Identification of monovinyl tripropionic acid porphyrins and metabolites from faeces of patients with hereditary coproporphyria by high-performance liquid chromatography/electrospray ionization quadrupole time-of-flight tandem mass spectrometry

Liquid chromatography-tandem mass spectrometry of porphyrins and porphyrinogens in biological materials: separation and identification of interfering poly(ethylene) glycol by travelling wave ion mobility spectrometry/tandem mass spectrometry

Biological and clinical samples for porphyrin and porphyrinogen analyses by liquid chromatography-tandem mass spectrometry (LC-MS/MS) are often contaminated with poly(ethylene)glycol (PEG), which complicates the interpretation of mass spectra and characterisation of new porphyrin metabolites. Two contaminating PEG molecules (m/z 833 and m/z 835) were completely separated from uroporphyrin I (m/z 831) by travelling wave ion mobility spectrometry and characterised by tandem mass spectrometry. One of the PEG species (m/z 835) also co-eluted with uroporphyrinogen I (m/z 837) and was unresolvable by travelling wave ion mobility spectrometry/MS, therefore contaminating the MS/MS mass spectra owing to isotope distribution. These PEG species, with the [M + H](+) ions at m/z at 833 and/or m/z 835, co-eluted with uroporphyrin I and uroporphyrinogen I by LC-MS/MS and could be wrongly identified as uroporphomethenes.

Recent developments in the structural characterization of substituted meso-tetraarylporphyrins by electrospray tandem mass spectrometry

meso-tetraarylporphyrins with different substituents linked either to an aryl ring or to a β-pyrrolic position were studied by Electrospray (ESI) Tandem Mass Spectrometry (MS/MS). The electrospray mass spectra (ESI-MS) of meso-tetraarylporphyrins show the molecular ions and no significant fragmentation is noted. Structural information can be obtained by inducing fragmentation of the ions generated under ESI conditions. The product ions formed and registered in the tandem mass spectra (ESI-MS/MS) are characteristic of the chemical structure of the groups linked to the porphyrin and depend on their location. Also, the same functional group linked either to the aryl ring or to the β-pyrrolic position yields different product ions that confirm their position. Taking into consideration the Portugal-Spain special issue of the Journal of Porphyrins and Phthalocyanines, in this highlight we analyze the work done at the University of Aveiro related to the use of mass spectrometry in the structural characterization of meso-tetraarylporphyrins with carbohydrate, nitro and amino acid groups.

Travelling wave ion mobility mass spectrometry of 5-aminolaevulinic acid, porphobilinogen and porphyrins

RATIONALE

Human porphyrias, diseases caused by enzyme defects in haem biosynthesis, are characterised by the excessive production, accumulation and excretion of porphyrins and/or 5-aminolaevulinic acid (ALA) and porphobilinogen (PBG). A method for the simultaneous separation, detection and identification of ALA, PBG and porphyrins would greatly facilitate the screening and diagnosis of porphyrias. Such a method would also be invaluable for the biochemical study of the haem, chlorophyll and corrin pathways.

METHODS

An aqueous mixture containing ALA, PBG and type I isomer porphyrins was diluted with acetonitrile and infused (10 μL/min) into a Waters Synapt G2 high-definition mass spectrometer, equipped with a Z-Spray electrospray ionisation (ESI) source. Mass spectra were acquired in positive ionisation mode and the optimised ion mobility spectrometry (IMS) conditions were as follows: IMS wave height (V), 40; IMS wave velocity (m/s), 648; IMS gas flow (mL/min) 90.40; helium gas flow (mL/min), 182.60.

RESULTS

The IMS drift-time increased with increasing ion mass in the order of ALA, PBG, mesoporphyrin, coproporphyrin I, penta-, hexa- and heptacarboxylic acid porphyrin I and uroporphyrin I. The ESI-IMS-MS spectra shows that PBG could form two different positively charged ions by protonation [M+H](+) , m/z 227, or deprotonation [M - H](+) , m/z 225. The protonated PBG (m/z 227) easily eliminated ammonia in source and the fragment ion (m/z 210) was monitored instead. Doubly charged ions of porphyrins having different drift times from the protonated singly charged molecules were observed in high abundance, providing further structural characterisation.

CONCLUSIONS

We have shown, for the first time, an analytical method capable of simultaneously separating haem biosynthetic intermediates and metabolites, for a potential rapid clinical screening method for the porphyrias. IMS-MS allowed the separation of doubly charged porphyrin ions, which will be advantageous for the analysis of natural and synthetic tetrapyrrole compounds, while reducing the misinterpretation of contaminants.

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.

