Role of G protein-coupled receptor kinase 2 in oxidative and nitrosative stress-related neurohistopathological changes in a mouse model of sepsis-associated encephalopathy.

Sepsis-associated encephalopathy (SAE), characterized as diffuse brain dysfunction and neurological manifestations secondary to sepsis, is a common complication in critically ill patients and can give rise to poor outcome, but understanding the molecular basis of this disorder remains a major challenge. Given the emerging role of G protein-coupled receptor 2 (GRK2), first identified as a G protein-coupled receptor (GPCR) regulator, in the regulation of non-G protein-coupled receptor-related molecules contributing to diverse cellular functions and pathology, including inflammation, we tested the hypothesis that GRK2 may be linked to the neuropathogenesis of SAE. When mouse MG6 microglial cells were challenged with lipopolysaccharide (LPS), GRK2 cytosolic expression was highly up-regulated. The ablation of GRK2 by small interfering RNAs (siRNAs) prevented an increase in intracellular reactive oxygen species generation in LPS-stimulated MG6 cells. Furthermore, the LPS-induced up-regulation of inducible nitric-oxide synthase expression and increase in nitric oxide production were negated by GRK2 inhibitor or siRNAs. However, GRK2 inhibition was without effect on overproduction of tumor necrosis factor-α, interleukin (IL)-6, and IL-1ß in LPS-stimulated MG cells. In mice with cecal ligation and puncture-induced sepsis, treatment with GRK2 inhibitor reduced high levels of oxidative and nitrosative stress in the mice brains, where GRK2 expression was up-regulated, alleviated neurohistological damage observed in cerebral cortex sections, and conferred a significant survival advantage to CLP mice. Altogether, these results uncover the novel role for GRK2 in regulating cellular oxidative and nitrosative stress during inflammation and suggest that GRK2 may have a potential as an intriguing therapeutic target to prevent or treat SAE.

Critical role of endogenous histamine in promoting end-organ tissue injury in sepsis.

BACKGROUND: Histamine assumes an important role as a major mediator in various pathologic disorders associated with inflammation and immune reactions. However, the involvement of histamine in the pathological conditions and symptoms of sepsis remains entirely unknown. In this study, we establish that histamine is identified as a contributory mediator to promoting the development of organ injury in sepsis. METHODS: Histidine decarboxylase (HDC) gene knockout (HDC-/-) mice, histamine H1-/H2-receptor gene-double knockout (H1R-/-/H2R-/-) mice, and their littermate wild-type (WT) C57BL/6J mice underwent cecal ligation and puncture (CLP) or sham operation. Some WT mice were injected intraperitoneally with d-chlorpheniramine and famotidine 60 min before CLP to block H1- and H2-receptors, respectively. RESULTS: In mice rendered septic by CLP, tissue histamine levels were elevated in association with increased HDC expression. Sepsis-induced abnormal cytokine production and multiple organ injury (lung, liver, and kidney) were significantly less pronounced in HDC-/- mice as compared with WT controls, and HDC deficiency had improved survival in sepsis. This benefit corresponded with a significant reduction in activation levels of the nuclear factor (NF)-κB signaling pathway. H1R-/-/H2R-/- mice apparently behaved similar to HDC knockout mice in reducing sepsis-related pathological changes. Pharmacological interventions with H1- and H2-receptor antagonists indicated that both H1- and H2-receptors were involved in septic lung and liver injury, whereas only H2-receptors contributed to septic kidney injury. CONCLUSIONS: In the setting of sepsis, histamine, through activation of H1- and H2-receptors, serves as an aggravating mediator to contribute to the development of sepsis-driven major end-organ failure.