HIV envelope protein-induced neuronal damage and retardation of behavioral development in rat neonates

Cognitive and motor impairment are common symptoms among patients infected with the human immunodeficiency virus (HIV), including children who suffer neurological deficits and are frequently developmentally impaired. The HIV envelope protein, gp120, which has been shown to be toxic to neurons in culture, is shed in abundance by infected cells, and thus may play a significant role in the neuropathology of AIDS. To test this possible mechanism, neonatal rats were injected systematically with purified gp120 and the following consequences were observed: (1) radiolabeled gp120 and toxic fragments thereof were recovered in brain homogenates; (2) dystrophic changes were produced in pyramidal neurons of cerebral cortex; (3) retardation was evident in developmental milestones associated with complex motor behaviors. In parallel studies, co-treatment with peptide T, a gp120-derived peptide having a pentapeptide sequence homologous with vasoactive intestinal peptide, prevented or attenuated the morphological damage and behavioral delays associated with gp120 treatment. These studies suggest that gp120 and gp120-derived toxic fragments may contribute to the neurological and neuropsychiatric impairment related to HIV infection, and that peptide T appears to be effective in preventing gp120-associated neutoxicity in developing rodents.     

Calcium channel antagonists and human immunodeficiency virus coat protein-mediated neuronal injury.

Recent evidence in vitro has suggested that neuronal injury observed in the acquired immunodeficiency syndrome dementia complex may depend, at least in part, on toxic effects of the human immunodeficiency virus type 1 envelope protein, gp120. This laboratory previously reported that members of the dihydropyridine class of calcium channel antagonists, nimodipine and nifedipine, greatly attenuate the rise in intracellular calcium engendered by gp120 and prevent subsequent neuronal injury. The relatively low (nanomolar) concentrations of dihydropyridines that were effective suggested that their action might be exerted at the level of the L-type of voltage-dependent calcium channels. In the present study, I tested members of the three other major classes of Ca2+ channel antagonist drugs to determine if they too could prevent neurotoxicity induced by gp120. At the maximal dose that did not cause neuronal damage in and of itself, a diphenylalkylamine piperazine derivative (flunarizine, 10 microM) was the most effective, a phenylalkylamine (verapamil, 100 microM) was possibly effective, whereas a benzothiazepine (diltiazem, 1 microM) was ineffectual in protecting rat retinal ganglion cells from gp120-induced toxicity in vitro. To explain these results, previous work has shown that the various classes of Ca2+ channel antagonists may exhibit differential potency in blocking voltage-dependent Ca2+ current in neurons, with dihydropyridines and flunarizine being the most potent at neuronal calcium channels. Moreover, these channels on mammalian central neurons are relatively insensitive to agents such as verapamil and diltiazem compared with other cell types like muscle. The low micromolar concentrations necessary for potency of flunarizine is in keeping with that predicted by binding and electrophysiological studies for block of voltage-dependent calcium channels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Memantine reduces neuronal dysfunctions triggered by in vitro ischemia and 3-nitropropionic acid

Memantine, a low-affinity uncompetitive NMDA receptor antagonist, has been widely utilized for the treatment of Alzheimer's disease. A possible neuroprotective role of this drug in pathophysiological conditions involving an altered energetic metabolism of the basal ganglia has never been addressed. Thus, we have characterized the electrophysiological effect of memantine on striatal spiny neurons recorded under control conditions and after in vitro ischemia (oxygen and glucose deprivation). Memantine reduced in a dose-dependent manner (EC(50)=5 microM) the irreversible loss of field potential amplitude induced by in vitro ischemia. The neuroprotective effect of memantine against in vitro ischemia was even more potent (EC(50)=3.2 microM) in the absence of external magnesium, a condition enhancing NMDA-mediated glutamatergic transmission. Memantine was also able to block long-term potentiation recorded from spiny neurons following a brief ischemic episode. Moreover, memantine showed protection against irreversible field potential loss induced by 3-nitropropionic acid (3-NP), an inhibitor of the mitochondrial complex II, without influencing toxicity induced by rotenone, a complex I inhibitor. Memantine could represent a potential neuroprotective agent in pathophysiological conditions involving an altered energy metabolism of basal ganglia.     

