Human peroxisomal disorders

Protective effect of oleic acid against very long-chain fatty acid-induced apoptosis in peroxisome-deficient CHO cells

Very long-chain fatty acids (VLCFAs) are degraded exclusively in peroxisomes, as evidenced by the accumulation of VLCFAs in patients with certain peroxisomal disorders. Although accumulation of VLCFAs is considered to be associated with health issues, including neuronal degeneration, the mechanisms underlying VLCFAs-induced tissue degeneration remain unclear. Here, we report the toxic effect of VLCFA and protective effect of C18: 1 FA in peroxisome-deficient CHO cells. We examined the cytotoxicity of saturated and monounsaturated VLCFAs with chain-length at C20-C26, and found that longer and saturated VLCFA showed potent cytotoxicity at lower accumulation levels. Furthermore, the extent of VLCFA-induced toxicity was found to be associated with a decrease in cellular C18:1 FA levels. Notably, supplementation with C18:1 FA effectively rescued the cells from VLCFA-induced apoptosis without reducing the cellular VLCFAs levels, implying that peroxisome-deficient cells can survive in the presence of accumulated VLCFA, as long as the cells keep sufficient levels of cellular C18:1 FA. These results suggest a therapeutic potential of C18:1 FA in peroxisome disease and may provide new insights into the pharmacological effect of Lorenzo's oil, a 4:1 mixture of C18:1 and C22:1 FA.

SCA34 caused by ELOVL4 L168F mutation is a lysosomal lipid storage disease sharing pathology features with neuronal ceroid lipofuscinosis and peroxisomal disorders

Spinocerebellar ataxia 34 (SCA34) is a late-onset progressive ataxia caused by a mutation in ELOVL4, a gene involved in the biosynthesis of very long-chain fatty acids (VLCFAs). We performed post-mortem neuropathological examinations on four SCA34 patients with the ELOVL4 L168F mutation and compared the findings to age-matched controls. Specific gross findings of SCA34 were limited to pontocerebellar atrophy. On light microscopy, pontine base showed neuronal loss and storage of an autofluorescent lipopigment positive on oil red O, PAS and Hale's colloidal iron and negative on Alcian blue and Luxol fast blue (LFB). Among the swollen neurons were abundant CD68+ /CD163+ /IBA1- macrophages laden with a material with similar histochemical profile as in neurons except for the lack of autofluorescence and oil red O positivity and the presence of needle-like birefringent inclusions. Normal resting IBA1 + microglia were generally absent from pontine base nuclei but present in normal numbers elsewhere in the pons. In dentate nucleus neurons, atrophy was milder than in the pontine base and the coarser storage material was LFB-positive, closely resembling lipofuscin. On electron microscopy, dentate nucleus neurons showed neuronal storage of tridimensionally organized trilaminar spicules within otherwise normal lipofuscin, while in the more affected pontine base neurons, lipofuscin was almost completely replaced by the storage material. Storage macrophages were tightly packed with stacks of unorganized trilaminar spicules, reminiscent of the storage material seen in peroxisomal disorders and thought to represent VLCFAs incorporated in complex polar lipids. In summary, we provide histochemical and ultrastructural evidence that SCA34 is a lipid storage disease, the first among the currently known SCAs, and that the storage lipid is accumulating within neuronal lipofuscin. Our findings suggest that the storage lipid is similar to the one accumulating in non-neuronal cells in peroxisomal disorders and provide the first ultrastructural description of this type of material within neurons.

Peroxisomes attenuate cytotoxicity of very long-chain fatty acids

One of the major functions of peroxisomes in mammals is oxidation of very long-chain fatty acids (VLCFAs). Genetic defects in peroxisomal β-oxidation result in the accumulation of VLCFAs and lead to a variety of health problems, such as demyelination of nervous tissues. However, the mechanisms by which VLCFAs cause tissue degeneration have not been fully elucidated. Recently, we found that the addition of small amounts of isopropanol can enhance the solubility of saturated VLCFAs in an aqueous medium. In this study, we characterized the biological effect of extracellular VLCFAs in peroxisome-deficient Chinese hamster ovary (CHO) cells, neural crest-derived pheochromocytoma cells (PC12), and immortalized adult Fischer rat Schwann cells (IFRS1) using this solubilizing technique. C20:0 FA was the most toxic of the C16-C26 FAs tested in all cells. The basis of the toxicity of C20:0 FA was apoptosis and was observed at 5 μM and 30 μM in peroxisome-deficient and wild-type CHO cells, respectively. The sensitivity of wild-type CHO cells to cytotoxic C20:0 FA was enhanced in the presence of a peroxisomal β-oxidation inhibitor. Further, a positive correlation was evident between cell toxicity and the extent of intracellular accumulation of toxic FA. These results suggest that peroxisomes are pivotal in the detoxification of apoptotic VLCFAs by preventing their accumulation.

