In vitro hepatotoxicity of Petasites hybridus extract (Ze 339) depends on the concentration, the cytochrome activity of the cell system, and the species used.

Ze 339, a CO2 extract prepared from the leaves of Petasites hybridus, possesses antispasmodic and anti-inflammatory effects and is proven to be effective in the treatment of allergic rhinitis. To study possible hepatotoxic effects of Ze 339, its main constituents and metabolites, a series of in vitro investigations were performed. Furthermore, different reconstituted fractions of extract (petasins and fatty acid fraction) were examined in three in vitro test systems using hepatocytes: Two human cell lines, with lower and higher activity of cytochrome P450 enzymes (HepG2, HepaRG) as well as a rodent cell line with high cytochrome P450 activity (H-4-II-E), were used. Metabolic activity, assessed by the WST-1 assay, was chosen as indicator of cytotoxicity. To assess potential bioactivation of Ze 339 compounds, metabolic experiments using S9 fractions from rats, dogs, and humans and isolated cytochromes (human/rat) were performed, and the formation of reactive metabolites was assessed by measuring cellular concentrations of glutathione and glutathione disulphide. Our data revealed that the cytotoxicity of Ze 339, its single constituents, and main metabolites depends on the concentration, the cytochrome activity of the cell system, and the species used.

Development of an in vitro screening method of acute cytotoxicity of the pyrrolizidine alkaloid lasiocarpine in human and rodent hepatic cell lines by increasing susceptibility.

ETHNOPHARMACOLOGICAL RELEVANCE: Pyrrolizidine alkaloids (PAs) are secondary plant ingredients formed in many plant species to protect against predators. PAs are generally considered acutely hepatotoxic, genotoxic and carcinogenic. Up to now, only few in vitro and in vivo investigations were performed to evaluate their relative toxic potential. AIM OF THE STUDY: The aim was to develop an in vitro screening method of their cytotoxicity. MATERIALS AND METHODS: Human and rodent hepatocyte cell lines (HepG2 and H-4-II-E) were used to assess cytotoxicity of the PA lasiocarpine. At concentrations of 25 µM up to even 2400 µM, no toxic effects in neither cell line was observed with standard cell culture media. Therefore, different approaches were investigated to enhance the susceptibility of cells to PA toxicity (using high-glucose or galactose-based media, induction of toxifying cytochromes, inhibition of metabolic carboxylesterases, and inhibition of glutathione-mediated detoxification). RESULTS: Galactose-based culture medium (11.1 mM) increased cell susceptibility in both cell-lines. Cytochrome P450-induction by rifampicin showed no effect. Inhibition of carboxylesterase-mediated PA detoxification by specific carboxylesterase 2 inhibitor loperamide (2.5 µM) enhanced lasiocarpine toxicity, whereas the unspecific carboxylesterase inhibitor bis(4-nitrophenyl)phosphate (BNPP, 100 µM)) had a weaker effect. Finally, the inhibition of glutathione-mediated detoxification by buthionine sulphoximine (BSO, 100 µM) strongly enhanced lasiocarpine toxicity in H-4-II-E cells in low and medium, but not in high concentrations. CONCLUSIONS: If no toxicity is observed under standard conditions, susceptibility enhancement by using galactose-based media, loperamide, and BSO may be useful to assess relative acute cytotoxicity of PAs in different cell lines.

In Vitro and In Situ Absorption and Metabolism of Sesquiterpenes from Petasites hybridus Extracts.

Petasites hybridus extract is used in the treatment of seasonal allergic rhinitis. The aim of this study was to evaluate the active constituent petasin and its isomers isopetasin and neopetasin (petasins) in the P. hybridus extract Ze 339 for liberation, dissolution, absorption, and metabolism. The determination of pH-dependent thermodynamic solubility was performed via the shake-flask method. Petasins exhibited a low solubility that was pH independent. In vivo, the concentration of solute drugs is decreased continuously by intestinal absorption. Therefore, low solubility is not assumed to be critical for in vivo performance. Additionally, dissolution of an herbal medicinal product containing P. hybridus extract Ze 339 was assessed. Furthermore, high permeability through Caco-2 monolayers was evident. Using an in situ rat model, absorption capacity for petasins was found in all tested intestinal segments, namely, duodenum, jejunum, and ileum. Besides, high metabolism was evident both in Caco-2 monolayers and in the rat intestine. To compare intestinal and hepatic metabolism of petasins, in vitro enzyme assays using liver and intestinal cytosol and microsomes (S9 fraction) of rats and humans were performed. A significantly higher metabolic rate was found in the liver S9 fraction of both species compared with the intestinal S9 fraction.

