Uptake and metabolism of radioactively labeled sphingomyelin in cultured skin fibroblasts from controls and patients with Niemann-Pick disease and other lysosomal storage diseases

Consensus clinical management guidelines for acid sphingomyelinase deficiency (Niemann-Pick disease types A, B and A/B)

BACKGROUND

Acid Sphingomyelinase Deficiency (ASMD) is a rare autosomal recessive disorder caused by mutations in the SMPD1 gene. This rarity contributes to misdiagnosis, delayed diagnosis and barriers to good care. There are no published national or international consensus guidelines for the diagnosis and management of patients with ASMD. For these reasons, we have developed clinical guidelines that defines standard of care for ASMD patients.

METHODS

The information contained in these guidelines was obtained through a systematic literature review and the experiences of the authors in their care of patients with ASMD. We adopted the Appraisal of Guidelines for Research and Evaluation (AGREE II) system as method of choice for the guideline development process.

RESULTS

The clinical spectrum of ASMD, although a continuum, varies substantially with subtypes ranging from a fatal infantile neurovisceral disorder to an adult-onset chronic visceral disease. We produced 39 conclusive statements and scored them according to level of evidence, strengths of recommendations and expert opinions. In addition, these guidelines have identified knowledge gaps that must be filled by future research.

CONCLUSION

These guidelines can inform care providers, care funders, patients and their carers about best clinical practice and leads to a step change in the quality of care for patients with ASMD with or without enzyme replacement therapy (ERT).

The Niemann-Pick type diseases – A synopsis of inborn errors in sphingolipid and cholesterol metabolism

Disturbances of lipid homeostasis in cells provoke human diseases. The elucidation of the underlying mechanisms and the development of efficient therapies represent formidable challenges for biomedical research. Exemplary cases are two rare, autosomal recessive, and ultimately fatal lysosomal diseases historically named "Niemann-Pick" honoring the physicians, whose pioneering observations led to their discovery. Acid sphingomyelinase deficiency (ASMD) and Niemann-Pick type C disease (NPCD) are caused by specific variants of the sphingomyelin phosphodiesterase 1 (SMPD1) and NPC intracellular cholesterol transporter 1 (NPC1) or NPC intracellular cholesterol transporter 2 (NPC2) genes that perturb homeostasis of two key membrane components, sphingomyelin and cholesterol, respectively. Patients with severe forms of these diseases present visceral and neurologic symptoms and succumb to premature death. This synopsis traces the tortuous discovery of the Niemann-Pick diseases, highlights important advances with respect to genetic culprits and cellular mechanisms, and exposes efforts to improve diagnosis and to explore new therapeutic approaches.

Intracellular calcium dysregulation in autism spectrum disorder: An analysis of converging organelle signaling pathways

Autism spectrum disorder (ASD) is a group of complex, neurological disorders that affect early cognitive, social, and verbal development. Our understanding of ASD has vastly improved with advances in genomic sequencing technology and genetic models that have identified >800 loci with variants that increase susceptibility to ASD. Although these findings have confirmed its high heritability, the underlying mechanisms by which these genes produce the ASD phenotypes have not been defined. Current efforts have begun to "functionalize" many of these variants and envisage how these susceptibility factors converge at key biochemical and biophysical pathways. In this review, we discuss recent work on intracellular calcium signaling in ASD, including our own work, which begins to suggest it as a compelling candidate mechanism in the pathophysiology of autism and a potential therapeutic target. We consider how known variants in the calcium signaling genomic architecture of ASD may exert their deleterious effects along pathways particularly involving organelle dysfunction including the endoplasmic reticulum (ER), a major calcium store, and the mitochondria, a major calcium ion buffer, and theorize how many of these pathways intersect.

High-throughput screen detects calcium signaling dysfunction in typical sporadic autism spectrum disorder

Autism spectrum disorder (ASD) is a heterogeneous group of neurodevelopmental disorders without any defined uniting pathophysiology. Ca²⁺ signaling is emerging as a potential node in the genetic architecture of the disorder. We previously reported decreased inositol trisphosphate (IP₃)-mediated Ca²⁺ release from the endoplasmic reticulum in several rare monogenic syndromes highly comorbid with autism – fragile X and tuberous sclerosis types 1 and 2 syndromes. We now extend those findings to a cohort of subjects with sporadic ASD without any known mutations. We developed and applied a high throughput Fluorometric Imaging Plate Reader (FLIPR) assay to monitor agonist-evoked Ca²⁺ signals in human primary skin fibroblasts. Our results indicate that IP₃ -mediated Ca²⁺ release from the endoplasmic reticulum in response to activation of purinergic receptors is significantly depressed in subjects with sporadic as well as rare syndromic forms of ASD. We propose that deficits in IP₃-mediated Ca²⁺ signaling represent a convergent hub function shared across the spectrum of autistic disorders – whether caused by rare highly penetrant mutations or sporadic forms – and holds promise as a biomarker for diagnosis and novel drug discovery.

The Frequency, Characteristics, and Outcomes Among Cancer Patients With Delirium Admitted to an Acute Palliative Care Unit

BACKGROUND

Delirium is a common neuropsychiatric condition seen in patients with severe illness, such as advanced cancer. Few published studies are available of the frequency, course, and outcomes of standardized management of delirium in advanced cancer patients admitted to acute palliative care unit (APCU). In this study, we examined the frequency, characteristics, and outcomes of delirium in patients with advanced cancer admitted to an APCU.

METHODS

Medical records of 609 consecutive patients admitted to the APCU from January 2011 through December 2011 were reviewed. Data on patients' demographics; Memorial Delirium Assessment Scale (MDAS) score; palliative care specialist (PCS) diagnosis of delirium; delirium etiology, subtype, and reversibility; late development of delirium; and discharge outcome were collected. Delirium was diagnosed with MDAS score ≥7 and by a PCS using Diagnostic and Statistical Manual, 4th edition, Text Revision criteria. All patients admitted to the APCU received standardized assessments and management of delirium per best practice guidelines in delirium management.

RESULTS

Of 556 patients in the APCU, 323 (58%) had a diagnosis of delirium. Of these, 229 (71%) had a delirium diagnosis on admission and 94 (29%) developed delirium after admission to the APCU. Delirium reversed in 85 of 323 episodes (26%). Half of patients with delirium (n = 162) died. Patients with the diagnosis of delirium had a lower median overall survival than those without delirium. Patients who developed delirium after admission to the APCU had poorer survival (p ≤ .0001) and a lower rate of delirium reversal (p = .03) compared with those admitted with delirium.

CONCLUSION

More than half of the patients admitted to the APCU had delirium. Reversibility occurred in almost one-third of cases. Diagnosis of delirium was associated with poorer survival.

