Assim A. Alfadda

Reactive oxygen species in health and disease.

During the past decades, it became obvious that reactive oxygen species (ROS) exert a multitude of biological effects covering a wide spectrum that ranges from physiological regulatory functions to damaging alterations participating in the pathogenesis of increasing number of diseases. This review summarizes the key roles played by the ROS in both health and disease. ROS are metabolic products arising from various cells; two cellular organelles are intimately involved in their production and metabolism, namely, the endoplasmic reticulum and the mitochondria. Updates on research that tremendously aided in confirming the fundamental roles of both organelles in redox regulation will be discussed as well. Although not comprehensive, this review will provide brief perspective on some of the current research conducted in this area for better understanding of the ROS actions in various conditions of health and disease.

A Novel Function of Adipocytes in Lipid Antigen Presentation to iNKT Cells

ABSTRACT Systemic low-grade chronic inflammation has been intensively investigated in obese subjects. Recently, various immune cell types, such as macrophages, granulocytes, helper T cells, cytotoxic T cells, and B cells, have been implicated in the pathogenesis of adipose tissue inflammation. However, the roles of invariant natural killer T cells (iNKT cells) and the regulation of iNKT cell activity in adipose tissue are not thoroughly understood. Here, we demonstrated that iNKT cells were decreased in number in the adipose tissue of obese subjects. Interestingly, CD1d, a molecule involved in lipid antigen presentation to iNKT cells, was highly expressed in adipocytes, and CD1d-expressing adipocytes stimulated iNKT cell activity through physical interaction. iNKT cell population and CD1d expression were reduced in the adipose tissue of obese mice and humans compared to those of lean subjects. Moreover, iNKT cell-deficient Jα18 knockout mice became more obese and exhibited increased adipose tissue inflammation at the early stage of obesity. These data suggest that adipocytes regulate iNKT cell activity via CD1d and that the interaction between adipocytes and iNKT cells may modulate adipose tissue inflammation in obesity.

Obesity-induced DNA hypermethylation of the adiponectin gene mediates insulin resistance

Adiponectin plays a key role in the regulation of the whole-body energy homeostasis by modulating glucose and lipid metabolism. Although obesity-induced reduction of adiponectin expression is primarily ascribed to a transcriptional regulation failure, the underlying mechanisms are largely undefined. Here we show that DNA hypermethylation of a particular region of the adiponectin promoter suppresses adiponectin expression through epigenetic control and, in turn, exacerbates metabolic diseases in obesity. Obesity-induced, pro-inflammatory cytokines promote DNMT1 expression and its enzymatic activity. Activated DNMT1 selectively methylates and stimulates compact chromatin structure in the adiponectin promoter, impeding adiponectin expression. Suppressing DNMT1 activity with a DNMT inhibitor resulted in the amelioration of obesity-induced glucose intolerance and insulin resistance in an adiponectin-dependent manner. These findings suggest a critical role of adiponectin gene epigenetic control by DNMT1 in governing energy homeostasis, implying that modulating DNMT1 activity represents a new strategy for the treatment of obesity-related diseases.

Adipocytokine Orosomucoid Integrates Inflammatory and Metabolic Signals to Preserve Energy Homeostasis by Resolving Immoderate Inflammation

Orosomucoid (ORM), also called α-1 acid glycoprotein, is an abundant plasma protein that is an immunomodulator induced by stressful conditions such as infections. In this study, we reveal that Orm is induced selectively in the adipose tissue of obese mice to suppress excess inflammation that otherwise disturbs energy homeostasis. Adipose Orm levels were elevated by metabolic signals, including insulin, high glucose, and free fatty acid, as well as by the proinflammatory cytokine tumor necrosis factor-α, which is found in increased levels in the adipose tissue of morbid obese subjects. In both adipocytes and macrophages, ORM suppressed proinflammatory gene expression and pathways such as NF-κB and mitogen-activated protein kinase signalings and reactive oxygen species generation. Concomitantly, ORM relieved hyperglycemia-induced insulin resistance as well as tumor necrosis factor-α-mediated lipolysis in adipocytes. Accordingly, ORM improved glucose and insulin tolerance in obese and diabetic db/db mice. Taken together, our results suggest that ORM integrates inflammatory and metabolic signals to modulate immune responses to protect adipose tissue from excessive inflammation and thereby from metabolic dysfunction.

