The cytocidal effect of high energy shock waves on human prostatic tumour cell lines

In-vitro cell treatment with focused shockwaves-influence of the experimental setup on the sound field and biological reaction

Background

To improve understanding of shockwave therapy mechanisms, in vitro experiments are conducted and the correlation between cell reaction and shockwave parameters like the maximum pressure or energy density is studied. If the shockwave is not measured in the experimental setup used, it is usually assumed that the device’s shockwave parameters (=manufacturer’s free field measurements) are valid. But this applies only for in vitro setups which do not modify the shockwave, e.g., by reflection or refraction. We hypothesize that most setups used for in vitro shockwave experiments described in the literature influence the sound field significantly so that correlations between the physical parameters and the biological reaction are not valid.

Methods

To reveal the components of common shockwave in vitro setups which mainly influence the sound field, 32 publications with 37 setups used for focused shockwave experiments were reviewed and evaluated regarding cavitation, cell container material, focal sound field size relative to cell model size, and distance between treated cells and air. For further evaluation of the severity of those influences, experiments and calculations were conducted.

Results

In 37 setups, 17 different combinations of coupling, cell container, and cell model are described. The setup used mainly is a transducer coupled via water to a tube filled with a cell suspension. As changes of the shockwaves’ maximum pressure of 11 % can already induce changes of the biological reaction, the sound field and biological reactions are mainly disturbed by use of standard cell containers, use of coupling gel, air within the 5 MPa focal zone, and cell model sizes which are bigger than half the −6 dB focal dimensions.

Conclusions

Until now, correct and sufficient information about the shockwave influencing cells in vitro is only provided in 1 of 32 publications. Based on these findings, guidelines for improved in vitro setups are proposed which help minimize the influence of the setup on the sound field.

Electronic supplementary material

The online version of this article (doi:10.1186/s40349-016-0053-z) contains supplementary material, which is available to authorized users.

High-energy shockwaves and extracorporeal high-intensity focused ultrasound

We review the physical interactions of focused ultrasound with tissue, describe technical features of current high-energy shockwave (HESW) and extracorporeal high-intensity focused ultrasound (HIFU) devices, and summarize the experimental and human data available to date. Tissue destruction by extracorporeal HIFU is not new: the first clinical attempts were made almost half a century ago for ablating brain tissue. Despite recent progress in the knowledge of the interactions between HIFU and tissue and significant device modifications, this technique is still in its infancy. The most promising targets for this kind of therapy in the field of urology are the kidney, bladder, and testis. The largest clinical experience with HIFU therapy currently available is for benign prostatic enlargement and prostate cancer using transrectal HIFU devices, which are not the topic of this summary. In parallel with HIFU, HESW therapy has been tested in numerous experimental and preclinical settings. This technique is currently not in routine clinical use. Theoretically, in parallel with HIFU, any organ accessible to conventional diagnostic ultrasound examination is a potential target for this kind of therapy.

Effect of macroscopic air bubbles on cell lysis by shock wave lithotripsy in vitro

In studies of cells or stones in vitro, the material to be exposed to shock waves (SWs) is commonly contained in plastic vials. It is difficult to remove all air bubbles from such vials. Because SWs reflect at an air-fluid interface, and because existing gas bubbles can serve as nuclei for cavitation events, we sought to determine in our system whether the inclusion of small, visible bubbles in the specimen vial has an effect on SW-induced cell lysis. We found that even small bubbles led to increased lysis of red blood cells (1- to 3-mm diameter bubbles, 9.8+/-0.5% lysis, n = 7; no bubbles, 4.4+/-0.8%, n = 4), and that the degree of lysis increased with bubble size. Damage could not be reduced by centrifuging the cells to the opposite end of the vial, away from the bubble. B-scan ultrasound imaging of blood in polypropylene pipette bulbs showed that, with each SW, bubbles were recruited from the air interface, mixing throughout the fluid volume, and these appeared to serve as nuclei for increased echogenicity during impact by subsequent SWs; thus, bubble effects in vials could involve the proliferation of cavitation nuclei from existing bubbles. Whereas injury to red blood cells was greatly increased by the presence of bubbles in vials, lytic injury to cultured epithelial cells (LLC-PK1, which have a more complex cytoarchitecture than red blood cells) was not increased by the presence of small air bubbles. This suggests different susceptibility to SW damage for different types of cells. Thus, the presence of even a small air bubble can increase SW-induced cell damage, perhaps by increasing the number of cavitation nuclei throughout the vial, but this effect is variable with cell type.

