Lipophilic flavonoids from Orthosiphon spicatus prevent oxidative inactivation of 15-lipoxygenase

Biological Evaluations, NMR Analyses, Molecular Modeling Studies, and Overview of the Synthesis of the Marine Natural Product (-)-Mucosin

Natural products obtained from marine organisms continue to be a rich source of novel structural architecture and of importance in drug discovery, medicine, and health. However, the success of such endeavors depends on the exact structural elucidation and access to sufficient material, often by stereoselective total synthesis, of the isolated natural product of interest. (-)-Mucosin (1), a fatty acid derivative, previously presumed to contain a rare cis-bicyclo[4.3.0]non-3-ene moiety, has since been shown to be the trans-congener. Analytically, the fused bicyclic ring system in (-)-1 constitutes a particular challenge in order to establish its relative and absolute stereochemistry. Herein, data from biological evaluations, NMR and molecular modeling studies of (-)-1 are presented. An overview of the synthetic strategies enabling the exact structural elucidation of (-)-mucosin (1) is also presented.

Antibacterial and anti-inflammatory activity of plant species used in traditional poultry ethnomedicine in Zimbabwe: A first step to developing alternatives to antibiotic poultry feed additives

ETHNOPHARMACOLOGICAL RELEVANCE

Global interest in phytogenic feed additives as alternatives to antibiotics in feed has been spurred by the banning of antibiotic growth promoters by several countries. Suitable plant extracts for development of phytogenic feed additives should have therapeutic value and should also be safe.

AIM OF STUDY

The aim of this study was to evaluate the antibacterial, antioxidant and anti-lipoxygenase activities as well as cytotoxicity of selected plant species used in poultry ethnomedicine in Zimbabwe.

METHODS

Antibacterial activity was determined against three ATCC strains (Staphylococcus aureus, Escherichia coli, Salmonella Enteritidis) and two clinical strains isolated from chickens (Escherichia coli and Salmonella Gallinarum) using a two-fold serial microdilution assay. Qualitative antibacterial bioautography was also carried out using the ATCC strains. Antioxidant activities of crude acetone and methanol extracts were determined using free radical scavenging assays whilst anti-lipoxygenase activity was evaluated using a ferrous oxidation-xylenol orange (FOX) assay. Cytotoxicity was evaluated using a tetrazolium-based colorimetric assay (MTT assay) on Vero monkey kidney cells.

RESULTS

Erythrina abyssinica had the best antibacterial activity against both ATCC strains and clinical strains with minimum inhibitory concentration (MIC) values ranging from 0.02 to 0.156 mg/ml. Aloe greatheadii, Adenia gummifera (leaves), Senna singueana and Aloe chabaudii had moderate activity against the poultry pathogens. Bioautography showed that all ten plant species have antibacterial activity against the tested microorganisms with E. abyssinica and S. singueana having prominent bands of inhibition against both Gram-negative and Gram-positive bacteria. The acetone extract of S. singueana and the methanol extract of Euphorbia matabelensis had the most powerful antioxidant activities with mean IC₅₀ values of 1.43 μg/ml and 1.31 μg/ml respectively in the ABTS assay which were comparable with those of the positive controls (ascorbic acid and trolox). Bobgunnia madagascariensis, A. chabaudii, E. abyssinica and Tridactyle bicaudata extracts had reasonable antioxidant activity. The S. singueana extract had the most potent anti-lipoxygenase activity with a mean IC₅₀ value of 1.72 μg/ml. The cytotoxicity results showed that only the acetone extracts of A. greatheadii and S. singueana were relatively safe at concentrations that were active against the tested microorganisms (selective index >1). Regarding anti-lipoxygenase activity, extracts of B. madagascariensis, S. singueana, T. bicaudata and E. matabelensis were more active than toxic (selective index >5) indicating anti-inflammatory potential.

