Pharmacological properties of traditional medicines. XXII. Pharmacokinetic study of mulberroside A and its metabolites in rat

Metabolite identification and excretion of pinocembrin-7-O-β-D-glucoside in rats by UHPLC/MS

Pinocembrin-7-O-β-D-glucoside (PCBG) isolated from Penthorum chinense Pursh was proven to display a wide range of pharmacological effects including hepatoprotection, anti-hepatoma and antifungal activities, etc. The research aims to qualitatively analyze the metabolites of PCBG in rat plasma, urine, bile and feces, and further perform the excretion study of PCBG and its major metabolite pinocembrin (PCB). Fifteen rats were divided into three groups (n=5 for each group) for blood, bile, urine and feces collection, respectively. After PCBG suspension was intragastrically administered to rats at 50 mg/kg, biological samples were collected and processed. The metabolites in each matrix were detected by UHPLC-Q-Exactive-MS/MS. A total of 111 metabolites were observed in plasma, urine, bile and feces, which include hydroxylated, sulfated and glucuronized metabolites, etc. In addition, an UHPLC-MS/MS method was established and applied for the excretion quantification of PCBG and PCB in rat urine, bile, and feces samples. Studies on excretion have shown that PCBG is mainly excreted through feces. The cumulative excretion rates of PCBG and PCB in rat urine, bile and feces were (4.5±2.4)%, (0.2±0.1)% and (18.4±10.5)%, respectively. After hydrolysis by β-glucuronidase/sulfatase, the excretion rates of PCB in urine and bile were (5.7±2.8)% and (8.9±4.2)%. This study contributes to preclinical research on PCBG and explains its pharmacological effects.

Theoretical Exploration of Enhanced Antioxidant Activity in Copper Complexes of Tetrahydroxystilbenes: Insights into Mechanisms and Molecular Interactions

A theoretical investigation was conducted using DFT/PW91/TZP/DMSO calculations on a complete set of exhaustive lists of 18 compounds resulting from the complexation of trans-2,4,3',5'-tetrahydroxystilbene (T-OXY) and cis-2,4,1',3'-tetrahydroxystilbene (C-OXY) with copper metal cations (Cu+ and Cu2+). The ligand-binding sites are the critical points of Quantum Theory of Atoms in Molecules (QTAIM) analysis on neutral and deprotonated ligands. Various mechanisms, including hydrogen atom transfer (HAT), sequential proton loss electron transfer (SPLET), single electron transfer followed by proton transfer (SET-PT), and bond dissociation energy (BDE(E0)) calculations, were employed to quantify the antioxidant activity. The BDE(E0) mechanism emerged as the most suitable approach for such analyses to evaluate the departure of hydrogen atoms since the results show the HAT mechanism is the most likely occurring. Particularly intriguing were the anionic Cu+ complexes with ligands adopting trans configurations and deprotonated conformations, displaying superior antioxidant activity compared to their counterparts. Remarkably, a single ligand within the Cu+ complex exhibited exceptional antioxidant prowess, yielding a BDE(E0) value of 91.47 kcal/mol. Furthermore, a complex involving two deprotonated ligands demonstrated antioxidant activity of 31.12 kcal/mol, signifying its potential as a potent antiradical agent, surpassing T-OXY by a factor of 3.91 and even surpassing the antioxidant efficiency of Vitamin C.

Identification and mechanism prediction of mulberroside A metabolites in vivo and in vitro of rats using an integrated strategy of UHPLC-Q-Exactive Plus Orbitrap MS and network pharmacology

Mulberroside A is a polyhydroxylated stilbene active component of Morus alba L. Studies have shown that it has antitussive, antiasthmatic, tyrosinase and antioxidation activities. However, little is known about the metabolism of it in vitro and in vivo. In our study, an integrated strategy on the basis of UHPLC-Q-Exactive Plus Orbitrap MS and network pharmacology was established to comprehensively research the metabolic characteristic of mulberroside A for the first time. Plasma, urine, feces and liver tissues of rats in the blank group and drug group were collected after intragastric administration of mulberroside A at a dose of 150 mg/kg, and rat liver microsomes were cultured for in vitro metabolism experiment. The biological samples were processed by different methods and analyzed in positive and negative ion modes using UHPLC-Q-Exactive Plus Orbitrap MS. A total of 72 metabolites were finally identified based on the accurate molecular mass, retention time, MS/MS spectra and related literatures combined with the Compound Discoverer 3.1. The metabolic pathways were mainly hydrolysis, glucuronidation, hydrogenation, sulfation, hydroxylation, methylation and their composite reactions. In addition, a network pharmacology method was used to predict the mechanism of action of mulberroside A and its metabolites. In the end, 7 metabolites with high gastrointestinal absorption and drug-likeness and 167 targets were screened by Swiss ADME and Swiss Target Prediction. 1702 items of GO analysis and 158 related signaling pathways of KEGG were enriched using Metascape. This study established a novel integrated strategy based on UHPLC-Q-Exactive Plus Orbitrap MS and network pharmacology, which could systematically analyze the metabolism behavior of mulberroside A in vivo and in vitro of rats and provide basis for the further research of mulberroside A.

