Toxicity of dipyridyl compounds and related compounds

Design and Synthesis of Poly(2,2'-Bipyridyl) Ligands for Induction of Cell Death in Cancer Cells: Control of Anticancer Activity by Complexation/Decomplexation with Biorelevant Metal Cations

Chelation therapy is a medical procedure for removing toxic metals from human organs and tissues and for the treatment of diseases by using metal-chelating agents. For example, iron chelation therapy is designed not only for the treatment of metal poisoning but also for some diseases that are induced by iron overload, cancer chemotherapy, and related diseases. However, the use of such metal chelators needs to be generally carried out very carefully, because of the side effects possibly due to the non-specific complexation with intracellular metal cations. Herein, we report on the preparation and characterization of some new poly(bpy) ligands (bpy: 2,2'-bipyridyl) that contain one-three bpy ligand moieties and their anticancer activity against Jurkat, MOLT-4, U937, HeLa S3, and A549 cell lines. The results of MTT assays revealed that the tris(bpy) and bis(bpy) ligands exhibit potent activity for inducing the cell death in cancer cells. Mechanistic studies suggest that the main pathway responsible for the cell death by these poly(bpy) ligands is apoptotic cell death. It was also found that the anticancer activity of the poly(bpy) ligands could be controlled by the complexation (anticancer activity is turned OFF) and decomplexation (anticancer activity is turned ON) with biorelevant metal cations. In this paper, these results will be described.

Ca2+-Responsive Glyco-insulin

Chemical modification of peptides and proteins, such as PEGylation and lipidation, creates conjugates with new properties. However, they are typically not dynamic or stimuli-responsive. Self-assembly controlled by a stimulus will allow adjusting properties directly. Here, we report that conjugates of oligogalacturonic acids (OGAs), isolated from plant-derived pectin, are Ca²⁺-responsive. We report the conjugation of OGA to human insulin (HI) to create new glyco-insulins. In addition, we coupled OGA to model peptides. We studied their self-assembly by dynamic light scattering, small-angle X-ray scattering, and circular dichroism, which showed that the self-assembly to form nanostructures depended on the length of the OGA sequence and Zn²⁺ and Ca²⁺ concentrations. Subcutaneous administration of OGA12-HI with Zn²⁺ showed a stable decrease in blood glucose over a longer period of time compared to HI, despite the lower receptor binding affinity.

Coordination of siderophore gene expression among clonal cells of the bacterium Pseudomonas aeruginosa

There has been great progress in understanding how bacterial groups coordinate social actions, such as biofilm formation and public-goods secretion. Less clear is whether the seemingly coordinated group-level responses actually mirror what individual cells do. Here, we use a microscopy approach to simultaneously quantify the investment of individual cells of the bacterium Pseudomonas aeruginosa into two public goods, the siderophores pyochelin and pyoverdine. Using gene expression as a proxy for investment, we initially observe no coordination but high heterogeneity and bimodality in siderophore investment across cells. With increasing cell density, gene expression becomes more homogenized across cells, accompanied by a moderate shift from pyochelin to pyoverdine expression. We find positive associations in the expression of pyochelin and pyoverdine genes across cells, with cell-to-cell variation correlating with cellular metabolic states. Our work suggests that siderophore-mediated signalling aligns behaviour of individuals over time and spurs a coordinated three-phase siderophore investment cycle.

Mo(VI) Potential Metallodrugs: Explaining the Transport and Cytotoxicity by Chemical Transformations

