What Is Rhodiola Rosea Polysaccharide?

Rhodiola as a perennial herb or subshrub in the family Crassulaceae has tonic, invigorating and anti-stress effects similar to those of ginseng and Siberian ginseng [1-2]. Currently, 96 species of Rhodiola are known worldwide, most of which are distributed in the limestone and granite mountains of the northern hemisphere at an altitude of 3,500–5,000 m in the alpine zone. A small number grow at an altitude of about 2,000 m in alpine meadows, undergrowth in forests or near rocks along ditches[3]. The species of Rhodiola in China include 73 species, 2 subspecies, and 7 varieties, accounting for about 85% of the world's Rhodiola resources. They are mainly distributed in the southwest, northwest, north China, and northeast China, with 55 species on the Qinghai-Tibet Plateau[4].

The main medicinal part of Rhodiola rosea is the rhizome, which contains various active ingredients such as polysaccharides, glycosides, tyrosol, rhodioloside, phenols, flavonoids, amino acids, coumarins, organic acids, mineral elements, steroid compounds and alkaloids[5]. Rhodiola polysaccharides have the effects of anti-fatigue, anti-aging, anti-virus, hypoglycemic, immune regulation, antibacterial, antioxidant, hypoglycemic, regulation of glycolipid metabolism, anti-damage, anti-bad stimulation, etc.[6-10].

1 Chemical composition of Rhodiola polysaccharides

Luo Lipan et al. [11] and Teng Fei et al. [12] used gas chromatography-mass spectrometry to analyze the monosaccharide composition and ratio of Rhodiola polysaccharides extracted with water and alkali. The results showed that the monosaccharides of crude polysaccharides extracted from Rhodiola from different origins were all composed of rhamnose, mannose,

arabinose, glucose and galactose, but the proportions of the monosaccharides that make up the polysaccharides are different; the monosaccharide composition of the crude polysaccharides extracted from Rhodiola rosea from different origins is different. Therefore, the composition and content of the polysaccharides in Rhodiola rosea from different origins vary greatly, and the differences in the composition of the monosaccharides may lead to certain differences in biological activity. Jiang Kainian et al. [13] found that rhodiola polysaccharides contain uronic acid, which is a water-soluble acidic heteropolysaccharide. The weight-average molecular weight of the polysaccharide was measured to be 27.876 kDa by high-performance gel permeation chromatography.

2 Extraction and purification methods for Rhodiola polysaccharides

2.1 Extraction of polysaccharides

Currently, known polysaccharide extraction methods include water extraction, acid extraction, alkali extraction, protease hydrolysis, supercritical fluid extraction, ethanol extraction, ultrasound-microwave extraction, ultrasound-assisted extraction, microwave-assisted extraction, etc. [14-19]. Common methods for extracting rhodiola polysaccharides include water extraction, microwave-assisted extraction, and ultrasound extraction. The water extraction method does not damage the polysaccharide structure. It has the advantages of simple equipment, low cost, and no pollution, but it also has the disadvantages of being time-consuming and requiring multiple extractions [20].

Bona Nina et al. [21] found that at 80 °C and a material-to-liquid ratio of 1:30 g/mL, the extraction rate of Rhodiola polysaccharides using the water extraction method was 5.76% after 2.5 h of extraction. Microwave-assisted extraction uses microwaves to irradiate the solvent and penetrate through the cell wall to the inside of the cell, increasing the temperature and pressure inside the cell, rupturing the cell and releasing the active ingredients inside the cell, which are then dissolved by the solvent and extracted from the solvent to achieve the extraction effect [22]. Microwave-assisted extraction has the advantages of being environmentally friendly, high purity of the product, short extraction time and high solvent selectivity.

 However, it is not easy to extract on a large scale due to equipment limitations. Sun Ping et al. [23] used microwave-assisted water extraction and alcohol precipitation to extract polysaccharides from Rhodiola crassifolia. The polysaccharide content in the Rhodiola extract was measured to be 3.9%. Ultrasonic extraction uses cavitation, mechanical, and thermodynamic effects to extract polysaccharides. It has the advantages of not destroying physiological activity, being time-saving, and having a high extraction rate. However, it is not suitable for large-scale extraction due to equipment limitations [20]. Wang Li et al. [24] used an ultrasonic extraction method to extract polysaccharides from Rhodiola sachalinensis at a temperature of 69 °C, an ultrasonic power of 240 W, and a material-to-liquid ratio of 1:30 g/mL. The extraction time was 39 min, and the extraction yield was 4.305%.