Anti-Inflammatory Activity of Oxyresveratrol Tetraacetate, an Ester Prodrug of Oxyresveratrol, on Lipopolysaccharide-Stimulated RAW264.7 Macrophage Cells

Oxyresveratrol (OXY) has been reported for its anti-inflammatory activity; however, the pharmaceutical applications of this compound are limited by its physicochemical properties and poor pharmacokinetic profiles. The use of an ester prodrug is a promising strategy to overcome these obstacles. In previous researches, several carboxylate esters of OXY were synthesized and oxyresveratrol tetraacetate (OXY-TAc) was reported to possess anti-melanogenic and anti-skin-aging properties. In this study, in addition to OXY-TAc, two novel ester prodrugs of OXY, oxyresveratrol tetrapropionate (OXY-TPr), and oxyresveratrol tetrabutyrate (OXY-TBu), were synthesized. Results from the Caco-2-permeation assay suggested that synthesized ester prodrugs can improve the membrane-permeation ability of OXY. The OXY-TAc exhibited the most significant profile, then this prodrug was chosen to observe anti-inflammatory activities with lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. Our results showed that OXY-Tac significantly alleviated secretion of several pro-inflammatory mediators (nitric oxide (NO), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α)), mitigated expression of enzyme-regulated inflammation (inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2)), and suppressed the MAPK cascades. Interestingly, the observed anti-inflammatory activities of OXY-TAc were more remarkable than those of its parent compound OXY. Taken together, we demonstrated that OXY-TAc improved physicochemical and pharmacokinetic profiles and enhanced the pharmacological effects of OXY. Hence, the results in the present study would strongly support the clinical utilities of OXY-TAc for the treatment of inflammation-related disorders.

Synergistic inhibitory effects of the oxyresveratrol and dacarbazine combination against melanoma cells

Various therapies have been developed to target malignant melanoma, which is associated with a high mortality rate worldwide. Although dacarbazine (DTIC) is employed for treating melanoma, it is associated with several side effects. Hence, patients with melanoma are co-treated with additional drugs to mitigate the side effects of DTIC. In the present study, synergistic therapeutic effects of the DTIC/oxyresveratrol (ORT) combination were examined using the human malignant melanoma WM-266-4 cell line. Treatment with ORT and DTIC inhibited the proliferation of WM-266-4 cells. Compared with those in the ORT- and DTIC-treated groups, the proportion of cells arrested at the S phase, as well as apoptotic rates, were increased in the ORT and DTIC co-treatment group. In WM-266-4 cells, synergistic proliferation-inhibitory activities of the ORT/DTIC combination were assessed based on cell viability and migration, antioxidant capacity, cytokine production, cell cycle arrest, apoptotic rate and protein expression through WST-1 assay, wound healing assay, flow cytometry and western blotting. Furthermore, the expression levels of proteins, including NOTCH, involved in the pathogenesis of solid cancers, such as melanoma, were examined. Overall, the ORT/DTIC combination synergistically promoted cell cycle arrest at the S phase and the apoptosis of WM-266-4 cells. Thus, this combination treatment may serve as a novel therapeutic strategy for treating malignant melanoma.

Oxyresveratrol: Sources, Productions, Biological Activities, Pharmacokinetics, and Delivery Systems

Oxyresveratrol has recently attracted much research attention due to its simple chemical structure and diverse therapeutic potentials. Previous reviews describe the chemistry and biological activities of this phytoalexin, but additional coverage and greater accessibility are still needed. The current review provides a more comprehensive summary, covering research from 1955 to the present year. Oxyresveratrol occurs in both gymnosperms and angiosperms. However, it has never been reported in plants in the subclass Sympetalae, and this point might be of both chemotaxonomic and biosynthetic importance. Oxyresveratrol can be easily obtained from plant materials by conventional methods, and several systems for both qualitative and quantitative analysis of oxyresveratrol contents in plant materials and plant products are available. Oxyresveratrol possesses diverse biological and pharmacological activities such as the inhibition of tyrosinase and melanogenesis, antioxidant and anti-inflammatory activities, and protective effects against neurological disorders and digestive ailments. However, the unfavorable pharmacokinetic properties of oxyresveratrol, including low water solubility and poor oral availability and stability, have posed challenges to its development as a useful therapeutic agent. Recently, several delivery systems have emerged, with promising outcomes that may improve chances for the clinical study of oxyresveratrol.

