L’exposition à des polluants environnementaux est considérée comme l’un des facteurs pouvant expliquer l’augmentation exponentielle des maladies métaboliques dans le monde. Parmi ces polluants, plusieurs études épidémiologiques suggèrent une association entre exposition au cadmium (Cd) et incidence et sévérité des cas de diabète, mais le sujet reste controversé. Des travaux expérimentaux sur des modèles animaux montrent qu’une exposition au Cd induit des effets divers sur le métabolisme du glucose. Toutefois, ces études ont été réalisées avec des doses de Cd relativement fortes et avec des modèles d’exposition peu réalistes. De plus, très peu de données sont disponibles sur l’effet de l’exposition maternelle sur la descendance. L’objectif de ces travaux était donc d’étudier les possibles altérations du métabolisme du glucose après une exposition orale à des doses faibles de Cd, chez des rats adultes ainsi que sur des jeunes rats exposés via leur mère. Nos résultats montrent qu’à des niveaux de Cd proche des doses de références sans effets chez le rat, les femelles adultes présentent des perturbations du niveau d’insuline plasmatique ainsi qu’une légère diminution de la sensibilité à l’insuline. Ces effets diabétogènes ne sont pas retrouvés chez les mâles. Les résultats de notre seconde étude indiquent que l’exposition maternelle au Cd, pendant la gestation et la lactation, induit des modifications métaboliques précoces chez les descendance, 21, 26 et 60 jours après la naissance. A 21 jours, la tolérance au glucose est altérée. A 26 jours, la sensibilité périphérique à l’insuline est transitoirement restaurée mais la fonction pancréatique est impactée. Enfin, à 60 jours, le défaut de sensibilité à l’insuline est compensé par une sécrétion accrue. Ces travaux mettent en évidence les effets d’une exposition à doses faibles de Cd sur le métabolisme du glucose et renforcent l’idée que l’environnement périnatal, en particulier l’exposition aux polluants, impacte la santé de la descendance, à plus ou moins long terme. Au-delà de ces résultats, ces travaux portent une réflexion sur l’intérêt et la difficulté à mettre en place des modèles animaux d’exposition pertinents, pour répondre à l’enjeu de l’évaluation des risques de l’exposition chronique au Cd. / The exposure to environmental pollutants is considered one of the factors that could explain the exponential increase in metabolic illnesses worldwide. Among these pollutants, many epidemiological studies suggest a link between Cadmium (Cd) exposure and the occurrence and severity of diabetes, although the subject remains controversial. Experimental work on animals shows that exposure to Cd induces various effects on glucose metabolism. However, these studies were performed with relatively high doses of Cd and with unrealistic exposure models. In addition, very little data are available on the effect of maternal exposure and effect on descendants. The aim of this work was to study possible alterations in glucose metabolism after oral exposure to low doses of Cd in adult rats as well as in young rats exposed via their mothers. Results show that when exposed to Cd levels close to no-observed-effect reference values in rats, female rats show disturbances in plasma insulin level and a slight decrease in insulin sensitivity. These diabetogenic effects are not found in male rats. The results of the second study indicate that maternal exposure to Cd during pregnancy and lactation induces early metabolic changes in the offspring, 21, 26 and 60 days after birth. At 21 days, glucose tolerance is altered. At 26 days, the peripheral insulin sensitivity is transiently restored but the pancreatic function is impacted. Finally, at 60 days, the lack of insulin sensitivity is compensated by increased secretion. This work demonstrates the effects of low doses of Cd on glucose metabolism and reinforces the idea that the perinatal environment, in particular exposure to pollutants, affects the health of offspring in the long term. Beyond these results, this work allows the reader to reflect on the interest and difficulty of setting up relevant experimental animal models, in order to tackle the issue of risk assessment of chronic Cd exposure.

Background: Gestational Diabetes Mellitus (GDM) is defined as any degree of glucose intolerance diagnosed for the first time during pregnancy. Up to 60% of women who had a prior GDM will develop type II diabetes mellitus in the next 5 to 15 years after delivery. Our study aimed to examine perinatal factors associated with later development of impaired glucose metabolism in women with a recent history of GDM. Methods: We conducted a retrospective cohort study based on a 2-year follow-up of women with or without prior GDM. We recruited 39 women from the previous case-control study, including 19 women with prior GDM and 20 women without prior GDM. All the subjects were taken a 75-g oral glucose tolerance test (OGTT) and were interviewed with a questionnaire by research nurses. Chi-square tests were used to examine differences in proportions. Multiple log-linear regression models were used to determine whether there was an association between the prenatal potential risk factors and glucose metabolic abnormalities, after adjustment of various potential confounding variables. Results: Compared to women without a history of GDM, prior GDM women had significantly higher glucose and insulin concentration, increased insulin resistance and decreased β-cell function. Pre-pregnancy body mass index (BMI) and family history of diabetes were significantly reduced in early phase insulin responsiveness (IGI/HOMA-IR) and insulin secretion-sensitivity index (IS-SI) among women without prior GDM. Women’s parity was statistically significant decreased in Matsuda insulin sensitivity index (ISOGTT). Conclusion: Women with history of GDM have a significant higher risk of developing glucose metabolic abnormalities about two years after delivery. Pre-pregnancy BMI may have an association with later developing abnormal glucose metabolism in women without history of GDM. / acase@tulane.edu

