Sulfite triggers sustained calcium overload in cultured cortical neurons via a redox-dependent mechanism

Design and application of a novel "turn-on" fluorescent probe for imaging sulfite in living cells and inflammation models

Sulfite is one of the main existing forms of sulfur dioxide (SO2) in living system, which has been recognized as an endogenous mediator in inflammation. Evidence has accumulated to show that abnormal level of sulfite is associated with many inflammatory diseases, including neurological diseases and cancers. Herein, a novel fluorescent probe named QX-OA was designed and synthesized to detect sulfite. QX-OA was constructed by choosing quinolinium-xanthene as the fluorophore and levulinate as the specific and relatively steady recognition reaction. The probe showed remarkable green turn-on signal at 550 nm, together with high sensitivity (90-fold) and excellent selectivity to sulfite over other possible interfering species. In the meantime, QX-OA was successfully applied to visualize endogenous and exogenous sulfite in Hela cells. In the LPS-induced inflammation model, QX-OA could visualize the dose-dependent increase of sulfite level (0-2 mg/mL). Consequently, QX-OA was determined to be a potential method for detecting sulfite in pre-clinical diagnosis.

Sodium sulfite triggered hepatic apoptosis, necroptosis, and pyroptosis by inducing mitochondrial damage in mice and AML-12 cells

Sodium sulfite (SS) is a biological derivative of the air pollutant sulfur dioxide, and is often used as a food and pharmaceutical additive. Improper or excessive SS exposure in liver cell death. The phenomenon of simultaneous regulation of apoptosis, necroptosis, and pyroptosis is defined as PANoptosis. However, the specific types of programmed cell death (PCD) caused by SS and their interconnections remain unclear. In the present study, C57BL/6 mice were orally administered SS for 30 d, consecutively, to establish an in vivo mouse exposure model. AML-12 cells were treated with SS for 24 h to establish an in vitro exposure model. The results showed that SS-induced mitochondrial reactive oxygen species (mtROS) accumulation activated the BAX/Bcl-2/caspase 3 pathway to trigger apoptosis and RIPK1/RIPK3/p-MLKL to trigger necroptosis. Interestingly, ROS-activated p-MLKL perforated not the cell membrane as well as the lysosomal membrane. We determined that p-MLKL mediates lysosomal membrane permeabilization (LMP), resulting in cathepsin B (CTSB) release. Furthermore, knockdown of MLKL, a CTSB inhibitor (CA074-ME) and an NLRP3 inhibitor (MCC950) alleviated SS-induced pyroptosis. In summary, our study showed that SS induced apoptosis and necroptosis though mtROS accumulation, whereas the activation of p-MLKL mediated NLRP3-dependent pyroptosis by causing CTSB leakage through LMP. This study comprehensively explored the mechanism unerlying SS-induced PCD and provided an experimental basis for p-MLKL as a potential regulatory protein in PANoptosis.

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.

Non-Destructive Screening of Sodium Metabisulfite Residue on Shrimp by SERS with Copy Paper Loaded with AgNP

In order to prompt the appearance of the shrimp color, sodium metabisulfite is frequently added in shrimp processing, which is, however, prohibited in China and many other countries. This study aimed to establish a surface-enhanced Raman spectroscopy (SERS) method for screening sodium metabisulfite residues on shrimp surfaces, in a non-destructive manner. The analysis was carried out using a portable Raman spectrometer jointly with copy paper loaded with silver nanoparticles as the substrate material. The SERS response of sodium metabisulfite gives two fingerprint peaks at 620 (strong) and 927 (medium) cm^-1, respectively. This enabled unambiguous confirmation of the targeted chemical. The sensitivity of the SERS detection method was determined to be 0.1 mg/mL, which was equal to residual sodium metabisulfite on the shrimp surface at 0.31 mg/kg. The quantitative relationship between the 620 cm^-1 peak intensities and the concentrations of sodium metabisulfite was established. The linear fitting equation was y = 2375x + 8714 with R² = 0.985. Reaching an ideal balance in simplicity, sensitivity, and selectivity, this study demonstrates that the proposed method is ideally suitable for in-site and non-destructive screening of sodium metabisulfite residues in seafood.

Follow-up of the re-evaluation of sulfur dioxide (E 220), sodium sulfite (E 221), sodium bisulfite (E 222), sodium metabisulfite (E 223), potassium metabisulfite (E 224), calcium sulfite (E 226), calcium bisulfite (E 227) and potassium bisulfite (E 228)

