Effects of DETANONOate, a nitric oxide donor, on hemostasis in rabbits: an in vitro and in vivo thrombelastographic analysis

Inhibitory effect of nitrite on coagulation processes demonstrated by thrombelastography

Nitric oxide (NO) can be generated by two-step reduction pathway in which nitrate is converted first into nitrite and then into NO via several mechanisms, as well as from arginine by endogenous nitric oxide synthase (NOS). We have recently shown that nitrite ions in the presence of erythrocytes inhibit platelet aggregation and activation, as measured by aggregometry and flow cytometric analysis of P-selectin, through its reduction to NO under partially deoxygenated conditions. In the current study, we investigated how nitrite may affect overall clotting processes via modulating platelet function using thrombelastography (TEG). We measured three major TEG parameters, reaction time (R, time to initial fibrin formation), α angle (velocity of clot growth) and maximum amplitude (MA, maximum clot strength) using blood from healthy volunteers. An NO donor (DEANONOate) showed inhibitory effects on all TEG parameters in platelet rich plasma (PRP) and whole blood, resulting in delayed R, decreased angle, and reduced MA in a dose dependent manner. Nitrite ions also exhibited inhibitory effects in whole blood at 20% hematocrit, and this was greatly enhanced under hypoxic conditions, being demonstrable at 0.1 μM concentration. Neither compound changed any TEG parameters in plasma. Our results suggest that nitrite affects overall blood clotting and that TEG may be used to follow this process. Further the physiological effects of factors which determine NO bioavailability, such as endogenous levels of blood and tissue nitrite, may be useful as biomarkers for predicting hemostatic potential.

Endothelial cells influence the sodium nitroprusside mediated inhibition of platelet aggregation by an as yet unkown pathway

The clinical use of Sodium nitroprusside (SNP) may be associated with an alteration of platelet function. The main focus of this study was the effect of SNP on platelet aggregation in the absence or presence of endothelial cells.

Methods: Platelets were incubated with different concentrations of SNP with and without endothelial cells. Platelet aggregation was induced by ADP.

Results: Platelet aggregation was significantly inhibited by all concentrations of SNP. Endothelial cells significantly increased this inhibitory effect of SNP. Time course studies showed an inverse correlation of incubation time to platelet aggregation inhibition in the absence of endothelial cells, and a direct correlation in the presence of endothelial cells. Blocking platelet and endothelial cell guanylate cyclase with 1 H-(1,2,4)-oxadiazolo(4,3-a) quinoxalin-1-one (ODQ), or pretreatment of the endothelial cells with cyclooxygenase – inhibitors, had no influence on the increased inhibitory effect of the endothelial cells. Cyanide reversed the inhibitory effect of SNP completely.

Conclusion: Endothelial cells play an important role in the SNP mediated inhibition of platelet aggregation. The effect is reversible only by cyanide, not by blocking classical NO signal transduction.

Neutrophil extracellular traps contain mitochondrial as well as nuclear DNA and exhibit inflammatory potential

Neutrophils expel extracellular traps (NETs) to entrap and exterminate the invaded micro-organisms. Acute/chronic inflammatory disorders are often observed with aberrantly enhanced NETs formation and high nitric oxide (NO) availability. Recent study from this laboratory demonstrated release of NETs from human neutrophils following treatment with SNP or SNAP. This study is an extension of our previous finding to explore the extracellular bacterial killing, source of DNA in the expelled NETs, their ability to induce proinflammatory cytokines release from platelets/THP-1 cells, and assessment of NO-mediated free radical formation by using a consistent NO donor, DETA-NONOate. NO-mediated NETs exhibited extracellular bacterial killing as determined by colony forming units. NO-mediated NETs formation was due to the activation of NADPH oxidase and myeloperoxidase. NO- or PMA-mediated NETs were positive for both nuclear and mitochondrial DNA as well as proteolytic enzymes. Incubation of NETs with human platelets enhanced the release of IL-1β and IL-8, while with THP-1 cells, release of IL-1β, IL-8, and TNFα was observed. This study demonstrates that NO by augmenting enzymatic free radical generation release NETs to promote extracellular bacterial killing. These NETs were made up of mitochondrial and nuclear DNA and potentiated release of proinflammatory cytokines.

