The effects of hydrostatic pressure on pertussis toxin-catalyzed ribosylation of G proteins from deep-living macrourid fishes

Co-evolution of proteins and solutions: protein adaptation versus cytoprotective micromolecules and their roles in marine organisms

Organisms experience a wide range of environmental factors such as temperature, salinity and hydrostatic pressure, which pose challenges to biochemical processes. Studies on adaptations to such factors have largely focused on macromolecules, especially intrinsic adaptations in protein structure and function. However, micromolecular cosolutes can act as cytoprotectants in the cellular milieu to affect biochemical function and they are now recognized as important extrinsic adaptations. These solutes, both inorganic and organic, have been best characterized as osmolytes, which accumulate to reduce osmotic water loss. Singly, and in combination, many cosolutes have properties beyond simple osmotic effects, e.g. altering the stability and function of proteins in the face of numerous stressors. A key example is the marine osmolyte trimethylamine oxide (TMAO), which appears to enhance water structure and is excluded from peptide backbones, favoring protein folding and stability and counteracting destabilizers like urea and temperature. Co-evolution of intrinsic and extrinsic adaptations is illustrated with high hydrostatic pressure in deep-living organisms. Cytosolic and membrane proteins and G-protein-coupled signal transduction in fishes under pressure show inhibited function and stability, while revealing a number of intrinsic adaptations in deep species. Yet, intrinsic adaptations are often incomplete, and those fishes accumulate TMAO linearly with depth, suggesting a role for TMAO as an extrinsic 'piezolyte' or pressure cosolute. Indeed, TMAO is able to counteract the inhibitory effects of pressure on the stability and function of many proteins. Other cosolutes are cytoprotective in other ways, such as via antioxidation. Such observations highlight the importance of considering the cellular milieu in biochemical and cellular adaptation.

Water-soluble ruthenium complexes bearing activity against protozoan parasites

Parasitic illnesses are major causes of human disease and misery worldwide. Among them, both amebiasis and Chagas disease, caused by the protozoan parasites, Entamoeba histolytica and Trypanosoma cruzi, are responsible for thousands of annual deaths. The lack of safe and effective chemotherapy and/or the appearance of current drug resistance make the development of novel pharmacological tools for their treatment relevant. In this sense, within the framework of the medicinal inorganic chemistry, metal-based drugs appear to be a good alternative to find a pharmacological answer to parasitic diseases. In this work, novel ruthenium complexes [RuCl2(HL)(HPTA)2]Cl2 with HL=bioactive 5-nitrofuryl containing thiosemicarbazones and PTA=1,3,5-triaza-7-phosphaadamantane have been synthesized and fully characterized. PTA was included as co-ligand in order to modulate complexes aqueous solubility. In fact, obtained complexes were water soluble. Their activity against T. cruzi and E. histolytica was evaluated in vitro. [RuCl2(HL4)(HPTA)2]Cl2 complex, with HL4=N-phenyl-5-nitrofuryl-thiosemicarbazone, was the most active compound against both parasites. In particular, it showed an excellent activity against E. histolytica (half maximal inhibitory concentration (IC50)=5.2 μM), even higher than that of the reference drug metronidazole. In addition, this complex turns out to be selective for E. histolytica (selectivity index (SI)>38). The potential mechanism of antiparasitic action of the obtained ruthenium complexes could involve oxidative stress for both parasites. Additionally, complexes could interact with DNA as second potential target by an intercalative-like mode. Obtained results could be considered a contribution in the search for metal compounds that could be active against multiple parasites.

