Use of biopartitioning micellar chromatography and RP-HPLC for the determination of blood-brain barrier penetration of α-adrenergic/imidazoline receptor ligands, and QSPR analysis.

For this study, 31 compounds, including 16 imidazoline/α-adrenergic receptor (IRs/α-ARs) ligands and 15 central nervous system (CNS) drugs, were characterized in terms of the retention factors (k) obtained using biopartitioning micellar and classical reversed phase chromatography (log kBMC and log kwRP, respectively). Based on the retention factor (log kwRP) and slope of the linear curve (S) the isocratic parameter (φ0) was calculated. Obtained retention factors were correlated with experimental log BB values for the group of examined compounds. High correlations were obtained between logarithm of biopartitioning micellar chromatography (BMC) retention factor and effective permeability (r(log kBMC/log BB): 0.77), while for RP-HPLC system the correlations were lower (r(log kwRP/log BB): 0.58; r(S/log BB): -0.50; r(φ0/Pe): 0.61). Based on the log kBMC retention data and calculated molecular parameters of the examined compounds, quantitative structure-permeability relationship (QSPR) models were developed using partial least squares, stepwise multiple linear regression, support vector machine and artificial neural network methodologies. A high degree of structural diversity of the analysed IRs/α-ARs ligands and CNS drugs provides wide applicability domain of the QSPR models for estimation of blood-brain barrier penetration of the related compounds.

Polypharmacology of dopamine receptor ligands.

Most neurological diseases have a multifactorial nature and the number of molecular mechanisms discovered as underpinning these diseases is continuously evolving. The old concept of developing selective agents for a single target does not fit with the medical need of most neurological diseases. The development of designed multiple ligands holds great promises and appears as the next step in drug development for the treatment of these multifactorial diseases. Dopamine and its five receptor subtypes are intimately involved in numerous neurological disorders. Dopamine receptor ligands display a high degree of cross interactions with many other targets including G-protein coupled receptors, transporters, enzymes and ion channels. For brain disorders like Parkinsons disease, schizophrenia and depression the dopaminergic system, being intertwined with many other signaling systems, plays a key role in pathogenesis and therapy. The concept of designed multiple ligands and polypharmacology, which perfectly meets the therapeutic needs for these brain disorders, is herein discussed as a general ligand-based concept while focusing on dopaminergic agents and receptor subtypes in particular.

Imidazoline antihypertensive drugs: selective i(1) -imidazoline receptors activation.

Involvement of imidazoline receptors (IR) in the regulation of vasomotor tone as well as in the mechanism of action of some centrally acting antihypertensives has received tremendous attention. To date, pharmacological studies have allowed the characterization of three main imidazoline receptor classes, the I(1) -imidazoline receptor which is involved in central inhibition of sympathetic tone to lower blood pressure, the I(2) -imidazoline receptor which is an allosteric binding site of monoamine oxidase B (MAO-B), and the I(3) -imidazoline receptor which regulates insulin secretion from pancreatic ß-cells. All three imidazoline receptors represent important targets for cardiovascular research. The hypotensive effect of clonidine-like centrally acting antihypertensives was attributed both to α(2) -adrenergic receptors and nonadrenergic I(1) -imidazoline receptors, whereas their sedative action involves activation of only α(2) -adrenergic receptors located in the locus coeruleus. Since more selective I(1) -imidazoline receptors ligands reduced incidence of typical side effects of other centrally acting antihypertensives, there is significant interest in developing new agents with higher selectivity and affinity for I(1) -imidazoline receptors. The selective imidazoline receptors agents are also more effective in regulation of body fat, neuroprotection, inflammation, cell proliferation, epilepsy, depression, stress, cell adhesion, and pain. New agonists and antagonists with high selectivity for imidazoline receptor subtypes have been recently developed. In the present review we provide a brief update to the field of imidazoline research, highlighting some of the chemical diversity and progress made in the theoretical studies of imidazoline receptor ligands.

High-frequency limit of neural stimulation with ChR2.

Optogenetic technology based on light activation of genetically targeted single component opsins such as Channelrhodopsin-2 (ChR2) has been changing the way neuroscience research is conducted. This technology is becoming increasingly important for neural engineering as well. The efficiency of neural stimulation with ChR2 drops at high frequencies, often before the natural limit of the neuron is reached. This study aims to investigate the underlying mechanisms that limit the efficiency of the stimulation at high frequencies. The study analyzes the dynamics of the spikes induced by ChR2 in comparison to control stimulations using patch clamp current injection. It shows that the stimulation dynamics is limited by two mechanisms: 1) a frequency independent reduction in the conductance-to-irradiance yield due to the ChR2 light adaptation process and 2) a frequency dependent reduction in the conductance-to-current yield due to a decrease in membrane re-polarization level between spikes that weakens the ionic driving force. The effect of the first mechanism can be minimized by using ChR2 mutants with lower irradiance threshold. In contrast the effect of the second mechanism is fundamentally limited by the rate the native ion channels re-polarize the membrane potential.

QSAR study of selective I1-imidazoline receptor ligands.

