Effects Of gAd Research Articles

Globular Adiponectin Exerts a Pro-Inflammatory Effect via IκB/NF-κB Pathway Activation and Anti-Inflammatory Effect by IRAK-1 Downregulation.

Adiponectin, a hormone produced by adipose tissue, is very abundant in plasma, and its anti- and pro-inflammatory effects are reported. However, the mechanisms of these pro- and anti-inflammatory effects are not fully defined. Herein, we evaluated the dual inflammatory response mechanism of adiponectin in macrophages. Short-term globular adiponectin (gAd) treatment induced IκBα degradation, NF-κB nuclear translocation, and TNF-α production in RAW 264.7 cells. Polymyxin B pretreatment did not block gAd-induced IκBα degradation, and heated gAd was unable to degrade IκBα, suggesting that the effects of gAd were not due to endotoxin contamination. gAd activated IKK and Akt, and inhibition of either IKK or Akt by dominant-negative IKKβ (DN-IKKβ) or DN-Akt overexpression blocked gAd-induced IκBα degradation, suggesting that short-term incubation with gAd mediates inflammatory responses by activating the IκB/NF-κB and PI3K/Akt pathways. Contrastingly, long-term stimulation with gAd induced, upon subsequent stimulation, tolerance to gAd, lipopolysaccharide, and CpG-oligodeoxynucleotide, which is associated with gAd-induced downregulation of IL-receptor-associated kinase-1 (IRAK-1) due to IRAK-1 transcriptional repression. Conclusively, our findings demonstrate that the pro- and anti-inflammatory responses to gAd in innate immune cells are time-dependent, and mediated by the activation of the IκB/NF-κB pathway, and IRAK-1 downregulation, respectively.

Globular adiponectin acts as a melanogenic signal in human epidermal melanocytes.

Adiponectin is an adipocyte-derived cytokine that circulates as a full-length protein and a fragment containing the globular domain of adiponectin (gAd). A recent study has reported the antimelanogenic effects of full-length adiponectin. To examine the involvement of gAd in melanogenesis and its mechanisms of action. The effects of gAd on melanogenesis and its mechanisms of action were investigated in human epidermal melanocytes and reconstructed epidermis, including melanin content, cellular tyrosinase activity, cyclic adenosine monophosphate (cAMP) production and protein kinase A (PKA) activity, expression and phosphorylation of signalling molecules. Exogenous gAd increased melanin content, and the mRNA levels of microphthalmia-associated transcription factor (MITF) and its downstream genes TRP1, but not TRP2, were increased by gAd. However, cAMP production and PKA activity were not affected by gAd. Moreover, attempts to elucidate the underlying mechanism behind the gAd-mediated effect revealed that gAd could regulate melanogenesis by upregulating MITF through phosphorylation of the cAMP response element-binding protein (CREB). In addition, upregulation of MITF was mediated by activation of adenosine monophosphate-activated protein kinase (AMPK)-p38 mitogen-activated protein kinase (MAPK) signalling. Taken together, these findings indicate that promotion of melanogenesis by gAd occurs through increased expression of MITF, which is mediated by activation of the AMPK-p38 MAPK-CREB pathway. These findings suggest that gAd contributes to epidermal homeostasis via its effect on melanocyte biology, and products of adipose tissue could affect epidermal biology.

Adiponectin inhibits the generation of reactive oxygen species induced by high glucose and promotes endothelial NO synthase formation in human mesangial cells

The aim of this study was to investigate the effects of adiponectin (ADPN) on high glucose (HG)-induced reactive oxygen species (ROS) and the formation of endothelial nitric oxide (NO) synthase (eNOS) in human glomerular mesangial cells (HMCs), as well as to determine which signaling pathways are modulated by ADPN and the mechanisms involved. HMCs cultured in vitro were randomly divided into 4 groups: the control, HG, HG + globular adiponectin (gAd) and HG + gAd + adenine arabinoside (AraA). The generation of ROS was detected using a fluorescent probe. The mRNA expression and protein levels of eNOS were measured by RT-PCR and western blot analysis, respectively. The phosphorylation of AMP-activated protein kinase (AMPK) was assessed by western blot analysis. HMCs treated with ADPN revealed the time-dependent phosphorylation of AMPK. The treatment of HMCs with HG resulted in increased release of ROS and decreased expression of eNOS compared to the control group (p<0.05). Cells treated with ADPN showed a decrease in HG-induced ROS (p<0.05) and an upregulated eNOS expression. The effects of gAd were partly blocked by the AMPK inhibitor, AraA. The results from the present study show that ADPN inhibits the generation of HG-induced ROS in HMCs; it also stimulates eNOS activity, which has a protective effect. The mechanism partly occurs through the stimulation of the AMPK signaling pathway.

Impaired Activation of AMP-Kinase and Fatty Acid Oxidation by Globular Adiponectin in Cultured Human Skeletal Muscle of Obese Type 2 Diabetics

