Elevation of plasma retinol-binding protein 4 and reduction of plasma adiponectin in subjects with cerebral infarction

Biomarkers for prognostic functional recovery poststroke: A narrative review

Background and objective: Prediction of poststroke recovery can be expressed by prognostic biomarkers that are related to the pathophysiology of stroke at the cellular and molecular level as well as to the brain structural and functional reserve after stroke at the systems neuroscience level. This study aimed to review potential biomarkers that can predict poststroke functional recovery. Methods: A narrative review was conducted to qualitatively summarize the current evidence on biomarkers used to predict poststroke functional recovery. Results: Neurophysiological measurements and neuroimaging of the brain and a wide diversity of molecules had been used as prognostic biomarkers to predict stroke recovery. Neurophysiological studies using resting-state electroencephalography (EEG) revealed an interhemispheric asymmetry, driven by an increase in low-frequency oscillation and a decrease in high-frequency oscillation in the ipsilesional hemisphere relative to the contralesional side, which was indicative of individual recovery potential. The magnitude of somatosensory evoked potentials and event-related desynchronization elicited by movement in task-related EEG was positively associated with the quantity of recovery. Besides, transcranial magnetic stimulation (TMS) studies revealed the potential values of using motor-evoked potentials (MEP) and TMS-evoked EEG potentials from the ipsilesional motor cortex as prognostic biomarkers. Brain structures measured using magnetic resonance imaging (MRI) have been implicated in stroke outcome prediction. Specifically, the damage to the corticospinal tract (CST) and anatomical motor connections disrupted by stroke lesion predicted motor recovery. In addition, a wide variety of molecular, genetic, and epigenetic biomarkers, including hemostasis, inflammation, tissue remodeling, apoptosis, oxidative stress, infection, metabolism, brain-derived, neuroendocrine, and cardiac biomarkers, etc., were associated with poor functional outcomes after stroke. However, challenges such as mixed evidence and analytical concerns such as specificity and sensitivity have to be addressed before including molecular biomarkers in routine clinical practice. Conclusion: Potential biomarkers with prognostic values for the prediction of functional recovery after stroke have been identified; however, a multimodal approach of biomarkers for prognostic prediction has rarely been studied in the literature. Future studies may incorporate a combination of multiple biomarkers from big data and develop algorithms using data mining methods to predict the recovery potential of patients after stroke in a more precise way.

Correlation of serum RBP4 level with oxidative stress and unstable carotid plaque in patients with cerebral infarction

Objectives

This study aimed to investigate the changes in serum levels of retinol-binding protein 4 (RBP4) with cerebral infarction, relationship of RBP4 with oxidative stress and carotid atherosclerosis, and its possible role in cerebral infarction.

Materials and methods

According to the results of cervical vascular ultrasound, the experimental group was divided into three groups: intima thickening group (n = 31), stable plaque group (n = 51), and unstable plaque group (n = 54). Forty healthy subjects were selected as the control group. Their serum levels of RBP4, 8-iso-prostaglandin-F2alpha (8-iso-PGF2α), and catalase (CAT) were measured. Carotid vascular ultrasound was used to measure the plaque area and intima-media thickness (IMT).

Results

The serum RBP4 and 8-iso-PGF2α levels, IMT and plaque area in the control, intimal thickening, stable plaque, and unstable plaque groups increased, while the serum level of CAT decreased (P < 0.001). The serum levels of RBP4 positively correlated with 8-iso-PGF2α, IMT, and plaque area and negatively correlated with CAT level. The area under the receiver operating characteristic curve was 0.778 in predicting unstable plaques.

Conclusions

The serum levels of RBP4 were significantly elevated in elderly patients with cerebral infarction and correlated with oxidative stress injury and the degree of atherosclerosis. Serum RBP4 has diagnostic value for unstable plaques in carotid arteries.

Fluid biomarkers in stroke: From animal models to clinical care

Stroke is a leading cause of death and disability worldwide. Stroke prevention, early diagnosis, and efficient acute treatment are priorities to successfully impact stroke death and disability. Fluid biomarkers may improve stroke differential diagnostic, patient stratification for acute treatment, and post-stroke individualized rehabilitation. In the present work, we characterized the use of stroke animal models in fluid biomarker research through a systematic review of PubMed and Scopus databases, followed by a literature review on the translation to the human stroke care setting and future perspectives in the field. We found increasing numbers of publications but with limited translation to the clinic. Animal studies are very heterogeneous, do not account for several human features present in stroke, and, importantly, only a minority of such studies used human cohorts to validate biomarker findings. Clinical studies have found appealing candidates, both protein and circulating nucleic acids, to contribute to a more personalized stroke care pathway. Still, brain tissue complexity and the fact that different brain pathologies share lesion biomarkers make this task challenging due to biomarker low specificity. Moreover, the study design and lack of validation cohorts may have precluded a formal integration of biomarkers in different steps of stroke diagnosis and treatment. To overcome such issues, recent pivotal studies on biomarker dynamics in individual patients are providing added value to diagnosis and anticipating patients' early prognosis. Presently, the most consistent protein biomarkers for stroke diagnosis and short- and long-term prognosis are associated with tissue damage at neuronal (TAU), axonal (NFL), or astroglial (GFAP and S100β) levels. Most promising nucleic acids are microRNAs (miR), due to their stability in plasma and ease of access. Still, clinical validation and standardized quantitation place them a step behind compared protein as stroke biomarkers. Ultimately, the definition of clinically relevant biomarker panels and optimization of fast and sensitive biomarker measurements in the blood, together with their combination with clinical and neuroimaging data, will pave the way toward personalized stroke care.

