Combined HPLC-MS and HPLC-NMR on-line coupling for the separation and determination of lutein and zeaxanthin stereoisomers in spinach and in retina

A mechanistic review on growing multiple therapeutic applications of lutein and its global market research

Lutein is a naturally occurring carotenoid synthesized by plants and algae that has a beneficial effect on several biological processes and associated ailments. Its immediate application is in ophthalmology, where it significantly lowers the incidences of age-related macular degeneration (AMD). It also has anti-inflammatory action, treatment of diabetic retinopathy, and cataracts, and enhancement of visual contrast. To critically assess lutein biosynthesis, therapeutic applicability, and market research literature. We have discussed its theoretical frameworks, experimental evidence, limitations, as well as clinical trial results, and future research prospects. The literature for this review article was mined and compiled by collecting and analyzing articles from several databases, including ScienceDirect, Google Scholar, PubMed, Wiley Online Library, Patentscope, and ClinicalTrials.gov published until March 30, 2022. Patent publications were identified using the search terms like IC:(C07C67/56) AND EN_AB:(lutein) OR EN_TI:(lutein) OR EN_AB:(extraction) OR EN_TI:(process). According to the literature, lutein is an essential nutrient given that it cannot be synthesized in the human body and acts as an antioxidant, affecting AMD, diabetic retinopathy, Rheumatic diseases, inflammation, and cancer. Due to inadequate production and laborious extraction, lutein is expensive despite its high demand and applicability. Market research predicts a 6.3% compound annual growth rate for lutein by 2032. Optimizing lutein extraction for high yield and purity is necessary. Lutein has proven applicability in various ailments as well as cosmetics that can be developed as a candidate drug for various diseases discussed in the review.

Isomerization of carotenoids in photosynthesis and metabolic adaptation

In nature, carotenoids are present as trans- and cis-isomers. Various physical and chemical factors like light, heat, acids, catalytic agents, and photosensitizers can contribute to the isomerization of carotenoids. Living organisms in the process of evolution have developed different mechanisms of adaptation to light stress, which can also involve isomeric forms of carotenoids. Particularly, light stress conditions can enhance isomerization processes. The purpose of this work is to review the recent studies on cis/trans isomerization of carotenoids as well as the role of carotenoid isomers for the light capture, energy transfer, photoprotection in light-harvesting complexes, and reaction centers of the photosynthetic apparatus of plants and other photosynthetic organisms. The review also presents recent studies of carotenoid isomers for the biomedical aspects, showing cis- and trans-isomers differ in bioavailability, antioxidant activity and biological activity, which can be used for therapeutic and prophylactic purposes.

Lutein Isomers: Preparation, Separation, Structure Elucidation, and Occurrence in 20 Medicinal Plants

Lutein and its cis-isomers occur in a lot of plants, including a variety of flowers. In this study, lutein isomers were produced via iodine-catalyzed isomerization, and four cis-isomers (9Z-, 9'Z-, 13Z-, and 13Z') were isolated by means of column chromatography and semipreparative HPLC. The structures of the 9'Z- and 13'Z-isomers were elucidated via NMR measurements. These compounds were used as standards for the HPLC-DAD-MS determination of the carotenoid composition of the flowers of 20 plant species, in which lutein and its geometrical isomers are the main components. The flowers showed great variation in their cis- and trans-lutein content, and also in the presence or absence of other carotenoids, such as violaxanthin, neoxanthin, β-cryptoxanthin, and β-carotene. Some of the investigated flowers were found to be rich sources of lutein without zeaxanthin.

Investigation on the changes of carotenoids and capsaicinoids in chili oil at different frying temperature by using 1H NMR

