Parasites give clues to cancer treatments
cancer is a distinct possibility after researchers made a
surprising discovery about the immune system that details how the
body expels parasitic worms.
Scientists made the discovery, which may explain why some hosts were able to expel the worms naturally without the need for treatment. Essentially, the team discovered that the immune system controlled other physiological systems.
"The body naturally renews the lining of the gut every few days as cells rise to the surface and are discarded," said Dr Laura Cliffe in the Faculty of Life Sciences at the University of Manchester, who carried out the research.
The whipworm attaches itself to the lining and then must burrow faster than the rate of cell renewal in order to remain in the gut, similar to walking the wrong way down an escalator.
Cliffe's team found that hosts whose bodies generated a good allergic response to the worms were able to increase the rate of cell renewal in the intestine and force the parasites to the surface and out through the normal channels.
About 6 per cent of the population in Western countries develop bowel cancer at some time during their lives, making this the second commonest cause of cancer-related death. However, it is curable in 40-50 per cent of cases, usually by surgery.
The cancer develops when one of the cells in the colon develops a series of changes (mutations) in some of the genes that control how the cell divides and survives. As a result, the cell divides uncontrollably to form a clump of malignant (cancerous) cells.
Initially, these cell changes commonly produce a polyp (a clump of abnormal cells the size of a pea on the end of a stalk of normal cells) called an adenoma.
Professor Richard Grencis, who lead the research team said: "Once attached to the lining of the intestine, whipworm slows down the rate at which the host renews its cells allowing it to burrow further into the gut wall."
"We were able to counteract this by speeding up the cell 'escalator' artificially but some hosts we studied managed to do this naturally. It's ultimately our genes that determine whether we make the right immune response," he added.
No-one fully understands what causes bowel cancer but it is widely accepted to be a combination of factors. Studies of migrating populations, for example Japanese migrants who move to Hawaii, have shown that people rapidly acquire the risk of developing bowel cancer that is found in the country to which they have moved.
About 90 per cent of the risk for bowel cancer is thought to be due to dietary factors, with the other 10 per cent due to genetic (inherited) factors.
Dietary factors that increase bowel cancer risk are not yet clearly defined. Populations with a high-fibre intake tend to have a low risk of bowel cancer. However, the results of studies in which people, usually those who have already developed polyps, have been given high-fibre diets are disappointing. It now seems as though the beneficial effect of fibre is not simply due to its mechanical effect on helping the bowel to regularly pass faeces.
Although still controversial, it seems that taking aspirin regularly (300mg per day or more ie one standard tablet) reduces the risk by about 50 per cent. However, prolonged use of aspirin carries a risk of intestinal ulceration and bleeding, so whether the benefits would outweigh the risks is unclear at present.
Approximately 10 per cent of bowel cancers have a strong genetic factor. The commonest is hereditary non-polyposis colon cancer (HNPCC or Lynch syndrome). This condition is caused by mutation in any one of at least five different genes. These genes carry the instructions for manufacturing proteins that can repair damaged DNA.