The physiological functions of human peroxisomes

Peroxisomes are subcellular organelles that play a central role in human physiology by catalyzing a range of unique metabolic functions. The importance of peroxisomes for human health is exemplified by the existence of a group of usually severe diseases caused by an impairment in one or more peroxisomal functions. Among others these include the Zellweger spectrum disorders, X-linked adrenoleukodystrophy, and Refsum disease. To fulfill their role in metabolism, peroxisomes require continued interaction with other subcellular organelles including lipid droplets, lysosomes, the endoplasmic reticulum, and mitochondria. In recent years it has become clear that the metabolic alliance between peroxisomes and other organelles requires the active participation of tethering proteins to bring the organelles physically closer together, thereby achieving efficient transfer of metabolites. This review intends to describe the current state of knowledge about the metabolic role of peroxisomes in humans, with particular emphasis on the metabolic partnership between peroxisomes and other organelles and the consequences of genetic defects in these processes. We also describe the biogenesis of peroxisomes and the consequences of the multiple genetic defects therein. In addition, we discuss the functional role of peroxisomes in different organs and tissues and include relevant information derived from model systems, notably peroxisomal mouse models. Finally, we pay particular attention to a hitherto underrated role of peroxisomes in viral infections.

Peroxisome prognostications: Exploring the birth, life, and death of an organelle

Peroxisomes play a central role in human health and have biochemical properties that promote their use in many biotechnology settings. With a primary role in lipid metabolism, peroxisomes share a niche with lipid droplets within the endomembrane-secretory system. Notably, factors in the ER required for the biogenesis of peroxisomes also impact the formation of lipid droplets. The dynamic interface between peroxisomes and lipid droplets, and also between these organelles and the ER and mitochondria, controls their metabolic flux and their dynamics. Here, we review our understanding of peroxisome biogenesis to propose and reframe models for understanding how peroxisomes are formed in cells. To more fully understand the roles of peroxisomes and to take advantage of their many properties that may prove useful in novel therapeutics or biotechnology applications, we recast mechanisms controlling peroxisome biogenesis in a framework that integrates inference from these models with experimental data.

Potential Involvement of Peroxisome in Multiple Sclerosis and Alzheimer's Disease : Peroxisome and Neurodegeneration

Peroxisomopathies are rare diseases due to dysfunctions of the peroxisome in which this organelle is either absent or with impaired activities. These diseases, at the exception of type I hyperoxaluria and acatalasaemia, affect the central and peripheral nervous system. Due to the significant impact of peroxisomal abnormalities on the functioning of nerve cells, this has led to an interest in peroxisome in common neurodegenerative diseases, such as Alzheimer's disease and multiple sclerosis. In these diseases, a role of the peroxisome is suspected on the basis of the fatty acid and phospholipid profile in the biological fluids and the brains of patients. It is also speculated that peroxisomal dysfunctions could contribute to oxidative stress and mitochondrial alterations which are recognized as major players in the development of neurodegenerative diseases. Based on clinical and in vitro studies, the data obtained support a potential role of peroxisome in Alzheimer's disease and multiple sclerosis.

7-Ketocholesterol- and 7β-Hydroxycholesterol-Induced Peroxisomal Disorders in Glial, Microglial and Neuronal Cells: Potential Role in Neurodegeneration : 7-ketocholesterol and 7β-hydroxycholesterol-Induced Peroxisomal Disorders and Neurodegeneration

Peroxisomopathies are qualitative or quantitative deficiencies in peroxisomes which lead to increases in the level of very-long-chain fatty acids (VLCFA) and can be associated with more or less pronounced dysfunction of central nervous system cells: glial and microglial cells. Currently, in frequent neurodegenerative diseases, Alzheimer's disease (AD) and multiple sclerosis (MS), peroxisomal dysfunction is also suspected due to an increase in VLCFA, which can be associated with a decrease of plasmalogens, in these patients. Moreover, in patients suffering from peroxisomopathies, such as X-linked adrenoleukodystrophy (X-ALD), AD, or MS, the increase in oxidative stress observed leads to the formation of cytotoxic oxysterols: 7-ketocholesterol (7KC) and 7β-hydroxycholesterol (7β-OHC). These observations led to the demonstration that 7KC and 7β-OHC alter the biogenesis and activity of peroxisomes in glial and microglial cells. In X-ALD, AD, and MS, it is suggested that 7KC and 7β-OHC affecting the peroxisome, and which also induce mitochondrial dysfunctions, oxidative stress, and inflammation, could promote neurodegeneration. Consequently, the study of oxisome in peroxisomopathies, AD and MS, could help to better understand the pathophysiology of these diseases to identify therapeutic targets for effective treatments.

