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Visible light induced reversible extrusion of nitric oxide from a ruthenium(II) nitrosyl complex: a facile delivery of nitric oxide.

The new ruthenium compound [Ru(NO)(pysiS4)]Br (3) (pysiS4 = 2,6-bis(3-triphenylsilyl-2-sulfanylphenylthiomethyl)pyridine), containing sterically bulky SiPh3 groups ortho to the thiolate donors, has been synthesized. In solution, 3 releases NO efficiently on exposure to visible light (lambda >/= 455 nm) at room temperature to afford [Ru(Br)(pysiS4)] (4). Treatment of 4 with NO yielded exclusively 3 without any metal-bound side reaction.

Crystallography, X-Ray↗

Ruthenium-catalyzed regiospecific borylation of methyl C-H bonds.

We report the regiospecific, ruthenium-catalyzed borylation of saturated terminal C-H bonds. Alkylboronates were obtained in 78-98% yields. The borylations of alkanes, trialkylamines, protected alcohols, and fluoroalkanes occurred regiospecifically at the methyl group that is least sterically hindered. In contrast to most organometallic C-H activation, the reactions of alkanes occurred in higher yields than the reactions of arenes. Reactions were conducted that probed steric and electronic effects on the alkyl borylation. These reactions showed that the borylation occurred preferentially at the methyl group that is least sterically hindered and most electron-deficient. Ruthenium compounds containing boryl ligands were synthesized, and one was characterized by X-ray crystallography. One of these compounds contained a rare bridging boryl ligand and served as a catalyst precursor for the borylation of octane.

Boron Compounds↗

Synthesis and chemical-pharmacological characterization of the antimetastatic NAMI-A-type Ru(III) complexes (Hdmtp)[trans-RuCl4(dmso-S)(dmtp)], (Na)[trans-RuCl4(dmso-S)(dmtp)], and [mer-RuCl3(H2O)(dmso-S)(dmtp)] (dmtp = 5,7-dimethyl[1,2,4]triazolo[1,5-a]pyrimidine).

Ruthenium compounds have gained large interest for their potential application as chemotherapeutic agents, and in particular the complexes of the type (X)[trans-RuCl4(dmso-S)L] (X = HL or Na, NAMI-A or NAMI, respectively, for L = imidazole) are under investigation for their antimetastatic properties. The NAMI(-A)-like compounds are prodrugs that hydrolyze in vivo, and the investigation of their hydrolytic properties is therefore important for determining the nature of the potential active species. The NAMI-A-type Ru(III) complex 1, (Hdmtp)[trans-RuCl4(dmso-S)(dmtp)] (dmtp is 5,7-dimethyl[1,2,4]triazolo[1,5-a]pyrimidine), and the corresponding sodium analogue 2, (Na)[trans-RuCl4(dmso-S)(dmtp)], were synthesized. The hydrolyses of 1 and 2 in water as well as in buffered solutions were studied, and the first hydrolysis product, [mer-RuCl3(H2O)(dmso-S)(dmtp)].H2O (3), was isolated and characterized. The molecular structures of 1 and 3 were determined by single-crystal X-ray diffraction analyses and prove the importance of the hydrogen-bonding properties of dmtp to stabilize hydrolysis products. In vitro 1 (a) is not cytotoxic on tumor cells, following challenges from 1 to 72 h and concentrations up to 100 microM, (b) inhibits matrigel invasion at 0.1 mM and MMP-9 activity with an IC50 of about 1 mM, and (c) is devoid of pronounced effects on cell distribution among cell cycle phases. In vivo compound 1, similar to NAMI-A, significantly inhibits metastasis growth in mice bearing advanced MCa mammary carcinoma tumors. In the lungs, 1 is significantly less concentrated than NAMI-A, whereas no differences between these two compounds were found in other organs such as tumor, liver, and kidney. However, 1 caused edema and necrotic areas on liver parenchyma that are more pronounced than those caused by NAMI-A. Conversely, glomerular and tubular changes on kidney are less extensive than with NAMI-A. In conclusion, 1 confirms the excellent antimetastatic properties of this class of NAMI-A-type compounds and qualifies as an interesting alternative to NAMI-A for treating human cancers.