Mulberroside A repairs high fructose diet-induced damage of intestinal epithelial and blood-brain barriers in mice: A potential for preventing hippocampal neuroinflammatory injury

Our previous studies showed that high fructose diet (HFrD)-driven gut dysbiosis caused fecal short-chain fatty acids (SCFAs) reduction and intestinal epithelial barrier (IEB) damage in mice, which might play an important role in hippocampal neuroinflammatory injury. Mulberroside A is reported to have neuroprotective effects in animal experiments, while the underlying mechanisms are not yet fully elucidated. Here, we investigated whether and how mulberroside A prevented HFrD-induced neuroinflammatory injury. HFrD-fed mice were treated orally with mulberroside A (20 and 40 mg/kg) for 8 weeks. Mulberroside A was found to inhibit hippocampal neuroinflammation and neurogenesis reduction in HFrD-fed mice. It reshaped gut dysbiosis, increased fecal and serum SCFAs contents, reactivated signaling of the colonic NLR family, pyrin domain containing 6 (NLRP6) inflammasome, and up-regulated Muc2 expression to prevent IEB damage, as well as subsequently, reduced serum endotoxin levels in this animal model. Additionally, mulberroside A inhibited oxidative stress in colon of HFrD-fed mice and hydrogen peroxide (H₂ O₂ )-stimulated Caco-2 cells. Blood-brain barrier (BBB) structure defects were also observed in HFrD-driven hippocampal neuroinflammatory injury of mice. Interestingly, mulberroside A maintained astrocyte morphology and up-regulated tight junction proteins to repair BBB structure defects in hippocampus dentate gyrus (DG). Our results demonstrated that mulberroside A was capable of preventing HFrD-induced damage of IEB and BBB in mice, which might contribute to the suppression of hippocampal neuroinflammatory injury.

Metabolic profile and structure-activity relationship of resveratrol and its analogs in human bladder cancer cells

Purpose: Resveratrol (RV), a promising anti-cancer candidate, is limited in application for its poor bioavailability. However, the better bioavailability has been found in some RV derivatives. So in this paper, we explore the structure–activity relationship and the metabolic profiles of RV and its analogs (polydatin [PD], oxyresveratrol [ORV], acetylresveratrol [ARV]) in human bladder cancer T24 cells, and then evaluate their active forms and key chemical functional groups which may determine the fate of tumor cells.

Methods: Drug sensitivity is evaluated by MTT assay, HE staining and flow cytometry analysis after T24 cells treated with RV, PD, ORV and ARV, respectively. Then the drug metabolites, in alive and dead T24 cells, also in T24 cell supernatant and lysates, are qualitatively and quantitatively analyzed by high-performance liquid chromatography, liquid chromatography coupled with tandem mass spectrum and high-resolution mass spectrometry technologies, respectively.

Results: RV, ORV and ARV inhibit bladder cancer cells growth in a dose- and time-dependent manner, and exert the anti-tumor potency to T24 cells in order of ORV>ARV>RV>PD. Meanwhile, similar metabolic profiles of the above compounds are found not only in cell supernatant and lysate, but also in dead and alive T24 cells after drug treatment, and the main metabolites of RV, ORV and PD are their prototypes, but ARV is mainly metabolized to RV.

Conclusion: The inhibitory potencies to T24 cells in the order of ORV>ARV>RV>PD are related to the structure and metabolism of RV and its analogs. Meanwhile, the number and position of free phenolic hydroxyl groups play a prominent role in antitumor activities. Therefore, protecting phenolic hydroxyl groups, and inhibiting drug metabolism to keep phenolic hydroxyl groups free would be the promising strategies to ensure the bioactivity of RV and its analogs, and thus to improve RV’s bioactivity and promote RV clinical translation.

Comparison of the Hepatoprotective Effects of the Three Main Stilbenes from Mulberry Twigs

The purpose of this study was to compare the hepatoprotective effects of Oxy (oxyresveratrol), Res (resveratrol), and MulA (mulberroside A) (80 mg/kg body weight/d, i.g.) on acute liver injury (ALI) induced by lipopolysaccharide (LPS)/d-galactosamine (d-GalN) in mice. After 7 h of LPS (50 μg/kg body weight, i.p.) and d-GalN (500 mg/kg body weight, i.p.) exposure, the activities of serum transaminases and antioxidant enzymes were determined. The expressions of the Kelch-like ECH-associated protein 1 (Keap1)-nuclear factor erythroid 2-related factor 2 (Nrf2) signal pathway, the nuclear factor-kappa B (NF-κB) signal pathway, and the mitogen-activated protein kinase (MAPK) signal pathway related proteins were evaluated by Western blot assays. Histopathological analysis was performed by hematoxylin-eosin (H&E) staining on the separated livers of mice. The results showed that treatment with Oxy, Res, and MulA could significantly decreases the levels of alanine transaminase (ALT) and aspartate transaminase (AST) ( P < 0.01). MulA was the most effective ingredient among the three, and the ALT and AST levels were reduced at 90.3 ± 1.3% and 93.9 ± 1.1% compared with the LPS/D-GalN treated group ( P < 0.01). Meanwhile, the stilbenes curbed the expression of inflammatory factors, NF-κB pathway activation, and MAPKs phosphorylation and upregulated antioxidant enzymes, Nrf2, NAD (P) H:quinone oxidoreductase (NQO1), and heme oxygenase-1 (HO-1) expression levels. Stilbenes might protect the ALI caused by LPS/d-GalN through inhibiting the negative effectiveness of oxidation stress and inflammation. The protective performance of MulA was better than those of Oxy and Res, and we hypothesize that it might be due to the mediation of the specific metabolic pathway of the MulA in vivo. All of these results implied that stilbenes in mulberry twigs might be promising as natural additives.