Localisation of oxysterols at the sub-cellular level and in biological fluids

Oxysterols are oxidized derivatives of cholesterol that are formed enzymatically or via reactive oxygen species or both. Cholesterol or oxysterols ingested as food are absorbed and packed into lipoproteins that are taken up by hepatic cells. Within hepatic cells, excess cholesterol is metabolised to form bile acids. The endoplasmic reticulum acts as the main organelle in the bile acid synthesis pathway. Metabolised sterols originating from this pathway are distributed within other organelles and in the cell membrane. The alterations to membrane oxysterol:sterol ratio affects the integrity of the cell membrane. The presence of oxysterols changes membrane fluidity and receptor orientation. It is well documented that hydroxylase enzymes located in mitochondria facilitate oxysterol production via an acidic pathway. More recently, the presence of oxysterols was also reported in lysosomes. Peroxisomal deficiencies favour intracellular oxysterols accumulation. Despite the low abundance of oxysterols compared to cholesterol, the biological actions of oxysterols are numerous and important. Oxysterol levels are implicated in the pathogenesis of multiple diseases ranging from chronic inflammatory diseases (atherosclerosis, Alzheimer's disease and bowel disease), cancer and numerous neurodegenerative diseases. In this article, we review the distribution of oxysterols in sub-cellular organelles and in biological fluids.

Octadecaneuropeptide (ODN) Induces N2a Cells Differentiation through a PKA/PLC/PKC/MEK/ERK-Dependent Pathway: Incidence on Peroxisome, Mitochondria, and Lipid Profiles

Neurodegenerative diseases are characterized by oxidative stress, mitochondrial damage, and death of neuronal cells. To counteract such damage and to favor neurogenesis, neurotrophic factors could be used as therapeutic agents. Octadecaneuropeptide (ODN), produced by astrocytes, is a potent neuroprotective agent. In N2a cells, we studied the ability of ODN to promote neuronal differentiation. This parameter was evaluated by phase contrast microscopy, staining with crystal violet, cresyl blue, and Sulforhodamine 101. The effect of ODN on cell viability and mitochondrial activity was determined with fluorescein diacetate and DiOC₆(3), respectively. The impact of ODN on the topography of mitochondria and peroxisomes, two tightly connected organelles involved in nerve cell functions and lipid metabolism, was evaluated by transmission electron microscopy and fluorescence microscopy: detection of mitochondria with MitoTracker Red, and peroxisome with an antibody directed against the ABCD3 peroxisomal transporter. The profiles in fatty acids, cholesterol, and cholesterol precursors were determined by gas chromatography, in some cases coupled with mass spectrometry. Treatment of N2a cells with ODN (10^-14 M, 48 h) induces neurite outgrowth. ODN-induced neuronal differentiation was associated with modification of topographical distribution of mitochondria and peroxisomes throughout the neurites and did not affect cell viability and mitochondrial activity. The inhibition of ODN-induced N2a differentiation with H89, U73122, chelerythrine and U0126 supports the activation of a PKA/PLC/PKC/MEK/ERK-dependent signaling pathway. Although there is no difference in fatty acid profile between control and ODN-treated cells, the level of cholesterol and some of its precursors (lanosterol, desmosterol, lathosterol) was increased in ODN-treated cells. The ability of ODN to induce neuronal differentiation without cytotoxicity reinforces the interest for this neuropeptide with neurotrophic properties to overcome nerve cell damage in major neurodegenerative diseases.

Hepatic symptoms and histology in 13 patients with a Zellweger spectrum disorder

Patients with a Zellweger spectrum disorder (ZSD) have a defect in the assembly or maintenance of peroxisomes, leading to a multisystem disease with variable outcome. Liver disease is an important feature in patients with severe and milder phenotypes and a frequent cause of death. However, the course and histology of liver disease in ZSD patients are ill-defined. We reviewed the hepatic symptoms and histological findings of 13 patients with a ZSD in which one or several liver biopsies have been performed (patient age 0.2-39 years). All patients had at least some histological liver abnormalities, ranging from minor fibrosis to cirrhosis. Five patients demonstrated significant disease progression with liver failure and early death. In others, liver-related symptoms were absent, although some still silently developed cirrhosis. Patients with peroxisomal mosaicism had a better prognosis. In addition, we show that patients are at risk to develop a hepatocellular carcinoma (HCC), as one patient developed a HCC at the age of 36 years and one patient a precancerous lesion at the age of 18 years. Thus, regular examination to detect fibrosis or cirrhosis should be included in the standard care of ZSD patients. In case of advanced fibrosis/cirrhosis expert consultation and HCC screening should be initiated. This study further delineates the spectrum and significance of liver involvement in ZSDs.

