Antagonism of α2A-adrenoceptor: a novel approach to inhibit inflammatory responses in sepsis

Abstract

Sepsis is a systemic inflammatory response syndrome (SIRS) when an infection is the etiology of SIRS. Our previous studies have indicated that the release of the sympathetic neurotransmitter, norepinephrine (NE), from the gut is increased in sepsis, and that NE potentiates endotoxin-induced tumor necrosis factor (TNF)-alpha upregulation via the A subtype of alpha(2)-adrenoceptors (i.e., alpha(2A)-AR) expressed on the surface of Kupffer cells. A specific antagonist for alpha(2A)-AR, 2-[(4,5-dihydro-1H-imidazol-2-yl) methyl]-2,3-dihydro-1-methyl-1H-isoindole maleate (BRL-44408 maleate), reduces TNF-alpha secretion in cultured Kupffer cells. We, therefore, hypothesize that administration of BRL-44408 maleate inhibits inflammatory responses and reduces organ injury in sepsis. To study this, sepsis was induced in male rats by cecal ligation and puncture (CLP). At 5 h after CLP, BRL-44408 maleate (0.3125, 0.625, 1.25, 2.5, or 5.0 mg/kg BW) or vehicle (1-ml normal saline) were administered intravenously over a period of 30 min. Blood and intestinal samples were collected at 20 h after CLP. Serum levels of TNF-alpha, interleukin (IL)-6, IL-10, keratinocyte-derived chemokine (KC), macrophage inflammatory protein-2 (MIP-2), liver enzymes (i.e., aspartate aminotransferase (AST) and alanine aminotransferase (ALT)), and lactate were measured. The intestinal levels of TNF-alpha, IL-6, and myeloperoxidase (MPO) activities were also analyzed. In additional groups of animals, the necrotic cecum was excised at 20 h post-CLP, and the 10-day survival was recorded. Our results showed that serum levels of proinflammatory cytokines (TNF-alpha and IL-6), anti-inflammatory cytokine (IL-10), chemokines (KC, MIP-2), liver enzymes (AST and ALT), lactate, and intestinal levels of TNF-alpha, IL-6, and MPO were significantly elevated at 20 h after CLP. Administration of BRL-44408 maleate significantly reduced serum levels of proinflammatory cytokines, chemokines, liver enzymes, and lactate, and dramatically decreased TNF-alpha, IL-6, and MPO levels in the gut. However, it has no statistical effects on the elevated serum levels of IL-10. Moreover, BRL-44408 maleate at the doses of 2.5 or 5.0 mg/kg BW significantly increased the survival rate after CLP and cecal excision. In conclusion, modulation of the sympathetic nervous system by blocking alpha(2A)-AR appears to be a novel treatment for inflammatory conditions such as sepsis.