**2. Physicochemical properties and peculiarities of biological action of astaxanthin**

Astaxanthin is a secondary carotenoid, which belongs to the group of xanthophylls and has two additional oxygen atoms on each benzene ring in comparison with β-carotene. This gives astaxanthin a rich red color and greatly increases its antioxidant properties. Unlike β-carotene, astaxanthin is not a vitamin A precursor [8].

Empirical formula: C40H52O4 Molar weight: 596.84 g/M

In contrast to primary carotenoids, which are associated with the structural and functional components of the photosynthetic apparatus, secondary carotenoids, which include astaxanthin, are in the cell in oil droplets, and their main function is to form a protective layer to prevent the damages, which are provoked by stress conditions [9, 10].

Because the astaxanthin molecule contains conjugated double bonds, hydroxyl and keto groups, it has both lipophilic and hydrophilic properties [11]. Astaxanthin has two chiral centers and can exist in three different stereoisomers—3S, 3′S; 3R, 3′S; and 3R, 3′R. The probability of obtaining these isomers of astaxanthin in the process of chemical synthesis is 1:2:1 [12, 13].

for new safe and effective radioprotectors, preferably of natural origin, for prevention and treatment of radiation-induced damages in humans, especially which cause genome alterations and cancer. For that purpose, carotenoids, due to its chemical and biological properties,

Astaxanthin is a carotenoid of xanthophyll group, and it is one of the most common red pigments of algae, yeasts, krill, shrimps, crayfish, trout, and salmon [2]. It is known that astaxanthin is the most powerful antioxidant, which has the ability to scavenge free radicals in tens of times higher than α-tocopherol or β-carotene [3], and has anti-inflammatory [2],

Since 2015, we have started the investigation of the radioprotective effects of astaxanthin studying parameters of genome damages in human somatic cells. In this chapter, we have concentrated on physicochemical properties of astaxanthin and its biological effects with the main focus on the data from our investigations concerning the impact of astaxanthin on radiation-induced genome damages in human somatic cells and have discussed eventual

**2. Physicochemical properties and peculiarities of biological action** 

Astaxanthin is a secondary carotenoid, which belongs to the group of xanthophylls and has two additional oxygen atoms on each benzene ring in comparison with β-carotene. This gives astaxanthin a rich red color and greatly increases its antioxidant properties. Unlike β-carotene,

In contrast to primary carotenoids, which are associated with the structural and functional components of the photosynthetic apparatus, secondary carotenoids, which include astaxanthin, are in the cell in oil droplets, and their main function is to form a protective layer to

prevent the damages, which are provoked by stress conditions [9, 10].

are the most promising substances [1].

122 Progress in Carotenoid Research

mechanisms of its action.

Empirical formula: C40H52O4 Molar weight: 596.84 g/M

astaxanthin is not a vitamin A precursor [8].

**of astaxanthin**

immunomodulating [4], and anticarcinogenic [5–7] effects.

Nowadays natural astaxanthin mainly derived from microalgae (hyperproducer *Haematococcus pluvialis*), yeast (*Phaffia rhodozyma*) and animal-consumers included a number of small marine crustaceans (Euphausiacea) and the salmon family (Salmonidae*)* [2]. Microalgae *Haematococcus pluvialis* produces astaxanthin mainly 3S, 3′S stereoisomeric form; precisely, such molecular structure is considered the most valuable [14].

As shown in experiments *in vitro*, astaxanthin effectively protects cells from nonspecific oxidation by quenching singlet oxygen, effectively inhibits lipid peroxidation in biological samples, and owing to the capture of free radical prevents or stops the chain reaction of oxidation [2, 15, 16]. In addition to direct protective effect, astaxanthin inhibits the activation of the H<sup>2</sup> O2 mediated transcription of the factor NF-kB (the nuclear factor "kappa-b"—a universal transcription factor) that controls the expression of heme oxygenase 1 (HMOX1), one of the markers of oxidative stress, and nitric oxide synthase (iNOS) [17, 18]. Astaxanthin blocks the cytokine production declined by modulating the expression of protein tyrosine phosphatase 1 [18].

Experiments on the determination of astaxanthin toxicity showed a high level of safety—LD<sup>50</sup> was not established after single administration of substance to rats. The studies confirmed the absence of histopathological changes and the dose-effect dependence upon oral administration of astaxanthin in doses ranging from 4.161–17.076 to 465.0–557.0 mg/kg per day [19].

The accumulated published data have shown the multifaceted positive effect of astaxanthin in mammals by reducing the manifestations of oxidative stress, including during inflammation processes; it can prevent the development of atherosclerotic cardiovascular diseases and participate in the regulation of lipid and glucose metabolism [19–23].

These properties of astaxanthin primarily attributed to its ability to exhibit activity both at the level of the cell membrane and in the area of the cytoplasm, thus affecting the flow of intracellular processes [2]. Due to these unique properties, astaxanthin exhibits significantly higher biological activity in comparison with other antioxidants [24].

Thus, the above data indicate that astaxanthin complies with all the requirements that apply to radioprotectors (low toxicity, high antiradical and antioxidant activity, the ability to act both at the membrane level and in the intracellular space). These properties of astaxanthin suggest that it may have antimutagenic activity and, as consequence, radioprotective effect on the human genome.
