Induction of heme oxygenase-1 in the rat brain by kainic acid-mediated excitotoxicity: the dissociation of mRNA and protein expression in hippocampus

Paeonol exerts neuroprotective and anticonvulsant effects in intrahippocampal kainate model of temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is presented the most common form of focal epilepsy with involvement of oxidative stress and neuroinflammation as important factors in its development. About one third of epileptic patients are intractable to currently available medications. Paeonol isolated from some herbs with traditional and medicinal uses has shown anti-oxidative and anti-inflammatory effects in different models of neurological disorders. In this research, we tried to evaluate the possible protective effect of paeonol in intrahippocampal kainate murine model of TLE. To induce TLE, kainate was microinjected into CA3 area of the hippocampus and paeonol was administered at two doses of 30 or 50mg/kg. The results of this study showed that paeonol at the higher dose significantly reduces incidence of status epilepticus, hippocampal aberrant mossy fiber sprouting and also preserves neuronal density. Beneficial protective effect of paeonol was in parallel with partial reversal of some hippocampal oxidative stress markers (reactive oxygen species and malondialdehyde), caspase 1, glial fibrillary acidic protein, heme oxygenase 1, DNA fragmentation, and inflammation-associated factors (nuclear factor-kappa B, toll-like receptor 4, and tumor necrosis factor α). Our obtained data indicated anticonvulsant and neuroprotective effects of paeonol which is somewhat attributed to its anti-oxidative and anti-inflammation properties besides its attenuation of apoptosis, pyroptosis, and astrocyte activity.

Effect of status epilepticus on expression of brain UDP-glucuronosyltransferase 1a in rats

Status epilepticus (SE) involves severe epileptic seizures that cause oxidative stress in the brain. Oxidative stress is known to influence uridine 5'-diposphate-glucuronosyltransferase (UGT) 1A expression. The present study aimed at elucidating the effect of SE on Ugt1a1, Ugt1a6 and Ugt1a7 expression in the rat brain. Kainic acid was used to create an animal model of SE. Sprague-Dawley rats were treated intraperitoneally with 10 mg/kg kainic acid. Ugt1a1 and Ugt1a7 mRNA levels were increased by SE in the cortex and hippocampus (Ugt1a1: 4.0- and 5.3-fold, respectively; Ugt1a7: 2.8- and 2.5-fold, respectively). Moreover, the induction degree of heme oxygenase-1 mRNA, an oxidative stress marker, was high in these regions, suggesting that oxidative stress could be involved in Ugt1a1 and Ugt1a7 induction. Ugt1a6 was elevated by 1.8-fold in the cortex in both SE and non-response (non-epileptic seizure response) rats, implying that Ugt1a6 induction may be independent from SE. An intraperitoneal single administration of 25 mg/kg diazepam (DZP) for the treatment of SE could attenuate heme oxygenase-1 induction in the cortex, whereas Ugt1a1 was decreased in the hippocampus, but not in the cortex, suggesting that there likely exists an alternative mechanism for Ugt1a1 reduction by DZP treatment. Continuous 14-day administration of DZP inhibited Ugt1a1 induction in the cortex, but did not have an effect on Ugt1a7 induction. This study indicated that SE altered the expression of brain Ugt1a1 and Ugt1a7, which could alter glucuronidation in the brain.

Regulation and expression of heme oxygenase enzymes in aged-rat brain: age related depression in HO-1 and HO-2 expression and altered stress-response

