Lovastatin in X-linked adrenoleukodystrophy

In vivo adenine base editing rescues adrenoleukodystrophy in a humanized mouse model

X-linked adrenoleukodystrophy (ALD), an inherited neurometabolic disorder caused by mutations in ABCD1, which encodes the peroxisomal ABC transporter, mainly affects the brain, spinal cord, adrenal glands, and testes. In ALD patients, very-long-chain fatty acids (VLCFAs) fail to enter the peroxisome and undergo subsequent β-oxidation, resulting in their accumulation in the body. It has not been tested whether in vivo base editing or prime editing can be harnessed to ameliorate ALD. We developed a humanized mouse model of ALD by inserting a human cDNA containing the pathogenic variant into the mouse Abcd1 locus. The humanized ALD model showed increased levels of VLCFAs. To correct the mutation, we tested both base editing and prime editing and found that base editing using ABE8e(V106W) could correct the mutation in patient-derived fibroblasts at an efficiency of 7.4%. Adeno-associated virus (AAV)-mediated systemic delivery of NG-ABE8e(V106W) enabled robust correction of the pathogenic variant in the mouse brain (correction efficiency: ∼5.5%), spinal cord (∼5.1%), and adrenal gland (∼2%), leading to a significant reduction in the plasma levels of C26:0/C22:0. This established humanized mouse model and the successful correction of the pathogenic variant using a base editor serve as a significant step toward treating human ALD disease.

ABCD1 Transporter Deficiency Results in Altered Cholesterol Homeostasis

X-linked adrenoleukodystrophy (X-ALD), the most common peroxisomal disorder, is caused by mutations in the peroxisomal transporter ABCD1, resulting in the accumulation of very long-chain fatty acids (VLCFA). Strongly affected cell types, such as oligodendrocytes, adrenocortical cells and macrophages, exhibit high cholesterol turnover. Here, we investigated how ABCD1 deficiency affects cholesterol metabolism in human X-ALD patient-derived fibroblasts and CNS tissues of Abcd1-deficient mice. Lipidome analyses revealed increased levels of cholesterol esters (CE), containing both saturated VLCFA and mono/polyunsaturated (V)LCFA. The elevated CE(26:0) and CE(26:1) levels remained unchanged in LXR agonist-treated Abcd1 KO mice despite reduced total C26:0. Under high-cholesterol loading, gene expression of SOAT1, converting cholesterol to CE and lipid droplet formation were increased in human X-ALD fibroblasts versus healthy control fibroblasts. However, the expression of NCEH1, catalysing CE hydrolysis and the cholesterol transporter ABCA1 and cholesterol efflux were also upregulated. Elevated Soat1 and Abca1 expression and lipid droplet content were confirmed in the spinal cord of X-ALD mice, where expression of the CNS cholesterol transporter Apoe was also elevated. The extent of peroxisome-lipid droplet co-localisation appeared low and was not impaired by ABCD1-deficiency in cholesterol-loaded primary fibroblasts. Finally, addressing steroidogenesis, progesterone-induced cortisol release was amplified in X-ALD fibroblasts. These results link VLCFA to cholesterol homeostasis and justify further consideration of therapeutic approaches towards reducing VLCFA and cholesterol levels in X-ALD.

Multivariate analysis and model building for classifying patients in the peroxisomal disorders X-linked adrenoleukodystrophy and Zellweger syndrome in Chinese pediatric patients

BACKGROUND

The peroxisome is a ubiquitous single membrane-enclosed organelle with an important metabolic role. Peroxisomal disorders represent a class of medical conditions caused by deficiencies in peroxisome function and are segmented into enzyme-and-transporter defects (defects in single peroxisomal proteins) and peroxisome biogenesis disorders (defects in the peroxin proteins, critical for normal peroxisome assembly and biogenesis). In this study, we employed multivariate supervised and non-supervised statistical methods and utilized mass spectrometry data of neurological patients, peroxisomal disorder patients (X-linked adrenoleukodystrophy and Zellweger syndrome), and healthy controls to analyze the role of common metabolites in peroxisomal disorders, to develop and refine a classification models of X-linked adrenoleukodystrophy and Zellweger syndrome, and to explore analytes with utility in rapid screening and diagnostics.

RESULTS

T-SNE, PCA, and (sparse) PLS-DA, operated on mass spectrometry data of patients and healthy controls were utilized in this study. The performance of exploratory PLS-DA models was assessed to determine a suitable number of latent components and variables to retain for sparse PLS-DA models. Reduced-features (sparse) PLS-DA models achieved excellent classification performance of X-linked adrenoleukodystrophy and Zellweger syndrome patients.

CONCLUSIONS

Our study demonstrated metabolic differences between healthy controls, neurological patients, and peroxisomal disorder (X-linked adrenoleukodystrophy and Zellweger syndrome) patients, refined classification models and showed the potential utility of hexacosanoylcarnitine (C26:0-carnitine) as a screening analyte for Chinese patients in the context of a multivariate discriminant model predictive of peroxisomal disorders.

