Sterol regulatory element-binding protein-1c mediates increase of postprandial stearic acid, a potential target for improving insulin resistance, in hyperlipidemia

Female mice exposed to varying ratios of stearic to palmitic acid in a high-fat diet during gestation and lactation shows differential impairments of beta-cell function

AIMS

While emerging evidence implicates an abnormal stearic-to-palmitic acid ratio in saturated fats in beta-cell dysfunction, their gestational/lactational impacts remain underexplored. This study evaluates the differential transient and long-lasting effects of high-fat diets with contrasting stearic-to-palmitic acid ratios on maternal beta-cell function.

MATERIALS AND METHODS

Female mice were fed high-fat diets with high/low stearic-to-palmitic acid ratios during gestation/lactation, followed by a recovery period and subsequent exposure to an obesogenic diet. Beta-cell function was assessed using ex-vivo glucose-stimulated insulin secretion (GSIS) and immunohistochemistry. Islets mRNA profiling was performed using RNA-sequencing.

KEY FINDINGS

Both high- and low-ratio groups showed impaired GSIS post-lactation. High-ratio-fed dams exhibited pronounced compensatory responses, including increased islet size, number, and elevated Stx1a, Stx4, Pdx1, Mafa expression. Following metabolic re-challenge, high-ratio group demonstrated more severely impaired ex vivo insulin release. No significant differences in islet apoptosis and senescence were observed between the two groups. Transcriptomic profiling, however, revealed distinct mechanistic pathways: the high-ratio diet was likely to disrupt beta-cell organelles ultrastructure, while the low-ratio diet predominantly dysregulated chemokine-mediated immune signaling networks.

SIGNIFICANCE

Gestational/lactational exposure to high-fat diets with both high and low ratios of stearic-to-palmitic acid exerts pronounced transient impacts on beta-cell function, with the high-ratio diet inducing more severe and persistent detrimental effects. These findings highlight the critical influence and importance of dietary saturated fatty acid composition in maternal metabolic programming and beta-cell vulnerability.

Impact of Olive Oil Components on the Expression of Genes Related to Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is a multifactorial metabolic disorder characterized by insulin resistance and beta cell dysfunction, resulting in hyperglycemia. Olive oil, a cornerstone of the Mediterranean diet, has attracted considerable attention due to its potential health benefits, including reducing the risk of developing T2DM. This literature review aims to critically examine and synthesize existing research regarding the impact of olive oil on the expression of genes relevant to T2DM. This paper also seeks to provide an immunological and genetic perspective on the signaling pathways of the main components of extra virgin olive oil. Key bioactive components of olive oil, such as oleic acid and phenolic compounds, were identified as modulators of insulin signaling. These compounds enhanced the insulin signaling pathway, improved lipid metabolism, and reduced oxidative stress by decreasing reactive oxygen species (ROS) production. Additionally, they were shown to alleviate inflammation by inhibiting the NF-κB pathway and downregulating pro-inflammatory cytokines and enzymes. Furthermore, these bioactive compounds were observed to mitigate endoplasmic reticulum (ER) stress by downregulating stress markers, thereby protecting beta cells from apoptosis and preserving their function. In summary, olive oil, particularly its bioactive constituents, has been demonstrated to enhance insulin sensitivity, protect beta cell function, and reduce inflammation and oxidative stress by modulating key genes involved in these processes. These findings underscore olive oil's therapeutic potential in managing T2DM. However, further research, including well-designed human clinical trials, is required to fully elucidate the role of olive oil in personalized nutrition strategies for the prevention and treatment of T2DM.

Comparison of the effects of monounsaturated fatty acids and polyunsaturated fatty acids on the lipotoxicity of islets

Background

Monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs) have been reported to combat saturated fatty acid (SFA)-induced cellular damage, however, their clinical effects on patients with metabolic diseases such as diabetes and hyperlipidemia are still controversial. Since comparative studies of the effects of these two types of unsaturated fatty acids (UFAs) are still limited. In this study, we aimed to compare the protective effects of various UFAs on pancreatic islets under the stress of SFA-induced metabolic disorder and lipotoxicity.

Methods

Rat insulinoma cell line INS-1E were treated with palmitic acid (PA) with or without UFAs including eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), arachidonic acid (AA), and oleic acid (OA) to determine cell viability, apoptosis, endoplasmic reticulum (ER) stress, and inflammatory. In vivo, male C57BL/6 mice were fed a 60% high-fat diet (HFD) for 12 w. Then the lard in HFD was partially replaced with fish oil (FO) and olive oil (OO) at low or high proportions of energy (5% or 20%) to observe the ameliorative effects of the UFA supplement.

Results

All UFAs significantly improved PA-induced cell viability impairment in INS-1E cells, and their alleviation on PA induced apoptosis, ER stress and inflammation were confirmed. Particularly, OA had better effects than EPA, DHA, and AA on attenuating cellular ER stress. In vivo, the diets with a low proportion of UFAs (5% of energy) had limited effects on HFD induced metabolic disorder, except for a slight improved intraperitoneal glucose tolerance in obese mice. However, when fed diets containing a high proportion of UFAs (20% of energy), both the FO and OO groups exhibited substantially improved glucose and lipid metabolism, such as decrease in total cholesterol (TC), low-density lipoprotein (LDL), fasting blood glucose (FBG), and fasting blood insulin (FBI)) and improvement of insulin sensitivity evidenced by intraperitoneal glucose tolerance test (IPGTT) and intraperitoneal insulin tolerance test (IPITT). Unexpectedly, FO resulted in abnormal elevation of the liver function index aspartate aminotransferase (AST) in serum. Pathologically, OO attenuated HFD-induced compensatory hyperplasia of pancreatic islets, while this effect was not obvious in the FO group.

Conclusions

Both MUFAs and PUFAs can effectively protect islet β cells from SFA-induced cellular lipotoxicity. In particular, both OA in vitro and OO in vivo showed superior activities on protecting islets function and enhance insulin sensitivity, suggesting that MUFAs might have greater potential for nutritional intervention on diabetes.

Palmitoylation-driven PHF2 ubiquitination remodels lipid metabolism through the SREBP1c axis in hepatocellular carcinoma

Palmitic acid (PA) is the most common fatty acid in humans and mediates palmitoylation through its conversion into palmitoyl coenzyme A. Although palmitoylation affects many proteins, its pathophysiological functions are only partially understood. Here we demonstrate that PA acts as a molecular checkpoint of lipid reprogramming in HepG2 and Hep3B cells. The zinc finger DHHC-type palmitoyltransferase 23 (ZDHHC23) mediates the palmitoylation of plant homeodomain finger protein 2 (PHF2), subsequently enhancing ubiquitin-dependent degradation of PHF2. This study also reveals that PHF2 functions as a tumor suppressor by acting as an E3 ubiquitin ligase of sterol regulatory element-binding protein 1c (SREBP1c), a master transcription factor of lipogenesis. PHF2 directly destabilizes SREBP1c and reduces SREBP1c-dependent lipogenesis. Notably, SREBP1c increases free fatty acids in hepatocellular carcinoma (HCC) cells, and the consequent PA induction triggers the PHF2/SREBP1c axis. Since PA seems central to activating this axis, we suggest that levels of dietary PA should be carefully monitored in patients with HCC.