The heme oxygenase isozymes, HO-1 and HO-2, oxidatively cleave the heme molecule to produce biliverdin and the gaseous messenger, CO. The cleavage results in the release of iron, a regulator of transferrin, ferritin, and nitric oxide (NO) synthase gene expression. Biliverdin reductase (BVR) then catalyzes the reduction of biliverdin, generating the potent intracellular antioxidant, bilirubin. We report an age-related decrease in HO-1 and HO-2 expression present in select brain regions including the hippocampus and the substantia nigra, that are involved in the high order cognitive processes of learning and memory. The age-related loss of monoxide-producing potential in select regions of the brain was not specific to the HO system but was also observed in neuronal NO-generating system. Furthermore, compared to 2-month old rats, the ability of aged brain tissue to respond to hypoxic/hyperthermia was compromised at both the protein and the transcription levels as judged by attenuated induction of HO-1 immunoreactive protein and its 1.8 Kb transcript. Neotrofin (AIT), a cognitive-enhancing and neuroprotective drug, caused a robust increase in HO-1 immunoreactive protein in select neuronal regions and increased the expression of HO-2 transcripts. The potential interplay between regulation of HO-2 gene expression and the serum levels of the adrenal steroids is discussed. We suggest the search for therapeutic agents that reverse the decline and aberrant stress response of HO enzymes may lead to effective treatment regimens for age-associated neuronal deficits.

Glial overexpression of heme oxygenase-1: a histochemical marker for early stages of striatal damage

The level of heme oxygenase-1 (HO-1) in the normal striatum is below the limit of immunodetection. However, HO-1 is overexpressed in both neural and non-neural cells in response to a wide range of lesions. We induced different types of lesions affecting the striatal cells or the main striatal afferent systems in rats to investigate if overexpression of HO-1 could be a useful histochemical marker of striatal damage. Thirty-six hours after intrastriatal or intraventricular injection of excitotoxins that affect striatal neurons (ibotenic acid) or of neurotoxins that affect striatal dopaminergic (6-hydroxydopamine) or serotonergic (5,7-dihydroxytriptamine) afferent terminals, or after surgical lesioning of cortico-striatal projections, there was intense induction of striatal HO-1 immunoreactivity (HO-1-ir). Double immunolabeling revealed that the HO-1-ir was located in glial cells. After intrastriatal injection of ibotenic acid, a central zone of neuronal degeneration contained numerous round and pseudopodic HO-1-ir cells, and was surrounded by a ring of HO-1-ir cells, most of which were immunoreactive for astroglial markers. Intraventricular injection of neurotoxins induced astroglial HO-1-ir cells which were more evenly distributed throughout the lesioned or denervated areas. HO-1-ir microglial cells were also observed in areas subjected to mechanical damage. The HO-1-ir was markedly lower or absent 1 week after lesion, and even more so 3 weeks after, although some HO-1-ir cells were still observed after intrastriatal injection of ibotenic acid or surgical corticostriatal deafferentation. The results indicate that determination of glial HO-1-ir is a useful histochemical marker for early stages of striatal damage.

Inhibition of aconitase in astrocytes increases the sensitivity to chemical convulsants

Although there is evidence that astrocytes support neuronal function, the contribution of astrocytes to seizure onset and termination is not known. To determine whether there are changes in seizure susceptibility or neuronal damage when the ability of astrocytes to generate ATP is reduced, 0.5 nmol of fluorocitrate (FC) was injected into the right ventricle. Injection of FC alone did not produce electrographic or behavioral seizures and did not stress or injure neurons or astrocytes, as measured with silver stain and immunohistochemistry for HSP32 or HSP72. However, in animals pretreated with FC, administration of kainic acid, at a dose that does not initiate seizures in control animals (7 mg/kg), caused wet dog shakes and neuronal damage in the hilus. Wet dog shakes did not cause any neuronal damage in control animals. If the dose of FC was increased to 0.75 nmol, then subsequent administration of the same dose of kainic acid (7 mg/kg) caused stage 3-5 seizures. Injection of FC also reduced the dose of pilocarpine needed to produce seizures. Given simultaneously with FC, isocitrate, which bypasses the biochemical inhibition of aconitase, blocked the effects of FC in both kainic acid and pilocarpine treated animals. The data demonstrate that inhibition of aconitase in astrocytes lowers the doses of both kainic acid and pilocarpine that will cause behavioral seizures and may increase neuronal vulnerability to seizures.

