Elisabetta Gerace

Neuroprotection by group I mGlu receptors in a rat hippocampal slice model of cerebral ischemia is associated with the PI3K-Akt signaling pathway: a novel postconditioning strategy?

Ischemic postconditioning is defined as a repetitive series of brief interruptions of reperfusion applied immediately after ischemia. In this study, postconditioning was investigated by first exposing rat organotypic hippocampal slices to 30min oxygen-glucose deprivation (OGD), which promotes selective CA1 pyramidal cell death, and 5min later to either a brief period (3min) of OGD or to a low dose (10microM) of 3,5-dihydroxyphenylglycine (DHPG) for 30min. Both protocols attenuated CA1 neuronal injury, as revealed 24h later by measuring the intensity of propidium iodide fluorescence in this region. The beneficial effects were observed when DHPG postconditioning was applied up to 15min after OGD, but not at later time points, and was not additive with the neuroprotective effects of a preconditioning DHPG treatment. The attenuation of the OGD-induced CA1 injury evoked by postconditioning was prevented when mGlu1 and mGlu5 receptor antagonists and inhibitors of phosphatidylinositol 3-kinase and Akt activity were present in the incubation medium during the 5min recovery period after OGD and the 30min exposure to DHPG. The PI3K inhibitor was also able to prevent the reduction of NMDA toxicity induced by the DHPG treatment. Finally, DHPG increased the phosphorylation of Akt in a transient and mGlu1/mGlu5-dependent manner. Our results show that activation of the mGlu1/mGlu5-PI3K-Akt signaling pathway plays a crucial role in the mechanisms of postconditioning evoked by DHPG and point to this strategy as a possible novel therapeutic tool for stroke and cerebral ischemia.

Pharmacological effects of 3‐iodothyronamine (T1AM) in mice include facilitation of memory acquisition and retention and reduction of pain threshold

3‐Iodothyronamine (T1AM), an endogenous derivative of thyroid hormones, is regarded as a rapid modulator of behaviour and metabolism. To determine whether brain thyroid hormone levels contribute to these effects, we investigated the effect of central administration of T1AM on learning and pain threshold of mice either untreated or pretreated with clorgyline (2.5 mg·kg−1, i.p.), an inhibitor of amine oxidative metabolism.

Ischemic neuroprotection by TRPV1 receptor-induced hypothermia

Although treatment of stroke patients with mild hypothermia is a promising therapeutic approach, chemicals inducing prompt and safe reduction of body temperature are an unmet need. We measured the effects of the transient receptor potential vanilloid-1 (TRPV1) agonist rinvanil on thermoregulation and ischemic brain injury in mice. Intraperitoneal or intracerebroventricular injection of rinvanil induces mild hypothermia that is prevented by the receptor antagonist capsazepine. Both intraischemic and postischemic treatments provide permanent neuroprotection in animals subjected to transient middle cerebral artery occlusion (MCAo), an effect lost in mice artificially kept normothermic. Data indicate that TRPV1 receptor agonists are promising candidates for hypothermic treatment of stroke.

Selective PARP-2 inhibitors increase apoptosis in hippocampal slices but protect cortical cells in models of post-ischaemic brain damage

Background and purpose:  Poly(ADP‐ribose) polymerases (PARP)‐1 and PARP‐2 play complementary tasks in the maintenance of genomic integrity, but their role in cell death or survival processes is rather different. A recently described series of selective PARP‐2 inhibitors (UPF‐1035, UPF‐1069) were used to study the role of PARP‐1 and PARP‐2 in post‐ischaemic brain damage.

Mild activation of poly(ADP‐ribose) polymerase (PARP) is neuroprotective in rat hippocampal slice models of ischemic tolerance

