Summary: New research indicates that a toxic build-up of urea in the brain can cause damage that may lead to dementia, with potential implications for earlier diagnosis and new treatment strategies.
Source: University of Manchester
International research team identifies elevated brain urea as a likely major contributor to age-related dementia
An international team of scientists, led in Manchester by Professor Garth Cooper, reports strong evidence that accumulation of urea in the brain to toxic levels can cause neuronal damage and contribute to dementia. This finding links metabolic dysfunction directly to neurodegeneration and opens new avenues for diagnosis and potential intervention.
Professor Cooper, from The University of Manchester’s Division of Cardiovascular Sciences, and collaborators from institutions in New Zealand, Australia and the United States examined human brain tissue and a transgenic sheep model of Huntington’s disease (HD). Their results, published in the Proceedings of the National Academy of Sciences, show that Huntington’s disease is associated with markedly increased brain urea levels and related metabolic changes.
The team’s earlier work had already found increased brain urea in Alzheimer’s disease. Together, those findings suggest that disrupted urea metabolism may be a common feature across several major age-related dementias. Notably, in the Huntington’s study the rise in brain urea occurred before clear clinical dementia, suggesting a potential window for earlier diagnosis and treatment.
Urea and its precursor ammonia are breakdown products of protein metabolism. Under normal circumstances the kidneys and liver help remove these compounds from the body. If urea and ammonia accumulate—whether from systemic metabolic defects or impaired clearance—they can be toxic to neural tissue and impair brain function.
Professor Cooper said: “This study provides a crucial piece of evidence linking high brain urea to dementia. Huntington’s and Alzheimer’s sit at different points on the dementia spectrum, so finding elevated urea in both disorders increases the likelihood that altered urea metabolism is relevant across multiple forms of age-related dementia.”
He added that further research is needed to identify the source of elevated urea in Huntington’s disease, including whether ammonia or a broader systemic metabolic defect contributes to the rise. Understanding these mechanisms could reshape our view of how dementia begins at the molecular level and which therapies might be effective.
The researchers used donated human brain tissue and a prodromal transgenic sheep model. Manchester researchers applied gas chromatography–mass spectrometry to obtain sensitive measurements of brain urea. According to Professor Cooper, urea must rise roughly fourfold or more above normal brain levels to reach toxicity and cause damage.
Huntington’s disease is caused by a genetic expansion in the Huntingtin gene that produces an abnormal protein. While the genetic cause has long been known, the downstream biochemical events that drive neuronal dysfunction and cell loss have been less clear. This study links altered urea transport and metabolism to those early pathogenic events.
The HD sheep model used in the study carries a human Huntingtin transgene and represents a prodromal stage of the disease with minimal neuropathology and no detectable neuronal loss. In these animals the researchers found increased expression of the urea transporter SLC14A1 and other osmotic regulators in the striatum, together with elevated urea levels in both striatum and cerebellum. The same pattern of increased urea was observed in postmortem human HD brains, including cases with low-level neuropathology.
Elevated brain urea likely reflects altered protein catabolism and metabolic stress, possibly with protein breakdown providing an alternative energy source in the context of broader metabolic defects. Dysregulation of the urea cycle and consequent increases in ammonia and urea are known to impair neurological function, supporting the idea that aberrant urea metabolism could be a primary biochemical disruption triggering neuropathogenesis in HD and potentially other dementias.
Professor Cooper noted that some existing treatments used for systemic disorders that alter urea and ammonia levels might be repurposed or adapted for brain metabolic states. For example, lactulose is used in other contexts to reduce ammonia absorption in the gut. While translating such approaches to the brain remains speculative at this stage, the new findings raise the possibility that metabolic therapies could slow progression or, in the long term, support tissue recovery.
The authors thank families who donated brain tissue to enable this research, including contributions to the Douglas Human Brain Bank at the Centre for Brain Research, New Zealand. This work was supported by the CHDI Foundation (A‑8247) and Brain Research New Zealand.
Source: Mike Addelman, University of Manchester. Publisher: NeuroscienceNews (organized overview of the research). Image: adapted from University of Manchester materials.
Brain urea increase is an early Huntington’s disease pathogenic event observed in a prodromal transgenic sheep model and HD cases
Huntington’s disease (HD) is a neurodegenerative disorder marked by progressive loss of striatal neurons and midlife onset of motor, cognitive and psychiatric symptoms. HD is caused by a CAG repeat expansion in the Huntingtin (HTT) gene, producing an elongated polyglutamine tract in the huntingtin protein, but downstream mechanisms that lead to cellular dysfunction and death remain incompletely understood. To characterize early molecular events, the researchers performed RNA sequencing and metabolite analysis on striatal tissue from 5‑year‑old OVT73 transgenic sheep that express human mutant HTT. These prodromal animals show minimal pathology and no neuronal loss. The study found increased expression of the urea transporter SLC14A1 and elevated urea levels in the striatum and cerebellum of OVT73 sheep, consistent with previously reported increases in postmortem human HD brain. Analysis of a larger cohort of HD cases, including low‑grade neuropathology, confirmed elevated brain urea. The findings point to increased protein catabolism and disrupted urea cycle metabolism as early biochemical events in HD pathogenesis, implicating aberrant urea metabolism as a potential initiating factor in neurodegeneration.
Reference: Handley RR et al. “Brain urea increase is an early Huntington’s disease pathogenic event observed in a prodromal transgenic sheep model and HD cases.” Proceedings of the National Academy of Sciences. Published online December 11, 2017. DOI: 10.1073/pnas.1711243115
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