Ultra high-performance liquid chromatography of porphyrins

An ultra high-performance liquid chromatographic (UHPLC) system was developed and optimized for the separation of porphyrins of clinical interest. Optimum conditions for the simultaneous separation of uroporphyrin, hepta-, hexa-, penta-carboxylic acid porphyrins and coproporphyrin and their type I and III isomers on a Thermo Hypersil BDS C18 column (2.4 µm particle size, 100 × 2.1 mm i.d.) using a gradient elution with 10% (v/v) acetonitrile in 1.0 m ammonium acetate buffer (pH 5.16) and 10% (v/v) acetonitrile in methanol at a flow-rate of 0.4 mL/min. The effect of mobile phase buffer molarity on the sensitivity of fluorescence detection and resolution of porphyrin isomers was investigated. The method was successfully applied to the analysis of porphyrins extracted from the urine and faeces of patients with various human porphyrias.

Normal and abnormal heme biosynthesis. Part 7. Synthesis and metabolism of coproporphyrinogen-III analogues with acetate or butyrate side chains on rings C and D. Development of a modified model for the active site of coproporphyrinogen oxidase

Analogues of coproporphyrinogen-III have been prepared with acetate or butyrate groups attached to the C and D pyrrolic subunits. The corresponding porphyrin methyl esters were synthesized by first generating a,c-biladienes by reacting a dipyrrylmethane with pyrrole aldehydes in the presence of HBr. Cyclization with copper(II) chloride in DMF, followed by demetalation with 15% H(2)SO(4)-TFA and reesterification, gave the required porphyrins in excellent yields. Hydrolysis with 25% hydrochloric acid and reduction with sodium-amalgam gave novel diacetate and dibutyrate porphyrinogens 9. Diacetate 9a was incubated with chicken red cell hemolysates (CRH), but gave complex results due to the combined action of two of the enzymes present in these preparations. Separation of uroporphyrinogen decarboxylase (URO-D) from coproporphyrinogen oxidase (CPO) allowed the effects of both enzymes on the diacetate substrate to be assessed. Porphyrinogen 9a proved to be a relatively poor substrate for CPO compared to the natural substrate coproporphyrinogen-III, and only the A ring propionate moiety was processed to a significant extent. Similar results were obtained for incubations of 9a with purified human recombinant CPO. Diacetate 9a was also a substrate for URO-D and a porphyrinogen monoacetate was the major product in this case; however, some conversion of a second acetate unit was also evident. The dibutyrate porphyrinogen 9b was only recognized by the enzyme CPO, but proved to be a modest substrate for incubations with CRH. However, 9b was an excellent substrate for purified human recombinant CPO. The major product for these incubations was a monovinylporphyrinogen, but some divinyl product was also generated in incubations using purified recombinant human CPO. The incubation products were converted into the corresponding porphyrin methyl esters, and these were characterized by proton NMR spectroscopy and mass spectrometry. The results extend our understanding of substrate recognition and catalysis for this intriguing enzyme and have allowed us to extend the active site model for CPO. In addition, the competitive action of both URO-D and CPO on the same diacetate porphyrinogen substrate provides additional perspectives on the potential existence of abnormal pathways for heme biosynthesis.

Normal and abnormal heme biosynthesis. 6. Synthesis and metabolism of a series of monovinylporphyrinogens related to harderoporphyrinogen. Further insights into the oxidative decarboxylation of porphyrinogen substrates by coproporphyrinogen oxidase

A series of vinylporphyrinogens were prepared to probe the enzyme coproporphyrinogen oxidase (CPO). Six (2-chloroethyl)porphyrins were synthesized from a common dipyrrylmethane via a,c-biladiene intermediates in excellent yields. Subsequent dehydrohalogenation with DBU in refluxing DMF then gave the required vinylporphyrin methyl esters, including harderoporphyrin-I, harderoporphyrin-III, and isoharderoporphyrin. The corresponding porphyrinogen carboxylic acids were incubated with chicken red cell hemolysates, which contain the enzyme CPO, and the products analyzed. The 17-ethyl analogue of harderoporphyrinogen-III, but not its 13-ethyl isomer, was shown to be an excellent substrate for CPO in accord with a proposed model for the active site of this enzyme. In addition, harderoporphyrinogen-VII, the monovinyl intermediate in the metabolism of coproporphyrinogen-IV, was shown to be an equally good substrate for this enzyme. However, isoharderoporphyrinogen, which lacks the correct ordering of peripheral substituents, was also a substrate for CPO. Furthermore, a nonnatural type I isomer of harderoporphyrinogen was shown to be acted on by CPO, but in this case further metabolism was noted and this afforded an unprecedented trivinyl porphyrinogen product. The corresponding porphyrin methyl ester was isolated and characterized by FAB MS and proton NMR spectroscopy. The results from these studies allow the binding requirements of CPO to be further assessed and provide a series of substrates to investigate this poorly understood enzyme.