Immunocytochemical localization and expression of heme oxygenase-1 in primary astroglial cell cultures during differentiation: effect of glutamate

Heme oxygenase-1 (HO-1) catalyzes the rate-limiting step in heme degradation releasing iron, carbon monoxide (CO), and biliverdin. We investigated subcellular localization of HO-1 using confocal laser scanning microscopy (CLSM) and the expression by Western blot in primary astroglial cells during differentiation and after exposure to glutamate (100microM). CLSM analysis of immunostained HO-1 in cultured astroglial cells during differentiation showed an increase of fluorescence between 7 and 14 days and a decrease between 14 and 21, although HO-1 peaked at 14 days it remained at high levels. The distribution of HO-1 protein undergoes modification in the various cellular compartments. Furthermore, localization of the protein in untreated astrocytes at 7 days appeared prevalently localized in the cytosol and in the perinuclear region. In contrast, at 14 and 21 days, fluorescence detection suggests that HO-1 was present also in the nucleus, and in the nucleoli. Fluorescence intensity significantly increased in glutamate-treated astrocytes during all development stages and the protein appeared in the cytosol, in the nucleus and in the nucleoli. The involvement of AMPA/Ka receptors was studied in glutamate-treated astroglial cells at 14 days by the preincubation of the cells with GYKI 52466, a specific receptor inhibitor, of AMPA/Ka receptor demonstrating the involvement of these receptors. Western blot analysis of HO-1 confirmed the CLSM results. Our results demonstrate that changes in HO-1 protein expression and localization in primary cultured astroglial cells may be part of the underlying mechanisms involved in brain development as well as in neurodegenerative diseases.

Neotrofin increases heme oxygenase-1 selectively in neurons

There is evidence that heme oxygenase plays a role in cellular defense against reactive oxygen species and thereby has neuroprotective effects. We examined the interaction of Neotrofin, a cognitive-enhancing and neuroprotective drug, with the heme oxygenase system. In adult rats, both a single administration or seven daily injections of Neotrofin at 10, 30 or 100 mg/kg intraperitoneally increased HO-1 immunoreactivity in neurons of the hippocampal formation and its connections including CA1-4, fornix, septal nuclei, hippocampal commissure, septohippocampal nucleus, fimbria, anteroventral thalamic nucleus, frontal and parietal cortex. Prominent HO-1 staining of neuronal cells in the proximity of blood vessels and circumventricular organs was also observed. Increasing doses of Neotrofin resulted in an increase in the number of neuronal populations expressing HO-1 with 100 mg/kg evoking a widespread neuronal cell response in brain. Quantification by ELISA confirmed that intraperitoneal administration of 100 mg/kg Neotrofin caused a significant increase in HO-1 protein expression in the hippocampus. The increase was evident by 6 h post-injection, peaked at 24 h with a 4-fold increase, and persisted for at least 48 h. Similarly, oral administration of 100 mg/kg Neotrofin produced a 5-fold increase in HO-1 protein 24 h post-administration. The effect of Neotrofin on HO-1 appears to be at the transcriptional level, as suggested by an increase in HO-1 mRNA levels. Neotrofin treatment was also associated with a significant increase in HO-2 mRNA levels in whole brain homogenate. These data may explain the neuroprotective effects of Neotrofin in models of excitotoxic neuronal injury.

Upregulation and activation of the Nrf-1 transcription factor in the lesioned hippocampus

The Nrf-1 and Nrf-2 transcription factors play a pivotal role in the cellular defence against the toxic effects of reactive oxygen species (ROS). Although ROS are key effectors of neuronal death after ischaemic and traumatic brain injury, it is not known whether Nrf-1 and Nrf-2 are involved in neuroprotective signalling. Here, we analysed the temporal and spatial expression pattern of Nrf-1 and Nrf-2 after unilateral excitotoxic lesion of mouse hippocampus. In marked contrast to previous in vitro studies, where upregulation of these transcription factors on the mRNA level was never detected, we found a strong induction of Nrf-1 mRNA and protein expression in neurons of the lesioned hippocampus, accompanied by a weak elevation of Nrf-2 mRNA levels. Nrf-1 predominantly localized to the nucleus in the injured hippocampus. Furthermore, expression of the cytoprotective enzyme, heme oxygenase-1, a major target of Nrf-1 and Nrf-2 action, was coregulated with Nrf-1 in the same hippocampal neurons, suggesting that Nrf-1 is functionally active. Because Nrf-1 and Nrf-2 are potent inducers of various cytoprotective proteins, our data suggest a role of Nrf-1 and Nrf-2 in neuronal survival after acute brain injury.

