In vitro effect of quinolinic acid on energy metabolism in brain of young rats

Mitochondrial Impairment: A Common Motif in Neuropsychiatric Presentation? The Link to the Tryptophan-Kynurenine Metabolic System

Nearly half a century has passed since the discovery of cytoplasmic inheritance of human chloramphenicol resistance. The inheritance was then revealed to take place maternally by mitochondrial DNA (mtDNA). Later, a number of mutations in mtDNA were identified as a cause of severe inheritable metabolic diseases with neurological manifestation, and the impairment of mitochondrial functions has been probed in the pathogenesis of a wide range of illnesses including neurodegenerative diseases. Recently, a growing number of preclinical studies have revealed that animal behaviors are influenced by the impairment of mitochondrial functions and possibly by the loss of mitochondrial stress resilience. Indeed, as high as 54% of patients with one of the most common primary mitochondrial diseases, mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome, present psychiatric symptoms including cognitive impairment, mood disorder, anxiety, and psychosis. Mitochondria are multifunctional organelles which produce cellular energy and play a major role in other cellular functions including homeostasis, cellular signaling, and gene expression, among others. Mitochondrial functions are observed to be compromised and to become less resilient under continuous stress. Meanwhile, stress and inflammation have been linked to the activation of the tryptophan (Trp)-kynurenine (KYN) metabolic system, which observably contributes to the development of pathological conditions including neurological and psychiatric disorders. This review discusses the functions of mitochondria and the Trp-KYN system, the interaction of the Trp-KYN system with mitochondria, and the current understanding of the involvement of mitochondria and the Trp-KYN system in preclinical and clinical studies of major neurological and psychiatric diseases.

Crosstalk between Tryptophan Metabolism via Kynurenine Pathway and Carbohydrate Metabolism in the Context of Cardio-Metabolic Risk-Review

Scientific interest in tryptophan metabolism via the kynurenine pathway (KP) has increased in the last decades. Describing its metabolites helped to increase their roles in many diseases and disturbances, many of a pro-inflammatory nature. It has become increasingly evident that KP can be considered an important part of emerging mediators of diabetes mellitus and metabolic syndrome (MS), mostly stemming from chronic systemic low-grade inflammation resulting in the aggravation of cardiovascular complications. An electronic literature search of PubMed and Embase up to March 2021 was performed for papers reporting the effects of tryptophan (TRP), kynurenine (KYN), kynurenic acid (KYNA), xanthurenic acid (XA), anthranilic acid (AA), and quinolinic acid (QA), focusing on their roles in carbohydrate metabolism and the cardiovascular system. In this review, we discussed the progress in tryptophan metabolism via KP research, focusing particular attention on the roles in carbohydrate metabolism and its complications in the cardiovascular system. We examined the association between KP and diabetes mellitus type 2 (T2D), diabetes mellitus type 1 (T1D), and cardiovascular diseases (CVD). We concluded that tryptophan metabolism via KP serves as a potential diagnostic tool in assessing cardiometabolic risk for patients with T2D.

Kynurenines and Neurofilament Light Chain in Multiple Sclerosis

Multiple sclerosis is an autoimmune, demyelinating, and neurodegenerative disease of the central nervous system. In recent years, it has been proven that the kynurenine system plays a significant role in the development of several nervous system disorders, including multiple sclerosis. Kynurenine pathway metabolites have both neurotoxic and neuroprotective effects. Moreover, the enzymes of the kynurenine pathway play an important role in immunomodulation processes, among others, as well as interacting with neuronal energy balance and various redox reactions. Dysregulation of many of the enzymatic steps in kynurenine pathway and upregulated levels of these metabolites locally in the central nervous system, contribute to the progression of multiple sclerosis pathology. This process can initiate a pathogenic cascade, including microglia activation, glutamate excitotoxicity, chronic oxidative stress or accumulated mitochondrial damage in the axons, that finally disrupt the homeostasis of neurons, leads to destabilization of neuronal cell cytoskeleton, contributes to neuro-axonal damage and neurodegeneration. Neurofilaments are good biomarkers of the neuro-axonal damage and their level reliably indicates the severity of multiple sclerosis and the treatment response. There is increasing evidence that connections exist between the molecules generated in the kynurenine metabolic pathway and the change in neurofilament concentrations. Thus the alterations in the kynurenine pathway may be an important biomarker of the course of multiple sclerosis. In our present review, we report the possible relationship and connection between neurofilaments and the kynurenine system in multiple sclerosis based on the available evidences.

