Stanford researchers found a way to reversibly pause liver cell metabolism at normal temperature and oxygen levels: pausing metabolism during storage reduced tissue damage fourfold in rat liver transplants
Stanford researchers found a way to reversibly pause liver cell metabolism at normal temperature and oxygen levels: pausing metabolism during storage reduced tissue damage fourfold in rat liver transplants
Hiromitsu Nakauchi’s laboratory developed TorPause, a solution combining the cell growth inhibitor GSK212 with the mitochondrial hydrogen sulfide donor AP39. In a rat liver transplant model involving five hours of storage at room temperature, TorPause reduced the graft’s structural damage score from 8 to 2 and significantly reduced the risk of death.
More than 100 thousand people in the United States are waiting for an organ transplant, and about 17 die each day before a donor becomes available. The short time an organ remains viable after retrieval contributes to the shortage: cold storage slows metabolism but does not prevent ischemia-reperfusion injury, the damage caused when blood flow stops and then resumes. Machine perfusion is more effective, but it is expensive and available at few hospitals.
On October 9, the team led by Stanford geneticist Hiromitsu Nakauchi, known for his work on growing human organs in animals, proposed another approach: pausing an organ’s metabolism from within, as cells do during embryonic diapause and hibernation. A similar idea was tested in 2005, when mice inhaling hydrogen sulfide entered a state resembling suspended animation. Later work, however, attributed the effect to the accompanying oxygen shortage in the chamber rather than the gas itself, and the effect largely disappeared in larger mammals.
Nakauchi and his colleagues hypothesized that earlier attempts had induced the pause by targeting only mTOR, while oxygen deprivation suppressed the parallel PI3K pathway that remained active. After screening 18 molecules individually and in pairs in mouse stem cells, the team found that blocking a single pathway was insufficient: even a potent mTOR inhibitor reduced cell growth by only a third, whereas blocking both pathways produced an effect much greater than the sum of the individual effects. They identified one molecule that blocked both: GSK2126458 (GSK212) inhibited both pathways and, unlike RapaLink-1, allowed cells to recover after washout. In whole embryos under normal oxygen conditions, GSK212 maintained the pause for 8,5 days (78% survived), whereas INK128, previously used under low-oxygen conditions, proved toxic under the same conditions.
The researchers combined GSK212 with AP39, which protects mitochondria when blood flow resumes after the pause. They added TorPause to University of Wisconsin solution, which is already used clinically, and tested it in liver transplantation. Rat livers were stored for five hours at room temperature, exposing them to severe warm ischemia instead of cold storage.
This differs from an earlier finding: controlled torpor in mice slowed blood aging only when accompanied by a drop in body temperature; reduced metabolism alone did not produce that effect.
Control livers remained dark and congested; livers treated with TorPause had a normal color.
During the 14-day follow-up, all animals in the control and AP39 groups died within the first day. In both the GSK212 group and the group receiving the full combination, one in four rats survived to day 14, and both survivors’ livers recovered completely. The risk analysis indicated that GSK212 reduced the risk of death eightfold (p = 0,04).
“True organ biostasis requires a shift from controlling the external environment to control at the level of the cell itself,” the authors write in their preprint.
The method protects the organ during the transplant operation itself, before it is connected to the recipient’s circulation. Stanford has already filed a patent application for TorPause, and Nakauchi holds equity in several biotechnology companies unrelated to this work.