BACKGROUND: Microvascular dysfunction (MD: impaired performance of blood flow, tissue perfusion, blood pressure, etc.) is one of the earliest stages in the progression of various chronic diseases. OBJECTIVE: The aim of this study was to determine if a difference in microvascular function existed between two metabolically healthy groups that differed in BMI and waist circumference. DESIGN: This study employed a causal comparative design, with two groups: I) normal weight (n =14, BMI 28 kg/m2). METHODS: Microvascular function was assessed by measuring skin blood flow (SkBF) using laser Doppler flowmetry during postocclusive reactive hyperemia (PORH). The area under the SkBF time curve during the 60-second PORH response was used to quantify the magnitude of the microvascular response. RESULTS: Group I (control) had a significantly higher average area under the SkBF time curve (3240 ± 879) than Group II (1948 ± 808) (Z= -3.0094, p = 0.0026). CONCLUSIONS: The overweight/obese subjects exhibited a diminished skin blood flow response to occlusion compared to their normal-weight counterparts. This supports the hypothesis that overweight/obese subjects who are otherwise metabolically healthy exhibit a biological change that is linked to chronic disease.

Übergewichtige Personen, die keine fettleibigkeitsbedingten metabolischen Komplikationen zeigen, wurden als 'metabolisch gesund fettleibig' (MHO, Metabolically healthy obesity) definiert. Im Gegensatz zu metabolisch ungesunden fettleibigen (MUO, Metabolically unhealthy obesity) Individuen zeigen MHOs keine metabolischen Störungen wie Bluthochdruck, Dyslipidämie, Insulinresistenz und Entzündung [50]. Aufgrund des Mangels an allgemein akzeptierten Kriterien ist die genaue Definition des MHO-Status jedoch immer noch umstritten. Es wird allgemein angenommen, dass die MHO-Definition von der Einführung zusätzlicher Biomarker profitieren könnte, welche wiederum zur Klärung der zugrunde liegenden Mechanismen metabolischer Komplikationen herangezogen werden können [24]. Darüber hinaus hat sich die klinische Forschung hauptsächlich auf Erwachsene konzentriert, und es liegen nur wenige Studien zu MHO bei jungen Menschen vor. Daher wird die Untersuchung des MHO-Status in der jungen Bevölkerung unter Verwendung gut etablierter und potentiell neuer Indikatoren als wesentlich angesehen, um einen positiven Beitrag zur Prävention und/oder Behandlung von zukünftigen fettleibigkeitsbezogenen Krankheiten zu leisten. Unter den möglichen neuen Biomarkern wurde festgestellt, dass Serumharnsäure (Serum-UA) eine wichtige Rolle als kardiometabolischer Risikofaktor [22] für Adipositas-assoziierte Komorbiditäten bei Kindern und Jugendlichen spielt. Dennoch haben nur wenige Studien den Zusammenhang zwischen dieser biochemischen Variablen und MHO in der jungen Bevölkerung untersucht. Der Schwerpunkt der vorliegenden Studie lag auf der Identifizierung potenzieller klinischer und metabolischer Indikatoren, die zur Unterscheidung zwischen MHO- und MUO-Phänotypen beitragen können. Die anthropometrischen, klinischen und biochemischen Merkmale von 458 Kindern und Jugendlichen wurden analysiert und diskutiert. MHO- und MUO-Individuen repräsentieren 38% bzw. 16% der dieser Grupe. Der häufigste kardiovaskuläre Risikofaktor bei MUO-Patienten war Hypertriglyceridämie (54,2%), gefolgt von niedrigem Serum-HDL-C (45,8%), Hypertonie (19,5%) und gestörter Glukosetoleranz (14,7%). Zusammenfassend deuten diese Ergebnisse darauf hin, dass eine frühzeitige Identifizierung von MUO in der Jugend möglich ist, wodurch eine frühzeitige Erkennung möglicher metabolischer Komplikationen gewährleistet ist. Verglichen mit der MUO-Gruppe zeigten MHO-Individuen niedrigere Nüchterninsulinwerte, Triglyceride, Blutdruck, Nüchternglucose und höhere Insulinsensitivität sowie niedrigere Serumharnsäure-, hs-CRP-, Albumin- und C-Peptidspiegel. Interessanterweise wurden im Gegensatz zu früheren Studien in den MHO- und MUO-Gruppen ähnlich hohe Werte für die Marker der Leberfunktion, einschließlich der zirkulierenden Konzentrationen von ALT, AST und alkalischer Phosphatase, festgestellt. Dieses Ergebnis legt nahe, dass niedrigere Leberenzyme zu dem günstigen metabolischen Profil von MHO-Individuen beitragen könnten. Darüber hinaus fördert diese Forschung ein besseres Verständnis der Wirkung potenzieller Indikatoren, die