The influence of major dietary fatty acids on insulin secretion and action

Plasma lipidic fingerprint associated with type 2 diabetes in patients with coronary heart disease: CORDIOPREV study

OBJECTIVE

We aimed to identify a lipidic profile associated with type 2 diabetes mellitus (T2DM) development in coronary heart disease (CHD) patients, to provide a new, highly sensitive model which could be used in clinical practice to identify patients at T2DM risk.

METHODS

This study considered the 462 patients of the CORDIOPREV study (CHD patients) who were not diabetic at the beginning of the intervention. In total, 107 of them developed T2DM after a median follow-up of 60 months. They were diagnosed using the American Diabetes Association criteria. A novel lipidomic methodology employing liquid chromatography (LC) separation followed by HESI, and detection by mass spectrometry (MS) was used to annotate the lipids at the isomer level. The patients were then classified into a Training and a Validation Set (60-40). Next, a Random Survival Forest (RSF) was carried out to detect the lipidic isomers with the lowest prediction error, these lipids were then used to build a Lipidomic Risk (LR) score which was evaluated through a Cox. Finally, a production model combining the clinical variables of interest, and the lipidic species was carried out.

RESULTS

LC-tandem MS annotated 440 lipid species. From those, the RSF identified 15 lipid species with the lowest prediction error. These lipids were combined in an LR score which showed association with the development of T2DM. The LR hazard ratio per unit standard deviation was 2.87 and 1.43, in the Training and Validation Set respectively. Likewise, patients with higher LR Score values had lower insulin sensitivity (P = 0.006) and higher liver insulin resistance (P = 0.005). The receiver operating characteristic (ROC) curve obtained by combining clinical variables and the selected lipidic isomers using a generalised lineal model had an area under the curve (AUC) of 81.3%.

CONCLUSION

Our study showed the potential of comprehensive lipidomic analysis in identifying patients at risk of developing T2DM. In addition, the lipid species combined with clinical variables provided a new, highly sensitive model which can be used in clinical practice to identify patients at T2DM risk. Moreover, these results also indicate that we need to look closely at isomers to understand the role of this specific compound in T2DM development. Trials registration NCT00924937.

Acute effects of prior dietary fat ingestion on postprandial metabolic responses to protein and carbohydrate co-ingestion in overweight and obese men: A randomised crossover trial

BACKGROUND

Obesity and insulin resistance are associated with an impaired sensitivity to anabolic stimuli such as dietary protein (anabolic resistance). Omega-3 polyunsaturated fatty acids (n-3 PUFA) may be protective against the deleterious effects of saturated fatty acids (SFA) on insulin resistance. However, the contribution of excess fat consumption to anabolic and insulin resistance and the interaction between SFA and n-3 PUFA is not well studied.

AIM

The primary aim of this study was to investigate the effects of an oral fat pre-load, with or without the partial substitution of SFA with fish oil (FO)-derived n-3 PUFA, on indices of insulin and anabolic sensitivity in response to subsequent dietary protein and carbohydrate (dextrose) co-ingestion.

METHODS

Eight middle-aged males with overweight or obesity (52.8 ± 2.0 yr, BMI 31.8 ± 1.4 kg·m^-2) ingested either an SFA, or isoenergetic SFA and FO emulsion (FO), or water/control (Con), 4 h prior to a bolus of milk protein and dextrose.

RESULTS

Lipid ingestion (in particular FO) impaired the early postprandial uptake of branched chain amino acids (BCAA) into the skeletal muscle in response to protein and dextrose, and attenuated the peak glycaemic response, but was not accompanied by differences in whole body (Matsuda Index: Con: 4.66 ± 0.89, SFA: 5.10 ± 0.94 and FO: 4.07 ± 0.59) or peripheral (forearm glucose _netAUC: Con: 521.7 ± 101.7; SFA: 470.2 ± 125.5 and FO: 495.3 ± 101.6 μmol·min^-1·100 g lean mass·min [t = 240-420 min]) insulin sensitivity between visits. Postprandial whole body fat oxidation was affected by visit (P = 0.024) with elevated rates in SFA and FO, relative to Con (1.85 ± 0.55; 2.19 ± 0.21 and 0.65 ± 0.35 kJ·h^-1·kg^-1 lean body mass, respectively), however muscle uptake of free fatty acids (FFA) was unaffected.