Emodin prevents hypoxic-ischemic neuronal injury Involvement of the activin A pathway

Emodin, an extract of dried rhizomes and the root of the Rhizoma Polygoni Cuspidati, can protect neurons from hypoxic-ischemic brain damage. This study aimed to verify the underlying mechanism. After PC12 cells had differentiated into neuron-like cells under the induction of mouse nerve growth factor, cells were subjected to oxygen-glucose deprivation and treated with emodin. Results showed that the viability of neuron-like cells cultured under an ischemia-hypoxia environment decreased, while the expression of activin A and caspase-3 in cells increased. Emodin raised the survival rate of oxygen-glucose deprived neuron-like cells, increased activin A expression, and decreased caspase-3 expression. Experimental findings indicate that emodin can inhibit neuronal apoptosis and alleviate the injury of nerve cells after oxygen-glucose deprivation through the activin A pathway.     

Requirement for macrophages in neuronal injury induced by HIV envelope protein gp120.

HIV-1-related neuronal injury may involve a complex web of viral proteins and cytokines, but neurons themselves are not infected. The HIV envelope protein gp120 has been shown to engender an early increase in neuronal free calcium followed by delayed excitotoxic-like damage, which is prevented by N-methyl-D-aspartate (NMDA) antagonists. In the present study, we found that the injurious effects of gp120 on retinal ganglion cell neurons require the presence of macrophages in mixed neuronal glial cultures of postnatal retina. Within 24 hours of incubation, 20 pM gp120 injured nearly 40% of retinal ganglion cells in cultures containing macrophages and other glial cells, whereas no deleterious effects of gp120 were noted on retinal ganglion cells in cultures depleted of macrophages. Thus, the toxic effect of gp120 on neurons appears to be an indirect one, mediated by activation of macrophages and perhaps other glial cells.     

Selective neuronal vulnerability in HIV encephalitis.

Recent studies of human immunodeficiency virus type 1 (HIV-1) encephalitis have shown that in addition to well established white matter damage, the neocortex shows thinning, loss of large neurons and dendritic damage. In order to identify neuronal populations affected in HIV encephalitis and to determine how neuronal damage relates to the severity of HIV infection within the nervous system, we quantified parvalbumin (PV+) and neurofilament (NF+) immunoreactive neurons in the frontal cortex and hippocampus. We found that in the neocortex, the density of NF+ and PV+ neurons was independent of severity of HIV encephalitis, and therefore changes in these neuronal subsets did not account for previously reported neuronal loss. However, neuritic processes of PV+ neurons were fragmented, atrophic and in some cases distended. In contrast to the frontal cortex, there was a trend toward decreased density of PV+ neurons in the hippocampus which only reached significance in the CA3 layer where there was a 50-90% decrease in PV+ neurons. This decrease was closely correlated with the severity of HIV encephalitis. Double-label immunocytochemical analysis confirmed neuritic damage to interneurons. These results suggest that HIV encephalitis differentially involves specific subpopulations of neurons. Since direct HIV infection of neuronal cells was not detected, damage to PV+ cells and fibers may be indirectly mediated by cytokines released by HIV-infected microglia.     

Polydatin prevents the induction of secondary brain injury after traumatic brain injury by protecting neuronal mitochondria

