Clotrimazole, an antimycotic drug, inhibits the sarcoplasmic reticulum calcium pump and contractile function in heart muscle

G45 and V386 in Transmembrane Domains 1 and 8 Are Critical for the Activation of OATP1B3-Mediated E17βG Uptake by Clotrimazole

Organic anion-transporting polypeptides (OATPs) 1B1 and 1B3 are two highly homologous transport proteins. However, OATP1B1- and 1B3-mediated estradiol-17β-glucuronide (E17βG) uptake can be differentially affected by clotrimazole. In this study, by functional characterization on chimeric transporters and single mutants, we find that G45 in transmembrane domain 1 (TM1) and V386 in TM8 are critical for the activation of OATP1B3-mediated E17βG uptake by clotrimazole. However, the effect of clotrimazole on the function of OATP1B3 is substrate-dependent as clotrimazole does not stimulate OATP1B3-mediated uptake of 4',5'-dibromofluorescein (DBF) and rosuvastatin. In addition, clotrimazole is not transported by OATP1B3, but it can efficiently permeate the plasma membrane due to its lipophilic properties. Homology modeling and molecular docking indicate that E17βG binds in a substrate binding pocket of OATP1B3 through hydrogen bonding and hydrophobic interactions, among which its sterol scaffold forms hydrophobic contacts with V386. In addition, a flexible glycine residue at position 45 is essential for the activation of OATP1B3. Finally, clotrimazole is predicted to bind at an allosteric site, which mainly consists of hydrophobic residues located at the cytoplasmic halves of TMs 4, 5, 10, and 11.

Sarco/Endoplasmic Reticulum Calcium ATPase Inhibitors: Beyond Anticancer Perspective

The sarco/endoplasmic reticulum calcium ATPase (SERCA), which plays a key role in the maintenance of Ca²⁺ ion homeostasis, is an extensively studied enzyme, the inhibition of which has a considerable impact on cell life and death decision. To date, several SERCA inhibitors have been thoroughly studied and the most notable one, a derivative of the sesquiterpene lactone thapsigargin, is gradually approaching a clinical application. Meanwhile, new compounds with SERCA-inhibiting properties of natural, synthetic, or semisynthetic origin are being discovered and/or developed; some of these might also be suitable for the development of new drugs with improved performance. This review brings an up-to-date comprehensive overview of recently discovered compounds with the potential of SERCA inhibition, discusses their mechanism of action, and highlights their potential clinical applications, such as cancer treatment.

VDAC1 as Pharmacological Target in Cancer and Neurodegeneration: Focus on Its Role in Apoptosis

Cancer and neurodegeneration are different classes of diseases that share the involvement of mitochondria in their pathogenesis. Whereas the high glycolytic rate (the so-called Warburg metabolism) and the suppression of apoptosis are key elements for the establishment and maintenance of cancer cells, mitochondrial dysfunction and increased cell death mark neurodegeneration. As a main actor in the regulation of cell metabolism and apoptosis, VDAC may represent the common point between these two broad families of pathologies. Located in the outer mitochondrial membrane, VDAC forms channels that control the flux of ions and metabolites across the mitochondrion thus mediating the organelle's cross-talk with the rest of the cell. Furthermore, the interaction with both pro-apoptotic and anti-apoptotic factors makes VDAC a gatekeeper for mitochondria-mediated cell death and survival signaling pathways. Unfortunately, the lack of an evident druggability of this protein, since it has no defined binding or active sites, makes the quest for VDAC interacting molecules a difficult tale. Pharmacologically active molecules of different classes have been proposed to hit cancer and neurodegeneration. In this work, we provide an exhaustive and detailed survey of all the molecules, peptides, and microRNAs that exploit VDAC in the treatment of the two examined classes of pathologies. The mechanism of action and the potential or effectiveness of each compound are discussed.

Sub-lethal effects and bioconcentration of the human pharmaceutical clotrimazole in rainbow trout (Oncorhynchus mykiss)

The aim of this study was to characterize biomarker responses, haematological profiles, structural changes and uptake in juvenile rainbow trout exposed to clotrimazole (CLO) at three concentrations (0.01 - [lowest environmentally relevant concentration], 1.0 [highest environmentally relevant concentration] and 10 μg L(-1)) in a semi-static system over a period of 42 days. Antioxidant defence enzymes, which responded to CLO exposure, changed the oxidative stress status of cells, but no differences were observed in lipid peroxidation. Clotrimazole triggered a biphasic response of CYP3A-like activity in liver microsomes, which may indicate a detoxification process in the liver. Histopathological alterations were most pronounced in kidneys and testes in the group exposed to 10 μg L(-1). Structural changes in the kidney included tubulonephrosis and hyaline droplet degeneration in the tubular epithelial cells. The relative proportions of germ cells in testes were changed: The number of spermatozoa was reduced, and the spermatogonia and spermatocytes were increased. The highest CLO concentration was detected in fish liver (3710 ng per gram wet tissue) and kidney (4280 ng per gram wet tissue). Depuration half-life was estimated to be 72, 159, and 682 h in liver, muscle, and kidney, respectively. Taken together, these results provide valuable toxicological data on the effects of CLO on aquatic non-target organisms, which could be useful for further understanding of the potential risks in the real aquatic environment.

