The neuroprotective properties of calorie restriction, the ketogenic diet, and ketone bodies

Both calorie restriction and the ketogenic diet possess broad therapeutic potential in various clinical settings and in various animal models of neurological disease. Following calorie restriction or consumption of a ketogenic diet, there is notable improvement in mitochondrial function, a decrease in the expression of apoptotic and inflammatory mediators and an increase in the activity of neurotrophic factors. However, despite these intriguing observations, it is not yet clear which of these mechanisms account for the observed neuroprotective effects. Furthermore, limited compliance and concern for adverse effects hamper efforts at broader clinical application. Recent research aimed at identifying compounds that can reproduce, at least partially, the neuroprotective effects of the diets with less demanding changes to food intake suggests that ketone bodies might represent an appropriate candidate. Ketone bodies protect neurons against multiple types of neuronal injury and are associated with mitochondrial effects similar to those described during calorie restriction or ketogenic diet treatment. The present review summarizes the neuroprotective effects of calorie restriction, of the ketogenic diet and of ketone bodies, and compares their putative mechanisms of action.     

Comparison of seizure reduction and serum fatty acid levels after receiving the ketogenic and modified Atkins diet

The ketogenic diet (KD) and the modified Atkins diet are effective therapies for intractable epilepsy. We compared retrospectively the KD and modified Atkins diet in 27 children and also assessed serum long chain fatty acid profiles. After 3 months, using an intent-to-treat analysis, the KD was more successful, with >50% seizure reduction in 11/17 (65%) vs. 2/10 (20%) with the modified Atkins diet, p = 0.03. After 6 months, however, the difference was no longer significant: 7/17 (41%) vs. 2/10 (20%) (p = 0.24). We observed a preventive effect of both diets on the occurrence of status epilepticus. After 1 and 3 months of either diet, responders experienced a significant decrease in serum arachidonic acid concentration compared to non-responders. The KD and modified Atkins diet led to seizure reduction in this small pilot series, with slightly better results after 3 months with the KD, but not after 6 months. The decrease of serum arachidonic acid levels might be involved in the anticonvulsive effects of KD or modified Atkins diet.     

Dietary fat, ketosis, and seizure resistance in rats on the ketogenic diet

PURPOSE: Fat is the major component of the ketogenic diet (KD), yet no studies have examined whether the type of fat used in the diet can be optimized to provide additional benefits. The purpose of the present experiments was to compare the efficiency of different fats in inducing ketosis and affording seizure resistance. METHODS: The effects of KDs that incorporate lard, butter, medium-chain triglycerides (MCT), or flaxseed oil or a mixture of the latter three fats were examined in rats fed KD for up to 98 days. The maximal electroshock (MES) or pentylenetetrazole (PTZ) threshold tests were used to assess seizure susceptibility in two separate experiments. RESULTS: The rank order of induced ketosis was MCT > mixture > or = flaxseed oil > or = lard = butter > or = control. MES failed to reveal anticonvulsant effects, but the PTZ test indicated that up to 50% of rats fed the KD were seizure protected (p < 0.05). The measures of seizure protection, seizure incidence and score, did not correlate, however, with the level of ketosis in the range of 0. 7-5.2 mmol/L for beta-hydroxybutyrate. In the long-term study, flaxseed oil KD maintained stable ketosis throughout 98 days, whereas ketones declined with lard and butter KD to the control level. CONCLUSIONS: Seizure protection with the versions of the KD did not improve with the higher level of ketosis. The focus of the KD improvement, therefore, is not the achievement of higher ketosis per se but rather designing a diet that provides steady ketosis, exploits advantages of certain fats for neurological development or seizure protection via a nonketogenic mechanism, and is nutritionally balanced.     

