Ic dysfunction and cell death by induction of caspase activation [28,29]. In the present study we showed that the hepatic Zn level was decrease in TPEN-treated normal mice and further decrease in TPEN-treated diabetic mice (Fig. 1). Therefore the hepatic toxicity of TPEN-treatment in normal and diabetic mice should be mediated by Zn deficiency. To further confirm our speculation, we further provided experimental evidence that TPEN-treated hepatic cells also showed the induction of apoptotic cell death in a 1676428 dose-dependent FCCP web manner (Fig. 7A) and the apoptotic effect of TPEN in the hepatic cells was able to be completelyFigure 7. TPEN induced apoptosis in HepG2 cells is prevented by supplementation of Zn. HepG2 cells were treated by indicated concentrations of TPEN for 30 h and then the cell death was detected by DNA fragmentation assay (A). HepG2 cells were also treated with 1 mM TPEN in the absence or presence of Zn at indicated concentrations for 30 h and then the cell death was detected by DNA fragmentation assay (B). Experiments were repeated three times at least and the data are presented as mean 6 SD. * P,0.05 vs. control group; # P,0.05 vs. TPEN group. doi:10.1371/journal.pone.0049257.grescued by supplementation of Zn at 30?0 mM, but not at lower level such as 15 mM (Fig. 7B). The in vitro study suggests that the apoptotic effect of TPEN treatment is mediated 25837696 by its chelation of Zn, rather than its direct toxicity. Type 1 diabetic patients with the liver disease often have systemic increases of inflammatory cytokines such as TNF-a [30,31]. Zn deficiency also induces systemic inflammatory response [32,33] and hepatic injury [14?6]. Therefore, we Microcystin-LR biological activity assumed that Zn deficiency in diabetic patients might exacerbate hepatic injury. In support of our hypothesis, we demonstrated here that Zn deficiency significantly exacerbated diabetes-induced hepatic inflammation, oxidative stress, lipid accumulation, and hepatic cell death along with the increased serum hepatic enzyme (Figs. 2,3,4). Our finding is consistent with a previous study that showed the exacerbation of carbon tetrachloride hepatic toxicity by Zn deficiency [34]. Endoplasmic reticulum (ER) stress was found to play a critical role in diabetes pathogenesis and diabetes-induced testicular and cardiac apoptosis [22,35]. To date, however, there was no report whether ER stress also plays certain role in diabetes-induced hepatic cell death. In fact, hepatocytes contain abundant ER that is essential 
for protein metabolism and stress signaling. Hepatic cells cope with ER stress by an adaptive or protective response, termed unfolded protein response (UPR). UPR includes both the enhancement of protein folding and degrading in the ER and the down-regulation of overall protein synthesis. When the UPR to ER stress is insufficient, the ER 
stress response unleashesZn Deficiency Exacerbates Diabetic Liver InjuryFigure 8. Possible mechanism for hepatic damage induced by diabetes and Zn deficiency. Both Zn deficiency-induced PTEN/ PTP1B activation and diabetes-increased TRB3 expression via induction of oxidative stresses and ER stress inhibit the activation of Akt, which in turn increase GSK3b activity, leading to Fyn-nuclear accumulation that stimulates Nrf2 exporting to cytosol where to be degraded. Downregulation of Nrf2 activity leads to the decrease in antioxidants, which cause hepatic oxidative stress, inflammation, cell death, damage, and steatosis. doi:10.1371/journal.pone.0049257.gpathologica.Ic dysfunction and cell death by induction of caspase activation [28,29]. In the present study we showed that the hepatic Zn level was decrease in TPEN-treated normal mice and further decrease in TPEN-treated diabetic mice (Fig. 1). Therefore the hepatic toxicity of TPEN-treatment in normal and diabetic mice should be mediated by Zn deficiency. To further confirm our speculation, we further provided experimental evidence that TPEN-treated hepatic cells also showed the induction of apoptotic cell death in a 1676428 dose-dependent manner (Fig. 7A) and the apoptotic effect of TPEN in the hepatic cells was able to be completelyFigure 7. TPEN induced apoptosis in HepG2 cells is prevented by supplementation of Zn. HepG2 cells were treated by indicated concentrations of TPEN for 30 h and then the cell death was detected by DNA fragmentation assay (A). HepG2 cells were also treated with 1 mM TPEN in the absence or presence of Zn at indicated concentrations for 30 h and then the cell death was detected by DNA fragmentation assay (B). Experiments were repeated three times at least and the data are presented as mean 6 SD. * P,0.05 vs. control group; # P,0.05 vs. TPEN group. doi:10.1371/journal.pone.0049257.grescued by supplementation of Zn at 30?0 mM, but not at lower level such as 15 mM (Fig. 7B). The in vitro study suggests that the apoptotic effect of TPEN treatment is mediated 25837696 by its chelation of Zn, rather than its direct toxicity. Type 1 diabetic patients with the liver disease often have systemic increases of inflammatory cytokines such as TNF-a [30,31]. Zn deficiency also induces systemic inflammatory response [32,33] and hepatic injury [14?6]. Therefore, we assumed that Zn deficiency in diabetic patients might exacerbate hepatic injury. In support of our hypothesis, we demonstrated here that Zn deficiency significantly exacerbated diabetes-induced hepatic inflammation, oxidative stress, lipid accumulation, and hepatic cell death along with the increased serum hepatic enzyme (Figs. 2,3,4). Our finding is consistent with a previous study that showed the exacerbation of carbon tetrachloride hepatic toxicity by Zn deficiency [34]. Endoplasmic reticulum (ER) stress was found to play a critical role in diabetes pathogenesis and diabetes-induced testicular and cardiac apoptosis [22,35]. To date, however, there was no report whether ER stress also plays certain role in diabetes-induced hepatic cell death. In fact, hepatocytes contain abundant ER that is essential for protein metabolism and stress signaling. Hepatic cells cope with ER stress by an adaptive or protective response, termed unfolded protein response (UPR). UPR includes both the enhancement of protein folding and degrading in the ER and the down-regulation of overall protein synthesis. When the UPR to ER stress is insufficient, the ER stress response unleashesZn Deficiency Exacerbates Diabetic Liver InjuryFigure 8. Possible mechanism for hepatic damage induced by diabetes and Zn deficiency. Both Zn deficiency-induced PTEN/ PTP1B activation and diabetes-increased TRB3 expression via induction of oxidative stresses and ER stress inhibit the activation of Akt, which in turn increase GSK3b activity, leading to Fyn-nuclear accumulation that stimulates Nrf2 exporting to cytosol where to be degraded. Downregulation of Nrf2 activity leads to the decrease in antioxidants, which cause hepatic oxidative stress, inflammation, cell death, damage, and steatosis. doi:10.1371/journal.pone.0049257.gpathologica.
