PharmacotheraPeutic Potential of astaxanthin: human and animal targeting roles – a review

the recent pandemic stress and the impacts of climatic changes on humans’ and animals’ health status and well-being resulted in severe drawbacks. initially, stress-induced oxidation resulting from the generation of free radicals led to the impairment of cellular function and a high possibility of attack with infection. Astaxanthin is a bioactive material derived from fish, crustaceans

Astaxanthin is one of the carotenoids with bioactive natural substances and sourced from plants, photosynthetic microorganisms, and crustaceans (Brotosudarmo et al., 2020;Raza et al., 2021). Many carotenoids play a vital role in the photosynthetic reactions while some other play a role in protection of organisms from photooxidation (Brotosudarmo et al., 2020). Astaxanthins are among the most abundant xanthophyll pigments, which are responsible for the characteristic red to pink color of salmon, crustaceans and some birds (Galasso et al., 2017). Astaxanthin was first isolated from lobsters in 1938 (Lorenz and Cysewski, 2000). Naturally, many organisms are a natural source of astaxanthin including green algae, bacteria, fungi, crawfish, shrimp, crabs, Antarctic krill, marine copepoda, and salmonids (Ambati et al., 2014;Domınguez-Bocanegra et al., 2004;Kusdiyantini et al., 1998). Several marine organisms are abundant in astaxanthins which are responsible for the coloration of skin and flesh of fish, shells, and crustaceans (Breithaupt, 2007). Astaxanthins are known for their pigmentation effects which are required for the coloration of some aquatic animals (Lim et al., 2018). Further, astaxanthin is consumed by the ornamental fish species to enhance the coloration of egg yolk and skin. In the poultry industry, astaxanthin can also enhance coloration and reduce lipid peroxidation in birds' meat (Akiba et al., 2001). Astaxanthin inclusion enhanced the antioxidative capacity in aging roosters, leading to high semen quality . Further, astaxanthin addition did not affect the titer of antibodies to Newcastle disease, infectious bronchitis, avian rhinotracheitis, and egg drop syndrome in the serum of vaccinated laying hens (Shevchenko et al., 2021). In fact, fishes, and animals are unable to synthesize astaxanthin, while the color of these animals is the result of bioconcentration of the pigment due to consumption of algae and other microorganisms (Fitton et al., 2015;Shekarabi et al., 2020).
Haematococcus pluvialis is the most prevalent and promising producer of astaxanthin, it can produce 10-15% d.w. under certain stress conditions (Ambati et al., 2014). Astaxanthin has a lot of health benefits including its strong antioxidant effects, anti-lipid peroxidation effect, anti-inflammatory effect, anticancer, antidiabetic effects in addition to the protection from heart diseases (Lauver et al., 2005;Park et al., 2010;Rao et al., 2013;Uchiyama et al., 2002). Many patents are available for the use of astaxanthin in pharmaceutical applications (Lu et al., 2021;Ng et al., 2021;Radice et al., 2021). Recently, astaxanthin have been produced commercially in many forms including for instance tablet, capsule, soft gel, biomass powder, cream, and oil in the market (Table 1). The global market of astaxanthin was estimated to be USD 600 in 2018 and it is expected to reach USD 880 million by 2024 with the increasing awareness of the various nutritional and pharmaceutical roles and the safety of its use (Donoso et al., 2021). While chemically synthesized astaxanthin is most cost effective, pharmaceutical, food, and cosmetics industries use exclusively the natural one (Fakhri et al., 2020). The COVID-19 pandemic has recently threatened humanity, and massive efforts were made to counteract its fatal consequences (Brendler et al., 2021;Hamulka et al., 2021). Antiviral drugs were prepared and offered to people with the hope of inhibiting this fatal pandemic (Butters and Whitehouse, 2021). However, these antivirals are not fully approved as treatments against COVID-19 (Chowdhury et al., 2021). The possibility of infection with COVID-19 varies among people due to the differences in immune responses and health status (Feng et al., 2021). The resistance against infection with COVID-19 relies on natural immunity, which can be activated by using natural functional substances such as astaxanthin (Bogan-Brown et al., 2021). Although no investigations confirmed the possible protective roles of astaxanthin against COVID-19 infection, astaxanthin can be proposed as a natural supplement involved in the protection against oxidative stress, immunosuppression (Lu et al., 2021;Oslan et al., 2021), and features associated with COVID-19 infection.
The potential effects of marine-derived astaxanthins on the health and well-being of ruminants, birds, and aquatic animals as leading sources for animal protein are presented in this review. The antibacterial, antiviral, antioxidative, anticancer, anti-inflammation, and immunostimulant effects are also investigated. Comprehensively, herein we present an optional supplement that may relieve the negative impacts of COVID-19 infection.

