Vanadate oligomer interactions with myosin

Vanadium in Biological Action: Chemical, Pharmacological Aspects, and Metabolic Implications in Diabetes Mellitus

Vanadium compounds have been primarily investigated as potential therapeutic agents for the treatment of various major health issues, including cancer, atherosclerosis, and diabetes. The translation of vanadium-based compounds into clinical trials and ultimately into disease treatments remains hampered by the absence of a basic pharmacological and metabolic comprehension of such compounds. In this review, we examine the development of vanadium-containing compounds in biological systems regarding the role of the physiological environment, dosage, intracellular interactions, metabolic transformations, modulation of signaling pathways, toxicology, and transport and tissue distribution as well as therapeutic implications. From our point of view, the toxicological and pharmacological aspects in animal models and humans are not understood completely, and thus, we introduced them in a physiological environment and dosage context. Different transport proteins in blood plasma and mechanistic transport determinants are discussed. Furthermore, an overview of different vanadium species and the role of physiological factors (i.e., pH, redox conditions, concentration, and so on) are considered. Mechanistic specifications about different signaling pathways are discussed, particularly the phosphatases and kinases that are modulated dynamically by vanadium compounds because until now, the focus only has been on protein tyrosine phosphatase 1B as a vanadium target. Particular emphasis is laid on the therapeutic ability of vanadium-based compounds and their role for the treatment of diabetes mellitus, specifically on that of vanadate- and polioxovanadate-containing compounds. We aim at shedding light on the prevailing gaps between primary scientific data and information from animal models and human studies.

A novel supermolecular tetrameric vanadate-selective colorimetric and "off-on" sensor with pyrene ligand

Tris(2-((ethylimino)methyl)pyren-1-ol)amine (1) was synthesized and introduced as the first tetrameric vanadate fluorescence sensor, the entire binding of which was successfully accomplished in two steps with distinct colorimetric changes and "off-on" fluorescent enhancement.

Binding modes of decavanadate to myosin and inhibition of the actomyosin ATPase activity

Decavanadate, a vanadate oligomer, is known to interact with myosin and to inhibit the ATPase activity, but the putative binding sites and the mechanism of inhibition are still to be clarified. We have previously proposed that the decavanadate (V(10)O(28)(6-)) inhibition of the actin-stimulated myosin ATPase activity is non-competitive towards both actin and ATP. A likely explanation for these results is that V(10) binds to the so-called back-door at the end of the Pi-tube opposite to the nucleotide-binding site. In order to further investigate this possibility, we have carried out molecular docking simulations of the V(10) oligomer on three different structures of the myosin motor domain of Dictyostelium discoideum, representing distinct states of the ATPase cycle. The results indicate a clear preference of V(10) to bind at the back-door, but only on the "open" structures where there is access to the phosphate binding-loop. It is suggested that V(10) acts as a "back-door stop" blocking the closure of the 50-kDa cleft necessary to carry out ATP-gamma-phosphate hydrolysis. This provides a simple explanation to the non-competitive behavior of V(10) and spurs the use of the oligomer as a tool to elucidate myosin back-door conformational changes in the process of muscle contraction.

Myosin light chain phosphorylation inhibits muscle fiber shortening velocity in the presence of vanadate

We have shown that myosin light chain phosphorylation inhibits fiber shortening velocity at high temperatures, 30 degrees C, in the presence of the phosphate analog vanadate. Vanadate inhibits tension by reversing the transition to force-generating states, thus mimicking a prepower stroke state. We have previously shown that at low temperatures vanadate also inhibits velocity, but at high temperatures it does not, with an abrupt transition in inhibition occurring near 25 degrees C (E. Pate, G. Wilson, M. Bhimani, and R. Cooke. Biophys J 66: 1554-1562, 1994). Here we show that for fibers activated in the presence of 0.5 mM vanadate, at 30 degrees C, shortening velocity is not inhibited in dephosphorylated fibers but is inhibited by 37 +/- 10% in fibers with phosphorylated myosin light chains. There is no effect of phosphorylation on fiber velocity in the presence of vanadate at 10 degrees C. The K(m) for ATP, defined by the maximum velocity of fibers partially inhibited by vanadate at 30 degrees C, is 20 +/- 4 microM for phosphorylated fibers and 192 +/- 40 microM for dephosphorylated fibers, showing that phosphorylation also affects the binding of ATP. Fiber stiffness is not affected by phosphorylation. Inhibition of velocity by phosphorylation at 30 degrees C depends on the phosphate analog, with approximately 12% inhibition in fibers activated in the presence of 5 mM BeF(3) and no inhibition in the presence of 0.25 mM AlF(4). Our results show that myosin phosphorylation can inhibit shortening velocity in fibers with large populations of myosin heads trapped in prepower stroke states, such as occurs during muscle fatigue.

