Determination of L-carnitine, acetyl-L-carnitine and propionyl-L-carnitine in human plasma by high-performance liquid chromatography after pre-column derivatization with 1-aminoanthracene

Determination of L-Carnitine in Infant Powdered Milk Samples after Derivatization

Herein, a novel analytical method using a high-performance liquid chromatography-fluorescence detector (HPLC/FLD) is developed for rapidly measuring an L-carnitine ester derivative in infant powdered milk. In this study, solid-phase extraction cartridges filled with derivatized methanol and distilled water were used to effectively separate L-carnitine. Protein precipitation pretreatment was carried out to remove the protein and recover the analyte extract with a high recovery (97.16%–106.56%), following which carnitine in the formula was derivatized to its ester form. Precolumn derivation with 1-aminoanthracene (1AA) was carried out in a phosphate buffer using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) as the catalyst. Method validation was performed following the AOAC guidelines. The calibration curves were linear in the L-carnitine concentration range of 0.1–2.5 mg/L. The lower limit of quantitation and limit of detection of L-carnitine were 0.076 and 0.024 mg/L, respectively. The intra- and interday precision and recovery results were within the allowable limits. The results showed that our method helped reduce the sample preparation time. It also afforded higher resolution and better reproducibility than those obtained by traditional methods. Our method is suitable for detecting the quantity of L-carnitine in infant powdered milk containing a large amount of protein or starch.

Analysis of Choline, Carnitine, Acetylcarnitine and Acetylcholine in Animal Feeds, Blood and Urine Using Ion Chromatography Coupled with Tandem Mass Spectrometry

A simple and sensitive method was proposed for choline, carnitine, acetylcarnitine (ACa) and acetylcholine (ACh) separation in feed, blood and urine of animals by using ion chromatography (IC) and detection by tandem mass spectrometry (MS/MS). Analytes were extracted using a mixture of acetonitrile and water, purified by C18 solid-phase extraction columns, separated via IC with an IonPac SCS-1 column and detected by an MS/MS detector by using isotopic internal standards for quantification. The effects of different chromatographic parameters on the separation were also investigated. Under optimal conditions, the recovery was >90%, with the relative standard deviations of <15%. The proposed method was highly reliable for the simultaneous determination of choline, carnitine, ACa and ACh in feed, blood and urine.

Bioanalysis and enantioseparation of dl-carnitine in human plasma by the derivatization approach

BACKGROUND

L-carnitine is an over the counter drug, used to treat disorders like cardiomyopathy, skeletal myopathy, hypoglycemia and hyperammonemia. Preparations containing D-carnitine should be avoided by dialysis patients because it has toxic influence on biochemical processes by inhibiting the carnitine acetyltransferase. Therefore, it is of utmost importance to assess and control the content of D-carnitine.

METHODS

A HPLC method was developed and validated for determination and enantiomeric resolution of DL-carnitine in human plasma by derivatization approach. (S)-Naproxen-based three derivatizing reagents were synthesized and applied.

CONCLUSION

The limit of detection values were found to be 1.26 and 1.35 ng ml(-1) for the two isomers. The method is simple, reproducible, and can be used for routine analysis in laboratories for control of enantiomeric purity of carnitine.

L-carnitine preserves endothelial function in a lamb model of increased pulmonary blood flow

BACKGROUND

In our model of a congenital heart defect (CHD) with increased pulmonary blood flow (PBF; shunt), we have recently shown a disruption in carnitine homeostasis, associated with mitochondrial dysfunction and decreased endothelial nitric oxide synthase (eNOS)/heat shock protein (Hsp)90 interactions that contribute to eNOS uncoupling, increased superoxide levels, and decreased bioavailable nitric oxide (NO). Therefore, we undertook this study to test the hypothesis that L-carnitine therapy would maintain mitochondrial function and NO signaling.

METHODS

Thirteen fetal lambs underwent in utero placement of an aortopulmonary graft. Immediately after delivery, lambs received daily treatment with oral L-carnitine or its vehicle.

RESULTS

L-Carnitine-treated lambs had decreased levels of acylcarnitine and a reduced acylcarnitine:free carnitine ratio as compared with vehicle-treated shunt lambs. These changes correlated with increased carnitine acetyl transferase (CrAT) protein and enzyme activity and decreased levels of nitrated CrAT. The lactate:pyruvate ratio was also decreased in L-carnitine-treated lambs. Hsp70 protein levels were significantly decreased, and this correlated with increases in eNOS/Hsp90 interactions, NOS activity, and NOx levels, and a significant decrease in eNOS-derived superoxide. Furthermore, acetylcholine significantly decreased left pulmonary vascular resistance only in L-carnitine-treated lambs.

CONCLUSION

L-Carnitine therapy may improve the endothelial dysfunction noted in children with CHDs and has important clinical implications that warrant further investigation.

Disposition and Metabolite Kinetics of Oral L-carnitine in Humans

The pharmacokinetics of L-carnitine and its metabolites were investigated in 7 healthy subjects following the oral administration of 0, 0.5, 1, and 2 g 3 times a day for 7 days. Mean plasma concentrations of L-carnitine across an 8-hour dose interval increased significantly (P < .05) from a baseline of 54.2 +/- 9.3 microM to 80.5 +/- 12.5 microM following the 0.5-g dose; there was no further increase at higher doses. There was a significant increase (P < .001) in the renal clearance of L-carnitine indicating saturation of tubular reabsorption. Trimethylamine plasma levels increased proportionately with L-carnitine dose, but there was no change in renal clearance. A significant increase in the plasma concentrations of trimethylamine-N-oxide from baseline was evident only for the 2-g dose of L-carnitine (from 34.5 +/- 2.0 to 149 +/- 145 microM), and its renal clearance decreased with increasing dose (P < .05). There was no evidence for nonlinearity in the metabolism of trimethylamine to trimethylamine-N-oxide. In conclusion, the pharmacokinetics of oral L-carnitine display nonlinearity above a dose of 0.5 g 3 times a day.

Urinary excretion of L-carnitine, acetyl-L-carnitine, propionyl-L-carnitine and their antioxidant activities after single dose administration of L-carnitine in healthy subjects

The urine excretion of L-carnitine (LC), acetyl-L-carnitine (ALC) and propionyl-Lcarnitine (PLC) and their relations with the antioxidant activities are presently unknown. Liquid L-carnitine (2.0 g) was administered orally as a single dose in 12 healthy subjects. Urine concentrations of LC, ALC and PLC were detected by HPLC. Superoxide dismutase (SOD), total antioxidative capacity (T-AOC), malondialdehyde (MDA) and nitrogen monoxidum (NO) activities were measured by spectrophotometric methods. The 0~2 h, 2~4 h, 4~8 h, 8~12 h, 12~24 h excretion of LC was 53.13±31.36 µmol, 166.93±76.87 µmol, 219.92±76.30 µmol, 100.48±23.89 µmol, 72.07±25.77 µmol, respectively. The excretion of ALC was 29.70±14.43 µmol, 80.59±32.70 µmol, 109.85±49.21 µmol, 58.65±18.55 µmol, and 80.43±35.44 µmol, respectively. The urine concentration of PLC was 6.63±4.50 µmol, 15.33±12.59 µmol, 15.46±6.26 µmol, 13.41±11.66 µmol and 9.67±7.92 µmol, respectively. The accumulated excretion rate of LC was 6.1% within 24h after its administration. There was also an increase in urine concentrations of SOD and T-AOC, and a decrease in NO and MDA. A positive correlation was found between urine concentrations of LC and SOD (r = 0.8277) or T-AOC (r = 0.9547), and a negative correlation was found between urine LC excretions and NO (r = -0.8575) or MDA (r = 0.7085). In conclusion, a single oral LC administration let to a gradual increase in urine L-carnitine excretion which was associated with an increase in urine antioxidant enzymes and the total antioxidant capacities. These data may be useful in designing therapeutic regimens of LC or its analogues in the future.

