In vitro analysis of iron chelating activity of flavonoids

Flavonoids have been demonstrated to possess miscellaneous health benefits which are, at least partly, associated with iron chelation. In this in vitro study, 26 flavonoids from different subclasses were analyzed for their iron chelating activity and stability of the formed complexes in four patho/physiologically relevant pH conditions (4.5, 5.5, 6.8, and 7.5) and compared with clinically used iron chelator deferoxamine. The study demonstrated that the most effective iron binding site of flavonoids represents 6,7-dihydroxy structure. This site is incorporated in baicalein structure which formed, similarly to deferoxamine, the complexes with iron in the stoichiometry 1:1 and was not inferior in all tested pH to deferoxamine. The 3-hydroxy-4-keto conformation together with 2,3-double bond and the catecholic B ring were associated with a substantial iron chelation although the latter did not play an essential role at more acidic conditions. In agreement, quercetin and myricetin possessing all three structural requirements were similarly active to baicalein or deferoxamine at the neutral conditions, but were clearly less active in lower pH. The 5-hydroxy-4-keto site was less efficient and the complexes of iron in this site were not stable at the acidic conditions. Isolated keto, hydroxyl, methoxyl groups or an ortho methoxy-hydroxy groups were not associated with iron chelation at all.     

Synthesis and characterization of new beta-diketo derivatives with iron chelating ability

Here we report the synthesis, the characterization and a theoretical study on new glycosylated phenyl substituted beta-diketones; two classes of compounds are obtained according to the condensation reaction: central and side derivatives. Their iron(III) chelating ability is tested by means of UV-visible (UV-vis), potentiometric and NMR techniques. The conformation of central derivatives does not allow any metal chelation, while side derivatives bind iron(III) through the beta-dioxo moiety. The glycosyl moiety does not interact with metal ion but it helps to stabilize metal/ligand (1/3) complexes by means of hydrophylic interactions. The pK(a) of the ligands and the stability constants of their Fe(III) complexes are evaluated by means of UV-vis spectroscopy and potentiometry. A comparison with other iron-chelating agents, on the basis of lipophilicity and the pFe(III), is finally reported.     

In vitro metabolic stability of obestatin: kinetics and identification of cleavage products

The in vitro metabolic stability testing on synthetic obestatin peptides from two different species (human hOb and mouse mOb) using HPLC analysis is described. A reversed-phase C(18) column of 300A pore size was used, with a gradient system based on aqueous formic acid and acetonitrile. Electrospray ionization (ESI) ion trap mass spectrometry was used for identification of the chromatographic eluting peptide metabolic products, while UV (DAD) and fluorescence served quantitative purposes. Differences in the metabolic degradation kinetics of hOb and mOb were found in plasma, liver and kidney homogenate, with half-lives ranging between 12.6 and 138.0min. Proteolytic hydrolysis at the N-terminal Phe residue and cleavage at Pro(4)-Phe(5) were found to be two major metabolic pathways, accounting for more than 50% of the metabolic degradation. Several other labile peptide bonds were located. The influence of a standard protease inhibitor cocktail was investigated, as well as the metabolism of iodinated human obestatin in liver homogenate. Our results indicate that the major instability of obestatin peptides, as currently used in biomedical investigations, should be taken into account in the interpretation of the obtained results.     

In vitro studies of iron bioavailability

The bioavailability of iron from foods is ultimately determined by interactions between iron and other components in the digestive milieu. Perhaps the most important factor is the concentration of Fe2+ during transit through the duodenum. During in vitro simulations of human digestion it is possible to probe the concentration of Fe2+, the rate of Fe2+ formation, and total iron concentration using ferrous chromogens. It is crucial, of course, that the chromogen not interfere with the redox reactions occurring during digestion. Accordingly, ferrozine was examined with regard to its ability to reduce complexes Fe3+, alter rates of Fe3+ production, detect Fe2+ present in the digestive mixture and differentiate the effects of chelating and reducing agents in the mobilization of iron from pinto beans. The chromogen was found to be free from apparent artefacts and to be a sensitive and reproducible probe of the state of iron in digestive mixtures.     

