Modification of NMDA receptor by in vitro lipid peroxidation in fetal guinea pig brain

Tumor cell survival pathways activated by photodynamic therapy: a molecular basis for pharmacological inhibition strategies

Photodynamic therapy (PDT) has emerged as a promising alternative to conventional cancer therapies such as surgery, chemotherapy, and radiotherapy. PDT comprises the administration of a photosensitizer, its accumulation in tumor tissue, and subsequent irradiation of the photosensitizer-loaded tumor, leading to the localized photoproduction of reactive oxygen species (ROS). The resulting oxidative damage ultimately culminates in tumor cell death, vascular shutdown, induction of an antitumor immune response, and the consequent destruction of the tumor. However, the ROS produced by PDT also triggers a stress response that, as part of a cell survival mechanism, helps cancer cells to cope with the PDT-induced oxidative stress and cell damage. These survival pathways are mediated by the transcription factors activator protein 1 (AP-1), nuclear factor E2-related factor 2 (NRF2), hypoxia-inducible factor 1 (HIF-1), nuclear factor κB (NF-κB), and those that mediate the proteotoxic stress response. The survival pathways are believed to render some types of cancer recalcitrant to PDT and alter the tumor microenvironment in favor of tumor survival. In this review, the molecular mechanisms are elucidated that occur post-PDT to mediate cancer cell survival, on the basis of which pharmacological interventions are proposed. Specifically, pharmaceutical inhibitors of the molecular regulators of each survival pathway are addressed. The ultimate aim is to facilitate the development of adjuvant intervention strategies to improve PDT efficacy in recalcitrant solid tumors.

Fe2+ and Fe3+ initiated peroxidation of sonicated and non-sonicated liposomes made of retinal lipids in different aqueous media

Retina is highly susceptible to oxidative damage due to its high content of polyunsaturated fatty acids (PUFAs), mainly docosahexaenoic acid (22:6 n3). Lipid peroxidation process is thought to be involved in many physiological and pathological events. Many model membranes can be used to learn more about issues that cannot be studied in biological membranes. Sonicated liposomes (SL) and non-sonicated liposomes (NSL) prepared with lipids isolated from bovine retina and characterized by dynamic light-scattering, were submitted to lipid peroxidation, under air atmosphere at 22 degrees C, with Fe(2+) or Fe(3+) as initiator, in different aqueous media. Conjugated dienes and trienes, determined by absorption at 234 and 270 nm respectively, and thiobarbituric acid-reactive substances were measured as a function of time. Peroxidation of SL or NSL initiated with 25 microM FeSO(4) in 20mM Tris-HCl pH 7.4 resulted in an increase in TBARS production after a lag phase of 60 min. Incubation of both types of liposomes in water resulted in shortening of the lag phase at 30 min. When lipid peroxidation was performed in 0.15M NaCl, lag phase completely disappeared. On the other hand, FeCl(3) (25 microM) induced a limited production of TBARS only just after 30 min of incubation. When Fe(2+)- or Fe(3+)-lipid peroxidation of both types of liposomes was carried out in water or 0.15M NaCl, formation of conjugated dienes and conjugated trienes were higher than in reactions carried out in 20mM Tris-HCl pH 7.4. Our results established that both liposome types were susceptible to Fe(2+)- and Fe(3+)-initiated lipid peroxidation. However, Fe(2+) showed a clearly enhanced effect on peroxidation rate and steady state concentration of oxidation products. We verified that peroxidation of liposomes made of retinal lipids is affected not only by type of initiator but also by aqueous media. This model constitutes a useful system to study formation of lipid peroxidation intermediaries and products in an aqueous environment.

