Saw Palmetto Uses and Pharmacology
Benign prostatic hyperplasia
Saw palmetto's mechanism of action in suppressing the symptoms of BPH
is poorly understood. Animal and human in vitro studies have led to
several different hypotheses.
Animal data
The leading hypothesis involves the inhibition of testosterone
5-alpha reductase, an enzyme that converts testosterone to
5-alpha-dihydrotestosterone in the prostate. Hexane extracts of saw
palmetto inhibited the enzyme from human foreskin fibroblasts, while
they had no direct effect on androgen receptor binding.
10
Investigators found various saw palmetto extracts to be much weaker
5-alpha reductase inhibitors in vitro than the synthetic drug
finasteride.
11 Similarly, in humans, serum levels of dihydrotestosterone (DHT) were reduced markedly by finasteride, but not by saw palmetto.
12
Further studies using both known 5-alpha reductase isozymes found
that finasteride inhibited only type 1 reductase, while saw palmetto
inhibited formation of all testosterone metabolites in cultured prostate
epithelial cells and fibroblasts.
13
A different saw palmetto extract, IDS 89, dose dependently inhibited
5-alpha reductase in both the stroma and epithelium of human BPH tissue.
This inhibition was related to the free fatty acids present in the
extract.
14
A tracer study found that radiolabeled oleic acid in saw palmetto
extract was taken up preferentially by rat prostate compared with other
tissues.
15
Studies in a coculture model of human prostate epithelial cells and
fibroblasts found that saw palmetto inhibited types 1 and 2 isoforms of
5-alpha reductase without altering the secretion of prostate-specific
antigen.
16
Other work has shown that saw palmetto extract inhibits trophic as well
as androgenic effects of prolactin in a rat model of prostatic
hyperplasia.
17
Structure-activity studies of pure fatty acid inhibition of steroid
5-alpha reductase found gamma-linolenic acid was the most potent and
specific inhibitor of the enzyme.
18
It is possible that the C18 monounsaturated fatty oleic acid in saw
palmetto was partly responsible for the observed effects on 5-alpha
reductase, though more extensive analysis of saw palmetto fatty acids is
required.
There is less support for other hormonal mechanisms. One study found
5-alpha reductase inhibition and inhibition of DHT binding to androgen
receptors,
19 and another study demonstrated inhibition of DHT and testosterone receptor binding.
20
Administration of saw palmetto extract over 30 days led to no changes
in plasma levels of testosterone, follicle-stimulating hormone, or
luteinizing hormone.
21
Hormonal pathways were invoked to explain reduced prostate weights in
castrated rats treated with estradiol, testosterone, and saw palmetto
extract as opposed to estradiol and testosterone alone.
22
In the human prostate cancer line LNCaP, saw palmetto induced a mixed
proliferative/differentiative effect that was not seen in the
nonhormone-responsive PC3 human prostate cancer cell line.
23
Treatment of patients for 3 months with saw palmetto preceding
prostatectomy caused a reduction in DHT levels in BPH tissue, along with
a corresponding rise in testosterone levels. A marked reduction in
epidermal growth factor concentration was also observed in the
periurethral region of the prostate.
24
Other observations of saw palmetto extracts include the following: a
spasmolytic effect on rat uterus, suggested to be caused by effects on
cyclic AMP and calcium mobilization
25
; an inhibition of smooth muscle contraction in rat deferens and guinea
pig ileum and bladder, postulated as alpha-adrenoreceptor antagonistic,
26 as found in other studies to be noncompetitive in nature
27 ; and interference with 5-lipoxygenase metabolites in neutrophils.
28 A few studies have suggested an increase in apoptosis with administration in mice and humans.
29 ,
30
Clinical data
Although the mechanism of action of saw palmetto is not completely
understood, clinical trials in BPH have shown convincing evidence of
moderate efficacy. A 6-month, double-blind, head-to-head study versus
finasteride in 1,098 men found equivalent efficacy and a superior
adverse reaction profile for saw palmetto.
31 Likewise, a 3-year study of IDS 89 in 435 patients with BPH found clear advantage to placebo in reduction of BPH symptoms.
32
A 1-year study of 132 patients comparing 2 dose levels of saw palmetto
demonstrated efficacy in symptom reduction, but little difference
between dose levels.
33
One study observed Serona repens compared with placebo in 189 patients
with a mild International Prostate Symptom Score (IPSS). Patients were
observed for clinical progression into moderate or severe IPSS. After 24
months the Serona repens group had fewer patients with clinical
progression of bladder outlet obstruction.