Polydatin is thought to protect mitochondria in different cell types in various diseases. Mitochondrial dysfunction is a major contributing factor in secondary brain injury resulting from traumatic brain injury. To investigate the protective effect of polydatin after traumatic brain injury, a rat brain injury model of lateral fluid percussion was established to mimic traumatic brain injury insults. Rat models were intraperitoneally injected with polydatin(30 mg/kg) or the SIRT1 activator SRT1720(20 mg/kg, as a positive control to polydatin). At 6 hours post-traumatic brain injury insults, western blot assay was used to detect the expression of SIRT1, endoplasmic reticulum stress related proteins and p38 phosphorylation in cerebral cortex on the injured side. Flow cytometry was used to analyze neuronal mitochondrial superoxide, mitochondrial membrane potential and mitochondrial permeability transition pore opened. Ultrastructural damage in neuronal mitochondria was measured by transmission electron microscopy. Our results showed that after treatment with polydatin, release of reactive oxygen species in neuronal mitochondria was markedly reduced; swelling of mitochondria was alleviated; mitochondrial membrane potential was maintained; mitochondrial permeability transition pore opened. Also endoplasmic reticulum stress related proteins were inhibited,including the activation of p-PERK, spliced XBP-1 and cleaved ATF6. SIRT1 expression and activity were increased; p38 phosphorylation and cleaved caspase-9/3 activation were inhibited. Neurological scores of treated rats were increased and the mortality was reduced compared with the rats only subjected to traumatic brain injury. These results indicated that polydatin protectrd rats from the consequences of traumatic brain injury and exerted a protective effect on neuronal mitochondria. The mechanisms may be linked to increased SIRT1 expression and activity, which inhibits the p38 phosphorylation-mediated mitochondrial apoptotic pathway. This study was approved by the Animal Care and Use Committee of the Southern Medical University, China(approval number: L2016113) on January 1, 2016.     

Alzheimer-associated neuronal thread protein-induced apoptosis and impaired mitochondrial function in human central nervous system-derived neuronal cells

In Alzheimer Disease (AD), dementia is due to cell loss and impaired synaptic function. The cell loss is mediated by increased apoptosis, predisposition to apoptosis, and impaired mitochondrial function. Previous studies demonstrated that the AD7c-NTP neuronal thread protein gene is over-expressed in AD beginning early in the course of disease, and that in AD, AD7c-NTP protein accumulation in neurons co-localizes with phospho-tau-immunoreactivity. To determine the potential contribution of AD7c-NTP over-expression to cell loss in AD, we utilized an inducible mammalian expression system to regulate AD7c-NTP gene expression in human CNS-derived neuronal cells by stimulation with isopropyl-1-beta-D-thiogalactopyranoside (IPTG). IPTG induction of AD7c-NTP gene expression resulted in increased cell death mediated by apoptosis, impaired mitochondrial function, and increased cellular levels of the p53 and CD95 pro-apoptosis gene products as occur in AD. In addition, over-expression of AD7c-NTP was associated with increased levels of phospho-tau, but not amyloid-beta immunoreactivity. These results suggest that AD7c-NTP over-expression may have a direct role in mediating some of the important cell death cascades associated with AD neurodegeneration, and further establish a link between AD7c-NTP overexpression and the accumulation of phospho-tau in preapoptotic CNS neuronal cells.     

NBQX or topiramate treatment after perinatal hypoxia-induced seizures prevents later increases in seizure-induced neuronal injury

PURPOSE: To evaluate the efficacy of NBQX (2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(f) quinoxaline-2,3-dione) and topiramate (TPM) given after hypoxia-induced seizures in preventing the delayed effect of hypoxia on subsequent susceptibility to seizures and neuronal injury. METHODS: We used "two-hit" rodent seizure model to study the long-term effect of perinatal hypoxia on later kainate (KA) seizure-induced neuronal damage and investigated the therapeutic efficacy of a postseizure treatment protocol in reversing the conditioning effect of early-life seizures. RESULTS: Hypoxia at P10 induces seizures without cell death but causes an increase in susceptibility to second seizures induced by KA as early as 96 h after hypoxia, and this lowered seizure threshold persists to adulthood. Furthermore, perinatal hypoxia increases KA-induced neuronal injury at postnatal day (P)21 and 28/30. Repeated doses of NBQX (20 mg/kg) or TPM (30 mg/kg) given for 48 h after hypoxia-induced seizures prevent the increase in susceptibility to KA seizure-induced hippocampal neuronal injury at P28/30. CONCLUSIONS: Our results suggest that alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor blockade after hypoxia prevents the priming effect of perinatal hypoxia-induced seizures and that this protection occurs independent of its anticonvulsant action.     

