1-Methyl-1-nitrosourea Depression of Brain Nicotinamide Adenine Dinucleotide in the Production of Neurologic Toxicity

Abstract

1-Methyl-1-nitrosourea (MNU) has been shown to be both a potent carcinogenic and antitumor compound (1, 2). These effects have been attribted to the liberation of diazomethane, a highly reactive agent capable of alkylating protein, RNA, DNA, and inhibiting the incorporation of amino acids into protein (3, 4). Recent investigations demonstrated that MNU can produce a rapid dose-related depression in liver nicotinamide-adenine dinucleotide (NAD) concentrations 5, 6). During the course of these studies there appeared a transient neurologic syndrome which was temporally related to the acute lowering of brain NAD levels. This communication correlates these findings with measurements of drug concentration in the acid-soluble fraction of brain, and with brain NAD glycohydrolase activity and histology.

Methods. Male albino mice, Swiss strain, weighing 20-25 g were used for all studies, and were maintained on Purina laboratory chow pellets and water ad libitum. 1-Methyl-1-nitrosourea, NCS-23909, and nicotinamide (Calbiochem) were prepared in distilled water. Streptozotocin, NSC-85998, a diabetogenic compound composed of the union of glucosamine and MNU at the carbon 2 position of the glucose moiety (7), wa sdissolved in 0.005 M citrate buffer, pH 4.0. The drugs were administered at a volume of 1 ml/100 g of body weight intravenously via the tail vein, or intraperitoneally. The NAD content of brain was assayed enzymatically using alcohol dehydrogenase (Sigma) after the organ was homogenized 1:5 weight:volume in 0.6 N perchloric acid at 4°, and the supernate wa sneutralized using 3 N KOH (8). The NAD glycohydrolase activity of brain homogenate was assayed using the method of Kaplan as modified by Waravdekar (9). The concentration of MNU in the acid-soluble fraction of brain, liver, and serum was measured colorimetically using a modification of the Forist method for streptozotocin (10, 6). For histologic study of brain, mice were anesthetized with ethyl ether, and 10% formalin was perfused through the heart.