Fred W. Quimby

Western-Style Diets Induce Oxidative Stress and Dysregulate Immune Responses in the Colon in a Mouse Model of Sporadic Colon Cancer

A Western-style diet (WD), defined by high-fat, low-calcium, and vitamin D content, is associated with increased risk of human colorectal cancer. Understanding molecular mechanisms altered by the WD is crucial to develop preventive and therapeutic strategies. Effects of a WD on the colonic transcriptome of C57Bl/6J mice, a model for sporadic colon cancer, were studied at endpoints before tumors occur. To assess whether a WD induces inflammatory changes, expression profiles of a broad spectrum of inflammatory proteins were performed and numbers of lamina propria macrophages were determined with semiquantitative morphometry. Transcriptome changes were translated into molecular interaction network maps and pathways. Pathways related to oxidative stress response; lipid, glutathione, and xenobiotic metabolism; and the immune response were perturbed by the WD. Several nuclear factor-erythroid 2-related factor 2- and aryl hydrocarbon receptor-dependent genes, including those coding for enzymes involved in phase 1 and 2 drug metabolism and oxidative stress responses, were induced. Oxidative stress was demonstrated by measurements of endogenous colonic redox-sensitive compound concentrations. Perturbations in immune response-related pathways, expression of inflammatory proteins, and increased numbers of lamina propria macrophages showed that the WD significantly alters the local colonic immune response. Collectively, these data suggest that consumption of a WD interferes with networks of related biological response pathways involving colonic lipid metabolism, oxidative stress, and the immune response. These new findings impact our understanding of links between consumption of WD and colon carcinogenesis, providing additional information for developing preventive means for decreasing colorectal cancer risk.

Cox-2 expression, PGE2 and cytokines production are inhibited by endogenously synthesized n-3 PUFAs in inflamed colon of fat-1 mice

There is great interest in the role of polyunsaturated fatty acids (PUFAs) in promoting (n-6 class) or inhibiting (n-3 class) inflammation. Mammalian cells are devoid of desaturase that converts n-6 to n-3 PUFAs. Consequently, essential n-3 fatty acids must be supplied with the diet. We have studied the effect of endogenously produced n-3 PUFAs on colitis development in fat-1 transgenic mice carrying the Caenorhabditis elegans fat-1 gene encoding n-3 desaturase. Colonic cell lipid profile was measured by capillary gas chromatography in fat-1 and wild-type (WT) littermates fed standard diet supplemented with 10% (w/w) safflower oil rich (76%) in n-6 polyunsaturated linoleic acid (LA). Experimental colitis was induced by administrating 3% dextran sodium sulphate (DSS). Colitis was scored by histopatological analysis. Cyclooxygenase-2 (Cox-2) expression was evaluated by real time polymerase chain reaction. Prostaglandin E(2) (PGE(2)) levels and cytokine production were determined by enzyme and microsphere-based immunoassays, respectively. The n-6/n-3 PUFA ratios in colonic cells of fat-1 mice were markedly lower (9.83±2.62) compared to WT (54.5±9.24, P<.001). Results also showed an attenuation of colonic acute and chronic inflammation in fat-1 mice with significant decreases in PGE(2) production (P<.01) and Cox-2 expression (P<.01). High levels of colitis-induced proinflammatory cytokines, interleukin (IL)-18, IL-1α, IL-1β, IL-6, monocytes chemotactic proteins 1, 2 and 3 (MCP 1,2,3), matrix metalloproteinase 9 and tumor necrosis factor α (TNF-α) were down-regulated in DSS acutely and chronically treated fat-1 mice. The expression of fat-1 gene in the colon was associated with endogenous n-3 PUFAs production, decreased Cox-2 expression, increased PGE(2) and cytokine production.

Impacts of glutathione peroxidase-1 knockout on the protection by injected selenium against the pro-oxidant-induced liver aponecrosis and signaling in selenium-deficient mice.

Previous research has suggested that repletion of cellular glutathione peroxidase (GPX1) activity by a single injection of Se was dissociated from the Se protection against the pro-oxidant-induced liver necrosis in Se-deficient rodents. Using the GPX1 knockout (GPX1-/-) mice, TUNEL assay, and apoptosis gene expression microarray, we have demonstrated strikingly different impacts of GPX1 knockout on hepatotoxicity and the related signaling induced by an intraperitoneal injection of 12.5 mg paraquat/kg body weight (b.wt.). In both Se-deficient GPX1-/- and wild-type (WT) mice, the paraquat did not induce typical liver necrosis, rather aponecrosis or necrapoptosis, a syncretic process of cell death sharing characteristics of both apoptosis and necrosis. The severity of liver aponecrosis and the associated mortality were reduced to a much greater extent by an injection of Se (ip, 50 microg/kg b.wt. as Na2SeO3) prior to paraquat stress in the WT mice, compared with the GPX1-/- mice. The induced liver aponecrosis seemed to be more apoptotic in the GPX1-/- mice but more necrotic in the WT mice. The paraquat-mediated gene or protein expression of proapoptotic Bax, Bcl-w, and Bcl-X(S), cell survival/death factors GADD45, MDM2, c-Myc, and caspase-3 was upregulated, but that of antiapoptotic Bcl-2 was downregulated in the GPX1-/- mice vs. the WT mice. Overall, these differences between the two groups of mice were related to a low level of liver GPX1 activity in the WT mice that represented < 4% of the normal physiological level. Therefore, the low level of GPX1 activity in the Se-deficient mice can exert a potent role in defending against liver aponecrosis induced by moderate oxidative stress.

