Recombinant porphobilinogen deaminase targeted to the liver corrects enzymopenia in a mouse model of acute intermittent porphyria

Correction of enzymatic deficits in hepatocytes by systemic administration of a recombinant protein is a desired therapeutic goal for hepatic enzymopenic disorders such as acute intermittent porphyria (AIP), an inherited porphobilinogen deaminase (PBGD) deficiency. Apolipoprotein A-I (ApoAI) is internalized into hepatocytes during the centripetal transport of cholesterol. Here, we generated a recombinant protein formed by linking ApoAI to the amino terminus of human PBGD (rhApoAI-PBGD) in an attempt to transfer PBGD into liver cells. In vivo experiments showed that, after intravenous injection, rhApoAI-PBGD circulates in blood incorporated into high-density lipoprotein (HDL), penetrates into hepatocytes, and crosses the blood-brain barrier, increasing PBGD activity in both the liver and brain. Consistently, the intravenous administration of rhApoAI-PBGD or the hyperfunctional rApoAI-PBGD-I129M/N340S (rApoAI-PBGDms) variant efficiently prevented and abrogated phenobarbital-induced acute attacks in a mouse model of AIP. One month after a single intravenous dose of rApoAI-PBGDms, the protein was still detectable in the liver, and hepatic PBGD activity remained increased above control values. A long-lasting therapeutic effect of rApoAI-PBGDms was observed after either intravenous or subcutaneous administration. These data describe a method to deliver PBGD to hepatocytes with resulting enhanced hepatic enzymatic activity and protection against AIP attacks in rodent models, suggesting that the approach might be an effective therapy for AIP

Nutritional Interventions with Bacillus coagulans Improved Glucose Metabolism and Hyperinsulinemia in Mice with Acute Intermittent Porphyria

Acute intermittent porphyria (AIP) is a metabolic disorder caused by mutations in the porphobilinogen deaminase (PBGD) gene, encoding the third enzyme of the heme synthesis pathway. Although AIP is characterized by low clinical penetrance (~1% of PBGD mutation carriers), patients with clinically stable disease report chronic symptoms and frequently show insulin resistance. This study aimed to evaluate the beneficial impact of nutritional interventions on correct carbohydrate dysfunctions in a mouse model of AIP that reproduces insulin resistance and altered glucose metabolism. The addition of spores of Bacillus coagulans in drinking water for 12 weeks modified the gut microbiome composition in AIP mice, ameliorated glucose tolerance and hyperinsulinemia, and stimulated fat disposal in adipose tissue. Lipid breakdown may be mediated by muscles burning energy and heat dissipation by brown adipose tissue, resulting in a loss of fatty tissue and improved lean/fat tissue ratio. Probiotic supplementation also improved muscle glucose uptake, as measured using Positron Emission Tomography (PET) analysis. In conclusion, these data provide a proof of concept that probiotics, as a dietary intervention in AIP, induce relevant changes in intestinal bacteria composition and improve glucose uptake and muscular energy utilization. Probiotics may offer a safe, efficient, and cost-effective option to manage people with insulin resistance associated with AIP

mRNA-based therapy in a rabbit model of variegate porphyria offers new insights into the pathogenesis of acute attacks

Variegate porphyria (VP) results from haploinsufficiency of protoporphyrinogen oxidase (PPOX), the seventh enzyme in the heme synthesis pathway. There is no VP model that recapitulates the clinical manifestations of acute attacks. Combined administrations of 2-allyl-2-isopropylacetamide and rifampicin in rabbits halved hepatic PPOX activity, resulting in increased accumulation of a potentially neurotoxic heme precursor, lipid peroxidation, inflammation, and hepatocyte cytoplasmic stress. Rabbits also showed hypertension, motor impairment, reduced activity of critical mitochondrial hemoprotein functions, and altered glucose homeostasis. Hemin treatment only resulted in a slight drop in heme precursor accumulation but further increased hepatic heme catabolism, inflammation, and cytoplasmic stress. Hemin replenishment did protect against hypertension, but it failed to restore action potentials in the sciatic nerve or glucose homeostasis. Systemic porphobilinogen deaminase (PBGD) mRNA administration increased hepatic PBGD activity, the third enzyme of the pathway, and rapidly normalized serum and urine porphyrin precursor levels. All features studied were improved, including those related to critical hemoprotein functions. In conclusion, the VP model recapitulates the biochemical characteristics and some clinical manifestations associated with severe acute attacks in humans. Systemic PBGD mRNA provided successful protection against the acute attack, indicating that PBGD, and not PPOX, was the critical enzyme for hepatic heme synthesis in VP rabbits