Targeted and untargeted metabolomic approach for GDM diagnosis

Gestational diabetes mellitus (GDM) is a disorder which manifests itself for the first time during pregnancy and is mainly connected with glucose metabolism. It is also known that fatty acid profile changes in erythrocyte membranes and plasma could be associated with obesity and insulin resistance. These factors can lead to the development of diabetes. In the reported study, we applied the untargeted analysis of plasma in GDM against standard glucose-tolerant (NGT) women to identify the differences in metabolomic profiles between those groups. We found higher levels of 2-hydroxybutyric and 3-hydroxybutyric acids. Both secondary metabolites are associated with impaired glucose metabolism. However, they are products of different metabolic pathways. Additionally, we applied lipidomic profiling using gas chromatography to examine the fatty acid composition of cholesteryl esters in the plasma of GDM patients. Among the 14 measured fatty acids characterizing the representative plasma lipidomic cluster, myristic, oleic, arachidonic, and α-linoleic acids revealed statistically significant changes. Concentrations of both myristic acid, one of the saturated fatty acids (SFAs), and oleic acid, which belong to monounsaturated fatty acids (MUFAs), tend to decrease in GDM patients. In the case of polyunsaturated fatty acids (PUFAs), some of them tend to increase (e.g., arachidonic), and some of them tend to decrease (e.g., α-linolenic). Based on our results, we postulate the importance of hydroxybutyric acid derivatives, cholesteryl ester composition, and the oleic acid diminution in the pathophysiology of GDM. There are some evidence suggests that the oleic acid can have the protective role in diabetes onset. However, metabolic alterations that lead to the onset of GDM are complex; therefore, further studies are needed to confirm our observations.

Inhibition of miR-146a-5p and miR-8114 in Insulin-Secreting Cells Contributes to the Protection of Melatonin against Stearic Acid-Induced Cellular Senescence by Targeting Mafa

BACKGRUOUND

Chronic exposure to elevated levels of saturated fatty acids results in pancreatic β-cell senescence. However, targets and effective agents for preventing stearic acid-induced β-cell senescence are still lacking. Although melatonin administration can protect β-cells against lipotoxicity through anti-senescence processes, the precise underlying mechanisms still need to be explored. Therefore, we investigated the anti-senescence effect of melatonin on stearic acid-treated mouse β-cells and elucidated the possible role of microRNAs in this process.

METHODS

β-Cell senescence was identified by measuring the expression of senescence-related genes and senescence-associated β-galactosidase staining. Gain- and loss-of-function approaches were used to investigate the involvement of microRNAs in stearic acid-evoked β-cell senescence and dysfunction. Bioinformatics analyses and luciferase reporter activity assays were applied to predict the direct targets of microRNAs.

RESULTS

Long-term exposure to a high concentration of stearic acid-induced senescence and upregulated miR-146a-5p and miR- 8114 expression in both mouse islets and β-TC6 cell lines. Melatonin effectively suppressed this process and reduced the levels of these two miRNAs. A remarkable reversibility of stearic acid-induced β-cell senescence and dysfunction was observed after silencing miR-146a-5p and miR-8114. Moreover, V-maf musculoaponeurotic fibrosarcoma oncogene homolog A (Mafa) was verified as a direct target of miR-146a-5p and miR-8114. Melatonin also significantly ameliorated senescence and dysfunction in miR-146a-5pand miR-8114-transfected β-cells.

CONCLUSION

These data demonstrate that melatonin protects against stearic acid-induced β-cell senescence by inhibiting miR-146a- 5p and miR-8114 and upregulating Mafa expression. This not only provides novel targets for preventing stearic acid-induced β-cell dysfunction, but also points to melatonin as a promising drug to combat type 2 diabetes progression.

Empagliflozin activates Sestrin2-mediated AMPK/mTOR pathway and ameliorates lipid accumulation in obesity-related nonalcoholic fatty liver disease

Empagliflozin (EMPA) therapy has led to improvements in patients with non-alcoholic fatty liver disease (NAFLD). Sestrin2 is a stress-inducible protein that controls the AMPK-mTOR pathway and inhibits oxidative damage in cells. This study investigated the functional implications of EMPA on the multifactorial pathogenesis of NAFLD and potential underlying molecular mechanisms of pathogenesis. An in vitro model of NAFLD was established by treating HepG2 cells with palmitic acid (PA); an in vivo model of NAFLD was generated by feeding C57BL/6 mice a high-fat diet. Investigations of morphology and lipid deposition in liver tissue were performed. Expression patterns of Sestrin2 and genes related to lipogenesis and inflammation were assessed by reverse transcription polymerase chain reaction. Protein levels of Sestrin2 and AMPK/mTOR pathway components were detected by Western blotting. NAFLD liver tissues and PA-stimulated HepG2 cells exhibited excessive lipid production and triglyceride secretion, along with upregulation of Sestrin2 and increased expression of lipogenesis-related genes. EMPA treatment reversed liver damage by upregulating Sestrin2 and activating the AMPK-mTOR pathway. Knockdown of Sestrin2 effectively increased lipogenesis and enhanced the mRNA expression levels of lipogenic and pro-inflammatory genes in PA-stimulated HepG2 cells; EMPA treatment did not affect these changes. Furthermore, Sestrin2 knockdown inhibited AMPK-mTOR signaling pathway activity. The upregulation of Sestrin2 after treatment with EMPA protects against lipid deposition-related metabolic disorders; it also inhibits lipogenesis and inflammation through activation of the AMPK-mTOR signaling pathway. These results suggest that Sestrin2 can be targeted by EMPA therapy to alleviate lipogenesis and inflammation in obesity-related NAFLD.

Postprandial Free Fatty Acids at Mid-Pregnancy Increase the Risk of Large-for-Gestational-Age Newborns in Women with Gestational Diabetes Mellitus

BACKGROUND

To investigate the association between free fatty acid (FFA) level at mid-pregnancy and large-for-gestational-age (LGA) newborns in women with gestational diabetes mellitus (GDM).

METHODS

We enrolled 710 pregnant women diagnosed with GDM from February 2009 to October 2016. GDM was diagnosed by a 'two-step' approach with Carpenter and Coustan criteria. We measured plasma lipid profiles including fasting and 2-hour postprandial FFA (2h-FFA) levels at mid-pregnancy. LGA was defined if birthweights of newborns were above the 90th percentile for their gestational age.