Molecular characterisation of the colicin E2 operon and identification of its products

Summary The DNA sequence of the entire colicin E2 operon was determined. The operon comprises the colicin activity gene, ceaB, the colicin immunity gene, ceiB, and the lysis gene, celB, which is essential for colicin release from producing cells. A potential LexA binding site is located immediately upstream from ceaB, and a rho-independent terminator structure is located immediately downstream from celB. A comparison of the predicted amino acid sequences of colicin E2 and cloacin DF13 revealed extensive stretches of homology. These colicins have different modes of action and recognise different cell surface receptors; the two major regions of heterology at the carboxy terminus, and in the carboxy-terminal end of the central region probably correspond to the catalytic and receptor-recognition domains, respectively. Sequence homologies between colicins E2, A and E1 were less striking, and the colicin E2 immunity protein was not found to share extensive homology with the colicin E3 or cloacin DF13 immunity proteins. The lysis proteins of the ColE2, ColE1 and CloDF13 plasmids are almost identical except in the aminoterminal regions, which themselves have overall similarity with lipoprotein signal peptides. Processing of the ColE2 prolysis protein to the mature form was prevented by globomycin, a specific inhibitor of the lipoprotein signal peptidase. The mature ColE2 lysis protein was located in the cell envelope. The results are discussed in terms of the functional organisation of the colicin operons and the colicin proteins, and the way in which colicins are released from producing cells.     

Recent advances in microbial production of aromatic natural products and their derivatives

Applied Microbiology and Biotechnology - Aromatic natural products represent a diverse class of chemicals with great industrial significance. Usually, they serve as the building blocks for...     

In vitro double transposition for DNA identification

We present a double transposition technique that inserts two different transposons into target DNA to act as priming sites for amplifying the region between the two transposons for sequencing applications. Unlike some current sequencing approaches, the genome of the unknown target remains intact in this method. The transposition reaction, DNA repair, and subsequent sequencing were performed entirely in vitro, without the need for transformation into bacteria, and resulted in sequence homology with the plasmid DNA target. This approach can reduce the time required for the assay by more than a day compared with standard techniques and reduces the number of required enzymatic steps. In addition, the in vitro method enables transposition to be carried out in automated microfluidic platforms without the need for significant sample manipulation. As a demonstration of incorporating transposition techniques into high-throughput technologies, single transposition reactions were carried out in picoliter-sized droplets generated on a microfluidic platform.     

In vitro antioxidant profile of phenolic acid derivatives

Several caffeic acid esters isolated from propolis exhibit interesting antioxidant properties, but their in vivo use is compromised by hydrolysis of the ester bond in the gastrointestinal tract. Therefore, a series of caffeic acid amides were synthesized and their in vitro antioxidant profile was determined. A series of hydroxybenzoic acids, hydroxycinnamic acids, and the synthesized caffeic acid amides were tested for both their 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging and microsomal lipid peroxidation-inhibiting activity. Some of the highly active antioxidants were further tested by means of electron paramagnetic resonance for their hydroxyl radical scavenging activity. Since a promising antioxidant compound should show a lipid peroxidation-inhibiting activity at micromolar level and a low cytotoxicity, the cytotoxicity of the phenolic compounds was also studied. In all the assays used, the caffeic acid anilides and the caffeic acid dopamine amide showed an interesting antioxidant activity.     

In vitro laser ablation of natural marine biofilms

We studied the efficiency of pulsed low-power laser irradiation of 532 nm from an Nd:YAG (neodymium-doped yttrium-aluminum-garnet) laser to remove marine biofilm developed on titanium and glass coupons. Natural biofilms with thicknesses of 79.4 +/- 27.8 microm (titanium) and 107.4 +/- 28.5 microm (glass) were completely disrupted by 30 s of laser irradiation (fluence, 0.1 J/cm2). Laser irradiation significantly reduced the number of diatoms and bacteria in the biofilm (paired t test; P < 0.05). The removal was better on titanium than on glass coupons.     

In vitro production and identification of autotetraploids of Scutellaria baicalensis

The roots of Scutellaria baicalensis are a major traditional Chinese medicine. We report research on induction, characteristics and chemical analysis of polyploid plants of S. baicalensis. Immersing calluses in 0.2% colchicine solution for 12 h prior to culture induced a high number of tetraploid plants. The induction rate reached as high as 40% of treated calluses. More than 50 lines of tetraploid plants were obtained. All tetraploid plants showed typical polyploidy characteristics. Twenty selected tetraploid lines were transferred to the field for determination of morphological characteristics and for chemical assays. Seven elite lines have been selected for further selection and breeding into new varieties for commercial production.     

