Flavonoids of the liverwort Marchantia polymorpha

The major flavonoids of Marchantia polymorpha var. polymorpha and aquatica are the 7-O-β-d-glucuronides of apigenin and luteolin, luteolin 3′-O-β-d-glucuronide, luteolin 7,3′-di-O-β-d-glucuronide, and the 7,4′-di-O-β-d-glucuronides of apigenin and luteolin. These are accompanied by minor amounts of apigenin, luteolin, luteolin 3′,4′-di-O-β-d-glucuronide and luteolin 7,3′,4′-tri-O-β-d-glucuronide. All the luteolin di- and triglucuronides except the 3′,4′-di- substituted compound are new natural products.     

A chemotaxonomic study of flavonoids in Thymbra capitata

5,6,4′-Trihydroxy-7,3′-dimethoxyflavone, 5,6-dihydroxy-7,3′,4′-trimethoxyflavone, luteolin, diosmetin, vicenin-2 and luteolin 7-rutinoside have been isolated and identified from Thymbra capitata. The occurrence of these compounds supports the inclusion of this plant in the genus Thymbra, rather than Thymus or Corydothymus.     

Flavone 5-O-glucosides from Daphne sericea

The aerial parts of Daphne sericea yielded two new flavonoids, luteolin 7-methyl ether 5-β-d-glucoside and luteolin 7,3′-dimethyl ether 5-β-d-glucoside, as well as luteolin 7-methyl ether, isovitexin, apigenin and its 7-β-d-glucoside.     

Metabolic fate of luteolin and its functional activity at focal site

Luteolin has been shown to possess potent antioxidant and anti-inflammatory/anti-allergic activities. In order to evaluate a chemopreventive role of luteolin in inflammatory responses involved in the pathogenesis of atherosclerosis and cancer etc., the metabolic fate of luteolin in rats and humans was investigated by HPLC analysis, and its effect on cell surface expression of adhesion molecules in human umbilical vein endothelial cells(HUVECs) was examined by ELISA. Luteolin monoglucuronide, which was a main metabolite, and free luteolin were detected in rat plasma and human serum. Luteolin monoglucuronide was hydrolyzed to free luteolin by beta-glucuronidase released from neutrophils stimulated with lonomycin and Cytocharasine B. Luteolin suppressed the TNF-alpha induced ICAM-1 expression significantly. Among nine flavonoids (40 microM) examined, chrysin, apigenine, quercetin and galangin also demonstrated suppressive effct on it. These results suggest the posssibility that deconjugation of luteolin monoglucuronide occurs and that free luteolin showed functional acyivities such as suppression of TNF-alpha induced ICAM- 1 expression at inflammation site.     

Acylated luteolin glucosides from Salix gilgiana

Besides apigenin and luteolin 7-glucoside, four novel luteolin glucosides acylated with acetic,trans-cinnamic,p-coumaric andferulic acids, re acyl groups was determined to be at C-6″ by the¹³C NMR spectral data.     

In vitro study of macrophage barrier function in mice vaccinated against tick-borne encephalitis and infection with flaviviruses of varying virulence

Tick-borne encephalitis (TBE) and Langat viruses were shown to be equally capable of multiplication in mouse peritoneal macrophages (PM) in vitro. The reproduction dynamics of TBE virus proved to be the same in PM of mice both highly sensitive and relatively less sensitive to TBE virus. The preliminary immunization of PM donors with commercial inactivated or experimental concentrated TBE virus vaccine produced no effect on the capacity of the virus for multiplication in PM. These facts indicate the absence of correlation between the capacity of the viruses under study for multiplication in PM in vitro and their virulence in vivo, as well as the insignificant role of circulating macrophages in the realization of the barrier function in an immune or nonimmune body.     

Effects of luteolin on arylamine N-acetyltransferase activity in rat blood and liver.

In this study we investigated inhibition of Arylamine N-acetyltransferase (NAT) activity in rat blood and liver tissue cytosols by luteolin. Using high-performance liquid chromatography, NAT activity for acetylation of 2-aminofluorene and remaining unacetylated 2-aminofluorene were examined. The NAT activity in rat blood and liver tissue was inhibited by luteolin in a dose-dependent manner: higher concentrations of luteolin in the reaction resulted in greater inhibition of NAT activities in both examined tissues. The data also indicated that luteolin decreased apparent Km and Vmax of NAT enzymes from rat blood and liver tissue cytosols. This report is the first demonstration that luteolin can affect rat blood and liver tissue NAT activity.     

