Comparison of the effects of the novel vasodilator FK409 with those of nitroglycerin in isolated coronary artery of the dog

Computational Investigation of the Formation of Substituted Isoindole N-Oxides through the Photo-oxidative Cyclization of 2'-Alkynylacetophenone Oximes

Our recently published joint experiment-theory study of the photo-oxidative intramolecular cyclization of 2'-alkynylacetophenone oximes, performed in collaboration with the de Lijser group, presented the first reported formation of isoindole N-oxides. That study focused on determining a mechanistic explanation for the unexpected chemistry observed when three 2'-alkynylacetophenone oximes were photo-oxidized with 9,10-dicyanoanthracene (DCA), specifically the derivatives with a phenyl, isopropyl, or n-butyl substituent at the alkynyl group. Here, we use density functional theory to develop a broader understanding of the scope of this chemistry. In particular, we demonstrate that substituents on the alkynyl group and on the central benzene ring can significantly modulate the thermodynamic driving force for oxime radical cation generation when DCA is used as the photosensitizer. In contrast, substituents are shown to have a small impact on the chemical reactivity of the radical cation intermediates. In particular, 5-exo radical cation cyclization, which ultimately results in an isoindole N-oxide product, is always kinetically and sometimes also thermodynamically preferred over 6-endo radical cation cyclization, which would produce an isoquinoline N-oxide product. Overall, this study provides mechanistic insights into the diversity of isoindole N-oxides that can be produced through the photo-oxidative cyclization of 2'-alkynylacetophenone oximes.

Mechanistic Investigation of the Formation of Isoindole N-Oxides in the Electron Transfer-Mediated Oxidative Cyclization of 2'-Alkynylacetophenone Oximes

This paper describes a joint experiment-theory investigation of the formation and cyclization of 2'-alkynylacetophenone oxime radical cations using photoinduced electron transfer (PET) with DCA as the photosensitizer. Using a combination of experimental ¹H and ¹³C nuclear magnetic resonance (NMR) spectra, high-resolution mass spectrometry, and calculated NMR chemical shifts, we identified the products to be isoindole N-oxides. The reaction was found to be stereoselective; only one of the two possible stereoisomers is formed under these conditions. A detailed computational investigation of the cyclization reaction mechanism suggests facile C-N bond formation in the radical cation leading to a 5-exo intermediate. Back-electron transfer from the DCA radical anion followed by barrierless intramolecular proton transfer leads to the final product. We argue that the final proton transfer step in the mechanism is responsible for the stereoselectivity observed in experiment. As a whole, this work provides new insights into the formation of complex heterocycles through oxime and oxime ether radical cation intermediates produced via PET. Moreover, it represents the first reported formation of isoindole N-oxides.

Modulating the Bioactivity of Nitric Oxide as a Therapeutic Strategy in Cardiac Surgery

Cardiac surgery, including cardioplegic arrest and extracorporeal circulation, causes endothelial dysfunction, which can lead to no-reflow phenomenon and reduction of myocardial pump function. Nitric oxide (NO) deficiency is involved in this pathologic process, thereby providing a fundamental basis for the use of NO replacement therapy. Presently used drugs and additives to cardioplegic and heart preservation solutions are not able to reliably protect endothelial cells and cardiomyocytes from ischemia-reperfusion injury. This review discusses promising NO-releasing compounds of various chemical classes for cardioplegia and reperfusion, which effectively maintain NO homeostasis under experimental conditions, and presents the mechanisms of their action on the cardiovascular system. Incomplete preclinical studies and a lack of toxicity assessment, however, hinder translation of these drug candidates into the clinic. Perspectives for modulation of endothelial function using NO-mediated mechanisms are discussed. They are based on the cardioprotective potential of targeting vascular gap junctions and endothelial ion channels, intracoronary administration of progenitor cells, and endothelial-specific microRNAs. Some of these strategies may provide important therapeutic benefits for human cardiovascular interventions.

Quinone-sensitized Steady-state Photolysis of Acetophenone Oximes Under Aerobic Conditions: Kinetics and Product Studies†

Oxidation of oximes via photosensitized electron transfer (PET) results in the formation of the corresponding ketones as the major product via oxime radical cations and iminoxyl radicals. The influence of electron-releasing and electron-accepting substituents on these reactions was studied. The observed substituent effect strongly supports formation of iminoxyl radicals from the oximes via an electron transfer-proton transfer sequence rather than direct hydrogen atom abstraction. Correlation of the relative conversion of the oximes with Hammett parameters shows that radical effects dominate for the meta-substituted acetophenone oximes (rho(rad)/rho(pol) = 5.4; r2 = 0.93), whereas the para-substituted oximes are influenced almost equally by radical and ionic effects (rho(rad)/rho(pol) = -1.1; r2 = 0.98). From these data sets we conclude that the follow-up reactions proceed through a number of intermediates with both radical and ionic character. This was confirmed by product studies with the use of an isotopically labeled nucleophile. In addition to the major oxidation product (ketone), a chlorine-containing product was often identified as well. Studies on the formation of this product show that the most likely pathway is either via a direct nucleophilic addition in a complex formed between the oxime radical cation and the chloranil radical anion or via a radical substitution (SH2) mechanism. These studies show that with the increasing use of oximes as drugs and pesticides, intake of these chemicals followed by enzymatic oxidation may result in the formation of a variety of reactive intermediates, which may lead to cell and tissue damage.

