Effect of Isoniazid on Protoporphyrin Levels in Erythropoietic Protoporphyria

Erythropoietic Protoporphyria (EPP) Clinical Trial

— INHEPP  

Official title:

Quantification of the Effects of Isoniazid Treatment on Erythrocyte and Plasma Protoporphyrin IX Concentration and Plasma Aminolevulinic Acid in Patients With Erythropoietic Protoporphyria

Clinical Trial Details — Status: Withdrawn

Administrative data

• NCT number: NCT01550705
• Other study ID #: UTINH
• Secondary ID: U54DK083909
• Status: Withdrawn
• Phase: N/A
• First received: March 5, 2012
• Last updated: December 1, 2015
• Start date: March 2012
• Est. completion date: December 2015

Study information

• Verified date: December 2015
• Source: University of Utah
• Contact: n/a
• Is FDA regulated: No
• Health authority: United States: Food and Drug Administration
• Study type: Interventional

Clinical Trial Summary

In erythropoietic protoporphyria there is an accumulation of protoporphyrin IX in the plasma and liver. The reason it builds up is either the last step to make heme, insertion of iron into protoporphyrin IX, is rate limiting or there is an increase in activity in the first step in the heme pathway.

It may be possible to decrease the amount of protoporphyrin IX made and see a decrease in symptoms. The first step to make heme is the key step in the pathway and it uses vitamin B6 as a cofactor. If the investigators can limit the amount of vitamin B6 the investigators can possibly reduce the activity of this rate limiting step. With decreased activity of the enzyme it may be possible for the body to utilize all the protoporphyrin IX that is made so that none builds up.

Description:

Clinically, both aEPP and XLEPP are characterized by painful, non-blistering cutaneous photosensitivity with onset in early childhood. EPP is the most common porphyria in children and the third most common in adults (after porphyria cutanea tarda and acute intermittent porphyria). Reports of prevalence vary between 5 and 15 cases per million population.

EPP is due in most cases to decreased activity of FECH, the enzyme that catalyzes the incorporation of ferrous iron into PPIX, the final step in the production of heme. The pattern of inheritance is autosomal recessive. However, homozygosity for a FECH mutation is rare. Rather, the decreased activity is a consequence of a combination of an inherited inactivating mutation affecting one FECH allele and an intronic polymorphism that alters splicing of the other allele. The alternative splice site, when used, produces a non-functional FECH mRNA. The alternative splice site is used approximately 40% of the time. Therefore, the polymorphic allele produces approximately 60% of normal FECH activity, and for this reason, is termed hypomorphic. When the hypomorphic FECH allele is in trans with the non-functional mutant allele the result is 30% or less of the normal FECH enzyme activity. This subnormal FECH activity becomes rate-limiting, resulting in accumulation of intracellular PPIX. Although the defect is presumably expressed in all tissues, the PPIX responsible for photosensitivity derives primarily from marrow reticulocytes.

ALAS1 and ALAS2 ALAS, the first, and rate-limiting enzyme in the heme biosynthetic pathway, catalyzes the condensation of glycine and succinyl-CoA to form ALA, and requires pyridoxal 5'-phosphate as a cofactor. ALAS in mammalian cells is localized to the mitochondrial matrix. The enzyme is synthesized as a precursor protein in the cytosol and transported into mitochondria. Two separate ALA synthase genes encode housekeeping (tissue-nonspecific) and erythroid specific forms of the enzyme (ALAS1 and ALAS2, respectively). The gene for human ALAS1 is on 3p.21 and the locus for ALAS2 the X-chromosome, at Xp11.2.

The two forms of ALAS are differentially regulated, ALAS1 is a housekeeping gene expressed in all cells and ALAS2 is driven by erythroid specific transcription factors GATA1 and NF-E2. Additionally, ALAS2 mRNA contains an iron-responsive element (IRE) in its 5'-untranslated region, similar to mRNAs encoding ferritin and the transferrin receptor (in which the IRE is in the gene's 3' UTR). Gel retardation analysis showed that the iron-responsive element in ALAS2 mRNA is functional [as evidenced by binding to iron regulator protein 2 (IRP2)], indicating that translation of the erythroid-specific mRNA is directly linked to the availability of iron and heme in erythroid cells.[9] In this case, when intracellular iron concentration is relatively high, it is available for binding to IRP2, a process that enhances ubiquitin-mediated degradation of IRP2. Under these conditions, IRP2 is unavailable for binding to the IRE element in ALAS2, clearing the message for efficient translation. Conversely, when intracellular iron is relatively low, IRP2 degradation is restricted, making the protein available for binding to the IRE and thereby blocking translation of ALAS2 mRNA.

