Acid Sphingomyelinase Inhibition Stabilizes Hepatic Ceramide Content and Improves Hepatic Biotransformation Capacity in a Murine Model of Polymicrobial Sepsis.

Liver dysfunction during sepsis is an independent risk factor leading to increased mortality rates. Specifically, dysregulation of hepatic biotransformation capacity, especially of the cytochrome P450 (CYP) system, represents an important distress factor during host response. The activity of the conserved stress enzyme sphingomyelin phosphodiesterase 1 (SMPD1) has been shown to be elevated in sepsis patients, allowing for risk stratification. Therefore, the aim of the present study was to investigate whether SMPD1 activity has an impact on expression and activity of different hepatic CYP enzymes using an animal model of polymicrobial sepsis. Polymicrobial sepsis was induced in SMPD1 wild-type and heterozygous mice and hepatic ceramide content as well as CYP mRNA, protein expression and enzyme activities were assessed at two different time points, at 24 h, representing the acute phase, and at 28 days, representing the post-acute phase of host response. In the acute phase of sepsis, SMPD1+/+ mice showed an increased hepatic C16- as well as C18-ceramide content. In addition, a downregulation of CYP expression and activities was detected. In SMPD1+/- mice, however, no noticeable changes of ceramide content and CYP expression and activities during sepsis could be observed. After 28 days, CYP expression and activities were normalized again in all study groups, whereas mRNA expression remained downregulated in SMPD+/+ animals. In conclusion, partial genetic inhibition of SMPD1 stabilizes hepatic ceramide content and improves hepatic monooxygenase function in the acute phase of polymicrobial sepsis. Since we were also able to show that the functional inhibitor of SMPD1, desipramine, ameliorates downregulation of CYP mRNA expression and activities in the acute phase of sepsis in wild-type mice, SMPD1 might be an interesting pharmacological target, which should be further investigated.

Acid Sphingomyelinase Inhibition Prevents Development of Sepsis Sequelae in the Murine Liver.

The molecular mechanisms of maladaptive response in liver tissue with respect to the acute and post-acute phase of sepsis are not yet fully understood. Long-term sepsis survivors might develop hepatocellular/hepatobiliary injury and fibrosis. Here, we demonstrate that acid sphingomyelinase, an important regulator of hepatocyte apoptosis and hepatic stellate cell (HSC) activation, is linked to the promotion of liver dysfunction in the acute phase of sepsis as well as to fibrogenesis in the long-term. In both phases, we observed a beneficial effect of partial genetic sphingomyelinase deficiency in heterozygous animals (smpd1+/-) on oxidative stress levels, hepatobiliary function, macrophage infiltration and on HSC activation. Strikingly, similar to heterozygote expression of SMPD1, either preventative (p-smpd1+/+) or therapeutic (t-smpd1+/+) pharmacological treatment strategies with desipramine - a functional inhibitor of acid sphingomyelinase (FIASMA) - significantly improved liver function and survival. The inhibition of sphingomyelinase exhibited a protective effect on liver function in the acute-phase, and the reduction of HSC activation diminished development of sepsis-associated liver fibrosis in the post-acute phase of sepsis. In summary, targeting sphingomyelinase with FDA-approved drugs is a novel promising strategy to overcome sepsis-induced liver dysfunction.

Stimulation of vasculogenesis and leukopoiesis of embryonic stem cells by extracellular transfer RNA and ribosomal RNA.

OBJECTIVE: Cell injury releases nucleic acids supporting inflammation and stem cell activation. Here, the impact of extracellular ribonucleic acid, especially transfer RNA (ex-tRNA), on vasculogenesis and leukopoiesis of mouse embryonic stem (ES) cells was investigated. APPROACH AND RESULTS: ex-tRNA, whole cell RNA and ribosomal RNA (ex-rRNA) but not DNA increased CD31-positive vascular structures in embryoid bodies. Ex-tRNA and ex-rRNA increased numbers of VEGFR2(+), CD31(+) and VE-cadherin(+) vascular cells as well as CD18(+), CD45(+) and CD68(+) cells, indicating leukocyte/macrophage differentiation. This was paralleled by mRNA and protein expression of hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor-165 (VEGF165) and neuropilin 1 (NRP1), phosphorylation of phosphatidyl inositol 3-kinase (PI3K) and VEGF receptor 2 (VEGFR2) as well as mRNA expression of α-smooth muscle actin (α-SMA). ex-tRNA was taken up by endosomes, increased expression of the pro-angiogenic semaphorin B4 receptor plexin B1 as well as the ephrin-type B receptor 4 (EphB4) and ephrinB2 ligand and enhanced cell migration, which was inhibited by the VEGFR2 antagonist SU5614 and the PI3K inhibitor LY294002. This likewise abolished the effects of ex-tRNA on vasculogenesis and leukopoiesis of ES cells. Ex-tRNA increased NOX1, NOX2, NOX4 and DUOX2 mRNA and boosted the generation of superoxide and hydrogen peroxide which was inhibited by radical scavengers, the NADPH oxidase inhibitors apocynin, VAS2870, ML171, and plumbagin as well as shRNA silencing of NOX1 and NOX4. CONCLUSIONS: Our findings indicate that ex-tRNA treatment induces vasculogenesis and leukopoiesis of ES cells via superoxide/hydrogen peroxide generated by NADPH oxidase and activation of VEGFR2 and PI3K.

