[Frontiers in Bioscience S3, 372-384, January 1, 2011]

Roles of phytochemicals in amino acid nutrition

Xiangfeng Kong1, Guoyao Wu1-3, Yinlong Yin1

1Hunan Engineering and Research Center of Animal and Poultry Science and Key Laboratory for Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, the Chinese Academy of Sciences, Changsha, Hunan, China 410125, 2Department of Animal Science, Texas A&M University, College Station, TX, USA 77843, 3State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China 100193


1. Abstract
2. Introduction
3. Amino Acid composition in typical Chinese herbs 4. Effects of dietary supplementation with Chinese herbal powder on ileal digestibilities of amino acids in weaned piglets
5. Effects of dietary supplementation with Acanthopanax senticosus extracts on ileal digestibilities of amino acids in weaned piglets
6. Effects of dietary supplementation with Astragalus polysaccharide on ileal digestibilities of amino acids in weaned piglets
7. Effects of dietary supplementation with glycyrrhetinic acid on endogenous arginine provision in early-weaned piglets
8. Effects of steroidal saponin from Yucca schidigera extract (BIOPOWDER) on intestinal arginase activity
9. Summary and perspective
10. Acknowledgements
11. References


Chinese herbal medicine (CHM) is often used as dietary supplements to maintain good health in animals and humans. Here, we review the current knowledge about effects of CHM (including ultra-fine Chinese herbal powder, Acanthopanax senticosus extracts, Astragalus polysaccharide, and glycyrrhetinic acid) as dietary additives on physiological and biochemical parameters in pigs, chickens and rodents. Additionally, we propose possible mechanisms for the beneficial effects of CHM on the animals. These mechanisms include (a) increased digestion and absorption of dietary amino acids; (b) altered catabolism of amino acids in the small intestine and other tissues; (c) enhanced synthesis of functional amino acids (e.g., arginine, glutamine and proline) and polyamines; and (d) improved metabolic control of nutrient utilization through cell signaling. Notably, some phytochemicals and glucocorticoids share similarities in structure and physiological actions. New research findings provide a scientific and clinical basis for the use of CHM to improve well-being in livestock species and poultry, while enhancing the efficiency of protein accretion. Results obtained from animal studies also have important implications for human nutrition and health.


Chinese traditional veterinary medicine (CTVM) has been practiced for several thousand years on the basis of a five-element (phase) theory and the principle that every healthy organism is in a Yin-Yang balance (1). Balance is considered to be a complex interplay between body and mind, which is reflected at all levels, ranging from the biochemical component perspective to the energetic system control of the physical body. Chinese herbal medicine (CHM) is the foundation of CTVM, in which more than 80% constituents of preparations are derived from plants (2). CHM is often used to maintain good health rather than to cure illness, much in the same way as amino acid (AA), vitamin or mineral supplements are used in Western countries (3). Based on a belief that CHM is natural, safe, and of relatively low cost, global use of CHM as herbal supplements continuously increases. In recent years, animal producers and veterinarians have begun to use the herbs to improve health and growth performance of pigs and poultry (4). Here, we review the current state of knowledge about the effects of CHM (including ultra-fine Chinese herbal powder, Acanthopanax senticosus extracts, Astragalus polysaccharide, and glycyrrhetinic acid) on physiological parameters and their use as growth and health promoters. We also propose the underlying mechanisms for the beneficial effects of CHM on the basis of studies with swine, an excellent animal model for studying human nutrition and metabolism (5-9).


