Interaction of ascorbic acid with the neurotoxic effects of NMDA and sodium nitroprusside

Combination of nitrate and sodium nitroprusside dosing for sulfide control with low carbon source loss in sewer biofilm reactors

Nitrate has been widely used in sewer systems for sulfide control. However, significant chemical consumption and the loss of carbon source were observed in previous studies. To find a feasible and cost-effective control strategy of the sulfide control, the effect of nitrate combined with sodium nitroprusside (SNP) dosage strategy was tested in lab-scale sewer biofilm reactors. Results showed that nitrate and SNP were strongly synergistic, with 30 mg N/L nitrate and 20 mg/L SNP being sufficient for sulfide control in this study. While large amount of nitrate alone (100 mg N/L) is required to achieve the same sulfide control effectiveness. Meanwhile, the nitrate combined with SNP could reduce the organic carbon source loss by 80%. Additionally, the high-throughput sequencing results showed that the relative abundance of autotrophic, nitrate reducing-sulfide oxidizing bacteria genera (a-NR-SOB) such as Arcobacter and Sulfurimonas was increased by around 18%, while the heterotrophic, nitrate-reducing bacteria (hNRB) such as Thauera was substantially reduced. It demonstrated that the sulfide control was mainly due to the a-NR-SOB activity under the nitrate and SNP dosing strategy. The microbial functional prediction further revealed that nitrate and SNP promoted the dissimilatory nitrate reduction process which utilizes sulfide as an effective electron donor. Moreover, economic assessment indicated that using the combination of nitrate and SNP for sulfide control in sewers would lower the chemical costs by approximately 35% compared with only nitrate addition.

Old Things New View: Ascorbic Acid Protects the Brain in Neurodegenerative Disorders

Ascorbic acid is a key antioxidant of the Central Nervous System (CNS). Under brain activity, ascorbic acid is released from glial reservoirs to the synaptic cleft, where it is taken up by neurons. In neurons, ascorbic acid scavenges reactive oxygen species (ROS) generated during synaptic activity and neuronal metabolism where it is then oxidized to dehydroascorbic acid and released into the extracellular space, where it can be recycled by astrocytes. Other intrinsic properties of ascorbic acid, beyond acting as an antioxidant, are important in its role as a key molecule of the CNS. Ascorbic acid can switch neuronal metabolism from glucose consumption to uptake and use of lactate as a metabolic substrate to sustain synaptic activity. Multiple evidence links oxidative stress with neurodegeneration, positioning redox imbalance and ROS as a cause of neurodegeneration. In this review, we focus on ascorbic acid homeostasis, its functions, how it is used by neurons and recycled to ensure antioxidant supply during synaptic activity and how this antioxidant is dysregulated in neurodegenerative disorders.

Astrocytic-neuronal crosstalk: implications for neuroprotection from brain injury

The older neurocentric view of the central nervous system (CNS) has changed radically with the growing understanding of the many essential functions of astrocytes. Advances in our understanding of astrocytes include new observations about their structure, organization, function and supportive actions to other cells. Although the contribution of astrocytes to the process of brain injury has not been clearly defined, it is thought that their ability to provide support to neurons after cerebral damage is critical. Astrocytes play a fundamental role in the pathogenesis of brain injury-associated neuronal death, and this secondary injury is primarily a consequence of the failure of astrocytes to support the essential metabolic needs of neurons. These needs include K+ buffering, glutamate clearance, brain antioxidant defense, close metabolic coupling with neurons, and the modulation of neuronal excitability. In this review, we will focus on astrocytic activities that can both protect and endanger neurons, and discuss how manipulating these functions provides a novel and important strategy to enhance neuronal survival and improve the outcome following brain injury.

Increased expression of tumor necrosis factor-alpha in the rat hippocampus after acute homocysteine administration

Background and Purpose:

This paper evaluated the effect of acute homocysteine administration on inflammatory cytokine tumor necrosis factor-alpha (TNF-α) expression and neuronal apoptosis in the rat hippocampus and investigated the effects of vitamin C treatment on homocysteine-induced inflammation and neuronal death.

Methods:

Subjects were three-week-old, male Sprague-Dawley rats. Rats for the control group, we injected saline solution into the rats’ abdominal cavities for one week. Rats in the second group received 1 injection of homocysteine (11 mmol/kg) into their abdominal cavities after 1 week of saline solution administration. For the third group, we injected the rats with vitamin C (100 mg/kg) for a week, followed by 1 injection of homocysteine. The hippocampi were stained with an anti-TNF-α antibody, and apoptosis was evaluated using the TUNEL staining method.

Results:

The homocysteine-injected rats had strong TNF-α expression in every hippocampal region. Vitamin C significantly reduced TNF-α expression in the hippocampus’s CA1 region. Acute homocysteine administration did not cause apoptosis in the hippocampus.

Conclusions:

The pro-inflammatory cytokine TNF-α may mediate elevated homocysteine levels’ contributions to inflammatory reactions, and vitamin C has some protective effect on inflammatory reactions in the CA1 hippocampal region.

