Studies of porphyrin synthesis in fibroblasts of patients with congenital erythropoietic porphyria and one patient with homozygous coproporphyria

Monk seal faeces as a non-invasive technique to monitor the incidence of ingested microplastics and potential presence of plastic additives

Anthropogenic debris, including plastics, has recently been identified as a major threat for marine mammals and the Marine Strategy Framework Directive aims to achieve the good environmental status of European waters by addressing among other criteria, the effects of marine litter on biota. This study implemented for the first time a non-invasive technique for collecting monk seal samples to assess microdebris ingestion in combination with identifying plastic additives and porphyrins biomarkers. A total of 12 samples of monk seal faeces were collected from marine caves in Zakynthos Island, Greece. A total of 166 microplastic particles were identified; 75 % of the particles were smaller than 3 mm. Nine phthalates and three porphyrins were detected. A strong correlation was found between the number of microplastics and the concentration of phthalates. The values of both phthalates and porphyrins were found lower than in other marine mammal tissues, suggesting that seals might not be impacted by them yet.

Persistent organic pollutants and porphyrins biomarkers in penguin faeces from Kopaitic Island and Antarctic Peninsula

Polychlorinated biphenyl (PCB) levels were determined in the faeces of three Antarctic Peninsula penguin species to assess viability as a non-invasive approach for sampling PCBs in Antarctic biota. These determinations were complemented with stable isotope and porphyrins assessments, and together this methodology determined the role of diet and metabolic disruption in penguins. Up to 60% of the collected faecal samples evidenced low molecular weight PCBs, of which, the more volatile compounds were predominant, in agreement with previous results. The highest PCB levels were reported in the gentoo penguin (Pygoscelis papua; 35.3ngg^-1 wet weight average), followed by the chinstrap (Pygoscelis antarctica; 6.4ngg^-1 wet weight average) and Adélie penguins (Pygoscelis adeliae; 12.9ngg^-1 wet weight average). Stable isotope analyses (δ¹⁵N and δ¹³C) demonstrated that gentoo feeding and foraging habits differed from those of Adélie and chinstrap penguins. A strong positive correlation was found between PCB concentrations and δ¹⁵N, indicating the role of diet on the observed pollutant levels. Porphyrins metabolite levels were also directly correlated with PCB concentrations. These results suggest that PCB levels impair the health of Antarctic penguins.

Pilot study on levels of chemical contaminants and porphyrins in Caretta caretta from the Mediterranean Sea

Perfluorinated compounds (PFCs), synthetic musks compounds (SMCs), bisphenol A (BPA), para-nonylphenol (p-NP) and polybrominated diphenyl ethers (PBDEs) are known for their toxicity and ability to interfere with the endocrine system. The aim of this study was to determine levels and distribution of the above mentioned compounds in liver samples of Caretta caretta and levels of porphyrins that have been proposed as sensitive biomarkers of exposure to contaminants. This paper reports the results for 9 specimens yet analysed. Musk ketone was never detected, PFOA was found in one sample, while PFOS was the prevalent contaminant. For PFCs the levels are lower than the results of studies of comparison. The porphyrins profile showed a predominance of protoporphyrins on coproporphyrins and uroporphyrins, with a positive statistical correlation between levels of PFOS and uroporphyrins. These data represent, for several parameters, the first evidence of contaminant levels and biomarker responses in loggerhead turtles.

Role of genetic testing in the management of patients with inherited porphyria and their families

The porphyrias are a group of mainly inherited metabolic conditions that result from partial deficiency of individual enzymes in the haem biosynthesis pathway. Clinical presentation is either with acute neurovisceral attacks, skin photosensitivity or both, and is due to overproduction of pathway intermediates. The primary diagnosis in the proband is based on biochemical testing of appropriate samples, preferably during or soon after onset of symptoms. The role of genetic testing in the autosomal dominant acute porphyrias (acute intermittent porphyria, hereditary coproporphyria and variegate porphyria) is to identify presymptomatic carriers of the family specific pathogenic mutation so that they can be counselled on how to minimize their risk of suffering an acute attack. At present the additional genetic factors that influence penetrance are not known, and all patients are treated as equally at risk. Genetic testing in the erythropoietic porphyrias (erythropoietic protoporphyria, congenital erythropoietic porphyria and X-linked dominant protoporphyria) is focused on predictive and preconceptual counselling, prenatal testing and genotype-phenotype correlation. Recent advances in analytical technology have resulted in increased sensitivity of mutation detection with success rates of greater than 90% for most of the genes. The ethical and consent issues are discussed. Current research into genetic factors that affect penetrance is likely to lead to a more refined approach to counselling for presymptomatic gene carriers.

Reduction in porphyrin excretion as a sensitive indicator of lead toxicity in primary cultures of adult rat hepatocytes

Alterations of specific metabolic pathways can be used as sensitive indicators of toxicity by chemicals and can give valuable information on the mechanism(s) involved. Short-term effects of lead on hepatic haem biosynthesis were studied in an in vitro system. Primary cultures of adult rat hepatocytes were exposed for 24-48 hr to lead (0.024-3.6 mm), and excreted and intracellular porphyrins were measured in untreated and lead-treated cultures. Cytotoxicity, as estimated by enzyme leakage, and morphological alterations were also evaluated. Control hepatocytes produced porphyrins at a rate of 387 pmol/mg cellular protein/day. Most of the released and intracellular porphyrins were protoporphyrins, although uro- and coproporphyrins were also detected in lower amounts. After 24 hr of exposure to 0.1-3.6 mm Pb(2+) , excreted porphyrins decreased by 24-92% and intracellular porphyrins by 36-60%, while 48 hr of exposure to 0.024-3.6 mm Pb(2+) caused a progressive reduction of 77-97% in porphyrin excretion and of 49-67% in intracellular porphyrins. Lead exposure also produced a differential decrease of proto-, copro- and uro-porphyrin excretion. These lead effects can be explained mainly by inhibition of the enzyme 5-aminolaevulinate dehydratase, resulting in a decreased monopyrrole supply for porphyrin biosynthesis, and probably by inhibition of the enzyme uroporphyrinogen decarboxylase. Morphological alterations and enzyme leakage were detected only after 24 hr of exposure to 2.4 mm and 48 hr of exposure to 3.6 mm Pb(2+), respectively. The results show that changes in porphyrin production, and particularly in their excretion, in cultured rat hepatocytes are useful indicators of lead toxicity, since they are more sensitive than enzyme leakage and can give preliminary information on the enzyme(s) that could be affected. They also suggest the potential benefits of the use of this method for the evaluation of compounds that alter haem biosynthesis.

Preliminary field study of hepatic porphyrin profiles of Astyanax fasciatus (Teleostei, Characiformes) to define anthropogenic pollution

The implementation of eco-toxicological assessment in South America is presently limited due to significant scientific information gaps concerning native species and their potential use as biomarkers. Recently, a common southern hemisphere fish species, Astyanax fasciatus, has been pointed out as a potential bio-indicator to anthropogenic pollution. This is a small, abundant, Neotropical characid, which is widely distributed from Central America south, to the Rio de la Plata Basin of western Uruguay. Our study found a statistically significant increase of coproporphyrin, uroporphyrin and protoporphyrin concentrations in hepatic tissues of A. fasciatus collected from a stream segment with high anthropogenic disturbance (due mainly to agricultural derivatives and motor vehicle transportation activities). Although the area studied showed differences in up and downstream limno-chemical parameters, these differences were not related to the increase of hepatic porphyrin concentrations. Based on the results of our study, we conclude that A. fasciatus is a good bio-indicator of exposure to environmental contaminants, and we propose that this abundant fish species be considered as a sentinel organism for monitoring potential disturbances to freshwater ecosystems.