Amino acids (AA) play important roles in gene expression, protein synthesis, cell signaling, metabolism, physiology, and health (10-13). Therefore, as an initial step to define the mechanisms responsible for the beneficial effects of typical Chinese herbs on health and growth performance of animals, we determined the contents of AA in seventeen Chinese herbs (Table 1). The herbs included Polyporus, Radix glycyrrhizae, Radix angelicae sinensis, Radixginseng, Gold Theragran, Radix polygoni multiflori, Semen Allii Tuberosi, Radix paeoniae alba, Rhizoma atractylodis macrocephalae, Astragalus membranaceus, Radix codonopsis, Radix rehmanniae preparata, Rhizoma dioscoreae, Radix Salvia miltiorrhizae, Poria, Fructus crataegi and Acanthopanax senticosus. Results are expressed on the dry matter (DM) basis. Percentages (%) of DM in Radix glycyrrhizae (95.1) and Astragalus membranaceus (93.6) were highest, followed by Fructus crataegi (93.0), Radix paeoniae alba (92.9) and Radix angelicae sinensis (92.5). The content (%) of crude protein was highest in Semen Allii Tuberosi (26.4), followed by Radix codonopsis (16.7), Astragalus membranaceus (16.3) and Gold Theragran (16.0). The content (%) of total AA in Semen Allii Tuberosi (17.2) was highest, followed by Astragalus membranaceus (11.0), Gold Theragran (8.9) and Radix angelicae sinensis (8.2). Aromatic AA (Phe + Tyr) were most abundant (% of ingredient) in Semen Allii Tuberosi (1.2) and Astragalus membranaceus (0.9); branched-chain AA (Leu + Ile + Val) in Semen Allii Tuberosi (2.7) and Polyporus (2.1); small neutral AA (Ala + Gly) in Semen Allii Tuberosi (1.6), Gold Theragran (1.1), and Astragalus membranaceus (1.0); acidic AA + Cys + Pro (Asp + Glu) in Semen Allii Tuberosi (6.4), Astragalus membranaceus (4.3) and Radix glycyrrhizae (3.6); basic AA (His + Lys + Arg) in Semen Allii Tuberosi (3.5), Radix angelicae sinensis(3.0), and Radix ginseng (2.5); as well as hydroxy AA (Thr + Ser) in Semen Allii Tuberosi (1.6), Gold Theragran (1.0), and Astragalus membranaceus (0.9) (Table 2). The composition of AA in the Chinese herbs is largely similar to that in feeds of plant origin, which indicate that typical Chinese herbs are not unique in the composition of protein-precursor AA among plants. Other components in the herbs are likely major active components that beneficially regulate intestinal barrier integrity, absorption and metabolism of nutrients (including AA), immune function, health, and protein synthesis in animals (14, 15).


Our previous studies have demonstrated that the ultra-fine Chinese herbal (UCH) powder is safe and effective in preventing intestinal dysfunction, improving growth performance (16), as well as exerting beneficial effects on immune responses (17) and gut microbiota development (18) in weanling piglets. However, the underlying mechanisms are largely unknown. Considering that most of composition herbs in the UCH powder are commonly employed for treatment of dyspepsia and poor appetite, and because AA are not only building blocks for protein synthesis but also serve as regulators of key metabolic pathways (19-22) and the immune response (23), we hypothesized that the UCH powder may affect the digestion of dietary protein, the intestinal absorption of AA, and circulating levels of AA in weanling piglets.

There have been published studies to determine effects of the herbal powder as a dietary additive on serum concentrations and apparent ileal digestibilities (AID) of AA in piglets weaned at 21 days of age (16,24). Dietary supplementation with the herbal powder (2 g/kg) increased (P < 0.05) serum concentrations and AID of most AA by 10% - 50% and 10% - 16%, respectively (Table 3 and 4). As an indicator of improved intestinal function, AID values of calcium were also enhanced in piglets supplemented with the herbal powder. Dietary supplementation of colistin (an antibiotic as a positive control) increased serum concentrations and AID values of some AA by 8% - 44% and 10% - 15%, respectively (Table 3 and 4), in comparison with the non-supplemented group (24).

Amino acids regulate key metabolic pathways that are crucial for maintenance, health, and growth of animals (19, 20, 25-27). An increase in the amounts of nutrients (particularly AA) that enter the portal vein from the small intestine can be sufficient to promote tissue protein synthesis in piglets (13, 28). At present, it is not clear how dietary UCH-powder supplementation can improve AA digestibilities in pigs. However, it is known that the UCH powder increased the growth of beneficial Lactobacillus (e.g. Bifidobacteria and Lactobacilli) and arrested the growth of bacterial pathogens (E. coli) (18), which suggested that the UCH powder could effectively promote the development of the normal gut microbiota and healthy intestinal environment in the weaned piglets. These Lactobacillus are also beneficial for maintaining the integrity and function of the small intestine (29, 30), which then promotes the absorption and transport of AA, glucose, calcium and other nutrients across the intestinal epithelium into the portal vein (31). Furthermore, the UCH powder may affect the metabolism of nutrients (particularly AA) in the lumen of the small intestine by altering the growth and metabolism of gut microbiota, therefore resulting in changes in the amounts of AA (free and protein-bound) in the ileal digesta (32). The variation of AID values for different AA may be explained by the different actions of microbes on metabolism in the lumen of the small intestine (29, 33). Because the underlying mechanisms are likely to multifactorial, future studies are warranted to determine the effects of active components of the UCH powder on the digestion and absorption of dietary nutrients.