An update on the diagnosis and treatment of adrenoleukodystrophy

PURPOSE OF REVIEW

The present review summarizes recent advances in the diagnosis and management of patients with X-linked adrenoleukodystrophy (ALD).

RECENT FINDINGS

Although ALD screening has been on the list of Recommended Uniform Screening Panel since 2016, only 30 states in the United States are currently testing their newborns for this disease. Hematopoietic stem cell transplant (HSCT) remains the only successful treatment option available for early cerebral ALD but does not reverse neurological changes or affect the course of adrenal insufficiency. There remains a significant knowledge gap in our understanding and treatment of this disease. Novel therapies such as gene therapy and gene editing have shown promising results in animal models and are exciting potential treatment options for the future.Recently, the American Academy of Neurologists released their consensus guidelines on the diagnosis, surveillance, and management of ALD.

SUMMARY

Early diagnosis and HSCT are key to improving the morbidity and mortality associated with ALD. The implementation of universal newborn screening for ALD and rigorous investigations of novel diagnostic and therapeutic agents is the need of the hour.

The Role of Oxidative Stress and Inflammation in X-Link Adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is an inherited disease caused by a mutation in the ABCD1 gene encoding a peroxisomal transmembrane protein. It is characterized by the accumulation of very-long-chain fatty acids (VLCFAs) in body fluids and tissues, leading to progressive demyelination and adrenal insufficiency. ALD has various phenotypes, among which the most common and severe is childhood cerebral adrenoleukodystrophy (CCALD). The pathophysiological mechanisms of ALD remain unclear, but some in vitro/in vivo research showed that VLCFA could induce oxidative stress and inflammation, leading to damage. In addition, the evidence that oxidative stress and inflammation are increased in patients with X-ALD also proves that it is a potential mechanism of brain and adrenal damage. Therefore, normalizing the redox balance becomes a critical therapeutic target. This study focuses on the possible predictors of the severity and progression of X-ALD, the potential mechanisms of pathogenesis, and the promising targeted drugs involved in oxidative stress and inflammation.

Stem cell transplantation for pediatric patients with adrenoleukodystrophy: A nationwide retrospective analysis in Japan

BACKGROUND

Adrenoleukodystrophy (ALD) is an X-linked recessive disorder and 30-40% of patients develop progressive cerebral neurodegeneration. For symptomatic ALD patients, allogeneic stem cell transplantation (SCT) is considered the standard treatment modality to stabilize or prevent the progression of neurological symptoms.

METHODS

We retrospectively analyzed the transplant outcomes of 99 pediatric patients with cerebral ALD in Japan. The conditioning regimens included Regimen A: fludarabine/melphalan/low-dose total body irradiation (TBI) with brain sparing (n = 39), Regimen B; busulfan/cyclophosphamide ± others (n = 23), Regimen C: melphalan/total lymphoid irradiation/thoracoabdominal irradiation ± anti-T lymphocyte globulin ± fludarabine (n = 27), and Regimen D: others (n = 10).

RESULTS

The 5-year overall survival (OS) and event-free survival (EFS) of all patients were 90.0% and 72.9%, respectively. The 5-year OS was 100.0% for Regimen A, 91.1% for Regimen B, 84.4% for Regimen C, and 67.5% for Regimen D (p = 0.028). The 5-year EFS was 78.3% for Regimen A, 78.0% for Regimen B, 70.4% for Regimen C, and 48.0% for Regimen D (p = 0.304). The OS marginally improved after 2007 compared with before 2006 (95.3% vs. 85.2%, p = 0.066), due to the improvement of cord blood transplantation (CBT) outcomes after 2007 compared with before 2006 (96.6% vs. 68.4%, p = 0.005). On magnetic resonance imaging of the brain, a reduced Loes score after SCT was only observed in one of the 15 bone marrow transplantation (BMT) patients, but in 5 of the 15 CBT patients (p = 0.173).

CONCLUSIONS

Our study revealed that a reduced conditioning regimen with fludarabine/melphalan/low-dose TBI provides better outcomes, and the results of CBT significantly improved after 2007.