Adiposity and insulin resistance correlate with telomere length in middle-aged Arabs: the influence of circulating adiponectin

Objective Studies in obesity have implicated adipocytokines in the development of insulin resistance, which in turn may lead to accelerated aging. In this study, we determined associations of chromosomal telomere length (TL) to markers of obesity and insulin resistance in middle-aged adult male and female Arabs with and without diabetes mellitus type 2 (DMT2). Design and methods One hundred and ninety-three non-diabetic and DMT2 subjects without complications (97 males and 96 females) participated in this cross-sectional study. Clinical data, as well as fasting blood samples, were collected. Serum glucose and lipid profile were determined using routine laboratory methods. Serum insulin, leptin, adiponectin, resistin, tumor necrosis factor-α, and PAI-1 were quantified using customized multiplex assay kits. High sensitive C-reactive protein (hsCRP) and angiotensin II (ANG II) were measured using ELISAs. Circulating leukocyte TL was examined by quantitative real-time PCR. Results Circulating chromosomal leukocyte TL had significant inverse associations with body mass index (BMI), systolic blood pressure, fasting insulin, homeostasis model assessment of insulin resistance (HOMA-IR), low-density lipoprotein (LDL)- and total cholesterol, ANG II and hsCRP levels. Adiponectin, BMI, systolic blood pressure, and LDL cholesterol predicted 47% of the variance in TL (P<0.0001). HOMA-IR was the most significant predictor for TL in males, explaining 35% of the variance (P=0.01). In females, adiponectin accounted for 28% of the variance in TL (P=0.01). Conclusion Obesity and insulin resistance are associated with chromosomal TL among adult Arabs. Evidence of causal relations needs further investigation. The positive association of adiponectin to TL has clinical implications as to the possible protective effects of this hormone from accelerated aging.

Differential patterns of serum concentration and adipose tissue expression of chemerin in obesity: Adipose depot specificity and gender dimorphism

Chemerin, a recognized chemoattractant, is expressed in adipose tissue and plays a role in adipocytes differentiation and metabolism. Gender- and adipose tissue-specific differences in human chemerin expression have not been well characterized. Therefore, these differences were assessed in the present study. The body mass index (BMI) and the circulating levels of chemerin and other inflammatory, adiposity and insulin resistance markers were assessed in female and male adults of varying degree of obesity. Chemerin mRNA expression was also measured in paired subcutaneous and visceral adipose tissue samples obtained from a subset of the study subjects. Serum chemerin concentrations correlated positively with BMI and serum leptin levels and negatively with high density lipoprotein (HDL)-cholesterol levels. No correlation was found between serum chemerin concentrations and fasting glucose, total cholesterol, low density lipoprotein (LDL)-cholesterol, triglycerides, insulin, C-reactive protein or adiponectin. Similarly, no relation was observed with the homeostasis model assessment for insulin resistance (HOMA-IR) values. Gender- and adipose tissue-specific differences were observed in chemerin mRNA expression levels, with expression significantly higher in women than men and in subcutaneous than visceral adipose tissue. Interestingly, we found a significant negative correlation between circulating chemerin levels and chemerin mRNA expression in subcutaneous fat. Among the subjects studied, circulating chemerin levels were associated with obesity markers but not with markers of insulin resistance. At the tissue level, fat depot-specific differential regulation of chemerin mRNA expression might contribute to the distinctive roles of subcutaneous vs. visceral adipose tissue in human obesity.

Association between Osteocalcin, Metabolic Syndrome, and Cardiovascular Risk Factors: Role of Total and Undercarboxylated Osteocalcin in Patients with Type 2 Diabetes

Studies have demonstrated that total osteocalcin (TOC) is associated with metabolic syndrome (MetS) and therefore might influence the risk of cardiovascular disease in humans. Undercarboxylated osteocalcin (uOC) regulates insulin secretion and sensitivity in mice, but its relation to MetS in humans is unclear. We aimed to determine whether uOC is related to MetS and/or its individual components and other cardiovascular risk factors in patients with type 2 diabetes mellitus (T2DM), and whether TOC and uOC have utility in predicting the cardiovascular risk. We studied 203 T2DM patients with and without MetS. MetS was defined based on the NCEP-ATP III criteria. A correlation analysis was performed between the three outcome variables: (i) TOC, (ii) uOC, and (iii) carboxylated osteocalcin (cOC) and MetS components and other cardiovascular risk factors. Both TOC and uOC were significantly lower in patients with MetS compared to those without MetS, independent of body mass index. In patients with MetS, uOC was significantly and positively correlated with HDL cholesterol, while TOC was significantly and negatively correlated with serum triglycerides. We report for the first time that uOC is related to lipid indices in patients with T2DM. Further studies are necessary to determine whether uOC can be utilized for cardiovascular risk assessments in these patients.

