Structure elucidation of chlorophyll catabolites (phyllobilins) by ESI-mass spectrometry-Pseudo-molecular ions and fragmentation analysis of a nonfluorescent chlorophyll catabolite (NCC)

Structural Characterization, and Antioxidative and Anti-inflammatory Activities of Phylloxanthobilins in Tropaeolum majus, a Plant with Relevance in Phytomedicine

Tropaeolum majus (garden nasturtium) is a plant with relevance in phytomedicine, appreciated not only for its pharmaceutical activities, but also for its beautiful leaves and flowers. Here, we investigated the phytochemical composition of senescent nasturtium leaves. Indeed, we identified yellow chlorophyll catabolites, also termed phylloxanthobilins, which we show to contribute to the bright yellow color of the leaves in the autumn season. Moreover, we isolated and characterized the phylloxanthobilins from T. majus, and report the identification of a pyro-phylloxanthobilin, so far only accessible by chemical synthesis. We show that the phylloxanthobilins contribute to bioactivities of T. majus by displaying strong anti-oxidative effects in vitro and in cellulo, and anti-inflammatory effects as assessed by COX-1 and COX-2 enzyme inhibition, similar to other bioactive ingredients of T. majus, isoquercitrin, and chlorogenic acid. Hence, phylloxanthobilins could play a role in the efficacy of T. majus in the treatment of urinary tract infections, an established indication of T. majus. With the results shown in this study, we aid in the completion of the phytochemical profile of T. majus by identifying additional bioactive natural products as relevant components of this medicinal plant.

Chemical composition and effects of ethanolic extract and gel of Cochlospermum regium (Schrank) Pilg. Leaves on inflammation, pain, and wounds

ETHNOPHARMACOLOGICAL RELEVANCE

Cochlospermum regium is well-known as "Algodãozinho do cerrado" in folk Brazilian medicine, and is used to fight infections, inflammation and skin disorders.

AIM OF THE STUDY

To identify the phytochemical constituents and the effects of the ethanolic extract of C. regium leaves (EECR) on inflammation and pain, and the effects of C. regium gel (GEECR) on wound healing.

MATERIALS AND METHODS

Animals were treated with EECR (30-300 mg/kg) or GEECR (1.25 and 2.5%) and studies were conducted using carrageenan-induced pleurisy and paw edema tests, formalin-induced pain model, and excision wound model.

RESULTS

In total, 25 compounds, including quercitrin, methyl gallate, and 1,2,3,4,6-pentagalloylhexose, with highest detectability were identified. The treatments reduced leukocyte migration, nitric oxide production, protein extravasation, edema, mechanical hyperalgesia, pain in both phases (neurogenic and inflammatory), cold hypersensitivity, and improved wound closure and tissue regeneration.

CONCLUSIONS

The present findings established the anti-inflammatory, anti-nociceptive, and wound healing potential of the leaves of C. regium, confirming the potential therapeutic effect of this plant.

A yellow chlorophyll catabolite in leaves of Urtica dioica L.: An overlooked phytochemical that contributes to health benefits of stinging nettle

Stinging nettle is appreciated for its antioxidant and anti-inflammatory properties, which renders the plant a popular ingredient in a healthy diet in form of salads or smoothies. The most common use, presumably, is of dried leaves as ingredient in tea mixtures. The plant's health benefits are attributed primarily to phenolic phytochemicals. Here we describe the characterization and quantification of a phylloxanthobilin (PxB), a yellow chlorophyll catabolite, in nettle tea. Despite their abundance in the plant kingdom, chlorophyll catabolites have been overlooked as phytochemicals and as part of human nutrition. Our investigations of tea reveal that one cup of nettle tea contains about 50 µg of PxB with large variations depending on the supplier. When investigating the bioactivities of PxB, our observations show that PxB has antioxidative and anti-inflammatory activities comparable to known bioactive small molecules found in nettle, indicating the phylloxanthobilin to be an overlooked ingredient of nettle tea.