sources, structure, and bioavailability of astaxanthin
Astaxanthin pigment (3,3′-dihydroxy-β,β-carotene-4,4′-dione) is a 40 carbon tetraterpenoid with molecular weight of 596.8 g/mol and density of 1.081 g/L (Stachowiak and Szulc, 2021). The xanthophyll pigment which is a metabolic product of zeaxanthin and/or canthaxanthin consists of two terminal β-ionone-type rings joined by a polyene chain with two asymmetric carbons located at the 3,3′-position of the β-ionone ring and hydroxyl group of both ends of the molecule (Higuera-Ciapara et al., 2006). Astaxanthin may be present in free form inside the cell or esterified form as the hydroxyl group (OH) of one or both rings can bind to a number of fatty acids such as oleic, palmitic, stearic, and linoleic acid and form monoor diesters (Udayan et al., 2017). Three geometrical isomers are known for astaxanthin, two of them are enantiomers (3R,3′ R) and 3S,3′ S) and one is a meso form (3R,3′ S) ( Figure 1). The green alga Haematococcus in addition to wild salmon are famous for synthesizing the 3S,3′ S isomer, while the Euphausia superba (Antarctic krill) produce the 3R,3′ R as the primary isomer (Ambati et al., 2014). Unlike the natural astaxanthin which exists in esterified or in complex with proteins or lipids, the synthetic one is never esterified and contains the three isomers 3S,3′ S, 3R,3′ S, and 3R,3′ R in a 1: 2: 1 ratio, respectively (Higuera-Ciapara et al., 2006).  (Donoso et al., 2021) As a lipophilic compound astaxanthin absorption increases when combined in dietary oils. Bioavailability of astaxanthin in human plasma was confirmed after consumption of a single dose of 100 mg of H. pluvialis as a source of astaxanthin (Okada et al., 2009). Interestingly, the bioavailability of astaxanthin was enhanced with the use of lipid base formulation (Olson, 1994). In another study 28 volunteers were given either 250 mg of wild salmon or aquaculture salmon, the astaxanthin levels in plasma were higher at 3, 6, 10, and 14 days during the farming season rather than wild salmon, with the (3-S, 3′-S) isomer of astaxanthin showing the higher level in plasma (Rüfer et al., 2008). The bile salt plays a crucial role in the absorption of different carotenoids as carotenoids should be hydrolyzed before absorption (Olson, 1994). The absorption of the carotenoids is enhanced with fat-based diet and reduced in the low-fat diets. After ingestion, astaxanthin with the bile salt makes micelles in the intestinal tenue. The astaxanthin is finally assimilated via lipoprotein lipase and then distributed into different tissues (Olson, 1994). In general, the half-life of plasma elimination of astaxanthin from blood is 52 ± 4 h (Coral-Hinostroza et al., 2004).

mode of action
Although astaxanthin has been linked to various health advantages, they have been proven to differ depending on the astaxanthin source (natural or synthetic), its isomeric variation, and even the consumer's diet (Donoso et al., 2021). This might be one of the reasons why various research obtained inconsistent findings when analyzing the same parameters and pharmacokinetics of astaxanthin (Nagao, 2009). Hence, we included astaxanthin's main mode of action based on the in vivo and in vitro studies in the following lines.