CONCLUSIONS

This study showed that S. singueana had a cocktail of therapeutic activity and supports further investigation of this plant species for development of phytogenic poultry feed additives. Other plant species with noteworthy biological activities include B. madagascariensis, E. abyssinica, A. greatheadii, T. bicaudata and E. matabelensis.

Toll-Like Receptor 4: A Promising Therapeutic Target for Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease that primarily manifests as memory deficits and cognitive impairment and has created health challenges for patients and society. In AD, amyloid β-protein (Aβ) induces Toll-like receptor 4 (TLR4) activation in microglia. Activation of TLR4 induces downstream signaling pathways and promotes the generation of proinflammatory cytokines, such as tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β), which also trigger the activation of astrocytes and influence amyloid-dependent neuronal death. Therefore, TLR4 may be an important molecular target for treating AD by regulating neuroinflammation. Moreover, TLR4 regulates apoptosis, autophagy, and gut microbiota and is closely related to AD. This article reviews the role of TLR4 in the pathogenesis of AD and a range of potential therapies targeting TLR4 for AD. Elucidating the regulatory mechanism of TLR4 in AD may provide valuable clues for developing new therapeutic strategies for AD.

Bioassay Guided Fractionation of Senna singueana and Its Potential for Development of Poultry Phytogenic Feed Additives

There has been burgeoning interest in plant-based feed additives following restrictions placed on the use of antibiotic feed additives in many countries. Phytogenic feed additives are recommended to have a range of useful properties to support the growth and development of poultry to a similar level as that obtained by supplementing feed with antibiotics. The aim of this study was to evaluate the antibacterial, anti-lipoxygenase and antioxidant activity, and in vitro safety of fractions and isolated compounds from leaves of Senna singueana. Antibacterial activities of the fractions and isolated compounds were determined against a panel of bacteria using a two-fold serial microdilution assay and qualitative bioautography assays. Anti-lipoxygenase activity was evaluated using the ferrous oxidation-xylenol orange (FOX) method. Antioxidant activity was assessed qualitatively and quantitatively using radical scavenging assays. Dichloromethane and ethyl acetate fractions from solvent-solvent partitioning had the best antibacterial activity with MIC values ranging from 156 to 313 μg/ml. Fractions obtained from column chromatography had significant to weak antibacterial activity with MIC values ranging from 50 to 1,250 μg/ml. Bioautography showed clear bands of bacterial inhibition, indicating the presence of a number of active compounds in several fractions. The ethyl acetate fraction and all the tested column fractions had potent anti-lipoxygenase activity with IC₅₀ values of ≤2.5 μg/ml which were lower than that of quercetin (positive control), indicating anti-inflammatory potential. The ethyl acetate fraction and several column fractions had powerful antioxidant activity with IC₅₀ values of ≤5 μg/ml in the ABTS assay. Cytotoxicity values against Vero kidney cells ranged from LC₅₀ = 40.0–989.3 μg/ml. Bioassay-guided fractionation led to the isolation and identification of a known bioactive compound, luteolin. S. singueana is a promising candidate for the development of poultry phytogenic feed additives.

Sinensetin Attenuates Amyloid Beta25-35-Induced Oxidative Stress, Inflammation, and Apoptosis in SH-SY5Y Cells Through the TLR4/NF-κB Signaling Pathway

Sinensetin (SIN) is an important active compound that exists widely in citrus plants, and has been reported to exhibit various pharmacological properties, including anti-oxidative, anti-inflammatory, and anti-tumor. This study was designed to examine whether SIN can protect against amyloid beta (Aβ)-induced neurotoxicity and to elucidate the underlying mechanism. Our results showed that pretreatment with SIN for 1 h, followed by co-treatment with Aβ plus SIN for 24 h, attenuated Aβ_25-35-induced cell viability reduction, oxidative stress, inflammation, and apoptosis in a dose-dependent manner. Aβ_25-35-induced upregulation of Toll-like receptor 4 (TLR4) expression and nuclear translocation of nuclear factor-kappaB (NF-κB) p65 subunit were inhibited by pretreatment with SIN. Furthermore, the protective effect of SIN was abrogated by TLR4 overexpression. Hence, our data suggested that SIN attenuated Aβ_25-35-induced neurotoxicity through the TLR4/NF-κB pathway.

