Serum omentin-1 levels as a possible risk factor of mortality in patients with diabetes on haemodialysis

Omentin roles in physiology and pathophysiology: an up-to-date comprehensive review

Omentin (intelectin) was first detected in the visceral omental adipose tissue. It has mainly two isoforms, omentin-1 and -2, with isoform-1 being the main form in human blood. It possesses insulin-sensitizing, anti-inflammatory, anti-atherogenic, cardio-protective, and oxidative stress-decreasing effects. Omentin's cardiovascular protective actions are caused by the improved endothelial cell survival and function, increased endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) bioavailability, enhanced vascular smooth muscle cells (VSMCs) relaxation with reduced proliferation, decreased inflammation, and suppressed oxidative stress. Omentin may also have a potential role in different cancer types and rheumatic diseases. Thus, omentin is an excellent therapeutic target in many diseases, including diabetes mellitus (DM), metabolic syndrome (MetS), cardiovascular diseases (CVDs), inflammatory diseases, and cancer. This review demonstrates the physiological functions of omentin in ameliorating insulin resistance (IR), vascular function, and inflammation and its possible share in managing obesity-linked diseases, such as metabolic disorders, DM, and cardiovascular conditions.

The Role of Adipokines in the Pathologies of the Central Nervous System

Adipokines are protein hormones secreted by adipose tissue in response to disruptions in physiological homeostasis within the body's systems. The regulatory functions of adipokines within the central nervous system (CNS) are multifaceted and intricate, and they have been identified in a number of pathologies. Therefore, specific adipokines have the potential to be used as biomarkers for screening purposes in neurological dysfunctions. The systematic review presented herein focuses on the analysis of the functions of various adipokines in the pathogenesis of CNS diseases. Thirteen proteins were selected for analysis through scientific databases. It was found that these proteins can be identified within the cerebrospinal fluid either by their ability to modify their molecular complex and cross the blood-brain barrier or by being endogenously produced within the CNS itself. As a result, this can correlate with their measurability during pathological processes, including Alzheimer's disease, amyotrophic lateral sclerosis, multiple sclerosis, depression, or brain tumors.

The Potency of Serum Omentin-1 Quantification in Predicting Major Adverse Cardiac and Cerebrovascular Events Risk in Patients Receiving Hemodialysis

Omentin-1 regulates inflammation, lipid accumulation, endothelial dysfunction, and atherosclerosis; the latter factors contribute to the occurrence of major adverse cardiac and cerebrovascular events (MACCE). This study aimed to explore the predictive implication of serum omentin-1 for MACCE risk in patients receiving hemodialysis. A total of 319 patients receiving hemodialysis and 160 healthy controls were prospectively enrolled in this study. Omentin-1 from serum was detected by enzyme-linked immunosorbent assay. MACCE was recorded during follow-up (median 18.9 months; range 1.9-62.9 months) in patients receiving hemodialysis. Omentin-1 was reduced in patients receiving hemodialysis versus healthy controls (P < 0.001). In patients receiving hemodialysis, omentin-1 was negatively related to C-reactive protein, total cholesterol, and low-density lipoprotein cholesterol (all P < 0.05); whereas omentin-1 was not related to other clinical characteristics. Notably, the 1-year, 2-year, 3-year, 4-year, and 5-year accumulating MACCE rates in patients receiving hemodialysis were 7.9%, 18.3%, 25.9%, 36.1%, and 41.4%, respectively. Interestingly, high omentin-1 related to decreased accumulating MACCE rate (P = 0.003), which was further validated by multivariate Cox regression analysis (hazard ratio = 0.458, P = 0.006). Additionally, by direct comparison, omentin-1 was reduced in hemodialysis patients who experienced MACCE compared to those who did not (P < 0.001); meanwhile, the receiver operator characteristic curve displayed that omentin-1 had an acceptable ability to estimate MACCE risk with an area under the curve (95% confidence interval) of 0.703 (0.628-0.777). Serum omentin-1 reflects reduced inflammation and lipid accumulation, as well as predicts decreased MACCE risk in patients receiving hemodialysis.

Omentin-1 Levels and Outcomes in Incident Peritoneal Dialysis Patients

Rationale & Objective

Omentin-1 is an adipokine with anti-inflammatory and cardioprotective properties. The objective of this study was to determine the prognostic role of plasma omentin-1 levels in incident peritoneal dialysis (PD) patients.

Study Design

Retrospective analysis of prospective cohort.

Setting & Participants

152 incident PD patients.

Predictors

Plasma omentin-1 level, adipose tissue omentin-1 messenger RNA (mRNA) expression.

Outcomes

Patient survival, technique survival, hospital admission, and duration of stay.

Analytical Approach

Time-to-event survival analyses; linear regression for hospitalization.

