L-Palmitoylcarnitine

Studies on Novel Diagnostic and Predictive Biomarkers of Intrahepatic Cholestasis of Pregnancy Through Metabolomics and Proteomics

Background: Intrahepatic cholestasis of pregnancy (ICP) usually occurs in the third trimester and is associated with increased risks in fetal complications. Currently, the exact mechanism of this disease is unknown. The purpose of this study was to develop potential biomarkers for the diagnosis and prediction of ICP. Methods: We enrolled 40 pregnant women diagnosed with ICP and 40 healthy pregnant controls. The number of placental samples and serum samples between the two groups was 10 and 40 respectively. Ultra-performance liquid chromatography tandem high-resolution mass spectrometry was used to analyze placental metabolomics. Then, we verified the differentially expressed proteins and metabolites, both placental and blood serum, in the first, second, and third trimesters. Results: Metabolomic analysis of placental tissue revealed that fatty acid metabolism and primary bile acid biosynthesis were enriched. In the integrated proteomic and metabolomic analysis of placental tissue, peroxisomal acyl-CoA oxidase 1 (ACOX1), L-palmitoylcarnitine, and glycocholic acid were found to be three potential biomarkers. In a follow-up analysis, expression levels of both placental and serum ACOX1, L-palmitoylcarnitine, and glycocholic acid in both placenta and serum were found to be significantly higher in third-trimester ICP patients; the areas under the ROC curves were 0.823, 0.896, and 0.985, respectively. Expression levels of serum ACOX1, L-palmitoylcarnitine, and glycocholic acid were also significantly higher in first- and second-trimester ICP patients; the areas under the ROC curves were 0.726, 0.657, and 0.686 in the first trimester and 0.718, 0.727, and 0.670 in the second trimester, respectively. Together, levels of the three aforementioned biomarkers increased the value for diagnosing and predicting ICP (AUC: 0.993 for the third, 0.891 for the second, and 0.932 for the first trimesters). Conclusions: L-palmitoylcarnitine, ACOX1, and glycocholic acid levels taken together may serve as a new biomarker set for the diagnosis and prediction of ICP.

Inhibition of sodium pump by l-palmitoylcarnitine in single guinea-pig ventricular myocytes

We reinvestigated the issue of whether l-palmitoylcarnitine inhibits the Na/K pump in the heart. The effects of l-palmitoylcarnitine or ouabain on the Na/K pump current were studied with the voltage-clamp technique in isolated guinea-pig ventricular myocytes. In myocytes bathed in Tyrode's solution, l-palmitoylcarnitine shifted the current-voltage relation inward at all potentials between -80 and 20 mV. the "U"-shaped difference current seen in l-palmitoylcarnitine was maximal at -30 mV and declined at potentials more positive and negative than this. Under conditions that minimized time-dependent currents, ouabain or l-palmitoylcarnitine shifted membrane current inward in the presence of 5.4 mM extracellular potassium. Reduction of extracellular potassium to 0 mM for 2 min also shifted membrane current inward. When extracellular potassium was returned to 5.4 mM, the intracellular sodium that had accumulated was extruded and a transient outward current was generated as a result of Na/K pump stimulation. Ouabain or l-palmitoylcarnitine reversibly suppressed this transient outward current and reduced the rate constant for the decline of this current. The ability of l-palmitoylcarnitine to imitate the actions of ouabain on membrane current and on the transient outward current indicates that this amphiphile inhibits the Na/K pump current in guinea-pig ventricular myocytes. This results is consistent with the suppression by l-palmitoylcarnitine of the activity of Na/K ATPase in cardiac sarcolemmal vesicles.