Relationship between adiponectin multimer levels and subtypes of cerebral infarction

Aim

Serum adiponectin levels are decreased in patients with cerebral infarction. Adiponectin in circulation exists in three isoforms: high molecular weight (HMW), medium molecular weight (MMW), and low molecular weight (LMW) adiponectin. We measured serum levels of total adiponectin and adiponectin multimers (HMW, MMW, and LMW) in patients with cerebral infarction and compared the serum levels of the three adiponectin multimers in stroke subtypes. We also evaluated the clinical value of adiponectin multimer levels as a biomarker for cerebral infarction.

Methods

We assessed a total of 132 patients with cerebral infarctions. The serum levels of total and adiponectin multimers were measured using enzyme-linked immunosorbent assay (ELISA).

Results

The total and HMW adiponectin levels were significantly lower in atherothrombotic infarction (AI) than in cerebral embolism (CE) (total, p < 0.05; HMW, p < 0.05). In male patients, the MMW adiponectin level was significantly lower in the lacunar infarction (LI) group than in the AI group (p < 0.05). The LMW adiponectin level was significantly lower in the AI group than in the LI and CE groups (LI, p < 0.001; CE, p = 0.001). However, there were no significant differences in adiponectin multimer levels among the stroke subtypes in female subjects. Additionally, in female patients with AI and LI, the LMW adiponectin levels were negatively associated with C-reactive protein (CRP; AI, p < 0.05; LI, p < 0.05).

Conclusion

These findings suggest that a decrease in adiponectin is associated with AI and that serum LMW adiponectin level represents a potential biomarker for AI.

Left Ventricular Diastolic Dysfunction as Predictor of Unfavorable Prognosis After ESUS

Objective

Identification of echocardiographic, hemodynamic and biochemical predictors of unfavorable prognosis after embolic strokes of undetermined etiology (ESUS) in patients at age <65.

Patients and Methods

Out of 520 ischemic stroke patients we selected 64 diagnosed with ESUS and additional 36 without stroke but with similar risk profile. All patients underwent echocardiography, non-invasive assessment of hemodynamic parameters using SphygmoCor tonometer and measurements of selected biomarkers. Follow-up time was 12 months.

Results

Nine percent of patients died, and recurrent ischemic stroke occurred in 9% of patients only in the ESUS group. Atrial fibrillation (AF) occurred in 10% of patients and the ESUS group had a significantly poorer outcome of AF in the first 2 months after hospitalization. The outcome of re-hospitalization was 28% in the ESUS group and 17% in the control group. In the multivariate analysis mean early diastolic (E’) mitral annular velocity (OR 0.75, 95% CI: 0.6–0.94; p=0.01) was significantly associated with cardiovascular hospitalizations. The only independent predictor of recurrent stroke was the ratio of peak velocity of early diastolic transmitral flow to peak velocity of early diastolic mitral annular motion (E/E’) (OR 0.75, 95% CI: 0.6–0.94; p=0.01). E/E’ was independently associated with composite endpoint (death, hospitalization and recurrent stroke) (OR 1.90, 95% CI 1.1–3.2, p=0.01).

Conclusion

The indices of diastolic dysfunction are significantly associated with unfavorable prognosis after ESUS. There is a robust role for outpatient cardiac monitoring especially during the first 2 months after ESUS to detect potential AF.

Retinol-Binding Protein 4 Predicts Lesion Volume (Determined by MRI) and Severity of Acute Ischemic Stroke

Retinol-binding protein 4 (RBP4) is an adipocyte-secreted molecule and is associated with cardiovascular risk factors. The aim of this study was to assess the clinical significance of serum levels of RBP4 in Chinese patients with acute ischemic stroke (AIS). We sequentially screened patients with first-ever AIS who were admitted to our Hospital between September 2016 and October 2017. Serum levels of RBP4 were assayed with solid-phase sandwich ELISA, and severity of stroke was evaluated with the National Institutes of Health Stroke Scale (NIHSS) score on admission. We used logistic regression models to assess the relationship between RBP4 levels and stroke risk and severity. During the inclusion period, 323 patients completed the study. Our results indicated that the median serum RBP4 levels were significantly (P < 0.001) higher in patients with AIS than in those normal cases [28.9 (IQR, 17.3-39.6) μg/ml vs. 23.7 (14.6-32.3) μg/ml]. In logistic regression analysis, for each 1 unit increase of serum level of RBP4, the unadjusted and adjusted risks of AIS increased by 4% (OR 1.04 [95% CI 1.02-1.05], P < 0.001) and 3% (1.03 [1.01-1.04], P < 0.001), respectively. At admission, 116 patients (35.9%) had a minor stroke (NIHSS < 6). In logistic regression analysis, for each 1 unit increase of serum level of RBP4, the unadjusted and adjusted risks of moderate-to-high stroke increased by 7% (OR 1.07 [95% CI 1.05-1.09], P < 0.001) and 5% (1.05 [1.02-1.07], P < 0.001), respectively. Elevated levels of RBP4 could be considered an independent diagnosis marker of AIS. Elevated levels of RBP4 were significantly associated with higher stroke severity in Chinese sample.