亚肉座菌天然产物的分离鉴定及抗肿瘤活性

亚肉座菌能侵染粉虱和介壳虫,具有悠久的生物防治历史,但关于其天然产物的种类及抗肿瘤活性研究尚不深入。本研究借助硅胶柱、HPLC等色谱技术从亚肉座菌发酵液中分离纯化到6个化合物。基于核磁共振和质谱数据解析,化合物1–6依次鉴定为:5α,8α-表二氧-24(R)-甲基胆甾-6,22-二烯-3β-醇5α,8α-epidioxy-24(R)-methylcholesta-6,22-diene-3β-ol(1),杜斯塔宁dustanin(2),3β-乙酸基-15α,22-二羟基何伯烷3β-acetoxy-15α,22-dihydroxyhopane(3),麦角固醇ergosterol(4),7β,15α,22-三羟基何伯烷7β,15α,22-trihydroxyhopane(5)和5-(羟甲基)呋喃-3-羧酸flufuran(6),化合物1和6为首次从虫生真菌中获得。对化合物进行抗肿瘤活性测试发现,化合物1和5对人肝癌细胞(BEL-7404)展示显著的抗肿瘤活性,IC50值分别为28μmol/L和12.4μmol/L,而它们对人正常肝脏细胞(HL-7702)和肾脏上皮细胞(HEK-293T)均未呈现出明显活性。该研究对阐明亚肉座菌代谢产物及其活性提供了重要数据,为开发抗肿瘤新药提供了理论参考。     

In vitro inhibition of bacterial growth by iron chelators

The antimicrobial activity of the iron(III)-selective 3-hydroxypyridin-4-one chelators, CP251(1) and CP252(2), was evaluated in comparison with that of diethylenetriamine-penta acetic acid (3). CP251 was found to exhibit an inhibitory effect on the growth of both Gram-positive and Gram-negative bacteria. CP251 may find application in the treatment of external infections such as those associated with wounds.     

In vitro cytotoxicity evaluation of some substituted isatin derivatives

A range of substituted 1H-indole-2,3-diones (isatins) were synthesized using standard procedures and their cytotoxicity evaluated against the human monocyte-like histiocytic lymphoma (U937) cell line in vitro. SAR studies identified C(5), C(6), and C(7) substitution greatly enhanced activity with some di- and tri-halogenated isatins giving IC(50) values <10 microM. Of the 23 compounds tested, four were selected for further screening against a panel of five human cancer cell lines. These compounds, in general, showed greater selectivity toward leukemia and lymphoma cells over breast, prostate, and colorectal carcinoma cell lines. The most active compound, 5,6,7-tribromoisatin (2p), was found to be antiproliferative at low micromolar concentrations and also activated the effector caspases 3 and 7 in a dose-dependent manner. These results indicate that di- and tri-substituted isatins may be useful leads for anticancer drug development in the future.     

In vitro inhibition of Sphaeropsis sapinea by natural stilbenes

The effects of pinosylvin, pinosylvin monomethyl ether, pinosylvin dimethyl ether, and resveratrol on the fungal shoot blight and canker pathogen of conifers Sphaeropsis sapinea were examined in vitro. Effects of compounds, isolates, and concentrations on both conidial germination and mycelial growth were significant (values of P < 0.001), indicating inhibitory activity of these compounds.     

In vitro and in vivo evaluation of O-alkyl derivatives of tramadol

Tramadol is a centrally acting opioid analgesic structurally related to codeine and morphine. O-Alkyl, N-desmethyl, and non-phenol containing derivatives of tramadol were synthesized to probe their effect on metabolic stability and both in vitro and in vivo potency.     

LC-NMR: a new tool to expedite the dereplication and identification of natural products

The rapid identification of known or undesirable compounds from natural products extracts — “dereplication” — is an important step in an efficiently run natural products discovery program. Dereplication strategies use analytical techniques and database searching to determine the identity of an active compound at the earliest possible stage in the discovery process. In the past few years, advances in technology have allowed the development of tandem analytical techniques such as liquid chromatography mass spectrometry (LC-MS), LC-MS-MS, liquid chromatography nuclear magnetic resonance (LC-NMR), and LC-NMR-MS. LC-NMR, despite its lower sensitivity as compared to LC-MS, provides a powerful tool for rapid identification of known compounds and identification of structure classes of novel compounds. LC-NMR is especially useful in instances where the data from LC-MS are incomplete or do not allow confident identification of the active component of a sample. LC-NMR has been used to identify the marine alkaloid aaptamine as the active component in an extract of the sponge Aaptos sp. This extract had been identified as an enzyme inhibitor by a high throughput screening (HTS) effort. Isolated aaptamine exhibited an IC₅₀=120 μM against this enzyme. Strategies for the identification of aaptamine and for the use of LC-NMR in a natural products HTS program are discussed. Journal of Industrial Microbiology & Biotechnology (2000) 25, 342–345. Received 30 March 2000/ Accepted in revised form 03 July 2000