Seasonal and tissue variation in taxane concentrations of Taxus brevifolia

Microscopic distribution of taxanes in freeze-fixed stems of Taxus cuspidata

Introduction

Taxus species contain the anticancer alkaloid paclitaxel, as well as other taxanes similar in structure and potentially in effect to paclitaxel. Tissue-specific distribution patterns and seasonal variations of taxanes in some Taxus species have been reported; however, it is still under-presented for the taxanes in Taxus cuspidata.

Methods

The radial distributions of eight taxanes in the transverse surface of freeze-fixed T. cuspidata stems from the late summer and the spring seasons were investigated by cryo-time-of-flight secondary ion mass spectrometry and scanning electron microscopy (cryo-TOF-SIMS/SEM) visualization and liquid chromatography-mass spectrometry (LC-MS) quantitative analysis. By optical microscopic observation, seasonal differences in the amounts and distribution patterns of target taxanes were further characterized in specific tissues.

Results and Discussion

The overall amount of taxanes was higher in the late summer than in the spring. Also, taxanes' radial distribution was generally found at higher concentration in the phloem, the cambium and lower level in the periderm, the latest-forming xylem, with different taxanes showing several patterns with distinction between seasons, which were considered related to seasonal plant physiological behaviors. In addition, the distribution of baccatin III (BAC) was investigated at the cellular level, which was regarded in specific cells suggesting its transport in the radial and axial directions in the T. cuspidata stem. Characterizing the microscopic distribution of taxanes in the T. cuspidata stem is expected to play a role in the further study of their biosynthesis and in planta behaviors.

Seasonal and Circadian Variation of Non-Volatile Metabolites in Lippia alba Leaves

The present study describes the seasonal and circadian variations of the major compounds from Lippia alba leaves. SPSS was used to identify, quantify, and associate the variations in the secondary metabolites of this species through HPLC/DAD analysis of the leaves hydroethanolic extracts of six selected L. alba specimens. For the circadian study, the samples were collected at four different daily hours in each year's season. For the seasonal study, the samples were collected monthly from the same individuals for two consecutive years (2018 and 2019). These samples were analyzed and quantified using a validated HPLC method for flavonoids, iridoids, and phenyl ethanoid glycoside. Mussaenoside, acteoside, and tricin-7-O-diglucuronide showed a moderate positive correlation between their biosynthesis and the precipitation index, while epi-loganin had a moderate negative correlation. Acteoside showed a moderate positive correlation between the minimum registered temperature and its production. Compared with previous studies, a drastic reduction (about 95 %) in the production of tricin-7-O-diglucuronide compared with previous study and this difference could be attributed to the plant's aging. Thus, the data demonstrated that lower temperatures and high rainfall could favor the production of the major L. alba active compounds (acteoside and tricin-7-O-diglucuronide) and that older plants harm their production.

Screening and selection of camptothecin producing endophytes from Nothapodytes nimmoniana

Endophytic fungi with the ability to produce plant based secondary metabolites are a potential alternative for producing the host plant metabolite and to prevent natural plants from extinction. To isolate a high metabolite yielding endophytic strain from plants, hundreds of endophytic strains are screened and tested for product yield separately under axenic state, before shortlisting the potential endophyte, which involves huge time consumption. In this study, strategies for screening and selection of high camptothecin yielding endophytes from their natural habitat were proposed. A correlation was built between the camptothecin yield in the explants and the endophytes isolated from them. In addition, camptothecin yield was compared between the endophytes isolated from young and matured plants. Further, camptothecin producers and non-producers strains were compared for their tolerance toward camptothecin. The study indicates that high camptothecin yielding endophytes were isolated from high yielding explants and younger plants and they were more tolerant to camptothecin in comparison to non-camptothecin yielding endophytes. Thus, choosing a young and high yielding explant for endophyte isolation, and use of camptothecin as a selective agent in the growth medium, can be instrumental in screening and selection of high camptothecin yielding endophytes from nature in relatively less time.