A knock-in mouse model of congenital erythropoietic porphyria

Congenital erythropoietic porphyria (CEP) is a recessive autosomal disorder characterized by a deficiency in uroporphyrinogen III synthase (UROS), the fourth enzyme of the heme biosynthetic pathway. The severity of the disease, the lack of specific treatment except for allogeneic bone marrow transplantation, and the knowledge of the molecular lesions are strong arguments for gene therapy. An animal model of CEP has been designed to evaluate the feasibility of retroviral gene transfer in hematopoietic stem cells. We have previously demonstrated that the knockout of the Uros gene is lethal in mice (Uros(del) model). This work describes the achievement of a knock-in model, which reproduces a mutation of the UROS gene responsible for a severe UROS deficiency in humans (P248Q missense mutant). Homozygous mice display erythrodontia, moderate photosensitivity, hepatosplenomegaly, and hemolytic anemia. Uroporphyrin (99% type I isomer) accumulates in urine. Total porphyrins are increased in erythrocytes and feces, while Uros enzymatic activity is below 1% of the normal level in the different tissues analyzed. These pathological findings closely mimic the CEP disease in humans and demonstrate that the Uros(mut248) mouse represents a suitable model of the human disease for pathophysiological, pharmaceutical, and therapeutic purposes.

Effects of repeated administration with CP-55,940, a cannabinoid CB1 receptor agonist on the metabolism of the hepatic heme

Drugs metabolised by cytochrome P450 (CYP) such as analgesics may induce acute attacks in patients with hepatic porphyrias. In recent years, preclinical and clinical studies have suggested that cannabinoid pharmaceutical preparations may be potentially useful in the treatment of pain. The purpose of the study was to examine the effects of CP-55,940, a cannabinoid CB1 receptor agonist, on the hepatic heme metabolism in mice. To this end, hepatic activities of aminolevulinic acid synthase (ALAS), heme oxygenase (HO) and CYP levels were determined in mice treated with CP-55,940 (0.5 mg/kg/day; i.p.; 5 or 24 days). Results showed that treatment with CP-55,940 decreased CYP concentrations by 80% and increased HO activity by 158%. However, ALAS activity also decreased by 37%, suggesting that regulatory free heme pool was not modified. Our findings indicate that CP-55,940 and its metabolites do not behave as porphyrinogenic drugs and may potentially be safe for treating pain in patients with acute porphyrias.

Inducing coproporphyria in rat hepatocyte cultures using cyclic AMP and cyclic AMP-releasing agents

Cyclic AMP (c-AMP), added on its own to rat hepatocyte cultures, caused a marked accumulation of coproporphyrin III. The results obtained by comparing the effect of c-AMP to that of exogenous 5-aminolevulinate (ALA), and from adding c-AMP and ALA together, indicated that the coproporphyrinogen III metabolism was blocked, even though no inhibition of the relevant enzyme, coproporphyrinogen oxidase, could be demonstrated. Preferential accumulation of coproporphyrin could also be produced in cultures of rat hepatocytes by agents that raise the cellular levels of cyclic AMP, such as glucagon. The effect of supplementing the culture medium with triiodothyronine (T3) on the response of rat hepatocytes to c-AMP was also investigated. T3, which is known to stimulate mitochondrial respiration, uncoupling O2 consumption from ATP synthesis, produced a c-AMP-like effect when given on its own and potentiated the effect of c-AMP, with an apparent increase in the severity of the metabolic block. It is suggested that an oxidative mechanism may be activated in c-AMP and T3-induced coproporphyria, preferentially involving the mitochondrial compartment, leading to oxidation of porphyrinogen intermediates of haem biosynthesis, especially coproporphyrinogen. Coproporphyin, the fully oxidized aromatic derivative produced, cannot be metabolized and will therefore accumulate.

Hepatic gene expression in protoporphyic Fech mice is associated with cholestatic injury but not a marked depletion of the heme regulatory pool

BALB/c Fech(m1Pas) mice have a mutated ferrochelatase gene resulting in protoporphyria that models the hepatic injury occurring sporadically in human erythropoietic protoporphyria. We used this mouse model to study the development of the injury and to compare the dysfunction of heme synthesis with hepatic gene expression of liver metabolism, oxidative stress, and cellular injury/inflammation. From an early age expression of total cytochrome P450 and many of its isoforms was significantly lower than in wild-type mice. However, despite massive accumulation of protoporphyrin in the liver, expression of the main genes controlling heme synthesis and catabolism (Alas1 and Hmox1, respectively) were only modestly affected even in the presence of the cytochrome P450-inducing CAR agonist 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene. In contrast, in BALB/c mice exhibiting griseofulvin-induced hepatic protoporphyria with induction and destruction of cytochrome P450, both Alas1 and Hmox1 genes were markedly up-regulated. Other expression profiles in BALB/c Fech(m1Pas) mice identified roles for oxidative mechanisms in liver injury while modulated gene expression of hepatocyte transport proteins and cholesterol and bile acid synthesis illustrated the development of cholestasis. Subsequent inflammation and cirrhosis were also shown by the up-regulation of cytokine, cell cycling, and procollagen genes. Thus, gene expression profiles studied in Fech(m1Pas) mice may provide candidates for human polymorphisms that explain the sporadic hepatic consequences of erythropoietic protoporphyria.

Uroporphyria and hepatic carcinogenesis induced by polychlorinated biphenyls–iron interaction: Absence in the Cyp1a2(−/−) knockout mouse

Aryl hydrocarbon receptor ligands, such as polychlorinated biphenyls (PCBs), cause inhibition of the heme biosynthesis enzyme, uroporphyrinogen decarboxylase; this leads to uroporphyria and hepatic tumors, which are markedly enhanced by iron overload in C57BL/10 and C57BL/6 strains of mice. Cyp1a2(-/-) knockout mice were used to compare the effects of CYP1A2 expression on uroporphyria and liver carcinogenesis. PCBs in the diet (100ppm) of Cyp1a2(+/+) wild-type mice caused hepatic uroporphyria, which was strongly increased by iron-dextran (800mg Fe/kg). In contrast, uroporphyria was not detected in Cyp1a2(-/-) knockout mice, although expression of CYP1A1 and CYP2B10 was greatly induced. After 57 weeks on this diet, hepatic preneoplastic foci and tumors were seen in the Cyp1a2(+/+) mice; numbers and severity were enhanced by iron. No foci or tumors were detected in Cyp1a2(-/-) mice, although evidence for other forms of liver injury was observed. Our findings suggest a link not only between CYP1A2, iron metabolism, and the induction of uroporphyria by PCBs, but also with subsequent hepatocarcinogenesis.

Rapid and Simultaneous Determination of Coproporphyrin and Protoporphyrin in Feces by Derivative Matrix Isopotential Synchronous Fluorescence Spectrometry

Background: Measurement of fecal porphyrins is important in the diagnosis of porphyria, but conventional methods to measure them have drawbacks. We explored the use of derivative matrix isopotential synchronous fluorescence (MISF) spectrometry for the measurement of coproporphyrin and protoporphyrin.

Methods: The MISF scanning route was selected based on information from the three-dimensional fluorescence spectrum, which was a combination of the contour line of protoporphyrin via a detection point of coproporphyrin and that of coproporphyrin via a detection point of protoporphyrin. Derivative technique eliminated the constant interfering signals. MISF was used to measure porphyrins in stools from 2 pregnant women and 20 healthy volunteers.

Results: The coproporphyrin and protoporphyrin spectra were resolved with almost no mutual interference. The amplitudes of the derivative peaks were linearly related to the concentrations of coproporphyrin up to 310 nmol/L and protoporphyrin up to 590 nmol/L. The detection limits for coproporphyrin and protoporphyrin were 1.2 and 1.7 nmol/L, respectively. The within-run imprecision (CV; n = 6) was 2.2% at 175 nmol/L for coproporphyrin and 2.3% at 500 nmol/L for protoporphyrin. Bland–Altman analysis indicated no significant differences between the proposed MISF method and conventional spectrophotometry or fluorimetry. Mean (SD) recoveries of porphyrins added to fecal samples were of 98 (7)% for coproporphyrin and 102 (4)% for protoporphyrin.

Conclusions: This technique provides spectral resolution of coproporphyrin and protoporphyrin, obviating the need for chromatographic separation, and measurements can be made in a single scanning. The method also appears suitable for routine testing of large numbers of samples.

