Functional partitioning of lipoic acid decouples cellular abundance from mitochondrial utilization

Area of Science:

• Biochemistry
• Cellular Biology
• Mitochondrial Medicine

Background:

• Alpha-lipoic acid (ALA) is commonly included in "mitochondrial cocktails" for primary mitochondrial disorders.
• The precise mechanism of ALA's action and its cellular utilization in these conditions remain poorly understood.

Purpose of the Study:

• To elucidate the intracellular availability and functional utilization of ALA in mammalian cells.
• To clarify the mechanism of action of ALA as a mitochondrial supplement.

Main Methods:

• Investigated ALA's intracellular pools: free and protein-bound via mitochondrial fatty acid synthesis (mtFAS).
• Examined the impact of disrupting mtFAS on protein lipoylation and oxidative phosphorylation.
• Assessed effects of exogenous ALA supplementation on cellular ALA levels, lipoylation, mitochondrial respiration, and proliferation.

Main Results:

• ALA exists in distinct intracellular pools: a low-abundance free pool and a protein-bound pool formed by mtFAS.
• Disrupting mtFAS impaired oxidative phosphorylation and abolished protein lipoylation, independent of free ALA levels.
• Exogenous ALA increased free intracellular ALA but did not restore protein lipoylation, mitochondrial respiration, or cell proliferation.

Conclusions:

• Cellular ALA abundance does not directly correlate with its functional utilization in mitochondria.
• The cellular effects of ALA supplementation resemble those of antioxidants like N-acetylcysteine, not direct mitochondrial restoration.
• Findings challenge the rationale for using ALA supplementation to restore mitochondrial function in primary mitochondrial disorders.