β-adrenoceptor agonists downregulate adiponectin, but upregulate adiponectin receptor 2 and tumor necrosis factor-α expression in adipocytes

Agonism of β3-Adrenoceptors Inhibits Pathological Retinal Angiogenesis in the Model of Oxygen-Induced Retinopathy

Purpose

In response to hypoxia, sympathetic fibers to the retina activate β-adrenoceptors (β-ARs) that play an important role in the regulation of vascular and neuronal functions. We investigated the role of β3-AR using the mouse model of oxygen-induced retinopathy (OIR).

Methods

Mouse pups were exposed to 75% oxygen at postnatal day 7 (PD7) followed by a return to room air at PD12. The β3-AR preferential agonist BRL37344 was subcutaneously administered once daily at different times after the return to room air. At PD17, the OIR mice underwent flash and pattern electroretinogram. After sacrifice, retinal wholemounts were used for vessel staining or immunohistochemistry for astrocytes, Müller cells, or retinal ganglion cells (RGCs). In retinal homogenates, the levels of markers associated with neovascularization (NV), the blood-retinal barrier (BRB), or astrocytes were determined by western blot, and quantitative reverse-transcription polymerase chain reaction was used to assess β3-AR messenger. Administration of the β3-AR antagonist SR59230A was performed to verify BRL37344 selectivity.

Results

β3-AR expression is upregulated in response to hypoxia, but its increase is prevented by BRL37344, which counteracts NV by inhibiting the pro-angiogenic pathway, activating the anti-angiogenic pathway, recovering BRB-associated markers, triggering nitric oxide production, and favoring revascularization of the central retina through recovered density of astrocytes that ultimately counteracts NV in the midperiphery. Vasculature rescue prevents dysfunctional retinal activity and counteracts OIR-associated retinal ganglion cell loss.

Conclusions

β3-AR has emerged as a crucial intermediary in hypoxia-dependent NV, suggesting a role of β3-AR agonists in the treatment of proliferative retinopathies.

β-Adrenoceptor regulates contraction and inflammatory cytokine expression of human bladder smooth muscle cells via autophagy under pathological hydrostatic pressure

AIMS

Abnormal intravesical pressure created by partial bladder outlet obstruction (PBOO) triggered the progression from chronic inflammation to fibrosis, initiating structural and functional alterations of bladder. To elucidate the underlying mechanisms of contraction and inflammatory response, we investigated the isolated human bladder smooth muscle cells (hBSMC) under pathological hydrostatic pressure (HP) mimicking the in vivo PBOO condition.

METHODS

hBSMCs were subjected to HP of 200 cm H₂ O to explore the contraction and inflammatory cytokine expression of hBSMC treated with β-adrenoceptors (ADRBs) and/or autophagy signaling pathway agonists and/or antagonists.

RESULTS

We showed that pathological HP induced the release of the proinflammatory cytokines, including monocyte chemotactic protein-1, regulated upon activation normal T cell expressed and secreted factor, and interleukin-6. HP downregulated ADRB2 and ADRB3 expression, which was consistent with the results of the PBOO rat model. ADRB2 or autophagy activation repressed pathological HP-induced proinflammatory cytokine production. ADRB2, ADRB3 or autophagy activation ameliorated the HP-enhanced contraction. The increased contraction and autophagy activity by ADRB2 agonist under HP conditions were reversed by pretreatment with antagonists of adenosine monophosphate-activated protein kinase (AMPK).

CONCLUSION

The present study provides evidence that the ADRB3 agonist suppresses hBSMC contraction under pathological HP conditions. Moreover, the ADRB2 agonist negatively regulates the contraction and inflammatory response of hBSMCs through AMPK/mTOR-mediated autophagy under pathological HP. These findings provide a theoretical basis for potential therapeutic strategies for patients with PBOO.

Metoprolol Inhibits Profibrotic Remodeling of Epicardial Adipose Tissue in a Canine Model of Chronic Obstructive Sleep Apnea

Background Whether chronic obstructive sleep apnea ( OSA ) could promote epicardial adipose tissue ( EAT ) secretion of profibrotic adipokines, and thereby contribute to atrial fibrosis, and the potential therapeutic effects of metoprolol remain unknown. Methods and Results A chronic OSA canine model was established by repeatedly clamping the endotracheal tube for and then reopening it for 4 hours every other day for 12 weeks. In a metoprolol treatment group, metoprolol succinate was administered daily for 12 weeks. The EAT infiltration and left atrial fibrosis were examined. The expressions of adipokines secreted by EAT and hypoxic 3T3-L1 adipocytes were detected. The changes in collagen synthesis, transforming growth factor-β1 expression, and cell differentiation and proliferation in cardiac fibroblasts induced by hypoxic 3T3-L1 adipocyte-derived conditioned medium were further analyzed. Chronic OSA induced infiltration of EAT into the left atrium. OSA enhanced the profibrotic effect of EAT on the adjacent atrial myocardium. Moreover, OSA induced profibrotic cytokine secretion from EAT . We also found that hypoxia induced adipokine secretion in cultured adipocytes, and the medium conditioned by the hypoxic adipocytes increased collagen and transforming growth factor-β1 protein expression and cell proliferation of cardiac fibroblasts. More importantly, metoprolol attenuated infiltration of EAT and alleviated the profibrotic effect of EAT by inhibiting adipokine secretion. Metoprolol also inhibited hypoxia-induced adipokine secretion in adipocytes and thereby blocked the hypoxic adipocyte-derived conditioned medium-induced fibrotic response of cardiac fibroblasts. Conclusions Chronic OSA enhanced the profibrotic effect of EAT on the neighboring atrial myocardium by stimulating the secretion of profibrotic adipokines from EAT , which was significantly attenuated by metoprolol. This study gives insights into mechanisms underlying OSA -induced atrial fibrillation and also provides experimental evidence for the protective effects of metoprolol.

Hypothalamic POMC deficiency increases circulating adiponectin despite obesity

Objective

The steep rise in the prevalence of obesity and its related metabolic syndrome have become a major worldwide health concerns. Melanocortin peptides from hypothalamic arcuate nucleus (Arc) POMC neurons induce satiety to limit food intake. Consequently, Arc Pomc-deficient mice (ArcPomc^−/−) exhibit hyperphagia and obesity. Previous studies demonstrated that the circulating levels of adiponectin, a protein abundantly produced and secreted by fat cells, negatively correlate with obesity in both rodents and humans. However, we found that ArcPomc^−/− mice have increased circulating adiponectin levels despite obesity. Therefore, we investigated the physiological function and underlying mechanisms of hypothalamic POMC in regulating systemic adiponectin levels.

Methods

Circulating adiponectin was measured in obese ArcPomc^−/− mice at ages 4–52 weeks. To determine whether increased adiponectin was a direct result of ArcPomc deficiency or a secondary effect of obesity, we examined plasma adiponectin levels in calorie-restricted mice with or without a history of obesity and in ArcPomc^−/− mice before and after genetic restoration of Pomc expression in the hypothalamus. To delineate the mechanisms causing increased adiponectin in ArcPomc^−/− mice, we determined sympathetic outflow to adipose tissue by assessing epinephrine, norepinephrine, and tyrosine hydroxylase protein levels and measured the circulating adiponectin in the mice after acute norepinephrine or propranolol treatments. In addition, adiponectin mRNA and protein levels were measured in discrete adipose tissue depots to ascertain which fat depots contributed the most to the high level of adiponectin in the ArcPomc^−/− mice. Finally, we generated compound Adiopoq^−/−:ArcPomc^−/− mice and compared their growth, body composition, and glucose homeostasis to the individual knockout mouse strains and their wild-type controls.

Results

Obese ArcPomc^−/− female mice had unexpectedly increased plasma adiponectin compared to wild-type siblings at all ages greater than 8 weeks. Despite chronic calorie restriction to achieve normal body weights, higher adiponectin levels persisted in the ArcPomc^−/− female mice. Genetic restoration of Pomc expression in the Arc or acute treatment of the ArcPomc^−/− female mice with melanotan II reduced adiponectin levels to control littermate values. The ArcPomc^−/− mice had defective thermogenesis and decreased epinephrine, norepinephrine, and tyrosine hydroxylase protein levels in their fat pads, indicating reduced sympathetic outflow to adipose tissue. Injections of norepinephrine into the ArcPomc^−/− female mice reduced circulating adiponectin levels, whereas injections of propranolol significantly increased adiponectin levels. Despite the beneficial effects of adiponectin on metabolism, the deletion of adiponectin alleles in the ArcPomc^−/− mice did not exacerbate their metabolic abnormalities.

