Motoyoshi Ikebuchi

Abnormal glutathione metabolism and increased cytotoxicity caused by H2O2 in human umbilical vein endothelial cells cultured in high glucose medium

SummaryTo determine whether increased oxidative stress in diabetes mellitus is due to an impaired freeradical scavenger function in endothelial cells, GSH-dependent H2O2 degradation in human umbilical vein endothelial cells was studied. The GSH-dependent, NaN3-uninhibitable H2O2-degradation in endothelial cells was reduced by 48% (p <0.001) when the cells were exposed to 33 mmol/l d-glucose vs 5.5 mmol/l d-glucose. This impairment was dependent not only on the d-glucose concentration in the medium but also on d-glucose specific metabolism, since neither 27.5 mmol/l l-glucose nor 27.5 mmol/l d-raffinose had any effect on the peroxide degradation activity. Activation of the glutathione redox cycle by H2O2 in cells exposed to high glucose concentrations was attenuated as compared with 5.5 mmol/l d-glucose because of: 1) a 42% decrease (p <0.001) in intracellular NADPH content, and 2) a 34% reduction (p <0.01) in glutathione release into the media. This results in an accumulation of GSSG in the cells following exposure to H2O2. Both H2O2-evoked 51Cr-release and H2O2-induced endothelial cell damage were significantly (p <0.01) greater in the 33 mmol/l d-glucose group than in the 5.5 mmol/l d-glucose group. These results indicate that the abnormal glutathione redox cycle observed in endothelial cells is induced by high glucose concentrations in the medium, resulting in an impairment of reduced GSH-dependent H2O2-degradation. These abnormalities may associate with the increased cellular damage following an exogenous exposure to H2O2.

Demonstration, of Insulin Resistance in Coronary Artery Disease Documented With Angiography

OBJECTIVE To evaluate the relation between insulin resistance and coronary atherosclerosis, insulin sensitivity in lean nondiabetic, normotensive subjects with and without obstructive coronary artery disease (CAD). The correlation between insulin resistance and degree of coronary stenosis was also investigated. RESEARCH DESIGN AND METHODS Four groups were studied: 1) nine subjects with normal glucose tolerance(NGT) without CAD, 2) 10 subjects with NGT with CAD, 3) nine subjects withimpaired glucose tolerance (IGT) without CAD, and 4) 10 subjects with IGT with CAD. Insulin sensitivity was determined by the steady-state plasma glucose (SSPG) method using Sandostatin. Coronary angiography was performed in all study subjects, and the severity of coronary artery atherosclerosis wasquantified in a modified Gensini score. RESULTS The SSPG (millimoles per liter) levels were significantly higher in the patients with CAD compared with control subjects (control vs. patient group: 4.8 ±0.5 vs. 7.9 ± 0.9 with NGT, P < 0.05; 5.6 ± 0.5 vs. 11.1 ± 0.8 with IGT, P < 0.001), indicating the presence of insulin resistance in patients with CAD. The coronary atherosclerosis score (CAS) was significantly and positively correlated with SSPG (r = 0.74, P < 0.05) and 2-h insulin area (r = 0.78, P < 0.01) in NGT subjects with CAD. On the other hand, the percentage fall of plasma free fatty acid (0–30 min) during an insulin sensitivity test was significantly decreased in the subjects with CAD and was inversely correlated with the CAS (r = −0.43, P < 0.05), especially in NGT subjects with CAD. CONCLUSIONS These data suggest that in patients with CAD, insulin-mediated glucose metabolism is significantly impaired, and a significant correlation was noted between insulin resistance and severity of CAD. Therefore, the hyperinsulinemia often observed in patients with CAD is attributable to the compensatory mechanism of the β-cell to the inadequate action of insulin for glucose metabolism. Hyperinsulinemia in the presence of insulin resistance aggravates dyslipidemia and may stimulate the atheromatous process by an as-yet-unknown mechanism.