RESULTS

Mean age of pregnant women in this study was 33.1 years. Mean pre-pregnancy body mass index (BMI) was 22.4 kg/m2. The prevalence of LGA was 8.3% (n=59). Levels of 2h-FFA were higher in women who delivered LGA newborns than in those who delivered non-LGA newborns (416.7 μEq/L vs. 352.5 μEq/L, P=0.006). However, fasting FFA was not significantly different between the two groups. The prevalence of delivering LGA newborns was increased with increasing tertile of 2h-FFA (T1, 4.3%; T2, 9.8%; T3, 10.7%; P for trend <0.05). After adjustment for maternal age, pre-pregnancy BMI, and fasting plasma glucose, the highest tertile of 2h-FFA was 2.38 times (95% confidence interval, 1.11 to 5.13) more likely to have LGA newborns than the lowest tertile. However, there was no significant difference between groups according to fasting FFA tertiles.

CONCLUSION

In women with GDM, a high 2h-FFA level (but not fasting FFA) at mid-pregnancy is associated with an increasing risk of delivering LGA newborns.

Homocysteine inhibits pro-insulin receptor cleavage and causes insulin resistance via protein cysteine-homocysteinylation

Elevation in homocysteine (Hcy) level is associated with insulin resistance; however, the causality between them and the underlying mechanism remain elusive. Here, we show that Hcy induces insulin resistance and causes diabetic phenotypes by protein cysteine-homocysteinylation (C-Hcy) of the pro-insulin receptor (pro-IR). Mechanistically, Hcy reacts and modifies cysteine-825 of pro-IR in the endoplasmic reticulum (ER) and abrogates the formation of the original disulfide bond. C-Hcy impairs the interaction between pro-IR and the Furin protease in the Golgi apparatus, thereby hindering the cleavage of pro-IR. In mice, an increase in Hcy level decreases the mature IR level in various tissues, thereby inducing insulin resistance and the type 2 diabetes phenotype. Furthermore, inhibition of C-Hcy in vivo and in vitro by overexpressing protein disulfide isomerase rescues the Hcy-induced phenotypes. In conclusion, C-Hcy in the ER can serve as a potential pharmacological target for developing drugs to prevent insulin resistance and increase insulin sensitivity.

Inhibition of lncRNA TCONS_00077866 Ameliorates the High Stearic Acid Diet-Induced Mouse Pancreatic β-Cell Inflammatory Response by Increasing miR-297b-5p to Downregulate SAA3 Expression

Long-term consumption of a high-fat diet increases the circulating concentration of stearic acid (SA), which has a potent toxic effect on β-cells, but the underlying molecular mechanisms of this action have not been fully elucidated. Here, we evaluated the role of long noncoding (lnc)RNA TCONS_00077866 (lnc866) in SA-induced β-cell inflammation. lnc866 was selected for study because lncRNA high-throughput sequencing analysis demonstrated it to have the largest fold-difference in expression of five lncRNAs that were affected by SA treatment. Knockdown of lnc866 by virus-mediated shRNA expression in mice or by Smart Silencer in mouse pancreatic β-TC6 cells significantly inhibited the SA-induced reduction in insulin secretion and β-cell inflammation. According to lncRNA-miRNAs-mRNA coexpression network analysis and luciferase reporter assays, lnc866 directly bound to miR-297b-5p, thereby preventing it from reducing the expression of its target serum amyloid A3 (SAA3). Furthermore, overexpression of miR-297b-5p or inhibition of SAA3 also had marked protective effects against the deleterious effects of SA in β-TC6 cells and mouse islets. In conclusion, lnc866 silencing ameliorates SA-induced β-cell inflammation by targeting the miR-297b-5p/SAA3 axis. lnc866 inhibition may represent a new strategy to protect β-cells against the effects of SA during the development of type 2 diabetes.

TCONS_00230836 silencing restores stearic acid-induced β cell dysfunction through alleviating endoplasmic reticulum stress rather than apoptosis

BACKGROUND

Chronic exposure of pancreatic β cells to high levels of stearic acid (C18:0) leads to impaired insulin secretion, which accelerates the progression of type 2 diabetes mellitus (T2DM). Recently, long noncoding RNAs (lncRNAs) were found to participate in saturated fatty acid-induced metabolism dysfunction. However, their contribution to stearic acid-induced β-cell dysfunction remains largely unknown. This study evaluated the possible role of the lncRNA TCONS_00230836 in stearic acid-stimulated lipotoxicity to β cells.

METHOD

Using high-throughput RNA-sequencing, TCONS_00230836 was screened out as being exclusively differentially expressed in stearic acid-treated mouse β-TC6 cells. Co-expression network was constructed to reveal the potential mRNAs targeted for lncRNA TCONS_00230836. Changes in this lncRNA's and candidate mRNAs' levels were further assessed by real-time PCR in stearic acid-treated β-TC6 cells and islets of mice fed a high-stearic-acid diet (HSD). The localization of TCONS_00230836 was detected by fluorescent in situ hybridization. The endogenous lncRNA TCONS_00230836 in β-TC6 cells was abrogated by its Smart Silencer.

RESULTS

TCONS_00230836 was enriched in mouse islets and mainly localized in the cytoplasm. Its expression was significantly increased in stearic acid-treated β-TC6 cells and HSD-fed mouse islets. Knockdown of TCONS_00230836 significantly restored stearic acid-impaired glucose-stimulated insulin secretion through alleviating endoplasmic reticulum stress. However, stearic acid-induced β cell apoptosis was not obviously recovered.

CONCLUSION

Our findings suggest the involvement of TCONS_00230836 in stearic acid-induced β-cell dysfunction, which provides novel insight into stearic acid-induced lipotoxicity to β cells. Anti-lncRNA TCONS_00230836 might be a new therapeutic strategy for alleviating stearic acid-induced β-cell dysfunction in the progression of T2DM.

Effects of Agaricus blazei Murrill polysaccharides on hyperlipidemic rats by regulation of intestinal microflora

The present research envisaged the effects of Agaricus blazei Murrill polysaccharides (ABPs) on blood lipids and its role in regulation of the intestinal microflora in hyperlipidemic rats. The acidic polysaccharide fraction of Agaricus blazei Murrill was obtained by DEAE-cellulose ion exchange column chromatography. The sugar content of ABP was 75.1%. Compared with the model group (MG), the serum TC, TG, and LDL-C levels decreased (p < .05 or p < .01) and the HDL-C levels increased (p < .01) significantly in the ABP group. Expression of CYP7A1 was up-regulated (p < .01), and that of SREBP-1C (p < .05) was down-regulated significantly in the liver tissue of rats in the ABP group. Additionally, the disordered hepatic lobules and the steatosis of hepatocytes were found to be significantly alleviated in the ABP group. We believe that ABP can reduce the ratio of Firmicutes/Bacteroidetes and reduce the relative abundance of Firmicutes, Ruminococcaceae_unclassified, and Ruminococcaceae, increasing the relative abundance of Proteobacteria, Clostridium_sensu_stricto, Allobaculum, Peptostreptococcaceae, Clostridiaceae_1, and Erysipelotrichaceae as targets to regulate blood lipids. The results showed ABP could regulate the dyslipidemia in rats with hyperlipidemia. The mechanism may be through the regulation of the imbalance of intestinal microflora induced by the high-fat diet in rats, which may be one of the important ways of its intervention on the dyslipidemia induced by high-fat diet.