Proteomic analysis of plasma from children with sickle cell anemia and silent cerebral infarction

Silent cerebral infarction is the most common neurological abnormality in children with sickle cell anemia, affecting 30-40% of 14 year olds. There are no known biomarkers to identify children with silent cerebral infarcts, and the pathological basis is also unknown. We used an unbiased proteomic discovery approach to identify plasma proteins differing in concentration between children with and without silent cerebral infarcts. Clinical parameters and plasma samples were analysed from 51 children (mean age 11.8 years, range 6-18) with sickle cell anemia (HbSS). A total of 19 children had silent cerebral infarcts and 32 normal MRI; the children with silent infarcts had lower HbF levels (8.6 vs. 16.1%, P=0.049) and higher systolic blood pressures (115 vs. 108.6, P=0.027). Plasma proteomic analysis showed 13 proteins increased more than 1.3 fold in the SCI patients, including proteins involved in hypercoagulability (α2-antiplasmin, fibrinogen−γ chain, thrombospondin-4), inflammation (α2-macroglobulin, complement C1s and C3), and atherosclerosis (apolipoprotein B-100). Higher levels of gelsolin and retinol-binding protein 4 were also found in the population with silent infarcts, both of which have been linked to stroke. We investigated the genetic basis of these differences by studying 359 adults with sickle cell disease (199 with silent cerebral infarcts, 160 normal MRIs), who had previously undergone a genome-wide genotyping array. None of the genes coding for the differentially expressed proteins were significantly associated with silent infarction. Our study suggests that silent cerebral infarcts in sickle cell anemia may be associated with higher systolic blood pressure, lower HbF levels, hypercoagulability, inflammation and atherosclerotic lipoproteins.

Different Associations of Plasma Biomarkers in Alzheimer's Disease, Mild Cognitive Impairment, Vascular Dementia, and Ischemic Stroke

Background and Purpose

Cognitive and cerebrovascular diseases are common in the elderly, but differences in the plasma levels and associations of plasma biomarkers in these diseases remain elusive.

Methods

The present study investigated differences in plasma fatty acids [eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)], adiponectin, reptin, plasma markers of inflammation [high-sensitivity C-reactive protein (hsCRP) and serum amyloid A (serum AA)], and plasma lipids [high-density lipoprotein and low-density lipoprotein (LDL)] in patients with Alzheimer's disease (AD) (n=266), mild cognitive impairment (MCI) (n=44), vascular dementia (VaD) (n=33), and ischemic stroke (IS) (n=200) in comparison to normal controls (n=130).

Results

The serological data showed that lower EPA and DHA levels and higher reptin and LDL levels were associated with AD and IS, the reptin/adiponectin ratio was strongly associated with IS, the hsCRP level was more strongly associated with VaD and IS, and the serum AA level was associated with all three cognitive diseases and IS.

Conclusions

This is the first report of differences in the expression levels of plasma biomarkers and peripheral arterial tonometry among AD, MCI, VaD, and IS patients and normal controls. These different associations indicate that diverse pathological mechanisms underlie these diseases.

Plasma Retinol-Binding Protein 4 Levels and the Risk of Ischemic Stroke among Women

BACKGROUND

Plasma retinol-binding protein 4 (RBP4) levels have been associated with cardiovascular risk factors and risk of coronary heart disease, but little is known about the association between RBP4 and the risk of ischemic stroke. We hypothesized that elevated RBP4 levels would be associated with an increased risk of ischemic stroke among women.

METHODS

We performed a nested case-control study among women enrolled in the Nurses' Health Study who provided blood samples between 1989 and 1990 and were free of prior stroke and cancer. We measured prediagnostic RBP4 levels in 471 ischemic stroke cases who were confirmed by medical record review and in 471 controls who were matched 1:1 to the cases on age, race, blood collection date, menopausal status, postmenopausal hormone use, and smoking status. We analyzed the association between RBP4 levels and ischemic stroke using multivariable conditional logistic regression conditional on the matching factors and adjusted for physical activity, body mass index, aspirin use, alcohol consumption, diet, history of diabetes, high cholesterol, high blood pressure, or heart disease, and cholesterol and hemoglobin A1C levels.

RESULTS

Median levels of RBP4 were similar in cases (31.1 µg/mL) and controls (31.0 µg/mL; P value from the Wilcoxon rank-sum test = .82). Quartiles of RBP4 were not associated with an increased risk of ischemic stroke (highest quartile compared to lowest quartile: multivariate-adjusted odds ratio, .75; 95% confidence interval, .48, 1.17). We also did not observe associations between RBP4 and ischemic stroke of thrombotic or embolic origin.

