Palmitic acid acutely stimulates glucose uptake via activation of Akt and ERK1/2 in skeletal muscle cells

Gintonin Stimulates Glucose Uptake in Myocytes: Involvement of Calcium and Extracellular Signal-Regulated Kinase Signaling

Ginseng has anti-hyperglycemic effects. Gintonin, a glycolipoprotein derived from ginseng, also stimulates insulin release from pancreatic beta cells. However, the role of gintonin in glucose metabolism within skeletal muscle is unknown. Here, we showed the effect of gintonin on glucose uptake, glycogen content, glucose transporter (GLUT) 4 expression, and adenosine triphosphate (ATP) content in C2C12 myotubes. Gintonin (3-30 μg/mL) dose-dependently stimulated glucose uptake in myotubes. The expression of GLUT4 on the cell membrane was increased by gintonin treatment. Treatment with 1-3 μg/mL of gintonin increased glycogen content in myotubes, but the content was decreased at 30 μg/mL of gintonin. The ATP content in myotubes increased following treatment with 10-100 μg/mL gintonin. Gintonin transiently elevated intracellular calcium concentrations and increased the phosphorylation of extracellular signal-regulated kinase (ERK). Gintonin-induced transient calcium increases were inhibited by treatment with the lysophosphatidic acid receptor inhibitor Ki16425, the phospholipase C inhibitor U73122, and the inositol 1,4,5-trisphosphate receptor antagonist 2-aminoethoxydiphenyl borate. Gintonin-stimulated glucose uptake was decreased by treatment with U73122, the intracellular calcium chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl) ester, and the ERK inhibitor PD98059. These results show that gintonin plays a role in glucose metabolism by increasing glucose uptake through transient calcium increases and ERK signaling pathways. Thus, gintonin may be beneficial for glucose metabolism control.

Targeting the immunoproteasome in hypothalamic neurons as a novel therapeutic strategy for high-fat diet-induced obesity and metabolic dysregulation

OBJECTIVE

Obesity represents a significant global health challenge characterized by chronic low-grade inflammation and metabolic dysregulation. The hypothalamus, a key regulator of energy homeostasis, is particularly susceptible to obesity's deleterious effects. This study investigated the role of the immunoproteasome, a specialized proteasomal complex implicated in inflammation and cellular homeostasis, during metabolic diseases.

METHODS

The levels of the immunoproteasome β5i subunit were analyzed by immunostaining, western blotting, and proteasome activity assay in mice fed with either a high-fat diet (HFD) or a regular diet (CHOW). We also characterized the impact of autophagy inhibition on the levels of the immunoproteasome β5i subunit and the activation of the AKT pathway. Finally, through confocal microscopy, we analyzed the contribution of β5i subunit inhibition on mitochondrial function by flow cytometry and mitophagy assay.

RESULTS

Using an HFD-fed obese mouse model, we found increased immunoproteasome levels in hypothalamic POMC neurons. Furthermore, we observed that palmitic acid (PA), a major component of saturated fats found in HFD, increased the levels of the β5i subunit of the immunoproteasome in hypothalamic neuronal cells. Notably, the increase in immunoproteasome expression was associated with decreased autophagy, a critical cellular process in maintaining homeostasis and suppressing inflammation. Functionally, PA disrupted the insulin-glucose axis, leading to reduced AKT phosphorylation and increased intracellular glucose levels in response to insulin due to the upregulation of the immunoproteasome. Mechanistically, we identified that the protein PTEN, a key regulator of insulin signaling, was reduced in an immunoproteasome-dependent manner. To further investigate the potential therapeutic implications of these findings, we used ONX-0914, a specific immunoproteasome inhibitor. We demonstrated that this inhibitor prevents PA-induced insulin-glucose axis imbalance. Given the interplay between mitochondrial dysfunction and metabolic disturbances, we explored the impact of ONX-0914 on mitochondrial function. Notably, ONX-0914 preserved mitochondrial membrane potential and attenuated mitochondrial ROS production in the presence of PA. Moreover, we found that ONX-0914 reduced mitophagy in the presence of PA.

CONCLUSIONS

Our findings strongly support the pathogenic involvement of the immunoproteasome in hypothalamic neurons in the context of HFD-induced obesity and metabolic disturbances. Targeting the immunoproteasome highlights a promising therapeutic strategy to mitigate the detrimental effects of obesity on the insulin-glucose axis and cellular homeostasis. This study provides valuable insights into the mechanisms driving obesity-related metabolic diseases and offers potential avenues for developing novel therapeutic interventions.

Saturated fatty acids inhibit unsaturated fatty acid induced glucose uptake involving GLUT10 and aerobic glycolysis in bovine granulosa cells

Fatty acids have been shown to modulate glucose metabolism in vitro and in vivo. However, there is still a need for substantial evidence and mechanistic understanding in many cell types whether both saturated and unsaturated fatty acids (SFAs and UFAs) pose a similar effect and, if not, what determines the net effect of fatty acid mixes on glucose metabolism. In the present study, we asked these questions by treating granulosa cells (GCs) with the most abundant non-esterified fatty acid species in bovine follicular fluid. Results revealed that oleic and alpha-linolenic acids (UFAs) significantly increased glucose consumption compared to palmitic and stearic acids (SFAs). A significant increase in lactate production, extracellular acidification rate, and decreased mitochondrial activity indicate glucose channeling through aerobic glycolysis in UFA treated GCs. We show that insulin independent glucose transporter GLUT10 is essential for UFA driven glucose consumption, and the induction of AKT and ERK signaling pathways necessary for GLUT10 expression. To mimic the physiological conditions, we co-treated GCs with mixes of SFAs and UFAs. Interestingly, co-treatments abolished the UFA induced glucose uptake and metabolism by inhibiting AKT and ERK phosphorylation and GLUT10 expression. These data suggest that the net effect of fatty acid induced glucose uptake in GCs is determined by SFAs under physiological conditions.

Dietary protein restriction regulates skeletal muscle fiber metabolic characteristics associated with the FGF21-ERK1/2 pathway

Under conditions of dietary amino acid balance, decreasing the dietary crude protein (CP) level in pigs has a beneficial effect on meat quality. To further elucidate the mechanism, we explored the alteration of muscle fiber characteristics and key regulators related to myogenesis in the skeletal muscle of pigs fed a protein restricted diet. Compared to pigs fed a normal protein diet, dietary protein restriction significantly increased the slow-twitch muscle fiber proportion in skeletal muscle, succinic dehydrogenase (SDH) activity, the concentrations of ascorbate, biotin, palmitoleic acid, and the ratio of s-adenosylhomocysteine (SAM) to s-adenosylhomocysteine (SAH), but the fast-twitch muscle fiber proportion, lactate dehydrogenase (LDH) activity, the concentrations of ATP, glucose-6-phosphate, SAM, and SAH in skeletal muscle, and the ratio of serum triiodothyronine (T3) to tetraiodothyronine (T4) were decreased. In conclusion, we demonstrated that dietary protein restriction induced skeletal muscle fiber remodeling association the regulation of FGF21-ERK1/2-mTORC1 signaling in weaned piglets.

Explicit mechanistic insights of Prosopis juliflora extract in streptozotocin-induced diabetic rats at the molecular level

Background

The Ancient system of medicine showed the limelight on the use of herbal remedies and was found to possess minimal side effects and acceptable therapeutic outcomes. In this context, Prosopis juliflora gained importance in managing chronic diseases such as cancer, dermatological diseases, and chronic inflammatory disorders. Hence, P. juliflora was selected for further investigation associated with diabetes and inflammation.

Aim

The present study aimed to evaluate the anti-diabetic activity in chemically induced experimental rats and explore the nature of phytocomponents that may produce this activity.

Methods

Experimentally, diabetes was induced by a single administration of streptozotocin at 50 mg/kg intraperitoneally in Wistar rats. The animals were treated orally with P. juliflora at low and high doses (200 and 400 mg/kg) for 10 days. Blood collected from the retro-orbital plexus was analyzed for parameters like blood glucose levels, insulin, adiponectin, Keap1 and Nrf2. PPAR-γ, AMPK and GLUT 2 levels were analyzed in the pancreatic tissue. Besides, at the end of the experiment, animals were sacrificed, and the pancreatic tissue sections were subjected for histopathological, morphometrical and immune histochemical exploration. The phytochemical composition of the plant was investigated by GC-MS.

Results

The administration of P. juliflora higher dose showed a significant decrease (**p< 0.001) in blood glucose levels with a rise in adiponectin, PPARγ, Keap1, Nrf2, Glut 2, and AMPK significantly (**p< 0.001). The inflammatory cytokine TNFα was also estimated and was found to be lowered significantly (**p< 0.001) in test drug-treated animals. Furthermore, in the pancreatic tissue, the number of Islets, the area, and the number of β-cells were improved significantly with the sub-chronic treatment of P. juliflora extract. The structure and function of β-cells were also revamped.

