Citrus reticulata Blanco peel extract ameliorates hepatic steatosis,oxidative stress and inflammation in HF and MCD diet-induced NASH C57BL/6 J mice

Excessive lipid deposition, oxidative stress and inflammation in liver tissues are regarded as crucial inducers of nonalcoholic steatohepatitis (NASH), which is the most frequent chronic liver disease and closely related to obesity and insulin resistance. In this work, the preventive and therapeutic effects of Citrus reticulata Blanco (Jizigan) peel extract (JZE) on NASH induced by high fat (HF) diet and methionine choline-deficient (MCD) diet in C57BL/6 mice were investigated. We found that daily supplementation of JZE with an HF diet effectively ameliorated glucose tolerance and insulin resistance. In addition, the key indexes of lipid profiles, oxidative stress, hepatic steatosis and inflammatory factors were also ameliorated in both NASH mouse models. Furthermore, JZE treatment activated nuclear factor erythroid-2-related factor 2 (Nrf2) in the livers of diet- induced NASH mice. Our study suggests that JZE might alleviate NASH via the activation of Nrf2 signaling and that citrus Jizigan could be used as a dietary therapy for NASH and related metabolic syndrome.     

Dietary zinc supplementation attenuates hyperglycemia in db/db mice

Although zinc (Zn) deficiency has been associated with insulin resistance, and altered Zn metabolism (e.g., hyperzincuria, low-normal plasma Zn concentrations) may be present in diabetes, the potential effects of Zn on modulation of insulin action in Type II diabetes have not been established. The objective of this study was to compare the effects of dietary Zn deficiency and Zn supplementation on glycemic control in db/db mice. Weanling db/db mice and lean littermate controls were fed Zn-deficient (3 ppm Zn; dbZD and InZD groups), Zn-adequate control (30 ppm Zn; dbC and InC groups) or Zn-supplemented (300 ppm Zn; dbZS and InZS groups) diets for 6 weeks. Mice were assessed for Zn status, serum and urinary indices of diabetes, and gastrocnemius insulin receptor concentration and tyrosine kinase activity. Fasting serum glucose concentrations were significantly lower in the dbZS group compared with the dbZD group (19.3 +/- 2.9 and 27.9 +/- 4.1 mM, respectively), whereas the dbC mice had an intermediate value. There was a negative correlation between femur Zn and serum glucose concentrations (r = -0.59 for lean mice, P = 0.007). The dbZS group had higher pancreatic Zn and lower circulating insulin concentrations than dbZC mice. Insulin-stimulated tyrosine kinase activity in gastrocnemius muscle was higher in the db/db genotype, and insulin receptor concentration was not altered. In summary, dietary Zn supplementation attenuated hyperglycemia and hyperinsulinemia in db/db mice, suggesting that the roles of Zn in pancreatic function and peripheral tissue glucose uptake need to be further investigated.     

Loss of resistin ameliorates hyperlipidemia and hepatic steatosis in leptin-deficient mice

Resistin has been linked to components of the metabolic syndrome, including obesity, insulin resistance, and hyperlipidemia. We hypothesized that resistin deficiency would reverse hyperlipidemia in genetic obesity. C57Bl/6J mice lacking resistin [resistin knockout (RKO)] had similar body weight and fat as wild-type mice when fed standard rodent chow or a high-fat diet. Nonetheless, hepatic steatosis, serum cholesterol, and very low-density lipoprotein (VLDL) secretion were decreased in diet-induced obese RKO mice. Resistin deficiency exacerbated obesity in ob/ob mice, but hepatic steatosis was drastically attenuated. Moreover, the levels of triglycerides, cholesterol, insulin, and glucose were reduced in ob/ob-RKO mice. The antisteatotic effect of resistin deficiency was related to reductions in the expression of genes involved in hepatic lipogenesis and VLDL export. Together, these results demonstrate a crucial role of resistin in promoting hepatic steatosis and hyperlipidemia in obese mice.     

