Thiol-mediated NTA-Fe(III) reduction and lipid peroxidation

Area of Science:

• Biochemistry
• Toxicology
• Metal Metabolism

Background:

• Nephrotoxicity of nitrilotriacetate chelated Fe(III) (NTA-Fe(III)) is associated with glutathione (GSH) metabolism.
• Enzymatic breakdown of GSH yields cysteinyl-glycine (cys-gly) and cysteine (cys).
• These metabolites are implicated as reductants causing NTA-Fe(III)-induced oxidative damage.

Purpose of the Study:

• To investigate the differential rates of NTA-Fe(III) reduction by GSH and its metabolites.
• To elucidate the mechanisms underlying NTA-Fe(III) nephrotoxicity related to GSH metabolism.
• To determine the role of thiol pKa versus liganding in the reduction kinetics.

Main Methods:

• In vitro lipid peroxidation assays.
• Measurement of NTA-Fe(III) reduction rates by GSH, cys-gly, cys, and GSH esters.
• pH-dependent studies to assess the role of thiol ionization.

Main Results:

• Cys-gly and cys significantly accelerated NTA-Fe(III) reduction and lipid peroxidation compared to GSH.
• GSH did not stimulate lipid peroxidation, indicating a slower reduction rate.
• Dimethyl ester of GSH showed a markedly faster NTA-Fe(III) reduction rate than GSH or monomethyl ester.
• pH adjustments did not proportionally increase GSH's iron reduction rate.

Conclusions:

• The distinct rates of NTA-Fe(III) reduction by GSH, cys-gly, and cys are attributed to differences in their liganding interactions with iron.
• GSH's slower reduction rate is due to liganding, not solely thiol pKa differences.
• Understanding these metabolic and liganding interactions is crucial for NTA-Fe(III) nephrotoxicity mechanisms.