Activation of human ribosomal genes by 5-azacytidine

Cultured human fibroblasts were exposed to 5-azacytidine which inhibits methylation of newly synthesized DNA. A significant increase in the mean number of Ag-stained active nucleolus organizers has been observed in treated cells. This suggests that DNA methylation is involved in modulation of human rRNA synthesis.     

Evidence for an in vivo and in vitro modulation of endogenous cortical GABA release by α-glycerylphosphorylcholine

The effects of α-glycerylphosphorylcholine (α-GPC) on endogenous cortical GABA release were studied both in vivo and in vitro. In freely moving rats, equipped with epidural cups, α-GPC (30–300 mg/kg i.p.) increased GABA release. This effect was potentiated by atropine, both systematically administered (5 mg/kg i.p.) and locally applied (1.4 μM), but not by mecamylamine (4 mg/kg i.p.). The α-GPC-induced increasein GABA release was abolished in rats pretreated with the α₁ receptor antagonist prazosin (14 μg/kg i.p.). In cortical slices α-GPC (0.4 mM) increased the spontaneous GABA efflux. This effectwas abolished by tetrodotoxin (0.5 μM) and prazosin (1 μM), but not by atropine (0.15 μM) ormecamylamine (2.5μM). These results indicate that the facilitatory response by α-GPC on GABArelease does not depend on a direct activation of either muscarinic or nicotinic receptors, but suggest the involvement of the noradrenergic system.     

Effects of phototherapy with blue light on chromosomes from human lymphocytes

The dangerous effects of phototherapy have been matter of discussion in recent years. In order to evaluate its in vitro action on the human DNA, the authors have performed the karyotypic analysis on 20 cultures of lymphocytes. In different times 16 cultures have been exposed to the action of a "blue light" fluorescent lamp, commonly used for the treatment of neonatal jaundice. The authors have not evidenced any morphological or numerical change of the karyotype in any of the cultures.     

Analysis of the DNA replication pattern of a translocation (tX/X,qter→p221::p223→qter) chromosome in leukocyte and fibroblast cultures

Summary The results of a detailed analysis of DNA replication in a late replicating tX/X chromosome (qter p221::p223 » qter) are reported. The chronology of DNA replication has been analyzed by comparing (a) the replication patterns of each of the two moieties of the translocation chromosome in different cells and (b) the two moieties with each other in the same cell. The study has been done on leukocyte and fibroblast cultures after BUdR incorporation. A comparison with the late replication pattern of the normal X chromosome has also been done.     

Deoxynucleotide pools and DNA synthesis in resting and PHA-stimulated human lymphocytes treated with mutagens.

In resting and PHA-stimulated PBL treated with uv light or MMS we measured the sizes of the dTTP and dATP pools and the variation of ATP content taken as an indicator of cytotoxicity. The effects on DNA synthesis were examined by measuring DNA repair (unscheduled DNA synthesis) in resting PBL and the inhibition of DNA replication in stimulated PBL. While both treatments affected DNA synthesis, only MMS perturbed dNTP pools and decreased the intracellular concentration of ATP. All the effects were more evident in cycling than in resting lymphocytes.     

L-carnitine delays the killing of cultured hepatocytes by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

The role of fatty acid metabolism in chemical-dependent cell injury is poorly understood. Addition of L-carnitine to the incubation medium of cultured hepatocytes delayed cell killing initiated by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Protection by L-carnitine was stereospecific and observed as late as 1 h following addition of MPTP. D-Carnitine, but not iodoacetate, reversed the L-carnitine effect. Monoamine oxidase A and B activities, MPTP/N-methyl-4-phenyl-pyridinium levels, and MPTP-dependent loss of mitochondrial membrane potential measured by release of [3H]triphenylmethylphosphonium were not altered by addition of L-carnitine. Significant changes in MPTP-induced depletion of total cellular ATP did not occur with excess L-carnitine. Although the mechanism of cytoprotection exerted by L-carnitine remains unresolved, the data suggest that L-carnitine does not significantly alter: (i) mitochondrial-dependent bioactivation of MPTP; (ii) MPTP-dependent loss of mitochondrial membrane potential; or (iii) MPTP-mediated depletion of total cellular ATP content. We conclude that alterations of fatty acid metabolism may contribute to the toxic consequences of exposure to MPTP. Moreover, the lack of L-carnitine-mediated cytoprotection of monolayers incubated with 4-phenylpyridine or potassium cyanide suggests: (i) a link between fatty acid metabolism and mitochondrial membrane-mediated, bioactivation-dependent cell killing; and (ii) that inhibition of NADH dehydrogenase may not totally explain the mechanism of MPTP cytotoxicity.     

In vitro attachment of Treponema hyodysenteriae to mammalian epithelial cells.

The interaction between Treponema hyodysenteriae and isolated swine intestinal epithelial cells or mouse adrenal cells in culture was examined. Studies were performed in which treponemes were incubated with each type of anomal cell in an atmosphere of 5% CO2 in air. Coincubation was terminated at various time intervals, and the percentage of treponemal attachment evaluated by light microscopy. The extent of attachment was dependent on both incubation time and temperature. The mechanism of attachment to the animal cell surface was examined by scanning electron microscopy. Interaction of the parasite with the host cell did not appear to alter cellular morphology or result in changes of the cell surface at the site of attachment. Preference for a cellular site of attachment was not found.     

Effects of in vivo exposure to antineoplastic drugs on DNA repair and replication in human lymphocytes

In peripheral blood lymphocytes of 12 nurses and 3 patients exposed to antineoplastic drugs we determined the ability to repair DNA after UV irradiation and DNA replicative synthesis after stimulation by PHA. In nurses the levels of unscheduled DNA synthesis and DNA replication were not different than in a control group, whereas in patients significant changes were observed during and after chemotherapy in the level of both types of DNA synthesis.