Muscle lipid metabolism and insulin secretion are altered in insulin-resistant rats fed a high sucrose diet

Salvia hispanica L. (chia) seed improves redox state and reverts extracellular matrix collagen deposition in skeletal muscle of sucrose-rich diet-fed rats

Skeletal muscle (SkM) is a plastic and dynamic tissue, essential in energy metabolism. Growing evidence suggests a close relationship between intramuscular fat accumulation, oxidative stress (OS), extracellular matrix (ECM) remodeling, and metabolic deregulation in SkM. Nowadays natural products emerge as promising alternatives for the treatment of metabolic disorders. We have previously shown that chia seed administration reverts SkM lipotoxicity and whole-body insulin resistant (IR) in sucrose-rich diet (SRD) fed rats. The purpose of the present study was to assess the involvement of OS and fibrosis in SkM metabolic impairment of insulin-resistant rats fed a long-term SRD and the effects of chia seed upon these mechanisms as therapeutic strategy. Results showed that insulin-resistant SRD-fed rats exhibited sarcopenia, increase in lipid peroxidation, altered redox state, and ECM remodeling-increased collagen deposition and lower activity of the metalloproteinase 2 (MMP-2) in SkM. Chia seed increased ferric ion reducing antioxidant power and glutathione reduced form levels, and the activities of glutathione peroxidase and glutathione reductase enzymes. Moreover, chia seed reversed fibrosis and restored the MMP-2 activity. This work reveals a participation of the OS and ECM remodeling in the metabolic alterations of SkM in our experimental model. Moreover, current data show novel properties of chia seed with the potential to attenuate SkM OS and fibrosis, hallmark of insulin-resistant muscle.

Differential effects of fish-oil and cocoa-butter based high-fat/high-sucrose diets on endocrine pancreas morphology and function in mice

Introduction

A high-fat/high-sucrose diet leads to adverse metabolic changes that affect insulin sensitivity, function, and secretion. The source of fat in the diet might inhibit or increase this adverse effect. Fish oil and cocoa butter are a significant part of our diets. Yet comparisons of these commonly used fat sources with high sucrose on pancreas morphology and function are not made. This study investigated the comparative effects of a fish oil-based high-fat/high-sucrose diet (Fish-HFDS) versus a cocoa butter-based high-fat/high-sucrose diet (Cocoa-HFDS) on endocrine pancreas morphology and function in mice.

Methods

C57BL/6 male mice (n=12) were randomly assigned to dietary intervention either Fish-HFDS (n=6) or Cocoa-HFDS (n=6) for 22 weeks. Intraperitoneal glucose and insulin tolerance tests (IP-GTT and IP-ITT) were performed after 20-21 weeks of dietary intervention. Plasma concentrations of c-peptide, insulin, glucagon, GLP-1, and leptin were measured by Milliplex kit. Pancreatic tissues were collected for immunohistochemistry to measure islet number and composition. Tissues were multi-labelled with antibodies against insulin and glucagon, also including expression on Pdx1-positive cells.

Results and discussion

Fish-HFDS-fed mice showed significantly reduced food intake and body weight gain compared to Cocoa-HFDS-fed mice. Fish-HFDS group had lower fasting blood glucose concentration and area under the curve (AUC) for both GTT and ITT. Plasma c-peptide, insulin, glucagon, and GLP-1 concentrations were increased in the Fish-HFDS group. Interestingly, mice fed the Fish-HFDS diet displayed higher plasma leptin concentration. Histochemical analysis revealed a significant increase in endocrine pancreas β-cells and islet numbers in mice fed Fish-HFDS compared to the Cocoa-HFDS group. Taken together, these findings suggest that in a high-fat/high-sucrose dietary setting, the source of the fat, especially fish oil, can ameliorate the effect of sucrose on glucose homeostasis and endocrine pancreas morphology and function.

Thermostability improvement of sucrose isomerase PalI NX-5: a comprehensive strategy

OBJECTIVE

To increase the thermal stability of sucrose isomerase from Erwinia rhapontici NX-5, we designed a comprehensive strategy that combines different thermostabilizing elements.

RESULTS

We identified 19 high B value amino acid residues for site-directed mutagenesis. An in silico evaluation of the influence of post-translational modifications on the thermostability was also carried out. The sucrose isomerase variants were expressed in Pichia pastoris X33. Thus, for the first time, we report the expression and characterization of glycosylated sucrose isomerases. The designed mutants K174Q, L202E and K174Q/L202E, showed an increase in their optimal temperature of 5 °C, while their half-lives increased 2.21, 1.73 and 2.89 times, respectively. The mutants showed an increase in activity of 20.3% up to 25.3%. The Km values for the K174Q, L202E, and K174Q/L202E mutants decreased by 5.1%, 7.9%, and 9.4%, respectively; furthermore, the catalytic efficiency increased by up to 16%.

CONCLUSIONS

With the comprehensive strategy followed, we successfully obtain engineered mutants more suitable for industrial applications than their counterparts: native (this research) and wild-type from E. rhapontici NX-5, without compromising the catalytic activity of the molecule.

It's What and When You Eat: An Overview of Transcriptional and Epigenetic Responses to Dietary Perturbations in Pancreatic Islets

Our ever-changing modern environment is a significant contributor to the increased prevalence of many chronic diseases, and particularly, type 2 diabetes mellitus (T2DM). Although the modern era has ushered in numerous changes to our daily living conditions, changes in "what" and "when" we eat appear to disproportionately fuel the rise of T2DM. The pancreatic islet is a key biological controller of an organism's glucose homeostasis and thus plays an outsized role to coordinate the response to environmental factors to preserve euglycemia through a delicate balance of endocrine outputs. Both successful and failed adaptation to dynamic environmental stimuli has been postulated to occur due to changes in the transcriptional and epigenetic regulation of pathways associated with islet secretory function and survival. Therefore, in this review we examined and evaluated the current evidence elucidating the key epigenetic mechanisms and transcriptional programs underlying the islet's coordinated response to the interaction between the timing and the composition of dietary nutrients common to modern lifestyles. With the explosion of next generation sequencing, along with the development of novel informatic and -omic approaches, future work will continue to unravel the environmental-epigenetic relationship in islet biology with the goal of identifying transcriptional and epigenetic targets associated with islet perturbations in T2DM.

Investigation of d-allulose effects on high-sucrose diet-induced insulin resistance via hyperinsulinemic-euglycemic clamps in rats

d-Allulose, a C-3 epimer of d-fructose, is a rare sugar that has no calories. Although d-allulose has been reported to have several health benefits, such as anti-obesity and anti-diabetic effects, there have been no reports evaluating the effects of d-allulose on insulin resistance using a hyperinsulinemic-euglycemic clamp (HE-clamp). Therefore, we investigated the effects of d-allulose on a high-sucrose diet (HSD)-induced insulin resistance model. Wistar rats were randomly divided into three dietary groups: HSD containing 5% cellulose (HSC), 5% d-allulose (HSA), and a commercial diet. The insulin tolerance test (ITT) and HE-clamp were performed after administration of the diets for 4 and 7 weeks. After 7 weeks, the muscle and adipose tissues of rats were obtained to analyze Akt signaling via western blotting, and plasma adipocytokine levels were measured. ITT revealed that d-allulose ameliorated systemic insulin resistance. Furthermore, the results of the 2-step HE-clamp procedure indicated that d-allulose reversed systemic and muscular insulin resistance. d-Allulose reversed the insulin-induced suppression of Akt phosphorylation in the soleus muscle and epididymal fat tissues and reduced plasma TNF-α levels. This study is the first to show that d-allulose improves systemic and muscle insulin sensitivity in conscious rats.