The UCH powder had an average granule diameter of 30 μm as a phytochemical dietary additive and was composed of Acanthopanax senticosus (AS), Astragalus membranaceus (AM), Codonopsis pilosula (COP), Crataegus pinnatifida (CRP), Salvia miltiorrhiza (SM), and chitosan (16, 17). As one of the major components in the herbal power, AS is highly effective in treating allergies (34), stress-induced pathophysiologic changes (35), and inflammation (36). The AS extract also enhances immune responses (37) and physiological development of the gut microflora (38) in weaned piglets. AM is known for its effect on stimulating energy metabolism, tissue regeneration, and immunity in the body (39). COP possesses immuno-modulatory, anti-oxidant, free-radical scavenging, and anti-ulcer activities, and is commonly employed for treatment of dyspepsia, poor appetite, and psychoneurosis (40). Traditionally, CRP has a strong anti-bacterial activity against pathogenic bacteria (41), whereas SM is mainly used for treatment of infectious and inflammatory diseases (42). In addition, dietary supplementation of chitosan improves growth performance, feed efficiency, and the immune response in weaned piglets (43). Our novel findings demonstrate that the herbal powder can enhance the digestibility of dietary protein and the intestinal absorption of AA into the systemic circulation in post-weaning pigs, therefore providing a new mechanism for its growth-promoting efficacy.


Acanthopanax senticosus (AS), a tonic and sedative Chinese herb, is well known to be highly effective in treating various diseases, which include stress-induced pathophysiologic changes (35) and inflammation (36). The AS compounds include acanthosides, triterpenic saponin, polysaccharide, flavone, senticoside, organic acids, AA, vitamins and minerals (44). Saponin may be responsible for the biological activities of AS (45). Some evidence suggests that diterpenoids and phenolic substances are biologically active ingredients in Acanthopanax species (46).

Based on the above findings, we prepared the extracts of AS by decocting the dried herb in boiling distilled water (200 g/L) for 2 h. The AS decoction were filtered, lyophilized and kept at 4 �C. The yield of extraction was 25% (w/w). Percentages of total polysaccharides, flavone and organic acids in the AS extracts were 2.94%, 0.19% and 1.04%, as determined by vitriol-anthracene ketone, rutin (47) and alkalimetrictitration (48) methods, respectively. Concentrations (g/kg) of AA in the extracts, as analyzed by high-pressure liquid chromatography (HPLC, Hitachi L-8800 Auto-Analyzer, Tokyo, Japan) method (49) were: Phe 4.11; Leu 2.32; Ile 0.67; Val 0.77; Ala 2.14; Gly 1.87; Asp 2.86; Glu 4.71; Cys 2.45; His 0.41; Lys 0.95; Arg 3.78; Thr 1.30; Ser 2.47 and Met 0.28. Our previous study indicated that the AS extracts enhanced the cellular and humoral immune responses of weaned piglets by modulating the production of immunocytes, cytokines and antibodies (37). On the basis of the foregoing, we hypothesized that dietary supplementation with the AS extracts enhances the digestibility of AA in weaned piglets.

Further studies were conducted to determine the effects of AS extracts (1g/kg) as a dietary additive on serum concentrations and AID of AA in piglets weaned at 21 days of age. Collectively, results indicate that the serum concentrations and AID of most AA in the AS extracts-supplemented group were gradually increased by 15.3% - 80.8% and 4.1% - 30.8%, respectively, in comparison with the colistin-additive group and/or control group (Table 5 and 6). These findings suggest that the AS extracts could enhance the ability of digestion and absorption of AA, which may be a potential mechanism of its growth-promoting efficacy (50).

Growth of animals is an outcome of complex metabolic transformations, including AA and glucose utilization, intracellular protein turnover and fat deposition as well as their regulation by hormones and other factors (11, 51-55). Consistent with this view, dietary supplementation with the AS extracts enhance the serum concentrations and AID of most AA in 21- to 49-day-old weaned piglets. Therefore, the AS extracts improves the digestion and absorption of dietary protein/AA, and may also directly regulate the metabolism of absorbed nutrients through signal transduction mechanisms (20, 56, 57). Because the large numbers of components in the Chinese herb make their screening and analysis extremely challenging, our findings help identify the water soluble extracts of the AS as a natural green dietary additive for promoting the healthy growth in weaned piglets.


