الفهرس 
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Abstract
Mucositis induced by radiotherapy is defined as the reactive inflammation of the oral and oropharyngeal mucous membrane during radiotherapy in the head and neck region. It is characterized by atrophy of squamous epithelial tissue, absence of vascular damage, and an inflammatory infiltrate concentrated at the basement membrane. Oral Mucositis is considered one of oral side effects that develop early during radiotherapy.
Given the regenerative and anti-inflammatory properties of stem cells; the current work aimed to investigate the effect of intravenous infusion of bone marrow derived mesenchymal stem cells (BM-MSCS) before or after head and neck radiation in ameliorating the side effects of ionizing radiation.
Five rats served as control group (NC) and 45 five rats received a single radiation dose 13 Gy to head and neck region ,then they were equally divided into 3 groups: group II (PC) Consisted of 15 rats that and served as (Positive Control), group III (Pre-MSCs) Consisted of 15 rats in which BM-MSCs (5x106 cells) were infused one hour before irradiation (single dose 13Gy) and considered the test group for (Pre-radiation Stem Cell infusion) and group IV (Post-MSCs) Consisted of 15 rats in which BM-MSCs (5x106 cells) were infused on day 2 after irradiation (single dose 13Gy) and considered the test group for (Post-radiation Stem Cell infusion).
For Groups II, III, and IV; 5 rats were weighted then sacrificed every 3, 5, 7 days after radiation macroscopic examination of area of mucositis and histological and immunohistochemical analysis using anti PCNA, Caspase antibodies.
The reduction in body weight was observed in all irradiated groups (GII, II, IV) from baseline to 3 days and from 3 to 5days while mean body weight of non-radiated rats in group I was almost the same through the study period. Between 5 and 7 days increase in body weight was observed in group II and III only but the differences between groups was significant only from base to 3 days and from 5 to 7 days. The lowest reduction in body weight was observed in group IV in the first 3 days of radiation and between 3 and 5 days followed by group II but was significantly different from other groups in first interval only.
A gradual decrease in mean area of mucositis was noted between 3 days and 5 days and between 5 days and 7 days in group II, group III and group IV. However, the area of mucositis remains the lowest in group IV by the end of each interval but statistically there was no significance difference between groups regarding area of mucositis at any interval.
H & E stained sections of the irradiated tongue revealed reduction in epithelial thickness in 3 and 5 days in all groups compared to normal control. However by the end of 7 days in group IV the epithelium almost recovered its normal thickness. While in group III slight increase in thickness more than after 5 days was observed, but was still lower than normal control and group IV. In group II gradual increase in epithelial thickness was attained after 7 days and was very comparable to that of group III.
Obvious reduction PCNA in 3 and 5 days was observed in group II, III and IV then gradually raised at 7 day. However, the highest increase in mean area fraction of PCNA was seen in treated group IV post radiation followed by group II, then group III. The expression of Caspase was significantly higher in all irradiated group than normal control and gradually decreased at 3, 5 and 7 days in group II while in Groups infused with stem cells it increased gradually but was still lower than group II by the end of each interval however doesn’t reach normal. Moreover, the percentage reduction in Caspase expression was significantly higher in post infusion group than pre-infusion group between 5 and 7 days in contrast to the percentage increase which was significantly lower between 3 and 5 days
The injection of BM-MSCs seemed to promote proliferation of the epithelial cells when injected after radiation compared to pre-infusion timing. Thus showed positive effect in protecting oral mucosa from the side effects of head and neck radiotherapy; as manifested by reduction in area of mucositis and rapid restoration of oral function confirmed by increase in body weight