Sample Preparation Techniques Prior to HPLC Analysis of Serum Nucleosides and Their Bases

Analysis of submicromolar concentrations of adenosine in plasma using reversed phase high-performance liquid chromatography

A method is described for the determination of adenosine in small samples of plasma (< 1 ml) using reversed-phase high-performance liquid chromatography (HPLC) in either a simple isocratic or a gradient elution system which gives a clear separation of adenosine from other plasma constituents. Acetone is used to deproteinize plasma and chloroform to remove unwanted lipid soluble material prior to HPLC. 6-Methyladenosine is used as an internal standard for making corrections for changes in concentration during sample processing. Adenosine in plasma could be reliably detected at concentrations lower than its minimum effector concentration as a vasodilator (4 x 10(-8) Mol l(-1) using the isocratic system and 1.9 x 10(-8) Mol l(-1) with gradient elution). The recoveries of adenosine added to blood at concentrations ranging from 2 x 10(-8) Mol l(-1) to 1.4 x 10(-6) Mol l(-1) were from 101.4 +/- 16.9% (n = 4) to 100.0 +/- 3.6% (n = 5). The present method provides a simple, sensitive and selective assay for submicromolar concentrations of adenosine in plasma with good recovery.

Reversed-phase and ion-pair separations of nucleotides, nucleosides and nucleobases: analysis of biological samples in health and disease

Methods for the assay of nucleotides, nucleosides and nucleobases in biological samples in health and disease are reviewed, with emphasis on reversed-phase and ion-pair reversed-phase techniques for their determination. Modes of extraction from biological samples are discussed with respect of the determination of in vivo concentrations. Advantages and limitations of ion-pair reversed-phase chromatography are discussed with examples from biochemistry and clinical chemistry. The capacity of the high-performance capillary electrophoresis is compared with that of ion-pair reversed-phase chromatography.

Quantitation of hypoxanthine in plasma from patients with ischemic heart disease: adaption of a high-performance liquid chromatographic method

A high-performance liquid chromatographic method is described for the separation and quantitation of several purine compounds, including hypoxanthine. The isocratic separation of a standard mixture of nine compounds is achieved within 20 min on a reversed-phase Nucleosil 100-5C18 column, with a mobile phase of KH2PO4 (300 mM, pH 4.0)-methanol-acetonitrile-tetrahydrofuran (97.9:1:1:0.1, v/v). Uric acid, guanine, hypoxanthine, uridine, xanthine, allopurinol, inosine, guanosine and 7-methylxanthine were almost completely baseline-separated, with detection limits in the range 0.5-1.2 pmol per injection. The influence of the concentrations of buffer and tetrahydrofuran on the quality of separation are described. The within-day and the day-to-day precision were satisfactory (e.g. coefficients of variation of less than 1.5 and ca. 6.0%, respectively, for peak heights). The recovery of [3H]hypoxanthine added to samples was 86 +/- 1%. Hypoxanthine was quantified in human plasma samples obtained at various times during coronary artery bypass grafting. The hypoxanthine levels measured immediately after release of the aortic cross-clamp were significantly higher than those determined under control conditions (18.8 +/- 7.0 and 3.4 +/- 1.0 microM, respectively).

Metabolic alterations in burn patients: detection of adenosine triphosphate degradation products and lipid peroxides

Seven patients admitted to the University of Michigan Burn Center with greater than 20 per cent total body surface area burns were studied for evidence of oxygen radical production, as demonstrated by serum lipid peroxides, and adenosine triphosphate (ATP) degradation, based upon ATP degradation products in blood (serum purines) and urine (urine purines and urine uric acid). Lipid peroxides (conjugated dienes) were elevated beginning on day 1 postburn and remained elevated up to day 5, the duration of the study. ATP degradation products were elevated during the initial 24 h postburn but rapidly fell to normal levels. This study provides evidence of biochemical alterations in thermally injured patients similar to observations in animal models which demonstrate that ATP degradation and the production of oxygen radicals are part of the initial response to thermal trauma.

