Effect of High Fat Diet With AICAR Treatment on Mitochondrial Biogenesis of Male Rats

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David Mills and Professor Chad Hancock, Nutrition, Dietetics, and Food Science

The original goal for my project was to study how a high-fat diet affects insulin resistance in slow twitch and fast twitch muscle fibers in rats. We hypothesized that administering a drug named acipamox, which lowers cellular free fatty acid levels, would restore insulin sensitivity in both slow twitch and fast twitch muscle fibers. Previously published research showed that acipamox restored insulin sensitivity in slow twitch fibers (1) but this study did not address what happened in the fast twitch muscle fibers.

The experimental design for our project used three groups of male wistar rats. We fed one group a control diet with normal amounts of fat, carbohydrates and protein. We fed the other two groups a diet that was high in fat. This diet induces insulin resistance similar to that experienced by humans prior to the development of type 2 diabetes. We fed the rats their respective diets for five weeks. During the fifth week, we administered myriocin via an intraperitoneal injection to one of the high fat diet groups. At the end of the fifth week, we collected muscle samples from the rats and conducted various tests to analyze the effects of the high fat diet and the myriocin group. Our results did not show a significant difference in insulin resistance in the slow or fast twitch muscles between the high fat fed group and the myriocin with high fat diet group.

We are not sure why we did not see our expected results. It is possible that the way we administered the drug was not effective or that our dose was not high enough. We are currently in the process of following up on previous results in terms of insulin signaling and elevated FFA. Preliminary results suggest that a signaling defect due to elevated FFA may be clear in slow twitch muscle but not in fast twitch muscles. We will need to perform the feeding protocol with acipimox one more time to increase the number of samples in order to determine if this effect is real or not.

Additional work I have done regards the mechanisms responsible for stimulation of mitochondrial biogenesis in skeletal muscle. Published studies have shown that high fat diets increase mitochondrial markers in muscle cells (2). Other studies have shown that chronic activation of AMPK using a drug called AICAR also increases mitochondrial markers in skeletal muscle (3). We hypothesized that there would be an additive effect on mitochondrial content if rats were put on a high fat diet and given AICAR.

Our new study model included four groups of male wistar rats. We fed two groups a control diet and two groups a high fat diet. We administered AICAR daily via subcutaneous injections to one group with the control diet and high fat diet. We ran the study for six weeks and then at the end we collected muscle samples for our study. We conducted several tests on our muscle samples to asses the effect on mitochondrial biogenesis in the slow twitch and fast twitch muscle fibers.

In 2009, we presented some of our findings at the 14th International Biochemistry of Exercise Conference at the University of Guelph, in Canada. The graduate student who I helped came to present her work. She answered most of the questions that people there asked about the project but I was also able to answer a few questions. While at the conference, I was able to listen to presentations about the research conducted in this area around the world. I learned a great deal about the importance of conferences. Not only is it a place to present research but you can gain valuable feedback about your project from other researchers in your field.

The results that we obtained from our project supported our hypothesis. In fast twitch muscles there was a greater additive effect on markers for mitochondrial biogenesis than in slow twitch muscles but both groups had a significant increase in some markers of mitochondrial content. We are currently preparing the manuscript to be submitted in the Journal of Applied Physiology.

As mentioned above, we are following up on the experiments that on insulin resistance and FFA’s. In addition, we are interested in seeing if the increase in mitochondrial markers seen with the combined effects of AICAR and high fat feeding involve the regulation of a recently recognized co-repressor of mitochondrial transcription factors RIP140. Further, we would also like to see if exercise induced increases in mitochondrial content are limited by preventing the normal increase in FFA’s that occur during endurance training.

References

  • Holland, W. L., Brozinick, J., Wang, L., Hawkins, E., Sargent, K., Liu, Y., et al. (2007). Inhibition of Ceramide Synthesis Ameliorates Glucocorticoid-, Saturated-Fat-, and Obesity-Induced Insulin Resistance. Cell Metabolism, 5, 167-79.
  • Garcia-Roves P, Huss JM, Han DH, Hancock CR, Iglesias-Gutierrez E, Chen M, Holloszy JO. (2007). Raising plasma fatty acid concentration induces increased biogenesis of mitochondria in skeletal muscle. Proc Natl Acad Sci U S A. Jun 19;104(25):10709-13.
  • Merrill GF, Kurth EJ, Hardie DG, Winder WW. (1997). AICA riboside increases AMP-activated protein kinase, fatty acid oxidation, and glucose uptake in rat muscle. Am J Physiol. Dec;273: E1107-12.