Jacques Attoumbré

Development of antibodies against secoisolariciresinol – Application to the immunolocalization of lignans in Linum usitatissimum seeds

Lignans are widely distributed plant metabolites associated with a large range of biological activities. In order to gain insight into their biosynthesis and their spatio-temporal accumulation an immunological probe was developed. Secondary metabolites generally have too small molecular weight to be antigenic and have to be associated with a carrier protein. Secoisolariciresinol was chosen as the hapten and was linked to bovine serum albumin via a spacer arm, the p-aminohippuric acid. The artificial antigen was injected to New Zealand rabbits. The successful production of polyclonal antibodies against secoisolariciresinol was assessed with indirect enzyme immunosorbent assay (ELISA) by comparison with pre-immune serum and by competitive assays using dilutions of secoisolariciresinol standards. The antibodies had an IC(50) value of 94 μg/ml and showed moderate cross-reactivities with structurally related compounds. They were thus used to immunolocalize lignans in flaxseed (Linum usitatissimum), one of the richest sources of lignans. The immunohistochemical labeling allowed us to localize for the first time lignans in planta. They are mainly localized in the secondary wall of the sclerite cells of the outer integument of the seed. A very light labeling is also observed in cytoplasmic inclusions of the endosperm. The results were correlated with HPLC analytical results which enabled to evaluate the relative lignan quantities: in flaxseed about 90% of the metabolites are localized in the outer integument.

Extraction of lignans from flaxseed and evaluation of their biological effects on breast cancer MCF-7 and MDA-MB-231 cell lines.

Over the last decade, there has been an increasing interest in using flaxseed (Linum usitatissimum) in diet in order to improve nutritional and health status. Lignans are major components of flaxseed. Therefore an extraction procedure for lignans from flaxseed has been optimized. The influence of some parameters was investigated: first the preliminary extraction step with alcoholic solvent, and then the solvent polarity and pH of the extract. All these conditions affected the total lignan content, but the most critical variables were preliminary extraction and solvent polarity. The optimized procedure, consisting of a direct hydrolysis in hydrochloric acid (1 M) at 100 degrees C for 1 hour followed by an extraction with a mixture of ethyl acetate/hexane (90:10 vol/vol), was applied to 340 g of defatted flaxseed and resulted in the isolation of secoisolariciresinol and anhydrosecoisolariciresinol with a purity of 97% and 98%, respectively, as determined by high-performance liquid chromatography. The ability of these two compounds and that of secoisolariciresinol diglucoside to modulate the growth of human breast cancer MCF-7 and MDA-MB-231 cell lines was assessed. Our results show that lignans modulate development of breast cancer cells. The most intense effect was observed for anhydrosecoisolariciresinol, which significantly decreased cell growth at 50 and 100 microM.

Solanidine isolation from Solanum tuberosum by centrifugal partition chromatography.

The aim of this investigation was the preparative isolation of solanidine (aglycone of the two main potato glycoalkaloids: α-chaconine and α-solanine) from fresh Solanum tuberosum (cv. Pompadour) material by implementing a new preparation scheme using centrifugal partition chromatography (CPC). A setup for obtaining solanidine by hydrolysis of the glycoalkaloids found in the skin and sprouts of S. tuberosum was first developed. Then its isolation was carried out by the development of CPC conditions: the solvent system used for separation was ethyl acetate/butanol/water in the ratio 42.5:7.5:50 v/v/v, 0.6 g of crude extract were separated with a 8 mL/min flow rate of mobile phase while rotating at 2500 rpm. A run yielded 98 mg of solanidine (86.7% recovery from the crude extract) in a one-step separation. The purity of the isolated solanidine was over 98%. Thus, CPC has proven to be the method of choice to get solanidine of very high purity from S. tuberosum biomass in large quantities.

Preparative separation of glycoalkaloids α-solanine and α-chaconine by centrifugal partition chromatography

The main glycoalkaloids of a commercial potato cultivar, α-chaconine and α-solanine, were extracted from sprouts of Solanum tuberosum cv. Pompadour by a mixture of MeOH/H(2)O/CH(3)COOH (400/100/50, v/v/v). In these conditions, 2.8±0.62g of crude extract were obtained from 50g of fresh sprouts and the total glycoalkaloid content was determined by analytical HPLC at 216.5mg/100g. α-Chaconine and α-solanine were separated in a preparative scale using centrifugal partition chromatography (CPC). In a solvent system composed of a mixture of ethyl acetate/butanol/water (15/35/50, v/v/v), α-chaconine (54mg) and α-solanine (15mg) were successfully isolated from the crude extract in one step of purification. The purity of isolated compounds was determined to be higher than 92% by HPLC analysis.

5-O-caffeoylshikimic acid from Solanum somalense leaves: advantage of centrifugal partition chromatography over conventional column chromatography.

Solanum somalense leaves, used in Djibouti for their medicinal properties, were extracted by MeOH. Because of the high polyphenol and flavonoid contents of the extract, respectively, determined at 80.80 ± 2.13 mg gallic acid equivalent/g dry weight and 24.4 ± 1.01 mg quercetin equivalent/g dry weight, the isolation and purification of the main polyphenols were carried out by silica gel column chromatography and centrifugal partition chromatography. Column chromatography led to 11 enriched fractions requiring further purification, while centrifugal partition chromatography allowed the easy recovery of the main compound of the extract. In a solvent system composed of CHCl3/MeOH/H2O (9.5:10:5), 21.8 mg of this compound at 97% purity was obtained leading to a yield of 2.63%. Its structure was established as 5-O-caffeoylshikimic acid by mass spectrometry and NMR spectroscopy. This work shows that S. somalense leaves contain very high level of 5-O-caffeoylshikimic acid (0.74% dry weight), making it a potential source of production of this secondary metabolite that is not commonly found in nature but could be partly responsible of the medicinal properties of S. somalense leaves.

Synthesis and insecticidal activities of novel solanidine derivatives: Solanidine derivatives

BACKGROUND Potato (Solanum tuberosum) is the fourth culture in the world and is widely used in the agri-food industries. They generate by-products in which α-chaconine and α-solanine, the two major solanidine-based glycoalkaloids of potato, are present. As secondary metabolites, they play an important role in the protection system of potato and are involved in plant protection against insects. To add value to these by-products, we described here new glycoalkaloids that could have phytosanitary properties. RESULTS Solanidine, as a renewable source, was modified with an azido linker and coupled by copper-catalyzed alkyne azide cycloaddition to alkynyl derivatives of the monosaccharides found in the natural potato glycoalkakoids: D-glucose, D-galactose and L-rhamnose. The efficacy of our compounds was evaluated on the potato aphid Macrosiphum euphorbiae. The synthetic compounds have stronger aphicidal properties against nymphs than unmodified solanidine. They also showed strong aphicidal activities on adults and a negative impact on fecundity. CONCLUSION Our synthetic neoglycoalkaloids affected Macrosiphum euphorbiae survival at the nymphal stage as well as at the adult stage. Furthermore, they induced a decrease in fecundity. Our results show that chemical modifications of by-products may afford new sustainable compounds for crop and plant protection.