Hypoxic stress induces transient receptor potential melastatin 2 (TRPM2) channel expression in adult rat cardiac fibroblasts

When cardiac tissue is exposed to hypoxia, myocytes are damaged, while fibroblasts are activated. However, it is unknown what changes are induced by hypoxia in cardiac fibroblasts. In this study, using the whole cell patch-clamp technique, we investigated the effect of hypoxia on membrane currents in fibroblasts primarily cultured from adult rat hearts. Cardiac fibroblasts were incubated for 24 h under normoxic or hypoxic conditions using Anaeropack. Hypoxia increased a current which reversed at around -20 mV in the cardiac fibroblasts. This current was inhibited by clotrimazole, which is an inhibitor of transient receptor potential melastatin 2 (TRPM2) channel and intermediate-conductance Ca(2+)-activated K(+) channel (KCa3.1). ADP ribose in the pipette solution enhanced this current. Quantitative RT-PCR revealed that mRNA of TRPM2, but not that of KCa3.1, was increased by hypoxia. RNA interference of TRPM2 prevented the development of the hypoxia-induced current. H(2)O(2), an activator of TRPM2 channel, induced a higher [Ca(2+)](i) elevation in hypoxia-exposed cardiac fibroblasts than that in normoxia-exposed cells. We conclude that hypoxia induces TRPM2 channel expression in adult rat cardiac fibroblasts.

Synthesis and characterization of tritylthioethanamine derivatives with potent KSP inhibitory activity

Assembly of a bipolar mitotic spindle requires the action of class 5 kinesins, and inhibition or depletion of this motor results in mitotic arrest and apoptosis. S-Trityl-l-cysteine is an allosteric inhibitor of vertebrate Kinesin Spindle Protein (KSP) that has generated considerable interest due to its anti-cancer properties, however, poor pharmacological properties have limited the use of this compound. We have modified the triphenylmethyl and cysteine groups, guided by biochemical and cell-based assays, to yield new cysteinol and cysteamine derivatives with increased inhibitory activity, greater efficacy in model systems, and significantly enhanced potency against the NCI60 tumor panel. These results reveal a promising new class of conformationally-flexible small molecules as allosteric KSP inhibitors for use as research tools, with activities that provide impetus for further development as anti-tumor agents.

Discovery of novel SERCA inhibitors by virtual screening of a large compound library

Two screening protocols based on recursive partitioning and computational ligand docking methodologies, respectively, were employed for virtual screens of a compound library with 345,000 entries for novel inhibitors of the enzyme sarco/endoplasmic reticulum calcium ATPase (SERCA), a potential target for cancer chemotherapy. A total of 72 compounds that were predicted to be potential inhibitors of SERCA were tested in bioassays and 17 displayed inhibitory potencies at concentrations below 100 μM. The majority of these inhibitors were composed of two phenyl rings tethered to each other by a short link of one to three atoms. Putative interactions between SERCA and the inhibitors were identified by inspection of docking-predicted poses and some of the structural features required for effective SERCA inhibition were determined by analysis of the classification pattern employed by the recursive partitioning models.

Intrasperm Ca2+ modulation and human ejaculated sperm viability: influence of miconazole, clotrimazole and loperamide

Elevation of intrasperm Ca2+ is reported to influence viability of ejaculated spermatozoa. Human spermatozoa possess inositol triphosphate (IP3)-sensitive Ca2+ stores, which can be targeted for increasing intrasperm Ca2+ level. The influence of agents affecting Ca2+ homeostasis has been investigated. Miconazole nitrate, clotrimazole and loperamide hydrochloride produced a dose- and time-dependent decrease in viability, each requiring respectively 0.5, 1.0 and 1.0 mM for producing death of all sperm cells immediately upon addition to ejaculated human semen samples. The reduction in sperm viability was accompanied by elevation of intrasperm Ca2+ and was not affected by presence or absence of extracellular Ca2+. Significantly (P < 0.05) less time was required for producing complete loss of sperm viability and increasing intrasperm Ca2+ when any of these drugs was added to sperm cells previously treated with selected agents affecting Ca2+ homeostasis. This enhanced spermicidal activity of miconazole, clotrimazole and loperamide appeared to be due to further mobilization of Ca2+ from partially depleted intrasperm Ca2+ stores. Synergism of spermicidal activity and intrasperm Ca2+ elevation by miconazole or clotrimazole was observed when Ca2+ efflux from sperm cells was simultaneously inhibited by 2′,4′-dichlorobenzamil hydrochloride, a Na+-Ca2+ exchange inhibitor. The spermicidal activity of miconazole, clotrimazole or loperamide due to elevation of intrasperm Ca2+ and its synergism, therefore, has great potential for exploitation of these drugs as contact spermicides.

Structure-based virtual screening for novel inhibitors of the sarco/endoplasmic reticulum calcium ATPase and their experimental evaluation

A public compound library with 260,000 compounds was screened virtually by computational docking for novel inhibitors of the transmembrane enzyme sarco/endoplasmic reticulum calcium ATPase (SERCA). Docking was performed with the program GOLD in conjunction with a high resolution X-ray crystal structure of SERCA. Compounds that were predicted to be active were tested in bioassays. Nineteen novel compounds were discovered that were capable of inhibiting the ATP hydrolysis activity of SERCA at concentrations below 50 microM. Crucial enzyme/inhibitor interactions were identified by analyzing the docking-predicted binding poses of active compounds. Like other SERCA inhibitors, the newly discovered compounds are of considerable medicinal interest because of their potential for cancer chemotherapy.

