Association of Serum Angiopoietin-Like Protein 8 With Albuminuria in Type 2 Diabetic Patients: Results From the GDMD Study in China

Angiopoietin-2 and Angiopoietin-like Proteins with a Prospective Role in Predicting Diabetic Nephropathy

Angiopoietins are crucial growth factors for maintaining a healthy, functional endothelium. Patients with type 2 diabetes (T2D) exhibit significant levels of angiogenic markers, particularly Angiopoietin-2, which compromises endothelial integrity and is connected to symptoms of endothelial injury and failure. This report examines the levels of circulating angiopoietins in people with T2D and diabetic nephropathy (DN) and explores its link with ANGPTL proteins. We quantified circulating ANGPTL3, ANGPTL4, ANGPTL8, Ang1, and Ang2 in the fasting plasma of 117 Kuwaiti participants, of which 50 had T2D and 67 participants had DN. The Ang2 levels increased with DN (4.34 ± 0.32 ng/mL) compared with T2D (3.42 ± 0.29 ng/mL). This increase correlated with clinical parameters including the albumin-to-creatinine ratio (ACR) (r = 0.244, p = 0.047), eGFR (r = -0.282, p = 0.021), and SBP (r = -0.28, p = 0.024). Furthermore, Ang2 correlated positively to both ANGPTL4 (r = 0.541, p < 0.001) and ANGPTL8 (r = 0.41, p = 0.001). Multiple regression analysis presented elevated ANGPTL8 and ACRs as predictors for Ang2's increase in people with DN. In people with T2D, ANGPTL4 positively predicted an Ang2 increase. The area under the curve (AUC) in receiver operating characteristic (ROC) analysis of the combination of Ang2 and ANGPTL8 was 0.77 with 80.7% specificity. In conclusion, significantly elevated Ang2 in people with DN correlated with clinical markers such as the ACR, eGFR, and SBP, ANGPTL4, and ANGPTL8 levels. Collectively, this study highlights a close association between Ang2 and ANGPTL8 in a population with DN, suggesting them as DN risk predictors.

Silencing ANGPTL8 reduces mouse preadipocyte differentiation and insulin signaling

ANGPTL8, expressed mainly in the liver and adipose tissue, regulates the activity of lipoprotein lipase (LPL) present in the extracellular space and triglyceride (TG) metabolism through its interaction with ANGPTL3 and ANGPTL4. Whether intracellular ANGPTL8 can also exert effects in tissues where it is expressed is uncertain. ANGPTL8 expression was low in preadipocytes and much increased during differentiation. To better understand the role of intracellular ANGPTL8 in adipocytes and assess whether it may play a role in adipocyte differentiation, we knocked down its expression in normal mouse subcutaneous preadipocytes. ANGPTL8 knockdown reduced adipocyte differentiation, cellular TG accumulation and also isoproterenol-stimulated lipolysis at day 7 of differentiation. RNA-Seq analysis of ANGPTL8 siRNA or control siRNA transfected SC preadipocytes on days 0, 2, 4 and 7 of differentiation showed that ANGPTL8 knockdown impeded the early (day 2) expression of adipogenic and insulin signaling genes, PPARγ, as well as genes related to extracellular matrix and NF-κB signaling. Insulin mediated Akt phosphorylation was reduced at an early stage during adipocyte differentiation. This study based on normal primary cells shows that ANGPTL8 has intracellular actions in addition to effects in the extracellular space, like modulating LPL activity. Preadipocyte ANGPTL8 expression modulates their differentiation possibly via changes in insulin signaling gene expression.

