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The discovery of leptin in 1994 sparked dramatic new interest in the study of white adipose tissue. It is now recognised to be a metabolically active endocrine organ, producing important chemical messengers – adipokines and cytokines (adipocytokines). The search for new adipocytokines or adipokines gained added fervour with the prospect of the reconciliation between cardiovascular diseases (CVDs), obesity and metabolic syndrome. The role these new chemical messengers play in inflammation, satiety, metabolism and cardiac function has paved the way for new research and theories examining the effects they have on (in this case) CVD. Adipokines are involved in a ‘good–bad’, yin–yang homoeostatic balance whereby there are substantial benefits: cardioprotection, promoting endothelial function, angiogenesis and reducing hypertension, atherosclerosis and inflammation. The flip side may show contrasting, detrimental effects in aggravating these cardiac parameters.

Adipolin is a novel adipokine with anti-inflammatory and glucose-lowering properties. Lower levels of adipolin are found in obese and diabetic mice. Polycystic ovary syndrome (PCOS) is a pro-inflammatory state associated with obesity and diabetes. To date, there are no human studies on adipolin. Therefore, we measured serum (ELISA) and adipose tissue adipolin mRNA expression (RT-PCR) and protein concentrations (western blotting) in PCOS and control subjects. We also investigated the ex vivo effect of glucose and metformin on adipolin protein production in human subcutaneous adipose tissue explants. We report novel data that serum and subcutaneous adipose tissue adipolin mRNA expression and protein concentrations were significantly lower in women with PCOS compared with control subjects. Furthermore, Spearman's rank analysis showed that serum adipolin concentrations were significantly negatively correlated with BMI, waist-to-hip ratio, and glucose (P<0.05). However, when subjected to multiple regression analysis, none of these variables were predictive of serum adipolin concentrations (P>0.05). Also, subcutaneous adipose tissue adipolin mRNA expression and protein concentrations were only significantly negatively correlated with glucose (P<0.05). No significant correlations were found with omental adipose tissue adipolin mRNA expression and protein concentrations (P>0.05). Moreover, glucose profoundly reduced and metformin significantly increased adipolin protein production in human adipose tissue explants respectively. Importantly, metformin's effects appear to be via the AMP-activated protein kinase signaling pathway.

There has been intense interest in the adipokines of the C1q complement/TNF-related protein (CTRP) superfamily. Adipolin (CTRP12) has been described as a novel adipokine, abundantly expressed in adipose tissue with insulin-sensitising and anti-inflammatory effects. We wanted to investigate the effects of acute and chronic hyperinsulinaemia on circulating adipolin concentrations (ELISA) via a prolonged insulin–glucose infusion in humans. We also examined the effects of insulin and the insulin sensitiser, rosiglitazone, on adipolin concentrations (western blotting) in human adipose tissue explants. We found that hyperinsulinaemic induction in healthy lean human subjects significantly increased circulating levels of adipolin (P<0.05 and P<0.01). Furthermore, in subcutaneous adipose tissue explants, insulin significantly increased adipolin protein expression and secretion (P<0.05 and P<0.01). This effect was attenuated by the phosphatidylinositol 3-kinase inhibitor, LY294002 (P<0.05). Moreover, the insulin-sensitising peroxisome proliferator-activated receptor γ (PPARγ) agonist, rosiglitazone, significantly increased adipolin protein expression and secretion in subcutaneous adipose tissue explants (P<0.05 and P<0.01). This effect was inhibited by the PPARγ antagonist, GW9662 (P<0.05). Our data provide novel insights into adipolin physiology in human subjects.

Orexins A and B (ORA and ORB) are neuropeptide hormones found throughout the central nervous system and periphery. They are required for a host of physiological processes including mitogen-activated protein kinase (MAPK) regulation, steroidogenesis, appetite control and energy regulation. While some signalling mechanisms have been proposed for individual recombinant orexin receptors in generic mammalian cell types, it is clear that the peripheral effects of orexin are spatially and temporally complex. This study dissects the different G-protein signalling and MAPK pathways activated in a pluripotent human adrenal H295R cell line capable of all the physiological steps involved in steroidogenesis. Both extracellular receptor kinase 1/2 (ERK1/2) and p38 were phosphorylated rapidly with a subsequent decline, in a time- and dose-dependent manner, in response to both ORA and ORB. Conversely, there was little or no direct activation of the ERK5 or JNK pathway. Analysis using signalling and MAPK inhibitors as well as receptor-specific antagonists determined the precise mediators of the orexin response in these cells. Both ERK1/2 and p38 activation were predominantly G_q- and to a lesser extent G_s-mediated; p38 activation even had a small G_i-component. Effects were broadly comparable for both orexin sub-types ORA and ORB and although most of the effects were transmitted through the orexin receptor-1 subtype, we did observe a role for orexin receptor-2-mediated activation of both ERK1/2 and p38. Cortisol secretion also differed in response to ORA and ORB. These data suggest multiple roles for orexin-mediated MAPK activation in an adrenal cell-line, this complexity may help to explain the diverse biological actions of orexins with wide-ranging consequences for our understanding of the mechanisms initiated by these steroidogenic molecules.

NUCB2/nesfatin and its proteolytically cleaved product nesfatin-1 are recently discovered anorexigenic hypothalamic neuroproteins involved in energy homeostasis. It is expressed both centrally and in peripheral tissues, and appears to have potent metabolic actions. NUCB2/nesfatin neurons are activated in response to stress. Central nesfatin-1 administration elevates circulating ACTH and corticosterone levels. Bilateral adrenalectomy increased NUCB2/nesfatin mRNA levels in rat paraventricular nuclei. To date, studies have not assessed the effects of nesfatin-1 stimulation on human adrenocortical cells. Therefore, we investigated the expression and effects of nesfatin-1 in a human adrenocortical cell model (H295R). Our findings demonstrate that NUCB2 and nesfatin-1 are expressed in human adrenal gland and human adrenocortical cells (H295R). Stimulation with nesfatin-1 inhibits the growth of H295R cells and promotes apoptosis, potentially via the involvement of Bax, BCL-XL and BCL-2 genes as well as ERK_1/2, p38 and JNK1/2 signalling cascades. This has implications for understanding the role of NUCB2/nesfatin in adrenal zonal development. NUCB2/nesfatin may also be a therapeutic target for adrenal cancer. However, further studies using in vivo models are needed to clarify these concepts.