Some polysaccharide phytochemicals can profoundly affect the immune system (58) and intestinal function (17,37). Such work raised an attractive possibility that these natural substances may be highly effective in ameliorating the problems of weaning-associated gut dysfunction and growth retardation syndrome in pigs. In this regard, it is noteworthy that polysaccharide fractions of Astragalus membranaceus and Astragalus polysaccharide (APS) have been reported to reduce fatigue, the loss of appetite, and the incidence of diarrhea in animals (47, 59-61). Additionally, there is evidence that dietary supplementation with APS can improve growth performance in early-weaned pig (62). To elucidate the underling mechanisms, we conducted a study using APS isolated from AM (37), as previously described (63). Sliced rhizomes of AM grown in Liaoning Province of China were extracted three times with boiling water. The supernatant was applied to a DEAE-Sephacel (2.6 � 100 cm) column, and bound materials were eluted with a linear gradient of 0 to 2 mM NaCl. The fractions containing carbohydrates were pooled and precipitated three times with ethanol. The resultant polysaccharide extract was dialyzed against several changes of water and then lyophilized. The final product contained 95% carbohydrate but no detectable protein or nuclear acids, as measured at 280 and 260 nm wavelengths (37). The molecular weight of the extract was approximately 3.5�103 to 1.55�106, as determined by the gel filtration method.

Testing the hypothesis that dietary APS supplementation may stimulate the digestion of dietary protein and the absorption of resultant AA, therefore improving growth performance in weaned piglets, we determined AID of AA and their serum concentrations in the piglets weaned at 21 days of age after dietary supplementation with APS. We found that addition of APS to the diet increased AID and serum concentrations of most nutritionally essential and nonessential AA (including arginine, proline, glutamate, lysine, methionine, tryptophan, and threonine) on Days 14 and 28. Circulating levels of total AA were affected by the age of pigs and treatment � time interaction (Table 7 and 8). These findings indicate that APS may ameliorate the digestive and absorptive function and regulate AA metabolism to beneficially increase the entry of dietary AA into the systemic circulation, which provide a mechanism to explain the growth-promoting effect of APS in weaned piglets (64).

Although AID of threonine and valine on Day 14 or AID of leucine, isoleucine, methionine, and phenylalanine on Day 28 did not differ between APS-supplemented pigs and the control group, serum concentrations of these essential AA were higher in APS-supplemented pigs. Because these AA cannot be synthesized in enterocytes or extra-intestinal cells of pigs (31) but can be extensively degraded by intestinal luminal bacteria (65), an increase in their serum concentrations in APS-treated pigs may result from a reduction in their catabolism by the gut microorganisms. This raised a possibility that APS may beneficially modulate the number, population, and activity of intestinal microbes to favor the entry of dietary AA into the portal circulation. We suggest that this phytochemical may be an effective, as well as a useful alternative of antibiotics in swine production. On this basis, APS can be classified as a prebiotic to replace antibiotics in swine diets.


Radix Glycyrrhizae, the root or root plus the rhizome of legume such as Glycyrrhiza uralensis Fisch., Glycyrrhiza inflat Bat. and Glycyrrhiza glabra L., is thought to possess the effects of invigorating spleen, replenishing qi (vigor), eliminating phlegm, arresting cough, clearing away heat and toxins, relieving spasm and pain, and moderating the properties of other drugs and so on (66). Modern pharmacological studies reveal that glycyrrhetinic acid (GA) is a major constituent of licorice and has many therapeutic properties, including anti-inflammatory, anti-ulcer, anti-allergic, anti-viral, hepaprotective, anti-tumor, and immumodulatory actions (67). Interestingly, some herbal extracts contain GA (a pentacyclic triterpenoid derivative of the �-type amyrin), which has a chemical structure similar to cortisol (Figure 1). Therefore, GA inhibits the activity of 11-beta- hydroxysteroid dehydrogenase type 2, enhances the function of cortisol, and is often used clinically as a substitute for cortisol (68). Of particular note, cortisol has recently been reported to enhance the synthesis of arginine (an essential AA for neonates), generation of polyamines (key regulators of DNA and protein synthesis), and intestinal growth in neonatal pigs (69-71).

