Arsenic induces diabetic effects through beta-cell dysfunction and increased gluconeogenesis in mice

Abstract

Arsenic as a potential risk factor for type 2 diabetes has been received attention recently. However, the roles of arsenic on development of diabetes are unclear. In this study, we compared the influences of inorganic arsenic (iAs) on normal and diabetic mice by systems toxicology approaches. Although iAs exposure did not change glucose tolerance in normal mice, it caused the pancreatic β-cell dysfunction and increased gluconeogenesis and oxidative damages in liver. However, iAs exposure worsened the glucose tolerance in diabetic mice, which might be due to increased gluconeogenesis and impairment of pancreatic β-cell function. It is interesting that iAs exposure could improve the insulin sensitivity based on the insulin tolerance testing by the activation of glucose uptake-related genes and enzymes in normal and diabetic individuals. Our data suggested that iAs exposure could cause pre-diabetic effects by altering the lipid metabolism, gluconeogenesis and insulin secretion in normal individual, and worsen diabetic effects in diabetes individual by these processes. Insulin resistance might be not the reason of diabetic effects caused by iAs, indicating that mechanism of the diabetogenic effects of iAs exposure is different from the mechanism associated with traditional risk factors (such as obesity)-reduced type 2 diabetes.

Figure 1. Influences of arsenic on food intake (A), body weight (B), relative liver weight (C) and relative pancreas weight (D).

CK means control mice. DB means diabetic mice. Values are mean values ± standard deviation (n = 7–8). Differences of results among groups were calculated using ANOVA followed by Tukey's post hoc test. * means significant difference compared to CK group or between special groups (p < 0.05).

Figure 2. Arsenic intake and excretion by mice exposed to deionized water with or without 3 mg/L sodium arsenite.

(A) Daily water intake; (B) Arsenic species in urine; (C) Arsenic species in feces. Four As species, including iAs (III), iAs (V), methyl-As (MMA) and dimethyl-As (DMA) were measured by HPLC-ICP-MS. CK means control mice. DB means diabetic mice. Values are mean values ± standard deviation (n = 7–8). Differences of results among groups were calculated using ANOVA followed by Tukey's post hoc test. * means significant difference (p < 0.05) compared to control mice.

Figure 3. Effects of arsenic exposure on blood glucose and insulin tolerance.

(A) Fasting blood glucose; (B) Fasting blood insulin; (C) HOMA-IR; (D) HOMA-%β; (E) and (F) OGTT; (G) OGTT AUC, calculated according to OGTT; (H) and (I) ITT; (J) ITT AUC, calculated according to ITT. CK means control mice. DB means diabetic mice. Values are mean values ± standard deviation (n = 7–8). Differences of results among groups were calculated using ANOVA followed by Tukey's post hoc test. In general, * means significant difference (p<0.05) compared to db/m control mice or between special groups. In (F) and (I), * means significant difference (p<0.05) compared to db/db control mice at the same time.

Figure 4. Effects of arsenic on oxidative stress and inflammation.

(A) Gene expressions in liver; (B) Gene expressions in adipose; (C) Gene expressions in pancreas; (D) pathological maps of liver; (E) SOD activities; (F) MDA levels; (G) GSH levels and (H) 8-OHdG levels. SOD, MDA, GSH and 8-OHdG were measured by ELISA assays. CK means control mice. DB means diabetic mice. Values are mean values ± standard deviation (n = 7–8). Differences of results among groups were calculated using ANOVA followed by Tukey's post hoc test. * means significant difference (p<0.05) compared to db/m control mice.

Figure 5. Effects of arsenic on lipid metabolism.

(A) Gene expressions in liver; (B) Gene expressions in adipose; (C) PPAR-r levels; (D) Na⁺K⁺-ATP activities; (E) Ca²⁺Mg²⁺-ATP activities; and (F) free fatty acid (FFA) levels. PPAR-r, Na⁺K⁺-ATP, Ca²⁺Mg²⁺-ATP and FFA were measured by ELISA assays. CK means control mice. DB means diabetic mice. Values are mean values ± standard deviation (n = 7–8). Differences of results among groups were calculated using ANOVA followed by Tukey's post hoc test. * means significant difference (p<0.05) compared to db/m control mice.

Figure 6. Effects of arsenic on (A) glucose-related genes, (B) hepatic Ptp1b levels, (C) hepatic leptin levels and (D) impair of pancreas.

Ptp1b and leptin were measured by ELISA assays. CK means control mice. DB means diabetic mice. Values are mean values ± standard deviation (n = 7–8). Differences of results among groups were calculated using ANOVA followed by Tukey's post hoc test. * means significant difference (p < 0.05) compared to db/m control mice or between special groups.

Figure 7. PLS-DA plot of ¹H NMR spectra of serum metabolites from control (green), control+As (red), diabetes control (cyan) and diabetes+As (blue) groups.

PLS-DA was performed by MetaboAnalyst 2.0 (http://www.metaboanalyst.ca/MetaboAnalyst).