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Frequency of sister chromatid exchanges (SCEs), which has been considered an index to the synthetic and sharp genotoxic and clastogenic potencies, was examined by using the infant lymphocytes postnatal of around ten months, in order to evaluate the genotoxic or clastogenic potency of exposures to PCBs and dioxins through the breast milk. SCE frequency (mean±S.D.) as the control culture treated with the solvent, DMSO, alone (SCEcontrol) was 8.3±1.1/cell and that as the culture treated with 7,8-benzoflavone (SCEANF) was 11.9±1.5/cell. In addition, the difference between SCEANF and SCEcontrol, that is, A SCEs was calculated 3.6 ± 1.5/cell. The intake of PCBs (mean ± S.D.) through the breast milk in these infants was 133 ± 85 mg/kg body weight and that of dioxins 24±13 TEQ-ng/kg body weight. PCBs intake in the average was about 5,500 times greater than that of dioxins. We however, could not find any significant effect of PCBs on the frequencies of SCEs. Dioxins, on the contrary, showed a significant negative relationship to the frequency of A SCEs. Therefore, exposure to dioxins through the breast milk seemed to elicit some genotoxic or clastogenic effects on Japanese general infants postnatal of around ten months., 姉妹染色分体交換(Sisterchromatid exchanges,SCEs)はこれまで総合的で鋭敏な遺伝毒性あるいは染色体傷害性の指標として知られている. この研究では授乳によるPCBsとダイオキシン類への曝露と遺伝毒性の関係を調べる目的で, 生後10ケ月前後の一見健康な乳児の末梢血リンパ球細胞のSCEs頻度とPCBsやダイオキシン類への曝露との関係を統計学的に解析した. 溶媒のみ処理したコントロール群のSCEs頻度(SCEcontrol)(平均値± 標準偏差,以下同様)は8.3±1.1/細胞であり, 7,8-ベンゾフラボン(ANF)処理した場合のそれ(SCEANF)は11.9±1.5/細胞であった. また両者の差, つまり, △SCEs(SCEANF-SCEcontro1)は3.6±1.5/細胞であった. また, これらの乳児のPCBsの母乳からの摂取量は133±85mg/kg体重であり, ダイオキシン類では24±13TEQ-ng/kg体重であった. したがって授乳によるPCBsの摂取量はダイオキシン類よりも約5,500倍多かった. PCBへの授乳による乳児の曝露量はダイオキシン類よりもはるかに多いにもかかわらず, PCBsとSCEs頻度との関連性はSCEcontrol, SCEANFおよび△SCEsのいずれに対しても認められなかった. しかしダイオキシン類の場合には, 統計的に有意ではないけれども母乳からの摂 取量が増えるにしたがってSCEcontrolが上昇し, また逆にSCEANFは減少する傾向を示した. その結果, △SCEsの有意な低下が観察された. このようなSCEs頻度への影響がどのような臨床上の疾病と関連するのか現時点では定かでないが, ダイオキシン類への授乳期の曝露が次世代に対して何らかの遺伝毒性あるいは染色体傷害性作用を有する可能性が示唆されたのであり, 今後, さらに詳細な研究を行う必要がある.

Changes in the frequency of sister chromatid exchanges (SCEs) in cultured mammalian cells have been considered as indices to the synthetic and sharp genotoxic and clastogenic potencies. Frequency of SCEs in cultured lymphocyte obtained from infants postnatal of around ten months was examined to evaluate the genotoxic or clastogenic potency of lactational exposures to some organochlorine pesticides such as HCHs, DDT and chlordane in this study. Frequency (median, min. ～ max.) of SCEs as the control culture treated with the solvent, DMSO, alone (SCE control) was 8.0/cell, 6.5 ～ 12.4/cell, that as the culture treated with 7,8-benzoflavone (SCEANF) was 11.8/cell, 9.1 ～ 15.6/cell and the difference between SCEANF and SCEcontrol, that is, Δ SCEs was 3.9/cell, 0.2 : 7.2/cell. Lactational exposures (median, min. ～ max.) to the three organochlorine pesticides were as follows : HCHs ; 341 mg/kg body weight, 43 ～ 1449 mg/kg body weight, DDT ; 272 mg/kg body weight, 33 ～ 1361 mg/kg body weight and chlordane ; 69 mg/kg body weight, 13 ～ 379 mg/kg body weight. The median exposure level to chlordane through the breast milk was one fourth to one fifth times lower than that to HCHs or DDT and probably due to such small amounts of it's intake, we could not find any correlation of chlordane with frequencies of SCEcontrol, SCEANF and Δ SCEs in cultured lymphocytes of Japanese infants postnatal of about ten months. In the meantime, frequencies of SCEcontrol and SCEANF showed increasing and decreasing tendencies with the increasing exposure to DDT and also HCHs through the breast milk. In consequence, the frequency of Δ SCEs was significantly lowered. Therefore, lactational exposure to DDT and HCHs seemed to elicit some genotoxic or clastogenic effects on Japanese general infants at ages of around the months. These compounds were also considered rather potent S-dependent clastogens than non-S-dependent ones. So, further detailed studies are needed not only to get conclusive findings but also from this viewpoint., 総合的で鋭敏な遺伝毒性指標として知られている姉妹染色分体交換(Sisterchromatid exchanges,SCEs)頻度を用いて, 授乳によるHCHs, DDTおよびクロルデンへの曝露と乳児リンパ球細胞のSCEs頻度との関係を数理統計学的に調べた. リンパ球細胞の培養中に溶媒(DMSO)のみ処理したコントロール群のSCEs頻度すなわちSCEcontro1(中央値,最小値～ 最大値,以下同様) は8.0/細胞, 6.5～12.4/細胞, 7,8-ベンゾフラボン(ANF)処理した場合のSCEs頻度, SCEANFは11.8/細胞, 9.1～15.6/細胞, また両者の差SCEANF-SCEcontrol, △SCEsは3.9/細胞, 0.2～7.2/細胞であった. 母乳からの有機塩素系農薬の摂取量は次のようである. HCHs;341mg/kg 体重, 43～1449mg/kg 体重, DDT;272mg/kg 体重, 33～1361mg/kg 体重, クロルデン;69mg/kg 体重, 13～379mg/kg 体重.クロルデンの授乳による曝露量は中央値で比較するとHCHsとDDTの4分の1から5分の1程度と少なく, SCEs頻度との関係も認められなかった. 一方, HCHsとDDTについては母乳からのこれらの農薬の摂取量が増加するにつれて有意ではないけれどもSCEcontrolが上昇し, 逆にSCEANFが減少する傾向が観察された. その結果, いずれの農薬でも△SCEs頻度の有意な低下が認められた. このようなSCEsへの影響が臨床上どのような意義があるのか不明であるが, HCHsやDDTへの授乳期の曝露が次世代に対して何らかの遺伝毒性作用を及ぼす可能性が示唆されたのであり, 今後, さらに詳細な研究が必要である. また同様の結果は母乳からのダイオキシン類への曝露でも観察されているが, SCEsへの影響は細胞分裂のS期依存型遺伝毒性物質とみなされ, この視点からの研究も重要である.