Sonochemically induced radicals generated by pulsed high-energy ultrasound in vitro and in vivo

The aim of this study was to evaluate the role of radicals as a mechanism of tissue damage induced by pulsed high-energy ultrasound. Transient cavitation has proved to be an important mechanism for the generation of reactive radical species during pulsed high-energy ultrasound applications. The amount of radicals studied in in vitro experiments using a chemical dosimeter based on iodine release is proportional to the number of pulses. Sonications of the R3327-AT1 subline of the Dunning prostate rat tumor transplanted in the thigh of Copenhagen rats were performed applying 500 and 2000 pulses at a pulse repetition frequency of 1 Hz. Tumor growth after treatment was compared with sham-treated controls. We were able to assess a significant growth delay, but could not find a significant difference between the two groups treated. In conclusion, radical formation does not seem to be the major mechanism for tissue necrosis induced by pulsed high-energy ultrasound.

Mechanisms of shockwave action in the human kidney

The effects on the human kidney parenchyma of high-energy shockwaves (HESW) with different energy densities were examined. Kidneys of patients treated by radical nephrectomy for renal cell carcinoma were perfused with cold HTK solution immediately after nephrectomy and kept in hypothermia (8 degrees C) for a maximum of 4 hours. The tumor-free parenchyma was treated with 2000 shocks at energy outputs of 15 kV (16 MPa, 0.15 mJ/mm2), 17 kV (32 MPa, 0.25 mJ/mm2), 19 kV (50 MPa, 0.4 mJ/mm2), and 21 kV (65 MPa, 0.6 mJ/mm2) in an experimental electromagnetic shockwave system (Siemens Co., Erlanger, Germany). Resulting tissue effects were analyzed by histologic and immunohistochemical examinations and confocal laser scanning microscopy. Different sensitivities of cell components, blood vessels, and tubules were found. Laser scanning microscopy revealed nuclear alterations in the vicinity of the focus up to a distance of approximately 10 mm. Severe histologic changes were found in a smaller zone, while immunohistochemistry studies revealed negative collagen IV staining in an area of approximately 4 x 4 mm (all distances measured within the plane perpendicular to the acoustic axis). From these results, it can be concluded that HESW directly damage the tubules and the vascular system, which might explain the clinical changes after extracorporeal shockwave lithotripsy in human patients. The extent of these effects seems to be dependent on the applied energy.

Cytocidal effect of high energy shock wave on tumour cells enhanced with larger dose and multiple exposures

Cultured LLC-WRC256 (Walker rat carcinoma) cells were exposed to different doses of high energy shock waves (HESW). The immediate viabilities were 98% in the control cells, and 74%, 53% and 18% following 400, 800, and 1500 HESW treatment, respectively. Surviving cells in the 400 and 800-treated HESW demonstrated delayed upward growth rate curves, and the 1500 HESW-treated a downward curve. Agar clonogenic efficiencies for surviving cells were 36% (control), 20% (400 HESW), 15% (800 HESW) and 3% (1500 HESW). LLC-WRC256 tumours in Wistar rats were treated once every other day with 1500 HESW on a total of three occasions. Tumours treated with HESW grew more slowly (4.9 cm3) than those in the control (13.5 cm3). HESW fragmented cells and destroyed cell membranes and intracellular organelles. A histological examination of tumours treated with HESW demonstrated local haemorrhage with necrosis in the HESW focus area. Damage to the surrounding skin and soft tissue was slight and transient. These findings suggest that the growth of tumour cells can be suppressed in vitro and in vivo by treatment with HESW.

Current role of extracorporeal shockwave therapy in surgery

In urology the introduction of extracorporeal shockwave therapy brought a revolutionary change to the management of urinary calculi. This inspired the introduction of shockwave therapy in several fields of surgery; it has been applied as a potential alternative to several operative procedures but is still experimental. So far, the major application of shockwave therapy has been lithotripsy of stones in the gallbladder, common bile duct, pancreatic duct and salivary gland ducts. Other applications are in the non-operative management of bone healing disturbances and in the inhibition of tumour growth. Steps towards selective thrombus ablation and pretreatment of heavily calcified arteries have also been made. In this review, the applications of extracorporeal shockwave therapy in several areas of surgery are discussed. It is concluded that, for selected patients, shockwave treatment may serve as a useful addition to the surgical armamentarium.

