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For the first time, scientists have used a new imaging technique to painlessly and accurately measure the loss of the sense of smell, known as anosmia. The probe targets the olfactory nerve, offering the potential to eliminate the need for biopsies used to diagnose some cases of anosmia and help develop therapeutic interventions.
Is loss of smell common?
Research suggests that about 13.3 million adults in the United States suffer from a wide range of smell disorders, and that 3.4 million people have severe impairment or complete loss of their sense of smell. These numbers were drawn from studies conducted before the coronavirus pandemic, and thus greatly underestimate the number of people who currently suffer from smell disorders.
“Despite the fundamental importance of smell to quality of life and the high prevalence of smell loss, there are currently no objective, user-independent methods for assessing smell, either clinically or in animals or humans in research,” said Doreen Adelby, MD, assistant professor in the Department of Otolaryngology-Head and Neck Surgery at the Medical University of South Carolina in Charleston, South Carolina. “We sought to explore a new method for diagnosing smell loss using a specific fluorescent imaging agent, called Tsp1a-IR800P.”
Some chemicals have the ability to emit visible light after absorbing radiation that is not normally visible, such as ultraviolet light, a process known as fluorescence.
Olfaction and voltage-gated sodium channels
Voltage-dependent sodium channels are a type of small membrane proteins that are widely distributed on the membranes of excitable cells such as neurons, and are primarily responsible for the transport of sodium across the membrane. Voltage-dependent sodium channels are the most important ion channels for neurons to generate excitation and carry out normal physiological functions. To date, 10 subtypes of voltage-dependent sodium channels have been successfully identified in mammals, and 10 of them have been discovered so far, and they have been named with serial numbers from 1.1 to 1.9, in addition to channel number 10.
The fluorescent imaging agent used in the study targets voltage-dependent sodium channels 1.7 (Nav1.7), which play a critical role in olfaction by helping to transmit signals to the olfactory bulb. To determine the expression of voltage-dependent sodium channels 1.7, the researchers injected and imaged mice with the fluorescent agent. The experiment was conducted in mice with a normal sense of smell and in mice that had been chemically induced to lose smell. Additional imaging studies were also performed on olfactory epithelial tissue from non-human primates, the olfactory epithelium of hamsters infected with the novel coronavirus, and the cadavers of humans who had previously been diagnosed with the virus and died from it.
If you lose your sense of smell, the material will not light up.
The results of the study, published in Journal of Nuclear Medicine Last July 3, the voltage-dependent sodium channel 1.7 was highly expressed in people with a normal sense of smell, while in people with anosmia, the expression of voltage-dependent sodium channel 1.7 was significantly reduced, as shown by the fluorescence signal. It was also observed that the decrease in signal intensity was proportional to the degree of damage, which means that low fluorescence signals may indicate anosmia, and high signals may indicate a response to treatment and restoration of the sense of smell.
The study's authors noted, according to the website, Youre AlertThis fluorescent agent can be used in the doctor's office using an endoscope to diagnose smell disorders, and can also be immediately applied in preclinical studies on animal models (where objective, non-invasive tools are lacking) to evaluate the effectiveness of pharmacological interventions that restore the sense of smell, thus helping to develop new treatments.
“Early detection of olfactory disorders could lead to early interventions that may treat or slow the progression of the disease, improving patients’ quality of life,” added Naga Vara Kishore Pillarsetti, MD, professor in the Department of Radiology at Memorial Sloan Kettering Cancer Center in New York. “This innovation could lead to the development of similar imaging agents for other sensory and neurological disorders, expanding the scope of molecular imaging.”
