Ingredientsγ-L-Glutamyl-L-cysteine, also known as γ-glutamylcysteine (GGC), is a dipeptide found in animals, plants, fungi, some bacteria, and archaea. It possesses a relatively unusual γ-bond between its two constituent amino acids, L-glutamic acid and L-cysteine, and is a key intermediate in the γ-glutamyl cycle first described by Meister in the 1970s. The compound is variously abbreviated in the scientific literature as GGC, γ-GC, or γ-EC. Its IUPAC name is (2S)-2-amino-5-[[(1R)-1-(carboxymethylcarbamoyl)-2-sulfanylethyl]amino]-5-oxopentanoic acid. The CAS registry number is 636-58-8.
GGC is the most immediate precursor to the antioxidant glutathione. It is synthesized from L-glutamic acid and L-cysteine in the cytoplasm of virtually all cells in an adenosine triphosphate (ATP)-requiring reaction catalyzed by the enzyme glutamate-cysteine ligase (GCL, EC 6.3.2.2; formerly γ-glutamylcysteine synthetase).
The intracellular concentration of gamma-glutamylcysteine is generally low because it reacts rapidly with glycine to form glutathione. This second and final reaction step in glutathione biosynthesis is catalyzed by the ATP-dependent glutathione synthase (GS) enzyme.
GGC is a dipeptide found in animals, plants, fungi, some bacteria, and archaea, making it a ubiquitous molecule in biology rather than a compound restricted to any single biological kingdom. Within the human body it is synthesized endogenously in the cytosol of all cell types as an obligatory metabolic intermediate.
Garlic (Allium sativum L.) is a particularly rich source of organosulfur compounds, which are currently under investigation for their potential to prevent and treat disease. The two main classes of organosulfur compounds found in whole garlic cloves are L-cysteine sulfoxides and γ-glutamyl-L-cysteine peptides. Fresh garlic cloves contain about 2 to 6 mg/g of γ-glutamyl-S-allyl-L-cysteine (0.2%–0.6% fresh weight) and 6 to 14 mg/g of alliin (0.6%–1.4% fresh weight).
A garlic bulb has about 0.9% γ-glutamylcysteine, which naturally undergoes hydrolysis and oxidation to form S-allyl cysteine. Garlic contains several characteristic organosulfur compounds, including diallyl sulfide, allicin (diallyl thiosulphate), γ-glutamylcysteine, and S-allyl cysteine (alliin) and ajoene. Beyond garlic and other Allium species (such as onions, leeks, and chives), GGC occurs as an endogenous metabolic intermediate in virtually every aerobic organism that biosynthesizes glutathione.
The predominant sulfur-containing natural ingredient in whole garlic is γ-glutamyl-S-allyl-L-cysteine, which is catabolized to water-soluble compounds like S-allyl cysteine (SAC) by the enzyme γ-glutamyl transpeptidase during the natural aging process of aged garlic extract (AGE).
Gamma-glutamylcysteine is available in several distinct chemical and commercial forms:
While the direct historical documentation of gamma-glutamylcysteine as a distinct medicinal remedy is limited, its significance is deeply intertwined with centuries-old practices focusing on health, vitality, and detoxification. Traditional remedies from various cultures have long valued ingredients rich in its constituent amino acids, such as garlic and onions, which have been used for promoting liver health, detoxifying the body, and enhancing immunity. These effects are now understood to be partly due to their ability to support gamma-glutamylcysteine and glutathione synthesis within the body.
Garlic has long been known as a disease-impeding and health-boosting foodstuff, and it has been utilized as a therapeutic medicine for treating a variety of ailments. Garlic, a component of Allium plants, has been utilized for therapeutic purposes since ancient times. Ancient Egyptian, Greek, Roman, and Chinese medical traditions documented the use of garlic for conditions ranging from infections and wounds to cardiovascular complaints.
GGC as a specifically identified, isolated molecule is a product of modern biochemistry. It was characterized as a distinct enzymatic intermediate during the 20th-century elucidation of the glutathione biosynthesis pathway. It is a key intermediate in the γ-glutamyl cycle first described by Meister in the 1970s. Thus, no traditional medical system used or named GGC as a discrete compound; rather, it was present in high-GGC food sources such as fresh garlic that were valued long before the compound's identity was known.
γ-Glutamylcysteine, an intermediate for the biosynthesis of glutathione, is a thiol compound expected to have a flavor-improving effect similar to that of cysteine, and has been considered as a potential therapeutic agent for lifestyle-related diseases and Alzheimer's disease. Its specific investigation and supplemental use are entirely modern phenomena, beginning primarily in the early 21st century.
