Energy metabolism after 2 y of energy restriction: the biosphere 2 experiment.

BACKGROUND: An adaptive decrease in energy expenditure (EE) in response to 6 mo of severely restricted energy intake was shown in a classic semistarvation study-the Minnesota experiment. OBJECTIVE: Our objective was to examine whether such adaptation also occurs in response to less severe but sustained energy restriction. DESIGN: Body composition, 1-wk total EE (TEE), 24-h sedentary EE, and spontaneous physical activity were measured in 8 healthy subjects (4 men and 4 women) at the end of a 2-y confinement inside Biosphere 2. Unexpectedly, the food supply was markedly restricted during most of the confinement and all subjects experienced a marked, sustained weight loss (9.1 +/- 6.6 kg; P: < 0.001) from the low-energy (7000-11000 kJ/d), low-fat (9% of energy), but nutrient-dense, diet they consumed. RESULTS: The TEE inside Biosphere 2, assessed 3 wk before exit, averaged 10700 +/- 560 kJ/d (n = 8). Within 1 wk after exit, the adjusted 24-h EE and spontaneous physical activity were lower in the biospherians (n = 5) than in 152 control subjects (6% and 45%, respectively; both P: < 0.01). Six months after exit and return to an ad libitum diet, body weight had increased to preentry levels; however, adjusted 24-h EE and spontaneous physical activity were still significantly lower than in control subjects. CONCLUSIONS: In lean humans, an adaptive decrease in EE appears to occur not only in states of life-threatening undernutrition, but also in response to less severe energy restriction sustained over several years.

Physiologic changes in humans subjected to severe, selective calorie restriction for two years in biosphere 2: health, aging, and toxicological perspectives.

Biosphere 2 is a closed ecological space of 7-million cubic feet near Tucson, AZ, containing 7 biomes: rain forest, Savannah, ocean, marsh, desert, agricultural station, and habitat for humans and domestic animals. Sealed inside, 4 men and 4 women maintained themselves and the various systems for 2 years. All organic material, all water, and nearly all air was recycled, and virtually all food was grown inside. On the low calorie but nutrient-dense diet available, the men sustained 18% and the women 10% weight loss, mostly within the first 6 to 9 months. The nature of the diet duplicated rodent diets that had been shown to enhance health, lower disease incidence, and retard aging. Using blood specimens frozen at different points during and after the 2 years, determinations were made of a number of biochemical parameters judged to be pertinent based on past studies of rodents and monkeys on similar diets. These included blood lipids, glucose, insulin, glycosylated hemoglobin, renin, and others. The results clearly suggest that humans react to such a nutritional regime similarly to other vertebrates. In addition to these studies, and because this was a tightly closed, isolated environment, the levels of insecticides or pollutants or their derivatives were determined in the sera of 2 crew members. It was found that levels of the lipophilic toxicant DDE and the "total PCB" load increased with the loss of body fat during the first 12-18 months inside Biosphere 2, then decreased.

Atmospheric dynamics and bioregenerative technologies in a soil-based ecological life support system: initial results from Biosphere 2.

Biosphere 2 is the first man-made, soil-based, bioregenerative life support system to be developed and tested. The utilization and amendment of local space resources, e.g. martian soil or lunar regolith, for agricultural and other purposes will be necessary if we are to minimize the requirement for Earth materials in the creation of long-term off-planet bases and habitations. Several of the roles soil plays in Biosphere 2 are 1) for air purification 2) as a key component in created wetland systems to recycle human and animal wastes and 3) as nutrient base for a sustainable agricultural cropping program. Initial results from the Biosphere 2 closure experiment are presented. These include the accelerated cycling rates due to small reservoir sizes, strong diurnal and seasonal fluxes in atmospheric CO2, an unexpected and continuing decline in atmospheric oxygen, overall maintenance of low levels of trace gases, recycling of waste waters through biological regeneration systems, and operation of an agriculture designed to provide diverse and nutritionally adequate diets for the crew members.

Biosphere 2 Test Module: a ground-based sunlight-driven prototype of a closed ecological life support system.

Constructed in 1986, the Biosphere 2 Test Module has been used since the end of that year for closed ecological systems experiments. It is the largest closed ecological facility ever built, with a sealed variable volume of some 480 cubic meters. It is built with a skin of steel spaceframes with double-laminated glass panels admitting about 65 percent Photosynthetically Active Radiation (PAR). The floor is of welded steel and there is an underground atmospheric connection via an air duct to a variable volume chamber ("lung") permitting expansion and contraction of the Test Module's air volume caused by changes in temperature and barometric pressure, which causes a slight positive pressure from inside the closed system to the outside thereby insuring that the very small leakage rate is outward. Several series of closed ecological system investigations have been carried out in this facility. One series of experiments investigated the dynamics of higher plants and associated soils with the atmosphere under varying light and temperature conditions. Another series of experiments included one human in the closed system for three, five and twenty-one days. During these experiments the Test Module had subsystems which completely recycled its water and atmosphere; all the human dietary needs were produced within the facility, and all wastes were recycled using a marsh plant/microbe system. Other experiments have examined the capability of individual component systems used, such as the soil bed reactors, to eliminate experimentally introduced trace gases. Analytic systems developed for these experiments include continuous monitors of eleven atmospheric gases in addition to the complete gas chromatography mass spectrometry (GCMS) examinations of potable, waste system and irrigation water quality.

