Enzymatic synthesis of butyryl-rutin ester in organic solvents and its cytogenetic effects in mammalian cells in culture

In vitro genotoxicity assessment of functional ingredients: DHA, rutin and α-tocopherol

The in vitro genotoxicity of three compounds widely used as functional ingredients, docosahexaenoic acid (DHA), rutin and α-tocopherol, was assessed. A miniaturized version of the Ames test in Salmonella typhimurium TA97a, TA98, TA100, TA102, and TA1535 strains (following the principles of OECD 471), and the in vitro micronucleus test in TK6 cells (OECD 487) were performed. This strategy is recommended by the European Food Safety Authority for the in vitro genotoxicity assessment of food and feed. In addition, this approach was complemented with the in vitro standard and enzyme-modified comet assay (S9-/S9+) using hOGG1, EndoIII and hAAG in order to assess potential premutagenic lesions in TK6 cells. Rutin showed an equivocal response in the in vitro micronucleus test and also was a potent Salmonella typhimurium revertant inductor in the Ames test. DHA showed equivocal results in the in vitro micronucleus test. In this regard, DHA and rutin seemed to interact with the DNA at a chromosomal level, but rutin is also capable of producing frameshift mutations. No genotoxicity was observed in cells treated with α-tocopherol. This article complements the evidence already available about the genotoxicity of these compounds. However, more studies are needed in order to elucidate the consequences of their use as functional ingredients in human health.

Rutin derivatives obtained by transesterification reactions catalyzed by Novozym 435: Antioxidant properties and absence of toxicity in mammalian cells

Flavonoids are one of the most important and diversified phenolic groups among products of natural origin. An important property of this metabolite class is the antioxidant action. This study evaluated the antioxidant and cytotoxic activities and oxidative stress of transesterification products of the flavonoid rutin, catalyzed by Novozym^® 435. The presence of monoacetate and diacetate was confirmed by quantitative evaluation of the retention times (rutin, 15.68 min; rutin monoacetate, 18.14 min; and rutin diacetate, 18.57 min) and by the data from LC-MS and NMR ¹H and ¹³C. The experiment showed excellent conversion values of 96% in total acetates (rutin monoacetate and diacetate). These results confirmed that rutin derivatives have antioxidant potential, as evaluated by the ORAC method (rutin standard: 0.53 ± 0.08 μM Trolox/g and rutin derivatives: 2.33 ± 1.08 μM Trolox/g) and also show low cytotoxicity in human and animal cells. Rutin derivatives reduced the production of reactive oxygen species in RAW macrophages as well. Many qualities attributed to rutin derivatives make them promising potential candidates for use as nutraceuticals, including their high amounts of antioxidants, biological potential and low toxicity, which contribute to the reduction of oxidative stress.

Synthesis of New Glycosylated Flavonoids with Inhibitory Activity on Cell Growth

Natural flavonoids and xanthone glycosides display several biological activities, with the glycoside moiety playing an important role in the mechanism of action of these metabolites. Herein, to give further insights into the inhibitory activity on cell growth of these classes of compounds, the synthesis of four flavonoids (5, 6, 9, and 10) and one xanthone (7) containing one or more acetoglycoside moieties was carried out. Acetyl groups were introduced using acetic anhydride and microwave irradiation. The introduction of one or two acetoglycoside moieties in the framework of 3,7-dihydroxyflavone (4) was performed using two synthetic methods: the Michael reaction and the Koenigs-Knorr reaction. The in vitro cell growth inhibitory activity of compounds 5, 6, 7, 9, and 10 was investigated in six human tumor cell lines: A375-C5 (malignant melanoma IL-1 insensitive), MCF-7 (breast adenocarcinoma), NCI-H460 (non-small cell lung cancer), U251 (glioblastoma astrocytoma), U373 (glioblastoma astrocytoma), and U87MG (glioblastoma astrocytoma). The new flavonoid 3-hydroxy-7-(2,3,4,6-tetra-O-acetyl-β-glucopyranosyl) flavone (10) was the most potent compound in all tumor cell lines tested, with GI₅₀ values < 8 μM and a notable degree of selectivity for cancer cells.