Effect of clotrimazole on the pump cycle of the Na,K-ATPase

The effect of the antimycotic drug clotrimazole (CLT) on the Na,K-ATPase was investigated using fluorescence and electrical measurements. The results obtained by steady-state fluorescence experiments with the electrochromic styryl dye RH421 were combined with those achieved by a pre-steady-state method based on fast solution exchange on a solid supported membrane that adsorbs the protein. Both techniques are suitable for monitoring the electrogenic steps of the pump cycle and are in general complementary, yielding distinct kinetic information. The experiments show clearly that CLT affects specific partial reactions of the pump cycle of the Na,K-ATPase with an affinity in the low micromolar range and in a reversible manner. All results can be consistently explained by proposing the CLT-promoted formation of an ion-occluded-CLT-bound conformational E(2) state, E(2)(CLT)(X(2)) that acts as a "dead-end" side track of the pump cycle, where X stands for H+ or K+. Na+ binding, enzyme phosphorylation, and Na+ transport were not affected by CLT, and at high CLT concentrations approximately (1/3) of the enzyme remained active in the physiological transport mode. The presence of Na+ and K+ destabilized the inactivated form of the Na,K-ATPase.

Clotrimazole, an antifungal drug possessing diverse actions, increases membrane permeation of cadmium in rat thymocytes

In previous study, clotrimazole, an antifungal drug, exerted potent cytotoxic action on rat thymocytes in presence of metal divalent cations such as Cd(2+) and Pb(2+). To reveal one of toxicological characteristics of clotrimazole, we examined the effect of clotrimazole on intracellular concentration of metal divalent cations by flow cytometer with fluo-3, a fluorescent. Simultaneous application of clotrimazole and CdCl(2) significantly decreased the cell viability although their concentrations were not cytotoxic, respectively. Clotrimazole alone increased the intensity of fluo-3 fluorescence, suggesting an increased concentration of intracellular Ca(2+). The intensity of fluo-3 fluorescence augmented by the combination of clotrimazole and CdCl(2) was much higher than that by respective agents. Removal of external Ca(2+) further increased the intensity of fluorescence augmented by the combination. Furthermore, the application of MnCl(2) did not attenuate the intensity in the presence of CdCl(2). Therefore, it is suggested that the augmentation of fluo-3 fluorescence in the simultaneous presence of clotrimazole and CdCl(2) is Cd(2+)-dependent. Clotrimazole may increase membrane permeation of Cd(2+).

Complete inhibition of the Pdr5p multidrug efflux pump ATPase activity by its transport substrate clotrimazole suggests that GTP as well as ATP may be used as an energy source

The yeast Pdr5p transporter is a 160 kDa protein that effluxes a large variety of xenobiotic compounds. In this study, we characterize its ATPase activity and demonstrate that it has biochemical features reminiscent of those of other ATP-binding cassette multidrug transporters: a relatively high Km for ATP (1.9 mM), inhibition by orthovanadate, and the ability to specifically bind an azidoATP analogue at the nucleotide-binding domains. Pdr5p-specific ATPase activity shows complete, concentration-dependent inhibition by clotrimazole, which is also known to be a potent transport substrate. Our results indicate, however, that this inhibition is noncompetitive and caused by the interaction of clotrimazole with the transporter at a site that is distinct from the ATP-binding domains. Curiously, Pdr5p-mediated transport of clotrimazole continues at intracellular concentrations of substrate that should eliminate all ATPase activity. Significantly, however, we observed that the Pdr5p has GTPase and UTPase activities that are relatively resistant to clotrimazole. Furthermore, the Km(GTPase) roughly matches the intracellular concentrations of the nucleotide reported for yeast. Using purified plasma membrane vesicles, we demonstrate that Pdr5p can use GTP to fuel substrate transport. We propose that Pdr5p increases its multidrug transport substrate specificity by using more than one nucleotide as an energy source.

Clotrimazole inhibits and modulates heterologous association of the key glycolytic enzyme 6-phosphofructo-1-kinase

Clotrimazole is an antifungal azole derivative recently recognized as a calmodulin antagonist with promising anticancer effects. This property has been correlated with the ability of the drug to decrease the viability of tumor cells by inhibiting their glycolytic flux and consequently decreasing the intracellular concentration of ATP. The effects of clotrimazole on cell glycolysis and ATP production are considered to be due to the detachment of the glycolytic enzymes from the cytoskeleton. Here, we show that clotrimazole directly inhibits the key glycolytic enzyme 6-phosphofructo-1-kinase (PFK). This property is independent of the anti-calmodulin activity of the drug, since it is not mimicked by the classical calmodulin antagonist compound 48/80. However, the clotrimazole-inhibited enzyme can be activated by calmodulin, even though calmodulin has no effect on PFK activity in the absence of the drug. Clotrimazole alone induces the dimerization of PFK reducing the population of tetramers, which is not observed when calmodulin is also present. Since PFK dimers are less active than PFK tetramers, this can explain the inhibitory effect of clotrimazole on the enzyme. Additionally, clotrimazole positively modulates the association of PFK with erythrocyte membranes. Altogether, our data support a hitherto unrecognized action of clotrimazole as a negative modulator of glycolytic flux through direct inhibition of the key enzyme PFK.

