Neofunctionalization of an OMT cluster dominates polymethoxyflavone biosynthesis associated with the domestication of citrus

Polymethoxyflavones (PMFs) are a class of abundant specialized metabolites with remarkable anticancer properties in citrus. Multiple methoxy groups in PMFs are derived from methylation modification catalyzed by a series of hydroxylases and O-methyltransferases (OMTs). However, the specific OMTs that catalyze the systematic O-methylation of hydroxyflavones remain largely unknown. Here, we report that PMFs are highly accumulated in wild mandarins and mandarin-derived accessions, while undetectable in early-diverging citrus species and related species. Our results demonstrated that three homologous genes, CreOMT3, CreOMT4, and CreOMT5, are crucial for PMF biosynthesis in citrus, and their encoded methyltransferases exhibit multisite O-methylation activities for hydroxyflavones, producing seven PMFs in vitro and in vivo. Comparative genomic and syntenic analyses indicated that the tandem CreOMT3, CreOMT4, and CreOMT5 may be duplicated from CreOMT6 and contributes to the genetic basis of PMF biosynthesis in the mandarin group through neofunctionalization. We also demonstrated that N17 in CreOMT4 is an essential amino acid residue for C3-, C5-, C6-, and C3'-O-methylation activity and provided a rationale for the functional deficiency of OMT6 to produce PMFs in early-diverging citrus and some domesticated citrus species. A 1,041-bp deletion in the CreOMT4 promoter, which is found in most modern cultivated mandarins, has reduced the PMF content relative to that in wild and early-admixture mandarins. This study provides a framework for reconstructing PMF biosynthetic pathways, which may facilitate the breeding of citrus fruits with enhanced health benefits.

Identification of Polymethoxyflavones (PMFs) from Orange Peel and Their Inhibitory Effects on the Formation of Trimethylamine (TMA) and Trimethylamine-N-oxide (TMAO) Using cntA/B and cutC/D Enzymes and Molecular Docking

This study investigates the inhibitory effects of polymethoxyflavones (PMFs) on enzymes involved in the production of trimethylamine (TMA) and trimethylamine-N-oxide (TMAO). PMFs were isolated from Valencia orange peel and identified using column separation and NMR techniques. The findings reveal that nobiletin and 3,6,7,8,2',5'-hexamethoxyflavone significantly suppress cntA/B and cutC/D, respectively. Furthermore, 3,6,7,8,2',5'-hexamethoxyflavone decreases the level of TMAO formation by suppressing the FMO3 mRNA level. This study elucidates that specific structural features of PMFs can contribute to their interactions with enzymes. Our study represents the first demonstration of the ability of PMFs to mitigate the risk of cardiovascular disease (CVD) by inhibiting enzymes responsible for TMA production, which are generated by gut microbiomes. Furthermore, we introduce a novel model system utilizing TMA-induced HepG2 cells to assess and compare the inhibitory effects of PMFs on TMAO production. These findings could pave the way for the development of novel therapeutic approaches to manage CVD.

The Polymethoxyflavone Sudachitin Modulates the Circadian Clock and Improves Liver Physiology

SCOPE

Polymethoxylated flavones (PMFs) are a group of natural compounds known to display a wide array of beneficial effects to promote physiological fitness. Recent studies reveal circadian clocks as an important cellular mechanism mediating preventive efficacy of the major PMF Nobiletin against metabolic disorders. Sudachitin is a PMF enriched in Citrus sudachi, and its functions and mechanism of action are poorly understood.

METHODS AND RESULTS

Using circadian reporter cells, it shows that Sudachitin modulates circadian amplitude and period of Bmal1 promoter-driven reporter rhythms, and real-time qPCR analysis shows that Sudachitin alters expression of core clock genes, notably Bmal1, at both transcript and protein levels. Mass-spec analysis reveals systemic exposure in vivo. In mice fed with high-fat diet with or without Sudachitin, it observes increased nighttime activity and daytime sleep, accompanied by significant metabolic improvements in a circadian time-dependent manner, including respiratory quotient, blood lipid and glucose profiles, and liver physiology. Focusing on liver, RNA-sequencing and metabolomic analyses reveal prevalent diurnal alteration in both gene expression and metabolite accumulation.

