Rescue of Suppressed Mitochondrial Superoxide Alleviates Vascular Restenosis

Objectives: A deranged balance between smooth muscle cell (SMC) proliferation and apoptosis is the hallmark of progressive myointimal hyperplasia, a primary stage of arterial vascular disease. Dichloroacetate (DCA) was recently reported to prevent injury-induced myointimal formation via revocation of associated SMC apoptosis resistance, although mechanistic details remained elusive. We therefore sought to investigate DCA's mode of action.

Methods: Male Lewis rats underwent balloon injury of their abdominal aortas using Fogarty catheters. DCA was administered via the drinking water (0.75 g/L). As Pdk2 is the main target of DCA, mice carrying a homozygous knockout mutation for Pdk2 (Pdk2−/−) were generated. C57BL/6 wildtype (wt) mice and Pdk2−/− mice underwent aortic balloon injury using the stiff end of a PCI wire.

Results: Compared with highly proliferative and apoptosis-resistant early lesions in control rats with elevated smooth muscle cell (SMC) mitochondrial membrane potential (ΔΨm) and suppressed mitochondrial superoxide (mO₂-), DCA increased apoptosis and prevented both ΔΨm elevation and mO₂ ^- suppression. We could establish a mechanistic framework for DCAs mode of action and demonstrate that DCA restores suppressed mO₂ via the activation of pyruvate dehydrogenase. The downstream electron transport chain complexes I and III were identified as the sources for mO₂- leakage. Enhanced mO₂- then suppresses MYC, rescues hyperpolarized ΔΨm, and facilitates apoptosis. Pdk2−/− mice similarly showed maintain vascular SMC mO₂- after vascular injury and mitigated myointimal formation, thus confirming the regulatory role of Pdk2. As we attribute DCA's anti-restenotic effect to its enhancement of suppressed mO₂-, we hypothesized that other drugs that elevate mO₂- would have similar vasculoprotective effects. We therefore tested the five cancer drugs piperlongumine, 3-bromopyruvate, β-lapachone, buthionine sulfoximine, and doxorubicin, all of which are known to induce oxidative stress via mO₂- generation. All tested drugs maintained SMC mO₂- levels and reduced myointimal formation. Administration of mO₂- scavengers abolished the anti-restenosis effects.

Conclusion: Although antioxidants have been heavily promoted for vascular health, they have failed to provide any benefit in clinical trials. In contrast, we herein reveal that restoration of suppressed mO₂- emerges as a beneficial strategy to combat restenosis.