Novel hits for acetylcholinesterase inhibition derived by docking-based screening on ZINC database

The inhibition of the enzyme acetylcholinesterase (AChE) increases the levels of the neurotransmitter acetylcholine and symptomatically improves the affected cognitive function. In the present study, we searched for novel AChE inhibitors by docking-based virtual screening of the standard lead-like set of ZINC database containing more than 6 million small molecules using GOLD software. The top 10 best-scored hits were tested in vitro for AChE affinity, neurotoxicity, GIT and BBB permeability. The main pharmacokinetic parameters like volume of distribution, free fraction in plasma, total clearance, and half-life were predicted by previously derived models. Nine of the compounds bind to the enzyme with affinities from 0.517 to 0.735?µM, eight of them are non-toxic. All hits permeate GIT and BBB and bind extensively to plasma proteins. Most of them are low-clearance compounds. In total, seven of the 10 hits are promising for further lead optimisation. These are structures with ZINC IDs: 00220177, 44455618, 66142300, 71804814, 72065926, 96007907, and 97159977.     

The influence of selenium and caffeine on chemical carcinogenesis in rats,mutagenesis in bacteria,and unscheduled DNA synthesis in human lymphocytes

The influence of sodium selenite (Na₂SeO₃) and caffeine on chemical carcinogenesis induced in rats by diethylnitrosamine (DEN), N-nitrosomorpholine (NM), andN-methyl-N-nitro-N-nitrosoguanidine (MNNG) was investigated. A dose-dependent inhibitory effect of Na₂SeO₃ (l–10 ppm) on hepatocarcinogenesis induced by DEN was demonstrated. Na₂SeO₃ also increased the latency period for stomach tumor formation in rats treated with MNNG. Combined treatment of rats with Na₂SeO₃ plus vitamin C added to the diet resulted in a slight inhibition of NM-induced liver carcinogenesis. Supplementation of diet with Na₂SeO₃ plus butylated hydroxytoluene, vitamin C, and vitamin E did not reveal any additive inhibitory effect compared to the inhibitory effect of Na₂SeO₃ given alone. Caffeine (600 rag/L) reduced the number of liver tumors induced in rats by DEN. Preliminary experiments have indicated that combined treatment of rats with selenium and caffeine could result in more effective inhibition of DEN-induced liver carcinogenesis. Further experiments are being conducted to study the influence of selenium and caffeine on mutagenic activity of 1-methyl-l-nitrosourea (MNU) inSalmonella typhimurium TA 1535. The pretreatment of bacteria cells with Na₂SeO₃ (3–10 p.g/mL) increased the mutagenic response of bacteria to MNU. A synergistic stimulation of mutagenic activity of MNU was observed in bacteria pretreated simultaneously with Na₂SeO₃ and caffeine. In addition the influence of Na₂SeO₃ on UDS induced by DEN in human lymphocytes was investigated. The trace element inhibited the UDS up to 82%. The possible role of potentiation by NazSeO3 of the cell killing effect of DEN in inhibition of liver carcinogenesis was discussed.     

Sand fly specificity of saliva-mediated protective immunity in Leishmania amazonensis-BALB/c mouse model

Immune response of BALB/c mice to the salivary antigens of sand flies was found to vary with different species used, i.e. Phlebotomus papatasi, Phlebotomus sergenti and Lutzomyia longipalpis. Exposure of mice to bites of these sand flies elicits production of antibodies, which are largely specific to different saliva antigens previously identified as unique to the respective fly species. When immunized intradermally (i.d.) with salivary gland lysates (SGL) of L. longipalpis, BALB/c mice developed partial protective immunity against challenges in the contralateral ears with Leishmania amazonensis plus the gland lysates. Preimmunization of these mice with the lysates from the other two species was ineffective, further indicative of the specificity of saliva-mediated immune response. The partial protective immunity observed is significant, although it is not as dramatic as reported previously in a different sand fly-mouse model. There is a correlation of this immunity with a lower number of mononuclear and polymorphonuclear phagocytes at the site of parasite inoculation. Vector species-specificity of this immunity implies its elicitation by unique saliva antigen-an issue which requires attention when designing saliva-based vaccines against leishmaniasis.     