Conclusion

In summary, to the best of our knowledge, this study provides the first evidence that despite obesity, the ArcPomc^−/− mouse model has high circulating adiponectin levels, which demonstrated that increased fat mass is not necessarily correlated with hypoadiponectinemia. Our investigation also found a previously unknown physiological pathway connecting POMC neurons via the sympathetic nervous system to circulating adiponectin, thereby shedding light on the biological regulation of adiponectin.

•

Obese female hypothalamic-specific Pomc-deficient mice have unexpectedly elevated circulating adiponectin.

•

Restoration of Pomc expression in the hypothalamus reduces plasma adiponectin.

•

Low sympathetic output to subcutaneous fat depots in the Pomc-deficient mice contributes to high adiponectin levels.

•

Deletion of adiponectin in hypothalamic-specific Pomc-deficient mice does not alter their metabolic phenotype.

Selected adipocytokines in patients with an incidentally discovered pheochromocytoma

BACKGROUND

Adipose tissue secretes many adipokines and cytokines, which may be an additional risk factor of cardiovascular and metabolic diseases in patients with an incidentally discovered pheochromocytoma (PHEO). The aim of the study was to investigate levels of selected adipocytokines in these patients.

METHODS

This prospective study included 12 patients with an incidentally discovered PHEO and 18 healthy participants. In all participants plasma/serum concentrations of triglycerides, HDL and LDL cholesterol, insulin, glucose, adipocytokines (adiponectin, leptin, resistin, TNFα, IL6, and MCP1) were determined, hormonal tests were performed in patients.

RESULTS

Patients and controls did not differ significantly in terms of age, sex, and body mass index. Among incidentally discovered PHEO patients, adiponectin levels were lower, while TNFα concentrations higher than in controls. Concentrations of adiponectin correlated with 24-hour urinary excretion of normetanephrine in women. Significantly higher TNFα concentrations were found in hypertensive than in normotensive PHEO patients as well as in non-diabetic PHEO patients than controls. Further, resistin concentration was higher in PHEO patients with diabetes than in non-diabetic ones (P<0.001). Incidentally discovered PHEO tumor size correlated with leptin and IL6 levels. Adiponectin levels were higher, while TNFα and resistin lower among five patients re-examined after tumor resection.

CONCLUSIONS

Among patients with an incidentally discovered pheochromocytoma, lower adiponectin, and higher resistin and TNFα levels may constitute additional factors for HT and DM. In our study, for the first time, correlations between incidentally discovered PHEO tumor size and concentrations of leptin as well as IL6 were found.

Sleep and body temperature in TNFα knockout mice: The effects of sleep deprivation, β3-AR stimulation and exogenous TNFα

Increased production of pro-inflammatory cytokines is assumed to mediate increased sleep under inflammatory conditions, such as systemic infections or recovery from sleep loss. The role of cytokines in sleep regulation under normal conditions is less clear. In the present study, we investigated the role of endogenous tumor necrosis factor alpha (TNFα) in sleep regulation using TNFα knockout (KO) mice. Under control conditions at thermoneutral ambient temperature, total sleep time did not differ between TNFα KO and wild-type (WT) mice, but TNFα KO mice had increased rapid-eye-movement sleep (REMS), accompanied by decreased motor activity and body temperature. Exposure to 17 °C induced decreases in total sleep time similarly in both genotypes. Sleep deprivation by gentle handling elicited robust rebound increases in non-rapid-eye movement sleep (NREMS), REMS and electroencephalographic (EEG) slow-wave activity (SWA), accompanied by suppressed motor activity and decreased body temperature; there was no significant difference between the responses of WT and KO mice. Systemic injection of the beta3-adrenergic receptor (β3-AR) agonist CL-316,243 induced increases in NREMS and body temperature. The temperature response, but not the sleep effect, was attenuated in the KO animals. Systemic injection of TNFα induced increased NREMS, reduced REMS and biphasic temperature responses in both genotypes. In the KO mice, the NREMS-promoting effects of exogenously administered TNFα was decreased, while REMS suppression was enhanced, and the first, hypothermic, phase of temperature response was attenuated. Overall, TNFα KO mice did not show any deficiency in sleep regulation which suggests that the role of endogenous TNFα in sleep regulation is less pronounced than previously suggested.

Beta 3 Adrenergic Receptor Activation Rescues Metabolic Dysfunction in Female Estrogen Receptor Alpha-Null Mice

Metabolic disease risk escalates following menopause. The mechanism is not fully known, but likely involves reduced signaling through estrogen receptor alpha (ERα), which is highly expressed in brown and white adipose tissue (BAT and WAT).

Objective: Test the hypothesis that uncoupling protein (UCP1) activation mitigates metabolic dysfunction caused by loss of signaling through ERα.

Methods: At 8 weeks of age, female ERα knock out (KO) and wild-type mice were housed at 28°C and fed a Western-style high-fat, high sucrose diet (HFD) or a normal low-fat chow diet (NC) for 10 weeks. During the final 2 weeks, they received daily injections of CL 316,256 (CL), a selective β3 adrenergic agonist, or vehicle control (CTRL), creating eight groups: WT-CTRL, WT-CL, KO-CTRL, and KO-CL on HFD or NC; n = 4–10/group.

Results: ERαKO demonstrated exacerbated HFD-induced adiposity gain (P < 0.001) and insulin resistance (P = 0.006). CL treatment improved insulin sensitivity (P < 0.05) and normalized ERαKO-induced adiposity increase (P < 0.05). In both genotypes, CL increased resting energy expenditure (P < 0.05) and induced WAT beiging indicated by increased UCP1 protein in both perigonadal (PGAT) and subcutaneous (SQAT) depots. These effects were attenuated under HFD conditions (P < 0.05). In KO, CL reduced HFD energy consumption compared to CTRL (P < 0.05). Remarkably, CL increased WAT ERβ protein levels of both WT and KO (P < 0.001), revealing CL-mediated changes in estrogen signaling may have protective metabolic effects.

Conclusion: CL completely restored metabolic dysfunction in ERαKO mice. Thus, UCP1 may be a therapeutic target for treating metabolic dysfunction following loss of estrogen receptor signaling.

Sustained stimulation of β2- and β3-adrenergic receptors leads to persistent functional pain and neuroinflammation

Functional pain syndromes, such as fibromyalgia and temporomandibular disorder, are associated with enhanced catecholamine tone and decreased levels of catechol-O-methyltransferase (COMT; an enzyme that metabolizes catecholamines). Consistent with clinical syndromes, our lab has shown that sustained 14-day delivery of the COMT inhibitor OR486 in rodents results in pain at multiple body sites and pain-related volitional behaviors. The onset of COMT-dependent functional pain is mediated by peripheral β2- and β3-adrenergic receptors (β2- and β3ARs) through the release of the pro-inflammatory cytokines tumor necrosis factor α (TNFα), interleukin-1β (IL-1β), and interleukin-6 (IL-6). Here, we first sought to investigate the role of β2- and β3ARs and downstream mediators in the maintenance of persistent functional pain. We then aimed to characterize the resulting persistent inflammation in neural tissues (neuroinflammation), characterized by activated glial cells and phosphorylation of the mitogen-activated protein kinases (MAPKs) p38 and extracellular signal-regulated kinase (ERK). Separate groups of rats were implanted with subcutaneous osmotic mini-pumps to deliver OR486 (15 mg/kg/day) or vehicle for 14 days. The β2AR antagonist ICI118551 and β3AR antagonist SR59230A were co-administrated subcutaneously with OR486 or vehicle either on day 0 or day 7. The TNFα inhibitor Etanercept, the p38 inhibitor SB203580, or the ERK inhibitor U0126 were delivered intrathecally following OR486 cessation on day 14. Behavioral responses, pro-inflammatory cytokine levels, glial cell activation, and MAPK phosphorylation were measured over the course of 35 days. Our results demonstrate that systemic delivery of OR486 leads to mechanical hypersensitivity that persists for at least 3 weeks after OR486 cessation. Corresponding increases in spinal TNFα, IL-1β, and IL-6 levels, microglia and astrocyte activation, and neuronal p38 and ERK phosphorylation were observed on days 14-35. Persistent functional pain was alleviated by systemic delivery of ICI118551 and SR59230A beginning on day 0, but not day 7, and by spinal delivery of Etanercept or SB203580 beginning on day 14. These results suggest that peripheral β2- and β3ARs drive persistent COMT-dependent functional pain via increased activation of immune cells and production of pro-inflammatory cytokines, which promote neuroinflammation and nociceptor activation. Thus, therapies that resolve neuroinflammation may prove useful in the management of functional pain syndromes.

