Sulfite is generated from PAPS by activated neutrophils

Click and release: bioorthogonal approaches to “on-demand” activation of prodrugs

This review summarizes recent developments in using bioorthogonal chemistry in prodrug design for the delivery of traditional small molecule- and gasotransmitter-based therapeutics.

Adaptation of Candida albicans to Reactive Sulfur Species

Candida albicans is an opportunistic fungal pathogen that is highly resistant to different oxidative stresses. How reactive sulfur species (RSS) such as sulfite regulate gene expression and the role of the transcription factor Zcf2 and the sulfite exporter Ssu1 in such responses are not known. Here, we show that C. albicans specifically adapts to sulfite stress and that Zcf2 is required for that response as well as induction of genes predicted to remove sulfite from cells and to increase the intracellular amount of a subset of nitrogen metabolites. Analysis of mutants in the sulfate assimilation pathway show that sulfite conversion to sulfide accounts for part of sulfite toxicity and that Zcf2-dependent expression of the SSU1 sulfite exporter is induced by both sulfite and sulfide. Mutations in the SSU1 promoter that selectively inhibit induction by the reactive nitrogen species (RNS) nitrite, a previously reported activator of SSU1, support a model for C. albicans in which Cta4-dependent RNS induction and Zcf2-dependent RSS induction are mediated by parallel pathways, different from S. cerevisiae in which the transcription factor Fzf1 mediates responses to both RNS and RSS. Lastly, we found that endogenous sulfite production leads to an increase in resistance to exogenously added sulfite. These results demonstrate that C. albicans has a unique response to sulfite that differs from the general oxidative stress response, and that adaptation to internal and external sulfite is largely mediated by one transcription factor and one effector gene.

Click and Release: SO2 Prodrugs with Tunable Release Rates

Employing an intramolecular cycloaddition reaction, we have developed a series of SO₂ prodrugs with tunable release rates with half-lives ranging from minutes to days.

Endogenous sulfur dioxide protects against isoproterenol-induced myocardial injury and increases myocardial antioxidant capacity in rats

Recently, sulfur dioxide (SO(2)) was discovered to be produced in the cardiovascular system and to influence important biological processes. Here, we investigated changes in endogenous SO(2)/glutamic oxaloacetic transaminase (GOT) pathway in the development of isoproterenol (ISO)-induced myocardial injury in rats and the regulatory effect of SO(2) on cardiac function, myocardial micro- and ultrastructure, and oxidative stress. Wistar male rats were divided into control, ISO-treated, ISO+SO(2), and SO(2) groups. At the termination of the experiment, parameters of cardiac function and hemodynamics were measured and the micro- and ultrastructure of myocardium and stereological ultrastructure of mitochondria were analyzed. Myocardial SO(2) content was detected by high-performance liquid chromatography. GOT (key enzyme for endogenous SO(2) production) activity and gene (GOT1 and GOT2) expressions were measured, and superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), hydrogen peroxide, and superoxide radical levels were assayed. SOD (SOD1 and SOD2) and GSH-Px (GSH-Px1) gene expressions were also detected. The results showed that SO(2) donor at a dose of 85 mg/(kg day) did not impact the cardiac function and structure of rats, but exerted a subtle influence on myocardial redox status. ISO-treated rats exhibited decreased cardiac function, damaged myocardial structures, and downregulated endogenous SO(2)/GOT pathway. Meanwhile, myocardial oxidative stress increased, whereas antioxidative capacity downregulated. Administration of SO(2) markedly improved cardiac function and ISO-induced myocardial damage by ameliorating the pathological structure of the myocardium and the mitochondria. At the same time, myocardial products of oxidative stress decreased, whereas antioxidative capacity increased. These results suggest that downregulation of the endogenous SO(2)/GOT pathway is likely involved in the pathogenesis of ISO-induced myocardial injury. SO(2) protects against ISO-induced myocardial injury associated with increased myocardial antioxidant capacity in rats.

Effects of endogenous sulfur dioxide on monocrotaline-induced pulmonary hypertension in rats

AIM

The present study aimed to explore the protective effect of endogenous sulfur dioxide (SO2) in the development of monocrotaline (MCT)-induced pulmonary hypertension (PH) in rats.

METHODS

Forty Wistar rats were randomly divided into the MCT group receiving MCT treatment, the MCT+L-aspartate-beta- hydroxamate (HDX) group receiving MCT plus HDX treatment, the MCT+SO2 group receiving MCT plus SO2 donor treatment, and the control group. Mean pulmonary artery pressure (mPAP) and structural changes in pulmonary arteries were evaluated. SO2 content, aspartate aminotransferase activity, and gene expression were measured. Superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT), reduced glutathione (GSH), oxidized glutathione, and malondialdehyde (MDA) levels were assayed.

RESULTS

In the MCT-treated rats, mPAP and right ventricle/(left ventricle+septum) increased significantly (P<0.01), pulmonary vascular structural remodeling developed, and SOD, GSHPx, CAT, GSH, and MDA levels of lung homogenates significantly increased (P<0.01) in association with the elevated SO2 content, aspartate aminotransferase activity, and gene expression, compared with the control rats. In the MCT+HDXtreated rats, lung tissues and plasma SO2 content and aspartate aminotransferase activities decreased significantly, whereas the mPAP and pulmonary vascular structural remodeling were markedly aggravated with the decreased SOD, CAT, and GSH levels of lung tissue homogenates compared with the MCT-treated rats (P<0.01). In contrast, with the use of a SO2 donor, the pulmonary vascular structural remodeling was obviously lessened with elevated lung tissue SOD, GSH-Px, and MDA content, and plasma SOD, GSH-Px, and CAT levels.

