Structure of asteroid bodies in the vitreous of galactose-feddogs

[摘要] Purpose: Asteroid hyalosis is a condition in which white sphericalparticles (asteroid bodies) are suspended in the vitreous, usually inthe dependent part of the vitreous. These particles seldom cause seriousvisual symptoms; however, their presence can be a source of irritation.It has been suggested, but not confirmed, that asteroid hyalosis may beassociated with systemic diseases such as diabetes, hyperlipidemia, orhypertension. Studies indicate that these particles are composed oflipid material and calcium; however, the specific composition andstructure of asteroid bodies remains unknown. We have observed thatasteroid hyalosis occurs in galactose-fed dogs, and this represents thefirst animal model which consistently forms this vitreal condition. Thepurpose of this study was to identify the main structural component ofthe asteroid bodies present in the vitreous of these dogs.Methods: Vitreous humor containing asteroid bodies was collected andfrozen from long-term galactose-fed beagles and from age-matched normalcontrols where asteroid bodies were absent. A portion of the frozenvitreous was sent out for elemental analysis. Thawed vitreous sampleswere sonicated with HPLC grade water and the aqueous layer was extractedthree times with chloroform and then three times with n-butanol. Thethree organic layers from each extraction were combined and the solventsremoved in vacuo. The residue from each extraction was re-dissolved inmethanol and analyzed by electrospray ionization mass spectrometry(ESI-MS).Results: Vitreous-containing asteroid bodies had significantlyhigher levels of calcium and phosphorus. Negative mode ESI-MS analysisof the n-butanol extracts from vitreous samples with and withoutasteroid bodies were similar with both containing a predominant peakwith a mass to charge ratio (m/z) of 538.4. However, similar analyses ofthe chloroform extracts indicated that three peaks with m/z values of547.1, 690.5, and 1430.6 were present only in vitreous samplescontaining asteroid bodies. Subtraction analysis indicated that the m/zof 690.5 peak corresponded to the main component present. This peak wasidentified and confirmed to be the quasimolecular ion of1,2-dipalmitoyl-glycero-3-phosphoethanolamine (DPPE).Conclusions: Based on the current belief that asteroid bodies arecomposed of lipid-calcium complexes, we propose that the main componentof asteroid hyalosis in the galactose-fed dog is a quasimolecular ion ofDPPE in which two molecules of DPPE are complexed through theirphosphates groups with calcium.

[学科分类] 生物化学/生物物理