Katsuhiro Koyama

Oxidative stress stimulates skeletal muscle glucose uptake through a phosphatidylinositol 3-kinase-dependent pathway

We determined the acute effects of oxidative stress on glucose uptake and intracellular signaling in skeletal muscle by incubating muscles with reactive oxygen species (ROS). Xanthine oxidase (XO) is a superoxide-generating enzyme that increases ROS. Exposure of isolated rat extensor digitorum longus (EDL) muscles to Hx/XO (Hx/XO) for 20 min resulted in a dose-dependent increase in glucose uptake. To determine whether the mechanism leading to Hx/XO-stimulated glucose uptake is associated with the production of H2O2, EDL muscles from rats were preincubated with the H2O2 scavenger catalase or the superoxide scavenger superoxide dismutase (SOD) prior to incubation with Hx/XO. Catalase treatment, but not SOD, completely inhibited the increase in Hx/XO-stimulated 2-deoxyglucose (2-DG) uptake, suggesting that H2O2 is an intermediary leading to Hx/XO-stimulated glucose uptake with incubation. Direct H2O2 also resulted in a dose-dependent increase in 2-DG uptake in isolated EDL muscles, and the maximal increase was threefold over basal levels at a concentration of 600 micromol/l H2O2. H2O2-stimulated 2-DG uptake was completely inhibited by the phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin, but not the nitric oxide inhibitor NG-monomethyl-l-arginine. H2O2 stimulated the phosphorylation of Akt Ser473 (7-fold) and Thr308 (2-fold) in isolated EDL muscles. H2O2 at 600 micromol/l had no effect on ATP concentrations and did not increase the activities of either the alpha1 or alpha2 catalytic isoforms of AMP-activated protein kinase. These results demonstrate that acute exposure of muscle to ROS is a potent stimulator of skeletal muscle glucose uptake and that this occurs through a PI3K-dependent mechanism.

Role of xanthine oxidase in delayed lipid peroxidation in rat liver induced by acute exhausting exercise

Abstract The aim of this study was to examine whether xanthine oxidase (XOD)-derived hepatic oxidative damage occurs in the main not during but following strenuous exercise. The degree of damage to hepatic tissue catalyzed by XOD was investigated immediately and 3 h after a single bout of exhausting exercise, in allopurinol and saline injected female Wistar rats. Allopurinol treatment resulted in increased hypoxanthine and decreased uric acid contents in the liver compared with the saline treated group, immediately and 3 h after the exercise. Analysis immediately after the exercise showed no changes in hepatic hypoxanthine, uric acid, and thiobarbituric acid-reactive substance (TBARS) contents in the saline treated group, when compared with the resting controls. However, significant increases in uric acid contents in the saline treated livers were observed 3 h after the exercise, relative to the controls. Hepatic TBARS content in the saline treated group were markedly greater than those in both the control and allopurinol treated groups after 3 h of recovery following the exercise. It was concluded that a single bout of exhausting exercise may impose XOD-derived hepatic oxidative damage, primarily during the recovery phase after acute severe exercise.

Effects of decreased plasma glutamine concentrations on peripheral lymphocyte proliferation in rats

Abstract The relationship between exercise-induced lowering of plasma glutamine concentrations and proliferation of peripheral lymphocytes was investigated in male Wistar rats. The T-lymphocyte proliferative responses to the mitogen, concanavalin A, were determined by incorporation of radiolabelled thymidine into the DNA in vitro. The rats ran 2 h · day−1, 6 days · week−1 for 4 weeks. Analysis immediately after the final period of exercise showed T-lymphocyte proliferation to be significantly depressed, together with a marked decrease in plasma glutamine concentrations. There were also significant increases in serum corticosterone concentrations immediately after exercise. However, following 24-h recovery, this exercise-induced immunosuppression was not statistically significant when compared with the age-matched control group. In the second experiment, in order to clarify the importance of glutamine for immunological function in vivo, methionine sulfoximine, an effective inhibitor of glutamine synthetase was injected intraperitoneally (12.5 mg · kg body mass−1). Plasma glutamine concentrations were decreased 4 h after the injection, compared with the placebo control group, and this resulted in a significant decrease in the rate of T-lymphocyte proliferation. This treatment had no effects on serum corticosterone concentrations. These results would suggest that the chronic exercise-induced reduction in proliferation of peripheral T-lymphocytes is a transient reversible phenomenon, which returns to normal levels within 24 h of the final training period. It is also conceivable that this exercise-induced immunosuppression is associated with a decrease in circulating glutamine concentrations.

