Total Synthesis of Mycalolides A and B through Olefin Metathesis.

An asymmetric total synthesis of the trisoxazole marine macrolides mycalolides A and B is described. This synthesis involves the convergent assembly of highly functionalized C1-C19 trisoxazole and C20-C35 side-chain segments through the use of olefin metathesis and esterification as well as Julia-Kocienski olefination and enamide formation as key steps.

A novel JNK2/SREBP-1c pathway involved in insulin-induced fatty acid synthesis in human adipocytes.

Insulin plays important roles in apoptosis and lipid droplet (LD) formation, and it is one of the determinants involved in increasing fat mass. However, the mechanisms underlying insulin-induced enlargement of fat mass remain unclear. Our previous study suggested that insulin-induced increases in LDs are related to c-Jun N-terminal kinase (JNK)2-mediated upregulation of cell death-inducing DNA fragmentation factor-α-like effector (CIDE)C in human adipocytes. However, other genes involved in insulin/JNK2-induced LD formation are unknown. Here, we explored insulin/JNK2-regulated genes to clarify the mechanism of enlargement of LDs. Microarray analysis revealed that an insulin/JNK2 pathway mostly regulates expression of genes involved in lipid metabolism, including sterol regulatory element binding protein (SREBP)-1, a key transcription factor of lipogenesis. The JNK inhibitor SP600125 blocked insulin-induced upregulation of SREBP-1c expression. Small interfering RNA-mediated depletion of JNK2 suppressed insulin-induced nuclear accumulation of the active form of SREBP-1 protein and upregulation of SREBP-1c. Furthermore, depletion of JNK2 attenuated insulin-induced upregulation of SREBP-1c target lipogenic enzymes, leading to reduced de novo fatty acid synthesis. In addition, JNK2 coimmunoprecipitated with SREBP-1, reinforcing the correlation between JNK2 and SREBP-1. These results suggest that SREBP-1c is a novel insulin/JNK2-regulated gene and that the JNK2/SREBP-1c pathway mediates insulin-induced fatty acid synthesis, which may lead to enlargement of LDs in human adipocytes.

Impaired insulin signaling in endothelial cells reduces insulin-induced glucose uptake by skeletal muscle.

In obese patients with type 2 diabetes, insulin delivery to and insulin-dependent glucose uptake by skeletal muscle are delayed and impaired. The mechanisms underlying the delay and impairment are unclear. We demonstrate that impaired insulin signaling in endothelial cells, due to reduced Irs2 expression and insulin-induced eNOS phosphorylation, causes attenuation of insulin-induced capillary recruitment and insulin delivery, which in turn reduces glucose uptake by skeletal muscle. Moreover, restoration of insulin-induced eNOS phosphorylation in endothelial cells completely reverses the reduction in capillary recruitment and insulin delivery in tissue-specific knockout mice lacking Irs2 in endothelial cells and fed a high-fat diet. As a result, glucose uptake by skeletal muscle is restored in these mice. Taken together, our results show that insulin signaling in endothelial cells plays a pivotal role in the regulation of glucose uptake by skeletal muscle. Furthermore, improving endothelial insulin signaling may serve as a therapeutic strategy for ameliorating skeletal muscle insulin resistance.

Direct evidence for leptin-induced lipid oxidation independent of long-form leptin receptor.

Leptin administration has been shown to enhance muscle lipid oxidation in relation to the energy expenditure. Both long-form (Ob-R(L)) and short-form leptin receptors (Ob-R(S)) are expressed in skeletal muscle, but the role of Ob-R(S) is unclear. In the present study, the role of Ob-R(S) in leptin-induced lipid oxidation in skeletal muscles was investigated using primary murine myotubes from m/m and db/db mice. Primary myotubes were treated with leptin (0.1, 1, 10, 100nM) for 24h. Lipid oxidation was determined by (14)CO(2) production rate from [1-(14)C] palmitate. Leptin was found to increase lipid oxidation in a dose- and time-dependent manner in db/db myotubes as well as in m/m myotubes. Leptin significantly increased phosphorylation of JAK2 and STAT3 in both types of myotube. Leptin-induced lipid oxidation was abolished by STAT3 siRNA. To investigate the mechanism underlying leptin-induced lipid oxidation, the effects of pharmacological inhibitors were examined. JAK2 or p38 MAPK inhibitor suppressed leptin-induced lipid oxidation and decreased STAT3 phosphorylation in both types of myotube, respectively. Leptin significantly increased phosphorylation of p38 MAPK, and leptin-induced lipid oxidation was abolished by treatment with p38 MAPK siRNA in both types of myotube. These results suggest that leptin induces lipid oxidation in skeletal muscle through the JAK2/p38 MAPK/STAT3 signaling pathway via not only Ob-R(L) but also Ob-R(S).

