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J. C. Eule, A. M. Borowiak, I. A. Butovich; Evaluation of Tear Lipid Pattern in Healthy Dogs by HPLC-Mass Spectrometry. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4159.
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Integrity of the human tear film (hTF), and of its outermost part called TF lipid layer (TFLL), which is formed mostly of meibomian gland secretions (hMGS), is critical for maintaining the health of the ocular surface. Various abnormalities in the hMGS composition were shown to be associated with dry eye (DE) in humans. The same is expected to be true for domestic and laboratory animals, some of which have already been exhaustively studied and used as animal models of hTF in DE studies. However, to the best of our knowledge, no information about the TFLL and MGS of dogs - one of the most common pets and laboratory animals - is currently available. The aim of this study was to evaluate the lipid spectrum of MGS in healthy dogs (cMGS) of different breeds and compare it with hMGS.
Ophthalmic evaluation of the canine subjects using slit lamp biomicroscopy, interferometry, meibometry, Schirmer tear tests, and blood chemistry including cholesterol, triglyceride and thyroid globulin confirmed their healthy state. Dogs with health problems and ocular abnormalities were excluded from the study. MGS specimens from dogs of 10 different breeds (1 to 9 years old, both genders) were studied. Meibum was soft-squeezed from meibomian glands and collected using a spatula. The samples were evaluated using ion trap atmospheric pressure chemical ionization HPLC-MSn and lipid mapping was performed by using a shotgun lipidomic approach.
Between 0.1 and 0.2 mg of dry cMGS/animal was collected. The main lipid classes found in cMGS were very long chain cholesteryl esters, wax esters, triacylglycerols, di- and triesters (as defined by Nicolaides et al) and a novel class of (O-acyl)-omega-hydroxy fatty acids which was recently detected in hMGS. A shotgun lipidomic analysis showed that the major individual lipid species found in cMGS were structurally close to those found in hMGS. However, the canine samples displayed relatively high inter-breed variability in the ratio of the detected lipid species, and generally a several-fold higher ratio of di- and triesters compared to the rest of the lipid pool.
These results suggest that canine meibum closely resembles the human one, but there are some quantitative differences between the two. Also, we observed noticeable inter-breed differences in cMGS samples. Further detailed structural and quantitative studies of cMGS are warranted.
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