Osteoprotegerin is associated with cardiovascular risk in hypertension and/or diabetes

Distinct Roles of Common Genetic Variants and Their Contributions to Diabetes: MODY and Uncontrolled T2DM

Type 2 diabetes mellitus (T2DM) encompasses a range of clinical manifestations, with uncontrolled diabetes leading to progressive or irreversible damage to various organs. Numerous genes associated with monogenic diabetes, exhibiting classical patterns of inheritance (autosomal dominant or recessive), have been identified. Additionally, genes involved in complex diabetes, which interact with environmental factors to trigger the disease, have also been discovered. These genetic findings have raised hopes that genetic testing could enhance diagnostics, disease surveillance, treatment selection, and family counseling. However, the accurate interpretation of genetic data remains a significant challenge, as variants may not always be definitively classified as either benign or pathogenic. Research to date, however, indicates that periodic reevaluation of genetic variants in diabetes has led to more consistent findings, with biases being steadily eliminated. This has improved the interpretation of variants across diverse ethnicities. Clinical studies suggest that genetic risk information may motivate patients to adopt behaviors that promote the prevention or management of T2DM. Given that the clinical features of certain monogenic diabetes types overlap with T2DM, and considering the significant role of genetic variants in diabetes, healthcare providers caring for prediabetic patients should consider genetic testing as part of the diagnostic process. This review summarizes current knowledge of the most common genetic variants associated with T2DM, explores novel therapeutic targets, and discusses recent advancements in the pharmaceutical management of uncontrolled T2DM.

Osteoprotegerin as an Emerging Biomarker of Carotid Artery Stenosis? A Scoping Review with Meta-Analysis

Objective: In developed countries, stroke is the fifth cause of death, with a high mortality rate, and with recovery to normal neurological function in one-third of survivors. Atherosclerotic occlusive disease of the extracranial part of the internal carotid artery and related embolic complications are common preventable causes of ischemic stroke (IS), attributable to 7-18% of all first-time cases. Osteoprotegerin (OPG), a soluble member of the tumor necrosis factor receptor (TNFR) superfamily, is considered a modulator of vascular calcification linked to vascular smooth muscle cell proliferation and collagen production in atherosclerotic plaques. Therefore, OPG emerges as a potential biomarker (BM) of calcified carotid plaques and carotid artery stenosis (CAS). Methods: We performed a literature search of PubMed on OPG in CAS and atherosclerosis published until 2024. Results: Increased levels of serum OPG were reported in both patients with symptomatic and asymptomatic CAS, and higher values were observed in those with unstable atherosclerotic plaques. Notably, increased OPG levels were observed regardless of the location of atherosclerosis, including coronary and other peripheral arteries. In addition, chronic kidney disease, the most significant confounder disturbing the association between vascular damage and circulating OPG levels, decreases the usefulness of OPG as a BM in CAS. Conclusions: Osteoprotegerin may be considered an emerging BM of global rather than cerebrovascular atherosclerosis. Its diagnostic significance in identifying patients with asymptomatic CAS and their monitoring is limited.

Circulating osteoprotegerin as a cardiac biomarker for left ventricular diastolic dysfunction in patients with pre-dialysis chronic kidney disease: the KNOW-CKD study

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) is a major cause of mortality in patients with chronic kidney disease (CKD), and diagnosis is challenging. Moreover, no specific biomarker for HFpEF has been validated in patients with CKD. The present study aimed to investigate the association between serum osteoprotegerin (OPG) levels and the risk of left ventricular diastolic dysfunction (LVDD), a surrogate of HFpEF, in patients with pre-dialysis CKD.

METHODS

A total of 2039 patients with CKD at stage 1 to pre-dialysis 5 were categorized into quartiles (Q1 to Q4) by serum OPG levels, and were cross-sectionally analyzed. The study outcome was LVDD, which was operationally defined as the ratio of early transmitral blood flow velocity to early diastolic velocity of the mitral annulus (E/e') > 14.

RESULTS

In the analysis of baseline characteristics, higher serum OPG levels were clearly related to the risk factors of HFpEF. A scatter plot analysis revealed a moderate correlation between serum OPG levels and E/e' (R = 0.351, P < 0.001). Logistic regression analysis demonstrated that the risk of LVDD in Q3 (adjusted odds ratio 2.576, 95% confidence interval 1.279 to 5.188) and Q4 (adjusted odds ratio 3.536, 95% confidence interval 1.657 to 7.544) was significantly higher than that in Q1.

CONCLUSIONS

Elevated serum OPG levels are associated with the risk of LVDD in patients with pre-dialysis CKD. The measurement of serum OPG levels may help the diagnosis of LVDD, which is an important echocardiographic feature of HFpEF.

Osteoprotegerin is associated with subclinical left ventricular systolic dysfunction in non-dipper hypertensive patients: a 2D speckle tracking echocardiographic study

BACKGROUND

Past studies have shown that non-dipper hypertensive patients have more frequent subclinical left ventricular (LV) systolic dysfunction compared to dippers. Many different parameters have been examined to predict subclinical LV dysfunction. The role of osteoprotegerin (OPG) in the pathogenesis of heart failure and LV systolic dysfunction through different mechanisms had well described. In the present study, we hypothesized that increased OPG levels could predict subclinical LV systolic dysfunction in non-dipper hypertensive patients.

PATIENTS AND METHODS

Hypertensive patients were divided into two groups according to the results of ambulatory blood pressure (BP) monitoring. Non-dipper patients were subsequently divided into two further groups (normal LV function and impaired LV function) according to LV global longitudinal strain (GLS).

RESULTS

A total of 103 hypertensive patients (51 dippers, 52 non-dippers) were included in the study. In the non-dipper group, LV GLS was normal in 21 patients and impaired in 31 patients. Based on the results of the multivariate logistic regression test, it was determined that OPG levels (OR: 2.413, 95% CI: 1.284-4.535, P  = 0.006) and LVMI (OR: 1.086, 95% CI: 1.013-1.165, P  = 0.021) were independently associated with impaired GLS.

CONCLUSION

Higher OPG values were associated with subclinical LV systolic dysfunction in non-dipper hypertensive patients. It could be used for the early diagnosis of subclinical LV systolic dysfunction, which would allow for strategies to be designed to reduce the cardiovascular event rate in this patient population.

