Refsum disease, peroxisomes and phytanic acid oxidation: a review

Interaction between fatty acid oxidation and ethanol metabolism in liver

Fatty acid oxidation (FAO) releases the energy stored in fat to maintain basic biological processes. Dehydrogenation is a major way to oxidize fatty acids, which needs NAD+ to accept the released H+ from fatty acids and form NADH, which increases the ratio of NADH/NAD+ and consequently inhibits FAO leading to the deposition of fat in the liver, which is termed fatty liver or steatosis. Consumption of alcohol (ethanol) initiates simple steatosis that progresses to alcoholic steatohepatitis, which constitutes a spectrum of liver disorders called alcohol-associated liver disease (ALD). ALD is linked to ethanol metabolism. Ethanol is metabolized by alcohol dehydrogenase (ADH), microsomal ethanol oxidation system (MEOS), mainly cytochrome P450 2E1 (CYP2E1), and catalase. ADH also requires NAD+ to accept the released H+ from ethanol. Thus, ethanol metabolism by ADH leads to increased ratio of NADH/NAD+, which inhibits FAO and induces steatosis. CYP2E1 directly consumes reducing equivalent NADPH to oxidize ethanol, which generates reactive oxygen species (ROS) that lead to cellular injury. Catalase is mainly present in peroxisomes, where very long-chain fatty acids and branched-chain fatty acids are oxidized, and the resultant short-chain fatty acids will be further oxidized in mitochondria. Peroxisomal FAO generates hydrogen peroxide (H2O2), which is locally decomposed by catalase. When ethanol is present, catalase uses H2O2 to oxidize ethanol. In this review, we introduce FAO (including α-, β-, and ω-oxidation) and ethanol metabolism (by ADH, CYP2E1, and catalase) followed by the interaction between FAO and ethanol metabolism in the liver and its pathophysiological significance.

Phytanic acid, an inconclusive phytol metabolite: A review

Phytanic acid (PA: 3,7,11,15-tetramethylhexadecanoic acid) is an important biometabolite of the chlorophyll-derived diterpenoid phytol. Its biological sources (occurrence) and ADME (absorption, distribution, metabolism, and elimination) profile are well-discussed in the literature. Cumulative literature suggests that PA has beneficial as well as harmful biological roles in humans and other animals. This study aimed to sketch a brief summary of PA's beneficial and harmful pharmacological effects in test systems on the basis of existing literature reports. Literature findings propose that PA has anti-inflammatory and immunomodulatory, antidiabetic, anti-obesity, anticancer, and oocyte maturation effects. Although a high plasma PA-level mediated SLS remains controversial, it is evident to link it with Refsum's disease and other peroxisomal enzyme deficiency diseases in humans, including RCDP and LD; ZHDA and Alzheimer's disease; progressive ataxia and dysarthria; and an increased risk of some lymphomas such as LBL, FL, and NHL. PA exerts toxic effects on different kinds of cells, including neuronal, cardiac, and renal cells, through diverse pathways such as oxidative stress, mitochondrial disturbance, apoptosis, disruption of Na+/K+-ATPase activity, Ca2+ homeostasis, alteration of AChE and MAO activities, etc. PA is considered a cardiac biomarker in humans. In conclusion, PA may be one of the most important biometabolites in humans.

Adult Refsum Disease in Puerto Rico: A Case Report

Patients with adult Refsum Disease (ARD) have retinitis pigmentosa and thus nyctalopia, anosmia, sensorineural deafness, polyneuropathy, and ataxia. Upon physical examination, patients with ARD have congenital short metacarpals, metatarsals, and cardiac arrhythmias. Manifestations due to the lack of phytanoyl-CoA hydroxylase in peroxisomes needed for alpha-oxidation of phytanic acid lead patients to accumulate phytanic acid in their body tissues. To our knowledge, no consensus for clinical diagnostic criteria for patients with ARD has been published. Our patient had nyctalopia, retinal findings, and visual field results compatible with retinitis pigmentosa. Additionally, the patient had decreased macular thickness and volume in both eyes, the findings being worse in the left eye. The patient had undergone hand surgery due to chronic pain in both hands, as well as his fourth and fifth metatarsal bones were shortened. Interestingly, audiology evaluation showed mild hearing loss in the right ear and mild to moderate hearing loss in the left ear. Inheritance patterns in patients with ARD have been described. Physical examination, phytanic acid evaluation, and genetic studies may all help reach an ARD diagnosis. This is the first report of adult Refsum disease in Puerto Rico.

Phytanic Acid Intake and Lifestyle Modifications on Quality of Life in Individuals with Adult Refsum Disease: A Retrospective Survey Analysis

Adult Refsum disease (ARD) is a rare peroxisomal biogenesis disorder inherited in an autosomal recessive fashion and is often characterized by retinitis pigmentosa, cerebellar ataxia, and polyneuropathy. Many patients with ARD require diet modification, psychosocial support, and various specialist visits to manage their symptoms. In this study, we explored the quality of life in individuals with ARD by analyzing retrospective survey data collected by the Coordination of Rare Diseases at Sanford (CoRDS) Registry and Global Defeat Adult Refsum Everywhere (DARE) Foundation. Statistical tests used were frequencies, mean, and median. There were 32 respondents, ranging between 11 and 32 responses for each question. The mean age at diagnosis was 35.5 ± 14.5 years (range 6-64) with 36.4% male and 63.6% female respondents. The average age for retinitis pigmentosa diagnosis was 22.8 ± 15.7 years (range 2-61). Dieticians were the most frequently seen (41.7%) for management of low-phytanic-acid diets. Most participants exercise at least once per week (92.5%). Depression symptoms were reported in 86.2% of the participants. Early diagnosis of ARD is important for managing symptoms and preventing progression of visual impairment due to phytanic acid buildup. Interdisciplinary approach should be used for patients to address physical and psychosocial impairments of ARD.