Quinolinic Acid-Induced Huntington Disease-Like Symptoms Mitigated by Potent Free Radical Scavenger Edaravone-a Pilot Study on Neurobehavioral, Biochemical, and Histological Approach in Male Wistar Rats

In this study, we demonstrated for the first time the neuroprotective role of edaravone (Eda) (5 and 10 mg/kg b.w.), a potent free radical scavenger against the unilateral stereotaxic induction of quinolinic acid (QA) (300 nm/4 μl saline)-induced Huntington disease (HD)-like symptoms in behavioral, biochemical, and histological features in male Wistar rats striatum. QA induction, which mimics the early stage of HD, commonly causes oxidative stress to the cell and decreases the antioxidant defense mechanism by altering the level of lipid peroxidation (LPO), protein carbonyls, and nitrate concentration (NO) and the activities of glutathione family enzymes (GPx, GST, GR) and acetyl choline esterase concentration (AChE) which was found to be ameliorated by Eda treatment in both the tested doses 5 and 10 mg/kg b.w. in the significance of P < 0.05 and P < 0.01, respectively. Finally histopathological analysis by hematoxylin and eosin stain concluded the promising neurodefensive role of Eda in rat striatum at the dosage of 10 mg/kg b.w., with the decreased tissue damage and the number of damaged granular cells when compared to QA-induced groups.

Kynurenic Acid Restores Nrf2 Levels and Prevents Quinolinic Acid-Induced Toxicity in Rat Striatal Slices

Kynurenic acid (KYNA) and quinolinic acid (QUIN) are metabolites produced in the degradation of tryptophan and have important neurological activities. KYNA/QUIN ratio changes are known to be associated with central nervous system disorders, such Alzheimer, Parkinson, and Huntington diseases. In the present study, we investigate the ability of KYNA in prevent the first events preceding QUIN-induced neurodegeneration in striatal slices of rat. We evaluated the protective effect of KYNA on oxidative status (reactive oxygen species production, antioxidant enzymes activities, lipid peroxidation, nitrite levels, protein and DNA damage, and iNOS immunocontent), mitochondrial function (mitochondrial mass, membrane potential, and respiratory chain enzymes), and Na⁺,K⁺-ATPase in striatal slices of rats treated with QUIN. Since QUIN alters the levels of Nrf2, we evaluated the influence of KYNA protection on this parameter. Striatal slices from 30-day-old Wistar rats were preincubated with KYNA (100 μM) for 15 min, followed by incubation with 100-μM QUIN for 30 min. Results showed that KYNA prevented the increase of ROS production caused by QUIN and restored antioxidant enzyme activities and the protein and lipid damage, as well as the Nrf2 levels. KYNA also prevented the effects of QUIN on mitochondrial mass and mitochondrial membrane potential, as well as the decrease in the activities of complex II, SDH, and Na⁺,K⁺-ATPase. We suggest that KYNA prevents changes in Nrf2 levels, oxidative imbalance, and mitochondrial dysfunction caused by QUIN in striatal slices. This study elucidates some of the protective effects of KYNA against the damage caused by QUIN toxicity.

Brain bioenergetics in rats with acute hyperphenylalaninemia

Phenylketonuria (PKU) is a disorder of phenylalanine (Phe) metabolism caused by deficient phenylalanine hydroxylase (PAH) activity. The deficiency results in increased levels of Phe and its metabolites in fluids and tissues of patients. PKU patients present neurological signs and symptoms including hypomyelination and intellectual deficit. This study assessed brain bioenergetics at 1 h after acute Phe administration to induce hyperphenylalaninemia (HPA) in rats. Wistar rats were randomized in two groups: HPA animals received a single subcutaneous administration of Phe (5.2 μmol/g) plus p-Cl-Phe (PAH inhibitor) (0.9 μmol/g); control animals received a single injection of 0.9% NaCl. In cerebral cortex, HPA group showed lower mitochondrial mass, lower glycogen levels, as well as lower activities of complexes I-III and IV, ATP synthase and citrate synthase. Higher levels of free Pi and phospho-AMPK, and higher activities of LDH, α-ketoglutarate dehydrogenase and isocitrate dehydrogenase were also reported in cerebral cortex of HPA animals. In striatum, HPA animals had higher LDH (pyruvate to lactate) and isocitrate dehydrogenase activities, and lower activities of α-ketoglutarate dehydrogenase and complex IV, as well as lower phospho-AMPK immunocontent. In hippocampus, HPA rats had higher mRNA expression for MFN1 and higher activities of α-ketoglutarate dehydrogenase and isocitrate dehydrogenase, but decreased activities of pyruvate dehydrogenase and complexes I and IV. In conclusion, our data demonstrated impaired bioenergetics in cerebral cortex, striatum and hippocampus of HPA rats.

