Dataset Information

Oral administration of ?-glutamylcysteine increases intracellular glutathione levels above homeostasis in a randomised human trial pilot study.

ABSTRACT:

Objective

To determine if orally dosed ?-glutamylcysteine (?-GC) can increase cellular glutathione (GSH) levels above homeostasis. Many chronic and age-related disorders are associated with down-regulation, or impairment, of glutamate cysteine ligase (GCL). This suggests that ?-GC supply may become limiting for the maintenance of cellular GSH at the normal levels required to effectively protect against oxidative stress and any resulting physiological damage.

Methods

GSH levels were measured in lymphocytes of healthy, non-fasting participants before and after single oral doses (2 and 4g) of ?-GC. Blood samples were immediately processed using high speed fluorescence-activated cell sorting to isolate 10⁶ lymphocytes that were then assayed for GSH content.

Results

A single 2g dose of ?-GC increased lymphocyte GSH content above basal levels (53±47%, p<0.01, n=14) within 90min of administration. A randomized dosage (2 and 4g ?-GC) crossover design was used to explore the pharmacokinetics of this GSH increase. In general, for both dose levels (n=9), GSH increased from initial basal levels over 3h (t_max) before reaching maximum GSH concentrations (C_max) that were near two (2g ?-GC) to three (4g ?-GC) fold basal levels (0.4 nmol/10⁶ lymphocytes). Beyond t_max, GSH levels progressively declined reaching near basal levels by 5h. The GSH half-life was between 2 and 3h with exposure (AUC) to increased GSH levels of 0.7 (2g ?-GC) and 1.8 (4g ?-GC) nmol.h/10⁶ lymphocytes.

Conclusions

Oral ?-GC is a non-toxic form of cysteine that can be directly taken up by cells and transiently increase lymphocyte GSH above homeostatic levels. Our findings that ?-GC can increase GSH levels in healthy subjects suggests that it may have potential as an adjunct for treating diseases associated with chronic GSH depletion. This trial was registered at anzctr.org.au as ACTRN12612000952842.

SUBMITTER: Zarka MH

PROVIDER: S-EPMC5284489 | biostudies-literature | 2017 Apr

REPOSITORIES: biostudies-literature

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Publications

Oral administration of γ-glutamylcysteine increases intracellular glutathione levels above homeostasis in a randomised human trial pilot study.

Zarka Martin Hani MH Bridge Wallace John WJ

Redox biology 20170122

<h4>Objective</h4>To determine if orally dosed γ-glutamylcysteine (γ-GC) can increase cellular glutathione (GSH) levels above homeostasis. Many chronic and age-related disorders are associated with down-regulation, or impairment, of glutamate cysteine ligase (GCL). This suggests that γ-GC supply may become limiting for the maintenance of cellular GSH at the normal levels required to effectively protect against oxidative stress and any resulting physiological damage.<h4>Methods</h4>GSH levels wer ...[more]

PMID: 28131081

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Project description:gamma-Glutamylcysteine synthetase (GCS) is reported to catalyse the rate-limiting step in glutathione biosynthesis, and is a heterodimer composed of a catalytic subunit [heavy subunit (GCSh) of Mr 73000] and a regulatory subunit [light subunit (GCSl) of Mr 31000]. In the present study, we have demonstrated for the first time a potential role for GCSl in resistance towards doxorubicin and cadmium chloride. Addition of recombinant GCSl to HeLa cell extracts in vitro was found to result in an increase in GCS activity of between 2- and 3-fold. Transient transfections of COS-1 cells with the GCSl cDNA cause an increase in GCS activity of approx. 2-fold, and a small but significant (P=0.008) increase in glutathione levels from 126.9+/-4. 2 nmol/mg protein to 178.8+/-19.1 nmol/mg protein. We proceeded to make a HeLa cell line (LN73), which stably overexpresses GCSl. These cells overexpress GCSl approx. 20-fold above basal levels. LN73 was found to have a 2-fold increase in GCS activity (437.3+/-85.2 pmol/min per mg) relative to the control cell line, HL9 (213.4+/-71. 8 pmol/min per mg). In contrast with the transient transfections in COS-1 cells, stable overexpression of GCSl was found not to be associated with an increase in glutathione content. However, when the LN73 and HL9 cells were treated with the glutathione-depleting agent, diethylmaleate, the LN73 cells were found to have an enhanced ability to regenerate glutathione, compared with HL9 cells. The cell lines were treated with various anti-cancer drugs, and their cytotoxicity was examined. No obvious differences in toxicity were observed between the different cell lines following treatment with cisplatin and melphalan. The redox-cycling agent doxorubicin, however, was found to be more toxic (approx. 2-fold) to the HL9 cells than the LN73 cells. When the cells were treated with the carcinogenic transition-metal compound, cadmium chloride, LN73 cells were found to be approx. 3-fold more resistant than HL9 cells.

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