Recently, a variant form of EPP, inherited in an X-linked pattern (XLEPP), was shown to be due to an ALAS2 gain-of-function mutation in exon 11. The mutation results in a truncated form of the protein that has supranormal specific activity as a result of less constrained enzyme-substrate interactions, resulting in overproduction of PPIX. This situation is in contrast to EPP with mutated FECH in which PPIX accumulates because of deficient heme formation.

ALAS1 and 2 use pyridoxal phosphate (PLP) as a cofactor. PLP is a modified form of vitamin B6. It has been shown that PLP complexes with isoniazid depleting the cofactor. This PLP depletion has been one of the causes of sideroblastic anemia.

The investigators will test the hypothesis that depletion of PLP will lead to decreased activity of ALAS.

Recruitment information / eligibility

• Status: Withdrawn
• Enrollment: 0
• Est. completion date: December 2015
• Est. primary completion date: December 2015
• Accepts healthy volunteers: No
• Gender: Both
• Age group: 18 Years and older

Eligibility

Inclusion Criteria:

• All subjects will be enrolled in the Longitudinal Study of the Porphyrias.

• In patients with EPP the inclusion criteria are based on

1. clinical features

2. biochemical findings, as documented by laboratory reports of porphyria-specific testing performed after 1980

3. molecular findings documenting the identification of a mutation in FECH or ALAS2 genes (molecular evidence of EPP is required for inclusion in the study).

These data will be obtained from the Porphyria Rare Disease Clinical Research Consortium Longitudinal Study (RDCRN Protocol 7201). An individual must be willing to give written informed consent and be 18 years of age or greater.

Autosomal EPP (EPP) and X-linked protoporphyria (XLEPP)

Clinical features - a or b required

• A history of nonblistering cutaneous photosensitivity, usually with early age of onset.

• A diagnosis of EPP or XEPP in a relative.

Biochemical findings

• A marked increase in erythrocyte protoporphyrin [total erythrocyte protoporphyrin >200 ug/dL, or more than 1.5-fold increase relative to upper limit of normal of 80 ug/dL, with a predominance of free protoporphyrin (85-100% in EPP and 50-85% in XLEPP). Note: Methods in some laboratories for measuring free erythrocyte protoporphyrin (FEP) actually measure zinc protoporphyrin, so these results cannot be relied upon for diagnosis or characterizing the phenotype in EPP and XLEPP.

• Increased plasma porphyrins with a fluorescence emission peak at ~634 nm.

• Normal urinary porphyrins (except in patients with hepatobiliary impairment), and normal ALA and porphobilinogen (PBG).

Molecular findings - one of the following:

• A disease causing FECH mutation trans to the IVS3-48C>T low expression FECH allele (aEPP)

• Two disease-causing FECH mutations (EPP, recessive variant)

• A gain-of-function ALAS2 C-terminal deletion/exon 11 mutation (XLEPP)

Exclusion Criteria:

• We will exclude patients with a diagnosis of EPP that cannot be documented by DNA testing.

• Patients with evidence of active liver injury as defined by serum transaminase concentrations greater than three times the upper limit of normal, those with a history of recent (within 3 months of enrollment) or ongoing alcohol abuse, those with diabetes mellitus requiring therapy, renal insufficiency (serum creatinine >2.0 mg/ml) or evidence of malnutrition (based on subnormal plasma concentration of transthyretin) will be ineligible for participation in the study.

• Pregnant and/or lactating women will be excluded from the study.

Study Design

Endpoint Classification: Safety/Efficacy Study, Intervention Model: Single Group Assignment, Masking: Open Label, Primary Purpose: Treatment

Related Conditions & MeSH terms

• Erythropoietic Protoporphyria (EPP)
• X Linked Erythropoietic Protoporphyria

Intervention

Drug:
• Isoniazid
Isoniazid 5 mg/Kg up to 300 mg per day. Oral tablets. 2 months.

Locations

Country	Name	City	State
United States	University of Utah School of Medicine	Salt Lake City	Utah

Sponsors (6)

Lead Sponsor	Collaborator
University of Utah	Icahn School of Medicine at Mount Sinai, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), University of Alabama at Birmingham, University of California, San Francisco, University of Texas

Country where clinical trial is conducted

United States, 

Outcome

Type	Measure	Description	Time frame	Safety issue
Primary	Decrease in plasma protoporphyrin	Plasma protoporphyrin will be measured ever 2 weeks for 3 months.	3 months	No
Secondary	Sun sensitivity	Patients will be asked if there is a change in sun sensitivity	3 months	No

External Links

•   American Porphyria Foundation
•   Porphyria Rare Disease Consortium