A concentrated extract from broccoli sprouts may cut the development of bladder cancer by more than 50 per cent, according to results of an animal study.
The study adds to an ever-growing body of science, particularly human epidemiologic studies, that report a protective effect of cruciferous vegetables for bladder cancer (for example, International Journal of Cancer, Vol. 120, pp. 2208-2213)
The new study is published in the new issue of the journal Cancer Research.
"Although this is an animal study, it provides potent evidence that eating vegetables is beneficial in bladder cancer prevention," said co-author Yuesheng Zhang from Roswell Park Cancer Institute in New York.
The tissue of cruciferous vegetables, like broccoli, cauliflower, cabbage and Brussels sprouts, contain high levels of the active plant chemicals glucosinolates. These are metabolised by the body into isothiocyanates, which are known to be powerful anti-carcinogens. The main isothiocyanate from broccoli is sulphoraphane.
"The bladder is particularly responsive to this group of natural chemicals," explained Zhang. "In our experiments, the broccoli sprout isothiocyanates after oral administration were selectively delivered to the bladder tissues through urinary excretion."
Broccoli sprouts have previously been shown to reduce blood pressure in rats with hypertension due to the presence of a compound called glucoraphanin (Grn+). Sprouts are the richest source of Grn+, containing up to 50 times more than mature broccoli.
Glucoraphanin, also known as sulforaphane glucosinolate (SGS), is the precursor of sulforaphane.
The new study used a freeze-dried aqueous extract of broccoli sprouts that contained approximately 600 times the isothiocyanates content of mature broccoli.
Despite using such a highly concentrated extract, Zhang said that people at increased risk for bladder cancer probably do not need to eat huge amounts of broccoli sprouts in order to derive protective benefits.
"Because epidemiologic studies have shown that dietary isothiocyanates and cruciferous vegetable intake are inversely associated with bladder cancer risk in humans, it is possible that isothiocyanate doses much lower than those given to the rats in the present study may be adequate for bladder cancer prevention," explained the researchers in Cancer Research.
Female Sprague-Dawley rats were assigned to one of five groups. All groups were fed a control diet for two weeks. After a further 2 weeks, three groups were given a chemical, N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) in drinking water, which induces bladder cancer. Two of these groups were given the broccoli extract in diet (low and high dose), beginning two weeks before the carcinogenic chemical was delivered.
The two control groups were fed either the control diet, while the second received only the broccoli extract to test for safety.
At the end of the study, about 96 per cent animals given only BBN developed an average of almost two tumours each of varying sizes, report the researchers. However, in the animals given BBN and the low dose extract tumours developed in only 22 per cent fewer animals, and the number of tumours per rat was 1.39.
Furthermore, animals given BBN and the high dose extract developed about 58 per cent fewer tumours, and the average number of tumours per animal was only 0.46.
In comparison, in both control groups, no tumours developed, and no toxicity from the extract was observed in the animals.
Analysis of the urine of the animals showed that 70.3 and 4.3 per cent of the isothiocyanate dose were excreted in the urine during the first and second 12-hour period, respectively, wrote the researchers. This results demonstrated that the compounds were passed via the bladder.
"These findings show for the first time that broccoli sprout extract strongly inhibits carcinogenesis in the bladder," wrote the researchers. "The results are consistent with epidemiologic studies showing that increased consumption of broccoli and other cruciferous vegetables is associated with reduced bladder cancer risk."
The exact mechanism behind these apparent benefits is unclear, they added, and future work should include studies to elucidate how isothiocyanates in cruciferous vegetables may protect against the formation of tumours in the bladder.
Bladder cancer is diagnosed in about 336,000 people every year worldwide, and it is three times more likely to affect men than women, according to the European School of Oncology.
The researchers were affiliated with Ruakura Agricultural Research Center (New Zealand), Roswell Park Cancer Institute (USA), Massey University (New Zealand), The New Zealand Institute for Crop and Food Research Limited, and the Johns Hopkins University (USA),
Source: Cancer Research
Volume 68, Issue 5, Pages 1593-1600
"Inhibition of Urinary Bladder Carcinogenesis by Broccoli Sprouts"
Authors: R. Munday, P. Mhawech-Fauceglia, C.M. Munday, J.D. Paonessa, L. Tang, J.S. Munday, C. Lister, P. Wilson, J.W. Fahey, W. Davis, Y. Zhang