The transport and cytotoxicity of molybdenum-based drugs have been explained with the concept of chemical transformation, a very important idea in inorganic medicinal chemistry that is often overlooked in the interpretation of the biological activity of metal-containing systems. Two monomeric, [MoO₂(L¹)(MeOH)] (1) and [MoO₂(L²)(EtOH)] (2), and two mixed-ligand dimeric Mo^VIO₂ species, [{MoO₂(L^1-2)}₂(μ-4,4'-bipy)] (3-4), were synthesized and characterized. The structures of the solid complexes were solved through SC-XRD, while their transformation in water was clarified by UV-vis, ESI-MS, and DFT. In aqueous solution, 1-4 lead to the penta-coordinated [MoO₂(L^1-2)] active species after the release of the solvent molecule (1 and 2) or removal of the 4,4'-bipy bridge (3 and 4). [MoO₂(L^1-2)] are stable in solution and react with neither serum bioligand nor cellular reductants. The binding affinity of 1-4 toward HSA and DNA were evaluated through analytical and computational methods and in both cases a non-covalent interaction is expected. Furthermore, the in vitro cytotoxicity of the complexes was also determined and flow cytometry analysis showed the apoptotic death of the cancer cells. Interestingly, μ-4,4'-bipy bridged complexes 3 and 4 were found to be more active than monomeric 1 and 2, due to the mixture of species generated, that is [MoO₂(L^1-2)] and the cytotoxic 4,4'-bipy released after their dissociation. Since in the cytosol neither the reduction of Mo^VI to Mo^V/IV takes place nor the production of reactive oxygen species (ROS) through Fenton-like reactions of 1-4 with H₂O₂ occurs, the mechanism of cytotoxicity should be attributable to the direct interaction with DNA that happens with a minor-groove binding which results in cell death through an apoptotic mechanism.

New Sodium Mefenamate - Nicotinamide Multicomponent Crystal Development to Modulate Solubility and Dissolution: Preparation, Structural, and Performance Study

A cocrystal of mefenamic acid (MA) - nicotinamide (NA) has been reported to increase the solubility of MA, but it still does not exceed the solubility of sodium mefenamate (SM). Accordingly, this research dealt with a new salt cocrystal arrangement of SM - NA. Cocrystal screening was performed, followed by powder and single-crystal preparation. Solvent drop grinding and slow evaporation at cold and ambient temperatures were employed to produce the multicomponent crystal. Two new salt cocrystals were found as hemihydrates and monohydrates, named SMN-HH and SMN-MH, respectively. SMN-MH single crystals were successfully isolated and structurally analyzed using a single crystal X-ray diffractometer. Pharmaceutical properties were investigated, including hydrate stability, solubility, and intrinsic dissolution. The experiments showed that the hemihydrate was stable under ambient humidity and temperature, and that the monohydrate rapidly changed to hemihydrate. Both hydrates improved the solubility and intrinsic dissolution of SM, but SMN-HH was superior. The data showed that SMN salt cocrystals combine the advantages of salt and cocrystals and show potential for dosage form development.

Recent Advances in Iron Chelation and Gallium-Based Therapies for Antibiotic Resistant Bacterial Infections

Iron is essential for multiple bacterial processes and is thus required for host colonization and infection. The antimicrobial activity of multiple iron chelators and gallium-based therapies against different bacterial species has been characterized in preclinical studies. In this review, we provide a synthesis of studies characterizing the antimicrobial activity of the major classes of iron chelators (hydroxamates, aminocarboxylates and hydroxypyridinones) and gallium compounds. Special emphasis is placed on recent in-vitro and in-vivo studies with the novel iron chelator DIBI. Limitations associated with iron chelation and gallium-based therapies are presented, with emphasis on limitations of preclinical models, lack of understanding regarding mechanisms of action, and potential host toxicity. Collectively, these studies demonstrate potential for iron chelators and gallium to be used as antimicrobial agents, particularly in combination with existing antibiotics. Additional studies are needed in order to characterize the activity of these compounds under physiologic conditions and address potential limitations associated with their clinical use as antimicrobial agents.

