Effect of sildenafil on human aromatase activity: From in vitro structural analysis to catalysis and inhibition in cells

Aromatase catalyses the conversion of androgens into estrogens and is a well-known target for breast cancer therapy. As it has been suggested that its activity is affected by inhibitors of phosphodiesterase-5, this work investigates the potential interaction of sildenafil with aromatase. This is carried out both at molecular level through structural and kinetics assays applied to the purified enzyme, and at cellular level using neuronal and breast cancer cell lines. Sildenafil is found to bind to aromatase with a K_D of 0.58±0.05μM acting as a partial and mixed inhibitor with a maximal inhibition of 35±2%. Hyperfine sublevel correlation spectroscopy and docking studies show that sildenafil binds to the heme iron via its 6th axial water ligand. These results also provide information on the starting molecular scaffold for the development of new generations of drugs designed to inhibit aromatase as well as phosphodiesterase-5, a new emerging target for breast cancer therapy.

The effect of a C298D mutation in CaHydA [FeFe]-hydrogenase: Insights into the protein-metal cluster interaction by EPR and FTIR spectroscopic investigation

A conserved cysteine located in the signature motif of the catalytic center (H-cluster) of [FeFe]-hydrogenases functions in proton transfer. This residue corresponds to C298 in Clostridium acetobutylicum CaHydA. Despite the chemical and structural difference, the mutant C298D retains fast catalytic activity, while replacement with any other amino acid causes significant activity loss. Given the proximity of C298 to the H-cluster, the effect of the C298D mutation on the catalytic center was studied by continuous wave (CW) and pulse electron paramagnetic resonance (EPR) and by Fourier transform infrared (FTIR) spectroscopies. Comparison of the C298D mutant with the wild type CaHydA by CW and pulse EPR showed that the electronic structure of the center is not altered. FTIR spectroscopy confirmed that absorption peak values observed in the mutant are virtually identical to those observed in the wild type, indicating that the H-cluster is not generally affected by the mutation. Significant differences were observed only in the inhibited state Hox-CO: the vibrational modes assigned to the COexo and Fed-CO in this state are shifted to lower values in C298D, suggesting different interaction of these ligands with the protein moiety when C298 is changed to D298. More relevant to the catalytic cycle, the redox equilibrium between the Hox and Hred states is modified by the mutation, causing a prevalence of the oxidized state. This work highlights how the interactions between the protein environment and the H-cluster, a dynamic closely interconnected system, can be engineered and studied in the perspective of designing bio-inspired catalysts and mimics.

Isolation and characterization of a new [FeFe]-hydrogenase from Clostridium perfringens

This paper reports the first characterization of an [FeFe]-hydrogenase from a Clostridium perfringens strain previously isolated in our laboratory from a pilot-scale bio-hydrogen plant that efficiently produces H2 from waste biomasses. On the basis of sequence analysis, the enzyme is a monomer formed by four domains hosting various iron-sulfur centres involved in electron transfer and the catalytic center H-cluster. After recombinant expression in Escherichia coli, the purified protein catalyzes H2 evolution at high rate of 1645 ± 16 s(-1) . The optimal conditions for catalysis are in the pH range 6.5-8.0 and at the temperature of 50 °C. EPR spectroscopy showed that the H-cluster of the oxidized enzyme displays a spectrum coherent with the Hox state, whereas the CO-inhibited enzyme has a spectrum coherent with the Hox -CO state. FTIR spectroscopy showed that the purified enzyme is composed of a mixture of redox states, with a prevalence of the Hox ; upon reduction with H2 , vibrational modes assigned to the Hred state were more abundant, whereas binding of exogenous CO resulted in a spectrum assigned to the Hox -CO state. The spectroscopic features observed are similar to those of the [FeFe]-hydrogenases class, but relevant differences were observed given the different protein environment hosting the H-cluster.

EPR investigation of TiCl3 dissolved in polar solvents--implications for the understanding of active Ti(III) species in heterogeneous Ziegler-Natta catalysts

Multi-frequency continuous-wave and pulsed EPR techniques are employed to investigate Ti(III)-chloro complexes obtained by dissolving TiCl3 in anhydrous and hydrated methanol. Two distinctly different species, characterized by different g matrices are observed in the two cases. Hyperfine sublevel correlation (HYSCORE) spectroscopy is found to be a powerful method to identify the type of nuclei surrounding the Ti(3+) ion. For the first time, the hyperfine and nuclear quadrupole data of Ti(III)-bound (35/37)Cl nuclei are reported together with (1)H and (13)C hyperfine data of the coordinated methanol molecules. DFT modelling allows interpreting the measured spin Hamiltonian parameters in terms of microscopic models of the solvated species. The theoretical observable properties (g matrix, (35/37)Cl, (1)H and (13)C hyperfine tensors) are in quantitative agreement with the experiments for two families of complexes: [TiCln(CH3OH)6-n]((3-n)+) (with n ranging from 1 to 3) and [Ti(CH3OH)5(OH)](2+) or [Ti(CH3OH)5(OCH3)](2+). The first complex is observed in anhydrous methanol, while the second type of complex is observed when water is added to the solution, the presence of OH(-) and/or CH3O(-) species being promoted by water hydrolysis. The results obtained for the frozen solutions are critically compared to EPR spectra recorded for a MgCl2-supported Ti-based Ziegler-Natta model catalyst.

