Differential response of iron metabolism to oxidative stress generated by antimycin A and nitrofurantoin

Can iron, zinc, copper and selenium status be a prognostic determinant in COVID-19 patients?

In severe COVID-19, the levels of iron (Fe), copper (Cu), zinc (Zn) and selenium (Se), do not only regulate host immune responses, but modify the viral genome, as well. While low serum Fe concentration is an independent risk factor for the increased death rate, Zn controls oxidative stress, synthesis of inflammatory cytokines and viral replication. Therefore, Zn deficiency associates with a worse prognosis. Although Cu exposure inactivates the viral genome and exhibits spike protein dispersal, increase in Cu/Zn due to high serum Cu levels, are correlated with enhanced risk of infections. Se levels are significantly higher in surviving COVID-19 patients. Meanwhile, both Zn and Se suppress the replication of SARS-CoV-2. Since the balance between the deficiency and oversupply of these metals due to a reciprocal relationship, has decisive effect on the prognosis of the SARS-CoV-2 infection, monitoring their concentrations may facilitate improved outcomes for patients suffering from COVID-19.

Potential therapeutic use of ebselen for COVID-19 and other respiratory viral infections

Ebselen is an organoselenium compound exhibiting hydroperoxide- and peroxynitrite-reducing activity, acting as a glutathione peroxidase and peroxiredoxin enzyme mimetic. Ebselen reacts with a multitude of protein thiols, forming a selenosulfide bond, which results in pleiotropic effects of antiviral, antibacterial and anti-inflammatory nature. The main protease (M^pro) of the corona virus SARS-CoV-2 is a potential drug target, and a screen with over 10,000 compounds identified ebselen as a particularly promising inhibitor of M^pro (Jin, Z. et al. (2020) Nature 582, 289-293). We discuss here the reaction of ebselen with cysteine proteases, the role of ebselen in infections with viruses and with other microorganisms. We also discuss effects of ebselen in lung inflammation. In further research on the inhibition of M^pro in SARS-CoV-2, ebselen can serve as a promising lead compound, if the inhibitory effect is confirmed in intact cells in vivo. Independently of this action, potential beneficial effects of ebselen in COVID-19 are ascribed to a number of targets critical to pathogenesis, such as attenuation of inflammatory oxidants and cytokines.

Role of cytochrome P450 reductase in nitrofurantoin-induced redox cycling and cytotoxicity

The one-electron reduction of redox-active chemotherapeutic agents generates highly toxic radical anions and reactive oxygen intermediates (ROI). A major enzyme catalyzing this process is cytochrome P450 reductase. Because many tumor cells highly express this enzyme, redox cycling of chemotherapeutic agents in these cells may confer selective antitumor activity. Nitrofurantoin is a commonly used redox-active antibiotic that possesses antitumor activity. In the present studies we determined whether nitrofurantoin redox cycling is correlated with cytochrome P450 reductase activity and cytotoxicity in a variety of cell lines. Recombinant cytochrome P450 reductase was found to support redox cycling of nitrofurantoin and to generate superoxide anion, hydrogen peroxide, and, in the presence of redox-active iron, hydroxyl radicals. This activity was NADPH dependent and inhibitable by diphenyleneiodonium, indicating a requirement for the flavin cofactors in the reductase. Nitrofurantoin-induced redox cycling was next analyzed in different cell lines varying in cytochrome P450 reductase activity including Chinese hamster ovary cells (CHO-OR) constructed to overexpress the enzyme. Nitrofurantoin-induced hydrogen peroxide production was 16-fold greater in lysates from CHO-OR cells than from control CHO cells. A strong correlation between cytochrome P450 reductase activity and nitrofurantoin-induced redox cycling among the cell lines was found. Unexpectedly, no correlation between nitrofurantoin-induced ROI production and cytotoxicity was observed. These data indicate that nitrofurantoin-induced redox cycling and subsequent generation of ROI are not sufficient to mediate cytotoxicity and that cytochrome P450 reductase is not a determinant of sensitivity to redox-active chemotherapeutic agents.

Studies on resistance characteristic and cDNA sequence conservation of transferrin from crucian carp, Carassius auratus

Transferrin (Tf) is a kind of non-heme beta-globulin with two iron ions (Fe(3+))-binding sites. To prove Tf's physiological functions, Fe(3+)-proteins, serum iron contents, and total iron-binding capabilities were tested for Tfs of crucian carps (Carassius auratus) and sliver carps (Hypophthalmichthys molitrix). The above results demonstrated that sliver carps shared 1/3 Tf alleles with crucian carps; Tf of crucian carps had stronger Fe(3+)-binding ability and transportation ability in plasma than that of sliver carps. In addition, the results of oxygen consumption experiments indicated that crucian carps had the higher oxygen utility rate than sliver carps. For acute hypoxia exposure assay, normoxic gas mixture, hypoxic gas mixture A, and hypoxic gas mixture B were used to induce oxygen-regulated gene expression of crucian carps in acute hypoxia. The results of quantitative real-time PCR revealed that mRNA levels of Tf gene, Tfr gene and ATPase gene were down-regulated in acute hypoxia but mRNA level of LDHa gene was up-regulated in acute hypoxia. The results of crucian carp Tf-cDNA sequence analysis showed that cDNA regions of two Fe(3+)-binding sites were T(747)-T(1026) and T(1737)-A(1884) based on the principle of bioinformatics. The sequence conservation of two Fe(3+)-binding sites was higher than that of the other five regions, which were confirmed according to the subregion model of Tf-cDNA sequence.