Biomedical subjects

J B Nixon

Publications and source records attributed to J B Nixon.

11 recordsLinked to original sources

PubMed2005

Profiling and modelling of thermal changes in a large waste stabilisation pond.

A thermal profiling study was undertaken at four depths at each of nine sites, and at the inlets and outlets of a large waste stabilisation pond (WSP). Results were collected simultaneously using a network of 42 thermistors and dataloggers. Profiles at each site were categorised as either "stratified" or "unstratified", and persistence analysis was used to determine the frequency and persistence of stratification events at each of the nine sites. Stratification was found to persist most strongly at the site furthest upwind in the WSP, with respect to prevailing wind during the study, leading to the conclusion that stratification induced short-circuiting will be greatest in this region of the WSP. A computational fluid dynamics (CFD) model was constructed of the WSP, including an energy balance to predict the bulk stratification gradient in the pond. Environmental conditions and WSP inlet temperature during one day in June 2001 were used as boundary conditions. The pond thermal profiles measured during the profiling study, together with outlet temperature during the day, were used to validate the CFD model results. The model predicted mean pond temperature with a high degree of accuracy (r2 = 0.92). However it was evident that even modest winds (> or = 1.5 m/s) partially broke down stratification, leading to poor prediction of the gradient by the CFD model, which did not directly account for the impact of wind shear stress on mixing in the WSP.

Models, Biological↗

PubMed2003

Evaluation of eicosanoids and NSAIDs as PPARgamma ligands in colorectal carcinoma cells.

The activation of peroxisome proliferator activated receptor gamma (PPARgamma) may play a role in the control of colorectal carcinogenesis. The expression of PPARgamma was examined by Western blotting in human colorectal tumors and matched normal adjacent tissues, as well as in various colorectal carcinoma cell lines. In the tissues, the expression of PPARgamma was elevated in tumors relative to the adjacent normal tissues. Each colorectal carcinoma cell line expressed PPARgamma. The ability of various eicosanoids to bind PPARgamma in colorectal carcinoma cells was investigated using luciferase reporter assays. The well-known PPARgamma ligands, troglitazone and 15-deoxy-Delta(12,14)-prostaglandin J(2) strongly induced PPARgamma binding activity. Products of lipoxygenases displayed moderate binding activity, while other prostaglandins and fatty acids displayed little or no reporter activation. The activation of PPARgamma by 13(S)-HODE, the major metabolite of 15-lipoxygenase-1 from linoleic acid, was concentration dependent reaching maximum at 10 micro M (35-fold activation). The endogenous production of 13(S)-HODE by expression of 15-LO-1 did not activate PPARgamma. The ability of various nonsteroidal anti-inflammatory drugs (NSAIDs) to induce PPARgamma activation was also evaluated. The conventional NSAIDs that inhibit both cyclooxygenases (COX-1 and COX-2) also induced PPARgamma binding activity. In general, however, neither COX-1- nor COX-2-specific inhibitors induced the activation of PPARgamma. Taken together, the metabolites of 15-lipoxygenase and the conventional NSAIDs were confirmed as exogenous ligands for PPARgamma in colorectal carcinoma cells.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed2003

The spatial significance of water quality indicators in waste stabilization ponds--limitations of residence time distribution analysis in predicting treatment efficiency.

Over the past fifty years, considerable research in waste stabilization pond operation has led to the development of a number of models used to describe the hydraulic regime and predict treatment efficiency. Models range in complexity from plug or completely mixed simplifications to computational fluid dynamics (CFD) models which are able to predict flow hydraulics at a local level. Information about the exit age of pond effluent can be used to estimate pollutant decay. However, a mechanistic approach to understanding pond operation highlights the importance of knowing both the time and spatial history of pond effluent. A CFD model of a large pond system was constructed to demonstrate various hydraulic scenarios under different boundary conditions. Two scenarios were compared to visually demonstrate the effects of differing hydraulic conditions. Typical mechanistic models were applied to each condition to quantify biological differences. This simple example indicates that integrating biological and localised flow models will lead to a more holistic understanding of pond operation and treatment efficiency.

