Oligoesculin fraction induces anti-tumor effects and promotes immune responses on B16-F10 mice melanoma.

Laccase was used to enzymatically polymerize esculin. Oligoesculin fraction was obtained after ultrafiltration through a 5-kDa membrane. Several studies have been carried out to prove the effectiveness of natural substances such as immunomodulators to promote the anti-cancer activity in situ. The purpose of our report was to explore whether the anti-tumor potential of the oligoesculin fraction in vitro and in vivo is linked to its immunological mechanisms in melanoma-bearing mice. We revealed that oligoesculin fraction reduced B16-F10 proliferation and migration in vitro in a dose-related manner. Moreover, melanin synthesis and tyrosinase activity were inhibited in these melanoma cells in a concentration-dependent way. The anti-tumor potential of oligoesculin fraction was also assessed in vivo. Our results showed that intraperitoneal administration of oligoesculin fraction, at 50 mg/kg body weight (b.w.) for 21 days, reduced tumor size and weight with percentages of inhibition of 94 and 87 %, respectively. Oligoesculin fraction was effective in promoting lysosomal activity and nitric oxide (NO) production by peritoneal macrophages in tumor-implanted mice. In addition, the activities of natural killer (NK), cytotoxic T lymphocytes, and macrophages were significantly enhanced by oligoesculin fraction. These findings suggested that this polymer with its anti-tumor and immunomodulatory properties could be used for the treatment of melanoma.

Esculin and its oligomer fractions inhibit adhesion and migration of U87 glioblastoma cells and in vitro angiogenesis.

Cancer metastasis is the major cause of cancer-related death. Chemoprevention is defined as the use of natural or synthetic substances to prevent cancer formation or cancer progress. In the present study, we investigate the antitumor activity of esculin and its oligomer fractions in U87 glioblastoma cells. We showed that esculin and its oligomers reduced U87 cell growth in a dose dependent manner. They also inhibited cell adhesion to collagen IV and vitronectin by interfering with the function of their respective receptors α2ß1 and αvß5 integrins. Furthermore, the tested samples were able to reduce migration of U87 cells towards another extracellular matrix fibronectin. Moreover, esculin and its oligomer fractions inhibited in vitro angiogenesis of endothelial cells (HMEC-1). In summary, our data provide the first evidence that esculin and its oligomer fractions are able to reduce adhesion, migration of glioblastoma cells and in vitro angiogenesis. Esculin and its oligomers may thus exert multi-target functions against cancer cells.

Oligomerization of esculin improves its antibacterial activity and modulates antibiotic resistance.

In this particular study, the antibacterial activity of esculin and oligomer fractions was assessed. MIC values of esculin and its oligomer fractions as well as of some antibiotics against Gram-positive and Gram-negative strains and against Escherichia coli multiresistant variants were determined by the standard broth microdilution method. Both esculin and oligoesculin fractions exhibited antibacterial effect against reference strains; Staphylococcus aureus, Enterococcus faecalis, Salmonella enteritidis and Salmonella typhimurium. It appears that E3 oligomer fraction had the greatest antibacterial activity against these reference strains. Besides, as E2 and E3 revealed the best antibacterial effect against multiresistant variants of E. coli, we decided to test the effect of each, combined to the antibiotic against which the variants were resistant. In the interaction study, E2 and E3 oligoesculin fractions were found to be effective in reducing the resistance of E. coli 6574 to ofloxacin and the resistance of E. coli 6228 to amoxicillin. Only E3 oligoesculin fraction showed a synergetic interaction with amoxicillin and tetracyclin against E. coli 6708, but no interaction was found either with E2 or E3 fractions against E. coli 6234. Our study allowed us to conclude that oligomerization of esculin increases its antibacterial potential, according to the degree of polymerization.

Evaluation of mutagenic and antimutagenic activities of oligorutin and oligoesculin.

Rutin and esculin have been polymerised by laccase. Five fractions with M(w)¯ between 2127.42 and 8331.85g/mol for oligorutins, and between 688.12 and 6973g/mol for oligoesculins, were obtained. Fourier transformed infrared analysis showed that oligorutins were formed through C-C, C-O and CO linkages, while oligoesculins were obtained through C-C linkages. Monomers, their oligomers and their metabolites exhibited no mutagenic effect. Oligorutins and oligoesculins were more efficient in reducing the mutagenicity of methyl methanesulphonate, by, respectively, 69% and 64.8% in the presence of Salmonella typhimurium TA104, and 79.7% and 68.9% in the presence of S. typhimurium TA102, than were their monomers. The same oligomers revealed greater significant inhibitory effect of 2-aminoanthracene mutagenicity (respectively 82.4% and 79.3% in the presence of S. typhimurium TA104, and 89.2% and 82.9% in the presence of S. typhimurium TA102), than their monomers. Our results strongly suggest the enhancement of the tested monomer antimutagenicity after polymerisation.

Solubilities inferred from the combination of experiment and simulation. Case study of quercetin in a variety of solvents.

A strategy to infer solubilities from the combination of experiment and all-atom simulations is presented. From a single experimental estimate, the solubility of a substrate can be predicted in various environments from the related free energies of solvation. In the case of quercetin, the methodology was shown to reproduce the experimental solubilities in chloroform, water, acetonitrile, acetone, and tert-amyl alcohol within 0.5 log unit. The reliability of the estimates is markedly correlated to the accuracy of the experimental measure and to both the accuracy and precision of the computed free energies of solvation.

Enzymatic acylation of flavonoids: effect of the nature of the substrate, origin of lipase, and operating conditions on conversion yield and regioselectivity.

The conversion yield at equilibrium, the initial rate, and the regioselectivity of the enzymatic acetylation of aglycone flavonoids (quercetin, naringenin, hesperetin, and chrysin) were investigated and compared to those obtained with a glycosylated one (isoquercitrin). The effects of a wide range of operating conditions were quantified. Fourier transform infrared spectrometry (FT-IR), NMR, and high performance liquid chromatography electrospray ionization mass spectrometry (HPLC-ESI-MS) analyses showed that for glycosylated flavonoids, in the presence of Candida antarctica (CAL-B), the acetylation occurred on the 2''-OH, 3''-OH, and 6''-OH of the glucose part, while with Pseudomonas cepacea lipase (PSL-C) acetylation takes place on 6''-OH of the sugar and 4'-OH of the B-ring. For aglycone flavonoids, the acetylation occurred only with PSL-C on 4'-OH, 3'-OH, and 7-OH hydroxyls. The conversion yield and the number and the relative proportions of the synthesized products were found dependent on the nature of the enzyme, the molar ratio, and the flavonoid structure. The initial rate was affected only by the origin of the enzyme.