Green tea extract improves running endurance in mice by stimulating lipid utilization during exercise

A series of polyphenols known as catechins are abundant in green tea, which is consumed mainly in Asian countries. The effects of catechin-rich green tea extract (GTE) on running endurance and energy metabolism during exercise in BALB/c mice were investigated. Mice were divided into four groups: nonexercise control, exercise control (Ex-cont), exercise+0.2% GTE, and exercise+0.5% GTE groups. Treadmill running time to exhaustion, plasma biochemical parameters, skeletal muscle glycogen content, beta-oxidation activity, and malonyl-CoA content immediately after exercise were measured at 8-10 wk after the initiation of the experiment. Oxygen consumption and respiratory exchange ratio were measured using indirect calorimetry. Running times to exhaustion in mice fed 0.5% GTE were 30% higher than in Ex-cont mice and were accompanied by a lower respiratory exchange ratio, higher muscle beta-oxidation activity, and lower malonyl-CoA content. In addition, muscle glycogen content was high in the GTE group compared with the Ex-cont group. Plasma lactate concentrations in mice fed GTE were significantly lower after exercise, concomitant with an increase in free fatty acid concentrations. Catechins, which are the main constituents of GTE, did not show significant effects on peroxisome proliferator-activated receptor-alpha or delta-dependent luciferase activities. These results suggest that the endurance-improving effects of GTE were mediated, at least partly, by increased metabolic capacity and utilization of fatty acid as a source of energy in skeletal muscle during exercise.     

Cardiac and skeletal muscle adaptations to voluntary wheel running in the mouse.

In this paper, we describe the effects of voluntary cage wheel exercise on mouse cardiac and skeletal muscle. Inbred male C57/Bl6 mice (age 6-8 wk; n = 12) [corrected] ran an average of 4.3 h/24 h, for an average distance of 6.8 km/24 h, and at an average speed of 26.4 m/min. A significant increase in the ratio of heart mass to body mass (mg/g) was evident after 2 wk of voluntary exercise, and cardiac atrial natriuretic factor and brain natriuretic peptide mRNA levels were significantly increased in the ventricles after 4 wk of voluntary exercise. A significant increase in the percentage of fibers expressing myosin heavy chain (MHC) IIa was observed in both the gastrocnemius and the tibialis anterior (TA) by 2 wk, and a significant decrease in the percentage of fibers expressing IIb MHC was evident in both muscles after 4 wk of voluntary exercise. The TA muscle showed a greater increase in the percentage of IIa MHC-expressing fibers than did the gastrocnemius muscle (40 and 20%, respectively, compared with 10% for nonexercised). Finally, the number of oxidative fibers as revealed by NADH-tetrazolium reductase histochemical staining was increased in the TA but not the gastrocnemius after 4 wk of voluntary exercise. All results are relative to age-matched mice housed without access to running wheels. Together these data demonstrate that voluntary exercise in mice results in cardiac and skeletal muscle adaptations consistent with endurance exercise.     

Voluntary physical activity alterations in endothelial nitric oxide synthase knockout mice