Association of rs2073618 polymorphism and osteoprotegerin levels with hypertension and cardiovascular risks in patients with type 2 diabetes mellitus

There are reports of link of osteoprotegerin (OPG) gene polymorphism to type-2 diabetes (T2D) and hypertension (HTN). The objective of the study was to assess the allele frequency of OPG (rs2073618) gene polymorphism and its association with heart rate variability (HRV) and blood pressure variability profile as CVD risks in diabetes mellitus patients with hypertension undergoing treatment. T2D patients on treatment without hypertension (n = 172), with hypertension (n = 177) and 191 healthy volunteers were recruited for the study. Their blood pressure variability including baroreflex sensitivity (BRS), heart rate variability (HRV), OPG, insulin, lipid profile, receptor-activator for NFkB (RANK), receptor-activator for NFkB-Ligand (RANKL), and tumor necrosis factor-α (TNF-α) were estimated. Allele frequency of OPG (rs2073618) gene polymorphism was assessed from the DNA samples. BRS and HRV indices were decreased, and RANKL/OPG and TNF-α were increased in T2D and T2D + HTN groups, respectively compared to healthy control group. The reduction in BRS was contributed by increased inflammation and reduced SDNN of HRV in GG genotype in T2D + HTN. In GG + GC subgroup, it was additionally contributed by rise in RANKL/OPG level (β - 0.219; p 0.008). Presence of mutant GG genotype contributed to the risk of hypertension among T2D patients (OR 3.004) as well as in general population (OR 2.79). It was concluded that CV risks are more in T2D patients with HTN expressing OPG rs2073618 gene polymorphism.

Serum Osteoprotegerin Levels and the Vascular Reactivity Index in Patients with Hypertension

Background and Objectives: Osteoprotegerin (OPG), a soluble glycoprotein found in serum, has been associated with both the presence and severity of atherosclerosis. OPG is regarded as the mediator in the process of vascular endothelial dysfunction. Impaired endothelial function has an intimate link with hypertension (HTN) and is associated with significant morbidity and mortality. This study was to investigate the connection between OPG and endothelial dysfunction in patients having HTN. Materials and Methods: There are 102 patients with HTN included. For the purpose of determining the levels of OPG, a commercial enzyme-linked immunosorbent test kit was applied. The vascular reactivity index (VRI), which is assessed via the digital thermal monitoring, provides information on endothelial function. Results: Ten patients with HTN (9.8%) were classified as having poor vascular reactivity (VRI < 1.0), 46 HTN patients (45.1%) as having intermediate vascular reactivity (1.0 ≤ VRI < 2.0), and 46 HTN patients (45.1%) were classified as having high vascular reactivity (VRI ≥ 2.0). A greater serum OPG level (p < 0.001) and older age (p = 0.022) were linked to impaired vascular reactivity. The estimated glomerular filtration rate (r = 0.196, p = 0.048) was positively correlated with VRI values in hypertensive participants, while advanced age (r = -0.222, p = 0.025) and the log-transformed OPG level (log-OPG, r = -0.357, p < 0.001) were negatively correlated with VRI. Serum log-OPG level was shown to be strongly and independently correlated with VRI values in HTN individuals after multivariable forward stepwise linear regression analysis (β = -0.357, adjusted R2 change = 0.119, p < 0.001). Conclusions: In patients with HTN, serum OPG levels were adversely correlated with VRI and probably had a role in endothelial dysfunction.

Role of cerebral microbleeds in acute ischemic stroke and atrial fibrillation

Cerebral microbleeds (CMBs) are commonly detected in the brains of patients with acute ischemic stroke (AIS). With the development of neuroimaging, clinicians are paying more attention to the presence of CMBs. CMBs were found to significantly increase the risk of intracranial hemorrhagic transformation and hemorrhage in patients with AIS, especially in patients with concurrent atrial fibrillation (AF). Additionally, the presence of CMBs is thought to be a symbol of a high risk of recurrent ischemic stroke (IS). A few researchers have found that the presence of CMBs has no significant effect on the prognosis of patients with AIS. Therefore, the current views on the role of CMBs in the prognoses of patients with IS are controversial. The use of anticoagulants and other drugs has also become a dilemma due to the special influence of CMBs on the prognosis of these patients. Due to the large number of patients with AF and CMBs, many studies have been conducted on the effects of CMBs on these patients and subsequent pharmacological treatments. However, at present, there are no relevant guidelines to guide the secondary preventive treatment of patients with stroke, CMBs, and AF. In this paper, we summarized the role of CMBs in AIS combined with AF and relevant preventive measures against the recurrence of stroke and the occurrence of intracerebral hemorrhage to help clarify the specifics of drug therapies for this group of patients.

Roles of osteoprotegerin in endocrine and metabolic disorders through receptor activator of nuclear factor kappa-B ligand/receptor activator of nuclear factor kappa-B signaling

Endocrine and metabolic diseases show increasing incidence and high treatment costs worldwide. Due to the complexity of their etiology and mechanism, therapeutic strategies are still lacking. Osteoprotegerin (OPG), a member of the tumor necrosis factor receptor superfamily, appears to be a potential candidate for the treatment of these diseases. Studies based on clinical analysis and rodent animal models reveal the roles of OPG in various endocrine and metabolic processes or disorders, such as bone remodeling, vascular calcification, and β-cell proliferation, through the receptor activator of nuclear factor kappa-B ligand (RANKL) and the receptor activator of NF-κB (RANK). Thus, in this review, we mainly focus on relevant diseases, including osteoporosis, cardiovascular disease (CVD), diabetes, and gestational diabetes mellitus (GDM), to summarize the effects of the RANKL/RANK/OPG system in endocrine and metabolic tissues and diseases, thereby providing a comprehensive insight into OPG as a potential drug for endocrine and metabolic diseases.

A missense mutation sheds light on a novel structure-function relationship of RANKL

The tumor necrosis factor (TNF)-like core domain of receptor activator of nuclear factor-κB ligand (RANKL) is a functional domain critical for osteoclast differentiation. One of the missense mutations identified in patients with osteoclast-poor autosomal recessive osteopetrosis (ARO) is located in residue methionine 199 that is replaced with lysine (M199K) amid the TNF-like core domain. However, the structure-function relationship of this mutation is not clear. Sequence-based alignment revealed that the fragment containing human M199 is highly conserved and equivalent to M200 in rat. Using site-directed mutagenesis, we generated three recombinant RANKL mutants M200K/A/E (M200s) by replacing the methionine 200 with lysine (M200K), alanine (M200A), and glutamic acid (M200E), representative of distinct physical properties. TRAcP staining and bone pit assay showed that M200s failed to support osteoclast formation and bone resorption, accompanied by impaired osteoclast-related signal transduction. However, no antagonistic effect was found in M200s against wild-type rat RANKL. Analysis of the crystal structure of RANKL predicted that this methionine residue is located within the hydrophobic core of the protein, thus, likely to be crucial for protein folding and stability. Consistently, differential scanning fluorimetry analysis suggested that M200s were less stable. Western blot analysis analyses further revealed impaired RANKL trimerization by M200s. Furthermore, receptor-ligand binding assay displayed interrupted interaction of M200s to its intrinsic receptors. Collectively, our studies revealed the molecular basis of human M199-induced ARO and elucidated the indispensable role of rodent residue M200 (equivalent to human M199) for the RANKL function.

