Quantitative detection of C-deuterated drugs by CARS microscopy and Raman microspectroscopy.

The introduction of carbon-deuterium (C-D) bonds into drug compounds by organic synthesis is a non-invasive labelling approach, which does not alter the chemical and physiological properties of the drug itself. C-deuterated drugs exhibit characteristic vibrational signatures in the C-D stretching region around 2100-2300 cm(-1), which avoids spectral interference with contributions from a complex biological environment. In this paper, the quantitative detection of C-deuterated drugs by Raman microspectroscopy and single-band CARS microscopy is examined. Concentration-dependent studies on drugs with aliphatic and aromatic C-D moieties were performed in a two-channel microfluidic chip, using the corresponding non-deuterated (C-H) isotopologues as an internal reference.

Formation of a cyclic derivative of ethacrynic acid with diazomethane.

Samples of ethacrynic acid were treated with methanol-hydrochloric acid or with diazomethane. GLC and mass spectrometric analysis indicated that the methanol-hydrochloric acid reaction gave the expected methyl ester, whereas diazomethane treatment gave a compound containing an additional 14 mass units. Accurate mass measurement and PMR and IR spectra showed that this product was a cyclic derivative of the methyl ester of ethacrynic acid, methyl 4-(2,3-dihydro-4-ethyl-5-furyl)-2,3-dichlorophenoxyacetate. Either derivatization method can be used for development of an assay for ethacrynic acid.

Liquid chromatographic analysis of ethacrynic acid and degradation products in pharmaceutical systems.

An accurate, reproducible, and specific reversed-phase high-performance liquid chromatographic (HPLC) system was developed for the determination of ethacrynic acid and its degradation products. The method was used in stability studies of the drug in the solid state, in solution, and in dosage forms. Three degradation products were isolated by preparative chromatography and identified by several techniques, principally NMR and MS. TLC Rt and HPLC response factors are quoted. A degradation scheme consistent with the observed stability profiles is proposed.

New specific and sensitive HPLC-assays for ethacrynic acid and its main metabolite--the cysteine conjugate--in biological material.

A reversed-phase high-performance liquid chromatography (HPLC) method was developed and validated for the determination of the loop diuretic ethacrynic acid and its potentially active main metabolite, the ethacrynic acid-cysteine conjugate, in biological material. Simple and rapid sample preparation procedures were established using solid-phase extraction for the parent drug and direct injection after one washing step for the metabolite. HPLC separation was performed on a Spherisorb ODS II (3 microns) analytical column using isocratic elution with different mixtures of mobile phases (phosphoric acid-methanol-acetonitrile-tetrahydrofuran or triethylamine buffer-methanol, respectively). The analytes were detected by measuring the UV absorption of the eluate at 275 nm. Stability studies revealed that considerable amounts of ethacrynic acid may be released from the cysteine conjugate unless the urine samples are pH stabilized (pH 3-4). The assay provided high sensitivity with limits of quantification of 20 ng ml-1 for ethacrynic acid in plasma and urine, and 240 ng ml-1 for the cysteine conjugate in urine. All validation parameters were within the required limits. For the presented assays, the applicability to pharmacokinetic studies and routine analyses was proved.

Liquid chromatographic determination of hippuric acid for the evaluation of ethacrynic acid as angiotensin converting enzyme inhibitor.

A rapid, simple and interference-free method is described to evaluate the inhibitory effects of organic compounds on the activity of angiotensin converting enzyme irrespective of their acid-base properties. The assay is based on the high performance liquid chromatographic separation of the synthetic substrate hippuryl-L-histidyl-L-leucine, the hydrolysis product hippuric acid and the test compound. Using the new method, the diuretic drug ethacrynic acid was found to act as an inhibitor for the enzyme in a non competitive mode.

Application of diffusion-edited NMR spectroscopy for the structural characterization of drug metabolites in mixtures.