Conclusion

The study results demonstrated a significant effect of P. juliflora on glycemic status, inflammatory condition, and the architecture of pancreatic tissue. In the identification and isolation process by GC MS, it was noticed that P. juliflora contained few phytochemical constituents from which it might be considered a promising drug for type 2 diabetes mellitus.

Butyrate promotes C2C12 myoblast proliferation by activating ERK/MAPK pathway

Sarcopenia has garnered considerable interest in recent years as ageing-associated diseases constitute a significant worldwide public health burden. Nutritional supplements have received much attention as potential tools for managing sarcopenia. However, the specific nutrients responsible are still under-investigated. In the current study, we first determined the levels of short chain fatty acids (SCFAs) and intestinal flora in the feces of elderly sarcopenia subjects and elderly healthy individuals by ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). Then cell viability detection, flow cytometry and transcriptome analysis were adopted to experimentally evaluate the effect and the underlying mechanism of SCFA on C2C12 cells proliferation in vitro. The results suggested that patients with sarcopenia exhibited decreased levels of butyrate. And butyrate may stimulate C2C12 myocyte proliferation via promoting G1/S cell cycle transition. Transcriptomic analyses pointed to upregulation of the Mitogen-activated protein kinase (MAPK) signaling pathway in butyrate-treated cells. In addition, the above proliferative phenotypes could be suppressed by the combination of ERK/MAPK inhibitor. A combined transcriptomic and metabolomic approach was applied in our study to investigate the potential effect of microbiota-derived butyrate yield on muscular proliferation which may indicate a protective effect of nutritional supplements.

Protective Effects of Hemp (Cannabis sativa) Root Extracts against Insulin-Deficient Diabetes Mellitus In Mice

The pharmacological potential of industrial hemp (Cannabis sativa) has been widely studied. However, the majority of studies have focused on cannabidiol, isolated from the inflorescence and leaf of the plant. In the present study, we evaluated the anti-diabetic potential of hemp root water (HWE) and ethanol extracts (HEE) in streptozotocin (STZ)-induced insulin-deficient diabetic mice. The administration of HWE and HEE ameliorated hyperglycemia and improved glucose homeostasis and islet function in STZ-treated mice (p < 0.05). HWE and HEE suppressed β-cell apoptosis and cytokine-induced inflammatory signaling in the pancreas (p < 0.05). Moreover, HWE and HEE normalized insulin-signaling defects in skeletal muscles and apoptotic response in the liver and kidney induced by STZ (p < 0.05). Gas chromatography-mass spectrometry analysis of HWE and HEE showed possible active compounds which might be responsible for the observed anti-diabetic potential. These findings indicate the possible mechanisms by which hemp root extracts protect mice against insulin-deficient diabetes, and support the need for further studies geared towards the application of hemp root as a novel bioactive material.

Effects of saturated versus unsaturated fatty acids on metabolism, gliosis, and hypothalamic leptin sensitivity in male mice

BACKGROUND

Development of obesity and its comorbidities is not only the result of excess energy intake, but also of dietary composition. Understanding how hypothalamic metabolic circuits interpret nutritional signals is fundamental to advance towards effective dietary interventions.

OBJECTIVE

We aimed to determine the metabolic response to diets enriched in specific fatty acids.

METHODS

Male mice received a diet enriched in unsaturated fatty acids (UOLF) or saturated fatty acids (SOLF) for 8 weeks.

RESULTS

UOLF and SOLF mice gained more weight and adiposity, but with no difference between these two groups. Circulating leptin levels increased on both fatty acid-enriched diet, but were higher in UOLF mice, as were leptin mRNA levels in visceral adipose tissue. In contrast, serum non-esterified fatty acid levels only rose in SOLF mice. Hypothalamic mRNA levels of NPY decreased and of POMC increased in both UOLF and SOLF mice, but only SOLF mice showed signs of hypothalamic astrogliosis and affectation of central fatty acid metabolism. Exogenous leptin activated STAT3 in the hypothalamus of all groups, but the activation of AKT and mTOR and the decrease in AMPK activation in observed in controls and UOLF mice was not found in SOLF mice.

CONCLUSIONS

Diets rich in fatty acids increase body weight and adiposity even if energy intake is not increased, while increased intake of saturated and unsaturated fatty acids differentially modify metabolic parameters that could underlie more long-term comorbidities. Thus, more understanding of how specific nutrients affect metabolism, weight gain, and obesity associated complications is necessary.

Supplementation of palmitoleic acid improved piglet growth and reduced body temperature drop upon cold exposure

Piglet survival is a major challenge in the first few days postpartum and interventions during this period may improve survival and growth. This study investigated the effects of palmitoleic acid (C16:1n-7; PA) supplementation on growth performance, body temperature, fatty acid (FA), and energy metabolism in milk-replacer-fed piglets. Forty-eight piglets were stratified by body weight and randomly assigned to one of four dietary treatments (0%, 1%, 2%, and 3% PA supplementation as a percent of milk replacer) and given the diet through an orogastric tube. They were fed dietary treatments every 2 h for 4 d in the first week postpartum and all were sacrificed at the end of the experiment. The piglets were weighed daily, and half in each dietary treatment group, the same piglets each day, were exposed daily to a lower temperature for 2 h. Plasma samples were collected immediately before sacrifice for analyses of FA and other plasma metabolites. The weight of organs and empty body weight were determined after sacrifice. Liver and semimembranosus muscle tissue samples were collected and analyzed for FA content. Contents of C16:1n-7 and C18:1n-7 in both plasma and liver (P < 0.001), and C16:1n-7 in semimembranosus muscle (P < 0.001) increased linearly as PA supplementation increased. Most plasma FA levels (except C16:1n-7, C16:1n-9, and C22:5n-3) were lower in piglets exposed to lower temperatures than those that were not. Plasma glucose, triglycerides, and lactate dehydrogenase levels increased linearly with PA supplementation (P < 0.001). Piglets' average daily gain, liver glycogen pool, liver weight, and gallbladder weight increased linearly (P < 0.05, P < 0.01, P < 0.05, and P < 0.001, respectively), but lung weight, liver nitrogen content, and body temperature drop decreased linearly (P < 0.01, P < 0.001, and P < 0.05, respectively) with PA supplementation. Piglets exposed to low temperature had greater liver nitrogen (P < 0.05) and lactate dehydrogenase (P < 0.001) contents but had lower liver weight (P < 0.01) and plasma lactate concentration (P < 0.05) than those that were not. In conclusion, this study demonstrated the importance of PA on the growth performance of the piglets by increasing their average daily gain and decreasing a drop in body temperature upon cold exposure, most likely due to a modified energy metabolism.

Modulation of Milk and Lipid Synthesis and Secretion in a3-Dimensional Mouse Mammary Epithelial Cell Culture Model: Effects of Palmitate and Orlistat

Human milk synthesis is impacted by maternal diet, serum composition, and substrate uptake and synthesis by mammary epithelial cells (MECs). The milk of obese/high-fat-diet women has an increased fat content, which promote excess infant weight gain and the risk of childhood/adult obesity. Yet, the knowledge of milk synthesis regulation is limited, and there are no established approaches to modulate human milk composition. We established a 3-dimensional mouse MEC primary culture that recreates the milk production pathway and tested the effects of the major saturated fatty acid in human milk (palmitate) and a lipoprotein lipase inhibitor (orlistat) on triglyceride production. Positive immunostaining confirmed the presence of milk protein and intracellular lipid including milk globules in the cytoplasm and extracellular space. The treatment with palmitate activated "milk" production by MECs (β-casein) and the lipid pathway (as evident by increased protein and mRNA expression). Consistent with these cellular changes, there was increased secretion of milk protein and triglyceride in MEC "milk". The treatment with orlistat suppressed milk triglyceride production. Palmitate increased milk and lipid synthesis, partly via lipoprotein lipase activation. These findings demonstrate the ability to examine MEC pathways of milk production via both protein and mRNA and to modulate select pathways regulating milk composition in MEC culture.

Exploring Visceral and Subcutaneous Adipose Tissue Secretomes in Human Obesity: Implications for Metabolic Disease

Adipose tissue secretions are depot-specific and vary based on anatomical location. Considerable attention has been focused on visceral (VAT) and subcutaneous (SAT) adipose tissue with regard to metabolic disease, yet our knowledge of the secretome from these depots is incomplete. We conducted a comprehensive analysis of VAT and SAT secretomes in the context of metabolic function. Conditioned media generated using SAT and VAT explants from individuals with obesity were analyzed using proteomics, mass spectrometry, and multiplex assays. Conditioned media were administered in vitro to rat hepatocytes and myotubes to assess the functional impact of adipose tissue signaling on insulin responsiveness. VAT secreted more cytokines (IL-12p70, IL-13, TNF-α, IL-6, and IL-8), adipokines (matrix metalloproteinase-1, PAI-1), and prostanoids (TBX2, PGE2) compared with SAT. Secretome proteomics revealed differences in immune/inflammatory response and extracellular matrix components. In vitro, VAT-conditioned media decreased hepatocyte and myotube insulin sensitivity, hepatocyte glucose handling, and increased basal activation of inflammatory signaling in myotubes compared with SAT. Depot-specific differences in adipose tissue secretome composition alter paracrine and endocrine signaling. The unique secretome of VAT has distinct and negative impact on hepatocyte and muscle insulin action.

