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K Valko

Publications and source records attributed to K Valko.

9 recordsLinked to original sources
PubMed2003

A cell-based approach for the early assessment of the phospholipidogenic potential in pharmaceutical research and drug development.

Phospholipidosis is a term commonly used to indicate a phospholipid storage disorder; in affected cells, phospholipids accumulate in lysosomes that acquire a multilamellar morphological appearance. Cationic amphiphilic drugs (CADs) are suggested to induce phospholipidosis by direct interaction of xenobiotics with intracellular phospholipids or by the action of xenobiotics on the synthesis and metabolism of phospholipids. To date, electron microscopy (EM) represents the most reliable and the preferred method for the demonstration of phospholipidotic cell damage. Nevertheless, EM has a low throughput, it is expensive, and it is not suitable for screening purposes. We discuss here the assessment of the the phospholipidogenic potential of drugs using a cell culture-based model. In this test, intracellular phospholipids of treated U-937 cells (a human monocyte-derived cell line) were measured using the fluorescent probe Nile red. Eleven CADs reported to induce phospholipidosis in vivo and eight nonphospholipidogenic drugs were tested. Results obtained with the U-937 model confirmed the phospholipidogenic potential of drugs tested as described in the literature. Results have also been correlated with data obtained with a physical-chemical model (chromatographic hydrophobicity index measurement). Good correlation was obtained, confirming that the physical-chemical properties of CADs play a crucial role in the development of phospholipidosis. This work demonstrates that the U-937 model is a rapid and sensitive method for the determination of phospholipidosis-mediated cell damage. The specificity and the predictive potency observed make this method suitable for screening purposes in pharmaceutical development.

Cations↗
PubMed2001

Rapid method for the estimation of octanol/water partition coefficient (log P(oct)) from gradient RP-HPLC retention and a hydrogen bond acidity term (zetaalpha(2)(H)).

We propose a rapid method for the measurement of octanol/water partition coefficients (log P(oct)) via fast gradient reversed phase retention and the calculation of the hydrogen bond acidity of the compounds. The cycle time of the generic gradient HPLC method is 5 minutes. The general solvation equation obtained for the log Poct values and the fast gradient Chromatographic Hydrophobicity Indices with acetonitrile (CHI(ACN)) and methanol

Chemical Phenomena↗
PubMed2000

Rapid-gradient HPLC method for measuring drug interactions with immobilized artificial membrane: comparison with other lipophilicity measures.

A fast-gradient high-performance liquid chromatographic (HPLC) method has been suggested to characterize the interactions of drugs with an immobilized artificial membrane (IAM). With a set of standards, the gradient retention times can be converted to Chromatographic Hydrophobicity Index values referring to IAM chromatography (CHI(IAM)) that approximates an acetonitrile concentration with which the equal distribution of compound can be achieved between the mobile phase and IAM. The CHI(IAM) values are more suitable for interlaboratory comparison and for high throughput screening of new molecular entities than the log k(IAM) values (isocratic retention factor on IAM). The fast-gradient method has been validated against the isocratic log k(IAM) values using the linear free energy relationship solvation equations based on the data from 48 compounds. The compound set was selected to provide a wide range and the least cross-correlation between the molecular descriptors in the solvation equation: (2) where SP is a solute property (e.g., logarithm of partition coefficients, reversed-phase (RP)-HPLC retention parameters, such as log k, log k(w), etc.) and the explanatory variables are solute descriptors as follows: R(2) is an excess molar refraction that can be obtained from the measured refractive index of a compound, pi(2)(H) is the solute dipolarity/polarizability, summation operatoralpha(2)(H) and summation operatorbeta(2)(0) are the solute overall or effective hydrogen-bond acidity and basicity, respectively, and V(x) is the McGowan characteristic volume (in cm(3)/100 mol) that can be calculated for any solute simply from molecular structure using a table of atomic constants. It was found that the relative constants of the solvation equation were very similar for the CHI(IAM) and for the log k(IAM). The IAM lipophilicity scale was quite similar to the octanol/water lipophilicity scale for neutral compounds. The effect of charge on the interaction with IAM was studied by varying the mobile phase pH.

Chromatography, High Pressure Liquid↗
PubMed2000

Characterizing the selectivity of stationary phases and organic modifiers in reversed-phase high-performance liquid chromatographic systems by a general solvation equation using gradient elution.