Lipid peroxidation of membrane phospholipids generates hydroxy-alkenals and oxidized phospholipids active in physiological and/or pathological conditions

Polyunsaturated fatty acids (PUFAs) and their metabolites have a variety of physiological roles including: energy provision, membrane structure, cell signaling and regulation of gene expression. Lipids containing polyunsaturated fatty acids are susceptible to free radical-initiated oxidation and can participate in chain reactions that increase damage to biomolecules. Lipid peroxidation, which leads to lipid hydroperoxide formation often, occurs in response to oxidative stress. Hydroperoxides are usually reduced to their corresponding alcohols by glutathione peroxidases. However, these enzymes are decreased in certain diseases resulting in a temporary increase of lipid hydroperoxides that favors their degradation into several compounds, including hydroxy-alkenals. The best known of these are: 4-hydroxy-2-nonenal (4-HNE) and 4-hydroxy-2-hexenal (4-HHE), which derive from lipid peroxidation of n-6 and n-3 fatty acids, respectively. Compared to free radicals, these aldehydes are relatively stable and can diffuse within or even escape from the cell and attack targets far from the site of the original event. These aldehydes exhibit great reactivity with biomolecules, such as proteins, DNA, and phospholipids, generating a variety of intra and intermolecular covalent adducts. At the membrane level, proteins and amino lipids can be covalently modified by lipid peroxidation products (hydoxy-alkenals). These aldehydes can also act as bioactive molecules in physiological and/or pathological conditions. In addition this review is intended to provide an appropriate synopsis of identified effects of hydroxy-alkenals and oxidized phospholipids on cell signaling, from their intracellular production, to their action as intracellular messenger, up to their influence on transcription factors and gene expression.

Peroxidation of liposomal lipids

Free radicals, formed via different mechanisms, induce peroxidation of membrane lipids. This process is of great importance because it modifies the physical properties of the membranes, including its permeability to different solutes and the packing of lipids and proteins in the membranes, which in turn, influences the membranes' function. Accordingly, much research effort has been devoted to the understanding of the factors that govern peroxidation, including the composition and properties of the membranes and the inducer of peroxidation. In view of the complexity of biological membranes, much work was devoted to the latter issues in simplified model systems, mostly lipid vesicles (liposomes). Although peroxidation in model membranes may be very different from peroxidation in biological membranes, the results obtained in model membranes may be used to advance our understanding of issues that cannot be studied in biological membranes. Nonetheless, in spite of the relative simplicity of peroxidation of liposomal lipids, these reactions are still quite complex because they depend in a complex fashion on both the inducer of peroxidation and the composition and physical properties of the liposomes. This complexity is the most likely cause of the apparent contradictions of literature results. The main conclusion of this review is that most, if not all, of the published results (sometimes apparently contradictory) on the peroxidation of liposomal lipids can be understood on the basis of the physico-chemical properties of the liposomes. Specifically: (1) The kinetics of peroxidation induced by an "external" generator of free radicals (e.g. AAPH) is governed by the balance between the effects of membrane properties on the rate constants of propagation (k (p)) and termination (k (t)) of the free radical peroxidation in the relevant membrane domains, i.e. in those domains in which the oxidizable lipids reside. Both these rate constants depend similarly on the packing of lipids in the bilayer, but influence the overall rate in opposite directions. (2) Peroxidation induced by transition metal ions depends on additional factors, including the binding of metal ions to the lipid-water interface and the formation of a metal ions-hydroperoxide complex at the surface. (3) Reducing agents, commonly regarded as "antioxidants", may either promote or inhibit peroxidation, depending on the membrane composition, the inducer of oxidation and the membrane/water partitioning. All the published data can be explained in terms of these (quite complex) generalizations. More detailed analysis requires additional experimental investigations.

Lipid Peroxidation Induces Cholesterol Domain Formation in Model Membranes

Numerous reports have established that lipid peroxidation contributes to cell injury by altering the basic physical properties and structural organization of membrane components. Oxidative modification of polyunsaturated phospholipids has been shown, in particular, to alter the intermolecular packing, thermodynamic, and phase parameters of the membrane bilayer. In this study, the effects of oxidative stress on membrane phospholipid and sterol organization were measured using small angle x-ray diffraction approaches. Model membranes enriched in dilinoleoylphosphatidylcholine were prepared at various concentrations of cholesterol and subjected to lipid peroxidation at physiologic conditions. At cholesterol-to-phospholipid mole ratios (C/P) as low as 0.4, lipid peroxidation induced the formation of discrete, membrane-restricted cholesterol domains having a unit cell periodicity or d-space value of 34 A. The formation of cholesterol domains correlated directly with lipid hydroperoxide levels and was inhibited by treatment with vitamin E. In the absence of oxidative stress, similar cholesterol domains were observed only at C/P ratios of 1.0 or higher. In addition to changes in sterol organization, lipid peroxidation also caused reproducible changes in overall membrane structure, including a 10 A reduction in the width of the surrounding, sterol-poor membrane bilayer. These data provided direct evidence that lipid peroxidation alters the essential organization and structure of membrane lipids in a manner that may contribute to changes in membrane function during aging and oxidative stress-related disorders.

