Elevation of serum apelin-13 associated with proliferative diabetic retinopathy in type 2 diabetic patients

Protamine as a barrier against the angiogenic effect of insulin: a possible role of apelin

Insulin is proved to have angiogenic ability thereby may worsen the diabetic retinopathy (DR) progression. Insulin also triggers the expression of endogenous angiogenic peptide, apelin. Since protamine was introduced as an inhibitor of the apelin receptor, we hypothesized that use of protaminated insulin instead of non-protaminated insulin can decrease the negative role of insulin in progression of DR. Firstly, the incidence of DR was compared among three diabetic patient groups: an oral medication, non-protaminated insulin, and protaminated insulin (PIns). Proliferation and migration rate of HUVECs was measured after insulin, apelin, and protamine exposure. In clinical study, the chance of developing DR was 8.5 and 4.1 times higher in insulin group and PIns groups compared with oral group respectively. Insulin group had a chance of 9.5-folds of non-proliferative DR compared to oral group. However, the difference of non-proliferative DR between PIns and oral group wasn't significant. In-vitro tests showed that concomitant use of insulin and apelin increases viability and migratory potential of HUVECs. However, protamine could reverse this effect. Protamine present in some insulins might show a promising protective role against diabetic retinopathy. Thus, protaminated insulins may be preferable in the treatment of diabetes.

Association between adipocytokines and diabetic retinopathy: a systematic review and meta-analysis

Background

Diabetic retinopathy (DR) is a common complication of diabetes. The adipocytokines are closely associated with the occurrence and development of diabetes and its related complications. Literature confirms that the level of adiponectin in patients with DR is significantly higher; however, the relationship between other adipocytokines (leptin, chemerin, apelin, and omentin-1) and DR remains unclear.

Aim

This study aimed to systematically evaluate the association between adipocytokines (leptin, chemerin, apelin, and omentin-1) and DR.

Methods

The PubMed, Web of Science, Embase, EBSCO and Willy databases were used to search for potential studies with keywords such as "diabetic retinopathy" or "DR" in combination with the terms "leptin," "chemerin", "apelin" or "omentin-1" in the search titles or abstracts. Standardized mean differences (SMD) with corresponding 95% confidence intervals (CIs) were determined as the results of the meta-analysis.

Results

After screening, 18 articles were included in the meta-analysis including 750 DR cases and 993 controls. Leptin and chemerin levels in patients with DR were significantly higher than those in the control group (SMD: 0.68, 95% CI [0.1, 1.26]; SMD: 0.79, 95% CI [0.35, 1.23]). The omentin-1 levels in patients with DR were significantly lower than those in the controls (SMD: -0.85, 95% CI [-1.08, -0.62]).

Conclusions

To the best of our knowledge, this is the first meta-analysis to evaluate the leptin, chemerin, apelin, and omentin-1 levels in patients with DR. Further high-quality studies are warranted to support the association between these adipocytokines and DR.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=443770, identifier CRD42023443770.

The role of apelinergic system in metabolism and reproductive system in normal and pathological conditions: an overview

Lifestyle changes have made metabolic disorders as one of the major threats to life. Growing evidence demonstrates that obesity and diabetes disrupt the reproductive system by affecting the gonads and the hypothalamus-pituitary-gonadal (HPG) axis. Apelin, an adipocytokine, and its receptor (APJ) are broadly expressed in the hypothalamus nuclei, such as paraventricular and supraoptic, where gonadotropin-releasing hormone (GnRH) is released, and all three lobes of the pituitary, indicating that apelin is involved in the control of reproductive function. Moreover, apelin affects food intake, insulin sensitivity, fluid homeostasis, and glucose and lipid metabolisms. This review outlined the physiological effects of the apelinergic system, the relationship between apelin and metabolic disorders such as diabetes and obesity, as well as the effect of apelin on the reproductive system in both gender. The apelin-APJ system can be considered a potential therapeutic target in the management of obesity-associated metabolic dysfunction and reproductive disorders.

Potential impact of epicardial fat thickness, pentraxin-3, and high-sensitive C-reactive protein on the risk of non-proliferative diabetic retinopathy

Purpose

We tried to clarify the potential association between systemic inflammatory markers like high-sensitive C-reactive protein (Hs-CRP), pentraxin-3 (PTX3), and epicardial fat thickness (EFT) with the non-proliferative diabetic retinopathy (NPDR) in patients with type 2 diabetes mellitus (T2D). Previous studies dealt with diabetic retinopathy as a whole entity rather than early stages of diabetic retinopathy. Early detection of various determinants of NPDR is prioritized in clinical practice.

