الفهرس 
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Abstract
Iron Oxide Nanoparticles (IONPs) are among those most widely manufactured on a global scale. They have widespread applications in many fields including food industry, electronic field, environmental remediation and nanomedicine. Human exposure to IONPs is getting more day-by-day through various routes; therefore their potential toxicity effects should be studied.
The nanoparticles have different physical and chemical properties compared to their conventional bulk counterparts, even if they are of the same composition, which might alter their bioactivity. Their ability to induce toxicity has been attributed to their increased surface reactivity. The smaller the particles are, the more surface they have per unit mass and the more reactive they are in the cellular environment.
Investigating the potential hazardous effect of IONPs on the thyroid follicular cells of adult male albino rats has been a point of interest in the recent research work.
Oxidative stress has been suggested to be the main mechanism of toxicity caused by the NPs including the iron oxide ones. Therefore, using antioxidants may play a role in ameliorating their potential hazardous effects.
Beta-carotene is a naturally occurring carotenoid. It has various important properties making it suitable to act as antioxidant, anti-inflammatory agent, immune enhancer and anticancerous agent. It can scavenge free radicals and inactivate ROS and prevent oxidation of membrane lipids, oxidative modification of proteins and DNA fragmentation. The possible protective role of beta-carotene against IONPs’ toxic effects on the thyroid follicular cells also needed further studies.
The aim of the present study was to investigate the possible histological alterations that might occur in the thyroid follicular cells of adult male albino rats following administration of IONPs for 15 days. In addition, it attempted to throw the light on the possible protective role of Beta-carotene as an antioxidant, when administered concomitantly with IONPs.
The present study was carried out on 40 adult male albino rats, each with an average weight of 150-200 gm. The rats were divided randomly into 4 equal groups as follows:
• group I: 10 rats were used as a control group, that was further subdivided randomly into 2 subgroups:
Subgroup IA: 5 rats, each received distilled water orally for 15 days.
Subgroup IB: 5 rats, each received 2 ml corn oil for 15 days.
• group II: 10 rats, each received oral beta-carotene at a dose of 40 mg/kg body weight/day dissolved in 2 ml corn oil for 15 days.
• group III (the treated group): 10 rats, each treated with oral administration of 300 mg/kg body weight/ day IONPs dissolved in one ml of distilled water for 15 days.
• group IV (the protected group): 10 rats, each treated with IONPs as in group III and simultaneously received oral beta-carotene as in group II for 15 days.
The oral route was done by gastric gavage. Each group was sacrificed under anesthesia as scheduled, 24 hours after the last administration. The following studies were done:
I. Biochemical study:
Trunk blood samples were collected and processed for hormonal assay.
II. Histological study:
Thyroid gland of each sacrificed albino rat was dissected out carefully.
1. One lobe was cut into small pieces (1-2 mm3) fixed immediately in 3% phosphate buffered glutaraldehyde solution and processed to get ultrathin sections for transmission electron microscopic examination.
2. The other lobe was fixed in 10% neutral buffered formalin and processed to get 6 μm thick paraffin sections. These sections were stained with hematoxylin and eosin (H&E) stain for light microscopic examination.