Asiatic acid prevents the quinolinic acid-induced oxidative stress and cognitive impairment

Increased accumulation of endogenous neurotoxin quinolinic acid has been found in various neurodegenerative diseases. Oxidative stress caused by quinolinic acid is considered as imperative factor for its toxicity. Asiatic acid, a natural triterpene is widely studied for its various medicinal values. In the present study the effects of asiatic acid in preventing the cognitive impairment and oxidative stress caused by quinolinic acid was investigated. Male Spraque-Dawley rats were orally administered asiatic acid (30 mg/kg/day) for 28 days, while quinolinic acid toxicity-induced animals received quinolinic acid (1.5 mmol/kg/day) from day 15 to day 28 for 14 days. Asiatic acid administration prevented the loss of spatial memory caused due to quinolinic acid-induced toxicity as determined using the novel object location test. In addition, asiatic acid administration alleviated the deleterious effect of quinolinic acid in brain such as increased oxidative stress, decreased antioxidant status and mitochondrial oxidative phosphorylation dysfunction. These data demonstrate that asiatic acid through its potent antioxidant and cognition enhancement property prevented the neuronal impairments caused by quinolinic acid.

Neurodegeneration Alters Metabolic Profile and Sirt 1 Signaling in High-Fat-Induced Obese Mice

Different factors may contribute to the development of neurodegenerative diseases. Among them, metabolic syndrome (MS), which has reached epidemic proportions, has emerged as a potential element that may be involved in neurodegeneration. Furthermore, studies have shown the importance of the sirtuin family in neuronal survival and MS, which opens the possibility of new pharmacological targets. This study investigates the influence of sirtuin metabolic pathways by examining the functional capacities of glucose-induced obesity in an excitotoxic state induced by a quinolinic acid (QA) animal model. Mice were divided into two groups that received different diets for 8 weeks: one group received a regular diet, and the other group received a high-fat diet (HF) to induce MS. The animals were submitted to a stereotaxic surgery and subdivided into four groups: Standard (ST), Standard-QA (ST-QA), HF and HF-QA. The QA groups were given a 250 nL quinolinic acid injection in the right striatum and PBS was injected in the other groups. Obese mice presented with a weight gain of 40 % more than the ST group beyond acquiring an insulin resistance. QA induced motor impairment and neurodegeneration in both ST-QA and HF-QA, although no difference was observed between these groups. The HF-QA group showed a reduction in adiposity when compared with the groups that received PBS. Therefore, the HF-QA group demonstrated a commitment-dependent metabolic pathway. The results suggest that an obesogenic diet does not aggravate the neurodegeneration induced by QA. However, the excitotoxicity induced by QA promotes a sirtuin pathway impairment that contributes to metabolic changes.

Centella asiatica and Its Fractions Reduces Lipid Peroxidation Induced by Quinolinic Acid and Sodium Nitroprusside in Rat Brain Regions

Oxidative stress has been implicated in several pathologies including neurological disorders. Centella asiatica is a popular medicinal plant which has long been used to treat neurological disturbances in Ayurvedic medicine. In the present study, we quantified of compounds by high performance liquid chromatography (HPLC) and examined the phenolic content of infusion, ethyl acetate, n-butanolic and dichloromethane fractions. Furthermore, we analyzed the ability of the extracts from C. asiatica to scavenge the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) radical as well as total antioxidant activity through the reduction of molybdenum (VI) (Mo(6+)) to molybdenum (V) (Mo(5+)). Finally, we examined the antioxidant effect of extracts against oxidant agents, quinolinic acid (QA) and sodium nitroprusside (SNP), on homogenates of different brain regions (cerebral cortex, striatum and hippocampus). The HPLC analysis revealed that flavonoids, triterpene glycoside, tannins, phenolic acids were present in the extracts of C. asiatica and also the phenolic content assay demonstrated that ethyl acetate fraction is rich in these compounds. Besides, the ethyl acetate fraction presented the highest antioxidant effect by decreasing the lipid peroxidation in brain regions induced by QA. On the other hand, when the pro-oxidant agent was SNP, the potency of infusion, ethyl acetate and dichloromethane fractions was equivalent. Ethyl acetate fraction from C. asiatica also protected against thiol oxidation induced by SNP and QA. Thus, the therapeutic potential of C. asiatica in neurological diseases could be associated to its antioxidant activity.