A comparison of the ability of a 4:1 ketogenic diet and a 6.3:1 ketogenic diet to elevate seizure thresholds in adult and young rats

PURPOSE: The pentylenetetrazol (PTZ) infusion test was used to compare seizure thresholds in adult and young rats fed either a 4:1 ketogenic diet (KD) or a 6.3:1 KD. We hypothesized that both KDs would significantly elevate seizure thresholds and that the 4:1 KD would serve as a better model of the KD used clinically. METHODS: Ninety adult rats and 75 young rats were placed on one of five experimental diets: (a) a 4:1 KD, (b) a control diet balanced to the 4:1 KD, (c) a 6.3:1 KD, (d) a standard control diet, or (e) an ad libitum standard control diet. All subjects were seizure tested by using the PTZ infusion test. Blood glucose and beta-hydroxybutyrate (beta-OHB) levels were measured. RESULTS: Neither KD elevated absolute "latencies to seizure" in young or adult rats. Similarly, neither KD elevated "threshold doses" in adult rats. In young rats, the 6.3:1 KD, but not the 4:1 KD, significantly elevated threshold doses. The 6.3:1 KD group showed poorer weight gain than the 4:1 KD group when compared with respective controls. The most dramatic discrepancies were seen in young rats. CONCLUSIONS: "Threshold doses" and "latency to seizure" data provided conflicting measures of seizure threshold. This was likely due to the inflation of threshold doses calculated by using the much smaller body weights found in the 6.3:1 KD group. Ultimately, the PTZ infusion test in rats may not be a good preparation to model the anticonvulsant effects of the KD seen clinically, especially when dietary treatments lead to significantly mismatched body weights between the groups.     

Lack of benefit of linoleic and alpha-linolenic polyunsaturated fatty acids on seizure latency, duration, severity or incidence in rats

BACKGROUND: Polyunsaturated fatty acids have been reported to increase seizure threshold and to reduce seizure duration and severity in rats. OBJECTIVE: The purpose of the present study was to test the anticonvulsant effects of an essential fatty acid mixture containing linoleic and alpha-linolenic acids at a 4:1 ratio (SR-3 compound), using the pentylenetetrazol seizure model in Long-Evans hooded rats. RESULTS: There were no significant effects of SR-3 on seizure latency, duration or severity (P>0.05). There were also no significant differences in the incidence of myoclonic jerks, forelimb and hindlimb clonus, forelimb and hindlimb tonus or running fits in rats that received SR-3, as compared to control rats (P>0.05). CONCLUSION: Linoleic and alpha-linolenic polyunsaturated fatty acids have no beneficial effects on seizure latency, duration, average severity or incidence.     

Effects of acute valproic acid administration on carnitine plasma concentrations in epileptic patients

Serial plasma samples collected after an acute administration of valproic acid, (VPA, 15 mg/kg as oral solution) in epileptic patients were selected for this study. The plasma samples were selected from three different groups of patients; patients on phenobarbital and phenytoin with clinical VPA intolerance (group A); patients on phenobarbital and phenytoin without clinical VPA toxicity (group B); and patients without phenobarbital and phenytoin and without clinical VPA toxicity (group C). Plasma samples from 6 patients per group were analyzed for carnitines and ammonia. Ammonia levels during acute study increased significantly (P less than 0.05) in patients who experienced VPA intolerance, while no changes were found in the other patients. After acute VPA administration, total carnitine was unchanged but free carnitine was decreased (P less than 0.05) and carnitine esters were increased (P less than 0.05) in all groups of patients studied. No difference in carnitine profiles was seen between patients with or without evidence of VPA administration has an important effect on carnitine metabolism. However, unlike the acute effect on ammonia metabolism, this acute effect does not seem to be correlated with any associated antiepileptic therapy, nor does it predict clinical VPA intolerance.     

Intravenous infusion of docosahexaenoic acid increases serum concentrations in a dose-dependent manner and increases seizure latency in the maximal PTZ model

Docosahexaenoic acid (DHA) is an omega-3 polyunsaturated fatty acid (n − 3 PUFA) that has been shown to raise seizure thresholds in the maximal pentylenetetrazole model following acute subcutaneous (s.c.) administration in rats. Following s.c. administration, however, the dose–response relationship for DHA has shown an inverted U-pattern. The purposes of the present experiment were as follows: (1) to determine the pattern of serum unesterified concentrations resulting from the intravenous (i.v.) infusions of various doses of DHA, (2) to determine the time course of these concentrations following the discontinuation of the infusions, and (3) to determine whether seizure protection in the maximal PTZ model would correlate with serum unesterified DHA levels.Animals received 5-minute i.v. infusions of saline or 25, 50, 100, or 200 mg/kg of DHA via a cannula inserted into one of the tail veins. Blood was collected during and after the infusions by means of a second cannula inserted into the other tail vein (Experiment 1). A separate group of animals received saline or 12.5-, 25-, 50-, 100-, or 200 mg/kg DHA i.v. via a cannula inserted into one of the tail veins and were then seizure-tested in the maximal PTZ model either during infusion or after the discontinuation of the infusions.Slow infusions of DHA increased serum unesterified DHA concentrations in a dose-dependent manner, with the 200-mg/kg dose increasing the concentration approximately 260-fold compared with saline-infused animals. Following discontinuation of the infusions, serum concentrations rapidly dropped toward baseline, with half-lives of approximately 40 and 11 s for the 25-mg/kg dose and 100-mg/kg dose, respectively. In the seizure-tested animals, DHA significantly increased latency to seizure onset in a dose-dependent manner. Following the discontinuation of infusion, seizure latency rapidly decreased toward baseline. Overall, our study suggests that i.v. infusion of unesterified DHA results in transient anticonvulsant effects which parallel unesterified DHA serum concentrations.     

