Hyperpipecolic acidemia associated with hepatomegaly, mental retardation, optic nerve dysplasia and progressive neurological disease

Pipecolic acid mitigates ferroptosis in diabetic retinopathy by regulating GPX4-YAP signaling

Diabetic retinopathy (DR) is currently recognized as the leading cause of end-stage eye disease. Pipecolic acid, a metabolite, has a significant regulatory effect on several pathological processes. However, the exact mechanism by which it causes damage in diabetic retinopathy is unknown. Between September 2021 and December 2022, 40 patients were retrospectively examined and divided into two groups: the healthy group (n = 20) and the DR group (n = 20). Metabolomic analysis found that pipecolic acid plays an important role in this process. Streptozotocin-induced diabetic mice and high-glucose cultured human retinal capillary endothelial cells (HRCECs) were then treated with pipecolic acid. Several oxidative stress measurements and RNA sequencing of retinal cells were tested. A gene interaction study was conducted using bioinformatics. Comparison of serological metabolites between healthy volunteers and DR patients showed that pipecolic acid was significantly lower in DR patients, and there was a negative correlation between the level of pipecolic acid with blood glucose and glycated hemoglobin. Yes-associated protein (YAP) mRNA, Malondialdehyde (MDA), and reactive oxygen species (ROS) levels were significantly higher in diabetic mice, but glutathione peroxidase (GSH-Px) levels were significantly lower. Pipecolic acid significantly alleviated oxidative stress and YAP expression. The number of vascular tubes was significantly higher in the DR group, and pipecolic acid treatment significantly reduced tube formation. RNA-Sequencing analysis revealed that YAP and glutathione-dependent lipid hydroperoxidase glutathione peroxidase 4 (GPX4) expression was reduced, and functional enrichment analysis revealed that ferroptosis and Hippo signaling pathways play an important role in this process. Additionally, pipecolic acid's ability to improve DR is diminished after YAP and GPX4 ablation. This study found that pipecolic acid, as a metabolite, may impede the progression of DR by inhibiting the YAP-GPX4 signaling pathway.

Dysfunctional peroxisomal lipid metabolisms and their ocular manifestations

Retina is rich in lipids and dyslipidemia causes retinal dysfunction and eye diseases. In retina, lipids are not only important membrane component in cells and organelles but also fuel substrates for energy production. However, our current knowledge of lipid processing in the retina are very limited. Peroxisomes play a critical role in lipid homeostasis and genetic disorders with peroxisomal dysfunction have different types of ocular complications. In this review, we focus on the role of peroxisomes in lipid metabolism, including degradation and detoxification of very-long-chain fatty acids, branched-chain fatty acids, dicarboxylic acids, reactive oxygen/nitrogen species, glyoxylate, and amino acids, as well as biosynthesis of docosahexaenoic acid, plasmalogen and bile acids. We also discuss the potential contributions of peroxisomal pathways to eye health and summarize the reported cases of ocular symptoms in patients with peroxisomal disorders, corresponding to each disrupted peroxisomal pathway. We also review the cross-talk between peroxisomes and other organelles such as lysosomes, endoplasmic reticulum and mitochondria.

Pipecolic Acid, a Putative Mediator of the Encephalopathy of Cerebral Malaria and the Experimental Model of Cerebral Malaria

BACKGROUND

We explored a metabolic etiology of cerebral malaria (CM) coma.

METHODS

Plasma metabolites were compared between Malawian children with CM and mild Plasmodium falciparum malaria. A candidate molecule was further studied in animal models of malaria.

RESULTS

Clinically abnormal concentrations of pipecolic acid (PA) were present in CM plasma, and nearly normal in mild malaria samples. PA is renally cleared and the elevated PA blood levels were associated with renal insufficiency, which was present only in CM subjects. Prior studies demonstrate that PA has neuromodulatory effects and is generated by malaria parasites. PA brain levels in Plasmodium berghei ANKA-infected animals in the experimental cerebral malaria (ECM) model inversely correlated with normal behavior and correlated with blood-brain barrier (BBB) permeability. Mice infected with malaria species that do not induce neurological abnormalities or manifest BBB permeability had elevated plasma PA levels similar to ECM plasma at 7 days postinfection; however, they had low PA levels in the brain compared to ECM mice brains at 7 days postinfection.

CONCLUSIONS

Our model suggests that malaria-generated PA induces coma in CM and in ECM. The role of BBB permeability and the mechanisms of PA neuromodulation in CM will require additional investigation.

Plasma and Urine Amino Acid Profiles in a Healthy Adult Population of Singapore

Introduction: The analysis of amino acids in plasma and urine was introduced in Singapore when a laboratory for the investigation of inherited metabolic disorders was established by the Ministry of Health. Reference ranges are required for interpreting test results and making diagnoses. Initially, reference ranges established for Caucasians were used as there were no local data and we were unable to find data obtained by the same analytical method for Asian populations. This was not considered an ideal and long-term solution, as Singaporeans may have amino acid concentrations quite different from those of Caucasians due to genetic factors, dietary difference, environment, and other influences. This study was therefore undertaken when a number of healthy laboratory personnel volunteered to provide specimens for the study. Materials and Methods: Sixty healthy male and female laboratory workers not on any form of medication were recruited. They consisted of 24 males (range, 23 to 58 years) and 36 females (range, 20 to 60 years), with a mean age of 38.7 years. Non-fasting random blood and urine specimens were collected on ice. Removal of protein and peptides from heparinised plasma and urine was achieved by ultrafiltration through protein-exclusion membrane. Amino acid analysis on the ultrafiltrate was performed by a dedicated Beckman 6300 Amino Acid Analyzer using a cation exchange resin column and post-column colour reaction with ninhydrin reagent. Urine creatinine was measured by a Beckman LX 20 PRO Analyzer. Results for urine amino acids were expressed as µmol/mmol of creatinine. Results: Reference ranges for 32 amino acids in blood plasma and 36 amino acids in urine were calculated by a non-parametric method using the SPSS statistical calculation software. The ranges cover 95% of the population and the low and high limits of each reference range represent the 2.5th percentile and 97.5th percentile of the frequency distribution respectively. Conclusions: We observed differences in the reference ranges of several plasma and urine amino acids between Singaporean and Caucasian populations. Moreover, the list of urine amino acids for Caucasian population is incomplete. We have therefore discontinued the use of reference values established for Caucasians and adopted the results of this study for our patient diagnostic work. Key words: Blood amino acid, Normal ranges, Reference values, Urine amino acids

Metabolic and molecular basis of peroxisomal disorders: a review

The group of peroxisomal disorders now includes 17 different disorders with Zellweger syndrome as prototype. Thanks to the explosion of new information about the functions and biogenesis of peroxisomes, the metabolic and molecular basis of most of the peroxisomal disorders has been resolved. A review of peroxisomal disorders is provided in this paper.

