Potential effect of chronic Helicobacter pylori infection on glucose metabolism of Mongolian gerbils

Abstract

Aim: To assess the effect of Helicobacter pylori (H. pylori) infection on metabolic parameters in Mongolian gerbils.

Methods: A total of 40 male, 5- to 8-wk-old, specific-pathogen-free Mongolian gerbils (30-50 g) were randomly allocated into two groups: a control group (n = 20) and an H. pylori group (n = 20). After a two-week acclimation period, the control group was administered Brucella broth and the H. pylori group was challenged intra-gastrically five times every other day with approximately 10(9)/CFU H. pylori ATCC43504 (CagA+, VacA+). Each group was then divided into two subgroups, which were sacrificed at either 6 or 12 mo. The control and H. pylori subgroups each contained 10 Mongolian gerbils. Body weight, abdominal circumference, and body length were measured, and body mass index (BMI) and Lee's index were calculated. Biochemical assays were used to detect serum indexes, including glucose, glycated hemoglobin (GHb), glycated hemoglobin A1c (HbA1c), triacylglycerol, and total cholesterol, using an automatic biochemistry analyzer. Inflammatory cytokines, including interleukin (IL)-1β, IL-2, IL-4, IL-10, IL-12, tumor necrosis factor-α (TNF-α) and interferon (IFN)-γ, were assayed using ELISA. The expression of insulin and insulin-like growth factor 1 (IGF-1) was detected by immunohistochemistry, and islet apoptosis was measured using the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay.

Results: At each time point, body weight, abdominal circumference, BMI, and Lee's index were increased after H. pylori infection. However, these differences were not significant. H. pylori infection significantly increased the GHb (5.45 ± 0.53 vs 4.98 ± 0.22, P < 0.05) and HbA1c (4.91 ± 0.61 vs 4.61 ± 0.15, P < 0.05) levels at 12 mo. We observed no significant differences in serum biochemical indexes, including fasting blood glucose, triacylglycerol and total cholesterol, at 6 or 12 mo after infection. H. pylori infection significantly increased the expression of IGF-1 (P < 0.05). Insulin levels from the pancreas and the apoptotic rate of islet β-cells remained unchanged. Also, we observed no significant differences among cytokines levels, including IL-1β, IL-2, IL-4, IL-10, IL-12, TNF-α and IFN-γ. IL-4 was the only exception, which increased at 6 (44.36 ± 25.17 vs 17.38 ± 3.47, P < 0.05) and 12 mo (33.41 ± 10.00 vs 18.91 ± 5.31, P < 0.05) after H. pylori infection.

Conclusion: Long-term H. pylori infection is significantly associated with high levels of HbA1c in Mongolian gerbils, indicating a potential role of H. pylori infection in glucose dysregulation.

Keywords: Glucose metabolism; Glycated hemoglobin A1c; Helicobacter pylori; Inflammatory cytokines.

Figure 1

Effects of Helicobacter pylori infection on body indexes of Mongolian gerbils at different time points. The body weight, body length, and abdominal circumference were measured, and body mass index and Lee’s index were calculated at 6 and 12 mo after Helicobacter pylori (H. pylori) infection. The data denote an upward trend of these parameters, although there were no significant differences (P > 0.05). Bars represent the mean ± SEM, n = 8-10 mice per group.

Figure 2

Measurements of serum biochemical parameters of Mongolian gerbils after Helicobacter pylori infection at different time points. Serum concentration of fasting glucose (Glu), triacylglycerol (TG), total cholesterol (TC), and glycated hemoglobin (GHb) and hemoglobin A1c (HbA1c) were measured at 6 and 12 mo after Helicobacter pylori (H. pylori) infection. Data are presented as mean ± SEM from eight to ten mice per group. ^aP < 0.05 between H. pylori infected mice and their controls at 12 mo concerning GHb and HbA1c.

Figure 3

Effects of chronic Helicobacter pylori infection on the serum inflammatory cytokines in Mongolian gerbils at different time points. The serum levels of cytokines including IL-1β, IL-2, IL-12, IL-4, IL-10, IFN-γ, and TNF-α were measured by ELISA at 6 and 12 mo after Helicobacter pylori (H. pylori) infection. Data are presented as mean ± SEM from eight to ten mice per group. Cytokines were not significant different except IL-4 (^aP < 0.05 between H. pylori infected mice and their controls). IL: Interleukin; TNF: Tumor necrosis factor; IFN: Interferon.

Figure 4

Effects of chronic Helicobacter pylori infection on the expression of insulin-like growth factor-1 and insulin in the pancreas of Mongolian gerbils. A: Immunohistochemistry scores of insulin-like growth factor-1 (IGF-1) and insulin were determined in the control and Helicobacter pylori (H. pylori) groups at 6 and 12 mo (n = 8-10). Data are expressed as the mean ± SEM. ^aP < 0.05 between H. pylori infected mice at 6 mo and their controls concerning the expression of IGF-1; B: Representative immunohistochemical staining of IGF-1 and insulin expression in the pancreas of Mongolian gerbils at 6 mo after H. pylori infection (magnification × 400).

Figure 5

Effects of chronic Helicobacter pylori infection on the apoptosis of islet β-cells in Mongolian gerbils. A: Apoptotic rate of islet β-cells was detected by TUNEL assay in the control and Helicobacter pylori (H. pylori) groups at 6 and 12 mo. Data are expressed as the means ± SEM (n = 8-10 mice/group). P > 0.05 was observed between H. pylori infected mice and their controls; B: Representative images of islet β-cells in the pancreas of Mongolian gerbils at 6 mo after H. pylori infection by TUNEL staining (magnification × 400).

Figure 6

Insulin-like growth factor-1 signaling with regard to Helicobacter pylori associated glucose dysregulation. Insulin-like growth factor-1 (IGF-1), upon binding to its receptor IGF-1R, activates the intrinsic tyrosine kinase activity. IGF-1R then phosphorylates substrate proteins, including members of the IRS family such as IRS1 and Shc on selective tyrosine residues. Downstream to the receptors are two major pathways: the phosphatidylinositol-3 kinase (PI3K)/Akt pathway and MAPK pathway. IGF-1 acts via the MAPK pathway to mediate growth responses. The PI3K pathway is thought to have predominantly metabolic effects. We supposed that this pathway might play a part in Helicobacter pylori (H. pylori) associated abnormal glucose metabolism and the upregulation of HbA1c. SHC: Spontaneous human combustion.