Osteopontin and osteoprotegerin in atherosclerotic plaque - are they significant markers of plaque vulnerability?

Atherosclerosis (ATS) is still considered as a major, global health problem. For a deeper understanding of its pathogenesis, in the last years the research was translated from tissue visible events to molecular mechanisms. Osteopontin (OPN) and osteoprotegerin (OPG) are two molecules that have been associated with the initiation and progression of ATS lesions. The aim of our study was to assess the OPN and OPG expression in advanced stages of carotid ATS, to analyze the correlation between these markers and the ultrasonographic plaque properties, pointing out the identification of possible patterns that can predict plaque vulnerability and risks of restenosis. The study group comprised 49 consecutive patients (38 males and 11 females) diagnosed with carotid stenotic lesions by using ultrasonography. The carotid endarterectomy specimens were standardly processed for histopathological and immunohistochemical exams. The OPN and OPG expression was semi-quantitatively assessed. Our results sustained the relationship between histological American Heart Association (AHA) type and ultrasonographic classification (echogenic versus echolucent) (p<0.001). The semi-quantitative analysis showed that in most cases (31 plaques) OPG and OPN had opposite expressions, whereas in the remaining cases (18 plaques) the expression was similar. There were no correlations between low versus high expression of intra-plaque OPN and OPG (p=0.335). We found significant correlation for OPN and plaque echogenicity (p=0.011), but not for OPG (p=0.079). OPN expression (low versus high) was correlated with plaque type (stable versus unstable) (p=0.036), plaque ulceration (p=0.009) and inflammation (p<0.001). OPG expression (low versus high) did not reveal statistically significant differences with plaque type (stable versus unstable) and vulnerability plaque parameters, respectively. OPG and OPN co-exist in carotid atherosclerotic plaque demonstrating a modulatory role in inflammatory and calcification processes. OPG is strongly expressed in stable, calcified plaques, while OPN is poorly expressed in calcified plaques and in plaques without hemorrhage, ulceration, inflammation, or necrosis. Starting from the molecular mechanisms, further studies of biomarkers are important to identify new therapeutic resources meant to prevent and treat vascular calcification.

Association of Alk1 and Endoglin Polymorphisms with Cardiovascular Damage

Cardiovascular diseases are associated to risk factors as obesity, hypertension and diabetes. The transforming growth factor-β1 receptors ALK1 and endoglin regulate blood pressure and vascular homeostasis. However, no studies relate the association of ALK1 and endoglin polymorphisms with cardiovascular risk factors. We analysed the predictive value of the ALK1 and endoglin polymorphisms on cardiovascular target organ damage in hypertensive and diabetic patients in 379 subjects with or without hypertension and diabetes in a Primary Care setting. The ALK1 rs2071219 polymorphism (AA genotype) is associated with a lower presence of diabetic retinopathy and with the absence of altered basal glycaemia. Being carrier of the ALK1 rs3847859 polymorphism (G allele) is associated with lower basal heart rate and with higher LDL-cholesterol levels. The endoglin rs3739817 polymorphism (AA genotype) is associated with higher levels of LDL-cholesterol, and being carrier of the endoglin rs10987759 polymorphism (C allele) is associated with higher haemoglobin levels and with an increased heart rate. Summarizing, several ALK1 and endoglin gene polymorphisms increase the risk of cardiovascular events. The analysis of these polymorphisms in populations at risk, in combination with the determination of other parameters and biomarkers, could implement the diagnosis and prognosis of susceptibility to cardiovascular damage.

Serum osteoprotegerin level is independently related to subclinical left atrial mechanical function in patients with hypertension and diabetes

OBJECTIVES

Previous studies showed that subclinical abnormal left atrial (LA) function could be diagnosed with LA speckle tracking evaluation long before chamber enlargement. Osteoprotegerin (OPG) is a member of the tumor necrosis factor (TNF) receptor superfamily and was recently found to be an indicator for adverse cardiovascular outcomes and a risk factor for new onset atrial fibrillation. The authors hypothesized that OPG values could predict LA mechanical dysfunction and LA remodeling assessed by two-dimensional speckle tracking echocardiography (2D-STE) in patients with hypertension (HT) and diabetes mellitus (DM).

METHODS

A single center study was conducted including consecutive patients presenting to the authors' outpatient clinic. Enrolled patients needed to have been treated for HT and DM for at least 1 year.

RESULTS

The study included 80 patients (mean age, 57.5 ± 8.3 years). Patients in the impaired LA strain group were older (p = 0.035), had lower low density lipoprotein (LDL) cholesterol (mg/dl) (p = 0.021), and higher OPG (pmol/l) (p = 0.004) values than patients in the normal LA strain group. Univariate logistic regression analysis demonstrated that age (p = 0.039), LDL cholesterol (mg/dl) (p = 0.025), and OPG (pmol/l) (p = 0.008) values were associated with impaired LA strain. Backward multivariate logistic regression analysis showed that LDL cholesterol (mg/dl) (OR: 0.982, CI 95% 0.964-0.999, p = 0.049) and OPG (pmol/l) (OR: 1.438, CI 95% 1.043-1.983, p = 0.027) were independently associated with impaired LA strain.

CONCLUSION

In hypertensive and diabetic patients, higher OPG values were associated with impaired LA function assessed by 2D-STE. In this high-risk patient group, serum OPG can be used as a risk predictor for LA mechanical dysfunction.