The Changing Face of Adrenoleukodystrophy

Adrenoleukodystrophy (ALD) is a rare X-linked disorder of peroxisomal oxidation due to mutations in ABCD1. It is a progressive condition with a variable clinical spectrum that includes primary adrenal insufficiency, myelopathy, and cerebral ALD. Adrenal insufficiency affects over 80% of ALD patients. Cerebral ALD affects one-third of boys under the age of 12 and progresses to total disability and death without treatment. Hematopoietic stem cell transplantation (HSCT) remains the only disease-modifying therapy if completed in the early stages of cerebral ALD, but it does not affect the course of adrenal insufficiency. It has significant associated morbidity and mortality. A recent gene therapy clinical trial for ALD reported short-term MRI and neurological outcomes comparable to historical patients treated with HSCT without the associated adverse side effects. In addition, over a dozen states have started newborn screening (NBS) for ALD, with the number of states expecting to double in 2020. Genetic testing of NBS-positive neonates has identified novel variants of unknown significance, providing further opportunity for genetic characterization but also uncertainty in the monitoring and therapy of subclinical and/or mild adrenal insufficiency or cerebral involvement. As more individuals with ALD are identified at birth, it remains uncertain if availability of matched donors, transplant (and, potentially, gene therapy) centers, and specialists may affect the timely treatment of these individuals. As these promising gene therapy trials and NBS transform the clinical management and outcomes of ALD, there will be an increasing need for the endocrine management of presymptomatic and subclinical adrenal insufficiency. (Endocrine Reviews 41: 1 - 17, 2020).

Comparison of the Diagnostic Performance of C26:0-Lysophosphatidylcholine and Very Long-Chain Fatty Acids Analysis for Peroxisomal Disorders

Peroxisomes are subcellular organelles that are involved in various important physiological processes such as the oxidation of fatty acids and the biosynthesis of bile acids and plasmalogens. The gold standard in the diagnostic work-up for patients with peroxisomal disorders is the analysis of very long-chain fatty acid (VLCFA) levels in plasma. Alternatively, C26:0-lysophosphatidylcholine (C26:0-LPC) can be measured in dried blood spots (DBS) using liquid chromatography tandem mass spectrometry (LC-MS/MS); a fast and easy method but not yet widely used. Currently, little is known about the correlation of C26:0-LPC in DBS and C26:0-LPC in plasma, and how C26:0-LPC analysis compares to VLCFA analysis in diagnostic performance. We investigated the correlation between C26:0-LPC levels measured in DBS and plasma prepared from the same blood sample. For this analysis we included 43 controls and 38 adrenoleukodystrophy (ALD) (21 males and 17 females) and 33 Zellweger spectrum disorder (ZSD) patients. In combined control and patient samples there was a strong positive correlation between DBS C26:0-LPC and plasma C26:0-LPC, with a Spearman's rank correlation coefficient of r (114) = 0.962, p < 0.001. These data show that both plasma and DBS are suitable to determine blood C26:0-LPC levels and that there is a strong correlation between C26:0-LPC levels in both matrices. Following this, we investigated how VLCFA and C26:0-LPC analysis compare in diagnostic performance for 67 controls, 26 ALD males, 19 ALD females, and 35 ZSD patients. For C26:0-LPC, all ALD and ZSD samples had C26:0-LPC levels above the upper limit of the reference range. For C26:0, one out of 67 controls had C26:0 levels above the upper reference range. For 1 out of 26 (1/26) ALD males, 1/19 ALD females and 3/35 ZSD patients, the C26:0 concentration was within the reference range. The C26:0/C22:0 ratio was within the reference range for 0/26 ALD males, 1/19 ALD females and 2/35 ZSD patients. Overall, these data demonstrate that C26:0-LPC analysis has a superior diagnostic performance compared to VLCFA analysis (C26:0 and C26:0/C22:0 ratio) in all patient groups. Based on our results we recommend implementation of C26:0-LPC analysis in DBS and/or plasma in the diagnostic work-up for peroxisomal disorders.

The Pleiotropic Effects of Statins in Endocrine Disorders

BACKGROUND

The 3-Hydroxy-3-MethylGlutaryl-CoA reductase inhibitors, better known as statins, are used extensively in the treatment of dyslipidemia and cardiovascular risk reduction. They have also demonstrated a variety of non-lipid lowering, or pleiotropic effects. Pertaining to the endocrine system the benefits of statins can extend to patients with the polycystic ovarian syndrome and thyroid disease. However, there is also increasing evidence that statin use can lead to deleterious effects in different organs, including worsening glycemia and the development of diabetes mellitus.

OBJECTIVE

The aim of this review is to describe the most relevant and updated evidence regarding the pleiotropic effects of statins in endocrine disorders.

METHODS

We did a systematic review of scientific articles published in PubMed regarding the effects of statins on the different aspects of the endocrine system up until June 5th of 2018.

RESULTS

We identified preliminarily 61 publications, of which 4 were excluded due to having abstract format only, and 5 were excluded for not containing pertinent information to the study.

CONCLUSION

Several aspects of the endocrine system have been shown to be influenced by the pleiotropic effects that statins exert, however, the benefits of statins on cardiovascular morbidity and mortality largely outweigh this deleterious effect, and statin therapy should continue to be recommended.