Evaluation of the oral subchronic toxicity of AHTN (7-Acetyl-1,1,3,4,4,6-hexamethyl-1,2,3,4-tetrahydronaphthalene) in the rat

7-Acetyl-1,1,3,4,4,6-hexamethyl-1,2,3,4-tetrahydronaphthalene (AHTN) is used as a fragrance material in a wide variety of consumer products. Because of its widespread exposure, a 90-day oral feeding study, with 4-week recovery periods for selected rats, was conducted. AHTN was added to the diet of rats at levels calculated to result in mean daily doses of 1.5, 5, 15 or 50 mg AHTN/kg body weight/day. On completion of the treatment period, 3 males and 3 females from each of the high dose groups and controls were maintained for a treatment free period of 4 weeks. There were no adverse effects revealed upon clinical examination or following extensive histopathological examinations. Histopathological examination of the prostate, seminal vesicles, mammary gland and testes of males and ovaries, mammary gland, uterus and vagina of females, undertaken on all animals in all test groups, revealed no evidence of hormonal effects of AHTN. A statistically significant decrease in body weight gain was observed in both sexes in the high dose group only. Statistically significant effects were observed in hematology and blood chemistry, although these effects were all within the range for historical controls and were not proportional to dose. A green to dark brown coloration in the livers and mesenteric lymph nodes was also seen in high dose animals. At the end of the treatment-free period, the color change was almost completely reversed; one high dose male still had green colored lymph nodes, but the liver appeared normal. A green coloration of the lacrimal glands in females, but not males, was also seen in 8/12, 4/15 and in 1 female given 50, 15 and 5 mg/kg body weight/day, respectively. This green color was still present in 2/3 of the high dose females after the treatment-free period. Microscopic examination of unstained sections of frozen livers under UV illumination did not reveal any fluorescence that might have been consistent with porphyrin accumulation. These findings were clearly related to administration of AHTN, but were not accompanied by any histopathological changes. In discolored livers, all fractions of liver homogenate were abnormally colored; the change was most prominent in the mitochondria. Some dissolved pigment was obtained by extraction of liver homogenates with DMSO/trichloroacetic acid mixtures, but its identity remains to be established. Further work on the mechanism of production of the abnormal color is in progress. Based on these results, the 90-day conservative no-observed-effect level (NOAEL) is 1.5 mg/kg body weight/day.

Correction of the biochemical defect in porphobilinogen deaminase deficient cells by non-viral gene delivery

Porphobilinogen deaminase (PBGD), the third enzyme in the biosynthesis of heme, is deficient in acute intermittent porphyria (AIP). AIP is a genetic disease characterized by neurovisceral and psychiatric disturbances. Despite a palliative treatment, it may still be lethal. An initial step towards gene therapy was recently taken by showing that PBGD could be expressed to correct the enzyme deficiency in AIP fibroblasts. The aim of the present study was to investigate whether the biochemical defect can be corrected by using non-viral gene delivery. The biochemical defect in human and mouse PBGD deficient fibroblasts was demonstrated by analyzing synthesis of the heme precursor, protoporphyrin (PP), after addition of 5-aminolevulinic acid (ALA). Human AIP fibroblasts synthesized 21% and mouse PBGD deficient fibroblasts only 11% of the PP amount synthesized in respective control cells. Gene delivery increased the PBGD activity 88-200 fold in human AIP fibroblasts and synthesis of PP was increased from 21-152% of normal after ALA incubation. Similar results were obtained in mouse PBGD deficient cells, although the PP levels were several-fold lower as compared to human cells. HPLC analysis confirmed that PP was the main porphyrin intermediate that was formed. Addition of porphobilinogen (PBG) resulted in 3-7 fold lower synthesis of PP as compared to ALA addition. These results show that non-viral gene delivery of plasmids encoding PBGD results in a high expression of functional PBGD shown by induced synthesis of PP in PBGD deficient cells after supplementation of ALA and PBG.

The use of porphyrins as a non-destructive biomarker of exposure to contaminants in two sea lion populations

This study was carried out in two populations of Otariaflavescens, living in a polluted and in a reference site, in order to validate the use of porphyrins as a non-destructive biomarker of exposure to environmental contaminants. Analysis of porphyrins was carried out in the feces, blood and fur of free ranging sea lions and in the liver and kidney of stranded specimens. The results show that: (a) all biological materials used were useful for porphyrin determinations; (b) no clear seasonal variations in porphyrin accumulation and excretion were found; (c) differences in fecal porphyrin levels existed between the two colonies.

Multi-trial biomarker approach in Meganyctiphanes norvegica: a potential early indicator of health status of the Mediterranean "whale sanctuary."

The aim of this study was to propose a suite of biomarkers (BPMO activity, NADPH-cytocrome c reductase, NADH-ferricyanide reductase. esterases, porphyrins, vitellogenin and zona radiata proteins) and residue levels (organochlorines, PAHs and heavy metals) in the zooplanktonic euphausiid Meganyctiphanes norvegica as a potential multi-disciplinary diagnostic tool for assessment of the health status of the Mediterranean "whale sanctuary". Very little difference in BPMO was detected between sites, with values ranging from 0.75 to 2.68 U.A.F./mg prot/h. On the other hand larger differences between sites were found for reductase activities. Esterases (AChE), porphyrins (Copro-, Uro-, Proto-porphyrins) vitellogenin and zona radiata proteins were also detectable in this zooplanctonic species. Hg showed mean levels of 0.141 ppm d.w., Cd 0.119 ppm d.w. and Pb 0.496 ppm d.w. Total PAHs ranged from 860.7 to 5,037.9 ng/g d.w., carcinogenic PAHs from 40.3 to 141.7 ng/g d.w., HCB from 3.5 to 11.6 ng/g d.w., DDTs from 45.3 to 163.2 ng/g d.w. and the PCBs from 84.6 to 210.2 ng/g d.w.

Non-ahr gene susceptibility Loci for porphyria and liver injury induced by the interaction of 'dioxin' with iron overload in mice

Among the actions of 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) in mice is the induction of hepatic porphyria. This is similar to the most common disease of this type in humans, sporadic porphyria cutanea tarda (PCT). Evidence is consistent with the actions of dioxin being mediated through binding to the aryl hydrocarbon receptor (AHR) with different Ahr alleles in mouse strains apparently accounting for differential downstream gene expression and susceptibility. However, studies of dioxin-induced porphyria and liver injury indicate that the mechanisms must involve interactions with other genes, perhaps associated with iron metabolism. We performed a quantitative trait locus (QTL) analysis of an F(2) cross between susceptible C57BL/6J (Ahr(b1) allele) and the highly resistant DBA/2 (Ahr(d) allele) strains after treatment with dioxin and iron. For porphyria we found QTLs on chromosomes 11 and 14 in addition to the Ahr gene (chromosome 12). Studies with C57BL/6.D2 Ahr(d) mice confirmed that the Ahr(d) allele alone did not completely negate the response. SWR mice are syngenic for the Ahr(d) allele with the DBA/2 strain but are susceptible to porphyria after elevation of hepatic iron. Analysis of SWRxD2 F(2) mice treated with iron and dioxin showed a QTL on chromosome 11, as well as finding other loci on chromosomes 1 (and possibly 9), for both porphyria and liver injury. These findings show for the first time the location of genes, other than Ahr, that modulate the mechanism of hepatic porphyria and injury caused by dioxin in mice. Orthologous loci may contribute to the pathogenesis of human sporadic PCT.

The 5-aminolevulinic acid-induced porphyrin biosynthesis in benign and malignant cells of the skin

In fluorescence diagnosis and photodynamic therapy of neoplastic tissues 5-aminolevulinic acid is used to synthesize endogenous porphyrins as photosensitizers. The efficacy of neoplastic tissues to fluorescence diagnosis and photodynamic therapy is thought to be dependent on the total level of intralesional formed porphyrins. The available profiles of porphyrin metabolites in normal and in neoplastic cell lines after administration of 5-aminolevulinic acid vary considerably. Thus, this is the first in-vitro study which compares the porphyrin biosynthesis in normal skin cells (HaCaT, fibroblasts) with melanoma cells (Bro, SKMel-23, SKMel-28). After incubation with 1 mM 5-aminolevulinic acid, kinetics of porphyrin levels and metabolites were determined in the cells and the corresponding supernatants. Exogenous 5-aminolevulinic acid induced porphyrin formation in all cells with maximum values after an incubation period of 16-36 h. Increase of porphyrin levels varied from 10- to 80-fold (SKMel-28>HaCaT>fibroblasts>SKMel-23>>Bro) with minimum 1.5 times higher levels of porphyrins in the supernatants than in the cells. In cells and supernatants protoporphyrin and coproporphyrin were the predominantly formed porphyrin metabolites. Metastatic melanoma cells (SKMel-23, SKMel-28) accumulated much higher porphyrin levels than primary melanoma cells (Bro). In conclusion, by optimizing the treatment modalities, especially the light source, topical photodynamic therapy (PDT) could become a treatment alternative of melanoma metastases in progressive disease.