Identification of lipidomic biomarkers for coexposure to subtoxic doses of benzo[a]pyrene and cadmium: the toxicological cascade biomarker approach

The search for model bioassay systems indicating activation of different toxicological signaling pathways is one of the paramount goals of modern toxicology. Especially coexposure scenarios need to be investigated with respect to synergistic and interdependent effects for the activation of toxicological signaling pathways. The present study introduces an experimental in vitro model system for nontoxic and low-dose coexposures of human mammary carcinoma MCF-7 cells against polycyclic aromatic hydrocarbons (PAHs) such as benzo[a]pyrene (BP) and heavy metals such as cadmium. For the first time, a multivariate model that identifies 18 metabolic biomarkers has been shown to be sufficient to separate BP-treated cells from coexposed or control cells. A "toxicological pathway color code model" is introduced to visualize the results. Different biomarker subsets can be associated with specific HER2 signaling steps. A tiered cascade biomarker approach is proposed that could be used to identify profiles associated with tumorigenic potency of environmental toxicants in coexposure scenarios, including possible synergistic or additive effects.

Gangliosides and gangliosidoses: principles of molecular and metabolic pathogenesis

Gangliosides are the main glycolipids of neuronal plasma membranes. Their surface patterns are generated by coordinated processes, involving biosynthetic pathways of the secretory compartments, catabolic steps of the endolysosomal system, and intracellular trafficking. Inherited defects in ganglioside biosynthesis causing fatal neurodegenerative diseases have been described so far almost exclusively in mouse models, whereas inherited defects in ganglioside catabolism causing various clinical forms of GM1- and GM2-gangliosidoses have long been known. For digestion, gangliosides are endocytosed and reach intra-endosomal vesicles. At the level of late endosomes, they are depleted of membrane-stabilizing lipids like cholesterol and enriched with bis(monoacylglycero)phosphate (BMP). Lysosomal catabolism is catalyzed at acidic pH values by cationic sphingolipid activator proteins (SAPs), presenting lipids to their respective hydrolases, electrostatically attracted to the negatively charged surface of the luminal BMP-rich vesicles. Various inherited defects of ganglioside hydrolases, e.g., of β-galactosidase and β-hexosaminidases, and of GM2-activator protein, cause infantile (with tetraparesis, dementia, blindness) and different protracted clinical forms of GM1- and GM2-gangliosidoses. Mutations yielding proteins with small residual catabolic activities in the lysosome give rise to juvenile and adult clinical forms with a wide range of clinical symptomatology. Apart from patients' differences in their genetic background, clinical heterogeneity may be caused by rather diverse substrate specificities and functions of lysosomal hydrolases, multifunctional properties of SAPs, and the strong regulation of ganglioside catabolism by membrane lipids. Currently, there is no treatment available for neuronal ganglioside storage diseases. Therapeutic approaches in mouse models and patients with juvenile forms of gangliosidoses are discussed.

Ceramides and other bioactive sphingolipid backbones in health and disease: lipidomic analysis, metabolism and roles in membrane structure, dynamics, signaling and autophagy

Sphingolipids are comprised of a backbone sphingoid base that may be phosphorylated, acylated, glycosylated, bridged to various headgroups through phosphodiester linkages, or otherwise modified. Organisms usually contain large numbers of sphingolipid subspecies and knowledge about the types and amounts is imperative because they influence membrane structure, interactions with the extracellular matrix and neighboring cells, vesicular traffic and the formation of specialized structures such as phagosomes and autophagosomes, as well as participate in intracellular and extracellular signaling. Fortunately, "sphingolipidomic" analysis is becoming feasible (at least for important subsets such as all of the backbone "signaling" subspecies: ceramides, ceramide 1-phosphates, sphingoid bases, sphingoid base 1-phosphates, inter alia) using mass spectrometry, and these profiles are revealing many surprises, such as that under certain conditions cells contain significant amounts of "unusual" species: N-mono-, di-, and tri-methyl-sphingoid bases (including N,N-dimethylsphingosine); 3-ketodihydroceramides; N-acetyl-sphingoid bases (C2-ceramides); and dihydroceramides, in the latter case, in very high proportions when cells are treated with the anticancer drug fenretinide (4-hydroxyphenylretinamide). The elevation of DHceramides by fenretinide is befuddling because the 4,5-trans-double bond of ceramide has been thought to be required for biological activity; however, DHceramides induce autophagy and may be important in the regulation of this important cellular process. The complexity of the sphingolipidome is hard to imagine, but one hopes that, when partnered with other systems biology approaches, the causes and consequences of the complexity will explain how these intriguing compounds are involved in almost every aspect of cell behavior and the malfunctions of many diseases.

ESI-MS quantitation of increased sphingomyelin in Niemann-Pick disease type B HDL

HDLs have been proposed to have antiatherogenic properties because of their role in reverse cholesterol transport as lipid acceptors. To elucidate the phospholipid profile of these particles, we used electrospray ionization mass spectrometry to examine the phosphatidylcholine (PC) and sphingomyelin (SM) composition of HDLs purified from plasma and nascently generated in vitro from fibroblasts. We also quantitatively compared the phospholipids present in these lipoproteins between normal and Niemann-Pick disease type B (NPD-B) subjects characterized by sphingomyelinase (SMase) deficiency. We demonstrated that plasma HDLs from NPD-B were significantly enriched in SM by an average of 28%, particularly the palmitoyl SM (with an increase of 95%), which accounted for approximately 25-44% of total SM molecular species. Similarly, we observed an increase of approximately 63% in total SM levels in nascent HDLs prepared from NPD-B fibroblasts. Although PC levels in nascent HDLs were comparable between control and NPD-B cells, there was a 95% increase in total PC levels similar to that of SM in plasma HDLs extracted from NPD-B subjects. These data provide insight into the structure of HDLs and identify potential new roles for SMase in lipoprotein metabolism.

Quantification of Cellular Acid Sphingomyelinase and Galactocerebroside β-Galactosidase Activities by Electrospray Ionization Mass Spectrometry

Background: Diagnosis of Niemann-Pick (A and B) and Krabbe diseases is achieved by measurement of the lysosomal enzymes acid sphingomyelinase (ASM) and galactocerebroside β-galactosidase (GCG), respectively. Conventional assays use radiolabeled or fluorescent substrates and do not allow simultaneous determination of two or more enzymes in the sample.

Methods: We developed a sensitive and specific method to assay ASM and GCG in skin fibroblast homogenates using biotinylated substrate conjugates. The products were purified by bioaffinity capture on streptavidin-agarose beads and, following release, were analyzed by electrospray ionization mass spectrometry. Quantification was achieved using stable-isotope-labeled internal standards that were chemically identical to the products of the enzymatic reactions.

Results: The method demonstrated excellent linearity of ASM and GCG enzymatic product formation with the amount of cellular protein and incubation time. The range of ASM activities in fibroblast lysates from six healthy patients was 39–70 nmol · mg−1 · h−1 compared with 3.7–5.1 nmol · mg−1 · h−1 in cell lysates from two patients affected with Niemann-Pick A disease. The GCG activities toward the corresponding substrate conjugate were 4.0–6.8 nmol · mg−1 · h−1 in cell lysates from healthy patients compared with 0.1–0.2 nmol · mg−1 · h−1 in cell lysates from two patients affected with Krabbe disease. The amounts of substrate conjugates needed per analysis were 15 nmol (14 μg) for both ASM and GCG.

Conclusions: Electrospray mass spectrometry combined with the use of biotinylated substrate conjugates and bioaffinity purification represents a new approach for the diagnosis of lysosomal storage diseases as demonstrated for Niemann-Pick A and Krabbe diseases. No radioactive substrates are used, and the method uses a single instrumental platform to determine both ASM and GCG in one cell sample.