Resistance to Bipyridyls Mediated by the TtgABC Efflux System in Pseudomonas putida KT2440

Resistance-nodulation-division (RND) transporters are involved in antibiotic resistance and have a broad substrate specificity. However, the physiological significance of these efflux pumps is not fully understood. Here, we have investigated the role of the RND system TtgABC in resistance to metal ion chelators in the soil bacterium Pseudomonas putida KT2440. We observed that the combined action of an RND inhibitor and the chelator 2,2'-bipyridyl inhibited bacterial growth. In addition, the deletion of ttgB made the strain susceptible to 2,2'-bipyridyl and natural bipyridyl derivatives such as caerulomycin A, indicating that TtgABC is required for detoxification of compounds of the bipyridyl family. Searching for the basis of growth inhibition by bipyridyls, we found reduced adenosine triphosphate (ATP) levels in the ttgB mutant compared to the wild type. Furthermore, the expression of genes related to iron acquisition and the synthesis of the siderophore pyoverdine were reduced in the mutant compared to the wild type. Investigating the possibility that 2,2'-bipyridyl in the ttgB mutant mediates iron accumulation in cells (which would cause the upregulation of genes involved in oxidative stress via the Fenton reaction), we measured the expression of genes coding for proteins involved in intracellular iron storage and the response to oxidative stress. However, none of the genes was significantly upregulated. In a further search for a possible link between 2,2'-bipyridyl and the observed phenotypes, we considered the possibility that the ion chelator limits the intracellular availability of metabolically important metal ions. In this context, we found that the addition of copper restores the growth of the ttgB mutant and the production of pyoverdine, suggesting a relationship between copper availability and iron acquisition. Taken together, the results suggest that detoxification of metal chelating compounds of the bipyridyl family produced by other bacteria or higher ordered organisms is one of the native functions of the RND efflux pump TtgABC. Without the efflux pump, these compounds may interfere with cell ion homeostasis with adverse effects on cell metabolism, including siderophore production. Finally, our results suggest that TtgABC is involved in resistance to bile salts and deoxycholate.

Oxadiazon affects the expression and activity of aldehyde dehydrogenase and acylphosphatase in human striatal precursor cells: A possible role in neurotoxicity

Exposure to herbicides can induce long-term chronic adverse effects such as respiratory diseases, malignancies and neurodegenerative diseases. Oxadiazon, a pre-emergence or early post-emergence herbicide, despite its low acute toxicity, may induce liver cancer and may exert adverse effects on reproductive and on endocrine functions. Unlike other herbicides, there are no indications on neurotoxicity associated with long-term exposure to oxadiazon. Therefore, we have analyzed in primary neuronal precursor cells isolated from human striatal primordium the effects of non-cytotoxic doses of oxadiazon on neuronal cell differentiation and migration, and on the expression and activity of the mitochondrial aldehyde dehydrogenase 2 (ALDH2) and of the acylphosphatase (ACYP). ALDH2 activity protects neurons against neurotoxicity induced by toxic aldehydes during oxidative stress and plays a role in neurodegenerative conditions such as Alzheimer's disease and Parkinson's disease. ACYP is involved in ion transport, cell differentiation, programmed cell death and cancer, and increased levels of ACYP have been revealed in fibroblasts from patients affected by Alzheimer's disease. In this study we demonstrated that non-cytotoxic doses of oxadiazon were able to inhibit neuronal striatal cell migration and FGF2- and BDNF-dependent differentiation towards neuronal phenotype, and to inhibit the expression and activity of ALDH2 and to increase the expression and activity of ACYP2. In addition, we have provided evidence that in human primary neuronal precursor striatal cells the inhibitory effects of oxadiazon on cell migration and differentiation towards neuronal phenotype were achieved through modulation of ACYP2. Taken together, our findings reveal for the first time that oxadiazon could exert neurotoxic effects by impairing differentiative capabilities of primary neuronal cells and indicate that ALDH2 and ACYP2 are relevant molecular targets for the neurotoxic effects of oxadiazon, suggesting a potential role of this herbicide in the onset of neurodegenerative diseases.

