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Document Type

Campus Access

Degree Program

Nutrition

Degree Type

Master of Science (M.S.)

Year Degree Awarded

2011

Month Degree Awarded

September

Keywords

obesity, inflammation, vitamin D, TNF-alpha, adipocyte, cytokine

Abstract

Obesity accounts for $168 billion in annual medical expenses and increases the risk of cardiovascular disease, cancer, and type-2 diabetes, three diseases responsible for over 50% of deaths in the United States. It is well established that the pattern of adiposity is an important factor in the relationship with disease risk and that visceral adiposity, which favors hypertrophy (characterized by enlarged cells) is more dangerous than subcutaneous adiposity, which tends to be hyperplastic (characterized by an increase in cell number). Hypertrophy is associated with inflammation and insulin resistance, and hyperplasia (adipogenesis, i.e., the formation of new adipocytes), is associated with improved insulin sensitivity. Tumor necrosis factor-alpha (TNF-alpha) is a potent pro-inflammatory cytokine that activates a nuclear factor-kappa B (NFKB) intracellular pathway that is an important mediator of obesity-associated insulin resistance and increased risk of type-2 diabetes. Interestingly, obesity has been positively associated with both low vitamin D status and elevated levels of TNF-alpha. Our studies focused on examining the influence of the active vitamin D hormone, 1,25-dihydroxyvitamin D, and TNF-alpha on adipogenesis and inflammation in human primary adipocytes and determining whether the balance of these two factors influences the extent to which adipocytes accumulate lipid or express pro-inflammatory cytokines. We found no effect of 1,25-dihydroxyvitamin D on adipogenesis or pro-adipogenic gene expression despite a clear upregulation of a vitamin D responsive gene, 24-hydroxylase, in response to treatment with 1,25-dihydroxyvitamin D. TNF-alpha clearly inhibited adipogenesis and expression of PPAR-gamma and C/EBP-alpha and enhanced expression of the pro-inflammatory cytokines IL-6 and MCP-1, but not IL-8. There was a trend towards a dose-dependent downregulation of MCP-1 by 1,25-dihydroxyvitamin D in three individuals; however, this effect was not statistically significant. While we found no interaction between TNF-alpha and 1,25-dihydroxyvitamin D on adipogenesis, there is a potential anti-inflammatory action of 1,25-dihydroxyvitamin D in human primary adipocytes. Future studies into this potential are warranted in light of the growing obesity epidemic and the interest in finding nutritionally modifiable treatment or prevention strategies to mitigate the negative consequences of obesity.

First Advisor

Richard J Wood

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