Mesoionic oxatriazoles (MOTA): NO-donating characteristics and pharmacology.

Biological role of nitric oxide (NO), functioning of isoforms of NO synthetases (NOS) and pharmacology of principle NO-donors were reviewed. NO donating characteristics and pharmacology of 23 mesoionic oxatriazoles (MOTA) were compared with those of 5-morpholinosydnonimine (SIN-1), S-nitroso-N-acetylpenicillamine (SNAP), sodium nitroprusside (NaNP) and glyceryl trinitrate (GTN). It is concluded that in vitro NO donating profile of MOTA hardly can be used as a predicting measure for their pharmacological activities either in vitro or in vivo. If anything, fast NO releasers seem to be stronger vasorelaxants than MOTA with slow NO releasing properties. Still, among representatives of this last category of MOTA one may find efficient antithrombotic and thrombolytic agents. For instance, MOTA 5-oxides were more potent thrombolytics than SIN-1, SNAP or NaNP. Also MOTA with potent anti-platelet action in vitro seem to be potent relaxants of tracheal strips. In summary, by manipulating the chemical structures of MOTA one may obtain relative selectivity towards vasorelaxant, anti-platelet, thrombolytic or tracheorelaxant properties. Thus different categories of MOTA might be designed with a hope of achieving hypotensive, antithrombotic, thrombolytic or anti-asthmatic drugs.

Significance of endothelial prostacyclin and nitric oxide in peripheral and pulmonary circulation.

BACKGROUND: Vasoprotective function of endothelial cells is associated, among others, with biosynthesis and release of nitric oxide (NO), prostacyclin (PGI2), prostaglandin E2 (PGE2), carbon monoxide (CO) and plasminogen activator (t-PA). These endothelial mediators calm down activated platelets and leukocytes, prevent the occurrence of parietal thrombotic events, promote thrombolysis, maintain tissue perfusion and protect vascular wall against acute damage and against chronic remodeling. Endothelial dysfunction in patients suffering from atherosclerosis or diabetes type 2 is associated not only with suppression in release of the above mediators but also with deleterious discharge of prostaglandin endoperoxides (PGH2, PGG2), superoxide anion (O2-, peroxynitrite (ONOO-), and plasminogen activator inhibitor (PAI-1). We looked for mechanisms of protective endothelial function, with a special respect to the differences between peripheral and pulmonary circulation. METHODS: Cultured endothelial cells of bovine aorta (BAEC) were used to study physiological and pharmacological mechanisms of increasing free cytoplasmic calcium [Ca2+]i. A porphyrinic sensor quantified the release of NO from BAEC. In cultured human umbilical vein endothelial cells (HUVEC) we looked for induction by bradykinin (Bk) of mRNAs for a number of enzymes. In blood perfused rat lungs we studied protective role of NO against injury inferred by lipopolysaccharide on pulmonary microcirculation that was accomplished by thromboxane A2 (TXA2), platelet activating factor (PAF), cysteinyl-leukotrienes (cyst-LTs) and the complement system. In vivo we analyzed the influence of Bk, perindopril and quinapril ('tissue type' angiotensin converting enzyme inhibitors, ACE-Is) on endothelial function in entire circulation of anaesthetized rats using a thrombolytic bioassay and EIA for 6-keto-PGF1 alpha and t-PA antigen. RESULTS: In BAEC Bk via kinin B2 receptors raised in a concentration-dependent manner (1 pM-10 nM) free cytoplasmic calcium ions [Ca2+]i, that triggered the release of NO from BAEC. Calcium ionophore (A23187, 1-100 nM) as well as receptor agonists such as adenosine diphosphate (ADP, 10 nM-1 microM), adrenaline (Adr, 1-10 microM) or acetylcholine (Ach, 10-100 microM) produced a similar rise in endothelial [Ca2+]i as did Bk at a nanomolar concentration. 'Tissue type' ACE-Is, e.g. quinapril or perindopril acted through accumulation of endogenous Bk. However, the potency of ACE-I to change endothelial function is by several orders of magnitude lower than that for exogenous Bk. In vivo the major difference between thrombolytic actions by quinapril or perindopril on one hand, and by exogenous Bk on the other was longevity of thrombolysis by ACE I and a distinct hypotensive action of exogenous Bk. Still, the long-lasting isolated thrombolytic effect of ACE I was mediated entirely by endogenous BK as evidenced by the preventive action of icatibant, a kinin B2 receptor antagonist. Moreover, in vivo the immediate thrombolysis by ACE-I was mediated by PGI2 rather than by NO or t-PA, as shown by pharmacological analysis, and by direct blood assays of 6-keto-PGF1 alpha and t-PA antigen. Bradykinin as a mediator of pleiotropic endothelial action of several cardiovascular drugs (e.g. ACE-I) may complete its mission not only through B2 receptor and [Ca2+]i--mediated release of PGI2 or NO. Here, we describe a new route of the Bk action. Bk mediated induction of the [Ca2+]i-independent, so called 'inducible', endothelial isoenzymes required for generation of CO, PGI2 and PGE2. After 4 hours of incubation of HUVEC with Bk (10 nM) it induced mRNAs for haemooxygenase 1 (HO-1), cyclooxygenase 2 (COX-2), prostaglandin E synthase (PGE-S) whereas mRNA for nitric oxide synthase 2 (NOS-2) was weakly affected. We proved also that unlike in peripheral circulation, in pulmonary circulation only NO but not PGI2 would play a protective role. In the blood-perfused lung, endotoxaemia liberates lipids, such as TXA2, PAF and cyst-LTs. These toxic lipids along with the activated complement mediate pulmonary damage. Pulmonary endothelial nitric oxide is the only local protector against lung injury evoked by the phagocytised bacterial lipopolysaccharide. SUMMARY: Summing up, in peripheral circulation endogenous Bk is the most efficient activator of protective endothelial function. For instance, thrombolytic action of 'tissue type' ACE-I depends on the Bk-released PGI2. Acting as an agonist of endothelial B2 kinin receptors Bk rises [Ca2+]i with a subsequent activation of constitutive COX 1 and NOS-3. This is followed by an immediate release of PGI2 and NO. Moreover, acting as 'microcytokine' Bk induces mRNAs for HO-1, COX-2 and PGE S, the isoenzymes responsible for a delayed endothelial biosynthesis of CO, PGI2 and PGE2. (ABSTRACT TRUNCATED)