Effect of lead exposure on dopaminergic transmission in the rat brain

Lead is a neurotoxicant with known behavioral and neurochemical effects. In this study we attempted to relate the behavioral effects of lead to neurotransmission. Oral administration of 1000 ppm of lead acetate to young rats for 30 days caused a reduction in locomotor activity and stereotypic exploratory behavior during a 20 min testing period. This locomotor hypoactivity induced by lead was accompanied by a reduction in stereotypic behavior (sniffing, lickings, biting and grooming). These outcomes suggested that lead might interfere with catecholaminergic and particularly dopaminergic neurotransmission. Therefore, we examined the effect of the lead acetate on the uptake of dopamine in striatal synaptosomal preparations. The collected data showed a clear inhibition of the uptake of 3H-DA with an IC50 of 3.5 x 10(-5)M. This inhibition of the uptake of dopamine suggests that the behavioral effects of lead may be involved in dopaminergic neurotransmission.

Role of nitric oxide in ethanol-induced ascorbic acid release in striatum of freely moving mice

In the present study, in vivo brain microdialysis coupled with high performance liquid chromatography (HPLC) and electrochemical detection were used to evaluate the effects of either L-arginine (L-Arg), the substrate of nitric oxide synthase (NOS), Nomega-nitro-L-arginine methyl ester hydrochloride (L-NAME), a non-selective NOS inhibitor, or sodium nitroprusside (SNP), a donor of NO, on the ethanol-induced release of ascorbic acid (AA) in the striatum of freely moving mice. Drugs were administered intrastriatally via the microdialysis probe and ethanol (2-4 g/kg) was administered intraperitoneally. The results showed that L-arginine (1-10 mg/ml) had no effect on either the basal AA contents in striatal extracellular fluid or the ethanol-induced release of AA. L-NAME (10(-4) to 10(-3) mg/ml) and SNP (10(-4) to 10(-3) mg/ml) both reduced the basal AA concentrations in striatal extracellular fluid. L-NAME significantly inhibited ethanol-induced release of AA, while SNP only had a transient inhibitory effect on the ethanol-induced release of AA. SNP significantly increased dehydroascorbic acid (DHAA) contents and DHAA/AA ratio but had no effect on the total AA contents (AA and DHAA contents) in striatal extracellular fluid, while L-NAME had no effect on DHAA contents but decreased the total AA contents in striatal extracellular fluid. Only high concentration L-NAME induced a transient increase in DHAA/AA ratio. Our results suggest that nitric oxide (NO) might not directly be involved in the mechanism of ethanol-induced release of AA in mouse striatum.

Glutamate stimulates ascorbate transport by astrocytes

The concentrations of glutamate and ascorbate in brain extracellular fluid increase following seizure activity, trauma and ischemia. Extracellular ascorbate concentration also rises following intracerebral glutamate injection. We hypothesized that glutamate triggers the release of ascorbate from astrocytes. We observed in primary cultures of rat cerebral astrocytes that glutamate increased ascorbate efflux significantly within 30 min. The half-maximal effective concentration of glutamate was 180+/-30 microM. Glutamate-stimulated efflux of ascorbate was attenuated by hypertonic media. 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid inhibited both Na(+)-dependent glutamate uptake and ascorbate efflux. Two other inhibitors of volume-sensitive organic anion channels (1, 9-dideoxyforskolin and 5-nitro-2-(3-phenylpropylamino) benzoic acid) did not slow glutamate uptake but prevented stimulation of ascorbate efflux. Glutamate also stimulated the uptake of ascorbate by ascorbate-depleted astrocytes. In contrast, glutamate uptake was not affected by intracellular ascorbate, thus ruling out a putative glutamate-ascorbate heteroexchange mechanism. These results are consistent with activation by glutamate of ascorbate-permeant channels in astrocytes.

Ascorbic acid is neuroprotective against global ischaemia in striatum but not hippocampus: histological and voltammetric data

