Pharmacokinetics of K117 and K127, two novel antidote candidates to treat Tabun poisoning.

AIMS: K117 and K127 are bis-pyridinium aldoximes but K117 is a bis-pyridinium bis-aldoxime while K127 has only one single aldoxime in addition to its amide substituent. Is there any difference in pharmacokinetics in these compounds that otherwise have the same chemical structure? Both K117 and K127 are developed as antidotes in acetylcholinesterase and butyrylcholinesterase poisoning in terrorist attacks or intoxication with other organophosphorous compounds. Their distributions have been scouted in the bodies of rats. MAIN METHODS: White male Wistar rats were intramuscularly injected. The animals were sacrificed, tissue samples were homogenized, and either K117 or K127 concentrations were determined using reversed-phase high-performance liquid chromatography. KEY FINDINGS: Both K117 and K127 were present in all tissues that were analyzed including blood (serum), the brains, cerebrospinal fluid, the eyes, livers, kidneys, lungs and testes. Their pharmacokinetics and body distributions are similar. SIGNIFICANCE: Either K117 or K127 meets the essential requirements for antidotes. Dose dependence and kinetics of their distribution were compared to that of other pyridinium aldoximes.

Mini review on blood-brain barrier penetration of pyridinium aldoximes.

This paper reviews the blood-brain barrier (BBB) penetration of newly developed pyridinium aldoximes. Pyridinium aldoximes are highly charged hydrophilic compounds used in the treatment of subjects exposed to organophosphonates because they are effective as acetylcholinesterase reactivators. Pyridinium aldoximes have antidotal effects against poisoning with cholinesterase inhibitors, a frequent problem affecting people working with organophosphate-based insecticides and pesticides. Toxic organophosphonate products such as sarin and tabun can be used by terrorists as chemical warfare agents. This poses a severe challenge to all innocent and peace-loving people worldwide. This review gives a brief summary of BBB transporters and description of the current in vitro and in vivo methods for the characterization of BBB penetration of established and novel pyridinium aldoximes. The authors provide a putative mechanism of penetration, outline some future ways of formulation and discuss the possible advantages and disadvantages of increasing BBB penetration.

Metabolism of selegiline [(-)-deprenyl)].

Selegiline (1) [(-)-deprenyl] is used to treat patients with Parkinson's disease. Nevertheless, in much higher doses it has beneficial effects in depression, and dementia of the aged patients. Selegiline (1) undergoes a complex metabolic pathway. Its major metabolites include (-)-desmethyldeprenyl (2), (-)-methamphetamine (3) and (-)-amphetamine (4), deprenyl-N-oxide (5) and formaldehyde (6) as a small metabolic fragment. In addition, more than 40 minor metabolites of selegiline (1) have also been either detected or proposed by investigators and researchers. This review analyses the pharmacological activity, generation pathway and the detection method of the major metabolites of selegiline (1).

Medicinal chemistry of antimigraine drugs.

Migraine is one of the most frequent neurological disorder with high impact on the quality of life. Primary headaches such as migraine are pathophysiologically complex disorders. The concept of the trigeminovascular system dysfunction in migraine has led to a number of drug discoveries dramatically changing the treatment options. Acute and prophylactic therapy targeting either the trigeminovascular system or central structures involve several groups of drugs with peculiar medicinal chemistry. In the proposed review up to date concept of treatment strategy, medicinal chemistry data of the drugs used will be summarized. The present review gives detailed information on drugs effective in aborting migraine attacks (by inhibiting prostanoid synthesis, are agonists of serotonin 5-HT1B/D receptors, on the recently introduced CGRP-receptor antagonists) and the drugs recommended for prophylactic treatment (selected beta-adrenergic receptor antagonists, Ca-channel inhibitors, antiepileptics, antidepressants). The pharmacokinetics, fate in the body (absorption, distribution, metabolism, excretion) and significant pharmacological effects as well as the recent bioanalytical methods for their determination are presented.

Study on medicinal chemistry of K203 in wistar rats and beagle dogs.

K203 is an experimental bis-pyridinium mono-aldoxime type cholinesterase reactivator of potential use in organophosphate/ organophosphonate poisoning. Pharmacokinetics of K203 were examined in Wistar rats and beagle dogs using ion-pair HPLC. Serum and cerebrospinal fluid concentrations of K203 were determined using ion-pair reversedphase chromatography on octadecyl silica column. HPLC with ultraviolet detection was used for determination of serum concentration of K203 higher than 0.1 µg/mL while its low concentrations in cerebrospinal fluid required electrochemical detection (0.015 through 4 µg/mL range). In rats the serum levels of K203 followed zero order pharmacokinetics from 15 to 120 minutes post administration. Zero order pharmacokinetics was also observed in beagle dogs after low dose (15 µmol/kg) of K203 administration. High dose administration (250 µmol/kg) led to subsequent hindered elimination from both cerebrospinal fluid and serum.