Induction of peroxisomal changes in oligodendrocytes treated with 7-ketocholesterol: Attenuation by α-tocopherol

The involvement of organelles in cell death is well established especially for endoplasmic reticulum, lysosomes and mitochondria. However, the role of the peroxisome is not well known, though peroxisomal dysfunction favors a rupture of redox equilibrium. To study the role of peroxisomes in cell death, 158 N murine oligodendrocytes were treated with 7-ketocholesterol (7 KC: 25-50 μM, 24 h). The highest concentration is known to induce oxiapoptophagy (OXIdative stress + APOPTOsis + autoPHAGY), whereas the lowest concentration does not induce cell death. In those conditions (with 7 KC: 50 μM) morphological, topographical and functional peroxisome alterations associated with modifications of the cytoplasmic distribution of mitochondria, with mitochondrial dysfunction (loss of transmembrane mitochondrial potential, decreased level of cardiolipins) and oxidative stress were observed: presence of peroxisomes with abnormal sizes and shapes similar to those observed in Zellweger fibroblasts, lower cellular level of ABCD3, used as a marker of peroxisomal mass, measured by flow cytometry, lower mRNA and protein levels (measured by RT-qPCR and western blotting) of ABCD1 and ABCD3 (two ATP-dependent peroxisomal transporters), and of ACOX1 and MFP2 enzymes, and lower mRNA level of DHAPAT, involved in peroxisomal β-oxidation and plasmalogen synthesis, respectively, and increased levels of very long chain fatty acids (VLCFA: C24:0, C24:1, C26:0 and C26:1, quantified by gas chromatography coupled with mass spectrometry) metabolized by peroxisomal β-oxidation. In the presence of 7 KC (25 μM), slight mitochondrial dysfunction and oxidative stress were found, and no induction of apoptosis was detected; however, modifications of the cytoplasmic distribution of mitochondria and clusters of mitochondria were detected. The peroxisomal alterations observed with 7 KC (25 μM) were similar to those with 7 KC (50 μM). In addition, data obtained by transmission electron microcopy and immunofluorescence microscopy by dual staining with antibodies raised against p62, involved in autophagy, and ABCD3, support that 7 KC (25-50 μM) induces pexophagy. 7 KC (25-50 μM)-induced side effects were attenuated by α-tocopherol but not by α-tocotrienol, whereas the anti-oxidant properties of these molecules determined with the FRAP assay were in the same range. These data provide evidences that 7 KC, at concentrations inducing or not cell death, triggers morphological, topographical and functional peroxisomal alterations associated with minor or major mitochondrial changes.

Lipid homeostasis and inflammatory activation are disturbed in classically activated macrophages with peroxisomal β-oxidation deficiency

Macrophage activation is characterized by pronounced metabolic adaptation. Classically activated macrophages show decreased rates of mitochondrial fatty acid oxidation and oxidative phosphorylation and acquire a glycolytic state together with their pro-inflammatory phenotype. In contrast, alternatively activated macrophages require oxidative phosphorylation and mitochondrial fatty acid oxidation for their anti-inflammatory function. Although it is evident that mitochondrial metabolism is regulated during macrophage polarization and essential for macrophage function, little is known on the regulation and role of peroxisomal β-oxidation during macrophage activation. In this study, we show that peroxisomal β-oxidation is strongly decreased in classically activated bone-marrow-derived macrophages (BMDM) and mildly induced in alternatively activated BMDM. To examine the role of peroxisomal β-oxidation in macrophages, we used Mfp2^-/- BMDM lacking the key enzyme of this pathway. Impairment of peroxisomal β-oxidation in Mfp2^-/- BMDM did not cause lipid accumulation but rather an altered distribution of lipid species with very-long-chain fatty acids accumulating in the triglyceride and phospholipid fraction. These lipid alterations in Mfp2^-/- macrophages led to decreased inflammatory activation of Mfp2^-/- BMDM and peritoneal macrophages evidenced by impaired production of several inflammatory cytokines and chemokines, but did not affect anti-inflammatory polarization. The disturbed inflammatory responses of Mfp2^-/- macrophages did not affect immune cell infiltration, as mice with selective elimination of MFP2 from myeloid cells showed normal monocyte and neutrophil influx upon challenge with zymosan. Together, these data demonstrate that peroxisomal β-oxidation is involved in fine-tuning the phenotype of macrophages, probably by influencing the dynamic lipid profile during macrophage polarization.

