alpha-Guanidinoglutaric acid in cobalt-induced epileptogenic cerebral cortex of cats

Relationship between structure and inhibitory effect of arginine analogues on neuronal nitric oxide synthase activity

Since nitric oxide (NO) is synthesized by nitric oxide synthase (NOS) from L-arginine (Arg) which has an amidino group in its molecule, we examined the effect of 29 kinds of Arg analogues on neuronal NOS (nNOS) activity in the rat brain. None of the Arg analogues acted as a substrate for nNOS. Diamidinocystamine, hirudonine, and guanethidine inhibited nNOS activity to 67.3%, 64.2% and 74.1%, respectively, but their inhibitory efficiency was lower than NG-monomethyl-L-arginine (to 36.5%) which is a well known NOS inhibitor. Dimethylguanidine and N-benzoylguanidine also significantly inhibited nNOS activity to 88.0% and 90.7%, respectively. Whereas almost all of the NOS inhibitors previously reported were synthesized by substituting the amidino nitrogen of Arg, none of these new inhibitors were substituted at this position. Furthermore, hirudonine, which is a naturally occurring compound, was thought to act as an agonist at polyamine binding site of the N-methyl-D-aspartate type of glutamate receptor complex. It is also interesting that guanethidine, an antihypertensive agent, inhibit nNOS activity. These new drugs are useful for the investigation not only of the chemical nature of nNOS but also of the physiologic function of NO.

Structure-activity relationships of arginine analogues on nitric oxide synthase activity in the rat brain

Nitric oxide (NO) is synthesized by nitric oxide synthase (NOS) from L-arginine (Arg) which has a guanidino group in its molecule. We examined the effect of 23 different Arg analogues on NOS activity in the rat brain. Though homoarginine, epsilon-guanidinocaproic acid and canavanine act as substrates of NOS, production of NO from them was lower than that from Arg. alpha-Guanidinoglutaric acid (2-GGA) and arcaine inhibited NOS activity at levels equal to NG-monomethyl-L-arginine (MeArg), a well known NOS inhibitor. Though almost all previously reported NOS inhibitors were synthesized by substituting the guanidino nitrogen of Arg, the guanidino nitrogens of arcaine and 2-GGA were not substituted. Furthermore, 2-GGA is a known endogenous convulsant in mammals, and arcaine, which was isolated from a marine mollusc, is also a convulsive substance. Hence, 2-GGA and arcaine will be excellent drugs to investigate not only the chemical nature of NOS but also the physiologic function of NO.

Synthesis of neuroactive guanidino compounds by rat kidney L-arginine: glycine amidinotransferase

Several neuroactive guanidino compounds have been reported to be synthesized in mammals by transamidination reactions. The enzyme(s) responsible for their synthesis and their location in the body has not been well established. The purpose of this investigation was to determine if purified homogeneous rat kidney alpha- and beta-L-arginine : glycine amidinotransferase (transamidinase) would catalyze the synthesis of certain neuroactive guanidino compounds, and if so, to determine if any catalytic specificity existed between the two forms of the enzymes. L-Arginine (Arg) was used as the amidino group donor and the following compounds were investigated for their ability to accept the amidino group: ethanolamine; 4-aminobutyric acid; lysine; 5-aminovaleric acid; 3-aminopropionic acid; taurine; L-glutamic acid (Glu); L-aspartic acid (Asp); and histidine (His). All of the above listed compounds served as amidino group acceptors for the enzyme except Glu, Asp and His. No differences were found between the alpha- and beta-transamidinase in any of the experiments reported, and the synthesis of 2-guanidinoethanol by the enzyme was by a sequential mechanism with a Km for Arg and ethanolamine of 14mM and 163mM, respectively. The possibility that the site of synthesis of the neuroactive guanidino compounds in the kidney and perhaps pancreas is discussed.

