Astaxanthin: a nature’s versatile compound utilized for diverse applications and its therapeutic effects

Abstract

Astaxanthin (ASTX), red-colored xanthophyll, also known as the “king of carotenoids” exhibits a strong antioxidant property that can be naturally found in green algae Haematococcus pluvialis, red yeast Phaffia rhodozyma, and various aquatic species including salmon, krill, trout, and fish eggs. Due to their strong antioxidant qualities, ASTX nanoparticles may be crucial in fighting against phytotoxicity caused by heavy metal ions. Similarly, it may also reduce the uptake of heavy metal, i.e. cadmium, and translocation by improving the morpho-physiological profiles of plants. Furthermore, it can also have the ability to scavenge free radicals, therefore, it can protect plants from reactive oxygen species (ROS). Implementing ASTX nanoparticles on crops can also help to achieve higher food production while minimizing toxic effects. Additionally, it can also possess several therapeutic activities including anti-cancerous, anti-diabetic, antioxidant, anti-aging, anti-inflammation, hepatoprotective, and cardiovascular, etc. that can be beneficial to treat various types of diseases in humans and animals. Recently, it has gained more interest in food, agriculture, aquaculture, neutraceuticals, and pharmaceutical industries due to its wide range of applications including food-coloring agents, food supplements, and strong antioxidant property that helps in skin protection, and boosts immune function. However, ASTX possesses poor water solubility and chemical stability so the implementation of ASTX on human health is facing various issues. Therefore, nanoencapsulation of ASTX is very crucial to improve its chemical stability and solubility, ultimately leading to its bioavailability and bioaccessibility. Recently, ASTX has been commercially available with specific dosages in the market mainly in the form of tablets, gels, powders, creams, syrups, etc. The current review mainly highlights the present state of ASTX nanoparticle applications in various fields explaining its natural and synthetic sources, extraction methods, chemical structure, stability, nanoformulations, nano encapsulation, and various commercial aspects.

Introduction

A xanthophyll carotenoid known as astaxanthin (ASTX), a red and fat-soluble pigment that can be produced artificially through chemical catalysis and is naturally present in aquatic animals, plants, and different microorganisms as well as the leaves of some plants along with chlorophyll (Higuera-Ciapara et al. 2006). ASTX is also present in a large number of flowering plants in the genus Adonis, and these plants’ vibrant colors help in drawing pollinators. Adonis aestivalis contains the highest concentration of ASTX among other plants, ensuring up to around 1% of its dry matter (Cunningham and Gantt 2007; Stachowiak and Szulc 2021). In animals, it disperses within fats or is mixed with protein in an aqueous solution but their usual solubility mainly occurs in fats. They serve as additives, coloring agents, or stabilizers that are crucial components in most of the foods. In the pharmaceutical industry, it can also be used as a coating agent to give drugs appealing colors and flavor combinations (Benjamin et al. 2023). When it is included in the diet of aquatic animals like crabs, prawns, salmon, and trout within an aquaculture environment, it imparts a recognizable reddish-orange color (Higuera-Ciapara et al. 2006b). ASTX has been licensed for use as a food color by the US Food and Drug Administration (FDA) (Pashkow et al. 2008).

ASTX has a potent ability to scavenge the effects of free radicals. Functional foods that are primarily the biologically active ingredients found in food or some other food additives have health-enhancing properties beyond their basic nutritional value derived from both plants and animals, such as vitamins, minerals, peptides, and antioxidants (Mordi et al. 2020). Because of their high antioxidant activity, ASTX has several therapeutic advantages that can be used to treat numerous diseases. ASTX is well known for its anti-aging and anti-cancerous properties, which may help to reduce the risk of many diseases. It is also a good option as a dietary supplement with outstanding properties including immune-boosting and antioxidant effects. Additionally, it helps in the prevention of many diseases, such as diabetes, heart disease, and neurological disorders (Cao et al. 2023). Many studies have proven that ASTX is a stronger antioxidant than other carotenoids available. It is assumed to be ten times more stronger than Beta-carotene and 100 times stronger than vitamin E (Fakhri et al. 2018; Ren et al. 2021). The major issues with ASTX are its low bioavailability, limited stability, and poor solubility, among others carotenoids that can significantly limit its wider use as a therapeutic agent in clinical settings (Jafari et al. 2022). A wide range of synthesis methods can be employed to circumvent these issues. One promising route to enhance the biological compatibility and bioavailability of ASTX is through nanoencapsulation. Likewise, an anti-solvent precipitation method was applied to develop carrier-free ASTX nanoparticles (ASTX-NP). These results showed a small average particle size of 74.29 ± 7.92 nm, with uniform morphology, and an impressive loading capacity of 94.57 ± 0.70%. These NPs can effectively enhance the solubility of ASTX in water by optimizing its physico-chemical properties (Li et al. 2023).

The various synthesis processes including high-energy top-down or low-energy bottom-up techniques can be used to reduce the size of ASTX NP. The process parameters should be adjusted to produce homogeneous ASTX NP with the largest net zeta potential, the smallest mean particle size, and the greatest amount of physical as well as chemical stabilities. These findings demonstrated the excellent chemical stability of ASTX NP in food-based systems, making them suitable for use as beneficial ingredients in various formulations utilized for food, feed, medicinal products or pharmaceuticals, cosmetics, and personal care products. Several scientific studies have reported the non-toxic behaviour of ASTX NP despite the presence of inorganic nanoparticles. More precisely, different preparation techniques were also used to produce different nanostructures such as solid lipid NP, metal/metal-oxide NP, nanoemulsions, nanoliposomes, polymeric/biopolymeric NP, nanostructured lipid NP, supercritical fluid-based NP, nanocarotenoids by utilizing both carotenoid extracts and standards (dos Santos et al. 2018; Rostamabadi et al. 2019; Rehman et al. 2020). However, ASTX can be still affected by several environmental factors including pH, heat, and light exposure. Because of some limitations, it can lead to alter its physiological and chemical characteristics via structural modification including isomerization, aggregation, or esterification. This issue might be resolved by encasing ASTX in naturally occurring or artificially synthesized biodegradable materials to synthesize nanoformulation that could potentially solve this issue.