Effects of postweaning calorie restriction on accelerated growth and adiponectin in nutritionally programmed microswine offspring

Poor prenatal development, followed by rapid childhood growth, conveys greater cardiometabolic risk in later life. Microswine offspring exposed to perinatal maternal protein restriction [MPR; "low protein offspring" (LPO)] grow poorly in late-fetal/neonatal stages. After weaning to an ad libitum (AL) diet, LPO-AL exhibit accelerated growth and fat deposition rates with low adiponectin mRNA, despite low-normal body fat and small intra-abdominal adipocytes. We examined effects of caloric restriction (CR) on growth and metabolic status in LPO and normal protein offspring (NPO) randomized to AL or CR diets from weaning. CR transiently reduced growth in both LPO and NPO, delaying recovery in female LPO-CR. Over 7.5-12.5 weeks, linear growth rates in LPO-CR were slower than LPO-AL ( P < 0.001) but exceeded NPO-AL; body weight growth rates fell but were lower in LPO-CR versus NPO-CR. Linear acceleration ceased after 12 weeks. At 16 weeks, percent catch-up in LPO-CR was reduced versus LPO-AL ( P < 0.001). Plasma growth hormone was low in LPO ( P < 0.02). CR normalized fat deposition rate, yet adiponectin mRNA remained low in LPO-CR ( P < 0.001); plasma adiponectin was low in all LPO-AL and in female LPO-CR. Insulin sensitivity improved during CR. We conclude that in LPO: 1) CR delays onset of, but does not abolish, accelerated linear growth, despite low growth hormone; 2) CR yields stunting via delayed onset, plus a finite window for linear growth acceleration; 3) MPR lowers adiponectin mRNA independently of growth, adiposity, or adipocyte size; and 4) MPR reduces circulating adiponectin in LPO-AL and female LPO-CR, potentially enhancing cardiometabolic risk.

The role of the brown adipose tissue in β3-adrenergic receptor activation-induced sleep, metabolic and feeding responses

Brown adipose tissue (BAT) is regulated by the sympathetic nervous system via β3-adrenergic receptors (β3-AR). Here we tested the hypothesis that pharmacological stimulation of β3-ARs leads to increased sleep in mice and if this change is BAT dependent. In wild-type (WT) animals, administration of CL-316,243, a selective β3-AR agonist, induced significant increases in non-rapid-eye movement sleep (NREMS) lasting for 4–10 h. Simultaneously, electroencephalographic slow-wave activity (SWA) was significantly decreased and body temperature was increased with a delay of 5–6 h. In uncoupling protein 1 (UCP-1) knockout mice, the middle and highest doses of the β3-AR agonist increased sleep and suppressed SWA, however, these effects were significantly attenuated and shorter-lasting as compared to WT animals. To determine if somnogenic signals arising from BAT in response to β3-AR stimulation are mediated by the sensory afferents of BAT, we tested the effects of CL-316,243 in mice with the chemical deafferentation of the intra-scapular BAT pads. Sleep responses to CL-316,243 were attenuated by ~50% in intra-BAT capsaicin-treated mice. Present findings indicate that the activation of BAT via β3-AR leads to increased sleep in mice and that this effect is dependent on the presence of UCP-1 protein and sleep responses require the intact sensory innervation of BAT.

White Adipocyte Adiponectin Exocytosis Is Stimulated via β3-Adrenergic Signaling and Activation of Epac1: Catecholamine Resistance in Obesity and Type 2 Diabetes

We investigated the physiological regulation of adiponectin exocytosis in health and metabolic disease by a combination of membrane capacitance patch-clamp recordings and biochemical measurements of short-term (30-min incubations) adiponectin secretion. Epinephrine or the β₃-adrenergic receptor (AR) agonist CL 316,243 (CL) stimulated adiponectin exocytosis/secretion in cultured 3T3-L1 and in primary subcutaneous mouse adipocytes, and the stimulation was inhibited by the Epac (Exchange Protein directly Activated by cAMP) antagonist ESI-09. The β₃AR was highly expressed in cultured and primary adipocytes, whereas other ARs were detected at lower levels. 3T3-L1 and primary adipocytes expressed Epac1, whereas Epac2 was undetectable. Adiponectin secretion could not be stimulated by epinephrine or CL in adipocytes isolated from obese/type 2 diabetic mice, whereas the basal (unstimulated) adiponectin release level was elevated twofold. Gene expression of β₃AR and Epac1 was reduced in adipocytes from obese animals, and corresponded to a respective ∼35% and ∼30% reduction at the protein level. Small interfering RNA-mediated knockdown of β₃AR (∼60%) and Epac1 (∼50%) was associated with abrogated catecholamine-stimulated adiponectin secretion. We propose that adiponectin exocytosis is stimulated via adrenergic signaling pathways mainly involving β₃ARs. We further suggest that adrenergically stimulated adiponectin secretion is disturbed in obesity/type 2 diabetes as a result of the reduced expression of β₃ARs and Epac1 in a state we define as "catecholamine resistance."

AG. Persistent Catechol-O-methyltransferase-dependent Pain Is Initiated by Peripheral β-Adrenergic Receptors

BACKGROUND

Patients with chronic pain disorders exhibit increased levels of catecholamines alongside diminished activity of catechol-O-methyltransferase (COMT), an enzyme that metabolizes catecholamines. The authors found that acute pharmacologic inhibition of COMT in rodents produces hypersensitivity to mechanical and thermal stimuli via β-adrenergic receptor (βAR) activation. The contribution of distinct βAR populations to the development of persistent pain linked to abnormalities in catecholamine signaling requires further investigation.

METHODS

Here, the authors sought to determine the contribution of peripheral, spinal, and supraspinal βARs to persistent COMT-dependent pain. They implanted osmotic pumps to deliver the COMT inhibitor OR486 (Tocris, USA) for 2 weeks. Behavioral responses to mechanical and thermal stimuli were evaluated before and every other day after pump implantation. The site of action was evaluated in adrenalectomized rats receiving sustained OR486 or in intact rats receiving sustained βAR antagonists peripherally, spinally, or supraspinally alongside OR486.

RESULTS

The authors found that male (N = 6) and female (N = 6) rats receiving sustained OR486 exhibited decreased paw withdrawal thresholds (control 5.74 ± 0.24 vs. OR486 1.54 ± 0.08, mean ± SEM) and increased paw withdrawal frequency to mechanical stimuli (control 4.80 ± 0.22 vs. OR486 8.10 ± 0.13) and decreased paw withdrawal latency to thermal heat (control 9.69 ± 0.23 vs. OR486 5.91 ± 0.11). In contrast, adrenalectomized rats (N = 12) failed to develop OR486-induced hypersensitivity. Furthermore, peripheral (N = 9), but not spinal (N = 4) or supraspinal (N = 4), administration of the nonselective βAR antagonist propranolol, the β2AR antagonist ICI-118,511, or the β3AR antagonist SR59230A blocked the development of OR486-induced hypersensitivity.

CONCLUSIONS

Peripheral adrenergic input is necessary for the development of persistent COMT-dependent pain, and peripherally-acting βAR antagonists may benefit chronic pain patients.

