E. W. Askew

Work at high altitude and oxidative stress: antioxidant nutrients

A significant portion of the worlds geography lies above 10,000 feet elevation, an arbitrary designation that separates moderate and high altitude. Although the number of indigenous people living at these elevations is relatively small, many people travel to high altitude for work or recreation, exposing themselves to chronic or intermittent hypoxia and the associated risk of acute mountain sickness (AMS) and less frequently, high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE). The symptoms of AMS (headache, nausea, anorexia, fatigue, lassitude) occur in those who travel too high, too fast. Some investigators have linked the development of these symptoms with the condition of altered blood-brain barrier permeability, possibly related to hypoxia induced free radical formation. The burden of oxidative stress increases during the time spent at altitude and may even persist for some time upon return to sea level. The physiological and medical consequences of increased oxidative stress engendered by altitude is unclear; indeed, hypoxia is believed to be the trigger for the cascade of signaling events that ultimately leads to adaptation to altitude. These signaling events include the generation of reactive oxygen species (ROS) that may elicit important adaptive responses. If produced in excess, however, these ROS may contribute to impaired muscle function and reduced capillary perfusion at altitude or may even play a role in precipitating more serious neurological and pulmonary crisis. Oxidative stress can be observed at altitude without strenuous physical exertion; however, environmental factors other than hypoxia, such as exercise, UV light exposure and cold exposure, can also contribute to the burden. Providing antioxidant nutrients via the diet or supplements to the diet can reduce oxidative stress secondary to altitude exposure. In summary, the significant unanswered question concerning altitude exposure and antioxidant supplementation is when does oxidative stress become potentially damaging enough to merit antioxidant therapy and conversely, what degree of oxidative stress is necessary to foster the adaptive response of altitude exposure?

Adipose tissue cellularity and lipolysis. Response to exercise and cortisol treatment.

Male rats a 5 wk of age were subjected to 13 wk of intensive treadmill running to study the effect of exercise on adipose tissue cellularity and lipolysis. Untrained controls of the same age remained sedentary in their cages for the duration of the experiment. Adipocyte numbers were similar in eqidiymal fat pads from trained and untrained rats (12.7 plus or minus 1.3 X 10(6) vs. 15.3 plus or minus 1.3 X 10(6) cells/pad), however trained rats had smaller fat pads containing smaller cells (0.09 plus of minus 0.01 vs. 0.20 plus or minus 0.04 mug triglyceride/cell). Adipocytes from trained rats possessed greater epinephrine-sensitive lipase activity than sedentary rats on a per cell, per milligram protein, per gram adipose tissue, or per fat pad basis. Although the smaller cells of the trained rats had greater epinephrine-sensitive lipase activity than the larger cells of the untrained rats, lipolysis was positively correlated with cell size within both treatment groups. Cortisol treatment of intact animals did not significantly affect in vitro adipose tissue lipolysis. The results of this study indicate that exercise training increased the potential of adipose tissue cells to release free fatty acids in response to epinephrine stimulation. Exercise training initiated at 5 wk of age had only a small effect on adipose tissue cell numbers but significantly decreased cell size.

Oxidative Stress in Humans Training in a Cold, Moderate Altitude Environment and Their Response to a Phytochemical Antioxidant Supplement

OBJECTIVE This study examined the effectiveness of an antioxidant mixture containing vitamin E, beta-carotene, ascorbic acid, selenium, alpha-lipoic acid, N-acetyl 1-cysteine, catechin, lutein, and lycopene to reduce oxidative stress in US Marines undergoing 24 days of cold-weather field training at a moderate altitude. METHODS Forty physically active male volunteers (ages 18-40) were randomly assigned to a treatment (antioxidant) group (n = 21) or a control (placebo) group (n = 19). Breath pentane (BP), serum lipid hydroperoxides (LPO), urine malondialdehyde (MDA), urine 8-hydroxy deoxyguanosine (8-OHdG), ferric-reducing ability of plasma (FRAP), and serum and urine oxygen radical absorption capacity (ORAC) were measured as indicators of oxidative stress and antioxidant status. Urine was sampled at days 0, 12, and 24. Serum and breath were sampled on days 0 and 24. RESULTS Both groups exhibited increased levels of oxidative stress after 24 days of field training, as indicated by an increased LPO, pentane, and 8-OHdG. There was no significant difference between the treatment and placebo groups at day 24; however, there was some indication that test subjects with initially low antioxidant capacity (ORAC) may have benefited from the antioxidant supplement. CONCLUSIONS An increased level of oxidative stress was associated with high levels of physical exertion of training in a cold environment at moderate altitude. The antioxidant mixture tested did not attenuate the mean oxidative stress levels in the entire group of test subjects, but it may have reduced the oxidative stress of some individuals with low initial antioxidant status.

