Jen‐Fu Chiu

Silver nanoparticles (nano-Ag) are potent and broad-spectrum antimicrobial agents. In this study, spherical nano-Ag (average diameter = 9.3 nm) particles were synthesized using a borohydride reduction method and the mode of their antibacterial action against E. coli was investigated by proteomic approaches (2-DE and MS identification), conducted in parallel to analyses involving solutions of Ag(+) ions. The proteomic data revealed that a short exposure of E. coli cells to antibacterial concentrations of nano-Ag resulted in an accumulation of envelope protein precursors, indicative of the dissipation of proton motive force. Consistent with these proteomic findings, nano-Ag were shown to destabilize the outer membrane, collapse the plasma membrane potential and deplete the levels of intracellular ATP. The mode of action of nano-Ag was also found to be similar to that of Ag(+) ions (e.g., Dibrov, P. et al, Antimicrob. Agents Chemother. 2002, 46, 2668-2670); however, the effective concentrations of nano-Ag and Ag(+) ions were at nanomolar and micromolar levels, respectively. Nano-Ag appear to be an efficient physicochemical system conferring antimicrobial silver activities.

Wound healing is a complex process and has been the subject of intense research for a long time. The recent emergence of nanotechnology has provided a new therapeutic modality in silver nanoparticles for use in burn wounds. Nonetheless, the beneficial effects of silver nanoparticles on wound healing remain unknown. We investigated the wound-healing properties of silver nanoparticles in an animal model and found that rapid healing and improved cosmetic appearance occur in a dose-dependent manner. Furthermore, through quantitative PCR, immunohistochemistry, and proteomic studies, we showed that silver nanoparticles exert positive effects through their antimicrobial properties, reduction in wound inflammation, and modulation of fibrogenic cytokines. These results have given insight into the actions of silver and have provided a novel therapeutic direction for wound treatment in clinical practice.

Targeted drug delivery is an important research area in specific therapy. Transferrin-conjugated nanoparticles are an attractive formulation as a vehicle for specific cellular uptake and targeted drug delivery. In this report, atomic force microscopy imaging was used to visualize the process of cellular uptake of transferrin-coupled gold nanoparticles on the surfaces of live cells for the first time. High-resolution images were captured, showing the endocytosis of transferrin-conjugated nanoparticles taking place during the process of internalization. This specific transferrin-mediated nanoparticle uptake was validated by confocal scanning imaging and transferrin competition experiments.

Reactive oxygen species (ROS) are natural products inevitably generated along cellular metabolism. Due to their highly reactive nature, which can damage DNA, proteins and lipids, cells utilize antioxidative or defense systems to balance these toxic products to keep the cells in a state of redox homeostasis. However, under the situation of imbalance in redox status, depending on the magnitude of ROS encountered, high levels of ROS can induce apoptosis, whereas chronic low levels of ROS promote vascular diseases such as arteriosclerosis. Although ROS seem to be catastrophic to life, accumulating evidence points to the beneficial roles of ROS by virtue of the ability as chemotherapeutic agents to cure human diseases. Many anti-cancer drugs have been developed in this way which can generate ROS and cause oxidative stress-induced apoptosis in cancer cells. The effects of ROS are paradoxical because they can act as both disease culprits and chemotherapeutic agents. In this review, the current knowledge of ROS and the potential applications of ROS in cancer therapeutic will be discussed.

Apoptosis is a tightly controlled multistep mechanism of cell death, and mitochondria are considered to play a central role in this process. Mitochondria initiate two distinct apoptosis pathways, one caspase-dependent and the other caspase-independent. In addition, mitochondrial production of reactive oxygen species (ROS) seems to play a role in cell death. Most chemotherapeutic agents induce apoptosis through at least one of these pathways. The post-initiation mechanisms of gold(III) porphyrin 1a were investigated in this study. HONE1 cells exposed to gold(III) porphyrin 1a underwent apoptosis after 24 hours. Functional proteomic studies revealed the alteration of several cytoplasmic protein expressions in HONE1 cells after treatment with the drug. These proteins include enzymes participating in energy production and proteins involved in cellular redox balance. There was a quick attenuation of mitochondrial membrane potential (DeltaPsi(m)) with the alterations of Bcl-2 family proteins, the release of cytochrome c, and apoptosis-inducing factor (AIF) following gold(III) porphyrin 1a treatment. Cytochrome c in turn activated caspase-9 and caspase-3. Cotreatment with caspase inhibitor (zVAD-fmk) showed that the activated caspases worked in conjunction with AIF-initiated apoptosis pathways. Further study showed that ROS played a part in gold(III) porphyrin 1a-induced apoptosis by regulating DeltaPsi(m). In summary, gold(III) porphyrin 1a induced apoptosis through both caspase-dependent and caspase-independent mitochondrial pathways, and intracellular oxidation affected gold(III) porphyrin 1a-induced apoptosis. These results support a role for gold(III) porphyrin 1a as a promising anticancer drug lead and as a possible novel therapeutic agent directed toward the mitochondria.