Comparison of endothelial pleiotropic actions of angiotensin converting enzyme inhibitors and statins.

Two in vitro and one in vivo assay were performed to study the endothelial pleiotropic actions of "tissue type" angiotensin converting enzyme inhibitors (ACE-Is) such as perindopril and quinapril, their active forms, that is, quinaprilat and peridoprilat, or of statins belonging to natural (lovastatin), semisynthetic (simvastatin), and synthetic enantiomeric (atorvastatin, cerivastatin) classes. Cytoplasmic [Ca2+]i levels in cultured bovine aortic endothelial cells and endothelium-dependent nitric oxide-mediated coronary vasodilatation in the Langendorff preparation of guinea pig heart constituted our in vitro assays. The in vivo assay consisted of study of PGI2-mediated thrombolytic response in arterial blood of rats after intravenous administration of drugs. In this last assay, perindopril and quinapril proved to be, by two orders of magnitude, more potent PGI2-dependent thrombolytics than the most potent statin (atorvastatin). However, in both in vitro assays we found a higher endothelial efficacy of statins as compared to ACE-Is. In particular, those statins that contain the lactone ring in their molecules (lovastatin, simvastatin) were the most potent coronary vasodilators. In summary, the in vivo profile of action of ACE-Is and statins contrasted with their reversed order of potency in vitro. We hypothesize that the endocrine-like function of the pulmonary circulation [28-31] may be responsible for the in vivo bradykinin-triggered, PGI2-mediated thrombolysis by ACE-Is, whereas the pleiotropic action of statins, possibly involving inhibition of prenylation [14-19], is diffused throughout many vascular beds.

Thienopyridines: effects on cultured endothelial cells.

