N-Hydroxyguanidine compound 1-(3,4-dimethoxy- 2-chlorobenzylideneamino)-3-hydroxyguanidine inhibits the xanthine oxidase mediated generation of superoxide radical

NG-hydroxyguanidines from primary amines

A concise and general method for the preparation of N(G)-hydroxyguanidines from primary amines is reported. Using available and readily prepared materials, primary amines are converted to protected N(G)-hydroxyguanidines in a one-pot procedure followed by deprotection under nonreducing conditions. The method has been successfully applied to a number of examples including a high-yielding preparation of N(G)-hydroxy-L-arginine, the intermediate in the enzymatic conversion of L-arginine to nitric oxide and L-citrulline by nitric oxide synthase.

Investigations on the pharmacology of the cardioprotective guanidine ME10092

The guanidine compound ME10092 (1-(3,4-dimethoxy-2-chlorobenzylideneamino)-guanidine), which possesses a strong cardioprotective effect to ischemia-reperfusion, was assessed for different pharmacological actions that may underlie its cardioprotective effect. In the living rat ME10092 decreased the blood pressure and heart rate in a dose-dependent manner. We found ME10092 to bind to alpha 1- and alpha 2-adrenoreceptors with moderate affinity (Ki values 1-4 microM), and to block adrenaline-elicited contractile responses in isolated guinea pig aortas. Our results indicate that ME10092 possesses a certain anti-oxidant profile. Thus, in a competitive manner and with low affinity it inhibited the bovine milk xanthine oxidase enzyme, as well as NAD(P)H oxidase driven oxyradical formation in membrane fractions isolated from the rat brain. By using electron paramagnetic resonance we here show that, after its systemic administration, ME10092 modulates the nitric oxide (NO) content in several tissues of the rat in a time-dependent manner. However, in vitro ME10092 inhibited the activities of nitric oxide synthases nNOS and eNOS, but not that of iNOS. Our data give evidence that the cardioprotective effect of ME10092 could be mediated through pharmacological mechanisms that include some modulation of NO production, as well as possible inhibition of radical formation during ischemia-reperfusion.

In vivo measurements of the cerebral perfusion and cardiovascular effects of the novel guanidine ME10092 in the non-human primate, Papio ursinus

The novel guanidines N-(3,4-dimethoxy-2-chlorobenzylideneamino)-guanidine (ME 10092) and N-(3,4-dimethoxy-2-chlorobenzylideneamino)-N1-hydroxyguanidine (PR5) were recently reported to exhibit promising cardioprotective activities in myocardial ischaemia and reperfusion in rats. The current study investigated for the first time pharmacological effects of ME10092 in the primate, viz. the Cape baboon Papio ursinus. The effects of ME10092 (1 and 2 mg/kg doses) on the cerebral blood flow, heart rates and the systolic and diastolic blood pressure were investigated after intravenous injection to the baboon under anaesthesia. The cerebral perfusion effects of ME10092 were assessed using Single Photon Emission Computed Tomography according to the split-dose approach and 99mTc-hexamethyl-propylene amine oxime as brain perfusion tracer. The observation that the recovery times from the anaesthesia were unacceptably prolonged excluded doses beyond 2 mg/kg. The data indicate that no cerebral perfusion changes were induced at both the 1 and 2 mg/kg doses of ME10092. Both these doses of ME10092 showed blood pressure and heart rate effects, with the latter being more significant. Decreases in heart rate were seen directly after ME10092 administration reaching levels of about 20% for the 2 mg/kg dose and about 15% for the 1 mg/kg dose at around 6 min post drug administration. A transient decrease in both systolic and diastolic blood pressure was observed for the higher dose. The blood pressure data further suggest an attenuation of the anaesthesia induced increase in pressure usually present in non-intervention studies. ME10092 clearly exhibits mycocardial effects in the non-human primate, similar to the effects previously observed in the ischaemia-reperfusion rat model, where ME10092 showed strong protection.

Synthesis and quantitative structure-activity relationship of hydrazones of N-amino-N'-hydroxyguanidine as electron acceptors for xanthine oxidase

A series of new N-hydroxyguanidines were synthesized and tested for electron acceptor activity on bovine milk xanthine oxidase using xanthine as reducing substrate. Manual inspection of the structure-activity data revealed that molecules containing nitro groups ("set A") show a different structure-activity relationship pattern compared to non-nitro compounds ("set B"). Accordingly separate QSAR models were built and validated for the two sets. Substantial differences were found in properties governing acceptor activity for the models, the only common property being sterical access to the imino nitrogen atom of the hydroxyguanidinimines. For set A molecules the presence of a nitro substituent at a certain distance range from the hydroxuguanidino group was most important. In addition, the presence of a nitro group in the ortho position interacting with NH(2) of the hydroxyguanidino group, and the mutual geometry of the phenyl ring, hydroxyguanidine, and imine groups was important for this set. By contrast, for set B molecules the acceptor activity was most influenced by the geometry of methoxy groups and the size and geometry of meta and para substituents of the phenyl ring.