Electrophysiological effects of L-palmitoylcarnitine in single ventricular myocytes

In isolated guinea pig ventricular myocytes, L-palmitoylcarnitine (L-PC) produced concentration- and time-dependent changes of resting potential (RP) and action potential duration at 50% repolarization (APD50). At 10(-8) to 10(-6) M, L-PC increased APD50 without changing RP. At 10(-5) M, the amphiphile initially increased (0-10 min) and eventually decreased (greater than 10 min) APD50; the membrane depolarized when APD50 decreased. Additionally, transient depolarizations (TDs) were consistently induced in 10(-5) M L-PC within 10 min, and TD amplitude progressively increased with continued exposure to L-PC. The TDs induced in L-PC were augmented by membrane depolarization, elevated extracellular Ca2+ concentration ([Ca2+]o), and increased number of stimuli. Elevated [Ca2+]o or neuraminidase treatment also allowed TDs. In neuraminidase, the changes of RP, APD50, and TD amplitude were qualitatively similar to those seen with L-PC. These results are consistent with the hypothesis that 10(-5) M L-PC causes intracellular Ca2+ overload. The blockade of L-PC and neuraminidase-induced TDs by ryanodine is consistent with the intracellular Ca2+ overload hypothesis.

Mechanisms for depolarization by l-palmitoylcarnitine in single guinea pig ventricular myocytes

Introduction: The changes of the resting potential (RP) and of the current-voltage (I-V) relationship induced by l-palmitoylcarnitine (l-PC) in the presence of the IKI blocker, cesium, or in the presence of the INa/K blocker, ouabain, were tested in guinea pig ventricular myocytes to ascertain the relative contributions of IKI and INa/K suppression to the membrane depolarization caused by this amphiphile.
Methods and results: Ramp voltages were applied to myocytes with the whole cell, patch clamp technique. l-PC (10 microM) produced additional membrane depolarization in the presence of either 10 mM Cs+ or 30 microM ouabain. In the presence of Cs+, l-PC, like 3 microM ouabain, shifted current inward at potentials negative to -20 mV as a result of INa/K blockade. In the presence of 30 microM ouabain, l-PC, like Cs+, shifted current inward at potentials between -27 and -88 mV and outward at potentials negative to -88 mV. This is attributed to IKI block because the current was inwardly rectifying, with a reversal potential near EK. When l-PC or ouabain inhibited INa/K, the presence of an Ni(2+)-sensitive component attributed to INa/Ca distorted the membrane I-V relationship, particularly in the presence of Cs+. The relative contributions of IKI and INa/K block by l-PC were voltage dependent. At the RP, l-PC produced a greater block of INa/K than of IKI.
Conclusion: l-PC depolarizes the resting membrane by inhibiting both IKI and INa/K. It is concluded that suppression of INa/K by l-PC predominates over block of IKI to depolarize the membrane at the RP.

Alteration of the membrane lipid environment by L-palmitoylcarnitine modulates K(ATP) channels in guinea-pig ventricular myocytes

Sarcolemmal adenosine 5'-triphosphate-sensitive K+ channels (K(ATP)) are dramatically up-regulated by a membrane phospholipid, phosphatidyl-inositol-4,5-bisphosphate (PIP2). During ischaemia, L-palmitoylcarnitine (L-PC), a fatty acid metabolite, accumulates in the sarcolemma and deranges the membrane lipid environment. We therefore investigated whether alteration of the membrane lipid environment by L-PC modulates the K(ATP) channel activity in inside-out patches from guinea-pig ventricular myocytes. L-PC (1 microM) inhibited KATP channel activity, without affecting the single channel conductance, through interaction with Kir6.2. L-PC simultaneously enhanced the ATP sensitivity of the channel [concentration for half-maximal inhibition (IC50) fell from 62.0+/-2.7 to 30.3+/-5.5 microM]. In contrast, PIP2 attenuated the ATP sensitivity (IC50 343.6+/-54.4 microM) and restored Ca2+-induced inactivation of KATP channels (94.1+/-13.7% of the control current immediately before the Ca2+-induced inactivation). Pretreatment of the patch membrane with 1 microM L-PC, however, reduced the magnitude of the PIP2-induced recovery to 22.7+/-6.3% of the control (P<0.01 vs. 94.1+/-13.7% in the absence of L-PC). Conversely, after the PIP2-induced recovery, L-PC's inhibitory action was attenuated, but L-PC partly reversed the PIP2-mediated decrease in the ATP sensitivity (IC50 fell from 310+/-19.2 to 93.1+/-9.8 microM). Thus, interaction between L-PC and PIP2 in the plasma membrane appears to regulate K(ATP) channels.