Isolation and quantification of tuliposides and tulipalins in tulips (Tulipa) by high-performance liquid chromatography

Identification of tuliposides K-M in tulip bulbs via an enzyme reaction-based screening method using a tuliposide-converting enzyme

Tuliposides (Pos) are major defense-related secondary metabolites in tulip, having 4-hydroxy-2-methylenebutanoyl and/or (3S)-3,4-dihydroxy-2-methylenebutanoyl groups at the C-1 and/or C-6 positions of d-glucose. The acyl group at the C-6 position is converted to antimicrobial lactones (tulipalins) by an endogenous Pos-converting enzyme. Based on this enzyme activity, we examined tulip bulb extracts and detected HPLC peaks that disappeared following the reaction by the Pos-converting enzyme. Spectroscopic analyses of the three purified compounds revealed that one of them was a glucose ester-type Pos, while the other two were identified as a glucoside ester-type Pos. These compounds were designated as PosK, L, and M. They were specific to bulbs, with the highest content in the outermost layer, but they were markedly less abundant than PosG, the minor bulb Pos we identified earlier. The study results suggest that tulip bulbs contain at least four minor Pos in addition to the major 6-PosA. Although PosK-M were present in almost all of the tested tulip cultivars, they were detected in only a few wild species, indicative of their potential utility as chemotaxonomic markers in tulip. Identification of PosK-M as 6-PosA derivatives unveils the biosynthetic diversity of Pos, the well-known group of secondary metabolites in tulip.

Tuliposides H-J and Bioactive Components from the Bulb of Amana edulis

Three new tuliposides H-J (1-3) and 11 known compounds were obtained from the methanolic extracts of the bulbs of Amana edulis for the first time. Their structures were elucidated by NMR, MS, and IR spectroscopic data, optical rotation, and Mosher's method. The melanogenesis properties of all the isolates were evaluated in B16 melanoma cells. Consequently, tributyl citrate (9) had anti-melanogenesis activity but was cytotoxic toward B16. (+)-Pyroglutamic acid (4), (+)-butyl 5-oxopyrrolidine-2-carboxylate (6), (-)-3-hydroxy-2-methylbutyrolactone (10), and 5-(hydroxymethyl)furfural (12) had increased melanin productions and tyrosinase activities. Those active components could be further studied as the candidates against melanoma and vitiligo for skin diseases or whitening/hypopigmentation for hair.

Identification of tuliposide G, a novel glucoside ester-type tuliposide, and its distribution in tulip

Tuliposides (Pos) are major defensive secondary metabolites in tulip (genus Tulipa), having 4-hydroxy-2-methylenebutanoyl and/or (3S)-3,4-dihydroxy-2-methylenebutanoyl groups at the C-1 and/or C-6 positions of d-glucose. The acyl group at the C-6 position is converted to antimicrobial lactones, tulipalins, by tuliposide-converting enzymes (TCEs). In the course of a survey of tulip tissue extracts to identify novel Pos, we found a minute high-performance liquid chromatography peak that disappeared following the action of a TCE, and whose retention time differed from those of known Pos. Spectroscopic analyses of the purified compound, as well as its enzymatic degradation products, revealed its structure as 5″-O-(6-O-(4'-hydroxy-2'-methylenebutanoyl))-β-d-glucopyranosyl-(2″R)-2″-hydroxymethyl-4″-butyrolactone, which is a novel glucoside ester-type Pos. We gave this compound the trivial name 'tuliposide G' (PosG). PosG accumulated in bulbs, at markedly lower levels than 6-PosA (the major Pos in bulbs), but was not found in any other tissues. Quantification of PosG in bulbs of 52 types of tulip, including 30 cultivars (Tulipa gesneriana) and 22 wild Tulipa spp., resulted in the detection of PosG in 28 cultivars, while PosG was present only in three wild species belonging to the subgenus Tulipa, the same subgenus to which tulip cultivars belong, suggesting the potential usefulness of PosG as a chemotaxonomic marker in tulip.

