Glutamine Inhibits Lipopolysaccharide-Induced Cytoplasmic Phospholipase A2 Activation and Protects Against Endotoxin Shock in Mouse

Abstract

Glutamine (Gln) supplementation is known to play a beneficial role in a number of settings of critical illness as well as laboratory models of endotoxin shock. We have investigated a molecular mechanism of the protective role of Gln in lipopolysaccharide (LPS)-induced shock using a mouse model. To examine the effectiveness of Gln, Gln was administered before or after LPS injection. Treatment of Gln before, but not after, LPS injection resulted in inhibition of nuclear factor kappaB activation and tumor necrosis factor alpha synthesis. In contrast, protection of animal from LPS-mediated death by Gln was observed when the Gln treatment was performed after LPS injection, suggesting that nuclear factor kappaB/tumor necrosis factor alpha signaling does not play an important role in this process. LPS injection induced phosphorylation of cytoplasmic phospholipase A2 (cPLA2), which was blocked by Gln treatment after LPS injection. Similarly, the LPS-stimulated cPLA2 activity was also inhibited by Gln treatment after LPS injection. Moreover, a cPLA2 inhibitor not only inhibited LPS-induced activation of cPLA2, but also significantly prevented LPS-mediated death. These observations indicate that Gln has a capability to inhibit cPLA2 phosphorylation and activation and suggest that Gln might be of a great therapeutic value for controlling inflammatory diseases in which cPLA2 plays an important role in the pathogenesis of the diseases.

Glutamine Protects Mice from Lethal Endotoxic Shock via a Rapid Induction of MAPK Phosphatase-1

“…Gln was dissolved in Hartmann's solution (30 mg/ml), and 750 mg/kg of Gln was i.p. administered as described previously (14). Quercetin from Sigma-Aldrich (400 mg/kg) was administered i.p.…”

“…The protective effects of PLA 2 inhibitors in endotoxic shock (10,11), or reduced septic symptoms in PLA 2 -deficient mice (12,13), indicate that PLA 2 is an essential component in the pathogenesis of endotoxic shock. We have previously shown that Gln protects animals from endotoxic shock through its inhibition of cPLA 2 activity (14), and this activity of Gln was also associated with suppression of asthma in mice (15).…”

Mechanism of glutamine inhibition of cytosolic phospholipase a2 (cPLA2): Evidence of physical interaction between glutamine-Induced mitogen-activated protein kinase phosphatase-1 and cPLA2

“…Both MKP-1 induction and MKP-1 mediated p38 dephosphorylation within 5 min following Gln administration, suggesting that Gln dephosphorylated cPLA 2 indirectly through MKP-1-mediated p38 dephosphorylation. However, Gln dephosphorylated p-cPLA 2 rapidly within 5 min, as in the case of p38 in LPS-injected mice [13,14,20], suggesting that phosphatase is involved. Gln injection resulted in a rapid induction of MKP-1 within 5 min, which coincided with Gln-induced dephosphorylation of cPLA 2 (Fig.…”

“…Gln was dissolved in sterilized distilled water to 3%. A volume of 0Á5 ml (750 mg/ kg) [12][13][14][15] was administered intraperitoneally (i.p.) 10 min before or 10 min after LPS injection.…”

“…To understand the molecular mechanism of Gln antiinflammatory activity, we have shown that Gln can protect animals effectively from endotoxin shock as well as inhibit bronchial allergic asthma by inhibiting cPLA 2 phosphorylation [13,14]. To decipher the mechanism of Gln inhibition of cPLA 2 , we demonstrated recently that Gln deactivated p38 and Janus kinase (JNK) mitogenactivated protein kinases (MAPKs) by rapidly inducing MAPK phosphatase (MKP)-1 protein [15], which preferentially dephosphorylated p38 and JNK [16,17], suggesting that Gln inhibited cPLA 2 phosphorylation indirectly by blocking the kinase activity of p38, a major upstream pathway for cPLA 2 phosphorylation [18].…”