Toxic trans-crotonaldehyde in mitochondria intercepted by oxyresveratrol contributing to anticancer

The aim of this study was to explore how the toxic trans-crotonaldehyde (TCA) in mitochondria or aldehyde dehydrogenase (ALDH) at different pHs was intercepted by oxyresveratrol (Oxy-Res) contributing to anticancer. Ultraviolet-visible (UV-vis) spectroscopy and Raman spectroscopy were employed. UV-vis spectra showed that the Oxy-Res red shifted the peak of the toxic TCA from 316 nm to 325 nm, while the peaks of the Oxy-Res shifted from 329 nm with 290 nm and 300 nm to 325 nm with 303 nm. In the mitochondria, the Oxy-Res blue shifted the peaks of the toxic TCA from 325 nm with 303 nm to 321 nm with 301 nm. Raman spectra revealed that the Oxy-Res caused shifting of the CHO of the toxic TCA from 1,689 cm^-1 to 1,671 cm^-1 with band decline. The CC of the toxic TCA at 1641 cm^-1 was split into 1,639 cm^-1 and 1,642 cm^-1 with band decline. The bands of the Oxy-Res at 1634 cm^-1 , 1,617 cm^-1 , and 1,595 cm^-1 disappeared. In the mitochondria, the CC of the toxic TCA at 1641 cm^-1 splitting disappeared. In ALDH, with the decrease of pH from 7.8 to 6.5, the CHO of the toxic TCA did not red shift from 1,689 cm^-1 to 1,674 cm^-1 up to pH 6.5. There was no change in the CC of the toxic TCA at 1640 cm^-1 in ALDH at different pHs. The conclusion of the study was that the CHO of the toxic TCA was intercepted by the Oxy-Res under the action of ALDH in the mitochondria, particularly at pH 7.8. © 2019 IUBMB Life, 2019.

Regioselective Glucosylation of Oxyresveratrol by Cell Suspension Cultures of Solanum Mammosum

The glucosylation of oxyresveratrol by cell suspension cultures of Solanum mammosum has been investigated.

Improvement of stilbenoid production by 2-hydroxypropyl-β-cyclodextrin in white mulberry (Morus alba L.) callus cultures

Mulberroside A, oxyresveratrol and resveratrol, commonly found in Morus alba L., are potent anti-aging phytostilbenes. In this study, the effect of the addition of 2-hydroxypropyl-β-cyclodextrin on the levels of phytostilbenes in M. alba callus cultures was investigated. Commercial cyclodextrin was used in the hydrolytic and culture processes of the M. alba callus cultures. The hydrolytic study indicated that 2-hydroxypropyl-β-cyclodextrin acted as a retardant for stilbenoid hydrolysis. It reduced mulberroside A deglycosylation and stabilised oxyresveratrol. The elicitation result showed that extracellular oxyresveratrol was increased by adding 2-hydroxypropyl-β-cyclodextrin to the culture media of both free and immobilised M. alba callus (>730-fold and >169-fold, respectively) compared with those of the control. However, the intracellular mulberroside A levels in the treatment groups did not increase compared with those of the control. The results show that the addition of 2-hydroxypropyl-β-cyclodextrin significantly changed the patterns and levels of the stilbenoids in M. alba callus cultures.

Anti-diabetic effects of mulberry (Morus alba L.) branches and oxyresveratrol in streptozotocin-induced diabetic mice

Despite with accumulating evidences on the anti-diabetic effects of mulberry branch (MB), the major active component for the activity has not been known. Oral administration of MB ethanol (EtOH) extracts [0.5 or 1 g/kg body weight (BW)] once a day for 22 days to streptozotocin-induced diabetic ICR mouse significantly reduced fasting blood and plasma glucose level in a dose dependent manner compared to those of the diabetic control. Administration of oxyresveratrol [ORT, 0.6 g/kg BW], a major compound of MB EtOH extracts, to diabetic ICR mouse also significantly reduced fasting plasma glucose level. Further, ORT increased hepatic glucose transporter 2 transcription and glycogen content. Plasma insulin concentration and intestinal disaccharidase activity were not different between diabetic control and ORT groups. This suggests that ORT reduced plasma glucose by stimulating hepatic glucose uptake and glycogen storage. MB EtOH extracts and ORT could be potential adjunct therapies for diabetes management.