Effect of educational intervention using the Internet on quantitative ultrasound parameters in prevention of osteoporosis: a randomized controlled trial in young Japanese women.

Background The objective of this study was to determine whether or not educational intervention using the Internet, to prevent osteoporosis, is able to increase bone strength in young women. Methods Subjects were 253 healthy female university and junior college students aged 18–25 years. After initial measurements of bone stiffness index, a bone formation marker, and a bone absorption marker, the minimization method was used to allocate the subjects to an intervention group (n = 126) or a control group (n = 127) according to whether the measurements were above or below average. Subjects in the intervention group were instructed to perform osteoporosis prevention activities, ie, jump on the spot as high as possible ten times per day and increase calcium intake by 300 mg per day to a total of 800 mg or more per day on average. In addition, they were instructed to report the implementation status of the recommended measures via email. The researcher sent out information on osteoporosis and preventive behaviors to the subjects five times via email. Results A total of 182 subjects, comprising 87 (69.0%) in the intervention group and 95 (74.8%) in the control group, underwent remeasurement 6 months later. Of the subjects in the intervention group, 54 (42.9%) reported their daily additional calcium intake amount and number of jumps via email. The mean amount of additional calcium taken was 216.3 ± 85.9 mg per day, and mean number of jumps performed was 6.4 ± 4.2 per day. Subjects in the intervention group were further divided into an implementation group (n = 54), consisting of subjects who sent in reports and a nonimplementation group (n = 72) who did not. No significant difference was found among the groups for rate of change in bone stiffness index and speed of sound, but there was a significant difference for broadband ultrasound attenuation (BUA) (P = 0.017). Sheffe’s multiple comparison test was performed using baseline body weight and BUA values as covariates, and revealed that the rate of decrease in bone strength in the control group was larger than that in the implementation group (P = 0.049). Conclusion Health education for preventing osteoporosis via Internet email was performed over 6 months for women aged 18 to 25 and a comparison was performed between the intervention group and control group. The intervention consisted of high jumps on the spot (ten times a day), which reduced the drop in BUA, and thus indicates robustness of the trabecular structure. This suggests that a longer intervention period may maintain or improve bone strength.

Reference range of blood biomarkers for oxidative stress in Thoroughbred racehorses (2–5 years old)

ABSTRACT The oxidant and antioxidant equilibrium is known to play an important role in equine medicine and equine exercise physiology. There are abundant findings in this field; however, not many studies have been conducted for reference ranges of oxidative stress biomarkers in horses. This study was conducted to determine the reference values of reactive oxygen metabolites (d-ROMs) and biological antioxidant potential (BAP) using blood samples from 372 (191 males, 181 females) Thoroughbred racehorse aged 2 to 5 (3.43 ± 1.10 (mean ± SD)) years old. There were obvious gender differences in oxidative biomarkers, and growth/age-related changes were observed especially in females. Gender and age must be considered when interpreting obtained oxidative stress biomarkers for diagnosis of disease or fitness alterations in Thoroughbred racehorses.

Rotational Acceleration during Head Impact Resulting from Different Judo Throwing Techniques

Most severe head injuries in judo are reported as acute subdural hematoma. It is thus necessary to examine the rotational acceleration of the head to clarify the mechanism of head injuries. We determined the rotational acceleration of the head when the subject is thrown by judo techniques. One Japanese male judo expert threw an anthropomorphic test device using two throwing techniques, Osoto-gari and Ouchigari. Rotational and translational head accelerations were measured with and without an under-mat. For Osoto-gari, peak resultant rotational acceleration ranged from 4,284.2 rad/s2 to 5,525.9 rad/s2 and peak resultant translational acceleration ranged from 64.3 g to 87.2 g; for Ouchi-gari, the accelerations respectively ranged from 1,708.0 rad/s2 to 2,104.1 rad/s2 and from 120.2 g to 149.4 g. The resultant rotational acceleration did not decrease with installation of an under-mat for both Ouchi-gari and Osoto-gari. We found that head contact with the tatami could result in the peak values of translational and rotational accelerations, respectively. In general, because kinematics of the body strongly affects translational and rotational accelerations of the head, both accelerations should be measured to analyze the underlying mechanism of head injury. As a primary preventative measure, throwing techniques should be restricted to participants demonstrating ability in ukemi techniques to avoid head contact with the tatami.

