The role of lipogenesis in the development of obesity and diabetes in Israeli sand rats (Psammomys obesus)

A comparative transcriptomics analysis reveals ethylene glycol derivatives of squalene ameliorate excessive lipogenesis and inflammatory response in 3T3-L1 preadipocytes

Squalene (SQ) is a natural compound with anti-inflammatory, anti-cancer, and anti-oxidant effects, but due to its low solubility, its biological properties have been greatly underestimated. This study aims to explore the differences in gene expression patterns of four newly synthesized amphipathic ethylene glycol (EG) derivatives of SQ by whole-genome transcriptomics analysis using DNA microarray to examine the mRNA expression profile of adipocytes differentiated from 3T3-L1 cells treated with SQ and its EG derivatives. Enrichment analyses of the transcriptional data showed that compared with SQ, its EG derivatives exerted different, in most cases desirable, biological responses. EG derivatives showed increased enrichment of mitochondrial functions, lipid and glucose metabolism, and inflammatory response. Mono-, di-, and tetra-SQ showed higher enrichment of the cellular component-ribosome. Histological staining showed EG derivatives prevented excessive lipid accumulation. Additionally, mitochondrial transcription factors showed upregulation in tetra-SQ-treated cells. Notably, EG derivatives showed better anti-inflammatory effects. Further, gene-disease association analysis predicted substantial improvement in the bioactivities of SQ derivatives in metabolic diseases. Cluster analyses revealed di- and tetra-SQ had more functional similarities than others, reflected in their scanning electron microscopy images; both di- and tetra-SQ self-organized into similar sizes and shapes of vesicles, subsequently improving their cation binding activities. Protein-protein interaction networks further revealed that cation binding activity might explain a major part, if not all, of the differences observed in functional analyses. Altogether, the addition of EG derivatives may improve the biological responses of SQ and thus may enhance its health-promoting potential.

Anti-obesity effect of Lythri herba water extracts in vitro and in vivo

ETHNOPHARMACOLOGICAL RELEVANCE

Lythrum salicaria L., also called purple loosestrife, has traditionally been used as a medicinal plant to treat internal dysfunction, such as gastrointestinal disorders or hemorrhages. It contains numerous phytochemical compounds, including orientin, and has been reported to have anti-diarrheal, anti-inflammatory, antioxidant, and antimicrobial properties.

AIM OF THE STUDY

The effects of Lythrum salicaria L. on obesity have not been explored. Therefore, we investigated the anti-obesity effects of Lythri Herba, the aerial part of this plant, in vitro and in vivo.

MATERIALS AND METHODS

Using distilled water, Lythri Herba water extracts (LHWE) were prepared by extracting Lythri Herba at 100°Ϲ. The contents of orientin in LHWE were identified using High Performance Liquid Chromatography (HPLC) analysis. To evaluate the anti-obesity effect of LHWE, 3T3-L1 adipocytes and a high-fat diet (HFD)-fed mice were used. Oil-red O staining was performed to examine the anti-adipogenic effects of LHWE in vitro. The histological changes in epididymal white adipose tissue (epiWAT) by LHWE were examined using hematoxylin and eosin staining. Serum leptin levels were measured by enzyme-linked immunosorbent assay. Specific quantification kits measured total cholesterol and triglyceride levels in the serum. The relative fold induction of protein and mRNA was determined using western blot and Quantitative real-time Polymerase Chain Reaction analysis, respectively.

RESULTS

HPLC analysis demonstrated the presence of orientin in LHWE. LHWE treatment markedly reduced lipid accumulation in differentiated 3T3-L1 adipocytes. LHWE administration also conferred resistance to HFD-induced weight gain in mice and reduced epiWAT mass. Mechanistically, LHWE significantly decreased lipogenesis by downregulating lipoprotein lipase (LPL), glucose-6-phosphate dehydrogenase, ATP-citrate lyase, fatty acid synthase, stearoyl-CoA desaturase 1, sterol regulatory element binding transcription factor 1, and carbohydrate response element binding protein expression and increased the expression of genes involved in fatty acid oxidation (FAO), peroxisome proliferator-activated receptor α and carnitine palmitoyltransferase 1 in 3T3-L1 adipocytes and epiWAT. Furthermore, LHWE significantly up-regulated the phosphorylation of AMP-activated protein kinase in 3T3-L1 adipocytes and epiWAT.

CONCLUSION

LHWE decreases white adipogenesis in vitro and HFD-induced weight gain in vivo, which is associated with reduced lipogenesis and enhanced FAO.

