gamma-L-Glutamyl-L-cysteine

γ -L-Glutamyl-L-cysteine, also known as γ-glutamylcysteine (GGC), is a dipeptide found in animals, plants, fungi, some bacteria, and archaea. It has a relatively unusual γ-bond between the constituent amino acids, L-glutamic acid and L-cysteine and is a key intermediate in the gamma (γ) -glutamyl cycle first described by Meister in the 1970s.[1][2] It is the most immediate precursor to the antioxidant glutathione.[3]

γ-l-Glutamyl-l-cysteine
Names
Systematic IUPAC name
(2S)-2-Amino-5-[[(1R)-1-carboxy-2-sulfanylethyl]amino]-5-oxopentanoic acid
Other names
gamma-Glutamylcysteine
Identifiers
3D model (JSmol)
3DMet
1729154
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.164.128
KEGG
MeSH gamma-glutamylcysteine
Properties
C8H14N2O5S
Molar mass 250.27 g·mol−1
Appearance White, opaque crystals
log P −1.168
Acidity (pKa) 2.214
Basicity (pKb) 11.783
Related compounds
Related alkanoic acids
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Biosynthesis

GGC is synthesized from L-glutamic acid and L-cysteine in the cytoplasm of virtually all cells in an adenosine triphosphate (ATP) requiring reaction catalysed by the enzyme glutamate-cysteine ligase (GCL, EC 6.3.2.2; formerly γ-glutamylcysteine synthetase).  The production of GGC is the rate limiting step in glutathione synthesis.

Occurrence

GGC occurs in human plasma in the range of 1 – 5 µM[2][3] and intracellularly at 5 – 10 µM.[4] The intracellular concentration is generally low because GGC is rapidly bonded with a glycine to form glutathione.  This second and final reaction step in glutathione biosynthesis is catalysed by the activity of the ATP dependent glutathione synthetase enzyme.

Importance

GGC is essential to mammalian life. Mice that have had the glutamate-cysteine ligase (GCL) gene knocked out do not develop beyond the embryo stage and die before birth.[5] This is because GGC is vital for the biosynthesis of glutathione. Since the production of cellular GGC in humans slows down with age, as well as during the progression of many chronic diseases, it has been postulated that supplementation with GGC could offer health benefits. Such GGC supplementation may also be of benefit in situations where glutathione has been acutely lowered below optimum, such as following strenuous exercise, during trauma or episodes of poisoning.

Several review articles have been published exploring the therapeutic potential of GGC to replenish glutathione in age related[6] and chronic disease states such as Alzheimer’s disease.[7]

GGC is also capable of being a powerful antioxidant in its own right.[8][9][10]

Availability

GGC synthesis for commercial use is exceedingly difficult and, until recently, no commercially viable process for large scale production had been developed. The major drawback preventing the commercial success of chemical synthesis of GGC is the number of steps involved due to the three reactive groups on L-glutamic acid and L-cysteine molecules, which must be masked to achieve the correct regioisomer.  Similarly, there have been numerous attempts at biological production of GGC by fermentation over the years and none have been successfully commercialised.[11][12][13][14]

Towards the end of 2019, a biocatalytic process was developed in Australia and has been patented[15] and commercialised. GGC is now available as a supplement in the US under the trademarked name of Glyteine and sold as a formulated supplement under the Continual G brand.

Bioavailability and supplementation

A human clinical study in healthy, non-fasting adults demonstrated that orally administered GGC can significantly increase lymphocyte GSH levels indicating systemic bioavailability, validating the therapeutic potential of GGC,[16]

Animal model studies with GGC have supported a potential therapeutic role for GGC in both the reduction of oxidative stress induced damage in tissues, including the brain[17] and as a treatment for sepsis.[18]

In contrast, supplementation with glutathione is incapable of increasing cellular glutathione since the GSH concentration found in the extracellular environment is much lower than that found intracellularly by about a thousand-fold. This large difference means that there is an insurmountable concentration gradient that prohibits extracellular glutathione from entering cells.  Although currently unproven, GGC may be the pathway intermediate of glutathione transportation in multicellular organisms[19][20]