CONCLUSION

Oral lipid preloads, consisting of SFA and FO, impair the early postprandial BCAA uptake into skeletal muscle, which occurs independent of changes in insulin sensitivity.

CLINICAL TRIAL REGISTRY NUMBER

ClinicalTrials.gov Identifier NCT03146286.

Study on chemical composition and physical properties of the Hamri (Barbus luteus) and Balaout (Chondrostoma regium) fish meat, oil and impact of its oils on cholesterol, triglyceride, HDL and blood sugar of laboratory rats

The study aimed at investigating the meat chemical composition and physical properties of oil of the Hamri (Barbus luteus) and Balaout (Chondrostoma regium) fish and its oil content or fatty acids, and also to know the impact of its oils on the level of cholesterol, triglyceride, high density lipoprotein (HDL) and blood sugar levels of laboratory rats. The study area extended from the province of Shirqat and Balad district to the province of Salah al-Din. The approximate percentages of meat from Hamri were 72.13, 19.74, 5.07 and 1.60 % for the moisture, protein, fat and ash respectively, and 71.63, 19.98, 4.96 and 2.04% respectively from Balaout. The extract oil from 2 types of fish differed significantly in Iodine value, Peroxide value, and Acid value and in saponification number. The fatty acids profiles results showed that oils from Hamri and Balaout fish meat consisted of 44.31 and 55.76% of Saturated fatty acid, 36.10 and 25.41% of poly unsaturated fatty acid, and 18.17 and 25.41% poly unsaturated fatty acids respectively. The experiment laboratory rats showed decreases in cholesterol, triglyceride and blood sugar level, and increases in high density lipoprotein (HDL). In conclusion, it is recommended that this oil can be used in human diet for health benefits.

Protective Effects of Almond Oil on Streptozotocin-Induced Diabetic Rats via Regulating Nrf2/HO-1 Pathway and Gut Microbiota

Almond oil has been used as a medicine substitution for its numerous health benefits. This study aimed to evaluate the effect of almond oil on streptozotocin- (STZ-) induced diabetic rats for 4 weeks. The results showed that the administration of almond oil could significantly increase body weight, attenuate abnormally elevated blood glucose, promote insulin secretion, and improve glucose tolerance. Almond oil treatment also suppressed oxidative stress, reduced inflammation reaction, improved liver and kidney function, upregulated the expressions of Nrf2, HO-1, and NQO1, while downregulating the expression of Keap1. Furthermore, almond oil reversed the gut microbiota change by STZ and regulated the gut microbiota associated with glucose metabolism. At the phylum level, the relative abundance of Firmicutes was decreased, while Bacteroidetes was increased by almond oil treatment. More importantly, the ratio of Firmicutes/Bacteroidetes was significantly increased. At the genus level, administration of almond oil increased the abundances of Lactobacillus, Bacteroides, and Lachnospiraceae_NK4A136_group, while decreased the abundances of Ruminococcaceae_UCG-014, Clostridium_sensu_stricto_1, and Fusicatenibacter. These results provided evidence for the regulating effect of almond oil on diabetic rats via the Nrf2/HO-1 pathway and gut microbiota.

Saturated fatty acids entrap PDX1 in stress granules and impede islet beta cell function

AIMS/HYPOTHESIS

Failure of pancreatic and duodenal homeobox factor 1 (PDX1) to localise in the nucleus of islet beta cells under high-fat diet (HFD) conditions may be an early functional defect that contributes to beta cell failure in type 2 diabetes; however, the mechanism of PDX1 intracellular mislocalisation is unclear. Stress granules (SGs) are membrane-less cytoplasmic structures formed under stress that impair nucleocytoplasmic transport by sequestering nucleocytoplasmic transport factors and components of the nuclear pore complex. In this study, we investigated the stimulators that trigger SG formation in islet beta cells and the effects of SGs on PDX1 localisation and beta cell function.

METHODS

The effect of palmitic acid (PA) on nucleocytoplasmic transport was investigated by using two reporters, S-tdTomato and S-GFP. SG assembly in rat insulinoma cell line INS1 cells, human islets under PA stress, and the pancreas of diet-induced obese mice was analysed using immunofluorescence and immunoblotting. SG protein components were identified through mass spectrometry. SG formation was blocked by specific inhibitors or genetic deletion of essential SG proteins, and then PDX1 localisation and beta cell function were investigated in vitro and in vivo.