verwendet werden können, um MHO von MUO zu unterscheiden, insbesondere mit dem Fokus auf Serum-UA. Die Ergebnisse dieser Arbeit zeigen, dass Serum-UA mit mehreren kardiometabolischen Risikofaktoren assoziiert ist, die normalerweise mit Fettleibigkeit in Verbindung gebracht werden, wie Serumtriglycerid SDS, systolischer Blutdruck, C-Peptid und Cystatin C. Keine signifikante Beziehung zwischen Glukose-SDS und Serum-UA-Spiegeln wurde gefunden. Höhere Serumspiegel von UA erwiesen sich als signifikanter Indikator für den MUO-Phänotyp. Höhere C-Peptid-Spiegel, Taillenumfangs-SDS und Pubertätstadium sind mit einer höheren Wahrscheinlichkeit des MUO-Status assoziiert. Umgekehrt zeigte das Geschlecht der Person keine signifikante Wirkung. Hs-CRP und Albumin waren keine signifikanten MUO-Indikatoren, wenn sie nach Alter, Geschlecht, Pubertät und BMI-SDS kontrolliert wurden. Die in dieser Arbeit präsentierten Ergebnisse könnten für eine bessere Unterscheidung zwischen MUO- und MHO-Phänotypen nützlich sein und adipositasbedingte Komorbiditäten frühzeitig im Leben behandeln. Längsschnittstudien in größeren Kohorten mit jüngeren Individuen werden als ein vernünftiger nächster Schritt angesehen, um das Ergebnis dieser Arbeit zu bestätigen und zu erweitern. Mögliche zukünftige Untersuchungen könnten zusätzliche Eigenschaften und Wirkungen von MHO/MUO-Indikatoren betreffen. Zum Beispiel, wie der Serum-UA-Spiegel durch Konsum zuckergesüßter Erfrischungsgetränke und Alkohol beeinfluss wird.:LIST OF ABBREVIATIONS III I. BIBLIOGRAPHISCHE BESCHREIBUNG IV 1 INTRODUCTION 1.1 Obesity and associated diseases, a world health threat 1.1.1 Definitions and classifications of overweight and obesity 1.2 A ‘metabolic healthy’ type of obesity 1.2.1 Distinguishing characteristics of healthy obesity 1.3 Physiology of uric acid (UA) 1.3.1 Serum UA and cardiometabolic risk factors 1.3.2 Serum UA and type 2 diabetes 1.3.3 Serum UA and hypertension 1.3.4 Serum UA and kidney-related complications 1.3.5 Connection between Serum UA levels and metabolic health status THE PROJECT RESEARCH 1.4 Research question and hypotheses 1.5 The LIFE-Child study 2 PUBLICATION MANUSCRIPT REFERENCES 3 ZUSAMMENFASSUNG DER ARBEIT REFERENCES ANLAGEN II. Supplement Material III. Erklärung über die eigenständige Abfassung der Arbeit IV. Curriculum Vitae V. List of publications and conference participations VI. Acknowledgments / Obese individuals that do not show obesity-related metabolic complications have been defined as “metabolically healthy obese” (MHO). Unlike metabolic unhealthy obese (MUO) individuals, MHO do not show several metabolic disorders, such as hypertension, dyslipidemia, insulin resistance and inflammation. However, due to the lack of universally accepted criteria, the precise definition of the MHO status is still controversial. It is widely believed that the MHO definition might benefit from the introduction of additional biomarkers, which in turn can be used to clarify the underlying mechanisms of metabolic complications. Futhermore, clinical research has mostly focused on adults and few studies addressing MHO in young individuals are available. Therefore, the investigation of the MHO status in the young population, by using well-established and potential new indicators, is considered essential to positively contribute to prevention and/or treatment of future obese-related diseases. Among the possible potential new biomarker, serum uric acid (serum UA) has been found to play an important role as a cardiometabolic risk factor44 for obesity-related comorbidities in children and adolescents. Nonetheless, very few studies have investigated the association between this biochemical variable and MHO in the young population. The focus of the present study was to identify potential clinical and metabolic indicators that may help to distinguish between MHO and MUO phenotypes. The anthropometric, clinical and biochemical characteristics of 458 children and adolescents were analyzed and discussed. MHO and MUO individuals represent 38% and 16% of the overweight/obese population, respectively. The most frequent cardiovascular risk factor found in MUO individuals was hypertriglyceridemia (54.2%), followed by low serum HDL-C (45.8%), hypertension (19.5%) and impaired glucose tolerance (14.7%). Altogether, these findings suggest that early identification of MUO