Chemosensory context effects: role of perceived similarity and neural commonality. (41/761)

Seven experiments investigated how stimulus context affects judgements of the magnitude of chemosensory stimuli. In each experiment, subjects gave magnitude estimates of the intensity of several concentrations of two substances, with the contextual set of concentrations varying across experimental conditions. Different experiments used different pairs of substances, which could be tastants (sucrose or NaCl) that were sipped, odorants (orange or vanillin) that were sipped (i.e. presented retronasally) or the same odorants sniffed (i.e. presented orthonasally). Varying the stimulus context affected the judgements differentially when the two substances were compositionally different (sucrose and NaCl; sucrose and orange; sucrose and vanillin) but not when they were the same (vanillin or orange presented orally and nasally). Judgements of qualitative similarity of the same pairs of substances, obtained in a separate experiment, failed to predict accurately the pattern of differential context effects. Taken together, the results suggest that differential effects of context relate only indirectly to perceptual dissimilarity per se but may primarily reflect the result of stimulus-specific adaptation-like processes.  (+info)

Xylella genomics and bacterial pathogenicity to plants. (42/761)

Xylella fastidiosa, a pathogen of citrus, is the first plant pathogenic bacterium for which the complete genome sequence has been published. Inspection of the sequence reveals high relatedness to many genes of other pathogens, notably Xanthomonas campestris. Based on this, we suggest that Xylella possesses certain easily testable properties that contribute to pathogenicity. We also present some general considerations for deriving information on pathogenicity from bacterial genomics.  (+info)

Effects of daily oral administration of quercetin chalcone and modified citrus pectin on implanted colon-25 tumor growth in Balb-c mice. (43/761)

The health benefits of fruits and vegetables have been the subject of numerous investigations over many years. Two natural substances, quercetin (a flavonoid) and citrus pectin (a polysaccharide found in the cell wall of plants) are of particular interest to cancer researchers. Two modified versions of these substances - quercetin chalcone (QC) and a pH-modified citrus pectin (MCP) - are the focus of this study. Previous research has confirmed that quercetin exhibits antitumor properties, likely due to immune stimulation, free radical scavenging, alteration of the mitotic cycle in tumor cells, gene expression modification, anti-angiogenesis activity, or apoptosis induction, or a combination of these effects. MCP has inhibited metastases in animal studies of prostate cancer and melanoma. To date, no study has demonstrated a reduction in solid tumor growth with MCP, and there is no research into the antitumor effect of QC. This study examines the effects of MCP and QC on the size and weight of colon-25 tumors implanted in balb-c mice. Fifty mice were orally administered either 1 ml distilled water (controls), low-dose QC (0.8 mg/ml), high-dose QC (1.6 mg/ml), low-dose MCP (0. 8 mg/ml) or high-dose MCP (1.6 mg/ml) on a daily basis, beginning the first day of tumor palpation (usually eight days post-implantation). A significant reduction in tumor size was noted at day 20 in all groups compared to controls. The groups given low-dose QC and MCP had a 29-percent (NS) and 38-percent (p<0.02) decrease in size, respectively. The high-dose groups had an even more impressive reduction in size; 65 percent in the QC group and 70 percent in the mice given MCP (both p<0.001). This is the first evidence that MCP can reduce the growth of solid primary tumors, and the first research showing QC has antitumor activity. Additional research on these substances and their effect on human cancers is warranted.  (+info)

Modified citrus pectin-monograph. (44/761)

Modified citrus pectin (MCP), also known as fractionated pectin, is a complex polysaccharide obtained from the peel and pulp of citrus fruits. Modified citrus pectin is rich in galactoside residues, giving it an affinity for certain types of cancer cells. Metastasis is one of the most life-threatening aspects of cancer and the lack of effective anti-metastatic therapies has prompted research on MCP's effectiveness in blocking metastasis of certain types of cancers, including melanomas, prostate, and breast cancers.  (+info)

Genomic characterization of a liberibacter present in an ornamental rutaceous tree, Calodendrum capense, in the Western Cape Province of South Africa. Proposal of 'Candidatus Liberibacter africanus subsp. capensis'. (45/761)

In 1994, the uncultured phloem-restricted bacteria of citrus huanglongbing (ex-greening) disease in Asia and Africa were characterized as 'Candidatus Liberobacter asiaticum' and 'Candidatus Liberobacter africanum', respectively. Following the rules of the International Code of Nomenclature of Bacteria, the two bacterial species have now been renamed 'Candidatus Liberibacter asiaticus' and 'Candidatus Liberibacter africanus'. A third liberibacter was detected by PCR in an ornamental rutaceous tree, Cape chestnut (Calodendrum capense), in South Africa. The new liberibacter was characterized by serology and from the sequences of its 16S rDNA, intergenic 16S/23S rDNA and ribosomal protein genes of the beta operon. Phylogenetic analysis showed that the liberibacter present in C. capense differed from the two previously described liberibacter species from citrus and that it was more closely related to 'Candidatus Liberibacter africanus' than to 'Candidatus Liberibacter asiaticus'. It is proposed that the liberibacter from C capense be assigned a subspecies status, 'Candidatus Liberibacter africanus subsp. capensis'.  (+info)

Effect of grapefruit juice on Sandimmun Neoral absorption among stable renal allograft recipients. (46/761)

