Reaction of cysteine and glutathione (GSH) at the freshly fractured quartz surface: a possible role in silica-related diseases?
The reactivity of quartz dusts towards glutathione (GSH) and cysteine (Cys) has been investigated. Cys and GSH react, without being adsorbed (UV-Vis spectroscopy), with commercial quartz dusts in an exposed surface-dependent way, but not with amorphous silica. GSH and Cys have been contacted with freshly ground quartz (agate jar QZg-a and steel jar QZg-s) and quartz heated in air at 500 degrees C (QZs-500) and with a dust generated from a purified quartz (99.9999%) to detect the nature of the reacting surface sites. With both GSH and Cys, the highest reactivity was found on the particles ground in a steel jar, while pure quartz was fully inactive. Detection of the radical GS* (spin trapping) suggests a radical mechanism of oxidation to disulphide onto surface-bound iron traces, more abundant on QZg-s and absent on the pure quartz. Oxidation of thiol groups occurs at surface sites different from those involved in the homolytic rupture of a C-H bond. Both reactions are more pronounced on freshly ground samples, but the C-H rupture takes place at silicon-based surface radicals and Fe2+ centers, while oxidation of GSH and Cys requires Fe3+ centers. As all commercial quartz dusts contain surface iron as an impurity, depletion of extracellular or intracellular GSH may contribute to the oxidative damage caused by particle-derived and cell-derived reactive oxygen species.
Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Materiali and Interdepartmental Center for Studies on Asbestos and other Toxic Particulates, Università degli Studi di Torino, Torino, Italy.
Ivana
I
Fenoglio
Stefania
S
Fonsato
Bice
B
Fubini
D000327:Adsorption; D001665:Binding Sites; D003545:Cysteine / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000737:chemistry; D005978:Glutathione / Q000737:chemistry*; D006358:Hot Temperature; D010084:Oxidation-Reduction; D011791:Quartz / Q000737:chemistry*; D012829:Silicosis / Q000209:etiology* / Q000473:pathology*; D013056:Spectrophotometry, Ultraviolet; D013499:Surface Properties
D005609:Free Radicals; D011791:Quartz; D005978:Glutathione; D003545:Cysteine