Electrophoretic study of pipecolic acid, a biogenic imino acid, in the mammalian brain

919 Syrup Alleviates Postpartum Depression by Modulating the Structure and Metabolism of Gut Microbes and Affecting the Function of the Hippocampal GABA/Glutamate System

Postpartum depression (PPD) is a mental disorder that affects pregnant women around the world, with serious consequences for mothers, families, and children. Its pathogenesis remains unclear, and medications for treating PPD that can be used during lactation remain to be identified. 919 syrup (919 TJ) is a Chinese herbal medicine that has been shown to be beneficial in the treatment of postpartum depression in both clinical and experimental studies. The mechanism of action of 919 TJ is unclear. 919 syrup is ingested orally, making the potential interaction between the drug and the gut microbiome impossible to ignore. We therefore hypothesized that 919 syrup could improve the symptoms of postpartum depression by affecting the structure and function of the intestinal flora, thereby altering hippocampal metabolism. We compared changes in hippocampal metabolism, fecal metabolism, and intestinal microflora of control BALB/c mice, mice with induced untreated PPD, and mice with induced PPD treated with 919 TJ, and found that 4-aminobutyric acid (GABA) in the hippocampus corresponded with PPD behaviors. Based on changes in GABA levels, multiple key gut bacterial species (Mucispirillum schaedleri, Bifidobacterium pseudolongum, Desulfovibrio piger, Alloprevotella tannerae, Bacteroides sp.2.1.33B and Prevotella sp. CAG:755) were associated with PPD. Metabolic markers that may represent the function of the intestinal microbiota in mice with PPD were identified (Met-Arg, urocanic acid, thioetheramide-PC, L-pipecolic acid, and linoleoyl ethanolamide). The relationship between these factors is not a simple one-to-one correspondence, but more likely a network of staggered functions. We therefore believe that the composition and function of the entire intestinal flora should be emphasized in research studying the gut and PPD, rather than changes in the abundance of individual bacterial species. The introduction of this concept of “GutBalance” may help clarify the relationship between gut bacteria and systemic disease.

Plasma metabolic profiling after cortical spreading depression in a transgenic mouse model of hemiplegic migraine by capillary electrophoresis – mass spectrometry

Cortical spreading depression-induced brain metabolic changes have been captured in the plasma of a transgenic migraine mouse model using CE-MS.

Cerebral low-molecular metabolites influenced by intestinal microbiota: a pilot study

Recent studies suggest that intestinal microbiota influences gut-brain communication. In this study, we aimed to clarify the influence of intestinal microbiota on cerebral metabolism. We analyzed the cerebral metabolome of germ-free (GF) mice and Ex-GF mice, which were inoculated with suspension of feces obtained from specific pathogen-free mice, using capillary electrophoresis with time-of-flight mass spectrometry (CE-TOFMS). CE-TOFMS identified 196 metabolites from the cerebral metabolome in both GF and Ex-GF mice. The concentrations of 38 metabolites differed significantly (p < 0.05) between GF and Ex-GF mice. Approximately 10 of these metabolites are known to be involved in brain function, whilst the functions of the remainder are unclear. Furthermore, we observed a novel association between cerebral glycolytic metabolism and intestinal microbiota. Our work shows that cerebral metabolites are influenced by normal intestinal microbiota through the microbiota-gut-brain axis, and indicates that normal intestinal microbiota closely connected with brain health and disease, development, attenuation, learning, memory, and behavior.

Determination of D- and L-pipecolic acid in food samples including processed foods

BACKGROUND

Pipecolic acid, a metabolite of lysine, is found in human physiological fluids and is thought to play an important role in the central inhibitory gamma-aminobutyric acid system. However, it is unclear whether plasma D- and L-pipecolic acid originate from oral food intake or intestinal bacterial metabolites.

METHODS

We analyzed the contents of D- and L-pipecolic acid in several processed foods including dairy products (cow's milk, cheese and yogurt), fermented beverages (beer and wine) and heated samples (beef, bovine liver, bread and tofu) to clarify the relationship between plasma D- and L-pipecolic acid and dietary foods.

RESULTS

Our study revealed that some of the samples contained high concentrations of total pipecolic acid, and a higher proportion of L- than D-isomers. The other samples also showed high proportions of L-pipecolic acid. It was also shown that there is no significant change in the ratio of the D-isomer before and after heat treatment. The heat treatments could not cause the racemization of pipecolic acid in this study.

CONCLUSION

These findings suggest that plasma pipecolic acid, particularly the D-isomer, does not originate from direct food intake and that D- and L-pipecolic acid can possibly be derived from intestinal bacterial metabolites.

