic delivery to the central laboratory. The rapid diagnosis of the acute hemostasis state of a patient should be performed in the 24-hour central laboratory that is connected to all hospital wards via a good pneumatic delivery.

Singlet Oxygen Enhances Intrinsic Thrombolysis: The Intrinsic Oxidative Clot Lysis Assay (INOXCLA)

Granulocytes are important cells of inflammation and cellular thrombolysis. They produce urokinase (u-PA) and chloramines. In this study, u-PA/chloramine—mediated fibrinolysis is imitated in a microtiter-plate. Seventy-five microliters plasma are incubated with 50 μL 50% Pathromtin SL, 6% BSA, and 38 mM CaCl2 for 30 minutes (37°C). Then, 50 μL 10 mM chloramine-T in PBS are added. After 30 minutes (37°C), 50 μL 0, 100, or 10 IU/mL u-PA in 6% BSA-PBS are added and the turbidity is determined at 405 nm after 0, 3, or 16 hours. Clot lysis was increased more than tenfold by 0.5 to 1 μmoles chloramine (ED50 after 3h = about 0.25 μmoles = 2mM final concentration). The normal range for the present intrinsic oxidative clot lysis assay (INOXCLA) is 100% ± 25% (MV ± SD; 100 relative % of norm; the normal lysis being 60 absolute %; CVs < 10%). Fifty percent lysis of adherent microclots occurred after 0.75 hours, 2 hours, 14 hours, 13 days, or 17 days when using 1000, 100, 10, 1, or 0 IU/mL u-PA reagent. If the u-PA activity is quenched by PAI-2, no clot lysis appears. Chloramines are important physiologic generators of nonradical excited singlet oxygen and enhance u-PA—mediated lysis of plasma clots. Based on the u-PA/chloramines coaction, a new global fibrinolysis assay has been derived.

Monitoring of platelet activation in platelet concentrates using transmission electron microscopy

OBJECTIVE

The quality of platelet concentrates (PC) is important for the in vivo recovery of thrombostasis in patients suffering from bleeding disorders and in tumor patients after chemotherapy. In this respect, activated platelets (PLT) cannot display their full functionality in the recipient and even can cause adverse effects. Therefore, we developed a transmission electron microscopy (TEM) method for quality assessment of PC.

METHODS

Score values taken from panorama TEM images describe the progress of PLT activation. To exemplify this method, i) 19 apheresis PC isolated with the Baxter Amicus system (BA) were compared with 14 PC obtained from pooled buffy coats (BC). ii) The score values of 33 PC derived from BA as well from BC were compared with flow-cytometric CD62P determinations by cross correlation. iii) Changes in the score value profiles during storage of a single pathogen-reduced BA PC were monitored over a period of 7 days.

RESULTS

The TEM evaluation described allows for demonstrating particular PLT activation stages. i) Significant differences between the percentages of the score values 0, 1 and 2 could be demonstrated in both processing groups. No significant differences were found comparing these two groups. ii) A weak correlation could be shown when comparing the percentages of score values 2 plus 3 with the percentage of CD62P-positive PLT. iii) The pathogen reduction affected slightly the score profiles during storage due to an increase of dead PLT.

CONCLUSION

Our investigations demonstrate the unique detailed quality information of PC obtained by the TEM method. This method can be performed in every routine electron microscopy laboratory.

