Meibomian gland studies: comparison of steer and human lipids

Simple surgery gave whole meibomian glands of steer yielding approximately 47 mg of lipid per pair of lids. This lipid gave a thin-layer chromatography pattern similar to that of steer or human excreta. Column chromatography of pooled steer gland lipids and pooled human lipid (excreta) gave 0.06% and 7.54% hydrocarbons, respectively, containing no squalene. Excluding human hydrocarbons (as exogenous material) the percentage composition of steer and human lipids were, respectively, sterol esters 31.7 and 29.5; wax esters 31.2 and 35.0; material in the diester region 11.4 and 8.4; triacyl glycerols 1.6 and 4.0; material in the post-triacyl glycerol region 2.8 and 3.2; free sterols 3.0 and 1.8; free fatty acids 5.1 and 2.1; and polar lipids 13.3 and 16.0. Glass capillary gas-liquid chromatography revealed the following: a series of normal odd- and even-chain hydrocarbons (C16 to C32) for the steer and a complex pattern for the human samples; unsubstituted fatty acids in total lipids and various lipid classes ranging from C12 to C31 with n-even, n-odd, iso-even and iso-odd, and anteiso-odd chains for both samples; and fatty alcohols in total lipids and wax esters ranging from C18 to C31. Anteiso structures predominated in the steer, and iso structures in the human samples. Steer fatty acids favored anteiso branching and saturation, whereas human acids favored iso branching and unsaturation. Fatty acids of sterol esters in both samples showed a wider range of chain lengths than did other lipid classes. Similarity of the fatty acid pattern suggests that the free fatty acids are derived from the triacyl glycerols as in human sebum. Identification of saturated fatty acids was confirmed by a gas liquid chromatography--mass spectrometry--data system (GLC-MS-DS). We define "meibum" and "meibocyte" as the meibomian gland equivalent of sebum and sebocyte.