Tissue distribution and histopathological effects of titanium dioxide nanoparticles after intravenous or subcutaneous injection in mice.

Nanoparticles can be formed following degradation of medical devices such as orthopedic implants. To evaluate the safety of titanium alloy orthopedic materials, data are needed on the long-term distribution and tissue effects of injected titanium nanoparticles in experimental animals. In this study, we evaluated the tissue distribution and histopathological effects of titanium dioxide (TiO(2)) nanoparticles (approximately 120 nm diameter) in mice after intravenous (i.v.; 56 or 560 mg kg(-1) per mouse) or subcutaneous (s.c.; 560 or 5600 mg kg(-1) per mouse) injection on two consecutive days. Animals were examined 1 and 3 days, and 2, 4, 12 and 26 weeks after the final injection. When examined by light microscopy, particle agglomerates identified as TiO(2) were observed mainly in the major filtration organs - liver, lung and spleen - following i.v. injection. Particles were still observed 26 weeks after injection, indicating that tissue clearance is limited. In addition, redistribution within the histological micro-compartments of organs, especially in the spleen, was noted. Following s.c. injection, the largest particle agglomerates were found mainly in the draining inguinal lymph node, and to a lesser extent, the liver, spleen and lung. With the exception of a foreign body response at the site of s.c. injection and the appearance of an increased number of macrophages in the lung and liver, there was no histopathological evidence of tissue damage observed in any tissue at any time point.

Developmental exposure of mice to pulsed ultrasound.

Exposure of pregnant mice on gestation day (gd) 8 to 1 MHz continuous-wave ultrasound (0, 0.05, 0.50, or 1.00 W/cm2) was reported previously to result in a slight (nonsignificant) increase in malformations. The present study was conducted in a similar fashion using pulsed ultrasound but was designed to maximize the likelihood of finding effects of gd 8 ultrasound exposure on prenatal development. Pregnant ICR mice (approximately 60 animals/group) were exposed on gd 8 to pulsed ultrasound with a center frequency of 1 MHz at levels of 0 (sham control), 0.05, 0.50, or 1.00 W/cm2 (spatial average, temporal average intensities; ISATA) with a spatial peak, pulse average intensity (ISPPA) of 90 W/cm2 and pulse duration of 6.5 microseconds. Anesthetized animals were placed in a degassed water bath (30 degrees C) and exposed for two 10 min intervals during which the beam was centered 1 cm on either side of the abdominal midline. On gd 17, dams were killed; the uterus and its contents were weighed and examined; and live fetuses were weighed and examined for external, visceral, and skeletal malformations. Although one female in the 0.50 W/cm2 group and seven animals in the 1.00 W/cm2 group died following exposure, no other significant change from controls was seen in any maternal or fetal parameter evaluated. Thus the results of this study indicate that there was no detectable effect on prenatal development of mice following exposure to ultrasound on gd 8 (a time of maximal sensitivity), even at exposure intensities that were lethal to some maternal animals.

The embryotoxic effects of ultrasound exposure in pregnant ICR mice.

The embryotoxicity of ultrasound exposure during pregnancy was investigated in DUB:(ICR) mice. On day 0 of gestation (day of plug), pregnant mice were assigned to one of five groups: cage control, sham exposed (0 W/cm2), 0.05 W/cm2, 0.50 W/cm2. or 1.00 W/cm2. Females were anesthetized on day 8 of gestation and their abdomens were shaved to assure good acoustic coupling. The animals were strapped on a lucite board and placed vertically into a distilled degassed water bath (30 degrees C) so that the abdomen was fully submerged and centered in the axis of the ultrasonic beam. Insonation was carried out using a PZT transducer with a radius of 1.27 cm and a frequency of 1 MHz under continuous wave conditions. Each animal was placed at a distance of 25 cm from the transducer and exposed to the appropriate intensity for 120 seconds. On day 17 of gestation, the maternal animals were killed, the uterine contents were examined, and live fetuses were weighed and then shipped in cold lactated Ringer's solution from Maryland to Arkansas. Fetuses were examined on the day following maternal sacrifice for external and visceral defects and skeletons were prepared and examined subsequently. Slight but significant differences were detected between the cage control and sham-exposed groups. No statistically significant changes were seen that could be attributed to ultrasound exposure, although there was a slight increase in the incidence of malformed fetuses and the occurrence of multiple malformations in individual fetuses as intensity of the ultrasonic exposure increased.

Biological effects of ultrasound.

In summary, there are many deficiencies and gaps in the current data base for ultrasound-induced bioeffects. More information is needed on the effects of low intensity ultrasound, the effects of pulsed ultrasound, the relationship between peak intensities and average intensities of pulsed ultrasound, the possibility of cumulative effects, and the possibility of long-term effects. Also, very little of the data, either positive or negative, has been verified by other laboratories. Although there is presently no evidence to indicate that diagnostic ultrasound involves a significant risk, the evidence is insufficient to justify an unqualified acceptance of safety. The potential for acute adverse effects has not been systematically explored, and the potential for delayed effects has been virtually ignored. Because of the difficulties involved in searching for and defining potential risks from exposure to low levels of chemicals, radiation, or other forms of energy, it is unreasonable to expect that in the near future, the degree of risk, if any, will be clearly defined for diagnostic ultrasound. As in other areas (e.g., the effects of ionizing radiation) no single study, epidemiological or experimental, can accomplish this goal. In the meantime, a prudent public health policy calls for judicious use of diagnostic ultrasound, using it only when diagnostic benefits to patients are indicated, and keeping any exposure to diagnostic ultrasound as low as practicable, consistent with its intended purpose.