Simultaneous determination of paraquat and atrazine in water samples with a white light reflectance spectroscopy biosensor

An optical immunosensor based on White Light Reflectance Spectroscopy for the simultaneous determination of the herbicides atrazine and paraquat in drinking water samples is demonstrated. The biosensor allows for the label-free real-time monitoring of biomolecular interactions taking place onto a SiO₂/Si chip by transforming the shift in the reflected interference spectrum due to reaction to effective biomolecular layer thickness. Dual-analyte determination is accomplished by functionalizing spatially distinct areas of the chip with protein conjugates of the two herbicides and scanning the surface with an optical reflection probe. A competitive immunoassay format was adopted, followed by reaction with secondary antibodies for signal enhancement. The sensor was highly sensitive with detection limits of 40 and 50 pg/mL for paraquat and atrazine, respectively, and the assay duration was 12 min. Recovery values ranging from 90.0 to 110% were determined for the two pesticides in spiked bottled and tap water samples, demonstrating the sensor accuracy. In addition, the sensor could be regenerated and re-used at least 20 times without significant effect on the assay characteristics. Its excellent analytical performance and short analysis time combined with the small sensor size should be helpful for fast on-site determinations of these analytes.

Proteomic response of Streptococcus pneumoniae to iron limitation

Iron is an essential trace element and involved in various key metabolic pathways in bacterial lifestyle. Within the human host, iron is extremely limited. Hence, the ability of bacteria to acquire iron from the environment is critical for a successful infection. Streptococcus pneumoniae (the pneumococcus) is a human pathobiont colonizing symptomless the human respiratory tract, but can also cause various local and invasive infections. To survive and proliferate pneumococci have therefore to adapt their metabolism and virulence factor repertoire to different host compartments. In this study, the response of S. pneumoniae to iron limitation as infection-relevant condition was investigated on the proteome level. The iron limitation was induced by application of the iron chelator 2,2'-bipyridine (BIP) in two different media mimicking different physiological traits. Under these conditions, the influence of the initial iron concentration on pneumococcal protein expression in response to limited iron availability was analyzed. Interestingly, one major difference between these two iron limitation experiments is the regulation of proteins involved in pneumococcal pathogenesis. In iron-poor medium several proteins of this group were downregulated whereas these proteins are upregulated in iron-rich medium. However, iron limitation in both environments led to a strong upregulation of the iron uptake protein PiuA and the significant downregulation of the non-heme iron-containing ferritin Dpr. Based on the results, it is shown that the pneumococcal proteome response to iron limitation is strongly dependent on the initial iron concentration in the medium or the environment.

Vanadium Compounds as PTP Inhibitors

Phosphotyrosine signaling is regulated by the opposing actions of protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs). Here we discuss the potential of vanadium derivatives as PTP enzyme inhibitors and metallotherapeutics. We describe how vanadate in the V oxidized state is thought to inhibit PTPs, thus acting as a pan-inhibitor of this enzyme superfamily. We discuss recent developments in the biological and biochemical actions of more complex vanadium derivatives, including decavanadate and in particular the growing number of oxidovanadium compounds with organic ligands. Pre-clinical studies involving these compounds are discussed in the anti-diabetic and anti-cancer contexts. Although in many cases PTP inhibition has been implicated, it is also clear that many such compounds have further biochemical effects in cells. There also remain concerns surrounding off-target toxicities and long-term use of vanadium compounds in vivo in humans, hindering their progress through clinical trials. Despite these current misgivings, interest in these chemicals continues and many believe they could still have therapeutic potential. If so, we argue that this field would benefit from greater focus on improving the delivery and tissue targeting of vanadium compounds in order to minimize off-target toxicities. This may then harness their full therapeutic potential.

Case Series of Paraquat Poisoning in Tuen Mun Hospital

Paraquat is highly toxic to human and is widely used in agriculture as a contact herbicide. However, it is easily accessible in agricultural product shops. Seven cases of paraquat poisoning were treated in Tuen Mun Hospital from 1998–2005. The mortality (4 out of 7) was very high. One patient died after oral exposure to paraquat despite immunosuppressive and antioxidant therapies. The mechanism of toxicity and potential new therapies of paraquat poisoning are discussed in the article.

