In vitro formation of crocetin glucosyl esters by Crocus sativus callus extract

Research progress on the pharmacological activity, biosynthetic pathways, and biosynthesis of crocins

Crocins are water-soluble apocarotenoids isolated from the flowers of crocus and gardenia. They exhibit various pharmacological effects, including neuroprotection, anti-inflammatory properties, hepatorenal protection, and anticancer activity. They are often used as coloring and seasoning agents. Due to the limited content of crocins in plants and the high cost of chemical synthesis, the supply of crocins is insufficient to meet current demand. The biosynthetic pathways for crocins have been elucidated to date, which allows the heterologous production of these valuable compounds in microorganisms by fermentation. This review article provides a comprehensive overview of the chemistry, pharmacological activity, biosynthetic pathways, and heterologous production of crocins, aiming to lay the foundation for the large-scale production of these valuable natural products by using engineered microbial cell factories.

A New Glycosyltransferase Enzyme from Family 91, UGT91P3, Is Responsible for the Final Glucosylation Step of Crocins in Saffron (Crocus sativus L.)

Crocetin is an apocarotenoid formed from the oxidative cleavage of zeaxanthin, by the carotenoid cleavage enzymes CCD2 (in Crocus species) and specific CCD4 enzymes in Buddleja davidii and Gardenia jasminoides. Crocetin accumulates in the stigma of saffron in the form of glucosides and crocins, which contain one to five glucose molecules. Crocetin glycosylation was hypothesized to involve at least two enzymes from superfamily 1 UDP-sugar dependent glycosyltransferases. One of them, UGT74AD1, produces crocins with one and two glucose molecules, which are substrates for a second UGT, which could belong to the UGT79, 91, or 94 families. An in silico search of Crocus transcriptomes revealed six candidate UGT genes from family 91. The transcript profiles of one of them, UGT91P3, matched the metabolite profile of crocin accumulation, and were co-expressed with UGT74AD1. In addition, both UGTs interact in a two-hybrid assay. Recombinant UGT91P3 produced mostly crocins with four and five glucose molecules in vitro, and in a combined transient expression assay with CCD2 and UGT74AD1 enzymes in Nicotiana benthamiana. These results suggest a role of UGT91P3 in the biosynthesis of highly glucosylated crocins in saffron, and that it represents the last missing gene in crocins biosynthesis.

The effect of salt stress on the production of apocarotenoids and the expression of genes related to their biosynthesis in saffron

Saffron stigmas are widely used as food additives and as traditional medicine in Iran and many other countries. The unique taste, flavor and pharmaceutical properties of saffron stigmas are due to the presence of three apocarotenoids secondary metabolites crocin, picrocrocin and safranal. There is limited knowledge about the effect of environmental stresses on the metabolism of apocarotenoids in saffron. We analyzed the content of crocin and picrocrocin and the expression of key genes of apocarotenoid biosynthesis pathways (CsCCD2, CsCCD4, CsUGT2, CsCHY-β and CsLCYB) in saffron plants exposed to moderate (90 mM) and high (150 mM) salt (NaCl) concentrations. Measuring ion concentrations in leaves showed an increased accumulation of Na⁺ and decreased uptake of K⁺ in salt treated compared to control plants indicating an effective salt stress. HPLC analysis of apocarotenoids revealed that crocin production was significantly halted (P < 0.05) with increasing salt concentration while picrocrocin level did not change with moderate salt but significantly dropped by high salt concentration. Real-time PCR analysis revealed a progressive decrease in transcript levels of CsUGT2 and CsLCYB genes with increasing salt concentration (P < 0.05). The expression of CsCCD2 and CsCHY-β tolerated moderate salt concentration but significantly downregulated with high salt concentration. CsCCD4 however responded differently to salt concentration being decreased with moderate salt but increased at higher salt concentration. Our result suggested that salt stress had an adverse effect on the production of saffron apocarotenoids and it is likely influencing the quality of saffron stigma produced.