is possible during youth, thereby ensuring the early addressing of potential metabolic complications. Compared to the MUO group, MHO individuals showed lower fasting insulin values, triglycerides, blood pressure, fasting glucose and higher insulin sensitivity, as well as lower serum uric acid, hs-CRP, albumin and C-peptide levels. Interestingly, in contrast to previous studies, markers of liver function, including circulating concentrations of ALT, AST and alkaline phosphatase, were found to be similarly high in MHO and MUO groups. This finding suggests that lower levels of hepatic enzymes could contribute to the favorable metabolic profile of MHO individuals. In addition, the research promotes a better understanding of the action of potential indicators that can be used to distinguish MHO from MUO, especially focusing on serum UA. The results of this thesis revealed that serum UA is associated with several cardiometabolic risk factors usually linked with obesity, such as serum triglyceride SDS, systolic blood pressure, C-peptide and Cystatin C. No significant relationship between glucose-SDS and serum UA levels has been found. Higher levels of serum UA were found to be a significant indicator of the MUO phenotype. Higher levels of C-peptide, waist circumference SDS and pubertal stage are associated to higher likelihood of MUO status. Conversely, the individual’s gender showed no significant effect. Hs-CRP and albumin were non-significant MUO indicators when controlled for age, gender, pubertal stage and BMI-SDS. The results presented in this thesis might be valuable for a better distinction between MUO and MHO phenotypes and to properly address obesity-related comorbidities early in life. Longitudinal studies in larger cohorts with younger individuals are seen as a sensible next step to confirm and expand the outcome of this work. Possible future investigations might address additional properties and effects of MHO/MUO indicators, for instance by studying how serum UA levels are affected by alcohol consumption and sugar-sweetened soft drinks.:LIST OF ABBREVIATIONS III I. BIBLIOGRAPHISCHE BESCHREIBUNG IV 1 INTRODUCTION 1.1 Obesity and associated diseases, a world health threat 1.1.1 Definitions and classifications of overweight and obesity 1.2 A ‘metabolic healthy’ type of obesity 1.2.1 Distinguishing characteristics of healthy obesity 1.3 Physiology of uric acid (UA) 1.3.1 Serum UA and cardiometabolic risk factors 1.3.2 Serum UA and type 2 diabetes 1.3.3 Serum UA and hypertension 1.3.4 Serum UA and kidney-related complications 1.3.5 Connection between Serum UA levels and metabolic health status THE PROJECT RESEARCH 1.4 Research question and hypotheses 1.5 The LIFE-Child study 2 PUBLICATION MANUSCRIPT REFERENCES 3 ZUSAMMENFASSUNG DER ARBEIT REFERENCES ANLAGEN II. Supplement Material III. Erklärung über die eigenständige Abfassung der Arbeit IV. Curriculum Vitae V. List of publications and conference participations VI. Acknowledgments

The Hedgehog signaling pathway regulates many processes during embryogenesis and the homeostasis of adult organs. Recent data suggest that central metabolic processes and signaling cascades in the liver are controlled by the Hedgehog pathway and that changes in hepatic Hedgehog activity also affect peripheral tissues, such as the reproductive organs in females. Here, we show that hepatocyte-specific deletion of the Hedgehog pathway is associated with the dramatic expansion of adipose tissue in mice, the overall phenotype of which does not correspond to the classical outcome of insulin resistance-associated diabetes type 2 obesity. Rather, we show that alterations in the Hedgehog signaling pathway in the liver lead to a metabolic phenotype that is resembling metabolically healthy obesity. Mechanistically, we identified an indirect influence on the hepatic secretion of the fibroblast growth factor 21, which is regulated by a series of signaling cascades that are directly transcriptionally linked to the activity of the Hedgehog transcription factor GLI1. The results of this study impressively show that the metabolic balance of the entire organism is maintained via the activity of morphogenic signaling pathways, such as the Hedgehog cascade. Obviously, several pathways are orchestrated to facilitate liver metabolic status to peripheral organs, such as adipose tissue.

