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

Porphyrinogen fragmentation profiles by ultra-high-performance liquid chromatography/electrospray ionisation tandem mass spectrometry

An ultra-high-performance liquid chromatography/electrospray ionisation tandem mass spectrometry system is described for the separation and characterisation of uroporphyrinogen, heptacarboxylic acid porphyrinogen, hexacarboxylic acid porphyrinogen, pentacarboxylic acid porphyrinogen and coproporphyrinogen. The separation was carried out on a 100 mm × 2.1 mm Thermo-Hypersil BDS column (2.4 µm average particle size) by gradient elution with a mixture of acetonitrile, methanol and 1 mol/L aqueous ammonium acetate buffer, pH 5.16, as eluent. The fragmentation pattern of each compound was established by collision-induced dissociation tandem mass spectrometry. The most characteristic fragmentation was ring opening at one of the four methylene bridges of the protonated porphyrinogen molecule followed by further cleavages of methylene bridges linking the four pyrrole rings at various points to give product ions with methylenepyrrolenine, methylene-dipyrrolenine and methylene-tripyrrolenine structures.

Mutations in human CPO gene predict clinical expression of either hepatic hereditary coproporphyria or erythropoietic harderoporphyria

Hereditary coproporphyria (HCP), an autosomal dominant acute hepatic porphyria, results from mutations in the gene that encodes coproporphyrinogen III oxidase (CPO). HCP (heterozygous or rarely homozygous) patients present with an acute neurovisceral crisis, sometimes associated with skin lesions. Four patients (two families) have been reported with a clinically distinct variant form of HCP. In such patients, the presence of a specific mutation (K404E) on both alleles or associated with a null allele, produces a unifying syndrome in which hematological disorders predominate: 'harderoporphyria'. Here, we report the fifth case (from a third family) with harderoporphyria. In addition, we show that harderoporphyric patients exhibit iron overload secondary to dyserythropoiesis. To investigate the molecular basis of this peculiar phenotype, we first studied the secondary structure of the human CPO by a predictive method, the hydrophobic cluster analysis (HCA) which allowed us to focus on a region of the enzyme. We then expressed mutant enzymes for each amino acid of the region of interest, as well as all missense mutations reported so far in HCP patients and evaluated the amount of harderoporphyrin in each mutant. Our results strongly suggest that only a few missense mutations, restricted to five amino acids encoded by exon 6, may accumulate significant amounts of harderoporphyrin: D400-K404. Moreover, all other type of mutations or missense mutations mapped elsewhere throughout the CPO gene, lead to coproporphyrin accumulation and subsequently typical HCP. Our findings, reinforced by recent crystallographic results of yeast CPO, shed new light on the genetic predisposition to HCP. It represents a first monogenic metabolic disorder where clinical expression of overt disease is dependent upon the location and type of mutation, resulting either in acute hepatic or in erythropoietic porphyria.

Neonatal Hemolytic Anemia Due to Inherited Harderoporphyria: Clinical Characteristics and Molecular Basis

Porphyrias, a group of inborn errors of heme synthesis, are classified as hepatic or erythropoietic according to clinical data and the main site of expression of the specific enzymatic defect. Hereditary coproporphyria (HC) is an acute hepatic porphyria with autosomal dominant inheritance caused by deficient activity of coproporphyrinogen III oxidase (COX). Typical clinical manifestations of the disease are acute attacks of neurological dysfunction; skin photosensitivity may also be present. We report a variant form of HC characterized by a unifying syndrome in which hematologic disorders predominate: harderoporphyria. Harderoporphyric patients exhibit jaundice, severe chronic hemolytic anemia of early onset associated with hepatosplenomegaly, and skin photosensitivity. Neither abdominal pain nor neuropsychiatric symptoms are observed. COX activity is markedly decreased. In a first harderoporphyric family, with three affected siblings, a homozygous K404E mutation has been previously characterized. In the present study, molecular investigations in a second family with neonatal hemolytic anemia and harderoporphyria revealed two heterozygous point mutations in the COX gene. One allele bore the missense mutation K404E previously described. The second allele bore an A→G transition at the third position of the donor splice site in intron 6. This new COX gene mutation resulted in exon 6 skipping and the absence of functional protein production. In contrast with other COX gene defects that produce the classical hepatic porphyria presentation, our data suggest that the K404E substitution (either in the homozygous or compound heterozygous state associated with a mutation leading to the absence of functional mRNA or protein) is responsible for the specific hematologic clinical manifestations of harderoporphyria.

