Does astaxanthin help with blood-brain barrier damage in mice?

 Clinical studies have shown that the number of patients with diabetes mellitus associated with dementia is on the rise, making hyperglycemia an established risk factor for dementia [1]. Functional and structural disruption of the blood brain barrier (BBB) in the capillary blood vessels of the brain during hyperglycemia leads to a reduction in cerebrovascular integrity, which is a key and early event in cognitive decline leading to dementia [2].

Inflammation is a key mediator of BBB dysfunction. Hyperglycemia can cause chronic inflammation throughout the body, which promotes cerebrovascular inflammation, causing disruption of the BBB tight junction complex and increasing its permeability [3]. At the same time, when hyperglycemia occurs, a large amount of inflammatory factors can enter the brain through the damaged BBB, aggravating neuroinflammation and leading to cognitive decline [4]. The application of anti-inflammatory drugs can inhibit the inflammatory reaction in the brain and improve diabetic BBB damage and cognitive impairment [5]. However, long-term use of anti-inflammatory drugs may cause serious complications and drug tolerance in multiple tissues and organs throughout the body. Therefore, further research is needed to find more effective drugs to protect diabetic BBB.

 

Astaxanthin (ASTA) is a kind of carotenoid with deep red color, which can be produced by freshwater and marine microorganisms such as microalgae [6]. ASTA has powerful antioxidant, anti-inflammatory and anti-apoptotic functions, and it can pass through the BBB to exert neuroprotective effects, so the brain is considered to be an important target organ for ASTA [7]. Studies have confirmed that ASTA can improve cognitive dysfunction in diabetes mellitus and reduce BBB damage caused by dementia and stroke [8]. However, the effect of ASTA on BBB damage caused by diabetes mellitus and the related mechanism have not been reported.

 

In this paper, we observed the effects of ASTA on the expression of CD31, zonula occluden-1 (ZO-1) and clau- din5 (Cldn5) proteins and inflammatory factors, as well as learning and memory ability in the brain of db/db mice, a model of type 2 diabetes, by gavage for 4 weeks, to clarify the effects of ASTA on BBB injury and related mechanisms in db/db mice, and to provide a new basis for the prevention and treatment of diabetic BBB injury. In order to clarify the effect of ASTA on BBB injury in db/ db mice and the related mechanism, we provide a new theoretical basis for the prevention and treatment of diabetic BBB injury.

 

1 Materials and Methods

1.1 Materials

1 . 1 . 1 Main reagents    

ASTA (sc-391 006, purity ≥99%) was purchased from Jingdao Sifu Biotechnology Co., Ltd, BSA Protein Assay Kit (P001 0S) and Immunoblotting Gel Preparation Kit (P001 2A) were purchased from Biyuntian, CD31 antibody (M1 51 1-8) was purchased from HUABIO, China, and ZO-1 antibody (sc-1 0804) was purchased from Santa Cruz, Santa Cruz, Santa Cruz, Santa Cruz, Santa Cruz, Santa Cruz, Santa Cruz, USA. ZO-1 antibody (sc-1 0804) was purchased from Santa Cruz, Cldn5 antibody (352588) was purchased from Invitrogen, USA.  IL-6 ELISA kit (KGEMC004-1), IL-1 β ELISA kit (KGEMC001b), and TNF-α ELISA kit (KGEMC1 02a) were purchased from Nanjing KGI, and the water labyrinth equipments were purchased from Anhui Zhenghua Equipment Company. Other chemical reagents were purchased from Shanghai National Pharmaceutical Reagent Co.

 

1 . 1 . 2 Animal    

Type 2 diabetes model mice db/db and control heterozygous db/m mice were purchased from the Model Animal Research Institute of Nanjing University, under the license of SYXK (Su) 2020-0048. They were housed in the SPF barrier system of the Experimental Animal Center of Xuzhou Medical University and fed with sterile feed and water. The mice were acclimatized for 1 week and then subjected to experiments.

 

1.2 Methodology

1 . 2 . 1 Experimental grouping 8-week-old male db/db mice were randomly divided into type 2 diabetes mellitus group (db/db, no treatment); diabetes mellitus oral ASTA low, medium, and high groups (ASTA-L, ASTA-M, and ASTA-H, respectively, were given 5, 10, and 20 mg kg-1 ASTA by gavage to select the appropriate ASTA dose); in order to exclude the effect of ASTA solvent corn oil on experimental results, a corn oil group (Oil, db/db mice were given the same volume of corn oil by gavage) was set up in this experiment. In order to exclude the influence of corn oil, the solvent of ASTA, on the results of the experiment, a corn oil group (Oil, db/db mice were given the same volume of corn oil by gavage) was set up in this experiment, with 8 mice in each group. Eight male db/m mice of the same age were used as normal controls. After 4 weeks of administration, behavioral tests were performed, and then the brains were executed.

