Lipasin, a novel nutritionally-regulated liver-enriched factor that regulates serum triglyceride levels

Serum Concentrations of Betatrophin and Its Association with Indirect Indices of Insulin Resistance and Beta Cell Function in Women with Polycystic Ovary Syndrome

INTRODUCTION

Data underline the role of betatrophin in glucose homeostasis. Polycystic ovary syndrome (PCOS) is characterized by insulin resistance (IR). The aim of our study was to investigate the relationship of serum betatrophin concentrations with indirect indices of IR and insulin secretion in women with PCOS, compared to the control group.

METHODS

The study group comprised 43 women with PCOS and 16 controls. IR was assessed by HOMA-IR and Matsuda index. Insulin secretion was evaluated with HOMA-B. An oral glucose tolerance test (OGTT) with estimation of serum betatrophin concentrations was performed.

RESULTS

Glucose load resulted in an increase in serum betatrophin concentrations in the control group (p = 0.02). Serum betatrophin concentrations at 120 min of OGTT were lower in women with PCOS than in the control group (p = 0.02). We observed positive correlations between baseline serum betatrophin concentrations and HOMA-IR (r = 0.39, p = 0.008), negative correlations with Matsuda index (r = -0.31, p = 0.004), and a positive relationship with HOMA-B (r = 0.38, p = 0.01) in women with PCOS. Multiple regression analysis revealed that HOMA-B (β = 0.47, p = 0.001) was an independent factor connected to serum betatrophin levels in PCOS.

CONCLUSIONS

Serum concentrations of betatrophin are connected with insulin resistance and beta cell function and did not change after glucose load in women with PCOS.

The ANGPTL3-4-8 model, a molecular mechanism for triglyceride trafficking

Lipoprotein lipase (LPL) is a rate-limiting enzyme for hydrolysing circulating triglycerides (TG) into free fatty acids that are taken up by peripheral tissues. Postprandial LPL activity rises in white adipose tissue (WAT), but declines in the heart and skeletal muscle, thereby directing circulating TG to WAT for storage; the reverse is true during fasting. However, the mechanism for the tissue-specific regulation of LPL activity during the fed–fast cycle has been elusive. Recent identification of lipasin/angiopoietin-like 8 (Angptl8), a feeding-induced hepatokine, together with Angptl3 and Angptl4, provides intriguing, yet puzzling, insights, because all the three Angptl members are LPL inhibitors, and the deficiency (overexpression) of any one causes hypotriglyceridaemia (hypertriglyceridaemia). Then, why does nature need all of the three? Our recent data that Angptl8 negatively regulates LPL activity specifically in cardiac and skeletal muscles suggest an Angptl3-4-8 model: feeding induces Angptl8, activating the Angptl8–Angptl3 pathway, which inhibits LPL in cardiac and skeletal muscles, thereby making circulating TG available for uptake by WAT, in which LPL activity is elevated owing to diminished Angptl4; the reverse is true during fasting, which suppresses Angptl8 but induces Angptl4, thereby directing TG to muscles. The model suggests a general framework for how TG trafficking is regulated.

Angiopoietin-like protein 8 (ANGPTL8) in pregnancy: a brown adipose tissue-derived endocrine factor with a potential role in fetal growth

Angiopoietin-like protein 8 (ANGPTL8), a protein implicated in lipid and glucose homeostasis, is present only in mammals, suggesting that it is involved in processes unique to these vertebrates such as pregnancy and homeothermy. We explored the role of ANGPTL8 in maternal-fetal crosstalk and its relationship with newborn adiposity. In a longitudinal analysis of healthy pregnant women, ANGPTL8 levels decreased progressively during pregnancy although remained higher than levels in the postpartum period. In a cross-sectional observational study of women with or without gestational diabetes mellitus (GDM), and their offspring, ANGPTL8 levels were higher in venous cord blood than those in maternal blood and were significantly lower in GDM patients than those in healthy women. Infants small for gestational age and with low-fat mass had the highest ANGPTL8 cord blood levels. Studies in vitro revealed that ANGPTL8 was secreted by brown adipocytes and its expression was increased in experimental models of white-to-brown fat conversion. In addition, ANGPTL8 induced the expression of markers of brown adipocytes. The high levels of ANGPTL8 found in fetal life together with its relationship with newborn adiposity and brown adipose tissue point to ANGPTL8 as a potential new player in the modulation of the thermogenic machinery during the fetal-neonatal transition.

Fasting and Feeding Signals Control the Oscillatory Expression of Angptl8 to Modulate Lipid Metabolism

Emerging evidence implies a key role of angiopoietin-like protein 8 (Angptl8) in the metabolic transition between fasting and feeding, whereas much less is known about the mechanism of its own expression. Here we show that hepatic Angptl8 is rhythmically expressed, which involving the liver X receptor alpha (LXRα) and glucocorticoid receptor (GR) modulation during feeding and fasting periods, respectively. In addition, Angptl8 mRNA is very unstable, which contributes to the nature of its daily rhythmicity by rapidly responding to fasting/feeding transition. To explore its pathological function in dexamethasone (DEX)-induced fatty liver, we reversed its suppression by glucocorticoids through adenoviral delivery of Angptl8 gene in mouse liver. Surprisingly, hepatic overexpression of Angptl8 dramatically elevated plasma triglyceride (TG) and non-esterified fatty acid (NEFA) levels in DEX-treated mice, suggesting a metabolic interaction between Angptl8 and glucocorticoid signaling. Moreover, intracellular hepatic Angptl8 is implicated in the regulation of lipid homeostasis by the experiments with ectopic expression of a nonsecreted Angptl8 mutant (Δ25-Angptl8). Altogether, our data demonstrate the molecular mechanism of the diurnal rhythm of Angptl8 expression regulated by glucocorticoid signaling and LXRα pathway, and provide new evidence to understand the role of Angptl8 in maintaining plasma TG homeostasis.

Increased ANGPTL3, 4 and ANGPTL8/betatrophin expression levels in obesity and T2D

Background

Hypertriglyceridemia is associated with increased risk for cardiovascular diseases and type 2 diabetes (T2D). Angiopoietin like proteins particularly 3, 4 and recently 8 are well established regulators of plasma triglyceride level through regulating the activity of lipoprotein lipase. Plasma level and association between ANGPTL3, 4 and 8 is not well established in human subjects. This study was designed to establish the level of these proteins in plasma and adipose tissues and investigate the association between ANGPTL8 with ANGPTL3 and 4 in T2D and non-diabetics subjects.

Methods

A total of 235 subjects were enrolled in this study, 144 non-diabetics and 91 T2D. ANGPTL 3, 4 and 8 levels were measured in plasma by ELISA and using real time RT-PCR in adipose tissues.

Results

In this study, we showed that ANGPTL3, 4 and 8 were higher in T2D subjects. Dividing the non-diabetic subjects according to their BMI showed higher level of ANGPTL3, 4 and 8 in obese subjects compared to non-obese subjects. No significant difference was observed between the T2D subjects. ANGPTL8 was showed positive correlation with ANGPTL3 in the non-diabetic subjects in the non-obese (r = 0.2437, p-Value = 0.0543) and obese subjects (r = 0.418, p-Value = 0.0125). No association was observed in the T2D subjects. On the other hand, ANGPTL4 was positively associated with the obese subjects in both the non-diabetics (r = 0.3322, p-Value = 0.0316) and the obese T2D subjects (r = 0.3161, p-Value = 0.0211).

Conclusion

In conclusion, our data shows that ANGPTL3, 4 and 8 are increased in obesity and T2D. ANGPTL8 associates with ANGPTL3 in the non-diabetic subjects while it associated more with ANGPTL4 in the obese and T2D subjects. Taken together, this data highlight the role of these proteins in metabolic diseases and how they interact with each other’s under different physiological and pathophysiological conditions.

Vitamin D modifies the associations between circulating betatrophin and cardiometabolic risk factors among youths at risk for metabolic syndrome

Background

Betatrophin has been recently reported to play a role in glucose homeostasis by inducing beta-cell proliferation in mice. However, studies in human are inconsistent. As a nutritionally-regulated liver-enriched factor, we hypothesize that betatrophin might be regulated by vitamin D, and ignorance of vitamin D status may explain the discrepancy in previous human studies. The aims of this study were to assess the association between circulating betatrophin and glucose homeostasis as well as other cardiometabolic variables in a cohort of youths at risk for metabolic syndrome and test the possible influence of vitamin D status on the association.