A liquid chromatography and tandem mass spectrometry method for the determination of potential biomarkers of cardiovascular disease

A simple, accurate and sensitive liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantitation of α-ketoglutaric acid (α-KG), L-carnitine (L-CAR) and acetyl-L-carnitine (acetyl-L-CAR) in human urine as potential biomarkers of cardiovascular disease. The separation was performed using an isocratic elution of 0.1% formic acid in water and acetonitrile (97:3, v/v) on an Acclaim 120 C8 column (150 mm × 4.6 mm, 3.0 μm). The flow rate of the mobile phase was 1.2 mL/min and the total assay run time was 3 min. Detection was performed on a triple-quadrupole mass spectrometer in selected reaction monitoring (SRM) mode via an electrospray ionization (ESI) source in positive and negative ion modes. This method covered a linearity range of 0.1-500 ng/mL for L-CAR and acetyl-L-CAR and 1-1000 ng/mL for α-KG with lower limits of quantification (LLOQ) of 0.08 ng/mL for L-CAR, 0.04 ng/mL for acetyl-L-CAR and 0.8 ng/mL for α-KG. The intra-day and inter-day precision and accuracy of the quality control samples exhibited relative standard deviations of less than 5.54% and relative error values from -5.95% to 3.11%. Analyte stability was evaluated under various sample preparation, analysis and storage conditions and varied from -9.89% to -0.47%. A two-step solid-phase extraction (SPE) procedure using silica gel and quaternary amine cartridges was used for urine sample cleanup. The average recoveries for all analyzed compounds were better than 86.64% at three concentrations. The method was successfully applied for the quantitation of α-KG, L-CAR and acetyl-L-CAR in human urine samples.

Determination of l-carnitine using enantioselective, potentiometric membrane electrodes based on macrocyclic antibiotics

In order to determine the enantiopurity of l-carnitine three enantioselective, potentiometric membrane electrodes were proposed for the assay of l-carnitine. The electrodes were designed using macrocyclic glycopeptide antibiotics-vancomycin and teicoplanin. Acetonitrile was added to the teicoplanine to design a modified teicoplanine based electrode. The linear concentration ranges for the proposed enantioselective membrane electrodes were 10(-4) to 10(-2)moll(-1) for electrodes based on vancomycin and teicoplanin and 10(-5) to 10(-2)moll(-1) for electrode based on teicoplanin modified with acetonitrile. The slopes of the electrodes were 56.5mV per pl-carnitine; 54.5mV per pl-carnitine and 58.3mV per pl-carnitine for vancomycin-, teicoplanin- and teicoplanin modified with acetonitrile-based electrodes, respectively. The enantioselectivity was determined over d-carnitine. The proposed electrodes could be employed reliably for the assay of l-carnitine raw material and its pharmaceutical formulation, Carnilean((R)) capsules. The surfaces of the electrodes are stable and easily renewable by polishing on alumina paper.

Metformin rescues the myocardium from doxorubicin-induced energy starvation and mitochondrial damage in rats

Clinical use of doxorubicin (DOX) is limited by its cardiotoxic side effects. Recent studies established that metformin (MET), an oral antidiabetic drug, possesses an antioxidant activity. However, whether it can protect against DOX-induced energy starvation and mitochondrial damage has not been reported. Our results, in a rat model of DOX-induced cardiotoxicity, show that DOX treatment significantly increased serum levels of LDH and CK-MB, indicators of cardiac injury, and induced expression of hypertrophic gene markers. DOX also caused marked decreases in the cardiac levels of glutathione, CoA-SH and ATP, and mRNA expression of catalase and NQO-1. These biochemical changes were associated with myocardial histopathological and ultrastructural deteriorations, as observed by light and electron microscopy, respectively. Cotreatment with MET (500 mg/kg) eliminated all DOX-induced biochemical, histopathological, and ultrastructural changes. These findings demonstrate that MET successfully prevents DOX-induced cardiotoxicity in vivo by inhibiting DOX-induced oxidative stress, energy starvation, and depletion of intramitochondrial CoA-SH.

Single dose administration of L-carnitine improves antioxidant activities in healthy subjects

L-carnitine has been used as a supplement to treat cardiovascular or liver disease. However, there has been little information about the effect of L-carnitine on anti-oxidation capability in healthy human subjects. This study was designed to investigate the correlation between plasma L-carnitine concentration and antioxidant activity. Liquid L-carnitine (2.0 g) was administered orally as a single dose in 12 healthy subjects. Plasma concentration of L-carnitine was detected by HPLC. The baseline concentration of L-carnitine was 39.14 ± 5.65 µmol/L. After single oral administration, the maximum plasma concentration (C(max)) and area under the curve (AUC(0-∞)) were 84.7 ± 25.2 µmol/L and 2,676.4 ± 708.3 µmol/L·h, respectively. The half-life and the time required to reach the C(max) was 60.3 ± 15.0 min and 3.4 ± 0.46 h, respectively. There was a gradual increase in plasma concentrations of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase and total antioxidative capacity (T-AOC) in the first 3.5 h following L-carnitine administration. The plasma concentrations of SOD, GSH-Px, catalase and T-AOC returned to baseline levels within 24 h. A positive correlation was found between L-carnitine concentration and the antioxidant index of SOD (r = 0.992, P < 0.01), GSH-Px (r = 0.932, P < 0.01), catalase (r = 0.972, P < 0.01) or T-AOC (r = 0.934, P < 0.01). In conclusion, L-carnitine increases activities of antioxidant enzymes and the total antioxidant capacity in healthy subjects. It may be useful as a supplementary therapy for chronic illnesses involving excessive oxidative stress.

Acetyl-L-carnitine improves aged brain function

The effects of acetyl-L-carnitine (ALCAR), an acetyl derivative of L-carnitine, on memory and learning capacity and on brain synaptic functions of aged rats were examined. Male Fischer 344 rats were given ALCAR (100 mg/kg bodyweight) per os for 3 months and were subjected to the Hebb-Williams tasks and AKON-1 task to assess their learning capacity. Cholinergic activities were determined with synaptosomes isolated from brain cortices of the rats. Choline parameters, the high-affinity choline uptake, acetylcholine (ACh) synthesis and depolarization-evoked ACh release were all enhanced in the ALCAR group. An increment of depolarization-induced calcium ion influx into synaptosomes was also evident in rats given ALCAR. Electrophysiological studies using hippocampus slices indicated that the excitatory postsynaptic potential slope and population spike size were both increased in ALCAR-treated rats. These results indicate that ALCAR increases synaptic neurotransmission in the brain and consequently improves learning capacity in aging rats.

Progression of diethylnitrosamine-induced hepatic carcinogenesis in carnitine-depleted rats

AIM: To investigate whether carnitine deficiency is a risk factor during the development of diethylnitrosamine (DENA)-induced hepatic carcinogenesis.