Quinolinic acid: an endogenous neurotoxin with multiple targets

Quinolinic acid (QUIN), a neuroactive metabolite of the kynurenine pathway, is normally presented in nanomolar concentrations in human brain and cerebrospinal fluid (CSF) and is often implicated in the pathogenesis of a variety of human neurological diseases. QUIN is an agonist of N-methyl-D-aspartate (NMDA) receptor, and it has a high in vivo potency as an excitotoxin. In fact, although QUIN has an uptake system, its neuronal degradation enzyme is rapidly saturated, and the rest of extracellular QUIN can continue stimulating the NMDA receptor. However, its toxicity cannot be fully explained by its activation of NMDA receptors it is likely that additional mechanisms may also be involved. In this review we describe some of the most relevant targets of QUIN neurotoxicity which involves presynaptic receptors, energetic dysfunction, oxidative stress, transcription factors, cytoskeletal disruption, behavior alterations, and cell death.

Cooperation of non-effective concentration of glutamatergic system modulators and antioxidant against oxidative stress induced by quinolinic acid

Excessive formation of reactive oxygen species (ROS) and disruption of glutamate uptake have been hypothesized as key mechanisms contributing to quinolinic acid (QA)-induced toxicity. Thus, here we investigate if the use of diphenyl diselenide (PhSe)(2), guanosine (GUO) and MK-801, alone or in combination, could protect rat brain slices from QA-induced toxicity. QA (1 mM) increased ROS formation, thiobarbituric acid reactive substances (TBARS) and decreased cell viability after 2 h of exposure. (PhSe)(2) (1 μM) protected against this ROS formation in the cortex and the striatum and also prevented decreases in cell viability induced by QA. (PhSe)(2) (5 μM) prevented ROS formation in the hippocampus. GUO (10 and 100 μM) blocked the increase in ROS formation caused by QA and MK-801 (20 and 100 μM) abolished the pro-oxidant effect of QA. When the noneffective concentrations were used in combination produced a decrease in ROS formation, mainly (PhSe)(2) + GUO and (PhSe)(2) + GUO + MK-801. These results demonstrate that this combination could be effective to avoid toxic effects caused by high concentrations of QA. Furthermore, the data obtained in the ROS formation and cellular viability assays suggest different pathways in amelioration of QA toxicity present in the neurodegenerative process.

In vivo manganese exposure modulates Erk, Akt and Darpp-32 in the striatum of developing rats, and impairs their motor function

Manganese (Mn) is an essential metal for development and metabolism. However, exposures to high Mn levels may be toxic, especially to the central nervous system (CNS). Neurotoxicity is commonly due to occupational or environmental exposures leading to Mn accumulation in the basal ganglia and a Parkinsonian-like disorder. Younger individuals are more susceptible to Mn toxicity. Moreover, early exposure may represent a risk factor for the development of neurodegenerative diseases later in life. The present study was undertaken to investigate the developmental neurotoxicity in an in vivo model of immature rats exposed to Mn (5, 10 and 20 mg/kg; i.p.) from postnatal day 8 (PN8) to PN12. Neurochemical analysis was carried out on PN14. We focused on striatal alterations in intracellular signaling pathways, oxidative stress and cell death. Moreover, motor alterations as a result of early Mn exposure (PN8-12) were evaluated later in life at 3-, 4- and 5-weeks-of-age. Mn altered in a dose-dependent manner the activity of key cell signaling elements. Specifically, Mn increased the phosphorylation of DARPP-32-Thr-34, ERK1/2 and AKT. Additionally, Mn increased reactive oxygen species (ROS) production and caspase activity, and altered mitochondrial respiratory chain complexes I and II activities. Mn (10 and 20 mg/kg) also impaired motor coordination in the 3^rd, 4^th and 5^th week of life. Trolox™, an antioxidant, reversed several of the Mn altered parameters, including the increased ROS production and ERK1/2 phosphorylation. However, Trolox™ failed to reverse the Mn (20 mg/kg)-induced increase in AKT phosphorylation and motor deficits. Additionally, Mn (20 mg/kg) decreased the distance, speed and grooming frequency in an open field test; Trolox™ blocked only the decrease of grooming frequency. Taken together, these results establish that short-term exposure to Mn during a specific developmental window (PN8-12) induces metabolic and neurochemical alterations in the striatum that may modulate later-life behavioral changes. Furthermore, some of the molecular and behavioral events, which are perturbed by early Mn exposure are not directly related to the production of oxidative stress.