X-linked adrenoleukodystrophy: Pathology, pathophysiology, diagnostic testing, newborn screening and therapies

Adrenoleukodystrophy (ALD) is a rare X-linked disease caused by a mutation of the peroxisomal ABCD1 gene. This review summarizes our current understanding of the pathogenic cell- and tissue-specific roles of lipid species in the context of experimental therapeutic strategies and provides an overview of critical historical developments, therapeutic trials and the advent of newborn screening in the USA. In ALD, very long-chain fatty acid (VLCFA) chain length-dependent dysregulation of endoplasmic reticulum stress and mitochondrial radical generating systems inducing cell death pathways has been shown, providing the rationale for therapeutic moiety-specific VLCFA reduction and antioxidant strategies. The continuing increase in newborn screening programs and promising results from ongoing and recent therapeutic investigations provide hope for ALD.

X-linked Adrenoleukodystrophy: Pathology, Pathophysiology, Diagnostic Testing, Newborn Screening, and Therapies

Adrenoleukodystrophy (ALD) is a rare X-linked disease caused by a mutation of the peroxisomal ABCD1 gene. This review summarizes our current understanding of the pathogenic cell- and tissue-specific role of lipid species in the context of experimental therapeutic strategies and provides an overview of critical historical developments, therapeutic trials, and the advent of newborn screening in the United States. In ALD, very long chain fatty acid (VLCFA) chain-length-dependent dysregulation of endoplasmic reticulum stress and mitochondrial radical generating systems inducing cell death pathways has been shown, providing the rationale for therapeutic moiety-specific VLCFA reduction and antioxidant strategies. The continuing increase in newborn screening programs and promising results from ongoing and recent therapeutic investigations provide hope for ALD.

Exogenous Addition of 25-Hydroxycholesterol Reduces Level of Very Long-Chain Fatty Acids in X-Linked Adrenoleukodystrophy

X-Linked adrenoleukodystrophy (X-ALD) is a severe metabolic disorder characterized by the accumulation of very long-chain fatty acids (VLCFAs). Recently, we demonstrated that levels of 25-hydroxycholesterol (25-HC) and cholesterol 25-hydroxylase (CH25H) were found to be elevated in X-ALD. Herein, we report that the exogenous addition of 25-HC significantly reduces C26:0 levels in X-ALD patient-derived fibroblasts and oligodendrocytes differentiated from induced pluripotent stem cells (iPSCs) derived from X-ALD patients. Moreover, 25-HC treatment was found to down-regulate the expression of ELOVL1, a key enzyme for the synthesis of C26. In addition, activation of liver X receptor (LXR), a molecular target of endogenous 25-HC, also reduced C26:0 level. The reduction of C26:0 levels by 25-HC treatment might result, at least partially, from the decrease of ELOVL1 expression as well as the activation of LXR. Our findings could provide a better understanding of the role of 25-HC in X-ALD and useful information to find therapeutic agents to treat X-ALD.

Allogeneic stem cell transplantation with reduced intensity conditioning for patients with adrenoleukodystrophy

Objective

The prognosis of adrenoleukodystrophy (ALD)with neurological involvement is generally dismal; however, allogeneic stem cell transplantation (SCT) is recognized as effective to stabilize or improve the clinical symptoms of ALD. Herein, we report the clinical outcomes of patients with ALD who consecutively underwent allogeneic stem cell transplantation with reduced intensity conditioning at our institution.

Patients

Sixteen patients with ALD, who were symptomatic (n = 14) or presymptomatic (n = 2), received SCT from 2010 to 2016. The stem cell source was cord blood (n = 14), or bone marrow from a human leukocyte antigen identical sibling (n = 2). The conditioning regimen prior to transplantation was reduced intensity and consisted of fludarabine (125 mg/m²), melphalan (140 mg/m²) and low dose total body irradiation (TBI) of 4Gy (n = 15) or 3Gy (n = 1).

Results

Primary engraftment was obtained in 11 patients, and 4 of the 5 patients who lost the primary graft received a second cord blood transplantation and were engrafted. Five years overall and event-free survival were 90.9% and 61.1% respectively, with a median of 45 months (range 16–91). Loes score stabilized or improved by 18 months after transplantation except for patients with internal capsule involvement.

Conclusion

Allogeneic SCT with reduced intensity conditioning for patients with ALD was safely performed without major transplant-related complications even in symptomatic patients and neurological symptoms were stabilized after SCT in patients without internal capsule involvement.

Peroxisomal disorders: Improved laboratory diagnosis, new defects and the complicated route to treatment

Peroxisomes catalyze a number of essential metabolic functions of which fatty acid alpha- and beta-oxidation, ether phospholipid biosynthesis, glyoxylate detoxification and bile acid synthesis are the most important. The key role of peroxisomes in humans is exemplified by the existence of a group of peroxisomal disorders, caused by mutations in > 30 different genes which code for proteins with a role in either peroxisome biogenesis or one of the metabolic pathways in peroxisomes. Technological advances in laboratory methods at the metabolite-, enzyme-, and molecular level have not only allowed the identification of new peroxisomal disorders but also new phenotypes associated with already identified genetic defects thus extending the clinical spectrum. Unfortunately, progress in the field of pathogenesis and treatment has lagged behind although there are certainly new and hopeful developments with respect to X-linked adrenoleukodystrophy and hyperoxaluria type 1.