One of the main factors that control vasoreactivity and angiogenesis is nitric oxide produced by endothelial nitric oxide synthase (eNOS). We recently showed that knocking out eNOS induces an important reduction of mitochondrial oxidative capacity in slow-twitch skeletal muscle. Here we investigated eNOS's role in physical activity and contribution to adaptation of muscle energy metabolism to exercise conditions. Physical capacity of mice null for the eNOS isoform (eNOS-/-) was estimated for 8 wk with a voluntary wheel-running protocol. In parallel, we studied energy metabolism enzyme profiles and their response to voluntary exercise in cardiac and slow-twitch soleus (Sol) and fast-twitch gastrocnemius (Gast) skeletal muscles. Weekly averaged running distance was two times lower for eNOS-/- (4.09 +/- 0.42 km/day) than for wild-type (WT; 7.74 +/- 0.42 km/day; P < 0.01) mice. Average maximal speed of running was also lower in eNOS-/- (17.2 +/- 1.4 m/min) than WT (21.2 +/- 0.9 m/min; P < 0.01) mice. Voluntary exercise influenced adaptation to exercise specifically in Sol muscle. Physical activity significantly increased Sol weight by 22% (P < 0.05) in WT but not eNOS-/- mice. WT Sol muscle did not change its metabolic profile in response to exercise, in contrast to eNOS-/- muscle, in which physical activity decreased cytochrome-c oxidase (COX; -36%; P < 0.05), citrate synthase (-37%; P < 0.06), and creatine kinase (-24%, P < 0.01) activities. Voluntary exercise did not change energy enzyme profile in heart (except for 39% increase in COX activity in WT) or Gast muscle. These results suggest that eNOS is necessary for maintaining a suitable physical capacity and that when eNOS is downregulated, even moderate exercise could worsen energy metabolism specifically in oxidative skeletal muscle.     

Bitter melon seed oil increases mitochondrial content in gastrocnemius muscle and improves running endurance in sedentary C57BL/6J mice

The α-eleostearic acid (α-ESA) in bitter melon seed oil (BMSO) is efficiently converted by the body into rumenic acid. The objective of this study was to investigate effects of BMSO on skeletal muscle fiber-type switch and endurance capacity in mice, with or without exercise training. In a 3×2 factorial design, C57BL/6J mice were fed a 30% high-fat diet composed of soybean oil, butter or a 1:1 mixture of BMSO and soybean oil, i.e., SB, BT and BM diets, respectively, and were allocated to be sedentary or undergo exercise (Ex). The Ex groups received a 15-min training regimen on a motorized treadmill 5 times a week. After 3-week intervention, endurance capacity was evaluated (total running time and distance until exhaustion). Mice fed a BM diet had significantly less body fat, with increased muscle percentage and improved endurance capacity. Combining sedentary and Ex groups, mice fed a BM diet ran 33% longer and 50% further than those fed SB, or 25% longer and 36% further than those fed BT (P<.01). The BM-diet-increased gastrocnemius cytochrome c protein and mitochondrial DNA content was more prominent in sedentary than in trained mice. Histochemical staining shows sedentary BM-fed mice had a higher succinate dehydrogenase activity among groups. Based on a reporter assay, rumenic acid, rather than α-ESA itself, activated PPARδ ligand binding domain. We concluded that BMSO improved endurance capacity via stimulation of mitochondrial biogenesis and function, potentially influencing muscle metabolism and fiber-type composition in sedentary mice.     

Alpha-lipoic acid supplementation: tissue glutathione homeostasis at rest and after exercise.

Antioxidant nutrients have demonstrated potential in protecting against exercise-induced oxidative stress. alpha-Lipoic acid (LA) is a proglutathione dietary supplement that is known to strengthen the antioxidant network. We studied the effect of intragastric LA supplementation (150 mg/kg, 8 wk) on tissue LA levels, glutathione metabolism, and lipid peroxidation in rats at rest and after exhaustive treadmill exercise. LA supplementation increased the level of free LA in the red gastrocnemius muscle and increased total glutathione levels in the liver and blood. The exercise-induced decrease in heart glutathione S-transferase activity was prevented by LA supplementation. Exhaustive exercise significantly increased thiobarbituric acid-reactive substance levels in the liver and red gastrocnemius muscle. LA supplementation protected against oxidative lipid damage in the heart, liver, and red gastrocnemius muscle. This study reports that orally supplemented LA is able to favorably influence tissue antioxidant defenses and counteract lipid peroxidation at rest and in response to exercise.     

