Plasma analysis of di- and trihydroxycholestanoic acid diastereoisomers in peroxisomal α-methylacyl-CoA racemase deficiency

Autoantibody Positivity in Two Bahraini Siblings With a Novel Alpha-Methylacyl-CoA Racemase Mutation

Bile acid synthesis disorders (BASD) are a group of rare autosomal recessive disorders. Of the nine different versions, BASD type 4 is characterized by a gene mutation in alpha-methylacyl-CoA racemase (AMACR), which is located on chromosome 5p13. These disorders generally present with a normal gamma-glutamyl transferase with cholestasis, absence of pruritis, and malabsorption of fat, which can lead to fat-soluble vitamin deficiencies. In adulthood, patients usually develop neurological sequelae. Initial testing can be done through the measurement of urine metabolites; however, confirmation of the diagnosis is achieved through whole exome sequencing. Treatment involves supplementation of oral cholic acid and modification of diet. Only 23 patients with this disease have been described. Here, we report two cases of siblings from a family in Bahrain with a novel AMACR mutation and a unique association with autoimmune antibodies alongside a literature review.

Development of a system adapted for the diagnosis and evaluation of peroxisomal disorders by measuring bile acid intermediates

OBJECTIVE

Bile acid intermediates, 3α,7α,12α-trihydroxycholestanoic acid (THCA) and 3α,7α-dihydroxycholestanoic acid (DHCA), are metabolized in peroxisomes. Some peroxisomal disorders (PDs), such as Zellweger spectrum disorder (ZSD), show an accumulation of bile acid intermediates. In particular, ABCD3 deficiency and acyl-CoA-oxidase 2 deficiency are characterized by these metabolite abnormalities. In patients with ZSD, levels of bile acid intermediates can be lowered by a primary bile acid supplementation treatment; therefore, measuring their levels could help evaluate treatment effectiveness. Here, we established a method for the quantitative determination of bile acid intermediates (THCA/DHCA) for differentiating PDs and assessing bile acid treatment.

METHODS

Serum samples, obtained from patients with several forms of ZSD as well as peroxisomal β-oxidation enzyme deficiencies, were deproteinized and analyzed using liquid chromatography-mass spectrometry.

RESULTS

Levels of the bile acid intermediates increased significantly in patients with Zellweger syndrome (ZS) and slightly in patients with neonatal adrenoleukodystrophy and infantile Refsum disease (IRD), reflecting the severity of these diseases. One patient with ZS treated with primary bile acids for 6 months showed slightly decreased serum DHCA levels but significantly increased serum THCA levels. One patient with IRD who underwent living-donor liver transplantation showed a rapid decrease in serum THCA and DHCA levels, which remained undetected for 6 years. In all controls, THCA and DHCA levels were below the detection limit.

CONCLUSION

The analytical method developed in this study is useful for diagnosing various PD and validating bile acid treatment. Additionally, it can help predict the prognosis of patients with PD and support treatment strategies.

The physiological functions of human peroxisomes

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

Current Knowledge on the Function of α-Methyl Acyl-CoA Racemase in Human Diseases

Branched chain fatty acids perform very important functions in human diet and drug metabolism. they cannot be metabolized in mitochondria and are instead processed and degraded in peroxisomes due to the presence of methyl groups on the carbon chains. Oxidative degradation pathways for lipids include α- and β-oxidation and several pathways. In all metabolic pathways, α-methyl acyl-CoA racemase (AMACR) plays an essential role by regulating the metabolism of lipids and drugs. AMACR regulates β-oxidation of branched chain lipids in peroxisomes and mitochondria and promotes chiral reversal of 2-methyl acids. AMACR defects cause sensory-motor neuronal and liver abnormalities in humans. These phenotypes are inherited and are caused by mutations in AMACR. In addition, AMACR has been found to be overexpressed in prostate cancer. In addition, the protein levels of AMACR have increased significantly in many types of cancer. Therefore, AMACR may be an important marker in tumors. In this review, a comprehensive overview of AMACR studies in human disease will be described.

