Diabetes Downregulates Allergen-Induced Airway Inflammation in Mice

Abstract

Previous studies described that allergic diseases, including asthma, occur less often than expected in patients with type 1 diabetes. Here, we investigated the influence of diabetes on allergic airway inflammation in a model of experimental asthma in mice. Diabetes was induced by intravenous injection of alloxan into 12 h-fasted A/J mice, followed by subcutaneous sensitization with ovalbumin (OVA) and aluminum hydroxide (Al(OH)₃), on days 5 and 19 after diabetes induction. Animals were intranasally challenged with OVA (25 μg), from day 24 to day 26. Alloxan-induced diabetes significantly attenuated airway inflammation as attested by the lower number of total leukocytes in the bronchoalveolar lavage fluid, mainly neutrophils and eosinophils. Suppression of eosinophil infiltration in the peribronchiolar space and generation of eosinophilotactic mediators, such as CCL-11/eotaxin, CCL-3/MIP-1α, and IL-5, were noted in the lungs of diabetic sensitized mice. In parallel, reduction of airway hyperreactivity (AHR) to methacholine, mucus production, and serum IgE levels was also noted under diabetic conditions. Our findings show that alloxan diabetes caused attenuation of lung allergic inflammatory response in A/J mice, by a mechanism possibly associated with downregulation of IgE antibody production.

Figure 1

Brief scheme of animal sensitization and challenge with ovalbumin (OVA). i.v.: intravenous; s.c.: subcutaneous; i.n.: intranasal.

Figure 2

Alloxan diabetes attenuates OVA-induced airway inflammation in lung tissue of sensitized mice. Profile of cells in BAL and lung tissue in diabetic allergen-challenged mice. (a) Total cell counts were determined on 1.5 mL BAL, and differential cell counts were assessed by May-Grünwald Giemsa staining. (b–e) Lung sections were stained with hematoxylin and eosin (H&E) for measurement of inflammatory cells around the airways. Data revealed a different extent of cellular infiltration of the peribronchiolar area. Sections were obtained from lungs of nondiabetic saline-challenged mice (b), diabetic saline-challenged mice (c), nondiabetic OVA-challenged mice (d), and diabetic OVA-challenged mice (e). Lungs were removed 24 h after the last challenge. Six animals were assigned to each group. Scale bar 100 μm. (f) Eosinophil count in lung tissue from nondiabetic or diabetic mice challenged with saline or ovalbumin (OVA). The analysis proceeded 24 h after the last OVA challenge. Data were expressed as mean ± SEM (n = 6). ⁺P < 0.05 and ⁺⁺⁺P < 0.001 versus nondiabetic saline-challenged mice; ^∗P < 0.05, ^∗∗P < 0.01 and ^∗∗∗P < 0.001 versus nondiabetic OVA-challenged mice.

Figure 3

Alloxan diabetes attenuates lung PAS staining of goblet cells in the airways of OVA-induced lung inflammation in mice. Panels (a–d) show photomicrographs of PAS staining (arrows) of lung sections from nondiabetic saline-challenged, diabetic saline-challenged, nondiabetic OVA-challenged, and diabetic OVA-challenged mice, respectively. In (e), quantification of PAS staining in lungs from nondiabetic and diabetic mice. Each value indicates the mean ± SEM from six animals per group. ⁺⁺P < 0.01 versus nondiabetic saline-challenged mice; ^∗∗P < 0.01 versus nondiabetic OVA-challenged mice. Scale bar 100 μm.

Figure 4

Alloxan diabetes suppressed cytokine production in the lung tissue of sensitized OVA-challenged mice. IL-5 (a), CCL-11/eotaxin (b), and CCL-3/MIP-1α (c) production in lung tissue from nondiabetic or diabetic mice challenged with saline or ovalbumin (OVA) was analyzed by ELISA. The analysis proceeded 24 h after the last OVA challenge. Each value indicates the mean ± SEM from six animals per group. ⁺⁺⁺P < 0.001 versus nondiabetic saline-challenged mice; ^∗P < 0.05 and ^∗∗∗P < 0.001 versus nondiabetic OVA-challenged mice.

Figure 5

Alloxan diabetes reduces serum OVA-specific IgE antibody levels in mice sensitized with ovalbumin. The levels of OVA-specific IgE were measured at 24 h after the last allergen challenge. Blood was collected by cardiac puncture for measurement of OVA-specific IgE by ELISA. Each value indicates the mean ± SEM from six animals per group. ⁺⁺⁺P < 0.001 versus nondiabetic nonsensitized group. ^∗∗∗P < 0.001 versus nondiabetic sensitized group.

Figure 6

Alloxan diabetes attenuates AHR caused by OVA challenge in sensitized mice. The AHR to aerosolized methacholine was measured 24 h after the last allergen challenge in unrestrained conscious mice. Mice were placed in the main chamber and aerosolized first with PBS followed by increasing doses of methacholine (3 and 6 mg/mL), 2 min for each aerosolization. Readings of breathing parameters were taken for 5 min after each nebulization during which Penh values were determined. Each value indicates the mean ± SEM from five animals per group. ⁺⁺P < 0.01 and ⁺⁺⁺P < 0.001 versus nondiabetic saline-challenged mice; ^∗∗P < 0.01 and ^∗∗∗P < 0.001 versus nondiabetic OVA-challenged mice.