Ursolic acid: apple anabolic
The fatty layer on apple peel contains a compound that has an anabolic effect, write researchers from the University of Iowa in Cell Metabolism. It's called ursolic acid, but also goes by the shorter name of malol [structural formula shown below]. In tests on mice, the compound caused their muscles to grow and fat mass to shrink.
Ursolic acid is also present in basil, blueberries, cranberries, rosemary, oregano, thyme and plums. And while we're on the subject of plums: researchers at the American department of agriculture discovered in 2006 that prunes [dried plums] boost the concentration of IGF-1. [Bone. 2006 Dec;39(6):1331-42.] They had no explanation for this, but it might be that ursolic acid explains the special effects of prunes.
The researchers from Iowa stumbled upon the anabolic properties of ursolic acid when they were examining cells from muscle tissue that was wasting. They determined which genes in the cells were active during the process of muscular atrophy. Then they searched databases for substances that had precisely the opposite effect. The most promising substance that they found was ursolic acid.
The researchers gave this to fasting mice and observed that the ursolic acid led to a reduction in the processes of muscle atrophy. They then did a second round of experiments, in which the mice were given as much to eat as they wanted. A control group was given ordinary feed and another group was given feed containing 0.27 percent ursolic acid.
The figures immediately below show that a five-week course of malol resulted in growth of the quadriceps and that the mice grew stronger. The activity of the catabolic genes MuRF-1 and Atrogin-1 declined in the muscle cells. In contrast, the activity of the gene for IGF-1 increased, as did the concentration of IGF-1 in the blood. Molecular signalling molecules, like the receptor for IGF-1, Akt and S6K, were switched on.
The graphs are on ergo-log.com, I cannot put them here.
The figure above describes the effect on muscle and fat mass of seven weeks of supplementation with increasing doses of ursolic acid.
In the animal studies ursolic acid also reduced the fat cells' emission of leptin, the concentrations of triglycerides and cholesterol, and even the fasting glucose level. All of these are positive effects.
The researchers suspect that ursolic acid's prime target is the IGF-1 receptor. This becomes more sensitive and as a result the IGF-1 that is present in the body works better.
"Given the current lack of therapies for skeletal muscle atrophy, we speculate that ursolic acid might be investigated as a potential therapy for illness- and age-related muscle atrophy", the researchers conclude. "It may be useful as a monotherapy or in combination with other strategies that have been considered, such as myostatin inhibition. A systematic search for ursolic acid derivatives that are more potent and/or efficacious could also be undertaken."
Cell Metab. 2011 Jun 8; 13(6): 627-38.