Changes in tryptophan and kynurenine pathway metabolites in the blood of children treated with ketogenic diet for refractory epilepsy.

PURPOSE: There is growing evidence to support the role of the kynurenine pathway in the anticonvulsant efficacy of ketogenic diets (KDs) in refractory epilepsy. The aim of the present study was to measure blood levels of tryptophan (TRP) and its kynurenine derivatives and correlate them with seizure reduction after starting the KD in children with refractory epilepsy. METHODS: Sixteen children (9 F/7 M; 7.1 ± 5.1 years) with refractory epilepsy were treated with the KDs. Clinical efficacy and metabolic ketosis were monitored throughout the study; blood levels of TRP, kynurenine (KYN), kynurenic acid (KYNA), and 3-OH-kynurenine (3-OH-KYN) were measured at 3, 6, and 12 months on the diet and compared to the pre-KD levels. RESULTS: Out of 16 children, 14 attained a ≥50% reduction (responders) in seizure frequency 3 months after starting the KD. In the 14 responders, TRP levels decreased numerically (18-25%) but not significantly (P = 0.077) compared to the pre-KD control values. KYN levels decreased significantly (30-57%; P = 0.001) compared to the pre-KD control levels while KYNA levels significantly increased (38-96%; P < 0.001). KYNA/KYN ratios significantly increased (100-323%; P = 0.003) while 3-OH-KYN levels (P = 0.680) and KYN/TRP ratios (P = 0.385) remained unchanged. Higher concentrations of KYNA and lower concentrations of KYN (P < 0.05) were found in patients who attained a higher reduction in seizure frequencies on the KD. CONCLUSIONS: We report a pattern of changes in the blood level of kynurenines in patients with refractory epilepsy who started the KD. The results of this study further support the role of specific kynurenines (e.g. KYNA) in the efficacy of the KD in refractory epilepsy.

Influence of picolinic acid on seizure susceptibility in mice.

BACKGROUND: The mechanism of drug resistance in epilepsy remains unknown. Picolinic acid (PIC) is an endogenous metabolite of the kynurenine pathway and a chelating agent added to dietary supplements. Both inhibitory and excitatory properties of PIC were reported. The aim of this study was to determine the influence of exogenously applied PIC upon the electroconvulsive threshold and the activity of chemical convulsants in eight models of epilepsy in mice. METHODS: All experiments were performed on adult male Swiss albino mice. Electroconvulsions were induced through ear clip electrodes. The electroconvulsive threshold (current strength necessary to induce tonic seizures in 50% of the tested group - CS50) was estimated for control animals and animals pretreated with PIC. To determine the possible convulsant activity of PIC, it was administered subcutaneously or intracerebroventricularly in increasing doses to calculate the CD50 values (doses of convulsants necessary to produce seizures in 50% of the animals). Chemical convulsions were induced by challenging the animals with increasing doses of convulsant to calculate the CD50 values. The following convulsants were used: 4-aminopyridine, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, bicuculline, N-methyl-d-aspartate, nicotine, pentylenetrazole, pilocarpine hydrochloride and strychnine nitrate. RESULTS: PIC significantly decreased the electroconvulsive threshold and, after intracerebroventricular injection, but not subcutaneous, produced convulsions. Of the studied convulsants, only the activity of pilocarpine hydrochloride was significantly enhanced by PIC. CONCLUSIONS: PIC enhances seizure activity and potentially may play a role in the pathogenesis of drug resistant epilepsy. Future studies should focus on the interactions between PIC and antiepileptic drugs.

Effect of oral administration of kynurenic acid on the activity of the peripheral blood leukocytes in mice.

Kynurenic acid (KYNA), an endogenous tryptophan metabolite, is a selective ligand of the GPR35 receptor, expressed mainly on the immune cells. In inflammatory conditions, by affecting this receptor, KYNA inhibits the synthesis of pro-inflammatory cytokines and probably protects tissues from oxidative damage. However, we lack data regarding the effect of exogenous KYNA on the activity of immune cells in healthy individuals. The objective of this study has been to determine the influence of kynurenic acid administered to mice in different doses (2.5, 25 or 250 mg/l) and for different time periods (3, 7, 14, 28 days) in drinking water, on the activity of their peripheral blood leukocytes. The determinations comprised the proliferative activity of lymphocytes (MTT assay) and the phagocytic activity as well as the respiratory burst activity of granulocytes and monocytes (Phagotest, Phagoburst). It was only the lowest KYNA dose that influenced the mitogenic response of lymphocytes, namely by increasing the proliferation of T cells. The impact on the phagocytic activity was varied with KYNA dose and administration time. However, all the KYNA doses significantly lowered the activity of oxidative burst in phagocytes, which was probably associated with its antioxidant properties. In the light of the research results, kynurenic acid may find applications as an immuno-modulating agent able to correct an excessive or insufficient response of phagocytizing cells, protecting an organism from oxidative stress.

