Lysosome lipid storage disorder in NCTR-BALB/c mice. II. Morphologic and cytochemical studies.

Electron-microscopic and cytochemical studies were carried out on tissues of NCTR-BALB/c mice. These mice are affected with a neurovisceral genetic disorder involving excessive tissue accumulation of lipid. Distinctive polymorphic intracellular inclusions, bounded by a membrane and containing lamellated bodies, were found in many cells of liver, spleen, lung, kidney, intestine, lymph nodes, and brain. The inclusions transformed reticuloendothelial cells into massive foam cells. Acid phosphatase cytochemical studies performed on sections of liver demonstrated that the inclusions were lysosomes. Fixation of liver in the presence of digitonin produced "spicules" in the inclusions characteristic of digitonin-cholesterol complexes. Clefts of cholesterol crystals were seen in the inclusions in liver, spleen, and lung. We conclude that the NCTR-BALB/c mice are affected by a lysosome lipid storage disease and that cholesterol is a major storage product.     

Lysosome lipid storage disorder in NCTR-BALB/c mice. I. Description of the disease and genetics.

We describe a strain of BALB/c mice, designated NCTR-BALB/c, carrying a new genetic disorder characterized by excessive tissue deposition of cholesterol and phospholipid. The mice exhibit progressive incoordination, grow less rapidly, and die 80-120 days after birth. In comparison with control animals of the same age, organ weights in the affected animals are lower in absolute value but higher relative to body weight, except for the thymus, which is atrophied, and for the lung and testes, whose absolute weights are not changed. Vacuolated cells are found in many tissues, and large foam cells are present in reticuloendothelial system (RES)-rich organs. Compared with those of BALB/c controls, serum lipoproteins migrate more slowly on electrophoresis; the amount of beta-lipoproteins is increased, while alpha-lipoprotein content is decreased. Serum total cholesterol remains normal. The serum activities of aspartate aminotransferase, creatine phosphokinase, and N-acetyl-beta-glucosaminidase are elevated. Free cholesterol levels are increased 8-10-fold in liver, spleen, and thymus, and about 2-fold in other tissues; but esterified cholesterol levels are normal. The phospholipid content of several tissues is increased 50-100%, largely as a result of an increase in sphingomyelin content. Significant increases in phosphatidylcholine occur also in spleen and lung. The disorder is inherited, affecting both sexes equally, and appears to be transmitted as an autosomal recessive mutation.     

Infantile sialic acid storage disease: Biochemical studies

Infantile free sialic acid storage disease (ISSD), is an inherited metabolic disorder characterized by hyperexcretion of free sialic acid in the urine and by its storage in the lysosomes of different tissues. In order to obtain more reliable data on the amount of total and free sialic acid, we analyzed the urine, brain, cerebellum, liver, spleen, and kidneys from a 3-month-old baby who died with a diagnosis of ISSD. The lysosomal nature of the disease was confirmed by an electron microscopic study of cells in culture. No significant abnormalities were found involving cholesterol, total phospholipids, glycolipids, and gangliosides in the tissues examined. However, differences in the tissue distribution of individual glycolipids and gangliosides were observed. The amount of free and total sialic acid was markedly increased, due to the storage of free sialic acid accompanied by its hyperexcretion in the urine. These results demonstrate and confirm that only acid monosaccharide transport from the lysosome compartment is involved in the pathogenesis of ISSD. © 1995 Wiley-Liss, Inc.     

Effects of the diazafluoranthen derivative AC-3579 (NSC-170561), a new experimental antitumour drug, on rat hepatoma.

The effects of AC-3579 (NSC-170561), a new experimental antitumour drug which depresses phospholipid catabolism in liver, were compared in rat aflatoxin-induced hepatoma and in non-neoplastic hepatocytes surrounding the tumour. Ultrastructural lesions, characterized by the hypertrophy of the smooth endoplasmic reticulum and the presence of lamellate cytosomes appeared in both tissues. They were less marked in hepatoma than in non-neoplastic cells. As in control livers, they were related to an invrease in pohspholipid concentration due to the decrease of phospholipid breakdown. In addition, chemical analysis demonstrated differences between hepatoma, non-neoplastic aflatoxin-treated liver and control liver: total and free cholesterol were decreased, relative concentration of sphingomyelin increased and that of phosphatidylethanolamine decreased by about 50%, in both hepatoma and non-neoplastic liver. Phospholipid concentration was decreased by 50% in tumour cells. After AC-3579 treatment total cholesterol was increased 3.2 fold in non-neoplastic liver and 2.5 fold in hepatoma but not in control liver.     