This review mainly highlights the importance of ASTX in diverse field applications including the food industry, aquaculture industry, pharmaceutical industry, cosmetic industry, and agriculture sector. In previous literature, source, stability, storage, and therapeutic applications of ASTX were reported. However, in this review, we mainly emphasize therapeutic activities and nanoformulations of ASTX. ASTX is a natural carotenoid pigment that has the highest antioxidant activity but poor solubility. Therefore, the preparation of ASTX nanoformulation is crucial to overcome this limitation. Therefore, various nanoencapsulation methods via nanoemulsion, nanoliposome, biopolymeric carriers, etc. are widely utilized. Nanoformulation of ASTX can be advantageous as it can increase their strength, stability, and integrity. Additionally, it can also protect ASTX from various environmental stresses like pH, light, temperature, heat, salt stress, nutrient stress, heavy metals stress, etc. Similarly, it can also contribute to significantly enhance the antioxidant properties and DPPH free radical scavenging activity in both plant and animal studies. In agriculture, the hydroponics application of ASTX NP on wheat, showed a significant increase in the morphological and physiological parameters of cadmium (Cd)-affected plants. These result demonstrated the enhanced shoot length/root length, fresh weight/dry weight, nitrogen (N), and phosphorous (P) concentration while maintaining the optimum nutrient level in Cd-affected plants.

Natural and synthetic astaxanthin

Synthetic and natural ASTX, have numerous known variations. Natural ASTX consists of the cultivation and extraction of microalgae which is an expensive and time-consuming process whereas synthetic ASTX is less expensive as compared to natural ASTX. The second reason is that synthetic ASTX is mainly unesterified whereas ASTX derived from microalgae is esterified (Ambati et al. 2014; Sui et al. 2020). Typically, ASTX exists in nature as monoesterand diesters, including the shells of an algae and crustaceans (Jackson et al. 2008). Different forms of geometrical as well as optical isomers are present both in synthetic and microalgal or natural ASTX (Sui et al. 2020). Although the commercial value of 1 kg of synthetic ASTX exceeds 2000$, the production expenses are estimated to be around $1000. For instance, 1 Kg of ASTX derived from algae, Haematococcus pluvialis costs 7000$, while 1 Kg of the organic pigment produced from Xanthophyllomyces dendrorhous yeasts costs up to around $2550 (Panis and Carreon 2016). The characteristics of natural ASTX involve enhanced assimilation, better stability, and a greater capability for absorbing free radicals of oxygen. This variation is due to the presence of ASTX stereoisomers in synthetic preparations. Therefore, in the present scenario, biologically derived ASTX may be the only ingredients present in human nutritional supplements (Calo et al. 1995b; Yuan and Chen 2001).

This review aims to provide the current overview of the physical and chemical properties of ASTX and its various sources of extraction. It also highlights the effects of ASTX on human health, based on the current research. The research investigating the use of nanoencapsulation approaches to enhance their bioavailability and physicochemical stabilities are also highlighted.

Sources of natural astaxanthin

ASTX is found naturally in a wide range of organisms, including green algae, bacteria, fungi, archaea, chromista, crabs, lobster, antarctic krill, marine copepods, and salmonids as mentioned in Fig. 1. Humans mostly obtain ASTX from seafood, with wild sockeye salmon (Oncorhynchus nerka) having the highest ASTX content (26–38 mg kg^–1) (Lim et al. 2018). Marine organisms contain ASTX in large quantities, some of which are shown in Table 1. It is the cause of the known reddish-orange hue of salmon flesh, as well as the skin and flesh of crayfish and prawns because they are unable to produce ASTX from scratch, crustaceans and fish must rely on eating algae and other microbes to provide them with ASTX precursors (Lim et al. 2018). Nowadays, aquaculture accounts for about 72% of global salmon production. A significant commercial characteristics of farmed salmon is its flesh pigmentation, which can frequently be attributed to product quality (Luthman et al. 2019). The flesh of farmed atlantic salmon is said to contain 6–8 mg/kg of ASTX. Large trout serve as sources of ASTX, marketed in Europe at 6 mg/kg of flesh and in Japan at 25 mg/kg.

Fig. 1.

Various sources of astaxanthin (ASTX) including its primary and secondary sources

Table 1.

Represents the groups of different organisms in which astaxanthin is present

Group of varied organisms	Representative	References
Plantae (microalgae)	Haematococcus Pluvialis, Monoraphidium Chlorella zofingiensis, Chlorococcum spp., Scenedesmus spp., Chlamydomonas nivalis, Nannochloropsis spp., Chlamydocapsa spp., Chlorella vulgaris, Eremosphaera viridis, Neochloris wimmeri, Coelastrella striolata Diatoms,	(Ranga Rao et al. 2010; Kaha et al. 2021; Wang and Peng 2008; Zhang et al. 1997) (Remias et al. 2005) (Ritu et al. 2023) (Ritu et al. 2023) (Yang et al. 2020)
Bacteria	Paracoccus carotinifaciens, Agrobacterium aurantiacum Escherichia coli Cyanobacteria Brevundimonas sp., Sphingomonas sp. Corynebacterium glutamicum	(Fang et al. 2019) (Henke et al. 2016)
Yeast	Xanthophyllomyces dendrorhous (Phaffia rhodozyma) Yarrowia lipolytica Saccharomyces cerevisiae Candida utilis	(Schmidt et al. 2011; Tramontin et al. 2019) (Kildegaard et al. 2017)
Animal	Salmon, Trout, Flamingos, and Crustaceans (shrimp, crab, krill, and crayfish) Redfish Wild salmon (Oncorhynchus species)	(Stachowiak and Szulc 2021) (Turujman et al. 1997)
Lichens	Clodia aggregata, Concamerella fistulata, Usnea amaliae, Usnea densirostra	(Aziz et al. 2020)
Archaea	Halobacterium salinarium NRC-1 Haloarcula hispanica ATCC 33960	(Calo et al. 1995a)
Fishes	Atlantic salmon (Salmo salar) Chinook salmon (Oncorhynchus tshawytscha) Chum salmon (Oncorhynchus keta)	(Ambati et al. 2014; Lim et al. 2018)
Crabs	Chionoecetes opilio Eriocheir sinensis	(Higuera-Ciapara et al. 2006; Wang et al. 2018)
Zooplankton	Acartia bifilosa Pseudocalanus acuspes Diaptomus nevadensis Leptodiaptomus minutus	(Holeton et al. 2009) (Lotocka 2004) (Hairston 1979) (Oester et al. 2022)
Phytoplankton	Chlorococcum sp. Chromochloris zofingiensis	(Zhang and Lee 1997; Chen et al. 2020)