CCAAT/enhancer-binding protein beta deletion reduces adiposity, hepatic steatosis, and diabetes in Lepr(db/db) mice

CCAAT/enhancer-binding protein beta (C/EBPbeta) plays a key role in initiation of adipogenesis in adipose tissue and gluconeogenesis in liver; however, the role of C/EBPbeta in hepatic lipogenesis remains undefined. Here we show that C/EBPbeta inactivation in Lepr(db/db) mice attenuates obesity, fatty liver, and diabetes. In addition to impaired adipogenesis, livers from C/EBPbeta(-/-) x Lepr(db/db) mice had dramatically decreased triglyceride content and reduced lipogenic enzyme activity. C/EBPbeta deletion in Lepr(db/db) mice down-regulated peroxisome proliferator-activated receptor gamma2 (PPARgamma2) and stearoyl-CoA desaturase-1 and up-regulated PPARalpha independent of SREBP1c. Conversely, C/EBPbeta overexpression in wild-type mice increased PPARgamma2 and stearoyl-CoA desaturase-1 mRNA and hepatic triglyceride content. In FAO cells, overexpression of the liver inhibiting form of C/EBPbeta or C/EBPbeta RNA interference attenuated palmitate-induced triglyceride accumulation and reduced PPARgamma2 and triglyceride levels in the liver in vivo. Leptin and the anti-diabetic drug metformin acutely down-regulated C/EBPbeta expression in hepatocytes, whereas fatty acids up-regulate C/EBPbeta expression. These data provide novel evidence linking C/EBPbeta expression to lipogenesis and energy balance with important implications for the treatment of obesity and fatty liver disease.     

Oral glucagon-like peptide 1 analogue ameliorates glucose intolerance in db/db mice

Objectives

We constructed a recombinant oral GLP-1 analogue in Lactococcus lactis (L. lactis) and evaluated its physiological functions.

Results

In silico docking suggested the alanine at position 8 substituted with serine (A8SGLP-1) reduced binding of DPP4, which translated to reduced cleavage by DPP4 with minimal changes in stability. This was further confirmed by an in vitro enzymatic assay which showed that A8SGLP-1 significantly increased half-life upon DPP4 treatment. In addition, recombinant L. lactis (LL-A8SGLP-1) demonstrated reduced fat mass with no changes in body weight, significant improvement of random glycemic control and reduced systemic inflammation compared with WT GLP-1 in db/db mice.

Conclusion

LL-A8SGLP-1 adopted in live biotherapeutic products reduce blood glucose in db/db mice without affecting its function.

     

Antidiabetic effects of Vigna nakashimae extract in db/db mice

The inhibitory activity of Vigna nakashimae extract against intestinal α-glucosidase was investigated in vitro and in vivo. The extract exerted a significant inhibitory effect against intestinal α-glucosidases. With sucrose-loading, it reduced the peak responses of blood glucose significantly in normal mice. Next, it was administrated to 8-week-old db/db mice for 2 weeks, and then plasma glucose, triglyceride, and total cholesterol levels were measured. The extract significantly suppressed postprandial hyperglycemia and blood glycated hemoglobin in the db/db mice. In addition, it lowered fasting glucose and improved glucose tolerance. Furthermore, it led to significant decreases in plasma triglyceride levels. It reduced endoplasmic reticulum stress in thapsigargin-induced HepG2 cells. Taken together, these results suggest that Vigna nakashimae extract has hypoglycemic and hypolipidemic effects that occur via inhibition of α-glucosidase activity and endoplasmic reticulum stress.     

Green tea extract attenuates hepatic steatosis by decreasing adipose lipogenesis and enhancing hepatic antioxidant defenses in ob/ob mice

