Liver Of Otsuka Long-Evans Tokushima Fatty Rats Research Articles

Soy β-Conglycinin Peptide Attenuates Obesity and Lipid Abnormalities in Obese Model OLETF Rats.

We previously reported that soy β-conglycinin (βCG) improves obesity-induced metabolic abnormalities, but not obesity, in obese model Otsuka Long-Evans Tokushima fatty (OLETF) rats. In the present study, we aimed to investigate the effects of βCG-derived peptide consumption on obesity and lipid abnormality in OLETF rats. To this end, wild-type Long-Evans Tokushima Otsuka and OLETF rats were provided a normal diet containing 20% casein for four weeks as a control. In addition, we prepared βCG peptide by enzymatic hydrolysis, and OLETF rats were fed a diet in which half of the casein was replaced by βCG peptide (βCG peptide group). Consequently, rats in the βCG peptide group showed decreased abdominal white adipose tissue weight and lipid content (serum and liver triglycerides, and serum and liver cholesterol) compared to control OLETF rats. Further analysis demonstrated that βCG peptide consumption decreased lipogenic enzyme activity and increased lipolytic enzyme activity in the liver of OLETF rats. In addition, suppressive effects on both synthesis and absorption of cholesterol were observed in βCG peptide-fed OLETF rats. These findings suggest that peptidization of βCG enhanced the anti-obese and hypolipidemic effects of βCG.

The effects of herbal composition Gambigyeongsinhwan (4) on hepatic steatosis and inflammation in Otsuka Long‐Evans Tokushima fatty rats and HepG2 cells

Ethnopharmacological relevanceHepatic steatosis has risen rapidly in parallel with a dramatic increase in obesity. The aim of this study was to determine whether the herbal composition Gambigyeongsinhwan (4) (GGH(4)), composed of Curcuma longa L. (Zingiberaceae), Alnus japonica (Thunb.) Steud. (Betulaceae), and the fermented traditional Korean medicine Massa Medicata Fermentata, regulates hepatic steatosis and inflammation. Materials and methodsThe effects of GGH(4) on hepatic steatosis and inflammation in Otsuka Long-Evans Tokushima fatty (OLETF) rats and HepG2 cells were examined using Oil red O, hematoxylin and eosin, and toluidine blue staining, immunohistochemistry, quantitative real-time polymerase chain reaction, and peroxisome proliferator-activated receptor α (PPARα) transactivation assay. ResultsAdministration of GGH(4) to OLETF rats improved hepatic steatosis and lowered serum levels of alanine transaminase, total cholesterol, triglycerides, and free fatty acids. GGH(4) increased mRNA levels of fatty acid oxidation enzymes (ACOX, HD, CPT-1, and MCAD) and decreased mRNA levels of lipogenesis genes (FAS, ACC1, C/EBPα, and SREBP-1c) in the liver of OLETF rats. In addition, infiltration of inflammatory cells and expression of inflammatory cytokines (CD68, TNFα, and MCP-1) in liver tissue were reduced by GGH(4). Treatment of HepG2 cells with a mixture of oleic acid and palmitoleic acid induced significant lipid accumulation, but GGH(4) inhibited lipid accumulation by regulating the expression of hepatic fatty acid oxidation and lipogenic genes. GGH(4) also increased PPARα reporter gene expression. These effects of GGH(4) were similar to those of the PPARα activator fenofibrate, whereas the PPARα antagonist GW6471 reversed the inhibitory effects of GGH(4) on lipid accumulation in HepG2 cells. ConclusionsThese results suggest that GGH(4) inhibits obesity-induced hepatic steatosis and that this process may be mediated by regulation of the expression of PPARα target genes and lipogenic genes. GGH(4) also suppressed obesity-related hepatic inflammation. Thus, GGH(4) may be a promising drug for the treatment of obesity-related liver diseases.

α‐lipoic acid prevents non‐alcoholic fatty liver disease in OLETF rats

Insulin resistance, oxidative stress, inflammation and innate immune system activation contribute to the development of non-alcoholic fatty liver disease (NAFLD) through steatosis and inflammation in the liver. The powerful antioxidant α-lipoic acid (ALA) has been shown to improve insulin sensitivity and suppress inflammatory responses. This study explores how ALA administration protects against NAFLD. Otsuka Long-Evans Tokushima Fatty (OLETF) rats were divided into two groups (treated with 200 mg/kg/day of ALA or untreated) at 12 weeks of age and sacrificed at 28 weeks of age. Serum levels of insulin, free fatty acids, total cholesterol, triglyceride, leptin, IL-6 and blood glucose were decreased in ALA-treated rats. Serum adiponectin levels were higher in ALA-treated rats. ALA treatment decreased the expression of sterol regulatory element binding protein-1 and acetyl CoA carboxylase, and increased glucose transporter-4 expression in the livers of OLETF rats. Expression of the antioxidant enzymes heme oxygenase-1 and Cu/Zn-superoxide dismutase was increased in the livers of ALA-treated rats. The lipid peroxidation marker 4-hydroxynonenal was decreased in the liver of ALA-treated rats. Proteins associated with innate immune activation (Toll-like receptor-4 and high-mobility group protein box-1) and inflammatory markers (vascular cell adhesion molecule-1, intercellular adhesion molecule-1, and cyclooxygenase-2) were decreased in the livers of ALA-treated rats. Chronic ALA supplementation prevents NAFLD through multiple mechanisms by reducing steatosis, oxidative stress, immune activation and inflammation in the liver.