Isoprenoid alcohols utilization by malaria parasites

Plasmodium falciparum is the etiological agent of human malaria, one of the most widespread diseases in tropical and subtropical regions. Drug resistance is one of the biggest problems in controlling the disease, which leads to the need to discover new antimalarial compounds. One of the most promissory drugs purposed is fosmidomycin, an inhibitor of the biosynthesis of isoprene units by the methylerythritol 4-phosphate (MEP) pathway, which in some cases failed in clinical studies. Once formed, isoprene units are condensed to form longer structures such as farnesyl and geranylgeranyl pyrophosphate, which are necessary for Heme O and A formation, ubiquinone, and dolichyl phosphate biosynthesis as well as for protein isoprenylation. Even though the natural substrates of polyprenyl transferases and synthases are polyprenyl pyrophosphates, it was already demonstrated that isoprenoid alcohols (polyprenols) such as farnesol (FOH) and geranylgeraniol (GGOH) can rescue parasites from fosmidomycin. This study better investigated how this rescue phenomenon occurs by performing drug-rescue assays. Similarly, to FOH and GGOH, it was observed that phytol (POH), a 20-carbon plant isoprenoid, as well as unsaponifiable lipid extracts from foods rescue parasites from the antimalarial effect of fosmidomycin. Contrarily, neither dolichols nor nonaprenol rescue parasites from fosmidomycin. Considering this, here we characterized the transport of FOH, GGOH, and POH. Once incorporated, it was observed that these substances are phosphorylated, condensed into longer isoprenoid alcohols, and incorporated into proteins and dolichyl phosphates. Through proteomic and radiolabelling approaches, it was found that prenylated proteins are naturally attached to several isoprenoids, derived from GGOH, dolichol, and POH if exogenously added. Furthermore, the results suggest the presence of at least two promiscuous protein prenyltransferases in the parasite: one enzyme which can use FPP among other unidentified substrates and another enzyme that can use GGPP, phytyl pyrophosphate (PPP), and dolichols, among other substrates not identified here. Thus, further evidence was obtained for dolichols and other isoprenoid products attached to proteins. This study helps to better understand the apicoplast-targeting antimalarial mechanism of action and a novel post-translational modification of proteins in P. falciparum.

Treatable Ataxias: How to Find the Needle in the Haystack?

Treatable ataxias are a group of ataxic disorders with specific treatments. These disorders include genetic and metabolic disorders, immune-mediated ataxic disorders, and ataxic disorders associated with infectious and parainfectious etiology, vascular causes, toxins and chemicals, and endocrinopathies. This review provides a comprehensive overview of different treatable ataxias. The major metabolic and genetic treatable ataxic disorders include ataxia with vitamin E deficiency, abetalipoproteinemia, cerebrotendinous xanthomatosis, Niemann-Pick disease type C, autosomal recessive cerebellar ataxia due to coenzyme Q10 deficiency, glucose transporter type 1 deficiency, and episodic ataxia type 2. The treatment of these disorders includes the replacement of deficient cofactors and vitamins, dietary modifications, and other specific treatments. Treatable ataxias with immune-mediated etiologies include gluten ataxia, anti-glutamic acid decarboxylase antibody-associated ataxia, steroid-responsive encephalopathy associated with autoimmune thyroiditis, Miller-Fisher syndrome, multiple sclerosis, and paraneoplastic cerebellar degeneration. Although dietary modification with a gluten-free diet is adequate in gluten ataxia, other autoimmune ataxias are managed by short-course steroids, plasma exchange, or immunomodulation. For autoimmune ataxias secondary to malignancy, treatment of tumor can reduce ataxic symptoms. Chronic alcohol consumption, antiepileptics, anticancer drugs, exposure to insecticides, heavy metals, and recreational drugs are potentially avoidable and treatable causes of ataxia. Infective and parainfectious causes of cerebellar ataxias include acute cerebellitis, postinfectious ataxia, Whipple's disease, meningoencephalitis, and progressive multifocal leukoencephalopathy. These disorders are treated with steroids and antibiotics. Recognizing treatable disorders is of paramount importance when dealing with ataxias given that early treatment can prevent permanent neurological sequelae.

Genetics behind Cerebral Disease with Ocular Comorbidity: Finding Parallels between the Brain and Eye Molecular Pathology

Cerebral visual impairments (CVIs) is an umbrella term that categorizes miscellaneous visual defects with parallel genetic brain disorders. While the manifestations of CVIs are diverse and ambiguous, molecular diagnostics stand out as a powerful approach for understanding pathomechanisms in CVIs. Nevertheless, the characterization of CVI disease cohorts has been fragmented and lacks integration. By revisiting the genome-wide and phenome-wide association studies (GWAS and PheWAS), we clustered a handful of renowned CVIs into five ontology groups, namely ciliopathies (Joubert syndrome, Bardet–Biedl syndrome, Alstrom syndrome), demyelination diseases (multiple sclerosis, Alexander disease, Pelizaeus–Merzbacher disease), transcriptional deregulation diseases (Mowat–Wilson disease, Pitt–Hopkins disease, Rett syndrome, Cockayne syndrome, X-linked alpha-thalassaemia mental retardation), compromised peroxisome disorders (Zellweger spectrum disorder, Refsum disease), and channelopathies (neuromyelitis optica spectrum disorder), and reviewed several mutation hotspots currently found to be associated with the CVIs. Moreover, we discussed the common manifestations in the brain and the eye, and collated animal study findings to discuss plausible gene editing strategies for future CVI correction.

Ophthalmic Diagnosis and Novel Management of Infantile Refsum Disease with Combination Docosahexaenoic Acid and Cholic Acid

Infantile Refsum disease is a rare peroxisomal biogenesis disorder characterized by impaired alpha-oxidation and accumulation of phytanic acid in the tissues. Patients often present with fundus changes resembling retinitis pigmentosa, developmental delay, sensorineural hearing loss, ataxia, and hepatomegaly. Traditionally, mainstay treatment for this condition has been a phytanic acid-restricted diet, although supplementation with either docosahexaenoic acid or cholic acid has rarely been described in the literature. We present a case of infantile Refsum disease in a child with retinitis pigmentosa-like ocular findings, sensorineural hearing loss, and self-resolving hepatic disease, who developed novel findings of macular edema refractory to carbonic anhydrase inhibitors. We describe management with a phytanic acid-restricted diet and combination docosahexaenoic acid, and cholic acid therapy, which helped to limit progression of her disease.

Crosstalk between Peroxisomal Activities and Nrf2 Signaling in Porcine Embryos

Melatonin and phytanic acid (PA) are known to be involved in lipid metabolism and β-oxidation, in which peroxisomal activities also significantly participate. In addition, other studies have reported that the nuclear factor-erythroid-derived 2-like 2 (Nrf2 or NFE2L2) signaling pathway mediates lipid metabolism and its subsequent cascades. As these mechanisms are partially involved in porcine oocytes or embryonic development, we hypothesized that the factors governing these mechanisms could be interconnected. Therefore, we aimed to investigate possible crosstalk between peroxisomal activities and Nrf2 signaling in porcine embryos following melatonin and PA treatment. Porcine embryos were cultured for seven days after parthenogenetic activation, and subsequently treated with melatonin and PA, or injected with Pex19-targeted siRNAs. Real-time PCR, immunocytochemistry, and BODIPY staining were used to evaluate peroxisomal activities, Nrf2 signaling, and subsequent lipid metabolism. We found that melatonin/PA treatment enhanced embryonic development, whereas injection with Pex19-targeted siRNAs had the opposite effect. Moreover, melatonin/PA treatment upregulated peroxisomal activities, Nrf2 signaling, lipid metabolism, and mitochondrial membrane potentials, whereas most of these mechanisms were downregulated by Pex19-targeted siRNAs. Therefore, we suggest that there is a connection between the action of melatonin and PA and the Nrf2 signaling pathway and peroxisomal activities, which positively influences porcine embryonic development.

