Merima Čajlaković

Increased Adipose Tissue Oxygen Tension in Obese Compared With Lean Men Is Accompanied by Insulin Resistance, Impaired Adipose Tissue Capillarization, and Inflammation

Background— Adipose tissue (AT) dysfunction in obesity contributes to chronic, low-grade inflammation that predisposes to type 2 diabetes mellitus and cardiovascular disease. Recent in vitro studies suggest that AT hypoxia may induce inflammation. We hypothesized that adipose tissue blood flow (ATBF) regulates AT oxygen partial pressure (AT PO2), thereby affecting AT inflammation and insulin sensitivity. Methods and Results— We developed an optochemical measurement system for continuous monitoring of AT PO2 using microdialysis. The effect of alterations in ATBF on AT PO2 was investigated in lean and obese subjects with both pharmacological and physiological approaches to manipulate ATBF. Local administration of angiotensin II (vasoconstrictor) in abdominal subcutaneous AT decreased ATBF and AT PO2, whereas infusion of isoprenaline (vasodilator) evoked opposite effects. Ingestion of a glucose drink increased ATBF and AT PO2 in lean subjects, but these responses were blunted in obese individuals. However, AT PO2 was higher (hyperoxia) in obese subjects despite lower ATBF, which appears to be explained by lower AT oxygen consumption. This was accompanied by insulin resistance, lower AT capillarization, lower AT expression of genes encoding proteins involved in mitochondrial biogenesis and function, and higher AT gene expression of macrophage infiltration and inflammatory markers. Conclusions— Our findings establish ATBF as an important regulator of AT PO2. Nevertheless, obese individuals exhibit AT hyperoxia despite lower ATBF, which seems to be explained by lower AT oxygen consumption. This is accompanied by insulin resistance, impaired AT capillarization, and higher AT gene expression of inflammatory cell markers. Clinical Trial Registration— URL: http://www.trialregister.nl. Unique identifier: NTR2451.

Combined sensing platform for advanced diagnostics in exhaled mouse breath

Breath analysis is an attractive non-invasive strategy for early disease recognition or diagnosis, and for therapeutic progression monitoring, as quantitative compositional analysis of breath can be related to biomarker panels provided by a specific physiological condition invoked by e.g., pulmonary diseases, lung cancer, breast cancer, and others. As exhaled breath contains comprehensive information on e.g., the metabolic state, and since in particular volatile organic constituents (VOCs) in exhaled breath may be indicative of certain disease states, analytical techniques for advanced breath diagnostics should be capable of sufficient molecular discrimination and quantification of constituents at ppm-ppb - or even lower - concentration levels. While individual analytical techniques such as e.g., mid-infrared spectroscopy may provide access to a range of relevant molecules, some IR-inactive constituents require the combination of IR sensing schemes with orthogonal analytical tools for extended molecular coverage. Combining mid-infrared hollow waveguides (HWGs) with luminescence sensors (LS) appears particularly attractive, as these complementary analytical techniques allow to simultaneously analyze total CO2 (via luminescence), the 12CO2/13CO2 tracer-to-tracee (TTR) ratio (via IR), selected VOCs (via IR) and O2 (via luminescence) in exhaled breath, yet, establishing a single diagnostic platform as both sensors simultaneously interact with the same breath sample volume. In the present study, we take advantage of a particularly compact (shoebox-size) FTIR spectrometer combined with novel substrate-integrated hollow waveguide (iHWG) recently developed by our research team, and miniaturized fiberoptic luminescence sensors for establishing a multi-constituent breath analysis tool that is ideally compatible with mouse intensive care stations (MICU). Given the low tidal volume and flow of exhaled mouse breath, the TTR is usually determined after sample collection via gas chromatography coupled to mass spectrometric detection. Here, we aim at potentially continuously analyzing the TTR via iHWGs and LS flow-through sensors requiring only minute (< 1 mL) sample volumes. Furthermore, this study explores non-linearities observed for the calibration functions of 12CO2 and 13CO2 potentially resulting from effects related to optical collision diameters e.g., in presence of molecular oxygen. It is anticipated that the simultaneous continuous analysis of oxygen via LS will facilitate the correction of these effects after inclusion within appropriate multivariate calibration models, thus providing more reliable and robust calibration schemes for continuously monitoring relevant breath constituents.