Effect of graded hypoxia on the high-affinity CPP binding site of the NMDA receptor in the cerebral cortex of newborn piglets

Previous studies have shown that the N-methyl-D-aspartate (NMDA) receptor is modified during hypoxia in the cerebral cortex of newborn piglets. The present study tests the hypothesis that the NMDA receptor 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) high-affinity binding site is modified during hypoxia and that the degree of modification correlates with the progressive decrease in cerebral cellular energy metabolism and increase in lipid peroxidation induced by hypoxia. Studies were conducted in twelve anesthetized, ventilated newborn piglets, five normoxic and seven hypoxic which were exposed to decreased fraction of inspired oxygen (FiO2) to achieve varying phosphocreatine (PCr) levels. 3[H]-CPP binding was performed with CPP concentrations ranging from 0.5 to 1500 nM at 23 degrees C for 40 min in P2 membrane fractions. Brain tissue PCr levels were determined biochemically. Conjugated dienes (CDs) were measured as an index of lipid peroxidation. In the normoxic group, B(max) (receptor number) for the CPP binding site was 329+/-93 fmol/mg protein and Kd (dissociation constant) 137+/-44 nM, the mean PCr value was 2.5+/-0.4 micromol/g brain and the CD level was 0.0 nmol/g brain. As tissue hypoxia worsened, there was a gradual decline in tissue PCr as well as receptor B(max) and K(d) values, and there was an increase in conjugated dienes. Both the receptor B(max) (r=0.90) and Kd (r=0.72) decreased in a linear relationship as PCr decreased. As the levels of CDs increased both the receptor B(max) (r=0.88) and Kd (r=0.68) decreased in a linear fashion. The data show that there is not a critical hypoxic threshold for modification of the CPP binding site of the NMDA receptor, but that modification is coupled to a gradual decrease in brain cell energy metabolism and increase in lipid peroxidation. We speculate that hypoxia-induced modification of the NMDA receptor is mediated not only by changes in the receptor recognition site but also by an alteration of brain cell membrane structure secondary to conjugated diene formation.

D-serine is an endogenous ligand for the glycine site of the N-methyl-D-aspartate receptor

Functional activity of N-methyl-D-aspartate (NMDA) receptors requires both glutamate binding and the binding of an endogenous coagonist that has been presumed to be glycine, although D-serine is a more potent agonist. Localizations of D-serine and it biosynthetic enzyme serine racemase approximate the distribution of NMDA receptors more closely than glycine. We now show that selective degradation of d-serine with D-amino acid oxidase greatly attenuates NMDA receptor-mediated neurotransmission as assessed by using whole-cell patch-clamp recordings or indirectly by using biochemical assays of the sequelae of NMDA receptor-mediated calcium flux. The inhibitory effects of the enzyme are fully reversed by exogenously applied D-serine, which by itself did not potentiate NMDA receptor-mediated synaptic responses. Thus, D-serine is an endogenous modulator of the glycine site of NMDA receptors and fully occupies this site at some functional synapses.

Spermine dependent activation of the N-methyl-D-aspartate receptor and the effect of nitric oxide synthase inhibition during hypoxia in the cerebral cortex of newborn piglets