Methods

A case-control study was conducted at Mansoura University Hospital, included 207 Egyptian subjects divided into 3 groups; 69 diabetic patients without retinopathy, 69 diabetic patients with NPDR, and 69 healthy control subjects. Participants were subjected to clinical history taking, physical examination, and laboratory assessment of Hs-CRP and plasma PTX3. Transthoracic echocardiography was applied to estimate EFT.

Results

Hs-CRP, PTX3, and EFT were significantly higher in patients with T2D without retinopathy than control cohort (p = 0.033, p < 0.00 and p < 0.00, respectively). Moreover, patients with NPDR showed significantly higher values of Hs-CRP, PTX3, and EFT than diabetic comparators without retinopathy (p = 0.002, p = 0.012, and p < 0.001, respectively). Although, NPDR was positively correlated with Hs-CRP, PTX3, and EFT (p < 0.001), Hs-CRP was not an independent determinant of NPDR meanwhile, EFT (OR = 1.094, 95%CI: 1.036-1.154, P = 0.001) and PTX3 (OR = 16.145, 95%CI: 1.676-155.551, P = 0.016) were.

Conclusion

Plasma pentraxin-3 and epicardial fat thickness showed more significant association with NPDR than high-sensitive C-reactive protein in patients with type 2 diabetes mellitus.

Low serum apelin levels are associated with mild cognitive impairment in Type 2 diabetic patients

BACKGROUND

Apelin is a new adipokine that is secreted by adipocytes, and is associated with insulin resistance (IR), inflammation, and obesity. This study was designed to investigate the role of apelin in type 2 diabetes mellitus (T2DM) patients with mild cognitive impairment (MCI).

METHODS

A total of 235 patients with T2DM were included. The cognitive function of patients was evaluated using Montreal Cognitive Assessment (MoCA) tool, then patients were divided into MCI group and non-MCI group according to the MoCA score. Blood sample was analyzed for the level of apelin by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The MCI group (n = 73) presented lower serum apelin levels compared with the patients with normal cognitive function (P < 0.001). Apelin levels showed significantly negative correlation with diabetes duration, triglyceride (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C, creatinine and high sensitivity C-reactive protein (hs-CRP), and positive correlation with high-density lipoprotein cholesterol (HDL-C) and brain-derived neurotrophic factor (BDNF). Multivariable logistic regression analysis indicated that serum apelin (OR = 0.304, 95%CI: 0.104-0.886, P = 0.029), as well as education levels, diabetes duration, cardiovascular disease, serum HbA1c, HDL-C, creatinine, and BDNF, were independent risk factors of MCI in patients with T2DM.

CONCLUSIONS

Serum apelin level is reduced in T2DM patients with MCI. Apelin might has protective effect against cognitive impairment and serve as a serum biomarker of T2DM.

The therapeutic potential of apelin in kidney disease

Chronic kidney disease (CKD) is a leading cause of global morbidity and mortality and is independently associated with cardiovascular disease. The mainstay of treatment for CKD is blockade of the renin-angiotensin-aldosterone system (RAAS), which reduces blood pressure and proteinuria and slows kidney function decline. Despite this treatment, many patients progress to kidney failure, which requires dialysis or kidney transplantation, and/or die as a result of cardiovascular disease. The apelin system is an endogenous physiological regulator that is emerging as a potential therapeutic target for many diseases. This system comprises the apelin receptor and its two families of endogenous ligands, apelin and elabela/toddler. Preclinical and clinical studies show that apelin receptor ligands are endothelium-dependent vasodilators and potent inotropes, and the apelin system has a reciprocal relationship with the RAAS. In preclinical studies, apelin regulates glomerular haemodynamics and acts on the tubule to promote aquaresis. In addition, apelin is protective in several kidney injury models. Although the apelin system has not yet been studied in patients with CKD, the available data suggest that apelin is a promising potential therapeutic target for kidney disease.

VEGF, apelin and HO-1 in diabetic patients with retinopathy: a correlation analysis

BACKGROUND

It's necessary to analyze the role of VEGF, apelin, and HO-1 in patients with type 2 diabetes (T2DM), and to evaluate its relevance to diabetic retinopathy (DR).

METHODS

T2DM patients who were treated in our hospital from December 1, 2018 to November 30, 2019 were included. T2DM patients were divided into non-DR (NDR) group, non-proliferative DR (NPDR) group, and proliferative DR (PDR) group. and healthy participants were selected as the control group. The value of VEGF, apelin, and HO1 in predicting PDR were analyzed by receiver operating characteristic (ROC) curve, and the relations of VEGF, apelin, HO-1 and clinical factors in PDR patients were analyzed by Pearson correlation analysis.