Immunomodulation
Carotenoids, especially astaxanthin, offer very good protection for the immune system from free radicals which affect the immune system badly (Lu et al., 2021;Oslan et al., 2021). Although there are many reports about the effect of astaxanthin on animals, there is limited clinical research on humans. Jyonouchi et al. (1995) concluded that astaxanthin enhances the production of immunoglobulins in vitro by peripheral blood mononuclear cells in response to T-dependent recall antigen (Ag). In another study, Park et al. (2010) reported that supplementation of astaxanthin for 8 weeks increases natural killer cell cytotoxic activity and increases generally the total T and B cell subpopulations. Additionally, they reported a lower rate of DNA damage and significantly lower levels of CRP proteins in the astaxanthin supplemented group.

Antimicrobial activity
A number of studies, although few, indicate antimicrobial activity of astaxanthin especially against bacterial organisms (Table 2). Ushakumari and Ramanujan (2013) proved moderate antibacterial activity of astaxanthin when compared to chloramphenicol antibiotic against bacterial pathogens including Bacillus subtilis, Salmonella typhi, Staphylococcus aureus and Pseudomonas aeruginosa. In another study, high antimicrobial activity was noticed via the carotenoid pigment extracted from Sporobolomyces sp. against Escherichia coli and S. aureus (Manimala and Murugesan, 2014). In the same context, Suganya and Asheeba (2015) concluded high antibacterial activity of crab isolated astaxanthin against E. coli isolated from spoiled milk and rotten meat. In a recent study Rather et al. (2021) studied the antimicrobial activity of astaxanthin against E. coli, S. typhi, Vibrio cholera and S. aureus. The highest antibacterial activity was observed against E. coli with inhibition zone of 10.2 ±0.20 mm, while the lowest activity was displayed against V. cholera with inhibition zone of 6.1±0.0 mm. Astaxanthin was also found to have an antimicrobial effect against Helicobacter pylori and protect from gastric ulcers (Wang et al., 2000). In fact, there are few studies that explain the mechanism of antimicrobial activity of astaxanthin, but the antimicrobial effect may be due to many factors including for instance alteration of the composition of the bacterial cell wall and cell membrane (Devine and Hancock, 2002).

Antioxidant and anti-lipid peroxidation activity
Antioxidants are molecules with a protective function against free radicals, which has a determinable effect on human body . Free radicals are molecules with one or more unpaired electrons so as to have a high chemical reactivity (Bolarin et al., 2016). These radicals are normally produced through normal aerobic metabolism or through exposure to ionizing radiation, cigarette smoking, drug ingestion, chemicals such as acetyl phenyl hydrazine and hydrogen peroxide (Ekpe et al., 2018). The presence of excessive free radicals reacting with proteins, lipids and DNA molecules causes damage of these molecules which result in a number of disorders (Flaman et al., 2001). Antioxidants which may be either enzymes like superoxide dismutase, catalase, and glutathione reductase or dietary antioxidants such as vitamins A, C, E play a vital role in the inhibition of these free radicals (Table 3). Carotenoids are mainly composed of polyene chain in addition to long conjugated double bonds, which are responsible for the antioxidant activity (Naguib, 2000). Comparing to other carotenoids, astaxanthin is considered to have higher antioxidant activity as well as lowering lipid peroxidation (Naguib, 2000). Astaxanthin adjusts the redox state within the cellular mitochondrial membrane via lipophilic property (Ge et al., 2013). Karppi et al. (2007) assessed that the astaxanthin supplementation for three months decreased the in vivo oxidation of fatty acids in healthy non-smoking men. In another study, Iwamoto et al. (2000) concluded that consumption of astaxanthin from marine sources inhibited LDL oxidation. Astaxanthin is showed also to inhibit glycation in human umbilical vein endothelial cells though preventing lipid/protein oxidation (Nishigaki et al., 2010).

