Making Scents of Alzheimer’s

Between animals that can detect cancer and tuberculosis (1) and humans who can smell Parkinson’s disease (2), it seems clear that – when it comes to detecting disease – there’s something in the air. Until now, it has been a challenge to detect that unique “something,” but a new study from the Monell Chemical Senses Center has reported evidence of an identifiable odor signature for Alzheimer’s disease (3). What makes these findings particularly strong is that they were demonstrated by two independent tests: both a bioassay and a chemical assay showed alterations in the urine of mice overexpressing the protein associated with Alzheimer’s disease in man.

“We believe that the mice in the bioassay are responding to a unique pattern of volatiles,” says Bruce Kimball, one of the study’s authors. “Likewise, we approached the chemometric portion of the study in the same manner – looking for patterns of up- and downregulated odorants.” It’s not that new compounds appear in the urine of Alzheimer’s mouse models; rather, the same compounds exist in mice with no disease, but because they exist in different concentrations, they emit a unique odor. “Our results suggest that the odor signal may be present well before any pathological changes occur,” adds Kimball, although he notes that this first study did not monitor the progression of the disease.

Could this lead to a simple Alzheimer’s test in humans? Perhaps one day, but right now the work is still at the proof-of-concept stage. “If an alteration is identified in the human population, the desired result would be some sort of chemical confirmation – be that by chromatographic analysis at a laboratory or perhaps even some sort of urine dipstick.” Kimball believes that the next step is to examine urinary volatiles in humans, but we’re much more variable than APP mice – meaning that a huge number of samples will be required to investigate even one disease. And Kimball doesn’t want to stop at just one. “We currently think that all inflammatory processes result in alteration of body odors, and much work is required to evaluate the specificity of such alterations,” he says. “There is much to be done!”