Glutaraldehyde release from vascular prostheses of biologic origin

The inhibition of growth by adult human venous endothelial cells in culture forms the basis of a sensitive assay of glutaraldehyde (GA) concentration, valid between 0 and 5 parts per million. This cytotoxicity assay was used to measure residual (unbound) GA in commercial vascular prostheses of biologic origin following manufacturer-recommended rinsing procedures, from which as much as 13.8 ppm GA per gram of tissue per 24 hours continued to be released after 1 month. A brief (1 hour) exposure of cultured endothelial cells to 2 ppm GA delayed growth, while continuous exposure to 4 ppm totally prevented growth for at least 12 days. Endothelial cells exposed to GA demonstrated a reduced efficiency of attachment to standard test surfaces, although prior GA treatment of these surfaces was not detrimental to subsequent cell attachment. GA release from vascular prostheses may contribute to their lack of endothelial cell coverage in human implants and may be indicative of collagen cross-link instability. If so, in vitro cytotoxicity may be helpful in identifying the potential for aneurysm formation in preserved biologic grafts.

Modulation of in vitro response to adriamycin by verapamil in murine P388 leukaemia, Ehrlich ascites carcinoma and sarcoma 180

Experiments were carried out in vitro on adriamycin (ADR) accumulation and cytotoxicity alone and in combination with calcium channel antagonist, verapamil (VRP), in ascites murine tumour models of Ehrlich carcinoma (EAC), sarcoma 180 (S180) and P388 lymphocytic leukaemia (P388). The cytotoxicity was assayed as the inhibition of [3H]-thymidine incorporation into the cellular DNA. ADR, a broad-spectrum anticancer drug, at a concentration of 10 micrograms/ml showed a cytotoxic effect in the order S180 greater than P388 greater than EAC. VRP alone exhibited the DNA synthesis inhibiting activity. The enhanced DNA biosynthesis inhibition of ADR along with VRP was maximal in S180 and marginal in P388 and EAC. The ADR retention after 3 hr of incubation in these tumour models correlated with the cytotoxicity. VRP enhanced the accumulation of ADR in all these cell lines. The property of potentiation in the activity and accumulation of ADR in these tumours exposed to a non-toxic concentration of VRP can best be utilized in cancer chemotherapy where the massive cytotoxic therapy, with a single large dose of ADR, can be substituted with a low dose, along with this drug-response modulator, for better therapeutic results.

Ribavirin antagonizes the effect of azidothymidine on HIV replication

Azidothymidine and ribavirin both inhibit replication of human immunodeficiency virus in vitro and show promise of clinical utility in patients infected with this virus. In this study, the possible interactions of these drugs were examined in vitro, and a reproducible antagonism between azidothymidine and ribavirin was found to occur under a variety of experimental conditions. The mechanism responsible for this antagonism appeared to be inhibition of azidothymidine phosphorylation by ribavirin. Because similar effects may occur in vivo, clinical trials of these two drugs in combination must be performed only under carefully controlled conditions.

Biochemical analysis of toxic effects of 5-hydroxymethyl-2'-deoxyuridine in mammalian cells

Cellular and biochemical analyses of the toxic effects of the thymidine analog, 5-hydroxymethyl-2'-deoxyuridine (hmdUrd), were carried out using V79.5 Chinese hamster cells. It was found that the toxic effects of hmdUrd could be totally suppressed by the addition of thymidine at 1/10th the concentration of hmdUrd. When other pyrimidines were tested, deoxyuridine was found to also suppress toxicity, although not as well as thymidine, while orotate, uridine, cytidine, and deoxycytidine did not have significant effect. Biochemical analyses of the metabolic fate of hmdUrd demonstrated low but significant levels of hmdUrd triphosphate and the incorporation of 5-hydroxymethyluracil (hmUra) residues into DNA. Surprisingly, in addition to these metabolites, relatively high levels of free hmUra were also detected in the acid-soluble cell extracts. Further analysis demonstrated that when V79.5 cells were exposed to hmdUrd significant amounts of hmUra were released into the culture medium. In vitro assays provided evidence that hmdUrd was first phosphorylated to its monophosphate and then degraded to hmUra, possibly via the action of a new enzyme, hydroxymethyldeoxyuridylate phosphorylase. Exposure of cells to hmUra alone, at concentrations as high as 3 mM, had no effect on viability. However, when V79.5 cells were simultaneously exposed to low, nontoxic concentrations of hmdUrd and high, nontoxic concentrations of hmUra, a synergistic reduction in viability was observed. This synergistic effect was found to correlate with increased incorporation of hmUra into DNA, possibly via end-product inhibition of an hmUra-DNA glycosylase.