Following reports that ascorbic acid (AA) blocks NMDA receptors, we examined its possible neuroprotective properties in vivo (gerbil bilateral carotid artery occlusion model: BCAO) and in vitro (ischaemia-induced dopamine (DA) release in brain slices). Five minutes of BCAO caused substantial cell loss of 90-95% and 40-50% in gerbil CA1 hippocampus and striatum, respectively, measured in haematoxylin and eosin-stained sections, 5 days post-insult. AA (500 mg kg(-1) day(-1) i.p. for 312 days, first dose 1 h before occlusion) significantly (P<0.05) reduced striatal cell loss (from 40 to 13%) while only reducing CA1 cell loss from 95 to 88%. A lower dose (250 mg kg(-1) day(-1) i.p. for 312 days) was ineffective in either region. AA (750 mg kg(-1) day(-1) i.p. for 312 days) caused significant striatal protection (cell loss reduced from 49 to 20%) if treatment was initiated 1 h before occlusion. Initiation of treatment immediately post occlusion did not cause significant protection. Neither treatment regime protected CA1 hippocampus. In separate experiments we examined the effect of AA on DA release, monitored by voltammetry, in an in vitro model of striatal ischaemia. Four DA release variables were measured: T(on)--time from initiation of ischaemia to the onset of DA release, T(pk)--the time from onset of DA release to maximum, deltaDA/deltat--the mean rate of DA release and [DA](max)-- the maximum extracellular DA concentration. Control values in drug-naive slices were: T(on)=193+/-8 s, T(pk) = 24 +/- 4 s, [DA](max) = 69 +/- 6 microM and deltaDA/deltat = 4.2 +/- 0.7 microM s(-1) (means+/-S.E.M., n=15). 212 h pretreatment with AA (0.4 to 10 mM) did not affect T(on) or [DA](max) but increased T(pk) and decreased deltaDA/deltat (P<0.05) with an EC50 of 1.66 mM. NMDA (100 microM) shortened T(on). N-ethylmaleimide (20 microM) had no effect on the response to AA but potentiated the action of NMDA on T(on). AA (2 or 10 mM) had no effect on the response to NMDA. We conclude that AA is neuroprotective against global ischaemia in the striatum and that some of this action may be due to attenuation of ischaemia-induced DA release. This action is mediated neither by blockade of the NMDA receptor nor modulation of its redox status.

Involvement of the corticostriatal glutamatergic pathway in ethanol-induced ascorbic acid release in rat striatum

The mechanism of ethanol-induced ascorbic acid (AA) release in striatum is not well understood. In the present work, the possible involvement of NMDA receptors in the corticostriatal pathway was studied by microdialysis coupled to high performance liquid chromatography with electrochemical detection. Ethanol (3.0 g/kg i.p.) stimulated significant striatal AA release to more than 200% above the baseline. This effect of ethanol could be partially antagonized by amantadine, a non-selective NMDA receptor antagonist and dopamine releaser, at a dose of 200 mg/kg i.p. and significantly antagonized by MK-801, a non-competitive NMDA receptor antagonist, at the doses of 0.5 and 1.0 mg/kg i.p. Furthermore, deafferentation of the glutamatergic projection from cortex to striatum by undercutting the prefrontal cortex completely eliminated ethanol-induced AA release in rat striatum. The basal level of AA in striatum could only be reduced by high doses of MK-801, but not by low doses of MK-801, amantadine or decortication. The results further confirm that NMDA receptors are involved in ethanol-induced AA release and provide the first evidence for the necessity of the activation of corticostriatal glutamatergic pathway in ethanol-induced AA release in rat striatum.

Interaction of nitric oxide donors and ascorbic acid on D-[3H] aspartate efflux from rat striatal slices

There are conflicting reports in the literature concerning the neuroprotective effect of ascorbic acid on excitotoxic processes in which excessive glutamate release and nitric oxide are supposed to be major factors. To study the influence of ascorbate on the nitric oxide modulated glutamate release rat striatal slices, preloaded with the tritiated glutamate analog D-aspartate, were used. The high potassium-induced efflux of D-[3H]aspartate was concentration dependently stimulated by the nitric oxide donors sodium nitroprusside, S-nitroso-N-acetylpenicillamine (SNAP) or 5-amino 3-morpholinyl-1,2,3-oxadiazolium chloride (SIN-1), as well as by solutions of gaseous nitric oxide and, interestingly, by cyanide. Only the stimulation of D-[3H]aspartate release by SNAP and nitroprusside was affected by ascorbate in terms of a highly significant potentiation. Ascorbate was shown to exert its effect primarily by influencing the decomposition of these nitric oxide donors rather than by a direct interaction of ascorbate with nitric monoxide on glutamate release.

Free radicals in Alzheimer's dementia: currently available therapeutic strategies

Substantial evidence now exists that oxidative stress may play an important role in the etiopathogenesis of DAT. The different sources of oxidative stress in DAT are suggesting several pharmacological opportunities for influencing the disease. It is possible to distinguish 2 major types of possible therapeutic agents according to their pharmacological point of attack. 1. Radical scavengers, agents directly interacting with free radicals. Candidates of this type are gingko biloba, vitamins A, C, E and estrogen. 2. Antioxidants, which are able to prevent or decrease the production of free radicals by use of specific neuropharmacological properties. Candidates are selegiline, a MAO-B inhibitor well established in the therapy of Parkinson's disease, and tenilsetam, which is believed to be an AGE-inhibitor. Recent in vitro studies have demonstrated the efficacy of both types of therapeutic agents by preventing or delaying oxidative neural damage. Some clinical data exist regarding the antidementive properties particularly in terms of gingko biloba, selegiline and vitamin E. The efficacy studies about these compounds seem to indicate a promising future strategy in the therapy of DAT. But it is too early to draw definite conclusions since it is well known that all of our candidate substances do not act specifically as radical scavengers or antioxidants.