Pipecolic acid induces apoptosis in neuronal cells

Pipecolic acid, a lysine metabolite, is thought to be a factor responsible for hepatic encephalopathy; however, the underlying mechanism is far from understood. Twenty minutes treatment with D-, L-, and DL-pipecolic acid at concentrations ranging from 1 to 100 microM, except for 1 microM L-pipecolic acid, had no inhibitory effect on excitatory postsynaptic responses in the dentate gyrus of rat hippocampal slices. In a whole-cell voltage-clamp configuration, DL-pipecolic acid (10 and 100 microM) did not affect voltage-sensitive Na(+) channel currents and K(+) channel currents, but it potentiated voltage-sensitive Ca(2+) channel currents, but to a lesser extent, in cultured rat cortical neurons and Neuro-2A cells, a mouse neuroblastoma cell line. Notably, 72-h treatment with D-, L-, and DL-pipecolic acid reduced Neuro-2A cell viability in a dose-dependent manner at concentrations ranging from 1 to 100 microM in a 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay, in parallel with reactions to propidium iodide, a marker of cell death, and Hoechst 33,342, a marker of apoptosis in a fluorescent microscopic study, with DL-pipecolic acid being the most potent. The results of the present study suggest that pipecolic acid could cause hepatic encephalopathy by inducing neuronal cell death, perhaps apoptosis, rather than by depressing neurotransmissions.

Hyperpipecolic acidemia: clinical, biochemical, and radiologic observations

Pipecolic acid is a biochemical marker frequently detected in group 1 peroxisomal disorders (peroxisomal biogenesis disorders). Its presence, in addition to the constellation of particular phenotypic manifestations and pathologic findings, has led to its recent classification under disorders of peroxisomal biogenesis as a separate disease entity (hyperpipecolic acidemia or hyperpipecolatemia). The clinical, biochemical, and radiologic findings observed in three patients diagnosed with hyperpipecolic acidemia are reported.

Identification of L-amino acid/L-lysine alpha-amino oxidase in mouse brain

Lysine, an essential amino acid is catabolized in brain through only the pipecolic acid pathway. During the formation of pipecolic acid, alpha-deamination of lysine, and the formation of the alpha-keto acid as well as its cyclized product are pre-requisites. The enzyme mediated alpha-deamination of L-lysine and the formation of the alpha-keto acid and the cyclized product are not demonstrated so far. Both lysine and pipecolic acid are known to increase in brain under the conditions of fasting, studies were therefore undertaken to identify the enzyme responsible for the alpha-deamination of L-lysine in the brain tissue of mice which were fasted. The detection of the alpha-keto acid of L-lysine -alpha-keto-epsilon-amino caproic acid and its cyclized product-delta-piperidine-2-carboxylate was facilitated by the use of L-[U-14C]-lysine as the substrate. The quantitation of the radioactivity in reaction products was done after separation by ion exchange chromatographic methods. The formation of the alpha-keto acid was enzyme mediated, the alpha-keto acid formed was established by reaction with N-methyl benzothiazolinone hydrazone hydrochloride. The cyclized product was accounted in a fraction which matched the resolution of authentic pipecolic acid on the Dowex column, and the cyclized product was confirmed by spectrophotometry. The hitherto undemonstrated alpha-amino deaminating enzyme of L-lysine in brain tissue, the alpha-keto acid of L-lysine and its cyclized product in a mammalian system could thus be demonstrated in the present study. These findings confirm the involvement of L-lysine oxidase/L-amino acid oxidase in the formation of pipecolic acid from L-lysine.

Biochemistry of peroxisomes in health and disease

The ubiquitous distribution of peroxisomes and the identification of a number of inherited diseases associated with peroxisomal dysfunction indicate that peroxisomes play an essential part in cellular metabolism. Some of the most important metabolic functions of peroxisomes include the synthesis of plasmalogens, bile acids, cholesterol and dolichol, and the oxidation of fatty acids (very long chain fatty acids > C22, branched chain fatty acids (e.g. phytanic acid), dicarboxylic acids, unsaturated fatty acids, prostaglandins, pipecolic acid and glutaric acid). Peroxisomes are also responsible for the metabolism of purines, polyamines, amino acids, glyoxylate and reactive oxygen species (e.g. O-2 and H2O2). Peroxisomal diseases result from the dysfunction of one or more peroxisomal metabolic functions, the majority of which manifest as neurological abnormalities. The quantitation of peroxisomal metabolic functions (e.g. levels of specific metabolites and/or enzyme activity) has become the basis of clinical diagnosis of diseases associated with the organelle. The study of peroxisomal diseases has also contributed towards the further elucidation of a number of metabolic functions of peroxisomes.

