Biological activities of cyclophellitol

Cyclophellitol [1S,2R,3S,4R,5R,6R)-5-hydroxymethyl-7-oxabicyclo[4,1,0] heptane-2,3,4-triol) was tested against 9 glycosidases and found to be a specific inhibitor of almond beta-glucosidase. Cyclophellitol inhibited almond beta-glucosidase activity by 50% at 0.8 micrograms/ml and was a competitive inhibitor of almond beta-glucosidase as revealed by Lineweaver-Burk plot. Cyclophellitol was inactive against yeast alpha-glucosidase, beta-galactosidase, beta-glucuronidase, alpha-L-fucosidase, end-beta-N-acetyl glucosaminidase, alpha-mannosidase, and cellulase. It was weakly active toward fungal beta-xylosidase. Cyclophellitol-treated almond beta-glucosidase was equally suppressed after dialysis; thus cyclophellitol is likely to bind to almond beta-glucosidase irreversibly. The inhibitor was found by fluorimetric assay to be active against beta-glucosidase but inactive toward alpha-glucosidase in Molt-4 microsomal fraction. It also inhibited Molt-4 beta-glucocerebrosidase completely at 2 micrograms/ml when the enzyme was assayed with a synthetic labeled substrate, and the inhibitory activity was more than one hundred times higher than that of nojirimycin, castanospermine, or of deoxynojirimycin. Mice administered 1 mg of cyclophellitol daily for 5 days began to exhibit severe abnormalities of nervous system similar to those found in Gaucher's mouse.     

Effects of concanavalin A on 5-hydroxytryptamine uptake by rabbit blood platelets and on their ultrastructure.

1. Effects of concanavalin A (Con A) and other lectins on 5-hydroxytryptamine (5-HT) uptake by rabbit blood platelets and on their ultrastructure were studied. 2. Uptake of [3H]-5-HT by platelets was decreased by application of Con A, E-PHA (lectin from Phaseolus vulgaris) and lentil-PHA (lectin from Lens culinaris), but not by wheat germ agglutinin (WGA). Con A induced specific changes in the ultrastructure of platelets, causing (i) a change in external appearance from a discoid to an irregularly spherical shape, (ii) re-arrangement of the canalicular system and formation of a concentric structure. These effects of Con A on platelets were antagonized by pretreatment with alpha-methyl-D-mannoside (alpha-MM), a specific inhibitor of Con A binding to glycoprotein. 3. The inhibition of 5-HT uptake by Con A was antagonized by colchicine, vinblastine and sodium nitroprusside (SNP), but not by cytochalasin B. 4. Theophylline, papaverine and dibutyryl cyclic adenosine 3',5'-monophosphate (db cyclic AMP) antagonized the effect of Con A on 5-HT uptake, but dibutyryl cyclic guanosine 3',5'-monophosphate had no effect. Theophylline and db cyclic AMP did not influence the effect of Con A on the ultrastructure of platelets. 5. It is suggested that binding of Con A to specific receptor glycoproteins can inhibit the 5-HT uptake system of platelets. Microtubules, contractile protein and the membrane adenylate cyclase system of platelets may also be regulatory factors in this mechanism.     

牛膝多糖硫酸酯体外和体内抗艾滋病病毒作用

牛膝多糖硫酸酯(Achyranthes bidentata polysaccharide sulfate，ABPS)为牛膝多糖经硫酸酯化修饰后获得的产物，其结构清楚、理化性质稳定及分子质量小，具有抗单纯疱疹病毒、柯萨奇病毒和乙型肝炎病毒等作用。本文研究其在体外和体内的抗艾滋病病毒1型(human immunodeficiency virus type 1，HIV-1)活性。体外采用 ³H掺入法和酶联免疫吸附法测定ABPS对HIV-1逆转录酶和整合酶的活性，其半数抑制浓度(50% inhibiting concentrations,IC₅₀)分别为(2.948±0.556) μmol·L^-1和(0.155±0.030) μmol·L^-1， 但25 μmol·L^-1 ABPS对HIV-1蛋白酶无效。ABPS在MT-4细胞培养内对HIV-1实验病毒株IIIB和在人外周血单核细胞培养内对AZT耐药病毒株的急性感染有较强的抑制作用， 但在HIV-1 IIIB慢性感染的H9细胞培养中则无效。血清药理学研究表明，单次腹腔注射大鼠ABPS 125 mg·kg^-1或连续腹腔注射小鼠ABPS 3 mg·kg^-1(qd×20)后鼠血清在MT-4细胞培养内对HIV-1 P24抗原都有抑制作用，但口服ABPS生物利用度低，灌胃大鼠ABPS 2 g·kg^-1或灌胃小鼠ABPS 300 mg·kg^-1无效。实验结果提示ABPS有抗HIV-1作用，有可能用于防治HIV-1感染，值得进一步研究。     

A quantitative evaluation of radiolabelled lectin retention on oral mucosa in vitro and in vivo.

Previous work has identified lectins that bind to the cells present on the oral mucosa for their potential use as a means of retaining a drug delivery system on the mucosal surfaces of the mouth. In this study, a radiolabelling technique was developed to allow the quantification of lectin binding to human buccal cells in vitro, and the retention of the lectins in the oral cavity of a rat model in vivo. Lectins were labelled with 99mTc using a cyclic diethylene triamine pentaacetic acid conjugation technique. In the in vitro study, human buccal cells were obtained by scraping the inner surface of the cheek. The suspended cells were exposed to the labelled lectin solution for 30 min and after washing with buffer the activity associated with the cells determined. In the in vivo study, male Wistar rats were briefly anaesthetized during which 10 microl of a solution containing labelled lectin was applied into the buccal pouch. At set times the rats were killed and the lower buccal cavity mucosal tissue and tongue dissected out and monitored for bound lectin. The in vitro study indicated that the lectins from Arachis Hypogaea, Canavalia ensiformis and Triticum vulgaris bound to oral mucosal cells. The T. vulgaris lectin showed the greatest binding, calculated to be 6.77 x 10(9) molecules per cell. The in vivo retention of C. ensiformis and T. vulgaris lectins on rat oral mucosal tissue was also evident. The T. vulgaris lectin showed significantly higher levels of retained lectin after 30 min (29.54 +/- 4.20 microg SD) on the oral mucosal tissue and 28.37 microg (+/-2.13 SD) on the tongue and was still detected at similar levels after 2 h. These studies indicate that significant lectin binding to human buccal cells occurs in vitro and retention in an animal model occurs for over 2 h in vivo. The T. vulgaris lectin showed most promise for further work.