Additive effects of training and high-fat diet on energy metabolism during exercise

This study was conducted to obtain additional information about the adaptations after 12 wk of high-fat diet (HFD) per se or HFD combined with endurance training in the rat using a two [diet: carbohydrate (CHO) or HFD] by two (training: sedentary or trained) by two (condition at death: rested or exercised) factorial design. Adaptation to prolonged HFD increases maximal O2 uptake (VO2max; 13%, P less than 0.05) and submaximal running endurance (+64%, P less than 0.05). This enhancement in exercise capacity could be attributed to 1) an increase in skeletal muscle aerobic enzyme activities (3-hydroxyacyl-CoA dehydrogenase and citrate synthase in soleus and red quadriceps) or 2) a decrease in liver glycogen breakdown in response to 1 h exercise at 80% VO2max. When training is superimposed to HFD, the most prominent finding provided by this study is that the diet-induced effects are cumulative with the well-known training effect on VO2max, exercise endurance, oxidative capacity of red muscle, and metabolic responses to exercise, with a further reduction in liver glycogen breakdown.     

Catechins attenuate eccentric exercise-induced inflammation and loss of force production in muscle in senescence-accelerated mice

Catechins have a great variety of biological actions. We evaluated the potential benefits of catechin ingestion on muscle contractile properties, oxidative stress, and inflammation following downhill running, which is a typical eccentric exercise, in senescence-accelerated prone mice (SAMP). Downhill running (13 m/min for 60 min; 16° decline) induced a greater decrease in the contractile force of soleus muscle and in Ca(2+)-ATPase activity in SAMP1 compared with the senescence-resistant mice (SAMR1). Moreover, compared with SAMR1, SAMP1 showed greater downhill running-induced increases in plasma CPK and LDH activity, malondialdehyde, and carbonylated protein as markers of oxidative stress; and in protein and mRNA expression levels of the inflammatory mediators such as tumor necrosis factor-α and monocyte chemoattractant protein-1 in muscle. SAMP1 exhibited aging-associated vulnerability to oxidative stress and inflammation in muscle induced by downhill running. Long-term (8 wk) catechin ingestion significantly attenuated the downhill running-induced decrease in muscle force and the increased inflammatory mediators in both plasma and gastrocnemius muscle. Furthermore, catechins significantly inhibited the increase in oxidative stress markers immediately after downhill running, accompanied by an increase in glutathione reductase activity. These findings suggest that long-term catechin ingestion attenuates the aging-associated loss of force production, oxidative stress, and inflammation in muscle after exercise.     

The role of reactive oxygen species in the hearts of dystrophin-deficient mdx mice

Duchenne muscular dystrophy (DMD) is caused by deficiency of the cytoskeletal protein dystrophin. Oxidative stress is thought to contribute to the skeletal muscle damage in DMD; however, little is known about the role of oxidative damage in the pathogenesis of the heart failure that occurs in DMD patients. The dystrophin-deficient (mdx) mouse is an animal model of DMD that also lacks dystrophin. The current study investigates the role of the antioxidant N-acetylcysteine (NAC) on mdx cardiomyocyte function, Ca(2+) handling, and the cardiac inflammatory response. Treated mice received 1% NAC in their drinking water for 6 wk. NAC had no effect on wild-type (WT) mice. Immunohistochemistry experiments revealed that mdx mice had increased dihydroethidine (DHE) staining, an indicator of superoxide production; NAC-treatment reduced DHE staining in mdx hearts. NAC treatment attenuated abnormalities in mdx cardiomyocyte Ca(2+) handling. Mdx cardiomyocytes had decreased fractional shortening and decreased Ca(2+) sensitivity; NAC treatment returned mdx fractional shortening to WT values but did not affect the Ca(2+) sensitivity. Immunohistochemistry experiments revealed that mdx hearts had increased levels of collagen type III and the macrophage-specific protein, CD68; NAC-treatment returned collagen type III and CD68 expression close to WT values. Finally, mdx hearts had increased NADPH oxidase activity, suggesting it could be a possible source of increased reactive oxygen species in mdx mice. This study is the first to demonstrate that oxidative damage may be involved in the pathogenesis of the heart failure that occurs in mdx mice. Therapies designed to reduce oxidative damage might be beneficial to DMD patients with heart failure.     

