Circadian rhythms in acute intermittent porphyria--a pilot study

Abstract

Background: Acute intermittent porphyria (AIP) is an inherited disorder of haem synthesis wherein a partial deficiency of porphobilinogen (PBG) deaminase (PBGD) with other factors may give rise to biochemical and clinical manifestations of disease. The biochemical hallmarks of active AIP are relative hepatic haem deficiency and uncontrolled up-regulation of hepatic 5-aminolevulinic acid (ALA) synthase-1 (ALAS1) with over-production of ALA and PBG. The treatment of choice is intravenous haem, which restores the deficient regulatory haem pool of the liver and represses ALAS1. Recently, haem has been shown to influence circadian rhythms by controlling their negative feedback loops. We evaluated whether subjects with AIP exhibited an altered circadian profile.

Materials and methods: Over a 21-h period, we measured levels of serum cortisol, melatonin, ALA, PBG and mRNA levels (in peripheral blood mononuclear cells) of selected clock-controlled genes and genes involved in haem synthesis in 10 Caucasian (European-American) women who were either postmenopausal or had been receiving female hormone therapy, six of whom have AIP and four do not and are considered controls.

Results: Four AIP subjects with biochemical activity exhibited higher levels of PBG and lower levels and dampened oscillation of serum cortisol, and a trend for lower levels of serum melatonin, than controls or AIP subjects without biochemical activity. Levels of clock-controlled gene mRNAs showed significant increases over baseline in all subjects at 5 a.m. and 11 p.m., whereas mRNA levels of ALAS1, ALAS2 and PBGD were increased only at 11 p.m. in subjects with active AIP.

Conclusions: This pilot study provides evidence for disturbances of circadian markers in women with active AIP that may trigger or sustain some common clinical features of AIP.

Figure 1. Time course of serum cortisol concentrations in subjects studied

Subjects had blood samples drawn and processed as described in Methods. (A) Concentrations of serum cortisol in control (n=3) and all AIP subjects (n=6). *= Control group significantly different from all other time points within control except for 5am, and AIP group significantly different from all other time points within AIP. (B) Concentrations of serum cortisol in control (n=3) and AIP subjects with (n=4) and without (n=2) biochemical activity for time course studied. †= AIP subjects with biochemical activity significantly different from other time points within group, AIP subjects without biochemical activity significantly different from 8pm and 11pm time points within group, and control group significantly different from all other time points within control except 5am. ‡= AIP subjects with biochemical activity significantly different from control at same time point. Shaded boxes represent times of usual sleep. Data are means ± SE.

Figure 2. Time course of serum melatonin concentrations in subjects studied

Subjects had blood samples drawn and processed as described in Methods. (A) Concentrations of serum melatonin in control (n=3) and all AIP subjects (n=6). *= mean value for AIP group at 5 am significantly greater than mean values for this at 11am, 2pm, and 5pm time points. (B) Concentrations of serum melatonin in control (n=3) and AIP subjects with (n=4) and without (n=2) biochemical activity. Shaded boxes represent times of usual sleep. Data are means ± SE.

Figure 3. Time course of plasma ALA and PBG concentrations in subjects studied

Subjects had blood samples drawn and processed as described in Methods. Mean concentrations of plasma (A) ALA and (B) PBG in control (n=3) and AIP subjects with (n=4) and without (n=2) biochemical activity. *= All groups significantly different from each other at 8pm time point. †= AIP subjects without biochemical activity significantly different from other subject groups within time point. ‡= AIP subjects with biochemical activity significantly different from other subject groups within time point. Shaded boxes represent times of usual sleep. Data are means ± SE.

Figure 4. Selected clock-controlled gene mRNA expression in PBMCs in subjects studied

Subjects had blood samples drawn and processed as described in Methods. mRNA expression for (A) PER2, (B) CRY1 and (C) NR1D1 using ΔΔC_t method in PBMCs for control (n=3) and AIP subjects with (n=4) and without (n=2) biochemical activity. *= Significantly different from other time points within respective subject group. Data are means ± SE.

Figure 5. mRNA expression of selected genes involved in heme synthesis in PBMCs in subjects studied

Subjects had blood samples drawn and processed as described in Methods. mRNA expression for (A) ALAS1, (B) ALAS2 and (C) PBGD using ΔΔC_t method in PBMCs for control (n=3) and AIP subjects with (n=4) and without (n=2) biochemical activity. *= AIP subjects with biochemical activity significantly different from other time points within group, and also different from other subject groups within same time point. Data are means ± SE.