Results

The mean age was 58.4 ± 11.7 years; 102 were men, and 92 had diabetes. There was no significant correlation between plasma omentin-1 level and its adipose tissue mRNA expression. A higher plasma omentin-1 level quartile was not associated with patient survival (P = 0.92) or technique survival (P = 0.83) but had a modest correlation with a lower number of hospital admissions (P = 0.07) and shorter duration of hospital stay (P = 0.04). In adjusted models using multivariable linear regression, a higher plasma omentin-1 level quartile remained significantly associated with fewer hospital admissions (β, -0.13; 95% CI, -0.26 to -0.002; P = 0.05) and shorter hospitalization duration (β, -0.20; 95% CI, -0.38 to -0.02; P = 0.03).

Limitations

Observational study with baseline measures only.

Conclusions

Plasma omentin-1 level was not associated with patient survival, technique survival, or peritonitis, but higher plasma omentin-1 levels were associated with fewer hospital admissions and shorter duration of hospitalization among incident PD patients.

Circulating Omentin-1, Sustained Inflammation and Hyperphosphatemia at the Interface of Subclinical Atherosclerosis in Chronic Kidney Disease Patients on Chronic Renal Replacement Therapy

Background and Objectives: Subclinical atherosclerosis, reflected by abnormal carotid intima–media thickness (cIMT), is pervasive among chronic kidney disease patients on chronic renal replacement therapy (RRT), being mostly influenced by uremia-related rather than traditional risk factors. Materials and Methods: In this pilot study, we measured circulating levels of Omentin-1, a recently discovered adipokine with strong anti-atherogenic properties, in a heterogeneous cohort of 77 asymptomatic RRT individuals (40 chronic kidney transplant recipients, Ktx; and 37 chronic hemodialysis patients, HD) and in 30 age-matched controls. Results: Omentin-1 was increased in RRT individuals as compared with controls (p = 0.03). When stratifying for renal replacement modality, we found Ktx patients to have significantly lower Omentin-1 than HD patients (p = 0.01). Lower Omentin-1 levels were also found among RRT individuals with pathological cIMT (168.7 [51.1–457.8] vs. 474.9 [197.2–1432.1]; p = 0.004). Our multivariate correlations analysis revealed Omentin-1 as the most robust independent predictor of carotid atherosclerosis (β-0.687; p = 0.03), even more than total cholesterol, diastolic BP and age, and this adipokine was at the crossroad of a complex interplay with sustained inflammation (high CRP and ferritin) and hyperphosphatemia in predicting higher cIMT values. Conclusion: The findings reported extend to renal patients with advanced disease, with the possible involvement of Omentin-1 in the pathogenesis of atherosclerosis. This may set the stage for future interventional studies of Omentin-1 replacement to retard atherosclerosis progression, as it is currently being investigated in other disease settings.

Circulating Omentin-1 levels and altered iron balance in chronic haemodialysis patients

Background

Iron deficiency is highly prevalent among patients undergoing chronic haemodialysis (HD) but its correct identification is often problematic as common biomarkers of iron status, such as transferrin saturation (TSAT) and ferritin, can be altered by inflammation or malnutrition.

Methods

In this pilot multicentre study, we aimed at evaluating circulating levels of Omentin-1, a novel fat depot-specific adipokine that is also involved in iron regulation, in a cohort of 85 chronic HD patients with relation to their iron status.

Results

Omentin-1 levels in HD were statistically higher than in healthy controls (P = 0.03) and there was a significant, growing trend in all iron parameters across Omentin-1 tertiles (P < 0.001). Compared with patients with optimal iron status, Omentin-1 levels were lower in subjects categorized according to TSAT ≤20% or serum ferritin ≤200 μg/L (both P < 0.001) and even more reduced in 19 patients (22%) simultaneously displaying low levels of both markers (P < 0.001). In this latter group, Omentin-1 levels increased in parallel to all other iron markers after iron correction by i.v. supplementation. At multivariate regression analyses, ferritin (β = 0.71; P < 0.001) and TSAT (β = 0.32; P = 0.03) remained the sole independent predictors of Omentin-1 levels. This biomarker also showed a remarkable diagnostic capacity at receiver operating characteristic analyses in identifying iron-depleted HD patients according to a criterion of TSAT ≤20% [area under the curve (AUC) 0.827], ferritin ≤200 μg/L (AUC 0.863) or low levels of both parameters (AUC 0.907).

Conclusions

Findings obtained indicate that Omentin-1 is somewhat involved in iron balance regulation and might be a candidate biomarker for diagnosing and managing altered iron conditions in HD patients.

