Broccoli Sprouts May Protect Against Bladder Cancer

By Crystal Phend
BUFFALO, N.Y., Feb. 28 -- Even before broccoli matures, the much-maligned vegetable shows promise in prevention of bladder cancer. Rats given high doses of freeze-dried broccoli sprout extract were less than half as likely to develop bladder cancer when exposed to a potent carcinogen as rats not fed the extract, reported Yuesheng Zhang, M.D., Ph.D., of the Roswell Park Cancer Institute here, and colleagues in the March 1 issue of the journal Cancer Research. Broccoli sprouts are a particularly good source of a class of phytochemicals called isothiocyanates, which have been linked to reduced risk of bladder cancer in observational studies.
The sprouts contain about 30 times more isothiocyanates than mature broccoli. The broccoli sprout extract fed to the rats contained about 600 times more.
The daily intake of total isothiocyanate in humans through consumption of cruciferous vegetables is estimated to be 0.14 to 1.43 µmol/kg. Although it's probably not possible to eat enough broccoli sprouts to replicate the doses used in the study (40 to 160 µmol/kg), Dr. Zhang acknowledged, he said it likely wouldn't be necessary.
"The carcinogen exposure we as humans have is going to be much lower than those animals had," he said. "I think if we just simply extrapolate these data to humans, the dose of broccoli sprout extract required to have a similar impact on carcinogenesis is going to be much, much lower."
Dr. Zhang's group previously showed that broccoli sprout extract induced production of enzymes in the bladder that protect against carcinogens and oxidants.
To see whether this would result in lower rates of bladder cancer, the researchers randomly assigned 24 rats to each of five groups.
The control group got regular chow and water. Another group got regular chow but received N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) in their water as a bladder-specific carcinogen representative of nitrosamines, an important class of human carcinogens.
Another two groups got the carcinogen in their water starting two weeks after initiation of the broccoli sprout extract in their diet at a dose of either 40 or 160 µmol isothiocyanate per kg body weight per day.
The final group received broccoli sprout extract without the carcinogen.
After 12 weeks of treatment, all rats were switched to regular diets and water and were sacrificed 24 weeks later.
None of the rats in the control group or the group that received only the extract developed bladder cancer.
All the rats in the group that received only the carcinogen developed dysplasia (4.2%) or carcinoma (95.8%) of the bladder with an average of 1.96 tumors each.
Broccoli sprouts reduced the likelihood of bladder cancer in a dose-dependent manner.
In the lower dose group, 73.9% of the rats developed cancer (a 22.9% reduction) with an average of 1.39 tumors each a 29.1%).
In the higher dose group, only 37.5% developed cancer (60.9% inhibition) with an average of 0.46 tumors per animal (76.5% inhibition).
Tumor size and progression were similarly lower in extract-treated rats.
Another group of rats sacrificed at various times after being given the broccoli sprout extract showed that isothiocyanate equivalents were rapidly absorbed with a peak at one hour after dosing and excreted in the urine over the next 12 hours.
The researchers said the most remarkable finding was that urinary concentrations were two to three orders of magnitude higher in the urine than in the plasma.
Likewise, levels in the bladder were 2.7 to 3.6 times higher in the bladder than in the liver in the first 12 hours after the extract was given and 19.7 times higher at 24 hours.
Isothiocyanate levels in the bladder epithelium, which is directly exposed to urine, were likely substantially higher than those measured in the bladder tissue overall, Dr. Zhang and colleagues noted, suggesting the isothiocyanate selectively reached the target tissue.
"Given that nearly all bladder cancers occur in the epithelium," the researchers concluded, "isothiocyanate-enriched broccoli sprout extract and other cruciferous vegetables rich in isothiocyanates may be particularly useful for prevention of bladder cancer."
The study was supported by Vital Vegetables Research Program of Australia and New Zealand, which is funded by Horticulture Australia and the New Zealand Foundation for Research Science and Technology; by grants from the National Cancer Institute; and the Roswell Park Alliance Foundation.
One of the authors was a founder of Brassica Protection Products, a company that sells broccoli sprouts, and reported being an unpaid consultant for and owning stock in the company. Neither the broccoli sprout extract used in the present study nor the study itself involved the company.
Primary source: Cancer ResearchSource reference:Munday R, et al "Inhibition of Urinary Bladder Carcinogenesis by Broccoli Sprouts" Cancer Res 2008; 68: 1593-1600.