Comparison of toxicity of radiocontrast agents to renal tubule cells in vitro

We have previously reported that radiocontrast agents induce direct renal tubule cell toxicity in vitro. The observed toxic effects were markedly potentiated by concomitant hypoxia. In addition, we have reported that the ionic radiocontrast agent diatrizoic acid is more toxic than the nonionic radiocontrast agent iopamidol in this system. Using suspensions enriched in rabbit renal proximal tubule segments, we compared the direct toxicities of the ionic dimeric ioxaglic acid to the nonionic monomeric compound iopamidol. Toxicity was assessed by comparing tubule potassium and calcium content, ATP levels, and respiratory rates after exposure to clinically achievable concentrations of radiocontrast agents. Ioxaglate (25 mM) produced significant declines in tubule cation content and respiratory rate with 30 min of hypoxia followed by 60 min of reoxygenation compared to molar-equivalent concentrations of iopamidol under similar conditions. Meglumine, a cationic compound frequently present in ionic contrast agent solutions, and ioxaglate tubule toxicity was additive. Iopamidol and ioxaglate exhibited similar tubule cell toxicity when comparison was based on iodine content. These experimental results suggest that the intrinsic nephrotoxic potential of ioxaglic acid is greater than that of iopamidol on a molar basis, but that the nephrotoxic potential of the two radiocontrast agents is similar when comparison is based upon iodine content.

Amino acid analysis utilizing phenylisothiocyanate derivatives

Advances in liquid chromatography have brought about the development of new techniques in amino acid analysis which take full advantage of precolumn derivatization procedures. Using phenylisothiocyanate as the reagent, detection limits under 1 pmol can be routinely achieved, allowing the analysis of submicrogram protein samples. Analysis times as short as 10 min for samples after hydrolysis and 1 h for physiologic samples are possible. Accurate, reproducible quantitation of amino acids can be obtained from complex matrices such as plasma, urine, feed, and food samples. This level of performance and flexibility gives the analyst the first realistic alternative to ion-exchange analysis without compromising desirable features of the traditional methodology.

Hypoxanthine, xanthine and uridine in body fluids, indicators of ATP depletion

Measurements of hyp, xan and urd in body fluids can provide evidence of energy, ATP, depletion in the body, in organs or in cells. Such information is clinically useful in the many diseases in which cellular energy supplies cannot be maintained like perinatal asphyxia, hydrocephalus and vascular insufficiency in brain, heart, limbs, kidneys or other organs. Similar HPLC methods using reversed-phase C18 columns and quantitation by UV absorption have been employed in a variety of centres to yield almost identical results. These have been assembled in this review to form a series of reference values. The current analytical problems are reviewed. Since concentrations of hyp and xan may alter independently situations are discussed in which separate measurements rather than their summed, total oxypurine concentrations are needed. The biochemistry and physiology underlying the use of such analyses is examined to guide sampling of the appropriate body fluid at a relevant time and to avoid oversimplified interpretation of results as well as unnecessary arguments. Specifically: (1) Intracellular concentrations of hyp and xan are inversely related to adenylate energy change and therefore to the energy currency of the cell ATP. Uridine in tissues is similarly 'controlled'. (2) There is extensive evidence that large increases in hyp, xan and urd in body fluids indicate ATP depletion. (3) Small changes in hyp probably reflect alterations of ATP turnover. (4) Xanthine arises mainly from guanine and can change independently of hyp. (5) Clinically useful information is obtainable from hyp and xan concentrations in CSF, amniotic fluid, urine and plasma. Extensive clinical correlations are reviewed. At present we are in a development phase for which HPLC is ideal but the most efficient way to perform and use such analyses in routine clinical practice remains to be established.