Argan Oil-Mediated Attenuation of Organelle Dysfunction, Oxidative Stress and Cell Death Induced by 7-Ketocholesterol in Murine Oligodendrocytes 158N

Argan oil is widely used in Morocco in traditional medicine. Its ability to treat cardiovascular diseases is well-established. However, nothing is known about its effects on neurodegenerative diseases, which are often associated with increased oxidative stress leading to lipid peroxidation and the formation of 7-ketocholesterol (7KC) resulting from cholesterol auto-oxidation. As 7KC induces oxidative stress, inflammation and cell death, it is important to identify compounds able to impair its harmful effects. These compounds may be either natural or synthetic molecules or mixtures of molecules such as oils. In this context: (i) the lipid profiles of dietary argan oils from Berkane and Agadir (Morocco) in fatty acids, phytosterols, tocopherols and polyphenols were determined by different chromatographic techniques; and (ii) their anti-oxidant and cytoprotective effects in 158N murine oligodendrocytes cultured with 7KC (25-50 µM; 24 h) without and with argan oil (0.1% v/v) or α-tocopherol (400 µM, positive control) were evaluated with complementary techniques of cellular and molecular biology. Among the unsaturated fatty acids present in argan oils, oleate (C18:1 n-9) and linoleate (C18:1 n-6) were the most abundant; the highest quantities of saturated fatty acids were palmitate (C16:0) and stearate (C18:0). Several phytosterols were found, mainly schottenol and spinasterol (specific to argan oil), cycloartenol, β-amyrin and citrostadienol. α- and γ-tocopherols were also present. Tyrosol and protocatechic acid were the only polyphenols detected. Argan and extra virgin olive oils have many compounds in common, principally oleate and linoleate, and tocopherols. Kit Radicaux Libres (KRL) and ferric reducing antioxidant power (FRAP) tests showed that argan and extra virgin olive oils have anti-oxidant properties. Argan oils were able to attenuate the cytotoxic effects of 7KC on 158N cells: loss of cell adhesion, cell growth inhibition, increased plasma membrane permeability, mitochondrial, peroxisomal and lysosomal dysfunction, and the induction of oxiapoptophagy (OXIdation + APOPTOsis + autoPHAGY). Altogether, our data obtained in 158N oligodendrocytes provide evidence that argan oil is able to counteract the toxic effects of 7KC on nerve cells, thus suggesting that some of its compounds could prevent or mitigate neurodegenerative diseases to the extent that they are able to cross the blood-brain barrier.

7-Ketocholesterol is increased in the plasma of X-ALD patients and induces peroxisomal modifications in microglial cells: Potential roles of 7-ketocholesterol in the pathophysiology of X-ALD

X-linked adrenoleukodystrophy (X-ALD) is a genetic disorder induced by a mutation in the ABCD1 gene, which causes the accumulation of very long-chain fatty acids in tissue and plasma. Oxidative stress may be a hallmark of X-ALD. In the plasma of X-ALD patients with different forms of the disease, characterized by high levels of C24:0 and C26:0, we observed the presence of oxidative stress revealed by decreased levels of GSH, α-tocopherol, and docosahexaenoic acid (DHA). We showed that oxidative stress caused the oxidation of cholesterol and linoleic acid, leading to the formation of cholesterol oxide derivatives oxidized at C7 (7-ketocholesterol (7KC), 7β-hydroxycholesterol (7β-OHC), and 7α-hydroxycholesrol (7α-OHC)) and of 9- and 13-hydroxyoctadecadienoic acids (9-HODE, 13-HODE), respectively. High levels of 7KC, 7β-OHC, 7α-OHC, 9-HODE and 13-HODE were found. As 7KC induces oxidative stress, inflammation and cell death, which could play key roles in the development of X-ALD, the impact of 7KC on the peroxisomal status was determined in microglial BV-2 cells. Indeed, environmental stress factors such as 7KC could exacerbate peroxisomal dysfunctions in microglial cells and thus determine the progression of the disease. 7KC induces oxiapoptophagy in BV-2 cells: overproduction of H₂O₂ and O₂^-, presence of cleaved caspase-3 and PARP, nuclear condensation and/or fragmentation; elevated [LC3-II/LC3-I] ratio, increased p62 levels. 7KC also induces several peroxisomal modifications: decreased Abcd1, Abcd2, Abcd3, Acox1 and/or Mfp2 mRNA and protein levels, increased catalase activity and decreased Acox1-activity. However, the Pex14 level was unchanged. It is suggested that high levels of 7KC in X-ALD patients could foster generalized peroxisomal dysfunction in microglial cells, which could in turn intensify brain damage.