Structure of astaxanthin

A chain of double bonds with conjugation, or polyene systems, connects the two terminal ring systems that make up the primary structural element of carotenoids, which are hydrocarbons with 40 carbon atoms. Carotenes, which are only made of carbon and hydrogen, and xanthophylls, which contain oxygen derivatives, are the two main groups of carotenoids that can be distinguished from one another based on their structural and chemical elements. As in the case of ASTX, oxygen is expressed in the xanthophylls as either hydroxyl (OH) groups, keto-moieties (C = O) groups, or as a mixture of both (Jackson et al. 2008). Isomers of two enantiomers (3S, 3′S), (3R, 3′R), and one mesomer (3R, 3′S), are found in synthetic ASTX. The most common form of ASTX in nature includes isomer i.e. 3S, 3′S. However, in synthetic ASTX, R, S distributions are present in an equal proportion at each chiral center.The predominant ASTX stereoisomer in antarctic krill, Euphausia superba, is 3R, 3′R, primarily consisting of esterified form, while in wild atlantic salmon, it is 3S, 3′S, occurring as the free form (Coral-Hinostroza and Bjerkeng 2002). Furthermore, in the case of salmon-fed ASTX derived from yeast, the predominant isomer is 3R,3R (whereas the predominant isomer in salmon-fed ASTX derived from artificially produced sources is 3R,3S (Megdal et al. 2009). Additionally, ASTX has geometrical cis-or trans-isomers because its polyene chain contains multiple double bonds. Trans-ASTX esters are frequently found in nature, while cis-ASTX esters are less stable thermodynamically but still identifiable (Qiu et al. 2012). Molecularly, ASTX is composed of C₄₀H₅₂O₄ as shown in the Fig. 2. It weighs 596.84 g/mole.

Fig. 2.

Chemical structure of astaxanthin (ASTX) derived from PubChem (https://pubchem.ncbi.nlm.nih.gov/compound/Astaxanthin)

Based on its molecular structure, ASTX exhibits distinct chemical properties besides the general metabolic and physiological roles associated with carotenoids. As an antioxidant and free radical scavenger, the conjugated double-bond hydrocarbon chain in the ASTX molecule, along with the unsaturated ketone and hydroxyl groups at the chain's end, can draw unpaired electrons or donate electrons to free radicals (Ambati et al. 2014). Because of the presence of oxygen in its rings, ASTX has a more polar nature that enables it to remove free radicals and donate electrons, making it a potent antioxidant (Jafari et al. 2022).

There are various types of carotenoids including Beta-carotene, canthaxanthin, zeaxanthin, cryptoxanthin, astaxanthin, lutein, and vitamin C, etc. as shown in Fig. 3 but as compared to other carotenoids, ASTX has the strongest natural antioxidant activity, with values between 10 and 65 times higher than already available carotenoid molecules (Shah et al. 2016a).

Fig. 3.

Chemical structure of some other carotenoids (Beta-carotene, Zeaxanthin, and Cryptoxanthin) present in nature

The antioxidant activity of ASTX can be measured in different units, which mainly depend on the processes or assays used to evaluate its efficacy. For instance, carotenoid production was performed using technological approaches including various magnetic field (MF) intensities of 0–60 MT and agitation i.e.150–210 rpm. Implementing MF during inoculum culture resulted in a 12.4% improvement in cell growth. In addition, a peak volumetric carotenoid concentration of 1898.60 µg L⁻¹ was reached in 96 h by applying a 60 mT MF and stirring at 150 rpm. The results presented showed a 66% increase in productivity and a 22.7% increase in carotenoid concentration (Silva et al. 2023).

Carotenoids, vitamins C and E, and phenolic compounds are the major antioxidants that occur naturally in food produced from plants. These secondary metabolites are important factors for improving the food's shelf life as they make it more stable, therefore it lasts longer (Kaur and Kapoor 2001). Similarly, canthaxanthin is another type of red–orange colored carotenoid that is classified within the xanthophylls. It is an isolated compound that occurs in various species of fungi, algae, and bacteria naturally (Esatbeyoglu and Rimbach 2017). Some of the foods comprise maize and several vegetables, that contain zeaxanthin; i.e. the dihydroxy derivative of Beta-carotene (Lu et al. 2021). The molecular formula for Beta-cryptoxanthin is C₄₀H₅₆O. Being a monohydroxy derivative of Beta-carotene, with a hydroxyl group at the 3' position on one of its β-rings.

Astaxanthin (ASTX) extraction process

The process of extraction is a crucial step for isolating carotenoid pigments from various natural sources including microalgae and crustaceans, additionally, it can also produced artificially via different synthetic production methods. Solvents and oils, as well as enzymatic and microwave-assisted methods, can all be used for the extraction process (Kapoore et al. 2018). This pigment is widely employed in industries such as food, medicine, and cosmetics because of its red color pigments and strong anti-oxidant properties. The extraction process's main goal is to produce concentrated ASTX. Samples are typically taken from a variety of aquatic organisms and microalgae to accomplish this extraction method, and the compound is then synthesized using the reaction mixture. For instance, with the aid of acetone powder, cellulose, and catalase, the compound present in encysted Haematococcus cells was extracted using 40% acetone at 80 °C for 2 min (Sarada et al. 2006; Mota et al. 2022).

