Modulation of benzodiazepine by lysine and pipecolic acid on pentylenetetrazol-induced seizures

Synthesis and Biological Evaluation of Amino Acid Based Mutual Amide Prodrugs of Phenytoin as Anticonvulsant Agents

BACKGROUND

Phenytoin (5,5-diphenyl hydantoin) has poor water solubility, which results in incomplete oral availability. Other problems associated with the oral and intramuscular administration of phenytoin are gastric irritation and inflammation at the site of injection.

OBJECTIVE

The purpose of this study was to synthesize mutual amide prodrugs of phenytoin by using amino acids like glycine, L-tryptophan, L-lysine and taurine.

METHODS

These prodrugs were synthesized and characterized by Fourier Transform Infrared (FTIR), Proton nuclear magnetic resonance (1H NMR) and Mass Spectra. Physical and spectral characterization was performed by determination of solubility, maximum wavelength, partition coefficient (log P), ionization constant (pKa), specific (α) and molar rotation (μ), refractive index (n), specific refraction (RS) and molar refraction (RM).

RESULTS

The results obtained from solubility and log P values determination indicated that phenytoin prodrugs can be administered by oral as well as a parenteral route by minimizing the limitations associated with phenytoin. Anticonvulsant activity of prodrugs (4a-4d) was evaluated by using maximal electroshock (MES) and strychnine induced seizure test on albino mice of either sex weighing 25-30 g in which 4b and 4d were found to have significant anticonvulsant activity for MES and strychnine induced seizure test. In vitro enzymatic hydrolysis study of 4b and 4d was performed on liver, intestinal mucosa and plasma sample of male Sprague Dawley rats weighing 280-300 g in which phenytoin was eluted at 10.13 to 10.68 minutes at 220 nm.

CONCLUSION

The results obtained from the present work showed that amino acid-based mutual prodrug strategy can be a promising method to increase the solubility and anticonvulsant activity of phenytoin for the development of anticonvulsant agents.

Homostachydrine is a Xenobiotic Substrate of OCTN1/SLC22A4 and Potentially Sensitizes Pentylenetetrazole-Induced Seizures in Mice

Understanding of the underlying mechanism of epilepsy is desired since some patients fail to control their seizures. The carnitine/organic cation transporter OCTN1/SLC22A4 is expressed in brain neurons and transports food-derived antioxidant ergothioneine (ERGO), L-carnitine, and spermine, all of which may be associated with epilepsy. This study aimed to clarify the possible association of this transporter with epileptic seizures. In both pentylenetetrazole (PTZ)-induced acute seizure and kindling models, ocnt1 gene knockout mice (octn1^-/-) showed lower seizure scores compared with wild-type mice. Up-regulation of the epilepsy-related genes, c-fos and Arc, and the neurotrophic factor BDNF following PTZ administration was observed in the hippocampus of wild-type, but not octn1^-/- mice. To find the OCTN1 substrate associated with the seizure, untargeted metabolomics analysis using liquid chromatography-quadrupole time-of-flight mass spectrometry was conducted on extracts from the hippocampus, frontal cortex, and plasma of both strains, leading to the identification of a plant alkaloid homostachydrine as a compound present in a lower concentration in octn1^-/- mice. OCTN1-mediated uptake of deuterium-labeled homostachydrine was confirmed in OCTN1-transfected HEK293 cells, suggesting that this compound is a substrate of OCTN1. Homostachydrine administration increased PTZ-induced acute seizure scores and the expression of Arc in the hippocampus and that of Arc, Egr1, and BDNF in the frontal cortex. Conversely, administration of the OCTN1 substrate/inhibitor ERGO inhibited PTZ-induced kindling and reduced the plasma homostachydrine concentration. Thus, these results suggest that OCTN1 is at least partially associated with PTZ-induced seizures, which is potentially deteriorated by treatment with homostachydrine, a newly identified food-derived OCTN1 substrate.