Hepatic dysfunction in peroxisomal disorders

The peroxisomal compartment in hepatocytes hosts several essential metabolic conversions. These are defective in peroxisomal disorders that are either caused by failure to import the enzymes in the organelle or by mutations in the enzymes or in transporters needed to transfer the substrates across the peroxisomal membrane. Hepatic pathology is one of the cardinal features in disorders of peroxisome biogenesis and peroxisomal β-oxidation although it only rarely determines the clinical fate. In mouse models of these diseases liver pathologies also occur, although these are not always concordant with the human phenotype which might be due to differences in diet, expression of enzymes and backup mechanisms. Besides the morphological changes, we overview the impact of peroxisome malfunction on other cellular compartments including mitochondria and the ER. We further focus on the metabolic pathways that are affected such as bile acid formation, and dicarboxylic acid and branched chain fatty acid degradation. It appears that the association between deregulated metabolites and pathological events remains unclear.

Peroxisomes in zebrafish: distribution pattern and knockdown studies

Peroxisomes are organelles that are essential for normal development in men and mice. In order to explore whether zebrafish could be used as a model system to study the role of peroxisomes, we examined their distribution pattern in developing and adult zebrafish and we tested different approaches to eliminate them during the first days after fertilization. In 4-day-old embryos, catalase-containing peroxisomes were obvious in the liver, the pronephric duct and the wall of the yolk sac, but transcripts for peroxisomal matrix and membrane proteins were also detected in the head region from 24 h post-fertilization. In adult zebrafish, catalase-containing peroxisomes remained prominent in the hepatocytes, the renal proximal tubules and the intestinal epithelium. Several peroxins, essential proteins for the biogenesis of peroxisomes, were targeted using knockdown approaches. Two morpholinos, blocking, respectively, splice sites in pex3 and pex13, only induced a short in frame deletion or insertion in the transcripts and did not result in the elimination of peroxisomes after injection into one-cell embryos. A morpholino blocking translation of pex13 was able to reduce the number of peroxisomes to variable extents. Finally, overexpression of a potential dominant negative fragment of Pex3p did not result in deletion of peroxisomes from developing zebrafish. We conclude that in zebrafish (1) peroxisomes, as visualized by DAB cytochemistry for catalase activity, are most conspicuous in the liver and renal tubular epithelium; this pattern is reminiscent of peroxisome occurrence in mammalian organs, (2) our approaches to eliminate these organelles during development by targeting peroxins were not successful.

Brain damage in a large cohort of solvent abusers

The neuropathology of solvent inhalation consists of patchy myelin loss with white matter macrophages that contain granular inclusions. It has been described only in a small number of cases. We sought to characterize the abnormalities in greater detail. In a retrospective study from 1995 to 2009, we encountered 88 autopsy cases with documented history of solvent abuse by inhalation and 1 with industrial exposure. Among these are 6 fetuses and infants with maternal exposure, 23 children (12-17 years), and 60 adults (18-66 years). Available brain samples from 75 cases were stained with solochrome cyanein (to demonstrate myelin) and periodic acid-Schiff (PAS) (to highlight the inclusions). Forty brains of ethanol and/or illicit drug exposed individuals and ten cases of multiple sclerosis were examined as controls. We found that 16 cases (age 23-49, median 37 years) had well-established leukoencephalopathy with multifocal myelin loss and abundant macrophages that stain with PAS and which contain birefringent inclusions. Six cases (age 15-55, median 27 years) had early leukoencephalopathy with scattered macrophages but no obvious myelin changes. Clusters of PAS-staining but non-birefringent macrophages were seen in 2/10 cases of (active) multiple sclerosis and in none of the ethanol/drug exposed brains. Ultrastructurally, inclusions from solvent cases differed from multiple sclerosis cases. Although exposure to solvents is impossible to quantify, there appears to be a duration-dependent effect. Brain damage related to solvent abuse can begin within only a few years of the onset. In the context of substance abuse, the changes are relatively specific for solvent inhalation and do not appear to result from demyelination alone. Interaction with ethanol cannot be excluded as a compounding risk factor.

Refsum disease due to the splice-site mutation c.135-2A>G before exon 3 of the PHYH gene, diagnosed eight years after detection of retinitis pigmentosa

OBJECTIVES

If Refsum disease (RD) is not considered as a differential at onset of the initial manifestations the diagnosis of RD remains unrecognized for a long time as in the following case.

CASE REPORT

A 55-y old Caucasian female with hyperextensible joints developed progressive visual impairment due to retinitis pigmentosa and sensorimotor polyneuropathy of the lower limbs since age 32 y. Screening for causes of polyneuropathy at age 40 y revealed markedly elevated serum phytanic acid (PA) with a maximum value of 293.6 microg/ml (n:<6 microg/ml) why RD was diagnosed. Since age 48 y slowly progressive hypacusis was noted. RD was caused by the known transition A135G in exon 3 of the PHYH gene. Additionally, the polymorphism T153C in exon 3 of the PHYH gene was detected. Upon strict adherence to the Chelsea diet PA levels slightly decreased since onset of this therapy.

