Physical, chemical and pharmacological characterization of a new oleogel-forming triterpene extract from the outer bark of birch (betulae cortex).

Triterpenes are biologically active secondary plant substances that display antimicrobial, hepatoprotective and anti-inflammatory effects. However, the poor solubility of triterpenes in both polar and non-polar solvents as well as expensive purification procedures have prevented the large-scale isolation of these compounds for medicinal purposes. Here, we describe a novel quantitative extraction method of triterpenes from the outer bark of birch (Betula species) in which betulin, a lupan triterpene, predominates. The resulting highly purified triterpene extract (TE) in the form of a dry powder contains betulin as the major compound, but also betulinic acid, lupeol, erythrodiol and oleanolic acid. We have found that this TE is able to form an oleogel, thus providing an opportunity for the topical application of pharmacologically relevant amounts of triterpenes. Furthermore, we have investigated the TE in comparison to its major isolated compounds in cell culture experiments with human immortalized keratinocytes and skin cancer cells. We could demonstrate dose-dependent cytotoxic and apoptosis-inducing effects of TE and betulin. These experimental data support the notion from a previous clinical study that TE from the outer bark of birch might represent a new tool for the topical treatment of skin cancer and skin cancer precursors like actinic keratoses.