Peripheral arterial and venous response to tilt test after a 60-day bedrest with and without countermeasures (ES-IBREP)

Vascular and Microvascular Dysfunction Induced by Microgravity and Its Analogs in Humans: Mechanisms and Countermeasures

Weightlessness and physical inactivity have deleterious cardiovascular effects. The space environment and its ground-based models offer conditions to study the cardiovascular effects of physical inactivity in the absence of other vascular risk factors, particularly at the macro- and microcirculatory levels. However, the mechanisms involved in vascular dysfunction and remodeling are not sufficiently studied in the context of weightlessness and its analogs including models of physical inactivity. Here, we summarize vascular and microvascular changes induced by space flight and observed in models of microgravity and physical inactivity and review the effects of prophylactic strategies (i.e., countermeasures) on vascular and microvascular function. We discuss physical (e.g., exercise, vibration, lower body negative pressure, and artificial gravity) and nutritional/pharmacological (e.g., caloric restriction, resveratrol, and other vegetal extracts) countermeasures. Currently, exercise countermeasure appears to be the most effective to protect vascular function. Although pharmacological countermeasures are not currently considered to fight vascular changes due to microgravity, nutritional countermeasures are very promising. Dietary supplements/natural health products, especially plant extracts, should be extensively studied. The best prophylactic strategy is likely a combination of countermeasures that are effective not only at the cardiovascular level but also for the organism as a whole, but this strategy remains to be determined.

Bone protection effects of a novel Chinese herbal formula, taikong yangxin prescription, in hindlimb unloaded rats against bone deterioration

OBJECTIVE

To investigate the protective effects of a Chinese herbal formula, taikong yangxin prescription (TKYXP) against bone deterioration in a hindlimb unloaded (tail-suspension) rat model.

METHODS

Thirty-two male Sprague-Dawley rats were divided into 4 groups: tail-suspension group fed with 2.5 g•kg(-1)•day(-1) of TKYXP extract (high dose), tail-suspension group fed with 1.25 g•kg(-1)•day(-1) (low dose), tail-suspended group treated with water placebo (placebo control group) and non tail-suspended group. The effects of TKYXP on bone were assessed using peripheral quantitative computed tomography (pQCT), microcomputerized tomography (micro-CT) and three-point bending biomechanical test on the femur in vivo.

RESULTS

TKYXP had a significant protective effect against bone loss induced by tail-suspension on day 28, as shown in the reduction in bone mineral density (BMD) loss, preservation of bone micro-architecture and biomechanical strength. The administration ofhigh dose TKYXP could significantly reduce the total BMD loss by 4.8% and 8.0% at the femur and tibia regions, respectively, compared with the placebo control group (P<0.01) on day 28. Its bone protective effect on the femur was further substantiated by the increases of the trabecular BMD (by 6.6%), bone volume fraction (by 20.9%), trabecular number (by 9.5%) and thickness (by 11.9%) as compared with the placebo control group.

CONCLUSION

TKYXP may protect the bone under weightless influence from gradual structural deterioration in the tail-suspension model.

Effect of Chinese herbal medicine on vascular functions during 60-day head-down bed rest

PURPOSE

Chinese herbal medicine is a promising countermeasure against cardiovascular dysfunction associated with a sedentary lifestyle. We examined the impact of the Chinese herb, Taikong Yangxin, on the micro- and macrovascular dysfunction associated with a 60-day bed rest.

METHODS

Fourteen healthy men were randomly divided into two groups: those given herbal supplement, and the control group; the two groups underwent a 60-day bed rest. The macrovasculature was assessed by sonography. Skin microvascular functions were assessed with laser Doppler. The plasma level of endothelial microparticles (EMPs), markers of endothelial injury, was determined.

RESULTS

Bed rest induced a 33 % decrease in the femoral artery diameter and compliance whereas carotid wall thickness, diameter, and compliance remained unchanged. The early phase of endothelium-dependent vasodilation to ACh was unmodified by bed rest, while the late phase was reduced by 30 % along with a twofold increase in EMPs. In those given Taikong Yangxin, the early phase was amplified by 2.5-fold, and the effects of bed rest on the late phase were prevented.

CONCLUSION

These findings indicate that Taikong Yangxin ameliorates endothelium-dependent vasodilation, likely by improving the NO pathway. The study suggests Taikong Yangxin as a new countermeasure to prevent the changes in microvascular function induced by physical inactivity.

Inhibition of autophagy recovers cardiac dysfunction and atrophy in response to tail-suspension

AIMS

Physical inactivity during space flight or prolonged bed rest may cause cardiac dysfunction and atrophy, but the exact mechanism that governs the regulation of myocardial dysfunction and cardiac atrophy remains poorly understood. Autophagy, a protein degradation pathway, has recently been shown to be involved in the regulation of cardiac dysfunction and atrophy. In this study, we investigated the relationships between dysfunction and inactivity-induced atrophy and autophagy in rat cardiac tissue.

MAIN METHODS

Physical inactivity was simulated by a tail suspension model, and cardiac function was examined by echocardiography. Cardiac atrophy was measured by wheat germ agglutinin staining and autophagic activity was detected by Western blot analysis and immunofluorescence staining.

KEY FINDINGS

We demonstrated that cardiac function, especially contractility, declined and the area of cardiac atrophy increased in the tail-suspended cardiac tissue. Additionally, the cross-sectional area of myocardial cells decreased; however, apoptosis did not increase with tail suspension. Similarly, the expression of autophagy-related proteins and the number of autophagosomes were elevated in the tail-suspended cardiac tissue. Moreover, the administration of chloroquine, an autophagy inhibitor, reversed cardiac dysfunction and atrophy via the suppression of autophagic activity during suspension. Our results indicate that autophagy facilitates the development and progression of cardiac dysfunction and atrophy induced by tail suspension.

SIGNIFICANCE

Our studies hint that the components of the autophagy-related signaling pathway are potential therapeutic targets for the treatment of cardiac diseases induced by physical inactivity.