Kathrin Türk

IL-6 blockade by monoclonal antibodies inhibits apolipoprotein (a) expression and lipoprotein (a) synthesis in humans

Lipoprotein (a) [Lp(a)] is a highly atherogenic lipid particle. Although earlier reports suggested that Lp(a) levels are mostly determined by genetic factors, several recent studies have revealed that Lp(a) induction is also caused by chronic inflammation. Therefore, we aimed to examine whether cytokine blockade by monoclonal antibodies may inhibit Lp(a) metabolism. We found that interleukin 6 (IL-6) blockade by tocilizumab (TCZ) reduced Lp(a) while TNF-α-inhibition by adalimumab in humans had no effect. The specificity of IL-6 in regulating Lp(a) was further demonstrated by serological measurements of human subjects (n = 1,153) revealing that Lp(a) levels are increased in individuals with elevated serum IL-6. Transcriptomic analysis of human liver biopsies (n = 57) revealed typical IL-6 response genes being correlated with the LPA gene expression in vivo. On a molecular level, we found that TCZ inhibited IL-6-induced LPA mRNA and protein expression in human hepatocytes. Furthermore, examination of IL-6-responsive signal transducer and activator of transcription 3 binding sites within the LPA promoter by reporter gene assays, promoter deletion experiments, and electrophoretic mobility shift assay analysis showed that the Lp(a)-lowering effect of TCZ is specifically mediated via a responsive element at −46 to −40. Therefore, IL-6 blockade might be a potential therapeutic option to treat elevated Lp(a) serum concentrations in humans and might be a noninvasive alternative to lipid apheresis in the future.

Interleukin-6 and Tumour Necrosis Factor-α differentially regulate lincRNA transcripts in cells of the innate immune system in vivo in human subjects with rheumatoid arthritis

lincRNAs recently have been discovered as evolutionary conserved transcripts of non-coding DNA sequences and have been implicated in the regulation of cellular differentiation. In humans, molecular studies have suggested a functional role for lincRNAs in cancer development. The aim of the present study was to examine whether these novel molecules are specifically regulated by different cytokines in cells of the innate immune system in humans in vivo and whether lincRNAs thereby might be involved in the pathophysiology of rheumatoid arthritis (RA). Therefore, CD14(+) monocytes were isolated from RA patients before and after anti-IL-6R (tocilizumab) or anti-TNF-α (adalimumab) therapy and lincRNA transcription was analysed by a microarray based experiment. As expected, we found lincRNAs to be present in CD14(+) monocytes of RA patients. However, of the total number of 7.419 lincRNAs examined in this study only a very small number was significantly regulated by either IL-6 or TNF-α (85 lincRNAs, corresponding to 1.1%). The numbers of lincRNAs regulated was higher due to TNF-α compared to IL-6. Interestingly, none of the identified lincRNAs was influenced by both, IL-6 and TNF-α, suggesting the regulation of lincRNA transcription to be highly specific for distinct cytokines. Taken together, our results suggest (1) that lincRNAs are novel intracellular molecular effectors of specific cytokines in cells of the innate immune system in humans in vivo and (2) that lincRNAs might be involved in the molecular pathophysiology of RA.

Hypothalamic Inflammation in Human Obesity is Mediated by Environmental and Genetic Factors

Obesity is associated with hypothalamic inflammation (HI) in animal models. In the current study, we examined the mediobasal hypothalamus (MBH) of 57 obese human subjects and 54 age- and sex- matched nonobese control subjects by MRI and analyzed the T2 hyperintensity as a measure of HI. Obese subjects exhibited T2 hyperintensity in the left but not the right MBH, which was strongly associated with systemic low-grade inflammation. MRS revealed the number of neurons in the left hypothalamic region to be similar in obese versus control subjects, suggesting functional but not structural impairment due to the inflammatory process. To gain mechanistic insights, we performed nutritional analysis and 16S rDNA microbiome sequencing, which showed that high-fat diet induces reduction of Parasutterella sp. in the gut, which is significantly correlated with MBH T2 hyperintensity. In addition to these environmental factors, we found subjects carrying common polymorphisms in the JNK or the MC4R gene to be more susceptible to HI. Finally, in a subgroup analysis, bariatric surgery had no effect on MBH T2 hyperintensity despite inducing significant weight loss and improvement of peripheral insulin sensitivity. In conclusion, obesity in humans is associated with HI and disturbances in the gut-brain axis, which are influenced by both environmental and genetic factors.