Safety

Safety assessment of GGC sodium salt in rats has shown that orally administered (gavage) GGC was not acutely toxic at the limit single dosage of 2000 mg/kg (monitored over 14 days) and demonstrated no adverse effects following repeated daily doses of 1000 mg/kg over 90 days.[21]

History

In 1983, pioneers of glutathione research, Mary E. Anderson and Alton Meister, were the first to report on the ability of GGC to augment cellular GSH levels in a rat model [3]. Intact GGC, which was synthesised in their own laboratory, was shown to be taken up by cells, bypassing the rate-limiting step of the GCL enzyme to be converted to glutathione. Control experiments with combinations of the constituent amino acids that make up GGC, including L-glutamic acid and L-cysteine, were ineffective. Since this initial work, only a few studies using GGC were performed due to the fact that there was no commercial source of GGC on the market. Subsequently, GGC has become commercially availabe and studies investigating its efficacy have commenced.[16][18][22]

References
  1. Orlowski, M.; Meister, A. (1970-11-01). "The Gamma-Glutamyl Cycle: A Possible Transport System for Amino Acids". Proceedings of the National Academy of Sciences. 67 (3): 1248–1255. doi:10.1073/pnas.67.3.1248. ISSN 0027-8424.
  2. Meister, A; Anderson, M E (1983). "Glutathione". Annual Review of Biochemistry. 52 (1): 711–760. doi:10.1146/annurev.bi.52.070183.003431. ISSN 0066-4154.
  3. Anderson, M. E.; Meister, A. (1983-02-01). "Transport and direct utilization of gamma-glutamylcyst(e)ine for glutathione synthesis". Proceedings of the National Academy of Sciences. 80 (3): 707–711. doi:10.1073/pnas.80.3.707. ISSN 0027-8424.
  4. Mårtensson, Johannes (1987). "Method for determination of free and total glutathione and γ-glutamylcysteine concentrations in human leukocytes and plasma". Journal of Chromatography B: Biomedical Sciences and Applications. 420: 152–157. doi:10.1016/0378-4347(87)80166-4. ISSN 0378-4347.
  5. Dalton, Timothy P.; Chen, Ying; Schneider, Scott N.; Nebert, Daniel W.; Shertzer, Howard G. (2004). "Genetically altered mice to evaluate glutathione homeostasis in health and disease". Free Radical Biology and Medicine. 37 (10): 1511–1526. doi:10.1016/j.freeradbiomed.2004.06.040. ISSN 0891-5849.
  6. Ferguson, Gavin; Bridge, Wallace (2016). "Glutamate cysteine ligase and the age-related decline in cellular glutathione: The therapeutic potential of γ-glutamylcysteine". Archives of Biochemistry and Biophysics. 593: 12–23. doi:10.1016/j.abb.2016.01.017. ISSN 0003-9861.
  7. Braidy, Nady; Zarka, Martin; Welch, Jeffrey; Bridge, Wallace (2015-04-27). "Therapeutic Approaches to Modulating Glutathione Levels as a Pharmacological Strategy in Alzheimer's Disease". Current Alzheimer Research. 12 (4): 298–313. doi:10.2174/1567205012666150302160308. ISSN 1567-2050.
  8. Quintana-Cabrera, Ruben; Bolaños, Juan (2013-01-29). "Glutathione and γ-glutamylcysteine in the antioxidant and survival functions of mitochondria". Biochemical Society Transactions. 41 (1): 106–110. doi:10.1042/bst20120252. ISSN 0300-5127.
