Temporal and spatial dynamics of organic chemicals in the environment with a multimedia fate model.

In this PhD thesis we have deal with different aspects of treatment and pathogenesis of diabetes mellitus. With regard to type 1 diabetes, we followed three different research lines clarifying aspects not yet well known on different types of patient transplants. Regarding type 2 diabetes, we studied the role of insular amyloid in the development and progression of the disease. Transplantation is one of the possible therapies for type 1 diabetes and can be performed in patients who no longer respond to insulin therapy in satisfactory manner. For type 1 diabetes treatment there are three possible types of transplantation: • Pancreas, often associated with kidney transplantation, is the only treatment for type 1 diabetes that can maintain long-term insulin independence and normoglycemia. In type 1 diabetes patients, chronic hyperglycemia leads to both microvascular and macrovascular damages probably due to overproduction of superoxides by the mitochondrial electron transport chain. In patients subjected to pancreas transplantation, it has been noted improvements in the microcirculation and in particular at the level of endothelial cells. In order to identify possible mechanisms by which transplantation improves microcirculation, we analyzed the expression of proteins involved in cellular response to oxidative stress in skin biopsies. According to the results obtained in our studies, some of the identified proteins may be considered as therapeutic targets for a new class of drugs, potentially able to correct cell modifications in cases where normoglycemia cannot be restored. • Human purified pancreatic islet transplantation. The transplantation of human islets can successfully restore long-term insulin independence and improve glycemic control. However, the number of patients that remain insulin-independent decreases gradually in 2-3 years. Several hypotheses have been formulated in order to explain this negative response. One hypothesis is the “functional exhaustion" of a chronically overstimolated β cells mass. To better understand this possible mechanism, we studied at morphological, immunohistochemical and ultrastructural level the pancreatic islets before and after human islet cells transplantation in athymic nude mice made diabetic. • Stem cell transplantation. Stem cells seem to be the new frontier for the treatment of type 1 diabetes. Several stem cell types have been identified as potential progenitors of pancreatic β cells and mesenchymal stem cells (MSC) seem to be a possible source of them. In addition, MSCs have immunomodulatory effects as demonstrated in several researches in which these cells have been used to reduce the burden of a variety of immune-mediated diseases. Since type 1 diabetes is an autoimmune disorder, we explored the possibility to use MSCs transplantation as a therapeutic approach. For this reason, we characterized MSCs obtained from diabetes susceptible (NOD) mice and from diabetes-resistant (BALB/c) mice. After, we injected MSCs into pre-diabetic NOD mice and we evaluated their immunomodulatory effects in vivo. It has been demonstrated that amyloid deposits are one of the main morphological alteration of the islets of Langerhans in patients affects by long-standing type 2 diabetes. Typically, islet amyloid derives from deposition of amylin which is synthesized and stored in pancreatic β cells together with insulin. Amylin is produced as a pro-peptide and cut by specific proteases. It has been showed in Alzheimer's patients that the protease BACE 1 is involved in amyloid plaques production. In addition, a BACE 1 homologue called BACE 2 has been identified and localised in most adult tissues such as the pancreatic one. However, the role of BACE 2 still remains unclear. By using immunohistochemical, ultrastructural and immunocytochemical techniques, we identified and localised BACE 2 in secretory granules of mice and rats pancreatic β cells. The data collected in our studies could be considered as a starting point for further investigations on human normal and diabetic pancreases. For instance, the correlation between BACE 2 expression and amyloid deposition could help to better understand a possible role of BACE 2 in islet amyloidosis and consequently could improve our understanding of the type 2 diabetes disorder. However, it is not yet clear if amyloidosis is a primary or secondary event in the pathogenesis of diabetes. In order to better understand this situation, we used the Papio hamadryas (baboon) as an in vivo model. Indeed, baboons spontaneously develop type 2 diabetes associated with obesity as in humans, hypothesizing a similarity in diabetes pathogenesis between the two species. Our results strongly support that the insular amyloidosis associated with β cell apoptosis, α cell proliferation and hypertrophy are determinants of islets dysfunctional remodeling and hyperglycemia in baboons. In addition, our studies allow to hypothise a correlation between severity of amyloidosis, age and fasting plasma glucose levels.