Evidence for lipase abnormality: high levels of free and triacylglycerol forms of unsaturated fatty acids in neuronal ceroid-lipofuscinosis tissue.

Total lipid obtained from normal and different forms of neuronal ceroid-lipofuscinoses (NCL) tissues was analyzed by high performance thin layer chromatography (HPTLC). We observed a large (greater than 6-fold) increase in a lipid band corresponding to triolein for NCL dog pancreas and spleen and juvenile human NCL brain and infantile NCL spleen. The accumulation was less pronounced for the brain samples but apart from increased dolichol-monophosphate levels, other lipids appeared normal. Normal dog, goat, or human spleen contained virtually no triacylglycerol, and of the pathological controls, beta-mannosidosis goat spleen showed no triacylglycerol band at all. A sample of human spleen from a patient with lymphoma-associated splenomegaly displayed a strong triacylglycerol band, but gas chromatography-mass spectrometry (GC/MS) of the bands showed an equal increase in both saturated and unsaturated fatty acid containing triacylglycerols in the splenomegaly sample, in keeping with the notion of non-specific fat deposition in damaged tissue. In contrast, in all the NCL samples (spleen, pancreas, and brain) a prominent increase in the proportion of unsaturated fatty acids was observed in both free fatty acid and/or triacylglycerol bands following GC/MS. The NCL-English setter dog pancreas showed a major presence of oleic acid (18:1) (twofold increase) as compared to normal, while dog and infantile human NCL spleen samples and juvenile Batten brain (human) displayed a robust increase in linoleic acid (18:2) and sometimes in oleic acid and arachidonic acid (20:4) (for infantile human NCL spleen). For the infantile human NCL spleen sample an increase in linoleic acid in both free fatty acid (3.2-fold) and triacylglycerol (10-fold) was observed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Protease inhibitors as a model for NCL disease, with special emphasis on the infantile and adult forms.

An animal model of NCL disease has been developed with the use of protease inhibitors. Young rats received a continuous infusion of various specific protease inhibitors or of physiological saline into the lateral ventricle of the brain using osmotic mini-pumps. Treatment lasted for 2 weeks, at which time animals were sacrificed and the brains were removed and processed for light or electron microscopic analysis. The thiol protease inhibitors leupeptin and E64C, but not saline or the serine protease inhibitor aprotinin, caused a massive accumulation of ceroid-lipofuscin (CL) in brain cells that bore a strong morphological resemblance to the CL in the infantile and adult forms of NCL disease, and bore similarity to the CL of the late infantile and juvenile forms. Leupeptin also caused the death of cerebellar Purkinje cells, as is seen in the infantile and adult forms of NCL. Further evidence is presented in support of the hypothesis (Ivy et al.: Science 226:985-987, 1984) that decreased or defective lysosomal thiol proteases or their substrates may underly the pathogenesis of at least the infantile and adult forms of NCL disease. Administration of protease inhibitors to the brains of young rats provides an important model for studying the cellular mechanisms of ceroid-lipofuscino-genesis.     

Abnormal acid phosphatases in neuronal ceroid-lipofuscinoses

Acid phosphatases in brain and cultured lymphoblasts from patients affected with neuronal ceroid-lipofuscinoses (NCL) were studied by starch gel electrophoresis. After electrophoresis the gel was incubated with 4-methyl umbelliferyl phosphate at pH 4.5 and the fluorescent reaction product was visualized under ultraviolet light. Control brain showed a single band with mobility of about 1 cm while NCL patients showed two additional fast moving bands. In the lateinfantile, and in the adult form (Kufs disease), the middle band was prominent while the fast moving band was predominant in juvenile NCL. In long-term lymphoblasts, controls showed a single band of acid phosphatase activity while both juvenile and late-infantile NCL showed two additional fast moving bands. Obligate heterozygotes showed reduced levels of the fast moving bands. Fluorometric assay of acid phosphatase using 4-methylumbelliferyl phosphate as substrate showed a 2-fold increase in activity in the patients. The increased acid phosphatase activity is completely inhibited by tartrate. Lymphocyte hexosamnidase activities were unchanged in NCL patients lymphoblasts. Studies on brains of NCL patients and on cultured lymphoblasts from families with late-infantile and juvenile form of NCL showed that abnormal acid phosphatase is characteristic of NCL © 1995 Wiley-Liss, Inc.     