Nutritional Models of Type 2 Diabetes Mellitus

In order to better understand the events that precede and precipitate the onset of type 2 diabetes (T2DM), several nutritional animal models have been developed. These models are generated by manipulating the diet of either the animal itself, or its mother during her pregnancy, and in comparison to traditional genetic and knock out models, have the advantage that they more accurately reflect the etiology of human T2DM. This chapter will discuss some of the most widely used nutritional models of T2DM: Diet-induced obesity (DIO) in adult rodents, and studies of offspring of mothers fed a low-protein, high-fat and/or high-sugar diet during pregnancy and/or lactation. Several common mechanisms have been identified through which these nutritional manipulations can lead to metabolic disease, including pancreatic beta-cell dysfunction, impaired insulin signaling in skeletal muscle, and the excess accumulation of visceral adipose tissue and consequent deposition of nonesterified fatty acids in peripheral tissues. In addition, there is an emerging concept that obesity/poor quality diets result in increased production and release of pro-inflammatory cytokines from adipose tissue leading to a state of chronic low-grade inflammation, and that this is likely to represent an important link between obesity/diet and metabolic dysfunction. The following chapter will discuss the most common nutritional models of T2DM in experimental animals, their application, and relationship to human etiology, and will highlight the important insights these models have provided into the pathogenesis of T2DM.

Stressing the importance of choice: Validity of a preclinical free-choice high-caloric diet paradigm to model behavioural, physiological and molecular adaptations during human diet-induced obesity and metabolic dysfunction

Humans have engineered a dietary environment that has driven the global prevalence of obesity and several other chronic metabolic diseases to pandemic levels. To prevent or treat obesity and associated comorbidities, it is crucial that we understand how our dietary environment, especially in combination with a sedentary lifestyle and/or daily-life stress, can dysregulate energy balance and promote the development of an obese state. Substantial mechanistic insight into the maladaptive adaptations underlying caloric overconsumption and excessive weight gain has been gained by analysing brains from rodents that were eating prefabricated nutritionally-complete pellets of high-fat diet (HFD). Although long-term consumption of HFDs induces chronic metabolic diseases, including obesity, they do not model several important characteristics of the modern-day human diet. For example, prefabricated HFDs ignore the (effects of) caloric consumption from a fluid source, do not appear to model the complex interplay in humans between stress and preference for palatable foods, and, importantly, lack any aspect of choice. Therefore, our laboratory uses an obesogenic free-choice high-fat high-sucrose (fc-HFHS) diet paradigm that provides rodents with the opportunity to choose from several diet components, varying in palatability, fluidity, texture, form and nutritive content. Here, we review recent advances in our understanding how the fc-HFHS diet disrupts peripheral metabolic processes and produces adaptations in brain circuitries that govern homeostatic and hedonic components of energy balance. Current insight suggests that the fc-HFHS diet has good construct and face validity to model human diet-induced chronic metabolic diseases, including obesity, because it combines the effects of food palatability and energy density with the stimulating effects of variety and choice. We also highlight how behavioural, physiological and molecular adaptations might differ from those induced by prefabricated HFDs that lack an element of choice. Finally, the advantages and disadvantages of using the fc-HFHS diet for preclinical studies are discussed.

Dietary fish oil ameliorates adipose tissue dysfunction in insulin-resistant rats fed a sucrose-rich diet improving oxidative stress, peroxisome proliferator-activated receptor γ and uncoupling protein 2

This work aims to assess the possible beneficial effects of dietary fish oil (FO) on the pre-existing adipose tissue dysfunction through the improvement or reversion of the mechanisms underlying oxidative stress and pro-inflammatory cytokines in dyslipemic insulin-resistant rats. Wistar rats were fed a sucrose rich diet (SRD) for 6 months. After that half of the animals continued with the SRD until month 8 while in the other half corn oil was replaced by FO for 2 months (SRD + FO). A reference group consumed a control diet all the time. In an epididymal fat pad, we analyzed antioxidant and oxidant enzyme activities, ROS content, glutathione redox state, the protein level of peroxisome proliferator-activated receptor gamma (PPARγ) and the expression and protein levels of uncoupling protein 2 (UCP2) as well as oxidative stress biomarkers and TNF-α and IL-6 plasma levels. Besides these, insulin sensitivity and the composition of fatty acid phospholipids of adipose tissue were measured. Compared with the SRD the SRD + FO fed group showed a decrease of fat pad weight and the antioxidant and oxidant enzyme activities and ROS content returned to control values along with normal plasma TNF-α and IL-6 levels. FO normalized both the decrease of PPARγ protein and the increase of protein and expression of UCP2. Furthermore, FO increased the n-3/n-6 fatty acid ratio in the adipose tissue phospholipids and normalized dyslipidemia and insulin resistance. Finally, these findings reinforce the view that dietary FO may exert a beneficial effect in ameliorating the dyslipidemia and insulin resistance in this animal model.

High Fat With High Sucrose Diet Leads to Obesity and Induces Myodegeneration

Skeletal muscle utilizes both free fatty acids (FFAs) and glucose that circulate in the blood stream. When blood glucose levels acutely increase, insulin stimulates muscle glucose uptake, oxidation, and glycogen synthesis. Under these conditions, skeletal muscle preferentially oxidizes glucose while the oxidation of fatty acids (FAs) oxidation is reciprocally decreased. In metabolic disorders associated with insulin resistance, such as diabetes and obesity, both glucose uptake, and utilization muscle are significantly reduced causing FA oxidation to provide the majority of ATP for metabolic processes and contraction. Although the causes of this metabolic inflexibility or disrupted "glucose-fatty acid cycle" are largely unknown, a diet high in fat and sugar (HFS) may be a contributing factor. This metabolic inflexibility observed in models of obesity or with HFS feeding is detrimental because high rates of FA oxidation in skeletal muscle can lead to the buildup of toxic metabolites of fat metabolism and the accumulation of pro-inflammatory cytokines, which further exacerbate the insulin resistance. Further, HFS leads to skeletal muscle atrophy with a decrease in myofibrillar proteins and phenotypically characterized by loss of muscle mass and strength. Overactivation of ubiquitin proteasome pathway, oxidative stress, myonuclear apoptosis, and mitochondrial dysfunction are some of the mechanisms involved in muscle atrophy induced by obesity or in mice fed with HFS. In this review, we will discuss how HFS diet negatively impacts the various physiological and metabolic mechanisms in skeletal muscle.

Impaired endocrine-metabolic homeostasis: underlying mechanism of its induction by unbalanced diet

To characterize the intrinsic mechanism by which sucrose induces β-cell dysfunction. Normal rats received for 3 weeks a standard diet supplemented with 10% sucrose in the drinking water (high sucrose (HS)) with/out an antioxidant agent (R/S α-lipoic acid). We measured plasma glucose, insulin, triglyceride, leptin, and lipid peroxidation levels; homeostasis model assessment (HOMA)-insulin resistance (HOMA-IR) and HOMA for β-cell function (HOMA-β) indexes were also determined. Insulin secretion, β-cell apoptosis, intracellular insulin and leptin mediators, and oxidative stress (OS) markers were also measured in islets isolated from each experimental group. HS rats had increased plasma triglyceride, insulin, leptin, and lipid peroxidation (OS marker) levels associated with an insulin-resistant state. Their islets developed an initial compensatory increase in glucose-induced insulin secretion and mRNA and protein levels of β-cell apoptotic markers. They also showed a significant decrease in mRNA and protein levels of insulin and leptin signaling pathway mediators. Uncoupling protein 2 (UCP2), peroxisome proliferator-activated receptor (PPAR)-α and -δ mRNA and protein levels were increased whereas mRNA levels of Sirtuin-1 (Sirt-1), glutathione peroxidase, and catalase were significantly lower in these animals. Development of all these endocrine-metabolic abnormalities was prevented by co-administration of R/S α-lipoic acid together with sucrose. OS may be actively involved in the mechanism by which unbalanced/unhealthy diet induces β-cell dysfunction. Since metabolic-endocrine dysfunctions recorded in HS rats resembled those measured in human pre-diabetes, knowledge of its molecular mechanism could help to develop appropriate strategies to prevent the progression of this metabolic state toward type 2 diabetes (T2D).