Regulatory Effects and Interactions of the Wnt and OPG-RANKL-RANK Signaling at the Bone-Cartilage Interface in Osteoarthritis

Cartilage and the bordering subchondral bone form a functionally active regulatory interface with a prominent role in osteoarthritis pathways. The Wnt and the OPG-RANKL-RANK signaling systems, as key mediators, interact in subchondral bone remodeling. Osteoarthritic osteoblasts polarize into two distinct phenotypes: a low secretory and an activated, pro-inflammatory and anti-resorptive subclass producing high quantities of IL-6, PGE2, and osteoprotegerin, but low levels of RANKL, thus acting as putative effectors of subchondral bone sclerosis. Wnt agonists, Wnt5a, Wisp-1 initiate excessive bone remodeling, while Wnt3a and 5a simultaneously cause loss of proteoglycans and phenotype shift in chondrocytes, with decreased expression of COL2A, aggrecan, and Sox-9. Sclerostin, a Wnt antagonist possesses a protective effect for the cartilage, while DKK-1 inhibits VEGF, suspending neoangiogenesis in the subchondral bone. Experimental conditions mimicking abnormal mechanical load, the pro-inflammatory milieu, but also a decreased OPG/RANKL ratio in the cartilage, trigger chondrocyte apoptosis and loss of the matrix via degradative matrix metalloproteinases, like MMP-13 or MMP-9. Hypoxia, an important cofactor exerts a dual role, promoting matrix synthesis via HIF-1α, a Wnt silencer, but turning on HIF-2α that enhances VEGF and MMP-13, along with aberrant collagen expression and extracellular matrix deterioration in the presence of pro-inflammatory cytokines.

Arterial Stiffness in CKD: A Review

This narrative review summarizes a decade of experience examining the cross-sectional and longitudinal relationships of arterial stiffness, as assessed using carotid-femoral pulse wave velocity, with outcomes in patients with chronic kidney disease enrolled in the Chronic Renal Insufficiency Cohort. Our goal is to review the importance of the pulse wave contour and pulse wave velocity and present data on the reproducibility of pulse wave velocity measurements, determinants of pulse wave velocity, and the relationship that velocity measurements have with longitudinal kidney and cardiovascular outcomes. Measures of arterial stiffness have contributed substantially to our understanding of mechanisms of cardiovascular disease, kidney disease progression, and all-cause mortality. Given the independent relationship of arterial stiffness to a variety of outcomes, it is our hope that future developments in behavioral, nutritional, and pharmacologic approaches to vascular destiffening will provide interventions that benefit patients with chronic kidney diseases.

Carotid intima media thickness and associations with serum osteoprotegerin and s-RANKL in children and adolescents with type 1 diabetes mellitus with increased risk for endothelial dysfunction

Background Although carotid intima media thickness (CIMT) is an established marker of endothelial dysfunction, limited data exist on relative laboratory biomarkers in youngsters with type 1 diabetes mellitus (T1DM). Our aim was to study CIMT and the biomarkers of the osteoprotegerin (OPG)/RANKL system in young T1DM patients and controls, and also in subgroups of patients with increased risk for endothelial dysfunction, such as those with overweight/obesity, poor metabolic control or the presence of microalbuminuria. Methods CIMT and OPG/RANKL of 56 T1DM children and adolescents were compared to 28 healthy controls. Results Anthropometric, laboratory, CIMT and OPG/RANKL measurements were similar between patients and controls. Overweight/obese patients had greater CIMT than the normal weight ones (0.50 vs. 0.44 mm, p=0.001). Microalbuminuric patients had greater CIMT (0.49 vs. 0.44 mm, p=0.035) than the normoalbuminuric ones, with no difference in terms of OPG/RANKL. In the microalbuminuric group, OPG (r=-0.90, p=0.036) and RANKL (r=-0.92, p=0.024) were significantly negatively associated with CIMT. Following linear regression analysis, in the total patients group, microalbuminuria was the only factor significantly associated with CIMT (beta±SE: 0.050±0.021, p=0.035), body mass index (BMI)-z-scores were negatively associated with OPG (beta±SE: -0.25±0.12, p=0.05), while in the microalbuminuric group, CIMT was negatively associated with OPG (beta±SE: -0.070±0.019, p=0.036). During the forward stepwise procedure, microalbuminuria and age were the only variables negatively associated with RANKL (b=-0.334, p=0.034, b=-35.95, p=0.013, respectively). Conclusions In T1DM pediatric patients, overweight/obesity and microalbuminuria were associated with greater CIMT and with impaired OPG/RANKL levels, as biochemical indices of calcification of the atherosclerotic plaque.

Spotty Carotid Plaques Are Associated with Inflammation and the Occurrence of Cerebrovascular Symptoms

Background

Echolucent carotid plaques have been related to an increased risk of ischemic cerebrovascular events. The aim of the present study was to evaluate whether a new objective ultrasonographic parameter, the statistical geometric feature (SGF), reflecting spottiness of carotid plaques, can be associated with cerebrovascular symptoms and with a rupture-prone plaque phenotype.

Methods

The plaques of 144 patients who underwent carotid endarterectomy were included in this study. SGF and plaque area were estimated by outlining the plaque on ultrasound (US) images. The correlation coefficient for inter- and intraobserver variability was 0.69 and 0.93, respectively. The SGF values were normalized to the degree of stenosis (SGF/DS). The plaques collected at surgery 1 day after the US were analyzed histologically, and inflammatory markers and matrix metalloproteinases (MMPs) were measured.

Results

Patients with ipsilateral hemispheric symptoms had higher SGF/DS compared to patients without symptoms (0.82 [0.59–1.16] vs. 0.70 [0.56–0.89], p = 0.01). Analysis of plaque components revealed a positive correlation between SGF/DS and the percentage of the plaque area stained for lipids, macrophages, and hemorrhage. A correlation was also found between SGF/DS and plaque expression of interleukin-6, monocyte chemoattractant protein-1, macrophage inflammatory protein-1β, vascular endothelial growth factor A, C-C motif chemokine 3 and 20, and MMP-9. An inverse correlation was found with plaque levels of osteoprotegerin.

Conclusions

The present study supports the concept that spottiness is a feature of the carotid plaques rich in inflammation and can be associated with the typical phenotype of high-risk plaques.

T2DiACoD: A Gene Atlas of Type 2 Diabetes Mellitus Associated Complex Disorders

We performed integrative analysis of genes associated with type 2 Diabetes Mellitus (T2DM) associated complications by automated text mining with manual curation and also gene expression analysis from Gene Expression Omnibus. They were analysed for pathogenic or protective role, trends, interaction with risk factors, Gene Ontology enrichment and tissue wise differential expression. The database T2DiACoD houses 650 genes, and 34 microRNAs associated with T2DM complications. Seven genes AGER, TNFRSF11B, CRK, PON1, ADIPOQ, CRP and NOS3 are associated with all 5 complications. Several genes are studied in multiple years in all complications with high proportion in cardiovascular (75.8%) and atherosclerosis (51.3%). T2DM Patients' skeletal muscle tissues showed high fold change in differentially expressed genes. Among the differentially expressed genes, VEGFA is associated with several complications of T2DM. A few genes ACE2, ADCYAP1, HDAC4, NCF1, NFE2L2, OSM, SMAD1, TGFB1, BDNF, SYVN1, TXNIP, CD36, CYP2J2, NLRP3 with details of protective role are catalogued. Obesity is clearly a dominant risk factor interacting with the genes of T2DM complications followed by inflammation, diet and stress to variable extents. This information emerging from the integrative approach used in this work could benefit further therapeutic approaches. The T2DiACoD is available at www.http://t2diacod.igib.res.in/ .