Excess hepatic lipid accumulation and oxidative stress contribute to nonalcoholic fatty liver disease (NAFLD). Thus, we hypothesized that the hypolipidemic and antioxidant activities of green tea extract (GTE) would attenuate events leading to NAFLD. Obese mice (ob/ob; 5 weeks old, n=38) and their lean littermates (n=12) were fed 0%, 0.5% or 1% GTE for 6 weeks. Then, hepatic steatosis, oxidative stress and inflammatory markers were measured. Obese mice, compared to lean controls, had greater hepatic lipids and serum alanine aminotransferase (ALT). GTE at 1% lowered (P<.05) hepatic lipids and ALT in obese mice. The GTE-mediated attenuation in hepatic steatosis was accompanied by decreased mRNA expression of adipose sterol regulatory element-binding protein-1c, fatty acid synthase, stearoyl CoA desaturase-1, and hormone-sensitive lipase and decreased serum nonesterified fatty acid concentrations. Immunohistochemical data indicated that steatotic livers from obese mice had extensive accumulation of tumor necrosis factor-α (TNF-α), whereas GTE at 1% decreased hepatic TNF-α protein and inhibited adipose TNF-α mRNA expression. Hepatic total glutathione, malondialdehyde and Mn- and Cu/Zn-superoxide dismutase activities in obese mice fed GTE were normalized to the levels of lean littermates. Also, GTE increased hepatic catalase and glutathione peroxidase activities, and these activities were inversely correlated with ALT and liver lipids. Collectively, GTE mitigated NAFLD and hepatic injury in ob/ob mice by decreasing the release of fatty acids from adipose and inhibiting hepatic lipid peroxidation as well as restoring antioxidant defenses and decreasing inflammatory responses. These findings suggest that GTE may be used as an effective dietary strategy to mitigate obesity-triggered NAFLD.     

Constitutive hepatic glucokinase activity db/db and ob/ob mice

The specific activity of hepatic glucokinase (ATP: d-glucose 6-phosphotransferase, EC 2.7.1.2) in db/db mice and ob/ob mice was higher than in normal mice. All enzymes had a similar K_m and, thus, the difference in activity was not due to differences in the affinity of enzyme molecules to substrates. Mixing liver extracts with high or low enzyme activities yielded additive results, as expected, which ruled out the involvement of an inhibitor or activator of the enzyme. Fasting normal mice of either strain for three days decreased glucokinase activity. However, fasting db/db or ob/ob mice for as long as 10 days had no effect on enzyme activity, indicating that glucokinase in db/db or ob/ob mice was out of regulation of constitutive. The constant, abnormally high glucokinase activity may be a contributing factor to the obesity of ob/ob or db/db mice. These mice provide a model system to study the regulation of this rate-limiting enzyme of glucose metabolism.     

Effects of oxytetracycline treatment on enzymes of hepatic glycogen metabolism in genetically diabetic (db/db) mice

The effects of daily oxytetracycline treatment on the activities of hepatic glycogen synthase, glycogen phosphorylase, plasma glucose, and insulin, and on liver glycogen, free fatty acid, and triglyceride levels were examined in 8- to 15-week-old genetically diabetic and lean mice. Oxytetracycline administration resulted in substantial reductions in the plasma glucose and immunoreactive-insulin levels in both diabetic and lean mice. The drug had no significant effect on the liver glycogen content in either phenotype, regardless of age, but it increased hepatic lipids and depressed body weights in lean animals. The most prominent effect of the drug was in markedly altering the activities of both glycogen synthase and phosphorylase in the liver of older diabetic mice. Oxytetracycline treatment produced a three-fold increase in the percentage of glycogen synthase I activity and reduced by one-third the percentage of glycogen phosphorylase a activity in 15-week-old diabetic mice. In age-matched lean mice treated with oxytetracycline, the percentage of glycogen synthase I activity increased significantly, but the percentage of phosphorylase a activity was unchanged. These data suggest that the drug may alter an aspect of hepatic glycogen metabolism which might lead to an inhibition of glycogenolysis and subsequent diminution of blood sugar levels in the diabetic. The present results show that, while oxytetracycline may be effective in reducing the severity of some of the diabetic symptoms associated with carbohydrate metabolism in this animal model of maturity-onset diabetes, the drug may have adverse effects on aspects of protein and lipid metabolism in these animals.     

Anti-hyperlipidemic effect of soybean extract fermented by Bacillus subtilis MORI in db/db mice

The purpose of this study was to investigate the anti-hyperlipidemic effect of soy bean extract solution fermented by Bacillus subtilis MORI (BTD-1E) in obese db/db mice. Eight-week-old male db/db mice were administered 33.3 mg/kg BTD-1E solution orally once a day for four weeks. The BTD-1E group showed significantly lower body weight compared with the db control group (P<0.05). The BTD-1E group showed significantly lower serum total cholesterol and LDL cholesterol levels compared with the db control group, respectively (P<0.05, P<0.01). The BTD-1E group showed significantly decreased liver weight relative to final body weight compared with the db control group (P<0.01). After four weeks of BTD-1E administration, lipid droplets in the liver were apparently decreased in the BTD-1E group compared to the db control group. In summary, our results suggest that BTD-1E has an anti-hyperlipidemic effect in the obese mouse model.     

