Yanying Fan

Carnosine protects against permanent cerebral ischemia in histidine decarboxylase knockout mice by reducing glutamate excitotoxicity

Recently, we showed that carnosine protects against NMDA-induced excitotoxicity in differentiated PC12 cells through a histaminergic pathway. However, whether the protective effect of the carnosine metabolic pathway also occurs in ischemic brain is unknown. Utilizing the model of permanent middle cerebral artery occlusion (pMCAO) in mice, we found that carnosine significantly improved neurological function and decreased infarct size in both histidine decarboxylase knockout and the corresponding wild-type mice to the same extent. Carnosine decreased the glutamate levels and preserved the expression of glutamate transporter-1 (GLT-1) but not the glutamate/aspartate transporter in astrocytes exposed to ischemia in vivo and in vitro. It suppressed the dissipation of Delta Psi(m) and generation of mitochondrial reactive oxygen species (ROS) induced by oxygen-glucose deprivation in astrocytes. Furthermore, carnosine also decreased the mitochondrial ROS and reversed the decrease in GLT-1 induced by rotenone. These findings are the first to demonstrate that the mechanism of carnosine action in pMCAO may not be mediated by the histaminergic pathway, but by reducing glutamate excitotoxicity through the effective regulation of the expression of GLT-1 in astrocytes due to improved mitochondrial function. Thus, our study reveals a novel antiexcitotoxic agent in ischemic injury.

Activation of the Central Histaminergic System is Involved in Hypoxia-Induced Stroke Tolerance in Adult Mice

We hypothesized that activation of the central histaminergic system is required for neuroprotection induced by hypoxic preconditioning. Wild-type (WT) and histidine decarboxylase knockout (HDC-KO) mice were preconditioned by 3 hours of hypoxia (8% O2) and, 48 hours later, subjected to 30 minutes of middle cerebral artery (MCA) occlusion, followed by 24 hours of reperfusion. Hypoxic preconditioning improved neurologic function and decreased infarct volume in WT or HDC-KO mice treated with histamine, but not in HDC-KO or WT mice treated with α-fluoromethylhistidine (α-FMH, an inhibitor of HDC). Laser-Doppler flowmetry analysis showed that hypoxic preconditioning ameliorated cerebral blood flow (CBF) in the periphery of the MCA territory during ischemia in WT mice but not in HDC-KO mice. Histamine decreased in the cortex of WT mice after 2, 3, and 4 hours of hypoxia, and HDC activity increased after 3 hours of hypoxia. Vascular endothelial growth factor (VEGF) mRNA and protein expressions showed a greater increase after hypoxia than those in HDC-KO or α-FMH-treated WT mice. In addition, the VEGF receptor-2 antagonist SU1498 prevented the protective effect of hypoxic preconditioning in infarct volume and reversed increased peripheral CBF in WT mice. Therefore, endogenous histamine is an essential mediator of hypoxic preconditioning. It may function by enhancing hypoxia-induced VEGF expression.

Oxygen-Glucose Deprivation Induced Glial Scar-Like Change in Astrocytes

Background It has been demonstrated that cerebral ischemia induces astrocyte reactivity, and subsequent glial scar formation inhibits axonal regeneration during the recovery phase. Investigating the mechanism of glial scar formation will facilitate the development of strategies to improve axonal regeneration. However, an in vitro model of ischemia-induced glial scar has not yet been systematically established. Methodology and Principal Findings In the present study, we at the first time found that oxygen-glucose deprivation (OGD) in vitro can induce rat cortical astrocytes to present characteristics of glial scar. After OGD for 6 h, astrocytes showed a remarkable proliferation following 24 h reperfusion, evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and BrdU immunocytochemistry. Meanwhile, the expression of glial fibrillary acidic protein significantly increased, so did the expression of neurocan, which is a hallmark of the glial scar. In further experiments, neurons were co-cultured with astrocytes, which had been exposed to OGD, and then the immunostaining of class III β-tubulin was carried out to assess the neurite growth. When the co-culture was performed at 48 h reperfusion of astrocytes, the neurite growth was obviously inhibited, and this inhibition could be reversed by chondroitinase ABC, which digests glycosaminoglycan chains on CSPGs, including neurocan. However, the processes of neurons were elongated, when the co-culture was performed immediately after OGD. Conclusions and Significance Our results indicated that after conditioned OGD the astrocytes presented the characteristics of the glial scar, which are also comparable to the astrocytes in acute and chronic phases after cerebral ischemia in vivo. Therefore, the present system may be used as an in vitro model to explore the mechanisms underlying glial scar formation and the treatments to improve axonal regeneration after cerebral ischemia.

