Paracetamol perturbs neuronal arborization and disrupts the cytoskeletal proteins SPTBN1 and TUBB3 in both human and chicken in vitro models.

Epidemiological studies have linked long-term/high-dose usage of paracetamol (N-acetyl-para-aminophenol, APAP) during pregnancy to adverse neuropsychiatric outcomes, primarily attention-deficit hyperactive disorder (ADHD), in the offspring. Though variable, ADHD has been associated with phenotypic alterations characterized by reductions in grey matter densities and aberrations in structural connectivity, effects which are thought to originate in neurodevelopment. We used embryonic chicken cerebellar granule neurons (CGNs) and neuronally differentiating human NTERA2 cells (NT2Ns) to investigate the in vitro effects of APAP on cell viability, migration, neuritogenesis, and the intracellular levels of various proteins involved in neurodevelopment as well as in the maintenance of the structure and function of neurites. Exposure to APAP ranging from 100 to 1600 µM yielded concentration- and time-dependent reductions in cell viability and levels of neurite arborization, as well as reductions in the levels of the cytoskeletal protein ß2-spectrin, with the highest APAP concentration resulting in between 50 and 75% reductions in the aforementioned metrics over the course of 72 h. Exposure to APAP also reduced migration in the NT2Ns but not CGNs. Moreover, we found concentration- and time-dependent increases in punctate aggregation of the cytoskeletal protein ß3-tubulin following exposure to APAP in both cell model systems, with the highest APAP concentration approximately doubling the number of aggregates over 72-120 h. Our findings demonstrate that APAP negatively perturbs neurite arborization degree, with concurrent reductions in the protein levels of ß2-spectrin and disruption of the integrity of ß3-tubulin, both proteins of which play important roles in neuronal structure and function.

Peripherally administered persistent organic pollutants distribute to the brain of developing chicken embryo in concentrations relevant for human exposure.

Persistent organic pollutants (POPs) can reach the fetal brain and contribute to developmental neurotoxicity. To explore the distribution of POPs to the fetal brain, we exposed chicken embryos to a POP mixture, containing 29 different compounds with concentrations based on blood levels measured in the Scandinavian human population. The mixture was injected into the allantois at embryonic day 13 (E13), aiming at a theoretical concentration of 10 times human blood levels. POPs concentrations in the brain were measured at 0.5, 1, 2, 4, 6, 24, 48, and 72 h after administration. Twenty-seven of the individual compounds were detected during at least one of the time-points analyzed. Generally, the concentrations of most of the measured compounds were within the order of magnitude of those reported in human brain samples. Differences in the speed of distribution to the brain were observed between the per- and polyfluoroalkyl substances (PFASs), which have protein binding potential, and the lipophilic polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and brominated flame retardants (BFRs). Based on pharmacokinetic modeling, PFASs were best described by a one compartment model. PFASs displayed relatively slow elimination (Kel) and persisted at high levels in the brain. Lipophilic OCPs and PCBs could be fitted to a 2-compartment model. These showed high levels in the brain relative to the dose administrated as calculated by area under the curve (AUC)/Dose. Altogether, our study showed that chicken is a suitable model to explore the distribution of POPs into the developing brain at concentrations which are relevant for humans.

Chicken embryo as animal model to study drug distribution to the developing brain.

INTRODUCTION: Rodent models are routinely used to assess the safety and developmental toxicity of pharmaceuticals, along with analysis of their distribution. These models require sacrifice of parent females, have challenges in the estimation of the number of embryos and stage of development, and are expensive and time-consuming. In this study, we used fertilized chicken eggs as an alternative model to address drug distribution to the developing brain of two antiepileptic drugs, valproic acid (VPA) and lamotrigine (LTG) at two developmental stages. METHODS: VPA or LTG was injected into the allantois of the egg on embryonic day 13 (E13) or E16. Whole chicken brains were harvested at time-points of 5 min to 24 h and the concentrations of the drugs determined using GC/MS and LC-MS/MS, for VPA and LTG, respectively. RESULTS: VPA and LTG had distinct absorption and elimination phases and were found in the brain as early as 5-15 min after injection. Both drugs reached the brain in clinically relevant concentrations, with Cmax 10-30% of the calculated concentration assuming uniform distribution throughout the egg. LTG concentrations were higher when injected at E13 compared to E16. CONCLUSION: The chicken embryo model may be a suitable alternative animal model for preclinical drug distribution studies. It enables to easily approach antenatal development on an individual level, with a precise number of experimental animals, high reproducibility and low time and cost. Knowledge of the concentrations reaching the brain at different developmental stages with different drugs is important for the planning and interpretation of neurodevelopmental toxicity studies.

