Cyanide inhibition and pyruvate-induced recovery of cytochrome c oxidase

Tumor necrosis factor induces pathogenic mitochondrial ROS in tuberculosis through reverse electron transport

Tumor necrosis factor (TNF) is a critical host resistance factor against tuberculosis. However, excess TNF produces susceptibility by increasing mitochondrial reactive oxygen species (mROS), which initiate a signaling cascade to cause pathogenic necrosis of mycobacterium-infected macrophages. In zebrafish, we identified the mechanism of TNF-induced mROS in tuberculosis. Excess TNF in mycobacterium-infected macrophages elevates mROS production by reverse electron transport (RET) through complex I. TNF-activated cellular glutamine uptake leads to an increased concentration of succinate, a Krebs cycle intermediate. Oxidation of this elevated succinate by complex II drives RET, thereby generating the mROS superoxide at complex I. The complex I inhibitor metformin, a widely used antidiabetic drug, prevents TNF-induced mROS and necrosis of Mycobacterium tuberculosis-infected zebrafish and human macrophages; metformin may therefore be useful in tuberculosis therapy.

The two faces of cyanide: an environmental toxin and a potential novel mammalian gasotransmitter

Cyanide is traditionally viewed as a cytotoxic agent, with its primary mode of action being the inhibition of mitochondrial Complex IV (cytochrome c oxidase). However, recent studies demonstrate that the effect of cyanide on Complex IV in various mammalian cells is biphasic: in lower concentrations (nanomolar to low micromolar) cyanide stimulates Complex IV activity, increases ATP production and accelerates cell proliferation, while at higher concentrations (high micromolar to low millimolar) it produces the previously known (‘classic’) toxic effects. The first part of the article describes the cytotoxic actions of cyanide in the context of environmental toxicology, and highlights pathophysiological conditions (e.g., cystic fibrosis with Pseudomonas colonization) where bacterially produced cyanide exerts deleterious effects to the host. The second part of the article summarizes the mammalian sources of cyanide production and overviews the emerging concept that mammalian cells may produce cyanide, in low concentrations, to serve biological regulatory roles. Cyanide fulfills many of the general criteria as a ‘classical’ mammalian gasotransmitter and shares some common features with the current members of this class: nitric oxide, carbon monoxide, and hydrogen sulfide.

Distinguishing chemically induced NADPH- and NADH-related metabolic responses using phasor analysis of UV-excited autofluorescence

NADPH and NADH are well known for their role in antioxidant defense and energy metabolism, respectively, however distinguishing their cellular autofluorescence signals is a challenge due to their nearly identical optical properties. Recent studies applying spectral phasor analysis to autofluorescence emission during chemically induced metabolic responses showed that two-component spectral behavior, i.e., spectral change acting as a superposition of two spectra, depended on whether one or multiple metabolic pathways were affected. Here, we use this property of spectral behavior to show that metabolic responses primarily involving NADPH or NADH can be distinguished. We start by observing that the cyanide-induced response at micro- and millimolar concentrations does not follow mutual two-component spectral behavior, suggesting their response mechanisms differ. While respiratory inhibition at millimolar cyanide concentration is well known and associated with the NADH pool, we find the autofluorescence response at micromolar cyanide concentration exhibits two-component spectral behavior with NADPH-linked EGCG- and peroxide-induced responses, suggesting an association with the NADPH pool. What emerges is a spectral phasor map useful for distinguishing cellular autofluorescence responses related to oxidative stress versus cellular respiration.

A phasor approach was used to show that chemically induced cellular autofluorescence responses linked to NADPH and NADH pathways can be distinguished.

Rationally designed molecules for resurgence of cyanide mitigated cytochrome c oxidase activity

Cytochrome c oxidase (CcOX) containing binuclear heme a₃-Cu B centre (BNC) mechanises the process of electron transfer in the last phase of cellular respiration. The molecular modelling based structural analysis of CcOX - heme a₃-Cu B complex was performed and the disturbance to this complex under cyanide poisoning conditions was investigated. Taking into consideration the results of molecular docking studies, new chemical entities were developed for clipping cyanide from the enzyme and restoring its normal function. It was found that the molecules obtained by combining syringaldehyde, oxindole and chrysin moieties bearing propyl/butyl spacing groups occupy the BNC region and effectively remove cyanide bound to the enzyme. The binding constant of compound 2 with CN^- was 2.3 × 10⁵ M^-1 and its ED₅₀ for restoring the cyanide bound CcOX activity in 10 min was 16 µM. The compound interacted with CN^- over the pH range 5-10. The comparison of the loss of enzymatic activity in the presence of CN^- and resumption of enzymatic activity by compound 2 mediated removal of CN^- indicated the efficacy of the compound as antidote of cyanide.

The pathomechanism of cytochrome c oxidase deficiency includes nuclear DNA damage

Mitochondrial cytochrome c oxidase (COX, respiratory chain complex IV), contributes to ATP production via oxidative phosphorylation (OXPHOS). Clinical presentation of COX deficiency is heterogeneous ranging from mild to severe neuromuscular diseases. Anemia is among the symptoms and we have previously reported Fanconi anemia like features in COX4-1 deficiency, suggesting genomic instability and our preliminary results detected nuclear double stranded DNA breaks (DSB). We now quantified the DSB by phospho histone H2AX Ser139 staining of COX4-1 and COX6B1 deficient fibroblasts (225% and 215% of normal, respectively) and confirmed their occurrence by neutral comet assay. We further explored the mechanism of DNA damage by studying normal fibroblasts treated with micromolar concentrations of cyanide (KCN). Present results demonstrate elevated nuclear DSB in cells treated with 50 μM KCN for 24 h (170% of normal) in high-glucose medium conditions where ROS and ATP remain normal, although Glutathione content was partially decreased. In glucose-free and serum-free medium, where growth is hampered, DSB were not elevated. Additionally we demonstrate the benefit of nicotinamide riboside (NR) which ameliorated DSB in COX4-1, COX6B1 and KCN treated cells (130%, 154% and 87% of normal cells, respectively). Conversely a negative effect of a poly[ADP-ribose] polymerase (PARP) inhibitor was found. Although additional investigation is needed, our findings raise the possibility that the pathomechanism of COX deficiency and possibly also in other OXPHOS defects, include nuclear DNA damage resulting from nicotinamide adenine dinucleotide (NAD⁺) deficit combined with a replicative state, rather than oxidative stress and energy depletion.