1 . 2 . 2.2.2 Water Maze Experiment The water maze consists of a pool of 50 cm in height and 1 50 cm in diameter, with a depth of 30 cm, and a water temperature of 20-22 °C and a room temperature of 24-26 °C. The pool is divided into four virtual quadrants using Anymaze software. Before the experiment, the pool was divided into four virtual quadrants using Anymaze software, and cards of different colors and shapes were attached to the walls of the pool. A camera was placed directly above the pool and connected to the computer software to track the mice's movements, swimming time and speed. In quadrant 4, an 8-cm diameter object below the surface of the water was placed.

A 1 cm platform was used and set as the 5th quadrant. The exploration experiment was conducted for 5 days, 4 times per day. Mice were immersed in water from the middle of each of the four quadrants with their heads facing the wall of the pool, and the time from immersion to finding the 5th quadrant (latency), i.e., the time to find the platform, was recorded, and the mice were allowed to observe the platform for 20 s. If the mice did not find the 5th quadrant within 60 s, the latency was recorded as 60 s, and the mice were guided to the platform and allowed to observe the environment for 20 s. On day 6, the platform quadrant was removed, and the mice were allowed to enter the water from the quadrant opposite to the platform quadrant. On day 6, the platform quadrant was removed and the mice were allowed to enter the water from the opposite quadrant of the platform quadrant, and the time and distance spent in quadrant 4 where the platform was located during the 60-s period was recorded as a percentage of the total time and distance for assessing the learning and memory ability of the mice in each group.

1 . 2 . 3 Extraction and concentration determination of brain tissue proteins  

1 . The mice were anesthetized by intraperitoneal injection of 5% pentobarbital (0.6 mL-g-1 ), and then the brains were rapidly removed by decapitation, and the brain tissues were stripped out and placed in EP tubes. Cytoplasmic proteins were extracted according to the instructions for protein extraction: the brain tissue was homogenized by adding an equal volume of homogenate on ice, then centrifuged at 12,000 r-min-1 for 10 min, and the supernatant was removed. Determine the concentration of each group of proteins with the BCA kit, and use the homogenizing solution to level the concentration and volume according to the concentration of the samples. Add 5 × Loading Buffer, mix thoroughly, boil for 10 min, and store in the refrigerator at -20 ℃ for use.

 

1 . 2 . 4 Western blot for protein expression of CD31, ZO-1 and Cldn5   

Depending on the molecular weight of the protein, different concentrations of electrophoresis gel are used. Add about 40~80 μg of protein per well in a volume of about 20~30 μL for electrophoresis, and electrotransfer the protein to the NC membrane. Then, the NC membrane was immersed in 3% BSA for 2 h, and then immersed in primary antibodies (CD31: 1:2,000; ZO-1: 1:3,000; Cldn5: 1:1,500) at the appropriate ratio and incubated at 4 ℃ overnight. On the following day, the NC membrane was washed five times with Washing Buffer and incubated for 1 h at room temperature on a shaker with a fluorescent secondary antibody of suitable origin (1:10 000), and the bands were scanned with an Odyssey Infrared Fluorescence Scanning Imaging System. The bands were scanned with Odyssey Red Extra-Fluorescence Scanning Imaging System. Gray scale analysis of the protein bands was performed using ImageJ software.

 

1 . 2 . 5 Detection of brain tissue inflammatory factors    

Brain tissue samples were first homogenized in phosphate buffer and centrifuged (10 000 r-min-1 , 5 min), and then the supernatant was collected for the assay. The supernatant was collected and used for the assay. The kit and specimens were equilibrated for 30 min at room temperature according to the instructions of the kit. 96-well plates were used to measure the absorbance at 450 nm, and the levels of the inflammatory factors IL-6, IL-1 β, and TNF-α in the hippocampal tissues were expressed as ng-L-1 .

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1.3 Statistical Processing    

Data were expressed as x ± s and plotted using GraphPad Prism 7. 0 software. The statistical data were analyzed by SPSS 1 8.0 software, and the data on the latency period of the water maze were analyzed by one-way ANOVA and multiple comparisons. For other experiments, one-way ANOVA was used for comparison between groups, and t-test was used for comparison between two groups.

 

2 Results

2.1 Medium and high doses of ASTA attenuate BBB injury in db/db mice    

After 4 weeks of gavage with different doses of ASTA, the protein expression of CD31, ZO-1 and Cldn5 in the brain of mice was detected by Western blot. The results showed that the protein expression of CD31, ZO-1 and Cldn5 in the brains of db/db mice was significantly lower than that in the db/m group, and the expression of CD31, ZO-1 and Cldn5 in the brains of db/db mice was significantly increased by gavage of medium-dose and high-dose ASTA (Fig. 1). These results suggest that ASTA can improve the BBB injury induced by hyperglycemia in mice. ASTA was selected as a medium dose (10 mg kg-1 ) for subsequent experiments.

