13 C-labelling and non-invasive detection of glutathione in human liver

Introduction Oxidative stress in a tissue results from an excess of reactive oxygen species, resulting in an inability of cells to maintain a reduced intracellular environment. Liver disease arises from broad range of processes, but oxidative stress is common to these processes and central to the mechanisms by which liver tissue damage occurs (1). The liver has multiple defences against oxidative stress, and glutathione (a tripeptide) is the principal intracellular antioxidant in liver tissue. Glutathione has a central role in maintaining a reduced intracellular environment, detoxifying xenobiotics and protecting against reactive oxygen species (2). Many studies have validated the importance of glutathione in liver disease, often using invasive (eg biopsy) methods to monitor glutathione content. We have developed non-invasive methods to measure in vivo liver glutathione concentration and synthesis rate, providing a dynamic measurement that is responsive to changing cellular oxidative stress defences (3). Our preclinical studies (3) have demonstrated that we can incorporate a C label into glutathione by administering C -labelled glycine to rats, as glycine is one of the building blocks of glutathione. By measuring the rate of appearance and magnitude of the C -label in glutathione we can report on glutathione concentration and synthesis rate, allowing quantification of tissue oxidative stress defences. Here we report the translation of our methods to human studies, successfully showing non-invasive in vivo detection of metabolically produced C-labelled glutathione in the liver of human subjects.