Nature: Nanoparticles can cause neurological damage

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GMW: Nanoparticles can cause neurological damage - Nature

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Tue, 20 Jun 2006 11:25:19 +0100

 

 

 

 

 

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Nanoparticles are also going into food supplements and there's also

work on nano-biotech.

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Nanoparticles in sun creams can stress brain cells

Philip Ball

Published in Nature

Published online: 16 June 2006; | doi:10.1038/news060612-14

http://info.nature.com/cgi-bin24/DM/y/eYjT0BfGwN0C304AC0ES

 

Tiny grains send cells into potentially dangerous overdrive.

 

Tiny particles used in some sun creams have the potential to cause

neurological damage, researchers in the United States have found

 

The research does not necessarily imply that these microscopic grains,

which are also used in consumer products such as some toothpastes and

cosmetics, are harmful in the human body. But it adds to a growing body

of evidence that suggests that their safety cannot be taken for granted

simply because larger particles of the same substance have no ill

effects.

 

Bellina Veronesi of the US Environmental Protection Agency's research

laboratories in North Carolina and her co-workers have studied the

effect of nanoparticles of titania (titanium oxide) on cultures of mice

cells called microglia, which protect neurons in the brain from harm.

 

They find that the particles provoke the cells to manufacture chemicals

that are protective in the short term but potentially damaging when

released in the prolonged manner seen in the experiments.

 

Gunter Oberdsrster, a specialist in nanoparticle toxicity at the

University of Rochester in New York, stresses that it is too early to say

whether the findings reveal a real health hazard. " These are valuable

results, " he says, " but you have to be very careful about extrapolating

them to live organisms. "

 

Into the brain

 

Nanoparticles are fragments of a material just a few nanometres

(millionths of a millimetre) in size. Titania is the white pigment

used in

paints, and is generally considered non-toxic. It has long been used as a

fine powder in many sun creams because of its ability to absorb

ultraviolet light.

 

Some of these creams use titania nanoparticles, which are so small that

they appear transparent rather than white. This means that applying the

creams on skin does not leave it looking pallid.

 

The chemicals industry has tended to assume that if large grains are

safe, smaller ones will be too. But that assumption is coming under

increasing scrutiny, and is not necessarily always valid. " In most cases

nanoparticles are unlikely to be dangerous, " says Oberdsrster, " but we

need to look at it on a case-by-case basis. "

 

Scientists working with nanoparticles have known for a long time that

size matters: at these very small scales, the properties of materials

can change. For one thing, the chemical reactivity of powders depends on

their surface area, which increases as the particles get smaller.

 

But the behaviour of small particles can also be altered by more exotic

influences. Quantum-mechanical effects make the colour of

light-emitting nanoparticles change with their size, for example.

 

Nanoparticles may also travel around natural environments, including

the human body, in different ways to bigger particles. In particular,

they can enter the brain from the bloodstream, whereas big particles

cannot. " The blood-brain barrier is normally very tight, " says

Oberdsrster,

but nanoparticles can slip through. Many researchers now think that the

safety of such particles should be examined as if they were completely

new chemicals.

 

That caution seems to be warranted for titania nanoparticles. Previous

studies have suggested that they might be toxic to various types of

cell, such as skin, bone and liver cells. Veronesi says that nothing

previously was known about their effects on brain cells, however.

 

Burst or bust?

 

The researchers used commercially available titania nanopartices about

30 nanometres across, which they added to cultures of mouse microglia.

These cells protect neurons in the brain by engulfing foreign particles

and releasing a burst of chemicals known as reactive oxygen species

(ROS) to 'burn up' the invading substances.

 

This is a risky strategy, because ROS are also potentially damaging to

neighbouring cells. It's a bit like releasing poison gas in a room

containing invaders and hoping that it won't seep out into the rest of

the

building.

 

Veronesi and colleagues found that titania nanoparticles are swallowed

by microglia and that they trigger the release of ROS not as a burst

but in a prolonged manner, over an hour or more. That could subject the

brain to so-called oxidative stress, which is thought to be the

underlying cause of some neurodegenerative diseases such as

Parkinson's and

Alzheimer's.

 

It's too early to know how worrying the findings are. No one knows

whether nanoparticles applied on the skin, inhaled or ingested can find

their way to the brain, or at what concentrations. Effects seen for

cultured mice cells might not be duplicated in living mice, let alone

in the

human body. And there is no firm evidence that this oxidative stress

could damage neurons, although Veronesi says they have preliminary

results showing that titania nanoparticles can trigger cell death in

neurons.

 

References

 

Long T. C., et al, Envir. Sci. Technol, doi:10.1021/es060589n (2006).

 

Visit our newsblog to read and post comments about this story.

http://blogs.nature.com/news/blog/2006/06/nanoparticles_in_sun_creams_st.html

 

 

 

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