Long-term outcome of patients with X-linked adrenoleukodystrophy: A retrospective cohort study

BACKGROUND

X-linked adrenoleukodystrophy (X-ALD) is a peroxisomal disorder associated with leukodystrophy, myeloneuropathy and adrenocortical insufficiency. We performed a retrospective cohort study to evaluate long-term outcome of patients with X-ALD.

METHOD

All patients with X-ALD diagnosed between 1989 and 2012 were included. Electronic patient charts were reviewed for clinical features, biochemical investigations, molecular genetic testing, neuroimaging, long-term outcome and treatment.

RESULTS

Forty-eight patients from 18 unrelated families were included (15 females; 33 males). Seventeen patients were symptomatic at the time of the biochemical diagnosis including 14 with neurocognitive dysfunction and 3 with Addison disease only. Thirty-one asymptomatic individuals were identified by positive family history of X-ALD. During follow-up, eight individuals developed childhood cerebral X-ALD (CCALD), one individual developed adrenomyeloneuropathy (AMN), six individuals developed Addison disease only, and five individuals remained asymptomatic. Direct sequencing of ABCD1 confirmed the genetic diagnosis in 29 individuals. Seven patients with CCALD underwent hematopoietic stem cell transplantation (HSCT). Nine patients lost the follow-up. There was no correlation between clinical severity score, Loes score and elevated degree of elevated very long chain fatty acid (VLCFA) levels in CCALD.

CONCLUSION

Our study reports forty-eight new patients with X-ALD and their long-term outcome. Only 35% of the patients presented with neurological features or Addison disease. The remaining individuals were identified due to positive family history. Close monitoring of asymptomatic males resulted in early HSCT to prevent progressive lethal neurodegenerative disease. Identification of patients with X-ALD is important to improve neurodevelopmental outcome of asymptomatic males.

Adrenoleukodystrophy - neuroendocrine pathogenesis and redefinition of natural history

X-Linked adrenoleukodystrophy (ALD) is a peroxisomal metabolic disorder with a highly complex clinical presentation. ALD is caused by mutations in the ABCD1 gene, which leads to the accumulation of very long-chain fatty acids in plasma and tissues. Virtually all men with ALD develop adrenal insufficiency and myelopathy. Approximately 60% of men develop progressive cerebral white matter lesions (known as cerebral ALD). However, one cannot identify these individuals until the early changes are seen using brain imaging. Women with ALD also develop myelopathy, but generally at a later age than men and adrenal insufficiency or cerebral ALD are very rare. Owing to the multisystem symptomatology of the disease, patients can be assessed by the paediatrician, general practitioner, endocrinologist or a neurologist. This Review describes current knowledge on the clinical presentation, diagnosis and treatment of ALD, and highlights gaps in our knowledge of the natural history of the disease owing to an absence of large-scale prospective cohort studies. Such studies are necessary for the identification of new prognostic biomarkers to improve care for patients with ALD, which is particularly relevant now that newborn screening for ALD is being introduced.

Regulation of the adrenoleukodystrophy-related gene (ABCD2): focus on oxysterols and LXR antagonists

The regulation of the ABCD2 gene is recognized as a possible therapeutic target for X-linked adrenoleukodystrophy, a rare neurodegenerative disease caused by mutations in the ABCD1 gene. Up-regulation of ABCD2 expression has indeed been demonstrated to compensate for ABCD1 deficiency, restoring peroxisomal β-oxidation of very-long-chain fatty acids. Besides the known inducers of the ABCD2 gene (phenylbutyrate and histone deacetylase inhibitors, fibrates, dehydroepiandrosterone, thyroid hormone and thyromimetics), this review will focus on LXR antagonists and 22S-hydroxycholesterol, recently described as inducers of ABCD2 expression. Several LXR antagonists have been identified and their possible indication for neurodegenerative disorders will be discussed.

ABCD2 is a direct target of β-catenin and TCF-4: implications for X-linked adrenoleukodystrophy therapy

