Cells ingest things by engulfing them. When a long cylindrical fibre like a carbon nanotube comes near, the cell senses only its tip, mistakes it for a sphere, and begins engulfing something too long to fully ingest. This can have a detrimental affect on the cell.
Credit: Gao Lab/Brown University
SHROPSHIRE: Cells are tricked into swallowing carbon nanotubes that are too long for them to completely ingest, resulting in inflammation and possibly cell death, new research shows.
A study published in this week's Nature Nanotechnology describes how cells can mistake cylindrical nanotubes for spherical particles, leading to problems when the nanotubes cannot be fully ingested.
"Our work explains how one-dimensional nanomaterials enter the cell tip-first," said Xinghua Shi, lead author of the study, now at the Chinese Academy of Sciences in Beijing.
"We reveal that the entry starts with tip recognition, followed by tube rotation. Once the nanotube enters, the cell cannot feel the end point, causing inflammation."
Sword-swallowing cells
Carbon nanotubes are essentially rolled up, one-atom-thick sheets of carbon.
With their incredible strength, sub-microscopic size, and other fascinating properties, nanotubes have potential applications in fields such as engineering, computer technology, sport and medicine.
However, the spiky structure of these nanotubes - not dissimilar to that of hazardous asbestos fibres - has led some researchers to highlight their possible health risks.
Cells have been observed trying to swallow carbon nanotubes and asbestos fibres that are longer than the cell itself. And just like someone attempting to devour a javelin, this can cause a few problems.
Unable to fully ingest the fibre, the cell triggers an immune response that can lead to inflammation. Damage to DNA and chromosomes may also contribute to the development of lung cancer or mesothelioma, a rare form of cancer that can affect the lungs' protective lining.
Mistaken identity
It's been previously known that long asbestos fibres can wreak havoc with human cells, and scientists have seen the gory evidence, observing the fibres protruding out through the cell wall.
Exactly why a cell would ingest a potentially damaging fibre was not previously understood. But Xinghua Shi and researchers at Brown University in Rhode Island, U.S., have shown that carbon nanotubes fool cells by entering them tip-first.
This behaviour was discovered with scanning electron microscopy (SEM) imagery of nanomaterials entering cells. These materials - nanotubes, gold nanowires and asbestos fibres - entered the cells perpendicularly and
tip-first in about 90 percent of cases.
The cells ingest these one-dimensional materials - a process known as 'endocytosis' - because they mistake the tip of the fibre for a spherical particle.
By the time the cell has realised that the fibre is too long to be fully engulfed, it is too late for the process to be halted.
"It’s in trouble and calls for help, triggering an immune response that can cause repeated inflammation,” said nanoengineer Huajian Gao from Brown University, a co-author of the study
