Vera Ribeiro

DNA cleavage activity of VIVO(acac)2 and derivatives

The DNA cleavage activity of several beta-diketonate vanadyl complexes is examined. Vanadyl acetylacetonate, V(IV)O(acac)(2), 1, shows a remarkable activity in degrading plasmid DNA in the absence of any activating agents, air and photoirradiation. The cleaving activity of several related complexes V(IV)O(hd)(2) (2, Hhd=3,5-heptanedione), V(IV)O(acac-NH(2))(2) (3, Hacac-NH(2)=acetoacetamide) and V(IV)O(acac-NMe(2))(2) (4, Hacac-NMe(2)=N,N-dimethylacetoacetamide) is also evaluated. It is shown that 2 exhibits an activity similar to 1, while 3 and 4 are much less efficient cleaving agents. The different activity of the complexes is related to their stability towards hydrolysis in aqueous solution, which follows the order 1 approximately 2>>3 approximately 4. The nature of the pH buffer was also found to be determinant in the nuclease activity of 1 and 2. In a phosphate buffered medium DNA cleavage by these agents is much more efficient than in tris, hepes, mes or mops buffers. The reaction seems to take place through a mixed mechanism, involving the formation of reactive oxygen species (ROS), namely OH radicals, and possibly also direct cleavage at phosphodiester linkages induced by the vanadium complexes.

Determination of ABCB1 polymorphisms and haplotypes frequencies in a French population.

The ATP‐binding cassette (ABC) transporter ABCB1, or P‐glycoprotein, is a transmembrane efflux pump well known for its implication in drug transport and chemoresistance. ABCB1 substrates include either drugs, such as antiretrovirals and immunomodulators, or physiological molecules like phospholipids. Pharmacogenetic analysis of ABCB1 polymorphisms, in addition to other xenobiotic metabolizing enzymes, might help to personalize and optimize drug therapy. Indeed, some polymorphisms of ABCB1 have been implicated in susceptibility to diseases, changes in drug pharmacokinetics, and in variation of the biological response to drug treatment. In addition, variant and haplotype distributions differ depending on ethnicity. Thus, some ethnies may be at higher risk for adverse events, inefficacy of treatment or prevalence of pathologies. This study aimed to determine frequencies of ABCB1 polymorphisms and haplotypes in a sample of French healthy individuals. DNA was isolated from blood‐EDTA. Polymerase chain reaction‐restriction fragment length polymorphism and TaqMan single nucleotide polymorphism genotyping assays were used to genotype 227 individuals for T‐129C, G‐1A, A61G, G1199A, C1236T, T‐76A, G2677T/A and C3435T polymorphisms. The observed frequencies of the variant allele for these eight polymorphisms are 0.04, 0.08, 0.09, 0.06, 0.42, 0.46, 0.45 and 0.46 respectively. These polymorphisms are in linkage disequilibrium and haplotype frequencies were determined, the most frequent haplotype being the one with variants at position 1236, 2677 and 3435 and wild‐type alleles at the other positions. Finally, the frequencies of these eight ABCB1 polymorphisms in our French individuals supposed to be healthy population are quite similar to those described in other Caucasian populations except for the C3435T polymorphism.

Plasmodium infection alters Anopheles gambiae detoxification gene expression.

BackgroundAnopheles gambiae has been shown to change its global gene expression patterns upon Plasmodium infection. While many alterations are directly related to the mosquitos innate immune response, parasite invasion is also expected to generate toxic by-products such as free radicals. The current study aimed at identifying which loci coding for detoxification enzymes are differentially expressed as a function of Plasmodium berghei infection in midgut and fat body tissues.ResultsUsing a custom-made DNA microarray, transcript levels of 254 loci primarily belonging to three major detoxification enzyme families (glutathione S-transferases, cytochrome P450 monooxygenases and esterases) were compared in infected and uninfected mosquitoes both during ookinete invasion and the release of sporozoites into the hemocoel. The greatest changes in gene expression were observed in the midgut in response to ookinete invasion. Interestingly, many detoxification genes including a large number of P450s were down-regulated at this stage. In the fat body, while less dramatic, gene expression alterations were also observed and occurred during the ookinete invasion and during the release of sporozoites into the hemocoel. While most gene expression changes were tissue-related, CYP6M2, a CYP previously associated with insecticide resistance, was over-expressed both in the midgut and fat body during ookinete invasion.ConclusionsMost toxicity-related reactions occur in the midgut shortly after the ingestion of an infected blood meal. Strong up-regulation of CYP6M2 in the midgut and the fat body as well as its previous association with insecticide resistance shows its broad role in metabolic detoxification.

