Noriyuki Yabunaka

Effect of thermal stress on glutathione metabolism in human erythrocytes.

This is the first experiment to investigate the effect of heat and cold stress on glutathione metabolism in human erythrocytes. We immersed men at three different water temperatures for 10 min. At 39°C, no remarkable changes were observed. Levels of glutathione (GSH) decreased from 2.44 (0.14) to 1.80 (0.10) μmol·ml red blood cells−1 [μmol·ml RBC−1; mean (SEM);P<0.0005] and those of lipid peroxides increased from 1.87 (0.03) to 2.06 (0.04) nmol · ml RBC−1 (P<0.01) after the immersion at 42°C. In contrast, levels of GSH increased from 2.46 (0.17) to 2.91 (0.17) μmol · ml RBC−1 (P<0.05) and those of lipid peroxides did not change after the immersion at 25°C. The activities of glutathione peroxidase decreased from 35.90 (1.83) to 34.33 (1.66) IU · g Hb−1 (P < 0.01) after the immersion at 42°C; however, these activities did not change after the immersion at 25°C. The activities of glutathione reductase (both active and inactive forms) showed no changes at any temperatures. These changes indicate that heat stress causes oxidative stress in the human body; however, cold stress is thought to augment the activity of the antioxidative defence system. It is suggested that body exposure to hot environmental conditions should not be recommended for patients suffering from a damaged antioxidative defence system.

Elevated levels of heat-shock protein 70 (HSP70) in the mononuclear cells of patients with non-insulin-dependent diabetes mellitus

Increased free radicals and reduced levels of antioxidants have been reported in diabetes mellitus. Since heat-shock protein 70 (HSP70) is a stress-induced protein and is suggested to play a protective role against oxidative stress, we have investigated whether HSP7O acts as one of the defense systems against this stress. We separated mononuclear cells from diabetic patients (N=12) and age- and sex-matched healthy controls (N =12), and detected HSP70 by western blot analysis. The results were expressed by the ratio of the density determined by laser densitometry, to that of 10 mu g of purified HSP70. HSP70 levels in the mononuclear cells of diabetic patients (0.78 + or- 0.56) were significantly high, compared with healthy subjects (0.43 + or - 0.23) (P < 0.05). No correlation was found between HSP7O and hemoglobin A1c, fasting plasma glucose, duration of diabetes or diabetic complications except age. A negative correlation was found between HSP70 and age (r = -0.658, P < 0.05). These results suggest that HSP70 levels in the mononuclear cells are elevated reflecting increased oxidative stress in patients with diabetes.

Balneotherapy and platelet glutathione metabolism in type II diabetic patients

Effects of balneotherapy on platelet glutathione metabolism were investigated in 12 type II (non-insulin-dependent) diabetic patients. Levels of the reduced form of glutathione (GSH) on admission were well correlated with those of fasting plasma glucose (FPG;r=0.692,P<0.02). After 4 weeks of balneotherapy, the mean level of GSH showed no changes; however, in well-controlled patients (FPG <150 mg/dl), the level increased (P<0.01) and in poorly controlled patients (FPG >150 mg/dl), the value decreased (P<0.05). There was a negative correlation between glutathione peroxidase (GPX) activities and the levels of FPG (r=−0.430,P<0.05). After balneotherapy, the activity increased in 5 patients, decreased in 3 patients and showed no changes (alteration within ±3%) in all the other patients. From these findings in diabetic patients we concluded: (1) platelet GSH synthesis appeared to be induced in response to oxidative stress; (2) lowered GPX activities indicated that the antioxidative defense system was impaired; and (3) platelet glutathione metabolism was partially improved by 4 weeks balneotherapy, an effect thought to be dependent on the control status of plasma glucose levels. It is suggested that balneotherapy is beneficial for patients whose platelet antioxidative defense system is damaged, such as those with diabetes mellitus and coronary heart disease.

