Experimental porphyric neuropathy: a preliminary report

Protoporphyrin IX-induced phototoxicity: Mechanisms and therapeutics

Protoporphyrin IX (PPIX) is an intermediate in the heme biosynthesis pathway. Abnormal accumulation of PPIX due to certain pathological conditions such as erythropoietic protoporphyria and X-linked protoporphyria causes painful phototoxic reactions of the skin, which can significantly impact daily life. Endothelial cells in the skin have been proposed as the primary target for PPIX-induced phototoxicity through light-triggered generation of reactive oxygen species. Current approaches for the management of PPIX-induced phototoxicity include opaque clothing, sunscreens, phototherapy, blood therapy, antioxidants, bone marrow transplantation, and drugs that increase skin pigmentation. In this review, we discuss the present understanding of PPIX-induced phototoxicity including PPIX production and disposition, conditions that lead to PPIX accumulation, symptoms and individual differences, mechanisms, and therapeutics.

Dichloroacetate-induced peripheral neuropathy

Dichloroacetate (DCA) has been the focus of research by both environmental toxicologists and biomedical scientists for over 50 years. As a product of water chlorination and a metabolite of certain industrial chemicals, DCA is ubiquitous in our biosphere at low μg/kg body weight daily exposure levels without obvious adverse effects in humans. As an investigational drug for numerous congenital and acquired diseases, DCA is administered orally or parenterally, usually at doses of 10-50mg/kg per day. As a therapeutic, its principal mechanism of action is to inhibit pyruvate dehydrogenase kinase (PDK). In turn, PDK inhibits the key mitochondrial energy homeostat, pyruvate dehydrogenase complex (PDC), by reversible phosphorylation. By blocking PDK, DCA activates PDC and, consequently, the mitochondrial respiratory chain and ATP synthesis. A reversible sensory/motor peripheral neuropathy is the clinically limiting adverse effect of chronic DCA exposure and experimental data implicate the Schwann cell as a toxicological target. It has been postulated that stimulation of PDC and respiratory chain activity by DCA in normally glycolytic Schwann cells causes uncompensated oxidative stress from increased reactive oxygen species production. Additionally, the metabolism of DCA interferes with the catabolism of the amino acids phenylalanine and tyrosine and with heme synthesis, resulting in accumulation of reactive molecules capable of forming adducts with DNA and proteins and also resulting in oxidative stress. Preliminary evidence in rodent models of peripheral neuropathy suggest that DCA-induced neurotoxicity may be mitigated by naturally occurring antioxidants and by a specific class of muscarinic receptor antagonists. These findings generate a number of testable hypotheses regarding the etiology and treatment of DCA peripheral neuropathy.

Recurrent attacks of acute hepatic porphyria: major role of the chronic inflammatory response in the liver

BACKGROUND

Acute intermittent porphyria (AIP) is an inherited disorder of haem metabolism characterized by life-threatening acute neurovisceral attacks due to the induction of hepatic δ-aminolevulinic acid synthase 1 (ALAS1) associated with hydroxymethylbilane synthase (HMBS) deficiency. So far, the treatment of choice is hemin which represses ALAS1. The main issue in the medical care of AIP patients is the occurrence of debilitating recurrent attacks.

OBJECTIVE

The aim of this study was to determine whether chronic hemin administration contributes to the recurrence of acute attacks.

METHODS

A follow-up study was conducted between 1974 and 2015 and included 602 French AIP patients, of whom 46 had recurrent AIP. Moreover, we studied the hepatic transcriptome, serum proteome, liver macrophage polarization and oxidative and inflammatory profiles of Hmbs^-/- mice chronically treated by hemin and extended the investigations to five explanted livers from recurrent AIP patients.

RESULTS

The introduction of hemin into the pharmacopeia has coincided with a 4.4-fold increase in the prevalence of chronic patients. Moreover, we showed that both in animal model and in human liver, frequent hemin infusions generate a chronic inflammatory hepatic disease which induces HO1 remotely to hemin treatment and maintains a high ALAS1 level responsible for recurrence.

CONCLUSION

Altogether, this study has important impacts on AIP care underlying that hemin needs to be restricted to severe neurovisceral crisis and suggests that alternative treatment targeting the liver such as ALAS1 and HO1 inhibitors, and anti-inflammatory therapies should be considered in patients with recurrent AIP.

Cationic dendritic starch as a vehicle for photodynamic therapy and siRNA co-delivery

Cationic enzymatically synthesized glycogen (cESG) is a naturally-derived, nano-scale carbohydrate dendrite that has shown promise as a cellular delivery vehicle owing to its flexibility in chemical modifications, biocompatibility and relative low cost. In the present work, cESG was modified and evaluated as a vehicle for tetraphenylporphinesulfonate (TPPS) in order to improve cellular delivery of this photosensitizer and investigate the feasibility of co-delivery with short interfering ribonucleic acid (siRNA). TPPS was electrostatically condensed with cESG, resulting in a sub-50nm particle with a positive zeta potential of approximately 5mV. When tested in normal ovarian surface epithelial and ovarian clear cell carcinoma cell culture models, encapsulation of TPPS in cESG significantly improved cell death in response to light treatment compared to free drug alone. Dosages as low as 0.16μM TPPS resulted in cellular death upon illumination with a 4.8J/cm² light dosage, decreasing viability by 96%. cESG-TPPS was then further evaluated as a co-delivery system with siRNA for potential combination therapy, by charge-based condensation of an siRNA directed at reducing expression of manganese superoxide dismutase (Sod2) as a proof of principle target. Simultaneous delivery of TPPS and siRNA was achieved, reducing Sod2 protein expression to 48%, while maintaining the photodynamic properties of TPPS under light exposure and maintaining low dark toxicity. This study demonstrates the versatility of cESG as a platform for dual delivery of small molecules and oligonucleotides, and the potential for further development of this system in combination therapy applications.