In cultured endothelial cells harvested from human umbilical vein (HUVEC) or bovine aorta (BAEC) the 30 min incubation with calcium ionophore A 23187 (1 microM) or ticlopidine (100 microM) caused an increase in nitrite generation in HUVEC from basal 227 +/- 37 to 372 +/- 60 or to 325 +/- 33 pmoles per 10(6) cells, respectively, and in BAEC from basal 182 +/- 17 to 378 +/- 18 or to 423 +/- 66 pmoles per 106 cells (n = 6), respectively. Calcium ionophore A 23187 (1 microM) or ticlopidine (100 microM) next to 30 min incubation with BAEC increased release of 6-keto-PGF 1alpha from basal level of 9.4 +/- 1.8 to 96.2 +/- 5.1 or to 99.5 +/- 10.2 pmoles per 10(6) cells, respectively. The pretreatment with aspirin (300 microM) cut down this rise to 4.2 +/- 0.1 pmoles per 10(6) cells (n = 8). Basal cytoplasmic calcium levels, [Ca2+]i, in immortalised HUVEC cell line - ECV304, HUVEC and BAEC were 47.7 +/- 3.3 nM (n = 53), 68.3 +/- 5.0 nM (n = 30) and 53.1 +/- 3.0 nM (n = 15), respectively. In these cultured endothelial cells calcium ionophore A 23187 (0.1 microM) produced net maximum rise in [Ca2+]i by 157 +/-27 nM (n = 16)[ ECV304], by 107 +/- 58 nM (n=4) [HUVEC], and by 231.0 +/- 41.3 nM (n = 8) [BAEC], respectively, while ticlopidine (30 microM) produced net maximum rise in [Ca2+]i by 30.0 +/- 3.2 nM (n=9)[ECV304], 48.8 +/- 15.6 nM (n = 4)[HUVEC] and 28.4 +/- 5.4 nM (n = 8)[BAEC], respectively. Effect of ticlopidine on [Ca2+]i was not only weaker than that of calcium A 23187 but also its maximum appeared after a lag period that was 2 3 times longer than that for A23187. In ECV304 clopidogrel at concentrations of 10, 30 and 100 microM produced maximum increment of [Ca2+]i by 16.5 +/- 3.8 nM (n = 7), 47.0 +/- 6.9 nM (n = 8) and 67.2 +/- 8.3 nM (n = 8), respectively. Incubation of BAEC with A23187 (microM), ticlopidine or clopidogrel (100 microM) for 2 h did not influence viability of cultured endothelial cells. We claim that thienopyridines, independently of their delayed anti-platelet properties ex vivo do release NO and PGI2 from cultured endothelial cells in vitro. The above endothelial action of thienopyridines might be mediated by a rise in [Ca2+]i, however, this possibility has not been proved.

Thrombolytic activity of beta-adrenolytic drug, sotalol.

Sotalol is a beta-adrenoreceptor blocking drug, the clinical efficacy of which has been linked up to its negative chrono- and inotropic effects and its hypotensive action. In addition, beta-adrenolytic drugs are known to inhibit platelet aggregation in vitro possibly through lowering of calcium ions level. Here, we report that in rats sotalol at a dose of 10-20 mg/kg i.v., apart from hypotension, evokes instantaneous thrombolytic effect. This is associated with an increase in plasma level of tissue plasminogen activator (t-PA). In vitro, sotalol at a concentration of 1-100 microM inhibits thrombogenesis on surface of rabbit aorta endothelium superfused with blood. Sotalol also has a weak anti-aggregatory activity (IC50 approximately 500-1000 microM) in human platelet rich plasma (PRP). Since the thrombolytic and fibrinolytic but not hypotensive effects of sotalol were inhibited by cyclooxygenase inhibitor, indomethacin, while its hypotensive but not thrombolytic potency was dimished by an inhibitor of nitric oxide synthase, NG-nitro-L-arginine (L-NNA), we have linked up the sotalol-induced effects in vivo with the release of prostacyclin and nitric oxide. Our data point out to a possibility that prostacyclin and nitric oxide concomitantly released from endothelium and/or from other blood cells after administration of sotalol, may play different roles: prostacyclin may be responsible for fibrinolytic, thrombolytic and antithrombotic properties, while nitric oxide may take part in the mechanism of sotalol-induced hypotension.

Nitric oxide donation and nitrite assays in the presence of thiols and albumin as determined by Griess' and Werringloer's methods.

Nitric oxide (NO) or nitrite (NO2-) were assayed using the Werringloer's method or the Griess' method, respectively, in the presence or absence of various thiols, amino acids, or albumin. This has been done because both methods are used to determine the generation of endogenous NO from L-arginine or exogenous NO from drugs in vivo, paying little attention to biological constituents which may affect results of these assays. Albumin, reduced glutathione (GSH), cysteine and N-acetylcysteine, but not other amino acids lowered the amount of NO2- as detected by Griess' method no matter whether sodium nitrite or 3-morpholinosydnonimine (SIN-1) were used as a source of NO2-. This happened probably because at low pH of the reaction mixture the corresponding nitrosothiols were formed and thus NO2- was not accessible for detection. However, this phenomenon was not seen when instead of SIN-1 another NO donor--S-nitroso-N-acetylpenicillamine (SNAP) was used. SNAP is a nitrosothiol itself and physiological low molecular thiols (e.g. GSH or cysteine) displaced NO from SNAP. An increase in the amount of released NO was detectable by both Werringloer's and Griess' methods. Only the presence of 700 microns of albumin steadily suppressed the detection of NO or NO2- no matter what was the source of these species. It is concluded that low molecular thiols and albumin may differently influence the detection of both NO and NO2- which derive from various NO donors or sodium nitrite.