When compared to other biological sources like Phaffia rhodozyma (0.4 Wt.%), Euphausia pacifica (Pacific krill, 0.012 Wt.%), and Pandalus borealis (Arctic prawn, 0.12 Wt.%), H. pluvialis is the most powerful source of ASTX (Lorenz and Cysewski 2000; Praveenkumar et al. 2015). Once the green stage has produced algal biomass under ideal growth and development conditions, ASTX synthesis is initiated and conducted under a stressful environment, as ASTX is synthesized, a resistant cell wall is also produced. The different parameters including light, temperature, pH, phosphate and nitrate deficiencies, and changes in salt concentration may affect the synthesis of ASTX (Shah et al. 2016b). Furthermore, H. pluvialis can develop in phototrophic, mixotrophic, or heterotrophic environments, and it usually takes two stages to complete. In the downstream process, cysts of H. pluvialis are harvested, dried, and mechanically disrupted after that, ASTX is extracted using supercritical CO₂ (Mutale-joan and El Arroussi 2023). The biotechnological flow chart of Hematococcus pluvalis is shown in Fig. 4.

Fig. 4.

Flowchart of the various biotechnological approaches, i.e. cultivation, harvesting, and extraction are used to produce red-color carotenoids, astaxanthin by using microalgae, Haematococcus pluvialis (H. pluvialis)

Because it is a lipophilic compound, ASTX dissolves easily in organic solvents. Hexane, ethyl acetate, and acetone are frequently used solvents for its extraction. Similarly, HCl was used to assess the maximum ASTX yield when it was kept at different temperatures for about 15–30 min. (Gallego et al. 2019). Furthermore, the mixture was sonicated and mechanically stirred to extract the compounds from the material's cellular and structural constituents. To extract ASTX (1.3 mg/g) from the algae Phaffia rhodozyma, acid stimulation was also used (Ruen-ngam et al. 2010). Similarly, the compound was heated up to 75 °C for 5 min, during which about 75% of the compound condensed into microvapour to extract 75% of the total ASTX content. Additionally, a combination of centrifugation and filtration was used to separate ASTX from the solid residues. Following this separation method, all solvents were removed from the reaction mixture using a rotary vacuum evaporator to concentrate the solvents and raise the ASTX concentration. For instance, ASTX compounds derived from Hematococcus pluvialis have been produced with a yield of roughly 80–90% using a variety of supercritical fluids, including solvents (ethanol and sunflower oils) (Machmudah et al. 2006; Nobre et al. 2006; Wang et al. 2012).

To find the ASTX concentration, the material was separated using several solvents after that, the extract was then collected, and condensed using a rotary evaporator that was finally dissolved in an organic solution.

Further, the absorbance of the extract was measured between 476 nm and 480 nm respectively (Ranga Rao et al. 2010). This procedure will improve the ASTX solution's concentration, after which it will be further refined by removing impurities using solid-phase extraction or column chromatography techniques while undergoing an additional purification steps. NMR spectroscopy, LC–MS, HPLC, and other methods are the few examples of an additional extraction techniques (Seger et al. 2013).

Preservation and storage of astaxanthin

ASTX degradation can be minimized by using suitable preservation methods, such as complexing with calcium ions or cyclodextrin, microencapsulating, and incorporating it into chitosan matrices, liposomes, emulsions, or suspensions (Higuera-Ciapara et al. 2004; Ribeiro et al. 2005; Chen et al. 2007; Tachaprutinun et al. 2009). In rice-bran, gingelly, and palm oils, ASTX showed stability between 70 °C and 90 °C, retaining 84% to 90% of its content for use in food, pharmaceutical, and nutraceutical applications. However, at 120 °C and 150 °C, ASTX content decreased (Rao et al. 2007). It was suggested that the presence of flavonoids, polyphenols, tocopherols, and vitamin E compounds contributed to the stability of carotenoids in oil. Additionally, it has been discovered that ASTX incorporated into lipid solid particles or colloidal systems raised the compound's bioavailability (Anarjan et al. 2013). Similarly, storage conditions had an impact on ASTX's stability even after it had been preserved with the best practices. The decomposition of ASTX may be accelerated by various factors such as light, oxygen, and ozone (Niamnuy et al. 2008). ASTX's stability and rate of degradation can be effectively maintained and delayed by using vacuum packaging as a storage technique (Gouveia and Empis 2003).

Food products storage temperature, oxygen content, light conditions, medium pH, product type, fat content, antioxidant levels, and the activity of internal lipolytic enzymes are just a few of the factors that affects ASTX stability. For instance, the least amount of ASTX was degraded when dried microalgae biomass was stored for 9 weeks at  21 °C in a nitrogen atmosphere (Raposo et al. 2012). Further, the addition of chelators and antioxidants may also enhance ASTX's chemical stability. The degradation of ASTX in nanodispersions could be effectively mitigated by adding ascorbic acid and α-tocopherol in ratios of 0.4 and 0.6, respectively (Anarjan et al. 2013).

Astaxanthin: an innovative carotenoid utilized for agriculture farming practices

The most potent and naturally occurring antioxidant known as ASTX, possesses a lipophilic chemical structure that causes inadequate solubility and low bioavailability in water. The issues related to the solubility of functional lipid compounds can be significantly resolved and their solubility, bioavailability, and chemical stability can be greatly enhanced by size-reduction technique to convert these large molecules into nano ranges.

ASTX NPs possess a high surface-to-volume ratio, and involve a wide range of applications in various fields. For instance, when compared to free ASTX, the ASTX-loaded NP demonstrated a greater aqueous phase ABTS (2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid)) radical scavenging capacity and significantly higher anti-fibrogenic activity in LX-2 cells, which were used as an HSC (Hematopoietic stem cells) cell model. In 2022, Sorasitthiyanukarn et al. fabricated NPs prepared using chitosan oligosaccharide and alginate combined with the loaded ASTX using an oil-in-water emulsification process via ionotropic gelation. The resulting NPs possessed higher stability; increased bioaccessibility and bioavailability; as well as better antioxidant activities, along with an excellent storage stability at 4 °C up to 60 days (Sorasitthiyanukarn et al. 2022). According to Kim et al. (2022), synthesized chitosan and tripolyphosphate NP, specifically designed to encapsulate ASTX, using an ionic gelation method. These NPs significantly enhanced antioxidant activity, as shown in both laboratory (in vitro) and living organism (in vivo) studies (Kim et al. 2022).

