Protective vascular and myocardial effects of adiponectin

Endothelial dysfunction, inflammation, and apoptosis in diabetes mellitus

Endothelial dysfunction is regarded as an important factor in the pathogenesis of vascular disease in obesity-related type 2 diabetes. The imbalance in repair and injury (hyperglycemia, hypertension, dyslipidemia) results in microvascular changes, including apoptosis of microvascular cells, ultimately leading to diabetes related complications. This review summarizes the mechanisms by which the interplay between endothelial dysfunction, inflammation, and apoptosis may cause (micro)vascular damage in patients with diabetes mellitus.

Adipocyte factors, high-sensitive C-reactive protein levels and lipoxidative stress products in overweight postmenopausal women with normal and impaired OGTT

OBJECTIVE

In obese postmenopausal women we assessed leptin and adiponectin, high-sensitive C-reactive protein (hsCRP), serum lipids and lipoxidative stress products: oxidized LDL (oxLDL) and malondialdehyde (MDA), in relation to impaired glucose tolerance (IGT).

METHODS

Thirty-eight overweight/obese postmenopausal women were included in the study. Eighteen with normal glucose metabolism (NGT) and twenty with IGT, as it is diagnosed by OGTT. Serum leptin, adiponectin, hsCRP and MDA were measured at time 0 and 120 min of OGTT while total-cholesterol, LDL, HDL, triglycerides, oxLDL and anti-oxLDL autoantibodies at time 0. Insulin resistance (HOMA)/sensitivity (QUICKI) indexes were estimated.

RESULTS

In subjects with NGT, hsCRP was positively correlated with fasting leptin and HOMA, while in subjects with IGT negatively with QUICKI. In both groups, hsCRP was positively correlated with fasting insulin, body mass index and waist circumference. Fasting adiponectin was positively associated with HDL in both groups and negatively with triglycerides in subjects with NGT as well as with serum glucose levels at time 120 min of OGTT in subjects with IGT. No association was observed between oxLDL and adipokines. A significant positive association was found between oxLDL and HOMA in subjects with IGT. During OGTT there was a significant increase of leptin and MDA levels in both groups.

CONCLUSIONS

A relationship exists between obesity, insulin and sub-clinical inflammation. Leptin and lipid peroxidation are linked to hyperglycaemic state while oxLDL might be considered as a predictor of insulin resistance. Adiponectin could exert its antiatherogenic effect through HDL independently of the presence of IGT.

Plasma adiponectin levels are associated with left ventricular hypertrophy in a random sample of middle-aged subjects

BACKGROUND

A low adiponectin level is associated with high blood pressure which, in turn, often results in left ventricular hypertrophy. We evaluated the association between plasma adiponectin concentrations and echocardiographic measurements, including left ventricular mass index (LVMI), in 933 middle-aged subjects consisting of 453 hypertensives and 480 controls.

METHODS

Plasma adiponectin concentrations were measured with an enzyme-linked immunosorbent assay (ELISA) method. One experienced cardiologist performed echocardiographic examinations, and LVMI was calculated according to Devereux's method.

RESULTS

Low plasma adiponectin levels were independently associated with increased intraventricular septum thickness, posterior ventricular wall thickness, and left ventricular mass index (P<0.001) in the whole cohort. In the subgroup analysis, the association between these echocardiographic parameters and adiponectin concentrations was observed only in the hypertensive cohort although fractional shortening revealed an association with adiponectin levels also in the control cohort (P=0.021). Findings remained significant after adjustment for the major risk factors for LVMI, such as age, sex, smoking, and systolic blood pressure.

CONCLUSIONS

This study in a large population sample detected an association between low plasma adiponectin concentration and LVMI, a marker of left ventricular hypertrophy. This association may be one of the factors that could explain the reported increased cardiovascular risk in subjects with low adiponectin levels.

