Protective effects of morphine in peroxynitrite-induced apoptosis of primary rat neonatal astrocytes: potential involvement of G protein and phosphatidylinositol 3-kinase (PI3 kinase)

Glycogen synthase kinase-3 beta inhibition reduces secondary damage in experimental spinal cord trauma

Glycogen synthase kinase-3 (GSK-3) has recently been identified as an ubiquitous serine-threonine protein kinase that participates in a multitude of cellular processes and plays an important role in the pathophysiology of a number of diseases. The aim of this study was to investigate the effects of GSK-3beta inhibition on the degree of experimental spinal cord trauma induced by the application of vascular clips (force of 24 g) to the dura via a four-level T5-T8 laminectomy. Spinal cord injury (SCI) in mice resulted in severe trauma characterized by edema, neutrophil infiltration, production of a range of inflammatory mediators, tissue damage, and apoptosis. Treatment of the mice with 4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione (TDZD-8), a potent and selective GSK-3beta inhibitor, significantly reduced the degree of 1) spinal cord inflammation and tissue injury (histological score); 2) neutrophil infiltration (myeloperoxidase activity); 3) inducible nitric-oxide synthase, nitrotyrosine, and cyclooxygenase-2 expression; and 4) and apoptosis (terminal deoxynucleotidyl transferase dUTP nick-end labeling staining and Bax and Bcl-2 expression). In a separate set of experiments, TDZD-8 significantly ameliorated the recovery of limb function (evaluated by motor recovery score). Taken together, our results clearly demonstrate that treatment with TDZD-8 reduces the development of inflammation and tissue injury associated with spinal cord trauma.

Signal transduction induced by opioids in immune cells: a review

New data regarding signal transduction triggered by opioid ligands in immune cells are reviewed, and the signal transduction in neuronal cells is documented. Similar signaling pathways are induced by opioids in immune as well as neuronal cells. Opioids altered second messenger cAMP, intracellular calcium, and second messenger-induced kinases in immune cells. Met-enkephalin, preferentially delta-opioid, was bimodally regulated, while kappa-opioids inhibited these second messengers. delta-, kappa- and micro-opioids altered nitric oxide secretion, inducing cGMP as the second messenger in immune cells. Coupling of opioid agonists to opioid receptors activated mitogen-activated protein/extracellular signal-regulated protein kinases and various transcription factors in immune cells. Activator protein 1 (AP-1), c-fos, and nuclear factor-kappaB (NF-kappaB) are transcription factors shared by neuronal and immune cells. Delta-opioids activated AP-1, c-fos, activating transcription factor 2, Ikaros-1 and Ikaros-2 transcription factors in immune cells. Induction of kappa-opioid receptor gene by retinoic acid resulted in increased binding of Sp1 transcription factor to the promoter of the kappa-opioid receptor. Micro-opioids inhibited synthesis of common transcription factors AP-1, c-fos, NF-kappaB, and nuclear factor of activated T cells in activated or stimulated immune cells, whereas micro-opioids activated NF-kappaB, GATA-3, and Kruppel-like factor 7 transcription factors in non-stimulated immune cells.

Protection from neuronal damage evoked by a motivational excitation is a driving force of intentional actions

Motivation may be understood as an organism's subjective attitude to its current physiological state, which somehow modulates generation of actions until the organism attains an optimal state. How does this subjective attitude arise and how does it modulate generation of actions? Diverse lines of evidence suggest that elemental motivational states (hunger, thirst, fear, drug-dependence, etc.) arise as the result of metabolic disturbances and are related to transient injury, while rewards (food, water, avoidance, drugs, etc.) are associated with the recovery of specific neurons. Just as motivation and the very life of an organism depend on homeostasis, i.e., maintenance of optimum performance, so a neuron's behavior depends on neuronal (i.e., ion) homeostasis. During motivational excitation, the conventional properties of a neuron, such as maintenance of membrane potential and spike generation, are disturbed. Instrumental actions may originate as a consequence of the compensational recovery of neuronal excitability after the excitotoxic damage induced by a motivation. When the extent of neuronal actions is proportional to a metabolic disturbance, the neuron theoretically may choose a beneficial behavior even, if at each instant, it acts by chance. Homeostasis supposedly may be directed to anticipating compensation of the factors that lead to a disturbance of the homeostasis and, as a result, participates in the plasticity of motivational behavior. Following this line of thought, I suggest that voluntary actions arise from the interaction between endogenous compensational mechanisms and excitotoxic damage of specific neurons, and thus anticipate the exogenous compensation evoked by a reward.

