BackgroundThe development of new anticoagulants is an important goal for the improvement of thromboses treatments.ObjectivesThe design, synthesis and experimental testing of new safe and effective small molecule direct thrombin inhibitors for intravenous administration.MethodsComputer-aided molecular design of new thrombin inhibitors was performed using our original docking program SOL, which is based on the genetic algorithm of global energy minimization in the framework of a Merck Molecular Force Field. This program takes into account the effects of solvent. The designed molecules with the best scoring functions (calculated binding energies) were synthesized and their thrombin inhibitory activity evaluated experimentally in vitro using a chromogenic substrate in a buffer system and using a thrombin generation test in isolated plasma and in vivo using the newly developed model of hemodilution-induced hypercoagulation in rats. The acute toxicities of the most promising new thrombin inhibitors were evaluated in mice, and their stabilities in aqueous solutions were measured.ResultsNew compounds that are both effective direct thrombin inhibitors (the best KI was <1 nM) and strong anticoagulants in plasma (an IC50 in the thrombin generation assay of approximately 100 nM) were discovered. These compounds contain one of the following new residues as the basic fragment: isothiuronium, 4-aminopyridinium, or 2-aminothiazolinium. LD50 values for the best new inhibitors ranged from 166.7 to >1111.1 mg/kg. A plasma-substituting solution supplemented with one of the new inhibitors prevented hypercoagulation in the rat model of hemodilution-induced hypercoagulation. Activities of the best new inhibitors in physiological saline (1 µM solutions) were stable after sterilization by autoclaving, and the inhibitors remained stable at long-term storage over more than 1.5 years at room temperature and at 4°C.ConclusionsThe high efficacy, stability and low acute toxicity reveal that the inhibitors that were developed may be promising for potential medical applications.

(1) Background. A one-time moderate hypobaric hypoxia (HBH) has a preconditioning effect whose neuronal mechanisms are not studied well. Previously, we found a stable correlation between the HBH efficiency and acoustic startle prepulse inhibition (PPI). This makes it possible to predict the individual efficiency of HBH in animals and to study its potential adaptive mechanisms. We revealed a bi-directional action of nicotinic α7 receptor agonist PNU-282987 and its solvent dimethyl sulfoxide on HBH efficiency with the level of PPI > or < 40%. (2) The aim of the present study was to estimate cholinergic mechanisms of HBH effects in different brain regions. (3) Methods: in rats pretested for PPI, we evaluated the activity of synaptic membrane-bound and water-soluble choline acetyltransferase (ChAT) in the sub-fractions of ‘light’ and ‘heavy’ synaptosomes of the neocortex, hippocampus and caudal brainstem in the intact brain and after HBH. We tested the dose-dependent influence of PNU-282987 on the HBH efficiency. (4) Results: PPI level and ChAT activity correlated negatively in all brain structures of the intact animals, so that the values of the latter were higher in rats with PPI < 40% compared to those with PPI > 40%. After HBH, this ChAT activity difference was leveled in the neocortex and caudal brainstem, while for membrane-bound ChAT in the ‘light’ synaptosomal fraction of hippocampus, it was reversed to the opposite. In addition, a pharmacological study revealed that PNU-282987 in all used doses and its solvent displayed corresponding opposite effects on HBH efficiency in rats with different levels of PPI. (5) Conclusion: We substantiate that in rats with low and high PPI two opposite hippocampal cholinergic mechanisms are involved in hypoxic preconditioning, and both are implemented by forebrain projections via nicotinic α7 receptors. Possible causes of association between general protective adaptation, HBH, PPI, forebrain cholinergic system and hippocampus are discussed.

Moderate one-off hypobaric hypoxia (HBH) provokes preconditioning and prolongs the resistance (T, the time before apnoea) to severe hypobaric hypoxia (SHBH). Hypoxic preconditioning has therapeutic potential; however, the efficiency of hypoxic preconditioning varies greatly and the methods for its preliminary evaluation are absent in both animals and humans. This rodent study evaluates the dependence of SHBH resistance, initiated by HBH, on the rate of sensorimotor gating estimated in the model of the acoustic startle prepulse inhibition (PPI). A stable negative correlation was found between PPI and T. Low doses of the α7 nicotinic receptor agonist, PNU-282987 (PNU), and more pronouncedly dimethyl sulfoxide (DMSO) (a PNU solvent), inverted the correlation between PPI and T from negative to positive. The DMSO and PNU effects were reversed at PPIs of 0.36 -0.40 (36% -40%). DMSO increased T values by 52.2% ± 9.7% in the region of lower HBH efficiency (PPI ≥ 0.40) and reduced it by 35.2% ± 9.3% in the region of higher HBH efficiency (PPI < 0.40). PNU reduced both DMSO effects. The involvement of the central cholinergic mechanisms was substantiated in both DMSO and PNU influences on HBH. In conclusion, 1) PPI can be used to predict the efficiency of hypoxic preconditioning and to study its mechanisms, 2) two opposite cholinergic PPI-related mechanisms participate in the preconditioning effects of HBH, 3) the sensitivity of rats to DMSO and PNU diverges when the PPI is 0.36 -0.40,

In rats, a single moderate hypobaric hypoxia (HBH) increased the resistance to severe hypoxia (SHBH). The HBH efficiency and neurotransmitter mechanisms of its preconditioning action were investigated by biochemical and pharmacological methods. It will be substantiated in the chapter: (1) HBH preconditioning has its own mechanisms that do not depend on an innate resistance to SHBH and prior hypoxic experience of rats; (2) the same preconditioning effect can be achieved by diverse neuronal pathways and synaptic plasticity means; (3) cholinergic and, presumably, serotoninergic, GABAergic and/or glutamatergic systems of the caudal brainstem, cortex and some other brain structures are involved in HBH realisation; (4) the rate of sensorimotor gating estimated in the model of acoustic startle pre-pulse inhibition (PPI) predicts the efficiency of hypoxic preconditioning and (5) the cholinergic system, including α7 nicotinic receptors, is involved in the mechanisms of HBH-PPI-dependent preconditioning effects.

Experiments were performed on Wistar rats with high and low locomotor activities. In rats with high locomotor activity, activities of acetylcholine transferase, acetylcholine esterase, and monoamine oxidase A increased in the subcellular fractions of the sensorimotor cortex and arcuate nucleus, while monoamine oxidase B activity decreased compared to those in rats with low locomotor activity. The peculiarities of neurotransmitter systems in brain structures of rats with different behavioral patterns were related to genetic and functional organization of the central nervous system.