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.

Intracerebroventricular administration of GABA-A and GABA-B receptor antagonists attenuate feeding and sleeping-like behavior induced by L-pipecolic acid in neonatal chicks

It has been demonstrated that L-pipecolic acid (L-PA), a major metabolic intermediate of L-lysine (L-Lys) in the mammalian and chicken brain, is involved in the functioning of the GABAergic system. A previous study has shown that intracerebroventricular (i.c.v.) injection of L-PA suppressed feeding and induced sleep-like behavior in neonatal chicks; however, the precise relationship between the GABAergic system and L-PA has not been clarified. In the present study, the role of the GABA-A or GABA-B receptors in the suppression of food intake and induction of sleeping-like behavior by L-PA was investigated. Chicks were injected i.c.v. with the GABA-A antagonist picrotoxin or GABA-B antagonist CGP54626 along with L-PA. Although suppression of food intake by L-PA was restored partially by co-injection with CGP54626, but not picrotoxin, sleep-like behavior induced by L-PA was suppressed significantly by both antagonists. These results suggested that L-PA activated both GABA-A and GABA-B receptors, and GABA-B receptors alone contributed to food intake whereas both receptors contributed to sleep-like behavior.

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.

Uptake and metabolism of delta 1-piperidine-2-carboxylic acid by synaptosomes from rat cerebral cortex

delta 1-Piperidine-2-carboxylic acid (P2C), an intermediate of the L-lysine metabolic pathway in the brain, was studied for its uptake and metabolism in the synaptosome of the rat cerebral cortex. The results of this study showed that the uptake of P2C into the synaptosome was NA+- and temperature-dependent with a two-tier transport kinetic (Km = 2.6 and 0.7 microM; Vmax = 1.6 and 0.73 pmol/min/mg). P2C uptake was only moderately inhibited (approximately 20%) by L-lysine and its metabolites, L-pipecolic acid and L-alpha-aminoadipic acid at up to 100 microM, and the putative amino acid neurotransmitters, gamma-aminobutyric acid, L-glutamic acid and L-aspartic acid (25-31%) at 5-500 microM. The synaptosomal preparation only has a very low activity for metabolizing P2C to its product L-pipecolic acid. The metabolic activity for P2C was mainly contained in the 27,000 x g supernatant S2 fraction. Since P2C is the precursor of the putative neuromodulator L-pipecolic acid, the understanding of its uptake and metabolic characteristics in the brain should be of significance.

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.

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.

Treatment of infantile phytanic acid storage disease: clinical, biochemical and ultrastructural findings in two children treated for 2 years

Two patients with infantile phytanic acid storage disease (infantile Refsum disease), one of whom showed the presence of morphologically normal peroxisomes in a liver biopsy, were treated with a low phytanic acid diet for more than 2 years and the effects of treatment on certain clinical, biochemical and ultrastructural parameters were examined. Both patients showed evidence of either an improvement or stabilisation in their clinical condition. Plasma phytanic acid levels decreased to near normal values in approximately 6 weeks after the introduction of the diet; plasma pipecolic acid also declined markedly but the decrease was not so rapid and its level remained abnormal. C26:C22 fatty acid ratios decreased very slowly and even after 2 years the values remained grossly abnormal. Despite the marked reduction of phytanic acid in the liver, there was an increase in the C26:C22 fatty acid ratios and this appeared to be paralleled by an increase in inclusion bodies. Our data suggest that some patients with the infantile form of Refsum disease may show some clinical benefit from dietary management and this is reflected biochemically by decreases in the plasma levels of phytanic acid and pipecolic acid.

Stable isotope dilution analysis of pipecolic acid in cerebrospinal fluid, plasma, urine and amniotic fluid using electron capture negative ion mass fragmentography

A sensitive and accurate stable isotope dilution assay was developed for the measurement of pipecolic acid in body fluids using electron capture negative ion mass fragmentography. The method utilizes [2H11]pipecolic acid as the internal standard. Sample preparation consisted of derivatization in aqueous solution (pH 11.5) of the amine moiety with methyl chloroformate to the N-methylcarbamate, followed by acidic ethyl acetate extraction (pH 2) and further derivatization of the carboxyl moiety to the pentafluorobenzyl ester. Normal values have been determined in cerebrospinal fluid (mean means = 0.041 mumol/l, range 0.010-0.120 mumol/l), in plasma of at term infants (age less than 1 wk, means = 5.73 mumol/l, range 3.75-10.8 mumol/l; age greater than 1 wk, means = 1.46 mumol/l, range 0.70-2.46 mumol/l), in urine of at term infants (age less than 6 mth, means = 32.5 mumol/g. creat., range 9.81-84.5 mumol/g. creat; age greater than 6 mth, means = 6.35 mumol/g. creat., range 0.15-13.6 mumol/g. creat.) and in amniotic fluid (means = 4.65 mumol/l, range 2.24-8.40 mumol/l). The utility of the method was demonstrated for the pipecolic acid quantification in these biofluids of patients with peroxisomal disorders. As affected fetuses with infantile Refsum's disease and Zellweger syndrome showed no significant elevation of pipecolic acid in their surrounding amniotic fluids, the measurement of pipecolic acid in amniotic fluid seemed not to be useful for prenatal diagnosis in these disorders.