Clotrimazole, an antifungal drug possessing diverse actions, increases the vulnerability to cadmium in lymphocytes dissociated from rat thymus

Since clotrimazole, known as an antifungal drug, exerts diverse actions on cellular functions, it is expected that clotrimazole can be used for other purposes. This antifungal drug protects the cells overloaded with Ca(2+) by A23187, a calcium ionophore. Therefore, the agent may prevent the cells from death induced by heavy metals such as CdCl(2), PbCl(2), or HgCl(2) that are respectively proposed to increase intracellular Ca(2+) concentration. To test this possibility, we have examined the effect of clotrimazole on the cells simultaneously treated with CdCl(2), PbCl(2), or HgCl(2) using rat thymocytes and a flow cytometer with fluorescent probes. The simultaneous application of clotrimazole and CdCl(2) significantly decreased cell viability, even though the concentrations of both were ineffective at affecting the viability. The significant decrease in cell viability was not due to the inhibition of Ca(2+)-ATPase and Ca(2+)-dependent K(+) channels that were induced by clotrimazole. The simultaneous application increased the population of cells with phosphatidylserine exposed on membrane surface, indicating the change in asymmetrical distribution of membrane phospholipids. Furthermore, the cytotoxicity induced by the combination of clotrimazole and CdCl(2) under nominally Ca(2+)-free condition was more profound than that under normal Ca(2+) condition. Therefore, the membrane may be a target for the cytotoxic action of clotrimazole and CdCl(2) that were simultaneously applied. It is also the case for PbCl(2), but not the case for HgCl(2). It is concluded that clotrimazole can modulate the cytotoxicity of some heavy metals.

Cytochrome P450 enzymes: Central players in cardiovascular health and disease

Cardiovascular disease (CVD) is a human health crisis that remains the leading cause of death worldwide. The cytochrome P450 (CYP) class of enzymes are key metabolizers of both xenobiotics and endobiotics. Many CYP enzyme families have been identified in the heart, endothelium and smooth muscle of blood vessels. Furthermore, mounting evidence points to the role of endogenous CYP metabolites, such as epoxyeicosatrienoic acids (EETs), hydroxyeicosatetraenoic acids (HETEs), prostacyclin (PGI(2)), aldosterone, and sex hormones, in the maintenance of cardiovascular health. Emerging science and the development of genetic screening have provided us with information on the differences in CYP expression among populations and groups of individuals. With this information, a link between CYP expression and activity and CVD, such as hypertension, coronary artery disease (CAD), myocardial infarction, heart failure, stroke, and cardiomyopathy and arrhythmias, has been established. In fact many currently used therapeutic modalities in CVD owe their therapeutic efficacy to their effect on CYP metabolites. Thus, the evidence for the involvement of CYP in CVD is numerous. Concentrating on treatment modalities that target the CYP pathway makes ethical sense for the affected individuals and decreases the socioeconomic burden of this disease. However, more research is needed to allow the integration of this information into a clinical setting.

Clotrimazole Inhibits the Ca2+-ATPase (SERCA) by Interfering with Ca2+ Binding and Favoring the E2 Conformation

Clotrimazole (CLT) is an antimycotic imidazole derivative that is known to inhibit cytochrome P-450, ergosterol biosynthesis and proliferation of cells in culture, and to interfere with cellular Ca(2+) homeostasis. We found that CLT inhibits the Ca(2+)-ATPase of rabbit fast-twitch skeletal muscle (SERCA1), and we characterized in detail the effect of CLT on this calcium transport ATPase. We used biochemical methods for characterization of the ATPase and its partial reactions, and we also performed measurements of charge movements following adsorption of sarcoplasmic reticulum vesicles containing the ATPase onto a gold-supported biomimetic membrane. CLT inhibits Ca(2+)-ATPase and Ca(2+) transport with a K(I) of 35 mum. Ca(2+) binding in the absence of ATP and phosphoenzyme formation by the utilization of ATP in the presence of Ca(2+) are also inhibited within the same CLT concentration range. On the other hand, phosphoenzyme formation by utilization of P(i) in the absence of Ca(2+) is only minimally inhibited. It is concluded that CLT inhibits primarily Ca(2+) binding and, consequently, the Ca(2+)-dependent reactions of the SERCA cycle. It is suggested that CLT resides within the membrane-bound region of the transport ATPase, thereby interfering with binding and the conformational effects of the activating cation.

A low toxicity maintenance regime, using eicosapentaenoic acid and readily available drugs, for mantle cell lymphoma and other malignancies with excess cyclin D1 levels

Mantle cell lymphoma is a difficult to treat non-Hodgkin's lymphoma (NHL) whose biochemistry is unusually well characterised. Almost all and perhaps all patients overexpress the cyclin D1 protein which is crucial in driving cells from the G1 to the S phase. This overexpression may be responsible for the refractoriness. Despite this understanding, treatments for mantle cell lymphoma are based on standard NHL regimes of cyclophosphamide, doxorubicin, vincristine and prednisone, perhaps supplemented with the monoclonal antibody rituximab. There has never been any attempt to direct treatment to the cyclin D1 mechanism or to angiogenesis which is now known to be important in all lymphomas. Both these targets lend themselves to long-term maintenance regimes of relatively low toxicity which can be used as adjuvants to standard therapy. Agents which have recently been shown to block cyclin D1 translation by regulating calcium levels are the unsaturated essential fatty acid, eicosapentaenoic acid (EPA), the antidiabetic thiazolidinediones, and the antifungal agent, clotrimazole. Two types of agent which have been shown to inhibit angiogenesis are the teratogen, thalidomide, and the selective inhibitors of cyclo-oxygenase 2 (COX-2). Retinoids exert synergistic effects with EPA and have been shown to inhibit both tumour growth and angiogenesis. The mechanisms of action of these various agents are discussed, and specific suggestions are made for low toxicity maintenance therapy of mantle cell lymphoma and of other tumours which overexpress cyclin D1.