Glial expression of small heat shock proteins following an excitotoxic lesion in the immature rat brain

Heat shock proteins (HSPs) are chaperones induced under pathological conditions and involved in protein stabilization and cellular protection. In this study, we have evaluated the expression pattern of the glial cell-related HSP27, HSP32, and HSP47 following an excitotoxic lesion in the immature rat brain. Postnatal day 9 rats received an intracortical injection of N-methyl-D-aspartate and tissue was processed immunohistochemically for HSPs and double labeling using astroglial and microglial markers. HSP expression was quantified by image analysis. Excitotoxic damage caused primary cortical degeneration and secondary damage in the corresponding thalamus. In the injured cortex, reactive microglia/macrophages expressed HSP32 from 10 h until 14 days postlesion (PL), showing maximal levels at days 3-5. In parallel, most cortical reactive astrocytes showed expression of HSP47 from 10 h until 14 days PL and a population of them also displayed HSP27 labeling from 1 day PL. In addition, some cortical reactive astrocytes showed a temporary expression of HSP32 at day 1. In general, astroglial HSP expression in the cortex achieved maximal levels at days 3-5 PL. In the damaged thalamus, HSP32 was not significantly induced, but reactive astrocytes expressed HSP47 and some of them also HSP27. Thalamic astroglial HSP induction was transient, peaked at 5 days PL and reached basal levels by day 14. The injury-induced expression of HSP32, HSP27, and HSP47 in glial cells may contribute to glial cell protection and adaptation to damage, therefore playing an important role in the evolution of the glial response and the excitotoxic lesion outcome. HSP32 may provide antioxidant protective mechanisms to microglia/macrophages, whereas HSP47 could contribute to extracellular matrix remodeling and HSP27 may stabilize the astroglial cytoskeleton and participate in astroglial antioxidant mechanisms.

Kainate-induced genes in the hippocampus: lessons from expression patterns

Kainate, the analog of the excitatory amino acid L-glutamate, upon binding to non-NMDA glutamate receptors, causes depolarization of neurons followed by severe status epilepticus, neurodegeneration, plasticity and gliosis. These events are best observed in hippocampus, the limbic structure implicated in learning and long-term memory formation. Neurons in all hippocampal structures undergo hyper-activation, however, whereas the cells in the CA subfields degenerate within 2--3 days following the application of kainate, the granule cells of the dentate gyrus are resistant to any form of neurodegeneration and even initiate new synaptic contacts. These physiological and histological changes are modulated by short-term and long-term alterations in gene expression. Perhaps close examination of the changing spatio-temporal patterns of mRNAs of various genes may help in generating a clearer picture of the molecular events leading to complex cognitive functions.

Heme oxygenase-1 (HSP-32) and heme oxygenase-2 induction in neurons and glial cells of cerebral regions and its relation to iron accumulation after focal cortical photothrombosis

