Characterization of toxicological properties of L-lysine polymers in CD-1 mice.

We recently showed that polylysine, the polymer of lysines, retains anti-prion activity. Although the effectiveness of prion inhibition by polylysine was demonstrated with the regimen tolerated in mice, a determination of quantitative polylysine toxicity is necessary to precisely address the in vivo toxicity level of polylysine. In this communication, we report the results of body weight monitoring and hematologic tests performed in CD-1 mice that received two different tolerable dosages of polylysine for an either 5-day or 4-week period. We found that there was no significant alteration in overall serum chemistry, blood cell count, and body weight gain compared with controls. The only notable quantitative change with statistical significance was the decrease of platelet numbers in mice subchronically administered with polylysine. Our results suggest that polylysine is harmless in mice if administered for a short period, but administrations of polylysine in mice may require considerate attention for safety in future investigations as mice chronically receive tolerable doses of polylysine.