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

Transport characteristics of guanidino compounds at the blood-brain barrier and blood-cerebrospinal fluid barrier: relevance to neural disorders

Guanidino compounds (GCs), such as creatine, phosphocreatine, guanidinoacetic acid, creatinine, methylguanidine, guanidinosuccinic acid, γ-guanidinobutyric acid, β-guanidinopropionic acid, guanidinoethane sulfonic acid and α-guanidinoglutaric acid, are present in the mammalian brain. Although creatine and phosphocreatine play important roles in energy homeostasis in the brain, accumulation of GCs may induce epileptic discharges and convulsions. This review focuses on how physiologically important and/or neurotoxic GCs are distributed in the brain under physiological and pathological conditions. Transporters for GCs at the blood-brain barrier (BBB) and the blood-cerebrospinal fluid (CSF) barrier (BCSFB) have emerged as substantial contributors to GCs distribution in the brain. Creatine transporter (CRT/solute carrier (SLC) 6A8) expressed at the BBB regulates creatine concentration in the brain, and represents a major pathway for supply of creatine from the circulating blood to the brain. CRT may be a key factor facilitating blood-to-brain guanidinoacetate transport in patients deficient in S-adenosylmethionine:guanidinoacetate N-methyltransferase, the creatine biosynthetic enzyme, resulting in cerebral accumulation of guanidinoacetate. CRT, taurine transporter (TauT/SLC6A6) and organic cation transporter (OCT3/SLC22A3) expressed at the BCSFB are involved in guanidinoacetic acid or creatinine efflux transport from CSF. Interestingly, BBB efflux transport of GCs, including guanidinoacetate and creatinine, is negligible, though the BBB has a variety of efflux transport systems for synthetic precursors of GCs, such as amino acids and neurotransmitters. Instead, the BCSFB functions as a major cerebral clearance system for GCs. In conclusion, transport of GCs at the BBB and BCSFB appears to be the key determinant of the cerebral levels of GCs, and changes in the transport characteristics may cause the abnormal distribution of GCs in the brain seen in patients with certain neurological disorders.

Creatine and creatinine metabolism

The goal of this review is to present a comprehensive survey of the many intriguing facets of creatine (Cr) and creatinine metabolism, encompassing the pathways and regulation of Cr biosynthesis and degradation, species and tissue distribution of the enzymes and metabolites involved, and of the inherent implications for physiology and human pathology. Very recently, a series of new discoveries have been made that are bound to have distinguished implications for bioenergetics, physiology, human pathology, and clinical diagnosis and that suggest that deregulation of the creatine kinase (CK) system is associated with a variety of diseases. Disturbances of the CK system have been observed in muscle, brain, cardiac, and renal diseases as well as in cancer. On the other hand, Cr and Cr analogs such as cyclocreatine were found to have antitumor, antiviral, and antidiabetic effects and to protect tissues from hypoxic, ischemic, neurodegenerative, or muscle damage. Oral Cr ingestion is used in sports as an ergogenic aid, and some data suggest that Cr and creatinine may be precursors of food mutagens and uremic toxins. These findings are discussed in depth, the interrelationships are outlined, and all is put into a broader context to provide a more detailed understanding of the biological functions of Cr and of the CK system.

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.