Hana Farhangkhoee

Curcumin prevents diabetes-associated abnormalities in the kidneys by inhibiting p300 and nuclear factor-κB

OBJECTIVE Diabetic nephropathy is a debilitating disease that leads to end-stage renal failure in the Western world. Hyperglycemia is the initiating factor in several chronic diabetic complications which mediates increased oxidative stress and eventually the increased production of vasoactive factors and extracellular matrix proteins. We hypothesized that curcumin, a potent antioxidant, might be beneficial in preventing the development of diabetic nephropathy because this compound has been shown to inhibit p300, a histone acetyltransferase that plays a role in regulating gene expression through its interaction with the transcription factor nuclear factor-kappaB. METHODS To test this hypothesis, male Sprague-Dawley rats were injected with streptozotocin to induce diabetes. These animals were subsequently treated with curcumin for a period of 1 mo. RESULTS Real-time reverse transcriptase polymerase chain reaction analyses showed that diabetes-induced upregulation of vasoactive factors (endothelial nitric oxide synthase and endothelin-1), transforming growth factor-beta1 and extracellular matrix proteins (fibronectin and extradomain-B-containing fibronectin) in the kidneys. These changes were associated with increased oxidative stress, mesangial expansion, and p300 and nuclear factor-kappaB activity that were prevented with curcumin treatment. CONCLUSION These beneficial effects of curcumin were mediated through the inhibition of p300 and nuclear factor-kappaB.

EDB fibronectin and angiogenesis -- a novel mechanistic pathway

Extra domain-B containing fibronectin (EDB+ FN), a recently proposed marker of angiogenesis, has been shown to be expressed in a number of human cancers and in ocular neovascularization in patients with proliferative diabetic retinopathy. To gain molecular understanding of the functional significance of EDB+ FN, we have investigated possible regulatory mechanisms of induction and its role in endothelial cell proliferation and angiogenesis. Human vascular endothelial cells were cultured in high levels of glucose, and fibrogenic growth factors, transforming growth factor-β1 (TGF-β1) and endothelin-1 (ET-1). Our results show that high glucose levels, TGF-β1, and ET-1 upregulated EDB+ FN expression. Treatment of cells exposed to high glucose with TGF-β1 neutralizing antibody and ET receptor antagonist prevented high glucose-induced EDB+ FN expression. In order to elucidate the functional significance of EDB+ FN upregulation, cells were subjected to in vitro proliferation and angiogenesis assays following EDB peptide treatment and specific EDB+ FN gene silencing. Our results show that exposure of cells to EDB peptide increased vascular endothelial growth factor (VEGF) expression, endothelial proliferation, and tube formation. Furthermore, specific EDB+ FN gene silencing prevented both basal and high glucose-induced VEGF expression and reduced the proliferative capacity of endothelial cells. In conclusion, these results indicate that EDB+ FN is involved in endothelial cell proliferation and vascular morphogenesis, findings which may provide novel avenues for the development of anti-angiogenic therapies.

Towards Newer Molecular Targets for Chronic Diabetic Complications

Prior to the discovery of insulin, the major cause of death in the diabetic population was ketoacidosis. Although insulin and improved glycemic control have improved the longevity of diabetic patients, they still suffer from significant morbidity and mortality due to chronic secondary complications. Long standing diabetes leads to structural and functional alterations in both the micro- and macrovasculature. These complications, involving the retina, kidney, and peripheral nerves, as well as cardiovascular system, severely compromise the quality and expectancy of life. Large scale clinical trials have identified hyperglycemia as the key determinant for the development of such complications. Therapeutic modalities have been developed to target glucose-induced alterations, such as protein kinase C activation, augmented polyol pathway activity, non-enzymatic glycation and oxidative stress to ameliorate chronic complications. However, clinical trials targeting these biochemical alterations have failed to show significant beneficial effects. The plethora of biochemical anomalies that govern the development of chronic diabetic complications may therefore be subject to cross-interaction and complex interplays. Studies in both animal and human diabetes have, however, showed alteration of several vasoactive effector molecules such as endothelins. These molecules may be instrumental in mediating diabetes-induced structural and functional deficits at both the early and late stages of the disease. This review will discuss the current mechanistic understanding of chronic diabetic complications and will explore the potential novel therapeutic interventions.

PARP mediates structural alterations in diabetic cardiomyopathy.

Diabetic cardiomyopathy is characterized by structural alterations such as cardiomyocyte hypertrophy, necrosis and focal fibrosis. Hyperglycemia-induced oxidative damage may play an important role in this pathogenetic process. Recent studies have shown that poly (ADP-ribose) polymerase (PARP) is activated in response to oxidative stress and cellular damage as well, plays a role in gene expression. This study investigated mechanisms of diabetes-induced, PARP-mediated development of structural alterations in the heart. Two models of diabetic complications were used to determine the role of PARP in oxidative stress, cardiac hypertrophy and fibrosis in the heart. PARP-1 knockout (PARP(-/-)) mice and their respective controls were fed a 30% galactose diet while male Sprague-Dawley rats were injected with streptozotocin and subsequently treated with PARP inhibitor 3-aminobenzamide (ABA). The in vivo experiments were verified in in vitro models which utilized both neonatal cardiomyocytes and endothelial cells. Our results indicate that hyperhexosemia caused upregulation of extracellular matrix proteins in association with increased transcriptional co-activator p300 levels, cardiomyocyte hypertrophy and increased oxidative stress. These pathogenetic changes were not observed in the PARP(-/-) mice and diabetic rats treated with ABA. Furthermore, these changes appear to be influenced by histone deacetylases. Similar results were obtained in isolated cardiomyocytes and endothelial cells. This study has elucidated for the first time a PARP-dependent, p300-associated pathway mediating the development of structural alterations in the diabetic heart.

Endothelin-mediated remodeling in aortas of diabetic rats

Smooth muscle cells proliferation and extracellular matrix (ECM) protein deposition are key features of diabetic macroangiopathy. In the present study, we have studied the role of endothelinA (ETA) receptor, the predominant receptor on smooth muscle cells, in diabetes‐induced vascular hypertrophy and remodeling.

Glucose-induced regulation of novel iron transporters in vascular endothelial cell dysfunction

Increased iron indices have been associated with the development of diabetes and its complications. In the present study, we have investigated the glucose-induced alteration of iron transporters, divalent metal transporter-1 (DMT-1), iron regulated transporter protein-1 (IREG-1), and transferrin receptor (TfR), in endothelial cell iron accumulation and oxidative stress. Cells were exposed to high glucose levels and subjected to gene expression, protein expression, iron measurement and assessment of oxidative stress. Our results show, for the first time, expression of DMT-1 and IREG-1 in vascular endothelial cells. Our data further indicates upregulation of DMT-1 and IREG-1 mRNA and protein in response to high levels of glucose. TfR, however, exhibited a modest decrease in response to high levels of glucose. Increased expression of DMT-1 and IREG-1 was associated with iron accumulation and oxidative stress. Furthermore, our results show differential expression of iron transporters with treatment of high glucose-exposed cells with two different iron chelators. In conclusion, our study suggests that glucose-induced alteration of iron transporters may arbitrate iron accumulation and oxidative stress in endothelial cells.