Methods

559 subjects aged 14–28 years were recruited from Beijing children and adolescents metabolic syndrome study. All underwent a 2 h-oral glucose tolerance test. Serum levels of betatrophin, 25-hydroxy-vitamin D as well as adipokines including adiponectin and fibroblast growth factor 21 (FGF21) were measured by immunoassays. The relationships between betatrophin and insulin resistance, beta-cell function, other cardiometabolic variables and vitamin D status were evaluated.

Results

Participants in the highest quartile of betatrophin levels had the highest levels of total cholesterol (P < 0.001), triglyceride (P < 0.001) and low-density lipoprotein cholesterol (P < 0.001) and the lowest levels of vitamin D (P = 0.003). After stratification by vitamin D status, betatrophin in subjects with vitamin D deficiency were positively correlated with unfavorable metabolic profiles including high blood pressures, dyslipidemia and hyperglycemia, whereas betatrophin in those with higher vitamin D levels only showed negative association with fasting insulin, 2 h-insulin, and insulin resistance. In addition, adiponectin and FGF21 demonstrated the expected associations with metabolic parameters.

Conclusions

Elevated betatrophin levels were associated with cardiometabolic risk factors in this young population, but the association was largely dependent on vitamin D status. These findings may provide valuable insights in the regulation of betatrophin and help explain the observed discrepancies in literature.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-016-0461-y) contains supplementary material, which is available to authorized users.

Increased angiopoietin-like protein 8 levels in patients with type 2 diabetes and cardiovascular disease

In the present study, we recruited 124 patients with type 2 diabetes, among which 22 had a history of cardiovascular disease (CVD). The study demonstrated that compared with type 2 diabetes without CVD, those with CVD had remarkably higher levels of angiopoietin-like protein 8 (ANGPTL8). Moreover, the close relationship between ANGPTL8 and CVD was independent of conventional CVD risk factors.

Different relationship between ANGPTL3 and HDL components in female non-diabetic subjects and type-2 diabetic patients

Background

Angiopoietin-like protein 3 (ANGPTL3) is a major lipoprotein regulator and shows positive correlation with high-density lipoprotein-cholesterol (HDL-c) in population studies and ANGPTL3 mutated subjects. However, no study has looked its correlation with HDL components nor with HDL function in patients with type 2 diabetes mellitus (T2DM).

Methods

We studied 298 non-diabetic subjects and 300 T2DM patients who were randomly recruited in the tertiary referral centre. Plasma levels of ANGPTL3 were quantified by ELISA. Plasma samples were fractionated to obtain HDLs. HDL components including apolipoprotein A-I (apoA-I), triglyceride, serum amyloid A (SAA), phospholipid and Sphingosine-1-phosphate were measured. HDLs were isolated from female controls and T2DM patients by ultracentrifugation to assess cholesterol efflux against HDLs. A Pearson unadjusted correlation analysis and a linear regression analysis adjusting for age, body mass index and lipid lowering drugs were performed in male or female non-diabetic participants or diabetic patients, respectively.

Results

We demonstrated that plasma level of ANGPTL3 was lower in female T2DM patients than female controls although no difference of ANGPTL3 levels was detected between male controls and T2DM patients. After adjusting for confounding factors, one SD increase of ANGPTL3 (164.6 ng/ml) associated with increase of 2.57 mg/dL cholesterol and 1.14 μg/mL apoA-I but decrease of 47.07 μg/L of SAA in HDL particles of non-diabetic females (p < 0.05 for cholesterol and SAA; p < 0.0001 for apoA-I). By contrast, 1-SD increase of ANGPTL3 (159.9 ng/ml) associated with increase of 1.69 mg/dl cholesterol and 1.25 μg/mL apoA-I but decrease of 11.70 μg/L of SAA in HDL particles of female diabetic patients (p < 0.05 for cholesterol; p < 0.0001 for apoA-I; p = 0.676 for SAA). Moreover, one SD increase of ANGPTL3 associated with increase of 2.11 % cholesterol efflux against HDLs in non-diabetic females (p = 0.071) but decrease of 1.46 % in female T2DM patients (p = 0.13) after adjusting for confounding factors.

Conclusions

ANGPTL3 is specifically correlated with HDL-c, apoA-I, SAA and HDL function in female non-diabetic participants. The decrease of ANGPTL3 level in female T2DM patients might contribute to its weak association to HDL components and function. ANGPTL3 could be considered as a novel therapeutic target for HDL metabolism for treating diabetes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-016-0450-1) contains supplementary material, which is available to authorized users.

The Rise and the Fall of Betatrophin/ANGPTL8 as an Inducer of β-Cell Proliferation

Diabetes is a global health problem that is caused by impaired insulin production from pancreatic β-cells. Efforts to regenerate β-cells have been advancing rapidly in the past two decades with progress made towards identifying new agents that induce β-cells regeneration. ANGPTL8, also named betatrophin, has been recently identified as a hormone capable of inducing β-cells proliferation and increasing β-cells mass in rodents. Its discovery has been cherished as a breakthrough and a game changer in the field of β-cells regeneration. Initially, ANGPTL8 has been identified as atypical member of the angiopoietin-like protein family as a regulator of triglyceride in plasma through its interaction with ANGPTL3 and its regulation of lipoprotein lipase activity. In this review, we will review literature on the proposed role of ANGPTL8 in β-cells proliferation, the controversy regarding this role, and the emerging data questioning its involvement in β-cells proliferation. Additionally we will discuss new clinical data that describes its role in diabetes and the putative therapeutic targeting of this protein.

Relationship between serum betatrophin levels and the first-phase of glucose-stimulated insulin secretion

AIMS

To examine circulating betatrophin concentrations in subjects with different glucose tolerance status and to investigate the relationship between serum betatrophin levels and first-phase of glucose-stimulated insulin secretion.

METHODS

Serum betatrophin concentrations were measured in 110 age- and sex-matched subjects: 47 newly diagnosed type 2 diabetes mellitus (T2DM), 29 impaired glucose tolerance (IGT) and 34 normal glucose tolerance (NGT). Oral glucose tolerance test and intravenous glucose tolerance test were performed to assess glucose tolerance and first-phase of glucose-stimulated insulin secretion.

RESULTS

Serum betatrophin levels were significantly higher in the T2DM and IGT group than in the NGT group (2.10±1.16ng/mL vs 0.77±0.44ng/mL, 1.73±1.28ng/mL vs 0.77±0.44ng/mL; P<0.01). The AIR and AUC among the three groups showed a progressive decrease from the NGT to IGT group with the lowest value in the T2DM group (P<0.01). Betatrophin were found to be positively correlated with BMI, waist circumference (WC), homeostatic model assessment of insulin resistance (HOMA-IR) and triglyceride (TG), and inversely associated with HDL-c (all P<0.01), but not significantly correlated with 0-10min insulin the area under the curve (AUC) and acute insulin response (AIR) (P>0.05). Stepwise multiple regression analysis showed that HOMA-IR and TG were independently related to betatrophin (P<0.05).

CONCLUSION

Serum betatrophin concentrations were higher in T2DM and IGT, and were closely related to glucolipid disorder, insulin resistance, but not related to the first-phase of glucose-stimulated insulin secretion.

Betatrophin expression is promoted in obese hyperinsulinemic type 2 but not type 1 diabetic mice

Regeneration of pancreatic β-cell mass benefits both type 1 and type 2 diabetic patients. A recent study identified betatrophin as a β-cell proliferation factor. However, the expressional regulation of betatrophin remains less defined. In this study, we aimed to clarify the regulation of betatrophin expression in obese type 2 vs. type 1 diabetes model animals. We experimented type 2 diabetes models, diet-induced-obesity (DIO) mice and db/db mice, and type 1 diabetes models, C57B6 mice receiving streptozotocin (STZ) or 70% pancreatectomy to destroy or remove β-cells. Serum betatrophin levels and betatrophin mRNA expressions in the liver, white adipose tissue (WAT) and brown adipose tissue (BAT) were measured. In DIO mice and db/db mice, serum betatrophin and betatrophin mRNA expressions in the liver, WAT and BAT were elevated in parallel with increases in body weight and plasma insulin. These elevated betatrophin mRNA expressions were not altered by treatment with SGLT2 inhibitor that ameliorated hyperglycemia. In pancreatectomized mice, betatrophin expression in WAT decreased in parallel with reductions in weight and insulin. In STZ-treated mice, betatrophin expressions in the liver, WAT and BAT were reduced. However, when the mouse liver slices were cultured with STZ, betatrophin expression was significantly reduced, indicating a direct action of STZ on the liver. These results indicate that the expression of betatrophin is upregulated in the liver, WAT and BAT in obese hyperinsulinemic type 2 diabetes but decreased in WAT in hypoinsulinemic type 1 diabetes, suggesting its positive correlation with body weight and plasma insulin but not blood glucose.

