A novel insight into the mechanism of the antithrombotic action of defibrotide

Defibrotide: properties and clinical use of an old/new drug

The drug named defibrotide (DFT) has been studied for many years. It has been shown to possess many activities: profibrinolytic, antithrombotic-thrombolytic, antiischemic (heart, liver, kidney, skin, brain), antishock, antiatherosclerotic, antirejection and anti-angiogenic. The previously displayed activities, as antithrombotic, profibrinolytic and anti-inflammatory, suggested its use in vascular disorders, as in the treatment of peripheral obliterative arterial disease and in thrombophlebitis. Some years after, the use of DFT in hepatic veno-occlusive disease has been also proposed. Even if DFT was considered for long time a multi-target drug, now it could be considered on the whole as a drug able to protect endothelium against activation. The present work reviews the more important experimental and clinical studies performed to detect DFT effects.

Defibrotide normalizes cardiovascular function hampered by established atherosclerosis in the rabbit

In a previous paper we gave evidence that chronic oral defibrotide antagonizes the noxious effect of developing atherosclerosis in the cardiovascular system. In the present paper we give evidence that defibrotide is still capable of exerting beneficial effects on cardiovascular function once atherosclerosis is established. In fact, there was statistically significant amelioration by defibrotide infusion in the following, all of which were hampered by established atherosclerosis: in rabbit aorta relaxation to acetylcholine, prostaglandin E2, and 6-keto-prostaglandin F1alpha generation from rabbit aortas, rabbit heart left ventricular end-diastolic pressure, coronary perfusion pressure, and left ventricular developed pressure, vasopressor activity of acetylcholine and endothelin-1 on coronary perfusion pressure, and 6-keto-prostaglandin F1alpha generation from the rabbit heart. Since prostacyclin takes part in NO generation, is cellular protective, and inhibits 5-lipoxygenase product synthesis, its increase, caused by defibrotide, could explain defibrotide cardioprotective activity. Prostacyclin activity could be backed by prostaglandin E2, another cardioprotective prostaglandin.

Defibrotide activity in experimental frostbite injury

The pathogenesis of frostbite injury has not been completely elucidated although the available evidence suggests it is an inflammatory reaction following reperfusion injury. Defibrotide given i.p. at 40 mg/kg/ day for three days to rabbits, the ears of which were subjected to frostbite, decreased the presence of inflammatory cells (mast cells -76%; neutrophils -40.4%) and increased prostaglandin I2 (PGI2) (as 6-Keto-PGF1 alpha) in the involved skin. Thromboxane A2 (TxA2) (as TxB2) was unaffected. These data strengthen the view that an inflammatory process is the underlying cause of frostbite injury and that Defibrotide is active in pathological situations involving an inflammatory process like in frostbite.

Effects of defibrotide on leukocytosis in rabbits with diet-induced atherosclerosis

The antithrombotic drug Defibrotide (DFT) (a polydeoxyribonucleotide with a mean MW of 20,000 Daltons) reduces the number of leukocytes and platelets in thrombi. Because leukocytes and platelets are of importance in the genesis of endothelial lesions leading to atherosclerosis, DFT was given to challenge leukocytosis in rabbits with diet-induced atherosclerosis (0.25% cholesterol for 16 weeks). After 9 weeks of cholesterol feeding and at the end of experiment, oral DFT (60 mg/Kg per day) had decreased the leukocyte count raised by the cholesterol diet. Leukocyte stickiness and leukocyte differential counts were not modified by either oral cholesterol or by oral cholesterol plus oral DFT. At the end of experiment, oral DFT had normalized the platelet count increased by cholesterol diet. The red blood cell count decreased by oral cholesterol at 9 weeks and at the end of experiment was normalized by DFT. The % of aortae endothelial surface involved in the atherosclerotic process was decreased by oral DFT. The frequencies of intimal thickening in blood vessels of kidneys and hearts and in cardiac valves were reduced by oral DFT by 47%, 29% and 17%, although these reductions were not statistically significant. It is suggested that DFT, by preventing the increase in the number of leukocytes and platelets and deactivating them, as demonstrated in papers already published, was able to counteract against the atherosclerotic process.

Defibrotide protects endothelial cells, but not L929 tumour cells, from tumour necrosis factor-alpha-mediated cytotoxicity

The effect of defibrotide on the cytotoxicity of tumour necrosis factor-alpha was investigated in cultured bovine pulmonary artery endothelial cells and L929 mouse tumour cells. In endothelial cells, a 72-h incubation with tumour necrosis factor-alpha (1 and 10 ng mL-1) reduced the number of viable cells to 63 and 51% of control, respectively. Simultaneous incubation with defibrotide (0.03-0.3 mg mL-1) protected endothelial cells from tumour necrosis factor-alpha-mediated cytotoxicity, and increased viability in a concentration-dependent fashion to 98% of control at 1 ng mL-1 tumour necrosis factor-alpha and to 80% of control at 10 ng mL-1 tumour necrosis factor-alpha. However, under the same conditions a similar cytotoxic response to tumour necrosis factor-alpha in L929 tumour cells remained unaltered in the presence of defibrotide. These findings demonstrate protection from tumour necrosis factor-alpha-mediated toxicity by defibrotide in endothelial cells but not in a tumour cell line. It is concluded that defibrotide might serve as a therapeutic agent to limit the vascular toxicity of tumour necrosis factor-alpha without affecting its antineoplastic activity.

Defibrotide's activity on leukocytes and platelets in rabbits with diet-induced atherosclerosis

Oral Defibrotide decreased leukocyte and platelet counts, raised by cholesterol diet, and the area (%) of aorta endothelial surface involved in atherosclerosis. Frequency of intimal thickening in blood vessels of kidneys and hearts and in cardiac valves was reduced by oral Defibrotide by 47%, 29% and 17%. It is suggested that oral Defibrotide reduced the involvement of the aorta in the atherosclerotic process by acting on leukocytes and platelets, to both reduce their number and deactivate them.