Green tea extract attenuates hepatic steatosis by decreasing adipose lipogenesis and enhancing hepatic antioxidant defenses in ob/ob mice

Excess hepatic lipid accumulation and oxidative stress contribute to nonalcoholic fatty liver disease (NAFLD). Thus, we hypothesized that the hypolipidemic and antioxidant activities of green tea extract (GTE) would attenuate events leading to NAFLD. Obese mice (ob/ob; 5 weeks old, n=38) and their lean littermates (n=12) were fed 0%, 0.5% or 1% GTE for 6 weeks. Then, hepatic steatosis, oxidative stress and inflammatory markers were measured. Obese mice, compared to lean controls, had greater hepatic lipids and serum alanine aminotransferase (ALT). GTE at 1% lowered (P<.05) hepatic lipids and ALT in obese mice. The GTE-mediated attenuation in hepatic steatosis was accompanied by decreased mRNA expression of adipose sterol regulatory element-binding protein-1c, fatty acid synthase, stearoyl CoA desaturase-1, and hormone-sensitive lipase and decreased serum nonesterified fatty acid concentrations. Immunohistochemical data indicated that steatotic livers from obese mice had extensive accumulation of tumor necrosis factor-α (TNF-α), whereas GTE at 1% decreased hepatic TNF-α protein and inhibited adipose TNF-α mRNA expression. Hepatic total glutathione, malondialdehyde and Mn- and Cu/Zn-superoxide dismutase activities in obese mice fed GTE were normalized to the levels of lean littermates. Also, GTE increased hepatic catalase and glutathione peroxidase activities, and these activities were inversely correlated with ALT and liver lipids. Collectively, GTE mitigated NAFLD and hepatic injury in ob/ob mice by decreasing the release of fatty acids from adipose and inhibiting hepatic lipid peroxidation as well as restoring antioxidant defenses and decreasing inflammatory responses. These findings suggest that GTE may be used as an effective dietary strategy to mitigate obesity-triggered NAFLD.     

Green tea extract improves endurance capacity and increases muscle lipid oxidation in mice

Green tea contains a high level of polyphenolic compounds known as catechins. We investigated the effects of green tea extract (GTE), which is rich in catechins, on endurance capacity, energy metabolism, and fat oxidation in BALB/c mice over a 10-wk period. Swimming times to exhaustion for mice fed 0.2-0.5% (wt/wt) GTE were prolonged by 8-24%. The effects were dose dependent and accompanied by lower respiratory quotients and higher rates of fat oxidation as determined by indirect calorimetry. In addition, feeding with GTE increased the level of beta-oxidation activity in skeletal muscle. Plasma lactate concentrations in mice fed GTE were significantly decreased after exercise, concomitant with increases in free fatty acid concentrations in plasma, suggesting an increased lipid use as an energy source in GTE-fed mice. Epigallocatechin gallate (EGCG), a major component of tea catechins, also enhanced endurance capacity, suggesting that the endurance-improving effects of GTE were mediated, at least in part, by EGCG. The beta-oxidation activity and the level of fatty acid translocase/CD36 mRNA in the muscle was higher in GTE-fed mice compared with control mice. These results indicate that GTE are beneficial for improving endurance capacity and support the hypothesis that the stimulation of fatty acid use is a promising strategy for improving endurance capacity.     

Effect of short-term exercise training on muscle glycogen in resting conditions in rats fed a high fat diet.

