A B S T R A C T We sought to determine whether the third component of complement (C3)

Castanospermine, an inhibitor of a-glucosidase activity, was injected into rats to determine its effects in vivo. Daily injections of alkaloid, at levels of 0.5 mg/g of body weight, or higher, for 3 days decreased hepatic a-glucosidase to 40% of control values, whereas a-glucosidase in brain was reduced to 25% of control values and that in spleen and kidney was reduced to about 40%. In liver, both the neutral (pH 6.5) and the acidic (pH 4.5) a-glucosidase activities were inhibited, but the former was more susceptible. On the other hand, 13-Nacetylhexosaminidase activity was elevated in the livers of treated animals, whereas f8-galactosidase activity was unchanged and a-mannosidase activity was somewhat inhibited. Livers of treated animals were examined by light and electron microscopy and compared to control animals to determine whether changes in morphology had occurred. In treated animals fed normal rat chow, the hepatocytes were smaller in size and simplified in structure, whereas the high-glucose diet lessened these alterations. Furthermore, in those animals receiving castanospermine at 1.0 mg or higher per g of body weight for 3 days, there was a marked decrease in the amount of glycogen in the cytoplasm, while a large number of lysosomes were observed that were full of dense, granular material. That this dense material was indeed glycogen was shown by the fact that it disappeared when blocks of fixed tissue were pretreated with a-amylase. Glycogen levels in liver, as measured either colorimetrically or enzymatically, were somewhat depressed at the higher levels of castanospermine.Castanospermine (1,6,7,8-tetrahydroxyoctahydroindolizine) is an indolizine alkaloid that is found in the seeds of the Australian tree Castanospermum australe (1). These seeds have been reported to be toxic to animals and to cause various symptoms, including gastrointestinal upset. We recently found that this alkaloid was a potent inhibitor of lysosomal a-and ,3-glucosidase but had no effect on a number of other glycosidases (2). In addition, castanospermine also inhibits the neutral glucosidase(s) that participates in the processing of the oligosaccharide chains of the N-linked glycoproteins (3). Thus, in cultured mammalian cells, castanospermine prevents the formation of complex chains and gives rise to glycoproteins having mostly Glc3Man7_9GlcNAc2 structures.Since glucosidases are very important enzymes in a number of metabolic sequences, including glycogen degradation, we were interested in determining whether this alkaloid would affect glycogen metabolism if injected into animals. Based on preliminary experiments, we postulated that castanospermine would inhibit the lysosomal a-glucosidase and produce a lysosomal block leading to the abnormal storage of glycogen. The data presented in this paper show that this alkaloid markedly depressed the activity levels of a-glucosidase in liver and other tissues. Coupled with this decreased activity was the finding that the livers of rats given this alkaloid for several days had...

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Lovastatin, an inhibitor of protein prenylation, was reported to inhibit DNA synthesis and induce apoptosis in cultured cells. This report describes the morphological consequences of lovastatin treatment. Lovastatin (50 microM) induced mesangial cell rounding and disassembly of actin stress fibers within 24 to 48 h. After 48 to 72 h of lovastatin treatment, the cells detached from the substratum and underwent apoptotic cell death as evidenced by condensed nuclear chromatin, nuclear fragmentation, cell blebbing and decrease in cell size. Time lapse cinematography revealed that lovastatin caused cell rounding by either inhibiting cytokinesis or cell spreading following cytokinesis. Lovastatin-induced cell rounding, detachment, and apoptosis were dependent upon cell proliferation. These effects were prevented by serum deprivation to inhibit cell proliferation or by plating cells at densities which resulted in contact inhibition of cell growth. Lovastatin-induced mesangial cell rounding and apoptosis were also prevented by the inclusion of the isoprenoids all-trans-farnesol or all-trans-geranylgeraniol in the incubation medium. These results indicate that the effects of lovastatin were mediated by inhibition of protein isoprenylation because exogenous all-trans-geranylgeraniol can be used only in protein prenylation. The small GTP-binding protein RhoA, which may be important for cell spreading and cytokinesis, accumulated in the cytosol following treatment with lovastatin, suggestive of its inactivation. This effect was also prevented by the inclusion of either farnesol or geranylgeraniol in the incubation medium. Thus, lovastatin-induced apoptosis in mesangial cells occurs by interfering with prenylation dependent mitotic and post-mitotic events.

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