Clinical approach to inherited peroxisomal disorders

At least 21 genetic disorders have now been found that are linked to peroxisomal dysfunction. Whatever the genetic defect might be, peroxisomal disorders should be considered in various clinical conditions, dependent on the age of onset. The prototype of peroxisomal disorders is represented by 'classical' Zellweger syndrome (ZS) which is the most severe disorder combining all the characteristic symptoms. ZS is characterized by the association of errors of morphogenesis, severe neurological dysfunction, neurosensory defects, regressive changes, hepatodigestive involvement with failure to thrive, usually early death, and absence of recognizable liver peroxisomes. Other peroxisomal disorders (pseudo-Zellweger syndrome, neonatal adrenoleukodystrophy (NALD), pseudo-neonatal adrenoleukodystrophy, rhizomelic chondrodysplasia punctata (RCDP), and hyperpipecolic acidaemia) share some of these symptoms, but with varying organ involvement, severity of dysfunction, and duration of survival. The diagnosis should not cause difficulty when all the characteristic manifestations are present. Depending on the main presenting sign, peroxisomal disorders in neonates should be suspected in two categories of circumstances: polymalformative syndrome with craniofacial dysmorphism, and severe neurological dysfunction. During the first 6 months of life, the predominant symptoms may be hepatomegaly, prolonged jaundice, liver failure, anorexia, vomiting and diarrhoea leading to failure to thrive resembling a malabsorption syndrome; severe psychomotor retardation, hearing loss and ocular abnormalities become evident. Beyond 4 years of age, behavioural changes, intellectual deterioration, visual impairment and gait abnormalities may be the presenting symptoms. Independently of the clinical symptoms and age of onset, most peroxisomal disorders described so far can be clinically screened by recordings of electroretinogram, visual-evoked responses, and brain auditory-evoked responses, which are almost always abnormal. Nine of the 17 peroxisomal disorders with neurological involvement are associated with an accumulation of very long-chain fatty acids (VLCFA), which suggests that assay of plasma VLCFA should be used as a primary test. However, assays of plasma phytanic acid and plasma/urine bile acid intermediates should also be performed in view of the recent reports of atypical chondrodysplasia variants (without rhizomelic shortening) and isolated trihydroxycholestanoic aciduria. The differential diagnoses in various clinical conditions and age periods are discussed.

Peroxisomal disorders: a review

Until recently peroxisomal disorders were considered to be extremely rare and the diagnostic procedures available for postanatal and prenatal diagnosis were not widely known. At present, 17 human disorders are linked to peroxisomal dysfunction. The clinical, biochemical and morphological peroxisome heterogeneity described in the different diseases illustrate that only combined analysis of all the different approaches will lead to a correct diagnosis and a coherent pathophysiological model to guide ongoing research. With the study of human peroxisomal disease, advances have been gained as to the function of the peroxisome in normal and pathological conditions. Genetic analysis of peroxisome biogenesis and research on peroxisomal targeting signals are now in progress. Peroxisomal disorders are usually classified according to the degree of biochemical impairment. In this paper, a tentative classification of peroxisomal disorders will be proposed, based on the degree of biochemical abnormalities combined with new data obtained on whether or not defective peroxisome assembly is involved: (1) disorders with peroxisome assembly deficiencies; (2) disorders with single enzyme deficiencies. The clinical onset and the major symptoms of the various disorders, and the recently discovered findings are discussed.

L-pipecolic acid oxidation in rat: subcellular localization and developmental study

By using a sensitive radioactive assay method, we present here evidence that L-pipecolic acid oxidase is localized in both mitochondria and peroxisomes of rat liver. Brain white matter contained a more than 2-fold higher activity of L-pipecolic acid oxidation than the brain cortex. Suborganellar fractionation studies indicate that while the enzyme is a matrix protein in mitochondria, it is membrane-associated in peroxisomes. Both rotenone and antimycin A completely inhibited the enzyme activity in mitochondria but not in peroxisomes. The enzyme was shown to be inducible in mitochondria and peroxisomes of rat liver and brain tissues by glucagon and di-(2-ethylhexyl)phthalate, respectively. We report here for the first time the developmental aspects of L-pipecolic acid oxidation activity in rat liver and brain tissues. L-Pipecolic acid oxidase activity was detectable in whole rat embryo at 10 days of gestation, suggesting active L-pipecolic acid metabolism early during development. In both liver and brain tissues L-pipecolic acid oxidation activity was highest at 15 days of gestation and decreased with age in prenatal and postnatal conditions.

Update on genetic and molecular investigations of diseases with general impairment of peroxisomal functions

A group of genetically determined peroxisomal diseases is characterized by both multiple enzymatic deficiencies and abnormal structural features of the organelle. The primary cause of the phenotypes is likely to involve peroxisome assembly impairment. Complementation analyses performed on fibroblasts of patients revealed the existence of at least eight groups that do not reflect the clinical classifications. Recently, the use of experimental models led to the identification of a gene encoding for a peroxisomal membrane protein (PAF-1) in which a mutation was associated with the altered phenotype in a complementation group of the Zellweger syndrome (paradigm of these diseases). Also revealed in Zellweger probands are mutations of a gene encoding another peroxisomal protein (PMP70).

Assay for L-pipecolate oxidase activity in human liver: detection of enzyme deficiency in hyperpipecolic acidaemia

A direct assay method is described for L-pipecolate oxidase. The assay uses NaHSO3 to trap the L-alpha-amino [3H]adipate delta-semialdehyde (AAS) formed as a direct reaction product of L-pipecolate oxidase from L-[3H]pipecolic acid. The adduct so formed was separated from the substrate on Dowex 50 (H+) column. The product was identified as [3H]AAS by amino acid analysis after breaking down the adduct by boiling under acidic conditions. The assay is simpler and more specific than fluorometric methods; it is also more sensitive, requiring at most 16 micrograms of liver peroxisome-enriched protein per assay. We have used this assay procedure to detect L-pipecolate oxidase in skin fibroblasts obtained from a control subject and from patients of hyperpipecolic acidaemia and Zellweger syndrome and found that this enzyme activity is present in the control, but absent or decreased in the patients with the peroxisomal disorders.

