Scientist - News - 19-11-2009:

Gut microbiota influences lens and retina
Beintema, Nienke

Finnish researchers have discovered that gut microbiota affects the lipid composition of the lens and retina in mouse eyes. This opens up new possibilities for treatment of eye diseases and for early diagnosis of various conditions.

The gut microbiota is known to affect various metabolic processes in both animals and humans. Many effects on the immune system are now known, as well as on digestive processes and various other health parameters. Recent studies have also shown that the gut microbiota affects the host lipid metabolism. This influence is not always beneficial – obesity, for instance, has been associated with an altered gut microbiota and mice without gut microbiota (so-called germ-free mice) seem to be protected against obesity.
A team of Finnish researchers has investigated whether the gut microbiota also affects the lipid composition of the eye. This organ has a relatively high lipid content, but does not metabolize lipids itself, in contrast with metabolically active organs such as the liver. In addition, the eye's lipid composition is not affected by dietary lipids, but merely by metabolic processes in the body. For that reason, the researchers argue that the eye can become a 'reporter' of metabolic processes. They published their results in the November issue of the journal Experimental Eye Research.

New area of investigation
The Fins made a detailed lipid profile of the eyes of germ-free mice and of conventionally raised mice. Both in the lens and in the retina, they found significant differences between the two groups: one class of lipids, called phosphatidylcholines, were lower in the lenses of conventionally raised mice, and another class, called phosphatidylethanolamine plasmalogens, were elevated in their retinas. The researchers do not speculate about how this may affect the eyes' health; however, they do note that the lower level of lens phosphatidylcholines in the presence of gut microbiota suggests that the conventionally raised mice experience more oxidative stress - a negative side-effect of normal metabolism - than germ-free mice. Consistent with this, their lifespan is also shorter.
This is another sign, next to the recent findings on obesity, that gut microbiota might actually have a negative impact on health parameters. "Our findings may open a new area of investigation how modulation of gut microbiota, for instance via a probiotic intervention, affects eye health," write the authors. "Comparative lipid analysis of the lens and surrounding tissues could also be a novel approach to identifying the early onset of various conditions or diseases."

More information:
Article in Experimental Eye Research