Florian W. Kiefer

CC Chemokine and CC Chemokine Receptor Profiles in Visceral and Subcutaneous Adipose Tissue Are Altered in Human Obesity

BACKGROUND/AIMS Obesity is associated with a low-grade inflammation, insulin resistance, and macrophage infiltration of adipose tissue. The role of CC chemokines and their respective receptors in human adipose tissue inflammation remains to be determined. METHODS sc and visceral adipose tissue of obese patients (body mass index 53.1 +/- 11.3 kg/m(2)) compared with lean controls (body mass index 25.9 +/- 3.8 kg/m(2)) was analyzed for alterations in inflammatory gene expression. RESULTS Macrophage infiltration was increased in sc and visceral adipose tissue of obese patients as determined by increased mRNA expression of a macrophage-specific marker (CD68) and by elevated macrophage infiltration. Gene expression of CC chemokines involved in monocyte chemotaxis (CCL2, CCL3, CCL5, CCL7, CCL8, and CCL11) and their receptors (CCR1, CCR2, CCR3, and CCR5) was higher in sc and visceral adipose tissue of obese patients. Serum concentrations of the inflammatory marker IL-6 and C-reactive protein were elevated in obese patients compared with lean controls. Obese patients revealed increased insulin resistance as assessed by the homeostasis model assessment of insulin resistance index and reduced plasma adiponectin concentrations. Adipose tissue expression of many CC chemokines and their receptors in the obese group positively correlated with CD68 expression. CONCLUSION Up-regulation of the CC chemokines and their respective receptors in adipose tissue occurs in human obesity and is associated with increased systemic inflammation.

Neutralization of Osteopontin Inhibits Obesity-Induced Inflammation and Insulin Resistance

OBJECTIVE Obesity is associated with a state of chronic low-grade inflammation mediated by immune cells that are primarily located to adipose tissue and liver. The chronic inflammatory response appears to underlie obesity-induced metabolic deterioration including insulin resistance and type 2 diabetes. Osteopontin (OPN) is an inflammatory cytokine, the expression of which is strongly upregulated in adipose tissue and liver upon obesity. Here, we studied OPN effects in obesity-induced inflammation and insulin resistance by targeting OPN action in vivo. RESEARCH DESIGN AND METHODS C57BL/6J mice were fed a high-fat diet to induce obesity and were then intravenously treated with an OPN-neutralizing or control antibody. Insulin sensitivity and inflammatory alterations in adipose tissue and liver were assessed. RESULTS Interference with OPN action by a neutralizing antibody for 5 days significantly improved insulin sensitivity in diet-induced obese mice. Anti-OPN treatment attenuated liver and adipose tissue macrophage infiltration and inflammatory gene expression by increasing macrophage apoptosis and significantly reducing c-Jun NH2-terminal kinase activation. Moreover, we report OPN as a novel negative regulator for the activation of hepatic signal transducer and activator of transcription 3 (STAT3), which is essential for glucose homeostasis and insulin sensitivity. Consequently, OPN neutralization decreased expression of hepatic gluconeogenic markers, which are targets of STAT3-mediated downregulation. CONCLUSIONS These findings demonstrate that antibody-mediated neutralization of OPN action significantly reduces insulin resistance in obesity. OPN neutralization partially decreases obesity-associated inflammation in adipose tissue and liver and reverses signal transduction related to insulin resistance and glucose homeostasis. Hence, targeting OPN could provide a novel approach for the treatment of obesity-related metabolic disorders.

Increased bone resorption and impaired bone microarchitecture in short-term and extended high-fat diet–induced obesity

Although obesity traditionally has been considered a condition of low risk for osteoporosis, this classic view has recently been questioned. The aim of this study was to assess bone microarchitecture and turnover in a mouse model of high-fat diet-induced obesity. Seven-week-old male C57BL/6J mice (n = 18) were randomized into 3 diet groups. One third (n = 6) received a low-fat diet for 24 weeks, one third was kept on an extended high-fat diet (eHF), and the remaining was switched from low-fat to high-fat chow 3 weeks before sacrifice (sHF). Serum levels of insulin, leptin, adiponectin, osteocalcin, and cross-linked telopeptides of type I collagen (CTX) were measured. In addition, bone microarchitecture was analyzed by micro-computed tomography; and lumbar spine bone density was assessed by dual-energy x-ray absorptiometry. The CTX, body weight, insulin, and leptin were significantly elevated in obese animals (sHF: +48%, +24%, +265%, and +102%; eHF: +43%, +52%, +761%, and +292%). The CTX, body weight, insulin, and leptin showed a negative correlation with bone density and bone volume. Interestingly, short-term high-fat chow caused similar bone loss as extended high-fat feeding. Bone volume was decreased by 12% in sHF and 19% in eHF. Bone mineral density was 25% (sHF) and 27% (eHF) lower when compared with control mice on low-fat diet. As assessed by the structure model index, bone microarchitecture changed from plate- to rod-like appearance upon high-fat challenge. Trabecular and cortical thickness remained unaffected. Short-term and extended high-fat diet-induced obesity caused significant bone loss in male C57BL/6J mice mainly because of resorptive changes in trabecular architecture.

