Low-Resveratrol Muscadine Grape Skin Extract (MSKE) Inhibits Prostate Cancer Cell Growth

A press release came in from the US NIH before the weekend noting that NCI's Dr Jeffrey Green has identified potential anticancer activities from a grape skin extract that is not dependent on the presence of the well-known compound, resveratrol. The report is to appear in the 1 September issue of Cancer Research, but the article is not yet online.

Green's group investigated a skin extract from muscadine grapes (Vitis rotundifolia) that was apparently nearly devoid of resveratrol but contained high levels of compunds called anthocyanins (they called it MSKE for "muscadine skin extract"). The press release notes that muscadines have low levels of resveratrol but that is not true based on published data. A 1996 paper notes that muscadines have up 10-fold more resveratrol than conventional Vitis vinifera red wine grapes. In fact, another group showed in 2000 that the resveratrol in muscadines was responsible for its apoptosis-promoting effects in cancer cells. So, that's why I need to get my hands on this Cancer Research paper to investigate the chemical characterization of the extract. It's also not yet clear to me if the work of Green's group is only on human prostate cancer cells grown in culture or in tumors grown in immunocompromised mice.

I should note briefly for those hitting on this post from internet searches for "resveratrol" that resveratrol from wine is not abundant enough to have any anticancer or antiaging action. In fact, a recent Phase I dose-escalation study where patients were given up to 5 grams of resveratrol revealed that even these high doses failed to give plasma levels consistent with reported in vitro effects of the compound. Keeping in mind that the maximum reported concentration of resveratrol in any wine is about 40 mg/L, a 5 gram dose is the equivalent of 125 liters, or 167 bottles, of wine - well beyond the capabilities of even the most voracious wine enthusiast.

But back to muscadines. My interest in muscadines stems (pun intended) from their identity with the American South, although the grape grows as far north as Delaware and as far west as Missouri. They have a tough skin and a pulpy interior that squeezes out whole, as opposed to table grapes that just go "crunch." Muscadines have a terrifically fragrant and distinct aroma that permeates farmers markets, signaling that fall has arrived.

Wines are also made from muscadine grapes, although they are usually fermented to include a fair bit of residual sugar. So, they are kind of sweet and syrupy and not considered "serious" wines by the cognoscenti. In fact, I've never tasted a muscadine wine fermented dry (i.e., devoid of all residual sugar).

A well-known subtype of the muscadine grape is the Scuppernong. The North Carolina Department of Agriculture and Consumer Services recently posted this press release drawing attention to the history of the muscadine and the distinction of the Scuppernong:

Early North Carolina settlers found the "Mother Vine" of this secret treasure on Roanoke Island. It was home to the Scuppernong variety, large bronze grapes with thick skins. They were growing in loose clusters of eight to 10 grapes and averaging about 1½ inches in size, encasing rich antioxidants in their outer cover. When ripe, the Scuppernong exudes a sweet and distinctly musky taste. The grapes create a delectable flavor in wines popular throughout the South.

Confusion exists about the difference between the Scuppernong and the Muscadine. A popular saying is, "All Scuppernongs are Muscadines, but not all Muscadines are Scuppernongs." There are now numerous varieties of Muscadines for fresh eating and other products. They tend to vary in appearance, depending on the type, and range in hue from bronze to black. So, to be accurate, it is better to use the term Muscadine when the species is unknown.

The Scuppernong was the first grape cultivated in America and the history of this twisted vine dates back 400 years ago when Florentine navigator Giovanni de Verrazzano first recorded its existence in 1524. Today the Scuppernong and its kin enjoy popularity in North Carolina grocery stores, roadside stands and farmers' markets, which take pride in promoting North Carolina offerings. Several Muscadine vineyards sell their fresh grapes but also showcase their wines at festivals throughout the year.

But back to biology and medicine. Muscadines have also been investigated for their anti-inflammatory activities in animal models and companies have already sprung up selling muscadine extracts as dietary supplements (i.e., products not evaluated by the FDA for either effectiveness or safety). There is also some weak evidence (in abstract form) that suggests muscadine grape extracts may increase HDL-cholesterol ("good" cholesterol).

Obviously, the company that made the muscadine extract for the Cancer Research paper is bound to experience a bump in sales. I'll report back on that issue once the paper is formally published.