Stoffwechselerkrankungen

Entsprechend ihrer Wanderung bei isoelektrischer Fokussierung werden die allelen Varianten des α1-AT als Proteinaseinhibitorphänotypen (Pi) klassifiziert. Die dominierende Isoform ist der normale Phänotyp M, daneben gibt es die Mangelvarianten S und Z sowie eine 0-Variante.

How were new medicines discovered?

Preclinical strategies that are used to identify potential drug candidates include target-based screening, phenotypic screening, modification of natural substances and biologic-based approaches. To investigate whether some strategies have been more successful than others in the discovery of new drugs, we analysed the discovery strategies and the molecular mechanism of action (MMOA) for new molecular entities and new biologics that were approved by the US Food and Drug Administration between 1999 and 2008. Out of the 259 agents that were approved, 75 were first-in-class drugs with new MMOAs, and out of these, 50 (67%) were small molecules and 25 (33%) were biologics. The results also show that the contribution of phenotypic screening to the discovery of first-in-class small-molecule drugs exceeded that of target-based approaches - with 28 and 17 of these drugs coming from the two approaches, respectively - in an era in which the major focus was on target-based approaches. We postulate that a target-centric approach for first-in-class drugs, without consideration of an optimal MMOA, may contribute to the current high attrition rates and low productivity in pharmaceutical research and development.

Porphyrias

Hereditary porphyrias are a group of eight metabolic disorders of the haem biosynthesis pathway that are characterised by acute neurovisceral symptoms, skin lesions, or both. Every porphyria is caused by abnormal function of a separate enzymatic step, resulting in a specific accumulation of haem precursors. Seven porphyrias are the result of a partial enzyme deficiency, and a gain of function mechanism has been characterised in a new porphyria. Acute porphyrias present with acute attacks, typically consisting of severe abdominal pain, nausea, constipation, confusion, and seizure, and can be life-threatening. Cutaneous porphyrias present with either acute painful photosensitivity or skin fragility and blisters. Rare recessive porphyrias usually manifest in early childhood with either severe cutaneous photosensitivity and chronic haemolysis or chronic neurological symptoms with or without photosensitivity. Porphyrias are still underdiagnosed, but when they are suspected, and dependent on clinical presentation, simple first-line tests can be used to establish the diagnosis in all symptomatic patients. Diagnosis is essential to enable specific treatments to be started as soon as possible. Screening of families to identify presymptomatic carriers is crucial to decrease risk of overt disease of acute porphyrias through counselling about avoidance of potential precipitants.

ALA and its clinical impact, from bench to bedside

ALA-induced protoporphyrin IX (PpIX) is used for fluorescence diagnosis (ALA-FD) and for fluorescence-guided resection of both (pre)malignant and non-malignant diseases. ALA is also applied in photodynamic therapy (ALA-PDT) of superficial (pre)malignant lesions in dermatology, urology, neurosurgery, otorhinolaryngology, gynecology and gastroenterology. Today, ALA is approved as Levulan for actinic keratoses, the ALA-methyl ester Metvix for actinic keratoses and basal cell carcinoma, the ALA-hexyl ester Hexvix for the diagnosis of bladder cancer and Gliolan for malignant glioma. The use of ALA for PDT and FD was established around 25 years ago, with most of the fundamental knowledge gained at the "bench" and implemented at the "bedside" due to the diligence of a few researchers within the first 10 years of research. After 1993 ALA research was taken up by many groups. For patient treatment, several factors are relevant. Administered mainly in a topical or oral form, ALA penetrates tissue in a sub-optimal way, which is currently improved by special techniques and the use of ALA-esters. PpIX accumulation is elevated in many malignant tissues, several tissue abnormalities, and in mucosa. It is also found at elevated levels in macrophages, dendritic cells and activated lymphocytes. Following sufficient PpIX accumulation in the target cells, irradiation is carried out which may be accompanied by a burning sensation at the treatment site. Due to a saturation process of PpIX formation and rapid photobleaching during irradiation the risk of overtreatment is relatively low. Pharmacokinetical studies have demonstrated a low systemic photosensitivity and excretion of PpIX via natural routes.

Mechanistic studies on delta-aminolevulinic acid uptake and efflux in a mammary adenocarcinoma cell line

Delta-aminolevulinic acid (ALA) is the precursor in the biosynthesis of porphyrins. The knowledge of both the regulation of ALA entrance and efflux from the cells and the control of porphyrin biosynthesis is essential to improve ALA-mediated photodynamic therapy. In this work, we studied the regulation of ALA uptake and efflux by endogenously accumulated ALA and/or porphyrins in murine mammary adenocarcinoma cells. Under our set of conditions, the haem synthesis inhibitor succinyl acetone completely prevented porphobilinogen and porphyrin synthesis from ALA, and led to an increase in the intracellular ALA pool. However, neither intracellular ALA nor porphyrin pools regulate ALA uptake or efflux during the first 15 min of the process. Based on temperature dependence data, ALA but not gamma-aminobutyric acid (GABA) efflux is mediated by a diffusion mechanism. Moreover, the addition of extracellular GABA not only did not influence the rate of ALA efflux but on the contrary it affected ALA uptake, showing the contribution of a saturable mechanism for the uptake, but not for the efflux of ALA from the cells.