Enzyme therapy for lysosomal acid lipase deficiency in the mouse

Lysosomal acid lipase (LAL) is the critical enzyme for the hydrolysis of the triglycerides (TG) and cholesteryl esters (CE) delivered to lysosomes. Its deficiency produces two human phenotypes, Wolman disease (WD) and cholesteryl ester storage disease (CESD). A targeted disruption of the LAL locus produced a null (lal( -/-)) mouse model that mimics human WD/CESD. The potential for enzyme therapy was tested using mannose terminated human LAL expressed in Pichia pastoris (phLAL), purified, and administered by tail vein injections to lal( -/-) mice. Mannose receptor (MR)-dependent uptake and lysosomal targeting of phLAL were evidenced ex vivo using competitive assays with MR-positive J774E cells, a murine monocyte/macrophage line, immunofluorescence and western blots. Following (bolus) IV injection, phLAL was detected in Kupffer cells, lung macrophages and intestinal macrophages in lal( -/-) mice. Two-month-old lal( -/-) mice received phLAL (1.5 U/dose) or saline injections once every 3 days for 30 days (10 doses). The treated lal( -/-) mice showed nearly complete resolution of hepatic yellow coloration; hepatic weight decreased by approximately 36% compared to PBS-treated lal( -/-) mice. Histologic analyses of numerous tissues from phLAL-treated mice showed reductions in macrophage lipid storage. TG and cholesterol levels decreased by approximately 50% in liver, 69% in spleen and 50% in small intestine. These studies provide feasibility for LAL enzyme therapy in human WD and CESD.     

Targeted disruption of the mouse lysosomal acid lipase gene: long-term survival with massive cholesteryl ester and triglyceride storage

Lysosomal acid lipase (LAL) is essential for the hydrolysis of the triglycerides and cholesteryl esters in lysosomes. Its deficiency produces two phenotypes, a severe infantile-onset variant, Wolman disease (WD), and a later onset variant, cholesteryl ester storage disease (CESD). A mouse model with a LAL null mutation was produced by targeting disruption of the mouse gene. Homozygote knockout mice (lal - /lal-) produce no LAL mRNA, protein or enzyme activity. The lal-/lal- mice are born in Mendelian ratios, are normal appearing at birth, and follow normal development into adulthood. However, massive accumulation of triglycerides and cholesteryl esters occurs in several organs. By 21 days, the liver develops a yellow-orange color and is approximately 1.5- 2.0x larger than normal. The accumulated cholesteryl esters and triglycerides are approximately 30-fold greater than normal. The lal+/lal- mice have approximately 50% of normal LAL activity and do not show lipid accumulation. Male and female lal-/lal- mice are fertile and can be bred to produce progeny. This mouse model is a phenotypic model of human CESD, and a biochemical and histopathologic mimic of human WD. The lal-/lal- mice provide a model to determine the role of LAL in lipid metabolism and the pathogenesis of its deficiency states.      

The effect of prostaglandins on experimental storage disease in rats.

The aim of this study was to investigate the effect of prostaglandins (PGs) on the release of lysosomes into the extracellular space in experimentally-induced storage disease in rats. The generalized phospholipidosis was induced by oral administration of chlorphentermine to Wistar rats. PG-E2 or PG-F2 alpha (50 micrograms/100 g) was injected intravenously into rats with phospholipidosis. Control rats were injected with the same amount of saline. Twenty-four hours later, extracellular and intracellular lysosomes were analysed morphometrically in electromicrographs of the liver, kidney, myocardium, skeletal muscle, aorta and cervix uteri, having been stained with acid-phosphatase. The morphometric parameters used were the numerical density of lysosomes per unit volume and the volume density of lysosomes per unit volume. The results show that, in comparison with the controls, a volumetric increase of extracellular lysosomes and a volumetric decrease of intracellular lysosomes were achieved by PG-E2 or PG-F2 alpha administration in several organs, but not in the myocardium or skeletal muscles. The effect of PG-F2 alpha was greater than that of PG-E2 in the liver and kidney, while the effect of PG-E2 was greater than that of PG-F2 alpha in the aorta and cervix uteri. These results indicate that PGs influence the discharge of storage lysosomes in bipolar epithelial cells in the liver and kidney, and also influence the release of non-storing lysosomes in apolar mesenchymal cells in the aorta and cervix uteri.     

