Influence of melatonin on free radical‐induced changes in rat pancreatic beta‐cells in vitro

Abstract

Free radicals may produce cytotoxicity to pancreatic islets under pathophysiological conditions. The aim of our in vitro investigations was to compare functional and morphological changes in pancreatic beta-cells induced by reactive oxygen species (ROS) generated by alloxan or xanthine oxidase/hypoxanthine (XO/HX), respectively. We demonstrate that short-term exposure to alloxan or to XO/HX leads to a temporarily elevated insulin release from isolated pancreatic islets. On application of alloxan, this effect is caused by beta-cell necrosis and can be prevented by administration of melatonin, while in contrast, XO/HX did not lead to long-term morphological changes in the majority of the cells. Among the cells destroyed by alloxan, only necrosis could be detected, while in contrast, some apoptotic cells were identified by the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) reaction and electron microscopic examinations of cells treated with XO/HX. Melatonin was able to prevent the changes caused by alloxan, but failed to influence the alterations caused by XO/HX. Using electron spin resonance and lipid peroxidation assay, respectively, it was confirmed that melatonin effectively detoxifies hydroxyl radicals. Therefore, we believe that hydroxyl radicals are the toxic principle of alloxan, but not of XO/HX toxicity.

Reactive Oxygen Species as a Signal in Glucose-Stimulated Insulin Secretion

“…Wollheim's group found in rat islets that H 2 O 2 and alloxan, another agent like DEM that can increase intracellular H 2 O 2 , caused a rapid and transient elevation of intracellular Ca 2ϩ accompanied by insulin release at basal nonstimulatory glucose concentrations (39,40). Similarly, Ebelt et al (41) reported that short-term exposure of isolated rat islets to alloxan and xanthine oxidase/hypoxanthine, a well-known ⅐O 2 Ϫ generating system, evoked an acute elevation in insulin release. Additional indirect support for the notion that ROS in ␤-cells might contribute to GSIS also comes from Leloup et al (42), who recently reported that mitochondrial ROS are required for hypothalamic glucose sensing.…”

The effects of melatonin on the oxidants and antioxidants in the pancreatic tissue during the aging process

“…Pankreas üzerinde yapılmış çalışmalarda da, melatoninin pankreasta koruyucu etkisi olduğu göste-rilmiştir [21]. Pankreasta oksidatif stresi artırmaya yönelik diğer deneysel modellemelerde de antioksidanların koruyucu etkileri araştırılmıştır.…”

Cytoprotective Effect of Costus Speciosus on Pancreatic Β-Cells in Alloxan-Treated Rats.

“…Furthermore, the cytotoxic action of alloxan is mediated mainly by the generation of reactive oxygen species (ROS) (Dahech, Belghith et al 2011). ROS produce fragmentation and damage of DNA of β -cells exposed to alloxan (Ebelt, Peschke et al 2000).…”