Experimental photodynamic therapy with MESO-tetrakisphenylporphyrin (TPP) in liposomes leads to disintegration of human amelanotic melanoma implanted to nude mice

Liposomal meso-tetrakis-phenylporphyrin (TPP) was tested for photodynamic therapy (PDT) of human amelanotic melanomas implanted in nude mice. After intratumoural TPP application (15 mg x kg(-1)) followed by PDT lamp irradiation (600-700 nm, 635 nm peak), tumours retained their original volume up to the 23rd day post-PDT, whereas volumes increased 6 times in controls. PDT with intravenously (i.v.) administered liposomal (3.2 mg x kg(-1)) TPP mostly disintegrated tumours to zero volumes. Melanoma remissions were accompanied by tumour surface necroses and were documented by the appearance of nontumourous cells with nonpycnotic nuclei. Spatial arrangement of capillaries in remissing tumour was the same as in healthy surrounding tissue. Lower TPP doses (1, 0.3 and 0.1 mg x kg(-1)) were more or equally efficient than hydrophilic TPPS(4) (3.2 mg x kg(-1), i.e., sulfonated TPP), i.v. administered also in liposomes. Liposomal TPPS(4) only delayed the onset of subsequent tumour growth. Commercial Photosan 3 disintegrated tumours only in doses of approx. 7.5 mg x kg(-1); in lower doses it was less efficient than TPPS(4). The second PDT cycle (3.2 mg x kg(-1) TPP or 7.5 mg x kg(-1) Photosan 3), performed in a few unsuccessfully cured mice, predominantly led again to tumour remissions. Since the measured TPP and TPPS(4) content in melanomas was similar, these results demonstrate the advantage of PDT with a hydrophobic photosensitizer such as TPP. Photophysical properties of TPP and TPPS(4) are equal, but TPP has probably more favorable intracellular distribution, as documented by our studies, which leads to more efficient PDT. Consequently, liposomal TPP is suggested as a potentially suitable efficient preparation for PDT.

The use of 5-aminolaevulinic acid as a photosensitiser in photodynamic therapy and photodiagnosis

Photodynamic therapy (PDT) is a treatment for cancer and pre-malignant conditions, which involves the administration of a photosensitising agent followed by exposure of the tissue to light. 5-Aminolaevulinic acid (ALA) is a naturally occurring compound in the haem biosynthetic pathway, which is metabolised to a photosensitive product, protoporphyrin IX (PpIX). The major advantage of ALA when compared to synthetic photosensitisers is the rapid metabolism, which significantly reduces the period of cutaneous photosensitivity. This review focuses on the development of ALA as a photosensitiser in photodynamic therapy and photodiagnosis, and the wide range of clinical applications in which ALA is now being used as a therapeutic modality.

Neurotoxicity of tetraphenylporphinesulfonate (TPPS4) and a hematoporphyrin derivative (Photosan) in organotypic cultures of chick embryonic dorsal root ganglia

The neurotoxic effect of tetraphenylporphinesulfonate (TPPS4) and a hematoporphyrin derivative (HPD, Photosan) has been studied in organotypic cultures of chick dorsal root ganglia maintained in a semi-solid culture medium. The changes in two characteristics of neurite outgrowth, the mean radial length of neurites growing out from the ganglia and the area of neurite outgrowths, are used as parameters to evaluate the toxic effect. The porphyrins are tested over the concentration range 10-160 micrograms ml-1. TPPS4 is slightly more toxic than the HPD Photosan. The median inhibitory concentration (IC50) for TPPS4 is 45-50 micrograms ml-1 and for the HPD Photosan 50-60 micrograms ml-1, respectively. Nevertheless, the toxicity of the two drugs is relatively low compared to that of commonly used anticancer drugs, such as cisplatin or taxol.

Effect of reactive oxygen species promoted by delta-aminolevulinic acid on porphyrin biosynthesis and glucose uptake in rat cerebellum

1. delta-Aminolevulinic acid (ALA) has been reported to promote reactive oxygen species (ROS). Overproduction and accumulation of ALA, as it occurs in acute intermittent porphyria (AIP), can be the origin of an endogenous source of ROS, which can then exert their oxidative damage to cell structures. 2. To investigate the induction of lipid peroxidation by ALA, thiobarbituric acid reactive substances and conjugated diene formation were measured by using minimal tissue units (MTUs) obtained from rat cerebellum. Malondialdehyde levels increased with ALA concentration and incubation time (72% at 1.0 mM ALA and 127% at 4.0 mM ALA for 4 hr), and conjugated diene formation was enhanced 50% in incubations with 1.0 mM ALA for 4 hr. 3. ALA-promoted ROS by exposure of cerebellum MTUs to 1.0 mM ALA during different intervals (1-4 hr) was partly reduced by the addition of antioxidants such as superoxide dismutase (SOD; 50 U/ml), catalase (4.5 microM) and dimethylsulfoxide (150 mM), demonstrating the involvement of O2-., H2O2 and OH. in ALA autooxidation. 4. Porphobilinogen biosynthesis was 170% increased when cerebellum MTUs were incubated with 1.0 mM ALA for 4 hr in the presence of SOD, suggesting that protein damage was promoted by ALA autooxidation. 5. These findings provide the first experimental evidence of the involvement of ALA-promoted ROS in the damage of proteins related to porphyrin biosynthesis, specially ALA-D. Oxidation of this enzyme would lead to further accumulation of ALA in AIP patients, which may be the origin of the well-known neuropsychiatric manifestations.