Osteopontin Is an Activator of Human Adipose Tissue Macrophages and Directly Affects Adipocyte Function

Osteopontin (OPN) is highly up-regulated in adipose tissue in human and murine obesity and has been recently shown to be functionally involved in the pathogenesis of obesity-induced adipose tissue inflammation and associated insulin resistance in mice. OPN is a protein with multiple functions and acts as a chemokine and an inflammatory cytokine through a variety of different receptors (CD44, integrins). It is expressed in many cell types including adipose tissue macrophages (ATM). However, the target cells of OPN action in obese adipose tissue are still elusive. Here, we investigated expression of OPN receptors and the impact of OPN on ATM, adipocytes, and other cells of human adipose tissue. We found broad expression of OPN receptors in different adipose tissue cell types including adipocytes. OPN stimulated inflammatory signaling pathways and secretion of cytokines in model macrophages as well as isolated human ATM. Moreover, OPN impaired differentiation and insulin sensitivity of primary adipocytes as determined by peroxisomal proliferator-activated receptor-γ and adiponectin gene expression and insulin-stimulated glucose uptake. Furthermore, OPN induced inflammatory signaling in human adipocytes. In conclusion, OPN activates ATM and interferes with adipocyte function. Thus these data underline the potential of OPN as a therapeutic target for obesity-induced complications.

Liver X receptors interfere with cytokine-induced proliferation and cell survival in normal and leukemic lymphocytes

Liver X receptors (LXRs) are nuclear receptors regulating lipid and cholesterol metabolism. Recent data indicate an additional role of LXR in immunity by controlling dendritic cell and T‐cell function and in breast and prostate cancer cells. Here, we show that LXR activation interferes with IL‐2 and IL‐7‐induced proliferation and cell cycle progression of human T‐cell blasts mainly through inhibited phosphorylation of the retinoblastoma protein and decreased expression of the cell cycle protein cyclin B. Comparable results were obtained with IL‐2‐dependent chronic lymphoblastic leukemia (CLL) T cells. Furthermore, we show for B‐CLL cells that LXR are functionally active and inhibit expression of survival genes bcl‐2 and MMP‐9, and significantly reduce cell viability, suggesting an interference of LXR with cytokine‐dependent CLL cell survival. In conclusion, our data reveal LXR as a potent modulator of cytokine‐dependent proliferation and survival of normal and malignant T and B lymphocytes. This novel LXR action could find clinical application in immunosuppressive and antileukemic therapies.

Brown adipose tissue and thermogenesis.

Abstract The growing understanding of adipose tissue as an important endocrine organ with multiple metabolic functions has directed the attention to the (patho)physiology of distinct fat depots. Brown adipose tissue (BAT), in contrast to bona fide white fat, can dissipate significant amounts of chemical energy through uncoupled respiration and heat production (thermogenesis). This process is mediated by the major thermogenic factor uncoupling protein-1 and can be activated by certain stimuli, such as cold exposure, adrenergic compounds or genetic alterations. White adipose tissue (WAT) depots, however, also possess the capacity to acquire brown fat characteristics in response to thermogenic stimuli. The induction of a BAT-like cellular and molecular program in WAT has recently been termed “browning” or “beiging”. Promotion of BAT activity or the browning of WAT is associated with in vivo cold tolerance, increased energy expenditure, and protection against obesity and type 2 diabetes. These preclinical observations have gained additional significance with the recent discovery that active BAT is present in adult humans and can be detected by 18fluor-deoxy-glucose positron emission tomography coupled with computed tomography. As in rodents, human BAT can be activated by cold exposure and is associated with increased energy turnover and lower body fat mass. Despite the tremendous progress in brown fat research in recent years, pharmacological concepts to harness BAT function therapeutically are currently still lacking.

Circulating Betatrophin Is Strongly Increased in Pregnancy and Gestational Diabetes Mellitus.

Aims/hypothesis Betatrophin has recently been introduced as a novel hormone and promotor of beta cell proliferation and improved glucose tolerance in mouse models of insulin resistance. In obese and diabetic humans altered levels were reported and a role in pathophysiology of metabolic diseases was therefore hypothesized. However its release and regulation in women with gestational diabetes mellitus (GDM), as well as its associations with markers of obesity, glucose and lipid metabolism during pregnancy still remain unclear. Methods Circulating betatrophin was quantified in 21 women with GDM and 19 pregnant body mass index-matched women with normal glucose tolerance (NGT) as well as 10 healthy age-matched non-pregnant women by enzyme-linked immunosorbent assay. Additionally we performed radioimmunassay (RIA) to confirm the results. Results Betatrophin concentrations measured by ELISA were significantly higher in GDM than in NGT (29.3±4.4 ng/ml vs. 18.1±8.7 ng/ml, p<0.001) which was confirmed by RIA. Betatrophin did not correlate with BMI or insulin resistance but showed a weak association with leptin levels in pregnancy and negative relationship with fasting C-peptide levels in all women. Moreover it correlated significantly with lipid parameters including triglycerides and total cholesterol in pregnancy, as well as estrogen, progesteron and birth weight. Conclusions/interpretation Circulating betatrophin concentrations are dramatically increased in pregnancy and are significantly higher in GDM versus pregnant NGT. In the light of the previously reported role in lipid metabolism, betatrophin may represent a novel endocrine regulator of lipid alterations in pregnancy. However additional studies are needed to elucidate whether hormonal factors, such as estrogen, control the production of betatrophin and if targeting betatrophin could hold promise in the fight against metabolic disease.

