Long-term fructose consumption prolongs hepatic stearoyl-CoA desaturase 1 activity independent of upstream regulation in rats

Spirulina (Arthrospira platensis) Improved Nonalcoholic Fatty Liver Disease Characteristics and Microbiota and Did Not Affect Organ Fibrosis Induced by a Fructose-Enriched Diet in Wistar Male Rats

Spirulina (Arthrospira platensis) is reported to play a role in improving nonalcoholic fatty liver disease (NAFLD) and intestinal microbiota (IM). To study spirulina's effects in the improvement of NAFLD characteristics, IM, and pancreatic-renal lesions induced by a fructose-enriched diet, 40 Wistar healthy male rats, weighing 200-250 g, were randomly divided into four groups of 10, and each rat per group was assigned a diet of equal quantities (20 g/day) for 18 weeks. The first control group (CT) was fed a standardized diet, the second group received a 40% fructose-enriched diet (HFr), and the third (HFr-S5) and fourth groups (HFr-S10) were assigned the same diet composition as the second group but enriched with 5% and 10% spirulina, respectively. At week 18, the HFr-S10 group maintained its level of serum triglycerides and had the lowest liver fat between the groups. At the phylae and family level, and for the same period, the HFr-S10 group had the lowest increase in the Firmicutes/Bacteroidetes ratio and the Ruminococcaceae and the highest fecal alpha diversity compared to all other groups (p < 0.05). These findings suggest that at a 10% concentration, spirulina could be used in nutritional intervention to improve IM, fatty liver, metabolic, and inflammatory parameters associated with NAFLD.

Influence of different types of sugar on overfeeding performance-part of meat quality

Previous research in our lab showed that 10% glucose, 10% fructose, and 10% sucrose can induce lipid deposition in goose fatty liver formation process more efficiently. However, whether the overfeeding diet supplement with sugar can affect the meat quality is unclear. The aim of this research was to estimate the meat quality of geese overfed with overfeeding diet adding with different types of sugar. The results indicated there were no significant differences in the diameter of muscle fiber, the muscle fiber density, pH0, pH24, the meat color, the cooking loss, the drip loss, the shear force and the dry matter in breast muscle and thigh muscle between corn flour groups and three sugars groups (P > 0.05). The crude fat content of breast muscle in fructose group was significantly higher than that in sucrose group (P < 0.05); the inosinic acid content of leg muscle in fructose group was significantly higher than that in the sucrose group (P < 0.05); the ratios of essential amino acids to total amino acids (EAA/TAA) in the breast muscle of maize flour group, fructose group, sucrose group and glucose group were 42%, 35%, 32% or 34%;57%, 64%, 64%, and 62%, respectively; the ratios of essential amino acids to total amino acids in leg muscle of maize flour group, fructose group, sucrose group and glucose group were 31%, 33%, 35%, and 34%, respectively. The contents of C16:1 and C18:1 n-9c in breast muscle in fructose group were significantly higher than that in sucrose group (P < 0.05). Compared with maize flour group, the contents of C18:0 and C20:0 were lower in leg muscle of sugar group (P < 0.05). Compared with the maize flour group, the activities of hydrogen peroxide (H2O2) and glutathione peroxidase (GSH-PX) in breast muscle were higher than those of sucrose group (P < 0.05), the total antioxidant capacity (T-AOC) levels in breast muscle was higher than that of fructose group and sucrose group (P < 0.05). Cluster analysis and principal component analysis (PCA) showed that there was no difference in meat quality between maize flour and sugar group. In conclusion, the overfeeding with maize flour supplement with 10% sugar had no evident influence on the meat quality.

