Toxic dark effects of protoporphyrin on the cytochrome P-450 system in rat liver microsomes

Radioprotective effect of chloropyllin, protoporphyrin-IX and bilirubin compared with amifostine® in Drosophila melanogaster

The identification of substances that prevent or minimize the detrimental effects of ionizing radiation is an essential undertaking. The aim of this paper was to evaluate and compare the radioprotective potential of chlorophyllin, protoporphyrin and bilirubin, with amifostine®, an US Food & Drug Administration approved radioprotector Using the somatic mutation and recombination assay in the Drosophila melanogaster wing, it was found that pretreatment (1-9 h) with any of the porphyrins or amifostine® alone, did not affect the larva-adult viability or the basal frequency of mutation. However, they were associated with significant reductions in frequency of somatic mutation and recombination compared with the gamma-irradiated (20 Gy) control as follows: bilirubin (69.3 %)> chlorophyllin (40.0 %)> protoporphyrin (39.0 %)> amifostine® (19.7 %). Bilirubin also caused a 16 % increase in larva-adult viability with 3 h of pretreatment respect to percentage induced in 20 Gy control group. Whilst amifostine® was associated with lower genetic damage after pre-treatment of 1 and 3 h, this did not attain significance. These findings suggest that the tested porphyrins may have some potential as radioprotectant agents.

Chronic Treatment with Isoniazid Causes Protoporphyrin IX Accumulation in Mouse Liver

Isoniazid (INH) can cause hepatotoxicity. In addition, INH is contraindicated in patients suffering from porphyrias. Our metabolomic analysis revealed that chronic treatment with INH in mice causes a hepatic accumulation of protoporphyrin IX (PPIX). PPIX is an intermediate in the heme biosynthesis pathway, and it is also known as a hepatotoxin. We further found that INH induces delta-aminolevulinate synthase 1 (ALAS1), the rate-limiting enzyme in heme biosynthesis. We also found that INH downregulates ferrochelatase (FECH), the enzyme that converts PPIX to heme. In summary, this study illustrated that chronic treatment with INH causes PPIX accumulation in mouse liver in part through ALAS1 induction and FECH downregulation. This study also highlights that drugs can disrupt the metabolic pathways of endobiotics and increase the risk of liver damage.

Lamin aggregation is an early sensor of porphyria-induced liver injury

Oxidative liver injury during steatohepatitis results in aggregation and transglutaminase-2 (TG2)-mediated crosslinking of the keratin cytoplasmic intermediate filament proteins (IFs) to form Mallory-Denk body (MDB) inclusions. The effect of liver injury on lamin nuclear IFs is unknown, though lamin mutations in several human diseases result in lamin disorganization and nuclear shape changes. We tested the hypothesis that lamins undergo aggregation during oxidative liver injury using two MDB mouse models: (i) mice fed the porphyrinogenic drug 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) and (ii) mice that harbor a mutation in ferrochelatase (fch), which converts protoporphyrin IX to heme. Dramatic aggregation of lamin A/C and B1 was noted in the livers of both models in association with changes in lamin organization and nuclear shape, as determined by immunostaining and electron microscopy. The lamin aggregates sequester other nuclear proteins including transcription factors and ribosomal and nuclear pore components into high molecular weight complexes, as determined by mass-spectrometry and confirmed biochemically. Lamin aggregate formation is rapid and precedes keratin aggregation in fch livers, and is seen in liver explants of patients with alcoholic cirrhosis. Exposure of cultured cells to DDC, protoporphyrin IX or N-methyl-protoporphyrin, or incubation of purified lamins with protoporphyrin IX, also results in lamin aggregation. In contrast, lamin aggregation is ameliorated by TG2 inhibition. Therefore, lamin aggregation is an early sensor of porphyria-associated liver injury and might serve to buffer oxidative stress. The nuclear shape and lamin defects associated with porphyria phenocopy the changes seen in laminopathies and could result in transcriptional alterations due to sequestration of nuclear proteins.