Dietary soy protein improves adipose tissue dysfunction by modulating parameters related with oxidative stress in dyslipidemic insulin-resistant rats

The present study investigates the benefits of the dietary intake of soy protein on adipose tissue dysfunction in a rat model that mimics several aspects of the human metabolic syndrome. Wistar rats were fed a sucrose-rich diet (SRD) for 4 months. After that, half of the animals continued with SRD until month 8 while in the other half, casein protein was replaced by isolated soy protein for 4 months (SRD-S). A reference group consumed a control diet all the time. In adipose tissue we determined: i) the activities of antioxidant enzymes, gene expression of Mn-superoxide dismutase (SOD) and glutathione peroxidase (GPx), and glutathione redox state ii) the activity of xanthine oxidase (XO), ROS levels and the gene expression of NAD(P)H oxidase iii) the expression of the nuclear factor erythroid-2 related factor-2 (Nrf2). Besides, adiposity visceral index, insulin sensitivity, and tumor necrosis factor-α (TNF-α) in plasma were determined. Compared with the SRD-fed rats, the animals fed a SRD-S showed: activity normalization of SOD and glutathione reductase, improvement of mRNA SOD and normalization of mRNA GPx without changes in the expression of the Nrf2, and improvement of glutathione redox state. These results were accompanied by a normalization of XO activity and improvement of both the ROS production as well as TNF-α levels in plasma. Besides, adipocyte size distribution, adiposity visceral index and insulin sensitivity improved. The results suggest that soy protein can be a complementary nutrient for treating some signs of the metabolic syndrome.

A High-Fat High-Sucrose Diet Rapidly Alters Muscle Integrity, Inflammation and Gut Microbiota in Male Rats

The chronic low-level inflammation associated with obesity is known to deleteriously affect muscle composition. However, the manner in which obesity leads to muscle loss has not been explored in detail or in an integrated manner following a short-term metabolic challenge. In this paper, we evaluated the relationships between compromised muscle integrity, diet, systemic inflammatory mediators, adipose tissue, and gut microbiota in male Sprague-Dawley rats. We show that intramuscular fat, fibrosis, and the number of pro-inflammatory cells increased by 3-days and was sustained across 28-days of high-fat high-sugar feeding compared to control-diet animals. To understand systemic contributors to muscle damage, dynamic changes in gut microbiota and serum inflammatory markers were evaluated. Data from this study links metabolic challenge to persistent compromise in muscle integrity after just 3-days, a finding associated with altered gut microbiota and systemic inflammatory changes. These data contribute to our understanding of early consequences of metabolic challenge on multiple host systems, which are important to understand as obesity treatment options are developed. Therefore, intervention within this early period of metabolic challenge may be critical to mitigate these sustained alterations in muscle integrity.

Effects of post-suckling n-3 polyunsaturated fatty acids: prevention of dyslipidemia and liver steatosis induced in rats by a sucrose-rich diet during pre- and post-natal life

The interaction between fetal programming and the post-natal environment suggests that the post-natal diet could amplify or attenuate programmed outcomes. We investigated whether dietary n-3 long-chain polyunsaturated fatty acids (n-3 PUFAs) at weaning resulted in an amelioration of dyslipidemia, adiposity and liver steatosis that was induced by a sucrose-rich diet (SRD; where the fat source is corn oil) from the onset of pregnancy up to adulthood. During pregnancy and lactation, dams were fed an SRD or the standard powdered rodent commercial diet (RD). At weaning and until 150 days of life, male offspring from SRD-dams were divided into two groups and fed an SRD or SRD-with-fish oil [where 6% of the corn oil was partially replaced by fish oil (FO) 5% and corn oil (CO) 1%], forming SRD-SRD or SRD-FO groups. Male offspring from RD-dams continued with RD up to the end of the experimental period, forming an RD-RD group. The presence of FO in the weaning diet showed the following: prevention of hypertriglyceridemia and liver steatosis, together with increased lipogenic enzyme activity caused by a maternal SRD; the complete normalization of CPT I activity and PPARα protein mass levels; a slight but not statistically significant accretion of visceral adiposity; and limited body fat content and reduced plasma free fatty acid levels. All of these results were observed even in the presence of a high-sucrose diet challenge after weaning. SRD-dams' breast milk showed a more saturated fatty acid composition. These results suggest the capacity of n-3 PUFAs to overcome some adverse outcomes induced by a maternal and post-weaning sucrose-rich diet.

Dose-related antihyperglycemic and hypolipidemic effects of two novel thiazolidin-4-ones in a rodent model of metabolic syndrome

BACKGROUND

The replacement of the thiazolidinedione moiety with a thiazolidinone may yield antidiabetic compounds with similar pleiotropic effects. Hence, the aim of the present study was to explore the dose-related antihyperglycemic and hypolipidemic effects of two synthesized novel thiazolidin-4-one derivatives, one with a nicotinamide and the other with a p-chlorophenoxyacetamide substitution at the N3 position of the thiazolidinone ring (NAT1 and PAT1, respectively), in a rodent model of metabolic syndrome (MetS).

METHODS

Metabolic syndrome was induced in Wistar rats by neonatal administration of monosodium glutamate (i.p.) on 4 consecutive days followed by high-sucrose diet feeding for 6 months. The effects of NAT1 (33 and 66 mg/kg) and molar equivalent doses of PAT1 (40 and 80 mg/kg) on relevant biochemical parameters were evaluated. Because MetS is a state of chronic low-grade inflammation, we also evaluated the effects of these compounds on proinflammatory markers, namely interleukin (IL)-6, tumor necrosis factor (TNF)-α, reactive oxygen species (ROS), and nitric oxide (NO).

RESULTS

Both NAT1 and PAT1 attenuated hyperglycemia, hypertriglyceridemia, hypoalphalipoproteinemia, and glucose intolerance. PAT1 exhibited superior antihyperglycemic and antihypoalphalipoproteinemic effects than NAT1. However, NAT1 had a better triglyceride-lowering effect. At the lower dose tested, both compounds significantly reduced elevated malondialdehyde levels. In addition, PAT1 (80 mg/kg) restored hepatic superoxide dismutase enzyme levels. There was a tendency for NAT1 and PAT1 to inhibit elevated hepatic IL-6 and TNF-α levels, but the differences did not reach statistical significance. In addition, PAT1 exhibited in vitro anti-inflammatory activity by reducing proinflammatory ROS and NO levels in RAW264.7 macrophages.

CONCLUSIONS

The novel thiazolidin-4-ones NAT1 and PAT1 could be potential pleiotropic drug candidates targeting MetS.

The combined action of omega-3 polyunsaturated fatty acids and grape proanthocyanidins on a rat model of diet-induced metabolic alterations

It has been suggested that food components such as ω-3 polyunsaturated fatty acids (ω-3 PUFAs) and (poly)phenols counteract diet-induced metabolic alterations by common or complementary mechanisms. To examine the effects of a combination of ω-3 PUFAs and (poly)phenols on such alterations, adult Wistar-Kyoto rats were fed an obesogenic high-fat high-sucrose diet supplemented, or not, for 24 weeks with: eicosapentaenoic acid (EPA)/docosahexaenoic acid (DHA) 1 : 1 (16.6 g kg(-1) feed); proanthocyanidin-rich grape seed extract (GSE, 0.8 g kg(-1) feed); or EPA/DHA 1 : 1 + GSE. Body weight, feed intake, and plasma glucose were evaluated every 6 weeks, while adipose tissue weight, insulin, glucagon, ghrelin, leptin, adiponectin, cholesterol, and triglycerides were evaluated at the end of the experiment. ω-3 PUFAs reduced plasma leptin and cholesterol levels, but did not modify diet-induced perigonadal fat or plasma insulin levels; while GSE increased plasma triglyceride levels. The combined action of ω-3 PUFAs and the proanthocyanidins reduced plasma insulin and leptin, as well as partially prevented perigonadal fat accumulation. While separate supplementation with ω-3 PUFAs or grape proanthocyanidins may not counteract all the key metabolic changes induced by a high-energy-dense diet, the combination of both supplements reverts altered insulin, leptin and triglyceride levels to normal.