Melatonin-Nrf2 Signaling Activates Peroxisomal Activities in Porcine Cumulus Cell-Oocyte Complexes

Melatonin and Nrf2 signaling synergistically improve mammalian oocyte maturation and embryonic development. Furthermore, previous studies have suggested an interplay between peroxisomes and Nrf2 signaling in cells, but it is still unclear whether peroxisomes are involved in oocyte maturation. The aim of the present study was to identify the possible roles of peroxisomes in the melatonin-Nrf2 signaling pathway during in vitro maturation (IVM) of porcine oocytes. Porcine oocytes were treated with melatonin (10^-9 M) and brusatol, a Nrf2 specific inhibitor, in order to investigate the mechanism. Then, the rates of maturation and related gene and protein expression were analyzed. During oocyte maturation, melatonin upregulated the expression of gene and protein related to Nrf2 signaling and peroxisomal activities; RNA sequencing partially validated these results. Our results demonstrate that melatonin can activate Nrf2 signaling by binding to melatonin receptor 2, resulting in the upregulation of catalase. Moreover, peroxisomes were also found to be activated in response to melatonin treatment, causing the activation of catalase; together with Nrf2 signaling, peroxisomes synergistically prevented the generation of reactive oxygen species and enhanced oocyte quality. Thus, we suggest that a crosstalk might exist between Nrf2 signaling and peroxisomal activities in porcine oocytes.

Phytanic acid-derived peroxisomal lipid metabolism in porcine oocytes

Lipid metabolism plays an important role in oocyte maturation. The peroxisome is the fundamental mediator for this mechanism. In this study, we investigated the peroxisomal lipid metabolism in porcine oocytes. Phytanic acid (PA) was chosen as an activator of alpha-oxidation in peroxisomes. Oocyte maturation, embryo development, immunocytochemistry of peroxisomal lipid activities, and staining of mitochondrial potentials were assessed. We found that 40 μM PA not only increased porcine oocyte maturation and embryonic development, but also upregulated the expression of genes and proteins related to activities of the peroxisomal lipid metabolism (PHYH, PEX19, and PEX subfamilies) and mitochondrial potentials (NRF1 and PGC1α). Moreover, PA upregulated the lipid droplet and fatty acid content in the oocytes. Moreover, mitochondria were activated and the mitochondrial membrane potential was increased after PA treatment, resulting in the production of more ATPs in the oocytes. Our findings suggest that the degradation of PA via alpha-oxidation in the peroxisome may potentiate oocyte maturation processes, peroxisomal lipid oxidation, and mitochondria activities.

Severe thiamine deficiency in eastern Baltic cod (Gadus morhua)

The eastern Baltic cod (Gadus morhua) population has been decreasing in the Baltic Sea for at least 30 years. Condition indices of the Baltic cod have decreased, and previous studies have suggested that this might be due to overfishing, predation, lower dissolved oxygen or changes in salinity. However, numerous studies from the Baltic Sea have demonstrated an ongoing thiamine deficiency in several animal classes, both invertebrates and vertebrates. The thiamine status of the eastern Baltic cod was investigated to determine if thiamine deficiency might be a factor in ongoing population declines. Thiamine concentrations were determined by chemical analyses of thiamine, thiamine monophosphate and thiamine diphosphate (combined SumT) in the liver using high performance liquid chromatography. Biochemical analyses measured the activity of the thiamine diphosphate-dependent enzyme transketolase to determine the proportion of apoenzymes in both liver and brain tissue. These biochemical analyses showed that 77% of the cod were thiamine deficient in the liver, of which 13% had a severe thiamine deficiency (i.e. 25% transketolase enzymes lacked thiamine diphosphate). The brain tissue of 77% of the cod showed thiamine deficiency, of which 64% showed severe thiamine deficiency. The thiamine deficiency biomarkers were investigated to find correlations to different biological parameters, such as length, weight, otolith weight, age (annuli counting) and different organ weights. The results suggested that thiamine deficiency increased with age. The SumT concentration ranged between 2.4–24 nmol/g in the liver, where the specimens with heavier otoliths had lower values of SumT (P = 0.0031). Of the cod sampled, only 2% of the specimens had a Fulton’s condition factor indicating a healthy specimen, and 49% had a condition factor below 0.8, indicating poor health status. These results, showing a severe thiamine deficiency in eastern Baltic cod from the only known area where spawning presently occurs for this species, are of grave concern.

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.

Clinical and Neuroimaging Spectrum of Peroxisomal Disorders

Peroxisomes play vital roles in a broad spectrum of cellular metabolic pathways. Defects in genes encoding peroxisomal proteins can result in a wide array of disorders, depending upon the metabolic pathways affected. These disorders can be broadly classified into 2 main groups; peroxisome biogenesis disorders (PBDs) and single peroxisomal enzyme deficiencies. Peroxisomal enzyme deficiencies are result of dysfunction of a specific metabolic pathway, while PBDs are due to generalized peroxisomal dysfunction. Mutations in PEX1 gene are the most common cause of PBDs, accounting for two-thirds of cases. Peroxisomal fission defects is a recently recognized entity, included under the subgroup of PBDs. The aim of this article is to provide a comprehensive review on the clinical and neuroimaging spectrum of peroxisomal disorders.

Phytol Promotes the Formation of Slow-Twitch Muscle Fibers through PGC-1α/miRNA but Not Mitochondria Oxidation

Phytol is a side chain of chlorophyll belonging to the side-chain double terpenoid. When animals consume food rich in chlorophyll, phytol can be broken down to phytanic acid after digestion. It was reported that feeding animals with different varieties and levels of forage could significant improve pH and marbling score of steer and lamb carcasses, but the internal mechanism for this is still not reported. The marbling score and pH of muscle was mainly determined by skeletal muscle fiber type, which is due to expression of different myosin heavy-chain (MHC) isoforms. Here, we provide evidence that phytol can indeed affect the diversity of muscle fiber types both in vitro and in vivo and demonstrate that phytol can increase the expression of MHC I (p < 0.05), likely by upgrading the expression of PPARδ, PGC-1α, and related miRNAs. This fiber-type transformation process may not be caused by activated mitochondrial metabolism but by the structural changes in muscle fiber types.