CONCLUSION

This study elucidates Sudachitin as a new clock-modulating PMF with beneficial effects to improve diurnal metabolic homeostasis and liver physiology, suggesting the circadian clock as a fundamental mechanism to safeguard physiological well-being.

Endothelium-Independent Vasorelaxant Effects of Sudachitin and Demethoxysudachitin, Polymethoxyflavone from the Peel of Citrus sudachi on Isolated Rat Aorta

Although polymethoxyflavones have been reported to exhibit various pharmacological actions, the effects of polymethoxyflavones sudachitin and demethoxysudachitin from the peel of Citrus sudachi on the cardiovascular system have not been clarified. This study investigated the mechanisms of vasorelaxation induced by sudachitin and demethoxysudachitin in rat aorta. Both compounds inhibited phenylephrine-induced contractions in a concentration-dependent manner. This was also observed in the case of potassium chloride (KCl)-induced contractions although the inhibitory effect was weak. In both contraction types, no differences were found in the inhibitory effects of sudachitin and demethoxysudachitin between endothelium-intact and -denuded aorta. The relaxant effects of sudachitin in endothelium-intact aortas were not affected by the nitric oxide synthase inhibitor N-nitro-L-arginine methyl ester hydrochloride (L-NAME) or the cyclooxygenase inhibitor indomethacin. In endothelium-denuded aorta, propranolol did not affect the relaxant effect of sudachitin. Both the adenylate cyclase activator forskolin- and soluble guanylate cyclase activator sodium nitroprusside-induced relaxant effects were potentiated by preincubation of sudachitin. Furthermore, the relaxant effect of sudachitin was not affected by the adenylate and guanylate cyclase inhibitors SQ22536 and or 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxaline-1-one (ODQ), respectively. Finally, we examined the effect of phosphodiesterase inhibition. Phosphodiesterase inhibitors (3-isobutyl-1-methylxanthine, cilostamide or sildenafil) alone, sudachitin alone, and a combination of phosphodiesterase inhibitors with sudachitin exhibited relaxant effects, while the lack of any interaction between each phosphodiesterase inhibitor and sudachitin indicated an additive effect between the two substance categories. These results suggest that sudachitin and demethoxysudachitin cause endothelial-independent relaxation, and that the mechanism of vasorelaxation by sudachitin is associated with the enhancement of cAMP- and guanosine 3',5'-cyclic monophosphate (cGMP)-dependent pathways.

Preclinical Pharmacokinetic and Pharmacodynamic Investigation of 5'-Methoxynobiletin from Ageratum conyzoides: In vivo and In silico Approaches

PURPOSE

5'-methoxynobiletin (5'-MeONB), a polymethoxyflavone isolated from A. conyzoides, has shown anti-inflammatory property. Nevertheless, the antinociceptive activity and pre-clinical pharmacokinetics (PK) characteristics of 5'-MeONB remain unknown. Considering the anti-inflammatory potential of the 5'-MeONB, this study aimed to investigate the pre-clinical PK behavior of 5'-MeONB, as well as its time course antinociceptive activity.

METHODS

5'-MeONB plasma concentrations were determined in Wistar rats after intravenous (i.v.) (10 mg/kg) and oral (50 mg/kg) administration, and in Swiss mice after oral administration (100 mg/kg). Plasma samples were deproteinization and 5'-MeONB quantified by a validated UPLC-MS method. Additionally, the antinociceptive activity of 5'-MeONB was evaluated after 15, 30, 60, 180 and 360 min following oral administration on the acute nocifensive behavior of mice induced by formalin.

RESULTS

5'-MeONB rats and mice plasma concentration-time profiles were best one-compartment model. After i.v. administration to rats, a short half-life, a high clearance and moderate volume of distribution at steady state were observed. Similar results were obtained after oral administration. The oral bioavailability ranged from 8 to 11%. Additionally, 5'-MeONB exhibited antinociceptive activity in both formalin phases, especially in the inflammatory phase of the model, inhibiting 68% and 91% of neurogenic and inflammatory responses, respectively, after 30 min of oral administration.

CONCLUSIONS

The results described here provide novel insights on 5'-MeONB pharmacokinetics and pharmacodynamic effect, serving as support for future studies to confirm this compound as anti-nociceptive and anti-inflammatory effective agent.