Cellular damage to human hepatocytes through repeated application of 5-aminolevulinic acid

BACKGROUND/AIMS

5-Aminolevulinic acid (ALA), a precursor of porphyrins is used for photodynamic diagnosis and therapy within topical or systemic applications. A potential toxic effect on the human liver is of major interest and therefore we investigated the impact of a repeated application of ALA without illumination on cultures of human hepatocytes.

METHODS

After ALA treatment of hepatocytes in vitro the porphyrin synthesis, albumin secretion, liver-specific enzyme release, and malondialdehyde levels were determined. In order to reduce levels of reactive oxygen substances, mannitol and the antioxidant enzymes superoxide dismutase and catalase were supplemented.

RESULTS

Porphyrin biosynthesis by human hepatocytes in vitro was repeatedly stimulated by ALA (0.001-1.0 mM), which was indicated by an accumulation of protoporphyrin IX. A repetitive treatment (up to four times) of hepatocytes with ALA resulted in an impairment of the hepatic function and viability, depending on the ALA concentration (0.1-1.0 mM) and frequency of application (2-3 times). This was also accompanied by increased malondialdehyde levels indicating enhanced lipid peroxidation. Only superoxide dismutase was able to reduce cellular damage and prevent specific function.

CONCLUSIONS

Repeated, not single, ALA treatment without illumination may cause deleterious effects to the liver, which are mediated by oxygen radicals and inhibited by an antioxidant.

Liver pathology and hepatocarcinogenesis in a long-term mouse model of erythropoietic protoporphyria

Erythropoietic protoporphyria (EPP) is an inherited disease of haem synthesis caused by a mutation in one of the alleles of the enzyme ferrochelatase. This mutation leads to partial deficiency of the enzyme, resulting in increased concentrations of protoporphyrin (PP) in blood, liver, and faeces. Five to ten per cent of patients with EPP develop severe liver disease characterized by the presence of PP deposits. This study used histochemistry and immunohistochemistry to investigate the histopathological features present in the livers of 44 mice with a heterozygous or homozygous point mutation in the ferrochelatase gene (fch/+ and fch/fch mice, respectively). Some fch/+ mouse livers showed mixed steatosis and large cell dysplasia. The livers of fch/fch mice showed periportal or septal fibrosis accompanied by an atypical ductular reaction. These findings suggest that the obstruction and damage of a proportion of large and small bile ducts by PP deposits cause an accumulation of PP in the parenchyma, which leads to damage and loss of hepatocytes due to the toxic effects of PP. The classical stages of hepatocarcinogenesis were observed and hepatic progenitor cells appear to be involved in this process. PP acts as the promoting agent and is probably also the initiating agent.

DNA Damage and Repair in Gorlin Syndrome and Normal Fibroblasts After Aminolevulinic Acid Photodynamic Therapy: A Comet Assay Study¶

Using normal, untransformed, human fibroblasts, the effectiveness of aminolevulinic (ALA)-mediated photodynamic therapy (PDT) was investigated in terms of both clonogenic survival and DNA damage. The response of normal fibroblasts was then compared with Gorlin syndrome-derived fibroblasts (basal cell nevus syndrome [BCNS]). In terms of clonogenic survival, no significant differences were observed between the two groups of cells. Using the alkaline comet assay, initial DNA damage after PDT was measured. Some DNA damage was detected at higher doses, but this was fully repaired within 24 h of treatment. The BCNS-derived cells showed levels of initial damage that did not differ significantly from normal lines.