Follow-up after liver transplantation for protoporphyric liver disease

Protoporphyria is a genetic disorder in which patients may develop severe protoporphyrin-induced liver damage and require transplantation. Because unique problems occur in the perioperative period and because excess production of protoporphyrin by the bone marrow continues after liver transplantation, the efficacy of this procedure for protoporphyric liver disease is uncertain. We present follow-up of nine patients who underwent liver transplantation. Two patients died within 2 months of transplantation, one from complications of abdominal bleeding and the other from sepsis after bowel perforations. The remaining seven patients had follow-up at 14 months to 8 years after transplantation (mean, 3.8 years). Two of the seven had suffered skin burns from exposure to operating room lights, which healed without scarring. Three had axonal neuropathies in the postoperative period requiring prolonged mechanical ventilation, and motor defects persisted in two. Five patients had normal liver chemistries at follow-up (mean, 3.5 years), with liver biopsy results normal or showing mild portal triad abnormalities, but erythrocyte protoporphyrin levels remained significantly elevated (1,765 +/- 365 mcg/dL; normal, < 65). The other two patients, both of whom had rejection, cytomegalovirus infection, and biliary tract obstruction requiring endoscopic therapy, had a recurrence of protoporphyric liver disease as indicated by liver biopsy features. One died 5 years after transplantation from complications of the liver disease. The other was stable 3.3 years after transplantation and was being monitored for possible retransplantation. Thus, liver transplantation can be performed successfully in patients with protoporphyric liver disease, with intermediate survival rates comparable to the general transplant population. However, disease may recur in the graft, particularly if there are complications that cause cholestasis.

Enhancement of photodynamic therapy with 5-aminolaevulinic acid-induced porphyrin photosensitisation in normal rat colon by threshold and light fractionation studies

5-Aminolaevulinic acid (ALA)-induced prophyrin photosensitisation is an attractive option for photodynamic therapy (PDT) since skin photosensitivity is limited to 1-2 days. However, early clinical results on colon tumours using the maximum tolerated oral dose of 60 mg kg-1 showed only superficial necrosis, presumably owing to insufficient intratumoral porphyrin levels, although inadequate light dosimetry may also be a factor. We undertook experiments using ALA, 25-400 mg kg-1 intravenously, to establish the threshold doses required for a PDT effect. Laser light at 630 nm (100 mW, 10-200 J) was delivered to a single site in the colon of photosensitised normal Wistar rats at laparotomy. The animals were killed 3 days later and the area of PDT-induced necrosis measured. No lesion was seen with 25 mg kg-1. The lesion size increased with larger ALA doses and with the light dose but little benefit was seen from increasing the ALA dose above 200 mg kg-1 or the light dose above 100 J. Thus there is a fairly narrow window for optimum doses of drug and light. Further experiments showed that the PDT effect can be markedly enhanced by fractionating the light dose. A series of animals was sensitized with 200 mg kg-1 ALA and then treated with 25 J. With continuous irradiation, the lesion area was 13 mm2, but with a single interruption of 150 s the area rose to 94 mm2 with the same total energy. Results were basically similar for different intervals between fractions (10-900 s) and different numbers of fractions (2-25). This suggests that a single short interruption in the light irradiation may dramatically reduce the net light dose required to achieve extensive necrosis.

Fluorescence localization in tumour and normal brain after intratumoral injection of haematoporphyrin derivative into rat brain tumour

In the intracerebral 9L rat gliosarcoma, the spatial distribution of the photosensitizer haematoporphyrin derivative (HpD) was studied after intratumoral injection. The fluorescence volume was measured in histological sections from 10 min up to 5 days after injection. Complete sensitization of the tumours could not be achieved by slow stereotactical injection of 4 mm3 HpD (mean HpD fluorescence volume, 13 +/- 11 mm3). Larger parts of the tumour could be loaded with HpD (39 +/- 23 mm3, p = 0.0001) by increasing the injection velocity and the volume to 50 mm3. Again, complete sensitization of the tumours was not achieved during a time scale of 5 days after intratumoral injection. Although the fluorescence volume did not change significantly with time, it was influenced by the injection site within the tumour. Injection of HpD within 1 mm from the tumour border resulted in significantly smaller fluorescence volumes in the tumour than injection into the tumour centre. Large injection volumes caused an increased leakage of HpD to normal brain, leading to the loss of selectivity of photosensitizer content and the occurrence of dark toxicity of normal brain while the tumours still appeared vital.

Photodynamic therapy of experimental colonic tumours with 5-aminolevulinic-acid-induced endogenous porphyrins

5-Aminolevulinic acid (5-ALA) is a precursor in the biosynthesis of haem. External application of 5-ALA leads to the formation of protoporphyrin IX, the last intermediate product before haem, which is an effective sensitiser. The 5-ALA-induced endogenous photosensitisation of tumour cells has been exploited for photodynamic therapy (PDT). Experimental human G-3 colonic tumours were transplanted into nude mice, and ten mice were treated by PDT. Ten animals served as controls. We measured a fluorescence intensity of the tumour that was about eight times higher than in the surrounding tissue; a good correlation between the fluorescence intensity and the photodynamic effect was found. Tumour growth was inhibited significantly after PDT, two tumours being destroyed completely after the second PDT treatment. In addition, on-line fluorescence detection during PDT showed a change in the intensity and the fluorescence spectrum of protoporphyrin IX caused by photobleaching and the formation of photoproducts.