Opposite effects of pre- and postischemic treatments with nitric oxide donor on ischemia/reperfusion-induced renal injury

We have demonstrated previously that preischemic treatment with FK409 [(+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide], a spontaneous nitric oxide (NO) donor, markedly improves ischemia/reperfusion-induced renal injury. However, there is conflicting information (renoprotective or cytotoxic) as to the contribution of NO to ischemic acute renal failure (ARF). In the present study, we investigated the effect of postischemic treatment with FK409 (1, 3, and 10 mg/kg i.v.) at 6 h after reperfusion on ischemic ARF, in comparison with the preischemic treatment effect. Ischemic ARF was induced by clamping of the left renal artery and vein for 45 min, followed by reperfusion, 2 weeks after contralateral nephrectomy. Renal function in ARF rats markedly decreased at 24 h after reperfusion. Histopathological examination of the kidney of ARF rats revealed severe renal damage. In contrast to the renoprotective effect by preischemic treatment, postischemic treatment with FK409 aggravated the ischemia/reperfusion-induced renal dysfunction and histological damage. Immunohistochemical analysis of renal sections obtained from ARF rats revealed positive staining for nitrotyrosine, a biomarker of peroxynitrite formation, in injured tubular cells, and more intense staining was observed in renal tissues from the animals that received postischemic treatment with FK409. On the other hand, the formation of nitrotyrosine, neutrophil infiltration into renal tissues, and renal superoxide production, all of which were enhanced in ARF rats, were efficiently attenuated by the preischemic treatment with FK409. These results demonstrate that, although preischemic treatment with an NO donor is renoprotective, postischemic treatment with the same agent aggravates the ischemia/reperfusion-induced renal injury, probably through peroxynitrite overproduction.

Cellular infiltrates and injury evaluation in a rat model of warm pulmonary ischemia-reperfusion

Introduction

Beside lung transplantation, cardiopulmonary bypass, isolated lung perfusion and sleeve resection result in serious pulmonary ischemia–reperfusion injury, clinically known as acute respiratory distress syndrome. Very little is known about cells infiltrating the lung during ischemia–reperfusion. Therefore, a model of warm ischemia–reperfusion injury was applied to differentiate cellular infiltrates and to quantify tissue damage.

Methods

Fifty rats were randomized into eight groups. Five groups underwent warm ischemia for 60 min followed by 30 min and 1–4 hours of warm reperfusion. An additional group was flushed with the use of isolated lung perfusion after 4 hours of reperfusion. One of two sham groups was also flushed. Neutrophils and oedema were investigated by using samples processed with hematoxylin/eosin stain at a magnification of ×500. Immunohistochemistry with antibody ED-1 (magnification ×250) and antibody 1F4 (magnification ×400) was applied to visualize macrophages and T cells. TdT-mediated dUTP nick end labelling was used for detecting apoptosis. Statistical significance was accepted at P < 0.05.

Results

Neutrophils were increased after 30 min until 4 hours of reperfusion as well as after flushing. A doubling in number of macrophages and a fourfold increase in T cells were observed after 30 min until 1 and 2 hours of reperfusion, respectively. Apoptosis with significant oedema in the absence of necrosis was seen after 30 min to 4 hours of reperfusion.

Conclusions

After warm ischemia–reperfusion a significant increase in infiltration of neutrophils, T cells and macrophages was observed. This study showed apoptosis with serious oedema in the absence of necrosis after all periods of reperfusion.

Novel nitric oxide donor (FK409) ameliorates liver damage during extended liver resection with warm ischemia in dogs

BACKGROUND

Nitric oxide attenuates ischemia-reperfusion injury by maintaining organ circulation through its actions as a vasoregulator, an inhibitor of platelet aggregation, and an attenuator of leukocyte adhesion. Otherwise, the harmful effects of enhanced nitric oxide production induced by inducible nitric oxide synthase mediate ischemia-reperfusion injury. FK409 has been characterized as a spontaneous nitric oxide donor. The aim of this study was to evaluate the effects of FK409 on extended liver resection with ischemia using a canine model.