Animals↗

Pharmacological control of lung metastases of solid tumours by a novel ruthenium complex.

Imidazolium trans-imidazoledimethylsulphoxidetetrachlororuthenate ImH[trans-RuCl4(DMSO)Im] (NAMI-A), a ruthenium compound that replaces Na+ with ImH+ in the molecule of Na[trans-RuCl4(DMSO)Im] (NAMI), was studied for the anti-metastasis effects in models of solid metastasizing tumours of the mouse. NAMI-A, given i.p. at 35 mg/kg/day for six consecutive days, a dose equimolar to that of NAMI, to mice bearing Lewis lung carcinoma and MCa mammary carcinoma, markedly reduces lung metastasis weight by 80-90%, with an effect equal or even superior to that of NAMI, depending on the experimental system adopted. Correspondingly, NAMI-A increases the content of connective tissue in the tumour matrix, around blood vessels, and in the tumour capsule, augments the percentage of tumour cells in G2/M phase and reduces the amount of CD45+ cells infiltrating the tumour parenchyma. The effects of the same doses on spleen lymphocytes correspond to an increase of CD8+ subset without any change of the distribution of cells in G0/G1, S and G2/M phases. The study shows that NAMI-A behaves similarly to NAMI on the several parameters examined in comparison experiments and therefore we suggest to credit NAMI-A with all the biological actions already described for NAMI during the last 3 years. The replacement of Na+ with ImH+ therefore, besides the better chemical stability of the molecule, confers to [trans-RuCl4(DMSO)Im]- a closer similarity with a true drug to be used in humans, and suggests this molecule for future studies of preclinical toxicology and phase I and II clinical trials.

Animals↗

EELS data acquisition, processing and display for the Zeiss CEM 902 based on LOTUS 1-2-3: application examples from a biological system and inorganic transition metal compounds.

A personal computer combined with LOTUS 1-2-3 software, including the RS232 module of LOTUS MEASURE and a 12-bit ADC, has been used for data acquisition of electron energy-loss spectroscopy (EELS) spectra with the Zeiss CEM 902. The internal macro language of LOTUS 1-2-3 allows a menu-driven procedure. Macro-programs partly combined with external FORTRAN programs can be chosen from the menu for background subtraction, removal of multiple scattering effects by deconvolution, elemental quantification and several utilities. For special applications or conditions the macro programs can easily be modified. Spectra from crystals of two inorganic transition metal compounds, ruthenium trichloride and vanadium disulphide, and from a biological sample are presented as examples of the application of this software.

Animals↗

Comparative kinetic study of D-glucose oxidation by ruthenium(III) compounds catalyzed by FAD-dependent glucose oxidase and PQQ-dependent glucose dehydrogenase.

The comparative kinetic study of two glucose oxidizing enzymes, FAD-dependent glucose oxidase and PQQ-dependent glucose dehydrogenase, is presented in the artificial electron transfer mediator system based on ruthenium(III) compounds. It is demonstrated that FAD-dependent glucose oxidase and PQQ-dependent glucose dehydrogenase follow Michaelis kinetics in the D-glucose/ruthenium(III) system. PQQ-dependent glucose dehydrogenase is more active than FAD-dependent glucose oxidase in the process of D-glucose oxidation by ruthenium(III) compounds, this being due to the different catalytic mechanisms of these enzymes.

Catalysis↗

Coordination and cluster compounds of ruthenium with the [hypho-1,2-S2B6H9]- ligand.