Obesity enhances gastrointestinal tumorigenesis in Apc-mutant mice.

Epidemiological evidence indicates a link between obesity and human colon cancer. A putative association between obesity and colon tumorigenesis has been explored experimentally using chemical carcinogens administered to obese rodents. The main objective of this study was to generate a new mouse line that displays both obesity and intestinal tumorigenesis. To this end, we have generated C57BLKS-mLeprdb/db; Apc1638N/+ mice combining both db and Apc mutations. The db mutation results in obesity and type 2 diabetes, the Apc mutation is a key initiating event of intestinal neoplasia. All mice were euthanized at 6 months of age and all regions of the gastrointestinal tract examined for tumors. The results show that the combination of Apc1638N/+ and db mutations not only enhanced mutant Apc-driven small intestinal tumorigenesis but also induced gastric and colonic tumors. Homozygous db mice did not develop gastrointestinal neoplasia. These findings indicate that obesity associated with type 2 diabetes promotes gastrointestinal tumorigenesis in Apc-deficient mice and provides evidence of a mechanistic link between obesity and colorectal neoplasia.

Animal Models in Biomedical Research

The use of animals in biomedical research has an extensive history which no single chapter could hope to completely cover. This chapter examines both the historical use of animals in research and contemporary uses. The chapter focuses on several fields of animal research to illustrate the progressive nature of research and puts research findings into their perspective by illustrating how multiple disciplines, investigators, and animal models are often necessary to make historic progress. Principles of animal model selection are highlighted as methods to create animal models.

Reproductive impairment in zebra finches (Taeniopygia guttata)

The effects of polychlorinated biphenyls (PCBs) as compounds that may disrupt endocrine activity and, consequently, alter reproductive performance were investigated in altricial zebra finches (Taeniopygia guttata). The breeding performance and breeding cycle of zebra finches differed significantly between nonexposed birds and those experimentally pulse-exposed to Aroclor 1248, a PCB compound (40 microg/bird). Aroclor-exposed birds showed significantly increased numbers of clutches laid, nests constructed per pair, incubation time per pair, and percentage of hatchling mortality compared to controls. Not all reproductive parameters were affected. Those traditionally regarded as indicators of reproductive capacity (number of eggs laid per clutch, number of eggs laid per pair, hatchlings per clutch, and fledglings per clutch) did not differ statistically between exposed and control birds. Findings support the hypothesis that very low PCB doses may be associated with endocrine disruption. It is suggested that evaluation of reproductive parameters related to parental care is more adequate to assess endocrine disruption than is evaluation of reproductive success parameters. Given its short breeding cycle, altricial breeding behavior, and other advantages not possessed by precocial birds, we propose using the zebra finch for evaluations of chemicals with endocrine-disruptive activity.

Effect of caloric intake on Western-style diet-induced intestinal tumors in a mouse model for hereditary colon cancer.

Increased caloric intake has been associated with increased risk for cancer of the large intestine. We studied caloric intake effect on tumor formation in Apc1638 N/+ mice, a preclinical model for human familial adenomatous polyposis. Mice were fed a controlled AIN-76A diet or a new Western-style diet (NWD). Intestinal tumor development was evaluated after 6 mo of feeding 1) AIN-76A diet (fed ad libitum) vs. AIN-76A (caloric intake reduced 30%); 2) NWD (fed ad libitum) vs. NWD (caloric intake reduced 30%); and 3) AIN-76A (fed ad libitum) vs. NWD (paired-fed with NWD providing equal caloric intakes to AIN-76A). Intestinal tumor incidences were 78–100% with intergroup variation P > 0.05; however, tumor multiplicity responded differently to dietary treatment: 1) Tumor multiplicity was unchanged after AIN-76A (caloric intake reduced 30% vs. mice fed AIN-76A ad libitum); 2) tumor multiplicity was unchanged after NWD (caloric intake reduced 30% vs. NWD ad libitum); and 3) tumor multiplicity increased 130% after NWD was paired-fed with the same caloric intake as mice fed AIN-76A ad libitum (P < 0.05). Body weights showed no association with tumor development. Findings indicated modified nutrients in NWD were mainly responsible for increased tumors in mice fed NWD vs. AIN-76A in this preclinical mouse model for human FAP.