Broccoli may prevent or stop the growth of breast cancer by modifying the expression of certain human genes, according to a new study published in the latest issue of the journal Cell Research.
The vegetable, which is part of the cruciferous, or cabbage, family, has long been known for its health effects, including potential anti-cancer effects targeting the mouth, throat, neck and head.
The latest study suggested that it works by transferring genetic agents called micro RNA (miRNA) into the body. These are short, single strands of nucleic acid involved in genetic coding, decoding and expression, according to the paper.
The research team confirmed for the first time that miR159, which is commonly found in plants but has a particularly high presence in broccoli, can inhibit the growth of tumour cells in the human breast, it said.
The team was led by Dr Emily Wang at the City of Hope Beckman Research Institute And Medical Centre in California.
The study demonstrated for the first time that a plant’s micro RNA (miRNA) can inhibit cancer growth in mammals. A dose of miR159 (pictured) can significantly suppress the growth of breast tumours in mice, it found. Credit: Cell Research
Further experiments with mice showed that feeding them this form of miRNA could reduce the onset and progression of breast cancer.
“Oral delivery of tumour-suppressive plant micro RNA may provide a new non-invasive strategy for cancer prevention and treatment in humans,” Wang said.
But because the animals were not directly fed with broccoli, “it remains to be seen whether therapeutic levels of plant micro RNAs can be reached through consumption of specific foods,” she said.
“If this is the case, then dietary changes may improve currently existing cancer therapies,” she added.
Dr Jiang Peng, a biological researcher with the School of Life Science at Tsinghua University in Beijing, said it would be “really exciting” if the study’s findings were confirmed.
“It means plants can meddle in our genes, and that has long been regarded as impossible,” he said.
RNA is less stable than DNA due to its single-strand structure, but miRNA can be almost impossible to destroy and can be passed from plants to humans to influence gene expression. Credit: SCMP Pictures
Previous studies in the United States have also shown that certain vegetables may have anti-cancer properties.
In December 2012, researchers at the Baylor College of Medicine in Texas found a concentrated form of sulforaphane in broccoli. This compound has been shown in laboratory tests to reduce the number of acute lymphoblastic leukaemia cells – a cancer of the white blood cells common in children.
“There is about an 80 per cent cure rate, but some children don’t respond to treatment,” Dr Daniel Lacorazza, assistant professor of pathology and immunology at the college, said at the time.
“For those cases, we are in need of alternative treatments.”
Nonetheless, the majority of biologists remain skeptical about whether a plant’s RNA can actually enter the human body. Typically, it perishes quickly after exiting a living organism because of its unstable, single-stranded structure.
In order to enter the human body as food, the genetic agent has to go through a number of destructive processes, namely, being cooked, masticated and then digested. If it manages to survive all of these, it still has to contend with the human immune system, which is nothing if not hostile to “alien” genes.
Emily Wang, Ph.D., associate professor in the department of cancer biology at the City of Hope Beckman Research Institute And Medical Centre in California, led the research team. Photo: Handout.
But a few years ago, a team led by Professor Zhang Chenyu at China’s Nanjing University in eastern Jiangsu province discovered for the first time that miRNA can be passed from plants to humans directly.
The team claimed to have found traces of the plant’s physically intact miRNA in the human body, despite the plant having been boiled, fried or steamed before it was consumed and digested.
A follow-up study by Zhang’s team reportedly went on to show how miRNA from the arching shrub honeysuckle could enter the human lungs to bind and kill the flu virus, or common cold.
But attempts by researchers at Harvard and Stanford universities to replicate Zhang’s success failed. Some have argued that if the Chinese scientists’ claims were indeed true, the phenomenon may be limited to Asians.
But the latest study by Wang’s team seems to support Zhang’s results.
Wang detected miR159, which is only produced by plants, in the blood of human donors from Western countries like the US and breast cancer patients.
Farmers harvest broccoli at a vegetable base in Hefei, capital of East China’s Anhui province, last Thursday. A protracted cold spell has taken a heavy toll on the supply of fresh produce in the country. Photo: Xinhua
Her team also found that the higher the level of miR159 found the blood, the less likely a person was to get breast cancer. For patients already afflicted with one or more tumours, higher doses in the blood were found to retard the development of such tumours.
The main problem with previous studies is that they restricted their compass to traditional compounds like sulforaphane because of their stable chemical structure.
Xue Yuanchao, a researcher with the Chinese Academy of Sciences’ Institute of Biophysics in Beijing, said Wang’s results were encouraging for cancer patients, but that much work remained to be done in studying the exact role and function of miRNA.
“This is one of the most controversial topics in biology today, namely, miRNA. They seem to be indestructible, but nobody can fully explain why,” said Xue.
Plants are not believed to be able to pass their genetic information on to animals, which is why some scientists have a hard time believing they can influence humans.
Moreover, this is used a key argument by purveyors of genetically modified food when selling their products as safe for human consumption.
But if future studies confirm miRNA can be passed from plant to person, the safety evaluation codes of GM foods may need to be rewritten, Xue said.