Bezafibrate activation of PPAR drives disturbances in mitochondrial redox bioenergetics and decreases the viability of cells from patients with VLCAD deficiency

Iain P. Hargreaves,Niels Gregersen,Rikke K.J. Olsen,Kathrine G. Andersen,Robert Heaton,Martin Lund

doi:10.1016/j.bbadis.2021.166100

Abstract

Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is the most common inborn long-chain fatty acid oxidation (FAO) disorder. VLCAD deficiency is characterized by distinct phenotypes. The severe phenotypes are potentially life-threatening and affect the heart or liver, with a comparatively milder phenotype characterized by myopathic symptoms. There is an unmet clinical need for effective treatment options for the myopathic phenotype. The molecular mechanisms driving the gradual decrease in mitochondrial function and associated alterations of muscle fibers are unclear.The peroxisome proliferator-activated receptor (PPAR) pan-agonist bezafibrate is a potent modulator of FAO and multiple other mitochondrial functions and has been proposed as a potential medication for myopathic cases of long-chain FAO disorders. In vitro experiments have demonstrated the ability of bezafibrate to increase VLCAD expression and activity. However, the outcome of small-scale clinical trials has been controversial.We found VLCAD deficient patient fibroblasts to have an increased oxidative stress burden and deranged mitochondrial bioenergetic capacity, compared to controls. Applying heat stress under fasting conditions to bezafibrate pretreated patient cells, caused a marked further increase of mitochondrial superoxide levels. Patient cells failed to maintain levels of the essential thiol peptide antioxidant glutathione and experienced a decrease in cellular viability. Our findings indicate that chronic PPAR activation is a plausible initiator of long-term pathogenesis in VLCAD deficiency. Our findings further implicate disruption of redox homeostasis as a key pathogenic mechanism in VLCAD deficiency and support the notion that a deranged thiol metabolism might be an important pathogenic factor in VLCAD deficiency.

Highlights

Very long-chain acyl-coenzyme A (CoA) dehydrogenase (VLCAD) deficiency was first described in 1993 [1]
Dermal fibroblast cells derived from six patients, diagnosed with Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency based on 4 clinical presentation, abnormal acyl-carnitines, and biallelic pathogenic VLCAD variations were included in the study
We found that mitochondrial metabolic capacity and the essential peptide GSH is affected by bezafibrate treatment of VLCAD deficient fibroblasts, even at basal conditions

Summary

Introduction

Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency was first described in 1993 [1]. As the most common of the inborn long-chain fatty acid oxidation (FAO) disorders, VLCAD deficiency is clinically well-described and is part of neonatal screening programs in many countries [2]. VLCAD can process long-chain fatty acids with chain lengths from 12 to 22 carbons, with each β-oxidation cycle removing two carbons [3]. The worst phenotypes are characterized by ATP homeostasis failure that in the most severe cases results in death. The most severe phenotypes do involve the heart or liver respectively and are associated with episodes of hypoketotic hypoglycemia, risk of multi-organ failure, and sudden death [6,7,8]. The most severe phenotype is typically associated with biallelic loss-of-function variations, resulting in very low residual enzymatic capacity. For the missense variations, associated with milder myopathic phenotypes, there is less predictability with regard to genotype-phenotype relationships [7, 9]

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