Mixed results with mixed disulfides

S-adenosyl-L-methionine (SAMe) halts the autoimmune response in patients with primary biliary cholangitis (PBC) via antioxidant and S-glutathionylation processes in cholangiocytes

S-adenosyl-L-methionine is an endogenous molecule with hepato-protective properties linked to redox regulation and methylation. Here, the potential therapeutic value of SAMe was tested in 17 patients with PBC, a cholestatic disease with autoimmune phenomena targeting small bile ducts. Nine patients responded to SAMe (SAMe responders) with increased serum protein S-glutathionylation. That posttranslational protein modification was associated with reduction of serum anti-mitochondrial autoantibodies (AMA-M2) titers and improvement of liver biochemistry. Clinically, SAMe responders were younger at diagnosis, had longer duration of the disease and lower level of serum S-glutathionylated proteins at entry. SAMe treatment was associated with negative correlation between protein S-glutathionylation and TNFα. Furthermore, AMA-M2 titers correlated positively with INFγ and FGF-19 while negatively with TGFβ. Additionally, cirrhotic PBC livers showed reduced levels of glutathionylated proteins, glutaredoxine-1 (Grx-1) and GSH synthase (GS). The effect of SAMe was also analyzed in vitro. In human cholangiocytes overexpressing miR-506, which induces PBC-like features, SAMe increased total protein S-glutathionylation and the level of γ-glutamylcysteine ligase (GCLC), whereas reduced Grx-1 level. Moreover, SAMe protected primary human cholangiocytes against mitochondrial oxidative stress induced by tBHQ (tert-Butylhydroquinone) via raising the level of Nrf2 and HO-1. Finally, SAMe reduced apoptosis (cleaved-caspase3) and PDC-E2 (antigen responsible of the AMA-M2) induced experimentally by glycochenodeoxycholic acid (GCDC). These data suggest that SAMe may inhibit autoimmune events in patients with PBC via its antioxidant and S-glutathionylation properties. These findings provide new insights into the molecular events promoting progression of PBC and suggest potential therapeutic application of SAMe in PBC.

The glutathione system and the related thiol network in Caenorhabditis elegans

Advances in the field of redox biology have contributed to the understanding of the complexity of the thiol-based system in mediating signal transduction. The redox environment is the overall spatiotemporal balance of oxidation-reduction systems within the integrated compartments of the cell, tissues and whole organisms. The ratio of the reduced to disulfide glutathione redox couple (GSH:GSSG) is a key indicator of the redox environment and its associated cellular health. The reaction mechanisms of glutathione-dependent and related thiol-based enzymes play a fundamental role in the function of GSH as a redox regulator. Glutathione homeostasis is maintained by the balance of GSH synthesis (de novo and salvage pathways) and its utilization through its detoxification, thiol signalling, and antioxidant defence functions via GSH-dependent enzymes and free radical scavenging. As such, GSH acts in concert with the entire redox network to maintain reducing conditions in the cell. Caenorhabditis elegans offers a simple model to facilitate further understanding at the multicellular level of the physiological functions of GSH and the GSH-dependent redox network. This review discusses the C. elegans studies that have investigated glutathione and related systems of the redox network including; orthologs to the protein-encoding genes of GSH synthesis; glutathione peroxidases; glutathione-S-transferases; and the glutaredoxin, thioredoxin and peroxiredoxin systems.

Exercise redox biochemistry: Conceptual, methodological and technical recommendations

Exercise redox biochemistry is of considerable interest owing to its translational value in health and disease. However, unaddressed conceptual, methodological and technical issues complicate attempts to unravel how exercise alters redox homeostasis in health and disease. Conceptual issues relate to misunderstandings that arise when the chemical heterogeneity of redox biology is disregarded: which often complicates attempts to use redox-active compounds and assess redox signalling. Further, that oxidised macromolecule adduct levels reflect formation and repair is seldom considered. Methodological and technical issues relate to the use of out-dated assays and/or inappropriate sample preparation techniques that confound biochemical redox analysis. After considering each of the aforementioned issues, we outline how each issue can be resolved and provide a unifying set of recommendations. We specifically recommend that investigators: consider chemical heterogeneity, use redox-active compounds judiciously, abandon flawed assays, carefully prepare samples and assay buffers, consider repair/metabolism, use multiple biomarkers to assess oxidative damage and redox signalling.

Redox status in a model of cancer stem cells

Reversible oxidation of Cys residues is a crucial element of redox homeostasis and signaling. According to a popular concept in oxidative stress signaling, the oxidation of targets of signals can only take place following an overwhelming of the cellular antioxidant capacity. This concept, however, ignores the activation of feedback mechanisms possibly leading to a paradoxical effect. In a model of cancer stem cells (CSC), stably overexpressing the TAZ oncogene, we observed that the increased formation of oxidants is associated with a globally more reduced state of proteins. Redox proteomics revealed that several proteins, capable of undergoing reversible redox transitions, are indeed more reduced while just few are more oxidized. Among the proteins more oxidized, G6PDH emerges as both more expressed and activated by oxidation. This accounts for the observed more reduced state of the NADPH/NADP⁺ couple. The dynamic redox flux generating this apparently paradoxical effect is rationalized in a computational system biology model highlighting the crucial role of G6PDH activity on the rate of redox transitions eventually leading to the reduction of reversible redox switches.