Nutritional status assessment before, during, and after long-duration head-down bed rest.

INTRODUCTION: Bed rest is a valuable ground-based model for many of the physiological changes that are associated with spaceflight. Nutritional changes during and after 60 or 90 d of head-down bed rest were evaluated. METHODS: A total of 13 subjects (8 men, 5 women; ages 26-54 yr) participated in either 60 or 90 d of bed rest. Blood and urine were collected twice before bed rest and about once per month during bed rest. Samples were stored frozen and batch analyzed. Data were analyzed using repeated-measures analysis of variance. RESULTS: During bed rest, markers of bone resorption (such as N-telopeptide excretion, P < 0.001) increased and serum concentration of parathyroid hormone decreased (P < 0.001). Also, oxidative damage markers such as superoxide dismutase increased (P < 0.05), and after 90 d of bed rest, total antioxidant capacity decreased (P < 0.05). During bed rest, iron status indices showed patterns of increased iron stores with a decreased concentration of transferrin receptors (P < 0.01). DISCUSSION: These changes are similar to some of those observed during spaceflight, and further document the utility of bed rest as a model of spaceflight.

Body iron stores and oxidative damage in humans increased during and after a 10- to 12-day undersea dive.

The National Aeronautics and Space Administration Extreme Environment Mission Operations (NEEMO) underwater habitat is a useful analogue for spaceflight. However, the increased air pressure in the habitat exposes crewmembers to higher oxygen pressures, which increases their risk for oxidative damage to DNA, proteins, and lipids. Studies from a previous NEEMO mission suggested that DNA oxidation occurs at an increased level, similar to that in smokers and astronauts returning from space. Astronauts in space and NEEMO crewmembers also have similar changes in iron metabolism. Newly formed RBC are destroyed and body iron stores are elevated. Because excess iron can act as an oxidant and cause tissue damage, we investigated aspects of oxidative damage and tested whether toxic forms of iron were present when iron stores increased during NEEMO missions. Subjects (n = 12) participated in 10- to 12-d saturation dives, and blood and 24-h urine samples were collected twice before, twice during, and twice after the dive. During the dive, ferritin was higher (P < 0.001), transferrin was lower (P < 0.001), and transferrin receptors were lower (P < 0.01). Serum iron was higher during and immediately after the dive (P < 0.001). Total homocysteine (P < 0.001) and superoxide dismutase (SOD) (P < 0.05) activity were affected by time; homocysteine increased during the dive and SOD decreased during and after the dive. Labile plasma iron was measurable only during the dive. These data indicate that the NEEMO environment increases body iron stores and labile forms of iron, which may contribute to oxidative damage.

Energy metabolism in brain cells: effects of elevated ammonia concentrations.

Both neurons and astrocytes have high rates of glucose utilization and oxidative metabolism. Fully 20% of glucose consumption is used for astrocytic production of glutamate and glutamine, which during intense glutamatergic activity leads to an increase in glutamate content, but at steady state is compensated for by an equally intense oxidation of glutamate. The amounts of ammonia used for glutamine synthesis and liberated during glutamine hydrolysis are large, compared to the additional demand for glutamine synthesis in hyperammonemic animals and patients with hepatic encephalopathy. Nevertheless, elevated ammonia concentrations lead to an increased astrocytic glutamine production and an elevated content of glutamine combined with a decrease in glutamate content, probably mainly in a cytosolic pool needed for normal activity of the malate-asparate shuttle (MAS); another compartment generated by glutamine hydrolysis is increased. As a result of reduced MAS activity the pyruvate/lactate ratio is decreased in astrocytes but not in neurons and decarboxylation of pyruvate to form acetyl coenzyme A is reduced. Elevated ammonia concentrations also inhibit decarboxylation of alpha-ketoglutarate in the TCA cycle. This effect occurs in both neurons and astrocytes, is unrelated to MAS activity and seen after chronic treatment with ammonia even in the absence of elevated ammonia concentrations.

Nutritional status is altered in the self-neglecting elderly.