Identification and quantification of 5-hydroxypipecolic acid and hydroxyproline in mammalian brain and blood by selected ion monitoring

A method for the analysis of 5-hydroxypipecolic acid and 4-hydroxyproline in mammalian brain and blood is reported. The identification and quantification of the two hydroxyimino acids were accomplished with gas chromatography/mass spectrometry including a selected ion-monitoring technique following HPLC prepurification. The lower limit of detection for the method is 2 to 10 pmol. The amounts of 5-hydroxypipecolic acid and 4-hydroxyproline in blood were 20 to 30 pmol/ml and 3 to 6 nmol/ml, respectively. Their concentrations in the rabbit whole brain were determined to be 5 and 120 pmol/g, respectively.

Piperidine: a microelectrophoretic study in the mammalian brain

Using unit recording and electrophoretic techniques, the action of piperidine on unit activity of the brain of the rat was studied. Piperidine excited 31%, and inhibited 4% of cortical cells tested. In the hippocampus and caudate nucleus, piperidine excited larger proportions of the cells tested. The actions of piperidine were blocked by tetraethylammonium but not by scopolamine.

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.

Dose pipecolic acid interact with the central GABA-ergic system?

Several previous studies have suggested a strong GABA-mimetic action of the endogenous brain imino acid, L-pipecolic acid (L-PA). In the present study, these observations were evaluated using electrophysiological and neurochemical methods. In contrast to published data our electrophysiological studies on rat cortical neurones in situ showed only a weak, but bicuculline-sensitive depressant action of L-PA on cortical neurones. Furthermore, L-PA proved to have no affinity for any of the three components of the GABA-benzodiazepine-chloride channel receptor complex. However, using a modification of published methods a weak affinity for the GABA-B receptor site was demonstrated (IC50 = 1.8 X 10(-3) M). L-PA showed no anticonvulsive activity in several tests; in particular, it did not protect mice from seizures induced by inhibition of L-glutamate-1-decarboxylase (EC 4.1.1.15: GAD). L-PA had a very weak action on brain GABA levels of mice, and did not modify the rate of GABA synthesis. In conclusion, these results are not compatible with a strong in vivo interaction between L-PA and GABA-mediated inhibitory transmission.

Pipecolic acid antagonizes barbiturate-enhanced GABA binding to bovine brain membranes

L-Pipecolic acid, a brain L-lysine metabolite, is found to inhibit GABA binding to bovine synaptic membranes strongly in the presence of hexobarbital (IC50 = 2 X 10(-10)M) or pentobarbital (IC50 = 2 X 10(-9)M), but only slightly (less than 10%) by itself. Longer dialysis increases this binding inhibition. Hill plots indicate heterogeneity of L-pipecolic acid displaceable GABA binding sites. L-Pipecolic acid may be an endogenous ligand acting as a neuromodulator on the GABA receptor ionophore complex, or it may act on its own membrane binding sites exerting an allosteric effect on the GABA receptor complex. This discovery may be useful for further defining pharmacological and biochemical differences between the GABA receptors in the brain.

Pipecolic acid receptors in rat cerebral cortex

Identification of [14C]pipecolic acid (PA) receptors was attempted in the solubilized membrane fraction from rat cerebral cortex. Specific binding proteins for both PA and muscimol, a potent gamma-aminobutyric acid (GABA) agonist, were detected in the same preparation. Separation of labeled PA and GABA binding proteins by glycerol gradient centrifugation has shown labeled protein bands of similar sedimentation rates, suggesting that PA and GABA may be binding to identical proteins. It seems likely that the PA binding receptor either may possess the same sedimentation characteristics as that of the GABA receptor, or both GABA and PA which is an endogenous and weak GABA agonist may bind to the same receptor complex, if not to the same binding site.

Pipecolic acid enhancement of GABA response in single neurons of rat brain

Using unit recording and microelectrophoresis, influence of pipecolic acid (PA), a major metabolite of lysine in the brain, on GABA and glycine responses was studied in the cerebral cortical and hippocampal pyramidal neurons of rats. With small currents, PA had no effect on the single neuron activities but enhanced GABA response without affecting glycine response. The finding provides a new evidence that PA may have a connection with central GABA system.

