cPseudomonas aeruginosa produces N-(3-oxo-dodecanoyl)-L-homoserine lactone (3OC12), a crucial signaling molecule that elicits diverse biological responses in host cells thought to subvert immune defenses. The mechanism mediating many of these responses remains unknown. The intracellular lactonase paraoxonase 2 (PON2) hydrolyzes and inactivates 3OC12 and is therefore considered a component of host cells that attenuates 3OC12-mediated responses. Here, we demonstrate in cell lines and in primary human bronchial epithelial cells that 3OC12 is rapidly hydrolyzed intracellularly by PON2 to 3OC12 acid, which becomes trapped and accumulates within the cells. Subcellularly, 3OC12 acid accumulated within the mitochondria, a compartment where PON2 is localized. Treatment with 3OC12 caused a rapid PON2-dependent cytosolic and mitochondrial pH decrease, calcium release, and phosphorylation of stress signaling kinases. The results indicate a novel, PON2-dependent intracellular acidification mechanism by which 3OC12 can mediate its biological effects. Thus, PON2 is a central regulator of host cell responses to 3OC12, acting to decrease the availability of 3OC12 for receptor-mediated effects and acting to promote effects, such as calcium release and stress signaling, via intracellular acidification. P seudomonas aeruginosa is a common pathogen causing serious infections in immunocompromised and ill individuals due to the bacteria's ability to evade host immune responses and acquire antibiotic resistance (1). Many Gram-negative bacteria, including P. aeruginosa, produce acyl-homoserine lactone (AHL) signaling molecules which regulate the cell density-dependent expression of virulence factors in a process termed quorum sensing (QS) (1). The AHL N-(3-oxododecanoyl)-L-homoserine lactone (3OC12) is a key P. aeruginosa QS signal that has been shown to be necessary for biofilm maturation and full expression of virulence in P. aeruginosa animal infection models (2-5). Concentrations up to 600 M 3OC12 have been measured in P. aeruginosa biofilms in vitro (6). Concentrations of over 6 M 3OC12 have been detected in the sputum of individuals with pulmonary P. aeruginosa infections (7), suggesting active 3OC12 signaling in the human disease as well.In addition to modulating bacterial gene expression, 3OC12 elicits a multitude of biological responses in diverse mammalian cell types (8). Depending upon the cell type and dose, 3OC12 (10 to 100 M) can induce apoptosis, endoplasmic reticulum (ER) stress, chemotaxis, and proinflammatory gene expression (8-10). Conversely, 3OC12 inhibited lipopolysaccharide (LPS) induction of proinflammatory mediators in macrophages, fibroblasts, and epithelial cells and in vivo by repressing nuclear factor -light chain enhancer of activated B-cell (NF-B) signaling (11). In antigen-stimulated T-lymphocytes, 3OC12 inhibits cell proliferation and production of gamma interferon and interleukin-4 (IL-4), critical regulators of immunity (8,12). These diverse responses suggest that 3OC12 acts through multiple, and cell-...

BackgroundDelayed cerebral ischemia (DCI) occurs after aneurysmal subarachnoid hemorrhage (aSAH). Continuous intraarterial nimodipine infusion (CIAN) is a promising approach in patients with intracranial large vessel vasospasm (LVV). The objective of this retrospective single-center cohort study was to evaluate the outcome in aSAH-patients treated with CIAN.MethodsCIAN was initiated and ended based on the clinical evaluation and transcranial Doppler (TCD), CT-angiography, CT-perfusion (PCT), and digital subtraction angiography (DSA). Nimodipine (0.5–2.0 mg/h) was administered continuously through microcatheters placed in the extracranial internal carotid and/or vertebral artery. Primary outcome measures were Glasgow Outcome Scale (GOS) at discharge and within 1 year after aSAH, and the occurrence of minor and major (<⅓ and >⅓ of LVV-affected territory) DCI-related infarctions in subsequent CT/MRI-scans. Secondary outcome measures were CIAN-associated complications.ResultsA total of 17 patients underwent CIAN. Median onset of CIAN was 9 (3–13) days after aSAH, median duration was 5 (1–13) days. A favorable outcome (GOS 4–5) was achieved in 9 patients (53%) at discharge and in 13 patients within 1 year (76%). One patient died of posthemorrhagic cerebral edema. Minor cerebral infarctions occurred in five and major infarctions in three patients. One patient developed cerebral edema possibly due to CIAN. Normalization of PCT-parameters within 2 days was observed in 9/17 patients. Six patients showed clinical response and thus did not require PCT imaging.ConclusionThe favorable outcome in 76% of patients after 1 year is in line with previous studies. CIAN thus may be used to treat patients with severe therapy-refractory DCI.

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