Zinc levels linked to prostate cancer spread
zinc, suggest preliminary findings by the US Agricultural Research
Service, and this may lead to the cancer's spread.
Scientists have known for decades that zinc may play an important part in the health of the prostate, a walnut-sized gland in males, that secretes a zinc-containing liquid in seminal fluid.
They already have evidence that cancerous prostate cells contain less zinc than healthy prostate cells and the new findings may explain why. However they still need to test whether an increase of zinc in cancerous prostate cells may help prevent their proliferation.
Prostate cancer is the second most common cancer in men after lung cancer. It was the most common form of cancer diagnosed among men in the European Union during 2004, representing 15 per cent of male cancers and 238,000 new cases, according to the International Agency for Research on Cancer (IARC).
This high prevalence is pushing researchers to investigate nutritional invervention that could help prevent the disease.
ARS research geneticist Liping Huang compared the amounts of zinc taken up by the prostate's epithelial cells. She used noncancerous and cancerous human cells that had the same genetic source, or genotype. (Genes can influence the take-up and use of nutrients in food, including zinc.)
Cultured cells were exposed to zinc sulphate for two days.
"The cancerous cells accumulated about one-third less zinc than did the noncancerous cells," Huang reports.
The team also looked for significant differences in levels of zinc transporter proteins. These specialized proteins ferry zinc throughout the body, such as from storage in the liver, kidney, or bone to other sites. The amount of one such zinc transporter protein-ZIP1-was reduced in the cancerous cells. As a result, those cells had low ability to take in zinc.
In addition, analyses showed that even though a second zinc transporter protein, ZIP3, was present in the cancerous cells, it was not in its correct location.
"This error may have blunted any of ZIP3's potential protective effects," explained Huang.
She added that the study "provides the first direct comparison of zinc-transporter-protein levels in noncancerous and cancerous prostate epithelial cells with the same genetic background and the first evidence of significant differences in the levels and localizations of the proteins."
"Though these results are preliminary, they suggest that reduced levels of one transporter protein and mislocation of another may play a role in cancer's progression in the prostate."
To learn more, the team developed another experiment with ZIP1, artificially stepping up its manufacture in the cancerous cells by overexpressing the genes that cue production of this protein.
"Overexpressing ZIP1 significantly suppressed growth and spread of the cancerous cells," Huang reported. "We don't yet have enough evidence to say with certainty that zinc in our foods acts as a chemopreventive. But zinc's natural abundance in the prostate of healthy men, and its performance in our tests, suggest it may be an important natural defense."
The research is described in the June 2005 issue of Agricultural Research magazine.
