Comparing vibrational spectra of free bumetanide and its solutions

Bumetanide, which is known as a potent diuretic, is currently under investigation for its potential anti-epileptic effects in neonatal seizures. The purpose of this study was to examine the molecular structure of bumetanide both in the free form and its solutions via vibrational spectra (FT-IR, FT-Raman spectroscopies) and quantum chemical calculations. FT-IR and FT-Raman spectra of the title compound were recorded for the solid phase and the solutions of DMSO and ethanol. Optimized molecular geometry and vibrational wavenumbers of bumetanide were calculated by DFT/B3LYP functional with 6-31G(d,p), 6-31G++(d,p) and 6-311++G(d,p) basis sets. The assignment of the vibrational modes were performed based on total energy distribution (TED). The same calculations were performed for the molecule in DMSO and ethanol solutions using the polarizable conductor continuum model (CPCM) method. Lastly, probable donor-acceptor interactions of the molecule were examined with NBO analysis in different media. In all forms of bumetanide (the free molecule and the other solvents), some significant changes were observed in the dihedral angles and the vibrational frequencies.

A novel prodrug-based strategy to increase effects of bumetanide in epilepsy

OBJECTIVE

There is considerable interest in using bumetanide, a chloride importer Na-K-Cl cotransporter antagonist, for treatment of neurological diseases, such as epilepsy or ischemic and traumatic brain injury, that may involve deranged cellular chloride homeostasis. However, bumetanide is heavily bound to plasma proteins (~98%) and highly ionized at physiological pH, so that it only poorly penetrates into the brain, and chronic treatment with bumetanide is compromised by its potent diuretic effect.

METHODS

To overcome these problems, we designed lipophilic and uncharged prodrugs of bumetanide that should penetrate the blood-brain barrier more easily than the parent drug and are converted into bumetanide in the brain. The feasibility of this strategy was evaluated in mice and rats.

RESULTS

Analysis of bumetanide levels in plasma and brain showed that administration of 2 ester prodrugs of bumetanide, the pivaloyloxymethyl (BUM1) and N,N-dimethylaminoethylester (BUM5), resulted in significantly higher brain levels of bumetanide than administration of the parent drug. BUM5, but not BUM1, was less diuretic than bumetanide, so that BUM5 was further evaluated in chronic models of epilepsy in mice and rats. In the pilocarpine model in mice, BUM5, but not bumetanide, counteracted the alteration in seizure threshold during the latent period. In the kindling model in rats, BUM5 was more efficacious than bumetanide in potentiating the anticonvulsant effect of phenobarbital.

INTERPRETATION

Our data demonstrate that the goal of designing bumetanide prodrugs that specifically target the brain is feasible and that such drugs may resolve the problems associated with using bumetanide for treatment of neurological disorders.

Diuretics prime plant immunity in Arabidopsis thaliana

Plant activators are agrochemicals that activate the plant immune system, thereby enhancing disease resistance. Due to their prophylactic and durable effects on a wide spectrum of diseases, plant activators can provide synergistic crop protection when used in combination with traditional pest controls. Although plant activators have achieved great success in wet-rice farming practices in Asia, their use is still limited. To isolate novel plant activators applicable to other crops, we screened a chemical library using a method that can selectively identify immune-priming compounds. Here, we report the isolation and characterization of three diuretics, bumetanide, bendroflumethiazide and clopamide, as immune-priming compounds. These drugs upregulate the immunity-related cell death of Arabidopsis suspension-cultured cells induced with an avirulent strain of Pseudomonas syringae pv. tomato in a concentration-dependent manner. The application of these compounds to Arabidopsis plants confers disease resistance to not only the avirulent but also a virulent strain of the pathogen. Unlike salicylic acid, an endogenous phytohormone that governs disease resistance in response to biotrophic pathogens, the three diuretic compounds analyzed here do not induce PR1 or inhibit plant growth, showing potential as lead compounds in a practical application.

Diuretics prime plant immunity in Arabidopsis thaliana

Plant activators are agrochemicals that activate the plant immune system, thereby enhancing disease resistance. Due to their prophylactic and durable effects on a wide spectrum of diseases, plant activators can provide synergistic crop protection when used in combination with traditional pest controls. Although plant activators have achieved great success in wet-rice farming practices in Asia, their use is still limited. To isolate novel plant activators applicable to other crops, we screened a chemical library using a method that can selectively identify immune-priming compounds. Here, we report the isolation and characterization of three diuretics, bumetanide, bendroflumethiazide and clopamide, as immune-priming compounds. These drugs upregulate the immunity-related cell death of Arabidopsis suspension-cultured cells induced with an avirulent strain of Pseudomonas syringae pv. tomato in a concentration-dependent manner. The application of these compounds to Arabidopsis plants confers disease resistance to not only the avirulent but also a virulent strain of the pathogen. Unlike salicylic acid, an endogenous phytohormone that governs disease resistance in response to biotrophic pathogens, the three diuretic compounds analyzed here do not induce PR1 or inhibit plant growth, showing potential as lead compounds in a practical application.