X-linked adrenoleukodystrophy (X-ALD) is a peroxisomal disorder caused by mutations in the ABCD1 gene that encodes the peroxisomal ATP-binding cassette (ABC) transporter subfamily D member 1 protein (ABCD1), which is referred to as the adrenoleukodystrophy protein (ALDP). Induction of the ABCD2 gene, the closest homolog of ABCD1, has been mentioned as a possible therapeutic option for the defective ABCD1 protein in X-ALD. However, little is known about the transcriptional regulation of ABCD2 gene expression. Here, through in silico analysis, we found two putative TCF-4 binding elements between nucleotide positions -360 and -260 of the promoter region of the ABCD2 gene. The transcriptional activity of the ABCD2 promoter was strongly increased by ectopic expression of β-catenin and TCF-4. In addition, mutation of either or both TCF-4 binding elements by site-directed mutagenesis decreased promoter activity. This was further validated by the finding that β-catenin and the promoter of the ABCD2 gene were pulled down with a β-catenin antibody in a chromatin immunoprecipitation assay. Moreover, real-time PCR analysis revealed that β-catenin and TCF-4 increased mRNA levels of ABCD2 in both a hepatocellular carcinoma cell line and primary fibroblasts from an X-ALD patient. Interestingly, we found that the levels of very long chain fatty acids were decreased by ectopic expression of ABCD2-GFP as well as β-catenin and TCF-4. Taken together, our results demonstrate for the first time the direct regulation of ABCD2 by β-catenin and TCF-4.

CYP4 enzymes as potential drug targets: focus on enzyme multiplicity, inducers and inhibitors, and therapeutic modulation of 20-hydroxyeicosatetraenoic acid (20-HETE) synthase and fatty acid ω-hydroxylase activities

The Cytochrome P450 4 (CYP4) family of enzymes in humans is comprised of thirteen isozymes that typically catalyze the ω-oxidation of endogenous fatty acids and eicosanoids. Several CYP4 enzymes can biosynthesize 20- hydroxyeicosatetraenoic acid, or 20-HETE, an important signaling eicosanoid involved in regulation of vascular tone and kidney reabsorption. Additionally, accumulation of certain fatty acids is a hallmark of the rare genetic disorders, Refsum disease and X-ALD. Therefore, modulation of CYP4 enzyme activity, either by inhibition or induction, is a potential strategy for drug discovery. Here we review the substrate specificities, sites of expression, genetic regulation, and inhibition by exogenous chemicals of the human CYP4 enzymes, and discuss the targeting of CYP4 enzymes in the development of new treatments for hypertension, stroke, certain cancers and the fatty acid-linked orphan diseases.

Bezafibrate lowers very long-chain fatty acids in X-linked adrenoleukodystrophy fibroblasts by inhibiting fatty acid elongation

X-linked adrenoleukodystrophy (X-ALD) is caused by mutations in the ABCD1 gene encoding ALDP, an ATP-binding-cassette (ABC) transporter located in the peroxisomal membrane. ALDP deficiency results in impaired peroxisomal β-oxidation and the subsequent accumulation of very long-chain fatty acids (VLCFA; > C22:0) in plasma and tissues. VLCFA are primarily derived from endogenous synthesis by ELOVL1. Therefore inhibiting this enzyme might constitute a feasible therapeutic approach. In this paper we demonstrate that bezafibrate, a PPAR pan agonist used for the treatment of patients with hyperlipidaemia reduces VLCFA levels in X-ALD fibroblasts. Surprisingly, the VLCFA-lowering effect was independent of PPAR activation and not caused by the increase in either mitochondrial or peroxisomal fatty acid β-oxidation capacity. In fact, our results show that bezafibrate reduces VLCFA synthesis by decreasing the synthesis of C26:0 through a direct inhibition of fatty acid elongation activity. Taken together, our data indicate bezafibrate as a potential pharmacotherapeutic treatment for X-ALD. A clinical trial is currently ongoing to evaluate the effect in patients with X-ALD.

Adrenoleukodystrophy: a forgotten diagnosis in children with primary Addison's disease

The X linked adrenoleukodystrophy (X-ALD) is a peroxisomal disease caused by defects of the ABCD1 gene on chromosome Xq28 leading to accumulation of very long chain fatty acids (VLCFA), progressive demyelination and adrenal insufficiency. An 8-year-old boy was referred to our paediatric endocrinology clinic due to fatigue and hyperpigmentation with onset at 2-years old. Blood tests revealed mineralocorticoid insufficiency. Serum adrenocorticotropic hormone and cortisol concentrations were compatible with adrenal insufficiency. Adrenal antibodies were negative. The elevated plasmatic concentration of VLCFA and the genotype analysis with sequencing of ABCD1 gene established the diagnosis of X-ALD. Brain MRI showed demyelination of white matter in the peritrigonal regions. Steroid replacement was started with good response. He initiated restriction of VLCFA by reducing the intake of fatty foods. The authors highlight the importance of suspecting of X-ALD in the aetiology of primary adrenal insufficiency as the first sign of the disease.

X-linked adrenoleukodystrophy (X-ALD): clinical presentation and guidelines for diagnosis, follow-up and management

X-linked adrenoleukodystrophy (X-ALD) is the most common peroxisomal disorder. The disease is caused by mutations in the ABCD1 gene that encodes the peroxisomal membrane protein ALDP which is involved in the transmembrane transport of very long-chain fatty acids (VLCFA; ≥C22). A defect in ALDP results in elevated levels of VLCFA in plasma and tissues. The clinical spectrum in males with X-ALD ranges from isolated adrenocortical insufficiency and slowly progressive myelopathy to devastating cerebral demyelination. The majority of heterozygous females will develop symptoms by the age of 60 years. In individual patients the disease course remains unpredictable. This review focuses on the diagnosis and management of patients with X-ALD and provides a guideline for clinicians that encounter patients with this highly complex disorder.

