Long chain saturated and unsaturated fatty acids exert opposing effects on viability and function of GLP-1-producing cells: Mechanisms of lipotoxicity

Multiomics analysis revealed the mechanism of the anti-diabetic effect of Salecan

Salecan, a natural β-glucan compromising nine residues connected by β-(1 → 3)/α-(1 → 3) glycosidic bonds, is one of the newly approved food ingredients. Salecan has multiple health-improving effects, yet its mechanism against Type 2 diabetes mellitus (T2DM) remains poorly understood. In this study, the hypoglycemic effect and underlying mechanism of Salecan intervention on STZ-induced diabetic model mice were investigated. After 8 weeks of gavage, Salecan attenuated insulin resistance and repaired pancreatic β cells in a dose-dependent manner. In addition, Salecan supplement remodel the structure of the gut microbiota and altered the level of intestinal metabolites. Serum metabolites, especially unsaturated fatty acids, were also affected significantly. In addition, tight junction proteins in the colon and autophagy-related proteins in the pancreas were upregulated. Multiomics analysis indicated that Lactobacillus johnsonii, Muribaculaceae, and Lachnoclostridium were highly associated with fatty acid esters of hydroxy fatty acids (FAHFA) levels in the colon, accordingly enhancing arachidonic acid and linoleic acid in serum, and promoting GLP-1 release in the intestine and insulin secretion in the pancreas, thus relieving insulin resistance and exhibiting hypoglycemic effects. These findings provide a novel understanding of the anti-diabetic effect of Salecan in mice from a molecular perspective, paving the way for the wide use of Salecan.

Tripterygium glycosides improve abnormal lipid deposition in nephrotic syndrome rat models

OBJECTIVE

The purpose of this study was to determine the effect of tripterygium glycosides (TGs) on regulating abnormal lipid deposition in nephrotic syndrome (NS) rats.

METHODS

Sprague-Dawley (SD) rats were injected with 6 mg/kg doxorubicin to construct nephrotic syndrome models (n = 6 per group), and then administered with TGs (10 mg/kg·d^-1), prednisone (6.3 mg/kg·d^-1), or pure water for 5 weeks. Biomedical indexes, such as urine protein/creatinine ratio (PCR), blood urea nitrogen (BUN), serum creatinine (Scr), serum albumin (SA), triglycerides (TG), total cholesterol (TC)were investigated to evaluate the renal injury of rats. H&E staining experiment was used to assess the pathological alterations. Oil Red O staining was used to assess the level of renal lipid deposition. Malondialdehyde (MDA) and glutathione (GSH) were measured to assess the extent of oxidative damage to the kidney. TUNEL staining was used to assess the status of apoptosis in the kidney. Western blot analysis was performed to examine the levels of relevant intracellular signaling molecules.

RESULTS

After treatment with TGs, those tested biomedical indexes were significantly improved, and the extent of kidney tissue pathological changes and lipid deposition in the kidney was diminished. Treatment with TGs decreased renal oxidative damage and apoptosis. Regarding the molecular mechanism, TGs significantly increased the protein expression levels of Bcl-2 but decreased the levels of CD36, ADFP, Bax, and Cleaved caspase-3.

CONCLUSION

TGs alleviates renal injury and lipid deposition induced by doxorubicin, suggesting that it may be a new strategy for reducing renal lipotoxicity in NS.

Regulation of semen quality by fatty acids in diets, extender, and semen

Fatty acids (FAs) are classified into different types according to the degree of hydrocarbon chain saturation, including saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), omega-3 polyunsaturated fatty acids (omega-3 PUFAs) and omega-6 polyunsaturated fatty acids (omega-6 PUFAs), which play an important role in maintaining semen quality. This review focuses on the regulation of FAs in semen, diet and extender on semen quality, and expounds its effects on sperm motility, plasma membrane integrity, DNA integrity, hormone content, and antioxidant capacity. It can be concluded that there are species differences in the FAs profile and requirements in sperm, and their ability to regulate semen quality is also affected by the addition methods or dosages. Future research directions should focus on analyzing the FAs profiles of different species or different periods of the same species and exploring suitable addition methods, doses and mechanism of regulating semen quality.