Decavanadate effects in biological systems

Vanadium biological studies often disregarded the formation of decameric vanadate species known to interact, in vitro, with high-affinity with many proteins such as myosin and sarcoplasmic reticulum calcium pump and also to inhibit these biochemical systems involved in energy transduction. Moreover, very few in vivo animal studies involving vanadium consider the contribution of decavanadate to vanadium biological effects. Recently, it has been shown that an acute exposure to decavanadate but not to other vanadate oligomers induced oxidative stress and a different fate in vanadium intracellular accumulation. Several markers of oxidative stress analyzed on hepatic and cardiac tissue were monitored after in vivo effect of an acute exposure (12, 24 h and 7 days), to a sub-lethal concentration (5 mM; 1 mg/kg) of two vanadium solutions ("metavanadate" and "decavanadate"). It was observed that "decavanadate" promote different effects than other vanadate oligomers in catalase activity, glutathione content, lipid peroxidation, mitochondrial superoxide anion production and vanadium accumulation, whereas both solutions seem to equally depress reactive oxygen species (ROS) production as well as total intracellular reducing power. Vanadium is accumulated in mitochondria in particular when "decavanadate" is administered. These recent findings, that are now summarized, point out the decameric vanadate species contributions to in vivo and in vitro effects induced by vanadium in biological systems.

Cadmium and vanadate oligomers effects on methaemoglobin reductase activity from Lusitanian toadfish: in vivo and in vitro studies

Cadmium and two vanadate solutions as 'metavanadate' (containing ortho and metavanadate species) and 'decavanadate' (containing decameric species) (5 mM) were injected intraperitoneously in Halobatrachus didactylus (Lusitanian toadfish), in order to evaluate the effects of cadmium and oligomeric vanadate species on methaemoglobin reductase activity from fish red blood cells. Following short-term exposure (1 and 7 days), different changes were observed on enzyme activity. After 7 days of exposure, 'metavanadate' increased methaemoglobin reductase activity by 67% (P < 0.05), whereas, minor effects were observed on enzymatic activity upon cadmium and 'decavanadate' administration. However, in vitro studies indicate that decameric vanadate, in concentrations as low as 50 microM, besides strongly inhibiting methaemoglobin reductase activity, promotes haemoglobin oxidation to methaemoglobin. Although decameric vanadate species showed to be unstable in the different media used in this work, the rate of decameric vanadate deoligomerization is in general slow enough, making it possible to study its effects. It is concluded that the increase in H. didactylus methaemoglobin reductase activity is more pronounced upon exposition to 'metavanadate' than to cadmium and decameric species. Moreover, only decameric vanadate species promoted haemoglobin oxidation, suggesting that vanadate speciation is important to evaluate in vivo and in vitro effects on methaemoglobin reductase activity.

Oxidative stress in toadfish (Halobactrachus didactylus) cardiac muscle. Acute exposure to vanadate oligomers

Vanadate solutions as "metavanadate" (containing ortho and metavanadate species) and "decavanadate" (containing mainly decameric species) (5 mM; 1 mg/kg) were injected intraperitoneously in Halobatrachus didactylus (toadfish), in order to evaluate the contribution of decameric vanadate species to vanadium (V) intoxication on the cardiac tissue. Following short-term exposure (1 and 7 days), different changes on antioxidant enzyme activities-superoxide dismutase (SOD), catalase (CAT), selenium-glutathione peroxidase (Se-GPx), total glutathione peroxidase (GPx), lipid peroxidation and subcellular vanadium distribution were observed in mitochondrial and cytosolic fractions of heart ventricle toadfish. After 1 day of vanadium intoxication, SOD, CAT and Se-GPx activities were decreased up to 25%, by both vanadate solutions, except mitochondrial CAT activity that increased (+23%) upon decavanadate administration. After 7 days of exposure, decavanadate versus metavanadate solutions promoted different effects mainly on cytosolic CAT activity (-56% versus -5%), mitochondrial CAT activity (-10% versus +10%) and total GPx activity (+1% versus -35%), whereas lipid peroxidation products were significantly increased (+82%) upon 500 microM decavanadate intoxication. Accumulation of vanadium in total (0.137+/-0.011 microg/g) and mitochondrial (0.022+/-0.001 microg/g) fractions was observed upon 7 days of metavanadate exposure, whereas for decavanadate, the concentration of vanadium increased in cytosolic (0.020+/-0.005 microg/g) and mitochondrial (0.021+/-0.009 microg/g) fractions. It is concluded that decameric vanadate species are responsible for a strong increase on lipid peroxidation and a decrease in cytosolic catalase activity thus contributing to oxidative stress responses upon vanadate intoxication, in the toadfish heart.