Morphinans attenuate cortical neuronal injury induced by glucose deprivation in vitro

The non-narcotic dextrorotatory morphinan, dextrorphan, as well as its levorotatory opioid enantiomer, levorphanol, and its O-methyl derivative, dextromethorphan, have recently been shown to antagonize N-methyl-D-aspartate receptor-mediated neurotoxicity. Consistent with in vivo data suggesting that this neurotoxicity contributes to the neuronal damage associated with hypoglycemia, micromolar concentrations of these morphinans markedly attenuated the injury of cultured mouse cortical neurons produced by acute glucose deprivation. These observations lend specific support to the possibility that morphinan compounds may prove to have clinical therapeutic utility in hypoglycemic encephalopathy.     

Glucose deprivation neuronal injury in vitro is modified by withdrawal of extracellular glutamine

Cultured cortical neurons deprived of glucose in a defined solution containing 2 mM glutamine became acutely swollen and went on to degenerate over the next day; this neuronal loss could be substantially attenuated by an N-methyl-D-aspartate (NMDA) antagonist. Removal of extracellular glutamine produced two effects: an increase in overall neuronal injury and a decrease in the protective effect of an NMDA antagonist. Both effects of glutamine removal were glutamine concentration dependent (EC50 for both approximately 300 microM) and not reversed by substitution of equimolar concentrations of alanine or arginine. These observations suggest that glucose deprivation neuronal injury may be tonically regulated by the presence of extracellular glutamine. We speculate that glutamine may reduce overall injury by serving as an energy substrate in the absence of glucose, but may increase NMDA receptor-mediated injury by serving as a precursor for transmitter excitatory amino acids.     

Brain-derived neurotrophic factor prevents neuronal cell death induced by corticosterone.

Corticosterone (CORT), one of the glucocorticoids, causes neuronal damage in the hippocampus, but the mechanism(s) of action underlying its effects remains unknown. Brain-derived neurotrophic factor (BDNF) is a neurotrophic factor that belongs to the neurotrophin family, affects the survival and/or differentiation of various types of neurons in vitro, and is able to antagonize neuronal death induced by various brain insults or neurotoxins in vivo. In this study, the effects of CORT on BDNF protein contents and mRNA expression were investigated in relation to neuronal survival/death of cultured rat hippocampal neurons, because the colocalization of BDNF with its receptor, TrkB, suggests that BDNF may exert its putative protective and trophic effects through an autocrine mechanism in the hippocampus. Administration of CORT accelerated the neuronal death that proceeds after serum deprivation, and simultaneously reduced the levels of BDNF mRNA and intracellular BDNF content. Exogenously added BDNF actually attenuated CORT-induced neuronal death, but not in the presence of K252a, an inhibitor of the tyrosine kinase activity of Trk family receptors. These observations suggest that CORT induces damage to hippocampal neurons, at least partly, via reducing their BDNF synthesis.     

Memantine attenuates staurosporine-induced activation of caspase-3 and LDH release in mouse primary neuronal cultures

Developmental aspects of pro- and antiapoptotic action of some NMDA receptor antagonists in the central nervous system have been postulated. In order to further elucidate this problem, we investigated effect of memantine, an uncompetitive NMDA receptor antagonist and staurosporine alone and in combination on caspase-3 activity and lactate dehydrogenase (LDH) release in primary hippocampal, neocortical and striatal cell cultures on 7 and 12 days in vitro. The data showed that the vulnerability of neuronal cells to induction of caspase-3 activity by staurosporine was higher on 7 DIV than on 12 DIV, whereas staurosporine-mediated LDH release increased with days in vitro in striatal culture only. A specific inhibitor of caspase-3, AcDEVDCHO (60 microM), completely abolished the effect of staurosporine on this enzyme's activity, but only partially attenuated staurosporine-induced LDH release in hippocampal cells. Memantine alone (0.05-2.0 microM) did not induce any cytotoxic effect but attenuated the staurosporine-induced caspase-3 activity and LDH release in hippocampal cultured neurons on each investigated day in vitro. In striatal culture, memantine had a moderate inhibitory effect on staurosporine-evoked LDH release only on 7 DIV with no significant influence on caspase-3 activity. As for neocortical cultures, memantine partially inhibited staurosporine-induced neuronal injury only on 7 DIV. These data showed that the induction of caspase-3 activity by staurosporine was more profound in immature cells, however, the staurosporine neurotoxicity, as reflected by LDH release, only partially depended on caspase-3 activation and stage of cell development. Furthermore, memantine attenuated staurosporine-induced apoptosis more efficiently in hippocampal cultures than in neocortical and striatal ones, which points to tissue specificity of effects of this neuroprotectant.     