Anti-inflammatory activity
Astaxanthin is a potent antioxidant playing a vital role in the inhibition of inflammation in the biological systems, especially human (Ambati et al., 2014). Haines et al. (2011) concluded that a combination of astaxanthin, vitamin C, and Ginkgo biloba extract suppressed inflammation with efficiency superior to Ibuprofen (widely used non-steroidal anti-inflammatory drug, NSAID). Park et al. (2010) observed the reduction in DNA oxidative damage biomarker inflammation, which improved young women's immunity. Additionally, astaxanthin plays a vital role in minimizing inflammation at local and systematic levels (Bhuvaneswari et al., 2010).

astaxanthin for human health
Although there are many studies that evaluated the medical and pharmacological importance of astaxanthin, studies on humans are very few and most of them conducted on healthy volunteers. Majority of these studies are performed to assess the perfect dose, bioavailability, and safety of astaxanthin (Table 4).
Cancer represents the second cause of mortalities globally and was encountered to be responsible for about 8.8 million deaths in 2015 (McGuire, 2016) and reached around 10 million deaths in 2020 (Ferlay et al., 2020). Healthy cells are controlled by signals that manage the cell division and discriminate into another cell or die. These signals give cancer cells a sense of autonomy, resulting in unregulated differentiation and division (Weinberg, 2013). Antioxidants, especially carotenoids, are known for their ability to decrease carcinogenesis (Chatterjee et al., 2012). The anticancer activity of carotenoids may be a result of enhancing cell to cell communication as the carotenoids increase the synthesis of the gapjunction protein and connexin-43 (Woolfe, 1992). Astaxanthin induced apoptosis and inhibition of growth and proliferation of LS-180 colorectal cancer cells through increasing expression of BAX and caspase-3 and decreasing Bcl-2 expression (Hormozi et al., 2019). Similarly, the different stereoisomers of astaxanthin induce apoptosis of HCT-116 and HT-29 colon cancer cells (Liu  (Iwamoto et al., 2000) In vivo n=40 (healthy non-smokers) mg/ day 12 weeks Decrease the oxidation of fatty acids (Karppi et al., 2007) In vitro human umbilical-vein endothelial cells (HUVEC) 0-100 µg 24-72 h Inhibit glycation and and glycated protein induced cytotoxicity in HUVEC (Nishigaki et al., 2010)  In vivo n=3 100 mg 2 weeks Proved that astaxanthin taken up via VLDL chylomicrons. (Østerlie et al., 2000) In vivo n=35 6 mg/day 8 weeks Prove the safety of astaxanthin through measuring of blood pressure and blood biochemistry parameters. (Spiller and Dewell, 2003) In vivo n=27 4 mg/day 12 months Improve the retinal function. (Parisi et al., 2008) In vivo n=20 6 mg/day 10 days Improve the blood rheology. (Miyawaki et al., 2008) et al., 2016 b). It also inhibits the growth and the proliferation of breast, embryonic fibroblasts and prostate cancer cells (Palozza et al., 2009). It is found that astaxanthin inhibits STAT3 protein which is activated in the cancerous cells and plays a vital role in inhibiting the expression of crucial immune response, STAT3 is greatly accompanied to prostate cancer in addition to breast cancer and human leukemia, multiple myeloma, head and neck squamous cell carcinoma (Franceschelli et al., 2014;Zou et al., 2020).

