Castanospermine inhibits alpha-glucosidase activities and alters glycogen distribution in animals.

Abstract

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...

Castanospermine, a Potent Inhibitor of Dengue Virus Infection In Vitro and In Vivo

“…Castanospermine was well tolerated and prevented DEN-associated mortality over a broad range of doses from 10 to 250 mg/kg/day. Doses in excess of 250 mg/kg/day in mice were associated with gastrointestinal toxicity, results that are consistent with previous observations in rats (42). The treatment success with castanospermine was in spite of the relatively unfavorable pharmacokinetics, as the rate of its renal clearance in mice is up to 20 times higher than in humans (24).…”

Transformation by the v-fms oncogene product: role of glycosylational processing and cell surface expression.

“…4). No overt toxicity was observed either in vitro (unpublished observations) or in short-term tests (3 to 7 days) in vivo (43). High dosage levels, however, were toxic to mice (A. D. Elbein, personal communication).…”

Glycan-dependent and -independent Interactions Contribute to Cellular Substrate Recruitment by Calreticulin

“…6B). Castanospermine is an inhibitor of glucose trimming (36) that is required for the generation of monoglucosylated glycans from their triglucosylated precursors. Pretreatment of cells with castanospermine prior to the methionine pulse abrogated preferential binding of cellular proteins to mCRT(WT) relative to mCRT(Y92A) (Fig.…”