Phytanic acid attenuates insulin-like growth factor-1 activity via nitric oxide-mediated γ-secretase activation in rat aortic smooth muscle cells: possible implications for pathogenesis of infantile Refsum disease

BACKGROUND

Infantile Refsum disease (IRD), a peroxisomal disease with defective phytanic acid oxidation, causes neurological impairment and development delay. Insulin-like growth factor-1 (IGF-1) regulates child development and to understand molecular mechanism(s) of IRD, we examined the effect of phytanic acid (PA) on IGF-1 activity.

METHODS

Bromodeoxyuridine (BrdU) incorporation was measured in rat aortic smooth muscle cell (SMC) cultures following treatment with fetal bovine serum (FBS), basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF) or IGF-1 in the absence or presence of PA. Gene expression and protein contents of IGF-1 receptor (IGF-1R) and PDGF receptor (PDGFR) were examined using quantitative PCR and western blotting.

RESULTS

PA inhibited mitogenic activities of FBS, PDGF and IGF-1 with more pronounced effect on IGF-1-induced bromodeoxyuridine (BrdU) incorporation. Palmitic acid or lignoceric acids did not inhibit IGF-1 activity. PA had no effect on PDGFR mRNA/protein levels but markedly increased IGF-1R mRNA levels. PA and nitric oxide (NO) markedly decreased IGF-1R protein. L-NAME, a NO synthase inhibitor and DAPT, a γ-secretase inhibitor, alleviated PA-induced decrease in IGF-1R protein. Both PA and NO donor increased γ-secretase activity which was alleviated by L-NAME.

CONCLUSION

This study demonstrates that PA attenuates IGF-1 activity possibly through IGF-1R impairment and NO-mediated modulation of γ-secretase activity.

Inherited ichthyosis: Syndromic forms

Among diseases that cause ichthyosis as one of the symptoms, there are some diseases that induce abnormalities in organs other than the skin. Of these, diseases with characteristic signs are regarded as syndromes. Although these syndromes are very rare, Netherton syndrome, Sjögren-Larsson syndrome, Conradi-Hünermann-Happle syndrome, Dorfman-Chanarin syndrome, ichthyosis follicularis, atrichia and photophobia (IFAP) syndrome, and Refsum syndrome have been described in texts as representative ones. It is important to know the molecular genetics and pathomechanisms in order to establish an effective therapy and beneficial genetic counseling including a prenatal diagnosis.

Phytanic acid activates NADPH oxidase through transactivation of epidermal growth factor receptor in vascular smooth muscle cells

BACKGROUND

Phytanic acid (PA) has been implicated in development of cancer and its defective metabolism is known to cause life-threatening conditions, such as Refsum disease, in children. To explore molecular mechanisms of phytanic acid-induced cellular pathology, we investigated its effect on NADPH oxidase (NOX) and epidermal growth factor receptor (EGFR) in rat aortic smooth muscle cells (RASMC).

METHODS

Smooth muscle cells were isolated from rat aortae using enzymic digestion with collagenase and elastase. Cultured RASMC were treated with varying concentrations (0.5-10 μg/ml) of phytanic acid in the presence/absence of fetal bovine serum (FBS) and/or EGFR inhibitor, AG1478. Following treatment with experimental agents, NOX activity was assayed in RASMC cultures by luminescence method. Gene expression of NOX-1 and p47phox was assessed using RT-PCR. NOX-1, p47phox and, total EGFR protein and its phosphorylated form were measured by Western blotting.

RESULTS

Treatment of RASMC with supraphysiological concentrations (>2.5 μg/ml) of PA significantly (p < 0.01) increased the NOX activity. PA also significantly increased gene/protein expression of NOX-1 and p47phox whereas p22phox and p67phox remained unaffected. Interestingly, PA (2.5-10 μg/ml) markedly (2-3 folds) increased the total and phosphorylated EGFR. Treatment of cells with EGFR inhibitor, AG1478, significantly blocked the PA-induced enhancement of NOX activity.

CONCLUSIONS

Our findings that PA transactivates EGFR and induces NOX activity in vascular smooth muscle cells provide new insights into molecular mechanisms of PA's role in cancer and Refsum disease.

Peroxisomal Disorders: A Review on Cerebellar Pathologies

Peroxisomes are organelles with diverse metabolic tasks including essential roles in lipid metabolism. They are of utmost importance for the normal functioning of the nervous system as most peroxisomal disorders are accompanied with neurological symptoms. Remarkably, the cerebellum exquisitely depends on intact peroxisomal function both during development and adulthood. In this review, we cover all aspects of cerebellar pathology that were reported in peroxisome biogenesis disorders and in diseases caused by dysfunction of the peroxisomal α-oxidation, β-oxidation or ether lipid synthesis pathways. We also discuss the phenotypes of mouse models in which cerebellar pathologies were recapitulated and search for connections with the metabolic abnormalities. It becomes increasingly clear that besides the most severe forms of peroxisome dysfunction that are associated with developmental cerebellar defects, milder impairments can give rise to ataxia later in life.

Ataxia

Ataxia is a disorder of balance and coordination resulted from dysfunctions involving cerebellum and its afferent and efferent connections. While a variety of disorders can cause secondary ataxias, the list of genetic causes of ataxias is growing longer. Genetic abnormalities may involve mitochondrial dysfunction, oxidative stress, abnormal mechanisms of DNA repair, possible protein misfolding, and abnormalities in cytoskeletal proteins. Few ataxias are fully treatable while hope for efficacious gene therapy and pharmacotherapy is emerging. A discussion of the ataxias is presented here with brief mention of acquired ataxias, and a greater focus on inherited ataxias.

