Chronic nitrate administration increases the expression the genes involved in the browning of white adipose tissue in female rats

Nitrate, a nitric oxide (NO) donor, has antiobesity effect in female rats. This study hypothesized that the antiobesity effect of nitrate in female rats is due to the browning of white adipose tissue (WAT). Female Wistar rats (aged 8 months) were divided into two groups (n=10/group): the control group received tap water and the nitrate group received water containing 100mg/L of sodium nitrate for 9 months. At months 0, 3, 6, and 9, obesity indices were measured. At month 9, gonadal adipose tissue was used to measure messenger RNA (mRNA) and protein levels of peroxisome proliferator-activated receptor-gamma (PPAR-gamma), PPAR-gamma coactivator 1-alpha (PGC1-alpha), uncoupling protein 1 (UCP1), and adipocyte density and area. After the 9-month intervention, nitrate-treated rats had lower body weight, body mass index, thoracic circumference, and abdominal circumference by 6.4% (p=.012), 9.1% (p=.029), 6.0% (p=.056), and 5.7% (p=.098), respectively. In addition, nitrate-treated rats had higher PPAR-gamma (mRNA: 1.78-fold, p=.016 and protein: 19%, p=.076), PGC1-alpha (mRNA: 1.69-fold, p=.012 and protein: 68%, p=.001), and UCP1 (mRNA: 2.50-fold, p=.001 and protein: 81%, p=.001) in gonadal adipose tissue. Nitrate also reduced adipocyte area by 35% (p=.054) and increased adipocyte density by 31% (p=.086). In conclusion, antiobesity effect of nitrate in female rats is associated with increased browning of gonadal adipose tissue as indicated by higher expression of PPAR-gamma, PGC1-alpha, and UCP1 and reduced adipocyte area and increased adipocyte density.