Bioreactors↗

PubMed2001

Effect of PPAR activators on cytokine-stimulated cyclooxygenase-2 expression in human colorectal carcinoma cells.

Cyclooxygenase-2 (COX-2) expression is up-regulated in colorectal cancer tissue. Peroxisome proliferator-activated receptors (PPARs) are expressed in human colorectal tissue and activation of PPARs can alter COX-2 expression. In macrophages, activation of PPARs down-regulates COX-2 expression. We examined the effect of PPARalpha and PPARgamma ligands on untreated and TNF-alpha-induced COX-2 expression in the human colorectal epithelial cell line HT-29. The expression of PPARalpha and PPARgamma was confirmed in these cells. TNF-alpha, an inflammatory cytokine, increased COX-2 expression via the NFkappaB pathway. In the absence of TNF-alpha, WY14643 (PPARalpha activator) caused an increase, while BRL49653 (PPARgamma activator) did not alter COX-2 expression. When HT-29 cells were incubated with TNF-alpha and WY14643, a further increase in COX-2 expression was detected. Incubation with TNF-alpha and BRL49653 caused an additional twofold increase in COX-2 expression. Our results suggest that both PPARalpha signaling and TNF-alpha signaling increase COX-2 expression by independent pathways, while PPARgamma stimulates COX-2 expression by up-regulation of the TNF-alpha pathway.

Adenocarcinoma↗

PubMed2001

Overexpression of 15-lipoxygenase-1 in PC-3 human prostate cancer cells increases tumorigenesis.

The effect of overexpression of 15-lipoxygenase-1 (15-LO-1) was studied in the human prostate cancer cell line, PC-3. Stable PC-3 cell lines were generated by transfection with 15-LO-1-sense (15-LOS), 15-LO-1-antisense (15-LOAS) or vector (Zeo) and selection with Zeocin. After characterization by RT-PCR, western and HPLC, a PC3-15LOS clone was selected that possessed 10-fold 15-LO-1 enzyme activity compared with parental PC-3 cells. The PC3-15LOAS clone displayed little or no 15-LO-1 activity. These PC-3 cell lines were characterized for properties of tumorigenesis. The proliferation rates of the cell lines were as follows: PC3-15LOS > PC-3 = PC3-Zeo > PC3-15LOAS. Addition of a specific 15-LO-1 inhibitor, PD146176, caused a dose-dependent inhibition of proliferation in vitro. Overexpression of 15-LO-1 also caused [(3)H]thymidine incorporation to increase by 4.0-fold (P < 0.01). Compared with parental and PC-3-Zeo cells, PC3-15LOS enhanced whereas PC3-15LOAS reduced the ability of PC-3 cells to grow in an anchorage-independent manner, as assessed by colony formation in soft agar. These data suggested a pro-tumorigenic role for 15-LO-1 in PC-3 cells in vitro. Therefore, to clarify the role of 15-LO-1 in vivo, the effect of 15-LO-1 expression on the growth of tumors in nude mice was investigated. The PC-3 cell lines were inoculated subcutaneously into athymic nude mice. The frequency of tumor formation was increased and the sizes of the tumors formed were much larger in the PC3-15LOS compared with PC3-15LOAS, parental PC-3 and PC-3-Zeo cells. Immunohistochemistry for 15-LO-1 confirmed expression throughout the duration of the experiment. The expression of factor VIII, an angiogenesis marker, in tumor sections was increased in tumors derived from PC3-15LOS cells and decreased in those from PC3-15LOAS cells compared with tumors from parental or Zeo cells. These data further supported the evaluation by ELISA of vascular endothelial growth factor (VEGF) secretion by PC-3 cells in culture. Secretion of this angiogenic factor was elevated in PC3-15LOS cells compared with the other cell lines. These results support a role for 15-LO-1 in a novel growth-promoting pathway in the prostate.

Adenocarcinoma↗

PubMed2001

Cyclooxygenase inhibitors regulate the expression of a TGF-beta superfamily member that has proapoptotic and antitumorigenic activities.