Increased Levels of Circulating IGFBP4 and ANGPTL8 with a Prospective Role in Diabetic Nephropathy

Diabetic nephropathy (DN) is a complicated condition related to type 2 diabetes mellitus (T2D). ANGPTL8 is a hepatic protein highlighted as a risk factor for DN in patients with T2D; additionally, recent evidence from DN studies supports the involvement of growth hormone/IGF/IGF-binding protein axis constituents. The potential link between ANGPTL8 and IGFBPs in DN has not been explored before. Here, we assessed changes in the circulating ANGPTL8 levels in patients with DN and its association with IGFBP-1, -3, and -4. Our data revealed a significant rise in circulating ANGPTL8 in people with DN, 4443.35 ± 396 ng/mL compared to 2059.73 ± 216 ng/mL in people with T2D (p < 0.001). Similarly, levels of IGFBP-3 and -4 were significantly higher in people with DN compared to the T2D group. Interestingly, the rise in ANGPTL8 levels correlated positively with IGFBP-4 levels in T2DM patients with DN (p < 0.001) and this significant correlation disappeared in T2DM patients without DN. It also correlated positively with serum creatinine and negatively with the estimated glomerular filtration rate (eGFR, All < 0.05). The area under the curve (AUC) on receiver operating characteristic (ROC) analysis of the combination of ANGPTL8 and IGFBP4 was 0.76 (0.69-0.84), p < 0.001, and the specificity was 85.9%. In conclusion, our results showed a significant increase in ANGPTL8 in patients with DN that correlated exclusively with IGFBP-4, implicating a potential role of both proteins in the pathophysiology of DN. Our findings highlight the significance of these biomarkers, suggesting them as promising diagnostic molecules for the detection of diabetic nephropathy.

Potential Role of N-Cadherin in Diagnosis and Prognosis of Diabetic Nephropathy

Diabetic nephropathy (DN) is a serious complication of diabetes affecting about half the people with diabetes and the leading cause of end stage renal disease (ESRD). Albuminuria and creatinine levels are currently the classic markers for the diagnosis of DN. However, many shortcomings are arising from the use of these markers mainly because they are not specific to DN and their levels are altered by multiple non-pathological factors. Therefore, the aim of this study is to identify better markers for the accurate and early diagnosis of DN. The study was performed on 159 subjects including 42 control subjects, 50 T2D without DN and 67 T2D subjects with DN. Our data show that circulating N-cadherin levels are significantly higher in the diabetic patients who are diagnosed with DN (842.6 ± 98.6 mg/l) compared to the diabetic patients who do not have DN (470.8 ± 111.5 mg/l) and the non-diabetic control group (412.6 ± 41.8 mg/l). We also report that this increase occurs early during the developmental stages of the disease since N-cadherin levels are significantly elevated in the microalbuminuric patients when compared to the healthy control group. In addition, we show a significant correlation between N-cadherin levels and renal markers including creatinine (in serum and urine), urea and eGFR in all the diabetic patients. In conclusion, our study presents N-cadherin as a novel marker for diabetic nephropathy that can be used as a valuable prognostic and diagnostic tool to slow down or even inhibit ESRD.

Association of Circulating ANGPTL8 Levels With Renal Dysfunction: A Case-Control Study