Potential mechanism of the anti-trypanosomal activity of organoruthenium complexes with bioactive thiosemicarbazones

In the search for new metal-based drugs against diseases produced by trypanosomatid parasites, four organoruthenium(II) compounds [Ru2(p-cymene)2(L)2]X2, where L are bioactive 5-nitrofuryl-containing thiosemicarbazones and X = Cl or PF6, had been previously obtained. These compounds had shown activity on Trypanosoma brucei, the etiological agent of African trypanosomiasis. Because of genomic similarities between trypanosomatides, these ruthenium compounds were evaluated, in the current work, on Trypanosoma cruzi, the parasite responsible of American trypanosomiasis (Chagas disease). Two of them showed significant in vitro growth inhibition activity against the infective trypomastigote form of T. cruzi (Dm28c clone, IC50 = 11.69 and 59.42 μM for [Ru2(p-cymene)2(L4)2]Cl2 and [Ru2(p-cymene)2(L1)2]Cl2, respectively, where HL4 = 5-nitrofuryl-N-phenylthiosemicarbazone and HL1 = 5-nitrofurylthiosemicarbazone), showing fairly good selectivities toward trypanosomes with respect to mammalian cells (J774 murine macrophages). Moreover, [Ru2(p-cymene)2(L2)2]Cl2, where HL2 = 5-nitrofuryl-N-methylthiosemicarbazone, was synthesized in order to evaluate the effect of improved solubility on biological behavior. This new chloride salt showed higher activity against T. cruzi than that of the previously synthesized hexafluorophosphate one (Dm28c clone, IC50 = 14.30 μM for the former and 231.3 μM for the latter). In addition, the mode of antitrypanosomal action of the organoruthenium compounds was investigated. The complexes were not only able to generate toxic free radicals through bioreduction but they also interacted with two further potential parasite targets: DNA and cruzipain, a cysteine protease which plays a fundamental role in the biological cycle of these parasites. The results suggest a "multi-target" mechanism of trypanosomicidal action for the obtained complexes.

Antimicrobial Activity of Some Derivatives of 1,4-Dihydropyridines

Hantzsch reported the synthesis of functionalized 1,4-dihydropyridines via three-component condensation of an aromatic aldehyde, ketoester, and ammonium hydroxide. This multicomponent reaction is of much importance due to excellent pharmacological properties of dihydropyridines. In this account, we synthesized some halo- and nitrophenyl dihydropyridines and evaluated their antimicrobial activity. The minimum inhibitory concentration (MIC) was determined by microdilution technique in Mueller Hinton broth. The MICs were recorded after 24 hours of incubation at 37°C. These results showed that these compounds exhibited significant to moderate activities against both Gram-(+) and Gram-(−) organisms.

Oral Therapy with Amlodipine and Lacidipine, 1,4-Dihydropyridine Derivatives Showing Activity against Experimental Visceral Leishmaniasis

Amlodipine and lacidipine, conventional antihypertensive drugs, inhibited Leishmania donovani infection in vitro and in BALB/c mice when administered orally. These 1,4-dihydropyridine derivatives functioned through dose-dependent inhibition of oxygen consumption, triggering caspase 3-like activation-mediated programmed cell death of the parasites.

Pressure effects on the GTPase activity of brain membrane G proteins of deep-living marine fishes

In marine fishes, heterotrimeric guanyl nucleotide binding proteins (G proteins), which couple cell surface membrane receptors to their effector elements, are sensitive to hydrostatic pressure. The intrinsic high affinity GTPase activity of the alpha subunits of G proteins in three signaling systems coupled to adenylyl cyclase, the A(1) adenosine receptor, the muscarinic cholinergic receptor and the beta-adrenergic receptor, was tested at pressures up to 340 atm. Brain membrane preparations from four members of the deep-sea teleost fish family Macrouridae were studied. Coryphaenoides armatus, C. filifer, C. rupestris and Macrourus berglax have depth distributions which together span 100-5810 m. Increased pressure inhibited basal GTPase activity only in M. berglax, which of the four species has the shallowest center of abundance. Increased hydrostatic pressure did not alter the response of GTPase activity to the beta-adrenergic receptor agonist isoproterenol. Increased pressure decreased the stimulation of GTPase activity by the A(1) adenosine receptor agonist cyclopentyladenosine (CPA) in C. armatus and M. berglax, and by the muscarinic cholinergic receptor agonist carbamyl choline in C. armatus, C. filifer and M. berglax. Decreased agonist-stimulation of the GTPase activity at elevated pressure may result from pressure-induced changes in conformational states or inhibition of agonist binding. The binding of the non-hydrolyzable GTP analog guanosine 5'-[gamma-thio]triphosphate (GTP[S]) in response to CPA was determined at 5 degrees C and atmospheric pressure. Six macrourid species and a morid were studied. The halftime (t(1/2)) values for GTP[S] binding, ranging from 20.8 to 40.9 min, are similar to values previously reported for two other cold-adapted fishes.