Sites of biosynthesis and storage of Taxol in Taxus media (Rehder) plants: Mechanism of accumulation

Taxol is a cytotoxic agent against various types of cancers. The cytotoxic activities of Taxol can be extended to its synthesizing plant. Here, Taxol is shown to have special synthesis, storage and transport mechanisms that avoid the toxic effects on its source plant. The sites of Taxol biosynthesis, transport and storage were revealed by quantification of plant Taxol, its intermediate baccatin III, the polyphenol side chain precursor , gene expression analysis of the major Taxol biosynthetic genes and in situ immuno-labeling. Although the biosynthesis of Taxol was limited by the expression of its biosynthetic genes and the presence of baccatin III, its presence did not correlate to baccatin III accumulation, nor to the expression of biosynthetic genes. However, Taxol presence positively correlated to polyphenol accumulation (late stage in Taxol assembly) and the resin-like hydrophobic bodies (HB, storage organelles). These results indicate that the presence of Taxol requires two complementary steps, biosynthesis followed by storage. Each step is limited by the availability of different precursors, which differ in their localization within the plant. Thus, the sites of biosynthesis, transport and storage of Taxol are different. Taxus media (Rehder) plant wood showed high concentrations of baccatin III and the expression of biosynthetic genes. However, the concentrations of Taxol, polyphenol and HB were very high in the plant outer layers including phloem and dead bark (rhytidome). Furthermore, in situ immuno-labeling showed that taxadiene synthase (the rate-limiting enzyme in Taxol biosynthesis) was mainly found in the wood, while Taxol primarily localized to the outer tissues. Conclusively, wood can be considered as the site of Taxol biosynthesis. Our data also propose that Taxol then accumulates into HB in order to permit its transport within the living plant tissues without causing toxic effects. This is followed by Taxol storage in the outer tissues including phloem and dead bark.

Seasonal Dynamics of Metabolites in Needles of Taxus wallichiana var. mairei

Seasonal variations of the phytochemicals contents in needles of T. wallichiana var. mairei due to the effects of growth meteorological parameters were investigated in this study. The needles of T. wallichiana var. mairei were collected from different months and the contents of taxoids (paclitaxel, 10-deacetylbaccatin III (10-DAB), baccatin III, cephalomannine, 10-deacetyltaxol (10-DAT)), flavones (ginkgetin, amentoflavone, quercetin) and polysaccharides were quantified by ultra performance liquid chromatography (UPLC) and the resonance light scattering (RIL) method. The content of taxoids gave the highest level of 1.77 ± 0.38 mg·g-1 in January, and the lowest value of 0.61 ± 0.08 mg·g-1 in September. Unlike taxoids, the content of flavonoids was the highest in August. The content of polysaccharides reached peak value of 28.52 ± 0.57 mg·g-1 in September, which was two times higher than the lowest content of 9.39 ± 0.17 mg·g-1 in January. The contents of paclitaxel, 10-DAB, 10-DAT and polysaccharides significantly depended on meteorological parameters. The mean of minimum temperature (R = -0.61) and length of daylight (R = -0.60) were significantly correlated to 10-DAB content, while 10-DAT level showed significant correlation with length of daylight (R = -0.70) and relative humidity (R = 0.70). In addition, temperature had significantly negative effect on the content of paclitaxel and a significantly positive effect on that of polysaccharides. This study enriched the knowledge on the accumulation pattern of metabolites and could help us to determine the collecting time of T. wallichiana var. mairei for medicinal use.

Seasonal-based temporal changes fluctuate expression patterns of TXS, DBAT, BAPT and DBTNBT genes alongside production of associated taxanes in Taxus baccata

