Niemann-Pick disease type D: lipid analyses and studies on sphingomyelinases

Bis(monoacylglycero)phosphate, a peculiar phospholipid to control the fate of cholesterol: Implications in pathology

Bis(monoacylglycero)phosphate (BMP) is a structural isomer of phosphatidylglycerol that exhibits an unusual sn1:sn1' stereoconfiguration, based on the position of the phosphate moiety on its two glycerol units. Early works have underlined the high concentration of BMP in the lysosomal compartment, especially during some lysosomal storage disorders and drug-induced phospholipidosis. Despite numerous studies, both biosynthetic and degradative pathways of BMP remained not completely elucidated. More recently, BMP has been localized in the internal membranes of late endosomes where it forms specialized lipid domains. Its involvement in both dynamics and lipid/protein sorting functions of late endosomes has started to be documented, especially in the control of cellular cholesterol distribution. BMP also plays an important role in the late endosomal/lysosomal degradative pathway. Another peculiarity of BMP is to be naturally enriched in docosahexaenoic acid and/or to specifically incorporate this fatty acid compared to other polyunsaturated fatty acids, which may confer specific biophysical and functional properties to this phospholipid. This review summarizes and updates our knowledge on BMP with an emphasis on its possible implication in human health and diseases, especially in relation to cholesterol homeostasis.

Screening for the drug-phospholipid interaction: correlation to phospholipidosis

Phospholipid bilayers represent a complex, anisotropic environment fundamentally different from bulk oil or octanol, for instance. Even "simple" drug association to phospholipid bilayers can only be fully understood if the slab-of-hydrocarbon approach is abandoned and the complex, anisotropic properties of lipid bilayers reflecting the chemical structures and organization of the constituent phospholipids are considered. The interactions of drugs with phospholipids are important in various processes, such as drug absorption, tissue distribution, and subcellular distribution. In addition, drug-lipid interactions may lead to changes in lipid-dependent protein activities, and further, to functional and morphological changes in cells, a prominent example being the phospholipidosis (PLD) induced by cationic amphiphilic drugs. Herein we briefly review drug-lipid interactions in general and the significance of these interactions in PLD in particular. We also focus on a potential causal connection between drug-induced PLD and steatohepatitis, which is induced by some cationic amphiphilic drugs.

An enzymatic assay for quantifying sphingomyelin in tissues and plasma from humans and mice with Niemann-Pick disease

Sphingomyelin is an important lipid component of cell membranes and lipoproteins which can be hydrolyzed by sphingomyelinases into ceramide and phosphorylcholine. The type A and B forms of Niemann-Pick disease (NPD) are lipid storage disorders due to the deficient activity of the enzyme acid sphingomyelinase, and the resultant accumulation of sphingomyelin in cells and tissues. In this paper we report a new, enzyme-based method to quantify the levels of sphingomyelin in tissues and plasma of normal individuals and NPD patients. The method utilizes sphingomyelinase from Bacillus cereus to completely hydrolyze the sphingomyelin into ceramide. Quantification of the sphingomyelin-derived ceramide is accomplished using Escherichia coli diacylglycerol (DAG) kinase and [gamma-(32)P]ATP. The resulting [(32)P]ceramide is quantified using a phosphor-imager system following TLC separation. This procedure allowed quantification of sphingomyelin over a broad range from 10 pmol to 1 nmol. To validate this assay we quantified sphingomyelin in plasma and tissues obtained from normal and NPD mice and humans. The sphingomyelin content in adult homozygous (-/-) or heterozygous (+/-) NPD mouse plasma was significantly elevated compared to that of normal mice (up to twofold). Moreover, the accumulated sphingomyelin in the tissues of NPD mice was 4 to 40 times higher than that in normal mice depending on the tissue analyzed. The sphingomyelin levels in plasma from several type B NPD patients also were significantly elevated compared to normal individuals of the same age. Based on these results we propose that this new, enzyme-based procedure can provide sensitive and reproducible sphingomyelin quantification in tissues and fluids from normal individuals and NPD patients. It could be a useful tool for the diagnosis of NPD and the evaluation of NPD treatment protocols, as well as for the study of ceramide-mediated apoptosis since the method provides the simultaneous determination of sphingomyelin and ceramide in the same lipid extract.