In the first step of glutathione biosynthesis, γ-glutamylcysteine synthetase (γ-GCL) catalyzes the formation of γ-glutamylcysteine from glutamate and cysteine in an ATP-dependent reaction. Gamma-glutamylcysteine is defined as a dipeptide formed from the combination of cysteine and glutamate, serving as a precursor in the synthesis of glutathione (GSH), which is critical for maintaining redox balance in cells.
The therapeutic potential for GGC to increase GSH is related to the second GSH biosynthetic enzyme, glutathione synthetase (GS), which is not regulated by non-allosteric feedback inhibition by GSH. GS catalyzes the addition of glycine to GGC to produce GSH. This provides support for the benefits of GGC as an immediate precursor to GSH.
γ-Glutamylcysteine synthetase (γGCS), a rate-limiting enzyme in glutathione biosynthesis, plays a central role in glutathione homeostasis and is a target for development of potential therapeutic agents against parasites and cancer.
The limiting factors for strategies aimed at elevating GSH levels include: (1) the inability of GSH to cross the cell membrane via direct absorption; (2) feedback inhibitory effects of GSH on glutamate cysteine ligase (GCL) activity (the first biosynthetic enzyme), which is regulated by the availability of cysteine; and (3) reduced activity of GCL with advanced age. Because GGC is a substrate for the second biosynthetic enzyme (glutathione synthetase, GS), and GS is not subject to the same feedback inhibition, exogenous GGC can raise intracellular GSH above homeostatic levels in a way that other precursor strategies cannot reliably accomplish.
To address GSH depletion arising from dysregulated GCL, the exogenous supply of γ-glutamylcysteine (γ-GC) could offer a means for increasing GSH levels, providing it is taken up by cells intact.
A particularly important mechanistic discovery established that GGC is not merely a passive precursor but an independent antioxidant molecule. By directing the biosynthesis of γ-glutamylcysteine—the immediate glutathione precursor—to mitochondria, it efficiently detoxifies hydrogen peroxide and superoxide anion, regardless of cellular glutathione concentrations. Knocking down glutathione peroxidase-1 drastically increases superoxide anion in cells synthesizing mitochondrial γ-glutamylcysteine. In vitro, γ-glutamylcysteine is as efficient as glutathione in disposing of hydrogen peroxide by glutathione peroxidase-1.
Glutathione reductase (GR) does not recognize γ-glutamylcysteine or its disulfide form as substrates, meaning the compound participates in a non-recyclable antioxidant pathway distinct from the GSH/GSSG redox cycle. This places GGC in an unusual biochemical position: it can act as a GPx-1 cofactor to neutralize reactive oxygen species, but unlike GSH, it cannot be regenerated (recycled) by glutathione reductase after oxidation.
GGC is a dipeptide which exhibits potent antioxidant properties in several experimental models. It serves as an essential cofactor for the antioxidant enzyme glutathione peroxidase (GPx) and is a precursor for GSH synthesis.
In vivo investigation showed that γ-GC reduced sepsis lethality and attenuated systemic inflammatory responses in mice, as well as inhibited lipopolysaccharide (LPS)-stimulated production of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). Mechanistically, γ-GC suppressed LPS-induced reactive oxygen species accumulation and GSH depletion. Inflammatory stimuli, such as LPS treatment, upregulated the expression of glutathione synthetase via activating nuclear factor-erythroid 2-related factor (Nrf2) and nuclear factor kappa B (NF-κB) pathways, thereby promoting synthesis of GSH from γ-GC.
Both in vivo and in vitro experiments demonstrated that γ-GC exhibited better therapeutic effects against inflammation compared with N-acetyl-L-cysteine (NAC) and GSH.
Pretreatment with γ-GC increases the ratio of reduced:oxidized GSH levels in both neurons and astrocytes and increases total GSH levels in neurons. In addition, γ-GC pretreatment decreases isoprostane formation in both neurons and astrocytes, as well as nuclear factor erythroid 2-related factor 2 (Nrf2) nuclear translocation in astrocytes in response to H2O2-induced oxidative stress.
A consistent underlying index of aging is a decline in the cellular levels of the tripeptide glutathione (GSH). GSH is an essential thiol antioxidant produced in the cytosol of all cells and plays a key role in protecting against oxidative stress by neutralizing free radicals and reactive oxygen species (ROS). The decline in GSH has been associated with changes in the expression and activity of the rate-limiting enzyme glutamate cysteine ligase (GCL), which produces the intermediate dipeptide γ-glutamylcysteine (γ-GC).