STUDY DESIGN

Adult mongrel dogs were subjected to 60 minutes of warm ischemia by partial inflow occlusion. After reperfusion the nonischemic lobes were resected and the remnant liver function was evaluated. The dogs were divided into two groups: the control group (n = 7) and the FK409 group (n = 6), which was given FK409 through the portal vein.

RESULTS

The hepatic tissue blood flow, serum liver enzymes levels, and serum endothelin-1 level after reperfusion were significantly better in the FK409 group than in the control group. Electron microscopy demonstrated that endothelial cells and Ito cells were well-preserved in the FK409 group. The 3-day survival rate was statistically better in the FK409 group (67%) than in the control group (14%).

CONCLUSIONS

FK409 appears to have protective effects during extended liver resection with ischemia.

A spontaneous nitric oxide donor ameliorates small bowel ischemia-reperfusion injury in dogs

Nitric oxide (NO) appears to play an important role in tissue injury during reperfusion. FK409 is the first spontaneous NO donor that increases plasma guanosine 3',5'-cyclic monophosphate. We investigated the effects of the NO donor FK409 (FK) on ischemia-reperfusion injury in a canine warm ischemia model. Fourteen adult mongrel dogs were divided into two groups: the control group and the FK group, which received FK. The superior mesenteric artery and vein were both clamped for 2 h and then reperfused for 12 h. Arterial and intramucosal pH were well maintained in the FK group in comparison with the control group. Histologically, ischemia-reperfusion injury was significantly more severe in the control group than in the FK group. The serum NO levels were significantly higher in the FK group than in the control group during FK administration. FK409 has protective effects on ischemia-reperfusion injury of the small intestine due to NO release.

Nitric oxide donor FK409 and 8-bromoguanosine-cyclic monophosphate attenuate cardiac contractility assessed by Emax

FK409 decomposes and releases nitric oxide (NO) spontaneously when it is dissolved in phosphate buffer solution at 37 degrees C. With the use of this NO donor, the effect of exogenous NO on cardiac contractility was examined by assessing Emax. alpha-chloralose-anaesthetized dogs were instrumented for measurements of left ventricular (LV) pressure and volume and coronary blood flow (CBF) in the left anterior descending artery (LAD). FK409, 8-bromoguanosine-cyclic-monophosphate (8-Br-cGMP) and papaverine were infused into the LAD, and Emax was determined by transient inferior vena cava occlusion when CBF was increased and reached its peak. Neither drug affected heart rate nor LV pressure just before the measurement of Emax. FK409 increased CBF and decreased Emax in a dose-dependent manner. 8-Br-cGMP also increased CBF and decreased Emax in a dose-dependent manner. Pretreating with propranolol did not affect the effects of FK4098-Br-cGMP on CBF and Emax. Papaverine increased mean CBF but did not affect Emax. In conclusion NO attenuates cardiac contractility in vivo, while increasing CBF. This effect seems to be mediated by cyclic-guanosine monophosphate, a second messenger of NO.

The effect of FK409-a nitric oxide donor-on canine lung transplantation

BACKGROUND

Nitric oxide (NO) is known to have beneficial effects in ischemia-reperfusion (I/R) injury through maintaining endothelial integrity, inhibiting leukocyte adhesion and platelet aggregation, and inducing vasodilation. The effect of FK409 (FK), a spontaneous NO donor, was investigated in a canine lung transplantation model.

METHODS

Ten pairs of weight-matched dogs were used. Five pairs were assigned to the FK group, to which FK (5 microg/kg/min) was administered intravenously from 30 minutes prior to ischemia until the induction of ischemia in the donor, and from 15 minutes prior to reperfusion until 45 minutes after reperfusion in the recipient. The others were assigned to the control group. After 8-hour preservation in 4 degrees C Euro-Collins solution, orthotopic single-lung transplantation was performed. During a 5-minute clamping test of the right pulmonary artery, left pulmonary arterial pressure (L-PAP), left pulmonary vascular resistance (L-PVR), arterial oxygen pressure (PaO(2)), and alveolar-arterial oxygen pressure difference (A-aDO(2)) were measured. The lung specimens were harvested for histologic study, and polymorphonuclear neutrophils (PMNs) were counted. Pulmonary perfusion and ventilation scintigraphy (Tc-99m-MAA and Xe-133) were performed.

RESULTS

PAP, L-PVR, PaO(2), and A-aDO(2) revealed significantly (p < 0.05) better function in the FK group than in the control group. Histologically, edema was more mild, and PMN infiltration was significantly (p < 0.05) lower in the FK group than in the control group. Xe-133 and Tc-99m-MAA were widely distributed throughout the graft lung in the FK group. The 2-day survival rate was 100% in the FK group, which was significantly (p < 0.05) better than the rate (40%) in the control group.