Background: Chronic kidney disease (CKD) is recognized as a major public health problem with high morbidity and mortality worldwide. Recently, angiopoietin-like protein 8 (ANGPTL8) was found to regulate lipid metabolism. Previous studies suggested that serum ANGPTL8 levels increased in patients with diabetes, especially in diabetic patients with albuminuria. This study aimed to investigate the association between circulating levels of ANGPTL8 and kidney function in the general population. Methods: The subjects were patients with renal dysfunction [estimated glomerular filtration rate (eGFR) <60/min/1.73 m²] from Risk Evaluation of cAncers in Chinese diabeTic Individuals: a lONgitudinal study (the REACTION study). Each case was matched by age, sex, and body mass index (BMI) with one control whose eGFR was ≥ 90 ml/min/1.73 m². The case and control groups were compared using a paired t-test. Binary logistic regression analysis was used to calculate the odds ratio (OR) of renal dysfunction (RD). Results: Among 135 case-control pairs, circulating ANGPTL8 levels were elevated in patients with RD compared to control subjects [799.96 (410.12-1086.44) vs. 609.58 (365.13-740.06) pg/ml, p < 0.05]. Partial correlations showed that ANGPTL8 levels were negatively correlated with eGFR (r = -0.26, p < 0.05). Multivariable-adjusted binary logistic regression analysis showed that elevated ANGPTL8 levels were associated with an increased risk of RD (OR in quartile 4 vs. 1, 3.80; 95% CI, 1.71-8.41). Interestingly, the association between ANGPTL8 levels and RD was consistent with the overall findings in both nondiabetic individuals (OR, 1.44; 95% CI, 1.09 to 1.91) and diabetic patients (OR, 2.71; 95% CI, 1.13-6.49) in the subgroup analyses. Furthermore, the estimates for this association were also significant in females (OR, 2.12; 95% CI, 1.33-3.37), individuals aged > 60 years (OR, 1.55; 95% CI, 1.16-2.07), individuals with a BMI <24 (OR, 1.66; 95% CI, 1.16-2.39), and individuals without hyperlipidaemia (OR, 1.61; 95% CI, 1.16-2.23) (all p-values <0.05). Conclusion: Elevated circulating ANGPTL8 levels were associated with increased risk of RD in the general population, especially among females, individuals aged > 60 years, individuals with a BMI < 24, individuals without diabetes mellitus, individuals with diabetes mellitus (DM), and individuals without hyperlipidaemia. This finding implies that ANGPTL8 may play a role in the pathological process of RD.

Nonenzymatic function of DPP4 in diabetes-associated mitochondrial dysfunction and cognitive impairment

Dipeptidyl peptidase-4 (DPP4) has been proven to exert its functions by both enzymatic and nonenzymatic pathways. The nonenzymatic function of DPP4 in diabetes-associated cognitive impairment remains unexplored. We determined DPP4 protein concentrations or its enzymatic activity in type 2 diabetic patients and db/db mice and tested the impact of the non-enzymatic function of DPP4 on mitochondrial dysfunction and cognitive impairment both in vivo and in vitro. The results show that increased DPP4 activity was an independent risk factor for incident mild cognitive impairment (MCI) in type 2 diabetic patients. In addition, DPP4 was highly expressed in the hippocampus of db/db mice and contributed to mitochondria dysfunction and cognitive impairment. Mechanistically, DPP4 might bind to PAR2 in the hippocampus and trigger GSK-3β activation, which downregulates peroxisome proliferator-activated receptor gamma coactivator 1 alpha expression and leads to mitochondria dysfunction, thereby promoting cognitive impairment in diabetes. Our findings indicate that the nonenzymatic function of DPP4 might promote mitochondrial dysfunction and cognitive impairment in diabetes.

Circulating ANGPTL8 levels and risk of kidney function decline: Results from the 4C Study

Background

ANGPTL8, an important regulator of lipid metabolism, was recently proven to have additional intracellular and receptor-mediated functions. This study aimed to investigate circulating levels of ANGPTL8 and its potential association with the risk of kidney function decline in a cohort study.

Methods

We analysed 2,311 participants aged 40 years old and older from the China Cardiometabolic Disease and Cancer Cohort (4C) Study. Kidney function decline was defined as an estimated glomerular filtration rate (eGFR) less than 60 mL per minute per 1.73 m² of body surface area, a decrease in eGFR of ≥ 30% from baseline, chronic kidney disease (CKD)-related hospitalization or death, or end-stage renal disease. The association between baseline ANGPTL8 levels and kidney function decline was assessed using multivariable-adjusted Cox proportional hazards models, and inverse possibility of treatment weight (IPTW) was utilized to prevent overfitting.