The Role of Oxidative Stress and Inflammation in Obesity and Its Impact on Cognitive Impairments-A Narrative Review

Obesity is a chronic low-grade inflammatory condition that induces the generation of oxidative stress and inflammation. This oxidative stress and inflammation stimulate brain atrophy and some morphological changes in the brain that eventually result in cognitive impairments. However, there is no exact study that has summarized the role of oxidative stress and inflammation in obesity and its impact on cognitive impairments. Thus, the objective of this review is to recapitulate the current role of oxidative stress and inflammation in cognitive decline based on in vivo evidence. A comprehensive search was performed in Nature, Medline and Ovid, ScienceDirect, and PubMed, and the search was limited to the past 10 years of publication. From the search, we identified 27 articles to be further reviewed. The outcome of this study indicates that a greater amount of fat stored in individual adipocytes in obesity induces the formation of reactive oxygen species and inflammation. This will lead to the generation of oxidative stress, which may cause morphological changes in the brain, suppress the endogenous antioxidant system, and promote neuroinflammation and, eventually, neuronal apoptosis. This will impair the normal function of the brain and specific regions that are involved in learning, as well as memory. This shows that obesity has a strong positive correlation with cognitive impairments. Hence, this review summarizes the mechanism of oxidative stress and inflammation that induce memory loss based on animal model evidence. In conclusion, this review may serve as an insight into therapeutic development focusing on oxidative stress and inflammatory pathways to manage an obesity-induced cognitive decline in the future.

Spirulina reduces diet-induced obesity through downregulation of lipogenic genes expression in Psammomys obesus

The present study evaluates the protective effect of spirulina against diet-induced obesity and metabolic disorders in Psammomys obesus, an animal model of metabolic syndrome. Psammomys obesus lives on a low-energy diet, in order to remain healthy. However, under a standard laboratory chow diet (SLCD), this animal exhibits insulin resistance, which occurs as a result of obesity. Psammomys obesus was maintained on SLCD, in order to evaluate the effect of spirulina on obesity development with a particular focus on glucose and lipid metabolism, as well as the mRNA expression of some pro-inflammatory cytokines. After 12 weeks of treatment with spirulina, there was a significant reduction in body weight gain, plasma glucose, insulin and triglyceride levels. There was also a significant reduction in the mRNA expression of genes involved in lipogenesis and inflammation. Spirulina improved insulin sensitivity, glucose and lipid metabolism. These findings highlight the positive effect of spirulina on weight maintenance.

Adipocytes in Breast Cancer, the Thick and the Thin

It is well established that breast cancer development and progression depend not only on tumor-cell intrinsic factors but also on its microenvironment and on the host characteristics. There is growing evidence that adipocytes play a role in breast cancer progression. This is supported by: (i) epidemiological studies reporting the association of obesity with a higher cancer risk and poor prognosis, (ii) recent studies demonstrating the existence of a cross-talk between breast cancer cells and adipocytes locally in the breast that leads to acquisition of an aggressive tumor phenotype, and (iii) evidence showing that cancer cachexia applies also to fat tissue and shares similarities with stromal-carcinoma metabolic synergy. This review summarizes the current knowledge on the epidemiological link between obesity and breast cancer and outlines the results of the tumor-adipocyte crosstalk. We also focus on systemic changes in body fat in patients with cachexia developed in the course of cancer. Moreover, we discuss and compare adipocyte alterations in the three pathological conditions and the mechanisms through which breast cancer progression is induced.

Protectin DX ameliorates palmitate- or high-fat diet-induced insulin resistance and inflammation through an AMPK-PPARα-dependent pathway in mice

Protectin DX (PDX), a double lipoxygenase derivative of docosahexaenoic acid, has been reported to attenuate inflammation and insulin resistance. In the current study, we explored the effects of PDX on hyperlipidemia-induced insulin resistance and inflammation through AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor α (PPARα). PDX attenuated the impairment of insulin receptor substrate 1/Akt-mediated insulin signaling in palmitate-treated differentiated C2C12 cells and soleus skeletal muscle of HFD-fed mice. Furthermore, PDX treatment significantly ameliorated HFD-induced weight gain and improved glucose tolerance in mice. Nuclear factor kB nuclear translocation, inhibitory kBα phosphorylation, and expression of proinflammatory cytokines were markedly attenuated by PDX in both in vitro and in vivo models. PDX treatment markedly augmented AMPK phosphorylation and PPARα expression in C2C12 cells and in skeletal muscle of mice. AMPK- and PPARα-specific siRNAs significantly abrogated the suppressive effects of PDX on palmitate-induced insulin resistance and inflammation. Furthermore, PDX markedly stimulated the expression of genes related to fatty acid oxidation. These effects of PDX were significantly suppressed by AMPK and PPARα siRNAs. In conclusion, our results demonstrate that PDX ameliorates insulin resistance and inflammation and stimulates fatty acid oxidation through AMPK- and PPARα-mediated pathways in skeletal muscle.