  9. Quintana-Cabrera, Ruben; Fernandez-Fernandez, Seila; Bobo-Jimenez, Veronica; Escobar, Javier; Sastre, Juan; Almeida, Angeles; Bolaños, Juan P. (2012). "γ-Glutamylcysteine detoxifies reactive oxygen species by acting as glutathione peroxidase-1 cofactor". Nature Communications. 3 (1): 718. doi:10.1038/ncomms1722. ISSN 2041-1723.
  10. Nakamura, Yukiko K.; Dubick, Michael A.; Omaye, Stanley T. (2012). "γ-Glutamylcysteine inhibits oxidative stress in human endothelial cells". Life Sciences. 90 (3–4): 116–121. doi:10.1016/j.lfs.2011.10.016. ISSN 0024-3205.
  11. , "Microorganism and method for overproduction of gamma-glutamylcysteine and derivatives of this dipeptide by fermentation", issued 2014-04-15
  12. , "Candida utilis containing gamma-glutamylcysteine", issued 2003-03-26
  13. , "Gamma-glutamylcysteine-producing yeast and method of screening the same", issued 2002-11-21
  14. , "Method for producing γ-glutamylcysteine", issued 2003-12-11
  15. , "Process for the production of γ-glutamylcysteine", issued 2006-03-31
  16. Zarka, Martin Hani; Bridge, Wallace John (2017). "Oral administration of γ-glutamylcysteine increases intracellular glutathione levels above homeostasis in a randomised human trial pilot study". Redox Biology. 11: 631–636. doi:10.1016/j.redox.2017.01.014. ISSN 2213-2317.
  17. Le, Truc M.; Jiang, Haiyan; Cunningham, Gary R.; Magarik, Jordan A.; Barge, William S.; Cato, Marilyn C.; Farina, Marcelo; Rocha, Joao B.T.; Milatovic, Dejan; Lee, Eunsook; Aschner, Michael (2011). "γ-Glutamylcysteine ameliorates oxidative injury in neurons and astrocytes in vitro and increases brain glutathione in vivo". NeuroToxicology. 32 (5): 518–525. doi:10.1016/j.neuro.2010.11.008. ISSN 0161-813X. PMC 3079792.
  18. Yang, Yang; Li, Ling; Hang, Qiyun; Fang, Yuan; Dong, Xiaoliang; Cao, Peng; Yin, Zhimin; Luo, Lan (2019). "γ-glutamylcysteine exhibits anti-inflammatory effects by increasing cellular glutathione level". Redox Biology. 20: 157–166. doi:10.1016/j.redox.2018.09.019. ISSN 2213-2317.
  19. Wu, Guoyao; Fang, Yun-Zhong; Yang, Sheng; Lupton, Joanne R.; Turner, Nancy D. (2004-03-01). "Glutathione Metabolism and Its Implications for Health". The Journal of Nutrition. 134 (3): 489–492. doi:10.1093/jn/134.3.489. ISSN 0022-3166.
  20. Stark, Avishay-Abraham; Porat, Noga; Volohonsky, Gloria; Komlosh, Arthur; Bluvshtein, Evgenia; Tubi, Chen; Steinberg, Pablo (2003). "The role of γ-glutamyl transpeptidase in the biosynthesis of glutathione". BioFactors. 17 (1–4): 139–149. doi:10.1002/biof.5520170114. ISSN 0951-6433.
  21. Chandler, S.D.; Zarka, M.H.; Vinaya Babu, S.N.; Suhas, Y.S.; Raghunatha Reddy, K.R.; Bridge, W.J. (2012). "Safety assessment of gamma-glutamylcysteine sodium salt". Regulatory Toxicology and Pharmacology. 64 (1): 17–25. doi:10.1016/j.yrtph.2012.05.008. ISSN 0273-2300.
  22. Braidy, Nady; Zarka, Martin; Jugder, Bat-Erdene; Welch, Jeffrey; Jayasena, Tharusha; Chan, Daniel K. Y.; Sachdev, Perminder; Bridge, Wallace (2019-08-08). "The Precursor to Glutathione (GSH), γ-Glutamylcysteine (GGC), Can Ameliorate Oxidative Damage and Neuroinflammation Induced by Aβ40 Oligomers in Human Astrocytes". Frontiers in Aging Neuroscience. 11. doi:10.3389/fnagi.2019.00177. ISSN 1663-4365.
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