Impact of two different dehydration methods on saffron quality, concerning the prevalence of Saffron latent virus (SaLV) in Iran

The dehydration process is a prerequisite to preserve saffron for a long time. According to this process, saffron shows differences in the main compounds responsible for its quality (colour, taste, aroma, and flavonol content). At present, the freeze-drying method obtains dried products with the highest quality. Viruses can modify the physiology and metabolism of plants, being able to affect the activities of several enzymes. For this reason, the main compounds of saffron have been analyzed under two different dehydrating processes, freeze-drying and dark-drying, considering their infection status with the Saffron latent virus (SaLV). Results showed that the picrocrocin and safranal content enables to differ dark-dried samples from freeze-dried ones. Besides, the kaempferol-3-O-sophoroside-7-O-glucoside content allows differentiating between SaLV-infected (SaLV⁺) and uninfected (SaLV^-) saffron samples. Moreover, our data suggest that the freeze-drying would decrease crocins content, and dark-drying can nullify the adverse effect of SaLV on crocins content.

Effect of ultrasonic waves on crocin and safranal content and expression of their controlling genes in suspension culture of saffron (Crocus sativus L.)

The expression of biosynthesis controlling genes of crocin and safranal in saffron (Crocus sativus) can be influenced by ultrasonic waves. Sterilized saffron corms were cultured in a ½-MS medium supplemented by 2-4-D and BAP.  Saffron callus cells were treated with ultrasonic waves in a cellular suspension culture under optimal growth conditions. The samples were collected at 24 and 72 hours after treatment in three replications. The secondary metabolites were measured by high-performance liquid chromatography and the gene expression was analysed by the real-time polymerase chain reaction. Results indicate that this elicitor can influence the expressions of genes CsBCH, CsLYC and CsGT-2; the ultrasonic waves acted as an effective mechanical stimulus to the suspension cultures. The analysis of variance of the ultrasonically produced amounts of safranal and crocin indicates that there is a significant difference between once- and twice-treated samples in that the amount of safranal was the highest within the samples taken from the twice-treated suspension culture at 72 h after the ultrasound treatment, and the crocin was maximised after 24 h passed the twice-applied ultrasound treatment.

Anti-tumor effects of crocetin and related molecular targets

Natural products have gained a wide popularity as chemopreventive and anti-cancer agents owing to their multi-mechanistic mode of action, availability and synergism with several conventional chemotherapeutic agents. Crocetin is a carotenoid compound isolated from the stigma of Crocus sativus L. (saffron). Crocetin has shown promising effects as an anti-tumor agent in animal models and cell culture systems. Crocetin retards the growth of cancer cells via inhibiting nucleic acid synthesis, enhancing anti-oxidative system, and inducing apoptosis and differentiation pathways. The present review outlines natural sources of crocetin, and its pharmacokinetic and pharmacological properties relevant to the prevention and treatment of cancer. Also, we discuss molecular targets underlying the putative anti-tumor effects of crocetin.

Saffron: Its Phytochemistry, Developmental Processes, and Biotechnological Prospects

The present state of knowledge concerning developmental processes and the secondary metabolism of saffron, Crocus sativus L. (Iridaceae), along with the genes involved in these processes so far known, is reviewed. Flowers and corms constitute the most valuable parts of saffron. Corm and flower development are two key aspects to be studied in saffron to increase the yield and quality of the spice, to raise its reproductive rate, and to implement new production systems. Important knowledge about the physiology of flowering and vegetative growth has been acquired in recent years, but there is still only limited information on molecular mechanisms controlling these processes. Although some genes involved in flower formation and meristem transition in other species have been isolated in saffron, the role of these genes in this species awaits further progress. Also, genes related with the synthesis pathway of abscisic acid and strigolactones, growth regulators related with bud endodormancy and apical dominance (paradormancy), have been isolated. However, the in-depth understanding of these processes as well as of corm development is far from being achieved. By contrast, saffron phytochemicals have been widely studied. The different flower tissues and the corm have been proved to be an important source of phytochemicals with pharmacological properties. The biotechnological prospects for saffron are here reviewed on the basis of the discovery of the enzymes involved in key aspects of saffron secondary metabolism, and we also analyze the possibility of transferring current knowledge about flowering and vegetative propagation in model species to the Crocus genus.