Zapotin, a Polymethoxyflavone, with Potential Therapeutic Attributes

The use of plants as traditional medicines is common and has prevailed in many different cultures over time. Polymethoxyflavones (PMFs) are natural polyphenols from the group of flavonoids. Zapotin, a member of the PMFs, is found mainly in citrus plants and is almost exclusively limited to their peels. The chemical structure of zapotin has been questioned from the very beginning, since the structure of flavonoids with a single oxygen atom in the C2′ position is extremely rare in the plant kingdom. To clarify this, the structural determination and bio-inspired synthesis of zapotin are discussed in detail in this review. Due to the broad biological potential of PMFs, the complication in the isolation process and characterization of PMFs, as well as their purification, have been estimated by adapting various chromatographic methods. According to available data from the literature, zapotin may be a promising curative agent with extensive biological activities, especially as a chemopreventive factor. Apart from that, zapotin acts as an antidepressant-like, anticancer, antifungal, and antioxidant agent. Finally, accessible studies about zapotin metabolism (absorption, distribution, metabolism, excretion, and toxicity) underline its potential in use as a therapeutic substance.

Biotransformation and Quantification of Sinensetin and Its Metabolites in Plasma, Urine, and Feces of Rats

As one of the major polymethoxyflavones in citrus peels, sinensetin (Sin) has been reported to possess numerous bioactivities. However, its detailed in vivo metabolic fate has not been uncovered yet. In the present study, the possible metabolites of Sin were synthesized, and all five mono-demethylated metabolites were successfully identified via ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) analysis in rats fed with 100 mg/(kg·bw) Sin. The excretion and pharmacokinetic studies were then carried out to quantitatively investigate their variation in content with time in urine, feces, and plasma samples. Results showed that 4'-demethylsinensetin, 6-demethylsinensetin, and 3'-demethylsinensetin were the three most abundant metabolites generated in the above-mentioned biological samples. In addition, the total amount of Sin with its metabolites showed a significantly higher content in urine than in feces, indicating that Sin may be easily absorbed in the small intestine.

Nobiletin suppresses the development of experimental autoimmune encephalomyelitis mediated by modulation of T helper 17 cell differentiation

Multiple sclerosis is an organ-specific autoimmune disease that targets the myelin antigen in the central nervous system. Nobiletin is a dietary polymethoxylated flavonoid found in citrus fruits. In this study, we investigated how nobiletin affects the disease state and immune responses to myelin oligodendrocyte glycoprotein in experimental autoimmune encephalomyelitis mice. Nobiletin was administered orally from 14 days before immunization until the end of the experiment, and clinical scores were determined. The production levels of interleukin-17A and interferon-γ were measured in a culture supernatant of splenocytes stimulated with myelin oligodendrocyte glycoprotein. In addition, flow cytometric analysis was performed to examine the effect of nobiletin on T cell differentiation in vitro. Admin-istration of nobiletin significantly decreased the clinical score and interleukin-17A production in splenocytes. Furthermore, in vitro analysis showed that nobiletin significantly suppressed Th17 cell differentiation and interleukin-17A production in a dose-dependent manner. The results suggest that nobiletin attenuates experimental autoimmune encephalomyelitis severity through modulation of Th17 cell differentiation.

Polymethoxyflavones in orange peel extract prevent skeletal muscle damage induced by eccentric exercise in rats

Polymethoxyflavones (PMFs) contained in the peel of citrus fruits have anti-inflammatory, anticancer, and antidepressant effects. However, their effects on skeletal muscle are unknown. We investigated whether PMFs could prevent skeletal muscle damage induced by eccentric exercise in rats. Downhill running for 90 min increased the levels of the inflammatory cytokines, monocyte chemotactic protein-1 (MCP-1), and interleukin-1β (IL-1β) in skeletal muscles, especially in vastus lateralis, and the plasma creatine kinase levels. These increases were attenuated by a single oral administration of orange peel extract (OPE) 30 min before downhill running. A mixture of nobiletin, sinensetin, 3,5,6,7,8,3',4'-heptamethoxyflavone, and tangeretin, which are the major PMFs of OPE, also showed similar effects on muscle damage. These results suggest that OPE has a protective effect against eccentric exercise-induced skeletal muscle damage, and that the effects may be attributed to the 4 major PMFs.