Inhibition of intrathecally administered picrotoxin- and bicuculline-induced convulsions in mice by pipecolic acid or GABA

Pipecolic acid (PA) is an alicyclic amino acid and putative neurotransmitter which may modulate GABAergic transmission in the central nervous system. The present study was designed to investigate the anticonvulsant effect of intrathecally (i.t.) injected PA on picrotoxin- and bicuculline-induced convulsions which are thought to be produced by interactions with GABAergic systems. Intrathecal injections of picrotoxin and bicuculline in mice produced convulsions which were characterized by a rapid onset and short duration. Coadministration of GABA with either bicuculline or picrotoxin, but not strychnine, attenuated the severity of the convulsions. Coadministration of PA also protected against bicuculline- and picrotoxin-induced convulsions. Intrathecal injections of PA produced a dose-related increase in the latency to the onset of these convulsions as well as a decrease in their duration, however PA failed to inhibit the duration of strychnine-induced seizures. The D isomer of PA was found to be more effective than the L isomer as an anticonvulsant in this study. When administered in a high dose (500 micrograms i.t.), the D isomer produced flaccid paralysis while injection of high doses (100-500 micrograms i.t.) of the L isomer actually elicited convulsions. These results further support an interaction between PA and GABAergic activity.

Identification and characterization of pipecolic acid binding sites in mouse brain

Pipecolic acid (PA, piperidine-2-carboxylic acid) is the major product of lysine metabolism in the mammalian brain (Giacobini et al., 1980). In this study we have characterized the binding of [3H]PA to P2 fraction membranes and its distribution in the mouse brain. The binding was found to be saturable (70 nM), temperature and Na+ and Cl- dependent. A high affinity binding site with an apparent KD of 33.2 nM and a Bmax of 0.2 pmol/mg protein was demonstrated. The regional distribution of [3H]PA specific binding in mouse brain showed the highest concentration in cerebral cortex, thalamus and olfactory bulb. Unlabeled PA (10(-3)-10(-11) M) displaced specific binding of [3H]PA in a concentration dependent manner. Out of several substances tested, only proline showed a similar pattern of displacement. Pre-incubation of the membrane preparation with GABA (10(-3)-10(-11) M) resulted in either an increase or decrease of [3H]PA binding depending on the concentrations of GABA and PA. These results suggest a modulatory action of GABA on PA binding sites. The postnatal development of [3H]PA specific binding was studied in the whole brain of the mouse. [3H]Pipecolic acid binding increased progressively (8-fold) from one day after birth to 16 days. Following this developmental peak, the binding decreased gradually to 30 days at which age, adult values were attained.

A microiontophoretic study of the actions of the putative sleep factor, piperidine, in the rat brainstem

By means of microiontophoresis, we have compared the actions of a putative sleep substance, piperidine, with other neurotransmitters in the rat anaesthetized with urethane. In the pons and midbrain, piperidine mimicked the actions of acetylcholine on more than 200 neurones. Piperidine- and acetylcholine-induced excitations were equally effectively antagonized by hexamethonium or atropine. In 32 neurones piperidine showed no affinity for the receptors for the excitatory amino acid agonists, quisqualate and N-methyl-D-aspartate, piperidine-evoked excitations being unaffected by the antagonists glutamate diethylester or 2-amino-5-phosphonovalerate. Similarly, piperidine-evoked excitations in 23 neurones were unaffected by alpha-methylnoradrenaline, suggesting that piperidine does not act at receptors for noradrenaline. Twenty per cent of neurones responsive to piperidine were inhibited. These inhibitions in 12 neurones were insensitive to either strychnine or bicuculline indicating that piperidine does not act on receptors for glycine or gamma-aminobutyric acid. In a further 68 neurones, neither hexamethonium (4 out of 59 cells) nor atropine (0 out of 9 cells) was effective in antagonizing the inhibitions evoked by piperidine or by acetylcholine. It is suggested that piperidine may exert its central hypnogenic effects by an action at cholinoceptors in brainstem areas involved in sleep regulation.

Infantile Refsum's disease (phytanic acid storage disease): a variant of Zellweger's syndrome?

The activity of phytanic acid oxidase is low in infantile and adult Refsum's disease, and in the cerebro-hepato-renal (Zellweger's) syndrome. The plasma of patients with the infantile but not the adult form of Refsum's disease contains increased amounts of pipecolic acid and of at least two abnormal bile acids, one of which has been identified as 3 alpha, 7 alpha, 12 alpha trihydroxy-5 beta-cholestan-26-oic acid. These changes are similar to those reported in the Zellweger syndrome and indicate that there may be similarities in the metabolic defects in Zellweger's syndrome and the infantile form of Refsum's disease.

