Coupling deep transcriptome analysis with untargeted metabolic profiling in Ophiorrhiza pumila to further the understanding of the biosynthesis of the anti-cancer alkaloid camptothecin and anthraquinones.

The Rubiaceae species, Ophiorrhiza pumila, accumulates camptothecin, an anti-cancer alkaloid with a potent DNA topoisomerase I inhibitory activity, as well as anthraquinones that are derived from the combination of the isochorismate and hemiterpenoid pathways. The biosynthesis of these secondary products is active in O. pumila hairy roots yet very low in cell suspension culture. Deep transcriptome analysis was conducted in O. pumila hairy roots and cell suspension cultures using the Illumina platform, yielding a total of 2 Gb of sequence for each sample. We generated a hybrid transcriptome assembly of O. pumila using the Illumina-derived short read sequences and conventional Sanger-derived expressed sequence tag clones derived from a full-length cDNA library constructed using RNA from hairy roots. Among 35,608 non-redundant unigenes, 3,649 were preferentially expressed in hairy roots compared with cell suspension culture. Candidate genes involved in the biosynthetic pathway for the monoterpenoid indole alkaloid camptothecin were identified; specifically, genes involved in post-strictosamide biosynthetic events and genes involved in the biosynthesis of anthraquinones and chlorogenic acid. Untargeted metabolomic analysis by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) indicated that most of the proposed intermediates in the camptothecin biosynthetic pathway accumulated in hairy roots in a preferential manner compared with cell suspension culture. In addition, a number of anthraquinones and chlorogenic acid preferentially accumulated in hairy roots compared with cell suspension culture. These results suggest that deep transcriptome and metabolome data sets can facilitate the identification of genes and intermediates involved in the biosynthesis of secondary products including camptothecin in O. pumila.

Mutational analysis of conserved outer sphere arginine residues of chalcone synthase.

Chalcone synthase (CHS), a key enzyme in flavonoid biosynthesis, catalyses sequential decarboxylative condensations of p-coumaroyl-CoA with three malonyl-CoA molecules and cyclizes the resulting tetraketide intermediate to produce chalcone. Phenylglyoxal, an Arg selective reagent, was found to inactivate the enzyme, although no Arg is found at the active site. Conserved, non-active site Arg residues of CHS were individually mutated and the results were discussed in the context of the 3D structure of CHS. Arg199 and Arg350 were shown to provide important interactions to maintain the structural integrity and foldability of the enzyme. Arg68, Arg172 and Arg328 interact with highly conserved Gln33/Phe215, Glu380 and Asp311/Glu314, respectively, thus helping position the catalytic Cys-His-Asn triad and the (372)GFGPG loop in correct topology at the active site. In particular, a mutation of Arg172 resulted in selective impairment in the cyclization activities of CHS and stilbene synthase, a related enzyme that catalyses a different cyclization of the same tetraketide intermediate. These Arg residues and their interactions are well conserved in other enzymes of the CHS superfamily, suggesting that they may serve similar functions in other enzymes. Mutations of Arg68 and Arg328 had been found in mutant plants that showed impaired CHS activity.

Astaxanthin ameliorates features of metabolic syndrome in SHR/NDmcr-cp.

Glucose and lipid metabolic parameters play crucial roles in metabolic syndrome and its major feature of insulin resistance. This study was designed to investigate whether dietary astaxanthin oil (ASX-O) has potential effects on metabolic syndrome features in an SHR/NDmcr-cp (cp/cp) rat model. Oral administration of ASX (50 mg/kg/day) for 22 weeks induced a significant reduction in arterial blood pressure in SHRcp. It also significantly reduced the fasting blood glucose level, homeostasis index of insulin resistance (HOMA-IR), and improved insulin sensitivity. The results also showed an improved adiponectin level, a significant increase in high-density lipoprotein cholesterol, a significant decrease in plasma levels of triglycerides, and non-esterified fatty acids. Additionally, ASX showed significant effects on the white adipose tissue by decreasing the size of the fat cells. These results suggest that ASX ameliorates insulin resistance by mechanisms involving the increase of glucose uptake, and by modulating the level of circulating lipid metabolites and adiponectin.

