Methyl Cinnamate (MC) Alleviates Free Fatty Acids (FFAs) Induced Lipid Accumulation Through the AMPK Pathway in HepG2 Cells

Background

AMP-activated protein kinase (AMPK) plays a critical role in energy metabolism. Its activation leads to the phosphorylation of downstream proteins such as acetyl-CoA carboxylase (ACC) and sterol regulatory element-binding protein-1 (SREBP1), subsequently inhibiting de novo fatty acid synthesis, thereby reducing intracellular triglyceride accumulation. MC is a compound found in extracts from Zanthoxylum armatum DC plants. Research has shown that MC can inhibit the differentiation of 3T3-L1 adipocytes through the CAMKK2-AMPK pathway. However, the biological effect of MC in HepG2 cells remains unknown.

Methods

In this study, we utilized HepG2 cells to establish a model of MAFLD through FFAs stimulation. We investigated the biological effects of MC on HepG2 cells and studied its impact on lipid metabolism. Small interfering RNA was employed to explore the mechanism by which MC activates AMPK. Finally, molecular docking was conducted, establishing a model of the interaction between AMPK and MC.

Results

We observed that MC can alleviate triglyceride accumulation in HepG2 cells. We observed the elevated p-AMPK/AMPK, P-ACC/ ACC, and elevated CPT1a after treatment of MC in HepG2 cells. The interference of CAMKK2 mRNA did not impact the ability of MC to phosphorylate AMPK. Compound C attenuates the ability of MC to increase p-AMPK. Molecular docking results led us to hypothesize that MC directly interacts with AMPK, resulting in AMPK phosphorylation and improved lipid accumulation in HepG2 cells.

Encapsulation of resveratrol-loaded Pickering emulsions in alginate/pectin hydrogel beads: Improved stability and modification of digestive behavior in the gastrointestinal tract

In this study, alginate/pectin hydrogel beads were prepared with different mixing ratios (9:1, 8:2, 7:3, 6:4, and 5:5) to encapsulate resveratrol-loaded Pickering emulsions using Ca²⁺ crosslinking. The system with a suitable ratio of pectin and alginate can enhance the encapsulation efficiency and loading capacity. Scanning electron microscopy (SEM) study confirmed that the hydrogel beads were spherical, in which Pickering emulsion was distributed evenly within the polymer network. Fourier Transform Infrared Spectroscopy (FTIR) study indicated that the hydrogel beads were formed by physical cross-linking. X-ray diffraction (XRD) study demonstrated that resveratrol existed in hydrogel beads with an amorphous or dissolved form. Besides, the stability and antioxidant capacity suggested that hydrogel beads could offer protection to resveratrol by preventing degradation through environmental stresses, while maintaining its antioxidant capacity. Importantly, hydrogels significantly reduced the release of free fatty acids and resveratrol during in vitro digestion compared to emulsions, especially with the appropriate ratio of sodium alginate and pectin. Overall, Pickering emulsions-loaded alginate/pectin hydrogel beads could offer a novel option for the preparation of low-calorie foods and a potential substitute model for controlling the release of free fatty acids contributing to the transportation of resveratrol.

Effect of free fatty acids on insulin secretion, insulin sensitivity and incretin effect - a narrative review

Deleterious effects of free fatty acids, FFAs, on insulin sensitivity are observed in vivo studies in humans. Mechanisms include impaired insulin signaling, oxidative stress, inflammation, and mitochondrial dysfunction, but the effects on insulin secretion are less well known. Our aim was to review the relationship of increased FFAs with insulin resistance, secretion and mainly with the incretin effect in humans. Narrative review. Increased endogenous or administered FFAs induce insulin resistance. FFAs effects on insulin secretion are debatable; inhibition and stimulation have been reported, depending on the type and duration of lipids exposition and the study subjects. Chronically elevated FFAs seem to decrease insulin biosynthesis, glucose-stimulated insulin secretion and β-cell glucose sensitivity. Lipids infusion decreases the response to incretins with unchanged incretin levels in volunteers with normal glucose tolerance. In contrast, FFAs reduction by acipimox did not restore the incretin effect in type-2 diabetes, probably due to the dysfunctional β-cell. Possible mechanisms of FFAs excess on incretin effect include reduction of the expression and levels of GLP-1 (glucagon like peptide-1) receptor, reduction of connexin-36 expression thus the coordinated secretory activity in response to GLP-1, and GIP (glucose-dependent insulinotropic polypeptide) receptors downregulation in islets cells. Increased circulating FFAs impair insulin sensitivity. Effects on insulin secretion are complex and controversial. Deleterious effects on the incretin-induced potentiation of insulin secretion were reported. More investigation is needed to better understand the extent and mechanisms of β-cell impairment and insulin resistance induced by increased FFAs and how to prevent them.