The reaction between [tmndH][hypho-1,2-S(2)B6H9](tmnd =N,N,N',N'-tetramethylnaphthalene-1,8-diamine) and [RuCl(PPh3)2(eta5-Cp)] in CH2Cl2 at room temperature afforded two ruthenathiaboranes, [5-(eta(5)-Cp)-5-(PPh3)-5,4,6-RuS2B6H9], 1, and [Ru(eta(1)-1,2-S2B6H9)(PPh3)2(eta5-Cp)], 2, in 6 and 48% yields, respectively. The heating of a solution of [Ru(eta(1)-1,2-S2B6H9)(PPh3)2(eta5-Cp)] 2 in CH2Cl2 at reflux temperature afforded 1 in 59% yield. Compound 1 could be described as either a hypho nine-vertex {RuS2B6} cluster or a coordination compound of ruthenium which contains a bidentate eta2-dithiaborate cluster ligand; the latter description is preferred. Compound 2 contains an eight-atom hypho-type {1,2-S2B6} cage bonded to the ruthenium atom of the {Ru(PPh3)2(eta5-Cp)} unit by one sulfur atom and may be described as a compound of ruthenium coordinated eta(1)- to the dithiaborate cluster ligand. The reaction between [tmndH][hypho-1,2-S2B6H9] and [RuCl2(eta6-MeC6H4Pri)]2 in CH2Cl2 at room temperature afforded [5-(eta6-MeC6H4Pri)-arachno-5,4,6-RuS2B6H8], 3, in 94% yield. Further reaction of 3 and PMePh2 afforded another arachno{RhS2B6}cluster, [5-(eta6-MeC6H4Pri)-8-(PMePh2)-arachno-5,4,6-RuS2B6H6], 4, in 25% yield. Compounds 1, 2, and 4 were characterised with single crystal X-ray analyses.

Journal Article↗

Ruthenium complexes as anticancer agents.

Cancer is one of the major cases of death in the world. Current treatment of cancer is limited to surgery, radiotherapy, and the use of cytotoxic agents, despite their well known side effects and problems associated with the development of resistance. For most forms of disseminated cancer, however, no curative therapy is available, and the discovery and development of novel active chemotherapeutic agents is largely needed. Since the development of cisplatin, an inorganic platinum complex, numerous platinum and non-platinum metal complexes were synthesized and tested for anticancer activity. Very few match the clinical efficacy of cisplatin. Ruthenium complexes were prepared to ameliorate cisplatin activity, particularly on resistant tumours, or to reduce host toxicity at active doses. Since many years a lot of scientific groups have actively worked in the field of inorganic antitumor drugs and have developed a number of Ru(II) and Ru(III) complexes, which were shown to possess good antitumor and, above all, antimetastatic properties against animal models. Ruthenium complexes are presently an object of great attention in the field of medicinal chemistry, as antitumor agents with selective antimetastatic properties and low systemic toxicity. Ruthenium compounds appear to penetrate reasonably well the tumor cells and bind effectively to DNA. In this review, the achievements in the field of medicinal chemistry, DNA binding modes, and the development status of Ru(II) and Ru(III) complexes as anticancer agents are discussed. The aim of this review is therefore that of critically examining the past and the actual work on ruthenium compounds with emphasis on their proposed role in cancer therapy.

Animals↗

A comparative study of adduct formation between the anticancer ruthenium(III) compound HInd trans-[RuCl4(Ind)2] and serum proteins.

Formation of adducts between the antitumor ruthenium(III) complex [HInd]trans-[RuCl(4)(Ind)(2)] (KP1019) and the plasma proteins serum albumin and serum transferrin was investigated by UV-vis spectroscopy, for metal-to-protein ratios ranging from 1:1 to 5:1. In both cases, formation of tight metal-protein conjugates was observed. Similar spectroscopic features were observed for both albumin and transferrin derivatives implying a similar binding mode of the ruthenium species to these proteins. Surface histidines are the probable anchoring sites for the bound ruthenium(III) ions in line with previous crystallographic results. In order to assess the stability of the KP1019-protein adducts the influence of pH, reducing agents and chelators was analysed by UV-vis spectroscopy. Notably, there was no effect of addition of EDTA on the UV-vis spectra of the conjugates. The pH-stability was high in the pH range 5-8. Experiments with sodium ascorbate showed that there was just some alteration of selected bands. The implications of the present results are discussed in relation to the pharmacological behavior of this novel class of antitumor compounds.