Recently, persistent organic pollutants such as polychlorinated biphenyls (PCBs) were classified as “metabolic disruptors” for their suspected roles is altering metabolic and energy homeostasis through bioaccumulation in liver and adipose tissues. Among PCBs, a specific congener, 3,3',4,4',5-pentachlorobiphenyl (PCB126), is a potent arylhydrocarbon receptor (AhR) agonist and elicits toxicity similar to the classic dioxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). PCB126 levels found in human blood are particularly associated with diabetes and nonalcoholic fatty liver disease (NAFLD) in humans, however the mechanisms are unclear. We hypothesized that the accumulation of PCB126 disrupts carbohydrate and lipid metabolism by altering the functions of liver and adipose tissues. Hence, our objective was to characterize PCB126 induced-metabolic disruption and the underlying molecular mechanisms that cause toxicity. Separate animal studies were performed using a rat model to understand the time- and dose-dependent effects after PCB126 administration. The chronology of PCB126 toxicity showed early decreases in serum glucose level at 9 h, worsened in a time-dependent way until the end of the study at 12 d. Lipid accumulation and the liver pathology also worsened over time between 3 d and 12 d post administration. These observed effects in the liver were also found to be dose-dependent. The decrease in serum glucose was a result of a decrease in the transcript levels of gluconeogenic and glycogenolytic enzymes, necessary for hepatic glucose production and hence the maintenance of steady glucose levels in the blood. Phosphoenolpyruvate carboxykinase (PEPCK-C), the rate limiting enzyme of gluconeogenesis, was found to be significantly decreased upon exposure to PCB126. The expression levels of peroxisome proliferator-activated receptor alpha (Pparα) and some of its targets involved in fatty acid oxidation were also found to be time and dose-dependently decreased upon exposure to PCB126. In an attempt to understand the molecular targets that may cause these dual effects on both gluconeogenic and fatty acid oxidation, we found that PCB126 significantly decreases phosphorylation of the cAMP response element-binding protein (CREB). CREB is a nuclear transcription factor that is activated in the liver through phosphorylation; to switch-on the transcription of enzymes that catalyze gluconeogenesis and fatty acid oxidation, in order to meet energy demands, especially during fasting. Further, to understand the toxicity of PCB126 on adipose tissue, a human pre-adipocyte model that can be differentiated into mature adipocytes was used. In these studies, we found that exposure of preadipocytes to PCB126 resulted in a significant reduction in their ability to differentiate into adipocytes. This results in decreased lipid accumulation in the adipocyte. Reduction in the differentiation by PCB126 was associated with down regulation in transcript levels of a key adipocyte transcription factor, PPARγ and its transcriptional targets necessary for adipogenesis and adipocyte function. These inhibitory effects of PCB126 on the regulation of PPARγ and the initiation of adipogenesis were mediated through activation of AhR. Overall, this work shows that PCB126 disrupts nutrient homeostasis through its effects on the function of target tissues; liver and adipose. PCB126 significantly alters the nutrient homeostasis through its effects on gluconeogenesis and fatty-acid oxidation necessary for glucose and energy regulation during fasting. In addition, PCB126 interrupts the storage functions of adipose tissue by inhibiting adipogenesis and thus disrupts lipid storage and distribution

The desert-adapted frogs Cyclorana platycephala and Cyclorana maini survive long periods of inhospitably hot and dry conditions by retreating underground and aestivating. While aestivating they suspend food and water intake as well as physical activity, depress their metabolic rate by ~80 %, and form cocoons that protect them against desiccation. How these frogs function during this exceptional state is largely unknown. This work characterized a number of physiological parameters in three metabolic states spanning their natural metabolic range: during aestivation (depressed metabolism), at rest (normal metabolism), and where possible, during exercise (elevated metabolism). The primary objective was to identify by comparison, physiological adjustments in these parameters to metabolic depression, as well as the scope of these parameters in frogs capable of aestivation. The parameters measured for C. maini were (a) the glucose transport kinetics and (b) the fluid balance of an extensive number of their individual organs. For C. platycephala, the parameters measured were (a) the activity of the cardiovascular system as indicated by heart rate and blood pressure and (b) the roles of pulmonary and cutaneous respiratory systems in gas exchange