Estradiol production of granulosa cells is unaffected by the physiological mix of non-esterified fatty acids in follicular fluid

Ovarian cycle is controlled by circulating levels of the steroid hormone 17-β-estradiol, which is predominantly synthesized by the granulosa cells (GCs) of ovarian follicles. Our earlier studies showed that unsaturated fatty acids (USFs) downregulate and saturated fatty acids (SFAs) upregulate estradiol production in GCs. However, it was unclear whether pituitary gonadotropins induce accumulation of free fatty acids (FFAs) in the follicular fluid since follicle-stimulating hormone induces and luteinizing hormone inhibits estradiol production in the mammalian ovary. Interestingly, we show here the gas chromatography analysis of follicular fluid revealed no differential accumulation of FFAs between pre- and post-luteinizing hormone surge follicles. We therefore wondered how estradiol production is regulated in the physiological context, as USFs and SFAs are mutually present in the follicular fluid. We thus performed in vitro primary GC cultures with palmitate, palmitoleate, stearate, oleate, linoleate, and alpha-linolenate, representing >80% of the FFA fraction in the follicular fluid, and analyzed 62 different cell culture conditions to understand the regulation of estradiol biosynthesis under diverse FFA combinations. Our analyses showed co-supplementation of SFAs with USFs rescued estradiol production by restoring gonadotropin receptors and aromatase, antagonizing the inhibitory effects of USFs. Furthermore, transcriptome data of oleic acid–treated GCs indicated USFs induce the ERK and Akt signaling pathways. We show SFAs inhibit USF-induced ERK1/2 and Akt activation, wherein ERK1/2 acts as a negative regulator of estradiol synthesis. We propose SFAs are vital components of the follicular fluid, without which gonadotropin signaling and the ovarian cycle would probably be shattered by USFs.

Pharmacologically Active Phytomolecules Isolated from Traditional Antidiabetic Plants and Their Therapeutic Role for the Management of Diabetes Mellitus

Diabetes mellitus is a chronic complication that affects people of all ages. The increased prevalence of diabetes worldwide has led to the development of several synthetic drugs to tackle this health problem. Such drugs, although effective as antihyperglycemic agents, are accompanied by various side effects, costly, and inaccessible to the majority of people living in underdeveloped countries. Medicinal plants have been used traditionally throughout the ages to treat various ailments due to their availability and safe nature. Medicinal plants are a rich source of phytochemicals that possess several health benefits. As diabetes continues to become prevalent, health care practitioners are considering plant-based medicines as a potential source of antidiabetic drugs due to their high potency and fewer side effects. To better understand the mechanism of action of medicinal plants, their active phytoconstituents are being isolated and investigated thoroughly. In this review article, we have focused on pharmacologically active phytomolecules isolated from medicinal plants presenting antidiabetic activity and the role they play in the treatment and management of diabetes. These natural compounds may represent as good candidates for a novel therapeutic approach and/or effective and alternative therapies for diabetes.

Drug Discovery of Plausible Lead Natural Compounds That Target the Insulin Signaling Pathway: Bioinformatics Approaches

The growing smooth talk in the field of natural compounds is due to the ancient and current interest in herbal medicine and their potentially positive effects on health. Dozens of antidiabetic natural compounds were reported and tested in vivo, in silico, and in vitro. The role of these natural compounds, their actions on the insulin signaling pathway, and the stimulation of the glucose transporter-4 (GLUT4) insulin-responsive translocation to the plasma membrane (PM) are all crucial in the treatment of diabetes and insulin resistance. In this review, we collected and summarized a group of available in vivo and in vitro studies which targeted isolated phytochemicals with possible antidiabetic activity. Moreover, the in silico docking of natural compounds with some of the insulin signaling cascade key proteins is also summarized based on the current literature. In this review, hundreds of recent studies on pure natural compounds that alleviate type II diabetes mellitus (type II DM) were revised. We focused on natural compounds that could potentially regulate blood glucose and stimulate GLUT4 translocation through the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) pathway. On attempt to point out potential new natural antidiabetic compounds, this review also focuses on natural ingredients that were shown to interact with proteins in the insulin signaling pathway in silico, regardless of their in vitro/in vivo antidiabetic activity. We invite interested researchers to test these compounds as potential novel type II DM drugs and explore their therapeutic mechanisms.

Hypoglycaemic activity of Smilax canellifolia Mill. rhizomes: a bioassay-guided isolation and identification of synergistic compounds

Background

Smilax canellifolia Mill. is a native shrub used in commercial root tonics as an aphrodisiac, stimulant, and pain reliever. Traditional medicine incorporates the rhizomes of S. canellifolia for the treatment of anaemia, rheumatoid arthritis, and diabetes in Jamaica and its diaspora. In particular, the use of this plant in the management of diabetes has yet to receive any scientific evaluation. In this study, the hexane crude extract of S. canellifolia rhizomes (SCH) was investigated to determine its hypoglycaemic activity in normal Sprague-Dawley rats and to identify the compounds contributing to this activity.

Methods

The hypoglycaemic compounds were isolated using bioactivity-guided purification which involved hypoglycaemic screening using an Oral Glucose Tolerance Test (via intravenous administration of SCH and its fractions). Purification was performed using column chromatography, and the bioactive fractions were elucidated using spectroscopic techniques (IR; GC-MS; 1H NMR and 13C NMR).

Results

Administration of SCH at 50 mg/kg body weight (BW) to normal S-D rats produced a reduced glycaemic response, notably from the 90 to the 150-min intervals when compared with the control, dimethyl sulfoxide (p < 0.05). Purification of this extract yielded four main fractions, SCH1 – SCH4, of which SCH3 and SCH4 displayed significant hypoglycaemia. Further purification of both SCH3 and SCH4 led to the isolation of sub-fractions SCH3.6 and SCH4.2, respectively. Using spectroscopic techniques stigmasterol (1) and β-sitosterol (2) from SCH3.6; and the fatty acids palmitic acid (3), oleic acid (4), and stearic acid (5) from SCH4.2 were identified as the major compounds with significant hypoglycaemic activities comparable to that of glibenclamide.

Conclusion

This study demonstrates that the rhizomes of Smilax canellifolia contain several bioactive constituents that are responsible for its hypoglycaemic activity and may be beneficial in the management of hyperglycaemia and complications associated with diabetes.

Cardiac metallothionein overexpression rescues diabetic cardiomyopathy in Akt2-knockout mice

To efficiently prevent diabetic cardiomyopathy (DCM), we have explored and confirmed that metallothionein (MT) prevents DCM by attenuating oxidative stress, and increasing expression of proteins associated with glucose metabolism. To determine whether Akt2 expression is critical to MT prevention of DCM, mice with either global Akt2 gene deletion (Akt2-KO), or cardiomyocyte-specific overexpressing MT gene (MT-TG) or both combined (MT-TG/Akt2-KO) were used. Akt2-KO mice exhibited symptoms of DCM (cardiac remodelling and dysfunction), and reduced expression of glycogen and glucose metabolism-related proteins, despite an increase in total Akt (t-Akt) phosphorylation. Cardiac MT overexpression in MT-TG/Akt2-KO mice prevented DCM and restored glucose metabolism-related proteins expression and baseline t-Akt phosphorylation. Furthermore, phosphorylation of ERK1/2 increased in the heart of MT-TG/Akt2-KO mice, compared with Akt2-KO mice. As ERK1/2 has been implicated in the regulation of glucose transport and metabolism this increase could potentially underlie MT protective effect in MT-TG/Akt2-KO mice. Therefore, these results show that although our previous work has shown that MT preserving Akt2 activity is sufficient to prevent DCM, in the absence of Akt2 MT may stimulate alternative or downstream pathways protecting from DCM in a type 2 model of diabetes, and that this protection may be associated with the ERK activation pathway.