Investigation of the photochemical properties and in vitro phototoxic potential of bumetanide

The photophysical and photochemical properties of bumetanide, a sulfonamide diuretic drug, have been investigated and the photodegradation of the drug on exposure to UV-B and UV-A radiation monitored by fluorimetric and chromatographic (HPLC) methods. The main photoproducts were isolated by solid-phase extraction and liquid chromatographic procedures, and their structure elucidated by 1H-NMR and mass spectrometry. Bumetanide generates only extremely small quantities of singlet oxygen (1O2) upon irradiation in the presence of oxygen. The in vitro 3T3 N RU phototoxicity test yielded no evidence of phototoxic action.

Effect of Curing Conditions and Plasticizer Level on the Release of Highly Lipophilic Drug from Coated Multiparticulate Drug Delivery System

The study aimed to investigate the effect of triethyl citrate (TEC) plasticizer level (10, 15, and 20%), curing temperature (40, 50, and 60 degrees C) and time (0 to 168 h) on the release of a highly lipophilic drug bumetanide from pellets coated with methacrylate ester copolymer (Eudragit RS). Bumetanide was layered onto sugar pellets followed by coating with 6% Eudragit RS with and without hydroxypropyl methyl cellulose (HPMC) seal coat using Wurster Fluid Bed equipment. Coated pellets were stored for 3 months at room temperature and the release was tested in USP purified water. At 10% TEC level, increasing curing time and temperature lead to slower drug release. At 15 and 20% TEC levels, curing initially decreased drug release followed by increase in the release at longer curing time and higher temperature. Drug release from coated pellets plasticized with 15% TEC and completely cured followed zero order kinetic models. At plasticizer level of 20%, bumetanide release from the completely cured pellets was better modeled using the Higuchi's equation reflecting possible drug migration during curing. Storage led to an increase in drug release. The use of HPMC seal coat stabilized drug release after storage. It was concluded that bumetanide migration into Eudragit RS film coat was the main cause of the accelerated release after curing and storage. The drug migration during storage at room temperature was prevented by seal coating the pellets with HPMC.

Effect of the location of hydrogen abstraction on the fragmentation of diuretics in negative electrospray ionization mass spectrometry

The diuretic agents bumetanide, xipamide, indapamide, and related compounds were investigated in order to determine the effect of different ionization sites on their collisionally activated dissociation and the corresponding fragmentation pathways. Therefore, analytes were selectively alkylated, and structural analogues as well as deuterium labeled compounds synthesized, which contain a reduced number of ionizable hydrogen atoms. Thus, specific hydrogen abstractions and their correlated dissociation routes of the negatively charged molecules were eliminated, providing evidence for the influence of the location of ionization on product ion spectra. Fragment ions such as m/z 78 indicate ionization at the commonly present sulfamoyl residue of diuretics but does not exclude additional ionization sites. Product ion spectra of the investigated diuretic agents proved to be composed by fragmentations initiated from different hydrogen abstractions. Moreover, the generation of radical anions by collision-activated dissociation of even-electron precursor ions was observed, the generation of which is discussed by proposed fragmentation pathways.

Rat NKCC2/NKCC1 cotransporter selectivity for loop diuretic drugs

It is generally assumed that bumetanide possesses some selectivity for the renal Na-K-Cl cotransporter NKCC2, although the results are scarce in the literature and comparisons were done with extra-renal NKCC1 at its basal, almost silent state. Here we investigated NKCC2/NKCC1 selectivity of loop diuretic drugs (bumetanide, piretanide and furosemide) as a function of the NKCC1 activated state (NKCC1 was activated by hypertonic media). NKCC2 activity was measured in isolated rat medullary thick ascending limb (mTAL) and NKCC1 in rat thymocytes and erythrocytes. When NKCC2 was compared with NKCC1at its activated state, all three diuretic drugs inhibited NKCC2 and NKCC1 with the same potency (bumetanide pIC50=6.48, 6.48 and 6.47; piretanide pIC50=5.97, 5.99 and 6.29; and furosemide pIC50=5.15, 5.04 and 5.21 for mTAL NKCC2, erythrocyte NKCC1 and thymocyte NKCC1, respectively). Basal NKCC1 exhibited a lower diuretic sensitivity, although with marked differences depending on the diuretic drug and the cell type in consideration and with the notable exception of furosemide in erythrocytes. Molecular modelling showed that bumetanide and piretanide possess four potentially active groups, of which three are shared with furosemide at similar intergroup distances. Of these three common groups, one should not bind to basal NKCC1 in thymocytes. The fourth (phenoxy) group (absent in furosemide) confers higher lipophilicity and should not bind to basal NKCC1 in erythrocytes. In conclusion, loop diuretics had no NKCC2/NKCC1 selectivity, when NKCC1 is measured at its activated state. Basal NKCC1 has a reduced diuretic sensitivity, of very different magnitude depending on the diuretic drug and cell type in consideration.