GCS activity was significantly decreased with increased age in liver, kidney, lung, and red blood cells. Parallel with the decreased enzyme activity, the protein and mRNA contents of both GCS subunits also changed inversely with age in liver, kidney, and lung, implying decreased GCS gene expression during aging. Such a reduced GCS gene expression was accompanied by a decline in total GSH content without any change in cysteine concentration.
An age-related truncation of the enzyme γ-glutamylcysteine ligase catalytic subunit (GCLC) has been discovered, a critical enzyme involved in GSH biosynthesis. This truncation impairs intracellular GSH synthesis and contributes to diminished GSH levels in aged lenses. Blocking GCLC truncation preserves GSH levels in aged lenses and significantly delays cataract formation.
Impairment of the transcriptional activity of Nrf2 has been demonstrated to contribute to GCL dysregulation in aged rats. A 2016 review by Ferguson and Bridge focused on the suitability of treatment with exogenous γ-GC to raise GSH levels by circumventing the age-related dysregulation of the rate-limiting step of GSH biosynthesis, providing promise for future research for the treatment of chronic oxidative stress-related diseases.
Mice that have had the glutamate-cysteine ligase (GCL) gene knocked out do not develop beyond the embryo stage and die before birth. This is because gamma-glutamylcysteine is vital for the biosynthesis of glutathione (GSH).
The most direct clinical evidence for GGC concerns its capacity to elevate intracellular glutathione above baseline in human subjects. A randomised human trial pilot study published by Zarka and Bridge (2017) investigated whether orally dosed γ-glutamylcysteine can increase cellular GSH levels above homeostasis. Many chronic and age-related disorders are associated with down-regulation or impairment of glutamate cysteine ligase (GCL), suggesting that γ-GC supply may become limiting. GSH levels were measured in lymphocytes of healthy, non-fasting participants before and after single oral doses (2 and 4 g) of γ-GC. Blood samples were processed using high-speed fluorescence-activated cell sorting to isolate lymphocytes. A single 2 g dose of γ-GC increased lymphocyte GSH content above basal levels (53±47%, p<0.01, n=14) within 90 min of administration.
A randomized dosage (2 and 4 g γ-GC) crossover design was used to explore the pharmacokinetics of this GSH increase. A randomised human pilot study found that single doses of oral administered GGC at 2 g and 4 g significantly increased GSH levels in lymphocytes within 3 hours, with a return to normal homeostatic levels by 5 hours.
A randomized human pilot study demonstrated that oral doses of 2 mg/kg and 4 mg/kg γ-glutamylcysteine produced significant elevations in intracellular erythrocyte GSH levels above baseline, whereas equivalent oral GSH doses did not increase intracellular GSH.
Evidence strength: This evidence is preliminary. The trial is a single small pilot study with short-term single-dose measurements in healthy adults. It establishes proof-of-concept bioavailability but does not establish efficacy for any clinical condition, and no chronic dosing or disease-state data exist from randomized controlled trials in humans as of the available literature.
Many chronic and age-related diseases are associated with a decline in cellular GSH levels or impairment in the catalytic activity of the GSH biosynthetic enzyme glutamate cysteine ligase (GCL). γ-Glutamylcysteine, a precursor to glutathione, can replenish depleted GSH levels under oxidative stress conditions by circumventing the regulation of GSH biosynthesis and providing the limiting substrate. Soluble amyloid-β (Aβ) oligomers have been shown to induce oxidative stress, synaptic dysfunction, and memory deficits reported in Alzheimer's disease.
A 2019 cell-based study by Braidy et al. (published in Frontiers in Aging Neuroscience) examined GGC in primary human astrocytes exposed to Aβ₄₀ oligomers. It has been shown that administration of γ-glutamylcysteine (GGC) increases cellular levels of GSH, circumventing the regulation of GSH biosynthesis by providing the limiting substrate. The study used human-derived cells, making it more translationally relevant than purely rodent work, but it remains an in vitro model.
In animal models, supplementation with γ-GC can reduce brain oxidative stress and neuroinflammation and maintain antioxidant status in an AD mouse model. Supplementation with γ-GC can also reduce amyloid pathology and improve learning and memory deficits in an AD mouse model.
The ethyl ester prodrug form (GCEE) has been studied in neuronal cultures: administration of gamma-glutamylcysteine ethyl ester (GCEE) increases cellular levels of GSH, circumventing the regulation of GSH biosynthesis by providing the limiting substrate. In one study, the protective role of GSH up-regulation by GCEE was evaluated against the oxidative and neurotoxic effects of Aβ(1-42) in primary neuronal culture. Addition of GCEE to neurons led to an elevated mean cellular GSH level compared with untreated control.