Gundelia tournefortii: Fractionation, Chemical Composition and GLUT4 Translocation Enhancement in Muscle Cell Line

Type 2 diabetes (T2D) is a chronic metabolic disease, which could affect the daily life of patients and increase their risk of developing other diseases. Synthetic anti-diabetic drugs usually show severe side effects. In the last few decades, plant-derived drugs have been intensively studied, particularly because of a rapid development of the instruments used in analytical chemistry. We tested the efficacy of Gundelia tournefortii L. (GT) in increasing the translocation of glucose transporter-4 (GLUT4) to the myocyte plasma membrane (PM), as a main strategy to manage T2D. In this study, GT methanol extract was sub-fractionated into 10 samples using flash chromatography. The toxicity of the fractions on L6 muscle cells, stably expressing GLUTmyc, was evaluated using the MTT assay. The efficacy with which GLUT4 was attached to the L6 PM was evaluated at non-toxic concentrations. Fraction 6 was the most effective, as it stimulated GLUT4 translocation in the absence and presence of insulin, 3.5 and 5.2 times (at 250 μg/mL), respectively. Fraction 1 and 3 showed no significant effects on GLUT4 translocation, while other fractions increased GLUT4 translocation up to 2.0 times. Gas chromatography-mass spectrometry of silylated fractions revealed 98 distinct compounds. Among those compounds, 25 were considered anti-diabetic and glucose disposal agents. These findings suggest that GT methanol sub-fractions exert an anti-diabetic effect by modulating GLUT4 translocation in L6 muscle cells, and indicate the potential of GT extracts as novel therapeutic agents for T2D.

Acute and Subacute Toxicity and Cytotoxicity of Opuntia Dillenii (Ker-Gawl) Haw. Seed Oil and Its Impact on the Isolated Rat Diaphragm Glucose Absorption

This study aims to assess the safety of the Opuntia dillenii (Ker-Gawl) haw. seed oil (ODSO) and its effect on the glucose absorption activity of the isolated rat hemidiaphragm. This oil's safety was studied by exploring its acute (doses 1, 3, 5, and 7 mL/kg) and subacute (doses 1 and 2 mL/kg) toxicities in albino mice and Wistar rats, respectively. The safety of the ODSO was also assessed by studying its effect on the HepG2 cell viability in vitro. The effect of ODSO, or combined with the insulin, on the glucose absorption activity of isolated rat hemidiaphragm was evaluated at the dose 1 g/L in vitro. The results demonstrated the safety of ODSO. Indeed, this study showed that this oil does not produce any mortality or signs of toxicity after the single-dose administration in mice. Additionally, the daily intake of the ODSO during four weeks does not induce a significant variation in the biochemical parameters and body weight of rats compared with the control group. Besides, the cell viability of HepG2 did not change in the presence of ODSO. On the other hand, the ODSO increased the glucose absorption activity of the isolated rat hemidiaphragm, and this activity was significantly enhanced when combined with insulin. This study confirms, on one side, the safety of this oil and its efficacy and, on the other side, encourages its potential use as a complement to treat diabetes.

Impact of Conventional and Atypical MAPKs on the Development of Metabolic Diseases

The family of mitogen-activated protein kinases (MAPKs) consists of fourteen members and has been implicated in regulation of virtually all cellular processes. MAPKs are divided into two groups, conventional and atypical MAPKs. Conventional MAPKs are further classified into four sub-families: extracellular signal-regulated kinases 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK1, 2 and 3), p38 (α, β, γ, δ), and extracellular signal-regulated kinase 5 (ERK5). Four kinases, extracellular signal-regulated kinase 3, 4, and 7 (ERK3, 4 and 7) as well as Nemo-like kinase (NLK) build a group of atypical MAPKs, which are activated by different upstream mechanisms than conventional MAPKs. Early studies identified JNK1/2 and ERK1/2 as well as p38α as a central mediators of inflammation-evoked insulin resistance. These kinases have been also implicated in the development of obesity and diabetes. Recently, other members of conventional MAPKs emerged as important mediators of liver, skeletal muscle, adipose tissue, and pancreatic β-cell metabolism. Moreover, latest studies indicate that atypical members of MAPK family play a central role in the regulation of adipose tissue function. In this review, we summarize early studies on conventional MAPKs as well as recent findings implicating previously ignored members of the MAPK family. Finally, we discuss the therapeutic potential of drugs targeting specific members of the MAPK family.

Palmitate-induced toxicity is associated with impaired mitochondrial respiration and accelerated oxidative stress in cultured cardiomyocytes: The critical role of coenzyme Q9/10

Impaired mitochondrial function concomitant to enhanced oxidative stress-induced damage are well established mechanisms involved in hyperlipidemia-induced cardiotoxicity. Currently, limited information is available on the direct effect of myocardial lipid overload on endogenous coenzyme Q_9/10 (CoQ_9/10) levels in association with mitochondrial respiration and oxidative stress status. Here, such effects were explored by exposing H9c2 cardiomyocytes to various doses (0.15 to 1 mM) of palmitate for 24 h. The results demonstrated that palmitate doses ≥0.25 mM are enough to impair mitochondrial respiration and cause oxidative stress. Although endogenous CoQ_9/10 levels are enhanced by palmitate doses ≤0.5 mM, this is not enough to counteract oxidative stress, but is sufficient to maintain cell viability of cardiomyocytes. Palmitate doses >0.5 mM caused severe mitochondrial toxicity, including reduction of cell viability. Interestingly, enhancement of CoQ_9/10 levels with the lowest dose of palmitate (0.15 mM) was accompanied by a significantly reduction of CoQ₉ oxidation status, as well as low cytosolic production of reactive oxygen species. From the overall findings, it appears that CoQ_9/10 response may be crucial to improve mitochondrial function in conditions linked to hyperlipidemia-induced insult. Confirmation of such findings in relevant in vivo models remains essential to better understand the cardioprotective effects in association with improving endogenous CoQ_9/10 content.

Modulation of adiponectin receptors AdipoR1 and AdipoR2 by phage display-derived peptides in in vitro and in vivo models

Type 2 diabetes (T2D) is often linked to metabolic syndrome, which assembles various risk factors related to obesity. Plasma levels of adiponectin are decreased in T2D and obese subjects. Aiming to develop a peptide able to bind adiponectin receptors and modulate their signalling pathways, a 12-amino acid sequence homologous in AdipoR1/R2 has been targeted by phage display with a linear 12-mer peptide library. The selected peptide P17 recognises AdipoR1/R2 expressed by skeletal muscle, liver and pancreatic islets. In HepaRG and C2C12 cells, P17 induced the activation of AMPK (AMPKα-pT172) and the expression of succinate dehydrogenase and glucokinase; no cytotoxic effects were observed on HepaRG cells. In db/db mice, P17 promoted body weight and glycaemia stabilisation, decreased plasma triglycerides to the range of healthy mice and increased adiponectin (in high fat-fed mice) and insulin (in chow-fed mice) levels. It restored to the range of healthy mice the tissue levels and subcellular distribution of AdipoR1/R2, AMPKα-pT172 and PPARα-pS12. In liver, P17 reduced steatosis and apoptosis. The docking of P17 to AdipoR is reminiscent of the binding mechanism of adiponectin. To conclude, we have developed an AdipoR1/AdipoR2-targeted peptide that modulates adiponectin signalling pathways and has therapeutic relevance for T2D and obesity associated pathologies.

Mechanisms of electrical remodeling in lipotoxic guinea pig heart

OBJECTIVES

To develop an adult guinea pig model of lipotoxicity and explore the underlying mechanisms associated with changes in the expression of the delayed rectifier potassium current (I_K).

BACKGROUND

Lipotoxicity may represent a common link among metabolic disorders and a higher vulnerability to arrhythmias.

METHODS

Whole-cell patch clamp, and palmitic acid (PA, a potent inducer of lipotoxicity), were used to assess mechanisms of short-term (∼50 days) high-fat diet (HFD) feeding on atrial electrophysiology in guinea pig hearts and myocytes.

RESULTS

HFD fed guinea pigs were significantly heavier, displayed hypertriglyceridemia and hypercholesterolemia; but no signs of hyperglycemia or inflammation compared to low-fat diet fed controls. Increasing cardiac PA levels, resulted in shortened atrial action potential duration, and increased I_K density. Inhibition of phosphoinositide 3-kinase (PI3K) prevented increases in I_K due to PA. Acute (≥1hr) exposure of atrial myocytes to exogenous PA (1 mM) increased the density of the rapid delayed rectifier potassium current I_Kr, while it was decreased with the unsaturated oleic acid (OA, 1 mM). Serine-threonine protein phosphatase-2 (PP2A) inhibition with cantharidin reversed the effect of OA on I_Kr.

CONCLUSION

Our data provide evidence of a novel lipotoxic guinea pig model with signs of vulnerability to arrhythmias. Inhibition of PA/PI3K/I_K and/or activation of the OA/PP2A/I_Kr pathways may be therapeutically beneficial for lipotoxic arrhythmias.

