Separation of porphyrin isomers by high-performance liquid chromatography

Heme Determination and Quantification Methods and Their Suitability for Practical Applications and Everyday Use

Many research institutions, clinical diagnostic laboratories, and blood banks are desperately searching for a possibility to identify and quantify heme in different physiological and pathological settings as well as various research applications. The reasons for this are the toxicity of the heme and the fact that it acts as a hemolytic and pro-inflammatory molecule. Heme only exerts these severe and undesired effects when it is not incorporated in hemoproteins. Upon release from the hemoproteins, it enters a biologically available state (labile heme), in which it is loosely associated with proteins, lipids, nucleic acids, or other molecules. While the current methods and procedures for quantitative determination of heme have been used for many years in different settings, their value is limited by the challenging chemical properties of heme. A major cause of inadequate quantification is the separation of labile and permanently bound heme and its high aggregation potential. Thus, none of the current methods are utilized as a generally applicable, standardized approach. The aim of this Feature is to describe and summarize the most common and frequently used chemical, analytical, and biochemical methods for the quantitative determination of heme. Based on this overview, the most promising approaches for future solutions to heme quantification are highlighted.

HPLC methods for analysis of porphyrins in biological media

Changes in porphyrin concentrations in biological media may serve as biological indicators of exposure and toxicity from a wide variety of drugs and chemical agents. This unit describes procedures for quantitative extraction of porphyrins from urine, feces, blood, and biological tissues as well as their separation and analysis by HAPLY spectrofluorometrc techniques.

HPLC study of chlorin e6 and its molecular complex with polyvinylpyrrolidone

Several HPLC methods with UV detection were developed for qualitative and quantitative analysis of chlorin e(6) and photosensitizer Photolon either in the free form or upon pre-derivatization (methylation) under reversed- and normal-phase conditions. Optimum analysis conditions providing the best resolution of analytes were found at acidic pH where polar groups are completely protonated. The separation was performed by gradient elution with mobile phases of 0.08% trifluoroacetic acid and acetonitrile on an XTerra RP(18) column. The method was specific, accurate and precise, allowing the analysis of chlorin e(6) in the presence of numerous degradation products useful in the manufacturing process and quality control of chlorin e(6) and Photolon.

Separation of porphyrin-based photosensitizer isomers by laser-induced fluorescence capillary electrophoresis

Methods for the separation of photosensitizer isomers, such as benzoporphyrin derivative monoacid, benzoporphyrin ethyl monoacid, 2-[1-hexyloxyethyl]-2-devinylpyropheophorbide-a, diethyleneglycol diester benzoporphyrin derivative, tin ethyl etiopurpurin, and phthalocyanine tetrasulfonate, have been systematically developed by CE. Detection was accomplished by UV absorption at 214 nm or by LIF with excitation at 442/488 nm and emission at 690 nm. The effects of three major experimental parameters of buffer types, organic solvents, and surfactant additives are described. The optimized separation conditions were determined so as to provide satisfactory separation efficiency and analysis time. The methods are shown to be suitable for the separation and determination of porphyrin and phthalocyanines regioisomers, diastereoisomers, and enantiomers.

Rapid analysis of porphyrins at low ng/l and μg/l levels in human urine by a gradient liquid chromatography method using octadecylsilica monolithic columns

Rapid gradient RP-HPLC method with fluorimetric detection for trace analysis of diagnostically significant porphyrins in human urine was developed for clinical and diagnostic purposes. Results show that optimized high-pressure gradient elution and monolithic column Chromolith SpeedRod RP18e enabled separation of seven urine porphyrins including baseline separation of I and III positional isomers of uro- and coproporphyrins within 3.2 min. Problems associated with high metal cation complexing ability of the analytes and common stainless steel based instrumentation were substantially reduced by use of 0.1 mol/l ammonium citrate buffer (pH 5.47) and methanol as a mobile phase components. Good reproducibilities of retention times (within +/- 0.36% RSD) and peak areas (from +/- 0.6 to +/- 2.5% RSD) at 5-20 microg/l level of the analytes were achieved. Determined LOQ (10 x S/N) values of diagnostically important porphyrins using fluorimetric detection (ex.405 nm/em.620 nm) were 82 pmol/l (65 ng/l, 1.30 pg/injection) for uroporphyrin I, 44 pmol/l (33 ng/l, 0.66 pg/injection) for uroporphyrin III, 50 pmol/l (40 ng/l, 0.80 pg/injection) for coproporphyrin I and 47 pmol/l (39 ng/l, 0.78 pg/injection) for coproporphyrin III. Attained LOQ concentration level is approximately 20-120 times lower than concentration of porphyrins in a urine of healthy person. Calculated LOD's (3 x S/N) were at a low ng/l levels, what enabled quantification of carry-over effect to be from 2.0% to 0.2% in each of three consecutive blank runs and from 2.5% to 7% in total after injection of mixed standard of porphyrins with 5-20 microg/l concentrations. Recovery of porphyrins at low microg/l concentration levels was from 93% to 97.5%. Devised method increases productivity of clinical laboratory from 2 to 10 times in dependence of duration of currently used method.

