Takahito Kondo

Effect of insulin on impaired antioxidant activities in aortic endothelial cells from diabetic rabbits

The defense system of aortic endothelial cells against oxidative stress was studied in alloxan-induced diabetic rabbits, and the effect of insulin on the antioxidant activities was estimated. Endothelial cells were prepared from 10 diabetic rabbits, 18 diabetic rabbits treated with insulin, and 10 age-matched controls after 17 days of diabetes. These cells were used for the estimation of glutathione (GSH) levels and its related enzyme activities. The antioxidant activities in these endothelial cells from diabetic rabbits were compared with those from control subjects. The concentration of GSH decreased in diabetic rabbits (1.6 +/- 0.2 nmol/mg protein [mean +/- SD] v 3.7 +/- 0.6 nmol/mg protein). Decreases in the activities of Cu, Zn-superoxide dismutase (Cu,Zn-SOD) (62.7 +/- 11.0 U/mg protein v 172.9 +/- 20.2 U/mg protein), catalase (7.6 +/- 2.1 U/mg protein v 12.3 +/- 3.2 U/mg protein), and GSH peroxidase (134.0 +/- 27.0 mU/mg protein v 179.1 +/- 26.2 mU/mg protein) were observed. The activities of other GSH-related enzymes such as GSH S-transferase or GSH reductase did not change in endothelial cells from diabetic rabbits. Most of these antioxidant activities were prevented when diabetic rabbits were treated with insulin (1 to 2 U/kg/d). These antioxidant activities were also determined in the diabetic liver and kidney. Similar decreases in the cellular defense activities and prevention of the decrease in activities by insulin were observed in the diabetic liver, while these antioxidant enzyme activities in the kidney were resistant to diabetic conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and characterization of glutathione disulfide-stimulated Mg2+-ATPase from human erythrocytes

We have previously shown the presence of two different forms of glutathione disulfide (GSSG)-stimulated Mg2+-ATPases in human erythrocytes. We have now investigated a low-Km form of the enzyme from human erythrocytes. Purification of the enzyme was performed to apparent homogeneity involving procedures of affinity chromatography and gel filtration. The enzyme was composed of two non-identical subunits of Mr = 82K and 62K. The enzyme reconstituted into phospholipid vesicles showed both GSSG-stimulated Mg2+-ATPase activity (285 nmol Pi released/mg protein/min) and active GSSG transport activity (320 nmol GSSG/mg protein/min). The amino acid composition of the enzyme was similar to that of the enzyme purified from cytoplasmic membranes of human hepatocytes. These enzymes were immunologically cross reactive. These results indicate that this enzyme functions in the active transport of GSSG as it possibly does in hepatocytes.

Estimation and characterization of glycosylated carbonic anhydrase I in erythrocytes from patients with diabetes mellitus

Glycosylated form of carbonic anhydrase isozyme I was found in human erythrocytes. The percent of glycosylated enzyme of the total erythrocyte carbonic anhydrase I of patients with diabetes mellitus was significantly higher than that from normal controls. Characterization of the glycosylated carbonic anhydrase I was studied using an enzyme purified from diabetic patients. The glycosylated enzyme showed a slightly acidic isoelectric point in comparison with that of a nonglycosylated enzyme. The specific activity of the glycosylated enzyme was approximately 40% of that of the normal enzyme, and the immunological activity decreased to 52% of that of the normal enzyme. Estimation of carbohydrates which may form a ketoamine linkage with the enzyme was studied using [3H]-labelled glycosylated enzyme synthesized by incubation of the enzyme with [3H]-D-glucose in vitro, and it was found that one mol of glucose binds to one mol of enzyme. Exposure of red cells to a higher concentration of glucose in diabetics brought about glycosylation of carbonic anhydrase, which is associated with its low activity enzymatically and immunologically.

Purification of nucleosidediphosphatase of rat liver by metal-chelate affinity chromatography

A procedure is presented for the purification of nucleosidediphosphatase (nucleosidediphosphate phosphohydrolase, EC 3.6.1.6) of rat liver by affinity chromatography using metal conjugated to epoxy-activated Sepharose 6B. The enzyme is eluted from the conjugate by a solution of L-histidine. The enzyme, when bound to metal-chelate gel, is active in a suspended form, suggesting that the catalytic site is different from the site that binds to the metal-chelate gels. Substrate specificity and Km value of the enzyme obtained are similar to those of the enzyme obtained from the same sources by a conventional procedure, indicating that the metal-chelate affinity chromatography does not bring about any substantial change in the catalytic properties.

A solid-phase radioimmunoassay for human carbonic anhydrase B.