Medicinal chemistry of drugs with active metabolites (N-, O-, and S-desalkylation and some specific oxidative alterations).

Metabolic fate plays an important role in the elimination of drugs and other foreign compounds from the body. Metabolism through various enzyme systems, makes the parent compound more hydrophilic, thus, it can be readily excreted from the body. Some active metabolites of drugs are produced following N-, O-, and S-desalkylation. These metabolites are either more or less potent, or as potent as their parent drugs. The removal of alkyl groups from tertiary aliphatic and acyclic amines is carried out by hepatic cytochrome P450 mixed-function oxidase enzymes. Several drugs undergo this process, which yields free hydroxyl-, or amino-groups, in addition to aldehyde from the splitted alkyl group. Metabolism of drugs into clinically active compounds indicates an extra target of therapeutic drug monitoring. Numerical data of logP values show how lipophilicity changes through metabolism to facilitate excretion. The example of phenacetin - paracetamol opened up a way for improving pharmacological effect by the use of a metabolite. This review gives a detailed description of these drugs, their active and major metabolites found in humans or animals, metabolizing cytochrome P450s, and the most recent analytical methods for their determination.

Active metabolites resulting from decarboxylation, reduction and ester hydrolysis of parent drugs.

Decarboxylation, reduction and hydrolysis can yield active metabolites from the parent drug. Major therapeutic indications and metabolic routes of these drugs are reviewed. Changes in the logP values (determined and calculated) from the parent drug to the active metabolite show certain characteristics in comparison to other phase I metabolic alterations. Metabolic decarboxylation of parent drug is commonly associated with increase in lipophilicity. However, in some cases, decarboxylation may cause a reduction in lipophilicity. Ester hydrolysis generally unmasks either the polar carboxylic or hydroxyl group with the outcome of an increase in hydrophilicity. On the contrary, hydrolysis of phosphate ester means a huge increase in the lipophilic character of the drug, as the highly polar phosphate group is removed.

Aliphatic and aromatic oxidations, epoxidation and S-oxidation of prodrugs that yield active drug metabolites.

About one hundred and fifty of the several thousands of drugs on the market are known to have active metabolites. Medicinal chemistry of the parent drugs as well as that of the metabolites are very important both in medical practice and drug research. The efficacy of a drug will depend on a number of properties including, pharmacokinetic behavior, absorption, tissue distribution, pharmacological potency, toxicity and tissue-specificity. The production and release of active metabolites are important because active drug metabolites may influence the clinical outcome of a drug by increasing the gross level of pharmacologically active compounds (drug + active metabolite) and/or essentially increasing the duration of drug effect, when t(1/2) of active metabolite is much longer than that of the parent drug. Furthermore, certain drug metabolizing enzymes can either be inhibited or induced by other drugs and a variety of food and environmental factors. A careful control of the clinical effects of any drug with active metabolites is important especially in the treatment of the elderly population where the administration of several drugs is not unusual.This review provides a detailed description of the medicinal chemistry of drugs yielding active metabolites after undergoing transformation via aliphatic and aromatic oxidations, epoxidation and S-oxidation. Their respective pharmacologically active metabolites, metabolizing enzymes and changes in lipophilicity are also summarized. The most recent analytical methods used for the reliable quantification of both the parent drugs and their metabolites are also included.

Chromatographic separation of antiviral/anticancer nucleoside reverse transcriptase inhibitor drugs.

This paper discusses the current methods used for quantitative determination of analogues of nucleotide reverse transcriptase inhibitors (NtRTIs) in body fluids, cells, and tissues. Nucleoside reverse transcriptase inhibitors (NRTIs) prodrugs given to AIDS/herpes/cancer patients conjugate with phosphates at the site of their action. Separation of phosphorylated NRTIs is generally performed by reversed-phase chromatography. After separation, plasma NRTIs can be detected using a variety of methods, including immunoassay through monitoring of UV absorbance, fluorescence, and mass spectrometry. The most recent development in the field of detection of plasma NtRTIs shows a tendency toward the use double- or triple-focusing mass spectrometry, the most specific and sensitive monitoring technique.

