Search Results (5)

Background/Objectives: Vitexin and isovitexin are bioactive flavonoids with promising pharmacological effects; however, they have poor bioavailability. Microencapsulation with biodegradable polymers is a promising strategy for improving their stability, bioavailability, and biocompatibility. This study aimed to optimize the formulation parameters to obtain microspheres with desired properties in terms of size, loading ratio, and vitexin–isovitexin release. Methods: Microspheres were prepared using alginate as the core matrix and a chitosan outer layer. A Design of Experiment approach using response surface methodology was employed. The hypoglycemic effects of the obtained microspheres were evaluated. Results: The formulation using 1.17% low-viscosity alginate, 7.60% calcium chloride, 5.78% Tween 80, and 5.00% Span 80 resulted in microspheres with optimal mean size (10.78 µm), high loading ratio (22.45%) and encapsulation efficiency (68.92%). The in vitro release of vitexin–isovitexin from microspheres was completed within 24 h in controlled manner. The microspheres were found to be non-toxic in vivo and exhibited hypoglycemic effects after 21 days at doses equivalent to 30 and 60 mg/kg of vitexin–isovitexin. The potential mechanisms might involve increasing the size of Islets of Langerhans and improving pancreatic β-cell function and insulin resistance, as observed in alloxan-induced diabetic mice. Conclusions: This work successfully developed alginate–chitosan-based microspheres for the controlled release of vitexin–isovitexin while maintaining their bioactivities. Full article

Ryanodine receptors (RyRs) are large intracellular Ca²⁺ release channels primarily found in muscle and nerve cells and also present at low levels in pancreatic islet endocrine cells. This review examines the role of RyRs in islet cell function, focusing on calcium signaling and hormone secretion, while addressing the ongoing debate regarding their significance due to their limited expression. We explore conflicting experimental results and their potential causes, synthesizing current knowledge on RyR isoforms in islet cells, particularly in beta and delta cells. The review discusses how RyR-mediated calcium-induced calcium release enhances, rather than drives, glucose-stimulated insulin secretion. We examine the phosphorylation-dependent regulation of beta-cell RyRs, the concept of “leaky ryanodine receptors”, and the roles of RyRs in endoplasmic reticulum stress, apoptosis, store-operated calcium entry, and beta-cell electrical activity. The relationship between RyR dysfunction and the development of impaired insulin secretion in diabetes is assessed, noting their limited role in human diabetes pathogenesis given the disease’s polygenic nature. We highlight the established role of RyR-mediated CICR in the mechanism of action of common type 2 diabetes treatments, such as glucagon-like peptide-1, which enhances insulin secretion. By integrating findings from electrophysiological, molecular, and clinical studies, this review provides a balanced perspective on RyRs in islet cell physiology and pathology, emphasizing their significance in both normal insulin secretion and current diabetes therapies. Full article

Calcium (Ca²⁺) is a ubiquitous and fundamental signaling component that is utilized by cells to regulate a diverse range of cellular functions, such as insulin secretion from pancreatic β-cells of the islets of Langerhans. Cyclic ADP-ribose (cADPR), synthesized from NAD⁺ by ADP-ribosyl cyclase family proteins, such as the mammalian cluster of differentiation 38 (CD38), is important for intracellular Ca²⁺ mobilization for cell functioning. cADPR induces Ca²⁺ release from endoplasmic reticulum via the ryanodine receptor intracellular Ca²⁺ channel complex, in which the FK506-binding protein 12.6 works as a cADPR-binding regulatory protein. Recently, involvements of the CD38-cADPR signal system in several human diseases and animal models have been reported. This review describes the biochemical and molecular biological basis of the CD38-cADPR signal system and the diseases caused by its abnormalities. Full article

In type 1 diabetes (T1D) development, proinflammatory cytokines (PIC) released by immune cells lead to increased reactive oxygen species (ROS) production in β-cells. Nonetheless, the temporality of the events triggered and the role of different ROS sources remain unclear. Isolated islets from C57BL/6J wild-type (WT), NOX1 KO and NOX2 KO mice were exposed to a PIC combination. We show that cytokines increase O₂^•− production after 2 h in WT and NOX1 KO but not in NOX2 KO islets. Using transgenic mice constitutively expressing a genetically encoded compartment specific H₂O₂ sensor, we show, for the first time, a transient increase of cytosolic/nuclear H₂O₂ in islet cells between 4 and 5 h during cytokine exposure. The H₂O₂ increase coincides with the intracellular NAD(P)H decrease and is absent in NOX2 KO islets. NOX2 KO confers better glucose tolerance and protects against cytokine-induced islet secretory dysfunction and death. However, NOX2 absence does not counteract the cytokine effects in ER Ca²⁺ depletion, Store-Operated Calcium Entry (SOCE) increase and ER stress. Instead, the activation of ER stress precedes H₂O₂ production. As early NOX2-driven ROS production impacts β-cells’ function and survival during insulitis, NOX2 might be a potential target for designing therapies against early β-cell dysfunction in the context of T1D onset. Full article

Sustained high concentration of glucose has been verified toxic to β-cells. Glucose augments Ca²⁺-stimulated insulin release in pancreatic β-cells, but chronic high concentration of glucose could induce a sustained level of Ca²⁺ in β-cells, which leads to cell apoptosis. However, the mechanism of high glucose-induced β-cell apoptosis remains unclear. In this study, we use a calcium channel blocker, nifedipine, to investigate whether the inhibition of intracellular Ca²⁺ concentration could protect β-cells from chronic high glucose-induced apoptosis. It was found that in a concentration of 33.3 mM, chronic stimulation of glucose could induce INS-1 β-cells apoptosis at least through the endoplasmic reticulum stress pathway and 10 μM nifedipine inhibited Ca²⁺ release to protect β-cells from high glucose-induced endoplasmic reticulum stress and apoptosis. These results indicated that inhibition of Ca²⁺ over-accumulation might provide benefit to attenuate islet β-cell decompensation in a high glucose environment. Full article