<p>Primary hyperparathyroidism (pHPT), characterized by elevated serum levels of calcium and parathyroid hormone (PTH), is associated with a number of metabolic derangements causing secondary manifestations. These include osteoporosis and increased risk of fractures, but also risk factors for cardiovascular morbidity and mortality. These risk factors include impaired glucose tolerance (IGT), dyslipidemia, increased body mass index and hypertension. While the skeletal abnormalities are mainly due to elevated PTH, the latter disturbances are still unexplained. Non-insulin dependent diabetes mellitus (NIDDM), IGT, dyslipidemia and hypertension are all included in the metabolic syndrome, also associated with morbidity and mortality in cardiovascular diseases.</p><p>In this thesis, decreased bone mineral density (BMD) and variables of the metabolic syndrome are explored in patients with mild and normocalcemic pHPT before and after parathyroidectomy. To further investigate the relationship between insulin sensitivity and calcium, a community-based cohort was investigated.</p><p>In two different patient cohorts of pHPT, lipoprotein alterations with decreased levels of HDL-cholesterol and elevated triglycerides were found in association with a high frequency of IGT, NIDDM and decreased insulin sensitivity. Parathyroidectomy had effects on the dyslipidemia and in part on the glucose metabolism. The disturbed glucose metabolism in pHPT was substantiated by results from the general population by a negative association between insulin sensitivity, measured by hyperinsulinemic clamp, and serum calcium.</p><p>In conclusion, normocalcemic, mild and overt pHPT are associated with a range of risk factors for cardiovascular diseases, development of NIDDM and decreased BMD in cortical as well as trabecular bone. These findings explain, at least in part, the elevated morbidity and mortality from cardiovascular disease as well as fractures, reported in pHPT patients. Moreover, in the general population, serum calcium is associated with decreased insulin sensitivity. Parathyroidectomy has positive effects on several, but not all, of the investigated metabolic parameters.</p>

Primary hyperparathyroidism (pHPT), characterized by elevated serum levels of calcium and parathyroid hormone (PTH), is associated with a number of metabolic derangements causing secondary manifestations. These include osteoporosis and increased risk of fractures, but also risk factors for cardiovascular morbidity and mortality. These risk factors include impaired glucose tolerance (IGT), dyslipidemia, increased body mass index and hypertension. While the skeletal abnormalities are mainly due to elevated PTH, the latter disturbances are still unexplained. Non-insulin dependent diabetes mellitus (NIDDM), IGT, dyslipidemia and hypertension are all included in the metabolic syndrome, also associated with morbidity and mortality in cardiovascular diseases. In this thesis, decreased bone mineral density (BMD) and variables of the metabolic syndrome are explored in patients with mild and normocalcemic pHPT before and after parathyroidectomy. To further investigate the relationship between insulin sensitivity and calcium, a community-based cohort was investigated. In two different patient cohorts of pHPT, lipoprotein alterations with decreased levels of HDL-cholesterol and elevated triglycerides were found in association with a high frequency of IGT, NIDDM and decreased insulin sensitivity. Parathyroidectomy had effects on the dyslipidemia and in part on the glucose metabolism. The disturbed glucose metabolism in pHPT was substantiated by results from the general population by a negative association between insulin sensitivity, measured by hyperinsulinemic clamp, and serum calcium. In conclusion, normocalcemic, mild and overt pHPT are associated with a range of risk factors for cardiovascular diseases, development of NIDDM and decreased BMD in cortical as well as trabecular bone. These findings explain, at least in part, the elevated morbidity and mortality from cardiovascular disease as well as fractures, reported in pHPT patients. Moreover, in the general population, serum calcium is associated with decreased insulin sensitivity. Parathyroidectomy has positive effects on several, but not all, of the investigated metabolic parameters.