Glucose challenge metabolomics implicates the change of organic acid profiles in hyperlipidemic subjects

Hyperlipidemia (HLP) is a major risk factor of diabetes and cardiovascular disease. Here, we applied gas chromatography-mass spectrometry to study differences in postprandial organic acid profiles in healthy and HLP subjects. In fasting status, six intermediates of the tricarboxylic acid cycle showed significant differences in HLP and healthy controls (P < 0.05). The percentage changes of 17 metabolites including three intermediates of the tricarboxylic acid cycle were significantly different during the oral glucose tolerance test. Postprandial changes in ethylmalonic acid and pimelic acid were negatively associated with HOMA-IR (homeostasis model assessment of insulin resistance; all P < 0.05) in the HLP group. Postprandial metabolism of organic acid profiles revealed energy metabolism perturbations in HLP. Our findings provide new insights into the complex physiological regulation of HLP postprandial metabolism.

Overexpression of miR-297b-5p protects against stearic acid-induced pancreatic β-cell apoptosis by targeting LATS2

Chronic exposure to high concentrations of stearic acid (C18:0) can result in β-cell dysfunction, leading to development of type 2 diabetes. However, the molecular mechanisms underlying the destructive effects of stearic acid on β-cells remain largely unknown. In this study, we aimed to investigate the role of miR-297b-5p on stearic acid-induced β-cell apoptosis. Differential expression of microRNAs (miRNAs) was assessed in a β-TC6 cell line exposed to stearic acid, palmitic acid, or a normal culture medium by high-throughput sequencing. The apoptosis rate was measured by flow cytometry after miR-297b-5p mimic/inhibitor transfection, and large-tumor suppressor kinase 2 (LATS2) was identified as a target of miR-297b-5p using a luciferase activity assay. In vivo, C57BL/6 mice were fed with normal and high-stearic-acid diet, respectively. Mouse islets were used for similar identification of miR-297b-5p and Lats2 in β-TC6 cell. We selected two differentially expressed miRNAs in stearic acid compared with those in the palmitic acid and control groups. miR-297b-5p expression was significantly lower in β-TC6 cells and mouse islets in stearic acid than in control group. Upregulation of miR-297b-5p alleviated the stearic acid-induced cell apoptosis and reduction in insulin secretion by inhibiting Lats2 expression in vitro. Meanwhile, silencing Lats2 significantly reversed the stearic acid-stimulated β-cell dysfunction in both β-TC6 cells and islets. Our findings indicate a suppressive role for miR-297b-5p in stearic acid-induced β-cell apoptosis, which may reveal a potential target for the treatment of β-cell dysfunction in the pathogenesis of type 2 diabetes.

Metabolomics Study of Metabolic Changes in Renal Cells in Response to High-Glucose Exposure Based on Liquid or Gas Chromatography Coupled With Mass Spectrometry

Diabetic nephropathy (DN) is one of the most serious microvascular complications and the leading causes of death in diabetes mellitus (DM). To find biomarkers for prognosing the occurrence and development of DN has significant clinical value for its prevention, diagnosis, and treatment. In this study, a non-targeted cell metabolomics–based ultra-performance liquid chromatography coupled with quadrupole time of flight mass spectrometry and gas chromatography coupled with mass spectrometry was developed and performed the dynamic metabolic profiles of rat renal cells including renal tubular epithelial cells (NRK-52E) and glomerular mesangial cells (HBZY-1) in response to high glucose at time points of 12 h, 24 h, 36 h, and 48 h. Some potential biomarkers were then verified using clinical plasma samples collected from 55 healthy volunteers, 103 DM patients, and 57 DN patients. Statistical methods, such as principal component analysis and partial least squares to latent structure-discriminant analysis were recruited for data analyses. As a result, palmitic acid and linoleic acid (all-cis-9,12) were the potential indicators for the occurrence and development of DN, and valine, leucine, and isoleucine could be used as the prospective biomarkers for DM. In addition, rise and fall of leucine and isoleucine levels in plasma could be used for prognosing DN in DM patients. Through this study, we established a novel non-targeted cell dynamic metabolomics platform and identified potential biomarkers that may be applied for the diagnosis and prognosis of DM and DN.

Impact of GPR1 signaling on maternal high-fat feeding and placenta metabolism in mice

Chemerin and G protein-coupled receptor 1 (GPR1) are increased in serum and placenta in mice during pregnancy. Interestingly, we observed increased serum chemerin levels and decreased GPR1 expression in placenta of high-fat-diet-fed mice compared with chow-fed mice at gestational day 18. GPR1 protein and gene levels were significantly decreased in gestational diabetes mellitus (GDM) patient placentas. Therefore, we hypothesized that chemerin/GPR1 signaling might participate in the pathogenic mechanism of GDM. We investigated the role of GPR1 in carbohydrate homeostasis during pregnancy using pregnant mice transfected with small interfering RNA for GPR1 or a negative control. GPR1 knockdown exacerbated glucose intolerance, disrupted lipid metabolism, and decreased β-cell proliferation and insulin levels. Glucose transport protein-3 and fatty acid binding protein-4 were downregulated with reducing GPR1 in vivo and in vitro via phosphorylated AKT pathway. Taken together, our findings first demonstrate the expression of GPR1, the characterization of its direct biological effects in humans and mice, as well as the molecular mechanism that indicates the role of GPR1 signaling in maternal metabolism during pregnancy, suggesting a novel feedback mechanism to regulate glucose balance during pregnancy, and GPR1 could be a potential target for the detection and therapy of GDM.

Effects of liraglutide on lipolysis and the AC3/PKA/HSL pathway

BACKGROUND

Liraglutide reduces blood glucose, body weight and blood lipid levels. Hormone-sensitive lipase (HSL) is a key enzyme in lipolysis. Evidence from our and other studies have demonstrated that adenylate cyclase 3 (AC3) is associated with obesity and can be upregulated by liraglutide in obese mice. In the present study, we investigated whether hepatic HSL activity is regulated by liraglutide and characterized the effect of liraglutide in the AC3/protein kinase A (PKA)/HSL signalling pathway.