The color and pungency are important indicators for evaluating the quality of chili oil, which are mainly determined by the carotenoids and capsaicinoids, respectively. In this study, the effect of frying temperature on the changes of carotenoids and capsaicinoids in chili oil was qualitatively and quantitatively analyzed by ¹H NMR. The increasing frying temperature caused the thermal degradation of carotenoids to be intensified, and the degradation of red carotenoids was greater than that of yellow carotenoids. After 10 min of frying at 130, 150, 170 and 190 °C, the contents of capsanthin in chili oil were 40.3, 15.4, 9.6 and 6.2 mg/kg, respectively. Meanwhile, the contents of total carotenoids were 63.0, 25.5, 17.7 and 13.3 mg/kg, respectively. The observed change of R/Y values correlated well with the degradation of carotenoids. The contents of capsaicinoids were 14.8, 20.9, 19.4 and 7.4 mg/kg, respectively. The best frying temperature for the extraction of carotenoids was 130 °C, and over 90% of the carotenoids were dissolved in the frying oil at this frying condition. However, capsaicinoids were more stable than carotenoids, and the best frying temperature for capsaicinoids was 150-170 °C with over 90% extraction rate. Therefore, the temperature fried at 130-150 °C was suitable for the quality of chili oil, considering the higher extraction rates of both total carotenoids and capsaicinoids. This study is of great significance for the quality control of chili oil.

An efficient process for the extraction of lutein and chemical characterization of other organic volatiles from marigold (Tagetes erecta L.) flower

Marigold (Tagetes erecta L.) petals are the primary industrial source of lutein, which is used as a colouring agent and nutrient supplement to foods. This research extracted marigold petals using different solvents, covering conventional and non-toxic green solvents. The oleoresin, free lutein, and recrystallized lutein yields varied from 8.47-16.67%, 2.56-9.62%, and 1.11-1.61%, respectively. The purity of lutein was achieved up to 92.57% and 97.64% in conventional and newly established green methods, respectively. The present study described an efficient green process to isolate lutein with significantly improved yield (2.56%) and purity (97.33%) over the conventional methods. Based on the results, 2-methyltetrahydrofurancould be a practical green alternative to the traditional toxic solvents for the processing of lutein. Further, the chemical analysis of the essential oil of the residual receptacles obtained after removing petals revealed the presence of important organic volatiles, including piperitone (54.7%) and piperitenone oxide (6.5%), indicating its usefulness for value-addition.

Isolation and Analysis of Carotenoids in Hungary from Zechmeister until Today

László Zechmeister, one of the most important pioneers of carotenoid chemistry, died 50 years ago. He founded a carotenoid research group in Pécs (Hungary), which is the only place in the world where carotenoid research has been conducted continuously over the past 95 years. This review presents the life of Zechmeister and gives a summary about the evolution of the methods of analysis, isolation, and structure elucidation of carotenoids from the 1930s until today, based on the results of the research group founded by Zechmeister.

Antrocaryon amazonicum: An unexploited Amazonian fruit with high potential of scavenging reactive oxygen and nitrogen species

Antrocaryon amazonicum fruits are unexploited sources of bioactive compounds found in the Amazonia region of Brazil. In this study, for the first time, the carotenoid and phenolic compound profiles of the pulp and peel of A. amazonicum fruits, from two varieties at two harvest periods, were determined by LC-MS. Additionally, the potential of the peel and pulp extracts to scavenge physiologically relevant reactive oxygen species (ROS) and reactive nitrogen species (RNS) was assessed. The major carotenoids in both parts of the fruits were lutein, accounting for ≈42% of the identified carotenoids in the peel and ≈25% in the pulp, whereas catechin and hydroxybenzoic acid derivatives were the major phenolics in both parts. The peel extract, which presented the highest bioactive compound contents, was more efficient to scavenge ROS than the pulp. The peel extract showed high scavenging efficiency (IC₅₀ ) for singlet oxygen (¹ O₂ ; 16 µg/ml), hypochlorous acid (HOCl; 20 µg/ml), peroxynitrite (ONOO^- ; 38 µg/ml), and superoxide radical (O₂ ^•- ; 47 µg/ml), whereas the pulp extract exhibited high efficiency for ONOO^- (13 µg/ml), followed by HOCl (30 µg/ml), ¹O₂ (76 µg/ml), and less efficient for O₂ ^•- (44 µg/ml). Therefore, A. amazonicum fruits can be seen as an expressive source of bioactive compounds with high antioxidant potential to be further investigated to inhibit or delay oxidative processes both in food and physiological systems triggered by ROS and RNS. PRACTICAL APPLICATION: Bioactive compound extracts of Antrocaryon amazonicum fruits have high potential to be exploited for inhibiting or delaying oxidative processes and increase food stability.

