Pharmacological Toxicological Effects 51 In Vitro Animal Studies

Saw palmetto's benefits in treatment of BPH are hypothesized to be caused in part by antiandrogen effects (6). Saw palmetto is a multisite inhibitor of androgen action. In an in vitro study (7), a liposterolic saw palmetto extract called Permixon® was shown to compete with a radiolabeled synthetic androgen for the cytosolic androgenic receptor of rat prostate tissue. Another in vitro study found that saw palmetto lipid extract inhibits 5a-reductase, the enzyme responsible for the conversion of testosterone to its active metabolite dihydrotestosterone (DHT); inhibits 3-ketosteroid reductase, the enzyme responsible for DHT metabolism to other active androgens; and blocks androgen receptors (8). Saw palmetto may also improve BPH signs and symptoms by inhibiting estrogen receptors in the prostate (6). A study of the effects of saw palmetto on cancer cell lines (9) has demonstrated that saw palmetto can inhibit 5a-reductase activity without affecting prostate-specific antigen (PSA) expression, confirming that saw palmetto can be administered without interfering with this biomarker (PSA) of tumor progression. Finally, it has recently been demonstrated in vitro that saw palmetto extracts do not affect a1-adrenoceptor subtypes, suggesting that its primary mechanism of action is on androgen metabolism (10).

An in vivo study in rats evaluated the effects of saw palmetto and cernitin (another natural product) and finasteride on prostate growth (11). In castrated rats who were given testosterone, all three treatments significantly reduced prostate size as compared to rats (castrated + testosterone) who were not given any treatment. Though finasteride produced the greatest effect on prostate size, no statistical difference was noted among any of the three treatments.

Anti-inflammatory effects of saw palmetto also have been hypothesized to improve BPH symptoms (6). An acidic, lipophilic saw palmetto extract (Talso®) was shown in vitro to inhibit both the cyclooxygenase and 5-lipoxygenase pathways, preventing the formation of inflammatory-producing prostaglandins and leukotrienes (12). Finally, saw palmetto has been purported to stimulate immune function (13).

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