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Biomedical subjects

I Miwa

Publications and source records attributed to I Miwa.

At least 55 records · Page 3Linked to original sources
PubMed1995

Tissue and subcellular distribution of glucokinase in rat liver and their changes during fasting-refeeding.

The distribution of glucokinase in rat liver under both normal feeding and fasting-refeeding conditions was investigated immunohistochemically. Under normal feeding conditions, glucokinase immunoreactivity was observed in both nuclei and cytoplasm of parenchymal cells. The nuclei were stained intensely and evenly, whereas the cytoplasm showed weak immunoreactivity of different degrees of staining intensity depending on the location of the cells. The cytoplasm of perivenous hepatocytes was stained more intensely, though not so much more, than that of periportal hepatocytes. The cytoplasm of hepatocytes surrounding the terminal hepatic venule (THV), of hepatocytes surrounding the portal triad, and of some other hepatocytes showed a stronger immunoreactivity than that of residual hepatocytes. The nuclear immunoreactivity in hepatocytes surrounding the portal triad and in some other hepatocytes was weak or absent, and positive immunoreactivity was detected at the plasma membrane of some of these cells. After 72 h of fasting, glucokinase immunoreactivity was markedly decreased in all hepatocytes. After the start of refeeding, the cytoplasmic immunoreactivity began to increase first in the parenchymal cells surrounding the THV and extended to those in the intermediate zone followed by those in the periportal zone. In contrast, the increase in nuclear immunoreactivity started in hepatocytes situated in the intermediate zone adjacent to the perivenous zone and then extended to those in the perivenous zone followed by those in the periportal zone. Hepatocytes surrounding either THV or portal triad showed a distinctive change in immunoreactivity during the refeeding period. After 10 h of refeeding, strong immunoreactivity was observed in both the cytoplasm and the nuclei of all hepatocytes, and appreciable glucokinase immunoreactivity was detected at the plasma membrane of some hepatocytes. These findings are discussed from the standpoint of a functional role of glucokinase in hepatic glucose metabolism.

Animals↗
PubMed1995

Clinical efficacy of pravastatin for hyperlipidemia in patients with type 2 diabetes mellitus.

The efficacy of pravastatin (CAS 81131-70-6) on serum lipid levels in 91 type 2 diabetic patients with mean glycosylated hemoglobin of 8.5% was investigated up to 12 weeks. Oral administration of 10 to 20 mg/d of pravastatin significantly decreased total cholesterol by 18.4 +/- 1.5% after 4 weeks. When analyzed separately in type IIa and IIb hyperlipidemia, the reduction of total cholesterol by pravastatin was more prominent in the former. Low-density lipoprotein cholesterol were also significantly decreased 22.2 +/- 2.7% after 4 weeks. The effect of pravastatin in reducing triglyceride was more prominent in patients with higher triglyceride compared to those with lower triglyceride before the administration of the drug. High-density lipoprotein cholesterol showed a slight but significant increase by 4.2 +/- 1.9% after 4 weeks. Among the apolipoproteins examined, apolipoprotein B was significantly decreased after 4 weeks. Atherogenic index and apolipoprotein B/apolipoprotein A-I ratio were also significantly decreased after 4 weeks. The efficacy of pravastatin was also observed after 12 weeks to the same extent as after 4 weeks. No major side effects or abnormalities of laboratory parameters have been observed. These data lead to the conclusion that pravastatin is useful for the treatment of hyperlipidemia in type 2 diabetic patients with poor glycemic control without major adverse effects.

Adult↗
PubMed1994

Evidence for glucokinase translocation by glucose in rat hepatocytes.

By an immunohistochemical technique, we examined changes in the subcellular distribution of rat liver glucokinase in response to external stimuli. Glucokinase immunoreactivity was found predominantly in the nucleus of hepatocytes. In situ perfusion of the liver with 20 mM glucose for 10 min caused a marked decrease in nuclear immunoreactivity and an increase in cytoplasmic immunoreactivity. Insulin (10 nmol/l) potentiated this glucose effect. However, no change took place when 5 mM glucose was perfused. These results indicate that glucokinase is translocated from the nucleus to the cytoplasm in response to a high concentration of glucose.

Animals↗
PubMed1994

Correlation between circadian periods and cellular activities in Paramecium bursaria.