34
In contrast, a 1-year double-blind study of 225 men compared American
Urological Association BPH Symptom Index in saw palmetto versus
placebo-treated patients and found no difference between the 2 groups.
35
The general consensus has been that saw palmetto extracts reduce BPH
symptoms without reducing prostate size, therefore delaying surgical
intervention.
36
A meta-analysis that included a total of 18 clinical trials in BPH
concluded that saw palmetto was better tolerated than finasteride and
equivalent in efficacy.
37
A clinical trial in BPH of the saw palmetto constituent beta-sitosterol
showed efficacy similar to that seen with saw palmetto itself.
38
Studies have compared the use of saw palmetto in combination with
other products versus current prescription therapy. A randomized
double-blind trial compared PRO 160/120 ( Prostagutt ), a fixed
combination preparation of 160 mg sabal fruit extract WS 1473 and 120 mg
Urtica root extract WS 1031 , per capsule versus tamsulosin in lower
urinary tract symptoms. In the 140 subjects with moderate to severe
IPSS, there was a decrease in IPSS total scores in both groups after 60
weeks.
39 Similar results were found in an earlier trial comparing PRO 160/120 with placebo.
40
An open-label extension of this trial observed patients for a total of
96 weeks. All patients received PRO 160/120 for the last 48 weeks. A
decrease was found in IPSS total score and residual urine volume, along
with an increase in peak and average urinary flow.
41
Another study had 3 arms comparing Serenoa repens 320 mg daily,
tamsulosin 0.4 mg daily, and S. repens 320 mg plus tamsulosin 0.4 mg
daily. After 6 months of therapy in the 60 study subjects, the groups
were not statistically different in urinary flow rate and decrease in
IPSS.
42
Dosage
The crude saw palmetto berries are usually administered at a dosage
of 1 to 2 g/day; however, lipophilic extracts standardized to 85% to 95%
fatty acids in soft native extract or 25% fatty acids in a dry extract
are more common. Brand-name products include Permixon , Prostaserene ,
Prostagutt , Remigeron , Quanterra Prostate , and LG 166/S . Typical
dosages of standardized extracts range from 100 to 400 mg given twice
daily for benign prostatic hypertrophy to the most commonly used dosage
in clinical trials of 160 mg twice daily or 320 mg daily.
21 ,
25 ,
38 ,
43 ,
44 ,
45
Pregnancy/Lactation
Information regarding safety and efficacy in pregnancy and lactation
is lacking; however, antiandrogenic activity suggests that saw palmetto
should not be used in pregnancy.
Interactions
Two men stabilized on warfarin experienced an increase in the
international normalized ratio (INR) after taking an herbal combination
containing cucurbita, saw palmetto, and vitamin E.
46
In both patients, the INR returned to previous values when the herbal
product was discontinued. Although neither cucurbita nor saw palmetto
can be ruled out as the cause of the increase in INR, it is more likely
that vitamin E interfered with vitamin K-dependent clotting factors,
adding to the anticoagulant effects of warfarin.
Adverse Reactions
Saw palmetto products are generally well tolerated, with occasional reports of adverse GI effects.
Because of well-documented antiandrogen and antiestrogenic activity,
avoid taking with any hormone therapy, including oral contraceptive and
hormone replacement therapy.
A study assessing the affects of several herbal medications including
saw palmetto on platelet function in adult volunteers found no effect
of saw palmetto on platelets after 2 weeks at the recommended dose.
47 However, there has been 1 case report linking saw palmetto to intraoperative hemorrhage.
48
A 53-year-old white man with normal preoperative prothrombin time and
activated partial thromboplastin time underwent surgical resection of
meningioma. Surgery was terminated early after administration of 4
liters of crystalloid fluids, 4r units of packed red blood cells, 3
units of pooled platelets, and 3 units of fresh frozen plasma. After
surgery, the patient had an elevated bleeding time, which normalized
over the next 5 days. No other medication use or events were reported
that could be linked to the elevated bleeding time; saw palmetto dose,
duration of therapy, or manufacturer were not reported in the case
report.
Two case reports link saw palmetto to intraoperative floppy-iris syndrome, which is also associated with multiple alpha
1 -adrenergic antagonist. This condition can cause complications during cataract surgery.
49
Toxicology
Research reveals little or no information regarding toxicology with the use of saw palmetto.
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