Regional muscle loss after short duration spaceflight

BACKGROUND

Muscle strength and limb girth measurements during Skylab and Apollo missions suggested that loss of muscle mass may occur as a result of spaceflight. Extended duration spaceflight is important for the economical and practical use of space. The loss of muscle mass during spaceflight is a medical concern for long duration flights to the planets or extended stays aboard space stations. Understanding the extent and temporal relationships of muscle loss is important for the development of effective spaceflight countermeasures.

HYPOTHESIS

We hypothesized that significant and measurable changes in muscle volume would occur in Shuttle crewmembers following 8 d of weightlessness.

METHODS

MRI was used to obtain the muscle volumes of the calf, thigh and lower back before and after the STS-47 Shuttle mission.

RESULTS

Statistical analyses demonstrated that the soleus-gastrocnemius (-6.3%), anterior calf (-3.9%), hamstrings (-8.3%), quadriceps (-6.0%) and intrinsic back (-10.3%) muscles were decreased, p < 0.05, compared to baseline, 24 h after landing. At 2 weeks post recovery, the hamstrings and intrinsic lower back muscles were still below baseline, p < 0.05.

CONCLUSIONS

These results demonstrate that even short duration spaceflight can result in significant muscle atrophy.

Bone and body mass changes during space flight

Body mass, calcium and skeletal changes occur in humans who have worked in microgravity. Physiologic changes are seen as early as one week and are still occurring 312 days into space flight. The physiologic changes in bone and mineral metabolism may be among those which limits long duration space flight if an adequate countermeasure is not developed. The purpose of this paper is to summarize what is known about calcium dynamics and bone mineral changes as well as associated changes of body mass induced by space flight. The data reported is from a variety of studies conducted in both actual and simulated space flight.

Terminal differentiation-dependent alteration in the expression of translation elongation factor-1 alpha and its sister gene, S1, in neurons

Elongation factor-1 alpha (EF-1 alpha) is a highly conserved, abundantly expressed protein that functions in peptide elongation during mRNA translation. Mammalian species contain a second EF-1 alpha gene, S1, whose expression is limited to brain, heart, and skeletal muscle. Such tissue specificity in S1 gene expression led us to hypothesize that this specialized member of the EF-1 alpha family is possibly essential to terminally differentiated, long-lived cells such as neurons, cardiomyocytes, and myocytes. We report here that during development, EF-1 alpha mRNA levels remain unchanged in S1-negative tissues, but sharply decrease in S1-positive tissues. RNase protection as well as tissue distribution analyses of the S1 message suggest that down-regulation of EF-1 alpha expression coincides well with that of S1 up-regulation during postnatal development. Analysis of primary cultures of the rat neonatal cerebral cortex cells has shown that S1 gene expression is indeed restricted to neurons only, whereas nonneuronal cell types such as astrocytes and microglia are S1-negative. EF-1 alpha mRNA on the other hand was detected in all three cell types, namely, neurons, astrocytes, and microglia. This report confirms the terminal differentiation-dependent expression of the S1 gene in neurons of the cerebral cortex.

Calcium absorption, endogenous excretion, and endocrine changes during and after long-term bed rest