Cadmium-dependent enzyme activity alteration is not imputable to lipid peroxidation

The effect of cadmium on the liver-specific activities of NADPH-cytochrome P450 reductase (CPR), malic dehydrogenase (MDH), glyceraldehyde-3-phosphate dehydrogenase (GADPH), and sorbitol dehydrogenase (SDH) was assessed 6, 24, and 48 h after administration of the metal to rats (2.5 mg/kg of body weight, as CdCl2, single ip injection). CPR specific activity increased after 6 h and afterward decreased significantly, while MDH specific activity increased up to 24 h and then remained unchanged. Both SDH and GADPH specific activities reduced after 6 h, the former only a little but the latter much more, and after 24 and 48 h were strongly inhibited. In vitro experiments, by incubating rat liver microsomes, mitochondria, or cytosol with CdCl2 in the pH range 6.0-8.0, excluded cadmium-induced lipid peroxidation as the cause of the reduction in enzyme activity. In addition, from these experiments, we obtained indications on the type of interactions between cadmium and the enzymes studied. In the case of CPR, the inhibitory effect is probably due to Cd2+ binding to the histidine residue of the apoenzyme, which, at physiological pH, acts as a nucleophilic group. In vitro, mitochondrial MDH was not significantly affected by cadmium at any pH, indicating that this enzyme is probably not involved in the decrease in mitochondrial respiration caused by this metal. As for GADPH specific activity, its inhibition at pH 7.4 and above is imputable to the binding of cadmium to the SH groups present in the enzyme active site, since in the presence of dithiothreitol this inhibition was removed. SDH was subjected to a dual effect when cytosol was exposed to cadmium. At pH 6.0 and 6.5, its activity was strongly stimulated up to 75 microM CdCl2 while at higher metal concentrations it was reduced. At pH 7.4 and 8.0, a stimulation up to 50 microM CdCl2 occurred but above this concentration, a reduction was found. These data seem to indicate that cadmium can bind to different enzyme sites. One, at low cadmium concentration, stimulates the SDH activity while the other, at higher metal concentrations, substitutes for zinc, thus causing inhibition. This last possibility seems to occur in vivo essentially at least 24 h after intoxication. The cadmium-induced alterations of the investigated enzymes are discussed in terms of the metabolic disorders produced which are responsible for several pathological conditions.

Treatment of viral infections with 5-aminolevulinic acid and light

BACKGROUND AND OBJECTIVE

When 5-aminolevulinic acid (ALA) is exogenously supplied, protoporphyrin IX (PpIX) is accumulated in various cells and makes them light sensitive. The possibility of using such an approach for the treatment of viral infections was studied in this work.

STUDY DESIGN/MATERIALS AND METHODS

ALA was added to cultured cells infected with human immunodeficiency virus (HIV). Accumulation of PpIX in the cells as well as virus infectivity after photodynamic treatment (PDT) were assessed. For in vivo studies, guinea pigs were infected with herpes simplex virus (HSV) and then administered ALA at intervals after infection. The animals were exposed to PDT at the site of infection 3 hours after ALA administration. Clinical observations and virus titration were made daily. For clinical studies, two patients with Molluscum contagiosum and Verrucae vulgares were treated with ALA fortified with an iron chelating agent and dimethylsulfoxide, followed 4 hours later by PDT.

RESULTS

Cells that are infected with HIV accumulated PpIX upon addition of ALA in vitro. This accumulation was enhanced approximately two-fold in the presence of an iron chelator. Subsequent exposure to red light PDT drastically reduced the virus titer (> 99% for U1 cells latently infected with HIV). In guinea pigs infected with HSV, subsequent administration of ALA and exposure of the lesions to red light shortened the duration of vesicles' appearance from more than a week to a few days and reduced HSV titer in the lesions by > or = 5 log10. ALA-PDT treated AIDS patient suffering from Molluscum contagiosum or a kidney transplant patient with Verrucae vulgares showed greatly improved clinical symptoms one month after treatment.

CONCLUSION

It is concluded that ALA-PDT could be effective in treating certain viral infections, particularly those resulting in warts.