Plasma Neutrophil Gelatinase-Associated Lipocalin Is Primarily Related to Inflammation during Sepsis: A Translational Approach.

Acute kidney injury (AKI) during sepsis is common and underestimated. Plasma neutrophil gelatinase-associated lipocalin (plasma-NGAL) is discussed as new biomarker for AKI diagnosis, but during inflammation its function and diagnostic impact remain unclear. The association between plasma-NGAL and inflammatory markers in septic patients, but also in healthy controls and patients with chronic inflammation before and after either maximum exercise test or treatment with an anti-TNF therapy were investigated. In-vitro blood stimulations with IL-6, lipopolysaccharide, NGAL or its combinations were performed to investigate cause-effect-relationship. Plasma-NGAL levels were stronger associated with inflammation markers including IL-6 (Sepsis: r = 0.785 P < 0.001; chronic inflammation after anti-TNF: r = 0.558 P < 0.001), IL-8 (Sepsis: r = 0.714 P<0.004; healthy controls after exercise r = 0.786 P < 0.028; chronic inflammation before anti-TNF: r = 0.429 P < 0.041) and IL-10 (healthy controls before exercise: r = 0.791 P < 0.028) than with kidney injury or function. Correlation to kidney injury or function was found only in septic patients (for creatinine: r = 0.906 P < 0.001; for eGFR: r = -0.686 P = 0.005) and in patients with rheumatic disease after anti-TNF therapy (for creatinine: r = 0.466 P < 0.025). In stimulation assays with IL-6 and lipopolysaccharide plasma-NGAL was increased. Co-stimulation of lipopolysaccharide with plasma-NGAL decreased cellular injury (P < 0.05) and in trend IL-10 levels (P = 0.057). Septic mice demonstrated a significantly improved survival rate after NGAL treatment (P < 0.01). Plasma-NGAL seams to be strongly involved in inflammation. For clinical relevance, it might not only be useful for AKI detection during severe inflammation - indeed it has to be interpreted carefully within this setting - but additionally might offer therapeutic potential.

Impact of antibiotic treatment intensity on long-term sepsis-associated kidney injury in a polymicrobial peritoneal contamination and infection model.

BACKGROUND/AIMS: Long-term kidney affections after sepsis are poorly understood. Animal models for investigating kidney damage in the late phase of disease progression are limited. The aim of this study was to investigate the impact of two antibiotic regimes on persistence of kidney injury after peritonitis. METHODS: Kidney damage was investigated 65 days after polymicrobial peritoneal contamination and infection (PCI) sepsis induction in C57BL/6 mice. Short-term antibiotic therapy (STA, 4 days) was compared to long-term (LTA, 10 days) treatment using plasma creatinine, plasma and urine neutrophil gelatinase-associated lipocalin (NGAL), urine albumin/creatinine ratio and renal histology. RESULTS: Sepsis resulted in mortality rates of 68.2% (STA) and 61.0% (LTA). Surviving STA animals showed the most pronounced kidney damage indicated by significantly elevated levels of creatinine and acute tubular damage (ATD), whereas NGAL was significantly increased in LTA survivors only. A creatinine level above 0.3 mg/dl was used to define kidney injury, found in 21.4% of STA animals and 7.8% of LTA animals. While animals with kidney injury demonstrated significantly higher ATD scores and persistent tubular damage, no significant differences were found for plasma or urine NGAL levels or urine albumin/creatinine ratios. CONCLUSION: Prolonged antibiotic treatment reduced the rate of ongoing peritonitis-induced kidney injury in a C57BL/6 mouse model. Plasma or urine NGAL levels were not able to identify animals with or without persistent kidney injury. The kidney injury after the PCI mouse model represents prototypic clinical findings and should be used for further studies investigating disease mechanisms.