Osteoprotegerin as a marker of cardiovascular risk in children and adolescents with type 1 diabetes

BACKGROUND

Elevated osteoprotegerin (OPG) levels have been reported in patients with diabetes complications. We investigated whether plasma OPG levels can be used as a marker of cardiovascular risk in children and adolescents with type 1 diabetes (T1D).

METHODS

Plasma blood samples were obtained from 243 subjects (143 children and adolescents with T1D and 100 healthy controls). OPG concentrations were measured by enzyme-linked immunosorbent assay (ELISA) method. All data were analyzed by using PASW statistics 18.

RESULTS

A significant higher plasma OPG level was found in children with T1D compared to controls (p < 0.001). A significant increase of OPG levels has been related to the glucose level ≥ 7 mmol/L (2.44 [0.01-6.22] vs. 2.16 [0.13-6.22] pmol/L, p = 0.019), microalbuminuria ≥ 30 mg/24 h (3.71 [0.160-6.03] vs. 2.26 [0.01-6.22] pmol/L, p < 0.001), and cystatin-C ≥ 0.789 mg/L (2.64 [0.37-6.22] vs. 2.11 [0.01-5.82] pmol/L, p < 0.001). We noted a significant higher frequency of children with increased cystatin-C levels in the group with elevated plasma level of OPG compared with those with normal levels (49 vs. 18%, respectively) with an odds ratio (OR) = 4.42 [1.41-13.84] (p = 0.006). We showed a significant increase of OPG levels when the number of cardiovascular risk factors exceeds 3 (p = 0.001).

CONCLUSION

OPG may be a potential biomarker of cardiovascular risk in T1D. Implementation of OPG determination in the clinical laboratory setting would be useful in order to better stratify patients and to assess the most adequate treatment.

Does the OPG/RANKL system contribute to the bone-vascular axis in chronic kidney disease? A systematic review

Vascular calcification (VC) is highly prevalent in patients with chronic kidney disease (CKD) and is strongly associated with cardiovascular mortality and morbidity. Accumulating evidence over the past decade has challenged the hypothesis of close interaction between bone and VC what raises the possibility of a common underlying pathophysiological mechanism. Lately, bone regulatory proteins such as: osteoprotegerin (OPG) and Receptor Activator for Nuclear Factor κB Ligand (RANKL) has attracted attention of researchers as a possible key mediators of bone-vascular calcification imbalance. The literature search was carried out using the MEDLINE/PubMed database and a combination of keywords and MeSH terms, and only papers published since January 2005 to July 2016 were selected. The search resulted in 562 potential articles. After selection according to the eligibility criteria, 107 studies fulfilled were included (102 full texts and 5 was case reports). OPG and RANKL plays essential role in the regulation of bone metabolism and may be regarded as a possible link between VC, bone and mineral metabolism in CKD patients. Further studies are required to determine the diagnostic significance of these proteins in evaluation of progression and severity of VC process in CKD patients. Finally, the efficacy and safety, especially in regard to VC, of anti-RANKL therapy in CKD patients requires well-designed prospective, randomized trials.

High circulating osteoprotegerin levels are associated with non-zero blood groups

BACKGROUND

Osteoprotegerin (OPG) and von Willebrand factor (VWF) form complex within endothelial cells and following secretion. The nature of blood group antigens strongly influences the levels of circulating VWF, but there is no available data concerning its ascendancy on OPG levels. We aimed to assess the relationship of AB0 blood groups with OPG, VWF levels (VWF: Ag) and collagen binding activity (VWF: CB) in peripheral arterial disease (PAD) patients.

METHODS

Functional and laboratory parameters of 105 PAD patients and 109 controls were examined. Results of OPG, VWF: Ag, VWF: CB (ELISA-s) were analysed by comparative statistics, together with clinical data.

RESULTS

OPG levels were higher in patients than in controls (4.64 ng/mL vs. 3.68 ng/mL, p < 0.001). Among patients elevation was marked in the presence of critical limb ischemia (5.19 ng/mL vs. 4.20 ng/mL, p = 0.011). The OPG in patients correlated positively with VWF: Ag and VWF: CB (r = 0.26, p = 0.008; r = 0.33, p = 0.001) and negatively with ankle-brachial pressure index (r = -0.22, p = 0.023). Furthermore, OPG was significantly elevated in non-0 blood groups compared to 0-groups both in patients and controls (4.95 ng/mL vs. 3.90 ng/mL, p = 0.012 and 4.09 ng/mL vs. 3.40 ng/mL, p = 0.002).

CONCLUSIONS

OPG levels are associated to blood group phenotypes and higher in non-0 individuals. Increased OPG levels in PAD characterize disease severity. The significant correlation between OPG and VWF:CB might have functional importance in an atherothrombosis-prone biological environment.

Osteoprotegerin and TRAIL in Acute Onset of Atrial Fibrillation

Background. There is a growing amount of evidence that inflammatory processes are involved in the development of atrial fibrillation (AF) and its complications. We decided to investigate the behavior of osteoprotegerin (OPG) and TNF-related apoptosis inducing ligand (TRAIL) in terms of acute onset of AF. Methods and Results. We included 60 patients with acute onset of AF, candidates for pharmacological cardioversion. The presence of cardiovascular comorbidities was connected with higher concentration of OPG and lower level of TRAIL right from the first hours of AF paroxysm. The initial TRAIL level correlated also positively with left ventricle ejection fraction and negatively with left atrium diameter. We found subsequent increase of OPG in subgroups selected on the basis of CHA₂DS₂-VASc scoring. Although basal concentrations of studied markers did not allow prediction of the restoration of sinus rhythm, we observed important increase of TRAIL concentration in subgroup with sinus rhythm maintenance (94.11 ± 29.46 versus 111.39 ± 30.23 pg/mL; p = 0.002). Conclusions. OPG and TRAIL are associated with the underlying cardiovascular damage in AF, but their balance is modulated by the fact of sinus rhythm restoration. Determining the suitability of OPG and TRAIL as predictive markers in AF requires further prospective studies.