Environmental cues have synergistic or antagonistic regulatory roles on transcription activity and taxanes accumulation in yew, though DBAT activity is less influenced, could be accordingly a rate-limiting enzyme. The current work was undertaken to elucidate the consequences of some environmental cues (i.e., day length, temperature, sunlight and relative humidity) on the expression patterns of TXS, DBAT, BAPT and DBTNBT genes contributed to the taxol biosynthetic pathway along with the accumulation of some taxanes in needles and stems of Taxus baccata over year 2013-2014. In both tissues, light intensity and temperature correlated with the production of 10-DAB III and total taxanes, and TXS activity, while a lack of significant association was deduced for day length and relative humidity. Furthermore, in both tissues, a weak correlation was observed between BAC III and light intensity, temperature, day length and relative humidity, and the corresponding gene, DBAT. Surprisingly, DBAT activity was not co-induced with TXS in both tissues, and remained expressed at basal levels over year, supporting that the conversion of 10-DAB III into BAC III could presumably be a rate limiting step in the taxol biosynthetic pathway. Similar to BAC III, no strong correlation was detected between production of taxol in both tissues and all the meteorological data, while the corresponding genes BAPT and DBTNBT, in some cases, exhibited significant correlated results. Notably, despite higher activities of BAPT and DBTNBT in both tissues over year, taxol production was still in small quantities, probably owing to the low amounts of its precursors rather than low volumes of BAPT and DBTNBT transcripts. The results, altogether, could provide us new insights towards the potential regulatory roles of environmental cues on the production of taxanes in yew trees.

Influence of seasonal variation on the phenology and liriodenine content of Annona lutescens (Annonaceae)

Annona lutescens Saff. (Annonaceae) grows as a native tree in Chiapas, Mexico in Tropical Dry Forest habitat. Like most Annonaceae, it biosynthesizes benzylisoquinoline alkaloids, mostly liriodenine. To determine the influence of seasonal changes in the accumulation of liriodenine, the monthly variation of liriodenine content in roots, stems and leaves of mature and young trees was observed. These parts of young and mature A. lutescens trees were collected monthly over a 1 year period and the alkaloids were extracted; the liriodenine was quantified by high-resolution liquid chromatography. The phenological stages of the species were also assessed (leaf development, flowering and fruiting) using the Biologische Bundesanstalt, Bundessortenamt und Chemische Industrie (BBCH) scale. The analysis of both young and mature trees showed a significant increase in the liriodenine concentration occurs within roots during the dry season, which coincides with leaf fall. A significant decrease also occurred at the beginning of the rainy season (the period of leaf growth); the liriodenine content for the next rainy season did not reach the levels of the previous dry season. The climatic variation induced phenological and physiological changes in this species.

A fungal endophyte induces transcription of genes encoding a redundant fungicide pathway in its host plant

BACKGROUND

Taxol is an anti-cancer drug harvested from Taxus trees, proposed ecologically to act as a fungicide. Taxus is host to fungal endophytes, defined as organisms that inhabit plants without causing disease. The Taxus endophytes have been shown to synthesize Taxol in vitro, providing Taxus with a second potential biosynthetic route for this protective metabolite. Taxol levels in plants vary 125-fold between individual trees, but the underlying reason has remained unknown.

RESULTS

Comparing Taxus trees or branches within a tree, correlations were observed between Taxol content, and quantity of its resident Taxol-producing endophyte, Paraconiothyrium SSM001. Depletion of fungal endophyte in planta by fungicide reduced plant Taxol accumulation. Fungicide treatment of intact plants caused concomitant decreases in transcript and/or protein levels corresponding to two critical genes required for plant Taxol biosynthesis. Taxol showed fungicidal activity against fungal pathogens of conifer wood, the natural habitat of the Taxol-producing endophyte. Consistent with other Taxol-producing endophytes, SSM001 was resistant to Taxol.

CONCLUSIONS

These results suggest that the variation in Taxol content between intact Taxus plants and/or tissues is at least in part caused by varying degrees of transcriptional elicitation of plant Taxol biosynthetic genes by its Taxol-producing endophyte. As Taxol is a fungicide, and the endophyte is resistant to Taxol, we discuss how this endophyte strategy may be to prevent colonization by its fungal competitors but at minimal metabolic cost to itself.