TFAM Enhances Fat Oxidation and Attenuates High-Fat Diet-Induced Insulin Resistance in Skeletal Muscle

Diet-induced insulin resistance (IR) adversely affects human health and life span. We show that muscle-specific overexpression of human mitochondrial transcription factor A (TFAM) attenuates high-fat diet (HFD)-induced fat gain and IR in mice in conjunction with increased energy expenditure and reduced oxidative stress. These TFAM effects on muscle are shown to be exerted by molecular changes that are beyond its direct effect on mitochondrial DNA replication and transcription. TFAM augmented the muscle tricarboxylic acid cycle and citrate synthase facilitating energy expenditure. TFAM enhanced muscle glucose uptake despite increased fatty acid (FA) oxidation in concert with higher β-oxidation capacity to reduce the accumulation of IR-related carnitines and ceramides. TFAM also increased pAMPK expression, explaining enhanced PGC1α and PPARβ, and reversing HFD-induced GLUT4 and pAKT reductions. TFAM-induced mild uncoupling is shown to protect mitochondrial membrane potential against FA-induced uncontrolled depolarization. These coordinated changes conferred protection to TFAM mice against HFD-induced obesity and IR while reducing oxidative stress with potential translational opportunities.

4-hydroxy-3-methoxy cinnamic acid accelerate myoblasts differentiation on C2C12 mouse skeletal muscle cells via AKT and ERK 1/2 activation

BACKGROUND

The dietary intake of plant-based supplements has a vital role in human health and development. However, the actions of secondary plant metabolites on cell growth, differentiation and their signaling mechanisms are still unclear.

PURPOSE

In this study, we aim to investigate the C2C12 myoblast cells proliferation and differentiation by 4-hydroxy-3-methoxy cinnamic acid (=HMCA, ferulic acid) in a dose-dependent manner and to reveal its underlying mechanism of action.

METHODS

The effect of HMCA on C2C12 cell proliferation and differentiation were evaluated by expression of BMP's marker genes (-2, -4, -6, -7) and related myogenic proteins were analyzed by quantitative PCR and western blot techniques, respectively.

RESULTS

The in vitro findings confirmed that the HMCA upregulates BMPs (including BMP-2, -4, -6, and-7), gene expression in C2C12 skeletal muscle cells. Exposure to the lower dose of HMCA caused a significantly greater induction of myogenic differentiation than the higher dose during three- and six-day treatments. Further, the C2C12 myogenic differentiation signaling proteins MyoD, myogenin, JAK-1, -2, -3, STAT -2, -3, AMPK-α, ERK(1/2), and AKT were more preferentially activated by HMCA exposure cells than by untreated models. Thus, the experiment with inhibitors revealed that the HMCA induced muscle cell proliferation and differentiation through AKT and ERK (1/2) signaling cascades. Also, HMCA enhanced the C2C12 muscle cell differentiation protein markers such as myogenin, AKT and ERK (1/2) significantly (p ≤ 0.05) at day three in chemical inhibitors of LY 294002 and PD98056 treated samples.

CONCLUSION

The HMCA has a significant effect on muscle cell differentiation through ERK(1/2) and AKT signaling activation. Also, the HMCA promotes C2C12 muscle cell proliferation and differentiation via activation of osteogenic genes and myogeneic protein markers. Therefore, this study suggests that the natural phenolic compound HMCA has a potent function in muscle cell proliferation, differentiation, and development.

"Insulin-like" effects of palmitate compromise insulin signalling in hypothalamic neurons

Saturated fatty acids are implicated in the development of metabolic diseases, including obesity and type 2 diabetes. There is evidence, however, that polyunsaturated fatty acids can counteract the pathogenic effects of saturated fatty acids. To gain insight into the early molecular mechanisms by which fatty acids influence hypothalamic inflammation and insulin signalling, we performed time-course experiments in a hypothalamic cell line, using different durations of treatment with the saturated fatty acid palmitate, and the omega-3 polyunsaturated fatty acid, docosahexaenoic acid (DHA). Western blot analysis revealed that palmitate elevated the protein levels of phospho(p)AKT in a time-dependent manner. This effect is involved in the pathogenicity of palmitate, as temporary inhibition of the PI3K/AKT pathway by selective PI3K inhibitors prevented the palmitate-induced attenuation of insulin signalling. Similar to palmitate, DHA also increased levels of pAKT, but to a weaker extent. Co-administration of DHA with palmitate decreased pAKT close to the basal level after 8 h, and prevented the palmitate-induced reduction of insulin signalling after 12 h. The monounsaturated fatty acid oleate had a similar effect on the palmitate-induced attenuation of insulin signalling, the polyunsaturated fatty acid linoleate had no effect. Measurement of the inflammatory markers pJNK and pNFκB-p65 revealed tonic elevation of both markers in the presence of palmitate alone. DHA alone transiently induced elevation of pJNK, returning to basal levels by 12 h treatment. Co-administration of DHA with palmitate prevented palmitate-induced inflammation after 12 h, but not at earlier timepoints.

Is palmitate truly proinflammatory? Experimental confounders and context-specificity

Based primarily on cell culture results, saturated fatty acids (SFAs) are proposed to promote inflammation and contribute to metabolic dysfunction through Toll-like receptor activation. Studies are often complicated by a requirement for carriers (e.g., BSA) or solvents (e.g., ethanol) to increase SFA solubility. To ascertain whether these factors influence interpretations of SFA-associated inflammation activity, we measured responses of RAW264.7 monocyte/macrophages and C₂C₁₂ myotubes to various BSA, ethanol, and cyclodextrin (alternative FA carrier) conditions. Fatty acid-free, low-endotoxin BSA preparations (0.33% to 2% wt/vol) activated whereas 0.5-1.0% ethanol inhibited RAW264.7 TNFα release. Ethanol modestly increased IL-6 secretion in C₂C₁₂ myotubes. Cyclodextrins (0.3-6.0 mM) were tested as alternative carriers of palmitate, but their usefulness was limited due to toxicity and solubility issues. Using a lower-inflammation BSA source and no ethanol, ∼24-h sodium palmitate treatment (≤600 µM) failed to trigger RAW264.7 TNFα release and, in fact, significantly dampened BSA-induced inflammation by >50%. In C₂C₁₂ myotubes, only high palmitate concentrations (500-600 µM) elicited IL-6 secretion (>2.5-fold increase). Acute palmitate (200 or 500 µM) treatment did not activate MAP kinase pathways above that of fresh BSA-containing media alone in either cell type. These results highlight the importance of experimental conditions in studies exploring SFA inflammation effects. The limited (or even anti-inflammatory) effects of palmitate that we observed indicate that immunomodulatory effects of SFAs are context-specific. Thus, caution is needed when interpreting the literature related to putative proinflammatory effects of SFA.

Mebendazole exhibits potent anti-leukemia activity on acute myeloid leukemia

Acute myeloid leukemia (AML) is one of the most common types of acute leukemia in adults with the lowest survival rate of all leukemia. Resistance to cytarabine and anthracycline-based chemotherapy is a major cause of treatment failure. Thus, finding new drugs with anti-leukemia activities and minimal side effect is urgently needed. Here through screening more than 1000 drugs approved by the Food and Drug Administration (FDA) of United States, the anthelmintic drug mebendazole (MBZ) was found to inhibit the growth of AML cell lines (THP-1, U937, NB4 and K562) and bone marrow mononuclear cells (BM-MNCs) from AML patients at pharmacologically achievable concentrations. In contrast, similar concentration of MBZ had little inhibitory effect on the growth of normal peripheral blood mononuclear cells (PBMC) or human umbilical vein endothelial cells (HUVEC). In addition, MBZ induced mitotic arrest and mitotic catastrophe in AML cells based on nuclear morphology, cell cycle distribution, mitotic marker analyses and the number of multinucleated cells and apoptotic cells. Furthermore, MBZ treatment inhibited activation of Akt and Erk in AML leukemic cells. Finally, MBZ repressed the progression of leukemic cells in vivo and prolonged survival in AML xenograft mouse model. Taken together, our results suggest that MBZ could be a potential new therapeutic agent for the treatment of AML patients.

Relaxin activates AMPK-AKT signaling and increases glucose uptake by cultured cardiomyocytes

PURPOSE

Many evidences show that the hormone relaxin plays a pivotal role in the physiology and pathology of the cardiovascular system. This pleiotropic hormone exerts regulatory functions through specific receptors in cardiovascular tissues: in experimental animal models it was shown to induce coronary vasodilation, prevent cardiac damage induced by ischemia/reperfusion and revert cardiac hypertrophy and fibrosis. A tight relationship between this hormone and important metabolic pathways has been suggested, but it is at present unknown if relaxin could regulate cardiac metabolism. Our aim was to study the possible effects of relaxin on cardiomyocyte metabolism.

METHODS

Neonatal rat cardiomyocytes were treated with relaxin and (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assays (MTT) were performed to assess metabolic activity; while 2-deoxy-D-[³H] glucose and BODIPY-labelled fatty acid incorporations were analyzed to measure glucose and fatty acid uptakes, and western blot was utilized to study the intracellular signaling pathways activated by the hormone.

