Elevated frequency of sister chromatid exchanges of lymphocytes in sarin-exposed victims of the Tokyo sarin disaster 3 years after the event

Abstract

We previously reported that the frequency of sister chromatid exchanges (SCEs) among victims of the Tokyo subway sarin disaster was significantly higher than that of controls 2–3 months after the disaster. It has been reported that the victims were also exposed to the by-products generated during sarin synthesis, i.e., diisopropyl methylphosphonate (DIMP), diethyl methylphosphonate (DEMP) and N,N-diethylaniline (DEA) during the disaster and we previously found that DIMP, DEMP and DEA induced a significant SCE increase in human lymphocytes in vitro. To monitor the genetic aftereffects of the sarin exposure, SCEs of peripheral blood lymphocytes were measured in fire fighters and police officers involved in the disaster 3 years after the event. We found that the frequency of SCEs was still significantly higher in the exposed subjects than the controls, suggesting a risk of the genetic aftereffects of the sarin exposure. We further found a significant positive correlation between the frequency of SCEs and the inhibition of serum cholinesterase activity in the exposed subjects, suggesting that the elevated frequency of SCEs is related to the sarin exposure. On the other hand, there was no significant difference in natural killer activity between the exposed and the controls.

Introduction

On March 20, 1995, the nerve gas sarin (isopropylmethylphosphonofluoridate; CSA registry No. 107-44-8) was released by members of the Aum cult on subway trains in the Tokyo metropolitan area, killing 12 people and injuring over 5000 (Masuda et al., 1995, Nozaki and Aikawa, 1995). We previously found that the frequency of sister chromatid exchanges (SCEs) was significantly higher in the victims of the attack than in controls 2–3 months after the disaster (Li et al., 1998), suggesting a risk of the genetic aftereffects of sarin exposure. Sarin is an organophosphorus nerve agent, and a strong cholinesterase (ChE) inhibitor (Richardson and Gangolli, 1994). Although the genotoxicity of sarin was found to be negative using animal cells in vitro and in the Ames test (Klein et al., 1987, Nasr et al., 1988, Richardson and Gangolli, 1994), there has been no report on SCEs induced by sarin using human lymphocytes. In the Tokyo sarin disaster, the materials released were thought to contain not only sarin, but also by-products generated during its synthesis such as diisopropyl methylphosphonate (DIMP) and diethyl methylphosphonate (DEMP) (Minami et al., 1997a, Ogawa et al., 2000, Hui and Minami, 2000). And we also found that DIMP and DEMP significantly inhibited ChE activity in vitro (Minami et al., 1997b). In addition, a high concentration (37%) of N,N-diethylaniline (DEA) was detected as a stabilizing reagent in the plastic bags left in the subway cars: these bags were 35% full of sarin (Ogawa et al., 2000). Therefore, the victims were probably exposed to DEA as well. We also found that DIMP, DEMP and DEA induced a significantly higher rate of SCE in human lymphocytes in vitro (Li and Minami, 1997, Li et al., 1998), suggesting that DIMP, DEMP and DEA partially contribute to the elevated SCE levels in the victims. To monitor the genetic aftereffects of sarin exposure, SCEs of peripheral blood lymphocytes were measured 2 years and 10 months to 3 years and 9 months after the attack in the fire fighters and police officers who rescued the victims. These rescuers were dispatched to the sites of the accident and also exposed to sarin, primarily or secondarily and hospitalized due to poisoning from sarin. Since we previously found that DIMP, DEMP and DEA markedly decreased human and murine natural killer (NK) and/or cytotoxic T lymphocyte (CTL) activities (Li et al., 2000a, Li et al., 2000b), we also measured NK activity in the exposed subjects to monitor the aftereffects of sarin on NK function.