Opto-chemical method for ultra-low oxygen transmission rate measurement

A highly sensitive alternative to established methods for measuring oxygen transmission rates of ultra-barrier membranes is presented. The key idea is the employment of an opto-chemical sensor (a luminescent dye immobilized in a matrix) which has vital advantages over electrochemical sensors, such as consumption-less detection and extraordinary sensitivity. The luminescent response to modulated light, which is altered in the presence of oxygen, is recorded by an opto-electronic instrument in a non-invasive manner. Provided with said sensing system, a reusable stand-alone permeation cell was developed. Unlike in conventional devices, the permeating oxygen is accumulated while being simultaneously monitored. The demonstrator unit achieves a limit of detection in the 10−5 cm3 m−2 day−1 bar−1 regime. It is therefore among the most sensitive O2 permeability testers, outperforming commercial instruments by two orders of magnitude, yet offering reusability and similar convenience in operation.

Diet-induced weight loss decreases adipose tissue oxygen tension with parallel changes in adipose tissue phenotype and insulin sensitivity in overweight humans

BACKGROUND/OBJECTIVES:Although adipose tissue (AT) hypoxia is present in rodent models of obesity, evidence for this in humans is limited. Here, we investigated the effects of diet-induced weight loss (WL) on abdominal subcutaneous AT oxygen tension (pO2), AT blood flow (ATBF), AT capillary density, AT morphology and transcriptome, systemic inflammatory markers and insulin sensitivity in humans.SUBJECTS/METHODS:Fifteen overweight and obese individuals underwent a dietary intervention (DI), consisting of a 5-week very-low-calorie diet (VLCD, 500 kcal day−1; WL), and a subsequent 4-week weight stable diet (WS). Body composition, AT pO2 (optochemical monitoring), ATBF (133Xe washout), and whole-body insulin sensitivity were determined, and AT biopsies were collected at baseline, end of WL (week 5) and end of WS (week 9).RESULTS:Body weight, body fat percentage and adipocyte size decreased significantly during the DI period. The DI markedly decreased AT pO2 and improved insulin sensitivity, but did not alter ATBF. Finally, the DI increased AT gene expression of pathways related to mitochondrial biogenesis and non-mitochondrial oxygen consumption.CONCLUSIONS:VLCD-induced WL markedly decreases abdominal subcutaneous AT pO2, which is paralleled by a reduction in adipocyte size, increased AT gene expression of mitochondrial biogenesis markers and non-mitochondrial oxygen consumption pathways, and improved whole-body insulin sensitivity in humans.

New developments of an optochemical measurement system for the continuous monitoring in subcutaneous tissue by microdialysis

The monitoring of dissolved 02 in blood and organic tissues is extremely useful for physiological and respiratory studies and for monitoring the health conditions of hospitalized patients. Based on these demands an optochemical measurement system for the continuous monitoring of 02 in subcutaneous adipose tissue of critically ill patients is reported The system consists of a miniaturized flow trough cell including an 02 sensitive layer, an optoelectronic measuring unit and a microdialysis catheter for the extraction of the biological fluid. The measurement principle is the phase modulation fluorometry. The sensor allows the 02 measurement in the range 0-300 mmHg, with a resolution better than 1 mmHg and an accuracy better than plusmn1 mmHg. With respect to a previously reported instrumentation, this measurement system shows a high degree of miniaturization and an improved production reproducibility of the optochemical sensing layers. This new instrumentation has been extensively validated in laboratory and in-vivo tests.

Synthesis and characterization of naphthalimide-functionalized polynorbornenes

Highly fluorescent and photostable (2-alkyl)-1H-benzo[de]isoquinoline-1,3(2H)-diones with a polymerizable norbornene scaffold have been synthesized and polymerized using ring-opening metathesis polymerization. The monomers presented herein could be polymerized in a living fashion, using different comonomers and different monomer ratios. All obtained materials showed good film-forming properties and bright fluorescence caused by the incorporated push–pull chromophores. Additionally, one of the monomers containing a methylpiperazine functionality showed protonation-dependent photoinduced electron transfer which opens up interesting applications for logic gates and sensing.Graphical abstract

Simultaneously monitoring of tissue O 2 and CO 2 partial pressures by means of miniaturized implanted fiber optical sensors

A novel opto-chemical sensor instrumentation based on fiber optical micro-sensors for the simultaneous detection of pO2 and pCO2 in tissues is presented. The adopted sensing principle for both parameters is the measurement of luminescence lifetime via phase modulation fluorometry. Respect to currently used blood-gas analysers that require blood sampling and are associated with blood loss, this instrumentation allows on-line continuous measurements. Compared to electrochemical micro sensors, it is advantageous because of intrinsic higher sensitivity, no analyte consumption and less electromagnetic interferences. The results of the laboratory characterization and of tests in in vivo experiments of the proposed instrumentation are reported.

