Inhibition of tissue plasminogen activator inhibitor by defibrotide in atherosclerotic patients

Kinetics of Anti-Xa Activity during Combined Defibrotide - Heparin Administration in Hemodialysis

Defibrotide, a polydesoxyribonucleotide derivative with antithrombotic and fibrinolytic activity, capable of inducing the release of PGI2 from vascular endothelia, was proposed as an alternative to standard heparin coverage during blood dialysis for patients at risk of bleeding. The original procedure featured the preliminary washing of the dialysis circuit with heparin, which was then recirculated and eliminated, and the two drugs, heparin and defibrotide, are known to interact with each other. The purpose of this present study was to explore the ex-vivo heparin activity (assessed as anti-Xa activity) in diverse hemodialysis models using defibrotide (800 mg intravenous, in 4 bolus injections) and various dosages of heparin. Anti-Xa activity is negligible in dialysis conducted with defibrotide alone. When the circuit was prewashed with heparin (5000 and 2500 IU), there was evident anti-Xa activity (0.3-0.5 U/ml) in the first 30-60 minutes of dialysis; continuous heparin infusion (500 U/hour) resulted in high anti-Xa activity levels at the end of dialysis. Thus the best hemodialysis procedure for patients at high risk of bleeding should be one utilizing only defibrotide, or defibrotide plus small amounts of calcium heparin infused at the rate of 500 U/hour for not more than two hours.

Defibrotide: a review on clinical use and future development

BACKGROUND

Defibrotide is a deoxyribonucleic acid derivative that has been developed for the treatment of different vascular disorders.

OBJECTIVE

The authors reviewed the literature to give due representation to the spectrum of pharmacological properties and clinical application of this drug, evaluating consolidate and innovative application.

METHODS

The authors used PubMed from November 1982 to December 2007 and meeting abstracts (form American Society of Hematology Annual Meeting) with updated data as the sources for this review and selecting the most relevant papers when two or more articles covered the same point of interest.

CONCLUSIONS

Defibrotide has been used effectively in the treatment of endothelial complications of allogeneic stem cell transplantation and recent preclinical evidences suggest an antiangiogenic effect and an anticancer activity. Further in vivo and in vitro investigations are needed.

Effective DNA inhibitors of cathepsin g by in vitro selection

Cathepsin G (CatG) is a chymotrypsin-like protease released upon degranulation of neutrophils. In several inflammatory and ischaemic diseases the impaired balance between CatG and its physiological inhibitors leads to tissue destruction and platelet aggregation. Inhibitors of CatG are suitable for the treatment of inflammatory diseases and procoagulant conditions. DNA released upon the death of neutrophils at injury sites binds CatG. Moreover, short DNA fragments are more inhibitory than genomic DNA. Defibrotide, a single stranded polydeoxyribonucleotide with antithrombotic effect is also a potent CatG inhibitor. Given the above experimental evidences we employed a selection protocol to assess whether DNA inhibition of CatG may be ascribed to specific sequences present in defibrotide DNA. A Selex protocol was applied to identify the single-stranded DNA sequences exhibiting the highest affinity for CatG, the diversity of a combinatorial pool of oligodeoxyribonucleotides being a good representation of the complexity found in defibrotide. Biophysical and biochemical studies confirmed that the selected sequences bind tightly to the target enzyme and also efficiently inhibit its catalytic activity. Sequence analysis carried out to unveil a motif responsible for CatG recognition showed a recurrence of alternating TG repeats in the selected CatG binders, adopting an extended conformation that grants maximal interaction with the highly charged protein surface. This unprecedented finding is validated by our results showing high affinity and inhibition of CatG by specific DNA sequences of variable length designed to maximally reduce pairing/folding interactions.

BMT: Bone Marrow Transplant Associated Thrombotic Microangiopathy

Thrombotic microangiopathy is a severe microvascular disorder which may occur in up to 70% of patients undergoing bone marrow transplant. Clinically the term thrombotic microangiopathy encompasses a wide spectrum of syndromes, most importantly the thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS). Thrombotic microangiopathy is characterized by the presence of thrombocytopenia, microangiopathic hemolytic anemia, renal impairment, neurological disturbances and multiorgan failure. Several causative agents have been advocated as triggering factors for bone marrow transplant associated thrombotic microangiopathy, including cyclosporine, FK506, the use of total body irradiation, infections and the presence of severe graft-versus-host disease. Plasma exchange represents the standard treatment for patients who develop TTP/HUS after bone marrow transplant, however, the mortality rate still remains high despite aggressive therapy.