Eicosapentaenoic acid modulates fatty acid metabolism and inflammation in Psammomys obesus

The desert gerbil, Psammomys obesus, is a unique polygenic animal model of metabolic syndrome (insulin resistance, obesity and type 2 diabetes), and these pathological conditions resemble to those in human beings. In this study, the animals were fed ad libitum either a natural diet (ND) which contained desertic halophile plants or a standard laboratory diet (STD) or a diet which contained eicosapentaenoic acid (EPA), hence, termed as EPA diet (EPAD). In EPAD, 50% of total lipid content was replaced by EPA oil. By employing real-time PCR, we assessed liver expression of key genes involved in fatty acid metabolism such as PPAR-α, SREBP-1c, LXR-α and CHREBP. We also studied the expression of two inflammatory genes, i.e., TNF-α and IL-1β, in liver and adipose tissue of these animals. The STD, considered to be a high caloric diet for this animal, triggered insulin resistance and high lipid levels, along with high hepatic SREBP-1c, LXR-α and CHREBP mRNA expression. TNF-α and IL-1β mRNA were also high in liver of STD fed animals. Feeding EPAD improved plasma glucose, insulin and triacylglycerol levels along with hepatic lipid composition. These observations suggest that EPA exerts beneficial effects in P. obesus.

Quantitative histopathological assessment of retardation of islets of langerhans degeneration in rosiglitazone-dosed obese ZDF rats using combined insulin and collagens (I and III) immunohistochemistry with automated image analysis and statistical modeling

Islets of Langerhans represent a heterogeneous population in insulin resistant and diabetic animals and humans as histological appearances and function vary substantially. Mathematical representation that reflects this morphological diversity will assist in assessment of degeneration and regeneration, enabling comparisons between species, strains, and experimental investigations. Our investigative approach used a model of islet degeneration in diabetic male obese Zucker Diabetic Fatty (ZDF) rats and evaluated its prevention using rosiglitazone treatment. Immunohistochemical staining (insulin and collagens I/III) with automated image analysis reliably measured numbers, area, clustering, and staining intensity of β-cells and degree of islet fibrosis. Finite mixture mathematical modeling for the joint probability distribution of seven islet parameters to represent islet numerical data variation provided an automatic procedure for islet category allocations as normal or abnormal. Allocations for obese ZDF controls and rosiglitazone-treated animals were significantly different, with no significant difference between the latter and lean ZDF controls, indicative of differences within islet populations of individual animals, between lean and obese rat strains and following drug treatment. Islet morphology showed clear association with mathematical characterization. Information on islet morphology obtained by histopathological assessment of single pancreatic tissue sections was confirmed by this method showing drug-induced retardation of islet of Langerhans degeneration.

Lipogenesis in arterial wall and vascular smooth muscle cells of Psammomys obesus: its regulation and abnormalities in diabetes

AIM

Lipogenesis is expressed in vascular smooth muscle cells (VSMCs), and such in situ lipogenesis could be providing the fatty acids for triglyceride synthesis and cholesterol esterification, and contributing to lipid accumulation in the arterial wall. This study investigated both the expression and regulation of lipogenesis in VSMCs to determine if they are modified in Psammomys obesus gerbils fed a high-fat diet as a model of insulin resistance and diabetes.

METHODS

Aortas were collected from diabetic and non-diabetic P. obesus for histological examination, measurement of lipogenic gene expression and VSMC culture.

RESULTS

The aortas of diabetic animals exhibited lipid deposits and foam cells as well as disorganization of elastic fibres. However, lipogenic gene expression was not modified. VSMCs in vitro from the aortas of diabetic animals had, compared with cells from non-diabetic animals, lower mRNA levels of SREBP-1c and ChREBP. An adipogenic medium stimulated moderate FAS and ACC1 expression in cells from both diabetic and non-diabetic animals, but glucose and insulin on their own had no such stimulatory action. Also, triiodothyronine (T3) had a clear stimulatory action, while angiotensin II had a moderate effect, in cells from non-diabetic P. obesus, but not from diabetic animals, whereas LXR agonists stimulated lipogenesis in cells from both animal groups.

