Study Of Isolation, Characteristics And Pharmacological Effects Of Components With Biological Activities From Aloe Species

Three lectins:Lecl, Lec2, Lec3, which showed strong hemagglutination effect on rabbit red blood cells(RBCs), have been isolated from leaves of Aloe vera L. var. chinensis Haw, Aloe barbadensis Mill and Aloe arborescens Mill by DEAE-cellulose chromatography and gel filtration. They are glycoproteins tested by special colour reactions and SDS-PAGE with molecular weight of 23kDa, 26kDa and23kDa. Lec2 from Aloe barbadensis Mill and Lecl from Aloe chinensis showed the higher hemagglutinating activity of 204.8 (HA/mg) .Lectins had evident hemagglutination effect on A type human RBCs, weak effect on B and AB tpye human RBCs and showed no effect on O type human RBCs. Blood type specificity was related with different structures of glycoside receptors on RBC surface. Glycoside of lectins was mainly composed of D-mannose, D-glucose and N-GlcNAc. However ,Lec3 also contain some fucose. Results showed that among three lectins only Lec3 can be inhibited by maltose. Lec3 is first reported aloe lectin inhibited by maltose. These lectins are stable under 40℃ and pH range of 2-8. Their hemagglutination activities do not need divalent cations. Lectins from aloe had the recognition ability of K562 tumor cells and inhibited their growth. Lec3 exhibited stronger inhibition activity with an IC50 of 1.418mg/ml than Lecl (IC50=4.193mg/ml) and Lec2 (IC50=2.305mg/ml). These lectins showed no cytotoxic effect on FC cells. Anti-tumor effect of aloe lectins was further proved by animal experiment. Meanwhile, lectins from aloe can prevent the invasion of tumor cells by activating the immunity system of the living organisms. According to the results, anti-tumor effects of aloe lectins may be due to their special combination with glycoside receptors on tumor cells surface and affect the inside physiology functions. Moreover, they may also affect the connection and cohesive effect between tumor cells, therefore, inhibit tumor cells invasion and transmigration. Lectins can promote the proliferation of lymphocytes and activate immune defence system.The free radical scavenging properties (O2 and OH) of six Aloe species are to beinvestigated in some modified chemical system. The antioxidant was purified by silica column and thin layer chromatography and analyzed by HPLC. A fraction (FA) was purified from A.brevifolia Mill showed the most effective scavenging activities on o2 and OH (66.01% and 38.98% respectively). With the analysis of IR spectrum, UV spectrum and mass spectrum, the structure of FA was identifed as8-C-D-glucopyranosyl-2-[2-hydroxy]propyl-5-methyl-7-hydroxychromone.Its scavenging activity on free radicals is higher than that of aloe-emodin. Its antioxidant activity may be due to the phenoxyl on glucosyl chromone which can be react with free radicals and form relatively stable free radicals.Its protection on red blood cells was studied with in vitro red blood cells culture system. FA showed strong inhibitory activity on the H2O2 induced hemolysis of red blood cells. Its IC50 of inhibition was 0.856 mg/ml, stronger than VC(IC50 is 1.41 mg/ml) and aloe-emodin(IC50 is 1.57 mg/ml). The antioxidant activities of FA in vivo were assessed by monitoring the activity of SOD, GPx and the value of MDA in blood and liver tissue of young and aged rats. Aged rats treated with FA exhibited a significant increase of enzymic antioxidant activities and a significant decrease of the level of lipid peroxdiation. The results of animal experiment suggest that FA treatment can recover the activities of enzymic antioxidants in aged rats and protect them from the damage of lipid peroxidation with aging in which free radicals are the major causes. FA showed no cytotoxic effect on normal cells.Different tissue (outer leaf and leaf gel) extracts of six selected species of aloe were screened for their antibacterial activities by the method of agar diffusion. Extracts from the outer leaf of aloe showed remarkable antibacterial activities compared with their leaf gel preparations and the activity was correlative with anthraquinone content. The...