Cerebral ischemic injury results in the liberation of heme from degenerating heme-containing proteins. The neurotoxic heme is usually detoxified by the constitutive heme oxygenase-2 (HO-2) and its inducible isoform HO-1(heat shock protein 32) resulting in the formation of biliverdin which becomes reduced to bilirubin, carbon monoxide (CO), and iron. Biliverdin and bilirubin have antioxidative properties whereas CO is discussed as a signaling molecule. Iron if it remains free could catalyze Haber--Weiss and Fenton reactions causing the formation of highly toxic radicals. We have studied the alterations of cerebral HO-2 and HO-1 in relation to iron accumulations after defined cortical photothrombosis within the hindlimb area of the rat. HO-2 immunohistochemistry showed that the number of HO-2-positive neurons in most perilesional regions remained constant. However, much stronger systemic immunoreactivity for HO-2 was observed between days 1 and 7 postlesion. For HO-1 a systemic increase of immunoreactivity occurred also between days 1 and 7. In addition HO-1-positive astrocytes and microglia appeared as early as 4 h postlesion and increased up to day 3 followed by a sharp decline toward day 14 within the injured hemisphere. HO-1-positive astrocytes and microglia occurred in ipsilateral cortex, corpus callosum, hippocampus, striatum, and thalamic nuclei. Additionally an increase of HO-1 in myelin-associated globulin-positive oligodendrocytes was found in ipsilateral and contralateral cortex. Next to the lesion iron accumulation occurred after day 3 and increased strongly toward day 14 at times when HO-1 and -2 had decreased, suggesting that HO activity does not directly contribute to postlesional iron deposition.

Astrocyte phenotype and prevention against oxidative damage in neurotoxicity

Astrocytes possess a potent array of protective systems. These are chiefly targeted against oxidised products and radicals, which are frequently present in increased amounts following exposure of nervous tissue to a range of toxic insults. Following exposure to the toxic chemicals astrocytes commonly respond by alteration in phenotype with upregulation of a large number of molecules, including those controlling the protective systems. This article summarizes evidence, largely obtained from in vitro studies, which supports the concept that some of the changes in astrocyte phenotype are associated with increased protection against the cytotoxicity caused by the oxidative damage that results from exposure to range of neurotoxicants.

Unilateral upregulation of cyclooxygenase-2 following cerebral, cortical photothrombosis in the rat: suppression by MK-801 and co-distribution with enzymes involved in the oxidative stress cascade

Cyclooxygenase-2 (COX-2) is an essential enzyme for prostaglandin synthesis from arachidonic acid, during which considerable amounts of superoxide are produced. During pathological conditions, superoxide and nitric oxide (NO) rapidly form peroxynitrite, a potent cytotoxin, causing symptoms referred to as oxidative stress response. Superoxide is controlled by enzymes such as manganese- or copper-zinc-dependent superoxide dismutase (Mn-SOD, CuZn-SOD), glutathione peroxidase (GPx) and antioxidants derived from heme oxygenase (HO) activity such as biliverdin and bilirubin. NO derives from 3 NO-synthases (NOS I-III) from which the calcium-dependent NOS-I and III are activated rapidly due to hyperexcitation. We studied the induction of COX-2 by immunohistochemistry at days 1, 2 and 5 following cortical photothrombosis in normal and MK-801 treated rats. The results showed a weak constitutive, neuronal expression of COX-2 in cortex and amygdala. Layers II+III contained considerably more COX-2 than infragranular layers. One and 2 days following injury COX-2 was highly upregulated in the supragranular layers of the whole injured hemisphere compared with sham-operated animals and compared to the contralateral unlesioned hemisphere, whereas at day 5 COX-2 levels had returned to baseline. MK-801 treatment caused a reduction in COX-2 upregulation at day one and by day 2 no significant differences between injured and contralateral hemisphere were measurable. COX-2 positive neurons were found in close association with NOS-I containing neurons and their fibers but were not colocalized. In addition, codistribution of COX-2 was found with HO-1, CuZn-SOD and GPx containing cells, whereas COX-2 was colocalized with HO-2 and/or MnSOD in cortical neurons.