RESULTS

We showed that saturated fatty acids (SFAs) are endogenous stressors that disrupted nucleocytoplasmic transport and stimulated SG formation in pancreatic beta cells. Using mass spectrometry approaches, we revealed that several nucleocytoplasmic transport factors and PDX1 were localised to SGs after SFA treatment, which inhibited glucose-induced insulin secretion. Furthermore, we found that SFAs induced SG formation in a phosphoinositide 3-kinase (PI3K)/eukaryotic translation initiation factor 2α (EIF2α) dependent manner. Disruption of SG assembly by PI3K/EIF2α inhibitors or genetic deletion of T cell restricted intracellular antigen 1 (TIA1) in pancreatic beta cells effectively suppressed PA-induced PDX1 mislocalisation and ameliorated HFD-mediated beta cell dysfunction.

CONCLUSIONS/INTERPRETATION

Our findings suggest a link between SG formation and beta cell dysfunction in the presence of SFAs. Preventing SG formation may be a potential therapeutic strategy for treating obesity and type 2 diabetes.

Determination of glycemic index of enteral formulas used in clinical practice

Glycemic Index (GI) is a measure of carbohydrate quality and is recognised as a valid and reproducible method of classifying carbohydrate foods according to its effects on postprandial glycaemia. In this randomised crossover trial (RBR-7rjx3k) we determined the GI of nine enteral formulas, following the Food and Agriculture Organisation/World Health Organisation method. Forty healthy participants were included in the study (85% female mean age 27.1 ± 6.7 years). GI of the enteral formulas ranged from 40.5 to 85.2; four formulas had high GI (Nutrienteral 1.5^®, Novasource GI Control^®, Diamax^®, Isosource Soya^®), two intermediate GI (Fresubin 1.2 HP Fibre^®, Nutrison Energy Multifiber 1.5^®) and three low GI (Trophic 1.5^®, Glucerna^®, Novasource GC HP^®). The GI coefficient of variation ranged from 22.9% to 83.6%. The effect of the enteral formulas with low GI in glycemic control of patients with enteral nutrition prescription needs to be test in future studies.

Coconut oil consumption improves fat-free mass, plasma HDL-cholesterol and insulin sensitivity in healthy men with normal BMI compared to peanut oil

BACKGROUND & AIMS

The existing scientific evidence on coconut oil consumption and its health effects remains inconclusive due to varied reasons. In this context, we conducted a well-controlled metabolic study, eliminating some of the confounding factors and assessed the effects of the consumption of coconut oil-based diet on various anthropometric, biochemical and inflammatory markers and compared with peanut oil-diet.

METHODS

Nine healthy male volunteers with BMI ≤25 kg/m² were enrolled for this study and given balanced diets prepared with coconut oil (CO; ~35 g) for a period of eight weeks. After a wash-out period of six weeks, the same subjects were provided with diets prepared with peanut oil (~35 g) for eight weeks. Except fat source, the composition of the diets was identical in all aspects.

RESULTS

Compared to basal values, there were significant increases in fat-free mass (p ≤ 0.022), plasma HDL-cholesterol (HDL-C) (p ≤ 0.047) and insulin sensitivity of the subjects at the end of CO-consumption. Further, compared to peanut oil, increase in plasma HDL-C was significant (p = 0.004) in CO treatment. On the other hand, plasma inflammatory markers-associated with cardiovascular diseases (CVD), namely soluble vascular cell adhesion molecule 1 (sVCAM1) and matrix metalloproteinase levels were reduced significantly by CO-intake. Further, these subjects displayed elevated levels of myristic acid (14:0) in plasma phospholipids at the end of CO-consumption, which correlated positively with HDL-C and negatively with sVCAM1. However, no such changes were observed after peanut oil diet consumption.

CONCLUSIONS

In conclusion, compared to peanut oil, the consumption of coconut oil in a balanced diet resulted in increased fat-free mass, plasma HDL-C, elicited favourable changes on insulin sensitivity and CVD risk-associated parameters in healthy men with normal BMI.