Rat colonic lipid peroxidation and antioxidant status: the effects of dietary luteolin on 1,2-dimethylhydrazine challenge

Colon cancer is the third most common cancer and second leading cause of cancer-related death in the United States. A number of recent articles demonstrate the importance of natural products as cancer chemopreventive agents. In this study, we evaluated the chemopreventive efficacy of luteolin, a flavonoid, on tissue lipid peroxidation and antioxidant status, which are used as biomarkers in DMH-induced experimental colon carcinogenesis. Rats were given a weekly subcutaneous injection of DMH at a dose of 20 mg/kg body weight for 15 weeks. Luteolin (0.2 mg/kg body weight/everyday p.o.) was given to the DMH-treated rats at the initiation and post-initiation stages of carcinogenesis. The animals were killed after 30 weeks. After a total experimental period of 32 weeks (including 2 weeks of acclimatization), tumor incidence was 100% in DMH-treated rats. In those DMH-treated rats that had received luteolin during the initiation or post-initiation stages of colon carcinogenesis, the incidence of cancer and the colon tumor size was significantly reduced as compared to that for DMH-treated rats not receiving luteolin. In the presence of DMH, relative to the results for the control rats, there were decreased levels of lipid peroxidation, as denoted by thiobarbituric acid reactive substances (TBARS), conjugated dienes and lipid hydroperoxides, decreased activities of the enzymic antioxidants superoxide dismutase (SOD) and catalase (CAT), and elevated levels of glutathione and the glutathione-dependent enzymes reduced glutathione (GSH), glutathione peroxidase (GPx), glutathione-S-transferase (GST) and glutathione reductase (GR), and of the non-enzymic antioxidants vitamin C and vitamin E. Our study shows that intragastric administration of luteolin inhibits colon carcinogenesis, not only by modulating lipid peroxidation and antioxidant status, but also by preventing DMH-induced histopathological changes. Our results thus indicate that luteolin could act as a potent chemopreventive agent for colon carcinogenesis.     

Prevention of selenite induced oxidative stress and cataractogenesis by luteolin isolated from Vitex negundo

Free radical mediated oxidative stress plays a crucial role in the pathogenesis of cataract and the present study was to determine the efficacy of luteolin in preventing selenite induced oxidative stress and cataractogenesis in vitro. Luteolin is a bioactive flavonoid, isolated and characterized from the leaves of Vitex negundo. Lenses were extracted from Sprague-Dawley strain rats and were organ cultured in DMEM medium. They were divided into three groups with eight lenses in each group as follows: lenses cultured in normal medium (G I), supplemented with 0.1mM sodium selenite (G II) and sodium selenite and 2 μg/ml luteolin (G III). Treatment was from the second to fifth day, while selenite administration was done on the third day. After the experimental period, lenses were taken out and various parameters were studied. The antioxidant potential of luteolin was assessed by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity. In the selenite induced group, morphological examination of the lenses showed dense cortical opacification and vacuolization. Biochemical examinations revealed a significant decrease in activities of antioxidant enzymes and enzymes of the glutathione system. Additionally decreased glutathione level and increased reactive oxygen species (ROS) and thiobarbituric acid reactive substances (TBARS) were observed. Luteolin treatment abated selenite induced oxidative stress and cataractogenesis by maintaining antioxidant status, reducing ROS generation and lipid peroxidation in the lens. These finding demonstrated the anticataractogenic effect of luteolin by virtue of its antioxidant property, which has been reported in this paper for the first time.     

Characterization of monoclonal antibodies against Hokkaido strain tick-borne encephalitis virus

A tick-borne encephalitis (TBE) patient was found in Hokkaido in 1993, and TBE viruses were isolated from animals and ticks in our previous studies. To develop a diagnostic reagent to identify TBE viruses, monoclonal antibodies (Mabs) were produced against the TBE virus strain Hokkaido (Oshima 5-10). Seven Mabs were obtained which reacted with the envelope protein of the Oshima 5-10 strain. These Mabs were flavivirus genus-specific, TBE virus complex-specific or TBE virus type-specific. The Mabs are applicable for identification of TBE virus strains.     

