Incretins are gastric hormones released by intestinal K-cells in response to food consumption and stimulate insulin secretion from pancreatic beta cells. One of these hormones, glucose-dependent insulinotropic peptide (GIP) is also anabolic in bone. Individuals with diabetes experience diminished bone quality caused by a low bone formation osteopenia. The present study seeks to identify a mechanism for diabetic osteopenia in which diabetes interferes with GIP-stimulated increases in the collagen cross-linking enzyme lysyl oxidase (LOX) in osteoblasts, leading to decreased collagen integrity and the trabecular abnormalities seen in diabetic bone. Micro-CT analysis and picrosirius red histology of long bones from LOX +/- and wild type mice made diabetic by low dose streptozotocin induction revealed a profound exacerbation of the decreased bone volume, impaired trabecular structure, and disorganized collagen matrix seen in diabetic mice when the mice were also haploinsufficient for LOX. Furthermore, qPCR of RNA isolated from diabetic long bones revealed a more than 20 fold decrease in LOX expression in diabetic bone from wild type mice. Treatment of wild type osteoblasts in culture with GIP results in a significant increase in LOX transcript and protein levels. Interestingly in our diabetic mice there is a decrease in osteoblast derived LOX and an abnormal increase in serum levels of the anti-incretin gut-derived dopamine, which is known to inhibit the effects of GIP in the pancreas. Therefore the ability of dopamine to inhibit GIP-stimulated signaling in osteoblasts was examined. Data indicate a strong dose-dependent inhibition of GIP-stimulated LOX expression when primary osteoblast cultures are pretreated with dopamine. Finally, pretreatment of primary osteoblasts with the dopamine receptor inhibitor amisulpride restored the impaired GIP stimulated increases in LOX expression in osteoblasts isolated from diabetic mice. This study defines a potential mechanism for diabetic bone disease and suggests that interference with dopamine signaling would likely restore bone health in diabetes.

Made available in DSpace on 2014-12-17T14:13:36Z (GMT). No. of bitstreams: 1 ValeriaMGDML_TESE.pdf: 5877760 bytes, checksum: 33cd720eef775e51bdd077da12942ba1 (MD5) Previous issue date: 2010-11-19 / Funda??o de Amparo a Pesquisa do Estado de S?o Paulo / The relationship between lipid peroxidation, antioxidant defense and diabetic osteopenia remains unclear. This study evaluated the relationship between lipid peroxidation index, antioxidant defense parameter and bone metabolism in a premenopausal diabetic model by measurements such as thiobarbituric acid-reactive substances concentration (TBARS) and reduced glutathione (GSH) content in brain homogenates, histomorphometric analysis, biomechanical testing and bone mineral density (BMD). Female Wistar rats with regular estrous cycle were divided into two groups: Group 1: control rats (n = 15) and Group 2: diabetic rats (n = 15). Diabetes mellitus was induced by alloxan and confirmed by glycemia &#61619;250 mg/dL. The experimental period understood 1 and 5 after days induction and 45, 75 and 120 days after the installation of diabetes mellitus.The lipid peroxidation index, measured by TBARS concentration, showed a significant increase (p<0.05) in diabetic animals in comparison to animals control. However, the antioxidant parameter, measured by GSH content, was significantly decrease (p<0.05) in diabetic animals. Histomorphometric analysis showed a significant increase (p<0.05) in femoral trabecular separation together with a significant decrease (p<0.05) in trabecular thickness and reduced trabecular bone volume in diabetic rats. Moreover, biomechanical testing and BMD values were significant decrease (p<0.05) in diabetic group. Thus, our results demonstrated that increased lipid peroxidation and altered antioxidant defense could be related to the development of oxidative stress and diabetic osteopenia in premenopausal rats / A rela??o entre peroxida??o lip?dica, defesa antioxidante e osteopenia diab?tica permanece obscura. Este estudo avaliou a associa??o entre ?ndice de peroxida??o lip?dica, par?metro de defesa antioxidante e metabolismo ?sseo em um modelo diab?tico pr?-menopausado atrav?s de medidas como a concentra??o de subst?ncias reativas ao ?cido tiobarbit?rico (SRAT) e conte?do de glutationa reduzida (GSH) no homogenato cerebral, an?lises histomorfom?tricas, teste biomec?nico e densidade mineral ?ssea (DMO). Ratas Wistar com ciclo estral regular foram distribu?das em dois grupos: Grupo 1 - ratas controle (n = 15) e Grupo 2 - ratas diab?ticas (n = 15). O diabetes mellitus foi induzido pela aloxana e confirmado pela glicemia &#61619;250 mg/dL. O per?odo experimental compreendeu 1 e 5 dias ap?s a indu??o e 45, 75 e 120 dias ap?s a instala??o do diabetes mellitus. O ?ndice de peroxida??o lip?dica, medido pela concentra??o de SRAT, demonstrou um aumento significativo (p<0.05) nos animais diab?ticos, em rela??o aos animais controle. Entretanto, o par?metro de defesa antioxidante, mensurado pelo conte?do de GSH, foi reduzido significativamente (p<0.05) nos animais diab?ticos. As an?lises histomorfom?tricas mostraram um aumento significativo (p<0.05) da separa??o trabecular do f?mur, associado ? diminui??o significativa da espessura trabecular (p<0.05) e volume ?sseo trabecular reduzido nas ratas diab?ticas. Al?m disso, o teste biomec?nico, medido pela for?a m?xima de compress?o, e valores de DMO foram reduzidos significativamente (p<0.05) no grupo diab?tico. Dessa maneira, nossos resultados demonstraram que a peroxida??o lip?dica aumentada e defesa antioxidante modificada podem estar relacionadas ao desenvolvimento do estresse oxidativo e osteopenia diab?tica em ratas pr?-menopausadas