Effects of dietary bovine lactoferrin on intestinal lymphocytes of mice after dextran sulfate sodium or acute exercise challenge.

摘要

The primary objective of this research was to determine whether dietary bovine lactoferrin (bLf) affects mouse intestinal lymphocytes (IL) apoptosis and cytokine concentrations in: (1) a normal, non-inflamed state, (2) following acute exercise (AE) challenge and (3) following dextran sulfate sodium (DSS) treatment. A second objective was to directly examine the potential protective effects of dietary bLf from inflammatory damage caused by DSS and AE challenge when administered alone or in combination with a carcinogen.;Results from the first experiment determined that 2.0% bLf was effective at reducing mouse IL levels of TNF-alpha (p0.05) (pro-inflammatory) and increasing the percentage of apoptotic CD4+ IL (CD4 +/ANN+, p0.05) in healthy mice. Thus, 2.0% bLf was used for the subsequent experiments. Dietary bLf administration in mice exposed to AE was associated with lower levels in mouse IL of the anti-apoptotic protein Bcl-2 (p0.01) and of TNF-alpha (p0.05) and NFkappaB (p0.05), both pro-inflammatory proteins. Further, the exercise protocol resulted in oxidative stress, as measured by 8-iso prostaglandin F2alpha levels in plasma, but did not induce intestinal inflammation, evident by the absence of both tissue damage and infiltration of immune cells. Following DSS treatment, mice supplemented with bLf enriched diets had lower levels of both TNF-alpha (non-significant, 34% reduction) and NFkappaB (p0.05) and increased concentrations (p0.01) of cytochrome c, a mitochondrial protein associated with cell death. DSS exposure in mice resulted in gross morphological alterations and infiltration of immune cells in the small and large intestine; these changes in tissue histology were not affected by the addition of bLf. Mice injected with AOM and then subjected to DSS, but not AE, had increased numbers (p0.001) of aberrant crypts, preneoplastic colonic lesions, compared to animals only receiving AOM injection. Dietary bLf did not affect any of these carcinogenic processes.;Collectively, these results suggest that dietary bLf administration reduces pro-inflammatory cytokine levels and has limited effects on apoptosis of mouse IL. Moreover, these modifying effects of bLf did not result in mucosal protection, as evident in the inability of this protein to reduce DSS-induced tissue damage or formation of aberrant crypts. Although the long term physiological consequences of bLf supplementation in the regulation of intestinal immune homeostasis require further study, the following clinical implications are tentatively suggested by the findings from this thesis research. First, dietary bLf supplementation does not provide direct protection of the intestine during inflammation either with or without exposure to the carcinogen (i.e., AOM); hence, bLf (at least in the dietary concentration and exposure used in these experiments) may not be useful in reducing the formation of aberrant crypts and carcinogenesis. Second, dietary bLf should not be recommended as a supplement at this time for athletes experiencing intestinal distress since it had no impact on tissue indicators of disease in a model (DSS) shown to produce extensive inflammation and tissue pathology. Nonetheless, the findings raise the possibility that bLf can modify both cytokines and apoptotic protein expression in IL and may influence some aspects of inflammatory processes in the gut. (Abstract shortened by UMI.);Methods: A total of 252 female C57BL/6 mice were used in the experiments. Mice were exposed to bLf containing diets for 4 d or 12 d prior to sacrifice. DSS was provided at 5% in the drinking water for 4 consecutive days prior to sacrifice. Animals were subjected to three repeated bouts of AE (each separated by 24 h rest) involving treadmill running and sacrificed either immediately or 24 h after the final exercise bout. In the experiment involving carcinogenesis, mice were given two subcutaneous injections of azoxymethane (AOM), followed by a two week incubation period, and subsequently exposed to bLf or the control diet.