Mechanisms Involved in the Improvement of Lipotoxicity and Impaired Lipid Metabolism by Dietary α-Linolenic Acid Rich Salvia hispanica L (Salba) Seed in the Heart of Dyslipemic Insulin-Resistant Rats

This study explores the mechanisms underlying the altered lipid metabolism in the heart of dyslipemic insulin-resistant (IR) rats fed a sucrose-rich diet (SRD) and investigates if chia seeds (rich in α-linolenic acid 18:3, n-3 ALA) improve/reverse cardiac lipotoxicity. Wistar rats received an SRD-diet for three months. Half of the animals continued with the SRD up to month 6. The other half was fed an SRD in which the fat source, corn oil (CO), was replaced by chia seeds from month 3 to 6 (SRD+chia). A reference group consumed a control diet (CD) all the time. Triglyceride, long-chain acyl CoA (LC ACoA) and diacylglycerol (DAG) contents, pyruvate dehydrogenase complex (PDHc) and muscle-type carnitine palmitoyltransferase 1 (M-CPT1) activities and protein mass levels of M-CPT1, membrane fatty acid transporter (FAT/CD36), peroxisome proliferator activated receptor α (PPARα) and uncoupling protein 2 (UCP2) were analyzed. Results show that: (a) the hearts of SRD-fed rats display lipotoxicity suggesting impaired myocardial lipid utilization; (b) Compared with the SRD group, dietary chia normalizes blood pressure; reverses/improves heart lipotoxicity, glucose oxidation, the increased protein mass level of FAT/CD36, and the impaired insulin stimulated FAT/CD36 translocation to the plasma membrane. The enhanced M-CPT1 activity is markedly reduced without similar changes in protein mass. PPARα slightly decreases, while the UCP2 protein level remains unchanged in all groups. Normalization of dyslipidemia and IR by chia reduces plasma fatty acids (FAs) availability, suggesting that a different milieu prevents the robust translocation of FAT/CD36. This could reduce the influx of FAs, decreasing the elevated M-CPT1 activity and lipid storage and improving glucose oxidation in cardiac muscles of SRD-fed rats.

Time course of adipose tissue dysfunction associated with antioxidant defense, inflammatory cytokines and oxidative stress in dyslipemic insulin resistant rats

Time course of adipose tissue dysfunction in dyslipemic insulin resistant rats.

Approach to assessing determinants of glucose homeostasis in the conscious mouse

Obesity and type 2 diabetes lessen the quality of life of those afflicted and place considerable burden on the healthcare system. Furthermore, the detrimental impact of these pathologies is expected to persist or even worsen. Diabetes is characterized by impaired insulin action and glucose homeostasis. This has led to a rapid increase in the number of mouse models of metabolic disease being used in the basic sciences to assist in facilitating a greater understanding of the metabolic dysregulation associated with obesity and diabetes, the identification of therapeutic targets, and the discovery of effective treatments. This review briefly describes the most frequently utilized models of metabolic disease. A presentation of standard methods and technologies on the horizon for assessing metabolic phenotypes in mice, with particular emphasis on glucose handling and energy balance, is provided. The article also addresses issues related to study design, selection and execution of metabolic tests of glucose metabolism, the presentation of data, and interpretation of results.

Ingestion of a moderate high-sucrose diet results in glucose intolerance with reduced liver glucokinase activity and impaired glucagon-like peptide-1 secretion

Aims/Introduction:  Excessive intake of sucrose can cause severe health issues, such as diabetes mellitus. In animal studies, consumption of a high‐sucrose diet (SUC) has been shown to cause obesity, insulin resistance and glucose intolerance. However, several in vivo experiments have been carried out using diets with much higher sucrose contents (50–70% of the total calories) than are typically ingested by humans. In the present study, we examined the effects of a moderate SUC on glucose metabolism and the underlying mechanism.

Materials and Methods:  C57BL/6J mice received a SUC (38.5% sucrose), a high‐starch diet (ST) or a control diet for 5 weeks. We assessed glucose tolerance, incretin secretion and liver glucose metabolism.

Results:  An oral glucose tolerance test (OGTT) showed that plasma glucose levels in the early phase were significantly higher in SUC‐fed mice than in ST‐fed or control mice, with no change in plasma insulin levels at any stage. SUC‐fed mice showed a significant improvement in insulin sensitivity. Glucagon‐like peptide‐1 (GLP‐1) secretion 15 min after oral glucose administration was significantly lower in SUC‐fed mice than in ST‐fed or control mice. Hepatic glucokinase (GCK) activity was significantly reduced in SUC‐fed mice. During the OGTT, the accumulation of glycogen in the liver was suppressed in SUC‐fed mice in a time‐dependent manner.

Conclusions:  These results indicate that mice that consume a moderate SUC show glucose intolerance with a reduction in hepatic GCK activity and impairment in GLP‐1 secretion. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2012.00208.x, 2012)

Cognitive and behavioural effects of sugar consumption in rodents. A review

The pronounced global rise in sugar consumption in recent years has been driven largely by increased consumption of sugar-sweetened beverages. Although high sugar intakes are recognised to increase the risk of obesity and related metabolic disturbances, less is known about how sugar might also impair cognition and learned behaviour. This review considers the effects of sugar in rodents on measures of learning and memory, reward processing, anxiety and mood. The parallels between sugar consumption and addictive behaviours are also discussed. The available evidence clearly indicates that sugar consumption can induce cognitive dysfunction. Deficits have been found most consistently on tasks measuring spatial learning and memory. Younger animals appear to be particularly sensitive to the effects of sugar on reward processing, yet results vary according to what reward-related behaviour is assessed. Sugar does not appear to produce long-term effects on anxiety or mood. Importantly, cognitive impairments have been found when intake approximates levels of sugar consumption in people and without changes to weight gain. There remain several caveats when extrapolating from animal models to putative effects of sugar on cognitive function in people. These issues are discussed in conjunction with potential underlying neural mechanisms and directions for future research.

Dietary Salba (Salvia hispanica L) seed rich in α-linolenic acid improves adipose tissue dysfunction and the altered skeletal muscle glucose and lipid metabolism in dyslipidemic insulin-resistant rats

This work reports the effect of dietary Salba (chia) seed rich in n-3 α-linolenic acid on the morphological and metabolic aspects involved in adipose tissue dysfunction and the mechanisms underlying the impaired glucose and lipid metabolism in the skeletal muscle of rats fed a sucrose-rich diet (SRD). Rats were fed a SRD for 3 months. Thereafter, half the rats continued with SRD while in the other half, corn oil (CO) was replaced by chia seed for 3 months (SRD+chia). In control group, corn starch replaced sucrose. The replacement of CO by chia seed in the SRD reduced adipocyte hypertrophy, cell volume and size distribution, improved lipogenic enzyme activities, lipolysis and the anti-lipolytic action of insulin. In the skeletal muscle lipid storage, glucose phosphorylation and oxidation were normalized. Chia seed reversed the impaired insulin stimulated glycogen synthase activity, glycogen, glucose-6-phosphate and GLUT-4 protein levels as well as insulin resistance and dyslipidemia.

Short-term and long-term effects of excessive consumption of saturated fats and/or sucrose on metabolic variables in Sprague Dawley rats: a pilot study

BACKGROUND

Feeding high-fat and/or high-sugar diets to rats leads to a change in markers of metabolic syndrome. However, types and amounts of fat and sugar as well as the length of the experiment for establishing diet-induced metabolic syndrome in the Sprague Dawley (SD) rat model remain uncertain. This study was designed to investigate the effects in SD rats of consuming excess lard, sucrose or a combination of lard and sucrose for a short (4 week) or long (8 week) period of time.

RESULTS

Consumption of the high-fat high-sugar (HFHS) diet significantly increased weight gain and abdominal fat weights (P < 0.05), and the rats also began to develop signs of impaired glucose tolerance and had increased fasting blood lipids glucose and insulin concentrations. The high-fat (HF) diet mainly affected weight gain and fat deposition, whereas the high-sugar (HS) diet induced glucose intolerance but not the obesity-related parameters. Control rats showed a tendency towards insulin resistance and glucose intolerance when fed for a long-term period.

CONCLUSION

The lard plus sucrose-based HFHS diet is the most efficient one for inducing signs of metabolic syndrome, and SD rats fed this diet for 8 weeks successfully develop obesity and insulin resistance, which can be used as a model for metabolic syndrome research.