Neuroprotective effect of carnosine on necrotic cell death in PC12 cells

The nervous tissue of many vertebrates, including humans, can synthesize beta-alanyl-L-histidine (carnosine). The biological functions of carnosine are still open to question, although several theories supported by strong experimental data have been proposed. The objective of this study was to examine the effects of carnosine on neurotoxicity in differentiated rat pheochromocytoma (PC12) cells. Neurotoxicity was induced by N-methyl-D-aspartate (NMDA), which caused time- and concentration-dependent cell death as measured by MTT and LDH assays. Pretreatment with carnosine significantly prevented the neurotoxicity in a concentration-dependent manner. The protective effect of carnosine was antagonized by the H1 receptor antagonist pyrilamine, but not by the H2 receptor antagonist cimetidine. In addition, alpha-fluoromethylhistidine, a histidine decarboxylase inhibitor, slightly reversed the protective action of carnosine. These results indicate that carnosine can effectively protect against NMDA-induced necrosis in PC12 cells, and its protection may in part be due to the activation of the postsynaptic histamine H1 receptor. The study suggests that carnosine may be an endogenous protective factor and calls for its further study as a new anti-excitotoxic agent.

Chronic H1‐Antihistamine Treatment Increases Seizure Susceptibility After Withdrawal by Impairing Glutamine Synthetase

To investigate the effect of chronic H1‐antihistamine treatment on seizure susceptibility after drug withdrawal in nonepileptic rats and to further study its relation to glutamine synthetase (GS), which is the key enzyme for glutamate metabolism and gamma aminobutyric acid (GABA) synthesis.

A Novel Neuroprotective Strategy for Ischemic Stroke: Transient Mild Acidosis Treatment by CO2 Inhalation at Reperfusion

Acidosis is one of the key components in cerebral ischemic postconditioning that has emerged recently as an endogenous strategy for neuroprotection. We set out to test whether acidosis treatment at reperfusion can protect against cerebral ischemia/reperfusion injury. Adult male C57BL/6 J mice were subjected to 60-minute middle cerebral arterial occlusion followed by 24-hour reperfusion. Acidosis treatment by inhaling 10%, 20%, or 30% CO2 for 5 or 10 minutes at 5, 50, or 100 minutes after reperfusion was applied. Our results showed that inhaling 20% CO2 for 5 minutes at 5 minutes after reperfusion-induced optimal neuroprotection, as revealed by reduced infarct volume. Attenuating brain acidosis with NaHCO3 significantly compromised the acidosis or ischemic postconditioning-induced neuroprotection. Consistently, both acidosis-treated primary cultured cortical neurons and acute corticostriatal slices were more resistant to oxygen–glucose deprivation/reperfusion insult. In addition, acidosis inhibited ischemia/reperfusion-induced apoptosis, caspase-3 expression, cytochrome c release to cytoplasm, and mitochondrial permeability transition pore (mPTP) opening. The neuroprotection of acidosis was inhibited by the mPTP opener atractyloside both in vivo and in vitro. Taken together, these findings indicate that transient mild acidosis treatment at reperfusion protects against cerebral ischemia/reperfusion injury. This neuroprotection is likely achieved, at least partly, by inhibiting mPTP opening and mitochondria-dependent apoptosis.

Postconditioning-induced neuroprotection, mechanisms and applications in cerebral ischemia.

