This review is focused on formation and biological significance of hydropersulfides, i.e. S-sulfhydration process. Biogenesis and properties of reactive sulfur species and their role in redox signaling are presented. The effect of S-sulfhydration on protein function is discussed.

The aim of the present studies was to determine whether the mechanism of biological action of garlic-derived sulfur compounds in human hepatoma (HepG2) cells can be dependent on the presence of labile sulfane sulfur in their molecules. We investigated the effect of allyl sulfides from garlic: monosulfide, disulfide and trisulfide on cell proliferation and viability, caspase 3 activity and hydrogen peroxide (H(2)O(2)) production in HepG2 cells. In parallel, we also examined the influence of the previously mentioned compounds on the levels of thiols, glutathione, cysteine and cysteinyl-glycine, and on the level of sulfane sulfur and the activity of its metabolic enzymes: rhodanese, 3-mercaptopyruvate sulfurtransferase and cystathionase. Among the compounds under study, diallyl trisulfide (DATS), a sulfane sulfur-containing compound, showed the highest biological activity in HepG2 cells. This compound increased the H(2)O(2) formation, lowered the thiol level and produced the strongest inhibition of cell proliferation and the greatest induction of caspase 3 activity in HepG2 cells. DATS did not affect the activity of sulfurtransferases and lowered sulfane sulfur level in HepG2 cells. It appears that sulfane sulfur containing DATS can be bioreduced in cancer cells to hydroperthiol that leads to H(2)O(2) generation, thereby influencing transmission of signals regulating cell proliferation and apoptosis.

Liver abnormalities have been reported to occur in up to 20 % of patients on a long-term therapy with the tricyclic antidepressant drug imipramine (IMI). The mechanism involved in this IMI-induced process is unknown but a contribution of oxidative stress is highly likely. Chronic mild stress (CMS) is widely used for modeling depressive-like behavior in rats. In the present study, we examined the effects of CMS and chronic IMI treatment, applied alone or in combination, on the levels of oxidative stress markers, such as reactive oxygen species (ROS), malondialdehyde (MDA), non-protein sulfhydryl groups, and sulfane sulfur as well as on activities of key antioxidant enzymes: catalase (CAT), glutathione peroxidase (GPx), and superoxide dismutase in the rat liver. Administration of IMI for 5 weeks to rats subjected to CMS resulted in a gradual significant reduction of anhedonia measured by sucrose intake, in a majority of animals (CMS IMI-reactive, CMS IMI-R), although about 20 % of rats did not respond to the IMI treatment (CMS IMI non-reactive, CMS IMI-NR). CMS-induced hepatic oxidative stress, estimated by increased ROS and MDA concentrations, was not prevented by the IMI administration, moreover, in CMS IMI-NR animals, the level of the marker of lipid peroxidation, i.e., MDA was increased in comparison to CMS-subjected rats and activity of antioxidant enzymes (GPx and CAT) was decreased compared to IMI-treated rats. The clinical significance of this observation remains to be established.

Diallyl sulfide (DAS), diallyl disulfide (DADS) and diallyl trisulfide (DATS) are major oil-soluble organosulfur compounds of garlic responsible for most of its pharmacological effects. The present study investigated the influence of repeated intraperitoneally (ip) administration of DAS, DADS and DATS on the total level of sulfane sulfur, bound sulfur (S-sulfhydration) and hydrogen sulfide (H2S) and on the activity of enzymes, which catalyze sulfane sulfur formation and transfer from a donor to an acceptor in the normal mouse kidney, i.e., γ-cystathionase (CSE) and rhodanese (TST). The activity of aldehyde dehydrogenase (ALDH), which is a redox-sensitive protein, containing an –SH group in its catalytic center, was also determined. The obtained results indicated that all tested compounds significantly increased the activity of TST. Moreover, DADS and DATS increased the total sulfane sulfur level and CSE activity in the normal mouse kidney. ALDH activity was inhibited in the kidney after DATS administration. The results indicated also that none of the studied allyl sulfides affected the level of bound sulfur or H2S. Thus, it can be concluded that garlic-derived DADS and DATS can be a source of sulfane sulfur for renal cells but they are not connected with persulfide formation.