Mice deficient in Neu4 sialidase exhibit abnormal ganglioside catabolism and lysosomal storage

Mammalian sialidase Neu4, ubiquitously expressed in human tissues, is located in the lysosomal and mitochondrial lumen and has broad substrate specificity against sialylated glycoconjugates. To investigate whether Neu4 is involved in ganglioside catabolism, we transfected beta-hexosaminidase-deficient neuroglia cells from a Tay-Sachs patient with a Neu4-expressing plasmid and demonstrated the correction of storage due to the clearance of accumulated GM2 ganglioside. To further clarify the biological role of Neu4, we have generated a stable loss-of-function phenotype in cultured HeLa cells and in mice with targeted disruption of the Neu4 gene. The silenced HeLa cells showed reduced activity against gangliosides and had large heterogeneous lysosomes containing lamellar structures. Neu4(-/-) mice were viable, fertile and lacked gross morphological abnormalities, but showed a marked vacuolization and lysosomal storage in lung and spleen cells. Lysosomal storage bodies were also present in cultured macrophages preloaded with gangliosides. Thin-layer chromatography showed increased relative level of GD1a ganglioside and a markedly decreased level of GM1 ganglioside in brain of Neu4(-/-) mice suggesting that Neu4 may be important for desialylation of brain gangliosides and consistent with the in situ hybridization data. Increased levels of cholesterol, ceramide and polyunsaturated fatty acids were also detected in the lungs and spleen of Neu4(-/-) mice by high-resolution NMR spectroscopy. Together, our data suggest that Neu4 is a functional component of the ganglioside-metabolizing system, contributing to the postnatal development of the brain and other vital organs.     

Early atherogenesis in the White Carneau pigeon. III. Lipid accumulation in nascent foam cells.

The role of lysosomes in aortic atherogenesis in White Carneau pigeons was examined by means of acid phosphatase cytochemistry. Foam cells were the major constituent of nascent atherosclerotic lesions in pigeons fed a 0.5% cholesterol diet for either 5 or 10 weeks. Seventy-four percent of foam cell lipid from animals at 5 weeks was in cytoplasmic droplets. The remaining lipid appeared in secondary lysosomes. After 10 weeks of cholesterol feeding, lysosomal lipid accounted for 73% of the lipid volume. The lipid accumulation correlated with increases in both size and number of lysosomes. An average of 2.4 lysosomes per 10(4) cu mu of cytoplasm was observed at 5 weeks. This value doubled by 10 weeks. The average lysosome diameter also increased between 5 and 10 weeks from 2.2 mu to 5.75 mu. Concomitantly, the complexity of lysosomes increased from simple, spherical organelles at 5 weeks to complex, multichambered organelles at 10 weeks. In contrast, lipid storage within cytoplasmic lipid droplets did not change either in size or in number. These observations suggest that by 5 weeks lipid storage within cytoplasmic droplets was maximized, and continued increases in lipid stores occurred predominantly through lysosomal loading.     

Cholesterol ester storage disease in an adult presenting with sea-blue histiocytosis

An adult patient is described with hepatomegaly and sea-blue histiocytes in the bone marrow. A diagnosis of cholesterol ester storage disease was established following enzyme and lipid analyses on liver biopsy and cultured skin fibroblasts. Acid esterase activity was deficient (approx. 5% of controls) in liver and fibroblasts using [14C]-triolein or 4-methylumbelliferyl palmitate as substrates. Cholesterol ester levels were raised about 70-fold in liver, whereas triglyceride levels were only marginally raised. Marked accumulation of cholesterol esters was also demonstrated in cultured fibroblasts. Clinically, the patient responded favourably to phenobarbitone treatment. However, this was not reflected in liver acid esterase or lipid levels.     