Paramecium bursaria shows a circadian rhythm of photoaccumulation: photoaccumulation is stronger during the day than at night. We obtained five strains of P. bursaria having different circadian periods under continuous light conditions, ranging from 20.9 to 27.9 h. Various physiological activities were compared in the cells of these strains. The periods of contractile vacuole contraction were in the range 10-15 s, which was almost proportional to the periods of the circadian rhythm in each strain. Swimming velocities were inversely proportional to the circadian period; i.e. swimming velocities were high in strains whose circadian periods were short. Resting membrane potential was more depolarized in strains with longer circadian periods. Finally, the membrane resistance of the resting state was reduced in proportion to the increase of the circadian period. Such correlation between the cellular properties and the circadian period suggests that the circadian clock mechanism is associated with various physiological activities of the cell.

Animals↗
PubMed1994

Purification and characterization of triokinase from porcine kidney.

In order to be able to use triokinase for the enzymatic assay of tissue glyceraldehyde, we purified the enzyme to homogeneity from porcine kidney and characterized its biochemical properties. The purification was performed by polyethylene glycol fractionation, anion exchange chromatography, hydroxyapatite chromatography, hydrophobic chromatography, and gel filtration. The enzyme was purified 937-fold from the crude extract with an overall yield of 28%. It had a molecular weight of 122,000 and was a dimer composed of identical subunits. The optimal pH and optimal temperature were 7.0 and 60 degrees C, respectively. This enzyme was stable when incubated at pH 7.0 at 40 degrees C for 1 h in the presence of 0.1 mg/ml bovine serum albumin. No loss of activity occurred for at least 1 month when the enzyme was stored at 4 degrees C in the presence of 1 mM dithiothreitol and 15 mM NaN3 under N2. Only three compounds, i.e., D-glyceraldehyde, dihydroxyacetone, and glycolaldehyde, acted as the substrate of the enzyme, having Km's of 11, < 5, and 260 microM, respectively. The Km for ATP-Mg2+ was 68 microM. These results indicate that porcine kidney triokinase has properties advantageous for the glyceraldehyde assay using glyceraldehyde-3-phosphate dehydrogenase as a coupling enzyme.

Amino Acid Sequence↗
PubMed1994

Purification of rat liver glucokinase.

A new purification method for rat liver glucokinase was developed. Glucokinase was purified to homogeneity in a yield of 70% in 5 days. The procedure consists of DEAE-cellulose ion-exchange chromatography, QAE-Toyopearl ion-exchange chromatography, glucosamine-Sepharose affinity chromatography, and HiLoad Superdex 200 gel filtration. Purified glucokinase had a specific activity of 200 units/mg protein and was highly stable in the presence of 100 mM glucose, 300 mM KCl, and 20% glycerol. We found that some of the methionine residues of glucokinase were oxidized to methionine sulfoxide residues during dialysis in the presence of glucose. It would appear that this oxidation is caused by formation of hydroxyl radicals in the presence of glucose and contaminating transition metal(s).

Animals↗
PubMed1994

The effects of altering extracellular potassium ion concentration on the membrane potential and circadian clock of Paramecium bursaria.

In some neural models of circadian rhythmicity, membrane potential and transmembrane flux of potassium and calcium ions appear to play important roles in the entrainment and central mechanisms of the biological clock. We wondered whether these cellular variables might be generally involved in circadian clocks, even non-neural clocks. Therefore, we tested the impact of changing extracellular potassium level on the circadian rhythm of photoaccumulation of Paramecium cells, whose membrane potential responds to changes of extracellular potassium in a manner similar to that of neurones. We found that pulse or step changes of extracellular potassium concentration did not phase-shift the circadian clock of P. bursaria cells in a phase-specific manner. Furthermore, modifying the extracellular concentration of calcium did not affect the magnitude of light-induced phase resetting. Therefore, while membrane potential and calcium fluxes may be crucial components of the circadian clock system in some organisms, especially in neural systems that involve intercellular communication, the P. bursaria data indicate that membrane potential changes are not necessarily an intrinsic component of circadian organization at the cellular level.

Animals↗
PubMed1993

Stimulatory effect of phospholipase A2 treatment on glucose utilization in human erythrocytes.