Cardiomyocyte-derived adiponectin is biologically active in protecting against myocardial ischemia-reperfusion injury

Adiponectin (APN) has traditionally been viewed as an adipocyte-specific endocrine molecule with cardioprotective effects. Recent studies suggest that APN is also expressed in cardiomyocytes. However, biological significances of this locally produced APN remain completely unknown. The aim of this study was to investigate the pathological and pharmacological significance of cardiac-derived APN in cardiomyocyte pathology. Adult cardiomyocytes from wild-type littermates (WT) or gene-deficient mice were pretreated with vehicle (V) or rosiglitazone (RSG) for 6 h followed by simulated ischemia-reperfusion (SI/R, 3 h/12 h). Compared with WT cardiomyocytes, myocytes from APN knockout (APN-KO) mice sustained greater SI/R injury, evidenced by greater oxidative/nitrative stress, caspase-3 activity, and lactate dehydrogenase (LDH) release (P < 0.05). Myocytes from adiponectin receptor 1 knockdown (AdipoR1-KD) or AdipoR1-KD/AdipoR2-KO mice had slightly increased SI/R injury, but the difference was not statistically significant. RSG significantly (P < 0.01) increased APN mRNA and protein expression, upregulated AdipoR1/AdipoR2 expression, reduced SI/R-induced apoptosis, and decreased LDH release in WT cardiomyocytes. However, the anti-oxidative/anti-nitrative and cell protective effects of RSG were completely lost in APN-KO cardiomyocytes (P > 0.05 vs. vehicle group), although a comparable degree of AdipoR1/AdipoR2 upregulation was observed. The upregulatory effect of RSG on APN mRNA and protein expression was significantly potentiated in AdipoR1-KD/AdipoR2-KO cardiomyocytes. However, the cellular protective effects of RSG were significantly blunted, although not completely lost, in these cells. These results demonstrated that cardiomyocyte APN is biologically active in protecting cells against SI/R injury. Moreover, this locally produced APN achieves its protective effect primarily through paracrine/autocrine activation of APN receptors.

Disulfide-dependent self-assembly of adiponectin octadecamers from trimers and presence of stable octadecameric adiponectin lacking disulfide bonds in vitro

Adiponectin is a circulating insulin-sensitizing hormone that homooligomerizes into trimers, hexamers, and higher molecular weight (HMW) species. Low levels of circulating HMW adiponectin appear to increase the risk for insulin resistance. Currently, assembly of adiponectin oligomers and, consequently, mechanisms responsible for decreased HMW adiponectin in insulin resistance are not well understood. In the work reported here, we analyzed the reassembly of the most abundant HMW adiponectin species, the octadecamer, following its collapse to smaller oligomers in vitro. Purified bovine serum adiponectin octadecamer was treated with reducing agents at pH 5 to obtain trimers. These reduced trimers partially and spontaneously reassembled into octadecamers upon oxidative formation of disulfide bonds. Disulfide bonds appear to occupy a greater role in the process of oligomerization than in the structural stabilization of mature octadecamer. Stable octadecamers lacking virtually all disulfide bonds could be observed in abundance using native gel electrophoresis, dynamic light scattering, and collision-induced dissociation nanoelectrospray ionization mass spectrometry. These findings indicate that while disulfide bonds help to maintain the mature octadecameric adiponectin structure, their more important function is to stabilize intermediates during the assembly of octadecamer. Adiponectin oligomerization must proceed through intermediates that are at least partially reduced. Accordingly, fully oxidized adiponectin hexamers failed to reassemble into octadecamers at a rate comparable to that of reduced trimers. As the findings from the present study are based on in vitro experiments, their in vivo relevance remains unclear. Nevertheless, they describe a redox environment-dependent model of adiponectin oligomerization that can be tested using cell-based approaches.

Vascular inflammation in patients with impaired glucose tolerance and type 2 diabetes: analysis with 18F-fluorodeoxyglucose positron emission tomography

BACKGROUND

Type 2 diabetes mellitus (T2DM) is associated with an increased risk of atherosclerotic cardiovascular disease. Vascular inflammation is a key factor in both the pathogenesis and outcome of atherosclerosis. (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET) is a promising tool for indentifying and quantifying vascular inflammation within atherosclerotic plaques. This study was designed to examine the vascular inflammation measured using FDG-PET in patients with impaired glucose tolerance and T2DM, in comparison with age- and sex-matched control subjects with normal glucose tolerance.