RESULTS

We observed that relaxin at 10 ng/ml was able to increase the level of metabolic activity of cultured neonatal rat cardiomyocytes; the rate of 2-deoxy-D-[³H]glucose incorporation demonstrated that relaxin also induced an increase in glucose uptake. First evidence is also offered that relaxin can activate the master energy sensor and regulator AMPK in cardiomyocytes. Moreover, the treatment of cardiomyocytes with relaxin also induced dose-dependent increases in ERK1/2, AKT, and AS160 phosphorylation. That raise in AS160 phosphorylation induced by relaxin was prevented by the pretreatment with AMPK and AKT pathways inhibitors, indicating that both molecules play important roles in the relaxin effects reported.

CONCLUSION

Relaxin can regulate cardiomyocyte metabolism and activate AMPK, the central sensor of energy status that maintains cellular energy homeostasis, and also ERK and AKT, two molecular sensing nodes that coordinate dynamic responses of the cell's metabolic responses.

Cigarette smoke induced urocystic epithelial mesenchymal transition via MAPK pathways

Cigarette smoke has been shown to be a major risk factor for bladder cancer. Epithelial-mesenchymal transition (EMT) is a crucial process in cancer development. The role of MAPK pathways in regulating cigarette smoke-triggered urocystic EMT remains to be elucidated. Human normal urothelial cells and BALB/c mice were used as in vitro and in vivo cigarette smoke exposure models. Exposure of human normal urothelial cells to cigarette smoke induced morphological change, enhanced migratory and invasive capacities, reduced epithelial marker expression and increased mesenchymal marker expression, along with the activation of MAPK pathways. Moreover, we revealed that ERK1/2 and p38 inhibitors, but rather JNK inhibitor, effectively attenuated cigarette smoke-induced urocystic EMT. Importantly, the regulatory function of ERK1/2 and p38 pathways in cigarette smoke-triggered urocystic EMT was further confirmed in mice exposed to CS for 12 weeks. These findings could provide new insight into the molecular mechanisms of cigarette smoke-associated bladder cancer development as well as its potential intervention.

In vitro contraction protects against palmitate-induced insulin resistance in C2C12 myotubes

We are interested in understanding mechanisms that govern the protective role of exercise against lipid-induced insulin resistance, a key driver of type 2 diabetes. In this context, cell culture models provide a level of abstraction that aid in our understanding of cellular physiology. Here we describe the development of an in vitro myotube contraction system that provides this protective effect, and which we have harnessed to investigate lipid-induced insulin resistance. C2C12 myocytes were differentiated into contractile myotubes. A custom manufactured platinum electrode system and pulse stimulator, with polarity switching, provided an electrical pulse stimulus (EPS) (1 Hz, 6-ms pulse width, 1.5 V/mm, 16 h). Contractility was assessed by optical flow flied spot noise mapping and inhibited by application of ammonium acetate. Following EPS, myotubes were challenged with 0.5 mM palmitate for 4 h. Cells were then treated with or without insulin for glucose uptake (30 min), secondary insulin signaling activation (10 min), and phosphoinositide 3-kinase-α (PI3Kα) activity (5 min). Prolonged EPS increased non-insulin-stimulated glucose uptake (83%, P = 0.002), Akt (Thr308) phosphorylation (P = 0.005), and insulin receptor substrate-1 (IRS-1)-associated PI3Kα activity (P = 0.048). Palmitate reduced insulin-specific action on glucose uptake (-49%, P < 0.001) and inhibited insulin-stimulated Akt phosphorylation (P = 0.049) and whole cell PI3Kα activity (P = 0.009). The inhibitory effects of palmitate were completely absent with EPS pretreatment at the levels of glucose uptake, insulin responsiveness, Akt phosphorylation, and whole cell PI3Kα activity. This model suggests that muscle contraction alone is a sufficient stimulus to protect against lipid-induced insulin resistance as evidenced by changes in the proximal canonical insulin-signaling pathway.

Palmitic Acid-BSA enhances Amyloid-β production through GPR40-mediated dual pathways in neuronal cells: Involvement of the Akt/mTOR/HIF-1α and Akt/NF-κB pathways

The pathophysiological actions of fatty acids (FAs) on Alzheimer’s disease (AD), which are possibly mediated by genomic effects, are widely known; however, their non-genomic actions remain elusive. The aim of this study was to investigate the non-genomic mechanism of extra-cellular palmitic acid (PA) regulating beta-amyloid peptide (Aβ) production, which may provide a link between obesity and the occurrence of AD. In an obese mouse model, a high-fat diet (HFD) significantly increased the expression levels of APP and BACE1 as well as the AD pathology in the mouse brain. We further found that PA conjugated with bovine serum albumin (PA-BSA) increased the expression of APP and BACE1 and the production of Aβ through the G protein-coupled receptor 40 (GPR40) in SK-N-MC cells. PA-BSA coupling with GPR40 significantly induced Akt activation which is required for mTOR/p70S6K1-mediated HIF-1α expression and NF-κB phosphorylation facilitating the transcriptional activity of the APP and BACE1 genes. In addition, silencing of APP and BACE1 expression significantly decreased the production of Aβ in SK-N-MC cells treated with PA-BSA. In conclusion, these results show that extra-cellular PA coupled with GPR40 induces the expression of APP and BACE1 to facilitate Aβ production via the Akt-mTOR-HIF-1α and Akt-NF-κB pathways in SK-N-MC cells.

Myristic Acid Enhances Diacylglycerol Kinase δ-Dependent Glucose Uptake in Myotubes

Decreased expression of diacylglycerol kinase (DGK) δ in skeletal muscles attenuates glucose uptake and is closely related to the pathogenesis of type 2 diabetes. Therefore, up-regulation of DGKδ expression is thought to protect and improve glucose homoeostasis in type 2 diabetes. We recently determined that myristic acid (14:0), but not palmitic (16:0) or stearic (18:0) acid, significantly increased DGKδ2 protein expression in mouse C2C12 myotubes. In the current study, we analyzed whether myristic acid indeed enhances glucose uptake in C2C12 myotubes. We observed that myristic acid caused ~1.4-fold increase in insulin-independent glucose uptake. However, palmitic and stearic acids failed to enhance glucose uptake. DGKδ-specific siRNA decreased myristic acid-dependent increase of glucose uptake. Moreover, overexpression of DGKδ2 enhanced glucose uptake in C2C12 cells in the absence of myristic acid treatment. Taken together, these results strongly suggest that myristic acid enhances basal glucose uptake in myotubes in a DGKδ2 expression-dependent manner.

Induction of Gnrh mRNA expression by the ω-3 polyunsaturated fatty acid docosahexaenoic acid and the saturated fatty acid palmitate in a GnRH-synthesizing neuronal cell model, mHypoA-GnRH/GFP

Gonadotropin-releasing hormone (GnRH) neurons coordinate reproduction. However, whether GnRH neurons directly sense free fatty acids (FFAs) is unknown. We investigated the individual effects of the FFAs docosahexaenoic acid (DHA), palmitate, palmitoleate, and oleate (100 μM each) on Gnrh mRNA expression in the mHypoA-GnRH/GFP neuronal cell model. We report that 2 h exposure to palmitate or DHA increases Gnrh transcription. Using the inhibitors AH7614, K252c, U0126, wortmannin, and LY294002, we demonstrate that the effect of DHA is mediated through GPR120 to downstream PKC/MAPK and PI3K signaling. Our results indicate that the effect of palmitate may depend on palmitoyl-coA synthesis and PI3K signaling. Finally, we demonstrate that both DHA and palmitate increase Gnrh enhancer-derived RNA levels. Overall, these studies provide evidence that GnRH neurons directly sense FFAs. This will advance our understanding of the mechanisms underlying FFA sensing in the brain and provides insight into the links between nutrition and reproductive function.

Evidence for DNA damage as a biological link between diabetes and cancer

Objective:

This review examines the evidence that: Diabetes is a state of DNA damage; pathophysiological factors in diabetes can cause DNA damage; DNA damage can cause mutations; and DNA mutation is linked to carcinogenesis.

Data Sources:

We retrieved information from the PubMed database up to January, 2014, using various search terms and their combinations including DNA damage, diabetes, cancer, high glucose, hyperglycemia, free fatty acids, palmitic acid, advanced glycation end products, mutation and carcinogenesis.

Study Selection:

We included data from peer-reviewed journals and a textbook printed in English on relationships between DNA damage and diabetes as well as pathophysiological factors in diabetes. Publications on relationships among DNA damage, mutagenesis, and carcinogenesis, were also reviewed. We organized this information into a conceptual framework to explain the possible causal relationship between DNA damage and carcinogenesis in diabetes.

Results:

There are a large amount of data supporting the view that DNA mutation is a typical feature in carcinogenesis. Patients with type 2 diabetes have increased production of reactive oxygen species, reduced levels of antioxidant capacity, and increased levels of DNA damage. The pathophysiological factors and metabolic milieu in diabetes can cause DNA damage such as DNA strand break and base modification (i.e., oxidation). Emerging experimental data suggest that signal pathways (i.e., Akt/tuberin) link diabetes to DNA damage. This collective evidence indicates that diabetes is a pathophysiological state of oxidative stress and DNA damage which can lead to various types of mutation to cause aberration in cells and thereby increased cancer risk.