Phenotypic heterogeneity in cultured skin fibroblasts from patients with disorders of peroxisome biogenesis belonging to the same complementation group

We have studied fibroblast cell lines derived from a control subject (cell line 85AD5035F) and three patients clinically described as having the Zellweger syndrome (cell line W78/515), the infantile form of Refsum disease (cell line BOV84AD) and hyperpipecolic acidaemia (cell line GM3605), respectively. The mutant cell lines belonged to the same complementation group. The fibroblasts were cultured under identical conditions and were harvested at different time intervals after reaching confluence. Several peroxisomal parameters were determined. In agreement with previous reports, a lowered enzymic activity of acyl-CoA: dihydroxyacetonephosphate acyltransferase and a decrease in latent catalase clearly distinguished the patient cell lines from the control cell line. However, the cell lines exhibited a phenotypic heterogeneity. This was most strikingly encountered when cells were processed for indirect immunofluorescence microscopy and stained with anti-(catalase). The control cells exhibited a punctate fluorescence, which is indicative of the presence of catalase in peroxisomes. In the mutant cell line W78/515 a diffuse fluorescence was observed, indicative of the presence of catalase in the cytosol. In the other two mutant cell lines a punctate fluorescence was observed in some of the cells. Moreover, clear differences in the extent of proteolytic processing of acyl-CoA oxidase were detected. The mutant cell line BOV84AD displayed a control-like pattern with all molecular forms of acyl-CoA oxidase (72, 52 and 20 kDa) present, whereas in the W78/515 cell line only the 72 kDa component could be visualised. The GM3605 cell line was intermediate in this respect.

The peroxisome and the eye

Several childhood multisystem disorders with prominent ophthalmological manifestations have been ascribed to the malfunction of the peroxisome, a subcellular organelle. The peroxisomal disorders have been divided into three groups: 1) those that result from defective biogenesis of the peroxisome (Zellweger syndrome, neonatal adrenoleukodystrophy, and infantile Refsum's disease); 2) those that result from multiple enzyme deficiencies (rhizomelic chondrodysplasia punctata); and 3) those that result from a single enzyme deficiency (X-linked adrenoleukodystrophy, primary hyperoxaluria type 1). Zellweger syndrome, the most lethal of the three peroxisomal biogenesis disorders, causes infantile hypotonia, seizures, and death within the first year. Ophthalmic manifestations include corneal opacification, cataract, glaucoma, pigmentary retinopathy and optic atrophy. Neonatal adrenoleukodystrophy and infantile Refsum's disease appear to be genetically distinct, but clinically, biochemically, and pathologically similar to Zellweger syndrome, although milder. Rhizomelic chondrodysplasia punctata, a peroxisomal disorder which results from at least two peroxisomal enzyme deficiencies, presents at birth with skeletal abnormalities and patients rarely survive past one year of age. The most prominent ocular manifestation consists of bilateral cataracts. X-linked (childhood) adrenoleukodystrophy, results from a deficiency of a single peroxisomal enzyme, presents in the latter part of the first decade with behavioral, cognitive and visual deterioration. The vision loss results from demyelination of the entire visual pathway, but the outer retina is spared. Primary hyperoxaluria type 1 manifests parafoveal subretinal pigment proliferation. Classical Refsum's disease may also be a peroxisomal disorder, but definitive evidence is lacking. Early identification of these disorders, which may depend on recognizing the ophthalmological findings, is critical for prenatal diagnosis, treatment, and genetic counselling.

Species variation in organellar location and activity of L-pipecolic acid oxidation in mammals

The oxidation of L-pipecolic acid to alpha-aminoadipic acid was studied in eight species of mammals using an assay system more sensitive than those previously employed. After percoll-gradient fractionation, activity was localized to the mitochondrial-enriched fractions in tissues from rabbit, guinea pig, pig, dog, and sheep, with guinea pig kidney cortex showing greatest specific activity. These results contrast with the peroxisomal oxidation of L-pipecolic acid observed in macaques and man (Mihalik and Rhead 1989; Mihalik et al. 1989). Rats and mice had undetectable levels of both peroxisomal and mitochondrial L-pipecolic acid oxidation. In the rat, peroxisomal oxidation activity was not induced by feeding with either clofibrate or clofibrate and L-pipecolic acid. Thus, among mammals, both the ability to oxidize L-pipecolic acid and the organellar location of this oxidation is species dependent.

Determination of pipecolic acid in serum or plasma by solid-phase extraction and isotope dilution mass spectrometry

The determination of pipecolic acid in serum or plasma by positive chemical ionization gas chromatography/mass spectrometry is assessed. This quantitative method involves stable isotope dilution and cation-exchange solid-phase extraction. Several derivatives of pipecolic acid and its octadeuterated analogue were investigated for their mass spectrometric characteristics. The heptafluorobutyric methyl ester derivatives afford optimal resolution on gas chromatography of biological extracts. Moreover, the derivatizing reagent (methanolic HCl) allows a combined elution and derivatization. Selected ion monitoring is performed on the [M + H]+ ions of both analyte and internal standard, at m/z 340 and 348, respectively. Serum or plasma samples from healthy subjects and patients suspected of peroxisomal diseases have been examined.

Peroxisomal disorders in neurology

Although peroxisomes were initially believed to play only a minor role in mammalian metabolism, it is now clear that they catalyse essential reactions in a number of different metabolic pathways and thus play an indispensable role in intermediary metabolism. The metabolic pathways in which peroxisomes are involved include the biosynthesis of ether phospholipids and bile acids, the oxidation of very long chain fatty acids, prostaglandins and unsaturated long chain fatty acids and the catabolism of phytanate and (in man) pipecolate and glyoxylate. The importance of peroxisomes in cellular metabolism is stressed by the existence of a group of inherited diseases, the peroxisomal disorders, caused by an impairment in one or more peroxisomal functions. In the last decade our knowledge about peroxisomes and peroxisomal disorders has progressed enormously and has been the subject of several reviews. New developments include the identification of several additional peroxisomal disorders, the discovery of the primary defect in several of these peroxisomal disorders, the recognition of novel peroxisomal functions and the application of complementation analysis to obtain information on the genetic relationship between the different peroxisomal disorders. The peroxisomal disorders recognized at present comprise 12 different diseases, with neurological involvement in 10 of them. These diseases include: (1) those in which peroxisomes are virtually absent leading to a generalized impairment of peroxisomal functions (the cerebro-hepato-renal syndrome of Zellweger, neonatal adrenoleukodystrophy, infantile Refsum disease and hyperpipecolic acidaemia); (2) those in which peroxisomes are present and several peroxisomal functions are impaired (the rhizomelic form of chondrodysplasia punctata, combined peroxisomal beta-oxidation enzyme protein deficiency); and (3) those in which peroxisomes are present and only a single peroxisomal function is impaired (X-linked adrenoleukodystrophy, peroxisomal thiolase deficiency (pseudo-Zellweger syndrome), acyl-CoA oxidase deficiency (pseudo-neonatal adrenoleukodystrophy) and probably, the classic form of Refsum disease.

