Antidiabetic effect of a glycoside of pelargonidin isolated from the bark of Ficus bengalensis Linn.

The antidiabetic effect of a dimethoxy derivative of perlargonidin 3-O-alpha-L rhamnoside (250 mg/kg, single dose study and 100 mg/kg/day long term study) isolated from the bark of Ficus bengalensis Linn. has been compared with that of glibenclamide (2 mg/kg and 0.5 mg/kg/day respectively) in moderately diabetic rats. The single dose glycoside treatment decreased fasting blood glucose by 19% and improved glucose tolerance by 29%. The corresponding effects of glibenclamide were 25% and 66% respectively over the control values. On one-month treatment the fasting blood glucose levels went down almost to half of the pretreatment levels in both the groups and their glucose tolerance improved by 41% in glibenclamide group and by 15% in glycoside treated group. Urine sugar decreased to traces in both the groups and they appeared healthy. In vitro studies showed that insulin secretion by beta-cells was more in presence of the pelargonidin derivative than in presence of a leucocyanidin derivative, reported to be a good anti-diabetic agent.     

Antigen presentation in the rat. II. An Ia+ radiosensitive T cell can present antigen to primed Ia- T cells

We demonstrated previously the presence of an Ia+ (OX-6+) antigen-presenting cell within the rat T cell fraction that is capable of presenting antigen to antigen-primed OX-6-T cells. This antigen-presenting cell (T-APC) reacted with the monoclonal antibodies W3/25 and W3/13, which is known to react mainly with rat T cells. Further characterization of the T-APC indicated that the cell also reacted with the monoclonal antibody OX-19, which is highly specific for rat T cells. Moreover, the antigen-presenting function of the T-APC was sensitive to treatment with mitomycin C or gamma-irradiation (2000 rad). Under similar conditions, antigen presentation by partially purified dendritic cells or macrophages was totally resistant to these treatments. The antigen-presenting activity of gamma-irradiated T-APC was not reconstituted by the addition of the lymphokines IL 1, IL 2, or Con A supernatants. Although unirradiated T-APC were able to stimulate an MLR response, this function was also sensitive to gamma-irradiation, whereas the MLR-stimulating ability of macrophages and dendritic cells was resistant to gamma-irradiation. These data indicate that Ia+ T cells from the rat are capable of presenting antigen to antigen-primed T lymphocytes and that, in contrast to antigen presentation by macrophages and dendritic cells, the function of T-APC is gamma-radiation sensitive.     

Influence of maternal mineral deficiency on the hepatic metallothionein and zinc in newborn rats

The effects of maternal Zn, Cu, or Fe deficiencies during late gestation on hepatic levels of metals and metallothionein (MT) and the binding of Zn and Cu to protein fractions were investigated in newborn rats. Timed pregnant rats were fed one of the following diets: Zn deficient (Zn-D), Cu-D, Fe-D, or control from day 12 of gestation until birth. The specific nutritional deficiency status of the dams was confirmed by low plasma levels of the deficient metal. Livers from pups were analyzed for MT, metal content, and metal-protein binding. Maternal Zn-D resulted in a greater than 50% reduction of hepatic MT levels in pups, whereas Cu-D and Fe-D had no significant effects. Pups in each deficient group showed a significant decrease in the hepatic levels of the respective metals. Fractionation of hepatic cytosols from the pups by Sephadex G-75 gel filtration showed that in both Fe-D and Cu-D pups the respective metals were depleted from the high molecular weight protein fraction, whereas in Zn-D pups the Zn was depleted mainly from the MT fraction (Ve/V0 approximately 2). Incorporation of [35S] cysteine into MT fractions was significantly lower in Zn-D pups as compared with control pups. These results indicate that there is a specific effect of the maternal Zn-D on the hepatic storage of Zn as MT in newborn rats.     

Metabolism of parenterally administered zinc and cadmium in livers of newborn rats

The interaction of injected zinc and cadmium with metallothionein was investigated in newborn rats. Tissues of 5-day-old rats were removed 24 h after a single injection (Sc) of saline or zinc (20 mg/kg, body wt.) or cadmium (1 mg/kg, body wt.) with 2.5 μCi of ⁶⁵Zn or ¹⁰⁹Cd or 5 μCi of [³⁵S]cysteine. Injection of zinc resulted in a 75% increase in the hepatic zinc concentration with a concomitant elevation of metallothionein (P < 0.001), zinc in metallothionein increased by 45% (P < 0.05); [³⁵S]cysteine incorporation indicated the induced synthesis of metallothionein. Injection of cadmium did not alter either metallothionein or zinc levels in liver, but cadmium in cytosol was preferentially bound to metallothionein. Neither treatment altered hepatic copper metabolism and copper in metallothionein, nor renal zinc and metallothionein levels. These data indicate that zinc injection can elevate hepatic zinc levels and induce metallothionein synthesis in newborn rats despite high basal levels; cadmium injection does not induce metallothionein synthesis, though cadmium is avidly sequestered by pre-existing metallothionein. The differences in the induction of metallothionein by these divalent cations can be explained by the differences in their binding affinities for thiol groups in intracellular metallothionein.     