Differential effects of a cafeteria diet and GSPE preventive treatments on the enterohormone secretions of aged vs. young female rats

Grape seed derived procyanidins (GSPE) have been shown to effectively prevent intestinal disarrangements induced by a cafeteria diet in young rats. However, little is known about the effects of procyanidins and cafeteria diet on enterohormone secretion in aged rats, as the ageing processes modify these effects. To study these effects in aged rats, we subjected 21-month-old and young 2-month-old female rats to two sub-chronic preventive GSPE treatments. After three months of cafeteria diet administration, we analysed the basal and stimulated secretion and mRNA expression of CCK, PYY and GLP-1, caecal SCFA and intestinal sizes. We found that the effects of a cafeteria diet on the basal duodenal CCK secretion are age dependent. GLP-1 in the ileum was not modified regardless of the rat's age, and GSPE preventive effects differed in the two age groups. GSPE pre-treatment reduced GLP-1, PYY and ChgA in mRNA in aged ileum tissue, while the cafeteria diet increased these in aged colon. The GSPE treatments only modified low-abundance SCFAs. The cafeteria diet in aged rats increases the caecum size differently from that in young rats and GSPE pre-treatment prevents this increase. Therefore, ageing modifies nutrient sensing, and the cafeteria diet acts mainly on the duodenum and colon, while procyanidins have a larger effect on the ileum.

Circadian secretion rhythm of GLP-1 and its influencing factors

Circadian rhythm is an inherent endogenous biological rhythm in living organisms. However, with the improvement of modern living standards, many factors such as prolonged artificial lighting, sedentarism, short sleep duration, intestinal flora and high-calorie food intake have disturbed circadian rhythm regulation on various metabolic processes, including GLP-1 secretion, which plays an essential role in the development of various metabolic diseases. Herein, we focused on GLP-1 and its circadian rhythm to explore the factors affecting GLP-1 circadian rhythm and its potential mechanisms and propose some feasible suggestions to improve GLP-1 secretion.

Slow digestion-oriented dietary strategy to sustain the secretion of GLP-1 for improved glucose homeostasis

Dysregulated glucose metabolism is associated with many chronic diseases such as obesity and type 2 diabetes mellitus (T2DM), and strategies to restore and maintain glucose homeostasis are essential to health. The incretin hormone of glucagon-like peptide-1 (GLP-1) is known to play a critical role in regulating glucose homeostasis and dietary nutrients are the primary stimuli to the release of intestinal GLP-1. However, the GLP-1 producing enteroendocrine L-cells are mainly distributed in the distal region of the gastrointestinal tract where there are almost no nutrients to stimulate the secretion of GLP-1 under normal situations. Thus, a dietary strategy to sustain the release of GLP-1 was proposed, and the slow digestion property and dipeptidyl peptidase IV (DPP-IV) inhibitory activity of food components, approaches to reduce the rate of food digestion, and mechanisms to sustain the release of GLP-1 were reviewed. A slow digestion-oriented dietary approach through encapsulation of nutrients, incorporation of viscous dietary fibers, and enzyme inhibitors of phytochemicals in a designed whole food matrix will be implemented to efficiently reduce the digestion rate of food nutrients, potentiate their distal deposition and a sustained secretion of GLP-1, which will be beneficial to improved glucose homeostasis and health.

Abnormal post-prandial glucagon-like peptide release in patients with Crohn's disease

BACKGROUND AND AIMS

Glucagon-like peptide GLP-1 and -2 have been shown to regulate immune responses in immune-mediated disorders, including Crohn's disease (CD). Our aim was to investigate post-prandial GLP release and its potential link to chronic inflammation, insulin secretion/sensitivity and body composition changes in CD patients.

METHODS

Fifteen patients with CD, 15 healthy controls (HC) and 15 patients with metabolic syndrome (MS) were recruited. All patients underwent assessment of body composition by means of bio-impedance followed by a meal tolerance test (MTT). Only one CD patient did not tolerate the MTT and was excluded.

RESULTS

Basal GLP-1 levels were up-regulated in CD, however, as compared to HC, stimulated GLP-1 secretion was significantly reduced in CD (-31 %, p < 0.05) as in MS (-52 %, p < 0.003). Similarly, basal GLP-2 levels were comparable to that of HC, while response to MTT in CD was virtually absent (p < 0.05). Similar fasting insulin sensitivity, estimated 1^st and 2^nd phase insulin secretion and insulinogenic index were found in CD and in HC. Post-prandial GLP secretion was positively correlated to insulin secretion indices, both in CD and MS. In CD, high-sensitive C reactive protein levels (hsCRP) and extra-cellular to intra-cellular water ratio (ECW/ICW), an index of cellular inflammation, were inversely correlated with stimulated GLP-1 (p < 0.05 and p < 0.01, respectively) levels.