ANGPTL8/betatrophin alleviates insulin resistance via the Akt-GSK3β or Akt-FoxO1 pathway in HepG2 cells

Angiopoietin-like protein 8 (ANGPTL8)/betatrophin, a newly identified protein, is primarily expressed in the liver and regulates the glucose metabolic transition during fasting and re-feeding in mice with or without insulin resistance. These findings strongly suggest that ANGPTL8/betatrophin could be a novel glucose-lowering candidate medicine for type 2 diabetes. However, the molecular mechanisms by which ANGPTL8/betatrophin regulates glucose metabolism are poorly understood in human. Two sub-clones of HepG2 cells, ANGPTL8/betatrophin knockouts and ANGPTL8/betatrophin over-expressors, were established using TALENs (transcription activator-like effector nucleases) and through stable transfection, respectively. Over-expression of ANGPTL8/betatrophin enhanced the insulin-stimulated activation of the Akt-GSK3β or Akt-FoxO1 pathway, no matter whether the cells were present with insulin resistance or not. In contrast, knockout of ANGPTL8/betatrophin did not affect the Akt-GSK3β or Akt-FoxO1 pathway unless the HepG2 cells were preset with insulin resistance. Our results suggest that ANGPTL8/betatrophin might play an important role in glucose metabolism in the context of insulin resistance.

Resolving Discrepant Findings on ANGPTL8 in β-Cell Proliferation: A Collaborative Approach to Resolving the Betatrophin Controversy

The β-cell mitogenic effects of ANGPTL8 have been subjected to substantial debate. The original findings suggested that ANGPTL8 overexpression in mice induced a 17-fold increase in β-cell proliferation. Subsequent studies in mice contested this claim, but a more recent report in rats supported the original observations. These conflicting results might be explained by variable ANGPTL8 expression and differing methods of β-cell quantification. To resolve the controversy, three independent labs collaborated on a blinded study to test the effects of ANGPTL8 upon β-cell proliferation. Recombinant human betatrophin (hBT) fused to maltose binding protein (MBP) was delivered to mice by intravenous injection. The results demonstrate that ANGPTL8 does not stimulate significant β-cell proliferation. Each lab employed different methods for β-cell identification, resulting in variable quantification of β-cell proliferation and suggests a need for standardizing practices for β-cell quantification. We also observed a new action of ANGPTL8 in stimulating CD45+ hematopoietic-derived cell proliferation which may explain, in part, published discrepancies. Overall, the hypothesis that ANGPTL8 induces dramatic and specific β-cell proliferation can no longer be supported. However, while ANGPTL8 does not stimulate robust β-cell proliferation, the original experimental model using drug-induced (S961) insulin resistance was validated in subsequent studies, and thus still represents a robust system for studying signals that are either necessary or sufficient for β-cell expansion. As an added note, we would like to commend collaborative group efforts, with repetition of results and procedures in multiple laboratories, as an effective method to resolve discrepancies in the literature.

Elevated circulating levels of betatrophin are associated with polycystic ovary syndrome

Betatrophin is a newly identified hormone determined to be a potent inducer of pancreatic beta cell proliferation in response to insulin resistance in mice. Polycystic ovary syndrome (PCOS) is an inflammatory-based metabolic disease associated with insulin resistance. However, no evidence is available indicating whether betatrophin is involved in women with PCOS. The objective of this study was to ascertain whether betatrophin levels are altered in women with PCOS. This study was conducted in secondary referral center. This cross-sectional study included 164 women with PCOS and 164 age- and BMI-matched female controls. Circulating betatrophin levels were measured using ELISA. Metabolic and hormonal parameters were also determined. Circulating betatrophin levels were significantly elevated in women with PCOS compared with controls (367.09 ± 55.78 vs. 295.65 ± 48.97 pg/ml, P < 0.001). Betatrophin levels were positively correlated with insulin resistance marker homeostasis model assessment of insulin resistance (HOMA-IR), free-testosterone, high-sensitivity C-reactive protein (hs-CRP), atherogenic lipid profiles, and BMI in PCOS. Multivariate logistic regression analyses revealed that the odds ratio for PCOS was 2.51 for patients in the highest quartile of betatrophin compared with those in the lowest quartile (95 % CI 1.31-4.81, P = 0.006). Multivariate regression analyses showed that HOMA-IR, hs-CRP, and free-testosterone were independent factors influencing serum betatrophin levels. Betatrophin levels were increased in women with PCOS and were associated with insulin resistance, hs-CRP, and free-testosterone in these patients. Elevated betatrophin levels were found to increase the odds of having PCOS. Further research is needed to elucidate the physiologic and pathologic significance of our findings.

The Effects of Serum ANGPTL8/betatrophin on the Risk of Developing the Metabolic Syndrome - A Prospective Study

ANGPTL8/betatrophin is a recently discovered hormone, which mainly synthesized and secreted by liver and adipose tissue, playing a critical role in pancreatic beta cell proliferation. Previous studies have suggested that serum ANGPTL8/betatrophin levels are associated with obesity and diabetes mellitus. Here, we evaluated the prospective association between ANGPTL8/betatrophin and the metabolic syndrome from a community-based cohort of 153 adults without metabolic syndrome. After 3.5-year follow-up, we observed an inverse correlation between the baseline ANGPTL8/betatrophin levels and the incidence of metabolic syndrome, even after multivariate adjustments. In receiver operating characteristic analysis, the area underneath the curve for ANGPTL8/betatrophin was 0.70 in males and 0.86 in females, and the optimal cut-off values were 23.9 ng/mL and 31.1 ng/mL, respectively. This article suggests that ANGPTL8/betatrophin might be useful in predicting newly-onset metabolic syndrome and its progression in clinical setting.

Adipokines and the Endocrine Role of Adipose Tissues

The last two decades have witnessed a shift in the consideration of white adipose tissue as a mere repository of fat to be used when food becomes scarce to a true endocrine tissue releasing regulatory signals, the so-called adipokines, to the whole body. The control of eating behavior, the peripheral insulin sensitivity, and even the development of the female reproductive system are among the physiological events controlled by adipokines. Recently, the role of brown adipose tissue in human physiology has been recognized. The metabolic role of brown adipose tissue is opposite to white fat; instead of storing fat, brown adipose tissue is a site of energy expenditure via adaptive thermogenesis. There is growing evidence that brown adipose tissue may have its own pattern of secreted hormonal factors, the so-called brown adipokines, having distinctive biological actions on the overall physiological adaptations to enhance energy expenditure.

Regulation of lipid metabolism by angiopoietin-like proteins

PURPOSE OF REVIEW

The angiopoietin-like proteins (ANGPTLs) 3, 4 and 8 have emerged as key regulators of plasma lipid metabolism by serving as potent inhibitors of the enzyme lipoprotein lipase (LPL). In this review, we provide an integrated picture of the role of ANGPTL3, ANGPTL4 and ANGPTL8 in lipid metabolism by focusing on their impact on LPL activity and plasma triglyceride clearance during physiological conditions such as fasting, refeeding, exercise and cold exposure.

RECENT FINDINGS

Upon refeeding, circulating ANGPTL3 and ANGPTL8 promote the replenishment of white adipose tissue depots by specifically inhibiting LPL activity in oxidative tissues. During exercise and cold exposure, ANGPTL4 represses local LPL activity to assure that plasma triglycerides are specifically shuttled to exercising muscle and brown adipose tissue, respectively. Overall, ANGPTL4 is the central component of a fatty acid-driven feedback mechanism that regulates plasma triglyceride hydrolysis and subsequent tissue fatty acid uptake in response to changes in lipid availability and cellular fuel demand.

SUMMARY

ANGPTL3, ANGPTL4 and ANGPTL8 together ensure that triglycerides from triglyceride-rich lipoproteins are adequately distributed during different physiological conditions. The impact of the ANGPTLs on plasma lipid levels has led to scrutiny of ANGPTLs as therapeutic targets for dyslipidemia.

The Arg59Trp variant in ANGPTL8 (betatrophin) is associated with total and HDL-cholesterol in American Indians and Mexican Americans and differentially affects cleavage of ANGPTL3

We previously identified a locus linked to total cholesterol (TC) concentration in Pima Indians on chromosome 19p. To characterize this locus, we genotyped >2000 SNPs in 1838 Pimas and assessed association with log(TC). We observed evidence for association with log(TC) with rs2278426 (3.5% decrease/copy of the T allele; P=5.045×10(-6)) in the ANGPTL8 (angiopoietin-like 8) gene. We replicated this association in 2413 participants of the San Antonio Mexican American Family Study (SAMAFS: 2.0% decrease per copy of the T allele; P=0.005842). In a meta-analysis of the combined data, we found the strongest estimated effect with rs2278426 (P=2.563×10(-7)). The variant T allele at rs2278426 predicts an Arg59Trp substitution and has previously been associated with LDL-C and HDL-C. In Pimas and SAMAFS participants, the T allele of rs2278426 was associated with reduced HDL-C levels (P=0.000741 and 0.00002, respectively), and the combined estimated effect for the two cohorts was -3.8% (P=8.526×10(-8)). ANGPTL8 transcript and protein levels increased in response to both glucose and insulin. The variant allele was associated with increased levels of cleaved ANGPTL3. We conclude that individuals with the variant allele may have lower TC and HDL-C levels due to increased activation of ANGPTL3 by ANGPTL8.