Extraction of adenine nucleotides from cultured endothelial cells

The goal of this work was to find a method suitable for the extraction of adenine nucleotides from cultured vascular endothelial cells. Extraction of cell monolayers with 80% methanol in water yielded extracts with a higher content of ATP than did extraction of cells with perchloric acid, trichloroacetic acid, or boiling water. The optimal extraction solution was 80% methanol with 0.5 mM ethylene glycol bis(beta-aminoethyl ether) N,N'-tetraacetic acid (EGTA) or EDTA, heated to 70 degrees C immediately before use. Extraction of nucleotides by this solution was rapid and the recovery of exogenous ATP added during the extraction process was generally greater than 90%. An aqueous methanol or ethanol solution may be applicable for the extraction of nucleotides and other metabolites from cultured animal cells, dispersed cells, and frozen, powdered tissues.

High-performance liquid chromatographic profiling of nucleic acid components in physiological samples

The papers reviewed represent recent progress in HPLC profiling of nucleic acid components in physiological samples. Each method was designed for a particular application and possesses certain inherent advantages and/or disadvantages. Many methods are simply modifications of previous procedures. Although some methodologies appear to be superior to others, there is no "best" method for universal usage. The analyst must use the procedure which is best suited for the particular application at hand. This review is meant to be a starting point for the chromatographer who is comparing and evaluating HPLC methods for a given application.

Sensitive analysis of asparagine and glutamine in physiological fluids and cells by precolumn derivatization with phenylisothiocyanate and reversed-phase high-performance liquid chromatography

The analytical methodologies for the determination of free amino acids in plasma, serum, erythrocytes and leukemic cells are described. Deproteinization of the sample by methanol or organic acids is followed by derivatization with phenylisothiocyanate to form stable phenylthiocarbamylamino acid derivatives. The derivatives are separated by reversed-phase high-performance liquid chromatography in 80 min using a 5-microns C18 column (250 X 4 mm I.D.) and monitored by ultraviolet detection at 254 nm. Twenty physiological amino acids are resolved and quantified in plasma and erythrocyte samples. The resolution and sensitivity of the analytical method permitted unequivocal quantification of very low asparagine and glutamine levels in leukemic cells and growth media following treatment with asparaginase and glutaminase enzymes despite the presence of high aspartic and glutamic acid levels.

PITC derivatives in amino acid analysis

Refined methods for separating PTC-amino acids on reverse phase columns may pose a challenge to traditional ion exchange techniques.

Useful sample handlings for reversed phase high performance liquid chromatography in emergency toxicology

Some physicochemical treatments of biological samples, before being injected into a liquid chromatograph, are discussed. The advantages of dilution, liquid and solid extraction are compared referring mainly to unpublished results. Assays of antiepileptic drugs, caffeine, theophylline, tricyclic antidepressants, valproic acid, and meprobamate are used to demonstrate the importance of sample handlings in toxicological analyses in which reversed phase high performance liquid chromatographies are applied.

Optimal extraction conditions for high-performance liquid chromatographic determination of nucleotides in yeast

Different extraction methods of nucleotides from the yeast Saccharomyces cerevisiae were compared. A new extraction solution--formic acid saturated with 1-butanol--was found to be more effective than the commonly used solutions of trichloroacetic acid, perchloric acid, or formic acid alone. Using this solution the optimal extraction conditions were established. Nucleotide recovery was evaluated by adding standard nucleotides to the extraction medium and carrying them together with the cells through the whole extraction procedure. Nucleotides were separated and quantitated by high-performance liquid chromatography on an anion-exchange column.

Current high-performance liquid chromatographic methodology in analysis of nucleotides, nucleosides, and their bases. I

This review of HPLC technology is presented in two parts. An introduction to chromatography, sample preparation, and basic information on chromatographic theory and terminology, modes, and instrumentation is presented here. A discussion of stationary and mobile phase parameters which can be varied to optimize separations is also presented here. The second part of the review, which will appear in the next issue, will cover peak identification, quantification, and selected applications. The applications include short discussions of applications of HPLC for metabolic profiling, for assays of adenosine and cyclic nucleotides in studies of disease processes, and for enzyme assays. The paper concludes with a short discussion of future trends for HPLC in biomedical research and clinical chemistry.

