Studies on drug-induced lipidosis. VIII. Correlation between drug accumulation and acidic phospholipids.

The effect of 4,4'-bis(beta-diethylaminoethoxy)alpha,beta-diethyldiphenylethane (DH) on lipid metabolism in the liver differed considerably in different animal species, humans, monkeys, and rats, because of differences in drug-metabolizing ability. Monkeys retain considerable drug-metabolizing ability as compared with humans, but the DH-hydroxylating activity in monkeys seems to be much lower than in rats. The hydroxyl derivative was the major substance which accumulated in rat liver following the administration of DH, while DH itself and its N-dealkylated substances accumulated in monkey liver. N-Dealkylated substances were also observed in human liver, but the amount was much smaller than in monkeys. Bis(monoacylglyceryl)phosphate (BMGP), which is characteristic of this kind of drug-induced lipidosis, did not increase as much in monkey liver as in human liver, but a marked increase in phosphatidyl inositol (PI) was observed in monkey liver during administration of DH. The concentration of acidic phospholipids (BMGP + PI) in liver showed a close correlation with the accumulation of the drug (DH + its metabolites), irrespective of species differences. Among subcellular particles isolated from a monkey liver following administration of DH, the crude mitochondrial fraction, including lysosomes, was richest in BMGP.     

Histochemical study on the pathogenesis of chlorocyclizine-induced pulmonary lipidosis.

Male rats were fed a diet containing chlorocyclizine in high concentrations for about 3 weeks. They lost weight and showed respiratory distress. The lungs contained clusters of foam cells in the alveoli. Acid esterase staining revealed reduction of activity in alveolar cells presumed to be granular pneumocytes and absence of activity in the foam cells. The lipid showed in the foam cells could not be stained with Sudan dyes, except at high temperature, and was not stained by phospholipid and cholesterol procedures. This indicated that the stored lipids are probably solid at room temperature, consisting of saturated triglycerides and/or phospholipids. It is suggested that the lipid originated in the granular pneumocytes. The drug might have deranged the esterase-phospholipase activity in these cells and in the macrophages.     

Renal lysosomal protein digestion in experimental lipidosis

The present study was undertaken to clarify whether or not chlorphentermine-induced lipidosis in the proximal tubules of the rat kidney interferes with lysosomal degradation of an absorbed exogenous protein. 125I-lysozyme was injected in vivo; its degradation was measured in vitro using slices from renal cortex. The subcellular distribution of the protein was examined by electron microscope autoradiography. Lysosomes structurally altered by the lipidosis were able to accumulate the protein, although to a smaller extent than normal-appearing lysosomes present in the same cells; the label persisted longer in the altered than in the normal-appearing lysosomes. Protein degradation was significantly decreased in renal cortical slices from chlorphentermine-treated rats compared with controls. The results indicate that experimentally-induced lipidosis is associated with decreased proteolytic efficiency of the lysosomes in proximal tubules.     

Peripheral nervous system affection in experimental lipidosis induced by 4,4'-diethylaminoethoxyhexesterol.

A picture of generalized phosphoglyceride and cholesterol storage was induced, in keeping with literary data, by the experimental administration of 4,4'-diethylaminoethoxyhexesterol to rats. An asset of this model lies in the discovery that considerable storage occurs in the peripheral nervous system in contrast to the CNS, whose resistance to hexesterol is generally known. The significance of this finding is briefly discussed.     

Histochemical study on the pathogenesis of chlorocyclizine-induced pulmonary lipidosis

Summary Male rats were fed a diet containing chlorocyclizine in high concentrations for about 3 weeks. They lost weight and showed respiratory distress. The lungs contained clusters of foam cells in the alveoli. Acid esterase staining revealed reduction of activity in alveolar cells presumed to be granular pneumocytes and absence of activity in the foam cells. The lipid showed in the foam cells could not be stained with Sudan dyes, except at high temperature, and was not stained by phospholipid and cholesterol procedures. This indicated that the stored lipids are probably solid at room temperature, consisting of saturated triglycerides and/or phospholipids. It is suggested that the lipid originated in the granular pneumocytes. The drug might have deranged the esterase-phospholipase activity in these cells and in the macrophages.With technical assistance of Nitza Deitsch     

Freeze-fracture studies of cytoplasmic inclusions occurring in experimental lipidosis as induced by amphiphilic cationic drugs.

The ultrastructure of cytoplasmic inclusions, which characterize experimental lipidosis as induced by several amphiphilic cationic drugs, was studied by means of freeze-fracturing and thin-sectioning. Retinal and adrenal tissues of rats chronically treated with high oral doses of chlorphentermine were used. In thin sections the cytoplasmic inclusions, which were previously shown to represent lysosomes overloaded with polar lipids, exhibit lamellated or lattice-like internal patterns. The present freeze-fracture observations are interpreted as to indicate that the lamellated inclusions contain polar lipids in the lamellar phase, whereas those with lattice-like patterns contain polar lipids in a hexagonal phase.     