Selective imidazoline(1)-receptor (I(1)-R) ligands are used clinically to reduce blood pressure. Thus, there is significant interest in developing new imidazoline analogs with high selectivity and affinity for I(1) receptors. A quantitative structure-activity relationship (QSAR) study was carried out on 11 potent I(1)-R ligands (derivatives of imidazoline, oxazoline and pyrroline) using a multiple linear regression (MLR) procedure. The selected compounds have been studied using B3LYP/3-21G(d, p) and B3LYP/6-31G(d, p) methods. Among the 42 descriptors that were considered in generating the QSAR model, three descriptors (partial atomic charges of nitrogen in the heterocyclic moiety (N-2 charge), log D and the dipole moment of the ligands) resulted in a statistically significant model with r(2) > 0.874 and [image omitted] > 0.802. The QSAR models were validated through cross-validation and external test set prediction. The aim of the developed MLR models for the I(1)-R ligands was to link the structures to their reported I(1)-R binding affinity log(1/Ki). The proposed QSAR models indicate that an increase in log D and the dipole moment value and a decrease in N-2 charge in the heterocyclic moiety are predictors of better selectivity and affinity for I(1) receptors. The developed QSAR model is intended to predict the I(1)-R binding affinity of related compounds and aid in the rational design of new potent and selective I(1)-R ligands.

Design and QSAR study of analogs of alpha-tocopherol with enhanced antiproliferative activity against human breast adenocarcinoma cells.

Quantitative structure-activity relationships (QSAR) have been established for two sets of the antitumor drugs, alpha-tocopherol derivatives. Constitutional, geometrical, physico-chemical and electronic descriptors (using the B3LYP/6-31G (d, p) basis set) were computed and analyzed. The most relevant of these descriptors were grouped and multiple linear regressions have been carried out. QSAR model with four variables, R2=0.98 and cross-validation parameter qpre2)=0.91, was selected. Analogs of alpha-tocopherol (compounds D-1 and D-2) have been designed and their antiproliferative activities were evaluated using the proposed regression model. Calculated antiproliferative activities of the designed lysine/alpha-tocopherol/cholesterol conjugates, IC50 (D-1)=2.25 microM and IC50 (D-2)=3.42 microM, were significantly stronger than activities of the other analyzed compounds IC50>4 microM.

A non-invasive retinal prosthesis - testing the concept.

We have developed a testing platform for a novel type of retinal prosthesis. Our system uses an array of light sources as non-contact stimulators. The platform consists of an imaging system based on a CMOS camera, PC based image processing, and a stimulation address system carried out on a Field Programmable Gated Array which addresses a matrix array of LEDs. Special optics are used to focus the light from the LED array onto light sensitized cells.

Coulometric determination of some antiinflammatory compounds.

A method is presented for the chlorocoulometric assay of small amounts of piroxicam and tenoxicam. This assay is carried out directly by coulometrically titrating the investigated substances with electrogenerated chloride in the presence of methyl orange as indicator. Results are accurate and reproducible. The method can be applied for routine analysis of these substances.

Coulometric determination of some antiasthmatics.

A simple and rapid method for the assay of microquantities of fenoterol hydrobromide, orciprenaline sulphate and terbutaline sulphate in pure state and various pharmaceutical formulations, is presented. The method is based on the coulometric titration of the investigated compounds with electrogenerated chlorine in the presence of methyl orange as indicator. The method requires a simple apparatus and gives accurate and reproducible results.

[Correlation of clinical and autopsy diagnosis during a 10-year period at the Institute for Pathology and Forensic Medicine at the Military Medicine Academy in Belgrade]. / Korelacija klinickih i autopsijskih dijagnoza na desetogodisnjem materijalu Instituta za patologiju i sudsku medicinu Vojnomedicinske akademije u Beogradu.

The comparison between the clinical and pathohistoanatomic diagnosis of 3.929 autopsied cases is performed. In 82.5% of cases the clinical and pathohistoanatomic diagnosis were in the absolute correlation; in 8% of cases the clinical diagnosis of the basic disease has no adequate pathoanatomic characteristics, while in 4.5% of cases the clinical diagnosis of the basic disease, immediate cause of death and condition which was important for the course and outcome of the treatment were not adequate. Among the pathologic states diagnosed as: pulmonary thromboembolism, myocardial infarction and cerebrovascular insult--pulmonary embolism most often was not confirmed by autopsy (47%), while in 58% of cases it remained clinically unrecognized. Malignant tumours of the liver, pancreas and kidneys have been most frequently clinically unrecognized compared to other malignancies. Duration of hospitalization has not had the essential influence on correct establishment of the clinical diagnosis.

Chlorocoulometric determination of hydrocortisone and hydrocortisone acetate.

A chlorocoulometric method for the determination of small amounts of hydrocortisone and hydrocortisone acetate is presented. The method is simple and rapid, the results obtained are accurate and reproducible. It can be successfully applied to the determination of hydrocortisone and hydrocortisone acetate in pharmaceutical formulations.

Coulometric determination of levodopa, methyldopa and carbidopa.

A simple and rapid method for the assay of small quantities of levodopa, methyldopa and carbidopa is presented. The method is based on coulometric titration of the investigated substances with electrogenerated chlorine in the presence of methyl orange as indicator. Results are accurate and reproducible. The method does not require any expensive instrumentation and can be applied in any laboratory for routine analysis of these substances.

Potentiometric determination of captopril.

A rapid, accurate and reproducible method for the potentiometric determination of captopril in aqueous solution, is described. The method is based on the reaction of the thiol and the carboxylic group of captopril with silver ions whereby an equivalent amount of the acid is liberated; thereafter, the amount of captopril is determined by the potentiometric titration with sodium hydroxide. This method can be applied also for direct determination of captopril content in tablets.

Coulometric determination of sulfadimethoxine and sulfafurazole.

A chlorocoulometric method for determination of sulfadimethoxine and sulfafurazole in pharmaceutical preparation is proposed. The electrogeneration of chloride is carried out in the supporting electrolyte consisting of 0.5 mole x dm(-3) sulphuric acid and 0.2 mole x dm(-3) sodium chloride. The results obtained show that the method is accurate and reproducible and can be applied for determination of small quantities of sulfafurazole and sulfadimethoxine.