Synthesis and in vitro trypanocide activity of several polycyclic drimane-quinone derivatives

The Diels-Alder reaction between two polygodial-derived dienes and simple quinones to yield substituted naphtho- and anthraquinones, is described. The in vitro trypanocide activity for the series was determined. Two of the new compounds showed an activity ten and two times higher, respectively, than nifurtimox and benznidazole, the medicines of choice for the treatment of the acute Chagas' disease.

The effects of the deep-sea environment on transmembrane signaling

Membrane-associated processes may be particularly susceptible to perturbation by the high hydrostatic pressures and low temperatures of the deep ocean. Transmembrane signaling by guanyl nucleotide binding protein (G protein) coupled receptors (GPCRs) is affected at a number of steps: (1) agonist activation of the GPCR; (2) the interaction of the receptor with the heterotrimeric G protein; (3) the G protein GTPase cycle; and (4) the activation and function of the effector element, adenylyl cyclase. The effects of low temperature and high hydrostatic pressures on the A(1) adenosine receptor-inhibitory G protein (G(i))-adenylyl cyclase signaling complex were examined in teleost fishes from three families, Scorpaenidae, Macrouridae and Moridae. In a comparison of teleost fishes, rat and chicken, species with body temperatures from 1 to 40 degrees C, at atmospheric pressure, A(1) adenosine receptor agonist binding is conserved at the body temperature of the species. In the marine teleost fishes examined, increased pressure decreases agonist efficacy. There are differences among species in the effects of increased hydrostatic pressure on G protein interactions with receptors, GTP binding to G protein alpha subunits and the intrinsic GTPase activity of alpha subunits. Adenylyl cyclase activity and modulation are affected by increased pressure in all the species examined, except Antimora rostrata which was unaffected by pressure changes. At pressures approximating those which the species experience in situ adenylyl cyclase activity retains its sensitivity to modulators. To understand the physiological consequences of impaired cell signaling several prototypical human diseases are discussed.

Fish at high pressure: a hundred year history

Two main periods can be considered in the history of fish metabolism under pressure. The first period (roughly from 1870 to 1970) was mainly descriptive: survival times and behavior were studied and some authors described an increase in oxygen consumption under pressure; later, the counteracting effects of high temperature on pressure were mentioned. The second period (from 1970 onwards) was more integrative and two major ways were explored. The first was to use shallow-water fish, experimentally exposed to hydrostatic pressure, which can induce a metabolic state resembling histotoxic hypoxia. The second way was to use deep-living fish which have, when compared to surface fish, muscle enzymes with higher structural stability, lower activity (in relationship with habitat depth) and kinetics that are less sensitive to pressure increase. Using this approach, it was also shown that muscle composition and function were somewhat different at depth and that deep fish are well adapted to pressure partly by maintaining membrane fluidity (homeoviscous theory). Since about 1990, the two above-mentioned approaches have still been pursued but by fewer researchers. Studies on deep-living fish are mainly concerned with enzyme kinetics whereas shallow water fish are used mainly for cellular energetic studies. Regarding this topic, it has been shown that yellow freshwater eels are able to acclimate to high-pressure effects, by optimizing membrane fluidity and composition (as achieved by deep-living fish), by improving oxidative phosphorylation (increase of P/O ratio) and the glycolytic pathway.