Singlet oxygen potentiates thrombolysis

Activated polymorphonuclear neutrophils (PMN) participate in physiologic thrombolysis. PMN produce large amounts of urokinase (u-PA) and oxidants of the hypochlorite/chloramine-type that generate nonradical excited singlet oxygen ((1)O(2)). The u-PA/(1)O(2)-mediated thrombolysis was imitated in vitro. One hundred microliters microclots of normal human plasma were oxidized with 25 microL 0 to 5.0 micromoles of chloramine-T in physiol. NaCl in the absence or presence of 100 microL 6% bovine serum albumin or 100 microL normal plasma. Twenty-five microliters 0 to 167 IU/mL (related to 150 microL added supernatant) u-PA or 0 to 2.08 microg/mL t-PA were added. The absorbance at 405 nm was determined after 0 to 27 hours (37 degrees C). The specific clot turbidity was calculated, subtracting the 100% lysis absorbance from the respective measured absorbance. The chloramine-effective dose 50% (ED(50)) after 27 hours was determined in the presence of 2.6 IU/mL u-PA. The plasminogen activator-ED(25) was determined after 2 hours (37 degrees C), and the ET(25); i.e., the time needed to lyse a microclot by 25%, was determined for each respective clot-oxidation. The ED(25) of u-PA depends on the oxidation of the microclots: 1.25 micromoles chloramine/100 microL clot enhances thrombolysis approximately 20-fold; here, 25% of clot lysis is achieved within 50 minutes (using approximately 20 IU/mL u-PA), whereas approximately 5 hours are needed to lyse an unoxidized microclot by 25%. The present global assay technique imitates the u-PA/(1)O(2) aspects of physiologic thrombolysis by PMN.

Pancreatic two P domain K+ channels TALK-1 and TALK-2 are activated by nitric oxide and reactive oxygen species

This study firstly shows with in situ hybridization on human pancreas that TALK-1 and TALK-2, two members of the 2P domain potassium channel (K(2P)) family, are highly and specifically expressed in the exocrine pancreas and absent in Langherans islets. On the contrary, expression of TASK-2 in mouse pancreas is found both in the exocrine pancreas and in the Langherans islets. This study also shows that TALK-1 and TALK-2 channels, expressed in Xenopus oocytes, are strongly and specifically activated by nitric oxide (obtained with a mixture of sodium nitroprussate (SNP) and dithiothreitol (DTT)), superoxide anion (obtained with xanthine and xanthine oxidase) and singlet oxygen (obtained upon photoactivation of rose bengal, and with chloramine T). Other nitric oxide and reactive oxygen species (NOS and ROS) donors, as well as reducing conditions were found to be ineffective on TALK-1, TALK-2 and TASK-2 (sin-1, angeli's salt, SNP alone, tBHP, H(2)O(2), and DTT). These results suggest that, in the exocrine pancreas, specific members of the NOS and ROS families could act as endogenous modulators of TALK channels with a role in normal secretion as well as in disease states such as acute pancreatitis and apoptosis.

The physiology and pharmacology of singlet oxygen

Reactive oxygen species (ROS) are generated by many different cells. Singlet oxygen (1O(2)) and a reaction product of it, excited carbonyls (C=O*), are important ROS. 1O(2) and C=O* are nonradicalic and emit light (one photon/molecule) when returning to ground state oxygen. Especially activated polymorphonuclear neutrophil granulocytes (PMN) produce large amounts of 1O(2). Via activation of the respiratory burst (NADPH oxidase and myeloperoxidase) they synthesize hypochlorite (NaOCl) and chloramines (in particular N-chlorotaurine). Chloramines are selective and stable chemical generators of 1O(2). In the human organism, 1O(2) is both a signal and a weapon with therapeutic potency against very different pathogens, such as microbes, virus, cancer cells and thrombi. Chloramines at blood concentrations between 1 and 2 mmol/L inactivate lipid enveloped virus and chloramines at blood concentrations below 0.5 mmol/L, i.e. at oxidant concentrations that do not affect thrombocytes or hemostasis factors, act antithrombotically by activation of the physiologic PMN mediated fibrinolysis; this thrombolysis is of selective nature, i.e. it does not impair the hemostasis system of the patient allowing the antithrombotic treatment in patients where the current risky thrombolytic treatment is contraindicated. The action of 1O(2) might be compared to the signaling and destroying gunfire of soldiers directed against bandits at night, resulting in an autorecruitment of the physiological inflammatory response. Chloramines (such as the mild and untoxic oxidant chloramine T (N-chloro-p-toluene-sulfonamide)) and their signaling and destroying reaction product 1O(2) might be promising new therapeutic agents against a multitude of up to now refractory diseases.