L’obésité est associée au développement de plusieurs complications métaboliques, dont la résistance à l’insuline (RI). Or, certains sujets obèses ne développent pas de RI. Ces obèses sensibles à l’insuline (ISO) représentent un modèle humain unique pour étudier les facteurs impliqués dans le développement de la RI. La fibrose du tissu adipeux a été directement associée au développement de la RI chez le rongeur. Nous avons donc évalué la fibrose dans les tissus adipeux sous-cutané (TASC) et viscéral (TAV) d’individus obèses ISO, résistants à l’insuline (IRO) et diabétiques de type 2 (DT2), avant et six mois après leur chirurgie bariatrique. Malgré un âge, IMC et pourcentage de masse grasse semblables, les ISO présentaient une RI inférieure à celle des IRO avant la chirurgie (p < 0,05). Aucune différence n’a été observée entre les sujets ISO, IRO et DT2 en ce qui concerne la fibrose totale et les niveaux d’expression de gènes associés à la fibrose, ni dans le TASC ni dans le TAV. Toutefois, le log du pourcentage de fibrose dans le TASC était positivement corrélé avec le log de HOMA-IR (r = 0,3847, p = 0,0476) avant la chirurgie. Six mois plus tard, les niveaux de fibrose demeurent inchangés dans le TASC, mais la RI est significativement réduite dans tous les groupes, particulièrement chez les DT2. Aucune corrélation n’a été observée entre la fibrose du TASC et l’HOMA-IR après la chirurgie. Ces résultats montrent une association significative, mais éphémère entre la fibrose du TASC et la RI chez l’humain obèse. / Obesity is associated to the development of metabolic complications, including insulin resistance. Yet, a distinctive subset of obese patients seems protected from insulin resistance. Such insulin-sensitive obese subpopulation (ISO) offers a unique opportunity to investigate factors underlying the development of insulin resistance in humans without the confounding effect of major differences in adiposity. Adipose tissue fibrosis has been directly linked to the development of obesity-associated insulin resistance in rodents. Therefore, we quantified total fibrosis and examined the expression of fibrosis-related genes in subcutaneous (SAT) and visceral (VAT) adipose tissue biopsies of diabetic (T2D) and non diabetic obese patients stratified into ISO or insulin-resistant obese (IRO) based on the OGTT-derived ISIMatsuda index, before and six months after bariatric surgery. Despite similar age, BMI, and percent fat mass, ISO had lower insulin resistance than IRO subjects (p<0.05) at baseline. No difference was found between ISO, IRO and T2D, neither in terms of total fibrosis, nor in the expression of fibrosis-related genes in the adipose tissues before surgery. However, log SAT fibrosis positively correlated with log HOMA-IR at baseline (r = 0.3847, p < 0.05). Six months after surgery, fibrosis levels remained unchanged in SAT, but insulin resistance was significantly reduced in all groups, especially in T2D patients. No correlation was found between SAT fibrosis and HOMA-IR after surgery. These results show a significant, yet ephemeral association between SAT fibrosis and insulin resistance in obese humans.