Isolation and identification of tuliposides D and F from tulip cultivars

6-Tuliposides A (6-PosA) and B (6-PosB) are major defensive secondary metabolites in tulip cultivars (Tulipa gesneriana), having an acyl group at the C-6 position of d-glucose. Although some wild tulip species produce 1,6-diacyl-glucose type of Pos (PosD and PosF), as well as 6-PosA/B, they have not yet been isolated from tulip cultivars. Here, aiming at verifying the presence of PosD and PosF in tulip cultivars, tissue extracts of 25 cultivars were analyzed by high-performance liquid chromatography (HPLC). Although no HPLC peaks for PosD nor PosF were detected in most cultivars, we found two cultivars giving a minute HPLC peak for PosD and the other two cultivars giving that for PosF. PosD and PosF were then purified from petals of cultivar 'Orca' and from pistils of cultivar 'Murasakizuisho', respectively, and their identities were verified by spectroscopic analyses. This is the first report that substantiates the presence of 1,6-diacyl-glucose type of Pos in tulip cultivars.

Substrate specificity of tuliposide-converting enzyme, a unique non-ester-hydrolyzing carboxylesterase in tulip: Effects of the alcohol moiety of substrate on the enzyme activity

6-Tuliposides A (PosA) and B (PosB) are glucose esters accumulated in tulip (Tulipa gesneriana) as major defensive secondary metabolites. Pos-converting enzymes (TgTCEs), which we discovered previously from tulip, catalyze the conversion reactions of PosA and PosB to antimicrobial tulipalins A (PaA) and B (PaB), respectively. The TgTCEs, belonging to the carboxylesterase family, specifically catalyze intramolecular transesterification, but not hydrolysis. In this report, we synthesized analogues of Pos with various alcohol moieties, and measured the TgTCE activity together with a determination of the kinetic parameters for these analogues with a view to probe the substrate recognition mechanism of the unique non-ester-hydrolyzing TgTCEs. It was found that d-glucose-like structure and number of the hydroxyl group in alcohol moiety are important for substrate recognition by TgTCEs. Among the analogues examined, 1,2-dideoxy analogues of PosA and PosB were found to be recognized by the TgTCEs more specifically than the authentic substrates by lowering K_m values. The present results will provide a basis for designing simple, stable synthetic substrate analogues for crystallographic analysis of TgTCEs.

One-Step Enzymatic Synthesis of 1-Tuliposide A Using Tuliposide-Converting Enzyme

6-Tuliposides A (6-PosA) and B (6-PosB) are major secondary metabolites in tulip (Tulipa gesneriana), having an acyl group at the C-6 position of D-glucose. They serve as precursors of the antimicrobial α-methylene-γ-butyrolactones tulipalins A (PaA) and B (PaB). The conversions of 6-PosA/6-PosB to PaA/PaB are catalyzed by tuliposide-converting enzymes A and B (TCEA and TCEB), respectively. A minor Pos, 1-PosA, which has the acyl group at the C-1 position of D-glucose, has been identified in some wild tulip species, but availability of this compound is limited. Here, by using the TCEs, we established a facile enzymatic process for 1-PosA synthesis from the naturally occurring 1,6-diacyl-glucose type of Pos (PosD and PosF). We first discovered that TCEA and TCEB react preferentially with PosD and PosF, respectively, to form 1-PosA and the corresponding Pa derived from the 6-acyl group, demonstrating that the TCEs specifically acted on the 6-acyl group, but not the 1-acyl group, of the substrates. Using TCEB, 300 mg of PosF was completely converted to 1-PosA and PaB in 10 min at room temperature. Then, 160 mg of 1-PosA (75% molar yield) was purified by column chromatography. This one-step enzymatic process dramatically improves accessibility to 1-PosA.

Molecular diversity of tuliposide B-converting enzyme in tulip (Tulipa gesneriana): identification of the third isozyme with a distinct expression profile

6-Tuliposide B (PosB), a major secondary metabolite that accumulates in tulip (Tulipa gesneriana), is converted to the antibacterial lactone, tulipalin B (PaB), by PosB-converting enzyme (TCEB). TgTCEB1 and TgTCEB-R, which encode TCEB, are specifically expressed in tulip pollen and roots, respectively, but are hardly expressed in other tissues (e.g. leaves) despite the presence of substantial PosB-converting activity, suggesting the existence of another TCEB isozyme. Here, we describe the identification of TgTCEB-L (“L” for leaf), a paralog of TgTCEB1 and TgTCEB-R, from leaves via native enzyme purification. The enzymatic characters of TgTCEB-L, including catalytic activity and subcellular localization, were substantially the same as those of TgTCEB1 and TgTCEB-R. However, TgTCEB-L did not exhibit tissue-specific expression. Identification of TgTCEB-L explains the PosB-converting activity detected in tissues where TgTCEB1 and TgTCEB-R transcripts could not be detected, indicating that tulip subtilizes the three TgTCEB isozymes depending on the tissue.

