Regenerative
Blood exosomes may keep shingles pain alive after the virus is gone
By Life and Health Today Staff, . Life and Health Today.
About one in five people who get shingles go on to develop post-herpetic neuralgia, or PHN, a condition where pain continues for more than three months after the rash has healed and the virus is no longer detectable. Why that happens has not been well understood. A team led by Andrew Bubak, an associate professor of neurology at the University of Colorado Anschutz who studies exosomes in infectious disease, now has a candidate explanation, reported in the journal Annals of Neurology.
Exosomes are microscopic packages that cells release into the bloodstream. They carry proteins and other molecules and are used by the body to send signals between tissues. Bubak's team found that in people with PHN, these packages appear to keep delivering damaging instructions to nerve cells long after the shingles virus itself has been cleared.
The core experiment was conducted in cells in a laboratory dish, not in people. When the researchers exposed healthy nerve cells to exosomes collected from the blood of people with PHN, those nerve cells showed many of the same harmful changes seen during an active viral infection, according to Genetic Engineering News, which reported the findings. The exosomes did not kill the nerve cells. Instead, they appeared to hold them in a persistently unhealthy, dysfunctional state, reducing the nerves' ability to grow and repair themselves and causing structural changes that may make them function abnormally.
One result surprised the team. They expected to see increases in the standard pain-signaling channels found on nerve cell surfaces. Instead, those channels were reduced. At the same time, levels of substance P, a chemical messenger involved in transmitting pain signals, went up. That combination suggests, the authors wrote, that chronic shingles pain may be driven less by conventional nerve firing and more by ongoing chemical signals that keep the pain system activated.
The researchers describe this as a "failure-to-resolve" model. Rather than PHN being caused by permanent damage done during the initial infection, the idea is that the body fails to switch off the healing response it mounted during acute illness. Exosomes generated during that acute phase persist in circulation and continue sending inflammatory signals that prevent nerves from recovering. Bubak said, as quoted by Genetic Engineering News: "We can completely stop the infection, yet in some patients the pain does not go away."
This framing matters for treatment. Standard antiviral drugs such as acyclovir and valacyclovir target the replicating virus, but the Annals of Neurology paper notes they do not consistently prevent PHN, which is consistent with a mechanism that operates independently of ongoing viral replication. If exosomes are sustaining the pain state, then blocking the virus alone would not be enough.
The team also raised two forward-looking possibilities, both speculative at this stage. First, exosome profiles measured early during an acute shingles infection might one day identify which patients are at higher risk of developing PHN, potentially allowing earlier intervention. Second, because exosomes naturally travel to nerve tissue, they might eventually be engineered to carry therapeutic agents that block specific proteins and help nerves recover. Neither of these applications has been tested in people.
What this study does not establish is whether targeting exosomes actually relieves pain in humans. The experiments were conducted in cells in a dish. The path from a lab finding to a clinical therapy is long, and many mechanisms that look promising at the cellular level do not translate into effective treatments. No human trial of an exosome-targeting therapy for PHN is described in the reports.
What the finding does offer is a more detailed picture of why some people remain in pain after shingles, and a set of molecular targets that did not previously exist. Whether those targets can be reached safely and effectively in people is the question that future research would need to answer. Anyone experiencing persistent pain after shingles should discuss it with a clinician who knows their full history.