Peroxisomal disorders: clinical commentary and future prospects

Recent progress in the classification, biochemistry, and molecular biology of peroxisomal disorders is reviewed from a clinical perspective. Diseases such as Zellweger syndrome, neonatal adrenoleukodystrophy, infantile Refsum disease, hyperpipecolic acidemia, chondrodysplasia punctata, and Leber amaurosis share a common phenotype and involve deficiency of multiple peroxisomal enzymes. These disorders are associated with diverse metabolic abnormalities which are useful in pre- or postnatal diagnosis and distinguish these disorders from others such as X-linked adrenoleukodystrophy, adult Refsum disease, hyperoxaluria type I, and acatalasemia. Peroxisome structure is difficult to quantify histologically, since recent studies emphasize its developmental variability and tissue heterogeneity. The ability to manipulate this structure by dietary or pharmaceutical means provides a novel approach to therapy. At the molecular level, deficiency of peroxisomal enzymes responsible for fatty acid beta-oxidation or ether lipid synthesis reflects enhanced protein degradation due to abnormal peroxisomes; messenger RNA for the beta-oxidation enzymes is transcribed normally in peroxisomal disorders and can be increased by peroxisome proliferators. At least one integral structural protein of the peroxisome is synthesized normally in Zellweger syndrome. Hypotheses for the basic defect include defective regulation, uptake, or coenzyme stimulation of imported proteins, as well as defective biosynthesis. One clue to this defect may be a similar evolutionary history of peroxisomes and mitochondria which would explain their common alteration in Zellweger syndrome.

Genetic heterogeneity in the cerebrohepatorenal (Zellweger) syndrome and other inherited disorders with a generalized impairment of peroxisomal functions. A study using complementation analysis

We have used complementation analysis after somatic cell fusion to investigate the genetic relationships among various genetic diseases in humans in which there is a simultaneous impairment of several peroxisomal functions. The activity of acyl-coenzyme A:dihydroxyacetonephosphate acyltransferase, which is deficient in these diseases, was used as an index of complementation. In some of these diseases peroxisomes are deficient and catalase is present in the cytosol, so that the appearance of particle-bound catalase could be used as an index of complementation. The cell lines studied can be divided into at least five complementation groups. Group 1 is represented by a cell line from a patient with the rhizomelic form of chondrodysplasia punctata. Group 2 consists of cell lines from four patients with the Zellweger syndrome, a patient with the infantile form of Refsum disease and a patient with hyperpipecolic acidemia. Group 3 comprises one cel line from a patient with the Zellweger syndrome, group 4 one cell line from a patient with the neonatal form of adrenoleukodystrophy, and group 5 one cell line from a patient with the Zellweger syndrome. We conclude that at least five genes are required for the assembly of a functional peroxisome.

Clinical biochemistry of peroxisomal disorders

Peroxisomes have been shown to participate in a variety of pathological processes. Peroxisomal anomalities are central features of Zellweger's cerebro-hepato-renal syndrome, neonatal adrenoleukodystrophy, infantile Refsum's disease and several other genetic metabolic disorders (pseudo-Zellweger syndrome, Leber congenital amaurosis, cerebrotendinous xanthomatosis, rhizomelic chondrodysplasia punctata). In disorders with general loss of peroxisomal functions (Zellweger syndrome, neonatal adrenoleukodystrophy, infantile Refsum's disease) an accumulation of very long-chain fatty acids and pathological bile acids are found. Patients have a defective synthesis of plasmalogens and show increased excretion of dicarboxylic acids of medium chain length and of pipecolic acid in the urine. These anomalities which are due to the lack of peroxisomal enzymes, supply the basis for clinical laboratory tests. The study of these peroxisomal disorders has presented valuable information on the normal function of peroxisomes.

Plasma levels of pipecolic acid in patients with chronic liver disease

Plasma levels of pipecolic acid, which is a minor metabolite of lysine, were determined by high-performance liquid chromatography in 22 patients with chronic liver disease, composed of 6 patients with chronic active hepatitis, 11 with liver cirrhosis and 5 with hepatocellular carcinoma. The plasma levels of pipecolic acid, when compared to those in normal subjects (1.00 +/- 0.08 nmoles per ml), were found to be significantly elevated (p less than 0.01) in patients with liver cirrhosis (1.93 +/- 0.24 nmoles per ml) and hepatocellular carcinoma (2.22 +/- 0.49 nmoles per ml), but did not show any significant change in patients with chronic active hepatitis. Plasma levels of pipecolic acid correlated positively with serum bile acid and bilirubin, and negatively with indocyanine green disappearance rate, cholinesterase and prothrombin time but not with plasma lysine levels. These results suggest that plasma levels of pipecolic acid increase almost parallel to the severity of liver damage, and that this increase in pipecolic acid may reflect the injury of liver peroxisomes which appear to be related to the degradation of pipecolic acid.

