Toxicity of colloidal silica nanoparticles administered orally for 90 days in rats

This study was undertaken to investigate the potential toxicity and establish the no observed adverse effect level (NOAEL) and target organ(s) of negatively charged colloidal silica particles of different sizes, ie, SiO₂^EN20(−) (20 nm) or SiO₂^EN100(−) 2(100 nm), administered by gavage in Sprague-Dawley rats. After verification of the physicochemical properties of the SiO₂ particles to be tested, a preliminary dose range-finding study and 90-day repeated dose study were conducted according to the Organisation for Economic Cooperation and Development test guideline. Based on the results of the 14-day dose range-finding study, a high dose was determined to be 2,000 mg/kg, and middle and low doses were set at 1,000 and 500 mg/kg, respectively. In the 90-day toxicity study, there were no animal deaths in relation to administration of SiO₂ particles of either size. In addition, no treatment-related clinical changes or histopathological findings were observed in any of the experimental groups. Moreover, no difference in toxic effects from chronic exposure to SiO₂^EN20(−)(20 nm) or SiO₂^EN100(−) (100 nm) was observed. The results of this study indicate that the NOAEL for SiO₂^EN20(−) and SiO₂^EN100(−) would most likely be 2,000 mg/kg, and no target organ was identified in rats of either sex.

Toxicity of 100 nm zinc oxide nanoparticles: a report of 90-day repeated oral administration in Sprague Dawley rats

Nanoparticles (NPs) are used commercially in health and fitness fields, but information about the toxicity and mechanisms underlying the toxic effects of NPs is still very limited. The aim of this study is to investigate the toxic effect(s) of 100 nm negatively (ZnO^AE100[−]) or positively (ZnO^AE100[+]) charged zinc oxide (ZnO) NPs administered by gavage in Sprague Dawley rats, to establish a no observed adverse effect level, and to identify target organ(s). After verification of the primary particle size, morphology, hydrodynamic size, and zeta potential of each test article, we performed a 90-day study according to Organisation for Economic Co-operation and Development test guideline 408. For the 90-day study, the high dose was set at 500 mg/kg and the middle and low doses were set at 125 mg/kg and 31.25 mg/kg, respectively. Both ZnO NPs had significant changes in hematological and blood biochemical analysis, which could correlate with anemia-related parameters, in the 500 mg/kg groups of both sexes. Histopathological examination showed significant adverse effects (by both test articles) in the stomach, pancreas, eye, and prostate gland tissues, but the particle charge did not affect the tendency or the degree of the lesions. We speculate that this inflammatory damage might result from continuous irritation caused by both test articles. Therefore, the target organs for both ZnO^AE100(−) and ZnO^AE100(+) are considered to be the stomach, pancreas, eye, and prostate gland. Also, the no observed adverse effect level for both test articles was identified as 31.25 mg/kg for both sexes, because the adverse effects were observed at all doses greater than 125 mg/kg.

Organization of research team for nano-associated safety assessment in effort to study nanotoxicology of zinc oxide and silica nanoparticles

Currently, products made with nanomaterials are used widely, especially in biology, bio-technologies, and medical areas. However, limited investigations on potential toxicities of nanomaterials are available. Hence, diverse and systemic toxicological data with new methods for nanomaterials are needed. In order to investigate the nanotoxicology of nanoparticles (NPs), the Research Team for Nano-Associated Safety Assessment (RT-NASA) was organized in three parts and launched. Each part focused on different contents of research directions: investigators in part I were responsible for the efficient management and international cooperation on nano-safety studies; investigators in part II performed the toxicity evaluations on target organs such as assessment of genotoxicity, immunotoxicity, or skin penetration; and investigators in part III evaluated the toxicokinetics of NPs with newly developed techniques for toxicokinetic analyses and methods for estimating nanotoxicity. The RT-NASA study was carried out in six steps: need assessment, physicochemical property, toxicity evaluation, toxicokinetics, peer review, and risk communication. During the need assessment step, consumer responses were analyzed based on sex, age, education level, and household income. Different sizes of zinc oxide and silica NPs were purchased and coated with citrate, L-serine, and L-arginine in order to modify surface charges (eight different NPs), and each of the NPs were characterized by various techniques, for example, zeta potentials, scanning electron microscopy, and transmission electron microscopy. Evaluation of the “no observed adverse effect level” and systemic toxicities of all NPs were performed by thorough evaluation steps and the toxicokinetics step, which included in vivo studies with zinc oxide and silica NPs. A peer review committee was organized to evaluate and verify the reliability of toxicity tests, and the risk communication step was also needed to convey the current findings to academia, industry, and consumers. Several limitations were encountered in the RT-NASA project, and they are discussed for consideration for improvements in future studies.

A 90-day study of sub-chronic oral toxicity of 20 nm positively charged zinc oxide nanoparticles in Sprague Dawley rats

Purpose

The study reported here was conducted to determine the systemic oral toxicity and to find the no-observed-adverse-effect level of 20 nm positively charged zinc oxide (ZnO^SM20(+)) nanoparticles in Sprague Dawley rats for 90 days.

Methods

For the 90-day toxicity study, the high dose was set as 500 mg per kg of body weight (mg/kg) and the middle and low dose were set to 250 mg/kg and 125 mg/kg, respectively. The rats were held for a 14-day recovery period after the last administration, to observe for the persistence or reduction of any toxic effects. A distributional study was also carried out for the systemic distribution of ZnO^SM20(+) NPs.

Results

No rats died during the test period. There were no significant clinical changes due to the test article during the experimental period in functional assessment, body weight, food and water consumption, ophthalmological testing, urine analysis, necropsy findings, or organ weights, but salivation was observed immediately after administration in both sexes. The total red blood cell count was increased, and hematocrit, albumin, mean cell volume, mean cell hemoglobin, and mean cell hemoglobin concentration were decreased significantly compared with control in both 500 mg/kg groups. Total protein and albumin levels were decreased significantly in both sexes in the 250 and 500 mg/kg groups. Histopathological studies revealed acinar cell apoptosis in the pancreas, inflammation and edema in stomach mucosa, and retinal atrophy of the eye in the 500 mg/kg group.

Conclusion

There were significant parameter changes in terms of anemia in the hematological and blood chemical analyses in the 250 and 500 mg/kg groups. The significant toxic change was observed to be below 125 mg/kg, so the no-observed-adverse-effect level was not determined, but the lowest-observed-adverse-effect level was considered to be 125 mg/kg in both sexes and the target organs were found to be the pancreas, eye, and stomach.