Pectin v galectin 3

By Sumana Narayanan
Published: Wednesday 31 December 2008

A crunchy apple a day (Credit: MEETA AHLAWAT) How fibre from fruits fights tumorous cells in human body

FRUITS and vegetables are known to promote normal cell growth and reduce cancer risks. Scientists have attributed these qualities to a major constituent of cell walls called pectin, a fibre composed of complex carbohydrates, that provides crunchiness to fruits and vegetables. But the mechanism by which pectin reduces the risk was not known. A study now demonstrates this.

A team from the Institute of Food Research in Britain studied interaction between pectin and cancer cells using various techniques.

They found that galactans, a complex carbohydrate compound present in pectin fragments, bind with and inhibit a cell protein called galectin 3, or Gal3. This protein is present on the surface of tumour cells and helps cells detach from tumours and spread the caner to other parts of the body.

Although pectin is sold as a food supplement in the market, the researchers recommend eating lots of fresh fruits and vegetables because they are more likely to supply bioactive pectin. "We still do not know how various extraction processes affect the properties of pectin, but we do know that pectin acts differently in different conditions. Until we do a study on pectin uptake by humans, we can only speculate about whether natural is better than commercially sold pectin," said Patrick Gunning, researcher with the Institute of Food Research, UK, and lead author of the study.

Pectin is usually extracted from leftovers of the juice industry--dried citrus peel or apple pomace. The leftovers first go through an alkali treatment and then an acid treatment. Alkali treatment reduces the size of the pectin molecule and makes it more soluble, making it easier to use in formulations. The acid treatment releases galactans responsible for the anti-cancer activity. These treatments could affect the activity of the commercial pectin, said the paper published online on October 2, 2008 in the faseb Journal.

This was also indicated earlier in a paper published in the August 2007 issue of Glycobiology. The study showed that treating commercial pectin with mild alkaline base decreased its anti-cancer properties, while heating increased its activity. Exposing prostate cancer cells to pectin reduced the number of cells by up to 40 per cent.

British researchers also revealed that a subtle stereochemistry is required for the galactans in pectin to bind with Gal3. "Knowing the mechanism of pectin's bioactivity will allow for better design of anti-cancer pectin fragments for therapeutic use," said Gunning.

Eating bad food is linked to about 30 per cent of all cancers in western countries and up to 20 per cent in developing countries. Diet is second only to tobacco as a preventable cause of cancer. Consumption of fruits and vegetables is linked to reduced risks of cancers of the oral cavity, oesophagus, stomach and colorectum.

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