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Monacolins in Red Yeast Rice —their composition, production and standardization

作者:天曲生物 日期:2020-10-02 15:14:15 点击数:3

Monacolins in Red Yeast Rice

—their composition, production and standardization

 

Lixin Wang1,3*, Chunzhen Chen1,2 and Zhanming Li1,2

 

1 Pharmatek China, Kunming, 650106, China

2 Yunnan Kangle Institute of Pharmacy, Kunming, 650200, China

3 Pharmatek Canada Inc. Mississauga, ON L5C 1H4 Canada

*Correspondence: +86-871-8311366, lxwang@ptkcn.com

  

Abstract:The composition of monacolins in red yeast rice reviewed has shown that all monacolin compounds possess two molecular structures: hydroxyl acid form and lactone form, and monacolin K is the major constituent among monacolins. The multiplicity phenomena of monacolin compounds in red yeast rice were observed during the solid state fermentation and downstream process. On the basis of recent researches, suggestions are made to improve current standard of red yeast rice products for quality control.

 

Introduction

Red yeast rice, also known as Hongqu or red Koji, is a fermented product of nonglutinous rice with fungus Monascus. It has been extensively used as both food additive and folk medicine for thousand years in China. In one of the famous ancient pharmacopeias Ben Cao Gang Mu authored by Li Shizhen in Ming Dynasty, Hongqu is described to promote food digestion and blood circulation, strengthen the spleen and dry the stomach. More recently, pigment of Monascus was authorized in China as a national standard of food additive, and red yeast rice by M. purpureus went was recognized medical material in current Chinese Pharmacopeias. Since Endo first reported the finding of monacolin K in Monascus ruber in 1979, and especially Mevacor (lovastatin) was successfully marketed in USA in 1986, more and more attention has been paid on red yeast rice, the traditional Chinese medicine. Many products of red yeast rice have been registered such as Xuezhikang from Weixin-Peking University, Zhibituo from Diao Pharm, Academia Sinica as authorized drug and Honglinzhi capsules and several others as health food in China, Cholestin as food dietary supplement in USA, and others in Japan, Singapore, Taiwan. Along with the marketing, great progress has been made in research of red yeast rice in academic sector, more and more papers have been published, which involved strain identification, constituents, standard, quantification, fermentation, downstream processing, pharmacology and clinic trials. However, since red yeast rice being such a complicated natural product, our knowledge about red yeast rice still need developing, more emphasis are to be made on standardization of red yeast rice.  

Monacolins In Red Yeast Rice

Since monacolin K was firstly reported from Monascus ruber in 1979, many monacolin compounds have been identified. They are monacolin J, K, L, M, X, dihydromonacolin K, methyl ester of monacolin L, methyl ester of monacolin K, and some very traced unnamed monacolin derivatives (Fig. 1). The striking characteristics of these monacolin compounds in red yeast rice is that they all share two kind of molecular structures: hydroxyl acid form and lactone form, e.g. hydroxyl acid form and lactone form of monacolin K (Fig. 2 ).  The ratio of these two structural monacolin Ks in red yeast rice from different sources varies very largely from 10:1 to 1:10. The total of these two kinds of monacolin Ks accounts for more than 90% of monacolin derivatives in red yeast rice.  

 

Figure1 Some molecular structures of monacolins in red yeast rice

 

Figure 2  nbsp;Two molecular structures of monacolin K

 

Production Of Monascolins

Biosynthesis of Monacolins

All monacolins share a common main polyketide portion, a hydroxyl-hexa-hydro napathalene ring, to which different side chains are linked at C6 and C8. Monacolin K (lovastatin) has a methylbutyryl side-chain 8-α and a methyl group in 6-α of the naphthalene ring. Monacolin K has two polyketide chains C-18 and C-14 synthesized from incorporation of acetate and methionine. The C-18 chain is cycled, oxidized at the 8-carbon, and esterified by the side chain. Monacolin L is considered to be the precursor of monacolin J. Thus, monacolins are expected in any red yeast rice product.