Chemical evidence of rare porphyrins in purple shells of Crassostrea gigas oyster

The colour of oyster shells is a very diverse characteristic morphotype, forming intriguing vivid patterns both on the inside and outside of the shell. In the present study, we have identified for the first time, the presence of several porphyrins as constituents of the shell pigmentation of the Crassostrea gigas oyster consumed worldwide. The precise molecular structures of halochromic, fluorescent and acid-soluble porphyrins, such as uroporphyrin and turacin, are unambiguously determined by reverse phase liquid chromatography combined with high resolution mass spectrometry. Their presence account for the purple colouration of shells but also for the dark colouration of adductor muscle scars. We have also defined the endogenous origin of these porphyrins, specifically secreted or accumulated by the shell forming tissue. These findings are pioneering analytical proofs of the existence of the haem pathway in the edible oyster Crassostrea gigas, evidenced by the chemical identification of haem side-products and supported by the recent publication of the corresponding oyster genome.

Profile of Chlorophyll Catabolites in Senescent Leaves of Epipremnun aureum Includes a Catabolite Esterified with Hydroxytyrosol 1-O-Glucoside

Despite the fact that chlorophyll degradation is a physiological phenomenon occurring daily in all photosynthetic tissues, chlorophyll catabolites are not fully identified. Three new forms (1, 3, and 4) of linear chlorophyll catabolites (phyllobilins) have been characterized in senescent leaves of Epipremnun aureum with spectroscopic data. Compound 1 is a hypermodified blue fluorescent chlorophyll catabolite (hmFCC) esterified with the potent antioxidant hydroxytyrosol. The sequestration of this phenol by a chlorophyll catabolite could explain the physiological meaning of the persistence of hmFCCs in some senescent plants. Compound 3, a yellow chlorophyll catabolite (YCC) originated from the oxidation at C-15 of 1. YCCs have been identified previously and are exclusively formed in the plant vacuole from the final nonfluorescent chlorophyll catabolites (NCCs). The presence of 3 in leaves implies a new reaction in chlorophyll catabolism, as the characterization of 3 implies that YCCs can be also be oxidized in the cytosol from FCCs. Finally, phyllobilin 4 represents a new type of YCC characterized by an inflexible bicyclo glucosyl moiety linked through an intramolecular esterification of the propionic acid residue with the C-3 hydroxy group. The corresponding NCC precursor was recently identified and now the characterization of 4 shows that even this rigid structure can be further oxidized. Undoubtedly, the characterization of phyllobilins is essential to completely comprehend chlorophyll degradation.

Effect-directed profiling and identification of bioactive metabolites from field, in vitro-grown and acclimatized Musa spp. accessions using high-performance thin-layer chromatography-mass spectrometry

Bananas and plantains (Musa spp.) are used as nutritious foods, and at the same time, are a source of phytoconstituents for the pharmaceutical industry. As biological activities of especially the pulp and peel of Musa spp. have been documented, this study investigated the variation in the secondary metabolite profiles of the leaves from field, in vitro-grown and acclimatized accessions. The genetic fidelity of the diverse accessions was assessed using diversity array technology sequencing. It showed that the in vitro-grown accessions were true-to-type with the field samples. The antioxidant and anticholinesterase activities of the samples from different culture systems (field and in vitro) were evaluated by UV-spectrophotometry and compared to high-performance thin-layer chromatography-effect-directed analysis (HPTLC-EDA). The latter was applied for the first time for effect-directed profiling of the polar and medium polar sample components via different biochemical and biological assays. Compound zones showed acetyl-/butylrylcholinesterase inhibition (zones 1-4), α-/β-glucosidase inhibition (zones 1 and 2) as well as antioxidative (zones 1-3) and antimicrobial (zone 4) activities. Structures were preliminary assigned by HPTLC-HRMS. The HPTLC was effective for bioactivity-guided characterization of the bioactive constituents in Musa spp. accessions. Accumulation of useful metabolites, especially compounds with antioxidant and anticholinesterase properties, was higher in samples from in vitro system. This validated the use of plant tissue culturing as an alternative method for large scale production of plant material and supply of bioactive constituents.

Isolation, characterization, and antioxidative activity of a dioxobilin-type phylloxanthobilin from savoy cabbage

The degradation of the green pigment chlorophyll in plants is known to yield phyllobilins as highly abundant linear tetrapyrroles. Recently, a split path of the degradation pathway has been discovered, leading to so-called dioxobilin-type (or type-II) phyllobilins. The first characterized type-II phyllobilin was colorless featuring four deconjugated pyrrole units. Similar to the type-I branch, for which yellow oxidation products of the colorless phyllobilins – the type-I phylloxanthobilins – are known, a type-II phylloxanthobilin has recently been characterized from senescent leaves of grapevine. Type-I phylloxanthobilins appear to be actively produced in the plant, are known to possess interesting chemical properties, and were shown to act as potent antioxidants that can protect cells from oxidative stress. Here we report the isolation and structural characterization of a type-II phylloxanthobilin from de-greened leaves of savoy cabbage, which turned out to be structurally closely related to bilirubin. Bilirubin is known to possess high antioxidative activity; in addition, savoy cabbage is considered to promote health benefits due to its high content in antioxidants. We therefore investigated the in vitro antioxidative potential of the newly identified type-II phylloxanthobilin using two different approaches, both of which revealed an even higher antioxidative activity for the type-II phylloxanthobilin from savoy cabbage compared to bilirubin.

