Zinc inhibition of caspase-3 activation does not protect HeLa cells from apoptotic cell death

Non-redox cycling mechanisms of oxidative stress induced by PM metals

Metallic compounds contribute to the oxidative stress of ambient particulate matter (PM) exposure. The toxicity of redox inert ions of cadmium, mercury, lead and zinc, as well as redox-active ions of vanadium and chromium is underlain by dysregulation of mitochondrial function and loss of signaling quiescence. Central to the initiation of these effects is the interaction of metal ions with cysteinyl thiols on glutathione and key regulatory proteins, which leads to impaired mitochondrial electron transport and persistent pan-activation of signal transduction pathways. The mitochondrial and signaling effects are linked by the production of H₂O₂, generated from mitochondrial superoxide anion or through the activation of NADPH oxidase, which extends the range and amplifies the magnitude of the oxidative effects of the metals. This oxidative burden can be further potentiated by inhibitory effects of the metals on the enzymes of the glutathione and thioredoxin systems. Along with the better-known Fenton-based mechanisms, the non-redox cycling mechanisms of oxidative stress induced by metals constitute significant pathways for cellular injury induced by PM inhalation.

Rational design of novel red-shifted BRET pairs: Platforms for real-time single-chain protease biosensors

Bioluminescence resonance energy transfer (BRET) systems to date have been dominated by use of blue-green Renilla luciferase (Rluc) as the energy donor. Although effective in many cases, the expense and unfavorable biochemical attributes of the substrate (phenylcoelenterazine) limit utility of Rluc-based BRET systems. Herein we report a series of novel BRET pairs based on luciferases that utilize D-luciferin, resulting in red-shifted photonic outputs, favorable biochemical attributes, and increased efficacy. We developed a modified Förster equation to predict optimal BRET luciferase donor-fluorophore pairs and identified tdTomato as the optimal red fluorophore acceptor for click beetle green luciferase (CBG). A prototypical single-chain protease biosensor, capable of reporting on executioner caspase activity in live cells and in real-time, was generated by inserting a DEVD linker between CBG and tdTomato and validated in vitro with recombinant caspases and in cellulo with apoptosis-sensitive and -resistant cell lines. High signal-to-noise ratios ( approximately 33) and Z' factors (0.85) were observed in live cell longitudinal studies, sufficient for high-throughput screening. Thus, we illustrate a general methodology for the rational design of new BRET systems and provide a novel single-chain BRET protease biosensor that is long lived, red-shifted, and utilizes D-luciferin.

Effect of zinc ions on apoptosis in PBMCs from healthy aged subjects

Immunosenescence features, such as thymic involution, alteration of T-cell repertoire, autoimmunity and accumulation of memory/effector T cells, may be the result, at least in part, of a zinc deficiency, which is often observed during ageing. Zinc, as essential trace element, affects the immune system function and it is an important regulator of apoptosis of immune cells. In this study we addressed the question whether zinc supplementation in vitro at physiological doses can affect spontaneous and oxidative stress-induced apoptosis in peripheral blood mononuclear cells from subjects of three different age groups: young (mean age 28 years), old (mean age 72 years) and nonagenarians. We studied different parameters related to apoptosis (phosphatydilserine exposure, mitochondrial membrane potential, caspase 3 cleavage) and we found that zinc, while decreasing spontaneous apoptosis, can increase oxidative stress-induced apoptosis in an age-related fashion, being this effect more evident in nonagenarians than in old or young subjects. In particular, zinc can increase late apoptosis/necrosis, a phenomenon that could trigger unnecessary inflammation in vivo. We surmise that these age-associated alterations in susceptibility to apoptosis may be due to a different effect of zinc on T cell subsets, that are altered in very old people, and finally that the zinc deficiency, which is often observed in aged subjects, could be a compensatory mechanism to counteract the inflammatory status of the elderly.

Metal and redox modulation of cysteine protein function

In biological systems, the amino acid cysteine combines catalytic activity with an extensive redox chemistry and unique metal binding properties. The interdependency of these three aspects of the thiol group permits the redox regulation of proteins and metal binding, metal control of redox activity, and ligand control of metal-based enzyme catalysis. Cysteine proteins are therefore able to act as "redox switches," to sense concentrations of oxidative stressors and unbound zinc ions in the cytosol, to provide a "storage facility" for excess metal ions, to control the activity of metalloproteins, and to take part in important regulatory and signaling pathways. The diversity of cysteine's multiple roles in vivo is equally as fascinating as it is promising for future biochemical and pharmacological research.

Suppression of Fas-mediated signaling pathway is involved in zinc inhibition of ethanol-induced liver apoptosis

Apoptosis is critically involved in hepatic pathogenesis induced by acute alcohol exposure. This study was undertaken to test the hypothesis that zinc interferes with an important Fas ligand-mediated pathway in the liver, leading to the inhibition of ethanol-induced apoptosis. Male 129/Sv(PC)J mice were injected subcutaneously with ZnSO4 (5 mg of Zn ion/kg) in 12-hr intervals for 24 hr before intragastric administration of ethanol (5 g/kg) in 12-hr intervals for 36 hr. Ethanol-induced apoptosis in the liver was detected by a terminal deoxynucleotidyl transferase nick-end labeling assay and was further confirmed by electron microscopy. The number of apoptotic cells in the livers pretreated with zinc was significantly decreased, being only 15% of that found in the animals treated with ethanol only. Characteristic apoptotic morphological changes observed by electron microscopy were also inhibited by zinc. Importantly, zinc inhibited ethanol-induced activation of caspase-3, the primary executioner protease responsible for alcohol-induced liver apoptosis, and caspase-8 as determined by enzymatic assay. Immunohistochemical analysis revealed that zinc inhibited ethanol-induced endogenous Fas ligand activation, which is a key component in signaling pathways leading to hepatic caspase-8 and subsequent caspase-3 activation and apoptosis. These results demonstrate that zinc is a potent inhibitor of acute ethanol-induced liver apoptosis, and this effect occurs primarily through zinc interference with Fas ligand pathway and the suppression of caspase-3.