An HPLC assay for rat liver ferrochelatase activity

A rapid, reliable, sensitive and reproducible HPLC method was developed for the assay of ferrochelatase activity in rat liver. The assay was carried out aerobically with Zn2+ and mesoporphyrin or protoporphyrin IX as substrates. Zn-porphyrins formed were extracted with dimethyl sulphoxide/methanol (30:70, v/v) containing Zn-deuteroporphyrin as the internal standard for separation and quantification by reversed-phase chromatography. The Km for mesoporphyrin was 5.9 microM, for protoporphyrin IX 8.8 microM and for zinc 6.0 microM. The specific activities were 33.1 +/- 5.0 nmol Zn-mesoporphyrin or 13.4 +/- 2.0 nmol Zn-protoporphyrin formed per hour per mg of protein for mitochondria and 12.3 +/- 2.2 nmol Zn-mesoporphyrin or 4.6 +/- 0.9 nmol Zn-protoporphyrin per hour per mg of protein for liver homogenate.

Assaying erythrocyte haem biosynthetic enzyme activities by high-performance liquid chromatography with the advanced automated sample processor

The four cytosolic haem biosynthetic enzymes in erythrocytes were assayed with the Varian advanced automated sample processor (AASP) for rapid sample concentration and clean-up with fast and effective high-performance liquid chromatography systems for separation and quantitation. In the assay for 5-aminolaevulinic acid dehydrase, the porphobilinogen (PBG) formed was extracted on a C18 AASP cartridge and separated by reversed-phase ion-pair chromatography with 32% methanol in 0.05 M sodium acetate buffer (pH 3.5), containing 5.4 mM of 1-heptane-sulphonic acid as eluent. PBG was the substrate for the simultaneous assay of hydroxymethylbilane synthase and uroporphyrinogen III synthase. The uroporphyrinogen I and III isomers formed were oxidised to porphyrins, concentrated on a C2 or C8 cartridge, and separated by reversed-phase chromatography with 13% acetonitrile in 1 M ammonium acetate buffer (pH 5.16) as eluent. Uroporphyrinogen decarboxylase was estimated with pentacarboxylic porphyrinogen III as substrate. The coproporphyrinogen formed was extracted on a C2 or C8 cartridge, oxidised to coproporphyrin and separated by reversed-phase chromatography with 30% acetonitrile in 1 M ammonium acetate buffer (pH 5.16) as mobile phase.

Assay of blood acetaldehyde by HPLC with fluorescence detection of its 2-diphenylacetyl-1,3-indandione-1-azine derivative

A simple sensitive method for the assay of blood acetaldehyde is described. Samples are collected into an organic solution of 2-diphenylacetyl-1,3-indandione-1-hydrazone. Proteins are precipitated immediately and carbonyl compounds react to form fluorescent azine derivatives. Methanol in the reagent mixture prevents the oxidation of any ethanol present, precipitates protein and releases any absorbed acetaldehyde. After protein removal, the reaction is completed by the addition of an acid catalyst and a portion of the reaction mixture is subjected to quantitative analysis by high performance liquid chromatography.

A high-performance-liquid-chromatographic method for the assay of coproporphyrinogen oxidase activity in rat liver

An h.p.l.c. method was developed for the assay of coproporphyrinogen oxidase activity in rat liver. The protoporphyrinogen IX formed is completely oxidized to protoporphyrin IX for separation and quantification by reversed-phase chromatography with mesoporphyrin as the internal standard. The Km of coproporphrinogen oxidase is 1.01 +/- 0.23 microM. The activities are 4.07 +/- 0.40 nmol of protoporphyrin IX/h per mg of mitochondrial protein and 224 +/- 19 nmol of protoporphyrin IX/h per g of liver tissue homogenate. The method is sensitive enough for measuring enzyme activity in small amounts of human tissue from needle biopsy.

High-performance liquid chromatography of uroporphyrinogen and coproporphyrinogen isomers with amperometric detection

A reversed-phase h.p.l.c. system, with an ODS-Hypersil column with acetonitrile or methanol in ammonium acetate buffer as mobile phase, is described for the separation of uro-and copro-porphyrinogen isomers. The porphyrinogens are detected amperometrically with sensitivity comparable with that of the fluorescent detection of porphyrins. The effects of pH, buffer concentration and organic modifiers on retention and resolution were studied. The method is suitable for both analytical and preparative separation of porphyrinogens.