 

2.2 ASTA inhibits brain inflammation in db/db mice    

The levels of IL-6, IL-1 β and TNF-α in the brains of mice in each group were detected by ELISA. The results showed that the levels of IL-6, IL-1 β and TNF-α in the brain tissue of mice in the db/db group were significantly higher than that of mice in the db/m group, and that ASTA significantly reduced the expression of inflammatory factors in the brains of mice in the db/db group, and that the levels of inflammatory factors in the corn oil group were higher than that of the ASTA group but did not differ from that of the db/db group (Fig. 2). The level of inflammatory factors in the corn oil group was higher than that in the ASTA group, but did not differ from that in the db/db group (Fig 2). These results suggest that ASTA reduces BBB damage in db/db mice by decreasing the expression of inflammatory factors in the brain.

 

2.3 ASTA improves cognitive impairment in db/db mice    

In order to further clarify the effect of ASTA on the cognitive impairment of db/db mice, we applied the water maze experiment to test the learning and memory functions of each group. The results showed that on days 1, 2 and 3 of the water maze exploration experiment, there was no difference in the time to find the platform in each group; on days 4 and 5, the time to find the platform in the db/db group was higher than that in the db/m group; the time to find the platform in the ASTA group was significantly lower than that in the db/db group; and the time to find the platform in the corn oil group was higher than that in the ASTA group, but there was no significant difference from that in the db/db group. In the water maze test on day 6, mice in the db/m group had a significantly higher time and distance to the platform quadrant than those in the db/db group; mice in the ASTA group had a significantly higher time and distance to the platform quadrant than those in the db/db group; and mice in the corn oil group had a significantly lower time and distance to the platform quadrant than those in the ASTA group, and there was no significant difference in comparison with those in the db/db group (Fig. 3). These results suggest that ASTA improves the cognitive function of db/db mice by inhibiting BBB damage.

 

3 Discussion

In this study, we demonstrated that ASTA inhibits the release of inflammatory factors IL-6, IL-1 β and TNF-α, and increases the protein expression of CD31, ZO-1 and Cldn5 in the brain of db/db mice, thereby reducing BBB damage and improving cognitive dysfunction in diabetes mellitus.

The BBB is a special semipermeable membrane with properties different from those of peripheral capillaries, including a basement membrane and tight junctions formed by pericytes, astrocytes, microglia, and neurons [9]. The BBB is a physical barrier separating the body circulation from the brain parenchyma, and it is also a natural barrier that prevents bacteria, harmful substances, and inflammatory factors in the peripheral blood from entering the brain parenchyma [10]. Clinical data and animal experiments have found that hyperglycemia not only reduces the homeostatic control of brain parenchyma due to glucose metabolism disorders, but also causes a decrease in the expression of tight junction proteins, such as ZO-1 and Cldn5, which destroys the tight junctions of the BBB, increases the permeability of the BBB, and facilitates the entry of more potentially neurotoxic substrates into the brain, resulting in neuronal dysfunction, which is associated with reduced cognitive function in diabetes mellitus [4, 4, 5, 6]. This leads to neuronal dysfunction, which in turn is accompanied by a decrease in cognitive function in diabetic patients [4, 11]. Therefore, BBB damage is an important cause of cognitive impairment in diabetes mellitus, and maintaining the normal function of the BBB may be a new therapeutic strategy for treating cognitive impairment in diabetes mellitus.

 

It has been found that type 1 and type 2 diabetes can cause an increase in BBB permeability through direct damage to endothelial and pericytes [2]. At the same time, circulating blood inflammatory markers such as TNF-α and intercellular cell adhesion molecule 1 are significantly increased in diabetic patients, resulting in decreased expression of ZO-1 and Claudin-5 proteins in the BBB, which further exacerbates BBB damage [4]. In addition, chronic hyperglycemia activates advanced glyco- sylation end product-specific receptor to exacerbate the inflammatory response, thereby damaging the BBB [12]. Therefore, inflammation is a key mechanism for BBB damage and cognitive dysfunction in diabetes mellitus.

ASTA is a beneficial dietary supplement with strong anti-inflammatory effects, inhibiting the expression of TNF-α, IL-6, and IL-1β, and blocking the activation of nitric oxide (NO)- and nucle- ar factor-κB-dependent mitogen- activated protein kinase signaling pathways [13]. kinase signaling pathway [13]. Meanwhile, ASTA also showed high metastatic properties to brain tissues, and both cellular and animal experiments demonstrated that ASTA was able to reduce microglia activation and pro-inflammatory cytokine release, thus protecting cerebral blood vessels and neurons from inflammatory stimuli in neurodegenerative diseases and strokes [14]. In our previous study, we found that ASTA was able to reduce the inflammatory response in the hippocampus induced by high glucose stimulation and alleviate diabetic cognitive dysfunction, but its specific mechanism needs to be further explored [15].

 

In this paper, we applied behavioral, ELISA and Western blot experiments to demonstrate that ASTA reduces BBB damage and improves learning and memory functions in db/db mice, a model of type 2 diabetes, by inhibiting inflammatory responses. The clarification of this mechanism provides a reliable experimental basis for the development of drugs for the treatment of diabetic cerebrovascular complications and cognitive dysfunction.