Structural characterization of highly glucosylated crocins and regulation of their biosynthesis during flower development in Crocus

Crocin biosynthesis in Crocus has been proposed to proceed through a zeaxanthin cleavage pathway catalyzed by carotenoid cleavage dioxygenase 2 (CCD2), and followed by glucosylation reactions catalyzed by CsGT2 (UGT74AD1). In Crocus ancyrensis flowers, crocins with eight (crocin-1), seven (crocin-2), and six glucose (crocin-3) moieties accumulated both in stigma and tepals. We have characterized the structure of these highly glucosylated crocins and follow up their accumulation by high-resolution liquid chromatography coupled with diode array detector along the development of both tissues, and coupled to the isolation and analysis of the expression of eighteen genes (PSY-I, PSY-II, PDS-(I-V), ISO-ZDS, ZDS, CtrISO, LYC-I and II, BCH, CaCCD2, UGT74AD2-5) related with the apocarotenoid metabolism in C. ancyrensis tepals and stigmas. Structure elucidation of crocin-1 and crocin-2 was done by the combined use of 1D and 2D [(1)H, (1)H] (gCOSY and TOCSY and ROESY) and [(1)H-(13)C] NMR experiments, revealing that for crocin-1 was all-trans-crocetin O-[β-D- Glucopyranosyl)-(1→4)-(β-D-glucopyranosyl)-(1→2)]-O-[β-D-glucopyranosyl-(1→6)]-β-D-glucopyranosyl diester, while crocin-2 showed an identical structure except for the absence of one glucose residue in one end of the molecule. Crocins accumulation was not synchronically regulated in stigma and tepals, although in both cases crocins accumulation parallels tissue development, decreasing at anthesis. The expression of the carotenogenic genes PSY, ZDS-V, BCH, and LCY-II was correlated with crocins accumulation. In addition, CaCCD2 and only one of the four glucosyltransferase encoding genes, UGT74AD2, were highly expressed, and the expression was correlated with high levels of crocins accumulation in stigma and tepals.

Bioactivity assessment and toxicity of crocin: a comprehensive review

Since ancient times, saffron, the dried stigma of the plant Crocus sativus L. has been extensively used as a spice and food colorant; in folk medicine it has been reputed to be efficacious for the alleviation and treatment of ailments. In addition to the three founded major constituents including crocin, picrocrocin and safranal, presence of carotenoids, carbohydrates, proteins, anthocyanins, vitamins and minerals provide valuable insights into the health benefits and nutritional value of saffron. Of the carotenoids present in saffron, highly water-soluble crocin (mono and diglycosyl esters of a polyene dicarboxylic acid, named crocetin) is responsible for the majority of its color, and appears to possess various health-promoting properties, as an antioxidant, antitumor, memory enhancer, antidepressant, anxiolytic and aphrodisiac. It is also worth noting that the crocin principle of saffron exhibited high efficacy along with no major toxicity in experimental models. We would be remiss to not consider the great potential of saffron and crocin, which benefits the cuisine and health of human life throughout the world. The present study provides a comprehensive and updated report of empirical investigations on bioactivities and biological characteristics of crocin.

Crocins with high levels of sugar conjugation contribute to the yellow colours of early-spring flowering crocus tepals

Crocus sativus is the source of saffron spice, the processed stigma which accumulates glucosylated apocarotenoids known as crocins. Crocins are found in the stigmas of other Crocuses, determining the colourations observed from pale yellow to dark red. By contrast, tepals in Crocus species display a wider diversity of colours which range from purple, blue, yellow to white. In this study, we investigated whether the contribution of crocins to colour extends from stigmas to the tepals of yellow Crocus species. Tepals from seven species were analysed by UPLC-PDA and ESI-Q-TOF-MS/MS revealing for the first time the presence of highly glucosylated crocins in this tissue. β-carotene was found to be the precursor of these crocins and some of them were found to contain rhamnose, never before reported. When crocin profiles from tepals were compared with those from stigmas, clear differences were found, including the presence of new apocarotenoids in stigmas. Furthermore, each species showed a characteristic profile which was not correlated with the phylogenetic relationship among species. While gene expression analysis in tepals of genes involved in carotenoid metabolism showed that phytoene synthase was a key enzyme in apocarotenoid biosynthesis in tepals. Expression of a crocetin glucosyltransferase, previously identified in saffron, was detected in all the samples. The presence of crocins in tepals is compatible with the role of chromophores to attract pollinators. The identification of tepals as new sources of crocins is of special interest given their wide range of applications in medicine, cosmetics and colouring industries.