KvAP-based model of the pore region of shaker potassium channel is consistent with cadmium- and ligand-binding experiments

Potassium channels play fundamental roles in excitable cells. X-ray structures of bacterial potassium channels show that the pore-lining inner helices obstruct the cytoplasmic entrance to the closed channel KcsA, but diverge in widely open channels MthK and KvAP, suggesting a gating-hinge role for a conserved Gly in the inner helix. A different location of the gating hinge and a narrower open pore were proposed for voltage-gated Shaker potassium channels that have the Pro-473-Val-Pro motif. Two major observations back the proposal: cadmium ions lock mutant Val-476-Cys in the open state by bridging Cys-476 and His-486 in adjacent helices, and cadmium blocks the locked-open double mutant Val-474-Cys/Val-476-Cys by binding to Cys-474 residues. Here we used molecular modeling to show that the open Shaker should be as wide as KvAP to accommodate an open-channel blocker, correolide. We further built KvAP-, MthK-, and KcsA-based models of the Shaker mutants and Monte-Carlo-minimized them with constraints Cys-476-Cd(2+)-His-486. The latter were consistent with the KvAP-based model, causing a small-bend N-terminal to the Pro-473-Val-Pro motif. The constraints significantly distorted the MthK-based structure, making it similar to KvAP. The KcsA structure resisted the constraints. Two Cd(2+) ions easily block the locked-open KvAP-based model at Cys-474 residues, whereas constraining a single cadmium ion to four Cys-474 caused large conformational changes and electrostatic imbalance. Although mutual disposition of the voltage-sensor and pore domains in the KvAP x-ray structure is currently disputed, our results suggest that the pore-region domain retains a nativelike conformation in the crystal.     

BAD is a pro-survival factor prior to activation of its pro-apoptotic function

The mammalian BAD protein belongs to the BH3-only subgroup of the BCL-2 family. In contrast to its known pro-apoptotic function, we found that endogenous and overexpressed BAD(L) can inhibit cell death in neurons and other cell types. Several mechanisms regulate the conversion of BAD from an anti-death to a pro-death factor, including alternative splicing that produces the N-terminally truncated BAD(S). In addition, caspases convert BAD(L) into a pro-death fragment that resembles the short splice variant. The caspase site that is selectively cleaved during cell death following growth factor (interleukin-3) withdrawal is conserved between human and murine BAD. A second cleavage site that is required for murine BAD to promote death following Sindbis virus infection, gamma-irradiation, and staurosporine treatment is not conserved in human BAD, consistent with the inability of human BAD to promote death with these stimuli. However, loss of the BAD N terminus by any mechanism is not always sufficient to activate its pro-death activity, suggesting that the N terminus is a regulatory domain rather than an anti-death domain. These findings suggest that BAD is more than an inert death factor in healthy cells; it is also a pro-survival factor, prior to its role in promoting cell death.     

Evolutionarily stable strategies for stochastic processes

The classical definition of evolutionary stability assumes that the fitness of each phenotype is fully determined by the composition of phenotypes in the population and by the strategies of each of these phenotypes. In natural populations, however, stochasticity often plays a crucial role in determining the fitness of an individual and a deterministic fitness function is probably rather rare. For example, choices of a new host plant, prey or oviposition patch are completely stochastic processes. Here we introduce a new definition of ESS that takes into account the effect of stochasticity on individual fitness. Then we show an application of this definition in a realistic system.     

Nuclear and division-plane positioning revealed by optical micromanipulation

The position of the division plane affects cell shape and size, as well as tissue organization. Cells of the fission yeast Schizosaccharomyces pombe have a centrally placed nucleus and divide by fission at the cell center. Microtubules (MTs) are required for the central position of the nucleus. Genetic studies lead to the hypothesis that the position of the nucleus may determine the position of the division plane. Alternatively, the division plane may be positioned by the spindle or by morphogen gradients or reaction diffusion mechanisms. Here, we investigate the role of MTs in nuclear positioning and the role of the nucleus in division-plane positioning by displacing the nucleus with optical tweezers. A displaced nucleus returned to the cell center by MT pushing against the cell tips. Nuclear displacement during interphase or early prophase resulted in asymmetric cell division, whereas displacement during prometaphase resulted in symmetric division as in unmanipulated cells. These results suggest that the division plane is specified by the predividing nucleus. Because the yeast nucleus is centered by MTs during interphase but not in mitosis, we hypothesize that the establishment of the division plane at the beginning of mitosis is an optimal mechanism for accurate symmetric division in these cells.