Negative calcium balance is a known consequence of bed rest, and is manifested in elevated urine and fecal calcium (Ca). Elevated fecal Ca can result from either decreased absorption, increased endogenous fecal excretion, or both. We measured the Ca absorption and endogenous fecal excretion in eight healthy male volunteers before and during 4 months of bed rest. Dual isotope (n = 6) or single isotope (n = 2) methods in conjunction with Ca balance were used to calculate true and net Ca absorption and endogenous fecal excretion. Stool Ca increased from 797 mg/day (mean intake 991 mg/day) to 911 mg/day during bed rest, whereas urine Ca excretion increased from 174 to 241 mg/day. True Ca absorption decreased from 31 +/- 7% of Ca intake pre-bed rest to 24 +/- 2% during bed rest, (p < 0.05) and returned toward pre-bed rest values within 5-6 weeks following reambulation. Endogenous fecal excretion did not change significantly, and therefore, most of the increased fecal Ca resulted from changes in absorption. However, in one individual, endogenous fecal Ca excretion was the major contributor to Ca loss. Ionized Ca and pyridinium crosslinks increased and 1,25(OH)2 vitamin D decreased during bed rest, similar to the decrease in Ca absorption; parathyroid hormone (PTH), calcitonin, serum albumin, phosphorus, and total serum Ca were unchanged. Although alkaline phosphatase, osteocalcin, and PTH were unchanged during bed rest, they were elevated during reambulation. These changes accompanied by increased Ca absorption and balance and decreased ionized and total serum Ca suggest a rebound in bone formation following immobilization.

Rapid, sensitive, and noninvasive sampling technique for determination of chloroform in alveolar breath

A sampling technique for the determination of chloroform in alveolar breath is presented. Subjects exhale in a homemade device for collection of the alveolar fraction. The collected sample is transferred to a partially evacuated headspace vial and subsequently analyzed by capillary gas chromatography using electron-capture detection. Concentrations greater than 50 micrograms/m3 can readily be detected. Good correlation observed between chloroform levels in alveolar breath and plasma validates the sampling technique.

Hologic QDR 2000 whole-body scans: a comparison of three combinations of scan modes and analysis software

This study reports on the short-term in vivo precision and absolute measurements of three combinations of whole-body scan modes and analysis software using a Hologic QDR 2000 dual-energy X-ray densitometer. A group of 21 normal, healthy volunteers (11 male and 10 female) were scanned six times, receiving one pencil-beam and one array whole-body scan on three occasions approximately 1 week apart. The following combinations of scan modes and analysis software were used: pencil-beam scans analyzed with Hologic's standard whole-body software (PB scans); the same pencil-beam analyzed with Hologic's newer "enhanced" software (EPB scans); and array scans analyzed with the enhanced software (EA scans). Precision values (% coefficient of variation, %CV) were calculated for whole-body and regional bone mineral content (BMC), bone mineral density (BMD), fat mass, lean mass, %fat and total mass. In general, there was no significant difference among the three scan types with respect to short-term precision of BMD and only slight differences in the precision of BMC. Precision of BMC and BMD for all three scan types was excellent: < 1% CV for whole-body values, with most regional values in the 1%-2% range. Pencil-beam scans demonstrated significantly better soft tissue precision than did array scans. Precision errors for whole-body lean mass were: 0.9% (PB), 1.1% (EPB) and 1.9% (EA). Precision errors for whole-body fat mass were: 1.7% (PB), 2.4% (EPB) and 5.6% (EA). EPB precision errors were slightly higher than PB precision errors for lean, fat and %fat measurements of all regions except the head, although these differences were significant only for the fat and % fat of the arms and legs. In addition EPB precision values exhibited greater individual variability than PB precision values. Finally, absolute values of bone and soft tissue were compared among the three combinations of scan and analysis modes. BMC, BMD, fat mass, %fat and lean mass were significantly different between PB scans and either of the EPB or EA scans. Differences were as large as 20%-25% for certain regional fat and BMD measurements. Additional work may be needed to examine the relative accuracy of the scan mode/software combinations and to identify reasons for the differences in soft tissue precision with the array whole-body scan mode.

