Milk Thistle
Silymarin officinalis, or milk thistle, is an herb
that contains a polyphenoloic flavonoid antioxidant, silymarin. Silymarin is
composed of silybin, dehydrosilybin, silydianin, silycristin. Of these, silybin
has been most well studied. European herbalists have used milk thistle for
hundreds of years for the treatment of liver diseases, specifically alcoholic
liver disease.
Efficacy
Data on milk thistle in
chemoprevention is almost entirely preclinical. These data describe
apoptogenic, antiproliferative and anti-angiogenesis effects of milk thistle
extracts in a variety of cancers. However, the estrogenic characteristics of
milk thistle flavonoids may preclude its use in breast carcinomas.
Preclinical in vitro studies have
shown that Silybinin inhibits growth of tumor cells in human prostate, breast
and cervical carcinoma cells. In vivo models have confirmed this effect. Using
the SENCAR mouse skin tumorigenesis model, silymarin has been shown to be a
highly effective inhibitor of stage I tumor promotion.
Silybin has also been studied for
its protective activity against cisplatin toxicity in an animal model of
testicular cancer. When silybin was infused into rats prior to infusion with
cisplatin, there
was a significant reduction in glomerular and tubular kidney toxicity.
Dose-response curves of human testicular cell lines for cisplatin combined with
silybin did not deviate significantly from those of cisplatin alone.
Of particular interest is the
indication of a synergistic effect of milk thistle extracts with various
chemotherapy agents. For example, silybin has been shown to potentiate the
cytotoxic effect of cisplatin. Orally delivered silibinin suppresses human
non-small cell lung carcinoma A549 xenograft growth and enhances the
therapeutic response of doxorubicin in athymic BALB/c nu/nu mice while
simultaneously preventing doxorubicin-caused adverse health effects.
Safety
Milk thistle is considered safe
in concentrations used by over the counter supplements, unless the patient is
allergic to the plant or related plants (such as ragweed, chrysanthemum,
marigold, and daisy). In large, carefully designed studies in patients with
liver disorders silymarin have shown in a few cases a laxative effect, nausea,
heartburn, or stomach upset. At high doses (more than 1,500 milligrams a day),
some mild allergic reactions have been observed.
Recommendations
Milk thistle is often prescribed
by to protect from the hepatoxic effects of chemotherapy drugs. While not a
cytochrome P450 inducer or inhibitor its concurrent use with chemotherapy is
still experimental. Current data suggest that it be used in secondary
prevention of liver cancer, both primary and metastatic, and in lowering iron
in patients with iron overload.
http://depts.washington.edu/integonc/clinicians/act/milk_thistle.shtml
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