Conclusions:

This review highlights the interrelationships amongst diabetes, DNA damage, DNA mutation and carcinogenesis, which suggests that DNA damage can be a biological link between diabetes and cancer.

In vitro evaluation of anti-diabetic activity and cytotoxicity of chemically analysed Ocimum basilicum extracts

The aim of this study was to evaluate the role of glucose transporter-4 (GLUT4) in the anti-diabetic effects of methanol, hexane and dichloromethane extracts of the aerial parts of Ocimum basilicum (OB) and to analyze their phytochemical composition. Phytochemical analysis of the three extracts by GC/MS using the silylation derivatization technique revealed 53 compounds, 17 of them were found for the first time in OB. Cytotoxic and anti-diabetic properties of the extracts were evaluated using L6-GLUT4myc muscle cells stably expressing myc epitope at the exofacial loop (GLUT4). No cytotoxic effects were observed in treated cells up to 0.25 mg/ml extract as measured with MTT and LDH-leakage assays. GLUT4 translocation to the plasma membrane was elevated by 3.5 and 7 folds (-/+ insulin) after treatment with OB extracts for 20 h. Our findings suggest that the observed anti-diabetic properties of OB extracts are possibly mediated in part through one or more of the 17 new identified compound.

Pentacyclic Triterpenoids from Astilbe rivularis that Enhance Glucose Uptake via the Activation of Akt and Erk1/2 in C2C12 Myotubes

Glucose uptake into insulin-sensitive tissues is important for the regulation of blood glucose. This study has investigated whether the pentacyclic triterpenoids substituted with a carboxylic acid at the C-27 position isolated from Astilbe rivularis can enhance glucose uptake and subsequently to also examine their underlying molecular mechanisms. The structure of the new pentacyclic triterpenoid 1 was assigned by spectroscopic data interpretation. To evaluate the activity of compounds 1 and 2, glucose uptake and glucose transporter 4 (GLUT4) translocation were measured in C2C12 myotubes. The C-27-carboxylated triterpenoids 1 and 2 significantly increased basal and insulin-stimulated glucose uptake and GLUT4 translocation to plasma membrane. Both compounds stimulated the phosphorylation of insulin receptor substrate-1 (IRS-1), protein kinase B (Akt), and extracellular signal-regulated kinase 1/2 (Erk1/2). Pretreatment with the Akt inhibitor triciribine or the Erk1/2 inhibitor U0126 decreased the ability of both compounds to enhance basal- and insulin-stimulated glucose uptake and stimulate GLUT4 translocation. These results indicate that compounds 1 and 2 activated both the IRS-1/Akt and Erk1/2 pathways and subsequently stimulated GLUT4 translocation, leading to enhanced glucose uptake. Thus, these observations suggest that C-27-carboxylated-pentacyclic triterpenoids may serve as scaffolds for development as agents for the management of blood glucose levels in disease states such as diabetes.

Fucosylated chondroitin sulfate from sea cucumber improves insulin sensitivity via activation of PI3K/PKB pathway

This study was to investigate the effects of fucosylated chondroitin sulfate (CHS) from sea cucumber on insulin sensitivity in skeletal muscle of type 2 diabetic mice induced by a high-fat high-sucrose diet (HFSD). CHS supplementation for 19 wk significantly improved insulin sensitivity by 20%, and reduced blood glucose and insulin levels. Western blotting assay showed that CHS significantly increased insulin-stimulated glucose transporter 4 (GLUT4) translocation to 1.7-fold, phosphorylation of phosphoinositide 3-kinase (PI3K) at p85 to 5.0-fold, protein kinase B (PKB) at Ser473 to 1.5-fold, and Thr308 to 1.6-fold in skeletal muscle. However, PI3K, PKB, and GLUT4 total proteins expression were unchangeable. In addition, qRT-PCR analysis proved that the insulin signaling was activated by CHS treatment, showing the increased mRNA expressions of glucose uptake-related key genes. It indicated that CHS improved insulin sensitivity by activation of PI3K/PKB signaling in skeletal muscle of type 2 diabetic mice. Identification of potential mechanism by which CHS increased insulin sensitivity might provide a new functional food or pharmaceutical application of sea cucumber.

Amelioration of palmitate-induced metabolic dysfunction in L6 muscle cells expressing low levels of receptor-interacting protein 140

We have shown that reduced expression of receptor-interacting protein 140 (RIP140) alters the regulation of fatty-acid (FA) oxidation in muscle. To determine whether a high level of FA availability alters the effects of RIP140 on metabolic regulation, L6 myotubes were transfected with or without RNA interference oligonucleotide sequences to reduce RIP140 expression, and then incubated with high levels of palmitic acid, with or without insulin. High levels of palmitate reduced basal (53%-58%) and insulin-treated (24%-44%) FA uptake and oxidation, and increased basal glucose uptake (88%). In cells incubated with high levels of palmitate, low RIP140 increased basal FA uptake and insulin-treated FA oxidation and glucose uptake, and decreased basal glucose uptake and insulin-treated FA uptake. Under basal conditions, low RIP140 increased the mRNA content of FAT/CD36 (159%) and COX4 (61%), as well as the protein content of Nur77 (68%), whereas the mRNA expression of FGF21 (50%) was decreased, as was the protein content of CPT1b (35%) and FGF21 (44%). Under insulin-treated conditions, low RIP140 expression increased the mRNA content of MCAD (84%) and Nur77 (84%), as well as the protein content of Nur77 (23%). Thus, a low level of RIP140 restores the rates of FA uptake in the basal state, in part via a reduction in upstream insulin signaling. Our data also indicate that the protein expression of Nur77 may be modulated by RIP140 when muscle cells are metabolically challenged by high levels of palmitate.

Proteomic analysis of the palmitate-induced myotube secretome reveals involvement of the annexin A1-formyl peptide receptor 2 (FPR2) pathway in insulin resistance

Elevated levels of the free fatty acid palmitate are found in the plasma of obese patients and induce insulin resistance. Skeletal muscle secretes myokines as extracellular signaling mediators in response to pathophysiological conditions. Here, we identified and characterized the skeletal muscle secretome in response to palmitate-induced insulin resistance. Using a quantitative proteomic approach, we identified 36 secretory proteins modulated by palmitate-induced insulin resistance. Bioinformatics analysis revealed that palmitate-induced insulin resistance induced cellular stress and modulated secretory events. We found that the decrease in the level of annexin A1, a secretory protein, depended on palmitate, and that annexin A1 and its receptor, formyl peptide receptor 2 agonist, played a protective role in the palmitate-induced insulin resistance of L6 myotubes through PKC-θ modulation. In mice fed with a high-fat diet, treatment with the formyl peptide receptor 2 agonist improved systemic insulin sensitivity. Thus, we identified myokine candidates modulated by palmitate-induced insulin resistance and found that the annexin A1- formyl peptide receptor 2 pathway mediated the insulin resistance of skeletal muscle, as well as systemic insulin sensitivity.

Dynamic changes in genes related to glucose uptake and utilization during pig skeletal and cardiac muscle development

Skeletal and cardiac muscle have important roles in glucose uptake and utilization. However, changes in expression of protein coding genes and miRNAs that participate in glucose metabolism during development are not fully understood. In this study, we investigated the expression of genes related to glucose metabolism during muscle development. We found an age-dependent increase in gene expression in cardiac muscle, with enrichment in heart development- and energy-related metabolic processes. A subset of genes that were up-regulated until 30 or 180 days postnatally, and then down-regulated in psoas major muscle was significantly enriched in mitochondrial oxidative-related processes, while genes that up-regulated in longissimus doris muscle was significantly enriched in glycolysis-related processes. Meanwhile, expression of energy-related microRNAs decreased with increasing age. In addition, we investigated the correlation between microRNAs and mRNAs in three muscle types across different stages of development and found many potential microRNA-mRNA pairs involved in regulating glucose metabolism.