We examined whether modification of membrane phospholipids of human erythrocytes by hydrolysis with phospholipase A2 (PLA2 from bee venom) would affect glucose utilization, chosen as a typical model of intracellular metabolism, and, if so, intended to clarify the mechanism of the alteration of glycolysis. Treatment of erythrocytes with PLA2 induced a marked shape change (i.e., crenation) and significantly increased the rate of lactate production from glucose. Available evidence indicated that there is no relevance of this cell-shape change to the alteration of glycolysis. The lack of a detectable effect of papain treatment on glycolysis in PLA2-treated cells suggested that the increase in glycolysis by PLA2 treatment might not be caused by the conformational change of band-3 protein through modulation of membrane phospholipids. The result of the measurement of lactate production in the presence and absence of ouabain did not support the idea that hydrolysis of phospholipids by PLA2 treatment makes plasma membranes leaky to Na+ and consequently enhances glycolysis through activation of Na+/K(+)-ATPase. The action of PLA2 on glycolysis was abolished by extraction of free fatty acids in the cell membrane with bovine serum albumin. Loading erythrocytes with free fatty acid (oleic acid, linoleic acid, or arachidonic acid) caused a significant increase in glycolysis. Analysis of glycolytic intermediates suggested that the enhancement of glycolysis was induced by activation of 6-phosphofructokinase. The data, thus, indicate that treatment of human erythrocytes with PLA2 significantly accelerates glucose utilization and suggest that the stimulation of glycolysis is caused by activation of 6-phosphofructokinase through liberation of free fatty acids of membrane phospholipids by PLA2.

Adult↗
PubMed1993

Alteration of anomeric preference of glucose-induced insulin secretion by glyceraldehyde.

Glucokinase activity in pancreatic islets was dose-dependently inactivated by D-glyceraldehyde, whereas islet hexokinase activity was not altered. In untreated islets, alpha-D-glucose stimulated insulin secretion more efficiently than beta-D-glucose at a glucose concentration of 10 mM. However, glyceraldehyde highly attenuated the insulin-secretory response of pancreatic islets to alpha-D-glucose compared with that to beta-D-glucose. Thus, there was apparently no anomeric preference of glucose-induced insulin secretion in glyceraldehyde-treated islets. Glyceraldehyde affected neither the alpha-preference of glucose phosphorylation by glucokinase nor the beta-preference of glucose phosphorylation by hexokinase. Our study suggests that defective discrimination of glucose anomers by glyceraldehyde-treated islets may be caused by inactivation of glucokinase.

Animals↗
PubMed1993

Inhibition of glucose-induced insulin secretion through inactivation of glucokinase by glyceraldehyde.

D-Glyceraldehyde irreversibly inhibited rat liver glucokinase in a concentration-dependent manner. The inactivation of glucokinase by glyceraldehyde was blocked by the presence of its substrates such as glucose and mannose. Glucokinase was highly sensitive to glyceraldehyde compared with some other glycolytic enzymes (from animal tissues) including hexokinase, glucose-6-phosphate isomerase, 6-phosphofructokinase, glyceraldehyde-3-phosphate dehydrogenase, and pyruvate kinase. The amino acid analysis of untreated and glyceraldehyde-treated glucokinase suggested that glyceraldehyde-induced inactivation of glucokinase is caused by glycation of Lys residues of the enzyme by the triose. Treatment of pancreatic islets with 6 mM glyceraldehyde for 1 h at 37 degrees C caused both inactivation of glucokinase and inhibition of glucose-induced insulin secretion. Another glucose-phosphorylating enzyme (hexokinase) in pancreatic islets, however, was little affected by glyceraldehyde. In addition, glyceraldehyde did not affect the insulin secretory responses of islets to nonglucose secretagogues such as glyceraldehyde and Leu. When pancreatic islets were cultured with a lower concentration (1 mM) of glyceraldehyde for a longer time (17 h) in the presence of 10 mM glucose to mimic the in vivo conditions, both glucokinase activity and glucose-induced insulin secretion were again decreased. This study demonstrates that glucose-induced insulin secretion is impaired by glyceraldehyde through the inactivation of glucokinase. The implication of this finding in the pathophysiology of type II diabetes is discussed.

Amino Acids↗
PubMed1993

Two interconvertible forms of glucose-6-phosphate isomerase in rat muscle.

