Age-related increase in liver retinyl palmitate. Relationship to lipofuscin

Lipofuscin is a general term assigned to fluorescent material that accumulates in cells as they age. It is apparent from this study that the fluorescent intensity of detergent-solubilized liver from Fisher-344 rats increased as a function of age. The fluorophore responsible for this increase was extracted with methanol and could be resolved from other cellular components when the methanol extracts were chromatographed over a reverse phase column. This compound was identified as retinyl palmitate and was found to increase throughout the entire life of the Fisher-344 rat (2-24 months), from a value of 0.26-1.77 mg/g of liver. In addition, the results presented here demonstrate that concentration, time between extraction and analysis, exposure to light, and degree of purity affect the observed fluorescent properties of retinyl palmitate. These factors affect many fluorophores and are likely to be, at least in part, responsible for the multiplicity of reported properties of lipofuscin. As has been reported for lipofuscin, retinyl palmitate accumulates in intracellular granules and exhibits fluorescence between 450 and 600 nm. Due to these similarities, the relationship between retinyl palmitate and lipofuscin warrants further investigation.