Retention data for a set of 69 compounds using rapid gradient elution are obtained on a wide range of reversed-phase stationary phases and organic modifiers. The chromatographic stationary phases studied are Inertsil (IN)-ODS, pentafluorophenyl, fluoro-octyl, n-propylcyano, Polymer (PLRP-S 100), and hexylphenyl. The organic solvent modifiers are 2,2,2-trifluoroethanol (TFE); 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP); isopropanol; methanol (MeOH); acetonitrile (AcN); tetrahydrofuran; 1,4-dioxane; N,N-dimethylformamide; and mixed solvents of dimethylsulfoxide (DMSO) with AcN and DMSO with MeOH (1:1). A total of 25 chromatographic systems are analyzed using a solvation equation. In general, most of the systems give reasonable statistics. The selectivity of the reversed phase-high-performance liquid chromatographic (HPLC) systems with respect to the solute's dipolarity-polarity, hydrogen-bond acidity, and basicity are reflected in correspondingly large coefficients in the solvation equation. We wanted to find the most orthogonal HPLC systems, showing the highest possible selectivity difference in order to derive molecular descriptors using the gradient retention times of a compound. We selected eight chromatographic systems that have a large range of coefficients of interest (s, a, and b) similar to those found in water-solvent partitions used previously to derive molecular descriptors. The systems selected are IN-ODS phases with AcN, MeOH, TFE, and HFIP as mobile phase, PLRP-S 100 phase with AcN, propylcyano phase with AcN and MeOH, and fluorooctyl phase with TFE. Using the retention data obtained for a compound in the selected chromatographic systems, we can estimate the molecular descriptors with the faster and simpler gradient elution method.

Journal Article↗
PubMed1999

Detection of the principal synthetic route indicative impurity in lamotrigine.

An analytical method has been developed for the detection of trace amounts of the principal synthetic route indicative impurity in lamotrigine (3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine). A sample extract was preconcentrated by normal-phase high-performance liquid chromatography (HPLC) and analysed by subsequent on-line reversed-phase HPLC-thermospray mass spectrometry (TSP-MS). During the sample extraction and concentration step, carried out by semipreparative normal-phase chromatography, the preliminary separation of the impurity from the lamotrigine takes place. The organic solvent (dichloroethane-methanol, 90:10, v/v) is evaporated from the collected fraction and the material is redissolved in a smaller volume of the reversed-phase mobile phase. The collected fraction is then subjected to reversed-phase HPLC-TSP-MS. The influence of an ultrasonic extraction step has been examined. When the method was applied to lamotrigine tablets, a shake flask partitioning step using 1 mg/ml EDTA in water-dichloroethane was used instead of the ultrasonic extraction. Detection limit and recovery measurements showed that the route indicative impurity formed during the synthesis could be detected in the 50-100 ppb (w/w) range.

Acetonitriles↗
PubMed1996

Binding measurements of indolocarbazole derivatives to immobilised human serum albumin by high-performance liquid chromatography.

The binding properties of six indolocarbazole derivative have been measured using immobilised human serum albumin (HSA) in an HPLC column. The compounds showed very strong binding to HSA which necessitated the application of a 30 to 40% concentration of 2-propanol in the mobile phase. This represents a much higher concentration than is recommended by the column manufacturers. This HSA column had not changed its binding property when it was used again with 4% 2-propanol and 96% phosphate buffer. The binding parameters were estimated by extrapolation to 0% 2-propanol and were above 99% for each indolocarbazole derivative. The correlation analysis, including the calculated octanol/water partition coefficient (log P), pKa values as well as measured reversed-phase retention data of the compounds revealed that the extremely strong binding can be explained by the hydrophobic and acidic properties of the compounds.

Antiviral Agents↗
PubMed1990

Relationship between the hydrophobic and hydrophilic molecular parameters of some synthetic nucleosides, determined by means of adsorptive and reversed-phase thin-layer chromatography.

The adsorption capacity, the specific adsorptive surface, the lipophilicity and the specific hydrophobic surface of 59 natural and synthetic nucleoside derivatives were determined by means of adsorptive chromatography and reversed-phase thin-layer chromatography for the future application of these molecular parameters in quantitative structure-activity relationship studies. Stepwise regression analysis and principal component analysis proved that each of the physico-chemical parameters has a different information content, and their application in the design of new bioactive derivatives is therefore justified.

Adsorption↗