Additional pathways of sterol metabolism: Evidence from analysis of Cyp27a1-/- mouse brain and plasma

Cytochrome P450 (CYP) 27A1 is a key enzyme in both the acidic and neutral pathways of bile acid biosynthesis accepting cholesterol and ring-hydroxylated sterols as substrates introducing a (25R)26-hydroxy and ultimately a (25R)26-acid group to the sterol side-chain. In human, mutations in the CYP27A1 gene are the cause of the autosomal recessive disease cerebrotendinous xanthomatosis (CTX). Surprisingly, Cyp27a1 knockout mice (Cyp27a1−/−) do not present a CTX phenotype despite generating a similar global pattern of sterols. Using liquid chromatography – mass spectrometry and exploiting a charge-tagging approach for oxysterol analysis we identified over 50 cholesterol metabolites and precursors in the brain and circulation of Cyp27a1−/− mice. Notably, we identified (25R)26,7α- and (25S)26,7α-dihydroxy epimers of oxysterols and cholestenoic acids, indicating the presence of an additional sterol 26-hydroxylase in mouse. Importantly, our analysis also revealed elevated levels of 7α-hydroxycholest-4-en-3-one, which we found increased the number of oculomotor neurons in primary mouse brain cultures. 7α-Hydroxycholest-4-en-3-one is a ligand for the pregnane X receptor (PXR), activation of which is known to up-regulate the expression of CYP3A11, which we confirm has sterol 26-hydroxylase activity. This can explain the formation of (25R)26,7α- and (25S)26,7α-dihydroxy epimers of oxysterols and cholestenoic acids; the acid with the former stereochemistry is a liver X receptor (LXR) ligand that increases the number of oculomotor neurons in primary brain cultures. We hereby suggest that a lack of a motor neuron phenotype in some CTX patients and Cyp27a1−/− mice may involve increased levels of 7α-hydroxycholest-4-en-3-one and activation PXR, as well as increased levels of sterol 26-hydroxylase and the production of neuroprotective sterols capable of activating LXR.

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Besides CYP27A1 an additional sterol 26-hydroxylase is present in mouse.

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Sterol-acids are observed as 7α-hydroxy-(25R/S)26-acid epimers.

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The (25S)26-acid is found in mouse brain of the CYP27A1−/− mouse.

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The (25R)26-acid is found in brain of the wild type animal.

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Both epimers are found in plasma of both genotypes.

Dietary fish, n-3 polyunsaturated fatty acid consumption, and depression risk in Japan: a population-based prospective cohort study

Systematic review of observational studies has revealed that fish consumption and levels of n-3 polyunsaturated fatty acids (PUFAs) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid are associated with a reduced risk of depression. A reverse J-shaped effect of n-3 PUFAs was suggested. However, there is limited evidence from populations with high fish consumption and no studies have used a standard psychiatrist-based diagnosis of major depressive disorder (MDD). Therefore, this population-based, prospective study investigated the association of dietary fish, n-3 PUFA, and n-6 PUFA consumption with risk of psychiatrist-diagnosed MDD in Japan. A total of 12 219 subjects were enrolled from the Saku area in 1990. Of these, we extracted 1181 participants aged 63-82 years who completed food frequency questionnaires in both 1995 and 2000 and also underwent a mental health examination in 2014-2015. Odds ratios (ORs) and 95% confidence intervals (CIs) for MDD according to fish intake and PUFA quartiles were calculated. Current MDD was diagnosed in 95 patients. We found a reduced risk of MDD in the third quartile for fish intake (111.1 g per day, OR=0.44, 95% CI=0.23-0.84), second quartile for EPA (307.7 mg per day, OR=0.54, 95% CI=0.30-0.99) and third quartile for docosapentaenoic acid (DPA) (123.1 mg per day, OR=0.42, 95% CI=0.22-0.85). ORs adjusted for cancer, stroke, myocardial infarction and diabetes remained significant for fish and DPA intake. Our results suggest that moderate fish intake could be recommended for the prevention of MDD in aged Japanese individuals.