CONCLUSION

CD is characterized by abnormal fasting and post-prandial GLP levels. Circulating GLP influences subclinical inflammation and glucose metabolism in CD patients, but not their body composition parameters.

Mediterranean Diet as an Antioxidant: The Impact on Metabolic Health and Overall Wellbeing

It has been established, worldwide, that non-communicable diseases such as obesity, diabetes, metabolic syndrome, and cardiovascular events account for a high percentage of morbidity and mortality in contemporary societies. Several modifiable risk factors, such as sedentary activities, sleep deprivation, smoking, and unhealthy dietary habits have contributed to this increase. Healthy nutrition in terms of adherence to the Mediterranean diet (MD), rich in fruits, legumes, vegetables, olive oil, herbs, spices, and high fiber intake may contribute to the decrease in this pandemic. The beneficial effects of the MD can be mainly attributed to its numerous components rich in anti-inflammatory and antioxidant properties. Moreover, the MD may further contribute to the improvement of reproductive health, modify the risk for neurodegenerative diseases, and protect against depression and psychosocial maladjustment. There is also evidence highlighting the impact of healthy nutrition in female people on the composition of the gut microbiota and future metabolic and overall health of their offspring. It is therefore important to highlight the beneficial effects of the MD on metabolic, reproductive, and mental health, while shaping the overall health of future generations. The beneficial effects of MD can be further enhanced by increased physical activity in the context of a well-balanced healthy lifestyle.

The Role of Fatty Acids in Ceramide Pathways and Their Influence on Hypothalamic Regulation of Energy Balance: A Systematic Review

Obesity is a global health issue for which no major effective treatments have been well established. High-fat diet consumption is closely related to the development of obesity because it negatively modulates the hypothalamic control of food intake due to metaflammation and lipotoxicity. The use of animal models, such as rodents, in conjunction with in vitro models of hypothalamic cells, can enhance the understanding of hypothalamic functions related to the control of energy balance, thereby providing knowledge about the impact of diet on the hypothalamus, in addition to targets for the development of new drugs that can be used in humans to decrease body weight. Recently, sphingolipids were described as having a lipotoxic effect in peripheral tissues and the central nervous system. Specifically, lipid overload, mainly from long-chain saturated fatty acids, such as palmitate, leads to excessive ceramide levels that can be sensed by the hypothalamus, triggering the dysregulation of energy balance control. However, no systematic review has been undertaken regarding studies of sphingolipids, particularly ceramide and sphingosine-1-phosphate (S1P), the hypothalamus, and obesity. This review confirms that ceramides are associated with hypothalamic dysfunction in response to metaflammation, endoplasmic reticulum (ER) stress, and lipotoxicity, leading to insulin/leptin resistance. However, in contrast to ceramide, S1P appears to be a central satiety factor in the hypothalamus. Thus, our work describes current evidence related to sphingolipids and their role in hypothalamic energy balance control. Hypothetically, the manipulation of sphingolipid levels could be useful in enabling clinicians to treat obesity, particularly by decreasing ceramide levels and the inflammation/endoplasmic reticulum stress induced in response to overfeeding with saturated fatty acids.

Lipidomics demonstrates the association of sex hormones with sebum

BACKGROUND

The regulation of sebocytes by hormones has been unanimously certified by scholars. But how sebocytes are affected has not been fully demonstrated by the regulation of multiple hormones.

AIMS

The regulation effect of sex hormone on sebocytes was further discussed.

PATIENTS/METHODS

Based on our previous studies, the changes of skin surface liposomes in different sex hormone levels were analyzed by comprehensive statistics.

RESULTS

We found that androgen can induce sebocytes to synthesis and secrete more fatty acids (FAs) and triglycerides (TGs) through comprehensive analysis of sebum content and composition, which is inhibited by estrogen.

CONCLUSIONS

We further confirmed the regulatory effect of hormones on sebocytes from a molecular point of view using lipidomics and found that sex hormones may dominate.