METHODS: A total of 60 male Wistar albino rats were divided into six groups with 10 animals in each group. Rats in group 1 (control group) received a single intraperitoneal (i.p.) injection of normal saline. Animals in group 2 (carnitine-supplemented group) were given L-carnitine (200 mg/kg per day) in drinking water for 8 wk. Animals in group 3 (carnitine-depleted group) were given D-carnitine (200 mg/kg per day) and mildronate (200 mg/kg per day) in drinking water for 8 wk. Rats in group 4 (DENA group) were injected with a single dose of DENA (200 mg/kg, i.p.) and 2 wk later received a single dose of carbon tetrachloride (2 mL/kg) by gavage as 1:1 dilution in corn oil. Animals in group 5 (DENA-carnitine depleted group) received the same treatment as group 3 and group 4. Rats in group 6 (DENA-carnitine supplemented group) received the same treatment as group 2 and group 4.

RESULTS: Administration of DENA resulted in a significant increase in alanine transaminase (ALT), gamma-glutamyl transferase (G-GT), alkaline phosphatase (ALP), total bilirubin, thiobarbituric acid reactive substances (TBARS) and total nitrate/nitrite (NOx) and a significant decrease in reduced glutathione (GSH), glutathione peroxidase (GSHPx), catalase (CAT) and total carnitine content in liver tissues. In the carnitine-depleted rat model, DENA induced a dramatic increase in serum ALT, G-GT, ALP and total bilirubin, as well as a progressive reduction in total carnitine content in liver tissues. Interestingly, L-carnitine supplementation resulted in a complete reversal of the increase in liver enzymes, TBARS and NOx, and a decrease in total carnitine, GSH, GSHPx, and CAT induced by DENA, compared with the control values. Histopathological examination of liver tissues confirmed the biochemical data, where L-carnitine prevented DENA-induced hepatic carcinogenesis while D-carnitine-mildronate aggravated DENA-induced hepatic damage.

CONCLUSION: Data from this study suggest for the first time that: (1) carnitine deficiency is a risk factor and should be viewed as a mechanism in DENA-induced hepatic carcinogenesis; (2) oxidative stress plays an important role but is not the only cause of DENA-induced hepatic carcinogenesis; and (3) long-term L-carnitine supplementation prevents the development of DENA-induced liver cancer.

Achiral liquid chromatography with circular dichroism detection for the determination of carnitine enantiomers in dietary supplements and pharmaceutical formulations

A simple and enantioselective method for the separation and determination of carnitine enantiomers in dietary supplements and pharmaceutical formulation samples is proposed. This method is based on achiral liquid chromatographic separation of carnitine enantiomers from interferences and direct circular dichroism (CD) detection. The calibration curve of the anisotropy factor (g) versus the enantiomeric excess was linear, with a correlation coefficient (R(2)) of 0.996. The precision evaluated by UV peak area and CD peak area was suitable (RSD <5% in all cases). The usefulness of the proposed method was demonstrated by analysing natural dietary supplements and pharmaceutical formulation samples. This method has the advantages of being rapid and precise, without using an expensive chiral column. The method was suitable for the simultaneous determination of both enantiomers and for assessing the chemical purity of carnitine.

Comparative metabolite profiling of carboxylic acids in rat urine by CE-ESI MS/MS through positively pre-charged and (2)H-coded derivatization

A new approach to the selective comparative metabolite profiling of carboxylic acids in rat urine was established using CE-MS and a method for positively pre-charged and (2)H-coded derivatization. Novel derivatizing reagents, N-alkyl-4-aminomethyl-pyridinum iodide (alkyl = butyl, butyl-d9 or hexyl), containing quaternary amine and stable-isotope atoms (deuterium), were introduced for the derivatization of carboxylic acids. CE separation in positive polarity showed high reproducibility (0.99-1.32% RSD of migration time) and eliminated problems with capillary coating known in CE-MS anion analyses. Essentially complete ionization and increased hydrophobicity after the derivatization also enhanced MS detection sensitivity (e.g. formic acid was detected at 0.5 pg). Simultaneous derivatization of one sample using two structurally similar reagents, N-butyl-4-aminomethyl-pyridinum iodide (BAMP) and N-hexyl-4-aminomethyl-pyridinum iodide, provided additional information for recognizing a carboxylic acid in an unknown sample. Moreover, characteristic fragmentation acquired by online CE-MS/MS allowed for identification and categorization of carboxylic acids. Applying this method on rat urine, we found 59 ions matching the characteristic patterns of carboxylic acids. From these 59, 32 ions were positively identified and confirmed with standards. For comparative analysis, 24 standard carboxylic acids were derivatized by chemically identical but isotopically distinct BAMP and N-butyl-d9-4-aminomethyl-pyridinium iodide, and their derivatization limits and linearity ranges were determined. Comparative analysis was also performed on two individual urine samples derivatized with BAMP and N-butyl-d9-4-aminomethyl-pyridinium iodide. The metabolite profiling variation between these two samples was clearly visualized.

Determination of the reference range of endogenous plasma carnitines in healthy adults

BACKGROUND

l-carnitine is an endogenous substance, vital in the transport of fatty acids across the inner mitochondrial membrane for oxidation. Disturbances in carnitine homeostasis can have a significant impact on human health; therefore, it is critical to define normal endogenous concentrations for l-carnitine and its esters to facilitate the diagnosis of carnitine deficiency disorders. This study was conducted to determine the normal concentrations of a number of carnitines in healthy adults using three analytical methods. The impact of age and gender on carnitine concentrations was also examined.

METHODS

Blood samples were collected from 60 healthy subjects of both genders and various ages. Plasma samples were analysed for endogenous carnitine concentrations by radioenzymatic assay, high-performance liquid chromatography and electrospray tandem mass spectrometry.

RESULTS

Precision and accuracy of results obtained for each assay were within acceptable limits. Average endogenous concentrations obtained from the three analytical methods in this study were in the range of 38-44, 6-7 and 49-50 mumol/L for l-carnitine, acetyl-l-carnitine and total carnitine, respectively. Comparison of results between the genders indicated that males had significantly higher endogenous plasma l-carnitine and total carnitine concentrations than females. Age was found to have no impact on plasma carnitine concentrations.

CONCLUSION

These results are useful in the evaluation of biochemical or metabolic disturbances and in the diagnosis and treatment of patients with carnitine deficiency.

Pharmacokinetics of acetyl-L-carnitine given in single or multiple doses to HIV-1 Infected patients with toxic peripheral polyneuropathy

The use of nucleoside reverse transcriptase inhibitors in the treatment of HIV infection is associated with antiretroviral toxic polyneuropathy (ATN). Previous studies suggest that long term treatment with Acetyl-L-carnitine (ALCAR) 1.5 gram twice daily improves symptoms and promotes nerve regeneration. It is unknown whether the drug’s pharmacokinetic profile would allow for a once daily administration. Twenty three HIV-1 infected subjects taking ALCAR for ATN were enrolled in a cross over trial and switched from twice to once daily dosing. Their regimen was changed from 1.5g twice daily to 1g (4 patients), 2g (7), and 3g (12) once daily, respectively. Twelve healthy volunteers served as control. Plasma levels of ALCAR and its metabolite L-carnitine were measured. Patients receiving ALCAR had higher pre-dose levels than control subjects. Post dose levels were not significantly higher than pre dose levels in any treatment group. The pre / post dose ALCAR concentrations were 7.6 / 7.7, 7.1 / 6.8, 7.7 / 6.8, and 7.1 / 7.5 µmol/l for 1.5g twice daily, 1g once daily, 2g once daily, and 3g once daily, respectively. All values were significantly higher than the mean concentration in the control group (4.3 µmol/l). For ALCAR and L-carnitine, measurements for once daily regimens did not differ from the twice daily regimen. Once daily dosing of ALCAR can achieve similar plasma levels as twice daily dosing but intra-mitochondrial levels remain unknown. The pharmacokinetic profile of orally administered ALCAR is complex and likely to be highly affected by endogenous concentrations.

