Huba Kalász

New planar liquid chromatographic technique: overpressured thin-layer chromatography

Abstract A novel planar liquid chromatographic technique using a pressurized ultramicro chamber (PUM chamber) has been developed. The sorbent layer is completely covered by a membrane under external pressure, so that the vapour phase above the layer is virtually eliminated. Solvent is admitted under pressure by means of a pump system. The main advantage of this technique, termed overpressured thin-layer chromatography (TLC), is the substantially shorter time required for separation than in classical column chromatography and TLC, with velocities of the mobile phase about as stable as in high-performance liquid chromatography, and aggressive reagents being applicable as in classical TLC. The method appears to be suitable for the accurate modelling of column chromatographic methods.

Entry of Oximes into the Brain: A Review

The passage of hydrophilic drugs, such as oxime acetylcholinesterase reactivators, into the central nervous system is restricted by the blood-brain and the blood-cerebrospinal fluid barriers. The present review summarizes morphological and functional properties of the blood-brain barrier, blood-cerebrospinal fluid barrier and cerebrospinal fluid-brain interface and reviews the existing data on brain entry of oximes. Due to the virtual absence of transcytosis, lack of fenestrations and unique properties of tight junctions in brain endothelial cells, the blood-brain barrier only allows free diffusion of small lipophilic molecules. Various carriers transport hydrophilic compounds and extrude potentially toxic xenobiotics. The blood-cerebrospinal fluid barrier is formed by the choroid plexus epithelium, whose tight junctions are more permeable than those of brain endothelial cells. The major function of plexus epithelium cells is active transport of ions for the production of the cerebrospinal fluid. The cerebrospinal fluid-brain interface is not a biological barrier and allows free diffusion. However, in contrast to passage via the blood-brain barrier or the blood-cerebrospinal fluid barrier, direct penetration from the cerebrospinal fluid into the brain is very slow, since much longer distances have to be covered. A bulk flow of brain interstitial fluid and cerebrospinal fluid speeds up exchange between these two fluid compartments. Oximes, by reactivating acetylcholinesterase, are important adjunct therapeutics in organophosphate poisoning. They are very hydrophilic and therefore cannot diffuse freely into the central nervous system. Changes in brain acetylcholinesterase activity, oxime concentration and some biological effects elicited by oxime administration in the periphery indicate, however, that oximes can gain access to the brain to a certain degree, probably by carrier-mediated transport, reaching in the brain about 4-10% of their respective plasma levels. The clinical relevance of this effect is hotly debated. Possible strategies to improve brain penetration of oximes are discussed.

Resolution and retention behaviour of some dyes in overpressured thin-layer chromatography

Abstract The performance of conventional and overpressured thin-layer chromatographic techniques was compared in different chamber systems (normal, ultramicro and pressurized chamber), on commercial normal and high-performance thin-layer chromatography (HPTLC) silica gel plates. Data obtained with three dyes demonstrated that separation in the pressurized chamber is similar to those observed in normal and ultramicro chambers, but the diameters of the spots are significantly smaller in separations carried out in pressurized chambers, principally owing to decreased diffusion. It was also observed that the velocity of the moving phase is very stable in the pressurized chamber, and has a linear relationship to solvent flow-rate. Owing to the substantially shorter separation time and stable flow-rates in the pressurized ultramicro chamber, the resolution values obtained on HPTLC plates are also better in the case of longer solvent migration distances.

Optimization of operating parameters in overpressured thin-layer chromatography

Abstract By adjusting the solvent by means of a pump system in overpressured thin-layer chromatography using a pressurized ultramicro (PUM) chamber it is possible to separate substances with optional development distances. In the PUM chamber the external pressure on the flexible cover membrane must always be higher than the input pressure of the solvent. The input pressure of the solvent increases linearly with increasing solvent migration distance. An increase in the solvent flow velocity always results in higher input pressures, which must be taken into account by choosing an appropriate external pressure on the membrane. The number of theoretical plates and the separation numbers obtained with a PUM chamber of the linear type on fine-particle sorbent layers are also better with longer solvent migration distances than in a normal TLC chamber. The advantages and the necessity for development with a longer migration distance are demonstrated with the example of the separation of amino acids on a fine-particle silica gel chromatoplate.

Medicinal chemistry of the anti-diabetic effects of momordica charantia: active constituents and modes of actions.

Diabetes mellitus (DM) is one of the oldest known human disease currently affecting more than 200 million people worldwide. Diabetes mellitus is derived from two Greek words meaning siphon and sugar. In DM, patients have high blood level of glucose and this passes out with urine. This is because the endocrine pancreas does not produce either or not enough insulin or the insulin which is produced is not exerting its biochemical effect (or insulin resistance) effectively. Insulin is a major metabolic hormone which has numerous functions in the body and one main role is to stimulate glucose uptake into body’s cells where it is utilized to provide energy. The disease is classified into type 1 and type 2 DM. Type 1 DM develops when the insulin producing β cells have been destroyed and are unable to produce insulin. This is very common in children and is treated with insulin. Type 2 DM (T2DM) develops when the body is unable to produce an adequate amount of insulin or the insulin which is provided does not work efficiently. This is due to life style habits including unhealthy diet, obesity, lack of exercise and hereditary and environmental factors. Some symptoms of DM include excess urination, constant thirst, lethargy, weight loss, itching, decreased digestive enzyme secretion, slow wound healing and other related symptoms. If left untreated, DM can result in severe long-term complications such as kidney and heart failure, stroke, blindness, nerve damage, exocrine glands insufficiency and other forms of complications. T2DM can be treated and controlled by prescribed drugs, regular exercise, diet (including some plant-based food) and general change in life style habits. This review is concerned with the role of plant-based medicine to treat DM. One such plant is Momordica charantia which is grown in tropical countries worldwide and it has been used as a traditional herbal medicine for thousands of years although its origin in unknown. This review examines the medicinal chemistry and use(s) of M. charantia and its various extracts and compounds, their biochemical properties and how they act as anti-diabetic (hypoglycemic) drugs and the various mechanisms by which they exert their beneficial effects in controlling and treating DM.

