Insulin resistance is a key pathophysiologic feature of pre-diabetes and a major contributor to the progression towards overt type 2 diabetes mellitus (T2DM). For many years, increased consumption of bioactives in blueberries (BB) has been a folk remedy in Canada for treating T2DM. Preliminary data in the applicant's laboratory found that dietary supplementation with BB for six weeks was well tolerated and increased whole-body insulin sensitivity in humans with pre-diabetes when compared to the placebo group. However, cellular mechanisms of action underlying the biological response of BB in improving insulin sensitivity were not evaluated previously. Therefore, the overall research objective in the application is to determine the underlying cellular mechanism(s) of action and therapeutic efficacy of BB and its bioactive component(s) in modulating insulin sensitivity in target tissues i vitro and in vivo. To attain the overall objective, the working hypothesis will be tested that BB wll improve insulin sensitivity by modulating glucose uptake and intracellular proteins in the insulin-dependent (i.e., Insulin receptor (IR), insulin receptor substrate (IRS), phosphatidylinositol-3 kinase (PI-3K), and Akt)) and -independent (i.e., AMP-activated protein kinase (AMPK)) pathways in target tissues in vitro and in vivo. The hypothesis will be addressed through the following Specific Aims: 1) determine cellular mechanism(s) by which whole BB enhances insulin sensitivity in insulin sensitive tissues in vitro (i.e., adipose and skeletal muscle cell cultures), 2) isolate and identify the bioactive component(s) in BB and their mechanism(s) of action by which insulin sensitivity is enhanced in insulin sensitive tissues in vitro, and 3) evaluate the therapeutic efficacy and tissue-specific site of action (i.e., liver, adipose tissue, and/or skeletal muscle) of whole BB and BB bioactive component(s) on ameliorating insulin sensitivity in mice using the hyperinsulinemic-euglycemic clamp. During this mentored career development, Dr. Stull will acquire detailed input from her mentors with relevant expertise and work to increase her versatility as a clinical researcher by learning new techniques and methodologies related to [molecular and cellular biology, botanical characterization, and animal biomethodology. Dr. Stull's long-term goal is to become an independent translational CAM investigator and leader in the study of complementary and alternative medicine with an emphasis in botanical dietary supplementation and its impact on insulin resistance.
The proposed research is relevant to public health because it will provide new insights on the effectiveness of phytochemicals found in a common fruit (i.e., blueberries) on glucose control and insulin sensitivity, which would potentially benefit the health quality of life, and well-being of an insulin-resistant population. Most importantly, the findings from this application will enable consumers to make more informed decisions about the use of bioactives in blueberries to treat insulin resistance in individuals with pre-diabetes or type 2 diabetes.