Correlations between osteoprotegerin serum levels and body composition parameters in patients with sleep apnea syndrome and the possible influence on cardiovascular risk

INTRODUCTION

Osteoprotegerin (OPG) is a member of the tumor necrosis factor family and a key regulator in bone turnover; it plays a role in the development of many cardiovascular diseases and may be treated as a marker of vascular damage. Bioelectrical impedance analysis (BIA) is a reliable, non-invasive and effective technique for measuring body composition. The aim of the study was to evaluate correlations between osteoprotegerin serum levels and body composition parameters in sleep apnea patients and their influence on cardiovascular risk.

MATERIAL AND METHODS

A total of 125 patients with newly diagnosed OSA were enrolled in the study (including 34 females). The mean age was 54.48±8.81 years, mean AHI 33.16±20.44/h and mean BMI 33.76±7.18. A control group comprised 59 healthy subjects with mean age of 51.27±12.97 years and mean BMI 29.47±5.42. All subjects underwent a nocturnal respiratory polygraphy and body composition measurements were taken with bioelectrical impedance analysis. OPG serum levels were measured using the enzyme-linked immunosorbent assay (ELISA) method.

RESULTS

In OSA patients OPG correlated negatively with muscle mass percentage (MM%), phase angle, fat free mass percentage (FFM%) and body cell mass percentage (BCM%), while there was a positive correlation between osteoprotegerin and fat mass percentage (FM%). We demonstrated higher OPG serum levels in OSA patients with cardiovascular diseases than in those without comorbidities (4.01 vs 3.46pmol/l, p<0.05).

CONCLUSION

Our findings, combined with previous observations in other diseases, suggest that elevated OPG serum levels together with selected body composition parameters may be helpful in identifying OSA patients with increased cardiovascular risk.

Osteoprotegerin in Cardiometabolic Disorders

Osteoprotegerin (OPG), a glycoprotein traditionally implicated in bone remodelling, has been recently related to cardiovascular disease (CVD). Human studies show a positive relationship between circulating OPG, vascular damage, and CVD, and as such OPG has emerged as a potential biomarker for CVD. This review focuses on the relationship between circulating OPG and different endocrine cardiometabolic alterations such as type 1 and 2 diabetes. The association of OPG with diabetic complications (neuropathy, nephropathy, or retinopathy) as well as with atherosclerosis, coronary artery calcification, morbidity, and mortality is pointed out. Moreover, OPG modulation by different treatments is also established. Besides, other associated diseases such as obesity, hypertension, and metabolic syndrome, which are known cardiovascular risk factors, are also considered.

Role of osteoprotegerin and its gene polymorphisms in the occurrence of left ventricular hypertrophy in essential hypertensive patients

The aim of the study was to investigate the role of osteoprotegerin (OPG) in left ventricular hypertrophy (LVH) development in patients with essential hypertension (EH). A total of 1092 patients diagnosed with EH were recruited. The LVHs were determined and OPG gene polymorphisms were genotyped. Patients with LVH had a significantly higher mean serum OPG level than those without LVH. The 1181CC genotype carriers had significantly lower risk for LVH compared with GC and GG genotype carriers. The serum OPG level and OPG 1181 G>C polymorphism were found to be independent risk factors for the occurrence of LVH in hypertensive patients. In vitro study shows that OPG overexpression upregulates cell surface size, protein synthesis per cell, and hypertrophy- and fibrosis-related proteins in both cardiomyocytes and cardiac fibroblasts, whereas OPG inhibition can abolish the above-mentioned changes. Consistent with the in vitro data, our in vivo study revealed that the OPG administration induced the LVH in hypertensive rats. This study is the first to report the close association between OPG and LVH development in EH patients and the regulatory effect of OPG on cardiomyocytes and cardiac fibroblasts.

Circulating osteoprotegerin is increased in the metabolic syndrome and associates with subclinical atherosclerosis and coronary arterial calcification

CONTEXT

The relationship between osteoprotegerin (OPG) a glycoprotein related to bone metabolism and the metabolic syndrome (MS) has not been established.

OBJECTIVE

The aim of this study is to evaluate OPG concentration in patients with MS and its association with subclinical atherosclerosis and coronary arterial calcification (CAC).

MATERIALS/METHODS

The study included 238 asymptomatic patients. MS was diagnosed according to the NCEP/ATPIII guidelines. OPG was measured by ELISA. All subjects underwent ultrasonography of the common carotid arteries to measure intima-media thickness (IMT) and evaluate the presence of atheroma plaques. In a subgroup (n=39) CAC was quantified by ECG-triggered cardiac computed tomography. Adipose tissue was excised from 25 patients and OPG expression by RT-PCR and immunohistochemistry was studied.

RESULTS

Patients with the MS (n=60) had higher OPG than patients without (n=178) (p<0.05). OPG correlated with IMT (r=0.2, p=0.005) and patients with atheroma plaques had higher OPG (p=0.008) and also those with coronary artery calcification (p<0.05). OPG expression was confirmed in adipose tissue (n=12) and the expression was significantly higher in patients with MS than in those without (p=0.003).

CONCLUSIONS

This study shows that OPG may potentially be a biomarker for cardiovascular risk/damage in the MS and identifies adipose tissue as a potential source of OPG.

Circulating osteoprotegerin and asymptomatic carotid atherosclerosis in postmenopausal non diabetic women

PURPOSE

Osteoprotegerin (OPG) is a bone metabolism regulator but it is also involved in vascular calcification. Its role in the development of atherosclerosis is still a subject of debate. Postmenopausal women seem to have an increased risk for cardiovascular disease. The aim of the study is to evaluate the relationship between serum OPG and asymptomatic carotid atherosclerosis in postmenopausal non-diabetic women.

MATERIAL/METHODS

Carotid artery examination was performed in 100 postmenopausal women without diabetes mellitus and overt cardiovascular disease, using B-mode ultrasonography to determine the carotid intima-media thickness (CIMT) and the presence of plaques. Serum OPG was measured in all study participants and its relationship with clinical, biochemical and vascular parameters was evaluated.

RESULTS

CIMT correlated with age (r=0.45, p<0.001), years since menopause (r=0.30, p=0.003), abdominal circumference (r=0.25, p=0.01) and OPG (r=0.23, p=0.02). Carotid plaques correlated with age (p<0.001), obesity (p=0.03), abdominal circumference (p=0.03) and CIMT (p<0.001), but not with serum OPG (p=0.86). In regression analyses the independent predictors for CIMT were age (β=0.717, p<0.001), OPG (β=0.214, p=0.02), and years since menopause (β=-0.334, p=0.04) and for the presence of carotid plaques were obesity (p=0.04, OR=3.90), CIMT (p<0.001, OR=6408.86) and smoking (p=0.02, OR=687.93).

CONCLUSION

OPG is associated with cardiovascular risk factors, CIMT, but not with the presence of asymptomatic carotid plaques in non diabetic postmenopausal women. OPG may be a marker of cardiovascular risk.

