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Methylmercury is a ubiquitous neurotoxic substance present in the environment, and health concerns, especially through the consumption of seafood, remain. Glutathione (GSH)-mediated detoxification and the excretion of methylmercury are known metabolic detoxification pathways. We have also discovered a mechanism by which endogenous super-sulfides convert methylmercury to nontoxic metabolites such as bis-methylmercury sulfide. However, these metabolites are present in very small quantities, and the significance of the detoxification of methylmercury by super-sulfides is not well understood. Methylmercury binds to thiol groups in vivo but can also react with highly reactive selenols (selenocysteine residues). Such covalent bonds (S-mercuration and Se-mercuration) are broken by nucleophilic substitution reactions with other thiol and selenols, however, the contribution of super-sulfides to this substitution reaction is not well understood. Interestingly, a recent study suggested that selenoprotein P, the major selenium transport protein in plasma, binds to methylmercury, however, Se-mercuration was not determined. In this review, we introduce these series of reactions and discuss their involvement with super-sulfides in methylmercury toxicity.

Cardiac redox homeostasis is precisely regulated by reactive oxygen species (ROS) or electrophilic molecules that are formed by ROS reacting with intracellular substrates, and their eliminating systems. We have focused on the role of nitric oxide (NO) generated from inducible NO synthase (iNOS) that is continuously upregulated from early stage of heart failure, and revealed that iNOS-derived NO acts as a protective factor in the early stage of heart failure, whereas it contributes to induction of cardiac early senescence in later stages. The switching mechanism of NO-mediated signaling includes formation of endogenous NO-derived electrophilic byproducts such as 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP), which selectively targets an oncogenic small GTPase H-Ras at Cys-184, leading to cardiac cell senescence via covalent modification (S-guanylation) and activation of H-Ras. We also found that hydrogen sulfide-related reactive sulfur species (RSS) function as potent nucleophiles to eliminate electrophilic modification of H-Ras and suppress the onset of chronic heart failure after myocardial infarction. Our results strongly suggest a new concept of redox biology in which suppression of electrophilic irreversible modification of protein cysteine thiols by RSS may be a new therapeutic strategy of cardiovascular diseases.

A 66-year-old man was referred to our hospital with obstructive jaundice. Computed tomography(CT)scan showed thickening of the gallbladder wall, invasion into the liver bed, and thickening of the rectal wall. Colonoscopy revealed a type 2 rectal cancer, in which adenocarcinoma was identified by endoscopic biopsy. He was diagnosed with double-cancer of the gallbladder and rectum. Because his gallbladder cancer was more life threatening than his rectal cancer, gemcitabine was administered at 1, 000 mg/m2 on days 1, 8, and 15 of a 28-day course. After 3 courses of gemcitabine, the CT scan showed that the lymph nodes in the hepatoduodenal ligament had been enlarged, and duodenal stenosis had occurred as a result of gallbladder cancer invasion. S-1 was administered orally at doses of 120 mg/day twice daily on days 1-28 of a 42-day course. Partial response was confirmed by CT scan. After 8 courses of S-1, the gallbladder cancer had progressed and liver metastases had appeared. He subsequently died of disease progression. He survived for 17 months after the first course of chemotherapy, and the progression-free survival with S-1 was 10 months. Therefore, S-1 could be an effective agent for synchronous double cancer of the gallbladder and rectum.

The patient was a 55-year-old man with a large hepatic tumor measuring 12 × 12 cm in the left lobe. To obtain the histological diagnosis, the target liver biopsy was performed. Histologically, the tumor revealed as a neuroendocrine carcinoma. After the diagnosis, he received the chemotherapy (CTX) with etoposide and cisplatin. Serum levels of NSE and the tumor size were decreased after the first course of CTX. We here report a case of primary hepatic neuroendocrine carcinoma treated with CTX following the diagnosis by the needle biopsy.