A reappraisal of the effect upon thymidine kinase of thymidine derivatives carrying large groups at the 5'-position

Several thymidine derivatives with hydrophobic 5'-substituents, linked by chemically stable amide and ether links, were synthesized as potential thymidine kinase inhibitors. None of these was active nor were several derivatives of thymidine 5'-acetate, which were previously reported to be inhibitors. It was shown that the apparent inhibition by the latter compounds was due to their facile hydrolysis in aqueous solution with release of thymidine. These results must cast doubt on any conclusions drawn from biological studies with 5'-esters of thymidine.

The in vivo uptake of tritiated thymidine as a potential short-term test of toxic effects of polycyclic aromatic hydrocarbons in different organs

A rapid in vivo test for toxicity is described where the test substance is allowed to distribute and metabolize in the intact mouse. Quantitative data are provided on the effect of 3 different polycyclic aromatic hydrocarbons on the DNA turnover in various organs, measured as the incorporation of tritiated thymidine. In accordance with previously reported carcinogenic potencies, 7,12-dimethylbenz[alpha]anthracene (DMBA) was more potent in inhibiting the thymidine incorporation than benzo[alpha]pyrene (B[alpha]P). The inhibitory effect was most pronounced in spleen, lung, pancreas, small intestine and kidney, resulting in a decrease of incorporated activity with up to 80%. There was no evidence for the existence of specific target organs for DMBAs effects on thymidine incorporation as indicated by an inhibitory action in all organs studied. A decreased thymidine incorporation after administration of DMBA could also be demonstrated with whole-body autoradiography. The inhibitory effect of B[alpha]P was most pronounced in thymus, spleen, small intestine and testis, the average decrease of incorporated activity being more than 40% after 48 h. Contrary to the wide action of the above mentioned polycyclic aromatic hydrocarbons, an equimolar dose of anthracene lacked significant effects on the various organs.

Mechanisms of recovery from sublethal damage and potentially lethal damage induced by BrdUrd/313 nm light treatment: alkali-labile lesions

BrdUrd pulse labelling of synchronous Chinese hamster cell cultures was used to correlate repair of sublethal damage with removal of alkali-labile lesions. Both processes were modified in a quantitatively similar manner by cysteamine. In addition, the age responses for repair of sublethal damage and for cysteamine reduction of repair agreed. Through the use of thymidine as an S-phase-blocking agent it was further demonstrated that progression past the S-phase of the cell cycle was required for the loss of resistance to UVB light in BrdUrd-substituted cells. Similarly, a thymidine block administered before synthesis upon the BrdUrd-substituted template prevented the cell from acquiring the sensitivity to UVB light normally associated with synthesis on a lesioned template. The UVB-light-sensitive mutant V79-UC was shown to have reduced capacities both for the accumulation of sublethal injury and for the removal of alkali-labile lesions. These data support the notion that alkali-labile lesions are responsible for sublethal damage in BrdUrd pulse-labelled Chinese hamster cells.

[Resistance of various herpes simplex virus strains to the action of chemical inhibitors]

The effect of chemical inhibitors on reproduction of 2 laboratory and 3 vaccine strains of herpes simplex virus (HSV), types 1 and 2, was studied. By the time of the study the vaccine strains had undergone from 27 to 69 passages in chick embryo fibroblast cultures. All the vaccine strains (L2, Us, and VN) exhibited 100-1000 fold higher resistance to phosphonoacetic acid than did the laboratory F+ and G strains, and the vaccine L2 strain (HSV-1) was also 1000-fold resistant to 1-beta-D-arabinofuranosine thymine.