Quantitative determination and regional distribution of pipecolic acid in rodent brain

A rapid and sensitive method for the quantitative determination of pipecolic acid (PA), one of the three cyclic secondary imino acids present in mammalian brain is described. The quantification and identification of PA are accomplished in rat and mouse brain using high performance liquid chromatography with electrochemical detection (LCEC) and nipecotic acid (NPA) as an internal standard. The cyclic imino acids are derivatized with 2,4-dinitrofluorobenzene (DNFB) to dinitrophenyl derivatives. The remaining time for LCEC analysis is less than 30 min and the limit of sensitivity is in the lower picomole range. The levels of PA found in rat and mouse brain are comparable to those reported using gas chromatography/mass spectrometry. The regional distribution of PA shows higher concentrations of PA in hypothalamus, pons-medulla oblongata and cerebellum. The present results demonstrate that LCEC is sensitive enough to determine endogenous levels of PA in mg amounts of rodent brain tissue. Due to its simplicity and rapidity, the technique represents an alternative to existing methods. This method can also be used for determination of PA in CSF, blood or urine of hyperpipecolic patients.

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.

Potentiation of phenobarbital-induced anticonvulsant activity by pipecolic acid

Pipecolic acid (PA) is an intermediate of lysine metabolism in the mammalian brain. Recent findings suggest a functional connection of PA as neuromodulator in GABAergic transmission. Since many drugs are postulated to produce their effects by interaction with the central GABA system, the influence of PA on the anticonvulsant activity of phenobarbital was examined. Pretreatment of mice with 50 mg . kg-1 of PA potentiated the suppressing effects of the barbiturate on electrically and chemically induced convulsions. However, there was no potentiation of the behavioral effects and hypothermia induced by phenobarbital. PA itself had no or only little effect on the convulsions, motor function and rectal temperature when given in i.p. doses up to 500 mg . kg-1. Intraventricular administration of 500 microgram of PA also did not suppress either type of convulsion, although it produced ptosis, hypotonia, sedation and hypothermia. The results are discussed in relation to GABA system.

Lysine metabolism in the human and the monkey: demonstration of pipecolic acid formation in the brain and other organs

Metabolism of L-[U-14C]lysine was studied in the human autopsy tissues and the intact monkeys through intracerebroventricular and intravenous injections. The human tissues were more active in the metabolism of L-[14C]lysine to [14C]pipecolate than the rat tissues previously reported. This metabolism was equally active in the phosphate (pH 7) and the glycyl-glycine (pH 8.6) buffers with the brain and the kidney having higher activity than the liver. Besides [14C]pipecolate, traces of [14C]saccharopine and alpha-[14C]aminoadipate were also detected in the liver incubation. Twenty-four hr after intraventricular injection of L-[14C]lysine to the monkey, substantial labeling of pipecolate and alpha-aminoadipate was observed in the brain and spinal cord, with the kidney, liver and the plasma having much reduced levels. Radioactivity levels of these two compounds were found low in the organs and plasma of the intravenously injected monkey. The urine of both monkeys contained only traces of [14C]pipecolate, even though it contained high levels of L-[14C]lysine and alpha-[14C]aminoadipate. It was concluded that L-lysine is actively metabolized to pipecolate and alpha-aminoadipate in the human and the monkey, that this reaction is most active in the brain when L-lysine is intraventricularly administered, and that in contrast to the rat, the monkey may have an effective renal reabsorption for pipecolate which is similar to the human.

Comparison of synaptosomal and glial uptake of pipecolic acid and GABA in rat brain

The active uptake of [3H]pipecolic acid increased with incubation time and its uptake at 3 min was half of that at 20 min. On the other hand, a ratio (pellet/medium) of [3H]pipecolic acid uptake into glial cell-enriched fractions, was much less (0.4 - 0.6) than that of [14C]GABA (25.8 - 74.1). GABA, 10(-4) M, and pipecolic acid, 10(-4) M, produced a significant inhibitor of [3H]pipecolic acid uptake into P2 fractions. Pipecolic acid, 10(-4) M, significantly reduced the synaptosomal and glial uptake of [14C]GABA. GABA, 10(-4) M, affected neither spontaneous nor high K+-induced release of [3H]pipecolic acid from brain slices. It is suggested that pipecolic acid is involved in either synaptic transmission or in its modulation at GABA synapses in the central nervous system.