Nordic Life Science 1
“In smell, the virus infects the supporting cells
of the sense organ, 84 and this provokes an anti-viral response in those cells as well as in the olfactory receptor neurons. This anti-viral response turns off the mRNA that encodes the proteins underlying the receptor responses to odors; hence the sense of smell is lost.” THOMAS FINGER B ut it is still unclear why taste cells do not resume operation. “In taste, the virus seems to infect the sensory cells themselves – at least the cells for sweet, bitter, and umami – and likely disrupts taste that way,” Finger says. “But that does not explain the prolonged loss of taste since the infected cells would be replaced in a matter of weeks. So maybe there is lingering inflammation that keeps the anti-viral response turned on, thereby reducing the cell's ability to make taste receptors and related proteins, such as Phospholipase C (PLC).” Some encouraging findings The recent study with which Finger was involved had some encouraging findings. Work with researchers from the Swedish University of Agricultural Sciences (SLU) and Uppsala University showed that some people with compromised taste had lower levels in their taste cells of mRNA that generate the protein PLCβ2. This protein boosts signals to receptor cells that identify sweet, bitter, and umami (savory) tastes. Taste cells for salty and sour flavors are not reliant on the protein so are usually not as affected. T Thomas Finger, Professor, University of Colorado Anschutz aste buds usually are replaced every two to four weeks, but the researchers found that in some people the cellular signals may be interrupted for a greater period. Unfortunately, since researchers still have not determined why PLC levels are low in some people, creating a treatment approach is difficult, according to Finger. The investigation collected data from 28 people in Sweden who had COVID, did not require hospitalization but still reported diminished taste and smell 12 months after contracting the virus. Eight out of the 28 people showed abnormal scores on a test measuring taste and 11 participants specifically cited losing tastes of sweet, bitter, and umami. While people reported not tasting anything, what they really were indicating is they did not perceive flavors, which are a combination of smell and taste, says Finger. The next step for the research is the further characterization of cell types and neurotransmitters in human taste buds to see which conditions in mice correspond with human taste sensations, describes Finger. For example, scientists have noted that in mice, sour and sweet cells communicate with nerves, but this process is not replicated in humans. “Things have to be wired up properly, and there’s a difference between human and mouse taste buds, and those differences may be significant,” he says. “There seem to be some biochemical differences in the different cell types. To restore normal function in any disease state, you need to know what normal is,” he says. NLS THE NOSE // SMELL AND TASTE