Studies on the anticarcinogenic effect of some vitamins

Abstract

간세포의 microsome분획내에는 mixed-function oxidase(또는 monooxygenase)라고 불리우는 중요한 산화효소군이 존재하며 이 효소계는 스테로이드, 지방산과 같은 내인적인 화합물 뿐만 아니라 외인적 화합물인 약물, 살충제 및 발암물질에 대한 대사과정에서 전자전달계의 역할을 하는 것으로 알려져 있다. Vitamin A와 Vitamin E는 항산화제이며 화학적인 발암현상에 대한 항암작용이 있는 것으로 보고되어있다. 한편 phenobarbital(PB)은 간 내 약물대사와 monooxygenase활성을 증가시켜 acetyl-aminofluorene(AAF)과 같은 발암물질의 대사를 촉진하는 것으로 알려져 있다. 본 연구는 이와 같은 Vitamin이나 PB에 관한 연구 결과와 연관하여 발암물질로 알려진 AAF와 DNA, RNA 및 protein과의 결합에 미치는 vitamin A, E 또는 C의 영향을 PB, AAF 또는 PB과 AAF를 투여한 쥐에서 관찰하고자 하였다. 체중 150~200g의 웅성 흰쥐를 사용하여 AAF, PB 및 vitamin A, E또는 C를 투여한 후 간 세포 microsome분획과 핵내의 cytochrome p-450, cytochrome b5, NADPH-cytochrome C resuctase 및 NADH-cytochrome C reductase 활성을 측정하였고 간 DNA 및 RNA와 AAF와의 결합량을 in vivo실험으로 조사하여 다음과 같은 결과를 얻었다. 1. vitamin A, E 또는 C를 구강투여하였을 때 간 세포 microsome분획과 핵내의 cytochrome P-450, cytochrome b5, NADPH-cytochrome C resuctase 및 NADH-cytochrome C reductase 활성이 크게 감소하였으며 lipid peroxide의 생성도 감소되었다. 또한 microsome분획과 핵내의 DNA, RNA 및 protein과 AAF의 결합량도 감소되었다. 2.PB을 투여하였을 때 간 세포 microsome분획과 핵내의 cytochrome P-450과 cytochrome b5활성이 증가되었다. 그러나 microsome분획과 핵내의 DNA, RNA 및 protein과 AAF의 결합량은 microsome분획에서의 약 1.5배였다. 이와 같은 실험결과는 AAF가 소포체나 핵막의 핵산과 결합하기 위해서는 활성화되어야 한다는 것을 의미하는 것이며 vitamin E나 vitamin C와 같은 vitamin의 항암작용은 AAF와 같은 발암물질이 핵산과 결합할 수 있는 활성형으로 변화하는 것을 억제하는 것으로 생각된다. ; Electron transport I known to be carried out by a nonspecific multienzyme system located in the nucleus as well as in the endoplasmic reticulum of the cell. The monooxygenase system consists of NADPH-cytochrome P-450 reductase and cytochrome P-450 itself. The effect of some vitamins on the electron transport chain of the microsomal and nuclear membranes has been examined in hepatocytes of 2-[9-14C]-acetyl-aminofluorene(AAF) and phenobarbital(PB) intraperitoneally administered rats. Vitamin(such as A, E, or C) was administered orally once a day for 28 days followed by intraperitoneal injection of PB once a day for the last 3 days and/or a single intraperitoneal injection of AAF at 3.5 hrs before sacrifice. And the content of AAF persistently bound to hepatic DNA, RNA or protein in vivo was assayed; the following results were obtained: 1.The activities of hepatic microsomal and nuclear cytochrome P-450 and cytochrome b5 as well as lipid peroxide contents in AAF and/or PB treated rats were increased whereas those in vitamin A, E or C fed rats were decreased. The contents of the nuclear cytochrome p-450, cytochrome b5, and lipid peroxide were approximately one-half of the corresponding value in the microsomal fraction respectively. 2.The hepatic microsomal NADPH-cytochrome C reductase activity in PB treated rats was increased; conversely the nuclear enzyme was decreased. The hepatic microsomal and nuclear NADPH-cytochrome C reductase activities in AAF administered rats were increased whereas those in vitamin A, E, or C fed rats were decreased. The activity of the nuclear NADPH-cytochrome C reductase was approximately one-third of that in the microsomal fraction. 3.The hepatic microsomal and nuclear NADH-cytochrome C reductase activities in PB/vitamin (A, E, C) administered rats were decreased whereas those in AAF treated rats were increased. The activity of the nuclear NADH-cytochrome C reductase was approximately of that in the microsomal fraction. 4.In vivo amounts of AAF bound to hepatic microsomal and nuclear DNA, RNA or protein in PB/vitamin (A, E, C) administered rats were decreased. The amount of AAF bound to DNA, RNA or protein in nuclei were found to be higher than those in the microsomes. It is, therefore, suggested that AAF may be activated to bind to nucleic acids of the endoplasmic reticulum and nuclear envelope under the intracellular conditions. Further the protective effect of vitamins against the hepatocarcinogenic action of AAF appears to be mediated by decreased cytochrome P-450 and cytochrome b5 activities and by alteration in the binding of the carcinogen to hepatic nucleic acid.