Sphingomyelin-degrading pathways in human cells role in cell signalling

The ubiquitous sphingophospholipid sphingomyelin (SM) can be hydrolysed in human cells to ceramide by different sphingomyelinases (SMases). These enzymes exert a dual role, enabling not only the turnover of membrane SM and the degradation of exogenous (lipoprotein) SM, but also the signal-induced generation of the lipid second messenger ceramide. This review focuses on the function(s) of the different SMases in living cells. While both lysosomal and non-lysosomal pathways that ensure SM hydrolysis in intact cells can be distinguished, the precise contribution of each of these SM-cleaving enzymes to the production of ceramide as a signalling molecule remains to be clarified.

A simple method for screening for Farber disease on cultured skin fibroblasts

Farber disease is an inborn lysosomal storage disorder characterized by accumulation of ceramide in the patient's tissues due to the deficient activity of acid ceramidase. Currently, confirmation of the diagnosis is performed in an extremely limited number of laboratories. We therefore developed a procedure which does not require any particular sphingolipid substrate and is based on the quantitation of ceramide levels in cultured skin fibroblasts. In the method we devised, the ceramide present in cellular lipid extracts subjected to mild alkaline hydrolysis was quantified using the commercially available diacylglycerol kinase kit. We show that both primary cultures of skin fibroblasts and SV40-transformed fibroblasts derived from a series of patients with Farber disease exhibit ceramide excess as compared to their normal counterparts (2345-17 153 pmol/mg cell protein in Farber cells vs. 432-1298 pmol/mg cell protein in controls). Use of this simple method should greatly facilitate the biochemical diagnosis of Farber disease.

Degradation of fluorescent and radiolabelled sphingomyelins in intact cells by a non-lysosomal pathway

The aim of the present study was to investigate the role of the entitled neutral, sphingomyelinase in the non-lysosomal pathway of sphingomyelin degradation by intact cells (Spence et al. (1983) J. Biol. Chem. 258, 8595-8600; Levade et al. (1991) J. Biol. Chem. 266, 13519-13529). The uptake and degradation of sphingomyelin by intact living cells was studied using cell lines exhibiting a wide range of activity levels of acid, lysosomal and neutral sphingomyelinases as determined in vitro on cell homogenates by their respective standard assays. For this purpose, neuroblastoma, skin fibroblasts, lymphoid and leukemic cell lines, some of them derived from patients with Niemann-Pick disease (deficient in the acid, lysosomal sphingomyelinase) were incubated with radioactive, [oleoyl-3H]sphingomyelin or fluorescent, pyrene-sulfonylaminoundecanoyl-sphingomyelin. Either compound was taken up by a pathway which was not receptor-mediated and hydrolyzed by all intact cells, including those derived from Niemann-Pick disease patients. Moreover, their degradation by the intact cells was not inhibited by treatment with chloroquine, indicating hydrolysis by a non-lysosomal sphingomyelinase. The intracellular sphingomyelin degradation rates showed no correlation with the activity of the 'classical' neutral sphingomyelinase as determined in vitro. In particular, fibroblasts derived from Niemann-Pick patients lacking the lysosomal sphingomyelinase, and having no detectable in vitro activity of the 'classical' neutral sphingomyelinase, were able to degrade the exogenously supplied sphingomyelins. Indeed, in vitro these cells were shown to exhibit neutral, magnesium- and dithiothreitol-dependent sphingomyelinase activities, that might contribute to the non-lysosomal pathway for sphingomyelin degradation to ceramide in intact cells.

Formation of bioactive sphingoid molecules from exogenous sphingomyelin in primary cultures of neurons and astrocytes

Exogenous sphingomyelin, radiolabelled at the sphingosine moiety, was administered to primary cultures of cerebellar granule cells and astrocytes for different pulse times (20 min-2 h) and the fate of the radioactivity was followed. Ceramide was the main metabolic product in both cells, whereas sphingosine, glucosyl-ceramide and gangliosides GM3 and GD3 were produced only in astrocytes. When endocytosis was prevented and the lysosomal apparatus inactivated, ceramide formation was reduced slightly in granule cells and almost completely blocked in astrocytes, with disappearance of sphingosine, glucosyl-ceramide, GM3 and GD3. These data indicate that (a) ceramide is rapidly produced in cerebellar granule cells and astrocytes, presumably at the level of the plasma membrane in the first cell type, and of the lysosomes in the second one; (b) sphingosine is produced in cerebellar astrocytes by lysosomal sphingomyelin degradation and is partly reused for glucosyl-ceramide and ganglioside biosynthesis.

A family with visceral course of Niemann-Pick disease, macular halo syndrome and low sphingomyelin degradation rate

We report a family with six patients suffering from a sphingomyelinase-deficient form of Niemann-Pick disease, all presenting with a visceral course of the disease. Retinal changes classified as macular halos in four members indicated neuronal storage and therefore an intermediate type of the disease. For further classification of the biochemical type, [choline-methyl-14C]sphingomyelin degradation studies were carried out in fibroblast cultures of all six members. The low degradation rates measured were similar to those usually found in the neuronopathic form (type A) of Niemann-Pick disease. This family illustrates the broad heterogeneity within the sphingomyelinase deficiency group of the Niemann-Pick disease. Apparently the finding of a low sphingomyelin degradation rate in fibroblast cultures does not necessarily imply a typical serious and lethal course of the disease.

Deletion of arginine (608) in acid sphingomyelinase is the prevalent mutation among Niemann-Pick disease type B patients from northern Africa

There is a high incidence of Niemann-Pick type B disease in the Maghreb region of North Africa, which includes Morocco, Algeria and Tunisia. A hypothesis that there may well be a common, predominant mutant acid sphingomyelinase allele responsible for the type B phenotype in this population has been tested. A deletion of an arginine codon at amino acid residue 608 was found in one patient. The same mutation was also observed in another of our cases. An original screening procedure using 3'-end digoxigenin-labeled allele-specific oligonucleotides and chemiluminescent detection was developed and used parallel to the conventional assay with 5'-end radiolabeled oligonucleotides. Of the 15 non-related, non-Jewish North African type B patients studied, 12 were homozygous and two compound heterozygous for this deletion (26 delta R608 alleles/30 mutant alleles). Among type B patients from other geographic regions (France, UK, Italy, Czechoslovakia), this mutation was observed in only one of the 16 alleles studied. Our results indicate that deletion of arginine 608 in the acid sphingomyelinase gene is the highly prevalent mutation underlying Niemann-Pick type B disease in the population of Maghreb. A varying severity of the clinical and enzymatic expression within the non-neuronopathic phenotype has however been observed in patients homozygous for the mutation.

