Determination of Porphyrins in Biological Materials

Models for human porphyrias: Have animals in the wild been overlooked?: Some birds and mammals accumulate significant amounts of porphyrins in the body without showing the injurious symptoms observed in human porphyrias

Humans accumulate porphyrins in the body mostly during the course of porphyrias, diseases caused by defects in the enzymes of the heme biosynthesis pathway and that produce acute attacks, skin lesions and liver cancer. In contrast, some wild mammals and birds are adapted to accumulate porphyrins without injurious consequences. Here we propose viewing such physiological adaptations as potential solutions to human porphyrias, and suggest certain wild animals as models. Given the enzymatic activity and/or the patterns of porphyrin excretion and accumulation, the fox squirrel, the great bustard and the Eurasian eagle owl may constitute overlooked models for different porphyrias. The Harderian gland of rodents, where large amounts of porphyrins are synthesized, presents an underexplored potential for understanding the carcinogenic/toxic effect of porphyrin accumulation. Investigating how these animals avoid porphyrin pathogenicity may complement the use of laboratory models for porphyrias and provide new insights into the treatment of these disorders.

Drug-Induced Protoporphyria in Beagle Dogs

As part of regulatory safety testing program, a 13-week oral toxicity study with a new antipsychotic drug candidate was performed in beagle dogs. During this study, dark red/brown feces were recorded in treated dogs and increases in liver parameters (alanine aminotransferase, alkaline phosphatase, bilirubin) were measured biochemically. At the end of the study, livers of high-dose (50 mg/kg) animals were (mottled) dark brown, sometimes with pale foci. Histopathological examination of these livers showed dark globular pigment deposits in the hepatocellular cytoplasm and within the bile canaliculi. Varying numbers of inflammatory cell infiltrates were additionally present in association with the deposits. These pigment deposits showed birefringency with characteristic “Maltese Cross”-like structures under polarized light. Electronmicroscopy revealed the typical, so-called “sunburst” pattern with radiating double-lined crystalline structures. These morphologic characteristics strongly indicated at the presence of porphyrins, which was definitely confirmed biochemically. Published reports of drug-induced hepatic porphyria in dogs are rare. The possible underlying mechanism in the dog and man is discussed.

Measurement of erythrocyte protoporphyrin concentration by double extraction and spectrofluorometry

Quantification of the level of erythrocyte protoporphyrin can be used as a screening assay for lead exposure. In this method, porphyrins and heme compounds are extracted from whole blood using ethyl acetate, and porphyrins are then separated from heme by back-extraction with HCl solution. The extracted porphyrins are then quantified using a spectrofluorometer calibrated with protoporphyrin IX standard solutions.

Acute hereditary coproporphyria induced by the androgenic/anabolic steroid methandrostenolone (Dianabol)

Acute attacks of porphyria can be induced by certain drugs. We report a case of acute coproporphyria induced by methandrostenolone. This is the first report of acute porphyria induced by an androgenic, anabolic steroid.

Saturnism caused by hand-made plates: partial diagnosis by a computer-aided program

A man, aged 41 years, suffering from anaemia and abdominal pains was admitted to the Department of Medicine. Over the previous 2 years he had had several periods in hospital for these symptoms. There was, apparently, no occupational or accidental exposure to toxic substances and a correct diagnosis of the condition had not been possible. The computer-aided program AIDEDIAG II was therefore used to attempt a diagnosis. This approach indicated possible saturnism which was confirmed by metabolic and lead analyses. The lead source was identified as the hand-made food-plates used by the patient for his meals.

Coexistent hereditary coproporphyria and congenital erythropoietic porphyria (Günther disease)

We present data on one patient with an inheritance pattern for two porphyrias. From her mother she inherited the trait of hereditary coproporphyria; from both parents she inherited the trait of congenital erythropoietic porphyria (Günther disease). Enzyme studies confirmed this new type of dual porphyria.

Decreased leukocyte ferrochelatase activity in erythropoietic protoporphyria

We studied the porphyrin metabolism of a 7-year-old Japanese boy with erythropoietic protoporphyria (EPP) and his family members. Leukocyte ferrochelatase activity was markedly decreased in this patient, being approximately 12% of the mean value of normal controls (4 aged-matched healthy boys). In contrast, leukocyte delta-aminolevulinic acid (ALA) synthase activity was normal. The free protoporphyrin content of erythrocytes was greatly increased (4.3 mg/100 ml RBC), while erythrocyte ALA dehydratase and porphobilinogen (PBG) deaminase activities were 1.7- and 2.2-fold of respective control values. A survey of his family revealed that 12 of 19 members probably had manifest EPP or were EPP carriers. These results suggest that, in EPP, there might be an inherited impairement of ferrochelatase activity which gives rise to an elevation of erythroblast ALA dehydratase and PBG deaminase activities to compensate for a resultant decrease in heme production.