Molecular targets of opiate drug abuse in neuroAIDS

Opiate drug abuse, through selective actions at mu-opioid receptors (MOR), exacerbates the pathogenesis of human immunodeficiency virus-1 (HIV-1) in the CNS by disrupting glial homeostasis, increasing inflammation, and decreasing the threshold for pro-apoptotic events in neurons. Neurons are affected directly and indirectly by opiate-HIV interactions. Although most opiates drugs have some affinity for kappa (KOR) and/or delta (DOR) opioid receptors, their neurotoxic effects are largely mediated through MOR. Besides direct actions on the neurons themselves, opiates directly affect MOR-expressing astrocytes and microglia. Because of their broad-reaching actions in glia, opiate abuse causes widespread metabolic derangement, inflammation, and the disruption of neuron-glial relationships, which likely contribute to neuronal dysfunction, death, and HIV encephalitis. In addition to direct actions on neural cells, opioids modulate inflammation and disrupt normal intercellular interactions among immunocytes (macrophages and lymphocytes), which on balance further promote neuronal dysfunction and death. The neural pathways involved in opiate enhancement of HIV-induced inflammation and cell death, appear to involve MOR activation with downstream effects through PI3-kinase/Akt and/or MAPK signaling, which suggests possible targets for therapeutic intervention in neuroAIDS.

Saeng-Ji-Hwang has a protective effect on adriamycin-induced cytotoxicity in cardiac muscle cells

This study examined the effect of Saeng-Ji-Hwang (SJH: Radix Rehmanniae) on cardiac muscle cells. Adriamycin-exposed H9C2 cardiac muscle cells were treated with a water extract of SJH. The adriamycin induced cell death and caspase-3 activation were significantly inhibited by SJH (2 mg/ml), which can be explained by the increase in Bcl-2 expression and the inhibition of Bax expression. Adriamycin reduced the Mn-SOD protein expression level in H9C2 cardiac muscle cells but a SJH treatment partially but significantly reversed this effect. Manganese (Mn)-TBAP or Mn-TMyM--mitochondria-specific SOD mimetic agent--reduced the adriamycin-induced cytotoxicity. It was also shown that SJH inhibits the release of H2O2 and prevents lipid peroxidation in the presence of adriamycin. This study examined the intracellular GSH level, which showed that adriamycin significantly decreased the intracellular GSH level but SJH increased it. BSO, a selective inhibitor of glutamyl cysteinyl ligase, which is a rate-limiting enzyme in GSH synthesis, did not affect the viability of the cardiac muscle cells. However, a combination of BSO with SJH in the presence of adriamycin reversed the SJH-induced protection. Overall, the results suggest that SJH-associated Mn-SOD and GSH are important factors in the mechanism of the SJH-induced protective mechanism in H9C2 cardiac muscle cells.