Sulfur dioxide-sulfites (E 220-228) were re-evaluated in 2016, resulting in the setting of a temporary ADI of 0.7 mg SO2 equivalents/kg bw per day. Following a European Commission call for data, the present follow-up opinion assesses data provided by interested business operators (IBOs) and additional evidence identified in the publicly available literature. No new biological or toxicological data addressing the data gaps described in the re-evaluation were submitted by IBOs. Taking into account data identified from the literature search, the Panel concluded that there was no substantial reduction in the uncertainties previously identified in the re-evaluation. Therefore, the Panel considered that the available toxicity database was inadequate to derive an ADI and withdrew the current temporary group acceptable daily intake (ADI). A margin of exposure (MOE) approach was considered appropriate to assess the risk for these food additives. A lower confidence limit of the benchmark dose of 38 mg SO2 equivalents/kg bw per day, which is lower than the previous reference point of 70 mg SO2 equivalents/kg bw per day, was estimated based on prolonged visual evoked potential latency. An assessment factor of 80 was applied for the assessment of the MoE. At the estimated dietary exposures, when using a refined exposure scenario (Data set D), MOEs at the maximum of 95th percentile ranges were below 80 for all population groups except for adolescents. The dietary exposures estimated using the maximum permitted levels would result in MOEs below 80 in all population groups at the maximum of the ranges of the mean, and for most of the population groups at both minimum and maximum of the ranges at the 95th percentile. The Panel concluded that this raises a safety concern for both dietary exposure scenarios. The Panel also performed a risk assessment for toxic elements present in sulfur dioxide-sulfites (E 220-228), based on data submitted by IBOs, and concluded that the maximum limits in the EU specifications for arsenic, lead and mercury should be lowered and a maximum limit for cadmium should be introduced.

Protective effects of antioxidants on striatal dopamine release induced by organophosphorus pesticides

Although the toxic effects of organophosphorus (OP) pesticides have been classically attributed to inhibition of the acetylcholinesterase, other neurotoxic mechanisms, as oxidative stress can also occur. Here we evaluated if antioxidants prevent the excessive dopamine release induced by OP pesticides in conscious and freely moving rats, using cerebral microdialysis technique. Intrastriatal infusion of paraoxon (5 mM), glufosinate (10 mM) or glyphosate (5 mM) significantly increased the dopamine release (1006 ± 106%, 991 ± 142%, and 1164 ± 128%, relative to baseline, respectively). To evaluate if these increased dopamine release could be related to oxidative stress, we pretreated animals with antioxidants glutathione (GSH, 400 or 800 μM), dithiothreitol (DTT, 5 or 10 μM), trolox (1 or 3 mM), and α-lipoic acid (ALA, 400 or 800 μM) before administration of OP pesticides. Intrastriatal administration of the antioxidants GSH, DTT, trolox, and ALA was highly effective in preventing the glyphosate and glufosinate-induced dopamine overflow. However, only GSH (800 μM) significantly decreased the effect of paraoxon on dopamine levels. The high toxicity of this pesticide and the low concentrations used could explain this lack of effect in our experimental conditions. The fact that ROS scavengers prevent the excessive dopamine release induced by OP pesticides, further supports the view that dopamine overflow can cause neuronal damage mediated, at least in part, by oxidative stress.

Sodium sulfite causes gastric mucosal cell death by inducing oxidative stress

Sulfites are commonly used as a preservative and antioxidant additives in the food industry. Sulfites are absorbed by the gastrointestinal tract and distributed essentially to all body tissues. Although sulfites have been believed to be safe food additives, some studies have shown that they exhibit adverse effects in various tissues. In this study, we examined the cytotoxic effect of sodium sulfite (Na₂SO₃) against rat gastric mucosal cells (RGM1) and further investigated its underlying molecular mechanism. We demonstrated that exposure to Na₂SO₃ exerts significant cytotoxicity in RGM1 cells through induction of oxidative stress. Exposure of RGM1 cells to Na₂SO₃ caused a significant formation of protein carbonyls and 8-hydroxy-2'-deoxyguanosine, major oxidative stress markers, with a concomitant accumulation of carbonylated protein-related aggregates. Furthermore, we found that incubation of lysozyme with Na₂SO₃ evokes protein carbonylation and aggregation via the metal ion-catalyzed free radical formation derived from Na₂SO₃. Our results suggest that Na₂SO₃ might lead to gastric tissue injury via induction of oxidative stress by the formation of Na₂SO₃-related free radicals.

Mechanism analysis of toxicity of sodium sulfite to human hepatocytes L02

Food additives are widely used in various food products to preserve the taste, color, and other qualities. However, if they are used improperly or exceed the standard, they will cause damage to the human body. Sulfite is a commonly used food additive to prevent oxidation from deteriorating the nutrients in foods, it has been widely used as a bleaching agent in the food industry for a long time. In this study, human hepatocytes L02 cells were used as a model cell line to evaluate the toxicity of sodium sulfite. The cell morphology and cell proliferation were affected by sodium sulfite treatment, and apoptosis was detected. Transcriptome sequencing showed 97 differentially expressed genes (DEGs) between the experimental group (IC50) and the control group (MOCK), and 27 differentially expressed genes related to cell apoptosis, metabolism and inflammation were selected for validation by qPCR. Among them, 13 significantly upregulated genes and 14 significantly downregulated genes were identified by qPCR. The results showed that with increase of sodium sulfite concentration, the morphology of L02 changed, cell proliferation and activity were inhibited, and sodium sulfite caused apoptosis in a concentration- and time-dependent manner. The resulting toxic mechanism inhibits proliferation, damages the mitochondrial integrity, and promotes apoptosis.