Biologic effects of ultrasound

Expression of heat shock proteins after ultrasound exposure in HL-60 cells

One of the important cellular defense mechanisms against stress is the induction of heat shock proteins (HSPs). We have recently demonstrated that a low frequency electromagnetic field is unable to induce the heat shock response (HSR). In the present study, we expanded our investigations to the induction of HSPs, particularly Hsp72, by ultrasound (US). Human promyelocytic leukemia HL-60 cells were exposed in suspension to US at 1, 3 and 10 MHz, as well as combinations of two of these frequencies. The ability of US to induce Hsp72 was tested for different frequencies, intensities and exposure times. In addition, the water bath temperature was varied from 30 to 36 degrees C. The Hsp72 protein expression was determined 4 and 24 h after treatment. We found that the amount of Hsp72 increased with increasing US frequency, reaching its highest level of about 1800%, induced by 10 MHz. After increasing the temperature of the water bath, the amount of Hsp72 in the treated cells was also increased, whereas no induction was observed at 30 degrees C. For all treatment conditions, ultrasound of 1 MHz was unable to significantly induce Hsp72. At 10 MHz, the exposure time was varied from 0 to 20 min. We found that the induction of Hsp72 took place after 5 min of exposure. For a fixed level of absorbed US energy, the continuous regime, as well as a pulsation of 1:2 (5 ms on and 5 ms off) induced the same Hsp72 level. Pulsation of 1:5 (2 ms on and 8 ms off) and 1:10 (1 ms on and 9 ms off) did not show any effect. A single sonication of 20 min, as well as a fractionated sonication of two 10 min exposures induced the same level of Hsp72, whereas four exposures of 5 min reduced the Hsp72 level. At the optimum exposure conditions (10 MHz, 10 min), the concentration of other HSPs was also determined. Hsp27 showed no effect but Hsp32, Hsp40 and Hsp72 were induced. Taken together, these results suggest a synergistic interaction between heat and US.

Effect of diagnostic ultrasound during the fetal period on learning and memory in mice

BACKGROUND

An experiment was conducted to find out whether in utero exposure to diagnostic ultrasound leads to changes in postnatal behavior in adult mice.

METHODS

A total of 15 pregnant Swiss albino mice were exposed to diagnostic levels of ultrasound (3.5 MHz, 65 mW/cm(2), intensity((spatial peak-temporal peak)) (I(SPTP))=1 mW/cm(2), intensity((spatial average-temporal average)) (I(SATA))=240 mW/cm(2)) for 30 min on day 14 or 16 of gestation. All exposed as well as control animals were left to complete gestation and parturition. Their offspring were used in our further studies. They were monitored during early postnatal life for standard developmental markers (such as pinna detachment, eye opening and fur development) and postnatal mortality was recorded up to 6 weeks of age. The litters were subjected to behavioral tests for learning and memory at 4 months of age. Representative animals from each group were sacrificed and the hippocampal region of the brain was assayed for biogenic amines, noradrenaline, dopamine, serotonin (5-HT) and 5-HT's metabolite, 5-hydroxy indoleacetic acid (5-HIAA), in order to determine whether ultrasound exposure produced any biochemical changes in the hippocampal region of the brain. Coronal sections from the dorsal hippocampus from the representative animals from each group were processed for staining and the number of neurons was counted.

RESULTS

Neither the standard developmental markers (such as pinna detachment, eye opening and fur development) nor the postnatal mortality was affected by ultrasound exposure. However, there was a significant impairment in learning (hole board test) and memory functions (shuttle box test) in both the exposure groups. Significant reductions in the biogenic amines and the decrease in the neuronal density were found only in day 14th pc ultrasound-exposed group compared with the control animals. The 16th day exposure group is relatively resistant to ultrasound-induced impairment of brain functions.

CONCLUSIONS

The results suggest that the early fetal brain is highly susceptible to induction of neurobehavioral changes by ultrasound exposure.

Gestational stage sensitivity to ultrasound effect on postnatal growth and development of mice

BACKGROUND

An experiment was conducted to find out whether ultrasound exposure leads to changes in postnatal growth and development in the mouse.

