Dose-related effects of ferric citrate supplementation on endoplasmic reticular stress responses and insulin signalling pathways in streptozotocin–nicotinamide-induced diabetes

Abstract

Diabetic patients are at high risk of developing anemia; however, pharmacological doses of iron supplementation may vary greatly depending on diabetes-related complications. The aim of this study was to investigate the dose-dependent effect of iron on glucose disposal with a special focus on endoplasmic reticular (ER) stress, iron metabolism, and insulin signalling pathways. Diabetes was induced in overnight fasted rats by intraperitoneal (i.p.) injections of 40 mg kg(-1) streptozotocin (STZ) and 100 mg kg(-1) nicotinamide. Diabetic rats were fed a standard diet (36.7 mg ferric iron per kg diet) or pharmacological doses of ferric citrate (0.5, 1, 2, and 3 g ferric iron per kg diet). Ferric citrate supplementation showed a dose-related effect on hepatic ER stress responses and total iron levels, which were associated with increased hepcidin and decreased ferroportin expressions. Iron-fed rats had increased sizes of their pancreatic islets and hyperinsulinemia compared to rats fed a standard diet. A western blot analysis revealed that iron feeding decreased total insulin receptor substrate 1 (IRS1), phosphorylated IRS1ser307, and AS160 but increased phosphorylated GSK-3β. Iron supplementation inhibited the nuclear translocation of AKT but promoted FOXO1 translocation to nuclei. Ferric citrate supplementation showed a dose-related effect on ER stress responses, hepatic iron, and the insulin signaling pathway. Adverse effects were more evident at high iron doses (>1 g ferric iron per kg diet), which is equivalent to a 60 kg human male consuming >500 mg elemental iron per day.

Hepcidin links gluco-toxicity to pancreatic beta cell dysfunction by inhibiting Pdx-1 expression

“…Liu’s study showed that the increase of body iron could also active AKT and FoxO1, which are important regulators of Pdx-1 (18). These results suggested that hepcidin would also play a role in the regulation of insulin synthesis.…”

Effect of Endoplasmic Reticular Stress on Free Hemoglobin Metabolism and Liver Injury

“…Total protein was extracted from whole-liver tissues as previously described [ 17 ]. Briefly, 50 mg of tissues was lysed in RIPA buffer, and the protein concentration was determined with a Pierce™ BCA Protein Assay Kit (Thermo Fisher Scientific, Waltham, MA, USA).…”

“…The ER is an organelle that plays a key role in nutrient metabolism. Our previous study showed that iron supplementation (>1 g ferric iron/kg diet) increased ER stress responses and impaired insulin signaling pathways in a rat model of streptozotocin/nicotinamide-induced diabetes [ 17 ]. ER stress-associated mechanisms are also required for ferritin-mediated macrophage [ 18 ] and hepatic stellate cell activation [ 19 ].…”

Ferric Citrate Supplementation Reduces Red‐Blood‐Cell Aggregation and Improves CD163+ Macrophage‐Mediated Hemoglobin Metabolism in a Rat Model of High‐Fat‐Diet‐Induced Obesity

“…Total protein was extracted from whole‐liver tissues as previously described . In brief, 50 mg of tissues was lysed in RIPA buffer, and the protein concentration was determined using a Pierce BCA Protein Assay Kit (Thermo Fisher Scientific, Waltham, MA, USA).…”