In vivo kinetics and spectra of 5-aminolaevulinic acid-induced fluorescence in an amelanotic melanoma of the hamster

For successful photodynamic diagnosis (PDD) and effective photodynamic therapy (PDT) with the clinically used 'photosensitiser' 5-aminolaevulinic acid (ALA), knowledge of the maximal fluorescence intensity and of the maximal tumour-host tissue fluorescence ratio following systemic or local application is required. Therefore, time course and type of porphyrin accumulation were investigated in neoplastic and surrounding host tissue by measuring the kinetics and spectra of ALA-induced fluorescence in vivo. Experiments were performed in the amelanotic melanoma A-Mel-3 grown in the dorsal skinfold chamber preparation of Syrian golden hamsters. The kinetics of fluorescent porphyrins was quantified up to 24 h after i.v. injection of 100 mg kg-1, 500 mg kg-1 or 1,000 mg kg-1 body weight ALA by intravital fluorescence microscopy and digital image analysis (n = 18). In separate experiments fluorescence spectra were obtained for each dose by a simultaneous optical multichannel analysing device (n = 3). A three-compartment model was developed to simulate fluorescence kinetics in tumours. Maximal fluorescence intensity (per cent of reference standard; mean +/- s.e.) in the tumour arose 150 min post injection (p.i.) (1,000 mg kg-1, 109 +/- 34%; 500 mg kg-1, 148 +/- 36%) and 120 min p.i. (100 mg kg-1, 16 +/- 8%). The fluorescence in the surrounding host tissue was far less and reached its maximum at 240 min (100 mg kg-1, 6 +/- 3%) and 360 min p.i. (500 mg kg-1, 50 +/- 8%) and (1,000 mg kg-1, 6 +/- 19%). Maximal tumour-host tissue ratio (90:1) was encountered at 90 min after injection of 500 mg kg-1. The spectra of tissue fluorescence showed maxima at 637 nm and 704 nm respectively. After 300 min (host tissue) and 360 min (tumour tissue) additional emission bands at 618 nm and 678 nm were detected. These bands indicate the presence of protoporphyrin IX (PPIX) and of another porphyrin species in the tumour not identified yet. Tumour selectivity of ALA-induced PPIX accumulation occurs only during a distinct interval depending on the administered dose. Based on the presented data the optimal time for PDD and PDT in this model following intravenous administration of 500 mg kg-1 ALA would be around 90 min and 150 min respectively. The transient selectivity is probably caused by an earlier and higher uptake of ALA in the neoplastic tissue most likely as a result of increased vascular permeability of tumours as supported by the mathematical model.

Porphyrinogenesis in rat cerebellum. Effect of high delta-aminolevulinic acid concentration

1. delta-Aminolevulinic acid (ALA) uptake as well as precursor accumulation and porphyrin biosynthesis were investigated in rat cerebellum, using as experimental approach minimal tissue units called particles. 2. ALA was shown to be taken up into cerebellum particles by a non saturable process up to 4.0 mM ALA whereas PBG and porphyrin formation exhibited a hyperbolic response reaching the plateau at about 1.0 and 1.5 mM ALA respectively. 3. Exposure of cerebellum particles to high exogenous ALA amounts (0.01-4.0 mM) indicated that ALA can be accumulated in relatively high concentrations in the cells (40 nmol/mg protein). Under these experimental conditions, PBG-D presented a low activity (3.25 pmol/mg protein/4 hr) showing to be a secondary control step in heme biosynthesis. 4. Incubation of cerebellum particles in the presence of a physiological concentration of glucose revealed that 1.0 mM ALA decreased glucose uptake by the cells (87% during 1 hr incubation), being consistent with the fact that acute attacks are precipitated by fasting and that sugar administration appeared to be an efficient treatment of AIP crisis. 5. These findings provide the basis for a useful model to study the nature of the metabolic mechanism underlying the acute attack.

Porphyrins, porphyrias, cancer and photodynamic therapy--a model for carcinogenesis

Porphyrins are the only and most powerful photosensitizers synthesized internally. To understand better the involvement of porphyrins in photosensitization reactions, the heme biosynthetic pathway is first described, as well as the main features of its regulation in both erythroid and hepatic cells. Most disorders of porphyrin metabolism, known as porphyrias, are characterized by porphyrin accumulation. A full discussion of these diseases, their classification and relevant biochemical and clinical signs are presented. Abnormalities in heme biosynthesis in disorders other than porphyrias, such as iron-deficient and sideroblastic anemias, lead poisoning, hereditary tyrosinemia, chronic renal disease and alcoholism, are briefly considered. A complete survey of the experimental research on the biosynthesis of porphyrins in tumors and of the important association between cancer and porphyrias is dealt with. The link to photodynamic therapy (PDT) emerges naturally and this is treated from the point of view of using porphyrins endogenously formed by the tumors for their localization and PDT. Finally, considering the nature of the alterations occurring in heme metabolism in tumors, and porphyrias and their ubiquity, a model is discussed where the abnormality of heme synthesis is involved in the initiating lesion of carcinogenesis. The model strongly predicts that the incidence of cancer will be high in cells with abnormal heme metabolism, suggesting that porphyric patients may be at greater risk of the development of cancer.

Distribution and photosensitizing efficiency of porphyrins induced by application of exogenous 5-aminolevulinic acid in mice bearing mammary carcinoma

