Monosodium glutamate or MSG is a much discussed food additive and the subject of studies highlighting possible problems with the cardiovascular system, the gastrointestinal system (1) and the kidneys (2).
Checking the European regulations in Article 9 of Regulation (EU) No. 1169/2011 together with the mandatory requirements of Regulation (EC) 853/2004 for meat preparations, it appears that this additive is not included among the authorised ingredients for the preparation of food meat (3).
 

It may also play a role in the pathology of obesity (4) and in migraine (5).

Glutamate plays an important role in major brain functions including synapse formation and stabilisation, memory, cognition, learning and cell metabolism. However, ingestion of MSG-rich foods can cause different health disorders such as neurotoxicity, hepatotoxicity, obesity and diabetes. The use of medicinal plants and their natural products as therapy against MSG used in the food industry has been suggested as protective. Calendula officinalis, Curcuma longa, Green Tea, Ginkgo biloba and vitamins are some of the main natural products with a protective effect against MSG toxicity mentioned through different mechanisms. This review provides a summary of MSG toxicity and the protective effects of natural products against MSG-induced toxicity (6).

Most relevant studies:

Chakraborty SP. Patho-physiological and toxicological aspects of monosodium glutamate. Toxicol Mech Methods. 2019 Jul;29(6):389-396. doi: 10.1080/15376516.2018.1528649.

Abstract. Nowadays, the life-line of urban population has been formed by commercial foods due to industrialization, urbanization, and rapid increase in working class. Commercial foods are time and energy saving foods but it compromising the nutritional value of foods. The term adulteration refers to the deliberate addition of compound which is usually not present in food. These compounds are known as food additives or food adulterant. Monosodium Glutamate (MSG) is one of the most common food additives. Several studies revealed that MSG has toxic effect on fetal development/fetus, children's, adolescent, and adults. Physiological complication associated with MSG toxicity are hypertension, obesity, gastrointestinal tract troubles, and impairment of function of brain, nervous system, reproductive, and endocrine system. The effect of MSG depends upon its dose, route of administration and exposure time. Public awareness may play a major role in controlling the food adulteration by working in collaboration with National testing facilities to scrutinize each commercial food article from time to time. The aim of this review article is to highlight the deleterious impact of MSG on human health.

Gürgen SG, Sayın O, Çeti N F, Sarsmaz HY, Yazıcı GN, Umur N, Yücel AT. The Effect of Monosodium Glutamate on Neuronal Signaling Molecules in the Hippocampus and the Neuroprotective Effects of Omega-3 Fatty Acids. ACS Chem Neurosci. 2021 Aug 18;12(16):3028-3037. doi: 10.1021/acschemneuro.1c00308.

Abstract. Monosodium glutamate (MSG) is a flavoring substance added to many ready-to-eat foods and has known neurotoxic effects. This study was performed in order to examine the potential toxic effect of MSG on neurons in various regions of the hippocampus in prepubertal rats.....In addition, we concluded that the use of omega-3 fatty acids such as eicosapentaenoic acid and docosahexaenoic acid in addition to Monosodium glutamate may protect against the neurotoxic effects of Monosodium glutamate.

Zhao L, Zhu X, Xia M, Li J, Guo AY, Zhu Y, Yang X. Quercetin Ameliorates Gut Microbiota Dysbiosis That Drives Hypothalamic Damage and Hepatic Lipogenesis in Monosodium Glutamate-Induced Abdominal Obesity. Front Nutr. 2021 Apr 29;8:671353. doi: 10.3389/fnut.2021.671353. 

Abstract. Monosodium glutamate (MSG)-induced abdominal obesity, conventionally caused by hypothalamic damage, is a critical risk factor for health problem. Microbiota-gut-brain axis plays important roles in a variety of metabolic diseases. However, whether gut microbiota is involved in the pathogenesis for MSG-induced abdominal obesity and the effect of quercetin on it remains unclear. Herein, we find that MSG-induced gut microbiota dysbiosis contributes to neuronal damage in the hypothalamus, as indicated by antibiotics-induced microbiota depletion and co-house treatment. Inspired by this finding, we investigate the mechanism in-depth for MSG-induced abdominal obesity. Liver transcriptome profiling shows retinol metabolism disorder in MSG-induced abdominal obese mice. In which, retinol saturase (RetSat) in the liver is notably up-regulated, and the downstream lipogenesis is correspondingly elevated. Importantly, microbiota depletion or co-house treatment eliminates the difference of RetSat expression in the liver, indicating gut microbiota changes are responsible for liver retinol metabolism disorder. Moreover, this study finds dietary quercetin could modulate MSG-induced gut microbiota dysbiosis, alleviate hypothalamic damage and down-regulate liver RetSat expression, thus ameliorating abdominal obesity. Our study enriches the pathogenesis of MSG-induced abdominal obesity and provides a prebiotic agent to ameliorate abdominal obesity. Copyright © 2021 Zhao, Zhu, Xia, Li, Guo, Zhu and Yang.

