Accumulating evidence suggests that the bactericidal activity of some antibiotics may not be directly initiated by target inhibition. The activity of isoniazid (INH), a key first-line bactericidal antituberculosis drug currently known to inhibit mycolic acid synthesis, becomes extremely poor under stress conditions, such as hypoxia and starvation. This suggests that the target inhibition may not fully explain the bactericidal activity of the drug. Here, we report that INH rapidly increased Mycobacterium bovis BCG cellular ATP levels and enhanced oxygen consumption. The INH-triggered ATP increase and bactericidal activity were strongly compromised by Q203 and bedaquiline, which inhibit mycobacterial cytochrome bc1 and FoF1 ATP synthase, respectively. Moreover, the antioxidant N-acetylcysteine (NAC) but not 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPOL) abrogated the INH-triggered ATP increase and killing. These results reveal a link between the energetic (ATP) perturbation and INH’s killing. Furthermore, the INH-induced energetic perturbation and killing were also abrogated by chemical inhibition of NADH dehydrogenases (NDHs) and succinate dehydrogenases (SDHs), linking INH’s bactericidal activity further to the electron transport chain (ETC) perturbation. This notion was also supported by the observation that INH dissipated mycobacterial membrane potential. Importantly, inhibition of cytochrome bd oxidase significantly reduced cell recovery during INH challenge in a culture settling model, suggesting that the respiratory reprogramming to the cytochrome bd oxidase contributes to the escape of INH killing. This study implicates mycobacterial ETC perturbation through NDHs, SDHs, cytochrome bc1, and FoF1 ATP synthase in INH’s bactericidal activity and pinpoints the participation of the cytochrome bd oxidase in protection against this drug under stress conditions.

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A silver amperometric detector coupled to liquid chromatography (LC) was used for the determination of 6-thioguanine (6-TG) and two of its metabolites, thiouric acid (TU) and 2-amino-6-mercaptopurine riboside (6-TGR). The silver detector coupled to LC operated at a low applied potential (0.08 V vs Ag/AgCl) and offered a chromatogram with peak responses corresponding to molecules interacting with silver, namely, chloride ions and small soluble biothiols in addition to the organothiol drug compounds investigated. Online electrochemical surface cleaning permitted the improvement of the repeatability and peak shape of the recorded signal compared to direct current amperometric detection (AD) when operating in chloride containing media. The studied molecules were eluted isocratically within 5 min on a reversed-phase C18 column without interference from endogenous biothiols present in urine samples. Diluted urine samples (1:1) were directly injected in the LC setup; a linear calibration curve was obtained between peak area and analyte concentration between 0.1 and 10 μM for all the studied molecules. Limits of detection (LODs) were 0.03, 0.008, and 0.01 μM, and the limits of quantification (LOQs) were 0.1, 0.02, and 0.03 μM for TU, 6-TG, and 6-TGR, respectively. Within-day RSDs were 2%, 0.8%, and 1% and between-day RSDs were 2%, 0.9%, 2% for TU, 6-TG, and 6-TGR, respectively. Recoveries in spiked urine were 99.8%, 99.9%, and 99.0% for TU, 6-TG, and 6-TGR, respectively.

Ethoxyquin (EQ) is an antioxidant widely used in the food industry. Some concerns for human health have been reported since its utilization in animal feed may lead to residues in human food such as salmon samples. This work aimed to investigate the electrochemical behavior of EQ and its major oxidation products namely a dimer of EQ (EQDM) and ethoxyquin quinone imine (EQI) by cyclic voltammetry (CV) at a carbon screen printed electrode (cSPE). The stability of these products and their reactivity against glutathione (GSH) were also studied. Oxidized products and thiol adducts were identified by a microelectrolysis of an EQ solution onto a cSPE in the absence and in the presence of GSH. The products were analyzed off‐line, by liquid chromatography coupled to a mass spectrometer (LC‐MS). One of the generated product (EQI) was shown to be highly reactive towards GSH. Based on the redox pattern of EQ, a flow injection analysis with a dual cSPE was developed in order to detect in a rapid manner EQ in salmon samples. Since matrix effects were observed, matrix‐matched calibration curves with spiked samples were built. A linear response was obtained between 20–100 μM and a limit of detection (LOD) of 7.5 μM (8.2 mg/kg of salmon). Trueness was assessed with recovery assays at three levels of concentration. The recovery was close to 100 %. Precision was determined as RSD (%) with values lower than 6 % in all cases.

A glassy carbon electrode (GCE) was modified by electrochemically reduced graphene oxide (ERGO) for subsequent dsDNA immobilization. The interaction of cisplatin with dsDNA was studied at this modified electrode. Quantitative investigations were performed by adsorptive transfer stripping voltammetry (AdTSV) using differential pulse voltammetry (DPV). The morphology and structure of graphene oxide (GO) and ERGO modified GCEs (GO/GCE and ERGO/GCE, respectively) were characterized by UV‐vis, FT‐IR, Raman spectroscopy and cyclic voltammetry. Compared with the bare GCE and the GO/GCE, the ERGO/GCE exhibited excellent electrocatalytic activity towards the oxidation of dsDNA due to guanine and adenine groups, testified by high oxidation peak currents and decreased oxidation potentials. The interaction of micromolar concentrations of cisplatin with surface confined dsDNA was readily detected as inferred from the decrease of the voltammetric oxidation peaks of guanine and adenine. This trend was significantly greater at the ERGO/GCE compared to the GO/GCE. The interaction of cisplatin with dsDNA was also studied in solution phase by AdTSV with detection at the ERGO/GCE.