Purpose: Uptake and degradation of naked plasmid DNA (pDNA) by liver sinusoidal endothelial cells (LSECs) were investigated.
Methods: Tissue distribution and intrahepatic localization were determined after an intravenous injection of 111In- or 32P-labeled pDNA into rats. Cellular uptake and degradation of fluorescein- or 32P-labeled pDNA were evaluated using primary cultures of rat LSECs.
Results: Following intravenous injection, pDNA was rapidly eliminated from the circulation and taken up by the liver. Fractionation of liver-constituting cells by centrifugal elutriation revealed a major contribution of LSECs to the overall hepatic uptake of pDNA. Confocal microscopic study confirmed intracellular uptake of pDNA in cultured LSECs. Apparent cellular association of pDNA was similar at 37 degrees C and 4 degrees C. However, trichloroacetic acid (TCA) precipitation experiments showed the TCA-soluble radioactivity in the culture medium increased in an accumulative manner at 37 degrees C. Involvement of a specific mechanism was demonstrated, as the uptake of pDNA was significantly inhibited by excess unlabeled pDNA and some polyanions (polyinosinic acid, dextran sulfate, heparin) but not by others (polycytidylic acid, dextran). These inhibitors also reduced the amount of TCA-soluble radioactivity in the culture medium. CONCLUSION. These results suggest that LSECs efficiently ingested and rapidly degraded naked pDNA in vivo and in vitro and released the degradation products into the extracellular space.