Elimination of POR expression correlates with red leaf formation in Amaranthus tricolor

Amaranthus tricolor L. tricolor cv. Earlysplendor, an ornamental amaranth, generates red leaves instead of green leaves in late summer to early autumn. Red leaf formation was promoted under short-day conditions and delayed by night-break treatments. Red leaves were characterized by lower levels of chlorophyll accumulation rather than higher levels of red pigment (betacyanin) accumulation. However, the metabolic activity toward the production of Mg-protoporphyrin, an intermediate in the biosynthesis pathway for chlorophyll, was detected in red leaves as well as in green leaves. RNA gel blot analysis was performed to assess the expression of nine genes encoding eight enzymes involved in chlorophyll biosynthesis. Among these enzymes, red-leaf-specific reduction of gene expression was observed only for NADPH-protochlorophyllide oxidoreductase (POR), a key enzyme catalyzing a later step of chlorophyll biosynthesis. In addition, immunoblot analysis showed no accumulation of POR protein(s) in red leaves. These data indicate that the repression of POR gene expression and resultant loss of chlorophyll synthesis activity plays a role in red leaf formation of A. tricolor.

Protection of the Cyp1a2(-/-) null mouse against uroporphyria and hepatic injury following exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin

The effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the liver of C57BL/6J mice is a model for clinical sporadic porphyria cutanea tarda (PCT). There is massive uroporphyria, inhibition of uroporphyrinogen decarboxylase (UROD) activity, and hepatocellular damage. A variety of evidence implicates the CYP1A2 enzyme as necessary for mouse uroporphyria. Here we report that, 5 weeks after a single oral dose of TCDD (75 microg/kg), Cyp1a2(+/+) wild-type mice showed severe uroporphyria and greater than 90% decreases in UROD activity; in contrast, despite exposure to this potent agent Cyp1a2(-/-) knockout mice displayed absolutely no increases in hepatic porphyrin levels, even after prior iron overload, and no detectable inhibition of UROD activity. Plasma levels of alanine-aminotransferase (ALT) and aspartate aminotransferase (AST)-although elevated in both genotypes after TCDD exposure-were significantly less in Cyp1a2(-/-) than in Cyp1a2(+/+) mice, suggesting that the absence of CYP1A2 also affords partial protection against TCDD-induced liver toxicity. Histological examination confirmed a decrease in hepatocellular damage in TCDD-treated Cyp1a2(-/-) mice; in particular, there was no bile duct damage or proliferation that in the Cyp1a2(+/+) mice might be caused by uroporphyrin. We conclude that CYP1A2 is both necessary and essential for the potent uroporphyrinogenic effects of TCDD in mice, and that CYP1A2 also plays a role in contributing to TCDD-induced hepatocellular injury. This study has implications for both the toxicity assessment of TCDD and the hepatic injury seen in PCT patients.

Successful therapeutic effect in a mouse model of erythropoietic protoporphyria by partial genetic correction and fluorescence-based selection of hematopoietic cells

Erythropoietic protoporphyria is characterized clinically by skin photosensitivity and biochemically by a ferrochelatase deficiency resulting in an excessive accumulation of photoreactive protoporphyrin in erythrocytes, plasma and other organs. The availability of the Fech(m1Pas)/Fech(m1Pas) murine model allowed us to test a gene therapy protocol to correct the porphyric phenotype. Gene therapy was performed by ex vivo transfer of human ferrochelatase cDNA with a retroviral vector to deficient hematopoietic cells, followed by re-injection of the transduced cells with or without selection in the porphyric mouse. Genetically corrected cells were separated by FACS from deficient ones by the absence of fluorescence when illuminated under ultraviolet light. Five months after transplantation, the number of fluorescent erythrocytes decreased from 61% (EPP mice) to 19% for EPP mice engrafted with low fluorescent selected BM cells. Absence of skin photosensitivity was observed in mice with less than 20% of fluorescent RBC. A partial phenotypic correction was found for animals with 20 to 40% of fluorescent RBC. In conclusion, a partial correction of bone marrow cells is sufficient to reverse the porphyric phenotype and restore normal hematopoiesis. This selection system represents a rapid and efficient procedure and an excellent alternative to the use of potentially harmful gene markers in retroviral vectors.

Comparison of spectrofluorometric and HPLC methods for the characterization of fecal porphyrins in river otters

A spectrofluorometric method (B. Grandchamp et al., 1980, Biochem. Biophys. Acta 629, 577-586) developed for the determination of amounts of uroporphyrin I (Uro I), coproporphyrin III (Copro III), and protoporphyrin IX (Proto IX) in skin fibroblasts was compared with a high-performance liquid chromatography (HPLC) method for the analysis of porphyrins in fecal samples of river otters (Lutra canadensis). Heptacarboxylate porphyrin I and coproporphyrin I, two porphyrins determined to be critical in defining the porphyrin profile in fecal samples of river otters with the HPLC method, contributed substantially to the calculation of the concentrations of Uro I and Copro III, respectively, in standard solutions of porphyrins with the spectrofluorometric method. Fluorescent components of the fecal matrix complicated the determination of the concentrations of Uro I, Copro III, and Proto IX with the spectrofluorometric method and resulted in erroneous values for the concentrations of these porphyrins compared with values determined with the HPLC method. These results indicate that the complexity of the sample, particularly with regard to the potential presence of interfering fluorescent compounds, as well as porphyrins additional to Uro I, Copro III, and Proto IX, should be considered prior to the application of the spectrofluorometric method. An alternative HPLC method developed for the rapid characterization of porphyrin profiles in fecal samples of river otters is described.

Reversion of hepatobiliary alterations By bone marrow transplantation in a murine model of erythropoietic protoporphyria

Erythropoietic protoporphyria (EPP) is characterized clinically by cutaneous photosensitivity and biochemically by the accumulation of excessive amounts of protoporphyrin in erythrocytes, plasma, feces, and other tissues, such as the liver. The condition is inherited as an autosomal dominant or recessive trait, with a deficiency of ferrochelatase activity. A major concern in EPP patients is the development of cholestasis with accumulation of protoporphyrin in hepatobiliary structures and progressive cellular damage, which can rapidly lead to fatal hepatic failure. The availability of a mouse model for the disease, the Fech(m1Pas)/Fech(m1Pas) mutant mouse, allowed us to test a cellular therapy protocol to correct the porphyric phenotype. When Fech/Fech mice received bone marrow cells from normal animals, the accumulation of protoporphyrin in red blood cells and plasma was reduced 10-fold but still remained 2.5 times above normal levels. Interestingly, in very young animals, bone marrow transplantation can prevent hepatobiliary complications as well as hepatocyte alterations and partially reverse protoporphyrin accumulation in the liver. Bone marrow transplantation may be an option for EPP patients who are at risk of developing hepatic complications.

Biomarker responses at different levels of biological organisation in crabs (Carcinus aestuarii) experimentally exposed to benzo(alpha)pyrene

The aim of this study was to validate a multi-trial biomarker approach for the evaluation of toxicological risk due to benzo(alpha)pyrene. Carcinus aestuarii, exposed to increasing concentrations of B(alpha)P in the water, was used as the bioindicator organism. A set of biomarkers were tested in order to: identify biological materials for biomarker and residue analysis; determine a group of sensitive techniques for the assessment of PAH contamination; investigate correlation between responses at different levels of biological organisation. The results underlined that BPMO activities in hepatopancreas and gills were a good biomarker of exposure to PAH-type compounds. B esterases activities in hemolymph and porphyrin patterns in excreta could be proposed as a non-destructive approach for evaluating chemical exposure in this species.