Evaluation of dermal and respiratory chloroform exposure in humans

Chloroform is a known contaminant of chlorinated drinking water and of swimming pool water disinfected with chlorine or one of its derivatives. Few data exist regarding the importance of dermal and inhalation exposure routes to the chloroform body burden resulting from domestic and recreational use of chlorinated water. In our experimental study involving 11 male swimmers, we quantified the body burden resulting from exposure to various concentrations of chloroform in water and air of an indoor swimming pool, during a daily 55-min exercise period. From the first to the sixth exercise period, CHCl3 mean concentration in water was increased from 159 micrograms/l to 553 micrograms/l. Corresponding mean air CHCl3 level ranged from 597 ppb to 1630 ppb. To dissociate the dermal exposure route from that of inhalation, swimmers used scuba tanks during an additional exercise period. Chloroform concentrations were measured in alveolar air before and after each exercise period, as well as after 35 min of physical activity. Chloroform levels in water and air were measured every 10 min. We examined the relationship between alveolar air concentration (a measure of body burden) at 35 and 55 min and environmental chloroform concentrations by using multiple regression models. The natural logarithm of alveolar air concentration was strongly correlated with aqueous chloroform concentration both at 35 (p2 < 0.001, r2 = 0.75) and 55 min (p < 0.001, r2 = 0.86). The relationship with air concentrations was also statistically significant (35 min: p < 0.001, r2 = 0.58, 55 min: p < 0.001, r2 = 0.63).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of retained diaphyseal plates on forearm bone density and grip strength

Numerous complications have been attributed to elective plate removal following successful treatment of both bone diaphyseal forearm fractures, yet the effects of retained implants are not known. Fourteen patients were reviewed for residual forearm grip strength (FGS) and bone mineral density (BMD) following uneventful union. Patients were analyzed in two groups based upon time from fixation: group I, > 2 years but < or = 5 years, and group II, > 5 years. In group I, mean 2.6 years follow-up (n = 6), mean FGS ratios (patient values/age matched general population means) were 0.65 and 0.77, respectively, for plated and normal limbs (p = 0.08). The mean BMD ratios of plated/normal sides adjacent to the plate were 0.99 (ulna) and 1.02 (radius); these values were not significantly different from more proximal forearm BMD ratios (p = 0.92 ulna; p = 0.44, radius). In group II, mean 8.4 years (n = 8), mean FGS ratios were 0.97 and 1.09, respectively, for plated and normal limbs (p > 0.05). The BMD ratio was 1.04 adjacent to the plate; this was not significantly different from the ratios measured away from the plate (p > 0.4). We conclude that retained forearm plates can be well tolerated and that their routine removal is not indicated based on FGS or BMD.

Evaluation of dermal and respiratory chloroform exposure in humans

Chloroform is a known contaminant of chlorinated drinking water and of swimming pool water disinfected with chlorine or one of its derivatives. Few data exist regarding the importance of dermal and inhalation exposure routes to the chloroform body burden resulting from domestic and recreational use of chlorinated water. In our experimental study involving 11 male swimmers, we quantified the body burden resulting from exposure to various concentrations of chloroform in water and air of an indoor swimming pool, during a daily 55-min exercise period. From the first to the sixth exercise period, CHCl3 mean concentration in water was increased from 159 micrograms/l to 553 micrograms/l. Corresponding mean air CHCl3 level ranged from 597 ppb to 1630 ppb. To dissociate the dermal exposure route from that of inhalation, swimmers used scuba tanks during an additional exercise period. Chloroform concentrations were measured in alveolar air before and after each exercise period, as well as after 35 min of physical activity. Chloroform levels in water and air were measured every 10 min. We examined the relationship between alveolar air concentration (a measure of body burden) at 35 and 55 min and environmental chloroform concentrations by using multiple regression models. The natural logarithm of alveolar air concentration was strongly correlated with aqueous chloroform concentration both at 35 (p2 < 0.001, r2 = 0.75) and 55 min (p < 0.001, r2 = 0.86). The relationship with air concentrations was also statistically significant (35 min: p < 0.001, r2 = 0.58, 55 min: p < 0.001, r2 = 0.63).(ABSTRACT TRUNCATED AT 250 WORDS)

A role for extracellular matrix degradation and matrix metalloproteinases in senile dementia?

