Accumulation and metabolism of pipecolic acid in the brain and other organs of the mouse

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.

In Vitro Fertilisation of Mouse Oocytes in L-Proline and L-Pipecolic Acid Improves Subsequent Development

Exposure of oocytes to specific amino acids during in vitro fertilisation (IVF) improves preimplantation embryo development. Embryos fertilised in medium with proline and its homologue pipecolic acid showed increased blastocyst formation and inner cell mass cell numbers compared to embryos fertilised in medium containing no amino acids, betaine, glycine, or histidine. The beneficial effect of proline was prevented by the addition of excess betaine, glycine, and histidine, indicating competitive inhibition of transport-mediated uptake. Expression of transporters of proline in oocytes was investigated by measuring the rate of uptake of radiolabelled proline in the presence of unlabelled amino acids. Three transporters were identified, one that was sodium-dependent, PROT (SLC6A7), and two others that were sodium-independent, PAT1 (SLC36A1) and PAT2 (SLC36A2). Immunofluorescent staining showed localisation of PROT in intracellular vesicles and limited expression in the plasma membrane, while PAT1 and PAT2 were both expressed in the plasma membrane. Proline and pipecolic acid reduced mitochondrial activity and reactive oxygen species in oocytes, and this may be responsible for their beneficial effect. Overall, our results indicate the importance of inclusion of specific amino acids in IVF medium and that consideration should be given to whether the addition of multiple amino acids prevents the action of beneficial amino acids.

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.

Identification of 1,4-thiomorpholine-3-carboxylic acid (TMA) in normal human urine

The sulfur-containing cyclic imino acid 1,4-thiomorpholine-3-carboxylic acid (TMA) has been identified in normal human urine. After the enrichment procedure with ion-exchange chromatography, the urine extracts were reacted with diazomethane. Gas-liquid chromatography revealed the presence of two peaks with the same retention times exhibited by authentic TMA after the same derivatization. The two compounds have been identified by mass-spectrometry as the monomethylated and dimethylated derivatives of TMA. This result represents the first indication of the occurrence of TMA in a mammalian sample.

Peroxisomal oxidases: cytochemical localization and biological relevance

(1) alpha-HAOX has a broad substrate specificity. In rat kidney, the enzyme reacts with aliphatic and aromatic alpha-hydroxy acids, in rat liver, however, only with aliphatic ones. (2) The best substrate for the demonstration of alpha-HAOX activity in rat and human liver is glycolate. (3) alpha-hydroxy butyric acid is the best substrate in the luminometric assay for the demonstration of alpha-HAOX activity in the rat kidney, whereas glycolate is not catalysed by the enzyme. (4) In the proximal tubulus epithelial cells of the rat kidney alpha-HAOX is concentrated in the peripheral matrix of the peroxisomes.

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.

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.

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.

Transport of pipecolic acid in adult and developing mouse brain

In an effort to develop an animal model of hyperpipecolatemia, the uptake of pipecolic acid (PA) in the brain and changes of PA levels in serum following administration of D,L-PA were studied in the mouse using a new sensitive HPLC-EC method. Following i.p. injections (250 mg/kg) to adult male mice, the brain concentration peaks at 5-10 min (40 nmol/g). The level remains relatively stable up to 5 hrs and then declines slowly to 24 hrs. In serum, the level of PA increases rapidly to reach the maximum value at 10 min and then decreases rapidly in the first hour and continues to decline more slowly to 24 hrs. The net uptake of PA following administration of various amounts of D,L-PA is saturable at low doses (3.9-15.6 mg/kg), and it increases linearly at higher doses in a dose-dependent manner up to the maximum dose (500 mg/kg) used in the present study. Kinetic analysis suggests the presence of two kinds of transport systems. These findings are in good agreement with the previous results using D,L-[3H]PA in the mouse (7) and L-[14C]PA in the rat (13). There were no significant differences between uptake of D-pipecolic acid and L-pipecolic acid (250 mg/kg, i.p., 10 min), suggesting the absence of stereospecificity for PA uptake in the mouse brain. Developmental changes in net brain uptake of PA following injections of D,L-PA (250 mg/kg, s.c., 10 min) showed an age-dependent decrease which continues until adult levels are reached at four weeks after birth. The results suggest that the blood brain barrier (BBB) for PA is completed during the first month of life. Following administration of D,L-PA (250 mg/kg, s.c.) to pregnant mice during the period 19-21 days of gestation, PA level increases in fetal brain to a maximum value at 2 hrs (420 nmol/g). This level is unchanged during 24 hrs. The maximum level of PA in fetal serum is reached at 30 min to 1 hr. The level gradually decreases after 1 hr over 24 hrs. These results indicate that PA taken up by the placenta and into the brain is transported from the fetal circulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Pipecolic acid levels and transport in developing mouse brain