Tick-borne encephalitis in a northern zone of coniferous and broad-leaved forests of a focal region of the Amur River basin

The geographical variability of the population of tick-borne encephalitis (TBE) virus in the northern part of the zone of combined coniferous and broad-leaved forests was established; this variability was manifested by higher virulence and homogeneity of TBE virus strains, as shown in experiments on white mice receiving the virus extraneurally, in comparison with the southern part of the zone and by higher virus carriership of the ticks Ixodes persulcatus. With the epizootic situation remaining tense and the danger of TBE virus infection still present, TBE morbidity and mortality rates decreased in the years of the construction of the Baikal-Amur Railroad, which was due to greater attention given to measures for the prophylaxis of TBE during this period.     

Phylogenetic analysis and pathogenicity of tick-borne encephalitis virus from Japan and far-east Russia

Phylogenetic analysis of tick-borne encephalitis (TBE) virus revealed that Hokkaido strain of TBE virus evolved several hundreds years ago in far-east Russia. TBE virus strains in Irkutsk area were identified as Siberian subtype of TBE virus. BHK-cell adapted mutant of TBE virus showed lower neuro-invasive virulence in mice than parent virus. The mutant carried one amino acid substitution in envelope protein which resulted in increase of positive charge of the protein. The mutant-infected mice showed lower virus titers in bloods and spleens than the parent-infected mice. Infectious c-DNA clone of TBE virus Hokkaido strain was successfully generated and was applied to examine the neurovirulence in mice. One amino acid change in envelope protein and 2 amino acid changes in Ns5 protein showed a synergistic effect on reduced neurovirulence in mice.     

Effects of luteolin on arylamine N-acetyltransferase activity in human liver tumour cells

The human liver tumour cell line (J5) was selected in order to evaluate whether or not luteolin affected arylamine N-acetyltransferase (NAT) activity. Using high performance liquid chromatography, the NAT activity for acetylation of arylamine substrates (2-aminofluorene and p-aminobenzoic acid) was determined. The cytosolic NAT activity in human liver tumour cells was 2.74+/-0.26 and 1.68+/-0.20 nmol/min/mg of protein for 2-aminofluorene and p-aminobenzoic acid, respectively. Luteolin displayed a dose-dependent inhibition to cytosolic NAT activity and intact human liver tumour cells. Time-course experiments showed that NAT activity measured from intact human liver tumour cells was inhibited by luteolin for up to 24 h. Using standard steady-state kinetic analysis, it was shown that luteolin was a possible noncompetitive inhibitor to NAT activity in cytosols. This report is the first to show how luteolin affects NAT activity in human liver tumour cells.     

A study of the antioxidant and membranotropic activities of luteolin using different model systems

Luteolin, a water-insoluble 3′,4′,5,7-tetrahydroxyflavon, is one of the best-studied representatives of bioflavonoids. Luteolin is an essential food component for humans and other mammals that possesses a wide spectrum of biological activities by affecting the activities of various metabolic enzymes, target receptors, and signal transduction pathways. In this study, we conducted a comparative study of the antioxidant (free-radical scavenging) properties of luteolin in 2,2′-azobis(2-methylpropionamidine) dihydrochloride–luminol and hemoglobin–hydrogen peroxide–luminol systems and assessed its effect on the permeability of planar lipid bilayer membranes. Trolox was used as a reference antioxidant, while ascorbic acid and dihydroquercetin were taken as standards. Luteolin shows moderate antioxidant activity, exhibiting a higher antioxidant capacity than trolox and ascorbic acid, but it was less effective than dihydroquercetin in tests for antioxidant activity in the studied systems. The studied compounds can be ranked according to the effectiveness of their antioxidant action: dihydroquercetin > luteolin > trolox > ascorbic acid. It should be noted that the antioxidant activity of a water-soluble form of luteolin, luteolin disulfate, is comparable with that of luteolin. Luteolin does not cause significant changes in the permeability of planar bilayer membranes in the dose range from 1.5 to 30 μM. Our findings indicate the presence of a high level of free-radical scavenging activity and the absence of a primary membranotropic effect for luteolin. It can be assumed that the multiple pleiotropic nature of luteolin activity towards a variety of biological systems is associated not only with a neutralizing effect in regard to reactive oxygen species, but also with the ability of luteolin to block and modulate different cell-signaling processes and biochemical pathways. The presumed mechanisms of the biological activity of luteolin and luteolin disulfate are discussed.     

