MONOSODIUM GLUTAMATE

MONOSODIUM GLUTAMATEGlutamate The most abundant amino acid in the central nervous system

Functions as an excitant neurotransmitter

Highly concentrated in those regions of the brain that are essential in cognitive processes mediation : cerebral cortex, hippocampal gyrus dentatus and striatum .

Glutamate receptors include 3 families of ionotropic receptors and 3 groups of metabotropic receptors.

Dispersed throughout the CNS : amygdala, hippocampus and hypothalamus . where they regulate metabolic and autonomic functions.

The body can produce glutamate on its own from various other protein sources.

The body itself generates approximately 50 grams of free glutamate per day for use as a component of metabolization .

Approximately two kgs of naturally occurring glutamate can be found in the bodys organs and tissues, including the brain, the kidneys, the liver and various muscle.

Monosodium glutamateMonosodium glutamate belongs to the larger group of chemicals that are labeled glutamate. MSG is the sodium salt of the amino acid, glutamic acid, and a form of glutamate.

MSG has no texture or smell of its own, and therefore serves to emphasize the natural flavor of the food itself, rather than adding an independent flavor.

The flavor-enhancing properties of MSG were first discovered in 1908 by Professor Kikunae Ikeda, a Japanese chemist at Tokyo Imperial University, who had been working to isolate the ingredient that gave a particular taste in kombu (a Japanese seaweed). Today, MSG is generally derived from starch, corn sugar, molasses, sugar cane or sugar beetsproduced through a natural fermentation process,like that which is used to produce yogurt and beer. also sold alone as a white crystal substance, similar in texture and appearance to salt or sugar currently found in thousands of different processed foods, including soups, salad dressings, mayonnaise, canned vegetables and frozen dishes.

In 1959, the U.S. Food and Drug Administration (FDA) classified monosodium glutamate as generally recognized as safe.

g/dayAverage MSG intake per person in respective countriesThe estimated average daily MSG intake per person in industrialized countries is 0.3 1.0 gAccording to a joint inquiry by the governments of Australia and New Zealand in 2003, a typical Chinese restaurant meal contains between 10 and 1500 mg of MSG per 100 g. NEUROLOGICAL EFFECTS

Glutamate is an endogenous neurotransmitter required for a variety of physiological functions of neurons.

Increased release of endogenous glutamate has been suggested to play an important role in neuronal injury

Previous studies have also shown that incubation of neurons with high concentrations of exogenously applied glutamate rapidly induces neuronal cell death .. Although the blood brain barrier (BBB) has been said to have low permeability to MSG

the presence of high affinity glutamate transporters located at the BBB capillary luminal membrane could facilitate the uptake of MSG into the brain

Assuming 10% of the blood concentration can be reached in the cerebral spinal fluid

it would yield ~5 M MSG in the brain which is above the threshold concentration of MSG

causing neuronal injury

* Studies proved that neuronal swelling takes place at ~30 min after MSG treatment is also consistent with the time course of MSG-induced headache in clinical studies EXCITOTOXICITY ?A pathological process by which nerve cells are damaged and killed by excessive stimulation by neurotransmitters such as glutamate and similar substances.

This occurs when receptors for the excitatory neurotransmitter glutamate (glutamate receptors) such as the N-methyl- D- aspartate (NMDA) receptor are over activated.

Excitotoxins like NMDA and kainic acid which bind to these receptors, as well as pathologically high levels of glutamate, can cause excitotoxicity

by allowing high levels of calcium ions (Ca2+) to enter the cell.

Ca2+ influx into cells activates a number of enzymes, including phospholipases, endonucleases, and proteases enzymes.

These enzymes go on to damage cell structures such as components of the cytoskeleton, membrane, and DNA In contrast to mature neurons, immature neurons are very resistant to MSG damage. It is suggested that the young and immature neurons are less sensitive to the MSG damage as compared to mature neurons.

This finding might explain why young children, whose brain neurons are not fully mature, do not experience headaches after MSG intake.

However , the reason why young neurons are not damaged by MSG is still yet to be proven. Since young neurons are not fully developed, they may be missing some receptors that are required for MSG binding or downstream signaling pathway(s) required for MSG toxicity .

pre-exposure of a low dose of MSG can generate tolerance may explain why Chinese populations do not experience headaches after MSG intake.

It is likely that they have already established tolerance to MSG due to previous exposures to low doses of MSG when they were young

Prevention of MSG toxic effectsVitamin C reduces MSG damage of neurons - Vitamin C is an important endogenous neuroprotectant in the brain.It has been showed to be neuroprotective in various conditions protective role against toxic nerve cell and astrocyte glial fibrillary acidic protein damage in cerebellar cortex

Boiling does not reduce damaging effect of MSG - Treatment of neurons with boiled MSG produced a similar injury of neurons as non-boiled MSG . - Therefore, boiling MSG is not sufficient to reduce its damaging effect and its toxicity and no preventable measures can be made by over-cooking of MSG containing food.