GSH and isoprostane levels significantly correlate with increased neuron and astrocyte viability in cells pretreated with γ-GC. Administration of a single intravenous injection of γ-GC to mice significantly increases GSH levels in the brain, heart, lungs, liver, and muscle tissue.
A clinical trial (NCT07583251) is now underway to evaluate GGC specifically in patients with mild cognitive impairment. Oxidative stress plays a key role in aging and neurodegenerative diseases, including Alzheimer's Disease. This study is designed as an open-label, single-center, dose escalation clinical trial to evaluate the safety and tolerability of GGC supplementation in patients with MCI, with the aim of identifying the maximum tolerated or recommended dose for further clinical evaluation.
Evidence strength: Currently limited to in vitro (cell culture) and in vivo (mouse model) data, with one clinical feasibility trial recruiting. No completed randomized controlled trials in human patients with Alzheimer's disease or other neurodegenerative conditions have been published.
γ-Glutamylcysteine (γ-GC), an intermediate dipeptide of the GSH-synthesis pathway and harboring anti-inflammatory properties, represents a relatively unexplored option for sepsis treatment. Research published in Redox Biology (Yang et al., 2019) examined GGC's effects both in vitro and in a mouse cecal ligation and puncture sepsis model. In vivo investigation showed that γ-GC reduced sepsis lethality and attenuated systemic inflammatory responses in mice, as well as inhibited LPS-stimulated production of TNF-α, IL-1β. These findings suggested that γ-GC might represent a potential therapeutic agent for sepsis treatment.
Evidence strength: Preclinical only (in vitro and mouse models). No human clinical trials for sepsis or inflammatory disease have been published.
Due to compromised glutathione transport into the extracellular environment, excessive ROS and inflammation are persistent in the CF lung. A considerable body of research has targeted glutathione supplementation as a therapeutic strategy to restore redox homeostasis in patients with CF.
Administered glutathione and cysteine prodrugs such as N-acetylcysteine (NAC) simply provide substrates for GCL and thereby cannot increase cellular glutathione levels above homeostasis. An inability to increase above homeostasis may explain why studies with oral and inhaled formulations of thiols (GSH and NAC) have repeatedly failed to demonstrate consistent improvements in CF clinical outcomes.
Research confirmed that GGC improves cell metabolic viability, tight junction activity, and attenuates LPS-induced oxidative stress and stress granule formation in a 3D-differentiated airway model constructed from primary cystic fibrosis human bronchial cells. The immediate precursor to glutathione, γ-glutamylcysteine (GGC), has shown superior efficacy in increasing intracellular GSH levels in cardiac, liver, and neural cells in vitro.
Evidence strength: In vitro evidence using human-derived CF cells is promising but preliminary. No human clinical trials in CF patients have been reported.
Gamma-glutamylcysteine ethyl ester (GCEE) is a precursor of glutathione with promising hepatoprotective effects. One investigation evaluated the hepatoprotective effects of GCEE against cyclophosphamide-induced toxicity, pointing to the possible role of peroxisome proliferator activated receptor gamma (PPARγ). Pretreatment with GCEE significantly alleviated cyclophosphamide-induced liver injury by reducing serum aminotransferases, increasing albumin, and preventing histopathological and hematological alterations. GCEE suppressed lipid peroxidation and nitric oxide production and restored GSH and enzymatic antioxidants in the liver, which were associated with downregulation of COX-2, iNOS, and NF-κB.
Evidence strength: Animal (rodent) data only. Findings support plausible hepatoprotective mechanisms but have not been replicated or tested in human clinical trials.
γ-Glutamylcysteine (GGC) is a dipeptide and precursor of GSH. Unlike GSH, supplemental GGC can be taken up into cells/tissues and directly used as a substrate for GSH synthesis. A study by Nakamura, Dubick, and Omaye investigated the efficacy of GGC at graded concentrations on GSH synthesis, oxidative stress, and redox-sensitive transcription factor DNA binding in human umbilical vein endothelial cells (HUVEC), finding evidence that GGC inhibits oxidative stress in this cell type.
Evidence strength: In vitro, cell culture only. No human vascular outcome trials exist.
The ethyl ester prodrug GCEE has been investigated for traumatic brain injury (TBI). The synthetic agent gamma-glutamylcysteinyl ethyl ester (GCEE) has been shown to be an effective way for boosting endogenous levels of the key antioxidant GSH and thus blocking oxidative neuronal damage in many experimental models. In one study, researchers investigated whether GCEE can reduce oxidative injury in brain endothelium. A Phase 1 clinical trial is listed as investigating GGC supplementation for repetitive head impacts and brain injury (ClinicalTrials.gov), but results have not yet been published.