Probing the coordination environment of Ti3+ ions coordinated to nitrogen-containing Lewis bases

A combined EPR and DFT study on model systems reveals fingerprint ¹⁴N hyperfine and quadrupole data to identify binding of nitrogen-containing Lewis bases to Ti(iii).

Chemical composition of an aqueous oxalato-/citrato-VO(2+) solution as determinant for vanadium oxide phase formation

Aqueous solutions of oxalato- and citrato-VO(2+) complexes are prepared, and their ligand exchange reaction is investigated as a function of the amount of citrate present in the aqueous solution via continuous-wave electron paramagnetic resonance (CW EPR) and hyperfine sublevel correlation (HYSCORE) spectroscopy. With a low amount of citrate, monomeric cis-oxalato-VO(2+) complexes occur with a distorted square-pyramidal geometry. As the amount of citrate increases, oxalate is gradually exchanged for citrate. This leads to (i) an intermediate situation of monomeric VO(2+) complexes with a mix of oxalate/citrate ligands and (ii) a final situation of both monomeric and dimeric complexes with exclusively citrato ligands. The monomeric citrato-VO(2+) complexes dominate (abundance > 80%) and are characterized by a 6-fold chelation of the vanadium(IV) ion by 4 RCO2(-) ligands at the equatorial positions and a H2O/R-OH ligand at the axial position. The different redox stabilities of these complexes, relative to that of dissolved O2 in the aqueous solution, is analyzed via (51)V NMR. It is shown that the oxidation rate is the highest for the oxalato-VO(2+) complexes. In addition, the stability of the VO(2+) complexes can be drastically improved by evacuation of the dissolved O2 from the solution and subsequent storage in a N2 ambient atmosphere. The vanadium oxide phase formation process, starting with the chemical solution deposition of the aqueous solutions and continuing with subsequent processing in an ambient 0.1% O2 atmosphere, differs for the two complexes. The oxalato-VO(2+) complexes turn into the oxygen-deficient crystalline VO2 B at 400 °C, which then turns into crystalline V6O13 at 500 °C. In contrast, the citrato-VO(2+) complexes form an amorphous film at 400 °C that crystallizes into VO2 M1 and V6O13 at 500 °C.

Marked difference in the electronic structure of cyanide-ligated ferric protoglobins and myoglobin due to heme ruffling

Electron paramagnetic resonance experiments reveal a significant difference between the principal g values (and hence ligand-field parameters) of the ferric cyanide-ligated form of different variants of the protoglobin of Methanosarcina acetivorans (MaPgb) and of horse heart myoglobin (hhMb). The largest principal g value of the ferric cyanide-ligated MaPgb variants is found to be significantly lower than for any of the other globins reported so far. This is at least partially caused by the strong heme distortions as proven by the determination of the hyperfine interaction of the heme nitrogens and mesoprotons. Furthermore, the experiments confirm recent theoretical predictions [Forti, F.; Boechi, L., Bikiel, D., Martí, M.A.; Nardini, M.; Bolognesi, M.; Viappiani, C.; Estrin, D.; Luque, F. J. J. Phys. Chem. B 2011, 115, 13771-13780] that Phe(G8)145 plays a crucial role in the ligand modulation in MaPgb. Finally, the influence of the N-terminal 20 amino-acid chain on the heme pocket in these protoglobins is also proven.

Biosynthesis, release and degradation of the novel endogenous cannabimimetic metabolite 2-arachidonoylglycerol in mouse neuroblastoma cells

