Saw palmetto: Background. Actions

2010

Common Name

Serenoa or saw palmetto

Other Names

American dwarf palm tree, cabbage palm, dwarf palmetto, fan palm, sabal fructus, sabal, serenoa

Botanical Name / Family

Sabal serrulata, Serenoa repens (family Arecaceae or Palmaceae)

Plant Part Used

Dried ripe fruit

Chemical Components

An ethanol extract of the berry contains free fatty acids rich in shorter chain-length fatty acids, such as capric, caprylic, lauric and myristic acid. Palmitic, stearic, oleic, linoleic and linolenic acid are also present in the extract. There are also lesser amounts of phytosterols (such as beta-sitosterol, stigmasterol, ampesterol, and cycloartenol), aliphatic alcohols and polyprenic compounds. The lipophilic extract is used medicinally.

Historical Note

Saw palmetto was used traditionally as a treatment for urogenital irritations, impotence and male infertility, among other conditions, and was described by the American Eclectic physicians as the ‘old man’s friend’. Between 1906 and 1917 saw palmetto was listed in the US Pharmacopoeia and between 1926 and 1950 it was in the National Formulary as a treatment for urogenital ailments; however, it fell out of favour for several decades as pharmaceutical medicines came to the forefront of mainstream medicine. Not so in Europe where, in the 1960s, French researchers began to chemically analyse the saw palmetto berry, and a breakthrough lipophilic preparation was eventually developed and subjected to countless clinical trials.

Saw palmetto:  Main Actions

The mechanism of action is not fully elucidated; however, it appears that several mechanisms are at work.

INHIBITION OF 5-ALPHA REDUCTASE

In different cell systems, the lipid-sterolic extract acts as a non-competitive inhibitor of both type 1 and type 2 5-alpha reductase activity, thereby preventing the conversion of testosterone to dihydrotestosterone. However, it is currently unclear whether the effect is apparent in humans, as contradictory evidence exists. Raynaud et al (2002) explained that the discrepancies found by different authors were due to different experimental conditions and selectivity for fatty acids, as only specific aliphatic unsaturated fatty acids have been shown to inhibit 5-alpha reductase activity.

One study that analysed and compared BPH samples taken from both untreated and treated subjects (320 mg saw palmetto extract taken for 3 months) found that local levels of testosterone were raised, whereas dihydrotestosterone levels were reduced, suggestive of local 5-alpha reductase inhibition. An earlier, short-term study found that a dose of 160 mg of a liposterolic extract (Permixon) produced no changes to serum dihydrotestosterone levels, whereas finasteride 5 mg induced a significant reduction. Since prostate levels were untested in this study, it is not known whether a local effect occurred, even though serum levels remained unchanged.

Unlike other 5-alpha reductase inhibitors, there is no interference with the cell’s capacity to secrete prostate-specific antigens because it does not affect the transcription of the gene for prostate-specific antigen (PSA), as demonstrated both in vitro and in vivo. Although having an obvious clinical advantage in regard to PSA screening for prostate cancer, this also suggests that 5-alpha reductase inhibition is not a major activity.

INHIBITS BINDING OF DIHYDROTESTOSTERONE AND TESTOSTERONE TO ANDROGEN RECEPTORS

Saw palmetto reduces receptor binding of dihydrotestosterone and testosterone by an average of 41%, as tested in 11 different tissue specimens from BPH patients. In 2003, results from two animal studies showed that saw palmetto (whole berry and extract) influenced prostatic hyperplasia via effects on androgen metabolism.

INHIBITS PROLACTIN

In vivo research has identified not only an inhibitory effect on androgens, but also on the trophic effect of prolactin in the rat prostate. The inhibitory effect on prolactin activity appears to be due to inhibition of several steps in prolactin receptor signal transduction, according to one animal model.

ANTI-INFLAMMATORY

Saw palmetto is a dual inhibitor of the COX and 5-lipoxygenase pathways, according to in vitro research. More recently, decreased expression of COX-2 has been identified, providing a further explanation for the observed anti-inflammatory activity.

ANTISPASMODIC

Both the lipid and saponifiable fractions have demonstrated antispasmodic activity in several in vitro studies (WHO 2003).

CYTOCHROMES

Saw palmetto failed to have a significant effect on CYP3A4 or CYP2D6 when tested in healthy individuals.

ANTIPROLIFERATIVE EFFECTS

In recent years, there has been interest in determining whether saw palmetto may have a role in prostate cancer, as an inhibitory activity has been observed in several test tube studies for prostatic cancer cell lines.

Saw palmetto:  Other Actions

Although alpha-1 adrenoreceptor activity has been reported in vitro, a clinical study found no evidence of this activity.

Traditionally, saw palmetto is believed to act as a mild diuretic, urinary antiseptic and expectorant.