Effects of immediate-release niacin and dietary fatty acids on acute insulin and lipid status in individuals with metabolic syndrome

BACKGROUND

The nature of dietary fats profoundly affects postprandial hypertriglyceridemia and glucose homeostasis. Niacin is a potent lipid-lowering agent. However, limited data exist on postprandial triglycerides and glycemic control following co-administration of high-fat meals with a single dose of niacin in subjects with metabolic syndrome (MetS). The aim of the study was to explore whether a fat challenge containing predominantly saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs) or MUFAs plus omega-3 long-chain polyunsaturated (LCPUFAs) fatty acids together with a single dose of immediate-release niacin have a relevant role in postprandial insulin and lipid status in subjects with MetS.

RESULTS

In a randomized crossover within-subject design, 16 men with MetS were given a single dose of immediate-release niacin (2 g) and ∼15 cal kg^-1 body weight meals containing either SFAs, MUFAs, MUFAs plus omega-3 LCPUFAs or no fat. At baseline and hourly over 6 h, plasma glucose, insulin, C-peptide, triglycerides, free fatty acids (FFAs), total cholesterol, and both high- and low-density lipoprotein cholesterol were assessed. Co-administered with niacin, high-fat meals significantly increased the postprandial concentrations of glucose, insulin, C-peptide, triglycerides, FFAs and postprandial indices of β-cell function. However, postprandial indices of insulin sensitivity were significantly decreased. These effects were significantly attenuated with MUFAs or MUFAs plus omega-3 LCPUFAs when compared with SFAs.

CONCLUSION

In the setting of niacin co-administration and compared to dietary SFAs, MUFAs limit the postprandial insulin, triglyceride and FFA excursions, and improve postprandial glucose homeostasis in MetS. © 2017 Society of Chemical Industry.

Yeast Cells Exposed to Exogenous Palmitoleic Acid Either Adapt to Stress and Survive or Commit to Regulated Liponecrosis and Die

A disturbed homeostasis of cellular lipids and the resulting lipotoxicity are considered to be key contributors to many human pathologies, including obesity, metabolic syndrome, type 2 diabetes, cardiovascular diseases, and cancer. The yeast Saccharomyces cerevisiae has been successfully used for uncovering molecular mechanisms through which impaired lipid metabolism causes lipotoxicity and elicits different forms of regulated cell death. Here, we discuss mechanisms of the “liponecrotic” mode of regulated cell death in S. cerevisiae. This mode of regulated cell death can be initiated in response to a brief treatment of yeast with exogenous palmitoleic acid. Such treatment prompts the incorporation of exogenously added palmitoleic acid into phospholipids and neutral lipids. This orchestrates a global remodeling of lipid metabolism and transfer in the endoplasmic reticulum, mitochondria, lipid droplets, and the plasma membrane. Certain features of such remodeling play essential roles either in committing yeast to liponecrosis or in executing this mode of regulated cell death. We also outline four processes through which yeast cells actively resist liponecrosis by adapting to the cellular stress imposed by palmitoleic acid and maintaining viability. These prosurvival cellular processes are confined in the endoplasmic reticulum, lipid droplets, peroxisomes, autophagosomes, vacuoles, and the cytosol.

Reduced first-phase insulin secretion increases postprandial lipidemia in subjects with impaired glucose tolerance

OBJECTIVE

It is not clear which phase of insulin secretion is more important to regulate lipoprotein lipase (LPL) activity. After a meal, insulin is released and acts as a major regulator of LPL activity. Postprandial hyperlipidemia is a common comorbidity in subjects with insulin resistance (IR). Therefore this study aimed to evaluate the role of the first-phase insulin secretion (FPIS) on postprandial lipidemia in subjects with IR and impaired glucose tolerance (IGT).

RESEARCH DESIGN AND METHODS

This is a cross-sectional, observational and comparative study. We included male and female subjects between 40 and 60 years with a body mass index (BMI) between 23 and 30 kg/m². Then, patients were divided into three groups. Group 1 consisted of control subjects with normal glucose tolerance and preserved FPIS. Group 2 included patients with IGT and a reduced FPIS. Group 3 consisted of subjects with IGT but normal FPIS. Both groups were paired by age and BMI with subjects in the control group. Subjects underwent an intravenous glucose tolerance test to classify each case, and then a load with a mixed meal load to measure postprandial lipidemia.