The effect of seasonal variation on the antineoplastic activity of Alstonia scholaris R. Br. in HeLa cells

In order to evaluate the seasonal variation as well as cytotoxicity of different fractions of Alstonia scholaris R. Br. (ASE), the HeLa cells were treated with different doses of various fractions of ASE collected in monsoon, winter and summer. The exposure of HeLa cells to different extracts prepared from the stem bark collected in monsoon, winter and summer seasons resulted in a dose dependent increase in the cell killing effect of ASE and the highest cell killing effect was observed for the extract prepared from the summer collections. Similarly, treatment of HeLa cells with different doses of various fractions of the Alstonia scholaris extract viz. residue (ASERS), steroidal (ASEST), chloroform (ASECH), petroleum ether (ASEPE), diethyl ether (ASEDE), ethyl acetate (ASEEA), n-butanol (ASENB), aqueous (ASEAQ) and echitamine chloride (ECL) also resulted in a dose dependent decline in the cell viability, where the greatest cytotoxic effect was observed for residue (ASERS), followed by the whole extract (ASE) and chloroform (ASECH) fraction, while the least activity was observed for the steroidal (ASEST) fraction. The cytotoxicity declined ASERS > ASE > ASECH >ECL > ASEEA > ASEDE > ASEPE > ASENB > ASEAQ > ASEST in order. Our study demonstrates that the extract prepared from the summer collection, and the fractions containing the alkaloids were highly effective in cell killing. The extract of ASE was more powerful than the active principle echitamine present in ASE.

Production of taxoids with biological activity by plants and callus culture from selected Taxus genotypes

Twenty seven different yew trees belonging to various genotypes and hybrids have been screened for their capacity to produce significant amounts of taxoids provided with biological activity in the tubulin test. From the three best genotypes selected, Taxus x media "Sargentii" proved to be able to produce viable calluses from excised roots placed in vitro. Taxoid composition at various times of the in vitro culture was determined and the carcinostatic efficiency of the extracts was established using the KB cell cytotoxicity test. In leaves and calluses, respectively, 0.069 and 0.032% paclitaxel (taxol) contents were found. These contents were significantly higher than those previously reported for other genotypes.

Solid-phase extraction and simplified high-performance liquid chromatographic determination of 10-deacetylbaccatin III and related taxoids in yew species

Solid-phase extraction was accomplished with specially prepared cartridges filled with silanised silica gel (RP-2) for the purpose of 10-deacetylbaccatin III (10-DAB III) and related taxoids extracts purification obtained from different yew materials. In the first method, the analysed taxoids eluted in 75% methanol, but in the second method, the preliminary elution with 30% methanol was made. DAB III and its six derivatives were separated from co-extractives in merely acetonitrile-water gradient mode during 25 min on Waters Symmetry C-18 column with photodiode array (PDA) detection. The total recoveries for 10-DAB III and paclitaxel in the first SPE method (all compounds were applied in amounts of 80 microg) were about 98 and 94%, respectively. Almost 100% recoveries for paclitaxel and baseline separation of 10-DAB III and co-extracted compounds were obtained when preliminary elution with 30% methanol was performed. This method can be applied as a routine, inexpensive and uncomplicated procedure for 10-DAB III and related taxoids determination in yew material.

Screening for pharmaceutically important taxoids in Taxus baccata var. Aurea corr. with CC/SPE/HPLC-PDA procedure

Needles of 'the golden yew' Taxus baccata var. Aurea Corr. were extracted with methanol followed by pre-purification of the crude extract and column chromatographic (CC) separation on florisil in gradient mode (an increasing concentration of acetone in dichloromethane). The obtained fractions were concentrated and purified on silanized silica gel SPE cartridges and taxoids eluted with 75% methanol were analysed by HPLC-PDA procedure using Waters Symmetry C(18) column with gradient elution. The applied method enabled not only determination of four taxoids commonly occurring in yew extracts (10-deacetylbaccatin III, baccatin III, paclitaxel and cephalomannine), but also, on the basis of chromatographic behaviour and UV spectrum, 10-deacetylated taxoids (10-deacetylpaclitaxel, 10-deacetylcephalomannine, 7-xyloside-10-deacetylpaclitaxel and 10-deacetyltaxol C) could be detected together with 7-epi-10-deacetylpaclitaxel. From the needles of Taxus baccata var. Aurea Corr. the largest amounts isolated were of 10-deacetylbaccatin III, then 10-deacetylpaclitaxel and 7-xyloside-10-deacetylpaclitaxel, all compounds considered to be paclitaxel precursors in semisynthesis. The efficient mechanism of the separation of 10-acetylated taxoids from their 10-deacetylated derivatives on florisil on the basis of electron acceptor-electron donor interactions is discussed.