LC–NMR for Natural Product Analysis: A Journey from an Academic Curiosity to a Robust Analytical Tool

Liquid chromatography (LC)–nuclear magnetic resonance (NMR) combines the advantage of the outstanding separation power of liquid chromatography (LC) and the superior structural elucidating capability of nuclear magnetic resonance (NMR). NMR has proved that it is a standout detector for LC by providing maximum structural information about plant originated extracts, particularly on the isolating ability of isomeric (same molecular formula) and/or isobaric (same molecular weight) compounds as compared to other detectors. The present review provides an overview of the developmental trends and application of LC–NMR in natural product analysis. The different LC–NMR operational modes are described, and how technical improvements assist in establishing this powerful technique as an important analytical tool in the analysis of complex plant-derived compounds is also highlighted. On-flow, stop-flow and loop-storage modes, as well as the new offline mode LC–solid phase extraction (SPE)–NMR and capillary LC (capLC)–NMR configurations which avoid the ingestion of expensive deuterated solvents throughout the experiment, are mentioned. Utilization of cryogenic probe and microprobe technologies, which are the other important promising approaches for guaranteeing sensitivity, are also described. Concluding remarks and future outlooks are also discussed.

Addition of either gastric lipase or cholesterol esterase to improve both β-cryptoxanthin ester hydrolysis and micellarization during in vitro digestion of fruit pulps

Using the INFOGEST in vitro digestion protocol adapted to carotenoids, the impact of additional rabbit gastric lipase (RGL) on the hydrolysis extent of β-cryptoxanthin esters was evaluated for the first time, and compared with the addition of porcine cholesterol esterase (CEL). Both the modifications increased the hydrolysis of (all-E)-β-cryptoxanthin esters from mandarin and peach pulps, although the outcomes were different. Addition of RGL consistently increased the average hydrolysis extent from 55.2% to 59.5% in mandarin pulp and from 22.7% to 48.8% in peach pulp (p < 0.05). The addition of CEL produced lower hydrolysis extents, i.e., 58.5% in mandarin (not statistically significant) and 28.4% in peach (p < 0.05), compared to those obtained with RGL. The hydrolysis extent positively correlated with the carotenoid ester concentration in both matrices. Bioaccessibility values were higher in mandarin pulp (range 32-34%) compared to those in peach pulp (range 16-21%), and were associated with the hydrolysis extent of the carotenoid esters during digestion. Addition of RGL and CEL produced no significant (p < 0.05) effect on the overall carotenoid bioaccessibility values of mandarin, while positively affected those in peach. Altogether these results corroborate that the hydrolysis extent of xanthophyll esters limits bioaccessibility. Additionally, hydrophobicity of the carotenoid inversely correlates with micellarization, as free (all-E)-xanthophylls micellarized in a higher extent compared to (all-E)-β-carotene and xanthophyll esters. The new information of our results is that the addition of rabbit gastric lipase substantially contributes to the hydrolysis of β-cryptoxanthin esters from fruit pulps, and consequently, to increase carotenoid bioaccessibility, being even more effective than CEL.

LC-NMR for Natural Products Analysis: A Journey from an Academic Curiosity to a Robust Analytical Tool

LC–NMR combines the advantage of the outstanding separation power of liquid chromatography (LC) and the superior structural elucidating capability of nuclear magnetic resonance (NMR). NMR has proved that it is a standout detector for LC by providing maximum structural information about plant originated extracts particularly in its isolating ability of isomeric (same molecular formula) and/or isobaric (same molecular weight) compounds as compared to other detectors. The present review provides an overview of the LC–NMR developmental trends and its application in natural products analysis. The different LC–NMR operational modes are described, as well as how technical improvements assist in establishing this powerful technique as an important analytical tool in the analysis of complex plant-derived compounds. On-flow, stop-flow and loop-storage modes, as well as the new offline mode LC–SPE–NMR and capLC-NMR configurations that avoid the ingestion of expensive deuterated solvents throughout the experiment are mentioned. Utilization of cryogenic probe and microprobe technologies which are the other important promising approaches for guaranteeing the sensitivity issues are also described. Concluding remarks and future outlooks are also discussed.