RESULTS

A total of 32 subjects were evaluated: 10 were control subjects, 8 subjects with IGT with a reduced FPIS and 14 subjects with IGT and preserved FPIS. After administration of a standardized meal, group 2 showed a greater glucose area under the curve (AUC) at 30 and 120 min (p=0.001, for both). This group also showed a statistically significant increase (p<0.001) in triglyceride AUC.

CONCLUSIONS

A reduced FPIS is significantly and independently associated with a larger postprandial hyperlipidemia in subjects with IGT.

n-3 Fatty acids and asthma

Asthma is one of the most common and prevalent problems worldwide affecting over 300 million individuals. There is some evidence from observational and intervention studies to suggest a beneficial effect of n-3 PUFA in inflammatory diseases, specifically asthma. Marine-based n-3 PUFA have therefore been proposed as a possible complementary/alternative therapy for asthma. The proposed anti-inflammatory effects of n-3 fatty acids may be linked to a change in cell membrane composition. This altered membrane composition following n-3 fatty acid supplementation (primarily EPA and DHA) can modify lipid mediator generation via the production of eicosanoids with a reduced inflammatory potential/impact. A recently identified group of lipid mediators derived from EPA including E-series resolvins are proposed to be important in the resolution of inflammation. Reduced inflammation attenuates the severity of asthma including symptoms (dyspnoea) and exerts a bronchodilatory effect. There have been no major health side effects reported with the dietary supplementation of n-3 fatty acids or their mediators; consequently supplementing with n-3 fatty acids is an attractive non-pharmacological intervention which may benefit asthma.

Clustering effects on postprandial insulin secretion and sensitivity in response to meals with different fatty acid compositions

Dietary fatty acids play a role in glucose homeostasis. The aim of this study was to assess the individual relationship between dietary saturated (SFA), monounsaturated (MUFA) and polyunsaturated (PUFA) fatty acids with postprandial β-cell function and insulin sensitivity in subjects with normal and high fasting triglycerides. We assessed postprandial β-cell function (by the insulinogenic index and the ratio of the insulin to glucose areas under the time-concentration curve) and insulin sensitivity (by the oral glucose and the minimal model insulin sensitivity indices) over four nonconsecutive, randomly assigned, high-fat meals containing a panel of SFA (palmitic and stearic acids), MUFA (palmitoleic and oleic acids) and PUFA (linoleic and α-linolenic acids) in 14 subjects with normal and in 14 subjects with high fasting triglycerides. The proportions of each fatty acid in the meals and the values for surrogate measures of postprandial β-cell function and insulin sensitivity were subjected to a Pearson correlation and hierarchical cluster analysis, which revealed two classes of dietary fatty acids for regulating postprandial glucose homeostasis. We successfully discriminated the adverse effects of SFA palmitic acid from the beneficial effects of MUFA oleic acid on postprandial β-cell function (r ≥ 0.84 for SFA palmitic acid and r ≥ -0.71 for MUFA oleic acid; P < 0.05) and insulin sensitivity (r ≥ -0.92 for SFA palmitic acid and r ≥ 0.89 for MUFA oleic acid; P < 0.001) both in subjects with normal and high fasting triglycerides. In conclusion, dietary MUFA oleic acid, in contrast to SFA palmitic acid, favours the tuning towards better postprandial glycaemic control in subjects with normal and high fasting triglycerides.

Reduced adiponectin signaling due to weight gain results in nonalcoholic steatohepatitis through impaired mitochondrial biogenesis

Obesity and adiponectin depletion have been associated with the occurrence of nonalcoholic fatty liver disease (NAFLD). The goal of this study was to identify the relationship between weight gain, adiponectin signaling, and development of nonalcoholic steatohepatitis (NASH) in an obese, diabetic mouse model. Leptin-receptor deficient (Lepr(db/db) ) and C57BL/6 mice were administered a diet high in unsaturated fat (HF) (61%) or normal chow for 5 or 10 weeks. Liver histology was evaluated using steatosis, inflammation, and ballooning scores. Serum, adipose tissue, and liver were analyzed for changes in metabolic parameters, messenger RNA (mRNA), and protein levels. Lepr(db/db) HF mice developed marked obesity, hepatic steatosis, and more than 50% progressed to NASH at each timepoint. Serum adiponectin level demonstrated a strong inverse relationship with body mass (r = -0.82; P < 0.0001) and adiponectin level was an independent predictor of NASH (13.6 μg/mL; P < 0.05; area under the receiver operating curve (AUROC) = 0.84). White adipose tissue of NASH mice was characterized by increased expression of genes linked to oxidative stress, macrophage infiltration, reduced adiponectin, and impaired lipid metabolism. HF lepr (db/db) NASH mice exhibited diminished hepatic adiponectin signaling evidenced by reduced levels of adiponectin receptor-2, inactivation of adenosine monophosphate activated protein kinase (AMPK), and decreased expression of genes involved in mitochondrial biogenesis and β-oxidation (Cox4, Nrf1, Pgc1α, Pgc1β and Tfam). In contrast, recombinant adiponectin administration up-regulated the expression of mitochondrial genes in AML-12 hepatocytes, with or without lipid-loading.

