Pedro Díaz-Vivancos. Researcher in CEBAS-CSIC
As we have already mentioned, glutathione (GSH) is one of the main non-enzymatic antioxidants compounds both in plants and animals (https://antioxidantsgroup.wordpress.com/2013/07/04/antioxidant-defense-mechanisms-i-non-enzymatic-mechanisms/).
Glutathione (GSH) is a very important non-protein thiol compound (thiol is a compound which contains the functional group composed of a sulphur atom and a hydrogen atom) in many organisms. The GSH is a non-protein tripeptide composed of amino acids L-cysteine, acid L-glutamate and glycine. GSH has multiple functions:
1. It is the main endogenous antioxidant produced by cells, directly acting in the neutralization of free radicals and reactive oxygen species (ROS) and in the maintenance of endogenous antioxidant as vitamin C and E in its reduced form (active).
2. By direct conjugation, it participates in the detoxification of foreign compounds (xenobiotic) and carcinogenic agents.
3. In plants it is essential in the regulation of its development and in the responses to the environment (defence against both biotic and abiotic stresses). In animals it is essential for the proper functioning of the immune system, taking part, for example, in the modulation of the antigen presentation to lymphocytes, in lymphocytes proliferation and in the regulation of processes of apoptosis or programmed cell death.
4. It has a crucial role in numerous metabolic and biochemical reactions: DNA synthesis and reparation, protein synthesis, amino acid transport, enzymatic reactions, metabolism of sulphur etc.
Therefore, glutathione plays numerous functions, but mainly it participates in the regulation of the cellular redox state (oxidation-reduction reactions). The state of glutathione is modulated by oxidants, nutritional factors and other factors such as defence responses to pathogens, etc. For these reasons, glutathione is considered as a signalling molecule which integrates environmental information in cellular network. Nowadays, there are clear evidences that glutathione is a multifunctional metabolite in plants and animals, being fundamental in numerous cellular processes.
Foods rich in GSH are asparagus, spinaches, broccoli, garlic, cabbage, onions, watercress and Brussels sprouts. Some species as cumin or cinnamon also elevate GSH levels in a modest way. Other foods, which contain glutathione in minor quantity, are melon, avocado, grapefruit, peaches, oranges, walnuts, turkey and chicken. Summing up, dairy products, cereals and bread are low in GSH; fruits and vegetables have moderate or high quantities of GSH, and meat freshly prepared has a relatively high content of GSH.
However, it is very important to mention that is much more significant to focus in foods that contain glutathione precursors than in foods which contain glutathione. That is because glutathione has a chemical structure that is weak to digestive process. Glutathione is not an essential nutrient, since it can be synthesized from amino acids L-cysteine, acid L-glutamate and glycine. Glutamic acid and glycine are in almost all foods that we eat, but cysteine is much lower, being in eggs, garlic and milk. It is recommended the consumption of foods rich in selenium, being known for helping to elevate glutathione levels.