Bile acid analysis in human disorders of bile acid biosynthesis

Bile acids facilitate the absorption of lipids in the gut, but are also needed to maintain cholesterol homeostasis, induce bile flow, excrete toxic substances and regulate energy metabolism by acting as signaling molecules. Bile acid biosynthesis is a complex process distributed across many cellular organelles and requires at least 17 enzymes in addition to different metabolite transport proteins to synthesize the two primary bile acids, cholic acid and chenodeoxycholic acid. Disorders of bile acid synthesis can present from the neonatal period to adulthood and have very diverse clinical symptoms ranging from cholestatic liver disease to neuropsychiatric symptoms and spastic paraplegias. This review describes the different bile acid synthesis pathways followed by a summary of the current knowledge on hereditary disorders of human bile acid biosynthesis with a special focus on diagnostic bile acid profiling using mass spectrometry.

Role of AMACR (α-methylacyl-CoA racemase) and MFE-1 (peroxisomal multifunctional enzyme-1) in bile acid synthesis in mice

Bile acid analysis of wild-type, Mfe-1−/−, Amacr−/− and Amacr−/−Mfe-1−/− mouse models shows that peroxisomal multifunctional enzyme 1 can participate in bile acid synthesis in both AMACR-dependent and AMACR-independent pathways.

MRI characterisation of adult onset alpha-methylacyl-coA racemase deficiency diagnosed by exome sequencing

BACKGROUND

Correct diagnosis is pivotal to understand and treat neurological disease. Herein, we report the diagnostic work-up utilizing exome sequencing and the characterization of clinical features and brain MRI in two siblings with a complex, adult-onset phenotype; including peripheral neuropathy, epilepsy, relapsing encephalopathy, bilateral thalamic lesions, type 2 diabetes mellitus, cataract, pigmentary retinopathy and tremor.

METHODS

We applied clinical and genealogical investigations, homozygosity mapping and exome sequencing to establish the diagnosis and MRI to characterize the cerebral lesions.

RESULTS

A recessive genetic defect was suspected in two siblings of healthy, but consanguineous parents. Homozygosity mapping revealed three shared homozygous regions and exome sequencing, revealed a novel homozygous c.367 G>A [p.Asp123Asn] mutation in the α-methylacyl-coA racemase (AMACR) gene in both patients. The genetic diagnosis of α-methylacyl-coA racemase deficiency was confirmed by demonstrating markedly increased pristanic acid levels in blood (169 μmol/L, normal <1.5 μmol/L). MRI studies showed characteristic degeneration of cerebellar afferents and efferents, including the dentatothalamic tract and thalamic lesions in both patients.

CONCLUSIONS

Metabolic diseases presenting late are diagnostically challenging. We show that appropriately applied, homozygosity mapping and exome sequencing can be decisive for establishing diagnoses such as late onset α-methylacyl-coA racemase deficiency, an autosomal recessive peroxisomal disorder with accumulation of pristanic acid. Our study also highlights radiological features that may assist in diagnosis. Early diagnosis is important as patients with this disorder may benefit from restricted dietary phytanic and pristanic acid intake.

Bile acids: the role of peroxisomes

It is well established that peroxisomes play a crucial role in de novo bile acid synthesis. Studies in patients with a peroxisomal disorder have been indispensable for the elucidation of the precise role of peroxisomes. Several peroxisomal disorders are associated with distinct bile acid abnormalities and each disorder has a characteristic pattern of abnormal bile acids that accumulate, which is often used for diagnostic purposes. The patients have also been important for determining the pathophysiological consequences of defects in bile acid biosynthesis. In this review, we will discuss all the peroxisomal steps involved in bile acid synthesis and the bile acid abnormalities in patients with peroxisomal disorders. We will show the results of bile acid measurements in several tissues from patients, including brain, and we will discuss the toxicity and the pathological effects of the abnormal bile acids.