Increase of methylguanidine and guanidinoacetic acid in the brain of amygdala-kindled rats

Guanidino compounds are intrinsic chemoconvulsants. We investigated the regional and time-dependent changes of these compounds in the amygdala (AM) of kindled rats versus electroconvulsive shock (ECS) seizures using high-performance liquid chromatography (HPLC). Twenty-eight days after the last AM-kindled seizure, guanidinoacetic acid (GAA) and methylguanidine (MG) levels were significantly increased in the bilateral AM as compared with those of control rats, which had been implanted with electrodes but were not stimulated. Both compounds, however, tended to decrease in the bilateral AM after ECS seizure. In addition, we measured these compounds after induction of one afterdischarge (AD) in the AM. These compounds increased significantly 7 days after AD was induced in the ipsilateral AM. We suggest that the increase of these compounds is coincident with AD generation and specific to AM kindling and the kindled state.

Guanidino compound levels in the serum of healthy adults and epileptic patients

Some guanidino compounds are known to be convulsants and to change in the brain during seizures. In this study, we examined the serum levels of guanidino compounds in healthy adults (controls), non-epileptic neurological patients (NENP) and epileptic neurological patients (ENP). In healthy adults, serum levels of guanidinoacetic acid (GAA), creatinine (CRN) and homoarginine (HArg) were significantly lower in women than in men. Serum levels of GAA in ENP and NENP were significantly lower than in controls, with the exception of female NENP. In the male patients, CRN levels were significantly lower in ENP and NENP compared to the controls. Significantly higher arginine (Arg) levels were observed in both male and female ENP and NENP. HArg levels in the male patients were significantly lower in ENP compared with both controls and NENP. With regard to serum levels of guanidino compounds in ENP with symptomatic generalized epilepsy and with symptomatic partial epilepsy, significantly lower levels of HArg were observed in male ENP with symptomatic generalized epilepsy than in NENP. Serum levels of GAA and HArg in uncontrolled female ENP were significantly lower than those in controlled ENP. Furthermore, Arg and HArg levels in uncontrolled male ENP were significantly lower than in controlled ENP. Serum levels of Arg in male ENP and HArg in both sexes of ENP taking valproic acid were significantly lower than those in ENP not taking valproic acid. These results suggest that some metabolic disorder of guanidino compounds may exist in ENP and NENP and that guanidino compounds may be affected by seizure types, seizure severity and anticonvulsants.

Measurement during convulsions of guanidino compound levels in cerebrospinal fluid collected with a catheter inserted into the cisterna magna of rabbits

An easy method for collecting cerebrospinal fluid (CSF) was developed using a catheter inserted into the cisterna magna of rabbits. Levels of guanidino compounds in CSF collected by this method were measured. Levels of guanidinoacetic acid and creatinine increased at the onset of a pentylenetetrazol (PTZ)-induced convulsion. These levels normalized 2 h after the convulsion. The arginine level started to decrease 2 h after the convulsion, continued to decrease gradually and normalized 4 days after the convulsion. These results suggest that guanidinoacetic acid and creatinine are related to the initiation of PTZ-induced convulsions, and that 4 days are required for the metabolism of guanidino compounds to return to normal after a convulsion in rabbits.

Biochemistry and neurotoxicology of guanidino compounds. History and recent advances

Guanidino compounds are known to have important biological roles, such as the participation of arginine in ureagenesis, and of creatine in muscular contraction. On the other hand, the high toxicity of guanidino compounds, such as methylguanidine and guanidine, has been under study for quite a long time in the biochemical as well as clinical fields. In this review, the author summarizes the experimental results of neurophysiological and neurochemical studies on guanidino compound-induced seizures, conducted by his colleagues since 1966, and introduces several topics arising from their recent investigations on guanidino compounds and seizure mechanism, i.e., (1) alpha-guanidino-glutaric acid in the cobalt epileptic focus and its convulsive activity; (2) guanidino-ethanesulfonic acid and epilepsy; (3) delta-guanidinovaleric acid, and endogenous and specific GABA receptor antagonist; and (4) guanidino compounds as radical generators.