animals responses to astaxanthin
Livestock and poultry A limited number of studies on the potential of astaxanthin in ruminants were reported . Kumar and Singh (2019) described positive Karan Fries heifers' responses to the daily dietary astaxanthin at 0.25 mg/kg body weight under heat stress conditions in terms of enhanced weight, feed efficiency, Bcl-2 (B-cell lymphoma 2), adipose leptin hormone, and lowered skin temperature, plasma cortisol, interleukins, and nuclear factor-kappa B (NF-κB), and caspase-3 expression patterns. In the same line, dietary astaxanthin increased the glucose and reduced plasma prolactin, non-esterified fatty acids, and respiration rate in the Egyptian buffalo (Carballo et al., 2019). Zenteno-Savıń et al. (2002) explained that feeding newborn lambs on a milk substitute enhanced with astaxanthin (6 mg/day) led to an improvement in the quality of meat by boosting meat and fat redness, stability of lipid, and reduced the accumulation of butylated hydroxytoluene (BHT) in meat.
The effect of using astaxanthin in the poultry industry has been studied at all stages e.g. broiler chicks, laying hens, and egg quality. Hosseindoust et al. (2020) investigated astaxanthin dietary implementation at levels of 0, 20, 40, and 80 ppm on heat-stressed broiler chickens, and trial results showed reduced hyperthermic stress while also improving meat quality (increased redness and yellowness of breast meat) and antioxidant status in muscle (increased total antioxidant capacity, 2,2-diphenyl-1-picrylhydrazyl radical scavenging, and 3-ethylbenzothiazo-line-6-sulfonate reduction activity as well as reduced malondialdehyde, MDA) and plasma (increased catalase, superoxide dismutase). Moreover, astaxanthin downregulates expressions of hepatic heat shock protein (HSP 27,70), tumor necrosis factor (TNF), and interleukin 6. Similarly, Gao et al. (2020) observed affirmative impacts of dietary astaxanthin on lipid/sterols metabolism genes, heat shock proteins (HSP90, HSTF1, and P38MAPK), tumor necrosis factor (TNF), interleukin-6, diacylglycerol acyltransferase 2 (DGAT2), c-Jun N-terminal kinase 1 (JNK1), and P38 mitogen-activated protein kinase (P38MAKP). Liang et al. (2009) stated that dietary astaxanthin increased the egg quality, yolk color, and storage time were positive, with no effect on the yolk index, Haugh units, yolk pH, weight loss, and eggshell strength in laying hens. In the same context, Goto et al. (2001) reported that dietary astaxanthin can help in the improvement of egg storage and reduce the lipid peroxidation leading to high quality eggs.

Aquaculture
The role and applications of astaxanthin in aquaculture are well-reviewed by Lim et al. (2018). Owing to the positive impacts of astaxanthin and the inability of aquatic animals to synthesize it, it is fundamentally important to provide an external supply of astaxanthin (Lim et al., 2018). The focus has been on the various stages of production, starting with brood stock, reproductive efficiency (egg and sperm production and qualities), growth performance, survival, resistance to diseases, and stressors (Paibulkichakul et al., 2008;Palma et al., 2017). Reproductive performance was boosted with astaxanthin application (Tables 5, 6, 7) at different levels in goldfish, Carassius auratus (150 mg astaxanthin/kg diet) (Tizkar et al., 2015), shrimp, Penaeus monodon (500 mg astaxanthin/kg diet) (Paibulkichakul et al., 2008), rainbow trout, Oncorhynchus mykiss (0.07-92.91 mg astaxanthin/kg diet) (Ahmadi et al., 2006). The functional role of astaxanthin may rely on its ability to accumulate within different tissues, including sex organs, which may indicate maturity and readiness for mating (Foote et al., 2004;Nie et al., 2011;Nordeide et al., 2006). Moreover, the major benefits of astaxanthin are due to its powerful antioxidant potential to quench immoderate levels of harmful free radicals, avoiding peroxidation or oxidative damage to reproductive cells and tissues, as well as developing eggs (Dufossé et al., 2005). Also, astaxanthin boosts the immunity system by heightening antibodies and proliferation of immune cells (Kiron, 2012;Magnadottir, 2010). Astaxanthin was suggested to be the first source of retinoids in eggs which has a key role in cell signaling during embryo development (Kin Ting Kam et al., 2012).

conclusion remarks
Astaxanthin offers broadly beneficial effects when delivered to animals, birds, and humans. In this regard, the antibacterial, anti-oxidative, anti-inflammation, antiapoptosis, and anti-stressor effects are widely illustrated in vivo and in vitro. Besides, immunostimulant potential is confirmed in several animal and human-related studies. Concurrently, astaxanthin is expected to enrich the entire body with high resistance and immunity against COVID-19 infection. However, no efforts were seen to confirm the anti-COVID-19 roles of astaxanthin. Therefore, further future studies are suggested to evaluate the possible antiviral roles of astaxanthin in humans.

author contributions
Authors shared equally in this work. All authors have read and agreed to the published version of the manuscript.
funding This research work was partially supported by Chiang Mai University.

Conflicts of interest
The authors declare no conflict of interest.