Evidence in obese children: contribution of tri-ponderal mass index or body mass index to dyslipidemia, obesity-inflammation, and insulin sensitivity

Background Chronic inflammation plays a critical role in the development of obesity-related metabolic dysfunction. The tri-ponderal mass index (TMI) may be more effective than body mass index (BMI) for estimating body fat levels. This study compared the efficacy of BMI and TMI in screening for dyslipidemia, insulin sensitivity, and inflammation in childhood obesity. Methods This study included 80 children who were classified as normal weight, overweight or obese using standardized BMI (BMI standard deviation score [SDS]) and TMI measurements. Fasting blood glucose, insulin, homeostasis model assessment of insulin resistance (HOMA-IR), high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C), triglycerides, total cholesterol, liver function enzymes, leptin, serum free fatty acid (FFA), fetuin-A, monocyte chemoattractant protein-1 (MCP-1), tumor necrosis factor-alpha (TNF-α), and interleukin (IL)-6 levels were evaluated using both classification systems. Results LDL-C levels significantly differed within the groups by BMI, and serum FFA levels differed only according to the TMI. Serum MCP-1, TNF-α, IL-6, and fetuin-A levels showed no difference according to the TMI or BMI SDS. Fetuin-A levels did not differ between the insulin-resistant and non-resistant cases. Fetuin-A was the only inflammatory marker positively correlated with BMI. No inflammatory markers correlated with TMI. Fetuin-A, MCP-1, TNF-α, and IL-6 correlated with each other, but not with metabolic parameters. Conclusions BMI SDS and TMI were associated with metabolic disturbances in childhood obesity. Weight versus heightn values may be related more to metabolic parameters than to inflammatory changes.

Serum FFAs profile analysis of Normal weight and obesity individuals of Han and Uygur nationalities in China

Background

Han and Uygur are the two main nationalities living in Xinjiang, China. There are significant differences in the incidence of metabolic diseases for two nationalities, but the specific reasons are not clear. Obesity is an important risk factor for the development of metabolic syndrome, which may be closely related to the increase of serum free fatty acids (FFAs) content. This study aims to use metabolomics to compare the changes of serum FFAs profiles between normal weight (NW) and obese (OB) individuals of two nationalities, screening out the differential FFAs, predicting and evaluating their relationship with diseases.

Methods

Thirty-four kinds of FFAs in serum were detected by ultra-high-pressure liquid chromatography–mass spectrometry (UHPLC-MS) and distinctions in FFAs profiles were evaluated using a metabolomics method while Receiver operating characteristics (ROC) and logistic regression models were used to explore FFAs significant for diagnosing obesity and obesity-associated comorbidities.

Results

In the Han nationality, ten kinds of FFAs (C7:0, C8:0, C9:0, C10:0, C11:0, C14:0, C18:2, C20:3, C20:4 and C22:6) showed significant differences between NW and OB individuals. These differential FFAs may be related to hypertension and gestational diabetes mellitus. In the Uygur nationality, C20:3 and C20:5 showed significant differences between NW and OB individuals. C9:0 and C19:0, which were screened out among the female subjects, showed a good ability to predict obesity status in Uygur females (AUC = 0.950).

Conclusion

In both the Han and Uygur nationalities, the FFAs profiles of NW individuals differed from those of OB individuals. The significantly differential FFAs are closely related to obesity and may be important risk factors for obesity and related metabolic diseases.