Metabolic effects of short-chain ceramide and glucosylceramide on sphingolipids and protein kinase C

Recent studies have identified a potential role for glucosylceramide (GlcCer) in growth promotion and hormonal signalling. In an effort to demonstrate a growth-promoting activity of GlcCer, we prepared a GlcCer having a short-chain acid (octanoyl), in the belief that this glycolipid could be absorbed more readily and more uniformly by cultured cells. By using a mixture of two specific lecithins, dioleoylglycerophosphocholine and 1-stearoyl-2-palmitoylglycerophosphocholine, we were able to prepare dispersions containing a high molar proportion of the GlcCer and the related ceramide, octanoyl sphingosine. Unexpectedly, both sphingolipids inhibited protein and DNA synthesis in Madin-Darby canine kidney cells and produced large increases in the levels of the natural lipids, GlcCer, ceramide, free sphingosine, and an amine that may be glucosylsphingosine (GlcSph). Decreases were seen in the level of sphingomyelin and the proportion of protein kinase C in the cell membranes. The level of lactosylceramide was diminished by octanoyl GlcCer but elevated considerably by octanoyl sphingosine. Diacylglycerols were increased by the lecithins in the liposomes, but the exogenous sphingolipids had no effect. Octanoyl sphingosine labeled in the sphingoid base yielded labeled GlcCer and sphingomyelin labeled in both long-chain and very-long-chain fatty acid families, as well as the octanoyl version. The two families of ceramides, however, had relatively little radioactivity. Some of these changes are attributed to rapid hydrolysis of the added lipids with the formation, particularly from the ceramide, of sphingosine and its anabolic metabolite, GlcSph. Several observations support the idea that the octanoyl sphingosine inhibited the phosphocholinetransferase that synthesizes sphingomyelin while the octanoyl GlcCer inhibited GlcCer beta-glucosidase and GlcCer galactosyltransferase. The use of unnatural short-chain lipids in the study of cell growth and other phenomena may result in unexpected changes in related metabolites and the findings from such experiments should therefore be interpreted cautiously.

Variation of choline-substituted lipid metabolism in doxorubicin-resistant leukemia cells

In adriamycin-resistant murine (FLC) and human (K562) leukemia cells, phosphatidylcholine increases and phosphatidylethanolamine decreases compared to adriamycin-sensitive lines. This change is due to an increase in phosphatidylethanolamine methylation. The choline pathway of phosphatidylcholine biosynthesis is also disturbed in resistant cells with a blocking step of CDP-phosphocholine transferase and a decrease in sphingomyelinase activity. These changes in phospholipid metabolism are suggested to be responsible for the changes in membrane fluidity reported previously (Tapiero et al, 1986) for resistant cells.

Administration of pyrene lipids by receptor-mediated endocytosis and their degradation in skin fibroblasts

Sphingomyelin and seven glycosphingolipids were labeled with the fluorescent probe pyrene and administered into cultured fibroblasts by receptor-mediated endocytosis. For this purpose pyrene sphingomyelin or mixtures of pyrene glycolipid and unlabeled sphingomyelin were dispersed as small, unilamellar liposomes. Apolipoprotein E was then added and the receptor for this ligand on the cell surface was utilized for uptake of the liposomes and their transport to the lysosomes, where the respective pyrene lipids were degraded. Following incubation with each of the respective pyrene lipids, only the administered compound and the pyrene ceramide were present; intermediate hydrolysis products were not detected. This indicated that, in skin fibroblasts, the lysosomal ceramidase was limiting and controlled the rate of total degradation of the pyrene sphingolipids.

Type C Niemann-Pick disease: spectrum of phenotypic variation in disruption of intracellular LDL-derived cholesterol processing

To investigate biochemical heterogeneity within Niemann-Pick type C disease (NPC), the two most characteristic abnormalities, namely (1) kinetics of LDL-stimulated cholesteryl ester formation and (2) intravesicular accumulation of LDL-derived unesterified cholesterol, evaluated by histochemical filipin staining, were studied in cultured skin fibroblasts from a population of 125 NPC patients. Profound alterations (esterification rates less than 10% of normal, very numerous and intensely fluorescent cholesterol-filipin granules) were demonstrated in 86% of the cases, depicting the 'classical' NPC phenotype. The remaining cell lines showed a graded less severe impairment and more transient delay in the induction of LDL-mediated cholesteryl esterification, along with an attenuated accumulation of unesterified cholesterol. In particular, cells from a small group (7%) of patients, which have been individualized as representative of a 'variant' phenotype, showed only slight alterations of esterification, restricted to the early phase of LDL uptake and undistinguishable from those in heterozygotes. In these cells, an abnormal cytochemical distribution of LDL-derived cholesterol, although moderate, was still evident provided rigorous experimental conditions were followed. A third, less clearly individualized group (7%), differing from the classical phenotype mostly by higher rates of cholesteryl ester formation, has been designated as an 'intermediary' phenotype to reflect a more difficult diagnosis of such patients. These findings have an important bearing with regard to diagnosis and genetic counselling, although the significance of such a phenotypic variation in terms of genetic heterogeneity has still to be demonstrated. A given biochemical phenotype was however a constant observation within a family (14 pairs of siblings tested so far). The unique feature of LDL-cholesterol processing alterations in NPC has been further established from comparative studies in Wolman disease and I-cell disease, showing normal or different intracellular distribution of unesterified LDL-derived cholesterol in the latter disorders. Correlation between biochemical and clinical NPC phenotypes was only partial, but a correlation between the severity of alterations in cholesterol processing and sphingomyelin catabolism could be established.

Uptake and degradation of several pyrenesphingomyelins by skin fibroblasts from control subjects and patients with Niemann-Pick disease. Effect of the structure of the fluorescent fatty acyl residue

Three fluorescent analogues of sphingomyelin (SPM), each containing pyrene in the fatty acyl residue, were synthesized and employed for the study of their mode of uptake by, and degradation within, intact cultured human skin fibroblasts. These were prepared by condensing sphingosylphosphocholine and the following fatty acids: pyrenedodecanoic acid (P12), pyrenesulphonylaminoundecanoic acid (PSA11) and pyrenepropenoic acid (P3:1). The cell association and catabolism of these SPM analogues by normal, Niemann-Pick-disease-Type-A and low-density-lipoprotein (LDL)-receptor-negative familial hypercholesterolaemia fibroblasts were investigated and compared with the metabolism of [cholinemethyl-14C]sphingomyelin. The catabolism of the fluorescent derivatives was monitored by measuring the appearance of the corresponding fluorescent ceramides. Two modes of uptake and degradation patterns were observed. Thus P12-SPM and radiolabelled SPM were taken up by LDL-receptor-mediated endocytosis when incubated with serum-containing medium, this conclusion being supported by the very low uptake by familial-hypercholesterolaemia fibroblasts, which lack the apolipoprotein-B/E receptor. After uptake, these compounds were metabolically degraded solely by the lysosomal sphingomyelinase, as evidenced by the fact that more than 98% of the SPM remained undegraded in Niemann-Pick-disease cells. By contrast, PSA11- and P3:1-SPMs were taken up by a receptor-independent endocytic pathway, as indicated by the similar rates of uptake in control and familial-hypercholesterolaemia cells in the absence or presence of fetal-calf serum in the culture medium. The degradation of PSA11-SPM and P3:1-SPM was brought about, in the main, by the lysosomal sphingomyelinase, but also by a yet uncharacterized process. The latter catabolic pathway, active in Niemann-Pick-disease-Type-A fibroblasts, seems to differ from the neutral Mg2(+)-dependent sphingomyelinase whose activity was undetectable in homogenates of skin fibroblasts. The present study emphasizes the influence of the structure of the fatty acyl moiety of SPM on its association with lipoproteins and/or cell membranes and on its intracellular routing and metabolic degradation.