Zeolite-like Metal-Organic Framework (MOF) Encaged Pt(II)-Porphyrin for Anion-Selective Sensing

The selectivity and sensitivity of sensors are of great interest to the materials chemistry community, and a lot of effort is now devoted to improving these characteristics. More specifically, the selective sensing of anions is one of the largest challenges impeding the sensing-research area due to their similar physical and chemical behaviors. In this work, platinum-metalated porphyrin (Pt(II)TMPyP) was successfully encapsulated in a rho-type zeolite-like metal-organic framework (rho-ZMOF) and applied for anion-selective sensing. The sensing activity and selectivity of the MOF-encaged Pt(II)TMPyP for various anions in aqueous and methanolic media were compared to that of the free (nonencapsulated) Pt(II)TMPyP. While the photoinduced triplet-state electron transfer of Pt(II)TMPyP showed a very low detection limit for anions with no selectivity, the Pt(II)TMPyP encapsulated in the rho-ZMOF framework possessed a unique chemical structure to overcome such limitations. This new approach has the potential for use in other complex sensing applications, including biosensors, which require ion selectivity.

Cold acclimation of NaCl secretion in a eurythermic teleost: mitochondrial function and gill remodeling

Active chloride secretion, measured as short-circuit current (Isc) in ionocytes of opercular epithelia (OE) in the eurythermic, euryoxic, and euryhaline killifish or mummichog (Fundulus heteroclitus) was studied in cold (5°C) and warm (20°C) acclimated fish to determine if homeoviscous adaptation aided chloride secretion in the cold. Isolated opercular epithelia were cooled from 30°C to 0.2°C for warm and cold acclimated fish; from 30 to 8°C, Isc decreased with Q10=1.68 for warm and Q10=1.56 for cold acclimated tissues. By Arrhenius plots, there is a critical temperature, 8°C, below which aerobic Isc decreased sharply (Q10=6.90 for warm and 4.23 for cold acclimated tissues), suggesting a shift in mitochondrial efficiency of oxidative phosphorylation. In anaerobic conditions (0.5mM NaCN; N2 saturation), chloride transport continued at a lower rate, and Isc decrease with cooling below 8°C was less pronounced (Q10=2.95 for warm and 3.08 for cold), suggesting a shift in transporter function in plasma membrane. Under anaerobic conditions, NaCl secretion at 20°C was reversibly inhibited by hypotonic shock, indicating normal regulation of transport. Chloride secretion in warm-acclimated fish was supported mostly (75% at 20°C) by aerobic metabolism, whereas that for cold-acclimated fish was lower (55% at 20°C), suggesting a greater reliance on anaerobic metabolism in the cold. Once acclimated to cold, ionocytes may be temporarily incapable of increasing their aerobic ATP supply, even when warmed to 30°C. In cold acclimated fish there was increased polyunsaturated fatty acid composition of gill epithelium (consistent with homeoviscous adaptation) and gill remodeling, wherein epithelial cells filled the interlamellar space (interlamellar cell mass, ILCM) by as much as 70%, thus increasing diffusion distance against passive ion gain. Most ionocytes in these thickened epithelial masses became taller, still connecting basal lamina with the environment, consistent with the continuing transport rates at low temperatures. Whereas the low aerobic scope of cold-acclimated fish and thickened gill epithelium is appropriate to winter inactivity, metabolic depression and anaerobiosis, the large aerobic scope of warm-acclimated fish favors active foraging at high temperatures.

Selective detection of iodide and cyanide anions using gold-nanoparticle-based fluorescent probes

We developed two simple, rapid, and cost-effective fluorescent nanosensors, both featuring bovine serum albumin labeled with fluorescein isothiocyanate (FITC))-capped gold nanoparticles (FITC-BSA-Au NPs), for the selective sensing of cyanide (CN(-)) and iodine (I(-)) ions in high-salinity solutions and edible salt samples. During the preparation of FITC-BSA-Au NP probes, when AuNPs were introduced to the mixture containing FITC and BSA, the unconjugated FITC and FITC-labeled BSA (FITC-BSA) adsorbed to the particles' surfaces. These probes operated on a basic principle that I(-) and CN(-) deposited on the surfaces of the Au NPs or the etching of Au NPs induced the release of FITC molecules or FITC-BSA into the solution, and thus restored the florescence of FITC. We employed FITC-BSA to protect the Au NPs from significant aggregation in high-salinity solutions. In the presence of masking agents such as S(2)O(8)(2-)/Pb(2+), FITC-BSA-Au NPs facilitated the selective detection of CN(-) (by at least 150-fold in comparison with other anions). We also demonstrated that the FITC-BSA-Au NPs in the presence of H(2)O(2) could selectively detect I(-) down to 50 nM. Taking advantages of their high stability and selectivity, we employed our FITC-BSA-Au NP-based probes for the detection of CN(-) and I(-) in water samples (pond water, tap water, and seawater) and detection of I(-) in edible salt samples, respectively. This simple, rapid, and cost-effective sensing system appears to demonstrate immense practical potential for the detection of anions in real samples.