In vitro cytotoxic properties of plasma samples from uremic patients

The effect of uremic plasma on the growth of cultured cells was compared to that of control and of nonuremic plasma. Multiplication of D98 and 3T3 cells was measured by cell counting and by 3H-Thymidine incorporation. Uremic plasma was taken from severely uremic children (plasma creat. greater than 0.45 mM) and from hemodialyzed (HD) patients; plasma samples from HD patients were obtained at the beginning and the end of dialysis sessions. The 3H-Thymidine incorporation in the presence of uremic plasma (3665 +/- 520 cpm, n - 23) was lower than in the presence of control plasma (7700 +/- 1.080 cpm, n = 14) (P less than 0.01). The rate of 3H-Thymidine incorporation decreased regularly in the presence of increasing amounts of uremic plasma. 3H-Thymidine incorporation in post dialysis plasma was greater than in predialysis plasma (3902 +/- 664 cpm vs 9430 +/- 1540 cpm, n = 8) (P less than 0.01). To investigate the properties of the cytotoxic material, studies were performed with plasma ultrafiltrate (UF) and ultrafiltrate fractions obtained by G-15 Sepadex filtration. Uremic UF and fractions displayed no cytotoxic properties when cultured alone. Preincubation of uremic UF and the "middle molecular" fraction with control plasma restored a cytotoxic effect which, for total ultrafiltrate, was similar to that observed with uremic plasma. Thus, uremic plasma displays cytotoxic properties related to ultrafiltrable molecules which are not cytotoxic by themseleves but which are cytotoxic in the presence of plasma macromolecules.

Mechanism of deoxycytidine rescue of thymidine toxicity in human T-leukemic lymphocytes

Cultured malignant human lymphocytes are highly sensitive to growth inhibition by thymidine (50% inhibitory dose congruent to 10(-5) M). Growth inhibition reflects sustained elevation of the deoxythymidine 5'-triphosphate pool associated with secondary elevation of the deoxyguanosine 5'-triphosphate pool and reduction in the deoxycytidine 5'-triphosphate (dCTP) pool. Deoxycytidine was capable of partially reversing thymidine growth inhibition at a concentration of 0.5 microM, and growth recovery was virtually complete at 8 microM. The dCTP pool remained depressed until growth inhibition reversal by deoxycytidine was complete, and at a higher concentration of deoxycytidine the dCTP rose above control levels, but the deoxythymidine 5'-triphosphate and deoxyguanosine 5'-triphosphate pools remained elevated. These results support the view that thymidine growth inhibition induces a critical deficiency of dCTP via allosteric inhibition of ribonucleotide reductase rather than inhibiting DNA replication directly by elevated deoxythymidine 5'-triphosphate or deoxyguanosine 5'-triphosphate pools.

5,6-Dihydro-5-azathymidine: in vitro antiviral properties against human herpesviruses

5,6-Dihydro-5-azathymidine (DHAdT), a novel water-soluble nucleoside antibiotic, inhibits herpes simplex virus type 1 (HSV-1) in appropriately infected cell cultures to a greater extent than herpes simplex virus type 2 (HSV-2). Vaccinia virus was less susceptible than HSV-2, and pseudorabies virus yields were not reduced at the concentrations studied. Plaque formation by varicella-zoster virus was suppressed by DHAdT. DHAdT was slightly toxic to cells at concentrations that were inhibitory for HSV-1 and varicella-zoster virus. Thymidine and deoxyuridine completely reversed the anti-HSV-1 activity of DHAdT, whereas deoxycytidine was partially effective. Compared with other nucleoside analogs with activity for HSV-1, DHAdT was less active than 5-iodo-2'-deoxyuridine or 1-beta-d-arabinofuranosylcytosine and nearly equipotent with 9-beta-d-arabinofuranosyladenine.