The monoacylglycerol 2-arachidonoylglycerol (2-AG) has been recently suggested as a possible endogenous agonist at cannabinoid receptors both in brain and peripheral tissues. Here we report that a widely used model for neuronal cells, mouse N18TG2 neuroblastoma cells, which contain the CB1 cannabinoid receptor, also biosynthesize, release and degrade 2-AG. Stimulation with ionomycin (1-5 microM) of intact cells prelabelled with [3H]arachidonic acid ([3H]AA) led to the formation of high levels of a radioactive component with the same chromatographic behaviour as synthetic standards of 2-AG in TLC and HPLC analyses. The amounts of this metabolite were negligible in unstimulated cells, and greatly decreased in cells stimulated in the presence of the Ca2+-chelating agent EGTA. The purified component was further characterized as 2-AG by: (1) digestion with Rhizopus arrhizus lipase, which yielded radiolabelled AA; (2) gas chromatographic-MS analyses; and (3) TLC analyses on borate-impregnated plates. Approx. 20% of the 2-AG produced by stimulated cells was found to be released into the incubation medium when this contained 0.1% BSA. Subcellular fractions of N18TG2 cells were shown to contain enzymic activity or activities catalysing the hydrolysis of synthetic [3H]2-AG to [3H]AA. Cell homogenates were also found to convert synthetic [3H]sn-1-acyl-2-arachidonoylglycerols (AcAGs) into [3H]2-AG, suggesting that 2-AG might be derived from AcAG hydrolysis. When compared with ionomycin stimulation, treatment of cells with exogenous phospholipase C, but not with phospholipase D or A2, led to a much higher formation of 2-AG and AcAGs. However, treatment of cells with phospholipase A2 10 min before ionomycin stimulation caused a 2.5-3-fold potentiation of 2-AG and AcAG levels with respect to ionomycin alone, whereas preincubation with the phospholipase C inhibitor neomycin sulphate did not inhibit the effect of ionomycin on 2-AG and AcAG levels. These results suggest that the Ca2+-induced formation of 2-AG proceeds through the intermediacy of AcAGs but not necessarily through phospholipase C activation. By showing for the first time the existence of molecular mechanisms for the inactivation and the Ca2+-dependent biosynthesis and release of 2-AG in neuronal cells, the present paper supports the hypothesis that this cannabimimetic monoacylglycerol might be a physiological neuromodulator.

Biosynthesis, uptake, and degradation of anandamide and palmitoylethanolamide in leukocytes

Anandamide (arachidonoylethanolamide, AnNH) and palmitoylethanolamide (PEA) have been proposed as the physiological ligands, respectively, of central and peripheral cannabinoid receptors. Both of these receptors are expressed in immune cells, including macrophages and mast cells/basophils, where immunomodulatory and/or anti-inflammatory actions of AnNH and PEA have been recently reported. We now provide biochemical grounds to these actions by showing that the biosynthesis, uptake, and degradation of AnNH and PEA occur in leukocytes. On stimulation with ionomycin, J774 macrophages and RBL-2H3 basophils produced AnNH and PEA, probably through the hydrolysis of the corresponding N-acylphosphatidylethanolamines, also found among endogenous phospholipids. Immunological challenge of RBL-2H3 cells also caused AnNH and PEA release. The chemical structure and the amounts of AnNH and PEA produced upon ionomycin stimulation were determined by means of double radiolabeling experiments and isotope dilution gas chromatography/electron impact mass spectrometry. Both cell lines rapidly sequestered the two amides from the culture medium through temperature-dependent, saturable and chemically inactivable mechanisms. Once uptaken by basophils, AnNH and PEA compete for the same inactivating enzyme which catalyzes their hydrolysis to ethanolamine. This enzyme was found in both microsomal and 10,000 x g fractions of RBL cell homogenates, and exhibited similar inhibition and temperature/pH dependence profiles but a significantly higher affinity for PEA with respect to neuronal "anandamide amidohydrolase." The finding of biosynthetic and inactivating mechanisms for AnNH and PEA in macrophages and basophils supports the previously proposed role as local modulators of immune/inflammatory reactions for these two long chain acylethanolamides.

Novel inhibitors of brain, neuronal, and basophilic anandamide amidohydrolase

Mammalian brain as well as mouse neuroblastoma (N18TG2) and rat basophilic leukaemia (RBL) cells were previously shown to contain "anandamide amidohydrolase', a membrane-bound enzyme sensitive to serine and cysteine protease inhibitors and catalyzing the hydrolysis of the endogenous cannabimimetic metabolite, anandamide (arachidonoyl-ethanolamide). With the aim of developing novel inhibitors of this enzyme, we synthesized three arachidonic acid (AA) analogues, i.e. arachidonoyl-diazo-methyl-ketone (ADMK), ara-chidonoyl-chloro-methyl-ketone (ACMK) and O-acetyl-arachidonoyl-hydroxamate (AcAHA), by adding to the fatty acid moiety three functional groups previously used to synthesize irreversible inhibitors of serine and cysteine proteases. The three compounds were purified and characterized by proton nuclear magnetic resonance and electron impact mass spectrometry. Their effect was tested on anandamide amidohydrolase partially purified from N18TG2 and RBL-1 cells and porcine brain. Pre-treatment of the enzyme with each compound produced a significant inhibition, with ADMK being the most potent (IC50 = 3, 2 and 6 microM) and AcAHA the weakest (IC50 = 34, 15 and 25 microM) inhibitors. The inactivated enzyme regained its full activity when chromatographed by anion-exchange chromatography, suggesting that none of the compounds inhibited the amidohydrolase in a covalent manner. Accordingly, Lineweaver-Burk profiles showed competitive inhibition by each compound. Conversely, the irreversible inhibitor of cytosolic phospholipase As, methyl-arachidonoyl-fluoro-phosphonate (MAFP), covalently inhibited the amidohydrolase. MAFP was active at concentrations 10(3) times lower than those reported for phospholipase A2 inhibition, and is the most potent anandamide amidohydrolase inhibitor so far described (IC50 = 1-3 nM). MAFP, ADMK and ACMK, probably by inhibiting anandamide degradation, produced an apparent increase of the in vitro formation of anandamide from its biosynthetic precursor N-arachidonoyl-phosphatidyl-ethanolamine.

