The role of mitochondrial DNA damage in the citotoxicity of reactive oxygen species

Mitochondria contain their own genome, a small circular molecule of around 16.5 kbases. The mitochondrial DNA (mtDNA) encodes for only 13 polypeptides, but its integrity is essential for mitochondrial function, as all 13 proteins are regulatory subunits of the oxidative phosphorylation complexes. Nonetheless, the mtDNA is physically associated with the inner mitochondrial membrane, where the majority of the cellular reactive oxygen species are generated. In fact, the mitochondrial DNA accumulates high levels of oxidized lesions, which have been associated with several pathological and degenerative processes. The cellular responses to nuclear DNA damage have been extensively studied, but so far little is known about the functional outcome and cellular responses to mtDNA damage. In this review we will discuss the mechanisms that lead to damage accumulation and the in vitro models we are establishing to dissect the cellular responses to oxidative damage in the mtDNA and to sort out the differential cellular consequences of accumulation of damage in each cellular genome, the nuclear and the mitochondrial genome.

Urea amperometric biosensors based on a multifunctional bipolymeric layer: Comparing enzyme immobilization methods

This paper outlines the results obtained with biosensors designed for urea amperometric detection. The incorporation of urease into a bipolymeric substrate consisting of poly(pyrrole) and poly(5-amino-1-naphthol) was performed through four different approaches: direct adsorption, entrapment in cellulose acetate layer. cross-linking with glutaraldehyde, and also covalent attachment to the polymeric matrix. Poly(pyrrole) acts as amperometric transducer in these biosensors, while poly(5-amino-1-naphthol) drastically reduces the interference signal of agents such as ascorbic and uric acids. The biosensors containing urease covalently attached to the substrate provided interesting results in terms of sensitivity towards urea (0.50 mu A cm(-2) mmol(-1) L), lifetime (20 days) and short response times, due to the enzyme immobilization method used. All biosensors analyzed showed also a wide linear concentration range (up to 100 mmol L(-1)) and low detection limits (0.22-0.58 mmol L(-1)). (C) 2009 Elsevier B.V. All rights reserved.

Copper hexacyanoferrate nanoparticles modified electrodes: A versatile tool for biosensors

Copper hexacyanoferrate nanoparticles of about 30 nm in size have been prepared by the sonochemical irradiation of a mixture of aqueous potassium ferricyanide and copper chloride solutions. The nanoparticles were immobilized onto fluorine doped tin oxide (FTO) electrodes by using the electrostatic deposition layer-by-layer technique (LbL), obtaining electroactive films with electrocatalytic properties towards H2O2 reduction, providing higher currents than those observed for electrodeposited bulk material, even in electrolytes containing NH4+, Na+ and K+. The nanoparticles assembly was used as mediator in a glucose biosensor by immobilizing glucose oxidase enzyme by both, cross-linking and LbL. techniques. Sensitivities obtained were dependent on the immobilization method ranging from 1.23 mu A mmol(-1) L cm(-2) for crosslinking to 0.47 mu A mmol(-1) L cm(-2) for LbL; these values being of the same order than those obtained with electrodes where the amount of enzyme used is much higher. Moreover, the linear concentration range where the biosensors can operate was 10 times higher for electrodes prepared with the LbL immobilization method than with the conventional crosslinking one. (C) 2008 Elsevier B.V. All rights reserved.

Studies on the resonance Raman spectra of polyaniline obtained with near-IR excitation

The effects of near-IR (NIR) laser power over the Raman spectra of poly(aniline) emeraldine salt (PANIES) and base (PANI-EB) were investigated. The reasons for the existence of several bands from 1324 to 1500 cm-1 in the Raman spectra of poly(aniline) obtained at NIR region were also studied. The bands from 1324 to 1375 cm-` were associated to vC-N of polarons with different conjugation lengths and the bands from 1450 to 1500 cm-1 in Raman spectra of PANI emeraldine and pernigraniline base forms were correlated to vC=N modes associated with quinoid units having different conjugation lengths. The increase of laser power at 1064.0 run causes the deprotonation of PANI-ES and the formation of cross-linking segments having phenazine and/or oxazine rings. For PANI-EB only a small spectral change is observed when the laser power is increased, owing to the low absorption of this form in the NIR region. Copyright (c) 2007 John Wiley & Sons, Ltd.

Spectroscopic characterization of the structural changes of polyaniline nanofibers after heating

The thermal behavior of PANI nanofibers doped with beta-naphthalenesulfonic acid (beta-NSA) was investigated and their morphological and structural changes after heating were monitored by SEM, XRD and Raman techniques, respectively. By using electron-scanning microscopy it is possible to verify that the nanofiber morphology is stable and no polymer degradation is observed in thermogravimetric (TG) data up to 200 degrees C. Nevertheless, the heating promotes the formation of cross-linking structures (phenazine and/or oxazine-like rings), that is clearly demonstrated by the presence of bands at ca. 578, 1398, and 1644 cm(-1) in resonance Raman spectra of heated PANI-NSA samples. The most important consequence of the formation of cross-linking structures in PANI-NSA samples is that these samples retain their nanofiber morphology upon HCl doping in contrast to PANI-NSA nanofibers without heating. (c) 2007 Elsevier Ltd. All rights reserved.