To determine how soy protein isolate (SPI) ameliorated liver steatosis in male obese Zucker rats, we conducted global transcriptomic expression (RNAseq) analysis on liver samples of male rats fed either the SPI or a control casein (CAS)-based diet (n = 8 per group) for 16 weeks. Liver transcriptomics were analyzed using an Ilumina HiSeq system with 2 × 100 base pair paired-end reads method. Bioinformatics was conducted using Ingenuity Pathway Analysis (IPA) software (Qiagen, CA) with P < 0.05 and 1.3-fold differential expression cutoff values. Regression analysis between RNAseq data and targeted mRNA expression analysis of 12 top differentially expressed genes (from the IPA program) using quantitative PCR (qPCR) revealed a significant regression analysis (r2 = 0.69, P = 0.0008). In addition, all qPCR values had qualitatively similar direction of up- or down-regulation compared to the RNAseq transcriptomic data. Diseases and function analyses that were based on differentially expressed target molecules in the dataset predicted that lipid metabolism would be enhanced whereas inflammation was predicted to be inhibited in SPI-fed compared to CAS-fed rats at 16 weeks. Combining upstream regulator and regulator effects functions in IPA facilitates the prediction of upstream regulators (e.g., transcription regulators) that could play important roles in attenuating or promoting liver steatosis due to SPI or CAS diets. Upstream regulators that were predicted to be activated (from expression of down-stream targets) linked to increased conversion of lipid and transport of lipid in SPI-fed rats included hepatocyte nuclear factor 4 alpha (HNF4A) and aryl hydrocarbon receptor (AHR). Upstream regulators that were predicted to be activated in CAS-fed rats linked to activation of phagocytosis and neutrophil chemotaxis included colony stimulating factor 2 and tumor necrosis factor. The results provide clear indication that long-term SPI-fed rats exhibited diminished inflammatory response and increased lipid transport in liver compared to CAS-fed rats that likely would contribute to reduced liver steatosis in this obese Zucker rat model.

Differential expression of genes provides insight into fundamental mechanisms associated with the ability of soy protein isolate to attenuate liver steatosis in genetically obese rats.

Non-alcoholic fatty liver disease (NAFLD) is the leading cause of liver disease in adolescents and adults, and the risk of developing NAFLD increases with obesity. In the present study, it was shown that obesity increased fatty liver (steatosis) using an obese Zucker rat model. Metformin is an oral anti-hyperglycemic agent approved by the FDA for treatment of type 2 diabetes in adults and children >10 years of age. There is insufficient evidence regarding the effects of metformin on pediatric liver steatosis. Thus, in the present study, the effects of 10 weeks metformin treatment on liver steatosis and related serum markers for liver damage was assessed. Lean and obese (n=16 per group) 5-week old female Zucker rats were provided an AIN-93 G diet for 8 weeks to induce NAFLD, and then rats were randomly assigned to 4 groups (8 rats/group): i) lean without metformin (LC), ii) lean + metformin (LM), iii) obese without metformin (OC), and iv) obese + metformin (OM). Rats were provided ad libitum access to the diet containing metformin (1 g metformin per kg of food). Rats were weighed twice weekly and were sacrificed 10 weeks later. Serum was collected to measure the levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), leptin and adiponectin. Livers were collected for histological analysis. The results showed that obese rats gained significantly more weight than lean rats in both the control and metformin treatment groups (P<0.001). OM treated rats exhibited a lower degree of liver steatosis compared with the OC rats (P<0.04). There were no significant differences in serum ALT levels between the groups. However, obesity significantly increased serum AST levels in both the control and metformin treatment groups (P=0.01). The ratio of leptin to adiponectin was increased in obese compared with the lean rats in both the control and metformin treatment groups (P<0.0001). There was no effect of metformin on serum biomarkers. In summary, short-term metformin treatment decreased liver steatosis but did not affect the serum markers of liver steatosis.

No abstract

Obesity can lead to chronic health complications such as nonalcoholic fatty liver disease (NAFLD). NAFLD is characterized by lipid aggregation in the hepatocytes and inflammation of the liver tissue as a consequence that can contribute to the development of cirrhosis and hepatocellular carcinoma (HCC). Previously, we reported that feeding obese Zucker rats with soy protein isolate (SPI) can reduce liver steatosis when compared with a casein (CAS) diet as a control. However, the effects of SPI on cytochrome P450 (CYP) in an obese rat model are less known. In addition, there is a lack of information concerning the consumption of soy protein in adolescents and its effect in reducing the early onset of NAFLD in this group. Our main goal was to understand if the SPI diet had any impact on the hepatic CYP gene expression when compared with the CAS diet. For this purpose, we used the transcriptomic data obtained in a previous study in which liver samples were collected from obese rats after short-term (eight-week) and long-term (16-week) feeding of SPI (n = 8 per group). To analyze this RNAseq data, we used Ingenuity Pathway Analysis (IPA) software. Comparing short- vs long-term feeding revealed an increase in the number of downregulated CYP genes from three at 8 weeks of SPI diet to five at 16 weeks of the same diet (P ≤ 0.05). On the other hand, upregulated CYP gene numbers showed a small increase in the long-term SPI diet compared to the short-term SPI diet, from 14 genes at 8 weeks to 17 genes at 16 weeks (P ≤ 0.05). The observed changes may have an important role in the attenuation of liver steatosis.