Increased Cord Blood Betatrophin Levels in the Offspring of Mothers with Gestational Diabetes

AIM

Exposing a fetus to hyperglycemia can increase the risk for later-life metabolic disorders. Betatrophin has been proposed as a key regulator of pancreatic beta cell proliferation and lipid regulation. Highly responsive to nutritional signals, serum betatrophin concentrations have been found to be altered by various physiological and pathological conditions. We hypothesized that betatrophin levels are increased in the cord blood in offspring exposed to intrauterine hyperglycemia.

METHODS

This was a cross-sectional study including 54 mothers who underwent uncomplicated Cesarean delivery in a university hospital. Maternal gestational glucose concentration was determined at 24-48 weeks gestation after a 75-g OGTT. Cord blood and placental tissue was collected immediately post delivery. Metabolic parameters were determined in the Clinical Laboratory. Cord blood betatrophin levels were assayed using a commercially available ELISA kit. Placental mitochondrial content was determined by real-time PCR.

RESULTS

Cord blood betatrophin levels were increased in the gestational diabetes mellitus (GDM) group compared with the normoglycemic group. Furthermore, betatrophin levels were positively correlated with maternal gestational 2h post-OGTT glucose, cord blood insulin, HOMA-IR, and inversely correlated with placental mitochondrial content.

CONCLUSIONS

Cord blood betatrophin may function as a potential biomarker of maternal intrauterine hyperglycemia and fetal insulin resistance, which may presage for long-term metabolic impact of GDM on offspring.

The Relationship between Betatrophin Levels in Blood and T2DM: A Systematic Review and Meta-Analysis

Background. In order to clarify previous ambiguous research conclusions, a meta-analysis was made to investigate the relationship between betatrophin levels in blood and type 2 diabetes mellitus (T2DM). Methods. We have searched all the English and Chinese references regarding the relationship between betatrophin and diabetes in database both manually and online. Strict criteria have been established to include and exclude articles, with Mean and Standard Deviation as statistics to evaluate strength of association. We have chosen either fixed- or random effect model according to heterogeneity inspection results and used Begg's test and Egger's test to analyze publication bias. Results. A total of 11 studies were included in this meta-analysis. Meta-analysis indicated a significant association between betatrophin and T2DM (Mean: 329.46; 95% confidence interval: 182.51 to 476.42, P < 0.0001). However, in the subgroup analysis, there was no significant statistic between betatrophin concentration and T2DM within Caucasian population (Mean: 98.40; 95% confidence interval: −1585.08 to 1781.88, P = 0.91). Conclusions. Such relationship may suggest preference for association between betatrophin and T2DM in different population.

Lipasin, a biomarker of diabetic retinopathy

The present study recruited 74 participants with type 2 diabetes, among which 23 had retinopathy. Those with retinopathy had a longer duration of diabetes and higher levels of lipasin compared with those without retinopathy. Logistic regression revealed that lipasin was independently and significantly associated with retinopathy even after adjustments for confounders.

Circulating Betatrophin Is Increased in Patients with Overt and Subclinical Hypothyroidism

Thyroid hormone (TH) affects many metabolic processes such as promoting oxidation of sugar, fat, and protein in many tissues. Thyroid dysfunction is associated with metabolic disorders. The newly discovered adipocyte- and hepatocyte-derived cytokine, betatrophin, has been reported to be involved in metabolic diseases, but its influence on thyroid dysfunction is uncertain. Therefore, the present study aims to evaluate circulating betatrophin levels in subjects with different thyroid function status and to predict the factors associated with betatrophin levels, especially whether thyroid stimulating hormone (TSH), TH, or thyroid autoantibodies are associated with betatrophin levels. In the study, serum betatrophin was measured in the subjects grouped as overt hypothyroidism (OH), subclinical hypothyroidism (SCH), euthyroid with isolated thyroid peroxidase antibody positivity (isolated Ab), and healthy control (HC), according to their thyroid functions. From our results, we found that betatrophin may be associated with thyroid insufficiency but not thyroid autoimmunity. Thus, when interpreting the results of betatrophin, thyroid functions should also be taken into consideration.

Association between betatrophin/ANGPTL8 and non-alcoholic fatty liver disease: animal and human studies

Betatrophin/angiopoietin-like protein 8 (ANGPTL8) is a liver-secreted protein recently identified as a potent stimulator of beta cell proliferation in mice. However, it is unclear how betatrophin is regulated in humans with non-alcoholic fatty liver disease (NAFLD). We investigated the role of betatrophin in mice and in humans with and without NAFLD. Serum betatrophin levels were examined by ELISA in 164 subjects, including 96 patients with NAFLD. Levels were significantly elevated in subjects with NAFLD compared with controls (1.301 ± 0.617 vs. 0.900 ± 0.574 μg/L, P < 0.001), even after stratification by diabetic or obesity status. Circulating betatrophin positively correlated with obesity or glycemic indices, liver enzyme profiles, and NAFLD status, and was confirmed by multivariate regression analyses (β = 0.195, P = 0.040). However, when including insulin resistance index in the model, the significant association between betatrophin level and NAFLD was diminished due to a mediation effect of insulin resistance on this relationship. Palmitate or tunicamycin increased betatrophin expression in HepG2 cells, while a chemical chaperone blocked its induction. Hepatic expression of betatrophin was elevated in mice with NAFLD including db/db or ob/ob mice and mice with a high-fat or methionine-choline deficient diet. In conclusion, circulating betatrophin was increased in mice and humans with NAFLD and its expression was induced by endoplasmic reticulum stress in hepatocytes (Clinical trial no. NCT02285218).

Circulating betatrophin concentration is negatively correlated with insulin resistance in obese children and adolescents

AIM

The current study aimed to investigate the relationship between serum betatrophin levels and metabolic and anthropometric parameters in obese children.

METHOD

The study included 40 obese children with a body mass index (BMI) above 95th centile, and 35 non-obese subjects with a BMI 3-85th centile, whose age and gender were similar to those of the patient group. Fasting serum glucose, insulin, lipid profile, alanine aminotransferase, aspartate aminotransferase, serum betatrophin, and leptin levels were measured to evaluate the metabolic parameters. Total cholesterol:high-density lipoprotein cholesterol and low-density lipoprotein cholesterol:high-density lipoprotein cholesterol ratios were calculated as "atherogenic indices".

RESULTS

Serum betatrophin levels of the obese subjects were significantly lower than that of non-obese subjects (p<0.05). Insulin resistant subjects had significantly lower betatrophin concentrations than those of non-insulin resistant subjects (p<0.05). Betatrophin levels were negatively correlated with the fasting serum insulin and, accordingly insulin resistance index.

CONCLUSION

Serum betatrophin levels are lower in obese and insulin resistant subjects and betatrophin might act as a potential biomarker of insulin resistance in obese children or adolescents.

Circulating angiopoietin-like protein 8 (betatrophin) association with HsCRP and metabolic syndrome

Background

ANGPTL8 also called betatrophin is a regulator of lipid metabolism through its interaction with ANGPTL3. It has also been suggested to play a role in insulin resistance and beta-cell proliferation. Based on its function, we hypothesized that ANGPTL8 will play a role in Metabolic Syndrome (MetS). To test this hypothesis we designed this study to measure ANGPTL8 level in subjects with MetS as well as its association with high sensitivity C-reactive protein (HsCRP) level in humans.

Methods

ANGPTL8 level was measured using ELISA in subjects with MetS as well as their controls, a total of 1735 subjects were enrolled. HsCRP was also measured and its association with ANGPTL8 was examined.