Bioaccessibility, cellular uptake and transport of luteins and assessment of their antioxidant activities

A rapid method for producing 9Z- and 13'Z-isomers from all-E-lutein was developed using I-TiO₂ as catalyst. In a simulated in vitro gastrointestinal digestion model, both trans-cis isomerization of all-E-lutein and cis-trans isomerization of Z-luteins occurred during the intestinal phase. The bioaccessibility of all isomers was between 14 and 23%, and it was higher for Z-luteins. In a Caco-2 cell monolayer model, all isomers were relatively stable during cellular uptake and transport across the membrane as no significant isomerization and degradation was detected, but all-E-lutein exhibited significantly higher cellular uptake and transport efficiencies. These results suggest that Z-luteins found in human plasma may likely be formed before intestinal absorption. 13'Z-Lutein also exhibited highest antioxidant activity in FRAP, DPPH and ORAC-L assays, but no significant difference in cell-based antioxidant assay compared with other isomers. Future studies on the different antioxidant activities of cis isomers of lutein in vivo will provide further explanation.

Chemical composition of microalgae Heterochlorella luteoviridis and Dunaliella tertiolecta with emphasis on carotenoids

BACKGROUND

Microalgae have been used as food supplements owing to their high protein, polyunsaturated fatty acid and carotenoid contents. As different carotenoids have distinct properties and the carotenoid composition of microalgae has been poorly explored in the literature, this study determined the complete carotenoid composition of two microalgae species, Heterochlorella luteoviridis and Dunaliella tertiolecta, using high-performance liquid chromatography coupled with diode array detection and tandem mass spectrometry (HPLC-DAD/MS² ). Additionally, the proximate composition and major minerals were evaluated.

RESULTS

The carotenoid composition of the two microalgae was similar, with 13 carotenoids being found in H. luteoviridis and 12 in D. tertiolecta. The major carotenoids were all-trans-lutein (1.18 mg g^-1 in H. luteoviridis and 1.59 mg g^-1 in D. tertiolecta), all-trans-violaxanthin (0.52 mg g^-1 in H. luteoviridis and 0.45 mg g^-1 in D. tertiolecta) and all-trans-β-carotene (0.50 mg g^-1 in H. luteoviridis and 0.62 mg g^-1 in D. tertiolecta). All-trans-lutein was the predominant carotenoid in both microalgae, representing around 40% (mass fraction) of the total carotenoids. The lutein content found in these microalgae was significantly higher (2-40 times) than that in other important food sources of lutein (e.g. parsley, carrot, red pepper and broccoli).

CONCLUSION

The microalgae H. luteoviridis and D. tertiolecta are excellent sources of lutein that could be commercially exploited by the food and pharmaceutical industries. Moreover, it was confirmed that both microalgae are good sources of protein, lipids and calcium. © 2016 Society of Chemical Industry.

The Pharmacological Effects of Lutein and Zeaxanthin on Visual Disorders and Cognition Diseases

Lutein (L) and zeaxanthin (Z) are dietary carotenoids derived from dark green leafy vegetables, orange and yellow fruits that form the macular pigment of the human eyes. It was hypothesized that they protect against visual disorders and cognition diseases, such as age-related macular degeneration (AMD), age-related cataract (ARC), cognition diseases, ischemic/hypoxia induced retinopathy, light damage of the retina, retinitis pigmentosa, retinal detachment, uveitis and diabetic retinopathy. The mechanism by which they are involved in the prevention of eye diseases may be due their physical blue light filtration properties and local antioxidant activity. In addition to their protective roles against light-induced oxidative damage, there are increasing evidences that L and Z may also improve normal ocular function by enhancing contrast sensitivity and by reducing glare disability. Surveys about L and Z supplementation have indicated that moderate intakes of L and Z are associated with decreased AMD risk and less visual impairment. Furthermore, this review discusses the appropriate consumption quantities, the consumption safety of L, side effects and future research directions.

Carotenoid esters in foods - A review and practical directions on analysis and occurrence

