Stearylamine permeabilizes the lysosomal membrane to cystine and sialic acid

Cystine efflux from isolated rat liver lysosomes was enhanced by concentrations of stearylamine that were above the critical micellar concentration. Lysosomal latency, pH, and activity of the proton-translocating ATPase were largely unaffected under controlled experimental conditions. Loss of lysosomal latency was observed at higher stearylamine to protein ratios consistent with a detergent-like mechanism of action. Partially purified cultured fibroblast lysosomes with either defective cystine or sialic acid transport lost their stored material upon exposure to stearylamine. Concentrations of stearylamine which were effective for lysosomal efflux were highly toxic for cultured fibroblasts, thus limiting its use. Under specific conditions, stearylamine apparently selectively permeabilizes the lysosomal membrane. A similar acting, but less toxic agent may be of use in the treatment of lysosomal transport disorders.