PKA-independent cAMP stimulation of white adipocyte exocytosis and adipokine secretion: modulations by Ca2+ and ATP

We examined the effects of cAMP, Ca(2+) and ATP on exocytosis and adipokine release in white adipocytes by a combination of membrane capacitance patch-clamp recordings and biochemical measurements of adipokine secretion. 3T3-L1 adipocyte exocytosis proceeded even in the complete absence of intracellular Ca(2+) ([Ca(2+)]i; buffered with BAPTA) provided cAMP (0.1 mm) was included in the intracellular (pipette-filling) solution. Exocytosis typically plateaued within ∼10 min, probably signifying depletion of a releasable vesicle pool. Inclusion of 3 mm ATP in combination with elevation of [Ca(2+)]i to ≥700 nm augmented the rate of cAMP-evoked exocytosis ∼2-fold and exocytosis proceeded for longer periods (≥20 min) than with cAMP alone. Exocytosis was stimulated to a similar extent upon substitution of cAMP by the Epac (exchange proteins activated by cAMP) agonist 8-Br-2'-O-Me-cAMP (1 mm included in the pipette solution). Inhibition of protein kinase A (PKA) by addition of Rp-cAMPS (0.5 mm) to the cAMP-containing pipette solution was without effect. A combination of the adenylate cyclase activator forskolin (10 μm) and the phosphodiesterase inhibitor IBMX (200 μm; forsk-IBMX) augmented adiponectin secretion measured over 30 min 3-fold and 2-fold in 3T3-L1 and human subcutaneous adipocytes, respectively. This effect was unaltered by pre-loading of cells with the Ca(2+) chelator BAPTA-AM and 2-fold amplified upon inclusion of the Ca(2+) ionophore ionomycin (1 μm) in the extracellular solution. Adiponectin release was also stimulated by the membrane-permeable Epac agonist 8-Br-2'-O-Me-cAMP-AM but unaffected by inclusion of the membrane-permeable PKA inhibitor Rp-8-Br-cAMPS (200 μm). The adipokines leptin, resistin and apelin were present in low amounts in the incubation medium (1-6% of measured adiponectin). Adipsin was secreted in substantial quantities (50% of adiponectin concentration) but release of this adipokine was unaffected by forsk-IBMX. We propose that white adipocyte exocytosis is stimulated by cAMP/Epac-dependent but Ca(2+)- and PKA-independent release of vesicles residing in a readily releasable pool and that the release is augmented by a combination of Ca(2+) and ATP. We further suggest that secreted vesicles chiefly contain adiponectin.

β3-Adrenoceptor activation attenuates atherosclerotic plaque formation in ApoE(-/-) mice through lowering blood lipids and glucose

AIM

To examine the effects of β3-adrenoceptor (β3-AR) activation on atherosclerotic plaque development in ApoE(-/-) mice.

METHODS

Thirty six week-old male ApoE(-/-) mice on a high-fat diet were treated with atorvastatin (10 mg·kg(-1)·d(-1), po), BRL37344 (β3-AR agonist, 1.65 or 3.30 μg/kg, ip, twice a week) or SR52390A (β3-AR antagonist, 50 μg/kg, ip, twice a week) for 12 weeks. Wild-type C57BL/6J mice receiving a normal diet were taken as healthy controls. At the end of the treatments, serum levels of triglycerides (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), non-high density lipoprotein cholesterol (nHDL-C), glucose and insulin were measured. The thoracic aortas were dissected out, the area of atherosclerotic plaques and extent of fibrosis in the plaques were examined using HE and Masson's trichome staining, respectively.

RESULTS

Compared to wild-type mice, ApoE(-/-) mice fed on a high-fat diet exhibited prominent hyperlipidemia and insulin resistance, associated with large area of atherosclerotic plaques and great extent of fibrosis in aortas. Atorvastatin significantly decreased the serum levels of TC and nHDL-C, and reduced the plaque area and collagen content in aortas. BRL37344 significantly decreased the serum levels of TG, TC, nHDL-C, glucose and insulin, and increased HDL-C and the insulin sensitivity, and dose-dependently reduced the plaque area and collagen content in aortas. SR52390A treatment did not affect any parameters studied.

CONCLUSION

The β3-AR agonist impedes the progression of atherosclerosis in ApoE(-/-) mice, through improvement of the lipid and glucose profiles.

Repeated immobilization stress induces catecholamine production in rat mesenteric adipocytes

Catecholamines (CATs), the major regulator of lipolysis in adipose tissue, are produced mainly by the sympathoadrenal system. However, recent studies report endogenous CAT production in adipocytes themselves. This study investigated the effects of single and repeated (7-14 times) immobilization (IMO) stress on CAT production in various fat depots of the rat. Single IMO quickly induced a rise of norepinephrine (NE) and epinephrine (EPI) concentration in mesenteric and brown adipose depots. Adaptive response to repeated IMO included robust increases of NE and EPI levels in mesenteric and subcutaneous adipose tissue. These changes likely reflect the activation of sympathetic nervous system in fat depots by IMO. However, this process was also paralleled by an increase in tyrosine hydroxylase gene expression in mesenteric fat, suggesting regulation of endogenous CAT production in adipose tissue cells. Detailed time-course analysis (time course 10, 30, and 120 min) clearly showed that repeated stress led to increased CAT biosynthesis in isolated mesenteric adipocytes resulting in gradual accumulation of intracellular EPI during IMO exposure. Comparable changes were also found in stromal/vascular fractions, with more pronounced effects of single than repeated IMO. The potential physiological importance of these findings is accentuated by parallel increase in expression of vesicular monoamine transporter 1, indicating a need for CAT storage in adipocyte vesicles. Taken together, we show that CAT production occurs in adipose tissue and may be activated by stress directly in adipocytes.

Brown fat expresses adiponectin in humans

The presence of brown adipose tissue (BAT) in humans is unclear. Pheochromocytomas (PHEO) are rare tumors of neuroectodermal origin which occur in 0.1-0.2% of patients with hypertension. We sought to evaluate the presence and activity of BAT surrounding adrenal PHEO in a well-studied sample of 11 patients who were diagnosed with PHEO and then underwent adrenalectomy. Areas of white fat (WAT) and BAT surrounding PHEO were obtained by Laser Capture Microdissection for analysis of uncoupling protein (UCP)-1 and adiponectin mRNA expression. Adiponectin and UCP-1 mRNA levels were significantly higher in BAT than in WAT (0.62 versus 0.15 and 362.4 versus 22.1, resp., P < 0.01 for both). Adiponectin mRNA levels significantly correlated with urinary metanephrines (r = 0.76, P < 0.01), vanilly mandelic acid (VMA) (r = 0.95, P < 0.01), and serum adiponectin levels (r = 0.95, P < 0.01). Serum adiponectin levels significantly decreased (24.2 ± 2  μ g/mL versus 18 ± 11  μ g/mL, P < 0.01) after adrenalectomy in PHEO subjects. This study provides the following findings: (1) BAT surrounding PHEO expresses adiponectin and UCP-1 mRNA, (2) expression of adiponectin mRNA is significantly higher in BAT than in WAT surrounding PHEO, and (3) catecholamines and serum adiponectin levels significantly correlate with BAT UCP-1 and adiponectin mRNA.

The effects of exercise training on obesity-induced dysregulated expression of adipokines in white adipose tissue

Obesity is recognized as a risk factor for lifestyle-related diseases such as type 2 diabetes and cardiovascular disease. White adipose tissue (WAT) is not only a static storage site for energy; it is also a dynamic tissue that is actively involved in metabolic reactions and produces humoral factors, such as leptin and adiponectin, which are collectively referred to as adipokines. Additionally, because there is much evidence that obesity-induced inflammatory changes in WAT, which is caused by dysregulated expression of inflammation-related adipokines involving tumor necrosis factor- α and monocyte chemoattractant protein 1, contribute to the development of insulin resistance, WAT has attracted special attention as an organ that causes diabetes and other lifestyle-related diseases. Exercise training (TR) not only leads to a decrease in WAT mass but also attenuates obesity-induced dysregulated expression of the inflammation-related adipokines in WAT. Therefore, TR is widely used as a tool for preventing and improving lifestyle-related diseases. This review outlines the impact of TR on the expression and secretory response of adipokines in WAT.

Acute regulation of 5'-AMP-activated protein kinase by long-chain fatty acid, glucose and insulin in rat primary adipocytes

Palmitate increased AMPK (5'-AMP-activated protein kinase) activity, glucose utilization and 2-DOG (2-deoxyglucose) transport in rat adipocytes. All three effects were blocked by the AMPK inhibitor Compound C, leading to the conclusion that in response to an increase in long-chain NEFA (non-esterified fatty acid) concentration AMPK mediated an enhancement of adipocyte glucose transport, thereby providing increased glycerol 3-phosphate for FA (fatty acid) esterification to TAG (triacylglycerol). Activation of AMPK in response to palmitate was not due to an increase in the adipocyte AMP:ATP ratio. Glucose decreased AMPK activity and effects of palmitate and glucose on AMPK activity were antagonistic. While insulin had no effect on basal AMPK activity insulin did decrease AMPK activity in the presence of palmitate and also decreased the percentage effectiveness of palmitate to increase the transport of 2-DOG. It is suggested that activation of adipocyte AMPK by NEFA, as well as decreasing the activity of hormone-sensitive lipase, could modulate adipose tissue dynamics by increasing FA esterification and, under certain circumstances, FA synthesis.

TNF-α involvement in insulin resistance induced by experimental scorpion envenomation

BACKGROUND

Scorpion venom induces systemic inflammation characterized by an increase in cytokine release and chemokine production. There have been few experimental studies assessing the effects of scorpion venom on adipose tissue function in vivo.