Lipid changes in Niemann-Pick disease type C brain: personal experience and review of the literature

Niemann-Pick disease type C (NPC) is a neurovisceral disorder characterized by lysosomal sequestration of endocytosed LDL-cholesterol, premature and abnormal enrichment of cholesterol in trans Golgi cisternae and accompanying anomalies in intracellular sterol trafficking. In addition to cholesterol, the NPC lesion has also been shown to impact the metabolism of sphingolipids. Lipids, more particularly glycolipids, were studied in brain tissue from eight cases with proven NPC, ranging from 21 fetal weeks to 19 years of age (one case with rapidly fatal neonatal cholestatic icterus, three cases with infantile neurological onset, one late infantile and two juvenile neurological cases). In gray matter, the concentrations of total cholesterol, sphingomyelin and total gangliosides were within the normal range in all cases. In white matter, a severe loss of galactosylceramide and other myelin lipids (including cholesterol) was prominent in patients with the neurological severe infantile form (levels similar to those in 6-8 month-old infants) or the late infantile form of the disease, but only a slight decrease was observed in patients with a juvenile neurological onset. Analysis of the ganglioside profiles and study of minor neutral glycolipids revealed striking abnormalities, although not present at the fetal stage. In cerebral cortex, gangliosides GM3 and GM2 showed a significant increase, 10-15 fold and 3-5-fold the normal level, respectively, with already some abnormalities in a 3-month-old patient. Except in the latter patient, a prominent storage of glucosylceramide, lactosylceramide and gangliotriaosylceramide (asialo-GM2) was observed, with 10-50-fold increases from the normal concentration. The fatty acid composition of these glycolipids suggests that they have a neuronal origin. A slight increase of globotriaosyl- and globotetraosylceramide and of more complex neutral glycolipids also occurred. While ganglioside changes were essentially similar in gray and white matter, changes of the neutral glycolipids were only minimal in the latter. Our data are in good accordance with previous studies and provide additional information. They emphasize that, apart a varying demyelinating process (most pronounced in children with a severe infantile neurological form) brain lipids abnormalities are essentially located to the gray matter. They confirm and give more precise information on the glycolipid nature of the neuronal storage, and establish that a similar type of changes occurs in the different neurological forms of the disease. Yet, our study indicates that glycolipid changes in brain do not occur before a few months after birth, possibly at a period concomitant with the onset of neurological symptoms, in contrast to the very early glycolipid abnormalities observed in non-neural organs. Glycolipid changes rather similar to those seen in NPC brain, in particular for gangliosides, have been described for other lysosomal disorders such as Niemann-Pick type A and mucopolysaccharidoses. The glucosyl-and lactosylceramide accumulation, however, is more striking in NPC, especially taking into account that there is no other known storage in NPC brain. Some neuropathological changes, such as ectopic neurites, could be related to the glycolipid changes. Metabolic studies in cultured fibroblasts combined to the observation that no lipids other than glycolipids accumulate in brain suggest that the NPC gene products possibly participate in intracellular transport or regulate metabolism of glycolipids.

Cholesterol and oxygenated cholesterol concentrations are markedly elevated in peripheral tissue but not in brain from mice with the Niemann-Pick type C phenotype

Niemann-Pick disease type C (NP-C) is a rare genetic disorder characterized by progressive neurodegeneration, frequent developmental delay and early death. Tissues of affected individuals accumulate large quantities of free cholesterol in lysosomes. Because cytotoxic oxygenated derivatives of cholesterol are known to form readily when cholesterol concentrations are elevated, we searched for these compounds in liver, kidney, spleen and brain from mice with the NP-C phenotype. In order of abundance, we identified 7 alpha- and 7 beta-hydroxycholesterol, 5 alpha, 6 alpha-epoxycholestan-3 beta-ol, 4 beta-hydroxycholesterol, cholest-4-en-3 beta, 7 alpha-diol and cholest-4-en-3 beta, 6 beta-diol in most tissue samples. Cholesterol concentrations in affected mice were increased 3-fold in kidney and 7- to 8-fold in spleen and liver compared to controls (all p < 0.001) but were unchanged in brain. Although oxysterol levels were markedly elevated in nonbrain tissue, the oxysterol and cholesterol concentrations increased proportionally so that oxysterols expressed as percentage of total sterols were the same for all animals (0.34 +/- 0.19% averaged over all organs in affected animals vs 0.40 +/- 0.42% in control mice). In contrast to peripheral tissue, we could not detect any increase in either absolute or relative oxysterol levels in the brains of affected and control mice (49 +/- 61 vs 53 +/- 43 micrograms/g wet weight and 0.45 +/- 0.52 vs 0.47 +/- 0.37%, respectively). Thus, brain sterols are normal in NP-C mice and it is unlikely that an accumulation of cytotoxic oxygenated derivatives of cholesterol could account for the progressive neuropathology seen in the disease.