CONCLUSIONS

Elevated levels of RBP4 were not associated with an increased risk of ischemic stroke.

Prospective Relation of Circulating Adipokines to Incident Metabolic Syndrome: The Framingham Heart Study

Background

Adipokines are elaborated by adipose tissue and are associated with glycemic, lipid, and vascular traits. We hypothesized that in a cross‐sectional analysis circulating adipokines are altered among subsets of obesity stratified by presence versus absence of metabolic syndrome (MetS) and prospectively predict the incidence of MetS.

Methods and Results

Participants in the community‐based Framingham Third Generation Cohort who attended examination cycle 1 were included in the study (2002–2005; N=3777, mean age, 40 years; 59% women). Circulating adiponectin, leptin, leptin receptor, fetuin‐A, fatty acid–binding protein 4, and retinol binding protein 4 were assayed and related to incident MetS in follow‐up (mean 6 years). The adipokines were compared among individuals with excess body weight (body mass index ≥25 kg/m²) and prevalent MetS, excess body weight without MetS (metabolically healthy obese), and normal‐weight with MetS (metabolically obese, normal‐weight) with normal‐weight participants without MetS as a referent. Metabolically healthy obese individuals (n=1467) had higher circulating levels of fetuin‐A and fatty acid–binding protein 4 but lower levels of leptin, leptin receptor, and adiponectin (P<0.001 for all). The adipokine panel was associated with incident MetS (263 new‐onset cases; P=0.002). Higher circulating concentrations of retinol‐binding protein 4 and fetuin‐A were associated with incidence of MetS (odds ratio per 1‐SD increment log marker, 1.21; 95% CI, 1.03–1.41 [P=0.02] and 1.17; 95% CI, 1.01–1.34 [P=0.03], respectively).

Conclusions

In our community‐based sample of young to middle‐aged adults, metabolically healthy obese individuals demonstrated an adverse adipokine profile. Higher circulating levels of retinol‐binding protein 4 and fetuin‐A marked future cardiometabolic risk.

The novel exercise-induced hormone irisin protects against neuronal injury via activation of the Akt and ERK1/2 signaling pathways and contributes to the neuroprotection of physical exercise in cerebral ischemia

BACKGROUND

Irisin is a novel exercise-induced myokine involved in the regulation of adipose browning and thermogenesis. In this study, we investigated the potential role of irisin in cerebral ischemia and determined whether irisin is involved in the neuroprotective effect of physical exercise in mice.

MATERIALS AND METHODS

The middle cerebral artery occlusion (MCAO) model was used to produce cerebral ischemia in mice. First, the plasma irisin levels and changes in expression of the irisin precursor protein FNDC5 in skeletal muscle were determined post ischemic stroke. Second, the association between plasma irisin levels and the neurological deficit score, brain infarct volume, or plasma concentrations of tumor necrosis factor-α (TNF-α), interleukin (IL)-6 and IL-1β in mice with MCAO were evaluated. Third, the therapeutic effect of irisin on ischemic brain injury was evaluated in vivo and in vitro. Recombinant irisin was injected directly into the tail vein 30min after the MCAO operation, and then the effects of irisin treatment on brain infarct volume, neurological deficit, neuroinflammation, microglia activation, monocyte infiltration, oxidative stress and intracellular signaling pathway activation (Akt and ERK1/2) were measured. Irisin was also administered in cultured PC12 neuronal cells with oxygen and glucose deprivation (OGD). Finally, to assess the potential involvement of irisin in the neuroprotection of physical exercise, mice were exercised for 2weeks and an irisin neutralizing antibody was injected into these mice to block irisin 1h before the MCAO operation.

RESULTS

The plasma irisin concentration and intramuscular FNDC5 protein expression decreased after ischemic stroke. Plasma irisin levels were negatively associated with brain infarct volume, the neurological deficit score, plasma TNF-α and plasma IL-6 concentrations. In OGD neuronal cells, irisin protected against cell injury. In mice with MCAO, irisin treatment reduced the brain infarct volume, neurological deficits, brain edema and the decline in body weight. Irisin treatment inhibited activation of Iba-1⁺ microglia, infiltration of MPO-1⁺ monocytes and expression of both TNF-α and IL-6 mRNA. Irisin significantly suppressed the levels of nitrotyrosine, superoxide anion and 4-hydroxynonenal (4-HNE) in peri-infarct brain tissues. Irisin treatment increased Akt and ERK1/2 phosphorylation, while blockade of Akt and ERK1/2 by specific inhibitors reduced the neuroprotective effects of irisin. Finally, the exercised mice injected with irisin neutralizing antibody displayed more severe neuronal injury than the exercised mice injected with control IgG.

CONCLUSION

Irisin reduces ischemia-induced neuronal injury via activation of the Akt and ERK1/2 signaling pathways and contributes to the neuroprotective effect of physical exercise against cerebral ischemia, suggesting that irisin may be a factor linking metabolism and cardio-cerebrovascular diseases.

