Cadmium Induces Apoptosis in Pancreatic β-Cells through a Mitochondria-Dependent Pathway: The Role of Oxidative Stress-Mediated c-Jun N-Terminal Kinase Activation

Kai-Chih Chang,Kuo-Liang Chen,Chin-Ching Wu,Yi-Chang Su,Ching-Cheng Hsu,Cheng-Chieh Yen,Chun-Fa Huang,Dong-Zong Hung,Shing-Hwa Liu,Tien-Hui Lu,Chin-Chuan Su,Ming-Jye Lee,Tsung-Jung Ho,Ya-Wen Chen

doi:10.1371/journal.pone.0054374

Abstract

Cadmium (Cd), one of well-known highly toxic environmental and industrial pollutants, causes a number of adverse health effects and diseases in humans. The growing epidemiological studies have suggested a possible link between Cd exposure and diabetes mellitus (DM). However, the toxicological effects and underlying mechanisms of Cd-induced pancreatic β-cell injury are still unknown. In this study, we found that Cd significantly decreased cell viability, and increased sub-G1 hypodiploid cells and annexin V-Cy3 binding in pancreatic β-cell-derived RIN-m5F cells. Cd also increased intracellular reactive oxygen species (ROS) generation and malondialdehyde (MDA) production and induced mitochondrial dysfunction (the loss of mitochondrial membrane potential (MMP) and the increase of cytosolic cytochrome c release), the decreased Bcl-2 expression, increased p53 expression, poly (ADP-ribose) polymerase (PARP) cleavage, and caspase cascades, which accompanied with intracellular Cd accumulation. Pretreatment with the antioxidant N-acetylcysteine (NAC) effectively reversed these Cd-induced events. Furthermore, exposure to Cd induced the phosphorylations of c-jun N-terminal kinases (JNK), extracellular signal-regulated kinases (ERK)1/2, and p38-mitogen-activated protein kinase (MAPK), which was prevented by NAC. Additionally, the specific JNK inhibitor SP600125 or JNK-specific small interference RNA (si-RNA) transfection suppressed Cd-induced β-cell apoptosis and related signals, but not ERK1/2 and p38-MAPK inhibitors (PD98059 and SB203580) did not. However, the JNK inhibitor or JNK-specific si-RNA did not suppress ROS generation in Cd-treated cells. These results indicate that Cd induces pancreatic β-cell death via an oxidative stress downstream-mediated JNK activation-triggered mitochondria-regulated apoptotic pathway.

Highlights

Cadmium (Cd) is a naturally occurring nonessential toxic heavy metal that is widely distributed in the earth’s crust
Exposure to CdCl2 (5 and 10 mM) for 24 h caused substantial MDA production in the cell membrane after exposure to CdCl2 (5 and 10 mM) for 24 h (Figure 2B); and plasma lipid peroxidation (LPO) analysis of mice exposed to Cd (0.5 and 1.0 mg/kg/day) over a 1 to 6 weeks period showed that plasma MDA levels dramatically increased in a time-dependent manner (Cd-0.5 mg/ kg group 1, 2, 4, and 6 week: 4.7960.18, 5.0060.19, 5.4960.14, and 5.6360.16 nmole MDA/mg-protein, respectively; Cd1.0 mg/kg group 1, 2, 4, and 6 week: 4.9860.17, 5.4660.13, 6.1660.20, and 6.3360.22 nmole MDA/mg-protein, respectively; age-matched control group 1, 2, 4 and 6 week: 4.5860.11, 4.5360.15, 4.5260.11, and 4.5360.14 nmole MDA/mg-protein, respectively, n = 15, p,0.05)(Figure S2–C)
We found that exposure of RIN-m5F cells to CdCl2 (5 and 10 mM) for 30 min resulted in a significant increase in the expression of phosphorylation of jun N-terminal kinases (JNK), ERK1/2, and p38-mitogen-activated protein kinase (MAPK) in a dosedependent manner, which could be reversed by NAC (1 mM) (Figure 6A)

Summary

Introduction

Cadmium (Cd) is a naturally occurring nonessential toxic heavy metal that is widely distributed in the earth’s crust It has many industrial applications, e.g., use in several alloys, color pigments, electroplating, and rechargeable nickel-cadmium batteries [1]. Animal studies have shown that Cd can cause pancreatic b-cell damage, suppress insulin secretion, increase glucose intolerance, and have diabetogenic effects [9,10]. A marked disturbance of glucose homeostasis, the destruction of pancreatic islets insulin secretion, the increase in gluconeogenic enzymes, and even significant enhance Cd toxicity in diabetic conditions are observed after rats exposed to Cd (0.5–2 mg/kg/day), which are accompanied with significant Cd accumulation in the blood and/or pancreas [9,11,12,13]. Some in vivo studies have indicated a possible link between Cd exposure and diabetogenic effects (blood glucose unbalance and pancreatic islets dysfunction); the precise mechanisms of Cd-induced toxicological effects on the function of pancreatic bcells and injuries remain unclear

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