Zinc diffusion through lipid bilayers

An overview of interactions between micronutrients and of micronutrients with drugs, genes and immune mechanisms

The objective of the present review is to examine critically the consequences of interactions that micronutrients undergo with nutrients and non-nutrients (mainly prescribed medicines) in diets and lifestyle factors (smoking, tea and alcohol consumption). In addition, the review describes recent work on interactions between nutrients and genes, the influence of gene polymorphisms on micronutrients, the impact of immune responses on micronutrients and specific interactions of antioxidant micronutrients in disease processes to minimise potential pro-oxidant damage.

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

Zinc is proposed to be antiapoptotic for it has been shown to inhibit late events of apoptotic pathways such as Ca(2+)/Mg(2+)-dependent endonuclease cleavage of chromatin DNA, poly-ADP ribose polymerase cleavage, and caspase-3 activity. Because caspase-3 is a critical executioner caspase in apoptosis, this study was undertaken to examine specifically a correlation between zinc inhibition of caspase-3 activation and apoptosis in HeLa cells. Cultured HeLa cells were exposed to 100 microM ZnCl(2) for 1 h prior to 12 h treatment with 1.0 microM doxorubicin (DOX), an important anticancer agent that causes apoptosis in a wide variety of tumor cells. Western blot analysis of HeLa cells treated with DOX for 12 h revealed that DOX caused proteolytic activation of caspase-3 and zinc inhibited this activation. Interestingly, zinc did not inhibit DOX-induced apoptosis as measured by a terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay. Furthermore, a microculture tetrazolium assay confirmed that cell death occurred in the presence of zinc. These results demonstrate that zinc specifically inhibits DOX-induced activation of caspase-3 in HeLa cells, but does not suppress DOX-induced apoptosis or otherwise cell death, thus suggesting DOX-induced caspase-3 activation may not play a major role in overall cell death and/or non-caspase-3 pathways are involved in DOX-induced apoptosis in HeLa cells.

Principal component analysis of the absorption and resonance Raman spectra of the metallochromic indicator antipyrylazo III

Metallochromic indicators, whose spectral properties are changed in the presence of metal cations, are used mainly in biological studies to monitor Ca2+ and Mg2+ ions. Antipyrylazo III is such indicator, employed for mid-range Ca2+ concentrations (10-1000 microM). The stoichiometry of the interactions of antipyrylazo III with Ca2+, Mg2+, Ba2+, Sr2+ and Zn2+ ions and the relevant binding constants were studied by principal component analysis (PCA) of the absorption spectral changes. The resonance Raman spectra of the above systems were measured as well, and the resolved Raman spectra of the various species were calculated and assigned. The vibrational spectra are more featured, more characteristic of the binding ions and exhibit stronger relative spectral changes upon binding the cations. The basis sets of Raman spectra could thus be used as an analytical tool for these divalent metallic cations.

Routes of zinc entry in mouse cortical neurons: role in zinc-induced neurotoxicity

Exposure of central neurons to Zn2+ triggers neuronal death. The routes of Zn2+ entry were investigated in living cortical neurons from the mouse using the specific Zn2+ fluorescent dye N-(6-methoxy-8-quinolyl)-p-toluene sulphonamide (TSQ), which preferentially detects membrane-bound Zn2+. Exposure of cortical neurons to increasing concentrations of Zn2+ (1-100 microM) induced a progressive increase in the fluorescence of TSQ. This fluorescence signal was not attenuated by the permeation of plasma membrane with digitonin. Accordingly, the major part of TSQ fluorescence (two-thirds) was associated to the particulate fraction of cortical neurons exposed to Zn2+. These results suggest that Zn2+ detected with TSQ in neurons is mainly bound to membranes. TSQ fluorescence measured in neurons exposed to 3 microM Zn2+ was enhanced by Na+-pyrithione, a Zn2+ ionophore, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), N-methyl-D-aspartate (NMDA) or KCl-induced depolarization. However, in the absence of any treatment, TSQ labelling of neurons exposed to 3 microM Zn2+ was only decreased by NMDA receptor antagonists, whereas it remained unaltered in the presence of antagonists of AMPA receptors or L-type voltage-gated Ca2+ channels. Zn2+ entry through NMDA receptors did not contribute to Zn2+-induced neuronal death, as it was prevented by antagonists of NMDA receptors only when they were added after the Zn2+ exposure. Finally, Zn2+ induced a delayed accumulation of extracellular glutamate which might be responsible for the delayed NMDA receptor activation that leads to neuronal death.

Zinc as an inducer of the membrane permeability transition in rat liver mitochondria

It is shown that 2-10 microM Zn2+ induces swelling of rat liver mitochondria incubated in a buffered sucrose medium either with valinomycin or with FCCP, Ca2+, ionophore A23187, oligomycin, and nigericin. This swelling was associated with the release of GSH from mitochondria. Both processes were sensitive to known inhibitors of the mitochondrial permeability transition (MPT), cyclosporin A, and Mg2+. Mitochondrial swelling induced by Zn2+ was also inhibited by rotenone, antymycin A, N-ethylmaleimide, butylhydroxytoluene, and spermine, whereas it was stimulated by tert-butyl hydroperoxide, diamide, and monobromobimane. It did not require the addition of phosphate. The same sensitivity to pH of the mitochondrial swelling induced by Zn2+ and by phenylarsine oxide suggests the same site of the interaction, namely, thiol groups. The ability of Zn2+ to induce mitochondrial swelling gradually decreased along with its increasing concentration above 10 microM. It is concluded that micromolar Zn2+ induces the MPT presumably by the interaction with cysteinyl residues. This process is independent of the mitochondrial membrane potential.