Opioids as modulators of cell death and survival--unraveling mechanisms and revealing new indications

Opioids are powerful analgesics but also drugs of abuse. Because opioid addicts are susceptible to certain infections, opioids have been suspected to suppress the immune response. This was supported by the finding that various immune-competent cells express opioid receptors and undergo apoptosis when treated with opioid alkaloids. Recent evidence suggests that opioids may also effect neuronal survival and proliferation or migrating properties of tumor cells. A multitude of signaling pathways has been suggested to be involved in these extra-analgesic effects of opioids. Growth-promoting effects were found to be mediated through Akt and Erk signaling cascades. Death-promoting effects have been ascribed to inhibition of nuclear factor-kappaB, increase of Fas expression, p53 stabilization, cytokine and chemokine release, and activation of nitric oxide synthase, p38, and c-Jun-N-terminal kinase. Some of the observed effects were inhibited with opioid receptor antagonists or pertussis toxin; others were unaffected. It is still unclear whether these properties are mediated through typical opioid receptor activation and inhibitory G-protein-signaling. The present review tries to unravel controversial findings and provides a hypothesis that may help to integrate diverse results.

Opioid neurotoxicity: comparison of morphine and tramadol in an experimental rat model

Histopathologic changes in rat brain due to chronic use of morphine and/or tramadol in progressively increased doses were investigated in this study. Thirty male Wistar rats (180-220 g) were included and divided into three groups. Normal saline (1 ml/kg) was given intraperitoneally as placebo in the control group (n = 10). Morphine group (n = 10) received morphine intraperitoneally at a dose of 4 mg/kg/day for the first 10 days, 8 mg/kg/day between 11-20 days, and 12 mg/kg/day between 21-30 days. The tramadol group (n = 10) received the drug intraperitoneally at doses of 20, 40, and 80 mg/kg/day in the first, second, and the third 10 days of the study, respectively. All rats were decapitated on the 30th day and the brain was removed intact for histology. The presence and the number of red neurons, which are a histologic marker of apoptosis, were investigated in the parietal, frontal, temporal, occipital, entorhinal, pyriform, and hippocampal CA1, CA2, CA3 regions. Red neurons were found in morphine and tramadol groups but not in the control group. The total number of red neurons was not different in morphine and tramadol groups, but the numbers of red neurons were significantly higher in the temporal and occipital regions in tramadol group as compared with the morphine group (p < .05). In conclusion, chronic use of morphine and/or tramadol in increasing doses is found to cause red neuron degeneration in the rat brain, which probably contributes to cerebral dysfunction. These findings should be taken into consideration when chrome use of opioids is indicated.

Morphine Prevents Glutamate‐Induced Death of Primary Rat Neonatal Astrocytes Through Modulation of Intracellular Redox

This study is designed to investigate the effect of morphine on glutamate-induced toxicity of primary rat neonatal astrocytes. Glutamate decreases the intracellular GSH level, and thereby induces cytolysis of astrocytes and C6 glial cells accompanied by apoptotic features. Glutamate-induced cytotoxicity is protected by morphine and antioxidants such as GSH and NAC, whereas MK-801, an antagonist of glutamate receptor NMDA does not protect astrocytes against glutamate toxicity. Also, morphine antagonist, naloxone, as well as selective ligands for opioid receptor subtypes, including DAMGO, DPDPE, and U69593, do not inhibit the protective effect of morphine on glutamate-induced cytotoxicity. Morphine significantly prevents the depletion of GSH by glutamate and thereby inhibits the generation of H2O2 in a dose-dependent manner. Furthermore, morphine prevents the change of mitochondrial permeability transition by glutamate. Taken together, we suggest that morphine protects the primary rat neonatal astrocytes from glutamate toxicity via modulation of intracellular redox status.

Ischemic preconditioning and morphine attenuate myocardial apoptosis and infarction after ischemia-reperfusion in rabbits: role of δ-opioid receptor

