Sulfite Impairs Bioenergetics and Redox Status in Neonatal Rat Brain: Insights into the Early Neuropathophysiology of Isolated Sulfite Oxidase and Molybdenum Cofactor Deficiencies.

Isolated sulfite oxidase (ISOD) and molybdenum cofactor (MoCD) deficiencies are genetic diseases biochemically characterized by the toxic accumulation of sulfite in the tissues of patients, including the brain. Neurological dysfunction and brain abnormalities are commonly observed soon after birth, and some patients also have neuropathological alterations in the prenatal period (in utero). Thus, we investigated the effects of sulfite on redox and mitochondrial homeostasis, as well as signaling proteins in the cerebral cortex of rat pups. One-day-old Wistar rats received an intracerebroventricular administration of sulfite (0.5 µmol/g) or vehicle and were euthanized 30 min after injection. Sulfite administration decreased glutathione levels and glutathione S-transferase activity, and increased heme oxygenase-1 content in vivo in the cerebral cortex. Sulfite also reduced the activities of succinate dehydrogenase, creatine kinase, and respiratory chain complexes II and II-III. Furthermore, sulfite increased the cortical content of ERK1/2 and p38. These findings suggest that redox imbalance and bioenergetic impairment induced by sulfite in the brain are pathomechanisms that may contribute to the neuropathology of newborns with ISOD and MoCD. Sulfite disturbs antioxidant defenses, bioenergetics, and signaling pathways in the cerebral cortex of neonatal rats. CII: complex II; CII-III: complex II-III; CK: creatine kinase; GST: glutathione S-transferase; HO-1: heme oxygenase-1; SDH: succinate dehydrogenase; SO32-: sulfite.

The Role of Oxidative Stress and Bioenergetic Dysfunction in Sulfite Oxidase Deficiency: Insights from Animal Models.

Sulfite oxidase (SO) deficiency is an autosomal recessive inherited neurometabolic disease caused by deficient activity of SO. It is biochemically characterized by tissue accumulation and high urinary excretion of sulfite, thiosulfate, and S-sulfocysteine. Severe neurological symptoms, including neonatal seizures, encephalopathy, and psychomotor retardation, are commonly observed in the affected patients, but the pathogenesis of the neurologic dysfunction is still poorly understood. In this minireview, we will briefly summarize the knowledge obtained from in vivo and in vitro findings from animal studies indicating that oxidative stress and mitochondrial dysfunction are involved in the pathophysiology of the brain damage in this disease. Recent reports have shown that sulfite induces free radical generation, impairs brain antioxidant defenses, and disturbs mitochondrial energy metabolism and biogenesis. Moreover, it has been evidenced that free radical scavengers and the pan-PPAR agonist bezafibrate are able to prevent most deleterious effects elicited by sulfite on the brain. These promising data offer new perspectives for potential therapeutic strategies for this condition, which may include the early use of appropriate antioxidants and PPAR agonists in addition to the available treatment.

The determination of sulfite levels and its oxidation in plant leaves.

Sulfur is the sixth most abundant element in life and an important building block of proteins and cellular metabolites. Plants like bacteria can synthesize their sulfur-containing biomolecules from sulfate, where sulfite is an intermediate of the sulfur assimilation pathway. Above a certain threshold SO(2)/sulfite is cytotoxic and is rapidly metabolized to avoid damage. However, the existing data show considerable differences in basal sulfite levels both between species and apparent discrepancies in measured levels in the same species. In order to resolve this question we employed a sulfite detection method using chicken sulfite oxidase and developed an independent enzymatic assay, based on the specific detection of sulfite by sulfite reductase and compared those measurements to a modified colorimetric fuchsin-based method, specific for sulfite detection. We show here that when properly used the sulfite levels detected by the three methods can yield identical results. Furthermore, to examine the capacity of the plant to detoxify sulfite we injected sub-lethal sulfite solutions (yet, several folds higher than the basal levels) into Arabidopsis and tomato leaves and monitored the excess sulfite turnover. Within 3h of sulfite injection, more than 80% of the injected sulfite in Arabidopsis and 91% in tomato were oxidized to sulfate, demonstrating the high capacity of the sulfite oxidation mechanism/s in plants.

Molecular cloning and functional characterization of a putative sulfite oxidase (SO) ortholog from Nicotiana benthamiana.

Sulfite oxidase (SO) catalyzes the oxidation of sulfite to sulfate and thus has important roles in diverse metabolic processes. However, systematic molecular and functional investigations on the putative SO from tobacco (Nicotiana benthamiana) have hitherto not been reported. In this work, a full-length cDNA encoding putative sulfite oxidase from N. benthamiana (NbSO) was isolated. The deduced NbSO protein shares high homology and typical structural features with other species SOs. Phylogenetic analysis indicates that NbSO cDNA clone encodes a tobacco SO isoform. Southern blot analysis suggests that NbSO is a single-copy gene in the N. benthamiana genome. The NbSO transcript levels were higher in aerial tissues and were up-regulated in N. benthamiana during sulfite stress. Reducing the SO expression levels through virus-induced gene silencing caused a substantial accumulation in sulfite content and less sulfate accumulation in N. benthamiana leaves when exposed to sulfite stress, and thus resulted in decreased tolerance to sulfite stress. Taken together, this study improves our understanding on the molecular and functional properties of plant SO and provides genetic evidence on the involvement of SO in sulfite detoxification in a sulfite-oxidizing manner in N. benthamiana plants.

Cysteine, sulfite, and glutamate toxicity: a cause of ALS?

