Turnt or Burnt: The Biochemical Mechanism Behind Margarita Burns
Most people are aware of the harmful effects of consuming alcoholic beverages, but are not aware that the preparation of certain cocktails, such as margaritas, can also have the potential for harm. Margarita burns get their name not because of the alcohol, but because of the lime in margaritas that can cause burns, blistering, rashes, and sun poisoning. Margarita burns are a type of phytophotodermatitis, meaning they occur when chemicals from phototoxic plants interact with skin cells in sunlight.
The most common phototoxic plant species are Umbelliferae and Rutaceae, which include celery, parsnips, and citrus fruits like limes and lemons. These plants contain a type of molecule referred to as furocoumarins. This subset of molecules generally are made up of three aromatic rings. Furocoumarins become active when exposed to UV light and cause cell destruction.
Furocoumarins enter skin cells when a phototoxic plant touches the skin. After entering the cell, furocoumarins reach the nucleus by passive diffusion where they are able to interact with the DNA of the cells.
The aromatic rings of the furocoumarin allow the molecule to insert itself between two adjacent pyrimidine bases (C or T) of the DNA double helix. Figure 2 illustrates how the furocoumarin molecule is able to sit above and below two base pairs in the DNA double helix, both of which contain a cytosine (C). The furocoumarin molecule sits in this molecular complex with DNA but does not cause any DNA damage. Only upon UV light does the furocoumarin become active and cause DNA destruction.
The two cytosines are able to form covalent bonds with the furocoumarin when the molecule has been excited by a photon. Figure 2 demonstrates the covalent bonds that form between the furocoumarin and the pyrimidine bases of the DNA double helix.
The covalent bonds are formed by a photochemical 2 + 2 cycloaddition reaction which occurs between a double bond of the pyrimidine base and another double bond of the furocoumarin molecule. It is possible for the cycloaddition to occur at the furan or the double bond next to the ester of the furocoumarin, as shown in figure 3.
When furocoumarin is bound to DNA, transcription and translation are prevented from occurring. Without transcription, proteins and RNA molecules that are essential for cellular function can no longer be synthesized. When there is DNA damage, the cell cycle is arrested which can trigger self-induced death, known as apoptosis. Furocoumarins have also been found to initiate other cell pathways that lead to apoptosis. When these skin cells die and become damaged by the photoactive furocoumarin, blisters, rashes, and sun poisoning can appear on the skin.
Because furocoumarins can cause apoptosis, the molecule class has been studied as a potential cancer therapy drug. Although furocoumarins are often associated with the harm of margarita burns, future research regarding the molecule’s anticancer properties may one day make furocoumarins an important remedy.
By Bella Leite