Acute tadalafil administration increases plasma fatty acids without changes in the inflammatory response in healthy men

PURPOSE

Tadalafil, the phosphodiesterase type 5 inhibitor (PDE5I), has been shown to reduce visceral adipose tissue in rabbit and to improve lean mass content in non-obese men. In order to clarify this effect in humans, in the present study we determined the impact of an acute oral tadalafil administration on lipolysis by evaluating plasma free fatty acids (FFAs) and glycerol. FFAs are potential modulator of inflammation response that we evaluated through tumor necrosis factor alpha (TNFα), interleukin 6 (IL6), interleukin 8 (IL8) and interleukin 10 (IL10) plasma levels. Moreover, we determined whether the effects of tadalafil would be reflected in variation of plasma levels of cGMP and NO, two important molecules involved in PDE5Is signaling.

METHODS

Twelve healthy subjects were supplemented with 20 mg of tadalafil or a placebo, in a double-blind, randomized, cross-over design. Blood samples were collected immediately before, and at 2, 6, and 24 hours post ingestion, and assayed for biochemical analysis.

RESULTS

A condition effect was noted for FFAs and glycerol, with values higher for tadalafil when compared to the placebo group, at 2 and 6 hours post ingestion. No statistically significant effects were noted for glucose, cGMP, nitrate and nitrite. No inflammatory response was induced by tadalafil.

CONCLUSION

Tadalafil, in human subjects, increases lipolysis as evidenced by a significant increase in circulating FFAs and glycerol, without affecting the plasma cGMP and NO levels; noticeably, the increase in FFAs did not develop an inflammatory response. Further well-controlled studies are warranted to assess the impact of tadalafil administration on weight/fat loss.

Intracellular and extracellular miRNome deregulation in cellular models of NAFLD or NASH: Clinical implications

BACKGROUND & AIMS

Nonalcoholic fatty liver disease (NAFLD) represents the most common chronic liver disease in industrialized countries. NAFLD has the potential to progress through the inflammatory phase of nonalcoholic steatohepatitis (NASH) to fibrosis, cirrhosis, and hepatocellular carcinoma. Identifying patients at risk for this transition is a relevant clinical challenge. The complexity of these phenotypes in vivo made necessary the development of in vitro models in order to dissect the molecular signalling affected in NAFLD and NASH, but also to identify potential circulating biomarkers.

METHODS AND RESULTS

We profiled the expression of 754 cellular and medium-secreted human miRNAs in HepG2 cells after lipotoxic (Palmitate, model of NASH) or not-lipotoxic stimuli (Oleate-Palmitate, model of NAFLD). Results were validated through Single TaqMan assays. We performed computational analysis of miRNA targets and pathways. Oleate-palmitate treatment induced a variation of 2.8% and 10% of total miRNAs in cells and medium, respectively; palmitate treatment caused 10% and 19% intracellular and extracellular miRNA deregulation, respectively. We validated miR-126, miR-150, miR-223, miR-483-3p, miR-1226*, and miR-1290 deregulation. Through computational analysis, we observed that targets of both intracellular and extracellular DE miRNAs were involved in processes associated with the onset and progression of NAFLD and NASH, such as fatty acid metabolism, apoptosis and inflammation.

CONCLUSIONS

These data would be useful to elucidate the role of miRNAs in the pathogenesis and progression of the NAFLD spectrum, but they also allow the identification of novel potential biomarkers for differential diagnosis to be tested in vivo.

A20 Attenuates FFAs-induced Lipid Accumulation in Nonalcoholic Steatohepatitis

A20 is a ubiquitin-editing enzyme that attenuates the activity of proximal signaling complexes at pro-inflammatory receptors. It has been well documented that A20 protein plays an important role in response to liver injury and hepatocytes apoptosis in pro-inflammatory pathways. However, there was little evidence showing that A20 protein was involving in fatty-acid homeostasis except the up-regulation of two fatty acid metabolism regulatory genes at mRNA level (PPARa and CPT1a) by adenovirus-mediated A20 protein overexpression. In this study we found that: 1) the expression level of A20 protein was significantly higher in the steatotic liver from MCD-fed mice than the controls; 2) Overexpression of A20 protein suppressed FFAs-stimulated triglyceride deposition in HepG2 cells while under expression of A20 protein increased FFAs-stimulated triglyceride deposition; 3) Overexpression of A20 protein in HepG2 cells upregulated genes that promote β-oxidation and decreased the mRNA levels of key lipogenic genes such as fatty acid synthase (FAS), indicating A20 function as anti-steatotic factor by the activation of mitochondrial β-oxidation and attenuation of de novo lipogenesis; 4) Nonalcoholic steatohepatitis (NASH) patients showed significantly higher A20 expression level in liver compared with control individuals. Our results demonstrated that A20 protein plays an important role in fatty-acid homeostasis in human as well as animals. In addition, our data suggested that the pathological function of A20 protein in hepatocyte from lipotoxicity to NASH is by the alleviation of triglyceride accumulation in hepatocytes. Elevated expression of A20 protein could be a potential therapeutic strategy for preventing the progression of nonalcoholic steatohepatitis.

