Overview

An Integrated Low-Volume Nutritional Countermeasure to Maintain Muscle Mass and Function During Space Exploration

Principal Investigator:
Douglas Paddon-Jones, Ph.D.

Organization:
University of Texas Medical Branch at Galveston

The loss of muscle mass and function is one of several health risks associated with spaceflight. Dr. Douglas Paddon-Jones and colleagues contend that this loss in microgravity is impacted by age: In particular, they are concerned with the progressive impairment of a person’s ability to use nutrients to reduce muscle mass loss as they age.

The scientists are conducting a study to determine if enriching daily meals with a low volume leucine supplement will reduce the loss of muscle mass and function during a 14-day bed-rest study. They will also examine whether leucine facilitates muscle mass recovery during a seven-day rehabilitation period. The age range of the participants is 45-60 years.

NASA Taskbook Entry

Technical Summary

This project's long-term goal is to identify, prevent and remedy defects in the metabolic pathway that contribute to the loss of muscle mass and function during exposure to microgravity.

Demographic data indicate that the average age of shuttle crew members has increased from 40.7 years in 1995 to 46.7 years in 2007, with an increasing number of astronauts over 50 years of age. Dr. Douglas Paddon-Jones and colleagues contend that the loss of muscle mass and function during spaceflight is facilitated by an age-associated, progressive impairment in the ability to mount an anabolic response to standard mixed-nutrient meals.

The project seeks to determine if enriching daily meals with a low-volume leucine supplement will reduce the deleterious effects of microgravity on skeletal muscle and facilitate recovery during rehabilitation. The study will use an established 14-day bed-rest protocol to model the skeletal muscle unloading that occurs during microgravity. It will also examine recovery of muscle mass and functional capacity during a seven-day rehabilitation period.

Hypotheses
1. Bed rest will blunt the anabolic response to a mixed-nutrient meal, facilitating a loss of muscle mass and functional capacity that is only partially restored during rehabilitation.

2. Enriching daily meals with leucine will promote protein synthesis and maintain the anabolic response to mixed-nutrient meal ingestion. This will preserve lean muscle mass and function during bed rest and facilitate the recovery of functional and metabolic capacity during rehabilitation.

This project builds on our recent series of bed-rest studies and seeks to provide a refined and practical countermeasure that is supported by comprehensive mechanistic evidence.

Earth-based Applications of Research Project
Our long-term goal is to identify, prevent and remedy defects in the metabolic pathway that contribute to the loss of muscle mass and function during exposure to microgravity. This research can also benefit individuals whose ability to perform physical activity is compromised.

Protein catabolism and muscle loss occurs in many circumstances. The regulatory mechanisms controlling protein turnover are particularly sensitive to a reduction in the neuromuscular stimulus that occurs during physical inactivity or exposure to microgravity, and it is clear that muscle loss is greatly exaggerated with increasing age.

The project team contends that the loss of muscle mass and function during spaceflight is facilitated by an age-associated, progressive impairment in the ability to mount an anabolic response to standard mixed-nutrient meals. Protein supplementation is routinely employed to combat inactivity and age-related muscle loss. However, aggressive supplementation regimens are often impractical or ineffective due to issues including increased satiety, poor palatability, cost and compliance.

The project is studying whether enriching daily meals with a low-volume leucine supplement will reduce the deleterious effects of microgravity on skeletal muscle and facilitate recovery during rehabilitation. This supplement has the potential to also benefit individuals whose ability to perform physical activity is compromised (e.g., hospitalized patients, frail elders).

Earth Applications

The researchers long-term goal is to identify, prevent and remedy defects in the metabolic pathway that contribute to the loss of muscle mass and function during exposure to microgravity. Protein catabolism and muscle loss occurs in many circumstances. The regulatory mechanisms controlling protein turnover are particularly sensitive to a reduction in the neuromuscular stimulus that occurs during physical inactivity or exposure to microgravity, and it is clear that muscle loss is greatly exaggerated with increasing age.

Demographic data indicate that the average age of shuttle crew members has increased from 40.7 yrs in1995 to 46.7 yrs in 2007 with an increasing number of astronauts over 50 yrs of age. The project team contends that the loss of muscle mass and function during spaceflight is facilitated by an age-associated, progressive impairment in the ability to mount an anabolic response to standard mixed-nutrient meals. Protein supplementation is routinely employed to combat inactivity and age-related muscle loss. However, aggressive supplementation regimens are often impractical or ineffective due to issues including increased satiety, poor palatability, cost and compliance.

The project is studying whether enriching daily meals with a low-volume leucine supplement will reduce the deleterious effects of microgravity on skeletal muscle and facilitate recovery during rehabilitation. This supplement has the potential to also benefit individuals whose ability to perform physical activity is compromised (e.g., hospitalized patients, frail elders).