Pharmacological aspects of (-)-Deprenyl

Deprenyl, the selective irreversible inhibitor of monoamine oxidase-B (MAO-B), has been synthesised as a potential antidepressant, however, due to its dopamine potentiating capacity, became a registered drug in the treatment of Parkinsons disease. Deprenyl possesses a wide range of pharmacological activities; some of them are not related to its MAO-B inhibitory potency. Beside its dopamine potentiating effect, it renders protection against a number of dopaminergic, cholinergic and noradrenergic neurotoxins with a complex mechanism of action. By inducing antioxidant enzymes and decreasing the formation of reactive oxygen species, deprenyl is able to combat an oxidative challenge implicated as a common causative factor in neurodegenerative diseases. In a dose substantially lower than required for MAO-B inhibition (10(-9)-10(-13) M), deprenyl interferes with early apoptotic signalling events induced by various kinds of insults in cell cultures of neuroectodermal origin, thus protecting cells from apoptotic death. Deprenyl requires metabolic conversion to a hitherto unidentified metabolite to exert its antiapoptotic effect, which serves to protect the integrity of the mitochondrion by inducing transcriptional and translational changes. Pharmacokinetic and metabolism studies have revealed that deprenyl undergoes intensive first pass metabolism, and its major metabolites also possess pharmacological activities. The ratio of the parent compound and its metabolites reaching the systemic circulation and the brain are highly dependent on the routes of administration. Therefore, in the treatment of neurodegenerative diseases, reconsideration of the dosing schedule, by lowering the dose of deprenyl and choosing the most appropriate route of administration, would diminish undesired adverse effects, with unaltered neuroprotective potency.

Biological role of formaldehyde, and cycles related to methylation, demethylation, and formaldehyde production.

An overview is given on the analysis, formation, role and occurrence of formaldehyde in living organisms. Various methods have been used for the determination of formaldehyde in tissues and body fluids. Gas chromatography, thin-layer chromatography and HPLC were employed for the analysis of formaldehyde, mainly after derivatization. The formaldehyde level of human blood and urine was found at the low ppm level. The formaldehyde level could be increased upto several ten micro g/mL(-1) following special dietary supply. Biochemical pathway of both the formaldehyde production and demethylation/methylation processes is generally connected to the methionine - homocysteine cycles. Another important way of demethylation generated formaldehyde production is given by microsomal cytochrome P-450 dependent oxidation of xenobiotics, such as various drugs prescribed by doctors. Semicarbazide sensitive amine oxidase also produces formaldehyde. Increased level of formaldehyde may be the indication of either patho-physiological processes, or environmental contamination, or malnutrition. The formaldehyde-related methylation and demethylation procedures are also detailed. DNA methylation may have an important role in the pathogenesis of certain diseases.

Urinary excretion of deprenyl metabolites

(+)-Deprenyl metabolites in rats urine, such as nordeprenyl. methamphetamine amphetamine and p-hydroxy. methamphetamine were identified by HPLC-MS. After oral administration of 10 mg of pure (-)- and (+)-deprenyl to human volunteers, their urine was analyzed by gas chromatography. The concentration of methamphetamine was found to be overwhelming in the case of the (-)-isomer, while amphetamine and methamphetamine were excreted in equal amounts when (+)-deprenyl was administered. The metabolic processes of deprenyl resulted in metabolites possessing different lipophilicity, as it has been shown by planar displacement chromatography.

Circular-Development with Overpressured Thin-Layer Chromatography

Abstract A novel type modification of circular thin-layer chromatography has been developed, in which the layer is tightly covered by a membrane, eliminating the vapour phase over the sorbent layer. The developing solvent is pumped through the apparatus.

Medicinal Chemistry and Actions of Dual and Pan PPAR Modulators

Peroxisome proliferator-activated receptor (PPAR) agonists are used as adjunct therapy in the treatment of diabetes mellitus. Fibrates, including fenofibrate, gemfibrozil, benzafibrate, ciprofibrate, and clofibrate act on PPAR alpha to reduce the level of hypertriglyceridemia. However, agonists (ligands) of PPAR-beta/delta receptors, such as tesaglitazar, muraglitazar, ragaglitazar, imiglitazar, aleglitazar, alter the bodys energy substrate preference from glucose to lipids and hence contribute to the reduction of blood glucose level. Glitazones or thiazolidinediones on the other hand, bind to PPAR-gamma receptors located in the nuclei of cells. Activation of PPAR-gamma receptors leads to a decrease in insulin resistance and modification of adipocyte metabolism. They reduce hyperlipidaemia by increasing the level of ATP-binding cassette A1, which modifies extra-hepatic cholesterol into HDL. Dual or pan PPAR ligands stimulate two or more isoforms of PPAR and thereby reduce insulin resistance and prevent short- and long-term complications of diabetes including micro-and macroangiopathy and atherosclerosis, which are caused by deposition of cholesterol. This review examines the chemical structure, actions, side effects and future prospects of dual and pan PPAR agonists.