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Biomedical subjects

S X Xu

Publications and source records attributed to S X Xu.

At least 19 recordsLinked to original sources
PubMed2006

Characterization of an anther- and tapetum-specific gene and its highly specific promoter isolated from tomato.

A full-length genomic clone of 2,233 bp long containing an anther- and tapetum-specific gene TomA108 was isolated and characterized from tomato. The gene was present in one copy per haploid genome. The isolated clone contained 5' and 3' untranslated regions of 810 and 170 nucleotides, respectively and a single intron with highly repetitive sequences. The cDNA encoded the protein with an apparent mass of 10.6 kDa and a pI (isoelectric point) of 5.3. It was cysteine-rich and had an N-terminal hydrophobic domain with characteristics of a secretory signal. Amino acid sequence comparisons demonstrated that the protein was closely related to a family of cereal seed storage proteins and protease inhibitors. The fusion of beta-glucuronidase to the TomA108 promoter demonstrated that the promoter was highly active from early-meiosis to free microspores production in tapetum of tobacco. This strong and highly specific promoter can be potentially used to generate male sterility for efficient production of plant hybrids.

Amino Acid Sequence↗
PubMed2005

Genetic transformation of Leymus chinensis with the PAT gene through microprojectile bombardment to improve resistance to the herbicide Basta.

Chinese leymus [Leymus chinensis (Trin.) Tzvel.] is a perennial grass (tribe Gramineae) that is widely distributed throughout northern China and Mongolia where it is produced as a forage product. Severe production losses due to weed growth have serious economic consequences, and as non-selective herbicides not only kill the weeds but are also harmful to this forage grass, the introduction of a foreign gene for resistance to the herbicide Basta is necessary since this species lacks herbicide resistance. We have investigated the transformation of a gene for phosphinothricin acetyltransferase (PAT) through microprojectile bombardment in Chinese leymus. Calli from immature inflorescences cultured on N6 medium supplemented with 2.0 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D) and 5.0 mg/l of glutamine were bombarded. The bombarded calli survived on selection medium with 1.0 mg/l of phosphinothricin (PPT). Twenty-three plantlets regenerated from resistant calli on differentiation medium supplemented with 1.0 mg/l 6-benzylaminopurine, 1.0 mg/l kinetin, and 1.0 mg/l PPT, and five of these regenerated plantlets survived on rooting medium with 1.0 mg/l of PPT. PCR and Southern blotting analyses indicated that the PAT gene had been integrated into the genomes of two Chinese leymus plantlets and that the gene was stably transferred to its clonal offsprings. There were no other phenotypic effects associated with transgene expression during vegetative growth except tolerance to the herbicide Basta.

Acetyltransferases↗
PubMed2004

Cloning of hypoxia-inducible factor 1alpha cDNA from a high hypoxia tolerant mammal-plateau pika (Ochotona curzoniae).

Hypoxia-inducible factor 1 is a transcription factor composed of HIF-1alpha and HIF-1beta. It plays an important role in the signal transduction of cell response to hypoxia. Plateau pika (Ochotona curzoniae) is a high hypoxia-tolerant and cold adaptation species living only at 3000-5000 m above sea level on the Qinghai-Tibet Plateau. In this study, HIF-1alpha cDNA of plateau pika was cloned and its expression in various tissues was studied. The results indicated that plateau pika HIF-1alpha cDNA was highly identical to those of the human (82%), bovine (89%), mouse (82%), and Norway rat (77%). The deduced amino acid sequence (822bp) showed 90%, 92%, 86%, and 86% identities with those of the human, bovine, house mouse, and Norway rat, respectively. Northern blot analyses detected two isoforms named pLHIF-1alpha and pSHIF-1alpha. The HIF-1alpha mRNA was highly expressed in the brain and kidney, and much less in the heart, lung, liver, muscle, and spleen, which was quite different from the expression pattern of mouse mRNA. Meanwhile, a new variant of plateau pika HIF-1alpha mRNA was identified by RT-PCR and characterized. The deduced protein, composed of 536 amino acids, lacks a part of the oxygen-dependent degradation domain (ODD), both transactivation domains (TADs), and the nuclear localization signal motif (NLS). Our results suggest that HIF-1alpha may play an important role in the pika's adaptation to hypoxia, especially in brain and kidney, and pika HIF-1alpha function pattern may be different from that of mouse HIF-1alpha. Furthermore, for the high ratio of HIF-1alpha homology among the animals, the HIF-1alpha gene may be a good phylogenetic performer in recovering the true phylogenetic relationships among taxa.