Reversed-phase high-performance liquid chromatography of conjugated and unconjugated bilirubins in body fluids

A novel high-performance liquid chromatography (HPLC) system is described for the separation of bilirubin and its conjugates in body fluids. Biliary bilirubin mono- and diglucuronide can be analysed directly on a C18 reversed-phase column with acetonitrile-dimethyl sulphoxide-0.1 M ammonium acetate (pH 5.16) (50:50:85, v/v/v) as mobile phase. However, the simultaneous determination of conjugated and unconjugated bilirubins in plasma required conversion of the conjugates into their methyl esters by alkaline methanolysis before HPLC separation of the C18 column eluted with acetonitrile-dimethyl sulphoxide-0.50 M ammonium acetate (pH 4.6) (50:50:40, v/v/v). The method is superior to, and more flexible than, previously described reversed-phase systems by allowing precise control of retention times by adjustment of pH, buffer concentration and the relative proportion of organic modifier in the mobile phase.

Analysis of tumour-localizing haematoporphyrin derivative by high-performance liquid chromatography and fast-atom bombardment mass spectrometry

Reversed-phase chromatography using a MOS-Hypersil (C8) column with methanol-1 M ammonium acetate buffer (pH 4.6) (60:40) as mobile phase has been developed for the isolation of tumour-localizing haematoporphyrin derivative (HPD). The system effectively resolved the diastereoisomers of haematoporphyrin and its acetyl derivatives. The chromatography peaks were identified by fast-atom bombardment mass spectrometry and were confirmed by chemical synthesis. The main components of HPD before alkaline hydrolysis were diacetylhaematoporphyrin, 8-(1-acetoxyethyl)haematoporphyrin and 3-(1-acetoxyethyl)haematoporphyrin with small amounts of haematoporphyrin, 8-(1-hydroxyethyl)-3-vinyldeuteroporphyrin, 3-(1-hydroxyethyl)-8-vinyldeuteroporphyrin, 8-(1-acetoxyethyl)-3-vinyldeuteroporphyrin, 3-(1-acetoxyethyl)-8-vinyldeuteroporphyrin and protoporphyrin. After hydrolysis with 0.1 M sodium hydroxide, the main components were haematoporphyrin, hydroxyethylvinyldeuteroporphyrins, and protoporphyrin.

The effects of ethanol and anticonvulsants on erythroid delta-aminolaevulinic acid synthase

The activity of delta-aminolaevulinic acid (ALA) synthase was measured in bone marrow from 13 control subjects, 12 chronic alcoholic patients and 9 patients on long term anticonvulsant therapy. The majority of patients in both groups had macrocytic red cells in the absence of megaloblastic changes in the marrow. There was a significant increase in ALA synthase activity in the alcoholic patients but no significant increase in enzyme activity in the patients on anticonvulsants and overall there was no correlation of activity with MCV. The macrocytosis associated with these drugs does not therefore appear to result from accelerated erythroid haem synthesis.

High-performance liquid chromatography of dicarboxylic porphyrins and metalloporphyrins: retention behaviour and biomedical applications

The retention behaviour of the main dicarboxylic porphyrins, haemato-, deutero-, meso- and protoporphyrins, together with the Fe, Co, Cu and Zn complexes of meso- and protoporphyrins have been systematically studied. Hydrophobic chromatography with methanol-ammonium acetate buffer systems on reversed-phase columns provided the best selectivity, efficiency and resolution. The retention of the porphyrins is controlled by the relative hydrophobicity of the porphyrin side-chain substituents. The insertion of a metal ion into the porphyrin macrocycle, however, completely alters the electronic environment around the central nitrogen atoms of the porphyrins. The retention is then greatly influenced by the species of inserted metal ion, to accept axial ligands from the mobile phase, although hydrophobic interaction of the side-chain substituents with the stationary phase surface is still an important factor. The retention behaviour can be precisely controlled by adjusting the pH, buffer concentrations and types and proportions of organic solvents in the mobile phase. The analysis of porphyrins and metalloporphyrins in blood, and the determination of ferrochelatase in bone marrow are examples of biomedical applications.

Ammonium acetate: a general purpose buffer for clinical applications of high-performance liquid chromatography

The chromatographic properties of ammonium acetate have been studied, and its use as a general purpose buffer for reversed-phase chromatography has been investigated. Simple ammonium acetate systems can often replace complicated and expensive buffers, with or without ion-pairing agents, with improved column selectivity and efficiency. A wide range of clinically important compounds have been successfully separated by ammonium acetate buffer systems. These include creatinine, bilirubin, verapamil and its metabolites, etoposide and teniposide, vitamin A, biogenic amines and porphyrins.

Pseudoporphyria associated with consumption of brewers' yeast

A case of pseudoporphyria associated with excessive consumption of brewers ' yeast was studied. Detailed analysis of the yeast tablets by high performance liquid chromatography showed the presence of dicarboxylic deuteroporphyrin , mesoporphyrin, and protoporphyrin; coproporphyrin I and III isomers; and uroporphyrin I and III isomers. The faecal porphyrin concentration of the patient taking yeast tablets was significantly increased, resembling the excretion pattern in variegate porphyria. Any patient showing an unusual porphyrin excretion pattern on high performance liquid chromatography should be investigated for a possible dietary cause.

