The old pharmaceutical oleoresin labdanum of Cistus creticus L. exerts pronounced in vitro anti-dengue virus activity

ETHNOPHARMACOLOGICAL RELEVANCE

The haemorrhagic dengue fever affects up to 500 million patients, annually causing 20.000 deaths, with no chemotherapeutic agent available. The oleoresin labdanum of Cistus creticus L. has been established as an anti-infective agent since antiquity in Mediterranean ethnopharmacology.

MATERIALS AND METHODS

We tested several extracts and fractions of labdanum - standardised on labdane-type diterpenes via GC-MS - on their activity against the dengue virus (DENV-2 strain 00st-22A) in in vitro Vero cell cultures (96-well-plates, 5 days). Preliminary experiments with a labdanum diethyl ether raw-extract did not yield measureable results due to cytotoxic effects against Vero cells. In all following experiments, cell viability was constantly checked using the MTT-test. Fractionation of this raw-extract by liquid-liquid-extraction and column-chromatography on silica-gel (gradient elution with hexane, EtOAc, CHCl₃, MeOH) succeeded in separating the anti-viral activity of labdanum from its cytotoxic effect.

RESULTS

In the most active fraction GS5 at 30 μg/ml, dengue virus proliferation was 100% suppressed and cell viability was over 90%. Structural elucidation of major constituents of GS5 is currently ongoing, but thin-layer chromatography showed that this fraction is mainly dominated by manoyloxides, a class of labdane-type diterpenes with known antimicrobial activity. Claims concerning the antiviral activity of above ground parts of C. creticus have been made previously, but these generally ascribe this activity to hot water soluble polyphenols and propose an unspecific tanning effect of the viral surface proteins as the mechanism of action. However, the water soluble fraction enhanced viral proliferation.

CONCLUSION

We therefore describe a direct, pharmacological, antiviral activity of a diethyl ether extract of labdanum against a virulent haemorrhagic fever like dengue for the first time.

Influence of Drying Method on Some Bioactive Compounds and the Composition of Volatile Components in Dried Pink Rock Rose (Cistus creticus L.)

This study investigates the effects of various drying methods applied to leaves of Cistus creticus L. on the contents of polyphenols and the composition of the volatile fraction. The following four drying methods were used: convection drying at a temperature of 40 °C (CD 40 °C), 50 °C (CD 50 °C), and 60 °C (CD 60 °C); vacuum-microwave (VMD 240 W); combined drying, involving convection pre-drying (50 °C) and vacuum-microwave (240 W) finish drying (CPD-VMFD) as well as freeze-drying (FD). Polyphenols in the dried leaves were determined using chromatography-photodiode detector-quadrupole/time of flight-mass spectrometry (UPLC-PDA-Q/TOF-MS). The contents of odoriferous substances in the dry material were determined by means of head space-solid phase microextraction (HS-SPME) with the use of a gas chromatograph (GC). Thirty-seven polyphenol components including 21 flavonols, eight flavan-3-ols, and eight hydrolyzed tannins in dry Pink Rock Rose material were found for the first time. The highest contents of polyphenols, totaling 2.8 g 100 g⁻¹ dry matter (d.m.), were found in the samples subjected to the CPD/VMFD drying method. Pink Rock Rose subjected to this drying method was characterized by large quantities of odoriferous compounds, mainly eugenol, thymol, and carvacrol, which contribute to its antiseptic properties. By using CPD/VMFD methods, it is possible to obtain fine quality dry material from the leaves of C. creticus.

Labdanum and Labdanes of Cistus creticus and C. ladanifer: Anti-Borrelia activity and its phytochemical profiling✰

BACKGROUND

Intrigued by testimonies of Saxon borreliosis self-help groups concerning considerabl improvements of their symptoms by ingestion of Cistus creticus L. (Cistaceae) leaf preparations, we recently reported on the growth inhibiting activity of extracts with different polarities and its volatile oil against Borrelia burgdorferi sensu stricto (Bbss) in vitro, determined by a bioassay guided procedure. The most active volatile oil (only about 0.10% in leaves) was found to be dominated by labdane-type manoyloxides as well as carvacrol, determined via GC-MS.

HYPOTHESIS

These terpenes are major active constituents of the old pharmaceutical oleoresin labdanum, which is secreted from the leaf surface of C. creticus and traditionally harvested, e.g., on Crete by brushing the shrubs.

METHODS

In order to elucidate the definite anti-Borrelia active principles of C. creticus, preparative scale separation of the diethyl‑ether soluble fraction of Cretan labdanum was achieved by combined silica gel 60-and RP-18 CC and analysed by novel TLC-Extractor/ES-MS as well as by 1d/2d-1H/13C-NMR data. For the antispirochaetal activity tests against Bbss in vitro, all samples were solubilised in water with addition of polysorbate 80, the effect of which on bacterial growth was examined and found to be negligible.

RESULTS

This led to isolation and identification of the monoterpene carvacrol as well as of the four major manoyloxides manoyloxide (A), 3-acetoxy-manoyloxide (B), 3‑hydroxy-manoyloxide (C), and epi‑manoyloxide (D). Additionally, 2-keto-manoyloxide (E) and sclareol (F) were identified via GC/EI-MS. In subsequent microbiological tests of the isolated compounds, epi‑manoyloxide (D) exhibited by far the strongest individual antispirochaetal effect, equal to the positive control amoxicilline. Furthermore, manoyloxide (A), carvacrol, and the diethyl‑ether soluble fraction of labdanum as a whole contribute to the strong antispirochaetal activity, while the other labdanes were less active. Isolated manoyloxides were further used as external standards for a GC-MS screening of labdanum samples from different origins, revealing exceptionally high contents of all analysed manoyloxides in the samples of Cretan labdanum from C. creticus, while their contents in other commercial available labdanum samples were lower by several orders of magnitude. Especially in Spanish labdanum samples, declared as Cistus ladanifer L., mainly simple alkanes and at most traces of epi‑manoyloxide (D) and of manoyloxide (A) could be detected.

CONCLUSION

The application of C. creticus preparations by Lyme disease self-help groups may be considered as a reasonable therapy approach. For the first time, isolated epi‑manoyloxide and carvacrol could be evaluated as most promising candidates for drug development and labdanum based phytomedicine development, respectively. They should serve as vital active markers for quality assessments of C. creticus preparations.