Transport processes in Plasmodium falciparum-infected erythrocytes: potential as new drug targets

Plasmodium falciparum infection induces alterations in the transport properties of infected erythrocytes that have recently been defined using electrophysiological techniques. Mechanisms responsible for transport of substrates into intraerythrocytic parasites have also been clarified by studies of three substrate-specific (hexose, nucleoside and aquaglyceroporin) parasite plasma membrane transporters. These have been characterised functionally using the Xenopus laevis oocyte heterologous expression system. The same expression system is currently being used to define the function of parasite 'P' type ATPases responsible for intraparasitic [Ca(2+)] homeostasis. We review studies on these transport processes and examine their potential as novel drug targets.

Neuroprotective effects of the antifungal drug clotrimazole

Pretreatment with 10 microM of the antifungal drug clotrimazole potently reduced the death of cultured rat cerebellar granule cells induced by oxygen/glucose deprivation, and the excitotoxic effect of glutamate on cultured hippocampal neurons and cerebellar granule cells. In patch-clamped hippocampal pyramidal neurons, 10-50 microM clotrimazole caused a decrease in the amplitude of N-methyl-D-aspartate (NMDA) receptor-mediated currents. Glutamate induced intracellular Ca(2+) overload, as measured by Fluo-3 confocal fluorescence imaging, while clotrimazole reduced Ca(2+) overload and promoted the recovery of intracellular calcium homeostasis after glutamate treatment. Using tetramethylrhodamine ethyl ester fluorescence as a marker of mitochondrial membrane potential we found that clotrimazole prevented the glutamate-induced loss of mitochondrial membrane potential. Our data provide evidence that the protective effect of clotrimazole against oxygen/glucose deprivation and excitotoxicity is due to the ability of this drug to partially block NMDA receptor-gated channel, thus causing both reduced calcium overload and lower probability of the mitochondrial potential collapse.

Testosterone, cytochrome P450, and cardiac hypertrophy

Cytochrome P450 mono-oxygenases (CYP) play an essential role in steroid metabolism, and there is speculation that sex hormones might influence cardiac mass and physiology. As CYP mono-oxygenases activity is frequently altered during disease, we tested our hypothesis that CYP mono-oxygenase expression and testosterone metabolism are altered in cardiac hypertrophy. We investigate major CYP mono-oxygenase isoforms and other steroid-metabolizing enzymes and the androgen receptor in normal, hypertrophic, and assist device-supported human hearts and in spontaneously hypertensive rats (SHR). We show increased and idiosyncratic metabolism of testosterone in hypertrophic heart and link these changes to altered CYP mono-oxygenase expression. We show significant induction of 5-alpha steroid reductase and P450 aromatase gene expression and enhanced production of dihydrotestosterone, which can be inhibited by the 5-alpha reductase inhibitor finasteride. We show increased gene expression of the androgen receptor and increased levels of lipid peroxidation in diseased hearts, the latter being markedly inhibited by CYP mono-oxygenase inactivation. We show alpha-MHC to be significantly repressed in cardiac hypertrophy and restored to normal on testosterone supplementation. We conclude that heart-specific steroid metabolism is of critical importance in cardiac hypertrophy

Inhibition of sarcoplasmic reticulum Ca2+-ATPase by miconazole

The inhibition of sarcoplasmic reticulum Ca2+-ATPase activity by miconazole was dependent on the concentration of ATP and membrane protein. Half-maximal inhibition was observed at 12 microM miconazole when the ATP concentration was 50 microM and the membrane protein was 0.05 mg/ml. When ATP was 1 mM, a low micromolar concentration of miconazole activated the enzyme, whereas higher concentrations inhibited it. A qualitatively similar response was observed when Ca2+ transport was measured. Likewise, the half-maximal inhibition value was higher when the membrane concentration was raised. Phosphorylation studies carried out after sample preequilibration in different experimental settings shed light on key partial reactions such as Ca2+ binding and ATP phosphorylation. The miconazole effect on Ca2+-ATPase activity can be attributed to stabilization of the Ca2+-free enzyme conformation giving rise to a decrease in the rate of the Ca2+ binding transition. The phosphoryl transfer reaction was not affected by miconazole.

Effects of clotrimazole on transport mediated by multidrug resistance associated protein 1 (MRP1) in human erythrocytes and tumour cells

Clotrimazole has been shown to have potent anti-malarial activity in vitro, one possible mechanism being inhibition of oxidized glutathione (GSSG) export from the infected human red blood cells or from the parasite itself. Efflux of GSSG from normal erythrocytes is mediated by a high affinity glutathione S-conjugate transporter. This paper shows that transport of the model substrate, 3 microm dinitrophenyl S-glutathione, across erythrocyte membranes is inhibited by multidrug resistance-associated protein 1 (MRP1)-specific antibody, QCRL-3, strongly suggesting that the high affinity transport is mediated by MRP1. The rates of transport observed with membrane vesicles prepared from erythrocytes or from multidrug resistant tumour cells show a similar pattern of responses to applied reduced glutathione, GSSG and MRP1 inhibitors (indomethacin, MK571) further supporting the conclusion that the high affinity transporter is MRP1. In both erythrocytes and MRP1-expressing tumour cells, MRP1-associated transport is inhibited by clotrimazole over the range 2-20 microm, and the inhibitory effect leads to increases in accumulation of MRP1 substrates, vincristine and calcein, and decreases in calcein efflux from intact MRP1-expressing human tumour cells. It also results in increased sensitivity to daunorubicin of the multidrug resistant cells, L23/R but not the sensitive parent L23/P cells. These results demonstrate that clotrimazole can inhibit the MRP1 which is present in human erythrocytes, an effect that may contribute to, though not fully account for, its anti-malarial action.

