Excess Folic Acid Increases Lipid Storage, Weight Gain, and Adipose Tissue Inflammation in High Fat Diet-Fed Rats

Abstract

Folic acid intake has increased to high levels in many countries, raising concerns about possible adverse effects, including disturbances to energy and lipid metabolism. Our aim was to investigate the effects of excess folic acid (EFA) intake compared to adequate folic acid (AFA) intake on metabolic health in a rodent model. We conducted these investigations in the setting of either a 15% energy low fat (LF) diet or 60% energy high fat (HF) diet. There was no difference in weight gain, fat mass, or glucose tolerance in EFA-fed rats compared to AFA-fed rats when they were fed a LF diet. However, rats fed EFA in combination with a HF diet had significantly greater weight gain and fat mass compared to rats fed AFA (p < 0.05). Gene expression analysis showed increased mRNA levels of peroxisome proliferator-activated receptor γ (PPARγ) and some of its target genes in adipose tissue of high fat-excess folic acid (HF-EFA) fed rats. Inflammation was increased in HF-EFA fed rats, associated with impaired glucose tolerance compared to high fat-adequate folic acid (HF-AFA) fed rats (p < 0.05). In addition, folic acid induced PPARγ expression and triglyceride accumulation in 3T3-L1 cells. Our results suggest that excess folic acid may exacerbate weight gain, fat accumulation, and inflammation caused by consumption of a HF diet.

Keywords: adipose tissue; folic acid; metabolic syndrome; obesity.

Figure 1

Excess folic acid intake does not influence body weight, body composition or glucose tolerance on a low fat diet (A); growth curves (B); fat mass (C); lean mass (D); glucose tolerance (E); area under the glucose curve, and (F) plasma ALT, of rats fed 15% LF diet with excess or adequate folic acid. Values are means ± SEM, * p < 0.05.

Figure 2

Excess folic acid intake increases weight gain and fat mass on a high fat diet. (A) Growth curves; (B) food intake; (C) fat mass; (D) lean mass; and (E) tissue weights. Values are means ± SEM, * p < 0.05.

Figure 3

Excess folic acid intake impairs glucose tolerance on a high fat diet. (A) Fasting plasma glucose; (B) fasting plasma insulin; (C) blood glucose concentrations at different time points (15, 30, 60, 90, 120 min) after an intraperitoneal (IP) glucose injection; and (D) area under the glucose curve, for male rats fed 60% HF diet with excess or adequate folic acid. Values are means ± SEM, * p < 0.05.

Figure 4

HF-EFA fed rats had larger adipocytes than HF-AFA fed rats. (A) Adipose tissue histology after H and E staining; (B) adipocyte size was quantified using ImageJ software. Values are means ± SEM,* p < 0.05.

Figure 5

Gene expression analysis in adipose tissue of HF-EFA shows increased levels of lipogenic mediators. Relative mRNA levels of (A) transcription factors and (B) genes involved in lipid synthesis, storage and transport, in adipose tissue of HF-AFA and HF-EFA fed rats. Values are means ± SEM, * p < 0.05.

Figure 6

Inflammatory markers are increased in adipose tissue of HF-EFA compared to HF-AFA fed rats. (A) Relative mRNA levels of genes related to inflammation; and (B) protein levels of TNFα, MCP-1, Rantes, IL-10 in pg/mg protein, in adipose tissue of HF-EFA and HF-AFA fed rats. Values are means ± SEM, * p < 0.05.

Figure 7

Folic acid increases PPARγ and triglyceride levels in a dose-dependent manner in cultured 3T3-L1 cells. (A) Relative PPARγ mRNA levels in cells cultured with 9 µM or 20 µM folic acid and (B) Triglyceride levels in cells after treatment with 9 µM compared to 20 µM folic acid. Values are means ± SEM, * p < 0.05.