The effects of inhibiting leukocyte migration with fucoidin in a rat peritonitis model.

OBJECTIVES: To study the effects of fucoidin on leukocyte rolling and emigration and bacterial colonization in a peritonitis sepsis model in rats. DESIGN AND INTERVENTIONS: A controlled study in 64 male Wistar rats, anesthetized and rendered septic by cecal ligation and puncture (CLP). Immediately after CLP 32 animals received a continuous infusion of fucoidin and 32 a continuous infusion of Ringer's lactate. MEASUREMENTS AND MAIN RESULTS: Systemic leukocyte counts were determined every 2 h after CLP. Surviving animals were anesthetized 24 h after CLP, and intravital measurements of leukocyte rolling in venules in the cremaster muscle were performed. The animals were then killed and their organs harvested for histological and microbiological examinations. The 24-h survival was comparable in the two groups. Fucoidin-treated animals had higher leukocyte counts in the systemic circulation and lower counts in the lungs, liver, abdominal cavity, and brain than control animals. The number of bacterial colony forming units in the abdominal cavity, lungs, liver, brain and blood did not differ in the two groups. Fucoidin treatment changed the type of bacteria predominantly found in the examined organs from Escherichia coli to Pseudomonas aeruginosa. CONCLUSIONS: In an intra-abdominal model of sepsis we found that treatment with fucoidin induces leukocytosis inhibits leukocyte rolling and reduces leukocyte emigration in the abdominal cavity, lungs, and liver. Reduction in the number of emigrating leukocytes was not associated with an increase in bacterial counts found in the examined organs.

Fucoidin, but not yeast polyphosphomannan PPME, inhibits leukocyte rolling in venules of the rat mesentery.

Leukocyte rolling in venules is inhibited by several sulfated polysaccharides, by antibodies to the leukocyte adhesion receptor L-selectin (LECAM-1), and by recombinant soluble L-selectin. The sulfated fucose polymer fucoidin and the polyphosphomannan PPME bind to L-selectin and inhibit L-selectin-mediated lymphocyte adhesion to lymph node high endothelial venules (LN-HEV). We investigated whether fucoidin and PPME also inhibit leukocyte rolling. Rolling leukocyte flux was determined by intravital microscopy in 47 venules (diameter 21 to 50 microns) of the rat mesentery with and without micro-infusion of each reagent through 8-microns glass micropipettes. Micro-infusion (1 mg/mL) or intravenous (IV) injection (25 mg/kg) of fucoidin, but not vehicle, reduced leukocyte rolling by greater than 90%. The half-effective concentration was approximately 2.5 micrograms/mL. Stroboscopic fluorescence video microscopy showed that fucoidin decreased the fraction of rolling leukocytes from 44% of all leukocytes passing the venules in control to less than 1%. PPME micro-infusion (1 mg/mL) or IV injection (14 mg/kg) did not reduce leukocyte rolling. Hence, leukocyte rolling differs from lymphocyte homing with respect to the effect of PPME. This may be related to fucoidin binding to L-selectin with greater affinity than PPME. Alternatively, inflamed venular endothelium may express a ligand for L-selectin different from that constitutively expressed on LN-HEV.