N-Acetyl Cysteine Reduces von Willebrand Factor Multimer Size In Vitro and In Vivo.

von Willebrand factor (VWF) shares a similar domain structure with many polymeric mucins, including the presence of D domains and a C-terminal cysteine knot, which allows these molecules to form polymeric structures that can reach immense sizes. Precipitation of polymeric lung mucins complicates the clinical course of cystic fibrosis and chronic obstructive lung disease, and in both cases the viscosity of the inspissated mucus can be reduced by treatment with N-acetyl cysteine (NAC), which presumably reduces the size of the mucin polymers by reducing sensitive disulfide bonds. Because of the similarity of VWF and mucin multimers, we examined whether NAC could also reduce VWF multimer size both in vitro and in vivo. In vitro, we incubated NAC at different concentrations and for different times with ultra-large VWF multimers (ULVWF) isolated from endothelial cell supernatant and examined the effect on multimer size using agarose gel electrophoresis. NAC reduced ULVWF size in a time- and concentration-dependent manner, with the peak effect reached at 5 min and at concentration of 0.5 mM. We then examined the effect of NAC on ULVWF/platelet “strings” formed on the surface of histamine-activated endothelial cells by perfusing the strings with NAC solutions. At 1 mM, NAC eliminated almost all of the adherent strings within 5 minutes. We next examined the effect of NAC in vivo by following VWF multimer size with time in C57B/6 injected with NAC either intraperitoneally or intravenously. NAC, at a single dose of 500 mg/kg, induced a sustained reduction in VWF multimer size in the treated mice within 4 hours after injection. The effects lasted up to 8 hours. These results suggest that NAC may be a rapid, safe, and effective treatment for patients suspected of suffering from thrombotic thrombocytopenic purpura, a disorder characterized by a failure to process ULVWF.