Modulation of benzodiazepine by lysine and pipecolic acid on pentylenetetrazol-induced seizures

L-lysine, an essential amino acid for man and animals, and its metabolite pipecolic acid (PA) have been studied for their effects on pentylenetetrazol (PTZ)-induced seizures in mice. L-Lysine or L-PA i.p. significantly increased clonic and tonic latencies in a dose-dependent manner against 90 mg/kg PTZ-induced seizures. L-Lysine but not L-PA enhanced the anticonvulsant effect of diazepam (DZ) (0.2 mg/kg). L-PA (0.1 mmol/kg) i.c.v. showed a slight decrease in clonic latency; it did not enhance the antiseizure activity of DZ; it caused seizures at 0.6 mmol/kg. D-PA (0.1 mmol/kg) i.c.v. displayed an opposite effect compared to its L-isomer. The anticonvulsant effect of L-lysine in terms of increase in seizure latency and survival was even more amplified when tested with a submaximal PTZ concentration (65 mg/kg). L-Lysine showed an enhancement of specific 3H-flunitrazepam (FZ) binding to mouse brain membranes both in vitro and in vivo. The possibility of L-lysine acting as a modulator for the GABA/benzodiazepine receptors was demonstrated. Since L-PA showed enhancement of 3H-FZ binding only in vitro but not in vivo, the anticonvulsant effect of L-PA may not be linked to the GABA/benzodiazepine receptor.

Phenotypic and genotypic variability of generalized peroxisomal disorders

This article classifies and describes the various entities that comprise the generalized peroxisomal disorder. The variability in both phenotype and genotype is stressed. A heretofore undescribed generalized peroxisomal disorder is reported.

Effect of immobilization stress on pipecolic acid transport in mouse brain areas and peripheral tissues

Transport activity of d-pipecolic acid and of l-pipecolic acid in mouse brain and peripheral tissues were tested, and the effect of immobilization stress was described, along with the method for preparative, enantiomeric resolution and purification of d,l-pipecolic acid using high performance liquid chromatography equipped with a chiral column. It was found that l-isomer, an endogenous substance, was more rapidly transported to brain and liver than the d-isomer, non-endogenous one, which was more rapidly eliminated into the kidney. Immobilization stress caused acceleration of transport of l-pipecolic acid into the brain region, liver and heart, but not that of d-pipecolic acid. From these results it was suggested that the elevation of pipecolic acid concentration caused by stress might be exerted through its stimulatory effect on the transport of l-pipecolic acid into the tissues.

Peroxisomal disorders. A review of a recently recognized group of clinical entities

The peroxisome is a small organelle present in almost all cells. The peroxisomal disorders are a newly recognized group of disease entities that share structural and/or functional abnormalities of the peroxisomes, are inherited, and may have profound neurologic and systemic effects. Some of the disorders lack peroxisomes in cells, while others have single or multiple peroxisomal enzymatic deficiencies despite the presence of normally appearing peroxisomes. The prototype of the peroxisomal disorders is Zellweger syndrome. X-linked adrenoleukodystrophy, neonatal adrenoleukodystrophy, infantile Refsum disease, hyperpipecolic acidemia and Refsum disease are some of the other disease entities presently classified as peroxisomal disorders. Accurate methods of pre- and postnatal diagnosis are available. Treatment strategies are being developed, but at this time prenatal diagnosis and appropriate genetic counseling is the best therapeutic intervention for those peroxisomal disorders characterized by profound neurologic handicap and early death.

Prenatal diagnosis of Zellweger syndrome by measurement of very long chain fatty acid (C26:0) beta-oxidation in cultured chorionic villous fibroblasts: implications for early diagnosis of other peroxisomal disorders

In this paper we show that cultured chorionic villous fibroblasts efficiently catalyse the peroxisomal beta-oxidation of hexacosanoic acid (cerotic acid), a saturated very long chain fatty acid containing 26 carbon atoms. Hexacosanoic beta-oxidation was found to be strongly impaired in cultured chorionic villous fibroblasts from a Zellweger foetus. This finding indicates that measurement of peroxisomal beta-oxidation can be used (in addition to measurement of acyl-CoA:dihydroxyacetone phosphate acyltransferase, de novo plasmalogen biosynthesis, the amount of particle-bound catalase and phytanic acid oxidase) for prenatal diagnosis in the first trimester of Zellweger syndrome, infantile Refsum disease and neonatal adrenoleukodystrophy. The method should be equally applicable to the early prenatal diagnosis of disorders in which there is a deficiency of a single peroxisomal beta-oxidation enzyme. Such diseases include X-linked adrenoleukodystrophy (peroxisomal very long chain fatty acyl CoA ligase deficiency), 'pseudo-Zellweger syndrome' (peroxisomal 3-oxoacyl-CoA thiolase deficiency) and 'pseudo-neonatal adrenoleukodystrophy' (acyl-CoA oxidase deficiency).

Peroxisomal disorders: clinical characterization

The peroxisomal disorders can be divided into three classes: firstly, those in which the activity of only one single enzyme is reduced; secondly, those in which the activities of multiple peroxisomal enzymes are deficient and also the number of peroxisomes is reduced; and thirdly, those in which the activities of multiple peroxisomal enzymes are lacking and at the same time the number of peroxisomes is normal at least in liver tissue. The cerebro-hepato-renal syndrome of Zellweger is the prototype of peroxisomal disorders of the second group. Clinical distinction between Zellweger syndrome and neonatal adrenoleukodystrophy or infantile Refsum disease can be impossible. The clinical abnormalities that should give rise to suspicion for the presence of a peroxisomal disorder and urge the necessity of further biochemical studies are proposed.

D-pipecolic acid inhibits ethanol tolerance in mice

The effects of graded doses of D-pipecolic acid (0.005-5 micrograms/animals s.c.) on tolerance to the hypothermic effect of ethanol (4 g/kg i.p.) were investigated in mice. D-Pipecolic acid itself did not change the core temperature or the acute hypothermic response to a single dose of ethanol. Repeated D-pipecolic acid administration, however, blocked the development of tolerance to the hypothermic effect of ethanol. The development of tolerance could be observed in the control group. It is assumed that D-pipecolic acid is capable of counteracting the tolerance effect of ethanol.