By means of a chemical extraction procedure and confocal laser scanning microscopy, we investigated the kinetic patterns of uptake and biolocalization of 5-aminolevulinic acid (ALA)-induced porphyrins in s.c. transplanted tumors, adjacent normal skin and muscle, and liver of mice bearing mammary carcinoma, after i.p. injection of 250 mg/kg ALA or topical application of ALA (20% in an oil-in-water emulsion). Furthermore, we evaluated the tumor responses after either i.p. injection or topical application of 5-ALA followed by laser irradiation (632 nm, 150 mW/cm2, 25 min) by measuring the treated tumor regression/regrowth time and by light and electron microscopy. Strong fluorescence of ALA-induced porphyrins was detected in the tumor, skin and liver tissues, while little fluorescence was seen in the adjacent muscle tissue. Moreover, the highest amounts of ALA-induced porphyrins in the tumor and skin tissues were found 1 hr after i.p. injection, whereas the amounts of the porphyrins in both tissues increased with increasing time after topical application of ALA. The fluorescence of the porphyrins was localized in several components of the skin tissue (epidermis, hair follicles and their associated sebaceous glands). Furthermore, the fluorescence was diffusely distributed in the s.c. transplanted tumor tissue. Little could be observed under a confocal laser scan microscope (CLSM) in the muscle tissue. The uptake and biolocalization data correlate well with the results of PCT efficiency of the same tumor model with ALA-induced porphyrins. Light and electron microscopy showed that the mitochondria of the tumor cells and of the endothelial cells and the basal lamina of vascular walls beneath the endothelium in the tumor tissue were initially extensively destroyed after PCT with ALA-induced porphyrins. Thereafter, diffuse degeneration followed by local and/or diffuse severe necrosis of the tumor cells was found. This may be due mainly to the initial damage to mitochondria in the cancerous and endothelial cells and also to the destruction of the vascular wall in the tumor tissue.

Photodynamic therapy of the normal rat stomach: a comparative study between di-sulphonated aluminium phthalocyanine and 5-aminolaevulinic acid

Dysplasia in the upper gastrointestinal tract carries a risk of invasive malignant change. Surgical excision of the affected organ is the only treatment available. Photodynamic therapy has been shown to be promising in the treatment of early and superficial tumours and may be useful for the ablation of dysplastic mucosa. Because of the diffuse nature of the disease, such treatment would necessarily involve destruction of large areas of mucosa and it is desirable to confine its effect to the mucosa in order that safe healing can take place. By means of photometric fluorescence microscopy, we have studied the pattern of photosensitisation in the normal rat stomach using di-sulphonated aluminium phthalocyanine (AlS2Pc) and 5-aminolaevulinic acid (ALA) as photosensitisizers. AlS2Pc resulted in a panmural photosensitisation of the gastric wall with the highest level encountered in the submucosa. The mucosa and muscularis propria were sensitised to equal extent. Following light exposure, a full thickness damage resulted. ALA is a natural porphyrin precursor and exogenous administration gave rise to accumulation of protoporphyrin IX (PPIX) in the cells. The resultant pattern of photosensitisation was predominantly mucosal and its photodynamic effect was essentially confined to the mucosa. ALA produced a selective photosensitisation of the gastric mucosa for its photodynamic ablation with sparing the underlying tissue layers.

Endogenous protoporphyrin IX, a clinically useful photosensitizer for photodynamic therapy

The tissue photosensitizer protoporphyrin IX (PpIX) is an immediate precursor of heme in the biosynthetic pathway for heme. In certain types of cells and tissues, the rate of synthesis of PpIX is determined by the rate of synthesis of 5-aminolevulinic acid (ALA), which in turn is regulated via a feedback control mechanism governed by the concentration of free heme. The presence of exogenous ALA bypasses the feedback control, and thus may induce the intracellular accumulation of photosensitizing concentrations of PpIX. However, this occurs only in certain types of cells and tissues. The resulting tissue-specific photosensitization provides a basis for using ALA-induced PpIX for photodynamic therapy. The topical application of ALA to certain malignant and non-malignant lesions of the skin can induce a clinically useful degree of lesion-specific photosensitization. Superficial basal cell carcinomas showed a complete response rate of approximately 79% following a single exposure to light. Recent preclinical studies in experimental animals and human volunteers indicate that ALA can induce a localized tissue-specific photosensitization if administered by intradermal injection. A generalized but still quite tissue-specific photosensitization may be induced if ALA is administered by either subcutaneous or intraperitoneal injection or by mouth. This opens the possibility of using ALA-induced PpIX to treat tumors that are too thick or that lie too deep to be accessible to either topical or locally injected ALA.

Fluorescence distribution and photodynamic effect of ALA-induced PP IX in the DMH rat colonic tumour model

Aminolaevulinic acid (ALA) is the first committed step in haem synthesis. In the presence of excess ALA the natural regulatory feedback system is disrupted allowing accumulation of protoporphyrin IX (PP IX) the last intermediate product before haem, and an effective sensitiser. This method of endogenous photosensitisation of cells has been exploited for photodynamic therapy (PDT). We have studied the fluorescence distribution and biological effect of induced PP IX in normal and tumour tissue in the rat colon. Fluorescence in normal colonic tissue was at a peak of 4 h with a rapid fall off by 6 h. The fluorescence had returned to background levels by 24 h. All normal tissue layers followed the same fluorescence profile but the mucosa showed fluorescent levels six times higher than the submucosa, with muscle barely above background values. At 6 h the ratio of fluorescence levels between normal mucosa and viable tumour was approximately 1:6. At this time laser treatment showed necrosis of normal mucosa and tumour with sparing of normal muscle. There was good correlation between the fluorescence distribution and the biological effect of ALA-induced photosensitisation on exposure to red light. ALA may be superior to conventional sensitisers for tumours that produce haem as the PP IX is synthesised in malignant cells while the other sensitisers mainly localise to the vascular stroma of tumours. There is also a greater concentration difference between the PP IX levels in tumours and in normal mucosa and normal muscle than with the other photosensitisers raising the possibility of more selective necrosis in tumours.