Leptospira spp. possess a complete haem biosynthetic pathway and are able to use exogenous haem sources

Unlike the spirochetes Borrelia burgdorferi and Treponema pallidum, Leptospira spp. contain genes encoding the enzymes for most biosynthetic pathways. In this study, we describe the first haem biosynthetic pathway genes in the order Spirochaetales. Sequence analysis of the L. interrogans genome shows that all haem biosynthetic genes (hemA, heml, hemB, hemC, hemE, hemN, hemY and hemH) are clustered in a 15 kb region of the CII secondary chromosome. Although no hemD homologue (encoding uroporphyrinogen III synthase) was found in the genome, the L. interrogans hemC gene (encoding porphobilinogen deaminase) was able to restore uroporphyrinogen III synthase activity in an Escherichia coli Delta hemD mutant, suggesting that the L. interrogans hemC gene encodes a bifunctional enzyme. Similarly, we show that the L. interrogans hemH gene (encoding ferrochelatase, the terminal enzyme of the haem biosynthetic pathway) is able to complement a ferrochelatase-defective E. coli Delta hemH mutant. Further investigation of ferrochelatases was undertaken in both saprophytic and pathogenic species of Leptospira. Ferrochelatase activity of 2.3 +/- 0.1 nmol h-1 mg-1 (in comparison with 0.25 +/- 0.02 nmol h-1 mg-1 in E. coli) was found in membrane fractions of pathogenic and saprophytic species, suggesting that ferrochelatase is a membrane-associated protein. Leptospira biflexa allelic exchange mutants containing an inactivated hemH gene were recovered only when exogenous haemin was present. The results indicate that haem is an essential growth factor for Leptospira, and that these spirochetes are capable of both de novo synthesis or uptake of haem. This may have implications in a better understanding of the pathogenesis of Leptospira.

An exon 10 deletion in the mouse ferrochelatase gene has a dominant-negative effect and causes mild protoporphyria

Protoporphyria is generally inherited as an autosomal dominant disorder. The enzymatic defect of protoporphyria is a deficiency in ferrochelatase, which chelates iron and protoporphyrin IX to form heme. Patients with protoporphyria have decreased ferrochelatase activities that range from 5% to 30% of normal caused by heterogeneous mutations in the ferrochelatase gene. The molecular mechanism by which the ferrochelatase activity is decreased to less than an expected 50% is unresolved. In this study, we assessed the effect of a ferrochelatase exon 10 deletion, a common mutation in human protoporphyria, introduced into the mouse by gene targeting. F1 crosses produced (+/+), (+/-), and (-/-) mice at a ratio of 1:2:0; (-/-) embryos were detected at 3.5 days postcoitus, consistent with embryonic lethality for the homozygous mutant genotype. Heterozygotes demonstrated equivalent levels of wild-type and mutant ferrochelatase messenger RNAs and 2 immunoreactive proteins that corresponded to the full-length and an exon 10-deleted ferrochelatase protein. Ferrochelatase activities in the heterozygotes were an average of 37% of normal, and protoporphyrin levels were elevated in erythrocytes and bile. Heterozygous mice exhibited skin photosensitivity but no liver disease. These results lend support for a dominant-negative effect of a mutant allele on ferrochelatase activity in patients with protoporphyria.

Stacking and separation of coproporphyrin isomers by acetonitrile-salt mixtures in micellar electrokinetic chromatography

The effectiveness of the addition of salt and acetonitrile in the sample matrix to induce narrowing of the analyte zones is demonstrated for the first time in micellar electrokinetic chromatography (MEKC). Using coproporphyrin (CP) I and III isomers as test compounds, the use of sodium cholate (SC) as the micelle in the separation buffer and a high concentration of sodium chloride in the aqueous sample solution (without the presence of an organic solvent) were found to provide enhancement in peak heights for both CP I and III, but yielded very poor resolution of these two positional isomers at sample size of 10% capillary volume or larger. With the addition of acetonitrile as the organic solvent in the aqueous sample solution (acetonitrile-salt mixtures), baseline/partial resolution of CP I and III was obtained even at large injection volumes, along with significant increase in peak heights for both isomers. Possible mechanisms responsible for the narrowing of analyte zones are briefly discussed. The effects of experimental parameters, such as concentrations of salt and acetonitrile, on peak heights and resolution of the test compounds were studied. Importantly, the usefulness of the present method was demonstrated for the MEKC determination of endogenous CP I and III present in normal urine samples with good separation and detection performances.