The regional distribution of pipecolic acid (PA) in newborn mouse brain, measured by a new sensitive high performance liquid chromatography with electrochemical detection (HPLC-EC) method, shows a two-fold difference among various areas. Diencephalon, olfactory bulb and anterior telencephalon show the highest PA levels, while the lowest PA levels are seen in mesencephalon and rhombencephalon. The pattern of regional distribution of PA is identical to the regional accumulation in brain of the newborn seen by us following i.p. injections of D,L-[3H]PA9. The highest levels of PA are seen in both brain and serum during the perinatal period of development. Pipecolic acid levels decrease in brain and serum at one day of age and reach adult values within two weeks postnatal. The brain/serum PA ratio (2.9-3.5) during the perinatal period declines gradually after birth to adult values (0.7-0.8) at 30 days. The liver and kidney follow the same pattern with higher levels of PA seen during the perinatal period; however, these levels decreased rapidly to adult levels within one week postnatal. Following injections (250 mg/kg, i.p. and s.c. in the adult and newborn, respectively), D,L-PA accumulates for up to 24 h in the newborn mouse brain. In adult, the cerebral concentration of PA increases rapidly and reaches its peak level in 5-10 min. It remains relatively constant up to 5 h and then declines slowly to 24 h. Pipecolic acid levels in serum show essentially the same pattern of accumulation between adult and newborn mice with some quantitative differences.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantification by selected ion monitoring of pipecolic acid, proline, gamma-aminobutyric acid and glycine in rat brain

A procedure for the simultaneous analysis of brain pipecolic acid, proline, gamma-aminobutyric acid and glycine--amino acids with potent inhibitory actions on the central nervous system--was developed. The identification and quantification of the amino acids were performed with a gas chromatographic--mass spectrometric--computer system using deuterium-labelled amino acids as the internal standards. After separation of the amino acids by high-performance liquid chromatography, the methyl ester heptafluorobutyryl derivatives were prepared. The lower limit of quantification for this method is at the picomole level. The usefulness of this chromatographic procedure has been demonstrated by measurement of trace amounts of pipecolic acid in rat brain.

Determination of pipecolic acid in rat brain areas by high-performance liquid chromatography of dansyl derivatives with fluorimetric detection

A method for the determination of pipecolic acid in the rat brain is reported. The identification and quantification of pipecolic acid is accomplished with reverse-phase high-performance liquid chromatography including precolumn dansylation procedure by using nipecotic acid, a regio-isomer of pipecolic acid, as an internal standard. The lower limit of quantification for the method is in the picomole range. Higher concentration of pipecolic acid in the rat brain regions were found in cerebellum, medulla oblongata, hypothalamus, and midbrain than the other regions. The method establishes the usefulness of dansyl chloride for the simple and sensitive detection of pipecolic acid, and is easily adapted to routine analysis of pipecolic acid in the rat brain regions.

Review: the cerebrohepatorenal syndrome of Zellweger, morphologic and metabolic aspects

The cerebrohepatorenal syndrome of Zellweger (CHRS) is remarkable not only for a distinctive combination of congenital anomalies, but also for an unusual variety of profound metabolic disturbances. After a discussion of the clinical diagnosis of CHRS, abnormalities in the metabolism of peroxisomes, mitochondria, iron, pipecolic acid, glycogen, bile acids, and organic acids are discussed and related to the clinical and other biochemical findings in the syndrome. Attention is also drawn to syndromes with biochemical or clinical abnormalities similar to those of CHRS. Although the biochemical findings indicate major abnormalities in oxidative metabolism, the primary defect remains obscure.