Vascular and metabolic dysfunction in Alzheimer's disease: a review

Alzheimer's disease (AD) is thought to start years or decades prior to clinical diagnosis. Overt pathology such as protein misfolding and plaque formation occur at later stages, and factors other than amyloid misfolding contribute to the initiation of the disease. Vascular and metabolic dysfunctions are excellent candidates, as they are well-known features of AD that precede pathology or clinical dementia. While the general notion that vascular and metabolic dysfunctions contribute to the etiology of AD is becoming accepted, recent research suggests novel mechanisms by which these/such processes could possibly contribute to AD pathogenesis. Vascular dysfunction includes reduced cerebrovascular flow and cerebral amyloid angiopathy. Indeed, there appears to be an interaction between amyloid β (Aβ) and vascular pathology, where Aβ production and vascular pathology both contribute to and are affected by oxidative stress. One major player in the vascular pathology is NAD(P)H oxidase, which generates vasoactive superoxide. Metabolic dysfunction has only recently regained popularity in relation to its potential role in AD. The role of metabolic dysfunction in AD is supported by the increased epidemiological risk of AD associated with several metabolic diseases such as diabetes, dyslipidemia and hypertension, in which there is elevated oxidative damage and insulin resistance. Metabolic dysfunction is further implicated in AD as pharmacological inhibition of metabolism exacerbates pathology, and several metabolic enzymes of the glycolytic, tricarboxylic acid cycle (TCA) and oxidative phosphorylation pathways are damaged in AD. Recent studies have highlighted the role of insulin resistance, in contributing to AD. Thus, vascular and metabolic dysfunctions are key components in the AD pathology throughout the course of disease. The common denominator between vascular and metabolic dysfunction emerging from this review appears to be oxidative stress and Aβ. This review also provides a framework for evaluation of current and future therapeutics for AD.

Effect of caffeic acid and rofecoxib and their combination against intrastriatal quinolinic acid induced oxidative damage, mitochondrial and histological alterations in rats

Oxidative stress has long been implicated in the neurotoxic effects of glutamate acting through N-methyl-D-aspartate (NMDA) receptors. Therefore, present study has been designed to explore the effect of rofecoxib and caffeic acid on the involvement of oxidative stress, mitochondrial dysfunction and neuronal linked with NMDA receptor-mediated excitotoxicity. Caffeic acid, is a well-known antioxidant flavanoid, implicate anti-inflammatory and immunomodulatory like actions. The present study is an attempt to investigate the antioxidant-like effect of caffeic acid and rofecoxib and their combination against QA-induced oxidative damage, mitochondrial dysfunction and histological alterations. Intrastriatal injection of quinolinic acid (300 nmol) significantly increased oxidative stress (raised lipid peroxidation, nitrite concentration, depleted SOD and catalase), altered mitochondrial complex enzyme activities and histological alteration in the ex vivo striatum. Caffeic acid (5 and 10 mg/kg, p.o.) and rofecoxib (10 and 20 mg/kg, p.o.) treatment for 21 days significantly attenuated oxidative damage and impairment in mitochondrial activities of complex enzymes in the ex vivo striatum. Further, combination of sub effective doses of rofecoxib (10 mg/kg, p.o.) and caffeic acid (5 mg/kg, p.o.) potentiated their protective effect which was significant as compared to their effect per se. The present study suggests the therapeutic effect of caffeic acid and rofecoxib combination against QA-induced ex vivo oxidative damage, mitochondrial and histological alterations in rats.

Effect of PK11195 on attenuating the enhancement of glucose utilization induced by quinolinic acid infusion in the rat brain