Animals↗

Phosphorus chemical shift tensors of phosphido ligands in ruthenium carbonyl compounds: (31)P NMR spectroscopy of single-crystal and powder samples and ab initio calculations.

The phosphorus chemical shift (CS) tensors of several ruthenium carbonyl compounds containing a phosphido ligand, micro), bridging a Ru [bond] Ru bond were characterized by solid-state (31)P NMR spectroscopy. As well, an analogous osmium compound was examined. The structures of most of the clusters investigated have approximate local C(2v) symmetry about the phosphorus atom. Compared to the "isolated" PH(2)(-) anion, the phosphorus nucleus of a bridging phosphido ligand exhibits considerable deshielding. The phosphorus CS tensors of most of the compounds have spans ranging from 230 to 350 ppm and skews of approximately zero. Single-crystal NMR was used to investigate the orientation of the phosphorus CS tensors for two of the compounds, Ru(2)(CO)(6)(mu(2)-C [triple bond] C [bond] Ph)(mu(2)-PPh(2)) and Ru(3)(CO)(9)(mu(2)-H)(mu(2)-PPh(2)). The intermediate component of the phosphorus CS tensor, delta(22), lies along the local C(2) axis in both compounds. The least shielded component, delta(11), lies perpendicular to the Ru [bond] P [bond] Ru plane while the most shielded component, delta(33), lies perpendicular to the C [bond]P [bond] C plane. The orientation of the phosphorus CS tensor for a third compound, Ru(2)(CO)(6)(mu(2)-PPh(2))(2), was investigated by the dipolar-chemical shift NMR technique and was found to be analogous, suggesting it to be the same in all compounds. Ab initio calculations of phosphorus magnetic shielding tensors have been carried out and reproduce the orientations found experimentally. The orientation of the CS tensor has been rationalized using simple frontier MO theory. Splittings due to (99,101)Ru [bond] (31)P spin-spin coupling have been observed for several of the complexes. A rare example of (189)Os [bond] (31)P spin-spin splittings is observed in the (31)P MAS NMR spectrum of the osmium cluster, where (1)J((189)Os, (31)P) is 367 Hz. For this complex, the (189)Os nuclear quadrupolar coupling constant is on the order of several hundred megahertz.

Journal Article↗

Antitumor activity of some ruthenium derivatives in human colon cancer cell lines in vitro.

Six ruthenium derivatives were evaluated in vitro in two human colon cancer cell lines (SW707 and SW948) utilizing the microculture tetrazolium test (MTT) and cell counting with a Coulter Counter. The ruthenium compound sodium-(tetrachloroimidazoledimethylsulfoxideruthenate)- bisdimethylsulfoxide (Na(RuDMSOimCl4)) showed the best efficacy in inhibiting cell proliferation of both colon cancer cell lines followed by the other DMSO ruthenium compound sodium-(tetrachloroindazoledimethylsulfoxideruthenate) - bisdimethylsulfoxide (Na(RuDMSOIndCl4)), as demonstrated by IC50 values (80 and 90 micrograms/ml in SW707 and SW948 cell lines for Na(RuDMSOImCl4); 155 and 165 micrograms/ml in SW707 and SW948 cell lines for Na(RuDMSOIndCl4), respectively). Out of the ruthenium derivatives without DMSO, transindazolium - [tetrachlorobis(1H - indazole)ruthenate (III,N2)] (HInd[RuInd2Cl4(N2)]), was as active as its DMSO-containing congener whereas trans-imidazolium- [tetrachlorobisimidazoleruthenate)(III)], (HIm(RuIm2Cl4)) was less active, as shown by the IC50 values: (HIm (RuIm2Cl4) = 250 and 260 micrograms/ml in cell lines SW707 and SW948; HInd[RuInd2Cl4(N2)] = 110 and greater than 200 micrograms/ml in cell lines SW707 and SW948, respectively). The other ruthenium derivatives containing pyrazole and triazole as ligands (trans - pyrazolium (tetrachlorobispyrazoleruthenate) (III), PzH(RuPz2Cl4) and triazolium(tetrachlorobistriazoleruthenate) (III), TrH(RuTr2Cl4)) were active only at high concentrations that cannot be regarded as realistic in vivo, as shown by the respective IC50 values: (PzH(RuPz2Cl4) = 1056 and 750 micrograms/ml in cell lines SW707 and SW948; TrH(RuTr2Cl4) = 350 and 300 micrograms/ml in cell lines SW707 and SW948). The promising activity of ruthenium compounds with DMSO, indazole and imidazole as ligands should be evaluated in vivo for elucidating their possible role in the treatment of colorectal cancer.

