Dynamic Fluorescence Microscopy of Cellular Uptake of Intercalating Model Drugs by Ultrasound-Activated Microbubbles.

PURPOSE: The combination of ultrasound and microbubbles can facilitate cellular uptake of (model) drugs via transient permeabilization of the cell membrane. By using fluorescent molecules, this process can be studied conveniently with confocal fluorescence microscopy. This study aimed to investigate the relation between cellular uptake and fluorescence intensity increase of intercalating model drugs. PROCEDURES: SYTOX Green, an intercalating fluorescent dye that displays >500-fold fluorescence enhancement upon binding to nucleic acids, was used as a model drug for ultrasound-induced cellular uptake. SYTOX Green uptake was monitored in high spatiotemporal resolution to qualitatively assess the relation between uptake and fluorescence intensity in individual cells. In addition, the kinetics of fluorescence enhancement were studied as a function of experimental parameters, in particular, laser duty cycle (DC), SYTOX Green concentration and cell line. RESULTS: Ultrasound-induced intracellular SYTOX Green uptake resulted in local fluorescence enhancement, spreading throughout the cell and ultimately accumulating in the nucleus during the 9-min acquisition. The temporal evolution of SYTOX Green fluorescence was substantially influenced by laser duty cycle: continuous laser (100 % DC) induced a 6.4-fold higher photobleaching compared to pulsed laser (3.3 % DC), thus overestimating the fluorescence kinetics. A positive correlation of fluorescence kinetics and SYTOX Green concentration was found, increasing from 0.6 × 10-3 to 2.2 × 10-3 s-1 for 1 and 20 µM, respectively. Finally, C6 cells displayed a 2.4-fold higher fluorescence rate constant than FaDu cells. CONCLUSIONS: These data show that the temporal behavior of intracellular SYTOX Green fluorescence enhancement depends substantially on nuclear accumulation and not just on cellular uptake. In addition, it is strongly influenced by the experimental conditions, such as the laser duty cycle, SYTOX Green concentration, and cell line.

Understanding ultrasound induced sonoporation: definitions and underlying mechanisms.

In the past two decades, research has underlined the potential of ultrasound and microbubbles to enhance drug delivery. However, there is less consensus on the biophysical and biological mechanisms leading to this enhanced delivery. Sonoporation, i.e. the formation of temporary pores in the cell membrane, as well as enhanced endocytosis is reported. Because of the variety of ultrasound settings used and corresponding microbubble behavior, a clear overview is missing. Therefore, in this review, the mechanisms contributing to sonoporation are categorized according to three ultrasound settings: i) low intensity ultrasound leading to stable cavitation of microbubbles, ii) high intensity ultrasound leading to inertial cavitation with microbubble collapse, and iii) ultrasound application in the absence of microbubbles. Using low intensity ultrasound, the endocytotic uptake of several drugs could be stimulated, while short but intense ultrasound pulses can be applied to induce pore formation and the direct cytoplasmic uptake of drugs. Ultrasound intensities may be adapted to create pore sizes correlating with drug size. Small molecules are able to diffuse passively through small pores created by low intensity ultrasound treatment. However, delivery of larger drugs such as nanoparticles and gene complexes, will require higher ultrasound intensities in order to allow direct cytoplasmic entry.

The diagnostic significance of increased urinary and serum amylase activity in bitches with pyometra.

The serum amylase and the serum lipase activities determined simultaneously were normal in 92 bitches with pyometra (group A). To determine the usefulness of the information provided by the measurement of urinary amylase activity in pyometra dogs, the relation of serum and urinary amylase activity to urinary protein and serum lipase activity in paired serum and urine samples was investigated in 39 control bitches and in a second group of 66 bitches with pyometra (group B). The 39 control bitches and 18 pyometra bitches (group B1) had normal urinary amylase activity and showed neither a change in urinary protein nor in serum amylase or lipase activities. There was no relationship between the urinary amylase activity and the urinary protein level or the serum amylase activity. The remaining forty-eight pyometra bitches (group B2) had normal serum lipase activity and increased urinary amylase activity (amylasuria), which correlated highly with the increased urinary protein concentration and to a lesser degree with the increased serum amylase activity. Renal failure in 15 of those bitches had no influence on the degree of increase in the urinary or serum amylase activity. It was concluded that, in the absence of any significant indication of pancreatic disease, amylasuria and amylasaemia in bitches with pyometra are a strong indication of renal glomerular disease. Amylasuria was indicative to some degree of an increased serum amylase activity, but was unrelated to renal failure.

Urinary gamma-glutamyl transferase and the degree of renal dysfunction in 75 bitches with pyometra.

In 75 bitches with pyometra single urine samples were examined for gamma-glutamyl transferase (gamma-GT), protein, glucose, specific gravity, bacteria, red blood cells and white blood cells. Serum samples were examined for urea, creatinine, inorganic phosphate and gamma-GT. Biochemical findings were compared with the degree of illness (clinical signs). Twenty one bitches had no signs of renal disease. Seventeen showed only glomerular damage indicated by proteinuria without signs of proximal tubular damage. Thirty seven bitches had increased urinary gamma-GT levels, indicating proximal tubular lesions, which were associated with proteinuria in 35 and renal failure in 16 of them, and worse clinical findings. In all bitches with pyometra serum levels of gamma-GT were comparable to values in control bitches. Glomerular dysfunction seemed to precede proximal tubular lesions, so that gamma-GT-uria in bitches with pyometra was not an early but rather a late indication of a more profound degree of renal dysfunction, that is, proximal tubular renal damage developed after glomerular dysfunction and preceding renal failure.

Renal injury in dogs with pyometra.

In a group of 58 dogs with proven pyometra, 10 bitches developed renal failure, combined with increased (p less than 0.01) urinary excretion of protein, glucose, gamma-glutamyltransferase (GGT), alkaline phosphatase (AP), amylase, lipase and casts. Thirty-two bitches without renal failure showed nevertheless signs of renal dysfunction as indicated by increased (p less than 0.01) urinary levels of protein, glucose, GGT, AP and amylase. Six bitches without significant proteinuria showed increased (p less than 0.02) urinary levels of GGT, AP as well as amylase. Thus renal injury was detected in 72 per cent of the bitches. Sixteen bitches showed normal urinary levels of protein, glucose, GGT, AP, amylase and lipase, indicating absence of renal disease.