Kamil Musilek

Redox- and non-redox-metal-induced formation of free radicals and their role in human disease.

Abstract Transition metal ions are key elements of various biological processes ranging from oxygen formation to hypoxia sensing, and therefore, their homeostasis is maintained within strict limits through tightly regulated mechanisms of uptake, storage and secretion. The breakdown of metal ion homeostasis can lead to an uncontrolled formation of reactive oxygen species, ROS (via the Fenton reaction, which produces hydroxyl radicals), and reactive nitrogen species, RNS, which may cause oxidative damage to biological macromolecules such as DNA, proteins and lipids. An imbalance between the formation of free radicals and their elimination by antioxidant defense systems is termed oxidative stress. Most vulnerable to free radical attack is the cell membrane which may undergo enhanced lipid peroxidation, finally producing mutagenic and carcinogenic malondialdehyde and 4-hydroxynonenal and other exocyclic DNA adducts. While redox-active iron (Fe) and copper (Cu) undergo redox-cycling reactions, for a second group of redox-inactive metals such as arsenic (As) and cadmium (Cd), the primary route for their toxicity is depletion of glutathione and bonding to sulfhydryl groups of proteins. While arsenic is known to bind directly to critical thiols, other mechanisms, involving formation of hydrogen peroxide under physiological conditions, have been proposed. Redox-inert zinc (Zn) is the most abundant metal in the brain and an essential component of numerous proteins involved in biological defense mechanisms against oxidative stress. The depletion of zinc may enhance DNA damage by impairing DNA repair mechanisms. Intoxication of an organism by arsenic and cadmium may lead to metabolic disturbances of redox-active copper and iron, with the occurrence of oxidative stress induced by the enhanced formation of ROS/RNS. Oxidative stress occurs when excessive formation of ROS overwhelms the antioxidant defense system, as is maintained by antioxidants such as ascorbic acid, alpha-tocopherol, glutathione (GSH), carotenoids, flavonoids and antioxidant enzymes which include SOD, catalase and glutathione peroxidase. This review summarizes current views regarding the role of redox-active/inactive metal-induced formation of ROS, and modifications to biomolecules in human disease such as cancer, cardiovascular disease, metabolic disease, Alzheimer’s disease, Parkinson’s disease, renal disease, blood disorders and other disease. The involvement of metals in DNA repair mechanisms, tumor suppressor functions and interference with signal transduction pathways are also discussed.

Design, evaluation and structure—Activity relationship studies of the AChE reactivators against organophosphorus pesticides

Organophosphate pesticides (OPPs; e.g. chlorpyrifos, diazinon, paraoxon) are a wide and heterogeneous group of organophosphorus compounds. Their biological activity of inhibiting acetylcholinesterase (AChE) or butyrylcholinesterase (BChE) ranks them as life endangering agents. The necessary treatment after OPP exposure involves the use of parasympatolytics (e.g. atropine), oxime reactivators (e.g. obidoxime), and anticonvulsive drugs (e.g. diazepam). Therefore, the reactivators of AChE are essential compounds in the treatment of OPP intoxications. Commercial AChE reactivators (e.g. pralidoxime, HI‐6, obidoxime, trimedoxime, methoxime) were originally developed for other members of the organophosphate family, such as nerve agents (e.g. sarin, soman, tabun, VX). Pralidoxime, HI‐6, and methoxime were found to be weak reactivators of OPP‐inhibited AChE. Obidoxime and trimedoxime showed satisfactory reactivation against various OPPs with minor toxicity issues. During the last two decades, the treatment of OPP exposure has become more widely discussed because of growing agricultural production, industrialization, and harmful social issues (e.g. suicides). In this review is the summarized design, evaluation, and structure–activity relationship studies of recently produced AChE reactivators. Since pralidoxime, over 300 oximes have been produced or tested against OPP poisoning, and several novel compounds show very promising abilities as comparable (or higher) to commercial oximes. Some of these are highlighted for their further testing of OPP exposure and, additionally, the main structure–activity relationship of AChE reactivators against OPP is discussed.