RESULTS

A total of 295 participants were included. The level of FPG and HbAlc in PDR group were significantly higher than that of other groups (all p < 0.05); the level of VEGF and apelin in PDR group were significantly higher than that of other groups (all p < 0.05), but the level of HO-1 in PDR group were significantly less than that of other groups(p = 0.017); the AUC of VEGF, apelin, HO-1 and combined use was 0.806(95%CI: 0.779-0.861), 0.819(95%CI: 0.765-0.878), 0.808(95%CI: 0.733-0.869) and 0.902(95%CI: 0.822-0.958) respectively, the AUC, sensitivity, specificity of the three combined use was significantly higher than that of single VEGF, apelin, HO-1 use(all p < 0.05). The cutoff values of serum VEGF, apelin, and HO-1 levels for predicting PDR were 163.85 pg/ml, 8.27 ng/ml, and 26.06 mmol/L respectively. Serum VEGF, apelin, and HO-1 in patients with PDR was related to the time course of DM, FPG and HbAlc (all p < 0.05).

CONCLUSIONS

VEGF, apelin and HO-1 are related to the progress of DR, and the combined use of VEGF, apelin and HO-1 is beneficial to the diagnosis and treatment of PDR.

Proteomic Biomarkers of Retinal Inflammation in Diabetic Retinopathy

Diabetic retinopathy (DR), a sight-threatening neurovasculopathy, is the leading cause of irreversible blindness in the developed world. DR arises as the result of prolonged hyperglycemia and is characterized by leaky retinal vasculature, retinal ischemia, retinal inflammation, angiogenesis, and neovascularization. The number of DR patients is growing with an increase in the elderly population, and therapeutic approaches are limited, therefore, new therapies to prevent retinal injury and enhance repair are a critical unmet need. Besides vascular endothelial growth factor (VEGF)-induced vascular proliferation, several other mechanisms are important in the pathogenesis of diabetic retinopathy, including vascular inflammation. Thus, combining anti-VEGF therapy with other new therapies targeting these pathophysiological pathways of DR may further optimize treatment outcomes. Technological advancements have allowed for high-throughput proteomic studies examining biofluids such as aqueous humor, vitreous humor, tear, and serum. Many DR biomarkers have been identified, especially proteins involved in retinal inflammatory processes. This review attempts to summarize the proteomic biomarkers of DR-associated retinal inflammation identified over the last several years.

Vascular effects of apelin: Mechanisms and therapeutic potential

Apelin is a vasoactive peptide and is an endogenous ligand for APJ receptors, which are widely expressed in blood vessels, heart, and cardiovascular regulatory regions of the brain. A growing body of evidence now demonstrates a regulatory role for the apelin/APJ receptor system in cardiovascular physiology and pathophysiology, thus making it a potential target for cardiovascular drug discovery and development. Indeed, ongoing studies are investigating the potential benefits of apelin and apelin-mimetics for disorders such as heart failure and pulmonary arterial hypertension. Apelin causes relaxation of isolated arteries, and systemic administration of apelin typically results in a reduction in systolic and diastolic blood pressure and an increase in blood flow. Nonetheless, vasopressor responses and contraction of vascular smooth muscle in response to apelin have also been observed under certain conditions. The goal of the current review is to summarize major findings regarding the apelin/APJ receptor system in blood vessels, with an emphasis on regulation of vascular tone, and to identify areas of investigation that may provide guidance for the development of novel therapeutic agents that target this system.

Apelin-13 Is an Early Promoter of Cytoskeleton and Tight Junction in Diabetic Macular Edema via PI-3K/Akt and MAPK/Erk Signaling Pathways

Diabetic macular edema is major cause of vision loss associated with diabetic retinopathy. Breakdown of blood-retinal barrier, especially inner BRB, is an early event in pathogenesis of DR. Apelin, an endogenous ligand of APJ, mediates angiogenesis and is involved in the development of DR. The present study aimed to investigate effects and mechanism of apelin-13 in vascular permeability during DME. We verified apelin-13 was upregulated in DME patients' vitreous. High glucose incubation led to a progressive increase of apelin-13, APJ, cytoskeleton, and tight junction proteins, including VE-Cadherin, FAK, Src, ZO-1, and occludin. Apelin-13 promoted HRMEC proliferation and migration and phosphorylation of both cytoskeleton and tight junction under both normal and high glucose conditions. Besides, apelin-13 activated PI-3K/Akt and MAPK/Erk signaling pathways, including PLCγ1, p38, Akt, and Erk both in HRMEC and in C57BL/6 mice. Meanwhile, F13A performed opposite effects compared with apelin-13. In in vivo study, apelin-13 was also upregulated in retina of db/db mice. Taken together, apelin-13 increased biologic activity of HRMEC, as well as expression of both cytoskeleton and tight junction in DME via PI-3K/Akt and MAPK/Erk signaling pathways. Apelin-13 as an early promoter of vascular permeability may offer a new perspective strategy in early treatment of DR.