Erythropoietic protoporphyria: unusual skin and neurological problems after liver transplantation

The case of a woman with protoporphyria who developed liver failure and underwent liver transplantation is described. During the pretransplant episode of liver failure she developed quadriparesis that rapidly progressed after transplantation to a severe polyneuropathy. Following transplantation she also developed a second-degree burn of the light-exposed abdominal wall. The neuropathy resembled that observed in other forms of porphyria, and it is proposed that the extreme disturbance of protoporphyrin levels associated with protoporphyrin-induced liver failure caused this neuropathy. Such a neuropathy has not previously been described in protoporphyria. Erythrocyte protoporphyrin levels remain high and fecal levels normal, although results of liver tests are normal. She remains photosensitive, which emphasizes that although liver transplantation may be lifesaving in this disorder, it is not curative, and care must be taken to prevent photosensitive damage to skin and light-exposed internal organs.

Photodynamic therapy with endogenous protoporphyrin IX: basic principles and present clinical experience

5-Aminolaevulinic acid (ALA) is a precursor of protoporphyrin IX (Pp IX) in the biosynthetic pathway for haem. Certain types of cells have a large capacity to synthesize Pp IX when exposed to an adequate concentration of exogenous ALA. Since the conversion of Pp IX into haem is relatively slow, such cells tend to accumulate photosensitizing concentrations of Pp IX. Pp IX photosensitization can be induced in cells of the epidermis and its appendages, but not in the dermis. Moreover, since ALA in aqueous solution passes readily through abnormal keratin, but not through normal keratin, the topical application of ALA in aqueous solution to actinic keratoses or superficial basal cell or squamous cell carcinomas induces Pp IX photosensitization that is restricted primarily to the abnormal epithelium. Subsequent exposure to photoactivating light selectively destroys such lesions. In our ongoing clinical trial of ALA-induced Pp IX photodynamic therapy, the response rate for basal cell carcinomas following a single treatment has been 90% complete response and 7.5% partial response for the first 80 lesions treated. The cosmetic results have been excellent, and patient acceptance has been very good.

Biodistribution of tritiated benzoporphyrin derivative (3H-BPD-MA), a new potent photosensitizer, in normal and tumor-bearing mice

The biodistribution of a new and very potent photosensitizer, benzoporphyrin derivative-monoacid, ring A (BPD-MA), was determined in normal and P815 (mastocytoma) or M1 (rhabdomyosarcoma) tumor-bearing DBA/2J mice. A dose of 80 micrograms of 3H-BPD-MA was determined at 3, 24, 48, 72, 96 and 168 h post injection. The following tissues were tested: blood, brain, heart, intestine, kidney, lung, liver, muscle, skin, stomach, spleen, thymus and tumor. The biodistribution of 3H-BPD-MA in normal and tumor-bearing mice was comparable overall. 3H-BPD-MA localized in tumors better than in other tissues except kidney, liver and spleen. The tumor to tissue ratios were in the range 1.5-3 at 24 h post injection and increased further during the next 72 h. The highest levels of 3H-BPD-MA were observed in all tissues at 3 h post injection and decreased rapidly during the first 24 h. After 24 h the clearance from tissues was rather slow. The preliminary clearance data obtained in a group of five normal mice indicated that the majority of the injected dose (60%) cleared from the body via the bile and feces, while only about 4% cleared via kidneys and urine. Studies in which 3H-BPD-MA was extracted from tumor, kidney and liver 3 and 24 h after injection showed that, at 3 h, all the photosensitizing activity in tumor was retained. At 24 h only 39% of the activity was retained and considerably less active material was present in liver and kidney.

Neurologic crises in hereditary tyrosinemia

Hereditary tyrosinemia results from an inborn error in the final step of tyrosine metabolism. The disease is known to cause acute and chronic liver failure, renal Fanconi's syndrome, and hepatocellular carcinoma. Neurologic manifestations have been reported but not emphasized as a common problem. In this paper, we describe neurologic crises that occurred among children identified as having tyrosinemia on neonatal screening since 1970. Of the 48 children with tyrosinemia, 20 (42 percent) had neurologic crises that began at a mean age of one year and led to 104 hospital admissions. These abrupt episodes of peripheral neuropathy were characterized by severe pain with extensor hypertonia (in 75 percent), vomiting or paralytic ileus (69 percent), muscle weakness (29 percent), and self-mutilation (8 percent). Eight children required mechanical ventilation because of paralysis, and 14 of the 20 children have died. Between crises, most survivors regained normal function. We found no reliable biochemical marker for the crises (those we evaluated included blood levels of tyrosine, succinylacetone, and hepatic aminotransferases). Urinary excretion of delta-aminolevulinic acid, a neurotoxic intermediate of porphyrin biosynthesis, was elevated during crises but also during the asymptomatic periods. Electrophysiologic studies in seven patients and neuromuscular biopsies in three patients showed axonal degeneration and secondary demyelination. We conclude that episodes of acute, severe peripheral neuropathy are common in hereditary tyrosinemia and resemble the crises of the neuropathic porphyrias.

Neuroaxonal dystrophy in distal symmetric sensory polyneuropathy of the diabetic BB-rat

We and others have previously described neuroaxonal dystrophic changes as one of the hallmarks of structural diabetic autonomic polyneuropathy involving sympathetic nerves. In the present study, a systemic search for similar changes was undertaken in the mainly sensory symmetric polyneuropathy of the spontaneously diabetic BB-rat. Changes identical to those described in sympathetic nerves in this model were found in sensory ganglion cells, in their proximal extramedullary axons, and in proximal and distal myelinated axons of the spinal dorsal columns. The dystrophic substructures consisted of tubulovesicles, tubular rings, layered membranes, electron-dense membranous bodies, and neurofilamentous changes. Neuroaxonal dystrophic abnormalities increased with increasing duration of diabetes, and exhibited a topographic distribution along the sensory neuroaxonal axis, suggesting metabolic abnormalities as well as abnormalities in the turn-around mechanism of fast axonal transport in the pathogenesis of dystrophic changes in diabetic nerves.