Synthesis, antioxidant activity and bioinformatics studies of L-3-hydroxytyrosine templated N-alkyl/aryl substituted urea/thioureas

A new series of urea/thiourea derivatives have been efficiently synthesized from the reaction of L-3-hydroxytyrosine with selective isocyanates/isothiocyanates and characterized by Infra-red, proton & carbon-13 nuclear magnetic resonance spectral and mass spectrometry studies. All the synthesized compounds have been screened for their antioxidant activity by 1,1-diphenyl1-2-picrylhydrazyl radical assay, ferric reducing antioxidant power assay and also studied their molecular docking interaction profiles against 1N8Q and 3NRZ enzymatic proteins. The in vitro antioxidant activity has further supported by quantitative structure activity relationship, absorption, distribution, metabolism, and excretion & toxicity studies, bioactivity studies & enzyme inhibition assay and identified that they were potentially bound to ASP490 & ASP361 aminoacid residue in chain A of 1N8Q protein and GLN1194 aminoacid residue in chain L of 3NRZ protein and are responsible for potential antioxidant activity. It is proved that urea derivatives linked with 4-fluoro & 4-nitro and thiourea derivatives linked with 3-chloro & 4-fluoro have exhibited promising antioxidant activity. In eventual synthesized compounds have been identified as potential blood-brain barrier penetrable compounds and proficient central nervous system active neuro-protective antioxidant agents as they have envisaged as easily penetrable to blood-brain barrier thresholds, a neuroprotective property.

Sinensetin: An Insight on Its Pharmacological Activities, Mechanisms of Action and Toxicity

Sinensetin, a plant-derived polymethoxylated flavonoid found in Orthosiphon aristatus var. aristatus and several citrus fruits, has been found to possess strong anticancer activities and a variety of other pharmacological benefits and promising potency in intended activities with minimal toxicity. This review aims to compile an up-to-date reports of published scientific information on sinensetin pharmacological activities, mechanisms of action and toxicity. The present findings about the compound are critically analyzed and its prospect as a lead molecule for drug discovery is highlighted. The databases employed for data collection are mainly through Google Scholar, PubMed, Scopus and Science Direct. In-vitro and in-vivo studies showed that sinensetin possessed strong anticancer activities and a wide range of pharmacological activities such as anti-inflammatory, antioxidant, antimicrobial, anti-obesity, anti-dementia and vasorelaxant activities. The studies provided some insights on its several mechanisms of action in cancer and other disease states. However, more detail mechanistic studies are needed to understand its pharmacological effects. More in vivo studies in various animal models including toxicity, pharmacokinetic, pharmacodynamic and bioavailability studies are required to assess its efficacy and safety before submission to clinical studies. In this review, an insight on sinensetin pharmacological activities and mechanisms of action serves as a useful resource for a more thorough and comprehensive understanding of sinensetin as a potential lead candidate for drug discovery.

Chemical composition, antioxidant, anti-inflammatory and antiproliferative activities of the essential oil of Cymbopogon nardus, a plant used in traditional medicine