CONCLUSION

Lepr(db/db) mice fed a diet high in unsaturated fat develop weight gain and NASH through adiponectin depletion, which is associated with adipose tissue inflammation and hepatic mitochondrial dysfunction. We propose that this murine model of NASH may provide novel insights into the mechanism for development of human NASH.

Reducing saturated fatty acids in Arabidopsis seeds by expression of a Caenorhabditis elegans 16:0-specific desaturase

Plant oilseeds are a major source of nutritional oils. Their fatty acid composition, especially the proportion of saturated and unsaturated fatty acids, has important effects on human health. Because intake of saturated fats is correlated with the incidence of cardiovascular disease and diabetes, a goal of metabolic engineering is to develop oils low in saturated fatty acids. Palmitic acid (16:0) is the most abundant saturated fatty acid in the seeds of many oilseed crops and in Arabidopsis thaliana. We expressed FAT-5, a membrane-bound desaturase cloned from Caenorhabditis elegans, in Arabidopsis using a strong seed-specific promoter. The FAT-5 enzyme is highly specific to 16:0 as substrate, converting it to 16:1∆9; expression of fat-5 reduced the 16:0 content of the seed by two-thirds. Decreased 16:0 and elevated 16:1 levels were evident both in the storage and membrane lipids of seeds. Regiochemical analysis of phosphatidylcholine showed that 16:1 was distributed at both positions on the glycerolipid backbone, unlike 16:0, which is predominately found at the sn-1 position. Seeds from a plant line homozygous for FAT-5 expression were comparable to wild type with respect to seed set and germination, while oil content and weight were somewhat reduced. These experiments demonstrate that targeted heterologous expression of a desaturase in oilseeds can reduce the level of saturated fatty acids in the oil, significantly improving its nutritional value.

Reduction of connexin36 content by ICER-1 contributes to insulin-secreting cells apoptosis induced by oxidized LDL particles

Connexin36 (Cx36), a trans-membrane protein that forms gap junctions between insulin-secreting beta-cells in the Langerhans islets, contributes to the proper control of insulin secretion and beta-cell survival. Hypercholesterolemia and pro-atherogenic low density lipoproteins (LDL) contribute to beta-cell dysfunction and apoptosis in the context of Type 2 diabetes. We investigated the impact of LDL-cholesterol on Cx36 levels in beta-cells. As compared to WT mice, the Cx36 content was reduced in islets from hypercholesterolemic ApoE-/- mice. Prolonged exposure to human native (nLDL) or oxidized LDL (oxLDL) particles decreased the expression of Cx36 in insulin secreting cell-lines and isolated rodent islets. Cx36 down-regulation was associated with overexpression of the inducible cAMP early repressor (ICER-1) and the selective disruption of ICER-1 prevented the effects of oxLDL on Cx36 expression. Oil red O staining and Plin1 expression levels suggested that oxLDL were less stored as neutral lipid droplets than nLDL in INS-1E cells. The lipid beta-oxidation inhibitor etomoxir enhanced oxLDL-induced apoptosis whereas the ceramide synthesis inhibitor myriocin partially protected INS-1E cells, suggesting that oxLDL toxicity was due to impaired metabolism of the lipids. ICER-1 and Cx36 expressions were closely correlated with oxLDL toxicity. Cx36 knock-down in INS-1E cells or knock-out in primary islets sensitized beta-cells to oxLDL-induced apoptosis. In contrast, overexpression of Cx36 partially protected INS-1E cells against apoptosis. These data demonstrate that the reduction of Cx36 content in beta-cells by oxLDL particles is mediated by ICER-1 and contributes to oxLDL-induced beta-cell apoptosis.