Continuous measurement of blood pressure, heart rate and left ventricular performance during and after isometric exercise in head-out water immersion

Experiments were performed to determine the changes in blood pressure (BP), heart rate (HR) and left ventricular function during and after isometric knee extension during thermoneutral (35°C) head-out water immersion (HWI) or in air. Seven healthy male subjects mean age 24 (SD 3) years kept their knees extended (60% maximal voluntary extension) until they reached exhaustion. The mean BP at rest was 80 (SD 10) and 78 (SD 8) mmHg [10.7 (SD 1.33) and 10.4 (SD 1.07) kPa] in air and during HWI, respectively, (NS). They increased progressively (P < 0.01) during contraction and reached maximal values of 148 (SD 22) and 143 (SD 26) mmHg [19.7 (SD 2.93) and 19.1 (SD 3.47) kPa] in air and in HWI, respectively, (NS). The mean HR at rest was 74 (SD 8) and 70 (SD 11) beats·min−1 in air and in HWI, respectively, (NS). They also increased progressively (P < 0.01) and reached 126 (SD 14) and 118 (SD 17) beats·min−1 in air and in HWI, respectively, (NS). The changes in BP and HR during contraction in HWI tended to be smaller than those in air (NS). Left ventricular end diastolic diameters (dd) at rest in HWI were greater than those in air and were maintained at higher values during and after isometric contraction. In contrast, dd decreased during isometric contraction in air (P < 0.01). The change of left ventricular systolic diameters (ds) in HWI was no different to those in air. From these findings, isometric exercise in thermoneutral HWI would seem to be characterized by a greater dd than in air and this could be useful for patients with deconditioning effects such as orthostatic hypotension.

Thermal stress and diabetic complications.

Activities of erythrocyte aldose reductase were compared in 34 normal subjects, 45 diabetic patients, and nine young men following immersion in water at 25, 39, and 42° C. Mean basal enzyme activity was 1.11 (SEM 0.12) U/g Hb and 2.07 (SEM 0.14) U/g Hb in normal controls and diabetic patients, respectively (P<0.0001). Activities of the enzyme showed a good correlation with hemaglobin A1 (HbA1) concentrations (P<0.01) but not with fasting plasma glucose concentrations. After immersion at 42° C for 10 min, enzyme activity was increased by 37.6% (P<0.01); however, the activity decreased by 52.2% (P<0.005) after immersion for 10 min at 39° C and by 47.0% (P<0.05) at 25° C. These changes suggest that heat stress might aggravate diabetic complications, and body exposure to hot environmental conditions is not recommended for diabetic patients.

The mechanism of high-density lipoprotein cholesterol elevation in patients treated with simvastatin

Fourteen patients with untreated hypercholesterolemia were given simvastatin 5 mg/d for 12 weeks. Cholesteryl ester transfer protein (CETP) activity and lecithin-cholesterol acyltransferase (LCAT) activity were determined every 4 weeks during treatment. Total cholesterol (TC) decreased from 279.1 ± 55.1 mg/dL before treatment to 224.6 ± 30.7 mg/dL after 12 weeks, and high-density lipoprotein cholesterol (HDL-C) rose from 56.2 ± 13 mg/dL to 61.2 ± 15.2 mg/dL. These changes were statistically significant. CETP activity decreased significantly from 26.8 ± 6.4% before treatment to 23.6 ± 6.3% after 12 weeks, and LCAT activity at 37 °C increased significantly from 43.3 ± 33.5 nmol/mL per hour to 68.4 ± 32.6 nmol/mL per hour. The changes in TC correlated with those in CETP activity at each time point (r = .674), but not with those in LCAT activity. The HDL-C level was negatively correlated with CETP activity at each time point (r = .655) but not with LCAT activity. These findings show that CETP activity may play a more important role than LCAT activity in simvastatin-induced HDL-C elevation and suggest that simvastatin increases HDL-C by reducing CETP activity secondary to low-density lipoprotein cholesterol reduction.