CONCLUSIONS

FK appears to generate a protective effect on I/R injury in lung transplantation.

Role of nitric oxide and prostaglandin in the protective effect of pibutidine hydrochloride, a novel histamine H2-receptor antagonist, on the gastric mucosal lesions in rats

1. The role of endogenous nitric oxide (NO) and prostaglandins (PGs) in the gastric mucosal protective action of pibutidine hydrochloride (IT-066), a novel histamine H2-receptor antagonist, was investigated in a 0.15 N hydrochloride (HCl) + 60% ethanol (EtOH)-induced gastric lesion model. 2. The 0.15 N HCl + 60% EtOH-induced lesion formation was reduced significantly by IT-066 (3 mg/kg, PO), NOR3 (spontaneous NO releaser; 0.03-0.1 mg/kg, SC) or PGE2 (0.01 mg/kg, PO) but was not reduced by famotidine (1-10 mg/kg, PO). 3. Pretreatment with NG-nitro-L-arginine methyl ester (L-NAME) (3 mg/kg, IV), an inhibitor of NO synthase, inhibited the protective action of IT-066 (3 mg/kg, PO), and the inhibitory effect of L-NAME was reversed by L-arginine (300 mg/kg, IV). The protective effect of PGE2 (0.01 mg/kg, PO) was not affected by the pretreatment with L-NAME (3 mg/kg, IV). 4. Infusion of carboxy-PTIO (1 mg/kg/min), a direct NO scavenger, inhibited the protective effect of IT-066 (3 mg/kg, SC) or NOR3 (0.1 mg/kg, SC). Pretreatment with indomethacin (5 mg/kg, SC) markedly reduced the protective effect of IT-066 (3 mg/kg, PO) or NOR3 (0.1 mg/kg, SC). 5. These results suggest that endogenous NO and PGs may be implicated in the gastric mucosal protection induced by IT-066 and that the endogenous PGs may contribute to the protective effect of NO.

Effects of FK409, a nitric oxide donor, on renal responses to renal nerve stimulation in anesthetized dogs

We examined the effects of (+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (FK409), a nitric oxide (NO) donor, on renal actions and norepinephrine overflow induced by renal nerve stimulation in anesthetized dogs, with or without N(G)-nitro-L-arginine (NOARG), a NO synthase inhibitor. Renal nerve stimulation at a low frequency (0.5-2.0 Hz) produced significant decreases in urine flow and urinary excretion of Na+ and increases in norepinephrine secretion rate. Renal nerve stimulation at a high frequency (2.5-5.0 Hz) which diminishes renal hemodynamics, elicited more marked decreases in urine formation and increases in norepinephrine secretion rate. Intrarenal arterial infusion of FK409 (0.25 microg/kg/min) failed to alter renal actions and increases in norepinephrine secretion rate in response to both low- and high frequency renal nerve stimulation. When NOARG (40 microg/kg/min) was administrated intrarenally, low-frequency renal nerve stimulation caused a potent antidiuresis and renal vasoconstriction. The renal nerve stimulation-induced increase in norepinephrine secretion rate was markedly enhanced by NOARG infusion. Simultaneous infusion of FK409 markedly attenuated the NOARG-induced enhancement of renal actions and increases in norepinephrine secretion rate, in response to low-frequency renal nerve stimulation. These results suggest that exogenous NO suppresses the renal nerve stimulation-induced norepinephrine overflow and renal actions in NO-depleted conditions. We also propose that endogenous NO functions tonically as an inhibitory modulator of renal noradrenergic neurotransmission.

The in vitro pulmonary vascular effects of FK409 (nitric oxide donor): a study in normotensive and pulmonary hypertensive rats

1. Vasorelaxant responses to the nitric oxide (NO) donor, FK409 ((+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide ), were evaluated on precontracted isolated ring preparations of main pulmonary artery and intralobar pulmonary artery from rats. 2. On main pulmonary artery FK409 fully reversed the precontractions. Responses were inhibited by methylene blue but were independent of the endothelium. The potency (-log EC50) of FK409 was the same on preparations contracted with noradrenaline (7.62) or the thromboxane-mimetic, U44619 (7.63). 3. On intralobar pulmonary artery FK409 caused only 80% reversal of the precontraction and was 2 fold less potent than on main pulmonary artery. These differences in maximum response and potency between main and intralobar arteries are in keeping with previous findings with other NO donors. 4. Pulmonary hypertension was induced in rats by chronic exposure to hypoxia (10% O2) for 1 or 4 weeks. Main pulmonary arteries from 1 week hypoxic rats had inherent tone and showed spontaneous contractile activity. In these arteries FK409 reversed not only the precontraction induced by noradrenaline but also the inherent tone. However, FK409 was 17 fold less potent than in control arteries, reflecting previous findings with other NO donors. Main pulmonary arteries from 4 week hypoxic rats had minimal inherent tone and were quiescent and FK409 was 4.5 fold less potent than in control arteries. In intralobar pulmonary arteries from 4 week hypoxic rats FK409 was 12 fold less potent than in controls. 5. Treatment of arteries with either (a) in vitro hypoxic conditions (PO2 of solution in organ bath < 10 mmHg) or (b) superoxide dismutase (SOD; 150 u ml-1) together with catalase (1200 u ml-1) significantly increased the potency of FK409 in preparations from hypoxic rats but had no effect on the potency in control preparations. Neither SOD nor catalase, alone, nor the nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester, had any effect on the potency of FK409 in preparations from control or hypoxic rats. 6. It is concluded that the reduction in potency of FK409 seen in pulmonary arteries from rats with chronic hypoxic pulmonary hypertension may be due in part to the presence of one or more reactive oxygen species (either hydroxyl or superoxide plus hydrogen peroxide).

