Astaxanthin, an antioxidant superior to beta-carotene?

Belonging to the carotenoid family, astaxanthin is a liposoluble pigment whose structure was first discovered by Professor Basil WEEDON in 1975. He determined that unlike other carotenoids, astaxanthin does not convert into vitamin A in the body, an interesting feature considering that an excess of vitamin A in the body can be harmful. Astaxanthin is obtained from unicellular algae, most often from the micro-algae Haematococcus pluvialis. In cosmetics, its INCI name is indeed Haematococcus Pluvialis Extract. It is also present in certain crustaceans and fish (shrimp, lobsters, crabs, lobsters, trout...) and is responsible for their red colouration.

Today, we find astaxanthin in many products where it is incorporated for its excellent antioxidant properties. These properties are based on the ability of this pigment to cross the cellular membrane. Indeed, the chemical structure of astaxanthin includes hydrophilic and lipophilic regions, which allows it to combine with the cellular membrane, from both the inside and outside. Thus, its polar groups overlap the external polar regions of the cellular membrane, while the non-polar central area of the molecule inserts itself into the internal non-polar region of the membrane.

Astaxanthin can therefore adopt a transmembrane alignment in biological membranes, assisting in maintaining membrane structure and reducing its fluidity. This enables it to act as a cellular shield to combat the spread of free radicals.

The particularly high antioxidant capacity of astaxanthin can also be explained by the presence of specific functional groups on its ionone rings. Each end of the molecule indeed features hydroxyl (-OH) and ketone (C=O) groups, which play a central role in neutralising free radicals. The oxo function (C=O), in particular, can stabilise carbon radicals by resonance, thus reducing their reactivity. Moreover, unlike some antioxidants, this stabilising ability of astaxanthin allows it to avoid any secondary pro-oxidant activity. In other words, astaxanthin protects cells without ever inducing oxidative damage in return. Astaxanthin is also effective in capturing and neutralising singlet oxygen, a highly reactive form of oxygen involved in many oxidative stress reactions in skin tissues.

Astaxanthin operates through various mechanisms to safeguard cellular membranes, proteins, and DNA from oxidative stress.

The astaxanthin is often compared to beta-carotene, with which it shares a similar linear polyenic chemical structure, with conjugated double bonds, giving them a high affinity for free radicals. However, the presence of polar functional groups at the ends of the astaxanthin significantly alters its biological properties. Unlike beta-carotene, astaxanthin can stably integrate into phospholipid membranes, with its polar ends interacting with intra- and extracellular aqueous environments, and its lipophilic central chain integrating into the membrane core. This arrangement gives the molecule an effective and lasting antioxidant shield role within the cell membranes themselves, unlike beta-carotene which cannot insert itself there.

Furthermore, a comparative study has highlighted the superiority of astaxanthin over beta-carotene in the inhibition of lipid peroxidation, a major process responsible for the formation of free radicals within cell membranes. Researchers observed that astaxanthin reduced the production of lipid peroxides with an efficiency approximately twice that of beta-carotene. As previously explained, this difference in activity is due to the three-dimensional conformation of the molecule. Thanks to its amphiphilic structure, astaxanthin is able to insert itself transversely through the lipid bilayer of membranes, unlike beta-carotene, which is exclusively lipophilic and only integrates into the core of the membrane.

Astaxanthin provides a more comprehensive protection to cell membranes than beta-carotene.

Other studies have also been conducted to measure the antioxidant power of astaxanthin and compare it to that of other active ingredients commonly found in skincare products. The research focused on both the action of astaxanthin on singlet oxygen and its overall ability to trap free radicals. The results of these various scientific studies are presented in the table below.

• GOTO S. & al. Efficient radical trapping at the surface and inside the phospholipid membrane is responsible for highly potent antiperoxidative activity of the carotenoid astaxanthin. Biochimica et Biophysica Acta (2001).

• GARCIA-GONZALEZ M. & al. Outdoor cultivation of microalgae for carotenoid production: Current state and perspectives. Applied Microbiology and Biotechnology (2007).

• DHANKHAR J. & al. Astaxanthin : A potential carotenoid. International Journal of Pharmaceutical Sciences and Research (2012).

• EKPE V. & al. Antioxidant effects of astaxanthin in various diseases - a review. Journal of molecular pathophysiology (2018).

• NAME J. J. & al. Antioxidant and anti-inflammatory mechanisms of action of astaxanthin in cardiovascular diseases (review). International Journal of Molecular Medicine (2021).

• ELSHOPAKEY G. E. & al. Recent progress in practical applications of a potential carotenoid astaxanthin in aquaculture industry: a review. Fish Physiology and Biochemistry (2023).