Objectives Natural products commonly used in traditional medicine, such as essential oils (EOs), are attractive sources for the development of molecules with anti-proliferative activities for future treatment of human cancers, e.g., prostate and cervical cancer. In this study, the chemical composition of the EO from Cymbopogon nardus was characterized, as well as its antioxidativeproperties and anti-inflammatory and antiproliferative activities on LNCaP cells derived from prostate cancer. Methods The chemical composition of the EO was determined by GC/FID and GC/MS analyses. The antioxidative properties were assessed using DPPH radical scavenging assay and ABTS+• radical cation decolorization assay, and the anti-inflammatory capacity was determined by the inhibition of the lipoxygenase activity. Antiproliferative activity was evaluated by MTT assay. Results Collectively, our data show that the major constituents of C. nardus EO are citronellal (33.06 %), geraniol (28.40 %), nerol (10.94 %), elemol (5.25 %) and delta-elemene (4.09 %). C. nardus EO shows modest antioxidant and anti-inflammatory activity compared to the standard galic acid. C. nardus EO exhibits the best antiproliferative activity on the prostate cancer cell line LNCaP with an IC50 of 58.0 ± 7.9 μg/mL, acting through the induction of the cell cycle arrest. Conclusions This study has determined that C. nardus EO efficiently triggers cytotoxicity and pens a new field of investigation regarding the putative use of this EO in vivo.

In Vitro and In Silico Antidiabetic and Antimicrobial Evaluation of Constituents from Kickxia ramosissima (Nanorrhinum ramosissimum)

Background and Aims:Kickxia ramosissima (Wall.) Janch (or Nanorrhinum ramosissimum (Wall.) Betsche is a well-known medicinal plant in Pakistan that is traditionally used in diabetic and inflammatory conditions. Because little information is available on its phytochemical composition, a range of constituents were isolated and evaluated in vitro in assays related to the traditional use.

Methods: Dried whole plant material was extracted and chromatographically fractionated. Isolated constituents were evaluated in silico and in vitro in assays related to the traditional use against diabetes (inhibition of α-glucosidase activity; inhibition of advanced glycation endproducts) and in inflammatory conditions (inhibition of AAPH induced linoleic acid peroxidation, inhibition of 15-LOX, antimicrobial activity).

Results: Phytochemical analysis of the extracts and fractions led to isolation of 7 compounds, including the iridoids kickxiasine (being a new compound), mussaenosidic acid, mussaenoside and linarioside; the flavonoids pectolinarigenin and pectolinarin; and 4-hydroxy-benzoic acid methyl ester. The iridoids showed weak antiglycation activity. The flavonoids, however, showed interesting results as pectolinarigenin was highly active compared to pectolinarin. In the α-glucosidase inhibition assay, only weak activity was observed for the iridoids. However, the flavonoid pectolinarigenin showed good activity, followed by pectolinarin. In the 15-LOX experiment, moderate inhibition was recorded for most compounds, the iridoids mussaenosidic acid and mussaenoside being the most active. In the AAPH assay, weak or no inhibition was recorded for all compounds. The in silico assays for the α-glucosidase and 15-LOX assays confirmed the results of respective in vitro assays. Pectolinarigenin showed moderate antimicrobial activity against Staphylococcus aureus, Plasmodium falciparum K1, and Trypanosoma cruzi, but it was not cytotoxic on a human MRC-5 cell line.

Conclusion: Our findings may in part contribute to explain the traditional use of K. ramosissima.

6-carboxydihydroresveratrol 3-O-β-glucopyranoside--a novel natural product from the Cretaceous relict Metasequoia glyptostroboides

Metasequoia glyptostroboides, a tree native to China, is described as a living fossil and has existed for millions of years. The oldest fossils recorded have been dated to the late Cretaceous era. During the time of its existence, the molecular defence system of the tree has apparently resisted millions of generations of pathogens, which encouraged search for novel natural product from this source. Eight compounds have been characterised from needles of M. glyptostroboides, including the novel natural product 6-carboxydihydroresveratrol 3-O-β-glucopyranoside. The structure determinations were based on extensive use of 2D NMR spectroscopic techniques and high-resolution mass spectrometry.

Novel GHB-derived natural products from European mistletoe (Viscum album)

CONTEXT

The European white-berry mistletoe [Viscum album L. (Loranthaceae)] is among the oldest known medicinal plants. At present the most important application of mistletoe extracts is in the treatment of cancer. However, natural products specific to mistletoe have rarely been encountered in the current literature.