ASTX possesses several nutritional and therapeutic advantages that are significant for human health and well-being. However, it has low solubility in water so, its absorption in the human body has very poor. To achieve the absorption rate of nano-ASTX for their effective use in therapeutic applications, ASTX NP was prepared using an emulsification/solvent evaporation method. The key findings demonstrated that well-defined ASTX NP with a 5% ASTX content was produced by combining polyethylene glycol–polylactic acid copolymer as an encapsulation agent and cremophor RH40 as a surfactant. Additionally, the average diameter of these NP was around 90 nm in size and showed a spherical shape. Nano ASTX exhibited higher DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging activity and significantly enhanced cell uptake. Similarly, it showed strong cytoprotective and hypolipidemia effects, and toxicity when compared to free-ASTX (Hien et al. 2023). Furthermore, there are different types of carriers used for the drug delivery system of nano-ASTX that mainly involve nano micelles, nanoemulsion, nano gel, nanoparticles, etc. For instance, a solvent diffusion method was used to prepare ASTX-loaded stealth lipid NPs (ASTX-SSLNs) that result in greater antioxidant properties, compared to carrier-free ASTX. This NP was used in therapeutic applications for the treatment of Alzheimer’s disease (Santonocito et al. 2021). Similarly, the rate of absorption of lipophilic components in water-based products can be increased by nanodispersions because they exhibit a smaller particle size that results in enhanced water solubility (Shen et al. 2018). Additionally, nanodispersions and nano micelles possess external hydrophilicity that results in the stability of ASTX, facilitates its transport in vivo, and provides significant benefits for drug delivery and targeting treatments (Anarjan and Ping Tan 2013; Chiu et al. 2021).

Different methods can be employed to reduce the size of ASTX NP which mainly includes high-energy top-down or low-energy bottom-up processes. The process parameters should be adjusted to produce the most homogenous ASTX NP with the smallest mean particle size, highest net zeta potential, and the strongest chemical and physical stabilities. Additionally, the research results have established that ASTX NP could be prepared through the process of anti-solvent precipitation with a high loading capacity of around 94.57 ± 0.70%, negative zeta potential, and average size of NPs observed around 74.29 ± 7.92 nm. DSC and XRD analysis has further proved the amorphous nature of nano-formulated astaxanthin (ASTX-NPs). ASTX-NPs were shown to be more stable and compatible over time than free ASTX. They also exhibit remarkable strength and stability under UV light and have stronger antioxidant activity than free ASTX as mentioned earlier. These results may imply that ASTX-NPs could be an efficient formulation method, opening the doors for innovative functional food applications (Yu et al. 2022). Utilizing the nanoprecipitation method, ASTX-PLGA NPs of 142.23 ± 0.96 nm size with approximately − 27.3 ± 4.67 mV zeta potential were observed. Further, the characterization techniques including Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) indicated the formation of NPs at nanoscale range with amorphous nature. However, even though ASTX-PLGA NPs exhibited excellent encapsulation efficiency, but the overall yield was relatively low. This study underscores how the nanoprecipitation technique significantly enhances ASTX bioavailability, thus providing great prospects for further applications (Ku Aizuddin et al. 2020).

ASTX, the reddish-orange lipid-soluble oxy carotenoid was first discovered in lobsters. It can also be synthesized using biological materials including bacteria, microalgae, plants, and different kinds of seafoods (Sztretye et al. 2019). Due to their antioxidative properties, ASTX NPs may be crucial in fighting against phytotoxicity caused by the presence of heavy metals as they have the ability to reduce the uptake and translocation of heavy- metals by improving the overall morphological and biochemical parameters of agricultural crops (Yuan et al. 2011). Various NPs can also be utilized in the agricultural sector to increase plant morphology (leaf number, roots/shoots length, length of plants, no. of nodes, fresh weight/dry weight, etc.) and biochemical parameters as shown in Fig. 5. Furthermore, these NPs can also be utilized in a variety of field applications including nanopesticides, nanobiosensors, nanofertilizers, and nano-based remediation.

Fig. 5.

Role of various nanoparticles in improving morpho-physiological profiles of plants (a) different types of nanoparticles utilized in nutrient-loaded or nutrient-containing nanoparticles. (b) nanoparticles are delivered to plants via foliar spray through various parts of plants including stomata, cuticles, lenticels, or wounds, or (c) soil applications via root hairs or root tips. (d) beneficial for plants i.e. increased crop growth, fruit yield, improved health of the soil by preserving soil microflora, improved water holding capacity, and more stress tolerance due to the presence of different heavy metal ions. Additionally, it can be used in various field applications in the form of nanosensors, nanopesticides, nanofertilizers, and nano-based remediation

In hydroponically grown 10 days old rice seedlings, elevated salinity i.e. 150 mM sodium chloride, stress was successfully lowered for 7 days by using 100 mg/L of synthesized ASTX and gold nanoparticles (AuNPs) more when compared to ASTX (100 mg/L) alone. This was achieved by first synthesizing ASTX-AuNPs using ASTX and chloroauric acid. The main reason was that ASTX and AuNPs reduced oxidative stress brought on by high salinity while inducing tetrapyrrole biosynthesis (Song et al. 2022). This research findings showed that ASTX especially when applied as ASTX-AuNPs strongly alleviates the damaging effects of high salinity in rice. The application of ASTX-AuNPs enhanced rice resistance to salt stress through the restoration of tetrapyrrole biosynthesis that consequently enhanced the performance of antioxidant enzymes that ultimately lowered the levels of ROS activity. Furthermore, ASTX-AuNPs reduced salt-induced toxicity in rice seedlings through the expression and regulation of genes involved in the scavenging of ROS. Conversely, the application of ASTX itself did not produce such a regulating effect. These results might indicate the exogenous application of ASTX-AuNPs as a novel approach for improving salt tolerance in rice seedlings.

