Cytoplasmic molecular delivery with shock waves: Importance of impulse

Cell permeabilization using shock waves may be a way of introducing macromo lecules and small polar molecules into the cytoplasm, and may have applicat ions in gene therapy and anticancer drug delivery. The pressure profile of a shock wave indicates its energy content, and shock-wave propagation in ti ssue is associated with cellular displacement, leading to the development o f cell deformation. In the present study, three different shock-wave source s were investigated; argon fluoride excimer laser, ruby laser, and shock tu be. The duration of the pressure pulse of the shock tube was 100 times long er than the lasers. The uptake of two fluorophores, calcein (molecular weig ht: 622) and fluorescein isothiocyanate-dextran (molecular weight: 71,600), into HL-60 human promyelocytic leukemia cells was investigated. The intrac ellular fluorescence was measured by a spectrofluorometer, and the cells we re examined by confocal fluorescence microscopy. A single shock wave genera ted by the shock tube delivered both fluorophores into approximately 50% of the cells (p < 0.01), whereas shock waves from the lasers did not. The cel l survival fraction was >0.95. Confocal microscopy showed that, in the case of calcein, there was a uniform fluorescence throughout the cell, whereas, in the case of FITC-dextran, the fluorescence was sometimes in the nucleus acid at other times not. We conclude that the impulse of the shock wave (i .e., the pressure integrated over time), rather than the peak pressure, was a dominant factor for causing fluorophore uptake into living cells, and th at shock waves might have changed the permeability of the nuclear membrane and transferred molecules directly into the nucleus.