Reversal of cisplatin-induced carnitine deficiency and energy starvation by propionyl-L-carnitine in rat kidney tissues

1. The present study examined whether propionyl-L-carnitine (PLC) could prevent the development of cisplatin (CDDP)-induced acute renal failure in rats. 2. Forty adult male Wistar albino rats were divided into four groups. Rats in the first group were injected daily with normal saline (2.5 mL/kg, i.p.) for 10 consecutive days, whereas the second group received PLC (250 mg/kg, i.p.) for 10 consecutive days. Animals in the third group were injected daily with normal saline for 5 consecutive days before and after a single dose of CDDP (7 mg/kg, i.p.). Rats in the fourth group received a combination of PLC (250 mg/kg, i.p.) for 5 consecutive days before and after a single dose of CDDP (7 mg/kg, i.p.). On Day 6 following CDDP treatment, animals were killed and serum and kidneys were isolated for analysis. 3. Injection of CDDP resulted in a significant increase in serum creatinine, blood urea nitrogen (BUN), thiobarbituric acid-reactive substances (TBARS) and total nitrate/nitrite (NO(x)), as well as a significant decrease in reduced glutathione (GSH), total carnitine, ATP and ATP/ADP in kidney tissues. 4. Administration of PLC significantly attenuated the nephrotoxic effects of CDDP, manifested as normalization of the CDDP-induced increase in serum creatinine, BUN, TBARS and NO(x) and the CDDP-induced decrease in total carnitine, GSH, ATP and ATP/ADP in kidney tissues. 5. Histopathological examination of kidney tissues from CDDP-treated rats showed severe nephrotoxicity, in which 50-75% of glomeruli and renal tubules exhibited massive degenerative changes. Interestingly, administration of PLC to CDDP-treated rats resulted in a significant improvement in glomeruli and renal tubules, in which less than 25% of glomeruli and renal tubules exhibited focal necrosis. 6. Data from the present study suggest that PLC prevents the development of CDDP-induced acute renal injury by a mechanism related, at least in part, to the ability of PLC to increase intracellular carnitine content, with a consequent improvement in mitochondrial oxidative phosphorylation and energy production, as well as its ability to decrease oxidative stress. This will open new perspectives for the use of PLC in the treatment of renal diseases associated with or secondary to carnitine deficiency.

Altered carnitine homeostasis is associated with decreased mitochondrial function and altered nitric oxide signaling in lambs with pulmonary hypertension

Utilizing aortopulmonary vascular graft placement in the fetal lamb, we have developed a model (shunt) of pulmonary hypertension that mimics congenital heart disease with increased pulmonary blood flow. Our previous studies have identified a progressive development of endothelial dysfunction in shunt lambs that is dependent, at least in part, on decreased nitric oxide (NO) signaling. The purpose of this study was to evaluate the possible role of a disruption in carnitine metabolism in shunt lambs and to determine the effect on NO signaling. Our data indicate that at 2 wk of age, shunt lambs have significantly reduced expression (P < 0.05) of the key enzymes in carnitine metabolism: carnitine palmitoyltransferases 1 and 2 as well as carnitine acetyltransferase (CrAT). In addition, we found that CrAT activity was inhibited due to increased nitration. Furthermore, free carnitine levels were significantly decreased whereas acylcarnitine levels were significantly higher in shunt lambs (P < 0.05). We also found that alterations in carnitine metabolism resulted in mitochondrial dysfunction, since shunt lambs had significantly decreased pyruvate, increased lactate, and a reduced pyruvate/lactate ratio. In pulmonary arterial endothelial cells cultured from juvenile lambs, we found that mild uncoupling of the mitochondria led to a decrease in cellular ATP levels and a reduction in both endothelial NO synthase-heat shock protein 90 (eNOS-HSP90) interactions and NO signaling. Similarly, in shunt lambs we found a loss of eNOS-HSP90 interactions that correlated with a progressive decrease in NO signaling. Our data suggest that mitochondrial dysfunction may play a role in the development of endothelial dysfunction and pulmonary hypertension and increased pulmonary blood flow.

Determination of highly soluble L-carnitine in biological samples by reverse phase high performance liquid chromatography with fluorescent derivatization

This study was performed in order to validate an effective high performance liquid chromatograpy (HPLC) method to determine L-carnitine in biological samples such as plasma, milk and muscle in cows. An L-carnitine derivative for fluorescence absorption was synthesized with 1-aminoanthracene (16 mg/mL in acetone) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDAC; 160 mg/mL in 0.01 M NaH2PO4 buffer) as a precolumn fluorescent derivative reagent. gamma-Butyrobetaine HCI was used as an internal standard. A reversed-phase column with fluorescence detection at the excitation and emission wavelengths of 248 and 418 nm were used. The mobile phase consisted of 30% acetonitrile with 0.1 M ammonium acetate in water (pH 3.5) adjusted with acetic acid and delivered at a flow rate of 1.5 mL/ min. The L-carnitine concentration in plasma, milk and muscle samples of cows after oral feeding with 24 g L-carnitine/day for 2 months was then determined. All biological samples were deproteinated by barium hydroxide and zinc sulfate heptahydrate before the derivative reaction. Blank cow plasma was dialyzed using cellulose membrane for standard calibration. The calibration curve showed good linearity (r2 > 0.999) over the concentration range of 50 to 5000 ng/mL. The precision and accuracy were also satisfactory with less than 15% intra- and interday coefficiency of variations. The peaks of L-carnitine and internal standard in HPLC chromatography were successfully separated in plasma, milk and muscle samples of cows. The current derivatization method of L-carnitine for fluorescence detection was simple and adequately sensitive and could be applied to determine L-carnitine in biological samples.

Inflammation and perturbation of thel-carnitine system in heart failure

BACKGROUND

Heart failure (HF) is accompanied by elevated levels of pro-inflammatory cytokines. Skeletal muscle myopathy with atrophy of fibres, decreased oxidative metabolism and preferential synthesis of fast myosin heavy chains (MHCs) occurs, which contributes to the worsening of symptoms. l-Carnitine has been shown to be protective against the apoptosis-induced atrophy of fibres and fast MHCs shift.

AIMS

To investigate the interrelationship between TNFalpha and sphingosine (SPH), which induce muscle wastage, and plasma levels of l-carnitine.

METHODS

We studied 18 heart failure patients and correlated NYHA class and ventricular function with the plasma concentration of these molecules.

RESULTS

TNFalpha and SPH levels were raised and correlated with the severity of HF. l-Carnitine levels were increased in HF patients, but decreased according to the severity of cardiac decompensation.

CONCLUSIONS

The increased levels of l-carnitine are likely due to release from the damaged muscle, reduced urinary excretion, decreased dietary intake and liver synthesis (malnutrition). It is possible that the cytokine-induced muscle wastage is not counterbalanced by the beneficial metabolic effects of l-carnitine, the metabolism of which is profoundly perturbed in CHF. l-Carnitine supplementation may produce positive effects on the skeletal muscle, as has been shown in animal models of HF.