Carotenoids are naturally found in both free form and esterified with fatty acids in most fruits and some vegetables; however, up to now the great majority of studies presents data on carotenoid composition only after saponification. The reasons for this approach are that a single xanthophyll can be esterified with several different fatty acids, generating a great number of different compounds with similar chemical and structural characteristics, thus, increasing the complexity of analysis compared to the respective saponified extract. This means that since UV/Vis spectrum does not change due to esterification, differentiation between free and acylated xanthophylls is dependent at least on elution order and mass spectrometry (MS) features. The presence of interfering compounds, especially triacylglycerides (TAGs), in the non-saponified extract of carotenoids can also impair carotenoid ester analyses by MS due to high background noise and ionization suppression since TAGs can be present in much higher concentrations than the carotenoid esters. This leads to the need of development of new and effective clean-up procedures to remove the potential interferents. In addition, only few standards of xanthophyll esters are commercially available, making identification and quantification of such compounds even more difficult. Xanthophyll esterification may also alter some properties of these compounds, including solubility, thermostability and bioavailability. Considering that commonly consumed foods are dietary sources of xanthophyll esters and that it is the actual form of ingestion of such compounds, an increasing interest on the native carotenoid composition of foods is observed nowadays. This review presents a compilation of the current available information about xanthophyll ester analyses and occurrence and a practical guide for extraction, pre-chromatographic procedures, separation and identification by liquid chromatography-tandem mass spectrometry (LC-MS/MS).

Two-step cleanup procedure for the identification of carotenoid esters by liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry

Carotenoids are naturally found in both free form and esterified with fatty acids in most fruits; however, up to now the great majority of studies only evaluated their composition after saponification. This fact is easily explained by the difficult to analyze carotenoid esters. Preliminary studies showed that cleanup procedures in the extract are necessary for further analysis by LC-MS/MS since triacylglycerols (TAGs) impair the MS detection. Considering these facts, we developed a new cleanup procedure to remove TAGs and other lipids from carotenoid fruit extracts. This procedure is based on physical removal of solid lipids at low temperature followed by open column chromatography on MgO and diatomaceous earth. Before cleanup, four carotenoid diesters and two free xanthophylls were identified in murici (Byrsonyma crassifolia), corresponding to about 65% of the total chromatogram area. After carrying out the two-step cleanup procedure, 35 carotenoids were identified, being 14 monoesters, six free carotenoids and 15 carotenoid diesters. We can conclude that this two-step procedure was successfully applied to murici, an Amazonian fruit, which contains high amounts of lipids.

Structures and Analysis of Carotenoid Molecules

Modifications of the usual C40 linear and symmetrical carotenoid skeleton give rise to a wide array of structures of carotenes and xanthophylls in plant tissues. These include acyclic, monocyclic and dicyclic carotenoids, along with hydroxy and epoxy xanthophylls and apocarotenoids. Carotenols can be unesterified or esterified (monoester) in one or two (diester) hydroxyl groups with fatty acids. E-Z isomerization increases the array of possible plant carotenoids even further. Screening and especially quantitative analysis are being carried out worldwide. Visible absorption spectrometry and near infrared reflectance spectroscopy have been used for the initial estimation of the total carotenoid content or the principal carotenoid content when large numbers of samples needed to be analyzed within a short time, as would be the case in breeding programs. Although inherently difficult, quantitative analysis of the individual carotenoids is essential. Knowledge of the sources of errors and means to avoid them has led to a large body of reliable quantitative compositional data on carotenoids. Reverse-phase HPLC with a photodiode array detector has been the preferred analytical technique, but UHPLC is increasingly employed. HPLC-MS has been used mainly for identification and NMR has been useful in unequivocally identifying geometric isomers.

Direct observation of differences of carotenoid polyene chain cis/trans isomers resulting from structural topology

In the present paper, trapped ion mobility spectrometry (TIMS) and theoretical calculations have been used to study carotenoid geometrical motifs generated by photoisomerization from the all-trans geometry. Multiple geometric isomers of the carotenoids lutein and zeaxanthin were separated using TIMS (R > 110) for [M](+), [M + H](+), and [M - 18](+) molecular species. Comparison of observed cross sections with those obtained from molecular dynamics calculations showed that the number of cis double bonds and s-cis single bonds in the polyene chain determine the topology space of the carotenoid. The intensities of IMS signals are correlated with the relative stability of these geometric isomers.1,2 The most stable isomer is the all-trans geometry regardless of the ionization state ([M - 18](+), [M](+), and [M + H](+)), and structural stability decreases with the increasing number of cis and/or s-cis bonds in the polyene chain.

