Identification of adropin as a secreted factor linking dietary macronutrient intake with energy homeostasis and lipid metabolism

Obesity and nutrient homeostasis are linked by mechanisms that are not fully elucidated. Here we describe a secreted protein, adropin, encoded by a gene, Energy Homeostasis Associated (Enho), expressed in liver and brain. Liver Enho expression is regulated by nutrition: lean C57BL/6J mice fed high-fat diet (HFD) exhibited a rapid increase, while fasting reduced expression compared to controls. However, liver Enho expression declines with diet-induced obesity (DIO) associated with 3 months of HFD or with genetically induced obesity, suggesting an association with metabolic disorders in the obese state. In DIO mice, transgenic overexpression or systemic adropin treatment attenuated hepatosteatosis and insulin resistance independently of effects on adiposity or food intake. Adropin regulated expression of hepatic lipogenic genes and adipose tissue peroxisome proliferator-activated receptor gamma, a major regulator of lipogenesis. Adropin may therefore be a factor governing glucose and lipid homeostasis, which protects against hepatosteatosis and hyperinsulinemia associated with obesity.

Kumar KG, et al. Cell Metab. 2008 Dec;8(6):468-81.

Identification of adropin as a secreted factor linking dietary macronutrient intake with energy homeostasis and lipid metabolism

Obesity and nutrient homeostasis are linked by mechanisms that are not fully elucidated. Here we describe a secreted protein, adropin, encoded by a gene, Energy Homeostasis Associated (Enho), expressed in liver and brain. Liver Enho expression is regulated by nutrition: lean C57BL/6J mice fed high-fat diet (HFD) exhibited a rapid increase, while fasting reduced expression compared to controls. However, liver Enho expression declines with diet-induced obesity (DIO) associated with 3 months of HFD or with genetically induced obesity, suggesting an association with metabolic disorders in the obese state. In DIO mice, transgenic overexpression or systemic adropin treatment attenuated hepatosteatosis and insulin resistance independently of effects on adiposity or food intake. Adropin regulated expression of hepatic lipogenic genes and adipose tissue peroxisome proliferator-activated receptor gamma, a major regulator of lipogenesis. Adropin may therefore be a factor governing glucose and lipid homeostasis, which protects against hepatosteatosis and hyperinsulinemia associated with obesity.

Analysis of Whole Body Energy Metabolism in Chow-Fed Adr-Tg and WT Mice (A) Total 24 hr energy expenditure (TEE) of male and female Adr-Tg mice compared to controls. (B and C) TEE expressed per g body weight (B) or FFM (C) (*p < 0.05). (D) RQ of male and female Adr-Tg and WT mice (*p < 0.05). (E and F) Spontaneous locomotory activity of female Adr-Tg and WT mice (*p < 0.05). In (E), the data are presented as mean X beam breaks over 24 hr, during the lights-on period (0600-1800 hr; L or white bar) and during the dark period (1800-0600 hr; D or black bar), by gender. All data are mean SEM and are the mean from 3 days of recordings; n = 7 each genotype and sex.

Short-Term Treatment with Synthetic Adropin(34-76) Improves Glucose Homeostasis in DIO B6 Mice Independently of Weight Loss or Reduced Food Intake (A-D) Treatment of male DIO mice with 90 nmol/kg/day adropin(34-76) administered as two i.p. injections/day over 2 days did not significantly affect food intake (A) or weight gain (B) (n = 8/group). Treatment followed a 5 day lead-in period, with the injection period marked by the gray area. Following treatment, there were significant improvements in glucose homeostasis, indicated by reductions in fasting insulin and HOMA-IR values (C) and improved glucose tolerance (D). *p < 0.05 compared to saline. However, there were no changes observed in serum TG (C). (E-J) A second study assessed a dose-response to 2 days of injections on glucose homeostasis (F-H) and liver metabolism (I, J) (n = 6/group). There was no significant effect of treatment on body weight (E, the white and solid bars are body weight pre- and posttreatment). There was evidence for improved glucose homeostasis (F-H), with significant reductions in fasting glucose (F) and HOMA-IR (H). While liver TG content was not significantly affected by treatment (I), there were changes in the expression of genes involved in fatty acid metabolism, which was statistically significant for Scd1 and diacylglycerol O-transferase 2 (Dgat2) (J). * p < 0.05 versus saline. The values shown are mean ± SEM.

Adropin(34-76) Therapy Affects Energy Metabolism in DIO B6 Mice and Cultured Adipocytes (A-J) Administration of adropin(34-76) by i.p. injection at 0900 and 1800 hr for 14 days is associated with reduced food intake (A and B) and weight loss (C). Adropin treatment reduced fasting insulin (D) without affecting blood glucose (E), and increased serum adiponectin (F), suggesting improved insulin sensitivity. Adropin treatment improves hepatic steatosis (G) and significantly reduces liver TG accumulation (H), associated with reduced expression of genes involved in lipid synthesis in liver (I). Pparg expression in WAT of mice treated with adropin(34-76) was not significantly different from controls treated with saline (J). The values shown are mean ± SEM with N = 12/treatment group.