Mildronate, an inhibitor of carnitine biosynthesis, induces an increase in gamma-butyrobetaine contents and cardioprotection in isolated rat heart infarction

The inhibition of gamma-butyrobetaine (GBB) hydroxylase, a key enzyme in the biosynthesis of carnitine, contributes to lay ground for the cardioprotective mechanism of action of mildronate. By inhibiting the biosynthesis of carnitine, mildronate is supposed to induce the accumulation of GBB, a substrate of GBB hydroxylase. This study describes the changes in content of carnitine and GBB in rat plasma and heart tissues during long-term (28 days) treatment of mildronate [i.p. (intraperitoneal) 100 mg/kg/daily]. Obtained data show that in concert with a decrease in carnitine concentration, the administration of mildronate caused a significant increase in GBB concentration. We detected about a 5-fold increase in GBB contents in the plasma and brain and a 7-fold increase in the heart. In addition, we tested the cardioprotective effect of mildronate in isolated rat heart infarction model after 3, 7, and 14 days of administration. We found a statistically significant decrease in necrotic area of infarcted rat hearts after 14 days of treatment with mildronate. The cardioprotective effect of mildronate correlated with an increase in GBB contents. In conclusion, our study, for the first time, provides experimental evidence that the long-term administration of mildronate not only decreases free carnitine concentration, but also causes a significant increase in GBB concentration, which correlates with the cardioprotection of mildronate.

Carnitine deficiency provokes cisplatin-induced hepatotoxicity in rats

This study investigates whether or not carnitine deficiency is a risk factor and could contribute to cisplatin-induced liver toxicity. A total of 60 adult male Wistar albino rats were divided into six groups. The first three groups were injected intraperitoneally with normal saline, propionyl-l-carnitine (500 mg/kg), and d-carnitine (500 mg/kg), respectively, for 10 successive days. The fourth, fifth and sixth groups were injected intraperitoneally with the same doses of normal saline, propionyl-l-carnitine and d-carnitine, respectively, for 5 successive days before and after a single dose of cisplatin (7 mg/kg). Administration of the standard nephrotoxic dose of cisplatin did not produce any changes in serum alanine transaminase and gamma-glutamyl transferase and no morphological changes in liver tissues. However, it did produce a significant increase in thiobarbituric acid reactive substances and total nitrate/nitrite and a significant decrease in reduced glutathione content in liver tissues. On the other hand, combined treatment with cisplatin and d-carnitine induced a dramatic increase in serum alanine transaminase and gamma-glutamyl transferase, as well as progressive reduction in total carnitine and ATP content in liver tissue. Moreover, histopathological examination of liver tissues confirmed the biochemical data, where cisplatin and d-carnitine combination showed signs of liver injury manifested as focal necro-inflammatory changes and portal inflammation. Interestingly, in carnitine supplemented rats using propionyl-l-carnitine, cisplatin did not produce any biochemical and histopathological changes in liver tissues. In conclusion, data from this study suggest for the first time that (1) carnitine deficiency is a risk factor and could precipitate cisplatin-induced hepatotoxicity, (2) oxidative stress is not the main cause of cisplatin-related hepatotoxicity and (3) propionyl-l-carnitine prevents the development of cisplatin-induced liver injury.

Rapid determination of short chain carnitines in human plasma by electrospray ionisation-ion trap mass spectrometry using capillary electrophoresis instrument as sampler

A capillary electrophoresis apparatus was used as sampler for flow injection analysis (FIA) in tandem mass spectrometry of L-carnitine and its acetyl- and propionyl-metabolites in human plasma. The capillary electrophoresis instrument was coupled to the ion trap mass spectrometer by an electrospray ionization coaxial sheath liquid interface. The electrophoresis capillary introduced the sample directly into the source by applying a prolonged sample injection. The use of the capillary electrophoresis apparatus miniaturised the FIA procedure, substantially reducing the quantities of solvents and samples used, and allowed rapid automated sequential analyses. The method was optimised and validated using a dialyzed human plasma matrix. The plasma samples were analysed after a simple, rapid deproteinisation procedure with acetonitrile and diluted 70 times before direct injection into the mass spectrometer for product ion scan MS/MS analysis in positive ionisation. The total analysis time was 5 min, including capillary preconditioning and acquisition time (3 min). The method was sensitive, allowing the determination of L-, L-acetyl- and L-propionyl-carnitines at 140, 14 and 3.6 nM concentrations (injected values) corresponding to lower limit of quantitation values in plasma of 10, 1 and 0.25 microM, respectively. The method was processed for full validation and applied to the analysis of L-carnitine and its short chain derivatives in human plasma samples.

Urinary excretion of L-carnitine and its short-chain acetyl-L-carnitine in patients undergoing carboplatin treatment

PURPOSE

To evaluate the effect of the anti-cancer drug carboplatin on plasma concentrations and urinary excretion of L-carnitine (LC) and its main ester, acetyl-L-carnitine (ALC), in cancer patients.

METHODS

Plasma and urine concentrations of LC and ALC from 11 patients on carboplatin therapy (1 h intravenous infusion; AUC dose 4.8 +/- 1.1 mg/ml min) in combination with docetaxel, paclitaxel or vinorelbine, were determined by high-performance liquid chromatography with fluorimetric detection.

RESULTS

Before carboplatin therapy, the mean +/- SD plasma concentrations of LC and ALC were 47.8 +/- 10.9 and 7.04 +/- 1.04 nmoles/ml, respectively, and remained constant throughout the entire study period. In contrast, urinary excretion of LC and ALC, increased significantly during the chemotherapy from 115 +/- 105 to 480 +/- 348 micromoles/day (P < 0.01) and from 41 +/- 41 to 89 +/- 52 micromoles/day (P < 0.05) for LC and ALC, respectively, subsequently reverting to normal 6 days after the end of chemotherapy. Similarly, the renal clearance of LC and ALC increased substantially during chemotherapy from 1.67 +/- 1.43 to 9.05 +/- 9.52 ml/min (P < 0.05) and from 4.02 +/- 4.51 to 7.97 +/- 5.05 ml/min (P = not significant) for LC and ALC, respectively, reverting to normal 6 days after the end of chemotherapy. Plasma concentrations and urinary excretion of glucose, phosphate and urea nitrogen and creatinine clearance, however, were not affected by carboplatin therapy, indicating no impaired kidney function.

CONCLUSION

Treatment with carboplatin was associated with a marked urinary loss of LC and ALC, most likely due to inhibition of carnitine reabsorption in the kidney.

Carnitine for the treatment of idiopathic asthenospermia: a randomized, double-blind, placebo-controlled trial

OBJECTIVE

To determine the effect of oral carnitine supplementation on the semen parameters of men with idiopathic asthenospermia.

DESIGN

Prospective, randomized, double-blind placebo-controlled study.

SETTING

Academic tertiary referral centers.

PATIENT(S)

Male patients presenting with infertility and with sperm motility of 10%-50% were selected.

INTERVENTION(S)

Patients were randomized to 24-week treatment arms of oral carnitine (2,000 mg L-carnitine and 1,000 mg L-acetyl-carnitine per day) or placebo.

MAIN OUTCOME MEASURE(S)

Sperm motility and total motile sperm counts at baseline, 12 weeks, and 24 weeks. Seminal plasma and sperm free, acetyl, and total L-carnitine levels at baseline and at week 24.

