Characterization of Radioprotective, Radiomitigative and Bystander Signaling Modulating Effects of Endogenous Metabolites - Phenylacetate, Ursodeoxycholate and Tauroursodeoxycholate - on HCT116 Human Colon Carcinoma Cell Line.

Exposures to ionizing radiation can cause depletion in stem cell reservoirs and lead to chronic injury processes that exacerbate carcinogenic and inflammatory responses. Therefore, radioprotective measures, against both acute and chronic biological effects of radiation, require frequent intake of nontoxic natural products, which have practical oral administration. The goal of this study was to characterize the radioprotective, radiomitigative and radiation-induced bystander effect-inhibiting properties of endogenous metabolites: phenylacetate, ursodeoxycholate and tauroursodeoxycholate. Compounds were administered pre- and postirradiation as well as in donor and recipient bystander flasks to analyze whether these might adequately protect against radiation injury as well as facilitate recovery from the exposures. The clonogenic HCT116 p53 wild-type cancer cell line in this study shares characteristics of stem cells, such as high reproductive viability, which is an effective marker to demonstrate compound effectiveness. Clonogenic assays were therefore used to characterize radioprotective, radiomitigative and bystander inhibiting properties of treatment compounds whereby cellular responses to radiation were quantified with macroscopic colony counts to measure cell survival in flasks. The results were statistically significant for phenylacetate and tauroursodeoxycholate when administered preirradiation, conferring radioprotection up to 2 Gy, whereas administration postirradiation and in bystander experiments did not confer radioprotection in vitro. These findings suggest that phenylacetate and tauroursodeoxycholate might be effective radioprotectors, although they possess no radiomitigative properties.

Design of clinical trials.

Clinical trial design for nuclear medicine diagnostic imaging radiopharmaceuticals must include a design for preclinical safety studies. These studies should establish that the investigational product (IP) does not have a toxic effect. As a further requirement, radiopharmaceutical clinical trials include a human study (phase 1) that provides biodistribution, pharmacokinetics, and radiation dosimetry information. These studies demonstrate to the Food and Drug Administration that the IP either meets or exceeds the toxicology and radiation exposure safety limits. Satisfying this requirement can result in the Food and Drug Administration approving the performance of late-phase (phase 2/3) clinical trials that are designed to validate the clinical efficacy of the diagnostic imaging agent in patients who have a confirmed diagnosis for the intended application. Emphasis is placed on the most typical trial design for diagnostic imaging agents that use a comparator to demonstrate that the new IP is similar in efficacy to an established standard comparator. Such trials are called equivalence, or noninferiority, trials that attempt to show that the new IP is not less effective than the comparator by more than a statistically defined amount. Importantly, the trial design must not inappropriately favor one diagnostic imaging agent over the other. Bias is avoided by the use of a core laboratory with expert physicians who are not involved in the trial for interpreting and objectively scoring the image sets obtained at the clinical trial sites. Clinical trial design must also follow Good Clinical Practice (GCP) guidelines. GCP stipulates the clinical trial process, including protocol and Case Report Form design, analyses planning, as well as analyzing and preparing interim and final clinical trial/study reports.

Metabolic flexibility revealed in the genome of the cyst-forming alpha-1 proteobacterium Rhodospirillum centenum.

BACKGROUND: Rhodospirillum centenum is a photosynthetic non-sulfur purple bacterium that favors growth in an anoxygenic, photosynthetic N2-fixing environment. It is emerging as a genetically amenable model organism for molecular genetic analysis of cyst formation, photosynthesis, phototaxis, and cellular development. Here, we present an analysis of the genome of this bacterium. RESULTS: R. centenum contains a singular circular chromosome of 4,355,548 base pairs in size harboring 4,105 genes. It has an intact Calvin cycle with two forms of Rubisco, as well as a gene encoding phosphoenolpyruvate carboxylase (PEPC) for mixotrophic CO2 fixation. This dual carbon-fixation system may be required for regulating internal carbon flux to facilitate bacterial nitrogen assimilation. Enzymatic reactions associated with arsenate and mercuric detoxification are rare or unique compared to other purple bacteria. Among numerous newly identified signal transduction proteins, of particular interest is a putative bacteriophytochrome that is phylogenetically distinct from a previously characterized R. centenum phytochrome, Ppr. Genes encoding proteins involved in chemotaxis as well as a sophisticated dual flagellar system have also been mapped. CONCLUSIONS: Remarkable metabolic versatility and a superior capability for photoautotrophic carbon assimilation is evident in R. centenum.

Rhodospirillum centenum utilizes separate motor and switch components to control lateral and polar flagellum rotation.

Rhodospirillum centenum is a purple photosynthetic bacterium that is capable of differentiating from vibrioid swimming cells that contain a single polar flagellum into rod-shaped swarming cells that have a polar flagellum plus numerous lateral flagella. Microscopic studies have demonstrated that the polar flagellum is constitutively present and that the lateral flagella are found only when the cells are grown on solidified or viscous medium. In this study, we demonstrated that R. centenum contains two sets of motor and switch genes, one set for the lateral flagella and the other for the polar flagellum. Electron microscopic analysis indicated that polar and lateral flagellum-specific FliG, FliM, and FliN switch proteins are necessary for assembly of the respective flagella. In contrast, separate polar and lateral MotA and MotB motor subunits are shown to be required for motility but are not needed for the synthesis of polar and lateral flagella. Phylogenetic analysis indicates that the polar and lateral FliG, FliM, and FliN switch proteins are closely related and most likely arose as a gene duplication event. However, phylogenetic analysis of the MotA and MotB motor subunits suggests that the polar flagellum may have obtained a set of motor genes through a lateral transfer event.