Antihypertensive potential and mechanism of action of astaxanthin: III. Antioxidant and histopathological effects in spontaneously hypertensive rats.

We investigated the effects of a dietary astaxanthin (ASX-O) on oxidative parameters in spontaneously hypertensive rats (SHR), by determination of the level of nitric oxide (NO) end products nitrite/nitrate (NO2-/NO3-) and lipid peroxidation in ASX-O-treated SHR. Oral administration of the ASX-O significantly reduced the plasma level of NO2-/NO3- compared to the control vehicle (p<0.05). The lipid peroxidation level, however, was reduced in both ASX-O- and olive oil-treated groups. We also analyzed the post-treatment effects of ASX-O on the vascular tissues by examining the changes in the aorta and coronary arteries and arterioles. The dietary ASX-O showed significant reduction in the elastin bands in the rat aorta (p<0.05). It also significantly decreased the [wall : lumen] aerial ratio of the coronary arteries. These results suggest that ASX-O can modulate the oxidative condition and may improve vascular elastin and arterial wall thickness in hypertension.

Astaxanthin, a carotenoid with potential in human health and nutrition.

Astaxanthin (1), a red-orange carotenoid pigment, is a powerful biological antioxidant that occurs naturally in a wide variety of living organisms. The potent antioxidant property of 1 has been implicated in its various biological activities demonstrated in both experimental animals and clinical studies. Compound 1 has considerable potential and promising applications in human health and nutrition. In this review, the recent scientific literature (from 2002 to 2005) is covered on the most significant activities of 1, including its antioxidative and anti-inflammatory properties, its effects on cancer, diabetes, the immune system, and ocular health, and other related aspects. We also discuss the green microalga Haematococcus pluvialis, the richest source of natural 1, and its utilization in the promotion of human health, including the antihypertensive and neuroprotective potentials of 1, emphasizing our experimental data on the effects of dietary astaxanthin on blood pressure, stroke, and vascular dementia in animal models, is described.

Antioxidant constituents of Caragana tibetica.

Caragana tibetica KOM. (Fabaceae) is a medicinal plant that has been traditionally used in western part of China. In the course of our screening study on antioxidant activity of medicinal plants, the 70% acetone extract of the stems of C. tibetica was found to have a potent superoxide anion scavenging activity. Tibeticanol (1), a new piceatannol dimer possessing antioxidant activity, was isolated along with eleven known aromatic compounds. Their structures were elucidated on the basis of NMR and MS data. Enzyme oxidation of monomeric stilbene, piceatannol (3), with horseradish peroxidase and hydrogen peroxide yielded cassigarol E (5) and G (6) as major products. Most of the isolated compounds exhibited superoxide anion scavenging activity.

Antihypertensive potential and mechanism of action of astaxanthin: II. Vascular reactivity and hemorheology in spontaneously hypertensive rats.

The current study was designed to determine the effects of a dietary astaxanthin (ASX-O) on vascular reactivity in spontaneously hypertensive rats (SHR), in order to verify its antihypertensive action mechanism. We evaluated contractions induced by phenylephrine (Phe), angiotensin II (Ang II) and the xanthine/xanthine oxidase (Xan/XOD) system, and relaxations induced by sodium nitroprusside (SNP) as well as endothelium-dependent relaxations mediated by acetylcholine (ACh) in thoracic aorta of the SHR, with and without ASX-O intervention. We also investigated the effects of ASX-O on blood rheology using a microchannel array system. In this study, ASX-O showed a significant modulatory effect on nitric oxide (NO)-induced vasorelaxation by the NO-donor SNP (p<0.05). However, it did not show significant effects in restoring the impaired endothelium-dependent relaxation to ACh in the SHR. On the other hand, the constrictive effects by Phe, Ang II and Xan/XOD were ameliorated by ASX-O (p<0.05). ASX-O also demonstrated significant hemorheological effect by decreasing the microchannel transit time of whole blood. In conclusion, the results suggest that ASX-O may act in modulating the blood fluidity in hypertension, and that the antihypertensive effects of ASX-O may be exerted through mechanisms including normalization of the sensitivity of the adrenoceptor sympathetic pathway, particularly [alpha]-adrenoceptors, and by restoration of the vascular tone through attenuation of the Ang II- and reactive oxygen species (ROS)-induced vasoconstriction.

