Monica Saladini

Curcuminoids as potential new iron-chelating agents: spectroscopic, polarographic and potentiometric study on their Fe(III) complexing ability

The pKa values of curcumin and diacetylcurcumin are, here doubtless, determined by means of spectroscopic and potentiometric measurements, and the enolic proton is the more acidic one. The interaction of Fe 3 + with curcumin and diacetylcurcumin, in water/methanol 1:1 solution, leads to the formation of the complex species [FeH2CU(OH)2] and [FeDCU(OH)2 ]( H 2CU and DCU=curcumin or diacetylcurcumin monoanion, respectively) which prevails near pH 7. At more basic condition the prevailing species are [FeH2CU(OH)3] − and [FeDCU(OH)3] − , which prevent metal hydroxide precipitation. 1 H NMR data state that the dissociated -diketo moiety of the ligands is involved in metal chelation. The pKa value of the deprotonation reaction is strongly anticipated by the metal ion, as shown by UV spectral data. The stability constants, evaluated from potentiometric data, are near to that of desferrioxamine, which is, by now, the only iron-chelating agent for clinical use.

Silybin, a new iron-chelating agent

Silybin, a natural occurring flavolignan isolated from the fruits of Silibum marianum, has been reported to exert antioxidant and free radical scavenging abilities. It was suggested to act also as an iron chelator. The complexation and protonation equilibria of the ferric complex of this compound have been studied by potentiometric, spectrophotometric and electrochemical techniques. The formation of the complex silybin-Ga(III) in anhydrous DMSO-d6 has been studied by 1H NMR spectroscopy. Mass spectrometry and infrared spectroscopy on silybin-Fe(III) complex confirm all data obtained by 1H NMR spectroscopy. The experimental results show that silybin binds Fe(III) even at acidic pH. Different ternary complexes were observed at increasing methoxide ion concentration and their stability constants have been calculated. The results show the possible role of silybin in relation to the chelation therapy of chronic iron overload, as occurs in the treatment of Cooleys anemia.

Synthesis, cytotoxic and combined cDDP activity of new stable curcumin derivatives

New curcumin derivatives are synthesized in order to improve chemical properties of curcumin. The aromatic ring glycosylation of curcumin provides more water-soluble compounds with a greater kinetic stability which is a fundamental feature for drug bioavailability. The glycosylation reaction is quite simple, low cost, with high yield and minimum waste. NMR data show that the ability of curcumin to coordinate metal ion, in particular Ga(III), is maintained in the synthesized products. Although the binding of glucose to curcumin reduces the cytotoxicity of the derivatives towards cisplatin (cDDP)-sensitive and -resistant human ovarian carcinoma cell lines, the compounds display a good selectivity since they are much less toxic against non-tumourigenic Vero cells. The combination of cDDP with the most active glycosyl-curcuminoid drug against both cDDP-sensitive and -resistant as well as against Vero cell lines is tested. The results show an improvement of cDDP efficacy with higher selectivity towards cancer cells than non-cancer cells. These studies indicate the need for developing new valid components of drug treatment protocols to cDDP-resistant cells as well.

Newly synthesized curcumin derivatives: crosstalk between chemico-physical properties and biological activity.

New curcumin analogues (ester and acid series) were synthesized with the aim to improve the chemical stability in physiological conditions and potential anticancer activity. Cytotoxicity against different tumorigenic cell lines (human ovarian carcinoma cells -2008, A2780, C13*, and A2780/CP, and human colon carcinoma cells HCT116 and LoVo) was tested to evaluate cellular specificity and activity. Physico-chemical properties such as acidity, lipophilicity, kinetic stability, and free radical scavenging activity were investigated to shed light on the structure-activity relationship and provide new attractive candidates for drug development. Most of ester derivatives show IC(50) values lower than curcumin and exhibit selectivity against colon carcinoma cells. Especially they are extremely active after 24 h exposure showing enhanced inhibitory effect on cell viability. The best performances of ester curcuminoids could be ascribed to their high lipophilicity that favors a greater and faster cellular uptake overcoming their apparently higher instability in physiological condition.

bis-Dehydroxy-Curcumin Triggers Mitochondrial-Associated Cell Death in Human Colon Cancer Cells through ER-Stress Induced Autophagy

Background The activation of autophagy has been extensively described as a pro-survival strategy, which helps to keep cells alive following deprivation of nutrients/growth factors and other stressful cellular conditions. In addition to cytoprotective effects, autophagy can accompany cell death. Autophagic vacuoles can be observed before or during cell death, but the role of autophagy in the death process is still controversial. A complex interplay between autophagy and apoptosis has come to light, taking into account that numerous genes, such as p53 and Bcl-2 family members, are shared between these two pathways. Methodology/Principal Findings In this study we showed a potent and irreversible cytotoxic activity of the stable Curcumin derivative bis-DeHydroxyCurcumin (bDHC) on human colon cancer cells, but not on human normal cells. Autophagy is elicited by bDHC before cell death as demonstrated by increased autophagosome formation -measured by electron microscopy, fluorescent LC3 puncta and LC3 lipidation- and autophagic flux -measured by interfering LC3-II turnover. The accumulation of poly-ubiquitinated proteins and ER-stress occurred upstream of autophagy induction and resulted in cell death. Cell cycle and Western blot analyses highlighted the activation of a mitochondrial-dependent apoptosis, which involves caspase 7, 8, 9 and Cytochrome C release. Using pharmacological inhibitions and RNAi experiments, we showed that ER-stress induced autophagy has a major role in triggering bDHC-cell death. Conclusion/Significance Our findings describe the mechanism through which bDHC promotes tumor selective inhibition of proliferation, providing unequivocal evidence of the role of autophagy in contrasting the proliferation of colon cancer cells.