High cytotoxicity of vanadium(IV) complexes with 1,10-phenanthroline and related ligands is due to decomposition in cell culture medium

Cytotoxic effects of Metvan (cis-[V^IVO(OSO₃)(Me₂phen)₂], where Me₂phen = 4,7-dimethyl-1,10-phenanthroline) and its analogues with 1,10-phenanthroline (phen) and 2,2'-bipyridine (bpy) ligands in cultured human lung cancer (A549) cells have been re-investigated in conjunction with reactivity of the V(IV) complexes in neutral aerated aqueous solutions and in cell culture medium. All the V(IV) complexes underwent rapid oxidation to the corresponding V(V) species (cis-[V^V(O)₂L₂]⁺), followed by release of free ligands (shown by electrospray mass spectrometry). Decomposition of V(IV) complexes in cell culture medium within minutes at 310 K was confirmed by UV-Vis and EPR spectroscopies. High cytotoxicities (low μM or sub-μM IC₅₀ range in 72 h assays) were observed for the phen and Me₂phen complexes, but they were not different from that of the corresponding free ligands, which confirmed that the original V(IV) complexes played no significant role in the observed biological activities. The cytotoxicities of the ligands were most likely due to their complexation of redox-active essential metal ions, such as Cu(II) and Fe(II), in the medium, and their increased cellular uptake, leading to oxidative stress-related cell death. These results emphasize the need to assess the stability of metal-based drugs under the conditions of biological assays, particularly when biologically active ligands, such as 1,10-phenanthroline and its derivatives, are used. These ligands have high systemic toxicities in vivo and their release in the GI tract and blood makes the complexes unsuitable for use as anti-cancer drugs.

Glycosylated metal chelators as anti-parasitic agents with tunable selectivity

Metal complexation imparts selective anti-parasitic activity to aminopyridyl ligands: Zn(ii) and Cu(ii) complexes show potent activity and remarkable selectivity indexes.

Hypoxia inducible factor stabilization improves defective ischemia-induced angiogenesis in a rodent model of chronic kidney disease

Chronic kidney disease (CKD) is associated with increased risk and worse prognosis of cardiovascular disease, including peripheral artery disease. An impaired angiogenic response to ischemia may contribute to poor outcomes of peripheral artery disease in patients with CKD. Hypoxia inducible factors (HIF) are master regulators of angiogenesis and therefore represent a promising target for therapeutic intervention. To test this we induced hind-limb ischemia in rats with CKD caused by 5/6 nephrectomy and administered two different treatments known to stabilize HIF protein in vivo: carbon monoxide and a pharmacological inhibitor of prolyl hydroxylation 2-(1-chloro-4- hydroxyisoquinoline-3-carboxamido) acetate (ICA). Expression levels of pro-angiogenic HIF target genes (Vegf, Vegf-r1, Vegf-r2, Ho-1) were measured by qRT-PCR. Capillary density was measured by CD31 immunofluorescence staining and HIF expression was evaluated by immunohistochemistry. Capillary density in ischemic skeletal muscle was significantly lower in CKD animals compared to sham controls. Rats with CKD showed significantly lower expression of HIF and all measured pro-angiogenic HIF target genes, including VEGF. Both HIF stabilizing treatments rescued HIF target gene expression in animals with CKD and led to significantly higher ischemia-induced capillary sprouting compared to untreated controls. ICA was effective regardless of whether it was administered before or after induction of ischemia and led to a HIF expression in skeletal muscle. Thus, impaired ischemia-induced angiogenesis in rats with CKD can be improved by HIF stabilization, even if started after onset of ischemia.

The ferric iron chelator 2,2'-dipyridyl attenuates basilar artery vasospasm and improves neurological function after subarachnoid hemorrhage in rabbits

We investigated the efficacy of the ferrous iron (Fe(2+)) chelator 2,2'-dipyridyl (DP) to attenuate cerebral vasospasm after subarachnoid hemorrhage (SAH). Thirty-six New Zealand white rabbits were randomly assigned to four groups: untreated control, SAH, SAH + dimethyl sulfoxide (DMSO) vehicle, and SAH + DP. SAH was induced by injection of autologous blood into the cisterna magna and then DP or vehicle was infused into the cistern magna for 5 days (20 mg/kg/day or an equal volume of DMSO). Neurological deficit score (NDS) was used to assess neurological function and cerebral angiography to measure basilar artery (BA) diameter following SAH. TUNEL staining was used to detect BA endothelial cell apoptosis, and immunohistochemistry and Western blotting to assess changes in caspase-3 protein levels 5 days post-SAH. The SAH + DP group had a significantly larger mean BA diameter and lower mean NDS post-SAH compared to the SAH + DMSO and SAH groups (p < 0.05). TUNEL-positive cell numbers and caspase-3 levels were significantly reduced in BA endothelial cells of the SAH + DP group as compared to the SAH and SAH + DMSO groups (p < 0.05). The iron chelator DP reduced vasospasm and neurological sequelae in rabbits, likely by chelating the Fe(2+) in oxyhemoglobin and reducing oxidative stress-induced endothelial cell apoptosis.

