Search

Currently available interventions for vascular occlusive diseases suffer from high failure rates due to re-occlusive vascular wall adaptations, a process called intimal hyperplasia (IH). Naturally occurring hydrogen sulfide (H 2 S) works as a vasculoprotective gasotransmitter in vivo. However, given its reactive and hazardous nature, H 2 S is difficult to administer systemically. Here, we developed a hydrogel capable of localized slow release of precise amounts of H 2 S and tested its benefits on IH. The H 2 S-releasing hydrogel was prepared from a short peptide attached to an S -aroylthiooxime H 2 S donor. Upon dissolution in aqueous buffer, the peptide self-assembled into nanofibers, which formed a gel in the presence of calcium. This new hydrogel delivered H 2 S over the course of several hours, in contrast with fast-releasing NaHS. The H 2 S-releasing peptide/gel inhibited proliferation and migration of primary human vascular smooth muscle cells (VSMCs), while promoting proliferation and migration of human umbilical endothelial cells (ECs). Both NaHS and the H 2 S-releasing gel limited IH in human great saphenous vein segments obtained from vascular patients undergoing bypass surgery, with the H 2 S-releasing gel showing efficacy at a 5x lower dose than NaHS. These results suggest local perivascular H 2 S release as a new strategy to limit VSMC proliferation and IH while promoting EC proliferation, hence re-endothelialization. Arterial occlusive disease is the leading cause of death in Western countries, yet current therapies suffer from high failure rates due to intimal hyperplasia (IH), a thickening of the vascular wall leading to secondary vessel occlusion. Hydrogen sulfide (H 2 S) is a gasotransmitter with vasculoprotective properties. Here we designed and synthesized a peptide-based H 2 S-releasing hydrogel and found that local application of the gel reduced IH in human vein segments obtained from patients undergoing bypass surgery. This work provides the first evidence of H 2 S efficacy against IH in human tissue, and the results show that the gel is more effective than NaHS, a common instantaneous H 2 S donor. [ABSTRACT FROM AUTHOR]

Background Somatostatin analogs (SSAs) are first-line medical therapy for the treatment of acromegaly and neuroendocrine tumors that express somatostatin receptors (SSTR). Somatostatin suppresses secretion of a large number of hormones through the stimulation of the five SSTR. However, unbalanced inhibition of secretion as observed with the highly potent SSAs pasireotide causes hyperglycaemia mainly by inhibiting insulin secretion. In contrast, AP102 a new SSAs has neutral effect on blood glucose while suppressing GH secretion. Our objective was to establish the cellular effects of AP102 on SSTR2 and SSTR5 that may explain the differences observed between AP102 and other SSAs. Methods We compared the binding and agonist activity of AP102 with somatostatin-14, octreotide and pasireotide in HEK293 cells transfected with human SSTR2 and SSTR5 receptors. SSAs signal transduction effects (cAMP concentrations) were measured in forskolin-treated cells in the presence of SSAs. Proliferation and apoptotic effects were determined and binding assays were performed using 125 I- somatostatin-14. Results AP102 has comparable affinity and agonist effect to octreotide at SSTR2 (IC50's of 112 pM and 244 pM, respectively; EC50's of 230 pM and 210 pM, respectively) in contrast to pasireotide that exhibits a 12–27 fold higher IC50 (3110 pM) and about 5-fold higher EC50 (1097 pM). At SSTR5, AP102 has much higher affinity and stimulating effect than octreotide (IC50's of 773 pM and 16,737 pM, respectively; EC50's of 8526 pM and 26,800 pM), and an intermediate affinity and agonist effect between octreotide and pasireotide. AP102, octreotide and pasireotide have variable anti-proliferative effects on HEK cells transfected with SSTR2 and SSTR5. Conclusion AP102 is a new SSA that better reduces signaling at SSTR2 than SSTR5 and prevents cell proliferation at both receptors. The euglycaemic effect of AP102 observed in preclinical studies may be related to this intermediate agonistic potency between pasireotide and octreotide at SSTR2 and SSTR5. [ABSTRACT FROM AUTHOR]

