The effect of tamoxifen on opening ATP-sensitive K+ channels enhances hydroxyl radical generation in rat striatum.

The present study was examined the antioxidant effect of tamoxifen, a synthetic non-steroidal antiestrogen, on cromakalim or nicorandil (ATP-sensitive K+ (KATP) channels opener)-enhanced hydroxyl radical (OH) generation induced by 1-methyl-4-phenylpyridinium ion (MPP+) in extracellular fluid of rat striatum. Rats were anesthetized, and sodium salicylate in Ringer's solution (0.5 mM or 0.5 nmol/µl/min) was infused through a microdialysis probe to detect the generation of OH as reflected by the non-enzymatic formation of 2,3-dihydroxybenzoic acid (DHBA) in the striatum. Cromakalim (100 µM) or nicorandil (1 mM) enhanced the formation of OH trapped as DHBA induced by MPP+ (5 mM). Concomitantly, these drugs enhanced dopamine (DA) efflux induced by MPP+. Tamoxifen (30 µM) significantly decreased the level of DA enhanced by cromakalim or nicorandil. Tamoxifen suppressed DHBA formation induced by MPP+ and cromakalim or nicorandil. When iron(II) was administered to cromakalim treated animals, a marked elevation of DHBA was observed, compared with the tamoxifen-treated rats These results indicated that the effects of tamoxifen on opening of KATP channels enhances OH generation in the extracellular space of striatum during of DA release by MPP+. These results indicated that estrogen protects against neuronal degeneration by as an anti-oxidant.

Glutaminergic tonic action potentiate MPP+-induced hydroxyl radical production in rat striatum.

The effect of glycine on 1-methyl-4-phenylpyridinium ion (MPP+)-induced hydroxyl radical (OH) formation in the extracellular fluid of rat striatum were investigated. Rats were anesthetized and sodium salicylate in Ringer's solution (0.5 nmol/µl/min) was infused through a microdialysis probe to detect the generation of OH as reflected by the non-enzymatic formation of 2,3-dihydroxybenzoic acid (2,3-DHBA) in rat striatum. MPP+ (5 mmol/L) produced an increase in OH formation. When glycine (1 mmol/L) was infused into the rat striatum through a microdialysis probe after MPP+ treatment, the marked in the level of 2,3-DHBA was observed in the brain dialysate. However, in the presence of MK-801 (100 µmol/L), a non competitive antagonist of N-methyl-D-aspartate (NMDA), glycine failed to increase the 2,3-DHBA formation by MPP+. When corresponding experiments were performed with nitro-L arginine (L-NNA) (1 mmol/L), a nitric oxide synthase (NOS) inhibitor, same result was obtained. These results suggest that MPP+-induced OH generation may modulated by glycine via NMDA receptor in rat striatum. This increase might be explained because of the presence of a glutaminergic tonic action.

Oxidative stress inactivates ecto-5'-nucleotidase by inhibiting protein kinase C in rat hearts in vivo.

Examined in the present study, allopurinol are xanthine oxidase inhibitors for use in rat hearts in vivo dialysis technology and ventricular myocardial intersitial adenosine production can increase. The microdialysis probe was implanted in the left ventricular myocardium of anesthetized rat hearts and the tissue in the vicinity of the dialysis was perfused with Tyrode's solution containing adenosine 5'-monophosphate (AMP) through the dialysis probe at a rate of 1.0ml/min to assess the activity of ecto-5'-nucleotidase. Allopurinol (10µM) significantly increased the level of adenosine in rat heart dialysate (n=6, p<0.05), which was inhibited by chelerythrine, 10µM, an antagonist of protein kinase C (PKC). Another free radical scavenger, coenzyme Q10 (CoQ10, 100µM) or ascorbic acid (Vitamin C; 100µM) also increased adenosine production. In addition, allopurinol enhanced the diacylglycerol (DAG; 50µM)-induced also increases in adenosine production by 71.5±12.0% (n=6, P<0.05), to a level significantly (P<0.05) greater than the increase caused by DAG alone (33.0±10.6%). In the presence of allopurinol (10µM), a marked elevation of AMP-primed dialysate adenosine in ischemia/reperfused rat hearts was observed. Free radical generation may suppress adenosine production via activation of PKC. The results suggest that oxidative stress may cause inactivation of nucleotidase, adenosine production in rat heart.