Ketogenic diet increases concentrations of kynurenic acid in discrete brain structures of young and adult rats.

Targeting mechanisms that result in increased concentrations of kynurenic acid (KYNA) in the brain has been considered as a therapeutic approach for the treatment of epilepsy and certain neurodegenerative disorders. Recently, KYNA has been implicated in the effects produced by the high-fat and low-protein/carbohydrate ketogenic diet (KD) in a report demonstrating an increased production of KYNA in vitro by one of the ketone bodies, ß-hydroxybutyrate, elevated by the KD. To further explore this association, brain concentrations of KYNA were compared in young (3 weeks old) and adult (8-10 weeks old) rats that were chronically exposed to the KD and regular diet. Exposure to the KD resulted in the anticipated elevations of ß-hydroxybutyrate with accompanying decreases in glucose concentrations. In comparison to rats fed the regular diet, KYNA concentrations were significantly (p < 0.05) increased in the hippocampus (256 and 363% increase in young and adult rats, respectively) and in the striatum (381 and 191% increase in young and adult rats, respectively) in KD-fed rats. KD-induced increases in KYNA concentrations in young versus adult rats in the hippocampus and striatum were comparable (p > 0.05). Exposure to the KD had no effect on KYNA concentrations in the cortex of young and adult rats (p > 0.05). In summary, chronic exposure to the KD resulted in several-fold increases in KYNA concentrations in discrete brain structures in the rats. Thus, the relevant clinical question for further exploration is whether KD-induced increases in KYNA concentrations can translate into clinically significant improvements in neuropsychiatric diseases associated with KYNA hypofunction.

Content of transfluthrin in indoor air during the use of electro-vaporizers.

The quality of indoor air evokes increasing interest; however, no standards have been developed which determine the content of pesticides in the air of living space. At present, insecticides are increasingly more frequently applied to control household pests, flies, mosquitoes, termites and other harmful insects. In this study, the content of transfluthrin was measured indoors after the application of two consumer products containing this active substance, using commercially available electro-vaporizers. It was found that during the application of insecticides in the form of gel and liquid the mean concentration of transfluthrin in the air was 1.295-2.422 ug/m(3) and 3.817-5.227 ug/m(3), respectively. The concentration of an active agent in the air did not depend on the day of application. The concentration of transfluthrin was higher when used in the form of a liquid than a gel preparation. 18-24 hours after the discontinuation of the use of the preparation no active agent was found in the air. As long as the standards are developed regulating the content of insecticides in the air of living spaces and utility rooms, the most important method of preventing their potential hazardous effect is informing the users of these preparations about the occurrence of active substances in indoor air, and eventual risk of exposure to the effect of pesticides during their application at home.

A selective method for transfection of retinal ganglion cells by retrograde transfer of antisense oligonucleotides against kynurenine aminotransferase II.

PURPOSE: Intravitreal administration of specific antisense oligonucleotides (ODNs) effectively downregulates gene expression in the retina but does not modulate it exclusively in retinal ganglion cells (RGCs). Expression of kynurenine aminotransferase II (KAT II) in RGCs has been well described in the literature. We describe a new method for downregulating cellular KAT II expression via transfection of RGC by retrograde transfer of ODN. METHODS: Fluorescently labeled, specific ODNs against KAT II were injected into rats either intravitreally or into the superior colliculi. Fluorescence microscopy of retinal flat-mounts and radial sections was used to compare the location, duration, and degree of transfection for both methods of delivery. The effects of both methods on KAT II expression in RGCs were studied immunohistochemically with unlabeled ODN. Retinal kynurenic acid (KYNA) contents were measured using high pressure liquid chromatography (HPLC). RESULTS: After intravitreal injection, fluorescently labeled ODN reached all retinal layers, whereas injections into the superior colliculus resulted in transfection of the RGC layer alone. Immunohistochemistry showed that both methods of ODN application had a similar effect on downregulation of KAT II expression in RGC. Retinal KYNA content decreased significantly 4 days after both types of ODN administration. CONCLUSIONS: This study demonstrated that retrograde transfer of specific ODN into RGC is feasible and induces downregulation of KAT II cellular expression. This may become a useful tool for modulating gene expression in the retinal ganglion cell layer in vivo without direct transfer of ODN to other retinal cell layers.