Dietary fish oil normalized glucose-stimulated insulin secretion in isolated pancreatic islets of dyslipemic rats through mechanisms involving glucose phosphorylation, peroxisome proliferator-activated receptor γ and uncoupling protein 2

This study evaluates some possible mechanisms behind the beneficial effects of dietary fish oil (FO) on β cell dysfunction in rats fed a sucrose-rich diet (SRD). Rats were fed a SRD for 6 months. Thereafter, half the rats received a SRD in which corn oil was partially replaced by FO up to 8 months. The other half continued consuming the SRD up to 8 months. A control group was fed a control diet throughout the experimental period. In isolated islets of SRD-fed rats dietary FO normalized the reduced glucose phosphorylation, the altered glucose oxidation, the triglyceride content, the increased protein mass levels of peroxisome proliferator-activated receptor γ (PPARγ) and uncoupling protein 2 without changes in GLUT2 and PPARα. These finding suggest that the changes mentioned above could be involved in the normalization of the altered glucose-stimulated insulin secretion pattern in this nutritional model of dyslipidemia and insulin resistance.

Fish oil reverses the altered glucose transporter, phosphorylation, insulin receptor substrate-1 protein level and lipid contents in the skeletal muscle of sucrose-rich diet fed rats

The role and underlying mechanisms by which n-3 polyunsaturated fatty acids (PUFA) prevent/reverse SRD-induced insulin resistance (IR) in the muscle are not completely understood. Therefore, we examined: triglyceride, diacylglycerol, PKCθ, Glut-4, enzymatic hexokinase activity, IRS-1 protein mass level, and fatty acid composition of muscle phospholipids. Rats were fed a SRD during 6 months. Thereafter, half the animals continued with SRD up to 8 months; the other half was fed a SRD in which CO (8% wt/wt) was replaced by FO (7%+1% CO) for 2 months. Results were compared with those obtained in rats fed a control diet (CD). In SRD-fed rats, FO oil normalized/improved lipid storage and PKCθ protein mass level. Effects of insulin were comparable with those of CD-fed rats. FO reversed impaired glucose phosphorylation, IRS-1, and, under insulin stimulation, Glut-4 protein mass level. FO normalized insulin resistance and increased n-3 PUFAs in muscle phospholipids.

Murine models for pharmacological studies of the metabolic syndrome

Metabolic syndrome has been described as the association of insulin resistance, hypertension, hyperlipidemia and obesity. Its prevalence increased dramatically, mainly in developed countries. Animal models are essential to understand the pathophysiology of this syndrome. This review presents the murine models of metabolic syndrome the most often used in pharmacological studies. The most common metabolic syndrome models exhibit a non-functional leptin pathway, or metabolic disorders induced by high fat diets. In a first part, and after a short introduction on leptin, its receptor and mechanism of action, we provide a detailed description of each model: SHROB, SHHF, JCR:LA-cp, Zucker, ZDF, Wistar Ottawa Karlsburg W, and Otsuka Long-Evans Tokushima Fatty rats, ob/ob, db/db, agouti yellow and Mc4R KO mice. The second part of this review is dedicated to metabolic syndrome models obtained by high fat feeding.

Sucrose-rich feeding during rat pregnancy-lactation and/or after weaning alters glucose and lipid metabolism in adult offspring

1. Adverse fetal and early life environments predispose to the development of metabolic disorders in adulthood. The present study examined whether offspring of normal Wistar dams fed a high-sucrose diet (SRD) developed impaired lipid and glucose homeostasis when fed a control diet (CD) after weaning. In addition, we investigated whether there were more pronounced derangements in lipid and glucose homeostasis when offspring of SRD-fed Wistar were fed an SRD after weaning compared with those in offspring of CD-fed dams weaned on an SRD. 2. During pregnancy and lactation, female rats were fed either an SRD or CD. After weaning, half the male offspring from both groups were fed a CD or SRD, up to 100 days of age (CD-CD, CD-SRD, SRD-SRD and SRD-CD groups). 3. Final bodyweight was similar between all groups, although offspring of SRD-fed dams had lighter bodyweight at birth. Plasma lipid and glucose levels were significantly higher (P < 0.05) without changes in insulin levels in the CD-SRD, SRD-SRD and SRD-CD groups compared with the CD-CD group. Dyslipidaemia in the CD-SRD and SRD-SRD groups resulted from increased secretion of very low-density lipoprotein triacylglycerol, as well as decreased triacylglycerol (TAG) clearance that was associated with increased liver TAG content (P < 0.05) compared with the CD-CD group. The hypertriglyceridaemia observed in the SRD-CD group was mostly associated with decreased TAG clearance. Altered glucose and insulin tolerance were observed when the SRD was fed during any period of life. 4. These data support the hypothesis that early life exposure to SRD is associated with changes in lipid and glucose metabolism, leading to an unfavourable profile in adulthood, regardless of whether offspring consumed an SRD after weaning.

Upregulated expression of brain enzymatic markers of arachidonic and docosahexaenoic acid metabolism in a rat model of the metabolic syndrome

Background

In animal models, the metabolic syndrome elicits a cerebral response characterized by altered phospholipid and unesterified fatty acid concentrations and increases in pro-apoptotic inflammatory mediators that may cause synaptic loss and cognitive impairment. We hypothesized that these changes are associated with phospholipase (PLA₂) enzymes that regulate arachidonic (AA, 20:4n-6) and docosahexaenoic (DHA, 22:6n-6) acid metabolism, major polyunsaturated fatty acids in brain. Male Wistar rats were fed a control or high-sucrose diet for 8 weeks. Brains were assayed for markers of AA metabolism (calcium-dependent cytosolic cPLA₂ IVA and cyclooxygenases), DHA metabolism (calcium-independent iPLA₂ VIA and lipoxygenases), brain-derived neurotrophic factor (BDNF), and synaptic integrity (drebrin and synaptophysin). Lipid concentrations were measured in brains subjected to high-energy microwave fixation.

Results

The high-sucrose compared with control diet induced insulin resistance, and increased phosphorylated-cPLA₂ protein, cPLA₂ and iPLA₂ activity and 12-lipoxygenase mRNA, but decreased BDNF mRNA and protein, and drebrin mRNA. The concentration of several n-6 fatty acids in ethanolamine glycerophospholipids and lysophosphatidylcholine was increased, as was unesterified AA concentration. Eicosanoid concentrations (prostaglandin E₂, thromboxane B₂ and leukotriene B₄) did not change.

Conclusion

These findings show upregulated brain AA and DHA metabolism and reduced BDNF and drebrin, but no changes in eicosanoids, in an animal model of the metabolic syndrome. These changes might contribute to altered synaptic plasticity and cognitive impairment in rats and humans with the metabolic syndrome.

Effects of Gosha-jinki-gan (Chinese herbal medicine: Niu-Che-Sen-Qi-Wan) on hyperinsulinemia induced in rats fed a sucrose-rich diet

We investigated the effects of a Chinese herbal medicine, Gosha-jinki-gan (GJG), on the regulation of insulin levels in rats fed a sucrose-rich diet (SRD). Normal Wistar rats in the SRD group were fed an SRD for 4 weeks. Increased dietary sucrose did not alter plasma glucose levels but it increased plasma insulin levels at 2 and 4 weeks in the SRD-fed rats relative to control rats that were fed standard chow. GJG treatment significantly suppressed the SRD-induced elevation in plasma insulin levels. These results suggest that GJG improves hyperinsulinemia caused by an SRD.