A novel nonenzymatic pathway for the generation of nitric oxide by the reaction of hydrogen peroxide and D- or L-arginine

Nitric oxide (NO) is a biologically active molecule known to be enzymatically synthesized from L-arginine in the presence of NO synthetase (NOS). In this study, we demonstrate a novel non-enzymatic pathway for NO synthesis involving hydrogen peroxide and D- or L-arginine. We employed two measures of NO generation. The first consists in the demonstration of the oxidative metabolites of NO (NO2 + NO3 = NOx) and the second is the confirmatory finding of chemiluminescence derived from NO. The results show that NOx increases in the incubation mixture containing hydrogen peroxide coupled with D-arginine, L-arginine, L-canavanine, and even the NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). However, chemiluminescence was detected only from the reactions of hydrogen peroxide and D- or L-arginine and was diminished by the addition of carboxy-2-phenyl-4, 4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (PTIO), a specific scavenger of NO, confirming NO generation in the reaction.

Renal hemodynamic and excretory responses in anesthetized rats to FK409, a novel nitric oxide donor

Renal hemodynamic and excretory responses to (+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (FK409), a novel nitric oxide (NO) donor, were examined using anesthetized rats. When FK409 was infused into the renal artery of normal rats at 10 micrograms/kg per min, a moderate renal vasodilating effect was observed with a decrease in mean arterial blood pressure. Urine flow, urinary excretion of sodium and fractional excretion of sodium significantly increased by about 85%, 110% and 75%, respectively, compared with each control value. Simultaneously, urinary excretion of NO metabolites (UNOxV) was markedly increased with the administration of FK409. In hypertensive rats treated with NG-nitro-L-arginine (NOARG), the NO synthase inhibitor, FK409 produced a potent renal vasodilation, although the hypotensive effect of the agent was comparable to that seen in normal rats. In addition, glomerular filtration rate was significantly elevated by the agent. There were marked increases in the excretory responses, i.e., levels of urine flow, urinary excretion of sodium and fractional excretion of sodium were increased to about 3-, 6- and 5-fold of each control value, respectively. The extent of increment of UNOxV was similar to that seen in normal rats. These results clearly indicate that FK409 causes renal vasodilation and diuresis, via NO formation. Renal hemodynamic and excretory responses to the agent are sensitive in NO-depleted conditions. FK409 and related compounds may be useful for the treatment of renal diseases, in cases where the basal NO formation is impaired.

A new nitric oxide (NO) releaser: spontaneous NO release from FK409

The remarkable vasorelaxant and anti-platelet effects of FK409 have been reported to be due to nitric oxide (NO) release. The purpose of the present study is to investigate the spontaneous NO-releasing pathway of FK409 in aqueous solutions. 1H-NMR spectra of FK409 suggested that the compound underwent a time-dependent elimination of the hydrogen atom at alpha-position of the nitro moiety (at the 5-position) in weakly alkaline solutions. In addition, the degradation of FK409 monitored by HPLC showed a pH-dependency accelerating with an increase of pH. These results revealed that the first step in the degradation of FK409 might be the hydroxyl ion-dependent subtraction of the hydrogen atom at the 5-position. On the other hand, NO release from FK409 also exhibited a pH-dependency, and the velocity of NO liberation was markedly enhanced above pH 6. Furthermore, a linear relationship between the rate of FK409 degradation and that of NO formation was observed, indicating that the rate-limiting step for NO formation is the same as that for degradation. Thus, the rate-limiting process of NO formation from FK409 is due to the deprotonation reaction of the hydrogen atom at the 5-position by hydroxyl ions. The deprotonation process appears to be an essential step for both FK409 degradation and NO release. On the basis of the results, a possible kinetic scheme for NO release from FK409 is proposed.