Chronic leptin treatment stimulates lipid oxidation in immortalized and primary mouse skeletal muscle cells.

Leptin administration enhances lipid oxidation in skeletal muscle. Nevertheless, direct and chronic effect of leptin has not been well characterized. Here, we measured the effect of leptin on skeletal muscles and their signaling pathways using differentiated C(2)C(12) myotubes and primary myotube cultures. Differentiated myotubes expressed both the short and long forms of leptin receptors. Leptin increased lipid oxidation in myotubes in a concentration- and time-dependent manner, with significant induction of lipid oxidation occurring after 6 h. Actinomycin D completely blocked leptin-induced lipid oxidation. Leptin significantly increased phosphorylation of JAK2 and STAT3 in myotubes, and leptin-induced lipid oxidation was abolished by treatment with a JAK2 inhibitor or STAT3 siRNA. We then used mouse myotubes to measure these effects under physiological conditions. Leptin increased lipid oxidation, which again was blocked by a JAK2 inhibitor and STAT3 siRNA. These results suggest that the JAK2/STAT3 signaling pathway may underlie the chronic effects of leptin on lipid oxidation in skeletal muscles.

A novel PPARalpha agonist ameliorates insulin resistance in dogs fed a high-fat diet.

Agonism of peroxisome proliferator-activated receptor (PPAR) alpha, a key regulator of lipid metabolism, leads to amelioration of lipid abnormalities in dyslipidemic patients. However, whether PPARalpha agonism is an effective form of therapy for obesity-related insulin resistance associated with lipid abnormalities is unclear. The present study investigated the effects of a potent and subtype-selective PPARalpha agonist, KRP-101, in a nonrodent insulin-resistant animal model under pair-fed conditions. Beagle dogs were fed a high-fat diet for 24 wk to induce insulin resistance. During the final 12 wk, 0.03 mg x kg(-1) x day(-1) KRP-101 (n = 5) or vehicle (n = 5) was administered orally once a day. KRP-101 administration resulted in a significantly lower weight of overall visceral fat, which is associated with increased adiponectin and decreased leptin in serum. KRP-101 administration improved hyperglycemia and hyperinsulinemia as well as dyslipidemia in dogs fed a high-fat diet. Oral glucose tolerance test showed that KRP-101 administration improved glucose intolerance. The KRP-101 group showed a markedly lower hepatic triglyceride concentration. Lipid oxidation was increased in the liver and skeletal muscles of the KRP-101 group. These findings in the dog model suggest that the use of potent and subtype-selective PPARalpha agonists as a potentially relevant therapeutic approach to treat human insulin resistance associated with visceral obesity.

Targeted disruption of AdipoR1 and AdipoR2 causes abrogation of adiponectin binding and metabolic actions.

Adiponectin plays a central role as an antidiabetic and antiatherogenic adipokine. AdipoR1 and AdipoR2 serve as receptors for adiponectin in vitro, and their reduction in obesity seems to be correlated with reduced adiponectin sensitivity. Here we show that adenovirus-mediated expression of AdipoR1 and R2 in the liver of Lepr(-/-) mice increased AMP-activated protein kinase (AMPK) activation and peroxisome proliferator-activated receptor (PPAR)-alpha signaling pathways, respectively. Activation of AMPK reduced gluconeogenesis, whereas expression of the receptors in both cases increased fatty acid oxidation and lead to an amelioration of diabetes. Alternatively, targeted disruption of AdipoR1 resulted in the abrogation of adiponectin-induced AMPK activation, whereas that of AdipoR2 resulted in decreased activity of PPAR-alpha signaling pathways. Simultaneous disruption of both AdipoR1 and R2 abolished adiponectin binding and actions, resulting in increased tissue triglyceride content, inflammation and oxidative stress, and thus leading to insulin resistance and marked glucose intolerance. Therefore, AdipoR1 and R2 serve as the predominant receptors for adiponectin in vivo and play important roles in the regulation of glucose and lipid metabolism, inflammation and oxidative stress in vivo.

Overexpression of monocyte chemoattractant protein-1 in adipose tissues causes macrophage recruitment and insulin resistance.