Impact of thrombotic thrombocytopenic purpura on leukemic children undergoing bone marrow transplantation

Thrombotic thrombocytopenic purpura (TTP) has emerged as one of the main transplant-related complications over the last 15 years. The current study defines the incidence and the risk factors for the occurrence of TTP in 131 consecutive leukemic children who were transplanted between January 1994 and December 1997 at four Italian pediatric centers. Patients with ALL (101), AML (21), MDS (9), underwent an HLA-identical sibling BMT (82) or an HLA-identical unrelated BMT (49), receiving a conditioning regimen consisting of high-dose chemotherapy in 24 patients and of F-TBI combined with high-dose chemotherapy in 107 patients. The diagnosis of TTP was retrospectively evaluated on the basis of parallel criteria. TTP treatment varied according to the protocol of each treatment center. Twenty-eight of 131 patients (21.4%) developed TTP at a median of 46 days (range 21-80) after BMT. Multivariate analysis demonstrated that the risk of TTP was higher in patients who underwent unrelated BMT (P value = 0.02). Acute GVHD, stage of disease at BMT, conditioning with TBI, gender, age, did not appear to be associated with the occurrence of TTP. As to the outcome, TTP resolved in 19 patients while in nine it was the principal cause of death (32.1%). In patients with TTP, LDH peak value was the only statistically significant factor (P = 0.001) related to severe TTP. In conclusion, our experience demonstrates that leukemic children undergoing BMT, especially from an unrelated donor, should be carefully assessed for TTP which appears to be a severe and relatively common transplant-related complication when strict diagnostic criteria are applied.

Defibrotide versus heparin in the prevention of coronary reocclusion after thrombolysis in acute myocardial infarction

A multicenter controlled study versus heparin was conducted to explore the activity of defibrotide, a polydesoxyribonucleotide drug, in preventing reocclusion after urokinase thrombolysis in patients with acute myocardial infarction (AMI). The study involved 137 consecutive patients with AMI and a time from the onset of symptoms < or = 6 hours, treated with urokinase (1,000,000 U intravenous bolus followed by 1,000,000 U slow-drip infusion over 12 hours). Immediately after thrombolysis, patients were allocated to treatment with defibrotide (group D: day 0, 3.6 g by intravenous infusion in 12 hours; days +1 to +6, 800 mg tid intravenously; days +7 to +10/+12, 400 mg tid intramuscularly), or heparin (group H: day 0, 1000 IU/hour infused over 12 hours; days +1 to +10/+12, 5000 IU tid subcutaneously). Coronary angiography was done, whenever possible, at +10/+12 days. The following parameters were assessed: (a) noninvasive estimate of myocardial reperfusion, through the analysis of CPK time-activity curves; (b) incidence of infarct-related artery (IRA) patency (TIMI scores 2-3) at coronary angiography. A total of 125 patients had a complete enzymatic curve (63 in group D and 62 in group H) and 106 had coronary angiography as well. IRA patency (the main end point) was observed in 63% of group D versus 43% of group H patients (p = 0.07). No statistically significant differences were found in the proportion of patients with indirect signs of early reperfusion (63% in group D versus 52% in group H patients).(ABSTRACT TRUNCATED AT 250 WORDS)

Defibrotide. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in vascular disorders

Defibrotide is a deoxyribonucleic acid derivative extracted from mammalian organs, which has been developed for the treatment of a number of vascular disorders. It appears to increase fibrinolysis and may possess antithrombotic, antiatherosclerotic and anti-ischaemic actions, probably due to its ability to selectively increase prostaglandin I2 and E2 levels and to increase tissue plasminogen activator and decrease plasminogen activator inhibitor function. Defibrotide is available as an intravenous and intramuscular preparation, and also as an oral formulation for long term use. Trials performed to date have provided initial evidence that defibrotide is effective in the treatment of peripheral obliterative arterial disease and acute thrombophlebitis, while preliminary data suggest possible use in preventing fibrin deposition in the circuitry of renal haemodialysis equipment. Efficacy in preventing deep vein thrombosis after surgery has been demonstrated but defibrotide does not appear to offer any therapeutic advantage over heparin. Further clinical experience is required in other disorders, including acute myocardial infarction, Raynaud's phenomenon, renal thrombotic microangiopathy and renal transplant rejection, before adequate assessment of efficacy in these areas can be made. Defibrotide is well tolerated, as assessed in trials of up to 6 months duration, with a low global incidence of adverse events (< 1 to 9%). Mild allergic reactions and gastrointestinal disturbances have occasionally been described, and a hypotensive effect has also infrequently been observed. Thus, available data suggest that defibrotide is a well tolerated agent with little or no anticoagulant activity, which is conveniently available in both parenteral and oral formulations. Initial data indicate that the drug may be a useful alternative in the treatment of peripheral obliterative arterial disease and thrombophlebitis, while its therapeutic potential in other vascular disorders and efficacy relative to established agents remains to be fully determined.