Urine and faecal porphyrin profiles by reversed-phase high-performance liquid chromatography in the porphyrias

A novel reversed-phase system is described for the simultaneous separation of type I and type III isomers of uro-, heptacarboxylic-, hexacarboxylic -, pentacarboxylic - and copro -porphyrins and the dicarboxylic meso- and proto-porphyrins. The porphyrins were resolved on a Hypersil -SAS column eluted with 10% (v/v) acetonitrile in 1 mol/l ammonium acetate, pH 5.16 (solvent A) and 10% (v/v) acetonitrile in methanol (solvent B) with a linear gradient from 100% A (0%B) to 35% A (65%B) in 30 min followed by isocratic elution at 65% B for a further 10 min. The method is simple and reproducible and has been applied to the analysis of porphyrins in urine and faeces from patients with acute intermittent, variegate, hereditary copro , congenital erythropoietic, erythrohepatic proto and symptomatic porphyrias.

High-performance liquid chromatography of naturally occurring 8-, 7-, 6-, 5- and 4-carboxylic porphyrin isomers

Naturally occurring 8-, 7-, 6-, 5- and 4-carboxylic porphyrin isomers are separated on C18 reversed-phase columns with various proportions (13-31%, v/v) of acetonitrile in 1 M ammonium acetate buffer (pH 5.16) as the mobile phases. Hydrophobic interaction between the porphyrin side chain substituents and the C18 hydrophobic surface is the main retention mechanism. Ion-exchange behaviour is also observed, but this does not influence the relative retention of the isomers. All possible forms of the decarboxylation intermediates of uroporphyrinogen III are detected in normal and porphyric urine, and the results provide conclusive evidence for the existence of decarboxylation pathways other than the currently accepted clockwise sequence, starting at the ring D acetic acid group of uroporphyrinogen III.

Simultaneous determination of hydroxymethylbilane synthase and uroporphyrinogen III synthase in erythrocytes by high-performance liquid chromatography

A high-performance-liquid-chromatographic method is developed for the simultaneous determination of hydroxymethylbilane synthase and uroporphyrinogen III synthase activity in erythrocytes. Effective separation of uroporphyrin I and III isomers allows the accurate quantification of individual isomers and the total uroporphyrin concentration. Total uroporphyrin production is used to calculate hydroxymethylbilane synthase activity, and the amount of uroporphyrin III formed represents the activity of uroporphyrinogen III synthase. Normal ranges are established for the two enzymes.

Assay of blood and tissue aldehydes by HPLC analysis of their 2,4-dinitrophenylhydrazine adducts

A new method for the assay of blood and tissue acetaldehyde is described. Samples are reacted with a methanolic solution of 2,4-dinitrophenylhydrazine (DNP) and the DNP-aldehyde adducts extracted into CHCl3. DNP-[14C]formaldehyde is added as internal standard. The CHCl3 extracts are washed with HCl and H2O and purified by aluminium oxide chromatography. The eluate is dried down, re-dissolved in methanol and subjected to quantitative analysis by HPLC. The acetaldehyde adduct was identified by co-chromatography with the authentic derivative and by mass spectrometry. Recoveries of added acetaldehyde were 85% and addition of 20 mmol ethanol to the sample gave no apparent increment in acetaldehyde content. This technique is suitable for assessment of acetaldehyde levels in clinical and experimental studies of ethanol metabolism.

Separation of porphyrin isomers by high-performance liquid chromatography

A reversed-phase gradient elution system is described for the simultaneous separation of the type I and type III isomers of 8-, 7-, 6-, 5- and 4-carboxylated porphyrins and isocoproporphyrins. The method, adaptable for isocratic and stepwise separation of individual groups of isomers, is also suitable for preparative isolation of pure porphyrins. The analyses of porphyrin isomers in the urine and faeces of porphyric patients are examples of applications.

High-performance liquid chromatography of coproporphyrin isomers

A reversed-phase system is described for the simultaneous isocratic separation of coproporphyrin I, II, III and IV isomers. The retention behaviour of coproporphyrin I and III is studied in detail. The method is suitable for both analytical and semi-preparative separation.

Metabolic and drug profiling

Over recent years, advances in analytical technology have greatly improved our ability to study the metabolism of compounds from either endogenous or erogenous sources. The application of gas-liquid chromatography, mass spectrometry, high-performance liquid chromatography and immunological approaches are discussed in relation to the analysis of steroids, bile acids, organic acids, prostaglandins, porphyrins and bile pigments, amino acids, proteins, nucleotides, catecholamines, vitamins and drugs.