Oleate prevents saturated-fatty-acid-induced ER stress, inflammation and insulin resistance in skeletal muscle cells through an AMPK-dependent mechanism.

AIMS/HYPOTHESIS: Although the substitution of saturated fatty acids with oleate has been recommended in the management of type 2 diabetes mellitus, the mechanisms by which oleate improves insulin resistance in skeletal muscle cells are not completely known. Here, we examined whether oleate, through activation of AMP-activated protein kinase (AMPK), prevented palmitate-induced endoplasmic reticulum (ER) stress, which is involved in the link between lipid-induced inflammation and insulin resistance. METHODS: Studies were conducted in mouse C2C12 myotubes and in the human myogenic cell line LHCN-M2. To analyse the involvement of AMPK, activators and inhibitors of this kinase and overexpression of a dominant negative AMPK construct (K45R) were used. RESULTS: Palmitate increased the levels of ER stress markers, whereas oleate did not. In palmitate-exposed cells incubated with a lower concentration of oleate, the effects of palmitate were prevented. The induction of ER stress markers by palmitate was prevented by the presence of the AMPK activators AICAR and A-769662. Moreover, the ability of oleate to prevent palmitate-induced ER stress and inflammation (nuclear factor-kappa B [NF-κB] DNA-binding activity and expression and secretion of IL6) as well as insulin-stimulated Akt phosphorylation and 2-deoxyglucose uptake was reversed in the presence of the AMPK inhibitor compound C or by overexpression of a dominant negative AMPK construct. Finally, palmitate reduced phospho-AMPK levels, whereas this was not observed in oleate-exposed cells or in palmitate-exposed cells supplemented with oleate. CONCLUSIONS/INTERPRETATION: Overall, these findings indicate that oleate prevents ER stress, inflammation and insulin resistance in palmitate-exposed skeletal muscle cells by activating AMPK.

The peroxisome proliferator-activated receptor (PPAR) ß/δ agonist GW501516 inhibits IL-6-induced signal transducer and activator of transcription 3 (STAT3) activation and insulin resistance in human liver cells.

AIM/HYPOTHESIS: IL-6 induces insulin resistance by activating signal transducer and activator of transcription 3 (STAT3) and upregulating the transcription of its target gene SOCS3. Here we examined whether the peroxisome proliferator-activated receptor (PPAR)ß/δ agonist GW501516 prevented activation of the IL-6-STAT3-suppressor of cytokine signalling 3 (SOCS3) pathway and insulin resistance in human hepatic HepG2 cells. METHODS: Studies were conducted with human HepG2 cells and livers from mice null for Pparß/δ (also known as Ppard) and wild-type mice. RESULTS: GW501516 prevented IL-6-dependent reduction in insulin-stimulated v-akt murine thymoma viral oncogene homologue 1 (AKT) phosphorylation and in IRS-1 and IRS-2 protein levels. In addition, treatment with this drug abolished IL-6-induced STAT3 phosphorylation of Tyr7°5 and Ser7²7 and prevented the increase in SOCS3 caused by this cytokine. Moreover, GW501516 prevented IL-6-dependent induction of extracellular-related kinase 1/2 (ERK1/2), a serine-threonine protein kinase involved in serine STAT3 phosphorylation; the livers of Pparß/δ-null mice showed increased Tyr7°5- and Ser7²7-STAT3 as well as phospho-ERK1/2 levels. Furthermore, drug treatment prevented the IL-6-dependent reduction in phosphorylated AMP-activated protein kinase (AMPK), a kinase reported to inhibit STAT3 phosphorylation on Tyr7°5. In agreement with the recovery in phospho-AMPK levels observed following GW501516 treatment, this drug increased the AMP/ATP ratio and decreased the ATP/ADP ratio. CONCLUSIONS/INTERPRETATION: Overall, our findings show that the PPARß/δ activator GW501516 prevents IL-6-induced STAT3 activation by inhibiting ERK1/2 phosphorylation and preventing the reduction in phospho-AMPK levels. These effects of GW501516 may contribute to the prevention of cytokine-induced insulin resistance in hepatic cells.