In brain as in cartilage, the extracellular matrix contains aggregates formed by hyaluronic acid (HA) and proteoglycans. In osteoarthritic cartilage, release of the proteoglycans from the aggregates by cleavage of the HA-binding region results in the accumulation of the HA-binding region and in the fragmentation of the released proteoglycans. Stromelysin, a matrix neutral metalloproteinase, is one of the enzymes responsible for the cleavage of the HA-binding region. We suggest that a similar process also occurs in senile dementia. The brain proteoglycan contains sequences identical to those of aggrecan, which are recognized and cleaved by stromelysin, and is, in fact, susceptible to stromelysin digestion. Monoclonal antibodies reacting with glial HA-binding protein, but not with the parent protein, stained several senile plaques as defined by their reactivity with antibodies to the amyloid-beta protein in double-labeling experiments.

Prevention of space flight induced soft tissue calcification and disuse osteoporosis

This paper emphasizes the devastating effects of displacement of calcium during space flight, due to increased bone turnover.

Countermeasures against space flight related bone loss

This paper reviews human data concerning bone loss and attempted countermeasures during spaceflight and bed rest, a commonly employed technique to simulate the effects of weightlessness on the musculoskeletal system.

Fatal familial insomnia

Fatal familial insomnia (FFI), a condition characterized by inability to sleep, dysautonomia, motor disturbances, and selective thalamic atrophy is a prion disease linked to a GAC→C mutation at codon 178 of the prion gene. These data were obtained from one kindred. We now report a second kindred affected by FFI and carrying the same mutation. The finding of the same disease phenotype and genotype in a second family further validates FFI as a distinct disease entity and a phenotype of the GAC→C mutation at codon 178 of the prion gene.

Fatal familial insomnia, a prion disease with a mutation at codon 178 of the prion protein gene

BACKGROUND

We previously described two members of a family affected by an apparently genetically determined fatal disease characterized clinically by progressive insomnia, dysautonomia, and motor signs and characterized pathologically by severe atrophy of the anterior ventral and mediodorsal thalamic nuclei. Five other family members who died of this disease, which we termed "fatal familial insomnia," had broader neuropathologic changes suggesting that fatal familial insomnia could be a prion disease.

METHODS

We used antibodies to prion protein (PrP) to perform dot and Western blot analyses, with and without proteinase K, on brain tissue obtained at autopsy from two patients with fatal familial insomnia, three patients with sporadic Creutzfeldt-Jakob disease, and six control subjects. The coding region of the PrP gene was amplified and sequenced in the samples from the two patients with fatal familial insomnia. Restriction-enzyme analysis was carried out with amplified PrP DNA from 33 members of the kindred.

RESULTS

Protease-resistant PrP was found in both patients with fatal familial insomnia, but the size and number of protease-resistant fragments differed from those in Creutzfeldt-Jakob disease. In the family with fatal familial insomnia, all 4 affected members and 11 of the 29 unaffected members had a point mutation in PrP codon 178 that results in the substitution of asparagine for aspartic acid and elimination of the Tth111 I restriction site. Linkage analysis showed a close relation between the point mutation and the disease (maximal lod score, 3.4 when theta was zero).

CONCLUSIONS

Fatal familial insomnia is a prion disease with a mutation in codon 178 of the PrP gene, but the disease phenotype seems to differ from that of previously described kindreds with the same point mutation.

Can the adult skeleton recover lost bone?

