Complexation of antimony (Sb(V)) with guanosine 5'-monophosphate and guanosine 5'-diphospho-D-mannose: formation of both mono- and bis-adducts

Supramolecular assemblies from antimony(V) complexes for the treatment of leishmaniasis

The pentavalent meglumine antimoniate (MA) is still a first-line drug in the treatment of leishmaniasis in several countries. As an attempt to elucidate its mechanism of action and develop new antimonial drugs with improved therapeutic profile, Sb(V) complexes with different ligands, including β-cyclodextrin (β-CD), nucleosides and non-ionic surfactants, have been studied. Interestingly, Sb(V) oxide, MA, its complex with β-CD, Sb(V)-guanosine complex and amphiphilic Sb(V) complexes with N-alkyl-N-methylglucamide, have shown marked tendency to self-assemble in aqueous solutions, forming nanoaggregates, hydrogel or micelle-like nanoparticles. Surprisingly, the resulting assemblies presented in most cases slow dissociation kinetics upon dilution and a strong influence of pH, which impacted on their pharmacokinetic and therapeutic properties against leishmaniasis. To explain this unique property, we raised the hypothesis that multiple pnictogen bonds could contribute to the formation of these assemblies and their kinetic of dissociation. The present article reviews our current knowledge on the structural organization and physicochemical characteristics of Sb-based supramolecular assemblies, as well as their pharmacological properties and potential for treatment of leishmaniasis. This review supports the feasibility of the rational design of new Sb(V) complexes with supramolecular assemblies for the safe and effective treatment of leishmaniasis.

Organotin (IV) complexes with sulphonyl hydrazide moiety. Design, synthesis, characterization, docking studies, cytotoxic and anti-leishmanial activity

Due to a lack of therapeutic options for the pathological condition of leishmaniasis, which is characterized by polymorphic lesions and skin surface infections, Leishmania genus parasites damaged dermis and mucosa. There was a need to synthesize and characterize some new complexes. This study evaluated the biological activities preferably anti-Leishmanial activity of organotin (IV) containing sulphonyl hydrazide derivatives. A series of six new organotin (IV) complexes 1-6 labeled as R2SnL2; R = Methyl (1), Butyl (2), Phenyl (3) and R3SnL; R = Methyl (4), Butyl (5), Phenyl (6) has been synthesized as reflux method derived from N'- (2,4-dinitrophenyl)-4-methylphenylsulfonylhydrazide (L). All compounds were characterized through FT-IR, 1HNMR, 13CNMR, and elemental analysis. Structural analysis confirms the formation of six complexes (1-6). All derivatives have been screened for their pharmacological activities. Interestingly, compound 1 showed promising activity against leishmania promastigotes with low cytotoxicity. All results were further elaborated through docking studies performed on leishmania donovoni synthetase PDB: ID 3QW3 that acts as an essential building block for the viability of Leishmania promastigotes. This research effectively synthesized sulphonyl hydrazide ligand and its six new organotin (IV) derivatives, which were tested for biological properties such as antibacterial, anti-fungal, anti-oxidant, and ideally anti-leishmanial activity and cytotoxicity. Studies have confirmed that these compounds have the potency to be a good candidate against leishmaniasis. Computational studies were carried out to recognize the binding affinities for leishmania donovoni synthetase.Communicated by Ramaswamy H. Sarma.

Do bismuth complexes hold promise as antileishmanial drugs?

Even after 70 years, pentavalent antimonials sodium stibogluconate and meglumine antimoniate remain the most important and cost-effective antileishmanial drugs. However, the drugs cannot be delivered orally and treatment involves intravascular or intramuscular injections for 28 days under strict medical monitoring due to the toxicity of Sb(III). The main alternatives, amphotericin B, pentamidine and miltefosine, are expensive and not without their own problems. Bismuth sits below antimony in the periodic table and is considered to be relatively nontoxic to humans while being capable of providing powerful antimicrobial activity. This review describes recent efforts into developing antileishmanial Bi(III) and Bi(V) drugs, which may resemble Sb analogs in effect and mode-of-action while providing lower mammalian cell toxicity and opportunities of oral delivery. Within the last 10 years, various studies concerning bismuth-based compounds as potential antileishmanial agents have been published. This review seeks to summarize the relevant studies and draw a conclusion as to whether bismuth complexes have the potential to be effective drugs.

