Castanospermine, a plant alkaloid that inhibits the glycoprotein processing enzyme glucosidase I, has been used to inhibit N-linked oligosaccharide modification, resulting in the production of glycoproteins having Glc3Man7-9(GlcNAc)2 oligosaccharides. This alkaloid caused a significant inhibition of LDL endocytosis in cultured primate smooth muscle cells and human skin fibroblasts. At an optimum concentration of 250 micrograms/mL, castanospermine caused a 40% decrease in cell surface receptor-mediated LDL binding at 4 degrees C, with no apparent change in affinity. Further, the inhibitor had no direct effect on LDL metabolism. This inhibition of LDL receptor expression and function occurred only when the drug was present during de novo receptor synthesis, i.e., during up-regulation. Although the number of cell surface LDL receptors was significantly reduced in the presence of castanospermine, the total number of receptors in the cell was only slightly reduced, indicating that castanospermine induced a redistribution rather than a reduction in the number of receptors. Similarly, subcellular fractionation studies confirmed that castanospermine treatment of fibroblasts results in an altered distribution of receptor activity compared with controls. These findings are consistent with the conclusion that the decrease in specific LDL binding to cells grown in the presence of castanospermine is due to intracellular redistribution of the LDL receptor so that more receptor remains in internal compartments as a result of a diminished rate of transport.

A limited number of contradictory reports have appeared in the literature about the ability of radiofrequency (rf) radiation to induce chromosome aberrations in different biological systems. The technical documentation associated with such reports is often absent or deficient. In addition, no information is available as to whether any additional genotoxic hazard would result from a simultaneous exposure of mammalian cells to rf radiation and a chemical which (by itself) induces chromosome aberrations. In the work described, we have therefore tested two hypotheses. The first is that rf radiation by itself, at power densities and exposure conditions which are higher than is consistent with accepted safety guidelines, can induce chromosome aberrations in mammalian cells. The second is that, during a simultaneous exposure to a chemical known to be genotoxic, rf radiation can affect molecules, biochemical processes, or cellular organelles, and thus result in an increase or decrease in chromosome aberrations. Mitomycin C (MMC) and Adriamycin (ADR) were selected because they act by different mechanisms, and because they might put normal cells at risk during combined-modality rf radiation (hyperthermia)-chemotherapy treatment of cancer. The studies were performed with suitable 37 degrees C and equivalent convection heating-temperature controls in a manner designed to discriminate between any thermal and possible nonthermal action. Radiofrequency exposures were conducted for 2 h under conditions resulting in measurable heating (a maximum increase of 3.2 degrees C), with pulsed-wave rf radiation at a frequency of 2450 MHz and an average net forward power of 600 W, resulting in an SAR of 33.8 W/kg. Treatments with MMC or ADR were for a total of 2.5 h and encompassed the 2-h rf radiation exposure period. The CHO cells from each of the conditions were subsequently analyzed for chromosome aberrations. In cells exposed to rf radiation alone, and where a maximum temperature of approximately 40 degrees C was achieved in the tissue culture medium, no alteration in the frequency from 37 degrees C control levels was observed. Relative to the chemical treatment with MMC alone at 37 degrees C, for two different concentrations, no alteration was observed in the extent of chromosome aberrations induced by either simultaneous rf radiation exposure or convection heating to equivalent temperatures. At the ADR concentration that was used, most of the indices of chromosome aberrations which were scored indicated a similar result.(ABSTRACT TRUNCATED AT 400 WORDS)

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Castanospermine (1,6,7,8-tetrahydroxyoctahydroindolizidine) is a plant alkaloid that inhibits alpha-glucosidases, including the glycoprotein processing glucosidase I. When endothelial cells were grown for 48 h, or longer, in the presence of this alkaloid, they produced scavenger receptors for modified low-density lipoproteins (LDL) that had mostly Glc3Man7-9(GlcNAc)2 structures rather than the usual complex types of oligosaccharides. Furthermore, growth in the presence of castanospermine resulted in a substantial inhibition in degradation of endocytosed 125I-acetylated LDL, as well as a dose-dependent inhibition of 125I-acetylated LDL binding to these cells. Scatchard analysis of binding curves indicated that the diminished binding was due to a decrease in the number of scavenger receptor molecules at the cell surface rather than to a change in the affinity of the receptors for their ligand. Since castanospermine-treated cells had the same total number of cellular receptor molecules as did controls cells, it seemed likely that castanospermine caused an alteration in receptor targeting, rather than an inhibition in receptor synthesis or a stimulation in receptor degradation. Density gradient fractionation of cell homogenates showed that castanospermine-treated cells did have a much greater percentage of scavenger LDL receptor molecules in the endoplasmic reticulum-Golgi fraction and fewer receptors in the plasma membrane fraction, whereas normal cells showed the opposite distribution.

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