Ischemic tolerance is a phenomenon in which exposure to a mild preconditioning stress results in resistance to a subsequent lethal ischemic insult. Here we investigated the role of poly(ADP‐ribose) polymerase (PARP) in the development of ischemic tolerance by using organotypic rat hippocampal slices exposed to 30 min oxygen‐glucose deprivation (OGD), which leads to selective injury of the CA1 subregion 24 h later. We developed models of pharmacological preconditioning by exposing slices to subtoxic concentrations of either N‐methyl‐d‐aspartate (NMDA) or (S)‐3,5‐dihydroxyphenylglycine (DHPG) and then, 24 h later, to 30 min OGD. Under these conditions, we observed a significant reduction in OGD‐induced CA1 damage. Exposure of slices to the PARP‐1 and ‐2 inhibitors TIQ‐A, PJ‐34 and UPF 1069 during preconditioning prevented the development of OGD tolerance in a concentration‐dependent manner. NMDA and DHPG preconditioning increased the activity of PARP, as detected by immunoblots using antibodies against the poly(ADP‐ribose) polymer product, but was not associated with consumption of cellular NAD+ or ATP. Neuroprotection induced by preconditioning was also prevented by the caspase inhibitor Z‐VAD‐FMK. The modest but significant increase in caspase‐3/7 induced by preconditioning, however, was not associated with PARP‐1 cleavage, as occurred with staurosporine. Finally, TIQ‐A prevented the activation of ERK1/2 and Akt induced by NMDA preconditioning, suggesting that the protective mechanism evoked by PARP requires activation of these prosurvival mediators. Our results suggest that preconditioning with appropriate pharmacological stimuli may promote neuroprotective mechanisms triggered by the sublethal activation of two otherwise deleterious executioners such as PARP and caspase‐3/7.

Rat Hippocampal Slice Culture Models for the Evaluation of Neuroprotective Agents

Organotypic slices cultured for weeks in vitro represent an extremely valuable strategy for the investigation of the long-term properties of neuronal circuits under physiological and pathological conditions. Here, we describe how to prepare rat organotypic hippocampal slice cultures and how to expose them for appropriate periods of time to excitotoxic agents or to oxygen and glucose deprivation conditions, in order to mimic the pattern of pyramidal cell damage which is observed in vivo and in other in vitro models. This preparation is very useful not only to study synaptic plasticity or the pathways and mechanisms of neurodegeneration but also to evaluate the effects of neuroprotective agents.

Poly(ADP-ribose) polymerase inhibition with HYDAMTIQ reduces allergen-induced asthma-like reaction, bronchial hyper-reactivity and airway remodelling.

Activation of poly(ADP‐ribose) polymerases (PARPs) is considered a key event in the molecular and cellular processes leading from acute asthma attacks to bronchial hyper‐reactivity, leucocyte recruitment, chronic inflammation, airway remodelling and lung damage. The present investigation has been carried out to investigate the action of hydroxyl‐dimethylaminomethyl‐thieno[2,3‐c]isoquinolin‐5(4H)‐one (HYDAMTIQ), a new potent PARP inhibitor, in the process leading from asthma‐like events to airway damage. Ovalbumin‐sensitized guinea pigs exposed two times to allergen inhalation were treated for 8 days with vehicle or HYDAMTIQ. Asthma‐like signs, bronchial hyper‐reactivity to methacholine, cytokine production, histamine release from mast cells, airway remodelling, collagen deposition and lung damage were evaluated. Repeated HYDAMTIQ administration (1‐10 mg/kg/day i.p.) reduced lung PARP activity, delayed the appearance and reduced the severity of allergen‐induced cough and dyspnoea and dampened the increased bronchial responses to methacholine. HYDAMTIQ‐treated animals presented reduced bronchial or alveolar abnormalities, lower number of eosinophils and other leucocytes in the lung and decreased smooth muscle or goblet cell hyperplasia. The treatment also reduced lung oxidative stress markers, such as malondialdehyde or 8‐hydroxy‐2′‐deoxyguanosine and the lung content of pro‐inflammatory cytokines (TNF‐α, interleukin (IL)‐1β, IL‐5, IL‐6 and IL‐18). Finally, mast cells isolated from the peritoneal or pleural cavities of sensitized, HYDAMTIQ‐treated animals had a reduced ability to release histamine when exposed to ovalbumin in vitro. Our findings support the proposal that PARP inhibitors could have a therapeutic potential to reduce chronic lung inflammation, airway damage and remodelling in severe unresponsive asthmatic patients.

Interplay between histone acetylation/deacetylation and poly(ADP-ribosyl)ation in the development of ischemic tolerance in vitro

Ischemic tolerance is an endogenous defense program in which exposure to a subtoxic preconditioning insult results in resistance to a subsequent, otherwise lethal, episode of ischemia. Herein, we evaluated the role of histone acetylation/deacetylation in an in vitro model of preconditioning, using rat organotypic hippocampal slices exposed to 30 min oxygen-glucose deprivation (OGD), which leads to CA1 injury 24 h later: tolerance was induced by exposing the slices to preconditioning bouts of NMDA (3 μM for 60 min) 24 h prior to the toxic OGD challenge. Under these conditions, CA1 damage induced by OGD was reduced. The induction of tolerance was prevented by incubating the slices with HDAC inhibitors. NMDA preconditioning was associated with a mild increase in poly(ADP-ribose) polymerase (PARP) activity that was apparently followed, 3 h later, by a mild increase in histone acetylation. Use of PARP and HDAC inhibitors suggests a possible interaction between PARP and HDAC activities in the development of ischemic tolerance. Finally, both PARP and HDAC inhibitors were able to prevent the increase in pERK1/2 induced by NMDA preconditioning. We propose a model in which mild histone acetylation and PARP activity cooperate in producing a neuroprotective response in the development of ischemic tolerance.