Reversed-phase liquid chromatographic investigation of UV-absorbing low-molecular-weight compounds in saliva

The reversed-phase mode of high-performance liquid chromatography was used to determine the intra- and inter-individual levels of UV-absorbing low-molecular-weight compounds in saliva. Many of the compounds known to occur in serum were also found in saliva; however, concentrations in saliva are lower. Both the intra- and inter-individual levels of these compounds vary significantly; in most cases, the inter-individual variance is 2-3 times the intra-individual variance. Caffeine and its metabolites in saliva are also reported. A greater number of metabolites were found in the saliva of habitual coffee drinkers. After caffeine was administered orally, paraxanthine, theobromine, theophylline, 1-methylxanthine, and 1-methyluric acid were found in the saliva of an individual who did not drink coffee regularly. In this subject, the serum half-life for caffeine was 3.49 h and the saliva half-life was 3.27 h. The half-life of caffeine in an habitual coffee drinker who had refrained from caffeine products for four days was 4.39 h.

Sample purification using a C18-bonded reversed-phase cartridge for the quantitative analysis of corticosteroids in adrenal cell cultures by high-performance liquid chromatography or gas chromatography--mass spectrometry

Quantitative extraction and subsequent purification of small biological samples often involve cumbersome procedures. We have devised a short and efficient method for the quantitative extraction of the corticosteroid and the 20 alpha reduced steroid series from culture medium containing 20% sera in a single, pure fraction with separation from cholesterol. Passage through a C18-bonded reversed-phase Sep-Pak cartridge of the acidified culture medium and subsequent extraction of the steroid fraction with methanol yields a single fraction containing all steroids in 90% recovery and reduced quantities of cholesterol down to 30%. The extract can then be used without further purification for quantitative analysis by high-performance liquid chromatography or derivatized and analyzed by gas chromatography and gas chromatography--mass spectrometry.

Determination of mimosine and 3-hydroxy-4(1h)-pyridone in Leucaena, avian excreta and serum using reversed-phase ion-pair high-performance liquid chromatography

The estimation of mimosine and 3-hydroxy-4(1H)-pyridone in Leucaena leucocephala, Leucaena seeds, chick excreta and chick serum using reversed-phase ion-pair high-performance liquid chromatography was investigated. Isocratic elution of both compounds was achieved in 11 min using sodium octyl sulphate as the pairing agent in a pH 2.25 buffer. Good recoveries of both mimosine and 3-hydroxy-4(1H)-pyridone in all but serum samples were obtained.

Separation of bilirubin species in serum and bile by high-performance reversed-phase liquid chromatography

A high-performance, reversed-phase liquid chromatographic (HPLC) procedure has been developed for the separation of at least three major bilirubin fractions in bile and four fractions in human serum. This procedure was unlike most others, in that serum was not totally deproteinized prior to injection onto the HPLC column; instead, serum was treated with an excess of sodium sulfate solution to precipitate primarily proteins larger than albumin. Injection of the filtered and diluted supernatant onto a reversed-phase column then resulted in the separation of the bilirubin species in a 24-min gradient elution run. Both the initial aqueous acidic mobile phase and the final isopropyl alcohol-based mobile phase contained 5% methoxyethanol (v/v) to facilitate elution of albumin still present in the treated sample. Bilirubin species eluting from the column were detected by absorbance at 450 nm. Results of a number of chromatographic separations of pathological sera indicated a wide variation in the relative proportions of the four bilirubin fractions observed. A correlation of the sum of the areas of the bilirubin peaks observed by HPLC was found with the total bilirubin value obtained by a standard reference procedure.