Heme biosynthesis in a chicken hepatoma cell line (LMH): comparison with primary chick embryo liver cells (CELC)

5-Aminolevulinic acid synthase (ALA synthase), the rate-controlling enzyme of hepatic heme biosynthesis, is feed-back repressed by heme. In the liver, chemicals such as barbiturates markedly induce ALA synthase, especially in the presence of partial defects of heme biosynthesis. The inducibility and regulation of ALA synthase have been investigated using a variety of models, including intact animals and liver cell culture systems. A widely used model that closely approximates what occurs in vivo and in humans is that of primary cultures of chick embryo liver cells (CELCs). However, CELCs have some limitations: the cells obtained are somewhat heterogeneous; isolation and culture must be repeated every week resulting in weekly variations; and cells are short-lived limiting the feasibility of time-course and transfection studies. The aim of this study was to determine if LMH cells, a chick hepatoma cell line, are a good model comparable to that of CELCs. In both cells similar patterns of response of, ALA synthase activities and mRNA levels, and of porphyrin accumulation were obtained following treatments known to affect heme biosynthesis. Similarly, heme repressed ALA synthase mRNA levels in both cell types and ALA synthase activities in LMH cells. We conclude that LMH cells are a useful model for the study of hepatic heme biosynthesis and regulation of ALA synthase.

Biomarker approach to evaluating the impact of scientific stations on the Antarctic environment using Trematomus bernacchii as a bioindicator organism

A biomonitoring study was performed to evaluate the human impact on two small coves adjacent to the Italian Scientific Station at Terra Nova Bay in November 1995. The study used the fish species Trematomus bernacchii as a bioindicator organism for a biomarker analysis based on porphyrin levels, and BPMO (Benzo(a)pyrene MonoOxygenase) and EROD (Ethoxyresorufin-O-deethylase) activities. Porphyrin levels and EROD and BPMO activities were found to be generally low. In contrast to previous years, no statistically significant difference was found between the potentially contaminated cove and the control cove after the Italian expedition had been active nearby for a period of one month. This indicates a marked decrease in certain types of contaminants such as organochlorines and trace metals, mainly due to improvements in waste disposal.

Effects of selected antihypertensives and analgesics on hepatic porphyrin accumulation: implications for clinical porphyria

When patients with acute porphyrias are treated with antihypertensives and analgesics, they could be placed at increased risk of developing porphyric attacks, since little is known about the potential for many of these drugs to induce these attacks. We used primary chick embryo liver cells, which maintain intact heme synthesis and regulation, to study the effects of antihypertensives and analgesics on porphyrin accumulation. Cells were treated with desferrioxamine to block heme synthesis partially, simulating conditions encountered in porphyric patients. Typically, cells were treated for 20 hr with the test drugs (3.16 to 1000 microM), along with desferrioxamine. Porphyrins were measured spectrofluorometrically, as uro-, copro,- and protoporphyrin. The evaluated drugs included six antihypertensives (two calcium channel blockers, an angiotensin receptor antagonist, and three inhibitors of angiotensin converting enzyme) and eight analgesics. Of the calcium channel blockers tested, nifedipine greatly increased porphyrin accumulation, whereas diltiazem caused only a slight increase. Losartan (an angiotensin receptor antagonist), captopril, or lisinopril (two angiotensin converting enzyme inhibitors) produced only small increases in porphyrin accumulation. In contrast, enalapril (another angiotensin converting enzyme inhibitor) substantially increased porphyrin accumulation when given in high concentrations. Among the analgesics tested, fentanyl and tramadol produced the highest porphyrin accumulations. Nalbuphine, hydrocodone, oxycodone, and dezocine were moderately or weakly porphyrogenic, whereas buprenorphine and morphine did not increase porphyrin accumulation. These studies suggest that patients with acute porphyrias may be at greater risk for developing porphyric attacks when treated with nifedipine (compared with diltiazem), enalapril (compared with captopril or lisinopril), and tramadol (compared with the other analgesics).

In vitro study of biosynthesis of protoporphyrin IX induced by delta-aminolevulinic acid in normal and cancerous cells of the human cervix

BACKGROUND

delta-Aminolevulinic acid (ALA) is recognized as the starter in the biosynthesis of the heme group, the structural basis of cytochromes, chlorophylls, biliary pigments, and other porphyrins. It is the first intermediary in the biosynthesis of protoporphyrin IX (PpIX), and of the heme group. PpIX is present in low concentration in normal cells, and in high concentration in tumor cells.

METHODS

The accumulation of protoporphyrin IX (PpIX) induced by delta-aminolevulinic acid (ALA) was tested in two cervico-uterine cancer cell lines (HeLa and CaLo), and in normal human cervical epithelial (NHCE) cells.

RESULTS

The optimal concentration of ALA that induced maximum levels of intra- and extracellular accumulation of PpIX in both HeLa and NHCE cells was 300 micrograms of ALA/mL, and for CaLo cells, 150 micrograms/mL. The viability of HeLa, CaLo, and NHCE cells exposed to ALA measured 81, 98, and 84%, respectively. The optimal time for accumulation of PpIX, both intra- and extracellular, was 4 h for HeLa and NHCE cells and 5 h for CaLo cells per 24 h of exposure to optimal concentrations of ALA. After the maximum level of PpIX accumulation was reached, there was a gradual decrease until there was only a small quantity. A statistically significant difference (p < 0.0001) was found in the accumulation of PpIX, depending on the concentrations of ALA used as well as between cervical cancer cell lines and NHCE cells (p < 0.0001). The concentration ratio of PpIX for NHCE and HeLa cells was 1:7, and for NHCE and CaLo cells, 1:5.

CONCLUSIONS

These results are important for determining the usefulness of the sensitizer (PpIX).

Effect of acute lead treatment on coproporphyrinogen oxidase activity in HepG2 cells

Acute toxic effects of lead were evaluated on porphyrin synthesis and coproporphyrinogen oxidase (CO) activity in an in vitro model, using HepG2 cells, a hepatoma cell line of human origin. Lead concentrations for exposure treatments were 0.5, 1.0, 2.5, 5.0 microM. No significant changes were found in treated cells with respect to uroporphyrin cellular or media concentrations. Cellular protoporphyrin increased in dose response shape, but no changes in extracellular content were found. Extracellular coproporphyrin concentration increased in a dose response manner without changes in cellular content. The CO activity was depressed in dose response shape, reaching 62% of control activity at 5.0 microM of lead treatment. The CO activity in Pb-treated cells was recovered after dithiothreitol (DTT) treatment, suggesting that sulphydryl groups play an essential role in the enzyme activity. The dose-response increase of coproporphyrin secretion accompanied by the depression of CO activity supports the suggestion that lead causes CO inhibition, as observed in this cellular model.

Formation of zinc protoporphyrin in cultured hepatocytes: effects of ferrochelatase inhibition, iron chelation or lead

The formation of zinc protoporphyrin in response to lead or iron depletion has previously been investigated in erythroid systems. Because of its possible metabolic role in non-erythroid tissue, we investigated the formation of zinc protoporphyrin in cultured hepatocytes. The effects of lead and inhibitors of ferrochelatase, the iron insertion step of heme synthesis, on the conversion of 5-aminolevulinic acid to zinc protoporphyrin, protoporphyrin and heme were compared in rat and chick embryo hepatocyte cultures. In rat cultures, zinc protoporphyrin was synthesized enzymatically by ferrochelatase, since N-methylmesoporphyrin, an inhibitor of ferrochelatase. caused 40% or greater decreases in both heme and zinc protoporphyrin accumulation and markedly stimulated protoporphyrin accumulation. In addition, chelation of ferrous iron with 2,2'-dipyridyl decreased heme accumulation by 50%, but increased ZPP accumulation by 200%. Zinc protoporphyrin formation in chick embryo hepatocytes required the addition of zinc as well as 5-aminolevulinic acid and apparently was non-enzymatic, since it was not inhibited by N-methylmesoporphyrin nor increased by iron chelation. In the presence of 5-aminolevulinic acid, lead had no effect on zinc protoporphyrin, protoporphyrin or heme accumulation in chick hepatocytes, but decreased all three in rat hepatocytes, with the decrease in protoporphyrin being far greater than that of zinc protoporphyrin or heme. These findings indicate that, in contrast to the effect of lead in erythroid tissue, it did not specifically increase zinc protoporphyrin accumulation or alter iron availability in cultured hepatocytes.