The loss of bone mineral with aging and subsequent development of osteoporosis is a common problem in elderly women, and as life expectancy increases, in elderly men as well. Space flight also causes bone loss and could be a limiting factor for long duration missions, such as, a Mars expedition or extended occupation of a space station. Before effective countermeasures can be devised, a thorough knowledge of the extent, location, and rate of bone loss during weightlessness is needed from actual space flight data or ground-based disuse models. In addition, the rate and extent that these losses are reversed after return from space flight are of primary importance. Although the mechanisms are not likely to be the same in aging and space flight, there are common elements. For example, strategies developed to prevent disuse bone loss or to enhance the rate of recovery following space flight might have direct applicability to clinical medicine. For various reasons, little attention has been given to recovery of bone mass following space flight. As a prelude to the design of strategies to enhance recovery of bone, this paper reviews published literature related to bone recovery in the adult. We conclude that recovery can be expected, but the rate and extent will be individual and bone site dependent. The development of strategies to encourage or enhance bone formation following space flight may be as important as implementing countermeasures during flight.

Bone density in eumenorrheic female college athletes

Information is limited on the effect of exercise on bone density in young eumenorrheic athletes. We studied 12 Caucasian intercollegiate volleyball players (V), nine basketball players (B), ten swimmers (S), and 13 non-athletes (N) with bone density measurements by photon absorptiometry of their calcaneus and lumbar spine (L2-L4). The effect of athletic status on bone density was analyzed by multivariate analysis of covariance, with height and weight as covariates. The bone densities reported below are mean +/- SE, adjusted for the covariates; units = g.cm-2, P less than 0.005. The swimmers had a significantly lower mean density in the lumbar spine than all other groups; the non-athletes' mean density was also lower than that of volleyball players (V = 1.31 +/- 0.03, B = 1.26 +/- 0.04, N = 1.18 +/- 0.03, S = 1.05 +/- 0.03). The volleyball and basketball players' mean calcaneal densities were greater than those of the swimmers and non-athletes (V = 0.530 +/- 0.017, B = 0.564 +/- 0.023, N = 0.438 +/- 0.018, S = 0.375 +/- 0.019). The higher bone densities for athletes in vertical weight-bearing activities are consistent with some but not all published data. The swimmers' low bone density in the lumbar spine, less than published values for amenorrheic runners, was unexpected.

Calf muscle area and strength changes after five weeks of horizontal bed rest

Nine male volunteers participated in a 10 week metabolic study in which subjects underwent 5 weeks of ambulatory control and 5 weeks of complete horizontal bed rest. Bed rest is a model commonly used to simulate space flight. The changes in muscle area and strength of the calf dorsiflexors and plantar flexors were measured before and after bed rest using magnetic resonance imaging (MRI) and a Cybex II dynamometer. The muscle area of the plantar flexors (gastrocnemius and soleus) decreased 12%, whereas the muscle area of the dorsiflexors was not significantly decreased. The maximal muscle strength of the plantar flexors decreased 26%; the muscle strength of the dorsiflexors was not significantly decreased. These results, which demonstrate differential muscle atrophy and a larger loss in strength relative to muscle area, have important implications in the development of exercise counter-measures to be implemented during space flight. The results also have implications for patients who have severe orthopaedic disorders and must be bed rested for long periods of time, and for persons who are voluntarily inactive (a large number of the elderly).

Spinal bone mineral after 5 weeks of bed rest

Patients put at bedrest for medical reasons lose 1-2% of spinal bone mineral per week. Losses of this magnitude during even short-term space flights of a few months would pose a serious limitation and require countermeasures. The spinal bone mineral (L2-L4) was determined in 6 healthy males (precision = 2%) before and after 5 weeks of complete bed rest. Only one individual had a significant loss (3%) and the -0.9% mean change for the 6, was not significant (P = 0.06). The average negative calcium balance during the 5 weeks was 4 g or 0.36% of total body calcium, similar to that reported in other bed-rest studies. Spinal bone loss, however, in healthy bed-rested males is significantly less than reported for bed-rested patients, suggesting that a large loss of spinal bone mineral does not occur during space flight missions lasting 5 weeks or less.