Soluble receptor for advanced glycation end products as a potential biomarker to predict weight loss and improvement of insulin sensitivity by a very low calorie diet of obese human subjects

INTRODUCTION Obesity is associated with low-grade systemic inflammation which is thought to trigger the development of comorbidities such as type 2 diabetes. The soluble receptor for advanced glycation end products (sRAGE) belongs to the innate immune system and has been linked to obesity, recently. The aim of the present study was to examine whether serum sRAGE concentrations are related to the grade of weight loss and improvement of insulin resistance due to a very low calorie diet (VLCD). METHODS 22 severe obese subjects (Median Body Mass Index (BMI): 44.5kg/m(2)) were included in a dietary intervention study of 6month, consisting of a very low calorie formula diet phase (VLCD: 800kcal/d) for 12 weeks and a following 12 week weight maintenance phase. Fasting glucose, fasting insulin, adiponectin, leptin and sRAGE were determined from sera. Insulin sensitivity was estimated by Homeostasis Model Assessment (HOMA) index and leptin-to-adiponectin-ratio (LAR). RESULTS Mean body weight reduction by VLCD accounted to 21.7kg with a significant improvement of insulin resistance. At baseline, sRAGE serum levels were significantly inversely related to BMI (rS=-0.642, p=0.001) and HOMA (rS=-0.419, p=0.041). Of interest, sRAGE serum levels at baseline were significantly lower in study subjects with greater reduction of BMI (p=0.017). In addition, a significantly greater HOMA reduction was observed in subjects with lower sRAGE serum levels at baseline (p=0.006). Finally, correlation analysis revealed, that changes of sRAGE serum levels were significantly correlated to changes of BMI (rS=-0.650, p=0.022) during intervention. CONCLUSION Anti-inflammatory sRAGE might be a potential future biomarker to predict weight loss and improvement of insulin resistance by a VLCD whereby lower baseline sRAGE serum levels indicate a better outcome of the dietary intervention.

Beneficial Effects of a Dietary Weight Loss Intervention on Human Gut Microbiome Diversity and Metabolism Are Not Sustained during Weight Maintenance

Objective: In the present study, we examined the effect of a very low-calorie diet(VLCD)-based obesity program on human gut microbiome diversity and metabolism during weight loss and weight maintenance. Methods: Obese subjects underwent 3 months of VLCD followed by 3 months of weight maintenance. A lean and an obese control group were included. The microbiome was characterized by performing high-throughput dual-indexed 16S rDNA amplicon sequencing. Results: At baseline, a significant difference in the Firmicutes/Bacteroidetes ratio between the lean and obese individuals was observed (p = 0.047). The VLCD resulted in significant alterations in gut microbiome diversity from baseline to 3 months (p = 0.0053). Acinetobacter represented an indicator species for the observed effect (indicator value = 0.998, p = 0.006). Metabolic analyses revealed alterations of the bacterial riboflavin pathway from baseline to 3 months (pnom = 0.0078). These changes in diversity and bacterial metabolism induced by VLCD diminished during the weight maintenance phase, despite sustained reductions in body weight and sustained improvements of insulin sensitivity. Conclusion: The present data show that a VLCD is able to beneficially alter both gut microbiome diversity and metabolism in obese humans, but that these changes are not sustained during weight maintenance. This finding might suggest that the microbiome should be targeted during obesity programs.

Identification of direct and indirect social network effects in the pathophysiology of insulin resistance in obese human subjects.

Objective The aim of the present study was to examine to what extent different social network mechanisms are involved in the pathogenesis of obesity and insulin-resistance. Design We used nonparametric and parametric regression models to analyse whether individual BMI and HOMA-IR are determined by social network characteristics. Subjects and Methods A total of 677 probands (EGO) and 3033 social network partners (ALTER) were included in the study. Data gathered from the probands include anthropometric measures, HOMA-IR index, health attitudes, behavioural and socio-economic variables and social network data. Results We found significant treatment effects for ALTERs frequent dieting (p<0.001) and ALTERs health oriented nutritional attitudes (p<0.001) on EGOs BMI, establishing a significant indirect network effect also on EGOs insulin resistance. Most importantly, we also found significant direct social network effects on EGOs insulin resistance, evidenced by an effect of ALTERs frequent dieting (p = 0.033) and ALTERs sport activities (p = 0.041) to decrease EGOs HOMA-IR index independently of EGOs BMI. Conclusions Social network phenomena appear not only to be relevant for the spread of obesity, but also for the spread of insulin resistance as the basis for type 2 diabetes. Attitudes and behaviour of peer groups influence EGOs health status not only via social mechanisms, but also via socio-biological mechanisms, i.e. higher brain areas might be influenced not only by biological signals from the own organism, but also by behaviour and knowledge from different human individuals. Our approach allows the identification of peer group influence controlling for potential homophily even when using cross-sectional observational data.

