Inter-strain variance in late phase of erythematous reaction or leg contracture after local irradiation among three strains of mice.
RadGenomics Project, National Institute of Radiological Sciences. Chiba-shi, Chiba, Japan
Aim Radiotherapy for the treatment of cancer are limited by the tolerance of normal tissues within the treatment area. It is of significance, from the point of view of mechanism, whether skin reaction after irradiation might be related with genetic variance. In this study, late phase of erythema, as a sequential endpoint of radiation effects on ski, and leg contracture as an endpoint for slowly responses of normal tissues was investigated among three strains of mice. We also examined the expression profiles of several genes to gain insights into inter-strain differences in radiosensitivity. Methods Female, 12 weeks old mice of the inbred strains A/J, C57BL/6J, and C3H/HeMs, were used through experiments. The mice were irradiated using a beam of Cs-137 gamma rays at graded doses ranging from 10 to 60 Gy. The late skin reaction following irradiation was scored every other day for 300 days after irradiation, using the arbitrary scale. The scoring system consisted of 10 degrees, ranging from 0.5 to 3.5. A measure of the Ågtotal biological effectÅh in the time window was obtained by the area under the curve (AUC). Leg contracture assay was performed by measurement of extensibility of the treated and untreated control hind legs of each mouse. Microarray analysis was done for skin irradiated to gain insight of mechanism of radiation injury using Agilent's Mouse cDNA Microarray Kit (Agilent Technologies, Palo alto, CA). Data were further processed using the Rosetta Resolver Data Analysis System (Rosetta Biosoftware, Kirkland, WA). Differentially expressed genes were selected based on an up- or down-regulation value of over 2-fold. Gene expression was quantified by quantitative RT-PCR assay. Results The three different strains showed various degrees of susceptibility to irradiation. A dose-response analysis using the average of AUC at each dose group resulted in various regression lines among three strains. Large interstrain differences were also detected in the lengths of contracture. After screening with microarray assay, real-time PCR validated the quantitation of cDNA for several genes from three strain mice and several genes characteristically appeared. The expression of Alad, Cap1, Il18 and Rad51ap1 increased in A/J, and C3H/HeMs, and that of Mmp12 increased 12 hours after irradiation in A/J mice. The expression of Ang and that of Rad51ap1 increased 72 and 1 hours after irradiation in C3H/HeMs mice respectively. Conclusions The continuum model of tissue injury supports the investigation of mechanism of radiosusceptibility. Our data suggest that genetic factors cause obvious variations in severity of damage after irradiation.
Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Nice, France; February 7 - 10, 2004; in oral session 892 (Genetic predisposition - Part II).