Quinolinic acid induces NMDA receptor-mediated lipid peroxidation in rat brain microvessels

Quinolinic acid increased the generation of lipid peroxidation products by isolated rat brain microvessels in vitro. The effect was inhibited both by a specific NMDA receptor antagonist D-2-amino-5-phosphonovaleric acid and by reduced glutathione (GSH). Furthermore, quinolinic acid displaced specific binding of [(3)H]-L-glutamate by cerebral microvessel membranes, particularly in the presence of NMDA receptor co-agonist (glycine) and modulator (spermidine). We conclude that quinolinic acid can cause potentially cytotoxic lipid peroxidation in brain microvessels via an NMDA receptor mediated mechanism.     

Ontogenic changes in metabolism and transport of glutathione in the rat

Changes in the level of glutathione (GSH), the turnover rate, and gamma-glutamyltransferase (GGT) activity were examined in newborn, weanling, and adult male Wistar rats, the objective being to elucidate the mechanisms which control the hepatic GSH level during maturation as well as under conditions of different degrees of protein ingestion. The hepatic GGT activity in the newborn rats was high at birth, decreased within a few days to 1 to 2% of the initial level, and remained unchanged thereafter, when these rats were fed a normal diet after 3 weeks of age. In contrast, the hepatic GSH level increased 3-4-fold while total GGT activity in the kidney increased 6-8-fold. When weanling rats were fed a low protein diet (containing 10% soy protein) for 3 weeks, the hepatic GSH level decreased markedly while the GGT activity increased 5-6-fold. The turnover rate of hepatic GSH also increased, as determined by the use of buthionine sulfoximine, a specific inhibitor of GSH synthesis; a value of 2.1 h was obtained in comparison with 3.5 h for that of rats fed the normal laboratory chow (CRF-1). On the other hand, feeding adult rats on the low protein diet resulted in a marked decrease in hepatic GSH level with no effect on either hepatic or renal GGT activity. These results together with other observations may suggest that GSH translocated out of liver cells in the newborn rats is degraded mainly by these cells, while the tripeptide secreted by hepatocytes of adult rats is metabolized predominantly in extrahepatic tissues, such as the kidney.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chronic administration of valproic acid induces a decrease in rat striatal glutamate and taurine levels

Summary The effect of acute and chronic (10 days) administration of 200 mg/kg (i.p.) of valproic acid (VPA) on endogenous levels of aspartate, glutamate, alanine, glycine and taurine in the cerebral frontal cortex and corpus striatum of rats was studied. Quantification of the amino acid levels was performed by HPLC.Valproic acid (VPA) did not either induce changes on these neurotransmitters contents in corpus striatum after acute treatment. After chronic administration we found a decrease on the endogenous levels of glutamic acid (24%, p < 0.05) which was related to an increase (250%, p < 0.02) of the in vitro KCl evoked release of glutamate. We found decrements in taurine endogenous levels (22%, p < 0.05) which was not associated with an increase of its release.In cerebral frontal cortex there was not found any change neither under the acute nor under the chronic condition.Thus, it may be conclude that chronic treatment with VPA produces decreases on the endogenous levels of glutamate and taurine. However the relevance of this effect concerning it therapeutic action remains unclear.     

Quinolinic acid is a potent lipid peroxidant in rat brain homogenates

In this study, we describe the lipoperoxidative effect of quinolinic acid (QUIN) in vitro. The formation of thiobarbituric acid reactive products (TBA-RP), an index of lipid peroxidation, was measured in rat brain homogenates after incubation at 37°C for 30 min in the presence of QUIN and some structurally and metabolically related compounds such as Kynurenine, Kynurenic acid, Glutamate, Aspartate and Kainate. Concentrations of QUIN in the range of 20 to 80 M increased lipid peroxidation in a concentration-dependent manner from about 15% to about 50%. Kynurenic acid, a compound metabollically related to QUIN that can block its neurotoxic actions in vivo, also inhibited completely the QUIN-induced TBA-RP formation in our system. Lipid fluorescent material, another index of lipid peroxidation was also found increased by 49% after incubation with 40 M QUIN. It is concluded that lipid peroxidation may be a damaging process involved in the neurotoxicity of QUIN.     

Fetal asphyxia induces acute and persisting changes in the ceramide metabolism in rat brain

Fetal asphyctic preconditioning, induced by a brief episode of experimental hypoxia-ischemia, offers neuroprotection to a subsequent more severe asphyctic insult at birth. Extensive cell stress and apoptosis are important contributing factors of damage in the asphyctic neonatal brain. Because ceramide acts as a second messenger for multiple apoptotic stimuli, including hypoxia/ischemia, we sought to investigate the possible involvement of the ceramide pathway in endogenous neuroprotection induced by fetal asphyctic preconditioning. Global fetal asphyxia was induced in rats by clamping both uterine and ovarian vasculature for 30 min. Fetal asphyxia resulted in acute changes in brain ceramide/sphingomyelin metabolic enzymes, ceramide synthase 1, 2, and 5, acid sphingomyelinase, sphingosine-1-phosphate phosphatase, and the ceramide transporter. This observation correlated with an increase in neuronal apoptosis and in astrocyte number. After birth, ceramide and sphingomyelin levels remained high in fetal asphyxia brains, suggesting that a long-term regulation of the ceramide pathway may be involved in the mechanism of tolerance to a subsequent, otherwise lethal, asphyctic event.     