Vinconate prevents ischemic neuronal damage in the rat hippocampus

The neuroprotective effect of vinconate, a novel vinca alkaloid derivative, was examined in a rat model of forebrain ischemia induced by 4-vessel occlusion. Hippocampal cell loss was quantified histologically 3 days after 10 or 15 min of ischemia. Intraperitoneal application of vinconate (25 and 50 mg/kg) 10 min before and immediately after 10 min of ischemia significantly reduced the neuronal cell loss in the CA1 sector of the hippocampus. Protective effect of vinconate against 15 min of ischemia was reduced, but there was still significant protection at the higher dose. Autoradiography using 14C-vinconate showed that the drug easily penetrates the blood-brain barrier and distributes in the hippocampus. The result suggests that vinconate prevents ischemic neuronal damage by direct action on the hippocampal CA1 neurons.     

Cobalt prevents nitric oxide-induced apoptotic motoneuron death in vitro.

We studied the mechanism of nitric oxide (NO) toxicity in cultured rat spinal motoneurons. Treatment with the NO donor NOC-18 (NOC) resulted in slow motoneuron death, ending in apoptosis. The observed motoneuron death was completely prevented by hemoglobin. Treatment with inhibitors of the known intracellular targets of NO, soluble guanylate cyclase, polyADP-ribose polymerase (PARP) and superoxide, did not result in any significant protection against NOC-induced motoneuron death. ATP levels were reduced as soon as 3 h after the start of NOC treatment, suggesting a direct inhibition of cellular energy production. NOC toxicity could be blocked by the general voltage-gated calcium channel blocker cobalt, but not by specific blockers of various subtypes of calcium channels.     

Dihydrolipoate reduces neuronal injury after cerebral ischemia.

It has been shown in vitro that dihydrolipoate (DL-6,8-dithioloctanoic acid) has antioxidant activity against microsomal lipid peroxidation. We tested dihydrolipoate for its neuroprotective activity using models of hypoxic and excitotoxic neuronal damage in vitro and rodent models of cerebral ischemia in vivo. In vitro, neuronal damage was induced in primary neuronal cultures derived form 7-day-old chick embryo telencephalon by adding either 1 mM cyanide or 1 mM glutamate to the cultures. Cyanide-exposed and dihydrolipoate-treated (10(-9)-10(-7) M) cultures showed an increased protein and ATP content compared with controls. The glutamate-exposed cultures treated with dihydrolipoate (10(-7)-10(-5) M) showed a decreased number of damaged neurons. In vivo, dihydrolipoate treatment (50 and 100 mg/kg) reduced brain infarction after permanent middle cerebral artery occlusion in mice and rats. Dihydrolipoate treatment (50 and 100 mg/kg) could not ameliorate neuronal damage in the rat hippocampus or cortex caused by 10 min of forebrain ischemia. A comparable neuroprotection was obtained by using dimethylthiourea, both in vitro (10(-7) and 10(-6) M) and at a dose of 750 mg/kg in the focal ischemia models. Lipoate, the oxidized form of dihydrolipoate, failed to reduce neuronal injury in any model tested. We conclude that dihydrolipoate, similarly to dimethylthiourea, is able to protect neurons against ischemic damage by diminishing the accumulation of reactive oxygen species within the cerebral tissue.