Singlet oxygen (1O2)-oxidazable lipids in the HIV membrane, new targets for AIDS therapy?

Human immunodeficiency virus (HIV) is a lipid enveloped virus. The lipid envelope differs significantly from the lipid membrane of normal human cells: it contains high amounts of cholesterol, that is of importance for the virus-cell interaction (for entry and exit of the virus) at so-called lipid rafts. Cholesterol, as a R-C=C-R compound possesses an oxidazable carbenic bond. The present work suggests the inactivation of HIV by oxidation of viral cholesterol and/or unsaturated fatty acids. For oxidation, the relatively mild oxidant singlet oxygen (1O(2)) might be used. 1O(2) is generated by redoxcyclers (e.g., of the quinone type, such as vitamin K) or by chloramines (e.g., taurine-chloramine). At the 1O(2) concentrations necessary to inactivate lipid enveloped virus in human blood the oxidation-sensible critical hemostasis parameters such as thrombocytes and fibrinogen are only partly inactivated. Therefore, it is proposed to consider generators of 1O(2) as a new form of AIDS therapy.

Platelets stimulated by IgG-coated surfaces bind and activate neutrophils through a selectin-dependent pathway

Blood platelets bind rapidly to foreign surfaces and interact with adsorbed proteins and neutrophil granulocytes. We demonstrate by use of luminol-amplified chemiluminescence under stirred and non-stirred conditions that platelets at IgG-coated surfaces amplify the neutrophil extracellular release of reactive oxygen species (ROS). The neutrophil response involved tyrosine phosphorylation, but was only in part induced by neutrophil F(c gamma)-receptor stimulation. The platelet mediated effects were contact-dependent since the respiratory burst was inhibited when the IgG-stimulated platelets were removed by filtration, but not when they were fixed in paraformaldehyde. Bodipyphallacidin-staining of filamentous actin (F-actin) revealed that an actin-dependent platelet adhesion supported the subsequent adhesion and spreading of neutrophils. The neutrophil ROS-response was lowered when the interaction between platelet P-selectin (CD62P) and neutrophil P-selectin glycoprotein ligand-l (PSGL-1 or CD162) was inhibited. The blocking of L-selectin (CD62L) or blocking of the interaction between platelet glycoprotein (Gp) IIb/IIIa and neutrophil complement receptor 3 (CR3) showed no effect. We conclude that platelet activation on immobilized IgG trigger a contact-dependent "frustrated" phagocytosis by neutrophils, associated with a release of toxic ROS.

Clinical application of the PFA-100

The PFA-100 (platelet function analyzer) is a relatively new tool for the investigation of primary hemostasis. Recent studies have shown its utility as a screening tool for investigating possible von Willebrand disorder (VWD) and various platelet disorders. More recently, the PFA-100 has been shown to be valuable in monitoring desmopressin acetate (DDAVP) therapy in both VWD and platelet disorders. The PFA-100 has also been evaluated in many other studies for its utility in assessing drug effects, for potential monitoring of antiplatelet medication (including aspirin), or for evaluation of overall primary hemostasis in various clinical disorders or during surgical procedures. This article reviews current findings and highlights the benefits and limitations of the clinical utility of the PFA-100. Ultimately, the greatest strengths of the PFA-100 are its simplicity of use and excellent sensitivity to particular hemostatic disturbances such as VWD, platelet disorders, and platelet-affecting medication. However, because it is thus a global test system, this also creates a significant limitation because the PFA-100 is not specific for, nor predictive of, any particular disorder. However, used appropriately, the PFA-100 can be considered a worthwhile addition to any hemostasis laboratory involved in the diagnosis or therapeutic monitoring of bleeding disorders and potentially of antiplatelet medication. This review should be valuable to both hemostasis scientists and clinical specialists.