Effect of antioxidant supplementation on urine and blood markers of oxidative stress during extended moderate-altitude training

OBJECTIVE To investigate the increase in oxidative stress during work at moderate altitudes due to additional energy expenditure, tissue anoxia, and UV light exposure. METHODS Thirty US Marine Corps volunteers were divided into placebo (P) and antioxidant supplement (S) groups and tested for markers of oxidative stress before (t0), at the midpoint of (t1), and after (t2) 14 days of winter training at a moderate altitude (approximately 2700 m). The antioxidant supplement consisted of a daily dose of 20,000 IU beta-carotene, 400 IU vitamin E, 500 mg vitamin C, 100 micrograms selenium, and 30 mg zinc. The following markers of oxidative stress were measured: urine thiobarbituric acid reactive substances (TBARSs), urine hydroxynonenal (HNE), urine 8-hydrodeoxyguanosine (8-OHdG), plasma total peroxyl radical trapping potential (TRAP), and plasma lipid hydroperoxides (LPOs). Urine was collected on a 24-hr basis at t0, t1, and t2; blood samples were collected at t0 and t2. RESULTS P group LPOs increased 30% (p < 0.05) between t0 and t2, whereas S group LPOs did not increase. Both groups exhibited significant increases in urine TBARSs, HNE, and 8-OHdG by t2. Urine TBARSs, HNE, and 8-OHdG increased between t0 and t1 in both groups, with the greater increase in the S group. The conflicting results between the plasma and urine markers of oxidative stress may be due to a time-phase relationship. CONCLUSIONS The results of this study suggest that work in a moderate-altitude cold-weather environment is accompanied by increased oxidative stress, despite relatively high intakes of dietary and supplemental antioxidants.

Environmental and physical stress and nutrient requirements.

When faced with hot, cold, or high-altitude environments, humans can either modify the microenvironment to fit human physiology, adapt their physiology to fit the environment, or use a combination of these two tactics. Metabolic adaptations to heat, cold, and high-altitude exposure may, in some instances, be accompanied by changes in nutrient requirements. Energy expenditure is increased in all three environments. B-vitamin cofactor requirements increase in proportion to energy expenditure (oxidation of fat and carbohydrate). Increased B-vitamin nutrient requirements are usually adequately met by an increased consumption of the diet to meet energy requirements. Other nutrients such as iron may be required in greater amounts to meet the altitude-induced hematopoietic response in females. Additional quantities of vitamins and minerals with antioxidant properties may be beneficial to reduce the increased oxidative stress associated with work in heat, cold, or high-altitude outdoor environments.

Characteristics of fatty acid esterification by homogenates of bovine mammary tissue.

Fatty acid esterifying activity of homogenates of bovine mammary tissue was associated with the particulate fraction of the cell, was strongly dependent upon ATP, CoA,d,l-glycerol-3-phosphate, and Mg2+, and was stimulated by NaF, dithiothreitol and bovine serum albumin. The system made phospholipids, mono-, di- and triglycerides but did not esterify butyrate. The inability to form greater than 58% triglyceride suggested some factor(s) was limiting the acylation of di-to triglyceride. The results were consistent with glyceride synthesis by the α-glycerophosphate pathway.Fatty acid esterifying activity of homogenates of bovine mammary tissue was associated with the particulate fraction of the cell, was strongly dependent upon ATP, CoA,d,l-glycerol-3-phosphate, and Mg2+, and was stimulated by NaF, dithiothreitol and bovine serum albumin. The system made phospholipids, mono-, di- and triglycerides but did not esterify butyrate. The inability to form greater than 58% triglyceride suggested some factor(s) was limiting the acylation of di-to triglyceride. The results were consistent with glyceride synthesis by the α-glycerophosphate pathway.

Response of Rat Tissue Lipases to Physical Training and Exercise

Summary The results of this study indicate that physical training causes an adaptive increase in epinephrine-stimulated fatty acid mobilization potential in adipose tissue of rested animals. Exhaustion caused an increase in ESL activity of similar magnitude in untrained animals. The exercise effect was not additive with the training effect when trained animals were exercised or exhausted. Lipoprotein lipase was unaffected by training and increased in heart and muscle of untrained animals following exhaustion. Trained animals exhibited a similar but smaller trend toward increased LPL activity with exercise or exhaustion. Taken together, the results of this study are compatible with the concept that exercise increases lipolysis in adipose tissue and LPL mediated triglyceride fatty acid uptake by muscular tissues. Physical training appeared to increase the responsiveness of adipose tissue to adrenergic stimulation. An increased adipokinetic response by adipose tissue of trained animals would be compatible with the observation in this (33) and other studies (34-35) that training increases the capacity of muscular tissue for fatty acid oxidation.