Oxyresveratrol abrogates oxidative stress by activating ERK-Nrf2 pathway in the liver

Oxyresveratrol is a polyphenolic phytoalexin produced by plants as an antioxidant. This study investigated the hepatoprotective effects of oxyresveratrol as well as its underlying mechanism of action. Here, we evaluated the protective effects of oxyresveratrol against tert-butyl hydroperoxide (tBHP)-induced severe oxidative stress in HepG2 cells as well as acute liver injury caused by carbon tetrachloride (CCl4) in mice. tBHP-induced reactive oxygen species production and cell death in hepatocytes were blocked by oxyresveratrol, as indicated by MTT, TUNEL, and FACS analyses. Moreover, pretreatment with oxyresveratrol increased nuclear translocation and transactivation of NF-E2-related factor 2 (Nrf2), as assessed by antioxidant response element reporter gene expression and immunofluorescence staining, and transactivated expression of both hemeoxygenase-1 and glutamate-cysteine ligase catalytic subunit. More importantly, oxyresveratrol induced phosphorylation of Nrf2 mediated through activation of extracellular signal-regulated kinase 1/2 (ERK1/2). Further, ERK inhibitors such as PD98059 and U0126 blocked phosphorylation of Nrf2 as well as the protective effect of oxyresveratrol in mitochondria. In mice, oral administration of oxyresveratrol significantly prevented hepatocyte degeneration, inflammatory cell infiltration, as well as elevation of plasma markers such as ALT and AST induced by CCl4 injection. In conclusion, this study confirmed that oxyresveratrol protected hepatocytes against oxidative stress and mitochondrial dysfunction, which might be associated with activation of Nrf2.

Modification of oral absorption of oxyresveratrol using lipid based nanoparticles

The aim of this study was to develop and assess nanostructured lipid carriers (NLC) compared to solid lipid nanoparticles (SLN) for improving the oral bioavailability of oxyresveratrol (OXY). The OXY formulated as SLN (OXY-SLN) and NLC (OXY-NLC) were prepared by a high shear homogenization technique. The optimized OXY-NLC (NLC3) produced smaller nanoparticle sizes (96±0.9nm) than that of the OXY-SLN (108±0.3nm) with a homogeneous size distribution and a high zeta potential. The spherical NLC had a significantly higher efficiency for OXY entrapment (89±0.1%) and a better stability than the SLN after storage for 12 months at 4±2°C according to parameters such as smaller particles, greater zeta potential and a higher loading capacity (p<0.05). Differential scanning calorimetry (DSC) showed a less ordered crystalline structure of NLC than SLN. The accumulated drug in an amorphous state in the NLC was also confirmed by powder X-ray diffraction (PXRD). The in vitro release profiles of the OXY-NLC showed a more sustained release compared to the SLN and unformulated OXY. The in vivo pharmacokinetic profiles implied enterohepatic recycling of OXY in the Wistar rat. Meanwhile, the oral absorption pattern of OXY was modified by both types of lipid nanoparticles. The SLN and NLC increased the relative bioavailability of OXY to 125% and 177%, respectively, compared with unformulated OXY. These findings indicated that NLC could be used as a potential carrier to improve the oral bioavailability of OXY.

An efficient preparation of mulberroside a from the branch bark of mulberry and its effect on the inhibition of tyrosinase activity

A bioactive ingredient in an ethanol extract from the branch bark of cultivated mulberry Husang-32 (Morus multicaulis Perr.) was isolated using a macroporous resin column. The primary component, which was purified by semi-preparative high-performance liquid chromatography diode array detection (HPLC-DAD), was identified as mulberroside A (MA) by liquid chromatograph-mass spectrometer (LC-MS), ¹H and ¹³C nuclear magnetic resonance (NMR) spectra. In total, 4.12 g MA was efficiently extracted from one kilogram of mulberry bark. The enzymatic analysis showed that MA inhibited the generation of dopachrome by affecting the activities of monophenolase and diphenolase of tyrosinase in vitro. This analysis indicated that MA and oxyresveratrol (OR), which is the the aglycone of mulberroside A, exhibited strong inhibition of the monophenolase activity with IC₅₀ values of 1.29 µmol/L and 0.12 µmol/L, respectively. However, the former showed weaker inhibitory activity than the latter for diphenolase. For the monophenolase activity, the inhibitory activity of MA and OR was reversible and showed mixed type 1 inhibition. Additionally, the inhibition constant KI (the inhibition constant of the effectors on tyrosinase) values were 0.385 µmol/L and 0.926 µmol/L, respectively, and the KIS (the inhibition constants of the enzyme-substrate complex) values were 0.177 µmol/L and 0.662 µmol/L, respectively. However, MA showed competitive inhibition of diphenolase activity, and K_I was 4.36 µmol/L. In contrast, OR showed noncompetitive inhibition and K_I = K_IS = 2.95 µmol/L. Taken together, these results provide important information concerning the inhibitory mechanism of MA on melanin synthesis, which is widely used in whitening cosmetics.