CYP2C8 polymorphism among the Portuguese

Abstract Cytochrome P450 2C8 (CYP2C8) is a polymorphic phase I drug-metabolising enzyme involved in the metabolism of a wide variety of xenobiotics, as well as a proposed player in the regulation of vascular tone. Polymorphisms in this gene may have an impact on the metabolism of therapeutic drugs such as paclitaxel and verapamil. In this report we have determined the frequencies of the main non-synonymous CYP2C8 alleles, 805A>T (CYP2C8*2), 416G>A/1196A>G (CYP2C8*3) and 792C>G (CYP2C8*4) in a sample representative of Portuguese Caucasians. The allelic frequencies determined were 1.2%, 19.8%, and 6.4% for CYP2C8*2, CYP2C8*3, and CYP2C*4, respectively. The observed CYP2C8*3 prevalence is significantly different from the frequencies previously reported in North European populations.

Analysis of binding modes of ligands to multiple conformations of CYP3A4.

Cytochromes P450 (CYPs) are extremely versatile enzymes capable of catalyzing a vast number of compounds, and CYP3A4 is no exception metabolizing approximately half of the currently marketed drugs, besides endogenous compounds. To metabolize such a variety of compounds, CYP3A4 has to be extremely flexible, which makes interaction studies difficult. We employ a multi-conformational docking setup where conformations are generated by several molecular dynamics simulations to analyze the binding modes of various ligands, and the docking is considered successful if the ligand site of catalysis (SOC) is within 6.0A of the haem Fe. While docking with the X-ray structure proved unsuccessful with all ligands, the multi-conformational docking achieved successful binding of each ligand to at least one protein conformation. Analysis of the docked solutions highlights residues in the active site cavity that may have an important role in access, binding and stabilization of the ligand.

The expression of the solute carriers NTCP and OCT-1 is regulated by cholesterol in HepG2 cells.

Drug disposition and response are greatly determined by the activities of drug‐metabolizing enzymes and transporters. While the knowledge in terms of CYP enzymes and efflux ABC transporters (such as MDR1, P‐glycoprotein) is quite extensive, influx transporters are increasingly being unveiled as key contributors to the process of drug disposition. There is little information on the regulation of these proteins in human cells, especially as regards the effect of endogenous compounds. In this study, we analysed the expression of CYP3A4 and three uptake transporters NTCP (SLC10A1), OATP‐A/OATP1A2 (SLCO1A2) and OCT‐1 (SLC22A1) in HepG2 cells following treatment with cholesterol. While CYP3A4 and OATP1A2 expression was unaffected, cholesterol treatment led to increased levels of NTCP and OCT‐1 mRNAs. Alterations in the functional characteristics and/or expression levels of drug transporters in the liver may conceivably contribute to the variability in drug oral bioavailability often observed in the clinical settings.

Electrochemical DNA sensor for detection of single nucleotide polymorphisms

Abstract In recent years there has been an increased interest in using biosensors for the recognition and monitoring of molecule interactions. DNA sensors and gene chips are particularly relevant for directly applying the information gathered from the genome projects. In this work electrochemical techniques are used to develop methodologies to detect DNA polymorphisms in human genes using cytochrome P450 3A4 (CYP3A4) as a model gene. CYP3A4*1B oligonucleotides were immobilized on the surface of a gold electrode and hybridized with fully complementary oligonucleotide sequences as well as with mismatched sequences corresponding to the CYP3A4*1A reference sequence. The methodology developed is based on double-stranded DNAs ability to transport charge along nucleotide stacking. The perturbation of the double helix pi-stack introduced by a mismatched nucleotide reduces electron flow and can be detected by measuring the attenuation of the charge transfer. The methodology developed could identify CYP3A4*1A homozygotes by the 5 μC charge attenuation observed when compared with DNA samples containing at least one CYP3A4*1B allele.

Ethnic differences in the prevalence of polymorphisms in CYP7A1, CYP7B1 AND CYP27A1 enzymes involved in cholesterol metabolism.

