Tatjana Momić

Effects of Digoxin and Gitoxin on the Enzymatic Activity and Kinetic Parameters of Na+/K+-ATPase

Inhibition of Na+/K+-ATPase activity from human erythrocyte membranes and commercial porcine cerebral cortex by in vitro single and simultaneous exposure to digoxin and gitoxin was investigated to elucidate the difference in the mechanism of the enzyme inhibition by structurally different cardiac glycosides. The drugs exerted a biphasic dose-dependent inhibitory effect on the enzyme activity in both tissues, supporting the existence of two sensitive Na+/K+-ATPase isoforms. The IC50 values for the low and high affinity isoforms were calculated from the inhibition curves using mathematical analysis. The Hill coefficient (n) fulfilled the relationship 1<n<3, suggesting cooperative binding of inhibitors to the enzyme. Kinetic analysis showed that digoxin and gitoxin inhibited Na+/K+-ATPase by reducing the maximum enzymatic velocity (Vmax) and Km, implying an uncompetitive mode of interaction. Both the isoforms were always more sensitive to gitoxin. The erythrocyte enzyme was more sensitive to the inhibitors in the range of low concentrations but the commercial cerebral cortex enzyme exerted a higher sensitivity in high inhibitors affinity concentration range. By simultaneous exposure of the enzyme to digoxin and gitoxin in combinations a synergistic effect was achieved by low inhibitor concentrations. An antagonistic effect was obtained with erythrocyte membrane enzyme at high inhibitors concentration.

Na + ,K + -ATPase as the Target Enzyme for Organic and Inorganic Compounds

This paper gives an overview of the literature data concerning specific and non specific inhibitors of Na+,K+-ATPase receptor. The immobilization approaches developed to improve the rather low time and temperature stability of Na+,K+-ATPase, as well to preserve the enzyme properties were overviewed. The functional immobilization of Na+,K+-ATPase receptor as the target, with preservation of the full functional protein activity and access of various substances to an optimum number of binding sites under controlled conditions in the combination with high sensitive technology for the detection of enzyme activity is the basis for application of this enzyme in medical, pharmaceutical and environmental research.

Oxidation of Quercetin by Myeloperoxidase

Study of effect of myeloperoxidase on quercetin at pH 6.0 indicated quercetin oxidation via the formation of the oxidation product. The stability of quercetin and oxidation product was investigated as a function of time by using spectrophotometric and HPLC techniques. The apparent pseudo first-order rate constants were calculated and discussed.

Modulators of Acetylcholinesterase Activity: from Alzheimer's Disease to Anti-cancer Drugs.

BACKGROUND Acetylcholinesterase (AChE) is involved in the termination of impulse transmission by rapid hydrolysis of the neurotransmitter acetylcholine in numerous cholinergic pathways in the central and peripheral nervous systems. The enzyme inactivation leads to acetylcholine accumulation, hyperstimulation of nicotinic and muscarinic receptors, and disrupted neurotransmission. Hence, acetylcholinesterase inhibitors, interacting with the enzyme as their primary target, are applied as relevant drugs for different neurodegenerative diseases (such as Alzheimers and Parkinsons) as well as toxins. At the same time, there are increasing evidence that in non-neuronal context, AChE is involved in the regulation of cell proliferation, differentiation, apoptosis and cell-cell interaction. An irregular expression of AChE has been found in different types of tumors, suggesting the involvement of AChE in the regulation of tumor development. Having all this in mind, there is a possibility that some AChE inhibitors could be used as anti-cancer agents. OBJECTIVE This contribution will discuss a broad range of possible application of different AChE inhibitors as drugs, from well-known anti-Alzheimers disease drugs to their use in cancer treatment in future. Emphasis will be put on various known AChE inhibitors classes, whose application as drugs could be controversy, as well as on newly investigated natural products, which can also modulate AChE activity. CONCLUSION It is not clear a patient treated for neurodegenerative condition prone to increased risk for some types of cancer and vice versa. This is necessary to keep in mind during rational drug design process for all therapies, which are based on AChE as a target molecule.

Influence of organophosphorus pesticides on peroxidase and chlorination activity of human myeloperoxidase

Inhibitory effects of five organophosphorus pesticides (diazinon, malathion, chlorpyrifos, azinphos-methyl and phorate) and their oxo-analogs on human myeloperoxidase (MPO) activity were investigated. While inspecting separately peroxidase and chlorination activity, it was observed that investigated OPs affect peroxidase activity, but not chlorination activity. Among investigated pesticides, malathion and malaoxon have showed the highest power to inhibit MPO peroxidase activity with IC50 values of the order of 3×10(-7) and 5×10(-9) M, respectively. It was proposed that inhibition trend is rendered by molecular structure which invokes steric hindrance for OPs interaction with MPO active center responsible for peroxidase activity. In addition, it was concluded that physiological function of MPO is not affected by any of the investigated OPs.

Adsorption of Organophosphate Pesticide Dimethoate on Gold Nanospheres and Nanorods

Organophosphorus pesticide dimethoate was adsorbed onto gold nanospheres and nanorods in aqueous solution using batch technique. Adsorption of dimethoate onto gold nanoparticles was confirmed by UV-Vis spectrophotometry, TEM, AFM, and FTIR analysis. The adsorption of nanospheres resulted in aggregation which was not the case with nanorods. Nanoparticles adsorption features were characterized using Langmuir and Freundlich isotherm models. The Langmuir adsorption isotherm was found to have the best fit to the experimental data for both types of nanoparticles. Adsorption capacity detected for nanospheres is 456 mg/g and for nanorods is 57.1 mg/g. Also, nanoparticles were successfully used for dimethoate removal from spiked drinking water while nanospheres were shown to be more efficient than nanorods.

Metal Based Compounds, Modulators of Na, K-ATPase with Anticancer Activity

Involvement of Na, K-ATPase in different biological processes and its overexpression in pathological states enables its use as a target in anticancer studies. For the past 10 years, a variety of metal-based complexes have been synthesized which offer good tolerance, potent action, selectivity, and less toxicity in cancer treatment. This chapter gives an overview of the interaction of platinum, gold, ruthenium, vanadium, and palladium complexes with Na, K-ATPase and their effect on the enzyme function and activity. The mechanism of Na, K-ATPase activity inhibition with metal based complexes is supported with extensive kinetic analysis. The inhibition can be achieved via the complexes interaction with –SH groups of the enzyme and cleavage of the disulfide bridges, required for the enzyme functionality. Moreover, the inhibitory effect of selected compounds can be prevented and recovered by the addition of –SH donors, l-cysteine and glutathione, the biomolecules usually present in physiological liquids. The conclusion is made that gold, ruthenium, and palladium complexes are expected to overcome platinum complexes toxic side effects.

Vasić, V. et al. Na+,K+-ATPase as the Target Enzyme for Organic and Inorganic Compounds. Sensors 2008, 8, 8321-8360

We found that reference 94 was incorrectly cited in our paper published in Sensors recently [1]. Therefore, reference 94 is corrected as follows: 94. Van Quaquebeke, E.; Simon, G.; Andr, A.; Dewelle, J.; El Yazidi, M.; Bruyneel, F.; Tuti, J.; Nacoulma, O.; Guissou, P.; Decaestecker, C.; Braekman, J.C.; Kiss, R.; Darro, F. Id entification of a novel cardenolide (2″-oxovoruscharin) from Calotropis procera and the hemisynthesis of novel derivatives displaying potent in vitro antitumor activities and high in vivo tolerance: structure-activity relationship analyses. J. Med. Chem. 2005, 48, 849-56.