Kainic acid causes redox changes in cerebral cortex extracellular fluid: NMDA receptor activity increases ascorbic acid whereas seizure activity increases uric acid

The value of serum uric acid levels to differentiate causes of transient loss of consciousness

BACKGROUND

Generalized tonic-clonic seizures (GTCS), syncope, and psychogenic nonepileptic seizures (PNES) are common emergent neurological conditions that cause transient disturbances of consciousness; however, it is sometimes difficult to distinguish them.

OBJECTIVE

This study aimed to explore the value of serum uric acid levels in differentiating among GTCS, syncope, and PNES by analyzing serum uric acid levels in patients with GTCS, syncope, and PNES.

METHODS

A total of 391 patients were retrospectively analyzed. Venous blood was drawn from the patients within 20 min of their arrival to the emergency department; serum uric acid levels were measured using the uricase method.

RESULTS

Serum uric acid levels and the percentage of patients with elevated uric acid (elevation percentage) were significantly higher in the group with GTCS (n = 179) than in the groups with syncope (n = 156) (p < 0.001) and PNES (n = 56) (p < 0.001). The result remained the same when the serum uric acid level of male or female patients in the group with GTCS were compared separately with that in the other two groups (all p < 0.001). In the group with GTCS, both the serum uric acid level (p < 0.001) and elevation percentage (p < 0.05) were significantly higher in males than in females. The receiver operating characteristics (ROC) analysis in male patients yielded a serum uric acid value of 428.50 μmol/L with a sensitivity of 0.78 and a specificity of 0.99 as the optimal cutoff value to distinguish GTCS from other events. In female patients, a cutoff value of 338.00 μmol/L had a sensitivity of 0.69 and a specificity of 0.91 to distinguish GTCS from other events. For the group with GTCS, the period of time between the onset of seizure and serum uric acid levels dropping to normal were analyzed in 40 patients. The duration was 44.56 ± 11.46 h for males (n = 23) and 40.37 ± 9.78 h for females (n = 17) with no significant difference (p = 0.325).

CONCLUSION

Serum uric acid levels provided certain clinical value for the differentiation of GTCS, syncope, and PNES; however, this requires verification in prospective studies with larger sample sizes.

Functional interaction between N-methyl-D-aspartate receptor and ascorbic acid during neuropathic pain induced by chronic constriction injury of the sciatic nerve

BACKGROUND

Neuropathic pain is a chronic pain condition, which is resistant to therapy. Ascorbate was released because of the activation of glutaminergic neurons. Due to the important role of N-methyl-D-aspartate (NMDA) receptors in the pathophysiology of neuropathic pain, this study investigated the analgesic efficacy of ascorbic acid (AA) in neuropathic pain condition and the role of NMDA receptors in this effect.

METHODS

For this purpose, adult male rats were randomly allocated to experimental groups (n=8 in each group). Neuropathic pain was induced by chronic constriction injury (CCI) of the sciatic nerve. During the second week after CCI, animals received a single injection of 1, 3, 5, or 10 mg/kg of AA intraperitoneally and pain threshold was determined 15 and 60 min later. The antinociceptive effect of chronic administration was also evaluated by intraperitoneal injection (IP) of 3 mg/kg AA for 3 weeks. To determine the role of NMDA receptors, separate groups of animals 30 min after single injection of AA (1 mg/kg) animals received i.p. injection of ketamine (5 mg/kg), MK-801 (0.01 mg/kg), or glutamate (1000 nmol) and were tested 20 min afterwards. Data analyzed by ANOVA and Newman-Keuls tests and p<0.05 were considered as significant.

RESULTS

IP of 3, 5 and 10 mg/kg increased the pain threshold during the second week after CCI (p<0.05, F=3 in tactile allodynia and p<0.01, F=3.2 in thermal and mechanical hyperalgeisa). Chronic administration of AA also produced antinociceptive effect. Ascorbic acid (1 mg/kg, i.p.) inhibited MK-801 and ketamine-induced antinociception response significantly (p<0.001, F=2). It also prevented the analgesic effect of glutamate administration (p<0.001, F=2).

CONCLUSIONS

The results indicated that AA produced a dose-dependent antinociceptive effect that seems to mediate through its interaction with NMDA receptors.

Uric acid and allopurinol aggravate absence epileptic activity in Wistar Albino Glaxo Rijswijk rats

