Isotopologue Profiling of Triterpene Formation under Physiological Conditions. Biosynthesis of Lupeol-3-(3′-R-hydroxy)-stearate in Pentalinon andrieuxii

A cytotoxic triterpenoid from a Periplaneta americana-derived, Gordonia hongkongensis WA12-1-1

The secondary metabolites produced by microorganisms are a source of novel compounds with antitumor activities. In this study, we isolated biologically active secondary metabolites produced by microorganisms in the intestinal tract of Periplaneta americana. Based on the 16S rRNA gene sequencing, Gordonia hongkongensis WA12-1-1 was identified as the main microorganisms in the intestinal tract of P. americana. The obtained sequence was deposited in the National Center for Biotechnology Information (NCBI) database under the accession number MZ348554. The isolated secondary metabolites were separated and purified by thin layer chromatography, silica gel column chromatography, Sephadex column chromatography, open octadecyl silane column chromatography, high-performance liquid chromatography (HPLC), and semipreparative HPLC. Next, the structure of individual compounds was determined by ultraviolet spectroscopy, nuclear magnetic resonance, and mass spectrometry. A total of 20 compounds were isolated from the secondary metabolites produced by G. hongkongensis WA12-1-1. A total of 12 compounds were obtained from the crude ethyl acetate extract of the culture supernatant and eight from the cellular fraction. Compound 1 was identified as a triterpenoid named gordonterpene and showed cytotoxicity against A549 and HepG2 cell lines. These findings form a basis for further studies on the bioactivity of gordonterpene to tumor cells.

Extraction and antioxidant activity of total triterpenoids in the mycelium of a medicinal fungus, Sanghuangporus sanghuang

The scientific name of the traditional Chinese medicinal fungus, Sanghuang, has been clarified and confirmed that it is a new species -Sanghuangporus sanghuang in the recently discovered genus, Sanghuangporus. To maximize the yield of the active ingredients such as the triterpenoids from authentic Sanghuangporus sanghuang, four parameters of the extraction process, including the extraction time, solid-liquid ratio, extraction temperature, and ethanol concentration were determined. The Box-Behnken experimental design and the response surface method were used to optimize the triterpenoid extraction processes of Sanghuangporus sanghuang mycelium. The results showed that the parameters of the triterpenoid extraction processes were not simple linear relationships. Optimum conditions of ultrasonic extraction required an 80% ethanol concentration, a 1:20 solid-liquid ratio, a 20-min extraction time, and a 60 °C extraction temperature, to obtain a maximum triterpenoid extraction of 13.30 mg/g. Antioxidant capacity tests showed that the Sanghuangporus sanghuang triterpenoids had high clearance capabilities for hydroxyl free radicals, superoxide anions, 2,2-diphenyl-1-picrylhydrazyl free radicals, and 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulfonate) radicals, indicating that the Sanghuangporus sanghuang triterpenoids had high antioxidant activities.

Antimicrobial effects of the ginsenoside Rh2 on monospecies and multispecies cariogenic biofilms

AIMS

To investigate the effects of the ginsenoside Rh2 on monospecies and multispecies cariogenic biofilms and explore the mechanism of the antibiofilm effect of Rh2 in vitro.

METHODS AND RESULTS

Streptococcus mutans, Streptococcus sobrinus and Streptococcus sanguinis were chosen to form the monospecies or multispecies biofilms. Crystal violet staining and laser scanning confocal microscopy were used to observe the effect of Rh2 on biofilms in vitro. Cytotoxicity was examined by the Cell Counting Kit-8. The effects of Rh2 on bacterial membranes were observed via transmission electron microscopy (TEM). The isobaric tags for relative and absolute quantification (iTRAQ) method were used to profile the common differentially expressed proteins. Gene expression was analysed by reverse transcription quantitative polymerase chain reaction. In general, the treatment of cariogenic biofilms with Rh2 significantly decreased biomass accumulation by inhibiting bacterial growth and extracellular polysaccharide synthesis without any cytotoxic effects. TEM imaging showed that Rh2 could disrupt the cell membranes of these bacteria. The iTRAQ results indicated that the levels of mannose-specific IIC/D and acetaldehyde/alcohol dehydrogenase were substantially down-regulated, while the mRNA expression of the corresponding genes were significantly changed.