A sensitive and specific radioimmunoassay method for human erythrocyte carbonic anhydrase B was developed using a solid-phase technique. The assay was found to be sensitive for the detection of nanogram amounts of the enzyme in incubation mixtures. Iodination of it gave rise to a loss of antigenicity and a solid-phase assay technique using antibody-coated paper discs was employed in order to exclude the chemical modification or conformational changes of the enzyme. The levels of carbonic anhydrase B in the erythrocytes of newborn infants and in some biological fluids were determined.

Determination of carbonic anhydrase C and β2-microglobulin by radioimmunoassay in urine of heavy-metal-exposed subjects and patients with renal tubular acidosis

Abstract Carbonic anhydrase C (CA-C) was measured by the radioimmunoassay in urine specimens from normal individuals, residents in mercury-polluted area, cadmium-exposed workers, lead-exposed workers, and patients with primary or secondary renal tubular acidosis. None of the urine in the normal subjects demonstrated CA-C levels above 40 μg/g creatinine. Some of the cadmium-exposed workers, residents in mercury-polluted area, and patients with renal tubular acidosis excreted large amounts of CA-C that were 10–250 times higher than the normal. Urinary β2-microglobulin (BMG) was also determined in relation to the CA-C levels. Most of the subjects exposed to heavy metals had high levels of urine CA-C or BMG or both. Some individuals had high levels of urine CA-C although BMG levels were within normal values. These findings seem to suggest that the mechanisms of urinary excretion of these two proteins were different and the quantitative determination of urinary CA-C by radioimmunoassay appears to be also a useful and sensitive test for detecting the renal tubular disorders in environmental exposure of heavy metals or those in renal tubular acidosis.

Inhibitory effect of thyroxine on carbonic anhydrase B isozyme biosynthesis in rabbit reticulocyte lysates.

Abstract Biosynthesis of rabbit red cell carbonic anhydrase isozyme B and C was demonstrated in reticulocyte cell-free lysates by the specific immunoprecipitin reaction. Using this homologous protein synthesis system, it was found that 10−5 to 10−7 M thyroxine preferentially inhibited the synthesis of carbonic anhydrase B isozyme without affecting that of C isozyme. These results suggested that this inhibitory action of the protein synthesis by thyroxine may be responsible for the decreased level of the B type isozymes in human hyperthyroidism or experimental hyperthyroidism of rabbits.

Decrease of the inhibition of lipid peroxidation by glutathione-dependent system in erythrocytes of non-insulin dependent diabetics.

SummaryThe inhibition of lipid peroxidation of erythrocyte membranes by glutathione-dependent protection was studied in patients with non-insulin dependent diabetes mellitus. Incubation of red cells from diabetics with 1.5 mM t-butyl hydroperoxide resulted in a lipid peroxidation increase greater than that of normal controls. Glutathione-dependent and glutathione-independent protection against oxidative damage was examined using an artificial system, in which erythrocyte ghosts were incubated with t-butyl peroxide and dialysed hemolysate in the presence or the absence of 2 mM glutathione. The glutathione-dependent protection of hemolysate from diabetics was approximately 70% of that from normal controls.The results suggest that decrease in glutathione-dependent protection against lipid peroxidation, along with decrease in glutathione levels, increases oxidative damage in erythrocyte membranes taken from diabetic patients.

Effects of cold stress on glutathione and related enzymes in rat erythrocytes

Effects of acute and chronic cold stress on glutathione and related enzymes in rat erythrocytes were investigated. Blood from both cold-acclimated (CA) and cold-adapted (CG) rats had significantly lower concentrations of glutathione than blood from control animals. Superoxide dismutase activity was increased significantly in CA rats and tended to rise in CG rats. Activity of glutathione peroxidase in erythrocytes was inconsistent in that it tended to increase in CA rats but decreased significantly in CG rats. The results may imply that CG rats suffered deleterious effects of hydrogen peroxide. On the other hand, there were marked decreases in glutathione peroxidase and glutathione reductase activities in acutely cold-exposed rats in conjunction with unchanged levels of glutathione. In all treatments the state of riboflavin metabolism was estimated to be adequate, since no increases were observed in the erythrocyte glutathione reductase activity coefficient.

Oxidative stresses induced the cystine transport activity in human erythrocytes

Cystine was transported into human erythrocytes in the presence of tertiary-butyl hydroperoxide (t-BH) or 1-chloro-2,4-dinitrobenzene (CDNB). The transport rate of cystine was dependent on the extracellular concentration of t-BH or CDNB, and on the incubation time. According to Dowex-1 column chromatography, the transported cystine was incorporated into fractions of glutathione disulfide (GSSG) and glutathione-S (GSH-S) conjugate. The transport of cystine was competitively inhibited by DL-homocystine and alanine. The inhibition rates by DL-homocystine and alanine were 75% and 68%, with similar Ki values of 0.7 mM and 0.6 mM, respectively. It is suggested that cystine transport is induced for glutathione synthesis when human erythrocytes are exposed to oxidative stresses. This transport system of cystine may serve as an emergency function in human erythrocytes.