Cyanidin 3-glucoside attenuates obesity-associated insulin resistance and hepatic steatosis in high-fat diet-fed and db/db mice via the transcription factor FoxO1

Obesity is a major risk factor for the development of type 2 diabetes, and both conditions are now recognized to possess significant inflammatory components underlying their pathophysiologies. Here, we hypothesized that cyanidin 3-glucoside (C3G), a typical anthocyanin reported to possess potent anti-inflammatory properties, would ameliorate obesity-associated inflammation and metabolic disorders, such as insulin resistance and hepatic steatosis in mouse models of diabesity. Male C57BL/6J obese mice fed a high-fat diet for 12 weeks and genetically diabetic db/db mice at an age of 6 weeks received dietary C3G supplementation (0.2%) for 5 weeks. We found that dietary C3G lowered fasting glucose levels and markedly improved the insulin sensitivity in both high-fat diet fed and db/db mice as compared with unsupplemented controls. White adipose tissue messenger RNA levels and serum concentrations of inflammatory cytokines (tumor necrosis factor-α, interleukin-6, and monocyte chemoattractant protein-1) were reduced by C3G, as did macrophage infiltration in adipose tissue. Concomitantly, hepatic triglyceride content and steatosis were alleviated by C3G. Moreover, C3G treatment decreased c-Jun N-terminal kinase activation and promoted phosphorylation and nuclear exclusion of forkhead box O1 after refeeding. These findings clearly indicate that C3G has significant potency in antidiabetic effects by modulating the c-Jun N-terminal kinase/forkhead box O1 signaling pathway and the related inflammatory adipocytokines.     

Kaempferol ameliorates hyperglycemia through suppressing hepatic gluconeogenesis and enhancing hepatic insulin sensitivity in diet-induced obese mice

Obesity-associated insulin resistance (IR) is a major risk factor for developing type 2 diabetes and an array of other metabolic disorders. In particular, hepatic IR contributes to the increase in hepatic glucose production and consequently the development of fasting hyperglycemia. In this study, we explored whether kaempferol, a flavonoid isolated from Gink go biloba, is able to regulate hepatic gluconeogenesis and blood glucose homeostasis in high-fat diet-fed obese mice and further explored the underlying mechanism by which it elicits such effects. Oral administration of kaempferol (50 mg/kg/day), which is the human equivalent dose of 240 mg/day for an average 60 kg human, significantly improved blood glucose control in obese mice, which was associated with reduced hepatic glucose production and improved whole-body insulin sensitivity without altering body weight gain, food consumption or adiposity. In addition, kaempferol treatment increased Akt and hexokinase activity, but decreased pyruvate carboxylase (PC) and glucose-6 phosphatase activity in the liver without altering their protein expression. Consistently, kaempferol decreased PC activity and suppressed gluconeogenesis in HepG2 cells as well as primary hepatocytes isolated from the livers of obese mice. Furthermore, we found that kaempferol is a direct inhibitor of PC. These findings suggest that kaempferol may be a naturally occurring antidiabetic compound that acts by suppressing glucose production and improving insulin sensitivity. Kaempferol suppression of hepatic gluconeogenesis is due to its direct inhibitory action on the enzymatic activity of PC.     

Dietary cholesterol exacerbates hepatic steatosis and inflammation in obese LDL receptor-deficient mice