Evidence for processing of dolichol-linked oligosaccharides in patients with neuronal ceroid-lipofuscinosis.

In agreement with reports from other laboratories, we have shown that patients with the juvenile or late infantile forms of neuronal ceroid-lipofuscinosis (NCL) have greatly increased levels (5-fold to 20-fold) of dolichyl pyrophosphoryl oligosaccharides in their cerebral gray matter. Oligosaccharides containing 2 GlcNAc residues and 3 to 9 mannose residues were liberated by mild acid hydrolysis. The oligosaccharide profile given by brain tissue from 2 patients with infantile NCL was markedly different from that of late infantile and juvenile NCL brain, with Man9GlcNAc2 as the most abundant component and decreasing amounts of Man8- Man7- and Man6GlcNAc2. By contrast, Man5GlcNAc2 was the most abundant oligosaccharide present in all juvenile NCL brain samples analyzed. Both the susceptibility of the isolated Man5GlcNAc2 to endoglucosaminidase H digestion and permethylation analysis clearly indicated that it is not an intermediate in the biosynthesis of Glc3Man9GlcNAc2-PP-dolichol but has undergone catabolism, probably either in the endoplasmic reticulum or in the Golgi apparatus. Treatment of cultured skin fibroblasts for 7 days with N-methyldeoxynojirimycin, a potent inhibitor of the endoplasmic reticulum processing enzymes glucosidase I and II, resulted in an accumulation of the same Man5GlcNAc2-PP-dolichol species that was elevated in juvenile NCL brain. The level in untreated fibroblasts was undetectable, suggesting that inhibition of processing glucosidases has interfered with the regulation and compartmentalization of lipid-linked oligosaccharides.     

Accumulation of arachidonate in triacylglycerols and unesterified fatty acids during ischemia and reflow in the isolated rat heart. Correlation with the loss of contractile function and the development of calcium overload.

Alterations in triacylglycerol and phospholipid metabolism are known to occur during the evolution of myocardial ischemic injury. The purpose of this study was to explore potential relationships between the accumulation of arachidonic acid and other fatty acids, the accumulation of triacylglycerol, and the progression of myocardial injury. Measurements of the fatty acid levels in triacylglycerol, unesterified fatty acids, and calcium content were correlated with myocardial function during ischemia and ischemia with reflow in an isolated perfused rat heart preparation. After 10 minutes of ischemia in this model, myocardial dysfunction was reversible, with recovery of left ventricular +dP/dt to 82.0% +/- 4.8% of control values upon reperfusion. Hearts did not recover with reperfusion after 30 minutes of ischemia and displayed a significant increase in tissue calcium content. A significant, nearly threefold increase in the arachidonic acid content of triacylglycerol was found after 10 minutes of ischemia and continued to increase with longer periods of ischemia and reflow. Other fatty acids also showed increased levels in triacylglycerol. The time course of accumulation of unesterified arachidonic acid paralleled the loss of myocardial function. Levels of free arachidonic acid were (in nanomoles per gram wet weight) 11.1 +/- 2.1 (SEM) for control hearts, 17.3 +/- 1.9 after 10 minutes of ischemia, and 38.4 +/- 2.5 after 30 minutes of ischemia. Increases in other free fatty acids contributed to a significant increase in total free fatty acid accumulation after 30 minutes of ischemia. Thus, the content of arachidonic and other fatty acids in triacylglycerol was found to increase early during ischemia, and a major increase in free arachidonic and other unesterified fatty acids occurred after a longer period of ischemia. These findings are consistent with an initial reincorporation of free fatty acids into triacylglycerol after release from membrane phospholipids, suggesting that membrane fatty acids may be a major source of triacylglycerol that accumulates in ischemic myocardium. In addition, these results suggest that a major increase in free fatty acids during ischemia and ischemia with reflow correlates temporally with the development of severe contractile dysfunction and accumulation of calcium in the heart.     