Characterization of porphobilinogen deaminase from rat liver

Porphobilinogen deaminase (porphobilinogen ammonia-lyase, EC 4.3.1.8) was isolated from rat liver. The final preparation was homogeneous according to polyacrylamide gel electrophoresis and immunodiffusion criteria. Electrophoresis of the native enzyme revealed a single band of activity which was distributed into three bands after incubation with porphobilinogen. When electrophoresed under denaturing condition it displayed a single polypeptide band with a molecular weight of 42,000 confirmed by exclusion chromatography and by sucrose density gradient centrifugation. The enzyme showed a pH optimum of 7.5 both in 0.1 M sodium phosphate and 0.05 M Tris-HCl buffer, when assayed at 37 degrees C. An isoelectric point of 4.9 for the native purified protein was found. Hepatic porphobilinogen deaminase was remarkably heat-stable showing maximum activity at 55-60 degrees C with one break in the Arrhenius plot. The kinetic behaviour of the purified enzyme followed the typical Michaelis-Menten kinetics with values of Km = 17 microM and Vmax = 29.4 units power mg in 0.1 M phosphate buffer at 37 degrees C. The amino acid composition was determined, showing that the enzyme had a low content of sulphur-containing amino acids and a considerable number of acidic residues per mol of polypeptide chain. Reagents known to interact with sulphydryl groups have small effect on rat liver enzyme activity.

Covalent binding to apoprotein is a major fate of heme in a variety of reactions in which cytochrome P-450 is destroyed

The heme in rat liver microsomal cytochrome P-450 was labeled with 14C or 3H and the microsomes were fractionated after in vitro incubations with a variety of agents known to destroy cytochrome P-450 heme. A major fraction of the heme label was irreversibly bound to apoprotein in all cases, including incubations with fluroxene, 1-octene, vinyl bromide, trichloroethylene, vinyl chloride, parathion, cumene hydroperoxide, NaN3, or iron-ADP complex. Label was also extensively bound to apoprotein when purified and reconstituted cytochrome P-450 was incubated with NADPH and vinyl chloride. This process appears to be widespread and involved to a significant extent in the cytochrome P-450 heme destruction observed with many compounds.

Determination of porphyrins by high performance liquid chromatography: fluorescence detection compared to absorbance detection

A comparison is made between determination of porphyrin methyl esters by high performance liquid chromatography (HPLC) with absorbance detection and with fluorimetric detection. Detection limits with absorbance detection vary from 0.8 pmol for 2-COOH-porphyrins to 5 pmol for 8-COOH-porphyrins. With fluorometric detection the corresponding figures are 0.04 pmol and 0.4 pmol. Fluorimetric detection also has a better reproducibility, and it is more specific than absorbance detection. The use of HPLC with fluorimetric detection thus permits rapid, highly efficient and specific quantitative detection and identification of porphyrins in complex biological samples.

Fluorometric measurement of tin-protoporphyrin in biological samples

Sn-protoporphyrin is a potent competitive inhibitor of heme oxygenase, can suppress neonatal and other forms of hyperbilirubinemia in laboratory animals, and represents a potential new approach to the treatment of neonatal jaundice in humans. In order to study the disposition of Sn-protoporphyrin in vivo we have developed a sensitive fluorometric method for the quantitation of this metalloporphyrin in biological samples. The method is sensitive to concentrations as low as 0.01 nmol/ml, and is specific for Sn-protoporphyrin even in the presence of other porphyrins such as protoporphyrin.

Protoporphyrinogen oxidase and ferrochelatase in porphyria variegata

Protoporphyrinogen oxidase activity and ferrochelatase activity were measured in leucocytes from patients with porphyria variegata. The mean activity of protoporphyrinogen oxidase (PPO) in porphyria variegata (PV) was about 50% of normal (P less than 0.05). The mean activity of ferrochelatase with 59Fe2+ sulphate and protoporphyrin as substrates (in the presence of ascorbic acid) was reduced by 40% (P less than 0.009). The mean activity of ferrochelatase with 59Fe3+ chloride and protoporphyrin as substrates (in the presence of reduced glutathione) was increased by 65% (P less than 0.005). Both are statistically highly significant. The findings are interpreted as follows: (a) The occurrence of a low level of protoporphyrinogen oxidase in PV is confirmed. (b) The findings indicate a concurrent structural change in ferrochelatase (this may be structurally related to (a) but no evidence of this is at present available).