Evidence strength: Primarily preclinical. A Phase 1 trial is underway. No completed clinical data are available.
The body systems with which GGC is associated span wherever glutathione physiology is relevant—which encompasses essentially all aerobic tissues:
Because GGC is still an early-stage investigational ingredient for human supplementation, the dosage evidence base is narrow:
No established chronic maintenance dose, therapeutic dose, or regulatory recommended daily intake exists for GGC as of current published literature. The 2 g and 4 g single-dose findings represent the totality of human dosage data published in peer-reviewed literature.
Animal safety trials have demonstrated that GGC is safe at a repeated limit dosage of 1000 mg/kg/day over a 90-day period. In acute studies, a 2000 mg/kg single sodium GGC dose was well tolerated by all animals with no fatalities and no observed abnormalities. These findings provide a foundation for the safety assessment, though translating such animal findings directly to human equivalent doses requires further study.
The published human pilot study (Zarka & Bridge, 2017) reported no serious adverse events at doses of 2 g and 4 g in healthy adults, but the study was small (n=14) and measured only a single administration. This study is designed to generate preliminary clinical safety data to inform the feasibility and design of larger controlled trials, indicating that formal safety profiling in patient populations is still at an early stage.
The feedback inhibitory effects of GSH on glutamate cysteine ligase (GCL) activity mean that exogenous GSH is limited in its capacity to raise intracellular GSH above homeostasis. Because GGC bypasses this step, supraphysiological GSH accumulation is theoretically possible with high-dose or repeated GGC supplementation, though no toxic threshold in humans has been established in the published literature.
Glutathione reductase (GR) does not recognize γ-glutamylcysteine or its disulfide form as substrates, meaning the compound participates in a non-recyclable antioxidant pathway distinct from the GSH/GSSG redox cycle. This means that once GGC is oxidized in its role as a GPx-1 cofactor, it is consumed and cannot be regenerated by the cell's normal recycling machinery, which is biochemically distinct from the behavior of glutathione itself.
The role of overexpression of γ-glutamylcysteine synthetase in terms of cancer chemotherapy has been a subject of research attention. Because many cytotoxic chemotherapy agents operate in part by inducing oxidative stress in cancer cells, strategies that dramatically elevate intracellular GSH (including GGC supplementation) could theoretically interfere with the mechanisms of action of alkylating agents and other GSH-sensitive drugs. This is a documented pharmacological consideration, not merely theoretical: buthionine sulfoximine (BSO), which inhibits GCL and depletes GSH, has actually been investigated as a chemotherapy sensitizer precisely because elevated GSH is linked to drug resistance.
Supplementation of NAC or L-cysteine may be ineffective in aging brain due to glutamylcysteine ligase (GCL) deficiency in the aging brain. Preclinical studies in rodent models and human nutraceutical trials show that NAC could be beneficial for AD; however, evidence supporting the beneficial effect of NAC alone in human AD cases is relatively weak, as NAC supplementation alone leads to limited benefits in human studies. GGC, by acting downstream of GCL, is hypothesized to circumvent this limitation, but clinical confirmation is lacking.
Administered glutathione and cysteine prodrugs such as N-acetylcysteine simply provide substrates for GCL and thereby cannot increase cellular glutathione levels above homeostasis. An inability to increase above homeostasis may explain why studies with oral and inhaled formulations of thiols have repeatedly failed to demonstrate consistent improvements in CF clinical outcomes.
Raw garlic can induce a variety of negative effects, including anemia, growth regression, and gut microbiome devastation, as well as affect serum protein levels. Fresh garlic can also cause indigestion and leave a pungent odor on the breath. These safety signals pertain to the whole food source rather than to isolated GGC as a supplement, and the amounts of GGC deliverable from culinary garlic doses are substantially lower than the gram-level doses studied in the clinical pilot trial.
As of the published literature, the evidence for GGC as a dietary supplement can be summarized as follows: its biochemistry is well characterized, the single human pilot pharmacokinetic trial demonstrates proof-of-concept bioavailability and short-term GSH elevation, and multiple preclinical (cell culture and animal) studies establish plausible mechanisms in neurodegeneration, inflammation, hepatoprotection, and pulmonary disease. However, randomized controlled trials with clinical endpoints, long-term safety and efficacy data, and regulatory approval as a therapeutic agent are lacking. GGC should currently be regarded as a research-stage compound with compelling mechanistic underpinnings and preliminary translational data.
Health conditions that Gamma-glutamylcysteine may help support.
Body systems that Gamma-glutamylcysteine may help support.
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