Regioselective glucuronidation of oxyresveratrol, a natural hydroxystilbene, by human liver and intestinal microsomes and recombinant UGTs

Oxyresveratrol (OXY) is a natural hydroxystilbene that shows similar bioactivity but better water solubility than resveratrol. This study aims to characterize its glucuronidation kinetics in human liver (HLMs) and intestinal (HIMs) microsomes and identify the main UDP-glucuronosyltransferase (UGT) isoforms involved. Three and four mono-glucuronides of OXY were generated in HIMs and HLMs, respectively, with oxyresveratrol-2-O-β-D-glucuronosyl (G4) as the major metabolite in both organs. The kinetics of G4 formation fit a sigmoidal model in HLMs and biphasic kinetics in HIMs. Multiple UGT isoforms catalyzed G4 formation with the highest activity observed with UGT1A9 followed by UGT1A1. G4 formation by both isoforms followed substrate inhibition kinetics. Propofol (UGT1A9 inhibitor) effectively blocked G4 generation in HLMs (IC50 63.7 ± 11.6 µM), whereas the UGT1A1 inhibitor bilirubin only produced partial inhibition in HLMs and HIMs. These findings shed light on the metabolic mechanism of OXY and arouse awareness of drug interactions.

Enhancement of the tyrosinase inhibitory activity of Mori Cortex Radicis extract by biotransformation using Leuconostoc paramesenteroides PR

Mori Cortex Radicis (MCR), the root bark of Morus alba L., consists of various phytochemicals and exhibits a strong inhibitory effect on tyrosinase. To enhance the tyrosinase inhibitory activity of MCR extract without further purification of bioactive compounds, whole MCR extract was biotransformed with crude enzyme extract from a selected lactic acid bacterium, Leuconostoc paramesenteroides PR (LP). Mulberroside A (MA), a major stilbene glucoside of MCR, contains two β-glucosyl residues at the C3 and C4' positions of oxyresveratrol (OXY). The crude enzyme of LP hydrolyzed the two glycosidic bonds of MA effectively, and 97.1% of MA was biotransformed into OXY within 2 h. Commercial almond β-glucosidase hydrolyzed only one site of the two glycosidic bonds of MA, and 68.7% of MA was biotransformed to OXY-glucoside. The tyrosinase inhibitory activity of the crude extract of MCR was increased approximately 6.5-fold by biotransformation using LP, and the IC(50) value of the transformed MCR was 3.7 µg/mL.

In vitro pharmacokinetic characterization of mulberroside A, the main polyhydroxylated stilbene in mulberry (Morus alba L.), and its bacterial metabolite oxyresveratrol in traditional oral use

Mulberroside A (MulA) is one of the main bioactive constituents in mulberry (Morus alba L.). This study examined the determining factors for previously reported oral pharmacokinetic profiles of MulA and its bacterial metabolite oxyresveratrol (OXY) on in vitro models. When incubated anaerobically with intestinal bacteria, MulA underwent rapid deglycosylation and generated two monoglucosides and its aglycone OXY sequentially. MulA exhibited a poor permeability and predominantly traversed Caco-2 cells via passive diffusion; yet, the permeation of OXY across Caco-2 cells was much more rapid and involved efflux (both p-glycoprotein and MRPs)-mediated mechanisms. Moreover, OXY underwent extensive hepatic glucuronidation; yet, the parent MulA was kept intact in liver subcellular preparations. There was insignificant species difference in intestinal bacterial conversion of MulA and the extent of OXY hepatic glucuronidation between humans and rats, while OXY exhibited a distinct positional preference of glucuronidation in the two species. Overall, these findings revealed a key role of intestinal bacterial conversion in absorption and systemic exposure of MulA and its resultant bacterial metabolite OXY in oral route in humans and rats and warranted further investigational emphasis on OXY and its hepatic metabolites for understanding the benefits of mulberry.

Evaluation of the inhibition of mushroom tyrosinase and cellular tyrosinase activities of oxyresveratrol: comparison with mulberroside A

The inhibitory effects of oxyresveratrol, the aglycone of mulberroside A, on mushroom and cellular tyrosinase activities and melanin synthesis were evaluated. Mulberroside A and oxyresveratrol showed inhibitory activity against mushroom tyrosinase, with oxyresveratrol demonstrating a greater inhibitory effect than that of mulberroside A. Oxyresveratrol and mulberroside A strongly inhibited melanin production in Streptomyces bikiniensis and exhibited dose-dependent inhibition of tyrosinase activity and inhibition of melanin synthesis in B16F10 melanoma cells. However, the compounds exhibited nearly similar inhibitory effects on the activity of cellular tyrosinase and melanin synthesis in murine melanocytes. The inhibition of melanin synthesis by mulberroside A and oxyresveratrol was involved in suppressing the expression level of melanogenic enzymes, tyrosinase, tyrosinase-related protein-1 (TRP-1), and tyrosinase-related protein-2 (TRP-2). These results indicate that the inhibition rate of mushroom tyrosinase might not provide an accurate estimate of the inhibition rate of melanin synthesis in melanocytes.