It has been reported that exercise training increases muscle glycogen storage in rats fed a high carbohydrate (CHO) diet in resting conditions. The purpose of this study was to examine whether a 3-week swimming training programme would increase muscle glycogen stores in rats fed a high-fat (FAT) diet in resting conditions. Rats were fed either the FAT or CHO diet for 7 days ad libitum, and then were fed regularly twice a day (between 0800 and 0830 hours and 1800 and 1830 hours) for 32 days. During this period of regular feeding, half of the rats in both dietary groups had swimming training for 3 weeks and the other half were sedentary. The rats were not exercised for 48 h before sacrifice. All rats were killed 2 h after their final meal (2030 hours). The glycogen contents in red gastrocnemius muscle, heart and liver were significantly higher in sedentary rats fed the CHO diet than in those fed the FAT diet. Exercise training clearly increased glycogen content in soleus, red gastrocnemius and heart muscle in rats fed the CHO diet. In rats fed the FAT diet, however, training did not increase glycogen content in these muscles or the heart. Exercise training resulted in an 87% increase of total glycogen synthase activity in the gastrocnemius muscle of rats fed the CHO diet. However, this was not observed in rats fed the FAT diet. The total glycogen phosphorylase activity in the gastrocnemius muscle of the rats of both dietary groups was increased approximately twofold by training.(ABSTRACT TRUNCATED AT 250 WORDS)     

Biochemical characterization of exercise-trained porcine myocardium.

The purpose of this study was to determine whether cardiac biochemical adaptations are induced by chronic exercise training (ET) of miniature swine. Female Yucatan miniature swine were trained on a treadmill or were cage confined (C) for 16-22 wk. After training, the ET pigs had increased exercise tolerance, lower heart rates during exercise at submaximal intensities, moderate cardiac hypertrophy, increased coronary blood flow capacity, and increased oxidative capacity of skeletal muscle. Myosin from both the C and ET hearts was 100% of the V3 isozyme, and there were no differences between the myosin adenosine triphosphatase (ATPase) or myofibrillar ATPase activities of C and ET hearts. Also, the sarcoplasmic reticulum Ca(2+)-ATPase activity and Na(+)-Ca2+ exchange activity of sarcolemmal vesicles were the same in cardiac muscle of C and ET hearts. Finally, the glycolytic and oxidative capacity of ET cardiac muscle was not different from control, since phosphofructokinase, citrate synthase, and 3-hydroxyacyl-CoA dehydrogenase activities were the same in cardiac tissue from ET and C pigs. We conclude that endurance exercise training does not provide sufficient stress on the heart of a large mammal to induce changes in any of the three major cardiac biochemical systems of the porcine myocardium: the contractile system, the Ca2+ regulatory systems, or the metabolic system.     

Lack of myostatin alters intermyofibrillar mitochondria activity, unbalances redox status, and impairs tolerance to chronic repetitive contractions in muscle

Loss of myostatin (mstn) function leads to a decrease in mitochondrial content, a reduced expression of cytochrome c oxidase, and a lower citrate synthase activity in skeletal muscle. These data suggest functional or ultrastructural mitochondrial abnormalities that can impact on muscle endurance characteristics in such phenotype. To address this issue, we investigated subsarcolemmal and intermyofibrillar (IMF) mitochondrial activities, skeletal muscle redox homeostasis, and muscle fiber endurance quality in mstn-deficient mice [mstn knockout (KO)]. We report that lack of mstn induced a decrease in the coupling of IMF mitochondria respiration, with significantly higher basal oxygen consumption. No lysis of mitochondrial cristae or excessive swelling were observed in mstn KO mice compared with wild-type (WT) mice. Concerning redox status, mstn KO gastrocnemius exhibited a significant decrease in lipid peroxidation levels (-56%; P < 0.01 vs. WT) together with a significant upregulation of the antioxidant glutathione system. In contrast, superoxide dismutase and catalase activities were altered in mstn KO, gastrocnemius and soleus with a reduction of up to 80% compared with WT animals. The force production observed after contractile endurance test was significantly lower in extensor digitorum longus and soleus muscles of mstn KO mice compared with the controls (17 ± 3 and 36 ± 5% vs. 28 ± 4 and 56 ± 5%, respectively, P < 0.05). Together, these findings indicate that, besides an increased skeletal muscle mass, genetic mstn inhibition has differential effects on redox homeostasis and mitochondrial function that would have functional consequences on muscle response to endurance exercise.     