Prolonged Changes in Hepatic Mitochondrial Activity and Insulin Sensitivity by High Fructose Intake in Adolescent Rats

Persistence of damage induced by unhealthy diets during youth has been little addressed. Therefore, we investigated the impact of a short-term fructose-rich diet on liver metabolic activity in adolescent rats and the putative persistence of alterations after removing fructose from the diet. Adolescent rats were fed a fructose-rich diet for three weeks and then switched to a control diet for further three weeks. Body composition and energy balance were not affected by fructose-rich diet, while increased body lipids and lipid gain were found after the rescue period. Switching to a control diet reversed the upregulation of plasma fructose, uric acid, lipocalin, and haptoglobin, while plasma triglycerides, alanine aminotransferase, lipopolysaccharide, and tumor necrosis factor alpha remained higher. Hepatic steatosis and ceramide were increased by fructose-rich diet, but reversed by returning to a control diet, while altered hepatic response to insulin persisted. Liver fatty acid synthase and stearoyl-CoA desaturase (SCD) activities were upregulated by fructose-rich diet, and SCD activity remained higher after returning to the control diet. Fructose-induced upregulation of complex II-driven mitochondrial respiration, peroxisome proliferator-activated receptor-gamma coactivator 1 alpha, and peroxisome proliferator activated receptor α also persisted after switching to control diet. In conclusion, our results show prolonged fructose-induced dysregulation of liver metabolic activity.

Cell-Type-Specific, Ketohexokinase-Dependent Induction by Fructose of Lipogenic Gene Expression in Mouse Small Intestine

BACKGROUND

High intakes of fructose are associated with metabolic diseases, including hypertriglyceridemia and intestinal tumor growth. Although small intestinal epithelia consist of many different cell types, express lipogenic genes, and convert dietary fructose to fatty acids, there is no information on the identity of the cell type(s) mediating this conversion and on the effects of fructose on lipogenic gene expression.

OBJECTIVES

We hypothesized that fructose regulates the intestinal expression of genes involved in lipid and apolipoprotein synthesis, that regulation depends on the fructose transporter solute carrier family 2 member a5 [Slc2a5 (glucose transporter 5)] and on ketohexokinase (Khk), and that regulation occurs only in enterocytes.

METHODS

We compared lipogenic gene expression among different organs from wild-type adult male C57BL mice consuming a standard vivarium nonpurified diet. We then gavaged twice daily for 2.5 d fructose or glucose solutions (15%, 0.3 mL per mouse) into wild-type, Slc2a5-knockout (KO), and Khk-KO mice with free access to the nonpurified diet and determined expression of representative lipogenic genes. Finally, from mice fed the nonpurified diet, we made organoids highly enriched in enterocyte, goblet, Paneth, or stem cells and then incubated them overnight in 10 mM fructose or glucose.

RESULTS

Most lipogenic genes were significantly expressed in the intestine relative to the kidney, liver, lung, and skeletal muscle. In vivo expression of Srebf1, Acaca, Fasn, Scd1, Dgat1, Gk, Apoa4, and Apob mRNA and of Scd1 protein increased (P < 0.05) by 3- to 20-fold in wild-type, but not in Slc2a5-KO and Khk-KO, mice gavaged with fructose. In vitro, Slc2a5- and Khk-dependent, fructose-induced increases, which ranged from 1.5- to 4-fold (P < 0.05), in mRNA concentrations of all these genes were observed only in organoids enriched in enterocytes.

CONCLUSIONS

Fructose specifically stimulates expression of mouse small intestinal genes for lipid and apolipoprotein synthesis. Secretory and stem cells seem incapable of transport- and metabolism-dependent lipogenesis, occurring only in absorptive enterocytes.

Effects of Quercetin on Expression of Genes of Carbohydrate and Lipid Metabolism Enzymes in the Liver of Rats Receiving High-Fructose Ration

We studied the expression of genes encoding enzymes of carbohydrate and lipid metabolism ketohexokinase (Khk), glucokinase (Gck), pyruvate kinase (Pklr), acetyl-Co-carboxylase (Acaca), fatty acid synthase (Fasn), stearoyl-CoA desaturase (Scd), and their transcription regulators ChREBP (Mlxipl), SREBP-1c (Srebf1), and PPARα (Ppara) in rat liver. Control group rats received a semisynthetic ration over 20 weeks. Experimental group 1 received a semisynthetic ration and 20% fructose solution instead of drinking water. Experimental group 2 rats received a semisynthetic ration with quercetin (0.1% fodder weight) and 20% fructose solution. Consumption of 20% fructose solution (experimental group 1) led to an increase in Scd expression in comparison with the control and did not affect the expression of other genes. Addition of quercetin to the ration (experimental group 2) led to a decrease in the expression of Khk, Gck, Fasn, Scd, Mlxipl, and Ppara genes in comparison with experimental group 1. The results suggest that quercetin reduced the expression of genes of carbohydrate and lipid metabolism enzymes in the liver of rats receiving high-fructose ration.