In Vitro and In Situ Characterization of Triterpene Glycosides From Cimicifuga racemosa Extract.

Cimicifuga racemosa products are widely used in the treatment of climacteric symptoms. The aim of this study was to evaluate C racemosa extract Ze 450 according to Biopharmaceutics Classification System (BCS). Triterpene glycosides served as analytical marker and were evaluated for solubility and absorption properties. pH-dependent thermodynamic solubility was tested via shake flask method, and dissolution performance of a herbal medicinal product containing C racemosa extract Ze 450 was assessed. Absorption was estimated by in vitro permeation through Caco-2 monolayers. Furthermore, different intestinal segments were screened for absorption performance using an in situ rat model. Over a physiological pH range, triterpene glycosides exhibited pH-dependent solubility with highest concentration at pH 7.5. Dissolution profiles showed rapid dissolution of actein and 23-epi-26-deoxyactein. Furthermore, 23-epi-26-deoxyactein as surrogate for contained triterpene glycosides showed a high permeability through Caco-2 monolayers. Results of in situ rat model showed absorption capacity for 23-epi-26-deoxyactein in duodenum, jejunum, ileum, and colon. The results indicate high bioavailability of triterpene glycosides from C racemosa extract Ze 450. With regard to BCS, triterpene glycosides can be classified into BCS class I (high solubility, high permeability).

UPLC TOF MS for sensitive quantification of naturally occurring pyrrolizidine alkaloids in Petasites hybridus extract (Ze 339).

Due to increasing regulatory awareness of their hepatotoxic, genotoxic and possibly carcinogenic potential, pyrrolizidine alkaloid (PA) content has to be thoroughly monitored in herbal medicinal preparations. Recently, new very low PA regulatory threshold concentrations have been requested by the authorities. Therefore, a highly sensitive and reproducible UPLC TOF MS method for the quantification of the PAs senkirkine, senecionine, seneciphylline, senecionine-N-oxide and seneciphylline-N-oxide in a CO2-extract of Petasites hybridus leaves (Ze 339) has been developed. The limit of quantification (LOQ) was 2ppb for all PAs. Recovery at the LOQ was between 88.9 and 141.9%, the repeatability precision between 3.5 and 13.6%. Linearity of the five PAs showed correlation coefficients between 0.9995 and 0.9998 and coefficients of variation between 7.44 and 8.56%. A working range between 2 ppb and 200 ppb could be fixed. In the tested batches of the P. hybridus extract Ze 339, the absence of PAs could be demonstrated. In conclusion, this assay allows to determine trace PA concentrations in P. hybridus extract Ze 339, making it suitable for analytical PA monitoring in accordance with regulatory requirements.

A novel screening strategy to identify ABCB1 substrates and inhibitors.

We tested the hypothesis whether data on ABCB1 ATPase activity and passive permeability can be used in combination to identify ABCB1 substrates and inhibitors. We determined passive permeability using an artificial membrane permeability assay (HDM-PAMPA) and ABCB1 function, i.e., vanadate-sensitive ATPase activity for a training set (40 INN drugs) and a validation set (26 development compounds). In parallel experiments, we determined ABCB1 function, i.e., vectorial transport in a Caco-2 cell monolayer, and ABCB1 inhibition, i.e., calcein AM extrusion out of K562-MDR cells, to cross-validate the results with cellular assays. We found that compounds that did not modulate ABCB1-ATPase did also not affect calcein AM extrusion and were not actively transported by ABCB1 in Caco-2 cell monolayers. The results corroborated the effect of passive permeability as an important covariate of active transport: active transport in Caco-2 monolayer was only apparent for compounds showing low passive permeability (<5.0 cmx10(-6)/s) in the HDM-PAMPA assay whereas compounds with high passive permeability (>50 cmx10(-6)/s) were shown to inhibit calcein AM efflux with IC50 values close to their respective Km value obtained for ABCB1-ATPase. The use of HDM-PAMPA in combination with ABCB1-ATPase offers a simple, inexpensive experimental approach capable of identifying ABCB1 inhibitors as well as transported substrates.