Endothelial cells play an important role in the antiaggregatory effect of nitric oxide

OBJECTIVE

To investigate the role of endothelial cyclooxygenase in the antiaggregatory effect of nitric oxide, and to investigate the significance of the time span between contact of nitric oxide and platelets and laboratory evaluation by platelet aggregation.

DESIGN

Prospective, controlled, in vitro study.

SETTING

Research laboratory of a university hospital.

PARTICIPANTS

Three healthy volunteers.

INTERVENTIONS

Incubation of platelets with different concentrations (30 microM, 100 microM, 500 microM, 1000 microM) of the nitric oxide-donor S-nitroso-N-acetyl-d,l-penicillamine (SNAP) for varying incubation times (0 hrs, 1 hr, 2 hrs, 4 hrs) with and without endothelial cells. Induction of platelet aggregation with adenosine diphosphate. Inhibition of the effect of SNAP by 100 microM of the guanylate cyclase inhibitor 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ). Inhibition of prostacyclin production by endothelial cells with COX inhibitors acetyl salicylic acid (1 mM) and indomethacin (10 microM).

MEASUREMENTS AND MAIN RESULTS

Incubation with endothelial cells (= controls) had no effect on platelet aggregation. Platelet aggregation was significantly inhibited by all concentrations of SNAP. Time course studies with 30 microM of SNAP showed an inhibitory effect only after 0, 1, and 2 hrs of incubation, whereas after 4 hrs of incubation the inhibition of platelet aggregation could not be detected any more. Endothelial cells significantly increased the inhibitory effect of SNAP after 1 and 2 hrs of incubation. Incubation with ODQ with and without endothelial cells reversed the SNAP-mediated inhibition of maximum platelet aggregation regardless of the incubation time. Pretreatment of the endothelial cells with the COX inhibitors acetyl salicylic acid and indomethacin blocked the increased inhibitory effect of the endothelial cells after 1 and 2 hrs of incubation.

CONCLUSIONS

The time span between nitric oxide contact with platelets and induction of platelet aggregation by adenosine 5'-diphosphate is important for correct estimation of the antiaggregatory effect of nitric oxide. Endothelial cyclooxygenase plays an important role in the nitric oxide-mediated inhibition of platelet aggregation.

Nitric oxide decreases coagulation protein function in rabbits as assessed by thromboelastography

Nitric oxide (NO) is administered via infusion of donors such as nitroglycerin or in inhaled form for treatment of ischemia and pulmonary hypertension, respectively. In rabbits, the NO donor, DETANONOate, decreases whole blood clotting function as assessed by thromboelastographic variables (R, reaction time; alpha, angle; and G, a measure of clot strength). I hypothesized that DETANONOate-derived NO would adversely affect coagulation protein and platelet function. Blood obtained from ear arteries of conscious rabbits (n = 8) anticoagulated with sodium citrate. The blood was then incubated with 0 or 10mM DETANONOate for 30 min. After incubation and recalcification, thromboelastography was performed for 60 min under four conditions: 1) 0mM DETANONOate, 2) 0mM DETANONOate with platelet inhibition with cytochalasin D, 3) 10mM DETANONOate, and 4) 10mM DETANONOate with platelet inhibition. DETANONOate significantly (P < 0.05) increased R and decreased alpha and G in samples with or without platelet inhibition, compared with samples not exposed to DETANONOate. Lastly, the percentage of total G (G(T)) attributable to platelet function (G(P)) was significantly more in the absence of DETANONOate (G(P) = 92.3% +/- 1.6%; mean +/- SD) than after exposure to DETANONOate (G(P) = 90.2% +/- 2.3%). DETANONOate-derived NO significantly decreased coagulation protein function and platelet function. Coagulation protein function may be similarly affected in clinical situations involving the administration of NO or NO donors.