Furthermore, the ASTX-loaded DNA/chitosan nanoparticles (ADC) were created as nanocarriers for the encapsulation and delivery of ASTX NP that contains about 65 μg/ml of ASTX content. These findings suggested that ASTX can effectively shield cells from oxidative damage and significantly enhance the ROS scavenging activity of ASTX NP than free ASTX. Hence, the increased antioxidant capacity and cellular uptake properties made the ADC NPs more suitable for efficient absorption and delivery of ASTX (Wang et al. 2017).

However, the practical uses of ASTX as NP are hindered by its extremely low water solubility, poor oral bioaccessibility, and low bioavailability. In addition, the chemical stability of ASTX is not very good, particularly when it comes to manufacturing and storage(Langhans 2018). It exhibits an unsaturated molecular structure due to which it can be broken down readily in the presence of heat, acidic and alkaline solutions, oxides, and UV light (Sorasitthiyanukarn et al. 2022). To improve the state of ASTX such as its solubility in water, stability, bioaccessibility, bioavailability, and biological activities, different types of NPs with distinct structures have been investigated for encapsulation i.e. lipid-based NPs, protein-based NPs, polysaccharides-based NPs were discovered (Li et al. 2023).

Health benefits of astaxanthin

ASTX exhibits different types of biological activities which are beneficial for human health and society. These include activities like antioxidants, anti-inflammatory, anti-gastric, anti- cancerous, anti-aging, anti-diabetics, and also provide protection from cardiovascular and neurological-related diseases.

Antioxidant activity

While ASTX is not available as an antiviral element, its unique properties including anti-inflammatory and antioxidant activity have proven its capacity to inhibit viral infections. The drugs derived from ASTX prevent the growth, development, and expression of genes and inhibit the replication of viruses and other microorganisms present in host cells (Nair et al. 2023). As compared to other numerous carotenoids present, ASTX exhibits strong antioxidant activity through the process of scavenging free radicals, eliminating singlet oxygen, preventing peroxidation of lipids, strengthening immunological response, and controlling the expression of genes. Hepatic stellate cells in the liver are inhibited by ASTX, as they prevent the gene expression of pro-fibrotic induced by transforming growth factor (TGF-β1) and hepatic fibrosis (Yang et al. 2016). When compared to other carotenoids like Beta-carotene, zeaxanthin, canthaxanthin, vitamin C, and vitamin E, the naturally occurring form of ASTX with its configuration of all-trans isomer has superior antioxidant properties. Plants produce various kinds of carotenoids, which are mainly natural pigments, responsible for giving vibrant hues to a variety of fruits and vegetables. The most explored carotenoid is Beta-carotene (β-Carotene) containing 40 carbon atoms which is the most prevalent in fruits and vegetables in the majority of countries. For instance, in the United States, lycopene present in tomatoes is now consumed at the same concentration that is equivalent to beta-carotene. It can also show strong antioxidant properties in both in vitro and in vivo animal models additionally, it can also exhibit enhanced activity against free radicals. In the same way, when taken as a dietary supplements, it can also boost immunity (Paiva and Russell 1999).

Previous research has been conducted in the lab both in vitro and in vivo conditions which showed that all trans naturally occurring ASTX isomers have shown antioxidant properties as well as a strong inhibitory effects on lipid peroxidation (Liu and Osawa 2007). The strong antioxidant qualities of ASTX are a result of its distinct molecular structure, which includes hydroxyl and keto moieties on each ionone ring (Brotosudarmo et al. 2020).

Anti-cancer activity

Several epidemiological laboratory research has been performed on carotenoids i.e. ASTX that conclude that it exhibits protective effects against different types of cancer (Rowles and Erdman 2020). Plant extracts derived from lycopene contain a lot of ASTX, an oxygen-rich byproduct, that is one of the members of the xanthophyll family. Due to the presence of strong antioxidant and anti-inflammatory properties, ASTX has been used to treat deadly diseases, i.e. Cancer and Parkinson's disease (Erzurumlu et al. 2023). More precisely, it has been discovered that consuming ASTX can also inhibit cell proliferation and trigger apoptosis of colonic adenocarcinomas while additionally inhibiting the expression of inflammation-associated cytokines such as nuclear factor (NF)-κB, tumor necrosis factor (TNF)-α, and interleukin (IL)−1β (Yasui et al. 2011). As compared to other carotenoids including canthaxanthin and β-carotene, ASTX exhibited significant anti-tumor activity (Ávila-Román et al. 2021). Furthermore, it can also lower the proliferation of embryonic fibroblasts, breast, prostate, and fibrosarcoma cells (Palozza et al. 2009). Research reports indicate that smokers who are regularly exposed to asbestos are at a higher risk of developing lung cancer because β-carotene has been shown to cause lung diseases and has no protective effects (Bertram 2004). This implies that the utilization of carotenoids i.e. ASTX, does not have pro-vitamin A activity that may provide protection and prevent retinoid toxicity (Bertram and Vine 2005).

Anti-diabetic activity

In general, people with Diabetes mellitus have extremely high levels of oxidative stress. This is due to Hyperglycemia which leads to the damage of tissues and dysfunction of pancreatic cells in patients. ASTX can significantly increase the levels of serum insulin and glucose while minimizing the damage caused by Hyperglycemia in pancreatic βeta-cells (Uchiyama et al. 2002). It was discovered that ASTX inhibits the development of diabetes-related nephropathy by protecting adjacent tubular epithelial cells against oxidative damage. This is mainly due to the scavenging effect of ROS in the cell organelle "mitochondria "of mesangial cells (Braga et al. 2022). Furthermore, ASTX promotes the expression of genes related to antioxidants and minimizes blood cholesterol and triglycerol levels in the liver. Moreover, ASTX also prevents liver damage and improves cell sensitivity towards the hormone known as “insulin” by lowering CYP2E1 expression (Bhuvaneswari et al. 2010). It t can also hindered the oxidation of lipids and proteins, which consequently prevent the process of glycation, and glycated protein-induced cytotoxicity takes place in cells of endothelial in the human umbilical vein (Nishigaki et al. 2010).