This study tests the hypothesis that brain tissue hypoxia results in modification of spermine-dependent activation of the cerebral N-methyl-D-aspartate (NMDA) receptor ion-channel in newborn piglet brains and that pretreatment with N(omega)-nitro-L-arginine (NNLA), an inhibitor of nitric oxide synthase, will reduce the hypoxia-induced modification of the spermine-dependent activation of the receptor. Piglets were assigned to one of four groups; normoxia or hypoxia with or without NNLA. The infusion of NNLA or vehicle lasted for 60 min while the animals were ventilated under either hypoxic or normoxic conditions. Cerebral tissue hypoxia was confirmed by measuring ATP and phosphocreatine (PCr) levels. P2 membranes were isolated and 3H-MK-801 binding was measured in the presence of spermine. Steady state 3H-MK-801 binding in the presence of spermine, showed an increase in receptor affinity in both normoxic (47% of control) and hypoxic (42% of control) animals without change in receptor density. During hypoxia, the spermine-dependent increase in the maximal response of the 3H-MK-801 binding correlated inversely with the ATP concentrations. NNLA pretreatment prior to hypoxia, resulted in a decrease in the slope of the regression line describing the relationship between cellular energy state (ATP) and percent change in maximal response to spermine compared with vehicle treated animals indicating attenuation of the response to hypoxia. We conclude that the spermine-dependent modification of the affinity of the NMDA receptor ion-channel as assessed by 3H-MK-801 binding is similar in hypoxic and normoxic cortical tissue. NNLA administration reduces the hypoxia-induced spermine-dependent activation of the receptor indicating that nitric oxide mediates modification of the spermine site activation of the NMDA receptor ion-channel complex.

Effect of allopurinol on hypoxia-induced modification of the NMDA receptor in newborn piglets

The present study tests the hypothesis that pretreatment with allopurinol, a xanthine oxidase inhibitor, will prevent modification of the NMDA receptor during cerebral hypoxia in newborn piglets. Eighteen newborn piglets were studied. Six normoxic control animals were compared to six untreated hypoxic and six allopurinol (20 mg/kg i.v.) pretreated hypoxic piglets. Cerebral hypoxia was induced by lowering the FiO2 to 0.05-0.07 for 1 hour and tissue hypoxia was confirmed biochemically by the measurement of ATP and phosphocreatine. Brain cell membrane Na+,K+-ATPase activity was determined to assess membrane function. Na+,K+-ATPase activity was decreased from control in both the untreated and treated hypoxic animals (46.0+/-1.0 vs 37.9+/-2.5 and 37.3+/-1.4 micromol Pi/mg protein/hr, respectively, p < 0.05). [3H]MK-801 binding was determined as an index of NMDA receptor modification. The receptor density (Bmax) in the untreated hypoxic group was decreased compared to normoxic control (1.09+/-0.17 vs 0.68+/-0.22 pmol/mg protein, p < 0.01). The dissociation constant (Kd) was also decreased in the untreated group (10.0+/-2.0 vs 4.9+/-1.4 nM, p < 0.01), indicating an increase in receptor affinity. However, in the allopurinol treated hypoxic group, the Bmax (1.27+/-0.09 pmol/mg protein) was similar to normoxic control and the Kd (8.1+/-1.2 nM, p < 0.05) was significantly higher than in the untreated hypoxic group. The data show that the administration of allopurinol prior to hypoxia prevents hypoxia-induced modification of the NMDA receptor-ion channel binding characteristics, despite neuronal membrane dysfunction. By preventing NMDA receptor-ion channel modification, allopurinol may produce a neuromodulatory effect during hypoxia and attenuate NMDA receptor mediated excitotoxicity.

Inflammatory pathogenesis of cortical polymicrogyria: an autopsy study

Polymicrogyria, a cortical abnormality usually classified among neuron migration disorders, is characterized by different etiologies and pathogeneses. Recently, it has been proposed that polymicrogyria could be acquired as a consequence of a lasting damage to the developing brain. In this study, we test the hypothesis that an infection in the fetal adnexa may give rise to distant brain defects and eventually polymicrogyria. Thirty-two fetuses spontaneously aborted for extensive ascending chorioamnionitis at 15-26 wk of gestation were evaluated. Control subjects were represented by 8 fetuses aborted at 15-24 wk of gestation. A complete autopsy was carried out between 4 and 12 h after fetal expulsion. We found different histologic alterations in the primitive cortical architecture, both isolated and combined (undulation of the cortical ribbon, untimely cortical folding/molecular layer fusion, and neuronal loss). A total of 25 cases presented one or more of the above-described morphologic alterations in the brain (78%). On the contrary, similar alterations were never observed in any of the control brains (p=0.019). Our findings indicate that chorioamnionitis significantly impairs brain cortex morphogenesis. Such neuron damage may be caused by an unspecific, indirect mechanism of injury to the developing cortex involving hypoxia and free radical generation. The reported brain abnormalities may even evolve into polymicrogyria in surviving fetuses.

