Acute Intermittent Porphyria (AIP) presents with abdominal pain, neuropsychiatric symptoms, and autonomic dysfunction. Urine analysis shows elevated ALA and PBG. Why does glucose infusion and heme arginate alleviate acute attacks?

• A Glucose provides energy for neural repair; heme arginate provides iron
• B Both glucose and heme activate porphobilinogen deaminase to bypass the deficient enzyme
• C Glucose converts PBG to uroporphyrinogen non-enzymatically
• D Glucose represses ALA synthase-1 (ALAS1) transcription via downregulation of PGC-1alpha; heme directly inhibits ALAS1 allosterically and decreases its transcription ✓

Explanation

AIP is caused by haploinsufficiency of PBGD (porphobilinogen deaminase, hydroxymethylbilane synthase). When ALAS1 is induced (by drugs, fasting, hormones), ALA and PBG accumulate proximal to the PBGD bottleneck. Glucose therapy: high carbohydrate/glucose intake suppresses PGC-1alpha coactivator activity, which is required for ALAS1 transcriptional upregulation (PGC-1alpha drives ALAS1 via NRF2/HNF4alpha), thereby reducing ALA/PBG production. Heme arginate (intravenous): exogenous heme enters hepatocytes and (1) inhibits ALAS1 directly (heme binds regulatory cysteine residues blocking ALAS1 mitochondrial import) and (2) represses ALAS1 gene transcription. Both reduce toxic precursor accumulation.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

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Written and medically reviewed by the StethoPrep medical team.