Reactive nitrogen species mediate oxidative stress and astrogliosis provoked by in vivo administration of phytanic acid in cerebellum of adolescent rats: A potential contributing pathomechanism of cerebellar injury in peroxisomal disorders

Phytanic acid (Phyt) accumulates in various peroxisomal diseases including Refsum disease (RD) and Zellweger syndrome (ZS). Since the pathogenesis of the neurological symptoms and especially the cerebellar abnormalities in these disorders are poorly known, we investigated the effects of in vivo intracerebral administration of Phyt on a large spectrum of redox homeostasis parameters in the cerebellum of young rats. Malondialdehyde (MDA) levels, sulfhydryl oxidation, carbonyl content, nitrite and nitrate concentrations, 2',7'-dichlorofluorescein (DCFH) oxidation, total (tGS) and reduced glutathione (GSH) levels and the activities of important antioxidant enzymes were determined at different periods after Phyt administration. Immunohistochemical analysis was also carried out in the cerebellum. Phyt significantly increased MDA and nitric oxide (NO) production and decreased GSH levels, without altering tGS, DCFH oxidation, sulfhydryl oxidation, carbonyl content and the activities of glutathione peroxidase (GPx), superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR) and glucose-6-phosphate dehydrogenase (G6PD). Furthermore, immunohistochemical analysis revealed that Phyt caused astrogliosis and protein nitrosative damage in the cerebellum. It was also observed that the NO synthase inhibitor Nω-Nitro-L-arginine methyl ester (L-NAME) prevented the increase of MDA and NO production as well as the decrease of GSH and the immunohistochemical alterations caused by Phyt, strongly suggesting that reactive nitrogen species (RNS) were involved in these effects. The present data provide in vivo solid evidence that Phyt disrupts redox homeostasis and causes astrogliosis in rat cerebellum probably mediated by RNS production. It is therefore presumed that disequilibrium of redox status may contribute at least in part to the cerebellum alterations characteristic of patients affected by RD and other disorders with Phyt accumulation.

Dietary influences on tissue concentrations of phytanic acid and AMACR expression in the benign human prostate

BACKGROUND

Alpha-methylacyl-CoA racemase (AMACR) is an enzyme involved in fatty acid metabolism that is markedly over-expressed in virtually all prostate cancers (PCa), relative to benign tissue. One of AMACR's primary substrates, phytanic acid, is derived predominately from red meat and dairy product consumption. Epidemiological evidence suggests links between dairy/red meat intake, as well as phytanic acid levels, and elevated PCa risk. This study investigates the relationships among dietary intake, serum and tissue concentrations of phytanic acid, and AMACR expression (mRNA and protein) in the histologically benign human prostate.

METHODS

Men undergoing radical prostatectomy for the treatment of localized disease provided a food frequency questionnaire (n = 68), fasting blood (n = 35), benign fresh frozen prostate tissue (n = 26), and formalin-fixed paraffin-embedded (FFPE) sections (n = 67). Serum and tissue phytanic acid concentrations were obtained by gas chromatography-mass spectrometry. We extracted RNA from epithelial cells using laser capture microdissection and quantified mRNA expression of AMACR and other genes involved in the peroxisomal phytanic acid metabolism pathway via qRT-PCR. Immunohistochemistry for AMACR was performed on FFPE sections and subsequently quantified via digital image analysis. Associations between diet, serum, and tissue phytanic acid levels, as well as AMACR and other gene expression levels were assessed by partial Spearman correlation coefficients.

RESULTS

High-fat dairy intake was the strongest predictor of circulating phytanic acid concentrations (r = 0.35, P = 0.04). Tissue phytanic acid concentrations were not associated with any dietary sources and were only weakly correlated with serum levels (r = 0.29, P = 0.15). AMACR gene expression was not associated with serum phytanic acid (r = 0.13, P = 0.47), prostatic phytanic acid concentrations (r = 0.03, P = 0.88), or AMACR protein expression (r = -0.16, P = 0.20).

CONCLUSIONS

Our data underscore the complexity of the relationship between AMACR and its substrates and do not support the unifying hypothesis that excess levels of dietary phytanic acid are responsible for both the overexpression of AMACR in prostate cancer and the potential association between PCa risk and intake of dairy foods and red meat.

Ultrastructure of skin from Refsum disease with emphasis on epidermal lamellar bodies and stratum corneum barrier lipid organization

Classic Refsum disease (RD) is a rare, autosomal recessively-inherited disorder of peroxisome metabolism due to a defect in the initial step in the alpha oxidation of phytanic acid (PA), a C16 saturated fatty acid with four methyl side groups, which accumulates in plasma and lipid enriched tissues (please see van den Brink and Wanders, Cell Mol Life Sci 63:1752-1765, 2006). It has been proposed that the disease complex in RD is in part due to the high affinity of phytanic acid for retinoid X receptors and peroxisome proliferator-activated receptors. Structurally, epidermal hyperplasia, increased numbers of cornified cell layers, presence of cells with lipid droplets in stratum basale and reduction of granular layer to a single layer have been reported by Blanchet-Bardon et al. (The ichthyoses, SP Medical & Scientific Books, New York, pp 65-69, 1978). However, lamellar body (LB) density and secretion were reportedly normal. We recently examined biopsies from four unrelated patients, using both OsO4 and RuO4 post-fixation to evaluate the barrier lipid structural organization. Although lamellar body density appeared normal, individual organelles often had distorted shape, or had non-lamellar domains interspersed with lamellar structures. Some of the organelles seemed to lack lamellar contents altogether, showing instead uniformly electron-dense contents. In addition, we also observed mitochondrial abnormalities in the nucleated epidermis. Stratum granulosum-stratum corneum junctions also showed co-existence of non-lamellar and lamellar domains, indicative of lipid phase separation. Also, partial detachment or complete absence of corneocyte lipid envelopes (CLE) was seen in the stratum corneum of all RD patients. In conclusion, abnormal LB contents, resulting in defective lamellar bilayers, as well as reduced CLEs, likely lead to impaired barrier function in RD.

Disruption of oxidative phosphorylation and synaptic Na(+), K(+)-ATPase activity by pristanic acid in cerebellum of young rats

AIMS

Peroxisomal biogenesis disorders (PBD) are inherited disorders clinically manifested by neurological symptoms and brain abnormalities, in which the cerebellum is usually involved. Biochemically, patients affected by these neurodegenerative diseases accumulate branched-chain fatty acids, including pristanic acid (Prist) in the brain and other tissues.

MAIN METHODS

In the present investigation we studied the in vitro influence of Prist, at doses found in PBD, on oxidative phosphorylation, by measuring the activities of the respiratory chain complexes I-IV and ATP production, as well as on creatine kinase and synaptic Na(+), K(+)-ATPase activities in rat cerebellum.

KEY FINDINGS

Prist significantly decreased complexes I-III (65%), II (40%) and especially II-III (90%) activities, without altering the activities of complex IV of the respiratory chain and creatine kinase. Furthermore, ATP formation and synaptic Na(+), K(+)-ATPase activity were markedly inhibited (80-90%) by Prist. We also observed that this fatty acid altered mitochondrial and synaptic membrane fluidity that may have contributed to its inhibitory effects on the activities of the respiratory chain complexes and Na(+), K(+)-ATPase.