 

References:

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［8］ Chik M W, Mohd Affandi M M R M, Singh G K S. Detection of astaxanthin at different regions of the brain in rats treated with Astaxanthin Nanoemulsion［J］.  J Pharm Bioallied Sci, 2022, 14 (1 ): 25 -30 .

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[1 1] Yoo D Y, Yim H S, Jung H Y, et al. Chronic type 2 diabetes re- duces the integrity of the blood-brain barrier by reducing tight junction proteins in the hippocampus[J].  J Vet Med Sci, 201 6, 78(6):957-62 .

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［1 3］ Kohandel Z, Farkhondeh T, Aschner M, et al. Anti-inflammatory action of astaxanthin and its use in the treatment of various diseases ［J］.  Biomed Pharmacother, 2022, 145:1 1 21 79 .

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Application of astaxanthin and its commercial production

 1 Astaxanthin and its distribution

Astaxanthin (Astaxanthin, 3,3 'a dihydroxy β , β 'a carotene a 4,4 'a diketone group, molecular formula c40 H52 O4) is a carotenoid whose molecular structure is very similar to that of the more familiar carotenoid a β a carotene (Figure 1), an oxidized carotene. (Figure 1), is an oxidized carotene. However, it is the subtle difference between them that makes astaxanthin and β-carotene very different in terms of chemical and biological properties. Astaxanthin is a naturally occurring carotenoid that is widely distributed in nature, and although we don't always talk about astaxanthin every day, we do consume it consciously or unconsciously in our diets. In nature, many crustaceans turn red due to the accumulation of astaxanthin in their bodies, and astaxanthin has also been found in some birds. In most cases, astaxanthin is a bright red or orange color, but in some crustaceans astaxanthin turns dark blue or green due to binding to proteins, and the original color of astaxanthin is restored during processing when heat destroys the binding of astaxanthin to the proteins (Weesie, 1999).

 

Figure 1 Molecular structure of astaxanthin

Astaxanthin is more easily esterified due to the presence of a hydroxyl group and a ketone group on the two dahuricone rings. Since free-standing astaxanthin is very sensitive to oxidizing agents, naturally occurring astaxanthin is often esterified in combination with proteins or, more commonly, with one or two fatty acids, making astaxanthin more stable. The presence of two asymmetric carbon atoms in the 3' and 3 positions on the two terminal dahuricone rings of the astaxanthin molecule results in the formation of different stereospecific configurations of the astaxanthin molecule, which are referred to as the R-configuration when the hydroxyl group is at the top of the molecule, and the S-configuration when the hydroxyl group is at the top of the molecule. Three conformations are commonly found in nature, namely 3S, 3 'S; 3R, 3 'S; and 3R, 3 'R. The isomers of astaxanthin from different sources are different. Analysis showed that astaxanthin from wild salmon and red algae is mainly the 3S,3 'S isomer; chemically synthesized astaxanthin is mainly 3R,3 'S; and astaxanthin from yeast phaffia is all the 3R,3 'R isomer. R isomer.

 

2 Applications of astaxanthin

Like other carotenoids, astaxanthin cannot be synthesized by animals themselves, and with the exception of a few shrimp species, animals cannot convert ingested carotenoids into astaxanthin, so all animals must consume it from their food, which in the marine environment is generally provided by microalgae or other microorganisms in the food chain. In the marine environment, astaxanthin is generally supplied by microalgae or other microorganisms in the food chain. Astaxanthin is more readily absorbed and accumulated by animals than other carotenoids. As a natural carotenoid, astaxanthin is widely used in aquaculture and has the following functions: 1 . 1. antioxidant. 2. precursor of certain hormones. 3. Antioxidant. 2. Precursor of certain hormones. 3. Improvement of immune function. 4. Vitamin A source activity. 5 . Improves reproduction. 6 . Promotes growth and development. 7 . Promotes maturation. 8 . Photoprotective effect. At present, many countries in the world have approved astaxanthin as an additive for animal feed.

 

2 . 1 Aquaculture

2 . 1 . 1 Marijuana salmon

Astaxanthin keeps the flesh of salmon pink, whereas in the case of farmed fish, a certain amount of astaxanthin must be added to the bait in order for the flesh to maintain its bright color. Furthermore, studies conducted by the U.S. Food and Drug Administration (FDA) have shown that wild salmon or rainbow trout can be differentiated from captive products by analyzing their astaxanthin composition because wild salmon contain mainly the 3S,3 'S isomer, which accumulates in the muscle of the fish only if added to the bait, because the 3S,3 'S isomer is a major constituent of the fish's muscle. The 3S,3 'S isomer can only accumulate in the muscle of the fish if the isomer is added to the bait, because salmon do not convert the 3R,3 'S isomer into the 3S,3 'S isomer. Furthermore, surveys have shown that consumers prefer species with a natural red color (Turujman et al., 1997).