PK11195, a selective PBR ligand, has been reported to exert a protective effect against the neuronal damage induced by the intrastriatal infusion of quinolinic acid, an excitatory amino acid. The neuroprotective effect of PK11195 observed at 48 h after the infusion was mediated by the inhibition of microglial activation. The aim of this study is to search the mechanism for the effect of PK11195 other than the inhibition of activation of microglia. In this study, the effect of PK11195 on glucose metabolism as well as neuroprotection in the early phase (2 h) after the injection of quinolinic acid was examined. Intrastriatal injection of quinolinic acid (60 nmol/microL) alone caused a significant enhancement of [(14)C]DG utilization in the infused striatum (about 160% vs. the contralateral side). This enhancement of glucose utilization might be due to an increase in phosphorylation rate of [(14)C]DG rather than delivery process from the plasma into the brain, since the initial uptake of [(14)C]DG (1 min) was not changed by quinolinic acid. Coinjection of PK11195 (10 nmol/microL) completely blocked the enhancement of [(14)C]DG uptake induced by quinolinic acid. The attenuating effect of PK11195 on glucose metabolic disturbance induced by quinolinic acid seemed to be related to voltage-dependent anion channels (VDAC), which are component of the PBR complex and associated with the regulation of hexokinase activity. PK11195 also showed neuroprotective effect at 2 h after the infusion of quinolinic acid, despite no significant activation of microglia was observed at this time-point. Thus, the neuroprotection of PK11195 might be related to normalization of the metabolic disturbance by the excitatory amino acid.

Cytoplasmic calcium mediates oxidative damage in an excitotoxic /energetic deficit synergic model in rats

Excessive calcium is responsible for triggering different potentially fatal metabolic pathways during neurodegeneration. In this study, we evaluated the role of calcium on the oxidative damage produced in an in vitro combined model of excitotoxicity/energy deficit produced by the co-administration of quinolinate and 3-nitropropionate to brain synaptosomal membranes. Synaptosomal fractions were incubated in the presence of subtoxic concentrations of these agents (21 and 166 microm, respectively). In order further to characterize possible toxic mechanisms involved in oxidative damage in this experimental paradigm, agents with different properties - dizocilpine, acetyl L-carnitine, iron porphyrinate and S-allylcysteine - were tested at increasing concentrations (10-1000 microm). Lipid peroxidation was assessed by the formation of thiobarbituric acid-reactive substances. For confirmatory purposes, additional fractions were incubated in parallel in the presence of the intracellular calcium chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester (BAPTA-AM). Under physiological conditions of extracellular calcium availability, synaptomes exposed to both toxins displayed an increased lipoperoxidation (76% above controls), and this effect was partially attenuated by the tested agents as follows: dizocilpine = iron porphyrinate > acetyl L-carnitine > S-allylcysteine. When the incubation medium was deprived of calcium, the lipoperoxidative effect achieved in this experimental paradigm was still high (49% above the control), and the order of attenuation was: iron porphyrinate > S-allylcysteine > acetyl L-carnitine > dizocilpine. BAPTA-AM was effective in preventing the pro-oxidant action of both toxins, promoting even lower peroxidative levels than those quantified under basal conditions. Our results suggest that the lipid peroxidation induced in synaptosomal fractions by quinolinate plus 3-nitropropionate is largely dependent on the cytoplasmic concentrations of calcium.

Evidence for a synergistic action of glutaric and 3-hydroxyglutaric acids disturbing rat brain energy metabolism

Glutaric acidemia type I is an inherited metabolic disorder caused by a severe deficiency of the mitochondrial glutaryl-CoA dehydrogenase activity leading to accumulation of predominantly glutaric and 3-hydroxyglutaric acids in the brain tissue of the affected patients. Considering that a toxic role was recently postulated for quinolinic acid in the neuropathology of glutaric acidemia type I, in the present work we investigated whether the combination of quinolinic acid with glutaric or 3-hydroxyglutaric acids or the mixture of glutaric plus 3-hydroxyglutaric acids could alter brain energy metabolism. The parameters evaluated in cerebral cortex from young rats were glucose utilization, lactate formation and (14)CO(2) production from labeled glucose and acetate, as well as the activities of pyruvate dehydrogenase and creatine kinase. We first observed that glutaric (5 mM), 3-hydroxyglutaric (1 mM) and quinolinic acids (0.1 microM) per se did not alter these parameters. Similarly, no change of these parameters occurred when combining glutaric with quinolinic acids or 3-hydroxyglutaric with quinolinic acids. In contrast, co-incubation of glutaric plus 3-hydroxyglutaric acids increased glucose utilization, decreased (14)CO(2) generation from glucose, inhibited pyruvate dehydrogenase activity as well as total and mitochondrial creatine kinase activities. The glutaric plus 3-hydroxyglutaric acids-induced inhibitory effects on creatine kinase were prevented by the antioxidants glutathione and catalase plus superoxide dismutase, indicating the participation of reactive oxygen species. Our data indicate a synergic action of glutaric and 3-hydroxyglutaric acids disturbing energy metabolism in cerebral cortex of young rats.