Adaptation, Physiological↗
PubMed2004

Binding affinities of ocular hypotensive beta-blockers levobetaxolol, levobunolol, and timolol at endogenous guinea pig beta-adrenoceptors.

The current study determined the relative affinities and selectivities of numerous beta-adrenoceptor antagonists at the endogenous beta(1)- and beta(2)-adrenoceptors in guinea pig heart and lung, respectively, using [(3)H]-CGP12177. Specific binding of [(3)H]-CGP12177 comprised 80 +/- 0.2% (n = 11) and 94 +/- 0.2% (n = 16) of the total binding in washed heart and lung homogenates, respectively. Concentration-dependent displacement of [(3)H]-CGP12177 binding from beta-adrenoceptors in both preparations was observed with nine different beta-adrenoceptor antagonists. Levobetaxolol, betaxolol, CGP-20712A, levobunolol, and timolol yielded bi-phasic (two-site-fit) competition curves in the heart, while CGP-20712A, ICI-118551 and levobunolol produced bi-phasic curves in the lung preparation. The high-affinity component of [(3)H]-CGP12177 binding in the heart and lung reflected binding to beta(1)-receptors and beta(2)-receptors, respectively. The binding inhibition parameters (IC(50)s) for displacement of [(3)H]-CGP12177 from these predominantly high-affinity sites were: levobetaxolol (24.9 +/- 1.6 nM heart, 4810 +/- 367 nM lung), racemic betaxolol (37.9 +/- 8.7 mM heart; 8840 +/- 424 mM lung), CGP-20712A (4.6 +/- 0.9 nM heart; 171,000 +/- 109,000 nM lung), ICI-118551 (9230 +/- 3240 nM heart; 2.9 +/- 0.6 nM lung), levobunolol (42 +/- 15 nM heart, 0.3 +/- 0.2 nM lung), (l)-timolol (3.1 nM heart, 2.9 +/- 1.5 nM lung), ICI-215001 (5840 +/- 114 nM heart; 26100 +/- 3200 nM lung), BRL-37344 (83,300 +/- 2660 nM heart; 13,200 +/- 1250 lung). These data indicated that while levobetaxolol and betaxolol possessed a 193-233-fold selectivity for beta(1)-receptors, levobunolol exhibited a 140-fold beta(2)-receptor selectivity and (l)-timolol was essentially nonselective.

Adrenergic beta-Antagonists↗
PubMed2004

Pharmacological characterization and identification of EP3 prostanoid receptor binding sites in hamster uterus homogenates.

The pharmacological properties of [(3)H]-prostaglandin E(2) ([(3)H]-PGE(2)) binding to washed homogenates of hamster uterus were determined. Scatchard analysis of competition data yielded dissociation constants (K(d)s) of 30.9 +/- 5.6 nM (n = 3) and apparent receptor density (B(max)) of 25.25 +/- 1.89 pmol g(-1) wet weight tissue (74 +/- 8% specific binding). Competition studies yielded the following affinity parameters (K(i)) for various prostanoids: GR63799X = 13 4 nM; PGE(2) = 17 +/- 3 nM; sulprostone = 64 +/- 5 nM; enprostil = 67 +/- 3 nM; misoprostol = 124 +/- 15 nM; cloprostenol = 187 +/- 33 nM; carba-prostacyclin = 260 +/- 167 nM; iloprost = 555 +/- 162 nM; PGF(2 alpha) = 767 +/- 73 nM; PGD(2) > 3560 nM; fluprostenol = 11 790 +/- 2776 nM; RS93520 = 21 558 +/- 14 228 nM. These data closely matched the pharmacological profile of previously described EP(3) receptors such as in bovine corpus luteum (BCLM) and the cloned mammalian EP(3) receptors. The high correlation between the current hamster uterus pharmacology data vs the EP(3) receptor binding in BCLM (r = 0.94; P < 0.0001), vs cloned human EP(3) receptor (r = 0.94, P < 0.0001), vs the cloned mouse EP(3) receptor binding (r = 0.78; P < 0.002), vs cloned rat EP(3) receptor (r = 0.9, P < 0.0004), and vs EP(3) receptor-mediated functional responses (r = 0.72, P < 0.02) substantiated the conclusion that the hamster uterus contains EP(3) receptor binding sites.

