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.

The effects of liposuction removal of subcutaneous abdominal fat on lipid metabolism are independent of insulin sensitivity in normal-overweight individuals.

BACKGROUND: Abdominal fat (both visceral and subcutaneous) accumulation is associated with an increased risk of developing insulin resistance. The latter stands as the basis upon which diabetes, hypertension, and atherogenic dyslipidemia tend to build up. Hence, abdominal liposuction (AL) could theoretically hold metabolic benefits. We undertook the present study to assess the effects of AL on carbohydrate and lipid metabolism. METHODS: This is a prospective study including 20 healthy volunteers (M2/F18) aged 39.6 +/- 7.7 years old (24-52), body mass index (BMI) = 25.3 +/- 4.7 kg/m(2) (19.8-36) who underwent AL. Before and 4 months after AL, we measured glucose and insulin concentrations, HOMA index [glucose (mM) x IRI (microUI/l)/22.5], free fatty acids (FFA), glycerol, total cholesterol and triglycerides, high-density lipoprotein (HDL)-cholesterol (HDL-c), low-density lipoprotein (LDL)-cholesterol (LDL-c), very low-density lipoprotein (VLDL)-cholesterol (VLDL-c) and apolipoproteins (apo) B, AI and AII, adiponectin (Adp), and ultra-sensitive C-reactive protein (CRP). RESULTS: Lipo-aspirate averaged 5.494 +/- 5.297 cc (600-19.000). Weight, BMI, and waist circumference decreased significantly 4 months after surgery by 4.6, 4.6 and 5.9%, respectively. There were significant decrements in FFA (-35%, p < 0.0001), glycerol (-63%, p < 0.0005), VLDL-c (-15.2%; p < 0.001), and triglycerides (-21.3%, p < 0.002), an increase in HDL-c (+10%, p < 0.03), Apo AI (+10.1%, p < 0.02), and Apo AII (+11.8%, p < 0.001). Total cholesterol, LDL-c, ApoB, and the LDL-c/ApoB ratio raised by +15% (p < 0.0005), +27.3% (p < 0.000), +15.1% (p < 0.008) and +2.76% (p < 0.008), respectively. Glucose, insulin, the HOMA index, Adp, and CRP were not significantly altered after AL. CONCLUSION: AL in healthy normal weight or slightly overweight subjects improves the major lipoprotein components of obesity-associated dyslipidemia. This improvement occurs independent of insulin sensitivity.

Role of vitamin D in the pathogenesis of type 2 diabetes mellitus.

Vitamin D deficiency has been shown to alter insulin synthesis and secretion in both humans and animal models. It has been reported that vitamin D deficiency may predispose to glucose intolerance, altered insulin secretion and type 2 diabetes mellitus. Vitamin D replenishment improves glycaemia and insulin secretion in patients with type 2 diabetes with established hypovitaminosis D, thereby suggesting a role for vitamin D in the pathogenesis of type 2 diabetes mellitus. The presence of vitamin D receptors (VDR) and vitamin D-binding proteins (DBP) in pancreatic tissue and the relationship between certain allelic variations in the VDR and DBP genes with glucose tolerance and insulin secretion have further supported this hypothesis. The mechanism of action of vitamin D in type 2 diabetes is thought to be mediated not only through regulation of plasma calcium levels, which regulate insulin synthesis and secretion, but also through a direct action on pancreatic beta-cell function. Therefore, owing to its increasing relevance, this review focuses on the role of vitamin D in the pathogenesis of type 2 diabetes mellitus.

Characterization of two divergent endo-beta-1,4-glucanase cDNA clones highly expressed in the nonclimacteric strawberry fruit.

Two cDNAs clones (Cel1 and Cel2) encoding divergent endo-beta-1, 4-glucanases (EGases) have been isolated from a cDNA library obtained from ripe strawberry (Fragaria x ananassa Duch) fruit. The analysis of the amino acid sequence suggests that Cel1 and Cel2 EGases have different secondary and tertiary structures and that they differ in the presence of potential N-glycosylation sites. By in vitro translation we show that Cel1 and Cel2 bear a functional signal peptide, the cleavage of which yields mature proteins of 52 and 60 kD, respectively. Phylogenetic analysis revealed that the Cel2 EGase diverged early in evolution from other plant EGases. Northern analysis showed that both EGases are highly expressed in fruit and that they have different temporal patterns of accumulation. The Cel2 EGase was expressed in green fruit, accumulating as the fruit turned from green to white and remaining at an elevated, constant level throughout fruit ripening. In contrast, the Cel1 transcript was not detected in green fruit and only a low level of expression was observed in white fruit. The level of Cel1 mRNA increased gradually during ripening, reaching a maximum in fully ripe fruit. The high levels of Cel1 and Cel2 mRNA in ripe fruit and their overlapping patterns of expression suggest that these EGases play an important role in softening during ripening. In addition, the early expression of Cel2 in green fruit, well before significant softening begins, suggests that the product of this gene may also be involved in processes other than fruit softening, e.g. cell wall expansion.