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07.02.2018

Carotenoids versus muscle atrophy?

A high intake of carotenoids as beta-carotene may protect against muscle breakdown, according to a Japanese animal study that was published in the British Journal of Nutrition in 2013. The researchers, affiliates with Osaka Prefecture University, gave their mice an unhealthy high-dose beta-carotene, which can turn out to be dangerous in humans. But fortunately there are more carotenoids which may have the same anti-catabolic effect, but not have any health risks...

Study
The researchers cut nerve pathways in mice's hindlibms so that the animals could no longer use a leg [Den]. In other mice they did not [Sham]. During the first week after the procedure the researchers looked at what happened in the denervated muscles.

The researchers gave some of the mice a substantial amount of beta-carotene daily through the oral route [B-Carotene]. Other mice received a placebo [Vehicle].

Results
In the mice that received beta-carotene [gray bars], the soleus muscle shrank less rapidly after cutting the nerve path than in the animals that had received a placebo [white bars].

In the muscle tissue of soleus, the amount of ubiquitin conjugates increased after cutting through the nerve. Ubiquitin conjugates are protein fragments to which the cell has glued ubiquitin molecules. This way the cell labels protein as 'ripe for scrapping'.

However, in the denevervated muscles of the mice that had received beta-carotene, the researchers found less ubiquitin conjugate than in the muscles of the mice in the other group.

The actual demolition of muscle cell proteins is done by enzymes such as Atrogin-1 and MuRF-1. These are the molecular equivalents of the shredder and the demolition ball. In the soleus the production of these proteins increased after the denervation, but supplementation with beta-carotene inhibited this process.

How exactly beta-carotene inhibits muscle breakdown the Japanese don't know. They present in vitro data that suggest the possibility that beta-carotene neutralises free radicals that play a role in the first phase of muscle breakdown, and inhibits FOXO3a, a molecular master switch that plays a key role in muscle decay.

Conclusion
"We have demonstrated that dietary supplementation of beta-carotene is useful as a chemopreventive agent for improvement of disuse-induced muscle mass loss at the early stage of soleus muscle atrophy", the researchers wrote.

Wild speculation
The human equivalent of the amount of beta-carotene that the researchers used is about 100 milligrams per day. That dosage is unhealthy for humans. A daily intake of 15 milligrams supplemental beta-carotene is enough to increase the risk of lung cancer. This is probably because beta-carotene turns into retinol, and high concentrations of retinol in combination with environmental factors increase the risk of some types of cancer.

Fortunately, there are all sorts of other substances in food that are chemically similar to beta-carotene, but can not or hardly convert into vitamin A. Alpha-carotene, for example, or beta-cryptoxanthine, or lycopene, or astaxanthin, or lutein. It could just be that those substances protect against muscle breakdown as well...

Source:
Br J Nutr. 2013 Apr 28;109(8):1349-58.

More:
AMPK-booster lutein speeds up transformation from lazybones into athlete 27.06.2014
Lycopene and beta-carotene protect against heart attacks 16.10.2015
Pumpkin (source of carotenoids) boosts endurance capacity and muscle strength 08.04.2013

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