Solubilization and stability of bumetanide in vehicles for intranasal administration, a pilot study

The solubility of bumetanide in vehicles of various polarities, suitable for intranasal administration in acute situations, has been investigated. The solubility at 4 degrees C in glycofurol and polyethylene glycol 200 was high (167 and 143 mg/mL, respectively), decreasing exponentially with addition of phosphate buffer or coconut oil. Vehicles containing coconut oil and glycofurol did not seem to improve the solubility relative to mixtures between glycofurol and buffer. Adequate solubility (approximately 50 mg/mL) was achieved in vehicles containing about 80% cosolvent. The stability of bumetanide was studied at 5 degrees C and 57 degrees C. No degradation was observed at low temperature. At high temperature, bumetanide decomposes in nonaqueous vehicles with half-lifes ranging from 69 to 400 days, but sufficient stability may be obtained by adjustment of pH to 7.4. It may be concluded that it is possible to prepare a clinically relevant formulation for intranasal delivery of bumetanide.

Selective inhibition of Cl(-) conductance in toad skin by blockers of Cl(-) channels and transporters

We compared the effects exerted by two classes of Cl(-) transport inhibitors on a Cl(-)-selective, passive anion transport route across the skin of Bufo viridis, the conductance (G(Cl)) of which can be activated by transepithelial voltage perturbation or high cAMP at short circuit. Inhibitors of antiporters (erythrosine, eosin) or cotransporters (furosemide) reduced voltage-activated G(Cl) with IC(50) of 6 +/- 1, 54 +/- 12, and 607 +/- 125 microM, respectively; they had no effect on the cAMP-induced G(Cl). The voltage for half-maximal activation of G(Cl) (V(50)) increased compared with controls, but effects on the maximal G(Cl) at more positive clamp potentials were small. Cl(-) channel blockers from the diphenylamino-2-carboxylic acid (DPC) family [dichloro-DPC, niflumic acid, flufenamic acid, and 5-nitro-2-(3-phenylpropylamino)benzoic acid] reduced the voltage-activated G(Cl) with IC(50) of 8.3 +/- 1.2, 10.5 +/- 0.6, 16.5 +/- 3.4, and 36.5 +/- 11.4 microM, respectively, and also inhibited the cAMP-induced G(Cl), albeit with slightly larger IC(50). V(50) was not significantly changed compared with controls; the maximal G(Cl) was strongly reduced. We conclude that the pathway for Cl(-) is composed of the conductive pore proper, which is blocked by the derivatives of DPC, and a separate, voltage-sensitive regulator, which is influenced by blockers of cotransporters or antiporters. This influence is partly overcome by increasing the clamp potential and removed by high concentrations of cAMP, which renders the pathway insensitive to voltage.

Application of multiple response optimization technique to extended release formulations design

The purpose of the present study was to apply response surface methodology and multiple response optimization utilizing superimposed contour diagrams to design extended release formulations with a preplanned release profile. Bumetanide solution was layered on sugar pellets followed by coating with various coating formulations according to a central composite statistical design using a Glatt GPCG 1 Wurster Fluid Bed. The coated pellets were tested for their release profiles and the percent of drug released after 1, 4 and 8 h were used to describe and optimize the release process. Statistical models describing the percent bumetanide released after 1, 4 and 8 h were developed and the corresponding contour diagrams were superimposed to predict the coating formulation parameters expected to produce target release profile. The pellets coated with the designed coating formulation were tested for their release profiles in comparison to the target profile. According to the model-independent approach using similarity factor (F2), the dissolution profile of the designed formulation and the expected target profile were found to be similar. It was concluded that response surface methodology and multiple response optimization could be successfully used to design and optimize extended release formulations with desired preplanned release profile.

Evaluation of bumetanide as a matrix for prompt fragmentation matrix-assisted laser desorption/ionization and demonstration of prompt fragmentation/post-source decay matrix-assisted laser desorption/ionization mass spectrometry

Bumetanide was evaluated as a matrix for prompt fragmentation matrix-assisted laser desorption/ionization (MALDI) experiments on peptides. Both the MALDI mass spectrum and some physical properties of bumetanide were compared with those of some commonly used matrices. Bumetanide was then evaluated for prompt fragmentation MALDI by comparing the prompt fragmentation produced using bumetanide with that for alpha-cyano-4-hydroxycinnamic acid and 2, 5-dihydroxybenzoic acid. Bumetanide was also evaluated for use in a mixed matrix with alpha-cyano-4-hydroxycinnamic acid. A 4 : 1 matrix mixture was found to be useful for the post-source decay analysis of a prompt fragment ion. The prompt fragmentation/post-source decay analysis experiment is demonstrated on a prompt fragment ion from the oxidized b-chain of insulin.