G protein-coupled receptors as potential targets for nonalcoholic fatty liver disease treatment

Nonalcoholic fatty liver disease (NAFLD) is a broad-spectrum disease, ranging from simple hepatic steatosis to nonalcoholic steatohepatitis, which can progress to cirrhosis and liver cancer. Abnormal hepatic lipid accumulation is the major manifestation of this disease, and lipotoxicity promotes NAFLD progression. In addition, intermediate metabolites such as succinate can stimulate the activation of hepatic stellate cells to produce extracellular matrix proteins, resulting in progression of NAFLD to fibrosis and even cirrhosis. G protein-coupled receptors (GPCRs) have been shown to play essential roles in metabolic disorders, such as NAFLD and obesity, through their function as receptors for bile acids and free fatty acids. In addition, GPCRs link gut microbiota-mediated connections in a variety of diseases, such as intestinal diseases, hepatic steatosis, diabetes, and cardiovascular diseases. The latest findings show that gut microbiota-derived acetate contributes to liver lipogenesis by converting dietary fructose into hepatic acetyl-CoA and fatty acids. GPCR agonists, including peptides and natural products like docosahexaenoic acid, have been applied to investigate their role in liver diseases. Therapies such as probiotics and GPCR agonists may be applied to modulate GPCR function to ameliorate liver metabolism syndrome. This review summarizes the current findings regarding the role of GPCRs in the development and progression of NAFLD and describes some preclinical and clinical studies of GPCR-mediated treatment. Overall, understanding GPCR-mediated signaling in liver disease may provide new therapeutic options for NAFLD.

Diet-induced obesity enhances postprandial glucagon-like peptide-1 secretion in Wistar rats, but not in diabetic Goto-Kakizaki rats

Glucagon-like peptide-1 (GLP-1) is postprandially secreted from enteroendocrine L-cells and enhances insulin secretion. Currently, it is still controversial whether postprandial GLP-1 responses are altered in obesity and diabetes. To address the issue and to find out possible factors related, we compared postprandial GLP-1 responses in normal rats and in diabetic rats chronically fed an obesogenic diet. Male Wistar rats and diabetic Goto-Kakizaki (GK) rats were fed either a control diet or a high-fat/high-sucrose (HFS, 30 % fat and 40 % sucrose) diet for 26 weeks. Meal tolerance tests were performed for monitoring postprandial responses after a liquid diet administration (62·76 kJ/kg body weight) every 4 or 8 weeks. Postprandial glucose, GLP-1 and insulin responses in Wistar rats fed the HFS diet (WH) were higher than Wistar rats fed the control diet (WC). Although GK rats fed the HFS diet (GH) had higher glycaemic responses than GK rats fed the control diet (GC), these groups had similar postprandial GLP-1 and insulin responses throughout the study. Jejunal and ileal GLP-1 contents were increased by the HFS diet only in Wistar rats. Furthermore, mRNA expression levels of fatty acid receptors (Ffar1) in the jejunum were mildly (P = 0·053) increased by the HFS diet in Wistar rats, but not in GK rats. These results demonstrate that postprandial GLP-1 responses are enhanced under an obesogenic status in normal rats, but not in diabetic rats. Failure of adaptive enhancement of GLP-1 response in GK rats could be partly responsible for the development of glucose intolerance.

Let-7e-5p Regulates GLP-1 Content and Basal Release From Enteroendocrine L Cells From DIO Male Mice

Characterization of enteroendocrine L cells in diabetes is critical for better understanding of the role of glucagon-like peptide-1 (GLP-1) in physiology and diabetes. We studied L-cell transcriptome changes including microRNA (miRNA) dysregulation in obesity and diabetes. We evaluated the regulation of miRNAs through microarray analyses on sorted enteroendocrine L cells from control and obese glucose-intolerant (I-HFD) and hyperglycemic (H-HFD) mice after 16 weeks of respectively low-fat diet (LFD) or high-fat diet (HFD) feeding. The identified altered miRNAs were studied in vitro using the mouse GLUTag cell line to investigate their regulation and potential biological functions. We identified that let-7e-5p, miR-126a-3p, and miR-125a-5p were differentially regulated in L cells of obese HFD mice compared with control LFD mice. While downregulation of let-7e-5p expression was observed in both I-HFD and H-HFD mice, levels of miR-126a-3p increased and of miR-125a-5p decreased significantly only in I-HFD mice compared with controls. Using miRNA inhibitors and mimics we observed that modulation of let-7e-5p expression affected specifically GLP-1 cellular content and basal release, whereas Gcg gene expression and acute GLP-1 secretion and cell proliferation were not affected. In addition, palmitate treatment resulted in a decrease of let-7e-5p expression along with an increase in GLP-1 content and release, suggesting that palmitate acts on GLP-1 through let-7e-5p. By contrast, modulation of miR-125a-5p and miR-126a-3p in the same conditions did not affect content or secretion of GLP-1. We conclude that decrease of let-7e-5p expression in response to palmitate may constitute a compensatory mechanism contributing to maintaining constant glycemia in obese mice.