Kupffer cells ameliorate hepatic insulin resistance induced by high-fat diet rich in monounsaturated fatty acids: the evidence for the involvement of alternatively activated macrophages

BACKGROUND

Resident macrophages (Kupffer cells, KCs) in the liver can undergo both pro- or anti-inflammatory activation pathway and exert either beneficiary or detrimental effects on liver metabolism. Until now, their role in the metabolically dysfunctional state of steatosis remains enigmatic. Aim of our study was to characterize the role of KCs in relation to the onset of hepatic insulin resistance induced by a high-fat (HF) diet rich in monounsaturated fatty acids.

METHODS

Male Wistar rats were fed either standard (SD) or high-fat (HF) diet for 4 weeks. Half of the animals were subjected to the acute GdCl3 treatment 24 and 72 hrs prior to the end of the experiment in order to induce the reduction of KCs population. We determined the effect of HF diet on activation status of liver macrophages and on the changes in hepatic insulin sensitivity and triacylglycerol metabolism imposed by acute KCs depletion by GdCl3.

RESULTS

We found that a HF diet rich in MUFA itself triggers an alternative but not the classical activation program in KCs. In a steatotic, but not in normal liver, a reduction of the KCs population was associated with a decrease of alternative activation and with a shift towards the expression of pro-inflammatory activation markers, with the increased autophagy, elevated lysosomal lipolysis, increased formation of DAG, PKCε activation and marked exacerbation of HF diet-induced hepatic insulin resistance.

CONCLUSIONS

We propose that in the presence of a high MUFA content the population of alternatively activated resident liver macrophages may mediate beneficial effects on liver insulin sensitivity and alleviate the metabolic disturbances imposed by HF diet feeding and steatosis. Our data indicate that macrophage polarization towards an alternative state might be a useful strategy for treating type 2 diabetes.

Effects of a meal rich in 1,3-diacylglycerol on postprandial cardiovascular risk factors and the glucose-dependent insulinotropic polypeptide in subjects with high fasting triacylglycerol concentrations

It was previously reported that compared to triacylglycerol (TAG) oil, diacylglycerol (DAG) oil improves postprandial lipid response. However, the effects of DAG oil on postprandial hyperglycemia and incretin response have not yet been determined. In this study, the effects of DAG oil on both postprandial hyperlipidemia and hyperglycemia and the response to the glucose-dependent insulinotropic polypeptide (GIP) were studied. This randomized, double-blind, crossover study analyzed data for 41 individuals with high fasting triacylglycerol concentrations. The subjects ingested test meals (30.3 g of protein, 18.6 g of fat, and 50.1 g of carbohydrate) containing 10 g of DAG oil (DAG meal) or TAG oil (TAG meal) after fasting for at least 12 h. Blood samples were collected prior to and 0.5, 2, 3, 4, and 6 h after ingestion of the test meal. Postprandial TAG concentrations were significantly lower after the DAG meal compared with the TAG meal. Postprandial TAG, insulin, and GIP concentrations were significantly lower after the DAG meal compared with the TAG meal in 26 subjects with fasting serum TAG levels between 1.36 and 2.83 mmol/L. DAG-oil-based meals, as a replacement for TAG oil, may provide cardiovascular benefits in high-risk individuals by limiting lipid and insulin excursions.

Negative association of acetate with visceral adipose tissue and insulin levels

BACKGROUND

The composition of gut flora has been proposed as a cause of obesity, a major risk factor for type 2 diabetes. The objective of this study was to assess whether serum short chain fatty acids, a major by-product of fermentation in gut flora, are associated with obesity and/or diabetes-related traits (insulin sensitivity and secretion).

METHODS

The association of serum short chain fatty acids levels with measures of obesity was assessed using body mass index, computerized tomography scan, and dual photon X-ray absorptiometry scan. Insulin sensitivity and insulin secretion were both determined from an oral glucose tolerance test and insulin sensitivity was also determined from a hyperinsulinemic euglycemic clamp.

RESULTS

In this population of young, obese women, acetate was negatively associated with visceral adipose tissue determined by computerized tomography scan and dual photon X-ray absorptiometry scan, but not body mass index. The level of the short chain fatty acids acetate, but not propionate or butyrate, was also negatively associated with fasting serum insulin and 2 hour insulin levels in the oral glucose tolerance test.