Antioxidants inhibit endothelin-1 (1-31)-induced proliferation of vascular smooth muscle cells via the inhibition of mitogen-activated protein (MAP) kinase and activator protein-1 (AP-1)

We previously found that human chymase cleaves big endothelins (ETs) at the Tyr(31)-Gly(32) bond and produces 31-amino acid ETs (1-31), without any further degradation products. In the present study, we investigated the effects of various antioxidants on the ET-1 (1-31)-induced change in intracellular signaling and proliferation of cultured rat aortic smooth muscle cells (RASMC). ET-1 (1-31) stimulated rapid and significant activation of the mitogen-activated protein (MAP) kinase family, i.e. extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun NH(2)-terminal kinase (JNK), and p38 MAPK, in RASMC to an extent similar to that of ET-1. All of the antioxidants examined, i.e. N-acetyl-L-cysteine (NAC), diphenyleneiodonium chloride (DPI), and L-(+)-ascorbic acid (ascorbic acid), inhibited both ET-1 (1-31)- and ET-1-induced JNK and p38 MAPK activation but not ERK1/2 activation. Electron paramagnetic resonance (EPR) spectroscopy measurements revealed that NAC, DPI, and ascorbic acid inhibited xanthine oxidase-induced superoxide (O(2)(.-)) generation in a cell-free system. ET-1 (1-31) in addition to ET-1 increased the generation of cellular reactive oxygen species (ROS) in RASMC. ET-1 (1-31)- and ET-1-induced cellular ROS generation was inhibited similarly by NAC, DPI, and ascorbic acid in RASMC. Gel-mobility shift analysis showed that ET-1 (1-31) and ET-1 caused an increase in activator protein-1 (AP-1)-DNA binding activity in RASMC that was inhibited by the above three antioxidants. ET-1 (1-31) increased [3H]thymidine incorporation into cells to an extent similar to that of ET-1. This ET-1 (1-31)-induced increase in [3H]thymidine incorporation was also inhibited by NAC and DPI, but not by ascorbic acid. These results suggest that antioxidants inhibit ET-1 (1-31)-induced RASMC proliferation by inhibiting ROS generation within the cells. The underlying mechanisms of the inhibition of cellular proliferation by antioxidants may be explained, in part, by the inhibition of JNK activation and the resultant inhibition of AP-1-DNA binding.

The novel guanidine ME10092 protects the heart during ischemia-reperfusion

The novel guanidine N-(3,4-dimethoxy-2-chlorobenzylideneamino)-guanidine [ME10092; a metabolite to the strongly cardioprotective hydroxyguanidine N-(3,4-dimethoxy-2-chlorobenzylideneamino)-N'-hydroxyguanidine (PR5)] was administered intravenously to rats subjected to left coronary artery clamping followed by reperfusion. Administration of 1-10 mg/kg of ME10092 1 or 5 min before 10 min of coronary artery occlusion followed by 20 min reperfusion significantly and dose-dependently inhibited the reperfusion-induced burst of arrhythmia, and markedly improved the survival of the animals. This dose schedule also dose-dependently and significantly inhibited the ST-segment elevation seen on the ECG during the artery occlusion, and attenuated the secondary rise in ST-segment during the reperfusion. Even when ME10092 was administered 5 min after the start of the reperfusion, the ST-segment elevation became significantly attenuated. Administration of ME10092 (3 plus 1.5 mg/kg) to animals subjected to 1 h left coronary occlusion followed by 2 h reperfusion reduced the heart infarction size by about 40%. ME10092 also dose-dependently reduced the heart rate, both during normal conditions and during ischemia and reperfusion. Moreover, the highest dose of ME10092 used (10 mg/kg) strongly attenuated the reduction in blood pressure seen during 10 min left coronary occlusion, as well as it attenuated the rebound rise in blood pressure seen during the 20 min reperfusion phase; that is, resulting in a normalisation of the blood pressure disturbances caused by the ischemia-reperfusion. We also showed that after its p.o. administration, the PR5 hydroxyguanidine became completely metabolised to its guanidine ME10092, with no detectable traces of PR5 being present 30 and 60 min after the administration. Moreover, after the p.o. administration of ME10092, no signs of the formation of PR5 were seen on analysis of the rats' plasma. In view of the practically indistinguishable pharmacological effects of ME10092 and PR5, we suggest the strong cardioprotective effects of these compounds to be mediated by a direct effect by ME10092 per se.

Improved method for EPR detection of DEPMPO-superoxide radicals by liquid nitrogen freezing

5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO) is frequently used as a spin trap for the measurement of superoxide by EPR spectrometry. However, its half life is fairly short in room temperature. We here show that superoxide radicals trapped by DEPMPO can be successfully recorded at -196 degrees C. Moreover, we show that the signal intensity remains unaltered for up to 7 days, when the samples are stored in liquid nitrogen. Our new approach for measurement of superoxide should greatly simplify the studies of this important radical in biological systems.