Diabetes mellitus-associated vascular impairment: novel circulating biomarkers and therapeutic approaches

It is widely accepted that diabetes mellitus (DM) impairs endothelial nitric oxide synthase activity as well as enhances the production of reactive oxygen species, thus resulting in diminished nitric oxide bioavailability and the consequent pro-atherogenetic alterations. Important biomarkers of the vasculature are related to endothelial dysfunction, to inflammatory and coagulation processes, and to oxidative stress in DM. Several therapeutic strategies might exert favorable effects on the vasculature of diabetic patients, such as insulin analogues, antihypertensive agents, statins, and hypoglycemic agents, whereas in spite of the prominent role of oxidative stress in diabetes, antioxidant therapy remains controversial. The use of specific biomarkers related to vascular function could be a useful therapeutic approach in such patients.

MicroRNA 375 mediates palmitate-induced enteric neuronal damage and high-fat diet-induced delayed intestinal transit in mice

BACKGROUND & AIMS

A high-fat diet (HFD) can cause serious health problems, including alteration of gastrointestinal transit, the exact mechanism of which is not clear. Several microRNAs (miRNAs) are involved in energy homeostasis, lipid metabolism, and HFD-induced weight gain. We investigated the role of miRNAs in HFD-induced damage to the enteric nervous system.

METHODS

Male mice were fed a HFD (60% calories from fat) or regular diets (18% calories from fat) for 11 weeks. Mice on regular diets and HFDs were given intraperitoneal injections of Mir375 inhibitor or a negative control. Body weights, food intake, stool indices, and gastrointestinal transit (following Evans blue gavage) were measured. An enteric neuronal cell line (immorto-fetal enteric neuronal) and primary enteric neurons were used for in vitro studies.

RESULTS

HFD delayed intestinal transit, which was associated with increased apoptosis and loss of colonic myenteric neurons. Mice fed a low-palmitate HFD did not develop a similar phenotype. Palmitate caused apoptosis of enteric neuronal cells associated with mitochondrial dysfunction and endoplasmic reticulum stress. Palmitate significantly increased the expression of Mir375 in vitro; transfection of cells with a Mir375 inhibitor prevented the palmitate-induced enteric neuronal cell apoptosis. Mir375 expression was increased in myenteric ganglia of mice fed HFD and associated with decreased levels of Mir375 target messenger RNAs, including Pdk1. Systemic injection of a Mir375 inhibitor for 5 weeks prevented HFD-induced delay in intestinal transit and morphologic changes.

CONCLUSIONS

HFDs delay colonic transit, partly by inducing apoptosis in enteric neuronal cells. This effect is mediated by Mir375 and is associated with reduced levels of Pdk1. Mir375 might be targeted to increase survival of enteric neurons and gastrointestinal motility.

A novel and robust recombinant Pichia pastoris yeast whole cell biocatalyst with intracellular overexpression of a Thermomyces lanuginosus lipase: preparation, characterization and application in biodiesel production

A novel and robust recombinant Pichia pastoris yeast whole cell catalyst (WCC) with functional intracellular expression of Thermomyces lanuginosus lipase (Tll) was constructed and characterized for biodiesel production from waste cooking oils. This permeabilized WCC was able to convert waste cooking oils to biodiesel with 82% yield within 84 h at 6% dosage whole cells. The WCC showed two fold catalytic activity of 0.73 U/mg DCW compared to its commercial counterpart Lipozyme TLIM (immobilized Tll). Short chain alcohol tolerance of this WCC was significantly improved compared to Lipozyme TLIM. This beneficial property enabled it to catalyze biodiesel production efficiently with one step addition of methanol. The reusability of this biocatalyst retained 78% activity after three batch cycles. This easily prepared and cost-effective WCC showed better catalytic performance than Lipozyme TLIM with respect to biodiesel yield and productivity, thus suggesting a promising cost-effective biocatalyst for biodiesel production.