CONCLUSION

Endogenous SO2 might play a protective role in the pathogenesis of MCT-induced PH and promote endogenous antioxidative capacities.

OXIDATIVE STRESS-DEPENDENT CONVERSION OF HYDROGEN SULFIDE TO SULFITE BY ACTIVATED NEUTROPHILS

Sulfite, which is known as a major constituent of volcanic gas, is endogenously produced in mammals, and its concentration in serum is increased in patients with pneumonia. It has been reported that sulfite is produced by oxidation from hydrogen sulfide (H2S) as an intermediate in the mammalian body. The objective of this study was to investigate the ability of reactive oxygen species from neutrophils to produce sulfite from H2S. Sulfite production from activated neutrophils stimulated with N-formyl-methionyl-leucyl-phenylalanine gradually increased with an increased concentration of sodium hydrosulfide (NaHS) in the medium. The production of sulfite was markedly suppressed with an NADPH oxidase inhibitor, diphenyleneiodonium. When NaHS was added to the supernatant of activated neutrophils, a significant amount of sulfite was synthesized in the test tubes. Furthermore, when a medium containing NaHS was incubated with a water-soluble radical initiator, 2,2'-azobis-(amidinopropane) dihydrochloride, sulfite was formed in the solution and this increase was markedly suppressed by ascorbic acid. Finally, we determined serum concentrations of sulfite and H2S in an in vivo model of neutrophil activation induced by systemic injection of lipopolysaccharide (LPS) into rats. We found a significant increase in serum sulfite and H2S after LPS injection. Importantly, coadministration of ascorbic acid with LPS further increased serum H2S but suppressed sulfite levels. This finding implies that oxidative stress-dependent conversion of H2S to sulfite might occur in vivo. Thus, the oxidation of H2S is a novel sulfite production pathway in the inflammatory condition, and this chemical synthesis might be responsible for the upregulation of sulfite production in inflammatory conditions such as pneumonia.

Increased levels of serum sulfite in patients with acute pneumonia

Sulfite, a common air pollutant, is toxic for humans, causing hypersensitivity or chronic airway diseases. We previously reported that sulfite is actively produced from neutrophils by stimulation with bacterial endotoxin, lipopolysaccharide (LPS). We also found that the serum sulfite concentration is increased in a rat model of sepsis induced by systemic injection of LPS. However, information on sulfite metabolism in human inflammatory conditions is limited. In the current study, the serum concentration of sulfite was determined in 25 patients with acute pneumonia. Serum sulfite concentration in pneumonia patients was significantly higher than that in control subjects (3.75 +/- 0.88 vs. 1.23 +/- 0.48 microM, respectively, P < 0.05). Among 20 patients, serum sulfite was serially determined before and after antibiotic therapy. The levels of serum sulfite were significantly reduced during the recovery phase compared with those during the acute phase (1.34 +/- 0.56 vs. 3.65 +/- 0.92 microM, respectively, P < 0.05). Moreover, neutrophils obtained from three patients during the acute phase of pneumonia spontaneously produced higher amounts of sulfite in vitro than those obtained after recovery. There was a close positive correlation (r = 0.71, P < 0.05) between serum sulfite and C-reactive protein (CRP) in patients with pneumonia. Taken together, the current findings suggest that serum sulfite increases during systemic inflammation in humans. Activated neutrophils might be responsible, at least in part, for the up-regulation of sulfite. Given various biological effects reported previously, sulfite may act as a mediator in inflammation.

Sulfite-mediated oxidative stress in kidney cells

BACKGROUND

Chronic renal failure has been associated with oxidative stress. Serum sulfite, sulfate, cysteine, homocysteine, cysteine sulfinic acid, and gamma-glutamylcysteine are elevated in patients on hemodialysis, suggesting an accelerated catabolism of sulfur-containing amino acids or a reduced elimination of sulfite/sulfate, or both. Administration of metabisulfite has also been shown to damage kidney cells.

METHODS

Measurement of reactive oxygen species (ROS) was performed with the fluorescence of dichlorofluorescein (DCF), and that of intracellular ATP was by the luciferin-luciferase reaction. Oxidation of sulfite and succinate by isolated mitochondria from rat kidney was monitored polarographically. The fluorescent probe, 5, 5', 6, 6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolcarbocyanine iodide (JC-1) was employed to assess any loss in membrane potential in energized respiring mitochondria. Activities of glutamate and malate dehydrogenases (GDH, MDH, respectively) were assayed by the spectrophotometric measurement of NADH. Sulfite was determined by HPLC-fluorimetric measurement of monochlorobimane-sulfite and cell viability was by the MTT procedure.

RESULTS

An immediate increase in ROS followed exposure of Madin-Darby canine kidney (MDCK), type II, and opossum kidney (OK) cells to 5-500 micromol/L sulfite. Depletion of intracellular ATP was also observed. A low rate of oxidation of 100 micromol/L sulfite was observed polarographically in isolated kidney mitochondria, but ADP-stimulated State 3 respiration was not apparent. ATP biosynthesis from the oxidation of glutamate in rat kidney mitochondria was significantly inhibited by coincubation with 100 micromol/L sulfite; this was not the case with malate, succinate, and TMPD/ascorbate. However, activities of both GDH and MDH in kidney mitochondrial extract were inhibited. The mitochondrial membrane potential and cell viability were not compromised.

CONCLUSION

Micromolar sulfite elicited an immediate increase in ROS in MDCK, type II, and OK cells. This was accompanied by a depletion of intracellular ATP, which could be explained by its inhibitory effect on mitochondrial GDH. Although MDH was similarly inhibited, the impact was buffered by the high level of this enzyme in kidney mitochondria.