Pivotal role of the alpha(2A)-adrenoceptor in producing inflammation and organ injury in a rat model of sepsis.
BACKGROUND
Norepinephrine (NE) modulates the responsiveness of macrophages to proinflammatory stimuli through the activation of adrenergic receptors (ARs). Being part of the stress response, early increases of NE in sepsis sustain adverse systemic inflammatory responses. The intestine is an important source of NE release in the early stage of cecal ligation and puncture (CLP)-induced sepsis in rats, which then stimulates TNF-alpha production in Kupffer cells (KCs) through the activation of the alpha(2)-AR. It is important to know which of the three alpha(2)-AR subtypes (i.e., alpha(2A), alpha(2B) or alpha(2C)) is responsible for the upregulation of TNF-alpha production. The aim of this study was to determine the contribution of alpha(2A)-AR in this process.


RESULTS
Adult male rats underwent CLP and KCs were isolated 2 h later. Gene expression of alpha(2A)-AR was determined. In additional experiments, cultured KCs were incubated with NE with or without BRL-44408 maleate, a specific alpha(2A)-AR antagonist, and intraportal infusion of NE for 2 h with or without BRL-44408 maleate was carried out in normal animals. Finally, the impact of alpha(2A)-AR activation by NE was investigated under inflammatory conditions (i.e., endotoxemia and CLP). Gene expression of the alpha(2A)-AR subtype was significantly upregulated after CLP. NE increased the release of TNF-alpha in cultured KCs, which was specifically inhibited by the alpha(2A)-AR antagonist BRL-44408. Equally, intraportal NE infusion increased TNF-alpha gene expression in KCs and plasma TNF-alpha which was also abrogated by co-administration of BRL-44408. NE also potentiated LPS-induced TNF-alpha release via the alpha(2A)-AR in vitro and in vivo. This potentiation of TNF-alpha release by NE was mediated through the alpha(2A)-AR coupled Galphai protein and the activation of the p38 MAP kinase. Treatment of septic animals with BRL-44408 suppressed TNF-alpha, prevented multiple organ injury and significantly improved survival from 45% to 75%.


CONCLUSIONS
Our novel finding is that hyperresponsiveness to alpha(2)-AR stimulation observed in sepsis is primarily due to an increase in alpha(2A)-AR expression in KCs. This appears to be in part responsible for the increased proinflammatory response and ensuing organ injury in sepsis. These findings provide important feasibility information for further developing the alpha(2A)-AR antagonist as a new therapy for sepsis.
Center for Immunology and Inflammation, The Feinstein Institute for Medical Research, Department of Surgery, North Shore University Hospital and Long Island Jewish Medical Center, Manhasset, NY, USA.
Michael
M
Miksa
Padmalaya
P
Das
Mian
M
Zhou
Rongqian
R
Wu
Weifeng
W
Dong
Youxin
Y
Ji
Sanna M
SM
Goyert
Thanjavur S
TS
Ravikumar
Ping
P
Wang
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive; D002432:Cecum / Q000601:surgery; D002478:Cells, Cultured; D004195:Disease Models, Animal; D004789:Enzyme Activation / Q000187:drug effects; D015870:Gene Expression / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D007093:Imidazoles / Q000008:administration & dosage / Q000494:pharmacology; D007249:Inflammation / Q000503:physiopathology*; D054833:Isoindoles / Q000008:administration & dosage / Q000494:pharmacology; D007728:Kupffer Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D008026:Ligation / Q000009:adverse effects; D008099:Liver / Q000293:injuries / Q000503:physiopathology*; D008297:Male; D009638:Norepinephrine / Q000008:administration & dosage / Q000494:pharmacology; D011677:Punctures; D011869:Radioligand Assay; D051381:Rats; D018341:Receptors, Adrenergic, alpha-2 / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D018805:Sepsis / Q000209:etiology / Q000503:physiopathology* / Q000517:prevention & control; D016019:Survival Analysis; D014409:Tumor Necrosis Factor-alpha / Q000097:blood / Q000235:genetics / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
C547770:Adra2a protein, rat; D000317:Adrenergic alpha-Antagonists; D007093:Imidazoles; D054833:Isoindoles; D018341:Receptors, Adrenergic, alpha-2; D014409:Tumor Necrosis Factor-alpha; D048051:p38 Mitogen-Activated Protein Kinases; D009638:Norepinephrine; C072125:BRL 44408