Multiplicity of Production of Monacolins

There are two kinds of red yeast rice: one is for its pigment, the other is for its functional substances i.e. monacolins. Though these two kinds are prepared by solid state fermentation of rice with Monascus strains, the differences in cultivated media, culture conditions, period of cultivation are very large. For example, the culture temperature of red yeast rice for pigment is higher than 37, the period of cultivation is shorter than 5 days, whereas, for monacolins, the culture temperature is lower than 30, the period of cultivation is longer than 10 days. In this paper, only the latter case is discussed. The manufacture of red yeast rice consists of two steps: fermentation and downstream processing, especially drying. Lots of work has been done to show that the initial monacolins produced by Monascus are in hydroxyl acid forms, i.e. all the hydroxyl acid forms of monacolins are produced at the fermentation step. Since hydroxyl acid form is not very stable, it is easily converted into its conger form of lactone by dehydration. Thus, in fermentation, monacolin K mainly possesses hydroxyl acid form, though the cultivation conditions vary dramatically. Figure 3 shows the monacolins in red yeast rice from different batches. In Fig.3, the highest peaks are hydroxyl acid form of monacolin K, the second highest peaks after the former monacolin K are their lactone forms. Though the fermentation is slightly different in strains, cultivation condition in different batches, all the chromatograms of red yeast rice from different batches share the same pattern, that is, most of the monacolin K is in hydroxyl acid form.  This pattern is also seen in submerged fermentation for production of lovastatin with Monascus, even with Aspergillus terreus.

Figure 3  Monacolins in red yeast rice from different batches

 

At the downstream processing, the chromatograms of red yeast rice from different processes vary dramatically. From Fig.4, it can be seen that the two forms of monacolin K are the major components of monacolins in red yeast rice, the ratio of these two forms is greatly different in these chromatograms. There are no explicit patterns for the monacolin peaks. The reason for these multiplicity of monacolin chromatograms is that the hydroxyl acid form of monacolin K is very active: most of its molecules are converted into its congener lactone form by dehydration, they are also changed into methyl ester, they can be degraded into other monacolins. Under mild conditions, in some

Figure4 Monacolins in red yeast rice from different downstream processes

 

cases, most of hydroxyl acid forms of monacolin K may be kept in red yeast rice; in some cases, they may be changed into lactone forms, in most cases, both forms co-exist in red yeast rice. Under rigorous condition such as high temperature, very lower pH, etc, most of hydroxyl acid form of monacolin K is converted into lactone form, and some new substances appear, and the total of monacolin K decreases. Thus, from the point of monacolins production with Monascus, lactones are artificial natural substances. The rigorous condition of downstream process will lead to the degradation of monacolin K in red yeast rice.  The multiplicity of monacolins in red yeast rice , therefore, is due to the choice of downstream processes of fermented products.

 

Standardization Of Monacolins In Red Yeast Rice

The Current National Standards of Red Yeast Rice Products in China

In China, since red yeast rice is considered as both food additive and folk medicine, products from red yeast rice have been registered as drugs, namely Xuezhikang capsules and Zhibituo tablets, as well as health food, such as Hongqu tablets, Tianqu capsules etc.  With the stimulation of successful clinical application of Mevacor worldwide, in China, the red yeast rice products began to be marketed in 1990s. Due to the lack of knowledge of active substances in red yeast rice, and of reference standards of other monacolin derivatives, the quantification of active component in these products is using HPLC with lovastatin (lactone form) as reference standard in all national standards for red yeast rice. Because the portion of open-ringed form monacolin K in monacolins in red yeast rice from many sources is significant, this may lead to safety problem among the comsumers. With more and more detailed research committed, these standards need amending.

 

The Rational of Hydroxyl Acid Form of Monacolin K (Lovastatin)

In the eye of the production of monacolins with Monascus, it is reasonable to consider hydroxyl acid form of monacolin K as one of the major active constituents in red yeast rice, however, in early days, it was found that this form of monacolin K is not very stable, which is one of the reasons for Mevacor (lovastatin) in lactone form.

Fig.5  Sodium salt of Monacolin K

 

In search of stable hydroxyl acid form of monacolin K, we have found that the sodium salt of monacolin K is very stable in red yeast rice. The stability experiments have shown that the decrease of this compound was less than 5% after 3 years at room temperature. It was reported that monacolin Ks sodium salt is more potent and less toxic than its lactone, comparisons between these two compounds are shown in Table 1 and 2. From Table 2, it could understand that for the similar reduction in cholesterol in clinic therapy, the doses of red yeast rice preparation are much lower than those of lovastatin tablets.