Discovery and synthesis of novel luteolin derivatives as DAT agonists

Luteolin, 5,7-dihydroxy-2-(3,4-dihydroxyphenyl)-4H-chromen-4-one, has been proposed and proved to be a novel dopamine transporter (DAT) activator. In order to develop this potential of luteolin, a series of novel luteolin derivatives were designed, synthesized, and evaluated for their DAT agonistic activities, utilizing constructed Chinese hamster ovary (CHO) cell lines stably expressing rat DAT. Biological screening results demonstrated that luteolin derivatives 1d, 1e, and 4c carry great DAT agonistic potency (EC(50)=0.046, 0.869, and 1.375μM, respectively) compared with luteolin 8 (EC(50)=1.45±0.29μM). Luteolin derivative 1d, notably, exhibited a 32-fold-higher DAT agonistic potency than luteolin. These luteolin derivatives represent a novel DAT agonist class, from which lead compounds useful for exploration of additional novel DAT agonists could be drawn.     

森林脑炎自然疫源地样本的监测及病毒的分离研究

为了解森林脑炎疫源地的分布变化趋势及样本分离病毒的特性,采集了森林脑炎高发区周边的森林全沟硬蜱、血蜱样本及森林脑炎患者的脑组织样本,用小白鼠脑内接种法检测、分离病毒分离的病毒经鉴别试验证明为森林脑炎病毒：蜱、脑两种标本检测的阳性率分别为50％和100％、结果表明森林脑炎的疫区有从林区向农业区扩散的趋势,且全沟硬蜱的带毒率较高;森脑患者的脑组织样本与蜱标本病毒的性状育差异     

Evidence of biosynthetic simplicity in the flavonoid chemistry of the ricciaceae

The major flavonoids in Riccia crystallina are naringenin and its 7-O-glucoside, apigenin 7-O-glucoside and apigenin 7-O-glucuronide and derivatives. Ricciocarpus natans is a rich source of luteolin 7,3′-di-O-glucuronide and also contains the 7-O-glucuronides of apigenin and luteolin and the 3′-O-glucuronide of luteolin. A parallel between the production of biosynthetically simple flavonoids and reduced morphology is evident among these liverworts.     

Chemotaxis of Rhizobium meliloti to the plant flavone luteolin requires functional nodulation genes.

Luteolin is a phenolic compound from plants that acts as a potent and specific inducer of nodABC gene expression in Rhizobium meliloti. We have found that R. meliloti RCR2011 exhibits positive chemotaxis towards luteolin. A maximum chemotactic response was observed at 10(-8) M. Two closely related flavonoids, naringenin and apigenin, were not chemoattractants. The presence of naringenin but not apigenin abolished chemotaxis of R. meliloti towards luteolin. A large deletion in the nif-nod region of the symbiotic megaplasmid eliminated all chemotactic response to luteolin but did not affect general chemotaxis, as indicated by swarm size on semisoft agar plates and chemotaxis towards proline in capillary tubes. Transposon Tn5 mutations in nodD, nodA, or nodC selectively abolished the chemotactic response of R. meliloti to luteolin. Agrobacterium tumefaciens GMI9050, a derivative of the C58 wild type lacking a Ti plasmid, responded chemotactically to 10(-8) M luteolin. The introduction of a 290-kilobase nif-nod-containing sequence of DNA from R. meliloti into A. tumefaciens GMI9050 enabled the recipient to respond to luteolin at concentrations peaking at 10(-6) M as well as at concentrations peaking at 10(-8) M. The response of A. tumefaciens GMI9050 to luteolin was also abolished by the presence of naringenin.