Synergistic Antimicrobial Effects of Silver/Transition-metal Combinatorial Treatments.

Due to the emergence of multi-drug resistant strains, development of novel antibiotics has become a critical issue. One promising approach is the use of transition metals, since they exhibit rapid and significant toxicity, at low concentrations, in prokaryotic cells. Nevertheless, one main drawback of transition metals is their toxicity in eukaryotic cells. Here, we show that the barriers to use them as therapeutic agents could be mitigated by combining them with silver. We demonstrate that synergism of combinatorial treatments (Silver/transition metals, including Zn, Co, Cd, Ni, and Cu) increases up to 8-fold their antimicrobial effect, when compared to their individual effects, against E. coli and B. subtilis. We find that most combinatorial treatments exhibit synergistic antimicrobial effects at low/non-toxic concentrations to human keratinocyte cells, blast and melanoma rat cell lines. Moreover, we show that silver/(Cu, Ni, and Zn) increase prokaryotic cell permeability at sub-inhibitory concentrations, demonstrating this to be a possible mechanism of the synergistic behavior. Together, these results suggest that these combinatorial treatments will play an important role in the future development of antimicrobial agents and treatments against infections. In specific, the cytotoxicity experiments show that the combinations have great potential in the treatment of topical infections.

In vitro effect of H2O 2, some transition metals and hydroxyl radical produced via fenton and fenton-like reactions, on the catalytic activity of AChE and the hydrolysis of ACh.

It is well known that the principal biomolecules involved in Alzheimer's disease (AD) are acetylcholinesterase (AChE), acetylcholine (ACh) and the amyloid beta peptide of 42 amino acid residues (Aß42). ACh plays an important role in human memory and learning, but it is susceptible to hydrolysis by AChE, while the aggregation of Aß42 forms oligomers and fibrils, which form senile plaques in the brain. The Aß42 oligomers are able to produce hydrogen peroxide (H2O2), which reacts with metals (Fe(2+), Cu(2+), Cr(3+), Zn(2+), and Cd(2+)) present at high concentrations in the brain of AD patients, generating the hydroxyl radical ((·)OH) via Fenton (FR) and Fenton-like (FLR) reactions. This mechanism generates high levels of free radicals and, hence, oxidative stress, which has been correlated with the generation and progression of AD. Therefore, we have studied in vitro how AChE catalytic activity and ACh levels are affected by the presence of metals (Fe(3+), Cu(2+), Cr(3+), Zn(2+), and Cd(2+)), H2O2 (without Aß42), and (·) OH radicals produced from FR and FLR. The results showed that the H2O2 and the metals do not modify the AChE catalytic activity, but the (·)OH radical causes a decrease in it. On the other hand, metals, H2O2 and (·)OH radicals, increase the ACh hydrolysis. This finding suggests that when H2O2, the metals and the (·)OH radicals are present, both, the AChE catalytic activity and ACh levels diminish. Furthermore, in the future it may be interesting to study whether these effects are observed when H2O2 is produced directly from Aß42.

Effect of transition metals in synaptic damage induced by amyloid beta peptide.

The amyloid beta-peptide (Abeta), which is thought to be the major cause of Alzheimer's disease (AD), is known to be capable of aggregating in different states: soluble monomers and oligomers, and insoluble aggregates. The Abeta aggregation state as well as its toxicity has been related to the interaction between the peptide and transition metals such as iron and copper. However, this relationship, as well as the effects of Abeta on the synaptic endings, is not fully understood. The aggregation states of Abeta in the presence of iron and copper, as well as their effects on synaptic viability and signaling were investigated in this work. During acute incubation treatments (5 min-4 h), Abeta/metal impaired mitochondrial function to the same extent as has been observed with the metal alone. However, in the presence of Abeta/iron (10 and 50 muM), plasma membrane integrity was disrupted to a greater extent than when generated by either iron or Abeta alone, indicating that the membrane constitutes the first target of synaptic injury. Akt activation by Abeta/iron was evident after 5 min of incubation and was higher than that observed in the presence of the metal alone. This activation was barely detected after 4 h of incubation, demonstrating that there is no correlation between the extent of synaptic damage and the activation of this kinase. Extracellular signal-regulated kinases 1 and 2 (ERK1/2) activation profile was different from that observed for Akt. Accordingly, the presence of Abeta/metal could differentially modulate the activity of these kinases. This work shows evidence of the initial events locally triggered at the synapse by Abeta and transition metals. As synapses have been proposed as the starting point of Abeta/metal-triggered events, the characterization of early mechanisms occurring in models that mimic AD could be important for the search of unexplored therapeutics tools.

Determination of reactions between free radicals and selected Chilean wines and transition metals by ESR and UV-vis technique.

Four different types of Chilean wines (Cabernet Sauvignon, Merlot, Carmenere and Syrah) were selected and examined in their free radical scavenging capacities by electron spin resonance (ESR) and spectrophotometric methods. The free radical scavenging properties were evaluated against 2,2-diphenyl-1-picrylhydrazyl (DPPH*) radical, 2,6-di-tert-butyl-alpha-(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-p-tolyloxy (Galvinoxyl) radical and hydroxyl radical (HO*). The possible effect on these scavenging properties of added transition metals to these wines was evaluated. Among the wines evaluated, Cabernet Sauvignon was the one with the highest activity against all radicals tested. The presence of added copper or iron to wines resulted in a reduced free radical scavenging capacity for all type of wines studied. The formation of redox inactive complexes between polyphenols of wine and transition metals is the possible cause of this reduction in antioxidant activity.