Medicinal chemistry of antiviral/anticancer prodrugs subjected to phosphate conjugation.

Certain xenobiotics are given in the "prodrug" form. Either the human body, or one compartment of the body, or the targeted virus itself metabolizes the prodrug into its active form. The bioprecursor form of drugs is used for a wide variety of reasons, namely: to make drug penetration into the target organ (mainly to the brain through the blood-brain-barrier) possible, eliminate unpleasant taste, alter (either increasing or decreasing) the half life of the active component or supply more than one active components to the body.

Pyridinium aldoxime analysis by HPLC: the method for studies on pharmacokinetics and stability.

Reversed-phase separation of various pyridinium aldoximes requires a certain concentration of ion-pairing agent, as their chemical structures contain two quaternary amines in the pyridinium ring. Adequate mobile phase is scouted on the basis of retention of pyridinium aldoxime (using the graph of k' versus concentration of an ion-pairing agent) compared to the chromatogram of the background peaks originated from the homogenate. Change in the ion-pairing agent concentration was more expressed for the elution of K-203 than that of the background peaks from the serum, brain and cerebrospinal fluid. Stability of K-203 was investigated using HPLC. Determination of K-203 in tissue samples requires homogenization using either trichloroacetic acid or perchloric acid. Fast degradation takes place at acidic pH. Adjusting pH to neutral in the possible shortest time frame helps to avoid degradation. Degradation of K-203 was easily followed by HPLC separation and monitoring the elution with an ultraviolet absorbance detector at 276 nm. Amperometric detection indicates only the decrease of K-203 content.

Nociceptin inhibits uterine contractions in term-pregnant rats by signaling through multiple pathways.

The actions of the endogenous peptide nociceptin (PNOC; previously abbreviated as N/OFQ) on the myometrium have not been investigated previously. Our aim was to study the presence and functional role of PNOC in the modulation of uterine contractility in pregnant rats at term. The presence of PNOC and its receptors (OPRL1; previously called NOP) in the uterus were detected by radioimmunoassay and radioligand-binding experiments. The PNOC-stimulated G protein activation was assessed by a [(35)S]GTPgammaS-binding technique. The effects of PNOC in uterine rings precontracted with KCl or oxytocin were also tested in vitro. Uterine levels of cAMP were measured by enzyme immunoassay. The K(+) channel blockers tetraethylammonium and paxilline were used to study the role of K(+) channels in mediating the uterine effects of PNOC. Both PNOC and OPRL1 were present in the uterus. PNOC revealed a maximum contraction inhibition of approximately 30%, which was increased to 40% by naloxone. Naloxone and pertussis toxin significantly attenuated the G protein-stimulating effect of PNOC. The uterine cAMP levels were elevated by PNOC and naloxone and after preincubation with pertussis toxin. Tetraethylammonium and paxilline reduced the contraction-inhibiting effect of PNOC and naloxone to approximately 10% and 15%, respectively. We presume that PNOC plays a role in regulating uterine contractility at term. Its effect is mediated partly by stimulatory heterotrimeric G (G(s)) proteins coupled to OPRL1 receptors and elevated cAMP levels, and also by Ca(2+)-dependent K(+) channels. Our results demonstrate a novel action and signaling pathway for PNOC that might be a potential drug target.

Monitoring the pharmacokinetics of pyridinium aldoximes in the body.

A huge number of organophosphate poisonings occurring in agriculture, and a constant threat of misapplication of organophosphates as warfare agents require antidotes that efficiently improve the health-condition of intoxicated subjects. Pyridinium aldoximes are medically used to reactivate the cholinesterase enzymes inhibited by organophosphates. This paper outlines pharmacokinetics, metabolic disposition and blood-brain-barrier penetration of pyridinium aldoximes into the human and animal body, and the methods of their pharmacological analysis.

Influence of perinatal stress on the hormone content in immune cells of adult rats: dominance of ACTH.

Rat dams were stressed by total deprivation of food and water for 48 h just before or directly after delivery and the offspring were studied when adult. The immune cells' hormone content (ACTH, histamine, serotonin, and T(3)) was measured by immunocytochemical flow cytometry. The elevation of ACTH content in males was convincing in each cell type (lymphocytes, monocytes and granulocytes, and mast cells). The change in histamine and T(3) content was inconsistent, while serotonin level did not change at all. As ACTH is the key hormone in the General Adaptation Syndrome, it seems likely that the perinatal stress primarily caused elevation in ACTH level and it was provoking the life-long hormonal imprinting. There was a difference between the reaction of males and females (with males' advance), which points to the gender dependence of the phenomenon. It is important that the effect of stress on the offspring was similar in case of direct (prenatal, in the mother) and indirect (postnatal, transmitted by milk) stress treatment, which calls attention to the danger of stress during this latter period.