"Biospheric medicine" as viewed from the two-year first closure of Biosphere 2.

Biosphere 2 is a 3.15-acre, 7-million ft. enclosed ecological space near Tucson, AZ. It contains five wilderness and two domestic biomes (rain forest, savanna, desert, ocean, marsh; agricultural station, living quarters), an original introduction of 3,800 species (approximately 20% extinctions have occurred), and a large basement "technosphere." Sealed inside Biosphere 2 in September 1991, four women and four men, including two of the authors, maintained themselves and the various systems for 2 yr, the longest-sustained "isolated confined environment" period on record. MMPI psychological profile scores for Biosphere 2 crewmembers correlated closely with those reported for astronauts and shuttle applicants. Major medical problems encountered during the 2 yr included adaptation to a low-calorie (1800-2200 kcal.d-1 per person) but otherwise nutritionally adequate diet, with substantial weight loss (18% for men, 10% for women), and a declining oxygen atmosphere (down to 14.2%). Life in a miniworld such as Biosphere 2 may differ substantially from life in a space station or temporary planetary base. These differences include multiple, shifting, sometimes opposing post-launch objectives; complete self-sustenance with recycling of virtually all materials within a highly complex biologic system; retooling of some areas of practical medicine; an attention to "culture" as a social dynamic and how that may influence crew and leadership selection in a societal rather than a quasi-military community. Assuming that long-term planetary colonies must be largely self-sustaining (due to costs of supply over great distances), they must of necessity approach the condition of biospheres. Subject to chaos dynamic (nonlinear dynamic) perturbations, the behavior of complex biospheres will be inherently non-predictable--as opposed to the linear dynamic situation of most space missions--and will require of the inhabitants, including the medical team, a wide range of coping abilities. Under the circumstances, and while strong similarities exist, important differences may serve to distinguish "biospheric medicine" from "space medicine."

Autonomous Biological System (ABS) experiments.

Three space flight experiments have been conducted to test and demonstrate the use of a passively controlled, materially closed, bioregenerative life support system in space. The Autonomous Biological System (ABS) provides an experimental environment for long term growth and breeding of aquatic plants and animals. The ABS is completely materially closed, isolated from human life support systems and cabin atmosphere contaminants, and requires little need for astronaut intervention. Testing of the ABS marked several firsts: the first aquatic angiosperms to be grown in space; the first higher organisms (aquatic invertebrate animals) to complete their life cycles in space; the first completely bioregenerative life support system in space; and, among the first gravitational ecology experiments. As an introduction this paper describes the ABS, its flight performance, advantages and disadvantages.

Analysis of water in Autonomous Biological Systems (ABS) samples.

Several soluble components, peptidase and amino acids, and carbon isotopic ratio in the water retrieved from flight experiments of Autonomous Biological Systems (ABS) as well as ground control samples are analyzed to interpret the condition, dynamics, material balance of the ABS ecosystems. Organic carbons in flight samples were found to be more abundant compared with the control ones, which suggested the uniform ecosystems in low gravity might easily dissolve more soluble components. The Mir-1997 flight sample showed higher C/N ratio probably because of the dissolution of carbon-rich plant materials.

Microorganisms and plant of Autonomous Biological Systems (ABS) samples.

Distribution of microorganisms and cellular structure of an Autonomous Biological Systems (ABS) were studied with a special attention to the effect of space environments. Viable cell densities measured by the direct fluorescence microscopic method were in the order of 10(5) cells/ml for fractions 1 (upper suspension) and 2 (lower suspension), and 10(6) cells/ml for fraction 3 (sediments). These values were 10 to 100 times larger than the values obtained by the classical colony forming unit method. No difference between flight and ground samples was observed in the vertical distribution of viable microorganisms when fractionation and analysis were carried out after recovery. Intracellular distribution of chloroplasts in higher green plants, Ceratophyllum demersum, of flight samples was disturbed after 10 days of flight (24hrs/day light on). After 4 months of flight (Mir/STS-79/81) with 24 hrs light on, Ceratophyllum demersum was completely disintegrated. On the other hand, in the second 4-months-flight experiment with 16 hrs/day light on, Ceratophyllum demersum was only slightly deteriorated.

Behavior and reproduction of invertebrate animals during and after a long-term microgravity: space experiments using an Autonomous Biological System (ABS).