CONCLUSION

Lipogenesis is expressed in the arterial walls and VSMCs of P. obesus. However, its expression was not increased in diabetes, and did not respond to either T3 or angiotensin II. Therefore, lipogenesis in situ is unlikely to contribute to the accumulation of lipids in the arterial walls of diabetic P. obesus gerbils.

A review of islet of Langerhans degeneration in rodent models of type 2 diabetes

Type 2 diabetes mellitus (TTDM) is characterized by progressive loss of glucose control through multifactorial mechanisms. The search for an understanding of TTDM has relied on animal models since the realization of the importance of the pancreas in controlling plasma glucose concentration. Rodent models of TTDM are developed to express hyperglycemia and not islet degeneration per se. Degeneration of the islets of Langerhans with beta-cell loss is secondary to insulin resistance and is regarded as the more important lesion. Despite this, differences between models are seen in the development and progression of islet degeneration. Assessing the differences between the models is important to appreciate the various aspects of TTDM and understand their advantages as well as their deficiencies. Relevant animal models of TTDM provide opportunities to investigate important physiological and cell biological processes that may ultimately lead to development of targeted therapies. This article reviews the importance, advantages, and limitations of rodent models of TTDM in relation to the histopathological changes that characterize islet degeneration. Pathophysiological mechanisms that contribute to islet degeneration are also discussed and are placed into the context of changes in islet histological appearances.

Low rate of glucose 6-phosphate hydrolysis in liver cells is a physiological feature of non-diabetic wild sand rats (Psammomys obesus)

OBJECTIVE

In this study we have compared glucose metabolism and liver gluconeogenesis in wild adult desert gerbil Psammomys obesus fed with their natural halophilic plants and Wistar rats fed on a laboratory chow. Psammomys obesus is a natural model of insulin resistance when fed a rodent laboratory chow.

METHODS

Basal glucose and insulin were determined in plasma of fasting animals. Hepatocyte gluconeogenesis from lactate-plus-pyruvate was investigated in perifused hepatocytes by assessing simultaneously glucose synthesis rate and intracellular oxaloacetate, phosphoenolpyruvate, 3-phosphoglycerate, fructose 6-phosphate and glucose 6-phosphate (G6P) under true steady state conditions.

RESULTS

Fasting blood glucose (2.8 +/- 0.1 vs 4.8 +/- 0.4 mmol.L(- 1)) and plasma insulin concentration (129 +/- 14 vs 150 +/- 21 pmol.L(-1)) were significantly lower in Psammomys as compared to albino rats. Maximal gluconeogenic rate was also lower in Psammomys (2.3 +/- 0.3 vs 5.1 +/- 0.3 micromol x min(-1) x g dry cells(-1)). This effect was related to a slower hydrolysis of G6P.

CONCLUSION

A lower G6P hydrolysis in Psammomys as compared to wistar was the main difference between the two groups of liver cells. Such feature may represent the major metabolic adaptation permitting Psammomys to survive despite its severe restrictive natural conditions. Indeed, a low G6P hydrolysis allows an insulin resistance state, with a high lipogenic activity, but associated with low blood glucose. The rise in blood glucose occurring when Psammomys are fed with exogenous carbohydrates perturbs such delicate metabolic equilibrium, resulting thus in a diabetic state because of the deleterious effect of hyperglycemia.

Increasing fructose 2,6-bisphosphate overcomes hepatic insulin resistance of type 2 diabetes

Hepatic glucose production is increased as a metabolic consequence of insulin resistance in type 2 diabetes. Because fructose 2,6-bisphosphate is an important regulator of hepatic glucose production, we used adenovirus-mediated enzyme overexpression to increase hepatic fructose 2,6-bisphosphate to determine if the hyperglycemia in KK mice, polygenic models of type 2 diabetes, could be ameliorated by reduction of hepatic glucose production. Seven days after treatment with virus encoding a mutant 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase designed to increase fructose 2,6-bisphosphate levels, plasma glucose, lipids, and insulin were significantly reduced in KK/H1J and KK.Cg-A(y)/J mice. Moreover, high fructose 2,6-bisphosphate levels downregulated glucose-6-phosphatase and upregulated glucokinase gene expression, thereby reversing the insulin-resistant pattern of hepatic gene expression of these two key glucose-metabolic enzymes. The increased hepatic fructose 2,6-bisphosphate also reduced adiposity in both KK mice. These results clearly indicate that increasing hepatic fructose 2,6-bisphosphate overcomes the impairment of insulin in suppressing hepatic glucose production, and it provides a potential therapy for type 2 diabetes.