Nova Scotia Niemann-Pick disease (type D): clinical study of 20 cases

Patients with Niemann-Pick type D have been traced to a single Acadian ancestor in Nova Scotia. The objective of this study was to describe the clinical course. A cohort of children with Niemann-Pick type D was identified by chart review. Some children were seen and a telephone interview with the remaining parents was conducted. Twenty children with Niemann-Pick type D were identified. The female to male ratio was 2:1. Five children had severe neonatal jaundice. Early milestones were normal in the majority. Neurologic symptoms generally developed between 5 and 10 years of age with a mean age of 7.2 years at diagnosis. Seizures developed in all between 4.5 and 16 years of age (mean, 10.5 yr), and were followed by significant physical and mental deterioration. The age at death ranged between 11 and 22.5 years (mean, 14.8 yr). In 61%, bronchopneumonia was the cause of death. There is significant variability in the presentation and clinical course of Niemann-Pick type D.

Niemann-Pick disease

Results of the investigation carried out during this decade brought unambigous evidence of biochemical heterogeneity inside the complex of Niemann-Pick disease according to which two entirely different metabolic disorders can be recognized. 1. Niemann-Pick sphingomyelinosis, a clear-cut enzymopathy, the pivotal lesion of which is the deficiency of lysosomal spingomyelinase leading to widespread lysosomal deposition of sphingomyelin liquid crystals. Two main allelic variants are known. The first one, neuronopathic (former type A) known as infantile with rapid course, may also manifest considerably prolonged course or an atypical course with predominantly visceral symptomatology. Patients with the second, visceral, variant (former type B), display mainly slow clinical course and often reach adulthood. With rare exceptions the neuronopathic variant can be biochemically recognized from the visceral one by much lower values of the in vivo sphingomyelin degradation test in the former. 2. The rest of the complex comprising types C-D differs substantially from the sphingomyelinase deficiency group by the remarkable heterogeneity in the lysosomal stored lipid pattern given by differences among the affected cell populations. Sphingomyelin storage could be proved histochemically solely in the histiocytic population together with cholesterol, neutral glycosphingolipids and lysobisphosphatidic acid, whereas the brain neurons displayed only neutral glycosphingolipid storage. There is an increasing evidence of the crucial biochemical lesion in this group being an altered intracellular traffic of exogenously derived cholesterol caused probably by its deficient translocation from lysosomes to other intracellular membrane sites. This leads to decreased cholesterol esterification rate which is the basis of the newly developed diagnostic test. Inconstant depression of sphingomyelinase activity is considered to be a secondary phenomenon. The so-called lactosylceramidosis is a rare variant pertinent to this group. The biochemical nature of type E still awaits clarification. Both groups of Niemann-Pick disease display clinical and especially histochemical features which allows to establish diagnosis in a highly efficient way already at the clinicopathological level.

Interindividual heterogeneity of molecular weight of human brain neutral sphingomyelinase determined by radiation inactivation method

The molecular weight (Mr) of the membrane-bound neutral sphingomyelinase from human brain was determined using the radiation inactivation procedure. Previous studies on three human brains suggested a Mr of 165 +/- 25 kDa (J. Neurochem. 1985, 45:630-632). We now report that in another human brain the neutral sphingomyelinase had a Mr of 740 +/- 100 kDa; this higher Mr was not accompanied by differences in enzymatic properties nor heat-stability.

Enzyme activities and phospholipid storage patterns in brain and spleen samples from Niemann-Pick disease variants: a comparison of neuropathic and non-neuropathic forms

Phospholipid levels and enzyme activities were measured in brain and spleen samples from patients with the three major variants of Niemann-Pick disease. Accumulations of sphingomyelin and bis(monoacylglycero)phosphate were demonstrated in spleen from types A and B and group C Niemann-Pick disease, whereas only in type A Niemann-Pick brain was the sphingomyelin concentration increased. Sphingomyelinase activity was markedly deficient in type A Niemann-Pick brain and spleen but residual activity of approximately 12% of control was measured in type B Niemann-Pick brain. Normal or raised sphingomyelinase and beta-glucosidase activities were measured in group C Niemann-Pick brain and spleen. Significant (17% of control) residual beta-glucosidase activity was also measured in non-neuropathic Gaucher brain. Normal levels of neutral sphingomyelinase activity were measured in brain samples from the three variants of Niemann-Pick disease. Acid sphingomyelinase activity in group C Niemann-Pick brain appeared normal with respect to enzyme extraction, pH optimum (pH 5.0) and apparent Km (approximately 0.4 mmol/L). Isoelectric focusing of brain sphingomyelinase revealed a degree of heterogeneity with activity peaks between pI 4.5 and 6.5. No defect was observed in group C Niemann-Pick brain and, although attenuated, all peaks were present in type B Niemann-Pick brain.

Molecular weight of human brain neutral sphingomyelinase determined in situ by the radiation inactivation method

The radiation inactivation method was used to determine the molecular weight of membrane-bound neutral sphingomyelinase from normal human brain. Inactivation curves showed a molecular mass of 167,000 +/- 32,000. Molecular weights of two control enzymes, beta-N-acetylglucosaminidase and nonspecific beta-glucosidase, determined by the same procedure, were consistent with previous reports.

