Early phase of allergic airway inflammation in diabetic rats: role of insulin on the signaling pathways and mediators.
BACKGROUND
Allergic lung inflammation is impaired in diabetic rats and is restored by insulin treatment. In the present study we investigated the effect of insulin on the signaling pathways triggered by allergic inflammation in the lung and the release of selected mediators.


METHODS
Diabetic male Wistar rats (alloxan, 42 mg/kg, i.v., 10 days) and matching controls were sensitized by s.c. injections of ovalbumin (OA) in aluminium hydroxide, 14 days before OA (1 mg/0.4 ml) or saline intratracheal challenge. A group of diabetic rats were treated with neutral protamine Hagedorn insulin (NPH, 4 IU, s.c.), 2 h before the OA challenge. Six hours after the challenge, bronchoalveolar lavage (BAL) was performed for mediator release and lung tissue was homogenized for Western blotting analysis of signaling pathways.


RESULTS
Relative to non-diabetic rats, the diabetic rats exhibited a significant reduction in OA-induced phosphorylation of the extracellular signal-regulated kinase (ERK, 59%), p38 (53%), protein kinase B (Akt, 46%), protein kinase C (PKC)-α (63%) and PKC-δ (38%) in lung homogenates following the antigen challenge. Activation of the NF-κB p65 subunit and phosphorylation of IκBα were almost suppressed in diabetic rats. Reduced expression of inducible nitric oxide synthase (iNOS, 32%) and cyclooxygenase-2 (COX-2, 46%) in the lung homogenates was also observed. The BAL concentration of prostaglandin (PG)-E(2), nitric oxide (NO) and interleukin (IL)-6 was reduced in diabetic rats (74%, 44% and 65%, respectively), whereas the cytokine-induced neutrophil chemoattractant (CINC)-2 concentration was not different from the control animals. Treatment of diabetic rats with insulin completely or partially restored all of these parameters. This protocol of insulin treatment only partially reduced the blood glucose levels.


CONCLUSIONS
The data presented show that insulin regulates MAPK, PI3K, PKC and NF-κB pathways, the expression of the inducible enzymes iNOS and COX-2, and the levels of NO, PGE(2) and IL-6 in the early phase of allergic lung inflammation in diabetic rats. It is suggested that insulin is required for optimal transduction of the intracellular signals that follow allergic stimulation.
Department of Immunology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, SP, Brazil. martinsj@usp.br
Joilson O
JO
Martins
Beatriz M
BM
Wittlin
Denise B C
DB
Anger
Daniel O
DO
Martins
Paulina
P
Sannomiya
Sonia
S
Jancar
D000537:Aluminum Oxide / Q000737:chemistry; D000818:Animals; D001992:Bronchoalveolar Lavage Fluid; D019743:Chemokines, CXC / Q000378:metabolism; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D015232:Dinoprostone / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology / Q000502:physiology*; D015850:Interleukin-6 / Q000378:metabolism; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D010047:Ovalbumin / Q000276:immunology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D011014:Pneumonia / Q000378:metabolism*; D051571:Protein Kinase C-alpha / Q000378:metabolism; D051745:Protein Kinase C-delta / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction
D000537:Aluminum Oxide; D019743:Chemokines, CXC; D015232:Dinoprostone; D048049:Extracellular Signal-Regulated MAP Kinases; D007328:Insulin; D015850:Interleukin-6; D020928:Mitogen-Activated Protein Kinases; D016328:NF-kappa B; D009569:Nitric Oxide; D052247:Nitric Oxide Synthase Type II; D010047:Ovalbumin; D019869:Phosphatidylinositol 3-Kinases; D051571:Protein Kinase C-alpha; D051745:Protein Kinase C-delta; D051057:Proto-Oncogene Proteins c-akt; C513294:Cxcl3 protein, rat