Based on the above findings, we designed one experiment to investigate the effects of GA on the early- weaned piglets fed with milk-replacing diet, as well as the effects of GA on the endocrine, plasma concentrations of the arginine family of amino acids (including arginine, praline and glutamate), activity of ornithine decarboxylase (ODC) in small intestine mucosa of piglets. Our data showed that dietary supplementation with 0.02% GA increased arginine concentration in plasma (Table 9) and the activity of ODC in the pig jejunum on day 21 (Figure 2), as previously reported for suckling piglets receiving intramuscular administration of cortisol (6) and weanling piglets with a natural surge of cortisol (72). The GA treatment did not affect circulating levels of cortisol, growth hormone, or insulin (P > 0.05), when compared with the control group. Small-intestinal villus height and daily weight gain were 30% and 21% higher, respectively, in pigs treated with 0.02% GA than in the control pigs on day 21. These findings indicate that 0.02% GA increases endogenous arginine provision and intestinal ODC expression, improves small-intestinal morphology, and enhances growth performance in young pigs (73).


The Yucca schidigera plant is endemic of the southwest desert in the United States and the north part of Baja California in Mexico (74). The Yucca schidigera extract (BIOPOWDER) is generally recognized as a safe (GRAS) product and approved by the U.S. Food and Drug Administration (FDA) as a natural food adjuvant under Title 21CFR 172.510. This unique substance is also fed to livestock species (including swine) and poultry to improve air quality (e.g., reductions in ammonia levels and odors) in production barns, health, and productivity parameters (75-77). Thus, BIOPOWDER is widely used in animal nutrition. Of particular interest, Yucca schidigera extract consists of steroidal derivatives (74), which may modulate intestinal remodeling as physiological glucocorticoids do (e.g., cortisol (69-72)). We have previously reported that administration of cortisol to sow-reared piglets increases intestinal arginase expression to promote the conversion of arginine into polyamines (71), which are substances essential for DNA and protein synthesis (13). Notably, similar results were obtained for intestinal arginase and ODC activities in postweaning pigs receiving dietary supplementation of 120 and 180 ppm BIOPOWDER (Table 10). Thus, Yucca schidigera extract can stimulate arginine degradation for polyamine synthesis in pig enterocytes (Table 10), as demonstrated for cortisol (69-72). The nutritional and physiological significance of this novel finding remains to be determined.


Composition of AA in CHM is not unique among ingredients of plant origin. Bioactive substances in CHM act through mechanisms involving multiple systems and cells, including the small intestine, muscle, and lymphoid organs. Thus, studies with animal models demonstrate that dietary supplementation with CHM phytochemicals enhances the AID and absorption of dietary AA, as well as growth and health. Because the underlying mechanisms are likely to be complex and multifactorial, future studies are warranted to determine the effects of active components of CHM phytochemicals on digestion of dietary nutrients, gene expression, cell signaling, and metabolism. Achievement of these long-term goals can be greatly facilitated using omics techniques (e.g., genomics, proteomics, and metabolomics) (78-80) and bioinformatics (81). Such new knowledge will aid in full understanding of how CHM ingredients regulate physiological processes in organisms. Results obtained from animal studies will also have important implications for human nutrition and health.


This research was jointly supported by grants from NSFC (30901040, 30928018), an ISA Young Scholar Project (ISACX-LYQY-QN-0703), K.C. Wang Education Foundation of Hong Kong, National 863 project (2008AA10Z316), GungDong and Chinese Academy Cooperative projects (2009B091300043, 2009B091300079, 2009B091300089), the Outstanding Overseas Chinese Scholars Fund of the Chinese Academy of Sciences (2005-1-4), the Thousand-People-Talent program at China Agricultural University, and the Texas AgriLife Research Hatch project (H-8200).


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Abbreviations: AA, amino acids; AID, apparent ileal digestibilities; AM, Astragalus membranaceus; APS, Astragalus polysaccharide; AS, Acanthopanax senticosus; CHM, Chinese herbal medicine; COP, Codonopsis pilosula; CRP, Crataegus pinnatifida; CTVM, Chinese traditional veterinary medicine; DM, dry matter; GA, Glycyrrhetinic Acid; HPLC, high-pressure liquid chromatography; ODC, ornithine decarboxylase; SM, Salvia miltiorrhiza; UCH, ultra-fine Chinese herbal

Key Words: Chinese herbal medicine, Amino acids, Nutrition, Pigs, Review

Send correspondence to: Yulong Yin, Hunan Engineering and Research Center of Animal and Poultry Science and Key Laboratory for Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, the Chinese Academy of Sciences, Changsha, Hunan, China 410125, Tel: 86-731-84619703, Fax: 86-731-84612685, E-mail:yinyulong@isa.ac.cn