Ischemic preconditioning protects from hepatic ischemia/reperfusion-injury by preservation of microcirculation and mitochondrial redox-state.

BACKGROUND/AIMS: Ischemic preconditioning (IP) is known to protect hepatic tissue from ischemia-reperfusion injury. However, the mechanisms involved are not fully understood yet. METHODS: Using intravital multifluorescence microscopy in the rat liver, we studied whether IP exerts its beneficial effect by modulating postischemic Kupffer cell activation, leukocyte-endothelial cell interaction, microvascular no-reflow, mitochondrial redox state, and, thus, tissue oxygenation. RESULTS: Portal triad cross-clamping (45 min) followed by reperfusion induced Kupffer cell activation, microvascular leukocyte adherence, sinusoidal perfusion failure (no-reflow) and alteration of mitochondrial redox state (tissue hypoxia) (P<0.05). This resulted in liver dysfunction and parenchymal injury, as indicated by decreased bile flow and increased serum glutamate dehydrogenase (GLDH) levels (P<0.05). IP (5 min ischemia and 30 min intermittent reperfusion) was capable to significantly reduce Kupffer cell activation (P<0.05), which was associated with a slight attenuation of leukocyte adherence. Further, IP markedly ameliorated sinusoidal perfusion failure (P<0.05), and, thereby, preserved adequate mitochondrial redox state (P<0.05). As a consequence, IP prevented the decrease of bile flow (P<0.05) and the increase in serum GLDH levels (P<0.05). CONCLUSIONS: IP may exert its beneficial effects on hepatic ischemia-reperfusion injury by preserving mitochondrial redox state, which is guaranteed by the prevention of reperfusion-associated Kupffer cell activation and sinusoidal perfusion failure.

Acute mast cell-dependent neutrophil recruitment in the skin is mediated by KC and LFA-1: inhibitory mechanisms of dexamethasone.

This study examined adhesive and signaling pathways and anti-inflammatory mechanisms of dexamethasone in acute mast cell-dependent neutrophil recruitment in the skin in mice. Mast cell activation dose- and time-dependently triggered influx of predominately neutrophils and secretion of cytokine-induced neutrophil chemoattractant (KC). Neutralization of KC attenuated neutrophil recruitment upon mast cell activation. Mast cell activation- and KC-induced neutrophil responses were significantly decreased in lymphocyte function-associated antigen-1 (LFA-1)-deficient mice. Dexamethasone inhibited neutrophil accumulation elicited by mast cell activation. It is interesting that dexamethasone significantly reduced the mast cell-dependent secretion of KC, whereas neutrophil recruitment induced by exogenous KC was insensitive to dexamethasone treatment. Thus, KC is a fundamental mediator of neutrophil recruitment in acute mast cell-dependent skin inflammation, and mast cell activation- and KC-induced neutrophil responses are LFA-1-dependent. Moreover, dexamethasone inhibits mast cell-regulated skin infiltration of neutrophils mainly by attenuating KC secretion. Thus, this study elucidates important interactions between chemokines and adhesion molecules in mast cell-dependent neutrophil recruitment and provides new insight into mechanisms of dexamethasone in skin inflammation.

Fundamental and distinct roles of P-selectin and LFA-1 in ischemia/reperfusion-induced leukocyte-endothelium interactions in the mouse colon.

OBJECTIVE: To study the adhesive mechanisms underlying ischemia/reperfusion (I/R)-induced leukocyte-endothelium interactions in the colon. SUMMARY BACKGROUND DATA: Leukocyte recruitment is a key feature in I/R-induced tissue injury, but the mechanisms regulating leukocyte rolling and adhesion in the colon are not known. The authors recently developed a new model to study the molecular mechanisms of I/R-provoked leukocyte-endothelium interactions in the colon microcirculation using inverted intravital fluorescence microscopy. METHODS: The superior mesenteric artery was occluded for 30 minutes and leukocyte responses were analyzed after 120 minutes of reperfusion in colonic venules in mice. The adhesive mechanisms underlying I/R-induced leukocyte rolling and adhesion were investigated using monoclonal antibodies against L-, E- and P-selectin, and CD11a gene-targeted mice were used to examine the role of lymphocyte function antigen-1 (LFA-1, CD11a/CD18). RESULTS: Reperfusion provoked a clear-cut increase in leukocyte rolling and adhesion in colonic venules compared to negative controls. Both P- and E-selectin mRNA were expressed in the colon after this I/R insult. Pretreatment with an anti-P-selectin antibody reduced leukocyte rolling and adhesion by 88% and 85%, respectively, whereas antibodies against L- and E-selectin had no effect. Moreover, I/R-induced leukocyte adhesion in LFA-1-deficient mice was reduced by more than 95%. CONCLUSIONS: This study provides evidence that leukocyte rolling is exclusively and nonredundantly mediated by P-selectin and that firm adhesion is supported by LFA-1 in I/R-induced leukocyte recruitment in the colon. Taken together, both P-selectin and LFA-1 may be important targets to control pathologic inflammation in I/R-induced tissue injury in the colon.