Four weeks of speed endurance training reduces energy expenditure during exercise and maintains muscle oxidative capacity despite a reduction in training volume

We studied the effect of an alteration from regular endurance to speed endurance training on muscle oxidative capacity, capillarization, as well as energy expenditure during submaximal exercise and its relationship to mitochondrial uncoupling protein 3 (UCP3) in humans. Seventeen endurance-trained runners were assigned to either a speed endurance training (SET; n = 9) or a control (Con; n = 8) group. For a 4-wk intervention (IT) period, SET replaced the ordinary training ( approximately 45 km/wk) with frequent high-intensity sessions each consisting of 8-12 30-s sprint runs separated by 3 min of rest (5.7 +/- 0.1 km/wk) with additional 9.9 +/- 0.3 km/wk at low running speed, whereas Con continued the endurance training. After the IT period, oxygen uptake was 6.6, 7.6, 5.7, and 6.4% lower (P < 0.05) at running speeds of 11, 13, 14.5, and 16 km/h, respectively, in SET, whereas remained the same in Con. No changes in blood lactate during submaximal running were observed. After the IT period, the protein expression of skeletal muscle UCP3 tended to be higher in SET (34 +/- 6 vs. 47 +/- 7 arbitrary units; P = 0.06). Activity of muscle citrate synthase and 3-hydroxyacyl-CoA dehydrogenase, as well as maximal oxygen uptake and 10-km performance time, remained unaltered in both groups. In SET, the capillary-to-fiber ratio was the same before and after the IT period. The present study showed that speed endurance training reduces energy expenditure during submaximal exercise, which is not mediated by lowered mitochondrial UCP3 expression. Furthermore, speed endurance training can maintain muscle oxidative capacity, capillarization, and endurance performance in already trained individuals despite significant reduction in the amount of training.     

Imbalance in SOD/CAT activities in rat skeletal muscles submitted to treadmill training exercise

The association between physical exercise and oxidative damage in the skeletal musculature has been the focus of many studies in literature, but the balance between superoxide dismutase and catalase activities and its relation to oxidative damage is not well established. Thus, the aim of the present study was to investigate the association between regular treadmill physical exercise, oxidative damage and antioxidant defenses in skeletal muscle of rats. Fifteen male Wistar rats (8-12 months) were randomly separated into two groups (trained n=9 and untrained n=6). Trained rats were treadmill-trained for 12 weeks in progressive exercise (velocity, time, and inclination). Training program consisted in a progressive exercise (10 m/min without inclination for 10 min/day). After 1 week the speed, time and inclination were gradually increased until 17 m/min at 10% for 50 min/day. After the training period animals were killed, and gastrocnemius and quadriceps were surgically removed to the determination of biochemical parameters. Lipid peroxidation, protein oxidative damage, catalase, superoxide dismutase and citrate synthase activities, and muscular glycogen content were measured in the isolated muscles. We demonstrated that there is a different modulation of CAT and SOD in skeletal muscle in trained rats when compared to untrained rats (increased SOD/CAT ratio). TBARS levels were significantly decreased and, in contrast, a significant increase in protein carbonylation was observed. These results suggest a non-described adaptation of skeletal muscle against exercise-induced oxidative stress.     

Protein malnutrition mitigates the effects of a high-fat diet on glucose homeostasis in mice

