Blockade of central histaminergic H2 receptors facilitates catecholaminergic metabolism and aggravates ischemic brain damage in the rat telencephalon

Drug Discovery Research for Traumatic Brain Injury Focused on Functional Molecules in Astrocytes

Traumatic brain injury (TBI) is severe damage to the head caused by traffic accidents, falls, and sports. Because TBI-induced disruption of the blood-brain barrier (BBB) causes brain edema and neuroinflammation, which are major causes of death or serious disabilities, protection and recovery of BBB function may be beneficial therapeutic strategies for TBI. Astrocytes are key components of BBB integrity, and astrocyte-derived bioactive factors promote and suppress BBB disruption in TBI. Therefore, the regulation of astrocyte function is essential for BBB protection. In the injured cerebrum of TBI model mice, we found that the endothelin ETB receptor, histamine H2 receptor, and transient receptor potential vanilloid 4 (TRPV4) were predominantly expressed in reactive astrocytes. We also showed that repeated administration of an ETB receptor antagonist, H2 receptor agonist, and TRPV4 antagonist alleviated BBB disruption and brain edema in a TBI mouse model. Furthermore, these drugs decreased the expression levels of astrocyte-derived factors promoting BBB disruption and increased the expression levels of astrocyte-derived protective factors in the injured cerebrum after TBI. These results suggest that the ETB receptor, H2 receptor, and TRPV4 are molecules that regulate astrocyte function, and might be attractive candidates for the development of therapeutic drugs for TBI.

Histidine provides long-term neuroprotection after cerebral ischemia through promoting astrocyte migration

The formation of glial scar impedes the neurogenesis and neural functional recovery following cerebral ischemia. Histamine showed neuroprotection at early stage after cerebral ischemia, however, its long-term effect, especially on glial scar formation, hasn’t been characterized. With various administration regimens constructed for histidine, a precursor of histamine, we found that histidine treatment at a high dose at early stage and a low dose at late stage demonstrated the most remarkable long-term neuroprotection with decreased infarct volume and improved neurological function. Notably, this treatment regimen also robustly reduced the glial scar area and facilitated the astrocyte migration towards the infarct core. In wound-healing assay and transwell test, histamine significantly promoted astrocyte migration. H2 receptor antagonists reversed the promotion of astrocyte migration and the neuroprotection provided by histidine. Moreover, histamine upregulated the GTP-bound small GTPase Rac1, while a Rac1 inhibitor, NSC23766, abrogated the neuroprotection of histidine and its promotion of astrocyte migration. Our data indicated that a dose/stage-dependent histidine treatment, mediated by H2 receptor, promoted astrocyte migration towards the infarct core, which benefited long-term post-cerebral ischemia neurological recovery. Therefore, targeting histaminergic system may be an effective therapeutic strategy for long-term cerebral ischemia injury through its actions on astrocytes.

Targeted disruption of organic cation transporter 3 (Oct3) ameliorates ischemic brain damage through modulating histamine and regulatory T cells

The organic cation transporters OCT1, 2, and 3 (SLC22A1-3) have been implicated in the elimination of biogenic amines such as histamine. Among them, OCT3 was identified as an uptake-2 transporter, responsible for clearance of histamine. Because increasing evidence suggests the involvement of histamine in cerebral ischemia, we investigated the effects of targeted disruption of organic cation transporter-3 (Oct3) on the severity of ischemic brain damage. Transient focal ischemia for 1 hour was induced by occlusion of the middle cerebral artery (MCA) of homozygous Oct3-deficient mice and their wild-type (Wt) littermates. Although targeted disruption of Oct3 did not affect physiological parameters after MCA occlusion, this disruption significantly increased histamine content in the ischemic cortex and significantly reduced the infarct volume after cerebral ischemia. Furthermore, targeted disruption of Oct3 prevented the reduction of regulatory T-cell proportion after cerebral ischemia while this disruption did not affect Th1 and Th2 cells proportions after ischemia. Since repeated administration of L-histidine (a precursor of histamine) to Wt mice also showed the same effects, our observations suggested that OCT3 is the molecule responsible for clearance of ischemia-induced histamine in the brain and targeted disruption of Oct3 ameliorated ischemic brain damage through an increase in regulatory T cells.