Effects of shock waves on the mouse fetus

Extracorporeal shock wave lithotripsy is contraindicated during pregnancy because its effects on the fetus remain to be ascertained. The purpose of this study was to elucidate the effects of shock waves on fetuses at various stages of pregnancy. Pregnant mice received 100, 250, or 500 shock waves on 8, 10, 12, 14, and 16 days postcoitum. The effect on fetal survival rate and weight was minimal in the early stages of pregnancy. In the later stages of pregnancy, however, the number of viable fetuses decreased in proportion to an increasing number of shock waves, and almost no viable fetuses were found in the group treated with 500 shock waves. Fusion and necrosis were found in many dead fetuses. Histological examination of the fetuses, which was obtained immediately after the shock wave treatment, revealed hemorrhages in the brain, lungs and subcutaneous tissue. This study indicated that shock waves lead to fetal damage and death in the late stage of pregnancy in mice.

Determination of the energy-dependent extent of vascular damage caused by high-energy shock waves in an umbilical cord model

To determine the spatial extent of shock-wave-induced vascular damage human umbilical cords were exposed to electromagnetically generated, focused ultrasound waves of different energy densities. During treatment macroscopically visible hematoma and superficial holes appeared. Following exposure specimens were fixed and examined histologically. In addition to vessel wall necrosis and rupture, complete detachment of endothelial cells in defined regions was observed. A correlation of the extent of the damage with the energy density distribution revealed that a local energy density of 0.3 mJ/mm2 is the lower threshold for the occurrence of severe vascular damage.

A review of the physical properties and biological effects of the high amplitude acoustic field used in extracorporeal lithotripsy

Extracorporeal shockwave lithotripsy (ESWL) has now been used for more than a decade in the treatment of urinary stone disease. During this period there has been a wide range of studies on the physical properties of the high-amplitude focussed fields used in ESWL and the biological effects of exposure to such fields, including their ability to fragment hard concretions. These studies form a distinct body of knowledge whose relevance to the broader literature on biological effects from lower amplitude exposures has yet to be fully evaluated. This review attempts to present the main results of biological-effects studies in ESWL along with what is known of the physical properties of lithotripsy fields with the aim of assisting this evaluation. In general, the reported biological effects of lithotripsy fields are compatible with those that have been observed at those lower amplitudes of focussed pulsed ultrasound in which transient cavitation is the dominant mechanism of interaction. The relatively large amplitudes and low frequencies in ESWL, however, make it a more potent generator of transient cavitation than most other forms of medical ultrasound. Biological-effects studies with lithotripsy fields may, therefore, be expected to extend our understanding of the nature of transient cavitation and, in particular, its effects in mammalian tissue.

Shock wave and THP-adriamycin for treatment of rabbit's bladder cancer

Focused high-energy shock waves (6,000 to 10,000 shots) were targeted under ultrasound guidance onto implanted urinary bladder cancer in rabbits to elucidate its effect. Although only focal necrosis of the tumor was seen following 6,000 to 10,000 shots daily for 3 days or following chemotherapy (THP-adriamycin) alone, almost total tumor necrosis was observed following a combined shock-wave therapy for one day and THP-adriamycin administration, demonstrating an additive and/or synergetic effect on rabbit urinary bladder cancer.

The effect of isolated high-energy shock wave treatments on subsequent bacterial growth

To determine whether high-energy shock waves possess bactericidal potential, ATCC strains of Escherichia coli, Streptococcus faecalis, Pseudomonas aeruginosa and Staphylococcus aureus were suspended in solution at concentrations approximating 10(6) bacteria per milliliter, placed in polypropylene cryovials, and immersed in the water bath of a Dornier HM3 lithotriptor. Each cryovial was then fluoroscopically guided to the epicenter of the f2 focal point and 2000 shocks at 20 kV applied. Suspensions were then serially diluted and colony counts obtained. The procedure was then repeated with 4000 shocks at 20 kV from the Dornier HM3 and 4000 shocks at intensity level 4 from a Wolff Piezolith 2200 shock wave lithotriptor. Comparison of shock-wave-treated and sham-treated bacterial suspensions revealed no significant difference in bacterial growth according to the colony count technique. We conclude that high-energy shock waves, whether generated by spark gap or piezoelectric array, do not possess significant bactericidal activity.