Subcutaneous adipocytes promote melanoma cell growth by activating the Akt signaling pathway: role of palmitic acid

Tumorigenesis involves constant communication between tumor cells and neighboring normal cells such as adipocytes. The canonical function of adipocytes is to store triglyceride and release fatty acids for other tissues. This study was aimed to find out if adipocytes promoted melanoma cell growth and to investigate the underlying mechanism. Here we isolated adipocytes from inguinal adipose tissue in mice and co-cultured with melanoma cells. We found that the co-cultured melanoma had higher lipid accumulation compared with mono-cultured melanoma. In addition, fluorescently labeled fatty acid BODIPY® FLC16 signal was detected in melanoma co-cultured with the adipocytes that had been loaded with the fluorescent dye, suggesting that the adipocytes provide fatty acids to melanoma cells. Compared with mono-cultured melanoma, co-cultured melanoma cells had a higher proliferation and phospho-Akt (Ser-473 and Thr-450) expression. Overexpression of Akt mutants in melanoma cells reduced the co-culture-enhanced proliferation. A lipidomic study showed that the co-cultured melanoma had an elevated palmitic acid level. Interestingly, we found that palmitic acid stimulated melanoma cell proliferation, changed the cell cycle distribution, and increased phospho-Akt (Ser-473 and Thr-450) and PI3K but not phospho-PTEN (phosphophosphatase and tensin homolog) expressions. More importantly, the palmitic acid-stimulated proliferation was further enhanced in the Akt-overexpressed melanoma cells and was reduced by LY294002 or knockdown of endogenous Akt or overexpression of Akt mutants. We also found that palmitic acid-pretreated B16F10 cells were grown to a significantly larger tumor in mice compared with control cells. Taken together, we suggest that adipocytes may serve as an exogenous source of palmitic acid that promotes melanoma cell growth by activating Akt.

Cyclooxygenase-2-dependent oxidative stress mediates palmitate-induced impairment of endothelium-dependent relaxations in mouse arteries

Palmitic acid, one of the saturated free fatty acids, impairs cardiovascular function as manifested by inducing vascular inflammation, apoptosis and over-production of reactive oxygen species (ROS) although the origin for ROS remains unclear. The present study investigated the cellular mechanisms underlying palmitate-induced impairment of endothelial function. Ex vivo treatment in tissue culture with palmitate concentration-dependently attenuated acetylcholine-induced endothelium-dependent relaxations, up-regulated the expression of cyclooxygenase-2 (COX-2) and elevated superoxide formation in mouse aortic endothelial cells (MAECs) measured by dihydroethidium (DHE) staining and electron paramagnetic resonance (EPR) spectroscopy. Superoxide scavengers, COX-2 inhibitor and thromboxane prostanoid (TP) receptor antagonist, but not COX-1 inhibitor reversed the harmful effects of palmitate. Furthermore, palmitate impaired acetylcholine-induced relaxations and raised superoxide in en face endothelium of aortas only from COX-1(-/-) mice but not from COX-2(-/-) mice. Palmitate increased the production and release of TXB2, a stable thromboxane A2 metabolite in mouse aortas, which was abolished by COX-2 inhibitor. Superoxide scavenger did not affect palmitate-induced up-regulated expression of COX-2 in MAECs. Both real time PCR and luciferase reporter gene assay confirmed COX-2 up-regulation in palmitate-treated MAECs and NF-κB was substantially involved in this up-regulation. The present study provides novel evidence that palmitate up-regulates COX-2 through NF-κB-dependent mechanism and resultant COX-2-associated oxidative stress impairs endothelium-dependent relaxations in mouse aortas.

Mitochondrial glycerol-3-phosphate acyltransferase-1 is essential for murine CD4(+) T cell metabolic activation

Glycerol-3-phosphate acyltransferase-1 is the first rate limiting step in de novo glycerophospholipid synthesis. We have previously demonstrated that GPAT-1 deletion can significantly alter T cell function resulting in a T cell phenotype similar to that seen in aging. Recent studies have suggested that changes in the metabolic profile of T cells are responsible for defining specific effector functions and T cell subsets. Therefore, we determined whether T cell dysfunction in GPAT-1 (-/-) CD4(+) T cells could be explained by changes in cellular metabolism. We show here for the first time that GPAT-1 (-/-) CD4(+) T cells exhibit several key metabolic defects. Striking decreases in both the oxygen consumption rate (OCR) and the extracellular acidification rate (ECAR) were observed in GPAT-1 (-/-) CD4(+) T cells following CD3/CD28 stimulation indicating an inherent cellular defect in energy production. In addition, the spare respiratory capacity (SRC) of GPAT-1 (-/-) CD4+ T cells, a key indicator of their ability to cope with mitochondrial stress was significantly decreased. We also observed a significant reduction in mitochondrial membrane potential in GPAT-1 (-/-) CD4(+) T cells compared to their WT counterparts, indicating that GPAT-1 deficiency results in altered or dysfunctional mitochondria. These data demonstrate that deletion of GPAT-1 can dramatically alter total cellular metabolism under conditions of increased energy demand. Furthermore, altered metabolic response following stimulation may be the defining mechanism underlying T cell dysfunction in GPAT-1 (-/-) CD4(+) T cells. Taken together, these results indicate that GPAT-1 is essential for the response to the increased metabolic demands associated with T cell activation.

The Baf60c/Deptor pathway links skeletal muscle inflammation to glucose homeostasis in obesity

Skeletal muscle insulin resistance in type 2 diabetes is associated with a shift from oxidative to glycolytic metabolism in myofibers. However, whether this metabolic switch is detrimental or adaptive for metabolic homeostasis has not been resolved. We recently demonstrated that the Baf60c/Deptor pathway promotes glycolytic metabolism in the muscle and protects mice from diet-induced insulin resistance. However, the nature of the signals that impinge on this pathway and the role of Baf60c in glucose homeostasis in the severe insulin-resistant state remain unknown. Here we show that expression of Baf60c and Deptor was downregulated in skeletal muscle in obesity, accompanied by extracellular signal-related kinase (ERK) activation. In cultured myotubes, inhibition of ERK, but not Jun NH2-terminal kinase and IκB kinase, blocked the downregulation of Baf60c and Deptor by the proinflammatory cytokine tumor necrosis factor-α. Treatment of obese mice with the ERK inhibitor U0126 rescued Baf60c and Deptor expression in skeletal muscle and lowered blood glucose. Transgenic rescue of Baf60c in skeletal muscle restored Deptor expression and Akt phosphorylation and ameliorated insulin resistance in ob/ob mice. This study identifies the Baf60c/Deptor pathway as a target of proinflammatory signaling in skeletal muscle that may link meta-inflammation to skeletal myofiber metabolism and insulin resistance.

Fatty acids increase neuronal hypertrophy of Pten knockdown neurons

Phosphatase and tensin homolog (Pten) catalyzes the reverse reaction of PI3K by dephosphorylating PIP3 to PIP2. This negatively regulates downstream Akt/mTOR/S6 signaling resulting in decreased cellular growth and proliferation. Co-injection of a lentivirus knocking Pten down with a control lentivirus allows us to compare the effects of Pten knockdown between individual neurons within the same animal. We find that knockdown of Pten results in neuronal hypertrophy by 21 days post-injection. This neuronal hypertrophy is correlated with increased p-S6 and p-mTOR in individual neurons. We used this system to test whether an environmental factor that has been implicated in cellular hypertrophy could influence the severity of the Pten knockdown-induced hypertrophy. Implantation of mini-osmotic pumps delivering fatty acids results in increased neuronal hypertrophy and p-S6/p-mTOR staining. These hypertrophic effects were reversed in response to rapamycin treatment. However, we did not observe a similar increase in hypertrophy in response to dietary manipulations of fatty acids. Thus, we conclude that by driving growth signaling with fatty acids and knocking down a critical regulator of growth, Pten, we are able to observe an additive morphological phenotype of increased soma size mediated by the mTOR pathway.

The effects of propionate and valerate on insulin responsiveness for glucose uptake in 3T3-L1 adipocytes and C2C12 myotubes via G protein-coupled receptor 41

Since insulin resistance can lead to hyperglycemia, improving glucose uptake into target tissues is critical for regulating blood glucose levels. Among the free fatty acid receptor (FFAR) family of G protein-coupled receptors, GPR41 is known to be the Gα_i/o-coupled receptor for short-chain fatty acids (SCFAs) such as propionic acid (C3) and valeric acid (C5). This study aimed to investigate the role of GPR41 in modulating basal and insulin-stimulated glucose uptake in insulin-sensitive cells including adipocytes and skeletal muscle cells. Expression of GPR41 mRNA and protein was increased with maximal expression at differentiation day 8 for 3T3-L1 adipocytes and day 6 for C2C12 myotubes. GPR41 protein was also expressed in adipose tissues and skeletal muscle. After analyzing dose-response relationship, 300 µM propionic acid or 500 µM valeric acid for 30 min incubation was used for the measurement of glucose uptake. Both propionic acid and valeric acid increased insulin-stimulated glucose uptake in 3T3-L1 adipocyte, which did not occur in cells transfected with siRNA for GPR41 (siGPR41). In C2C12 myotubes, these SCFAs increased basal glucose uptake, but did not potentiate insulin-stimulated glucose uptake, and siGPR41 treatment reduced valerate-stimulated basal glucose uptake. Therefore, these findings indicate that GPR41 plays a role in insulin responsiveness enhanced by both propionic and valeric acids on glucose uptake in 3T3-L1 adipocytes and C2C12 myotubes, and in valerate-induced increase in basal glucose uptake in C2C12 myotubes.