The combined effect of adiponectin and resistin on all-cause mortality in patients with type 2 diabetes: Evidence of synergism with abdominal adiposity

A case-cohort study of the association between adiponectin and mortality in EPIC-Heidelberg: NT-proBNP may explain the adiponectin paradox

BACKGROUND AND AIMS

NT-proBNP has been hypothesized as a possible explanation for the paradoxical association between adiponectin and cardiovascular and all-cause mortality. We examined the heterogeneities by NT-proBNP, sex, BMI, smoking status, hypertension and diabetes status in the association between adiponectin and cardiovascular disease risk and mortality.

METHODS AND RESULTS

We used a case-cohort design nested within the EPIC-Heidelberg cohort, including 1387 incident cases of myocardial infarction or stroke, 582 deaths from cardiovascular causes and 2352 total deaths. We estimated hazard ratios for the association between 1SD increase in log-transformed total adiponectin levels and cardiovascular disease risk, cardiovascular mortality and mortality using Prentice-weighted Cox-proportional hazard models and assessed heterogeneity of the associations across strata of covariates. Overall, adiponectin was significantly associated with all-cause mortality [HR = 1.09, 95% CI: 1.03-1.16, p = 0.004]. The association with cardiovascular mortality did not reach statistical significance [1.10 (0.99-1.37), p = 0.073]. There was significant heterogeneity by NT-proBNP in the association between total adiponectin and all-cause mortality (phet = 0.019) such that significant increase in hazards of mortality were restricted to participants in the highest tertile of NT-proBNP. Among these participants, adiponectin showed a dose-response relationship with total mortality such that; compared to participants in the lowest quintile, those in the third, fourth and fifth were at 1.22 (0.87-1.70), 1.50 (1.07-2.11), and 1.59 (1.15-2.21) higher hazards of mortality respectively.

CONCLUSIONS

Significant association between adiponectin and mortality was only observed in the context of high NT-proBNP. Our findings provide further support for hypothesis that NT-proBNP may explain the adiponectin paradox.

Adiponectin, a unique adipocyte-derived factor beyond hormones

Visceral fat accumulation has a marked impact on atherosclerotic cardiovascular diseases and metabolic syndrome clustering diabetes, dyslipidemia, and hypertension. Adiponectin, an adipocyte-derived circulating protein, is a representative adipocytokine and uniquely possesses two major properties: 1) its circulating concentration is approximately 3-6 orders of magnitude greater than ordinary hormones and cytokines; 2) its concentration inversely correlates with body fat mass despite its adipocyte-specific production. Low serum levels of adiponectin correlate with cardiometabolic diseases. Extensive experimental evidence has demonstrated that adiponectin possesses multiple properties, such as anti-atherosclerotic, anti-diabetic, and anti-inflammatory activities. It has been shown to play a central role against the development of metabolic syndrome and its complications. However, even approximately 25 years after its discovery, the properties of adiponectin, including how and why it exerts multiple beneficial effects on various tissues and/or organs, remain unclear. Furthermore, the mechanisms responsible for the very high circulating concentrations of adiponectin in the bloodstream have not been elucidated. Several adiponectin-binding partners, such as AdipoR1/2, have been identified, but do not fully explain the multi-functional and beneficial properties of adiponectin. Recent advances in adiponectin research may resolve these issues. Adiponectin binds to and covers cell surfaces with T-cadherin, a unique glycosylphosphatidylinositol (GPI)-anchored cadherin. The adiponectin/T-cadherin complex enhances exosomal production and release, excreting cell-toxic products from cells, particularly in the vasculature. In this review, we discuss adiponectin and the role of the adiponectin/T-cadherin system in the maintenance of whole body homeostasis and cardiovascular protection.

Resistin is a prognostic factor for death in type 2 diabetes

PURPOSE

To investigate the association of leptin, resistin, and tumour necrosis factor α (TNF-α) with prognosis in type 2 diabetes (T2D).

METHODS

Analysis included 284 T2D patients. Apart from routine laboratory parameters, baseline leptin, resistin, and TNF-α concentrations were measured. Patients were followed for a median of 5.4 years. The primary endpoint was all-cause death at follow-up. The secondary endpoint was a composite of death, acute coronary syndrome, and stroke or transient ischemic attack.

RESULTS

At baseline, median age was 68 years, and 48% of patients were female. Data on the primary endpoint were obtained for all patients: 32 (11%) died during follow-up. Data on the secondary endpoint were available for 230 patients, of whom 45 (20%) reached the secondary endpoint. In univariate analyses, older age, heart failure, lower-glomerular filtration rate, and higher resistin, TNF-α and NT-proBNP concentrations were predictors of the study endpoints. Of these variables, only resistin remained an independent predictor of both study endpoints in multivariate models. In receiver-operating characteristic analysis, area under the curve for resistin was 0.7. Resistin concentration of greater than or equal to 11.4 ng/mL had sensitivity of 41% and specificity of 91% for prediction of death at follow-up (Youden's index).

CONCLUSIONS

Higher resistin is associated with reduced survival in T2D, irrespectively of TNF-α. Resistin concentration of above 11 ng/mL indicates T2D patients at an increased risk of unfavourable outcomes. Leptin was not a prognostic factor. These results suggest that in T2D, association of resistin with unfavourable outcomes might, at least in part, result from its pro-inflammatory properties.