Evaluation of the Effects of Charged Amino Acids on Uncontrolled Seizures

Introduction. Epilepsy is one of the most common diseases of the central nervous system. The prevalence of epilepsy throughout the world is 0.5 to 1%, and the same rate is 7.8 per 1000 in Kerman. Almost 20 to 30% of epileptic patients do not respond properly to common medications. The present study investigated patients who did not respond to common and, even in some cases, adjuvant therapies, with two seizures or more per week, regardless of the type of the inflicted epilepsy. Methodology. The participants of the present double-blind study were randomly selected into three 10-member groups of uncontrolled epileptic patients (arginine, glutamic acid, and lysine). The patients used amino acid powder dissolved in water (three times the daily need) every day for two weeks before breakfast. The number of seizures was recorded one week prior to commencing amino acid use, as well as the first and the second weeks subsequent to use. Results. A total of 32 patients were studied in three groups. The decline rates of seizures were 53%, 41%, and 13%, and the P value was 0.013, 0.027, and 0.720, respectively. Conclusion. Administration of the charged amino acids, arginine, and glutamic acid can decrease the seizures of patients suffering from uncontrolled epilepsy.

Determination of D- and L-pipecolic acid in food samples including processed foods

BACKGROUND

Pipecolic acid, a metabolite of lysine, is found in human physiological fluids and is thought to play an important role in the central inhibitory gamma-aminobutyric acid system. However, it is unclear whether plasma D- and L-pipecolic acid originate from oral food intake or intestinal bacterial metabolites.

METHODS

We analyzed the contents of D- and L-pipecolic acid in several processed foods including dairy products (cow's milk, cheese and yogurt), fermented beverages (beer and wine) and heated samples (beef, bovine liver, bread and tofu) to clarify the relationship between plasma D- and L-pipecolic acid and dietary foods.

RESULTS

Our study revealed that some of the samples contained high concentrations of total pipecolic acid, and a higher proportion of L- than D-isomers. The other samples also showed high proportions of L-pipecolic acid. It was also shown that there is no significant change in the ratio of the D-isomer before and after heat treatment. The heat treatments could not cause the racemization of pipecolic acid in this study.

CONCLUSION

These findings suggest that plasma pipecolic acid, particularly the D-isomer, does not originate from direct food intake and that D- and L-pipecolic acid can possibly be derived from intestinal bacterial metabolites.

Plasma levels of pipecolic acid, both L- and D-enantiomers, in patients with chronic liver diseases, especially hepatic encephalopathy

Pipecolic acid is regarded as a gamma-aminobutyric acid receptor agonist. Stereochemical studies of pipecolic acid were performed in patients with chronic liver diseases. Plasma D- and L-pipecolic acid were significantly elevated in 15 liver cirrhotic patients with no history of hepatic encephalopathy (1.05+/-0.24 micromol/l, 1.58+/-0.13 micromol/l, p < 0.01) and in 27 patients with chronic hepatic encephalopathy (1.58+/-0.50 micromol/l, 2.38+/-0.58 micromol/l, p<0.001) compared to 15 normal subjects. In seven patients with chronic hepatic encephalopathy orally treated with kanamycin, plasma pipecolic acid significantly decreased (D-acid: before 1.62+/-0.23 micromol/l, after 0.61+/-0.15 micromol/l; p<0.01, L-acid: before 2.43-0.52 micromol/l, after 2.23+/-0.11 micromol/l; p< 0.05). These results suggest that plasma pipecolic acid, particularly D-acid, is produced from D-lysine by intestinal bacteria in liver cirrhotic patients and that pipecolic acid could be involved in the pathogenesis of hepatic encephalopathy.

Origin of D- and L-pipecolic acid in human physiological fluids: a study of the catabolic mechanism to pipecolic acid using the lysine loading test

Pipecolic acid, a metabolite of lysine, is found in human physiological fluids. It is known that plasma pipecolic acid levels are elevated in patients with Zellweger syndrome, a genetic disorder, and chronic liver diseases. However, it is uncertain if this acid originates directly from food intake or from mammalian or intestinal bacterial enzyme metabolism. To characterize the relationship between plasma pipecolic acid and diet, we analyzed the contents of pipecolic acid in 17 edible plants and changes in plasma and urinary pipecolic acid levels following soybean juice ingestion by 4 healthy volunteers. Our study revealed that some of the plants contained high concentrations of total pipecolic acid, and a higher portion of L-isomer than D-isomer. Loading tests demonstrated that plasma levels and urinary excretion of D-isomer increased significantly 2 h after soybean juice ingestion. Plasma lysine levels showed a similar increase to that of D-isomer. These findings suggest that plasma pipecolic acid, particularly the D-isomer, originates mainly from the catabolism of dietary lysine by intestinal bacteria rather than by direct food intake and that D- and L-isomer may have different mechanisms of metabolism. Moreover, these findings may be important for clarifying the pathogenesis of peroxisomal disorders.