Muscle oxygenation profiles between active and inactive muscles with nitrate supplementation under hypoxic exercise

Whether dietary nitrate supplementation improves exercise performance or not is still controversial. While redistribution of sufficient oxygen from inactive to active muscles is essential for optimal exercise performance, no study investigated the effects of nitrate supplementation on muscle oxygenation profiles between active and inactive muscles. Nine healthy males performed 25 min of submaximal (heart rate ~140 bpm; EXsub) and incremental cycling (EXmax) until exhaustion under three conditions: (A) normoxia without drink; (B) hypoxia (FiO2 = 13.95%) with placebo (PL); and (c) hypoxia with beetroot juice (BR). PL and BR were provided for 4 days. Oxygenated and deoxygenated hemoglobin (HbO2 and HHb) were measured in vastus lateralis (active) and biceps brachii (inactive) muscles, and the oxygen saturation of skeletal muscle (StO2; HbO2/total Hb) were calculated. During EXsub, BR suppressed the HHb increases in active muscles during the last 5 min of exercise. During EXmax, time to exhaustion with BR (513 ± 24 sec) was significantly longer than with PL (490 ± 39 sec, P < 0.05). In active muscles, BR suppressed the HHb increases at moderate work rates during EXmax compared to PL (P < 0.05). In addition, BR supplementation was associated with greater reductions in HbO2 and StO2 at higher work rates in inactive muscles during EXmax. Collectively, these findings indicate that short‐term dietary nitrate supplementation improved hypoxic exercise tolerance, perhaps, due to suppressed increases in HHb in active muscles at moderate work rates. Moreover, nitrate supplementation caused greater reductions in oxygenation in inactive muscle at higher work rates during hypoxic exercise.

Effect of progressive normobaric hypoxia on dynamic cerebral autoregulation

What is the central question of this study? Acute hypoxia reduces dynamic cerebral autoregulation (dCA); however, it is unclear what level of hypoxia is necessary to exert this effect. We sought to investigate whether dCA would be reduced during progressive periods of normobaric hypoxia using a duplex Doppler ultrasound technique to evaluate the volumetric blood flow. What is the main finding and its importance? We showed that dCA decreased linearly as inspired O2 decreased from 21 to 12%. Additionally, symptoms of acute mountain sickness were related to changes in dCA. Our results may provide a sensitive and clinically relevant test to evaluate the risk of acute mountain sickness.

Intravenous infusion of H2-saline suppresses oxidative stress and elevates antioxidant potential in Thoroughbred horses after racing exercise

Upon intensive, exhaustive exercise, exercise-induced reactive oxygen species may exceed the antioxidant defence threshold, consequently resulting in muscular damage or late-onset chronic inflammation. Recently, the therapeutic antioxidant and anti-inflammatory effects of molecular hydrogen (H2) for human rheumatoid arthritis have been demonstrated. However, it is also important to clarify the effects of administrating H2 in large animals other than humans, as H2 is thought to reach the target organ by passive diffusion upon delivery from the blood flow, indicating that the distance from the administration point to the target is critical. However, data on the effects of H2 on oxidative stress in real-life exhaustive exercise in large animals are currently lacking. We here investigated 13 Thoroughbred horses administered intravenous 2-L saline with or without 0.6-ppm H2 (placebo, N = 6; H2, N = 7) before participating in a high-intensity simulation race. Intravenous H2-saline significantly suppressed oxidative stress immediately, 3 h, and 24 h after the race, although the antioxidant capability was not affected throughout the study. The serum creatine kinase, lactate, and uric acid levels were increased in both groups. Taken together, these results indicate that intravenous H2-saline can significantly and specifically suppress oxidative stress induced after exhaustive racing in Thoroughbred horses.

Decreased energy expenditure during prolonged sub-maximal exercise in a warm environment

Abstract The purpose of this study was to investigate the influence of a warm environment on thermoregulation and energy expenditure during sub-maximal prolonged exercise in humans. Six healthy male subjects cycled for 120 min at an intensity of 60% maximal oxygen uptake (Vo2max) at three environmental temperatures (10°C, CT; 20°C, MT; and 30°C, WT). Although oxygen uptake at WT showed a significantly lower value compared to those at MT and CT, no significant differences of respiratory exchange ratio were observed among the three environmental trials. A remarkable decrease in total energy expenditure during the 120-min exercise at WT was observed in comparison with those at MT and CT (p<0.05). Changes in rectal temperature, mean skin temperature, and mean body temperature at WT were significantly higher than those at both MT and CT. Although increases in mean body temperature from rest every five minutes during exercise were not different among three environmental temperatures, mean energy expenditures every five minutes at WT were lower compared with those at MT and CT (p<0.05). These results suggest that the increase in energy expenditure for physical exertion is substantially reduced during prolonged sub-maximal exercise in a warm environment. This acute alteration in the energy metabolism may contribute to inhibition of excess heat production and enable prolonged exercise in a warm environment.