New selective inhibitors of cytochromes P450 2B and their application to antimutagenesis of tamoxifen

2-Isopropenyl-2-methyladamantane (2-PMADA) and 3-isopropenyl-3-methyldiamantane (3-PMDIA) showed potent and selective inhibition of cytochrome P450 (CYP) 2B6-mediated reactions with K(i) values of 5.27 and 2.17 microM, respectively. No effect on activities of other human CYP was found even at concentrations 100-fold higher than those inhibiting CYP2B6. These results indicate that 2-PMADA and 3-PMDIA belong among the most potent CYP2B6-selective inhibitors discovered to date. Both compounds also inhibited reactions catalyzed by CYP2B2 and CYP2B4 with K(i) values ranging between 0.23 and 2 microM. They are competitive inhibitors of all CYP2B. The activation of the anticancer drug tamoxifen by human and rabbit microsomes generating tamoxifen-DNA adducts, which are responsible for carcinogenic side effects of this drug, was strongly inhibited by both compounds. 2-PMADA and 3-PMDIA are very potent for inhibition of formation of these DNA adducts and warrant consideration as candidates for preventing endometrial cancer development by tamoxifen in humans treated with this anticancer drug.     

INDUCED DIMORPHIC LIFE CYCLE OF A COCCOLITHOPHORID,CALYPTROSPHAERA SPHAEROIDEA (PRYMNESIOPHYCEAE,HAPTOPHYTA)1

The holococcolith Calyptrosphaera sphaeroidea Schiller was collected at Miyake‐jima Island, Japan and unialgal cultures established. Alternation of the holococcolith and heterococcolith phases was induced using new culture media (MNK, TR, and LO). Cells synchronized in the holococcolith phase were transferred into TR medium to induce a life cycle change. The heterococcolith phase, which has never been reported before, appeared after more than 40 days. The heterococcoliths were very small elliptical discs, about 0.5 μm wide and 1 μm long. Typical diploid‐type organic scales on the cell surface were observed. This phase was very stable in culture and was tolerant of unfavorable conditions. To reverse the life phase, cells in the heterococcolith phase were transferred into cold LO medium and exposed to low temperature (4°C) and low light (2 μmol photons·m^?2·s^?1) for 30 min before culturing at normal conditions (22.5°C and 20 μmol photons· m^?2·s^?1). The swimming behavior of the holococcolith cells seemed to be an indicator of the life cycle phase transition. This article reports for the first time a set of conditions that could control the transition of a coccolithophorid from one life phase to the other. Selected vitamins and trace metals induced the heterococcolith phase, whereas a slightly higher concentration of components in the basic medium along with concomitant stresses of light and temperature induced the holococcolith phase. Based on the results, we propose a hypothesis that the alternation of coccolithophorid life phases is regulated by changes between pelagic and coastal environments coupled with changes in seasonal conditions.     

Biased distribution of adenine and thymine in gene nucleotide sequences

We analyzed occurrences of bases in 20,352 introns, exons of 25,574 protein-coding genes, and among the three codon positions in the protein-coding sequences. The nucleotide sequences originated from the whole spectrum of organisms from bacteria to primates. The analysis revealed the following: (1) In most exons, adenine dominates over thymine. In other words, adenine and thymine are distributed in an asymmetric way between the exon and the complementary strand, and the coding sequence is mostly located in the adenine-rich strand. (2) Thymine dominates over adenine not only in the strand complementary to the exon but also in introns. (3) A general bias is further revealed in the distribution of adenine and thymine among the three codon positions in the exons, where adenine dominates over thymine in the second and mainly the first codon position while the reverse holds in the third codon position. The product (A₁/T₁) × (A₂/T₂) × (T₃/A₃) is smaller than one in only a few analyzed genes. Correspondence to: J. Kypr     

Maintenance of the induced hypomethylated state of tobacco nuclear repetitive DNA sequences in the course of protoplast and plant regeneration

Previously, we established experimental conditions allowing us to induce hypomethylation of tandem arrays of highly repetitive DNA sequences in the Nicotiana tabacum L. nuclear genome (M. Bezdk et al. 1991, Planta 184, 487–490). In this paper, we demonstrate that loci containing the highly repetitive sequences of the HRS60 family can maintain the induced hypomethylated state through protoplast regeneration, non-differentiated callus growth, and plant regeneration. The hypomethylation, induced with 5-azacytidine and monitored on these sequences, did not substantially alter the capacity of calli to produce plants. It can be concluded that, in contradistinction of multiple copies of transgenes or ectopic genes which are usually recognized as methylation targets, endogenous tandem repeats, such as the HRS60, present at 10⁵ copies in the genome, can escape de-novo methylation.Abbreviation AzaC 5-azacytidine This project was supported by the Grant Agency of the Academy of Sciences of the Czech Republic. We thank Ms. Libue Jedliková, Ms. Hana Suchánková, and Ms. Emilie Koudelková for technical assistance.     

Index of names of syntaxa typified in 1990

Following the “Index of new names” (Theurillat andMoravec 1993), the present work collects the names of syntaxa (in the sense of the Code of Phytosociological Nomenclature, BARKMAN et al. 1986) above subassociation rank typified in 1990. The list comprises 36 names of syntaxa; 2 names are given in addition to the “Index 1987” (Theurillat andMoravec 1990).     

Serum selenium levels in Slovak population

Blood serum selenium levels were measured in 576 healthy middle aged adults (40–60 yr, 255 men and 321 women) residing in both urban and rural areas in four districts of Slovakia. Serum selenium was determined by electrothermal AAS. The mean (±SD) serum selenium concentration was 0.852±0.335 μmol/L, ranging from 0.219–2.30 μmol/L. A large proportion of the individuals (19.62%) exhibited serum selenium levels under 0.57 μmol/L (45 μmol/L). There was no significant correlation between serum, selenium concentration and age, sex, and smoking status. There were significant differences between districts. The lowest mean (±SD) serum selenium was 0.664±0.269 μmol/L, the highest mean serum selenium (±SD) was 0.975±0.361 μmol/L. This differences could probably be attributed to the selenium, content in the soil of the different areas, which would contribute to the average daily selenium intake. In comparison with serum selenium levels in other European countries, the concentrations of selenium in the Slovak population are relatively low.     

Specific cellular immunity detected by the in vitro monocyte spreading inhibition test in patients with bronchogenic carcinoma

Summary The test of the in vitro inhibition of monocyte spreading detected specific cell-mediated immunity (CMI) to melanoma-associated antigens in patients with melanoma. In this study we investigated the applicability of the test for assessment of specific antitumour immunity in patients with bronchogenic squamous-cell carcinoma (BSCa). Mononuclear blood cells of patients with the tumour were exposed to a soluble antigenic preparation, obtained by high-speed centrifugation of a homogenate of freshly excised BSCa tissue. The preparation inhibited the spreading of allogeneic monocytes from a group of 26 patients with BSCa (P=0.0023), but it did not inhibit monocytes from healthy laboratory personnel or those of patients with bronchogenic oat-cell carcinoma, benign lung tumours, or chronic tuberculosis. However, the same BSCa preparation inhibited (0.05>P>0.025) the spreading of monocytes from healthy hospital personnel (who were in prolonged contact with patients). At the same time, the monocytes of patients with BSCa were not inhibited by similarly obtained preparations from a normal lung, a benign thymoma, and a uterine squamous-cell carcinoma. We concluded that the in vitro test of monocyte spreading inhibition can detect specific CMI to antigens associated with the allogeneic BSCa in patients with the tumour.A summary of these results was presented at the 4th European Immunology Meeting, Budapest, Hungary, April 1978