Formation of N-ethylmaleimide (NEM)-glutathione conjugate and N-ethylmaleamic acid revealed by mass spectral characterization of intracellular and extracellular microbial metabolites of NEM

A mitochondria-specific NIR fluorescence probe for dual-detection of sulfur dioxide and viscosity in living cells and mice

The level of sulfur dioxide (SO2) and viscosity in mitochondria play vital roles in various physiological and pathological processes. Abnormalities in mitochondrial SO2 and viscosity are closely associated with numerous biological diseases. It is of great significance to develop novel fluorescence probes for simultaneous detection of SO2 and viscosity within mitochondria. Herein, we have developed a water-soluble, mitochondrial-targeted and near-infrared fluorescent probe, CMBT, for the simultaneous detection of SO2 and viscosity. The probe CMBT incorporates benzothiazolium salt as a mitochondrial targeting moiety and 7-diethylaminocoumarin as a rotor for viscosity detection, respectively. Based on the prompt reaction between nucleophilic HSO3-/SO32- and the backbone of the benzothiazolium salt derivative, probe CMBT displayed high sensitivity and selectivity toward SO2 with a limit of detection as low as 0.17 μM. As viscosity increased, the twisted intramolecular charge transfer (TICT) process was restricted, resulting in fluorescence emission enhancement at 690 nm. Moreover, probe CMBT demonstrated exceptional mitochondrial targeting ability and was successfully employed to image variations of SO2 and viscosity in living cells and mice. The work highlights the great potential of the probe as a convenient tool for revealing the relationship between SO2 and viscosity in biological systems.

The Potassium Efflux System Kef: Bacterial Protection against Toxic Electrophilic Compounds

Kef couples the potassium efflux with proton influx in gram-negative bacteria. The resulting acidification of the cytosol efficiently prevents the killing of the bacteria by reactive electrophilic compounds. While other degradation pathways for electrophiles exist, Kef is a short-term response that is crucial for survival. It requires tight regulation since its activation comes with the burden of disturbed homeostasis. Electrophiles, entering the cell, react spontaneously or catalytically with glutathione, which is present at high concentrations in the cytosol. The resulting glutathione conjugates bind to the cytosolic regulatory domain of Kef and trigger activation while the binding of glutathione keeps the system closed. Furthermore, nucleotides can bind to this domain for stabilization or inhibition. The binding of an additional ancillary subunit, called KefF or KefG, to the cytosolic domain is required for full activation. The regulatory domain is termed K⁺ transport-nucleotide binding (KTN) or regulator of potassium conductance (RCK) domain, and it is also found in potassium uptake systems or channels in other oligomeric arrangements. Bacterial RosB-like transporters and K⁺ efflux antiporters (KEA) of plants are homologs of Kef but fulfill different functions. In summary, Kef provides an interesting and well-studied example of a highly regulated bacterial transport system.

Near-Infrared Mitochondria-Targetable Single-Molecule probe for Dual-Response of viscosity and sulfur dioxide in vivo

Studies have demonstrated that the viscosity and SO₂ in mitochondria are involved in various physiological processes, which are both important for maintaining the normal function of mitochondria. In this research, we rationally designed and synthesized a novel mitochondria-targetable fluorescent probe Mito-MG with near-infrared absorption and emission for dual-response of viscosity and SO₂. Based on the TICT mechanism and Michael addition reaction, the probe Mito-MG responds to viscosity and SO₂ with different near-infrared fluorescence signals. Importantly, Mito-MG presented outstanding mitochondrial targeting ability (Pearson's colocalization coefficient is 0.8602) and has been successfully applied to imaging of the cells, zebrafish and mice. We believe that Mito-MG could be applied as a powerful tool for a deep understanding of the connection of viscosity and SO₂ in biological systems.

Antagonistic effect of N-ethylmaleimide on arsenic-mediated oxidative stress-induced poly(ADP-ribosyl)ation and cytotoxicity

Long-term exposure to arsenic has been known to induce neoplastic initiation and progression in several organs; however, the role of arsenic (As₂ O₃ ) in oxidative stress-mediated DNA damage remains elusive. One of the immediate cellular responses to DNA damage is poly(ADP-ribosyl)ation (PARylation), which mediates DNA repair and enhances cell survival. In this study, we found that oxidative stress (H₂ O₂ )-induced PARylation was suppressed by As₂ O₃ exposure in different human cancer cells. Moreover, As₂ O₃ treatment promoted H₂ O₂ -induced DNA damage and apoptosis, leading to increased cell death. We found that N-ethylmaleimide (NEM), an organic compound derived from maleic acid, could reverse As₂ O₃ -mediated effects, thus enhancing PARylation with attenuated cell death and increased cell survival. Pharmacologic inhibition of glutathione with l-buthionine-sulfoximine blocked the antagonistic effect of NEM on As₂ O₃ , thereby continuing As₂ O₃ -mediated suppression of PARylation and causing DNA damage. Our findings identify NEM as a potential antidote against As₂ O₃ -mediated DNA damage in a glutathione-dependent manner. Copyright © 2016 John Wiley & Sons, Ltd.

Glutathione sulfinamide serves as a selective, endogenous biomarker for nitroxyl after exposure to therapeutic levels of donors

Nitroxyl (HNO) donors exhibit promising pharmacological characteristics for treatment of cardiovascular disorders, cancer, and alcoholism. However, whether HNO also serves as an endogenous signaling agent is currently unknown, largely because of the inability to selectively and sensitively detect HNO in a cellular environment. Although a number of methods to detect HNO have been developed recently, sensitivity and selectivity against other nitrogen oxides or biological reductants remain problematic. To improve selectivity, the electrophilic nature of HNO has been harnessed to generate modifications of thiols and phosphines that are unique to HNO, especially compared to nitric oxide (NO). Given high bioavailability, glutathione (GSH) is expected to be a major target of HNO. As a result, the putative selective product glutathione sulfinamide (GS(O)NH2) may serve as a high-yield biomarker of HNO production. In this work, the formation of GS(O)NH2 after exposure to HNO donors was investigated. Fluorescent labeling followed by separation and detection using capillary zone electrophoresis with laser-induced fluorescence allowed quantitation of GS(O)NH2 with nanomolar sensitivity, even in the presence of GSH and derivatives. Formation of GS(O)NH2 was found to occur exclusively upon exposure of GSH to HNO donors, thus confirming selectivity. GS(O)NH2 was detected in the lysate of cells treated with low-micromolar concentrations of HNO donors, verifying that this species has sufficient stability to server as a biomarker of HNO. Additionally, the concentration-dependent formation of GS(O)NH2 in cells treated with an HNO donor suggests that the concentration of GS(O)NH2 can be correlated to intracellular levels of HNO.