Prediction of therapeutic response in acute leukaemia

The degree to which anticancer drugs suppressed incorporation of tritiated thymidine into leukaemic cells was measured in 26 patients with acute leukaemia. Subsequent achievement of remission correlated best with suppression by cytosine arabinoside (ara-C). 6 of 7 patients with acute myelocytic and myelomonocytic leukaemia whose cells demonstrated suppression by ara-C of 3H-thymidine incorporation of 15% or less of control counts subsequently achieved remission, while 4 of 6 patients whose cells showed smaller degrees of inhibition did not achieve remission. Patients with acute lymphocytic leukaemia showed a similar pattern.

[Attempts to characterize a tumor specific inhibitor extracted from the maternal part of the bovine placenta]

A fraction was isolated from the maternal part of bovine placenta, which significantly inhibits the incorporation of thymidine into the DNA of tumour cells. This factor has, however, only a limited effect on the same reaction in bone marrow cells or in fibroblasts. It is suggested that the factor enters the cell by an active transport mechanism and that the active part thereof is a protein. The protein pattern of the chromatin is not influenced by the factor as is the phosphorylation or acetylation of nuclear proteins.

Activation of murine lymphocytes by cyclic guanosine 3',5'-monophosphate: specificity and role in mitogen activity

Cyclic guanosine 3',5'-monophosphate (cyclic GMP) stimulates nucleic acid synthesis in lymphocytes, and has been implicated as the intracellular effector of the actions of mitogenic agents on these cells. In the present study, we examined the specificity of the mitogenic activity of cyclic GMP and of its 8-bromo (Br) derivatives, and the effects of the T cell mitogens, concanavalin A, phytohemagglutinin, and staphylococcal entertoxin B (SEB) on the cyclic GMP content and guanylate cyclase activity of mouse splenic lymphocytes. Cyclic GMP and guanosine modestly increased the incorporation of [3H] thymidine into DNA by cultured lymphocytes, but were far less effective than their 8-Br-guanosine and 8-Br-5'-GMP exceeded that of 8-Br-cyclic GMP, when tested in the presence and absence of serum in the culture media. Combined addition of maximal doses of these nucleotides did not give additive stimulatory effects, suggesting an action on a common subpopulation of cells, and possibly a common mechanism. By contrast, cyclic AMP, 8-Br-cyclic AMP, 8-Br-adenosine, cholera toxin and prostaglandin E1 suppressed both basal [3H]thymidine incorporation and stimulation of this parameter by T-cell mitogens and the guanine nucleotides. Rapid effects of concanavalin A, phytohemagglutinin, SEB, guanosine, 5'-GMP, 8-Br-guanosine, and 8-Br-5'-GMP on the cyclic GMP content of murine lymphocytes could not be demonstrated. Similarly, concanavalin A, phytohemagglutinin and SEB failed to alter guanylate cyclase activity when added directly to cellular homogenates or pre-incubated with intact cells. Conversely, carbamylcholine rapidly increased lymphocyte cyclic GMP but was not mitogenic. These results are consistent with the hypothesis that cyclic GMP and cyclic AMP are antagonistic in their influence on lymphocyte mitogenesis. However, they also demonstrate that related nucleotides are more potent mitogens than cyclic GMP itself and suggest that activation of murine lymphocytes by concanavalin A, phytohemagglutinin and SEB may not be mediated by rapid increases in cellular cyclic GMP content. Since high concentrations of exogenous cyclic GMP and related nucleotides must be used to influence DNA synthesis, the biologic significance of this effect remains uncertain.

Immunological observations on patients with Lesch-Nyhan syndrome, and on the role of de-novo purine synthesis in lymphocyte transformation

Three patients with the Lesch-Nyhan syndrome were found to have normal delayed hypersensitivity, peripheral-blood T-lymphocyte counts, lymphocyte responses to P.H.A., and serum IgM, IgA, and IgE levels. However, the percentages of B-lymphocytes, IgG levels, serum-isohaemagglutinin titres, and lymphocyte responses to pokeweed mitogen (P.W.M.) were subnormal. These observations suggest that activity of the salvage pathway of purine synthesis catalysed by hypoxanthine-guanine phosphoribosyl transferase (H.G.P.R.T.) is not required for the responses of T-lymphocytes to mitogenic or antigenic stimulation, but may contribute to the proliferation and function of B lymphocytes. The major role of the de-novo pathway of purine synthesis in human lymphocyte responses to mitogenic or antigenic stimulation is shown by the effects of inhibitors of this pathway, including immunosuppressive agents, and by the effects of congenital deficiency or inhibition of adenosine deaminase.