Ethanol Toxicity During Brain Development: Alterations of Excitatory Synaptic Transmission in Immature Organotypic Hippocampal Slice Cultures.

BACKGROUND The developing brain is particularly vulnerable to alcohol: Drinking during pregnancy can lead to a number of physical, learning, and behavioral disorders in the newborn. It has been demonstrated that immature and mature brain tissues display a differential sensitivity to ethanol (EtOH) toxicity and that cerebral structure and function are diversely impaired according to the stage of synaptic maturation. METHODS Rat organotypic hippocampal slice cultures were exposed for 7 days to EtOH (100 to 300 mM) after 2 days (immature) or 10 days (mature) of culture in vitro; EtOH was then removed from the medium, and 24 hours later, slices were analyzed by fluorescence microscopy, Western blotting, electrophysiology, and electron microscopy to explore the molecular mechanisms of EtOH toxicity in the developing hippocampus. RESULTS EtOH withdrawal elicited a selective CA1 pyramidal cell injury in mature slices, but not in immature slices. A significant increase in the expression of pre- and postsynaptic proteins in mature slices revealed that slice maturation is presumably associated with the development of new synapses. Incubation with chronic EtOH for 7 days and its removal from the medium induced a significant decrease in GluA1 and GluA2 expression levels; a significant reduction in the expression of synaptophysin and GluN2A was observed only after EtOH withdrawal. Whole-cell patch-clamp recordings showed that incubation with EtOH for 7 days induced a significant decrease in spontaneous excitatory postsynaptic current (sEPSC) frequency in CA1 pyramidal cells of immature slices and a trend toward a decrease in sEPSC amplitude. Electron microscopy revealed a disorganization of neurotubuli in immature slices after chronic exposure to EtOH. CONCLUSIONS These results indicate that prolonged incubation with EtOH and its subsequent withdrawal from the medium induce an impairment of excitatory synaptic transmission and possibly an incorrect formation of neuronal circuits in developing hippocampus in vitro, which is suggestive of mechanisms that may lead to mental retardation in fetal alcohol spectrum disorders.

Neuroprotective effects of topiramate and memantine in combination with hypothermia in hypoxic-ischemic brain injury in vitro and in vivo

Hypoxic-ischemic encephalopathy (HIE) is a major cause of perinatal mortality and subsequent severe neurological sequelae. Mild hypothermia is a standard therapy for HIE, but is used only in selected Reference Centers and in neonates >1800 g. Since neuronal death following HIE occurs by a cascade of events triggered by activation of glutamate receptors, we used in vitro and in vivo models of HIE to examine whether the AMPA/kainate receptor antagonist topiramate and the NMDA receptor antagonist memantine could exert neuroprotective effects, alone or in combination with hypothermia. For the in vitro experiments, rat organotypic hippocampal slices were exposed to a 30 min duration of oxygen-glucose deprivation (OGD): treatment with topiramate (1 μM) and memantine (10-30 μM) or hypothermia (35 °C or 32 °C) significantly attenuated CA1 damage after 24 h. The combination of hypothermia with topiramate and memantine enhanced their protective effect. For the in vivo experiments, we used 7 day-old rat pups subjected to permanent left common carotid artery occlusion followed by 120 min of hypoxia. Administration of topiramate or memantine (i.p., 20 mg/kg) immediately and 2 h after hypoxia or exposure to hypothermia (32 °C for 4 h beginning 1 h after hypoxia) significantly reduced the extent of the resulting infarct. The combination of topiramate or memantine with hypothermia elicited a reduction of the infarct that was greater than that produced by drugs or hypothermia alone. Notably, memantine displayed a higher degree of neuroprotection as compared to topiramate both in vitro and in vivo and, when used alone at 20 mg/kg in vivo, produced a greater reduction in brain damage than observed using topiramate in combination with hypothermia. These results suggest that memantine may be more advantageous than topiramate as a therapeutic agent in neonates with HIE treated with hypothermia.