We examined whether ischemic preconditioning (IPC) attenuates ischemia-reperfusion injury, in part, by decreasing apoptosis and whether the δ-opioid receptor (DOR) plays a pivotal role in the regulation of apoptosis. Rabbits were subjected to 30-min coronary artery occlusion (CAO) and 180 min of reperfusion. IPC was elicited with four cycles of 5-min ischemia and 10-min reperfusion before CAO. Morphine (0.3 mg/kg iv) was given 15 min before CAO. Naloxone (Nal; 10 mg/kg iv) and naltrindole (Nti; 10 mg/kg iv), the respective nonselective and selective DOR antagonists were given 10 min before either morphine or IPC. Infarct size (%risk area) was reduced from 46 ± 3.8 in control to 11.6 ± 1.0 in IPC and 19.5 ± 3.8 in the morphine group (means ± SE; P < 0.001 vs. control). Nal blocked the protective effects of IPC and morphine, as shown by the increase in infarct size to 38.6 ± 7.2 and 44.5 ± 1.8, respectively. Similarly, Nti blocked IPC and morphine-induced protection. The percentage of apoptotic cells (revealed by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay) decreased in IPC (3.6 ± 1.9) and morphine groups (5.2 ± 1.2) compared with control group (12.4 ± 1.6; P < 0.001). Nti pretreatment increased apoptotic cells 11.2 ± 2.2% in IPC and 12.1 ± 0.8% in morphine groups. Nal failed to block inhibition of apoptosis in the IPC group (% of cells: 5.7 ± 1.3 vs. 3.6 ± 1.9 in IPC alone; P > 0.05). These results were also confirmed by nucleosomal DNA laddering pattern. We conclude that IPC reduces lethal injury, in part, by decreasing apoptosis after ischemia-reperfusion and activation of the DOR may play a crucial role in IPC or morphine-induced myocardial protection.

Morphine mimics the antiapoptotic effect of preconditioning via an Ins(1,4,5)P3 signaling pathway in rat ventricular myocytes

Morphine has cardioprotective effects against ischemic-reperfusion injuries. This study investigates whether morphine could mimic the antiapoptotic effect of preconditioning using a model of cultured neonatal rat cardiomyocytes subjected to metabolic inhibition (MI). To quantify MI-induced apoptosis, DNA fragmentation and mitochondrial cytochrome c release levels were measured by ELISA. MI-dependent DNA fragmentation was prevented by both Z-VAD-fmk (20 microM), a pan-caspase inhibitor, and cyclosporine A (CsA; 5 microM), a mitochondrial pore transition blocker, added during MI (36% and 54% decrease, respectively). MI-dependent cytochrome c release was not blocked by Z-VAD-fmk but was decreased (38%) by CsA during MI. Metabolic preconditioning (MIP) and preconditioning with morphine (1 microM) were also assessed. MI-dependent DNA fragmentation and cytochrome c release were prevented by MIP (40% and 45% decrease, respectively) and morphine (34% and 45%, respectively). The antiapoptotic effect of morphine was abolished by naloxone (10 nM), a nonselective opioid receptor antagonist, or xestospongin C (XeC, 400 nM), an inhibitor of inositol (1,4,5)-trisphosphate [Ins(1,4,5)P(3)]-mediated Ca(2+) release. Ca(2+) preconditioning, induced by increasing extracellular Ca(2+) from 1.8 to 3.3 mM, mimicked the antiapoptotic effect of morphine on DNA fragmentation (24% decrease) and cytochrome c release (57% decrease). This effect mediated by extracellular Ca(2+) was also abolished by XeC. Measurements of intracellular Ca(2+) concentration using fura-2 microspectrofluorimetry showed that morphine induces Ins(1,4,5)P(3)-dependent Ca(2+) transients abolished by 2-aminoethoxydiphenyl borate (2-APB), a cell-permeable Ins(1,4,5)P(3) antagonist. These results suggest that morphine preconditioning prevents simulated ischemia-reperfusion-induced apoptosis via an Ins(1,4,5)P(3) signaling pathway in rat ventricular myocytes.