Comparative reverse screening approach to identify potential anti-neoplastic targets of saffron functional components and binding mode

BACKGROUND

In the last two decades, pioneering research on anti-tumour activity of saffron has shed light on the role of crocetin, picrocrocin and safranal, as broad spectrum anti-neoplastic agents. However, the exact mechanisms have yet to be elucidated. Identification and characterization of the targets of bioactive constituents will play an imperative role in demystifying the complex anti-neoplastic machinery.

METHODS

In the quest of potential target identification, a dual virtual screening approach utilizing two inverse screening systems, one predicated on idTarget and the other on PharmMapper was here employed. A set of target proteins associated with multiple forms of cancer and ranked by Fit Score and Binding energy were obtained from the two independent inverse screening platforms. The validity of the results was checked by meticulously analyzing the post-docking binding pose of the picrocrocin with Hsp90 alpha in AutoDock.

RESULTS

The docking pose reveals that electrostatic and hydrogen bonds play the key role in inter-molecular interactions in ligand binding. Picrocrocin binds to the Hsp90 alpha with a definite orientation appropriate for nucleophilic attacks by several electrical residues inside the Hsp90-alpha ATPase catalytic site.

CONCLUSION

This study reveals functional information about the anti-tumor mechanism of saffron bioactive constituents. Also, a tractable set of anti-neoplastic targets for saffron has been generated in this study which can be further authenticated by in vivo and in vitro experiments.

Role of saffron and its constituents on cancer chemoprevention

CONTEXT

Cancer dramatically impacts human life expectancy and quality of life. Natural substances from vegetables, herbs and spices could be beneficial in the prevention or treatment of a variety of cancers. Crocus sativus (Iridaceae), which has been used as a folk medicine for treating diseases for ages, showed obvious cancer chemoprevention potential.

OBJECTIVE

This article focuses on the effects of Crocus sativus and its main ingredients, such as crocin, on cancer therapeutics.

METHODS

We reviewed research data from saffron, a spice derived from the flower of Crocus sativus, and its constituents using the major databases, namely, Web of Science, SciFinder and PubMed.

RESULTS AND CONCLUSION

Saffron possesses free radical-scavenging properties and antitumor activities. Significant cancer chemopreventive effects have been shown in both in vitro and in vivo models. Based on current data, saffron and its ingredients could be considered as a promising candidate for clinical anticancer trials.

The anticancer effect of saffron in two p53 isogenic colorectal cancer cell lines

BACKGROUND

Saffron extract, a natural product, has been shown to induce apoptosis in several tumor cell lines. Nevertheless, the p53-dependency of saffron's mechanism of action in colon cancer remains unexplored.

MATERIAL AND METHODS

In order to examine saffron's anti-proliferative and pro-apoptotic effects in colorectal cancer cells, we treated two p53 isogenic HCT116 cell lines (HCT wildtype and HCT p53-/-) with different doses of the drug and analyzed cell proliferation and apoptosis in a time-dependent manner. MTT viability and crystal violet assays were performed in order to determine the effective dose of saffron on both cell lines. The cell cycle progress was examined by Flow cytometric analysis. Apoptosis was assessed using Annexin-PI-staining and Western Blotting for caspase 3 and PARP cleavage. Autophagy was determined by Western Blotting of the light chain 3 (LC3)-II and Beclin 1 proteins. The protein content of phospho-H2AX (γH2AX), a sensor of DNA double strand breaks, was also analyzed by Western Blotting.

