The Fiery but Powerful Antioxidant

When getting my mandatory flu shot for my volunteer work at Carle Hospital in Urbana, IL, I thought of the last time I had actually received the vaccination. It turns out it had been more than 10 years. How was it possible that I was able to survive every flu season without getting significantly sick? I realized that compared to my friends and family, I eat very spicy food and lots of it. I had always heard of speculations that eating spicy food boosts your immune system but I never understood how or what molecules were involved. So after researching, I found that the spice Capsaicin in cayenne pepper has been identified as providing benefits to the immune system. The LIVESTRONG website mentions that capsaicin could function as an anti-inflammatory, analgesic, and even as a treatment for cancer. Capsaicin benefits. I was particularly intrigued by its role as an antioxidant, which is a substance that protects cells against the harmful effects of free radicals. I had heard that antioxidants were very good for you but did not know how they helped the body. I wondered how capsaicin reacts with free radicals and wanted to find out the chemical details. In addition, I wondered how getting rid of free radicals improved one’s health? Finally, I was curious how scientists measured the antioxidant capacity of a molecule and how effective was capsaicin?

The LIVESTRONG post mentioned a few other journals from where they received their information. I instead decided to take the liberty of surfing the web in hopes of answering my questions. Google was my first destination with my search being antioxidant abilities of capsaicin. Considering I usually never read science journals for pleasure, I had to go out of my comfort zone and explore the various sources I encountered. Instead of Google, I switched gears to using the University’s library resources since I would be able to obtain full access to science journals. I was able to find a couple of articles that piqued my interest.

After concluding my search, I decided to go ahead and read the one out of Biochimica et Biophysica Acta published in 2002 entitled Mechanism of potent antiperoxidative effect of capsaicin by Kentaro Kogure et al. Judging from the abstract, I decided that this article would be my primary resource in order to answer my questions. The article had many data but I decided to first analyze the first figure, which would answer my question of the effectiveness of capsaicin.

The abstract of this article indicated that Capsaicin’s inhibitory effects on lipid peroxidation was much more significant than alpha-tocopherol, a well-known antioxidant that happened to be found in vitamin E. The data was presented both from rat liver mitochondria (A) as well as egg yolk phosphatidylcholine liposomes (B). TBARS (thiobarbituric acid-reactive substances) are formed as a byproduct of lipid peroxidation so a larger number indicates more peroxidation took place. From the methods and materials section, I learned that the Rat liver mitochondria (RLM) were isolated from male Wistar rats (which I researched and found out to be albino, common in scientific experimentation). The liposomes were made by drying the chloroform solution of egg yolk PC under nitrogen gas. The amount of TBARS was measured at an absorbance of 532nm. From the results, it clearly showed that the amount of capsaicin required to inhibit peroxidation was significantly less than the known antioxidant. While peroxidation abilities was not my specific goal, it was still important to the big picture since it helps protect against the generation of harmful lipid oxidation products. Since it was compared against an antioxidant, the date actually proved that it had better antioxidant capabilities.

The first article went on to make conclusions of how capsaicin becomes trapped in the liposomal membranes and proceeds to scavenge 1,1V-diphenyl-2-picrylhydrazyl (DPPH). DPPH is a free radical molecule commonly used to test radical scavenging activity. In addition, the authors concluded that it was at carbon atom 7 – a benzylic position - where the radical activity took place on capsaicin. One interesting note mentioned in the discussion is that while alpha-tocopherol is an effective antiperoxidant under physiological conditions, capsaicin could be an auxiliary antioxidant mainly coming from foods since its potency is larger. This definitely got me thinking that while alpha-tocopherol came from an essential vitamin (E), capsaicin primarily came from chili peppers.

Since this primary article had been published in 2002, I was curious to see if any more progress had been made since then. For this, I found another interesting article in the Journal of Physical Chemistry entitled Capsaicin, a Tasty Free Radical Scavenger: Mechanism of Action and Kinetics by Annia Galano and Ana Martinez in 2011. It turns out that the sites vary based on the free radical as well as the environment. If capsaicin were reacting with an OOH radical, site 1a (phenolic OH) was more preferred contributing to more than 90% of the overall reactivity of the molecule. When reacting with an OOCH3 radical, the main site was also 1a in a polar aqueous environment, whereas site 16 in a nonpolar environment. An OCH3 radical was found to be less selective as to where the reaction takes place. In this case, the majority occurred at site 13 and site 16 of the capsaicin molecule. This finding was definitely expanded upon from the data in the 2002 article because it turns out there are many other sites that have the ability as the primary areas other than just site 7. This article actually referenced my primary source, which discussed how the UV-Vis Spectra of Capsaicin produced a distinct band at 280 nm at physiological pH and shifted with an increase in pH, representing the phenolic OH group. In addition to this, Galano and her group also noted less reactive regions around 360-380 nm and 600 nm, with less reactive alkoxyl and peroxyl radicals.

I however, wanted to learn more about the specific mechanism in regards to the chemistry. I was able to find this in my second article, which broke down the mechanism into three possibilities: hydrogen transfer (HT), single electron transfer (SET), and radical adduct formation (RAF). Table 1 shows the free energies of reaction, calculated for three different reaction types along with the various sites of reactivity for each of the three types of free radicals tested. PE signifies pentyl ethanoate, a nonpolar solution, while W signifies the polar environment of water. After calculating the Gibbs Free Energy of each reaction with various radical molecules, it was found that hydrogen transfer was the primary mode of reaction of capsaicin with free radical species and that it most commonly took place with and OCH3 radical.  The mechanism for a hydrogen transfer reaction is shown below. 

While SET reactions did not necessarily contribute to the overall reactivity of Capsaicin towards the three free radicals explored, it was speculated that its importance could be with hydroxyl and chloride radicals. The entire basis of the second article’s study was to find the most viable mechanism, which molecule stimulated the greatest scavenging activity, and then where the most common site on the capsaicin molecule this took place.

Now that I had figured out the answers to two of my primary questions, I wanted to tie it all together with my one final question. So what? What is the big deal that capsaicin is such a good antioxidant. How did getting rid of free radicals improve someone’s health overall other than preventing aging diseases? Accordingly, I set out to search and read about the harmful effects of reactive oxygen species (ROS). While it is normal to have a certain amount of ROS, an excess can cause oxidative damage to important biomolecules leading to faster aging as well as diseases such as atherosclerosis and cancer. Specifically, oxidative damage to membranes (where many fatty acids reside) leads to increased membrane fluidity and possibly inactivation of receptors. Oxygen-damaged lipids in cellular and organelle membranes will damage important molecular components in cells such as DNA once the cell membrane’s integrity has become compromised as well (Luqman 2006, Protection of Lipid Peroxidation and Carbonyl Formation in Proteins by Capsaicin in Human Erythrocytes Subjected to Oxidative Stress). Preventing ROS from damaging lipids clearly have both short and long-term benefits.

I now have a better understanding of how the body protects itself against harmful free radicals. I found out the numerous health benefits of capsaicin and it has further encouraged me to continue to eat spicy foods, of course still in moderation, to prevent ulcers. Antioxidants now have a larger meaning in my life now that I know how they help the body and prevent diseases. Writing this blog has not only informed me about a new aspect of organic chemistry, but I was able to connect this to my life, and I now plan on eating even healthier with plenty of spices and antioxidants in fruits and vegetables as well.