Re-opening the stage for Echinacea research - Characterization of phylloxanthobilins as a novel anti-oxidative compound class in Echinacea purpurea

BACKGROUND

Phylloxanthobilins are tetrapyrrolic natural products that arise from the degradation of chlorophyll. Phylloxanthobilins have been discovered roughly 10 years ago in the leaves of deciduous trees, and are now considered a compound class with high and still unexplored potential of bioactivities. To date, however, there are no reports on the occurrence of phylloxanthobilins in parts of a medicinal plant used for pharmaceutical preparations.

PURPOSE

The relevance of Echinacea purpurea as medicinal plant is undoubtedly high, and a large variety of pharmaceutical preparations is available on the market, mostly for the treatment of the common cold. Nevertheless, its phytochemical profiling has been limited to analysis for previously characterized substances, and this has not explained all its pharmacological efficacies. We therefore set out to investigate the occurrence of phylloxanthobilins in Echinacea purpurea.

METHODS

Phylloxanthobilins in leaf extracts of Echinacea purpurea were detected using analytical HPLC. Identified phyllobilins were purified from plant material and characterized by UV/Vis, mass spectrometry, MS/MS, and confirmed by co-injections with previously published phyllobilins from different sources. The anti-oxidant activity of selected isolated phylloxanthobilins was assessed by an in vitro ferric reducing antioxidant power (FRAP) assay; in addition, the ability to scavenge ROS in cells caused by hydrogen peroxide stimulation was determined by measuring H₂DCF-DA fluorescence and by assessing cellular GSH levels.

RESULTS

In extracts of Echinacea purpurea leaves, an unprecedented diversity of phylloxanthobilins was detected; surprisingly, not only in senescent yellow leaves, but also in green leaves with no visible chlorophyll degradation. Six phylloxanthobilins were identified and structurally characterized. The uptake of phylloxanthobilins by human endothelial kidney cells was demonstrated. When investigating the anti-oxidative activity of these natural products, a potent in vitro activity was demonstrated; in addition, phylloxanthobilins possess intracellular ROS scavenging ability and can prevent oxidative stress as assessed by total cellular GSH levels.

CONCLUSION

Phylloxanthobilins are important constituents of Echinacea purpurea extracts, and our first exploratory studies hint towards promising bioactivities of these natural products, which may be relevant for understanding Echinacea efficacies.

Novel Types of Hypermodified Fluorescent Phyllobilins from Breakdown of Chlorophyll in Senescent Leaves of Grapevine (Vitis vinifera)

The tetrapyrrolic chlorophyll catabolites (or phyllobilins, PBs) were analyzed in yellow fall leaves of the grape Chardonnay, a common Vitis vinifera white wine cultivar. The major fractions in leaf extracts of V. vinifera, tentatively assigned to PBs, were isolated and their structures elucidated. The dominant fraction is a dioxobilin-type non-fluorescent Chl-catabolite of a previously observed type. Two less polar fluorescent PBs were characterized as a novel dioxobilin-type fluorescent Chl-catabolite with a bicyclo-1',6'-glycosyl architecture, and its new fluorescent formyloxobilin-type analogue. The discovery of persistent hypermodified fluorescent PBs with the architecture of bicyclo-[17.3.1]-PBs (bcPBs), suggests the activity of an unknown enzyme that forges the 20-membered macroring at the tetrapyrrolic core of a fluorescent PB. bcPBs may play specific physiological roles in grapevine plants and represent endogenous anti-infective agents, as found similarly for other organic bicyclo-[n.3.1]-1',6'-glycosyl derivatives.