CTX (Crosslaps) Rather than Osteopontin Is Associated with Disturbed Glucose Metabolism in Gestational Diabetes

Objective Reciprocal interaction between bone and glucose metabolism might play a pivotal role in the development of type 2 diabetes. We recently demonstrated that osteocalcin is increased in women with gestational diabetes (GDM) compared to healthy pregnant women and related to enhanced insulin secretion. Here, we aimed to investigate the role of the bone resorption marker CTX and osteopontin (OPN), a key molecule in subclinical inflammation underlying insulin resistance, in gestational diabetes. Methods Insulin sensitivity and secretion (derived from OGTT) as well as CTX and osteopontin were investigated in 26 GDM and 52 women with normal glucose tolerance during pregnancy [CON] between 24th and 28th gestational weeks; 24 women also underwent postpartum examination. Results CTX was significantly higher in GDM compared to CON (0.44±0.20 vs.0.28±0.12 ng/ml, p<.0001) and positively correlated with osteocalcin (R = 0.64, p<.0001) and parameters of insulin secretion. Osteopontin plasma concentrations were decreased in GDM compared to CON (28.81±22.12 vs.37.68±19.63 ng/ml, p = 0.04), and did not show any relation to insulin secretion or sensitivity, but were significantly correlated with CRP (R = 0.3, p<0.007) and liver enzymes. Twelve weeks after delivery CTX and OPN were increased compared to pregnancy (both p<.0001) and did not differ between GDM and CON. Conclusion Our findings support the idea of a tight regulation between bone and glucose metabolism, and suggest, that less curbed CTX during pregnancy might be involved in osteocalcin-mediated amelioration of insulin secretion in GDM. On the other hand, osteopontin was unrelated to insulin resistance in GDM, but associated with inflammatory markers and liver enzymes in all women.

Fetal/neonatal Thyrotoxicosis in a Newborn From a Hypothyroid Woman With Hashimoto’s Thyroiditis

Context Fetal/neonatal thyrotoxicosis is a rare but potentially life-threatening condition. It is most commonly observed in poorly controlled Graves disease during pregnancy. Case Description Here we describe a fetus/newborn patient with thyrotoxicosis who was born of a woman with Hashimoto thyroiditis and levothyroxine-treated hypothyroidism. Transplacental passage of stimulating thyrotropin (TSH) receptor antibodies, which were measured by a cell-based bioassay, was the underlying mechanism of fetal/neonatal thyrotoxicosis, although the mother had no history of hyperthyroidism. Conclusion Diagnosis and management of fetal hyperthyroidism can be challenging. TSH receptor antibody testing should be considered in pregnant women with any history of autoimmune thyroid disease and symptoms of fetal hyperthyroidism.

Cold-Induced Brown Adipose Tissue Activity Alters Plasma Fatty Acids and Improves Glucose Metabolism in Men

Context: Mounting evidence suggests beneficial effects of brown adipose tissue (BAT) activation on glucose and lipid metabolism in humans. It is unclear whether cold‐induced BAT activation affects not only insulin sensitivity but also insulin secretion. Likewise, the role in clearing circulating fatty acids (FAs) has not been fully explored. Objective: Exploring the effects of cold‐induced BAT activation on insulin sensitivity and secretion, as well as on plasma FA profiles. Design: Fifteen healthy men participated in a cross‐balanced repeated within‐subject study with two experimental conditions. Subjects were exposed to thermoneutrality (22°C) and to moderate cold (18.06°C, shivering excluded) by use of a water‐perfused whole body suit. Cold‐induced BAT activation was quantified by [18F]‐fluorodeoxyglucose positron emission tomography‐computed tomography in a subset of volunteers. A Botnia clamp procedure was applied to determine pancreatic first phase insulin response (FPIR) and insulin sensitivity. Hormones and metabolites, including 26 specific plasma FAs, were sampled throughout the experiment. Results: Cold exposure induced BAT activity. Plasma noradrenaline and dopamine concentrations increased in response to cold. Peripheral glucose uptake and insulin sensitivity significantly improved by ˜20%, whereas FPIR remained stable. Lignoceric acid (C24:0) concentrations increased, whereas levels of eicosanoic acid (C20:1n9), nervonic acid (C24:1n9), and behenic acid (C22:0) decreased. Conclusions: Cold‐exposure induces sympathetic nervous system activity and BAT metabolism in humans, resulting in improved glucose metabolism without affecting pancreatic insulin secretion. In addition, BAT activation is associated with altered circulating concentrations of distinct FAs. These data support the concept that human BAT metabolism significantly contributes to whole body glucose and lipid utilization in a coordinated manner.