2,3-dihydroxybenzoic acid-containing nanofiber wound dressings inhibit biofilm formation by Pseudomonas aeruginosa

Pseudomonas aeruginosa forms biofilms in wounds, which often leads to chronic infections that are difficult to treat with antibiotics. Free iron enhances biofilm formation, delays wound healing, and may even be responsible for persistent inflammation, increased connective tissue destruction, and lipid peroxidation. Exposure of P. aeruginosa Xen 5 to the iron chelator 2,3-dihydroxybenzoic acid (DHBA), electrospun into a nanofiber blend of poly(d,l-lactide) (PDLLA) and poly(ethylene oxide) (PEO), referred to as DF, for 8 h decreased biofilm formation by approximately 75%. This was shown by a drastic decline in cell numbers, from 7.1 log10 CFU/ml to 4.8 log10 CFU/ml when biofilms were exposed to DF in the presence of 2.0 mM FeCl3 6H2O. A similar decline in cell numbers was recorded in the presence of 3.0 mM FeCl3 6H2O and DF. The cells were more mobile in the presence of DHBA, supporting the observation of less biofilm formation at lower iron concentrations. DHBA at MIC levels (1.5 mg/ml) inhibited the growth of strain Xen 5 for at least 24 h. Our findings indicate that DHBA electrospun into nanofibers inhibits cell growth for at least 4 h, which is equivalent to the time required for all DHBA to diffuse from DF. This is the first indication that DF can be developed into a wound dressing to treat topical infections caused by P. aeruginosa.

Cellular growth and mitochondrial ultrastructure of leishmania (Viannia) braziliensis promastigotes are affected by the iron chelator 2,2-dipyridyl

Background

Iron is an essential element for the survival of microorganisms in vitro and in vivo, acting as a cofactor of several enzymes and playing a critical role in host-parasite relationships. Leishmania (Viannia) braziliensis is a parasite that is widespread in the new world and considered the major etiological agent of American tegumentary leishmaniasis. Although iron depletion leads to promastigote and amastigote growth inhibition, little is known about the role of iron in the biology of Leishmania. Furthermore, there are no reports regarding the importance of iron for L. (V.) braziliensis.

Methodology/Principal Findings

In this study, the effect of iron on the growth, ultrastructure and protein expression of L. (V.) braziliensis was analyzed by the use of the chelator 2,2-dipyridyl. Treatment with 2,2-dipyridyl affected parasites' growth in a dose- and time-dependent manner. Multiplication of the parasites was recovered after reinoculation in fresh culture medium. Ultrastructural analysis of treated promastigotes revealed marked mitochondrial swelling with loss of cristae and matrix and the presence of concentric membranar structures inside the organelle. Iron depletion also induced Golgi disruption and intense cytoplasmic vacuolization. Fluorescence-activated cell sorting analysis of tetramethylrhodamine ester-stained parasites showed that 2,2-dipyridyl collapsed the mitochondrial membrane potential. The incubation of parasites with propidium iodide demonstrated that disruption of mitochondrial membrane potential was not associated with plasma membrane permeabilization. TUNEL assays indicated no DNA fragmentation in chelator-treated promastigotes. In addition, two-dimensional electrophoresis showed that treatment with the iron chelator induced up- or down-regulation of proteins involved in metabolism of nucleic acids and coordination of post-translational modifications, without altering their mRNA levels.