Phosphatidylinositol-3 kinase is distinctively required for �-, but not ?-opioid receptor-induced activation of c-Jun N-terminal kinase

Opioid receptors are the therapeutic targets of narcotic analgesics. All three types of opioid receptors (mu, delta and kappa) are prototypical G(i)-coupled receptors with common signaling characteristics in their regulation of intracellular events. Nevertheless, numerous signaling processes are differentially regulated by the three receptors. We have recently demonstrated that stimulation of delta-opioid receptor can up-regulate the activity of the c-Jun N-terminal kinase (JNK) in a pertussis toxin-sensitive manner (Kam et al. 2003; J. Neurochem. 84, 503-513). The present study revealed that the mu-opioid receptor could stimulate JNK in both SH-SY5Y cells and transfected COS-7 cells. The mechanism by which the mu-opioid receptor stimulated JNK was delineated with the use of specific inhibitors and dominant-negative mutants of signaling intermediates. Activation of JNK by the mu-opioid receptor was mediated through G beta gamma, Src kinase, son-of-sevenless (Sos), Rac and Cdc42. Interestingly, unlike the delta-opioid receptors, the mu-opioid receptor required phosphatidylinositol-3 kinase (PI3K) to activate JNK. The mu-opioid receptor-induced JNK activation was effectively inhibited by wortmannin or the coexpression of a dominant negative mutant of PI3K gamma. Like the delta-opioid receptor, activation of JNK by the kappa-opioid receptor occurred in a PI3K-independent manner. These studies revealed that the mu-opioid receptor utilize a distinct mechanism to regulate JNK.

Astrocyte apoptosis: implications for neuroprotection

Astrocytes, the most abundant glial cell types in the brain, provide metabolic and trophic support to neurons and modulate synaptic activity. Accordingly, impairment in these astrocyte functions can critically influence neuronal survival. Recent studies show that astrocyte apoptosis may contribute to pathogenesis of many acute and chronic neurodegenerative disorders, such as cerebral ischemia, Alzheimer's disease and Parkinson's disease. We found that incubation of cultured rat astrocytes in a Ca(2+)-containing medium after exposure to a Ca(2+)-free medium causes an increase in intracellular Ca(2+) concentration followed by apoptosis, and that NF-kappa B, reactive oxygen species, and enzymes such as calpain, xanthine oxidase, calcineurin and caspase-3 are involved in reperfusion-induced apoptosis. Furthermore, we demonstrated that heat shock protein, mitogen-activated protein/extracellular signal-regulated kinase, phosphatidylinositol-3 kinase and cyclic GMP phosphodiesterase are target molecules for anti-apoptotic drugs. This review summarizes (1) astrocytic functions in neuroprotection, (2) current evidence of astrocyte apoptosis in both in vitro and in vivo studies including its molecular pathways such as Ca(2+) overload, oxidative stress, NF-kappa B activation, mitochondrial dysfunction, endoplasmic reticulum stress, and protease activation, and (3) several drugs preventing astrocyte apoptosis. As a whole, this article provides new insights into the potential role of astrocytes as targets for neuroprotection. In addition, the advance in the knowledge of molecular mechanisms of astrocyte apoptosis may lead to the development of novel therapeutic strategies for neurodegenerative disorders.

T-588, a Cognitive Enhancer, Protects Against Sodium Nitroprusside-Induced Toxicity in Cultured Astrocytes

The effects of (1R)-1-benzo[b]thiophen-5-yl-2-[2-(diethylamino)ethoxy]ethan-1-ol hydrochloride (T-588), a cognitive enhancer, on sodium nitroprusside (SNP)-induced cytotoxicity were examined in cultured rat astrocytes. Treatment with 100 microM SNP for 72 h decreased cell viability and mitochondrial function assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenil tetrazolium bromide (MTT) reduction activity, mitochondrial transmembrane potential, and intracellular ATP level. T-588 at 100 microM prevented SNP-induced mitochondrial dysfunction and cell injury. Furthermore, T-588 increased MTT reduction activity without affecting cell proliferation in astrocytes. These results suggest that T-588 has a protective effect against SNP-mediated toxicity via improvement of mitochondrial dysfunction in astrocytes.