Disodium ascorbyl phytostanol phosphate (FM-VP4), a modified phytostanol, is a highly active hypocholesterolaemic agent that affects the enterohepatic circulation of both cholesterol and bile acids in mice.

Disodium ascorbyl phytostanol phosphate (FM-VP4) is a synthetic compound derived from sitostanol and campestanol that has proved to be efficient as a cholesterol-lowering therapy in mice and human subjects. However, the mechanism of action of FM-VP4 remains unknown. The present study tests the ability of FM-VP4 to alter intestinal and liver cholesterol homeostasis in mice. Female C57BL/6J mice were fed either a control chow or a 2 % FM-VP4-enriched diet for 4 weeks. FM-VP4 reduced the in vivo net intestinal cholesterol absorption and plasma and liver cholesterol concentrations by 2.2-, 1.5- and 1.6-fold, respectively, compared with control mice. Furthermore, FM-VP4 also showed an impact on bile acid homeostasis. In FM-VP4 mice, liver and intestinal bile acid content was increased by 1.3- and 2.3-fold, respectively, whereas faecal bile acid output was 3.3-fold lower. FM-VP4 also increased the intestinal absorption of orally administered [3H]taurocholic acid to small intestine in vivo. Inhibition of intestinal cholesterol absorption by FM-VP4 was not mediated via transcriptional increases in intestine liver X receptor (LXR)-alpha, adenosine triphosphate-binding cassette transporter (ABC)-A1, ABCG5/G8 nor to decreases in intestinal Niemann-Pick C1-like 1 (NPC1L1) expression. In contrast, FM-VP4 up-regulated liver LXRalpha, ABCA1, ABCG5, scavenger receptor class BI (SR-BI) and hydroxymethylglutaryl coenzyme A reductase (HMGCoA-R) gene expression, whereas it down-regulated several farnesoid X receptor (FXR)-target genes such as cytochrome P450 family 7 subfamily A polypeptide 1 (CYP7A1) and Na+/taurocholate co-transporter polypeptide (NTCP). In conclusion, FM-VP4 reduced intestinal cholesterol absorption, plasma and liver cholesterol and affected bile acid homeostasis by inducing bile acid intestinal reabsorption and changed the liver expression of genes that play an essential role in cholesterol homeostasis. This is the first phytosterol or stanol that affects bile acid metabolism and lowers plasma cholesterol levels in normocholesterolaemic mice.

El ácido palmítico estimula la producción de interleucina 6 en células musculares esqueléticas por activación de la proteincinasa C y el factor nuclear kB / Palmitate stimulates interleukin-6 production in skeletal muscle cells through activation of protein kinase C and nuclear factor kB

Introducción. Los mecanismos causantes de la aparición de resistencia a la insulina mediada por ácidos grasos libres en el músculo esquelético no son bien conocidos. Diversos datos sugieren que existe una relación entre inflamación y diabetes mellitus tipo 2 que podría estar implicada en la aparición de esta patología. Material, métodos y resultados. La incubación de células musculares esqueléticas C2C12 con palmitato 0,5 mM incrementó los niveles de ARN mensajero (ARNm) (inducción de 3,5 veces, p < 0,05) y la secreción (control 375 ± 57 frente a palmitato 1.129 ± 177 pg/ml, p < 0,001) de la citocina proinflamatoria interleucina 6 (IL-6). El tratamiento con palmitato aumentó la activación del factor nuclear (NF)-kB y la coincubación de las células con palmitato y el inhibidor de NF-kB pirrolidina ditiocarbamato evitó tanto la expresión como la secreción de IL-6. Por otra parte, la incubación de las células tratadas con palmitato con un potente inhibidor específico de la proteincinasa C (PKC), la calfostina C, o con PMA, que disminuye los valores de PKC en incubaciones largas, suprimió la inducción de la producción de IL-6. Finalmente, las células musculares esqueléticas expuestas a palmitato mostraron una caída de los valores de ARNm y de proteína del transportador de glucosa 4 (GLUT4), pero en presencia de un anticuerpo contra la IL-6, que neutraliza su actividad biológica, se evitaron estas reducciones. Conclusiones. Estos estudios sugieren que la IL-6 puede mediar parte de los efectos del palmitato sobre la sensibilidad a la insulina (AU)