Paraquat induces behavioral changes and cortical and striatal mitochondrial dysfunction

Paraquat is a highly toxic quaternary nitrogen herbicide capable of increasing superoxide anion production. The aim of this research was to evaluate various behavioral changes and study cortical, hippocampal, and striatal mitochondrial function in an experimental model of paraquat toxicity in rats. Paraquat (10 mg/kg ip) was administered weekly for a month. Anxiety-like behavior was evidenced in the paraquat-treated group as shown by a diminished time spent in, and fewer entries into, the open arms of an elevated-plus maze. Also, paraquat treatment induced a deficit in the sense of smell. In biochemical assays, NADH-cytochrome c reductase activity was significantly inhibited by 25 and 34% in cortical and striatal submitochondrial membranes, respectively. Striatal cytochrome oxidase activity was decreased by 24% after paraquat treatment. Also, cortical and striatal mitochondria showed 55 and 74% increased State 4 respiratory rates, respectively. Paraquat treatment decreased striatal State 3 oxygen consumption by 33%. Respiratory controls were markedly decreased in cortical and striatal mitochondria, indicating mitochondrial dysfunction after paraquat treatment, together with mitochondrial depolarization and increased hydrogen peroxide production rates. We demonstrate that paraquat induced alterations in nonmotor symptoms and cortical and striatal mitochondrial dysfunction.     

Role of glutathione and glutathione peroxidase in human platelet arachidonic acid metabolism

Selective removal of intracellular glutathione (GSH) and inhibition of the GSH-dependent peroxidase (GSH-Px) by 1-chloro-2, 4-dinitrobenzene (CDNB) was used to evaluate the role of GSH and GSH-Px in arachidonic acid (AA) metabolism in human platelets. Although total conversion of AA through the lipoxygenase pathway is lowered by GSH depletion, significant 12-HETE formation was observed suggesting that GSH and GSH-Px are not required for the generation of 12-HETE in human platelets. Prolonged treatment of platelets with CDNB (2 h) completely destroyed GSH-Px activity creating a model in which the effects of GSH alone could be determined. Platelet homogenates replenished with GSH, but lacking GSH-Px activity converted significantly higher amounts of AA to 12-HPETE and 12-HETE than control. Platelet cytosolic metabolism of 15-HPETE to 15-HETE decreased after CDNB, while the membrane metabolism remained similar to control due to high GSH-independent peroxidase activity associated with the membranes. These results indicate that GSH and GSH-Px function to enhance lipoxygenase activity, rather than catalyse the reduction of 12-HPETE to 12-HETE.     

Role of glutathione and glutathione peroxidase in human platelet arachidonic acid metabolism

Selective removal of intracellular glutathione (GSH) and inhibition of the GSH-dependent peroxidase (GSH-Px) by 1-chloro-2,4-dinitrobenzene (CDNB) was used to evaluate the role of GSH and GSH-Px in arachidonic acid (AA) metabolism in human platelets. Although total conversion of AA through the lipoxygenase pathway is lowered by GSH depletion, significant 12-HETE formation was observed suggesting that GSH and GSH-Px are not required for the generation of 12-HETE in human platelets. Prolonged treatment of platelets with CDNB (2 h) completely destroyed GSH-Px activity creating a model in which the effects of GSH alone could be determined. Platelet homogenates replenished with GSH, but lacking GSH-Px activity converted significantly higher amounts of AA to 12-HPETE and 12-HETE than control. Platelet cytosolic metabolism of 15-HPETE to 15-HETE decreased after CDNB, while the membrane metabolism remained similar to control due to high GSH-independent peroxidase activity associated with the membranes. These results indicate that GSH and GSH-Px function to enhance lipoxygenase activity, rather than catalyse the reduction of 12-HPETE to 12-HETE.     

Perinatal changes in amino acid metabolism of rat brain,especially alanine and glutamic acid

The changes in both the levels of some free amino acids and their metabolism in the rat brain during the first 24 hr of postnatal life were studied. The content of glutamic acid decreased for the first 2 hr; it remained at the lowest level for the next 4 hr, when it began to increase. The content of alanine decreased for the first 6 hr and approached the adult level. Oxygen consumption, glucose oxidation, and pyruvate formation in the cerebral slices of the 24-hr-old rats were as much as 150% of that of the 19-day-old fetus. The distribution profile of radioactivity incorporated into the cerebral amino acids from the subarachnoid-injected [U¹⁴C]glucose was also changed. In the 2- and 6-hr-old rats, 50% of the total radio-activity recovered in the free amino acids was in alanine. Its rate decreased to 30% in the 24-hr-old and was 2% in the adult, while the radioactivity incorporated into glutamic acid increased. Alanine aminotransferase activity started to increase at birth and had the highest level at 24 hr after birth. It then decreased and finally reached the same level as shown at birth. However, aspartate aminotransferase increased during the first 6 hr after birth and did not change until the end of the first day of life.     

