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Neutrophil-mediated activation and injury of the endothelium play roles in the pathogenesis of diverse disease states ranging from autoimmunity to cancer to COVID-19. Neutralization of cationic proteins (such as neutrophil extracellular trap-derived [NET-derived] histones) with polyanionic compounds has been suggested as a potential strategy for protecting the endothelium from such insults. Here, we report that the US Food and Drug Administration-approved polyanionic agent defibrotide (a pleiotropic mixture of oligonucleotides) directly engages histones and thereby blocks their pathological effects on endothelium. In vitro, defibrotide counteracted endothelial cell activation and pyroptosis-mediated cell death, whether triggered by purified NETs or recombinant histone H4. In vivo, defibrotide stabilized the endothelium and protected against histone-accelerated inferior vena cava thrombosis in mice. Mechanistically, defibrotide demonstrated direct and tight binding to histone H4 as detected by both electrophoretic mobility shift assay and surface plasmon resonance. Taken together, these data provide insights into the potential role of polyanionic compounds in protecting the endothelium from thromboinflammation with potential implications for myriad NET- and histone-accelerated disease states.

Background/aim: In this study, we aimed to investigate the additive effect of mesenchymal stem cells (MSC) and defibrotide (DFT) in a rat model of femoral arterial thrombosis., Methods: Thirty Sprague Dawley rats were included. An arterial thrombosis model by ferric chloride (FeCl3) was developed in the left femoral artery. The rats were equally assigned to 5 groups: Group 1-Sham-operated (without arterial injury); Group 2-Phosphate buffered saline (PBS) injected; Group 3-MSC; Group 4-DFT; Group 5-MSC + DFT. All had two intraperitoneal injections of 0.5 ml: the 1st injection was 4 h after the procedure and the 2nd one 48 h after the 1st injection. The rats were sacrificed 7 days after the 2nd injection., Results: Although the use of human bone marrow-derived (hBM) hBM-MSC or DFT alone enabled partial resolution of the thrombus, combining them resulted in near-complete resolution. Neovascularization was two-fold better in hBM-MSC + DFT treated rats (11.6 ± 2.4 channels) compared with the hBM-MSC (3.8 ± 2.7 channels) and DFT groups (5.5 ± 1.8 channels) (P < 0.0001 and P= 0.002, respectively)., Conclusion: The combined use of hBM-MSC and DFT in a rat model of arterial thrombosis showed additive effect resulting in near-complete resolution of the thrombus.

Each year in the US, more than 10 000 patients benefit from allogeneic haematopoietic stem cell transplantation (HSCT), a modality that offers an excellent chance of eradicating malignancy but confers a higher risk of treatment-related mortality. An uncommon but devastating consequence of HSCT is transplantation-associated thrombotic microangiopathy (TA-TMA). The incidence of TA-TMA ranges from 0.5% to 76%, with a mortality rate of 60-90% despite treatment. Although there appears to be a consistent treatment approach to idiopathic thrombotic thrombocytopenic purpura (TTP) using plasma exchange, corticosteroids and rituximab, the treatment strategies for TA-TMA are perplexing, in part, because the literature regarding this complex condition does not provide true consensus for incidence, aetiology, diagnostic criteria, classification and optimal therapy. The classic definition of idiopathic TTP includes schistocytes on the peripheral blood smear, thrombocytopenia and increased serum lactate dehydrogenase. Classic idiopathic TTP has been attributed to deficient activity of the metalloproteinase responsible for cleaving ultra-large von Willebrand factor multimers. This protease is a member of the 'a disintegrin and metalloprotease with thrombospondin type 1 motif' family and is subsequently named ADAMTS-13. Severely deficient ADAMTS-13 activity (<5% of normal) is associated with idiopathic TTP in 33-100% of patients. In constrast to the pathophysiology of idiopathic TTP, patients with TA-TMA have >5% ADAMTS-13 serum activity. These data may explain why plasma exchange, a standard treatment modality for idiopathic TTP that restores ADAMTS-13 activity, is not effective in TA-TMA. TA-TMA has a multifactorial aetiology of endothelial damage induced by intensive conditioning therapy, irradiation, immunosuppressants, infection and graft-versus-host disease. Treatment consists of substituting calcineurin inhibitors with an alternative immunosuppressive agent that possesses another mode of action. One candidate may be daclizumab, especially in those with mild to moderate TMA. Rituximab therapy or the addition of defibrotide may also be beneficial. In general, plasma exchange is not recommended.

The authors report a case of a patient with a refractory ascites due to extrahepatic portal thrombosis in course of idiopathic thrombocythemia. A peritoneovenous shunt was applied and as a late complication a massive thrombosis of the intracardiac portion of the duct developed. Thrombolysis was obtained with tissue plasminogen activator at doses usually administered for acute myocardial infarction. Prophylaxis of recurrence was pursued with pictomide and defibrotide.

