Nutrition for the eye: different susceptibility of the retina and the lacrimal gland to dietary omega-6 and omega-3 polyunsaturated fatty acid incorporation

The purpose of this study was to compare the susceptibility of the retina and the exorbital lacrimal gland to dietary supplies of long-chain omega-3 (omega3) and omega-6 (omega6) polyunsaturated fatty acids (LC-PUFAs). Male Wistar rats were fed a 5% lipid diet containing: (1) 10% eicosapentaenoic acid (EPA) and 7% docosahexaenoic acid (DHA), or (2) 10% gamma-linolenic acid (GLA), or (3) 10% EPA, 7% DHA and 10% GLA or (4) a balanced diet deprived of EPA, DHA and GLA for 3 months. Lipids were extracted from plasma phospholipids, retina and exorbital lacrimal gland, and fatty acid composition was determined by gas chromatography. Dietary supplementation with EPA and DHA increased omega3 PUFA levels in plasma phospholipids as well as in the retina and the exorbital lacrimal gland. By contrast, GLA supplementation favored omega6 PUFA incorporation, and particularly the incorporation of the end-chain omega6 product, docosapentaenoic acid (DPA), into all tissues. Supplementation with EPA, DHA and GLA increased the levels of DHA, EPA and dihomo-GLA (dGLA), whereas arachidonic acid (AA) was unchanged and DPA decreased in the retina and the lacrimal gland. The ability of both tissues to incorporate PUFAs from blood was evaluated. The results showed that the retina was more selective than the lacrimal gland for EPA. In spite of the different susceptibility of the retina and the lacrimal gland to dietary PUFAs, these results suggest that the concomitant use of dietary omega3 and omega6 PUFAs may be useful in modulating inflammation in both tissues.

A dietary combination of omega-3 and omega-6 polyunsaturated fatty acids is more efficient than single supplementations in the prevention of retinal damage induced by elevation of intraocular pressure in rats

BACKGROUND

To evaluate the effect of a dietary combination of omega-3 and omega-6 polyunsaturated fatty acids (PUFAs) compared to single PUFA supplementations on the outcome of a substantial elevation of intraocular pressure (IOP) in rats.

METHODS

Sprague Dawley rats were fed for 6 months with either a control diet, a diet enriched with omega-3 PUFAs (eicosapentaenoic acid, EPA, and docosahexaenoic acid, DHA), a diet enriched with omega-6 PUFAs (gamma-linolenic acid, GLA) or a diet enriched with both omega-3 and omega-6 PUFAs (EPA + DHA and GLA). After 3 months of feeding, elevation of IOP was induced by photocoagulation of the episcleral veins, limbus and trabecular meshwork using a 532-nm laser. IOP and scotopic electroretinograms (ERGs) were monitored after the induction of IOP elevation until the end of the nutritional supplementation. Retinal morphometry and GFAP immunohistochemistry were performed 3 months after laser photocoagulation. Retinal ganglion cells (RGCs) were quantified using retrograde labelling.

RESULTS

A significant rise in IOP was observed in the laser-treated eyes. PUFA supplementation did not influence the time course of IOP in the laser-treated eyes. Three months after laser photocoagulation, the activation of glial cells observed in the laser-treated eyes was significantly lower in animals fed with the EPA + DHA + GLA diet when compared to those fed the control diet, while single supplementations with either EPA + DHA or GLA were not effective. The same protective effect of the EPA + DHA + GLA combination was observed on retinal structures in the laser-treated eyes. However, PUFA supplementation did not influence either ERG b-wave amplitude or the RGC loss in the laser-treated eyes.

CONCLUSIONS

This study demonstrates that a 6-month supplementation with a combination of omega-3 and omega-6 PUFAs is more effective than single supplementations, since the EPA + DHA + GLA dietary combination prevented retinal cell structure and decreased glial cell activation induced by the elevation of IOP in rats.

Dietary n-3 and n-6 PUFA enhance DHA incorporation in retinal phospholipids without affecting PGE(1) and PGE (2) levels

The purpose of this study was to determine whether dietary n-3 and n-6 PUFA may affect retinal PUFA composition and PGE(1) and PGE(2) production. Male Wistar rats were fed for 3 months with diets containing: (1) 10% eicosapentaenoic acid (EPA) and 7% docosahexaenoic acid (DHA), or (2) 10% gamma-linolenic acid (GLA), or (3) 10% EPA, 7% DHA and 10% GLA, or (4) a balanced diet deprived of EPA, DHA, and GLA. The fatty acid composition of retinal phospholipids was determined by gas chromatography. Prostaglandin production was measured by enzyme immunoassay. When compared to rats fed the control diet, the retinal levels of DHA were increased in rats fed both diets enriched with n-3 PUFA (EPA + DHA and EPA + DHA + GLA diets) and decreased in those supplemented with n-6 PUFA only (GLA diet). The diet enriched with both n-6 and n-3 PUFA resulted in the greatest increase in retinal DHA. The levels of PGE(1) and PGE(2) were significantly increased in retinal homogenates of rats fed with the GLA-rich diet when compared with those of animals fed the control diet. These higher PGE(1) and PGE(2) levels were not observed in animals fed with EPA + DHA + GLA. In summary, GLA added to EPA + DHA resulted in the highest retinal DHA content but without increasing retinal PGE(2) as seen in animals supplemented with GLA only.