Mika Tanaka

Acceleration of Regeneration of Mucosa in Small Intestine Damaged by Ionizing Radiation Using Anabolic Steroids

Abstract Damage to intestine is a serious problem after accidental radiation exposure. To examine substances to ameliorate damage by postirradiation administration, we focused on the regeneration process after irradiation of the intestine. Using experimental systems, the effects of clinically used sex hormones on regeneration were compared. An anabolic steroid, nandrolone (19-nortestosterone), stimulated proliferation in IEC-6 epithelial cells. A single injection of 19-nortestosterone ester with prolonged action into mice 24 h after abdominal irradiation at a lethal dose of 15.7 Gy showed significant life-saving effects. Regeneration indicators such as microcolonies of BrdU-incorporated cells at day 5 and c-myb mRNA expression levels at day 4 were enhanced by 19-nortestosterone administration. In contrast, high concentrations of estradiol inhibited growth of IEC-6 cells. Treatment of abdominally irradiated mice with estradiol ester decreased levels of regeneration indicators and survival. These results suggest the effectiveness of the anabolic steroid as well as the importance of manipulation of steroid receptors in the recovery of mucosa damaged by radiation.

Comparison of Absorbents and Drugs for Internal Decorporation of Radiocesium: Advances of Polyvinyl Alcohol Hydrogel Microsphere Preparations Containing Magnetite and Prussian Blue.

Radiocesium nuclides, used as a gamma ray source in various types of industrial equipments and found in nuclear waste, are strictly controlled to avoid their leakage into the environment. When large amounts of radiocesium are accidentally incorporated into the human body, decorporation therapy should be considered. Although standard decorporation methods have been studied since the 1960s and were established in the 1970s with the drug Radiogardase(®) (a Prussian blue preparation), application of recent advances in pharmacokinetics and ethical standards could improve these methods. Here we designed a modern dosage form of hydrogel containing cesium-absorbents to alleviate intestinal mucosa irritation due to the cesium-binding capacity of the absorbents. The effectiveness of the dosage form on fecal excretion was confirmed by quantitative mouse experiments. The total cesium excretion rate of the crystal form (1.37±0.09) was improved by the hydrogel form (1.52±0.10) at the same dose of Prussian blue, with a longer gastrointestinal tract transit time. Using a mouse model, we compared the effects of several drugs on fecal and urinary excretion of internal cesium, without the use of absorbents. Only phenylephrine hydrochloride significantly enhanced cesium excretion (excretion rate of 1.17±0.08) via the urinary pathway, whereas none of the diuretic drugs tested had this effect. These findings indicate that modifying the dosage form of cesium absorbents is important for the decorporation of internal radiocesium contamination.

Pharmaceutical drugs supporting regeneration of small-intestinal mucosa severely damaged by ionizing radiation in mice

Accidental exposure of the abdomen to high-dose radiation leads to severe consequences initiated by disruption of the mucosa in the small intestine. Therapeutic options are limited, even though various treatments have been investigated, particularly in the field of regenerative therapy. In order to identify readily available treatment methods, we included several current pharmaceutical drugs, for which the clinical trials have already been completed, in tests on mice that had undergone severe mucosal damage by radiation. The drugs were injected into mice 24 h after exposure to 15.7 Gy X-rays. The effects of the drugs on the damaged mucosa of the small intestine were evaluated using early regeneration indices [the expression of c-myb mRNA, and proliferation of epithelial cells in the form of microcolonies (MCs) by Days 4 and 5 post-irradiation] and the survival rate of the mice. Enhancement of mucosal regeneration at Day 4 (c-myb: P < 0.01, MC: P < 0.05) and improvement of the survival rate (P < 0.05) were observed when a clinical dose of gonadotropin, a stimulator of androgen, was injected. Similarly, a clinical dose of thiamazole (which prevents secretion of thyroid hormone) stimulated mucosal growth by Day 5 (c-myb: P < 0.01, MC: P < 0.05) and also improved the survival rate (P < 0.05). The nonclinical drugs histamine and high-dose octreotide (a growth hormone antagonist) also gave significant survival-enhancing benefits (P < 0.01 and P < 0.05, respectively). These results can be used to construct therapeutic programs and applied in various experimental studies to control the regeneration of damaged mucosa.

Quantification of damage due to low-dose radiation exposure in mice: construction and application of a biodosimetric model using mRNA indicators in circulating white blood cells

Abstract Biodosimetry, the measurement of radiation damage in a biologic sample, is a reliable tool for increasing the accuracy of dose estimation. Although established chromosome analyses are suitable for estimating the absorbed dose after high-dose irradiation, biodosimetric methodology to measure damage following low-dose exposure is underdeveloped. RNA analysis of circulating blood containing radiation-sensitive cells is a candidate biodosimetry method. Here we quantified RNA from a small amount of blood isolated from mice following low-dose body irradiation (<0.5 Gy) aimed at developing biodosimetric tools for situations that are difficult to study in humans. By focusing on radiation-sensitive undifferentiated cells in the blood based on Myc RNA expression, we quantified the relative levels of RNA for DNA damage-induced (DDI) genes, such as Bax , Bbc3 and Cdkn1a . The RNA ratios of DDI genes/ Myc in the blood increased in a dose-dependent manner 4 h after whole-body irradiation at doses ranging from 0.1 to 0.5 Gy (air-kerma) of X-rays, regardless of whether the mice were in an active or resting state. The RNA ratios were significantly increased after 0.014 Gy (air-kerma) of single X-ray irradiation. The RNA ratios were directly proportional to the absorbed doses in water ranging from 0.1 to 0.5 Gy, based on gamma-irradiation from 137 Cs. Four hours after continuous irradiation with gamma-rays or by internal contamination with a beta-emitter, the increased RNA ratios resembled those following single irradiation. These findings indicate that the RNA status can be utilized as a biodosimetric tool to estimate low-dose radiation when focusing on undifferentiated cells in blood.