Anti-inflammatory activity

The primary pathophysiological reason for numerous diseases, including Diabetes mellitus and several neurodegenerative disorders, is chronic inflammation. Immune cells are especially vulnerable to oxidative stress because their plasma membranes contain a high proportion of polyunsaturated fatty acids. Thus, the overproduction of ROS leads to the disturbance of antioxidant balance (Chew et al. 2011). In physiological processes, ASTX is an effective antioxidant that reduces inflammation. This valuable carotenoid can lower inflammation correlated with peripheral disease or control the immune response to it (Kim et al. 2005). According to study, mice infected with the bacteria, Helicobacter pylori, cell extracts of algae i.e. Haematococcus and Chlorococcum drastically reduced the number of bacterial loads and gastric inflammatory conditions (Bennedsen et al. 2000; Liu and Lee 2003; Ranga Rao et al. 2010; Liu et al. 2015). Subsequently, it has been demonstrated that ASTX prevents transcription factors related to inflammation in several laboratory models including NF-κB (Suzuki et al. 2006; Speranza et al. 2012), Protein kinases activated by mitogens (MAPK) (Li et al. 2015; Yang et al. 2019), Nuclear factor related to erythroid factor 2 (Nrf2) (Liu et al. 2015), and Pathways involving phosphatidylinositol-3-kinase (PI3K) (Xu et al. 2015). Additionally, ASTX controls the expression of inflammatory mediators such as chemokines and cytokines consisting of interferon-γ (IFN-γ), VEGFs (Vascular Endothelial Growth Factors), TNF-α, interleukin (IL-6), and interleukin (IL-1β) (Kohandel et al. 2022).

Prevention from cardiovascular diseases

Globally, cardiovascular diseases (CVDs) is the leading cause of death worldwide. The metabolic syndrome, which is considered as one of the potential risk causes of CVD, is a collection of metabolic disorders that together increase the chances of CVD. These diseases include dyslipidemia, hypertension, obesity, impaired glucose tolerance, and dysfunctions in glucose metabolism (Roberts and Sindhu 2009). In a rat model of myocardial ischemia–reperfusion, a different team of researchers evaluated a combination therapy known as vitae pro, which includes three carotenoids mainly lutein (8.1%), zeaxanthin (1.23%), and ASTX (2%), all in safflower oil. Compared to the control and vitamin E-treated groups, prior consumption of vitae pro for twenty-one days developed a significant cardioprotective effect (Adluri et al. 2013). Additionally, ASTX enhanced sensitivity towards insulin as well as lowered blood sugar levels in the rats (Preuss et al. 2011).

Improve immunity

To safeguard the immune system and other vital organs, natural ASTX, a powerful and efficient antioxidant, can be an excellent choice. This bright-orange substance has an enormous effect on human health as it helps to prevent heart diseases, cancers, diabetes, liver diseases, stomach issues, obesity, and the aging of cells. It also boosts the immune system. The antioxidant ASTX improves the body's capacity to fight against inflammation while balancing and strengthening the immune system (Ahmadi and Ayazi-Nasrabadi 2021). Damage caused by free radicals can cause severe harm to immune system cells. There are polyunsaturated fatty acids (PUFA) in the cell membrane, protecting the immune system from damage triggered by free radicals can be achieved with antioxidants, particularly ASTX (Jyonouchi et al. 1991). The immune cells are more sensitive to oxidative stress because their plasma membranes contain a high concentration of polyunsaturated fatty acids, which tend to produce more oxidative by-products. In a mouse model, ASTX exhibited greater immuno-modulating effects than β-carotene (Jyonouchi et al. 1991). Some of the health benefits of ASTX are shown in Fig. 6.

Fig. 6.

Potential and versatile therapeutic applications of ASTX for promoting and managing human health

Commercial applications of astaxanthin

Nowadays, one of the most prosperous biotechnological endeavors is the natural source of ASTX production. Applications for ASTX in food, feed, nutraceuticals, and medicines are highly desirable. This has led to significant efforts to enhance ASTX production from biological rather than synthetic sources. Products containing ASTX can be found in the market in the form of  oil, soft gel, tablet, powder, biomass, cream, energy drink, and capsules. Certain ASTX products were created by combining multivitamins, omega-3 fatty acids, and omega-6 fatty acids, herbal extracts, and other carotenoids available (Stoyneva-Gärtner et al. 2022). An additional synthetic ASTX preparation with at least 10% ASTX is called Lucantin® Pink (BASF Chemical Company, Ludwigshafen, Rhineland-Palatinate, Germany). Egg yolks, salmon, prawns, and grill skins can all be effectively colored with it. The FDA authorized the implementation of artificial ASTX as a carotenoid pigment in both fish and animal feed in May 1995 (Fang and Chiou 1996). Because ASTX-containing microorganisms and animals are used in a variety of commercial activities, similarly, ASTX-enriched microalgae production can offer more alluring advantages (Ambati et al. 2014). Patent applications for ASTX highlight its potential in preventing bacterial infections, reducing inflammation, and combating vascular issues, cancer, and cardiovascular diseases. It also inhibits lipid peroxidation, reduces cells damage, minimizes body fat, and significantly increases brain activity and skin thickness. A study determined that feeding ASTX at a dose of 50 mg/kg lowered blood pressure in stroke-prone rats for 5 weeks and in hypertensive rats for 14 days respectively. It also protected significantly against naproxen-induced gastric and antral ulcers and decreased lipid peroxidation concentration in the gastric mucosa (Kim et al. 2005).

