The researchers, led by Navinda Seeram from UCLA's Center for Human Nutrition, characterised the phenolic content of six berries and tested their ability to inhibit the growth of human oral, prostate, breast and colon cell lines.
While more research is needed to clarify the possible anti-cancer effects of the berries, the research does add to a growing body of evidence of the potential health benefits of berries that has filtered through to the consumers and has seen demand increase.
Indeed, sales of blueberries, for example, are reported to have rocketed by 130 per cent, raspberry sales are said to have grown by 62 per cent in the last two years, a strawberry sales in the UK are reported to have increased by 34 per cent during the last two years.
"Our studies provide preliminary data as to the ability of these compounds to inhibit the growth and induce apoptosis of different human cancer cells lines in vitro," wrote Seeram in the Journal of Agricultural and Food Chemistry.
The scientists used high performance liquid chromatography with ultraviolet (HPLC-UV) and electrospray ionisation mass spectrometry (LC-ESI-MS) to evaluate the phenolic content of red and black raspberries, cranberries, blackberries, blueberries, and strawberries.
They report that the main phenolic constituents were found to be anthocyanins, flavonols, flavanols, ellagitannins, galltannins, proanthocyanidins, and phenolic acids. Each berry had a different and unique phenolic content.
Seeram and colleagues then tested the extracts for anti-cancer potential for a range of human cancer cell lines. Concentrations of berry extracts from 25 to 200 microlitres per millilitre were tested for their ability to stop the spread and induction of programmed cell death (apoptosis) of human oral (KB, CAL-27), prostate (LNCaP), breast (MCF-7) and colon (HT-29, HCT116) cell lines.
"It is noteworthy that the test concentrations of the berry extracts used in these cell culture experiments far exceed levels of phenolics and/or their metabolites achievable physiologically, based on current knowledge of polyphenol bioavailability," said the researchers.
The Journal of Agricultural and Food Chemistry article reports that cancer cell proliferation was reduced in a dose-dependent manner. Using IC50 values, a measure of the extract concentration under which 50 per cent of the cell population growth was inhibited, the researchers report that extracts from black raspberries, blackberries and strawberries were the most effective against the cancer cell lines studied.
Measures of apoptosis also showed that black raspberries extracts were the most effective at inducing programmed cell death (300 per cent, compared to control), while strawberry extracts induced about 275 per cent higher apoptosis than found in the controls.
"Induction of apoptosis or cell cycle arrest can be an excellent approach to inhibit the promotion and progression of carcinogenesis and to remove genetically damaged, preinitiated, or neoplastic cells from the body," explained Seeram.
While many different forms of phenolics are present in the berry extracts, the research suggest that the anthocyanins may be the major contributors toward programmed cell death, but significant further study is required.
"Because extrapolations cannot be made between cell culture studies to humans, future animal and human studies should be designed to investigate the potential of berries for the prevention… of chronic human diseases such as cancer," they concluded.
Source: Journal of Agricultural and Food Chemistry Published on-line ahead of print (18 November 2006) doi: 10.1021/jf061750g S0021-8561(06)01750-X "Blackberry, Black Raspberry, Blueberry, Cranberry, Red Raspberry, and Strawberry Extracts Inhibit Growth and Stimulate Apoptosis of Human Cancer Cells In Vitro" Authors: N. Seeram, L. Adams, Y. Zhang, R. Lee, D. Sand, H. Scheuller, D. Heber.