Results

ANGPTL8 level was higher in subjects with MetS 1140.6 (171.9–11736.1) pg/mL compared to 710.5 (59.5–11597.2) pg/mL in the controls. Higher levels of ANGPTL8 were also observed with the sequential increase in the number of MetS components (p value = <0.0001). ANGPTL8 showed strong positive correlation with HsCRP (r = 0.15, p value = <0.0001). Stratifying the population into tertiles according to the level of HsCRP showed increased ANGPTL8 level at higher tertiles of HsCRP in the overall population (p value = <0.0001).A similar trend was also observed in MetS and non-MetS subjects as well as in non-obese and obese subjects. Finally, multiple logistic regression models adjusted for age, gender, ethnicity and HsCRP level showed that subjects in the highest tertiles of ANGPTL8 had higher odds of having MetS (odd ratio [OR] = 2.3, 95 % confidence interval [CI] = (1.6–3.1), p value <0.0001.

Conclusion

In this study we showed that ANGPTL8 is increased in subjects with MetS and it was significantly associated with HsCRP levels in different subgroups highlighting its potential role in metabolic and inflammatory pathways.

Characterisation of betatrophin concentrations in childhood and adolescent obesity and insulin resistance

BACKGROUND AND OBJECTIVE

Betatrophin, a novel hormone, is correlated with insulin resistance and promotes pancreatic β-cell growth in mice. The aim of this study was to determine circulating betatrophin levels in overweight or obese children and adolescents.

METHODS

The following pairs of subjects were included: (i) normal-weight healthy (n = 27) and overweight or obese (n = 28); (ii) non-insulin-resistant overweight or obese (n = 25) and insulin-resistant obese (n = 15); (iii) normal-weight males (n = 18) and females (n = 20); (4) 5 to 8 yr olds (n = 20) and 8 to 14 yr olds (n = 18). Circulating betatrophin levels were measured using enzyme-linked immunosorbent assay (ELISA). In addition, clinical data were recorded and anthropometrical measurements were performed.

RESULTS

Circulating betatrophin levels were increased significantly in obese children and adolescents with insulin resistance (365.77 ± 30.86 pg/mL) compared with overweight or obese subjects without insulin resistance (274.25 ± 26.52 pg/mL; p < 0.05). However, no differences in betatrophin levels were seen between lean and overweight or obese children (323.18 ± 25.91 vs. 348.27 ± 18.91 pg/mL, respectively; p > 0.05). In the normal-weight cohort, males had higher serum betatrophin level than did females, and subjects <8 yr old had lower serum betatrophin levels compared with those >8 yr. Surprisingly, betatrophin concentrations were correlated negatively with body mass index (BMI), but not with the BMI Z-score, in non-insulin-resistant children and adolescents.

CONCLUSIONS

These results demonstrated that circulating betatrophin levels were increased in insulin-resistant obese children or adolescents and might act as a potential biomarker of insulin resistance in these populations. Furthermore, serum betatrophin concentrations might vary during the development of children and adolescents, as well as between genders.

Structural characterization of ANGPTL8 (betatrophin) with its interacting partner lipoprotein lipase

Angiopoietin-like protein 8 (ANGPTL8) (also known as betatrophin) is a newly identified secretory protein with a potential role in autophagy, lipid metabolism and pancreatic beta-cell proliferation. Its structural characterization is required to enhance our current understanding of its mechanism of action which could help in identifying its receptor and/or other binding partners. Based on the physiological significance and necessity of exploring structural features of ANGPTL8, the present study is conducted with a specific aim to model the structure of ANGPTL8 and study its possible interactions with Lipoprotein Lipase (LPL). To the best of our knowledge, this is the first attempt to predict 3-dimensional (3D) structure of ANGPTL8. Three different approaches were used for modeling of ANGPTL8 including homology modeling, de-novo structure prediction and their amalgam which is then proceeded by structure verification using ERRATT, PROSA, Qmean and Ramachandran plot scores. The selected models of ANGPTL8 were further evaluated for protein-protein interaction (PPI) analysis with LPL using CPORT and HADDOCK server. Our results have shown that the crystal structure of iSH2 domain of Phosphatidylinositol 3-kinase (PI3K) p85β subunit (PDB entry: 3mtt) is a good candidate for homology modeling of ANGPTL8. Analysis of inter-molecular interactions between the structure of ANGPTL8 and LPL revealed existence of several non-covalent interactions. The residues of LPL involved in these interactions belong from its lid region, thrombospondin (TSP) region and heparin binding site which is suggestive of a possible role of ANGPTL8 in regulating the proteolysis, motility and localization of LPL. Besides, the conserved residues of SE1 region of ANGPTL8 formed interactions with the residues around the hinge region of LPL. Overall, our results support a model of inhibition of LPL by ANGPTL8 through the steric block of its catalytic site which will be further explored using wet lab studies in future.

Circulating ANGPTL8/Betatrophin Is Increased in Obesity and Reduced after Exercise Training

Objective

ANGPTL8 is a liver and adipose tissue produced protein that regulates the level of triglyceride in plasma as well as glucose homeostasis. This study was designed to evaluate the level of ANGPTL8 in obese and non-obese subjects before and after exercise training.

Methods

A total of 82 non-obese and 62 adult obese were enrolled in this study. Subjects underwent a three months of exercise training. Both full length and C-terminal 139–198 form of ANGPTL8 were measured by ELISA.

Results

Our data show that the full length ANGPTL8 level was increased in obese subjects (1150.04 ± 108.10 pg/mL) compared to non-obese (775.54 ± 46.12) pg/mL (p-Value = 0.002). C-terminal 139–198 form of ANGPTL8 was also increased in obese subjects 0.28 ± 0.04 ng/mL vs 0.20 ± 0.02 ng/mL in non-obese (p-value = 0.058). In obese subjects, the levels of both forms were reduced after three months of exercise training; full length was reduced from 1150.04 ± 108.10 pg/mL to 852.04 ± 51.95 pg/mL (p-Values 0.015) and c-terminal form was reduced from 0.28 ± 0.04 ng/mL to 0.19 ± 0.03 ng/mL (p-Value = 0.058). Interestingly, full length ANGPTL8 was positively associated with fasting blood glucose (FBG) in non-obese (r = 0.317, p-Value = 0.006) and obese subjects (r = 0.346, p-Value = 0.006) C-terminal 139–198 form of ANGPTL8 on the other hand, did not show any correlation in both groups.

Conclusion

In conclusion, our data demonstrate that ANGPTL8 was increased in obesity and reduced after exercise training supporting the potential therapeutic benefit of reducing ANGPTL8. The various forms of ANGPTL8 associated differently with FBG suggesting that they have different roles in glucose homeostasis.

Higher serum betatrophin level in type 2 diabetes subjects is associated with urinary albumin excretion and renal function

BACKGROUND

Betatrophin is a newly identified liver-derived hormone that is associated with glucose homeostasis and lipid metabolism. Although dysregulated lipid metabolism results in diabetic nephropathy (DN) development in patients with type 2 diabetes mellitus (T2DM), it is not understood whether betatrophin is associated with urinary albumin excretion and renal function.

METHODS

Based on albumin/creatinine ratio (ACR), 109 T2DM patients were divided into normoalbuminuria (ACR <30 mg/g), microalbuminuria (ACR between 30 and 300 mg/g), and macroalbuminuria (ACR > 300 mg/g). Serum betatrophin levels of 109 T2DM patients and 32 healthy subjects were determined by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Serum level of betatrophin was significantly increased in T2DM patients with normoalbuminuria, microalbuminuria, and macroalbuminuria as compared with healthy subjects (P < 0.001). Serum betatrophin level was positively correlated with sex, duration of diabetes, systolic blood pressure (SBP), body mass index (BMI), ACR, and triglyceride, whereas it was inversely correlated with estimated glomerular filtration rate (eGFR), total cholesterol, and high-density lipoprotein cholesterol (HDL-C) (P < 0.001). Furthermore, multivariate regression analysis showed the betatrophin was significantly and positively independent with triglyceride and low-density lipoprotein cholesterol (LDL-C) (P < 0.05), whereas it was inversely independent with eGFR, total cholesterol, and low-density lipoprotein cholesterol (HDL-C) (P < 0.05). In addition, the betatrophin had higher odds of having DN [odds ratio (OR) = 5.65, 95 % confidence interval (CI) 2.17-14.57, P < 0.001].

CONCLUSION

Betatrophin is significantly increased in T2DM patients with different stages of albuminuria. Betatrophin may be a novel endocrine regulator involved in DN development.

Circulating angiopoietin-like protein 8 (ANGPTL8) and ANGPTL3 concentrations in relation to anthropometric and metabolic profiles in Korean children: a prospective cohort study

Background

Previous studies have shown that angiopoietin-like protein 8 (ANGPTL8), also called as betatrophin, acts together with ANGPTL3 to regulate lipid metabolism, glucose metabolism, and energy homeostasis. Moreover, ANGPTL8 promotes proliferation of pancreatic β-cells and induces insulin secretion. However, there are no previous longitudinal studies in humans.