METHODS AND RESULTS

We investigated vascular inflammation using FDG-PET in 90 age- and sex-matched subjects with different glucose tolerance (30 normal glucose tolerance subjects, 30 impaired glucose tolerance subjects, and 30 T2DM subjects). Vascular 18F-FDG uptake was measured as both the mean and maximum blood-normalized standardized uptake value, known as the target-to-background ratio (TBR). Both mean and maximum TBR measurements were significantly different, based on glucose tolerance, although the carotid intima-media thickness measurements were not significantly different. The maximum TBR values in patients with impaired glucose tolerance and T2DM were significantly increased compared with the normal subjects. In addition, subjects with metabolic syndrome had increased maximum TBR values compared with those without metabolic syndrome. Age-, sex-, and body mass index-adjusted maximum TBR levels were positively correlated with triglyceride, hemoglobin A1c, insulin resistance, high-sensitivity C-reactive protein, and Framingham risk score and were negatively correlated with high-density lipoprotein cholesterol and adiponectin levels.

CONCLUSIONS

The results of the present study suggest that impaired glucose tolerance and T2DM are associated with vascular inflammation in carotid atherosclerosis detected by FDG-PET.

Increased serum nitric oxide concentration after bariatric surgery--a potential mechanism for cardiovascular benefit

BACKGROUND

It is believed that endothelial dysfunction associated with obesity contributes to reduced vascular production of nitric oxide (NO). Weight reduction after bariatric surgery is known to decrease the risk of cardiovascular disease. The purpose of this study was to determine whether bariatric surgery leads to improvement of metabolic markers of endothelial function: serum NO and its precursor (arginine) concentrations in obese patients.

METHODS

Serum NO and L-arginine concentrations were measured in 25 morbidly obese patients directly before and 6 months after bariatric surgery. Moreover, selected parameters that may be involved in development of endothelial dysfunction were also studied. Control group consisted of ten healthy individuals with normal body weight.

RESULTS

Six months after bariatric surgery, serum NO concentration was approximately 40% higher than before surgery. Surprisingly, serum NO concentration in nonobese controls was essentially similar to obese patients before surgery. In contrast, serum L-arginine concentration was higher in obese patients than in controls and decreased significantly after surgery. The body weight, blood pressure, triacylglycerols, LDL/HDL-cholesterol ratio, insulin, homeostasis model assessment score (HOMA-index), C-reactive protein, and white blood cell count were higher in obese patients as compared with controls and decreased significantly after surgery.

CONCLUSIONS

Our results indicate that improvement of insulin resistance, lipidemia, and blood pressure as well as reduction of systemic inflammation after bariatric surgery were associated with the increase of serum NO concentration. We propose that the increase in serum NO concentration contribute to diverse beneficial effects of weight loss after bariatric surgery especially in the context of risk of atherosclerosis.

Cardioprotective effect of adiponectin is partially mediated by its AMPK-independent antinitrative action