Aquatic invertebrate animals such as Amphipods, Gastropods (pond snails), Ostracods and Daphnia (water flea) were placed in water-filled cylindrical vessels together with water plant (hornwort). The vessels were sealed completely and illuminated with a fluorescent lamp to activate the photosynthesis of the plant for providing oxygen within the vessels. Such ecosystem vessels, specially termed as Autonomous Biological System or ABS units, were exposed to microgravity conditions, and the behavior of the animals and their reproduction capacity were studied. Three space experiments were carried out. The first experiment used a Space shuttle only and it was a 10-day flight. The other two space experiments were carried out in the Space station Mir (Shuttle/Mir mission), and the flight units had been kept in microgravity for 4 months. Daphnia produced their offspring during a 10-day Shuttle flight. In the first Mir experiment, no Daphnia were detected when recovered to the ground. However, they were alive in the second Mir experiment. Daphnia were the most fragile species among the invertebrate animals employed in the present experiments. All the animals, i.e., Amphipods, pond snails, Ostracods and Daphnia had survived for 4 months in space, i.e., they had produced their offspring or repeated their life-cycles under microgravity. For the two Mir experiments, in both the flight and ground control ecosystem units, an inverse relationship was noted between the number of Amphipods and pond snails in each unit. Amphipods at 10 hours after the recovery to the ground frequently exhibited a movement of dropping straight-downward to the bottom of the units. Several Amphipods had their legs bent abnormally, which probably resulted from some physiological alterations during their embryonic development under microgravity. From the analysis of the video tape recorded in space, for Ostracods and Daphnia, a half of their population were looping under microgravity. Such looping animals could be observed still at the end of the 4 month stay in space. No looping behavior was noted for Amphipods and pond snails.

Concluding remarks of Autonomous Biological Systems (ABS) experiments.

Team efforts for analysis on the Autonomous Biological Systems (ABS) space experiments are summarized here to conclude scientific findings, and to scope the extended studies in future. From the three experiments on Space Shuttle and Space Station Mir, a closed ecological system modeled by the ABS was verified to be capable of sustaining its members of animals and plants under space environment for a period of several months. The animals successfully completed their life cycle in space during the course of these experiments, this was the first time that the life cycle of higher organisms had been completed in space and ecological system. Importance of gravity for ecology was proven at the same time. Gravity is a dominant factor for ecology by formulating spatial patterns and distribution of members of ecological system. Under microgravity, the fate of ecological system was found highly sensitive against the variation of environmental factor, such as light illumination cycle.

Performance of a digital video camcorder for the Autonomous Biological System experiment onboard Space Station Mir.

A video imaging and recording system was utilized in the Autonomous Biological System experiment onboard the space station Mir. Video image of the mini-ecological system was successfully recorded. The whole system was retrieved to the ground after its operation in orbit for four months. Performance of the video system is summarized here together with technical problems encountered. Defects of pixel had been developed in the imaging device. Cause of these defects could be attributed to its exposure against space radiation. Auto white balance was another function of the camcorder that was deviated from normal range of its performance once in orbit but recovered to normal after a while. Possible use of imaging devices for dosimetry is proposed to record space radiation environment at the site close to the experiment.

Mini ecosystem in space--preliminary experiment on board STS-77.

An enclosed ecosystem which is stable on Earth will behave differently when brought into space. Micro-gravity and radiation will affect the dynamics of material circulation or the activities of small creatures of the ecosystem. One series of space experiments aiming to address such issues was planned in the United States (It is termed as ABS--Autonomous Biological System) and Japanese group has been involved with cooperating with the analysis of the flight samples. Before the ecosystem will be on board Russian Space Station "Mir" later 1996 for 3 months, a preliminary flight was carried out in May 1996 on Space Shuttle (STS-77) for 10 days flight. It was the first of such experiments to fly one whole ecosystem in space.

Acute methionine loading does not alter arterial stiffness in humans.

Hyperhomocystinemia is a risk factor for cardiovascular disease, and acute elevation of plasma homocysteine after methionine loading impairs endothelial function in healthy subjects. Interestingly, pretreatment with vitamin C can ameliorate this effect. We have already shown that acute oral vitamin C administration reduces arterial stiffness in healthy subjects, and the aim of the present study was to investigate the effect of methionine loading on arterial stiffness with and without concomitant vitamin C using the noninvasive technique of pulse wave analysis. Eight healthy male subjects (mean age, 29 years; range, 20-42 years) were studied on three occasions at weekly intervals. In a double-blind, double-dummy, randomized order they received orally either 100 mg/kg methionine, 100 mg/kg methionine plus 2 g of vitamin C, or matching placebos. Peripheral and central blood pressure, heart rate, cardiac index, arterial stiffness, and plasma homocysteine levels were assessed at baseline and 6 hours after dosing. Compared with placebo, there was no significant change in any of the hemodynamic parameters, including arterial stiffness, after oral methionine, although plasma homocysteine did increase from 11.5 +/- 1.6 to 28.7 +/- 4.4 microM (mean +/- SEM; p < 0.001). Combined methionine and vitamin C led to a similar increase in plasma homocysteine but significantly reduced augmentation index by 10.5 +/- 3.2% (p = 0.02). Acute hyperhomocystinemia does not significantly alter arterial stiffness, as assessed by pulse wave analysis, whereas a combination of methionine and vitamin C leads to a similar reduction in augmentation index to that previously described after vitamin C alone. These data reinforce evidence that vitamin C reduces arterial stiffness but do not indicate any important interaction with oral methionine.