Effects of food restriction on the periodicity of corticosteroids in plasma and on monoamine concentrations in discrete brain nuclei

The concentrations of plasma corticosteroids and of norepinephrine, dopamine and serotonin in microdissected brain regions were measured at 08.00, 12.00 and 20.00 h in male rats fed ad libitum and in rats whose food intake was restricted to 09.30–11.30 h. In ad libitum fed animals, plasma corticosteroids were lowest at 08.00 and highest at 20.00 h. As demonstrated previously, restriction of food availability was associated with appearance of a peak in corticosteroids at 08.00 h. In ad libitum fed animals, serotonin and dopamine concentrations in the median eminence were higher at 20.00 than at 08.00 h. Restriction of food availability significantly decreased the levels of these neurotransmitters at 20.00 h. In the paraventricular nucleus, amygdala, and hippocampus of ad libitum fed animals, serotonin levels were lower at 20.00 than at 08.00 or 12.00 h. In food-shifted animals, this pattern was reversed so that lowest levels of serotonin occured at 08.00 and markedly elevated levels were observed at 12.00 and 20.00 h. No changes were noted in norepinephrine content of the median eminence or paraventricular nucleus of ad libitum fed or food restricted animals. These results indicate that the shift in the periodicity of corticosteroid secretion produced by a restricted feeding regime is accompanied by changes in the periodicity of neurotransmitter concentrations in specific regions of the brain, and that such patterns are dissimilar in different regions.     

Effects of neuroleptic treatment on symptoms of schizophrenia and plasma homovanillic acid concentrations

Measurement of plasma concentrations of the dopamine metabolite, homovanillic acid, is an indirect tool to assess changes in dopamine turnover in schizophrenic patients. Plasma homovanillic acid concentrations have been reported to decrease during neuroleptic treatment, with the decrement correlating with symptomatic improvement in symptoms of schizophrenia. The present study tested the hypothesis that neuroleptic drugs decrease plasma homovanillic acid concentrations in those schizophrenic patients who improve with administration of neuroleptic drugs but not in patients who fail to display a treatment response. Twenty schizophrenic men who remained drug free for at least 2 weeks were treated with 20 mg/d of haloperidol for 5 weeks. Symptoms and plasma homovanillic acid concentrations were assessed on the last drug-free day and weekly for 5 weeks. Mean plasma homovanillic acid concentrations decreased in the group of patients who responded to neuroleptic treatment and did not change in the group of patients who did not improve. These findings suggest that there may be a qualitative distinction between responders and nonresponders to dopamine antagonists.     

Effects of acute or chronic omega-3 and omega-6 polyunsaturated fatty acid treatment on behavioral, neuroendocrine and cytokine changes elicited by exogenous interleukin-1beta challenge

Chronic omega-3 or omega-6 polyunsaturated fatty acid (n-3; n-6 respectively) treatment attenuated human interleukin-1beta (hIL-1beta; 5.0 microg/kg)-elicited rise of circulating ACTH levels and attenuated the sickness behavior and locomotor suppression elicited by the cytokine. Furthermore, hIL-1beta markedly elevated circulating levels of plasma IL-6, an effect attenuated by n-3, but not n-6 treatment. Such protective effects were not evident upon short-term (3 day) n-3 exposure. These results demonstrate that long-term administration of either n-3 or n-6 confers protection against several neuroendocrinological, immunological and behavioral actions of hIL-1beta challenge, although in general the effects of n-3 were more pronounced.     