Methods

We analyzed the age- and sex-matched data of 240 normal weight and overweight Korean children from the Korean Metabolic disorders and Obesity Study in Elementary School children (K-MOSES), a prospective observational cohort study.

Results

At baseline, ANGPTL8 concentrations were positively associated with triglycerides (TG) (r = 0.168, P = 0.010), whereas ANGPTL3 levels were associated with fasting insulin (r = 0.248, P < 0.001) and the homeostasis model assessment of insulin resistance (HOMA-IR) (r = 0.197, P = 0.002). Although both ANGPTL8 and ANGPTL3 levels did not differ between children with normal weight and children with overweight, ANGPTL8 levels were increased in males compared to females (341.2 [267.4–436.5] vs. 270.2 [213.9–378.8] pg/ml, P = 0.001). In particular, there was no significant inter-relationship between circulating ANGPTL8 and ANGPTL3 concentrations in Korean boys and girls (r = −0.073, P = 0.265). Multivariate analysis showed that baseline ANGPTL8 concentrations were independently associated with future changes of serum TG levels in Korean children after adjusting for confounding factors after a 3 year follow-up period (r = −0.165, P = 0.016).

Conclusions

This longitudinal study demonstrated for the first time that baseline ANGPTL8 levels were associated with baseline and future changes in TG levels in Korean children.

Circulating Levels of Betatrophin and Irisin Are Not Associated with Pancreatic β-Cell Function in Previously Diagnosed Type 2 Diabetes Mellitus Patients

Betatrophin and irisin are two recently identified hormones which may participate in regulating pancreatic β-cell function. However, the associations of these two hormones with β-cell function remain unclear. The present study aims to demonstrate the associations of circulating betatrophin and irisin levels with β-cell function, assessed by the area under the curve (AUC) of C-peptide, and the possible correlation between these two hormones in previously diagnosed type 2 diabetes mellitus (T2DM) patients. In total, 20 age-, sex-, and body mass index- (BMI-) matched normal glucose tolerance (NGT) subjects and 120 previously diagnosed T2DM patients were included in this study. Partial correlation analysis was used to evaluate the relationships between these two hormones and indexes of β-cell function and insulin resistance. Our results showed that betatrophin levels were significantly elevated, while irisin levels were significantly decreased, in patients with T2DM compared with NGT subjects. However, partial correlation analysis showed that betatrophin levels did not correlate with β-cell function-related variables or insulin resistance-related variables before or after controlling multiple covariates, while irisin correlated positively with insulin sensitivity but is not associated with β-cell function-related variables. Besides, no correlation was observed between betatrophin and irisin levels. Hence we concluded that betatrophin and irisin were not associated with β-cell function in previously diagnosed T2DM patients.

A lipasin/Angptl8 monoclonal antibody lowers mouse serum triglycerides involving increased postprandial activity of the cardiac lipoprotein lipase

Lipasin/Angptl8 is a feeding-induced hepatokine that regulates triglyceride (TAG) metabolism; its therapeutical potential, mechanism of action, and relation to the lipoprotein lipase (LPL), however, remain elusive. We generated five monoclonal lipasin antibodies, among which one lowered the serum TAG level when injected into mice, and the epitope was determined to be EIQVEE. Lipasin-deficient mice exhibited elevated postprandial activity of LPL in the heart and skeletal muscle, but not in white adipose tissue (WAT), suggesting that lipasin suppresses the activity of LPL specifically in cardiac and skeletal muscles. Consistently, mice injected with the effective antibody or with lipasin deficiency had increased postprandial cardiac LPL activity and lower TAG levels only in the fed state. These results suggest that lipasin acts, at least in part, in an endocrine manner. We propose the following model: feeding induces lipasin, activating the lipasin-Angptl3 pathway, which inhibits LPL in cardiac and skeletal muscles to direct circulating TAG to WAT for storage; conversely, fasting induces Angptl4, which inhibits LPL in WAT to direct circulating TAG to cardiac and skeletal muscles for oxidation. This model suggests a general mechanism by which TAG trafficking is coordinated by lipasin, Angptl3 and Angptl4 at different nutritional statuses.

Circulating Betatrophin Levels Are Associated with the Lipid Profile in Type 2 Diabetes

Betatrophin is a newly characterized circulating hormone that is produced in tissues such as adipose tissue and liver and stimulates pancreatic beta-cell proliferation. The purpose of the current study was to examine circulating betatrophin levels in Iranian patients with type 2 diabetes mellitus (T2DM) and in normal controls. Seventy-five subjects were enrolled in this case-control study in the following two groups: T2DM patients (n=40) and a group of age-, sex-, and BMI-matched normal control subjects (n=35). Circulating betatrophin concentrations as well as the blood lipid profile, body mass index (BMI), fasting blood sugar (FBS), glycated hemoglobin (HbA1c), and insulin resistance were determined. Circulating betatrophin levels were significantly higher in patients with T2DM than in the normal subjects (4.79±1.53 ng/mL vs. 2.79±1.11 ng/mL respectively; p=0.001). Serum triacylglycerol and total cholesterol were also significantly higher in patients with T2DM than in the control group. In the patients with T2DM, serum betatrophin was positively correlated with age, FBS, TG, total cholesterol, and HbA1c. The results of this initial study in Iran have shown that circulating betatrophin levels are significantly increased in Iranian patients with T2DM compared with a control group. Additionally, it is postulated that betatrophin as a novel hormone may be involved in the generation of an atherogenic lipid profile.

Betatrophin in Diabetes Mellitus: the Epidemiological Evidence in Humans

The prevalence of type 2 diabetes is increasing worldwide, and while numerous treatments exist, none of the current pharmacologic therapies is curative. Pharmacologic approaches that increase beta cell mass may present an avenue for actual cure. There have been numerous reports on factors that can induce beta cell proliferation in rodents, whereas there are still very limited data on the occurrence of beta cell proliferation in humans. The recent discovery of the hormone betatrophin, which in mice counteracted glucose intolerance induced by insulin resistance by potently stimulating beta cell proliferation, has boosted the hope for a new target for drug development for the treatment of diabetes mellitus in humans. With the encouraging preclinical findings as a background, this review presents the available clinical data on betatrophin and discusses its possible role in humans.

Circulating Betatrophin in Patients with Type 2 Diabetes: A Meta-Analysis

OBJECTIVE

To investigate the association between circulating betatrophin level and type 2 diabetes mellitus (T2DM) in human.

METHODS

A comprehensive literature search was performed in PubMed and Embase databases to identify eligible studies assessing the circulating levels of betatrophin in both T2DM patients and nondiabetic adults.

RESULTS

A total of nine eligible studies with twelve comparisons were included for the final meta-analysis. Circulating betatrophin levels in T2DM patients were higher than those in the nondiabetic controls (random-effect SMD 0.53; 95% CI 0.13 to 0.94; P = 0.010). In the subgroup of nonobese population but not the obese population, the overall betatrophin level in T2DM patients was much higher than that in the nondiabetic controls (nonobese: random-effect SMD, 0.82; 95% CI 0.42 to 1.21; P < 0.001; obese: random-effect SMD, -0.39; 95% CI, -0.95 to 0.18; P = 0.18). Metaregression indicated that body mass index of T2DM patients was associated with mean difference of betatrophin level between T2DM and nondiabetic adults (slope, -578.8; t = -2.7; P = 0.02).

CONCLUSION

Based on the findings of our meta-analysis, circulating betatrophin level of T2DM patients is higher than that of nondiabetic adults in the nonobese population, but not in the obese population.

Angptl4 links α-cell proliferation following glucagon receptor inhibition with adipose tissue triglyceride metabolism

Type 2 diabetes is characterized by a reduction in insulin function and an increase in glucagon activity that together result in hyperglycemia. Glucagon receptor antagonists have been developed as drugs for diabetes; however, they often increase glucagon plasma levels and induce the proliferation of glucagon-secreting α-cells. We find that the secreted protein Angiopoietin-like 4 (Angptl4) is up-regulated via Pparγ activation in white adipose tissue and plasma following an acute treatment with a glucagon receptor antagonist. Induction of adipose angptl4 and Angptl4 supplementation promote α-cell proliferation specifically. Finally, glucagon receptor antagonist improves glycemia in diet-induced obese angptl4 knockout mice without increasing glucagon levels or α-cell proliferation, underscoring the importance of this protein. Overall, we demonstrate that triglyceride metabolism in adipose tissue regulates α-cells in the endocrine pancreas.