Fatty acid specificity of glyceride synthesis by homogenates of bovine mammary tissue.

Fatty acid esterification by cell free preparations of bovine mammary tissue was investigated to determine if the type of long chain fatty acid supplied might influence the rate of triglyceride synthesis by that tissue. Homogenates of lactating bovine mammary tissue esterified14C-fatty acids into glycerides at rates dependent upon chain length and degree of unsaturation. Palmitic, stearic, oleic and linoleic acids were esterified at rates consistent with their concentration in milk fat. A comparison of free fatty acid concentrations of mammary tissue with levels saturating esterification suggested that supply of fatty acids does not limit glyceride synthesis. Certain combinations of fatty acids were facilitory, competitive or inhibitory to esterification. Stearic acid complimented esterification of palmitic and oleic acids. Unlabeledtrans-11-octadecenoic acid did not compete with14C-palmitate as efficiently in the esterification process as did unlabeledcis-9-octadecenoic acid, indicating that the mammary gland may preferentially esterify thecis-isomer of C-18∶1. Linoleic acid inhibited esterification of palmitic, stearic and oleic acids.

Response of lipogenesis and fatty acid synthetase to physical training and exhaustive exercise in rats.

The effect of physical training and exhaustive exercise on fatty acid synthesis in rat liver and adipose tissue has been investigated. Exercise training (treadmill running) significantly (P<0.05) decreased body wt, epididymal fat pad wt, adipocyte size, and hepatic fattya cid synthetase activity. Training did not significantly affect adipose tissue cell number, lipogenesis from glucose-U-14C, or fatty acid synthetase. Exercise to exhaustion immediately prior to sacrifice significantly (P<0.05) decreased lipogenesis from glucose-U-14C and fatty acid synthetase in adipose tissue from trained but not untrained rats. Liver fatty acid synthetase was not significantly influenced by exhaustive exercise. The results of this study indicate that rats may adapt to physical training by decreasing adipose tissue lipogenesis during exhaustive exercise. This adaptation in energy metabolism may facilitate physically trained animals in conserving blood glucose during exhaustive exercise, thereby prolonging endurance.

Antioxidant Status of Young Children:Response to an Antioxidant Supplement

OBJECTIVE To study oxidative stress indicators in healthy young children and their response to a commercially available fruit- and vegetable-based antioxidant supplement. DESIGN Healthy children were randomly assigned to a placebo and a supplement (commercial antioxidant supplement produced from dried fruit and vegetable extracts and fortified with antioxidants, resembling a gummy-type candy). The placebo and the supplement were taken in 2 doses per day for 21 days. SUBJECTS Participants were 39 children (26 boys and 13 girls) aged 5 to 10 years. Research was conducted at Primary Childrens Medical Center and the University of Utah, Salt Lake City. MAIN OUTCOME MEASURES Breath and urine samples were collected on days 1 and 21 and assayed for breath pentane and urine 8-hydroxydeoxyguanosine, malondialdehyde, nitrites, and 8-isoprostane as noninvasive indicators of oxidative stress. Urine oxygen radical absorbance capacity was measured at days 1 and 21 as an indirect indicator of the antioxidant capacity of the body. Three-day food records were collected at the beginning and end of the study to measure intake of dietary fruit; vegetable; and antioxidant vitamins A, C, and E. STATISTICAL ANALYSIS Descriptive statistics, repeated measures analysis of variance, paired t tests, and Pearson r correlations. RESULTS Markers of oxidative stress were not significantly different between the placebo and supplement groups at day 1 or day 21. The oxidative stress indicators of the healthy children in this study appear to be similar to those of healthy adults and were not changed by antioxidant supplementation. The diet record analyses indicated that mean fruit and vegetable intakes (2.75 servings/day) were similar to the national average intake for children in the United States. APPLICATIONS/CONCLUSIONS This research presents original information on the subject of oxidative stress in healthy children. The results of this study may be useful as reference baseline markers to use in conjunction with clinical dietary evaluations and for future research with healthy children and with children in disease states who are subject to elevated levels of oxidative stress.