Palmitate- and C6 ceramide-induced Tnnt3 pre-mRNA alternative splicing occurs in a PP2A dependent manner

Background

In a previous study, we showed that consumption of diets enriched in saturated fatty acids causes changes in alternative splicing of pre-mRNAs encoding a number of proteins in rat skeletal muscle, including the one encoding skeletal muscle Troponin T (Tnnt3). However, whether saturated fatty acids act directly on muscle cells to modulate alternative pre-mRNA splicing was not assessed. Moreover, the signaling pathway through which saturated fatty acids act to promote changes in alternative splicing is unknown. Therefore, the objective of the present study was to characterize the signaling pathway through which saturated fatty acids act to modulate Tnnt3 alternative splicing.

Methods

The effects of treatment of L6 myotubes with saturated (palmitate), mono- (oleate), or polyunsaturated (linoleate) fatty acids on alternative splicing of pre-mRNA was assessed using Tnnt3 as a marker gene.

Results

Palmitate treatment caused a two-fold change (p < 0.05) in L6 myotube Tnnt3 alternative splicing whereas treatment with either oleate or linoleate had minimal effects compared to control myotubes. Treatment with a downstream metabolite of palmitate, ceramide, had effects similar to palmitate on Tnnt3 alternative splicing and inhibition of de novo ceramide biosynthesis blocked the palmitate-induced alternative splicing changes. The effects of palmitate and ceramide on Tnnt3 alternative splicing were accompanied by a 40–50% reduction in phosphorylation of Akt on S473. However, inhibition of de novo ceramide biosynthesis did not prevent palmitate-induced Akt dephosphorylation, suggesting that palmitate may act in an Akt-independent manner to modulate Tnnt3 alternative splicing. Instead, pre-treatment with okadaic acid at concentrations that selectively inhibit protein phosphatase 2A (PP2A) blocked both palmitate- and ceramide-induced changes in Tnnt3 alternative splicing, suggesting that palmitate and ceramide act through PP2A to modulate Tnnt3 alternative splicing.

Conclusions

Overall, the data show that fatty acid saturation level and ceramides are important factors modulating alternative pre-mRNA splicing through activation of PP2A.

Electronic supplementary material

The online version of this article (10.1186/s12986-018-0326-3) contains supplementary material, which is available to authorized users.

Restoration of GLP-1 secretion by Berberine is associated with protection of colon enterocytes from mitochondrial overheating in diet-induced obese mice

Objective

L-cell dysfunction is reported for GLP-1 reduction in type 2 diabetes. However, the mechanism of dysfunction remains unknown. In this study, we examined mitochondrial function in the mechanistic study in diet-induced obese (DIO) mice.

Subjects

C57BL/6 mice were fed a high-fat diet (HFD) for 16 weeks to establish the DIO model for GLP-1 reduction. The mice were then treated with berberine (BBR) (100 mg/kg/day) for 8 weeks to test the impact on GLP-1 expression. Mitochondrial activities of the colon enterocytes were compared among three groups of mice (lean, DIO, and DIO + BBR) at the end of treatment. Gut microbiota and short-chain fatty acids (SCFAs) were examined to understand the mitochondrial responses. A cellular model treated with palmitic acid (PA) was used in the mechanism study.

Results

A reduction in GLP-1 expression was observed in DIO mice with mitochondrial stress responses in the colon enterocytes. The mitochondria exhibited cristae loss, membrane rupture, and mitochondrial swelling, which was observed with an increase in ATP abundance, complex I activity, and deficiency in the activities of complexes II and IV. Those changes were associated with dysbiosis and a reduction in SCFAs in the colon of DIO mice. In the cellular model, an increase in ATP abundance, loss of mitochondrial potential, and elevation of apoptosis were induced by PA. All of the alterations in DIO mice and the cellular model were attenuated by BBR.

Conclusion

The mitochondrial stress responses were observed in the colon enterocytes of DIO mice for GLP-1 reduction. The stress was prevented by BBR in the restoration of GLP-1 expression, in which BBR may act through direct and indirect mechanisms.