Naringin lauroyl ester inhibits lipopolysaccharide-induced activation of nuclear factor κB signaling in macrophages

Naringin (Nar) has antioxidant and anti-inflammatory properties. It was recently reported that enzymatic modification of Nar enhanced its functions. Here, we acylated Nar with fatty acids of different sizes (C2–C18) using immobilized lipase from Rhizomucor miehei and investigated the anti-inflammatory effects of these molecules. Treatment of murine macrophage RAW264.7 cells with Nar alkyl esters inhibited lipopolysaccharide (LPS)-induced nitric oxide (NO) production, with Nar lauroyl ester (Nar-C12) showing the strongest effect. Furthermore, Nar-C12 suppressed the LPS-induced expression of inducible NO synthase by blocking the phosphorylation of inhibitor of nuclear factor (NF)-κB-α as well as the nuclear translocation of NF-κB subunit p65 in macrophage cells. Analysis of Nar-C12 uptake in macrophage cells revealed that Nar-C12 ester bond was partially degraded in the cell membrane and free Nar was translocated to the cytosol. These results indicate that Nar released from Nar-C12 exerts anti-inflammatory effects by suppressing NF-κB signaling pathway.

Biotransformation of polyphenols for improved bioavailability and processing stability

Research on the functions and effects of polyphenols has gained considerable momentum in recent times. This is attributed to their bioactivities, ranging from antioxidant to anticancer activities. But their potential is seldom fully realized since their solubility and stability is quite low and their bioavailability is hampered due to extensive metabolism in the body. Biotransformation of polyphenols using enzymes, whole cell microbes, or plant cell cultures may provide an effective solution by modifying their structure while maintaining their original bioactivity. Lipase, protease, cellulase, and transferases are commonly used enzymes, with lipase being the most popular for carrying out acylation reactions. Among the whole cell microbes, Aspergillus, Bacillus, and Streptomyces sp. are the most widely used, while Eucalyptus perriniana and Capsicum frutescens are the plant cell cultures used for the production of secondary metabolites. This chapter emphasizes the development of green solvents and identification of different sources/approaches to maximize polyphenol transformation for varied applications.

Antimicrobial properties of prunin, a citric flavanone glucoside, and its prunin 6″-O-lauroyl ester

AIMS

To determine the antimicrobial potential of prunin (P), a flavanone glucoside resulting from the hydrolysis of naringin present in grapefruit, and of its prunin 6″-O-lauroyl ester (PL), synthesized by enzymatic catalysis.

METHODS AND RESULTS

P and its lauroyl ester were tested against Gram-negative and Gram-positive bacteria, yeasts and moulds. P showed no inhibitory effect against the micro-organisms assayed, but stimulated growth of Pseudomonas aeruginosa and different Bacilllus sp. However, 150 μg ml(-1) of PL inhibited Escherichia coli, Salmonella enterica serovar Enteritidis, Salmonella enterica serovar Typhimurium, many Bacillus sp., Staphylococcus aureus ATCC29213, Enterococcus avium DSMZ17511, and different Listeria monocytogenes strains. In the last case, L. monocytogenes, sensitive or bacteriocin-resistant cells, lost nearly 4-log reductions after 30 min of contact. A bactericidal mode of action was determined using both scanning and transmission electronic microscopies.

CONCLUSIONS

PL could be used as a food additive, because at low concentration (150 μg ml(-1)) it exhibited antimicrobial activity against important food-borne pathogens. A bactericidal effect was also determined on L. monocytogenes sensitive and bacteriocin-resistant mutant strains. P did not show any antimicrobial property at all.

SIGNIFICANCE AND IMPACT OF THE STUDY

PL is a potential antimicrobial compound with a high anti-Listeria property.

Lipases in lipophilization reactions

Lipases are used in various sectors, as pharmaceutical, food or detergency industry. Their advantage versus classical chemical catalysts is that they exhibit a better selectivity and operate in milder reaction conditions. Theses enzymes can also be used in lipophilization reactions corresponding to the grafting of a lipophilic moiety to a hydrophilic one such as sugar, amino acids and proteins, or phenolic compounds. The major difficulty to overcome in such enzyme-catalyzed reaction resides in the fact that the two involved substrates greatly differ in term of polarity and solvent affinity. Therefore, several key parameters are to be considered in order to achieve the reaction in satisfactory kinetics and yields. The present review discusses the nature of such parameters (eg solvent nature, water activity, chemical modification of substrates) and illustrates their effect with examples of lipase-catalyzed lipophilization reactions of various sugar, amino acids or phenolic derivatives.