Adipose tissue expression and circulating concentrations of monocyte chemoattractant protein-1 (MCP-1) correlate positively with adiposity. To ascertain the roles of MCP-1 overexpression in adipose, we generated transgenic mice by utilizing the adipocyte P2 (aP2) promoter (aP2-MCP-1 mice). These mice had higher plasma MCP-1 concentrations and increased macrophage accumulation in adipose tissues, as confirmed by immunochemical, flow cytometric, and gene expression analyses. Tumor necrosis factor-alpha and interleukin-6 mRNA levels in white adipose tissue and plasma non-esterified fatty acid levels were increased in transgenic mice. aP2-MCP-1 mice showed insulin resistance, suggesting that inflammatory changes in adipose tissues may be involved in the development of insulin resistance. Insulin resistance in aP2-MCP-1 mice was confirmed by hyperinsulinemic euglycemic clamp studies showing that transgenic mice had lower rates of glucose disappearance and higher endogenous glucose production than wild-type mice. Consistent with this, insulin-induced phosphorylations of Akt were significantly decreased in both skeletal muscles and livers of aP2-MCP-1 mice. MCP-1 pretreatment of isolated skeletal muscle blunted insulin-stimulated glucose uptake, which was partially restored by treatment with the MEK inhibitor U0126, suggesting that circulating MCP-1 may contribute to insulin resistance in aP2-MCP-1 mice. We concluded that both paracrine and endocrine effects of MCP-1 may contribute to the development of insulin resistance in aP2-MCP-1 mice.

Enhancement of insulin signaling through inhibition of tissue lipid accumulation by activation of peroxisome proliferator-activated receptor (PPAR) alpha in obese mice.

BACKGROUND: The aim of the present study was to investigate the effect of PPARalpha activation on insulin signaling and lipid accumulation in the liver and skeletal muscle of insulin-resistant (ob/ob) mice. MATERIAL/METHODS: A known subtype-selective PPARalpha agonist, Wy-14,643, was administered to lean and ob/ob mice at 30 mg/kg/day for 4 weeks. Insulin (100 units/kg) or saline was injected into the portal vein of anesthetized mice. The liver and skeletal muscles were used for the detection of tyrosine phosphorylation of the insulin receptor (IR) and insulin receptor substrates (IRSs), as well as for the determination of both IRS-associated PI3-K activity and lipid content; in addition, the measurement of mRNA levels of PPAR-regulated genes was carried out. RESULTS: The PPARalpha agonist lowered plasma levels of glucose, insulin, triglycerides, and free fatty acids in ob/ob mice. Several PPARalpha-upregulated genes related to the transport and oxidation of fatty acids in the liver were increased by treatment with the agonist. The PPARalpha agonist significantly increased IR- and IRS-tyrosine phosphorylation and IRS-associated PI3-K activity in the liver and muscle of ob/ob mice, without exerting the same effects in lean mice. Moreover, these effects in ob/ob mice were accompanied by decreased triglyceride and fatty acyl-CoA contents in the liver and skeletal muscle. CONCLUSIONS: The present results suggest that inhibition of lipid accumulation by hepatic PPARalpha activation leads to an improvement in impaired insulin signaling in muscle tissue as well as in the liver of insulin-resistant mice.

Pharmacological characterization of a human-specific peroxisome proliferater-activated receptor alpha (PPARalpha) agonist in dogs.

Peroxisome proliferator-activated receptor alpha (PPARalpha) is a key regulator in lipid metabolism and a potential therapeutic target for lipid-related metabolic diseases. It has been shown that there are species differences between human and mouse in response to several PPARalpha agonists in a transactivation assay. In the present study, we cloned a full length of dog PPARalpha and investigated the effects of a novel and potent agonist (KCL) for human PPARalpha. In a transactivation assay using the full length of PPARalpha, agonistic activity of KCL for dog PPARalpha (EC(50): 0.007 microM) was comparable to that for human PPARalpha (EC(50): 0.003 microM), but not that for rat PPARalpha (EC(50): 11.49 microM). Similar results were obtained from a transactivation assay using a GAL4/PPARalpha ligand-binding domain (LBD) chimera. A point-mutation study showed that I272 on PPARalphaLBD is a major contributor to species differences in response to KCL between human, dog, and rat PPARalpha. KCL also induced mRNA levels of HMG-CoA synthase in dog hepatocytes. When administered orally to dogs and rats, KCL significantly decreased plasma triglyceride levels in a dose-dependent manner. The triglyceride-lowering effects of KCL in dogs were >100-fold more potent than those in rats. These results suggest that KCL may induce activation of highly potent PPARalpha in humans as well as dogs, and that dog is a suitable animal model for studying and predicting the biological actions of potent agonists for human PPARalpha.