Mass production of biomass for biotechnological purposes involves managing many algae cultures in indoor and outdoor systems, such as open pond raceways and photobioreactors. Photobioreactors are ideal for mass production since they can provide controlled growth conditions, thereby minimizing the risk of contamination if specific culture parameters are maintained. For instance, Haematococcus lacustris recently demonstrated a biomass productivity of 6.5 mg/L per day using a closed photobioreactor system under controlled conditions with light intensity maintained at 80 μmol photons/m²/s. (Do et al. 2019). Similarly, closed photobioreactors (PBRs) are essential for scaling up from the laboratory to pilot and commercial levels in the ASTX production process. For this purpose, Illuminated photobioreactors (IPBRs) are specifically designed to ensure optimal biomass productivity and consequently results in the maximum ASTX yield. The process involves the optimization of light exposure, carbon dioxide supply, temperature, pH, air mixing, mass transfer, and fluid dynamics (Ho et al. 2021). Moreover, Haematococcus pluvialis can be cultivated in vertical or horizontal tubular PBRs with capacities starting from 1000 L or more, as well as in raceway ponds covering areas of 1000 square meters or more. Outdoor PBRs are usually located in sunny, open areas to capture solar radiation, which enhances the growth of algae. Tubular PBRs can have a photosynthetic efficiency of approximately 3%, while raceway ponds can only have around 1%. For instance, the BGG company, located in Yunnan province uses vertical tubular PBRs for both the growth phase of biomass and the accumulation of ASTX (Tam et al. 2021).

Furthermore, consumer demand for natural materials, including ASTX has increased dramatically within the last few years (Ren et al. 2021). To address the demands in the food, cosmetics, pharmaceutical, and feed industries for natural carotenoids, new microbial candidates are being explored, along with the development of upstream/downstream technologies for advanced production. These developments offer efficient production, lower costs, and increased ability for scaling up. Furthermore, to evaluate the commercial potential of Paracoccus carotinifaciens-based ASTX production, a SWOT analysis presents its strengths, weaknesses, opportunities, and threats, providing a comprehensive view of its viability in the market.

Conclusion

ASTX is a red-colored carotenoid pigment mainly found in marine organisms, plants, and animals; and can be synthesized using various biotechnological approaches. According to the study, ASTX NPs can also be utilized in the agriculture field as it can contribute to plant growth and development and protect plants from various stresses, i.e. salt stress, and heavy metal stress. In a research study, it was shown that ASTX-AuNPs are essential for ROS scavenging activity because they can help significantly to reduce the levels of ROS in rice by modifying the expression of gene that scavenges ROS activity in plants. Similarly, it can also help to protect plants from the accumulation of heavy metals including cadmium, lead, arsenic, and mercury that can cause toxicity to plants and affect soil microflora. A common and cost-effective substance for reducing salt stress in crops is ASTX that found most abundantly in prawns, crab shells, and algae. Furthermore, ASTX is also effective in treating numerous human diseases including cancer, Diabetes mellitus, cardiovascular diseases, autoimmune diseases, hypertension, etc. due to the presence of its strong antioxidant properties. These life-threatening diseases are mainly caused due to oxidative stress, so the main role of ASTX in biomedical applications is to suppress oxidative stress by neutralizing the free radicals present in cells and tissues of the human body. Similarly, it can also possess immune-modulating, DNA-repairing, and anti-inflammatory qualities that can successfully preserve skin health making it a very valuable ingredient in anti-aging skin products. However, the breakdown and utilization of ASTX in biological systems have not been extensively studied. Future studies should concentrate more on the physical and chemical features of ASTX structures, mechanisms of absorption, and ease of incorporation into metabolic processes. ASTX has diverse applications that can be utilized in various fields including aquaculture, food industry, agriculture sector, pharmaceutical industry, and cosmetic industry, etc. Furthermore, very limited studies on the agricultural field application of ASTX NPs have been reported so far. Therefore, more research is necessary to create opportunities for advancements in health and sustainability.

Abbreviations

ASTX NP

Astaxanthin nanoparticle

NPs

Nanoparticles

SEM

Scanning electron microscopy

XRD

X-ray diffraction

FTIR

Fourier transform infrared spectroscopy

β-carotene

Beta-carotene

ROS

Reactive oxygen species

AuNPs

Gold nanoparticles

Cd

Cadmium

CVDs

Cardiovascular diseases

PUFA

Polyunsaturated fatty acids

NF-κB

Nuclear factor kappa B

Nrf2

Nuclear factor erythroid 2-related factor 2

MAPK

Mitogen-activated protein kinase

PI3K

Phosphatidylinositol-3-kinase

γ (IFN-γ)

Interferon-gamma (or type II interferon)

VEGFs

Vascular endothelial growth factors

TNF-α

Tumor necrosis factor-alpha

IL-6

Interleukin-6

IL-1β

Interleukin-1β

ASTX-PLGA NPs

Astaxanthin -Poly (D, L-Lactide-co-glycolide) nanoparticles

DPPH

2,2-Diphenyl-1-picrylhydrazyl

H. pluvialis

Hematococcus pluvialis

P. rhodozyma

Phaffia rhodozyma

FDA

Food and drug administration

DSC

Differential scanning calorimetry

ABTS

2,2′-Azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid)

HSC

Hematopoietic stem cell

ADC

Astaxanthin-loaded DNA/chitosan

MF

Magnetic field

VEGFs

Vascular endothelial growth factors

UV

Ultraviolet

HPLC

High-performance liquid chromatography

ASTX-SSLNs

Astaxanthin-loaded stealth lipid nanoparticles

IPBRs

Illuminated photobioreactors

PBRs

Photobioreactors

BGG

Beijing gingko group biological technology co. ltd

P. carotinifaciens

Paracoccus carotinifaciens

H. lacustris

Haematococcus lacustris

SWOT

Strength, weakness, opportunities and threats

Funding

Received funding from SEED project (UPES/R&D-SoHST/08042024/43), UPES, Dehradun.

Declarations

Conflict of interest

The authors declare no competing interests.

Ethical approval

Not applicable.

Consent for publication

We, the authors of this manuscript, give our consent for the publication of identifiable details of the above-titled manuscript to be published in this journal.