RESULTS

Saffron extract induced a p53-dependent pattern of cell cycle distribution with a full G2/M stop in HCT116 p53 wildtype cells. However, it induced a remarkable delay in S/G2 phase transit with entry into mitosis in HCT116 p53 -/- cells. The apoptotic Pre-G1 cell fraction as well as Annexin V staining and caspase 3 cleavage showed a more pronounced apoptosis induction in HCT116 p53 wildtype cells. Obviously, the significantly higher DNA-damage, reflected by ɣH2AX protein levels in cells lacking p53, was coped by up-regulation of autophagy. The saffron-induced LC3-II protein level was a remarkable indication of the accumulation of autophagosomes, a response to the cellular stress condition of drug treatment.

CONCLUSIONS

This is the first study showing the effect of saffron in HCT116 colorectal cancer cells with different p53 status. Saffron induced DNA-damage and apoptosis in both cell lines. However, autophagy has delayed the induction of apoptosis in HCT116 p53 -/- cells. Considering the fact that most tumors show a functional p53 inactivation, further research is needed to elucidate the long-term effects of saffron in p53 -/- tumors.

UGT75L6 and UGT94E5 mediate sequential glucosylation of crocetin to crocin in Gardenia jasminoides

Crocin is an apocarotenoid glycosyl ester accumulating in fruits of Gardenia jasminoides and used as a food coloring and nutraceutical. For the first time, the two glucosyltransferases UGT75L6 and UGT94E5 that sequentially mediate the final glucosylation steps in crocin biosynthesis in G. jasminoides have been identified and functionally characterized. UGT75L6 preferentially glucosylates the carboxyl group of crocetin yielding crocetin glucosyl esters, while UGT94E5 glucosylates the 6' hydroxyl group of the glucose moiety of crocetin glucosyl esters. The expression pattern of neither UGT75L6 nor UGT94E5 correlated with the pattern of crocin accumulation in G. jasminoides.

The regulation of carotenoid pigmentation in flowers

Carotenoids fulfill many processes that are essential for normal growth and development in plants, but they are also responsible for the breathtaking variety of red-to-yellow colors we see in flowers and fruits. Although such visual diversity helps to attract pollinators and encourages herbivores to distribute seeds, humans also benefit from the aesthetic properties of flowers and an entire floriculture industry has developed on the basis that new and attractive varieties can be produced. Over the last decade, much has been learned about the impact of carotenoid metabolism on flower color development and the molecular basis of flower color. A number of different regulatory mechanisms have been described ranging from the transcriptional regulation of genes involved in carotenoid synthesis to the control of carotenoid storage in sink organs. This means we can now explain many of the natural colorful varieties we see around us and also engineer plants to produce flowers with novel and exciting varieties that are not provided by nature.

Saffron suppresses oxidative stress in DMBA-induced skin carcinoma: A histopathological study

Cancer chemoprevention is the use of natural, synthetic or biological substances to reverse or prevent the development of cancer. Saffron is a naturally derived plant product that acts as an antispasmodic, diaphoretic, carminative, emmenagogic and sedative. Our aim in this study was to investigate the chemopreventive effect of aqueous saffron on chemically induced skin carcinogenesis using a histopathological approach. Mice were divided into five groups: carcinogen control (CC), normal control (NC) and saffron-treated Groups A, B and C. Groups A, B, C and CC mice received three topical applications of 7,12 dimethylbenz[a]anthracene (DMBA) followed by croton oil on shaven dorsal skin for 8 weeks. NC mice received topical skin applications of the vehicle, acetone, only. Saffron infusion was fed orally to three groups of mice either before (Group A) or after (Group C) or both before and after (Group B) DMBA applications. The activities of antioxidant enzymes glutathione-S transferase (GST), glutathione peroxidase (GPx), catalase (CAT) and superoxide dismutase (SOD) in liver tissue samples taken at 0, 6, 10 and 12 weeks from all groups were assessed. Standard histological examination of skin demonstrated a beneficial action of saffron in mice where saffron treatments were given both before and after the induction of skin carcinogenesis. Saffron ingestion inhibited the formation of skin papillomas in animals and simultaneously reduced their size. In conclusion, saffron inhibits DMBA-induced skin carcinoma in mice when treated early. This may be due, at least in part, to the induction of cellular defense systems.