L’obésité est devenue un véritable problème de santé publique. Elle est fréquemment associée à plusieurs anomalies cardiométaboliques telles que l’hypertension artérielle, l’insulinorésistance et les dyslipidémies qui font le lit du diabète de type 2 et des maladies cardiovasculaires. Cependant la fréquence de ces anomalies varie considérablement parmi les sujets obèses faisant de cette maladie chronique une situation clinique très hétérogène. A ce titre un nouveau concept a émergé, impliquant une population de patients sans facteurs de risque apparents, appelé « obèse métaboliquement sain » ou « metabolically healthy obese » (MHO). Des efforts sont en cours pour comprendre les mécanismes sous-jacents à ce phénotype et ses conséquences à long terme. L’objectif principal de cette thèse était d’étudier le lien entre le phénotype MHO et diverses pathologies chroniques connues pour être associées à l’obésité. Les données provenant des cohortes Whitehall II et GAZEL ont été utilisées pour examiner les associations entre le phénotype MHO et la mortalité, les maladies cardiovasculaires, le diabète de type 2 et la dépression. En comparaison aux sujets de poids normal métaboliquement sains, les individus MHO ont un risque accru de mortalité globale et cardiovasculaire, de diabète de type 2 et de maladies cardiovasculaires mais pas de dépression. Comparés aux sujets obèses avec anomalies métaboliques, les individus MHO ont un risque similaire de mortalité et de maladies cardiovasculaires, mais un moindre risque de diabète de type 2 et dépression. Nos résultats suggèrent que l’obésité à profil cardiométabolique normal n’est pas une condition bénigne. Une meilleure compréhension de ce phénotype contribuera à améliorer la décision thérapeutique et aidera peut-être à identifier des cibles thérapeutiques nouvelles. / Obesity has become a major public health concern. It is frequently associated with several cardiometabolic abnormalities such as hypertension, insulin resistance and dyslipidemia leading to type 2 diabetes and cardiovascular disease. However, the frequency of these abnormalities varies widely among obese subjects, making this chronic condition a very heterogeneous clinical situation. As such a new concept has emerged, involving a population of patients without metabolic risk, called "metabolically healthy obese" (MHO). Intense interest surrounds the MHO phenotype with on-going efforts to understand the mechanisms underlying this phenotype and its long-term consequences. The main objective of this thesis was to study the relationship between the MHO phenotype and various chronic diseases known to be associated with obesity. Data from the Whitehall II and GAZEL cohorts were used to examine associations between this phenotype and mortality, cardiovascular diseases, type 2 diabetes, and depression. Compared to metabolically healthy normal weight subjects, MHO individuals have an increased risk of overall and cardiovascular mortality, type 2 diabetes and cardiovascular diseases, but not depression. Compared to metabolically unhealthy obese subjects, MHO individuals have a similar risk of mortality and cardiovascular disease, but a lower risk of type 2 diabetes, and depression. Our results suggest that obesity with normal cardiometabolic profile is not a benign condition. A better understanding of this phenotype will enhance therapeutic decision making and possibly help to identify new therapeutic targets.

This thesis investigates the complexity of the obesity phenotype by characterizing the inflammatory status of Metabolically Healthy Obese (MHO) individuals. More specifically, this work has examined circulating inflammatory markers in MHO individuals and compared it to Lean Healthy (LH) and Metabolically Abnormal Obese (MAO) subjects. Thirty participants (n=10/group) were recruited as part of the Diabetes Risk Assessment (DRA) study, and classified according to adiposity and metabolic status. Despite a similar level of adiposity compared to MAO individuals, MHO subjects presented a more favourable inflammatory profile. Specifically, MHO individuals had levels of hsCRP and IL-6 comparable to LH subjects and lower than MAO subjects. Also, MHO subjects presented similar levels of high molecular weight adiponectin as the MAO group, but PDGF-ββ levels were intermediate to those of the LH and MAO groups. Overall, the distinct inflammatory profile observed in MHO subjects demonstrates the unique status of these individuals, reinforcing that obesity is a complex and heterogeneous phenotype. / Public Health Agency of Canada, Ontario Graduate Scholarships, Queen Elizabeth II Graduate Scholarships in Science and Technology, Canada Foundation for Innovation