OBJECTIVE

To discover novel natural products specific to European mistletoe.

MATERIALS AND METHODS

European mistletoe was extracted with methanol, purified to partition against diethyl ether and further purified with XAD-7 column chromatography. Pure compounds were separated by Sephadex column chromatography and preparative HPLC. The structures of the novel compounds were established using a combination of several 2D NMR spectroscopic techniques and mass spectrometry.

RESULTS

A new type of natural product derived from the methyl ester of γ-hydroxybutyric acid (GHB) coupled to hydroxybenzoic acids, namely 3-(3'-carbomethoxypropyl) gallic acid and 3-(3'-carbomethoxypropyl)-7→3″-protocatechoyl galloate were characterized from European white-berry mistletoe. Condensation of the 3-hydroxyl of gallic acid with the 4-hydroxyl of GHB significantly reduced the radical scavenging properties of the former compound.

DISCUSSION AND CONCLUSION

The characterized compounds define a novel group of natural products that may be of particular interest because it appears that the two new compounds are not closely related to any known natural product.

Antioxidant, antiglycation and cytotoxicity evaluation of selected medicinal plants of the Mascarene Islands

Background

Many indigenous plants of Mascarene Islands have been used in folkloric medicine to manage diabetes but few species have received scientific attention. Selected traditional medicinal plants (Antidesma madagascariense Lam. -Euphorbiaceae (AM), Erythroxylum macrocarpum O.E.Schulz -Erythroxylaceae (EM), Pittosporum senacia Putterl -Pittosporaceae (PS), Faujasiopsis flexuosa Lam. C.Jeffrey -Asteraceae (FF), Momordica charantia Linn -Cucurbitaceae (MC) and Ocimum tenuiflorum L -Lamiaceae (OT) were evaluated for their antioxidant, antiglycation and cytotoxic potential in vitro.

Methods

Graded concentrations (1.25-100 μg/mL) of the crude methanolic and water extracts and fractions (dichloromethane, ethyl-acetate, n-butanol and water) were evaluated for abilities to scavenge 2,2-diphenyl-2-picrylhydrazyl hydrate (DPPH), nitric oxide (NO), superoxide (SO) radicals and to inhibit lipoxygenase and formation of advanced glycation endproduct (AGE) in vitro. The MTT (3-(4, 5-dimethylthazol-2-yl)-2,5-diphenyl tetrazonium bromide) cytotoxicity test was performed on 3T3 cell line.

Results

Only IC₅₀ for DPPH, SO, NO and lipoxygenase for AM, FF and OT crude extracts and fractions were comparable to ascorbic acid and quercetin activity. Crude aqueous extracts of AM and FF showed IC₅₀ of 4.08 and 3.89 μg/mL respectively for lipoxygenase which was significantly lower (p < 0.05) than quercetin (10.86 ± 0.68 μg/mL). The three crude aqueous extracts of these plants and their n-butanol fractions also showed antiglycation activities (p < 0.05) comparable to aminoguanidine. Increasing concentrations (250-2000 μg/mL) of the six crude extracts (Methanol and water) and their fractions did not inhibit mitochondrial respiration as measured by MTT cytotoxicity assay.

Conclusion

AM, FF and OT crude extracts and fractions have potent antioxidant and antiglycation properties with no apparent cytotoxicity and might have prophylactic and therapeutic potentials in the management of diabetes and related complications. Our study tends to validate the traditional use of these medicinal herbs and food plants as complementary and alternative medicines.