Deficiency of taurocholate-dependent phospholipase C acting on phosphatidylcholine in Niemann-Pick disease

Examination of release of labeled glyceride from 2-[1-14C]oleoyl phosphatidylcholine by a soluble extract of human fibroblasts confirmed the presence of phosphodiesterase which is stimulated strongly by sodium taurocholate. This activity was maximal at pH 4.5 and was inhibited by sphingomyelin and 5' AMP. Assay of the phosphatidylcholine phosphodiesterase activity in fibroblast cultures from patients with Niemann-Pick disease revealed a severe deficiency in those cultures also deficient in sphingomyelinase (3 type A and 4 type B) whereas assay of cultures from Niemann-Pick patients without sphingomyelinase deficiency (3 type C and 1 with neurovisceral lipidosis and vertical supranuclear ophthalmoplegia) gave activities similar to controls. The distribution of label in the products of the reactions catalyzed by both control and Niemann-Pick extracts indicates that the phosphodiesterase activity observed was phospholipase C and that phospholipase D was not involved. The close correlation of phosphatidylcholine phospholipase C and sphingomyelinase activities in the control and mutant fibroblasts strongly suggests that both activities are catalyzed by one enzyme. Various alterations in the regulation of the specificity of a multifunctional phospholipase C may underlie phenotypic variation in Niemann-Pick disease.

Chemical studies on postmortem tissues from an infant with a sphingomyelin storage disorder

Investigations of formalin-stored tissues from a female child 3 weeks old showed that the concentrations of sphingomyelin, cholesterol and other lipids were increased in spleen and other tissues. Although the disorder could not be confirmed enzymatically, the findings are most consistent with the patient having a sphingomyelin storage disorder. Tissue lipid data for a series of subjects without storage disorders are presented and may provide useful information for interpretation of results from autopsy samples.

Hepatic storage of bis(monoacylglycerol) phosphate without concomitant storage of sphingomyelin in a 72-year-old patient with a partial deficiency of sphingomyelinase

A 72-year-old patient with marked splenomegaly and low sphingomyelinase (6% of lowest control value) in peripheral blood leukocytes is described. Much higher but variable residual sphingomyelinase activity was observed in cultured skin fibroblasts (40-67% of lowest control value); reduced activity was also found in a liver biopsy sample. Excess storage of sphingomyelin was not observed in a liver biopsy; instead, a lipid tentatively identified as bis(monoacylglycerol) phosphate was present in amounts at least 20 times greater than in age-matched control livers. The biochemical relationship of this patient to patients with sphingomyelin storage disease (Niemann-Pick disease) and phospholipidosis Type II is discussed.

Chemical and biochemical studies in fetuses affected with Nieman-Pick disease type A

Chemical and biochemical studies were performed on two unrelated fetuses affected with Niemann-Pick disease type A, following abortion at about the 19th week of gestation. Abortion was performed as a consequence of previous findings, in amniotic fluid cell cultures, that sphingomyelinase activity was completely absent. Phospholipid analyses of various organs of the fetuses, spleen and liver were the organs mostly affected. Interestingly enough considerable accumulation of sphingomyelin was found in the placenta. The brain was the only organ in which sphingomyelin storage could not be proved. In addition to sphingomyelin a slight accumulation of cholesterol was noticed. Deficiency of sphingomyelinase activity measured at pH 5.0 was the general characteristic of the affected tissues. It is concluded that the accumulation of sphingomyelin in various organs throughout the body of fetuses affected with Niemann-Pick disease is suggestive of the essential role of the enzyme sphingomyelinase and its biochemical maturation, even during the early stages of gestation.

Chemical and biochemical studies in human fetuses affected with Niemann-Pick disease type A

Chemical and biochemical studies were performed on two unrelated fetuses affected with Niemann-Pick disease type A, following abortion at about the 19th week of gestation. Abortion was performed as a consequence of previous findings, in amniotic fluid cell cultures, that sphingomyelinase activity was completely absent. Phospholipid analyses of various organs of the fetuses revealed an excess of sphingomyelin in all viscera as compared to control nonaffected fetuses. Spleen and liver were the organs mostly affected. Interestingly enough considerable accumulation of sphingomyelin was found in the placenta. The brain was the only organ in which sphingomyelin storage could not be proved. In addition to sphingomyelin a slight accumulation of cholesterol was noticed. Deficiency of sphingomyelinase activity measured at pH 5.0 was the general characteristics of the affected tissues. It could be concluded that the accumulation of sphingomyelin in various organs throughout the body of fetuses affected with Niemann-Pick disease, was suggestive of the essential role of the enzyme sphingomyelinase and its biochemical maturation, even during the early stages of gestation.