Close correlation between nitric oxide (NO) formation from NO releasers and the biological activities of these agents in rats

The aim of this study was to clarify the difference in the profiles of nitric oxide (NO) formation of three NO releasers and to examine the correlation between NO formation from these drugs and their biological activities in rats. (+/-)-(E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (FK409) and 3-morpholinosydnonimine (SIN-1) spontaneously generated nitrite, an oxidative product of NO, in sodium phosphate buffer (PB) solution. On the other hand, sodium nitroprusside (SNP) did not generate nitrite. The rank order of the concentrations of nitrite generated was SIN-1 > FK409 >> SNP. In biological studies using rats, these drugs showed anti-platelet effects and in vitro vasorelaxant and hypotensive effects with potencies in the rank order of FK409 > SIN-1 > SNP and SNP > FK409 > SIN-1, respectively. These drugs generated nitrite with concentrations in the rank order of FK409 > SIN-1 > SNP and SNP > FK409 > SIN-1 in rat plasma and in PB solution with L-cysteine (Cys), respectively. In conclusion, three NO releasers liberate NO with NO-releasing rates of different rank orders under different incubation conditions, and the anti-platelet effects and vasorelaxant and hypotensive effects of these NO releasers closely correlate with NO formation from the compounds in the plasma and PB solution with Cys, respectively, but not with that in PB solution without Cys.

FK409, a new nitric-oxide donor, suppresses smooth muscle proliferation in the rat model of balloon angioplasty

The effect of FK409, a new nitric-oxide (NO) donor, on neointimal formation of rat carotid arteries following balloon injury was studied. The intimal thickening at 14 days was strongly suppressed by twice daily administration of FK409 at 10 mg/kg from 2 days before to 13 days after injury. The neointima area and neointima/media ratio were decreased by 48.0% (P < 0.01) and 38.5% (P < 0.01), respectively, compared with control. On the other hand, isosorbide dinitrate (ISDN), a classical nitro-vasodilator, did not suppress intimal thickening even at 100 mg/kg twice a day. An in vivo 5-bromo-2'-dedoxyuridine (BrdU) uptake study revealed that FK409 inhibited the proliferative response of smooth muscle cells (SMC) in media at early stage of injury. In fact, the neointimal formation at 14 days was inhibited by the short term administration of FK409 only from the day of injury to 4 days after at 10 mg/kg twice a day. In cultured rat SMC, FK409 (1-10 mumol/l) markedly enhanced intracellular c-GMP and inhibited the proliferation in 10% FBS-containing medium. These results suggest that FK409 suppresses intimal thickening following balloon injury of the rat carotid artery by inhibition of SMC proliferation.

A new class of furoxan derivatives as NO donors: mechanism of action and biological activity

1. The mechanism of action and biological activity of a series of R-substituted and di-R-substituted phenylfuroxans is reported. 2. Maximal potency as vasodilators on rabbit aortic rings, precontracted with noradrenaline (1 microM), was shown by phenyl-cyano isomers and by the 3,4-dicyanofuroxan, characterized by a potency ratio 3-10 fold higher than glyceryl trinitrate (GTN). This effect was reduced upon coincubation with methylene blue or oxyhaemoglobin (10 microM). 3. The furoxan derivatives showing maximal potency as vasodilators were also able to inhibit collagen-induced platelet aggregation, with IC50 values in the sub-micromolar range. 4. The furoxan derivatives were able to stimulate partially purified, rat lung soluble guanylate cyclase; among the most active compounds, the 3-R-substituted isomers displayed a higher level of stimulatory effect than the 4-R analogues. 5. Solutions (0.1 mM) of all the tested furoxans, prepared using 50 mM phosphate buffer, pH 7.4, (diluting 10 mM DMSO stock solutions) did not release nitric oxide (NO) spontaneously; however in presence of 5 mM L-cysteine, a significant NO-releasing capacity was observed, which correlated significantly with their stimulation of the guanylate cyclase activity.

Comparison of antiplatelet effects of FK409, a spontaneous nitric oxide releaser, with those of TRK-100, a prostacyclin analogue

The anti-platelet effects of FK409 ((+/-)-(E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexeneamide) , a new spontaneous nitric oxide releaser, and TRK-100 (sodium dl-4-[(1R,2R,3aS,8bS)-1,2,3a,8b-tetra-hydro-2-hydroxy-1-[(3S ,4RS)-3-hydroxy- 4-methyl-oct-6-yen-(E)-1-enyl]-5-cyclopenta[b]benzofuranyl]butyrate), a stable prostacyclin analogue, were studied both in vivo and in vitro. FK409 and TRK-100 inhibited ADP-induced platelet aggregation in rat platelet-rich plasma at 1.0 and 0.032 microM, respectively. In a rat extracorporeal shunt model, FK409 suppressed thrombus formation dose dependently and significantly at 1.0 mg/kg and showed the maximum inhibition (52% inhibition) at 10 mg/kg. TRK-100 showed 79% inhibition of thrombus formation at 1.0 mg/kg, but not at less than 1.0 mg/kg. At the doses required for antiplatelet effects, TRK-100 decreased mean blood pressure significantly but FK409 did not alter the blood pressure. These data suggest that FK409 shows more selective activities on platelets than TRK-100 in these experiments.

