19.4.2Plants

Aged rice seeds treated by cerium nitrates enhanced the activities of enzymes associated with reduction of oxidative stress, thus increasing the respiration rate. They were added in fertilizers and increased harvest [42]. Supplementation of 0.5Ð10 mM cerium nitrate to the culture medium signiÞcantly increased the height, the dry weight and average number of ßower bolting [43]. Using 7 nm CeO2 nanoparticles to treat corn, tomato, cucumber, and alfalfa seeds signiÞcantly reduced germination rate but root growth and shoot elongation were signiÞcantly promoted. Furthermore, X-ray absorption spectroscopy (XAS) revealed that the nanoparticles were within root seedlings. ICP-OES (inductively coupled plasma-optical emission spectroscopy) demonstrated that nanoparticles remained in the same oxidation state (+4) after uptake by roots [44].

19.4.3Medical Usage

19.4.3.1Radioprotectants

Radiation is one of the commonly used strategies for cancer treatment. It is unique and efÞcient in killing the cancer cells, but new free radicals are produced during radiation treatment and are harmful to the normal cells near the treated site [34]. Amifostine is currently the only free radical scavenger for clinical applications to protect normal cells against radiation, but one major disadvantage of amifostine is its very short half-life in serum [34]. Radiation at a dose of 10 Gy to an immortalized normal breast epithelial cell line, CRL8798, and human breast carcinoma cell, MCF-7, caused 40Ð50% of cell death when cell viability was measured at 24 and 48 h. If the cells were pretreated with 10 nM CNPs 24 h prior to irradiation, CRL8798 cells were almost completely protected, whereas there was no statistically signiÞcant protection for MCF-7 cells. CNP concentrations ranging from 0 to 5 mM did not have signiÞcant toxic effects on CRL8798 cells, while a slight effect on MCF-7 cells was induced when concentrations were higher than 50 nM [34]. This suggests that CNPs can act as effective radioprotectants for normal tissues. Their long-term retention suggests that CNPs will be better than amifostine for protection of normal cells during radiation therapy [34]. In mouse models, nanoceria prevent high dose radiation-induced pneumonitis [45]. Dextran-coated cerium oxide nanoparticles (DNC) have been shown to be unable to regenerate at pH 4.0 and maintain a relatively high amount of Ce4+ for 10 days after H2O2 addition [21]. Lung (A-549) and breast cancer (BT-474) cells have been shown to upregulate glycolytic activity and lactic acid production which results in an acidic microenviroment [46]. Treatment with DNC before administering H2O2 and other biological relevant radicals produces no protection of the cancer cells but long-term cytoprotection to nontransformed surrounding normal cells [21].