Adiponectin is an adipocyte-derived hormone associated with antidiabetic actions. In rodent skeletal muscle, globular adiponectin (gAD) activates AMP-kinase (AMPK) and stimulates fatty acid oxidation effects mediated through the adiponectin receptors, AdipoR1 and AdipoR2. In the present study, we examined the mRNA expression of adiponectin receptors and the effects of gAD on AMPK activity and fatty acid oxidation in skeletal muscle myotubes from lean, obese, and obese type 2 diabetic subjects. Myotubes from all groups expressed approximately 4.5-fold more AdipoR1 mRNA than AdipoR2, and obese subjects tended to have higher AdipoR1 expression (P = 0.052). In lean myotubes, gAD activates AMPKalpha1 and -alpha2 by increasing Thr172 phosphorylation, an effect associated with increased acetyl-coenzyme A carboxylase (ACCbeta) Ser221 phosphorylation and enhanced rates of fatty acid oxidation, effects similar to those observed after pharmacological AMPK activation by 5-aminoimidazole-4-carboxamide riboside. In obese myotubes, the activation of AMPK signaling by gAD at low concentrations (0.1 mug/ml) was blunted, but higher concentrations (0.5 mug/ml) stimulated AMPKalpha1 and -alpha2 activities, AMPK and ACCbeta phosphorylation, and fatty acid oxidation. In obese type 2 diabetic myotubes, high concentrations of gAD stimulated AMPKalpha1 activity and AMPK phosphorylation; however, ACCbeta phosphorylation and fatty acid oxidation were unaffected. Reduced activation of AMPK signaling and fatty acid oxidation in obese and obese diabetic myotubes was not associated with reduced protein expression of AMPKalpha and ACCbeta or the expression and activity of the upstream AMPK kinase, LKB1. These data suggest that reduced activation of AMPK by gAD in obese and obese type 2 diabetic subjects is not caused by reduced adiponectin receptor expression but that aspects downstream of the receptor may inhibit AMPK signaling.

GAd-globular Head Domain of Adiponectin Increases Fatty Acid Oxidation in Newborn Rabbit Hearts

Adiponectin is an adipocyte-derived hormone that has a number of metabolic effects in the body, including the control of both glucose and fatty acid metabolism. The globular head domain of adiponectin, gAd, has also been shown to increase fatty acid oxidation in skeletal muscle. Within days after birth, a rapid increase in fatty acid oxidation occurs in the heart. We examined whether adiponectin or gAd plays a role in this maturation of cardiac fatty acid oxidation. Plasma adiponectin increased in newborn rabbits following birth: 1.2 +/- 0.3 microg/ml in 1-day-old, 6.8 +/- 1.8 microg/ml in 7-day-old, and 45 +/- 5 microg/ml in 6-week-old rabbits. Because plasma insulin levels decrease and remain low throughout the suckling period, and because this decrease may contribute to the maturation of fatty acid oxidation, we examined the effects of adiponectin and gAd on fatty acid oxidation in isolated perfused 1-day-old rabbit hearts in the presence or absence of 100 microunits/ml insulin. Adiponectin (10 microg/ml) did not alter fatty acid oxidation in the presence of insulin. In the absence of insulin, the addition of recombinant gAd (1.5 microg/ml) increased fatty acid oxidation compared with control (129 +/- 18 versus 66 +/- 11 nmol.g dry weight(-1).min(-1), respectively (p < 0.05). In 7-day-old hearts, where fatty acid oxidation rates were 5-fold higher than 1-day-old hearts, gAd did not alter fatty acid oxidation rates. The increase in fatty acid oxidation in 1-day-old hearts occurred independently of changes in 5'-AMP-activated protein kinase, acetyl-CoA carboxylase, or malonyl-CoA. The effect of gAd on fatty acid oxidation was reversed in the presence of 100 microunits/ml insulin. These results suggest that a decrease in plasma insulin and increase in gAd are involved in the increase of cardiac fatty acid oxidation in the immediate newborn period.

Adiponectin suppresses proliferation and superoxide generation and enhances eNOS activity in endothelial cells treated with oxidized LDL

Adiponectin (also known as 30-kDa adipocyte complement-related protein or Acrp30) is an abundant adipocyte-derived plasma protein with anti-atherosclerotic and insulin-sensitizing properties. In order to investigate the potential mechanism(s) of the vascular protective effect of adiponectin, we used cultured bovine endothelial cells (BAECs) to study the effect of recombinant globular adiponectin (gAd) on cellular proliferation and the generation of reactive oxygen species (ROS) induced by oxidized LDL (oxLDL). By RT-PCR, we found that BAECs preferentially express AdipoR1, the high-affinity receptor for gAd. Treatment of BAECs with oxLDL (10 μg/ml) for 16 h stimulated cell proliferation by ∼60%, which was inhibited by co-incubation with gAd. Cell treatment with gAd also inhibited basal and oxLDL-induced superoxide release, and suppressed the activation of p42/p44 MAP kinase by oxLDL. The effects of gAd were blocked by a specific polyclonal anti-adiponectin antibody (TJ414). OxLDL-induced BAEC proliferation and superoxide release were inhibited by the NAD(P)H oxidase inhibitor diphenyleneiodonium (DPI), but not the eNOS inhibitor l-nitroarginine methyl ester ( l-NAME). Finally, gAd ameliorated the suppression of eNOS activity by oxLDL. These data indicate that gAd inhibits oxLDL-induced cell proliferation and suppresses cellular superoxide generation, possibly through an NAD(P)H oxidase-linked mechanism.

Effects of GAD and GABA-T inhibitors on GABA metabolism in vivo

Methods are described for the investigation of GABA metabolism in vivo following the administration of convulsant or anticonvulsant drugs to rats and mice. The ability of penicillins to inhibit glutamate decarboxylate did not correlate with their convulsant potency and no detectable change occurred in GABA metabolism in vivo following a dose of penicillin G sufficient to produced epileptiform spiking of the EEG. Ethanolamine-O-sulphate and sodium valproate both increased the relative incorporation of 14C from glucose into GABA at minimally anticonvulsant doses. L-penicillamine, which was convulsant at high doses, inhibited GAD at equivalent concentrations and reduced the incorporation of 14C into GABA. The role of the GABA system in the action of these drugs is discussed.