B Lymphocyte Stimulator (BLyS) Is Expressed in Human Adipocytes In Vivo and Is Related to Obesity but Not to Insulin Resistance

Inflammation and metabolism have been shown to be evolutionary linked and increasing evidence exists that pro-inflammatory factors are involved in the pathogenesis of obesity and type 2 diabetes. Until now, most data suggest that within adipose tissue these factors are secreted by cells of the innate immune system, e. g. macrophages. In the present study we demonstrate that B lymphocyte stimulator (BLyS) is increased in human obesity. In contrast to several pro-inflammatory factors, we found the source of BLyS in human adipose tissue to be the adipocytes rather than immune cells. In grade 3 obese human subjects, expression of BLyS in vivo in adipose tissue is significantly increased (p<0.001). Furthermore, BLyS serum levels are elevated in grade 3 human obesity (862.5+222.0 pg/ml vs. 543.7+60.7 pg/ml in lean controls, p<0.001) and are positively correlated to the BMI (r = 0.43, p<0.0002). In the present study, bariatric surgery significantly altered serum BLyS concentrations. In contrast, weight loss due to a very-low-calorie-formula-diet (800 kcal/d) had no such effect. To examine metabolic activity of BLyS, in a translational research approach, insulin sensitivity was measured in human subjects in vivo before and after treatment with the human recombinant anti-BLyS antibody belimumab. Since BLyS is known to promote B-cell proliferation and immunoglobulin secretion, the present data suggest that adipocytes of grade 3 obese human subjects are able to activate the adaptive immune system, suggesting that in metabolic inflammation in humans both, innate and adaptive immunity, are of pathophysiological relevance.

Targeted Microbiome Intervention by Microencapsulated Delayed-Release Niacin Beneficially Affects Insulin Sensitivity in Humans

OBJECTIVE Gut microbiota represent a potential novel target for future prediabetes and type 2 diabetes therapies. In that respect, niacin has been shown to beneficially affect the host-microbiome interaction in rodent models. RESEARCH DESIGN AND METHODS We characterized more than 500 human subjects with different metabolic phenotypes regarding their niacin (nicotinic acid [NA] and nicotinamide [NAM]) status and their gut microbiome. In addition, NA and NAM delayed-release microcapsules were engineered and examined in vitro and in vivo in two human intervention studies (bioavailability study and proof-of-concept/safety study). RESULTS We found a reduced α-diversity and Bacteroidetes abundance in the microbiome of obese human subjects associated with a low dietary niacin intake. We therefore developed delayed-release microcapsules targeting the ileocolonic region to deliver increasing amounts of NA and NAM to the microbiome while preventing systemic resorption to avoid negative side effects (e.g., facial flushing). In vitro studies on these delayed-release microcapsules revealed stable conditions at pH 1.4, 4.5, and 6.8, followed by release of the compounds at pH 7.4, simulating the ileocolonic region. In humans in vivo, gut-targeted delayed-release NA but not NAM produced a significant increase in the abundance of Bacteroidetes. In the absence of systemic side effects, these favorable microbiome changes induced by microencapsulated delayed-release NA were associated with an improvement of biomarkers for systemic insulin sensitivity and metabolic inflammation. CONCLUSION Targeted microbiome intervention by delayed-release NA might represent a future therapeutic option for prediabetes and type 2 diabetes.

Role of wnt5a in Metabolic Inflammation in Humans

Context Common nutrition-associated diseases like obesity and type 2 diabetes are linked to chronic low-grade inflammation. The secreted glycopeptide wingless-type mouse mammary tumor virus integration site family member 5a (wnt5a) has been implicated in metabolic inflammation in rodent models, suggesting a potential treatment target. Data on the role of wnt5a in human physiology have yielded conflicting results. Objective Serum concentrations of wnt5a were measured in a cross-sectional cohort of 896 people to gain deeper insights into wnt5a physiology. Design Serum concentrations of wnt5a were measured by ELISA and related to several phenotyping and genotyping data. In vitro experiments were performed in THP-1 macrophages to examine potential molecular mechanisms. Results Wnt5a levels were significantly positively correlated to IL-6 and triglyceride levels. In subjects with diabetes, wnt5a levels were elevated and significantly correlated with fasting plasma glucose concentrations. Although wnt5a levels were not influenced by common single-nucleotide polymorphisms in the human wnt5a gene, environmental factors significantly altered wnt5a concentrations, as follows: (1) wnt5a levels were reduced in subjects with high nutritional load of the long-chain eicosatetraenoic acid independent of the total caloric intake and overall composition of the macronutrients, and (2) wnt5a levels were lower in humans with a high gut microbiome α diversity. In vitro experiments revealed that stimulation of the IL-6 receptor or the long-chain fatty acid receptor GPR40 directly affected wnt5a expression in human macrophages. Conclusion Our data suggest that wnt5a is important in linking inflammation to metabolism. The nutrition and the microbiome might be interesting targets to prevent and/or treat wnt5a-mediated metabolic inflammation.