Cardiac lysosomal derangements in mouse heart after long-term exposure to nonmetabolizable sugars

Hearts of late fetal mice were maintained in organ culture in the presence of 30-100 mM sucrose or mannitol. Activities of several lysosomal enzymes (cathepsin D, beta-acetylglucosaminidase, acid phosphatase) were increased by up to 30% after 18-24 hours and by up to 50% after 48-72 hours, as compared to enzyme activities in litter-matched hearts maintained in control medium or medium supplemented with equimolar urea. Simultaneously, the ratio of nonsedimentable to sedimentable enzyme activity was significantly increased, suggesting increased lysosomal fragility. Light and electron microsopic examination of the hearts revealed marked vacuolization in myocytic, interstitial, and endothelial cells. The vacuoles were limited by single membranes, often contained particulate or amorphous cellular debris resulting from autophagocytosis, and in cytochemical preparations frequently exhibited an electron-dense reaction product indicative of acid phosphatase activity. Hydrocortisone failed to prevent the marked lysosomal activation induced by the sugars. In conclusion, prolonged exposure to nonmetabolizable sugars induces severe lysosomal derangements with prominent autophagy, in fetal mouse heart maintained in organ culture.