What's in a name?-"Lipolysosome": ultrastructural features of a lipid-containing organelle

The prevalence of fatty liver is rising not only in adults but also in children and adolescents. The authors describe the ultrastructure of 12 biopsies from 10 males and 2 females aged 7-18 years. All subjects had fatty liver by ultrasonography and were overweight or obese according to BMI classification. They all had elevated aminotransferases and/or lipid/cholesterol levels, ultimately confirmed by biopsy. Steatosis was mild in 2, moderate in 3, and severe in 7 cases. Nonalcoholic steatohepatitis was diagnosed in 7 and nonalcoholic fatty liver disease in 5 patients. Lipolysosomes, identified in all 12 biopsies, were defined as fat droplets surrounded by a trilaminar membrane and lipofuscin-like deposits within or adjacent to the enveloping membrane. The lysosome marker CD68 revealed lysosomal activity in all lipolysosomes identified by electron microscopy. The ultrastructural features, here illustrated in diverse human biopsies, enabled lipolysosome classification in 3 types: monolocular (type I), multilocular (type II), and giant multilocular (type III). Type II, previously described in some conditions with abnormal lipid metabolism, was found in all biopsies, though with variable frequency. Type III was observed only in severe steatosis and associated with prominent connective tissue and conspicuous lipofuscin deposits. These new findings demonstrate the presence of lipolysosomes in a variety of fatty livers, in conditions hitherto unknown, in relation to the severity of steatosis, fibrogenic process, autophagy, lipolysis, and lipofuscin formation.