METHODS

A total of 15 pregnant Swiss albino mice were exposed to diagnostic levels of ultrasound (3.5 MHz, 65 mW/cm2, I(SPTP) = 1 mW/cm2 Intensity(Spatial Peak-Temporal Peak), I(SATA) = 240 mW/cm2 Intensity(Spatial Average-Temporal Average)) for 30 min for a single day between days 10 and 18 of gestation (GD 10-18). Virgin female mice were placed with same age group males for mating in the ratio 2 females : 1 male and examined the next morning for the presence of vaginal plug, a sign of successful copulation. The females with vaginal plugs were separated and labeled as 0-day pregnant. Maternal vaginal temperature was also measured. A sham exposed control group of 15 pregnant mice was maintained for comparison. All exposed as well as control animals were left to complete gestation and parturition. Their offspring were used in our further studies. They were monitored during early postnatal life for standard developmental markers, postnatal mortality, body weight, body length, head length, and head width, and growth restriction was recorded up to 6 weeks of age.

RESULTS

An exposure to ultrasound induced nonsignificant deviations in the maternal vaginal temperature or developmental markers. Significant low birth weight was observed in the present study, after exposure at GD 11, 12, 14, and 16. However, 14 and 16 days postcoitus during the fetal period appears to be the most sensitive to the ultrasound effect, in view of the number of different effects as well as severity of most of the observed effects when exposed on these gestation days.

CONCLUSIONS

The results indicate that diagnostic ultrasound can induce harmful effects on mouse growth and development when given at certain critical periods of gestation.

Long-term effects of diagnostic ultrasound during fetal period on postnatal development and adult behavior of mouse

Pregnant Swiss albino mice were exposed to diagnostic levels of ultrasound (3.5 MHz, intensity 65 mW, I(SPTP) = 1 W/cm(2), I(SATA) = 240 W/cm(2)) for 10, 20 and 30 minutes on day 14 of gestation. Sham exposed controls were maintained for comparison. Fifteen pregnant mice were exposed for each group. Exposed as well as control animals were left to complete gestation and parturition. Ultrasound induced changes in maternal vaginal temperature was recorded. The changes in the physiological reflexes and postnatal mortality up to 6 weeks of age were recorded. The litters were subjected to behavioral tests for locomotor activity, learning and memory at 4 month and 1 year of age. Neither the physiological reflexes nor the postnatal mortality was affected by ultrasound exposure. However, there was a noticeable impairment in both locomotor and learning behavior even after a 10 min exposure, which further increased with increases in exposure time. Thus the present study demonstrates the neurotoxicity of diagnostic ultrasound and the high susceptibility of early fetal brain to induction of lasting detrimental changes by ultrasound exposure.

In vitro effects of low-intensity ultrasound stimulation on the bone cells

Mechanical perturbations serve as extracellular signals to a variety of cells, including bone cells. Low-intensity pulsed ultrasound produces significant multifunctional effects that are directly relevant to bone formation and resorption. Ultrasound stimulation has been shown to accelerate bone-defect healing and trabecular bone regeneration. In this study, we use an in vitro bone cell culture model to investigate the effect of low-intensity pulsed ultrasound. The rat alveolar mononuclear cell-calvaria osteoblast coculture system was used in this study. Before treatment, the bone cells were cultured for 3 days to facilitate their attachment and differentiation. Then, ultrasound exposure (frequency = 1 MHz, intensity = 0.068 W/cm(2)) or sham exposure for 20 min per day was applied until the end of the experiment. Half of the culture media were obtained on the 4th, 5th, 6th, 7th, 8th, 9th, and 10th days for the analysis of cytokines and biochemical parameters. At the end of the experiment, cells were fixed and stained for identification and quantification of the osteoblast and osteoclast cells. After low-intensity pulse ultrasound stimulation, the osteoblast cell counts were significantly increased, whereas the osteoclast cell counts were significantly decreased. The total alkaline phosphatase amount in the culture medium was increased after 7 days of ultrasound stimulation, and tumor necrosis factor-alpha in ultrasound-stimulated bone cells was significantly increased after the 7th day of culture and reached 474.77% of the control medium on the 10th day of culture. The results of this study suggest that low-intensity ultrasound treatment may have a stimulatory effect on bone-healing processes.