Study of conformational changes and protein aggregation of bovine serum albumin in presence of Sb(III) and Sb(V)

Antimony is a metalloid that affects biological functions in humans due to a mechanism still not understood. There is no doubt that the toxicity and physicochemical properties of Sb are strongly related with its chemical state. In this paper, the interaction between Sb(III) and Sb(V) with bovine serum albumin (BSA) was investigated in vitro by fluorescence spectroscopy, and circular dichroism (CD) under simulated physiological conditions. Moreover, the coupling of the separation technique, asymmetric flow field-flow fractionation, with elemental mass spectrometry to understand the interaction of Sb(V) and Sb(III) with the BSA was also used. Our results showed a different behaviour of Sb(III) vs. Sb(V) regarding their effects on the interaction with the BSA. The effects in terms of protein aggregates and conformational changes were higher in the presence of Sb(III) compared to Sb(V) which may explain the differences in toxicity between both Sb species in vivo. Obtained results demonstrated the protective effect of GSH that modifies the degree of interaction between the Sb species with BSA. Interestingly, in our experiments it was possible to detect an interaction between BSA and Sb species, which may be related with the presence of labile complex between the Sb and a protein for the first time.

Phenolic composition and antiparasitic activity of plants from the Brazilian Northeast "Cerrado"

This work describes the antiparasitic and cytotoxic activities of three plant species from the Cerrado biome, Northeastern Brazil. Significant antiparasitic inhibition was observed against Trypanosoma cruzi (63.86%), Leishmania brasiliensis (92.20%) and Leishmania infantum (95.23%) when using ethanol extract from leaves of Guazuma ulmifolia Lam. (Malvaceae), at a concentration of 500 μg/mL. However, low levels of inhibition were observed when assessing leishmanicidal and trypanocidal (Clone CL-B5) activities of crude ethanol extracts from leaves and bast tissue of Luehea paniculata (Malvaceae) and leaves and bark of Prockia crucis (Salicaceae) at a concentration of 500 μg/mL. The extracts revealed the presence of phenolic acids such as gallic acid, chlorogenic acid, caffeic acid and rosmarinic acid, as well as flavonoids such as rutin, luteolin, apigenin and quercetin - the latter detected only in G. ulmifolia. G. ulmifolia extract displayed higher leishmanicidal activity probably due to the presence of quercetin, a potent known leishmanicidal compound. A cytotoxicity test indicated values over 50% at the highest concentration (1000 μg/mL) for all natural products, which were considered cytotoxic. This points out the need for further tests to enable future in vivo trials, including antineoplastic activity on human tumor cells.

Antileishmanial activity of medicinal plants used in endemic areas in northeastern Brazil

This study investigates the leishmanicidal activity of five species of plants used in folk medicine in endemic areas of the state of Alagoas, Brazil. Data were collected in the cities of Colonia Leopoldina, Novo Lino, and União dos Palmares, Alagoas state, from patients with cutaneous leishmaniasis (Leishmania amazonensis) who use medicinal plants to treat this disease. Plants extracts were tested at a concentration of 1–100 μg/mL in all experiments, except in an assay to evaluate activity against amastigotes, when 10 μg/mL was used. All plants extracts did not show deleterious activity to the host cell evidenced by LDH assay at 100, 10, and 1 μg/mL after 48 h of incubation. The plants extracts Hyptis pectinata (L.) Poit, Aloe vera L., Ruta graveolens L., Pfaffia glomerata (Spreng.) Pedersen, and Chenopodium ambrosioides L. exhibited direct activity against extracellular forms at 100 μg/mL; these extracts inhibited growth by 81.9%, 82.9%, 74.4%, 88.7%, and 87.4%, respectively, when compared with promastigotes. The plants extracts H. pectinata, A. vera, and R. graveolens also significantly diminished the number of amastigotes at 10 μg/mL, inhibiting growth by 85.0%, 40.4%, 94.2%, and 97.4%, respectively, when compared with control. Based on these data, we conclude that the five plants exhibited considerable leishmanicidal activity.

Use of antimony in the treatment of leishmaniasis: current status and future directions

In the recent past the standard treatment of kala-azar involved the use of pentavalent antimonials Sb(V). Because of progressive rise in treatment failure to Sb(V) was limited its use in the treatment program in the Indian subcontinent. Until now the mechanism of action of Sb(V) is not very clear. Recent studies indicated that both parasite and hosts contribute to the antimony efflux mechanism. Interestingly, antimonials show strong immunostimulatory abilities as evident from the upregulation of transplantation antigens and enhanced T cell stimulating ability of normal antigen presenting cells when treated with Sb(V) in vitro. Recently, it has been shown that some of the peroxovanadium compounds have Sb(V)-resistance modifying ability in experimental infection with Sb(V) resistant Leishmania donovani isolates in murine model. Thus, vanadium compounds may be used in combination with Sb(V) in the treatment of Sb(V) resistance cases of kala-azar.