Effects of lithotripter-generated high energy shock waves of mammalian cells in vitro

The effects of high energy shock waves on an established human prostatic carcinoma cell line (PC-3) were investigated. HESW were administered to PC-3 cell suspensions using an electrohydraulic lithotripter (Dornier HM3). Experimental variables included the number of shocks to which the cells were exposed, spark generator potential, and the position of the cell sample in the acoustic field. Two types of cellular damage were observed: immediate cell destruction (lysis) as measured by electronic particle counting and the loss of reproductive capacity (viability) among the remaining cells as determined by colony formation assay. Over the range of the experimental variables studied, cell lysis was dependent to a greater extent on the number of shocks administered than the generator potential. Viability was affected less but was also dependent on both the generator potential and shock number. Cell lysis was strongly dependent on the position of the sample in the acoustic field with the extent of damage increasing as the sample was moved along the central axis of the shock wave from the f2 focus towards the electrodes. Possible mechanisms of damage and the relationship of the in vitro effects to the damage observed in normal tissues of patients undergoing extracorporeal lithotripsy for kidney stone disease are discussed.

Effects of high-energy shock waves on murine renal cell carcinoma

The effects of high-energy shock waves (HESW) on a murine renal cell carcinoma (RenCa) was investigated. In vitro exposure of tumor cells to HESW resulted in a dose-dependent reduction in cell viability as determined by trypan blue dye exclusion, plating efficiency, growth curve, and soft agar clonogenic assays. Activity of lactic dehydrogenase (LDH) was detected in the supernatant after the HESW treatment due to cellular destruction, and a dose-dependent increase in cytocidal effect was demonstrated. Ultrastructural changes with swelling and distorted cristae of mitochondria, vacuolation, ribosomal lysis, and chromatinolysis were observed in HESW-treated RenCa cells. Flow cytometric (FCM) study revealed that DNA content of RenCa cells diminished after 200 HESW treatment, and RNA content of tumor cells decreased markedly after 400 HESW treatments. Partial or complete inhibition of tumor growth was shown in both animal modalities of subcutaneous inoculation and intravenous injection with sequential lung metastases. This study stressed again that HESW may play a role in combinational protocol for the treatment of human renal cell carcinoma in certain circumstances.

High energy underwater shock wave treatment on implanted urinary bladder cancer in rabbits

The effects of focused high energy shock waves (SW) on the implanted urinary bladder cancer in rabbits were examined. The bladder cancer was exposed to 2000 to 8000 shots of focused SW under ultrasound guidance. Although only focal necrosis of the tumor was seen in the one day SW exposure, wider and deeper tumor necrosis was observed in the tumors following serial SW (2000 to 6000 shots, for two to three days). Eight to 10 day serial SW exposure (6000 to 8000 shots) decreased the tumor growth in comparison with that of the control. Lung metastases examined by periodic chest X-ray after SW treatment revealed that SW did not promote lung metastases. Pathological findings were also in accord with the X-ray examinations. Polyclonal antibody type 4 collagen was used for immunohistochemical staining of vascular wall in bladder cancer. Vascular wall destruction, not found in spontaneous necrotic tumor, were clearly visible in SW induced necrotic area. SW induces vascular damage in the tumor, which may be the primary cause promoting the tumor necrosis.

Extracorporeal shock wave treatment of common bile duct stones: experience with two different lithotriptors at a single institution

Extracorporeal shock wave lithotripsy (ESWL) is a new treatment modality for retained common bile duct stones. Sixty-two patients (mean age 75 years, range 27-95 years) with retained common bile duct stones were treated with two different lithotriptors. One of the lithotriptors operated on the electrohydraulic principle (Dornier HM-3) (n = 13), the other on the electromagnetic principle (Siemens Lithostar) (n = 49). All HM-3 patients were treated under general anaesthesia, whereas with the Lithostar one patients was treated under general anaesthesia, 43 received analgesia and sedation and five had no analgesia at all. Patients treated with the Lithostar had more sessions (mean 1.9 versus 1.3, P less than 0.05) and needed more stock waves (mean 8611 versus 2534, P less than 0.001) than patients treated with the HM-3. Fragmentation was achieved in all patients treated with the HM-3 and in 42 (86 per cent) patients treated with the Lithostar. In this latter group ten patients underwent common bile duct exploration without complications. Eleven patients had transient haematuria after treatment with the HM-3 and two patients (one in each group) had a subcapsular haematoma of the right kidney, all without clinical sequelae. At follow-up (median: HM-3 43 months, Lithostar 18 months), none of the patients had biliary complaints. We conclude that ESWL of retained common bile duct stones in safe and effective with both lithotriptors and should be considered before surgery in the elderly or high-risk patient.

