Effect of lepirudin on APAP hepatotoxicity. Mice were treated with 300 mg/kg APAP or vehicle IP at time 0 hour. Lepirudin (1 mg/kg) or saline was given IP at −0.5 hour, and at +0.5, +2.5, and +4.5 hours relative to administration of APAP. (A) Hepatic CD41 signal at 3 and 6 hours, intensity normalized to the CD41 signal of WT mice that were not treated with either APAP or lepirudin. (B) ALT activity in plasma. (C) Area of necrosis and degeneration as a percentage of total liver area. (D) RBC to total cell (%) in sections of liver tissue. (E) Nitrotyrosine label at 6 hours quantified as described in “Materials and methods.” (F) Representative photomicrographs of frozen liver sections labeled with anti-CD41 antibody to identify platelets, using 4,6 diamidino-2-phenylindole stain to identify nuclei. Platelets are pseudocolored red; nuclei are pseudocolored blue. (Original magnification ×100) (G) Representative liver sections from each group at 3 and 6 hours after APAP injection. (Original magnification ×200). *Significantly different from the saline-pretreated group at same time (N = 4 mice per group for each treatment/time).