Effect of Tirapazamine and Mild Temperature Hyperthermia on the Recovery from Radiation-Induced Damage in Pimonidazole-Unlabeled Quiescent Tumor Cell Population

The aim in this study is to examine the effect of tirapazamine (TPZ) and mild temperature hyperthermia (MTH) on the repair of radiation-induced damage in pimonidazole-unlabeled quiescent (Q) tumor cells. Labeling of proliferating (P) cells in C57BL/6J mice bearing EL4 tumors was achieved by continuous administration of 5-bromo-2-deoxyuridine (BrdU). Tumors were irradiated with γ-rays at 1 h after the administration of pimonidazole followed by TPZ treatment or MTH. Twenty-four hours later, assessment of the responses of Q and total (= P + Q) cells were based on the frequencies of micronucleation and apoptosis using immunofluorescence staining for BrdU. The response of the pimonidazole-unlabeled tumor cell fractions was assessed by means of apoptosis frequency using immunofluorescence staining for pimonidazole. With γ-rays only, the pimonidazole-unlabeled cell fraction showed significantly enhanced radio-sensitivity compared with the whole cell fraction more remarkably in Q cells than total cells. However, a significantly greater decrease in radio-sensitivity in the pimonidazole-unlabeled than the whole cell fraction, evaluated using a delayed assay, was more clearly observed in Q cells than total cells. Post-irradiation MTH more remarkably repressed the decrease in radio-sensitivity in the Q cell than the total cells. Post-irradiation TPZ administration produced a large radio-sensitizing effect on both total and Q cells, especially on Q cells. On the other hand, in pimonidazole-unlabeled cell fractions in both total and Q cells, TPZ suppressed the reduction in sensitivity due to delayed assay much more efficiently than MTH, whereas no radio-sensitizing effect was produced. Not only through suppressing the recovery from radiation-induced damage but also through radio-sensitizing effect, post-irradiation TPZ administration is very useful for repressing the increase in the difference in radio-sensitivity due to the delayed assay not only between total and Q tumor cells but also between the pimonidazole-unlabeled and the whole cell fractions within the total and Q tumor cells.

Exercise induces tissue hypoxia and HIF-1α redistribution in the small intestine

Background'. Exercise induces blood flow redistribution among tissues, leading to splanchnic hypoperfusion. Intestinal epithelial cells are positionedbetween the anaerobic lumen and the highly metabolic lamina propria with an oxygen gradient. Hypoxia-inducible factor (HIF)-la is piv・otal in the transcriptional response to the oxygen flux.Methods: In this study, the pimonidazole hydrochloride staining was applied to observe the tissue hypoxia in different organs, which might beaffected by the blood flow redistribution. The HIF-la luciferase reporter ROSA26 oxygen-dependent degradation domain (ODD)-Luc/+ mousemodel (ODD domain-Luc;female, n = 3—6/group) was used to detect the HIF-la expression in the intestine. We used 3 swimming models: mod・erate exercise for 30 min, heavy-intensity exercise bearing 5% bodyweight for 1.5 h, and long-time exercise for 3 h.Results'. We found that 1 session of swimming at different intensities could induce tissue hypoxia redistribution in the small intestine, colon, liverand kidney, but not in the spleen, heart, and skeletal muscle. Our data showed that exercise exacerbated the extent of physiological hypoxia in thesmall intestine. Next, using ODD-Luc mice, we found that moderate exercise increased the in vivo HIF-la level in the small intestine. The post・exercise HIF-la level was gradually decreased in a time-dependent manner. Interestingly, the redistribution of tissue hypoxia and the increase ofHIF-la expression were not related to the exercise intensity and duration.Conclusion'. This study provided evidence that the small intestine is the primary target organ for exercise-induced tissue hypoxia and HIF-laredistribution, suggesting that HIF-la may be a potential target for the regulation of gastrointestinal functions after exercise.