Role of Insulin Resistance Associated With Compensatory Hyperinsulinemia in Ischemic Stroke

BACKGROUND AND PURPOSE Although insulin resistance and hyperinsulinemia play a crucial role in the pathogenesis of atherosclerosis, little is known about their roles in ischemic stroke. The purpose of this study was to clarify whether insulin resistance and hyperinsulinemia are causative factors in the pathogenesis of ischemic stroke. METHODS Thirty-four consecutive patients with ischemic stroke, who were normotensive, nondiabetic, and not obese, were classified into three groups--atherothrombotic infarction (n = 16), lacunar infarction (n = 10), and cardioembolic infarction (n = 8)--based on clinical findings, brain imaging, and cerebral angiography. Both oral glucose tolerance tests and lipid analyses were performed. Insulin sensitivity was determined by the steady state plasma glucose method with the use of octreotide acetate. Data were compared with those of healthy control subjects (n = 15). RESULTS Steady state plasma glucose levels were significantly higher in the atherothrombotic infarction group compared with control subjects and the other two stroke groups, indicating the presence of insulin resistance in patients with atherothrombotic infarction. In the atherothrombotic infarction group, the 2-hour insulin area (area under the plasma insulin concentration curve) during a 75-g oral glucose tolerance test was significantly increased and dyslipidemic changes (increased triglyceride and apolipoprotein B, decreased high-density lipoprotein) were observed, whereas these changes were not found in the lacunar infarction and cardioembolic stroke groups. CONCLUSIONS Insulin resistance in association with compensatory hyperinsulinemia and dyslipidemia may be an important pathogenetic factor underlying the development of atherothrombotic infarction.

Impaired Activation of Glucose Oxidation and NADPH Supply in Human Endothelial Cells Exposed to H2O2 in High-Glucose Medium

The effects of glucose concentration on D-glucose oxidation and reduced nicotinamide adenine dinucleotide phosphate (NADPH) supply were studied during exposure of cultured human umbilical vein endothelial cells to hydrogen peroxide (H2O2). The activation of glucose oxidation via the pentose phosphate pathway (PPP), induced by exposure of cells to 200 μmol/l H2O2 for 1 h, was reduced by 50% (P < 0.01) in cells cultured for 5–7 days in 33 mmol/l D-glucose (HG) versus those cultured in 5.5 mmol/l D-glucose without (NG) or with (HR) 27.5 mmol/l D-raffinose. The intracellular NADPH content in HG cells, but not in NG or HR cells, was decreased by 42% (P < 0.01) by exposing cells to 200 μmol/l H2O2. The decrease in NADPH was dependent on D-glucose concentration in the medium and was prevented in glutathione (GSH)-depleted cells. The latter observation suggests that the decrease in NADPH is associated with activation of the GSH redox cycle. In the presence of 200 μmol/l H2O2, lactate release into the medium, NADH/NAD ratio, and phosphofructokinase activity in HG cells were 56, 53, and 68% greater, respectively, than in the NG group, which indicates that inhibition of glycolysis by H2O2 is less marked in the HG group compared with NG group. These results indicate that activation of the PPP was impaired in endothelial cells cultured under conditions of high-glucose and oxidative stress, resulting in a decreased supply of NADPH to various NADPH-dependent pathways, including the GSH redox cycle.

Glycation, oxidative stress, and scavenger activity: glucose metabolism and radical scavenger dysfunction in endothelial cells.

It has been reported that oxidative stress is increased in vivo in the diabetic state. Increased oxidative stress is caused not only by accelerated production of oxygen-free radicals but also by decreased scavenging of those molecules. Endothelial cells are extremely sensitive to oxidative stress, resulting in impairments of various endothelial cell function. In this report, we studied the association of intracellular glucose metabolism and oxygen radical scavenging function via the glutathione redox (GR) cycle in cells exposed to high-glucose conditions using cultured human umbilical vein endothelial cells. Glutathione-dependent H2O2 degradation in cells exposed to 33 mmol/1 glucose (HG) for 5–7 days was reduced by 48% vs. 5.5 mmol/1 glucose (NG). This impairment under the oxidative stress was D-glucose-specific and concentration-dependent and was also associated with a 42% decrease in intracellular NADPH content. Exposure of cells to 200 μmol/1 H2O2 stimulated the GR cycle and the pentose phosphate pathway (PPP) at the same time. In the HG condition, activation of PPP was reduced by 50%, which was consistent with a decrease in NADPH content. Inhibition of glycolysis by H2O2 was less marked in HG cells versus NG cells. Activation of polyol pathway in HG cells is not responsible for the decrease in intracellular NADPH content. These results indicate that activation of the PPP and NADPH supply to the GR cycle is impaired in HG cells exposed to H2O2, which may result in increased oxidative stress to endothelial cells.

