Microbial transformations of 6- and 7-methoxyflavones in Aspergillus niger and Penicillium chermesinum cultures.

A detailed study of the biotransformation of 6- and 7-methoxyflavones by four fungal strains (Aspergillus niger strains MB, KB, and SBP; Penicillium chermesinum 113) was carried out. Products of demethylation and also demethylation combined with hydroxylation at C-4' were identified. The biotransformation products were stronger antioxidants than the substrates.

8-Prenylnaringenin is an inhibitor of multidrug resistance-associated transporters, P-glycoprotein and MRP1.

Flavonoids with hydrophobic e.g. prenyl substituents might constitute the promising candidates for multidrug resistance (MDR) reversal agents. The interaction of 8-prenylnaringenin (8-isopentenylnaringenin), a potent phytoestrogen isolated from common hop (Humulus lupulus), with two multidrug resistance-associated ABC transporters of cancer cells, P-glycoprotein and MRP1, has been studied for the first time. Functional test based on the transport of fluorescent substrate BCECF revealed that the flavonoid strongly inhibited MRP1 transport activity in human erythrocytes (IC(50)=5.76+/-1.80muM). Expression of MDR-related transporters in drug-sensitive (LoVo) and doxorubicin-resistant (LoVo/Dx) human colon adenocarcinoma cell lines was characterized by RT-PCR and immunochemical methods and elevated expression of P-glycoprotein in resistant cells was found to be the main difference between these two cell lines. By means of flow cytometry it was shown that 8-prenylnaringenin significantly increased the accumulation of rhodamine 123 in LoVo/Dx cells. Doxorubicin accumulation in both LoVo and LoVo/Dx cells observed by confocal microscopy was also altered in the presence of 8-prenylnaringenin. However, the presence of the studied compound did not increase doxorubicin cytotoxicity to LoVo/Dx cells. It was concluded that 8-prenylnaringenin was not able to modulate MDR in human adenocarcinoma cell line in spite of the ability to inhibit both P-glycoprotein and MRP1 activities. To our best knowledge, this is the first report of 8-prenylnaringenin interaction with clinically important ABC transporters.

Substrates and modulators of the multidrug transporter Cdr1p of Candida albicans in antifungal extracts of medicinal plants.

The effective treatment of infections caused by the most frequent human fungal pathogens Candida albicans and Candida glabrata is hindered by a limited number of available antifungals and development of resistance. In this study, we identified new extracts of medicinal plants inhibiting the growth of C. glabrata, a species generally showing low sensitivity to azoles. The methanolic extract of Anacardium occidentalis with an MIC of 80 microg ml(-1) proved to be the most active. In contrast to higher azole sensitivity, C. albicans showed increased resistance to several extracts. Investigation of the possible contribution of the multidrug transporter of the ATP-binding cassette superfamily Cdr1p of C. albicans to extract tolerance revealed a differential response upon overproduction of this protein in Saccharaomyces cerevisiae. Whereas the growth inhibitory activity of many extracts was not affected by CDR1 overexpression, increased sensitivity to some of them was observed. In contrast, extracts showing no detectable anticandidal activity including the ethyl acetate extract of Trichilia emetica were detoxified by Cdr1p. The presence of a non-toxic Cdr1p-mediated ketoconazole resistance modulator accompanying growth-inhibitory Cdr1p substrates in this extract was revealed by further fractionation experiments.

Genistein derivatives decrease liposome membrane integrity--calcein release and molecular modeling study.

The ability of newly synthesized genistein benzyl and glycosylated derivatives to permeabilize the liposome membrane was studied by calcein-leakage method. All studied derivatives appeared to be more effective than their parent compound--genistein. Comparing the experimental results with theoretical calculations we found that in the case of benzyl derivatives the dipole moment of added benzene ring (with its substitutions) might be important for the strength of flavonoids-lipid interactions. This conclusion may have some implications for QSAR studies in which mostly the dipole moments of entire molecules are considered.

Repeated injections of PEG-PE liposomes generate anti-PEG antibodies.

Liposomes containing the polyethylene glycol (PEG) derivative of phosphatidyl ethanolamine (PE) have recently been found to be promising drug carriers, as they facilitate controlled and target-oriented release of therapeutics. They also reduce the side effects of many drugs. Here, we present the results of a study on antiliposomal properties of rabbit sera obtained after weekly injections of small liposomes containing 20% PEG-PE. The effect was analysed as the level of induced carboxyfluorescein release from these liposomes in vitro. The incubation of liposomes with rabbit serum taken after the injections induced the release of carboxyfluorescein at a higher level than was seen for incubation with untreated animal's serum. The strongest effect was observed for serum obtained after the second injection, i.e. during the second week of the study. The effect was much smaller after the serum samples were preheated at 56 degrees C. The binding of serum proteins by PEGylated liposomes was analysed via gel filtration and via the immunoblot technique using goat anti-rabbit IgG; this revealed that the serum protein which bound to the liposomes in vitro had a molecular weight of 55 kD and reacted with the anti-IgG antibody. Competition with PEG or lipids indicate that this IgG has an anti-PEG activity. We therefore assume that these antibodies are responsible for the activation of complement and leakage induction of PEG-liposomes. Such antibodies could be responsible for increased phagocytosis by RES macrophages (in particular liver macrophages) and decreased circulation time.