Antineoplastic Agents↗

Ruthenium bipyridyl compounds with two terminal alkynyl ligands.

Compounds of the form Ru(X2bipy)(PPh3)2(-C triple bond CC6H4NO2-p)2(X2bipy = 4,4'-X(2)-2,2'-bipyridine, X = Me 3a, Br 3b, I 3c) have been synthesised from the mono-alkynyl precursors Ru(X2bipy)(PPh3)2(-C triple bond CC6H4NO2-p)Cl (X = Me 2a, Br 2b, I 2c); the former are the first ruthenium bis-alkynyl compounds that also contain a bipyridyl ligand. Spectroelectrochemical investigation of 3a shows that the metal is readily oxidised to form the ruthenium(III) compound 3a+, and will also undergo a single-electron reduction at each nitro group to form 3a2-. ESR and UV/visible spectra of these redox congeners are presented. We also report the synthesis of [Ru(Me2bipy)(PPh3)2(-C triple bond CBut)(N triple bond N)][PF6] during the attempted synthesis of Ru(Me2bipy)(PPh3)2(-C triple bond CBut)2, and report its X-ray crystal structure and IR spectrum. X-Ray crystal structures of 3b and 3c(as two different solvates) are presented, and the nature of the intermolecular interactions seen therein is discussed. Z-Scan measurements on Ru(Me2bipy)(PPh3)2(-C triple bond CR)Cl (R = C6H4NO2-p2a, But, Ph, C6H4Me) are also reported, and show that Ru(Me2bipy)(PPh3)2(-C triple bond CR)Cl (R = C6H4NO2-p2a, Ph) exhibit moderate third-order non-linearities.

Journal Article↗

Covalent linkage of ruthenium polypyridyl compounds to poly(L-lysine), albumins, and immunoglobulin G.

A series of ruthenium polypyridyl complexes has been covalently bound to poly(L-lysine), bovine serum albumin, human serum albumin, ovalbumin, and immunoglobulin G using different binding methods. The conjugation ratios and the luminescence properties of the bioconjugates are reported. All conjugates show nonsingle-exponential decay curves. Quenching of the emission by oxygen has been studied.

Albumins↗

Compared effects of ruthenium red and cis [Ru(NH3)4Cl2]Cl on the isolated ischaemic-reperfused rat heart.

