Brown rice and its component, γ-oryzanol, attenuate the preference for high-fat diet by decreasing hypothalamic endoplasmic reticulum stress in mice

Abstract

Brown rice is known to improve glucose intolerance and prevent the onset of diabetes. However, the underlying mechanisms remain obscure. In the current study, we investigated the effect of brown rice and its major component, γ-oryzanol (Orz), on feeding behavior and fuel homeostasis in mice. When mice were allowed free access to a brown rice-containing chow diet (CD) and a high-fat diet (HFD), they significantly preferred CD to HFD. To reduce hypothalamic endoplasmic reticulum (ER) stress on an HFD, mice were administered with 4-phenylbutyric acid, a chemical chaperone, which caused them to prefer the CD. Notably, oral administration of Orz, a mixture of major bioactive components in brown rice, also improved glucose intolerance and attenuated hypothalamic ER stress in mice fed the HFD. In murine primary neuronal cells, Orz attenuated the tunicamycin-induced ER stress. In luciferase reporter assays in human embryonic kidney 293 cells, Orz suppressed the activation of ER stress-responsive cis-acting elements and unfolded protein response element, suggesting that Orz acts as a chemical chaperone in viable cells. Collectively, the current study is the first demonstration that brown rice and Orz improve glucose metabolism, reduce hypothalamic ER stress, and, consequently, attenuate the preference for dietary fat in mice fed an HFD.

FIG. 1.

Effects of BR on body weight in mice fed CD (A) and HFD (B). Effects of BR on blood glucose levels in mice fed CD (C) and HFD (D) in the fed state. Fecal triglyceride (TG) contents of mice fed CD (E) and HFDs (F). Data are expressed as mean ± SEM (n = 10–12). *P < 0.05, **P < 0.01 compared with control mice; †P < 0.05, ††P < 0.01 compared with WR-fed mice.

FIG. 2.

Effects of BR on glucose homeostasis in mice. Blood glucose levels and AUC during GTT in mice fed CD (A) and HFD (B) for 10 weeks. Blood glucose levels and the AUC during ITT after 10 weeks of BR feeding in mice fed the CD (C) and the HFD (D). Data are expressed as mean ± SEM (n = 3–6). *P < 0.05, **P < 0.01 compared with control mice; †P < 0.05, ††P < 0.01 compared with WR-fed mice.

FIG. 3.

Effects of BR on hypothalamic ER stress in mice. A: Comparison of Chop, ERdj4, and Xbp1s mRNA levels in the hypothalamus and liver. The tissues were dissected from mice fed CD. Mice were fed BR or WR for 10 weeks. Levels of mRNA in the hypothalamus are shown for Chop (B), ERdj4 (C), and Xbp1s (D). The mRNA levels were determined using real-time PCR. Values were normalized to that of 18S rRNA. E: Plasma leptin concentrations were measured by ELISA. F: Leptin-induced (1 μg, i.c.v.) STAT3 phosphorylation. Blots show phospho-STAT3 (p-STAT3) and STAT3, and graph shows the p-STAT3-to-STAT3 ratio. Data are expressed as mean ± SEM (n = 3–9). *P < 0.05, **P < 0.01.

FIG. 4.

Impact of BR on dietary preference in mice. A: Dietary fat preferences were evaluated in the two-food CD vs. HFD choice tests. Mice were allowed free access to CD and HFD. Mice were randomly divided into three groups: the control (CD vs. HFD), BR-containing diet (CD + BR vs. HFD + BR), and the WR-containing diet (CD + WR vs. HFD + WR) groups. HFD preference in mice fed BR (B) and 4-PBA–treated mice (D). C: Body weight of mice fed BR during two-food CD vs. HFD choice tests (n = 8–12; 4 mice per cage). Data are expressed as mean ± SEM. *P < 0.05, **P < 0.01 compared with control or vehicle mice; †P < 0.05, ††P < 0.01 compared with WR-fed mice. (A high-quality digital representation of this figure is available in the online issue.)

FIG. 5.

Effects of long-term administration of Orz on body weight (A) and blood glucose (B) were examined in mice fed the HFD ad libitum. Blood glucose levels and the AUC for glucose during the GTT (C) and the ITT (E) and plasma insulin levels (D) during the GTT after 10 weeks of Orz treatment at doses of 20, 80, and 320 μg⋅g body weight⁻¹⋅day⁻¹. Data are expressed as mean ± SEM (n = 3–6). *P < 0.05, **P < 0.01 compared with vehicle-treated mice.

FIG. 6.

Effects of Orz on the activities of ER stress–responsive cis-acting elements in HEK293 cells. Reporter genes-transfected HEK293 cells were cotreated with tunicamycin (2 μg/mL) and Orz (1 μmol/L) or 4-PBA (1 mmol/L) for 15 h (ERSEs) or 24 h (UPRE). The activities of ERSE-I (A), ERSE-II (B), and UPRE (C) were measured. Data are expressed as mean ± SEM (n = 4). *P < 0.05, **P < 0.01 compared with vehicle (Veh)-treated cells.

FIG. 7.

Effects of Orz on hypothalamic ER stress and dietary preference in mice. Murine primary neuronal cells were pretreated with Orz (0.1, 1 μmol/L) and then stimulated with tunicamycin (0.1 μg/mL). The mRNA levels are shown for Chop (A), ERdj4 (B), and Xbp1s (C). Values were normalized to that of 18S rRNA and are expressed as levels relative to that of vehicle (Veh)-pretreated cells (n = 4–8). Mice were treated with Orz at doses of 20, 80 and 320 μg⋅g body weight⁻¹⋅day⁻¹ for 13 weeks, and mRNA levels were measured in the hypothalamus for Chop (D), ERdj4 (E), and Xbp1s (F). Values were normalized to that of 18S rRNA and are expressed as levels relative to that of vehicle-treated mice (n = 8–11). The mRNA levels were determined using real-time PCR. G: HFD preference in Orz-treated mice (80 μg⋅g body weight⁻¹⋅day⁻¹). Mice were allowed free access to CD and HFD (n = 6; 2 mice per cage). Data are expressed as mean ± SEM. *P < 0.05, **P < 0.01 compared with vehicle-treated cells or mice.