METHODOLOGY/PRINCIPAL FINDINGS

To study the adipose tissue inflammation (ATI) induced by Androctonus australis hector (Aah) venom and to assess possible mechanisms of ATI, mice (n = 6, aged 1 month) were injected with Aah (0.45 mg/kg), toxic fraction of Aah (FTox-G50; 0.2 mg/kg) or saline solution (control). Inflammatory responses were evaluated by ELISA and cell sorting analyses in adipose tissue 45 minutes and 24 hours after injection. Quantitative real-time PCR was used to assess the regulation of genes implicated in glucose uptake. The titers of selected inflammatory cytokines (IL-1β, IL-6 and TNF-α) were also determined in sera and in insulin target tissues. The serum concentration of IL-1β rose 45 minutes after envenomation and returned to basal level after 24 hours. The pathophysiological effects of the venom after 24 hours mainly involved M1-proinflammatory macrophage infiltration in adipose tissue combined with high titers of IL-1β, IL-6 and TNF-α. Indeed, TNF-α was strongly induced in both adipose tissue and skeletal muscle. We studied the effects of Aah venom on genes implicated in insulin-stimulated glucose uptake. Insulin induced a significant increase in the expression of the mRNAs for hexokinase 2 and phosphatidylinositol 3-kinase in both skeletal muscle and adipose tissue in control mice; this upregulation was completely abolished after 24 hours in mice envenomed with Aah or FTox-G50.

CONCLUSIONS/SIGNIFICANCE

Our findings suggest that Aah venom induces insulin resistance by mechanisms involving TNF-α-dependent Map4k4 kinase activation in the adipose tissue.

Nutritional and hormonal modulation of adiponectin and its receptors adipoR1 and adipoR2

Adiponectin is the most abundant plasma protein synthesized mostly by adipose tissue and is an insulin-sensitive hormone, playing a central role in glucose and lipid metabolism. Adiponectin effects are mediated via two receptors, adipoR1 and adipoR2. Several hormones and diet components that are involved in insulin resistance may impair insulin sensitivity at least in part by decreasing adiponectin and adiponectin receptors. Adiponectin expression and serum levels are associated with the amount and type of fatty acids and carbohydrate consumed. Other food items, such as vitamins, alcohol, sodium, green tea, and coffee, have been reported to modify adiponectin levels. Several hormones, including testosterone, estrogen, prolactin, glucocorticoids, catecholamines, and growth hormone, have been shown to inhibit adiponectin production, but the studies are still controversial. Even so, adiponectin is a potential therapeutic target in the treatment of diabetes mellitus and other diseases associated with hypoadiponectinemia.

Effects of adrenal hormones on the expression of adiponectin and adiponectin receptors in adipose tissue, muscle and liver

BACKGROUND

Adiponectin, an insulin-sensitive hormone that is primarily synthesized in adipose tissue, exerts its effects by binding to two receptors, adipoR1 and adipoR2. Little is known regarding the effects of glucocorticoids on the expression of adiponectin receptors.

METHODS

Male Wistar rats were bilaterally adrenalectomized and treated with dexamethasone (0.2 mg/100 g) twice daily for 3 days. To analyze the potential effects of glucocorticoids, rats received two daily injections of the glucocorticoid receptor antagonist (RU-486, 5.0 mg) over the course of 3 days. Additionally, 3T3-L1 adipocytes and C2C12 myotubes were treated with dexamethasone, adrenaline or RU-486. The gene expression of adiponectin, adipoR1 and adipoR2 was determined by real-time PCR, and protein secretion was examined by Western blotting using lysates from retroperitoneal, epididymal and subcutaneous adipose tissue depots, liver and muscle.

RESULTS

In rats, excess glucocorticoids increased the levels of insulin in serum and decreased serum adiponectin concentrations, whereas adrenalectomy decreased the mRNA expression of adiponectin (3-fold) and adipoR2 (7-fold) in epididymal adipose tissue and increased adipoR2 gene expression in muscle (3-fold) compared to control group sham-operated. Dexamethasone treatment did not reverse the effects of adrenalectomy, and glucocorticoid receptor blockade did not reproduce the effects of adrenalectomy. In 3T3-L1 adipocytes, dexamethasone and adrenaline both increased adipoR2 mRNA levels, but RU-486 reduced adipoR2 gene expression in vitro.

CONCLUSION

Dexamethasone treatment induces a state of insulin resistance but does not affect adiponectin receptor expression in adipose tissue. However, the effects of catecholamines on insulin resistance may be due to their effects on adipoR2.

Concentrações sanguíneas de adiponectina e exercício físico: associações com a sensibilidade insulínica

O objetivo desta revisão foi apresentar e discutir a influência do exercício físico nas concentrações sanguíneas de adiponectina e a associação com a sensibilidade insulínica. Estudos realizados nos últimos 10 anos mostram que o exercício agudo, de intensidade alta, provoca redução nas concentrações sanguíneas de adiponectina, sem alterar as concentrações de insulina. Porém, exercícios agudos de intensidade moderada não alteram as concentrações sanguíneas de adiponectina, apesar de proporcionar melhoria na sensibilidade insulínica. O exercício crônico, por sua vez, aumenta os níveis sanguíneos de adiponectina, melhora a sensibilidade insulínica, mas altera a composição corporal em indivíduos obesos. Em indivíduos eutróficos, todavia, os níveis de adiponectina não são afetados, apesar dos benefícios do exercício crônico para a composição corporal e sensibilidade insulínica.

Adipocytes as a new source of catecholamine production

Catecholamines are an important regulator of lipolysis in adipose tissue. Here we show that rat adipocytes, isolated from mesenteric adipose tissue, express genes of catecholamine biosynthetic enzymes and produce catecholamines de novo. Administration of tyrosine hydroxylase inhibitor, alpha-methyl-p-tyrosine, in vitro significantly reduced concentration of catecholamines in isolated adipocytes. We hypothesize that the sympathetic innervation of adipose tissues is not the only source of catecholamines, since adipocytes also have the capacity to produce both norepinephrine and epinephrine.

Fish oil consumption prevents glucose intolerance and hypercorticosteronemy in footshock-stressed rats

BACKGROUND

Environmental stress plays an important role in the development of glucose intolerance influencing lipid and glucose metabolism through sympathetic nervous system, cytokines and hormones such as glucocorticoids, catecholamines and glucagon. Otherwise, fish oil prevents glucose intolerance and insulin resistance. Although the mechanisms involved are not fully understood, it is known that sympathetic and HPA responses are blunted and catecholamines and glucocorticoids concentrations can be modulated by fish consumption. The aim of the present study was to evaluate whether fish oil, on a normal lipidic diet: 1) could prevent the effect of footshock-stress on the development of glucose intolerance; 2) modified adiponectin receptor and serum concentration; and 3) also modified TNF-α, IL-6 and interleukin-10 (IL-10) levels in adipose tissue and liver. The study was performed in thirty day-old male Wistar randomly assigned into four groups: no stressed (C) and stressed (CS) rats fed with control diet, and no stressed (F) and stressed (FS) rats fed with a fish oil rich diet. The stress was performed as a three daily footshock stress sessions.

RESULTS

Body weight, carcass fat and protein content were not different among groups. FS presented a reduction on the relative weight of RET. Basal serum glucose levels were higher in CS and FS but 15 min after glucose load just CS remained with higher levels than other groups. Serum corticosterone concentration was increased in CS, this effect was inhibited in FS. However, 15 min after footshock-stress, corticosterone levels were similar among groups. IL-6 was increased in EPI of CS but fish oil consumption prevented IL-6 increase in FS. Similar levels of TNF-α and IL-10 in RET, EPI, and liver were observed among groups. Adipo R1 protein concentration was not different among groups. Footshock-stress did not modify AdipoR2 concentration, but fish oil diet increases AdipoR2 protein concentration.

CONCLUSIONS

Footshock-stress promotes glucose intolerance associated to corticosterone serum level and epididymal white adipose tissue IL-6 concentration increase. The fish oil consumption by stressed rats normalized the stress responses. These results suggested that fish oil intake could be useful to minimize or prevent the development of diseases associated to the stress.

