Abstract
There are certain concerns regarding the safety for the environment and human health from the use of engineered nanoparticles (ENPs) which leads to unintended exposures, as opposed to the use of ENPs for medical purposes. This review focuses on the unintended human exposure of ENPs. In particular, possible effects in the brain are discussed and an attempt to assess risks is performed.Animal experiments have shown that investigated ENPs (metallic nanoparticles, quantum dots, carbon nanotubes) can translocate to the brain from different entry points (skin, blood, respiratory pathways). After inhalation or instillation into parts of the respiratory tract a very small fraction of the inhaled or instilled ENPs reaches the blood and subsequently secondary organs, including the CNS, at a low translocation rate. Experimental in vivo and in vitro studies have shown that several types of ENPs can have various biological effects in the nervous system. Some of these effects could also imply that ENPs can cause hazards, both acutely and in the long term. The relevance of these data for risk assessment is far from clear. There are at present very few data on exposure of the general public to either acute high dose exposure or on chronic exposure to low levels of air-borne ENPs. It is furthermore unlikely that acute high dose exposures would occur. The risk from such exposures for damaging CNS effects is thus probably very low, irrespective of any biological hazard associated with ENPs.The situation is more complicated regarding chronic exposures, at low doses. The long term accumulation of ENPs can not be excluded. However, we do not have exposure data for the general public regarding ENPs. Although translocation to the brain via respiratory organs and the circulation appears to be very low, there remains a possibility that chronic exposures, and/or biopersistent ENPs, can influence processes within the brain that are triggering or aggravating pathological processes.In general, the present state of knowledge is unsatisfactory for a proper risk assessment in this area. Crucial deficits include lack of exposure data, the absence of a proper dose concept, and that studies often fail in adequate description of the investigated ENPs.
Highlights
The purpose of the present review is to give a short overview of how engineered nanoparticles (ENPs) can translocate from the respiratory tract to the circulation, pass the blood-brain-barrier (BBB), affect the brain, and to discuss possible adverse health effects and associated risks
We focus on engineered nanoparticles and their unintended exposure of the CNS
Researchers have agreed to use the term nanoparticle if the material size is smaller than 100 nm in three dimensions and are singular particles; different terms are still used in the literature, like nanosized materials, ultrafine particles (UFP), engineered nanomaterials, manmade nanoparticles [1]
Summary
The purpose of the present review is to give a short overview of how engineered nanoparticles (ENPs) can translocate from the respiratory tract to the circulation, pass the blood-brain-barrier (BBB), affect the brain, and to discuss possible adverse health effects and associated risks. Geiser and Kreyling [40] summarized the evidence for translocation of certain ENPs like gold, silver, TiO2, polystyrene and carbon nanoparticles in the size range of 5 - 100 nm across the air-blood barrier from animal studies. In drug delivery studies using polysorbate 80-coated nanoparticles, it was shown that the ENP adsorbs apolipoproteins from the blood after injection These particles mimic lipoprotein particles which could be taken up by the brain capillary endothelial cells via LDL receptors [15]. This time, brain tissues were collected at postinstillation time points of 2, 10, 20 and 30 days and evaluated for accumulation of TiO2, histopathology, oxidative stress, and inflammatory markers It is shown in this study, that instilled TiO2 nanoparticles entered the brain directly through the olfactory bulb during the whole exposure period. At the present state of knowledge, the risk assessment needs to be performed on a case by case basis
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