Association between Omentin-1 and Coronary Artery Disease: Pathogenesis and Clinical Research

Like other adipokines, omentin-1 is secreted from visceral adipose tissue and plays a vital role in the development of chronic inflammatory diseases, including cardiovascular events. Recent studies have shown that circulating omentin-1 levels are associated with various metabolic risk factors, such as high blood pressure, increased waist circumference, dyslipidemia, and glucose intolerance. The decrease in serum omentin level is an independent predictor of Coronary Artery Disease (CAD) and is associated with the severity of this disease. Since there is no relevant review in the literature, we aimed to summarize the studies on the relationship between omentin-1 and CAD.

Serum omentin-1 levels in hypertensive patients

Hypertension (HT) is a disease that can cause death due to multiple target organ damage and eventually related vascular system damage. High blood pressure is known increased inflammatory activity and to cause endothelial dysfunction has been showed in HT patients. Omentin-1 is a glucoprotein of the adiponectin family released from visceral adipose tissue, endothelial cells, and visceral fat stromal-vascular cells. It has anti-inflammatory effect and circulating omentin-1 concentration correlates negatively with waist circumference, insulin resistance, and body-mass index. Serum omentin-1 is used as a biomarker of coronary artery disease, obesity, cancer, metabolic syndrome, inflammatorydisease, atherosclerosis, and diabetes mellitus. The aim of our study is to investigate circulating omentin-1 levels in HT patients compared to healthy normotensive controls. Patients diagnosed with new essential HT (n = 61) and healthy normotensive individuals (n = 60) were enrolled in this study. The HT group was separated into two subgroups. There were 30 patients in stage 2 HT group and 31 patients in stage 1 HT group. Omentin-1 levels were significantly lower both in stage 1 and 2 HT subgroup as compared with the normotensive controls (72.19 ± 54.33 ng/ml for stage 1 HT subgroup; 62.45 ± 47.01 ng/ml for stage 2 HT subgroup; and, 147.84 ± 58.55 ng/ml for healthy normotensive controls; overall P < 0.001). The present study demonstrated that serum Omentin-1 levels decreased in patients with HT compared with normotensive controls. These lower concentrations may be attributed to a combined outcome of endothelial dysfunction, renal injury, and inflammation in the setting of hypertension.

The relation between epicardial fat tissue thickness and atrial fibrillation ın hemodialysis patients

The prevalence of arrhythmia has increased in hemodialysis (HD) patients and the most frequent is atrial fibrillation (AF). It was reported that the amount of epicardial fat tissue (EFT) in the population without renal disease is closely related to AF. In the present study of ours, the relation between EFT thickness and AF was examined in HD patients. A total of 79 patients who underwent HD for periods longer than 3 months were included in the study. The mean age of the patients was 53.6 ± 15.2 years and 50.6% were male. The mean EFT thicknesses were measured as 7.2 ± 2.3 mm (3-12). A positive correlation was found between the EFT thickness and age, C-reactive protein, and left ventricle rear wall thickness. AF was found in 18 (22.8%) patients in the Holter ECG examination. When the group with AF was compared with the non-AF group; although the mean HD duration of the group with AF was longer, there were no significant differences in terms of epicardial adipose tissue thickness and other parameters. In the present study, no relations were found between EFT thickness and AF frequency in HD patients. Further studies with a larger number of the patient population are needed in this regard.

New Insights into Adipokines as Potential Biomarkers for Type-2 Diabetes Mellitus

A large number of studies have been focused on investigating serum biomarkers associated with risk or diagnosis of type-2 diabetes mellitus. In the last decade, promising studies have shown that circulating levels of adipokines could be used as a relevant biomarker for diabetes mellitus progression as well as therapeutic future targets. Here, we discuss the possible use of recently described adipokines, including apelin, omentin-1, resistin, FGF-21, neuregulin-4 and visfatin, as early biomarkers for diabetes. In addition, we also include recent findings of other well known adipokines such as leptin and adiponectin. In conclusion, further studies are needed to clarify the pathophysiological significance and clinical value of these biological factors as potential biomarkers in type-2 diabetes and related dysfunctions.

The association between omentin and diabetes: a systematic review and meta-analysis of observational studies

AIMS

A number of studies have examined the association between the serum levels of omentin and diabetes, but the findings have been inconclusive. Herein, we systematically reviewed available observational studies to elucidate the overall relationship between omentin and diabetes, including type 1 diabetes mellitus (T1DM), type 2 diabetes mellitus (T2DM), and impaired glucose tolerance (IGT) among adolescent and adult population.

METHODS

PubMed, Cochrane's Library, Science Direct, Scopus, Google Scholar, and ISI Web of Science databases were searched for all available literature until January 2019 for studies assessing the association between omentin and diabetes. The Newcastle-Ottawa Quality Assessment Scale was used to assess the quality of each study.

