A Lipophilic Fucoxanthin-Rich Phaeodactylum tricornutum Extract Ameliorates Effects of Diet-Induced Obesity in C57BL/6J Mice

Abstract

Phaeodactylum tricornutum (P. tricornutum) comprise several lipophilic constituents with proposed anti-obesity and anti-diabetic properties. We investigated the effect of an ethanolic P. tricornutum extract (PTE) on energy metabolism in obesity-prone mice fed a high fat diet (HFD). Six- to eight-week-old male C57BL/6J mice were switched to HFD and, at the same time, received orally placebo or PTE (100 mg or 300 mg/kg body weight/day). Body weight, body composition, and food intake were monitored. After 26 days, blood and tissue samples were collected for biochemical, morphological, and gene expression analyses. PTE-supplemented mice accumulated fucoxanthin metabolites in adipose tissues and attained lower body weight gain, body fat content, weight of white adipose tissue (WAT) depots, and inguinal WAT adipocyte size than controls, independent of decreased food intake. PTE supplementation was associated with lower expression of Mest (a marker of fat tissue expandability) in WAT depots, lower gene expression related to lipid uptake and turnover in visceral WAT, increased expression of genes key to fatty acid oxidation and thermogenesis (Cpt1, Ucp1) in subcutaneous WAT, and signs of thermogenic activation including enhanced UCP1 protein in interscapular brown adipose tissue. In conclusion, these data show the potential of PTE to ameliorate HFD-induced obesity in vivo.

Keywords: Phaeodactylum tricornutum; brown adipose tissue; browning; eicosapentanoic acid; fucoxanthin; microalgae; obesity.

Figure 1

Phaeodactylum tricornutum ethanolic extract (PTE) ameliorates fat deposition in C57BL/6J mice fed with a high fat diet (HFD). Evolution of body weight (bw) gain (A), cumulative energy intake from food (B), and body composition (C) from day 1 to 26 of dietary challenge. Body weight lost upon a 6 h fast, on day 22 (D). Liver, interscapular brown adipose tissue (BAT), and inguinal, epididymal, and retroperitoneal white adipose tissue (iWAT, eWAT, and rWAT) weights (E), adiposity as eWAT weight as percent body weight (F), and mRNA expression levels of Mest in iWAT, eWAT, and BAT (G) at the end of the experiment. HFD-fed mice received daily an oral dose of PTE (100 mg or 300 mg/kg bw) or placebo (olive oil:water, 2:1, v:v) for 26 days. Data are mean ± SEM of 5–6 male mice/group. To compare between two groups, the non-parametric Mann–Whitney U test was used: *, different (p < 0.05) from vehicle; and #, different (p < 0.05) between doses.

Figure 2

Phaeodactylum tricornutum ethanolic extract (PTE) decreases adipocyte size in inguinal white adipose tissue (iWAT) of C57BL/6J mice fed with a high fat diet (HFD). Representative microphotographs illustrating adipocyte size and Mitofusin (MFN) 2 immunostaining (A), and distribution of adipocytes size (B) in iWAT at the end of the experiment. HFD-fed mice received daily an oral dose of PTE (100 mg or 300 mg/kg body weight) or placebo (olive oil:water, 2:1, v:v) for 26 days. Five to six animals per group and between 200 and 300 cells per animal were included in the analysis of distribution of adipocytes size. The area of individual adipocytes was measured using a quantitative morphometric method at 20× magnification with the assistance of Axio Vision software. Adipocyte size distribution was statistically different (p < 0.001) between the control and the PTE groups, according to the Kolmogorov–Smirnov test. The bottom panels in (B) correspond to the difference in frequency for each adipocyte size interval between the PTE-supplemented group (PTE100 or PTE300) and the control (vehicle receiving) group.

Figure 3

Phaeodactylum tricornutum ethanolic extract (PTE) down-regulates fatty acid uptake and lipid turnover capacities in epididymal white adipose tissue (eWAT) and increases oxidative/thermogenic capacity in inguinal WAT (iWAT) of C57BL/6J mice fed with a high fat diet (HFD). mRNA levels of selected genes as indicated were analyzed in eWAT (A) and iWAT (B) at the end of the experiment. HFD-fed mice received daily an oral dose of PTE (100 mg or 300mg/kg body weight) or placebo (olive oil:water, 2:1, v:v) for 26 days. Data are the mean ± SEM of 5–6 male mice/group and are expressed relative to the mean value of the vehicle group, which was set to 100. To compare between two groups, the non-parametric Mann–Whitney U test was used: *, different (p < 0.05) from vehicle.

Figure 4

Phaeodactylum tricornutum ethanolic extract (PTE) activates interscapular brown adipose tissue (BAT) in C57BL/6J mice fed with a high fat diet (HFD). Representative microphotographs illustrating BAT activation and Uncoupling protein (UCP) 1 immunostaining (A), UCP1 and Mitofusin (MFN) 2 protein levels as determined by immunoblotting in BAT (B), and mRNA levels of selected genes in BAT (C) at the end of the experiment. HFD-fed mice received daily an oral dose of PTE (100 mg or 300 mg/kg body weight) or placebo (olive oil:water, 2:1, v:v) for 26 days. Data are the mean ± SEM of 5–6 male mice/group and are expressed relative to the mean value of the vehicle group, which was set to 100. To compare between two groups the non-parametric Mann–Whitney U test was used: *, different from vehicle; and #, different between doses. Threshold of statistical significance was set at p < 0.05; in (B), p values < 0.1 are also indicated.

Figure 5

Phaeodactylum tricornutum ethanolic extract (PTE) and fucoxanthin effects on gene expression in mature 3T3-L1 adipocytes are not equivalent. mRNA levels of selected genes in mature 3T3-L1 adipocytes are shown. 3T3-L1 preadipocytes were grown and differentiated following a standard protocol. On day 7, cultures were treated with PTE (100 mg/L), fucoxanthin (5 µM; Sigma-Aldrich), or vehicle (ethanol 0.5%) for 24 h. Data are the mean ± SEM of two independent experiments made in triplicate and are expressed relative to the mean value of the vehicle group, which was set to 100. To compare between two groups the non-parametric Mann–Whitney test was used: *, different from vehicle; and ‡, different from fucoxanthin. Threshold of statistical significance was set at p < 0.05, p values < 0.1 are also indicated.