Acitretin mitigates uroporphyrin-induced bone defects in congenital erythropoietic porphyria models

Congenital erythropoietic porphyria (CEP) is a rare genetic disorder leading to accumulation of uro/coproporphyrin-I in tissues due to inhibition of uroporphyrinogen-III synthase. Clinical manifestations of CEP include bone fragility, severe photosensitivity and photomutilation. Currently there is no specific treatment for CEP, except bone marrow transplantation, and there is an unmet need for treating this orphan disease. Fluorescent porphyrins cause protein aggregation, which led us to hypothesize that uroporphyrin-I accumulation leads to protein aggregation and CEP-related bone phenotype. We developed a zebrafish model that phenocopies features of CEP. As in human patients, uroporphyrin-I accumulated in the bones of zebrafish, leading to impaired bone development. Furthermore, in an osteoblast-like cell line, uroporphyrin-I decreased mineralization, aggregated bone matrix proteins, activated endoplasmic reticulum stress and disrupted autophagy. Using high-throughput drug screening, we identified acitretin, a second-generation retinoid, and showed that it reduced uroporphyrin-I accumulation and its deleterious effects on bones. Our findings provide a new CEP experimental model and a potential repurposed therapeutic.

Oral aspects of porphyria

Porphyria is a diverse group of diseases in which the biosynthesis of heme is disrupted by either genetic defects or environmental factors. This review gives an overview of the different types of porphyria and describes possible causes, clinical signs, diagnosis and therapy. In addition, the oral manifestations of porphyria and the potential implications of the disease for dental management are discussed.

[Clinical manifestations of porphyrin metabolism disorders]

AIM

To characterize patients with various nosological unities [symbol: see text] of porphyria in accordance with their age, clinical symptoms, provoking factors, therapy and outcome.

MATERIAL AND METHODS

Patients with acute intermittent porphyria (43), hereditary coproporphyria (8), variegate porphyria (3), porphyria cutanea tarda (7), hepatoerythropoietic porphyria (1), and hereditary erythropoietic porphyria (2) were studied. One patient was suspected of porphyria caused by deficiency of delta-aminolevulenic acid dehydrogenase.

RESULTS

The patients were from the CIS. The overwhelming majority of them were young and middle-aged subjects. Rapid development of the disease and severe neurological symptoms were predominantly observed in patients with acute forms of porphyria.

CONCLUSION

Early diagnosis of porphyrin metabolism disorders makes it possible to decrease abruptly the number of cases leading to severe complications, disability, and fatal outcome. The use of inexpensive methods of screening of porphyrin metabolism disorders provides a promising approach to solving this problem. These methods should be used in municipal hospitals. In addition, asymptomatic carriers of defective gene should be revealed at the preclinical stage using various methods of molecular genetic assay.

An unusual case of purpuric erythropoietic protoporphyria

Erythropoietic protoporphyria (EPP) is the most common of the erythropoietic porphyrias. Recent advances in diagnostic laboratory tests have led to the discovery of a number of previously undiagnosed cases. We describe a case of EPP presenting late with a purpuric eruption and discuss the pathogenesis and significance of purpura in EPP.

Porphyrins in urine, plasma, erythrocytes, bile and faeces in a case of congenital erythropoietic porphyria (Gunther's disease) treated with blood transfusion and iron chelation: lack of benefit from oral charcoal

Congenital erythropoietic porphyria is a rare genetic disorder in which deficiency of uroporphyrinogen III synthase results in excessive production of Type I porphyrins. The main clinical features are severe photodestruction of the skin and haemolytic anaemia. Treatment consists of shielding from light, blood transfusions and splenectomy, but is generally unsatisfactory. Previous studies have suggested that oral charcoal may be of benefit by binding porphyrins in the gut. A trial was therefore undertaken to evaluate this possibility. Porphyrins in urine, plasma and erythrocytes were measured by HPLC in a 23-year-old male patient with congenital erythropoietic porphyria, during an 8 week "run-in" period, and for a further 3 weeks when oral charcoal was given. Total urinary porphyrin excretion was 79-283 mumol/24 h consisting of 75% uroporphyrin I, 15% coproporphyrin I and smaller amounts of hepta-, hexa-, and pentacarboxylic porphyrins. Similar proportions were found in plasma and erythrocytes. During the first 24 h of charcoal administration a minor decrease in plasma and erythrocyte porphyrins was detected but this was not maintained during the remainder of the trial. In bile and faeces coproporphyrin I constituted approximately 95% of the porphyrins, with 2-3% coproporphyrin III and smaller amounts of pentaporphyrins I and III, but only trace amounts of uroporphyrin I. Oral charcoal was of no value in this case. Reasons are discussed in the context of biochemical differences between this patient with classical Gunther's disease and the similar clinical syndrome due to deficiency of uroporphyrinogen decarboxylase.

Congenital erythropoietic porphyria associated with nephrotic syndrome and renal siderosis

A 9-year-old boy with typical features of congenital erythropoietic porphyria who had received more than 50 blood transfusions developed the steroid-resistant nephrotic syndrome in the presence of normal glomerular function and glucosuria. Renal biopsy showed focal segmental glomerulosclerosis and widespread iron deposits. Magnetic resonance scanning revealed advanced siderosis of liver and kidneys. During a 4 year treatment by desferrioxamine the serum ferritin level was reduced, proteinuria dropped and serum proteins increased whilst glomerular filtration decreased slowly. It is suggested that the nephrotic syndrome may be a consequence of renal siderosis amenable to iron-chelating therapy.

[Canthaxanthin retinopathy. Follow-up of over 6 years]

After long-term treatment with high dosages, canthaxanthin causes a characteristic retinopathy with circular, macula surrounding crystals. As changes in retinal functionning disappear relatively easily after withdrawal of the drug, the crystals dissolve rather slowly--over about several years. Five patients showing a profound crystalline retinopathy were re-examined with an average of 69.7 months after withdrawal of the canthaxanthin-containing drug. Three of the patients were treated for erythropoetic protoporphyria (EPP) with Phenoro (2/5 beta-carotene, 3/5 canthaxanthin), two sisters took a canthaxanthin-containing formulation (1/8 beta-carotene, 7/8 canthaxanthin) for cosmetic reasons. Two female patients complained about an increased glare sensitivity, which was explainable for one of them with a subcapsular cataract. The retinal crystals decreased quite differently. Minor deffects of the retinal pigment epithelium remained unchanged in two patients. They increased slightly in the female patient with the smallest crystal formation but highest plasma cholesterol. Shortly after withdrawal of the drugs usually an increase of a-wave amplituded of the electroretinograms was found. The a-waves returned to normal and the b-wave amplitudes showed an increase up to the final control paralleling the reduction of the retinal crystals. A- and b-wave peak latencies which were prolonged under treatment returned to normal.