2.2 Purification of polysaccharides

Polysaccharides extracted from plants usually contain a large amount of impurities, mainly proteins. The large amount of charge carried by the protein causes the polysaccharide to adsorb more impurities. In order to obtain a polysaccharide with a higher purity, the protein must be removed. At present, the methods for removing protein include the Sevage method, the trichloroacetic acid method, the enzymatic hydrolysis method, and the trifluoro-trichloroethane method [25]. The Sevage method is the most commonly used method for removing free protein. Compared with the trifluoroacetic acid method and the enzymatic hydrolysis method, the Sevage method can retain more polysaccharide components. In addition, the Sevage reagent is relatively inexpensive, easy to store, and convenient to prepare [26]. Ma Yinghui et al. [10] used the Sevage method to remove protein impurities from the crude polysaccharides of Rhodiola rosea from Changbai Mountain. The content of purified Rhodiola rosea polysaccharides was determined using the phenol-sulfuric acid method, and the optimal purification conditions were screened. Under the optimal purification conditions, the polysaccharide retention rate of the purified Rhodiola rosea polysaccharides was 68%.

3 Biological functions of rhodiola polysaccharides

3.1 Antioxidant

The antioxidant mechanism of polysaccharides is characterized by multiple pathways, multiple targets, and multiple effects. The antioxidant effect of polysaccharides is mainly achieved through three pathways: eliminating free radicals, regulating the activity of antioxidant enzymes, and antagonizing nitric oxide [27]. Xu et al. [28] used methylation to prove that Rhodiola polysaccharides can scavenge DPPH, hydroxyl and superoxide anion radicals, and maintain the body's free radical levels stable. Zhang Yu [29] conducted a comparative study of the active substances in Rhodiola rosea polysaccharides, and found that Rhodiola rosea polysaccharides have a strong DPPH · scavenging effect. Lin Xiaoyue et al. [30] used an in vitro antioxidant model to demonstrate that rhodiola polysaccharides have a certain scavenging capacity for OH ·, DPPH · and ·O2-. Guo Meng [31] tested the scavenging capacity of rhodiola polysaccharides for hydroxyl radicals and superoxide anions and found that the antioxidant capacity of rhodiola polysaccharides increased with increasing polysaccharide concentration.

3.2 Anti-injury

Xu Yao [32] used a model of acute liver injury induced by carbon tetrachloride in mice to investigate the hepatoprotective effect of Rhodiola rosea polysaccharide liposomes. The results showed that the liver hydrogen peroxidase, superoxide dismutase activity and reduced glutathione content increased in the liver tissue, and the activities of serum glutamic pyruvic transaminase and glutamic oxaloacetic transaminase and malondialdehyde content in liver tissue decreased. Song Xiaoyong et al. [33] found that the addition of Rhodiola polysaccharides enhanced the activities of superoxide dismutase and glutathione peroxidase in the lung tissue of rats, and reduced the levels of reactive oxygen species and malondialdehyde, indicating that Rhodiola polysaccharides have an anti-damaging effect on the lung cells of mice exposed to second-hand smoke. Rhodiola polysaccharides also have a certain protective effect against damage caused by radiation. Huang Bingyang et al. [34] used rhodiola polysaccharides to intervene in UVA-irradiated rats to observe the protective effect of rhodiola polysaccharides. The results showed that rhodiola polysaccharides can repair damage caused by UVA irradiation.

3.3 Regulate glycolipid metabolism

Ling Yuesheng et al. [9] used streptozotocin + high-fat diet to induce a mouse diabetes model, and compared the liver glycogen content of mice at different polysaccharide concentrations. The results showed that rhodiola polysaccharides can promote glycogen synthesis and increase glucose utilization. Wang Suhua et al. [35] used a model of male rats intervened with rhodiola polysaccharides after intravenous injection of 4-hydroxy-2-oxopyrimidine to detect fasting blood glucose in diabetic rats and found that rhodiola polysaccharides can reduce lipid oxidative damage in pancreatic tissue, thereby reducing blood glucose in rats. Ding Wenfang [36] injected a certain amount of Rhodiola polysaccharide into the abdominal cavity of diabetic mice for 3 consecutive weeks, and detected the fasting tail vein blood glucose. It was found that Rhodiola polysaccharide can lower blood glucose levels. Shuihao Jie [37] used rhodiola polysaccharide to intervene in a diabetic rat model and measured the rats' fasting blood glucose, insulin, liver glycogen and muscle glycogen, and found that rhodiola polysaccharide achieved a hypoglycemic effect by increasing insulin, glycogen and muscle glycogen levels. Mao [38] used rhodiola polysaccharides to gavage mice and found that rhodiola polysaccharides have a high blood glucose and blood lipid lowering effect.

