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Alfonso Pompella

Publications and source records attributed to Alfonso Pompella.

27 records · Page 2Linked to original sources
PubMed2002

Glutathione catabolism as a signaling mechanism.

Glutathione (GSH) is the main intracellular thiol antioxidant, and as such participates in a number of cellular antitoxic and defensive functions. Nevertheless, non-antioxidant functions of GSH have also been described, e.g. in modulation of cell proliferation and immune response. Recent studies from our and other laboratories have provided evidence for a third functional aspect of GSH, i.e. the prooxidant roles played by molecular species originating during its catabolism by the membrane ectoenzyme gamma-glutamyl transpeptidase (GGT). The reduction of metal ions effected by GSH catabolites is capable to induce redox cycling processes leading to the production of reactive oxygen species (superoxide, hydrogen peroxide), as well as of other free radicals. Through the action of these reactive compounds, GSH catabolism can ultimately lead to oxidative modifications on a variety of molecular targets, involving oxidation and/or S-thiolation of protein thiol groups in the first place. Modulating effects of this kind have been observed on several important, redox-sensitive components of the signal transduction chains, such as cell surface receptors, protein phosphatase activities and transcription factors. Against this background, the prooxidant reactions induced by GSH catabolism appear to represent a novel, as yet unrecognized mechanism for modulation of cellular signal transduction.

Animals↗
PubMed2002

Plasma total antioxidant capacity in hemodialyzed patients and its relationships to other biomarkers of oxidative stress and lipid peroxidation.

Patients undergoing long-term hemodialysis (HD) exhibit increased levels of oxidative stress, likely contributing to the increased rate of cardiovascular disease. The present study represents a critical evaluation of some of the most widely used oxidative indicators, as applied to the monitoring of hemodialysis-associated oxidative stress. Total plasma antioxidant capacity was determined by two independent procedures, the total antioxidant status (TAS) and the ferric reducing ability of plasma (FRAP) methods. Plasma lipid peroxidation was assessed by determining the peroxidation products malonaldehyde and 4-hydroxynonenal (MDA-4HNE) as well as lipid hydroperoxides ("Fox-2" and "d-ROMs" methods). Total plasma thiols and plasma alpha-tocopherol were also determined. MDA-4HNE levels were higher in HD patients and decreased following HD, possibly due to passive diffusion across dialysis filters. d-ROMs were also higher in HD patients but exhibited a further increase following the dialysis procedure. Serum alpha-tocopherol did not show any significant differences. Plasma thiols were lower in HD patients and were restored following HD. Plasma total antioxidant capacity determined with either method was unexpectedly higher in HD patients compared to controls, and decreased following HD. These data indicate that, of the biomarkers studied, d-ROMs level is the one more accurately reflecting the oxidative alterations taking place in HD patients, while determination of MDA-4HNE fails to detect oxidation occurring during the HD sessions. In addition, our findings point out that the determination of total antioxidant capacity in HD patients is severely affected by the concomitant fluctuations in plasma urate levels and therefore needs careful interpretation.

Adult↗
PubMedDate not supplied

Biomarkers.

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Amino Acids↗
PubMedDate not supplied

The S-thiolating activity of membrane gamma-glutamyltransferase: formation of cysteinyl-glycine mixed disulfides with cellular proteins and in the cell microenvironment.

Previous studies have documented that activity of the plasma membrane enzyme gamma-glutamyltransferase (GGT) is accompanied by prooxidant processes, with production of reactive oxygen species and oxidation of cellular protein thiols. The present work was aimed to verify the occurrence and extent of S-thiolation mediated by GGT and characterize the molecular species involved in mixed disulfide formation. Experiments show that the cysteinyl-glycine (CG) originating from cellular GGT-mediated glutathione (GSH) metabolism can efficiently thiolate cellular proteins, as well as proteins present in the extracellular environment. With cells presenting high levels of GGT expression, basal levels of CG-containing protein mixed disulfides are detectable, in cellular proteins, as well as in proteins of the culture medium. Stimulation of GGT activity in these cells by administration of substrates results in an increase of CG mixed disulfide formation and a concomitant decrease of GSH-containing disulfides, likely due to GGT-dependent removal of GSH from the system. The findings reported suggest that binding of CG ("protein S-cysteylglycylation") may represent an as yet unrecognized function of membrane GGT, likely playing a regulatory role(s) in the cell and its surroundings.

Cell Line, Tumor↗
PubMedDate not supplied

Redox modulation of NF-kappaB nuclear translocation and DNA binding in metastatic melanoma. The role of endogenous and gamma-glutamyl transferase-dependent oxidative stress.

AIMS AND BACKGROUND: The transcription factor NF-kappaB is implicated in the expression of genes involved in cell proliferation, apoptosis and metastasis. In melanoma, high constitutive levels of NF-kappaB activation are usually observed. NF-kappaB is regulated by oxidation/reduction (redox) processes, and the occurrence of constitutive oxidative stress in melanoma cells has been documented. Recent studies of our laboratories showed that the membrane-bound gamma-glutamyl transferase (GGT) enzyme activity--expressed by a number of malignancies, including melanoma--can act as a basal source of superoxide, hydrogen peroxide and other prooxidants. METHODS: In the present study we utilized the 2/60 clone of Me665/2 human metastatic melanoma, which displays high levels of GGT activity, in order to verify if the presence of this enzyme--through the promotion of redox processes--may influence the activation status of NF-kappaB. The latter was evaluated by determining the nuclear translocation of the p65 subunit (by immunoblot), the DNA binding of NF-kappaB (by electrophoretic mobility shift assay) and its transcriptional activity (by gene transactivation studies). RESULTS: Me665/2/60 cells displayed a basal production of hydrogen peroxide. Stimulation of GGT activity by its substrates glutathione and glycyl-glycine caused additional production of hydrogen peroxide, up to levels approx. double the basal levels. Nuclear translocation of the NF-kappaB p65 subunit, DNA-binding and gene transactivation were thus investigated in Me665/2/60 cells whose GGT activity was modulated by means of substrates or inhibitors. Stimulation of GGT activity resulted in increased nuclear translocation of p65, while on the other hand NF-kappaB DNA binding and gene transactivation were paradoxically decreased. NF-kappaB DNA binding could be restored by treating cell lysates with the thiol-reducing agent dithiothreitol (DTT). Treatment of cells with exogenous hydrogen peroxide did not affect NF-kappaB activation status. CONCLUSIONS: Altogether, the data obtained indicate that GGT activity may impair the redox status of thiols that is critical for NF-kappaB DNA binding and gene transactivation, through the production of prooxidant species allegedly distinct from hydrogen peroxide. GGT activity therefore appears to be an additional factor in modulation of NF-kappaB transcriptional activity in melanoma, capable of hindering NF-kappaB DNA binding even in conditions where continuous oxidative stress would favor NF-kappaB nuclear translocation.

Cell Line, Tumor↗