Role of bile acids and bile acid receptors in metabolic regulation

The incidence of the metabolic syndrome has taken epidemic proportions in the past decades, contributing to an increased risk of cardiovascular disease and diabetes. The metabolic syndrome can be defined as a cluster of cardiovascular disease risk factors including visceral obesity, insulin resistance, dyslipidemia, increased blood pressure, and hypercoagulability. The farnesoid X receptor (FXR) belongs to the superfamily of ligand-activated nuclear receptor transcription factors. FXR is activated by bile acids, and FXR-deficient (FXR(-/-)) mice display elevated serum levels of triglycerides and high-density lipoprotein cholesterol, demonstrating a critical role of FXR in lipid metabolism. In an opposite manner, activation of FXR by bile acids (BAs) or nonsteroidal synthetic FXR agonists lowers plasma triglycerides by a mechanism that may involve the repression of hepatic SREBP-1c expression and/or the modulation of glucose-induced lipogenic genes. A cross-talk between BA and glucose metabolism was recently identified, implicating both FXR-dependent and FXR-independent pathways. The first indication for a potential role of FXR in diabetes came from the observation that hepatic FXR expression is reduced in animal models of diabetes. While FXR(-/-) mice display both impaired glucose tolerance and decreased insulin sensitivity, activation of FXR improves hyperglycemia and dyslipidemia in vivo in diabetic mice. Finally, a recent report also indicates that BA may regulate energy expenditure in a FXR-independent manner in mice, via activation of the G protein-coupled receptor TGR5. Taken together, these findings suggest that modulation of FXR activity and BA metabolism may open new attractive pharmacological approaches for the treatment of the metabolic syndrome and type 2 diabetes.

A PEX10 defect in a patient with no detectable defect in peroxisome assembly or metabolism in cultured fibroblasts

Zellweger spectrum disorders (ZSD) are diagnosed by biochemical assay in blood, urine and cultured fibroblasts and PEX gene mutation identification. In most cases studies in fibroblasts corroborate results obtained in body fluids. In 1996 Clayton and colleagues described a 10-year old girl with evidence of a peroxisome disorder, based on elevated bile acid metabolites and phytanate. At the time it was not possible to distinguish whether she had a ZSD or a single peroxisomal protein defect. Studies in our laboratory showed that she also had elevated plasma pipecolate, supporting the former diagnosis. Despite the abnormal metabolites detected in blood (phytanate, bile acid intermediates and pipecolate), analysis of multiple peroxisomal pathways in fibroblasts yielded normal results. In addition, she had a milder clinical phenotype than usually associated with ZSD. Since complementation analysis to determine the gene defect was not possible, we screened this patient following the PEX Gene Screen algorithm (PGS). The PGS provides a template for sequencing PEX gene exons independent of complementation analysis. Two mutations in PEX10 were identified, a frameshift mutation inherited from her father and a de novo missense mutation in a conserved functional domain on the other allele. This case highlights that molecular analysis may be essential to the diagnosis of patients at the milder end of the ZSD spectrum. Furthermore, it supports the concept that some tissues are less affected by certain PEX gene defects than brain and liver.

Synthesis and use of isotope-labelled substrates for a mechanistic study on human alpha-methylacyl-CoA racemase 1A (AMACR; P504S)

Alpha-Methylacyl-CoA racemase (AMACR) is an important enzyme for the metabolism of branched-chain lipids and drugs. The enzyme is over-expressed in prostate and other cancers. AMACR 1A, the major splice variant, was purified from recombinant E. coli cells as a His-tag protein. Purified enzyme catalysed chiral inversion of both S- and R-2-methyldecanoyl-CoA, with an equilibrium constant of 1.09 +/- 0.14 (2S/2R). Reactions with (2)H-labelled substrate showed that loss of the alpha-proton was a prerequisite for chiral inversion. Reactions conducted in (2)H(2)O indicated that reprotonation was not stereospecific. These results are the first mechanistic study on any recombinant mammalian alpha-methylacyl-CoA racemase.

