illustration: Kei Mogari

Mosquito saliva activates the pain-sensitive TRP channel

You hardly feel painful when bitten by a mosquito. Rather, you feel itchy and notice that you have been bitten. Why you do not feel painful? It is said because the mosquito needle is very thin. A mosquito bite is called “painless puncture,” which inspired us to develop ultra-thin injection needles.

Recently, a new study was published on “mosquito saliva” which is also associated with painless puncture. The study was conducted by a team consisting of National Institute for physiological Sciences, Kansai University, and University of Toyama.^*1 The secret of painless puncture lies in the mosquito saliva and the TRP channel of our cell sensors.

“Mosquito saliva contains a compound that inhibits the pain-sensitive TRP channel and makes us hardly feel painful when bitten by a mosquito,” said Professor Makoto Tominaga at the National Institute for Physiological Sciences.

A mosquito bites us while injecting a lot of saliva……

Professor Tominaga, a Japanese leading researcher of the TRP channel, was requested by and started joint research four years ago with Professor Seiji Aoyagi, Faculty of Engineering Science, Kansai University, who had studied the mosquito needle for many years. A mosquito injects a lot of saliva when biting a human being or animal. The researchers focused on the “mosquito saliva,” wondering about its secret of “painless puncture.”

We feel pain when the TRP channel of cell sensors are activated to signal to the brain. TRPV1, which detects capsaicin, a pungent component of chilis, and heat over 43℃ as pain and TRPA1, which detects the strong, sharp smell or taste of wasabi when we eat it are both pain-sensitive TRP channels. Examination of the connection between the compounds of mosquito saliva and these two TRP channels “revealed that the mosquito saliva inhibits activation of these TRP channels” (Professor Tominaga).

Sialorphin, or the key compound, may lead to development of new pain medicine

Further examination of the saliva compounds identified a protein called “sialorphin” which inhibits both TRPV1 and TRPA1. “Not only mosquito but mouse saliva inhibited TRPV1 and TRPA1. This means that sialorphin in saliva inhibits activation of pain sensors and relieves pain. “As human beings do, animals lick the wound. It may be their natural instinct to relieve pain,” said Professor Tominaga.

According to Professor Tominaga, “Analyzing the saliva compounds of different animals may lead to development of safe and effective pain medicines.”

We may be able to develop pain-preventive compress or spray containing compounds derived from mosquito, mouse or human saliva in the near future. The TRP channel of cell sensors will continue to help us solve various “mysteries” and identify useful compounds for product development.

We do not feel the pain of a mosquito bite, just because its saliva compounds prevent us from noticing it. Now, we had better find a way to escape from the mosquito’s “secret operation of blood sucking.”