Dietary chia seed induced changes in hepatic transcription factors and their target lipogenic and oxidative enzyme activities in dyslipidaemic insulin-resistant rats

The present study analyses the effect of dietary chia seed rich in n-3 α-linolenic acid on the mechanisms underlying dyslipidaemia and liver steatosis developed in rats fed a sucrose-rich diet (SRD) for either 3 weeks or 5 months. The key hepatic enzyme activities such as fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC), glucose-6-phosphate dehydrogenase (G-6-PDH), carnitine palmitoyltransferase-1 (CPT-1) and fatty acid oxidase (FAO) involved in lipid metabolism and the protein mass levels of sterol regulatory element-binding protein-1 (SREBP-1) and PPARα were studied. (1) For 3 weeks, Wistar rats were fed either a SRD with 11 % of maize oil (MO) as dietary fat or a SRD in which chia seed replaced MO (SRD+Chia). (2) A second group of rats were fed a SRD for 3 months. Afterwards, half the rats continued with the SRD while for the other half, MO was replaced by chia for 2 months (SRD+Chia). In a control group, maize starch replaced sucrose. Liver TAG and the aforementioned parameters were analysed in all groups. The replacement of MO by chia in the SRD prevented (3 weeks) or improved/normalised (5 months) increases in dyslipidaemia, liver TAG, FAS, ACC and G-6-PDH activities, and increased FAO and CPT-1 activities. Protein levels of PPARα increased, and the increased mature form of SREBP-1 protein levels in the SRD was normalised by chia in both protocols (1 and 2). The present study provides new data regarding some key mechanisms related to the fate of hepatic fatty acid metabolism that seem to be involved in the effect of dietary chia seed in preventing and normalising/improving dyslipidaemia and liver steatosis in an insulin-resistant rat model.

Effects of long-term feeding of chitosan on postprandial lipid responses and lipid metabolism in a high-sucrose-diet-impaired glucose-tolerant rat model

This study was designed to investigate the effects of long-term feeding of chitosan on postprandial lipid response and lipid metabolism in a high-sucrose (HS)-diet-impaired glucose-tolerant rat model. As the results, HS-diet-fed rats supplemented with 5 and 7% chitosan in diets for 9 weeks had lower postprandial plasma total cholesterol (TC) levels, but 7% chitosan in the diet had higher postprandial plasma triglyceride (TG) and TG-rich lipoprotein TG levels. Supplementation of chitosan significantly decreased the postprandial ratio of apolipoprotein B (apoB)48/apoB100 in TG-rich lipoprotein fractions of HS-diet-fed rats. Long-term supplementation of 5 and 7% chitosan in diets for 16 weeks had lower plasma TC, low-density lipoprotein cholesterol (LDL-C) + very low density lipoprotein cholesterol (VLDL-C), TC/high-density lipoprotein (HDL-C) ratio, leptin, and tumor necrosis factor-α (TNF-α) levels in HS-diet-fed rats. Moreover, it was noticed that the VLDL receptor (VLDLR) protein expression in skeletal muscles of HS-diet-fed rats was significantly decreased, which could be significantly reversed by supplementation of 5 and 7% chitosan. Rats supplemented with 7% chitosan in the diet significantly elevated the lipolysis rate and decreased the accumulation of TG in epididymal fat pads of HS-diet-fed rats. The plasma angiopoietin-like 4 (ANGPTL4) protein expression was not affected in HS-diet-fed rats, but it was significantly increased in 7% chitosan-supplemented HS-diet-fed rats. Taken together, these results indicate that supplementation of chitosan in the diet can improve the impairment of lipid metabolism in a HS-diet-fed rat model, but long-term high-dose chitosan feeding may enhance postprandial plasma TG and TG-rich lipoprotein TG levels in HS-diet-fed rats through an ANGPTL4-regulated pathway.

Glycosphingolipid modification: structural diversity, functional and mechanistic integration of diabetes

Glycosphingolipids (GSLs) are present in all mammalian cell plasma membranes and intracellular membrane structures. They are especially concentrated in plasma membrane lipid domains that are specialized for cell signaling. Plasma membranes have typical structures called rafts and caveola domain structures, with large amounts of sphingolipids, cholesterol, and sphingomyelin. GSLs are usually observed in many organs ubiquitously. However, GSLs, including over 400 derivatives, participate in diverse cellular functions. Several studies indicate that GSLs might have an effect on signal transduction related to insulin receptors and epidermal growth factor receptors. GSLs may modulate immune responses by transmitting signals from the exterior to the interior of the cell. Guillain-Barré syndrome is one of the autoimmune disorders characterized by symmetrical weakness in the muscles of the legs. The targets of the immune response are thought to be gangliosides, which are one group of GSLs. Other GSLs may serve as second messengers in several signaling pathways that are important to cell survival or programmed cell death. In the search for clear evidence that GSLs may play critical roles in various biological functions, many researchers have made genetically engineered mice. Before the era of gene manipulation, spontaneous animal models or chemical-induced disease models were used.

N-acetylcysteine an allium plant compound improves high-sucrose diet-induced obesity and related effects

This study was designed to determine whether N-acetylcysteine (NAC, C(5)H(9)-NO(3)S), a compound from Allium species may be used as a complementary therapeutic agent, to inhibit high-sucrose induced-obesity and its effects on glucose tolerance, in vivo low-density lipoprotein (LDL)-oxidation and serum oxidative stress in rats. Initially, 24 male Wistar rats were divided into two groups: controls receiving standard chow (C, n = 6) and those receiving high-sucrose diet (HS, n = 18). After 22 days, (HS) group was divided into three groups (n = 6/group); (HS-HS) continued to eat high-sucrose diet and water; (HS-N) continued to eat high-sucrose diet and received 2 mg l(-1)-NAC in its drinking water; (HS-CN) changing high-sucrose to standard chow and receiving 2 mg l(-1)-NAC in its drinking water. After 22 days of the HS-group division (44 days of experimental period) body weight, body mass index and surface area were enhanced in HS-HS rats (P < .001). HS-HS rats had glucose intolerance, increased serum triacylglycerol (TG), very low-density lipoprotein (VLDL), oxidized-LDL (ox-LDL) and lipid-hydroperoxide (LH) than the others (P < .01). NAC in HS-N and HS-CN rats reduced the obesity markers, feed efficiency, LH and ox-LDL, as well normalized glucose response, TG and VLDL (P < .01) in these groups compared with HS-HS. Total antioxidant substances, GSH/GSSG ratio and glutathione-reductase, were higher in HS-N than in HS-HS (P < .01). In conclusion, NAC improved high-sucrose diet-induced obesity and its effects on glucose tolerance, lipid profile, in vivo LDL-oxidation and serum oxidative stress, enhancing antioxidant defences. The application of this agent may be feasible and beneficial for high-sucrose diet-induced obesity, which certainly would bring new insights on obesity-related adverse effects control.

Hyperphagia induced by sucrose: relation to circulating and CSF glucose and corticosterone and orexigenic peptides in the arcuate nucleus

Sucrose-rich diets compared to starch-rich diets are known to stimulate overeating under chronic conditions. The present study in normal-weight rats established an acute "preload-to-test meal" paradigm for demonstrating sucrose-induced hyperphagia and investigating possible mechanisms that mediate this behavioral phenomenon. In this acute paradigm, the rats were first given a small (15 kcal) sucrose preload (30% sucrose) for 30 min compared to an equicaloric, starch preload (25% starch with 5% sucrose) and then allowed to freely consume a subsequent test meal of lab chow. The sucrose preload, when compared to a starch preload equal in energy density and palatability, consistently increased food intake in the subsequent test meal occurring between 60 and 120 min after the end of the preload. Measurements of hormones, metabolites and hypothalamic peptides immediately preceding this hyperphagia revealed marked differences between the sucrose vs starch groups that could contribute to the increase in food intake. Whereas the sucrose group compared to the starch group immediately after the preload (at 10 min) had elevated levels of glucose in serum and cerebrospinal fluid (CSF) along with reduced expressions of neuropeptide Y (NPY) and agouti-related protein (AgRP) in the arcuate nucleus (ARC), the subsequent effects (at 30-60 min) just preceding the test meal hyperphagia were the reverse. Along with lower levels of glucose, they included markedly elevated serum and CSF levels of corticosterone and mRNA levels of NPY and AgRP in the ARC. In addition to establishing an animal model for sucrose-induced hyperphagia, these results demonstrate peripheral and central mechanisms that may mediate this behavioral phenomenon.