Evaluation of Oxime K203 as Antidote in Tabun Poisoning

Evaluation of Oxime K203 as Antidote in Tabun Poisoning We studied bispyridinium oxime K203 [(E)-1-(4-carbamoylpyridinium)-4-(4-hydroxyiminomethylpyridinium)-but-2-ene dibromide] with tabun-inhibited human acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) in vitro, and its antidotal effect on tabun-poisoned mice and rats in vivo. We compared it with oximes K048 and TMB-4, which have proven the most efficient oxime antidotes in tabun poisoning by now. Tabun-inhibited AChE was completely reactivated by K203, with the overall reactivation rate constant of 1806 L mol-1 min-1. This means that K203 is a very potent reactivator of tabun-inhibited AChE. In addition, K203 reversibly inhibited AChE (Ki = 0.090 mmol L-1) and BChE (Ki = 0.91 mmol L-1), and exhibited its protective effect against phosphorylation of AChE by tabun in vitro. In vivo, a quarter of the LD50 K203 dose insured survival of all mice after the application of as many as 8 LD50 doses of tabun, which is the highest dosage obtained compared to K048 and TMB-4. Moreover, K203 showed high therapeutic potency in tabun-poisoned rats, preserving cholinesterase activity in rat plasma up to 60 min after poisoning. This therapeutic improvement obtained by K203 in tabun-poisoning places this oxime in the spotlight for further development. Procjena oksima K203 kao antidota pri otrovanju tabunom Proučavali smo bispiridinijski oksim K203 [(E)-1-(4-karbamilpiridinij)-4-(4-hidroksiiminometilpiridinij)-but-2-ene dibromid] u uvjetima in vitro - studirajući njegove interakcije s ljudskom acetilkolinesterazom (AChE) i butirilkolinesterazom (BChe) inhibiranim tabunom te u uvjetima in vivo - određivanjem njegova antidotskog učinka na miševe i štakore otrovane tabunom. Radi usporedbe uključili smo rezultate dobivene s oksimima K048 i TMB-4 kao najučinkovitijim oksimima kod otrovanja tabunom. K203 je potpuno reaktivirao AChE inhibiranu tabunom sa sveukupnom brzinom reaktivacije od 1806 L mol-1 min-1 što ga svrstava u najučinkovitije reaktivatore AChE inhibirane tabunom. K203 je reverzibilno inhibirao AChE (Ki = 0,090 mmol L-1) i BChE (Ki = 0,91 mmol L-1) pokazujući svoja in vitro zaštitna svojstva od inhibicije tabunom. Terapija dozom K203 od 1/4 njegove LD50 omogućila je preživljavanje svih miševa nakon otrovanja dozom tabuna od 8,0 LD50. Time je K203 pokazao bolju učinkovitost u usporedbi s K048 ili TMB-4. K tome, K203 je značajno zaštitio štakore od otrovanja tabunom kompenzirajući toksični učinak tabuna na aktivnost kolinesteraze i do 60 min nakon trovanja. Pokazano poboljšanje terapeutske učinkovitosti K203 ističe ovaj oksim pretečom za daljnji razvoj antidota u otrovanju tabunom.

Synthesis of monooxime-monocarbamoyl bispyridinium compounds bearing (E)-but-2-ene linker and evaluation of their reactivation activity against tabun- and paraoxon-inhibited acetylcholinesterase.

Six AChE monooxime-monocarbamoyl reactivators with an (E)-but-2-ene linker were synthesized using modification of currently known synthetic pathways. Their potency to reactivate AChE inhibited by the nerve agent tabun and insecticide paraoxon was tested in vitro. The reactivation efficacies of pralidoxime, HI-6, obidoxime, K048, K075 and the newly prepared reactivators were compared. According to the results obtained, one reactivator seems to be promising against tabun-inhibited AChE and two reactivators against paraoxon-inhibited AChE. The best results were obtained for bisquaternary substances with at least one oxime group in position four.

Progress of Biosensors Based on Cholinesterase Inhibition

Biosensors are available and applicable for detection and characterization of specific inhibitors of many enzymes. In this review, biosensors based on fixed acetylcholinesterase (AChE) or butyrylcholinesterase (BChE) are presented. Inhibition of selected enzymes by various compounds, such as organophosphorus and carbamate pesticides, nerve agents (e.g. sarin or VX), and other natural toxins (e.g. aflatoxins), was employed to develop specific assays using biosensors only. Biosensor technology brings potential miniaturization and portability, when it is compared to standard methods. Construction of biosensors based on cholinesterases became a more important issue within the last decades. Novel approach with recombinant proteins, microelectrodes and immobilization protocol related to nanotechnologies opened new insight to the cholinesterase based biosensor construction and its perspective via routine assays. This review is focused on novel trends within such biosensors as a result of the known platform.