Bezafibrate for X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is caused by mutations in the ABCD1 gene and is characterized by impaired beta-oxidation of very-long-chain fatty acids (VLCFA) and subsequent VLCFA accumulation in tissues. In adulthood X-ALD most commonly manifests as a gradually progressive myelopathy, (adrenomyeloneuropathy; AMN) without any curative or disease modifying treatments. We recently showed that bezafibrate (BF), a drug used for the treatment of hyperlipidaemia, reduces VLCFA accumulation in X-ALD fibroblasts by inhibiting ELOVL1, an enzyme involved in the VLCFA synthesis. We therefore designed a proof-of-principal clinical trial to determine whether BF reduces VLCFA levels in plasma and lymphocytes of X-ALD patients. Ten males with AMN were treated with BF for 12 weeks at a dose of 400 mg daily, followed by 12 weeks of 800 mg daily. Every 4 weeks patients were evaluated for side effects and blood samples were taken for analysis. Adherence was good as indicated by a clear reduction in triglycerides. There was no reduction in VLCFA in either plasma or lymphocytes. Plasma levels of BF did not exceed 25 µmol/L. We concluded that BF, at least in the dose given, is unable to lower VLCFA levels in plasma or lymphocytes in X-ALD patients. It is unclear whether this is due to the low levels of BF reached in plasma. Our future work is aimed at the identification of highly-specific inhibitors of ELOVL1 that act at much lower concentrations than BF and are well tolerated. BF appears to have no therapeutic utility in X-ALD.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01165060.

Mammalian peroxisomal ABC transporters: from endogenous substrates to pathology and clinical significance

Peroxisomes are indispensable organelles in higher eukaryotes. They are essential for a number of important metabolic pathways, including fatty acid α- and β-oxidation, and biosynthesis of etherphospholipids and bile acids. However, the peroxisomal membrane forms an impermeable barrier to these metabolites. Therefore, peroxisomes need specific transporter proteins to transfer these metabolites across their membranes. The mammalian peroxisomal membrane harbours three ATP-binding cassette (ABC) transporters. In recent years, significant progress has been made in unravelling the functions of these ABC transporters. There is ample evidence that they are involved in the transport of very long-chain fatty acids, pristanic acid, di- and trihydroxycholestanoic acid, dicarboxylic acids and tetracosahexaenoic acid (C24:6ω3). Surprisingly, only one disease is associated with a deficiency of a peroxisomal ABC transporter. Mutations in the ABCD1 gene encoding the peroxisomal ABC transporter adrenoleukodystrophy protein are the cause for X-linked adrenoleukodystrophy, an inherited metabolic storage disorder. This review describes the current state of knowledge on the mammalian peroxisomal ABC transporters with a particular focus on their function in metabolite transport.

Fatty acid omega-oxidation as a rescue pathway for fatty acid oxidation disorders in humans

Fatty acids (FAs) can be degraded via different mechanisms including α-, β- and ω-oxidation. In humans, a range of different genetic diseases has been identified in which either mitochondrial FA β-oxidation, peroxisomal FA β-oxidation or FA α-oxidation is impaired. Treatment options for most of these disorders are limited. This has prompted us to study FA ω-oxidation as a rescue pathway for these disorders, based on the notion that if the ω-oxidation of specific FAs could be upregulated one could reduce the accumulation of these FAs and the subsequent detrimental effects in the different groups of disorders. In this minireview, we describe our current state of knowledge in this area with special emphasis on Refsum disease and X-linked adrenoleukodystrophy.

Biochemical aspects of X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is the most common peroxisomal disorder. The disease is characterized by the accumulation of very long-chain fatty acids (VLCFA; >C22) in plasma and tissues. X-ALD is caused by mutations in the ABCD1 gene encoding ALDP, an adenosine triphosphate (ATP)-binding-cassette (ABC) transporter located in the peroxisomal membrane. In this paper, we describe the current knowledge on the function of ALDP, its role in peroxisomal VLCFA beta-oxidation and the consequences of a defect in ALDP on VLCFA metabolism. Furthermore, we pay special attention to the role of the VLCFA elongation system in VLCFA homeostasis, with elongation of very long-chain fatty acids like-1 (ELOVL1) as key player, and its relevance to X-ALD.