 

Numerous studies have shown that, in addition to increasing or maintaining the color of fish flesh, astaxanthin has a beneficial effect on the health and productivity of farmed fish, and that in some species, particularly salmon, astaxanthin maintains normal growth and high adult survival rates. Currently, the most promising market for natural astaxanthin is as a bait additive for salmonids, and the increasing production of salmonids is also driving demand for astaxanthin. Salmon have a bright red coloration due to the intake and accumulation of astaxanthin, and a study conducted in Norway in 2000 showed that the growth and survival of Atlantic salmon fry was closely related to the astaxanthin content of the bait, with the fish being more likely to survive if the bait contained < 5.3 mg/kg of astaxanthin, than if the bait contained < 5.3 mg/kg. If astaxanthin in the bait was < 5.3mg/kg, the fry did not grow normally, while when astaxanthin was > 5.3mg/kg, the fry did not grow normally. When astaxanthin > 5.3mg/kg, the fry not only maintained normal growth, but also showed a significant increase in lipid content, while if astaxanthin < 1mg/kg, the survival rate dropped significantly to 20%, compared to the 90% survival rate of the control. Therefore, researchers have suggested that astaxanthin may have vitamin A activity in these species (Christiansen et al., 1995). Astaxanthin is particularly important for some farmed fish species that are unable to absorb other carotenoids, and studies have shown that astaxanthin should be maintained at a minimum level of 5 mg/kg of bait as an essential nutrient in order to maintain normal physiological functioning of the farmed species and to maintain the vibrant color of the meat (Lorenz and Cysewski, 2000).

 

2 . 1 . 2 Sea bream

Sea bream are often sold at high prices if they have a bright red coloration on their skin. It has been shown that this bright color is mainly caused by astaxanthin, and if the amount of astaxanthin in the bait is lowered, the color becomes significantly lighter. Experiments have shown that if other carotenoids such as carotenoids, zeaxanthin, lutein and keratine are added to the bait, it does not have a significant effect on the skin, and then due to the insufficient intake of astaxanthin and the inability of sea bream to convert the other carotenoids into astaxanthin, the original color of astaxanthin slowly disappears from the skin due to metabolic effects and secretion. It has also been shown that astaxanthin in the form of astaxanthin lipids is more easily absorbed than free astaxanthin molecules (Nakazoe et al., 1984).

 

2 . 1 . 3 Ornamental fish (ornamentalfish)

The vibrant colors of tropical ornamental fish are due to the presence of carotenoids in the fish themselves. These colors are not only critical for species identification and mating signals, but also play a vital role in the physiology of fish, which naturally consume carotenoids from algae, corals, and other carotenoid-containing foods.

One of the biggest challenges facing the tropical fish industry today is how to maintain their naturally vibrant coloration in nature, and many companies have had great success in breeding tropical fish, but ultimately failed due to the inability to maintain the original coloration of the fish when they are sold in the marketplace. A great deal of research has been carried out on this subject and it has been concluded that the only way to maintain the color of tropical fish is to add astaxanthin to the bait during feeding, especially from astaxanthin-rich red algae.

 

Studies have shown that the addition of 30 mg/kg of astaxanthin to bait in large-scale production resulted in a significant improvement in the coloration of most species. In a recently published study, the addition of 100 mg/kg astaxanthin to the bait of some ornamental fish species resulted in a significant improvement in skin coloration in most species after one week, and in some species, even a significant increase in growth rate. Although the amount of astaxanthin added in the experiment was on the high side, most companies prefer to use this method to rapidly improve the color of ornamental fish before selling them.

 

2 . 1 . 4 Other farming industries

In addition to aquaculture and ornamental fish farming, astaxanthin also has important applications in other aquaculture industries. For example, the addition of astaxanthin-containing Rhodococcus erythropolis powder to poultry feed resulted in a significant reddening of egg yolks. In another study, the addition of naturally occurring astaxanthin to chicken feed resulted in a significant increase in astaxanthin content in various tissues of the chickens, an improvement in the appearance of the chickens' color, and a significant increase in the hatchability of the eggs (Elwinger et al., 1997). Similarly, a lack of astaxanthin in shrimp bait resulted in blue syndrome, which disappeared after 4 weeks of supplementation with 50 mg/kg of astaxanthin in the bait. Analyses showed a 3-fold increase in astaxanthin content in shrimp tissues (Menasveta, 1993). Astaxanthin has been approved as a feed additive in many countries.