A human relevant mixture of persistent organic pollutants (POPs) and perfluorooctane sulfonic acid (PFOS) differentially affect glutamate induced excitotoxic responses in chicken cerebellum granule neurons (CGNs) in vitro.

Primary cultures of cerebellar granule neurons (CGNs) derived from chicken embryos were used to explore the effects on developmental neurotoxicity by a complex defined mixture of persistent organic pollutants (POPs). Its chemical composition and concentrations were based on blood levels in the Norwegian/Scandinavian population. Perfluorooctane sulfonic acid (PFOS) alone, its most abundant compound was also evaluated. Different stages of CGNs maturation, between day in vitro (DIV) 1, 3, and 5 were exposed to the POP mixture, or PFOS alone. Their combination with glutamate, an excitatory endogenous neurotransmitter important in neurodevelopment, also known to cause excitotoxicity was evaluated. Outcomes with the mixture at 500x blood levels were compared to PFOS at its corresponding concentration of 20 µM. The POP mixture reduced tetrazolium salt (MTT) conversion at earlier stages of maturation, compared to PFOS alone. Glutamate-induced excitotoxicity was enhanced above the level of that induced by glutamate alone, especially in mature CGNs at DIV5. Glutathione (GSH) concentrations seemed to set the level of sensitivity for the toxic insults from exposures to the pollutants. The role of N-methyl-D-aspartate receptor (NMDA-R) mediated calcium influx in pollutant exposures was investigated using the non-competitive and competitive receptor antagonists MK-801 and CGP 39551. Observations indicate a calcium-independent, but still NMDA-R dependent mechanism in the absence of glutamate, and a calcium- and NMDA-R dependent one in the presence of glutamate. The outcomes for the POP mixture cannot be explained by PFOS alone, indicating that other chemicals in the mixture contribute its overall effect.

Opioid receptor-mediated changes in the NMDA receptor in developing rat and chicken.

The use of opioids during pregnancy has been associated with neurodevelopmental toxicity in exposed children, leading to cognitive and behavioural deficits later in life. The N-methyl-D-aspartate receptor (NMDAR) subunit GluN2B plays critical roles in cerebellar development, and methadone has been shown to possess NMDAR antagonist effect. Consequently, we wanted to explore if prenatal opioid exposure affected GluN2B subunit expression and NMDAR function in rat and chicken cerebellum. Pregnant rats were exposed to methadone (10 mg/kg/day) or buprenorphine (1 mg/kg/day) for the whole period of gestation, using an osmotic minipump. To further examine potential effects of prenatal opioid exposure in a limited time window, chicken embryos were exposed to a 20 mg/kg dose of methadone or morphine on embryonic days 13 and 14. Western blot analysis of cerebella isolated from 14 days old rat pups exposed to buprenorphine showed significantly lower level of the GluN2B subunit, while the opioid exposed chicken embryo cerebellar GluN2B expression remained unaffected at embryonic day 17. However, we observed increased NMDA/glycine-induced calcium influx in cerebellar granule neurone cultures from opioid exposed chicken embryos. We conclude that prenatal opioid exposure leads to opioid receptor-dependent reduction in the postnatal expression of GluN2B in rat cerebella, and increase in NMDA-induced calcium influx in chicken embryo cerebella.

Oligodendrocytes Do Not Export NAA-Derived Aspartate In Vitro.

Oligodendroglial cells are known to de-acetylate the N-acetylaspartate (NAA) synthesized and released by neurons and use it for lipid synthesis. However, the role of NAA regarding their intermediary metabolism remains poorly understood. Two hypotheses were proposed regarding the fate of aspartate after being released by de-acetylation: (1) aspartate is metabolized in the mitochondria of oligodendrocyte lineage cells; (2) aspartate is released to the medium. We report here that aspartoacylase mRNA expression increases when primary rat oligodendrocyte progenitor cells (OPCs) differentiate into mature cells in culture. Moreover, characterising metabolic functions of acetyl coenzyme A and aspartate from NAA catabolism in mature oligodendrocyte cultures after 5 days using isotope-labelled glucose after 5-days of differentiation we found evidence of extensive NAA metabolism. Incubation with [1,6-13C]glucose followed by gas chromatography-mass spectrometry and high performance liquid chromatography analyses of cell extracts and media in the presence and absence of NAA established that the acetate moiety produced by hydrolysis of NAA does not enter mitochondrial metabolism in the form of acetyl coenzyme A. We also resolved the controversy concerning the possible release of aspartate to the medium: aspartate is not released to the medium by oligodendrocytes in amounts detectable by our methods. Therefore we propose that: aspartate released from NAA joins the cytosolic aspartate pool rapidly and takes part in the malate-aspartate shuttle, which transports reducing equivalents from glycolysis into the mitochondria for ATP production and enters the tricarboxylic acid cycle at a slow rate.