3.4 Antibacterial and antiviral

Qi Xiaoni et al. [39] investigated the inhibitory effect of Rhodiola polysaccharides on Staphylococcus aureus, Escherichia coli and Bacillus subtilis and found that Rhodiola polysaccharides have certain antibacterial activity and specific selectivity for the inhibition of different bacterial species. Zhang Yong et al. [40] found that rhodiola polysaccharides can effectively inhibit cell damage and virus reproduction caused by CVB3 virus. Sun Fei et al. [8] used rhodiola polysaccharides to intervene in a viral myocarditis model, and analyzed the activity of antioxidant enzymes through immunological indicators. They found that rhodiola polysaccharides can repair damage to cell membranes caused by the virus, enhance the activity of NK cells in the spleen, and increase the stimulation index of spleen lymphocytes. Yan Qi et al. [41] used sulfated alpine rhodiola polysaccharides to treat mice infected with CVB5 virus. After the mice took sulfated alpine rhodiola polysaccharides, the blood superoxide dismutase activity increased significantly, the damage of free radicals to body cells was reduced, and the function of the heart muscle and various organs was restored and improved.

4 The application of Rhodiola polysaccharides in animal production

4.1 Improving production performance

Adding polysaccharides to the diet can promote nutrient absorption in the animal's intestines, inhibit the growth of harmful intestinal flora, reduce the feed-to-weight ratio, improve feed utilization efficiency, and promote animal growth. Li Jing et al. [42] found that adding a compound plant polysaccharide to the diet of weaned piglets can significantly increase the daily weight gain of normal weaned piglets and reduce the feed conversion ratio. For thin and weak weaned piglets and fattening piglets, a compound plant polysaccharide can significantly increase their daily weight gain and reduce the feed conversion ratio, with no significant effect. Cheng [43] added rhodiola polysaccharides to the diet of red swamp crayfish and fed it for 8 weeks. It was found that the red swamp crayfish gained weight, and the feeding efficiency, survival rate, total blood cell count and number of hyaline cells were significantly higher, indicating that ingestion of a diet containing rhodiola polysaccharides can improve the growth performance of crayfish.

4.2 Enhancing immunity

Rhodiola polysaccharides have pharmacological functions such as antibacterial and antioxidant properties, which can improve the immunity and antioxidant function of animals. Luo Wenzhe et al. [44] found that rhodiola polysaccharides can increase the proportion of the CD4+ subset and the CD4+/CD8+ ratio in an aged model group of mice, thereby increasing the serum interleukin level and immunoglobulin G content of aged mice, returning them to normal levels. Cai et al. [45]  designed in vitro and in vivo experiments to find that Rhodiola polysaccharides can promote the production of interleukin-2, tumor necrosis factor-alpha (TNF-α) and interferon-gamma (IFN-γ) in the serum, and increase the CD4+/CD8+ ratio of peripheral blood T lymphocytes in mice carrying tumors. Park et al. [46] found in an in vitro experiment that Rhodiola polysaccharides can significantly increase the number of mouse specific antibody-secreting cells. In vivo experiments showed that Rhodiola polysaccharides at a certain concentration can enhance the phagocytic function of macrophages and reduce the activity of interleukin. Li Haixia et al. [47] used intraperitoneal and axillary inoculation of U14 cells to establish a mouse U14 ascites and solid tumor model, and demonstrated that purified Changbai Mountain Rhodiola polysaccharides can significantly promote mouse mouse macrophage proliferation and increase the secretion of TNF-α and IL-1β by macrophages. Rhodiola polysaccharides can inhibit tumor growth in U14 model mice with cervical cancer, and the mechanism is related to improving the immune system of mice.