Simultaneous determination of five characteristic stilbene glycosides in root bark of Morus albus L. (Cortex Mori) using high-performance liquid chromatography

INTRODUCTION

Cortex Mori, one of the well-known traditional Chinese herbal medicines, is derived from the root bark of Morus alba L. according to the China Pharmacopeia. Stilbene glycosides are the main components isolated from aqueous extracts of Morus alba and their content varies depending on where Cortex Mori was collected. We have established a qualitative and quantitative method based on the bioactive stilbene glycosides for control of the quality of Cortex Mori from different sources.

OBJECTIVE

To develop a high-performance liquid chromatography coupled with ultraviolet absorption detection for simultaneous quantitative determination of five major characteristic stilbene glycosides in 34 samples of the root bark of Morus alba L. (Cortex Mori) from different sources.

METHODOLOGY

The analysis was performed on an ODS column using methanol-water-acetic acid (18: 82: 0.1, v/v/v) as the mobile phase and the peaks were monitored at 320 nm.

RESULTS

All calibration curves showed good linearity (r ≥ 0.9991) within test ranges. This method showed good repeatability for the quantification of these five components in Cortex Mori with intra- and inter-day standard deviations less than 2.19% and 1.45%, respectively.

CONCLUSION

The validated method was successfully applied to quantify the five investigated components, including a pair of cis-trans-isomers 1 and 2 and a pair of isomers 4 and 5 in 34 samples of Cortex Mori from different sources.

Efficient synthesis of natural polyphenolic stilbenes: resveratrol, piceatannol and oxyresveratrol

The practical synthesis of important natural polyphenolic stilbenes, including resveratrol, piceatannol and oxyresveratrol, through Perkin methodology is described. Starting from 3,5-dihydoxyacetophenone (1), the common intermediate 3,5-dimethoxyphenylacetic acid (3) can be obtained via methylation and Willgerodt-Kindler reaction. Perkin condensations between (3) and substituted phenylaldehydes 4 furnished E-2,3-diarylacrylic acids 5, followed by decarboxylation in Cu/quinoline giving stilbene intermediates 6 which bear the Z-configuration. Finally, through a simultaneous demethylation/isomerization process in AlI₃/CH₃CN system, the target compounds 7a-c can be obtained respectively in good to high overall yields. The synthetic method proved to be more concise, trans-specific, mild, economical and commonly applicable.

High-performance liquid chromatographic analysis: applications to nutraceutical content and urinary disposition of oxyresveratrol in rats

A high-performance liquid chromatographic (HPLC) method was developed for the analysis of the stilbene, oxyresveratrol. This method involves the use of a Luna C(18) column with ultraviolet detection at 320 nm. The mobile phase consisted of acetonitrile, water and formic acid (30 : 70 : 0.04 v/v) with a flow rate of 0.6 mL/min. The calibration curves were linear over the range of 0.5-100.0 microg/mL. The mean extraction efficiency was between 98.9 and 109%. The precision of the assay was 0.069-18.4% (RSD%), and within 20% at the limit of quantitation (0.5 microg/mL). The bias of the assay was <15% and within 15% at the limit of quantitation. This assay was successfully applied to pre-clinical pharmacokinetic samples from rat urine and to nutraceutical product analysis.

In-vitro and in-vivo anti-inflammatory effect of oxyresveratrol from Morus alba L

The antioxidative effects of mulberroside A and oxyresveratrol obtained from Mori Cortex were examined. Mulberroside A and oxyresveratrol showed an inhibitory effect against FeSO4/H2O2-induced lipid peroxidation in rat microsomes and a scavenging effect on 1,1-diphenyl-2-picrylhydrazyl radical. The anti-inflammatory effects of mulberroside A and oxyresveratrol using the carrageenin-induced model of inflammation were investigated in rats. Mulberroside A and oxyresveratrol significantly reduced paw edema. To investigate the mechanism of the anti-inflammatory action of these compounds, we examined the effects of oxyresveratrol on lipopolysaccharide (LPS)-induced responses in murine macrophage cell line RAW 264.7. Exposure of LPS-stimulated cells to oxyresveratrol inhibited nitrite accumulation in the culture medium. Oxyresveratrol also inhibited the LPS-stimulated increase of inducible nitric oxide synthase (iNOS) expression in a concentration-dependent manner; however, it had little effect on iNOS enzyme activity, suggesting that the inhibitory activity of oxyresveratrol is mainly due to the inhibition of iNOS expression rather than iNOS enzyme activity. Oxyresveratrol significantly inhibited LPS-evoked nuclear translocation of NF-kB and cyclooxygenase-2 (COX-2) activity in RAW 264.7 cells. The results suggest that the anti-inflammatory properties of oxyresveratrol might be correlated with inhibition of the iNOS expression through down-regulation of NF-kB binding activity and significant inhibition of COX-2 activity.

