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Abstract The toxicity of nanoalumina (Al2O3NPs) as a result of accumulation in the tissues of living organisms has been recognized since the last decades of the twentieth centuries. It has been found that zinc, as bulk zinc salt, acts to encounter the accumulation of aluminum ions, due to its chemical interaction with this metal, and this gives zinc an excellent therapeutic potentials to counteract and possibly lessen its notorious toxicity. Nanomaterials, because of their physical and chemical properties, have a substantial ability to penetrate the biological membranes, including cell membrane, blood-brain, and testicle barriers among many others in living organisms. Nanoparticles, in general, are more capable of gradual accumulation inside the cells and vital organelles where they are retained until they reach concentrations sufficient to induce sever cellular toxicity. Accordingly, the hypothesis of this study is based on the rationale that nano-zinc oxide (ZnONPs) particles, with their presumably high penetration and accumulation capacity would be even more efficient in encountering the aluminum nanoparticles toxicity. To the author’s knowledge, and after thorough literature search, there is no mention of previous studies to evaluate the interactions between Al oxide nanoparticles with either nano-zinc or bulk zinc in mammalian tissues. This work attempts, for the first time, to compare and provide a full coverage of the bioaccumulation pattern of aluminum nanoparticles in tissues in the presence of nano-zinc oxide and bulk zinc chloride in attempt to evaluate their ameliorative potentials in precluding the accumulation of Al2O3NPs in various rat organ. To attain the objectives set for this work, the following parameters were computed and assessed; the lethality percentile doses, including the median lethal dose of Al2O3NPs at 24h, acute bioaccumulation of Al in different tissues, and the effect of [90] combined treatment of nano alumina with either nano- or bulk zinc after 24 h. A follow-up study with sub-acute experiments, which covered several time intervals extending to 21 days, was also performed. In addition, the nano-size and zeta potential of Al2O3NPs and ZnONPs were estimated. The TEM technique revealed the amorphous shape of the Al2O3NPs with a size average of 8.26 ± 1.987 nm whereas that of ZnONPs had a crystal shape with an average diameter of 35.71 ± 5.39nm. The Zeta potential for Al2O3NPs and ZnONPs was 43.8 mV and 34.1 mV respectively. In order to determine the acute and sub-acute doses of Al2O3NPs, ZnONPs, and B-ZnCl2, the lethality percentile dosages (LD1 to LD99) were estimated. In order to evaluate the influence of zinc, as Nano- or bulk zinc, during acute and sub-acute experimentation, on the bioaccumulation of Al2O3NPs, the following design was constructed. For the acute experiments, rats were divided into four groups. The first group was intranasally instilled with deionized water (group I), whereas those of groups II, III, and IV were instilled with a single acute dose of LD25@96h Al2O3NPs either alone (1.66 g/kg b. wt.), in combination with ZnONPs LD25@96h (0.52 g/kg b. wt.), or with B-ZnCl2 LD25@96h (0.06 g/kg b. wt.), respectively. The total sample size was estimated as twenty rats (N=20) which were then divided into four equal groups, each of five rats (n=5). For the sub-acute experiments, the total sample size of one-hundred rats (N=100) was allocated into four groups of V, VI, VII, and VIII, each of twenty-five rats. The first group was intranasally instilled with deionized water (group V), whereas the sixth to the eighth groups, were instilled with a sub-acute dose of LD5@96h Al2O3NPs alone (0.94 g), every other day, and in combination with a sub-acute dose of LD5@96h ZnONPs (0.18g) or the LD5@96h B-ZnCl2 (0.03g), respectively. In sub-acute experimentation, five rats were taken from each group after 1, 3, [91] 7, 14, and 21 days, euthanized and quickly dissected. The brain, liver, kidneys, heart, spleen, and lungs were excised and prepared for the metal assay. Aluminum ion content was measured according to Smichowski et al. (2005) with the aid of an Inductively Coupled Plasma Atomic Emission Spectrometer (ICPAES). The Al levels were expressed as µg/g dry wt. Statistically, the Kolmogorov-Smirnov test indicated that the present data was normally distributed, and therefore the parametric statistical analyses were used. Two-ways analysis of variances was applied to analyze the effect of nano- and bulk zinc on the LD50@24h of Al2O3NPs as well as the bioaccumulation of Al in the studied tissues, and their interactions during acute experimentation. In the sub-acute experiments, one-way ANOVA was applied to analyze the effect of the experimental periods (1, 3, 7, 14, and 21 days) on the accumulation of Al in each organ, followed by Duncan’s multiple range test (DMRT) and Tukey’s test post ANOVA hoc analysis. Regression analysis and Spearman’s correlation coefficient (r) were used to fit the relationships between the different studied variables. All the results were expressed as a mean ± standard error of the mean (SEM). The current results revealed that the B-ZnCl2 was more toxic than ZnONPs and Al2O3NPs, and this was indicated by its lethality percentile dosages that were greater than ZnONPs and Al2O3NPs. Additionally, the B-ZnCl2 and ZnONPs had a high affinity to increase the median lethal dose values of Al2O3NPs at 24h, and this confirmed that zinc reduces the nano alumina lethality. In other words, the average values of the median lethal dose at 24h (LD50@24h) of nano alumina were increased in response to both forms of zinc salts at 24, 48, 72, and 96 h. These results revealed their capability to reduce the Al2O3NPs lethality. In conclusion, either the nano- or the bulk zinc had the ability to reduce the bioaccumulation of Al inside the cells and [92] their organelles as reflected by the increased average values of the lethality percentile dosages of nano alumina. Accordingly, the potential full lethality of nano alumina is reduced which may help in reducing the notorious impact of their accumulation in living tissues. The statistical analysis revealed that ZnONPs are more efficient than B-ZnCl2 in diminishing the bioaccumulation and lethality of Al2O3NPs, thereby reducing their toxicity |