CONCLUSIONS

In this population, serum acetate was negatively associated with visceral adipose tissue and insulin levels. Future studies need to verify these findings and expand on these observations in larger cohorts of subjects.

Dietary fatty acids linking postprandial metabolic response and chronic diseases

Chronic diseases are by far one of the main causes of mortality in the world. One of the current global recommendations to counteract disability and premature death resulting from chronic diseases is to decrease the consumption of energy-dense high-fat diets, particularly those rich in saturated fatty acids (SFA). The most effective replacement for SFA in terms of risk factor outcomes for chronic disease are polyunsaturated fatty acids (PUFA) and monounsaturated fatty acids (MUFA). The biochemical basis for healthy benefits of such a dietary pattern has been widely evaluated under fasting conditions. However, the increasing amount of data available from multiple studies suggest that the postprandial state, i.e., "the period that comprises and follows a meal", plays an important, yet underappreciated, role in the genesis of numerous pathological conditions. In this review, the potential of MUFA, PUFA, and SFA to postprandially affect selected metabolic abnormalities related to chronic diseases is discussed.

Effects of meals rich in either monounsaturated or saturated fat on lipid concentrations and on insulin secretion and action in subjects with high fasting triglyceride concentrations

BACKGROUND

The nature of dietary fats and fasting concentrations of triglycerides affect postprandial hypertriglyceridemia and glucose homeostasis.

OBJECTIVES

The objectives were to examine the effects of meals enriched in monounsaturated fatty acids (MUFAs) or saturated fatty acids (SFAs) on postprandial lipid, glucose, and insulin concentrations and to examine the extent of β cell function and insulin sensitivity in subjects with high fasting triglyceride concentrations.

DESIGN

Fourteen men with fasting hypertriglyceridemia and normal glucose tolerance were given meals (≈10 kcal/kg body weight) containing MUFAs, SFAs, or no fat. Blood samples were collected at baseline and hourly over 8 h for analysis.

RESULTS

The high-fat meals significantly increased postprandial concentrations of triglycerides, nonesterified fatty acids, and insulin and postprandial indexes of β cell function. However, postprandial indexes of insulin sensitivity decreased significantly. These effects were significantly attenuated with MUFAs relative to SFAs.

CONCLUSIONS

MUFAs postprandially buffered β cell hyperactivity and insulin intolerance relative to SFAs in subjects with high fasting triglyceride concentrations. These data suggest that, in contrast with SFAs, MUFA-based strategies may provide cardiovascular benefits to persons at risk by limiting lipid and insulin excursions and may contribute to optimal glycemic control after meal challenges.

Possible contributions of lipoproteins and cholesterol to the pathogenesis of diabetes mellitus type 2

PURPOSE OF REVIEW

Low HDL cholesterol and hypertriglyceridemia as well as lowering of LDL cholesterol with statins increase the risk of T2DM. We discuss the recent findings on the effects of lipoproteins and cholesterol on the function and survival of pancreatic β-cells as well as on obesity and insulin sensitivity of muscle and liver.

RECENT FINDINGS

LDL inhibits glucose-stimulated insulin secretion and proliferation of β-cells by LDL-receptor dependent and independent mechanisms, respectively. ApoA-I and HDL stimulate insulin secretion by interaction with ABCA1, ABCG1 or SR-BI and also inhibit apoptosis of β-cells. Mice with targeted knockouts of ABCA1 or ABCG1 in β-cells show reduced insulin secretion and glucose tolerance. ABCG1 contributes to the enrichment of insulin secretory granules with cholesterol, which is needed for their formation and trafficking to the plasma membrane whereas ABCA1-mediated cholesterol efflux from the plasma membrane appears to be important for their subsequent exocytosis. In mice, overexpression of apoA-I decreases body fat accumulation and increases insulin sensitivity of muscle and liver by inducing the phosphorylation of AMP kinase.

SUMMARY

LDL, HDL and cholesterol regulate the function and survival of β-cells. HDL also exerts antiobesity and insulin-sensitizing effects. Thus dyslipidemias may not only be consequences but also contributors to the pathogenesis and hence targets for prevention of T2DM.