Thiazolidinedione induces a therapeutic effect on hepatosteatosis by regulating stearoyl-CoA desaturase-1, lipase activity, leptin and resistin

Hepatosteatosis is a disease present worldwide, which presents a number of health problems. Recently, thiazolidinedione (TZD) has been used as a therapy for lipid disorders. The present study demonstrates the potential of TZD as a treatment for hepatosteatosis and its mechanism of action, particularly focusing on its role in lipid metabolism. A total of 60 (80-90 g) rats were divided into three groups: A normal group with a standard diet, a high-fat, high-carbohydrate diet (HFCD) group or a HFCD+TZD group (n=20/group). The HFCD induced hepatosteatosis over a period of 12 weeks and the HFCD+TZD group were administered TZD in weeks 13-16. Blood and tissue samples were collected to measure hepatic function, the lipid profile, metabolism and hormone biomarkers, including serum triglyceride (TG), lipoprotein lipase (LPL), stearoyl-CoA desaturase (SCD-1), leptin and resistin. The HFCD-fed rats exhibited a significant increase in serum TG, total cholesterol, low-density lipoproteins, alanine transaminase and bilirubin compared with the normal group as well as a significant decrease in high-density lipoprotein. In addition, serum leptin and resistin were significantly elevated in the HFCD group compared with the normal group. The administration of TZD significantly increased SCD-1 activity and significantly inhibited LPL activity. It also attenuated the changes in the lipid profiles and normalized serum leptin and resistin levels. The results of the present study indicated that HFCD induced lipid abnormalities associated with hypertriglyceridemia, hypercholesterolemia and hepatosteatosis. These changes resulted from disruption to leptin and resistin, which may be due to alterations in LPL and SCD-1 activity. TZD mitigated the effects of HFCD-induced hepatosteatosis, indicating a possible regulatory effect of TZD in the development of hepatosteatosis. The authors suggest that the manipulation of SCD-1 and lipase by TZD may be useful as a treatment for hepatosteatosis.

miR-192-5p regulates lipid synthesis in non-alcoholic fatty liver disease through SCD-1

AIM

To evaluate the levels of miR-192-5p in non-alcoholic fatty liver disease (NAFLD) models and demonstrate the role of miR-192-5p in lipid accumulation.

METHODS

Thirty Sprague Dawley rats were randomly divided into three groups, which were given a standard diet, a high-fat diet (HFD), and an HFD with injection of liraglutide. At the end of 16 weeks, hepatic miR-192-5p and stearoyl-CoA desaturase 1 (SCD-1) levels were measured. MiR-192-5p mimic and inhibitor and SCD-1 siRNA were transfected into Huh7 cells exposed to palmitic acid (PA). Lipid accumulation was evaluated by oil red O staining and triglyceride assays. Direct interaction was validated by dual-luciferase reporter gene assays.

RESULTS

The HFD rats showed a 0.46-fold decrease and a 3.5-fold increase in hepatic miR-192-5p and SCD-1 protein levels compared with controls, respectively, which could be reversed after disease remission by liraglutide injection (P < 0.01). The Huh7 cells exposed to PA also showed down-regulation and up-regulation of miR-192-5p and SCD-1 protein levels, respectively (P < 0.01). Transfection with miR-192-5p mimic and inhibitor in Huh7 cells induced dramatic repression and promotion of SCD-1 protein levels, respectively (P < 0.01). Luciferase activity was suppressed and enhanced by miR-192-5p mimic and inhibitor, respectively, in wild-type SCD-1 (P < 0.01) but not in mutant SCD-1. MiR-192-5p overexpression reduced lipid accumulation significantly in PA-treated Huh7 cells, and SCD-1 siRNA transfection abrogated the lipid deposition aggravated by miR-192-5p inhibitor (P < 0.01).

