Toshiaki Nagafuji

Blockade of nitric oxide formation by Nω-nitro-l-arginine mitigates ischemic brain edema and subsequent cerebral infarction in rats

In order to investigate whether or not nitric oxide (NO) formation underlies the cellular mechanisms of ischemic brain damage, we examined the effects of N omega-nitro-L-arginine (L-NNA), a NO synthase inhibitor, on ischemic brain edema and subsequent infarction in rats with middle cerebral artery occlusion (MCAo). For this purpose, administrations of L-NNA (1 mg/kg, i.p.) to each animal were done at the time of 5 min, 3, 6 and 24 h after MCAo, respectively. It was shown from this study that L-NNA significantly mitigated ischemic cerebral edema, and histological examinations revealed that this compound markedly reduced infarction size that occurred following MCAo. These results strongly suggest that NO formation is at least partly involved in the pathogenetic mechanisms of ischemic brain edema and subsequent cerebral infarction.

The neuroprotective effect of a potent and selective inhibitor of type I NOS (L-MIN) in a rat model of focal cerebral ischaemia.

OUR newly synthesized δ-(S-methylisothioureidoJ-L-norvaline (L-MIN) was shown to have potent inhibitory effects on Ca2+-dependent and constitutively expressed neuronal nitric oxide synthase (type I NOS) when compared to other commonly recognized NOS inhibitors and produced an IC50 value of 5.7 nM. By contrast, this compound exhibited more than 40-fold weaker inhibitory effects on the other NOS isoforms. Administration of L-MIN (0.1, 0.3 and lmg kg-1, i.p.) to rats immediately after 2 h middle cerebral artery occlusion and 2 h reperfusion reduced infarct size in a dose-dependent manner. These results suggest that type I NOS activation has a crucial role in the pathogenic cellular mechanisms underlying cerebral ischaemia.

Nitric oxide synthase in cerebral ischemia. Possible contribution of nitric oxide synthase activation in brain microvessels to cerebral ischemic injury.

The results of our continuing studies on the role of nitric oxide (NO) in cellular mechanisms of ischemic brain damage as well as related reports from other laboratories are summarized in this paper. Repetitive ip administration of NG-nitro-L-arginine (L-NNA), a NO synthase (NOS) inhibitor, protected against neuronal necrosis in the gerbil hippocampal CA1 field after transient forebrain ischemia with a bell-shaped response curve, the optimal dose being 3 mg/kg. Repeated ip administration of L-NNA also mitigated rat brain edema or infarction following permanent and transient middle cerebral artery (MCA) occlusion with a U-shaped response. The significantly ameliorative dose-range and optimal dose were 0.01-1 mg/kg and 0.03 mg/kg, respectively. Studies using a NO-sensitive microelectrode revealed that NO concentration in the affected hemisphere was remarkably increased by 15-45 min and subsequently by 1.5-4 h after MCA occlusion. Restoration of blood flow after 2 h-MCA occlusion resulted in enhanced NO production by 1-2 h after reperfusion. Administration of L-NNA (1 mg/kg, ip) diminished the increments in NO production during ischemia and reperfusion, leading to a remarkable reduction in infarct volume. In brain microvessels obtained from the affected hemisphere, Ca(2+)-dependent constitutive NOS (cNOS) was activated significantly at 15 min, and Ca(2+)-independent inducible NOS (iNOS) was activated invariably at 4 h and 24 h after MCA occlusion. Two hour reperfusion following 2 h-MCA occlusion caused more than fivefold increases in cNOS activity with no apparent alterations in iNOS activity. Thus, we report here based on available evidence that there is good reason to think that NOS activation in brain microvessels may play a role in the cellular mechanisms underlying ischemic brain injury.

Role of Nitric Oxide in Pathogenesis Underlying Ischemic Cerebral Damage

Abstract1. Based upon the intriguing report that nitric oxide synthase (NOS) inhibitor dose-dependently reverses N-methyl-D-aspartate (NMDA)-induced neurotoxicity observed in primary cortical cell cultures, many laboratories have investigated whether NOS inhibition is beneficial as a treatment for cerebral ischemia.2. Although the results are variable, it is likely thought that nitric oxide plays a key role in pathomechanism underlying ischemic brain damage.3. We review the experimental studies on effects of NOS inhibition on cerebral ischemia and measuring nitric oxide produced in the brain subjected to cerebral ischemia.4. Finally, the possibility of NOS inhibitors as a therapeutical tool is discussed.