Screening of the needles of different yew species and cultivars for paclitaxel and related taxoids

The needles of several yew species and cultivars were analysed by high-pressure liquid chromatography for paclitaxel, 10-deacetylpaclitaxel, cephalomannine, baccatin III, 10-deacetylbaccatin III and brevifoliol. About 750 samples were collected from five different locations in the Netherlands and the UK. The results of this screening show a large variation in taxane content between the different species and cultivars. The content of paclitaxel and 10-deacetylbaccatin III varied from 0 to 500 micrograms/g and 0 to 4800 micrograms/g dried needles, respectively. Brevifoliol was found in a very high concentration in Taxus brevifolia. 10-Deacetylpaclitaxel, cephalomannine and baccatin III were found in concentrations ranging from 0 to 500 micrograms/g dried needles.

Seasonal changes in the concentrations of four taxoids in Taxus baccata L. during the autumn-spring period

The concentrations of four common taxoids: baccatin III, paclitaxel, cephalomannine and 10-deacetylbaccatin III (10-DAB III) were measured in fresh needles and stems of Taxus baccata L. during the late autumn-spring period (November'96-April'97) which has not been investigated to date in this species. Baccatin III, paclitaxel and 10-DAB III were present on the surface of the twigs in concentrations of 8-26 micrograms/1000 g (fresh weight). Changes in the levels of baccatin III and paclitaxel inside the needles and stems showed similar trends over the investigated period. From November to March the total level of taxoids differed between the needles and stems, and were the same only in April. Total levels in fresh needles were stable from December to March. The highest concentrations of 10-DAB III in the whole analysed period in fresh stems were measured, as well as in the fresh needles except for samples collected in November and December when the levels of cephalomannine were higher. The concentrations of paclitaxel were usually the lowest. These results confirm that epigenetic factors--date of collection (and thus phyllogenesis) and kind of plant tissue--determine taxoid levels during the late autumn-spring period in T. baccata. The opposite patterns of changes for 10-DAB III and cephalomannine, especially in the fresh needles, suggest a possible role for 10-DAB III in the biosynthetic pathway to cephalomannine, a less polar taxoid with a side-chain at position C-13. As well, owing to the thermolability of taxoids, the influence of low temperatures in December and January could explain the highest observed concentrations of 10-DAB III in the fresh stems and needles, respectively.

Cyclization of geranylgeranyl diphosphate to taxa-4(5),11(12)-diene is the committed step of taxol biosynthesis in Pacific yew

The biosynthesis of taxol (paclitaxel) and related taxoids in Pacific yew (Taxus brevifolia) is thought to involve the cyclization of geranylgeranyl diphosphate to a taxadiene followed by extensive oxygenation of this diterpene olefin intermediate. A cell-free preparation from sapling yew stems catalyzed the conversion of [1-3H]geranylgeranyl diphosphate to a cyclic diterpene olefin that, when incubated with stem sections, was converted in good radiochemical yield to several highly functionalized taxanes, including 10-deacetyl baccatin III and taxol itself. Addition of the labeled olefin to a yew bark extract, followed by radiochemically guided fractionation, provided sufficient product to establish the structure as taxa-4(5),11(12)-diene by two-dimensional NMR spectroscopic methods. Therefore, the first dedicated step in taxol biosynthesis is the conversion of the universal diterpenoid precursor geranylgeranyl diphosphate to taxa-4(5),11(12)-diene, rather than to the 4(20),11(12)-diene isomer previously suggested on the basis of the abundance of taxoids with double bonds in these positions. The very common occurrence of taxane derivatives bearing the 4(20)-ene-5-oxy functional grouping, and the lack of oxygenated derivatives bearing a 4(5)-double bond, suggest that hydroxylation at C-5 of taxadiene with allylic rearrangement of the double bond is an early step in the conversion of this olefin intermediate to taxol.