In a first-of-its-kind experiment, researchers injected mitochondria into the eyes of a patient suffering from severe vision loss, in an attempt to recharge the damaged cells and salvage what could be salvaged of her sight.
Although the patient has not yet regained her vision, preliminary results indicate that the procedure is safe, with some positive signs emerging that open the door to future research.
Mitochondria are the microscopic structures that convert food and oxygen into energy that cells use to perform their functions. Retinal ganglion cells, the nerve cells responsible for transmitting visual information from the retina to the brain, rely heavily on mitochondria and are among the most energy-intensive cells in the central nervous system.
When the blood and oxygen supply is cut off, the mitochondria are damaged, contributing to a series of reactions that lead to the death of these cells.
The patient is a 26-year-old woman who suffered a severe brain hemorrhage and did not arrive at the hospital until 18 hours after the accident. Although emergency surgery was successful in saving her life, the prolonged deprivation of blood and oxygen to her optic nerves left her almost blind in both eyes. After eight weeks, her optic nerves showed significant atrophy, and a follow-up examination three months later showed no noticeable improvement.
But the imaging showed that the layers of nerve fibers and ganglion cells in the retina had not disappeared completely, and that some visual information was still reaching the visual cortex in the brain, raising the possibility that mitochondrial transplantation might be able to reactivate the remaining cells.
To reduce the risk of an immune reaction, the doctors used the patient's own cells. They took a sample from her thigh muscle and extracted tens of millions of mitochondria from it, then injected them fresh into the gelatinous fluid inside both of her eyes.
In the days following the injections, some changes appeared: before the treatment, doctors recorded 45 measurements of the pupils' response to light, none of which showed a normal response. But a few days after the injections, both pupils began to show normal responses. Three brain imaging sessions also recorded an organized response in the visual cortex.
However, these results did not last long, as the left eye recorded its last normal response on day 11, while the right eye continued to show intermittent normal responses until day 39. Visual acuity did not improve significantly and remained at the level of light perception only.
Experts caution that this is just an isolated case without a control group, and there is no direct evidence that the transplanted mitochondria entered the retinal ganglion cells. They also warn that this single case is insufficient to establish a causal relationship. However, the procedure did not produce any serious side effects, and the patient's body did not respond with a severe immune reaction.
The researchers point out that the temporary nature of the changes may mean that the damaged cells require repeated doses of healthy mitochondria to maintain the benefit. "Now that we've shown we can do this safely, we're working with the FDA to develop a protocol for repeated mitochondrial injections," said David Buterino, a neuroscientist at Mount Sinai School of Medicine and lead author of the study published on Research Square.
These findings open up new possibilities for treating optic nerve damage, and may one day provide a new way to save damaged cells in the eye using cellular batteries borrowed from other parts of the patient's own body.