 

3 Medicinal and healthcare effects of astaxanthin

3 . 1 Antioxidant properties of astaxanthin

The human body produces a large number of free radicals during metabolism. In addition, adverse environmental conditions such as pollution, smoking, exposure to harmful chemicals, and exposure to ultraviolet rays increase the production of free radicals in the human body. Free radicals are also produced by phagocytes during the body's immune response, and some nitrogen-containing compounds such as N2 O and N2 O3 are also harmful to the human body. In addition, some nitrogen-containing compounds such as N2 O and N2 O3 are also harmful to the human body. These free radicals can easily react with surrounding macromolecules such as DNA, RNA, carbon and water compounds, and lipids to cause damage to these macromolecules, which can lead to serious consequences for the organism. The human body is constantly under attack by free radicals. This state is known as oxidative stress, which can lead to a variety of diseases: aging, Meniere's syndrome, atherosclerosis, bacterial meningitis, cerebrovascular disease, retinal plaque deterioration, Parkinson's syndrome, visual meningitis, neurological disorders, and many others.

 

Because the human body is constantly attacked by free radicals, mechanisms have evolved to neutralize free radicals and prevent disease. Although some enzymes with reparative properties can eliminate free radical damage, antioxidants, as a means of neutralizing these free radicals before they can cause damage, are also important. Antioxidants are also important as a mechanism to neutralize free radicals before they cause damage, which is important for supporting life and preventing disease. Since antioxidants can effectively neutralize free radicals, they can not only alleviate these diseases, but can even prevent them from occurring. Many chemicals have antioxidant properties, such as vitamin C, vitamin E and carotenoids. In vitro studies have shown that astaxanthin is at least 10 times more antioxidant than beta-carotene and 80 - 550 times more antioxidant than vitamin E. Astaxanthin has the ability to cross the boundary between vitamin C and vitamin E. At the same time, astaxanthin is able to cross the lipid/protein bilayer of biological membranes to realize its antioxidant function.

 

3 . 2 Anti-cancer effects of astaxanthin

As astaxanthin is a very active antioxidant, it can effectively remove free radicals in the body, inhibit the growth of tumors, so it can effectively prevent or slow down cancer, improve immunity, and even regulate the activity of some of the genes, inhibit the metastasis of malignant tumors. Chew (1999) used mice to study the activity of astaxanthin, keratin yellow and β - carotene against breast cancer, the results show that among the above three astaxanthin has the highest tumor inhibition rate and has a certain quantitative effect relationship, in addition, researchers also measured the three kinds of carotene in the transformation of tumor cells in the peroxidase activity, but also astaxanthin has the best activity, while keratin yellow is not effective. Astaxanthin was also found to be the most active, while Keratin was ineffective. Similar results to chew were obtained in the tumor inhibition of astaxanthin on bladder cancer in mice, and Tanaka (1994) showed that astaxanthin could also effectively inhibit carcinogens such as aflatoxin, chloroform, and 4-nitro-quonoLine-1-oxide. Recently, researchers have proposed an anticancer mechanism for astaxanthin, and it has been suggested that astaxanthin can be used as an antioxidant in the treatment of cancer. Recently, researchers have proposed the anti-cancer mechanism of astaxanthin, that is, it is related to the stability of the cell membrane and the gene promoting the gap junction protein conexin-43, which regulates cell-to-cell communication by altering the amount of conexin-43, thus improving the balance between cells and maintaining normal cell function. In addition, a study in mouse liver cells showed that astaxanthin induced the synthesis of xenobiotic metabolizing enzymes, a process that has also been implicated in the prevention of cancer (Gradeletetal, 1996). Natural killer (NK) cells play an important role in the fight against cancer and the inhibition of tumor metastasis, and Kurihara (2002) concluded that astaxanthin can inhibit tumor metastasis by inhibiting the damage to the anti-tumor capacity of NK cells caused by the adverse environment through its antioxidant effects.

 

3 . 3 Cardiovascular diseases

Low-density lipoprotein (LDL) is known as the "bad" lipoprotein, so the cholesterol in LDL is also known as the "bad" cholesterol, whereas in contrast, the cholesterol in HDL is also known as the "good" cholesterol. good" cholesterol. The higher the concentration of LDL, the higher the risk of atherosclerosis, which damages the walls of the arteries, and the thinning of the blood vessels due to platelet deposits, which ultimately impede the flow of blood through the arteries, leading to heart disease and stroke. On the other hand, a higher level of HDL in the blood decreases the risk of coronary artery disease, thus preventing atherosclerosis. The researchers are also convinced that atherosclerosis is related to the oxidation of LDL. Epidemiologic and clinical data suggest that increased dietary intake of antioxidants may protect against cardiovascular disease.