Cytotoxic and porphyrinogenic effects of diphenyl ethers in cultured rat hepatocytes: chlornitrofen (CNP), CNP-amino, chlomethoxyfen and bifenox

We studied the cytotoxic and porphyrinogenic effects of four diphenyl ethers (DPEs), chlornitrofen (CNP), CNP-amino, chlomethoxyfen and bifenox, in rat hepatocytes cultured on Matrigel. Cytotoxicity was determined as a decrease in viability measured by the release of lactate dehydrogenase. Of the DPEs examined. CNP-amino was the most cytotoxic, with an LC50 value of 0.36 mM (95% confidence interval, 0.33-0.40 mM). CNP also reduced the viability in a concentration-dependent manner at the concentrations of 0.50 mM or above. In contrast, no concentration-dependent decrease in viability was observed in the chlomethoxyfen- and bifenox-treated hepatocytes at the concentrations up to 1.0 mM. To identify the enzyme involved in the metabolic activation of CNP-amino, inhibition studies were carried out using SKF 525-A (0.050 mM) and methimazole (1.0 mM). SKF 525-A, a cytochrome P450 inhibitor. quickened the onset of cell killing by CNP-amino, while methimazole, an inhibitor of flavin-containing monooxygenase (FMO), partially suppressed the cytotoxicity of CNP-amino. These results suggest that FMO plays an important role in the cytotoxicity induced by CNP-amino, while cytochrome P450 participates in the detoxification, possibly via the ring-hydroxylation. The maximum porphyrin accumulation was observed at 0.13 mM for chlomethoxyfen (18-fold) and at 0.25 mM for CNP and bifenox (17- and 21-fold, respectively). In contrast to these DPEs, the porphyrinogenic effect of CNP-amino was weak, with the maximum accumulation at 0.13 mM (at least fivefold). The predominant species was protoporphyrin IX in all of the DPE-treated cultures. These results suggest that all of the DPEs examined, possibly including CNP-amino, inhibit protoporphyrinogen oxidase, resulting in the accumulation of protoporphyrin IX.

A fluorescence quenching study on protoporphyrin IX in a model membrane system

The interaction of protoporphyrin IX (3,7,12,15-tetramethyl-8, 13-divinyl-2,18-porphyrine-dipropionic acid) (PPIX) with unilamellar dimyristoyl-L-alpha-phosphatidylcholine (DMPC) phospholipid vesicles has been studied by means of steady-state fluorescence quenching spectroscopy. The method of fluorescence-quenching-resolved spectroscopy has been applied in order to resolve the complex emission spectrum of a membrane-bound PPIX into two component spectra, attributed to distinct fluorophore species with different accessibilities to the iodide quencher. It is shown that PPIX associated with liposomes exists in two different microenvironments. One part of the fluorophore is embedded inside the lipid bilayer and is inaccessible to iodide. Its fluorescence spectrum exhibits the maximum characteristic of protoporphyrin found in the apolar medium. The other fraction of PPIX is located near the membrane surface, close to the polar phospholipid heads. Its emission is blue-shifted, resembling that of PPIX in a polar environment. It is quenched by iodide, although it reveals significant shielding from the quencher as compared to a buffer PPIX solution. Fluorescence quenching using 1-oxyl-4-oxo-2,2,6,6-tetramethyl-piperidine (TEMPONE) does not discriminate between the two protoporphyrin species. However, the accessibility of protoporphyrin IX to this quencher is much lower in a liposome system than in water.

Photodynamic effects of protoporphyrin on the cellular level-an in vitro approach

The purpose of this study was characterizing the phototoxic action of protoporphyrin and cellular protection mechanisms, as studied on the cellular level. In this process, active oxygen is involved. As a biological system, rat hepatocyte short-term and primary cultures were used. Phototoxicity of protoporphyrin could be observed, after previous absorption of protoporphyrin to membrane structures. Damaging of several cell organelles occurred, such as mitochondria and lysosomes. Peroxisomes were not affected. Coated vesicles located at the periphery of the cells' interior suggested that protoporphyrin absorption is mediated by an active uptake (endocytosis), as well as passive diffusion. Lipid peroxidation played a role in protoporphyrin phototoxicity. Cellular protection mechanisms such as superoxide dismutase and the scavenger glutathione (GSH) protected the cells from active oxygen toxicity. In conclusion, protoporphyrin entered the cells by diffusion and endocytosis. Previous adsorption to the membrane structures was necessary for the expression of protoporphyrin phototoxicity. However, active oxygen itself could not be demonstrated. Lipid peroxidation was involved in cell-damaging processes. Mechanisms of protoporphyrin phototoxicity on the cellular level were studied. Rat hepatocyte primary and short-term cultures proved to be suitable in vitro systems for studying biochemical and morphological effects on the cellular level.

