Trevor D. Bailey

Immunomodulatory activities of polysaccharides isolated from Taxillus chinensis and Uncaria rhyncophylla

Taxillus chinensis and Uncaria rhyncophylla are the herbs used in traditional Chinese anticancer formulations. During the past decade, research on plant polysaccharides has gained importance due to their therapeutic value and minimum side effects. In this study, hot water extraction method was employed to isolate polysaccharides from the stems of T. chinensis and stems with hooks of U. rhyncophylla. Size-exclusion chromatography was then used for further fractionation. Separated fractions from T. chinensis were designated as TCP-1, TCP-2 and TCP-3 and those from U. rhyncophylla were termed UC-1 and UC-2. Their sugar compositions were estimated using gas chromatography that revealed the presence fructose, glucose, xylose, arbinose, and rhamnose. Amino acid analysis of these fractions has indicated that they are protein-bound polysaccharides. The antioxidant activities were investigated using DPPH and yeast assays. The ability of these polysaccharide fractions to stimulate mouse macrophages was measured using Griess reagent and ELISA test. The results revealed that some of the isolated fractions (TCP-2, TCP-3, UC-1 and UC-2) displayed significant antioxidant activities and were also found to be effective immunomodulators in a concentration-dependent manner. Outcomes of this research strongly indicate that U. rhyncophylla and T. chinensis have therapeutic potential to be used for the treatment of cancer.

Different Reactive Oxygen Species Lead to Distinct Changes of Cellular Metal Ions in the Eukaryotic Model Organism Saccharomyces cerevisiae

Elemental uptake and export of the cell are tightly regulated thereby maintaining the ionomic homeostasis. This equilibrium can be disrupted upon exposure to exogenous reactive oxygen species (ROS), leading to reduction or elevation of the intracellular metal ions. In this study, the ionomic composition in the eukaryotic model organism Saccharomyces cerevisiae was profiled using the inductively-coupled plasma optical emission spectrometer (ICP-OES) following the treatment with individual ROS, including hydrogen peroxide, cumen hydroperoxide, linoleic acid hydroperoxide (LAH), the superoxide-generating agent menadione, the thiol-oxidising agent diamide [diazine-dicarboxylic acid-bis(dimethylamide)], dimedone and peroxynitrite. The findings demonstrated that different ROS resulted in distinct changes in cellular metal ions. Aluminium (Al3+) level rose up to 50-fold after the diamide treatment. Cellular potassium (K+) in LAH-treated cells was 26-fold less compared to the non-treated controls. The diamide-induced Al3+ accumulation was further validated by the enhanced Al3+ uptake along the time course and diamide doses. Pre-incubation of yeast with individual elements including iron, copper, manganese and magnesium failed to block diamide-induced Al3+ uptake, suggesting Al3+-specific transporters could be involved in Al3+ uptake. Furthermore, LAH-induced potassium depletion was validated by a rescue experiment in which addition of potassium increased yeast growth in LAH-containing media by 26% compared to LAH alone. Taken together, the data, for the first time, demonstrated the linkage between ionomic profiles and individual oxidative conditions.

Transcriptomic insights into the molecular response of Saccharomyces cerevisiae to linoleic acid hydroperoxide

Abstract Eukaryotic microorganisms are constantly challenged by reactive oxygen species derived endogenously or encountered in their environment. Such adversity is particularly applied to Saccharomyces cerevisiae under harsh industrial conditions. One of the major oxidants to challenge S. cerevisiae is linoleic acid hydroperoxide (LoaOOH). This study, which used genome-wide microarray analysis in conjunction with deletion mutant screening, uncovered the molecular pathways of S. cerevisiae that were altered by an arresting concentration of LoaOOH (75 μM). The oxidative stress response, iron homeostasis, detoxification through PDR transport and direct lipid β-oxidation were evident through the induction of the genes encoding for peroxiredoxins (GPX2, TSA2), the NADPH:oxidoreductase (OYE3), iron uptake (FIT2, ARN2, FET3), PDR transporters (PDR5, PDR15, SNQ2) and β-oxidation machinery (FAA2, POX1). Further, we discovered that Gpx3p, the dual redox sensor and peroxidase, is required for protection against LoaOOH, indicated by the sensitivity of gpx3Δ to a mild dose of LoaOOH (37.5 μM). Deletion of GPX3 conferred a greater sensitivity to LoaOOH than the loss of its signalling partner YAP1. Deletion of either of the iron homeostasis regulators AFT1 or AFT2 also resulted in sensitivity to LoaOOH. These novel findings for Gpx3p, Aft1p and Aft2p point to their distinct roles in response to the lipid peroxide. Finally, the expression of 89 previously uncharacterised genes was significantly altered against LoaOOH, which will contribute to their eventual annotation.