Expression of nitric oxide, peroxynitrite, and apoptosis in loose total hip replacements

Nitric oxide (NO) is an effector molecule associated with inflammation, immune function, bone metabolism, and the induction of apoptosis. This study examined the role of NO, peroxynitrite (ONOO(-)), and apoptosis in cases of revision total hip replacements (THRs). We hypothesized that apoptosis and excess production of NO contribute to the inflammatory reaction to orthopedic biomaterial wear debris that is associated with loosening and osteolysis. Periprosthetic membranous specimens were collected from revised cemented acetabular components with simple loosening and ballooning osteolysis. Synovial samples from patients undergoing primary THR were used as controls. The presence of macrophages (CD68(+)) and levels of inducible nitric oxide synthase (INOS), endothelial nitric oxide synthase (EcNOS), ONOO(-) (Nitro, assayed by the amount of nitrated tyrosine residues), and apoptosis (TUNEL staining) were examined using immunohistochemistry. Increased expression for INOS, EcNOS, and ONOO(-) in both the loose/osteolytic and the loose/non-osteolytic groups was observed when compared to the synovium group. There were no significant differences between the loose/osteolytic group and loose/non-osteolytic group for these biologic markers. TUNEL staining showed a significant increase in apoptosis in the loose/osteolytic group compared to the loose/non-osteolytic group and synovial tissues. These findings suggest that NO and NO-derived molecules, such as ONOO(-), may be involved in sustaining the foreign-body reaction to wear debris. NO and ONOO(-) may prove to be useful markers of prosthetic loosening whereas apoptosis may be a marker distinguishing ballooning from simple osteolysis.

Glycogen synthase kinase 3beta-mediated apoptosis of primary cortical astrocytes involves inhibition of nuclear factor kappaB signaling

Recent studies have revealed a positive correlation between astrocyte apoptosis and rapid disease progression in persons with neurodegenerative diseases. Glycogen synthase kinase 3beta (GSK-3beta) is a molecular regulator of cell fate in the central nervous system and a target of the phosphatidylinositol 3-kinase (PI-3K) pathway. We have therefore examined the role of the PI-3K pathway, and of GSK-3beta, in regulating astrocyte survival. Our studies indicate that inhibition of PI-3K leads to apoptosis in primary cortical astrocytes. Furthermore, overexpression of a constitutively active GSK-3beta mutant (S9A) is sufficient to cause astrocyte apoptosis, whereas an enzymatically inactive GSK-3beta mutant (K85M) has no effect. In light of reports on the interplay between GSK-3beta and nuclear factor kappaB (NF-kappaB), and because of the antiapoptotic activity of NF-kappaB, we examined the effect of GSK-3beta overexpression on NF-kappaB activation. These experiments revealed strong inhibition of NF-kappaB activation in astrocytes upon overexpression of the S9A, but not the K85M, mutant of GSK-3beta. This was accompanied by stabilization of the NF-kappaB-inhibitory protein, IkappaBalpha and down-regulation of IkappaB kinase (IKK) activity. These findings therefore implicate GSK-3beta as a regulator of NF-kappaB activation in astrocytes and suggest that the pro-apoptotic effects of GSK-3beta may be mediated at least in part through the inhibition of NF-kappaB pathway.

Beta-phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids and compounds derived from them, including further products of oxidation, condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2001 to June 2002 is reviewed, with 581 references cited.

Dynorphin A toxicity in striatal neurons via an alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate/kainate receptor mechanism

