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DCA Discussion Forum
michele lee
Member since May-26-09
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Aug-04-09, 09:32 AM (PST) |
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"Grapefruit For Cancer and to Reverse Drug Resistance"
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The grapefruit continues to surge and decline in popularity with fad diets and as a breakfast dish since its arrival to the United States from Jamaica in the 1820s. Grapefruit is an offspring of a fruit called the pummelo, a rather unpopular fruit of Jamaica because of its bitter taste. The pummelo was imported from Indonesian into Jamaica in the 1700s, where it was accidently crossbred with an orange and gave birth to the grapefruit we have today.
The grapefruit rose in popularity in the United States until the 1940 and 50s when it actually commanded the manufacture of its own knife and spoon for eating grapefruit halves for breakfast. The knife loosened sections of fruit and the small pointy spoon was just right for plucking the fruit from the rind bite by bite. Then things began to quiet down for the grapefruit until the grapefruit diet was advertised in the 1970s as a way to drop 10 pounds in a matter of days. The theory was based on grapefruit’s abundance of enzymes which were supposed to burn away calories and fat.
The grapefruit diet did not produce enough accounts of miraculous weight loss to keep the diet alive, eventhough a recent study indicated it may actually work by lowering insulin levels. It does, however, provide an abundance of nutrients. The red and pink varieties are high in beta carotene and all varieties are good sources of B vitamins, vitamin C, minerals and enzymes. And every part of the grapefruit has been used for medicinal purposes from the blossoms, which are used to treat insomnia, to its seeds, which are antioxidant and antifungal.
Grapefruits are rich in flavonoids, such as naringen, which has been found to lower cholesterol and triglycerides 1, and provide antioxidant protection. Grapefruits also contain the flavanone, naringenin, which is an antioxidant, an antiestrogen, an inhibitor of osteoclastic bone resorption (osteoporosis) and an anti-inflammatory. Naringenin inhibits the ability of cancer cells to build their own network of blood vessels, a process called angiogenisis, by stopping growth factors VEGF and B1 that promote the process. Naringenin also inhibits cAMP-phosphodiesterase, an enzyme implicated in the metastasis of many cancers 2, 3. Phosphodiestrase (PDE) inhibitors are also known to thwart the production of tumor necrosis factor (TNF), a pro-inflammatory cytokine implicated in cancer. One study concluded that PDE bore responsibility for “numerous signaling processes that were heretofore thought to be mediated by tyrosine kinases 4 ,” which are growth and angiogenisis promoters in cancer.
Grapefruit affects the availability of certain drugs to the body by blocking certain cytochrome P450 enzymes (CYP3A4 and CYP2D6) that metabolize them. This prevents the breakdown of a number of drugs and keeps them in the body longer. Drugs that are particularly amplified by the addition of grapefruit, include nifedipine, felodipine and cyclosporine. This amplification effect had been attributed to naringenin for some time, but is now thought to be the work of furanocoumarins abundant in grapefruit 5. Researchers found that the furanocoumarins in grapefruit not only prevented the breakdown of certain drugs, but also accelerated the rate at which they entered the bloodstream.
This effect has resulted in warning labels to avoid grapefruit with certain drugs, but it can also be used to enhance the effect of drugs with poor absorption and to lower the dose of drugs with side effects or toxicities. For example, the efficacy of the cancer drug, rapamycin, has been found to be enhanced by grapefruit, which has been very beneficial in solving the drug’s problem of poor absorption. The down side to grapefruit’s ability to inhibit CYP enzymes may be that because these enzymes help metabolize estrogens, grapefruit may elevate estrogen levels and the risk of estrogen-sensitive cancers 6, 7. Further research is needed to clarify grapefruit’s effects on estrogen levels, especially in light of studies that find antiestrogenic activity in coumarins 8.
Grapefruit’s furanocoumarins are also responsible for inhibiting p-glycoprotein(Pgp) 9. This is significant for cancer patients receiving chemotherapy, because Pgp causes cancer cells to become resistant to chemotherapy. Inhibiting Pgp can make cancer drugs that had become ineffective work again. One study found several furanocoumarins more potent than curcumin 10. (a known cancer inhibitor) at supressing cancer. A study found bergapten, one of grapefruit’s fruanocoumarins also called a psoralen, enhances the tumor supressor gene, p53, and induces programmed cell death called apoptosis in human breast cancer cells11.
Grapefruit is a powerhouse of health promoting and cancer-fighting phytochemicals that shouldn’t disappear from our diet with a passing fad. The powers of grapefruit can protect us from free radical damage and to treat numerous conditions from high cholesterol to urinary tract infections to cancer. Grapefruit can modulate the bioavailability and concentraton of drugs in our bodies and prevent drug resistance in chemotherapy. In light of the possibility that it raises estrogen levels, grapefruit products should not be consumed on a regular basis for those at risk of estrogen-dependent cancers, but grapefruits are rich in phytochemicals that we can exploit to treat illnesses and improve our health.1.Journal of Agricultural and Food Chemistry published on-line, doi:10.1021/jf058171g
2.Prune cAMP phosphodiesterase binds nm23-H1 and promotes cancer metastasis Cancer Cell. 2004 Feb;5(2):137-49
3.Clinical and Experimental Metastasis, Volume 17, Number 6, August 1999 , pp. 525-530(6)
4.Molecular PharmacologyVol. 57, Issue 4, 738-745, April 2000
5.American Journal of Clinical Nutrition, Vol. 83, No. 5, 1097-1105, May 2006
6.British Journal of Cancer (2007) 97, 440–445. doi:10.1038/sj.bjc.6603880
7.Maturitas. 1994 Dec;20(2-3):155-63
8.J Biol Chem. 2004 Nov 12;279(46):48071-8. Epub 2004 Sep 8
9.Br J Pharmacol. 2000 July; 130(6): 1369–1377
10.Pharmaceutical biology 2006, vol. 44, no2, pp. 116-120
11.Curr Cancer Drug Targets. 2009 Jun;9(4):469-81
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