In vivo and in vitro modulation of intercellular adhesion molecule (ICAM)-1 expression by hypertonicity

Hepatic ischemia-reperfusion (I/R) is an important cause of organ dysfunction in the critically ill. With reperfusion, Kupffer cells release pro-inflammatory cytokines that promote endothelial cell (EC) expression of adhesion molecules such as intercellular adhesion molecule (ICAM)-1, facilitating neutrophil (PMN) infiltration. Studies suggest hypertonic saline (HTS) might exert beneficial effects on development of organ injury following shock on the basis of reduced PMN-EC interactions. We hypothesized that HTS alters expression of EC ICAM-1 and thus minimizes PMN-mediated injury. To test our hypothesis, we used an in vivo model of hepatic I/R and an in vitro model of activated EC. Rats underwent 30 min of hepatic ischemia after pretreatment with HTS (7.5% NaCl, 4cc/kg ia) or normal saline (NS). At 4 h reperfusion, plasma was taken for aspartate aminotransferase (AST) and liver tissue was harvested for assessment of hepatic ICAM-1 mRNA by Northern blot analysis. Human umbilical vein endothelial cells (HUVECs) were activated by lipopolysaccharide (LPS) and exposed to hypertonic medium (350-500 mOsM). HUVEC ICAM-1 protein was measured by cell ELISA and ICAM-1 mRNA by Northern blot analysis. HTS prevented hepatic I/R injury as measured by AST. AST of shams was 282.6 +/- 38.1 IU/L. I/R following NS pretreatment caused significant injury (AST 973.8 +/- 110.9 IU/L) compared to sham (SM) (P < 0.001). Pretreatment with HTS exerted significant protection following I/R with an AST of 450.9 +/- 56.3 IU/L (P < 0.05). There was no significant difference in AST levels between SM and HTS groups. Reduced hepatic injury after HTS and I/R was accompanied by inhibition of I/R-induced hepatic ICAM-1 mRNA expression compared to NS treated animals (P < 0.01), Similarly, hypertonicity inhibited HUVEC LPS-induced ICAM-1 protein (LPS: 1.86 +/- 0.19 absorbance units; 400 mOsM +/- LPS: 1.45 +/- 0.14 absorbance units; 450 mOsM + LPS: 1.02 +/-: 0.19 absorbance units, P < 0.001) and mRNA expression. Thus, hypertonicity modulates endothelial ICAM-1 expression as one possible protective mechanism against I/R injury.