Conclusions

Iron chelation leads to a multifactorial response that results in cellular collapse, starting with the interruption of cell proliferation and culminating in marked mitochondrial impairment in some parasites and their subsequent cell death, whereas others may survive and resume proliferating.

American tegumentary leishmaniasis (ATL) is a neglected disease that is widely distributed in the Americas. The protozoan parasite Leishmania (Viannia) braziliensis is one of the main causative agents of ATL, being responsible for the development of different clinical manifestations of the disease, which ranges from self-healing cutaneous lesions to disseminated and mucocutaneous forms. Because iron is essential for the survival and growth of Leishmania, as it is required for colonization of macrophages and development of lesions in mice, several chelating compounds have been tested for their effects on the growth of these parasites. In the present work, treatment of L. (V.) braziliensis with the iron chelator 2,2-dipyridyl inhibited the growth of promastigote forms in a dose- and time-dependent manner. However, multiplication of the parasites was recovered after reinoculation in fresh culture medium. The iron chelator also induced mitochondrial dysfunction and altered expression of proteins involved in metabolism of nucleic acids and coordination of post-translational modifications. The events described above ultimately caused the death of some parasites, most likely due to mitochondrial dysfunction, whereas others adapted and survived, suggesting a plasticity or resilience of the mitochondrion in this parasite.

Biophysical Characterization of α-Synuclein and Rotenone Interaction

Previous studies revealed that pesticides interact with α-synuclein and accelerate the rate of fibrillation. These results are consistent with the prevailing hypothesis that the direct interaction of α-synuclein with pesticides is one of many suspected factors leading to α-synuclein fibrillation and ultimately to Parkinson's disease. In this study, the biophysical properties and fibrillation kinetics of α-synuclein in the presence of rotenone were investigated and, more specifically, the effects of rotenone on the early-stage misfolded forms of α-synuclein were considered. The thioflavine T (ThT) fluorescence assay studies provide evidence that early-phase misfolded α-synuclein forms are affected by rotenone and that the fibrillation process is accelerated. Further characterization by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) shows that rotenone increases the amount of ordered secondary structure in this intrinsically disordered protein. Morphological characterization by transmission electron microscopy (TEM) and atomic force microscopy (AFM) provide visualization of the differences in the aggregated α-synuclein species developing during the early kinetics of the fibrillation process in the absence and presence of rotenone. We believe that these data provide useful information for a better understanding of the molecular basis of rotenone-induced misfolding and aggregation of α-synuclein.

Agrochemicals, α-synuclein, and Parkinson's disease

Epidemiological, population-based case-control, and experimental studies at the molecular, cellular, and organism levels revealed that exposure to various environmental agents, including a number of structurally different agrochemicals, may contribute to the pathogenesis of Parkinson's disease (PD) and several other neurodegenerative disorders. The role of genetic predisposition in PD has also been increasingly acknowledged, driven by the identification of a number of disease-related genes [e.g., α-synuclein, parkin, DJ-1, ubiquitin C-terminal hydrolase isozyme L1 (UCH-L1), and nuclear receptor-related factor 1]. Therefore, the etiology of this multifactorial disease is likely to involve both genetic and environmental factors. Various neurotoxicants, including agrochemicals, have been shown to elevate the levels of α-synuclein expression in neurons and to promote aggregation of this protein in vivo. Many agrochemicals physically interact with α-synuclein and accelerate the fibrillation and aggregation rates of this protein in vitro. This review analyzes some of the aspects linking α-synuclein to PD, provides brief structural and functional descriptions of this important protein, and represents some data connecting exposure to agrochemicals with α-synuclein aggregation and PD pathogenesis.

In vitro and in vivo biological activities of iron chelators and gallium nitrate against Acinetobacter baumannii

We investigated the ability of compounds interfering with iron metabolism to inhibit the growth of Acinetobacter baumannii. Iron restriction with transferrin or 2,2-bipyridyl significantly inhibited A. baumannii growth in vitro. Gallium nitrate alone was moderately effective at reducing A. baumannii growth but became bacteriostatic in the presence of serum or transferrin. More importantly, gallium nitrate treatment reduced lung bacterial burdens in mice. The use of gallium-based therapies shows promise for the control of multidrug-resistant A. baumannii.