Ischemic postconditioning (PostC) is defined as a series of rapid intermittent interruptions of blood flow at the phase of reperfusion, which produces neuroprotection against cerebral ischemia/reperfusion injury via mobilizing the brains own endogenous adaptive mechanisms. Now the concept of conventional ischemic PostC has been extended to limb remote ischemic PostC and chemical PostC with hypoxia, volatile anesthetic, CO2, etc. According to the different temporal profile of PostC, it is divided into rapid and delayed PostC. Rapid PostC is applied within a few seconds to minutes after reperfusion, while delayed PostC is applied at a few hours to days after reperfusion. Although the neuroprotective mechanisms of PostC are not completely elucidated, a series of mechanisms have been found to connect with PostC in the central nervous system, such as regulating synaptic signaling, attenuating oxidative stress and inflammation, maintaining mitochondrial integrity, inhibiting endoplasmic reticulum stress, regulating autophagy, activating PI3K/Akt pathway, inhibiting apoptosis, protecting neurovascular unit, etc. Based on these multiple protective mechanisms, PostC has high expectations to translate to the clinic, but a few issues should be resolved such as the time window, risks, efficiency, the impact of age, gender, hypertension, hyperlipidemia and t-PA, and clinical maneuverability. Even so, PostC could soon be at the bedside if the clinical trials are carefully planned.

AMELIORATIVE EFFECTS OF HISTAMINE ON SPATIAL MEMORY DEFICITS INDUCED BY SCOPOLAMINE INFUSION INTO BILATERAL DORSAL OR VENTRAL HIPPOCAMPUS AS EVALUATED BY THE RADIAL ARM MAZE TASK

1 The present study examined the role of the hippocampal histaminergic system in the regulation of spatial memory deficit in rats using the radial arm maze task after scopolamine injection into the bilateral dorsal (DH) or ventral (VH) hippocampus. 2 Bilateral injection of scopolamine (5 µg/site) into both the DH and VH impaired spatial memory in the retrieval memory process. Injection of histamine (50 or 100 ng/site) in the DH and intraperitoneal injection of histidine (100 mg/kg) markedly improved working memory and reference memory deficits induced by scopolamine injection into the DH. The histamine H1 receptor antagonist pyrilamine (1 µg/site) abolished the ameliorative effects of histidine on working memory deficits, whereas both pyrilamine and the H2 receptor antagonist cimetidine (0.5 µg/site) abolished the effect of histidine on reference memory. 3 Local injection of histamine (25 or 50 ng/site) into the VH and systemic injection of histidine (50 or 100 mg/kg) markedly improved working memory deficits induced by scopolamine injection into the VH, but did not improve the deficits in reference memory. Injection of both pyrilamine (0.2, 0.5 and 1 µg/site) and cimetidine (0.1 and 0.5 µg/site) into the VH reversed the effects of histidine. 4 The results of the present study indicate that histamine has different actions on cholinergic‐related memory in the the DH and VH. Histamine in the DH ameliorates spatial working memory deficits by acting on histamine H1 receptors and reference memory deficits through both H1 and H2 receptors. However, histamine in the VH ameliorates working memory deficits via an action on both H1 and H2 receptors.

Transient Lack of Glucose but not O2 is Involved in Ischemic Postconditioning-Induced Neuroprotection

Cerebral ischemic postconditioning has emerged recently as a kind of endogenous strategy for neuroprotection. We set out to test whether hypoxia or glucose deprivation (GD) would substitute for ischemia in postconditioning.

Acidic preconditioning protects against ischemia-induced brain injury

Ischemic preconditioning protects against cerebral ischemia. Recent investigations indicated that acidic preconditioning (APC) protects against ischemia-induced cardiomyocytes injury. However, it is not clear whether APC can protect against cerebral ischemia. To address this issue, C57BL/6 mice were exposed 3 times at 10-min intervals to a normoxic atmosphere containing 20% CO(2) for 5 min before being further subjected to bilateral common carotid artery occlusion. APC reversed the ischemia-induced brain injury as revealed by improved performance in passive avoidance experiments and decreased neuron loss in the hippocampal CA1 region. Consistently, both APC-treated brain slices and primary cultured neurons were more resistant to oxygen-glucose-deprivation (OGD)-induced injury, in a pH- and time-dependent manner, as revealed by reversed cell/tissue viability. In addition, the APC treatment prevented OGD-induced mitochondrial transmembrane potential loss and apoptosis, which was inhibited by the mitochondrial permeability transport pore opener atractyloside. Taken together, these findings indicated that APC protects against ischemia-induced neuronal injury. The beneficial effects may be attributed, at least in part, to decreased mitochondria-dependent neuronal apoptosis.