An ultrastructural, morphometric and autoradiographic study of the effects of 7,12-dimethylbenzanthracene on the rat adrenal cortex.

The effects of chronic treatment (up to 9 consecutive days) with 7,12-dimethylbenzathracene (DMBA) on the adrenal glands of adult male Wistar rats were investigated. Morphometry showed that DMBA provokes atrophy of the zona reticularis which was due to the decrease in both cell volume and number. The zona fasciculata showed only a decrease in the cell volume, whereas the zona glomerulosa did not display any significant changes. Autoradiography demonstrated that DMBA induces a significant increase in the number of mitoses and "S" phase cells in the zona glomerulosa and outer zona fasciculata, which may be interpreted as a repair mechanism of the DMBA-provoked slight necrosis in the inner adrenocortical layers. The mechanism(s) underlying the cytotoxic effect of DMBA is discussed in the light of our ultrastructural observations showing that the chemical causes a decrease in the volume of the mitochondrial and nuclear compartments and in the surface of smooth endoplasmic reticulum as well as an increase in the volume of the lipid compartment.     

Heterogeneous binding of high mobility group chromosomal proteins to nuclei

A dramatic difference is observed in the intracellular distribution of the high mobility group (HMG) proteins when chicken embryo fibroblasts are fractionated into nucleus and cytoplasm by either mass enucleation of cytochalasin-B-treated cells or by differential centrifugation of mechanically disrupted cells. Nuclei (karyoplasts) obtained by cytochalasin B treatment of cells contain more than 90 percent of the HMG 1, while enucleated cytoplasts contain the remainder. A similar distribution between karyoplasts and cytoplasts is observed for the H1 histones and the nucleosomal core histones as anticipated. The presence of these proteins, in low amounts, in the cytoplast preparation can be accounted for by the small percentage of unenucleated cells present. In contrast, the nuclei isolated from mechanically disrupted cells contain only 30-40 percent of the total HMGs 1 and 2, the remainder being recovered in the cytosol fraction. No histone is observed in the cytosol fraction. Unike the higher molecular weight HMGs, most of the HMGs 14 and 17 sediment with the nuclei after cell lysis by mechanical disruption. The distribution of HMGs is unaffected by incubating cells with cytochalasin B and mechanically fractionating rather than enucleating them. Therefore, the dramatic difference in HMG 1 distribution observed using the two fractionation techniques cannot be explained by a cytochalasin-B-induced redistribution. On reextraction and sedimentation of isolated nuclei obtained by mechanical cell disruption, only 8 percent of the HMG 1 is released to the supernate. Thus, the majority of the HMG 1 originally isolated with these nuclei, representing 35 percent of the total HMG 1, is stably bound, as is all the HMGs 14 and 17. The remaining 65 percent of the HMGs 1 and 2 is unstably bound and leaks to the cytosol fraction under the conditions of mechanical disruption. It is suggested that the unstably bound HMGs form a protein pool capable of equilibrating between cytoplasm and stably bound HMGs.     

N2-(p-n-Octylphenyl)dGTP: Synthesis and Inhibitory Activity Against DNA Polymerases

Abstract

N²-(p-n-Octylphenyl)-2′-deoxyguanosine 5′-triphosphate (OctPdGTP)has been synthesized chemically. OctPdGTP inhibited DNA polymerases (pol) α, δ and ε from calf thymus, with moderate selectivity for pol α. Mechanistic studies on pol α and bacteriophage T4 DNA polymerase revealed competitive and mixed kinetics of OctPdGTP with respect to the substrate dGTP when the enzymes were assayed on activated DNA and oligo dT:poly dA, respectively.

     

DNA as molecular target of analogous palladium and platinum anti-Trypanosoma cruzi compounds: a comparative study

In the search for drugs with anti-trypanosome activity, we had previously synthesized two series of platinum and palladium analogous compounds of the formula [M^IICl₂(HL)], where HL were bioactive 5-nitrofuryl or 5-nitroacroleine thiosemicarbazone derivatives. In this work, we thoroughly characterized [M^IICl₂(HL)] complexes interaction with DNA by using different techniques: gel electrophoresis, DNA viscosity measurements, circular dichroism (CD) and atomic force microscopy (AFM). Electrophoresis results showed that all complexes induced a withdrawal of DNA superhelicity demonstrated by a decrease in electrophoretic mobility of supercoiled DNA form. This effect on migration was dependent on dose but also on the nature of both the metal and the ligand. In general, the effect produced by palladium complexes was significantly more intense than that observed for the corresponding platinum analogs. Differences between palladium and platinum complexes were also observed in CD experiments. While palladium complexes induce evident calf thymus (CT)-DNA profile changes compatible with B-DNA to Z-DNA conformational transition, no clear effect was observed for platinum ones. Additionally, AFM studies showed that changes in the shape of plasmid DNA, like supercoiling, kinks and thickness increase resulted more intense for the former. In addition, either Pd or Pt complexes increased the viscosity of CT DNA solutions in a concentration dependent manner. Although the nature of DNA interaction of both series of analogous palladium and platinum complexes seemed to be similar, an explanation for the observed differential intensity of the effect could be related to the known kinetic stability differences between palladium and platinum compounds.     

7-Alkyl-N(2)-substituted-3-deazaguanines. Synthesis, DNA polymerase III inhibition and antibacterial activity

Several 2-anilino- and 2-benzylamino-3-deaza-6-oxopurines [3-deazaguanines] and selected 8-methyl and 8-aza analogs have been synthesized. 7-Substituted N²-(3-ethyl-4-methylphenyl)-3-deazaguanines were potent and selective inhibitors of Gram+ bacterial DNA polymerase (pol) IIIC, and 7-substituted N²-(3,4-dichlorobenzyl)-3-deazaguanines were potent inhibitors of both pol IIIC and pol IIIE from Gram+ bacteria, but weakly inhibited pol IIIE from Gram− bacteria. Potent enzyme inhibitors in both classes inhibited the growth of Gram+ bacteria (MICs 2.5-10 μg/ml), and were inactive against the Gram− organism Escherichia coli. Several derivatives had moderate protective activity in Staphylococcus aureus-infected mice.