Evidence for processing of dolichol-linked oligosaccharides in patients with neuronal ceroid-lipofuscinosis

In agreement with reports from other laboratories, we have shown that patients with the juvenile or late infantile forms of neuronal ceroid-lipofuscinosis (NCL) have greatly increased levels (5-fold to 20-fold) of dolichyl pyrophosphoryl oligosaccharides in their cerebral gray matter. Oligosaccharides cont ain-ing 2 GlcNAc residues and 3 to 9 mannose residues were liberated by mild acid hydrolysis. The oligosaccharide profile given by brain tissue from 2 patients with infantil e NCL was markedly different from that of late infantile and juvenile NCL brain, with Man₉GlcNAc₂ as the most abundant component and decreasing amounts of Man₈- Man₇-and Man₆GlcNAc₂. By contrast, Man₅GlcNAc₂ was the most abundant oligosaccharide present in all juvenile NCL brain samples analyzed. Both the susceptibility of the isolated Man₅GlcNAc₂ to endoglucosaminidase H digestion and permethylation analysis clearly indicated that it is not an intermediate in the biosynthesis of Glc₃Man₉GlcNAc₂-PP-dolichol but has undergone catabolism, probably either in the endoplasmic reticulum or in the Golgi apparatus. Treatment of cultured skin fibroblasts for 7 days with N-methyldeoxyno-jirimycin, a potent inhibitor of the endoplasmic reticulum processing enzymes glucosidase I and II, resulted in an accumulation of the same Man₅GlcNAc₂-PP-dolichol species that was elevated in juvenile NCL brain. The level in untreated fibroblasts was undetectable, suggesting that inhibition of processing glu- cosidases has interfered with the regulation and compartmentalization of lipid-linked oli-gosaccharides.     

Developmental changes in the expression of neuronal ceroid lipofuscinoses-linked proteins

Neuronal ceroid lipofuscinoses (NCL) form a distinct group of storage diseases where the normal development of the central nervous system is interrupted and neurons of the neocortex begin to degenerate. Mutations in genes encoding three lysosomal enzymes are the causes for three early-onset forms of NCLs: palmitoyl-protein thioesterase 1 (PPT1) is deficient in human infantile NCL, tripeptidyl peptidase 1 (TTP1) in late-infantile NCL, and cathepsin D in congenital ovine NCL. We wanted to compare the developmental expression profiles of these enzymes in rat brain. In conclusion, the PPT1 expression pattern differed from the two other lysosomal enzymes implicated in NCL diseases, thus suggesting a distinctive role for PPT1 in brain development.     

Interferon production by human lymphoblastoid cells is stimulated by inducers of Friend cell differentiation.

A variety of structurally unrelated substances stimulated production of human lymphoblastoid interferon in Namalwa cells. Active substances include short-chain fatty acids, dimethyl sulfoxide, and hexamethylene bisacetamide. These substances are established inducers of erythropoietic differentiation in mouse erythroleukemic spleen cells (Friend cells). When Namalwa cells were cultured for 24 hr or more in the presence of 1–2.5 mM n-butyric acid and then induced with Sendai virus, a 30-fold increase in interferon yields over untreated Namalwa cells was observed. Propionic acid and n-valeric acid at a concentration of 5 mM caused a similar increase in interferon production and caproic acid at 5 mM stimulated it 8-fold. Substituted or unsaturated fatty acids were inert. Dimethyl sulfoxide increased interferon production at 280 mM and hexamethylene bisacetamide at 10 mM. All substances which enhanced interferon production blocked thymidine incorporation into Namalwa cell DNA at concentrations equal to those effective in interferon stimulation.     