Uptake and metabolism of radiolabelled GM1-ganglioside in skin fibroblasts from controls and patients with GM1-gangliosidosis

The uptake and metabolism of [3-3H-sphingosine]GM1-ganglioside was measured in cultured skin fibroblasts from controls and patients with infantile, juvenile and adult GM1-gangliosidosis. When dissolved in medium with phosphatidylserine, GM1-ganglioside was efficiently taken up by cultured skin fibroblasts and transferred into lysosomes. A linear increase in GM1-ganglioside endocytosis was shown with phosphatidylserine concentrations of up to 40 micrograms/ml. A pulse-chase study revealed that [3H]GM1-ganglioside was metabolized to GM2-ganglioside, GM3-ganglioside, ceramide dihexoside, ceramide monohexoside, ceramide and sphingosine. Sphingosine was recycled to sphingomyelin. In a 20-h pulse study, cell lines from patients with GM1-gangliosidosis of infantile, juvenile and adult types hydrolysed 2-5%, 20-44% and 54-58% of the total endocytosed GM1-ganglioside respectively. These values were lower than in control cells (64.17 +/- 5.43% (n = 10]. The hydrolysis rates of exogenous [3H]GM1-ganglioside in cultured fibroblasts from patients with various types of GM1-gangliosidosis closely reflected the clinical severity.

Sorting of an internalized plasma membrane lipid between recycling and degradative pathways in normal and Niemann-Pick, type A fibroblasts

We examined the metabolism and intracellular transport of a fluorescent sphingomyelin analogue, N-(N-[6-[(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]caproyl])- sphingosylphosphorylcholine (C6-NBD-SM), in both normal and Niemann-Pick, type A (NP-A) human skin fibroblast monolayers. C6-NBD-SM was integrated into the plasma membrane bilayer by transfer of C6-NBD-SM monomers from liposomes to cells at 7 degrees C. The cells were washed, and within 3 min of warming to 37 degrees C, both normal and NP-A fibroblasts had internalized C6-NBD-SM from the plasma membrane, resulting in a punctate pattern of intracellular fluorescence. Rates for C6-NBD-SM internalization and transport from intracellular compartments to the plasma membrane (recycling) were similar for normal and NP-A cells. With increasing time at 37 degrees C, internalized C6-NBD-SM accumulated in the lysosomes of NP-A fibroblasts, while normal fibroblasts showed increasing Golgi apparatus fluorescence with no observable lysosomal labeling. Since NP-A fibroblasts lack lysosomal (acid) sphingomyelinase (A-SMase), this result suggested that hydrolysis of C6-NBD-SM prevented its accumulation in the lysosomes of normal fibroblasts during its transport along the degradative pathway. We used the amount of C6-NBD-SM hydrolysis by A-SMase in normal cells as a measure of C6-NBD-SM transported from the cell surface to the lysosomes. After a lag period, C6-NBD-SM was delivered to the lysosomes at a rate of approximately 8%/h. This rate was approximately 18-19 fold slower than the rate of C6-NBD-SM recycling from intracellular compartments to the plasma membrane. Thus, small amounts of C6-NBD-SM were transported along the degradative pathway, while most endocytosed C6-NBD-SM was sorted for transport along the plasma membrane recycling pathway.

The role of sphingomyelin in phosphatidylcholine metabolism in cultured human fibroblasts from control and sphingomyelin lipidosis patients and in Chinese hamster ovary cells

Human fibroblasts in culture take up exogenous [choline-Me-3H,32P]sphingomyelin (SM) from the medium and incorporate it into cellular SM and phosphatidylcholine [Spence, Clarke & Cook (1983) J. Biol. Chem. 258, 8595-8600]. The ratio of [3H]choline/[32P]Pi is similar in SM and phosphatidylcholine, indicating that the phosphocholine (P-Cho) moiety is transferred intact. Similar results are obtained with Niemann-Pick (NP) cells which are deficient in lysosomal sphingomyelinase activity, suggesting that the P-Cho transfer may not be mediated by the lysosomal sphingomyelinase and that alternative pathways of sphingomyelin catabolism are present in cultured cells. In this study we have shown that: (1) the P-Cho pool in control and NP cells incubated with exogenous labelled SM has a specific radioactivity intermediate between that of SM and PtdCho; (2) expansion of the intracellular P-Cho pool by incubation with exogenous choline reduces the incorporation of [3H]choline from SM into PtdCho; and (3) incorporation of P-Cho from SM into PtdCho is decreased at the non-permissive temperature in Chinese hamster ovary cells with a temperature-sensitive mutation in the cytidylyltransferase reaction. These results suggest that incorporation of P-Cho from SM into PtdCho involves a reaction sequence in which P-Cho is hydrolysed from SM by a sphingomyelinase, followed by incorporation of P-Cho into PtdCho via the cytidine pathway of biosynthesis (SM----P-Cho----CDP-Cho----PtdCho). The appreciable incorporation of P-Cho from SM into PtdCho in sphingomyelinase-deficient NP cells suggests a more substantial or effective lysosomal sphingomyelinase activity in intact cells than is measured in vitro, and/or a significant contribution by other sphingomyelinase activities in these cells.

An update of the enzymology and regulation of sphingomyelin metabolism

Sphingomyelin is found in plasma membranes and related organelles (such as endocytic vesicles and lysosomes) of all tissues, as well as in lipoproteins. Abnormalities in sphingomyelin metabolism have been associated with atherosclerosis, cancer and genetically transmitted diseases; however, except for Niemann-Pick disease, little is known about the mechanism for these disorders. Sphingomyelin biosynthesis de novo involves ceramide formation from serine and two mol of fatty acyl-CoA followed by addition of the phosphocholine headgroup. The headgroup appears to come from phosphatidylcholine, but other sources have not been ruled out. Factors that influence the rate of sphingomyelin synthesis include the availability of serine and palmitic acid, plus the relative activities of key enzymes of this pathway. Sphingomyelin turnover involves removal of the headgroup and amide-linked fatty acid by sphingomyelinases and ceramidases, respectively, which have been found in both lysosomes (with acidic pH optima) and plasma membranes (with neutral to alkaline pH optima). The enzymes of sphingomyelin turnover release ceramide and free sphingosine from endogenous substrates, which may have implications for the participation of a sphingomyelin/sphingosine cycle as another 'lipid second messenger' system.

