Ajinomoto's Excitotoxicity: A Bitter Taste
Glutamic acid primarily serves as an important excitatory neurotransmitter in central nervous system and is an important excitatory amino acid (EAA). EAA represent major brain neurotransmitters and they are present in numerous neuronal systems and are involved in almost all aspects of normal and pathological brain activity. Changes in EAA transmission have been associated with the functional impairments characterizing major neurological disorders, including epilepsy, Alzheimer's disease, Parkinson's disease and schizophrenia etc. EAA also underlie the neuronal death associated with acute CNS insults, such as ischemia and post-traumatic lesions. The neurotoxicity of EAA, referred to as excitotoxicity, is presumably mediated primarily through an excess of EAA synaptic receptor stimulation. Excitotoxins are the substances which are capable of inducing excitotoxicity. They induce excitotoxicity through over stimulation of the ionotropic NMDA or AMPA/kainate receptor subtypes. They have been shown to produce an intense membrane depolarization and a massive increase in intracellular calcium leading to cell damage. Excitotoxins also promote cancer growth and metastasis. On expopsure to glutamate cancer cells become more mobile and that enhances metastasis, or spread. Our food stuffs and diet contains these excitotoxins in high amount as they are deliberately added to food items to enhance/alter taste. Glutamate is one such toxin added to foods usually as purified monosodium salt called monosodium glutamate or MSG. MSG is a potent excitotoxin which is the sodium salt of glutamic acid and due to its flavor enhancing properties it is used as a food additive in Asian cuisine and other diets making it a relevant aspect of the human diet worldwide. It increases the appetite by stimulating the appetite center but presently it has been debated for its safety and harmful effects. It affects almost every major organ in the body. In the present review resultant pathways associated with excitotoxicty of ajinomoto are deliberated with special reference to calcium signaling.