Changes in the incorporation of free fatty acids upon the stimulation of human polymorphonuclear leukocytes

We have investigated the incorporation of free fatty acids into the cellular lipids of human polymorphonuclear leukocytes (PMN). Resting PMN incorporated both saturated and unsaturated fatty acids into triacylglycerol with only small amounts incorporated into the phospholipids. In contrast, PMN stimulated with the calcium ionophore A23187 incorporated significantly higher amounts of fatty acids, predominantly those other than arachidonic acid, into phosphatidylcholine and phosphatidylinositol, with reduced incorporation into triacylglycerol. Stimulation of PMN with serum-treated zymosan or the chemotactic peptide f-met-leu-phe but not phorbol myristate acetate, also increased the incorporation of fatty acids into these phospholipids. This stimulation-induced incorporation of fatty acids into cellular phospholipids was directed exlusively into position 2 of the lipid and probably reflects the reacylation of lysophospholipids after the release of arachidonic acid by phospholipase A2.     

Anomalies of mitochondrial ATP synthase regulation in four different types of neuronal ceroid lipofuscinosis

Several neuronal ceroid lipofuscinoses (NCL) show storage of subunit c of mitochondrial ATP synthase. The neurodegenerative process, however, remains obscure. We previously reported a decreased basal ATP synthase activity in fibroblasts from late-infantile NCL (CLN2) and juvenile NCL (CLN3) patients. We have now extended the study of the ATP synthase system to an ovine NCL (a model for the late-infantile NCL variant, CLN6) and the infantile NCL (CLN1). In fibroblasts from healthy sheep, active regulation of ATP synthase in response to cellular energy demand was present similar to human cells: ATP synthase was down-regulated under conditions of anoxia or functional uncoupling and was up-regulated in response to calcium. In fibroblasts from NCL sheep, basal ATP synthase activity was slightly elevated and down-regulation in response to anoxia or uncoupling of mitochondria also occurred. Calcium produced an unexpected down-regulation to 55% of basal activity. Activities of respiratory chain enzymes did not differ between healthy and NCL sheep. In fibroblasts from CLN1 patients, basal ATP synthase activity was reduced and regulation of the enzyme was absent. Activities of respiratory chain complexes II and IV were reduced. The defect of ATP synthase regulation found in fibroblasts from NCL sheep and infantile NCL patients is different from the ATP synthase deficiencies demonstrated in late-infantile and juvenile NCL, but problems of mitochondrial energy production, if also expressed in brain, would be a common feature of several NCL forms. Deficient ATP supply could result in degeneration of neurons, especially in those with high energy requirements.     

Progress in neuropathology of the neuronal ceroid lipofuscinoses

Since the last, 6th, International Congress on Neuronal Ceroid-Lipofuscinoses, neuropathological advances in neuronal ceroid lipofuscinoses (NCL) have been made in several areas: (1) In adult NCL (ANCL) lipopigments have now been repeatedly confirmed to contain subunit c of mitochondrial ATP synthase and even sphingolipid activators (saposins). ANCL lipopigments have also been confirmed in extracerebral tissues including skin, skeletal muscle, and spleen, but not yet lymphocytes (2). Among circulating blood cells not only B cells and subclasses of T lymphocytes, i.e., CD4(+), CD8(+), and CD56 cells, but also monocytes have been found to contain NCL lipopigments, indicating that this precursor cell in the digesting macrophage system also has an impaired metabolic catabolism for lipopigments (3). Immunohistochemical studies indicate that microglial reaction in NCL brain is limited to resident microglia without contribution by circulating monocytes (4). The granular osmiophilic deposit (GROD) type of NCL has now been established not only in infantile, but also in late-infantile, juvenile, and protracted-juvenile NCL (5). A European Tissue Registry established within the framework of a European Concerted Action on Neuronal Ceroid-Lipofuscinosis may form the basis for additional collaborative studies on NCL, including both biopsy and autopsy tissues.     

