A Membrane-Disruptive Action of VBIT-4 Challenges Its Role as a Widely Used VDAC Oligomerization Inhibitor

Area of Science:

• Mitochondrial physiology
• Membrane biophysics
• Pharmacology

Background:

• Voltage-dependent anion channel 1 (VDAC1) is crucial for mitochondrial function.
• VDAC1 oligomerization is implicated in mtDNA release and apoptosis, but mechanisms are unclear.
• VBIT-4 is widely used to inhibit VDAC1 oligomerization, yet lacks mechanistic validation.

Purpose of the Study:

• To investigate the molecular mechanisms of VBIT-4's effect on VDAC1.
• To characterize VBIT-4's interaction with mitochondrial outer membrane proteins and lipid bilayers.

Main Methods:

• High-speed atomic force microscopy (HS-AFM) for direct visualization of VDAC1 oligomerization.
• Single-channel electrophysiology, microscale thermophoresis, and coarse-grained molecular dynamics simulations.
• Cytotoxicity assays in HeLa cells.

Main Results:

• VBIT-4 partitions into lipid bilayers at micromolar concentrations, disrupting membrane structure independently of VDAC1.
• Electrophysiology, thermophoresis, and MD simulations confirmed VBIT-4's membrane destabilizing effects.
• VBIT-4 induced VDAC1-independent cytotoxicity in HeLa cells at concentrations >10 microM.

Conclusions:

• VBIT-4 primarily acts by disrupting membrane integrity through lipid partitioning, not by specific VDAC1 inhibition.
• Prior studies using VBIT-4 may need re-interpretation due to its non-specific membrane effects.
• Caution is advised when using VBIT-4, emphasizing the need for mechanistic validation.