How Lipids Prevent Dry Eyes

Scientists in Japan have discovered that an enzyme responsible for the elongation of fatty acid chains is necessary for keeping the eyes moist and free from infections.

AsianScientist (Feb. 27, 2018) – In a study published in the FASEB Journal, a research group in Japan has identified an enzyme that makes long-chain lipids in tears, with implications for dry eyes and ocular infections.

One out of every ten Japanese people suffers from dry eyes. This is due to a defect in the production or composition of tears. Many might think tears are merely water, but tear film is actually composed of three basic layers: mucin, water and lipids. Lipids within tears help prevent water evaporation from the ocular surface and protect the eye against infection.

About 80 percent of dry eye disease cases are caused by abnormalities in this lipid layer. Although drugs targeting the water and mucin layers are available, no drug has been manufactured to target the lipid layer. Moreover, while scientists know that tear film lipids are secreted by the meibomian gland and are called meibum, much about meibum remains unclear.

In the present study, a team of scientists led by Dr. Akio Kihara of Hokkaido University, Japan, created mice whose Elovl1 gene, which encodes an enzyme that elongates fatty acid chains of lipids, was deleted from everywhere but the skin. Deletion of Elovl1 gene in the skin is lethal, hence the conditional deletion of this gene was essential to the study.

The team observed that young knockout mice blinked frequently and exhibited signs of dry eye disease, such as increased water evaporation from the tear film. After five months, many of the mice developed cloudy corneas. The corneal abnormalities are believed to have been caused by prolonged dry eyes, which inhibited self-repair of the damaged cornea.

The researchers also found that the knockout mice produced less very long-chain meibum, but more short-chain meibum. These results indicate Elovl1 is closely linked to the synthesis of very long-chain meibum, which appear to be crucial for preventing dry eye disease.

“Our results could help develop new drugs to treat and prevent the dry eye disease, such as agents that promote the secretion of very long-chain meibum or eye drops containing these lipids,” said Kihara.

The article can be found at: Sassa et al. (2018) Very Long-chain Tear Film Lipids Produced by Fatty Acid Elongase ELOVL1 Prevent Dry Eye Disease in Mice.


Source: Hokkaido University; Photo: Shutterstock.
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