Fatty acid content and pattern of spleen phospholipids and triglycerides in normal and either type-1 or type-2 diabetic rats

The fatty acid pattern of spleen phospholipids and triglycerides was examined in fed or overnight fasted normal rats, streptozotocin-induced diabetic animals (type-1 diabetes) and Goto-Kakizaki rats (type-2 diabetes). In both phospholipids and triglycerides, differences were observed in the relative contribution of several fatty acids, as well as in the ratio between distinct fatty acids, when comparing fed to fasted rats, normal to diabetic animals and male to female Goto-Kakizaki rats. Diabetes increased to a greater extent the C22:6omega3 content of phospholipids in the spleen than in either the liver or the brain. However, the diabetes-induced changes in the C22:6omega3 content of triglycerides was closely comparable in the spleen, liver and brain. These findings suggest that the incorporation of fatty acids into triglycerides is controlled by comparable regulatory factor(s), e.g. insulinemia, in the spleen, liver and brain. In the case of phospholipids, however, an apparent adaptation to diabetic stress was more marked in the spleen than in the liver, and virtually absent in the brain. The proposed dichotomy in the environmental regulation of fatty acid synthesis and incorporation into phospholipids and triglycerides was further supported by distinct diabetes-related changes in the apparent activity of Delta9-desaturase in these two classes of lipids.     

Changes in phospholipid fatty acid composition and triacylglycerol content in mouse tissues after infection with bacille Calmette-Guérin.

Changes in the lipids of tissues from mice infected with bacille Calmette-Guérin (BCG) have been detected by gas-liquid chromatography. Infection with BCG resulted in (1) an increase in the polyunsaturated to saturated fatty acid ratio of phospholipids and (2) a decrease in the total triacylglycerol fatty acid content of spleen, liver and peritoneal macrophages. The alteration in fatty acid composition was significant in the phosphatidylethanolamine fraction of the phospholipids. The relation of these findings to an increased sensitivity to bacterial endotoxins is discussed.     

Changes in phospholipid fatty acid composition and triacylglycerol content in mouse tissues after infection with bacille Calmette-Guérin

Changes in the lipids of tissues from mice infected with bacille Calmette-Guérin (BCG) have been detected by gas-liquid chromatography. Infection with BCG resulted in (1) an increase in the polyunsaturated to saturated fatty acid ratio of phospholipids and (2) a decrease in the total triacylglycerol fatty acid content of spleen, liver and peritoneal macrophages. The alteration in fatty acid composition was significant in the phosphatidylethanolamine fraction of the phospholipids. The relation of these findings to an increased sensitivity to bacterial endotoxins is discussed.     

Variability in the clinical and pathological findings in the neuronal ceroid lipofuscinoses: Review of data and observations