The antitumorigenic activity of nonsteroidal anti-inflammatory drugs (NSAIDs), cyclooxygenase (COX) inhibitors, is well established, but responsible molecular mechanisms are not fully understood. NSAIDs stimulate apoptosis by COX dependent and independent mechanisms in colorectal cells in culture. Identification of genes regulated by COX inhibitors could lead to a better understanding of their proapoptotic and anti-neoplastic activities. Using subtractive hybridization, a cDNA which was designated as NSAID activated gene (NAG-1) was identified from NSAID-treated HCT-116, human colorectal cells. NAG-1 has an identical sequence with a novel member of the TGF-beta superfamily that has 5 different names. In the HCT-116 cells, NAG-1 expression is increased and apoptosis is induced by treatment with some NSAIDs in a concentration and time-dependent manner. NAG-1 transfected cells exhibited increased basal apoptosis, increased response to NSAIDs and reduced soft agar cloning efficiency. Furthermore, transplantable tumors derived from NAG-1 transfected HCT-116 cells showed reduced tumorigenicity in athymic nude mice compared with vector-transfected HCT-116 cells. The increased NAG-1 expression by NSAIDs provides a suitable explanation for COX-independent apoptotic effects of NSAIDs in cultured cells. These data demonstrate that NAG-1 is an antitumorigenic and proapoptotic protein, and its regulation by COX inhibitors may provide new clues for explaining their proapoptotic and antitumorigenic activities.

Animals↗

PubMed2000

Phorbol myristate acetate induces neutrophil NADPH-oxidase activity by two separate signal transduction pathways: dependent or independent of phosphatidylinositol 3-kinase.

The neutrophil NADPH-oxidase can be activated by protein kinase C (PKC) agonists such as phorbol myristate acetate (PMA), resulting in superoxide anion release. This superoxide release is independent of phosphatidylinositol 3-kinase (PI 3-kinase) because the inhibitor wortmannin does not affect the response. In this study, PMA is shown to also induce a wortmannin-sensitive NADPH-oxidase activation, however, not resulting in release of superoxide but in intracellular production of the radical. This indicates that two pools of NADPH-oxidase, one localized in the plasma membrane and the other in the granule membranes, are separately regulated and the signal transduction pathways leading to activation of these pools differ regarding involvement of PI 3-kinase. Activation of both pools was dependent on ERK/MAPK kinase (MEK) activity and protein phosphatase 1 and/or 2A. As the two oxidase responses were differently affected by the inhibitor Gö-6850, different PKC isozymes are suggested to take part in the two signal transduction pathways.

Androstadienes↗

PubMed1999

Protein kinase C (PKC) isoforms translocate to Triton-insoluble fractions in stimulated human neutrophils: correlation of conventional PKC with activation of NADPH oxidase.

The responses of human neutrophils (PMN) involve reorganization and phosphorylation of cytoskeletal components. We investigated the translocation of protein kinase C (PKC) isoforms to PMN cytoskeletal (Triton-insoluble) fractions, in conjunction with activation of the respiratory burst enzyme NADPH oxidase. In resting PMN, PKC-delta (29%) and small amounts of PKC-alpha (0.6%), but not PKC-betaII, were present in cytoskeletal fractions. Upon stimulation with the PKC agonist PMA, the levels of PKC-alpha, PKC-betaII, and PKC-delta increased in the cytoskeletal fraction, concomitant with a decrease in the noncytoskeletal (Triton-soluble) fractions. PKC-delta maximally associated with cytoskeletal fractions at 160 nM PMA and then declined, while PKC-alpha and PKC-betaII plateaued at 300 nM PMA. Translocation of PKC-delta was maximal by 2 min and sustained for at least 10 min. Translocation of PKC-alpha and PKC-betaII was biphasic, plateauing at 2-3 min and then increasing up to 10 min. Under maximal stimulation conditions, PKC isoforms were entirely cytoskeletal associated. Translocation of the NADPH oxidase component p47phox to the cytoskeletal fraction correlated with translocation of PKC-alpha and PKC-betaII, but not with translocation of PKC-delta. Oxidase activity in cytoskeletal fractions paralleled translocation of PKC-alpha, PKC-betaII, and p47phox. Stimulation with 1,2-dioctanoylglycerol resulted in little translocation of PKC isoforms or p47phox, and in minimal oxidase activity. We conclude that conventional PKC isoforms (PKC-alpha and/or PKC-betaII) may regulate PMA-stimulated cytoskeletal association and activation of NADPH oxidase. PKC-delta may modulate other PMN responses that involve cytoskeletal components.