A kinetic study on the chemical cleavage of nucleoside diphosphate sugars

Nucleoside diphosphate sugars serve in essential roles in metabolic processes. They have, therefore, been used in mechanistic studies on glycosylation reactions, and their analogues have been synthesised as enzyme and receptor inhibitors. Despite extensive biochemical research, little is known about their chemical reactions. In the present work the chemical cleavage of two different types of nucleoside diphosphate sugars has been studied. UDP-Glc is phosphorylated at the anomeric carbon, whereas in ADP-Rib C-1 is unsubstituted, allowing hence the equilibrium between cyclic hemiacetal and acyclic carbonyl forms. Due to the structural difference, these substrates react via different pathways under slightly alkaline conditions: while UDP-Glc reacts exclusively by a nucleophilic attack of a glucose hydroxyl group on the diphosphate moiety, ADP-Rib undergoes a complex reaction sequence that involves isomerisation processes of the acyclic ribose sugar and results in a release of ADP.

Pentavalent antimonials: new perspectives for old drugs

Pentavalent antimonials, including meglumine antimoniate and sodium stibogluconate, have been used for more than half a century in the therapy of the parasitic disease leishmaniasis. Even though antimonials are still the first-line drugs, they exhibit several limitations, including severe side effects, the need for daily parenteral administration and drug resistance. The molecular structure of antimonials, their metabolism and mechanism of action are still being investigated. Some recent studies suggest that pentavalent antimony acts as a prodrug that is converted to active and more toxic trivalent antimony. Other works support the direct involvement of pentavalent antimony. Recent data suggest that the biomolecules, thiols and ribonucleosides, may mediate the actions of these drugs. This review will summarize the progress to date on the chemistry and biochemistry of pentavalent antimony. It will also present the most recent works being done to improve antimonial chemotherapy. These works include the development of simple synthetic methods for pentavalent antimonials, liposome-based formulations for targeting the Leishmania parasites responsible for visceral leishmaniasis and cyclodextrin-based formulations to promote the oral delivery of antimony.

Characterization of sodium stibogluconate by online liquid separation cell technology monitored by ICPMS and ESMS and computational chemistry

High-performance liquid chromatography (HPLC), mass spectrometry (MS), and computational chemistry has been applied to resolve the composition and structure of the Sb species present in dilutions of Pentostam, a first-line treatment drug against Leishmania parasites. Using HPLC-inductively coupled plasma-MS and electrospray-MS, it was shown that the original drug consists of large Sb(V)-glyconate complexes of polymeric nature that degrade upon dilution. In dilution solution, the drug is a mixture of noncomplexed Sb(V), large polymeric complexes as well as several low molecular mass Sb(V)-glyconate complexes of various stoichiometry (1:1, 1:2, 1:3, 2:2, 2:3, 2:4, 3:3, 3:4). The 1:1 complex became the most abundant low molecular mass Sb(V) complex with dilution time. A novel mixed-mode chromatographic system was applied in order to separate complexes of various stoichiometry and isomers. Density functional theory was used to study the structure of the 1:1 Sb-gluconate complex with three or four solvent molecules bound. By computing the structures and the free energies of the various possible isomers in aqueous solvation models, the most likely structures of the species were deduced. Importantly, 6-coordination is always preferred over 5-coordination, and the species commonly adopt conformations involving tris-coordination of deprotonated hydroxyl groups from gluconate.

Identification of Sb(V) Complexes in Biological and Food Matrixes and Their Stibine Formation Efficiency during Hydride Generation with ICPMS Detection

Several studies have described the synthetic preparation of Sb(V) complexes with organic ligands, but only recently was such a complex identified to exist in beverages stored in PET containers. In the present study, we have investigated by using HPLC-ICPMS and HPLC-ES-MS(/MS), the formation of Sb(V) complexes in various biological (urine) and food matrixes (yoghurt and juice) spiked with noncomplexed inorganic Sb(V). Our results show that Sb(V) complex formation is matrix dependent and that several Sb(V) complexes form to a considerable extent in these matrixes. The results also suggest that the existence of Sb(V) complexes in natural samples may have previously been overlooked due to analytical method limitations, mainly chromatographic, but also detection limitations when hydride generation is used. To overcome some of these limitations, we have developed chromatographic methods suitable for preserving Sb-organic ligand complexes during their separation. When applying this mild nondestructive chromatographic method, we were able to identify novel Sb complexes in yoghurt spiked with inorganic Sb(V), i.e., 1:1 Sb(V)-citrate, 1:1 Sb(V)-lactate, 1:2 Sb(V)-lactate, and other Sb(V)-lactate complexes. This is the first characterization of Sb(V)-lactate complexes. Detailed studies on the hydride generation (HG) efficiency of Sb(V) complexes showed that Sb(V) complexes of high stability, such as Sb(V)-citrate, Sb(V)-(adenosine)n and Sb(V)-(lactate)n (n = 1 or 2), are nondetectable by HG-ICPMS. Furthermore, Sb(V) complexes formed in natural biological and food matrixes were only partly detectable by HG-ICPMS, confirming limitations of analytical methods based on HG volatilization and subsequent stibine detection in natural samples containing complexing ligands with affinity toward Sb(V).