Kumar KG, et al. Cell Metab. 2008 Dec;8(6):468-81.

Adropin (34-76) is a novel regulator of endothelial function.

Adropin is a recently identified protein that has been implicated in the maintenance of energy homeostasis and insulin resistance. Because vascular function and insulin sensitivity are closely related, we hypothesized that adropin may also exert direct effects on the endothelium. In vitro cell culture models were partnered with an in vivo murine injury model to determine the potential vascular effects of adropin. Adropin was expressed in human umbilical vein and coronary artery endothelial cells (ECs). Adropin-treated endothelial cells exhibited greater proliferation, migration and capillary-like tube formation and less permeability and tumor necrosis factor-a-induced apoptosis. In keeping with a vascular protective effect, adropin stimulated Akt Ser(473) and endothelial nitric oxide (NO) synthase Ser(1177) phosphorylation. The former was abrogated in the presence of the phosphatidylinositol 3-kinase inhibitor LY294002, whereas the latter was attenuated by LY294002 and by mitogen-activated protein kinase kinase 1 inhibition with PD98059. Together, these findings suggest that adropin regulates NO bioavailability and events via the phosphatidylinositol 3-kinase-Akt and extracellular signal regulated kinase 1/2 signaling pathways. Adropin markedly upregulated vascular endothelial growth factor receptor-2 (VEGFR2) transcript and protein levels, and in VEGFR2-silenced endothelial cells, adropin failed to induce phosphorylation of endothelial NO synthase, Akt, and extracellular signal regulated kinase 1/2, supporting VEGFR2 as an upstream target of adropin-mediated endothelial NO synthase activation. Last, adropin improved murine limb perfusion and elevated capillary density following induction of hindlimb ischemia. We report a potential endothelial protective role of adropin that is likely mediated via upregulation of endothelial NO synthase expression through the VEGFR2-phosphatidylinositol 3-kinase-Akt and VEGFR2-extracellular signal regulated kinase 1/2 pathways. Adropin represents a novel target to limit diseases characterized by endothelial dysfunction in addition to its favorable metabolic profile.

Lovren F. et al. Circulation 2010 Sep 14;122(11 Suppl):S185-92
(Note: this publication uses the bioactive peptide, Adropin, from Phoenix)

Adropin (34-76) is a novel regulator of endothelial function.

Adropin is a recently identified protein that has been implicated in the maintenance of energy homeostasis and insulin resistance. Because vascular function and insulin sensitivity are closely related, we hypothesized that adropin may also exert direct effects on the endothelium. In vitro cell culture models were partnered with an in vivo murine injury model to determine the potential vascular effects of adropin. Adropin was expressed in human umbilical vein and coronary artery endothelial cells (ECs). Adropin-treated endothelial cells exhibited greater proliferation, migration and capillary-like tube formation and less permeability and tumor necrosis factor-a-induced apoptosis. In keeping with a vascular protective effect, adropin stimulated Akt Ser(473) and endothelial nitric oxide (NO) synthase Ser(1177) phosphorylation. The former was abrogated in the presence of the phosphatidylinositol 3-kinase inhibitor LY294002, whereas the latter was attenuated by LY294002 and by mitogen-activated protein kinase kinase 1 inhibition with PD98059. Together, these findings suggest that adropin regulates NO bioavailability and events via the phosphatidylinositol 3-kinase-Akt and extracellular signal regulated kinase 1/2 signaling pathways. Adropin markedly upregulated vascular endothelial growth factor receptor-2 (VEGFR2) transcript and protein levels, and in VEGFR2-silenced endothelial cells, adropin failed to induce phosphorylation of endothelial NO synthase, Akt, and extracellular signal regulated kinase 1/2, supporting VEGFR2 as an upstream target of adropin-mediated endothelial NO synthase activation. Last, adropin improved murine limb perfusion and elevated capillary density following induction of hindlimb ischemia. We report a potential endothelial protective role of adropin that is likely mediated via upregulation of endothelial NO synthase expression through the VEGFR2-phosphatidylinositol 3-kinase-Akt and VEGFR2-extracellular signal regulated kinase 1/2 pathways. Adropin represents a novel target to limit diseases characterized by endothelial dysfunction in addition to its favorable metabolic profile.

Adropin stimulates neovascularization in vivo in an eNOS-dependent manner. A through D, Balb/c mice were subjected to unilateral (left) hindlimb ischemia before administration of the adropin or null plasmid. A, Quantification of blood flow recovery after hindlimb ischemia surgery; n=4 to 7; *P < 0.05 vs corresponding values for null group. B, Representative laser Doppler images with the highest perfusion level shown in red. C, Quantification of capillary density in gastrocnemius sections as discerned by rhodamine-conjugated isolectin-B4-positive areas; n=3, *P < 0.05 vs null group. D, Representative Western blot analyses for VEGFR2, phospho-eNOS, phospho-Akt, and phospho-ERK1/2 from ischemic gastrocnemius muscles harvested 28 days after hindlimb ischemia surgery. E, Quantification of blood flow recovery after hindlimb ischemia surgery in Nos3tm1Unc/J mice treated with either the adropin or the null plasmid; n=5.