Time-course of utilization of [stearic or lignoceric acid]sphingomyelin from high-density lipoprotein by rat tissues

Utilization of stearic and lignoceric acids supplied by high-density lipoprotein (HDL) sphingomyelin to different tissues was followed for 24 h after rats were injected with HDL containing [[1-14C]stearic (18:0) or [1-14C]lignoceric (24:0) acid [Me-3H]choline]sphingomyelin. Both isotopes reached a maximum in tissue lipids 3-12 h after injection and were recovered mainly in the liver (30%) and small intestine (3%), whereas the other tissues contained approx. 1% or less of the injected dose. All the tissues were able to take up some intact sphingomyelin from HDL and hydrolyze it. In the lung and erythrocytes, the 3H:14C ratio of sphingomyelin remained unchanged throughout the studied period, while an increase in the isotopic ratio was observed in the kidney due to the 3H choline moiety re-used for synthesis of new sphingomyelin. Conversely, the isotopic ratio of sphingomyelin decreased in the liver, indicating a saving of the 14C-labelled fatty acids, especially 24:0. Furthermore, [24:0]ceramide in the liver remained at a high level (6% of the injected dose), whereas [18:0]ceramide decreased to 1%. When the tissues were examined 24 h after injection, the proportion of the 14C linked to sphingomyelin in the total 14C was always higher for both kinds of sphingomyelin than the molar proportion of sphingomyelin in the whole of lipid classes. However, in the majority of the extra-hepatic tissues, more [14C]18:0 than [14C]24:0 was recovered in sphingomyelin, and more 14C radioactivity from 18:0 than from 24:0 was redistributed in the other lipids. The choline moiety from both kinds of sphingomyelin was re-used to synthesize phosphatidylcholine, especially in the liver (up to 20% of the injected dose). All these results show that utilization of sphingomyelin from HDL by tissues normally occurs in vivo and that this phenomenon should be taken into account in the study of the phospholipid turnover of cell membranes. They also show that metabolism of sphingomyelin from HDL in the liver and other tissues is dependent on the sphingomyelin acyl moiety.

Uptake and utilization of double-labeled high-density lipoprotein sphingomyelin in isolated brain capillaries of adult rats

Isolated rat brain capillaries were incubated in the presence of high-density lipoprotein (HDL) containing [stearic acid-14C, (methyl-3H)choline]sphingomyelin. This double-labeled sphingomyelin was taken up in a concentration-dependent manner. Cerebral capillary-associated sphingomyelin had a 3H/14C ratio close to that of the incubation medium, a result indicating uptake of sphingomyelin without prior hydrolysis. TLC of lipid extracted from capillaries showed that part of the sphingomyelin (up to 40%) was hydrolyzed in the brain capillaries to ceramide and free fatty acids. The hydrolysis was proportional to the amount of incorporated sphingomyelin and reached a plateau when the HDL sphingomyelin concentration in the medium was 237 nmol/ml. The results of "pulse-chase" experiments showed that the choline moiety of sphingomyelin was recovered in the incubation medium after the chase period and that there was no redistribution of liberated choline in phosphatidyl-choline of capillaries.

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.

Utilization of high-density lipoprotein sphingomyelin by the developing and mature brain in the rat

Utilization of very long chain saturated fatty acids by brain was studied by injecting 20-day-old and adult rats with high-density lipoprotein containing [stearic or lignoceric acid-14C, (methyl-3H)choline]sphingomyelin. Labeling was followed for 24 h. Very small amounts of 14C were recovered in the brain of all rats, and there was no preferential uptake of lignoceric acid. Approximately 20% of the entrapped 14C was located in the form of unchanged sphingomyelin 24 h after injection. This result shows that the rat brain utilizes very little very long chain fatty acids (greater than or equal to 20 C atoms) from high-density lipoprotein sphingomyelin, even during the myelinating period. The [3H]choline moiety from sphingomyelin was recovered in brain phosphatidylcholine in a higher proportion in comparison with the 14C uptake. The brain 3H increased throughout the studied period in all experiments, but was much higher in the myelinating brain than in the mature brain. From the radioactivity distribution in liver and plasma lipids, it is clear that the choline 3H in the brain originates from either double-labeled phosphatidylcholine of lipoproteins or tritiated lysophosphatidylcholine bound to albumin, both synthesized by the liver.

Niemann-Pick disease group C: clinical variability and diagnosis based on defective cholesterol esterification. A collaborative study on 70 patients

Seventy patients were selected to cover the range of variability in clinical expression of Niemann-Pick disease group C (NP-C). Their individual main clinical features and course of the disease (age at discovery and type of visceromegaly, age at onset and first neurological manifestation, later neurological symptoms) are schematically described. In cultured skin fibroblasts from these patients, sphingomyelinase activities measured in vitro showed decreased values only in approximately half of the cases, and when the metabolic fate of [14C]-sphingomyelin was studied in living cell cultures, still 20% of the cases had a normal hydrolysis rate. Esterification of exogenous cholesterol was investigated in cell lines from these and 5 additional patients and in 21 of their parents. Using a non-lipoprotein [3H]cholesterol source, very low esterification rates were obtained in more than 90% of the cases. All the numerous other pathological conditions studied, including Niemann-Pick disease types A and B, gave normal results. A more sensitive method was elaborated, in which the cells were challenged with pure human low density lipoproteins (LDL) and the early rate of esterification studied. With the latter procedure, a pronounced deficiency could also be demonstrated in the few cases which had shown a milder impairment using a [3H]cholesterol source, and intermediate rates of esterification were obtained in heterozygotes. Discrimination of these difficult cases and of heterozygotes could also be achieved replacing LDL with total unfrozen human serum. Correlations were established between given clinical phenotypes and the severity of the biochemical lesion. Defective intracellular cholesterol esterification is further established as an intrinsic feature of NP-C, and demonstration of this metabolic alteration appears as a major advance in diagnosing the condition.

Turnover and uptake of double-labelled high-density lipoprotein sphingomyelin in the adult rat

Rat HDL containing [stearic acid-14C, (methyl-3H)choline]sphingomyelin was prepared by incubating labelled sphingomyelin liposomes with serum. HDL was then separated by ultracentrifugation and purified by gel-filtration chromatography. The maximum transfer was reached when 1.5 microliter sphingomyelin was incubated in the presence of 1 ml of serum at 37 degrees C for 1 h. When transfer was limited to a 5-7% increase in HDL mass, no significant change was observed in the HDL electrophoretic pattern, and rats could therefore be injected with this type of HDL under physiological conditions. Plasma radioactivity decay was followed for 24 h, and the recovery of both isotopes in 11 tissues was studied 24 h after the injection. The decay in plasma of both isotopes followed three exponential phases. During the first two phases, both isotopes disappeared with the same velocity (t1/2 = 12.8 and 98-105 min for the first and second phases, respectively). 10 h after injection, 3H had disappeared more slowly than 14C (t1/2 = 862 and 502 min for 3H and 14C, respectively) and 24 h after injection, only 1.5% of 14C and 2.5% of 3H remained in the plasma. This radioactivity was located mainly in HDL (80-85% for 3H and 14C), with a 3H/14C ratio close to that of injected sphingomyelin, and in VLDL, with the same isotopic ratio as that of liver lipids. Some 3H was associated with non-lipoprotein proteins. 17.5% of 3H and 23.4% of 14C were recovered in the liver, 1.6% of each isotope in erythrocytes, and 1.4% of 3H and 0.6% of 14C in kidney. Less than 1% of each isotope was recovered in each of the other tissues. Phosphatidylcholine was the lipid most labelled, and in several tissues sphingomyelin had a 3H/14C ratio close to that of injected sphingomyelin, showing an uptake without prior hydrolysis.