Results

There were 136 (5.9%) cases of kidney function decline over a median of 3.8 years of follow-up. We found that serum ANGPTL8 levels at baseline were elevated in individuals with kidney function decline compared to those without kidney function decline during follow-up (718.42 ± 378.17 vs. 522.04 ± 283.07 pg/mL, p < 0.001). Compared with the first quartile, multivariable-adjusted hazard ratio (95% confidence intervals [CIs]) for kidney function decline was 2.59 (95% CI, 1.41–4.77) for the fourth ANGPTL8 quartile. Furthermore, compared with patients in the first ANGPTL8 quartile, those in the fourth ANGPTL8 quartile were more likely to report a higher stage of CKD (relative risk: 1.33; 95% CI, 1.01–1.74). The conclusions of the regression analyses were not altered in the IPTW models. Multivariable-adjusted restricted cubic spline analyses suggested a linear relationship of ANGPTL8 with kidney function decline (p for nonlinear trend = 0.66, p for linear trend < 0.001).

Conclusions

Participants with higher circulating ANGPTL8 levels were at increased risk for kidney function decline, highlighting the importance of future studies addressing the pathophysiological role of ANGPTL8 in CKD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12933-021-01317-3.

The multi-faces of Angptl8 in health and disease: Novel functions beyond lipoprotein lipase modulation

Angiopoietin-like protein (ANGPTL) family members, mainly ANGPTL3, ANGPTL4 and ANGPTL8, are physiological inhibitors of lipoprotein lipase (LPL), and play a critical role in lipoprotein and triglyceride metabolism in response to nutritional cues. ANGPTL8 has been described by different names in various studies and has been ascribed various functions at the systemic and cellular levels. Circulating ANGPTL8 originates mainly from the liver and to a smaller extent from adipose tissues. In the blood, ANGPTL8 forms a complex with ANGPTL3 or ANGPTL4 to inhibit LPL in fed or fasted conditions, respectively. Evidence is emerging for additional intracellular and receptor-mediated functions of ANGPTL8, with implications in NFκB mediated inflammation, autophagy, adipogenesis, intra-cellular lipolysis and regulation of circadian clock. Elevated levels of plasma ANGPTL8 are associated with metabolic syndrome, type 2 diabetes, atherosclerosis, hypertension and NAFLD/NASH, even though the precise relationship is not known. Whether ANGPTL8 has direct pathogenic role in these diseases, remains to be explored. In this review, we develop a balanced view on the proposed association of this protein in the regulation of several pathophysiological processes. We also discuss the well-established functions of ANGPTL8 in lipoprotein metabolism in conjunction with the emerging novel extracellular and intracellular roles of ANGPTL8 and the implicated metabolic and signalling pathways. Understanding the diverse functions of ANGPTL8 in various tissues and metabolic states should unveil new opportunities of therapeutic intervention for cardiometabolic disorders.

Association between plasma dipeptidyl peptidase-4 activity to brain-derived neurotrophic factor ratio and depressive symptoms in middle-aged and older adults with normal glucose tolerance: A cross-sectional study

Objectives: Attenuation of brain-derived neurotrophic factor (BDNF) availability and increased dipeptidyl peptidase-4 (DPP4) activity have both been reported to link to the pathogenesis of depression. The aim of this study was to test the correlation between depressive symptoms and plasma DPP4 activity to BDNF ratio (DBR).Methods: We evaluated DPP4 activity, BDNF, oxidative stress parameters and inflammatory markers and calculated DBR in a cross-sectional sample of 1640 non-diabetic participants.Results: DPP4 activity was negatively related to BDNF in participants with and without depressive symptoms (r= -0.351 and r= -0.404, p<.001). Nitrotyrosine and 8-iso-PGF2a mediated 18.4 and 12.6% of the total effect of DPP4 activity on BDNF, respectively. 8-iso-PGF2a, nitrotyrosine, C-reactive protein, interleukin-6 and PHQ-9 score progressively increased across DBR quartiles. Participants whose DBRs were in the highest quartile had 2.64-fold increased odds (OR = 3.03) of depressive symptoms. The depressive symptoms risk increased more with lower levels of BDNF and higher levels of DPP4 activity (p<.05).Conclusions: Our data suggested inverse correlation between DPP4 activity and BDNF through the oxidative stress mediator. The positive relationship between DBR and depressive symptoms risk raises feasibility of identifying DBR as a novel biological marker or even a possible therapeutic target for depression.