Influence of Apelin-13 on osteoporosis in Type-2 diabetes mellitus: A clinical study

Objective:

To investigate the relationship between serum level of Apelin-13 and bone mineral density (BMD) as well as other parameters, and determine the influence of Apelin-13 on osteoporosis in patients with Type-2 diabetes mellitus.

Methods:

Seventy-six patients with Type-2 diabetes mellitus were recruited from Department of Endocrinology of our hospital between January 2013 and July2017. The clinical data, including age, gender, height, weight, body mass index (BMI) and disease duration were recorded for all patients. Blood sample was collected for measurement of Apelin-13, Procollagen type-I N propeptide (PINP) and Cross-linked carboxy terminal telopeptide of type-I collagen (ICTP), and BMD was tested with a dual-energy X-ray absorptiometry scanner.

Results:

The patients were divided into three groups, in which 19 patients were assigned in osteoporosis group, 25 in osteopenia group and 32 in normal group. The level of Apelin-13 in osteoporosis group was significantly lower than that in osteopenia and normal groups (p<0.05), and the value in osteopenia group was significant lower than that in normal group (p<0.05). Correlation analysis showed in the included patients the level of Apelin-13 was positively correlated to the value of BMD and PINP (p<0.05), but negatively correlated to age and ICTP (p<0.05).

Conclusion:

In conclusion, this study demonstrated that there was a close relationship among Apelin-13, BMD, ICTP and PINP, and Apelin-13 plays an important role in the occurrence of osteoporosis in patients with Type-2 diabetes mellitus.

Molecular Markers of Diabetic Retinopathy: Potential Screening Tool of the Future?

Diabetic retinopathy (DR) is among the leading causes of new onset blindness in adults. Effective treatment may delay the onset and progression of this disease provided it is diagnosed early. At present retinopathy can only be diagnosed via formal examination of the eye by a trained specialist, which limits the population that can be effectively screened. An easily accessible, reliable screening biomarker of diabetic retinopathy would be of tremendous benefit in detecting the population in need of further assessment and treatment. This review highlights specific biomarkers that show promise as screening markers to detect early diabetic retinopathy or even to detect patients at increased risk of DR at the time of diagnosis of diabetes. The pathobiology of DR is complex and multifactorial giving rise to a wide array of potential biomarkers. This review provides an overview of these pathways and looks at older markers such as advanced glycation end products (AGEs), inflammatory markers, vascular endothelial growth factor (VEGF) as well as other newer proteins with a role in the pathogenesis of DR including neuroprotective factors such as brain derived neurotrophic factor (BDNF) and Pigment Epithelium Derived Factor (PEDF); SA100A12, pentraxin 3, brain natriuretic peptide, apelin 3, and chemerin as well as various metabolites such as lipoprotein A, folate, and homocysteine. We also consider the possible role of proteins identified through proteomics work whose levels are altered in the sera of patients with DR as screening markers though their role in pathophysiology remains to be characterized. The role of microRNA as a promising new screening marker is also discussed.

Relationship between C-Reactive Protein Level and Diabetic Retinopathy: A Systematic Review and Meta-Analysis

Objectives

To date, the relationship between C-reactive protein (CRP) level and diabetic retinopathy (DR) remains controversial. Therefore, a systematic review and meta-analysis was used to reveal the potential relationship between CRP level and DR.

Methods

A systematic search of PubMed, Embase.com, and Web of Science was performed to identify all comparative studies that compared the CRP level of two groups (case group and control group). We defined that diabetic patients without retinopathy and /or matched healthy persons constituted the control group, and patients with DR were the case group.

Results

Two cross sectional studies and twenty case control studies including a total of 3679 participants were identified. After pooling the data from all 22 studies, obvious heterogeneity existed between the studies, so a subgroup analysis and sensitivity analysis were performed. Removing the sensitivity studies, the blood CRP levels in the case group were observed to be higher than those in the control group [SMD = 0.22, 95% confidence interval (CI), 0.11–0.34], and the blood CRP levels in the proliferative diabetic retinopathy (PDR) group were also higher than those in the non-proliferative diabetic retinopathy (NPDR) group [SMD = 0.50, 95% CI, 0.30–0.70].

Conclusions

The results from this current meta-analysis indicate that the CRP level might be used as a biomarker to determine the severity of DR.