Fibrinolytic enhancement in diabetic microangiopathy with defibrotide

Skin microcirculation was evaluated in 117 patients with diabetic microangiopathy over a period of six months. They were divided into two groups. Group 1 (64 patients) was treated with oral defibrotide, a new profibrinolytic drug, in association with diet and oral antidiabetic drugs. Group 2 (53 patients) was treated only with diet and antidiabetic agents. The microcirculation was studied by means of laser-Doppler flowmetry transcutaneous partial pressure of oxygen and carbon dioxide pressure measurements, and evaluation of capillary filtration. After six months, patients in group 1 improved their microcirculatory parameters in association with an improvement in signs and symptoms. Moreover, 30 patients in group 1 and 36 in group 2 were followed up for eighteen months, and the authors observed that the deterioration of the microcirculatory parameters was significantly slowed in diabetics treated with defibrotide. A decrease in plasma fibrinogen during defibrotide treatment was observed in all treated patients in association with an increased fibrinolytic activity. In conclusion, it appears that defibrotide, enhancing fibrinolysis, improved the microcirculation in diabetics, preventing further, progressive deterioration.

Effect of oral defibrotide on tissue-plasminogen activator and tissue-plasminogen activator inhibitor balance

Defibrotide, a polydeoxyribonucleotide of mammalian origin, has been shown to reduce the blood level of the plasminogen activator inhibitor, and so to increase the activity of tissue plasminogen activator without any adverse effect. A randomized, double-blind, placebo-controlled study has been done in 22 patients, 14 with peripheral vascular disease, 6 with coronary heart disease and 2 with cerebrovascular disease. Patients were given defibrotide 400 mg b.d. or identical placebo for 30 days and the parameters of fibrinolysis were evaluated before and after the treatment. A significant increase in tissue plasminogen activator activity at rest and after venostasis was observed after defibrotide; tissue plasminogen activator antigen at rest and after venostasis was not affected by either treatment. Defibrotide significantly reduced plasminogen activator inhibitor activity and antigen at rest. Only one patient complained of gastric pain after placebo treatment. The study shows that defibrotide has profibrinolytic property and that it could be used to explore the role of plasminogen activator inhibitor in venous and arterial thrombosis.

Effects of defibrotide on fibrinolytic activity in diabetic patients with stable angina pectoris

18 type II diabetes mellitus patients with coronary artery disease (CAD) have been studied. Tissue plasminogen activator (t-PA) antigen and activity, plasminogen activator inhibitor (PAI) antigen and activity, thrombin-antithrombin III (TAT) complexes were determined in blood samples. Diabetic CAD patients showed higher TAT levels with clearly increased PAI levels whereas t-PA levels levels were similar in patients and controls. Long term defibrotide treatment induced marked changes in fibrinolytic parameters of these diabetic patients with CAD with increased t-PA activity, that could be related to an evident reduction of PAI antigen and activity. Drugs able to modulate PAI activity may be useful in clinical conditions at high risk of thrombotic vascular complications like diabetics with stable angina.

The venoarteriolar response in diabetics

Resting skin blood flow and the venoarteriolar response (VAR) were studied in 40 patients with diabetic microangiopathy and neuropathy, in 40 diabetics with microangiopathy, and in 30 normal subjects by means of laser-Doppler flowmetry. In patients with microangiopathy and neuropathy, resting flow (RF) was increased and the VAR was impaired to a greater extent than in patients without neuropathy. There was also a significant delay in the VAR in diabetics, particularly in patients with neuropathy. The microangiopathy index (VAR/RF) was on the average 71.3 in normal subjects, significantly lower (p less than 0.05) in diabetics without neuropathy (34.8), and even lower in those with neuropathy (13.6). The VAR was evaluated with different postural changes; The authors observed that in the passage from supine to standing the VAR is more evident. In conclusion these results confirm that the postural control of blood flow in the skin of the foot is impaired in diabetic microangiopathy, particularly in patients with neuropathy. The increased skin blood flow and the impaired VAR are causes of edema and may contribute to the thickening of capillary basement membranes observed in diabetes.