Influenza continues to present challenges for early detection, particularly because viral transmission can occur before symptom onset. In this study, published in ACS Central Science, researchers developed a taste-based influenza screening approach that uses viral neuraminidase activity to cleave a chemically engineered sensor. The design centers on N-acetylneuraminic acid derivatives linked to thymol, a taste-active compound. The researchers modified these derivatives to ensure that only viral neuraminidase, and not bacterial neuraminidase, would cleave the α-glycosidic bond and release thymol.
Two sensor variants were synthesized: an unmethylated reference compound and a modified α-linked sensor incorporating 4,7-di-O-methyl substitutions. Only the α-linked, methylated sensor demonstrated selectivity. In buffer systems, the unmethylated sensor responded to both viral and bacterial neuraminidases, whereas the methylated α-sensor responded only in the presence of viral neuraminidase. Structural data and molecular docking showed different binding interactions for methylated sensors with bacterial and viral neuraminidases.
To assess whether neuraminidase levels in patients matched the concentrations needed for sensor activation, the researchers measured neuraminidase activity in saliva from hospitalized, influenza-positive patients across two seasons. Activity levels ranged from approximately 8.9 to 13.4 mU/mL, which corresponds to the concentrations used in laboratory assays of the α-sensor. Additional experiments showed that the α-sensor released thymol when incubated with live H1N1 virus at clinically relevant viral titers.
Cytotoxicity testing in human kidney and mouse fibroblast cell lines indicated no reduction in cell viability at concentrations up to 1.0 mM. Stability studies showed that the α-sensor remained at least 95 percent intact for four weeks under typical storage conditions. Based on known taste-detection thresholds for thymol and neuraminidase activity observed in saliva, the researchers estimated that milligram-level quantities of sensor would be needed for oral use.
The researchers showed that modifying specific hydroxyl groups on N-acetylneuraminic acid allowed control of neuraminidase selectivity and that neuraminidase levels in influenza-positive saliva were sufficient to activate the sensor.
The sensor strategy could address needs for low-cost, rapid testing at the point of care. But the authors advise that its value will first need to be assessed against patient-reported outcomes.
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