Emerging mechanisms of drug-induced phospholipidosis.

Drug-induced phospholipidosis is a lysosomal storage disorder characterized by excessive accumulation of phospholipids. Its cellular mechanism is still not well understood, but it is known that cationic amphiphilic drugs can induce it. These drugs have a hydrophilic amine head group that can be protonated in the endolysosomal compartment. As cationic amphiphiles, they are trapped in lysosomes, where they interfere with negatively charged intralysosomal vesicles, the major platforms of cellular sphingolipid degradation. Metabolic principles observed in sphingolipid and phospholipid catabolism and inherited sphingolipidoses are of great importance for lysosomal function and physiological lipid turnover at large. Therefore, we also propose intralysosomal vesicles as major platforms for degradation of lipids and phospholipids reaching them by intracellular pathways like autophagy and endocytosis. Phospholipids are catabolized as components of vesicle surfaces by protonated, positively charged phospholipases, electrostatically attracted to the negatively charged vesicles. Model experiments suggest that progressively accumulating cationic amphiphilic drugs inserting into the vesicle membrane with their hydrophobic molecular moieties disturb and attenuate the main mechanism of lipid degradation as discussed here. By compensating the negative surface charge, cationic enzymes are released from the surface of vesicles and proteolytically degraded, triggering a progressive lipid storage and the formation of inactive lamellar bodies.

Sustained activation of sphingomyelin synthase by 2-hydroxyoleic acid induces sphingolipidosis in tumor cells.

The mechanism of action of 2-hydroxyoleic acid (2OHOA), a potent antitumor drug, involves the rapid and specific activation of sphingomyelin synthase (SMS), leading to a 4-fold increase in SM mass in tumor cells. In the present study, we investigated the source of the ceramides required to sustain this dramatic increase in SM. Through radioactive and fluorescent labeling, we demonstrated that sphingolipid metabolism was altered by a 24 h exposure to 2OHOA, and we observed a consistent increase in the number of lysosomes and the presence of unidentified storage materials in treated cells. Mass spectroscopy revealed that different sphingolipid classes accumulated in human glioma U118 cells after exposure to 2OHOA, demonstrating a specific effect on C16-, C20-, and C22-containing sphingolipids. Based on these findings, we propose that the demand for ceramides required to sustain the SMS activation (ca. 200-fold higher than the basal level) profoundly modifies both sphingolipid and phospholipid metabolism. As the treatment is prolonged, tumor cells fail to adequately metabolize sphingolipids, leading to a situation resembling sphingolipidosis, whereby cell viability is compromised.

Qualified method for the estimation of di-18:1 bis(monoacylglycero)phosphate in urine, a noninvasive biomarker to monitor drug-induced phospholipidosis.

Aim: Our objective was to develop and qualify a bioanalytical method for the estimation of di-18:1-bis(monoacylglycero)phosphate (di-18:1 BMP) as a urinary biomarker for the assessment of drug-induced phospholipidosis and demonstrate its application in a preclinical study. Methodology/results: di-18:1 BMP was extracted by liquid-liquid extraction using n-butanol and analyzed by LC-MS/MS. The qualified method was selective, precise, robust and accurate across the linearity range (0.2-250 ng/ml). Qualified method was then used to assess chloroquine-induced phospholipidosis in rats dosed at 120 mg/kg for 5 days. A fivefold increase in di-18:1 BMP was observed on Day 5 compared with predose. Conclusion: Di-18:1 BMP can be used as a noninvasive biomarker to assess/screen compounds that could cause drug-induced phospholipidosis in rats.

Arsenic induces oxidative stress, sphingolipidosis, depletes proteins and some antioxidants in various regions of rat brain.

OBJECTIVES: To seek an interrelationship, if any, between oxidant stress and neurochemical changes in various rat brain regions after arsenic exposure. MATERIALS AND METHODS: This study was carried out at the Department of Biochemistry, Al Arab Medical University, Benghazi, Libya. Seventy five male Spraque-Dawley rats were divided into three groups: CONTROL GROUP: Rats were administered 2 ml of normal saline solution/kg body weight (b.wt.) daily for 20 days by intraperitoneal (i.p.) route. ARSENIC-TREATED GROUP: Rats received elemental arsenic (as sodium arsenate) 2.0 mg/kg b.wt. daily for 20 days by i.p. route. RECOVERY GROUP: Rats received 2.0 mg/kg b.wt. elemental arsenic daily for 20 days by i.p. route and were allowed to recover for 20 days. Rats were sacrificed and brains were dissected into cerebral cortex, corpus striatum, cerebellum and brain stem. Tissue homogenized in respective mediums. And were analyzed for lipid classes, oxidative stress, concentration of proteins, glutathione and ascorbic acid by utilizing standard colorimetric procedures. RESULTS: Arsenic exposure increased the oxidant stress because lipid peroxidation was enhanced. And decreased the contents of lipid classes, proteins, glutathione and the ascorbic acid in various rat brain regions. However, thins-layer chromatography exhibited regional variations in phospholipids classes. CONCLUSION: These results suggested that arsenic-initiated oxidant stress by increasing lipid peroxidation. The losses of lipid classes, ascorbic acid and glutathione may be attributed to peroxidative damage and binding of arsenic with sulfhydryl groups of enzymes. Recovery of animals showed reversibility in most of studied parameters, but gangliosides and cerebrosides over shooted. And speculated "Sphingolipidosis". It is then likely that repeated exposures of humans to arsenic may result in hampering of cell signalling, apoptosis and mutagenesis.

A view on sphingolipids and disease.

Sphingolipid and glycosphingolipid levels and expression of sphingolipid metabolizing enzymes are altered in a variety of diseases or in response to drug treatment. Inherited defects of enzymes and other proteins required for the lysosomal degradation of these lipids lead to human sphingolipidoses. Also genetic defects that affect sphingolipid biosynthesis are known. Although the molecular details are often far from clear, (glyco)sphingolipids have been implicated to play a role in atherosclerosis, insulin resistance, cancer, and infections by pathogens. More general aspects of selected diseases are discussed.

Experimental polymer storage disease in rabbits. An approach to the histogenesis of sphingolipidoses.

Water-soluble polymer compound, polyvinyl alcohol(PVA), and water-insoluble polymer compounds, polyvinyl acetate (PVAc) and polystylol (PS), were administered in 297 rabbits. When high polymerized PVA, PVAc or PS were continuously injected intravenously for a long period of time, lesions resembled to those of Gaucher and Niemann-Pick diseases were developed. From these experimental results, pathological development of various sphingolipidoses found in the human body was discussed and pathological findings were analysed polymer-chemically from the chemical properties of the substances stored.