CONCLUSION

This case confirms that RD remains unrecognized for a long time if RD is not considered as a differential of retinitis pigmentosa as the initial manifestation of the disease. Early recognition of RD is important since there is the therapeutic option of starting a diet.

Review article: The function and regulation of proteins involved in bile salt biosynthesis and transport

BACKGROUND

Bile salts are produced and secreted by the liver and are required for intestinal absorption of fatty food components and excretion of endobiotics and xenobiotics. They are reabsorbed in the terminal ileum and transported back to the liver via the portal tract. Dedicated bile salt transporters in hepatocytes and enterocytes are responsible for the unidirectional transport of bile salts in the enterohepatic cycle.

AIM

To give an overview of the function and regulations of proteins involved in bile salt synthesis and transport.

METHODS

Data presented are obtained from PubMed-accessible literature combined with our own recent research.

RESULT

Hepatocytes and enterocytes contain unique bile salt importers (sodium-taurocholate cotransporting polypeptide and apical sodium-dependent bile acid transporter, respectively) and exporters (bile salt export pump and organic solute transporter alpha-beta, respectively). Enzymes involved in bile salt biosynthesis reside in different subcellular locations, including the endoplasmic reticulum, mitochondria, cytosol and peroxisomes. Defective expression or function of the transporters or enzymes may lead to cholastasis. The bile salt-activated transcription factor Farnesoid X receptor controls expression of genes involved in bile salt biosynthesis and transport.

CONCLUSIONS

Detailed knowledge is available about the enzymes and transporters involved in bile salt homeostasis and how their defective function is associated with cholestasis. In contrast, the process of intracellular bile salt transport is largely unexplored.

Retinitis pigmentosa, pigmentary retinopathies, and neurologic diseases

Retinitis pigmentosa (RP) refers to a group of inherited retinal diseases with phenotypic and genetic heterogeneity. The pathophysiologic basis of the progressive visual loss in patients with RP is not completely understood but is felt to be due to a primary retinal photoreceptor cell degenerative process mainly affecting the rods of the peripheral retina. In most cases RP is seen in isolation (nonsyndromic), but in some other cases it may be a part of a genetic, metabolic, or neurologic syndrome or disorder. Nyctalopia, or night blindness, is the most common symptom of RP. The classic fundus appearance of RP includes retinal pigment epithelial cell changes resulting in retinal hypo- or hyperpigmentation ("salt-and-pepper"), retinal granularity, and bone spicule formation. The retinal vessels are often narrowed or attenuated and there is a waxy pallor appearance of the optic nerve head. Electroretinography will demonstrate rod and cone photoreceptor cell dysfunction and is a helpful test in the diagnosis and monitoring of patients with RP. A detailed history with pedigree analysis, a complete ocular examination, and the appropriate paraclinical testing should be performed in patients complaining of visual difficulties at night or in dim light. This review discusses the clinical manifestations of RP as well as describing the various systemic diseases, with a special emphasis on neurologic diseases, associated with a pigmentary retinopathy.

Peroxisomal multifunctional protein-2 deficiency causes motor deficits and glial lesions in the adult central nervous system

In humans, mutations inactivating multifunctional protein-2 (MFP-2), and thus peroxisomal beta-oxidation, cause neuronal heterotopia and demyelination, which is clinically reflected by hypotonia, seizures, and death within the first year of life. In contrast, our recently generated MFP-2-deficient mice did not show neurodevelopmental abnormalities but exhibited aberrations in bile acid metabolism and one of three of them died early postnatally. In the postweaning period, all survivors developed progressive motor deficits, including abnormal cramping reflexes of the limbs and loss of mobility, with death at 6 months. Motor impairment was not accompanied by lesions of peripheral nerves or muscles. However, in the central nervous system MFP-2-deficient mice overexpressed catalase in glial cells, accumulated lipids in ependymal cells and in the molecular layer of the cerebellum, exhibited severe astrogliosis and reactive microglia predominantly within the gray matter of the brain and the spinal cord, whereas synaptic and myelin markers were not affected. This culminated in degenerative changes of astroglia cells but not in overt neuronal lesions. Neither the motor deficits nor the brain lesions were aggravated by increasing the branched-chain fatty acid concentration through dietary supplementation. These data indicate that MFP-2 deficiency in mice causes a neurological phenotype in adulthood that is manifested primarily by astroglial damage.