METHODS

Obese mice or their lean littermates were treated with liraglutide or saline for 8 weeks. Serum was collected for the measurement of insulin and lipids. We investigated hepatic AC3, HSL and phosphorylated HSL Ser-660 (p-HSL(S660)) protein expression levels andAC3 and HSL mRNA expression levels and cyclic adenosine monophosphate (cAMP), PKA activity in liver tissue.

RESULTS

Liraglutide treatment decreased triglycerides (TGs) and free fatty acids (FFAs), increased glycerol, and upregulated hepatic AC3 and p-HSL(s660) levels and cAMP and PKA activities.

CONCLUSION

The results suggest that liraglutide can upregulates AC3/PKA/HSL pathway and may promotes lipolysis.

Postprandial Saturated Fatty Acids Increase the Risk of Type 2 Diabetes: A Cohort Study in a Chinese Population

CONTEXT

Experimental evidence suggests saturated fatty acids (SFAs) are associated with insulin resistance, but results from epidemiological studies on fasting SFAs-diabetes risk are inconsistent.

OBJECTIVE

We investigated SFA (fasting and 2-hour postprandial) profiles and diabetes risk.

DESIGN SETTING

A total of 8940 participants were recruited for the Harbin People's Health Study in 2008. Serum SFAs (fasting and 2-hour postprandial) at baseline in Chinese men and women without diabetes were profiled, and type 2 diabetes was ascertained using World Health Organization criteria after 4 to 7 years of follow-up.

OUTCOME

Associations between 2-hour postprandial SFA (2h-SFA) and diabetes.

RESULTS

At baseline, incident cases of diabetes were older with a higher body mass index and waist circumference. After a mean follow-up of 6.7 years, 658 incident cases of diabetes occurred. After propensity score computation and inverse probability of treatment weighting (IPTW) estimation, fasting SFAs were unrelated to diabetes risk but IPTW-adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for the highest tertile of 2-hour postprandial stearic acid (2h-SA), 2-hour postprandial palmitic acid (2h-PA), and 2h-SFA for diabetes risk were 2.50 (2.08 to 3.16), 1.56 (1.23 to 2.02), and 1.70 (1.34 to 2.17), respectively (P-trend < 0.0001). Similarly, 2h-SA/fasting SA, 2h-PA/fasting PA, and 2h-SFA/fasting SFA ratios [IPTW-adjusted OR (95% CI): 2.94 (2.39 to 3.58), 2.31 (1.80 to 2.93), and 2.42 (1.91 to 3.11), respectively; P-trend < 0.0001] predicted the diabetes risk.

CONCLUSIONS

Higher serum 2h-SFA (but not fasting SFA) independently predicted diabetes risk.

Liraglutide reduces body weight by upregulation of adenylate cyclase 3

Objective:

According to recent studies, adenylate cyclase 3 (AC3) is associated with obesity. Liraglutide reduces blood glucose levels and body weight (BW). We performed a 2 × 2 factorial experiment to study the relationships among AC3, liraglutide and obesity and to obtain a more comprehensive understanding of the mechanisms underlying the physiological effects of liraglutide on obesity.

Methods:

A high-fat diet was used to induce obesity in C57BL/6J mice. Both the normal and obese mice were treated with liraglutide (1 mg kg⁻¹) or saline twice daily for 8 weeks. The hepatic levels of the AC3 and glucagon-like peptide receptor (GLP-1R) mRNAs and proteins were measured by quantitative real-time PCR and western blotting, respectively. The serum AC3 levels were detected using a rat/mouse AC3 enzyme-linked immunosorbent assay kit.

Results:

The administration of liraglutide significantly decreased the BW in obese mice and normal control mice. The BW of obese mice exhibited a more obvious decrease. Hepatic AC3 mRNA and protein levels and serum AC3 levels were significantly reduced in obese mice compared with those in normal control mice. The administration of liraglutide significantly increased the hepatic expression of the AC3 and GLP-1R mRNAs and proteins and serum AC3 levels. The hepatic expression of the AC3 mRNA and protein and serum AC3 levels were negatively correlated with BW loss in the liraglutide-treated group. Pearson’s correlation coefficients for these comparisons are r=−0.448, P=0.048; r=−0.478, P=0.046; and r=−0.909, P=0.000, respectively.

Conclusions:

Based on our research, liraglutide reduces BW, possibly by increasing the expression of AC3.

The Development of Diabetes after Subtotal Gastrectomy with Billroth II Anastomosis for Peptic Ulcer Disease

PURPOSE

A duodenal bypass after a Roux-en-Y gastric bypass operation for obesity can ameliorate the development of diabetes mellitus (DM). We attempted to determine the subsequent risk of developing DM after subtotal gastrectomy with Billroth II anastomosis (SGBIIA) for peptic ulcer disease (PUD).

METHODS

We identified 662 patients undergoing SGBIIA for PUD between 2000 and 2011 from the Longitudinal Health Insurance Database as the study cohort, and we randomly selected 2647 controls from the peptic ulcer population not undergoing SGBIIA and were frequency-matched by age, sex, and index year for the control cohort. All patient cases in both cohorts were followed until the end of 2011 to measure the incidence of DM. We analyzed DM risk by using a Cox proportional hazards regression model.

RESULTS

The patients who underwent SGBIIA demonstrated a lower cumulative incidence of DM compared with the control cohort (log-rank test, P < .001 and 6.73 vs 12.6 per 1000 person-y). The difference in the DM risk between patients with and without SGBIIA increased gradually with the follow-up duration. Age and sex did not affect the subsequent risk of developing DM, according to the multivariable Cox regression model. Nevertheless, the SGBIIA cohort exhibited a lower DM risk after we adjusted for the comorbidities of hypertension, hyperlipidemia, and coronary artery disease (adjusted hazard ratio (aHR): 0.56, 95% confidence interval (CI): 0.40-0.78). The incidence rate ratio (IRR) of DM in the SGBIIA cohort was lower than that in the control cohort for all age groups (age ≤ 49 y, IRR: 0.40, 95% CI: 0.16-0.99; age 50-64 y, IRR: 0.54, 95% CI: 0.31-0.96; age ≧ 65 y, IRR: 0.57, 95% CI: 0.36-0.91). Moreover, the IRR of DM was significantly lower in the SGBIIA cohort with comorbidities (IRR: 0.50, 95% CI: 0.31-0.78) compared with those without a comorbidity (IRR: 0.65, 95% CI: 0.40-1.04).

CONCLUSION

The findings of this population-based cohort study revealed that SGBIIA was associated with a reduced risk of DM development, and the inverse association was greater in the presence of a comorbidity.

