4-Hydroxybenzoate supplementation in primary CoQ deficiency due to COQ2 defects

Introduction: Coenzyme Q (CoQ) is lipophilic, redox-active lipid involved in multiple cellular pathways. Its main role is to transport electrons from complex I and II to complex III of the mitochondrial respiratory chain. Primary CoQ deficiency is a rare mitochondrial disorder caused by mutations in genes involved in CoQ10 biosynthesis. Primary CoQ deficiency can manifest with a broad spectrum of clinical manifestations, including neurological symptoms, renal failure, hypertrophic cardiomyopathy, retinopathy, muscle involvement, and sensorineural hearing loss. The current management of primary CoQ deficiency is based on high-dose oral CoQ10 supplementation along with symptomatic care. However, approximately 70% of patients show a poor response to the treatment due the low absorption and bioavailability of the molecule. Moreover, and even minor variation in the formula lead to a severe deterioration of the clinical condition. Aim of the study: In this study 4-hydroxybenzoate (4-HB), a precursor of CoQ, has been tested as an alternative treatment for primary CoQ deficiency caused by mutations in the COQ2 gene. Materials and Methods: Fibroblasts from a healthy control and three patients with primary CoQ deficiency due to COQ2 mutations were obtained by skin biopsy. COQ2 protein content was assessed by SDS-PAGE and Western Blot analysis. Control and patient-derived fibroblasts were divided into two experimental groups: one group was treated with 4-HB under low-glucose conditions for seven days, while the other group remained untreated under the same conditions. Mitochondrial respiration efficiency was evaluated using the Agilent Seahorse XF analysis. Cellular CoQ10 content was quantified by high-performance liquid chromatography (HPLC). Results: Western Blott analysis showed that the COQ2 missense variants, identified in the patients, did not affect COQ2 protein expression, but rather result in a functional impairment of the enzyme. Treatment with 4-HB was associated with a heterogeneous bioenergetic response across control and patient-derived fibroblasts, with a minimal effect observed in fibroblasts from Patient 1 and 2 and a more pronounced response in fibroblasts from Patient 3. A similar increase in CoQ10 levels was observed across all patients, with 4-HB inducing a significantly increase of CoQ10 levels compared to untreated (UT) cells. Conclusions: Our preliminary results support for the use of 4-HB as a promising therapeutic approach for COQ2-related primary CoQ10 deficiency. As proposed, this approach may represent a valuable alternative to conventional oral CoQ10 supplementation. More generally, this study highlights the value of precision medicine strategies targeting specific molecular defects and may contribute to the development of substrate-based bypass therapies for other primary CoQ defects.