Stimulation of human lymphocytes by galactose-specific abrus and ricinus lectins

Human lymphocyte cultures were incubated with the nontoxic abrus agglutinin and with ricin B chain, and the incorporation of 3H thymidine was measured. Abrus agglutinin stimulated strongly the thymidine incorporation whereas ricin B chain had a much lesser effect. When galactose or lactose was added to the cultures together with the lectins, the abrus agglutinin and ricin B chain induced thymidine incorporation was strongly reduced. There was a linear relationship between the concentration of lectin and the concentration of lactose required for inhibition of lymphocyte stimulation. N-acetyl-galactosamine had a much lesser inhibiting effect and alpha-methyl-mannoside did not cause any inhibition. The abrus agglutinin induced thymidine incorporation was not demonstrable before 36 to 40 hr and reached its maximum after 2 to 5 days. If lactose was added within the first 4 hr of incubation with abrus agglutinin no stimulation was observed.

[Effect of methotrexate on the leukemic cell cycle in mouse ascitic leukemia L1210]

In cells of L1210 ascite leukemia cells, methotrexate inhibited H3-thymidine incorporation, blocked shortly (during 4 hours) the G1 leads to S transition, and did not affect cells in G2-phase or in the late S phase. Almost half a cell population was degenerated and cells in S- and G1-phases were affected in equal proportion. This may suggest that methotrexate is not S-phase specific for cells of leukemia L1210. A simultaneous administration of vinblastine increases the antitumour effect of methotrexate. Cells in G2-phase constitute, presumably, a significant proportion of cells recovered after methotrexate administration. A comparison of the data obtained with literature evidence shows that in the sensitive (leukemia L1210) and resistant (acute mieloid leukemia of man) forms of leukemia, methotrexate affects cells that are in S-phase, whereas cells being in G1-phase are affected only when the sensitive tumours are treated.

Effects of ethanol and ethionine on DNA synthesis during experimental liver regeneration

Ethanol reversed the ethionine-induced inhibition of 3H-thymidine incoroporation into hepatic DNA in the male and female rat after partial hepatectomy.

An Ultrastructural and Radio-Autographic Study of the Effect Of Ethidium Bromide on the Interphase Nucleus of Meristematic Plant Cells

In the present work the effects of an intermediate dose (20µg/ml) of ethidium bromide on nuclear structures of meristematic plant cells (Raphanus sativus) have been studied under both light and electron microscopy. Radioautography was also exploited to assess the action of this drug on the incorporation activity of nucleic acid precursors.

After a 30-min treatment with ethidium bromide, no noticeable ultrastructural modifications are detected but the incorporation of both thymidine and uridine is already markedly impaired. As treatment is extended to 1 h, the numerous light lacunae characterizing the fibrillar nucleolar zones in normal cells transform into elongated areas which are often found to extend to the surface of this organelle and are continuous with perinucleolar chromatin masses. After 2 h, many small bodies consisting of granular material appear in the nucleoplasm. The nucleolus gradually loses most of its granular component and, eventually, becomes predominantly fibrillar in texture; in many cells it breaks up into a number of irregular masses. Throughout various stages of the experiment, certain cells show small spherical nucleoli characterized by the presence on their surface of one or two conspicuous reticulate masses which are heavily labelled with thymidine and, consequently, consist mostly of chromatin. In view of the fact that ethidium bromide has been observed in this study to induce a certain degree of condensation of chromatin within the nuclear cavity, it is surmised that this drug also brings about migration of intranucleolar DNA to the surface of this organelle.