Opening of ATP-sensitive K(+) (KATP) channels enhance hydroxyl radical generation induced by MPP(+) in rat striatum.

The present study examined whether opening of adenosine triphosphate (ATP) sensitive K(+) (KATP) channels can enhance 1-methyl-4-phenylpyridinium (MPP(+))-induced hydroxyl radical (OH) generation in rat striatum. Rats were anesthetized, and sodium salicylate in Ringer's solution (0.5nmol/ml per min) was infused through a microdialysis probe to detect the generation of OH as reflected by the non-enzymatic formation of 2.3-dihydroxybenzoic acid (DHBA) in the striatum. MPP(+) (5mM) enhanced generation of OH with concomitant increased efflux of dopamine (DA). Cromakalim (100µM), a KATP channel opener, through the microdialysis probe significantly increased both DA efflux and OH formation induced by MPP(+). Another KATP channel opener, nicorandil (1mM), also increased the level DA or DHBA, but these changes were not significant. However, in the presence of glibenclamide (10µM), a KATP channel antagonist, and the increase of MPP(+)-induced DA or DHBA were not observed. Cromakalim (10, 50 and 100µM) increased MPP(+)-induced DHBA formation in a concentration-dependent manner. However, the effects of cromakalim in the presence of glibenclamide were abolished. These results suggest that opening of KATP channels may cause OH generation by MPP(+).

Evidence for existence of thyroid hormone inducible semicarbazide-sensitive amine oxidase (SSAO) in rat heart cytosol.

BACKGROUND: Semicarbazide-sensitive amine oxidase (SSAO; EC; 1.4.3.6.) has widespread tissue distribution, and the physiological role of SSAO is quite well known through its involvement in several pathological states. AIMS: The present study examined modulators of SSAO which might be present in the rat heart cytosol and looked for changes in SSAO modulatory activity. METHODS: An endogenous inhibitor of SSAO was separated by gel filtration from 105,000g supernate of T4-treated rat heart cytosol. SSAO inhibition fraction was referred to as "endogenous SSAO inhibitor". RESULTS: The inhibition by this inhibitor was concentration-dependent. Inhibition of SSAO was not enhanced by varying the time of preincubation of the enzyme, indicating reversible inhibition of SSAO. The molecular weight of this inhibitor was estimated to be 1000-1100 by gel filtration. The isoelectric point (pI) value was determined to be 4.8 isoelectric focusing. This inhibitor was found to be heat-stable and resistant to protease treatment. SSAO inhibition activity was much lower in the cytosol of thyroidectomized, non-T4-treated rats than T4-treated rats, suggesting that this inhibitor was induced by thyroid hormone T4. SSAO activity in rat heart might be regulated by the level of this inhibitor. CONCLUSION: These results suggest the presence of SSAO inhibitor in T4-treated rat cytosol and that the level of this inhibitor is regulated by thyroid hormone.

Fluvastatin, an HMG-CoA reductase inhibitor, facilitate adenosine production in the rat hearts via activation of ecto-5'-nucleotidase.

OBJECTIVE: The present study was examined whether fluvastatin, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, can increase the production of interstitial adenosine via activation of ecto-5'-nucleotidase in the ventricular myocardium, with use of microdialysis techniques in in situ rat hearts. METHODS: Adenosine in the dialysate collected during perfusion with Tyrode's solution containing 100µM AMP (through the probe) originated from the hydrolysis of AMP catalyzed by endogenous ecto-5'-nucleotidase, so that the level of adenosine reflected the activity of ecto-5'-nucleotidase in this tissue. RESULTS: Fluvastatin (100µM), an inhibitor of low-density lipoprotein (LDL) oxidation, significantly increased the concentration of adenosine measured in the presence of 100µM AMP (i.e., the activity of ecto-5'-nucleotidase) by 154.7±16.0% (n=6, P<0.05), an increase which inhibited an antagonist of the α1-adrenoceptor (prazosin, 50µM) or of protein kinase C (PKC; chelerythrine, 10µM). Fluvastatin (10-500µM) increased the level of AMP-primed dialysate adenosine in a concentration-dependent manner. CONCLUSION: These results indicate that fluvastatin increases in adenosine concentrations in the dialysate which resulted from activation of PKC, mediated by stimulation of α1-adrenoceptors, through activation of ecto-5'-nucleotidase.