Photocatalysis of Titanium Dioxide for Water Disinfection: Challenges and Future Perspectives

The performance of metal oxides such as titanium dioxide (TiO2), in the conversion of solar energy into chemical energy, is determined by semiconducting properties. The conversion process is closely related to the light-induced reactivity between oxide semiconductors and water, which may lead to partial water oxidation and consequently water disinfection. Key performance-related properties are considered here, including light absorption, light-induced ionisation over the band gap, charge separation, charge transport, charge transfer, and the chemical reactions taking place at anodic and cathodic sites. Optimisation of these interconnected performance-related properties is discussed, along with the photocatalytic application in water disinfection.

Effects of metal ions and hydrogen peroxide on the phenotype of yeast hom6Δ mutant

HOM6 is a major gene in the aspartate pathway which leads to biosynthesis of threonine and methionine. The phenotypes of the gene deletion mutant (hom6∆) in a variety of cultural conditions have previously provided meaningful insights into the biological roles of HOM6 and its upstream intermediate metabolites. Here, we conducted a survey on a spectrum of metal ions for their effect on the aspartate pathway and broader sulphur metabolism. We show that manganese (Mn2+) promoted the growth of hom6∆ under both anaerobic and aerobic conditions. Unexpectedly, 4 mmol l−1 hydrogen peroxide (H2O2), a dose normally causing temporary cell growth arrest, enhanced the growth of hom6∆ under the anaerobic condition only, while it had no effect on the wild type strain BY4743. We propose that Mn2+ and H2O2 promote the growth of hom6∆ by reducing the accumulation of the toxic intermediate metabolite—aspartate β‐semialdehyde, via directing the aspartate pathway to the central sugar metabolism–tricarboxylic acid cycle.

Transcriptomic and biochemical evidence for the role of lysine biosynthesis against linoleic acid hydroperoxide-induced stress in Saccharomyces cerevisiae

Abstract Amino acid biosynthesis forms part of an integrated stress response against oxidants in Saccharomyces cerevisiae and higher eukaryotes. Here we show an essential protective role of the l-lysine biosynthesis pathway in response to the oxidative stress condition induced by the lipid oxidant-linoleic acid hydroperoxide (LoaOOH), by means of transcriptomic profiling and phenotypic analysis, and using the deletion mutant dal80∆ and lysine auxotroph lys1∆. A comprehensive up-regulation of lysine biosynthetic genes (LYS1, LYS2, LYS4, LYS9, LYS12, LYS20 and LYS21) was revealed in dal80Δ following the oxidant challenge. The lysine auxotroph (lys1∆) exhibited a significant decrease in growth compared with that of BY4743 upon exposure to LoaOOH, albeit with the sufficient provision of lysine in the medium. Furthermore, the growth of wild type BY4743 exposed to LoaOOH was also greatly reduced in lysine-deficient conditions, despite a full complement of lysine biosynthetic genes. Amino acid analysis of LoaOOH-treated yeast showed that the level of cellular lysine remained unchanged throughout oxidant challenge, suggesting that the induced lysine biosynthesis leads to a steady-state metabolism as compared to the untreated yeast cells. Together, these findings demonstrate that lysine availability and its biosynthesis pathway play an important role in protecting the cell from lipid peroxide-induced oxidative stress, which is directly related to understanding environmental stress and industrial yeast management in brewing, wine making and baking.

Proteomic response to linoleic acid hydroperoxide in Saccharomyces cerevisiae

&NA; Yeast AP‐1 transcription factor (Yap1p) and the enigmatic oxidoreductases Oye2p and Oye3p are involved in counteracting lipid oxidants and their unsaturated breakdown products. In order to uncover the response to linoleic acid hydroperoxide (LoaOOH) and the roles of Oye2p, Oye3p and Yap1p, we carried out proteomic analysis of the homozygous deletion mutants oye3&Dgr;, oye2&Dgr; and yap1&Dgr; alongside the diploid parent strain BY4743. The findings demonstrate that deletion of YAP1 narrowed the response to LoaOOH, as the number of proteins differentially expressed in yap1&Dgr; was 70% of that observed in BY4743. The role of Yap1p in regulating the major yeast peroxiredoxin Tsa1p was demonstrated by the decreased expression of Tsa1p in yap1&Dgr;. The levels of Ahp1p and Hsp31p, previously shown to be regulated by Yap1p, were increased in LoaOOH‐treated yap1&Dgr;, indicating their expression is also regulated by another transcription factor(s). Relative to BY4743, protein expression differed in oye3&Dgr; and oye2&Dgr; under LoaOOH, underscored by superoxide dismutase (Sod1p), multiple heat shock proteins (Hsp60p, Ssa1p, and Sse1p), the flavodoxin‐like protein Pst2p and the actin stabiliser tropomyosin (Tpm1p). Proteins associated with glycolysis were increased in all strains following treatment with LoaOOH. Together, the dataset reveals, for the first time, the yeast proteomic response to LoaOOH, highlighting the significance of carbohydrate metabolism, as well as distinction between the roles of Oye3p, Oye2p and Yap1p. Graphical Abstract Figure. Detailing the molecular response of Saccharomyces cerevisiae to the lipid oxidant, linoleic acid hydroperoxide ‐ LoaOOH, on the basis of four proteomic datasets. Figure. No caption abailable.