Characterization of reactions of antimoniate and meglumine antimoniate with a guanine ribonucleoside at different pH

It has been shown previously that Sb(V) forms mono- and bis-adducts with adenine and guanine ribonucleosides, suggesting that ribonucleosides may be a target for pentavalent antimonial drugs in the treatment of leishmaniasis. In the present work, the reactions of antimoniate (KSb(OH)(6)) and meglumine antimoniate (MA) with guanosine 5'-monophosphate (GMP) have been characterized at 37 degrees C in aqueous solution and two different pH (5 and 6.5), using ESI(-)-MS and (1)H NMR. Acid and base species for both 1:1 and 1:2 Sb(V)-GMP complexes were identified by ESI(-)-MS. The (1)H NMR anomeric region was explored for determining the concentrations of mono- and bis-adducts. This allows for the determination of stability constants for these complexes (5,900 L mol(-1) for 1:1 complex and 370 L mol(-1) for 1:2 complex, at pD 5 and 37 degrees C). Kinetic studies at different pH indicated that formation and dissociation of both 1:1 and 1:2 Sb-GMP complexes are slow processes and favored at acidic pH (2,150 L mol(-1) h(-1) for the rate constant of 1:1 complex formation and 0.25 h(-1) for the rate constant of 1:1 complex dissociation, at pD 5 and 37 degrees C). When MA was used, instead of antimoniate, formation of 1:1 Sb-GMP complex occurred, but with a slower rate constant. Assuming that MA consists essentially of a 1:1 Sb-meglumine complex, a stability constant for MA could also be estimated (8,600 L mol(-1) at pD 5 and 37 degrees C). Thermodynamic and kinetic data are consistent with the formation of 1:1 Sb-ribonucleoside complexes in vertebrate hosts, following treatment with pentavalent antimonial drugs.

Bioinorganic chemistry of bismuth and antimony: target sites of metallodrugs

The biocoordination chemistry of antimony and bismuth has been extensively investigated due to the historical use of these metals in medicine. Structures of bismuth antiulcer agents and interactions of Bi3+ with proteins and enzymes, such as transferrin and lactoferrin, the histidine-rich protein Hpn, and urease, have been characterized. Sb5+ is a prodrug and is bioreduced or activated to its active form Sb3+ intracellularly. Antimony binds to biomolecules, such as glutathione, trypanothione, and nucleotides, and forms binary and ternary complexes, which may allow it to be trafficked in cells. These studies have improved our understanding of the mechanism of action of bismuth and antimony drugs, which in turn allows the future design of drugs.

Mass spectrometric identification and characterization of antimony complexes with ribose-containing biomolecules and an RNA oligomer

Mass spectrometric techniques have been used to study the interaction of inorganic Sb(V) with biomolecules containing a ribose or deoxyribose moiety. Electrospray (ES) mass spectra of reaction mixtures containing inorganic Sb(V) and one of several biomolecules (adenosine, cytidine, guanosine, uridine, adenosine-5'-monophosphate, adenosine-3',5'-cyclic monophosphate, ribose, or 2'-deoxyadenosine) afforded high-mass antimony-containing ions corresponding to Sb(V)-biomolecule complexes of stoichiometry 1:1, 1:2, or 1:3. The complexes were characterized by collision-induced dissociation (CID) tandem mass spectrometry (MS) using ion-trap multistage MS. The CID results revealed that Sb(V) binds to the ribose or deoxyribose moiety. Structures are proposed for the Sb-biomolecule complexes. Analysis of the reaction mixtures by reversed-phase chromatography coupled on-line to either inductively coupled plasma (ICP) MS or ES-MS showed that in solution Sb(V) forms complexes with all the analyzed biomolecules with vicinal cis hydroxyl groups. Evidence (from size-exclusion chromatography ICP-MS and direct infusion ES-MS) of complexation of Sb(V) with an RNA oligomer, but not with a DNA oligomer, supports the suggestion that the presence of vicinal cis hydroxyl groups is critical for complexation to occur. This is the first direct evidence of complexation of Sb(V) with RNA. Results obtained by studying the effect of changing reaction conditions, i.e. pH, reaction time, and Sb/biomolecule molar ratio, on the extent of Sb-biomolecule formation suggest the reaction may be of physiological importance. Selected reaction monitoring (SRM) and precursor-ion-scanning tandem MS were investigated to determine their potential to detect trace levels of the Sb-biomolecule complexes in biological samples. Application of SRM MS-MS in combination with high-performance liquid chromatography enabled successful detection of an Sb-adenosine complex that had been spiked into a complex biological matrix (liver homogenate).