Determination of dissociation constants of loop diuretics in acetonitrile-water mixtures

The dissociation pK values of the representative loop diuretics furosemide, bumetanide and ethacrynic acid in 10, 30, 40, 50 and 70% (w/w) acetonitrile-water mixtures at 298.15 K were determined, according to the rules and procedures endorsed by IUPAC. The variation in pK values over the whole composition range studied can be explained by tacking into account the preferential solvation of ionizable substances in acetonitrile-water mixtures. With a view to determining the pK values of the loop diuretics studied in any of the binary solvent acetonitrile-water mixtures, correlations of pK values and different bulk properties of the solvent were examined, and the linear solvation energy relationships method, LSER, has been applied. The pK values were then correlated with the pi*, alpha and beta solvatochromic parameters of acetonitrile-water mixtures. The resulting equations allowed us to calculate pK values for the loop diuretics in any acetonitrile-water mixture up to 70% (w/w) acetonitrile.

Determination of furosemide in plasma and urine by gas chromatography/mass spectrometry

A new method for the determination of furosemide (CAS 54-31-9) in plasma and urine by gas chromatography/mass spectrometry (GC/MS) has been developed. After acidification the samples were extracted by ethyl acetate and methylated by methyl iodide. The chromatography was carried out on a fused-silica capillary column with SE-54 stationary phase. Detection was performed by selected ion monitoring (ions 81 and 372 were monitored for furosemide and ions 363 and 406 for internal standard bumetanide). Limit of quantitation was 10 ng/ml for plasma and 40 ng/ml for urine and the calibration curves were linear up to 100,000 ng/ml.

Interaction of bumetanide derivatives with hepatocellular bile acid uptake

The loop diuretic bumetanide is an organic monocarboxylic organic anion assumed to be transported into hepatocytes by a transport system for bile acids. The structural requirements of 22 bumetanide analogues were analyzed for an interaction with bile acid uptake into isolated rat hepatocytes. Whereas bumetanide inhibited the hepatocellular uptake of [14C]cholate to the same degree as its own uptake, derivatization altered affinity and specificity and yielded compounds that selectively inhibited either cholate or taurocholate uptake or uptake of both. No correlation was found between the diuretic potency of bumetanide derivatives, reflecting the affinity to the Na(+)-K(+)-Cl- cotransporter, and their affinity to hepatic bile salt transport. Computer-aided model building combined with the calculation of potential energy maps showed a strictly amphipathic charge separation in bumetanide analogues as in bile acids. Ranking bumetanide compounds by their mean inhibitory concentration values, inhibition constants, and their type of competition, we conclude that at least three binding domains in the proteins are essential for recognition by bile acid transporters, namely two hydrophobic and an anionic side, and that for the anionic binding region a carbonyl atom in the ligands as an electron donor group is sufficient for ligand interaction.

Identification, characterization and purification of a 160 kD bumetanide-binding glycoprotein from the rabbit parotid

We demonstrate the presence of a 160 kD protein in rabbit parotid basolateral membranes that can be labeled with the irreversible sulfhydryl reagent [14C]-N-ethylmaleimide in a bumetanide-protectable fashion. The specificity of this labeling, and our previous evidence for the existence of an essential sulfhydryl group closely associated with the bumetanide-binding site on the parotid Na(+)-K(+)-Cl-cotransporter (J. Membrane Biol. 112:51-58, 1989), provide strong evidence that this protein is a part or all of the parotid bumetanide-binding site. When this protein is treated with endoglycosidase F/N-glycosidase F to remove N-linked oligosaccharides, its apparent molecular weight decreases to 135 kD. The pI of this deglycosylated protein is approximately 6.4. The bumetanide-binding protein was purified using two preparative electrophoresis steps. First, a Triton X-100 extract enriched in this protein was run on preparative electrophoresis to obtain fractions containing proteins in the 160 kD range. These were then deglycosylated with endoglycosidase F/N-glycosidase F and selected fractions were pooled and rerun on preparative electrophoresis to obtain a final 135 kD fraction. The enrichment of the bumetanide-binding protein in this final 135 kD fraction estimated from [14C]-N-ethylmaleimide labeling was approximately 48 times relative to the starting membrane extract. Since the bumetanide-binding site represents approximately 2% of the total protein in this starting extract, this enrichment indicates a high degree of purity of this protein in the 135 kD fraction.