الفهرس 
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Abstract
Humans are exposed to radiation that comes from natural sources and also from man-made sources such as atomic energy stations and the scientific and medical instruments and equipments. Many studies set down the deleterious effects of radiation on the body systems, tissues and cells.
It is well documented that part of the biological effects of radiation is the direct result of free radicals produced in the watery medium, and the other part is due to direct ionization of critical biological molecules.
The present study lies in the domains of molecular biology and biochemistry. One of the targets of the present study – besides clarifying the direct effects of radiation – is to pinpoint its indirect effect, i.e. its effect on a body part that was not directly exposed to irradiation. This is known as the ”bystander effect”.
Besides, the present study aims at evaluating the probable protective effect of the shark cartilage extract against the notorious biological effects of irradiation.
In the present study, 96 male albino rats were divided into 4 groups, each group of 24 rats:
Group I: The controls, not exposed to ionizing radiation and
were not dieted on shark cartilage.
Group II: The animals were dieted on shark cartilage extract.
Group III: Using special devices, the animals’ right femurs were exposed to ionizing radiation at a sublethal dose of 100 rads (1 Gy) without dieting on shark cartilage extract.
Group IV: The animals were dieted on shark cartilage extract and using special devices, the animals’ right femurs were exposed to ionizing radiation at a sublethal dose of 100 rads (1 Gy).
The control group was dissected parallel to the treated groups. Shark cartilage (SC) suspension was administrated to rats of group II for 15 days and half of them were dissected. The rest were given SC for an additional week and then dissected.
In group III, the animal subgroups were dissected one and seven days after cessation of radiation. Rats of group IV were given SC daily for 14 days before irradiation and half of them were dissected after 1 additional dose. For the other half, SC continued 7 days after the radiation dose and then they were dissected. 6 rats of each subgroup were used for getting the RNA specimens and the other 6 were used for DNA.
The molecular studies were performed on whole bone marrow cell populations, while the biochemical studies were performed on blood plasma. Polymorphisms of exons 5 and 6 of gene p53 were detected by using PCR-SSCP analysis. The analysis showed that bystander effect significantly induced polymorphisms of exons 5 and 6 of gene p53 in bone marrow cells in non-irradiated femurs. The polymorphisms in exons 5 and 6 induced by bystander effect of gamma radiation decreased in 7 days period; whereas polymorphisms in exons 5 and 6 that were induced by direct effect continued to be significantly elevated compared to the control group.
Both the direct and the bystander effects induced polymorphisms of exons 5 and 6 of gene p53 in bone marrow cells in non-irradiated femurs decreased with administration of SC. This suggests the possible role of SC as an anti-mutagenic material.
The detection of p53 mRNA expression by using semi-quantitative PCR yielded negative results although primers were verified using other types of organ tissues (liver and brain tissues). This may be owing to the very low expression of gene p53 in bone marrow cell populations.
Biochemical investigations included nitrite concentration (as an indicator of nitric oxide concentration), MDA level (as an indicator of lipid peroxidation) and protein carbonyls (as an indicator of protein oxidation). Both MDA level and protein carbonyls are indicators of degree of oxidative damage to biological molecules. Also, catalase activity assay was carried out as an indicator of cell anti-oxidant activity and hydrogen peroxide level.
Nitric oxide and protein carbonyl levels in blood plasma were significantly increased by radiation and decreased again by shark cartilage administration. MDA levels in plasma also decreased significantly under the effect of shark cartilage administration if compared with the animal group exposed to radiation only. However, catalase activity in blood plasma showed no significant difference between the animal groups. The decrease observed in reactive nitrogen species and products of free radicals damage to the biological molecules indicate that SC can be used as an anti-oxidant.
Conclusion:
The present study shows that direct as well as bystander effects of gamma radiation can cause polymorphisms in exons 5 and 6 of the gene p53 in whole bone marrow cell population. Also, the direct effect persisted longer than the bystander effect. Nitric oxide was significantly increased in the blood plasma of femur-irradiated rats.
SC administration induced anti-mutagenic and anti-oxidant effects. It decreased polymorphisms in exons 5 and 6 of the gene p53 in whole bone marrow cell population of both radiated and non-irradiated femurs of rats. SC also decreased NO, MDA and protein carbonyls levels in the blood plasma. Catalase levels showed no significant difference between the animal groups of the present study.