Osteoprotegerin is associated with subclinical left ventricular systolic dysfunction in diabetic hypertensive patients: a speckle tracking study

BACKGROUND

Recently, the role of osteoprotegerin (OPG) in the pathogenesis of heart failure through different mechanisms has received much attention. Subclinical changes in left ventricular (LV) function can be identified using quantification of myocardial strain, and global longitudinal strain (GLS) is a superior predictor of outcomes than ejection fraction. We hypothesized that increased OPG levels could predict subclinical LV systolic dysfunction in treated diabetic hypertensive patients with preserved LV ejection fraction.

METHODS

The study was composed of 86 diabetic hypertensive and 30 nondiabetic hypertensive patients. All patients underwent echocardiography and venous blood samples were taken for determination of OPG. The relation between OPG levels and LV GLS was investigated using 2-dimensional speckle tracking echocardiography.

RESULTS

Diabetic hypertensive patients had higher diastolic peak early/early diastolic tissue velocity and lower systolic tissue velocity, GLS, GLS rate systolic, and GLS rate early diastolic than nondiabetic hypertensive patients (P = 0.009, P = 0.049, P < 0.001, P = 0.004, and P < 0.001, respectively). Diabetic hypertensive patients were divided into 2 groups according to median GLS value (> 18.5 and ≤ 18.5). The patients with GLS ≤ 18.5 had higher diastolic blood pressure (mm Hg; P = 0.048), OPG (pmol/L; P < 0.001), and hemoglobin A1c (%; P = 0.042) values than those with GLS > 18.5. In multivariate logistic regression analysis, OPG was found to be an independent predictor of impaired GLS (P = 0.001). Receiver operating characteristic curve analysis revealed that OPG values of > 6.45 (pmol/L) identified the patients with GLS ≤ 18.5.

CONCLUSIONS

Plasma OPG values could predict subclinical LV systolic dysfunction in diabetic hypertensive patients.

Osteoprotegerin and kidney disease

Vascular calcification in chronic kidney disease (CKD) patients is associated to increased mortality. Osteoprotegerin (OPG) is a soluble tumor necrosis factor (TNF) superfamily receptor that inhibits the actions of the cytokines receptor activator of nuclear factor kappa-B ligand (RANKL) and TNF-related apoptosis-inducing ligand (TRAIL) by preventing their binding to signaling receptors in the cell membrane. OPG-deficient mice display vascular calcification while OPG prevented calcification of cultured vascular smooth muscle cells and protected kidney cells from TRAIL-induced death. OPG may be a biomarker in patients with kidney disease. Circulating OPG is increased in predialysis, dialysis and transplant CKD patients and may predict vascular calcification progression and patient survival. By contrast, circulating OPG is decreased in nephrotic syndrome. In addition, free and exosome-bound urinary OPG is increased in human kidney disease. Increased urinary OPG has been associated with lupus nephritis activity. Despite the association of high OPG levels with disease, experimental functional information available suggests that OPG might be protective in kidney disease and in vascular injury in the context of uremia. Thus, tissue injury results in increased OPG, while OPG may protect from tissue injury. Recombinant OPG was safe in phase I randomized controlled trials. Further research is needed to fully define the therapeutic and biomarker potential of OPG in patients with kidney disease.

Heme oxygenase suppresses markers of heart failure and ameliorates cardiomyopathy in L-NAME-induced hypertension

Heart failure and related cardiac complications remains a great health challenge. We investigated the effects of upregulating heme-oxygenase (HO) on myocardial histo-pathological lesions, proinflammatory cytokines/chemokines, oxidative mediators and important markers of heart failure such as osteopontin and osteoprotergerin in N(ω)-nitro-l-arginine methyl ester (L-NAME)-induced hypertension. Treatment with the HO-inducer, heme-arginate improved myocardial morphology in L-NAME hypertensive rats by attenuating subendocardial injury, interstitial fibrosis, mononuclear-cell infiltration and cardiomyocyte hypertrophy. These were associated with the reduction of several inflammatory/oxidative mediators including chemokines/cytokines such as macrophage inflammatory protein-1 alpha (MIP-1α), macrophage chemoattractant protein-1 (MCP-1), tumor necrosis factor alpha (TNF-α), interleukin (IL)-6, IL-1β, endothelin-1, 8-isoprostane, nitrotyrosine, and aldosterone. Similarly, heme-arginate abated the elevated levels of extracellular matrix/remodeling proteins including transforming-growth factor beta (TGF-β1) and collagen-IV in the myocardium. These were accompanied by significant reduction of proteins of heart failure such as osteopontin and osteoprotegerin. Interestingly, the cardio-protective effects of heme-arginate were associated with the potentiation of adiponectin, atrial-natriuretic peptide (ANP), HO-1, HO-activity, cyclic gnanosine monophosphate (cGMP) and the total-anti-oxidant capacity, whereas the HO-inhibitor, chromium-mesoporphyrin nullified the effects of heme-arginate, exacerbating inflammatory injury and oxidative insults. We conclude that heme-arginate therapy protects myocardial damage by potentiating the HO-adiponectin-ANP axis, which in turn suppressed the elevated levels of aldosterone, pro-inflammatory chemokines/cytokines, mononuclear-cell infiltration and oxidative stress, with concomitant reduction of extracellular matrix/remodeling proteins and heart failure proteins. These data suggest a cardio-protective role of the HO system against L-NAME-induced hypertension that could be explored in the design of novel strategies against cardiomyopathy.

Osteoprotegerin in exosome-like vesicles from human cultured tubular cells and urine

Urinary exosomes have been proposed as potential diagnostic tools. TNF superfamily cytokines and receptors may be present in exosomes and are expressed by proximal tubular cells. We have now studied the expression of selected TNF superfamily proteins in exosome-like vesicles from cultured human proximal tubular cells and human urine and have identified additional proteins in these vesicles by LC-MS/MS proteomics. Human proximal tubular cells constitutively released exosome-like vesicles that did not contain the TNF superfamily cytokines TRAIL or TWEAK. However, exosome-like vesicles contained osteoprotegerin (OPG), a TNF receptor superfamily protein, as assessed by Western blot, ELISA or selected reaction monitoring by nLC-(QQQ)MS/MS. Twenty-one additional proteins were identified in tubular cell exosome-like vesicles, including one (vitamin D binding protein) that had not been previously reported in exosome-like vesicles. Twelve were extracellular matrix proteins, including the basement membrane proteins type IV collagen, nidogen-1, agrin and fibulin-1. Urine from chronic kidney disease patients contained a higher amount of exosomal protein and exosomal OPG than urine from healthy volunteers. Specifically OPG was increased in autosomal dominant polycystic kidney disease urinary exosome-like vesicles and expressed by cystic epithelium in vivo. In conclusion, OPG is present in exosome-like vesicles secreted by proximal tubular epithelial cells and isolated from Chronic Kidney Disease urine.