Identification of Xanthomicrol as a Major Metabolite of 5-Demethyltangeretin in Mouse Gastrointestinal Tract and Its Inhibitory Effects on Colon Cancer Cells

5-Demethyltangeretin (5DT) is a unique polymethoxyflavone mainly found in the peel of citrus, and has shown potent suppressive effects on multiple human cancer cells. Biotransformation plays a critical role in the biological activities of dietary bioactive components because their metabolites may exert significant bioactivities. In the present study, the metabolic fate of 5DT in mouse gastrointestinal (GI) tract after long-term oral intake and the anti-cancer effects of its major metabolite were determined. It was found that 5DT underwent extensive biotransformation after oral ingestion in mice. A major demethylated metabolite was produced via phase I metabolism, while conjugates (glucuronide and sulfate) were generated via phase II metabolism. Specifically, 4'-position on the B ring of 5DT was the major site for demethylation reaction, which led to the production of xanthomicrol (XAN) as a major metabolite. More importantly, the level of XAN in the colon was significantly higher than that of 5DT in 5DT-fed mice. Thus, we further determined the suppressive effects of XAN on human colon cancer HCT116 cells. We found that XAN effectively inhibited the proliferation of HCT116 cells by arresting cell cycle and inducing cellular apoptosis, which was further evidenced by upregulated p53 and p21 and downregulated cyclin D and CDK4/6 level. In conclusion, this study identified XAN as a major metabolite of 5DT in mouse GI tract, and demonstrated its suppressive effects on HCT116 colon cancer cells.

Blockade of STAT3 Signaling Contributes to Anticancer Effect of 5-Acetyloxy-6,7,8,4'-Tetra-Methoxyflavone, a Tangeretin Derivative, on Human Glioblastoma Multiforme Cells

Glioblastoma multiforme (GBM) is the most aggressive primary brain tumor with poor prognosis, largely due to resistance to current radiotherapy and Temozolomide chemotherapy. The constitutive activation of Signal Transducer and Activator of Transcription 3 (STAT3) is evidenced as a pivotal driver of GBM pathogenesis and therapy resistance, and hence, is a promising GBM drug target. 5-acetyloxy-6,7,8,4'-tetramethoxyflavone (5-AcTMF) is an acetylated derivative of Tangeretin which is known to exert anticancer effects on breast, colon, lung, and multiple myeloma; however, its effect on GBM remains elusive. Herein, we reported that 5-AcTMF suppressed the viability and clonogenicity along with inducing apoptosis in multiple human GBM cell lines. Mechanistic analyses further revealed that 5-AcTMF lowered the levels of Tyrosine 705-phosphorylated STAT3 (p-STAT3), a canonical marker of STAT3 activation, but also dampened p-STAT3 upregulation elicited by Interleukin-6. Notably, ectopic expression of dominant-active STAT3 impeded 5-AcTMF-induced suppression of viability and clonogenicity plus apoptosis induction in GBM cells, confirming the prerequisite of STAT3 blockage for the inhibitory action of 5-AcTMF on GBM cell survival and growth. Additionally, 5-AcTMF impaired the activation of STAT3 upstream kinase JAK2 but also downregulated antiapoptotic BCL-2 and BCL-xL in a STAT3-dependent manner. Moreover, the overexpression of either BCL-2 or BCL-xL abrogated 5-AcTMF-mediated viability reduction and apoptosis induction in GBM cells. Collectively, we, for the first time, revealed the anticancer effect of 5-AcTMF on GBM cells, which was executed via thwarting the JAK2-STAT3-BCL-2/BCL-xL signaling axis. Our findings further implicate the therapeutic potential of 5-AcTMF for GBM treatment.

Three Polymethoxyflavones Purified from Ougan (Citrus reticulata Cv. Suavissima) Inhibited LPS-Induced NO Elevation in the Neuroglia BV-2 Cell Line via the JAK2/STAT3 Pathway

