Gene Injections Pump Vigor Into Old Mice’s Muscles, Study Shows

WASHINGTON —  Injecting new genes into aging muscles can restore youthful vigor and strength, according to a laboratory study of mice. But researchers caution that many safety questions must be resolved before they can try the therapy on humans.

Old mice gained 27% of the muscle lost to age when they were injected with a gene that prompts muscle cell growth, the researchers at the University of Pennsylvania Medical Center said Monday.

For younger mice, the gain was about 15%, said Dr. H. Lee Sweeney, the study’s senior author.

Before the technique is ready for humans, however, there are both ethical and safety questions to be resolved, Sweeney said. For athletes, he said, the injections could be the “perfect performance enhancer.”

“You build muscle mass and strength even without exercise,” said Sweeney. “And it is not detectable in the blood.”

Olympic athletes are routinely tested for drugs that artificially improve strength and performance. Most such drugs are now outlawed.

The safety issue arises because the same gene that causes muscles to grow can also cause the overgrowth of unwanted cells.

“Abnormal growth could be a health risk,” said Sweeney. “For instance, you wouldn’t want your heart to grow larger.”

Nonetheless, the experimental gene therapy offers the promise of correcting one of the major problems of aging--muscle feebleness, the researcher said.

Some experts estimate that humans lose 10% of their muscle strength and mass each decade after the age of 50. Weakness from old age can cause falls, broken bones and loss of the ability to walk or care for oneself.

Once in place, the new gene caused the muscles to make a protein called insulin-like growth factor-1, which, in turn, led to more muscles. But the therapy worked only in the muscles directly receiving the injection. “You would inject only into the muscles necessary for walking or other daily functions,” Sweeney said.

Even if further studies succeed, Sweeney said, it will be at least two years before the gene therapy is ready for human experiments.