14 Dec 2018

Researchers have strengthened the case that certain medical procedures can transfer amyloid pathology between people. John Collinge and Sebastian Brandner at University College London previously reported finding amyloid plaques and cerebral amyloid angiopathy (CAA) in the brains of seven young to middle-aged adults who had died from prion disease. As children, they had been treated with human growth hormone extracted from the pituitary glands of human cadavers; the data then implied that the extracts contained Aβ seeds as well as prions. In the December 13 Nature, researchers led by Collinge now provide direct evidence for this. The authors report that archived vials of the same growth hormone extract given to patients accelerated amyloidosis in transgenic mice. “I was amazed we could seed so easily from this material, which had sat as a dry powder at room temperature for 30 or 40 years. It shows the resistance of these seeds to degradation,” Collinge said in a Nature press briefing.

Some patients treated with pituitary extracts developed prion disease and amyloidosis.

The same extracts accelerated amyloid deposition in transgenic mice.

This confirms the presence of long-lasting Aβ seeds in these extracts.

Other scientists said the finding supports the transmission hypothesis proposed in the 2015 paper. “These two articles combined provide a very strong case for transmission of Alzheimer’s pathology in a prion-like infectious manner in human beings,” Claudio Soto at the University of Texas Medical School, Houston, wrote to Alzforum (full comment below). In an accompanying editorial, Tien-Phat Huynh and David Holtzman at Washington University, St. Louis, wrote, “These results provide strong evidence that the Aβ pathology previously reported in people who died of CJD after receiving cadaveric human growth hormone was indeed caused by their treatment.”

Not everyone agreed, however. “It is a long way from the data presented in this paper to the idea that Aβ pathology can be transmitted between people by medical procedures,” John Trojanowski at the University of Pennsylvania, Philadelphia, wrote to Alzforum. He noted that the APP mutations in these transgenic mice are rare in humans, and that the same kind of seeding might not happen in most people. "We studied the U.S. cadaver growth hormone cohort and found no PD or AD in more than 6,000 subjects," Trojanowski said (Irwin et al., 2013). More recently, he recently argued that multiple system atrophy should not be considered a prion disease, and said the same arguments apply to AD (Wenning et al., 2018).

The practice of obtaining growth hormone from cadavers ended in 1985, after some recipients developed the fatal prion disorder Creutzfeldt-Jakob disease (CJD). In the U.K., clinicians treated a total of 1,883 people with the extract. So far, 80 of them have contracted CJD. Notably, all of these patients received at least one treatment with growth hormone purified by the Hartree-modified Wilhelmi procedure (HWP) (Swerdlow et al., 2003). Unlike other methods, HWP does not include a size-exclusion chromatography step, which may help filter out protein aggregates. When Collinge and colleagues analyzed postmortem brain samples from eight of the patients treated with HWP preparations, they found extensive amyloidosis and CAA in four of them, while three more had occasional plaques (Sep 2015 news).

To confirm the presence of Aβ seeds, Collinge obtained archived vials from three HWP batches used to treat the eight patients, as well as from two additional HWP batches, and compared them to 11 non-HWP batches that had also been administered to the same group. Co-author Dominic Walsh at Brigham and Women’s Hospital, Boston, tested each vial for the presence of Aβ40, Aβ42, and tau using sensitive ELISAs and electrochemiluminescent assays. All HWP preparations were positive for these proteins, whereas all non-HWP preparations were negative.

Were these peptides able to seed amyloidosis, however? First author Silvia Purro injected samples from two of the HWP vials into the right parietal lobe of six-week-old APP NL-F knock-in mice. These animals carry humanized APP bearing the Swedish and Iberian mutations, and begin depositing amyloid in the hippocampus and cerebral cortex at six months. However, APP NL-F mice treated with either of the HWP samples developed more extensive amyloidosis. Eight months after injection, they sported plaques in the cerebellum, where control transgenics injected with vehicle had none. They also displayed extensive vascular amyloid, whereas control transgenics had almost no CAA at that age.

Transgenic mice that received the HWP preparation deposited almost as much amyloid as those injected with homogenates from AD brain. On the other hand, mice that received recombinant human growth hormone, or extracts from healthy human postmortem brains, looked like controls. Wild-type mice injected with the HWP batches did not develop plaques; mice expressing human wild-type APP were not tested.

These findings are not isolated to U.K. samples. Charles Duyckaerts and Stéphane Haïk at Hôpital Pitié-Salpêtrière, Paris, noted that they have found Aβ and tau contaminants in French cadaver-derived human growth hormone preparations (Duyckaerts et al., 2018). They suggested comparing the amount of Aβ in preparations from France and the U.K. and correlating this with the average incubation period before amyloidosis appeared in patients. “This will help determine the effect of the inoculum dose on the transmission of amyloid pathology,” they wrote to Alzforum (full comment below).

Researchers puzzled over why the tau that is also present in these preparations did not seed tangles in human patients. “It’s possible the tau is not in a seed-competent form,” suggested Lary Walker at Emory University, Atlanta. To test this, Collinge plans to repeat these experiments in mouse models of tauopathy. Researchers speculated that the CJD patients might have developed tau tangles and full-blown Alzheimer’s disease if they had lived longer. They also noted that CAA by itself can be fatal, causing cerebral hemorrhages.

Other studies have found that Aβ aggregates can be transmitted by other medical procedures, such as dural grafts and perhaps even neurosurgery (Jan 2016 news; Feb 2018 news; Hervé et al., 2018). How concerned should physicians and indeed brain surgery patients be? Walker noted that the medical community improved sterilization procedures for neurosurgical tools in the 1970s, when the risks of prion contamination became widely known, and no new cases of prion disease have been reported as a result of surgeries performed since then. “The procedures appear to be effective,” he said.

Even so, Collinge believes the issue deserves more study. Ronald Melki at the French National Center for Scientific Research in Gif–sur–Yvette and Luc Bousset at the Université Paris-Saclay recently analyzed how well various cleansers removed aggregated protein from different surfaces. They found that the detergent sodium dodecyl sulfate (SDS) worked well to dislodge and break up aggregates of Aβ42, tau, and α-synuclein from glass, plastic, and steel. Other solvents, such as sodium hydroxide, the alkaline cleaning solution Hellmanex, and the detergent TFD4, performed poorly. Aggregates clung most stubbornly to aluminum surfaces, resisting cleaning with all reagents (Fenyi et al., 2018).

Mathias Jucker at the German Center for Neurodegenerative Disease in Tubingen, suggested that surgical instruments should be designated for use on either young or old patients to prevent cross-contamination. Because of the long incubation period for protein aggregation diseases, young people would be at the greatest risk from surgical tools (full comment below).

Are researchers who work with protein aggregates in danger? Walker thought this unlikely. “There’s no evidence whatsoever for transmission of Aβ through routine laboratory handling,” he told Alzforum. Nonetheless, Melki said his lab routinely uses biosafety level 2 or 3 procedures as a precaution when working with aggregated proteins. This means handling materials in a ventilated safety cabinet, wearing protective clothing, and taking extra care with contaminated sharps.—Madolyn Bowman Rogers