Lysosomes of the arterial wall. II. Subcellular fractionation of aortic cells from rabbits with experimantal atheroma

Cells were isolated from the aortas of control rabbits and of rabbits with experimental atheroma induced by cholesterol feeding. They were homogenized and fractionated by three different techniques relying mainly on differences in equilibrium density of cell particles in sucrose gradients.After cholesterol feeding, the aortic smooth muscle cells transformed progressively into foamy cells. Their protein to DNA ratio was unchanged. The mitochondrial marker cytochrome oxidase and the presumed plasma membrane markers 5′-nucleotidase and leucyl-β-naphthylamidase showed no significant change in specific activity, nor in density distribution, even in severely atheromatous lesions. Only minimal changes were seen for α-glucosidase, an enzyme probably associated largely with microsomes. Catalase was increased up to 7-fold; one-third of this activity was in particles of about 1.18 density, the rest was soluble.The specific activity of all lysosomal acid hydrolases increased with increasing severity of atheroma, up to a little more than 2-fold for N-acetyl-β-galactosaminidase and α-mannosidase, 3- to 4-fold for N-acetyl-β-glucosaminidase, acid phosphatase, and cathepsin C, more than 10-fold for β-galactosidase and β-glucuronidase. At the same time the lysosome became less fragile and their density distribution underwent a progressive broadening in the direction of decreasing density, extending to a value as low as 1.03. Incipient changes in lysosome density could be detected already in the early stages of the cholesterol-induced atheromatous transformation and in animals with moderate atheroma induced by a diet rich in saturated fatty acids.The cholesterol content of the cells increased up to 16-fold and the distribution of this substance was altered from a plasma membrane type in normal smooth muscle cells to one resembling that of lysosomal enzymes in foamy cells. Most likely, cholesterol storage is responsible for the decrease in lysosome density, and cholesterol-containing vacuoles in foamy cells are of lysosomal nature. Much of this cholesterol was in esterified form.In other experiments, no age- or sex-related changes in the aortic cell organelles could be demonstrated. After repeated intravenous injection of Triton WR-1339 there was a significant decrease in equilibrium density of the lysosomes indicating uptake of the detergent by this organelle. No change was observed after repeated injection of dextrans of various molecular weight, injection of neutral red, or starvation.     

Niemann-Pick disease

Summary The results of a complex analysis of liver tissue are presented (four biopsy and two autopsy samples) obtained from six patients with Niemann-Pick disease (NPD) with a gross deficiency of sphingomyelinase (SMase) accompanied by a typical increase in sphingomyelin (SM). There were five cases of NPD type A (four of them with an atypical, prolonged course) and one case of type B. By means of lipid histochemistry it was possible to demonstrate SM storage both in hepatocytes and in the reticuloendothelial system (RES) of the liver (Kupffer cells and portal macrophages) and to show in two siblings with NPD type A a so-far undescribed centrilobular storage pattern. Enzyme histochemistry revealed a secondary deficit of nonspecific esterase activity and acid -galactosidase in liver storage macrophages and varying degrees of suppression of hepatocytic enzyme activities as a reaction to lipid storage of sudden onset. Ultrastructurally, it was possible to demonstrate cholesterol in lysosomes by using digitonin fixation, the involvement of Ito cells in lipid storage, the aggregation of storage lysosomes with certain other organelles and their occasional connections with the endoplasmic reticulum. The problems of possible lipid extraction during processing were considered as a cause of pronounced lysosomal electron-lucidity and of the ultrastructural identification of the participating lipopigment. The significance of the findings is discussed in relation to the existing classification and, particularly, to the stored lipid dilemma of cases of NPD type C.     

Generalized glycogen storage and cardiomegaly in a knockout mouse model of Pompe disease

Glycogen storage disease type II (GSDII; Pompe disease), caused by inherited deficiency of acid alpha-glucosidase, is a lysosomal disorder affecting heart and skeletal muscles. A mouse model of this disease was obtained by targeted disruption of the murine acid alpha-glucosidase gene (Gaa) in embryonic stem cells. Homozygous knockout mice (Gaa -/-) lack Gaa mRNA and have a virtually complete acid alpha-glucosidase deficiency. Glycogen-containing lysosomes are detected soon after birth in liver, heart and skeletal muscle cells. By 13 weeks of age, large focal deposits of glycogen have formed. Vacuolar spaces stain positive for acid phosphatase as a sign of lysosomal pathology. Both male and female knockout mice are fertile and can be intercrossed to produce progeny. The first born knockout mice are at present 9 months old. Overt clinical symptoms are still absent, but the heart is typically enlarged and the electrocardiogram is abnormal. The mouse model will help greatly to understand the pathogenic mechanism of GSDII and is a valuable instrument to explore the efficacy of different therapeutic interventions.      