SIGNIFICANCE

Considering the importance of oxidative phosphorylation for mitochondrial homeostasis and of Na(+), K(+)-ATPase for the maintenance of cell membrane potential, the present data indicate that Prist compromises brain bioenergetics and neurotransmission in cerebellum. We postulate that these pathomechanisms may contribute to the cerebellar alterations observed in patients affected by PBD in which Prist is accumulated.

Disruption of mitochondrial homeostasis by phytanic acid in cerebellum of young rats

Phytanic acid (Phyt) brain concentrations are highly increased in Refsum disease, a peroxisomal disorder clinically characterized by neurological features, cardiac abnormalities, and retinitis pigmentosa. Considering that the pathogenesis of cerebellar ataxia, a common finding in this disease, is still unknown, in the present work we investigated the in vitro effects of Phyt at concentrations similar to those found in affected patients on important parameters of mitochondrial homeostasis in cerebellum from young rats. The respiratory parameters states 3 and 4 and respiratory control ratio (RCR) determined by oxygen consumption, membrane potential (∆Ψm), NAD(P)H pool content, and swelling were evaluated in mitochondrial preparations from this cerebral structure. Phyt markedly increased state 4 respiration, whereas state 3 respiration, the RCR, the mitochondrial matrix NAD(P)H content, and ∆Ψm were decreased by this fatty acid, being the latter effect partially prevented by N-acetylcysteine. These data indicate that Phyt behaves as an uncoupler of oxidative phosphorylation and as a metabolic inhibitor disrupting mitochondrial homeostasis in cerebellum. It is proposed that these pathomechanisms may contribute at least in part to the cerebellar alterations found in Refsum disease.

Marked inhibition of Na+, K(+)- ATPase activity and the respiratory chain by phytanic acid in cerebellum from young rats: possible underlying mechanisms of cerebellar ataxia in Refsum disease

Refsum disease is an autosomal recessive disorder of peroxisomal metabolism biochemically characterized by highly elevated concentrations of phytanic acid (Phyt) in a variety of tissues including the cerebellum. Reduction of plasma Phyt levels by dietary restriction intake ameliorates ataxia, a common clinical manifestation of this disorder, suggesting a neurotoxic role for this branched-chain fatty acid. Therefore, considering that the underlying mechanisms of cerebellum damage in Refsum disease are poorly known, in the present study we tested the effects of Phyt on important parameters of bioenergetics, such as the activities of the respiratory chain complexes I to IV, creatine kinase and Na(+), K(+)- ATPase in cerebellum preparations from young rats. The activities of complexes I, II, I-III and II-III and Na(+), K(+)- ATPase were markedly inhibited (65-85%) in a dose-dependent manner by Phyt. In contrast, creatine kinase and complex IV activities were not altered by this fatty acid. Therefore, it is presumed that impairment of the electron flow through the respiratory chain and inhibition of Na(+), K(+)- ATPase that is crucial for synaptic function may be involved in the pathophysiology of the cerebellar abnormalities manifested as ataxia in Refsum disease and in other peroxisomal disorders in which brain Phyt accumulates.

Phosphorylation-dependent Pex11p and Fis1p interaction regulates peroxisome division

Pex11p plays a conserved role in peroxisome division. Although Pex11p is phosphorylated, the exact role of this modification was either unknown or confusing. Phosphorylation of Pichia pastoris Pex11p at serine 173 occurs at the peroxisome and is necessary for its interaction with Fis1p, a key protein of the peroxisome division complex.

Peroxisome division is regulated by the conserved peroxin Pex11p. In Saccharomyces cerevisiae (Sc), induction of the phosphoprotein ScPex11p coincides with peroxisome biogenesis. We show that the ScPex11p homologue in Pichia pastoris (PpPex11p) is phosphorylated at serine 173. PpPex11p expression and phosphorylation are induced in oleate and coordinated with peroxisome biogenesis. PpPex11p transits to peroxisomes via the endoplasmic reticulum (ER). PpPex11p is unstable and ER restricted gin pex3Δ and pex19Δ cells, which are impaired in peroxisomal membrane protein biogenesis. In oleate medium, the P. pastoris mutants pex11A (constitutively unphosphorylated; S173A) and pex11D (constitutively phosphorylated; S173D) exhibit juxtaposed elongated peroxisomes (JEPs) and hyperdivided forms, respectively, although protein levels remain unchanged. In contrast with ScPex11p, the ER-to-peroxisome translocation in P. pastoris is phosphorylation independent, and the phosphorylation occurs at the peroxisome. We show that PpPex11p interacts with the peroxisome fission machinery via PpFis1p and is regulated by phosphorylation because PpPex11p and PpPex11Dp interact more strongly with PpFis1p than PpPex11Ap. Neither PpPex11p nor PpFis1p is necessary for peroxisome division in methanol medium. We propose a model for the role of PpPex11p in the regulation of peroxisome division through a phosphorylation-dependent interaction with the fission machinery, providing novel insights into peroxisome morphogenesis.

Estimated phytanic acid intake and prostate cancer risk: a prospective cohort study

Phytanic acid is a saturated fatty acid found predominantly in red meat and dairy products and may contribute to increases in prostate cancer risk that are observed with higher intakes of these foods. We constructed a novel summary measure of phytanic acid intake and prospectively examined its association with prostate cancer risk in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study--a cohort of Finnish male smokers aged 50-69 years. Diet was assessed at baseline in 27,111 participants using a validated 276-item dietary questionnaire. Since phytanic acid is not currently included in food composition tables, we used the published phytanic acid content of 151 major food items to estimate total daily intake. During up to 21 years of follow-up, a total of 1,929 incident prostate cancer cases (including 438 advanced cases) were identified. Higher phytanic acid intake, though unrelated to the risk of localized disease [relative risks (RR) and 95% confidence intervals (CI) for increasing quartiles of intake = 1.00 (ref), 0.83 (0.68-1.01), 0.76 (0.62-0.94) and 0.91 (0.74-1.13); p trend = 0.23], was associated with increased risks of advanced prostate cancer [RR and 95% CI = 1.00 (ref), 1.43 (1.09-1.89), 1.31 (0.99-1.75) and 1.38 (1.02-1.89); p trend = 0.06]. This association appeared to be driven predominantly by phytanic acid obtained from dairy products (particularly butter). Our study indicates that phytanic acid may contribute to previously observed associations between high-fat animal foods (particularly dairy products) and prostate cancer risk, although some caution is warranted as it may be acting as a surrogate marker of dairy fat.