AMP-activated protein kinase suppresses the expression of LXR/SREBP-1 signaling-induced ANGPTL8 in HepG2 cells

ANGPTL8 is a liver-derived secretory protein that leads to elevated serum triglyceride and the level of circulating ANGPTL8 is strongly associated with obesity and diabetes. Here we investigated the mechanisms of activation and inhibition of ANGPTL8 expression in hepatocytes. The expression of ANGPTL8 was significantly increased in HepG2 cells exposed to palmitic acid, tunicamycin, or T0901317, and was reversed in cells treated with AICAR. Palmitic acid, tunicamycin, and T0901317 increased LXRα and SREBP-1c mRNA expression. The inhibitory effect of AICAR on the expression of T0901317-induced ANGPTL8 was most strongly evident in cells that were transfected with SREBP-1 siRNA. AICAR increased phosphorylation of PPARα and the effect of AICAR was not observed in cells treated with PPARα inhibitor. Metformin had a similar effect on ANGPTL8 expression to that of AICAR. These data suggest that AMPK can suppress the expression of LXR/SREBP-1 signal-induced ANGPTL8 in HepG2 cells.

Interplay of atherogenic factors, protein intake and betatrophin levels in obese-metabolic syndrome patients treated with hypocaloric diets

CONTEXT

The understanding of the potential role of betatrophin in human metabolic disorders is a current challenge.

OBJECTIVE

The present research evaluated circulating betatrophin levels in obese patients with metabolic syndrome (MetSyn) features under energy-restricted weight-loss programs and in normal weight in order to establish the putative interplay between the levels of this hormone, diet and metabolic risk factors linked to obesity and associated comorbidities.

SUBJECTS AND METHODS

One hundred forty-three participants were enrolled in the study (95 obese-MetSyn; age 49.5±9.4 years; body mass index (BMI) 35.7±4.5 kg m(-2) and 48 normal weight; age 35.71±8.8 years; BMI 22.9±2.2 kg m(-2)). A nutritional therapy consisting in two hypocaloric strategies (control diet based on the AHA recommendations and the RESMENA (MEtabolic Syndrome REduction in Navarra) diet, a novel dietary program with changes in the macronutrient distribution) was only prescribed to obese-MetSyn participants who were randomly allocated to the dietary strategies. Dietary records, anthropometrical and biochemical variables as well as betatrophin levels were analyzed before (pre-intervention, week 0), at 8 weeks (post-intervention, week 8) and after 4 additional months of self-control period (follow-up, week 24).

RESULTS

Betatrophin levels were higher in obese-MetSyn patients than normal-weight subjects (1.24±0.43 vs 0.97±0.69 ng ml(-1), respectively, P=0.012), and levels were positively associated with body composition, metabolic parameters, leptin and irisin in all participants at baseline. Notably, low pre-intervention (week 0) betatrophin levels in obese patients were significantly associated with higher dietary-induced changes in atherogenic risk factors after 8 weeks. Moreover, protein intake, especially proteins from animal sources, was an independent determinant of betatrophin levels after dietary treatment (B=-0.27; P=0.012).

CONCLUSIONS

Betatrophin is elevated in obese patients with MetSyn features and is associated with poorer nutritional outcomes of adiposity and dyslipidemia traits after a weight-loss program. Dietary protein intake could be a relevant modulator of betatrophin secretion and activity.

Circulating Betatrophin Is Strongly Increased in Pregnancy and Gestational Diabetes Mellitus

Aims/hypothesis

Betatrophin has recently been introduced as a novel hormone and promotor of beta cell proliferation and improved glucose tolerance in mouse models of insulin resistance. In obese and diabetic humans altered levels were reported and a role in pathophysiology of metabolic diseases was therefore hypothesized. However its release and regulation in women with gestational diabetes mellitus (GDM), as well as its associations with markers of obesity, glucose and lipid metabolism during pregnancy still remain unclear.

Methods

Circulating betatrophin was quantified in 21 women with GDM and 19 pregnant body mass index-matched women with normal glucose tolerance (NGT) as well as 10 healthy age-matched non-pregnant women by enzyme-linked immunosorbent assay. Additionally we performed radioimmunassay (RIA) to confirm the results.

Results

Betatrophin concentrations measured by ELISA were significantly higher in GDM than in NGT (29.3±4.4 ng/ml vs. 18.1±8.7 ng/ml, p<0.001) which was confirmed by RIA. Betatrophin did not correlate with BMI or insulin resistance but showed a weak association with leptin levels in pregnancy and negative relationship with fasting C-peptide levels in all women. Moreover it correlated significantly with lipid parameters including triglycerides and total cholesterol in pregnancy, as well as estrogen, progesteron and birth weight.

Conclusions/interpretation

Circulating betatrophin concentrations are dramatically increased in pregnancy and are significantly higher in GDM versus pregnant NGT. In the light of the previously reported role in lipid metabolism, betatrophin may represent a novel endocrine regulator of lipid alterations in pregnancy. However additional studies are needed to elucidate whether hormonal factors, such as estrogen, control the production of betatrophin and if targeting betatrophin could hold promise in the fight against metabolic disease.

Hepatic ANGPTL3 regulates adipose tissue energy homeostasis

Angiopoietin-like protein 3 (ANGPTL3) is a circulating inhibitor of lipoprotein and endothelial lipase whose physiological function has remained obscure. Here we show that ANGPTL3 plays a major role in promoting uptake of circulating very low density lipoprotein-triglycerides (VLDL-TGs) into white adipose tissue (WAT) rather than oxidative tissues (skeletal muscle, heart brown adipose tissue) in the fed state. This conclusion emerged from studies of Angptl3(-/-) mice. Whereas feeding increased VLDL-TG uptake into WAT eightfold in wild-type mice, no increase occurred in fed Angptl3(-/-) animals. Despite the reduction in delivery to and retention of TG in WAT, fat mass was largely preserved by a compensatory increase in de novo lipogenesis in Angptl3(-/-) mice. Glucose uptake into WAT was increased 10-fold in KO mice, and tracer studies revealed increased conversion of glucose to fatty acids in WAT but not liver. It is likely that the increased uptake of glucose into WAT explains the increased insulin sensitivity associated with inactivation of ANGPTL3. The beneficial effects of ANGPTL3 deficiency on both glucose and lipoprotein metabolism make it an attractive therapeutic target.

Lack of associations between betatrophin/ANGPTL8 level and C-peptide in type 2 diabetic subjects

Background

Betatrophin has been suggested as an inducer of β-cell proliferation in mice in addition to its function in regulating triglyceride. Recent data showed that betatrophin was increased in Type 2 Diabetes (T2D), however, its ability to induce insulin production has been questioned. We hypothesized that the increased betatrophin in T2D is not affecting insulin production from β-cells. To test this hypothesis, we investigated the association between betatrophin and C-peptide level in humans, which acts as a measure of endogenous insulin production from β-cells.

Methods

This study was designed to examine the association between plasma betatrophin level and C-peptide in 749 T2D and non-diabetics.

Results

Betatrophin and C-peptide levels were higher in T2D subjects compared with non-diabetics subjects. Betatrophin showed strong correlation with C-peptide in non-diabetics subjects (r = 0.28, p = < 0.0001). No association between betatrophin and C-peptide were observed in T2D subjects (r = 0.07, p = 0.3366). Dividing obese and non-obese subjects into tertiles according to betatrophin level showed significantly higher C-peptide levels at higher tertiles of betatrophin in obese non-diabetics subjects P-trend = 0.0046. On the other hand, C-peptide level was significantly higher in subject with higher betatrophin level in non-diabetics subjects across all age groups but not in T2D subjects. Multiple logistic regression models adjusted for age, BMI, gender, ethnicity as well as C-peptide level showed that subjects in the highest tertiles of betatrophin had higher odds of having T2D [odd ratio (OR) = 7.3, 95 % confidence interval (CI) 4.0–13.3].

Conclusion

Increased betatrophin level in obese subjects is correlated with an increase in C-peptide level; which is possibly caused by the increased insulin resistance. On the other hand, no correlation is observed between increased betatrophin level and C-peptide in T2D subjects. In conclusion, the increased betatrophin in T2D subject does not cause any increase in insulin production as indicated by C-peptide level.

Circulating Betatrophin Correlates with Triglycerides and Postprandial Glucose among Different Glucose Tolerance Statuses--A Case-Control Study

Purpose

Previous researches of betatrophin on glucose and lipids metabolism under insulin-resistant condition have reached controversial conclusions. To further identify the possible impact of betatrophin, we measured the circulating betatrophin levels in newly diagnosed type 2 diabetes (T2DM) patients, and in subjects with both impaired glucose tolerance (IGT) and normal glucose tolerance (NGT) and investigated the relationship between serum betatrophin and other clinical parameters in these patients with different glucose tolerance statuses.