The inherited enzymatic defect in porphyria variegata

Protoporphyrinogen oxidase activity and ferrochelatase activity have been measured in blood lymphocytes from patients with prophyria variegata, and from some members of the family of one patient; the mean activity of protoporphyrinogen oxidase from patients was about 50% of that in lymphocytes from normal subjects; similar results were obtained from asymptomatic carriers in two generations of the patient's family. This finding confirms that a protoporphyrinogen oxidase decreased activity reflects the primary genetic defect in Porphyria Variegata. Data of ferrochelatase activity have been found usually in the normal range and these results are discussed.

Second derivative-high-performance liquid chromatographic-fluorometric detection of porphyrins in chick embryo liver cell culture medium

A high-performance liquid chromatographic system is described which is suitable for the separation and quantitative determination of a mixture of porphyrin esters in nanogram quantities from the culture medium used for maintenance of a monolayer culture of chick embryo liver cells. The desired sensitivity was obtained by coupling a high-performance liquid chromatograph with a second derivative-fluorometric detection system. The most effective method for preparation of the porphyrin methyl esters prior to chromatography was found to be lyophilization of the culture medium prior to esterification with 5% sulphuric acid in methanol.

Stool porphyrins determined by high pressure liquid chromatography and by fractional hydrochloric acid--ether extraction

When stool copro- and protoporphyrin were quantitated by spectrophotometry, after fractional hydrochloric acid-ether extraction, up to 30% of the protoporphyrins were recovered in the coproporphyrin extract. In disorders with elevated stool protoporphyrin excretion (e.g. erythropoietic protoporphyria), this method therefore may give falsely elevated coproporphyrin values. When the stool porphyrins were determined by high pressure liquid chromatography there was no carry-over of protoporphyrin to coproporphyrin. The recoveries were 82 and 87%, and the coefficients of variation 5.6 and 3.1% for proto- and coproporphyrin, respectively. Moreover, in specimens containing a more complex mixture of porphyrins, a complete separation of the C2-C8 porphyrins and porphyrin isomers was obtained in a single run. High pressure liquid chromatography should therefore be considered the method of choice to obtain a quantitative profile of stool porphyrins in the routine laboratory.

Biochemistry and measurement of environmental lead intoxication

Lead is probably the oldest and most widely distributed environmental intoxicant, but unlike many of the synthetic agents which cause the greatest concern in industrial societies today, it occurs naturally at low levels in the environment and was present during evolutionary times. Galena (PbS), the most important lead-bearing mineral, is abundant and it is readily smelted. The metal is easily shaped and does not corrode and its compounds have found innumerable uses, particularly as pigments. This explains, in brief, why lead has had great economic importance since ancient times and why lead disease has plagued civilized societies for thousands of years and continues to be a serious concern to health authorities today. (Grandjean, 1975; Eisinger, 1977).

Uroporphyrin-accumulating mutant of Escherichia coli K-12

An uroporphyrin III-accumulating mutant of Escherichia coli K-12 was isolated by neomycin. The mutant, designated SASQ85, was catalase deficient and formed dwarf colonies on usual media. Comparative extraction by cyclohexanone and ethyl acetate showed the superiority of the former for the extraction of the uroporphyrin accumulated by the mutant. Cell-free extracts of SASQ85 were able to convert 5-aminolevulinic acid and porphobilinogen to uroporphyrinogen, but not to copro- or protoporphyrinogen. Under the same conditions cell-free extracts of the parent strain converted 5-aminolevulinic to uroporphyringen, coproporphyrinogen, and protoporphyrinogen. The conversion of porphobilinogen to uroporphyrinogen by cell-free extracts of the mutant was inhibited 98 and 95%, respectively, by p-chloromercuribenzoate and p-chloromercuriphenyl-sulfonate, indicating the presence of uroporphyrinogen synthetase activity in the extracts. Spontaneous transformation of porphobilinogen to uroporphyrin was not detectable under the experimental conditions used [4 h at 37 C in tris(hydroxymethyl)aminomethane-potassium phosphate buffer, pH 8.2]. The results indicate a deficient uroporphyrinogen decarboxylase activity of SASQ85 which is thus the first uroporphyrinogen decarboxylase-deficient mutant isolated in E. coli K-12. Mapping of the corresponding locus by P1-mediated transduction revealed the frequent joint transduction of hemE and thiA markers (frequency of co-transduction, 41 to 44%). The results of the genetic analysis suggest the gene order rif, hemE, thiA, metA; however, they do not totally exclude the gene order rif, thiA, hemE, metA.