Glomerular lipidosis in a Syrian hamster of the APA strain

Spontaneous glomerular lipidosis was found in a 12-week-old male Syrian hamster of the APA strain. Lipids in the glomeruli were observed as droplets in a prominently expanded mesangial area and as emboli in a dilated capillary lumen. Lipid deposition was also, but less often, detected in tubular epithelial cells and interstitial cells around the lipid-laden glomeruli. This case of glomerular lipidosis was considered to be closely related to hyperglycaemia and hyperlipidaemia.     

Tilorone-induced lysosomal storage mimicking the features of mucopolysaccharidosis and of lipidosis in rat liver

This ultrastructural and histochemical study deals with the lysosomal storage phenomena occurring in the rat liver after repeated oral administration of tilorone, an agent with anti-tumor and anti-viral activities. In the sinusoidal endothelium and in Kupffer cells, the lysosomes were changed into large vacuoles which contained material with the histochemical characteristics of acid glycosaminoglycans. The alterations closely resembled those previously observed in the splenic red pulp of tilorone-treated rats. In hepatocytes, the lysosomes were converted into large multilamellated inclusions indicating storage of polar lipids. The results show that, in the rat liver, tilorone induces cellular alterations mimicking those of inherited mucopolysaccharidoses and lipidoses. After discontinuing drug treatment the two storage phenomena gradually faded at different rates: The lipidosis disappeared within 2 to 4 weeks, whilst mucopolysaccharidosis-like changes were still found 15 weeks after drug withdrawal. The occurrence of lipidosis is not surprising, since by its molecular structure tilorone can be regarded as belonging to the group of amphiphilic cationic drugs which often have this side effect. Much more surprising is the occurrence of mucopolysaccharidosis-like alterations. The exact biochemical identification of the polyanionic storage material and the molecular mechanisms responsible for this drug side effect remain to be established.     

Acylglycerol structure of mustard seed oil and of cardiac lipids of rats during dietary lipidosis

Stereospecific degradation and combined gas chromatographic--mass spectrometric (gc/ms) analysis were employed in a detailed investigation of the triacylglycerol structure of mustard seed oil and of the triacylglycerols transiently accumulating in the hearts of young rats receiving the oil in their diet. It was shown that feeding of mustard seed oil at 40% of the daily caloric requirement resulted in a deposition of cardiac triacylglycerols containing a high proportion of enantiomers of a positional distribution and molecular association of fatty acids which were closely similar to those found in the dietary oil. Complete structures were derived for a total of 88 species representing 75 to 85% of the triacylglycerols. About 90% of the accumulated triacylglycerol contained at least one long-chain (C20--C22) monounsaturated fatty acid per molecule. The long-chain acids were confined mainly to the primary positions and preferentially to the sn-3-position of the glycerol molecule. The dietary lipidosis, is, therefore, accompanied by little or no accumulation of the normal rat tissue triacylglycerols containing C16 and C18 fatty acids. It is suggested that the deposition and eventual clearance of the enantiomeric long-chain triacylglycerols in the rat heart during mustard seed oil feeding may be largely a result of a gradual change in specificity of the cardiac lipases.     

Deletion of the transmembrane transporter ABCG1 results in progressive pulmonary lipidosis

We show that mice lacking the ATP-binding cassette transmembrane transporter ABCG1 show progressive and age-dependent severe pulmonary lipidosis that recapitulates the phenotypes of different respiratory syndromes in both humans and mice. The lungs of chow-fed Abcg1(-/-) mice, >6-months old, exhibit extensive subpleural cellular accumulation, macrophage, and pneumocyte type 2 hypertrophy, massive lipid deposition in both macrophages and pneumocytes and increased levels of surfactant. No such abnormalities are observed at 3 months of age. However, gene expression profiling reveals significant changes in the levels of mRNAs encoding key genes involved in lipid metabolism in both 3- and 8-month-old Abcg1(-/-) mice. These data suggest that the lungs of young Abcg1(-/-) mice maintain normal lipid levels by repressing lipid biosynthetic pathways and that such compensation is inadequate as the mice mature. Studies with A-549 cells, a model for pneumocytes type 2, demonstrate that overexpression of ABCG1 specifically stimulates the efflux of cellular cholesterol by a process that is dependent upon phospholipid secretion. In addition, we demonstrate that Abcg1(-/-), but not wild-type macrophages, accumulate cholesterol ester droplets when incubated with surfactant. Together, these data provide a mechanism to explain the lipid accumulation in the lungs of Abcg1(-/-)mice. In summary, our results demonstrate that ABCG1 plays essential roles in pulmonary lipid homeostasis.