The effect of nitric oxide donors on the release of plasminogen activator inhibitor (PAI) from rabbit platelets in vitro.

Here we describe effects of four nitric oxide (NO) donors, 4-arylsubstituted oxatriazol derivatives and 3-morpholino-sydnonimine (SIN-1) at concentrations of 30-1000 microM on the release of plasminogen activator inhibitor (PAI) from rabbit platelets in vitro. At 37 degrees C, pH of 7.4 and a concentration of 30 microM, all compounds released NO as measured by the Werringloer's technique. The NO-generating potency of the compounds correlated with their capacity to inhibit the release of PAI from platelets and both phenomena were concentration-dependent. We conclude that various types of NO-donors activate plasma fibrinolytic system through inhibition of the release of PAI from platelets.

Scavenging of reactive oxygen species as the mechanism of drug action.

Reactive oxygen species (ROS) are generated when oxygen is supplied in excess and/or its reduction is insufficient. The best explored ROS are superoxide anions, hydroxyl radicals and hydrogen peroxide. The first two are free radicals. ROS are harmful for the living cells and are implicated in a variety of pathological processes and diseases. Drugs used in the treatment of these states are either stimulators of endogenous defense mechanisms against ROS or inhibitors of ROS formation. Six groups of anti-ROS substances have been described in this paper. 1) Antioxidant substances used in substitutive therapy such as enzymes (e.g. superoxide dismutase), substances containing thiol groups and vitamins (A, E, P, C). 2) Chelating agents (e.g. desferoxamine), which lower the level of prooxidative transition metal ions. 3) Inhibitors of superoxide ions generation by stimulated cells or xanthine oxidase. Such mechanism of action was described for xanthine oxidase inhibitor-allopurinol. 4) Superoxide scavengers. Many known drugs were investigated for this activity, but the best documentation was presented for flavonoids. 5) Substances which eliminate hydrogen peroxide, mainly glutathione and its precursors. 6) Scavengers of hydroxyl radicals. Studies of the above activity were conducted mainly using an unspecific method--estimation of malondialdehyde generated during the action of hydroxyl radicals on lipids or on desoxyribose. Inhibition of malondialdehyde formation was described for many drugs of plant and synthetic origin.

Mesoionic oxatriazole derivatives--a new group of NO-donors.

A number of new 3-aryl-1,2,3,4-oxatriazole-5-imine derivatives (GEA Compounds--GEAC) were synthetized. GEAC are NO-releasers as evidenced by direct measurement of NO in headspace/NO-analyzer, by cooxygenation of oxyhaemoglobin to methaemoglobin in the Werringloer's test and by generation of nitrite in the Griess' reaction. During the release of NO from GEAC the consumption of O2 could be detected only when high concentrations of GEAC were used. The mechanism of release of NO from molecules of GEAC still remains hypothetical. Some of GEAC were found to remain stable for long periods of time, even at 37 degrees C. Both mutagenic properties and the pharmacodynamic profile of GEAC can be controlled by a mindful choosing of appropriate substituents.

Prostacyclin and the mechanism of action of defibrotide.

Defibrotide (DEF) is a product of the controlled hydrolysis of DNA from mammalian lungs. In vitro DEF (1-2000 micrograms/ml) neither inhibited the aggregation of human, rabbit and cat platelets nor released PGI2 from cultured porcine aortic endothelial cells. Preincubated with platelet preparations, DEF (10 micrograms/ml) lowered the IC50 for the anti-aggregatory action of PGI2 from 2.1-6.5 nM to 0.6-2.4 nM. In vivo DEF (2-20 mg/kg i.v. or 0.1-10 micrograms/ml locally o.t.) dispersed platelet thrombi in the extracorporeal circulation of anaesthetized heparinized cats. In contrast to an immediate and reversible action of PGI2 (0.3-3 micrograms/kg i.v. or 1-3 ng/ml locally o.t.), the delayed and irreversible dispersion of thrombi by DEF in vivo was inhibited by aspirin (50 mg/kg i.v.), indomethacin (10 mg/kg i.v.) or dexamethasone (2 mg/kg i.v.). After pretreatment with these drugs DEF, although deprived of its own effect on thrombi, still enhanced their dispersion by exogenous and endogenous PGI2. Similarly, at its subthreshold effective concentration (10 ng/ml, o.t.) DEF potentiated the thrombolytic action of PGI2 (1 microgram/kg, i.v.), dazoxiben (1 mg/kg, i.v.) and nicotinamide (100 mg/kg i.v.). It is concluded that DEF potentiates the action of PGI2 on platelets. In vivo DEF may facilitate an interaction between platelets and endothelium, leading to augmented generation of PGI2 or of its biologically active products, which are endowed with fibrinolytic properties.