Melatonin attenuates L-cysteine-induced seizures and lipid peroxidation in the brain of mice

The effect of melatonin, a potent free radical scavenger, on L-cysteine-induced seizures and lipid peroxidation was investigated in mice. When L-cysteine (1.25, or 5.0 mumol/animal) was injected intracerebroventricularly (i.c.v.) into mice, severe tonic seizures were observed for over 20 sec in 75% and 100% of the treated mice, respectively. However, when melatonin (20 or 100 mg/kg) was injected subcutaneously (sc) into mice 15 min before L-cysteine injection (1.25 mumol/animal, i.c.v.), the incidence of seizures was observed in only 35% and 20% of the treated mice, respectively. Furthermore, when L-cysteine (1.25 or 5.0 mumol/animal, i.c.v.) was injected into mice, lipid peroxidation in whole brain 20 min after injection was significantly increased by 56% or 67% as compared to that of the control. However, when the seizures induced by L-cysteine (1.25 mumol/animal) were abolished by preadministration of melatonin, the increased lipid peroxidation induced by L-cysteine was prevented. These results suggest that there may be a positive correlation between free radical formation and seizures induced by L-cysteine and that melatonin affords protection against the seizures as well as against the associated lipid peroxidation.

Brain cell membrane Na+,K(+)-ATPase activity following severe hypoxic injury in the newborn piglet

This study tests the hypothesis that severe brain hypoxia causes decreased Na+,K(+)-ATPase activity, resulting in permanent alterations in the neuronal cell membranes. Seventeen anesthetized piglets (normoxic control (NC), no recovery after hypoxia (Group 1), 6 h normoxic recovery (Group 2), and 48 h normoxic recovery (Group 3)) were studied. Hypoxia was induced by lowering the FiO2 to maintain PCr/Pi ratio at 25% of baseline for 1 h as monitored by 31P-NMR spectroscopy. PCr/Pi returned to 57% of baseline by 6 h and was normal by 48 h. At termination, cortical tissue Na+,K(+)-ATPase activity was determined. Na+,K(+)-ATPase activity was measured in cortical membrane preparations by determining the rate of ATP hydrolysis. NC membranes had Na+,K(+)-ATPase activity of 58.3 +/- 1.3 microM Pi/mg protein/h (mean +/- S.E.M.). Na+,K(+)-ATPase activity was reduced in Groups 1, 2, and 3 (45.8 +/- 1.3, 47.4 +/- 3.6, 48.7 +/- 2.9 microM Pi/mg protein/h) (P < 0.05 compared to NC). There was no difference in enzyme activity among Groups 1, 2, or 3. The data show that in spite of recovery of neuronal oxidative phosphorylation (PCr/Pi) by 48 h, there is a permanent decrease in Na+,K(+)-ATPase activity in cells that have undergone severe hypoxic injury. The persistent decrease in Na+,K(+)-ATPase activity indicates ongoing cell injury following severe cerebral hypoxia, and that recovery of oxidative phosphorylation as indicated by PCr/Pi values cannot be used as an index of recovery of cell function.

Oxidative stress in acidic conditions increases the production of inositol phosphates in chick retinal cells in culture