Prevention of diet-induced hepatic steatosis and hepatic insulin resistance by second generation antisense oligonucleotides targeted to the longevity gene mIndy (Slc13a5)

Reducing the expression of the Indy (I'm Not Dead Yet) gene in lower organisms extends life span by mechanisms resembling caloric restriction. Similarly, deletion of the mammalian homolog, mIndy (Slc13a5), encoding for a plasma membrane tricarboxylate transporter, protects from aging- and diet-induced adiposity and insulin resistance in mice. The organ specific contribution to this phenotype is unknown. We examined the impact of selective inducible hepatic knockdown of mIndy on whole body lipid and glucose metabolism using 2′-O-methoxyethyl chimeric anti-sense oligonucleotides (ASOs) in high-fat fed rats. 4-week treatment with 2′-O-methoxyethyl chimeric ASO reduced mIndy mRNA expression by 91% (P<0.001) compared to control ASO. Besides similar body weights between both groups, mIndy-ASO treatment lead to a 74% reduction in fasting plasma insulin concentrations as well as a 35% reduction in plasma triglycerides. Moreover, hepatic triglyceride content was significantly reduced by the knockdown of mIndy, likely mediating a trend to decreased basal rates of endogenous glucose production as well as an increased suppression of hepatic glucose production by 25% during a hyperinsulinemic-euglycemic clamp. Together, these data suggest that inducible liver-selective reduction of mIndy in rats is able to ameliorate hepatic steatosis and insulin resistance, conditions occurring with high calorie diets and during aging.

Lack of association between SREBF-1c gene polymorphisms and risk of non-alcoholic fatty liver disease in a Chinese Han population

The transcription factor sterol regulatory element-binding protein-1c (SREBP-1c) is a key regulator of lipogenesis and insulin sensitivity, and is associated with non-alcoholic fatty liver disease (NAFLD). Here, we assessed the impact of common single nucleotide polymorphisms (SNPs) in SREBF-1c on NAFLD susceptibility and associated metabolic phenotypes in a Han Chinese population. Four common SNPs (rs62064119, rs2297508, rs11868035 and rs13306741) in the SREBP-1c gene were selected and genotyped in 593 patients with NAFLD and 593 healthy controls. Unconditional logistic regression was performed to assess the risk of NAFLD by determining odds ratios and 95% confidence intervals (CIs). No significant differences in genotype and allele frequencies of these four SNPs were found between the NAFLD population and the controls (all P > 0.05). In addition, we did not find any association between the SREBF-1c SNPs and the clinical and biochemical parameters, such as body mass index, total cholesterol, high density lipoprotein-and low density lipoprotein-cholesterol or systolic and diastolic blood pressure, except that the rs2297508 C-allele or rs11868035 G-allele showed significant associations with lower triglyceride levels in control subjects (P < 0.01). Our findings suggested that the four polymorphisms in SREBF-1c gene are not associated with risk of NAFLD in the Chinese Han population.

SREBP1c-CRY1 signalling represses hepatic glucose production by promoting FOXO1 degradation during refeeding

SREBP1c is a key lipogenic transcription factor activated by insulin in the postprandial state. Although SREBP1c appears to be involved in suppression of hepatic gluconeogenesis, the molecular mechanism is not thoroughly understood. Here we show that CRY1 is activated by insulin-induced SREBP1c and decreases hepatic gluconeogenesis through FOXO1 degradation, at least, at specific circadian time points. SREBP1c^−/− and CRY1^−/− mice show higher blood glucose than wild-type (WT) mice in pyruvate tolerance tests, accompanied with enhanced expression of PEPCK and G6Pase genes. CRY1 promotes degradation of nuclear FOXO1 by promoting its binding to the ubiquitin E3 ligase MDM2. Although SREBP1c fails to upregulate CRY1 expression in db/db mice, overexpression of CRY1 attenuates hyperglycaemia through reduction of hepatic FOXO1 protein and gluconeogenic gene expression. These data suggest that insulin-activated SREBP1c downregulates gluconeogenesis through CRY1-mediated FOXO1 degradation and that dysregulation of hepatic SREBP1c-CRY1 signalling may contribute to hyperglycaemia in diabetic animals.

The clock protein Cry regulates hepatic glucose metabolism. Here the authors show that SREBP1c, activated by insulin signalling after feeding, directly regulates Cry transcription at specific circadian time points, and that Cry represses hepatic glucose production by promoting proteasomal degradation of Foxo1.

Decreasing high postprandial stearic acid in impaired fasting glucose by dietary regulation

BACKGROUND/OBJECTIVES

The objective of this study was to determine the postprandial change in free fatty acid (FFA) profiles in subjects with impaired fasting glucose (IFG), and to evaluate the effect of low glycemic index (GI) load on postprandial FFA profiles and inflammation.

SUBJECTS/METHODS

First, 50 IFG and 50 healthy subjects were recruited; and 2 -h postprandial changes in FFA profiles were determined. Second, the 50 IFG subjects then received three different loads: glucose load (GL), high glycemic index (HGI) load and low glycemic index (LGI) load, respectively. FFA profile, glucose, insulin, glucagon-like peptide 1 (GLP-1) and inflammatory biomarkers were assayed at 0, 30, 60, 90 and 120 min.

RESULTS

Postprandial stearic acid (C18:0) increased compared with baseline in all subjects, whereas the change in postprandial C18:0 was more marked in IFG subjects than in healthy subjects. Compared with subjects who received the GL and HGI load, the area under the curve for insulin, GLP-1, C18:0 and tumor necrosis factor-alpha significantly decreased and adiponectin increased in subjects who received the LGI load.

CONCLUSIONS

The rise in postprandial C18:0 in IFG subjects was inhibited by LGI load.

Amino Acid and Biogenic Amine Profile Deviations in an Oral Glucose Tolerance Test: A Comparison between Healthy and Hyperlipidaemia Individuals Based on Targeted Metabolomics

Hyperlipidemia (HLP) is characterized by a disturbance in lipid metabolism and is a primary risk factor for the development of insulin resistance (IR) and a well-established risk factor for cardiovascular disease and atherosclerosis. The aim of this work was to investigate the changes in postprandial amino acid and biogenic amine profiles provoked by an oral glucose tolerance test (OGTT) in HLP patients using targeted metabolomics. We used ultra-high-performance liquid chromatography-triple quadrupole mass spectrometry to analyze the serum amino acid and biogenic amine profiles of 35 control and 35 HLP subjects during an OGTT. The amino acid and biogenic amine profiles from 30 HLP subjects were detected as independent samples to validate the changes in the metabolites. There were differences in the amino acid and biogenic amine profiles between the HLP individuals and the healthy controls at baseline and after the OGTT. The per cent changes of 13 metabolites from fasting to the 2 h samples during the OGTT in the HLP patients were significantly different from those of the healthy controls. The lipid parameters were associated with the changes in valine, isoleucine, creatine, creatinine, dimethylglycine, asparagine, serine, and tyrosine (all p < 0.05) during the OGTT in the HLP group. The postprandial changes in isoleucine and γ-aminobutyric acid (GABA) during the OGTT were positively associated with the homeostasis model assessment of insulin resistance (HOMA-IR; all p < 0.05) in the HLP group. Elevated oxidative stress and disordered energy metabolism during OGTTs are important characteristics of metabolic perturbations in HLP. Our findings offer new insights into the complex physiological regulation of metabolism during the OGTT in HLP.