Predictive values of ANGPTL8 on risk of all-cause mortality in diabetic patients: results from the REACTION Study

Background

Angiopoietin-like protein 8 (ANGPTL8), an important regulator of lipid metabolism, is increased in diabetes and is associated with insulin resistance. However, the role of ANGPTL8 in the outcomes of diabetic patients remains unclear. This study aimed to investigate circulating levels of ANGPTL8 in participants with and without diabetes and its potential associations with clinical outcomes in a 5 year cohort study.

Methods

Propensity-matched cohorts of subjects with and without diabetes from the Risk Evaluation of Cancers in Chinese Diabetic Individuals: A longitudinal (REACTION) study were generated on the basis of age, sex and body mass index at baseline. The primary outcome was all-cause mortality. The secondary outcomes were a composite of new-onset major adverse cardiovascular events, hospitalization for heart failure, and renal dysfunction (eGFR < 60/min/1.73 m²).

Results

We identified 769 matched pairs of diabetic patients and control subjects. Serum ANGPTL8 levels were elevated in patients with diabetes compared to control subjects (618.82 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pm$$\end{document}± 318.08 vs 581.20 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pm$$\end{document}± 299.54 pg/mL, p = 0.03). Binary logistic regression analysis showed that elevated ANGPTL8 levels were associated with greater risk ratios (RRs) of death (RR in quartile 4 vs. quartile 1, 3.54; 95% CI 1.32–9.50) and renal dysfunction (RR in quartile 4 vs. quartile 1, 12.43; 95% CI 1.48–104.81) only in diabetic patients. Multivariable-adjusted restricted cubic spline analyses revealed a significant, linear relationship between ANGPTL8 and all-cause mortality in diabetic patients (p for nonlinear trend = 0.99, p for linear trend = 0.01) but not in control subjects (p for nonlinear trend = 0.26, p for linear trend = 0.80). According to ROC curve analysis, the inclusion of ANGPTL8 in QFrailty score significantly improved its predictive performance for mortality in patients with diabetes.

Conclusion

Serum ANGPTL8 levels were associated with an increased risk of all-cause mortality and could be used as a potential biomarker for the prediction of death in patients with diabetes.

Association of Plasma DPP4 Activity and Brain-Derived Neurotrophic Factor With Moderate to Severe Depressive Symptoms in Patients With Type 2 Diabetes: Results From a Cross-Sectional Study

OBJECTIVE

The objective of this study was to assess the association of plasma dipeptidyl peptidase-4 (DPP4) activity, brain-derived neurotrophic factor (BDNF), and the DPP4/BDNF ratio (DBR) with moderate to severe depressive symptoms in patients with type 2 diabetes mellitus. Increased DPP4 activity and decreased BDNF in peripheral circulation have been implicated in the pathophysiology of depression.

METHODS

We performed a cross-sectional study using data from 1535 patients with type 2 diabetes mellitus. The main outcome measures were plasma DPP4 activity, BDNF levels, DBR, inflammation markers, and oxidative stress parameters. Depressive symptoms were assessed using the nine-item Patient Health Questionnaire.

RESULTS

DPP4 activity and BDNF were negatively correlated in patients with and without moderate to severe depressive symptoms (p < .001). Oxidative stress partially mediated the inverse correlation between DPP4 and BDNF. Nitrotyrosine, 8-iso-PGF2a, interleukin-6, C-reactive protein, and the nine-item Patient Health Questionnaire score increased significantly with rising quartiles of DBR. Patients in the highest quartile of DPP4 activity and DBR and lowest quartile of BDNF more often had moderate to severe depressive symptoms compared with those in the lowest quartile of DPP4 activity and DBR and the highest quartile of BDNF, respectively (p < .05). The likelihood of having moderate to severe depressive symptoms increased more with higher DPP4 activity and lower BDNF.