In order to establish an efficient method for separation of polymethoxyflavones (PMFs) and explore the anti-inflammatory mechanism of PMF monomers, a citrus variety rich in PMFs, Ougan (Citrus reticulata cv. Suavissima), was selected, and three monomers, including nobiletin, tangeretin, and 5-demethylnobiletin, were purified by ultrasonic-assisted extraction, solid phase extraction, and high-speed countercurrent chromatography separation. UPLC-MS was used to identify the three monomers. UPLC determined purities of 99.87% to nobiletin, 99.76% to tangeretin, and 98.75% to 5-demethylnobiletin with the standard curve method. A lipopolysaccharide (LPS)-induced NO releasing model was performed in the mouse microglia BV-2 cell line. Results illustrated that PMF monomers inhibited the NO release and the inflammation-related cytokines, including IL-1β, IL-6, and TNFα elevation. QRT-PCR revealed that PMFs alleviated LPS-induced upregulation of iNOS, IL-6, JAK2, TNFα, IL-1β, and NF-κB and LPS-induced downregulation of IκBα, while they did not affect TLR1, TLR2, TLR4, and TLR6. STAT3 expression was repressed by tangeretin and 5-demethylnobiletin, but not by nobiletin. Western blot assay also showed a suppression of expression and phosphorylation of JAK2 by all three PMF monomers, while STAT3 phosphorylation was restrained by tangeretin and 5-demethylnobiletin. The mechanism was primarily verified by the JAK2 inhibitor Ruxolitinib and the STAT3 inhibitor Stattic.

Polymethoxyflavones from Nicotiana plumbaginifolia (Solanaceae) Exert Antinociceptive and Neuropharmacological Effects in Mice

Polymethoxylavones (PMFs) are known to exhibit significant anti-inflammatory and neuroprotective properties. Nicotiana plumbaginifolia, an annual Bangladeshi herb, is rich in polymethoxyflavones that possess significant analgesic and anxiolytic activities. The present study aimed to determine the antinociceptive and neuropharmacological activities of polyoxygenated flavonoids namely- 3,3′,5,6,7,8-hexamethoxy-4′,5′-methylenedioxyflavone (1), 3,3′,4′,5′,5,6,7,8-octamethoxyflavone (exoticin) (2), 6,7,4′,5′-dimethylenedioxy-3,5,3′-trimethoxyflavone (3), and 3,3′,4′,5,5′,8-hexamethoxy-6,7-methylenedioxyflavone (4), isolated and identified from N. plumbaginifolia. Antinociceptive activity was assessed using the acetic-acid induced writhing, hot plate, tail immersion, formalin and carrageenan-induced paw edema tests, whereas neuropharmacological effects were evaluated in the hole cross, open field and elevated plus maze test. Oral treatment of compounds 1, 3, and 4 (12.5–25 mg/kg b.w.) exhibited dose-dependent and significant (p < 0.01) antinociceptive activity in the acetic-acid, formalin, carrageenan, and thermal (hot plate)-induced pain models. The association of ATP-sensitive K⁺ channel and opioid systems in their antinociceptive effect was obvious from the antagonist effect of glibenclamide and naloxone, respectively. These findings suggested central and peripheral antinociceptive activities of the compounds. Compound 1, 3, and 4 (12.5 mg/kg b.w.) demonstrated significant (p < 0.05) anxiolytic-like activity in the elevated plus-maze test, while the involvement of GABA_A receptor in the action of compound 3 and 4 was evident from the reversal effects of flumazenil. In addition, compounds 1 and 4 (12.5–25 mg/kg b.w) exhibited anxiolytic activity without altering the locomotor responses. The present study suggested that the polymethoxyflavones (1–4) from N. Plumbaginifolia could be considered as suitable candidates for the development of analgesic and anxiolytic agents.

Demethylation of Polymethoxyflavones by Human Gut Bacterium, Blautia sp. MRG-PMF1

Polymethoxyflavones (PMFs) were biotransformed to various demethylated metabolites in the human intestine by the PMF-metabolizing bacterium, Blautia sp. MRG-PMF1. Because the newly formed metabolites can have different biological activities, the pathways and regioselectivity of PMF bioconversion were investigated. Using an anaerobic in vitro study, 12 PMFs, 5,7-dimethoxyflavone (5,7-DMF), 5-hydroxy-7-methoxyflavone (5-OH-7-MF), 3,5,7-trimethoxyflavone (3,5,7-TMF), 5-hydroxy-3,7-dimethoxyflavone (5-OH-3,7-DMF), 5,7,4'-trimethoxyflavone (5,7,4'-TMF), 5-hydroxy-7,4'-dimethoxyflavone (5-OH-7,4'-DMF), 3,5,7,4'-tetramethoxyflavone (3,5,7,4'-TMF), 5-hydroxy-3,7,4'-trimethoxyflavone (5-OH-3,7,4'-TMF), 5,7,3',4'-tetramethoxyflavone (5,7,3',4'-TMF), 3,5,7,3',4'-pentamethoxyflavone (3,5,7,3',4'-PMF), 5-hydroxy-3,7,3',4'-tetramethoxyflavone (5-OH-3,7,3',4'-TMF), and 5,3'-dihydroxy-3,7,4'-trimethoxyflavone (5,3'-diOH-3,7,4'-TMF), were converted to chrysin, apigenin, galangin, kaempferol, luteolin, and quercetin after complete demethylation. The time-course monitoring of PMF biotransformations elucidated bioconversion pathways, including the identification of metabolic intermediates. As a robust flavonoid demethylase, regioselectivity of PMF demethylation generally followed the order C-7 > C-4' ≈ C-3' > C-5 > C-3. PMF demethylase in the MRG-PMF1 strain was suggested as a Co-corrinoid methyltransferase system, and this was supported by the experiments utilizing other methyl aryl ether substrates and inhibitors.