Chlorophyll Breakdown in a Fern-Discovery of Phyllobilin Isomers with a Rearranged Carbon Skeleton

All structure-based information on chlorophyll (Chl) breakdown in the higher plants relies on studies with angiosperms. Herein, the first investigation of a fern is reported, revealing a novel type of Chl catabolites (phyllobilins) in leaves of this large division of the vascular plants, and providing structural insights into an astounding metabolic process of the higher plants that appears to have played a role even in early phases of plant evolution. The tetrapyrrolic Chl catabolites in the cosmopolitan bracken fern were discovered to be phyllobilin isomers with an unprecedented skeleton, proposed to be the striking result of a rearrangement of a hypothetical phyllobilin precursor.

The biochemistry and molecular biology of chlorophyll breakdown

Chlorophyll breakdown is one of the most obvious signs of leaf senescence and fruit ripening. The resulting yellowing of leaves can be observed every autumn, and the color change of fruits indicates their ripening state. During these processes, chlorophyll is broken down in a multistep pathway, now termed the 'PAO/phyllobilin' pathway, acknowledging the core enzymatic breakdown step catalysed by pheophorbide a oxygenase, which determines the basic linear tetrapyrrole structure of the products of breakdown that are now called 'phyllobilins'. This review provides an update on the PAO/phyllobilin pathway, and focuses on recent biochemical and molecular progress in understanding phyllobilin-modifying reactions as the basis for phyllobilin diversity, on the evolutionary diversity of the pathway, and on the transcriptional regulation of the pathway genes.

Chlorophyll Catabolites in Senescent Leaves of the Plum Tree (Prunus domestica)

In cold extracts of senescent leaves of the plum tree (Prunus domestica ssp. domestica), six colorless non-fluorescent chlorophyll catabolites (NCCs) were characterized, named Pd-NCCs. In addition, several minor NCC fractions were tentatively classified. The structure of the most polar one of the NCCs, named Pd-NCC-32, featured an unprecedented twofold glycosidation pattern. Three of the NCCs are also functionalized at their 32 -position by a glucopyranosyl group. In addition, two of these glycosidated NCCs carry a dihydroxyethyl group at their 18-position. In the polar Pd-NCC-32, the latter group is further glycosidated at the terminal 182 -position. Four other major Pd-NCCs and one minor Pd-NCC were identified with five NCCs from higher plants known to belong to the 'epi'-series. In addition, tentative structures were derived for two minor fractions, classified as yellow chlorophyll catabolites, which represented (formal) oxidation products of two of the observed Pd-NCCs. The chlorophyll catabolites in leaves of plum feature the same basic structural pattern as those found in leaves of apple and pear trees.

A liquid chromatography-mass spectrometry platform for the analysis of phyllobilins, the major degradation products of chlorophyll in Arabidopsis thaliana

During senescence, chlorophyll is broken down to a set of structurally similar, but distinct linear tetrapyrrolic compounds termed phyllobilins. Structure identification of phyllobilins from over a dozen plant species revealed that modifications at different peripheral positions may cause complex phyllobilin composition in a given species. For example, in Arabidopsis thaliana wild-type, eight different phyllobilins have structurally been characterized to date. Accurate phyllobilin identification and quantification, which classically have been performed by high performance liquid chromatography (HPLC) and UV/vis detection, are, however, hampered because of their similar physiochemical properties and vastly differing abundances in plant extracts. Here we established a rapid method for phyllobilin identification and quantification that couples ultra-HPLC with high-resolution/high-precision tandem mass spectrometry. Using Arabidopsis wild-type and mutant lines that are deficient in specific phyllobilin-modifying reactions, we identified a total of 16 phyllobilins, among them two that have not been described before in Arabidopsis. The single and collision-induced dissociation tandem mass spectrometry data of all 16 Arabidopsis phyllobilins were collected in a mass spectrometry library, which is available to the scientific community. The library allows rapid detection and quantification of phyllobilins within and across Arabidopsis genotypes and we demonstrate its potential use for high-throughput approaches and genome-wide association studies in chlorophyll breakdown. By extending the library with phyllobilin data from other plant species in the future, we aim providing a tool for chlorophyll metabolite analysis as a measure of senescence for practical applications, such as post-harvest quality control.