Chromatography of crude rat muscle extracts on CM-cellulose resulted in separation of glucose-6-phosphate isomerase (GPI) into two active peaks (designated types I and II in order of elution). Incubation of type I and type II at pH 6.0, 7.0, or 8.0 in the presence and absence of KCI revealed that one type of GPI is converted to the other type under certain conditions and that the two types are interconvertible by changing the incubation conditions. The two types were similar in molecular weight, kinetic property, and optimum pH. A remarkable difference was observed in pH-activity profile: the activity of type I, but not type II, was detectable at pH 6-7. The present results suggest that rat muscle has two types of GPI which are interconvertible and that the two types may be conformational variants of the same enzyme. It is conceivable that the interconversion between the two types is related to the regulation of glycolysis at lower intracellular pHs.

Animals↗
PubMed1992

Anomeric preference of glucose utilization in rat erythrocytes.

The beta-anomer of glucose relative to the alpha-anomer was more rapidly metabolized into lactate by rat erythrocytes at 37 degrees C (beta/alpha ratio = ca. 1.3): the amounts of alpha- and beta-D-glucose metabolized into lactate during 3 min were 0.21 and 0.27 mumol/gHb, respectively. Also, the transport of beta-D-glucose into erythrocytes was more rapid than that of alpha-D-glucose: the amounts of alpha- and beta-D-glucose transported into erythrocytes during 3 min were approximately 3.5 and 5.0 mumol/gHb, respectively. Glucose phosphorylation by rat erythrocyte hexokinase (i.e., a possible rate-limiting step in glycolysis) occurred at higher velocities with the beta-anomer than with the alpha-anomer (beta/alpha ratio = 1.28). The Km value of hexokinase for either anomer of glucose was 53 microM. The glucose concentrations in erythrocytes incubated with alpha- and beta-D-glucose reached about 1 mM in 1 min, indicating that hexokinase is almost completely saturated with glucose within less than 1 min. The results suggest that glucose phosphorylation and glucose transport are major and minor determinants, respectively, for the anomeric preference of glucose utilization in rat erythrocytes.

Animals↗
PubMed1991

Alpha- and beta-anomeric preference of glucose-induced insulin secretion at physiological and higher glucose concentrations, respectively.

We determined the anomeric preference of glucose phosphorylation by islet glucokinase, glucose utilization by pancreatic islets, and insulin secretion induced by glucose over a wide range of glucose concentrations. alpha-D-Glucose was phosphorylated faster than beta-D-glucose by islet glucokinase at lower glucose concentrations (5 and 10 mM), whereas the opposite anomeric preference was observed at higher glucose concentrations (40 and 60 mM). At 20 mM, there was no significant difference in phosphorylation rate between the two anomers. Similar patterns of anomeric preference were observed both in islet glucose utilization and in glucose-induced insulin secretion. The present study affords strong evidence that glucokinase is responsible for the anomeric preference of glucose-stimulated insulin secretion through anomeric discrimination in islet glucose utilization.

Animals↗
PubMed1991

Effects of novel aldose reductase inhibitors, M16209 and M16287, on streptozotocin-induced diabetic neuropathy in rats.

We investigated the effects of novel aldose reductase inhibitors, M16209 (1-(3-bromobenzo[b]furan-2-ylsulfonyl)hydantoin) and M16287 (1-(3-chlorobenzo[b]furan-2-ylsulfonyl)hydantoin), on neuropathy in streptozotocin-induced (STZ) diabetic rats. Both compounds (3-100 mg/kg per day, p.o.) dose dependently improved the decreased motor nerve conduction velocity in the sciatic nerve during a 14-day treatment period. These compounds also partially ameliorated the diabetes-induced histological changes in the sciatic nerve. A distinct increase in sorbitol content and a slight decrease in myo-inositol content was observed in the sciatic nerve of STZ diabetic rats, and the sorbitol accumulation was dose dependently suppressed by treatment with M16209 and M16287. Treatment started at an earlier period was more effective in the suppression of sorbitol accumulation. There was a significant correlation between motor nerve conduction velocity and nerve sorbitol content, whereas there was none between motor nerve conduction velocity and myo-inositol content. The present study indicates that M16209 and M16287 are potent aldose reductase inhibitors expected to be useful for the treatment of diabetic complications.

Aldehyde Reductase↗
PubMed1991

Properties of novel aldose reductase inhibitors, M16209 and M16287, in comparison with known inhibitors, ONO-2235 and sorbinil.