Bone defect healing enhanced by ultrasound stimulation: an in vitro tissue culture model

Ultrasound has many medical applications. Previous animal and clinical studies have clearly shown a positive effect of ultrasound on the rate of osseous repair. The present in vitro study was designed to elucidate the specific response of bony tissue to ultrasound treatment. Bilateral femora were obtained from 36 mature male Wistar rats. A bone defect was created at the center of each distal metaphysis. The femora were maintained for either 7 or 14 days in in vitro tissue culture and received 15 min of ultrasound stimulation or a sham exposure. The ultrasound intensity used was either 320 or 770 mW/cm2. Healing of the bone defect was evaluated by histomorphological examination and by analysis for the synthesis and secretion of prostaglandin E2. The results showed that ultrasound stimulation can accelerate both defect healing and trabecular bone regeneration. All experimental femoral defects treated with ultrasound healed faster than the untreated cortical defects, but only the defects receiving 770 mW/cm2 reached a level that was significantly different. The healing rate for the 320-mW/cm2 stimulated defects was intermediate between that of the 770-mW/cm2 and sham-exposed defects. With ultrasound stimulation, prostaglandin E2 secretion by the experimental femora decreased significantly. Changes in the prostaglandin synthesis and concentration were found to correspond to changes in the amount of trabecular regeneration and to acceleration of bone healing. This highly controlled and well-studied model of ultrasound stimulation of bone healing in vitro can be used to further examine the biological mechanisms involved.

Low intensity ultrasound treatment increases strength in a rat femoral fracture model

Bilateral closed femoral shaft fractures were made in 22 male Long-Evans rats. In 16 animals, ultrasound was applied to one limb for 15 minutes daily 10 times within the first 14 postoperative days. The treated limbs received a 200 microseconds burst of 1.5 or 0.5 MHz sine waves repeated at 1.0 kHz at a spatial average and temporal average intensity of 30 mW/cm2. The contralateral limb of each animal served as a nontreated control. Six remaining animals with fractures and six additional animals without fractures received sham ultrasound treatment to control for the effects of anesthesia and handling. Fracture repair was evaluated on postoperative day 21 by radiography, mechanical testing in torsion, and histology. Five of 16 ultrasound-treated fractures showed obliteration of the fracture gap on radiographs, whereas none of the 28 controls did. The average maximum torque of fractures treated with either signal was 22% greater than that of the contralateral controls (p < 0.05). The stiffness of treated fractures was greater than that of control fractures, but the difference was significant only in animals treated with the 1.5 MHz signal (p < 0.02). Sham treatment did not affect repair in the control group. These results indicate that low-intensity pulsed ultrasound at either 0.5 or 1.5 MHz can accelerate fracture repair at 21 days in this highly controlled model.

Medical sonography: reproductive effects and risks

While it is clear that the levels and types of medical sonography that have been used in the past have no measurable risks, it would be inaccurate to label the modality of ultrasound as totally safe regardless of exposure. Most agents have reproductive risks and even teratogenic risks if the exposure is raised sufficiently. Thus the prudent use of sonography means that clinicians and designers of equipment have to maintain exposures far below the risks that have been demonstrated in animal studies and from the knowledge obtained about the physical changes that can be produced in humans as the absorbed dose is elevated. The reproductive risks were evaluated using five criteria: 1) human epidemiology, 2) secular trend data, 3) animal experiments, 4) dose response relationships, and 5) biologic plausibility. The analysis reveals that the human epidemiology does not indicate that diagnostic ultrasound presents a measurable risk to the developing embryo or fetus. Animal studies also indicate that diagnostic levels of ultrasound are safe and do not elevate the fetal temperature into the region where deleterious embryonic and fetal effects will occur. Because higher exposures of ultrasound can elevate the temperature of the embryo, the use of diagnostic procedures and the design of sonographic equipment should take into consideration the hyperthermic potential of higher exposures of ultrasound and the hypothetical additional risk of performing sonography on pregnant patients who are febrile. It would appear that if the embryonic temperature never exceeds 39 degrees C, then there is no measurable risk. We suggest that sonography (the field) and sonogram (the procedure) are the most appropriate and least anxiety provoking terms.