Interstitial pH, pO2 and pCO2 controlled by optical sensors

The continuous monitoring of interstitial pH, pO2 and pCO2 contained in the adipose tissue of intensive care patients, is one of the objective of the four year European project CLINICIP (Closed Loop Insulin Infusion in Critically Ill Patients). A glass capillary on line with the microfluidic system, is the solid support onto which the appropriate chemistry is immobilised. The optical working principle applied for the detection of oxygen and carbon dioxide is the modulation of the fluorescence lifetime, whereas absorption modulation is the approach followed for the pH detection. On this basis, two different optoelectronic units were developed for the interrogation of the glass capillary, one for life-time measurements and the other for absorption measurements. Preliminary tests demonstrated a resolution of 0.03 pH units for pH; ≤ 0.55 mmHg for oxygen and ≤ 0.6 mmHg for carbon dioxide; and an accuracy of 0.07 pH units for pH; ≤ 1 mmHg for oxygen and ≤ 1.5 mmHg for carbon dioxide.

Optochemical Sensor Systems for In-Vivo Continuous Monitoring of Blood Gases in Adipose Tissue and in Vital Organs

Merima Cajlakovic1, Alessandro Bizzarri1, Gijs H. Goossens2, Igor Knez3, Michael Suppan1, Ismar Ovcina3 and Volker Ribitsch1 1Joanneum Research Forschungsgesellschaft mbH, MATERIALS Institute for Surface Technologies and Photonic, Sensorsystems, Graz, 2Department of Human Biology, NUTRIM School for Nutrition, Toxicology and Metabolism, Maastricht University Medical Centre, Maastricht, 3Department of Cardiac Surgery, University Clinic of Surgery, Medical University Graz, Graz, 2The Netherlands 1,3Austria

Differences in Upper and Lower-body Adipose Tissue Oxygen Tension Contribute to the Adipose Tissue Phenotype in Humans.

Context and Objectives Upper and lower body adipose tissue (AT) exhibits opposing associations with obesity-related cardiometabolic diseases. Recent studies have suggested that altered AT oxygen tension (pO2) may contribute to AT dysfunction. Here, we compared in vivo abdominal (ABD) and femoral (FEM) subcutaneous AT pO2 in women who are overweight and have obesity, and investigated the effects of physiological AT pO2 on human adipocyte function. Design ABD and FEM subcutaneous AT pO2 and AT blood flow (ATBF) were assessed in eight [BMI (body mass index) 34.4 ± 1.6 kg/m2] postmenopausal women who were overweight with obesity and impaired glucose metabolism. ABD and FEM AT biopsy specimens were collected to determine adipocyte morphology and AT gene expression. Moreover, the effects of prolonged exposure (14 days) to physiological AT pO2 on adipokine expression/secretion, mitochondrial respiration, and glucose uptake were investigated in differentiated human multipotent adipose-derived stem cells. Results AT pO2 was higher in ABD than FEM AT (62.7 ± 6.6 vs 50.0 ± 4.5 mm Hg, P = 0.013), whereas ATBF was comparable between depots. Maximal uncoupled oxygen consumption rates were substantially lower in ABD than FEM adipocytes for all pO2 conditions. Low physiological pO2 (5% O2) decreased proinflammatory gene expression, increased basal glucose uptake, and altered adipokine secretion in ABD and FEM adipocytes. Conclusions We demonstrated for the first time, to our knowledge, that AT pO2 is higher in ABD than FEM subcutaneous AT in women who are overweight/with obesity, partly due to a lower oxygen consumption rate in ABD adipocytes. Moreover, low physiological pO2 decreased proinflammatory gene expression and improved the metabolic phenotype in differentiated human adipocytes, whereas more heterogeneous effects on adipokine secretion were found.