Meal-regulated Substrate Metabolism, Influence of Obesity and IL-6

The overall purpose of this explorative yet quantitative study project is to understand how blocking IL-6 signaling leads to the expansion of adipose tissue mass in humans in vivo. The aim is to gain in depth knowledge about how IL-6 receptor blockade affects human lipid, glucose and protein metabolism, specifically the uptake and storage of substrates from a meal vs. their utilization, hence the balance determining whether one gains or loses fat mass.

Lacking IL-6 signaling leads to an expansion of adipose tissue mass in rodents and humans. However, the underlying mechanisms have not been identified.This project aims to investigate the overall hypothesis that IL-6 receptor blockade changes substrate metabolism during postabsorptive and postprandial states to favor storage over mobilization of fat and to favor glucose over fat as a source for energy production. This hypothesis finds some support in the literature: Infusion of recombinant IL-6 into humans, leading to high concentrations of IL-6 in the circulation, stimulates lipolysis and free fatty acid oxidation. Therefore, the investigators hypothesize that IL-6 receptor blockade impairs the mobilization of FFA from adipose tissue and impairs fat oxidation in skeletal muscle in the postabsorptive state. In the postprandial, state the investigators hypothesize that IL-6 receptor blockade reduces the insulin-induced uptake and deposition of fat by adipose tissue and skeletal muscle, therefore contributing to ectopic fat deposition in the liver. In this study 12 lean and 12 obese male participants will be included. The participants will attend one screening visit and two study visits. The IL-6 receptor antibody tocilizumab will be infused on study visit 1. Isotope dilution techniques, blood flow measurements, arterio-venous differences across adipose tissue and skeletal muscle, fat and skeletal muscle biopsies will be used to assess lipid, glucose and protein kinetics on a whole-body as well as fat and skeletal muscle level in the fasting state and after the ingestion of a liquid mixed-meal. Respiratory exchange ratio will be measured by indirect calorimetry.

Interleukin-6, Tocilizumab, Postprandial, Postabsorptive, Substrate metabolism, Fat metabolism, Glucose metabolism, Protein metabolism, Isotope dilution technique

The study is designed in a placebo-controlled crossover manner, consisting of a screening visit and two study visits. Due to the 4-week wash out period of the IL-6 receptor antibody tocilizumab, the order of study visits will be identical in all subjects; hence, study visits will not be randomized. Subjects will be infused with tocilizumab at the end of study visit 1. This will allow us to study the effect of tocilizumab on study visit 2.

Post-intervention measurements: Participants will be under the influence of tocilizumab, which was injected at the end of study visit 1.

Baseline: Tocilizumab (infusion of 8 mg/kg bodyweight or a maximum of 800 mg) will be infused over 60 minutes at the end for the study day, therefore study visit 1 (study day 1) measurements are baseline.

Participants are under influence of tocilizumab since the effect of the drug will last for 4 weeks. Participants will be infused with saline at study visit 2 (study day 21). Placebo to tocilizumab will be saline (NaCl 0.9%) as tocilizumab is a colorless solution and has to be diluted with NaCl 0.9% prior to administration

Rate of appearance and disappearance of glycerol and palmitate, fatty acid oxidation and re-esterification, arterio-venous differences of glycerol, palmitate, triglycerides across adipose tissue and skeletal muscle, triglycerides fractional synthesis rate in the postabsorptive and postprandial state in the presence of tocilizumab as compared to placebo

Rate of appearance and disappearance of glucose, arterio-venous differences of glucose across adipose tissue and skeletal muscle, glycogen fractional synthesis rate in the postabsorptive and postprandial state in the presence of tocilizumab as compared to placebo

Rate of appearance and disappearance of amino acids, arterio-venous differences of amino acids across adipose tissue and skeletal muscle, protein fractional synthesis rate in the postabsorptive and postprandial state, in the presence of tocilizumab as compared to placebo

Uptake of fatty acids, glucose and amino acids from a meal in the presence of tocilizumab as compared to placebo

Change in postabsorptive and postprandial FFA levels in the presence of tocilizumab as compared to placebo

Change in postabsorptive and postprandial triglycerides levels in the presence of tocilizumab as compared to placebo

Change in postabsorptive and postprandial insulin levels in the presence of tocilizumab as compared to placebo

Change in postabsorptive and postprandial c-peptide levels in the presence of tocilizumab as compared to placebo

Change in postabsorptive and postprandial glucagon levels in the presence of tocilizumab as compared to placebo

Change in postabsorptive and postprandial cortisol levels in the presence of tocilizumab as compared to placebo

Change in postabsorptive and postprandial adrenaline levels in the presence of tocilizumab as compared to placebo

Change in postabsorptive and postprandial noradrenaline levels in the presence of tocilizumab as compared to placebo

Change in postabsorptive and postprandial cytokine levels in the presence of tocilizumab as compared to placebo

Change in postabsorptive and postprandial total and active GLP-1 levels in the presence of tocilizumab as compared to placebo

Change in postabsorptive and postprandial GIP levels in the presence of tocilizumab as compared to placebo

Change in postabsorptive and postprandial PYY postabsorptive and postprandial in the presence of tocilizumab as compared to placebo

Change in postabsorptive and postprandial leptin levels in the presence of tocilizumab as compared to placebo

Change in postabsorptive and postprandial GH levels in the presence of tocilizumab as compared to placebo

RNA sequencing on adipose tissue and skeletal muscle biopsies, monocytes with or without the influence of tocilizumab

Change in the postabsorptive and postprandial secretory profile of monocytes in the presence of tocilizumab as compared to placebo

IL-6 signaling pathway activation in monocytes from lean participants compared to from obese participants

Inclusion Criteria: Healthy males: Age ≥ 18 years and ≤ 40 years BMI < 18 and > 25 kg/m2 Healthy (based on screening) Stable body weight for 6 months Obese males: Age ≥ 18 years and ≤ 40 years BMI ≥ 30 and ≤ 40 kg/m2 Healthy (based on screening) Stable body weight for 6 months Exclusion Criteria: Smoking Evidence of severe thyroid or heart disease, inflammatory diseases, current infection, liver disease (transaminases >2x upper normal range), kidney disease (creatinine >1.5 mg/dl), known immunosuppressive disease, corticosteroid use, regular NSAID or paracetamol usage, aspirin use >100 mg/d, history of carcinoma, history of tuberculosis, anemia (hematocrit <33%), WBC <2 x 10^3/ul, platelets <100 x 10^3/ul, bleeding disorders, obstructive pulmonary disease Femoral hernia, vascular prosthesis, vascular thrombosis Previous nerve damage, many previous femoral catheter installations

Rigshospitalet, Centre of Inflammation and Metabolism (CIM) Centre for Physical Activity Research (CFAS)

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