Non-alcoholic fatty liver disease (NAFLD), the hepatic manifestation of the metabolic syndrome, can progress to steatohepatitis (NASH) and advanced liver disease. Mechanisms that underlie this progression remain poorly understood, partly due to lack of good animal models that resemble human NASH. We previously showed that several metabolic syndrome features that develop in LDL receptor-deficient (LDLR-/-) mice fed a diabetogenic diet are worsened by dietary cholesterol. To test whether dietary cholesterol can alter the hepatic phenotype in the metabolic syndrome, we fed LDLR-/- mice a high-fat, high-carbohydrate diabetogenic diet (DD) without or with added cholesterol (DDC). Both groups of mice developed obesity and insulin resistance. Hyperinsulinemia, dyslipidemia, hepatic triglyceride, and alanine aminotransferase (ALT) elevations were greater with DDC. Livers of DD-fed mice showed histological changes resembling NAFLD, including steatosis and modest fibrotic changes; however, DDC-fed animals developed micro- and macrovesicular steatosis, inflammatory cell foci, and fibrosis resembling human NASH. Dietary cholesterol also exacerbated hepatic macrophage infiltration, apoptosis, and oxidative stress. Thus, LDLR-/- mice fed diabetogenic diets may be useful models for studying human NASH. Dietary cholesterol appears to confer a second "hit" that results in a distinct hepatic phenotype characterized by increased inflammation and oxidative stress.     

Hydroxytyrosol ameliorates insulin resistance by modulating endoplasmic reticulum stress and prevents hepatic steatosis in diet-induced obesity mice

Endoplasmic reticulum (ER) is a principal organelle responsible for energy and nutrient management. Its dysfunction has been viewed in the context of obesity and related glucolipid metabolic disorders. However, therapeutic approaches to improve ER adaptation and systemic energy balance in obesity are limited. Thus, we examined whether hydroxytyrosol (HT), an important polyphenolic compound found in virgin olive oil, could correct the metabolic impairments in diet-induced obesity (DIO) mice. Here, we found that HT gavage for 10 weeks significantly ameliorated glucose homeostasis and chronic inflammation and decreased hepatic steatosis in DIO mice. At the molecular level, ER stress indicators, inflammatory and insulin signaling markers demonstrated that high-fat diet (HFD)-induced ER stress and insulin resistance (IR) in insulin sensitive tissue were corrected by HT. In vitro studies confirmed that HT supplementation (100 μM) attenuated palmitate-evoked ER stress, thus rescuing the downstream JNK/IRS pathway. As a result from suppression of ER stress in the liver, HT further decreased hepatic sterol regulatory element-binding protein-1 expression (SREBP1). Additionally, aberrant expression of genes involved in hepatic lipogenesis (SREBP1, ACC, FAS, SCD1) caused by HFD was restored by HT. These findings suggested that HT ameliorated chronic inflammation and IR and decreased hepatic steatosis in obesity by beneficial modulation of ER stress.     

Cranberry extract attenuates hepatic inflammation in high-fat-fed obese mice

Cranberry (Vaccinium macrocarpon) consumption has been associated with health beneficial effects. Nonalcoholic fatty liver disease (NAFLD) is a comorbidity of obesity. In the present study, we investigated the effect of a polyphenol-rich cranberry extract (CBE) on hepatic inflammation in high fat (HF)-fed obese C57BL/6J mice. Following dietary treatment with 0.8% CBE for 10 weeks, we observed no change in body weight or visceral fat mass in CBE-supplemented mice compared to HF-fed control mice. We did observe a significant decrease in plasma alanine aminotransferase (31%) and histological severity of NAFLD (33% decrease in area of involvement, 29% decrease in lipid droplet size) compared to HF-fed controls. Hepatic protein levels of tumor necrosis factor α and C-C chemokine ligand 2 were reduced by 28% and 19%, respectively, following CBE supplementation. CBE significantly decreased hepatic mRNA levels of toll-like receptor 4 (TLR4, 63%) and nuclear factor κB (NFκB, 24%), as well as a number of genes related to the nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing 3 inflammasome. In conclusion, CBE reduced NAFLD and hepatic inflammation in HF-fed obese C57BL/6J mice. These effects appear to be related to mitigation of TLR4-NFκB related signaling; however, further studies into the underlying mechanisms of these hepatoprotective effects are needed.     