Dynorphin A (1-17) is an endogenous opioid peptide that is antinociceptive at physiological concentrations, but in excess can elicit a number of pathological effects. Both kappa-opioid and N-methyl-D-aspartate receptor antagonists modulate dynorphin toxicity, suggesting that dynorphin is acting directly or indirectly through these receptor types. We found in spinal cord neurons that the neurotoxic effects of dynorphin A and several dynorphin-derived peptide fragments are largely mediated by N-methyl-D-aspartate receptors. Despite these findings, aspects of dynorphin A toxicity could not be accounted for by opioid or N-methyl-D-aspartate receptor mechanisms. To address this issue, neurons enriched in kappa-opioid, N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptors were isolated from embryonic day-15 mouse striata and the effects of extracellularly administered dynorphin A (1-17) and (13-17) on neuronal survival were examined in vitro. Unlike spinal cord neurons, N-methyl-D-aspartate receptors mature later than alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate/kainate receptors in striatal neurons, thus providing a strategy to elucidate non-N-methyl-D-aspartate receptor-mediated mechanisms of toxicity. Time-lapse photography was used to repeatedly follow the same neurons before and during experimental treatments. Dynorphin A (1-17 or 13-17; 10 microM) caused significant neuronal losses after 48 to 72 hours versus untreated controls. Dynorphin A or A (13-17) toxicity was unaffected by the opioid receptor antagonist naloxone (10 microM) or by dizocilpine (10 microM). In contrast, the AMPA/kainate receptor antagonist 6-cyano-7-nitroquinoxaline- 2,3-dione (10 microM) significantly attenuated only dynorphin A (1-17)-induced neuronal losses and not that induced by dynorphin A (13-17). Dynorphin A (1-17) toxicity was accompanied by a proportional loss of R2 and R3 subunits of the AMPA receptor complex, but not non-N-methyl-D-aspartateR1, expressing neurons and was mimicked by the ampakine 1-(1,4-benzodioxan-6-ylcarbonyl)piperidine. Although it is unclear whether dynorphin A activates alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate/kainate receptors directly or indirectly via glutamate release, our culture conditions do not support glutamate retention or accumulation. Our findings suggest that dynorphin A (1-17) can exert toxic effects on striatal neurons via an alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate/kainate receptor mechanism.

High glucose-induced oxidative stress causes apoptosis in proximal tubular epithelial cells and is mediated by multiple caspases

Diabetic nephropathy is the leading cause of end-stage renal disease in the Western world. Poor glycemic control contributes to the development of diabetic nephropathy, but the mechanisms underlying high glucose-induced tissue injury are not fully understood. In the present study, the effect of high glucose on a proximal tubular epithelial cell (PTEC) line was investigated. Reactive oxygen species (ROS) were detected using the fluorescent probes dichlorofluorescein diacetate, dihydrorhodamine 123, and 2,3-diaminonapthalene. Peroxynitrite (ONOO-) generation and nitrite concentrations were increased after 24 h of high glucose treatment (P<0.05). LLC-PK1 cells exposed to high D-glucose (25 mM) for up to 48 h had increased DNA fragmentation (P<0.01), caspase-3 activity (P<0.001), and annexin-V staining (P<0.05) as well as decreased expression of XIAP when compared with controls (5 mM D-glucose). The ONOO- scavenger ebselen reduced DNA fragmentation and caspase-3 activity as well as the high glucose-induced nitrite production and DCF fluorescence. High glucose-induced DNA fragmentation was completely prevented by an inhibitor of caspase-3 (P<0.01) and a pan-caspase inhibitor (P<0.001). Caspase inhibition did not affect ROS generation. This study, in a PTEC line, demonstrates that high glucose causes the generation of ONOO-, leading to caspase-mediated apoptosis. Ebselen and a caspase-3 inhibitor provided significant protection against high glucose-mediated apoptosis, implicating ONOO- as a proapoptotic ROS in early diabetic nephropathy.