Antiatherogenic properties of acetone extract of Alpinia zerumbet seeds

Oxidation of low-density lipoprotein (LDL) is the principal risk factor for the development of atherosclerosis. In this study, we used several methods to investigate the ability of the acetone extract from rhizomes, stems, leaves, flowers, pericarps and seeds of Alpinia zerumbet to inhibit atherosclerosis in vitro. The seed extract had the strongest activity against tyrosinase, pancreatic lipase (PL), 15-lipoxygenase (15-LO) and LDL oxidation activities (IC₅₀ = 2.30 ± 0.02, 5.00 ± 0.07, 1.29 ± 0.07 and 15.40 ± 0.86 µg/mL, respectively), amongst all different parts. It also had similar effects to the positive controls. Most of the extracts showed partial agonistic properties towards estrogenic activity. Cholest-4-ene-3,6-dione, a steroid present only in the seed extract seems to be the compound responsible for these activities. The results showed that cholest-4-ene-3,6-dione had similar ability to curcumin and quercetin against PL and LDL oxidation (IC₅₀ = 19.50 ± 1.17 and 16.12 ± 1.43 µg/mL, respectively). Furthermore, cholest-4-ene-3,6-dione (IC₅₀ = 34.21 ± 1.31 µg/mL) had higher inhibition against 15-LO than quercetin (IC₅₀ = 54.79 ± 1.12 µg/mL).

Primary, secondary metabolites, H2O2, malondialdehyde and photosynthetic responses of Orthosiphon stimaneus Benth. to different irradiance levels

The resource availability hypothesis predicts an increase in the allocation to secondary metabolites when carbon gain is improved relative to nutrient availability, which normally occurs during periods of low irradiance. The present work was carried out to confirm this hypothesis by investigating the effects of decreasing irradiance on the production of plant secondary metabolites (flavonoids and phenolics) in the herbal plant Orthosiphon stamineus, and to characterize this production by carbohydrate, H₂O₂, and malondialdehyde (MDA) levels, net photosynthesis, leaf chlorophyll content and carbon to nitrogen ratio (C/N). Four levels of irradiance (225, 500, 625 and 900 µmol/m²/s) were imposed onto two-week old seedlings for 12 weeks in a randomized complete block design experiment. Peak production of total flavonoids, phenolics, soluble sugar, starch and total non-structural carbohydrate ocurred under low irradiance of 225 µmol/m²/s, and decreased with increasing irradiance. The up-regulation of secondary metabolites could be explained by the concomitant increases in H₂O₂ and MDA activities under low irradiance. This condition also resulted in enhanced C/N ratio signifying a reduction in nitrogen levels, which had established significant negative correlations with net photosynthesis, total biomass and total chlorophyll content, indicating the possible existence of a trade-off between growth and secondary metabolism under low irradiance with reduced nitrogen content. The competition between total chlorophyll and secondary metabolites production, as exhibited by the negative correlation coefficient under low irradiance, also suggests a sign of gradual switch of investment from chlorophyll to polyphenols production.

HPLC and anti-inflammatory studies of the flavonoid rich chloroform extract fraction of Orthosiphon stamineus leaves

The aim of the present study was to verify the anti-inflammatory activity of Orthosiphon stamineus leaf extracts and to identify the active compound(s) contributing to its anti-inflammatory activity using a developed HPLC method. Active chloroform extract of O. stamineus was fractionated into three fractions using a dry flash column chromatography method. These three fractions were investigated for anti-peritoneal capillary permeability, in vitro nitric oxide scavenging activity, anti-inflammatory and nitric oxide (NO) inhibition using carrageenan-induced hind paw edema method. The flavonoid rich chloroform extract fraction (CF2) [containing sinensetin (2.86% w/w), eupatorin (5.05% w/w) and 3’-hydroxy-5,6,7,4’-tetramethoxyflavone (1.101% w/w)], significantly reduced rat hind paw edema, NO and decreased dye leakage to peritoneal cavity at p < 0.05. IC₅₀ of in vitro NO scavenging of CF2 was 0.3 mg/mL. These results suggest that the anti-inflammatory properties of these CF2 may possibly be due to the presence of flavonoid compounds capable of affecting the NO pathway.