Synthesis of a novel series of bispyridinium compounds bearing a xylene linker and evaluation of their reactivation activity against chlorpyrifos-inhibited acetylcholinesterase

Nine potential AChE reactivators were synthesized using a modification of currently known synthetic pathways. Their potency to reactivate AChE inhibited by insecticide chlorpyrifos was tested in vitro. 2,2′-Bis(hydroxyiminomethyl)-1,1′-(1,4-phenylenedimethyl)-bispyridinium dibromide seems to be the most potent AChE reactivator. The reactivation potency of these compounds depends on structural factors such as length of the linking chain between both pyridinium rings and position of the oxime moiety on the pyridinium ring.

Synthesis and in vitro evaluation of N-alkyl-7-methoxytacrine hydrochlorides as potential cholinesterase inhibitors in Alzheimer disease

All approved drugs for Alzheimer disease (AD) in clinical practice ameliorate the symptoms of the disease. Among them, acetylcholinesterase inhibitors (AChEIs) are used to increase the cholinergic activity. Among new AChEI, tacrine compounds were found to be more toxic compared to 7-MEOTA (9-amino-7-methoxy-1,2,3,4-tetrahydroacridine). In this Letter, series of 7-MEOTA analogues (N-alkyl-7-methoxytacrine) were synthesized. Their inhibitory ability was evaluated on recombinant human acetylcholinesterase (AChE) and plasmatic human butyrylcholinesterase (BChE). Three novel compounds showed promising results towards hAChE better to THA or 7-MEOTA. Three compounds resulted as potent inhibitors of hBChE. The SAR findings highlighted the C(6)-C(7)N-alkyl chains for cholinesterase inhibition.

Synthesis of a novel series of non-symmetrical bispyridinium compounds bearing a xylene linker and evaluation of their reactivation activity against tabun and paraoxon-inhibited acetylcholinesterase

Nine potential non-symmetrical xylene-bridged AChE reactivators were synthesized using modifications of currently known synthetic pathways. Their potency to reactivate AChE inhibited by the nerve agent tabun and the insecticide paraoxon together with nine symmetrical xylene-bridged compounds, was tested in vitro. Seven compounds were promising against paraoxon-inhibited AChE. Two compounds were found to be more potent against tabun-inhibited AChE than obidoxime at a concentration applicable in vivo.

7-MEOTA–donepezil like compounds as cholinesterase inhibitors: Synthesis, pharmacological evaluation, molecular modeling and QSAR studies

A novel series of 7-methoxytacrine (7-MEOTA)-donepezil like compounds was synthesized and tested for their ability to inhibit electric eel acetylcholinesterase (EeAChE), human recombinant AChE (hAChE), equine serum butyrylcholinesterase (eqBChE) and human plasmatic BChE (hBChE). New hybrids consist of a 7-MEOTA unit, representing less toxic tacrine (THA) derivative, connected with analogues of N-benzylpiperazine moieties mimicking N-benzylpiperidine fragment from donepezil. 7-MEOTA-donepezil like compounds exerted mostly non-selective profile in inhibiting cholinesterases of different origin with IC50 ranging from micromolar to sub-micromolar concentration scale. Kinetic analysis confirmed mixed-type inhibition presuming that these inhibitors are capable to simultaneously bind peripheral anionic site (PAS) as well as catalytic anionic site (CAS) of AChE. Molecular modeling studies and QSAR studies were performed to rationalize studies from in vitro. Overall, 7-MEOTA-donepezil like derivatives can be considered as interesting candidates for Alzheimers disease treatment.

New methods in synthesis of acetylcholinesterase reactivators and evaluation of their potency to reactivate cyclosarin-inhibited AChE

Nine potential AChE reactivators were synthesized using modification of currently known synthetic pathways. Their potency to reactivate AChE inhibited by cyclosarin nerve agent was tested in vitro. According to the previous results, 1,4-bis(2-hydroxyiminomethylpyridinium)butane dibromide seems to be the most potent AChE reactivator. The reactivation potency of these compounds depends on structural factors such as presence of quaternary nitrogens, length of the linking chain between both pyridinium rings, and position of the oxime moiety at the pyridinium ring.