Silybum marianum in vitro-flavonolignan production L. Tůmová1, J. Řimáková1, J. Tůma2, J. Dušek1 1School of Pharmacy, Charles University, Hradec Kralove, Czech Republic 2Faculty of Education, University of Hradec Kralove, Czech Republic ABSTRACT The effect of coniferyl alcohol as a precursor of flavonolignan biosynthesis on silymarin components production in Silybum marianum suspension culture was studied. Coniferyl alcohol showed the changes in silymarin complex production. Silydianin was detected mainly in the control samples of cultivated cells. A significant increase of sily- dianin was observed only after 72 h of the application of 46µM coniferyl alcohol. No other components of the sily- marin complex (silychristin and silybin) were detected; neither in control samples nor after the precursor feeding. But the increased accumulation of taxifolin (flavanole) was very interesting. The highest taxifolin production was reached after 48 hours of treatment (about 554% compared to control). Keywords: milk thistle; Silybum marianum; in vitro culture; flavonolignans; coniferyl alcohol Milk thistle, Silybum marianum (L.) Gaertn., The parts of silymarin complex are of a consid- Asteraceae is widely used for hepatic and biliary erable pharmacological interest owing to their disorders in Europe; it has been used medicinally strong anti-hepatotoxic and hepatoprotective since the first century. It was also mentioned in the activity (Valenzuela et al. 1986, Morazoni and writings of Dioscorides, Jacobus Theodorus and Bombardelli 1995), and a recent work has shown Culpepper. Its leaves, flowers and roots were his- that silymarin also acts as an anticholesterolaemic torically considered a vegetable in European diets, agent (Krecman et al. 1998). Milk thistle fruit is and fruits (achenes), which resemble seeds, were used for the prophylaxis and treatment of liver roasted as a coffee bean substitute. The leaves of damage caused by metabolite toxins, e.g. alco- the plant are eaten in fresh salads and as a spinach hol, tissue poison, in liver dysfunction and after substitute, the stalks like asparagus, and the flower hepatitis (post-hepatic syndrome), and in chronic heads serve as artichokes (Luper 1998). degenerative liver conditions (Wichtl 1994). The milk thistle is an annual herb or biannual In vitro culture of cells and tissues may offer an herbaceous plant that is widespread in temper- alternative for the production of silymarin but until ate climate of the American countries, Australia, now, only few studies addressing this possibility Southern and Western Europe. This plant is also have been carried out (Becker and Schrall 1977), cultivated in the Czech Republic. and in all cases flavonolignan production in in The dried seeds contain 1–4% of silymarin fla- vitro cultures is very low and even disappears in vonoids. Silymarin is a mixture of three flavono- prolonged cultures. This is a common occurrence lignans, including silybin (silibinin), silidianin, in the production of secondary metabolites in and silichrystin (Figure 1). Other flavonolignans many species. However, in some cases (Corchete identified in S. marianum include dehydrosily- et al. 1991, Hagendoorn et al. 1994), the manipu- bin, deoxysilycistin, deoxysilydianin, silandrin, lation of the components of the culture medium silybinome, silyhermin, and neosilyhermin. In substantially increased the production of these addition, milk thistle contains apigenin, taxifolin, compounds. silybonol, myristic, oleic, palmitin, and stearin Feeding experiments with the precursors of acids (Wichtl 1994). biosynthesis of secondary metabolites resulted Supported by the Ministry of Education, Youth and Sports of the Czech Republic, Project No. MSM 0021620822. 454 PLANT SOIL ENVIRON., 52, 2006 (10): 454–458 Silybin Silychristin Silydianin Taxifolin 2,3-Dihydroquercetin Figure 1. Main components of silymarin complex and taxifolin structure in a 3–5 fold increase in levels of secondary me- MATERIAL AND METHODS tabolites. For example precursor L-phenylalanine showed a 3–5 fold increase in 5-methoxypodophyl- Plant material. Cell suspensions were established lotoxin in suspension culture of Linum flavum from 3-month-old undifferentiated cotyledon cal- (van Uden et al. 1990). luses and grown in MS liquid medium (Murashige Coniferyl alcohol is a key precursor of biosyn- and Skoog 1962) supplemented with 10 mg/dm3 thetic pathway of flavonolignans. Flavonolignans NAA. These suspensions were cultivated in growth are adducts of flavanole taxifolin with coniferyl chambers at 25°C in the shaker at 120 rpm and alcohol (Figure 2). Coniferyl alcohol was chosen 16 hours daylight. Ethanolic coniferyl alcohol solu- 3 as a model substance in this study. The aim of our tion in concentrations c1 33.11 