Dietary sphingomyelin attenuates hepatic steatosis and adipose tissue inflammation in high-fat-diet-induced obese mice

Western-type diets can induce obesity and related conditions such as dyslipidemia, insulin resistance and hepatic steatosis. We evaluated the effects of milk sphingomyelin (SM) and egg SM on diet-induced obesity, the development of hepatic steatosis and adipose inflammation in C57BL/6J mice fed a high-fat, cholesterol-enriched diet for 10 weeks. Mice were fed a low-fat diet (10% kcal from fat) (n=10), a high-fat diet (60% kcal from fat) (HFD, n=14) or a high-fat diet modified to contain either 0.1% (w/w) milk SM (n=14) or 0.1% (w/w) egg SM (n=14). After 10 weeks, egg SM ameliorated weight gain, hypercholesterolemia and hyperglycemia induced by HFD. Both egg SM and milk SM attenuated hepatic steatosis development, with significantly lower hepatic triglycerides (TGs) and cholesterol relative to HFD. This reduction in hepatic steatosis was stronger with egg SM supplementation relative to milk SM. Reductions in hepatic TGs observed with dietary SM were associated with lower hepatic mRNA expression of PPARγ-related genes: Scd1 and Pparg2 in both SM groups, and Cd36 and Fabp4 with egg SM. Egg SM and, to a lesser extent, milk SM reduced inflammation and markers of macrophage infiltration in adipose tissue. Egg SM also reduced skeletal muscle TG content compared to HFD. Overall, the current study provides evidence of dietary SM improving metabolic complications associated with diet-induced obesity in mice. Further research is warranted to understand the differences in bioactivity observed between egg and milk SM.     

Salvianolate ameliorates oxidative stress and podocyte injury through modulation of NOX4 activity in db/db mice

Podocyte injury is associated with albuminuria and the progression of diabetic nephropathy (DN). NADPH oxidase 4 (NOX4) is the main source of reactive oxygen species (ROS) in the kidney and NOX4 is up-regulated in podocytes in response to high glucose. In the present study, the effects of Salvianolate on DN and its underlying mechanisms were investigated in diabetic db/db mice and human podocytes. We confirmed that the Salvianolate administration exhibited similar beneficial effects as the NOX1/NOX4 inhibitor GKT137831 treated diabetic mice, as reflected by attenuated albuminuria, reduced podocyte loss and mesangial matrix accumulation. We further observed that Salvianolate attenuated the increase of Nox4 protein, NOX4-based NADPH oxidase activity and restored podocyte loss in the diabetic kidney. In human podocytes, NOX4 was predominantly localized to mitochondria and Sal B treatment blocked HG-induced mitochondrial NOX4 derived superoxide generation and thereby ameliorating podocyte apoptosis, which can be abrogated by AMPK knockdown. Therefore, our results suggest that Sal B possesses the reno-protective capabilities in part through AMPK-mediated control of NOX4 expression. Taken together, our results identify that Salvianolate could prevent glucose-induced oxidative podocyte injury through modulation of NOX4 activity in DN and have a novel therapeutic potential for DN.     

A polyphenol extract of Hibiscus sabdariffa L. ameliorates acetaminophen-induced hepatic steatosis by attenuating the mitochondrial dysfunction in vivo and in vitro

Oxidative stress is the major contributor to acetaminophen (AAP)-caused liver damage. It promotes mitochondrial oxidative stress and collapses the mitochondrial membrane potential to cause cell death. We have previously shown that a polyphenol extract of Hibiscus sabdariffa L. (HPE) potentiated the antioxidative effect. We further examined in this study the possible mechanism of HPE against AAP-caused liver damage. BABL/c mice were orally fed with HPE (100, 200 or 300 mg/kg) for two weeks prior to an i.p. injection of 1000 mg/kg of AAP. The mice were decapitated 6 h after the AAP injection to collect the blood and liver for further determination. The results show that pretreating with HPE increased the level of glutathione (GSH), decreased the level of lipid peroxidation, and increased catalase activity in the liver. A histopathological evaluation shows that HPE could decrease AAP-induced liver sterosis accompanied by a decreased expression of AIF, Bax, Bid, and p-JNK in the liver. An in vitro assay revealed that HPE could reduce AAP-induced death of BABL/c normal liver cells (BNLs), reverse the lost mitochondrial potency and improve the antioxidative status, similarly to the results of the in vivo assay. We show in this study that HPE possessed the ability to protect the liver from AAP-caused injury. The protective mechanism might be regulated by decreasing oxidative stress and attenuating the mitochondrial dysfunction.