Regulation of Energy Homeostasis via GPR120

Free fatty acids (FFAs) are fundamental units of key nutrients. FFAs exert various biological functions, depending on the chain length and degree of desaturation. Recent studies have shown that several FFAs act as ligands of G-protein-coupled receptors (GPCRs), activate intracellular signaling and exert physiological functions via these GPCRs. GPR120 (also known as free fatty acid receptor 4) is activated by unsaturated medium- to long-chain FFAs and has a critical role in various physiological homeostasis mechanisms such as incretin hormone secretion, food preference, anti-inflammation, and adipogenesis. Recent studies showed that a lipid sensor GPR120 has a key role in sensing dietary fat in white adipose tissue and regulates the whole body energy homeostasis in both humans and rodents. Genetic study in human identified the loss-of-functional mutation of GPR120 associated with obesity and insulin resistance. In addition, dysfunction of GPR120 has been linked as a novel risk factor for diet-induced obesity. This review aims to provide evidence from the recent development in physiological function of GPR120 and discusses its functional roles in the regulation of energy homeostasis and its potential as drug targets.

Maladaptive immune and inflammatory pathways lead to cardiovascular insulin resistance

Insulin resistance is a hallmark of obesity, the cardiorenal metabolic syndrome and type 2 diabetes mellitus (T2DM). The progression of insulin resistance increases the risk for cardiovascular disease (CVD). The significance of insulin resistance is underscored by the alarming rise in the prevalence of obesity and its associated comorbidities in the Unites States and worldwide over the last 40-50 years. The incidence of obesity is also on the rise in adolescents. Furthermore, premenopausal women have lower CVD risk compared to men, but this protection is lost in the setting of obesity and insulin resistance. Although systemic and cardiovascular insulin resistance is associated with impaired insulin metabolic signaling and cardiovascular dysfunction, the mechanisms underlying insulin resistance and cardiovascular dysfunction remain poorly understood. Recent studies show that insulin resistance in obesity and diabetes is linked to a metabolic inflammatory response, a state of systemic and tissue specific chronic low grade inflammation. Evidence is also emerging that there is polarization of macrophages and lymphocytes towards a pro-inflammatory phenotype that contributes to progression of insulin resistance in obesity, cardiorenal metabolic syndrome and diabetes. In this review, we provide new insights into factors, such as, the renin-angiotensin-aldosterone system, sympathetic activation and incretin modulators (e.g., DPP-4) and immune responses that mediate this inflammatory state in obesity and other conditions characterized by insulin resistance.

The role of hepassocin in the development of non-alcoholic fatty liver disease

BACKGROUND & AIMS

While non-alcoholic fatty liver disease (NAFLD) is the most common risk factor of chronic liver disease, the mechanisms that initiate its development are obscure. Hepassocin (HPS) is a hepatokine that has been reported to be involved in liver regeneration. In addition to the mitogenic activity of HPS, HPS expression is decreased in patients with hepatoma. However, the role of HPS in NAFLD is still unknown.

METHODS

A total of 393 subjects with (n=194) or without (n=199) NAFLD were enrolled to evaluate the serum HPS concentration. In order to clarify the causal inference between HPS and NAFLD, we used experimental animal and cell models. Hepatic overexpression or silencing of HPS was achieved by lentiviral vector delivery in mice and lipofectamine transfection in HepG2 cells. Lipogenesis related proteins were detected by Western blots. The expression of inflammatory factors was determined by real-time polymerase chain reaction.

RESULTS

Subjects with NAFLD had a higher serum HPS concentration than those without it. Overexpression of HPS increased hepatic lipid accumulation and NAFLD activity scores (NAS), whereas deletion of HPS improved high fat diet-induced hepatic steatosis and decreased NAS in mice. Additionally, oleic acid, a steatogenic reagent, increased HPS expression in hepatocytes. Furthermore, overexpression of HPS in HepG2 cells induced lipid accumulation through an extracellular signal-regulated kinase 1/2 (ERK1/2)-dependent pathway, whereas deletion of HPS decreased oleic acid-induced lipid accumulation.