Contact dermatitis caused by tulips: identification of contact sensitizers in tulip workers of Kashmir Valley in North India

BACKGROUND

Tulip, belonging to the genus Tulipa and family Liliaceae, is a spring-blooming perennial that grows from bulbs. Owing to manual handling, contact dermatitis can occur in professionals at any stage of the growth cycle of the tulip plant.

OBJECTIVES

To determine the clinical pattern of contact dermatitis resulting from tulip plant cultivation, and to assess contact allergy in workers coming into contact with this plant.

METHODS

One hundred and sixty-four tulip workers were screened, and 48 patients with suspected contact dermatitis were patch tested with 39 allergens, including haptens from the Indian baseline series, a plant series, and extracts from different parts of the tulip plant.

RESULTS

Thirty-nine positive patch test reactions were observed in 21 patients. Seventeen patients showed positive reactions to either α-methylene-γ-butyrolactone or to tulip plant extract. Clinical relevance was observed for 13 of 17 positive patch test reactions.

CONCLUSIONS

Contact dermatitis is an important health hazard in workers dealing with tulip bulbs. Further studies to identify and isolate other possible tulip allergens, and to quantify the amounts of allergens in different parts of the tulip plant, are recommended.

Molecular identification of tuliposide B-converting enzyme: a lactone-forming carboxylesterase from the pollen of tulip

6-Tuliposides A (PosA) and B (PosB), which are the major secondary metabolites in tulip (Tulipa gesneriana), are enzymatically converted to the antimicrobial lactonized aglycons, tulipalins A (PaA) and B (PaB), respectively. We recently identified a PosA-converting enzyme (TCEA) as the first reported member of the lactone-forming carboxylesterases. Herein, we describe the identification of another lactone-forming carboxylesterase, PosB-converting enzyme (TCEB), which preferentially reacts with PosB to give PaB. This enzyme was isolated from tulip pollen, which showed high PosB-converting activity. Purified TCEB exhibited greater activity towards PosB than PosA, which was contrary to that of the TCEA. Novel cDNA (TgTCEB1) encoding the TCEB was isolated from tulip pollen. TgTCEB1 belonged to the carboxylesterase family and was approximately 50% identical to the TgTCEA polypeptides. Functional characterization of the recombinant enzyme verified that TgTCEB1 catalyzed the conversion of PosB to PaB with an activity comparable with the native TCEB. RT-qPCR analysis of each part of plant revealed that TgTCEB1 transcripts were limited almost exclusively to the pollen. Furthermore, the immunostaining of the anther cross-section using anti-TgTCEB1 polyclonal antibody verified that TgTCEB1 was specifically expressed in the pollen grains, but not in the anther cells. N-terminal transit peptide of TgTCEB1 was shown to function as plastid-targeted signal. Taken together, these results indicate that mature TgTCEB1 is specifically localized in plastids of pollen grains. Interestingly, PosB, the substrate of TgTCEB1, accumulated on the pollen surface, but not in the intracellular spaces of pollen grains.

Anti-oxidative and anti-inflammatory activities of caffeoyl hemiterpene glycosides from Spiraea prunifolia

Activity guided isolation of a Spiraea prunifolia extract yielded five caffeoyl hemiterpene glycosides: 4'-(6-O-caffeoyl-β-D-glucopyranosyl)-2'-methyl butyric acid, 1-O-caffeoyl-6-O-(4'-hydroxy-2'-methylene-butyroyl)-β-D-glucopyranoside, 1,2-O-dicaffeoyl-6-O-(4'-hydroxy-2'-methylene-butyroyl)-β-D-glucopyranoside, 1-O-caffeoyl-6-O-(4'-caffeoyl-2'-methylene-butyroyl)-β-D-glucopyranoside, and 1-O-caffeoyl-6-O-(4'-caffeoyl-3'-hydroxy-2'-methylene-butyroyl)-β-D-glucopyranoside, and nine known compounds. Structures were elucidated by analysis of 1D and 2D NMR spectra and FAB-MS. To evaluate the anti-oxidative and anti-inflammatory properties of all fourteen compounds, DPPH radical scavenging, NBT superoxide scavenging, and inhibition of nitric oxide production in LPS-stimulated RAW264.7 cells were examined. Three of the caffeoyl hemiterpene glycosides exhibited potent anti-oxidative and anti-inflammatory activities compared with Vitamin C and l-NMMA, which were used as positive controls.