The role of osteoprotegerin in cardiovascular disease

Osteoprotegerin (OPG) is a 401 amino acid N-glycosylated protein, which is highly expressed in a large number of tissues. OPG mainly binds to two ligands, i.e. RANKL (receptor activator of nuclear factor κB ligand) and TRAIL (tumor necrosis factor- related apoptosis-inducing ligand). Upon binding to the former ligand, OPG inhibits the activation of osteoclasts and promotes apoptosis of osteoclasts, whereas the binding of OPG with TRAIL prevents apoptosis of tumor cells. There is now emerging evidence that OPG participates in the pathogenesis of atherosclerosis and cardiovascular diseases by amplifying the adverse effects of inflammation and several traditional risk factors such as hyperlipidemia, endothelial dysfunction, diabetes mellitus, and hypertension. Some epidemiological studies also showed a positive association between OPG levels and cardiovascular morbidity and mortality. The aim of this article is to provide an overview of the main biochemical, physiological, and pathological aspects of OPG biology in cardiovascular disease.

Osteoprotegerin as a marker of atherosclerosis in diabetic patients

Atherosclerosis is the principal cause of cardiovascular disease (CVD) and has many risk factors, among which is diabetes. Osteoprotegerin (OPG) is a soluble glycoprotein, involved in bone metabolism. OPG is also found in other tissues, and studies have shown that it is expressed in vascular smooth muscle cells. OPG has been implicated in various inflammations and also has been linked to diabetes mellitus. Increased serum OPG levels were found in patients with diabetes and poor glycemic control. Furthermore, prepubertal children with type 1 diabetes have significantly increased OPG levels. Receptor activator of nuclear factor kappa-B ligand (RANKL) is not found in the vasculature in normal conditions, but may appear in calcifying areas. OPG and RANKL are important regulators of mineral metabolism in both bone and vascular tissues. Few data are available on the relationship between plasma OPG/RANKL levels and endothelial dysfunction as assessed using noninvasive methods like ultrasound indexes, neither in the general population nor, more specifically, in diabetic patients. The aim of our review study was to investigate, based on the existing data, these interrelationships in order to identify a means of predicting, via noninvasive methods, later development of endothelial dysfunction and vascular complications in diabetic patients.

Osteoprotegerin, Soluble Receptor Activator of Nuclear Factor- κ B Ligand, and Subclinical Atherosclerosis in Children and Adolescents with Type 1 Diabetes Mellitus

Aims. To evaluate carotid intima-media thickness (cIMT) and biomarkers of the osteoprotegerin/receptor activator of nuclear factor- κ B ligand (OPG/RANKL) system in type 1 diabetes (T1DM) children and adolescents and controls. Subjects and Methods. Fifty six T1DM patients (mean ± SD age: 12.0 ± 2.7 years, diabetes duration: 5.42 ± 2.87 years and HbA1c: 8.0 ± 1.5%) and 28 healthy matched controls, were studied with anthropometric and laboratory measurements, including serum OPG, soluble RANKL (sRANKL) and cIMT. Results. Anthropometric, laboratory, and cIMT measurements were similar between T1DM youngsters and controls. However patients with longer diabetes duration (>/7.0 years) had indicatively higher cIMT (cIMT = 0.49 vs 0.44 mm, P 0.072) and triglyceride levels than the rest of the patients (93.7 vs 64.6 mg/dl, P 0.025). Both in the total study population (β 0.418, P 0.027) and among T1DM patients separately (β 0.604, P 0.013), BMI was the only factor associated with cIMT. BMI was further associated with OPG in both groups (β -0.335, P 0.003 and β -0.356, P 0.008 respectively), while sRANKL levels were not associated with any factor. Conclusions. BMI was the strongest independent predictor of cIMT among the whole population, and especially in diabetics, suggesting a possible synergistic effect of diabetes and adiposity on atherosclerotic burden. BMI was overall strongly associated with circulating OPG, but the causes of this association remain unclear.

Secretion patterns of circulating osteoprotegerin and response to acute and chronic energy deprivation in young healthy adults

INTRODUCTION

Osteoprotegerin (OPGN) is a bone-remodeling marker that is associated with various metabolic and vascular complications. Cross-sectional studies in humans have demonstrated an inverse association between leptin, a marker of energy sufficiency, and OPGN. The physiology of OPGN has not been fully elucidated to date. We thus aim to elucidate 1) whether OPGN levels exhibit any gender dimorphism or day/night secretion pattern; and 2) whether there is any effect of acute and/or chronic energy deprivation on its circulating levels and whether such effects are mediated through leptin.

MATERIALS AND METHODS

Study A: To evaluate OPGN secretion patterns and OPGN response to acute energy deprivation, we studied 12 healthy subjects under three different conditions for 72 h-in the isocaloric fed state, and during a fasting state with administration of either placebo or metreleptin in replacement doses. Blood samples were obtained every 15 min and pooled hourly during the last 24 h of the study. Study B: To evaluate the effect of chronic energy deprivation on OPGN secretion, we measured its levels in 14 obese subjects before and during weight loss after bariatric surgery.

RESULTS

OPGN levels exhibited a statistically significant (P < 0.01), albeit clinically limited in magnitude, day/night variation pattern in both genders (R(2) = 14.68%; 10.7-14.8% reduction with lower levels around 1600-1800 h; P < 0.01). Males had lower OPGN levels compared to females (1.81 ± 0.04 vs. 3.65 ± 0.07 pmol/liter; P < 0.001). Three days of fasting with either placebo or metreleptin administration did not change OPGN levels. OPGN levels did not change during bariatric surgery-induced weight loss.

CONCLUSIONS

OPGN levels are lower in men and exhibit a statistically significant, albeit clinically limited in magnitude, day/night secretion pattern. Neither acute nor chronic energy deprivation leading to significant weight loss has any effects on OPGN levels. Nomenclature Comment: Use of the terms "circadian" and "day/night variation" is meant as follows: Circadian pattern is a functional term that implies a rhythm that has been proven to be regulated by the innate circadian apparatus (anatomical and/or molecular). Conversely, day/night variation pattern is a descriptive term that refers to serum levels that vary during a day, usually in a periodic fashion. It is not known whether this variation is an innate property of the organ that secretes this hormone or whether it is determined by exogenous factors.