Determination of pipecolic acid in urine and plasma by isotope dilution mass fragmentography

A capillary gas chromatographic method with mass spectrometric detection for the determination of pipecolic acid in urine and plasma (or serum) has been developed. Using a quantification based on stable isotope dilution mass fragmentography the concentration of pipecolic acid was determined in urines of 34 healthy children and 8 patients with Zellweger's syndrome. The urinary pipecolic acid excretion of healthy infants decreases with age. Its concentration in urines of patients with Zellweger's syndrome was not consistently elevated. Normal values for pipecolic acid in plasma were established for 19 healthy children. Pipecolic acid concentrations in 47 urine samples (range 0.02-228.3 mmol/mol of creatinine) and 6 serum samples of Zellweger patients after oral loading with DL-pipecolic acid (range 65-1334 mumol/l) were found to correlate satisfactorily with the results obtained by an amino acid analyzer method. The major advantage of the presented method over the amino acid analyzer method concerns its greater sensitivity and its much shorter analysis time.

Optic nerve hypoplasia: a review

Optic nerve hypoplasia is a developmental anomaly of the retina and optic nerves in which there is a reduction in the number of ganglion cells in the retina and of their centripetal fibers projecting through the optic nerve to the lateral geniculate body. The condition may be unilateral or bilateral and is frequently misdiagnosed as optic atrophy. In about 25% of cases, bilateral optic nerve hypoplasia is associated with a variety of cerebral malformations of which the commonest single disturbance is absence of the septum pellucidum (septo-optic dysplasia). Cerebral malformations and their endocrine accompaniments are also seen, though less frequently, in unilateral hypoplasia. The endocrine disturbances that may accompany optic nerve hypoplasia include growth hormone deficiency, adrenal insufficiency, hypothyroidism, and disturbances of antidiuretic hormone production. Precocious puberty and hypogonadism have also been observed. The prognosis of optic nerve hypoplasia depends upon the severity of the changes in the optic nerves and especially the degree of associated cerebral malformation. The finding of optic nerve hypoplasia should lead to thorough ophthalmologic, neurologic, and endocrinologic evaluation of the patient.

Profiling of amino acids in body fluids and tissues by means of liquid chromatography

The needs of urgent diagnoses and the needs emerging from acute forms of diseases have directed progress in amino acid profiling to modern, rapid, automated analyses that can be done at reasonable cost. The first step in this direction was the short programmes of classical ion-exchange chromatography. At the beginning of this review we attempted to survey methods of sample preparation and sample treatment, as these are frequently neglected stages where artefacts or erroneous results may arise. There are basically the following approaches in amino acid profiling by liquid chromatographic techniques. For preliminary screening of a large number of samples in clinical routine planar procedures are the methods of choice, as they allow large numbers of samples to be handled with minimum effort and at very reasonable cost. For more precise profiling, particularly where quantitative data are essential, one can choose between some of the modern procedures for separating underivatized amino acids using modern equipment for cation-exchange chromatography, by making use of a stepped series of lithium citrate buffers with ninhydrin, o-phthalaldehyde or 4-fluoro-7-nitrobenzo-2,1,3-oxadiazole detection. Ninhydrin detection is preferred in those situations where the demands on sensitivity are not high. Where, however, only small amounts of samples are available or high sensitivity is required, one of the latter two methods is preferred. The o-phthalaldehyde procedure is not suitable for the detection of secondary amines and, if these are of interest, then diazole derivatization is to be preferred. At present, however, the ninhydrin and o-phthalaldehyde detection procedures are the most popular. The other choice is to use one of the sophisticated HPLC systems equipped with fluorescence detection and to separate amino acids as derivatives. Here o-phthalaldehyde and 4-fluoro-7-nitrobenzo-2,1,3-oxadiazole derivatives offer the most versatile possibilities. Automation and computerization have penetrated both categories of liquid column separation and are applied to automated sample delivery, automated and computerized gradient formation and quantitation of the data obtained. The tables of metabolic disorders of amino acids and the roles of different amino acids in these disorders should provide preliminary information for clinical chemists.

Zellweger syndrome: diagnostic assays, syndrome delineation, and potential therapy

Patients with the cerebrohepatorenal syndrome of Zellweger lack peroxisomes and certain peroxisomal enzymes such as dihydroxyacetone phosphate acyltransferase in their tissues. Deficiency of this enzyme, which is necessary for glycerol ether lipid synthesis, provides a biochemical method for recognizing patients with subtle manifestations of Zellweger syndrome and suggests the utility of exogenous ether lipid precursors as a therapeutic strategy for these children. We describe the results of glycerol ether lipid supplementation to two children, one with classic Zellweger syndrome and 9% of control fibroblast dihydroxyacetone phosphate acyltransferase activity, and one with mild facial manifestations, wide sutures, hypotonia, developmental delay, hepatomegaly, peripheral retinal pigmentation, and 50% of control fibroblast dihydroxyacetone phosphate acyltransferase activity. An increase in erythrocyte plasmalogen levels following therapy was clearly demonstrated in the milder patient, and neither patient showed evidence of toxicity. Evaluation of therapy by comparison to the usual clinical course of Zellweger syndrome was not helpful because of the variability and incomplete documentation of 90 previously reported cases. The literature survey did provide criteria for classic Zellweger syndrome, which include hypotonia with or without deformation of limbs, large fontanels and split sutures, prominent forehead, flattened facial profile with hypoplastic supraorbital ridges, anteverted nares, highly arched palate, cryptorchidism or labial hypoplasia, hepatomegaly or elevated liver enzymes, peripheral pigmentation of the retina, renal cortical cysts, and characteristic neuropathology involving decreased myelinization, abnormal neuronal migration, and sudanophilic macrophages. Less severe patients, as exemplified by our case 2 and others from the literature, will not have all the classic features and can be recognized only by a growing panel of biochemical indicators. Our patient studies illustrate the complexity of designing comprehensive therapy for Zellweger-like conditions, suggest other diseases that may involve peroxisomal alterations, and emphasize the need for multicenter, collaborative studies to evaluate biochemical heterogeneity and therapy of peroxisomal disorders.