Evidence for both endogenous and exogenous sources of the sphingomyelin storage in lymphoid cell lines from patients with Niemann-Pick disease types A and B

Epstein-Barr virus-transformed lymphoid cell lines from normal individuals and from patients with Niemann-Pick disease types A, B or C were subjected to various culture conditions in order to study the source of the characteristic lysosomal storage of sphingomyelin observed in the tissues of Niemann-Pick patients. The culture medium was supplemented with a serum substitute devoid of lipoproteins or with one of the following lipid sources: fetal calf serum, human low-density lipoprotein (LDL), or human high-density lipoprotein (HDL). Storage of sphingomyelin was demonstrated under all tested culture conditions in cells deficient in acid sphingomyelinase (Niemann-Pick disease types A and B). In contrast, the sphingomyelin concentration in the lymphoid cell line from a Niemann-Pick type C patient (not deficient in sphingomyelinase) was normal. After more than 30 days in a medium devoid of sphingomyelin, the Niemann-Pick types A and B lymphoid cell lines showed accumulation of sphingomyelin about twice control. The concentrations was higher when cells were grown in a medium supplemented with lipids, particularly human LDL or HDL. These results are consistent with the hypothesis that both exogenous and endogenous sphingomyelins participate in the lysosomal storage observed in lymphoid cell lines from patients with Niemann-Pick disease types A and B.

Uptake and intracellular degradation of fluorescent sphingomyelin by fibroblasts from normal individuals and a patient with Niemann-Pick disease

Sphingomyelin, labelled with a fluorescent probe, pyrene, in the fatty acyl residue was associated with fetal calf serum; approx. 80% of the sphingomyelin was found in the low- and high-density lipoproteins. This was added to the growth medium of cultured human skin fibroblasts from normal individuals and a patient with Niemann-Pick disease type A, devoid of acid sphingomyelinase activity. The fluorescent sphingomyelin was taken up by both cell types, but only the former degraded it to produce fluorescent ceramide. Differences between normal and Niemann-Pick cells in sphingomyelin content or ceramide production were observed after several hours uptake. A more pronounced difference was noted when cells were incubated for 1 day with fluorescent sphingomyelin and then for two to three days in medium devoid of this compound. Under these conditions, the fluorescence intensity of the Niemann-Pick cells remained practically constant while that of their normal counterparts was almost completely eliminated from the cells. Comparison of fluorescence intensities of these two cell types could be made directly on aqueous suspensions of whole cells or, alternatively, on their lipid extracts. For evaluation of the degradation of fluorescent sphingomyelin to ceramide within the cells, several procedures were developed for the rapid isolation of the latter compound from the total lipid extract. The results suggest that when associated with the constituents of the fetal calf serum, sphingomyelin is taken up by the cells and transported into the lysosomal compartment where it is degraded to ceramide. Use of the fluorescent derivative of sphingomyelin provided a simple and rapid procedure for following the uptake by and degradation within the cultured cells. It also permitted the establishment of differences in the rates of degradation of the fluorescent sphingomyelin by cells with a normal metabolism and others lacking sphingomyelinase (i.e., Niemann-Pick disease type A cells).

Biosynthesis and maturation of glucocerebrosidase in Gaucher fibroblasts

The biosynthesis and maturation of glucocerebrosidase were studied in fibroblasts from patients with the neurological and non-neurological forms of Gaucher disease and in control cells. In control fibroblasts the precursor of glucocerebrosidase (62-63 kDa), observed after a short pulse with [35S]methionine, was converted during the chase period to a 66-kDa intermediate form and, finally, to the 59-kDa mature protein. In fibroblasts from patients with the non-neurological phenotype of Gaucher disease (type 1) the same biosynthetic forms were seen as in control fibroblasts. These biosynthetic forms correspond to the three-banded pattern seen in control and Gaucher type 1 fibroblast extracts analysed by the immunoblotting procedure, or after electrophoresis and fluorography of extracts of such fibroblasts cultured for 5 days with [14C]leucine. The 59-kDa protein seen in type 1 fibroblasts was unstable and disappeared after a prolonged chase; this disappearance was not observed when the cells were grown in the presence of leupeptin. In fibroblasts from patients with the neurological forms of Gaucher disease (types 2 and 3) the 62.5-kDa precursor of glucocerebrosidase was present in near-normal amounts after a short pulse, but the 59-kDa form was not detected even when cells were cultured with leupeptin. These results are in accordance with the absence of the 59-kDa band in immunoblots of types 2 and 3 fibroblast extracts. Culturing of type 1, type 2 and type 3 Gaucher fibroblasts in the presence of leupeptin led to an increase in the activity of glucocerebrosidase.

Biochemical and ultrastructural studies on an Epstein-Barr virus-transformed lymphoid cell line from a Niemann-Pick disease type C patient

Human lymphoid cell lines established from normal subjects and from a Niemann-Pick disease type C patient were investigated from a triple point of view of enzymology, metabolism and ultrastructure: Sphingomyelinase activities, isoenzyme electrofocusing profiles and properties of the major enzyme were quite similar in type C and normal lymphoid cell lines. Similarly, no significant difference was observed in non-specific phosphodiesterases hydrolysing bis(methylumbelliferyl)phosphate and bis(methylumbelliferyl)pyrophosphate. The study of the lipid composition of type C cells showed no obvious accumulation of sphingomyelin or other phospholipid, but only a higher amount of glycolipids (mainly GlcCer and GbOse3Cer), as visualized by bidimensional thin-layer chromatography. Ultrastructural studies demonstrated, in type C cells, the presence of an obvious lysosomal storage of amphiphilic lipids quite similar to that observed in tissues of type C patients. These studies, which demonstrate the validity of lymphoid cell lines as an experimental model system for type C disease, agree with the current opinion that an impairment of sphingomyelin catabolism is not the primary defect in type C disease.

Phospholipids in inflammatory synovial effusions

The concentration of phospholipids and proteins was determined in 23 inflammatory synovial fluids obtained from human knee joints. The synovial fluid to plasma phospholipid ratio (0.48 and 0.37 at high and low inflammatory state) was lower than the value found for the total protein content (0.68 and 0.53, respectively) indicating that phospholipids were more discriminated than proteins in their transfer from plasma to the synovial space. Constant amounts of phosphatidylinositol were found in all synovial fluids, whereas trace amounts of lysophosphatidylethanolamine and phosphatidylserine were more frequent in the active inflammatory state. A decrease in the relative amounts of phosphatidylcholine and phosphatidylinositol with respect to plasma suggested the possibility of phospholipid hydrolysis in the synovial compartment. In agreement, determinations of phospholipase activity disclosed the presence of a phospholipase A2 in the fluid phase of synovial effusions. Phospholipid derivatives formed in the synovial space may thus contribute to the amplification of the inflammatory response.

Modifications of sphingomyelin and phosphatidylcholine metabolism by tricyclic antidepressants and phenothiazines

Phenothiazines and tricyclic antidepressants, when added to culture medium, gave rise in several types of cells (C6 rat glioma cells and human fibroblasts), to a decrease in lysosomal sphingomyelinase activity. The effect of chlorpromazine and desipramine was dose dependent, and was observed after 3 hours of incubation with the drugs at concentrations ranging between 1 and 10 microM. In C6 glioma cell cultures, the decrease in sphingomyelinase activity was related to the clinical effectiveness of phenothiazines, tricyclic antidepressants and derivatives. Incorporation of (choline-14C) sphingomyelin showed that the metabolic pathway implying the synthesis of phosphatidylcholine from the hydrolysis of sphingomyelin and/or transfer of phosphorylcholine to phosphatidylcholine was also partially reduced.