Dietary oxyresveratrol prevents parkinsonian mimetic 6-hydroxydopamine neurotoxicity

Oxyresveratrol (OXY) is a polyhydroxylated stilbene existing in mulberry. Increasing lines of evidence have shown its neuroprotective effects against Alzheimer disease and stroke. However, little is known about its neuroprotective effect in Parkinson disease (PD). Owing to its antioxidant activity, blood-brain barrier permeativity, and water solubility, we hypothesized that OXY may exert neuroprotective effects against parkinsonian mimetic 6-hydroxydopamine (6-OHDA) neurotoxicity. Neuroblastoma SH-SY5Y cells have long been used as dopaminergic neurons in PD research. We found that both pretreatment and posttreatment with OXY on SH-SY5Y cells significantly reduced the release of lactate dehydrogenase, the activity of caspase-3, and the generation of intracellular reactive oxygen species triggered by 6-OHDA. Compared to resveratrol, OXY exhibited a wider effective dosage range. We proved that OXY could penetrate the cell membrane by HPLC analysis of cell extracts. These results suggest that OXY may act as an intracellular antioxidant to reduce oxidative stress induced by 6-OHDA. Western blot analysis demonstrated that OXY markedly attenuated 6-OHDA-induced phosphorylation of JNK and c-Jun. Furthermore, we proved that OXY increased the basal levels of SIRT1, which may disclose new pathways accounting for the neuroprotective effects of OXY. Taken together, our results suggest OXY, a dietary phenolic compound, as a potential nutritional candidate for protection against neurodegeneration in PD.

Syntheses of hydroxy substituted 2-phenyl-naphthalenes as inhibitors of tyrosinase

Oxyresveratrol and resveratrol, with hydroxy substituted trans-stilbene structure, exert potent inhibitory effects on cyclooxygenase, rat liver mitochondrial ATPase activity, and tyrosinase. As the isosteres of oxyresveratrol, a new family of hydroxyl substituted phenyl-naphthalenes were synthesized to show excellent inhibition of mushroom tyrosinase. Compound 10, which is isostere of resveratrol, showed IC50 value of 16.52 microM in mushroom tyrosinase activity. As compared to this, the reference compound, resveratrol, showed IC50 value of 55.61 microM. Compound 4, which is isostere of oxyresveratrol, showed IC50 value of 0.49 microM. Among the other three derivatives, compound 13 showed IC50 value of 0.034 microM.

Blood-brain barrier permeability to the neuroprotectant oxyresveratrol

We investigated to what extent the antioxidative hydroxystilbene oxyresveratrol (trans-2,3',4,5'-tetrahydroxystilbene, OXY), that we showed earlier to be strongly neuroprotective in a stroke model, may cross the blood-brain barrier (BBB) in healthy rats and in subjects submitted to focal infarction. Tissue extraction and in vivo microdialysis in the striatum show that systematically applied OXY is able to penetrate the BBB in control animals, but to a low extent. Microdialysis samples from animals that were subjected to a middle cerebral artery occlusion (MCAO) displayed strongly increased OXY levels (more than six-fold) in the infarct region as compared to sham-operated rats. Our data show that OXY may exert direct protective effects in the brain by crossing the BBB and may prove an excellent complementary drug for the treatment of neurodegenerative disorders that causally involve oxidative/nitrosative stress, especially in stroke.

Oxyresveratrol and resveratrol are potent antioxidants and free radical scavengers: effect on nitrosative and oxidative stress derived from microglial cells

Hydroxystilbenes are naturally occurring polyphenols with protective effects against reactive oxygen and nitrogen species (ROS/RNS). Here, we investigated oxyresveratrol (OXY), which is contained in high amounts in mulberry wood, in comparison to the antioxidant resveratrol (RES). We found that OXY is a more effective scavenger for 2,2-diphenyl-1-picryl-hydrazyl (DPPH, 100 microM) used as a general free radical model, compared to RES or trans-4-hydroxystilbene (IC(50)=28.9, 38.5, and 39.6 microM, respectively). When primary glial cell cultures were loaded with the ROS/RNS-sensitive fluorochrome 2,7-dichlorodihydrofluorescein, the lowest rise in the fluorescence signal after H(2)O(2) exposure was seen when the cells were pretreated with OXY. Using 4,5-diaminofluorescein (DAF-2) to monitor free nitric oxide levels (7.7 microM NO) in a spectrofluorimetric cell-free assay, we found again that OXY (at 5 microM) is a more effective scavenger. Accordingly, cultures of the murine microglial cell line N9 and primary mixed glial cultures were used to test the drug effects of NO production upon expression of the inducible isoform of nitric oxide synthase (iNOS). We found that both compounds considerably diminished NO (nitrite) levels, RES more effectively than OXY (IC(50)=22.36 and 45.31 microM). RES but not OXY down-regulated the expression of iNOS protein, but both did not alter iNOS activity. Furthermore, OXY displayed a generally lower cytotoxicity than RES. The radical and ROS scavenging properties, as well as the lower cytotoxicity towards microglia and the known good water solubility suggest OXY as a potential protectant against ROS/RNS.