Two novel classes of neuroactive fatty acid amides are substrates for mouse neuroblastoma 'anandamide amidohydrolase'

The endogenous cannabimimetic substance, anandamide (N-arachidonoyl-ethanolamine) and the recently isolated sleep-inducing factor, oleoyl-amide (cis-9,10-octadecenoamide), belong to two neuroactive fatty acid amide classes whose action in mammals has been shown to be controlled by enzymatic amide bond hydrolysis. Here we report the partial characterisation and purification of 'anandamide amidohydrolase' from membrane fractions of N18 neuroblastoma cells, and provide evidence for a further and previously unsuspected role of this enzyme. An enzymatic activity catalysing the hydrolysis of [14C]anandamide was found in both microsomal and 10,000 x g pellet fractions. The latter fractions, which displayed the highest Vmax for anandamide, were used for further characterisation of the enzyme, and were found to catalyse the hydrolysis also of [14C]oleoyl-amide, with an apparent Km of 9.0 +/- 2.2 microM. [14C]anandamide- and [14C]oleoyl-amide-hydrolysing activities: (i) exhibited identical pH- and temperature-dependency profiles; (ii) were inhibited by alkylating agents; (iii) were competitively inhibited by the phospholipase A2 inhibitor arachidonyl-trifluoromethyl-ketone with the same IC50 (3 microM); (iv) were competitively inhibited by both anandamide (or other polyunsaturated fatty acid-ethanolamides) and oleoyl-amide. Proteins solubilised from 10,000 x g pellets were directly analysed by isoelectric focusing, yielding purified fractions capable of catalysing the hydrolysis of both [14C]anandamide and [14C]oleoyl-amide. These data suggest that 'anandamide amidohydrolase' enzymes, such as that characterised in this study, may be used by neuronal cells also to hydrolyse the novel sleep-inducing factor oleoyl-amide.

Bacillus Calmette-Guerin in the treatment of stage T1 grade 3 transitional cell carcinoma of the bladder: long-term results

PURPOSE

We performed a retrospective long-term study to evaluate the results of immunotherapy in the treatment of high grade superficial bladder tumors.

MATERIALS AND METHODS

Between 1981 and 1993, 593 patients with superficial transitional cell carcinoma of the bladder underwent transurethral resection. Of 64 patients with stage T1 grade 3 disease 50 received intravesical bacillus Calmette-Guerin after transurethral resection of all visible tumor.

RESULTS

At a median followup of 42 months (range 12 to 112) 36 patients (72%) are disease-free and have not required further treatment. Superficial recurrence was noted in 8 patients (16%). Disease progressed in 6 patients (12%), including 5 with locally invasive and 1 with metastatic disease. Cystectomy was performed for progression in 4 patients and for recurrent stage T1 grade 3 disease in 1. There was 1 disease related death (2%). The overall survival rate is 94%.

CONCLUSIONS

Intravesical bacillus Calmette-Guerin appears to be the most effective conservative treatment for patients with stage T1 grade 3 bladder cancer.

Chemical and biological investigation of the polar constituents of the starfish Luidia clathrata, collected in the Gulf of Mexico

Ten new [1-10] and three known [11-13] polyhydroxysteroids were isolated, along with four known asterosaponins [14-17], from the starfish Luidia clathrata, collected from the offshore waters of the northern Gulf of Mexico. The EtOH extracts of this starfish showed feeding-deterrent properties against marine fish, and inhibited the settlement of larvae of barnacles and bryozoans, as well as the growth of several bacteria. The structures of the new compounds were determined by interpretation of their nmr spectral data and by comparison with the spectral data of known compounds. The assignment of the configurations of the side-chain stereogenic centers of compounds 1 and 3-10 were based on the comparison of their nmr data with those of the stereoisomeric model compounds after derivatization with the chiral auxiliary MTPA reagent. Larval settlement assays conducted on ten isolated compounds revealed they are all potent inhibitors of settlement. Two of these isolated compounds inhibited the growth of several bacteria.