β(3) Receptors: Role in Cardiometabolic Disorders

Pharmacological and molecular approaches have shown that an atypical β-adrenoceptor (AR), called β(3)-AR, that is distinct from β(1)-ARs and β(2)-ARs, exists in some tissues in heterogeneous populations such as β(3a)-ARs and β(3b)-ARs. β(3)-ARs belong to a superfamily of receptors linked to guanine nucleotide binding proteins (G proteins). The β(3)-AR gene contains two introns whereas the β(1)-AR and β(2)-AR genes are intronless, leading to splice variants. β(3)-ARs can couple to G(i) and G(s) and they are reported to be present in brown adipose tissue, vasculature, the heart, among other tissues. β(3)-ARs cause vasodilation of microvessels in the islets of Langerhans and may participate in the pathogenesis of cardiac failure, during which modification of β(1)-AR and β(2)-AR expression occurs. The development of β(3)-AR agonists has led to the elaboration of promising new drugs, including antiobesity and antidiabetic drugs. This article reviews the various pharmacological actions of β(3)-ARs and their clinical implications for diabetes and cardiovascular diseases.

Tamoxifen-inducible Cre-mediated recombination in adipocytes

To generate a mouse line which allows inducible, Cre/loxP-dependent recombination in adipocytes, we used RedE/RedT-mediated recombineering to insert the CreER(T)²-transgene, which encodes a fusion protein of Cre and a mutated tamoxifen-responsive estrogen receptor, into the start codon of the adipocyte-specific Adipoq gene. Adipoq encodes adiponectin, an adipokine specifically expressed in differentiated adipocytes. Tamoxifen treatment induced almost complete recombination in white adipose tissue of the AdipoqCreER(T)² mouse line (97%-99%), while no recombination was seen in vehicle-treated animals. Recombination in brown adipose tissue was about 15%, whereas other organs and tissues did not undergo recombination. In addition, mice expressing CreER(T)² in adipocytes did not show any alterations of metabolic functions like glucose tolerance, lipolysis, or energy expenditure compared to control mice. Therefore the AdipoqCreER(T)² mouse line will be a valuable tool for studying the consequences of a temporally controlled deletion of floxed genes in white adipose tissue.

Influence of acute aerobic exercise on adiponectin oligomer concentrations in middle-aged abdominally obese men

Exercise intensity may induce changes in total adiponectin and adiponectin oligomer levels. However, the effects of acute aerobic exercise on total adiponectin and adiponectin oligomers in middle-aged abdominally obese men remain unknown. The purpose of this study was to investigate the influence of aerobic exercise intensity on changes in the concentrations of total adiponectin and adiponectin oligomers (high-molecular weight [HMW] and middle- plus low-molecular weight [MLMW] adiponectin), and the endocrine mechanisms involved in exercise-induced changes in adiponectin oligomer profiles in middle-aged abdominally obese men. Using a crossover design, 9 middle-aged abdominally obese men (age, 54.1 ± 2.4 years; body mass index, 27.9 ± 0.6 kg/m²) underwent 2 trials that consisted of 60 minutes of stationary cycle exercise at either moderate-intensity (ME) or high-intensity (HE) aerobic exercise (50% or 70% of peak oxygen uptake, respectively). Blood samples were collected to measure the concentrations of adiponectin oligomers, hormones (catecholamines, insulin, and growth hormone), metabolites (free fatty acid, glycerol, triglyceride, and glucose), and cytokines (interleukin-6 and tumor necrosis factor-α). After exercise, plasma catecholamine concentrations were higher during HE than during ME (P < .05). Total adiponectin concentration decreased at the end of HE (P < .05), but remained unchanged after ME. The HMW adiponectin concentration did not change at either intensity, whereas the MLMW concentration decreased at the end of HE (P < .05). The ratio of HMW to total adiponectin concentration increased significantly (P < .05), whereas the ratio of MLMW to total adiponectin concentration decreased significantly (P < .05), at the end of HE. The percentage changes in epinephrine concentration from baseline to the end of exercise were correlated with the percentage changes in total adiponectin concentration (r = -0.67, P < .05) and MLMW adiponectin concentration (r = -0.82, P < .05) from baseline to the end of HE. Our results indicate that the change in total adiponectin was mainly due to a change in MLMW adiponectin concentration during high-intensity exercise in middle-aged abdominally obese men. Epinephrine may partially regulate the decrease in total and MLMW adiponectin concentrations during high-intensity exercise.

The crosstalks between adipokines and catecholamines

Adipocytes, which secrete a spectrum of adipokines, play an integral role in metabolism via communications with other endocrine cells. In the present work, we have studied the interplays between adipokines and catecholamines, using 3T3-L1 adipocytes and PC12 cells as the cell models and an integrative experimental platform. We demonstrate that all catecholamines inhibit vesicle trafficking and secretion of leptin and resistin through β-adrenergic receptors, while leptin and resistin enhance the vesicle trafficking and secretion of catecholamines through PKC, PKA, MAPK kinase and Ca(2+) dependent pathways. The crosstalks between adipokines and catecholamines were further corroborated by co-culturing 3T3-L1 adipocytes and PC12 cells. Our findings highlight the importance of adipo-adrenal axis in energy metabolism and the intricate interactions between metabolic hormones.

High-fat diet and glucocorticoid treatment cause hyperglycemia associated with adiponectin receptor alterations

BACKGROUND

Adiponectin is the most abundant plasma protein synthesized for the most part in adipose tissue, and it is an insulin-sensitive hormone, playing a central role in glucose and lipid metabolism. In addition, it increases fatty acid oxidation in the muscle and potentiates insulin inhibition of hepatic gluconeogenesis. Two adiponectin receptors have been identified: AdipoR1 is the major receptor expressed in skeletal muscle, whereas AdipoR2 is mainly expressed in liver. Consumption of high levels of dietary fat is thought to be a major factor in the promotion of obesity and insulin resistance. Excessive levels of cortisol are characterized by the symptoms of abdominal obesity, hypertension, glucose intolerance or diabetes and dyslipidemia; of note, all of these features are shared by the condition of insulin resistance. Although it has been shown that glucocorticoids inhibit adiponectin expression in vitro and in vivo, little is known about the regulation of adiponectin receptors. The link between glucocorticoids and insulin resistance may involve the adiponectin receptors and adrenalectomy might play a role not only in regulate expression and secretion of adiponectin, as well regulate the respective receptors in several tissues.

RESULTS

Feeding of a high-fat diet increased serum glucose levels and decreased adiponectin and adipoR2 mRNA expression in subcutaneous and retroperitoneal adipose tissues, respectively. Moreover, it increased both adipoR1 and adipoR2 mRNA levels in muscle and adipoR2 protein levels in liver. Adrenalectomy combined with the synthetic glucocorticoid dexamethasone treatment resulted in increased glucose and insulin levels, decreased serum adiponectin levels, reduced adiponectin mRNA in epididymal adipose tissue, reduction of adipoR2 mRNA by 7-fold in muscle and reduced adipoR1 and adipoR2 protein levels in muscle. Adrenalectomy alone increased adiponectin mRNA expression 3-fold in subcutaneous adipose tissue and reduced adipoR2 mRNA expression 2-fold in liver.

CONCLUSION

Hyperglycemia as a result of a high-fat diet is associated with an increase in the expression of the adiponectin receptors in muscle. An excess of glucocorticoids, rather than their absence, increase glucose and insulin and decrease adiponectin levels.

Adipose proinflammatory cytokine expression through sympathetic system is associated with hyperglycemia and insulin resistance in a rat ischemic stroke model

Patients who experience acute ischemic stroke may develop hyperglycemia, even in the absence of diabetes, but the exact mechanisms are still unclear. Adipose tissue secretes numerous proinflammatory cytokines and is involved in the regulation of glucose metabolism. This study aimed to determine the effects of acute stroke on adipose inflammatory cytokine expression. In addition, because sympathetic activity is activated after acute stroke and catecholamines can regulate the expression of several adipocytokines, this study also evaluated whether alterations in adipose proinflammatory cytokines following acute stroke, if any, were medicated by sympathetic system. Acute ischemic brain injury was induced by ligating the right middle cerebral artery and bilateral common carotid arteries in male adult Sprague-Dawley rats. Adipose tumor necrosis factor-α (TNF-α) and monocyte chemoattractant protein-1 (MCP-1) mRNA and protein levels were determined by RT-PCR and enzyme-linked immunoassay, respectively. The stroke rats developed glucose intolerance on days 1 and 2 after cerebral ischemic injury. The fasting blood insulin levels and insulin resistance index measured by homeostasis model assessment were higher in the stroke rats compared with the sham group. Epididymal adipose TNF-α and MCP-1 mRNA and protein levels were elevated one- to twofold, in association with increased macrophage infiltration into the adipose tissue. When the rats were treated with a nonselective β-adrenergic receptor blocker, propranolol, before induction of cerebral ischemic injury, the acute stroke-induced increase in TNF-α and MCP-1 was blocked, and fasting blood insulin concentration and homeostasis model assessment-insulin resistance were decreased. These results suggest a potential role of adipose proinflammatory cytokines induced by the sympathetic nervous system in the pathogenesis of glucose metabolic disorder in rats with acute ischemic stroke.