CONCLUSIONS

The present study provides evidence that HPS plays an important role in NAFLD and induces hepatic lipid accumulation through an ERK1/2-dependent pathway.

Overview of epidemiology and contribution of obesity to cardiovascular disease

The prevalence of obesity has increased worldwide and is a source of concern since the negative consequences of obesity start as early as in childhood. The most commonly used anthropometric tool to assess relative weight and classify obesity is the body mass index (BMI); BMI alone shows a U- or a J-shaped association with clinical outcomes and mortality. Such an inverse relationship fuels a controversy in the literature, named the 'obesity paradox', which associates better survival and fewer cardiovascular (CV) events in patients with elevated BMI afflicted with chronic diseases compared to non-obese patients. However, BMI cannot make the distinction between an elevated body weight due to high levels of lean vs. fat body mass. Generally, an excess of body fat (BF) is more frequently associated with metabolic abnormalities than a high level of lean body mass. Another explanation for the paradox is the absence of control for major individual differences in regional BF distribution. Adipose tissue is now considered as a key organ regarding the fate of excess dietary lipids, which may determine whether or not body homeostasis will be maintained (metabolically healthy obesity) or a state of inflammation/insulin resistance will be produced, with deleterious CV consequences. Obesity, particularly visceral obesity, also induces a variety of structural adaptations/alterations in CV structure/function. Adipose tissue can now be considered as an endocrine organ orchestrating crucial interactions with vital organs and tissues such as the brain, the liver, the skeletal muscle, the heart and blood vessels themselves. Thus, the evidence reviewed in this paper suggests that adipose tissue quality/function is as important, if not more so, than its amount in determining the overall health and CV risks of overweight/obesity.

tert-Butylhydroquinone (tBHQ) protects hepatocytes against lipotoxicity via inducing autophagy independently of Nrf2 activation

Saturated fatty acids (SFAs) induce hepatocyte cell death, wherein oxidative stress is mechanistically involved. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is a master transcriptional regulator of cellular antioxidant defense enzymes. Therefore, Nrf2 activation is regarded as an effective strategy against oxidative stress-triggered cellular damage. In this study, tert-butylhydroquinone (tBHQ), a widely used Nrf2 activator, was initially employed to investigate the potential protective role of Nrf2 activation in SFA-induced hepatoxicity. As expected, SFA-induced hepatocyte cell death was prevented by tBHQ in both AML-12 mouse hepatocytes and HepG2 human hepatoma cells. However, the protective effect of tBHQ is Nrf2-independent, because the siRNA-mediated Nrf2 silencing did not abrogate tBHQ-conferred protection. Alternatively, our results revealed that autophagy activation was critically involved in the protective effect of tBHQ on lipotoxicity. tBHQ induced autophagy activation and autophagy inhibitors abolished tBHQ's protection. The induction of autophagy by tBHQ exposure was demonstrated by the increased accumulation of LC3 puncta, LC3-II conversion, and autophagic flux (LC3-II conversion in the presence of proteolysis inhibitors). Subsequent mechanistic investigation discovered that tBHQ exposure activated AMP-activated protein kinase (AMPK) and siRNA-mediated AMPK gene silencing abolished tBHQ-induced autophagy activation, indicating that AMPK is critically involved in tBHQ-triggered autophagy induction. Furthermore, our study provided evidence that tBHQ-induced autophagy activation is required for its Nrf2-activating property. Collectively, our data uncover a novel mechanism for tBHQ in protecting hepatocytes against SFA-induced lipotoxicity. tBHQ-triggered autophagy induction contributes not only to its hepatoprotective effect, but also to its Nrf2-activating property.