High-energy shock waves: in vitro effects

To date, there have been multiple studies on the effects of high-energy shock waves (HESW) on benign and malignant cells under in vitro conditions. The major problem in comparing and contrasting these studies has been the wide range of mechanical, biological, and analytical variables facing the investigator. However, if one takes the time to select out only those studies in which a wide range of experimental variables have been defined or controlled, then it becomes possible to begin to understand the effects of HESW on cells in vitro. With this in mind, the literature has been thoroughly reviewed. It would appear that HESW do cause cellular damage regardless of the cell's doubling time. The cell damage is likely due to the impact of cavitation and the attendant shear forces and jets that are produced by the shock waves as it passes through the cell suspension. The damage occurs both at the cell membrane and within the cell itself. With regard to the latter, it would appear that the mitochondria are most sensitive to HESW; however, damage also occurs within the nucleus and along the endoplasmic reticulum and in other cell organelles (eg, lyosomes). Applications of HESW to other clinical situations are currently being studied. One example of interest is the in vitro combination of chemotherapeutic agents and HESW to enhance the effect of a specific chemotherapeutic regimen on a given tumor cell line. Several investigators have noted a beneficial effect of this combination therapy in vitro; however, similar favorable results have not been obtained when the same or similar tumor system was studied in vivo.

Cytotoxic effects of high energy shock waves in different in vitro models: influence of the experimental set-up

High energy shock waves (electromagnetically generated, Siemens Lithostar) were studied for their effects in vitro on different (tumor) cell types. Cells were exposed to the shock waves as a single cell suspension or as a cell pellet on the bottom of a test tube. In both cases, a dose dependent direct cytotoxicity, established by trypan blue dye exclusion, was observed after treatment with 1000 or 2000 shock waves. Also, the antiproliferative capacity as determined by clonogenic potential (double layer soft agar) and growth rate (plastic) were affected in this way. However, comparing the results after treatment in suspension or pellet, a discrepancy was evident. The cell lines showed a different susceptibility in pellet vs. suspension. Also the differential sensitivity of the cell types varied in these two treatment models. Furthermore the outcome depended on the cell concentration; direct cytotoxicity in a cell suspension was more pronounced at higher cell concentrations, while in a pellet this was increased by decreasing the number of cells. Finally, no shock wave induced cytotoxicity could be seen after fixation of cells in gelatine or by placing the pellet on a bottom layer of gelatine. Pressure measurements revealed no adequate explanation for this phenomenon. These results indicate that in vitro effects depend on the way cells are exposed to the shock waves and can be greatly influenced by changing the conditions of the microenvironment. Therefore, precise descriptions of the experimental set-up and careful interpretations of their outcome are obligatory.

In vivo assessment of shock-wave pressures. Implication for biliary lithotripsy

During extracorporeal shock-wave lithotripsy, the pressure profile, which is generated by the lithotriptor, determines the risk of tissue damage. In the present study, the pressure distribution of a lithotriptor (Lithostar; Siemens A.G., Erlangen, Federal Republic of Germany) was investigated in 10 pigs, five of which had gallstones surgically implanted into the gallbladder. The in vivo values were compared with in vitro data. Measurements were carried out along the shock-wave transmission path at the focus within the gallbladder, the adjacent liver, the diaphragmatic surface of the right lung, and the shock-wave exit site from the skin. Interposition of ribs did not cause a significant decrease in focal positive pressure. However, a gallstone positioned in the focus caused a 30%-65% reduction in pressure, recorded immediately behind the stone. Pressures obtained in vivo were always 15%-25% lower than those measured in vitro. The spatial distributions of the positive pressure in vivo and in vitro were almost identical. There was a high correlation between the pressures in vitro and in vivo (r = 0.88; P less than or equal to 0.01). This justifies assessment of shock-wave energies generated during biliary lithotripsy by extrapolation of in vitro data. It is concluded that it is possible to characterize different lithotriptors by in vitro pressure profile measurements.

The effect of high-energy underwater shock waves on implanted urinary bladder cancer in rabbits

We have examined the effects of high-energy shock waves (HESW) on implanted urinary bladder cancer in rabbits. The bladder cancer was exposed to 2000 to 6000 shots of focused HESW under ultrasound guidance. Although only focal necrosis of the tumor was seen in the one-day HESW exposure (2000 shots), wider and deeper necrosis was observed in the tumors following serial HESW (4000 or 6000 shots; 2 or 3 days). These results indicate that serial HESW exposure has destructive effects on implanted bladder cancer in rabbits.