Elder self-neglect is the most common form of elder mistreatment. Individuals who cannot provide basic needs for themselves may develop social, functional, and physical deficits. The systematic characterization of self-neglecting individuals is the goal of the Consortium for Research in Elder Self-Neglect of Texas project. This study reports on the nutritional status of self-neglecting elderly. Self-neglectors (SN) were recruited based on referrals along with matched control (CN) subjects. Data are for 40 SN subjects (age 76 +/- 7 y) and 40 CN subjects (76 +/- 7 y). Blood samples were collected and analyzed for indices of nutritional status. SN subjects had a greater serum concentration of total homocysteine than CN subjects (13.6 +/- 4.5 vs. 11.6 +/- 5.6 micromol/L, P < 0.05) and a lower concentration of red blood cell folate (1380 +/- 514 vs. 1792 +/- 793 nmol/L, P < 0.05). Plasma beta-carotene and alpha-tocopherol were lower in SN subjects (0.28 +/- 0.2 vs. 0.43 +/- 0.33 micromol/L; 23.2 +/- 9.3 vs. 27.8 +/- 9.3 micromol/L, P < 0.05). SN subjects had a lower serum concentration of 25-hydroxyvitamin D than CN subjects (33.7 +/- 16.4 vs. 44.1 +/- 19.6 nmol/L, P < 0.05). These differences in markers of nutritional status show that the self-neglecting elderly are at risk for altered nutritional status, particularly of folate, antioxidants, and vitamin D. Evaluation of these data in relation to other functional and cognitive assessments are critical for evaluating the relation between nutrition and self-neglect.

Survival and cell death in cells constitutively unable to synthesize glutathione.

We examined the role of GSH in survival and cell death using GCS-2 cells that are deficient in glutamate cysteine ligase (gamma-glutamyl cysteine synthetase, gammaGCS), an enzyme essential for GSH synthesis. Cells maintained in 2.5 mM GSH have GSH levels that are approximately 2% of wild type and grow indefinitely; however, they express both pro- and anti-apoptotic Bcl-2 family members and have detectable levels of cytoplasmic cytochrome C. Withdrawal of GSH from the medium results in a fall in intracellular GSH to undetectable levels, decreased mitochondrial dehydrogenase activity, decreased anti-apoptotic factor RNAs, increased pro-apoptotic factor RNAs, additional cytochrome C release, and a fall in ATP levels; however, cells continue to grow for another 24h. At 48 h, these trends continue with the exception that mitochondrial membrane potential and ATP levels rise; DNA fragmentation begins at 48 h. Thus, severe reduction of GSH to 2% of wild type produces a metastable state compatible with survival, but complete absence of GSH triggers apoptosis.

Ammonia effects on pyruvate/lactate production in astrocytes--interaction with glutamate.

Ammonia exerts a multitude of metabolic and non-metabolic effects on brain tissue. In the present communication we have investigated its effect on lactate production rates, pyruvate production rates and pyruvate/lactate ratios in mouse cerebrocortical astrocytes and neurons in primary cultures. No effects were found in neurons. All three parameters were affected by ammonia in astrocytes, but less potently and to a smaller degree in cells that had been treated with dibutyryl cyclic AMP (morphologically differentiated cells) than in untreated cells (morphologically undifferentiated cells). In the differentiated cells ammonia had virtually no effect up to a concentration of 1.0 mM, but at 3.0 mM it increased lactate production and decreased pyruvate/lactate ratio significantly. In the undifferentiated cells ammonia greatly increased lactate accumulation (by 80% at 3.0 mM) and it inhibited pyruvate accumulation (by 40% at 3.0 mM). It thereby reduced the pyruvate/lactate ratio progressively within the entire range 0.1-3.0 mM ammonia. In support of the hypothesis that the ammonia-induced reduction of pyruvate/lactate ratio is secondary to depletion of cellular glutamate by formation of glutamine (and glutathione) and a resulting interruption of the malate-aspartate shuttle (MAS), the addition of glutamate to the incubation medium significantly diminished the ammonia-induced reduction of pyruvate/lactate ratio, whereas it had no effect on the increased lactate production. It is discussed that MAS interruption may have additional consequences in astrocytes.

Formation and urinary excretion of arsenic triglutathione and methylarsenic diglutathione.

Taking advantage of mice deficient in gamma-glutamyl transpeptidase that are unable to metabolize glutathione (GSH), we have identified two previously unrecognized urinary metabolites of arsenite: arsenic triglutathione and methylarsenic diglutathione. Following administration of sodium arsenite to these mice, approximately 60-70% of urinary arsenic is present as one of these GSH conjugates. We did not detect the dimethyl derivative, dimethyl arsenic GSH; however, dimethyl arsenic (DMAV) represented approximately 30% of urinary arsenic. Administration of buthionine sulfoximine, an inhibitor of GSH synthesis, to wild-type mice reduced urinary arsenic excretion by more than 50%, indicating the GSH dependence of arsenic metabolism, transport, or both. Rodents deficient in three known ABC family transporters (MRP1, MRP2, and MDR1a/1b) exhibited urinary arsenic levels similar or greater than those in wild-type rodents; however, administration of MK571, an MRP inhibitor, reduced urinary arsenic excretion by almost 50%. MK571-treated mice showed approximately 50% reduction of AsIII, MMAV, and AsV as compared to untreated wild-type controls, while DMAV levels were unchanged. These findings suggest that arsenic excretion is in part dependent on GSH and on an MRP transporter other than MRP1 or 2.