Blood-brain barrier transport of L-pipecolic acid in various rat brain regions

Blood-brain barrier transport of L-[1-14C]pipecolic acid was studied in the ray by single intracarotid injection using 3H2O as a diffusible internal standard. Brain uptake index (BUI) for L-[14C]pipecolic acid (0.036 mM) was found to be 18.1, 10.5, and 12.6 for the cerebral cortex, brain stem, and cerebellum, respectively which was substantially higher than that reported for its analog L-proline in the whole brain. Influx of L-pipecolic acid into the brain was concentration dependent and differed significantly between the cerebral cortex and the brain stem, and between the cerebral cortex and the cerebellum, but not between the brain stem and the cerebellum. Kinetic study of L-pipecolic acid influx revealed a low- and a high-capacity uptake mechanisms. The low-capacity saturable component has Km values ranging from 38 to 73 microM, and Vmax values ranging from 10 to 13 nmol/g/min for the three brain regions. The nonsaturable component has a Km of 4 mM, a Vmax of 200 nmol/g/min and similar diffusion constant (Kd) (0.03 to 0.06 mlg-1 min-1) for all three brain regions. A possible role of the two-component brain uptake mechanism in the regulation of the neuronal function of L-pipecolic acid was suggested.

Metabolism of cadaverine and pipecolic acid in brain and other organs of the mouse

Cadaverine and pipecolic acid metabolism was investigated in vitro in several organs of the mouse by measuring 14CO2 formation from labeled precursors. The liver showed the highest formation of 14CO2 from [1,5-14C]-cadaverine, whereas brain demonstrated a much lower formation. Anaerobiosis or inhibition of monoamineoxidase (MAO) activity significantly reduced 14CO2 formation in every organ, but inhibition of diamine oxidase (DAO) activity had no effect in brain and kidney. Piperidine was formed from cadaverine in vitro only in the large intestine and its content. This formation is probably of bacterial origin. Under a variety of experimental conditions we were unable to demonstrate any formation of piperidine in brain from cadaverine. Biosynthesis in vitro of [3H]-piperidine from D,L-[3H]-pipecolic acid was very low in brain and kidney. With the exception of brain and kidney, no other organs showed any formation of [3H]-piperidine. Neither MAO nor DAO inhibition influenced [3H]-piperidine formation in the large intestine with its content. Following 1 hr incubation at 37 degrees C under aerobic conditions, the levels of [14C]-pipecolic acid and [3H]-piperidine recovered from mouse brain homogenate did not indicate any significant degradation of these two substances. Our results suggest that under in vitro conditions, cadaverine is not a precursor of piperidine in brain, liver, heart, and kidney and that only very low levels of piperidine can be formed from pipecolic acid in brain. Outside the brain, formation of piperidine from pipecolic acid is detectable only in kidney and in the content of the large intestine. The latter is probably of bacterial origin. Our results do not support previous findings from other authors on an endogenous origin of piperidine in brain from cadaverine and pipecolic acid, and they suggest that a) cadaverine is not a precursor of piperidine in brain, b) the conversion of pipecolic acid into piperidine in the brain does not constitute a major metabolic pathway, and c) the main source of piperidine in the CNS may be of nonneural origin.

Accumulation and metabolism of pipecolic acid in the developing brain of the mouse

In newborn mice, following i.p. injections of D,L-[3H]PA (pipecolic acid, 28 micrograms/kg), accumulation of radioactivity continues to increase up to 24 h. In adults, radioactivity peaks at 5 min and remains approximately constant up to 5 h, and then declines slowly to 24 h. Fifteen-day-old mice follow the newborn pattern, while 30-day-old mice show the same trend as the adult. Radioactivity in plasma shows essentially the same pattern of accumulation in adult and newborn animals with some quantitative differences. Secretion of radioactivity in the urine is significantly higher in the adult than in the newborn during the interval between 10 min and 5 h. Accumulation of radioactivity at 24 h in the newborn brain shows a preferential localization to the olfactory bulb, the anterior telencephalon and the diencephalon. Two hours after the i.p. injection, approximately 70% of the radioactivity recovered in brain is due to PA. This percentage increases to 75% and 87% at 5 and 24 h respectively. Alpha-aminoadipic acid (alpha-Aaa) a major metabolite of PA was identified in brain extracts at 5 h. The maximal formation of alpha-Aaa in relation to PA occurs approximately at 5 h. No other brain metabolites of PA could be identified with this chromatographic system. The present results show that access of PA to the brain is easier in the newborn mouse than in the adult. In addition, our results demonstrate, for the first time, the presence of PA metabolism in the newborn mouse.