Porphyrin synthesis in primary nervous tissue cultures from 10(-3) M delta-aminolaevulinic acid in the presence of melatonin and neuropeptides

Of the primary neuronal tissue cultures (glia cell, neuronal cells, mixed and retina cultures), the neuronal cells of (cells + medium) display the highest total porphyrin production from 10(-3) M delta-aminolaevulinic acid (ALA). In the presence of 10(-3)-10(-6) M melatonin, the quantity of total porphyrins produced by the neuronal cultures decreases in inverse proportion to the concentration. Oxytocin, lysine-vasopressin, CCK-8 sulphate ester and des-Tyr-gamma-endorphin in concentrations of 10(-5) and 10(-6) M block the porphyrin synthesis of the glia cells and display different effects on that of the neuronal cells. They enhance the total porphyrin synthesis of the cell cultures, with the exception of 10(-5) M des-Tyr-gamma-endorphin, which exerts an inhibitory effect on the glia cells.

An autopsy case of acute porphyria with a decrease of both uroporphyrinogen I synthetase and ferrochelatase activities

An autopsy case of a 37-year-old woman with acute porphyria is reported. The patient began to complain of severe menstrual pains, and later developed serious peripheral neuropathy and various autonomic nervous symptoms. The autopsy revealed a marked loss and degeneration of axons and myelin sheaths in the peripheral nervous system (PNS), and prominent central chromatolysis of the spinal anterior horn cells. The predominant process of the peripheral neuropathy appeared to be axonal degeneration. Biochemical analysis showed a marked increase of delta-aminolevulinic acid (ALA), porphobilinogen, uroporphyrin, and coproporphyrin in the urine, and an increase of coproporphyrin and protoporphyrin in the stools and blood. In the analysis of the enzymatic activities of the liver and bone narrow, the activity of ALA synthetase (ALA-S) was markedly increased, and the activities of both uroporphyrinogen I synthetase (URO-S) and ferrochelatase were decreased. It was characteristic in this case that the enzymatic abnormalities found in both acute intermittent porphyria (AIP) and variegate porphyria (VP) coexisted. Biochemical analysis of the sciatic nerve showed an increase of ALA-S activity and a decrease of both URO-S and ALA dehydrase activities. This was the first report that indicated the presence of abnormal activities of the heme biosynthetic enzymes in the peripheral nerves of porphyric patients. The possibility was discussed that these enzymatic abnormalities of the heme biosynthesis in the peripheral nerve itself might be strongly related to the pathogenesis of the porphyric neuropathy.

Inhibition of Na+, K+-ATPase activity by delta-aminolevulinic acid

delta-Aminolaevulinic acid (ALA) has been shown to be toxic to cultured neurons and glia at concentrations as low as 10 microM. In an attempt to elucidate the mechanism of toxicity, the effects of ALA on membrane ATPase activity were investigated. Exposure of neuron cultures to 1 mM ALA for 7 days caused a substantial decrease in both Na+, K+-ATPase and Mg2+-ATPase activities. At lower concentrations, ALA affected only the Na+, K+-component. ALA appeared to act directly, inhibiting Na+, K+-ATPase activity in rat brain cortex membrane preparations at 10 microM. Although this effect was slight, it may well represent the mechanism of action of ALA, since ouabain, a potent inhibitor of Na+, K+-ATPase activity, proved to be more toxic to cultured neurons than ALA. Furthermore, cardiac glycoside overdosage causes neurological disturbances which are very similar to those observed in the acute attack of porphyria.

Light-microscopic and microspectrofluorometric characterization of porphyrin-containing astrocytes in mouse optic nerve

Fluorescence spectroscopy has been employed to investigate the emission spectrum of unusual orange-red fluorescence found in the mouse optic nerve. Comparison of the spectra obtained with those of a number of porphyrins used as standards (protoporphyrin, uroporphyrin, and coproporphyrins) shows that the autofluorescence excited at about 400 nm (Soret band) is due to the presence of a mixture of these or other porphyrins in the nerve. Phase contrast, dark-field, and light-microscopy techniques demonstrated that the fluorescence is emitted by dense, coarse inclusions in the cytoplasm of astrocytes. The inclusions also exhibit high activity of endogenous peroxidase, a heme (porphyrin)- containing enzyme, characteristic for process of phagocytosis. A possible participation of these astrocytes in phagocytosis is delineated.

The effect of tetraphenylporphinesulfonate (TPPS) on muscle end-plates in mice. An ultrastructural and quantitative study

Motor end-plates were studied in mice at various intervals after a single injection of a synthetic porphyrin, tetraphenylporphinesulfonate (TPPS). Ultrastructurally, excess accumulation of neurofilaments constituted the earliest abnormality. These were followed by atrophy of many nerve terminals and their separation from the postsynaptic area by interposed Schwann cells. Five to 8 months after the injection some postsynaptic areas showed denervation and atrophy. These progressive changes in the nerve terminals were accompanied by secondary changes in the subneural apparatus. Morphometric analysis revealed marked atrophy of the end-plates and significant swelling of preterminal axons. The present findings are suggestive of partial denervation of muscle, occurring after the injection of a synthetic porphyrin.

Porphyric neuropathy: an ultrastructural and quantitative case study

We report a case of acute neuropathy in a 46 year old female with porphyria variegata. Histologic, electron microscopic, and quantitative examinations of peripheral nerves were performed at onset of the neuropathy and at autopsy. The results revealed severe qualitative and quantitative changes in myelinated and unmyelinated fibers showing features indicative of an axonopathy with a distribution in keeping with a dying-back phenomenon.