However, many challenges must be overcome if the application of nanotechnology is to realize the anticipated improved understanding of the patho-physiological basis of disease, bring more sophisticated diagnostic opportunities, and yield improved therapies. NPs have a relatively large (functional) surface which is able to bind, adsorb and carry other compounds such as drugs, probes and proteins. The reason why these nanoparticles (NPs) are attractive for medical purposes is based on their important and unique features, such as their surface to mass ratio that is much larger than that of other particles, their quantum properties and their ability to adsorb and carry other compounds. However, this does not necessarily has an impact on their functionality in medical applications. It has to be recognized that not all particles used for medical purposes comply to the recently proposed and now generally accepted definition of a size ≤100 nm ( The Royal Society and Royal Academy of Engineering 2004). Engineered nanoparticles are an important tool to realize a number of these applications.
Anticipated applications in medicine include drug delivery, both in vitro and in vivo diagnostics, nutraceuticals and production of improved biocompatible materials ( Duncan 2003 De Jong et al 20 European Technology Platform on Nanomedicine 2005 Ferrari 2005). There is increasing optimism that nanotechnology, as applied to medicine, will bring significant advances in the diagnosis and treatment of disease. Recent years have witnessed unprecedented growth of research and applications in the area of nanoscience and nanotechnology. So, probably additional more specific testing would be needed. Although for pharmaceutical use the current requirements seem to be adequate to detect most of the adverse effects of nanoparticle formulations, it can not be expected that all aspects of nanoparticle toxicology will be detected.
For such testing the lessons learned from particle toxicity as applied in inhalation toxicology may be of use. Besides the potential beneficial use also attention is drawn to the questions how we should proceed with the safety evaluation of the nanoparticle formulations for drug delivery.
This paper provides an overview on some of the currently used systems for drug delivery. It is obvious that the potential interaction with tissues and cells, and the potential toxicity, greatly depends on the actual composition of the nanoparticle formulation. A multitude of substances are currently under investigation for the preparation of nanoparticles for drug delivery, varying from biological substances like albumin, gelatine and phospholipids for liposomes, and more substances of a chemical nature like various polymers and solid metal containing nanoparticles. In addition, the nanosize also allows for access into the cell and various cellular compartments including the nucleus. From a positive viewpoint, especially the potential to cross the blood brain barrier may open new ways for drug delivery into the brain. For nanoparticles the situation is different as their size opens the potential for crossing the various biological barriers within the body. However, absorbed species may also influence the potential toxicity of the inhaled particles. This may vary from a rather high local exposure in the lungs and a low or neglectable exposure for other organ systems after inhalation. The toxicology of particulate matter differs from toxicology of substances as the composing chemical(s) may or may not be soluble in biological matrices, thus influencing greatly the potential exposure of various internal organs.
For nanoparticles the knowledge on particle toxicity as obtained in inhalation toxicity shows the way how to investigate the potential hazards of nanoparticles. The kind of hazards that are introduced by using nanoparticles for drug delivery are beyond that posed by conventional hazards imposed by chemicals in classical delivery matrices. Interestingly pharmaceutical sciences are using nanoparticles to reduce toxicity and side effects of drugs and up to recently did not realize that carrier systems themselves may impose risks to the patient. Currently many substances are under investigation for drug delivery and more specifically for cancer therapy. The use of nanotechnology in medicine and more specifically drug delivery is set to spread rapidly.