Adipokines and Non-Alcoholic Fatty Liver Disease: Multiple Interactions

Accumulating evidence links obesity with low-grade inflammation which may originate from adipose tissue that secretes a plethora of pro- and anti-inflammatory cytokines termed adipokines. Adiponectin and leptin have evolved as crucial signals in many obesity-related pathologies including non-alcoholic fatty liver disease (NAFLD). Whereas adiponectin deficiency might be critically involved in the pro-inflammatory state associated with obesity and related disorders, overproduction of leptin, a rather pro-inflammatory mediator, is considered of equal relevance. An imbalanced adipokine profile in obesity consecutively contributes to metabolic inflammation in NAFLD, which is associated with a substantial risk for developing hepatocellular carcinoma (HCC) also in the non-cirrhotic stage of disease. Both adiponectin and leptin have been related to liver tumorigenesis especially in preclinical models. This review covers recent advances in our understanding of some adipokines in NAFLD and associated HCC.

Cardiovascular Adiponectin Resistance: The Critical Role of Adiponectin Receptor Modification

For the past two decades, a great deal of research has been published concerning adiponectin (APN), an abundant protein responsible for regulating numerous biologic functions including antioxidative, antinitrative, anti-inflammatory, and cardioprotective effects. A review of APN and its two major receptors is timely because of new findings concerning the mechanisms by which APN signaling may be altered in pathologic processes such as diabetes and heart failure. In this review we elaborate on currently known information regarding the physiologic role of APN and the known mechanisms underlying pathologic APN resistance - namely, APN receptor downregulation and phosphorylation - and provide insight regarding the future directions of APN research including an assessment of the clinical applicability of preventing pathologic post-translational modification of the APN receptor.

Serum resistin is causally related to mortality risk in patients with type 2 diabetes: preliminary evidences from genetic data

Resistin has been firmly associated with all-cause mortality. We investigated, whether, in patients with type 2 diabetes (T2D), this association is sustained by a cause-effect relationship. A genotype risk score (GRS), created by summing the number of resistin increasing alleles of two genome-wide association studies (GWAS)-derived single nucleotide polymorphisms (SNPs), serum resistin measurements and all-cause death records were obtained in 1,479 (403 events/12,454 person-years), patients with T2D from three cohorts, Gargano Heart Study-prospective design (n = 350), Gargano Mortality Study (n = 698) and Foggia Mortality Study (n = 431), from Italy. GRS was strongly associated with serum resistin in a non-linear fashion (overall p = 3.5 * 10^-7) with effect size modest for GRS = 1 and 2 and much higher for GRS >3, with respect to GRS = 0. A significant non-linear association was observed also between GRS and all-cause mortality (overall p = 3.3 * 10^-2), with a low effect size for GRS = 1 and 2, and nearly doubled for GRS ≥ 3, with respect to GRS = 0. Based on the above-reported associations, each genetic equivalent SD increase in log-resistin levels showed a causal hazard ratio of all-cause mortality equal to 2.17 (95%CI: 1.22-3.87), thus providing evidence for a causal role of resistin in shaping the risk of mortality in diabetic patients.

Increased circulating resistin is associated with insulin resistance, oxidative stress and platelet activation in type 2 diabetes mellitus

Resistin is an adipokine that promotes inflammation and insulin resistance by targeting several cells including platelets. We hypothesised that in type 2 diabetes (T2DM), resistin may foster in vivo oxidative stress, thromboxane-dependent platelet activation and platelet-derived inflammatory proteins release, key determinants of atherothrombosis. A cross-sectional comparison of circulating resistin, sCD40L, as a marker of platelet-mediated inflammation, asymmetric dimethylarginine (ADMA), endothelial dysfunction marker, Dickkopf (DKK)-1, reflecting the inflammatory interaction between platelets and endothelial cells, and urinary 8-iso-PGF_2α and 11-dehydro-TxB₂, reflecting in vivo lipid peroxidation and platelet activation, respectively, was performed between 79 T2DM patients and 30 healthy subjects. Furthermore, we investigated the effects of the α-glucosidase inhibitor acarbose and the PPARγ agonist rosiglitazone, targeting hyperglycaemia or insulin resistance, versus placebo, in 28 and 18 T2DM subjects, respectively. Age- and gender-adjusted serum resistin levels were significantly higher in patients than in controls. HOMA (β=0.266, p=0.017) and 11-dehydro-TXB₂ (β=0.354, p=0.002) independently predicted resistin levels. A 20-week treatment with acarbose was associated with significant reductions (p=0.001) in serum resistin, DKK-1, urinary 11-dehydro-TXB₂ and 8-iso-PGF_2α with direct correlations between the change in serum resistin and in other variables. A 24-week rosiglitazone treatment on top of metformin was associated with significant decreases in resistin, DKK-1, 11-dehydro-TXB₂ and 8-iso-PGF_2α, in parallel with HOMA decrease. In conclusion, resistin, antagonising insulin action in part through PPARγ activation, may favour insulin resistance and enhance oxidative stress, endothelial dysfunction and platelet activation. The adipokine-platelet interactions may be involved in platelet insulin resistance and their consequent pro-aggregatory phenotype in this setting.