Design, synthesis, and evaluation of substituted phenylpropanoic acid derivatives as human peroxisome proliferator activated receptor activators. Discovery of potent and human peroxisome proliferator activated receptor alpha subtype-selective activators.

Substituted phenylpropanoic acid derivatives were prepared as part of a search for subtype-selective human peroxisome proliferator activated receptor alpha (PPARalpha) activators. Structure-activity relationship studies indicated that the nature and the stereochemistry of the substituent at the alpha-position of the head part containing the carboxyl group, the distance between the carboxyl group and the central benzene ring, the linking group between the central benzene ring and the distal benzene ring, and the substituent at the distal hydrophobic tail part of the molecule all play key roles in determining the potency and selectivity of PPAR subtype transactivation. This study has led to the identification of potent and human PPARalpha selective optically active alpha-alkylphenylpropanoic acid derivatives, which will be useful not only as pharmacological tools to investigate the physiology and pathophysiology of PPARalpha but also as candidate drugs for the treatment of altered metabolic homeostasis, such as dyslipidemia, obesity, and diabetes.

Cloning of adiponectin receptors that mediate antidiabetic metabolic effects.

Adiponectin (also known as 30-kDa adipocyte complement-related protein; Acrp30) is a hormone secreted by adipocytes that acts as an antidiabetic and anti-atherogenic adipokine. Levels of adiponectin in the blood are decreased under conditions of obesity, insulin resistance and type 2 diabetes. Administration of adiponectin causes glucose-lowering effects and ameliorates insulin resistance in mice. Conversely, adiponectin-deficient mice exhibit insulin resistance and diabetes. This insulin-sensitizing effect of adiponectin seems to be mediated by an increase in fatty-acid oxidation through activation of AMP kinase and PPAR-alpha. Here we report the cloning of complementary DNAs encoding adiponectin receptors 1 and 2 (AdipoR1 and AdipoR2) by expression cloning. AdipoR1 is abundantly expressed in skeletal muscle, whereas AdipoR2 is predominantly expressed in the liver. These two adiponectin receptors are predicted to contain seven transmembrane domains, but to be structurally and functionally distinct from G-protein-coupled receptors. Expression of AdipoR1/R2 or suppression of AdipoR1/R2 expression by small-interfering RNA supports our conclusion that they serve as receptors for globular and full-length adiponectin, and that they mediate increased AMP kinase and PPAR-alpha ligand activities, as well as fatty-acid oxidation and glucose uptake by adiponectin.

Globular adiponectin protected ob/ob mice from diabetes and ApoE-deficient mice from atherosclerosis.

The adipocyte-derived hormone adiponectin has been shown to play important roles in the regulation of energy homeostasis and insulin sensitivity. In this study, we analyzed globular domain adiponectin (gAd) transgenic (Tg) mice crossed with leptin-deficient ob/ob or apoE-deficient mice. Interestingly, despite an unexpected similar body weight, gAd Tg ob/ob mice showed amelioration of insulin resistance and beta-cell degranulation as well as diabetes, indicating that globular adiponectin and leptin appeared to have both distinct and overlapping functions. Amelioration of diabetes and insulin resistance was associated with increased expression of molecules involved in fatty acid oxidation such as acyl-CoA oxidase, and molecules involved in energy dissipation such as uncoupling proteins 2 and 3 and increased fatty acid oxidation in skeletal muscle of gAd Tg ob/ob mice. Moreover, despite similar plasma glucose and lipid levels on an apoE-deficient background, gAd Tg apoE-deficient mice showed amelioration of atherosclerosis, which was associated with decreased expression of class A scavenger receptor and tumor necrosis factor alpha. This is the first demonstration that globular adiponectin can protect against atherosclerosis in vivo. In conclusion, replenishment of globular adiponectin may provide a novel treatment modality for both type 2 diabetes and atherosclerosis.

Design, synthesis and evaluation of substituted phenylpropanoic acid derivatives as peroxisome proliferator-activated receptor (PPAR) activators: novel human PPARalpha-selective activators.

A series of substituted phenylpropanoic acid derivatives was prepared as part of a search for subtype-selective human peroxisome proliferator-activated receptor (PPAR) activators. Structure-activity relationship studies indicated that the substituent at the alpha-position of the carboxyl group plays a key role in determining the potency and the selectivity for PPAR transactivation.