RESULTS

A total of 28 articles met the inclusion criteria and were included in our systematic review and meta-analysis. There was a significant association between serum omentin and diabetes (WMD-1.68; 95% CI, -2.17 to -1.19; P<0.001). The result of our sub-group analysis based on participants' health status revealed that omentin was significantly lower in T2DM and IGT subjects but not in T1DM ones compared to healthy controls.

CONCLUSION

We found that serum omentin level is significantly lower in T2DM and IGT patients but not in T1DM ones. These data could be used by clinicians for early diagnosis and management of diabetes. Furthermore, we need more clinical trials to investigate new agents which could influence omentin levels.

The complex effects of adipokines in the patients with kidney disease

Kidney diseases are categorized as the highest prevalent ones with worldwide noticeable incidence. They cause accelerated cardiovascular diseases and noticeable mortalities. Adipose tissue and its messengers, adipokines, are reported to have the highest relationship with end-stage renal diseases or chronic kidney diseases. Over recent years, with shifting of scientists’ mindset from a simple overview of adipose tissue as a fat store to the complex paradigm of this issue as a multipotential secretory organ, the importance of studies on this tissue has emerged.

Immunometabolic Regulation of Vascular Redox State: The Role of Adipose Tissue

SIGNIFICANCE

Vascular oxidative stress plays a crucial role in atherogenesis and cardiovascular disease (CVD). Recent evidence suggests that vascular redox state is under the control of complex pathophysiological mechanisms, ranging from inflammation to obesity and insulin resistance (IR). Recent Advances: Adipose tissue (AT) is now recognized as a dynamic endocrine and paracrine organ that secretes several bioactive molecules, called adipokines. AT has recently been shown to regulate vascular redox state in both an endocrine and a paracrine manner through the secretion of adipokines, therefore providing a mechanistic link for the association between obesity, IR, inflammation, and vascular disease. Importantly, AT behaves as a sensor of cardiovascular oxidative stress, modifying its secretory profile in response to cardiovascular oxidative injury.

CRITICAL ISSUES

The present article presents an up-to-date review of the association between AT and vascular oxidative stress. We focus on the effects of individual adipokines on modulating reactive oxygen species production and scavenging in the vascular wall. In addition, we highlight how inflammation, obesity, and IR alter the biology and secretome of AT leading to a more pro-oxidant phenotype with a particular focus on the local regulatory mechanisms of perivascular AT driven by vascular oxidation.

FUTURE DIRECTIONS

The complex and dynamic biology of AT, as well as its importance in the regulation of vascular redox state, provides numerous opportunities for the development of novel, targeted treatments in the management of CVD. Therapeutic modulation of AT biology could improve vascular redox state affecting vascular disease pathogenesis. Antioxid. Redox Signal. 29, 313-336.

Adipose Tissue-Derived Omentin-1 Function and Regulation

Omentin-1, also known as intelectin-1, is a recently identified novel adipocytokine of 313 amino acids, which is expressed in visceral (omental and epicardial) fat as well as mesothelial cells, vascular cells, airway goblet cells, small intestine, colon, ovary, and plasma. The level of omentin-1 expression in (pre)adipocytes is decreased by glucose/insulin and stimulated by fibroblast growth factor-21 and dexamethasone. Several lines of experimental evidence have shown that omentin-1 plays crucial roles in the maintenance of body metabolism and insulin sensitivity, and has anti-inflammatory, anti-atherosclerotic, and cardiovascular protective effects via AMP-activated protein kinase/Akt/nuclear factor-κB/mitogen-activated protein kinase (ERK, JNK, and p38) signaling. Clinical studies have indicated the usage of circulating omentin-1 as a biomarker of obesity, metabolic disorders including insulin resistance, diabetes, and metabolic syndrome, and atherosclerotic cardiovascular diseases. It is also possible to use circulating omentin-1 as a biomarker of bone metabolism, inflammatory diseases, cancers, sleep apnea syndrome, preeclampsia, and polycystic ovary syndrome. Decreased omentin-1 levels are generally associated with these diseases. However, omentin-1 increases to counteract the acute phase after onset of these diseases. These findings indicate that omentin-1 may be a negative risk factor for these diseases, and also act as an acute-phase reactant by its anti-inflammatory and atheroprotective effects. Therapeutic strategies to restore omentin-1 levels may be valuable for the prevention or treatment of these diseases. Weight loss, olive oil-rich diet, aerobic training, and treatment with atorvastatin and antidiabetic drugs (metformin, pioglitazone, and exenatide) are effective means of increasing circulating omentin-1 levels. This review provides insights into the potential use of omentin-1 as a biomarker and therapeutic target for these diseases. © 2017 American Physiological Society. Compr Physiol 7:765-781, 2017.