We reviewed the clinical and pathological data on 319 neuronal ceroid lipofuscinosis (NCL) cases to determine the degree of variability within the different forms and among and within families. Thirty-six cases (11.3%) were the infantile form; 116 cases (36.3%), late infantile, 163 cases (51.1%), juvenile; and four cases (1.3%), the adult form (Kufs disease). Clinical variability was found in all forms studied, but was most striking in the juvenile and late infantile forms of NCL. The expected initial findings of seizures, dementia, blindness, or motor impairment were evident in 255 cases (80%), and rarer, less typical initial neurological symptoms were seen mainly in the 64 cases (20%) of the juvenile form: behavior abnormalities (18/64), psychoses (12/64), neuropathy (2/64), involuntary movements (15/64), ataxia (9/64), Six juvenile and two adult cases had no detectable impairment of vision. All 319 NCL cases had skin or conjunctiva biopsies or buffy that showed the characteristic ultrastructural abnormalities of NCL. Variability was evident in 16.7% in that a combination of fingerprint, curvilinear, and membranous profile inclusion bodies was observed in storage lysosomes, although one type of inclusion was distinctly predominant for each form. Postmortem examination of brains of 19 NCL cases (three with the infantile form, six with the late infantile form, nine with the juvenile form, and one with the adult form) revealed characteristic changes, Sixteen of the 19 NCL brains (84%) showed pathological variability in that they contained more than one kind of characteristic inclusion body in the neuronal lysosomal storage compartment. In all 19 NCL brains, small amounts of aging lipofuscin were also found. In three late infantile cases, neuronal cytoplasmic inclusion bodies were found mainly in the basal ganglia, midbrain, and cerebellar (BG), At the ultrastructural level, theses inclusions were found to be large lysosomes filled with very densely packed curvilinear profiles. Histological and immunocytochemical staining properties of these basal ganglial, midbrain, and cerebellar neurons were found to be different from those storage neurons of other brain regions in this subform and other NCL forms. Therefore, we conclude that these cases represent a distinct NCL subtype. More confounding was the discovery of several neuritic plaques in the fronto-temporal lobes of a 53-year-old female with the adult form. Our present results reveal theat not all epitopes of amyloid β-precursor protein (APP) can be detected in the NCL brain, and moreover, their distribution and intensity of immunostaining vary, not only among different NCL forms but in some instances with the same forms. The significance of high levels of epitope expression of certain APP domains in NCL brains is still unknown and needs further biochemical studies.     

A frame shift mutation in canine TPP1 (the ortholog of human CLN2) in a juvenile Dachshund with neuronal ceroid lipofuscinosis

The neuronal ceroid lipofuscinoses (NCLs) are inherited lysosomal storage diseases characterized by progressive neuropathy and the accumulation of autofluorescent cytoplasmic granules. Clinical signs of a new canine NCL began in a 9-month-old male Dachshund with vomiting, mental dullness, and loss of previously learned commands and rapidly progressed to include disorientation, ataxia, visual deficits, generalized myoclonic seizures, and death at 12 months of age. Neurons throughout the CNS contained autofluorescent storage granules that stained with periodic acid-Schiff and Luxol fast blue stains. Electron microscopy revealed that the storage granule contents consisted of curvilinear-appearing material characteristic of human late infantile NCL caused by CLN2 mutations. Nucleotide sequence analysis of canine TPP1, the ortholog of human CLN2, revealed a single nucleotide deletion in exon 4 which predicted a frame shift with a premature stop codon. Brain tissue from the affected dog lacked detectable activity of the tripeptidyl-peptidase enzyme encoded by TPP1, whereas the specific activities of 15 other lysosomal enzymes were higher than those in the brains of three control dogs. The affected Dachshund was homozygous for the mutant c.325delC allele, his sire and dam were heterozygotes, and 181 unrelated dogs, including 77 Dachshunds, were all homozygous for the wild-type allele. A DNA assay that detects the mutant allele will help Dachshund breeders avoid producing affected puppies in future generations. Furthermore, this Dachshund NCL may prove to be a useful model for studying the pathogenesis of neurodegeneration in human late infantile NCL and for evaluating novel therapeutic interventions for this disease.     