Lovren F. et al. Circulation 2010 Sep 14;122(11 Suppl):S185-92
(Note: this publication uses the bioactive peptide, Adropin, from Phoenix)

Elevated plasma levels of adropin in heart failure patients.

Recent studies have suggested that a higher body mass index (BMI) is associated with an improved prognosis in heart failure (HF). Adropin is a recently identified protein that has been implicated in the maintenance of energy homeostasis. In the present study, we investigated plasma adropin levels in patients with HF and evaluated the relationship between the levels and the severity of HF.
METHODS AND RESULTS: The study group comprised 56 patients with HF and 20 control subjects, who were divided into 4 subgroups according to New York Heart Association (NYHA) functional classification. Plasma levels of adropin, brain natriuretic peptide (BNP) and cardiac hemodynamics were determined. Plasma adropin levels were significantly increased according to the severity of NYHA class in the patients with HF; control: 6.0 ± 0.3; NYHA functional Class II: 7.6 ± 0.4; NYHA functional Class III: 9.8 ± 0.5; NYHA functional Class IV: 12.4 ± 0.6 ng/mL (p < 0.01). Similarly, plasma BNP levels were significantly increased in accordance with the NYHA class. Plasma adropin levels were correlated positively with BNP (r=0.723, p< 0.001), interleukin-6 (IL-6) (r=0.326, p=0.007) and body mass index (BMI) (r=0.295, p=0.014), and negatively with left ventricular ejection fraction (LVEF) (r=-0.710, p< 0.001).
CONCLUSION: Plasma adropin levels were significantly increased according to the severity of HF, and BNP and BMI had independent impact on the plasma adropin level. These findings suggest that the augmented release of adropin may be involved in the pathogenesis of HF and further study is necessary to explain the precise role of adropin in HF.

Lian W, et al. Intern Med. 2011;50(15):1523-7. Epub 2011 Aug 1.

Elevated plasma levels of adropin in heart failure patients.

Recent studies have suggested that a higher body mass index (BMI) is associated with an improved prognosis in heart failure (HF). Adropin is a recently identified protein that has been implicated in the maintenance of energy homeostasis. In the present study, we investigated plasma adropin levels in patients with HF and evaluated the relationship between the levels and the severity of HF.
METHODS AND RESULTS: The study group comprised 56 patients with HF and 20 control subjects, who were divided into 4 subgroups according to New York Heart Association (NYHA) functional classification. Plasma levels of adropin, brain natriuretic peptide (BNP) and cardiac hemodynamics were determined. Plasma adropin levels were significantly increased according to the severity of NYHA class in the patients with HF; control: 6.0 ± 0.3; NYHA functional Class II: 7.6 ± 0.4; NYHA functional Class III: 9.8 ± 0.5; NYHA functional Class IV: 12.4 ± 0.6 ng/mL (p < 0.01). Similarly, plasma BNP levels were significantly increased in accordance with the NYHA class. Plasma adropin levels were correlated positively with BNP (r=0.723, p< 0.001), interleukin-6 (IL-6) (r=0.326, p=0.007) and body mass index (BMI) (r=0.295, p=0.014), and negatively with left ventricular ejection fraction (LVEF) (r=-0.710, p< 0.001).
CONCLUSION: Plasma adropin levels were significantly increased according to the severity of HF, and BNP and BMI had independent impact on the plasma adropin level. These findings suggest that the augmented release of adropin may be involved in the pathogenesis of HF and further study is necessary to explain the precise role of adropin in HF.

Table 1. Correlation between Plasma Adropin Level and various clinical Parameter in the Patients with Heart Failure

No. of Sample (N) = 56 Log transformation was used to normalize the distribution of plasma levels of BNP and TNF-alpha. The parameters listed were variables associated with plasma adropin levels at the p < 0.1 level in the simple linear regression analysis (Figure 2).

Table 2. Multiple Regression Analysis of Variable Associated with Plasma Adropin Level in the Patients with Heart Failure

No. of Sample (N) = 56 The parameters listed were variables associated with plasma adropin levels at the p < 0.1 level in the simple linear regression analysis.

Figure 1. Plasma adropin levels in the patients with heart failure according to New York Heart Association (NYHA) functional class (p-value for Kruskal-Wallis H test, p<0.001).

Figure 2. Relationship of plasma adropin level with plasma level of brain natriuretic peptide (BNP) in patients with heart failure (r=0.728, p< 0.001). Log transformation was used to normalize the distribution of the plasma levels of BNP (n=56).

Lian W, et al. Intern Med. 2011;50(15):1523-7. Epub 2011 Aug 1.