Antioxidant and antiviral activities of plastoquinones from the brown alga Sargassum micracanthum, and a new chromene derivative converted from the plastoquinones.

Two plastoquinones were isolated from the methanolic extract of the brown alga Sargassum micracanthum, and these were identified as a known 2-geranylgeranyl-6-methylbenzoquinone and its hydroquinone, respectively, based on spectroscopic analysis. The absolute configuration of the secondary hydroxyl group was determined by the modified Mosher's method using the new chromene derivative converted from plastoquinones. One of the plastoquinones and the chromene exhibited significant antioxidant activities, such as an inhibitory effect on lipid peroxidation and a radical scavenging effect on 1,1-diphenyl-2-picrylhydrazyl (DPPH). The benzoquinone-type compound and the chromene derivative were found to have potent antiviral activity against human cytomegalovirus (HCMV).

Antihypertensive and neuroprotective effects of astaxanthin in experimental animals.

Astaxanthin is a natural antioxidant carotenoid that occurs in a wide variety of living organisms. We investigated, for the first time, antihypertensive effects of astaxanthin (ASX-O) in spontaneously hypertensive rats (SHR). Oral administration of ASX-O for 14 d induced a significant reduction in the arterial blood pressure (BP) in SHR but not in normotensive Wistar Kyoto (WKY) strain. The long-term administration of ASX-O (50 mg/kg) for 5 weeks in stroke prone SHR (SHR-SP) induced a significant reduction in the BP. It also delayed the incidence of stroke in the SHR-SP. To investigate the action mechanism of ASX-O, the effects on PGF(2alpha)-induced contractions of rat aorta treated with NG-nitro-L-arginine methyl ester (L-NAME) were studied in vitro. ASX-O (1 to 10 microM) induced vasorelaxation mediated by nitric oxide (NO). The results suggest that the antihypertensive effect of ASX-O may be due to a NO-related mechanism. ASX-O also showed significant neuroprotective effects in ischemic mice, presumably due to its antioxidant potential. Pretreatment of the mice with ASX-O significantly shortened the latency of escaping onto the platform in the Morris water maze learning performance test. In conclusion, these results indicate that astaxanthin can exert beneficial effects in protection against hypertension and stroke and in improving memory in vascular dementia.

Expression, purification, and characterization of AknX anthrone oxygenase, which is involved in aklavinone biosynthesis in Streptomyces galilaeus.

In streptomycete anthracycline biosynthetic gene clusters, small open reading frames are located just upstream of minimal polyketide synthase genes. aknX is such a gene found in the aklavinone-aclacinomycin biosynthetic gene cluster of Streptomyces galilaeus. In order to identify its function, the aknX gene was expressed in Escherichia coli. The cell extract prepared from E. coli cells overexpressing AknX protein exhibited anthrone oxygenase activity, which converted emodinanthrone to anthraquinone emodin. This indicates that AknX and related gene products such as DnrG and SnoaB are involved in the formation of aklanonic acid from its anthrone precursor, as suggested by their homology with TcmH and ActVA6. The AknX protein fused with a His(6) tag was efficiently purified to homogeneity by Ni(2+) affinity and anion-exchange column chromatography. The native molecular mass of AknX was estimated to be 42 kDa by gel filtration. Thus, native AknX is considered to have a homotrimeric subunit structure. AknX, like TcmH and ActVA6, possesses no apparent prosthetic group for oxygen activation. Site-directed mutagenesis was carried out to identify the key amino acid residue(s) involved in the oxygenation reaction. Of seven AknX mutants expressed, the W67F mutant showed significantly reduced oxygenase activity, suggesting the important role of the W67 residue in the AknX reaction. A possible mechanism for the reaction via peroxy anion intermediate is proposed.