The effect of oxidative stress on the production of [3H]inositol phosphates (InsP) by retinal cells in culture was analyzed. The process of oxidation was induced by incubating the cells with ascorbic acid and ferrous sulphate, and increased extent of oxidation was obtained by varying the pH from neutral to moderate acidosis (pH 6.5). The oxidative process significantly reduced cell viability (about 15%) by decreasing the capacity of mitochondria dehydrogenases to reduce tetrazolium salts, but had no effect on the leakage of lactate dehydrogenase. The production of [3H]InsP, in the absence of receptor activation, was increased dose dependently by oxidative stress. Maximal increases to 189 +/- 7%, 197 +/- 13%, and 329 +/- 22% were observed, respectively, for inositol monophosphates (InsP1), inositol bisphosphates (InsP2), and inositol trisphosphates (InsP3), at 2.5 nmol thiobarbituric acid reactive substances (TBARS)/mg protein. The response to cholinergic receptor activation was slightly decreased in cells oxidized in acidic conditions. Antagonists of glutamate receptors failed to inhibit the enhancement in InsP that occurred upon cellular oxidation, suggesting that the effect was not mediated by activation of glutamate receptors. Cellular oxidation increased by about two fold the uptake of 45Ca2+ in the absence of agonist stimulation. However, stimulation of phospholipase C by Ca2+ did not mediate the increase in [3H]InsP upon cell oxidation in acidic conditions, because the addition of 1-[6-[[17 beta-3-methoxyestra-1,3,5(10)-trien-17-yl]amino] hexyl]-1-H-pyrrole-2,5-dione (U-73122), an inhibitor of phospholipase C-dependent processes, did not affect the production of [3H]InsP in oxidized cells. Nevertheless, U-73122 significantly inhibited carbachol- and K(+)-stimulated accumulation of [3H]InsP. Furthermore, the enhancement of [3H]InsP induced by ascorbate/Fe2+ was still observed in the absence of external Ca2+. This increase in the production of InsP did not substantially induce the release of Ca2+ from internal stores. The results suggest that both Ca(2+)-dependent and Ca(2+)-independent pathways are involved in oxidative stress-mediated InsP increment, and that the enzymes of the InsP metabolism may be affected by oxidation.

Differential effects of in vitro peroxidation on peripheral- and central-type benzodiazepine receptors. Protection by diverse antioxidants

The influence of various concentrations of ferrous iron and ascorbate on in vitro peroxidation and drug binding of diverse membrane preparations (cerebral cortex and liver) was studied. Peroxidation was not simply dose-related to ascorbate and ferrous iron, but a complex relationship between iron and ascorbate when added in association was established. Under our conditions 0.01 mM Fe2+ and 0.5 mM ascorbate was the most peroxidative combination for cerebral and liver membranes. Under the same conditions, cerebral membranes were more peroxidated than liver membranes. Considering the consequences of drug binding, peripheral-type benzodiazepine receptors (PBRs) of liver were more affected by peroxidative events than central-type benzodiazepine receptors (CBRs) of the cerebral cortex. The degree of binding disturbance was generally inversely correlated to the degree of peroxidation and this was more significant for liver PBRs than for cerebral CBRs. The liver membrane model was retained for testing in vitro protection by diverse putative antioxidants. Under our conditions desferrioxamine, ethylene diamine tetra acetate (EDTA), trolox, and rutin were good protective antioxidants, whereas phenyl-butyl-nitrone (PBN) and tocopherol were not effective.

Change in fluidity of brain endoplasmic reticulum membranes by oxygen free radicals: a protective effect of stobadine, alpha-tocopherol acetate, and butylated hydroxytoluene

Effect of various oxygen free radical generating systems and an oxidant H2O2 on brain endoplasmic reticulum (ER) membrane fluidity was examined using fluorescent membrane probe 1,6-diphenyl-1,3,5-hexatriene, DPH. The relative potency of free radical generating systems to decrease membrane fluidity increased in this order: FeCl3-EDTA, FeSO4-EDTA, FeSO4-EDTA/hydrogen peroxide. Potency to decrease membrane fluidity correlated well with these systems' potencies to induce lipid peroxidation, as detected by conjugated diene formation. Treatment of ER membranes with H2O2 had no effect on fluidity or conjugated diene formation. Using the two most potent free radical generating systems, FeSO4-EDTA and FeSO4-EDTA/hydrogen peroxide, a protective effect of the novel antihypoxic and antiarrhytmic drug stobadine was tested. Stobadine and two well-known antioxidants, alpha-tocopherol acetate and butylated hydroxytoluene, demonstrated the ability to prevent free radical induced alterations in ER membrane fluidity. These results provide new evidence of stobadine's protective effect on membranes attacked by oxygen free radicals.

