Modulation of the production of reactive oxygen species (ROS) by cAMP-elevating agents in granulocytes from diabetic patients: an Akt/PKB-dependent phenomenon.
BACKGROUND
Granulocytes from healthy subjects and from patients suffering from diabetes mellitus present differences in reactivity to stimulation with cyclic nucleotide-elevating agents. The production of reactive oxygen species (ROS) is inhibited in cells from non-diabetic subjects following such stimulation, but activated through a PKA-independent signaling pathway in granulocytes from type 1 and type 2 diabetic patients. The aim of the present study was to understand better the changes in signaling mechanisms induced by the disease.


METHODS
ROS production in granulocytes from healthy subjects and from type 1 and type 2 diabetic patients was measured using a luminol-dependent chemiluminescence assay. Granulocytes were stimulated by the addition of the cAMP-elevating agent dibutyryl cAMP. In some experiments, granulocytes were pre-treated with an inhibitor of PKA or Akt/PKB prior to cAMP stimulation.


RESULTS
Intracellular elevation of cAMP induced a PKA-dependent and Akt/PKB-independent inhibition of ROS production in granulocytes from healthy subjects, but a significant activation in cells from both type 1 and type 2 diabetic patients. Most significantly, activation of ROS generation in cells from diabetic patients was shown to be Akt/PKB-dependent and PKA-independent.


CONCLUSIONS
These results suggest that chronic hyperglycaemia could induce metabolic adaptation in cAMP-related signaling mechanisms. Epac (exchange protein directly activated by cAMP) is a novel cAMP receptor besides PKA involved in different signaling pathways. The cAMP-stimulated inverse ROS response in granulocytes from type 1 and type 2 diabetic patients may be due to a change in signaling pathways from cAMP/PKA to cAMP/Epac/Akt/PKB. These preliminary results require further studies in order to evaluate their consequences on innate immunity and pathogenesis of diabetes mellitus.
Nogueira-Machado
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JA
Hospital Santa Casa de Belo Horizonte, Núcleo de Pesquisa e Pós, Graduação (NPPG), Brasil. nogueira.machado@pesquisador.cnpq.br
Lima e Silva
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Horta
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D000328:Adult; D003994:Bucladesine / Q000494:pharmacology*; D000242:Cyclic AMP / Q000097:blood*; D003922:Diabetes Mellitus, Type 1 / Q000097:blood*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood*; D005260:Female; D006098:Granulocytes / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D008297:Male; D051057:Proto-Oncogene Proteins c-akt / Q000097:blood* / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000097:blood*; D012016:Reference Values
D017382:Reactive Oxygen Species; D003994:Bucladesine; D000242:Cyclic AMP; D051057:Proto-Oncogene Proteins c-akt