Effect of a sulphated glycopeptide on rat gastric acid secretion stimulated by histamine, bethanechol, pentagastrin and dibutyryl cyclic AMP.

The antisecretory activity of a semisynthetic sulphated glycopeptide (GLPS) was studied in rats in which the secretion rates of gastric acid were detennined on the perfused stomach preparation. GLPS at 1 mg/kg i.v. reduced the hypersecretory effect of dibutyryl cyclic AMP, histamine, pentagastrin, bethanechol but not of theophylline.

Inhibition of gastric acid secretion by a glycoprotein isolated from human urine (human urinary gastric inhibitor).

The gastric antisecretory activity of an inhibitor newly isolated from human urine (Human Urinary Gastric Inhibitor or HUGI) has been studied. HUGI was given intravenously and its activity determined in the following test systems: gastric secretion in the rat with pyloric ligation; gastric secretion in the dog with a Heidenhain pouch stimulated with pentagastrin, histamine and a protein meal; acid secretion by the isolated gastric mucosa of the rat; gastrointestinal motility; bile flow and gall-bladder tone and arterial and venous blood pressure and heart rate. HUGI was found to have marked activity only in the pyloric-ligated rats and in the dogs with Heidenhain pouches stimulated by a protein meal. Particularly in the dog, HUGI (0.1 to 6.4 micrograms/kg, i.v) markedly inhibited gastric secretion, dose-dependently and without changing the plasma gastrin concentration. Negative results were obtained in the other tests, but these results serve to demonstrate that HUGI is an inhibitor well-differentiated from other glycoproteins or peptides with gastric antisecretory activity, such as urogastrone and GIP. The results obtained to date are not sufficient to allow the mechanism of action of HUGI to be defined.

Defibrotide, a single-stranded polydeoxyribonucleotide acting as an adenosine receptor agonist.

The binding of single-stranded polydeoxyribonucleotides to adenosine A1 and A2 receptors was investigated. Defibrotide, a natural substance with established anti-thrombotic and anti-ischaemic effects, displaced [3H]CHA (N6-cyclohexyl-adenosine) and [3H]NECA (5'-N-ethylcarboxamido-adenosine) concentration dependently, completely and competitively. Ki values of 371 +/- 68 and 688 +/- 115 micrograms/ml (mean +/- S.E.M. of 4-5 replications) were computed for adenosine A1 and A2 sites, respectively. Higher and lower molecular weight polydeoxyribonucleotides displayed comparable affinity, whereas a double-stranded polydeoxyribonucleotide and a polyanion with a negative charge comparable to that of defibrotide were inactive. Defibrotide did not affect the total number of binding sites in radioligand saturation experiments. Defibrotide relaxed the K(+)-contracted guinea-pig trachealis muscle (IC50 = 4001 micrograms/ml) about one-third as potently as the CHA-contracted preparation and as potently as the resting preparation. NECA, a mixed adenosine A1/A2 receptor agonist, behaved similarly. The effects were abolished by the adenosine A1/A2 receptor blocker 8-phenyltheophylline, but not by the selective A1 blocker, 1,3-dipropyl-8-(2-amino-4-chlorophenyl)-xanthine. These results demonstrate that defibrotide binds to adenosine receptors and triggers pharmacological responses comparable to those of a known agonist.

Pharmacokinetics of Defibrotide and of its profibrinolytic activity in the rabbit.

An extensive study of the pharmacokinetics and the pharmacokinetics of the profibrinolytic activity of Defibrotide (D) in the rabbit has been made. a two compartment model was used to describe D's pharmacokinetics. The parameters of drug disposition and the rate constant of release from tissues to central compartment were closely dose-dependent. The dose-response curves for elimination parameters were powers with a negative exponent indicating considerable saturation of this process. As a consequence, the T1/2, Co and AUC were also dose-dependent, as were the parameters describing the decrease in profibrinolytic activity in the blood stream.

Protective activity of defibrotide against lethal acute myocardial ischemia in the cat.

Defibrotide (D) is a natural polydeoxyribonucleotide from mammalian lungs with profibrinolytic and antithrombotic activities. D also has PGI2-stimulating and tissue plasminogen activator (TPA)-releasing activities, but has no anticoagulant properties. The protective effects of D were demonstrated very recently in a model for non-lethal ischemia in the cat. In the experiments reported here Defibrotide was tested in a model for acute myocardial ischemia leading to ventricular fibrillation (VF) and death of the cat. Occlusion of the coronary artery (LAD) at its origin induced VF and death in 17 of 20 control cats. When cats were treated with D (32 mg Kg-1, bolus i.v., + 32 mg Kg-1 h-1, i.v., after LAD occlusion) 19 of 20 animals survived until the end of experiments. D also prevented changes in plasma and myocardial CPK, hemodynamics and ECG. D was compared with a variety of pharmacological agents which are used clinically for specific cardiovascular diseases. The ability of D to promote considerable generation of PGI2 from vascular walls plus its ability to prevent the decreases in CPK-activity and ATP in the myocardial tissue may have roles in its beneficial effects against ischemic heart in the cat. However, the mechanism/s of the substantial protective effect of D against cardiac death has still to be clarified.

Cardioprotective effects of defibrotide in acute myocardial ischemia in the cat.

