An acquired acute hepatic porphyria: a novel type of delta-aminolevulinate dehydratase inhibition

5-Aminolevulinate dehydratase porphyria: Update on hepatic 5-aminolevulinic acid synthase induction and long-term response to hemin

BACKGROUND

5-Aminolevulinic acid dehydratase (ALAD) porphyria (ADP) is an ultrarare autosomal recessive disease, with only eight documented cases, all of whom were males. Although classified as an acute hepatic porphyria (AHP), induction of the rate limiting hepatic enzyme 5-aminolevulinic acid synthase-1 (ALAS1) has not been demonstrated, and the marrow may also contribute excess 5-aminolevulinic acid (ALA). Two patients have died and reported follow up for the others is limited, so the natural history of this disease is poorly understood and treatment experience limited.

METHODS

We report new molecular findings and update the clinical course and treatment of the sixth reported ADP patient, now 31 years old and the only known case in the Americas, and review published data regarding genotype-phenotype correlation and treatment.

RESULTS

Circulating hepatic 5-aminolevulinic acid synthase-1 (ALAS1) mRNA was elevated in this case, as in other AHPs. Gain of function mutation of erythroid specific ALAS2 - an X-linked modifying gene in some other porphyrias - was not found. Seven reported ADP cases had compound heterozygous ALAD mutations resulting in very low residual ALAD activity and symptoms early in life or adolescence. One adult with a germline ALAD mutant allele developed ADP in association with a clonal myeloproliferative disorder, polycythemia vera.

CONCLUSIONS

Elevation in circulating hepatic ALAS1 and response to treatment with hemin indicate that the liver is an important source of excess ALA in ADP, although the marrow may also contribute. Intravenous hemin was effective in most reported cases for treatment and prevention of acute attacks of neurological symptoms.

Highly heterogeneous nature of delta-aminolevulinate dehydratase (ALAD) deficiencies in ALAD porphyria

The properties of 9 delta-aminolevulinate dehydratase (ALAD) mutants from patients with ALAD porphyria (ADP) were examined by bacterial expression of their complementary DNAs and by enzymologic and immunologic assays. ALADs were expressed as glutathione-S-transferase (GST) fusion proteins in Escherichia coli and purified by glutathione-affinity column chromatography. The GST-ALAD fusion proteins were recognized by anti-ALAD antibodies and were enzymatically active as ALAD. The enzymatic activities of 3 ALAD mutants, K59N, A274T, and V153M, were 69.9%, 19.3%, and 41.0% of that of the wild-type ALAD, respectively, whereas 6 mutants, G133R, K59N/G133R, F12L, R240W, V275M, and delTC, showed little activity (< 8%). These variations generally reflect the phenotype of ALAD in vivo in patients with ADP and indicate that GST-ALAD fusion protein is indeed useful for predicting of the phenotype of ALAD mutants. The location of F12L mutation in the enzyme's molecular structure indicates that its disturbance of the quaternary contact of the ALAD dimer appears to have a significant influence on the enzymatic activity. Mouse monoclonal antibodies to human ALAD were developed that specifically recognized a carboxy terminal portion of ALAD, or other regions in the enzyme. This study represents the first complete analysis of 9 mutants of ALAD identified in ADP and indicates the highly heterogeneous nature of mutations in this disorder.

Nonsynergic effect of ethanol and lead on heme metabolism in rats

The heme biosynthetic pathway is a metabolic target of alcohol and lead poisoning. To analyze the interdependence of both xenobiotics on porphyrin metabolism, male Wistar rats (n=47) were divided into four groups and were fed Lieber-DeCarli semiliquid control or alcoholic diets containing or not containing lead acetate (160 mg/liter) for 8 weeks. After this period, hematocrit values and porphyrin concentration in liver and urine were similar in all groups, indicating that the goal of inducing only mild chronic intoxication was achieved. Compared with the control group, rats poisoned only with lead exhibited high levels of this metal in blood and liver, increased erythrocytic protoporphyrin, and hypoactivity of aminolevulinate dehydrase (ALA-D) in both blood and liver. Rats intoxicated only with alcohol exhibited mild hypoactivity of both hepatic and erythrocytic ALA-D, although such decreased enzymatic values did not achieve statistical significance. Rats receiving ethanol and lead simultaneously demonstrated abnormalities in heme biosynthesis similar to those in rats exposed to lead, although zinc hepatic levels decreased significantly only in animals exposed to both xenobiotics. Hepatic GSH and urinary ALA and porphyrin levels were maintained in a similar range in all groups.