Convulsive activity of alpha-guanidinoglutaric acid and the possible involvement of 5-hydroxytryptamine in the alpha-guanidinoglutaric acid-induced seizure mechanism

alpha-Guanidinoglutaric acid (alpha-GGA) was first found in cobalt-induced epileptogenic focus tissue in the cerebral cortex of cats. We examined the effect of alpha-GGA on the electroencephalogram and on the brain 5-hydroxytryptamine (5-HT) level after intraventricular administration into rats. Sporadic low-voltage spikes appeared 4 min after the administration of alpha-GGA. Spikes increased in voltage 6 min after the administration. Multiple spikes appeared 10 min after the administration, and they reached maximal frequency 30 min after the administration. The epileptic discharges disappeared 100 min after the administration. The 5-HT level increased in the right and left cortices 3 min after the administration. The 5-HT level decreased in the mid-brain 5 min after the administration and subsequently in all regions of the brain 10 min after the administration. No change in the 5-HT level was found 30 min and 100 min after the administration. These results show that alpha-GGA induces epileptic seizures in rats after intraventricular administration. The results also suggest that alpha-GGA-induced seizures are associated with abnormal serotonergic function and that they are initiated by a decrease in the 5-HT level.

The lactam of alpha-guanidinoglutaric acid (1-amidino-2-pyrrolidone-5-carboxylic acid)

alpha-Guanidinoglutaric acid (alpha-GGA) has been reported to occur in the cerebral cortex after epileptic seizures. No physical characteristics of alpha-GGA have been given. A practical procedure for the preparation of alpha-GGA is reported here. alpha-GGA forms a lactam in aqueous solution at 80 degrees C. It is proposed to substitute this lactam, 1-amidino-2-pyrrolidone-5-carboxylic acid (pAGlu), for pyroglutamic acid (pGlu) at the N-terminal position in neuropeptides to modify their biological characteristics. L(+)-Glutamic acid was reacted with S-methylisothiourea (I) at pH 10 in aqueous solution to form L(-)-alpha-guanidinoglutaric acid: mp 165-168 degrees C, [alpha]22D = -22.7 (C = 4, 2 M HCl). alpha-GGA reacted promptly with excess reagent to form a salt, S-methylisothiourea-alpha-guanidinoglutarate: mp 209-210 degrees C, [alpha]22D = -13.0 (C = 4, 2 M HCl). I was removed from the salt with aqueous picric acid, since I readily formed an insoluble picrate, S-methylisothiourea picrate (mp 225-228 degrees C). Alternatively, the salt was added to a cation exchange column, and the alpha-GGA was eluted with molar ammonium acetate buffer, pH 9.5. Its lactam, 1-amidino-2-pyrrolidone-5-carboxylic acid, mp 248-249 degrees C, [alpha]22D = +2.1 (C = 4, 2 M HCl), formed a picrate (mp 196-199 degrees C).

Isolation of an endogenous clonidine-displacing substance from rat brain

An endogenous substance which specifically displaces clonidine, yohimbine and rauwolscine from rat brain alpha 2-adrenergic receptors, has been isolated. The new compound, designed clonidine-displacing-substance (CDS), has been partially purified by ion exchange chromatography, zone electrophoresis and high performance liquid chromatography (HPLC). CDS binds specifically to alpha 2-adrenergic receptors by competing with either alpha 2-adrenergic agonists or alpha 2-antagonists, but has no effect on the specific binding of [3H]prazosin to alpha 1-adrenergic receptors in rat brain membranes. In the course of isolation, CDS was shown to be neither the endogenous neurotransmitter (-)norepinephrine (NE) nor the guanyl nucleotide GTP which lowers the specific binding of alpha 2-agonists to the alpha 2-adrenergic receptors.

Fluorometrical analysis of guanidino compounds in human cerebrospinal fluid

Guanidino compounds in CSF of 57 human subjects were determined fluorometrically after reaction with phenanthrenequinone in alkali solution, using HPLC. Creatinine (65.2 +/- 13.4 nmol/ml), arginine (24.7 +/- 6.4 nmol/ml), and homoarginine (0.7 +/- 0.3 nmol/ml) were found in all subjects. Trace amounts of guanidinosuccinic acid and guanidinoacetic acid were detected in some of the subjects. Brain guanidino compounds, taurocyamine, N-acetylarginine, and methylguanidine were not detected in CSF.