Peroxisomal multifunctional protein-2: the enzyme, the patients and the knockout mouse model

The mammalian multifunctional protein-2 (MFP-2, also called multifunctional enzyme 2, D-bifunctional enzyme or 17-beta-estradiol dehydrogenase type IV) was identified by several groups about a decade ago. It plays a central role in peroxisomal beta-oxidation as it handles most, if not all, peroxisomal beta-oxidation substrates. Deficiency of this enzyme in man causes a severe developmental syndrome with abnormalities in several organs but in particular in the brain, leading to death within the first year of life. Accumulation of branched-long-chain fatty acids and very-long-chain fatty acids and a disturbed synthesis of bile acids were documented in these patients. A mouse model with MFP-2 deficiency only partly phenocopies the human disease. Although the expected metabolic abnormalities are present, no neurodevelopmental aberrations are observed. However, the survival of these mice into adulthood allowed to document the importance of this enzyme for the normal functioning of the brain, eyes and testis. In the present review, the identification and biochemical characteristics of MFP-2, and the consequences of MFP-2 dysfunction in humans and in mice will be discussed.

Targeted disruption of the peroxisomal thiolase B gene in mouse: a new model to study disorders related to peroxisomal lipid metabolism

The peroxisomal beta-oxidation system consists of four steps catalysed by three enzymes: acyl-CoA oxidase, 3-hydroxyacyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase (multifunctional enzyme) and thiolase. In humans, thiolase activity is encoded by one gene, whereas in rodents, three enzymes encoded by three distinct genes (i.e. thiolase A, thiolase B and SCP2/thiolase) catalyse the thiolase activity. So far, acyl-CoA oxidase- and multifunctional enzyme-deficient patients have been identified and knock-out mice for these genes have been produced. Conversely, no isolated thiolase-deficient patient has been found, and no thiolase (A or B)-deficient mice have been generated. Hence, to better understand the cause of isolated human thiolase deficiency, we disrupted the catalytic site of the mouse thiolase B by homologous recombination in order to analyse the phenotype of these thiolase B-deficient mice. Mice, made homozygous for the mutation, lack expression of thiolase B mRNA and are viable, fertile and healthy at birth. They exhibit no detectable phenotype defects and no compensation, rather a slight decrease in other peroxisomal thiolase (thiolase A and SCPx) mRNAs, was found.

Activity of the yeast Tat2p tryptophan permease is sensitive to the anti-tumor agent 4-phenylbutyrate

4-Phenylbutyrate (PB) induces differentiation and is being intensively studied as a treatment for brain, prostate, breast, and hematopoietic cancer. While many different primary targets for PB have been proposed, the mechanism by which it causes cellular differentiation remains unknown. To identify the primary cellular target, we investigated its effects on Saccharomyces cerevisiae and showed that it inhibits tryptophan transport. We show here that PB and sorbic acid induce an ubiquitin-dependent turnover of the tryptophan permease Tat2p. However, the inhibition of transport is not a consequence of the loss of Tat2p, since it also occurs when turnover is prevented by deleting the Tat2p ubiquitination sites. When we tested the effects of PB and other growth inhibitory agents on the growth of amino acid auxotrophs, we found that several auxotrophs are hypersensitive to a number of chemically unrelated agents, including PB and some, but not all, weak acids; and this sensitivity is due to the inhibition of amino acid transport. For the inhibitory weak acids, inhibition is not confined to aromatic amino acid auxotrophs, nor is it a general weak acid stress response, since the degree of inhibition is independent of weak acid hydrophobicity and p Ka. Our results show that diverse agents affect the activity of the Tat2p permease rather than its stability and suggest the hypothesis that the anti-neoplastic action of PB is due to a decrease in the activity of surface receptors or other membrane proteins needed to maintain the transformed state.

Phenotypic variability (heterogeneity) of peroxisomal disorders

Peroxisomes perform a multitude of biosynthetic and catabolic functions, many of which are related to lipid metabolism. Peroxisomal disorders result either from deficiency of a single peroxisomal enzyme or protein, or from a defect in the complex mechanism of peroxisomal biogenesis, resulting in deficiency of several or multiple peroxisomal functions. These can be assessed by a battery of biochemical assays, enabling a biochemical phenotype to be defined that is specific and diagnostic for each of the peroxisomal disorders. Some peroxisomal disorders have unique and specific clinical phenotypes, which may be diagnostic. Others share patterns of clinical abnormalities (particularly neurological dysfunction, craniofacial dysmorphism, skeletal defects, sensory deafness, retinopathy) consistent with defined clinical phenotypes, but with considerable overlap and heterogeneity. To a certain extent, the clinical features of a particular disorder reflect the accumulation or deficiency of specific metabolites. Thus, the same clinical phenotypes may be caused by both single enzyme defects and PBDs. Furthermore, the same defect may present with different clinical phenotypes. In general, the severity of the clinical phenotype correlates with the degree of biochemical dysfunction. The clinical heterogeneity of peroxisomal disorders constitutes a diagnostic challenge demanding a high index of suspicion on the clinician's part.