Molecular diversity of tuliposide A-converting enzyme in the tulip

Tuliposide A-converting enzyme (TCEA) catalyzes the conversion of 6-tuliposide A to its lactonized aglycon, tulipalin A, in the tulip (Tulipa gesneriana). The TgTCEA gene, isolated previously from petals, was transcribed in all tulip tissues but not in the bulbs despite the presence of TCEA activity, which allowed prediction of the presence of a TgTCEA isozyme gene preferentially expressed in the bulbs. Here, the TgTCEA-b gene, the TgTCEA homolog, was identified in bulbs. TgTCEA-b polypeptides showed approximately 77% identity to the petal TgTCEA. Functional characterization of the recombinant enzyme verified that TgTCEA-b encoded the TCEA. Moreover, the TgTCEA-b was found to be localized to plastids, as found for the petal TgTCEA. Transcript analysis revealed that TgTCEA-b was functionally transcribed in the bulb scales, unlike the TgTCEA gene, whose transcripts were absent there. In contrast, TgTCEA-b transcripts were in the minority in other tissues where TgTCEA transcripts were dominant, indicating a tissue preference for the transcription of those isozyme genes.

A novel lactone-forming carboxylesterase: molecular identification of a tuliposide A-converting enzyme in tulip

Tuliposides, the glucose esters of 4-hydroxy-2-methylenebutanoate and 3,4-dihydroxy-2-methylenebutanoate, are major secondary metabolites in tulip (Tulipa gesneriana). Their lactonized aglycons, tulipalins, function as defensive chemicals due to their biological activities. We recently found that tuliposide-converting enzyme (TCE) purified from tulip bulbs catalyzed the conversion of tuliposides to tulipalins, but the possibility of the presence of several TCE isozymes was raised: TCE in tissues other than bulbs is different from bulb TCE. Here, to prove this hypothesis, TCE was purified from petals, which have the second highest TCE activity after bulbs. The purified enzyme, like the bulb enzyme, preferentially accepted tuliposides as substrates, with 6-tuliposide A the best substrate, which allowed naming the enzyme tuliposide A-converting enzyme (TCEA), but specific activity and molecular mass differed between the petal and bulb enzymes. After peptide sequencing, a novel cDNA (TgTCEA) encoding petal TCEA was isolated, and the functional characterization of the recombinant enzyme verified that TgTCEA catalyzes the conversion of 6-tuliposide A to tulipalin A. TgTCEA was transcribed in all tulip tissues but not in bulbs, indicating the presence of a bulb-specific TgTCEA, as suggested by the distinct enzymatic characters between the petal and bulb enzymes. Plastidial localization of TgTCEA enzyme was revealed, which allowed proposing a cytological mechanism of TgTCE-mediated tulipalin formation in the tulip defensive strategy. Site-directed mutagenesis of TgTCEA suggested that the oxyanion hole and catalytic triad characteristic of typical carboxylesterases are essential for the catalytic process of TgTCEA enzyme. To our knowledge, TgTCEA is the first identified member of the lactone-forming carboxylesterases, specifically catalyzing intramolecular transesterification.

Direct release of the allergen tulipalin A from Alstroemeria cut flowers: a possible source of airborne contact dermatitis?

The allergen tulipalin A was collected by dynamic headspace technique from cut flowers of 2 Alstroemeria hybrids and quantified and identified by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The amounts of tulipalin A released into the air were correlated with the tulipalin A and the total allergen content (tulipalin A and tuliposides) in the plant tissue, respectively. Tulipalin A was released primarily from the wounded areas, i.e. the stems, although small amounts were also emitted from the undamaged flowers in one of the hybrids. The tulipalin A concentrations in the stems of the Alstroemeria hybrids investigated were 0.06% and 0.13% of fresh weight, respectively, and the amounts directly released from the cut flowers were 0.4 and 2.2 microg (cut flower)(-1) h(-1), respectively. The content of tulipalin A exceeded that of tuliposides in leaves and flowers of both hybrids, whereas the content of tulipalin A in stems (in % fresh weight) was slightly lower than the content of tuliposides. The possibility that airborne tulipalin A from Alstroemeria could be a source of airborne contact dermatitis is discussed.