Liver enzymes but not free fatty acid levels predict markers of insulin sensitivity in overweight and obese, nondiabetic adults

Although obesity is a key predisposing risk factor in the development of insulin resistance (IR) and type 2 diabetes mellitus, not all obese individuals develop IR. This study aimed to identify key anthropometric and biochemical parameters that predict insulin sensitivity in overweight and obese adults. Based on previous literature, we hypothesized that markers of insulin sensitivity would be negatively correlated with plasma concentrations of free fatty acids and liver enzymes. Forty nondiabetic adult participants (body mass index ≥ 25.0 kg/m²) were recruited. Data collection included anthropometric measurements and fasting plasma samples for the quantification of liver enzymes (alanine transaminase, aspartate transaminase, γ-glutamyl transpeptidase), blood lipid profile, and markers of insulin sensitivity. Questionnaires relating to dietary intake, physical activity, and fatigue were also completed. Insulin and Homeostasis Model of Assessment (HOMA) scores were significantly correlated with indirect measures of central obesity (P < .05). Glycosylated hemoglobin, insulin, and HOMA scores for IR were all positively correlated with selected liver function markers (P < .05). Scores of HOMA-IR were significantly positively correlated with plasma phospholipid levels of n-3 fatty acids (P = .04) and ratio of n-3/n-6 fatty acids (P < .05) and negatively correlated with n-6 fatty acids (P = .03). No significant correlations were found between markers of insulin sensitivity and cholesterol levels, physical activity, or self-reported fatigue. These results have reinforced the integral role of liver function in the development of IR. Despite previous data linking elevations in free fatty acid to the development of IR, we found no relationship between these variables in this study.

Oleanolic acid improves hepatic insulin resistance via antioxidant, hypolipidemic and anti-inflammatory effects

Insulin resistance is the hallmark of type 2 diabetes mellitus (T2DM), which is closely related to disorder of lipid metabolism. The study was designed to evaluate the effects of oleanolic acid (OA) on hepatic insulin resistance and underlying mechanisms in Lep(db)(/)(db) obese diabetic mice. db/db Mice were administered with OA (20mg/kg/day, i.p.) for two weeks. OA reduced body weight, liver weight, and fat weight, and protected liver morphology and function. OA decreased fasting blood glucose, improved glucose and insulin tolerance, enhanced insulin signaling and inhibited gluconeogenesis. In livers, mitochondrial biogenesis, ultrastructure and function were influenced, accompanied by increased cellular and mitochondrial ROS production. OA inhibited all these changes, in which process Nrf2-GCLc mediated stabilization of mitochondrial glutathione pool may be involved. Moreover, OA decreased serum triglyceride, total cholesterol, LDL, HDL, and free fatty acids, increased serum HDL, and reduced hepatic lipid accumulation. Furthermore, inflammatory condition in db/db mice was improved by OA, as evidenced by decreased level of IL-1 β, IL-6, and TNFα in circulation and in liver. The evidence suggests that OA improves hepatic insulin resistance through inhibition of mitochondrial ROS, hypolipidemic and anti-inflammatory effects. The effectiveness of OA leads to interesting therapeutic perspectives.

High glucose, insulin and free fatty acid concentrations synergistically enhance perilipin 3 expression and lipid accumulation in macrophages

OBJECTIVE

Perilipin (PLIN) 3, an intracellular lipid droplet (LD)-associated protein, is implicated in foam cell formation. Since metabolic derangements found in metabolic syndrome, such as high serum levels of glucose, insulin and free fatty acids (FFAs), are major risk factors promoting atherosclerosis, we investigated whether PLIN3 expression is affected by glucose, insulin and oleic acid (OA) using RAW264.7 cells.

METHODS

Real-time PCR and Western blotting were performed to detect PLIN3 or PLIN2 expression. Oil-red O staining and Lipid Analysis were employed to measure cellular content of triacylglycerides (TAG) and cholesterol.

RESULTS

PLIN3 mRNA was stimulated by high glucose or insulin concentrations individually, but not by OA. A combination of any two factors did not enhance PLIN3 expression any more than that evoked by glucose alone at 24h. Interestingly, however, simultaneous addition of all three factors synergistically enhanced the PLIN3 expression. This synergistic effect was not apparent for PLIN2 mRNA expression. Inhibitors of Src family tyrosine kinase and/or phosphatidylinositol 3-kinase, both of which are activated by insulin and FFA signaling, partially suppressed PLIN3 expression induced by the combination of the three factors. While simultaneous addition of glucose, insulin and OA remarkably increased the cellular content of TAG and cholesterol, knocking-down of PLIN3 predominantly reduced TAG content.

