DMS-Woah?!: From Oxidant to Analgesic?
Edit: Props to Pat Knerr for forwarding along the SI article.
Every chemistry teacher has moments when students ask…odd questions. I had one such moment last week, when a student hung around after class to ask me what I knew about DMSO (yes organickers, that DMSO). A friend had advised the student to use DMSO on a running-related injury. Organic chemists know DMSO as the world’s most annoying NMR solvent and an oxidant…was there any truth to these claims of pain relief? After lowering the figurative raised eyebrow, I decided to investigate.
DMSO is perhaps the world’s most famous sulfoxide, and it sits on the oxidation ladder between the abhorrent dimethyl sulfide (Me2S) and dimethyl sulfone (Me2SO2). The latter has an interesting medical history of its own, as we’ll see shortly. DMSO may be used as a polar solvent in organic reactions, but it also finds application in the Swern oxidation and other alkoxysulfonium-based oxidations—organickers, check out the Pfitzner-Moffatt oxidation too. All those applications, of course, have nothing to do with the medicinal effects of DMSO. Could a choice reagent for oxidations also have anti-inflammatory and analgesic effects?
Let’s start with Exhibit A, a 1981 report from Sports Illustrated describing the use of DMSO by athletes for pain relief. Here’s a quote from a winner of the New York Marathon:
“I used to go the usual route when I got a strain or a sprain,” he said, “ice, ultrasound, acupuncture, whirlpool, massage, heat. But I’ve been using DMSO for about three years now, and it’s the answer. A strain like this used to keep me from training for four or five days, but with DMSO I can run full strength again in 24 to 48 hours. That’s important when you’re peaking for a race.”
Tommy LaSorda used DMSO to relieve arthritis pain, but Lou Piniella (then still a player) called it “nothing special.” Midwesterners, are you listening yet?! The article goes on to list contradictory opinions of both players and physicians.
DMSO is quite the polar molecule, thanks to its S–O bond. It hardly has a “complex molecular structure,” despite SI’s description—replace the carbon in acetone with sulfur, and voilà! Because DMSO is so polar, it has the ability to dissolve water and all kinds of other polar molecules at sites of inflammation. DMSO rapidly penetrates the skin and may carry all kinds of polar compounds with it. As it zips through the skin and the bloodstream, DMSO whisks away water, making healing easier (or so the story goes). Users report the taste of oysters in their mouths mere seconds after topical application of DMSO, due to the production of foul-smelling dimethyl sulfide in the lungs.
Although this mechanism of action is purely physical (no chemical change to be found), DMSO may have some chemical benefits in humans as well. Since it can be oxidized, DMSO has the potential to scavenge for reactive oxygen species (ROS) and protect against “oxidative stress”—in other words, it may act as an antioxidant. The compound has also been shown to trap free radical species. DMSO’s great permeability is associated with some dangers, too, as it can easily carry highly toxic compounds into the bloodstream.
The Protein Data Bank includes a useful summary page on DMSO. The compound has been crystallized in the active site of (bacterial) DMSO reductase, a metal-dependent enzyme that converts DMSO to dimethyl sulfide. Similar studies of DMSO’s interactions with human enzymes are non-existent, however. The current body of work on DMSO makes it clear that its mechanism of action in the body is far from well understood!
One last word on dimethyl sulfone, (CH3)2SO2 (popularly known as methylsulfonylmethane, or “MSM”). Oxidation of DMSO in the body produces this metabolite. Interestingly, dimethyl sulfone readily crosses the blood-brain barrier. However, unlike everyone’s favorite barrier crosser ethanol, short exposure to dimethyl sulfone appears to have no negative physiological effects. MSM has been used in combination with drugs such as glucosamine that treat arthritis and joint pain. The compound can act as an analgesic and anti-inflammatory itself (probably by the exact same mechanism as DMSO).
In conclusion, I wouldn’t bathe in DMSO. However, this compound isn’t as toxic as its structure and name might lead the more chemophobic to believe. Its mechanism of action appears to involve a simple physical effect. That said, the verdict is still out on DMSO’s chemical effects, and its permeability and knack for carrying other molecules around with it imply that it should be used only on clean skin in moderate amounts. Finally, IANAD (I am not a doctor)!
References & Further Reading
A Miracle! Or Is It A Mirage? – Sports Illustrated, April 20, 1981
BMB Reports 2010, 43, 622. (doi: 10.5483/BMBRep.2010.43.9.622)
Histochem. Cell Biol. 2000, 113, 341. (doi: 10.1007/s004180000151)
NMR Biomed. 2005, 18, 331. (doi: 10.1002/nbm.966)
Dimethyl sulfoxide on the Human Metabolome Database
Dimethyl sulfoxide on Wikipedia
Dimethyl sulfoxide on the Protein Data Bank
Dimethyl sulfone summary page