Application of delayed extraction matrix-assisted laser desorption ionization time-of-flight mass spectrometry for analysis of sphingolipids in tissues from sphingolipidosis patients.

Sphingolipidosis is due to defects in enzymes involved in hydrolysis of sphingolipids. We analyzed sphingolipids in tissues from patients with sphingolipidosis, including Farber disease (FD, acid ceramidase deficiency), Gaucher disease (GD), Niemann-Pick disease type C (NPDC), and GM1-gangliosidosis (GM1G), using delayed extraction matrix-assisted laser desorption ionization time-of-flight mass spectrometry (DE MALDI-TOF-MS). Crude lipids were extracted from about 100 mg wet weight of autopsied tissues, including liver, spleen, cerebrum or cerebellum. After mild alkaline treatment, a sphingolipid fraction was prepared from the crude lipids and analyzed by DE MALDI-TOF-MS. The results were as follows: (a) In FD liver both the ceramide/sphingomyelin and ceramide/monohexosylceramide ratios were significantly high; (b) in both liver and spleen from a GD patient, the glucosylceramide/sphingomyelin ratio was raised; (c) in liver from a NPDC patient, the monohexosylceramide/sphingomyelin ratio was markedly low, suggesting an increase of sphingomyelin; and (d) in all tissues examined in the GM1G patient, GM1-gangliosides or asialo-GM1-gangliosides, that are undetectable in a normal control, were increased. In conclusion, sphingolipids in human tissues could be directly determined by DE MALDI-TOF-MS, with only a small amount of specimens. This method will be useful for the diagnosis and biochemical evaluation of sphingolipidosis patients.     

Lipids and fatty acids of tachyzoites and purified pellicles ofToxoplasma gondii

Various lipids were extracted from tachyzoites and from purfied pellicles ofToxoplasma gondii. Extracts from both sources were found to have a low cholesterol/phospholipid ratio. The major phospholipid in these fractions was phosphatidylcholine associated with a low amount of sphingomyelin. Oleic acid represented one-third of whole-cell fatty acids and 44% of pellicular fatty acid content. The lipid composition of the pellicle ofT. gondii is consistent with the previously reported high fluidity of this membrane.     

A novel mutation in the coding region of the prosaposin gene leads to a complete deficiency of prosaposin and saposins, and is associated with a complex sphingolipidosis dominated by lactosylceramide accumulation

A fatal infantile storage disorder with hepatosplenomegaly and severe neurological disease is described. Sphingolipids, including monohexosylceramides (mainly glucosylceramide), dihexosylceramides (mainly lactosylceramide), globotriaosyl ceramide, sulphatides, ceramides and globotetraosyl ceramide, were stored in the tissues. In general, cholesterol and sphingomyelin levels were unaltered. The storage process was generalized and affected a number of cell types, with histiocytes, which infiltrated a number of visceral organs and the brain, especially involved. The ultrastructure of the storage lysosomes was membranous with oligolamellar, mainly vesicular, profiles. Infrequently, there were Gaucher-like lysosomes in histiocytes. The neuropathology was severe and featured neuronal storage and loss with a massive depopulation of cortical neurons and pronounced fibrillary astrocytosis. There was a paucity of myelin and stainable axons in the white matter with signs of active demyelination. Immunohistochemical investigations indicated that saposins A, B, C and D were all deficient. The patient was homozygous for a 1 bp deletion (c.803delG) within the SAP-B domain of the prosaposin gene which leads to a frameshift and premature stop codon. In the heterozygous parents, mutant cDNA was detected by amplification refractory mutation analysis in the nuclear, but not the cytoplasmic, fraction of fibroblast RNA, indicating that the mutant mRNA was rapidly degraded. The storage process in the proband resembled that of a published case from an unrelated family. Saposins were also deficient in this case, leading to its reclassification as prosaposin deficiency, and her mother was found to be a carrier for the same c.803delG mutation. Both of the investigated families came from the same district of eastern Slovakia.     

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

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

The lipid composition of highly differentiated human hepatomas,with special reference to fatty acids.