Proteomic analysis of mature adipo cytes from obese patients in relation to aging

Obesity and aging are interrelated conditions that both cause changes in adipocyte metabolism and affect the distribution of fat in both subcutaneous and visceral depots. In addition, both weight gain and aging can lead to similar clinical outcomes such as insulin resistance, cardiovascular disease, type 2 diabetes mellitus, atherosclerosis and stroke. Our objective was to examine the changes in protein expression within the subcutaneous adipose tissue of obese patients, matched for BMI, in relation to age. Mature adipocytes were isolated from liposuction samples of abdominal subcutaneous adipose tissue collected from both young (26.2±4.3 (mean age±SD); n=7) and old (52.2±4.7 (mean age±SD); n=7) obese individuals. Total protein extracts were then compared by two-dimensional difference in gel electrophoresis (2D DIGE). Thirty differentially expressed protein spots (ANOVA test, p≤0.05; fold-change ≥1.8) were detected, of which, 15 were identified by MALDI-TOF mass spectrometry. These were comprised of a total of thirteen unique protein sequences. Nine proteins were more abundant in the adipocytes isolated from old vs. young individuals. These proteins included prohibitin 1, protein disulphide isomerase A3, beta actin, profilin, aldo-ketoreductase 1 C2, alpha crystallin B and the annexins A1, A5 and A6. Four other proteins were less abundant in the adipocytes from old, obese subjects and these included keratin type 2 cytoskeletal 1, keratin type 2 cytoskeletal 10 and hemoglobins A and B. The differentially abundant proteins were investigated by Ingenuity Pathway Analysis (IPA) to reveal their associations with known biological functions. This analysis identified signal transducer and activator of transcription 3 as the central molecule in the connectivity map and the apoptotic pathway as the pathway with the highest score. Differences in the abundances of several proteins were confirmed by immunoblotting: i.e., prohibitin 1, protein disulphide isomerase A3, beta actin, profilin and signal transducer and activator of transcription 3 proteins. In conclusion, proteomic analysis of subcutaneous adipose tissue reveals differences in the abundance of proteins in adipocytes isolated from young vs. old individuals. These differentially abundant proteins are involved in the regulation of apoptosis, cellular senescence and inflammatory response. All these are common pathologic events in both obesity and aging.

Circulating Adipokines in Healthy versus Unhealthy Overweight and Obese Subjects

It is now well established that not all obese subjects are at increased risk of cardiometabolic complications; such patients are termed the metabolically healthy obese. Despite their higher-than-normal body fat mass, they are still insulin sensitive, with a favorable inflammatory and lipid profile and no signs of hypertension. It remains unclear which factors determine an individuals metabolic health. Adipose tissue is known to secrete multiple bioactive substances, called adipokines, that can contribute to the development of obesity-associated complications. The goal of this study was to determine whether the circulating adipokine profiles differs between metabolically healthy and metabolically unhealthy overweight and obese subjects, thereby obtaining data that could help to explain the link between obesity and its related cardiometabolic complications. We defined metabolic health in terms of several metabolic and inflammatory risk factors. The serum adiponectin levels were higher in the healthy group and showed a positive correlation with HDL cholesterol levels in the unhealthy group. There were no differences between the two groups in the levels of serum leptin, chemerin and orosomucoid. Accordingly, adiponectin might play a role in protecting against obesity-associated cardiometabolic derangements. More studies are needed to clarify the role of different chemerin isoforms in this system.

Orosomucoid Serum Concentrations and Fat Depot-Specific mRNA and Protein Expression in Humans

Obesity is associated with chronic low-grade inflammation, which contributes to systemic metabolic irregularities and obesity-linked metabolic disorders. Orosomucoid (ORM), an acute phase reactant protein, was shown to be produced in response to metabolic and inflammatory signals in the adipose tissue of obese mice, which protects them from severe inflammation and subsequent metabolic dysfunction. In this study, we examined whether there are site-specific differences between visceral and subcutaneous adipose tissue (VAT and SAT, respectively) ORM gene and protein expression from individuals with a wide range of obesity and the relationship between expressed and circulating ORM levels and measures of adiposity, insulin resistance, and pro- and anti-inflammatory markers and adipokines. The level of circulating ORM correlated positively with BMI, body fat mass, and serum leptin. It also correlated with fasting insulin, HOMA-IR values and C-reactive protein in men. There were no site-specific differences in ORM mRNA and protein expression between VAT and SAT, nor did we find a relationship between circulating ORM levels and its mRNA expression in either fat depot. We found that ORM mRNA expression correlated with mRNA expression of TNF-α, IL-6, and adiponectin in VAT, and with TNF-α and adiponectin in SAT. These observations are the first description linking adipose tissue ORM and pro- and anti-inflammatory molecules in humans. The close links of ORM and measures of adiposity, insulin resistance, and adipose tissue inflammation in humans reinforce previous experimental data and warrant further studies to explore a possible role of ORM in the pathogenesis of obesity-associated metabolic derangements.