Epoxide derivatives of pipecolic acid and proline are inhibitors of pipecolate oxidase

The cis-4,5-epoxide derivative of L-pipecolic acid (2S,4S,5R-epoxypipecolic acid, cis-3) was synthesized and found to serve as an excellent substrate for L-pipecolate oxidase (L-PO) and also to cause time-dependent, irreversible inactivation of the enzyme. Data are presented showing this compound is a mechanism-based inhibitor of L-PO, whereas 2S,3R,4S-epoxyproline acts as a reversible inhibitor.

Anticonvulsant activity of novel derivatives of 2- and 3-piperidinecarboxylic acid in mice and rats

The relative ability of derivatives of 2-piperidinecarboxylic acid (2-PC; pipecolic acid) and 3-piperidinecarboxylic acid (3-PC; nipecotic acid) to block maximal electroshock (MES)-induced seizures, elevate the threshold for electroshock-induced seizures and be neurotoxic in mice was investigated. Protective index (PI) values, based on the MES test and rotorod performance, ranged from 1.3 to 4.5 for 2-PC benzylamides and from < 1 to > 7.2 for 3-PC derivatives. PI values based on elevation of threshold for electroshock-induced seizures and rotorod performance ranged from > 1.6 to > 20 for both types of derivatives. Since preliminary data indicated that benzylamide derivatives of 2-PC displace [3H]1-[1-(2-thienyl)-cyclohexyl]piperidine (TCP) binding to the phencyclidine (PCP) site of the N-methyl-D-aspartate (NMDA) receptor in the micromolar range and such low affinity uncompetitive antagonists of the NMDA receptor-associated ionophore have been shown to be effective anticonvulsants with low neurological toxicity, the 2-PC derivatives were evaluated in rat brain homogenates for binding affinity to the PCP site. Although all compounds inhibited [3H]TCP binding, a clear correlation between pharmacological activity and binding affinity was not apparent. Select compounds demonstrated minimal ability to protect against pentylenetetrazol-, 4-aminopyridine- and NMDA-induced seizures in mice. Corneal and amygdala kindled rats exhibited different sensitivities to both valproic acid and the nonsubstituted 2-PC benzylamide, suggesting a difference in these two models. Enantiomers of the alpha-methyl substituted benzylamide of 2-PC showed some ability to reduce seizure severity in amygdala kindled rats.

L-lysine is a barbiturate-like anticonvulsant and modulator of the benzodiazepine receptor

Our earlier observations showed that L-lysine enhanced the activity of diazepam against seizures induced by pentylenetetrazol (PTZ), and increased the affinity of benzodiazepine receptor binding in a manner additive to that caused by gamma-aminobutyric acid (GABA). The present paper provides additional evidence to show that L-lysine has central nervous system depressant-like characteristics. L-lysine enhanced [3H]flunitrazepam (FTZ) binding in brain membranes was dose-dependent and stimulated by chloride, bromide and iodide, but not fluoride. Enhancement of [3H]FTZ binding by L-lysine at a fixed concentration was increased by GABA but inhibited by pentobarbital between 10(-7) to 10(-3)M. While GABA enhancement of [3H]FTZ binding was inhibited by the GABA mimetics imidazole acetic acid and tetrahydroisoxazol pyridinol, the enhancement by pentobarbital and L-lysine of [3H]FTZ binding was dose-dependently increased by these two GABA mimetics. The above results suggest that L-lysine and pentobarbital acted at the same site of the GABA/benzodiazepine receptor complex which was different from the GABA binding site. The benzodiazepine receptor antagonist imidazodiazepine Ro15-1788 blocked the antiseizure activity of diazepam against PTZ. Similar to pentobarbital, the anti-PTZ effect of L-lysine was not blocked by Ro15-1788. Picrotoxinin and the GABA, receptor antagonist bicuculline partially inhibited L-lysine's enhancement of [3H]FTZ binding with the IC50s of 2 microM and 0.1 microM, respectively. The convulsant benzodiazepine Ro5-3663 dose-dependently inhibited the enhancement of [3H]FTZ binding by L-lysine. This article shows the basic amino acid L-lysine to have a central nervous system depressant characteristics with an anti-PTZ seizure activity and an enhancement of [3H]FTZ binding similar to that of barbiturates but different from GABA.