Changes in the intracellular accumulation and distribution of metallothionein in rat liver and kidney during postnatal development

Metallothionein (MT) bound to zinc and copper was detected in high concentration in fetal and newborn rat livers by a cadmium saturation method. The levels of both hepatic zinc and MT remained high for the first 14 days after birth and decreased to adult levels by 24 days of age. There was a direct linear relationship between hepatic metallothionein and zinc concentrations during the first 31 days after birth. The ratio of MT to zinc levels also decreased with age suggesting a rapid degradation of MT during postnatal development. Immunohistochemical localization of MT by peroxidase-antiperoxidase technique, using a specific antibody to MT, showed intense intranuclear staining for MT in fetal and newborn rat liver which persisted until Day 9. The nuclear MT staining decreased with age; at 11 days it was equal both in nucleus and cytoplasm and at 14 days, MT was localized mainly in the cytoplasm, similar to adult rat liver pattern. The intranuclear localization of MT in neonates could be considered as a typical fetal-neonatal morphological pattern and its subsequent presence in the cytoplasm, an adult pattern.     

蚕豆叶片发育与衰老过程中超氧物歧化酶活性与丙二醛含量变化

蚕豆植株叶片随茎节自上而下表现出明显的发育与衰老顺序,可作为衰老特征的是叶绿素和蛋白质含量明显下降。蚕豆叶中SOD活性主要定位于12 000× g离心后所得的上清液和叶绿体组分。衰老叶片的SOD总活性和叶绿体组分的相对活性都有所下降,SOD同工酶谱也发生了改变。O_2~ 产生速率随叶龄增大而稍上升;而MDA含量在叶片外观表现枯黄衰老征兆前就急剧上升。可能因为衰老叶片过氧化氢酶活性大幅度下降与SOD之间的不平衡,致使O_2~ 代谢中间产物累积而引起膜的损伤.     

Chemical modifications of metallothionein. Preparation and characterization of polymers.

Reaction of rat liver metallothionein-II with two bifunctional cross-linking reagents, glutaraldehyde and dimethyl suberimidate, produces high yields of polymeric species. It is argued that cross-linking is trapping preformed aggregates of the protein, which therefore represent a stabilized quaternary structure of metallothionein. The two polymeric species differ in a number of respects. With dimethyl suberimidate, the polymer retains all metal-binding sites of the monomer, and has an unaltered isoelectric point. Reaction with glutaraldehyde causes loss of one or two Cd2+/Zn2+-binding sites and elevates the pI. Both species are nearly spherical aggregates, in contrast with the highly asymmetrical metallothionein. Both polymers are linked through lysine residues, and the thiol groups remain reduced. The biological significance of these aggregates is discussed.     

Biosynthesis of lysosomal hydrolases: their synthesis in bound polysomes and the role of co- and post-translational processing in determining their subcellular distribution

By in vitro translation of mRNA’s isolated from free and membrane-bound polysomes, direct evidence was obtained for the synthesis of two lysosomal hydrolases, β-glucuronidase of the rat preputial gland and cathespin D of mouse spleen, on polysomes bound to rough endoplasmic reticulum (ER) membranes. When the mRNA’s for these two proteins were translated in the presence of microsomal membranes, the in vitro synthesized polypeptides were cotranslationally glycosylated and transferred into the microsomal lumen. Polypeptides synthesized in the absence of microsomal membranes were approximately 2,000 daltons larger than the respective unglycosylated microsomal polypeptides found after short times of labeling in cultured rat liver cells treated with tunicamycin. This strongly suggests that nascent chains of the lysosomal enzymes bear transient amino terminal signals which determine synthesis on bound polysomes and are removed during the cotranslational insertion of the polypeptides into the ER membranes. In the line of cultured rat liver cells used for this work, newly synthesized lysosomal hydrolases showed a dual destination; approximately 60 percent of the microsomal polypeptides detected after short times of labeling were subsequently processed proteolytically to lower molecular weight forms characteristic of the mature enzymes. The remainder was secreted from the cells without further proteolytic processing. As previously observed by other investigations in cultured fibroblasts (A. Gonzalez-Noriega, J.H. Grubbs, V. Talkad, and W.S. Sly, 1980, J Cell Biol. 85: 839-852; A. Hasilik and E.F. Neufeld, 1980, J. Biol. Chem., 255:4937-4945.) the lysosomotropic amine chloroquine prevented the proteolytic maturation of newly synthesized hydrolases and enhanced their section. In addition, unglycosylated hydrolases synthesized in cells treated with tunicamycin were exclusively exported from the cells without undergoing proteolytic processing. These results support the notions that modified sugar residues serve as sorting out signals which address the hydrolases to their lysosomal destination and that final proteolytic cleavage of hydrolase precursors take place within lysosome itself. Structural differences in the carbohydrate chains of intracellular and secreted precursors of cathespin D were detected from their differential sensitivity to digestion with endoglycosidases H and D. These observations suggest that the hydrolases exported into the medium follow the normal secretory route and that some of their oligosaccharides are subject to modifications known to affect many secretory glycoproteins during their passage through the Golgi apparatus.     

Age dependent changes in metallothionein and accumulation of cadmium in horses

1. Analysis of livers and kidneys from 28 horses for cadmium, zinc and metallothionein showed low cadmium content in liver. There was a gradual increase in cadmium content in kidney with age. 2. Metallothionein values varied with zinc content in the liver and with cadmium content in the kidney; copper values did not vary in either tissue. 3. Metallothionein was localized mainly in the cytoplasms in liver and kidney of horses by immunohistochemistry.