AMACR expression in colorectal cancer is associated with left-sided tumor localization

Alpha-methylacyl-CoA racemase (AMACR) is an enzyme playing an important role in the beta-oxidation of branched-chain fatty acids and fatty acid derivatives. Altered expression levels of AMACR have been described in various cancers including colorectal cancer (CRC). To determine the potential prognostic impact of AMACR expression, we analyzed 1,315 CRC on a tissue microarray (TMA) by immunohistochemistry (IHC). Clinical follow-up data were available from all cancer patients. Positive AMACR staining was observed in 1,074 (81.7%) of the 1,315 cases including 276 cancers with weak (21.0%) and 798 cancers with strong staining (60.7%). AMACR IHC was significantly associated with tumor grade, stage, non-mucinous phenotype, and left-sided tumor localization (p < 0.0001 each). AMACR positivity was observed in 65.8% of cancers from the right-sided colon, in 73.2% of cancers from the colon transversum, in 81.1% of cancers from the colon descendens, and in 88.9% of the distal left-sided cancers (sigma and rectum; p < 0.0001). However, AMACR staining results were unrelated to clinical outcome. It is concluded that AMACR cannot serve as a prognostic marker in CRC. We hypothesize that the association of AMACR expression with tumor localization may be related to differences in the metabolism/exposure to fatty acids occurring along the colon.

Mechanisms of disease: Inborn errors of bile acid synthesis

Inborn errors of bile acid synthesis are rare genetic disorders that can present as neonatal cholestasis, neurologic disease or fat-soluble-vitamin deficiencies. There are nine known defects of bile acid synthesis, including oxysterol 7alpha-hydroxylase deficiency, Delta(4)-3-oxosteroid-5beta-reductase deficiency, 3beta-hydroxy-Delta(5)-C(27)-steroid dehydrogenase deficiency, cerebrotendinous xanthomatosis (also known as sterol 27-hydroxylase deficiency), alpha-methylacyl-CoA racemase deficiency, and Zellweger syndrome (also known as cerebrohepatorenal syndrome). These diseases are characterized by a failure to produce normal bile acids and an accumulation of unusual bile acids and bile acid intermediaries. Individuals with inborn errors of bile acid synthesis generally present with the hallmark features of normal or low serum bile acid concentrations, normal gamma-glutamyl transpeptidase concentrations and the absence of pruritus. Failure to diagnose any of these conditions can result in liver failure or progressive chronic liver disease. If recognized early, many patients can have a remarkable clinical response to oral bile acid therapy.

Alpha-methylacyl-CoA racemase--an 'obscure' metabolic enzyme takes centre stage

Branched-chain lipids are important components of the human diet and are used as drug molecules, e.g. ibuprofen. Owing to the presence of methyl groups on their carbon chains, they cannot be metabolized in mitochondria, and instead are processed and degraded in peroxisomes. Several different oxidative degradation pathways for these lipids are known, including alpha-oxidation, beta-oxidation, and omega-oxidation. Dietary branched-chain lipids (especially phytanic acid) have attracted much attention in recent years, due to their link with prostate, breast, colon and other cancers as well as their role in neurological disease. A central role in all the metabolic pathways is played by alpha-methylacyl-CoA racemase (AMACR), which regulates metabolism of these lipids and drugs. AMACR catalyses the chiral inversion of a diverse number of 2-methyl acids (as their CoA esters), and regulates the entry of branched-chain lipids into the peroxisomal and mitochondrial beta-oxidation pathways. This review brings together advances in the different disciplines, and considers new research in both the metabolism of branched-chain lipids and their role in cancer, with particular emphasis on the crucial role played by AMACR. These recent advances enable new preventative and treatment strategies for cancer.

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

BACKGROUND

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

AIM

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

METHODS

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

RESULT

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

CONCLUSIONS

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

Peroxisomes and bile acid biosynthesis

Peroxisomes play an important role in the biosynthesis of bile acids because a peroxisomal beta-oxidation step is required for the formation of the mature C24-bile acids from C27-bile acid intermediates. In addition, de novo synthesized bile acids are conjugated within the peroxisome. In this review, we describe the current state of knowledge about all aspects of peroxisomal function in bile acid biosynthesis in health and disease. The peroxisomal enzymes involved in the synthesis of bile acids have been identified, and the metabolic and pathologic consequences of a deficiency of one of these enzymes are discussed, including the potential role of nuclear receptors therein.