RESULT(S)

Twenty-one patients entered the study, with 12 patients in the carnitine arm and 9 in the placebo arm. There were no significant differences in baseline semen parameters between the carnitine and placebo arms. There was no statistically significant or clinically significant increase in motility or total motile sperm counts between baseline, 12 week, or 24 weeks in the carnitine or placebo arms.

CONCLUSION(S)

Carnitine supplementation demonstrated no clinically or statistically significant effect on sperm motility or total motile sperm counts in men with idiopathic asthenospermia.

Direct determination of acylcarnitines in amniotic fluid by column-switching liquid chromatography with electrospray tandem mass spectrometry

A direct, simple, and simultaneous determination of acylcarnitines in amniotic fluid was developed using column-switching liquid chromatography/tandem mass spectrometry (LC/MS/MS). The analytes can be assayed within 20 min without any sample preparation process, and we monitored separated acylcarnitines with positive electrospray ionization (ESI)-MS/MS. The calibration ranges of acylcarnitines were 1 to 100 nmol/L. The linearity of the method was 0.992 to 0.999, and the limits of detection at a signal-to-noise ratio of 3 were 1 nmol/L. The coefficients of variation were in the range of 5.2 to 13.3% for within-day variation and 6.7 to 11.9% for day-to-day, respectively. We detected acylcarnitines in the amniotic fluid of 22 women in the early stages of their pregnancies in the range of 2.2 to 17.2 nmol/L. The proposed method could be applied to diagnosis, monitoring, and biomedical investigations of inborn errors of the organic acid and fatty acid metabolism of the embryo.

Progression of Cisplatin-Induced Nephrotoxicity in a Carnitine-Depleted Rat Model

BACKGROUND

This study has been initiated to investigate whether endogenous carnitine depletion and/or carnitine deficiency is an additional risk factor and/or a mechanism in cisplatin-induced nephrotoxicity and to gain insights into the possibility of a mechanism-based protection by L-carnitine against this toxicity.

METHODS

60 male Sprague-Dawley rats were divided into six groups of 10 animals each and received one of the following treatments: The first three groups were injected intraperitoneally with normal saline, L-carnitine (500 mg/kg), and D-carnitine (750 mg/kg), respectively, for 10 successive days. The 4th, 5th, and 6th groups were injected intraperitoneally with the same doses of normal saline, L-carnitine and D-carnitine, respectively, for 5 successive days before and after a single dose of cisplatin (7 mg/kg). Six days after cisplatin treatment, the animals were sacrificed, and serum as well as kidneys were isolated and analyzed.

RESULTS

A single dose of cisplatin resulted in a significant increase in blood urea nitrogen (BUN), serum creatinine, malondialdehyde (MDA) and nitric oxide (NO) and a significant decrease in total carnitine, reduced glutathione (GSH) and adenosine triphosphate (ATP) content in kidney tissues. Interestingly, L-carnitine supplementation attenuated cisplatin-induced nephrotoxicity manifested by normalizing the increase of serum creatinine, BUN, MDA and NO and the decrease in total carnitine, GSH and ATP content in kidney tissues. In the carnitine-depleted rat model, cisplatin induced a progressive increase in serum creatinine and BUN as well as a progressive reduction in total carnitine and ATP content in kidney tissue. Histopathological examination of kidney tissues confirmed the biochemical data, i.e. L-carnitine supplementation protected against cisplatin-induced kidney damage, whereas D-carnitine aggravated cisplatin-induced renal injury.

CONCLUSION

Data from this study suggest that: (1) oxidative stress plays an important role in cisplatin-induced kidney damage; (2) carnitine deficiency should be viewed as an additional risk factor and/or a mechanism in cisplatin-induced renal dysfunction, and (3) L-carnitine supplementation attenuates cisplatin-induced renal dysfunction.

Impact of hemodialysis on endogenous plasma and muscle carnitine levels in patients with end-stage renal disease

BACKGROUND

End-stage renal disease (ESRD) patients undergoing hemodialysis treatment have reduced plasma L-carnitine levels; however, the relationship between dialysis age and carnitine status is poorly understood. This study examined the relationship between duration of dialysis and plasma and skeletal muscle concentrations of L-carnitine and its esters in ESRD patients.

METHODS

Blood samples were collected from 21 patients at baseline and throughout the first 12 months of hemodialysis. In 5 patients, muscle samples were obtained after 0, 6, and 12 months of hemodialysis. Blood and muscle samples were collected from an additional 20 patients with a mean dialysis age of 5.10 years. L-carnitine, acetyl-L-carnitine, and total L-carnitine were measured by high-performance liquid chromatography (HPLC).

RESULTS

The mean +/- SD plasma L-carnitine concentration in ESRD patients who had not yet started hemodialysis was 50.6 +/- 20.0 micromol/L. Significantly lower concentrations were observed after 12 months (29.7 +/- 10.5 micromol/L) and >12 months (22.0 +/- 5.4 micromol/L) of hemodialysis treatment. Acetyl-L-carnitine also declined with dialysis age, while plasma nonacetylated acylcarnitines continued to increase with the progression of hemodialysis therapy. An inverse relationship between dialysis age and muscle L-carnitine concentrations was observed.

CONCLUSION

Long-term hemodialysis treatment is associated with a significant reduction in endogenous plasma and muscle L-carnitine levels and a significant increase in plasma acylcarnitines. The majority of the change in plasma L-carnitine concentrations occurs within the first few months of hemodialysis, while muscle levels continue to decline after 12 months of treatment.

Acetyl-L-carnitine permeability across the blood-brain barrier and involvement of carnitine transporter OCTN2

OCTN2 (SLC22A5), an organic cation/carnitine transporter, is widely distributed throughout the body, including the brain. In the present study, the involvement of OCTN2 in acetyl-L-carnitine (ALCAR) permeation across the blood-brain barrier (BBB) was examined using a microdialysis method in mouse. OCTN2 function was examined by comparison of wild-type mice with jvs mice, which express defective OCTN2 and are considered a model for primary systemic carnitine deficiency. Zero-net-flux method analysis indicated higher in vivo recovery of ALCAR and lower physiological ALCAR concentration in thalamus extracellular fluid (ECF) in jvs mice compared with wild-type mice. Externally added ALCAR showed significantly slower initial uptake across the BBB in jvs mouse. These results indicated that OCTN2 is functionally involved in ALCAR transfer across the BBB. Total radioactivity in ECF after i.v. administration of radiolabelled ALCAR remained constant for the rest of the experimental period. Accordingly, our results indicate that ALCAR is transported from blood to brain ECF by OCTN2 at least in part, and its concentration in brain ECF is regulated by other events such as protein binding and anabolic reactions in the brain, as well as by transport across the BBB.

Hplc determination and pharmacokinetics of endogenous acetyl-l-carnitine (alc) in human volunteers orally administered a single dose of alc

Acetyl-L-carnitine (ALC), a naturally occurring endogenous compound, has been shown to improve the cognitive performance of patients with senile dementia Alzheimer's type, and to be involved in cholinergic neurotransmission. Because ALC is an endogenous compound, validation of the analytical methods of ALC in the biological fluids is very important and difficult. This study was presented validation and correction for plasma ALC concentrations and pharmacokinetics after oral administration of ALC to human volunteers. ALC concentrations in human plasma were corrected by subtracting the concentration of blank plasma from each sample. Precision and accuracy (bias %) for uncorrected ALC concentrations were below 2.6 and 6.5% for intra-days, and 4.0 and 9.4% for inter-days, respectively. Precision and accuracy (bias %) for corrected ALC concentrations were below 10.9 and 6.0% for intra-days, and 10.5 and 16.9% for inter-days, respectively. Quantitation limit was 0.1 microg/mL. After oral administration of a 500 mg ALC tablet to 8 healthy volunteers, the principle pharmacokinetic parameters were 4.2 h of the half-life (t(1/2,beta)), the area under the curve (AUC(0-8)) of 9.88 microg.h/mL, and 3.1 h of the time (Tmax) to reach Cmax. This study first describes the pharmacokinetic study after oral administration of a single dose of ALC in human volunteers.