4.3 Improves stress resistance

High-altitude environments can easily cause animals to have a stress response. Rhodiola polysaccharides have the effect of resisting cold, hypoxia, and adverse stress, and can effectively improve the stress caused by animals in high-altitude environments. Liu Yongqi et al. [48] showed that cold stress and high-altitude hypoxia can cause a decrease in the thymus index and spleen index of mice, as well as a decrease in the proliferation capacity of spleen lymphocytes. The use of Rhodiola rosea to gavage mice in a hypoxic high-altitude environment can slow down the abnormal decrease in the thymus index and spleen index and the abnormal decrease in the proliferation capacity of spleen lymphocytes, indicating that Rhodiola rosea can reduce the effects of the high-altitude environment on animals.

Ren Weihe[49] used Rhodiola rosea to treat mice for 10 days and found that it could improve the mice's tolerance to hypoxia, inhibit the oxidative stress in heart, lung and brain tissues caused by hypoxia, and alleviate the damage caused by hypoxia. Zhang Chen et al. [50] added crude powdered dried alpine rhodiola to the diet of tilapia raised in a low-temperature environment and found that the tilapia's ability to withstand low temperatures was significantly enhanced. Shi Xiaofeng [51] observed the hypoxia and cold tolerance of mice after they had been given compound Rhodiola extract orally for 10 consecutive days, and found that Rhodiola polysaccharides have obvious anti-stress capabilities. Therefore, adding Rhodiola polysaccharides to the diet can help animals overcome the harsh conditions of hypoxia and low temperatures in high-altitude environments.

4.4 Improve reproductive ability

During semen cryopreservation, exposure to light and high oxygen levels will generate a large number of free radicals, which will damage cell membranes and sperm[52]. Prolonged storage will cause lipid peroxidation in boar semen, a decrease in superoxide dismutase activity, and an increase in malondialdehyde content. It is necessary to add antioxidant components during semen cryopreservation[53]. Rhodiola polysaccharides can protect the quality of sperm in semen during the freezing and thawing process. Cao et al. [54] found that extender supplemented with rhodiola polysaccharides can improve the activities of superoxide dismutase, lactate dehydrogenase and glutamate oxaloacetate transaminase after semen is frozen and stored, indicating that rhodiola polysaccharides can give bull sperm stronger cryopreservation ability during the freezing and thawing process.

He Tao et al. [55] added different concentrations of rhodiola polysaccharides to the freezing dilution, and found that rhodiola polysaccharides can significantly improve the viability, plasma membrane integrity, acrosome integrity, mitochondrial activity and integrity of rooster sperm after freezing and thawing, indicating that rhodiola polysaccharides can improve the post-freezing viability of poultry sperm. Xilimeng et al. [56] measured the viability, acrosome integrity, plasma membrane integrity, mitochondrial activity, and glutathione (GSH) and malondialdehyde (MDA) levels of frozen and thawed goat sperm. They found that the addition of rhodiola polysaccharides to the dilution solution significantly improved the quality and antioxidant capacity of frozen goat sperm.

Chen Xiaoying et al. [57] found that rhodiola polysaccharides can effectively protect sperm stored at low temperatures and improve the quality of thawed sperm. Rhodiola polysaccharides can protect the quality of reproductive cells and improve their developmental capacity. Yu Dongdong et al. [58] cultured spermatogonial stem cells on a layer of Sertoli cells and found that the addition of rhodiola polysaccharide to the culture layer significantly increased the number of spermatogonial stem cells cultured in vitro. The addition of rhodiola polysaccharide to an in vitro culture system with Sertoli cells as the trophoblast layer significantly promoted the proliferation of spermatogonial stem cells. Xu Li et al. [59] found that adding an appropriate concentration of rhodiola polysaccharides can increase the nuclear maturation rate and promote cytoplasmic maturation during the maturation process of pig oocytes. Therefore, in the animal production process, rhodiola polysaccharides can improve animal reproductive capacity by promoting the development of germ cells.

5 Conclusion

Rhodiola rosea polysaccharides can be extracted using various methods. Due to the particularity of its living environment, the chemical composition of rhodiola rosea polysaccharides is different from that of other plant polysaccharides, and it has special pharmacological effects. Rhodiola polysaccharides have functions such as resisting cold, hypoxia, adverse stimuli, injury, lowering blood sugar, regulating glycolipid metabolism, resisting viruses and regulating immunity. Rhodiola polysaccharides have a regulatory effect on the adverse reactions of animals in high-altitude cold areas such as hypoxia, and can to a certain extent replace antibiotics and have therapeutic effects on animal diseases.

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