Phytic acid suppresses ischemia-induced hydroxyl radical generation in rat myocardium.

The present study examined whether ischemia-reperfusion-induced hydroxyl radical (·OH) generation was attenuated by myo-inositol hexaphosphoric acid (phytic acid). A flexibly mounted microdialysis technique was used to detect the generation of ·OH in in vivo rat hearts. To measure the level of ·OH, sodium salicylate in Ringer's solution (0.5mM or 0.5 nmol/µl/min) was infused directly through a microdialysis probe to detect the generation of ·OH as reflected by the nonenzymatic formation of 2,3-dihydroxybenzoic acid (2,3-DHBA). To confirm the generation of ·OH by Fenton-type reaction, iron(II) was infused through a microdialysis probe. A positive linear correlation between iron(II) and the formation of 2,3-DHBA (R(2)=0.983) was observed. However, the level of 2,3-DHBA in norepinephrine (100 µM) plus phytic acid (100 µM) treated group were significantly lower than those observed in norepinephrine-only-treated group (n=6, *p<0.05). To examine the effect of phytic acid on ischemia-reperfusion-induced ·OH generation, the heart was subjected to myocardial ischemia for 15 min by occlusion of the left anterior descending coronary artery (LAD). When the heart was reperfused, the normal elevation of 2,3-DHBA in the heart dialysate was not observed in animals pretreated with phytic acid. These results suggest that phytic acid is associated with antioxidant effect due to the suppression of iron-induced ·OH generation.

Protective effect of diltiazem, a L-type calcium channel antagonist, on lysophosphatidylcholine-enhanced hydroxyl radical generation by MPP(+) in rat striatum.

BACKGROUND: The interaction between the PKC and oxygen free radicals. OBJECTIVE AND METHODS: The present study examined the effects of lysophosphatidylcholine (LPC), an endogenous amphophilic lipid metabolite, on 1-methyl-4-phenylpyridinium ion (MPP(+))-induced hydroxyl radical (()OH) generation in rat striatum. LPC (50 µM) increased ()OH formation by MPP(+). Further, the effect of diltiazem, a L-type Ca(2+) channel antagonist, on MPP(+) (5mM)-induced ()OH generation was studied. RESULTS: Diltiazem (100 µM) significantly suppressed LPC and MPP(+)-induced ()OH generation. The results indicate ()OH generation, and diltiazem may have preventive effect on MPP(+)-induced ()OH generation. CONCLUSION: These results demonstrated that diltiazem suppressed LPC-induced generation of free radical through blockage of Ca(2+) channel in the rat striatum.

Effect of tyramine on the production of interstitial adenosine during perfusion with adenosine 5'-monophosphate in rat hearts in vivo.

The present study was examined whether tyramine-released norepinephrine enhances the production of interstitial adenosine via stimulation of ecto-5'-nucleotidase (a key enzyme responsible for adenosine production) using microdialysis techniques in in situ rat hearts. The microdialysis probe was implanted in the left ventricular myocardium of anesthetized rats and perfused in the presence of adenosine 5'-monophosphate. Tyramine (1mM) increased the adenosine concentration measured in the presence of 100 µM adenosine 5'-monophosphate, an increase which was inhibited by antagonist of the α(1)-adrenoceptors (prazosin, 50 µM) or of a protein kinase C inhibitor (chlerythrine, 10 µM), and in reserpinized rats, tyramine failed to increase the adenosine 5'-monophosphate-primed dialysate adenosine concentration. norepinephrine is known to activate α(1)-adrenoceptors and protein kinase C. Taken together, the results demonstrate that tyramine-released norepinephrine activates both α(1)-adrenoceptors and protein kinase C, which increased ecto-5'-nucleotidase activity and augmented release of adenosine in rat hearts.

Diabetes modulates ethanol-induced increase in serotonin release from rat hippocampus: an in vivo microdialysis study.