Unaltered metabolism of taurolithocholic acid with changes in composition of rat intestinal microflora

Changes in composition of both total aerobes and anaerobes of rat intestinal microflora do not appear to affect the metabolism of taurolithocholic acid.     

A phytol-enriched diet induces changes in fatty acid metabolism in mice both via PPARalpha-dependent and -independent pathways

Branched-chain fatty acids (such as phytanic and pristanic acid) are ligands for the nuclear hormone receptor peroxisome proliferator-activated receptor alpha (PPARalpha) in vitro. To investigate the effects of these physiological compounds in vivo, wild-type and PPARalpha-deficient (PPARalpha-/-) mice were fed a phytol-enriched diet. This resulted in increased plasma and liver levels of the phytol metabolites phytanic and pristanic acid. In wild-type mice, plasma fatty acid levels decreased after phytol feeding, whereas in PPARalpha-/- mice, the already elevated fatty acid levels increased. In addition, PPARalpha-/- mice were found to be carnitine deficient in both plasma and liver. Dietary phytol increased liver free carnitine in wild-type animals but not in PPARalpha-/- mice. Investigation of carnitine biosynthesis revealed that PPARalpha is likely involved in the regulation of carnitine homeostasis. Furthermore, phytol feeding resulted in a PPARalpha-dependent induction of various peroxisomal and mitochondrial beta-oxidation enzymes. In addition, a PPARalpha-independent induction of catalase, phytanoyl-CoA hydroxylase, carnitine octanoyltransferase, peroxisomal 3-ketoacyl-CoA thiolase, and straight-chain acyl-CoA oxidase was observed. In conclusion, branched-chain fatty acids are physiologically relevant ligands of PPARalpha in mice. These findings are especially relevant for disorders in which branched-chain fatty acids accumulate, such as Refsum disease and peroxisome biogenesis disorders.     

Lipoic acid metabolism in the rat

dl-[1,6-¹⁴C]Lipoic acid was administered by intraperitoneal injection to rats at the level of 0.5 mg/100 g body weight. Approximately 56% of the radioactivity was recovered in the urine. When acidified and extracted with benzene, 92% of the radioactivity remained in the aqueous phase. Gel-filtration and paper chromatography were used to identify three of the compounds in the benzene extract as lipoic, bisnorlipoic and tetranorlipoic acids. In addition, a keto compound appears to be present. The aqueous phase contained several radioactive components separable by ion-exchange and paper chromatographies. Two of these compounds were identified as lipoate and β-hydroxybisnorlipoate. No evidence for oxidation of the dithiolane ring of lipoic acid was observed. dl-[7,8-¹⁴C]Lipoic acid was administered to rats under the same conditions. The urine contained 81% of the radioactivity, 72% of which remained in the aqueous phase and 28% was extracted into benzene. In contrast to over 30% of the label from dl-(1,6-¹⁴C] lipoate being expired as ¹⁴CO₂, a negligible amount of ¹⁴CO₂ was produced by rats injected with dl-[7,8-¹⁴C]lipoate. The catabolites identified were the same as those found using the 1,6-labeled lipoate. Another dithiolane-intact compound was also isolated. It appears that the rat, similar to Pseudomonas putida LP, metabolizes lipoate mainly via β-oxidation of the valeric acid side chain.     

Gibberellic acid-induced changes in glutathione metabolism and anthocyanin content in plant tissue

Literature data point to a possible link between gibberellic acid (GA₃) and glutathione metabolism in plant tissue, as both are connected to dormancy breakage. In order to study the influence of GA₃ on glutathione metabolism, we treated an anthocyanin accumulating cell culture of periwinkle (Catharanthus roseus) and a shoot differentiated culture of pea (Pisum sativum) with GA₃. Glutathione reductase (GR; E.C. 1.6.4.2) activity increased to 135% and 190% of the control in C. roseus and P. sativum, respectively. The level of oxidized glutathione (GSSG) decreased to 60% of the control in the C. roseus culture while no change in GSSG was observed in the P. sativum culture. No changes in the tissue concentration of total glutathione was observed in the cultures after GA₃ treatment. Concomitant to the changes in GSSG and GR, an increase in anthocyanin accumulation was observed in the C. roseus culture in association with a strong increase in phenylalanine ammonia-lyase (PAL; E.C. 4.3.1.5) activity in response to GA₃. These data strongly suggest a link between GA₃ and glutathione metabolism.