Removal of cadmium ion by means of synthetic hydroxyapatite.

The reaction behaviour of synthetic hydroxyapatite [Ca10(PO4)6(OH)2] (HAP) toward cadmium ion was investigated for the Cd/Ca molar ratio in the range 1-0.005, by means of ions, pH measurements and XRD, SEM, IR techniques. The reaction behaviour between HAP and cadmium ion could be explained by a formation of an amorphous phase and/or a sorption mechanism.

Crystal structure of lead hydroxyapatite from powder X-ray diffraction data

Abstract The crystal structure of lead hydroxyapatite, Pb10(PO4)6(OH)2, is refined on powder XRD data using the Rietveld method. The unit cell is hexagonal, a=b=9.866(3) and c=7.426(2) A , space group P63/m, Z=1 (relative to the specified formula). Results are discussed and compared with previous structures of hydroxyapatite and partially lead-substituted hydroxyatites. Now that the entire range of lead substitution is covered, it is possible to detect a coherent trend in the distortions of the crystal packing introduced by the different ability of the two metallic crystal sites to accommodate Pb ions.

Synthesis and Characterization of 68Ga-Labeled Curcumin and Curcuminoid Complexes as Potential Radiotracers for Imaging of Cancer and Alzheimer’s Disease

Curcumin (CUR) and curcuminoids complexes labeled with fluorine-18 or technetium-99m have recently shown their potential as diagnostic tools for Alzheimers disease. Gallium-68 is a positron-emitting, generator-produced radionuclide, and its properties can be exploited in situ in medical facilities without a cyclotron. Moreover, CUR showed a higher uptake in tumor cells compared to normal cells, suggesting potential diagnostic applications in this field. In spite of this, no studies using labeled CUR have been performed in this direction, so far. Herein, (68)Ga-labeled complexes with CUR and two curcuminoids, namely diacetyl-curcumin (DAC) and bis(dehydroxy)curcumin (bDHC), were synthesized and characterized by means of experimental and theoretical approaches. Moreover, a first evaluation of their affinity to synthetic β-amyloid fibrils and uptake by A549 lung cancer cells was performed to show the potential application of these new labeled curcuminoids in these diagnostic fields. The radiotracers were prepared by reacting (68)Ga(3+) obtained from a (68)Ge/(68)Ga generator with 1 mg/mL curcuminoids solutions. Reaction parameters (precursor amount, reaction temperature, and pH) were optimized to obtain high and reproducible radiochemical yield and purity. Stoichiometry and formation of the curcuminoid complexes were investigated by matrix-assisted laser desorption ionization time-of-flight mass spectrometry, NMR, ultraviolet-visible, and fluorescence spectroscopy on the equivalent (nat)Ga-curcuminoids (nat = natural) complexes, and their structure was computed by theoretical density functional theory calculations. The analyses evidenced that CUR, DAC, and bDHC were predominantly in the keto-enol form and attested to Ga(L)2(+) species formation. Identity of the (68)Ga(L)2(+) complexes was confirmed by coelution with the equivalent (nat)Ga(L)2(+) complexes in ultrahigh-performance liquid chromatography analyses.(68)Ga(CUR)2(+), (68)Ga(DAC)2(+), and (68)Ga(bDHC)2(+) were highly (87 ± 4, 90 ± 1%) and moderately (48 ± 2%), respectively, retained by synthetic β-amyloid fibrils in vitro. All the Ga-curcuminoid complexes showed an uptake in A549 lung cancer cells, at least equivalent to the respective free curcuminoids, confirming potential applications as cancer-detecting radiotracers.

Sugar complexes with metal2+ ions: thermodynamic parameters of associations of Ca2+, Mg2+ and Zn2+ with galactaric acid

Abstract A solution study on the complex ability of galactaric acid (GalaH 2 ) for complexation with Ca 2+ , Mg 2+ and Zn 2+ ions is reported. The stability constants of the complex species are determined by means of potentiometric measurements. From the dependence of stability constants on temperature, the Δ H ° and Δ S ° values are also determined. The formation of the complex species is an endothermic process and Δ H ° and Δ S ° values suggest a chelate coordination mode of galactaric acid involving carboxylic oxygen and α-hydroxylic group. The prevailing species at acidic or neutral pH is [MGala] (M=Ca 2+ , Mg 2+ , Zn 2+ ) which is also isolated in the solid state and characterised by means of IR spectroscopy. On increasing pH, the [MGalaH −1 ] − species is also formed, where the coordinated OH group undergoes deprotonation.

Coordination properties of N-p-tolylsulfonyl-l-glutamic acid toward metalII: Part 1. Crystallographic study on ZnII and CdII complexes

Abstract A series of compounds of N-p-tolylsulfonyl- l -glutamic acid with divalent Cu, Zn and Cd are synthesized and characterized. For the complexes [Zn(tsgluO)(H2O)2]·H2O (1), [Cd2(tsgluO)2(H2O)6] (2) and [Cd(bipy)(tsgluO)] (3) the crystal and molecular structure have been determined by X-ray diffraction (tsgluO=N-p-tolylsulfonyl- l -glutamate dianion, bipy=2,2′-bipyridine). In compound 1 the ZnII ion exhibits a tetrahedral geometry arising from coordination of two carboxylic oxygens of two amino acid molecules and of two water molecules. In compound 2 each CdII ion of the dimeric unit is coordinated by oxygen atoms of tsgluO2− and water molecules in a distorted octahedral environment. In compound 3 the CdII ion is coordinated by 2,2′-bipyridine nitrogens and four oxygen atoms from three different tsgluO2− in a distorted octahedral geometry.