We examined whether diabetes mellitus (DM) affects the acute ethanol (EtOH)-induced increase in serotonin (5-HT) release from the rat hippocampus, and compared the findings with those obtained from non-DM rats. Hippocampal 5-HT was measured by using in vivo microdialysis. Rats were rendered diabetic by an injection of streptozotocin (STZ). EtOH (0.5, 1.0, or 2.0 g/kg) was intraperitoneally administered or EtOH (25, 50, 100, or 200 mM) was given by intracerebral infusion. EtOH enhanced the extracellular 5-HT levels in both non-DM and DM rats in a dose-dependent manner, especially in non-DM rats, irrespective of administration route. Among three kinds of alcohols tested at same concentration (100 mM), methanol was the most effective in increasing extracellular 5-HT levels of non-DM rats; then, in descending order, EtOH and isopropanol. However, no such tendency was observed in DM rats. Experiments using various antagonists and agonists of 5-HT receptors showed that the functions of 5-HT(1B), 5-HT(2), 5-HT(3), and/or 5-HT(4) receptors in the hippocampus of DM rats differ from those in non-DM rats, suggesting that DM induces dysfunction of central neurotransmitter systems including 5-HT receptors. Acetaldehyde (100 mM), a major metabolite of EtOH, also significantly increased 5-HT release in both non-DM and DM rats. Based on the results that EtOH could increase the 5-HT in non-DM rats than in DM rats while acetaldehyde worked on both rats, it is more likely that alcohol dehydrogenase 1B activity was decreased in DM rats. The present study is the first, to our knowledge, to show that DM modulated the EtOH-induced 5-HT release from the hippocampus in type-1 diabetic rats.

The protective effect of fluvastatin on hydroxyl radical generation by inhibiting low-density lipoprotein (LDL) oxidation in the rat myocardium.

The present study examined the effect of fluvastatin on Cu(2+)-induced hydroxyl radical generation (*OH) in the extracellular fluid of rat myocardium using microdialysis technique (O system). Fluvastatin, an inhibitor of low-density lipoprotein (LDL) oxidation, was administered at a dose of 5.0 mg/kg/day i.p. for 4 weeks. Rats were anesthetized and sodium salicylate in Ringer's solution (0.5 nmol/microl/min) was infused through a microdialysis probe to detect the generation of *OH as reflected by the nonenzymatic formation of 2,3-dihydroxybenzoic acid (DHBA) in the myocardium. When CuSO(4) was infused through the microdialysis probe, CuSO(4) clearly produced an increase in *OH formation trapped as 2,3-DHBA (R(2)=0.983). However, when corresponding experiments were performed with fluvastatin (5.0 mg/kg/day i.p. for 4 weeks) pretreated animals, small increases in the level of 2,3-DHBA products were observed. When LDL is oxidized by Cu(2+), Cu(2+) can be reduced to Cu(1+) by LDL. Fenton-type reactions in the presence of Cu(1+) yields highly cytotoxic *OH. These results suggest that Cu(2+)-induced *OH generation may be reduced by inhibiting LDL oxidation with fluvastatin.

Effect of antidepressant drug on semicarbazide-sensitive amine oxidase (SSAO) in dog brain.

The present study examined whether or not other cyclic antidepressants, such as the dicyclic drug zimeldine, the tricyclic drug imipramine, and tetracyclic drug maprotiline, and the noncyclic drug nomifensine, inhibit semicarbazide-sensitive amine oxidase (SSAO) activity in dog brain. After treatment with 100 nM clorgyline and 100 nM deprenyl, all four antidepressant drugs inhibit SSAO activity in dog brain. The most potent of inhibition was observed by imipramine, followed by maprotiline, zimeldine and nomifensine. All four drugs are noncompetitive inhibitor of SSAO in dog brain. We found the tricyclic antidepressant drug imipramine to be the most selective inhibitors of SSAO activity in dog brain, as compared with other type of antidepressant drugs.

The properties of B-form monoamine oxidase in mitochondria from monkey platelet.

