α-Lipoic Acid Improves Hepatic Metabolic Dysfunctions in Acute Intermittent Porphyria: A Proof-of-Concept Study

Abstract

Background: Acute intermittent porphyria (AIP) is caused by the haploinsufficiency of porphobilinogen deaminase (PBGD) enzymatic activity. Acute attacks occur in response to fasting, and alterations in glucose metabolism, insulin resistance, and mitochondrial turnover may be involved in AIP pathophysiology. Therefore, we investigated the metabolic pathways in PBGD-silenced hepatocytes and assessed the efficacy of an insulin mimic, α-lipoic acid (α-LA), as a potential therapeutic strategy. Methods: HepG2 cells were transfected with siRNA-targeting PBGD (siPBGD). Cells were cultured with low glucose concentration to mimic fasting and exposed to α-LA alone or with glucose. Results: At baseline, siPBGD cells showed a lower expression of genes involved in glycolysis and mitochondrial dynamics along with reduced total ATP levels. Fasting further unbalanced glycolysis by inducing ATP shortage in siPBGD cells and activated DRP1, which mediates mitochondrial separation. Consistently, siPBGD cells in the fasted state showed the lowest protein levels of Complex IV, which belongs to the oxidative phosphorylation (OXPHOS) machinery. α-LA upregulated glycolysis and prompted ATP synthesis and triglyceride secretion, thus possibly providing energy fuels to siPBGD cells by improving glucose utilization. Finally, siPBGD exposed to α-LA plus glucose raised mitochondrial dynamics, OXPHOS activity, and energy production. Conclusions: α-LA-based therapy may ameliorate glucose metabolism and mitochondrial dysfunctions in siPBGD hepatocytes.

Cutting-Edge Therapies and Novel Strategies for Acute Intermittent Porphyria: Step-by-Step towards the Solution

“…Disturbances in glucose metabolism associated with PBGD deficiency were also recently revealed by our group. We found that PBGD-mRNA silencing in human hepatoma cells (HepG2), especially during fasting stimulus, reduced the expression of glycolytic enzymes such as glucokinase (GCKR), phosphofructokinase (PFK) and pyruvate kinase (PK), suggesting that the downregulation of heme biosynthesis may even affect glycolysis [17].…”

“…The impairment of mitochondrial bioenergetics could even be influenced by the unbalancing of the mitochondrial lifecycle and turnover, including fusion, fission, and mitophagy, which leads to alterations in mitochondrial dynamics, mass, shape, and metabolism. It was observed in both AIP mice and humans that the derangement of mitochondrial biogenesis was correlated with aberrations in mitochondrial morphology and functionality [17,52,54,56]. The analysis of the hepatic transcriptome of AIP mice, after PB exposure, indicated that the majority of differentially expressed genes belong to mitochondrial biogenesis and OXPHOS, both regulated by the peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PPARGC1A, encoding the PGC1-α transcription factor).…”

“…Aberrations in mitochondrial shape and size may be caused by defects in mitochondrial dynamics and metabolism, which are both modulated by PGC1-α. It was demonstrated that the fasting stimulus in AIP mice triggered the expression of hepatic ALAS1 via PGC1α, underlining its implication in precipitating acute episodes of AIP [2,17,54,61]. Our group investigated metabolic dysfunction in response to PBGD downregulation in hepatocytes, focusing on mitochondrial failure in terms of bioenergetics sources and dynamics.…”

“…Conversely, dynamin-1-like protein (DRP1), which is involved in mitochondrial fission and OXPHOS activity, was upregulated. Furthermore, the protein levels of complexes I and IV of the respiratory chain appeared reduced, indicating that fasting could switch the mitochondrial dynamics towards fission rather than fusion, thereby promoting OXPHOS failure and ATP shortage [17]. Most recently, it was demonstrated that a deficiency of FETCH, a gene involved in the last step of heme production and responsible for the development of erythropoietic protoporphyria (EPP), worsened both glycolysis and OXPHOS, along with a decrease in mitochondrial fusion [56], which indicates that common mechanisms may arise in the presence of heme deficiency.…”

“…The major steps forward for the treatment of AIP were carried out in recent years with (1) the approval of givosiran (Alnylam Pharmaceuticals, Inc., Cambridge, MA, USA), which inhibits ALAS1 through RNA interference (RNAi) in patients aged at least 12 years, and (2) with the ongoing efforts in the development of therapies based on the replacement of nonfunctional PBGD with hepatic delivery of the mRNA or protein [11][12][13][14][15]. Interestingly, the characterization of metabolic profiles in AIP experimental models and humans has highlighted alterations in glucose and lipid metabolism, insulin resistance (IR), and hepatic mitochondrial dysfunction, which offers the possibility of considering insulin and insulinmimetics for the clinical management of AIP [16][17][18].…”