Calcium regulation in the intraerythrocytic malaria parasite Plasmodium falciparum

The regulation of intracellular Ca(2+) in the intraerythrocytic form of the human malaria parasite, Plasmodium falciparum, was investigated using parasites 'isolated' from their host cells by saponin-permeabilisation of the erythrocyte membrane. The isolated parasites maintained tight control over their resting cytosolic Ca(2+) concentration which ranged from approximately 100 nM in the absence of extracellular Ca(2+) to approximately 700 nM in the presence of 1 mM extracellular Ca(2+). The parasite has two functionally discrete intracellular Ca(2+) stores. One is an 'endoplasmic reticulum (ER)-like' store, the other an 'acidic store'. The ER-like store was discharged by cyclopiazonic acid (CPA), an inhibitor of sarco/endoplasmic reticulum Ca(2+)-ATPases (SERCAs) of animal and plant cells, but not by thapsigargin (TG), a more specific inhibitor of SERCAs of animal cells. The acidic store was discharged by nigericin and by NH(4)(+). The amount of Ca(2+) in the ER-like store increased with increasing extracellular Ca(2+) concentration, whereas the amount of Ca(2+) in the acidic store did not. Ca(2+) released from the ER-like store by CPA was cleared from the parasite cytosol by uptake into the acidic store (over a range of extracellular Ca(2+) concentrations), consistent with the acidic store serving as a Ca(2+) reservoir within the intracellular parasite.

Endoplasmic reticulum Ca2+-ATPase pump is up-regulated in calcium-transporting dental enamel cells: a non-housekeeping role for SERCA2b

Dental enamel-forming cells face a major challenge to avoid the cytotoxic effects of excess calcium. We have characterized sarcoplasmic/endoplasmic reticulum calcium-ATPase pumps (SERCA) in rat enamel cells to address the proposal that non-mitochondrial calcium stores play a dominant role in transcellular calcium transport. A single major isoform, SERCA2b, was detected during the protein-secretory and calcium-transport stages of enamel formation using reverse-transcriptase PCR, cDNA cloning, Northern analysis and immunoblotting. Most importantly, SERCA2b exhibited a specific 3-fold up-regulation to high expression levels during calcium transport, as determined by quantitative immunoblotting and ATPase assays. Sensitivity of the calcium-dependent ATPase to thapsigargin and three other SERCA inhibitors was characterized. These findings indicate that enamel cells are well-equipped to sequester calcium in endoplasmic reticulum stores and so protect against calcium toxicity, associate SERCA with transcellular calcium transport for the first time, and establish SERCA2b as a molecular and pharmacological target for future investigations of calcium transcytosis. The observed physiological regulation in enamel cells contradicts the widespread perception that SERCA2b is restricted to general housekeeping duties.

Glucocorticoid modulation of protein phosphorylation and sarcoplasmic reticulum function in rat myocardium

To decipher the mechanism(s) underlying glucocorticoid action on cardiac contractile function, this study investigated the effects of adrenalectomy and dexamethasone treatment on the contents of sarcoplasmic reticulum (SR) Ca(2+)-cycling proteins, their phosphorylation by endogenous Ca(2+)/calmodulin-dependent protein kinase II (CaM kinase II), and SR Ca(2+) sequestration in the rat myocardium. Cardiac SR vesicles from adrenalectomized rats displayed significantly diminished rates of ATP-energized Ca(2+) uptake in vitro compared with cardiac SR vesicles from control rats; in vivo administration of dexamethasone to adrenalectomized rats prevented the decline in SR function. Western immunoblotting analysis showed that the relative protein amounts of ryanodine receptor/Ca(2+)-release channel, Ca(2+)-ATPase, calsequestrin, and phospholamban were neither diminished significantly by adrenalectomy nor elevated by dexamethasone treatment. However, the relative amount of SR-associated CaM kinase II protein was increased 2.5- to 4-fold in dexamethasone-treated rats compared with control and adrenalectomized rats. Endogenous CaM kinase II activity, as judged from phosphorylation of ryanodine receptor, Ca(2+)-ATPase, and phospholamban protein, was also significantly higher (50--80% increase) in the dexamethasone-treated rats. The stimulatory effect of CaM kinase II activation on Ca(2+) uptake activity of SR was significantly depressed after adrenalectomy and greatly enhanced after dexamethasone treatment. These findings identify the SR as a major target for glucocorticoid actions in the heart and implicate modification of the SR CaM kinase II system as a component of the mechanisms by which dexamethasone influences SR Ca(2+)-cycling and myocardial contraction.