Nω-nitro-L-arginine attenuates early ischemic neuronal damage of prolonged focal cerebral ischemia and recirculation in rats

The present study aimed to examine the effects of N omega-nitro-L-arginine (LNA) on the early ischemic neuronal damage (EIND). All the experiments were carried out under general anesthesia, maintaining the blood gases and the body temperature within the physiological ranges. The local CBF, the topographically corresponding cortical specific gravity, and the volume of EIND were determined in each rat, which was subjected to prolonged or temporary occlusion of middle cerebral artery (MCA) using our original miniclip. Significant cortical edema developed only in the brain area where the local CBF value was below 200 ml 100 g-1 min-1. The prolonged MCA occlusion for 1, 2, and 4 h induced a time-dependent increase in the severity of cortical edema and the volume of EIND. Removal of the clip invariably induced recirculation. Compared to that induced by 4 h prolonged ischemia, the brain damage was improved by 1 h MCA occlusion followed by 3 h recirculation, whereas it was significantly worsened by 2 h ischemia followed by 2 h recirculation. While LNA [1 mg, i.p., given two times during the experiment] only partially inhibited the activity of brain nitric oxide synthase, it remarkably ameliorated EIND of both prolonged ischemia and recirculation in this model. The above findings indicate the pathogenic role of nitric oxide in prolonged ischemia as well as recirculation.

An Activation of Synaptosomal Na+, K+-ATPase by a Novel Dibenzoxazepine Derivative (BY-1949) in the Rat Brain: Its Functional Role in the Neurotransmitter Uptake Systems

Abstract: In search of factors mitigating the final outcome of ischemic and epileptic brain damage, we tested a novel dibenzoxazepine derivative (BY‐1949), as the compound has been shown to be effective under these two conditions. First, using rat brain, we assessed whether or not BY‐1949 affects the Na+,K+‐ATPase activity. Although in vitro applications of either BY‐1949 or its three major metabolites did not cause any apparent effects, both acute and chronic oral administrations of the compound (10 mg/kg) invariably increased the Na+,K+‐ATPase activity in the synaptosomal plasma membranes by increasing Vmax values. Second, it was shown by this study that the drug treatment caused marked increases in the uptake of both glutamic acid and γ‐aminobutyric acid into the synaptosomes. These results suggest that the activity against ischemic/epileptic brain damage by BY‐1949 is explicable, at least partly, in terms of improvement of ionic derangements across the neural membranes via Na+,K+‐ATPase activation.

Blockade of nitric oxide formation by Nω-nitro--arginine mitigates ischemic brain edema and subsequent cerebral infarction in rats

In order to investigate whether or not nitric oxide (NO) formation underlies the cellular mechanisms of ischemic brain damage, we examined the effects of N omega-nitro-L-arginine (L-NNA), a NO synthase inhibitor, on ischemic brain edema and subsequent infarction in rats with middle cerebral artery occlusion (MCAo). For this purpose, administrations of L-NNA (1 mg/kg, i.p.) to each animal were done at the time of 5 min, 3, 6 and 24 h after MCAo, respectively. It was shown from this study that L-NNA significantly mitigated ischemic cerebral edema, and histological examinations revealed that this compound markedly reduced infarction size that occurred following MCAo. These results strongly suggest that NO formation is at least partly involved in the pathogenetic mechanisms of ischemic brain edema and subsequent cerebral infarction.

Blockade of nitric oxide formation by mitigates ischemic brain edema and subsequent cerebral infarction in rats

In order to investigate whether or not nitric oxide (NO) formation underlies the cellular mechanisms of ischemic brain damage, we examined the effects of N omega-nitro-L-arginine (L-NNA), a NO synthase inhibitor, on ischemic brain edema and subsequent infarction in rats with middle cerebral artery occlusion (MCAo). For this purpose, administrations of L-NNA (1 mg/kg, i.p.) to each animal were done at the time of 5 min, 3, 6 and 24 h after MCAo, respectively. It was shown from this study that L-NNA significantly mitigated ischemic cerebral edema, and histological examinations revealed that this compound markedly reduced infarction size that occurred following MCAo. These results strongly suggest that NO formation is at least partly involved in the pathogenetic mechanisms of ischemic brain edema and subsequent cerebral infarction.