Animals↗
PubMed2003

Ocular hypotensive FP prostaglandin (PG) analogs: PG receptor subtype binding affinities and selectivities, and agonist potencies at FP and other PG receptors in cultured cells.

Natural prostaglandins (PGs) such as PGD2, PGE2, PGF2(2alpha), and PGI2 exhibited the highest affinity for their respective cognate receptors, but were the least selective agents when tested in receptor binding assays. Travoprost acid ([+]-fluprostenol) was the most FP-receptor-selective compound, exhibiting a high affinity (Ki = 35 +/- 5 nM) for the FP receptor, and minimal affinity for DP (Ki = 52,000 nM), EP1 (Ki = 9540 nM), EP3 (Ki = 3501 nM), EP4 (Ki = 41,000 nM), IP (Ki > 90,000 nM), and TP (Ki = 121,000 nM) receptors. Travoprost acid was the most potent PG analog tested in FP receptor functional phosphoinositide turnover assays in the following cell types: human ciliary muscle (EC50 = 1.4 nM), human trabecular meshwork (EC50 = 3.6 nM), and mouse fibroblasts and rat aortic smooth muscle cells (EC50 = 2.6 nM). Although latanoprost acid exhibited a relatively high affinity for the FP receptor (Ki = 98 nM), it had significant functional activity at FP (EC50 = 32-124 nM) and EP1 (EC50 = 119 nM) receptors. Bimatoprost acid was less selective, exhibiting a relatively high affinity for the FP (Ki = 83 nM), EP1 (Ki = 95 nM), and EP3 (Ki = 387 nM) receptors. Bimatoprost acid exhibited functional activity at the EP1 (EC50 = 2.7 nM) and FP (EC50 = 2.8-3.8 nM in most cells) receptors. Bimatoprost (nonhydrolyzed amide) also behaved as an FP agonist at the cloned human FP receptor (EC50 = 681 nM), in h-TM (EC50 = 3245 nM) and other cell types. Unoprostone and S-1033 bound with low affinity (Ki = 5.9 microM to > 22 microM) to the FP receptor, were not selective, but activated the FP receptor. In conclusion, travoprost acid has the highest affinity, the highest FP-receptor-selectivity, and the highest potency at the FP receptor as compared to the other ocular hypotensive PG analogs known so far, including free acids of latanoprost, bimatoprost, and unoprostone isopropyl ester.

Amides↗
PubMed2002

Pharmacological and molecular biological (RT-PCR) characterization of functional TP prostanoid receptors in immortalized human non-pigmented ciliary epithelial cells.

Immortalized human non-pigmented ciliary epithelial (NPE) cells (ODM-2) were shown to express the mRNA for the prostanoid TPalpha but not the TPbeta receptor using reverse transcription-polymerase chain reaction (RT-PCR). These TPalpha receptors were coupled to phospholipase C (PLC) and, thus, promoted phosphoinositide (PI) turnover. TP receptor agonists yielded the following potencies (EC50S) in the PI turnover assays: I-BOP = 8.2 +/- 1.1 nM; carbocyclic TA2 = 87.5 +/- 25.3 nM; U-44069 = 1.16 +/- 0.32 microM; U-46619 = 1.2 +/- 0.2 microM (n = 4-17). Agonists selective for other prostanoid receptor subtypes (e.g., fluprostenol and sulprostone) were inactive. The agonist effects of U-44619 and I-BOP were potently blocked, in an apparent non-competitive manner (ki = 53.9 +/- 12 nM; pA2s = 7.6-7.8; pKbs = 7.38), by the TP receptor-selective antagonist, SQ29,548, but were unaffected by other prostanoid receptor antagonists (e.g., AH6809, AL-8810). The PLC inhibitor (U73122) inhibited U-46619-induced PI turnover (IC50 = 4.3 +/- 0.6 microM). The functional potencies of the compounds stimulating or inhibiting the TP receptor-mediated PI turnover in the NPE cells correlated well with the TP receptor binding affinities of these compounds at human platelet TP receptors (r = 0.98). These studies have shown the presence of the mRNA for and the expression of functional TPalpha receptors coupled to PLC in human NPE cells. The TPalpha receptors on NPE cells may be responsible for inhibiting aqueous humor production and may help explain the intraocular pressure-lowering effects of certain TP agonists.