The lipid compositions of homogenates and microsomal fractions derived from surgical samples of highly differentiated human hepatoma, morphologically normal regions outside the tumours and from normal livers were analysed. A few enzyme activities were also assayed. Hepatoma microsomes demonstrated considerably lowered levels of cytochromes P-450 and b5. Hepatoma homogenates exhibited increased levels of cholesterol, normal amounts of dolichyl-P and slightly lowered levels of total phospholipid. The levels of dolichol, dolichol ester and ubiquinone in hepatoma homogenates were prominently decreased. In tumour microsomes the levels of cholesterol and dolichyl phosphate were increased considerably while the levels of phospholipid and dolichol were lowered. The phospholipid composition of tumour homogenates was roughly similar to that of control tissue. In tumour microsomes the relative amounts of phosphatidylserine and phosphatidylinositol were about 30% decreased, whereas the major phospholipids showed minor increases in amount. The rate and pattern of incorporation of [3H]glycerol into individual phospholipids in liver slices from control and hepatoma tissue did not differ to any larger extent. The fatty acid composition of tumour homogenates exhibited minor differences in comparison to the control with the greatest changes in the sphingomyelin fraction. In hepatoma microsomes the fatty acid compositions of the major phospholipids were altered moderately, with evident decreases in the relative amounts of the long-chain polyunsaturated fatty acids. In hepatoma homogenates the fatty acid composition of dolichol esters differed only slightly from the control pattern. These results indicate that the major disturbance in the lipid metabolism of highly differentiated hepatomas is localized to the mevalonate pathway, thus affecting mainly the levels of cholesterol, dolichol and ubiquinone.     

Overexpression of human lecithin:cholesterol acyltransferase in mice offers no protection against diet-induced atherosclerosis

Human lecithin:cholesterol acyltransferase (LCAT) is a key enzyme in the metabolism of cholesterol. We have used homozygous transgenic mice overexpressing the human LCAT transgene to study the effect of a "Western-type" atherogenic diet (30% fat, 5% cholesterol and 2% cholic acid) on their LCAT expression, activity, lipoprotein profile and tendency to develop atherosclerosis. The LCAT activity was 35-fold higher in serum of the homozygous transgenic mice than in murine control serum, and decreased 11-20% in the transgenic mice when fed the atherogenic diet. The total cholesterol and high-density lipoprotein cholesterol (HDL-C) concentrations were approximately doubled in the transgenic mice compared with the controls when both groups were fed a regular chow diet. In mice on the atherogenic diet, the triglyceride concentration decreased about 50% to the same level in transgenic and control mice. Total cholesterol and HDL-C concentrations increased and were 60-80% higher in the transgenic mice. The expression of LCAT mRNA in the liver was decreased by 49-60% in the transgenic mice when fed the atherogenic diet. The development of atherosclerosis was similar in transgenic and control mice. Thus, the 14- to 27-fold higher LCAT activity and the higher HDL-C concentrations in the homozygous LCAT transgenic mice had no significant protective influence on the development of diet-induced atherosclerosis.     

A mouse model for alpha-methylacyl-CoA racemase deficiency: adjustment of bile acid synthesis and intolerance to dietary methyl-branched lipids

alpha-Methylacyl-CoA racemase (Amacr) deficiency in humans leads to sensory motor neuronal and liver abnormalities. The disorder is recessively inherited and caused by mutations in the AMACR gene, which encodes Amacr, an enzyme presumed to be essential for bile acid synthesis and to participate in the degradation of methyl-branched fatty acids. To generate a model to study the pathophysiology in Amacr deficiency we inactivated the mouse Amacr gene. As per human Amacr deficiency, the Amacr(-/-) mice showed accumulation (44-fold) of C27 bile acid precursors and decreased (over 50%) primary (C24) bile acids in bile, serum and liver, however the Amacr(-/-) mice were clinically symptomless. Real-time quantitative PCR analysis showed that, among other responses, the level of mRNA for peroxisomal multifunctional enzyme type 1 (pMFE-1) was increased 3-fold in Amacr(-/-) mice. This enzyme can be placed, together with CYP3A11 and CYP46A1, to make an Amacr-independent pathway for the generation of C24 bile acids. Exposure of Amacr(-/-) mice to a diet supplemented with phytol, a source for branched-chain fatty acids, triggered the development of a disease state with liver manifestations, redefining the physiological significance of Amacr. Amacr is indispensable for the detoxification of dietary methyl-branched lipids and, although it contributes normally to bile acid synthesis from cholesterol, the putative pMFE-1-mediated cholesterol degradation can provide for generation of bile acids, allowing survival without Amacr. Based upon our mouse model, we propose elimination of phytol from the diet of patients suffering from Amacr deficiency.