Introduction. The mechanisms by which elevated levels of free fatty acids in skeletal muscle cause insulin resistance are not well understood. In addition, accumulating evidence suggests a link between inflammation and type 2 diabetes, which could be involved in the development of this disorder. Material, methods and results. Exposure of C2C12 skeletal muscle cells to 0.5 mM palmitate increased mRNA levels (3.5-fold induction, p<0.05) and secretion (control 375±57 vs palmitate 1129±177 pg/ml, p<0.001) of the proinflammatory cytokine interleukin (IL)-6. Palmitate increased nuclear factor (NF)-kB activation and coincubation of the cells with palmitate and the NF-kB inhibitor pyrrolidine dithiocarbamate prevented both IL-6 expression and secretion. Furthermore, incubation of palmitate-treated cells with calphostin C, a strong and specific inhibitor of protein kinase C (PKC), and PMA, which down-regulates PKC in long-term incubations, abolished induction of IL-6 production. Finally, exposure of skeletal muscle cells to palmitate decreased mRNA and protein levels of GLUT4. However, in the presence of anti-IL-6 antibody, which neutralizes the biological activity of mouse IL-6 in cell culture, these reductions were prevented. Conclusions. These findings suggest that IL-6 may mediate several of the prodiabetic effects of palmitate (AU)

La atorvastatina previene la reducción de los receptores activados por proliferadores peroxisómicos en la hipertrofia cardíaca / Atorvastatin prevents reduction in peroxisome proliferator activated receptors in cardiac hypertrophy

Introducción. La activación del factor nuclear (NF)-kB desempeña un papel clave en el desarrollo de la hipertrofia cardíaca. Aunque se ha demostrado que las estatinas inhiben la hipertrofia cardíaca por su capacidad para reducir la producción de especies reactivas del oxígeno, todavía se desconoce si estos fármacos previenen la activación de NF-kB y si la activación de este factor de transcripción está relacionada con la reducción de la actividad de la vía de los receptores activados por los proliferadores peroxisómicos (PPAR). Material y método. Este estudio ha examinado el papel de la atorvastatina sobre la actividad NF-kB y los PPAR en la hipertrofia cardíaca inducida por sobrecarga de presión. Resultados. Los resultados indican que la atorvastatina inhibe la hipertrofia cardíaca y previene la reducción de las concentraciones de proteína de PPAR α y β/δ. Además, el tratamiento con atorvastatina evitó la activación de NF-kB durante el desarrollo de la hipertrofia cardíaca, reduciendo la asociación proteína-proteína entre los PPAR y la subunidad p65 de NF-kB. Conclusiones. Los resultados obtenidos indican que la interacción entre NF-kB y los proliferadores peroxisómicos puede intereferir la capacidad de transactivación de los últimos, y provocar una reducción en la expresión de sus genes diana implicados en el metabolismo de los ácidos grasos. Estos cambios se evitaron con atorvastatina (AU)