An abnormality of arachidonic acid metabolism is not a generalized phenomenon in patients with aspirin-induced asthma.

Aspirin (ASA)-induced asthma is a distinct clinical syndrome in which bronchoconstrictive response to nonsteroidal anti-inflammatory drugs can be predicted on the basis of their in vitro activity as inhibitors of cyclooxygenase. In ten ASA-sensitive asthmatics and ten matched healthy controls we measured 12-hydroxy-eicosatetraenoic acid (12-HETE) production by platelets and 5-hydroxy-eicosatetraenoic acid (5-HETE) and leukotriene B4 (LTB4) production by polymorphonuclear leucocytes. The blood cells were obtained before administration of the threshold doses of ASA and during the ASA-induced reactions. Initial levels of eicosanoids determined did not differ between the two groups. In both groups, after ASA challenge, 12-HETE rose to similar levels while 5-HETE and LTB4 remained unchanged. These data do not support the concept that an abnormality in the regulation of arachidonic acid oxidative pathways in ASA-sensitive asthmatics is a generalized phenomenon which embraces the platelets and leucocytes; rather it is inhibition of cyclo-oxygenase within the tissues of the respiratory tract that triggers asthmatic attacks in the sensitive patients.

Salicylates and 12-lipoxygenase activity in human washed platelets.

In vitro salicylates /aspirin, salicylic acid, salicylamide and gentisic acid/ inhibited formation of 12-lipoxygenase products in intact human washed platelets which were stimulated with thrombin or arachidonic acid. Salicylates did not affect 12-lipoxygenase activity in platelet lysates. Ex vivo aspirin or salicylamide at a dose of 1 g given orally to healthy volunteers potentiated formation of 12-lipoxygenase products in washed platelets. It is concluded that the effect of salicylates on 12-lipoxygenase pathway is independent from their influence on cyclooxygenase activity in platelets and aspirin cannot be considered as a selective inhibitor of platelet cyclooxygenase.

Hypotensive effects of eicosapentaenoic acid (EPA) and its influence on eicosanoid metabolism in spontaneously hypertensive rats.

Oral administration of pure eicosapentaenoic acid (EPA) ethyl ester caused a reversible hypotensive effect in spontaneously hypertensive rats. Treatment with EPA also lowered the platelet response to ADP and inhibited the conversion of leucotrienes (LTs) A4 and LTB4 and other sulphidopeptide leucotrienes. Therefore, diet supplemented with EPA may lower blood pressure in hypertensive rats and affect cardiovascular functions which may be mediated through eicosanoid metabolism.

Hepatic transformation of prostaglandin D2 to a new prostanoid, 9 alpha,11 beta-prostaglandin F2, that inhibits platelet aggregation and constricts blood vessels.

The metabolic transformation of tritium-labeled prostaglandin D2 ([3H]PGD2) was investigated in the isolated Tyrode's-perfused rabbit liver. One major product was isolated and identified in the perfusate as a new prostanoid. The structure of this metabolite was further confirmed by gas chromatography-mass spectrometry and chemical methods to be 9 alpha,11 beta,15-L-trihydroxyprosta-5-cis, 13-trans-dienoic acid, namely (9 alpha,11 beta-PGF2). This new prostanoid was found to be an inhibitor of platelet aggregation and to cause constriction of canine coronary artery strips. These results suggested that on passage through the hepatic circulation exogenous PGD2 is converted to 9 alpha,11 beta-PGF2, the latter having a biological profile which differs from that of PGD2 and PGF2 alpha.

Dual actions of prostacyclin (PGI2) on the rat pregnant uterus.

Using strips of rat pregnant uterus, treated with indomethacin to suppress spontaneous contractility, the oxytocic activity of prostacyclin was compared with other prostaglandins. A prostacyclin concentration of 32 ng/ml elicited uterine contractions in all experiments. In this respect prostacyclin was 80 times more active than 6-oxo-PGF1 alpha but less active than PGE2 or PGF2 alpha. Apart from a direct stimulant effect, prostacyclin also exhibited an indirect potentiating action. In threshold concentrations prostacyclin caused a 3-fold potentiation of threshold doses of oxytocin. A lesser 1.5-fold potentiation of PGE2 alpha was also observed. The implications of these findings in relation to prostacyclin playing a role in parturition are discussed.