Human Toxicology and Effects of Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 359

not observed for the 260 nm particles. At higher concentrations (125 g/ml) cyto-

toxicity was also observed with the smaller, but not the larger, particles, and this
cytotoxicity could be prevented by antioxidants, suggesting that it is mediated via
oxidative stress. In animal studies, instillation into the lung of rats of nanoparticle
carbon black also led to a depletion of glutathione in the lung tissue (Li et al. , 1999 ).
These studies therefore provide evidence that carbon black nanoparticles, but not
larger particles induce oxidative stress in lung cells.
Nanoparticle (25 nm) TiO 2 has also been shown to induce ROS production by
BV2 microglia cells (Long et al. , 2007). This ROS production was associated with
up-regulation of an infl ammatory response, apoptosis and cell cycling pathways,
while energy metabolism was down-regulated. The same study indicated that
nanoparticle TiO 2 did not induce toxicity to N27 neuronal cells, indicating a cell
selective effect. More recently, Sayes et al. (2005) have also demonstrated that C 60
nanoparticles elicit oxidative stress mediated toxicity in cells in vitro , suggesting
that oxidative stress is not limited to carbon black.
Many of the respiratory and cardiovascular diseases associated with ambient
ultrafi ne particles and PM 10 are driven by infl ammation. Infl ammation is an activa-
tion of the immune system, including activation of the white blood cells known as
macrophages. Infl ammation is essential to fi ght infection, but when it is inappropri-
ate in amplitude or duration then it can lead to disease. Acute effects might include
exacerbation of disease symptoms, such as asthma, while chronic and more severe
effects might include fi brosis (scar tissue formation) and cancer. Oxidative stress
activates infl ammation via a number of intracellular signalling pathways. These
pathways transmit a signal to transcription factor proteins that enter the nucleus
of the cell and control the expression of genes involved in infl ammation. Such
transcription factors include nuclear factor kappa B (NF

µ

B) and activator protein
1 (AP1), both of which are sensitive to oxidative stress. Prior to activation NF

κ

B
is located in the cytoplasm of the cell where it is bound to an inhibitor subunit
called I

κ

B kinase which phosphorylates IkB,
resulting in dissociation and degradation, allowing active NF

κ B. I κ B is activated by the enzyme I κ

κ B to translocate to

the nucleus. Once in the nucleus, NF B binds specifi c promoter motifs and initiates

transcription of the genes driving infl ammation (e.g. tumour necrosis factor

κ

α ) and interleukin 8) (Christman et al. , 2000 ). Using immunofl uorescence

and confocal microscopy, Brown et al. (2004) demonstrated that 14 nm carbon black
induced nuclear translocation of NF

(TNF α

B in primary human macrophages in vitro .
This effect could be blocked by antioxidants, suggesting that the oxidative stress
induced by the particles was responsible for activating this transcription factor. In
addition, the same study also assessed the effect of 14 nm carbon black on AP1
DNA binding; this marker of activation was also enhanced by the particles and
prevented by the antioxidant. Treatment of the macrophages with 260 nm carbon
black had no signifi cant impact on either NF

κ

κ B or AP1 activation in this study,

indicating that the effect was size specifi c.
Oxidative stress also infl uences intracellular calcium signalling (Orrenius et al. ,
1992 ; Brown et al. , 2007a). Intracellular calcium signalling is very important in the
regulation of many essential cellular functions, including enzymes that control
transcription factor activation (Berridge, 2004). ROS are thought to affect calcium