Elevated circulating stearic acid leads to a major lipotoxic effect on mouse pancreatic beta cells in hyperlipidaemia via a miR-34a-5p-mediated PERK/p53-dependent pathway

AIMS/HYPOTHESIS

Serum stearic acid (C18:0) is elevated in individuals with hyperlipidaemia and type 2 diabetes. However, the lipotoxicity induced by increased stearic acid in beta cells has not been well described. This study aimed to examine the adverse effects of stearic acid on beta cells and the potential mechanisms through which these are mediated.

METHODS

Three groups of C57BL/6 mice were fed a normal diet or a high-stearic-acid/high-palmitic-acid diet for 24 weeks, respectively. The microRNA (miR) profiles of islets were determined by microarray screening. Islet injury was detected with co-staining using the TUNEL assay and insulin labelling. A lentiviral vector expressing anti-miRNA-34a-5p oligonucleotide (AMO-34a-5p) was injected into mice via an intraductal pancreatic route.

RESULTS

In both mouse islets and cultured rat insulinoma INS-1 cells, stearic acid exhibited a stronger lipotoxic role than other fatty acids, owing to repression of B cell CLL/lymphoma 2 (BCL-2) and BCL-2-like 2 (BCL-W) by stearic acid stimulation of miR-34a-5p. The stearic-acid-induced lipotoxicity and reduction in insulin secretion were alleviated by AMO-34a-5p. Further investigations in INS-1 cells revealed that p53 was involved in stearic-acid-induced elevation of miR-34a-5p, owing in part to activation of protein kinase-like endoplasmic reticulum kinase (PERK). Conversely, silencing PERK alleviated stearic-acid-induced p53, miR-34a-5p and lipotoxicity.

CONCLUSIONS/INTERPRETATION

These findings provide new insight for understanding the molecular mechanisms underlying not only the deleterious impact of stearic-acid-induced lipotoxicity but also apoptosis in beta cells and progression to type 2 diabetes.

Hepatic adenylate cyclase 3 is upregulated by Liraglutide and subsequently plays a protective role in insulin resistance and obesity

OBJECTIVE

Recent studies have demonstrated that adenylate cyclase 3 (AC3) has a protective role in obesity. This gene resides at the pathway with glucagon-like peptide (GLP)-1. Liraglutide is a GLP-1 analog and has independent glucose and body weight (BW)-reducing effects. In the present study, we aimed to examine whether hepatic AC3 activity was regulated by Liraglutide and to further understand the effect of AC3 in reduction of BW and insulin resistance.

SUBJECTS

The diabesity and obese mice were induced from db/db and C57BL/6 J mice, respectively, by high-fat diet. Liraglutide (0.1 mg kg(-1) per 12 h) was given to the mice twice daily for 12 weeks. C57BL/6 J mice fed with chow diet and obese or diabesity mice treated with saline were used as the controls. Hepatic AC3 gene expression at mRNA and protein levels was analyzed with real-time reverse transcription-PCR and western blot. Fasting blood glucose and serum insulin levels were measured and followed insulin resistance index (HOMA-IR) was evaluated according to the homeostasis model assessment.

RESULTS

After administration of Liraglutide, BW and HOMA-IR in obese and diabesity mice were decreased, whereas hepatic AC3 mRNA and protein expression levels were upregulated. The AC3 gene expression was negatively correlated with BW, HOMA-IR and the area ratio of hepatic fat deposition in the liver.

CONCLUSIONS

The present study thus provides the evidence that hepatic AC3 gene expression is upregulated by Liraglutide. The reduction of BW and improvement of insulin resistance with Liraglutide may be partially explained by AC3 activation.

The Harbin Cohort Study on Diet, Nutrition and Chronic Non-communicable Diseases: study design and baseline characteristics

Diet and nutrition have been reported to be associated with many common chronic diseases and blood-based assessment would be vital to investigate the association and mechanism, however, blood-based prospective studies are limited. The Harbin Cohort Study on Diet, Nutrition and Chronic Non-communicable Diseases was set up in 2010. From 2010 to 2012, 9,734 participants completed the baseline survey, including demographic characteristics, dietary intake, lifestyles and physical condition, and anthropometrics. A re-survey on 490 randomly selected participants was done by using the same methods which were employed in the baseline survey. For all participants, the mean age was 50 years and 36% of them were men. Approximately 99.4 % of cohort members donated blood samples. The mean total energy intake was 2671.7 kcal/day in men and 2245.9 kcal/day in women, the mean body mass index was 25.7 kg/m² in men and 24.6 kg/m² in women, with 18.4% being obese (≥28 kg/m²), 12.7% being diabetic, and 29.5% being hypertensive. A good agreement was obtained for the physical measurements between the baseline survey and re-survey. The resources from the cohort and its fasting and postprandial blood samples collected both at baseline and in each follow-up will be valuable and powerful in investigating relationship between diet, nutrition and chronic diseases and discovering novel blood biomarkers and the metabolism of these biomarkers related to chronic diseases.

Targeted metabolomic analysis reveals the association between the postprandial change in palmitic acid, branched-chain amino acids and insulin resistance in young obese subjects

Obesity is the result of a positive energy balance and often leads to difficulties in maintaining normal postprandial metabolism. The changes in postprandial metabolites after an oral glucose tolerance test (OGTT) in young obese Chinese men are unclear. In this work, the aim is to investigate the complex metabolic alterations in obesity provoked by an OGTT using targeted metabolomics. We used gas chromatography-mass spectrometry and ultra high performance liquid chromatography-triple quadrupole mass spectrometry to analyze serum fatty acids, amino acids and biogenic amines profiles from 15 control and 15 obese subjects at 0, 30, 60, 90 and 120 min during an OGTT. Metabolite profiles from 30 obese subjects as independent samples were detected in order to validate the change of metabolites. There were the decreased levels of fatty acid, amino acids and biogenic amines after OGTT in obesity. At 120 min, percent change of 20 metabolites in obesity has statistical significance when comparing with the controls. The obese parameters was positively associated with changes in arginine and histidine (P<0.05) and the postprandial change in palmitic acid (PA), branched-chain amino acids (BCAAs) and phenylalanine between 1 and 120 min were positively associated with fasting insulin and HOMA-IR (all P<0.05) in the obese group. The postprandial metabolite of PA and BCAAs may play important role in the development and onset of insulin resistance in obesity. Our findings offer new insights in the complex physiological regulation of the metabolism during an OGTT in obesity.