Properties and efficacies of novel aldose reductase (AR) inhibitors, M16209 (1-(3-bromobenzo[b]furan-2-ylsulfonyl)hydantoin) and M16287 (1-(3-chlorobenzo[b]furan-2-ylsulfonyl)hydantoin), were examined in vitro and in vivo, compared with known AR inhibitors, ONO-2235 and sorbinil. These four compounds inhibited partially purified aldose reductases from various origins, and the potencies of M16209 and M16287 were on the whole similar to ONO-2235, and were greater than that of sorbinil. The IC50 values of the four AR inhibitors did not substantially depend on the substrate used. Kinetic studies of inhibition of partially purified bovine lens (BLAR) revealed that M16209, M16287 and sorbinil were uncompetitive with glyceraldehyde and noncompetitive with nicotineamide adenine dinucleotide phosphate (NADPH), whereas ONO-2235 was noncompetitive with both glyceraldehyde and NADPH. Aldose reductase became less sensitive to the four inhibitors as enzyme purification progressed, although the susceptibility to inhibition was partially reversed by incubation with dithiothreitol. In addition, the four compounds slightly affected those enzymes of carbohydrate and glutathione metabolism which were tested. M16209 and M16287 prevented sorbitol accumulation in isolated rat tissues as potently as ONO-2235 and sorbinil. M16209 and M16287 were effective in the prevention of galactosemic cataracts and amelioration of diabetic neuropathy with almost the same potency, while ONO-2235 was effective only in neuropathy, and sorbinil was effective in galactosemic cataracts and diabetic neuropathy with a different potency. These results indicate that M16209 and M16287 are potent aldose reductase inhibitors, which could be applicable to treatment for diabetic complications.

Aldehyde Reductase↗
PubMed1990

Anomeric preference of glucose utilization in human erythrocytes loaded with glucokinase.

Human erythrocytes were loaded with homogeneous rat liver glucokinase by an encapsulation method based on hypotonic hemolysis and isotonic resealing. As assayed at 10 mM glucose, glucokinase and hexokinase activities in glucokinase-loaded erythrocytes were 218 and 384 nmol/min/gHb, respectively; whereas hexokinase activity in both intact and unloaded red cells, which contain no glucokinase activity, was about 400 nmol/min/gHb. No difference in the rate of lactate production from glucose anomers between intact and unloaded erythrocytes suggested that the encapsulation procedure itself did not affect glucose utilization in red cells. Alpha-anomeric preference in lactate production from glucose was observed in glucokinase-loaded erythrocytes, whereas the beta anomer of glucose was more rapidly utilized than the alpha anomer in intact and unloaded erythrocytes. The results indicate that the step of glucose phosphorylation determines the anomeric preference in glucose utilization by human erythrocytes, since glucokinase and hexokinase are alpha- and beta-preferential, respectively, in glucose phosphorylation.

Animals↗
PubMed1990

In vivo activities of aldose reductase inhibitors having a 1-(arylsulfonyl)hydantoin structure.

Two potent aldose reductase inhibitors, 1-[(2,5-dichlorophenyl)sulfonyl]hydantoin (Di-Cl-PSH) and 1-[beta-naphthyl)sulfonyl]hydantoin (beta-NSH), were tested for usefulness in the treatment of diabetic and galactosemic complications in animal experiments. Both drugs were effective for the treatment of diabetic neuropathy characterized by decreased motor nerve conduction velocity, that is, slowing of tail and sciatic-tibial motor nerve conduction velocities in streptozocin-induced diabetic rats was prevented during 3 weeks by intubating Di-Cl-PSH or beta-NSH at 50 mg/kg/day. Lenticular vacuole formation in rats fed a 30% galactose diet was blocked completely for at least 2 weeks by oral administration of Di-Cl-PSH or beta-NSH at both 30 and 100 mg/kg/day, whereas all of the eyes of vehicle-treated rats showed vacuole formation by day 4 on the galactose diet. The ED50 values of Di-Cl-PSH and beta-NSH for inhibition of sorbitol accumulation in the sciatic nerve and lens of streptozocin-induced diabetic rats were also estimated; the values of Di-Cl-PSH and beta-NSH were 1.1 and 3.4 mg/kg/day, respectively, for inhibition in the sciatic nerve and 4.8 and 16.0 mg/kg/day, respectively, for that in the lens. This study indicates that Di-Cl-PSH and beta-NSH have high potential for future clinical use as aldose reductase inhibitors.

Aldehyde Reductase↗