Gum Guar fiber associated with fructose reduces serum triacylglycerol but did not improve the glucose tolerance in rats

INTRODUCTION

The increased intake of dietary fructose can be associated with alterations on energy homeostasis and lipid/carbohydrate metabolism, such as insulin resistance and dislipidemia. On the other hand, the ingestion of soluble fiber gum guar could improve benefic mechanism on glucose tolerance and lipids profile.

OBJECTIVE

The aim of the present study were to investigate the effects of the supplemental feeding partially hydrolyzed gum guar on glucose and lipid homeostasis, in rats fed with fructose solution.

METHODS

The study was performed on thirty day-old male Wistar rats randomly assigned into four groups: control(C) or treated with fructose (F-20%), fiber (FB-5%), or fructose plus fiber (F-20% + FB-5% = FF) solution for 30 days on glucose tolerance (OGTT), triacylglycerol concentration in the liver by chloroform/methanol method, glucose, triacylglycerol and total cholesterol serum concentration by assayed by enzymatic colorimetric method, insulin receptor (IR) concentration in the liver by Western Blotting.

RESULTS

The total body weight gain was not different between groups; in regards of total caloric intake, in the F group was significantly higher and in the FB group was lower than other groups. The triacylglycerol concentration in the liver of FF group was significantly higher than F group, the triacylglycerol concentration in the serum was higher the F group compared with other groups. The OGTT reveal impaired on glucose tolerance in the F, FB, FF compared with C. The IR concentration in the liver was lower in the F, FB, FF compared with C, no significant difference was observed between groups for IR concentration in the gastrocnemius muscle. No significant difference was observed between groups for carcass fat content and serum total cholesterol.

CONCLUSION

Fructose induced important alterations on glucose tolerance and lipid metabolism, despite of fiber showed reversion of part this alterations. The association fructose plus fiber to seem decrease insulin receptor concentration in the liver, with consequent impair on glucose tolerance.

Nuclear receptors and hepatic lipidogenic enzyme response to a dyslipidemic sucrose-rich diet and its reversal by fish oil n-3 polyunsaturated fatty acids

A sucrose-rich diet (SRD), compared with a starch diet, induces time-dependent metabolic disorders and insulin resistance with hypertriglyceridemia, similar to type 2 diabetes. In this study, we examined the effect of SRD, after 8 mo, on nuclear receptors peroxisome proliferator-activated receptor-alpha (PPARalpha), and liver X receptor-alpha (LXRalpha), stearoyl-CoA desaturase-1 (SCD-1), and Delta6 and Delta5 desaturases mRNA and activity, hepatic enzymes involved in lipid metabolism, and fatty acid (FA) composition as well as the reversal produced by cod liver oil. SRD induced triglyceride increase in plasma and liver, increasing the anabolic FA synthase, malic enzyme, and glucose-6-phosphate dehydrogenase, but not the prooxidative enzymes FA oxidase and carnitine palmitoyltransferase I, and correspondingly decreased PPARalpha and increased LXRalpha expressions. Results suggest a contribution of both nuclear receptors' interaction on these enzymatic activities. SRD depressed SCD-1 without altering oleic acid proportion and increased Delta6 and Delta5 desaturases and the proportion of n-6 arachidonic acid. Therefore, the data do not support that SRD hypertriglyceridemia is produced by increased SCD-1-dependent oleic acid biosynthesis. The administration of 7% cod liver oil for 2 mo depressed LXRalpha, enhancing PPARalpha in control and SRD-fed rats, reversing the activity of the hepatic enzymes involved in lipid metabolism and therefore the hyperlipidemia produced by the SRD. Fish oil increased n-3 PUFA and depressed n-6 PUFA of liver lipids without altering the 18:1/18:0 ratio, suggesting that its effects were produced mainly by competition of dietary n-6 and n-3 FA and not through desaturase activity modification.

Soya protein reverses dyslipidaemia and the altered capacity of insulin-stimulated glucose utilization in the skeletal muscle of sucrose-rich diet-fed rats

The present study investigates the benefits of dietary intake of soya protein upon dyslipidaemia and insulin resistance in rats chronically (8 months) fed a sucrose-rich (63 %) diet (SRD). For this purpose, we analysed the effectiveness of soya protein isolate in improving or reversing these metabolic abnormalities. Wistar rats were fed a SRD for 4 months. By the end of this period, stable dyslipidaemia and insulin resistance were present in the animals. From months 4 to 8, half the animals continued with the SRD and the other half were fed a SRD in which the source of protein casein was substituted by soya. The control group received a diet in which the source of carbohydrate was maize starch. The results showed that: (1) soya protein normalized plasma TAG, cholesterol and NEFA levels in the SRD-fed rats. Moreover, the addition of soya protein reversed the hepatic steatosis. (2) Glucose homeostasis was normalized without changes in circulating insulin levels. Whole-body peripheral insulin sensitivity substantially improved. Besides, soya protein moderately decreases body weight gain limiting the accretion of visceral fat. (3) By shifting the source of dietary protein from casein to soya during the last 4 months of the feeding period it was possible to reverse both the diminished insulin-stimulated glucose oxidation and disposal in the skeletal muscle of SRD-fed rats. This study provides new data showing the beneficial effect of soya protein upon lipid and glucose homeostasis in the experimental model of dyslipidaemia and insulin resistance.

Dietary fish oil reverses lipotoxicity, altered glucose metabolism, and nPKCepsilon translocation in the heart of dyslipemic insulin-resistant rats

The present study analyzes several markers of energy metabolism in the heart muscle of dyslipemic insulin-resistant rats fed a sucrose-rich diet (SRD, 62.5% wt/wt) for 8 months. It also explores the possible beneficial effects of dietary fish oil supplementation on cardiac lipids and glucose metabolism. With this purpose, male Wistar rats were fed an SRD for 6 months. Whereas half of the animals continued with the same diet for up to 8 months, the other half was fed an SRD in which fish oil (7% + 1% corn oil wt/wt) replaced corn oil (8% wt/wt) from months 6 to 8. The results were compared with rats fed a control diet (starch 62.5% wt/wt). The cardiac muscle of SRD-fed rats showed (1) a significant reduction (P < .05) in key enzymes activities and metabolites involved in glucose metabolism, accompanied by a significant (P < .05) increase of lipid storage (triglyceride, long-chain acyl coenzyme A, and diacylglycerol), and (2) a significant increase (P < .05) of nPKCepsilon protein mass expression in the membrane fraction without changes in the cPKCbetaII. Dietary fish oil, which reduces the availability of plasma lipid flux and normalizes glucose homeostasis, was able to reverse heart muscle lipotoxicity. Fish oil benefits key enzymes activities in glucose metabolism and normalizes glycogen and glucose-6-phosphate concentration, and the altered nPKCepsilon protein mass expression translocation in the heart of SRD-fed rats. Our findings suggest that manipulation of dietary fats may play a key role in the management of lipid disorders, offering a protection against the development of cardiovascular diseases.

Dietary chia seed (Salvia hispanica L.) rich in alpha-linolenic acid improves adiposity and normalises hypertriacylglycerolaemia and insulin resistance in dyslipaemic rats

The present study investigates the benefits of the dietary intake of chia seed (Salvia hispanica L.) rich in alpha-linolenic acid and fibre upon dyslipidaemia and insulin resistance (IR), induced by intake of a sucrose-rich (62.5 %) diet (SRD). To achieve these goals two sets of experiments were designed: (i) to study the prevention of onset of dyslipidaemia and IR in Wistar rats fed during 3 weeks with a SRD in which chia seed was the dietary source of fat; (ii) to analyse the effectiveness of chia seed in improving or reversing the metabolic abnormalities described above. Rats were fed a SRD during 3 months; by the end of this period, stable dyslipidaemia and IR were present in the animals. From months 3-5, half the animals continued with the SRD and the other half were fed a SRD in which the source of fat was substituted by chia seed (SRD+chia). The control group received a diet in which sucrose was replaced by maize starch. The results showed that: (i) dietary chia seed prevented the onset of dyslipidaemia and IR in the rats fed the SRD for 3 weeks--glycaemia did not change; (ii) dyslipidaemia and IR in the long-term SRD-fed rats were normalised without changes in insulinaemia when chia seed provided the dietary fat during the last 2 months of the feeding period. Dietary chia seed reduced the visceral adiposity present in the SRD rats. The present study provides new data regarding the beneficial effect of chia seed upon lipid and glucose homeostasis in an experimental model of dislipidaemia and IR.