Does delta-aminolaevulinic acid induce genotoxic effects?

5-Aminolaevulinic acid (ALA) is a precursor of protoporphyrin IX (PpIX) in the biosynthetic pathway of haem. The presence of exogenous ALA bypasses the feedback control and may induce the accumulation of PpIX. Since haem-containing enzymes are essential for energy metabolism, every nucleated cell in the body must have at least a minimal capacity to synthesize PpIX. Photodynamic therapy (PDT), which is the treatment of malignant lesions with light following the administration of a tumour-localizing photosensitizer, leads to oxidative damage, including the formation of genotoxic membrane degradation products via lipid peroxidation. In addition, it has been demonstrated that ALA itself can form the reactive oxygen species Ox.-, H2O2 and OH. by auto-oxidation, suggesting that it could potentially induce DNA damage. Therefore cultures of rat hepatocytes, which have been demonstrated to be very sensitive indicators for genotoxic effects induced by the lipid peroxidation product 4-hydroxynonenal and analogous aldehydes, were examined for possible mutagenic effects after treatment with ALA in the absence of light. The cytogenetic endpoints determined were chromosomal aberrations and the induction of micronuclei. Compared with the controls, significantly elevated levels of chromosomal aberrations and micronuclei were observed at concentrations of 1 microgram ml-1 or greater. Chromosomal aberrations and micronuclei were found to increase up to a concentration of 100 micrograms ml-1 ALA. While micronuclei decrease at higher concentrations, chromosomal aberrations remain at the same level. The kinetics of PpIX formation after induction with 100 and 1000 micrograms ml-1 ALA appear to be the same for both concentrations, suggesting that the induction of chromosomal aberrations may be due to PpIX.

The pro- and antioxidant properties of protoporphyrin IX

The effect of protoporphyrin on lipid peroxidation in rat liver microsomes was investigated in the presence and absence of light. Protoporphyrin and light stimulated Fe(3+)-ADP/ascorbate-induced lipid peroxidation, whereas Fe(3+)-ADP/NADPH-mediated lipid peroxidation was inhibited. In the dark, on the other hand, protoporphyrin inhibited lipid peroxidation in both systems in a concentration-dependent manner. Protoporphyrin did not affect the reduction of the Fe(3+)-ADP complex by ascorbate, nor did it affect the activity of the NADPH-cytochrome P-450 reductase under these conditions. Uroporphyrin, a hydrophilic porphyrin and not localized in the membrane, did not inhibit lipid peroxidation in the dark in these systems, whereas bilirubin, a well-known radical scavenger and degradation product of protoporphyrin, inhibited lipid peroxidation in both systems. When peroxyl radicals were generated in solution by the azocompound 2,2'-azobis (2-amidino-propane)dihydrochloride lipid peroxidation was inhibited by both porphyrins and bilirubin. Reaction of bilirubin or protoporphyrin, in the presence of microsomes or human serum albumin, with these peroxyl radicals resulted in degradation of both compounds, which could be determined by a decrease in their absorbance at 460 or 407 nm, respectively. These results indicate that the inhibition of lipid peroxidation is most likely caused by scavenging of peroxyl radicals by protoporphyrin. Massive accumulation of protoporphyrin occurs in livers of erythropoietic protoporphyria patients. The fact that protoporphyrin was able to inhibit lipid peroxidation completely at micromolar concentrations also indicates that the deleterious effects of protoporphyrin, observed in these patients, are most likely not mediated by oxidation of lipids.