Red pepper (Capsicum annuum) carotenoids as a source of natural food colors: analysis and stability-a review

Carotenoids are increasingly drawing the attention of researchers as a major natural food color due to their inherent nutritional characteristics and the implicated possible role in prevention and protection against degenerative diseases. In this report, we review the role of red pepper as a source for natural carotenoids. The composition of the carotenoids in red pepper and the application of different methodologies for their analysis were discussed in this report. The stability of red pepper carotenoids during post-harvest processing and storage is also reviewed. This review highlights the potential of red pepper carotenoids as a source of natural food colors and also discusses the need for a standardized approach for the analysis and reporting of composition of carotenoids in plant products and designing model systems for stability studies.

Earthworm-derived pore-forming toxin lysenin and screening of its inhibitors

Lysenin is a pore-forming toxin from the coelomic fluid of earthworm Eisenia foetida. This protein specifically binds to sphingomyelin and induces erythrocyte lysis. Lysenin consists of 297 amino acids with a molecular weight of 41 kDa. We screened for cellular signal transduction inhibitors of low molecular weight from microorganisms and plants. The purpose of the screening was to study the mechanism of diseases using the obtained inhibitors and to develop new chemotherapeutic agents acting in the new mechanism. Therefore, our aim was to screen for inhibitors of Lysenin-induced hemolysis from plant extracts and microbial culture filtrates. As a result, we isolated all-E-lutein from an extract of Dalbergia latifolia leaves. All-E-lutein is likely to inhibit the process of Lysenin-membrane binding and/or oligomer formation rather than pore formation. Additionally, we isolated tyrosylproline anhydride from the culture filtrate of Streptomyces as an inhibitor of Lysenin-induced hemolysis.

Unravelling ionization and fragmentation pathways of carotenoids using orbitrap technology: a first step towards identification of unknowns

Vegetables are a major source of carotenoids and carotenoids are identified as potentially important natural antioxidants that may aid in the prevention of several human chronic degenerative diseases. Characterization of carotenoids in organic biological matrices is a crucial step in any research valorization trajectory. This study reports for the first time the use of high mass resolution and exact mass orbitrap technology for the elucidation of carotenoid fragmentation pathways. This contributes to the generation of new tools for identifying unknown carotenoids based on fragmentation patterns. Two different chromatographic methods making use of different mobile phases resulted in the generation of different ion species because of the large influence of the mobile phase solvent composition on ionization. It was shown that depending on the molecular ion species that are generated (protonated ions or radical molecular ions), different fragments are formed when applying higher energy collisional dissociation. Fragmentation and the abundance of fragments provide valuable structural information on the type of functional groups, the polyene backbone and the location of double bonds in ring structures of carotenoids. Furthermore, coherence between specific substructures in the molecules and characteristic fragmentation patterns was observed allowing the assignment of fragmentation patterns for carotenoid substructures that can theoretically be extrapolated to carotenoids with similar (sub)structures. Differentiation between isomeric carotenoids by compound specific fragments could however not be made for all the isomeric groups under study. As a wide variety of isomeric forms of carotenoids exist in nature, the combination of good chromatographic separation with high resolution mass spectrometry and other complementary qualitative structure elucidation techniques such as a photo diode array detector and/or nuclear magnetic resonance spectroscopy are indispensable for unambiguous identification of unknown carotenoids.

Promising interaction between nanoencapsulated lutein with low molecular weight chitosan: characterization and bioavailability of lutein in vitro and in vivo

This study aims to develop water-soluble low molecular weight chitosan (LMWC) nanoencapsules with lutein to improve its bioavailability. Lutein-LMWC nanoencapsules were prepared, characterized and bioavailability was studied in vitro and in vivo with lutein in mixed micelles (control). The particle size ranged between 80-600 nm, which was confirmed by Atomic Force Microscope. The interaction between LMWC and lutein in nanocencapsules by (1)H and (13)C NMR showed the essentiality of water molecules to hold the lutein between LMWC chains of nanoparticle with a reversible weak bond. Bioavailability of lutein (200 μM) in vitro showed that lutein-LMWC nanoencapsules was significantly higher (27.7%) than control. Postprandial lutein level in the plasma (54.5%), liver (53.9%) and eyes (62.8%) of mice fed on nanoencapsulated lutein were higher than the control. LMWC may serve as novel carrier for enhancing the lutein bioavailability and can be suggested as the better dietary compound in food and pharmaceutical applications.

