(December 5, 2015) People born with a rare genetic mutation are unable to feel pain, but previous attempts to recreate this effect with drugs have had surprisingly little success. Using mice modified to carry the same mutation, UCL researchers funded by the MRC and Wellcome Trust have now discovered the recipe for painlessness.
‘Channels’ that allow messages to pass along nerve cell membranes are vital for electrical signalling in the nervous system. In 2006, it was shown that sodium channel Nav1.7 is particularly important for signalling in pain pathways and people born with non-functioning Nav1.7 do not feel pain. Drugs that block Nav1.7 have since been developed but they had disappointingly weak effects.
The new study, published in Nature Communications, reveals that mice and people who lack Nav1.7 also produce higher than normal levels of natural opioid peptides.
To examine if opioids were important for painlessness, the researchers gave naloxone, an opioid blocker, to mice lacking Nav1.7 and found that they became able to feel pain. They then gave naloxone to a 39-year-old woman with the rare mutation and she felt pain for the first time in her life.
“After a decade of rather disappointing drug trials, we now have confirmation that Nav1.7 really is a key element in human pain,” says senior author Professor John Wood (UCL Medicine). “The secret ingredient turned out to be good old-fashioned opioid peptides, and we have now filed a patent for combining low dose opioids with Nav1.7 blockers. This should replicate the painlessness experienced by people with rare mutations, and we have already successfully tested this approach in unmodified mice.”
Broad-spectrum sodium channel blockers are used as local anaesthetics, but they are not suitable for long-term pain management as they cause complete numbness and can have serious side-effects over time. By contrast, people born without working Nav1.7 still feel non-painful touch normally and the only known side-effect is the inability to smell.