 

In the last decade, the preventive effects of various carotenoids on cardiovascular disease have been reported in the literature. In these studies, attention has been focused on the effects of carotenoids on cholesterol levels in different lipoproteins. Murillo (1992) showed that astaxanthin intake significantly reduced blood LDL levels in rats, whereas other carotenoids, including β-carotene, did not have a significant effect on LDL.7 The effects of dietary supplementation with vitamin A, vitamin E, β-carotene, and other carotenoids have been shown to be beneficial in the prevention of cardiovascular disease. Dietary supplementation with vitamin A, vitamin E, beta-carotene, and other carotenoids may reduce the likelihood of LDL oxidation. Because astaxanthin is transported in VLDL, LDL, and HDL in the blood, Miki (1998) demonstrated that astaxanthin protects cholesterol in LDL from oxidation in vitro, thus indirectly demonstrating that astaxanthin protects against the development of atherosclerosis. A final reason for astaxanthin's ability to alter LDL cholesterol and HDL cholesterol levels is that Murillo (1992) used animal studies to observe that dietary supplementation with astaxanthin increased blood levels of HDL, and that high levels of HDL were negatively correlated with the incidence of heart disease, while lower levels of LDL and lower LDL/HDL ratios were associated with reduced heart disease. On the other hand, lower levels of LDL and lower LDL/HDL ratios are associated with a lower chance of heart disease. In one trial, it was demonstrated that subjects taking 3.8mg or 19mg of a drug derived from HDL per day were more likely to have a heart attack. In one experiment, it was demonstrated that subjects who received either 3.8 mg or 19 mg of astaxanthin from red algae per day were analyzed over a period of time and showed significant reductions in both LDL and LDL/HDL ratios.

 

3 . 4 Astaxanthin and immune function

Because immune cells communicate with each other through receptors distributed on the cell membrane, immune cells are very sensitive to oxidative adversity and free radical damage to the cell membrane. During immunization, some phagocytic activities release free radicals, which can rapidly damage the cell membrane of immune cells if they are not neutralized in time in the body. It has been observed in many aquatic animals that astaxanthin can increase the immune function and resistance to disease. In the case of salmon, for example, astaxanthin is essential for the normal development and survival of juvenile fish, so some researchers believe that astaxanthin is equivalent to the vitamins in salmon. Astaxanthin has been shown to significantly improve the immune system of mammals in both ex vivo and in vivo assays using a number of model animals. jyonouchi et al. (1991) found that astaxanthin stimulated the production of antibodies in splenocytes in an ex vivo assay of mouse splenocytes, and a further study found that this stimulatory effect was mediated at least as much by the stimulation of antibodies as by the stimulation of, in particular, the T-helper cells. -Jyonouchi et al. (1994) found that astaxanthin partially restored the decline in humoral immunity caused by aging. Since lactating animals cannot convert astaxanthin to vitamin A, the immunomodulatory function of astaxanthin is independent of vitamin A activity (1991). Astaxanthin was also found to enhance immunoglobulin production in an in vitro assay of human blood cells (Jyonouchi et al., 1995). In addition, in a preliminary human trial, astaxanthin (8 mg) administered five times daily for 3 weeks significantly reduced gastritis in all patients, although bacterial tests remained positive (Wang et al., 2000).

 

3 . 5 Astaxanthin and neurological disorders

The nervous system, including the brain, spine, and peripheral nervous system, is rich in unsaturated fatty acids that are easily oxidized and in iron ions, which are highly oxidizing. The high levels of unsaturated fatty acids, strong aerobic metabolic activity, ample contact with blood vessels, and high levels of iron ions make neural tissues particularly susceptible to oxidant damage. There is considerable evidence that oxidative adversity is a pathogenetic mechanism, or at least an accessory factor, in a number of neurodegenerative diseases. A number of in vitro studies have shown that dietary intake of antioxidant vitamins and carotenoids protects against oxidative stress. Numerous in vivo and clinical studies have demonstrated that dietary supplementation with fat-soluble antioxidants can help combat neurological disorders, and a study by Tso (1996) and others demonstrated that astaxanthin crosses the mammalian blood-brain barrier more readily than other antioxidants, and thus astaxanthin may be expected to extend its antioxidant capacity to the brain. Since astaxanthin's antioxidant capacity far exceeds that of vitamin E and β-carotene, it is a candidate for the treatment of neurological disorders and Meniere's syndrome.

 

3 . 6 Other protective effects of astaxanthin

In addition to the above medicinal and healthcare effects, a large number of studies have shown that astaxanthin also has anti-inflammatory, detoxification, promotes liver function, protects the mitochondria in cells, protects the eyes, protects the skin, protects against light, and improves the health of cells, etc. Many tissues and organs are subjected to free radicals due to the physiological functions of the tissues and organs that are frequently exposed to free radicals or generate large amounts of free radicals during metabolic processes. Since astaxanthin is a very strong antioxidant and can easily cross the blood barrier to reach all tissues and organs, and since antioxidants must be in close contact with the tissues and organs to be protected in order to achieve their protective effects, many questionnaires and medical tests have demonstrated the above effects of astaxanthin (Guerin, 2002).

 

4 Commercialization of astaxanthin

Since animals are not able to synthesize astaxanthin on their own, and most of them are not able to convert other carotenoids into astaxanthin, astaxanthin has to be consumed in the diet. In 2000, the market for astaxanthin was estimated to be $200 million per year, mainly for aquaculture but also as a health product. The current price of astaxanthin is about 2500 $/kg, of which >95% is chemically synthesized, mainly from the Swiss company Hoffmann-LaRoche. As consumers increasingly prefer products of natural origin, there is a potential market for the production of natural astaxanthin using microorganisms.