Changes in nuclear magnetic resonance (T2) relaxation of limb tissue with bed rest

Bed rest is used to simulate the effects of weightlessness on human physiology. A spin-echo procedure was used to image the lower leg of 15 normal male volunteers before and after 5 weeks of horizontal bedrest. In addition to noninvasively measuring muscle size changes, accurate T2 images were produced to investigate possible relaxation time changes immediately (2-4 h) and 1-2 days after bed rest. Subcutaneous fat showed no change in T2, bone marrow showed a decrease, and muscle showed no change immediately after bed rest but increased 1-2 days following reambulation.

Relaxation times of normal and atrophied muscle

Magnetic resonance imaging is being used to investigate physiological changes induced by microgravity. Using human (bed rest) and animal (tail suspension) models simulating zero gravity, muscle atrophy was studied. Despite significant physiological changes in muscle mass, distribution of blood flow, and muscle water, no changes in muscle proton relaxation times were found at several different resonant frequencies (6, 10, 20, and 200 MHz). These results suggest that observed changes in relaxation times as reported in pathologic studies are likely due to the pathological changes and not the accompanying muscle atrophy.

Bone and muscle atrophy with suspension of the rat

A modification of the Morey tail suspension model was used to determine atrophic responses of rat bone and muscle with 14-90 days unloading of the hindlimbs. Bone uptake of methylene diphosphonate followed a phasic pattern similar to changes in bone formation rate in immobilized dogs and rats. Increased uptake at 60 days (P = 0.01, femur) indicated an increased bone metabolism. Regional densitometry demonstrated a preferential loss of bone mineral in the trabecular mass (P = 0.02) at 30 days and in the cortical shaft by 90 days (P = 0.03). Maximal muscle atrophy occurred within 14-30 days. The gastrocnemius was less severely affected by suspension than by immobilization techniques, whereas the soleus atrophied (by weight) similarly, suggesting that muscle atrophy in the suspension model is distinctly different from immobilization atrophy. One significant response of skeletal muscle to suspension was an altered blood distribution. Muscle blood distribution changes reflect the hypodynamic state of muscle that continues to contract but probably at an altered rate in response to altered functional demands.

Clomiphene protects against osteoporosis in the mature ovariectomized rat

Clomiphene citrate, a mixed estrogen agonist-antagonist, protects mature ovariectomized breeder rats from changes in total body calcium and from deterioration of femur structure. Over 6 months, mature ovariectomized rats took up calcium at the rate of 0.7 +/- 0.5 mg/day, while normal controls gained 2.5 +/- 0.7 mg/day (mean +/- SEM) as measured by whole body neutron activation analysis. Injections of clomiphene (20 mg/kg/week) kept ovariectomized rats in positive calcium balance at 2.0 +/- 0.5 mg/day. Reductions in total femur calcium content, cortical thickness, and visible trabeculae of femurs in ovariectomized animals were prevented by chronic clomiphene administration. These results in animals suggest a possible new line of investigation of the use of antiestrogenic drugs as therapeutic agents for hormone-dependent osteoporosis in animals and humans.

High resolution bone mineral densitometry with a gamma camera

A technique is described by which the regional distribution of bone mineral can be determined in bone samples from small animals. The technique employs an Anger camera interfaced to a medical computer. High resolution (less than 1 mm) imaging is possible by producing magnified images of the bone samples. Regional densitometry of femurs from oophorectomised and bone grafted rats demonstrated significant heterogenity of bone mineral loss.

Response of local vascular volumes to lower body negative pressure stress

The present study involved an intravenous injection of radio-active iodinated serum albumin, equilibration of this isotope within the vascular space, and the continuous measurement of isotope activity over selected anatomical areas before, during and following multiple human LBNP tests. Both rate and magnitude of vascular pooling were distinctly different within each of five selected lower body anatomical areas. In the upper body, all areas except the abdomen showed depletions from their resting vascular volumes during LBNP. The presence of uniquely different pooling patterns in the lower body, the apparent stability of abdominal vascular volumes, and a possible decrease in cerebral blood volume during LBNP represent the major findings of this study.