Nutrient malnutrition, during the early stages of development, may facilitate the onset of metabolic diseases later in life. However, the consequences of nutritional insults, such as a high-fat diet (HFD) after protein restriction, are still controversial. We assessed overall glucose homeostasis and molecular markers of mitochondrial function in the gastrocnemius muscle of protein-restricted mice fed an HFD until early adulthood. Male C57BL/6 mice were fed a control (14% protein-control diet) or a protein-restricted (6% protein-restricted diet) diet for 6 weeks. Afterward, mice received an HFD or not for 8 weeks (mice fed a control diet and HFD [CH] and mice fed a protein-restricted diet and HFD [RH]). RH mice showed lower weight gain and fat accumulation and did not show an increase in fasting plasma glucose and insulin levels compared with CH mice. RH mice showed higher energy expenditure, increased citrate synthase, peroxisome-proliferator-activated receptor gamma coactivator 1-alpha protein content, and higher levels of malate and α-ketoglutarate compared with CH mice. Moreover, RH mice showed increased AMPc-dependent kinase and acetyl coenzyme-A (CoA) carboxylase phosphorylation, lower intramuscular triacylglycerol content, and similar malonyl-CoA levels. In conclusion, protein undernourishment after weaning does not potentiate fat accumulation and insulin resistance in adult young mice fed an HFD. This outcome seems to be associated with increased skeletal muscle mitochondrial oxidative capacity and reduced lipids accumulation.     

Habitual exercise program protects murine intestinal, skeletal, and cardiac muscles against aging.

Aging and aerobic exercise are two conditions known to interfere with health and quality of life, most likely by inducing oxidative stress to the organism. We studied the effects of aging on the morphological and functional properties of skeletal, cardiac, and intestinal muscles and their corresponding oxidative status in C57BL/6 mice and investigated whether a lifelong moderate exercise program would exert a protective effect against some deleterious effects of aging. As expected, aged animals presented a significant reduction of physical performance, accompanied by a decrease of gastrocnemius cross-sectional area and cardiac hypertrophy. However, most interesting was that aging dramatically interfered with the intestinal structure, causing a significant thickening of the ileum muscular layer. Senescent intestinal myocytes displayed many mitochondria with disorganized cristae and the presence of cytosolic lamellar corpuscles. Lipid peroxidation of ileum and gastrocnemius muscle, but not of the heart, increased in aged mice, thus suggesting enhanced oxidative stress. With exception of the intestinal muscle responsiveness, animals submitted to a daily session of 60 min, 5 days/wk, at 13 up to 21 m/min of moderate running in treadmill during animal life span exhibited a reversion of all the observed aging effects on intestinal, skeletal, and heart muscles. The introduction of this lifelong exercise protocol prevented the enhancement of lipid peroxidation and sarcopenia and also preserved cellular and ultracellular structures of the ileum. This is the first time that the protective effect of a lifelong regular aerobic physical activity against the deleterious effects of aging on intestinal muscle was demonstrated.     

Upregulation of osteopontin expression is involved in the development of nonalcoholic steatohepatitis in a dietary murine model

The pathogenesis of nonalcoholic steatohepatitis (NASH) is poorly defined. Feeding mice a diet deficient in methionine and choline (MCD diet) induces experimental NASH. Osteopontin (OPN) is a Th1 cytokine that plays an important role in several fibroinflammatory diseases. We examined the role of OPN in the development of experimental NASH. A/J mice were fed MCD or control diet for up to 12 wk, and serum alanine aminotransferase (ALT), liver histology, oxidative stress, and the expressions of OPN, TNF-alpha, and collagen I were assessed at various time points. MCD diet-fed mice developed hepatic steatosis starting after 1 wk and inflammation by 2 wk; serum ALT increased from day 3. Hepatic collagen I mRNA expression increased during 1-4 wk, and fibrosis appeared at 8 wk. OPN protein expression was markedly increased on day 1 of MCD diet and persisted up to 8 wk, whereas OPN mRNA expression was increased at week 4. TNF-alpha expression was increased from day 3 to 2 wk, and evidence of oxidative stress did not appear until 8 wk. Increased expression of OPN was predominantly localized in hepatocytes. Hepatocytes in culture also produced OPN, which was stimulated by transforming growth factor-beta and TNF-alpha. Moreover, MCD diet-induced increases in serum ALT levels, hepatic inflammation, and fibrosis were markedly reduced in OPN(-/-) mice when compared with OPN(+/+) mice. In conclusion, our results demonstrate an upregulation of OPN expression early in the development of steatohepatitis and suggest an important role for OPN in signaling the onset of liver injury and fibrosis in experimental NASH.