Currently, the natural sources of astaxanthin are crustaceans, yeasts and microalgae, and due to the low content in crustaceans and fungi, the content of the product is in the range of 0.15% to 0.5%. 15% ~ 0.4%, while many green algae have low levels of astaxanthin. 4%, but many green algae can accumulate large amounts of carotenoids under specific culture conditions, so the production of natural astaxanthin by microalgae has a broad prospect and has aroused great interest among researchers from various countries. (Margalith, 1999), chlorococcumsp. (zhang&Lee, 1997) and chlorellavulgari. Especially, red algae, whose dry basis content can reach 8%, is the organism with the highest astaxanthin content discovered so far, and it is considered as a green algae with the most promising development prospect, which has been commercially exploited in some countries.

 

Haematococcus pluvialisFlotow belongs to the phylum chlorophyta, order volvocales, family Chlamydomonadaceae (Chen Feng, Jiang Yue, 1999). Chlamydomonas reinhardtii is a unicellular freshwater alga. Under normal growth conditions, the cells are green in color, ellipsoidal to ovoid, with two equal flagella at the front of the cell, and the cell is covered by a thin cell wall. Under certain growth conditions, free-living spores lose their ability to move and turn into dormant spores, which turn red due to the large accumulation of astaxanthin. In the process of transformation from mobile to dormant spores, there are obvious morphological changes, with the cell wall thickening, the flagellum disappearing, and the cell diameter increasing. The content of carotenoids in the different growth periods of Rhodococcus spp. was not only different, but also its composition was very different. In the green free-swimming spores, lutein accounted for 75% ~ 80% of the total carotenoids, β-carotene 10% ~ 20%, and the cells contained very little, if any, astaxanthin. The cells contained little or no astaxanthin, whereas in the red dormant spores, more than 80% of the total amount of astaxanthin was present. Astaxanthin in red algae exists mainly in the form of astaxanthin esters, especially in the form of monoesters, and is therefore comparable to astaxanthin from other sources. The bioavailability of astaxanthin in red algae is much higher than that of other sources. Therefore, in recent years, many countries have carried out research on the production of astaxanthin by large-scale commercial cultivation of red algae.

 

According to the life history of the red algae and the pattern of astaxanthin accumulation in the cells, the production process is generally divided into two phases: the first phase is the biomass cultivation phase, in which the zoospores are cultivated in near-optimal growth conditions, and when the biomass reaches a sufficient density, it is transferred to the second phase, where the zoospores are cultivated in unfavorable conditions such as strong light, nutrient salt deficiency, increased salinity, and temperature, etc., and are induced to grow in a large amount of red dormant zoospores for 1.5 to 1.5 hours. After a few days of induction, most of the swimming spores were transformed into red dormant spores and accumulated a large amount of astaxanthin (1.5%w/w - 4.5%w/w). After a few days of induction, most of the free spores were transformed into red dormant spores and accumulated a large amount of astaxanthin. 0%w/w, can be harvested. The bioavailability of astaxanthin is very limited due to the thick cell wall of the dormant spores of Rhodococcus erythropolis (Sommeretal., 1991). Although it is possible to extract astaxanthin from the dormant spores to improve astaxanthin bioavailability, this is not practical in large-scale production, and therefore mechanical or physical methods are used to break up the cells before application.

 

Although the culture and production of Rhodococcus spp. is theoretically very simple and the culture medium is also simple, commercial production of Rhodococcus spp. is limited by the fact that the medium is very neutral and the growth rate is relatively slow, and is therefore easily contaminated by other fast-growing micro-algae, protozoa and fungi (Lorenz and cysewski, 2000). Therefore, large-scale culture of Rhodococcus erythropolis requires a high degree of skill and care, and the biomass of the algal broth in current commercial production is relatively low (Lee- and zhang, 1999). There are two ways to increase the biomass, either by using a closed photobioreactor in the first stage (Guerin, 2002), or by using mixotrophic culture in the first stage, as Rhodococcus erythropolis can be heterotrophic (Chen, 1996; Hata, 2001). In addition, since many green algae are capable of accumulating carotenoids, some researchers have also conducted screening for other fast-growing species that can accumulate astaxanthin in large quantities (orosaetal, 2000; zhangetal, 1997).

 

5 Conclusion

Astaxanthin is a very powerful antioxidant and has great potential for use in feed additives and pharmaceuticals. At present, important progress has been made in promoting the physiological and environmental factors of astaxanthin biosynthesis in red algae. Although there are some technical difficulties in large-scale cultivation technology, with the continuous progress of bioreactors, the continuous improvement of cultivation technology, the continuous discovery of new algal species, especially the identification of astaxanthin biosynthesizing enzymes and breakthroughs in gene technology, the use of microalgae in the production of natural astaxanthin is a very promising industry. The production of natural astaxanthin from microalgae is a very promising industry.