Suppression of inflammatory cell recruitment by histamine receptor stimulation in ischemic rat brains

Inflammation is a crucial factor in the development of ischemia-induced brain injury. Since facilitation of central histaminergic activity ameliorates reperfusion injury, effects of postischemic administration of L-histidine, a precursor of histamine, and thioperamide, a histamine H3 receptor antagonist, on inflammatory cell infiltration were evaluated in a rat model of transient occlusion of the middle cerebral artery. After reperfusion for 12, 24, or 72 h following 2 h of occlusion, brain slices were immunohistochemically stained with antibodies against myeloperoxidase and CD68, which were markers of polymorphonuclear leukocytes and macrophages/microglia, respectively. After reperfusion for 12-24 h, the number of neutrophils on the ischemic side increased markedly, whereas the increase was not observed on the contralateral side. Administration of L-histidine (1000 mg/kg x 2, i.p.), immediately and 6 h after reperfusion, reduced the number of neutrophils to 52%. Simultaneous administration of thioperamide (5 mg/kg, s.c.) further decreased the number of neutrophils to 32%. Likewise, the ischemia induced increase in the number of CD68-positive cells after 24 h was suppressed by L-histidine injections. The L-histidine administration decreased the number of CD4+ T lymphocytes on both ischemic and contralateral sides after 12 h, and concurrent administration of thioperamide prolonged the effect. Although administration of mepyramine (3 nmol, i.c.v.) did not affect suppression of leukocyte infiltration, ranitidine tended to reverse the effect of L-histidine. These data suggest that enhancement of central histaminergic activity suppresses inflammatory cell recruitment after ischemic events through histamine H2 receptors, which may be a mechanism underlying the protective effect of L-histidine.

Cerebral ischemia and brain histamine

Cerebral ischemia induces excess release of glutamate and an increase in the intracellular Ca(2+) concentration in neurons, which provokes enzymatic process leading to irreversible neuronal injury. Histamine plays a role as a neurotransmitter in the mammalian brain, and histamine release from nerve endings is enhanced in ischemia by facilitation of histaminergic activity. Dissimilar to ischemia-induced release of glutamate, histamine release is gradual and long lasting. The enhancement may contribute to neuroprotection against ischemic damage, because suppression of histaminergic activity aggravates the histologic outcome caused by ischemia. Preischemic administration of histamine (i.c.v.) suppresses ischemic release of glutamate and ameliorates neuronal damage, whereas blockade of central histamine H(2) receptors aggravates ischemic injury. These suggest that histamine provides beneficial effects against ischemic damage through histamine H(2) receptors, when administered before induction of ischemia. Postischemic loading with histidine, a precursor of histamine, alleviates both brain infarction and delayed neuronal death. Since the alleviation is abolished by blockade of central histamine H(2) receptors, facilitation of central histamine H(2) action caused by histidine may prevent reperfusion injury after ischemic events. Because the ischemia-induced increase in the glutamate level rapidly resumes after reperfusion of cerebral blood flow, beneficial effects caused by postischemic loading with histidine may be due to other mechanisms besides suppression of excitatory neurotransmitter release. Anti-inflammatory action by histamine H(2) receptor stimulation is a likely mechanism responsible for the improvement.