System N transporters are critical for glutamine release and modulate metabolic fluxes of glucose and acetate in cultured cortical astrocytes: changes induced by ammonia.

Glutamine (Gln) is synthesized in astrocytes from glutamate (Glu) and ammonia, whereupon it can be released to be transferred to neurons. This study evaluated the as yet not definitely established role of the astrocytic Gln transporters SN1 and SN2 (Slc38a3 and Slc38a5 respectively) in Gln release and metabolic fluxes of glucose and acetate, the canonical precursors of Glu. Cultured neocortical astrocytes were grown in the absence or presence of ammonia (5 mM NH4 Cl, 24 h), which deregulates astrocytic metabolism in hyperammonemic encephalopathies. HPLC analyses of cell extracts of SN1/SN2 siRNA-treated (SN1/SN2-) astrocytes revealed a ~ 3.5-fold increase in Gln content and doubling of glutathione, aspartate, alanine and glutamate contents, as compared to SN1/SN2+ astrocytes. Uptake and efflux of preloaded [(3) H]Gln was likewise significantly decreased in SN1/SN2- astrocytes. The atom percent excess (13) C values (given as M + 1) for alanine, aspartate and glutamate were decreased when the SN1/SN2- cells were incubated with [1-(13) C] glucose, while Gln consumption was not changed. No difference was seen in M + 1 values in SN1/SN2- cells incubated with [2-(13) C] acetate, which were not treated with ammonia. In SN1/SN2- astrocytes, the increase in Gln content and the decrease in radiolabeled Gln release upon exposure to ammonia were found abrogated, and glutamate labeling from [2-(13) C]acetate was decreased as compared to SN1/SN2+ astrocytes. The results underscore a profound role of SN1 and/or SN2 in Gln release from astrocytes under physiological conditions, but less so in ammonia-overexposed astrocytes, and appear to manifest dependence of astrocytic glucose metabolism to Glu/Gln on unimpaired SN1/SN2- mediated Gln release from astrocytes. The astrocytic N system transporters SN1 and SN2 show preponderance to mediate glutamine (Gln) efflux. Under hyperammonemic conditions, accumulation of Gln, a direct product of ammonia detoxification, may deregulate astrocytic metabolism and seems to be responsible for astrocytic swelling. This study evaluated not definitely established role of SN1 and SN2 in Gln release and metabolic fluxes of radiolabeled glucose and acetate. Simultaneous silencing of SN1/SN2 transporters increase Gln, glutathione, aspartate, alanine and glutamate contents (Panel B; marked in red) as compare to non-silenced astrocytes (Panel A). The atom percent excess (13) C values (given as M + 1) for alanine, aspartate and glutamate were decreased when the cells with silenced transporters were incubated with [1-(13) C]glucose, whereas no difference was seen in M + 1 values when those cells were incubated with [2-(13) C]acetate. Ammonia abrogated the increase in Gln content and decrease in radiolabeled Gln release in astrocytes with silenced transporters, but caused a decrease in glutamate labeling from [2-(13) C]acetate.

Modification of Astrocyte Metabolism as an Approach to the Treatment of Epilepsy: Triheptanoin and Acetyl-L-Carnitine.

Epilepsy is a severe neurological disorder characterized by altered electrical activity in the brain. Important pathophysiological mechanisms include disturbed metabolism and homeostasis of major excitatory and inhibitory neurotransmitters, glutamate and GABA. Current drug treatments are largely aimed at decreasing neuronal excitability and thereby preventing the occurrence of seizures. However, many patients are refractory to treatment and side effects are frequent. Temporal lobe epilepsy (TLE) is the most common type of drug-resistant epilepsy in adults. In rodents, the pilocarpine-status epilepticus model reflects the pathology and chronic spontaneous seizures of TLE and the pentylenetetrazole kindling model exhibits chronic induced limbic seizures. Accumulating evidence from studies on TLE points to alterations in astrocytes and neurons as key metabolic changes. The present review describes interventions which alleviate these disturbances in astrocyte-neuronal interactions by supporting mitochondrial metabolism. The compounds discussed are the endogenous transport molecule acetyl-L-carnitine and the triglyceride of heptanoate, triheptanoin. Both provide acetyl moieties for oxidation in the tricarboxylic acid cycle whereas heptanoate is also provides propionyl-CoA, which after carboxylation can produce succinyl-CoA, resulting in anaplerosis-the refilling of the tricarboxylic acid cycle.