Multiple factors and pathways involved in hepatic very low density lipoprotein-apoB100 overproduction in Otsuka Long-Evans Tokushima fatty rats

AimsOverproduction of hepatic very low-density lipoprotein (VLDL) particles is a major abnormality of lipoprotein dysregulation in type 2 diabetes (T2D). We sought to examine the relationship between systemic/hepatic inflammation associated with insulin resistance and apolipoprotein (apo)B100-containing VLDL production. Methods and resultsAt the age of 19 wks, Otsuka Long-Evans Tokushima Fatty (OLETF) rats showed systemic inflammation (plasma TNF-α and interleukin (IL)-6 levels increased), insulin resistance (plasma retinol binding protein 4 and soluble CD36 levels were higher), dyslipidemia and fatty liver (plasma and liver triglyceride and cholesterol levels were higher as well as total VLDL-, VLDL1-, VLDL2-apoB100 and VLDL-triglycerides were overproduced), compared with the control rats. In livers of OLETF rats, mRNA levels of tnf, il1b and il6 were increased, but an anti-inflammatory protein, zinc finger protein 36, and its mRNA expression were decreased. We also found that the liver mRNA, protein levels, and tyrosine phosphorylation (pY) of insulin receptor (InsR) substrate (IRS) 2, but not IRS1, were decreased in OLETF rats; pY of InsR and Akt protein and phospho-Akt (ser437) were also reduced; but protein tyrosine phosphatase-1B protein was overexpressed. The gene expressions of glucose transporters 1 and 2, and glycogen synthase were decreased, but phosphatase and tensin homolog deleted on chromosome ten and glycogen synthase kinase 3β mRNAs were overexpressed, compared with the controls. Sterol regulatory element binding protein-1c mRNA, ATP-binding cassette transporter A1 mRNA, microsomal triglyceride transfer protein mRNA/protein, and CD36 mRNA/protein levels were increased and lipoprotein lipase and Niemann-Pick c1-like1 mRNA levels were decreased, which are all involved in lipogenesis. Decreased sirtuins1–3 mRNA levels were also observed in OLETF rats. ConclusionsThese abnormal genes, proteins expression and phosphorylation of multiple pathways related to inflammatory, insulin signaling and lipogenesis may be important underlying factors in VLDL-apoB100 particles overproduction observed in T2D. Our data contribute to the further understanding of an association of dyslipoproteinemia with systemic metabolic disorders, fatty liver and dysregulated hepatic metabolic pathways.

Olmesartan ameliorates a dietary rat model of non-alcoholic steatohepatitis through its pleiotropic effects

Insulin resistance is a major pathological condition associated with obesity and metabolic syndrome. Insulin resistance and the renin–angiotensin system are intimately linked. We evaluated the role of the renin–angiotensin system in the pathogenesis of insulin resistance-associated, non-alcoholic steatohepatitis by using the angiotensin II type 1 receptor blocker olmesartan medoxomil in a diabetic rat model. The effects of olmesartan on methionine- and choline-deficient (MCD) diet-induced steatohepatitis were investigated in obese, diabetic Otsuka Long–Evans Tokushima Fatty (OLETF) rats and control Long–Evans Tokushima Otsuka (LETO) rats. Components of the renin–angiotensin system were up-regulated in the livers of OLETF rats, compared with LETO rats. In OLETF, but not LETO, rats, oral administration of olmesartan for 8 weeks ameliorated insulin resistance. Moreover, olmesartan suppressed MCD diet-induced hepatic steatosis and the hepatic expression of lipogenic genes (sterol regulatory element-binding protein-1c and fatty acid synthase) in OLETF, but not LETO, rats. In both OLETF and LETO rats, olmesartan inhibited hepatic oxidative stress (4-hydroxy-2-nonenal-modified protein) and expression of NADPH oxidase. Olmesartan also inhibited hepatic fibrosis, stellate cell activation, and expression of fibrogenic genes (transforming growth factor-β, α1 [I] procollagen, plasminogen activator inhibitor-1) in both OLETF and LETO rats. In conclusion, pharmacological blockade of the angiotensin II type 1 receptor slows the development of steatohepatitis in the OLETF rat model. This angiotensin II type 1 receptor blocker may exert insulin resistance-associated effects against hepatic steatosis and inflammation as well as direct effects against the generation of reactive oxygen species and fibrogenesis.