Regulation of glycogen concentration and glycogen synthase activity in skeletal muscle of insulin-resistant rats

The aim of this study was to investigate the effect of insulin resistance on glycogen concentration and glycogen synthase activity in the red and white gastrocnemius muscles and to determine whether the inverse relationship existing between glycogen concentration and enzyme activity is maintained in insulin resistant state. These questions were addressed using 3 models that induce various degrees of insulin resistance: sucrose feeding, dexamethasone administration, and a combination of both treatments (dex+sucrose). Sucrose feeding raised triglyceride levels without affecting plasma glucose or insulin concentrations whereas dexamethasone and dex+sucrose provoked severe hyperinsulinemia, hyperglycemia and hypertriglyceridemia. Sucrose feeding did not alter muscle glycogen concentration but provoked a small reduction in the glycogen synthase activity ratio (-/+ glucose-6-phosphate) in red but not in white gastrocnemius. Dexamethasone administration augmented glycogen concentration and reduced glycogen synthase activity ratio in both muscle fiber types. In contrast, dex+sucrose animals showed decreased muscle glycogen concentration compared to dexamethasone group, leading to levels similar to those of control animals. This was associated with lower glycogen synthase activity compared to control animals leading to levels comparable to those of dexamethasone-treated animals. Thus, in dex+sucrose animals, the inverse relationship observed between glycogen levels and glycogen synthase activity was not maintained, suggesting that factors other than the glycogen concentration modulate the enzyme's activity. In conclusion, while insulin resistance was associated with a reduced glycogen synthase activity ratio, we found no correlation between muscle glycogen concentration and insulin resistance. Furthermore, our results suggest that sucrose treatment may modulate dexamethasone action in skeletal muscle.

Dietary palatinose and oleic acid ameliorate disorders of glucose and lipid metabolism in Zucker fatty rats

Excessive dietary intake of carbohydrates and fats has been linked to the development of obesity. However, the mechanism by which these dietary factors interact to bring about metabolic changes has not been elucidated. We examined the combined effects of different types of dietary carbohydrates and fats on the etiology of obesity and its complications in the Zucker fatty (fa/fa) rat, a model of obesity. Specifically, these rats were fed an isocaloric diet containing various combinations of carbohydrates [palatinose (P), an insulin-sparing sucrose analogue, and sucrose (S)] and fatty acids [oleic acid (O) and linoleic acid (L)]. After 8 wk, palatinose feeding (PO and PL) led to significant reductions in visceral fat mass, adipocyte cell size, hyperglycemia, and hyperlipidemia compared with sucrose feeding (SO and SL); pancreatic islet hypertrophy was also prevented by palatinose feeding. Linoleic-acid-fed rats (PL and SL) exhibited reduced insulin-immunoreactive staining of the pancreatic islets, enhanced macrophage infiltration in adipose tissue, and an elevated plasma tumor necrosis factor-alpha concentration when compared with oleic-acid-fed rats (PO and SO). Furthermore, sucrose and linoleic acid synergistically increased the expression of genes involved in hepatic gluconeogenesis and lipogenesis [sterol regulatory-element binding protein (SREBP)-1c and SREBP-2]. In conclusion, a diet containing palatinose and oleic acid may prevent diet-induced metabolic abnormalities. The combination of palatinose and oleic acid holds promise for a new approach to preventing and treating obesity and its complications.

The reduction of dietary sucrose improves dyslipidemia, adiposity, and insulin secretion in an insulin-resistant rat model

OBJECTIVE

The purpose of the present work was to investigate whether changes in the type of carbohydrate in the diet are able to improve and/or reverse hyperlipemia, impaired glucose homeostasis, and insulin secretion from beta-cells induced in rats by chronically feeding a high sucrose intake.

METHODS

For 30 wk male Wistar rats received a sucrose-rich diet (63% w/w) or a control diet in which sucrose was replaced by starch. After this period, the sucrose-fed animals were randomly divided into two groups: the first group continued with this diet up to 42 wk and the other received the same diet but with a 20% reduction in the amount of sucrose and the rest of the carbohydrate being replaced by starch. Rats were fed with this diet for the next 12 wk.

RESULTS

The reduction of the amount of sucrose in the diet showed a substantial improvement (P < 0.05) of dyslipidemia associated with an amelioration of "in vivo" very low-density lipoprotein-triacylglycerol secretion and triacylglycerol removal rate from the circulation. Glucose homeostasis and glucose-induced insulin release from beta-cells were improved (P < 0.05), although these values did not reach those observed in rats fed a control diet. Visceral adiposity was also significantly reduced (P < 0.05).

CONCLUSION

These data are consistent with the suggestion that the composition of the diet could contribute to improvements in dyslipidemia, insulin resistance, and adiposity by direct effects on the lipid metabolism and insulin action and indirectly through the reduction of visceral fat mass and distribution.

Enhanced muscle mixed and mitochondrial protein synthesis rates after a high-fat or high-sucrose diet

OBJECTIVE

Obesity and insulin resistance are associated with muscle mitochondrial dysfunction, which might be related to impairment of mitochondrial protein synthesis. This study aimed at investigating mixed and mitochondrial protein synthesis in skeletal muscle in response to dietary manipulations.

RESEARCH METHODS AND PROCEDURES

High-sucrose (SU) and high-fat, high-sucrose (F) diets were provided for 6 weeks to Wistar rats at standard (N) and high (H) energy intakes and compared with controls. Fractional synthesis rates of mixed (FSRPT) and mitochondrial (FSRm) proteins within the oxidative (soleus) and glycolytic (tibialis) muscles were measured using stable isotope flooding dose technique using L-[13C]-valine. Carbonyl content, citrate synthase, and cytochrome c oxidase activities were assayed spectrophotometrically on isolated mitochondria.

RESULTS

In the soleus, FSRPT was increased by 40% in the NSU and NF groups and by 65% in the HSU and HF groups (p<0.001 vs. control). FSRm was increased with high-fat diets (NF, +16%; HF, +32%; p<0.01). In the tibialis, FSR(PT) was enhanced in all experimental groups (+31% to 37%, p<0.05 vs. control). FSRm was augmented in the NSU, NF, and HF groups (+28% to 32%, p<0.01). Cytochrome c oxidase activity was significantly decreased in all experimental groups in the soleus (p<0.001).

DISCUSSION

Muscle mixed and mitochondrial protein FSR are enhanced after short-term dietary intervention known to induce insulin resistance and obesity. Adaptations are muscle type specific and may not explain alterations in mitochondrial oxidative capacity but might contribute to maintain mitochondrial functioning.

Metabolic Syndrome: Effects of n-3 PUFAs on a Model of Dyslipidemia, Insulin Resistance and Adiposity

Both genetic and environmental factors (e.g. nutrition, life style) contribute to the development of the plurimetabolic syndrome, which has a high prevalence in the world population. Dietary n-3 PUFAs specially those from marine oil (EPA and DHA) appear to play an important role against the adverse effects of this syndrome. The present work examined the effectiveness of fish oil (FO) in reversing or improving the dyslipidemia, insulin resistance and adiposity induced in rats by long-term feeding a sucrose-rich diet (SRD). We studied several metabolic and molecular mechanisms involved in both lipid and glucose metabolisms in different tissues (liver, skeletal muscle, fat pad) as well as insulin secretion patterns from perifused islets under the stimulation of different secretagogues. Dietary FO reverses dyslipidemia and improves insulin action and adiposity in the SRD fed rats. FO reduces adipocytes cell size and thus, the smaller adipocytes are more insulin sensitive and the release of fatty acids decreases. In muscle, FO normalizes both the oxidative and non-oxidative glucose pathways. Moreover, FO modifies the fatty acid composition of membrane phospholipids. In isolated beta cells, lipid contents and glucose oxidation return to normal. All these effects could contribute to the normalization of glucose-stimulated insulin secretion and muscle insulin insensitivity.