GAA and other guanidino compounds in the brain
Guanidino compounds of guanidinoethanesulfonic acid, guanidinoacetic acid, guanidinosuccinic acid, N-acetylarginine, beta-guanidinopropionic acid, creatinine, gamma-guanidinobutyric acid, arginine, guanidine, methylguanidine, homoarginine and alpha-guanidinoglutaric acid are present in the mammalian brain. These guanidino compounds except for arginine and guanidine induce seizures and convulsions in rat, rabbit and cat by intracisternal injection. Hirudonine, audonine, alpha-keto-delta-guanidinovaleric acid, N,N’-dibenzoylguanidine and phenylethylguanidine are also convulsants. Levels of creatinine, guanidinoethanesulfonic acid, creatinine, guanidinoacetic acid and methylguanidine in animal brain were changed at pre- and during convulsions induced by pentylentetrazol, amygdala kindling, iron-induced epileptogenesis and so on. These convulsions are thought to be due to depressed functions of serotonergic neurons and accumulated free radicals. Arginine is a substrate of nitric oxide production by nitric oxide synthase. alpha-Guanidinoglutaric acid is a generator of superoxide, hydroxyl radicals and nitric oxide, and induced C6 glial cell death. On the other hand, aminoguanidine is a free radical scavenger. Energy formation by creatine metabolism may inhibit apoptosis induced by pathogenesis. Free radical generation/ reaction and energy generation by guanidino compounds must be important key role in the brain.