The histaminergic signaling system exerts a neuroprotective role against neurodegenerative-induced processes in the hamster

The neurotoxic 3-nitropropionic acid (3-NP), a freckled milk vetch-derived inhibitor of mitochondrial enzymatic processes that is capable of mimicking the typical pathological features of neurodegenerative disorders, behaved in a differentiated manner in a hibernating rodent (hamster) with respect to a nonhibernating rodent (rat). Treatment of the two rodents with both an acute and chronic 3-NP dose supplied deleterious neuronal effects due to distinct histamine receptor (H(n)R) transcriptional activities, especially in the case of the rat. In hamsters, these treatment modalities accounted for overall reduced global activity in a freely moving environment and overt motor symptoms such as hindlimb dystonia and clasping with respect to the greater abnormal motor behaviors in rats. This behavioral difference appeared to be strongly related to qualitative fewer neuronal alterations and, namely, lesser crenated cell membranes, swollen mitochondria, and darkened nuclei in hamster brain areas. Moreover, a mixed H(1,3)R mRNA expression pattern was reported for both rodents treated with a chronic 3-NP dose as demonstrated by predominantly low H1R mRNA levels (>50%) in rat striatum and cortex, whereas extremely high H3R levels (>80%) characterized the lateral and central amygdala nuclei plus the striatum of hamsters. Interestingly, the H3R antagonist (thioperamide) blocked 3-NP-dependent behaviors plus induced an up-regulation of H1R levels in mainly the above-reported hamster amygdalar nuclei. Overall, these results show, for the first time, that a major protective role against neurodegenerative events appears to be strongly related to the expression activity of H(1,3)R subtypes of amygdalar neurons in this hibernating model.

Postischemic regulation of central histamine receptors

This study characterizes changes occurring in the central histaminergic system associated with ischemia-reperfusion pathology in the rat. Specifically, after a postocclusion time period of 48 h, we have analyzed histamine H(1) receptor mRNA expression, histamine H(2) receptor protein amount and binding densities, and histamine H(3) receptor mRNA expression and binding densities in brain regions that have been suggested to be selectively vulnerable to transient global ischemia, i.e. hippocampus, thalamus, caudate-putamen, and cerebral cortex. We found an increase in H(1) receptor mRNA expression in the caudate-putamen: given that ischemia reduces glucose uptake and H(1) receptor activation has been shown to decrease this effect, an increase of expression levels may result in mitigating tissue damage due to energy failure observed in ischemia. A decrease in H(2) receptor binding densities in the caudate-putamen was also observed; the ischemia-induced decrease in H(2) receptor protein was also detectable by Western blot analysis. This phenomenon may underlie the previously reported ischemia induced striatal dopamine release. H(3) receptor mRNA expression was increased in the caudate putamen of the postischemic brain but was decreased in the globus pallidus and the thalamus; in association with this, H(3) receptor binding densities were increased in the cortex, caudate-putamen, globus pallidus, and hippocampus. The upregulation of H(3) receptor ligand binding may be involved in the previously reported continuous neuronal histamine release. Our data suggest that central histamine receptor expression and ligand binding are altered in brain ischemia in distinct areas, and may participate in neuroprotection and/or ischemia-associated neuronal damage.

Effect of oxygen-glucose deprivation on degranulation and histamine release of mast cells

The purpose of this study was to investigate the effect of oxygen-glucose deprivation (OGD) on degranulation and histamine release of mast cells. Cultured mast cells were exposed to OGD for 1, 2, 4, 8, or 16 h. At 2 h of OGD exposure, the degranulation percentage of mast cells had increased and subsequently showed a progressive further increase, associated with a similar change in lactate dehydrogenase release. Histamine release increased significantly from 1 h of OGD exposure. These results indicate that OGD induces mast cells to degranulate, possibly via a cytotoxic response. This in vitro ischemic model of mast cells might clarify their roles in the pathological processes induced by cerebral ischemia.

Effect of cerebral ischemia on brain mast cells in rats

The purpose of this study was to investigate the effect of transient cerebral ischemia on brain mast cells in rats. The mast cells decreased significantly at 1 h, 2 h, 4 h and 7 days after ischemia. At 1 day following ischemia, the increase of the number of mast cells in the middle aspect of the thalamus (bregma -2.80 to -3.16 mm) was twice as that of other regions in the thalamus. In addition, histamine contents increased significantly in the thalamus and striatum after ischemia. These results indicate that brain mast cells participate in the pathological process after ischemia.