Alternative Splicing↗
PubMed2001

Five saponins from the root bark of Aralia elata.

Five saponins, 3-O-[beta-D-glucopyranosyl (1-->2)-[beta-D-glucopyranosyl (1-->3)]-beta-D-glucopyranosyl]-oleanolic acid 28-O-beta-D-glucopyranosyl ester (aralia-saponin V), 3-O-[beta-D-glucopyranosyl (1-->2)-[beta-D-glucopyranosyl (1-->3)]-beta-D-glucopyranosyl]-echinocystic acid 28-O-beta-D-glucopyranosyl ester (aralia-saponin VI), 3-O-beta-D-glucopyranosyl (1-->2)-[beta-D-glucopyranosyl (1-->3)]-beta-D-glucopyranosyl]-hederagenin 28-O-beta-D-glucopyranosyl ester (aralia-saponin VII), 3-O-[beta-D-glucopyranosyl-(1-->3)-beta-D-glucopyranosyl-(1-->3)-[beta-D-glucopyranosyl-(1-->2)]-beta-D-glucopyranosyl]-caulophyllogenin 28-O-beta-D-glucopyranosyl ester (aralia-saponin VIII), 3-O-[beta-D-glucopyranosyl (1-->2)-[beta-D-glucopyranosyl(1-->3)]-alpha-L-arabinopyranosyl]-hederagenin 28-O-beta-D-glucopyranosyl ester (aralia-saponin IX), were isolated from the root bark of Aralia elata (Miq.) Seem., together with four known compounds. Their structures were determined on the basis of chemical and spectroscopic methods.

Magnoliopsida↗
PubMed2001

A new sesquiterpene lactone glucoside from Ixeris sonchifolia.

A new sesquiterpene lactone glucoside, Ixerin Z1 (1), was isolated from the whole plants of Ixeris sonchifolia (Bge.) Hance, along with 15 known compounds. The structure of 1 was elucidated as 1(10),3,11(13)-guaiatriene-12,6-olide-2-one-3-O-[6'-(p-hydroxyphenylacetyl)]-glucopyranoside by spectroscopic methods including 2D-NMR techniques.

Asteraceae↗
PubMed2001

A pair of 24-hydroperoxyl epimeric dammarane saponins from flower-buds of Panax ginseng.

Further investigation on the saponins of the flower-buds of Panax ginseng C. A. Meyer has resulted in the isolation and structural elucidation of a pair of new 24-epimers of dammarane type saponins named ginsenoside I and II. The structures of the epimers were characterized on the basis of chemical and spectral evidence as 3-O-[beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranosyl]-20-S-O-beta-D-glucopyranosyl-3beta, 12beta,20(S)-trihydroxy-24xi-hydroperoxydammar-25-ene, except for their C-24 configurations. Ginsenoside I is a new triterpene glycoside, and ginsenoside II is a known compound first isolated from a natural plant.

Chromatography, High Pressure Liquid↗
PubMed2001

Levobetaxolol (Betaxon) and other beta-adrenergic antagonists: preclinical pharmacology, IOP-lowering activity and sites of action in human eyes.

The pharmacological characteristics of levobetaxolol, a single active isomer of betaxolol, were determined and compared with activities of other beta-adrenoceptor antagonists. Levobetaxolol (43-fold beta1-selective) exhibited a higher affinity at cloned human beta1 (Ki = 0.76 nM) than at beta2 (Ki = 32.6 nM) receptors, while dextrobetaxolol was much weaker at both receptors. Levobetaxolol potently antagonized functional activities at cloned human beta1 and beta2 receptors, and also at guinea pig atrial beta1, tracheal beta2 and rat colonic beta3 receptors (IC50s = 33.2 nM, 2970 nM and 709 nM, respectively). Thus, levobetaxolol was 89-times beta1-selective (vs beta2). Levobetaxolol (Ki = 16.4 nM) was more potent than dextrobetaxolol (Ki = 2.97 microM) at inhibiting isoproterenol-induced cAMP production in human non-pigmented ciliary epithelial cells. Levobunolol and (l)-timolol had high affinities at beta1 and beta2 receptors but were considerably less beta1-selective than levobetaxolol. Levo-, dextro- and racemic-betaxolol exhibited little or no affinity, except at sigma sites and Ca2+-channels (IC50s > 1 microM), at 89 other receptor/ligand binding sites. Levobetaxolol exhibited a micromolar affinity for L-type Ca2+-channels. In conscious ocular hypertensive cynomolgus monkeys, levobetaxolol was more potent than dextrobetaxolol, reducing intraocular pressure by 25.9+/-3.2% at a dose of 150 microg/eye (n = 15-30). Quantitative [3H]-levobetaxolol autoradiography revealed high levels of binding to human ciliary processes, iris, choroid/retina, and ciliary muscles. In conclusion, levobetaxolol is a potent, high affinity and beta1-selective IOP-lowering beta-adrenoceptor antagonist.