BACKGROUND: Amyotrophic lateral sclerosis (ALS) of nonmutant superoxide dismutase (SOD) type may be caused by toxicity of the reduced glutathione (GSH) precursors glutamate and cysteine, and sulfite (a metabolite of cysteine), which accumulate when one or more of the enzymes needed for GSH synthesis are defective. OBJECTIVES: A case is examined where the patient exhibited elevated sulfur on a hair mineral analysis, elevated blood cysteine, positive urine sulfite, elevated urine glutamate, and low whole blood GSH. During the time when strict dietary and supplement measures normalized the patient's whole blood GSH, blood cysteine, and urine sulfite, the patient did not experience additional physical decline. The possible causes of abnormalities of the patient's laboratory test results, as well as the nutrition measures used to normalize them, are discussed in relationship to the functions and importance of cysteine, sulfite, and glutamate in glutathione metabolism in ALS. CONCLUSIONS: Since elevated plasma cysteine has been reported in other ALS patients, sulfite and cysteine toxicity may be involved in other cases of ALS. Patients with ALS with nonmutant-SOD should be tested for sulfite toxicity, cysteine, glutamate and GSH levels, and whether they have low levels of GSH metabolism enzymes. Since glutamate metabolism appears to be inhibited by sulfite, research on the effect of sulfite on glutamate levels in patients with ALS should be pursued. Life might be prolonged in those patients with ALS with sulfite toxicity by closely monitoring the blood cysteine and urine sulfite levels and minimizing their dietary intake, as well as increasing GSH by using sublingual GSH. A long-term solution might be found through research to determine methods to increase GSH synthesis without using sulfur-containing supplements that may add to the cysteine and sulfite toxicity.

Effects of sulphite supplementation on vascular responsiveness in sulphite oxidase-deficient rats.

1. The aim of the present study was to explore the effect of dietary sulphite supplementation on vascular responsiveness in sulphite oxidase (SO)-deficient rats. 2. Male albino rats were divided into four groups, namely control (n = 8), sulphite-treated (n = 8), SO-deficient (n = 8) and sulphite-treated SO-deficient (n = 8) groups. Sulphite oxidase deficiency was induced by administration of a low-molybdenum diet with concurrent addition of 200 p.p.m. tungsten in the form of sodium tungstate in the drinking water for 9 weeks. Sulphite, in the form of sodium metabisulphite (Na(2)O(5)S(2); 25 mg/kg) was given in the drinking water to sulphite-treated and sulphite-treated SO-deficient groups for the last 6 weeks. The vascular responsiveness of isolated aortic rings to acetylcholine (ACh), sodium nitroprusside (SNP) and histamine was investigated in organ baths. 3. The responsiveness of aortic rings to SNP and histamine did not differ significantly between groups. Conversely, there was a significant decrease in ACh-induced relaxation in aortic rings from the sulphite-treated SO-deficient group compared with the control group (pD(2) 6.2 +/- 0.3 and 7.5 +/- 0.1, respectively; P < 0.05). Incubation of aortic rings in the presence of either l-arginine or superoxide dismutase significantly improved the ACh-induced vasorelaxation in sulphite-treated SO-deficient group (pD(2) 7.2 +/- 0.3 and 7.4 +/- 0.3, respectively). 4. The findings of the present study suggest that the increased production of reactive oxygen species and the resultant increment in l-arginine/nitric oxideconsumption may play a role in the reduced endothelium-dependent vasorelaxation in sulphite-treated SO-deficient rats.

Fed-batch cultivation of the marine bacterium Sulfitobacter pontiacus using immobilized substrate and purification of sulfite oxidase by application of membrane adsorber technology.

Sulfitobacter pontiacus, a gram-negative heterotrophic bacterium isolated from the Black Sea is well known to produce a soluble AMP-independent sulfite oxidase (sulfite: acceptor oxidoreductase) of high activity. Such an enzyme can be of great help in establishing biosensor systems for detection of sulfite in food and beverages considering the high sensitivity of biosensors and the increasing demand for such biosensor devices. For obtaining efficient amounts of the enzyme, an induction of its biosynthesis by supplementing sufficient concentrations of sodium sulfite to the fermentation broth is required. Owing to the fact that a high initial concentration of sodium sulfite decreases dramatically the enzyme expression, different fed-batch strategies can be applied to circumvent such inhibition or repression of the enzyme respectively. By the use of sulfite species immobilized in polyvinyl alcohol gels, an approach to the controlled and continuous feeding of sulfite to the cultivation media could be established to diminish inhibitory concentrations. Furthermore, the purification of the enzyme is described by using membrane adsorber technology.

Effect of sulfite exposure on zinc, iron, and copper levels in rat liver and kidney tissues.

Sulfite is a potentially toxic molecule that might enter the body via ingestion, inhalation, or injection. For cellular detoxification, mammalians rely on sulfite oxidase to convert sulfite to sulfate. The purpose of this research was to determine the effect of sulfite on zinc, iron, and copper levels in rat liver and kidney tissues. Forty normal and sulfite oxidase-deficient male albino rats were divided into four groups that included untreated controls (group C), a sulfite-supplemented group that received 70 mg sodium metabisulfite per kilogram per day (group S), a sulfite oxidase-deficient group (group D), and a sulfite oxidase-deficient group that was also given 70 mg sodium metabisulfite per kilogram per day (group DS). The iron and zinc levels in the liver and kidney in groups S and DS were not affected by sulfite treatment compared to their respective controls (groups C and D). Sulfite exposure led to an increase of kidney copper content in the S group when compared to untreated controls. The kidney copper levels were significantly increased in the unexposed deficient rats, but it was not different than that of the deficient rats that were given oral sulfite treatment. These results suggest that kidney copper levels might be affected by exogenous or endogenous sulfite.