Prospective association of fatty acids in the de novo lipogenesis pathway with risk of type 2 diabetes: the Cardiovascular Health Study

BACKGROUND

Experimental evidence suggests that hepatic de novo lipogenesis (DNL) affects insulin homeostasis via synthesis of saturated fatty acids (SFAs) and monounsaturated fatty acids (MUFAs). Few prospective studies have used fatty acid biomarkers to assess associations with type 2 diabetes.

OBJECTIVES

We investigated associations of major circulating SFAs [palmitic acid (16:0) and stearic acid (18:0)] and MUFA [oleic acid (18:1n-9)] in the DNL pathway with metabolic risk factors and incident diabetes in community-based older U.S. adults in the Cardiovascular Health Study. We secondarily assessed other DNL fatty acid biomarkers [myristic acid (14:0), palmitoleic acid (16:1n-7), 7-hexadecenoic acid (16:1n-9), and vaccenic acid (18:1n-7)] and estimated dietary SFAs and MUFAs.

DESIGN

In 3004 participants free of diabetes, plasma phospholipid fatty acids were measured in 1992, and incident diabetes was identified by medication use and blood glucose. Usual diets were assessed by using repeated food-frequency questionnaires. Multivariable linear and Cox regression were used to assess associations with metabolic risk factors and incident diabetes, respectively.

RESULTS

At baseline, circulating palmitic acid and stearic acid were positively associated with adiposity, triglycerides, inflammation biomarkers, and insulin resistance (P-trend < 0.01 each), whereas oleic acid showed generally beneficial associations (P-trend < 0.001 each). During 30,763 person-years, 297 incident diabetes cases occurred. With adjustment for demographics and lifestyle, palmitic acid (extreme-quintile HR: 1.89; 95% CI: 1.27, 2.83; P-trend = 0.001) and stearic acid (HR: 1.62; 95% CI: 1.09, 2.41; P-trend = 0.006) were associated with higher diabetes risk, whereas oleic acid was not significantly associated. In secondary analyses, vaccenic acid was inversely associated with diabetes (HR: 0.56; 95% CI: 0.38, 0.83; P-trend = 0.005). Other fatty acid biomarkers and estimated dietary SFAs or MUFAs were not significantly associated with incident diabetes.

CONCLUSIONS

In this large prospective cohort, circulating palmitic acid and stearic acid were associated with higher diabetes risk, and vaccenic acid was associated with lower diabetes risk. These results indicate a need for additional investigation of biological mechanisms linking specific fatty acids in the DNL pathway to the pathogenesis of diabetes.

Adipose tissue inflammation and metabolic dysfunction: role of exercise

Our current environment has led to a vicious cycle of physical inactivity, obesity, and chronic inflammation, creating the "perfect storm" for metabolic diseases. White adipose tissue (WAT) is the major source of obesity/ inactivity-related inflammation; in turn, inflammation leads to insulin resistance and metabolic dysfunction. Inactivity, even in the absence of weight gain, disrupts WAT metabolism, while exercise mitigates WAT inflammation. The antiinflammatory mechanism(s) of exercise require additional study. Two current hypotheses include: (1) exercise-mediated antiinflammatory cytokine secretion, and (2) exercise-mediated improvements in adipocyte oxidative capacity.

Impact of sterol regulatory element-binding factor-1c polymorphism on incidence of nonalcoholic fatty liver disease and on the severity of liver disease and of glucose and lipid dysmetabolism

BACKGROUND

Genetic factors that predispose individuals to nonalcoholic fatty liver disease (NAFLD) and associated diabetes and cardiovascular disease are unclear. The transcription factor sterol regulatory element-binding protein-1c (SREBP-1c) modulates lipogenesis and insulin sensitivity and was experimentally connected to NAFLD.

OBJECTIVE

We assessed the impact of a common SREBF-1c polymorphism on the incidence and severity of NAFLD and on associated glucose and lipoprotein dysmetabolism.

DESIGN

We followed up 212 randomly selected, nonobese, nondiabetic, insulin-sensitive participants in a population-based study without NAFLD or metabolic syndrome at baseline who were characterized for the common SREBF-1c gene rs11868035 A/G polymorphism, dietary habits, physical activity, adipokine profile, C-reactive protein (CRP), and circulating markers of endothelial dysfunction. A comparable cohort of NAFLD patients underwent a liver biopsy, an oral-glucose-tolerance test with minimal model analysis of glucose homeostasis variables, and an oral-fat-tolerance test with measurement of plasma lipoproteins, adipokines, and cytokeratin-18 fragments.

RESULTS

SREBF-1c predicted the 7-y incidence of NAFLD (OR: 1.71; 95% CI: 1.15, 2.53) and diabetes and the 7-y elevation in CRP and endothelial dysfunction markers. In biopsy-proven NAFLD patients, the SREBF-1c A allele conferred increased risk of severe steatosis and nonalcoholic steatohepatitis; more-severe hepatic, muscle, and adipose tissue insulin resistance; and pancreatic β cell dysfunction. SREBF-1c A allele carriers also had an impaired oral fat tolerance with a postprandial accumulation of large triglyceride-rich lipoproteins and oxidized LDLs, lower HDL cholesterol and adiponectin concentrations, and cytokeratin-18 fragment elevation.

CONCLUSION

SREBF-1c polymorphism is associated with increased risk of developing NAFLD with more severe liver histology and derangement in glucose and lipoprotein metabolism, which contribute to the presentation and natural history of NAFLD.

Dietary triacyglycerols rich in sn-2 palmitate alter post-prandial lipoprotein and unesterified fatty acids in term infants

Human milk TAG contain 20-25% 16:0, with over 70% of the 16:0 at the TAG sn-2 position. The benefits of TAG sn-2 16:0 have been ascribed to reducing 16:0 excretion as insoluble fatty acid soaps. This study builds on knowledge that infants conserve milk TG sn-2 16:0 post-absorption. Comparison of plasma lipids from 120 day old infants fed formula containing 25-27% 16:0 with 29% 16:0 or 5% 16:0 at the TAG sn-2 position showed higher formula sn-2 16:0 led to lower 18:1n-9, but higher 18:2n-6 and 22:6n-3 in the infant plasma unesterified fatty acids, higher 18:0 in LDL TAG, and higher apo B and lower apo A-1. TAG-sn-2 16:0 may provide 16:0 in remnant particles for hepatic elongation to 18:0, needed for plasma and tissue phospholipids. We suggest attention to the plasma unesterified fatty acids as possible sources of fatty acids for membrane phospholipid synthesis.