Influence of neonatal vitamin A or vitamin D treatment on the concentration of biogenic amines and their metabolites in the adult rat brain.

Newborn male rats were treated with a single dose of 3 mg vitamin A (retinol) or 0.05 mg vita-min D (cholecalciferol), and three months later five brain regions (frontopolar cortex, hypothalamus, hippocampus, striatum, and brainstem) were studied for tissue levels of dopamine (DA), serotonin (5HT), and metabolites such as homovanillic acid (HVA), as well as 5-hydroxyindole-3-acetic acid (5HIAA). Vitamin A treatment as hormonal imprinting significantly decreased 5HIAA levels in each brain region. Vitamin D imprinting significantly elevated DA only in the brainstem and HVA levels in striatum and hypothalamus. Present and earlier brain-imprinting results (with brain-produced substances), show that the profound and life-long effect of neonatal hormonal imprinting on neurotransmitter production of the adult brain seems to be well established. As prophylactic treatment with these vitamins is frequent in the perinatal period, the imprinting effect of vitamin A and vitamin D must be taken into consideration.

Analysis of pyridinium aldoximes - a chromatographic approach.

Pyridinium aldoximes are used as antidotes to organophosphorus cholinesterase inhibitors. All pyridinium aldoximes (oximes) are highly polar quaternary ammonium compounds showing low to minimal blood-brain-barrier (BBB) penetration. Oximes are separated using reversed-phase (RP) HPLC methods and/or thin-layer chromatography (TLC). The chemical structures, elementary compositions, molecular sizes and the calculated logP values of several mono- and bis-pyridinium aldoximes are given. Chromatographic and electrophoretic analyses of oximes are detailed, including the stationary and mobile phase composition and the mode of detection. Degradation pathways and products are also discussed. To characterize oximes lipophilicity/hydrophilicity an in silico method was used and expanded as to describe organophosphorus compound adducts with several pyridinium aldoximes.

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.

In vitro and in vivo metabolisms of K-48.

Metabolic pathways of the oxime K-48 have been elucidated by means of in vitro and in vivo experiments. K-48 exposure to rat liver microsomal fraction resulted in the formation of a hydroxylated derivative, in addition to a small molecular fragment. The in vivo metabolism in rats was investigated after intramuscular administration of 50 mumol oxime. K-48 was present in the rat serum in unchanged form. Similarly, the analysis of rat cerebrospinal fluid indicated the sole occurrence of unchanged K-48. In contrast, unchanged K-48 was not found in the rat urine, where only the metabolite generated by epoxidation on the alkyl chain connecting the two pyridinium rings was present. The presence of unchanged K-48 in the serum and cerebrospinal fluid facilitates quantitative determination using HPLC separation and ultraviolet absorbance detection.

Effect of neonatal benzpyrene imprinting on the brain serotonin content and nocistatin level in adult male rats.

Single neonatal treatment (imprinting) with 20 microg benzpyrene results in significant increase of the brain serotonin level in the striatum, while in the other four regions (cortex, brainstem, hippocampus, hypothalamus) when measured in adults can be detected. The nocistatin level of cerebrospinal fluid (CSF) significantly decreases, while there is no change in the plasma nocistatin level. The results call attention to the comprehensive imprinting effect of benzpyrene, which in addition to receptorial, hormonal and sexual behavioral disturbances causes lasting differences in the brain serotonin and nocistatin levels, probably influencing mood and pain tolerance.

Effect of beta-endorphin imprinting during late pregnancy on the brain serotonin and plasma nocistatin levels of adult male rats.

Female rats were treated with 10 microg of beta-endorphin on the 19th day of pregnancy. Offspring were studied when five months old. Serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) content in four brain regions were determined by HPLC-EC and the nocistatin levels of blood plasma using RIA methods. In each brain region studied, the 5-HT levels were highly significantly reduced and that of 5-HIAA in three regions was highly significantly increased. When 5HIAA/5HT ratios, as a measure of serotonin turnover, were calculated, imprinted animals showed extremely high values. Plasma nocistatin level was also significantly elevated. The results call attention to the effect of perinatal endorphin imprinting and its long-term consequences (e.g., setting of aggressiveness, pain tolerance).