Breakdown of Chlorophyll in Higher Plants--Phyllobilins as Abundant, Yet Hardly Visible Signs of Ripening, Senescence, and Cell Death

Fall colors have always been fascinating and are still a remarkably puzzling phenomenon associated with the breakdown of chlorophyll (Chl) in leaves. As discovered in recent years, nongreen bilin-type Chl catabolites are generated, which are known as the phyllobilins. Collaborative chemical-biological efforts have led to the elucidation of the key Chl-breakdown processes in senescent leaves and in ripening fruit. Colorless and largely photoinactive phyllobilins are rapidly produced from Chl, apparently primarily as part of a detoxification program. However, fluorescent Chl catabolites accumulate in some senescent leaves and in peels of ripe bananas and induce a striking blue glow. The structural features, chemical properties, and abundance of the phyllobilins in the biosphere suggest biological roles, which still remain to be elucidated.

Chlorophyll catabolites in conditioned media of green microalga Desmodesmus subspicatus

Although the appearance of coloured chlorophyll degradation products of higher plants is well known, knowledge about such compounds produced and released particularly by planktonic algae is still limited. Colourless conditioned media (CM) obtained from autotrophic cultures of unicellular green alga Desmosdemus subspicatus turn red after acidification. The accumulation of red pigments in the medium and the growth rate of algae were inversely correlated. The red, crude solution isolated from CM by dialysis and ion exchange chromatography, and next purified by means of high-performance liquid chromatography, appeared to be a mixture of three compounds with characteristic UV/VIS absorption maxima near 330 and 505 nm. Electrospray ionization (ESI) mass spectrometry analysis revealed that the molecular mass of the most polar and most abundant compound was 637 Da and molecular masses of two other ones were 641 and 607 Da. Addition of ¹⁵ N isotope to the culture medium and subsequent mass spectrometry measurements revealed the occurrence of four nitrogen atoms per each molecule. The data suggest that red pigments isolated from algal-conditioned media are chlorophyll degradation compounds, the production of which depends on light intensity, and are released mainly during the stationary phase of growth.

Systematic HPLC/ESI-High Resolution-qTOF-MS Methodology for Metabolomic Studies in Nonfluorescent Chlorophyll Catabolites Pathway

Characterization of nonfluorescent chlorophyll catabolites (NCCs) and dioxobilane-type nonfluorescent chlorophyll catabolite (DNCC) in peel extracts of ripened lemon fruits (Citrus limon L.) was performed by HPLC/ESI-high resolution-qTOF-MS method. Compounds were identified in samples on the basis of measured accurate mass, isotopic pattern, and characteristic fragmentation profile with an implemented software postprocessing routine. Three NCC structures already identified in other vegetal tissues were present in the lemon fruit peels (Cl-NCC1; Cl-NCC2; Cl-NCC4) while a new structure not defined so far was characterized (Cl-NCC3). This catabolite exhibits an exceptional arrangement of the peripheral substituents, allowing concluding that the preferences for the NCC modifications could be a species-related matter.

Stereo- and regioselective phyllobilane oxidation in leaf homogenates of the peace lily (Spathiphyllum wallisii): hypothetical endogenous path to yellow chlorophyll catabolites

In senescent leaves, chlorophyll typically is broken down to colorless and essentially photo-inactive phyllobilanes, which are linear tetrapyrroles classified as “nonfluorescent” chlorophyll catabolites (NCCs) and dioxobilane-type NCCs (DNCCs). In homogenates of senescent leaves of the tropical evergreen Spathiphyllum wallisii, when left at room temperature and extracted with methanol, the major endogenous, naturally formed NCC was regio- and stereoselectively oxidized (in part) to a mixture of its 15-hydroxy and 15-methoxy derivative. In the absence of methanol in the extract, only the 15-OH-NCC was observed. The endogenous oxidation process depended upon molecular oxygen. It was inhibited by carbon monoxide, as well as by keeping the leaf homogenate and extract at low temperatures. The remarkable “oxidative activity” was inactivated by heating the homogenate for 10 min at 70 °C. Upon addition of a natural epimeric NCC (epiNCC) to the homogenate of senescent or green Sp. wallisii leaves at room temperature, the exogenous epiNCC was oxidized regio- and stereoselectively to 15-OH-epiNCC and 15-OMe-epiNCC. The identical two oxidized epiNCCs were also obtained as products of the oxidation of epiNCC with dicyanodichlorobenzoquinone (DDQ). Water elimination from 15-OH-epiNCC occurred readily and gave a known “yellow” chlorophyll catabolite (YCC). The endogenous oxidation process, described here, may represent the elusive natural path from the colorless NCCs to yellow and pink coloured phyllobilins, which were found in (extracts of) some senescent leaves.