Antianginal effects of FK409, a new spontaneous NO releaser

1. The aim of this study was to compare antianginal effects of (+/-)-(E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexeneamide (FK409), a new spontaneous nitric oxide releaser, with those of isosorbide dinitrate (ISDN). We used two types of rat angina model; methacholine- and arginine vasopressin (AVP)-induced coronary vasospasm models. 2. In the in vitro study, FK409 showed 80 times more potent vasorelaxant effect in dog isolated coronary artery than ISDN (EC50 = 16.7 +/- 4.8 and 1340 +/- 320 nM, respectively). 3. In the rat methacholine-induced coronary vasospasm model, FK409 suppressed the elevation of ST segment dose-dependently and significantly at 0.1 mg kg-1, i.d. On the other hand, ISDN suppressed it significantly at 3.2 mg kg-1, i.d. In addition, the efficacy of 3.2 mg kg-1 ISDN in the model was almost the same as that of 0.1 mg kg-1 FK409. 4. In the above experiments, FK409 and ISDN decreased mean blood pressure significantly at the maximum dose tested (1.0 mg kg-1, i.d. and 3.2 mg kg-1, i.d., respectively) but did not change heart rate at these doses. Therefore, the hypotensive effect of FK409 was 10 times weaker than the antianginal effect of the compound, while those of ISDN were almost the same. 5. In the rat AVP-induced coronary vasospasm model, 32 mg kg-1 FK409 significantly inhibited the depression of ST segment 60 min after oral administration. On the other hand, 32 mg kg-1 ISDN did not inhibit it at 60 and 120 min after oral administration. 6. In conclusion, FK409 inhibits coronary vasospasm more potently in two types of rat angina models than ISDN. In addition, FK409 shows an antianginal effect more selectively that a hypotensive effect,compared with ISDN.

Antiplatelet activities of FK409, a new spontaneous NO releaser

1. We reported that (+/-)-(E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexeneamide (FK409) released nitric oxide (NO) spontaneously with a chemiluminescence analyzer. The aim of this study was to compare antiplatelet activities of FK409, a new NO releaser, with those of isosorbide dinitrate (ISDN) in vivo and in vitro. In order to elucidate the differences in antiplatelet activities between FK409 and ISDN, we compared their modes of action. 2. In in vitro experiments, FK409 had a more potent inhibitory effect on rat platelet aggregation induced by adenosine 5'-diphosphate (2.0 microM) than ISDN (IC50 = 4.32 +/- 0.95 microM and > 100 microM respectively). 3. In the rat extracorporeal shunt model (in vivo experiments), FK409 suppressed thrombus formation dose-dependently from 0.32 mg kg-1, p.o. and showed the maximum inhibition (52% inhibition vs. vehicle treatment) at 10 mg kg-1, p.o., while ISDN showed no inhibition at 10 mg kg-1 and only 17% inhibition at 32 mg kg-1, p.o. 4. FK409 could generate nitrite, which is an oxidative product of NO, much faster than ISDN in phosphate buffer solution and rat plasma during 60-min incubation at 37 degrees C. 5. These data show that FK409 has more potent antiplatelet effects than ISDN, by acting through spontaneously released NO.

Tolerance to the vascular effect of a novel nitric oxide-donating vasodilator, FK409

We investigated whether tolerance develops to the vasorelaxant effects of a new vasodilator, (+-)-(E)-4-ethyl-2-[(E)-hydroxy-imino]-5-nitro-3-hexenamide (FK409), in isolated canine coronary artery strips and to its hypotensive effect in rats, and whether FK409 activates soluble guanylate cyclase isolated from vascular tissues in the absence of L-cysteine. No tolerance to FK409 (0.46 nM to 0.46 microM or 1-1000 micrograms/kg, i.v.) or cross-tolerance between FK409 and glyceryl trinitrate was demonstrated in in vitro and in vivo experiments, whereas the tolerance to glyceryl trinitrate (0.44 nM to 4.4 microM or 1-1000 micrograms/kg, i.v.) was marked in both conditions. In addition, FK409 (0.1-10 microM) activated soluble guanylate cyclase without L-cysteine, but glyceryl trinitrate (1-100 microM) required the addition of L-cysteine (5 mM) for the activation of the enzyme. The results suggest that FK409 may be advantageous compared to tolerance-producing nitrates currently in clinical use, and that this property of FK409 is probably due to its independence of a sulfhydryl group donor.