Current and future pharmacological treatment strategies in X-linked adrenoleukodystrophy

Mutations in the ABCD1 gene cause the clinical spectrum of the neurometabolic disorder X-linked adrenoleukodystrophy/adrenomyeloneuropathy (X-ALD/AMN). Currently, the most efficient therapeutic opportunity for patients with the cerebral form of X-ALD is hematopoietic stem cell transplantation and possibly gene therapy of autologous hematopoietic stem cells. Both treatments, however, are only accessible to a subset of X-ALD patients, mainly because of the lack of markers that can predict the onset of cerebral demyelination. Moreover, for female or male X-ALD patients with AMN, currently only unsatisfying therapeutic opportunities are available. Thus, this review focuses on current and urgently needed future pharmacological therapies. The treatment of adrenal and gonadal insufficiency is well established, whereas applications of immunomodulatory and immunosuppressive drugs have failed to prevent progression of cerebral neuroinflammation. The use of Lorenzo's oil and the inefficacy of lovastatin to normalize very-long-chain fatty acids in clinical trials as well as currently experimental and therefore possible future therapeutic strategies are reviewed. The latter include pharmacological gene therapy mediated by targeted upregulation of ABCD2, the closest homolog of ABCD1, antioxidative drug treatment, small molecule histone deacetylase inhibitors such as butyrates and valproic acid, and other neuroprotective attempts.

Adrenal insufficiency: etiology, diagnosis and treatment

PURPOSE OF REVIEW

Adrenal insufficiency, first codified in 1855 by Thomas Addison, remains relevant in 2010 because of its lethal nature.

RECENT FINDINGS

Reports illuminate features of adrenal insufficiency cause, diagnosis and treatment, and the role of glucocorticoids in critical illness.

SUMMARY

Progress has been made in identifying human leukocyte antigen and major histocompatability complex alleles that predispose to the development of adrenal insufficiency in patients with antibodies to 21-hydroxylase, but their role in clinical care is not established. Reports of HIV-associated infections and medication-induced hypocortisolism are reminders that autoimmune adrenal destruction does not underlie all cases. The diagnosis is adequately established by the 250 microg adrenocortocotropin hormone stimulation test in most patients; the 1 microg test carries the risk of misdiagnosis of healthy individuals as adrenally insufficient. Glucocorticoids provide life-saving treatment, but long-term quality of life is impaired, perhaps because therapy is not given in a physiologic way. The current recommended total daily dose is lower than that often prescribed. Dehydroepiandrosterone replacement may be useful in pubertal girls with hypopituitarism, but not in adults. Supraphysiologic hydrocortisone doses may aid in the reversal of septic shock independent of underlying adrenal function.

The role of ELOVL1 in very long-chain fatty acid homeostasis and X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is caused by mutations in the ABCD1 gene encoding the peroxisomal ABC transporter adrenoleukodystrophy protein (ALDP). X-ALD is characterized by the accumulation of very long-chain fatty acids (VLCFA; ≥C24) in plasma and tissues. In this manuscript we provide insight into the pathway underlying the elevated levels of C26:0 in X-ALD. ALDP transports VLCFacyl-CoA across the peroxisomal membrane. A deficiency in ALDP impairs peroxisomal β-oxidation of VLCFA but also raises cytosolic levels of VLCFacyl-CoA which are substrate for further elongation. We identify ELOVL1 (elongation of very-long-chain-fatty acids) as the single elongase catalysing the synthesis of both saturated VLCFA (C26:0) and mono-unsaturated VLCFA (C26:1). ELOVL1 expression is not increased in X-ALD fibroblasts suggesting that increased levels of C26:0 result from increased substrate availability due to the primary deficiency in ALDP. Importantly, ELOVL1 knockdown reduces elongation of C22:0 to C26:0 and lowers C26:0 levels in X-ALD fibroblasts. Given the likely pathogenic effects of high C26:0 levels, our findings highlight the potential of modulating ELOVL1 activity in the treatment of X-ALD.

Clinical aspects and adrenal functions in eleven Japanese children with X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is a genetic disease associated with demyelination of the central nervous system, adrenocortical insufficiency and accumulation of very long chain fatty acids. It is a clinically heterogeneous disorder ranging from a severe childhood cerebral form to an asymptomatic form. The incidence in Japan is estimated to be between 1:30,000 and 1:50,000 boys as determined by a nationwide retrospective survey between 1990 and 1999, which found no cases with Addison's form. We reviewed the medical records of eleven Japanese boys with X-ALD from 1990 to 2010 in our institute. Eight patients were detected by neuropsychological abnormalities, whereas a higher prevalence of unrecognized adrenocortical insufficiency (5/11: 45%) was observed than previously recognized. While no neurological abnormalities were demonstrated in two brothers, the elder brother had moderate Addison's disease at diagnosis and the presymptomatic younger brother progressed to Addison's disease six months after the diagnosis of X-ALD. Early detection of impaired adrenal function as well as early identification of neurologically presymptomatic patients by genetic analysis is essential for better prognosis. Addison's form might be overlooked in Japan; therefore, X-ALD should be suspected in patients with adrenocortical insufficiency.