CONCLUSIONS

These results indicate that PLIN3 expression is synergistically stimulated by high glucose, insulin and FFA concentrations, in parallel with TAG accumulation in macrophages. This finding raises new evidence of PLIN3 involvement in conversion of macrophages into foam cells.

Amelioration of palmitate-induced insulin resistance in C₂C₁₂ muscle cells by rooibos (Aspalathus linearis)

Increased levels of free fatty acids (FFAs), specifically saturated free fatty acids such as palmitate are associated with insulin resistance of muscle, fat and liver. Skeletal muscle, responsible for up to 80% of the glucose disposal from the peripheral circulation, is particularly vulnerable to increased levels of saturated FFAs. Rooibos (Aspalathus linearis) and its unique dihydrochalcone C-glucoside, aspalathin, shown to reduce hyperglycemia in diabetic rats, could play a role in preventing or ameliorating the development of insulin resistance. This study aims to establish whether rooibos can ameliorate experimentally-induced insulin-resistance in C₂C₁₂ skeletal muscle cells. Palmitate-induced insulin resistant C₂C₁₂ cells were treated with an aspalathin-enriched green (unfermented) rooibos extract (GRE), previously shown for its blood glucose lowering effect in vitro and in vivo or an aqueous extract of fermented rooibos (FRE). Glucose uptake and mitochondrial activity were measured using 2-deoxy-[³H]-D-glucose, MTT and ATP assays, respectively. Expression of proteins relevant to glucose metabolism was analysed by Western blot. GRE contained higher levels of all compounds, except the enolic phenylpyruvic acid-2-O-glucoside and luteolin-7-O-glucoside. Both rooibos extracts increased glucose uptake, mitochondrial activity and ATP production. Compared to FRE, GRE was more effective at increasing glucose uptake and ATP production. At a mechanistic level both extracts down-regulated PKC θ activation, which is associated with palmitate-induced insulin resistance. Furthermore, the extracts increased activation of key regulatory proteins (AKT and AMPK) involved in insulin-dependent and non-insulin regulated signalling pathways. Protein levels of the glucose transporter (GLUT4) involved in glucose transport via these two pathways were also increased. This in vitro study therefore confirms that rooibos can ameliorate palmitate-induced insulin resistance in C₂C₁₂ skeletal muscle cells. Inhibition of PKC θ activation and increased activation of AMPK and AKT offer a plausible mechanistic explanation for this ameliorative effect.

Modulation of cellular insulin signaling and PTP1B effects by lipid metabolites in skeletal muscle cells

Normal glucose regulation is achieved by having adequate insulin secretion and effective glucose uptake/disposal. Excess lipids in peripheral tissues - skeletal muscle, liver and adipose tissue - may attenuate insulin signaling through the protein kinase B (AKt) pathway and up-regulate protein tyrosine phosphatase 1B (PTP1B), a negative regulator of insulin signaling. We studied accumulation of lipid metabolites [triglycerides (TAGs), diglycerides (DAGs)] and ceramides in relation to insulin signaling and expression and phosphorylation of PTP1B by preincubating rat skeletal muscle cells (L6 myotubes) with three saturated and three unsaturated free fatty acids (FFAs) (200 μM). Cells were also evaluated in the presence of wortmannin, an inhibitor of phosphatidylinositol 3-kinases and thus AKt (0-100 nM). Unsaturated FFAs increased DAGs, TAGs and PTP1B expression significantly, but cells remained insulin sensitive as assessed by robust AKt and PTP1B phosphorylation at serine (Ser) 50, Ser 398 and tyrosine 152. Saturated palmitic and stearic acids increased ceramides, up-regulated PTP1B, and had AKt and PTP1B phosphorylation at Ser 50 impaired. We show a significant correlation between phosphorylation levels of AKt and of PTP1B at Ser 50 (R(2)=0.84, P<.05). The same was observed with increasing wortmannin dose (R(2)=0.73, P<.05). Only FFAs that increased ceramides caused impairment of AKt and PTP1B phosphorylation at Ser 50. PTP1B overexpression in the presence of excess lipids may not directly cause insulin resistance unless it is accompanied by decreased PTP1B phosphorylation. A clear relationship between PTP1B phosphorylation levels at Ser 50 and its negative effect on insulin signaling is shown.