mg/dm (184µM); 3 3 experiment was to increase flavonolignan produc- c2 16.56 mg/dm (92µM) and c3 8.28 mg/dm (46µM) tion by feeding nutrient medium with precursor of was added into MS nutrient medium as biosyn- coniferyl alcohol. The same precursor – coniferyl thesis precursor of flavonolignans. After 12, 24, alcohol in the form of complex with β-cyclodex- 48, 72, and 168 hours of precursor application, the trin was used as precursor for podophyllotoxin suspension cells were taken out. The cells were accumulation in Podophyllum hexandrum cell separated from nutrient medium by a reduced suspension cultures. The β-cyclodextrin itself press filtration and were dried at the laboratory was proven to be non-toxic for cells. It did not temperature. The flavonolignan content was de- influence podophyllotoxin content and it was not tected not only in suspension cells but also in the metabolized or used as a carbon source by cells. nutrient medium. For comparison, coniferin, the water-soluble Analytical method (Řimáková 2005). Dried β-D-glucoside of coniferyl alcohol, was also fed in suspension cells were extracted in methanol for the same concentrations. The effect of coniferin 30 min and methanolic solution was concentrated on the podophyllotoxin accumulation was stronger to 5 ml and analyzed by HPLC. Solid fraction after than that of coniferyl alcohol complexed with evaporation of nutrient medium was dissolved in β-cyclodextrin, but coniferin is not commercially 5 ml of methanol. The content of flavonolignans available (Woerdenbag et al. 1990). was determined by HPLC on a UNICAM CRYSTAL PLANT SOIL ENVIRON., 52, 2006 (10): 454–458 455 Taxifolin + Coniferyl alcohol Silybin Figure 2. Biosynthesis of flavonolignans 200 Liquid Chromatograph, column LiChrospher (benzoic acid, N-benzoylglycine, serine, glycine) in- RP-18 (250 mm × 4 mm). HPLC conditions were creased taxol accumulation. The greatest increases developed in our laboratory as follows. The mobile in taxol accumulation were observed in the pres- phase consisted of methanol and water (both acidi- ence of various concentrations of phenylalanine, fied with 0.3% orthophosphoric acid p.a. – w/v). and benzoic acid (Fett-Neto et al. 2004). Flavonolignans were eluted with linear gradient Our experiments with coniferyl alcohol as a pre- from water to 50% methanol in 5 min, following cursor used in suspension culture of Silybum mari- by isocratic elution with 50% methanol for 20 min. anum showed the changes in silymarin complex The flow-rate was 1.4 ml/min. Substances were production. Silydianin was detected mainly in the detected by absorption at λ = 288 nm and their control samples of cultivated cells. A significant identification was carried out by the comparison increase of silydianin was observed only after of retention times and absorption spectra with 72 h of the application of 46µM coniferyl alcohol. standard complex of silymarin (Sigma-Aldrich). No other components of the silymarin complex All experimental analyses were carried out in (silychristin and silybin) were detected; neither a minimum of three independent complexes for in control samples nor after the precursor feed- each time and each concentration of precursor. ing. But the increased accumulation of taxifolin The content of flavonolignans was referred to (flavanole) was a very interesting phenomenon. the dry mass of suspension complex. Statistical A significant increase of taxifolin content in nutri- significance was calculated using Student’s t-test ent medium (about 170%; 554%; 343% and 320%) for unpaired data (P ≤ 0.05). was observed after 24; 48; 72 and 168 hours of treat- ment with 184µM of coniferyl alcohol (Figure 3). The greatest taxifolin production was reached RESULTS AND DISCUSSION after 48 hours (about 554% compared to control). High taxifolin production was detected also after The feeding of precursors to differentiated cell 72 and 168 hours (about 118% and 192%, respec- cultures, resembling organised tissue of intact tively) when coniferyl alcohol in concentration plant, may open new ways for the improvement of 92µM was used (Figure 3). These results were of secondary metabolites. Cell culture of Taxus achieved in comparison with the precursor-feed- cuspidata represents an alternative to whole plant ing experiments in podophyllotoxin production. extraction as a source of taxol and related taxanes. Feeding with 3mM coniferyl alcohol dissolved in Feeding phenylalanine to callus culture was pre- the culture medium as a β-CD complex, resulted in viously shown to result in increased taxol yields, an enhanced podophyllotoxin accumulation, with probably due to the involvement of this aminoacid a maximum of 0.012% on day 10 of the growth cycle. as a precursor or the N-benzoylphenylisoserine Non-complexed