The sequence ischaemia-reperfusion is characterized by reperfusion damage. The calcium overload occurring at the beginning of reperfusion is one of the main mechanisms responsible for reperfusion damage. Ruthenium red, a blocker of the mitochondrial calcium uniport system, could prevent this damage by preserving the ATP synthesis in the mitochondria. We tested ruthenium red and another ruthenium compound, cis-tetrammine dichlororuthenium (III) chloride in our experimental model of ischaemic-reperfused rat hearts. After a 15 minute-stabilization period, the hearts were submitted to a 30 minute global ischaemia period and then reperfused for 45 minutes with the standard perfusion solution or with ruthenium red or cis-tetrammine dichlororuthenium (III) chloride at 1, 3 or 9 microM. Ruthenium red at 3 microM exerted a protective effect in our experimental conditions by showing a significant improvement of the contractility recovery at the end of reperfusion and a significant decrease of the malondialdehyde production, which reflects free radical production. The cis-tetrammine dichlororuthenium (III) chloride (containing 1 Ru ion per molecule) at 9 microM was slightly less efficient than ruthenium red at 3 microM (containing 3 Ru ions per molecule). The heart ruthenium binding was better for the ruthenium red than for the cis-tetrammine dichlororuthenium (III) chloride, suggesting a role of the ruthenium ion complexation in the crossing of the membrane, whereas the cardiac effect seemed to be linked to the ruthenium ion heart concentration, which was similar for the ruthenium red at 3 microM and for the cis-tetrammine dichlororuthenium (III) chloride at 9 microM. One can hope that ruthenium compounds would limit reperfusion damage and infarct size after ischaemia in in vivo models.

Animals↗

The effects of ruthenium tetraammine compounds on vascular smooth muscle.

The time course of the relaxation effect induced by a single dose (3 x 10(-6) mol/L) of trans-[Ru(NH3)4L(NO)]3+ (L=nic, 4-pic, py, imN, P(OEt)3, SO(3)(2-), NH3, and pz) species and sodium nitroprusside (4 x 10(-9) mol/L) was studied in aortic rings without endothelium and pre-contracted with noradrenaline (1 x 10(-6) mol/L). All the compounds induced a relaxing effect in the aortic rings, but the intensity and time of relaxation were different. Only the species where L=py, 4-pic, and P(OEt)3 were able to induce 100% (99-100%) of the relaxing effect during the assay. trans-[Ru(NH3)4(L)(NO)]3+ (L=SO(3)(2-) and NH3) showed the lowest relaxing effect (36 and 37%, respectively) when compared with the other compounds. Relationship was observed between the time corresponding to half of the maximum relaxation intensity observed and, respectively, k-NO, E0'[Ru(NO)]3+/[Ru(NO)]2+ in trans-[Ru(NH3)4(L)(NO)]3+ species and E0'Ru(III)/Ru(II) in trans-[Ru(NH3)4(L)(H2O)]3+ ions. These relationships strongly suggested that the NO liberation from the reduced nitrosyl complexes was responsible for the observed relaxation.

Amines↗

Lack of In vitro cytotoxicity, associated to increased G(2)-M cell fraction and inhibition of matrigel invasion, may predict In vivo-selective antimetastasis activity of ruthenium complexes.

The ruthenium complexes trans-dichlorotetrakisdimethylsulfoxide ruthenium(II) (trans-Ru), imidazolium trans-imidazoletetrachlororuthenate (ICR), sodium trans-tetramethylensulfoxideisoquinolinetetrachlororuthenate (TEQU), and imidazolium trans-imidazoledimethylsulfoxidetetrachlororuthenate (NAMI-A) are tested in vitro by short exposure of MCF-7, LoVo, KB, and TS/A tumor cells to 10(-4) M concentration, and in vivo on Lewis lung carcinoma by a daily i.p. treatment for 6 consecutive days using equitoxic and maximum tolerated doses. NAMI-A 1) inhibited tumor cell invasion of matrigel, 2) induced a transient accumulation of cells in the G(2)-M phase, 3) did not modify in vitro cell growth, and 4) markedly reduced lung metastasis formation. TEQU showed significant cytotoxicity in vitro and was not antimetastatic in vivo. ICR and trans-Ru did not modify cell cycle distribution of in vitro tumor cells nor did they inhibit matrigel invasion; ICR was also devoid of antimetastasis effects in vivo. Ruthenium uptake by tumor cells did account for in vitro cytotoxicity but not for other in vitro actions or for in vivo antimetastasis activity. The contemporary absence of cytotoxicity, associated to inhibition of matrigel crossing and to transient block in the premitotic G(2)-M phase, appears to be prerequisites for a ruthenium compound to show in vivo-selective antimetastasis effect. The validation of this model for other classes of compounds will allow an understanding of the combined weight of the above-mentioned phenomena for tumor metastasis growth and control.