Improvement of insulin sensitivity for glucose metabolism with the long-acting Ca-channel blocker amlodipine in essential hypertensive subjects☆

To clarify whether the long-acting calcium-channel blocker amlodipine restores insulin insensitivity in essential hypertension, insulin sensitivity tests were performed at the physiological steady-state insulin level (45 to 55 microU/mL) before and after amlodipine (2.5 to 7.5 mg/d) administration for 2 to 4 months in borderline and mild essential hypertensive subjects. Instead of somatostatin, Sandostatin (Sandoz, Basel, Switzerland) was used for the determination of steady-state plasma glucose (SSPG) in the same way as previously described. SSPG, which was initially high (212.9 +/- 18.0 mg/dL, mean +/- SE), was significantly reduced to 169.8 +/- 14.7 after amlodipine treatment. Responses of ketone bodies during the test at 30 minutes, which reflect the insulin effect on lipolysis in adipose tissue and hepatic fatty acid oxidation, also improved after amlodipine treatment. Norepinephrine, noted to be mildly elevated after amlodipine treatment, decreased during the sensitivity test at 2 hours probably due to the sedative effect, without any change in the fractional extraction of Na. This indicates that the physiological level of insulin does not activate sympathetic nerve activity or stimulate Na reabsorption. The long-acting calcium-channel blocker amlodipine has significantly improved the initially decreased insulin sensitivity for glucose metabolism at least partially in borderline or mild essential hypertension.

Development of approximate formula for LDL-chol, LDL-apo B and LDL-chol:LDL-apo B as indices of hyperapobetalipoproteinemia and small dense LDL

Estimation of LDL-chol and LDL-apo B is useful for the diagnosis of hyperapobetalipoproteinemia (normal LDL-chol with increased LDL-apo B), which is one of the most commonly occurring lipoprotein disorders associated with atherosclerotic cardiovascular diseases. The LDL-chol/LDL-apo B ratio reflects the level of small dense LDL, which is an important risk factor for IHD, CVD and ASO. In order to estimate LDL-apo B and LDL-chol/LDL-apo B ratio from blood chol, TG, HDL-chol and apo B values, we developed a formula for LDL-chol ¿0.94Chol- 0.94HDL-chol - 0.19TG¿, LDL-apo B ¿apo B - 0.09Chol + 0.09HDL-chol-0.08TG¿, and LDL-chol/LDL-apo B [¿0.94Chol-0.94HDL-chol - 0.19TG¿/¿apo B - 0.09Chol + 0.09HDL-chol-0.08TG¿] using ultracentrifugal data from 2179 subjects. These were calculated by the least squares method on the assumption that a certain compositional relationship exists between Chol, TG and apo B in VLDL, IDL and LDL. Friedewalds formula for LDL-chol (Chol - HDL-chol - 0.2TG) includes IDL-chol, but the present new formula theoretically excludes IDL-chol. It suggests a better estimation for the correct LDL-chol. Estimated LDL-apo B is useful for the diagnosis of hyperapobetalipoproteinemia and detection of small dense LDL. Without performing ultracentrifuge, additional information is obtained for the quantitative and qualitative alteration of LDL, such as small dense LDL. The above formulae and a new classification of lipoproteinemia including apo B were applied to the analyses of lipoprotein profiles of subjects with cardiovascular diseases, which were compared with those in the general population. Hyperapobetalipoproteinemia with high TG was observed 2-3 times more frequently in subjects with CAD, MI and ASO than in the Suita population. Lower ratios of LDL-chol/LDL-apo B, reflecting preponderance of small dense LDL, were observed in the above three groups. Type IIb and combined low HDL-chol were also frequent phenotypes in CAD, A-Th and ASO. The present formulae are useful for the detailed analyses of lipoprotein disorders in both qualitative as well as quantitative aspects.