Diffusion-edited NMR spectroscopy is used to enable the structural characterization of low level metabolites in the presence of endogenous compounds, and organic solvents. We compared data from standard one-dimensional (1D) (1)H, 1D NOESY-presaturation, and 1D diffusion-edited experiments run on 20 microg and 100 microg samples of ethacrynic acid glutathione thioether (EASG) and a previously unreported metabolite of mefenamic acid, mefenamic acid glutathione thioester (MSG). The 1D NOESY-presaturation technique gave spectra with the best signal-to-noise (S/N) ratio, approximately three times that observed with the standard (1)H experiment, with respect to the metabolite signals. However, it was not selective for solvent signals as overlapping metabolite signals were also suppressed by this technique. In some cases, these signals were key to determining the site of glutathione attachment on the parent molecule. 1D NOESY-presaturation spectra also produced baseline distortions and inconsistent integration values. By comparison, 1D diffusion-edited experiments were found to selectively and simultaneously remove multiple solvent signals, resolve overlapping metabolite signals, and provide more uniform integration for metabolite signals overlapping with or proximal to solvent peaks, without producing baseline distortions. However, the diffusion-edited experiments caused significant signal attenuation of the metabolite signals when compared with a standard (1)H spectrum. Partially purified metabolites isolated from biological matrices were also characterized by using two-dimensional diffusion-ordered spectroscopy (DOSY). DOSY spectra acquired on a sample of EASG purified from rat bile proved useful in 'separating' the signals of EASG, from those of a co-eluting bile acid and parent drug ethacrynic acid (EA) in the diffusion-dimension in regions where there was no spectral overlap. In the low-field regions of high overlap, the DOSY experiment did not effectively separate the signals from the individual components. Diffusion based experiments provide a way to determine the total number of components that are present in a metabolite sample as well as an ability to identify them based on the chemical shift information, without the need for laborious chromatography on small samples.

Determination of ethacrynic acid in pharmaceutical formulations by difference ultraviolet spectrophotometry after derivatisation with N-acetylcysteine.

A selective difference spectrophotometric procedure is described for the assay of ethacrynic acid (a diuretic drug) in pharmaceutical dosage forms. The method is based on the reaction of the drug with N-acetylcysteine at pH 7.4 and ambient temperature, affording thiol adducts having different spectral properties, and involves the measurement of the absorbance of the reaction mixture relative to an equimolar solution of unreacted ethacrynic acid. The absorbance at 270 nm (A(270)) and the absorbance difference, delta A=A(270-A(244), obtained from the difference spectrum, were found to be linearly correlated with the drug concentration. The proposed spectrophotometric procedure was applied successfully to the determination of ethacrynic acid in pharmaceutical formulations using a reversed-phase high-performance liquid chromatographic procedure as a reference method.

The influence of virus transformation and cell population density on some membrane properties of mouse fibroblasts in culture.

The influence of cell population density and simian virus 40 transformation on the activity of the Na-K pump was studied in mouse fibroblasts cultured in medium supplemented with fetal bovine serum. The activity of the Na-K pump was determined from K+ influx, ethacrynate-sensitive K+ influx, (Na+ + K+)-ATPase assay, and the determinations of intracellular potassium and sodium ion concentrations in these cells. The activity of the Na-K pump was found to decrease in density-inhibited cultures of normal fibroblasts (designated as 3T3 cells), while in the virus-transformed cells (SV3T3) the activity remained fairly constant at all cell population densities.

Effect of ethacrynic acid on sodium pump alpha isoforms in SH-SY5Y cells.

BACKGROUND: Ethacrynic acid (ECA), a diuretic that has several cellular actions, increases expression of the sodium and potassium-activated adenosine triphosphatase (Na, K-ATPase or Na pump) in normal lymphocytes, but not in lymphocytes of bipolar patients. While this has been proposed to be important in the pathophysiology of bipolar illness, the response of neural tissues to ECA is unknown. METHODS: Human neuroblastoma SH-SY5Y cells differentiated with 10-microM retinoic acid were treated with various ECA concentrations for 3 days, and changes in Na-pump alpha-isoform expression were quantified with densitometric analysis of Western bands. RESULTS: Expression of alpha1 and alpha3 Na pump isoforms significantly increased with 10-5 M ECA. Cells treated with 10-6 or 10-7 M ECA showed no change in Na-pump expression, while cells treated with 10-4 M ECA died. The alpha2 isoform could not be detected in differentiated SH-SY5Y cells. CONCLUSIONS: The effect of ECA on alpha1-isoform in neural tissue is similar to that observed in lymphocytes. As alpha3 isoform is not expressed in lymphocytes, however, we conclude that lymphocytes are an incomplete model of neural tissue.