Alkyl-glycerol rescues plasmalogen levels and pathology of ether-phospholipid deficient mice

A deficiency of plasmalogens, caused by impaired peroxisomal metabolism affects normal development and multiple organs in adulthood. Treatment options aimed at restoring plasmalogen levels may be relevant for the therapy of peroxisomal and non-peroxisomal disorders. In this study we determined the in vivo efficacy of an alkyl glycerol (AG), namely, 1-O-octadecyl-rac-glycerol, as a therapeutic agent for defects in plasmalogen synthesis. To achieve this, Pex7 knockout mice, a mouse model for Rhizomelic Chondrodysplasia Punctata type 1 characterized by the absence of plasmalogens, and WT mice were fed a control diet or a diet containing 2% alkyl-glycerol. Plasmalogen levels were measured in target organs and the biochemical data were correlated with the histological analysis of affected organs. Plasmalogen levels in all peripheral tissues of Pex7 KO mice fed the AG diet for 2 months normalized to the levels of AG fed WT mice. In nervous tissues of Pex7 KO mice fed the AG-diet, plasmalogen levels were significantly increased compared to control fed KO mice. Histological analysis of target organs revealed that the AG-diet was able to stop the progression of the pathology in testis, adipose tissue and the Harderian gland. Interestingly, the latter tissues are characterized by the presence of lipid droplets which were absent or reduced in size and number when ether-phospholipids are lacking, but which can be restored with the AAG treatment. Furthermore, nerve conduction in peripheral nerves was improved. When given prior to the occurrence of major pathological changes, the AG-diet prevented or ameliorated the pathology observed in Pex7 KO mice depending on the degree of plasmalogen restoration. This study provides evidence of the beneficial effects of treating a plasmalogen deficiency with alkyl-glycerol.

Autosomal recessive cerebellar ataxia caused by mutations in the PEX2 gene

Objective

To expand the spectrum of genetic causes of autosomal recessive cerebellar ataxia (ARCA).

Case report

Two brothers are described who developed progressive cerebellar ataxia at 3 1/2 and 18 years, respectively. After ruling out known common genetic causes of ARCA, analysis of blood peroxisomal markers strongly suggested a peroxisomal biogenesis disorder. Sequencing of candidate PEX genes revealed a homozygous c.865_866insA mutation in the PEX2 gene leading to a frameshift 17 codons upstream of the stop codon. PEX gene mutations usually result in a severe neurological phenotype (Zellweger spectrum disorders).

Conclusions

Genetic screening of PEX2 and other PEX genes involved in peroxisomal biogenesis is warranted in children and adults with ARCA.

In vitro evidence that phytanic acid compromises Na(+),K(+)-ATPase activity and the electron flow through the respiratory chain in brain cortex from young rats

Phytanic acid (Phyt) tissue concentrations are increased in Refsum disease and other peroxisomal disorders characterized by neurologic damage and brain abnormalities. The present work investigated the in vitro effects of Phyt, at concentrations found in these peroxisomal disorders, on important parameters of energy metabolism in brain cortex of young rats. The parameters analyzed were CO(2) production from labeled acetate and glucose, the activities of the citric acid cycle enzymes citrate synthase, aconitase, isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, succinate dehydrogenase, fumarase and malate dehydrogenase, as well as of the respiratory chain complexes I-IV, creatine kinase and Na(+),K(+)-ATPase. Our results show that Phyt did not alter citric acid cycle enzyme activities, or CO(2) production from acetate, reflecting no impairment of the functionality of the citric acid cycle. In contrast, respiratory chain activities were reduced at complexes I, II, I-III, II-III and IV. Membrane synaptical Na(+),K(+)-ATPase activity was also reduced by Phyt, with no alteration of creatine kinase activity. Considering the importance of the electron flow through the respiratory chain for brain energy metabolism (oxidative phosphorylation) and of Na(+),K(+)-ATPase activity for maintaining membrane potential necessary for neurotransmission, the data indicate that Phyt impairs brain bioenergetics at the level of energy formation, as well as neurotransmission. It is presumed that Phyt-induced impairment of these important systems may be involved at least in part in the neurological damage found in patients affected by disorders in which brain Phyt concentrations are increased.

Sjogren-larsson syndrome: case report and review of neurologic abnormalities and ichthyosis

INTRODUCTION

Sjogren-Larsson syndrome (SLS) is characterized by the triad of ichthyosis, mental retardation, and spastic diplegia or quadriplegia. The hallmark of SLS is ichthyosis. We report a case and review the major differential diagnosis of SLS.

CASE REPORT

A 21-year-old woman presented with seizures, mental retardation, spastic diplegia, and ichthyosis since birth. Computed tomography scan revealed hypodense areas in the periventricular white matter. Skin biopsy demonstrated a lamellar ichthyosis. These findings were compatible with SLS.

CONCLUSION

When ichthyosis is associated with spasticity and mental retardation, one should consider SLS. If hypogonadism, ataxia, retinitis, cardiomyopathy, or dwarfism is present, other diagnosis rather than SLS should be investigated.

Autosomal recessive ataxias: 20 types, and counting

More than 140 years after the first description of Friedreich ataxia, autosomal recessive ataxias have become one of the more complex fields in Neurogenetics. Currently this group of diseases contains more than 20 clinical entities and an even larger number of associated genes. Some disorders are very rare, restricted to isolated populations, and others are found worldwide. An expressive number of recessive ataxias are treatable, and responsibility for an accurate diagnosis is high. The purpose of this review is to update the practitioner on clinical and pathophysiological aspects of these disorders and to present an algorithm to guide the diagnosis.

Alstrom syndrome (OMIM 203800): a case report and literature review

Background

Alstrom syndrome (AS) is a rare autosomal recessive disease characterized by multiorgan dysfunction. The key features are childhood obesity, blindness due to congenital retinal dystrophy, and sensorineural hearing loss. Associated endocrinologic features include hyperinsulinemia, early-onset type 2 diabetes, and hypertriglyceridemia. Thus, AS shares several features with the common metabolic syndrome, namely obesity, hyperinsulinemia, and hypertriglyceridemia. Mutations in the ALMS1 gene have been found to be causative for AS with a total of 79 disease-causing mutations having been described.

Case presentation

We describe the case of a 27-year old female from an English (Caucasian) kindred. She had been initially referred for hypertriglyceridemia, but demonstrated other features suggestive of AS, including blindness, obesity, type 2 diabetes, renal dysfunction, and hypertension. DNA analysis revealed that she is a compound heterozygote with two novel mutations in the ALMS1 gene – H3882Y and V424I. Examination of her family revealed that her phenotypically unaffected mother and younger sister also had heterozygous mutations in the ALMS1 gene. In addition to presenting these novel molecular findings for AS, we review the clinical and genetic features of AS in the context of our case.