Ferrous chelator 2,2'-dipyridyl attenuates cerebral vasospasm after experimental subarachnoid haemorrhage in rabbits

The effect of 2,2'-dipyridyl (DP) on cerebral vasospasm was investigated in a double-injection rabbit model of subarachnoid haemorrhage (SAH). Thirty-six animals were divided between four groups: control (sham-operated), SAH (model alone), SAH + DP (the SAH model in which DP dissolved in dimethyl sulphoxide [DMSO] was injected once daily for 5 days into the cisterna magna), and SAH + DMSO (the SAH model in which DMSO [vehicle] was injected daily for 5 days). There were significant differences in the basilar artery luminal area, wall thickness, neurological deficit score and vasospasm index between the SAH + DP and SAH groups. There was a significant negative correlation between arterial luminal area and arterial wall thickness, and also between the neurological deficit score and vasospasm index. Cells that were positive for terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labelling (TUNEL) and p53 expression were significantly increased in the SAH + DMSO and SAH groups, but not in the SAH + DP group, versus controls. Thus, DP may attenuate cerebral vasospasm after SAH by suppressing p53-induced apoptosis in the cerebral vessels.

Paraquat toxicity in a mouse embryonic stem cell model

The objective of this in vitro study was to use a mouse embryonic stem (mES) cell model to better understand pesticide injury that may adversely affect early pregnancy and to evaluate an antioxidant intervention. Undifferentiated D3 mES cells were incubated 24h with control, reference dose (RfD), no observed effect level (NOEL), or lowest observed effect level (LOEL) of paraquat, a commonly used, toxic agricultural herbicide. Pesticide effects were evaluated at 0 and 24h using assays for cell proliferation, total reactive oxygen species (ROS), viability, and alkaline phosphatase activity. Compared to 0 h, cell proliferation increased significantly in the 24h control treatment and was stalled in all paraquat dilutions tested. ROS production and percent necrotic and apoptotic cells were significantly increased at all paraquat concentrations examined. Alkaline phosphatase activity suggested that cells remained undifferentiated during the study period. Experiments with ascorbic acid suggested that pesticide effects on cell viability and ROS production were minimized by the recommended daily allowance (RDA) of vitamin C. Data suggest pesticide-induced injury can occur very early in development and at concentrations predicted without health consequences. Mouse ES cells may provide a useful in vitro model for rapidly screening developmental toxicants and protective interventions.

An HPLC method for the simultaneous determination of neurotoxic dipyridyl isomers in human plasma

Several studies on dipyridyl isomers have suggested that they are neurotoxic and that chronic exposure to these compounds could be a potential human health hazard. A reversed phase HPLC method was developed for the simultaneous quantitation of 2,2'-dipyridyl and its four positional isomers, 2,3'-, 2,4'-, 3,4'- and 4,4'-dipyridyl in human plasma. Plasma samples were basified, extracted with 1-chlorobutane, evaporated, the residue reconstituted in mobile phase, and an aliquot part was analyzed by HPLC. Chromatographic separations were performed on a C(18) reversed phase Sunfire column eluted with a mobile phase composed of potassium phosphate (pH 3.5; 25 mM)-acetonitrile (80:20, v/v). Isomers were separated with good resolution, and quantification was determined utilizing an internal standard of quinoxaline. The method has been validated over a range from 30 to 2000 ng/ml with correlation coefficients higher than 0.995. Extraction recoveries for the dipyridyl isomers averaged from 65 to 92%. Limit of detection and limit of quantitation for the dipyridyl isomers ranged from 15 to 70 ng/ml and 30 to 90 ng/ml, respectively. The inter- and intra-day variation did not exceed 7% with an accuracy range of 96-102%. The described analytical method was successfully utilized for the determination of dipyridyl isomers in human plasma and suggested the need for more routine monitoring of tobacco smokers and other individuals who are involuntarily exposed to environmental source of dipyridyl isomers.