The role of cocaine in modulating the metabolism of sulfur-containing compounds in the peripheral tissues is poorly understood. In the present study we addressed the question about the effects of acute and repeated (5 days) cocaine (10 mg/kg i.p.) administration on the total cysteine (Cys) metabolism and on the oxidative processes in the rat liver and kidney. The whole pool of sulfane sulfur, its bound fraction and hydrogen sulfide (H2S) were considered as markers of anaerobic Cys metabolism while the sulfate as a measure of its aerobic metabolism. The total-, non-protein- and protein- SH group levels were assayed as indicators of the redox status of thiols. Additionally, the activities of enzymes involved in H2S formation (cystathionine γ-lyase, CSE; 3-mercaptopyruvate sulfurtransferase, 3-MST) and GSH metabolism (γ-glutamyl transpeptidase, γ-GT; glutathione S-transferase, GST) were determined. Finally, we assayed the concentrations of reactive oxygen species (ROS) and malondialdehyde (MDA) as markers of oxidative stress and lipid peroxidation, respectively. In the liver, acute cocaine treatment, did not change concentrations of the whole pool of sulfane sulfur, its bound fraction, H2S or sulfate but markedly decreased levels of non-protein SH groups (NPSH), ROS and GST activity while γ-GT was unaffected. In the kidney, acute cocaine significantly increased concentration of the whole pool of sulfane sulfur, reduced the content of its bound fraction but H2S, sulfate and NPSH levels were unchanged while ROS and activities of GST and γ-GT were reduced. Acute cocaine enhanced activity of the CSE and 3-MST in the liver and kidney, respectively. Repeatedly administered cocaine enhanced the whole pool of sulfane sulfur and reduced H2S level simultaneously increasing sulfate content both in the liver and kidney. After repeated cocaine, a significant decrease in ROS was still observed in the liver while in the kidney, despite unchanged ROS content, a marked increase in MDA level was visible. The repeated cocaine decreased 3-MST and increased γ-GT activities in both organs but reduced GST in the kidney. Our results show that cocaine administered at a relatively low dose shifts Cys metabolism towards the formation of sulfane sulfur compounds which possess antioxidant and redox regulatory properties and are a source of H2S which can support mitochondrial bioenergetics.

The aim of the present study was to verify whether lipoic acid (LA) itself is a source of H2S and sulfane sulfur. It was investigated in vitro non-enzymatically and enzymatically (in the presence of rat tissue homogenate). The results indicate that both H2S and sulfane sulfur are formed from LA non-enzymatically in the presence of environmental light. These results suggest that H2S is the first product of non-enzymatic light-dependent decomposition of LA that is, probably, next oxidized to sulfane sulfur-containing compound(s). The study performed in the presence of rat liver and kidney homogenate revealed an increase of H2S level in samples containing LA and its reduced form dihydrolipoic acid (DHLA). It was accompanied by a decrease in sulfane sulfur level. It seems that, in these conditions, DHLA acts as a reducing agent that releases H2S from an endogenous pool of sulfane sulfur compounds present in tissues. Simultaneously, it means that exogenous LA cannot be a direct donor of H2S/sulfane sulfur in animal tissues. The present study is an initial approach to the question whether LA itself is a donor of H2S/sulfane sulfur.

Biological activity of garlic has been attributed to organosulfur compounds, most of all to oil-soluble allyl sulfides, such as diallyl sulfide (DAS), diallyl disulfide (DADS) and diallyl trisulfide (DATS). This study evaluated the effectiveness of garlic-derived allyl sulfides in influencing peroxidative processes, levels of thiols and sulfane sulfur and its metabolic enzymes in normal mouse liver cells. Various allyl sulfides (DAS, DADS and DATS) dissolved in corn oil were given intraperitoneally to mice for 10 days. After sacrificing the mice, biochemical assays were performed in liver homogenates and in plasma in order to establish liver function. All allyl sulfides under study had a beneficial effect in the mouse liver since they decreased reactive oxygen species and malondialdehyde levels and increased glutathione S-transferase activity and non-protein sulfhydryl group level. Moreover, DADS and DATS elevated total sulfane sulfur pool and activity of sulfane sulfur biosynthetic enzymes. The increase in sulfane sulfur level entailed augmentation of its antioxidant and regulatory capacities. Garlic-derived allyl sulfides exhibited antioxidant action in the liver and elevated anaerobic cysteine metabolism leading to the formation of sulfane sulfur-containing compounds. Thus, DADS and DATS showed beneficial action in the liver, which can be used for protection of normal liver cells during chemotherapy or for alleviation of liver damage.

Aldehyde dehydrogenase (ALDH) catalyzes the critical step of ethanol metabolism, i.e. transformation of toxic acetaldehyde to acetic acid. It is a redox sensitive protein with the key Cys in its active site. Recently, it has been documented that activity of some proteins can be modified by sulfur-containing molecules called reactive sulfur species leading to the formation of hydro- persulfides. The aim of the present study was to examine whether ALDH activity can be modified in this way. Studies were performed in vitro using yeast ALDH and various reactive sulfur species, including NaS, GSSH, KS, NaSO, and garlic-derived allyl sulfides. The effect of garlic-derived trisulfide on ALDH activity was also studied in vivo in the rat liver. The obtained results clearly demonstrated that ALDH could be regulated by sulfur species which inhibited its enzymatic activity. The results also suggested that not HS but polysulfides or hydropersulfides were the oxidizing species responsible for this modification. This process was easily reversible by reducing agents. After the treatment with polysulfides or hydropersulfides the level of protein-bound sulfur increased, while the activity of the enzyme dramatically decreased. Moreover, the study demonstrated that ALDH activity was inhibited in vivo in the rat liver after garlic-derived trisulfide administration. This is the first study reporting the regulation of ALDH activity by sulfane sulfur species and the results suggest that it leads to the inhibition of the enzyme.