Clotrimazole inhibits smooth muscle cell proliferation and has a vasodilator effect on resistance arteries

Clotrimazole (CLT) is a drug known to interfere with cellular calcium homeostasis, which in turn is reported to intervene in cell proliferation and in the reactivity of small blood vessels. Experiments were designed to test the influence of CLT on the proliferative and vasorelaxant effect of bradykinin (BK) and on calcium homeostasis in smooth muscle cells (SMC). To this purpose two model systems were employed: (i) cultured human smooth muscle cells (HSMC), and (ii) isolated resistance arteries maintained in an organ bath. The effect of various concentrations of CLT (2-15 microM) on BK-induced proliferation of HSMC was quantitated by spectrometry following [3H]-thymidine incorporation, and intracellular calcium [Ca+]i was determined by spectrofluorimetry using Fura 2-AM assay. In other experiments the roles of BK receptor (AB2) and of thapsigargin were assessed. The reactivity of the resistance arteries was measured by the myograph technique, and the effects of BK, CLT, and NO synthase blocker, L-NAME were evaluated. The results showed that 10 microM CLT: (i) inhibits the BK-induced proliferation of HSMC by 45-50%: (ii) prevents the rise of [Ca2+]i induced by BK (120.8 +/- 12.4 nM vs. 235.8 +/- 34.1 nM), an cffect similar to that of "classic" L-type calcium channels blockers: (iii) reduces the release of Ca2+ entry induced by thapsigargin suggesting a possible inhibition of the capacitative Ca2+ entry. Organ bath assays showed that CLT enhanced the BK-induced relaxation of the resistance arteries by an endothelium NO-independent pathway. Together, these data suggest that the mechanism of action of CLT on SMC implies mainly a modification of intracellular calcium homeostasis, with a minor contribution of BK B2 receptors. These new distinctive features of CLT effects suggest the potential use of this drug in the therapy of cardiovascular diseases associated with SMC increased proliferation and impeded relaxation in small arteries, such as atherosclerosis and restenosis.

Novel effects of clotrimazole on Ca2+ signaling in Madin Darby canine kidney cells

The effect of clotrimazole on Ca2+ signaling in Madin Darby canine kidney (MDCK) cells was investigated by using fura-2 as a Ca2+ indicator. Clotrimazole (1-30 microM) induced a concentration-dependent [Ca2+]i increase. The [Ca2+]i increase comprised an initial rise and a slow decay. External Ca2+ removal partly inhibited the Ca2+ signals by reducing both the initial rise and the decay phase, indicating that clotrimazole triggered both Ca2+ influx and Ca2+ release. Pretreatment with 30 microM clotrimazole in Ca2+-free medium abolished the Ca2+ release induced by thapsigargin (1 microM), an endoplasmic reticulum Ca2+ pump inhibitor, and conversely, pretreatment with thapsigargin prevented clotrimazole from releasing more Ca2+. This suggests that the thapsigargin-sensitive Ca2+ store is the source of clotrimazole-induced Ca2+ release. Clotrimazole (10 microM) triggered Mn2+ quench of fura-2 fluorescence which was partly inhibited by 1 mM La3+. Addition of 3 mM Ca2+ induced a [Ca2+]i increase after preincubation with 10 microM clotrimazole in Ca2+-free medium, indicating that clotrimazole activated capacitative Ca2+ entry. However, 10 and 30 microM clotrimazole inhibited 1 microM thapsigargin-induced capacitative Ca2+ entry by 21% and 74%, respectively. Pretreatment with 40 microM aristolochic acid to inhibit phospholipase A2 reduced 30 microM clotrimazole-induced Ca2+ release by 51%, but inhibiting phospholipase C with 2 microM U73122 had little effect. This implies that clotrimazole induces Ca2+ release in an IP3-independent manner, which could be modulated by phospholipase A2-coupled events.

Effect of cytochrome P-450 inhibitors econazole, bifonazole and clotrimazole on prostanoid formation

1. The present study was carried out to clarify the effect of the imidazole antimycotics econazole, bifonazole and clotrimazole on prostanoid biosynthesis. Osteoblast-like MC3T3-E1 cells stimulated by endothelin-1, melittin, ionomycin or arachidonic acid showed diminished prostaglandin E(2) (PGE(2)) production upon pretreatment with econazole. Following pretreatment with bifonazole, stimulation with ionomycin or arachidonic acid also resulted in decreased PGE(2) formation. Clotrimazole inhibited ionomycin but not arachidonic acid stimulated PGE(2) synthesis in MC3T3-E1 cells. 2. The results observed in osteoblast-like UMR-106 cells pretreated with econazole, bifonazole or clotrimazole and stimulated by arachidonic acid were similar with the exception of clotrimazole which was a more effective inhibitor of PGE(2) biosynthesis than in MC3T3-E1 cells. 3. Upon treatment with arachidonic acid thromboxane B(2) (TXB(2)) production in human platelets was abolished completely at concentrations of the three imidazole antimycotics higher than 5 microM (IC(50)<1 microM). 4. These data were confirmed by a direct assay using purified ram seminal vesicle prostaglandin H(2) synthase-1 (PGHS-1), which clearly showed inhibitory properties of econazole (IC(50) 4.7+/-2.3 microM), bifonazole (IC(50) 9.4+/-0.8 microM) and clotrimazole (IC(50) 4.4+/-0.6 microM). 5. Summarizing, these results indicate an inhibitory effect of econazole, bifonazole and clotrimazole on PGHS-1, varying in its potency dependent on the cell system used. In addition TXB(2) formation is affected at doses even lower than those needed to suppress PGE(2) biosynthesis.