CONCLUSIONS

Our hypothesis-generating study demonstrates that oxidative stress might partially play a mediating role in the negative relationship between DPP4 activity and BDNF. DBR is positively related to moderate to severe depressive symptoms and thus might be used as a novel biological measure associated with depressive symptoms in patients with type 2 diabetes mellitus.

Higher circulating levels of ANGPTL8 are associated with body mass index, triglycerides, and endothelial dysfunction in patients with coronary artery disease

Bac Coronary artery disease (CAD) is the leading cause of death worldwide and most commonly develops as a result of atherosclerosis. ANGPTL8 is a secreted adipokine that regulates lipid metabolism and is associated with cardiometabolic diseases, including type 2 diabetes and CAD. However, the association between circulating ANGPTL8 levels and CAD is inconsistent among studies and the mechanism by which ANGPTL8 contributes to CAD development remains poorly understood. Here we sought to evaluate the relationship between ANGPTL8 levels and endothelial dysfunction and adipose tissue inflammation in CAD patients. Concentrations of ANGPTL8, adiponectin, TNF-α, IL6, hsCRP, ICAM-1, and VCAM-1 were measured by ELISA in serum samples from 192 CAD patients diagnosed with stenosis > 50% in at least one coronary artery by angiography and 71 individuals with normal heart function. Serum ANGPTL8 levels were significantly higher in CAD patients compared to controls (83.84 ± 23.25 ng/mL vs. 50.45 ± 17.73; p < 0.001), independent of adjustment for age, sex, BMI, smoking and statin use. ANGPTL8 could also differentiate CAD patients from controls with 82.3% specificity and 81.4% sensitivity (p < 0.001). Adiponectin levels were lower in CAD patients, while ICAM-1, VCAM-1, TNF-α, IL6, and hsCRP levels were higher compared to non-CAD controls (all p < 0.001). ANGPTL8 levels were associated with BMI in controls and with BMI, TG, and ICAM-1 in CAD patients. The presence of elevated ANGPTL8 levels in CAD patients and independent association with TG and ICAM-1 suggest a possible role related to endothelial dysfunction in the pathogenesis of atherosclerosis.

The Relationship Between Plasma DPP4 Activity to BDNF Ratio and Mild Cognitive Impairment in Elderly Population With Normal Glucose Tolerance

Objective: Since decreased brain-derived neurotrophic factor (BDNF) and increased dipeptidyl peptidase-4 (DPP4) activity have both been implicated in the pathogenesis of mild cognitive impairment (MCI), the aim of our study was to evaluate the association of MCI with plasma DPP4 activity to BDNF ratio (DBR) in an elderly population with normal glucose tolerance.

Methods: We cross-sectionally measured C-reactive protein, interleukin-6, nitrotyrosine, 8-iso-PGF2a, DPP4 activity BDNF and calculated the DBR in a total of 1,066 elderly participants in China. MCI was determined by the Montreal Cognitive Assessment and finally confirmed by neurologists.

Results: An inverse correlation was found between DPP4 activity and BDNF (r = -0.456, P < 0.001) and this inverse correlation was partly mediated by nitrotyrosine and 8-iso-PGF2a. Across rising quartiles of DBR, nitrotyrosine, 8-iso-PGF2a, C-reactive protein and interleukin-6 progressively increased, whereas the Montreal Cognitive Assessment score progressively decreased. Subjects in the lowest quartile of BDNF and highest quartiles of DBR and DPP4 activity, had higher MCI risk compared with subjects in the highest quartile of the BDNF and lowest quartiles of DBR and DPP4 activity, respectively (all P < 0.05). The odds ratio for MCI became more pronounced with decreased BDNF and increased DPP4.

Conclusion: In conclusion, a negative correlation was found between DPP4 activity and BDNF, and this negative correlation was partly mediated by oxidative stress, not inflammation. The DBR was positively associated with MCI and thus may be used as a novel risk biomarker for MCI in an elderly population with normal glucose tolerance.