Spontaneous nitric oxide release accounts for the potent pharmacological actions of FK409

(+-)-(E)-Ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexeneamide (FK409), which was isolated from microbial products, has been reported to show a vasorelaxant effect through a mechanism similar to that of the organic nitrates such as isosorbide dinitrate. In solution at pH 7.4, FK409 decomposed and released nitric oxide (NO) spontaneously, while isosorbide dinitrate did not. In in vitro biological tests, FK409 inhibited norepinephrine-induced contraction in rat isolated aorta more potently than did isosorbide dinitrate (ED50 = 1.0 and 310 nM, respectively) and ADP-induced human platelet aggregation (IC50 = 0.75 and > 100 microM, respectively). Nitrite/nitrate was recovered in urine accumulated for 24 h after collection from rats given FK409 or isosorbide dinitrate (10 mg/kg p.o.). FK409 (10 mg/kg p.o.) increased the plasma cyclic GMP level and at the same time decreased the mean blood pressure in conscious rats, while isosorbide dinitrate (10 mg/kg p.o.) did not change these parameters significantly. These results suggest that FK409 produces these pharmacological actions via spontaneously released NO, unlike isosorbide dinitrate, and has a possibility of becoming a unique orally active drug for cardiovascular diseases as a new NO donor.

Vasorelaxant mechanism of the new vasodilator, FK409

To define the vasorelaxation mechanism of FK409, we examined the effect of the compound on vascular tension and cyclic nucleotide levels in isolated rat thoracic aorta contracted with norepinephrine, and on activities of guanylate cyclase and cyclic GMP phosphodiesterase prepared from rat or rabbit thoracic aorta. FK409 (1 x 10(-9) to 1 x 10(-6) M), like nitroglycerin (1 x 10(-9) to 1 x 10(-6) M), produced a potent vasorelaxant effect associated with an increase in cyclic GMP content of the tissue. There was no change in cyclic AMP levels. The vasorelaxant effect of FK409 was independent of the integrity of the endothelium, and was unaffected by L-NG-monomethylarginine (0.1 mM) or oxyhemoglobin (1 microM). On the other hand, FK409 (3.2 x 10(-7) M) activated soluble guanylate cyclase, and the activating effect was completely inhibited by oxyhemoglobin (10 nM). Cyclic GMP phosphodiesterase was unaffected by FK409 (1 x 10(-7) to 1 x 10(-5) M). Furthermore, in rat aortic soluble fraction FK409 (3 mM) was found to liberate nitric oxide (NO) which was evaluated spectrophotometrically after diazotization of sulfanilic acid and coupling with N-(1-naphthyl)-ethylenediamine. The liberation occurred even in the absence of L-cysteine (5 mM), in contrast to the case with nitroglycerin (3 mM). These results suggest that the vasorelaxant effect of FK409 is associated with an increase in intracellular cyclic GMP, and that the cyclic GMP accumulation is due to activation of soluble guanylate cyclase. The enzyme activation is probably due to NO released from the compound molecule in the vascular smooth muscle cells.

Comparative studies on the inhibitory effects of calcium antagonists on cytosolic Ca2+ levels increased by high-potassium or glutamate in cultured rat cerebellar granule cells

The inhibitory effects of calcium antagonists on high-potassium or glutamate (Glu) enhanced intracellular calcium ion ([Ca2+]i) levels were studied in cultured cerebellar granule cells. Dosages between 0.5 and 10 microM of flunarizine, nicardipine, SM6586 and SM12565 reduced the rise in [Ca2+]i induced by 50 mM KCl in a dose-dependent manner, although diltiazem, verapamil and nifedipine showed less effects on such [Ca2+]i increases. SM6586, SM12565 and flunarizine at dosages below 10 microM each reduced the magnitude of the [Ca2+]i increase induced by 25 microM Glu, but the other examined calcium antagonists were less effective. These results suggest the dissimilar efficacy of calcium antagonists on the inhibition of [Ca2+]i levels increased by high-potassium and Glu.

Cardiohemodynamic effect of FK409, a novel highly potent nitrovasodilator, in anesthetized dogs

The cardiohemodynamic effect of (+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (FK409), a novel potent vasodilator, was studied in anesthetized open-chest dogs. FK409 (1 to 10 micrograms/kg, i.v.) decreased mean blood pressure, cardiac output and venous return (sum of the flow through the inferior and the superior vena cava). These changes accompanied decreases in left ventricular pressure, in its maximum rate of rise and in right atrial pressure. This cardiovascular profile of FK409 is very similar to those of classical nitrates.