Animals↗

Diimine-acetylide compounds of ruthenium: the structural and spectroscopic effects of oxidation.

The reaction of Ru(Me(2)bipy)(PPh(3))(2)Cl(2) 1 with terminal alkynes HCCR in the presence of TlPF(6) leads to the formation of the vinylidene compounds [Ru(Me(2)bipy)(PPh(3))(2)Cl(=C=CHR)][PF(6)] (2) (2a, R = Bu(t); 2b, R = p-C(6)H(4)-Me; 2c, R = Ph). These compounds decompose in oxygenated solution to form the carbonyl compound [Ru(Me(2)bipy)(PPh(3))(2)Cl(CO)][PF(6)] (3), and may be deprotonated by K(2)CO(3) to give the ruthenium(II) terminal acetylide compounds Ru(Me(2)bipy)(PPh(3))(2)Cl(CC-R) (4) (4a, R = Bu(t); 4b, R = p-C(6)H(4)-Me; 4c, R = Ph). Cyclic voltammetry shows that 2a-c may also be reductively dehydrogenated to form 4a-c. 4a-c are readily oxidized to their ruthenium(III) analogues [4a](+)-[4c](+), and the changes seen in their UV/visible spectra upon performing this oxidation are analyzed. These show that whereas the UV/visible spectra of 4a-c show MLCT bands from the ruthenium atom to the bipyridyl ligand, those of [4a](+)-[4c](+) contain LMCT bands originating on the acetylide ligands. This is in agreement with the IR and ESR spectra of [4a](+)-[4c](+). The X-ray crystal structures of the redox pair 4a and [4a][PF(6)()] have been determined, allowing the bonding within the metal-acetylide unit to be analyzed, and an attempt is made to determine Lever electrochemical parameters (E(L)) for the vinylidene and acetylide ligands seen herein. Room temperature luminescence measurements on 4a-c show that the compounds are not strongly emissive.

Journal Article↗

Ruthenium red and compound 48/80 inhibit the smooth-muscle plasma-membrane Ca2+ pump via interaction with associated polyphosphoinositides.

We will demonstrate the compound 48/80 and ruthenium red inhibit the smooth-muscle plasma-membrane Ca2+ pump by counteracting the stimulant effect of negatively charged phospholipids. Both substances did not affect the purified enzyme re-activated by pure phosphatidylcholine or phosphatidylinositol and measured in the absence of calmodulin, indicating that under these conditions they did not have a direct effect on the ATPase protein. Ruthenium red and compound 48/80 however inhibited the (Ca2(+) + Mg2+)-ATPase in the presence of phosphatidylinositol 4-phosphate and especially phosphatidylinositol 4,5-bisphosphate. The K0.5 for inhibition was 25 microM ruthenium red and 9 micrograms/ml of compound 48/80. The inhibition by ruthenium red developed slowly with half maximal inhibition occurring after about 75 s while that by compound 48/80 developed immediately within the time required for mixing. The efficacy of ruthenium red increased as the concentration of the acidic phospholipid increased, while no such cooperativity was observed for compound 48/80. Ruthenium red reduced the Vmax for Ca2+ without affecting the affinity for Ca2+, while compound 48/80 decreased both parameters. In conclusion, although ruthenium red and compound 48/80 affect the ATPase differently, both substances most likely inhibit the plasma-membrane Ca2+ pumping by counteracting the stimulation by negatively charged phospholipids.

Animals↗