Metabolism and uptake of L-pipecolic acid by brain and heart

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.

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)

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.

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.