Peroxisomal disorders: the single peroxisomal enzyme deficiencies

Peroxisomal disorders are a group of inherited diseases in man in which either peroxisome biogenesis or one or more peroxisomal functions are impaired. The peroxisomal disorders identified to date are usually classified in two groups including: (1) the disorders of peroxisome biogenesis, and (2) the single peroxisomal enzyme deficiencies. This review is focused on the second group of disorders, which currently includes ten different diseases in which the mutant gene affects a protein involved in one of the following peroxisomal functions: (1) ether phospholipid (plasmalogen) biosynthesis; (2) fatty acid beta-oxidation; (3) peroxisomal alpha-oxidation; (4) glyoxylate detoxification, and (5) H2O2 metabolism.

Phytanic acid, AMACR and prostate cancer risk

The growing body of knowledge in cancer prevention demonstrates that for many cancers, risk must be defined in terms of both environmental and genetic factors. In prostate cancer, there is increasing evidence linking risk with polymorphisms in the alpha-methylacyl-CoA racemase (AMACR) gene and branched-chain fatty acids derived from specific sources of dietary fats. We are now at the point where we can begin to conceptualize possible inter-relationships between dietary and genetic risk as applied to prostate cancer, with the goal of generating testable hypotheses amenable to coordinated examinations. A greater understanding of such relationships should provide better ways to establish overall risk, to screen for the disease and perhaps to offer specific opportunities for prevention and treatment.

Contemporary clinical usage of LC/MS: analysis of biologically important carboxylic acids

OBJECTIVES

This review summarizes the current role of LC/MS in the diagnosis and screening of clinical conditions involving the analysis of biologically important carboxylic acids.

DESIGN AND METHODS

Carboxylic acids are divided into six logical categories of acid size and function. Details of chromatographic separation methods and modes of mass spectrometer operation are described for each category.

RESULTS

The use of LC/MS in clinical applications such as the diagnosis of inherited and acquired metabolic disorders, gastrointestinal disorders, cancer and diabetes and therapeutic drug monitoring is discussed.

CONCLUSIONS

The mild conditions, speed and sensitivity advantages of LC/MS analysis, over alternatives, are highlighted. The sensitivity and specificity afforded by the combination of tertiary and quaternary ammonium derivatives and tandem mass spectrometry for the analysis of carboxylic acids is emphasized. Potential for a greater range of LC/MS carboxylic analyses, including stereoisomeric intermediates, is predicted.

Peroxisomes, lipid metabolism, and peroxisomal disorders

Peroxisomes catalyse a large variety of different cellular functions of which most have to do with lipid metabolism. This paper deals with the role of peroxisomes in three key pathways of lipid metabolism, including: (1) etherphospholipid biosynthesis, (2) fatty acid beta-oxidation, and (3) fatty acid alpha-oxidation. Apart from a brief description of the peroxisomal enzymes involved in each of these pathways, the interaction between peroxisomes and other subcellular organelles, notably microsomes and peroxisomes, will be discussed. Finally, the current state of knowledge with respect to the different disorders of peroxisomal lipid metabolism will be described.

Alpha-methylacyl-CoA racemase: a variably sensitive immunohistochemical marker for the diagnosis of small prostate cancer foci on needle biopsy

Expression of the alpha-methylacyl-CoA racemase (AMACR) gene has recently been demonstrated by several groups to be markedly elevated in prostate cancer cells with little expression in benign prostate tissue and has been suggested as a molecular marker of prostate cancer on needle biopsy. There is scant data, however, as to the sensitivity and specificity of AMACR in the diagnosis of small foci of cancer on needle biopsy. A total of 209 needle biopsies of the prostate with small foci (<5% of a core) of prostatic adenocarcinoma were identified. A total of 175 cases were received in consultation by one of the authors (140 from a single institution and 35 from different outside institutions) and 34 cases were from our hospital file. Immunohistochemistry for high molecular weight cytokeratin and p63 was performed in all cases to confirm the diagnosis of cancer. Only AMACR staining that was significantly stronger than that of background benign glands was considered positive; 88% of all cases of prostate cancer were positive for AMACR. The sensitivity varied among the different groups: 100% for the in house cases, 87.1% for the cases from a single institution, and 80% for cases from different outside institutions. The mean percentage of stained glands in positive cases was 95.9%, with 150 (71.8%) cases showing 100% of the glands positive and 25 (12.0%) cases showing no staining. Because negative staining for basal cell markers, especially in a small focus of atypical glands, is not necessarily diagnostic of prostate cancer, positive staining for AMACR can increase the level of confidence in establishing a definitive malignant diagnosis. However, the sensitivity of AMACR staining may vary in specimens from different pathology laboratories, possibly related to differences in fixation and processing. It is important to optimize the staining technique for each laboratory and recognize that some small cancers on needle biopsy may be AMACR negative.