Permeation of Polymethoxyflavones into the Mouse Brain and Their Effect on MK-801-Induced Locomotive Hyperactivity

Accumulating data have indicated that citrus polymethoxyflavones (PMFs) have the ability to affect brain function. In the present study, we showed that 3,5,6,7,8,3',4'-heptamethoxy- flavone (HMF) given intraperitoneally to mice was immediately detected in the brain and that the permeability of the brain tissues to it was significantly higher than that of other citrus PMFs (nobiletin, tangeretin, and natsudaidain). The permeation of these PMFs into the brain well correlated with their abilities to suppress MK-801-induced locomotive hyperactivity, suggesting that HMF had the ability to act directly in the brain. We also obtained data suggesting that the suppressive effect of HMF on MK-801-induced locomotive hyperactivity was mediated by phosphorylation of extracellular signal-regulated kinases 1/2 (ERK1/2) in the hippocampus.

Characterization and Modulation of the Bitterness of Polymethoxyflavones Using Sensory and Receptor-Based Methods

An obstacle in the application of many "health ingredients" is their alleged off-flavor. We used a combination of chemical, sensory, and biological analyses to identify the bitter components in citrus peel-derived polymethoxyflavone preparations, claimed to be functional in the lowering of cholesterol. Nobiletin (56-81%) and tangeretin (10-33%) were found to be the main bitter components. Using in vitro receptor assays, hTAS2R14 was shown to be the main bitter receptor involved in their perception, with EC50 values of 14 and 63 μM, respectively. Our analysis provided several routes for off-flavor reduction. Purification is an option because a purified, single PMF species proved to be considerably less bitter upon application in emulsified foods, due to limited solubility in the aqueous phase. A second route, also demonstrated in vivo, is C5-specific demethoxylation, in line with the finding that 5-desmethylnobiletin does not activate hTAS2R14. A third route could be the use of TAS2R14 antagonists. As a proof of principle, several antagonists, with IC50 values ranging from 10 to 50 μM, were identified.

Direct Fluorescent Detection of a Polymethoxyflavone in Cell Culture and Mouse Tissue

Convenient detection methods for bioactive food compounds and their metabolites in biological samples are needed to better understand their mechanism of actions. Herein, we developed a novel approach to directly monitor and visualize the distribution of 5,3',4'-tridemethylnobiletin (TDN), a unique polymethoxyflavone metabolite derived from citrus polymethoxyflavone, in biological samples such as cultured cells and mouse colonic tissues. Our results showed that a fluorescent conjugate could be formed between TDN and 2-aminoethyl diphenyl borate (DPBA) under simple reaction conditions, which was confirmed by both Raman spectroscopy and mass spectroscopy. We further demonstrated the application of DPBA-based conjugation reaction in the characterization of TDN in different biological samples including floating cells, adherent cells, and animal tissues. This is the first report demonstrating direct fluorescent detection of polymethoxyflavone in biological samples.