Effect of Cleome arabica leaf extract, rutin and quercetin on soybean lipoxygenase activity and on generation of inflammatory eicosanoids by human neutrophils

The effects of Cleome arabica leaf extract, rutin and quercetin on soybean lipoxygenase (Lox) activity and on calcium ionophore (A23187)-stimulated generation of the leukotriene B4 and prostaglandin E2 by human neutrophils were examined. The extract (25 microg/ml), rutin (25 microM) and quercetin (25 microM) inhibited LTB4 synthesis at all concentrations of A23187 used. The extract at 1-100 microg/ml and rutin at 1-100 microM inhibited LTB4 generation by neutrophils stimulated with 1 microM A23187 by about 50%. PGE2 production in response to different concentrations of A23187 was affected in a biphasic manner by the extract and rutin. Quercetin at 1-100 microM caused concentration-dependent inhibition of LTB4 and PGE2 production. The extract, rutin and quercetin caused concentration-dependent inhibition of soybean Lox activity. These results indicate that rutin, quercetin and an extract of C. arabica containing these compounds inhibit Lox activity, consequently decreasing LTB4 production. Thus, these compounds or extracts containing them may be beneficial for the treatment of inflammatory conditions, particularly those characterised by excessive leukotriene generation.

Determination of flavonoids from Orthosiphon stamineus in plasma using a simple HPLC method with ultraviolet detection

A simple liquid chromatographic method was developed for the simultaneous determination of flavonoids from Orthosiphon stamineus Benth, namely sinensitin, eupatorin and 3'-hydroxy-5,6,7,4'-tetramethoxyflavone, in plasma. Prior to analysis, the flavonoids and the internal standard (naproxen) were extracted from plasma samples using a 1:1 mixture of ethyl acetate and chloroform. The detection and quantification limits for the three flavonoids were similar being 3 and 5 ng/ml, respectively. The within-day and between-day accuracy values, expressed as percentage of true values, for the three flavonoids were between 95 and 107%, while the corresponding precision, expressed as coefficients of variation, for the three flavonoids were less than 14%. In addition, the mean recovery values of the extraction procedure for all the flavonoids were between 92 and 114%. The calibration curves were linear over a concentration range of 5-4000 ng/ml. The present method was applied to analyse plasma samples obtained from a pilot study using rats in which the mean absolute oral bioavailability values for sinensitin, eupatorin and 3'-hydroxy-5,6,7,4'-tetramethoxyflavone was 9.4, 1.0 and 1.5%, respectively.

Inhibitors of 15-lipoxygenase from orange peel

A series of polymethoxylated flavonoids has been isolated from orange peel, and their inhibitory activity toward soybean 15-lipoxygenase was determined. The strongest inhibition was shown by 3,5,6,7,3',4'-hexamethoxyflavone (IC(50) = 49 +/- 5 microM). Sinensetin, nobiletin, tangeretin, tetramethylscutellarein, and 3,5, 6,7,8,3',4'-heptamethoxyflavone were somewhat less active, with IC(50) values of 70-86 microM, comparable to the positive control quercetin (IC(50) = 68 +/- 5 microM). Demethylation apparently results in less active compounds, with 5-O-demethylsinensetin having an IC(50) value of 144 +/- 10 microM. Some other orange peel constituents were isolated and tested as well, hesperidin (IC(50) = 180 +/- 10 microM) and ferulic acid (111 +/- 2 microM), showing moderate activity. The polymethoxylated flavonoids were virtually inactive as scavengers of the diphenylpicrylhydrazyl radical. Hesperidin was only slightly active (24.2 +/- 0.7% scavenged at a concentration of 2 mM), and ferulic acid showed good activity (IC(50) = 86.4 +/- 0.7 microM). From this, it appears that orange peel constituents may counteract enzymatic lipid peroxidation processes catalyzed by 15-lipoxygenase in vitro. The radical scavenging activity of orange peel extracts is only modest.