Interaction between iron metabolism and 2,3,7,8-tetrachlorodibenzo-p-dioxin in mice with variants of the Ahr gene: a hepatic oxidative mechanism

The binding of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) with the aryl hydrocarbon (AH) receptor and subsequent changes in gene expression have been studied intensively, but the mechanisms by which these lead to toxicity are unclear. We investigated the influence of iron, previously implicated in TCDD-induced hepatic porphyria, in mice with alleles of Ahr that encode receptors with varied affinity for TCDD. The administration of iron to Ahrb-1 C57BL/6J (AH-responsive) mice before a single dose of TCDD (75 micrograms/kg) markedly potentiated not only the hepatic porphyria but also general hepatocellular damage and elevation of plasma hepatic enzymes. The formation of hydroxylated and peroxylated derivatives of uroporphyrins formed from uroporphyrinogen and the induction of a mu-glutathione transferase (GST) were consistent with the operation of an oxidative mechanism. In a comparison of C57BL/6J mice with Ahrb-2 BALB/c (AH-responsive) and Ahrd SWR and DBA/2 (AH-nonresponsive) mice, iron overcame the weak hepatic porphyria and toxicity responses in BALB/c and SWR strains but not in DBA/2. CYP1A isoforms are strongly implicated in the mechanism of porphyria, but activities were lowered by 20-30% with iron treatment, and a comparison of levels between strains did not fully account for the resistance of DBA/2 mice. Studies with the use of gel shift assays and cytosolic aconitase of the capacity of the iron regulatory protein controlling the translation of some iron metabolism proteins showed a significant difference between C57BL/6J and DBA/2 mice after the administration of TCDD. We conclude that iron potentiates both the hepatic porphyria and toxicity of TCDD in susceptible mice in an oxidative process with disturbance of iron regulatory protein capacity. Iron even overcomes the AH-nonresponsive Ahrd allele in the SWR strain but not in DBA/2 mice, which remain resistant.

Congenital erythropoietic porphyria

Congenital erythropoietic porphyria is a rare autosomal-recessive disorder of the porphyrin metabolism caused by the homozygous defect of uroporphyrinogen III cosynthase. High amounts of uroporphyrin I accumulate in all cells and tissues, reflected by an increased erythrocyte porphyrin concentration and excretion of high porphyrin amounts in urine and feces. Dermal deposits of uroporphyrin frequently induce a dramatic phototoxic oxygen-dependent skin damage with extensive ulcerations and mutilations. Splenomegaly and hemolytic anemia are typical internal symptoms. Skeletal changes such as osteolysis and calcifications are frequent. To date 130 cases of congenital erythropoietic porphyria have been published and are summarized here. Splenectomy, erythrocyte transfusions, and bone marrow transplantation have shown some beneficial effect. The best therapy is the avoidance of sunlight. In the two patients with congenital erythropoietic porphyria described here, oral administration of the oxygen quenchers ascorbic acid and alpha-tocopherol resulted in an improvement in the reduced hemoglobin and erythrocyte concentrations.

Protoporphyria Induced by the Orally Active Iron Chelator 1,2-diethyl-3-hydroxypyridin-4-one in C57BL/10ScSn Mice

Administration in the drinking water of the orally-active iron chelator 1,2-diethyl-3-hydroxypyridin-4-one (CP94) to C57BL/10ScSn mice caused the development of hepatic protoporphyria. This was detected after 1 week and continued as long as the chelator was given (15 weeks). The more hydrophilic 1,2-dimethyl- and 1-hydroxyethyl,2-ethyl-analogues (CP20 and CP102) were also tested, but they were both inactive in inducing accumulation of protoporphyrin in the liver. Restriction of in vivo iron supply for ferrochelatase seemed a likely mode of action, but an approximately 30% decrease in activity of this enzyme was also observed when measured in vitro. Extracts of livers from mice given CP20, CP94, and CP102 showed no potential to inhibit mouse ferrochelatase, in contrast to the findings with an extract from mice treated with the known porphyrogenic chemical 4-ethyl - 3 , 5 - diethoxycarbonyl - 2 , 6 - dimethyl - 1 , 4 - dihydropyridine, -indicating that ferrochelatase inhibition did not occur by the formation of an N-ethyl-protoporphyrin derived from metabolism by cytochrome P450. CP20, CP94, CP102, and CP117 (the pivoyl ester of CP102) all caused significant depression of the levels of ferritin-iron and total nonheme iron, but only CP94 caused the significant accumulation of protoporphyrin. Protoporphyria did not occur with iron overloaded C57BL/10ScSn mice or in SWR mice that had elevated basal iron status. Although the protoporphyrin had only a small effect on the total levels of the hemoprotein cytochrome P450 in C57BL/10ScSn mice, the activity of the CYP2B isoforms of cytochrome P450 was actually induced in both strains. The results show that CP94 could cause protoporphyria in individuals of low iron status, perhaps through specifically targeting particular iron pools available to ferrochelatase and by concomitantly stimulating heme synthesis.

Uroporphyria induced by 5-aminolaevulinic acid alone in Ahrd SWR mice

In mice, depression of hepatic uroporphyrinogen decarboxylase (UROD) leading to porphyrin accumulation (uroporphyria) occurs with chlorinated ligands of the aryl hydrocarbon (AH) receptor especially after iron overload. However, in the absence of chlorinated ligands, iron itself will eventually cause uroporphyria, but this response is not associated with the Ahr genotype. These effects are potentiated by administration of the haem precursor 5-aminolaevulinate (ALA). The aim of this study was to investigate the effects of ALA alone. Prolonged administration of 2 mg ALA/mL in the drinking water to SWR mice also led to decarboxylase insufficiency (11% of control) and uroporphyria by 8 weeks, whereas DBA/2 mice did not show reduced enzyme activity. Both strains are considered AH nonresponsive and analysis of the Ahr gene using restriction fragment length polymorphism was consistent with SWR, like DBA/2, possessing the Ahrd allele. Exposure of isolated hepatocytes to ALA (150-500 microM) for up to 48 hr showed a significant accumulation of both uroporphyrin and coproporphyrin in the medium, which for uroporphyrin particularly was significantly greater with SWR than with DBA/2 cells. Basal in vivo CYP1A2 activity, measured as microsomal methoxyresorufin dealkylation, was significantly greater in SWR than in DBA/2 mice (1.3-fold), but it was unclear whether this was sufficient to explain the marked difference in sensitivities of the two strains. Despite SWR mice being AH nonresponsive, uroporphyria and decarboxylase depression after an initial iron overload and ALA for 3 weeks were greatly potentiated by a single dose (100 mg/kg) of hexachlorobenzene (a weak AH ligand). The results demonstrate that there is a genetic difference in mice independent of the Ahr genotype and response to iron, which influences the susceptibility to ALA-induced uroporphyria. Thus chemicals, iron and ALA can act independently, but also together, to cause porphyria in susceptible individuals.

3,5,5-Trimethylhexanoylferrocene induction of heme oxygenase activity in normal hepatocytes

Recent work showed that the combination of 50 microM glutethimide plus 50 microM ferric nitrilotriacetate (FeNTA) synergistically induces heme oxygenase (HO) activity in cultured chick embryo liver cells (Cable et al., Biochem Biophys Res Commun 168: 176-181, 1990). This synergistic induction is due to increased heme synthesis, which then acts to increase HO gene transcription. The aim of the current studies was to characterize the effects on hepatic heme metabolism of (3,5,5-trimethylhexanoyl)ferrocene (TMH-ferrocene), which causes hepatic iron-loading in rats. Unlike FeNTA, TMH-ferrocene alone maximally induced HO activity at 5-10 microM TMH-ferrocene. At higher concentrations, HO activities declined, as did total cellular protein synthesis. Induction of HO was maximal after a 12-hr exposure to TMH-ferrocene, similar to induction by glutethimide plus FeNTA. The effect of TMH-ferrocene on HO could not be ascribed to greater cellular uptake of iron, since cell-associated iron levels were higher after FeNTA than after TMH-ferrocene treatment. TMH-ferrocene (up to 20 microM) did not induce delta-aminolevulinic acid synthase activity. Uroporphyrin accumulation in cells treated with TMH-ferrocene was minimal, but the combination of TMH-ferrocene and glutethimide caused a synergistic increase in uroporphyrin accumulation, similar to treatment with glutethimide plus FeNTA. 4,6-Dioxoheptanoic acid, an inhibitor of heme synthesis, blocked the induction of HO caused by glutethimide and FeNTA, but did not decrease the induction of HO by TMH-ferrocene. TMH-ferrocene-mediated induction of HO does not appear to be due to lipid peroxidation, since malondialdehyde formation was greater for ferrocene (a structural analog of TMH-ferrocene that does not induce HO) than for TMH-ferrocene. Furthermore, the anti-oxidant, butylated hydroxyanisole, which prevented lipid peroxidation, decreased HO induced by glutethimide plus FeNTA, but butylated hydroxyanisole did not affect HO induced by TMH-ferrocene. We conclude that, unlike the combination of glutethimide plus FeNTA, TMH-ferrocene induces HO activity by a mechanism that is independent of cellular heme synthesis.

