Pharmacology of Saw Palmetto

Saw Palmetto is widely used as a remedy for urinary dysfunction due to enlarged prostate (benign prostatic hyperplasia (BPH)), and can be used for male pattern baldness, acne, excess hair in women and eczema

father daughter bikeSaw palmetto extracts of the ripe berries of the American dwarf palm (Serenoa repens), are widely used as a therapeutic remedy for urinary dysfunction due to enlarged prostate or benign prostatic hyperplasia (BPH) in the US and more so in Europe. 

Based on mechanisms of action, Saw Palmetto extracts can also be used for male pattern baldness (alopecia), excess hair in women (hirsutism), acne, inflammatory skin disorder (seborrhea) and eczema.

Mechanisms of Action

Saw Palmetto extracts inhibit 5α-reductase, which is an enzyme responsible for conversion of testosterone to dihydrotestosterone.  Inhibition of such conversion maintains prostate health.

There are two commonly associated male physiological events that have a similar etiology.  Enlarged prostate or benign prostatic hyperplasia (BPH) and male pattern baldness are both related to the enzyme 5- reductase.  Hirsutism in women is also related to this enzyme.  An excess in activity of 5- reductase has been shown to be responsible for enlarged prostate and male pattern baldness, as well as hirsutism in women.

5- Reductase catalyzes the conversion of testosterone to 5 dihydrotestosterone (5 DHT).  5 DHT is a physiological ligand for an intracellular androgen receptor.  The intracellular receptor has a higher affinity for 5 DHT than testosterone.  Once the ligand has interacted with its cognate receptor, the receptor-ligand complex enters the nucleus and regulates gene expression.  

Enlarged Prostate or Benign Prostatic Hyperplasia

Enlarged prostate or benign prostatic hyperplasia is the most common non-neoplastic disease process in men directly associated with aging.  Although BPH has traditionally been a term used to refer to non-malignant enlargement of the prostate gland resulting from hyperplasia of the prostate epithelium and subsequent urinary outflow obstruction, recent studies have suggested that prostatic enlargement and histologic hyperplasia are only one facet of a larger syndrome consisting of both irritative and obstructive lower urinary tract symptoms, diminished urinary flow rate, and bladder dysfunction.  

Histologic evidence of BPH has been demonstrated in men as young as forty years; however, microscopic nodular hyperplasia associated with irritative symptoms or outlet obstruction is more commonly seen in men aged fifty to seventy.  The frequency of symptomatic BPH is variable yet increases between the fifth and eighth decade of life.

Male Pattern Baldness

Androgenetic alopecia can occur in both males and females.  In men, hair loss generally occurs in the frontal, vertex, and upper occipital regions of the scalp while sparing the posterior and lateral margins.  The process may begin at any age after puberty, with temporal hair recession usually noted first.  There is no actual loss of hair, but rather a conversion of thick thermal hairs to fine, unpigmented hairs.  

In women, the pattern of hair loss is generally more diffuse with thinning throughout the scalp.  Women with elevated androgen levels, as occur in masculinizing disorders, have a balding pattern similar to that of men.  Treatment generally focuses on blocking the 5--reductase, the enzyme responsible for converting testosterone to dihydrotestosterone.

Hirsutism

Hirsutism is the presence of excess hair in women.  This phenomenon is usually an androgen-dependent process.  Twenty-five to 35% of young women have terminal hair over the lower abdomen, around the nipples, or over the upper lip.  

Most women gradually develop more androgen-dependent body hair with age.  Nevertheless, normal patterns of female hair growth are unacceptable to many women.  At the other extreme, severe hirsutism may rarely be the earliest signs of masculinizing diseases.  More often, however, severe hirsutism reflects only increased androgen production in women with a non serious underlying disorder.

Acne and Seborrhea

There are other diseases associated with 5--reductase activity such as acne and inflammatory skin disorder (seborrhea) and eczema.  The key for treating all of these diseases is the modulation of 5--reductase activity.

Urinary Dysfunction

Today, α1-adrenoceptor antagonists and muscarinic cholinoceptor antagonists are commonly used in the treatment of men with voiding symptoms secondary to enlarged prostate. The improvement of voiding symptoms in patients taking Saw Palmetto extract may arise from its binding to pharmacologically relevant receptors in the lower urinary tract, such as α1-adrenoceptors, muscarinic cholinoceptors, 1,4-dihyropyridine receptors and vanilloid receptors.

Furthermore, oral administration of Saw Palmetto extract has been shown to attenuate the up-regulation of α1-adrenoceptors in the rat prostate induced by testosterone. Thus, Saw Palmetto extract at relevant doses may exert a direct effect on the pharmacological receptors in the lower urinary tract, thereby improving urinary dysfunction in patients with enlarged prostate and an overactive bladder.

Anti-Androgenic and Anti-Inflammatory Activities

Studies with a liposterolic extract of Saw Palmetto berries showed that it reduced the uptake by tissue specimens of both testosterone and dihydrotestosterone (DHT) by more than 40% suggesting anti-androgenic activity.

Further, the extract inhibited binding of DHT to its receptor and blocked the conversion of testosterone to DHT by inhibiting the activity of 5-alpha-reductase. The berries also inhibit cyclooxygenase and 5-lipoxygenase pathways, thereby preventing the biosynthesis of inflammation-producing prostaglandins and leukotrienes.

References:

  • Castor TP. (2010). Compositions and Methods for Inhibiting 5- Reductase. United States Patent No. 7,744,935 B2.
  • Dvorkin L. (2013). Introduction To Herbal Supplements for Pharmacists and Other Health Care Professionals. Center for Integrative Pharmacy, Massachusetts College of Pharmacy and Health Sciences.  http://www.longwoodherbal.org
  • Feifer A, Fleshner N and Klotz L. (2002). Analytical accuracy and reliability of commonly used nutritional supplements in prostate disease. J Urol. 168:150-4.
  • Fagelman E and Lowe F. (2002). Herbal medications in the treatment of benign prostatic hyperplasia (BPH). Urol Clin N Am. 29:23-9.
  • Suzuki M, Ito Y, Fujino T, Abe M, Umegaki K, Onoue S, Noguchi H and Yamada S. (2009). Pharmacological effects of saw palmetto extract in the lower urinary tract. Acta Pharmalogica Sinica. 30: 271-281.