Coproporphyrin excretion and low thiol levels caused by point mutation in the Rhodobacter sphaeroides S-adenosylmethionine synthetase gene

A spontaneous mutant of Rhodobacter sphaeroides f. sp. denitrificans IL-106 was found to excrete a large amount of a red compound identified as coproporphyrin III, an intermediate in bacteriochlorophyll and heme synthesis. The mutant, named PORF, is able to grow under phototrophic conditions but has low levels of intracellular cysteine and glutathione and overexpresses the cysteine synthase CysK. The expression of molybdoenzymes such as dimethyl sulfoxide (DMSO) and nitrate reductases is also affected under certain growth conditions. Excretion of coproporphyrin and overexpression of CysK are not directly related but were both found to be consequences of a diminished synthesis of the key metabolite S-adenosylmethionine (SAM). The wild-type phenotype is restored when the gene metK encoding SAM synthetase is supplied in trans. The metK gene in the mutant strain has a mutation leading to a single amino acid change (H145Y) in the encoded protein. This point mutation is responsible for a 70% decrease in intracellular SAM content which probably affects the activities of numerous SAM-dependent enzymes such as coproporphyrinogen oxidase (HemN); uroporphyrinogen III methyltransferase (CobA), which is involved in siroheme synthesis; and molybdenum cofactor biosynthesis protein A (MoaA). We propose a model showing that the attenuation of the activities of SAM-dependent enzymes in the mutant could be responsible for the coproporphyrin excretion, the low cysteine and glutathione contents, and the decrease in DMSO and nitrate reductase activities.

High-performance liquid chromatography/electrospray ionization tandem mass spectrometry of hydroxylated uroporphyrin and urochlorin derivatives formed by photochemical oxidation of uroporphyrinogen I

Hydroxylated uroporphyrin I and urochlorin I derivatives formed by photochemical oxidation of uroporphyrinogen I were separated by high-performance liquid chromatography and fully characterized by electrospray ionization tandem mass spectrometry. The porphyrins and chlorins were identified by analysis of their product ion spectra with each hydroxylated derivative giving a characteristic collision-induced dissociation fragmentation pattern. The porphyrins and chlorins characterized were meso-hydroxyuroporphyrin I, alpha-hydroxypropionic acid uroporphyrin I, beta-hydroxypropionic acid uroporphyrin I, hydroxyacetic acid uroporphyrin I, trans-7-hydroxy-8-spirolactoneurochlorin I, cis-7-hydroxy-8-spirolactoneurochlorin I and trans- and cis-7,8-dihydroxyurochlorins I.

Porphyrin profiles in blood, urine and faeces by HPLC/electrospray ionization tandem mass spectrometry

A high-resolution high-performance liquid chromatography/electrospray ionization quadrupole time-of-flight tandem mass spectrometry method is described for the analysis of porphyrins in blood, urine and faeces. The gradient elution reversed-phase HPLC system using acetonitrile-methanol-1 m ammonium acetate/acetic acid buffer (pH 5.16) as gradient solvent mixtures was able to separate all porphyrin metabolites, including the type I and type III isomers of uroporphyrin, hepta-, hexa- and penta-carboxylic acid porphyrins and coproporphyrin. The porphyrins were positively identified by the protonated molecules [M+H](+) and further characterized by tandem mass spectrometric analysis with each porphyrin giving a characteristic collisioninduced dissociation product ion spectrum. The mass chromatograms obtained by HPLC/ESI MS are useful for the differential diagnosis of the porphyrias, since each type of porphyria has a typical porphyrin excretion pattern.

Electrospray tandem mass spectrometry of new porphyrin amino acid conjugates

Porphyrin amino acid conjugates with one or two porphyrin units were analyzed by electrospray ionization tandem mass spectrometry (ESI-MS/MS). The ESI-MS spectra of all the porphyrins studied, obtained in positive ion mode, show the presence of the corresponding protonated molecule [M+H]+; ESI-MS spectra of diporphyrinyl compounds also show the doubly charged ions [M+2H]2+. The fragmentations of these ions induced by collision with argon were studied (ESI-MS/MS). ESI-MS/MS gives detailed structural information about the amino acids associated with the porphyrin. Cleavage of the bonds in the vicinity of the porphyrin moiety and those involving the side chain of amino acid residues gives structural information about this type of association. A fragmentation common to all derivatives corresponds to the cleavage of the phenyl-CO bond. The expected cleavage of the amide bond, that links the porphyrin to the amino acid moiety, is a minor fragmentation, which in some cases is even absent. The MS/MS spectra of the monoporphyrinyl derivatives show product ions characteristic of the amino acid linked to the porphyrin; the fragmentation also indicates when the amino acids has a terminal carboxylic group or a terminal ester group. The fragmentations of the diporphyrinyl compounds occur mainly by the cleavage of the spacer, leading, in the case of the doubly charged ions, to predominantly mono-charged ions, indicating a preferential location of the two protons in separated porphyrinic units.