Sometimes bad breath is good

Who knew bad breath is applicable to stem cell biology - I sure didn't. I've got oral surgery coming up to remove my wisdom teeth (I may use this as an excuse to not post next week), so I started poking around Google for stem cell stories related to dental pulp and found this one. This recent story about the finding of a Japanese research group is attracting some attention, mostly for the "who'd have thunk it" factor.

This paper appeared in Journal of Breath Research last week and reported that stem cells isolated from tooth pulp can be persuaded into becoming liver cells in their serum-free culture by adding a low amount of hydrogen sulfide (H_sS), which is the main chemical responsible for bad breath, to the incubator atmosphere. I'm not all that blow away by the data. For starters, they should have shown the lack of hepatic cell markers at Day 0 and the gradual disappearance of stem cell markers at the later time points. I'm guessing they found the morphological changes significant enough to show a difference, but in general the molecular characterization was lacking. The functional data was a bit more convincing. It's tricky to obtain consistence function results, but the authors showed a significant difference between the normally incubated cells vs. cells in the smelly gas. Although, the amount of change reported by the authors is modest, and is generally expected from cell culture studies because cell populations are mixed and can dilute the readout. Overall, I think the authors succeed in saying H₂S-incubated cells are different from those incubated in a normal fashion. I'm not totally convinced they're liver cells.

The authors speculated that the H₂S may be acting like 2-mercaptoethanol, which is a kind of liquid sulfide that's included in some culture media recipes as an antioxidant. If so, the sulfide in the air may be dissolving into the media, and it's the reducing property of sulfide that spurs differentiation and hepatic cell commitment. That's just a speculation at this point, but oxidative stress can influence cell biology and so it's a plausible line for further questions. There's still work needed to figure out how all those parts play together from the metabolic point of view.

Image credit: ©candi candi via Flickr (http://www.flickr.com/photos/candicandicandi/6817110530/)

References:

Ishkitiev N, et al. Hydrogen sulfide increases hepatic differentiation in tooth-pulp stem cells. J Breath Res. 6(1): 017103. (2012)