Retinol-Binding Protein-Dependent Cholesterol Uptake Regulates Macrophage Foam Cell Formation and Promotes Atherosclerosis

BACKGROUND

Retinol-binding protein 4 (RBP4) is an adipokine that plays decisive roles in glucose metabolism and insulin sensitivity. Elevated circulating RBP4 levels were reported to be associated with increased risk for cardiovascular disease, but the precise role of RBP4 in atherosclerotic diseases and its mechanisms of action remain elusive.

METHODS

Serum RBP4 levels of 1683 participants from South China were evaluated and the occurrence of major adverse cardiovascular events was followed up for 5 years. Apolipoprotein E-deficient mice infected with RBP4-overexpressing/silencing adenovirus, J774A.1 macrophages, and primary peritoneal macrophages from RBP4 transgenic mice were used for investigating the function of RBP4 in foam cell formation.

RESULTS

Prospective cohort studies revealed that baseline serum RBP4 level was an independent predictor for incidence of adverse cardiovascular events after adjustment for traditional risk factors. Increased RBP4 expression was observed in atherosclerotic lesions of aortic specimens from both humans and apolipoprotein E-deficient mice, and RBP4 was localized to areas rich in macrophage foam cells. RBP4 inhibition attenuated whereas overexpression accelerated atherosclerosis progression in apolipoprotein E-deficient mice. Both treatment with exogenous recombinant RBP4 and overexpression of RBP4 gene promoted macrophage-derived foam cell formation through the activation of scavenger-receptor CD36-mediated cholesterol uptake, and RBP4 transcriptionally upregulated CD36 expression in a manner dependent on jun N-terminal kinase and signal transducer and activator of transcription 1. The tyrosine kinase c-Src was identified as the upstream regulator of jun N-terminal kinase-signal transducer and activator of transcription 1-mediated CD36-dependent cholesterol uptake, and RBP4 challenge was found to alter the membrane distribution of c-Src and cause c-Src to partition into lipid-raft membrane subdomains, where the kinase was activated. Lastly, Toll-like receptor 4, but not retinol or stimulated by retinoic acid 6, mediated the inductive effects of RBP4 in macrophages.

CONCLUSIONS

Inclusion of RBP4 levels in traditional models enhances the predictive ability for the incidence of atherosclerotic events. RBP4 promotes atherogenesis by inducing macrophage-derived foam cell formation.

The role of adipokines in ischemic stroke risk stratification

Background

Adiponectin, leptin, and resistin are the most well-studied adipokines and play important roles in the regulation of glucose metabolism, subclinical inflammation, and cardiovascular homeostasis. Accordingly, measurement of adipokine levels might be useful in cardiovascular risk stratification. Moreover, the study of single-nucleotide polymorphisms of genes that encode these adipokines might also represent a valuable predictive tool in cardiovascular disease prevention strategies.

Aims

To summarize the biologic role of the adipokines adiponectin, leptin, and resistin and the prognostic value of their serum levels regarding the occurrence and outcome of ischemic stroke. We also discuss the relationship of single-nucleotide polymorphisms of the adiponectin, leptin genes, and the −420C > G polymorphism of resistin gene with stroke risk.

Summary of review

Several studies in the general population evaluated the association between these adipokines and stroke risk, yielding conflicting results. There are more limited data regarding the effect of these adipokines on stroke severity and outcome. A small number of studies also assessed the predictive role of single-nucleotide polymorphisms of the adiponectin, leptin, and resistin genes regarding stroke risk, but the findings were also controversial.

Conclusions

It is unclear whether adiponectin, leptin, and resistin levels or the single-nucleotide polymorphisms of their encoding genes are independently associated with stroke risk. However, given the role of these adipokines in the pathogenesis of atherosclerosis, larger prospective studies, both in the general population and in patients with a history of stroke, are needed to determine whether the measurement of serum levels of these adipokines or the evaluation of single-nucleotide polymorphisms in their encoding genes could improve stroke risk prediction. If this relationship is proven, therapeutic interventions targeting adipokine levels might represent a novel approach to reduce stroke-related mortality and disability.

Transgenic Mice Overexpressing Serum Retinol-Binding Protein Develop Progressive Retinal Degeneration through a Retinoid-Independent Mechanism

Serum retinol-binding protein 4 (RBP4) is the sole specific transport protein for retinol in the blood, but it is also an adipokine with retinol-independent, proinflammatory activity associated with obesity, insulin resistance, type 2 diabetes, and cardiovascular disease. Moreover, two separate studies reported that patients with proliferative diabetic retinopathy have increased serum RBP4 levels compared to patients with mild or no retinopathy, yet the effect of increased levels of RBP4 on the retina has not been studied. Here we show that transgenic mice overexpressing RBP4 (RBP4-Tg mice) develop progressive retinal degeneration, characterized by photoreceptor ribbon synapse deficiency and subsequent bipolar cell loss. Ocular retinoid and bisretinoid levels are normal in RBP4-Tg mice, demonstrating that a retinoid-independent mechanism underlies retinal degeneration. Increased expression of pro-interleukin-18 (pro-IL-18) mRNA and activated IL-18 protein and early-onset microglia activation in the retina suggest that retinal degeneration is driven by a proinflammatory mechanism. Neither chronic systemic metabolic disease nor other retinal insults are required for RBP4 elevation to promote retinal neurodegeneration, since RBP4-Tg mice do not have coincident retinal vascular pathology, obesity, dyslipidemia, or hyperglycemia. These findings suggest that elevation of serum RBP4 levels could be a risk factor for retinal damage and vision loss in nondiabetic as well as diabetic patients.