[Hepatic porphyria: diagnostic and therapeutic strategies]

Acute hepatic porphyrias are genetic diseases of heme synthesis with severe prognosis due to strong or acute abdominal pain and neurological complications. Clinical evolution is characterized by acute attacks frequently induced by either forbidden drugs, or infections, alcohol intake or often unknown factors. Modern treatment is perfusion of hematin, which is a stable form of heme. Hematin will induce again delta-aminolévulinic (ALA)-synthase synthesis repression. Its tolerance is perfect whereas clinical and biochemical efficiency is absolute in our experience, if initiated very early. This drug is now considered as the treatment of acute intermittent porphyria crises.

Formation of N-methyl protoporphyrin in chemically-induced protoporphyria. Studies with a novel porphyrogenic agent

1-[4-(3-Acetyl-2,4,6-trimethylphenyl)-2,6-cyclohexanedionyl]-O-eth yl propionaldehyde oxime (for short ATMP) is a novel porphyrogenic agent causing hepatic protoporphyria in the mouse. Mice given a single dose of the drug showed 24 h later a 70% inhibition of liver ferrochelatase and marked accumulation of protoporphyrin. These changes were not seen in similarly treated rats, guinea pigs, hamsters or chick embryos. A green pigment was isolated from the liver of mice treated with ATMP and identified by its electronic absorption spectrum and chromatographic properties on HPLC as N-methyl protoporphyrin. The ATMP pigment markedly inhibited the enzyme ferrochelatase in vitro, thus supporting its identification as N-methyl protoporphyrin. Two inhibitors of liver cytochrome P450, compound SKF 525-A and piperonyl butoxide, when given before ATMP, afforded protection against ATMP-induced porphyria and production of N-methyl protoporphyrin, suggesting a role of cytochrome P450 in the induction of the metabolic disorder. The most likely interpretation for these findings is therefore that ATMP is metabolized in the mouse to a reactive species, which in turn alkylates the haem moiety of liver cytochrome P450, thus producing N-methyl protoporphyrin. This inhibits ferrochelatase and, as a secondary response, protoporphyrin accumulates. This pathway of metabolism to the postulated reactive metabolite presumably does not occur to a significant extent in the other species examined and hence is the likely basis for the species difference in protoporphyria.

Effects of diphenyl ether herbicides on porphyrin accumulation by cultured hepatocytes

Several diphenyl ether herbicides, such as acifluorfen methyl, have been previously shown to cause large accumulations of the heme and chlorophyll precursor, protoporphyrin, in plants. Light-induced herbicidal damage is mediated by the photoactive porphyrin. Here we investigate whether diphenyl ether herbicides can affect porphyrin synthesis in rat and chick hepatocytes. In rat hepatocyte cultures, protoporphyrin, as well as coproporphyrin, accumulated after treatment with acifluorfen or acifluorfen methyl. Combination of acifluorfen methyl with an esterase inhibitor to prevent the conversion of acifluorfen methyl to acifluorfen resulted in a greater accumulation of porphyrins than caused by acifluorfen methyl or acifluorfen alone. In vitro enzyme studies of hepatic mitochondria isolated from rat and chick embryos demonstrated that protoporphyrinogen oxidase, the penultimate enzyme of heme biosynthesis, was inhibited by low concentrations of acifluorfen, nitrofen, or acifluorfen methyl with the latter being the most potent inhibitor. These findings indicate that diphenyl ether treatment can cause protoporphyrin accumulation in rat hepatocyte cultures and suggest that this accumulation was associated with the inhibition of protoporphyrinogen oxidase. In cultured chick embryo hepatocytes, treatment with acifluorfen methyl plus an esterase inhibitor caused massive accumulation of uroporphyrin rather than protoporphyrin or coproporphyrin. Specific isozymes of cytochrome P450 were also induced in chick embryo hepatocytes. These effects were not observed in the absence of an esterase inhibitor. These results suggest that diphenyl ether herbicides can cause uroporphyrin accumulation similar to that induced by other cytochrome P450-inducing chemicals such as polyhalogenated aromatic hydrocarbons in the chick hepatocyte system.

Differential potency of atropisomers of polychlorinated biphenyls on cytochrome P450 induction and uroporphyrin accumulation in the chick embryo hepatocyte culture

The atropisomers of 2,2',3,4,6-pentachlorobiphenyl (PeCB), 2,2',3,4,4',6-hexachlorobiphenyl (HeCB), and 2,2',3,3',4,4',6,6'-octachlorobiphenyl (OCB) were studied in the chick embryo hepatocyte culture to determine if chirality plays a role in the recognition events associated with the induction of cytochromes P450 and the accumulation of uroporphyrin (URO). Concentration-related induction of cytochrome P450 content, ethoxyresorufin-O-deethylase (EROD) and benzphetamine N-demethylase (BPDM) activities were measured. The rank order of potency for total cytochrome P450 induction was HeCB greater than OCB greater than or equal to PeCB. The (+)- and (-)-enantiomers of PeCB and OCB were of equal potencies as inducers of cytochromes P450, whereas the (+)-HeCB was greater than the (-)-HeCB. HeCB was a much more potent inducer of EROD activity than was either PeCB or OCB. EROD activity was induced to a much greater extent by the (+)-enantiomers of all compounds, with the (-)-enantiomers of PeCB and OCB being inactive. BPDM activity was induced by all three compounds in the order of OCB greater than or equal to HeCB greater than PeCB. The (-)-enantiomers were more potent inducers of BPDM activities than were the (+)-enantiomers, except for HeCB, in which the (+)- was more potent than the (-)-enantiomer. Analysis of porphyrin accumulation in cultures treated with delta-aminolevulinic acid revealed that (+)-HeCB caused the greatest percent URO accumulation, which also correlated with the greatest increase in EROD activity. All other enantiomers caused up to 47% URO accumulation, which did not correlate with an increase in EROD activity.

Homozygous variegate porphyria: a case report

Homozygous variegate porphyria is described in a 14-year-old girl with a unique clinical presentation of photosensitivity from the second year of life, mental retardation, clinodactyly, and normal growth rate. The erythrocyte protoporphyrin concentration was raised with the protoporphyrin being predominantly zinc-chelated, which appears to be characteristic for all homozygous hepatic porphyrias. Protoporphyrinogen oxidase activity in lymphoblasts was decreased in both patient and parents despite the latter having normal porphyrin excretion.

Strain and sex differences in the response of mice to drugs that induce protoporphyria: role of porphyrin biosynthesis and removal

A hepatic green pigment, inhibitory toward ferrochelatase, has been isolated from the liver of mice treated with griseofulvin, isogriseofulvin, or 3,5-diethoxycarbonyl-1,4-dihydrocollidine and has been shown to exhibit identical chromatographic characteristics to authentic N-methyl protoporphyrin. All four possible structural isomers have been demonstrated, and each drug produced primarily the same isomer. N-Methyl protoporphyrin has also been found in very small amounts in the liver of untreated mice, but the isomeric composition appeared to differ from that of the drug-induced N-methyl protoporphyrin. Intraperitoneal administration of 3,5-diethoxy-carbonyl-1,4-dihydrocollidine to female C3H/He/Ola and NIH/Ola inbred mice produced a marked dose-related loss of hepatic ferrochelatase activity, which was identical in magnitude in the two strains. Induction of hepatic 5-aminolevulinate synthase (ALA-S), and accumulation of liver protoporphyrin, however, were greater in C3H/He/Ola mice. The strain difference in ALA-S response was most marked when inhibition of ferrochelatase (the "specific" effect of the drug) was maximal, and this suggests that a genetic variation exists in the sensitivity of ALA-S to a second drug action, the so-called nonspecific action, which is shared by many lipid-soluble compounds. Male mice of three strains accumulated greater amounts of hepatic protoporphyrin than females after treatment with griseofulvin, yet no significant difference was found between the two sexes in the extent of ferrochelatase inhibition. Stimulation of ALA-S activity was slightly greater in males, but when porphyria was very marked, ALA-S activities were significantly lower in this sex.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of polychlorinated biphenyls on cytochrome P450 induction in the chick embryo hepatocyte culture