Improvement of insulin sensitivity and dyslipidemia with a new α-glucosidase inhibitor, voglibose, in nondiabetic hyperinsulinemic subjects☆

This study was undertaken to investigate the effect of voglibose, a new alpha-glucosidase inhibitor, on glucose and lipid metabolism in nondiabetic hyperinsulinemic subjects. Sixteen nondiabetic subjects with hyperinsulinemia participated in the study. They were divided into two groups of eight subjects with normal (NGT) and impaired (IGT) glucose tolerance. A meal tolerance test and a 75-g oral glucose tolerance test (OGTT) were performed at the beginning (baseline phase) and end (treatment phase) of the 12-week treatment. Serum lipid levels were measured every 4 weeks throughout the treatment phase and follow-up phase (8 weeks). All patients received 1 0.2-mg tablet of voglibose before each test meal (3 tablets per day). We also measured insulin sensitivity using a steady-state plasma glucose (SSPG) method in eight normotensive hyperinsulinemic subjects and in eight age- and body mass index (BMI)-matched control subjects before and after the drug treatment. Voglibose significantly decreased the responses of plasma glucose and insulin on the meal tolerance test. The area under the curve for 2-hour insulin during the 75-g OGTT decreased after treatment, whereas that for 2-hour glucose did not change before and after treatment. SSPG was reduced after treatment, indicating improvement of insulin sensitivity. Moreover, treatment with voglibose resulted in a significant decline of triglyceride level and an elevation of high-density lipoprotein (HDL) cholesterol and apolipoprotein A-1. These values returned to near-baseline levels after the drug was discontinued. Consequently, we conclude that this agent not only has a direct hypoglycemic effect through decreased absorption of carbohydrate, but also a hypoinsulinemic and hypolipidemic effect via improved insulin sensitivity.

Increase in cardiac muscle fructose content in streptozotocin-induced diabetic rats.

To evaluate the activation of the sorbitol pathway in cardiac muscle in diabetic rats, we measured sorbitol, fructose, and myo-inositol content in cardiac tissue obtained from control and streptozotocin-diabetic rats, with or without an 8-week insulin treatment, using gas chromatography-mass spectrometry (GC-MS). Cardiac fructose and sorbitol content in 10-week diabetic rats increased by 60-fold and 3.9-fold of those of control rats, respectively (P less than .001). In contrast, cardiac myo-inositol content in 10-week diabetic rats decreased to 56% (P less than .025) of the control value. The abnormalities in cardiac fructose, sorbitol, and myo-inositol content were completely normalized by the 8-week insulin treatment, which was initiated 2 weeks after the induction of diabetes. There was no difference in cardiac aldose reductase activity between control and diabetic rats. However, cardiac sorbitol dehydrogenase activity in diabetic rats was 151% (P less than .005) higher than that of control rats, although hepatic sorbitol dehydrogenase activity was not different between the two groups. These results indicate that the sorbitol pathway is significantly activated in cardiac tissue obtained from streptozotocin-induced diabetic rats, which results in the marked cardiac accumulation of fructose.

Pyruvate Improves Deleterious Effects of High Glucose on Activation of Pentose Phosphate Pathway and Glutathione Redox Cycle in Endothelial Cells

In our previous study (Diabetes 44:520–526, 1995), endothelial cells cultured in high glucose condition showed impairment of an oxidant-induced activation of the pentose phosphate pathway (PPP) and a reduced supply of NADPH to the glutathione redox cycle. To gain insight into the mechanisms of this impairment, the protective effect of pyruvate was studied in human umbilical vein endothelial cells cultured in either 5.5 mmol/l glucose (normal glucose [NG] condition) or 33 mmol/l glucose (high glucose [HG] condition). Through pretreatment of cells with 0.2 mmol/l pyruvate for 5–7 days in the HG condition, glucose oxidation through the PPP and total cellular NADPH content in the presence of 0.2 mmol/l H2O2 were increased by 54 (P < 0.05) and 34%, respectively, and glutathione-dependent degradation of H2O2 in HG cells was enhanced by 41% (P < 0.01), when compared with those cells to which pyruvate was not added. The addition of pyruvate significantly reduced the fructose 1,6-bisphosphate (FDP) content and free cytoplasmic NADH/NAD ratio, estimated by increased pyruvate/lactate ratio in NG and HG cells exposed to H2O2. Furthermore, the addition of pyruvate also showed a 46% reduction (P < 0.01) of endothelial cell damage induced by H2O2 in HG cells. These results indicate that abnormalities in PPP activation and glutathione redox cycle activity induced by H2O2 in HG cells are compensated, and that the accentuated reductive stress is improved by an addition of pyruvate. These pyruvate effects are associated with protection against an oxidant-induced endothelial cell injury in the high glucose condition.