It is well known that drug disposition and response are greatly determined by the activities of drug metabolizing enzymes, which are polymorphic. Some of these polymorphisms are clinically relevant and presented an ethnic-dependent pattern of distribution. The characterization of the genetic distribution of different populations allows the selection of therapeutic options in accordance with the genetic background, with the objective to avoid adverse reactions and inefficacy of the treatment. In this work, we studied selected genetic polymorphisms in drug metabolizing enzymes in three different ethnic groups – Portugal, Mozambique and Colombia. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) genotyping methods were developed for drug metabolizing enzymes, namely, cholesterol 7α-hydroxylase (CYP7A1) (–203A>C, –346C>T, –496C>T, N233S, G347S), sterol 27-hydroxylase (CYP27A1) (R164W, A169V, D273N, V400A) and oxysterol 7α-hydroxylase (CYP7B1) (–116C>G, R324H, 1774C>T) to characterize the allelic distribution of these polymorphisms among three different ethnic/geographic origins. A total of 12 CYP7A1, CYP27A1 and CYP7B1 genetic variants were genotyped in a sample of 92 Portuguese, 151 Mozambican and 91 Colombian subjects. The variants N233S in CYP7A1 and 1774C>T in CYP7B1 were not detected in any population studied. The promoter polymorphisms in CYP7A1 (–203A>C, –346C>T, –496C>T) had high frequency in the three ethnic groups. G347S (CYP7A1), R164W, A169V and V400A (CYP27A1) were present in a low frequency but with a similar distribution in the three ethnic groups. Significant differences were observed for D273N (CYP27A1), –346C>T (CYP7A1), –116C>G and R324H (CYP7B1)Our results demonstrate a high variability of drug metabolizing enzymes between the different populations analyzed, indicating that at least some of these polymorphisms are ethnic specific.

Bioenergetic cues shift FXR splicing towards FXRα2 to modulate hepatic lipolysis and fatty acid metabolism

Objective Farnesoid X receptor (FXR) plays a prominent role in hepatic lipid metabolism. The FXR gene encodes four proteins with structural differences suggestive of discrete biological functions about which little is known. Methods We expressed each FXR variant in primary hepatocytes and evaluated global gene expression, lipid profile, and metabolic fluxes. Gene delivery of FXR variants to Fxr−/− mouse liver was performed to evaluate their role in vivo. The effects of fasting and physical exercise on hepatic Fxr splicing were determined. Results We show that FXR splice isoforms regulate largely different gene sets and have specific effects on hepatic metabolism. FXRα2 (but not α1) activates a broad transcriptional program in hepatocytes conducive to lipolysis, fatty acid oxidation, and ketogenesis. Consequently, FXRα2 decreases cellular lipid accumulation and improves cellular insulin signaling to AKT. FXRα2 expression in Fxr−/− mouse liver activates a similar gene program and robustly decreases hepatic triglyceride levels. On the other hand, FXRα1 reduces hepatic triglyceride content to a lesser extent and does so through regulation of lipogenic gene expression. Bioenergetic cues, such as fasting and exercise, dynamically regulate Fxr splicing in mouse liver to increase Fxrα2 expression. Conclusions Our results show that the main FXR variants in human liver (α1 and α2) reduce hepatic lipid accumulation through distinct mechanisms and to different degrees. Taking this novel mechanism into account could greatly improve the pharmacological targeting and therapeutic efficacy of FXR agonists.

The effect of phosphate on the nuclease activity of vanadium compounds

The nuclease activity of VO(acac)2 (1, acac = acetylacetone) and its derivatives VO(hd)2 (2, hd = 3,5-heptanedione), VO(Cl-acac)2 (3, Cl-acac = 3-chloro-2,4-pentanedione), VO(Et-acac)2 (4, Et-acac = 3-ethyl-2,4-pentanedione) and VO(Me-acac)2 (5, Me-acac = 3-methyl-2,4-pentanedione), is studied by agarose gel electrophoresis, UV-visible spectroscopy, cyclic and square wave voltammetry and (51)V NMR. The mechanism is shown to be oxidative and associated with the formation of reactive oxygen species (ROS). Hydrolytic cleavage of the phosphodiester bond is also promoted by 1, but at much slower rate which cannot compete with the oxidative mechanism. The generation of ROS is much higher in the presence of phosphate buffer when compared with organic buffers and this was attributed to the formation of a mixed-ligand complex containing phosphate, (V(IV)O)(V(V)O)(acac)2(HnPO4(n-3)), presenting a quasi-reversible voltammetric behavior. The formation of this species was further observed by Electrospray Ionization Mass Spectrometry (ESI-MS). Phosphate being an essential species in most biological media, the importance of the formation of mixed-ligand species in other vanadium systems is emphasized.