Channels formed by the gap junction protein connexin36 (Cx36) contribute to the proper control of insulin secretion. We investigated the impact of chronic hyperlipidemia on Cx36 expression in pancreatic β-cells. Prolonged exposure to the saturated free fatty acid palmitate reduced the expression of Cx36 in several insulin-secreting cell lines and isolated mouse islets. The effect of palmitate was fully blocked upon protein kinase A (PKA) inhibition by H89 and (Rp)-cAMP, indicating that the cAMP/PKA pathway is involved in the control of Cx36 expression. Palmitate treatment led to overexpression of the inducible cAMP early repressor (ICER-17), which bound to a functional cAMP-response element located in the promoter of the CX36 gene. Inhibition of ICER-1γ overexpression prevented the Cx36 decrease, as well as the palmitate-induced β-cell secretory dysfunction. Finally, freshly isolated islets from mice undergoing a long term high fat diet expressed reduced Cx36 levels and increased ICER-1γ levels. Taken together, these data demonstrate that chronic exposure to palmitate inhibits the Cx36 expression through PKA-mediated ICER-1γ overexpression. This Cx36 down-regulation may contribute to the reduced glucose sensitivity and altered insulin secretion observed during the pre-diabetic stage and in the metabolic syndrome. [ABSTRACT FROM AUTHOR]

Store-operated Ca2+ channels (SOCs) are voltage-independent Ca2+ channels activated upon depletion of the endoplasmic reticulum Ca2+ stores. Early studies suggest the contribution of such channels to Ca2+ homeostasis in insulin-secreting pancreatic β-cells. However, their composition and contribution to glucose-stimulated insulin secretion (GSIS) remains unclear. In this study, endoplasmic reticulum Ca2+ depletion triggered by acetylcholine (ACh) or thapsigargin stimulated the formation of a ternary complex composed of Orai1, TRPC1, and STIM1, the key proteins involved in the formation of SOCs. Ca2+ imaging further revealed that Orai1 and TRPC1 are required to form functional SOCs and that these channels are activated by STIM1 in response to thapsigargin or ACh. Pharmacological SOCs inhibition or dominant negative blockade of Orai1 or TRPC1 using the specific pore mutants Orai1-E106D and TRPC1-F562A impaired GSIS in rat β-cells and fully blocked the potentiating effect of ACh on secretion. In contrast, pharmacological or dominant negative blockade of TRPC3 had no effect on extracellular Ca2+ entry and GSIS. Finally, we observed that prolonged exposure to supraphysiological glucose concentration impaired SOCs function without altering the expression levels of STIM1, Orai1, and TRPC1.Weconclude that Orai1 and TRPC1, which form SOCs regulated by STIM1, play a key role in the effect of AChon GSIS, a process that may be impaired in type 2 diabetes. [ABSTRACT FROM AUTHOR]

Abstract: The saphenous vein is the conduit of choice in bypass graft procedures. Haemodynamic factors play a major role in the development of intimal hyperplasia (IH), and subsequent bypass failure. To evaluate the potential protective effect of external reinforcement on such a failure, we developed an ex vivo model for the perfusion of segments of human saphenous veins under arterial shear stress. In veins submitted to pulsatile high pressure (mean pressure at 100 mmHg) for 3 or 7 days, the use of an external macroporous polyester mesh 1) prevented the dilatation of the vessel, 2) decreased the development of IH, 3) reduced the apoptosis of smooth muscle cells, and the subsequent fibrosis of the media layer, 4) prevented the remodelling of extracellular matrix through the up-regulation of matrix metalloproteinases (MMP-2, MMP-9) and plasminogen activator type I. The data show that, in an experimental ex vivo setting, an external scaffold decreases IH and maintains the integrity of veins exposed to arterial pressure, via increase in shear stress and decrease wall tension, that likely contribute to trigger selective molecular and cellular changes. [Copyright &y& Elsevier]