Scientists from University College London (UCL) have presented further evidence in mice that the amyloid protein, which builds up in the brain during Alzheimer’s, can be transmitted through contaminated brain tissue extracts in a similar way to the prion protein responsible for Creutzfeldt-Jakob disease (CJD). The results are published today (13 December) in the scientific journal Nature.
Previously, the same group of researchers at UCL who carried out this work studied brain tissue donated after death by eight people who developed CJD years after receiving human-derived growth hormone before the mid-1980s. As well as finding the prion protein responsible for CJD in all eight people, the research team also found unusually high levels of amyloid in tissue and blood vessels in four of the brains.
As this study only showed an association between those who received the injection and the build-up of amyloid in the brain, it wasn’t possible for the researchers to conclude that the injection itself caused the abnormally high levels of amyloid seen in the brains of the growth hormone recipients. To test this theory, they went back to the original batches of growth hormone given to those people whose brains were examined in the first research study.
The researchers found that they could detect amyloid in several of the batches of growth hormone, which they then prepared and injected into mice genetically modified to be more susceptible to amyloid build-up in the brain.
The scientists found that 240 days after injection, they could detect amyloid at significantly higher levels in blood vessels in the brains of mice injected with the growth hormone samples compared to those injected with control samples without amyloid.
The build-up of amyloid seen in the blood vessels of the brain is known as cerebral amyloid angiopathy (CAA), which can also lead to stroke and an increased risk of developing dementia.
Dr David Reynolds, Chief Scientific Officer at Alzheimer’s Research UK, said:
“Previous research suggests that amyloid can spread through a person’s brain in a similar way to the prion protein responsible for Creutzfeldt-Jakob disease (CJD). This new work in mice strengthens the case already proposed by this team that amyloid may have been passed between humans through historical contaminated growth hormone injections. The new research does not, however, provide evidence that the amyloid build-up initiated by these injections causes Alzheimer’s disease itself, an important question that remains to be answered.
“Although scientifically interesting, this research focused on a small set of samples from people who had a very specific neurosurgical procedure, last carried out in the mid-1980s. Although the findings might sound concerning, strict guidelines surrounding the sterilisation and use of surgical equipment have already been introduced since the discovery of prion protein contamination and CJD.
“Importantly, there remains no evidence of Alzheimer’s disease being transmitted through blood transfusions and further work to understand the mechanics of amyloid transmission is ongoing.”