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.

A new variant of sphingomyelinase deficiency (Niemann-Pick): visceromegaly, minimal neurological lesions and low in vivo degradation rate of sphingomyelin

Three males (aged 10 years, 3 years 9 months and 2 years 8 months) with profound sphingomyelinase deficiency are presented. The sphingomyelin storage in the liver biopsies attained 30-fold, 65-fold and 16-fold increases against controls, respectively. Levels of bis(monoacylglyceryl) phosphate were also increased. In two cases the bone marrow contained foam cells with liquid crystals of sphingomyelin. Besides the visceral involvement dominated by hepatosplenomegaly, all three cases showed discrete, so far stationary (8 years, 42 months and 28 months) neuropathic features and retinal lesions resembling the classical cherry-red spot. Electrophysiological examinations showed a variable reduction of peripheral nerve conduction velocity and prolongation of the latencies of somatosensory, visual and auditory evoked potentials. Ultrastructural examination of skin nerves showed a slight storage, mainly in Schwann cells. In some myelinated fibres there were pseudomyelinic ovoids. The cases therefore displayed features of both A and B types of sphingomyelinase deficiency and should be conventionally classified as intermediate. However, the very low levels of in vivo sphingomyelin hydrolysis (not exceeding 6%, against 30 +/- 10% in type B and 77 +/- 5% in controls) were clearly within the range of type A values (5 +/- 2%). Accordingly, we suggest that the cases may be biochemically classified as variants of type A disease.

Niemann-Pick disease type C. Study on the nature of the cerebral storage process

A complex neuropathological study of two cases of Niemann-Pick disease (NPD) type C (NPDC) revealed some novel features in the chemical pathology of the neuronal storage. Lipid histochemistry showed the presence of a lipid which met the criteria of a neuronal glycosphingolipid. Sphingomyelin (SM) was not detected in the neurones in any of the regions examined. Lipid chemical analysis of total extracts and of partially purified lysosomal fraction of the brain cortex showed markedly increased levels of neutral ceramide hexosides especially of glucosylceramide and ceramide dihexoside (mostly of its slower band). Phospholipids were not significantly increased. Monosialogangliosides GM2 and GM3 were increased only slightly. The storage process displayed the well known fine structure and was accompanied by a marked secondary increase in some lysosomal enzyme activities. There was neuroaxonal dystrophy (NAD) of considerable intensity and extent. Many spheroids contained masses of degenerated organelles and neurofilaments in various proportions and displayed variable activities of acid phosphatase, nonspecific esterase and dehydrogenases. There was marked brain atrophy accompanied in one case by severe demyelination. Enzyme studies revealed partial decrease of sphingomyelinase (SMase) and beta-glucosidase activities in cultured fibroblasts, as well as lack of cathodic SMase activity on isoelectric focusing. No defects of these enzymes were found in the brain samples. The findings are regarded as significant since they indicate a biochemical defect in which SM is not primarily involved and which may thus be fundamentally different from that in type A of NPD.

A defect in cholesterol esterification in Niemann-Pick disease (type C) patients

The demonstration of a defect of cholesterol esterification in a mutant strain of BALB/c mice with an attendant reduction of sphingomyelinase activity [Pentchev, P. G., Boothe, A. D., Kruth, H.S., Weintroub, H., Stivers, J. & Brady, R. O. (1984) J. Biol. Chem. 259, 5784-5791] prompted us to examine the capacity of cultured human Niemann-Pick fibroblasts to esterify exogenously derived cholesterol. Cholesterol was supplied to cell cultures in the form of native or chemically modified, positively charged low density lipoprotein or as non-lipoprotein cholesterol. Cholesterol esterification was not impaired in cell cultures derived from patients with type A or B Niemann-Pick disease. However, esterification of exogenously administered cholesterol was deficient in 20 type C Niemann-Pick cell lines that were available for testing. Fluorescence histochemical staining of unesterified cholesterol in type C cells suggested that these cells were able to internalize and lysosomally process lipoprotein cholesterol. Acyl-CoA:cholesterol acyltransferase activity did not appear deficient in type C cell extracts. The error in cholesterol esterification may provide an opportunity for probing the molecular lesion in this disorder and may afford a useful and reliable means for establishing diagnosis.

Molecular forms of sphingomyelinase and non-specific phosphodiesterases in Epstein-Barr virus-transformed lymphoid cell lines from Niemann-Pick disease types A and B

Molecular forms of sphingomyelinase and phosphodiesterases from lymphocytes- and Epstein-Barr virus-transformed lymphoid cell lines were separated by preparative electrofocusing in granulated gels. In either type of cell derived from normal individuals, sphingomyelinase focused as a single peak (pI = 5.60 +/- 0.1) while phosphodiesterases hydrolyzing bis(4-methylumbelliferyl)phosphate and bis(4-methylumbelliferyl)diphosphate separated into seven and three molecular forms respectively; one of the latter showed sphingomyelinase as well as phosphodiesterase activities. Lymphoid cell lines derived from patients with Niemann-Pick disease, types A or B, were practically devoid of sphingomyelinase activity; this was not so for the phosphodiesterases which focussed essentially as normal. The protein peak, which in normal cells contained the three activities, had phosphodiesterase but no sphingomyelinase activity in the Niemann-Pick cells. In normal cells, sphingomyelinase and phosphodiesterase activities of this peak showed different responses to heating and several effectors. These data suggest that in lymphoid cell lines, which are a useful model for studies of Niemann-Pick disease, sphingomyelinase and phosphodiesterases are subject to separate genetic coding and that the latter activities are not a reliable measure for diagnosing Niemann-Pick disease.

Studies on a sphingolipid activator protein (SAP-2) in fibroblasts from patients with lysosomal storage diseases, including Niemann-Pick disease Type C

Sphingolipid activator protein-2 (SAP-2) has been found to stimulate the enzymatic hydrolysis of at least three sphingolipids, glucosylceramide, galactosylceramide and sphingomyelin. Using monospecific antibodies against SAP-2 the level of SAP-2 was determined in cultured skin fibroblasts by rocket immunoelectrophoresis. Extracts from 14 controls had 1.03 +/- 0.28 micrograms cross-reactive material/mg solubilized protein and extracts from 46 patients with Niemann-Pick disease Type C had 1.12 +/- 0.26. Extracts from other lysosomal storage diseases, including Gaucher disease, Krabbe disease and Niemann-Pick disease Types A, B and D, had normal or slightly elevated SAP-2 concentrations, while extracts from patients with I-Cell disease had half normal SAP-2 concentration. When the fibroblast extracts were subjected to sodium dodecylsulfate-polyacrylamide gel electrophoresis followed by electroblotting and immunochemical staining two major SAP-2 bands with estimated molecular weights of 9000 and 10000 were found. Extracts from patients with I-Cell disease showed only a faint higher molecular weight band. Isoelectric focusing followed by electroblotting and immunochemical staining demonstrated no significant difference in the charge of SAP-2 obtained from different cell lines. In this study we could not demonstrate any change in concentration, size or charge of SAP-2 in fibroblast extracts from Niemann-Pick disease Type C, and we provided evidence that SAP-2 might be subject to post-translational processing similar to that of lysosomal enzymes.