We investigated the effects of Defibrotide (D), a natural polydeoxyribonucleotide, on acute myocardial ischemia (AMI) in anesthetized cats. A permanent ligature was placed around the left anterior descending coronary artery (LAD) 12-14 mm from its origin. Ventricular fibrillation and death were exceptional and when they occurred the cats were not included in the evaluation. Pretreatment of cats with D, 32 mg Kg-1 h-1, i.v. infusion, maintained throughout the 5 h occlusion period, reduced AMI-ST segment increases and increased the diminished pressure-rate index (PRI). AMI-induced changes in lactate, ATP and CPK in ischemic tissue were prevented by D. PGI2 gave the same results as D. Atenolol prevented the loss of myocardial CPK, but had no favourable effects on lactate and ATP in ischemic tissue. The beneficial effects of D in AMI reported here could be partly attributed to its ability to enhance PGI2 release from vascular walls; D might also relieve ischemia by improvement of local tissue oxygenation, energy supplies and platelet function by its ability to deaggregate platelet clumps.

Profibrinolytic activities of chemically modified heparins with very low anticoagulant activities.

Many evidences indicate that heparin is an activator of fibrinolysis, but the most important side effect of heparin is bleeding which is a problem particularly in the high risk patient. Here we describe how chemical modifications, associated with separation techniques, can sharply reduce the anticoagulant activities of a heparin while its ability to stimulate fibrinolysis is retained.

Pharmacokinetics, absorption, distribution and disposition of [125I]-defibrotide following intravenous or oral administration in the rat.

Defibrotide (D) was labelled with 125I. The radiolabelled compound ([125I]-Defibrotide ([125I]-D)) retained the same profibrinolytic activity as the parent drug. Following single intravenous administration of [125I]-D the half lives of radioactivity associated with D components in plasma were 9.45 min and 11.27 h for alpha and beta phases respectively. Following single oral administration of [125I]-D the half life of radioactivity associated with D components in plasma was 12.83 h for the elimination phase. Bioavailability was apparently 58%. The areas under plasma total radioactivity versus time curves were dose-dependent following both intravenous and oral administration. No significant accumulation of total radioactivity in plasma was observed following multiple oral administration of [125I]-D. Following single intravenous administration of [125I]-D a larger proportion of administered radioactivity was excreted via urine than faeces while following single oral administration excretion via urine and faeces accounted for similar proportions of administered radioactivity. Following both single and oral administration the levels of total radioactivity in tissues and organs examined were generally highest in highly perfused organs and were very high in the thyroid despite pretreatment with non-radiolabelled potassium iodide. Radioactivity was also found to be associated with the aorta wall.

Defibrotide has antiischemic activity in perfused rabbit hearts, preventing tissue Ca++ overloading.

Defibrotide (D), a polydeoxyribonucleotide obtained from mammalian lungs, reduced the ischemic contracture due to low perfusion (0.2 ml/min) of the isovolumic left heart of the rabbit and abolished the irregularity of the rhythm of the heart, thereby restoring the cardiomechanical activity upon reperfusion (20 ml/min). D stimulated the release of PG-like material. Indomethacin infusion completely prevented both the antiischemic activity of D and its ability to increase the generation of prostaglandins in the rabbit heart. Measurement by atomic absorption spectroscopy of calcium content in ischemic heart tissue and its mitochondrial fraction indicated that the ischemic procedure significantly increased tissue calcium content in both. D, Prostacyclin (PGI2) and Nifedipine protected the heart from ischemic ventricular contracture and prevented accumulation of calcium in the heart. The effect of D on preventing Ca++ overload was completely abolished by indomethacin infusion. The results indicate that the beneficial effects of Defibrotide in experimental ischemia are primarily due to a release of Prostaglandin E2 (PGE2) and PGI2, which in turn may inhibit the detrimental effects of calcium overload in myocytes and mitochondria.

Defibrotide decreases cholesterol amount in hypercholesterolemic rabbit aorta, with no modification of plasma or lipoprotein cholesterol.

Defibrotide, (D) an antithrombotic agent, when administered i.v. to cholesterol-fed rabbits decreased cholesterol in the aorta without changing total plasma cholesterol, triglyceride or phospholipid, nor the cholesterol, triglyceride, phospholipid and protein of plasma lipoproteins. Platelet aggregation was decreased in rabbits treated with D. There were fewer vascular lesions in the hearts and kidneys of animals treated with D than in animals fed cholesterol and treated with placebo. These data suggest that the antithrombotic activity of D and its ability to reduce platelet sensitivity could help to reduce the amount of cholesterol in the cardiovascular system in atherosclerosis-prone situations.

Sulglycotide displays cytoprotective activity in rat gastric mucosa.

Sulglycotide, a well known antisecretory and antiulcer compound, has been further investigated for its ability to protect rat gastric mucosa against extensive necrosis induced by absolute ethanol, NaOH (0.2N) and NaCl (30%). Sulglycotide, which has been compared with cimetidine, displays a dose-dependent cytoprotective activity against the above necrotizing agents. The results obtained indicate that Sulglycotide requires a normal prostaglandin biosynthetic process in order to manifest its antiulcer activity. In fact gastric mucosa from animals treated with Sulglycotide releases in vitro a greater amount of PGl2-like activity; and furthermore no protection was observed against gastric lesions induced by indomethacin. As far as the mode of action of Sulglycotide is concerned it is tempting to speculate that the compound may interfere with prostaglandin degradation or it may trigger an adaptive cytoprotection which is important in maintaining the cellular integrity of rat gastric mucosa.