Adiponectin (APN) exerts its metabolic regulation largely through AMP-dependent protein kinase (AMPK). However, the role of AMPK in APN's antiapoptotic effect in ischemic-reperfused (I/R) adult cardiomyocytes remains incompletely understood. The present study was designed to determine the involvement of AMPK in the antiapoptotic signaling of APN. Cardiomyocytes from adult male mice overexpressing a dominant-negative alpha(2)-subunit of AMPK (AMPK-DN) or wild-type (WT) littermates were subjected to simulated I/R (SI/R) and pretreated with 2 microg/ml globular domain of APN (gAPN) or vehicle. SI/R-induced cardiomyocyte apoptosis was modestly increased in AMPK-DN cardiomyocytes (P < 0.05). Treatment with gAPN significantly reduced SI/R-induced apoptosis in WT cardiomyocytes as well as in AMPK-DN cardiomyocytes, indicating that the antiapoptotic effect of gAPN is partially AMPK independent. Furthermore, gAPN-induced endothelial nitric oxide synthase (eNOS) phosphorylation was significantly reduced in AMPK-DN cardiomyocytes, suggesting that the APN-eNOS signaling axis is impaired in AMPK-DN cardiomyocytes. Additional experiments demonstrated that treatment of AMPK-DN cardiomyocytes with gAPN reduced SI/R-induced NADPH oxidase overexpression, decreased superoxide generation, and blocked peroxynitrite formation to the same extent as that observed in WT cardiomyocytes. Collectively, our present study demonstrated that although the metabolic and eNOS activation effect of APN is largely mediated by AMPK, the superoxide-suppressing effect of APN is not mediated by AMPK, and this AMPK-independent antioxidant property of APN increased nitric oxide bioavailability and exerted significant antiapoptotic effect.

Adiponectin inhibits pro-inflammatory signaling in human macrophages independent of interleukin-10

Macrophages participate pivotally in the pathogenesis of many chronic inflammatory diseases including atherosclerosis. Adiponectin, a vasculoprotective molecule with insulin-sensitizing and anti-atherogenic properties, suppresses pro-inflammatory gene expression in macrophages by mechanisms that remain incompletely understood. This study investigated the effects of adiponectin on major pro-inflammatory signaling pathways in human macrophages. We demonstrate that pretreatment of these cells with adiponectin inhibits phosphorylation of nuclear factor kappaB inhibitor (IkappaB), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK), induced by either lipopolysaccharide (LPS) or tumor necrosis factor (TNF) alpha, as well as STAT3 phosphorylation induced by interleukin-6 (IL6). Antagonism of IL10 by either neutralizing antibodies or siRNA-mediated silencing did not abrogate the anti-inflammatory actions of adiponectin, indicating that the ability of adiponectin to render human macrophages tolerant to various pro-inflammatory stimuli does not require this cytokine. A systematic search for adiponectin-inducible genes with established anti-inflammatory properties revealed that adiponectin augmented the expression of A20, suppressor of cytokine signaling (SOCS) 3, B-cell CLL/lymphoma (BCL) 3, TNF receptor-associated factor (TRAF) 1, and TNFAIP3-interacting protein (TNIP) 3. These results suggest that adiponectin triggers a multifaceted response in human macrophages by inducing the expression of various anti-inflammatory proteins that act at different levels in concert to suppress macrophage activation.

Oral supplementation of propionyl-l-carnitine reduces body weight and hyperinsulinaemia in obese Zucker rats

Propionyl-L-carnitine (PLC) is an SCFA esterified to carnitine that plays an important role in fatty acid oxidation and energy expenditure, in addition to having a protective effect on the endothelium. In order to evaluate the effect of PLC on an animal model of obesity, insulin resistance and, consequently, endothelial dysfunction, lean and obese Zucker rats (OZR) received either vehicle- or PLC-supplemented drinking water (200 mg/kg per d) for 20 weeks. Body weight, food intake, systolic blood pressure and heart rate were controlled weekly and an oral glucose tolerance test was performed. Fasting glucose, TAG, cholesterol, HDL, NEFA, adiponectin and insulin were analysed in serum. Visceral adipose tissue and liver were weighed and liver TAG liver composition was evaluated. Endothelial and vascular functions were assessed in the aorta and small mesenteric arteries by response to acetylcholine, sodium nitroprusside and phenylephrine (Phe); NO participation was evaluated after incubation with the NO synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester (L-NAME) and endothelial NOS protein expression by Western blotting. PLC decreased body-weight gain, food intake, adiposity, insulin serum concentration and TAG liver content and improved insulin resistance. Aortae from OZR receiving either vehicle or PLC exhibited a lower contractile response to Phe. PLC-treated OZR showed an enhanced release of endothelial NO upon the adrenergic stimulation. The protection of vascular function found after treatment with PLC in an animal model of insulin resistance supports the necessity of clinical trials showing the effect of L-carnitine supplements on metabolic disorders.