Conclusion

Two novel mutations in the ALMS1 gene causative for AS have been reported here, thereby increasing the number of reported mutations to 81 and providing a wider basis for mutational screening among affected individuals.

Peroxisomal disorders affecting phytanic acid α-oxidation: a review

Peroxisomes are involved in the synthesis and degradation of complex fatty acids. They contain enzymes involved in the α-, β- and ω-oxidation pathways for fatty acids. Investigation of these pathways and the diseases associated with mutations in enzymes involved in the degradation of phytanic acid have led to the clarification of the pathophysiology of Refsum's disease, rhizomelic chondrodysplasia and AMACR (α-methylacyl-CoA racemase) deficiency. This has highlighted the role of an Fe(II)- and 2-oxoglutarate-dependent oxygenases [PhyH (phytanoyl-CoA 2-hydroxylase), also known as PAHX], thiamin-dependent lyases (phytanoyl-CoA lyase) and CYP (cytochrome P450) family 4A in fatty acid metabolism. The differential regulation and biology of these pathways is suggesting novel ways to treat the neuro-ophthalmological sequelae of Refsum's disease. More recently, the discovery that AMACR and other peroxisomal β-oxidation pathway enzymes are highly expressed in prostate and renal cell cancers has prompted active investigation into the role of these oxidation pathways and the peroxisome in the progression of obesity- and insulin resistance-related cancers.

Biochemistry of mammalian peroxisomes revisited

In this review, we describe the current state of knowledge about the biochemistry of mammalian peroxisomes, especially human peroxisomes. The identification and characterization of yeast mutants defective either in the biogenesis of peroxisomes or in one of its metabolic functions, notably fatty acid beta-oxidation, combined with the recognition of a group of genetic diseases in man, wherein these processes are also defective, have provided new insights in all aspects of peroxisomes. As a result of these and other studies, the indispensable role of peroxisomes in multiple metabolic pathways has been clarified, and many of the enzymes involved in these pathways have been characterized, purified, and cloned. One aspect of peroxisomes, which has remained ill defined, is the transport of metabolites across the peroxisomal membrane. Although it is clear that mammalian peroxisomes under in vivo conditions are closed structures, which require the active presence of metabolite transporter proteins, much remains to be learned about the permeability properties of mammalian peroxisomes and the role of the four half ATP-binding cassette (ABC) transporters therein.

Characterization of phytanic acid omega-hydroxylation in human liver microsomes

Phytanic acid is a 3-methyl branched-chain fatty acid which originates from dietary sources. Since the 3-methyl group blocks regular beta-oxidation, it is broken down by peroxisomal alpha-oxidation. Adult Refsum disease patients accumulate phytanic acid as a result of an impairment in peroxisomal alpha-oxidation, caused by the deficient activity of the enzyme phytanoyl-CoA hydroxylase in the majority of patients. In this paper, we studied an alternative degradation route for phytanic acid, namely omega-oxidation. During omega-oxidation a fatty acid is hydroxylated at its omega-end by a member of the cytochrome P450 multi-enzyme family. Subsequently, an alcohol dehydrogenase converts the formed hydroxyl group into an aldehyde, which is then converted into a carboxyl-group by an aldehyde dehydrogenase. In case of phytanic acid omega-hydroxylation would lead to the formation of phytanedioic acid, which can be degraded by beta-oxidation from the omega-end. Here, we show that phytanic acid indeed undergoes omega- and (omega-1)-hydroxylation in pooled human liver microsomes in an NADPH-dependent manner with a ratio of 15:1. Studies with imidazole antimycotics indicate that these reactions are catalyzed by one or more cytochrome P450 enzymes. Induction of the cytochrome P450 involved in phytanic acid omega-hydroxylation may increase the flux through the omega-oxidation pathway, causing increased clearance of phytanic acid in ARD patients. Hence, this alternative catabolic pathway is of potential therapeutic relevance.

Studies on the specificity of unprocessed and mature forms of phytanoyl-CoA 2-hydroxylase and mutation of the iron binding ligands

The mature form of phytanoyl-coenzyme A 2-hydroxylase (PAHX), a nonheme Fe(II)- and 2-oxoglutarate-dependent oxygenase, catalyzes the alpha-hydroxylation of phytanoyl-CoA within peroxisomes. Mutations in PAHX result in some forms of adult Refsum's disease. Unprocessed PAHX (pro-PAHX) contains an N-terminal peroxisomal targeting sequence that is cleaved to give mature PAHX (mat-PAHX). Previous studies have implied a difference in the substrate specificity of the unprocessed and mature forms of PAHX. We demonstrate that both forms are able to hydroxylate a range of CoA derivatives, but under the same assay conditions, the N-terminal hexa-His-tagged unprocessed form is less active than the nontagged mature form. Analyses of the assay conditions suggest a rationale for the lack of activity previously reported for some substrates (e.g. isovaleryl-CoA) for the (His)6pro-PAHX. Site-directed mutagenesis was used to support proposals for the identity of the iron binding ligands (His-175, Asp-177, His-264) of the 2-His-1-carboxylate motif of PAHX. Mutation of other histidine residues (His-213, His-220, His-259) suggested that these residues were not involved in Fe(II) binding.

The Refsum disease marker phytanic acid, a branched chain fatty acid, affects Ca2+ homeostasis and mitochondria, and reduces cell viability in rat hippocampal astrocytes

The saturated branched chain fatty acid, phytanic acid, a degradation product of chlorophyll, accumulates in Refsum disease, an inherited peroxisomal disorder with neurological clinical features. To elucidate the pathogenic mechanism, we investigated the influence of phytanic acid on cellular physiology of rat hippocampal astrocytes. Phytanic acid (100 microM) induced an immediate transient increase in cytosolic Ca2+ concentration, followed by a plateau. The peak of this biphasic Ca2+ response was largely independent of extracellular Ca2+, indicating activation of cellular Ca2+ stores by phytanic acid. Phytanic acid depolarized mitochondria without causing in situ swelling of mitochondria. The slow decrease of mitochondrial potential is not consistent with fast and simultaneous opening of the mitochondrial permeability transition pore. However, phytanic acid induced substantial generation of reactive oxygen species. Phytanic acid caused astroglia cell death after a few hours of exposure. We suggest that the cytotoxic effect of phytanic acid seems to be due to a combined action on Ca2+ regulation, mitochondrial depolarization, and increased ROS generation in brain cells.