In vitro bioavailability of fatty acids and fatty acid esters of two saw palmetto preparations

The latest HMPC monograph on saw palmetto (Serenoa repens) differentiates by use of either ethanol or hexane as extractant between products for well established and traditional use. The hexane extract is further specified as it should contain 92% of fatty acids (free or esterified) and 2% of an unsaponifiable part. Ethanolic extracts contain more esterified fatty acids than hexane extracts, nevertheless in total is hardly ever more than 15% of all fatty acids [1].

If the differences in the chemical composition are relevant in the clinical situation is not clear so far. Therefore we carried out experiments with a hexane (Permixon®) and an ethanolic extract (96% V/V)(Prostasan®) in a validated in vitro model. It contains an artificial digestive process which simulates the enzymatic conditions as well as pH changes during gastrointestinal passage and then the transport of substances through a Caco-2 layer simulating the penetration from the intestinal lumen into the interior of the body.

The two extracts were similar in their content of fatty acids but the ethanolic extract contained 11.8% fatty acid esters compared to 2.7% of the hexane extract. After simulated gastric digestion, there were still fatty acid esters detectable in the serum in similar amounts for both extracts. After intestinal digestion and then also after passage through the Caco-2 layer there were for both extracts no fatty acid esters detectable but only free fatty acids in similar concentrations.

These in vitro experiments show that after digestion of lipophylic saw palmetto extracts only free fatty acids are available and absorbed into the human body.The amount of fatty acid esters in a saw palmetto extract should thus not serve as a marker to predict limited efficacy as it was warranted for example by the HMPC [2].

[1] Habib FK, Wyllie MG. ProstateCancer Prostatic Dis. 2004;7:195 – 200.

[2] EMA. Assessment report on Serenoa repens (W.Bartram) Small, Fructus. EMA/HMPC/137250/2013. Nov 2015.