Histamine H2-receptor antagonist ranitidine protects against neural death induced by oxygen-glucose deprivation

BACKGROUND AND PURPOSE

Administration of histamine receptor antagonists has been reported to produce contradictory results, either reducing or increasing neural damage induced by ischemia. In this study, we investigated the neuroprotective effects of histamine H2-receptor antagonists in an "in vitro" model of ischemia.

METHODS

Cultured rat brain cortical neurons were exposed to oxygen-glucose deprivation (OGD) in the presence or absence of different histaminergic drugs. Cell viability was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide reduction assay. Necrosis and apoptosis were quantified by staining cells with propidium iodide and Hoechst 33258. Caspase 3 activation was determined by immunocytochemistry and Western blot.

RESULTS

Pretreatment with H2 antagonists effectively reduced neuronal cell death induced by OGD. Ranitidine decreased the number of necrotic and apoptotic cells. Caspase 3 activation and alteration of the neuronal cytoskeleton were also prevented by ranitidine pretreatment. The neuroprotective effect of ranitidine was still evident when added 6 hours after OGD.

CONCLUSIONS

H2-receptor antagonists protected against OGD-induced neuronal death. Ranitidine attenuated cell death even when administered after OGD. These data suggest that this drug, which is currently used for the treatment of gastric ulcers, may be useful in promoting recovery after ischemia.

Risk factors for dopaminergic neuron loss in human alpha-synuclein transgenic mice

Genetic background, pesticide exposure, age, gender, diet and lifestyle are implicated risk factors in Parkinson's disease. We demonstrate dopamine neuron loss and other features of Parkinsonism based on the interaction of several of these human risk factors in transgenic mice expressing human alpha-synuclein. Mice expressing different forms of human alpha-synuclein had progressive declines in locomotor activity and abnormal responses to apomorphine that were modified by transgenic status. Stereological counts of tyrosine hydroxylase-positive neurons significantly declined with age only in the transgenic lines, consistent with a constant or decreasing risk, with the line expressing a double-mutant form of human alpha-synuclein more severely affected than the line expressing wild-type human alpha-synuclein. Treatment with Mn2+-ethylenebisdithiocarbamate and paraquat resulted in significantly greater effects in the double-mutant line than the other lines. Inclusions were not identified in the transgenic lines. Overexpression of human alpha-synuclein had adverse effects on substantia nigra pars compacta dopaminergic neurons that were modified by risk factors interacting in humans, including human alpha-synuclein mutations, ageing, and exposure to pesticides.

Alleviation of ischemic neuronal damage by histamine H2 receptor stimulation in the rat striatum

Transient ischemia was produced for 15 min by occlusion of the middle cerebral artery in halothane-anesthetized rats, and changes in the extracellular concentrations of neurotransmitter monoamines and amino acids were examined in the striatum. The occlusion produced marked increases in the extracellular concentrations of both dopamine and glutamate in the striatum in the saline-injected control group, the peak values being 148 and 5.2 times those before ischemia, respectively. Preischemic administration of histamine (200 nmol, i.c.v.) suppressed the increase in dopamine and glutamate levels during ischemia, the peak values being 38% and 40% of those in the control group, respectively. Neither the dopamine nor glutamate level was affected by 6-[2-(4-imidazolyl)ethylamino]-N-(trifluoromethylphenyl)heptanecarboxamide (HTMT), an H(1) agonist (100 nmol, i.c.v.). However, dimaprit, an H(2) agonist (100 nmol, i.c.v.) suppressed the peak values to 42% and 32%, respectively. Most neurons were degenerated 7 days after ischemia in control animals. Histologic outcome was alleviated by either histamine or dimaprit treatment, whereas HTMT did not affect the outcome. Although postischemic administration of mepyramine, an H(1) antagonist (5 nmol, i.c.v.), did not affect the histologic alleviation caused by preischemic treatment with histamine, ranitidine, an H(2) antagonist (30 nmol, i.c.v.), partly abolished the improvement caused by histamine. These results suggest that suppression of ischemic release of excitatory neurotransmitters by histamine H(2) action is a contributing factor in alleviation of histologic outcome.