Effects of various direct or indirect dopamine agonists on the latency of the acoustic startle response in rats

Summary The effects of dopamine agonists were investigated on the latency of the acoustic startle response in male Wistar rats. Four indirect dopamine agonits were tested: GBR 12783 (5–20mg/kg), BTCP (5–20mg/kg), dexamphetamine (3–6mg/kg) and L-DOPA 100 mg/kg associated with benserazide 25 mg/kg; they induced an increase in startle latency. Apomorphine at a dose (50 g/kg) known to decrease dopaminergic transmissions, was ineffective on the startle response. On the contrary, at 0.6 or 2 mg/kg, apomorphine induced an increase in the startle latency. A similar effect was observed with bromocriptine at 10 mg/kg from the 10th min up to at least the 9th hour after treatment. The specific agonist of D2 receptors Ru 24926 (0.45 mg/kg) enhanced the startle latency as well as the specific agonist of D1 receptors SKF 38393 (10 mg/kg). The association of these drugs resulted in an apparent additivity of their individual effects. The effect of apomorphine (0.6 mg/kg) was only partially reduced by a high dose of the specific D2 antagonist amisulpride (80 mg/kg) and more clearly antagonized by the specific D1 antagonist SCH 23390 (50 g/kg). It is concluded that D2 and D1 receptors contribute to the increase in startle latency elicited by direct or indirect dopamine agonists.     

Effects of brain surgery and EEG operant conditioning on seizure latency following monomethylhydrazine intoxication in the cat

Monomethylhydrazine (MMH) is a highly convulsive methyl derivative of hydrazine. The generalized tonic-clonic seizures elicited by this compound are unusual because of a characteristic latent period between administration and seizures. Evidence indicates that the duration of this latent period can reflect seizure susceptibility in relation to this drug. In the present study this concept was utilized to evaluate the influence of chronic electrode implantation and subsequent EEG operant conditioning on seizure susceptibility in the cat. Thirty cats were studied in three groups of 10 each. One group consisted of unoperated animals, another of operated animals with a diversity of electrode placements and experimental treatments, and the third of operated animals provided with 3 months of sensorimotor EEG operant conditioning. The EEG pattern rewarded was rhythmic, 12 to 16 cps activity, termed the sensorimotor rhythm. Seizure response was measured as the latency, in minutes postinjection, to the onset of generalized tonic-clonic seizures following intraperitoneal administration of 10 mg/kg MMH. Operated animals with either no EEG conditioning or noncontingent conditioning showed significantly shorter and more stable seizure latencies than either the unoperated group or the operated group with sensorimotor-rhythm conditioning. These data indicate that the surgical procedures used increased seizure susceptibility in this paradigm, and that sensorimotor-rhythm operant conditioning countered this effect. Furthermore, the marked variability in seizure latencies noted among unoperated and trained animals suggested individual differences in seizure susceptibility and in response to operant conditioning, respectively.     

Twenty-four-hour rhythms of mitogenic responses, lymphocyte subset populations and amino acid content in submaxillary lymph nodes of growing male rats subjected to calorie restriction

Peripubertal male Wistar rats were submitted to a calorie restriction diet enriched in proteins and low in fat and carbohydrates for 4 weeks, and starting on day 35 of life. Mitogenic responses, lymphocyte subset populations, interferon (IFN)- gamma release and amino acid content were determined in submaxillary lymph nodes at six time intervals during the 24-h span. The diet employed completely arrested growth in growing rats. After caloric restriction, mean values of Con A response, lymph node T and CD4+ cell number and CD4+/CD8+ ratio augmented, whereas those of B cell number, IFN-gamma release and glutamine and glutamate concentration decreased. Calorie restriction modified 24-h rhythmicity of lymph node mitogenic responses to Con A and LPS, and of T, T-B, CD4+ and CD4+ -CD8+ lymph node cell subsets. It also changed the 24-h pattern of lymph node IFN-gamma release and glutamine, aspartate, glutamate and taurine lymph node content. Availability of nutrients presumably affects the mechanisms that modulate the circadian variation of immune responsiveness in growing rats.     