Thrombotic microangiopathy (TMA) can occur whenever pathogenetic events lead to fibrin deposition in the microcirculation. It has been suggested that intravascular coagulation is important in the development of renal as well as cerebral lesions. The mortality rate in adults varies from 50 to 70%; chronic or progressive renal failure occurs in approximately two thirds of children over 2 years of age. Poor success may be due to therapy being initiated too late or to inappropriate use of antagonistic drugs, or both. In the last 2 years we have treated 8 patients with TMA (5 with thrombotic thrombocytopenic purpura; 3 with hemolytic uremic syndrome) with defibrotide, a new antithrombotic agent extracted from mammalian lungs. At admission all patients had severe renal involvement (serum creatinine 5.3-14.9 mg/dl) and coagulation abnormalities (low platelet count; high levels of circulating fibrin degradation products). There were neurological manifestations in 6 patients. Defibrotide administration was followed in 6 patients by recovery of renal function. In all patients, defibrotide therapy induced the disappearance of neurological manifestations and normalization of coagulation abnormalities. Defibrotide caused no side effects. All patients are alive after 7-22 months of follow-up.

Total intraparenteral nutrition therapy using an endocaval catheter is subject to complications due to the catheter itself and to the onset of phlebothrombosis of the venous district involved. Two groups of patients suffering from abdominal surgical pathologies requiring prolonged postoperative parenteral treatment were subjected to antithrombotic prophylaxis. In the first group of 20 patients, calciheparin u.s. was used and in the second defibrotide in the doses recommended in the literature. Serial lab screening of certain clotting parameters was carried of the brachio-subclavio-caval district. In the calciheparin group, the trend of certain examinations shows, as usual, a change in parameters in agreement with the drug's anticlotting action; in the group treated with defibrotide, the haemostatic balance is respected: the angiographies never showed intimal lesion or phlebothrombosis in either group. The usefulness of correct antithrombotic prophylaxis in these patients is confirmed and it is pointed out that defibrotide is more flexible and handy and that it can be used in patients in whom calciheparin is potentially risk.

8 patients with thrombotic microangiopathy were treated with a new antithrombotic agent, defibrotide. This drug displays considerable fibrinolytic and antithrombotic activity, and induces generation and release of a prostacyclin-like substance from vascular tissue. At admission all patients presented severe renal involvement and coagulation abnormalities. Neurological manifestations were present in 6. Defibrotide administration was followed by recovery of renal function in 6, disappearance of neurological symptoms and coagulation abnormalities in all patients. The use of defibrotide was not associated with side effects. On the basis of the results obtained in these patients, we suggest that defibrotide might be considered as a valuable drug in the management of patients with thrombotic microangiopathy.

In an open multicenter comparative study aimed at the evaluation of the efficacy of defibrotide in the prophylaxis of postsurgical deep vein thromboses (DVT) an ad interim evaluation has been made on 2626 patients thus far enrolled. 1323 had received defibrotide (200 mg q.i.d. by IV route from day -1 to day +7th postoperative), 941 calcium heparin (5000 IU b.i.d. or t.i.d. by SC route from day 0 to day +7 postoperative) and 362 other treatments (antiaggregating agents, placebo or no therapy). This group has not been included in the final evaluation, due to its limited size. The diagnosis of DVT or pulmonary embolism (PE) was made according to clinical routinary criteria. The incidence of DTV has been 15/1323 (1.13%) in the defibrotide group and 21/941 (2.23%) in the heparin group (chi-square, p = 0.056) while the cases of suspected or ascertained PE have been respectively 3/1323 (0.22%) and 10/941 (1.06%) (p = 0.02). The incidence of adverse effects with defibrotide was less than 1%; occasional cases of increased serum transaminase levels were seen with heparin. These preliminary results supports the effectiveness of defibrotide in the prevention of post-surgery DVT, its effects being similar or more prominent than those of calcium heparin, currently regarded as the standard medication.

Eighty transplanted patients were randomized to receive either a new antithrombotic agent, defibrotide (group A), or dipyridamole (group B) in addition to immunosuppressive therapy, in order to evaluate the effectiveness of these drugs in preventing graft vascular damage. While the incidence of rejection and the occurrence of specific anti-HLA antibodies were similar in the two groups, the peak serum creatinine levels during rejection were significantly lower in patients treated with defibrotide (3.3 +/- 1.8 versus 5.6 +/- 2.4 mg/dl; P less than 0.01), 97.5 per cent of whom had a still-functioning graft after a mean follow-up period of 24 months, compared with 80.5 per cent of the patients treated with dipyridamole (P less than 0.05). Graft biopsy, carried out during rejection, showed less severe vascular lesions in patients from group A than in those from group B. Our results suggest that the prophylactic administration of defibrotide may play a role in improving the long-term results of renal transplantation.