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Selective transport

Silica nanoparticles carry antibiotics and eliminate bacteria without harming healthy cells

068-069_Nanopart LNLS_232One of the evolutionary trajectories of pharmaceutical drugs is to attempt to reach and eliminate a microorganism or tumor without harming the patient’s healthy cells or causing side effects. Among the biotechnological tools most often used in experiments with this objective are nanoparticles produced using various types of materials. At the National Synchrotron Light Laboratory (LNLS), an institution located in Campinas (São Paulo State) and maintained by the Ministry of Science, Technology and Innovation, silica was the material of choice for these nanostructures with diameters measuring 10 to 500 nanometers (one nanometer is one millionth of a millimeter). A new type of nanoparticle could transport antibiotics throughout the human body in order to fight bacteria. It transports the drug and contains a labyrinth of internal channels in which the drug is stored for release within or near the microorganisms. The LNLS study also led to the development of two other types of nanoparticles: one made out of silver with bactericidal properties, and another containing a silver core covered in silica, which transports the drug on its surface.

The principal author of the project, researcher Mateus Borba Cardoso, says that the principal advantage of the nanoparticle is its ability to carry a large quantity of the antibiotic. “Ours can be active against the microorganisms, but harmless to mammal cells,” says Cardoso. The experiments were carried out using standard human cell cultures used in biotechnology. The silver nanostructures also had no adverse side effects on the cells.

Cardoso’s research began in 2010 when he developed a strategy to imprison carbohydrates inside porous silica nanoparticles. The research led to a scientific article published in 2011 in the Journal of Pharmaceutical Sciences. He says he realized in this first work that he could control the size of the nanostructures quite precisely. The team worked with several different carbohydrates, which led researchers to wonder whether they could put biologically active molecules inside the porous nanoparticles.

Cardoso then tested the method with a protein called lysozyme, together with the group led by biologist Jörg Kobarg, formerly a researcher at the Brazilian Biosciences National Laboratory (LNBio), which operates next to LNLS. Today Kobarg is a professor in the Department of Biochemistry and Tissue Biology at the Institute of Biology at the University of Campinas (Unicamp). Lysozyme is present in human tears and is able to digest part of the wall of most bacteria and destroy them. “Surprisingly, we found that our structure had greater bactericidal power than that of pure lysozyme,” says Cardoso. “At that point we understood that surface properties and size were critical to whether or not a nanoparticle has a biological effect.” The work illustrated the cover of one of the issues of the periodical Journal of Materials Chemistry in 2012.

Thus, it was clear to the group that the joint use of the nanoparticle with the drug or active ingredient produces more pronounced biological effects than either produces individually. “After understanding how the size and surface of nanoparticles correlated with bactericidal properties, we began to work with more complex biological systems, such as the interaction of these nanostructures with tumor cells and different types of viruses,” he explains. “Thus, we begin to synthesize types of nanostructures that carry the drug within their channels or on their surfaces.”

This is what happens with silica. Upon interacting with the bacteria, two possible effects may occur: the nanoparticle enters the microorganism and releases the antibiotic, or it sticks to the outside of the microorganism and releases the drug near where it will act. This enhances its bactericidal power, because the action of the drug is added to that of the vehicle itself. “We tested this technology on two bacteria: one resistant only to tetracycline and the other resistant to tetracycline and ampicillin,” says Cardoso. “Our methodology was proven to be effective against those resistant to both drugs.” This article was published in the June 2014 issue of the journal Langmuir.

Molecular dynamics
More recently, the group started to develop a slightly more complex class of nanoparticles called “core-shell.” “The great advantage of this structure is that we link it to molecules of the antibiotic ampicillin chemically, which gives the combination great bactericidal power,” says Cardoso. “Furthermore, the antibiotic is not placed randomly on the surface, but rather in a predetermined orientation. Theoretical studies based on molecular dynamics conducted by chemist Hubert Stassen [professor at the Federal University of Rio Grande do Sul] suggested the configuration that gave us the greatest biological effect.” The team believes that this is the most promising strategy because it has three means of attack against the pathogen: the silver core, the silica shell, and the drug.

In the opinion of chemical engineer Antônio Hortencio Munhoz Júnior, coordinator of the Materials Engineering program at Mackenzie Presbyterian University, in São Paulo, the most advanced research in the area of drug delivery is to use organic polymers to transport the antibiotic and slowly release it inside the human body. “These polymers are commonly used both in the medical literature and in the pharmaceutical industry,” says Antonio. “However, I know of no cases in which silica nanoparticles are used to transport antibiotics.”

According to Cardoso, various nanostructures are already approved for use in treating different types of cancer in other countries. “But as far as I know this type of structure is not being used with antibiotics,” he says. “A group in the United States demonstrated the bactericidal properties of another class of nanoparticles against resistant bacteria. However, the technique and the materials needed to produce the nanoparticles are very expensive, which could make the use of these particles in an industrial application very difficult,” he concludes. “They use gold nanoparticles, whereas ours are made of silica, an inexpensive material that can easily be used on an industrial scale.

Functionalization of composite nanoparticles for biomedical applications (No. 2011/21954-7); Grant mechanism: Regular research project; Principal investigator: Mateus Borba Cardoso (LNLS); Investment: R$312,799.24 (FAPESP).
Functionalization of silica nanoparticles: increasing biological interaction (No. 2014/22322-2); Grant mechanism: Regular research project; Principal investigator: Mateus Borba Cardoso (LNLS); Investment: R$376,226.76 (FAPESP).

Scientific articles
CAPELETTI, L. B. et al. Tailored silica-antibiotic nanoparticles: Overcoming bacterial resistance with low cytotoxicity. Langmuir. V. 30, No. 25, p. 7456–64. 2014.
OLIVEIRA, L. F. et al. Mechanism of interaction between colloids and bacteria as evidenced by tailored silica lysozyme composites. Journal of Materials Chemistry. 22, p. 22851-58. 2012.
LEIROSE, G. D. S. and Cardoso, M. B. Silica-maltose composites: Obtaining drug carrier systems through tailored ultrastructural nanoparticles. Journal of Pharmaceutical Sciences. V. 100, p. 2826-34. 2011.