CONCLUSION

This study demonstrates that miR-192-5p has a negative regulatory role in lipid synthesis, which is mediated through its direct regulation of SCD-1.

Chronic consumption of fructose in combination with trans fatty acids but not with saturated fatty acids induces nonalcoholic steatohepatitis with fibrosis in rats

PURPOSE

Consumption of Western diet high in fat and fructose has been attributed to the recent epidemic of nonalcoholic fatty liver disease (NAFLD). However, the impact of specific fatty acids on the progression of NAFLD to nonalcoholic steatohepatitis (NASH) is poorly understood. In the present study, we investigated the chronic effects of consumption of fructose in combination with saturated fatty acids (SFA) or trans fatty acids (TFA) on the development of NAFLD.

METHODS

Male Sprague-Dawley rats were randomly assigned to six isocaloric starch/high fructose (44% of calories), high fat (39% calories) diet containing either starch-peanut oil, fructose-peanut oil, fructose-palmolein, fructose-clarified butter, fructose-coconut oil or fructose-partially hydrogenated vegetable oil and fed for 24 weeks. Palmolein, clarified butter and coconut oil were used as the source of SFA whereas partially hydrogenated vegetable oil was used as the source of TFA. Peanut oil was used as the reference oil.

RESULTS

Long-term feeding of fructose in combination with SFA or TFA induced hepatic steatosis of similar extent associated with upregulation of stearoyl CoA desaturase-1. In contrast, fructose in combination with TFA induced NASH with fibrosis as evidenced by upregulation of hepatic proinflammatory cytokine and fibrogenic gene expression, increased hepatic oxidative stress and adipocytokine imbalance. Histopathological analysis revealed the presence of NASH with fibrosis. Further, peanut oil prevented the development of NAFLD in fructose-fed rats.

CONCLUSION

Fructose in combination with TFA caused NASH with fibrosis by inducing oxidative stress and inflammation, whereas, fructose in combination with SFA caused simple steatosis, suggesting that the type of fatty acid is more important for the progression of NAFLD.

Response of genes involved in lipid metabolism in rat epididymal white adipose tissue to different fasting conditions after long-term fructose consumption

There has been much concern regarding the dietary fructose contributes to the development of metabolic syndrome. High-fructose diet changes the expression of genes involved in lipid metabolism. Levels of a number of hepatic lipogenic enzymes are increased by a high-carbohydrate diet in fasted-refed model rats/mice. Both the white adipose tissue (WAT) and the liver play a key role in the maintenance of nutrient homeostasis. Here, the aim of this study was to analyze the expression of key genes related to lipid metabolism in epididymal WAT (eWAT) in response to different fasting condition after long-term chronic fructose consumption. Rats were fed standard chow supplemented with 10% w/v fructose solution for 5 weeks, and killed after chow-fasting and fructose withdrawal (fasting) or chow-fasting and continued fructose (fructose alone) for 14 h. Blood parameters and the expression of genes involved in fatty acid synthesis (ChREBP, SREBP-1c, FAS, SCD1), triglyceride biosynthesis (DGAT-1, DGAT-2) and lipid mobilization (ATGL, HSL) in eWAT were analyzed. In addition, mRNA levels of PPAR-γ, CD36 and LPL were also detected. As expected, fructose alone increased the mRNA expression of FAS, SCD1, and correspondingly decreased ATGL and HSL mRNA levels. However, ChREBP, DGAT-2, ATGL and HSL mRNA levels restored near to normal while FAS and SCD1 tend to basic level under fasting condition. The mRNA expression of SREBP-1c, PPAR-γ and LPL did not changed at any situations but CD36 mRNA decreased remarkably in fructose alone group. In conclusion, these findings demonstrate that genes involved in lipid metabolism in rat eWAT are varied in response to different fasting conditions after long-term fructose consumption.