Acetyl-l-carnitine supplementation restores decreased tissue carnitine levels and impaired lipid metabolism in aged rats

The effects of long-term carnitine supplementation on age-related changes in tissue carnitine levels and in lipid metabolism were investigated. The total carnitine levels in heart, skeletal muscle, cerebral cortex, and hippocampus were approximately 20% less in aged rats (22 months old) than in young rats (6 months old). On the contrary, plasma carnitine levels were not affected by aging. Supplementation of acetyl-l-carnitine (ALCAR; 100 mg/kg body weight/day for 3 months) significantly increased tissue carnitine levels in aged rats but had little effect on tissue carnitine levels in young rats. Plasma lipoprotein analyses revealed that triacylglycerol levels in VLDL and cholesterol levels in LDL and in HDL were all significantly higher in aged rats than in young rats. ALCAR treatment decreased all lipoprotein fractions and consequently the levels of triacylglycerol and cholesterol. The reduction in plasma cholesterol contents in ALCAR-treated aged rats was attributable mainly to a decrease of cholesteryl esters rather than to a decrease of free cholesterol. Another remarkable effect of ALCAR was that it decreased the cholesterol content and cholesterol-phospholipid ratio in the brain tissues of aged rats. These results indicate that chronic ALCAR supplementation reverses the age-associated changes in lipid metabolism.

Pharmacokinetics of L-carnitine

L-Carnitine is a naturally occurring compound that facilitates the transport of fatty acids into mitochondria for beta-oxidation. Exogenous L-carnitine is used clinically for the treatment of carnitine deficiency disorders and a range of other conditions. In humans, the endogenous carnitine pool, which comprises free L-carnitine and a range of short-, medium- and long-chain esters, is maintained by absorption of L-carnitine from dietary sources, biosynthesis within the body and extensive renal tubular reabsorption from glomerular filtrate. In addition, carrier-mediated transport ensures high tissue-to-plasma concentration ratios in tissues that depend critically on fatty acid oxidation. The absorption of L-carnitine after oral administration occurs partly via carrier-mediated transport and partly by passive diffusion. After oral doses of 1-6g, the absolute bioavailability is 5-18%. In contrast, the bioavailability of dietary L-carnitine may be as high as 75%. Therefore, pharmacological or supplemental doses of L-carnitine are absorbed less efficiently than the relatively smaller amounts present within a normal diet.L-Carnitine and its short-chain esters do not bind to plasma proteins and, although blood cells contain L-carnitine, the rate of distribution between erythrocytes and plasma is extremely slow in whole blood. After intravenous administration, the initial distribution volume of L-carnitine is typically about 0.2-0.3 L/kg, which corresponds to extracellular fluid volume. There are at least three distinct pharmacokinetic compartments for L-carnitine, with the slowest equilibrating pool comprising skeletal and cardiac muscle.L-Carnitine is eliminated from the body mainly via urinary excretion. Under baseline conditions, the renal clearance of L-carnitine (1-3 mL/min) is substantially less than glomerular filtration rate (GFR), indicating extensive (98-99%) tubular reabsorption. The threshold concentration for tubular reabsorption (above which the fractional reabsorption begins to decline) is about 40-60 micromol/L, which is similar to the endogenous plasma L-carnitine level. Therefore, the renal clearance of L-carnitine increases after exogenous administration, approaching GFR after high intravenous doses. Patients with primary carnitine deficiency display alterations in the renal handling of L-carnitine and/or the transport of the compound into muscle tissue. Similarly, many forms of secondary carnitine deficiency, including some drug-induced disorders, arise from impaired renal tubular reabsorption. Patients with end-stage renal disease undergoing dialysis can develop a secondary carnitine deficiency due to the unrestricted loss of L-carnitine through the dialyser, and L-carnitine has been used for treatment of some patients during long-term haemodialysis. Recent studies have started to shed light on the pharmacokinetics of L-carnitine when used in haemodialysis patients.

Dialysis-related carnitine disorder and levocarnitine pharmacology

Among the homeostatic processes controlling the endogenous L-carnitine pool in humans, the kidney has a vital role through extensive and adaptive tubular reabsorption. Kidney disease can lead to disturbances in L-carnitine homeostasis, and long-term hemodialysis therapy can lead to a significant reduction in plasma and tissue L-carnitine levels and an increase in the ratio of acyl-L-carnitine to free L-carnitine. These alterations may interfere with the oxidation of fatty acids and removal from tissues of unwanted short-chain acyl groups. A dialysis-related carnitine disorder (DCD) arises when these biochemical abnormalities exist in association with such clinical symptoms as muscle weakness, cardiomyopathy, intradialytic hypotension, or anemia that is resistant to erythropoietin therapy. Exogenous L-carnitine, administered intravenously, is approved for the treatment of secondary carnitine deficiency caused by long-term hemodialysis. Although intravenous administration of 20-mg/kg doses at the end of each hemodialysis session leads to supraphysiological levels of the compound in plasma, these levels do not appear to be associated with adverse effects. Because more than 99% of the body's carnitine pool is located outside of plasma, supraphysiological plasma levels appear to be required to ensure that depleted muscle stores can be replenished. Although oral L-carnitine has been used for the treatment of DCD, the bioavailability of oral L-carnitine is low (<15%) in healthy subjects and unknown in patients with end-stage renal disease. Moreover, gastrointestinal degradation of L-carnitine to trimethylamine and other compounds might limit the usefulness of long-term oral L-carnitine administration in this patient group.

Determination of carnitine and acylcarnitines in urine by high-performance liquid chromatography-electrospray ionization ion trap tandem mass spectrometry

A high-performance liquid chromatography-mass spectrometry method has been developed for the simultaneous determination of native carnitine and eight acylcarnitines in urine. The procedure uses a solid-phase extraction on a cation-exchange column and the separation is performed without derivatization within 17 min on a reversed-phase C8 column in the presence of a volatile ion-pairing reagent. The detector was an ion trap mass spectrometer and quantification was carried out in the MS-MS mode. Validation was done for aqueous standards at ranges between 0.75 and 200 micromol/l, depending on the compound. Carnitine was quantified in urine and comparison with a radioenzymatic assay gave a satisfactory correlation (R2 = 0.981). The assay could be successfully applied to the diagnostic of pathological acylcarnitines profile of metabolic disorders in urines of patients suffering from different organic acidurias.