Enzymatic formation of apo-carotenoids from the xanthophyll carotenoids lutein, zeaxanthin and β-cryptoxanthin by ferret carotene-9',10'-monooxygenase

Xanthophyll carotenoids, such as lutein, zeaxanthin and β-cryptoxanthin, may provide potential health benefits against chronic and degenerative diseases. Investigating pathways of xanthophyll metabolism are important to understanding their biological functions. Carotene-15,15'-monooxygenase (CMO1) has been shown to be involved in vitamin A formation, while recent studies suggest that carotene-9',10'-monooxygenase (CMO2) may have a broader substrate specificity than previously recognized. In this in vitro study, we investigated baculovirus-generated recombinant ferret CMO2 cleavage activity towards the carotenoid substrates zeaxanthin, lutein and β-cryptoxanthin. Utilizing HPLC, LC-MS and GC-MS, we identified both volatile and non-volatile apo-carotenoid products including 3-OH-β-ionone, 3-OH-α-ionone, β-ionone, 3-OH-α-apo-10'-carotenal, 3-OH-β-apo-10'-carotenal, and β-apo-10'-carotenal, indicating cleavage at both the 9,10 and 9',10' carbon-carbon double bond. Enzyme kinetic analysis indicated the xanthophylls zeaxanthin and lutein are preferentially cleaved over β-cryptoxanthin, indicating a key role of CMO2 in non-provitamin A carotenoid metabolism. Furthermore, incubation of 3-OH-β-apo-10'-carotenal with CMO2 lysate resulted in the formation of 3-OH-β-ionone. In the presence of NAD(+), in vitro incubation of 3-OH-β-apo-10'-carotenal with ferret hepatic homogenates formed 3-OH-β-apo-10'-carotenoic acid. Since apo-carotenoids serve as important signaling molecules in a variety of biological processes, enzymatic cleavage of xanthophylls by mammalian CMO2 represents a new avenue of research regarding vertebrate carotenoid metabolism and biological function.

Combining genomics, metabolome analysis, and biochemical modelling to understand metabolic networks

Now that complete genome sequences are available for a variety of organisms, the elucidation of gene functions involved in metabolism necessarily includes a better understanding of cellular responses upon mutations on all levels of gene products, mRNA, proteins, and metabolites. Such progress is essential since the observable properties of organisms – the phenotypes – are produced by the genotype in juxtaposition with the environment. Whereas much has been done to make mRNA and protein profiling possible, considerably less effort has been put into profiling the end products of gene expression, metabolites. To date, analytical approaches have been aimed primarily at the accurate quantification of a number of pre-defined target metabolites, or at producing fingerprints of metabolic changes without individually determining metabolite identities. Neither of these approaches allows the formation of an in-depth understanding of the biochemical behaviour within metabolic networks. Yet, by carefully choosing protocols for sample preparation and analytical techniques, a number of chemically different classes of compounds can be quantified simultaneously to enable such understanding. In this review, the terms describing various metabolite-oriented approaches are given, and the differences among these approaches are outlined. Metabolite target analysis, metabolite profiling, metabolomics, and metabolic fingerprinting are considered. For each approach, a number of examples are given, and potential applications are discussed.

An introduction to liquid chromatography-mass spectrometry instrumentation applied in plant metabolomic analyses

Over the past decade the application of non-targeted high-throughput metabolomic analysis within the plant sciences has gained ever increasing interest and has truly established itself as a valuable tool for plant functional genomics and studies of plant biochemical composition. Whilst proton nuclear magnetic resonance ((1)H-NMR) spectroscopy is particularly appropriate for the analysis of bulk metabolites and gas chromatography mass spectrometry (GC-MS) to the analysis of volatile organic compounds (VOC's) and derivatised primary metabolites, liquid chromatography (LC)-MS is highly applicable to the analysis of a wide range of semi-polar compounds including many secondary metabolites of interest to plant researchers and nutritionists. In view of the recent developments in the separation sciences, leading to the advent of ultra high performance liquid chromatography (UHPLC) and MS based technology showing the ever improving resolution of metabolite species and precision of mass measurements (sub-ppm accuracy now being achievable), this review sets out to introduce the background and update the reader upon LC, high performance (HP)LC and UHPLC, as well as the large range of MS instruments that are being applied in current plant metabolomic studies. As well as covering the theory behind modern day LC-MS, the review also discusses the most relevant metabolomics applications for the wide range of MS instruments that are currently being applied to LC.