Background:
A functional anesthetic target has long been suspected to reside within mitochondria and disruption of bioenergetic capacity is believed to play a role in the anesthetic response. Unfortunately, the exact mechanism by which changes in mitochondrial target activity result in clinically relevant anesthetic endpoints remains unknown. Here we leveraged knowledge of propofol toxicity to guide drug discovery and uncover a previously unknown pharmacological target within mitochondria. We hypothesized that, like propofol, quinone analogs would interfere with electron transfer, cause excessive proton leak within mitochondria, and induce hypnosis. We tested our hypothesis using the short-chain coenzyme Q (CoQ) analog, ubiquinone-5 (Ub5), and aimed to characterize its anesthetic phenotype in the mouse and elucidate the source of Ub5-induced mitochondrial leak.
Methods:
Anesthetic phenotype was assessed in vivo in the mouse using behavioral and neurophysiological approaches. We measured biological activity in isolated mitochondria using polarography and spectrophotometry and identified source of proton leak using pharmacological inhibitors, mutant mouse strains, and transport activity assays in proteoliposomes. Finally, we assessed cardiotoxic effects in the isolated-perfused mouse heart ex-vivo.
Results:
CoQ analogs caused uncompensated proton leak in developing cardiomyocyte mitochondria and reversible cardiotoxicity in a manner reminiscent of propofol. Tail vein injection of Ub5 induced short-lived loss of righting, EEG changes consistent with a deep state of anesthesia, and reversible decreases in neuronal calcium transients and mitochondrial membrane potential (ΔΨm) in vivo. Precipitous decline in ΔΨm played a role in Ub5-induced unconsciousness and we identified the aspartate-glutamate carrier, Aralar, as a functional target and source of Ub5-mediated proton leak.
Conclusions:
The data indicate that uncompensated mitochondrial proton leak is an important mechanistic contributor to the anesthetic response in addition to electron transport inhibition. These findings advance our understanding of how anesthetics induce hypnosis and lay the foundation for next-generation drug discovery.