Adult↗

PubMed1999

A novel protein kinase target for the lipid second messenger phosphatidic acid.

Activation of phospholipase D occurs in response to a wide variety of hormones, growth factors, and other extracellular signals. The initial product of phospholipase D, phosphatidic acid (PA), is thought to serve a signaling function, but the intracellular targets for this lipid second messenger are not clearly identified. The production of PA in human neutrophils is closely correlated with the activation of NADPH oxidase, the enzyme responsible for the respiratory burst. We have developed a cell-free system, in which the activation of NADPH oxidase is induced by the addition of PA. Characterization of this system revealed that a multi-functional cytosolic protein kinase was a target for PA, and that two NADPH oxidase components were substrates for the enzyme. Partial purification of the PA-activated protein kinase separated the enzyme from known protein kinase targets of PA. The partially purified enzyme was selectively activated by PA, compared to other phospholipids, and phosphorylated the oxidase component p47-phox on both serine and tyrosine residues. PA-activated protein kinase activity was present in a variety of hematopoietic cells and cell lines and in rat brain, suggesting it has widespread distribution. We conclude that this protein kinase may be a novel target for the second messenger function of PA.

Animals↗

PubMed1998

The effects of gemcitabine and TPA on PKC signaling in BG-1 human ovarian cancer cells.

Protein kinase C (PKC) signaling pathways play an important role in cell survival and anticancer drug-induced apoptosis. We observed in clonogenicity assays of BG-1 human ovarian cancer cells that gemcitabine cytotoxicity was increased synergistically when drug treatment was followed or preceded by a 24-h exposure to 10 nM 12-O-tetradecanoylphorbol-13-acetate (TPA). Coincubation of 10 nM TPA with pharmacological inhibitors of PKC abrogated the synergism of TPA and gemcitabine. These observations prompted further investigation of PKC signaling events linked to TPA and gemcitabine cytotoxicity in BG-1 cells. Because PKC isoforms are differentially expressed in various cell types, we determined that BG-1 cells express the alpha, beta, delta, epsilon, and zeta isoforms of PKC. In addition, 1-h exposures to 10 microM gemcitabine triggered cytosol to membrane translocation of PKC isoforms alpha, delta, and epsilon, indicating these isoforms were activated by gemcitabine. We also explored the PKC mechanism(s) responsible for the synergism of TPA and gemcitabine, and determined that treatment with 10 nM TPA for 24 h in BG-1 cells: 1) downregulated PKCdelta and PKCalpha, without affecting PKCepsilon, 2) did not affect cell cycle distribution into S phase. 3) increased extracellular signal-regulated kinase signaling, and 4) increased intracellular alkaline phosphatase activity, a biochemical marker of cellular differentiation. Chronic exposure (24 h) to TPA enhanced gemcitabine cytotoxicity, perhaps by inducing cellular differentiation pathways in BG-1 cells. Therefore, the use of differentiating agents in combination with gemcitabine may improve its clinical efficacy.

Alkaline Phosphatase↗

PubMedDate not supplied

Premalignant changes in ulcerative colitis.

Colitis-associated carcinoma is often associated with, or preceded by, noninvasive epithelial neoplastic changes termed dysplasia. Surveillance colonoscopy with biopsies looking for dysplasia is now standard practice in the management of the cancer problem in ulcerative colitis. However, this practice continues to have a number of limitations and problems that need to be understood by surgeons who may be referring such patients. A number of recent reports indicate that colitis associated carcinoma is predominantly left-sided and incorporation of this distribution in the surveillance methods merits consideration. The molecular and genetic abnormalities involved in the pathogenesis of colitis associated neoplasia are being actively investigated and may yield supplementary methods to better define individual patient risk.

Adenocarcinoma↗