Use of ionic liquids as media for the biocatalytic preparation of flavonoid derivatives with antioxidant potency

Biocatalytic preparation of acylated derivatives of flavonoid glycosides was performed using various immobilized lipases in two different ionic liquids, namely 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF(4)) and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF(6)). The influence of various reaction parameters on the performance and the regioselectivity of the biocatalytic process was pointed out, using as model reaction the acylation of naringin and rutin with vinyl butyrate, catalyzed by immobilized Candida antarctica lipase at 60 degrees C. The biocatalytic modification of flavonoids strongly depended on the ionic liquid used, the molar ratio of substrates, as well as the acyl donor chain length. The highest conversion yield (about 65% after 96 h of incubation) was obtained with short chain acyl donors (up to four carbon atoms), at a relatively high molar ratio (10-15) in both ionic liquids used. The amount of monoacylated flavonoid derivatives produced in a single-step biocatalytic process in [bmim]BF(4) was up to 5.5 g/L for monoacylated rutin and 30 g/L for monoacylated naringin. The regioselectivity of the process was higher in [bmim]BF(4) than in [bmim]PF(6) or organic solvents. Reaction rates observed in ionic liquids were up to four times higher than those reported for organic media. The acylation of sugar moiety of rutin with various acyl donors affected its antioxidant potential towards both isolated LDL and total serum model in vitro. A significant increase of antioxidant activity was observed for rutin-4'''-O-oleate.

Biocatalytic preparation of acylated derivatives of flavonoid glycosides enhances their antioxidant and antimicrobial activity

Enzymatic synthesis of acylated derivatives of a monosaccharidic flavonoid chrysoeriol-7-O-beta-D-(3''-E-p-coumaroyl)-glucopyranoside as well as of a disaccharidic flavonoid chrysoeriol-7-[6'''-O-acetyl-beta-D-allosyl-(1-->2)-beta-D-glucopyranoside], isolated from Greek endemic plants, was performed using an immobilized Candida antarctica lipase in non-toxic organic solvents. The influence of the reaction parameters such as the molar ratio of acyl donor to flavonoid, as well as the nature of the acyl donor, on the performance of the biocatalytic process was pointed out using the acylation of naringin as a model reaction. With vinyl laurate as acyl donor, the highest conversion was observed at relatively high molar ratio (>or=10), using acetone as solvent. Lipase exhibits specificity towards primary alcohol of the glucose moiety of both flavonoid glycosides. The introduction of an acyl group into glucosylated flavonoids significantly improved their antioxidant activity towards both LDL and serum model in vitro. Furthermore, the acylated derivative of disaccharidic flavonoid increased its antimicrobial activity against two Gram-positive bacteria.

Perillyl alcohol is an angiogenesis inhibitor

Aberrant angiogenesis is essential for the progression of solid tumors and hematological malignancies. Thus, antiangiogenic therapy is one of the most promising approaches to control cancer. In the present work, we examined the ability of perillyl alcohol (POH), a dietary monoterpene with well-established tumor chemopreventive and chemotherapeutic activity, to interfere with the process of angiogenesis. POH remarkably prevented new blood vessel growth in the in vivo chicken embryo chorioallantoic membrane assay and proved to be effective in inhibiting the morphogenic differentiation of cultured endothelial cells into capillary-like networks both in collagen gel and Matrigel models. In addition, POH reduced the cell number in a proliferation assay and induced apoptosis of endothelial cells as indicated by the POH-mediated increase of caspase-3 activity and DNA fragmentation. Consistent with the observed antisurvival effect, POH treatment resulted in a significant inhibition of Akt phosphorylation in endothelial cells. Finally, POH was able to differentially modulate the release of two important angiogenic regulators: vascular endothelial growth factor (VEGF) and angiopoietin 2 (Ang2). POH decreased the release of VEGF from cancer cells but stimulated the expression of Ang2 by endothelial cells, indicating that it might suppress neovascularization and induce vessel regression. Overall, these data underscore the antiangiogenic potential of POH and suggest that POH, in addition to its anticancer activity, may be an effective agent in the treatment of angiogenesis-dependent diseases.

Novel enzymatic approach to the synthesis of flavonoid glycosides and their esters

Flavonoids such as (+)catechin can be efficiently solubilised in supersaturated solutions prepared with donor glycosides, e.g., p-nitrophenyl glycosides, di- and higher oligosaccharides, and poly(ethylene glycol) dimethyl ether in sufficiently high concentration for their efficient enzymatic glycosylation. Under these conditions several glycosidases readily accept (+)catechin as substrate and the target glycosides were prepared in one step in up to 26% yields. The regioselectivity of the reaction depends on the enzyme and substrate combination used; three positions, 5, 7, and 4', in the flavonoid can be glycosylated. The resulting and similar flavonoid glycosides were further modified by regioselective acylation with vinyl esters of arylpropenoic acids using lipases as biocatalyst. The efficiency of acylation was found to diminish in the order of vinyl cinnamate > vinyl ferulate > vinyl coumarate. This work demonstrates the feasibility of assembling complex flavonoid glycoside esters in just two steps by sequential use of commercially available glycosidases and lipases.