J Vet Sci.  2012 Sep;13(3):245-252. 10.4142/jvs.2012.13.3.245.

Exendin-4 improves resistance to Listeria monocytogenes infection in diabetic db/db mice

• Liu HY
• Chung CY
• Yang WC
• Liang CL
• Wang CY
• Chang CY
• Chang CL

• KMID: 1389763
• DOI: http://doi.org/10.4142/jvs.2012.13.3.245

Abstract

The incidence of diabetes mellitus is increasing among companion animals. This disease has similar characteristics in both humans and animals. Diabetes is frequently identified as an independent risk factor for infections associated with increased mortality. In the present study, homozygous diabetic (db/db) mice were infected with Listeria (L.) monocytogenes and then treated with the anti-diabetic drug exendin-4, a glucagon-like peptide 1 analogue. In aged db/db mice, decreased CD11b+ macrophage populations with higher lipid content and lower phagocytic activity were observed. Exendin-4 lowered high lipid levels and enhanced phagocytosis in macrophages from db/db mice infected with L. monocytogenes. Exendin-4 also ameliorated obesity and hyperglycemia, and improved ex vivo bacteria clearance by macrophages in the animals. Liver histology examined during L. monocytogenes infection indicated that abscess formation was much milder in exendin-4-treated db/db mice than in the control animals. Moreover, mechanistic studies demonstrated that expression of ATP binding cassette transporter 1, a sterol transporter, was higher in macrophages isolated from the exendin-4-treated db/db mice. Overall, our results suggest that exendin-4 decreases the risk of infection in diabetic animals by modifying the interaction between intracellular lipids and phagocytic macrophages.

Keyword

diabetes mellitus; exendin-4; Listeria monocytogenes; macrophage; mice

MeSH Terms

ATP-Binding Cassette Transporters/metabolism
Age Factors
Animals
Blood Chemical Analysis
Cholesterol/metabolism
Diabetes Mellitus, Type 2/*drug therapy/genetics
Dyslipidemias/drug therapy/genetics
Female
Hyperglycemia/drug therapy/genetics
Hypoglycemic Agents/*therapeutic use
Injections, Intraperitoneal
*Lipid Metabolism/drug effects
Listeria monocytogenes/*drug effects/immunology
Listeriosis/*drug therapy/immunology/microbiology
Macrophages/drug effects/*metabolism
Mice
Obesity/drug therapy/genetics
Peptides/*therapeutic use
Phagocytosis/drug effects
Venoms/*therapeutic use

Figure

• 

  Fig. 1 Levels of CD11b+ expression, lipid, and phagocytic activity in peritoneal exudate cells (PECs) isolated from db/m mice and db/db mice at the indicated ages. (A) These cells were stained with specific anti-mouse CD11b-PE and analyzed with fluorescence-activated cell sorter (FACS). The fraction in each plot represents the total number of PECs /number of CD11b cells. (B) PECs were stained with Nile red and analyzed with FACS. Inserted panels show PECs stained with Oil Red O to identify lipid-laden macrophages. (C) Phagocytic efficacy of PECs isolated from db/m mice and db/db mice were incubated with dextran 40-fluorescein isothiocyanate (DX40-FITC) and analyzed with FACS. db/db: homozygous diabetic mice, db/m: non-diabetic control littermates, wk: week-old.

• 

  Fig. 2 Effects of exendin-4 on lipid contents, phagocytic activity, and ABCA1 expression in macrophages. (A) Adherent PECs were stained with Nile red to detect intercellular lipid and analyzed with FACS. (B) DX40-FITC was phagocytized by adherent PECs and the cells were analyzed with FACS. (C) The PECs shown in panel (A) were also stained with specific anti-mouse ABCA1-FITC and analyzed with FACS.

• 

  Fig. 3 Analysis of blood from control and exendin-4 treated db/db mice. The blood glucose (A), triglyceride (B), total cholesterol (C), HDL (D) and LDL (E) levels of db/db mice treated with or without exendin-4 were measured when the mice were various ages (n = 3 for both groups). Results are expressed as the mean ± SD. Statistically significant differences between the control (mock) and exendin-4-treated db/db mice are indicated by an asterisk (*p < 0.05). HDL: high-density lipoprotein, LDL: low-density lipoprotein.

• 

  Fig. 4 Ex vivo Listeria (L.) monocytogenes clearance by macrophages and examination of livers from exendin-4 treated db/db mice. (A) CFU values of supernatants of DMEM contained Listeria-infected macrophages were determined using the plate method with trypticase soy agar (TSA) plate. (B) The number of L. monocytogene CFUs among centrifuged pellets of macrophages were lysed in sterile cold water and determined using the plate method with TSA plate. Results are expressed as the mean ± SD. Statistically significant differences between control (mock) and exendin-4 treated db/db mice are indicated by an asterisk (*p < 0.05). Liver sections from the control (C and E) and exendin-4-treated (D and F) db/db mice were obtained 48 h after L. monocytogenes infection. Mononuclear cell infiltrates (arrowheads) were more prominent in the exendin-4-treated db/db mice than the control animals. Abscess formation (arrowheads) was much milder in the exendin-4-treated animals than in the control. Listeria was more widely distributed in the hepatic abscesses of the control db/db mice (G) than ones treated with exendin-4 (H). (I and J) The magnified areas of panels G and H. H&E (A~E) and Gram (G~J) stain. Scale bars = 100 µm.

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