Improvement of Obesity and Glucose Tolerance by Acetate in Type 2 Diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) Rats

Acetate has been found to have an inhibitory effect on the activity of carbohydrate-responsive element-binding protein (ChREBP) in cultured hepatocytes, this being a transcription factor that regulates several genes required for the conversion of glucose to fatty acids in the liver. The aim of this study was to investigate whether an oral administration of acetate would contribute to reducing lypogenic genes and protecting against obesity. We orally injected 5.2 mg/kg BW of acetate to obesity-linked type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats. The treatment with acetate showed a marked reduction in lipid accumulation in the adipose tissue, protection against accumulation of fat in the liver, and improved glucose tolerance. An analysis by Northern blotting revealed that the transcripts of several lipogenic genes in the liver of OLETF rats were decreased by the acetate treatment. On the basis of those results, it was indicated that acetate was a potential compound to improve obesity and obesity-linked type 2 diabetes.

Effects of troglitazone on skeletal muscle and liver protein tyrosine phosphatase activity in insulin-resistant otsuka long-evans tokushima fatty rats

Background: Protein tyrosine phosphatases (PTPases) appear to play an essential role in the regulation of steady-state phosphorylation of the insulin receptor and other proteins in the insulin-signaling pathway. Objectives: This study determined the role of PTPases in skeletal muscle and liver in an insulin-resistant model and the in vivo effect of troglitazone on PTPases. Methods: We used 26-week-old male Otsuka Long-Evans Tokushima Fatty (OLETF) rats as models of insulin resistance. PTPase activity was assessed with reduced carboxyamido-methylated and -maleylated lysozyme as substrates. The protein levels of 3 major candidate PTPases—leukocyte common antigen-related PTPase (LAR), PTPase 1B (PTP1B), and src homology 2-containing PTPase (SH-PTP2)—in skeletal muscle and liver of OLETF rats were analyzed using Western blot. The activities and amounts of PTPases in skeletal muscle and liver of OLETF rats treated with troglitazone for 7 days also were examined. Results: Particulate and cytosolic PTPase activities in skeletal muscle of OLETF rats were increased compared with those in control rats. Similar changes were observed in the liver. The protein levels of LAR, PTP1B, and SH-PTP2 in particulate fractions of skeletal muscle of OLETF rats were increased, but levels of PTP1B and SH-PTP2 in cytosolic fractions were unchanged. Similar findings were observed in the liver. Troglitazone normalized the increased PTPase activity and each protein level except cytosolic fraction of the liver. Conclusions: The findings suggest that troglitazone decreases elevated activities and levels of PTPases in the particulate fraction of the skeletal muscle and liver of OLETF rats, and that PTPase plays important roles through regulating the insulin-signaling system in the pathogenesis of insulin resistance in OLETF rats.

Transplantation of normal islets into the portal vein of Otsuka Long Evans Tokushima Fatty rats prevents diabetic progression.

To investigate the long-term effects of normal pancreatic islet transplantation on progression of obese type 2 diabetes mellitus (DM), 1500 normal islets (per rat) from Wistar King A rats at 8 weeks of age were transplanted into the liver through the portal vein of Otsuka Long Evans Tokushima Fatty (OLETF) rats, an animal model of obese type 2 DM, at 12 weeks of age. Body weight in the transplanted OLETF (IT) rats 8 and 28 weeks after islet transplantation did not differ from that in the corresponding sham-operated (SO) rats, but was greater than that in lean littermates (LETO rats; P < 0.05 for each group). In the early phase, 8 weeks after transplantation, rats in both IT and SO groups were normoglycemic, but hyperinsulinemic (P < 0.05 for each compared with LETO rats), probably resulting from increased body weight. In the late phase, 28 weeks after transplantation, hyperglycemia in the IT group was greatly attenuated compared with the SO group (P < 0.05), but hyperinsulinemia remained in both the IT and the SO groups compared with that in the LETO group (P < 0.05 for each). Immunohistochemical studies demonstrated that hypertrophic and fibrotic changes in pancreatic islets, together with mesangial proliferation of the glomerular matrix, an indicator for diabetic nephropathy, were attenuated predominantly in the IT group at the late phase after transplantation compared with those in the corresponding phase of the SO group. Islet transplantation into the liver of OLETF rats thus prevented further progression of obese type 2 DM. A possible mechanism is that islet transplantation may prevent development of hyperglycemia by improving abnormal hepatic glucose metabolism and consequently insulin resistance, which may lead to blockade of a vicious cycle between advancing damage to pancreatic islet cells and increased demand for insulin secretion, thus sparing original pancreatic cells from exhaustion induced by increased demand for insulin secretion.