Relationship between Proinflammatory and Antioxidant Proteins with the Severity of Cardiovascular Disease in Type 2 Diabetes Mellitus

Type 2 diabetes mellitus patients are at significant risk of cardiovascular disease, however, the pathophysiology of these complications is complex and incompletely known in this population. The aim of this study was to compare the serum proteome of patients with type 2 diabetes mellitus presenting or not presenting cardiovascular disease with non-diabetic subjects to find essential proteins related to these cardiovascular complications. This cross-sectional study compares the serum proteome by a combination of protein depletion with 2D-DIGE (2-dimension Difference Gel Electrophoresis) methodology. The proteins differentially expressed were identified by MALDI TOF/TOF (Matrix-assisted laser desorption/ionization and Time-Of-Flight ion detector) or LC-MS/MS (Liquid Chromatography coupled to Mass-Mass Spectrometry). Type 2 diabetes mellitus patients with cardiovascular disease showed higher expression of plasma retinol binding protein and glutathione peroxidase-3 compared to those without cardiovascular disease and non-diabetic controls. These results show that proteins related to the inflammatory and redox state appear to play an important role in the pathogenesis of the cardiovascular disease in the type 2 diabetes mellitus patients.

Endocrine and Metabolic Effects of Adipose Tissue in Children and Adolescents

Adipose tissue is implicated in many endocrine and metabolic processes. Leptin was among the first identified adipose-secreted factors, which act in an auto-, para- and endocrine manner. Since leptin, many other adipose tissue factors were determined, some primarily secreted from the adipocytes, some from other cells of the adipose tissue.

So-called adipokines are not only involved in obesity and its complications, as are insulin resistance, type 2 diabetes and other components of the metabolic syndrome, but also in growth, reproduction, bone metabolism, immune response, cancer development and many other important biological processes. Research in the field of adipokines has revealed new insights into the physiological and pathophysiologal processes and opened new therapeutic possibilities. In the present article, a special emphasis is devoted to research in children and adolescents.

Retinol-binding protein 4 levels and susceptibility to ischaemic events in men

BACKGROUND

Many efforts in cardiovascular medicine have been focused in the identification of patients at risk of developing an acute ischaemic event. Biomarker discovery studies have become an essential research area, being proteomic technologies an excellent tool for biomarker identification. By applying proteomic approaches, we have detected changes in retinol-binding protein 4 (RBP4) in acute new-onset myocardial infarction patients (AMI) and in high-risk patients with heterozygous familial hypercholesterolaemia (FH).

MATERIALS AND METHODS

Differential serum proteome was analysed by two-dimensional electrophoresis and MALDI-TOF/TOF. Validation studies were performed by ELISA, and functional effects of RBP4 were tested in cell culture experiments.

RESULTS

Retinol-binding protein 4 proteomic characterization depicted two spots (pI = 5·4;Mw = 23·01/22·78 kDa) with decreased intensity in AMI patients. Total serum RBP4 levels were decreased in AMI patients (N = 68) compared with controls (N = 132; P < 0·0001). RBP4 was also decreased in FH patients who had an ischaemic event 2 years (±0·3) after their inclusion compared with FH patients without any cardiovascular episode at follow-up (P < 0·001; N = 187). In both cases, changes were limited to men. RBP4 induced a significant increase in eNOS expression in human endothelial vascular cells and in prostaglandin I2 release in coronary vascular smooth muscle cells.

CONCLUSIONS

We show decreased serum RBP4 levels in men in the acute phase of AMI, being this decrease already detected in men with FH previous to the presentation of an ischaemic event. The decrease in RBP4 levels could confer an increased susceptibility to the precipitation of an ischaemic event that could be mediated by the decrease in its vasculoprotective properties through NO and PGI2 .

Metabolic syndrome in youth: current insights and novel serum biomarkers

Paralleling the worldwide epidemic in childhood obesity, in the last decade we have observed a rise in the prevalence of metabolic syndrome (MetS) in pediatrics. The MetS comprises a cluster of cardiovascular risk factors. Multiple definitions have been proposed for the syndrome in the pediatric age group, but they are very difficult to test and validate. Thus, in this paper we will discuss the current knowledge in pediatric MetS and the potential role of novel biomarkers in the pathogenesis and diagnosis of MetS.