Chlamydiae are important human bacterial pathogens with an intracellular life cycle that consists of two distinct bacterial forms, an infectious form (EB) that infects the eukaryotic host cell, and a non-infectious form (RB) that allows intracellular proliferation. To be successful, chlamydiae need to alternate between EB and RB to generate infectious EB’s which are competent to infect new host cells. Chemical genetics is an attractive approach to study bacterial pathogenesis; in principal this approach relies on an inhibitory compound that specifically inhibits a protein of interest. An obstacle in using this approach is target identification, however whole genome sequencing (WGS) of spontaneous mutants resistant to novel inhibitory compounds has significantly extended the utility of chemical genetic approaches by allowing the identification of their target proteins and/or biological pathways. In this thesis, a chemical genetics approach is used, I have found that heme and glucose metabolism of C. trachomatis is specifically important for the transition from the RB form to the infectious EB form. Heme and glucose metabolism are both coupled to energy metabolism, which suggests a common link between the RB-to-EB transitions. In connection with the above findings I have developed strategies that enable the isolation of isogenic C. trachomatis mutant strains. These strategies are based on WGS of spontaneous mutant populations and subsequent genotyping of clonal strains isolated from these mutant populations. Experiments with the mutant strains suggest that the uptake of glucose-6-phosphate (G-6-P) regulates the RB-to-EB transition, representing one of the first examples where genetics has been used to study C. trachomatis pathogenesis. Additional experiments with the mutant strains indicate that G-6-P promotes bacterial growth during metabolic stress. In concert with other findings presented in this thesis, I have fine-tuned methods that could be employed to reveal how novel inhibitory chemical compounds affect chlamydiae. In a broader context, I suggest that C. trachomatis could be used as a model organism to understand how new inhibitory drugs affect other bacterial pathogens. In addition, I observed that C. pneumoniae infections resulted in generalized bone loss in mice and that these mice display a cytokine profile similar to infected bone cells in vitro. Thus, this study indicates that C. pneumoniae potentially can infect bone cells in vivo, resulting in bone loss, alternatively, the inflammatory responses seen in vivo could be the causative factor of the bone loss observed.

This study was done to examine the effects of detraining upon the metabolism of glucose by the rats. Thirty-nine female Wister rats were separated into three groups: trained, detrained, and sedentary. The training protocol consisted of swimming 6 hours/day for eight weeks. The detrained groups were then sacrificed at 7, 14, and 21 days after training. The parametrial fat pads were removed and digested into isolated cells. The cell volumes, cell concentrations, and glucose oxidation rates (radioactively labeled C-1 or C-6 glucose) were measured. The results showed that those adaptations in the fat cell brought about by exercise, i.e., 120% decreases adipocyte volume and increased glucose oxidation rates in both pentose phosphate (C-1) cycle and the glycolysis/citric acid cycles, return to the sedentary control levels by 14 days detraining.Ball State UniversityMuncie, IN 47306

Pancreatic β-cells secrete insulin in response to glucose. Intracellular glucose metabolism drives a cascade of events, including ATP production, calcium influx, and insulin processing, culminating in insulin granule exocytosis. However, insulin secretory mechanisms are incompletely understood. β-cells have the capacity to flow pyruvate into the TCA cycle via the anaplerotic enzyme pyruvate carboxylase to engage one of several pathways of pyruvate recycling. Previous work demonstrated that pyruvate cycling was correlated with insulin secretion, and that NADPH may be involved in granule exocytosis. We hypothesized that NADPH-producing cytosolic enzymes isocitrate dehydrogenase (ICDc) and malic enzyme (MEc) may be involved in both pyruvate cycling and insulin secretion. ICDc expression was reduced using siRNA in the INS-1 derived cell line 832/13 and in isolated rat islets, which led decreased glucose-stimulated insulin secretion (GSIS), pyruvate cycling, and NADPH. Organic acid profiling revealed that decreased pyruvate cycling was compensated by an increase in lactate and stable pyruvate levels. This work established an important role for ICDc in maintaining GSIS through pyruvate-isocitrate cycling. MEc expression was reduced using siRNA in two β-cell lines, 832/13 and 832/3, as well as isolated rat islets. MEc suppression inhibited GSIS in the 832/13 cells only, and these effects were not due to changes in pyruvate cycling, NADPH, or the organic acid profile. This suggests that in normal β-cells, MEc does not participate in pyruvate cycling. Acetyl CoA carboxylase 1 (ACC1) is essential in de novo lipogenesis, which has been implicated in GSIS by other laboratories. Chronic, but not acute, inhibition of ACC1 via siRNA reduced insulin secretion independent of lipogenesis. ACC1 siRNA decreased glucose oxidation, pyruvate cycling, and ATP:ADP, due to an unexpected decrease in glucokinase protein. This work questions the use of ACC inhibitors in obesity and diabetes therapy. In summary, these studies on ICDc, MEc, and ACC1, coupled with concurrent work in our laboratory, eliminate two potential pyruvate cycling pathways (pyruvate-malate and pyruvate-citrate) and establish that pyruvate-isocitrate cycling is the critical pathway for control of GSIS. Future work will focus on identifying the signaling intermediate generated in the pyruvate-isocitrate pathway that links to insulin granule exocytosis. / Dissertation

Faced with an environment of constantly changing nutrient availability, mammals have adapted complex homeostatic mechanisms to maintain energy balance. Deviations from this balance are largely corrected through a concerted, multi-organ effort that integrates hormonal signals with transcriptional regulatory networks. When these relationships are altered, as with over-nutrition and insulin resistance, metabolic disease ensues. Here, I present data concerning two distinct transcriptional pathways--one for thyroid hormone (TH) and one for insulin--that confer hormone responsiveness on metabolic gene programs that preserve energy homeostasis.