References_________________________________________________________________________

(1) López-Miranda V, Soto-Montenegro ML, Uranga-Ocio JA, Vera G, Herradón E, González C, Blas C, Martínez-Villaluenga M, López-Pérez AE, Desco M, Abalo R. Effects of chronic dietary exposure to monosodium glutamate on feeding behavior, adiposity, gastrointestinal motility, and cardiovascular function in healthy adult rats. Neurogastroenterol Motil. 2015 Nov;27(11):1559-70. doi: 10.1111/nmo.12653.

 (2) Sharma A  Monosodium glutamate-induced oxidative kidney damage and possible mechanisms: a mini-review. -  J Biomed Sci. 2015 Oct 22;22(1):93. doi: 10.1186/s12929-015-0192-5.

(3) Liuzzo G, Rossi R, Giacometti F, Piva S, Serraino A, Mescolini G, Militerno G. Mislabelling of Döner Kebab Sold in Italy. Ital J Food Saf. 2016 Nov 2;5(4):6149. doi: 10.4081/ijfs.2016.6149.

(4) Shannon M, Green B, Willars G, Wilson J, Matthews N, Lamb J, Gillespie A, Connolly L.  The endocrine disrupting potential of monosodium glutamate (MSG) on secretion of the glucagon-like peptide-1 (GLP-1) gut hormone and GLP-1 receptor interaction. -  Toxicol Lett. 2017 Jan

(5) Zaeem Z, Zhou L, Dilli E. Headaches: a Review of the Role of Dietary Factors. Curr Neurol Neurosci Rep. 2016 Nov;16(11):101. doi: 10.1007/s11910-016-0702-1.

(6) Hajihasani MM, Soheili V, Zirak MR, Sahebkar A, Shakeri A. Natural products as safeguards against monosodium glutamate-induced toxicity. Iran J Basic Med Sci. 2020 Apr;23(4):416-430. doi: 10.22038/IJBMS.2020.43060.10123. 

Monosodium glutamate also called MSG is the sodium salt of glutamic acid.(alpha-amino acid), is obtained from plants by an industrial process consisting of different steps: extraction, filtration, concentration, drying, crushing, mixing, sieving.

It appears in the form of a white crystalline powder.

Amino acids play a key metabolic function in the human body and are constituents of proteins. Amino acids together with their salts are used in cosmetics as conditioning agents for both hair and skin (e.g. as moisturisers and other similar functions). Moisturisers are different in nature: the best are the natural ones that exploit the mechanism of integration between the ingredient and the skin by moisturising the horny hydrolipid film, i.e. the thin protective layer that covers the epidermis protecting it from harmful external microbes, keeping the skin moisturised and supple and its pH or acidity value between 4 and 6.  Then there are the occlusive moisturisers, usually derived from petroleum (Paraffinum, Paraffinum liquidum and others), but also triglycerides, lanolin oil, natural or synthetic waxes, fatty acid esters and others that create an artificial occlusive layer on the stratum corneum of the skin with the advantage of accelerating the protective process but with the disadvantage of preventing the skin's natural transpiration.

α-amino acids that have similar physical structures undergo similar changes with regard to solubility in water/ethanol mixtures, and technologies to separate α-amino acids from industrial residues, which may not even be innocuous, are constantly being improved. However, many data on the solubility in water-ethanol and ethanol of some α-amino acids are contradictory or even lacking, and the effects of ethanol on the solubility of amino acids may be different. Overall, the scientific literature considers that α-amino acids do not pose significant problems for human health when taken orally, except in people with certain genetic diseases.

Food safety

Amino acid α generally considered safe, but with daily doses not to be exceeded. Ingredient included in the list of European food additives as E621, flavour enhancer.

Cosmetic safety

Amino acid α generally considered safe when formulated to be non-irritant.

What it is used for and where

Food

It is a food additive with E621 label on the list of European food additives.

MSG is the typical additive that is found in Chinese cuisine and it is added with the function of making foods tastier or flavor enhancer.

