Toxicity and neuronal transport of stable liposomes and phospholipid in the nervous system.

When unilamellar "stable" liposomes composed of a dialkyl analog of phosphatidylcholine, tetradecyloctadec-11-eno(1)phosphocholine (dialkyl-PC), plus cholesterol at 1:1 molar ratio, and a trace of [3H]dialkyl-PC were injected into the vitreous of the rabbit eye, macrophage infiltration and phagocytosis of lipid were observed in retina including the epiretinal myelinated nerve fiber bundles, with no other neurotoxic effects. Little or no incorporation of [3h]dialkyl-PC was observed in the distal tissues of the optic system. With "labile" vesicles composed of egg lecithin, trace amounts of [3H]dialkyl-PC, and phosphatidic acid, no morphological changes occurred. After a lag of more than 7 days [3H]dialkyl-PC appeared in superior colliculus, indicating axonal transport of the lipid in an anterograde direction. Experiments with submandibular and parotid gland indicated retrograde transport of the lipid. The data do not suggest axonal transport of intact (stable) liposomes, but suggest that intact phospholipid molecules can be axonally transported.