BACKGROUND: The oral formulation of cyclosporin A (CsA)-Sandimmun-has a highly variable absorption. The development of a CsA microemulsion-Sandimmun Neoral-resulted in increased bioavailability, and decreased variability of absorption. The first oral formulation (Sandimmun) interacted with numerous other drugs and grapefruit juice. Several of these interactions might be explained by decreased pre-systemic metabolism by a cytochrome-enzyme (e.g. CYP3A4) located in the enteral mucosa, and/or via the P-glycoprotein-mediated decreased transport of CsA back from enterocytes into the gut lumen. The purpose of this pharmacokinetic study was to investigate the interaction between Sandimmun Neoral and grapefruit juice. METHOD: Eight stable renal transplant recipients were studied during two 8-h sessions in a randomized cross-over design with 4 weeks interval. Following an overnight fast the patients ingested their habitual morning dose of Neoral either with water or with grapefruit juice. During the 8-h study period 10 blood samples were taken for determination of CsA concentration. These results formed the basis for calculation of area under curve (AUC), and half-life (t(1/2)). Maximum concentration (C(max)) and time until C(max) (t(max)) were obtained from the concentration-time profile. RESULTS: The median AUC increased by 38% (12-194%) (P<0.05) following co-administration of Neoral with grapefruit juice. There were no significant changes in C(max), t(max), and t((1/2)). CONCLUSION: Co-administration of Sandimmun Neoral with grapefruit juice resulted in an increased bioavailability of CsA, indicating unchanged pre-systemic enterocyte first-pass metabolism as compared to Sandimmun. There was no impact of an oral grapefruit juice load on systemic clearance of CsA. It seems prudent to advise renal allograft recipients treated with Sandimmun Neoral not to ingest their medication with grapefruit juice.  (+info)

Plasma kinetics and urinary excretion of the flavanones naringenin and hesperetin in humans after ingestion of orange juice and grapefruit juice. (47/761)

The flavanones naringenin and hesperetin exhibit estrogenic, anticarcinogenic and antioxidative properties. Orange juice and grapefruit juice contain high amounts of these compounds, and therefore their intake from the diet can be relatively high. No data are available regarding plasma concentrations or plasma kinetics of flavanones. The objectives of this study were to develop methods allowing the analysis of naringenin and hesperetin from plasma and urine and to study their plasma kinetics and urinary excretion. We also wanted to assess whether plasma or urine flavanone concentrations can be used as biomarkers of intake. Healthy volunteers ingested orange juice (five women and three men) or grapefruit juice (two women and three men) once (8 mL/kg). Eleven blood samples and urine were collected between 0 and 24 h after juice administration. Flavanones were analyzed by HPLC with electrochemical detection. Naringenin and hesperetin were bioavailable from the studied juices, but interindividual variation in bioavailability was remarkable. The resulting plasma concentrations were comparatively high, and the peak plasma concentrations (C(max)) were 0.6 +/- 0.4 micromol/L (means +/- SD) for naringenin from orange juice and 6.0 +/- 5.4 micromol/L for naringenin from grapefruit juice. The corresponding value for hesperetin from orange juice was 2.2 +/- 1.6 micromol/L. The elimination half-lives were between 1.3 and 2.2 h, and therefore plasma concentrations reflect short-term intake. The relative urinary excretion varied depending on the flavanone source and dose and was 30.2 +/- 25.5% and 1.1 +/- 0.8% for naringenin from grapefruit juice and orange juice, respectively, and 5.3 +/- 3.1% for hesperetin from orange juice. The considerable difference in the relative urinary excretion of naringenin from the two juices was most likely caused by dose-dependent renal clearance rather than differences in bioavailability (as indicated by the similar C(max)-to-dose ratios). The results indicate that urine flavanone concentrations are not good biomarkers of dietary intake. We conclude that because of the relatively high concentrations of flavanones in plasma after ingestion of orange juice or grapefruit juice, considerable health effects could ensue in individuals consuming them regularly.  (+info)

Amplification of Citrus tristeza virus from a cDNA clone and infection of citrus trees. (48/761)

Isolates of the Closterovirus, Citrus tristeza virus (CTV), are populations of disparate genotypes and defective RNAs developed during long periods of vegetative propagation of citrus trees. Because it has not been possible to obtain pure cultures of the virus, it is not known what components of the population are primarily responsible for induction of diseases. We previously developed an infectious cDNA clone from which in vitro-produced RNA transcripts could infect protoplasts (Satyanarayana et al., 1999, Proc. Natl. Acad. Sci. USA 96, 7433-7438). However, neither the RNA transcripts nor virions from transcript-infected protoplasts were competent for infection of citrus trees. Using a green fluorescent protein-marked virus as inoculum, we found that the approximately 20-kb RNA from virions or transcripts of cDNA infected only a small percentage of protoplasts ( approximately 0.01%), but virions could infect more than 80% of the protoplasts. Based on this information, we amplified the virus from the cDNA clone (recombinant virus) by successive passages in protoplasts using virions in crude sap as inoculum. By the third to seventh passages in protoplasts, maximal amounts of recombinant progeny virus were produced, which were used for inoculation of small citrus trees by slashing stems in the presence of virion preparations. A relatively high percentage of plants became infected with the recombinant virus from protoplasts, resulting in the first defined pure culture of CTV in plants. The comparative biology of the pure culture of recombinant CTV with that of the parental population in planta demonstrated that the recombinant virus retained through all of the recombinant DNA manipulations the normal functions of replication, movement, and aphid transmissibility, and had a symptom phenotype indistinguishable from that of the parental population. Additionally, fulfilling Koch's postulates of the first pure culture of CTV in plants suggested that the major genotype of the CTV T36 population is the primary determinant of the symptom phenotype. We could distinguish no biological contributions resulting from the minor genotypes and defective RNAs of the parental population.  (+info)