Catecholamines, adiponectin, and insulin resistance as measured by HOMA in children with obstructive sleep apnea

INTRODUCTION

Obstructive sleep apnea (OSA) has been implicated in the pathophysiology of metabolic syndrome. Its contribution to insulin resistance is complicated by obesity and puberty. We hypothesized that OSA is associated with worse insulin resistance and lower adiponectin after adjustment for obesity and puberty and that catecholamines might mediate these changes.

METHODS

Normal controls and children with suspected OSA were recruited and categorized as pubertal or prepubertal. Overnight polysomnography (PSG) was performed. Subjects were categorized as OSA for total apnea hypopnea index (Total-AHI) > or = 1.5 events/h. Fasting blood glucose, insulin, adiponectin, and 24-hour urinary catecholamines were obtained. Homeostatic model assessment of insulin resistance (HOMA) was calculated. The independent effects of OSA upon HOMA, adiponectin, and urinary catecholamines following adjustment for body mass index (BMI) were determined. RESULTS (median; min, max): Subjects (n = 98, 42F; 11 +/- 4 years, 37 prepubertal) were generally overweight (BMI-Z = 2.1; -3, 4.1) and had wide-ranging insulin sensitivities (HOMA = 2.7; 0.5, 27) and PSG parameters (Total-AHI = 1.6; 0, 185). The risks of elevated insulin (P = 0.04) and HOMA (P = 0.05) were higher in OSA vs non OSA obese pubertal children. Polysomnographic markers of OSA, including Total-AHI (P = 0.001, R2 = 0.32), were negatively associated with adiponectin in pubertal children. Total-AHI and oxygen desaturation were associated with higher urinary normetanephrine and norepinephrine.

CONCLUSIONS

In obese pubertal children, OSA was associated with worse insulin resistance. Worsening OSA was associated with lower adiponectin and increasing urinary catecholamines. Whether OSA directly lowers adiponectin and aggravates a predisposition to insulin resistance is unknown, but these preliminary findings highlight the importance of further studying pediatric OSA.

AMP-activated protein kinase (AMPK) activation regulates in vitro bone formation and bone mass

Adenosine 5'-monophosphate-activated protein kinase (AMPK), a regulator of energy homeostasis, has a central role in mediating the appetite-modulating and metabolic effects of many hormones and antidiabetic drugs metformin and glitazones. The objective of this study was to determine if AMPK can be activated in osteoblasts by known AMPK modulators and if AMPK activity is involved in osteoblast function in vitro and regulation of bone mass in vivo. ROS 17/2.8 rat osteoblast-like cells were cultured in the presence of AMPK activators (AICAR and metformin), AMPK inhibitor (compound C), the gastric peptide hormone ghrelin and the beta-adrenergic blocker propranolol. AMPK activity was measured in cell lysates by a functional kinase assay and AMPK protein phosphorylation was studied by Western Blotting using an antibody recognizing AMPK Thr-172 residue. We demonstrated that treatment of ROS 17/2.8 cells with AICAR and metformin stimulates Thr-172 phosphorylation of AMPK and dose-dependently increases its activity. In contrast, treatment of ROS 17/2.8 cells with compound C inhibited AMPK phosphorylation. Ghrelin and propranolol dose-dependently increased AMPK phosphorylation and activity. Cell proliferation and alkaline phosphatase activity were not affected by metformin treatment while AICAR significantly inhibited ROS 17/2.8 cell proliferation and alkaline phosphatase activity at high concentrations. To study the effect of AMPK activation on bone formation in vitro, primary osteoblasts obtained from rat calvaria were cultured for 14-17days in the presence of AICAR, metformin and compound C. Formation of 'trabecular-shaped' bone nodules was evaluated following alizarin red staining. We demonstrated that both AICAR and metformin dose-dependently increase trabecular bone nodule formation, while compound C inhibits bone formation. When primary osteoblasts were co-treated with AICAR and compound C, compound C suppressed the stimulatory effect of AICAR on bone nodule formation. AMPK is a alphabetagamma heterotrimer, where alpha is the catalytic subunit. RT-PCR analysis of AMPK subunits in ROS17/2.8 osteoblastic cells and in mouse tibia showed that the AMPKalpha1 subunit is the dominant isoform expressed in bone. We analysed the bone phenotype of 4month-old male wild type (WT) and AMPKalpha1-/- KO mice using micro-CT. Both cortical and trabecular bone compartments were smaller in the AMPK alpha1-deficient mice compared to the WT mice. Altogether, our data support a role for AMPK signalling in skeletal physiology.

Differences in AMPK expression between subcutaneous and visceral adipose tissue in morbid obesity

Adenine monophosphate (AMP) activated protein kinase (AMPK) is an important regulator of obesity. The objective of the present work was to study and compare AMPK protein expression in visceral vs. subcutaneous adipose tissue of morbid obese subjects and to correlate it with adipose tissue characteristics. We selected a total population of 17 extreme obese (BMI>or=40 kg/m2) aged 42.8+/-10.2 years were included in this study. We measured anthropometric and body composition parameters. Adiponectin expression by qRT-PCR, isoproterenol-stimulated lipolytic rates, and AMPK alpha subunits expression by Western blot in adipose tissue explants were determined. Finally plasma concentrations of glucose, triacylglycerols, total cholesterol, HDL-c, LDL-c and insulin were also measured. Our results showed that AMPK alpha expression was higher in subcutaneous than in visceral tissue. A positive correlation between AMPK expression and adiponectin expression in human subcutaneous adipose tissue was observed. Furthermore, a positive correlation between AMPK expression and isoproterenol evoked upregulation of lipolysis rate was also observed. In conclusion, AMPK alpha expression differed according to adipose tissue location. The positive correlation between subcutaneous adipose tissue AMPK and adiponectin or the evoked lipolysis rate could indicate a protective role of AMPK in this tissue, counteracting insulin resistance in morbid obese patients.

Sympathetic overstimulation during critical illness: adverse effects of adrenergic stress

The term ''adrenergic'' originates from ''adrenaline'' and describes hormones or drugs whose effects are similar to those of epinephrine. Adrenergic stress is mediated by stimulation of adrenergic receptors and activation of post-receptor pathways. Critical illness is a potent stimulus of the sympathetic nervous system. It is undisputable that the adrenergic-driven ''fight-flight response'' is a physiologically meaningful reaction allowing humans to survive during evolution. However, in critical illness an overshooting stimulation of the sympathetic nervous system may well exceed in time and scope its beneficial effects. Comparable to the overwhelming immune response during sepsis, adrenergic stress in critical illness may get out of control and cause adverse effects. Several organ systems may be affected. The heart seems to be most susceptible to sympathetic overstimulation. Detrimental effects include impaired diastolic function, tachycardia and tachyarrhythmia, myocardial ischemia, stunning, apoptosis and necrosis. Adverse catecholamine effects have been observed in other organs such as the lungs (pulmonary edema, elevated pulmonary arterial pressures), the coagulation (hypercoagulability, thrombus formation), gastrointestinal (hypoperfusion, inhibition of peristalsis), endocrinologic (decreased prolactin, thyroid and growth hormone secretion) and immune systems (immunomodulation, stimulation of bacterial growth), and metabolism (increase in cell energy expenditure, hyperglycemia, catabolism, lipolysis, hyperlactatemia, electrolyte changes), bone marrow (anemia), and skeletal muscles (apoptosis). Potential therapeutic options to reduce excessive adrenergic stress comprise temperature and heart rate control, adequate use of sedative/analgesic drugs, and aiming for reasonable cardiovascular targets, adequate fluid therapy, use of levosimendan, hydrocortisone or supplementary arginine vasopressin.

Adiponectin and adiponectin receptors in human pheochromocytoma

AIM

Recent studies have demonstrated that serum adiponectin and its receptors in adipose and muscle tissues are suppressed in diabetic or obese individuals. Patients with pheochromocytoma are frequently diabetic.

