Inhibition of protein synthesis by N-methyl-N-nitrosourea in vivo

Karyometric, cytophotometric and histoenzymatic studies on neuroglia of rats treated with 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU/lomoustine)

CCNU is a cytostatic drug, a nitrosourea derivative, used--among others--in therapy of tumors of the central nervous system. Even if the drug is regarded safe for central and peripheral nervous systems, a possibility of harmful effects of CCNU on the central nervous system should be examined caused by the affinity of all nitrosourea derivatives to lipids. This has prompted us to study the drug effect on neuroglia cells in corpus callosum and gyrus cinguli. The drug was administered to rats by the intragastric route in four doses--one dose a week. Three doses of 2.5 mg each were followed by one dose of 5 mg. Some brains were isolated for the studies, and paraffin sections were prepared for karyometric as well as cytophotometric studies and for section staining according to Nissl and Klüver-Barrer techniques 8 days after the last dosage. Brains of other experimental rats served for preparing cryostat sections for demonstration of phosphatase and esterase activities. The studies, conducted after CCNU administration, documented a significant decrease in size of oligodendroglia nuclei and an increase in size of astroglia nuclei. DNA content of neuroglia nuclei was markedly decreased. Histoenzymatic changes in experimental animals were not very pronounced and included a slight increase in TPPase and nonspecific esterase activities as well as a decrease in ATPase activity. Despite the changes in neuroglia cells no damage to corpus callosum myelin sheaths was observed.

Karyometric, cytophotometric, and histoenzymatic studies on neuroglia of young rats subjected to CCNU (Lomustine) action

Studies on the effects of CCNU on neuroglia cells of the central nervous system in young individuals were conducted on 19 Wistar strain rats, each given 2 mg doses of 0.25 CCNU in 7th and 12th d of life. Karyometric and cytophotometric studies proved that CCNU administered to young rats induced changes in oligodendroglia and astroglia of the central nervous system. The changes included significant increase in nuclei contour and in the area of nuclei cross-section in oligodendro- and astroglia cells, elongation of oligodendroglia nuclei and an augmented DNA content in the 2 neuroglia types. The observed karyometric and cytophotometric changes were more evident in oligodendroglia nuclei than in astroglia nuclei.

Age-dependent changes in brain protein synthesis in the rat

Brain protein synthesis was studied in vivo, in brain slices, and in cell-free systems in rats aged 1, 16, and 24 months. We observed a highly significant reduction in amino acid incorporation with advancing age. This reduction was observed in vivo, in slices, in postmitochondrial supernatant, microsomes, and membrane-bound polysomes. Free heavy polysomes showed no age-dependent decline but formed a smaller proportion of total ribosomes in older animals. These studies suggest that in the rat brain protein synthesis declines before senescence, possibly due to an impairment in the initiation process.

Studies on histones and non-histone proteins from rats treated with dimethylnitrosamine

A study has been made of the histone and non-histone chromosomal proteins of rat liver after treatment in vivo with dimethylnitrosamine (DMN) (2 mg/kg). DMN was found not to affect histone turnover, as measured by 3H-labelled amino-acids incorporation. A decrease was observed in specific activity of the histones with time after injection of [14C]DMN or [14C]-formate and this was attributable to demethylation of both abnormal and normal methylation sites in these proteins. In the case of the non-histone proteins, DMN was found to increase greatly the turnover of those non-histone proteins loosely associated with chromatin DNA and RNA; turnover of those non-histone proteins tightly bound to chromatin DNA and RNA was unaffected. Demethylation of both normal and abnormal methylation sites was found to take place from both non-histone protein fractions. In the case of the loosely bound non-histone proteins a lower rate of demethylation was observed after DMN treatment.

Acute biochemical and morphological effects of N-nitrosomorpholine in comparison to dimethyl- and diethylnitrosamine

Some biochemical and ultrastructural changes induced in the livers of rats treated with N-nitrosomorpholine are described and compared with parallel observations in rats given dimethyl- or diethylnitrosamine. Hepatotoxic doses of the nitrosamines caused inhibition of incorporation of [14C]leucine into hepatic proteins, accompanied by progressive disaggregation of polysomes which paralleled the known time course of metabolism of each compound. Dimethylnitrosamine (DMN) and N-nitrosomorpholine (NM) inhibited incorporation of [14C]orotate into liver RNA but diethylnitrosamine (DEN) caused a slight stimulation of orotate incorporation. Electron microscopy revealed similar hepatic cytoplasmic changed induced by each nitrosamine, including dilation and degranulation of the rough surfaced endoplasmic reticulum and subsequent increase of the smooth endoplasmic reticulum. Nuclear changes differed with each compound, N-nitrosomorpholine having more marked effects than either dialkyl compound. The results are discussed with particular reference to the metabolism of N-nitrosomorpholine in the liver.

Resuscitation of the monkey brain after one hour complete ischemia. III. Indications of metabolic recovery

Adult rhesus monkeys were subjected to complete cerebral ischemia for one hour and subsequent recirculation for up to 24 h. Animals with signs of functional recovery (e.g. spontaneous EEG activity) exhibited a partial replenishment of cellular energy sources (ATP, phosphocreatine) and a progressive normalization of cerebral lactate levels. Glucose and pyruvate concentrations showed a transient increase over control values during the early stages of postischemic recirculation. Monkeys without functional recovery lacked a significant resynthesis of energy-rich compounds; adenine nucleotides continued to decrease and lactate concentrations were higher than in animals subjected to ischemia without recirculation. Cerebral polysome profiles remained unaltered during the ischemic period but in all animals a marked disaggregation of polyribosomes with a concomitant increase in ribosomal subunits occurred after the onset of recirculation. In monkeys with indications of functional recovery these changes were reversible but a normal polysome profile was only observed after 24 h of recirculation. The results obtained indicate a postischemic depression of protein synthesis due to an inhibition of peptide chain initiation. After recirculation of the brain for 3-6 h there was evidence for an induction of enzymes involved in polyamine synthesis (ornithine decarboxylase and S-adenosylmethionine decarboxylase). No changes in the activity of these enzymes were observed at the end of the ischemic period, indicating that during complete cerebral ischemia not only the synthesis but also the catabolism of proteins is inhibited.

On the theory of clonal selection in carcinogenic transformation

A temperature sensitive variant (ts13) of African green monkey kidney cell line, carrying a temperature sensitive lesion in thymidine metabolism, was transformed by 40 μg/ml of methylnitrosourea (MNU) at the restricted temperature of 39·5°C, whereas the same cell line was not transformed by MNU at the permissive temperature of 33°C. Results presented in this paper raise the possibility that clones of cells carrying a biochemical lesion might possibly contribute to carcinogenesis with respect to certain chemical carcinogens.