Heme oxygenase-1 in lesions of rat experimental autoimmune encephalomyelitis and neuritis

The enzyme heme oxygenase-1 (HO-1) is reducing heme to the gaseous mediator carbon monoxide, to iron and the antioxidant biliverdin. The inducible expression of HO-1 is considered a protective cellular mechanism against reactive oxygen intermediates. Further, carbon monoxide (CO) is a regulator of cGMP synthesis, of NO-synthetases and cyclooxygenases, thereby indirectly modulating reactive processes. Here we report expression of HO-1 in rat experimental autoimmune encephalomyelitis (EAE) and neuritis (EAN). With both models, similar results were obtained: HO-1 was localized predominantly to infiltrating, monocytic, but only rarely to ramified microglial cells or astrocytes surrounding the inflammatory lesions. Prominent expression by monocytic cells was seen from day 11 after immunization correlating with the development of neurologic disease. Further, local expression is persistent for long after cessation of neurologic signs. Thus, HO-1 could be considered a factor in the formation and resolution of inflammatory autoimmune lesions of the nervous system.

Induction of heme oxygenase-1 in the brains of scrapie-infected mice

Heme oxygenase-1 (HO-1) is an inducible enzyme that catalyzes the rate-limiting step in the degradation of heme to biliverdin, carbon monoxide and iron, and its expression can be used as a marker for oxidative stress. Oxidative stress has been reported to be associated with neurodegenerative diseases including Alzheimer's disease. It is possible that oxidative stress is also involved in the disease process seen in scrapie, the archetype transmissible spongiform encephalopathy. In this study, we report that HO-1 is significantly increased in the scrapie-infected group compared to an age-matched control group. Immunohistochemistry showed a pronounced increase of immunostaining of this protein in the infected group compared to the minimal amount of staining in the control group. These results support that oxidative stress is closely associated with the pathogenesis of scrapie and that it might contribute to neurodegeneration in this disease.

MPTP selectively induces haem oxygenase-1 expression in striatal astrocytes

Parkinson's disease (PD) is characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta with accompanying evidence of increased oxidative damage, deficits in mitochondrial function and iron deposition. Recently, haem oxygenase-1 levels were reported to be elevated in PD brains. Because this enzyme is involved in the response to oxidative stress and is critical for cellular haem and iron homeostasis, it could play a role in the pathogenesis of PD. Therefore, we investigated the expression of haem oxygenase isoform 1 (HO-1) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. MPTP triggered a relatively rapid and persistent increase in HO-1 mRNA exclusively in the mouse striatum. In situ hybridization and immunohistochemistry showed HO-1 to be localized to striatal astrocytes. The induction of HO-1 by MPTP was blocked by selegiline and GBR-12909, indicating the protoxin had to be metabolized by monoamine oxidase B and taken up by dopaminergic neurons to exert its action in astrocytes. MPTP did not alter the expression of other enzymes of haem synthesis or degradation nor were the levels of mRNA for haem or iron-binding proteins changed. Thus, expression of HO-1 was not part of a cellular program involving haem biosynthesis or homeostasis. In addition, heat shock proteins were not induced by MPTP. Thus, MPTP elicited a selective transcriptional response in striatal astrocytes. This response appears to be mediated by molecules released from affected dopaminergic nerve terminals in the striatum acting upon neighbouring astrocytes. This signalling pathway and its potential relevance to PD are discussed.

Oxidative stress-related proteins A170 and heme oxygenase-1 are differently induced in the rat cerebellum under kainate-mediated excitotoxicity

A170 and heme oxygenase-1 (HO-1) are characterized as oxidative stress-inducible proteins whose induction depends upon common transcription factor via antioxidant responsive element. We investigated the expression of A170 and HO-1 in the cerebellum after kainate administration. In situ hybridization showed constitutive expression of A170 and HO-1 mRNA in Purkinje cell layer; mild induction of A170 or HO-1 was detected, respectively, 8 or 24 h after kainate administration. Immunohistochemical studies also demonstrated that constitutive expression and the induction of A170 protein in Purkinje cells; the induction of HO-1 protein was detected in Bergmann glia but not in Purkinje cells. Thus, the transcription factors involved in the induction of A170 might be different from those in the induction of HO-1 under kainate-mediated excitotoxicity. The existence of cell type-specific stress response was suggested.