Digestion and absorption of carotenoids in sheep given fresh red clover

Digestion and absorption of carotenoids were studied in sheep given, twice daily, fresh red clover. Digestive fluxes were measured in six sheep cannulated in the rumen, duodenum and ileum using the double marker technique. Another five sheep were fitted with catheters allowing nutrient net flux measurements across the portal-drained viscera. Carotenoids in the red clover consisted of lutein (136 μg/g dry matter (DM)), epilutein (40 μg/g DM),trans-β-carotene (16 μg/g DM) and 13-cis-β-carotene (13 μg/g DM). Intake was 174, 52, 21 and 17 mg/day, and faecal excretion was 181, 25, 50 and 41 mg/day, for lutein, epilutein,trans- and 13-cis-β-carotene respectively, indicating net production of β-carotene in the digestive tract. The difference between duodenum and intake was positive for all carotenoids (30, 4, 43 and 37 g for lutein, epilutein,trans-β-carotene and 13-cis-β-carotene, respectively) suggesting net production and/or release of carotenes and xanthophylls by rumen microbes. Apparent digestibility in the small and large intestines was 0·18 and −0·05 for lutein, 0·30 and 0·29 for epilutein, 0·39 and 0·26 fortrans-β-carotene, 0·53 and 0·21 for 13-cis-β-carotene. Only lutein and epilutein were recovered in arterial plasma, at a concentration of 14·3 and 10·8 μg/l, respectively. Their portal net appearance was not different from 0, suggesting that absorption occurred mainly via the lymphatic system.

Glucosylation of the saffron apocarotenoid crocetin by a glucosyltransferase isolated from Crocus sativus stigmas

Saffron, the dry stigma of Crocus sativus L., is considered to be the world's most expensive spice. Three major apocarotenoids--crocin, crocetin and picrocrocin--are responsible for the colour and bitter taste of saffron. The final step in the biosynthesis of the 20-carbon esterified carotenoid crocin is the transformation of the insoluble crocetin into a soluble and stable storage form by glucosylation. These glucosylation reactions are catalysed by glucosyltransferases (GTases) that play a crucial role in natural-product biosynthesis. Using degenerate primers designed to match the plant secondary product GTase (PSPG) box we cloned two cDNAs, UGTCs2 and UGTCs3, from C. sativus stigmas that encode putative polypeptides of 460 and 475 amino acids, respectively. These genes were expressed differentially in saffron tissues. UGTCs2 was mainly expressed in fully developed stigmas, whereas UGTCs3 was mainly expressed in stamens. The UGTCs2 transcript was not detected in the stigma tissue of a Crocus species that does not synthesize crocin, while UGTCs3 and other structural genes for carotenoid biosynthesis were expressed in the stigma of all tested Crocus species. To identify the biochemical function of UGTCs2, the isolated cDNA was expressed in Escherichia coli cells. The recombinant protein UGTCs2 had glucosylation activity against crocetin, crocetin beta-D-glucosyl ester and crocetin beta-D-gentibiosyl ester. These results might suggest that the isolated clone UGTCs2 codes for a saffron crocetin GTase.

Cancer chemopreventive and tumoricidal properties of saffron (Crocus sativus L.)

Since cancer is the most common cause of death in the world population, the possibility that readily available natural substances from plants, vegetables, herbs, and spices may be beneficial in the prevention of cancer warrants closer examination. Saffron in filaments is the dried, dark red stigmata of Crocus sativus L. flowers and it is used as a spice, food colorant, and a drug in medicine. A growing body of research has demonstrated that saffron extract itself and its main constituents, the carotenoids, possess chemopreventive properties against cancer. This review discusses recent literature data and our results on the cancer chemopreventive activities of saffron and its main ingredients.