CONCLUSIONS

Our data revealed a potential application for Rh2 in the protection against dental caries via the inhibition of cariogenic biofilms.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study describes the first application of a ginsenoside against multispecies cariogenic biofilms. Rh2 may serve as an alternative agent to prevent dental caries by effectively modulating the pathogenic potentials of oral biofilms.

Dynamics of Monoterpene Formation in Spike Lavender Plants

The metabolic cross-talk between the mevalonate (MVA) and the methylerythritol phosphate (MEP) pathways was analyzed in spike lavender (Lavandula latifolia Med) on the basis of ¹³CO₂-labelling experiments using wildtype and transgenic plants overexpressing the 3-hydroxy-3-methylglutaryl CoA reductase (HMGR), the first and key enzyme of the MVA pathway. The plants were labelled in the presence of ¹³CO₂ in a gas chamber for controlled pulse and chase periods of time. GC/MS and NMR analysis of 1,8-cineole and camphor, the major monoterpenes present in their essential oil, indicated that the C5-precursors, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) of both monoterpenes are predominantly biosynthesized via the MEP pathway. Surprisingly, overexpression of HMGR did not have significant impact upon the crosstalk between the MVA and MEP pathways indicating that the MEP route is the preferred pathway for the synthesis of C5 monoterpene precursors in spike lavender.

Decoding Biosynthetic Pathways in Plants by Pulse-Chase Strategies Using (13)CO₂ as a Universal Tracer †

(13)CO₂ pulse-chase experiments monitored by high-resolution NMR spectroscopy and mass spectrometry can provide (13)C-isotopologue compositions in biosynthetic products. Experiments with a variety of plant species have documented that the isotopologue profiles generated with (13)CO₂ pulse-chase labeling are directly comparable to those that can be generated by the application of [U-(13)C₆]glucose to aseptically growing plants. However, the application of the (13)CO₂ labeling technology is not subject to the experimental limitations that one has to take into account for experiments with [U-(13)C₆]glucose and can be applied to plants growing under physiological conditions, even in the field. In practical terms, the results of biosynthetic studies with (13)CO₂ consist of the detection of pairs, triples and occasionally quadruples of (13)C atoms that have been jointly contributed to the target metabolite, at an abundance that is well above the stochastic occurrence of such multiples. Notably, the connectivities of jointly transferred (13)C multiples can have undergone modification by skeletal rearrangements that can be diagnosed from the isotopologue data. As shown by the examples presented in this review article, the approach turns out to be powerful in decoding the carbon topology of even complex biosynthetic pathways.

Metabolic cross-talk between pathways of terpenoid backbone biosynthesis in spike lavender

The metabolic cross-talk between the mevalonate (MVA) and the methylerythritol phosphate (MEP) pathways in developing spike lavender (Lavandula latifolia Med) was analyzed using specific inhibitors and on the basis of (13)C-labeling experiments. The presence of mevinolin (MEV), an inhibitor of the MVA pathway, at concentrations higher than 0.5 μM significantly reduced plant development, but not the synthesis of chlorophylls and carotenoids. On the other hand, fosmidomycin (FSM), an inhibitor of the MEP pathway, at concentrations higher than 20 μM blocked the synthesis of chlorophyll, carotenoids and essential oils, and significantly reduced stem development. Notably, 1.2 mM MVA could recover the phenotype of MEV-treated plants, including the normal growth and development of roots, and could partially restore the biosynthesis of photosynthetic pigments and, to a lesser extent, of the essential oils in plantlets treated with FSM. Spike lavender shoot apices were also used in (13)C-labeling experiments, where the plantlets were grown in the presence of [U-(13)C6]glucose. GC-MS-analysis of 1,8-cineole and camphor indicated that the C5-precursors, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) of both monoterpenes are predominantly biosynthesized via the methylerythritol phosphate (MEP) pathway. However, on the basis of the isotopologue profiles, a minor contribution of the MVA pathway was evident that was increased in transgenic spike lavender plants overexpressing the 3-hydroxy-3-methylglutaryl CoA reductase (HMGR), the first enzyme of the MVA pathway. Together, these findings provide evidence for a transport of MVA-derived precursors from the cytosol to the plastids in leaves of spike lavender.