Pentacyclic triterpenes are secondary plant metabolites widespread in fruit peel, leaves and stem bark. In particular the lupane-, oleanane-, and ursane triterpenes display various pharmacological effects while being devoid of prominent toxicity. Therefore, these triterpenes are promising leading compounds for the development of new multi-targeting bioactive agents. Screening of 39 plant materials identified triterpene rich (> 0.1% dry matter) plant parts. Plant materials with high triterpene concentrations were then used to obtain dry extracts by accelerated solvent extraction resulting in a triterpene content of 50 ‑ 90%. Depending on the plant material, betulin (birch bark), betulinic acid (plane bark), oleanolic acid (olive leaves, olive pomace, mistletoe sprouts, clove flowers), ursolic acid (apple pomace) or an equal mixture of the three triterpene acids (rosemary leaves) are the main components of these dry extracts. They are quantitatively characterised plant extracts supplying a high concentration of actives and therefore can be used for development of phytopharmaceutical formulations.

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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.

During the last two decades triterpenes have attracted attention because of their pharmacological potential. Triterpene extract (TE) from outer bark of birch consisting mainly of betulin is able to form an oleogel which was successfully tested in the treatment of actinic keratosis. Some aspects of TE in vitro pharmacology are already known. Now we show preliminary pharmacokinetics of betulin and results of a subchronic toxicity study of TE in rats and dogs. Because of poor aqueous solubility of the TE-triterpenes (< 0.1 µg/mL respectively), for pharmacokinetic studies it was suspended in sesame oil (rats, i.p.) and PEG 400 / 0.9 % NaCl (dogs, s.c.). I.p. administered, betulin, the main component of TE, shows time dependency over a period of 4 h and reaches a dose-independent serum level of 0.13 µg/mL. Dose dependency was observed with s.c. administration. At 300 mg/kg a maximum plasma concentration of 0.33 µg/mL betulin was detected after 28 daily applications. The subchronic toxicity study showed no toxicity of TE in rats (i.p.) and dogs (s.c.). In conclusion, triterpene extract from birch bark is safe, its betulin is bioavailable and in addition to published triterpene biological activities TE provides high potential for further pharmaceutical and pharmacological research.

Keywords• actinic keratoses • betulin • betulinic acid • oleogel • skin cancer Summary Background: Actinic keratoses (AK) are squamous cell carcinomas in situ and require treatment. Betulin-based oleogel prepared from a standardized triterpene dry extract from birch bark represents a new topical agent with antiinflammatory and anti-tumor potential. Patients and Methods: In the prospective, randomized, monocentric phase 2a study 45 patients with ≤ 10 AK were included and randomly assigned to one of the three treatment groups. Intervention consisted of topical betulin-based oleogel twice daily versus cryotherapy with liquid nitrogen versus the combination of cryotherapy with topical betulin-based oleogel. Treatment response was assessed clinically after three months. The clinical response was graded into complete clearing (100 %), therapy responders (≥ 75 % clearing of the lesions) and non-responders (< 75 % clearing). Additionally, punch biopsies were obtained from some patients before and at the end of treatment. Results: Therapy with betulin-based oleogel was well tolerated. Three patients discontinued therapy because of personal reasons. After three months, the 100 % (and > 75 %) clearing rates of the lesions were as follows: 64 % (86 %) with betulin-based oleogel (n = 14), 79 % (93 %) with cryotherapy (n = 14), and 71 % (71 %) with the combined therapy (n = 14). Histological analysis of biopsies taken before and after treatment (n = 8) showed a reduced degree of dysplasia in the epidermis in all study arms. Conclusions: Betulin-based oleogel seems to be an effective novel approach in the topical treatment of actinic keratoses. However, the clinical and histological findings of the present pilot study have to be verified against placebo with larger case numbers.