Changes in Activity of Three Sulfurtransferases in Response to Exposure to Cadmium, Lead and Mercury Ions

Cadmium, lead and mercury are environmentally persistent toxicants that affect tissues and cellular components or exert an effect on generation of reactive oxygen species causing a decreased level of available antioxidant reserves. Sulfurtransferases are enzymes that are widespread in nature. Rhodanese, 3-mercaptopyruvate sulfurtransferase and γ-cystathionase play an important role in the metabolism of L-cysteine. Heavy metal ions can bind to -SH groups of cysteine residues in their active sites and, therefore, decrease the activity of these enzymes and result in changes in the level of sulfane sulfur-containing compounds, products of L-cysteine desulfuration. Changes in the activity of sulfurtransferases were investigated in the kidneys, heart, brain, liver and skeletal muscle of Marsh frogs (Pelophylax ridibundus) after 10 days of exposure to Pb(NO3)2 at the concentration of 28 mg/L and CdCl2 at the concentration of 40 mg or 80 mg/L, and in Xenopus laevies tissues after 7 and 14 days of exposure to HgCl2 at the concentration of 1.353 mg/L. The investigated heavy metal ions have a tendency to inhibit the activity of sulfurtransferases and decrease the level of glutathione, what can result in oxidative stress and oxidation of cysteine -SH groups to -SOH. This reversible oxidation and reduction of these redox sensitive groups can play a role in defenses against oxidative stress. Based on the presented results, one can surmise that also the expression of the three sulfurtransferases depends on heavy metal ions and/or some parameters of oxidative stress, what can explain the increase of the activity of MPST and CST in the kidney.

Therapeutic importance of hydrogen sulfide in age-associated neurodegenerative diseases

Hydrogen sulfide(H2S)is a gasotransmitter that acts as an antioxidant and exhibits a wide variety of cytoprotective and physiological functions in age-associated diseases.One of the major causes of age-related diseases is oxidative stress.In recent years,the importance of H2S has become clear,although its antioxidant function has not yet been fully explored.The enzymes cystathionineβ-synthase,cystathionineγ-lya-se,and 3-mercaptopyruvate sulfurtransferase are involved in the enzymatic production of H2S.Previously,H2S was considered a neuromodulator,given its role in long-term hippocampal potentiation,but it is now also recognized as an antioxidant in age-related neurodegeneration.Due to aerobic metabolism,the central nervous system is vulnerable to oxidative stress in brain aging,resulting in age-associated degenerative diseases.H2S exerts its antioxidant effect by limiting free radical reactions through the activation of antioxidant enzymes,including superoxide dismutase,catalase,and glutathione peroxidase,which protect against the effects of aging by regulating apoptosis-related genes,including p53,Bax,and Bcl-2.This review explores the implications and mechanisms of H2S as an antioxidant in age-associated neurodegenerative diseases,including Alzheimer’s disease,Parkinson’s disease,Huntington’s disease,and Down syndrome.