L-Carnitine: a potential treatment for blocking apoptosis and preventing skeletal muscle myopathy in heart failure

Skeletal muscle in congestive heart failure is responsible for increased fatigability and decreased exercise capacity. A specific myopathy with increased expression of fast-type myosins, myocyte atrophy, secondary to myocyte apoptosis triggered by high levels of circulating tumor necrosis factor-alpha (TNF-alpha) has been described. In an animal model of heart failure, the monocrotaline-treated rat, we have observed an increase of apoptotic skeletal muscle nuclei. Proapoptotic agents, caspase-3 and -9, were increased, as well as serum levels of TNF-alpha and its second messenger sphingosine. Treatment of rats with L-carnitine, known for its protective effect on muscle metabolism injuries, was found to inhibit caspases and to decrease the levels of TNF-alpha and sphingosine, as well as the number of apoptotic myonuclei. Staurosporine was used in in vitro experiments to induce apoptosis in skeletal muscle cells in culture. When L-carnitine was applied to skeletal muscle cells, before staurosporine treatment, we observed a reduction in apoptosis. These findings show that L-carnitine can prevent apoptosis of skeletal muscles cells and has a role in the treatment of congestive heart failure-associated myopathy.

Up-regulation of carnitine transporters helps maintain tissue carnitine levels in carnitine deficiency induced by pivalic acid

PURPOSE

Pivalic acid (PVA) forms conjugates with endogenous carnitine and enhances its excretion. The purpose of this study is to determine whether tissue carnitine levels decrease in parallel with plasma levels in carnitine deficiency induced by PVA.

METHODS

PVA was orally administered to rats for 5 days. Carnitine levels in plasma, liver, kidney, muscle, and heart were monitored. The tissue uptake clearance (CLuptake) was determined in vivo by the integration plot method. Hepatocytes were prepared from control and PVA-treated rats, and the uptake of L-carnitine was determined.

RESULTS

Plasma concentrations of L-carnitine decreased as a result of the enhanced carnitine elimination as pivaloylcarnitine (PCN) when rats were treated with PVA. However, L-carnitine concentrations in liver, muscle, and heart remained relatively constant during the study. period. CLuptake increased in liver and muscle and, thus, the rate of carnitine uptake from plasma into these tissues did not change even at low plasma concentrations. This helps maintain carnitine levels in these tissues. Up-regulation of carnitine transporters is suggested to be a mechanism for the increased CLuptake.

CONCLUSIONS

In the carnitine deficiency state induced by PVA, increased CLuptake owing to up-regulation of carnitine transporters is suggested to help maintain carnitine levels in some tissues.

Pharmacokinetics of propionyl-L-carnitine in humans: evidence for saturable tubular reabsorption

AIMS

Propionyl-L-carnitine (PLC) is an endogenous compound which, along with L-carnitine (LC) and acetyl-L-carnitine (ALC), forms a component of the endogenous carnitine pool in humans and most, if not all, animal species. PLC is currently under investigation for the treatment of peripheral artery disease, and the present study was conducted to assess the pharmacokinetics of intravenous propionyl-L-carnitine hydrochloride.

METHODS

This was a placebo-controlled, double-blind, parallel group, dose-escalating study in which 24 healthy males were divided into four groups of six. Four subjects from each group received propionyl-L-carnitine hydrochloride and two received placebo. The doses (1 g, 2 g, 4 g and 8 g) were administered as a constant rate infusion over 2 h and blood and urine were collected for 24 h from the start of the infusion. PLC, ALC and LC in plasma and urine were quantified by h.p. l.c.

RESULTS

All 24 subjects successfully completed the study and the infusions were well tolerated. In addition to the expected increase in PLC levels, the plasma concentrations and urinary excretion of LC and ALC also increased above baseline values following intravenous propionyl-L-carnitine hydrochloride administration. At a dose of 1 g, PLC was found to have a mean (+/- s.d.) half-life of 1.09 +/- 0.15 h, a clearance of 11.6 +/- 0.24 l h-1 and a volume of distribution of 18.3 +/- 2.4 l. None of these parameters changed with dose. In placebo-treated subjects, endogenous PLC, LC and ALC underwent extensive renal tubular reabsorption, as indicated by renal excretory clearance to GFR ratios of less than 0.1. The renal-excretory clearance of PLC, which was 0.33 +/- 0.38 l h-1 under baseline condition, increased (P < 0. 001) from 1.98 +/- 0.59 l h-1 at a dose of 1 g to 5.55 +/- 1.50 l h-1 at a dose of 8 g (95% confidence interval for the difference was 2.18,4.97). As a consequence, the percent of the dose excreted unchanged in urine increased (P < 0.001) from 18.1 +/- 5.5% (1 g) to 50.3 +/- 13.3% (8 g). The renal-excretory clearance of LC and ALC also increased substantially after PLC administration and there was evidence for renal metabolism of PLC to LC and ALC.

CONCLUSIONS

Intravenous administration of propionyl-L-carnitine hydrochloride caused significant increases in the renal excretory clearances of PLC, LC and ALC, due to saturation of the renal tubular reabsorption process - as a consequence there was a substantial increase with dose in the fraction excreted unchanged in urine. Despite the marked increase in the renal clearance of PLC, total clearance remained unchanged, suggesting a compensatory reduction in the clearance of the compound by non excretory routes.

Analysis of carnitine and acylcarnitines in urine by capillary electrophoresis

A capillary electrophoresis method is described for the simultaneous analysis of carnitine and short-chain acylcarnitines in aqueous standard solutions and urine samples. Samples were worked up using silica gel extraction and derivatization with 4'-bromophenacyl trifluoromethanesulfonate. Separation was performed in less than 8 min using a binary buffer system containing phosphate/phosphoric acid and sodium dodecyl sulfate. 3-(2,2,2-Trimethylhydrazinium)propionate (mildronate) was used as an internal standard. The method was developed with aqueous standard solutions and then applied successfully to spiked and unspiked human urine samples. The limit of detection for both carnitine and acetylcamitine is 3 microM.

Improved high-performance liquid chromatographic method for analysis of L-carnitine in pharmaceutical formulations

A reversed-phase high performance liquid chromatographic method for analysis of L-carnitine is described. The improved method is able to provide a high resolution between L-carnitine and crotonoylbetaine, a major impurity and degradation product, and suitable for quantitative analysis of L-carnitine in pharmaceutical formulations, such as solution, tablets, and capsules. The resolution, linearity, accuracy and reproducibility of the method are discussed.

Acetyl-L-carnitine infusion increases glucose disposal in type 2 diabetic patients

Little information is available in the literature on the effect of L-carnitine to improve glucose disposal in healthy control subjects and type 2 diabetic patients. No data are reported on the pharmacological properties of acetyl-L-carnitine (ALC) in type 2 diabetes mellitus. The present study evaluates glucose uptake and oxidation rates with either ALC or placebo administration in 18 type 2 diabetic patients. On different days, each patient received both a primed-constant infusion of ALC (5 mg/kg body weight [BW] priming bolus and either 0.025, 0.1, or 1.0 mg/kg BW/min constant infusion) and a comparable placebo formulation. During the infusion period, continuous indirect calorimetric monitoring and a euglycemic-hyperinsulinemic clamp (EHC) study were performed. The total end-clamp glucose tissue uptake (M value) was significantly increased by the administration of ALC (from 3.8 to 5.2 mg/kg/min, P = .006), and the dose dependence of this effect reached borderline statistical significance (P = .037). The increase in the M/I ratio was also highly significant after ALC administration (from 3.9 to 5.8 x 10(-2) mg/kg/min/(microUI/mL, P < .001), while no statistically significant effect was attributable to the different dosages. The increase in the M value was related to increased glucose storage (highly significant effect of ALC) rather than increased glucose oxidation (no statistical significance). In conclusion, the effect of ALC on glucose disposal has no relationship to the amount administered. This could be due to an effect of ALC on the enzymes involved in both the glycolytic and gluconeogenetic pathways, and a possible reversibility of glycogen synthase inhibition in diabetic subjects.