The present study was examined the effect of the properties of monkey platelet monoamine oxidase (MAO) based on inhibitor sensitivity. Monkey platelet showed a high MAO activity with beta-phenylethylamine (beta-PEA) as substrate and a very low A-form MAO activity with 5 hydroxytryptamine (5-HT) as substrate. Moreover, monkey platelet MAO was sensitive to the drugs deprenyl as B-form MAO inhibitor and less sensitive to clorgyline and harmaline as A form MAO inhibitor with beta-PEA as the B-form MAO substrate. B-form MAO from monkey platelet was more stable against heat treatment at 55 degrees C than B-form MAO in brain. After digestion with trypsin at 37 degrees C for 4 hrs, it was found that MAO from platelet was inhibited about 70% with beta-PEA as substrate with brain. The tricyclic antidepressant imipramine and nortriptyline inhibited B-form MAO activity more potency than B-form MAO in brain. However, when the noncyclic antidepressant nomifensine was used, monkey platelet B-form MAO activities were less potently inhibited. All these reagents were noncompetitive inhibitors of B form MAO in monkey platelet. The present studies demonstrated that monkey platelet MAO is a single of B-form MAO and sensitive to tricyclic antidepressants.

Changes in monoamine oxidase activity in hepatic injury: a review.

This review focuses on multiplicity of monoamine oxidase (MAO) activity in rat hepatic injury. MAO play a major role in the metabolism of biogenic amines. Stress such as immobilization stress (IMMO) or cold stress changes the multiple forms of MAO activity in rat liver. Thyroid hormone-inducible MAO inhibitor may play some role in regulating the MAO activity in rat liver. Carcinogen such as dimethylnitrosamine (DEN) might change the proportions of the forms of MAO activity in tumor cells. This compound is selective to and an irreversible inhibitor of MAO-B. These changes may account for the multiplicity of MAO by hepatic injury.

Protective effect of tamoxifen, a synthetic non-steroidal antiestrogen, on phenelzine and 1-methyl-4-phenylpyridinium ion (MPP+)-induced hydroxyl radical generation in rat striatum.

The present study examined whether tamoxifen could suppress antidepressant drug phenelzine can increase an active dopaminergic neurotoxin, 1-methyl-4-phenylpyridinium ion (MPP+)-induced hydroxyl radical (*OH) generation in the extracellular fluid of rat striatum, using in vivo microdialysis system. Rats were anesthetized, and sodium salicylate (0.5 nmol/microl/min) was infused through a microdialysis probe to detect the generation of *OH as reflected by the non-enzymatic formation of 2,3-dihydroxybenzoic acid (DHBA) in the striatum. Infusion of phenelzine (0.1 mM or 0.1 nmol/microl/min) into the striatum drastically increased dopamine (DA) efflux and the *OH formation, trapped as 2,3-DHBA by the possible increased production of MPP+. However, tamoxifen (100 microM) significantly suppressed phenelzine enhanced DA efflux and *OH formation by MPP+. These results in the pressent study is the first demonstration showing the protective effect of tamoxifen on *OH generation induced by phenelzine enhanced MPP+ by suppressing DA efflux.

Effect of antidepressant drug on semicarbazide-sensitive amine oxidase (SSAO) in dog brain.

The present study examined whether or not other cyclic antidepressants, such as the dicyclic drug zimeldine, the tricyclic drug imipramine, and tetracyclic drug maprotiline, and the noncyclic drug nomifensine, inhibit semicarbazide-sensitive amine oxidase (SSAO) activity in dog brain. After treatment with 100 nM clorgyline and 100 nM deprenyl, all four antidepressant drugs inhibit SSAO activity in dog brain. The most potent of inhibition was observed by imipramine, followed by maprotiline, zimeldine and nomifensine. All four drugs are noncompetitive inhibitor of SSAO in dog brain. We found the tricyclic antidepressant drug imipramine to be the most selective inhibitors of SSAO activity in dog brain, as compared with other type of antidepressant drugs.

The properties of B-form monoamine oxidase in mitochondria from monkey platelet.