Adrenergic beta-Agonists↗
PubMed2001

A new triterpenoidal saponin from Ixeris sonchifolia and its cytotoxic activity.

A new triterpenoidal saponin, echinocystic acid 3-O-beta-D-glucopyranosyl-(1-->3)-alpha-L-arabinopyranoside (1), was isolated from Ixeris sonchifolia. Its structure was elucidated on the basis of full spectral data analysis and chemical methods. The cytotoxic activity of compound 1 was evaluated using the tumor cell lines of A375, Hela, and L929 in vitro.

Antineoplastic Agents, Phytogenic↗
PubMed2001

[Quantitative determination of icariin in "tangzhi shuangjiang cha" by high performance liquid chromatography].

Icariin in "Tangzhi Shuangjiang Cha" was quantitatively determined by HPLC with ODS column, a mixture of MeOH-H2O(60:40, V/V) as mobile phase and UV detection at 270 nm. There was a good linear relationship within the range of 0.1 g/L-0.5 g/L(r = 0.9993). The average recovery was 101.4%, RSD was below 2.7%(n = 3). The method is rapid, simple, accurate and reproducible. And the method is proposed to be used for quality control of "Tangzhi Shuangjiang Cha".

Chromatography, High Pressure Liquid↗
PubMed2001

[Chemical constituents from the leaves of crataegus pinnatifida Bge. var. major N.E.Br].

AIM: To study the chemical constituents in the leaves of Crataegus pinnatifida Bge. var. major N.E.Br.. METHODS: Compounds were isolated by using porous resin, silica gel, polyamide chromatographic techniques etc. Their structures were elucidated by chemical and spectroscopic methods. RESULTS: Eight compounds were identified as pinnatifin I (1), quercetin (2), 3-O-beta-D-glucopyranosyl quercetin (3), 3-O-beta-D-galacopyranosyl quercetin (4), 3-O-beta-D-glucopyranosyl (6-->1)-alpha-L-rhamnosyl quercetin (5), 3-O-beta-D-galacopyranosyl (6-->1)-alpha-L-rhamnosyl quercetin (6), kaempferol (7), 7-O-alpha-L-rhamnosyl-3-O-beta-D- glucopyranosyl kaempferol (8). CONCLUSION: Compound 1 is a new compound. Compound 8 was isolated from this plant for the first time.

Crataegus↗
PubMed2000

Anti-proliferative effect of ginseng saponins on human prostate cancer cell line.

Ginseng is a medicinal herb widely used in Asian countries, and many of its pharmacological actions are attributed to the ginsenosides. In a study of the anti-proliferative activity of ginsenosides using human prostate carcinoma LNCaP cell line, ginsenoside Rg3 displayed growth inhibitory activity. The cells lost its adherent property after incubation in the presence of 250 microM of ginsenoside for 48h. The expression of biomarker genes, including prostate specific antigen (PSA), androgen receptor (AR) and 5alpha-reductase (5alphaR), and that of the proliferating cell nuclear antigen (PCNA), were suppressed. Ginsenoside Rg3 induced classic apoptotic morphology and interfered with the expression of apoptosis-related genes, bcl-2 and caspase-3, in LNCaP cells, as demonstrated by fluorescence microscopy, flow cytometry and reverse transcriptase-polymerase chain reaction. Taken our results together, we suggested that ginsenoside Rg3 activated the expression of cyclin-kinase inhibitors, p21 and p27, arrested LNCaP cells at G1 phase, and subsequently inhibited cell growth through a caspase3-mediated apoptosis mechanism.

5-alpha Reductase Inhibitors↗