Introduction

For Britons in 1997, hamburger suddenly became a source of national anxiety.¹ Mad cow disease, formally known as bovine spongiform encephalopathy, had been discovered in the hamburgers at McDonald’s and at least 21 people had died from its human version, variant-Jakob-Creutzfeldt disease (vJCD).² News stations reported daily on confirmed cases in herds thought to be immune, prion-positive meat being sold at restaurants, and on the grave, inexorable progress of the incurable disease.³

More than 20 years removed from this episode, “mad-cow mania” has long since passed but the threat of prion disease remains. Prions and viruses are the only non living infectious agents, but, unlike viruses, prions contain no genetic material with which to replicate.⁴ Instead, prions are incorrectly arranged versions of proteins healthy animals already have in their bodies.⁴ Healthy prion proteins provide support to other cells.⁵ When an infectious prion contacts a healthy prion, it induces a change in the shape of the healthy protein that leads to dangerous accumulations of mishapen proteins.⁵ These accumulations, called plaques, lead to the damage and death of neurons in the brain.⁵ 

While mad cow and vJCD are the best-known prion diseases, there exist many others targeting several species.² All known prion diseases target functional, as opposed to structural, brain tissue and thus share several main symptoms: rapid-onset dementia, muscle stiffness, difficulty with speech and movement, hallucinations, and idiopathic exhaustion.² Currently there are no known cures for prion diseases.⁶ Patients receive care to alleviate symptoms until the disease runs its course and death occurs, typically within a year.² Though prion disease is rare and often hereditary, there are infectious and acquired forms of the disease making anyone with a brain a potential victim.² New research from Chao Hu and a team from Guangdong Ocean University’s College of Agriculture demonstrated that resveratrol is capable of both removing prions from infected tissue and restoring key growth factors crucial to neuron health. 

Hu and his team of neuroscientists had conducted previous research indicating the ability of a natural polyphenol, resveratrol, to remove prions from brain tissue infected with scrapie, the form of BSE observed in sheep.^6,7 A separate project of theirs tracked the levels of different proteins and transcription factors expressed in brain tissue over the course of scrapie infection.⁸ They discovered that levels of cerebral neuron growth factor (NGF) decreased sharply during scrapie infection.⁸ NGF belongs to a family of proteins known as neurotrophins that encourage the growth and maintenance of nerves.⁶In their paper published in Neuroscience Research, Hu and his team attempt to quantify the effect, if any, resveratrol had on the levels of NGF in scrapie infected tissue.⁶ 

Methods

Hu et al. took brain tissue samples from three cell lines: SMB-S15, taken from a mouse  infected with scrapie; SMB-PS, from a mouse confirmed to have never been ill with a prion disease, and SMB-RES, infected SMB-S15 tissue that was then treated for 7 days  with a 10-nanomolar solution of resveratrol.⁶ Cell debris from each of these lines were  injected into the brains of 3 groups of 10 mice.⁶ The mice were monitored for disease until death or euthanasia 300 days after injection.⁶ Tissue samples were then taken from the 30 mice and fixed for further testing.⁶ First, the team wanted to determine the  levels of beneficial NGF in infected, healthy, and treated tissue. This was facilitated via western blotting, a technique that identifies amounts of specific substances in a mixture first by their mass and then by recognition of specially engineered antibodies.⁹ The antibodies only bind to the protein of interest, NGF, in this case, and researchers can then calculate the amount of protein present using a color or fluorescent signal.⁹ To further support their observations the team repeated the western blotting procedure for  transcription factors, proteins that control the rate at which other proteins are produced, associated with increased levels of NGF.⁶ Western blotting worked well for giving the researchers raw data about the amount of NGF and transcription factors, but they also wanted to know where in the brain tissue samples the proteins were being expressed.⁶ This involved washing the whole tissue samples in one antibody solution to detect the protein of interest, and a second, fluorescent antibody that bound to the first.⁶ After this process, the researchers could visualize where on the intact samples the proteins were expressed.⁶ 

Results

Though previously infected with scrapie, the resveratrol treated brain tissue performed similarly to the tissue that had never been infected with prions.⁶ While alive, the mice inoculated with SMB-PS and SMB-RES never showed symptoms of prion disease and their brain tissue was free of any visual sign of neurodegeneration.⁶ Both exhibited much higher levels of NGF than the scrapie infected tissue, and the treated tissue contained levels of NGF promoting transcription factors that were equivalent or comprable to those in the healthy tissue line.⁶ Interestingly, the researchers found the expression of both NGF and one of its transcription factors, CaMKK2, restricted to sites on neurons and were not expressed on other cells such as astrocytes and microglia.⁶ The colocalization of NGF and CaMKK2 bolster the researcher’s conjectures that NGF is primarily associated with the support of neurons, not brain cells in general, and that the decrease in NGF observed in scrapie infection is caused by the reduction of transcription factors upstream.⁶ Thus, neurodegeneration characteristic of prion diseases may be caused not only by mechanical damage from plaques, but also from a  dearth of supportive growth factor leading to neuron death.⁶ 

Conclusion

Since a prion diagnosis today is essentially a death sentence, the discovery that resveratrol removes prions from infected tissue, restores nutritive growth factors, and recovers a healthy brain microenvironment is quite an advancement towards the treatment of prion disease. Even more excitingly, the disease progression of other neurodegenerative disorders like Alzheimer’s disease, amyotrophic lateral sclerosis (ALS) and others includes the depletion of NGF and upstream transcription factors like CaMKK2.⁶ This implies that a treatment for prion disease may also prove beneficial to those with different neurodegenerative disorders. Finally, such treatments may even be effective in other species. The structure and function of NGF is similar across many mammalian species and thus those prion disorders affecting non-human animals may also respond to a resveratrol derived treatment.¹⁰ Hunters and hamburger connoisseurs worldwide would rejoice at the eradication of chronic wasting disease and mad cow disease. However exciting the implications, it must be remembered that this experiment was performed in vitro, or outside of the animal. To establish resveratrol as a viable treatment, its efficacy in removing prions from an intact, living animal would need to be ascertained. Nonetheless, this study reminds us that revolutionary advances in medicine arrive small bits at a time, and someday the eradication of prion disease will be within grasp. 

[+] References

[+] Other Work By Rachel Buzzelle