MSG – “AD LIBITUM” DIELEMMA

It had been repeatedly observed that very high doses of MSG in “ad libitum” method is needed to produce neuro degenerative damage in brains of experimental animals.

(“FREEDICTIONARY” defines “ad libitum” feeding as ‘food available at all times with the quantity and frequency of consumption being the free choice of the animal’.)

This is complete opposite to mice models who received MSG by forced oral route and by subcutaneous route where brain damage could be induced by 1/10 to 1/20 doses (2 g/kg to 4 g/kg) of MSG that was required to induce same lesions with “ad libitum feeding” (20.9 g/kg to 45.5 g/kg).

“The cause for this difference lies in the route of administration”, experts say. When MSG is given in oral route, body calls in multiple defenses to keep blood glutamate levels stable in order to prevent MSG toxicity. These defenses are;

1.      Metabolizing glutamate in gut.

2.      Extrusion from brain by active blood-brain transport systems.

3.      By local brain mechanisms regulating glutamate uptake and metabolism in brain.

These systems can buffer glutamate to maintain extracellular glutamate level (glutamate level outside brain cells) stable.

“However, mechanism of MSG neurotoxicity often attributed to a prolonged increase in extracellular glutamate concentrations in brain”, a recent review on toxic effects of MSG explain.

Sources:

1.      Olney JW. Excitotoxic amino acids: Research applications and safety implications, In Flier, L J, Garratini, S, Kare, M R Reynolds, W.A and Wurtman, R.J (Eds.), Glutamtc Acid Advances in Biochemistry and Physiology, Raven. New York, 1979.

2.      A Studies On Monosodium L- Glutamate Toxicity In Animal Models- A Review. Kumar Ganesan1, Kumeshini Sukalingam1, Kanaga Balamurali1, Siti Radziah Bt. Sheikh, Alaudeen1, Kumar Ponnusamy1, Indang Ariati Ariffin, Sharmila Banu Gani. International Journal Of Pharmaceutical, Chemical And Biological Sciences, 2013, 3(4), 1257-1268.