Chronic L-lysine develops anti-pentylenetetrazol tolerance and reduces synaptic GABAergic sensitivity

L-Lysine 10 mmol/kg given to mice for 1 to 10 days significantly increased clonic and tonic seizure latencies caused by 60 mg/kg pentylenetetrazol (PTZ). On day 1 the clonic and tonic seizure latencies were increased from 160.4 +/- 26.3 and 828.6 +/- 230.8 s to 286.1 +/- 103.3 and 982.3 +/- 98.6 s, respectively. Both clonic and tonic seizure latencies increased steadily with additional L-lysine treatment without significant change in survival rate. On day 10, the anticonvulsant effect reached its highest level with a block of tonic seizures and a survival rate of 100% without tolerance developing. Acute L-lysine treatment significantly increased the mean clonic latency from 85.8 +/- 5.24 to 128.2 +/- 9.0 s and the mean tonic seizure latency from 287.2 +/- 58.7 to 313.5 +/- 42.2 s with 80 mg/kg PTZ. On the day 10 of treatment, the anticonvulsant effect of L-lysine was highest, with a significant increase of 155 and 184% in clonic and tonic latencies over the control, respectively. After 15- and 20-day treatment, clonic and tonic seizures latencies and survival rate decreased, suggesting development of tolerance. Brain membranes from tolerant mice showed decreased enhancement by gamma-aminobutyric acid of specific [3H]flunitrazepam binding from 210 +/- 8 to 169 +/- 5% with EC50 values of 4.1 +/- 1.4 and 7.8 +/- 1.5 microM, respectively. Scatchard analysis of [3H] flunitrazepam binding showed no significant change of apparent binding affinity (KD) or binding density (Bmax) after chronic L-lysine exposure. L-Lysine enhanced the specific [35S]tert-butyl bicyclophosphorothionate (TBPS) binding in brain membranes dose dependently.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation between enhancement of [3H]flunitrazepam binding and suppression of pentylenetetrazol-induced seizures by L-lysine

L-Lysine enhanced the specific [3H]flunitrazepam (FTZ) binding of bovine brain membranes in vitro. Inhibition of specific [3H]FTZ binding to brain membranes in vitro by pentylenetetrazol (PTZ) at concentrations 0.46 mM and below was reversed by increasing L-lysine concentrations in the incubation mixture; further increase of L-lysine concentration enhanced this binding. However, inhibition of [3H]FTZ binding by PTZ higher than 2.3 mM was reversed only partially by L-lysine. L-Lysine enhanced specific [35S]t-butylbicyclophosphorothionate (TBPS) binding on mouse brain membranes in a dose-dependent manner (EC approximately 5 microM). This enhancement was inhibited by PTZ dose dependently. Inhibition of [35S]TBPS binding by PTZ was attenuated slightly by L-lysine. L-Lysine enhanced [3H]FTZ binding in intact mice in a dose- or concentration-dependent manner with an ED50 of 6 mmol/kg body weight or EC50 of 3 mumol/g brain tissue, respectively. Similar effect was observed for L-lysine in ex vivo [3H]FTZ binding study when [3H]FTZ was incubated in vitro with an ED50 of 1 mmol/kg mouse or EC50 of 0.7 mumol/g brain. PTZ not only induced seizures, but also inhibited specific [3H]FTZ binding to brain membranes in a dose-dependent manner. L-Lysine, in a dose-dependent manner, suppressed seizures caused by PTZ at 50 or 60 mg/kg, or prolonged the time of seizure onset (seizure latency) caused by higher doses of PTZ (90 or 100 mg/kg). Pretreatment with L-lysine at 1, 5, 10 or 20 mmol/kg not only reversed the inhibition of the specific [3H]FTZ binding caused by PTZ at 50, 90 or 100 mg/kg, but also enhanced this binding above control level.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhancement of benzodiazepine receptor binding by L-lysine is chloride-dependent and due to increase in binding affinity

L-Lysine enhanced specific [3H]flunitrazepam binding dose dependently on extensively washed bovine brain membrane in vitro. This enhancement was stimulated by chloride ions dose dependently. Scatchard analysis indicated this enhancement by L-lysine to be due to increase in binding affinity (KD) with no change in receptor density (Bmax). Since enhancement of [3H]flunitrazepam binding by L-lysine was partially inhibited by picrotoxinin, L-lysine may act on a distinct picrotoxinin-sensitive site which was distinct from the gamma-aminobutyric acid receptor site. This binding site, however, appears to have some features resembling that of the central nervous system-depressant barbiturates.