Thyroid hormone-induced overexpression of functional ryanodine receptors in the rabbit heart

Modifications in the Ca(2+)-uptake and -release functions of the sarcoplasmic reticulum (SR) may be a major component of the mechanisms underlying thyroid state-dependent alterations in heart rate, myocardial contractility, and metabolism. We investigated the influence of hyperthyroid state on the expression and functional properties of the ryanodine receptor (RyR), a major protein in the junctional SR (JSR), which mediates Ca(2+) release to trigger muscle contraction. Experiments were performed using homogenates and JSR vesicles derived from ventricular myocardium of euthyroid and hyperthyroid rabbits. Hyperthyroidism, with attendant cardiac hypertrophy, was induced by the injection of L-thyroxine (200 microg/kg body wt) daily for 7 days. Western blotting analysis using cardiac RyR-specific antibody revealed a significant increase (>50%) in the relative amount of RyR in the hyperthyroid compared with euthyroid rabbits. Ca(2+)-dependent, high-affinity [(3)H]ryanodine binding was also significantly greater ( approximately 40%) in JSR from hyperthyroid rabbits. The Ca(2+ )sensitivity of [(3)H]ryanodine binding and the dissociation constant for [(3)H]ryanodine did not differ significantly between euthyroid and hyperthyroid hearts. Measurement of Ca(2+)-release rates from passively Ca(2+)-preloaded JSR vesicles and assessment of the effect of RyR-Ca(2+)-release channel (CRC) blockade on active Ca(2+)-uptake rates revealed significantly enhanced (>2-fold) CRC activity in the hyperthyroid, compared with euthyroid, JSR. These results demonstrate overexpression of functional RyR in thyroid hormone-induced cardiac hypertrophy. Relative abundance of RyR may be responsible, in part, for the changes in SR Ca(2+) release, cytosolic Ca(2+) transient, and cardiac systolic function associated with thyroid hormone-induced cardiac hypertrophy.

Reversible inhibition of the calcium-pumping ATPase in native cardiac sarcoplasmic reticulum by a calmodulin-binding peptide. Evidence for calmodulin-dependent regulation of the V(max) of calcium transport

Calmodulin (CaM) and Ca(2+)/CaM-dependent protein kinase II (CaM kinase) are tightly associated with cardiac sarcoplasmic reticulum (SR) and are implicated in the regulation of transmembrane Ca(2+) cycling. In order to assess the importance of membrane-associated CaM in modulating the Ca(2+) pump (Ca(2+)-ATPase) function of SR, the present study investigated the effects of a synthetic, high affinity CaM-binding peptide (CaM BP; amino acid sequence, LKWKKLLKLLKKLLKLG) on the ATP-energized Ca(2+) uptake, Ca(2+)-stimulated ATP hydrolysis, and CaM kinase-mediated protein phosphorylation in rabbit cardiac SR vesicles. The results revealed a strong concentration-dependent inhibitory action of CaM BP on Ca(2+) uptake and Ca(2+)-ATPase activities of SR (50% inhibition at approximately 2-3 microM CaM BP). The inhibition, which followed the association of CaM BP with its SR target(s), was of rapid onset (manifested within 30 s) and was accompanied by a decrease in V(max) of Ca(2+) uptake, unaltered K(0.5) for Ca(2+) activation of Ca(2+) transport, and a 10-fold decrease in the apparent affinity of the Ca(2+)-ATPase for its substrate, ATP. Thus, the mechanism of inhibition involved alterations at the catalytic site but not the Ca(2+)-binding sites of the Ca(2+)-ATPase. Endogenous CaM kinase-mediated phosphorylation of Ca(2+)-ATPase, phospholamban, and ryanodine receptor-Ca(2+) release channel was also strongly inhibited by CaM BP. The inhibitory action of CaM BP on SR Ca(2+) pump function and protein phosphorylation was fully reversed by exogenous CaM (1-3 microM). A peptide inhibitor of CaM kinase markedly attenuated the ability of CaM to reverse CaM BP-mediated inhibition of Ca(2+) transport. These findings suggest a critical role for membrane-bound CaM in controlling the velocity of Ca(2+) pumping in native cardiac SR. Consistent with its ability to inhibit SR Ca(2+) pump function, CaM BP (1-2.5 microM) caused marked depression of contractility and diastolic dysfunction in isolated perfused, spontaneously beating rabbit heart preparations. Full or partial recovery of contractile function occurred gradually following withdrawal of CaM BP from the perfusate, presumably due to slow dissociation of CaM BP from its target sites promoted by endogenous cytosolic CaM.

Potent antimalarial activity of clotrimazole in in vitro cultures of Plasmodium falciparum

The increasing resistance of the malaria parasite Plasmodium falciparum to currently available drugs demands a continuous effort to develop new antimalarial agents. In this quest, the identification of antimalarial effects of drugs already in use for other therapies represents an attractive approach with potentially rapid clinical application. We have found that the extensively used antimycotic drug clotrimazole (CLT) effectively and rapidly inhibited parasite growth in five different strains of P. falciparum, in vitro, irrespective of their chloroquine sensitivity. The concentrations for 50% inhibition (IC(50)), assessed by parasite incorporation of [(3)H]hypoxanthine, were between 0.2 and 1.1 microM. CLT concentrations of 2 microM and above caused a sharp decline in parasitemia, complete inhibition of parasite replication, and destruction of parasites and host cells within a single intraerythrocytic asexual cycle (approximately 48 hr). These concentrations are within the plasma levels known to be attained in humans after oral administration of the drug. The effects were associated with distinct morphological changes. Transient exposure of ring-stage parasites to 2.5 microM CLT for a period of 12 hr caused a delay in development in a fraction of parasites that reverted to normal after drug removal; 24-hr exposure to the same concentration caused total destruction of parasites and parasitized cells. Chloroquine antagonized the effects of CLT whereas mefloquine was synergistic. The present study suggests that CLT holds much promise as an antimalarial agent and that it is suitable for a clinical study in P. falciparum malaria.