A PHARMACOLOGICAL EVALUATION OF THE MECHANISM OF CYTOTOXICITY OF 9-BETA-D- XYLOFURANOSYLADENINE IN CHINESE HAMSTER OVARY CELLS

The biochemical determinants of cytotoxicity of the purine nucleoside analog, 9-(beta)-D-xylofuranosyladenine (xyl-A) were studied in wild-type Chinese hamster ovary cells and in nucleoside kinase deficient mutants. It was found that {('3)H}xyl-A was readily phosphorylated to the triphosphate level in both the wild-type and deoxycytidine kinase deficient mutant, but not by the adenosine kinase deficient cells. Values for the apparent Km and Vmax of this uptake process were 43.9 (mu)M and 118.7 nmol/min/10('9) cells, respectively. Cloning procedures indicated that the viability of CHO cells was decreased 90 per cent by a 5-hr incubation with 10 (mu)M xyl-A. However, the toxicity of xyl-A was increased 100-fold by the addition of a nontoxic concentration (10 (mu)M) of the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) to the medium. High-pressure liquid chromatographic analysis indicated that after 5 hr, the concentration of 9-(beta)-D-xylofuranosyladenine 5'-triphosphate (xyl-ATP) in cells incubated with xyl-A plus EHNA was 2.0 mM, four times greater than in those cells incubated with xyl-A alone. Incubation with xyl-A plus EHNA had no significant effect on the cellular concentrations of 5-phosphoribosyl-1-pyrophosphate after 1 hr whereas, treatment with 3'-dexoyadenosine (cordycepin) decreased the concentration of this metabolite. Determinations of the cellular nucleoside triphosphates indicated that under conditions that resulted in an intracellular accumulation of 500 (mu)M xyl-ATP, the endogenous concentrations of neither the ribonucleoside triphosphates nor deoxyribonucleoside triphosphates were significantly different from those of control cells. The ID(,50) for {('3)H}thymidine incorporation into DNA, 105 (mu)M xyl-ATP, was four-fold less than the ID(,50) for {('3)H}uridine incorporation into RNA suggesting that the process of DNA synthesis is more sensitive to the presence of xyl-ATP. When removed from exogenous xyl-A, CHO cells failed to recover their ability to synthesize RNA and DNA, although the intracellular xyl-ATP concentration decreased to less than 35 (mu)M. The selective inhibition of RNA synthesis by 6-azauridine did not prevent the expression of toxicity by xyl-ATP. However, the selective inhibition of DNA synthesis by ara-C significantly spared toxicity in cells that had accumulated an otherwise lethal concentration of xyl-ATP. It is shown that in cells which had accumulated 1.27 mM {('3)H}xyl-ATP, {('3)H}xyl-A was found to terminate cellular RNA chains at a frequency of 1.42 (mu)mol of {('3)H}xyl-A 3' termini per mol of mononucleotide. These results indicate that a general mechanism for the toxicity of xyl-A to CHO cells includes the cellular accumulation of xyl-ATP, which serves as a substrate for RNA synthesizing enzymes and subsequently is incorporated into nascent RNA transcripts as a chain terminator. A specific mechanism involving the premature termination of RNA primers required for the initiation of DNA synthesis is proposed to account for the inhibitory action of xyl-ATP on DNA synthesis. ^

Genetic Analyses Reveal a Role for Vitamin D Insufficiency in HCV-Associated Hepatocellular Carcinoma Development

Background Vitamin D insufficiency has been associated with the occurrence of various types of cancer, but causal relationships remain elusive. We therefore aimed to determine the relationship between genetic determinants of vitamin D serum levels and the risk of developing hepatitis C virus (HCV)-related hepatocellular carcinoma (HCC). Methodology/Principal Findings Associations between CYP2R1, GC, and DHCR7 genotypes that are determinants of reduced 25-hydroxyvitamin D (25[OH]D3) serum levels and the risk of HCV-related HCC development were investigated for 1279 chronic hepatitis C patients with HCC and 4325 without HCC, respectively. The well-known associations between CYP2R1 (rs1993116, rs10741657), GC (rs2282679), and DHCR7 (rs7944926, rs12785878) genotypes and 25(OH)D3 serum levels were also apparent in patients with chronic hepatitis C. The same genotypes of these single nucleotide polymorphisms (SNPs) that are associated with reduced 25(OH)D3 serum levels were found to be associated with HCV-related HCC (P = 0.07 [OR = 1.13, 95% CI = 0.99–1.28] for CYP2R1, P = 0.007 [OR = 1.56, 95% CI = 1.12–2.15] for GC, P = 0.003 [OR = 1.42, 95% CI = 1.13–1.78] for DHCR7; ORs for risk genotypes). In contrast, no association between these genetic variations and liver fibrosis progression rate (P>0.2 for each SNP) or outcome of standard therapy with pegylated interferon-α and ribavirin (P>0.2 for each SNP) was observed, suggesting a specific influence of the genetic determinants of 25(OH)D3 serum levels on hepatocarcinogenesis. Conclusions/Significance Our data suggest a relatively weak but functionally relevant role for vitamin D in the prevention of HCV-related hepatocarcinogenesis.

Apologie für die unterdrückte Judenschaft in Deutschland : an d. Congreß in Rastadt gerichtet

[Andreas Riem]

Der Optimismus und der Pessimismus in der jüdischen Religionsphilosophie : eine Studie über die Behandlung d. Theodicee in derselben bis auf Maimonides

von H. Goitein

Unterthänigste Immediat-Eingabe des jüdischen Vorstandes des Kreises Simmern : die Rechtsverhältnisse d. Juden in Preussen, insbes. in Rheinpreussen betr.

[David Rothschild]

Der Austritt aus der Synagogengemeinde : das Gesetz u. dessen Berathung im Hause d. Abgeordneten in 1., 2. u. 3. Lesung, nach d. stenogr. Berichten d. Abgeordnetenhauses zsgest. u. mit e. Vorw. vers.

von S. Meyer

Auswahl von Bibelsprüchen und Liederversen über die mosaische Glaubens- und Sittenlehre : zum Gebr. bei d. Religionsunterricht in israelit. Schulen

hrsg. von Joseph Maier

Derek emunah : der Weg des Glaubens oder : die kleine Bibel; enthaltend einen vollst. Ausz. aus d. Bücher d. heiligen Schrift ; zunächst f. israelitische Frauen u. Mädchen, u. mit Rücksicht auf d. Unterricht in der Religion u. Sittenlehre f. Knaben u. Mädchen zum Schul- u. Privat-Unterrichte bearb.

von M. Büdinger

Derek emunah: der Weg des Glaubens oder : die kleine Bibel; enthaltend einen vollst. Ausz. aus d. Bücher d. heiligen Schrift ; zunächst f. israelitische Frauen u. Mädchen, u. mit Rücksicht auf d. Unterricht in der Religion u. Sittenlehre f. Knaben u. Mädchen zum Schul- u. Privat-Unterrichte bearb.

von M. Büdinger

Urbild und Ebenbild : Lehrbuch f. d. Unterricht in d. israelit. Religion

von I. Goldschmidt

Die Juden, dürfen sie "Verbrecher von Religions wegen" genannt werden? : Aktenstücke zugl. als e. Beitr. zur Kennzeichnung d. Gerechtigkeitspflege in Preussen

ges. von Hermann L. Strack