Pipecolic acid is oxidized by renal and hepatic peroxisomes. Implications for Zellweger's cerebro-hepato-renal syndrome (CHRS)

Increased levels of pipecolic acid have been reported in patients with cerebro-hepato-renal syndrome (CHRS) of Zellweger and the general deficiency of peroxisomal function has been implicated in its pathogenesis. We have therefore investigated the capacity of normal peroxisomes to metabolize pipecolic acid. Highly purified peroxisomes were obtained from rat liver and rat and beef kidney cortex by a recently developed method using metrizamide gradients and a vertical rotor. These preparations oxidized D,L-pipecolic acid as evidenced by the measurement of H2O2 production. Incubation with either the D- or L-isomer revealed that almost exclusively D-pipecolate is oxidized. The specific activities proved to be 20-50 times higher in renal than in hepatic peroxisomes. A commercially available crystalline suspension of D-amino acid oxidase from porcine kidney also oxidized the pipecolic acid with the following rates 54:36:1 respectively for D-:,D,L-:L-isomers. Incubation of vibratome sections of rat kidney and liver in a medium containing D-pipecolic acid and cerous ions, revealed electron-dense deposits over the matrix of peroxisomes confirming the localization also by fine structural cytochemistry. These observations demonstrate the capability of mammalian peroxisomes to oxidize pipecolic acid and suggest that the absence or deficiency of peroxisomal D-amino acid oxidase may be implicated in the pathogenesis of hyperpipecolatemia in Zellweger's CHRS.

Neonatal adrenoleukodystrophy: new cases, biochemical studies, and differentiation from Zellweger and related peroxisomal polydystrophy syndromes

Eight new cases of autopsy-confirmed or suspected neonatal adrenoleukodystrophy (NALD) are presented together with new biochemical data on very-long-chain fatty acids (VLCFA) and plasmalogens and a review of all previously published cases. The clinical, biochemical, and histopathologic abnormalities characteristic of this newly recognized form of adrenoleukodystrophy are analyzed in detail and compared to the principal characteristics of the similar disorder, the cerebrohepatorenal syndrome of Zellweger (ZS). Using strict pathologic criteria for the diagnosis of NALD, we find that, despite many clinical resemblances, NALD and the ZS are distinguishable on the basis of histology and peroxisomal biochemistry. Patients with NALD demonstrate adrenal atrophy, systemic infiltration by abnormal lipid-laden macrophages, and elevations of saturated VLCFA. In contrast, patients with ZS have chondrodysplasia, glomerulocystic disease of the kidney, central nervous system dysmyelination, and elevations of unsaturated as well as saturated VLCFA, but they lack adrenal atrophy. We conclude that NALD and the ZS probably represent at least two different genetic defects.

Dysmorphic syndrome with phytanic acid oxidase deficiency, abnormal very long chain fatty acids, and pipecolic acidemia: studies in four children

We describe a relatively new syndrome in four children with characteristic facial dysmorphism, sensorineural hearing loss, severe visual impairment with retinitis pigmentosa, hypotonia, hepatomegaly, and severe developmental delay. Two patients had intracranial hemorrhage secondary to a vitamin K-responsive clotting defect; both had steatorrhea. Liver biopsy specimens in two children showed an accentuated lobular architecture with prominent fibrous bands in the portal area. In one, the ultrastructure showed accumulation of abnormal substances and occasional trilaminar structures in hepatocytes and other cells. All four patients had elevated serum phytanic acid concentrations (0.3 to 2.7 mg/dl, normal less than 0.2 mg/dl) and deficient fibroblast phytanic acid oxidase activity (0.1 to 6.7 pmol/mg protein/hr, normal 23 to 87 pmol/mg protein/hr). Serum pipecolic acid was 7 to 55 times normal, and the ratio of C26/C22 very long chain fatty acids was increased (0.10 to 0.22; normal less than 0.03). This characteristic syndrome has been described in several children and called infantile Refsum disease or phytanic acid storage disease. Its relationship to neonatal adrenoleukodystrophy, hyperpipecolic acidemia, and Zellweger syndrome is discussed.

Cerebro-hepato-renal (Zellweger) syndrome, adrenoleukodystrophy, and Refsum's disease: plasma changes and skin fibroblast phytanic acid oxidase

Cerebro-hepato-renal (Zellweger) syndrome, adrenoleukodystrophy, and Refsum's disease patients can be divided into at least five distinct groups, according to the nature of their plasma changes and their fibroblast phytanic acid oxidase activities. The biochemical changes in the plasma vary from an increase in a single metabolite or group of structurally related metabolites, such as in X-linked adrenoleukodystrophy (ALD) and classical Refsum's disease, to an increase in a number of structurally distinct metabolites, as in neonatal ALD/Zellweger syndrome, and infantile Refsum's disease. All patients, with the exception of those with the X-linked form of adrenoleukodystrophy are deficient in phytanic acid oxidase activity. The great similarity observed in neonatal adrenoleukodystrophy/Zellweger syndrome and infantile Refsum's disease suggests that the basic biochemical lesion in each may be similar or at least closely related.

Pipecolic acid levels in serum and urine from neonates and normal infants: comparison with values reported in Zellweger syndrome

Pipecolic acid (PA) excretion from normal newborn, preterm and/or small-for-dates infants has been determined and correlated with gestational age, sex and age after birth. An effect of fetal sex was not detectable. Only small-for-dates infants with a gestational age of greater than 34-37 weeks had a lower urinary excretion of PA than the appropriate-for-dates infants with the same gestational age. Preterm infants had a higher excretion of PA than term neonates. PA excretion of infants decreases with age after birth. This higher excretion in "younger" infants can be explained by a higher serum concentration and less efficient tubular reabsorption. PA level in serum and urine remains a valuable tool for the confirmation of the clinical diagnosis of Zellweger syndrome when gestational age and age after birth are taken into consideration. No PA was detected in serum or urine of four children suffering from hyperthyroidism.