Retinol-binding protein 4 induces inflammation in human endothelial cells by an NADPH oxidase- and nuclear factor kappa B-dependent and retinol-independent mechanism

Serum retinol-binding protein 4 (RBP4) is the sole specific vitamin A (retinol) transporter in blood. Elevation of serum RBP4 in patients has been linked to cardiovascular disease and diabetic retinopathy. However, the significance of RBP4 elevation in the pathogenesis of these vascular diseases is unknown. Here we show that RBP4 induces inflammation in primary human retinal capillary endothelial cells (HRCEC) and human umbilical vein endothelial cells (HUVEC) by stimulating expression of proinflammatory molecules involved in leukocyte recruitment and adherence to endothelium, including vascular cell adhesion molecule 1 (VCAM-1), intercellular adhesion molecule 1 (ICAM-1), E-selectin, monocyte chemoattractant protein 1 (MCP-1), and interleukin-6 (IL-6). We demonstrate that these novel effects of RBP4 are independent of retinol and the RBP4 membrane receptor STRA6 and occur in part via activation of NADPH oxidase and NF-κB. Importantly, retinol-free RBP4 (apo-RBP4) was as potent as retinol-bound RBP4 (holo-RBP4) in inducing proinflammatory molecules in both HRCEC and HUVEC. These studies reveal that RBP4 elevation can directly contribute to endothelial inflammation and therefore may play a causative role in the development or progression of vascular inflammation during cardiovascular disease and microvascular complications of diabetes.

Endothelial impairment and bone marrow-derived CD34(+)/133(+) cells in diabetic patients with erectile dysfunction

Aims/Introduction

The present study was undertaken to determine vascular endothelial impairment and endothelial progenitor cells (EPCs) in patients with type 2 diabetes mellitus and erectile dysfunction (ED).

Materials and Methods

A total of 100 type 2 diabetic men were enrolled. Flow‐mediated dilatation (FMD) and anaerobic threshold (AT) were measured. Also, EPCs in the peripheral blood were determined by flow cytometry.

Results

In the 42 ED diabetic patients, FMD and AT were significantly less than those in the 58 patients with normal erectile function (FMD 2.84 vs 3.82%, P = 0.038, and AT 11.2 vs 12.7 mL/kg/min, P = 0.022). Exercise tolerance significantly increased the number of EPCs in the patients with and without ED (49–60 cells/100 μL, P = 0.015, and 72–99 cells/100 μL, P = 0.003). In the diabetic patients without autonomic neuropathy, FMD was significantly reduced in the patients with ED than those without ED (P = 0.015). In response to exercise tolerance, the number of EPCs increased in both the diabetic patients with ED (P = 0.003) and without ED (P = 0.007). In contrast, in the diabetic patients with autonomic neuropathy, there was no difference in FMD between the patients with and without ED. The exercise tolerance increased the number of EPCs in the patients without ED (P = 0.023), but it disappeared in those with ED.

Conclusions

ED diabetic patients have endothelial impairment during the early period of diabetic complications, whose deranged endothelial function is concomitantly repaired by promoting bone marrow‐derived EPCs.

Association among retinol-binding protein 4, small dense LDL cholesterol and oxidized LDL levels in dyslipidemia subjects

OBJECTIVES

To investigate retinol-binding protein 4 (RBP4), small dense low-density lipoprotein cholesterol (sdLDL-C) and oxidized low-density lipoprotein (ox-LDL) levels and their associations in dyslipidemia subjects.

DESIGN AND METHODS

We determined RBP4, sdLDL-C, ox-LDL levels in 150 various dyslipidemia subjects and 50 controls. The correlation analysis and multiple linear regression analysis were performed.

RESULTS

The RBP4, sdLDL-C and ox-LDL levels were found increased in various dyslipidemia subjects. The sdLDL-C levels were positively correlated with RBP4 (r=0.273, P=0.001) and ox-LDL (r=0.273, P=0.001). RBP4 levels were also correlated with ox-LDL (r=0.167, P=0.043). The multiple regression analysis showed that only sdLDL-C was a significant independent predictor for RBP4 (β coefficient=0.219, P=0.009; adjusted R(2)=0.041) and ox-LDL (β coefficient=0.253, P=0.003; adjusted R(2)=0.057) levels, respectively.

CONCLUSIONS

The independent associations of sdLDL-C with RBP4 and ox-LDL were observed in dyslipidemia subjects. RBP4 may play an important role in lipid metabolism of atherosclerosis, particularly in formation of sdLDL.

Prompt increases in retinol-binding protein 4 and endothelial progenitor cells during acute exercise load in diabetic subjects

The present study was undertaken to determine whether acute exercise load alters serum retinol-binding protein 4 (RBP4) and numbers of endothelial progenitor cells (EPC) in diabetic subjects. Sixty-two subjects with type 2 diabetes mellitus were enrolled in the present study. They were 50 males and 12 females with the ages of 65.1±8.1 (mean ± SD) years. Cardio-pulmonary exercise stress test (CPX) was carried out, and the numbers of EPC and serum RBP4 levels before and after the CPX were measured. RBP4 is a cytokine synthesized in hepatocytes, white adipose tissues and skeletal muscles, and serum RBP4 was determined by ELISA. EPC was determined as CD34(+)/133(+) cells by FACS. The subjects were subgrouped into two groups with or without nephropathy. Serum RBP4 levels promptly increased from 48.2±4.3 (mean±SEM) to 54.3±4.2 μg/mL after the CPX (mean exercise time of 8 min) in the diabetic subjects without nephropathy (p=0.0006), but did not in those with nephropathy. There was a positive correlation between changes in serum RBP4 during the exercise and estimated glomerular filtration rate (r=0.30, p=0.018). Also, an acute exercise load promptly increased the number of EPCs in the diabetic subjects with and without nephropathy. These findings suggest that a prompt increase in exercise-induced RBP4 is retarded by progression of nephropathy, and that an exercise-induced mobilization of EPCs could maintain endothelial cells in diabetic subjects.