The present study was examined the effect of the properties of monkey platelet monoamine oxidase (MAO) based on inhibitor sensitivity. Monkey platelet showed a high MAO activity with beta-phenylethylamine (beta-PEA) as substrate and a very low A-form MAO activity with 5 hydroxytryptamine (5-HT) as substrate. Moreover, monkey platelet MAO was sensitive to the drugs deprenyl as B-form MAO inhibitor and less sensitive to clorgyline and harmaline as A form MAO inhibitor with beta-PEA as the B-form MAO substrate. B-form MAO from monkey platelet was more stable against heat treatment at 55 degrees C than B-form MAO in brain. After digestion with trypsin at 37 degrees C for 4 hrs, it was found that MAO from platelet was inhibited about 70% with beta-PEA as substrate with brain. The tricyclic antidepressant imipramine and nortriptyline inhibited B-form MAO activity more potency than B-form MAO in brain. However, when the noncyclic antidepressant nomifensine was used, monkey platelet B-form MAO activities were less potently inhibited. All these reagents were noncompetitive inhibitors of B form MAO in monkey platelet. The present studies demonstrated that monkey platelet MAO is a single of B-form MAO and sensitive to tricyclic antidepressants.

Changes in monoamine oxidase activity in hepatic injury: a review.

This review focuses on multiplicity of monoamine oxidase (MAO) activity in rat hepatic injury. MAO play a major role in the metabolism of biogenic amines. Stress such as immobilization stress (IMMO) or cold stress changes the multiple forms of MAO activity in rat liver. Thyroid hormone-inducible MAO inhibitor may play some role in regulating the MAO activity in rat liver. Carcinogen such as dimethylnitrosamine (DEN) might change the proportions of the forms of MAO activity in tumor cells. This compound is selective to and an irreversible inhibitor of MAO-B. These changes may account for the multiplicity of MAO by hepatic injury.

Protective effect of tamoxifen, a synthetic non-steroidal antiestrogen, on phenelzine and 1-methyl-4-phenylpyridinium ion (MPP+)-induced hydroxyl radical generation in rat striatum.

The present study examined whether tamoxifen could suppress antidepressant drug phenelzine can increase an active dopaminergic neurotoxin, 1-methyl-4-phenylpyridinium ion (MPP+)-induced hydroxyl radical (*OH) generation in the extracellular fluid of rat striatum, using in vivo microdialysis system. Rats were anesthetized, and sodium salicylate (0.5 nmol/microl/min) was infused through a microdialysis probe to detect the generation of *OH as reflected by the non-enzymatic formation of 2,3-dihydroxybenzoic acid (DHBA) in the striatum. Infusion of phenelzine (0.1 mM or 0.1 nmol/microl/min) into the striatum drastically increased dopamine (DA) efflux and the *OH formation, trapped as 2,3-DHBA by the possible increased production of MPP+. However, tamoxifen (100 microM) significantly suppressed phenelzine enhanced DA efflux and *OH formation by MPP+. These results in the pressent study is the first demonstration showing the protective effect of tamoxifen on *OH generation induced by phenelzine enhanced MPP+ by suppressing DA efflux.

Protective effect of captopril and enalaprilat, angiotensin-converting enzyme inhibitors, on para-nonylphenol-induced *OH generation and dopamine efflux in rat striatum.

We recently reported that para-nonylphenol, an environmental chemical, induced hydroxyl radical (*OH) formation in rat striatum. In this study we examined the antioxidant effects of angiotensin-converting enzyme inhibitors (captopril or enalaprilat) on para-nonylphenol (nonylphenol) and 1-methyl-4-phenylpyridinium ion (MPP(+))-induced hydroxyl radical (*OH) formation and dopamine (DA) efflux in extracellular fluid of rat striatum, using a microdialysis technique. para-Nonylphenol clearly enhanced *OH formation and DA efflux induced by MPP(+). When captopril or enalaprilat was infused in nonylphenol and MPP(+)-treated rats, DA efflux and OH formation significantly decreased, as compared with that in the nonylphenol and MPP(+)-treated control. We compared the ability of non-SH-containing enalaprilat with a SH-containing captopril to scavenge OH and DA efflux. Both inhibitors were able to scavenge *OH and DA efflux induced by para-nonylphenol and MPP(+). The results suggest that angiotensin-converting enzyme inhibitors may protect against nonylphenol and MPP(+)-induced *OH formation via suppressing DA efflux in the rat striatum.