Methods

A total of 460 permanent residents of the Fengxian District, aged 40–60 years, were enrolled. Based on the results of a 75 g oral glucose tolerance test, we selected newly diagnosed T2DM (n = 50) patients and subjects with IGT (n = 51) and NGT (n = 50) according to their age, gender and body mass index (18–28 kg/m²). Anthropometric parameters, glycosylated haemoglobin, blood lipids and fasting insulin were measured. Serum betatrophin concentrations were determined via ELISA.

Results

Serum betatrophin levels in T2DM patients were increased significantly compared with IGT and NGT groups, and decreased in subjects with better islet beta cell function. Serum betatrophin was positively correlated with triglyceride, 2-hour postprandial glucose, alanine aminotransferase and aspartate transaminase after adjusting for age, sex and body mass index in all subjects. Multiple regression analysis showed that 2-hour postprandial glucose was independently associated with serum betatrophin significantly.

Conclusions

Circulating betatrophin is increased in newly-diagnosed T2DM patients and positively correlated with the triglycerides and postprandial glucose levels. The results suggest that betatrophin may participate in glucose and triglycerides metabolism.

Angiopoietin-like protein 8 (ANGPTL8)/betatrophin overexpression does not increase beta cell proliferation in mice

AIMS/HYPOTHESIS

The identification of novel targets that stimulate endogenous regeneration of beta cells would represent a significant advance in the treatment of patients with diabetes. The betatrophin hypothesis suggests that increased expression of angiopoietin-like protein 8 (ANGPTL8) induces dramatic and specific beta cell proliferation and subsequent beta cell mass expansion with improved glucose tolerance. In light of recent controversy, we further investigated the effects of ANGPTL8 overexpression on beta cell proliferation.

METHODS

We performed hydrodynamic tail vein injections of green fluorescent protein (GFP) or Angptl8 (also known as Gm6484) DNA in multiple cohorts of mice of different ages. We employed state-of-the-art methods to comprehensively quantify beta cell mass and proliferation, controlling for mouse age, genetic strain, source of DNA injected, Angptl8 gene expression and proliferation markers.

RESULTS

In two young and two aged cohorts of B6.129 mice, no substantial change in beta cell replication, mass or glucose homeostasis was observed following ANGPTL8 overexpression. Even in mice with extremely elevated Angptl8 expression (26-fold increase), beta cell replication was not significantly altered. Finally, we considered mice on the ICR background exactly as studied by Melton and colleagues, and still no beta cell mitogenic effect was detected following ANGPTL8 overexpression.

CONCLUSION/INTERPRETATION

ANGPTL8 does not stimulate beta cell replication in young or old mice.

Relationship of betatrophin with youth onset type 2 diabetes among Asian Indians

BACKGROUND AND AIMS

Betatrophin is emerging as a marker for compensatory beta cell proliferation. While betatrophin has been mainly investigated in adults, there is a lack of data on betatrophin levels in youth-onset type 2 diabetes mellitus (T2DM-Y). The aim of this study was to determine levels of betatrophin and its association with T2DM-Y in Asian Indian participants.

METHODS

We recruited 100 individuals with normal glucose tolerance (NGT; n=50) and newly-diagnosed cases (within 18 months of first diagnosis) of T2DM-Y (n=50) with onset between 12 and 24 years of age from a large tertiary diabetes center in Chennai in southern India. Insulin resistance was measured by homeostatic model (HOMA-IR) and insulin secretion by oral disposition index (DIO). Betatrophin levels were measured by enzyme-linked immunosorbent assay.

RESULTS

Betatrophin levels were significantly lower in the T2DM-Y group compared with the NGT group (803 vs 1104 pg/ml, p<0.001). Betatrophin showed a significant inverse correlation with waist circumference (p=0.035), HOMA-IR (p<0.001), fasting and 2 h postprandial glucose (p<0.01), glycated hemoglobin (p=0.019) and a positive correlation with fasting C-peptide (p<0.001) and DIO (p=0.012). In regression analysis, betatrophin was independently associated with T2DM-Y even after adjustment for age, gender, and waist circumference (OR per standard deviation: 0.562, 95% CI: 0.342-0.899, p=0.019). However, the association was lost when HOMA-IR was included in the model (OR: 1.141, 95% CI: 0.574-2.249; p=0.646).

CONCLUSION

Betatrophin levels are lower in T2DM-Y and this association is likely mediated through insulin resistance.

Increased Maternal and Cord Blood Betatrophin in Gestational Diabetes

AIM

The aim of the study was to compare maternal and cord blood levels of betatrophin--a new peptide potentially controlling beta cell growth--as well as in its mRNA expression in subcutaneous adipose tissue, visceral adipose tissue and placental tissue obtained from pregnant women with normal glucose tolerance (NGT) and gestational diabetes (GDM).

METHODS

Serum betatrophin and irisin concentrations were measured by ELISA in 93 patients with GDM and 97 women with NGT between 24 and 28 week of gestation. Additionally, maternal and cord blood betatrophin and irisin, as well as their genes (C19orf80 and Fndc5) expression were evaluated in 20 patients with GDM and 20 women with NGT at term.

RESULTS

In both groups, serum betatrophin concentrations were significantly higher in the patients with GDM than in the controls (1.91 [1.40-2.60] ng/ml vs 1.63 [1.21-2.22] ng/ml, p=0.03 and 3.45 [2.77-6.53] ng/ml vs 2.78 [2.16-3.65] ng/ml, p=0.03, respectively). Cord blood betatrophin levels were also higher in the GDM than in the NGT group (20.43 [12.97-28.80] ng/ml vs 15.06 [10.11-21.36] ng/ml, p=0.03). In both groups betatrophin concentrations in arterial cord blood were significantly higher than in maternal serum (p=0.0001). Serum irisin levels were significantly lower in the patients with GDM (1679 [1308-2171] ng/ml) than in the healthy women between 24 and 28 week of pregnancy (1880 [1519-2312] ng/ml, p=0.03). Both C19orf80 and Fndc5 mRNA expression in fat and placental tissue did not differ significantly between the groups studied.

CONCLUSIONS

Our results suggest that an increase in maternal and cord blood betatrophin might be a compensatory mechanism for enhanced insulin demand in GDM.

In vivo targeted delivery of ANGPTL8 gene for beta cell regeneration in rats

AIMS/HYPOTHESIS

ANGPTL8 is a circulatory hormone secreted from liver and adipose tissue that promotes pancreatic beta cell proliferation and interferes with triacylglycerol metabolism in mice. The clinical significance of its effects on inducing beta cell proliferation is limited because it causes severe hypertriacylglycerolaemia.

METHODS

We employed ultrasound-targeted microbubble destruction (UTMD) to deliver human ANGPTL8 gene plasmids to the pancreas, liver and skeletal muscle of normal adult rats.

RESULTS

Human ANGPTL8 was consistently detected in the circulation 1 month after UTMD. ANGPTL8 gene delivery promoted the proliferation of adult and aged beta cells, expanded the beta cell mass, improved glucose tolerance and increased the fasting blood insulin level after UTMD treatment without causing severe hypertriacylglycerolaemia. ANGPTL8 gene therapy significantly alleviated but did not totally reverse STZ-induced diabetes in a rat model.

CONCLUSIONS/INTERPRETATION

ANGPTL8 induced adult and aged beta cell regeneration in a rat model.

Correlation of circulating betatrophin concentrations with insulin secretion capacity, evaluated by glucagon stimulation tests

AIM

To investigate the relationship between plasma betatrophin concentrations and insulin secretion capacity in people with Type 2 diabetes.

METHODS

Glucagon stimulation tests (1 mg) were performed in 70 people with Type 2 diabetes after an overnight fast. Plasma betatrophin concentrations were measured using an enzyme-linked immunosorbent assay. Insulin secretion capacity was evaluated by measuring increments of C-peptide concentration in response to glucagon stimulation, and creatinine clearance was determined by comparing creatinine concentrations in serum and 24-h urine samples.

RESULTS

Plasma betatrophin concentrations were positively correlated with duration of Type 2 diabetes (r = 0.34, P = 0.003), and negatively correlated with increments of C-peptide concentration (r = 0.37, P = 0.001) and creatinine clearance (r = 0.37, P = 0.001). The correlation with increments of C-peptide concentration remained significant after adjustment for age and duration of Type 2 diabetes (r = 0.25, P = 0.037). Multivariate analysis identified age and increments of C-peptide concentration as independent factors associated with plasma betatrophin levels.

CONCLUSION

Plasma betatrophin levels inversely correlate with insulin secretion capacity, suggesting that betatrophin levels are regulated by insulin secretion capacity in humans.