The effects of pure synthetic polychlorinated biphenyl (PCB) congeners on the induction of cytochrome P450 and associated activities were examined in cultured chick embryo hepatocytes. Dose-response effects for the induction of total cytochrome P450 ethoxyresorufin-O-deethylase (EROD) activity, and benzphetamine demethylase (BPDM) activity were studied using 10 selected tetra- to hexachlorinated PCB congeners. These studies revealed that PCBs caused effects in the chick hepatocyte culture different from previously observed effects in rat liver. Based on their effects in chick hepatocytes, the PCBs could be categorized into two groups. The first group (consisting of 3,3',4,4'-PCB, 3,3',4,4',5-PCB, 3,3',4,4',5,5'-PCB, 2',3,3',4,5-PCB, 2,3,3',4,4',5'-PCB, and 2,3,4,4',5-PCB) induced total cytochrome P450 2.4- to 2.9-fold and EROD activity from 1-2 pmol/min/mg protein to 162-247. There was marked variation in potency, but all these congeners had a maximal inducing dose above which cytochrome P450 concentrations and EROD activities declined. BPDM activities were increased only slightly (1.2- to 1.6-fold) at the maximal cytochrome P450 inducing dose. The second group of congeners (consisting of 2,2',4,5,5'-PCB. 2,2',4,4',5,5'-PCB, and 2,2',3,4,4',6-PCB) induced total cytochrome P450 concentrations 4.0-fold and BPDM activities 2.2- to 2.6-fold with greatest activity occurring at the highest doses which could be added (10-50 microM). However, EROD activities were also increased by these congeners to 60-112 pmol/min/mg protein with declining activities seen at the highest PCB doses (i.e., resembling EROD induction patterns of the first group). The EROD induction patterns with these latter PCB congeners are noteworthy since these PCBs do not induce EROD activity in the rat. For both groups of PCB congeners, EROD induction was associated with increased accumulation of uroporphyrin in cultures exposed to exogenous 5-aminolevulinate. Studies investigating the reason for the depression of cytochrome P450 concentrations and/or EROD activities by high doses of the PCBs revealed that with the first group there was slightly decreased total protein synthesis, decreased total cell heme concentrations, and decreased accumulation of radiolabeled heme synthesized from 5-[14C]aminolevulinate. These changes might represent nonspecific toxic effects of the first group of PCBs. However, since these changes were not seen with the second group of PCBs, it is unlikely that either inhibition of heme synthesis or toxicity cause the depression of EROD activity with high PCB doses.

The degradation of haem by carbon tetrachloride: metabolic activation requires a free axial coordination site on the haem iron and electron donation

1. The ability of haem to catalyse the reductive activation of carbon tetrachloride (CCl4) in vitro has been investigated under anaerobic conditions, using methaemalbumin (MHA) and either sodium dithionite or NADPH together with NADPH-cytochrome P-450 reductase (EC 1.6.2.4) as the reducing agents. 2. In the non-enzymic system protohaem and other non-physiological haem analogues underwent rapid and extensive CCl4-dependent degradation, due to irreversible modification of their porphyrin tetrapyrrolic structure. 3. This mechanism of non-enzymic activation of CCl4 by protohaem mimics that catalyzed by cytochrome P-450 in that it requires a free, reduced haem iron and electron donation and it is largely prevented by carbon monoxide. 4. H.p.l.c. analysis of 14C-haem after anaerobic incubation with CCl4 and sodium dithionite gave radioactive products which eluted before and after haem, and exhibited significantly lower absorbance at 400 nm compared with authentic haem. When the products of CCl4-dependent haem degradation were methylated and applied to silica for t.l.c., two non-fluorescent pigments were isolated, purified and partially characterized. 5. On incubation of haem with 14CCl4 and sodium dithionite a 1:1 stoichiometry could be calculated for haem loss and 14CCl4-derived adduct formation, indicating that, as with microsomes, the loss of haem may be the result of a typical 'suicidal' inactivation reaction where the same haem moiety is both the site of CCl4 activation and the target of CCl4 reactive metabolites.

Mechanism of iron potentiation of hepatic uroporphyria: studies in cultured chick embryo liver cells

Effects of iron were studied in cultured chick embryo liver cells to help elucidate the effect of hepatic iron in the human disease porphyria cutanea tarda and in toxic porphyria caused by chemicals. These cultures have proven useful because (a) phenobarbital and phenobarbital-like drugs induce a common form(s) of cytochrome P-450 (P-450-phenobarbital) in these cultures; (b) 20-methylcholanthrene and certain other polycyclic hydrocarbons induce a different form(s) (P-450-methylchol-anthrene), and (c) uroporphyria can be produced rapidly by exposure to suitable chemicals. In these cultures, treatment with iron alone did not produce porphyrin accumulation, and treatment with iron + 5-aminolevulinate caused accumulation of protoporphyrin, as did treatment with 5-aminolevulinate alone. However, treatment with phenobarbital-like drugs and iron, the latter at a concentration as low as 0.2 microM, led to accumulation of uro- and heptacarboxylporphyrins. Potentiation of uroporphyrin accumulation by iron began before there was a detectable synergistic increase in activity of 5-aminolevulinate synthase, the rate-controlling enzyme of heme synthesis. In contrast, treatment of cultures with 20-methylcholanthrene, in the presence or absence of iron, did not result in uroporphyrin accumulation or an increase in the activity of 5-aminolevulinate synthase. Uroporphyrinogen decarboxylase activity was unchanged by drug and iron treatments. Inhibitors of P-450-phenobarbital, SKF525A and piperonyl butoxide, as well as cadmium and cycloheximide prevented the porphyrin accumulation produced by glutethimide + iron, even though, except with cycloheximide, these substances further increased 5-aminolevulinate synthase activity. In vitro, uroporphyrin was oxidized autocatalytically by iron. In intact hepatocytes, even low concentrations of iron (0.2 to 20 microM), in the presence of a form of cytochrome P-450 induced by phenobarbital-like chemicals, produces uroporphyria primarily by enhancing uroporphyrinogen oxidation, not by inhibition of the decarboxylase. Induction of 5-aminolevulinate synthase amplifies the porphyrin overproduction.

Hepatic mitochondrial oxidative metabolism and lipid peroxidation in experimental hexachlorobenzene-induced porphyria with dietary carbonyl iron overload

Both human porphyria cutanea tarda and experimental hexachlorobenzene-induced porphyria are associated with hepatic injury and are potentiated by excess hepatic iron. The mechanisms whereby cellular injury occurs and the synergistic role of iron overload are unknown. In the present experiments, we studied hepatic mitochondrial function and lipid peroxidation in rats with hexachlorobenzene-induced porphyria in which iron loading was achieved by dietary carbonyl iron supplementation. Female rats were treated for 8 weeks, receiving a chow diet supplemented with hexachlorobenzene (0.2%, w/w), carbonyl iron (1.0%, w/w) or hexachlorobenzene + iron. Hepatic total porphyrins were increased 100-fold in rats receiving hexachlorobenzene (hexachlorobenzene alone and hexachlorobenzene + Fe), and total hepatic iron was increased approximately 10-fold in rats receiving iron supplementation (Fe alone and hexachlorobenzene + Fe). There was a significant increase in mitochondrial lipid peroxidation in rats treated with hexachlorobenzene alone and hexachlorobenzene + Fe. A significant reduction in mitochondrial respiratory control ratios and in oxidative phosphorylation (ADP/O ratios) using glutamate and succinate as substrates was demonstrated when rats were treated with hexachlorobenzene + iron. The reductions in respiratory control ratios were due to a combination of an inhibitory defect in electron transport as evidenced by an irreversible decrease in State 3 respiration and an uncoupling effect as evidenced by an increase in State 4 respiration. These findings suggest that lipid peroxidation and mitochondrial dysfunction may contribute to the hepatotoxicity seen in hexachlorobenzene-induced porphyria.