Date of Award

12-2005

Degree Type

Thesis

Degree Name

Master of Science

Major

Comparative and Experimental Medicine

Major Professor

Michael D. Karlstad

Committee Members

Joseph W. Bartges, Ph.D., Jay Whelan, Ph.D.

Abstract

We previously found that enteral nutrition with diets containing elevated levels of eicosapentaenoic acid (EPA; 20:5 n-3) reduced the number of neutrophils in bronchoalveolar lavage fluid and improved clinical outcome of patients with or at risk for adult respiratory distress syndrome (ARDS). We have also shown that the treatment of the neutrophil-like cell line, HL-60, with EPA can induce apoptosis. It is not known, however, if the addition of EPA to the diet would result in similar occurrences in neutrophils.

It has been suggested that the use of diets enriched with stearidonic acid (SDA; 18:4 n-3) may provide a novel source of n-3 fatty acids while offering similar beneficial effects on health as diets containing EPA. Therefore, we examined whether dietary SDA can be used as a precursor to increase EPA content in liver tissue.

It is well known that endotoxin increases neutrophil lifespan and that this may be important in maintaining innate immune response. The second part of this study incorporated the use of glycogen-elicited peritoneal neutrophils from the rat to examine the effect of dietary intervention with n-3 fatty acids (either EPA or SDA) on constitutive and endotoxin induced neutrophil survival. Male Long-Evans rats (n=18) were randomly divided into 3 dietary groups and fed a modified US-17 diet providing 200kcal/kg/day and containing 2% oleic acid (OA; 18:1 n-9) (n=6), 1% EPA/1% OA (n=6), or 1% SDA/1% OA (n=6) for 2 weeks. Liver phospholipids were analyzed using gas chromatography and neutrophil lifespan was evaluated using flow cytometry.

Dietary supplementation with EPA significantly increased the concentration of EPA and docosapentaenoic acid (DPA, 22:5n3), but not docosahexaenoic acid (DHA, 22:6n3) in liver tissue as compared with animals fed OA. Dietary supplementation with SDA also increased tissue contents of EPA and DPA, but not DHA as compared with OA fed controls. The increase in

tissue EPA was about one-half as effective in animals fed a diet containing SDA as those fed EPA. SDA was about two-thirds as effective as EPA at increasing tissue DPA content. These results indicate that, when fed at current dietary levels, SDA can increase the incorporation of EPA and DPA into the membrane phospholipids of liver tissue in a similar manner to dietary EPA. This provides evidence that SDA may provide an alternative to EPA for increasing tissue levels of EPA and DPA, but not DHA.

Flow cytometry analysis of neutrophils following 20h incubation in either presence or absence of endotoxin indicated that diet did not significantly affect constitutive or endotoxin-mediated neutrophil survival when fed at current levels. There was a non-significant trend towards an increase in both constitutive viability and endotoxin mediated cell survival (p=0.069) in both SDA and EPA fed animals as compared with control animals that were fed OA. While these results do not fully explain the role that EPA or SDA play in reducing neutrophil influx during ARDS, they do provide evidence that it is not through an increase of neutrophil apoptosis or an attenuation of the neutrophil response to endotoxin. These findings may indicate the importance of dietary EPA for maintaining host immune response, while providing beneficial effects in regards to inflammation. Because of similar action between dietary EPA and SDA these results might also provide further proof as to the potential for dietary SDA to be used as an alternative for dietary EPA.

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