Uric acid has a role in several physiological and pathophysiological processes. For example, uric acid may facilitate seizure generalization while reducing uric acid level may evoke anticonvulsant/antiepileptic effects. Allopurinol blocks the activity of xanthine oxidase, by which allopurinol inhibits catabolism of hypoxanthine to xanthine and uric acid and, as a consequence, decreases the level of uric acid. Although the modulation of serum uric acid level is a widely used strategy in the treatment of certain diseases, our knowledge regarding the effects of uric acid on epileptic activity is far from complete. Thus, the main aim of this study was the investigation of the effect of uric acid on absence epileptic seizures (spike-wave discharges: SWDs) in a model of human absence epilepsy, the Wistar Albino Glaxo/Rijswijk (WAG/Rij) rat. We investigated the influence of intraperitoneally (i.p.) injected uric acid (100 mg/kg and 200 mg/kg), allopurinol (50 mg/kg and 100 mg/kg), a cyclooxygenase 1 and 2 (COX-1 and COX-2) inhibitor indomethacin (10 mg/kg) and inosine (500 mg/kg) alone and the combined application of allopurinol (50 mg/kg) with uric acid (100 mg/kg) or inosine (500 mg/kg) as well as indomethacin (10 mg/kg) with uric acid (100 mg/kg) and inosine (500 mg/kg) with uric acid (100 mg/kg) on absence epileptic activity. We demonstrated that both uric acid and allopurinol alone significantly increased the number of SWDs whereas indomethacin abolished the uric acid-evoked increase in SWD number. Our results suggest that uric acid and allopurinol have proepileptic effects in WAG/Rij rats.

Uric acid is released in the brain during seizure activity and increases severity of seizures in a mouse model for acute limbic seizures

Recent evidence points at an important role of endogenous cell-damage induced pro-inflammatory molecules in the generation of epileptic seizures. Uric acid, under the form of monosodium urate crystals, has shown to have pro-inflammatory properties in the body, but less is known about its role in seizure generation. This study aimed to unravel the contribution of uric acid to seizure generation in a mouse model for acute limbic seizures. We measured extracellular levels of uric acid in the brain and modulated them using complementary pharmacological and genetic tools. Local extracellular uric acid levels increased three to four times during acute limbic seizures and peaked between 50 and 100 min after kainic acid infusion. Manipulating uric acid levels through administration of allopurinol or knock-out of urate oxidase significantly altered the number of generalized seizures, decreasing and increasing them by a twofold respectively. Taken together, our results consistently show that uric acid is released during limbic seizures and suggest that uric acid facilitates seizure generalization.

Vitamin C: a new auxiliary treatment of epilepsy?

Although many approaches to the therapy of epilepsy exist, most of antiepileptic drugs, beside certain and unquestioned benefits, have convinced disadvantages. That is the reason for looking for new methods of treatment. Ascorbic acid, as an antioxidant and electron donor accumulated in central nervous system, seems to take part in diminishing reactions of oxidative stress in brain and cooperate with other antioxidants like alpha-tocoferol. Vitamin C, easily transported through the blood-brain barrier, is proved to reduce injury in the hippocampus during seizures. Depending on type of seizures, it has mostly inhibitory activity and even decreases mortality. Moreover, vitamin C acts as a neuroprotective factor by consolidating cell membranes and decreasing lipid peroxidation. A possible adjunctive role of vitamin C in epileptic patients needs to be considered.

Inhibitory action of antioxidants (ascorbic acid or α-tocopherol) on seizures and brain damage induced by pilocarpine in rats

Temporal lobe epilepsy is the most common form of epilepsy in humans. Oxidative stress is a mechanism of cell death induced by seizures. Antioxidant compounds have neuroprotective effects due to their ability to inhibit free radical production. The objectives of this work were to comparatively study the inhibitory action of antioxidants (ascorbic acid or α-tocopherol) on behavioral changes and brain damage induced by high doses of pilocarpine, aiming to further clarify the mechanism of action of these antioxidant compounds. In order to determinate neuroprotective effects, we studied the effects of ascorbic acid (250 or 500 mg/kg, i.p.) and α-tocopherol (200 or 400 mg/kg, i.p.) on the behavior and brain lesions observed after seizures induced by pilocarpine (400 mg/kg, i.p., P400 model) in rats. Ascorbic acid or α-tocopherol injections prior to pilocarpine suppressed behavioral seizure episodes. These findings suggested that free radicals can be produced during brain damage induced by seizures. In the P400 model, ascorbic acid and α-tocopherol significantly decreased cerebral damage percentage. Antioxidant compounds can exert neuroprotective effects associated with inhibition of free radical production. These results highlighted the promising therapeutic potential of ascorbic acid and α-tocopherol in treatments for neurodegenerative diseases.

The Effects of Ascorbic Acid on Penicillin-induced Epileptiform Activity in Rats

PURPOSE

Epileptic seizure results from excessive discharge in a population of hyperexcitable neurons. A number of studies help to document the effects of active oxygen free radical scavengers such as alpha-tocopherol or ascorbic acid (vitamin C). In the present study, we examined the effects of ascorbic acid, at the six different doses, on penicillin-induced epileptiform activity.