 

 

 

Table 1 Comparison of chemical properties

Property

Sodium salt of monacolin K

Lactone of monacolin K

Color and form

White powder

Colorless crystal

Molecular weight

444

404

Molecular formula

C24H37O6Na

C24H36O5

UV absorption spectrum(nm)

232  239  248

232 238 246

solubility

Soluble in water, insoluble in organic solvents

Soluble in methanol, ethanol, acetone, insoluble in hexane

 

Table 2 Comparison of pharmacologic properties


Sodium salt of

monacolin K

Lactone of

monacolin K

IC50(ngml)

0.14

2.0

LD50(mg/kg)

>2000

1000

Animal test

Dose(mg/kg)

2

10

Cholesterol reduction in blood(%)

27.5

22.4

Cholesterol reduction in liver(%)

18.9

16.7

  

In recent years, several large-scale clinic trials have revealed that red yeast rice products are more potent than the similar dose of lovastatin. These results has made many investigators reconsider the standards of these products, especially quantification of monacolins. Since monacolin Ks are the major components in monacolins in red yeast rice, it is feasible to quantify the hydroxyl acid form of monacolin K in red yeast rice for the purpose of quality control. For sake of no reference standard of acid form of monacolin K, lumped quantification methods by UV and HPLC were developed for total monacolin Ks. Because red yeast rice is one of our biggest sales, many efforts have been made on the improvement of fermentation technology and standard of quality control. So far, the purified sodium salt of Monacolin K, tested by UV, IR, MS, NMR etc was obtained from red yeast rice, and we are to promote this compound to be national reference standard for quantification of monacolin K in red yeast rice, after its stability testing is done.

 

Fingerprinting  an alternative for quality control?

Fingerprinting of constituents in natural products and herb medicine is considered as one of most effective way for quality control. More and more work has been published to show its feasibility. In China, fingerprinting is compulsory for herbal injection preparations. Monacolins are all synthesized through the same pathway, thus, the chemical fingerprint of monacolins should be unique to red yeast rice. However, as it can be seen from the multiplicity of production of monacolins discussed above, there may be some new substances generated during the downstream process, it is not feasible to find a universal fingerprint for all red yeast rice even if the fermentation processes are identical. Thus, for red yeast rice, fingerprinting could be an effective supplement for quality control, the best way for the quality control of red yeast rice is to quantify the monacolin Ks.

 

Conclutions

Monacolin derivatives in red yeast rice possess two forms of molecular structures: hydroxyl acid form and lactone form. Monacolin Ks are the major constituent among monacolins. The reason for multiplicity of production of monacolins in red yeast rice is discussed, which is associated with applying fingerprinting method for quality control. Progress in quantification of monacolin Ks in Pharmatek China is introduced. .

 

References

[1]Alberts, AW, Chen, J., Huron, G. et al. Mevinolin: A Highly Potent Competitive Inhibitor of Hydromethylglutaryl-coenzyme A Reductase and a Cholesterol-lowering Agent. Proc. Natl. Acad. Sci. USA. 1980, 77(7):3957

[2]Chen, Ch., Li, Zh., Wang, L. et al. Traditional Chinese Medicine Red Yeast Rice with Lovastatin Salt as Major Active Constituent and its Preparation. Chinese Patent CN1513451A, 2003.

[3]Du, F., Yu, Y., Li Zh. et al. Determination of Lovastatin Acid by High Performance Liquid Chromatography. Anal. Testing Tech. Instruments. 2003 9(2):95

[4]Endo, A. Monacolin K. A New Hypocholesterolemic Agent Produced by a Monascus Species. J. Antibiotics, 1979, 32(6):852

[5]Hong, Zh. and Mao, N. Study on the Cholesterol-lowering Constituents from Monascus.  Strait Pharm. J. 2002, 14(1):33

[6]Ma, J., Li, G., and Ye, Q. et al. Constituents of Red Yeast Rice, a Traditional Chinese Food and Medicine. J. Agric. Food Chem. 2000, 48:5220  

[7]Song, H., Mi, H. and Guo, T. Advances in Chinese Medicine Hongqu.  J. Pharm. Prac. 1999, 17(3):172

[8]Song, H., Mi, H. Guo, T. et al. Determination of Lovastatin in Hongqu from Various Source by HPLC.  Medica Materia Sinica. 1999, 30(2):100

[9]Song, H., Guo, T. and Zhang, Y. Studues on Pharmacognotic Identification and Quality Control Standard for Hongqu.  J. Chinese Medicine. 1999, 24(5):262

[10]Tong, Q.  Progress in Bioactive Substances produced by Monascus. Food Sci. 2003, 24(1):163

[11]Tsujita, Y., Kuroda, M., Tanzawa, K. et al. Monacolin K Derivatives. UK Patent Application GB2055100A. 1980.

[12]Wang, W., Xia, F. and Wu, S. Progress in the Research of Fermented Monacolin K y Using Monascus.  Pharm. Biotech. 2002, 9(5):301

[13]Zhu., H. Xu., G. and Chen, Y. HPLC Analysis of Acid Form and Lactone Form Monacolin K from Monascus Red Rice. J. Wuxi Univ. Light Ind. 2003, 22(3):45

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