Liver disease caused by failure to racemize trihydroxycholestanoic acid: gene mutation and effect of bile acid therapy

BACKGROUND & AIMS

Inborn errors of bile acid metabolism may present as neonatal cholestasis and fat-soluble vitamin malabsorption or as late onset chronic liver disease. Our aim was to fully characterize a defect in bile acid synthesis in a 2-week-old African-American girl presenting with coagulopathy, vitamin D and E deficiencies, and mild cholestasis and in her sibling, whose liver had been used for orthotopic liver transplantation (OLT).

METHODS

Bile acids were measured by mass spectrometry in urine, bile, serum, and feces of the patient and in urine from the unrelated recipient.

RESULTS

Liver biopsy specimens showed neonatal hepatitis with giant cell transformation and hepatocyte necrosis; peroxisomes were reduced in number. High concentrations of (25R)3alpha,7alpha,12alpha-trihydroxy-5beta-cholestanoic acid in the urine, bile, and serum established a pattern similar to that of Zellweger syndrome and identical to the Alligator mississippiensis. Serum phytanic acid was normal, whereas pristanic acid was markedly elevated. Biochemical, MRI, and neurologic findings were inconsistent with a generalized defect of peroxisomal function and were unique. Analysis of the urine from the recipient of the deceased sibling's liver confirmed the same bile acid synthetic defect. A deficiency in 2-methylacyl-CoA racemase, which is essential for conversion of (25R)THCA to its 25S-isomer, the substrate to initiate peroxisomal beta-oxidation to primary bile acids, was confirmed by DNA analysis revealing a missense mutation (S52P) in the gene encoding this enzyme. Long-term treatment with cholic acid normalized liver enzymes and prevented progression of symptoms.

CONCLUSIONS

This genetic defect further highlights bile acid synthetic defects as a cause of neonatal cholestasis.

alpha-Methylacyl-CoA racemase: expression levels of this novel cancer biomarker depend on tumor differentiation

alpha-Methylacyl-CoA racemase (AMACR) has previously been shown to be a highly sensitive marker for colorectal and clinically localized prostate cancer (PCa). However, AMACR expression was down-regulated at the transcript and protein level in hormone-refractory metastatic PCa, suggesting a hormone-dependent expression of AMACR. To further explore the hypothesis that AMACR is hormone regulated and plays a role in PCa progression AMACR protein expression was characterized in a broad range of PCa samples treated with variable amounts and lengths of exogenous anti-androgens. Analysis included standard slides and high-density tissue microarrays. AMACR protein expression was significantly increased in localized hormone-naive PCa as compared to benign (P < 0.001). Mean AMACR expression was lower in tissue samples from patients who had received neoadjuvant hormone treatment but still higher compared to hormone-refractory metastases. The hormone-sensitive tumor cell line, LNCaP, demonstrated stronger AMACR expression by Western blot analysis than the poorly differentiated cell lines DU-145 and PC-3. AMACR protein expression in cells after exposure to anti-androgen treatment was unchanged, whereas prostate-specific antigen, known to be androgen-regulated, demonstrated decreased protein expression. Surprisingly, this data suggests that AMACR expression is not regulated by androgens. Examination of colorectal cancer, which is not hormone regulated, demonstrated high levels of AMACR expression in well to moderately differentiated tumors and weak expression in anaplastic colorectal cancers. Taken together, these data suggest that AMACR expression is not hormone-dependent but may in fact be a marker of tumor differentiation.