METHODS

A single microinjection of penicillin (2.5 microl, 500 units, intracortically) into the left sensorimotor cortex induced epileptiform activity within 2-5 min, progressing to full seizure activity lasting approximately 3-5 h. In the first set of experiments, 30 min after penicillin injection, six different doses of ascorbic acid (25, 50, 100, 200, 400, or 800 mg/kg) were administered intraperitoneally (IP). The other group of animals received the effective dose of ascorbic acid (100 mg/kg, IP) for 7 days. Ascorbic acid administration was stopped 24 h before penicillin treatment. Another group of rats received the effective dose of ascorbic acid (100 mg/kg, IP) 30 min before penicillin treatment. In the second set of experiments, the lipid peroxidation (MDA) and reduced glutathione (GSH) levels of brain were measured in the control, control + ascorbic acid, penicillin, and penicillin + ascorbic acid groups.

RESULTS

Ascorbic acid, at the low dose (50, 100 mg/kg, 30 min after penicillin injection), decreased both the frequency and amplitude of penicillin-induced epileptiform activity in rats. Ascorbic acid, at intermediate doses (200, 400 mg/kg, 30 min after penicillin injection), decreased the frequency of epileptiform activity without changing the amplitude. Ascorbic acid, at the lowest dose (25 mg/kg) and highest dose (800 mg/kg) (30 min after penicillin injection), did not change either the frequency or amplitude of epileptiform activity. Ascorbic acid, at the low dose (100 mg/kg) was the most effective dose in changing the frequency and amplitude of penicillin-induced epileptiform activity. Pretreatment with ascorbic acid (100 mg/kg) 30 min before penicillin treatment caused a significant delay in the onset of penicillin-induced epileptiform activity. Pretreatment with ascorbic acid (100 mg/kg) for 7 days did not change the latency of epileptiform activity. The most effective dose of ascorbic acid (100 mg/kg) prevented both the decrease in GSH level and the increase in lipid peroxidation level (MDA) occurring after penicillin-induced epileptiform activity.

CONCLUSIONS

These data indicate that ascorbic acid has neuroprotective activity against penicillin-induced epileptiform electrocorticogram activity.

Soman-induced seizures: limbic activity, oxidative stress and neuroprotective proteins

Soman, a potent acetylcholinesterase inhibitor, induces status epilepticus in rats followed by conspicuous neuropathology, most prominent in piriform cortex and the CA3 region of the hippocampus. Cholinergic seizures originate in striatal-nigral pathways and with fast-acting agents (soman) rapidly spread to limbic related areas and finally culminate in a full-blown status epilepticus. This leads to neurochemical changes, some of which may be neuroprotective whereas others may cause brain damage. Pretreatment with lithium sensitizes the brain to cholinergic seizures. Likewise, other agents that increase limbic hyperactivity may sensitize the brain to cholinergic agents. The hyperactivity associated with the seizure state leads to an increase in intracellular calcium, cellular edema and metal delocalization producing an oxidative stress. These changes induce the synthesis of stress-related proteins such as heat shock proteins, metallothioneins and heme oxygenases. We show that soman-induced seizures cause a depletion in tissue glutathione and an increase in tissue 'catalytic' iron, metallothioneins and heme oxygenase-1. The oxidative stress induces the synthesis of stress-related proteins, which are indicators of 'stress' and possibly provide neuroprotection. These findings suggest that delocalization of iron may catalyze Fenton-like reactions, causing progressive cellular damage via free radical products.

Novel role for the NMDA receptor redox modulatory site in the pathophysiology of seizures

Redox-active compounds modulate NMDA receptors (NMDARs) such that reduction of NMDAR redox sites increases, and oxidation decreases, NMDAR-mediated activity. Because NMDARs contribute to the pathophysiology of seizures, redox-active compounds also may modulate seizure activity. We report that the oxidant 5, 5'-dithio-bis(2-nitrobenzoic acid) (DTNB) and the redox cofactor pyrroloquinoline quinone (PQQ) suppressed low Mg(2+)-induced hippocampal epileptiform activity in vitro. Additionally, in slices exposed to 4-7 microM bicuculline, DTNB and PQQ reversed the potentiation of evoked epileptiform responses by the reductants dithiothreitol and Tris(2-carboxyethyl)phosphine (TCEP). NMDA-evoked whole-cell currents in CA1 neurons in slices were increased by TCEP and subsequently decreased by DTNB or PQQ at the same concentrations that modulated epileptiform activity. However, DTNB and PQQ had little effect on baseline NMDA-evoked currents in control medium, and PQQ did not alter NMDAR-dependent long-term potentiation. In contrast, in slices returned to control medium after low Mg(2+)-induced ictal activity, DTNB significantly inhibited NMDAR-mediated currents, indicating endogenous reduction of NMDAR redox sites under this epileptogenic condition. These data suggested that PQQ and DTNB suppressed spontaneous ictal activity by reversing pathological NMDAR redox potentiation without inhibiting physiological NMDAR function. In vivo, PQQ decreased the duration of chemoconvulsant-induced seizures in rat pups with no effect on baseline behavior. Our results reveal endogenous potentiation of NMDAR function via mass reduction of redox sites as a novel mechanism that may enhance epileptogenesis and facilitate the transition to status epilepticus. The results further suggest that redox-active compounds may have therapeutic use by reversing NMDAR-mediated pathophysiology without blocking physiological NMDAR function.