Cytotoxic, Antiproliferative and Pro-Apoptotic Effects of 5-Hydroxyl-6,7,3',4',5'-Pentamethoxyflavone Isolated from Lantana ukambensis

Lantana ukambensis (Vatke) Verdc. is an African food and medicinal plant. Its red fruits are eaten and highly appreciated by the rural population. This plant was extensively used in African folk medicinal traditions to treat chronic wounds but also as anti-leishmanial or cytotoxic remedies, especially in Burkina Faso, Tanzania, Kenya, or Ethiopia. This study investigates the in vitro bioactivity of polymethoxyflavones extracted from a L. ukambensis as anti-proliferative and pro-apoptotic agents. We isolated two known polymethoxyflavones, 5,6,7,3′,4′,5′-hexamethoxyflavone (1) and 5-hydroxy-6,7,3′,4′,5′-pentamethoxyflavone (2) from the whole plant of L. ukambensis. Their chemical structures were determined by spectroscopic analysis and comparison with published data. These molecules were tested for the anti-proliferative, cytotoxic and pro-apoptotic effects on human cancer cells. Among them, 5-hydroxy-6,7,3′,4′,5′-pentamethoxyflavone (2) was selectively cytotoxic against monocytic lymphoma (U937), acute T cell leukemia (Jurkat), and chronic myelogenous leukemia (K562) cell lines, but not against peripheral blood mononuclear cells (PBMCs) from healthy donors, at all tested concentrations. Moreover, this compound exhibited significant anti-proliferative and pro-apoptotic effects against U937 acute myelogenous leukemia cells. This study highlights the anti-proliferative and pro-apoptotic effects of 5-hydroxy-6,7,3′,4′,5′-pentamethoxyflavone (2) and provides a scientific basis of traditional use of L. ukambensis.

Influence of processing parameters on morphology of polymethoxyflavone in emulsions

Polymethoxyflavones (PMFs) are groups of compounds isolated from citrus peels that have been documented with wide arrays of health-promoting bioactivities. Because of their hydrophobic structure and high melting point, crystallized PMFs usually have poor systemic bioavailability when consumed orally. To improve the oral efficiency of PMFs, a viscoelastic emulsion system was formulated. Because of the crystalline nature, the inclusion of PMFs into the emulsion system faces great challenges in having sufficient loading capacity and stabilities. In this study, the process of optimizing the quality of emulsion-based formulation intended for PMF oral delivery was systematically studied. With alteration of the PMF loading concentration, processing temperature, and pressure, the emulsion with the desired droplet and crystal size can be effectively fabricated. Moreover, storage temperatures significantly influenced the stability of the crystal-containing emulsion system. The results from this study are a good illustration of system optimization and serve as a great reference for future formulation design of other hydrophobic crystalline compounds.

Metabolism of Kaempferia parviflora polymethoxyflavones by human intestinal bacterium Bautia sp. MRG-PMF1

Poylmethoxyflavones (PMFs) are major bioactive flavonoids, which exhibit various biological activities, such as anticancer effects. The biotransformation of PMFs and characterization of a PMF-metabolizing human intestinal bacterium were studied herein for the first time. Hydrolysis of aryl methyl ether functional groups by human fecal samples was observed from the bioconversion of various PMFs. Activity-guided screening for PMF-metabolizing intestinal bacteria under anaerobic conditions resulted in the isolation of a strict anaerobic bacterium, which was identified as Blautia sp. MRG-PMF1. The isolated MRG-PMF1 was able to metabolize various PMFs to the corresponding demethylated flavones. The microbial conversion of bioactive 5,7-dimethoxyflavone (5,7-DMF) and 5,7,4'-trimethoxyflavone (5,7,4'-TMF) was studied in detail. 5,7-DMF and 5,7,4'-TMF were completely metabolized to 5,7-dihydroxyflavone (chrysin) and 5,7,4'-trihydroxyflavone (apigenin), respectively. From a kinetics study, the methoxy group on the flavone C-7 position was found to be preferentially hydrolyzed. 5-Methoxychrysin, the intermediate of 5,7-DMF metabolism by Blautia sp. MRG-PMF1, was isolated and characterized by nuclear magnetic resonance spectroscopy. Apigenin was produced from the sequential demethylation of 5,7,4'-TMF, via 5,4'-dimethoxy-7-hydroxyflavone and 7,4'-dihydroxy-5-methoxyflavone (thevetiaflavone). Not only demethylation activity but also deglycosylation activity was exhibited by Blautia sp. MRG-PMF1, and various flavonoids, including isoflavones, flavones, and flavanones, were found to be metabolized to the corresponding aglycones. The unprecedented PMF demethylation activity of Blautia sp. MRG-PMF1 will expand our understanding of flavonoid metabolism in the human intestine and lead to novel bioactive compounds.