Preparation and separation of hydroxy derivatives of uroporphyrinogen I by high-performance liquid chromatography with electrochemical detection

The preparation and high-performance liquid chromatography (HPLC) separation of meso-hydroxyuroporphyrinogen I, hydroxyacetic acid uroporphyrinogen I and beta-hydroxypropionic acid uroporphyrinogen I is described. meso-Hydroxyuroporphyrin I, hydroxyacetic acid uroporphyrin I and beta-hydroxypropionic acid uroporphyrin I were isolated from the urine of a patient with congenital erythropoietic porphyria. The porphyrins were reduced to the corresponding porphyrinogens with 3% (w/w) Na/Hg amalgam. The hydroxy porphyrinogens were separated on a Hypersil ODS column with 4% (v/v) acetonitrile in 1 M ammonium acetate buffer, pH 5.16, containing EDTA (0.27 mM) as the mobile phase, and detected electrochemically. Reduction of meso-hydroxyuroporphyrin I and hydroxyacetic acid uroporphyrin I, followed by HPLC analysis, showed that, in addition to the expected formation of meso-hydroxyuroporphyrinogen I and hydroxyacetic uroporphyrinogen I, respectively, uroporphyrinogen I was also produced. Reduction of beta-hydroxypropionic acid uroporphyrin I, however, gave beta-hydroxypropionic acid uroporphyrinogen I, acrylic acid uroporphyrinogen I and uroporphyrinogen I as the products. The peaks were identified by conversion into the porphyrin methyl esters and analysed by liquid secondary-ion mass spectrometry.

Preparation, high-performance liquid chromatographic separation and characterization of hexacarboxylic porphyrinogens

A simple method for the preparation and reversed-phase high-performance liquid chromatographic separation of hexacarboxylic porphyrinogen isomers is described. Uroporphyrin I or III was partially decarboxylated in 0.5 M hydrochloric acid at 150 degrees C. Unreacted uroporphyrin and the hepta-, hexa- and pentacarboxylic porphyrins formed were esterified and then group-separated by thin-layer chromatography. After hydrolysis, the porphyrins were reduced to the corresponding porphyrinogens with 3% (w/w) sodium amalgam. The hexacarboxylic porphyrinogens were separated on an ODS-Hypersil column by elution with acetonitrile-methanol-1 M ammonium acetate, pH 5.16 (8:12:80, v/v/v) as mobile phase. Isomers were identified by high-performance liquid chromatography of the characteristic mixture of two pentacarboxylic porphyrins formed after partial decarboxylation of individual isomers. Except for the two type I isomers, resolution of the hexacarboxylic porphyrinogens was superior to that of the corresponding porphyrins.

High-performance liquid chromatography of porphyrins

Techniques for the analysis of porphyrins in the biomedical fields are reviewed. The emphasis is on high-performance liquid chromatography and its aspplications in: (1) the quantitative analysis of porphyrins in blood, urine and faeces; (2) qualitative porphyrin profiles in normal subjects and in the porphyrias; (3) assay of haem biosynthetic enzyme activities and (4) resolution of type isomers of porphyrins and porphyrinogens. Detection systems, quantitation methods, peak identification and sample preparation procedures are discussed.

Detection of non-typical porphyrin isomers in human urines by ion-pair reversed-phase high-performance liquid chromatography

An improved ion-pair reversed-phase high-performance liquid chromatographic system has been developed for the separation of uroporphyrin isomers I, II and III, whereas the isomers III and IV could not be resolved. Application of this method to the analysis of urines from porphyric patients indicated the presence of small amounts of the non-typical uroporphyrin isomer II. The questionable presence of the isomer IV was confirmed by acid-catalyzed decarboxylation to the corresponding coproporphyrin isomers, which were completely separated by a modified ion-pair method at elevated column temperatures. These procedures enabled the detection of small fractions of the atypical isomers II (1-3%) and IV (8-15%) besides the normal isomers I and III in urines of patients suffering from attacks of acute intermittent porphyria. Because such urines contain large amounts of porphobilinogen, the nonenzymatic self-condensation of porphobilinogen to uroporphyrinogens was studied under mild reaction conditions. In these experiments quite similar isomeric compositions were observed as compared to those in urines of patients with acute intermittent porphyria. Thus the non-typical uroporphyrin isomers II and IV present in human urines originate from a simple non-enzymatic condensation of porphobilinogen.

High-performance liquid chromatography of type-III heptocarboxylic porphyrinogen isomers

A reversed-phase h.p.l.c. system is described for the separation of the four type-III heptacarboxylic porphyrinogen isomers. The effects of buffer concentration, pH and type and proportion of organic modifier in the mobile phase on retention and resolution of isomers were studied. Optimum separation on an ODS-Hypersil column was by elution with a ternary mobile phase of acetonitrile, methanol and 1 M-ammonium acetate, pH 5.16 (7:3:90, by vol.). Isomer identification was based on a comparison of their retention times with those of authentic standards, and was further confirmed by h.p.l.c. analysis of the characteristic mixture of three pentacarboxylic porphyrins formed after partial decarboxylation of individual isomers in 0.3 M-HCl at 160 degrees C.

Separation and characterization of pentacarboxylic porphyrinogen isomers by high-performance liquid chromatography with electrochemical detection

A reversed-phase h.p.l.c. system is described for the separation of all five naturally occurring pentacarboxylic porphyrinogen isomers. The compounds are detected electrochemically with high sensitivity. The peaks are positively identified by h.p.l.c. analysis of the pentacarboxylic porphyrinogens from reduction of pentacarboxylic porphyrins prepared by partial decarboxylation of hexa- and hepta-carboxylic porphyrin III of known structures. The resolution of pentacarboxylic porphyrinogens is superior to that of the porphyrins and the method is applicable to the small-scale preparative isolation of pure isomers.