HIV increases markers of cardiovascular risk: results from a randomized, treatment interruption trial

OBJECTIVES

Plasma soluble inflammatory molecules are associated with the risk of ischaemic cardiovascular events. We investigated whether HIV replication modified the levels of these proteins in a combination antiretroviral therapy (cART) interruption trial.

METHOD AND RESULTS

In 145 HIV-infected Thai patients (62% women, median CD4 cell count 271 cells/microl, median plasma HIV-RNA 4.66 log10 copies/ml) included in the Swiss-Thai-Australia Treatment Interruption Trial (STACCATO) trial, leptin, adiponectin, C-reactive protein, soluble vascular cell adhesion molecule-1 (s-VCAM-1), P-selectin, chemokine ligand 2, chemokine ligand 3, interleukin (IL)-6, IL-10, granulocyte macrophage colony-stimulating factor and D-dimer were measured before cART was initiated, after cART had suppressed HIV replication to less than 50 copies/ml plasma (median 8 months) and again 12 weeks after randomization to continued cART (n=48) or interrupted cART (n=97). Multiple linear regression and logistic regression were used to investigate the association between each cardiovascular marker and plasma HIV-RNA. Initiation of cART resulted in significant declines in s-VCAM-1, P-selectin, leptin and D-dimer, whereas mediators with anti-inflammatory properties, such as adiponectin and IL-10, increased. At 12 weeks after randomization, we found positive associations between levels of s-VCAM-1 and chemokine ligand 2 with an increase in plasma HIV-RNA (r=0.271, P=0.001 and r=0.24, P=0.005, respectively), whereas levels of adiponectin decreased for each 1 log increase in plasma HIVRNA (r=-0.24, P=0.002). Detectable IL-10 was less likely (odds ratio = 0.64, 95% confidence interval = 0.43-0.96) for each 1 log increase in plasma HIV-RNA.

CONCLUSION

Plasma levels of several inflammatory, anti-inflammatory and endothelial activation markers of cardiovascular disease are associated with HIV-RNA replication.

Adiponectin protects against cerebral ischemia-reperfusion injury through anti-inflammatory action

Adiponectin (APN), a circulating adipose-derived hormone regulating inflammation and energy metabolism, has beneficial actions on cardio- and cerebrovascular disorders. Hypoadiponectinemia is associated with ischemic cerebrovascular disease, however, little is known about the cerebroprotective action of APN as well as its molecular mechanisms. In the present study, the role of APN in the pathogenesis of acute cerebral injury was investigated. Rats were divided into three groups: (i) a sham operation group; (ii) an ischemia/reperfusion (I/R) group, rats were subjected to 1 h middle cerebral artery occlusion followed by 23 h reperfusion (I/R); (iii) a APN-treated group, two bolus of 5 microg APN was administered through jugular vein before and after operation. I/R resulted in obvious cerebral infarct size, neurological deficits, and increased expression of endogenous immunoglobin G and matrix metalloproteinase 9, which can be significantly diminished by administration of APN. We also found that APN can significantly inhibited cerebral expression of myeloperoxidase, a distinct indicator of inflammatory cell infiltration, and inflammatory cytokines, interleukin (IL)-1beta, tumor necrosis factor-alpha and IL-8 in response to I/R, suggesting that APN exerts potent anti-inflammatory actions. Furthermore, nuclear factor (NF)-kappaB (p65), a critical transcription factor involved in inflammatory reactions, was observed predominantly located in the nucleus after I/R, whereas APN can obviously inhibit its translocation from cytoplasm into the nucleus. Results of this study demonstrate that APN exerts a potent cerebroprotective function through its anti-inflammatory action, and NF-kappaB (p65) is a key component in this process. APN might be potential molecular targets for ischemic stroke therapy.