Effect of oxidative stress on the release of [3H]GABA in cultured chick retina cells

The effect of ascorbate (1.5 mM)/Fe2+ (7.5 microM)-induced oxidative stress on the release of pre-accumulated [3H]gamma-aminobutyric acid ([3H]GABA) from cultured chick retina cells was studied. Depolarization of control cells with 50 mM K+ increased the release of [3H]GABA by 1.01 +/- 0.16% and 2.5 +/- 0.3% of the total, in the absence and in the presence of Ca2+, respectively. Lipid peroxidation increased the release of [3H]GABA to 2.07 +/- 0.31% and 3.6 +/- 0.39% of the total, in Ca(2+)-free or in Ca(2+)-containing media, respectively. The inhibitor of the GABA carrier, 1-(2-(((diphenylmethylene)amino)oxy)ethyl)-1,2,5,6-tetrahydro-3-py ridine- carboxylic acid hydrochloride (NNC-711) blocked almost completely the release of [3H]GABA due to K(+)-depolarization in the absence of Ca2+, but only 65% of the release occurring in the presence of Ca2+ in control and peroxidized cells. Under oxidative stress retina cells release more [3H]GABA than control cells, being the Ca(2+)-independent mechanism, mediated by the reversal of the Na+/GABA carrier, the most affected. MK-801 (1 microM), a non-competitive antagonist of the NMDA receptor-channel complex, blocked by 80% the release of [3H]GABA in peroxidized cells, whereas in control cells the inhibitory effect was of 48%. The non-selective blocker of the non-NMDA glutamate receptors, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), inhibited the release of [3H]GABA by 30% and 70% in control and peroxidized cells, respectively. Glycine (5 microM) stimulated [3H]GABA release evoked by 50 mM K+-depolarization in control but not in peroxidized cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain cell membrane modification following hypercapnia and recovery in newborn piglets

The effect of hypercapnia on brain cell membrane structure and function was studied in anesthetized newborn piglets. Lipid peroxidation products (conjugated dienes and fluorescent compounds), Na+,K(+)-ATPase activity and enzyme affinity to ATP (substrate), K+ and Na+ ions (activators), and strophanthidin (inhibitor) were measured in three groups of animals: controls, those exposed to 90 minutes of PaCO2 > 80 mmHg (hypercapnia) and those exposed the same way, following restoration of normal PaCO2 (recovery). Enzyme activity was unchanged by hypercapnia, but enzyme affinity was altered as indicated by an increase in ATP affinity. Affinities to Na+, K+, and strophanthidin were unchanged. Restoration of normal PaCO2 resulted in an increase in conjugated dienes. The data demonstrate that hypercapnia followed by restoration of normal PaCO2 in healthy term newborn piglets is associated with mild modification of brain cell membrane Na+,K(+)-ATPase, possibly due to lipid peroxidation.

Effect of dithiothreitol on lipid peroxidation induced modification of NMDA receptor in fetal guinea pig brain

The present study examines if the NMDA receptor modification induced by lipid peroxidation is mediated through its redox site and is therefore reversible by dithiothreitol (DTT) by performing [3H]MK-801 binding in the fetal guinea pig brain. P2 membrane fractions were prepared from fetal guinea pig brains and were peroxidized in vitro by 100 microM ascorbate and 25 microM ferric chloride for 20 min. Control and peroxidized membranes were then incubated with 100 microM DTT for 30 min at 37 degrees C. [3H]MK-801 binding was performed in DTT treated and untreated membranes in the presence of 100 microM each of glutamate and glycine. In addition, to study the glutamate- and glycine-dependent activation, [3H]MK-801 binding was determined in the absence (basal) and presence (activated) of glutamate and glycine. Bmax (number of binding sites) and Kd (affinity) of the binding sites were used as indices of NMDA receptor modification and its reversibility by DTT. After lipid peroxidation, the Kd value increased from 4.44 +/- 0.12 in control to 10.39 +/- 1.78 nM (P < 0.01) suggesting decreased affinity following lipid peroxidation. Following treatment with DTT, there was no significant change in Kd, but Bmax was significantly (P < 0.007) decreased in the peroxidized membrane. This suggests that DTT did not improve the affinity of the NMDA receptor of the lipid peroxidized membrane but may have a deleterious effect by reducing the number of binding sites. However, in the control membrane DTT significantly increased the affinity (P < 0.004) and the Bmax (P < 0.01) of the NMDA receptors.(ABSTRACT TRUNCATED AT 250 WORDS)