RBP4: a controversial adipokine

Adipose tissue is an endocrine organ secreting biologically active factors called adipokines that act on both local and distant tissues. Adipokines have an important role in the development of obesity-related comorbidities not only in adults but also in children and adolescents. Retinol binding protein 4 (RBP4) is a recently identified adipokine suggested to link obesity with its comorbidities, especially insulin resistance, type 2 diabetes (T2D), and certain components of the metabolic syndrome. However, data, especially resulting from the clinical studies, are conflicting. In this review, we summarize up-to-date knowledge on RBP4's role in obesity, development of insulin resistance, and T2D. Special attention is given to studies on children and adolescents. We also discuss the role of possible confounding factors that should be taken into account when critically evaluating published studies or planning new studies on this exciting adipokine.

Adipokines as possible new predictors of cardiovascular diseases: a case control study

Background and Aims. The secretion of several adipocytokines, such as adiponectin, retinol-binding protein 4 (RBP4), adipocyte fatty acid binding protein (aFABP), and visfatin, is altered in subjects with abdominal adiposity; these endocrine alterations could contribute to increased cardiovascular risk. The aim of the study was to assess the relationship among adiponectin, RBP4, aFABP, and visfatin, and incident cardiovascular disease. Methods and Results. A case-control study, nested within a prospective cohort, on 2945 subjects enrolled for a diabetes screening program was performed. We studied 18 patients with incident fatal or nonfatal IHD (Ischemic Heart Disease) or CVD (Cerebrovascular Disease), compared with 18 matched control subjects. Circulating adiponectin levels were significantly lower in cases of IHD with respect to controls. Circulating RBP4 levels were significantly increased in CVD and decreased in IHD with respect to controls. Circulating aFABP4 levels were significantly increased in CVD, while no difference was associated with IHD. Circulating visfatin levels were significantly lower in cases of both CVD and IHD with respect to controls, while no difference was associated with CVD. Conclusions. The present study confirms that low adiponectin is associated with increased incidents of IHD, but not CVD, and suggests, for the first time, a major effect of visfatin, aFABP, and RBP4 in the development of cardiovascular disease.

Elevated serum retinol-binding protein 4 concentrations are associated with chronic kidney disease but not with the higher carotid intima-media thickness in type 2 diabetic subjects

To examine the association of serum retinol-binding protein 4 (RBP4) concentrations with carotid intima-media thickness (CIMT) in type 2 diabetic subjects with chronic kidney disease (CKD). A total of 239 type 2 diabetic patients (64 ± 13 years, 154 males) were divided into two groups: one with CKD, defined as estimated glomerular filtration rate (eGFR) below 60 mL/min/1.73m(2) (n = 86), and one without (n = 153). We recorded clinical and biochemical data as well as CIMT. The patients with CKD were older, had had diabetes mellitus longer, and had higher incidence of hypertension, dyslipidemia and microalbuminuria than those without. They also had higher serum concentrations of RBP4 (44.8 ± 6.4 vs 39.5 ± 4.9 µg/mL, p < 0.001), higher mean CIMT (0.75 ± 0.16 vs 0.69 ± 0.14 mm, p = 0.0070), and higher incidence of carotid plaques (27.9 vs 11.8 %, p = 0.002). The RBP4 were negatively correlated with eGFR (r = -0.514, p < 0.001). However, the RBP4 were not correlated with mean CIMT (r = 0.065, p = 0.318). Moreover, when dividing the patients into two groups by the mean CIMT, those with mean CIMT above 0.71 mm did not have different RBP4 concentrations compared with those below (41.5 ± 5.7 vs 41.3 ± 6.3 µg/mL, p = 0.856). In conclusion, we observed an elevation of serum RBP4 concentrations and CIMT levels in type 2 diabetic subjects with CKD. However, the elevated RBP4 were not associated with the higher CIMT among these patients.

Inflammation, a link between obesity and cardiovascular disease

Obesity, the most common nutritional disorder in industrialized countries, is associated with an increased mortality and morbidity of cardiovascular disease (CVD). Obesity is primarily considered to be a disorder of energy balance, and it has recently been suggested that some forms of obesity are associated with chronic low-grade inflammation. The present paper focuses on the current status of our knowledge regarding chronic inflammation, a link between obesity and CVDs, including heart diseases, vascular disease and atherosclerosis. The paper discusses the methods of body fat evaluation in humans, the endocrinology and distribution of adipose tissue in the genders, the pathophysiology of obesity, the relationship among obesity, inflammation, and CVD, and the adipose tissue-derived cytokines known to affect inflammation. Due to space limitations, this paper focuses on C-reactive protein, serum amyloid A, leptin, adiponectin, resistin, visfatin, chemerin, omentin, vaspin, apelin, and retinol binding protein 4 as adipokines.