Hepatic triacylglycerol and fatty-acid biosynthesis during hypoxia in vivo

Hepatic fatty acid biosynthesis and the activity of phosphatidate phosphohydrolase, the rate-limiting enzyme of triacylglycerol biosynthesis, were studied after hypoxic periods of 1 and 7 days under hypo-bark conditions at 40.8 kPa. Phosphatidate phosphohydrolase activity increased 2-fold in the soluble fraction of the liver after one day at 40.8 kPa, but had returned to normal by 7 days. This was accompanied by a significant increase in liver triacylglycerol and sn-glycerol-3-phosphate. The phosphatidate phosphohydrolase activity increased continuously over 7 days in the pair-fed controls, probably due to the restriction on food. Measured as in vivo incorporation of ³H₂O into lipids, the hepatic fatty acid synthesis rate increased somewhat in acute hypoxia, but returned to normal values during 7 days of hypoxia. Plasma free fatty acids increased markedly after 24 h in the fasting controls (90 %) with a smaller increase in the hypoxic group (50%) due to peripheral lipolysis. Hepatic glycogen stores decreased in the hypoxic and fasting animals both after 1 and 7 days. It Is concluded that hypoxia induces the accumulation of fat into the liver at least partly as a consequence of an increase in phosphatidate phosphohydrolase activity in the soluble fraction of the liver.     

Effects of Fatty Acids on Human Serum Albumin Binding Centers

Albumin is a carrier of nonesterified long-chain fatty acids and many other ligands. The status of its binding centers was studied for various proportions of nonesterified long-chain fatty acids and albumin as exemplified by palmitic acid. The status of the binding center was tested by recording K-35 probe fluorescence decay in the subnanosecond band. This method showed the work of three types of centers. Palmitic acid enhanced binding activity of all centers, though to a different degree: if the palmitic acid/albumin proportion increased to 2-3, the probe binding to type 1 centers (located in the drug center I region) increased 1.5 times, while binding to type 3 centers increased more than 3-fold. Modification of these centers by nonesterified long-chain fatty acids was similar in the isolated human albumin preparation and in diluted blood serum. Hence, K-35 probe showed the actual status of various albumin centers, their binding capacity depending to a different measure on the fatty acid charge of albumin.     

Neuronal ceroid-lipofuscinoses in Italy: An epidemiological study

To establish the incidence of neuronal ceroid-lipofuscinoses (NCL) in Italy, we sent a questionnaire to all Neuropediatric and Child Neuropsychiatric Departments (answer rate 15/34 = 44%). Diagnoses were accepted only when based on firm clinical and/or electron microscopic criteria. We collected 58 cases born between 1966–1991 (2 infantile NCL, 37 late infantile NCL, and 19 juvenile NCL). The incidence was calculated only on patients born between 1974–1984. In this period, the incidence of overall NCL in the Italian population was calculated to be 0.56 per 100,000 live births (0.36 for late infantile NCL, and 0.20 for juvenile NCL). Our data show that infantile NCL is very rare in Italy, and that late infantile seems to be the most frequent form of NCL. © 1995 Wiley-Liss, Inc.     

Lipid metabolism in human skeletal muscle cells: effects of palmitate and chronic hyperglycaemia

This review focuses on the effect of exogenous factors known to be of importance for the development of insulin resistance in differentiated human myotubes. Recent data from our laboratory on the effects of fatty acid pre-treatment and chronic glucose oversupply on fatty acid and glucose metabolism, without and with acute insulin are presented, and discussed in the context of other recent publications in the field. Pre-treatment of myotubes with palmitate, chronic hyperglycaemia, and acute high concentrations of insulin changed fatty acid metabolism in favour of accumulation of intracellular lipids. Acute insulin exposure increased (14)C-oleate uptake and levels of free fatty acids (FFA) and triacylglycerol (TAG). Palmitate pre-treatment further increased oleate uptake, both under basal conditions and in the presence of insulin, with a marked increase in the phospholipid (PL) fraction, with a concomitant reduction in oleate oxidation. Chronic hyperglycaemia also promoted increased lipogenesis and elevated levels of cellular lipids. Changes in fatty acid metabolism in human muscle, in particular fatty acid oxidation, are probably crucial for the molecular mechanism behind skeletal muscle insulin resistance and impaired glucose metabolism. Differentiated human skeletal muscle cells may be an ideal system to further explore the mechanisms regulating lipid metabolism.