Peroxynitrite-induced cytotoxicity: mechanism and opportunities for intervention

Peroxynitrite is formed in biological systems when superoxide and nitric oxide are produced at near equimolar ratio. Although not a free radical by chemical nature (as it has no unpaired electron), peroxynitrite is a powerful oxidant exhibiting a wide array of tissue damaging effects ranging from lipid peroxidation, inactivation of enzymes and ion channels via protein oxidation and nitration to inhibition of mitochondrial respiration. Low concentrations of peroxynitrite trigger apoptotic death, whereas higher concentrations induce necrosis with cellular energetics (ATP and NAD) serving as switch between the two modes of cell death. Peroxynitrite also damages DNA and thus triggers the activation of DNA repair systems. A DNA nick sensor enzyme, poly(ADP-ribose) polymerase-1 (PARP-1) also becomes activated upon sensing DNA breakage. Activated PARP-1 cleaves NAD(+) into nicotinamide and ADP-ribose and polymerizes the latter on nuclear acceptor proteins. Peroxynitrite-induced overactivation of PARP consumes NAD(+) and consequently ATP culminating in cell dysfunction, apoptosis or necrosis. This cellular suicide mechanism has been implicated among others in the pathomechanism of stroke, myocardial ischemia, diabetes and diabetes-associated cardiovascular dysfunction. Here, we review the cytotoxic effects (apoptosis and necrosis) of peroxynitrite focusing on the role of accelerated ADP-ribose turnover. Regulatory mechanisms of peroxynitrite-induced cytotoxicity such as antioxidant status, calcium signalling, NFkappaB activation, protein phosphorylation, cellular adaptation are also discussed.

Kainic acid modifies mu-receptor binding in young, adult, and elderly rat brain

Mu-receptor binding changes were evaluated following the kainic acid (KA)-induced status epilepticus (SE) in young, adult, and elderly animals. Male Wistar rats were used as follows: young rats (15 days old) were treated with KA (7 mg/kg) and sacrificed 72 h (YKA3d) or 35 days (YKA35d) after SE; adult (90 days old) (AKA1d and AKA40d) and elderly rats (1-year-old) (EKA1d and EKA40d) were injected with KA (10 mg/kg) and then sacrificed 24 h or 40 days following SE. Their brains were processed for an autoradiography assay for mu-receptors. The YKA3d group showed increased values in dentate gyrus (39%) and a decrease in substantia nigra (26%); YKA35d animals had a reduction in caudate putamen (29%) and in substantia nigra (20%). The AKA1d group exhibited increased mu-receptors in caudate putamen (49%), cingulate (415%), frontal (52%), and temporal (53%) cortices: substantia nigra (56%), dentate gyrus (48%). and CA2 field of hippocampus (53%). The AKA40d group showed increased values in sensorimotor cortex (45%), anterior (39%), medial (65%), basolateral (202%), and central (32%) amygdaloid nuclei; dentate gyrus (80%) as well as CA2 (80%) and CA3 (49%) fields of hippocampus. The EKA1d group presented decreased mu-receptor binding in piriform (16%) and enthorinal (22%) cortices as well as in anterior amygdala nucleus (17%). The EKA40d group showed reduced values in sensorimotor cortex (14%) and substantia nigra (27%). The present results indicate that the mu-binding changes following SE depend on the rate of brain maturation.

Functions of PI 3-kinase in development of the nervous system

In the nervous system, receptor regulated phosphoinositide (PI) 3-kinases (PI 3-kinases) participate in fundamental cellular activities that underlie development. Activated by trophic factors, growth factors, neuregulins, cytokines, or neurotransmitters, PI 3-kinases have been implicated in neuronal and glial survival and differentiation. PI 3-kinases produce inositol lipid second messengers that bind to pleckstrin homology (PH) domains in diverse groups of signal transduction proteins, and control their enzymatic activities, subcellular membrane localization, or both. Downstream targets of the inositol lipid messengers include protein kinases and regulators of small GTPases. The kinase Akt/PKB functions as a key component of the PI 3-kinase dependent survival pathway through its phosphorylation and regulation of apoptotic proteins and transcription factors. Furthermore, since members of the Rho GTPase and Arf GTPase families have been implicated in regulation of the actin cytoskeleton, vesicular trafficking, and transcription, the downstream targets of PI 3-kinase that control these GTPases are excellent candidates to mediate aspects of PI 3-kinase dependent neuronal and glial differentiation.