Monosodium glutamate (MSG, C5H8NO4Na) is the sodium salt of glutamic acid. Encoded E621, it is a food additive from a group of flavor enhancers, used in a wide range of foods, such as soups, sauces, mixed condiments, chips, meat products, and puddings. MSG is a natural neurotransmitter in the brain. In humans, the daily intake of free glutamate is greater than 1 g in different forms and the average daily intake of total glutamate is 10 g. High daily intake of MSG results in accumulation and rise of glutamic acid in the blood. The protein-bound glutamate become free only after it goes to the small intestine, hence protein-bound glutamate has no such effect of enhancing the taste of food at this level. Recent evidence suggests that the taste and palatability of MSG are mediated through specific glutamate receptors present in the stomach and intestine . Several studies highlighted the deleterious effects of MSG on many organs when consumed daily. The objective of the current study was to explore the neuroprotective effects of ginger and propolis against MSG-induced neuropathological and toxicological changes. This effect was evident by neurotransmitter and electrochemical assessment in addition to evaluating the oxidative stress markers and antioxidant activity of both treatments in vitro and in vivo in comparison to a standard antioxidant (1).

Cosmetics

Humectant, moisturising.

Safety

An excessive glutamate level can result in excitotoxic damage and death of central nervous system cells, and is involved in the pathogenesis of many central nervous system diseases. It may also be related to a failure of the blood-spinal cord barrier. This study was aimed at examining the effects of extended administration of monosodium glutamate on the BSCB and spinal cord cells in adult male Wistar rats (2).

A single intake of Monosodium glutamate (MSG) may cause headache and increased muscle sensitivity. MSG induced mechanical sensitization in masseter muscle and adverse effects such as headache and short-lasting blood pressure elevation for which tolerance did not develop over 5 days of MSG intake (3).

The intake of foods with high amounts of MSG can affect human health and create neurotoxicity, hepatotoxicity, obesity and diabetes. Some herbs such as Calendula officinalis, Curcuma longa, green tea, Ginkgo bilobae and vitamins have been suggested as remedies (4).

The most relevant studies on this ingredient have been selected with a summary of their contents:

Monosodium Glutamate studies

Caratteristiche tipiche del prodotto commerciale Monosodium Glutamate

• Molecular Formula    C₅H₈NNaO₄     C₅H₁₀NNaO₅      C₅H₈NNaO₄ · xH₂O
• Molecular Weight  169.11109
• Exact Mass  169.035110
• CAS  142-47-2, 6106-04-3
• UNII    C3C196L9FG
• EC Number   205-538-1
• DSSTox Substance ID  
• IUPAC  sodium;(2S)-2-amino-5-hydroxy-5-oxopentanoate
• InChl=1S/C5H9NO4.Na/c6-3(5(9)10)1-2-4(7)8;/h3H,1-2,6H2,(H,7,8)(H,9,10);/q;+1/p-1/t3-;/m0./s1
• InChl Key      LPUQAYUQRXPFSQ-DFWYDOINSA-M
• SMILES  C(CC(=O)O)C(C(=O)[O-])N.[Na+]
• MDL number  MFCD00013074
• PubChem Substance ID    24895069
• RTECS  MA1500000
• NCI    C82289
• FEMA  2756   
• RXCUI        1311588
• NACRES NA.32
• SCHEMBL16336

Synonyms:

• Monosodium glutamate
• L-Glutamic acid monosodium salt hydrate
• MSG
• monosodium L-glutamate
• sodium glutamate
• sodium L-glutamate

References________________________________________________________________________

(1) Hussein UK, Hassan NEY, Elhalwagy MEA, Zaki AR, Abubakr HO, Nagulapalli Venkata KC, Jang KY, Bishayee A. Ginger and Propolis Exert Neuroprotective Effects against Monosodium Glutamate-Induced Neurotoxicity in Rats. Molecules. 2017 Nov 8;22(11). pii: E1928. doi: 10.3390/molecules22111928.

(2) Sulejczak D, Taraszewska A, Chrapusta SJ, Dziewulska D, Nakielski P, Rafałowska J. Nanofiber mat spinal cord dressing-released glutamate impairs blood-spinal cord barrier. Folia Neuropathol. 2016;54(4):392-404. doi: 10.5114/fn.2016.64818. 

(3) Shimada A, Cairns BE, Vad N, Ulriksen K, Pedersen AM, Svensson P, Baad-Hansen L. Headache and mechanical sensitization of human pericranial muscles after repeated intake of monosodium glutamate (MSG). J Headache Pain. 2013 Jan 24;14:2. doi: 10.1186/1129-2377-14-2.

(6) Hajihasani MM, Soheili V, Zirak MR, Sahebkar A, Shakeri A. Natural products as safeguards against monosodium glutamate-induced toxicity. Iran J Basic Med Sci. 2020 Apr;23(4):416-430. doi: 10.22038/IJBMS.2020.43060.10123.