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  • 1
    ISSN: 1432-1335
    Keywords: Tumor promoters ; Diterpene esters ; EBV early antigens ; Raji cells ; Specific binding ; Protein kinase C ; Irritant/tumor-promoting activities
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Sixteen new diterpene esters (DTE) of the tigliane, ingenane, daphnane, and 1α-alkyldaphnane types were investigated in two in vitro assays: as inhibitors of specific binding of 3H-labeled 12-O-tetradecanoylphorbol 13-acetate (TPA) to protein kinase C in a receptor preparation from mouse brain, and as inducers of Epstein-Barr virus (EBV) early antigens in Raji cells. Inhibition of binding of [3H]TPA to the receptor preparation by tigliane and ingenane DTE correlates with irritant activity in vivo, while some daphnane and 1α-alkyldaphnane DTE inhibit binding of [3H]TPA in a less pronounced manner but still are very irritant. Tumor-promoting activity does not correlate consistently with the receptor-binding data. To test the hypothesis that early antigen induction in Raji cells by DTE is coupled to functional DTE receptors (protein kinase C), the latter were searched on these Raji cells by a ‘cold acetonefilter assay’ and shown to be present. The dependence of the early antigen induction rate on the concentration of the DTE tested was demonstrated. At a given concentration of DTE, differences in the induction rate between various DTE are seen. However, a clear quantiative correlation either between early antigen induction and receptor binding data in vitro, or early-antigen-inducing activity in vitro versus irritancy and tumor-promoting activity in vivo was not observed.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1335
    Keywords: Protein kinase C ; Diterpene esters ; Luminol enhanced chemoluminescence ; Tumour promoters ; Murine peritoneal neutrophils
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In binding competition assays using a protein kinase C preparation from mouse brain (particulate fraction)3H-labelled 12-O-tetradecanoylphorbol-13-acetate (TPA), for a series of new diterpene esters (DTE) the relative binding affinity [rba=K i a (TPA)/K i a (DTE)] in relation to TPA was determined. A wide range of values was noticed, some of the DTE binding more strongly than TPA (rba 〉1), others binding less strongly than TPA (rba 〈1) In comparative terms, competition for specific binding sites appears to correlate better with irritant than with promoting acitvity of the DTE. Using mouse peritoneal neutrophils, binding of [3H]-TPA was determined by a modification of the “cold-acetone filter assay”; saturation of high-affinity sites (K d a =0.2 nM) was obtained at concentrations ≦ 1 nM, but there was also evidence for specific binding at “low-affinity” sites (K d a =26 nM). Induction of chemoluminescence in the presence of luminol in mouse peritoneal neutrophils with a set of DTE usually elecited two peaks; at concentrations ≧10 nM DTE a short-lived, “spike-like” response lasting only from 0 to about 5 min (phase A) ist followed by a “plateau” response from about 5–120 min (phase B). This latter phase of chemoluminescence stimulation with luminol correlated well with theirritant potential of the DTE used. The sequence of the two phases can be inverted partially by using first TPA at 2,5 nM followed by a quick concentration increase to 100 nM; this indicates two different concentration-dependent events. As regards the intensity of the chemoluminescent response, quantitative but not qualitative differences between DTE were observed, which show some correlation with strong and weak tumour-promoting activity. Inhibition studies suggest the involvement of the myeloperoxidase/H2O2/Cl− system in the luminogenic response; it is suggested that the release of hypochlorite or a closely related oxidant may be instrumental in tumour promotion.
    Type of Medium: Electronic Resource
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