Introduction. Nuclear factor (NF)-kB signalling pathway plays a pivotal role in cardiac hypertrophy. Although statins have been reported to inhibit cardiac hypertrophy by reducing the generation of reactive oxygen species, it is not yet known whether statins prevent NF-kB activation and whether this effect can be related to the reduction in the peroxisome proliferator-activated receptor (PPAR) pathway. Material and method. In this study, we examined the role of atorvastatin on NF-kB activity and PPAR signaling in pressure overload-induced cardiac hypertrophy. Results. Our findings indicate that atorvastatin inhibits cardiac hypertrophy and prevents the fall in protein levels of PPARα and PPARβ/δ. Furthermore, atorvastatin treatment avoided NF-kB activation during cardiac hypertrophy, by reducing the protein-protein association between these PPAR subtypes and the p65 subunit of NF-kB. Conclusions. These findings indicate that negative cross-talk between NF-kB and PPAR may interfere in the transactivation capacity of the latter, leading to a fall in the expression of genes involved in fatty acid metabolism, and that these changes are prevented by atorvastatin (AU)

D) ¿Modula el metabolismo lipídico del miocardio la hipertrofia cardíaca? / No disponible

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Sexual dimorphism in lipid metabolic phenotype associated with old age in Sprague-Dawley rats.

PURPOSE: Aged male rats show a decrease in liver PPARalpha. We aimed to determine if the sexual dimorphism in lipid metabolism observed in the PPARalpha-/- mouse is also present in senescent rats. RESULTS: Eighteen-month old rats were obese and presented high plasma NEFA concentrations. Old male rats were more hypercholesterolemic and hyperleptinemic than females, presenting a higher content in hepatic triglycerides and cholesteryl esters, while 18-month old females were more hypertriglyceridemic than males. Although PPARalpha expression and binding activity was reduced in liver from old male and female rats, the mRNA for a PPARalpha target gene, such as CPT-I, was reduced in old males (-56%), while increased by 286% in old females. LXRalpha protein was increased, and its binding activity was decreased in livers of old males, while livers of old females showed an increase in DGAT1 (2.6-fold) and DGAT2 (4.9-fold) mRNA, with respect to 3-month old animals. The increases in DGAT1 and DGAT2 mRNAs matched in old females those of plasma (3.1-fold) and liver triglycerides (5.0-fold). CONCLUSIONS: These features disclose a marked sexual dimorphism in lipid metabolism associated to old age in rats that can be partially attributed not only to an age-related decrease in liver PPARalpha expression, but also to changes in other hepatic transcription factors and enzymes, such as liver X receptor alpha (LXRalpha) and diacylglycerol acyltransferases (DGAT).

Insulin analogues in the management of diabetes.

Insulin therapy has been strongly influenced by the results of the Diabetes Control and Complications Trial (DCCT) and the United Kingdom Prospective Diabetes Study (UKPDS), both of which support intensive antidiabetic therapy. Conventional insulin therapy can be limited, due to the difficulty in achieving tight glycemic control in people with diabetes, which is crucial to reducing the risk of long-term complications associated with diabetes. In recent years, three short-acting (insulin lispro, insulin aspart and insulin glulisine) and two long-acting (insulin glargine and insulin detemir) recombinant analogues of regular human insulin have been developed for the management of diabetes. Short-acting insulin analogues are an alternative to regular human insulin before meals. Compared with regular human insulin, these new short-acting insulin analogues show faster subcutaneous absorption, a more rapid onset of activity and a shorter duration of action. As a result of these pharmacokinetic differences, an improved postprandial glycemic control is achieved, without increasing the risk of hypoglycemia. In addition, these insulin analogues can be administered immediately before a meal, thereby synchronizing insulin administration and food absorption. The long-acting insulin analogue insulin glargine was developed to provide basal insulin levels for 24 h when administered once daily at bedtime. Compared with previous intermediate- or long-acting conventional insulin, insulin glargine shows a flat profile of plasma insulin levels with no prominent peak. The use of this long-acting insulin analogue appears to be associated with a reduced incidence of hypoglycemia, especially at night. Insulin detemir is another basal insulin that may reduce nocturnal hypoglycemia and variability in glycemic values. The availability of these new insulin analogues has the potential to significantly improve long-term control over blood glucose in diabetic patients.