Analysis of ferrochelatase expression during hematopoietic development of embryonic stem cells

Ferrochelatase, the last enzyme in the heme pathway, chelates protoporphyrin IX and iron to form heme and is mutated in protoporphyria. The ferrochelatase gene is expressed in all tissues at low levels to provide heme for essential heme-containing proteins and is up-regulated during erythropoiesis for the synthesis of hemoglobin. The human ferrochelatase promoter contains 2 Sp1 cis-elements and GATA and NF–E2 sites, all of which bind their cognatetrans-acting factors in vitro. To investigate the role of these elements during erythropoiesis, we introduced expression of the green fluorescent protein (EGFP) transgenes driven by various ferrochelatase promoter fragments into a single locus in mouse embryonic stem cells. EGFP expression was monitored during hematopoietic differentiation in vitro using flow cytometry. We show that a promoter fragment containing the Sp1 sites, the NF–E2 and GATA elements, was sufficient to confer developmental-specific expression of the EGFP transgene, with an expression profile identical to that of the endogenous gene. In this system the −0.275 kb NF–E2 cis-element is required for erythroid-enhanced expression, the GATA cis-element functions as a stage-specific repressor and enhancer, and elements located between −0.375kb and −1.1kb are necessary for optimal levels of expression. Ferrochelatase mRNA increased before the primitive erythroid-cell stage without a concomitant increase in ferrochelatase protein, suggesting the presence of a translational control mechanism. Because of the sensitivity of this system, we were able to assess the effect of an A-to-G polymorphism identified in the promoters of patients with protoporphyria. There was no effect of the G haplotype on transcriptional activity of the −1.1 kb transgene.

Analysis of ferrochelatase expression during hematopoietic development of embryonic stem cells

Ferrochelatase, the last enzyme in the heme pathway, chelates protoporphyrin IX and iron to form heme and is mutated in protoporphyria. The ferrochelatase gene is expressed in all tissues at low levels to provide heme for essential heme-containing proteins and is up-regulated during erythropoiesis for the synthesis of hemoglobin. The human ferrochelatase promoter contains 2 Sp1 cis-elements and GATA and NF–E2 sites, all of which bind their cognatetrans-acting factors in vitro. To investigate the role of these elements during erythropoiesis, we introduced expression of the green fluorescent protein (EGFP) transgenes driven by various ferrochelatase promoter fragments into a single locus in mouse embryonic stem cells. EGFP expression was monitored during hematopoietic differentiation in vitro using flow cytometry. We show that a promoter fragment containing the Sp1 sites, the NF–E2 and GATA elements, was sufficient to confer developmental-specific expression of the EGFP transgene, with an expression profile identical to that of the endogenous gene. In this system the −0.275 kb NF–E2 cis-element is required for erythroid-enhanced expression, the GATA cis-element functions as a stage-specific repressor and enhancer, and elements located between −0.375kb and −1.1kb are necessary for optimal levels of expression. Ferrochelatase mRNA increased before the primitive erythroid-cell stage without a concomitant increase in ferrochelatase protein, suggesting the presence of a translational control mechanism. Because of the sensitivity of this system, we were able to assess the effect of an A-to-G polymorphism identified in the promoters of patients with protoporphyria. There was no effect of the G haplotype on transcriptional activity of the −1.1 kb transgene.

Studies on the mechanism of uroporphyrinogen decarboxylase inhibition in hexachlorobenzene-induced porphyria in the female rat

Hexachlorobenzene (HCB)-induced porphyria occurs in female, but not male, rats after a delay of 35 days following HCB treatment. Uroporphyrinogen decarboxylase (UROD) inhibition has been proposed as a primary causative event. To determine whether there also exists a delay phase and a sexual dimorphism for UROD inhibition, groups of male and female rats were given HCB (100 mg/kg/day) from Days 1 to 5. Hepatic uroporphyrin III was markedly increased only after Day 33. Liver cytosol UROD activity in HCB-treated female rats with porphyria at Days 33, 40, 47, 54, and 100 was decreased by over 70% compared to concurrent control, whereas treated male rats as well as nonporphyric female rats had UROD activity comparable to control levels at Days 6, 12, 19, 26, 33, 40, 47, and 54. Level of immunoreactive UROD in cytosol of porphyric rats was not modified by HCB. No gender-related differences in liver cytosol radiolabel level ([14C]HCB given as the fifth dose) were found at Days 6 and 30. Chromatography of liver cytosol showed nonspecific binding of radiolabel to proteins for males, porphyric and nonporphyric females, and loss of UROD activity did not correlate with the amount of radiolabel in the UROD-containing fractions. Thus, the gender-specific decrease in UROD activity observed when porphyria develops in female rats (delay of about 4 weeks), as well as the persistence of low activity and porphyria for months, suggests that UROD inhibition was causally related to porphyria.

Improved method to extract and concentrate porphyrins from liver tissue for analysis by high-performance liquid chromatography

A new method to extract and concentrate porphyrins from liver tissue for analysis by high-performance liquid chromatography is described. Porphyrins were extracted with acetonitrile-hydrochloric acid, concentrated on disposable octadecylsilyl columns, brought to dryness, and reconstituted in 1.2 M hydrochloric acid. Dried porphyrins were stable at -80 degrees C for at least three weeks, and porphyrins reconstituted in hydrochloric acid were stable for at least 20 h. Yields of uro-, heptacarboxyl-, hexacarboxyl-, pentacarboxyl- and coproporphyrin were > or = 90%. The method allows determination of porphyrin concentrations in small (10-100 mg) samples of liver tissue.