Saliva 'may speed healing' but 'kissing it better' probably won't
"Kissing it better really works: Saliva found to have properties that help speed up the healing process," reports the Mail Online. Researchers in Chile investigated how human saliva may help wounds to heal more efficiently.
They used lab-grown skin cells and fertilised chicken eggs to see how a protein found in saliva, histatin-1, affects the way cells grow, spread and create new blood vessels. They found it encouraged cells to spread and move in a way that promoted the formation of blood vessels (a process called angiogenesis), which aids wound healing in skin.
The experiments help us to understand why wounds in the mouth heal faster, but we don't know that saliva would encourage wound healing on other parts of the body. While parents "kissing it better" might help children when they hurt themselves (possibly due to a placebo effect), that doesn't mean their saliva is helping a grazed knee to heal quicker. The quantity of saliva that would be required is neither a practical nor hygienic solution, but the research could pave the way for new aids to wound healing.
Where did the story come from?
The study was carried out by researchers from the Universidad de Chile and Pontificia Universidad Católica de Chile, and was funded by five Chilean research foundations. The peer-reviewed study was published in The FASEB Journal, which is the journal of the Foundation of American Societies for Experimental Biology.
Aside from the eye-catching but inaccurate headline, the Mail Online article gives a reasonable overview of the research. It includes speculation from the researchers that their work could lead to the development of better treatments to speed up the healing of wounds.
What kind of research was this?
This was a series of laboratory-based experiments using lab-grown skin cells and fertilised chicken eggs to look at biochemical reactions to the introduction of a specific protein found in saliva, histatin-1. While this type of research is important to better understand wound healing, it's a far cry from using naturally produced saliva on human skin wounds.
What did the research involve?
Researchers carried out a series of experiments using a chemically synthesised form of histatin-1.
First, they tested whether this form was biologically active by mixing it with cells infected with candida yeast (a type of fungus that can cause wound infections) to see if histatin-1 slowed the growth of the yeast.
Next, they tested the histatin-1 on skin cells that had been grown and then wounded to see how quickly the wound healed. Further experiments on lab-grown (cultured) skin cells included tests to see how histatin-1 affected the movement of cells, and their ability to spread, grow and stick to a protein-coated plate.
A further test was carried out on fertilised chicken eggs. The membrane around the embryo (called the chorioallantoic membrane) makes it easy to see the growth of new blood vessels. The researchers made a break in the membranes and introduced histatin-1 to some of them to see whether it affected the growth of new blood vessels.
Finally, some of the experiments were repeated with natural saliva from donors, and again with saliva that had the histatin-1 reduced or removed.
What were the basic results?
Experiments on cultured skin cells found:
- Histatin-1 slowed the growth of the yeast Candida albicans, showing that the protein was biologically active.
- Histatin-1 increased the area of the wound that had healed, depending on cell type. For the most common outer-skin cell (keratinocytes), it increased the area from 14.9% healed to 25.4%, and from 31.4% to 46.1% for cells that line blood vessels.
- More cells treated with histatin-1 moved to the area of the damaged skin cells, more spread around the damaged area and more adhered to protein-coated glass plates.
- Histatin-1 did not encourage the growth of more cells – it just affected the way in which they behaved.
Experiments using the chicken-egg membrane found that histatin-1 encouraged the formation of new blood vessels, with the effect comparable to other substances known to do this.
One further experiment found that using human saliva from donors encouraged cell movement, while saliva that had histatin-1 removed did not.
How did the researchers interpret the results?
The researchers said their study shows "histatin-1 is a proangiogenic factor [something that encourages the formation of new blood vessels] that promotes endothelial cell adhesion and spreading" and it will "help [in] understanding the mechanisms underlying the novel roles of histatin-1".
They said histatin-1 promotes cell movement as a "crucial step" in the formation of new blood vessels and that this has "important consequences for future research".
This complex study helps us understand the biological mechanisms behind wound healing in the mouth and the role of saliva in promoting wound healing. As well as keeping the mouth moist and reducing levels of harmful bacteria, saliva contains a protein that encourages the movement of cells in ways that help wounds to heal.
It's possible this might lead to the development of new wound-healing treatments in future; however, this study didn't look at future uses – it simply helps us better understand how the body heals itself.
Before any new treatment could be developed, further studies in cell lines and in animals, followed by extensive studies in humans, would be needed to ensure that any treatment was safe and effective. That's a long way off.
Next time you bite your tongue or the inside of your cheek, just imagine the proteins in your saliva working away to help to heal the wound as quickly as possible.
But it's best not to imagine any more than that. While kissing your child's grazed knee may have a powerful placebo effect, we'd recommend reaching for some antiseptic cream and a plaster too.
Links To The Headlines
Links To Science
Torres P, Díaz J, Acre M, et al. The salivary peptide histatin-1 promotes endothelial cell adhesion, migration, and angiogenesis. The FASEB Journal. Published online July 27 2017