Relative biological effectiveness of fast neutrons for apoptosis in mouse hair follicles

Abstract

This study compared the effects of high linear energy transfer (LET) fast neutrons on the induction of apoptosis in the hair follicles of ICR mice with those of low LET (60)Co gamma-rays. The changes that occurred from 0 to 24 h after exposing the mice to either 2 Gy of gamma-rays (2 Gy/min) or 0.8 Gy of neutrons (94 mGy/min, 35 MeV) were examined. The maximum frequency was found at 12 h (gamma-rays) or 8 h (neutrons) after irradiation. The mice that received 0-8 Gy of gamma-rays or 0-1.6 Gy of neutrons were examined 8 h after irradiation. The dose-response curves were analyzed using the best-fit curve model. The dose-response curves were linear-quadratic, and a significant relationship was found between the frequency of apoptotic cells and the dose. The morphological findings in the irradiated groups were typical apoptotic fragments in the matrix region of the hair follicle, but the spontaneous existence of apoptotic fragments was rarely observed in the control group. In the presence of an apoptosis frequency between 2 and 14 per follicle, the relative biological effectiveness values of neutrons in small and large follicles were 2.09 +/- 0.30 and 2.15 +/- 0.18, respectively.

Fig. 1

Photomicrograph of small (A, C) and large (B, D) hair follicles of mice sacrificed 8 h after irradiation. The apoptotic cells, which occur predominantly in the matrix region of the follicle, were easily recognized from the condensation of their cytoplasm and nuclear chromatin. A and B; H&E staining, C and D; TUNEL staining, ×400.

Fig. 2

Variation in apoptotic cell frequency in small (□) or large (▪) hair follicle with time after whole-body irradiation of ICR mice with 0.8 Gy of fast neutrons (A) and 2.0 Gy of γ-rays (B). Results are presented as means ± SD from four mice in each group.

Fig. 3

Dose-response for fast neutrons (▪) and γ-rays (•) induced apoptotic cells in small (A) or large (B) hair follicle. The lines represent the results of a linear-quadratic fit through the data indicated in the figure.