Effects of a single dose of erythropoietin on subsequent seizure susceptibility in rats exposed to acute hypoxia at P10

PURPOSE: To determine if posthypoxia treatment with erythropoietin (EPO) has protective effects against subsequent susceptibility to seizure related neuronal injury in rat pups subjected to acute hypoxia at P10. METHODS: Four groups of rats were manipulated at P10, as described below, then all received kainic acid (KA) (10 mg/kg i.p.) at P29: Hypoxia-NS-KA group (n = 11): subjected to acute hypoxia (down to 4% O2), and then immediately received saline i.p. Hypoxia-EPO-KA group (n = 10): subjected to acute hypoxia and then immediately received EPO (1,000 U/Kg i.p.). Normoxia-NS-KA group (n = 11): sham manipulated and injected with saline. Normoxia-EPO-KA group (n = 10): sham manipulated then immediately injected with EPO (1000 U/Kg i.p.). After receiving KA at P29, all rats were monitored using videotape techniques, and were sacrificed at P31. TUNEL and Hoechst stains to assess for apoptosis, and regular histology for hippocampal cell counts were performed. RESULTS: Administration of the single dose of erythropoietin directly after an acute hypoxic event at P10 resulted at P29 in increased latency to forelimb clonus seizures, reduced duration of these seizures, protection against hippocampal cell loss, and decreased hippocampal apoptosis in the Hypoxia-EPO-KA group as compared to the Hypoxia-NS-KA group. CONCLUSION: These data support the presence of favorable protective effects of erythropoietin against the long-term consequences of acute hypoxia in the developing brain and raise the possibility of its investigation as a potential neuroprotective agent after human neonatal hypoxic encephalopathy.     

The influence of seizure type on the efficacy of plasma concentrations of phenytoin, phenobarbital, and carbamazepine

Plasma concentrations of phenytoin, phenobarbital, or carbamazepine were monitored prospectively during successful single-drug therapy in 78 patients who had various types of epileptic seizures. Mean plasma concentrations necessary for complete control of tonic-clonic seizures alone were as follows: phenytoin, 14 micrograms/mL (n = 28); phenobarbital, 18 micrograms/mL (n = 10); and carbamazepine, 5.5 micrograms/mL (n = 2). Epilepsy with simple or complex partial seizures alone or together with tonic-clonic seizures was completely controlled at the following plasma concentrations: phenytoin, 23 micrograms/mL (n = 25); phenobarbital, 37 micrograms/mL (n = 5); and carbamazepine, 7 micrograms/mL (n = 7). Higher plasma concentrations of phenytoin, phenobarbital, and carbamazepine are necessary for control in epilepsy with simple or complex partial seizures compared with epilepsy with tonic-clonic seizures alone. The efficacy of plasma concentrations of phenytoin, phenobarbital, and carbamazepine varies with the type of seizure.     

厄贝沙坦对急性脑梗死患者血浆溶血磷脂酸、内皮素-1和血清一氧化氮含量的影响

目的研究厄贝沙坦对急性脑梗死患者血浆溶血磷脂酸（LPA）、内皮素-1（ET-1）和血清一氧化氮（NO）含量的影响。方法将53例急性脑梗死患者随机分为厄贝沙坦治疗组（25例）和常规治疗组（28例）,并以23例非脑血管病患者和7名健康志愿者作为对照组。厄贝沙坦治疗组给予厄贝沙坦150mg＋阿司匹林100mg,常规治疗组给予阿司匹林100mg,每天1次,其余治疗方法相同,连续治疗14d。分别在治疗前后抽取静脉血检测LPA、ET-1和NO含量,并对两脑梗死组治疗前后进行神经功能缺损程度评分（NDS）。结果（1）脑梗死患者血LPA、ET-1含量较对照组显著升高（均P〈0.05）,NO含量显著降低（P〈0.05）;NDS与NO含量呈负相关（r=-0.4345,P〈0.05）。（2）厄贝沙坦治疗组和常规治疗组治疗后血LPA、ET-1含量和NDS较治疗前显著降低（均P〈0.05）,NO含量显著升高（均P〈0.05）。（3）治疗后厄贝沙坦治疗组与常规治疗组相比,血LPA、ET-1、NO含量改善更为明显（均P〈0.05）。结论厄贝沙坦能显著降低急性脑梗死患者血LPA、ET-1含量,提高血NO水平,显示其有抗血小板活化及内皮保护作用。