Astrocyte-neuronal interactions in epileptogenesis.

Pentylenetetrazol, kainic acid, or pilocarpine can be used to induce seizures in animal models of epilepsy. The present Review describes disturbances in astrocyte-neuron interactions in the acute, latent, and chronic phases analyzed by magnetic resonance spectroscopy of brain tissue extracts from rats injected with [1-(13)C]glucose and [1,2-(13)C]acetate. The most consistent change after onset of seizures was the decrease in (13)C labeling of glutamate (GLU) from [1-(13) C]glucose regardless of brain area, severity, or duration of the period with seizures and toxin used. In most cases this decrease was accompanied by a reduction in glutamine (GLN) labeling from [1-(13)C]glucose, presumably as a direct consequence of the reduction in labeling of GLU and the GLU-GLN cycle. Amounts of GLN were never changed. Reduction in the content of N-acetyl aspartate (NAA) was first detectable some time after status epilepticus but before the occurrence of spontaneous seizures. This decrease can be an indication of neuronal death and/or mitochondrial impairment and might indicate beginning gliosis. It is known that gliosis occurs in the chronic phase of temporal lobe epilepsy in hippocampus, but astrocyte metabolism appears normal in this phase, indicating that the gliotic astrocytes have a somewhat reduced metabolism per volume. A decrease in (13)C labeling of GLU from [1-(13)C]glucose is a very sensitive measure for the onset of epileptogenesis, whereas reduction of NAA is first detectable later. In the chronic phases of the hippocampal formation, astrocyte metabolism is upregulated given that the number of neurons is reduced.

The anticonvulsant actions of carisbamate associate with alterations in astrocyte glutamine metabolism in the lithium-pilocarpine epilepsy model.

As reported previously, in the lithium-pilocarpine model of temporal lobe epilepsy (TLE), carisbamate (CRS) produces strong neuroprotection, leads to milder absence-like seizures, and prevents behavioral impairments in a subpopulation of rats. To understand the metabolic basis of these effects, here we injected 90 mg/kg CRS or vehicle twice daily for 7 days starting 1 h after status epilepticus (SE) induction in rats. Two months later, we injected [1-13 C]glucose and [1,2-13 C]acetate followed by head microwave fixation after 15 min. 13 C incorporation into metabolites was analyzed using 13 C magnetic resonance spectroscopy. We found that SE reduced neuronal mitochondrial metabolism in the absence but not in the presence of CRS. Reduction in glutamate level was prevented by CRS and aspartate levels were similar to controls only in rats displaying absence-like seizures after treatment [CRS-absence-like epilepsy (ALE)]. Glutamine levels in CRS-ALE rats were higher compared to controls in hippocampal formation and limbic structures while unchanged in rats displaying motor spontaneous recurrent seizures after treatment (CRS-TLE). Astrocytic mitochondrial metabolism was reduced in CRS-TLE, and either enhanced or unaffected in CRS-ALE rats, which did not affect the transfer of glutamine from astrocytes to neurons. In conclusion, CRS prevents reduction in neuronal mitochondrial metabolism but its effect on astrocytes is likely key in determining outcome of treatment in this model. To understand the metabolic basis of the strong neuroprotection and reduction in seizure severity caused by carisbamate (CRS) in the lithium-pilocarpine (Li-Pilo) model of temporal lobe epilepsy (TLE), we injected CRS for 7 days starting 1 h after status epilepticus and 2 months later [1-13 C]glucose and [1,2-13 C]acetate. 13 C Magnetic resonance spectroscopy analysis was performed on brain extracts and we found that CRS prevented reduction in neuronal mitochondrial metabolism but its effect on astrocytes was likely key in determining outcome of treatment in this model. ALE = absence like epilepsy; acetyl CoA = acetyl coenzyme A; GS = glutamine synthetase; PAG = phosphate activated glutaminase; PC = pyruvate carboxylase; OAA = oxaloacetate; TCA cycle = tricarboxylic acid cycle.