DOI: 10.14457/tu.the.2015.648
title: The effect of rice bran extract on cardiovascular lipotoxicity in rats fed a high-fat diet

description: Metabolic syndrome is commonly associated with the development of cardiovascular diseases. Among the various pathomechanisms, the cardiovascular lipotoxicity is one of the important mechanisms for the development of cardiovascular diseases. Rice bran extract (RBE) from Khao Dawk Mali 105 rice variety (Oryza sativa Linn.) has shown to decrease the risk factors for cardiovascular diseases; however, the mechanisms of cardiovascular protection by RBE have not been yet elucidated. Thus, the present study aimed at verifying the protective effects of RBE on cardiovascular abnormalities in rats fed a high-fat diet (HF) so as to provide a model for prevention of metabolic syndrome and cardiovascular diseases. This study was also designed to characterize the phenolic compounds, γ-oryzanol and α-tocopherol composition of RBE and to evaluate its antioxidant activity.  Male outbred Sprague-Dawley rats were randomly diveided into two groups including short- and intermediate-term groups. Short- and intermediate-term experiments were studied for 4 and 16 weeks, respectively. For short-term study, rats were subdivided into 4 groups including control (C), HF, HF + RBE (2,205 mg/kg/day, oral gavage) and HF + fenofibrate (F) (5 mg/kg/day for day 4 to day 16 and 15 mg/kg/day for the next 12 days, oral gavage) groups. HF + F group served as a positive control. For intermediate-term study, rats were subdivided into 3 groups including C, HF and HF + RBE groups. Body weight and food intake were recorded daily. After animal sacrifice, metabolic characteristics, blood biochemical parameters and histology were determined. Left ventricular and aortic gene expressions were analyzed by real-time polymerase chain reaction and Western blot analysis. The total phenolic compounds, γ-oryzanol and and α-tocopherol contents in RBE were determined using the Folin-Ciocalteu method and high-performance liquid chromatography (HPLC), respectively. The antioxidant activity of RBE was evaluated by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging assay. After 4 and 16 weeks of exclusive HF feeding, elevated body weight, abdominal fat weight, adipocyte size, liver weight, liver triglyceride (TG) levels, fasting blood glucose (FBG), area under the curve of blood glucose levels (AUC-G) and serum total-cholesterol (total-C) and low-density lipoprotein-cholesterol (LDL-C) levels were found. The short-term HF group also showed elevated blood levels of TG and glucose. High-density lipoprotein-cholesterol (HDL-C) levels were significantly reduced in HF group when compared with the C group. Compared with the HF group, only those which received the 4 weeks of RBE treatment had decreased body weight, abdominal obesity, liver weight, liver TG accumulation and levels of serum total-C and blood glucose. The serum TG levels and adipocyte size were lower in all RBE-treated groups. In addition, the serum LDL-C levels and AUC-G were slightly reduced in both HF + RBE groups. Consitent with a decrease in FBG and AUC-G, the pancreatic mass was normalized after the short-term treatment with RBE. The same trends were found for F treatment. However, the HF + F group exhibited a significant increase in the liver weight and serum alanine aminotransferase (ALT) levels, suggesting an important role of F in inducing hepatotoxicity in this model. Rats fed only with intermediate-term HF also showed left ventricular hypertrophy and early signs of atherosclerotic lesions compared to the C group. In this experiment, the levels of serum aspartate aminotransferase (AST) and ALT were all significantly increased in the HF group when compared with the C group. These changes were prevented by RBE treatment. Mechanistically, expression levels of peroxisome proliferator activated receptor α (PPARα) and glucose transporter-4 (GLUT-4) were up-regulated in the hearts of both HF + RBE groups. However, down-regulated expression of fatty acid translocase/cluster of differentiation 36 (FAT/CD36) were detected in the hearts of all HF + RBE groups as compared with the HF groups. There were no significant differences in the levels of cardiac TG, and serum creatine kinase-MB (CK-MB) and lactate dehydrogenase (LDH) between three groups. Compared with the HF group, the short-term RBE-treated group had significantly increased aortic expression levels of endothelial nitric oxide synthase (eNOS), whereas the intermediate-term RBE-treated group did not have any significant changes. Interestingly, all experimental periods of RBE treatment caused significant decrease in nuclear factor-kappa B p65 (NF-κB p65) expression levels in both cardiac and aortic tissues Nonetheless, all groups showed normal aortic wall area. In conclusion, the present results suggest that the RBE consumption can prevent the derangement of cardiac energy metabolism and cardiac hypertrophy, partly by improving the expression of genes involved in fatty acid uptake (FAT/CD36),  fatty acid oxidation (PPARα ), glucose uptake (GLUT4) and  cardiomycyte hypertrophy (NF-κB p65). In addition, it was also able to improve the expression of eNOS and NF-κB p65 in the vasculature in HF-induced metabolic stress. Collectively, all these findings indicate that RBE treatment is likely to prevent the initial development of cardiovascular diseases by regulating cardiovascular risk factors as well as their related target gene expression. In comparison with the intermediate-term study, short-term treatment with RBE is more effectively in attenuating metabolic derangements in rats fed an HF. Therefore, RBE could be a potential food supplement for the prevention of cardiovascular abnormalities in the setting of the MS. However, RBE contained low levels of total phenolic compounds, γ-oryzanol and α-tocopherol and showed low antioxidant activity. Based on previous studies, the cardiovascular protective effects of RBE are probably due to the presence of other bioactive constituents such as protein and phytic acid, which have the anti-metabolic disorder and anti-atherosclerotic effects. Thus, evaluation of the bioactive compounds in RBE will be further studied to correlate their effects on the prevention of cardiovascular disease.