METHODS

Using real-time PCR, we examined mRNA expressions of adiponectin (Adp) and adiponectin receptor 1 (AdpR1) and AdpR2 in pheochromocytoma tissues from 49 patients. We also measured levels of serum total and high molecular weight (HMW) adiponectin levels in 10 pheochromocytomas and 33 normal volunteers.

RESULTS

In pheochromocytoma tissue, AdpR1 mRNA expression was higher in adrenaline (A)-type tumors than in noradrenaline (NA)-type tumors. AdpR1 expression was significantly higher in A-type non-diabetics than in NA-type non-diabetics (p<0.05). AdpR1 mRNA expression was significantly associated with the tumor tissue adrenaline content (p<0.005) in linear regression analysis, which suggest that adrenaline positively regulates AdpR1 mRNA expression.Serum total and HMW Adp levels in patients with NA-type pheochromocytomas were approximately 3 times higher than those of healthy volunteers. After adrenalectomy, levels of adiponectin normalized.

CONCLUSION

Our results indicate that serum total and HMW Adp, and AdpR1 gene expressions in pheochromocytoma tissue, are associated with the level of catecholamine produced in the tumor. It is tempting to speculate that catecholamine induces adiponectin production and signaling.

Oleic acid and peanut oil high in oleic acid reverse the inhibitory effect of insulin production of the inflammatory cytokine TNF-alpha both in vitro and in vivo systems

BACKGROUND

Chronic inflammation is a key player in pathogenesis. The inflammatory cytokine, tumor necrosis factor-alpha is a well known inflammatory protein, and has been a therapeutic target for the treatment of diseases such as Rheumatoid Arthritis and Crohn's Disease. Obesity is a well known risk factor for developing non-insulin dependent diabetes melitus. Adipose tissue has been shown to produce tumor necrosis factor-alpha, which has the ability to reduce insulin secretion and induce insulin resistance. Based on these observations, we sought to investigate the impact of unsaturated fatty acids such as oleic acid in the presence of TNF-alpha in terms of insulin production, the molecular mechanisms involved and the in vivo effect of a diet high in oleic acid on a mouse model of type II diabetes, KKAy.

METHODS

The rat pancreatic beta cell line INS-1 was used as a cell biological model since it exhibits glucose dependent insulin secretion. Insulin production assessment was carried out using enzyme linked immunosorbent assay and cAMP quantification with competitive ELISA. Viability of TNF-alpha and oleic acid treated cells was evaluated using flow cytometry. PPAR-gamma translocation was assessed using a PPRE based ELISA system. In vivo studies were carried out on adult male KKAy mice and glucose levels were measured with a glucometer.

RESULTS

Oleic acid and peanut oil high in oleic acid were able to enhance insulin production in INS-1. TNF-alpha inhibited insulin production but pre-treatment with oleic acid reversed this inhibitory effect. The viability status of INS-1 cells treated with TNF-alpha and oleic acid was not affected. Translocation of the peroxisome proliferator- activated receptor transcription factor to the nucleus was elevated in oleic acid treated cells. Finally, type II diabetic mice that were administered a high oleic acid diet derived from peanut oil, had decreased glucose levels compared to animals administered a high fat diet with no oleic acid.

CONCLUSION

Oleic acid was found to be effective in reversing the inhibitory effect in insulin production of the inflammatory cytokine TNF-alpha. This finding is consistent with the reported therapeutic characteristics of other monounsaturated and polyunsaturated fatty acids. Furthermore, a diet high in oleic acid, which can be easily achieved through consumption of peanuts and olive oil, can have a beneficial effect in type II diabetes and ultimately reverse the negative effects of inflammatory cytokines observed in obesity and non insulin dependent diabetes mellitus.

Proteomic analysis of mitochondrial proteins of basal and lipolytically (isoproterenol and TNF-alpha)-stimulated adipocytes

The regulation of adipocyte lipolysis is increasingly believed to influence insulin resistance, in a process that may be associated with mitochondrial dysfunction. However, the molecular basis of the relationship between mitochondrial protein expression, lipolytic responsiveness, and insulin resistance remains unknown. A set of proteins that shows altered abundances in the mitochondria of untreated and treated 3T3-L1 adipocytes with TNF-alpha or isoproterenol was identified. These include the proteins associated with energy production, including fatty acid oxidation, TCA cycle, and oxidative phosphorylation. Proteins associated with oxidative stress dissipation were down-regulated in lipolytically stimulated adipocytes. Lipolytic stimulation with isoproterenol and TNF-alpha, which is also a potent proinflammatory cytokine, showed some noticeable differences in mitochondrial protein expression. For example, isoproterenol markedly enhanced the expression of prohibitin which is involved in the integrity of mitochondria but TNF-alpha did not. These results provide valuable information on mitochondrial dysfunction associated with oxidative stress induced by lipolytic stimulation.

Adipocyte CREB promotes insulin resistance in obesity

Increases in adiposity trigger metabolic and inflammatory changes that interfere with insulin action in peripheral tissues, culminating in beta cell failure and overt diabetes. We found that the cAMP Response Element Binding protein (CREB) is activated in adipose cells under obese conditions, where it promotes insulin resistance by triggering expression of the transcriptional repressor ATF3 and thereby downregulating expression of the adipokine hormone adiponectin as well as the insulin-sensitive glucose transporter 4 (GLUT4). Transgenic mice expressing a dominant-negative CREB transgene in adipocytes displayed increased whole-body insulin sensitivity in the contexts of diet-induced and genetic obesity, and they were protected from the development of hepatic steatosis and adipose tissue inflammation. These results indicate that adipocyte CREB provides an early signal in the progression to type 2 diabetes.

Could Beta blockade improve outcome after injury by modulating inflammatory profiles?

BACKGROUND

Cardioprotection with beta-receptor antagonists improves outcome in high risk patients undergoing elective surgery. Recent trials have demonstrated an association between beta blocker (BB) use and improved outcomes after injury. The mechanisms through which BB result in improved outcomes remain poorly elucidated. In vitro evidence supports that BB modulates the postinjury inflammatory response. The purpose of this study was to examine the effects of BB on inflammatory profiles in injured patients at increased risk for heart disease.

METHODS

A pseudo-randomized, controlled trial of injured patients over 55 admitted to the intensive care unit was conducted. Patients were randomized to receive continuous BB or standard of care. Patients with a reported history of prehospital BB use were enrolled into an observational arm of the trial, continued on BB, and analyzed with the continuous BB group. Plasma interleukin (IL)-6 and IL-1beta levels were measured by enzyme-linked immunosorbent assay at baseline and day 1, 2, and 4 after BB initiation. Cytokine data were log transformed for normality assumptions. Repeated measures analysis of variance was used to test for within-group differences in cytokine levels over time.

RESULTS

Forty-two patients were enrolled. Seventeen patients were randomized to the control group and 25 patients received continuous BB (10 randomized/15 observational). There was no difference in gender, age, prior history of heart disease, or admission heart rate, systolic blood pressure or initial base deficit between groups. Baseline levels of IL-6 and IL-1beta did not differ between groups. Levels of IL-6, but not IL-1beta, decreased over time in patients receiving BB (p = 0.04), whereas levels in controls remained unchanged (p = 0.27). There were no BB related complications.

CONCLUSIONS

Use of BB decreases serum IL-6 levels over time in injured patients at risk for heart disease. This may contribute to improved outcomes noted in trauma patients receiving BB. Additionally, BB use in this population of patients is safe after endpoints of resuscitation have been met.

The effects of beta(3)-adrenoceptor agonist CL-316,243 on adiponectin, adiponectin receptors and tumor necrosis factor-alpha expressions in adipose tissues of obese diabetic KKAy mice

We investigated the effects of beta(3)-adrenoceptor agonist, 5-[(2R)-2-[[(2R)-2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]-1,3-benzodioxole-2,2-dicarboxylate (CL-316,243) in obese diabetic KKAy mice. Two weeks' subcutaneous administration of CL-316,243 reduced serum levels of glucose, insulin, triglyceride, free fatty acid and tumor necrosis factor-alpha (TNF-alpha), and increased adiponectin. Adiponectin, adiponectin receptors and beta(3)-adrenoceptor mRNA expressions were reduced in epididymal white adipose tissue in KKAy mice, and CL-316,243 recovered these mRNA expressions. Meanwhile, CL-316,243 suppressed the overexpressed mRNA level of TNF-alpha in both epididymal white adipose tissue and brown adipose tissue. These data suggest that the normalization of adiponectin, adiponectin receptors and TNF-alpha may result in the amelioration of obesity-induced insulin resistance.